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University Microfilms International 300 N. Z eeb Road Ann Arbor, Ml 48106 8308945 Gregg, Jay Mason TOE ORIGIN OF XENOTOPIC DOLOMITE TEXTURE Michigan State University University Microfiims International PH.D. 1982 300 N. Zeeb Road. Ann Arbor. MI 48106 PLEASE NOTE: In all cases this material has been filmed in the best possible way from the available copy. Problems encountered with this document have been identified here with a check mark V . 1. Glossy photographs or pages ^ 2. Colored illustrations, paper or print_____ 3. Photographs with dark background 4. Illustrations are poor copy______ 5. Pages with black marks, not original copy______ 6. Print shows through as there is text on both sides of page______ 7. Indistinct, broken or small print on several 8. Print exceeds margin requirements_____ 9. Tig htly bound copy with print lost in spine______ 10. Computer printout pages with indistinct print______ 11. Page(s)___________ lacking when material received, and not available from school or author. 12. Page(s)___________ seem to be missing in numbering only as text follows. 13. Two pages numbered 14. Curling and wrinkled p ages______ 15. Other____________________________________________________________________ p a g e s_ Text follows. University Microfilms International THE ORIGIN OF XENOTOPIC DOLOMITE TEXTURE by J a y Mason G regg A DISSERTATION S u b m itted to M ichigan S ta t e U n iv e r s ity i n p a r t i a l f u l f i l l m e n t o f th e re q u ire m e n ts f o r th e d e g re e o f DOCTOR OF PHILOSOPHY D epartm ent o f G eology 1982 Fron tp late: "The E n tran ce to M arble Canyon, C u lb erso n County, T ex as." B ack p late : "G alena D olom ite O utcrop L o c a lity 33, G rant C ounty, W isconsin. THE ORIGIN OF XENOTOPIC DOLOMITE TEXTURE J a y M* Gregg Ph.D* D i s s e r t a t i o n M ichigan S t a t e U n iv e r s ity D epartm ent o f G eology 1982 ERRATA A b s tra c ts p. i i i s l i n e 3» o m it " e d r a l" l i n e 9 . o m it " in g " ACKNOWLEDGMENTS l i n e 9* Dr* K. C. Lohmann o f th e U n iv e r s ity o f M ichigan p ro v id e d th e oxygen and c a rb o n is o to p e d a t a and a id e d i n i t ' s in te rp re ta tio n • l i n e 1 5 , "K able" sh o u ld b e "K ahle" l i n e 2 1 , "The te rm i s " s h o u ld r e a d "The te rra a i s " eq« 1» " ( i- N ) " sh o u ld r e a d "(1-N a )" p* 1 1 i l i n e 3» s h o u ld r e a d " t h e o r e t i c a l l y p r e d ic te d a " p* 7 : p , 19s l i n e 2 , "10 p. 24: lin e 21, " id io to p ic - A " s h o u ld r e a d " id io to p ic - E " p . 25: lin e 12, " id io to p ic - B " s h o u ld r e a d " id io to p ic - S " p . 26: T a b le 2 c a p t i o n , p« 5 1 J l i n e 3 1 s h o u ld re a d (1 0 1 1 ), (4 0 5 1 ) p* 78s lin e 3* s h o u ld r e a d " th e f o s s i l s a r e " p . 83* lin e 1 2 , " J F l" s h o u ld r e a d "JF " p* 86s l i n e 1 4 , " x en o to p ic-C " s h o u ld r e a d " x e n o to p ic -P " p. 89: l i n e 19* " ( t a b l e 4 and fig * 5 4 )" s h o u ld r e a d " ( t a b l e 6 and f ig * 4 9 )" p* 9 1 : l i n e 1 , " t a b l e 6" s h o u ld r e a d " t a b l e 7" p. 95: l i n e 2 0 , r e a d " C 0 ^ “ " a t end o f t h e l i n e p* 9 8 : m" s h o u ld r e a d "10 pm" " id io to p ic - B " s h o u ld r e a d " id io to p ic - S " l i n e 1 7 , sh o u ld re a d " b e g in t o e q u a lly fa v o r " p* 1 0 2 i l i n e 2 4 , s h o u ld r e a d "was p ro b a b ly ro c k dom inated" p* 103 : l i n e 8 , " T a b le 6" s h o u ld r e a d "T a b le 7" p* 105 : l i n e 7» s h o u ld r e a d " i s t h a t i t r e s u l t e d " p« 107: l i n e 17» sh o u ld r e a d " o b s e r v a tio n o f x e n o to p ic " ABSTRACT The O rig in o f X en o to p ic D olom ite T e x tu re by Jay Mason Gregg X enotopic d o lo m ite t e x t u r e , commonly o b serv ed i n a n c ie n t r o c k s , i s d e fin e d a s a m osaic o f an h ed ra w ith i r r e g u l a r o r cu rv ed i n t e r g r a i n b o u n d a rie s and u s u a lly u n d u lo se e x t i n c t i o n . X enotopic d o lo m ite e d r a l t e x t u r e i s s im i la r in ap p ea ran ce to neom orphic lim e s to n e t e x t u r e s . X enotopic t e x tu r e c o n t r a s t s w ith i d i o t o p i c d o lo m ite t e x t u r e (e u h e d ra l to s u b h e d ra l c r y s t a l s w ith s t r a i g h t i n t e r g r a i n b o u n d a rie s ) t h a t i s common in b o th C enozoic and a n c ie n t d o lo m ite s . T ex tu re may be c o n t r o l le d by th e te m p e ra tu re a t w hich c r y s t a l s grow . C r y s ta l grow th th e o ry p r e d i c t s t h a t a t low te m p e r a tu r e , a in g smooth c r y s t a l s u r f a c e i s e n e r g e t i c a l l y fa v o re d , atoms a r e added to c r y s t a l fa c e s la y e r by l a y e r , w ith d is l o c a t i o n s a c tin g a s n u c le a tin g s i t e s . T his r e s u l t s in f a c e te d c r y s t a l s and e u h e d ra l to s u b h e d ra l c r y s t a l m o sa ic s. Above a " c r i t i c a l ro u g h en in g te m p e ra tu re " (CRT) a rough s u r f a c e i s e n e r g e t i c a l l y fa v o re d , s u r f a c e n u c le a tio n does n o t r e q u ir e d is l o c a t i o n s and atoms a r e random ly added to th e c r y s t a l s u r f a c e r e s u l t i n g in n o n -fa c e te d grow th and an a n h e d ra l c r y s t a l m o saic. I t i s h y p o th e siz e d th a t a " c r i t i c a l ro u g h en in g te m p e ra tu re " e x i s t s f o r d o lo m ite above 25°C. X enotopic d o lo m ite s a r e produced by d o lo m itiz a tio n o f lim e s to n e a n d /o r neom orphic r e c r y s t a l l i z a t i o n o f d o lo m ite a t e le v a te d te m p e ra tu re (above CRT) a f t e r b u r i a l . I d io to p ic d o lo m ite s a r e produced below CRT by n e a r s u r f a c e p r o c e s s e s . C a lc ite has a CRT below 25°C an d , t h e r e f o r e , p ro d u ces a n n h e d ra l g r a in m osaics (neom orphic t e x t u r e ) b o th a t n e a r s u r f a c e and e le v a te d te m p e ra tu re . S y n th e tic x e n o to p ic d o lo m ite was produced in th e la b o r a to r y by d o lo m itiz a tio n o f a r a g o n ite and c a l c i t e s k e l e t a l frag m e n ts and by r e c r y s t a l l i z a t i o n o f n o n s to ic h io m e tr ic C enozoic d o lo m ite s a t 250°C and 300°C. X en o to p ic d o lo m ite r e s u l t e d from th e m etam orphic r e c r y s t a l l i z a t i o n o f th e i d i o t o p i c Hueco d o lo m ite (P e rm ia n ), Texas n e a r th e M arble Canyon i n t r u s i o n , a t te m p e ra tu re betw een 350°C and 600°C. H ydrotherm al d o lo m itiz a tio n o f p e r i d a s e - c a l c i t e m arble n e a r th e i n t r u s i o n a ls o r e s u l t e d in a x e n o to p ic t e x t u r e . X enotopic d o lo m ite in th e G alen a Group (O r d o v ic ia n ) , W isco n sin , was produced by neomorphism o f a p r e - e x i s t i n g d o lo m ite d u rin g th e emplacment o f le a d - z in c s u f id e s a t te m p e ra tu re s betw een 80° and 120°C. In th e T rento n F orm ation (O rd o v ic ia n ), M ichigan, x e n o to p ic d o lo m ite r e p la c e d lim e s to n e , d u rin g th e m ig ra tio n o f h o t (>50°C) f l u i d s alo n g f r a c t u r e s y ste m s . X en o to p ic d o lo m ite was n o t o b se rv e d in Cenozoic d o lo m ite s w hich were s u b je c te d o n ly to n ear s u r f a c e te m p e ra tu re s . D ed icated to th e Memory o f my F a th e r Ja y B. Gregg ii ACKNOWLEDGEMENTS I w ish to e x p re s s my deep a p p r e c ia tio n to Dr. Duncan F . S ib le y f o r s u g g e s tin g t h i s to p i c and p ro v id in g g u id an ce and encouragem ent th ro u g h o u t t h i s p r o j e c t . I g r a t e f u l l y acknow ledge th e h e lp and s u g g e s tio n s o f D rs. David T. Long, James H. F is h e r and e s p e c i a ll y Dr. Thomas A. V ogel, who i n i t i a l l y su g g e ste d a r e l a t i o n s h i p between d o lo m ite te x tu r e and te m p e ra tu re . Mr. David J . Delgado o f P h i l l i p s P etro leu m Co. p ro v id e d in v a lu a b le a s s is ta n c e in p ro v id in g s t r a t i g r a p h i c in fo rm a tio n and o u tc ro p lo c a tio n s f o r th e G alena Group. Mr. Stu McDonnald o f th e U n iv e r s ity o f M ichigan p ro v id ed v a lu a b le a s s is ta n c e in lo c a tin g and sam pling T renton F orm ation c o r e . Mr. Jo e W illiam s o f Texas A r c h ite c tu r a l A g g re g a te s, San Saba, Texas k in d ly g ra n te d me p e rm issio n to c o l l e c t sam ples in M arble Canyon. 1 a ls o w ish to th a n k D r. K enneth A. Jack so n o f th e B e ll L a b o r a to r ie s , M urray H i l l , N .J . and D r. C h arles F. Kable o f Bowling Green S ta te U n iv e r s ity f o r v a lu a b le d is c u s s io n s d u rin g th e co u rse o f t h i s work. Dr. Lynton S. Land o f th e U n iv e r s ity o f T ex as, D r. C arl M. Cooper and Mr. Donald L. C h ild s o f M ichigan S ta te U n iv e rs ity C o lleg e o f E n g in eerin g made v a lu a b le s u g g e s tio n s f o r th e d e s ig n o f hy d ro th erm al bombs used in t h i s s tu d y , D rs. S ta n le y F le g le r and Karen Baker o f th e M ichigan S ta te U n iv e r s ity C enter f o r E le c tr o n O p tic s fo r th e u se o f and e x p e rt i n s t r u c t i o n on t h e i r scan n in g e le c tr o n m icro sco p es. iii T his stu d y was p a r t i a l l y su p p o rted by g r a n ts from th e N a tio n a l S cien ce F oundation (no. EAR-8023736), The G eo lo g ical S o c ie ty o f A merica (n o . 2 8 3 7 -8 1 ), Sigma X i, and S h e ll O il Company. 1 a ls o w ish to th a n k Sun O il Company and Hunt Energy C o rp o ratio n f o r c o n tr ib u tin g to my s u p p o rt d u rin g th e f i r s t y e a r o f my g ra d u a te stu d y a t M ichigan S ta te U n iv e r s ity . Thanks a r e due to many f r ie n d s in th e Geology D epartm ent who h elp ed me g e t th ro u g h fo u r y e a rs o f s tu d y . P a r t i c u l a r l y Dr. Thomas R. T a y lo r whose stu d y o f th e T ren to n F orm ation was c o n c u rre n t w ith mine and p o rv id ed in v a lu a b le i n s i g h t s and in fo rm a tio n , and Mr. A lan D. T r ip p e l w ith o u t whose a s s is ta n c e 1 d o ubt 1 co u ld ev er have o b ta in e d a s in g le t h i n s e c ti o n . For t h e i r encouragem ent and f r ie n d s h ip . I w ish to th an k Bud Ifoyer, Mary J a n k , M elissa Wardlaw, Mick H a r tz e l, A b o lfa z l Jam eo ssan aie, Tom Fox, Dan O rr, L o r e tta S a tc h e l and C a rl K arlo w sk i. sh o u ld n o t f o r g e t K athy C asw ell and L o r e tta Knutson f o r making s u re t h a t 1 g o t my m ail among o th e r th i n g s . A p a r t i c u l a r th a n k s goes to my s i s t e r M argaret Lynn Gregg H a e rtlin g who c o n trib u te d artw o rk used in some o f th e c o p ie s o f t h i s d is s e rta tio n . F i n a l l y , and most im p o rta n tly o f a l l , I w ish to th a n k my w ife , Mickey and my c h i ld r e n , N ich o las and T r i c i a , f o r p ro v id in g me w ith s u p p o rt and encouragem ent and f o r t h e i r p a tie n c e and u n d e rs ta n d in g , w ith o u t which 1 co u ld have n ev er com pleted t h i s s tu d y . iv 1 TABLE OF CONTENTS Page LIST OF TABLES v li LIST OF FIGURES v iii INTRODUCTION 1 D olom ite R e c r y s t a l l i z a t i o n - P rev io u s Wbrk 3 Tem perature R e la te d O rig in o f X enotopic Dolom ite 5 EFFECTS OF TEMPERATURE ON CRYSTAL GROWTH - THEORY 7 SAMPLES USED IN STUDY 12 The T ren to n and G alena D olom ites 12 The Hueco D olom ite and D olo m itic M arble 16 Cenozoic D olom ites 16 METHODS' 16 RESULTS 20 Proposed C l a s s i f i c a t i o n System f o r D olom ite T ex tu res 20 E x p erim en tal R e s u lts 29 A rag o n ite to D olom ite and LMC 34 HMC to D olom ite and LMC 42 R e c ry s ta lliz a tio n 46 Experim ents P e tro g ra p h y , SEM and D is tr ib u t io n of th e Hueco D olom ites 51 P e tro g ra p h y , SEM and D is tr ib u tio n of th e G alena D olom ites 60 P e tro g ra p h y , SEM and D is tr ib u t io n of th e T ren to n D olom ites 74 R e su lts o f S ta b le Is o to p e A nalyses 86 X -ray D i f f r a c t io n o f Hueco, G alena and T ren to n D olom ites 92 v TABLE OF CONTENTS (continued) Page DISCUSSION 92 A p p lic a tio n o f C r y s ta l Growth Theory to C arb o n ate T e x tu re 92 Neomorphism o f D olom ite 99 The O rig in o f X en o to p ic D olom ite: G alena Group 102 S ta b le Is o to p e S tu d ie s 102 O ther E vidence f o r Neomorphism o f G alena D olom ites 103 The O rig in o f X enotopic D olom ite: T ren to n F orm ation 104 S ig n if ic a n c e and F u r th e r Study 107 CONCLUSIONS 108 APPENDICES 111 BIBLIOGRAPHY 146 vi LIST OF TABLES Page T able 1. D olom ite T ex tu res and F a b ric s T ab le 2. Q u a lita tiv e D iffe re n c e s Between Id io to p ic -B and X enotopic-A T ex tu res i n D olom ites T ab le 3. 22 26 C r i t e r i a f o r R ecognizing a P re s e rv e d Rhombic C r y s ta l Face J u n c tio n i n A Compromise Boundary 30 T ab le 4„ P o in t C ounting R e s u lts f o r D olom ite C l a s s i f i c a t i o n 31 T able 5. E x p erim en tal R e su lts 32 T ab le 6 . S ta b le Is o to p e V alues f o r Hueco D olom ites 87 T able 7. S ta b le Is o to p e V alues f o r th e G alena Group 90 vii LIST OF FIGURES Page 2 F ig u re 1. I d io to p ic d o lo m ite t e x t u r e . F ig u re 2. X enotopic d o lo m ite t e x t u r e . 2 F ig u re 3. R e la tiv e s u r f a c e f r e e energy as a fu n c tio n o f th e f r a c t i o n o f s u r f a c e s i t e s on a c r y s t a l f a c e which a r e o c c u p ie d . 9 D is tr ib u t io n o f T ren to n F orm ation d o lo m ite f a c i e s in th e M ichigan B asin . 14 F ig u re 5 . Upper M is s is s ip p i V a lle y le a d - z in c d i s t r i c t . 15 F ig u re 6. M arble Canyon, C ulberson C ounty, Texas 17 F ig u re 7. Proposed d o lo m ite t e x t u r a l c l a s s i f i c a t i o n . 23 F ig u re 8. " C ry s ta l f a c e ju n c tio n s " p re s e rv e d by s t r a i g h t compromise b o u n d a rie s. 27 F ig u re 9. How a " c r y s t a l f a c e ju n c tio n " form s. 28 F ig u re 10 . U n a lte re d s k e l e t a l a r a g o n ite o f pelecypod Area, p o n d ero sa. 35 A rea pon d ero sa a f t e r a l t e r a t i o n to d o lo m ite X 2 4 "h rs. 0 300°C). 37 A rea pon d ero sa a l t e r e d to d o lo m ite (24 h r s @ 300*C). 37 Area pon d ero sa a l t e r e d to d o lo m ite (2 weeks @ 250®C). 39 Area p o n d ero sa a l t e r e d to d o lo m ite (23 h r s @ 250°C). 39 Area pon d ero sa a l t e r e d to c a l c i t e (2 weeks 0 250*0). 41 F ig u re 4 . F ig u re 11 F ig u re 12 . F ig u re 13 . F ig u re 14 . F ig u re 15 . F ig u re 16 . F ig u re 17 . F ig u re 18 . F ig u re 19 . Area pon d ero sa a l t e r e d to c a l c i t e (1 week 0 W c ). 41 HMC s k e l e t a l m a te r ia l from th e c o r a l l i n e a lg a e G o n io lith o n sp . 43 G o n io lith o n s p . (HMC) a l t e r e d to d o lo m ite (60 days 0 300°C ). 45 G o n io lith o n s p . (HMC) a l t e r e d to LMC (2 weeks 0 300°C). 45 viii LIST OF FIGURES (continued) F ig u re 20. U n altered s u p r a ti d a l d o lo m ite from Andros I s la n d , Bahamas. F ig u re 21. S u p r a tid a l n o n - s to ic h io m e tr ic d o lo m ite from Andros I s la n d , Bahamas. F ig u re 22. U n a lte re d d o lo m itiz e d c o r a l l i n e a lg a e from B o n a ire , N.A. F ig u re 23. D o lom itized c o r a l l i n e a lg a e from B o n aire, F ig u re 24. I d io to p ic -B d o lo m ite o f th e HuecoL im estone, M arble Canyon, Texas. F ig u re 25. I d io to p ic -B Hueco d o lo m ite . F ig u re 26. Tem perature g r a d ie n t a t M arble Canyon. F ig u re 27. D olom ite c r y s t a l te rm in a tio n s (D) in a c a l c i t e f i l l e d vug (C ). F ig u re 28. Hueco d o lo m ite m arb le. F ig u re 29. Hueco d o lo m ite m arb le. N.A. F ig u re 30. D olom ite produced by h y d ro th erm al a l t e r a t i o n o f a p e r i c l a s e m arb le. F ig u re 31. D olom ite produced by h y d ro th erm al a l t e r a t i o n o f a p e r ic la s e m arb le. F ig u re 32. Id io to p lc -D d o lo m ite r e p la c in g lim esto n e m i c r it e o f th e G alena Group ( l o c a l i t y 4 5 ). F ig u re 33. Id io to p ic -D d o lo m ite (d a rk ) r e p la c in g c a l c i t e m i c r it e ( l i g h t ) o f th e G alena Group. F ig u re 34. I d io to p ic -B G alena d o lo m ite from F ig u re 35. I d io to p ic B G alena d o lo m ite from l o c a l i t y 20. F ig u re 36. Id io to p ic -A G alena d o lo m ite from F ig u re 37. X enotopic-A G alena d o lo m ite from l o c a l i t y 45. F ig u re 38. X enotopic-A G alena d o lo m ite (d a rk ) re p la c in g c a l c i t e ( l i g h t ) from l o c a l i t y 45, F ig u re 39. X enotopic-A G alena d o lo m ite from l o c a l i t y 19. F ig u re 40. X enotopic-A G alena d o lo m tie from l o c a l i t y 19. l o c a l i t y 20. l o c a l i t y 28. LIST OF FIGURES (continued) Page F ig u re 41. F ig u re 42. F ig u re 43. F ig u re 44. F ig u re 45. F ig u re—46. F ig u re 47. F ig u re 48. F ig u re 49. I d io to p ic - B d o lo m ite r e p la c in g m ic r ite in th e "cap" o f th e T ren to n Form ation (Br c o r e ) . 76 I d io to p ic -B d o lo m ite from th e "cap" o f th e T ren to n F o rm atio n . 76 X enotopic-A f r a c t u r e r e l a t e d d o lo m ite from th e T ren to n F o rm atio n . 77 D o lo m itized b io m ic r ite from th e "cap" o f th e T ren to n F o rm atio n . 80 X enotopic-A d o lo m ite r e p la c in g a f o s s i l in th e "cap" o f th e T re n to n F orm ation. 80 Saddle shaped X enotopic-C d o lo m ite growing in to f r a c t u r e p o r o s ity o f th e T ren to n F orm ation. 82 Anhedra o f x en o to p ic-C d o lo m ite ( l i g h t ) p a r t i a l l y r e p la c in g a c a l c i t e b rach io p o d frag m en t in th e T ren to n F orm atin "cap ". 85 X enotopic-C d o lo m ite r e p la c in g lim e sto n e m ic r ite alo n g a f r a c t u r e in th e T ren to n F orm ation. 85 1»0 v a lu e s f o r Hueco d o lo m ite s p lo tte d a g a in s t te m p e ra tu re and d is ta n c e from th e in tru s io n . 88 x INTRODUCTION Dolom ite i s u s u a lly re c o g n iz e d in th i n s e c tio n by th e e u h e d ra l rhom bic c r y s t a l form , i . e . F ried m an 's (1965) i d i o to p ic te x tu r e ( f ig . 1 ). However, in a n c ie n t r o c k s , d o lo m ite s can o f te n be found a s m osaics o f a n h e d ra l c r y s t a l s w ith i r r e g u l a r g r a in b o u n d aries and u n d u lo se e x t i n c t i o n . This t e x t u r e ( f i g . 2) f a l l s in to F ried m an 's (1965) x en o to p ic t e x t u r a l c a te g o ry and i s s im ila r to neom orphic te x tu r e s o b serv ed in some lim e s to n e s , p a r t i c u l a r l y n eo sp ars and m ic ro sp a rs (F o lk , 1965 and B a th u r s t, 1 9 7 6 ). The h y p o th e s is i s in v e s t ig a t e d t h a t x e n o to p ic d o lo m ite te x tu r e r e s u l t s from th e rep la cem e n t o f lim e sto n e by d o lo m ite o r by neom orphic r e c r y s t a l l i z a t i o n o f a p r e - e x i s t in g d o lo m ite a t e le v a te d te m p e ra tu re (above %5 0 ° ) . T his h y p o th e s is i s te s t e d by: 1) p e tro g r a p h ic a n a ly s is to d eterm in e tim in g o f d o lo m itiz a tio n and th e d i s t r i b u t i o n o f t e x t u r a l ty p e s , 2) p e tro g r a p h ic a n a ly s is o f a c o n ta c t m etam orphic d o lo m ite , 3) la b o r a to r y ex p erim en ts u sin g h y d ro th erm al bombs to r e c r y s t a l l i z e d o lo m ite s and produce h ig h te m p e ra tu re rep lacem en t d o lo m ite s, and 4) im p lic a tio n o f c r y s t a l grow th th e o r y . R e c r y s t a l l i z a t i o n o r Neomorphism o f D olom ite Neomorphic d o lo m ite i s d e fin e d h e re a s any d o lo m ite te x tu r e r e s u l t i n g from th e r e c r y s t a l l i z a t i o n o f a p r io r e x i s t in g d o lo m ite . This vrould in c lu d e th e in v e r s io n p ro c e s s by which p ro to d o lo m ite (G a in e s, 1977) becomes s to ic h io m e tr ic , w e ll o rd e re d d o lo m ite . T his would n o t in c lu d e th e d o lo m itiz a tio n o f a c a l c i t e o r a r a g o n ite se d im en t. The usage o f B eals and Hardy (1976) to d e s c rib e " . . . a d o lo s to n e in which th e o r i g i n a l lim e s to n e te x tu r e i s e n t i r e l y 1 2 Figure 1 Idiotopic dolomite texture? idealized representation. Figure 2 . Xenotopic dolomite texture; idealized representation. o b l i t e r a t e d , " I s d is r e g a r d e d h e r e . F olk (1965) and B a th u rs t (1976) rec o g n iz e d s e v e r a l ty p e s o f neomorphism In lim e s to n e s . These I n c lu d e : 1) polym orphic tr a n s f o r m a tio n ( B a th u r s t, 1976) o r in v e r s io n (F o lk , 1965) w hich in v o lv e s th e change o f one polym orph in to a n o th e r such a s a r a g o n ite in t o c a l c i t e , 2) a g g ra d in g neomorphism, whereby f in e c r y s t a l l i n e c a rb o n a te i s re p la c e d by a c o a rs e c r y s t a l l i n e m osaic o f th e same m a te ria l. T h is p ro c e s s may b eg in in p a r t l y c o n s o lid a te d sed im en ts and r e s u l t i n a s p a r r y t e x t u r e t h a t i s d i f f i c u l t and sometimes im p o s s ib le to d i s t i n g u i s h from a v o id f i l l i n g cem ent. 3) Uet r e c r y s t a l l i z a t i o n in v o lv in g th e grow th o f la r g e g r a in s a t th e expense o f s m a lle r o n e s . T h is p ro c e ss may o c c u r d u rin g th e l a t e s ta g e s o f ag g ra d in g neom orphism . Neomorphic lim e s to n e s a re c h a r a c te r iz e d by a n h e d ra l c r y s t a l s w ith i r r e g u l a r i n t e r g r a i n b o u n d a rie s . Some a n c ie n t d o lo m ite s t e x t u r a l l y resem b le c a l c i t e n e o sp a rs i n t e r p r e t e d to have formed by ag g ra d in g neomorphism. T his le a d s to th e s p e c u la tio n t h a t su ch d o lo m ite te x tu r e s a r e th e r e s u l t o f a g g ra d in g neomorphism o r r e c r y s t a l l i z a t i o n o f a p r e - e x i s t in g f i n e r g ra in e d d o lo m ite . D olom ite R e c r y s t a l l i z a t i o n - P re v io u s Work C e rta in te x t u r e s have been re c o g n iz e d a s e v id en ce o f d o lo m ite neom orphism , o r r e c r y s t a l l i z a t i o n . The Sevey D olom ite (D ev o n ian ), Nevada was d e s c rib e d by Osmond (1954) a s an in t e r lo c k i n g m osaic o f d o lo m ite an h ed ra made up o f i r r e g u l a r sh ap ed , c lo s e ly packed, c l e a r c ry s ta ls . These c r y s t a l s ran g ed in s i z e from 0.02mm to 0.09mm w ith most ab o u t 0.05mm. S c a tte r e d s u b h e d ra l d o lo m ite p o rp h y ro to p es were th o u g h t to r e p r e s e n t r e c r y s t a l l i z a t i o n s o f th e s m a lle r a n h e d ra l c ry s ta ls . U n f o r tu n a te ly , Osmond d id n o t p ro v id e a pho to m icro g rap h w ith h i s d e s c r i p t i o n . A q u a n t i t a t i v e stu d y o f g r a in m osaic geom etry was made by K arez (1964) on s e v e r a l Cambrian d o lo m ite s from th e I s l e o f Skye, S c o tla n d . By r e c o rd in g th e fre q u e n c y and shape o f t r i p l e ju n c tio n s betw een c r y s t a l s and m easu rin g th e i n t e r f a c i a l a n g le s o f th e s e ju n c tio n s i t was d eterm in ed t h a t f e a t u r e s a t t r i b u t a b l e to r e c r y s t a l l i z a t i o n e x i s t . G rain grow th was in d i c a te d by an i n t e r f a c i a l a n g le freq u en cy d i s t r i b u t i o n w ith a maximum in th e ran g e o f 100° to 1 4 0 °, i . e . , g r e a t e r th a n 90% o f th e t r i p l e ju n c tio n s m easured were o b tu s e a n g le s . Schmidt (1965) re c o g n iz e d th r e e d i s t i n c t k in d s o f r e c r y s t a l l i z a t i o n o f d o lo m ite in th e G igas beds o f n o rth w e s te rn Germany: 1) R e c r y s ta lli z e d d o lo m ite t h a t i s a s s o c ia te d w ith ir o n s ilic a te . Here d o lo m ic r ite was r e c r y s t a l l i z e d in to a t e x t u r e made up o f a n h e d ra l and s u b h e d ra l c r y s t a l s . 2) D o lo a re n ite s w hich were r e c r y s t a l l i z e d to a h ig h ly p o ro u s medium w ith a f i n e g r a in i d i o t o p i c te x tu re . g h o s ts . In some a r e a s , th e o r i g i n a l allo ch em s can be o b serv ed as The o r i g i n a l i n t e r g r a n u l a r p o r o s ity and allo ch em mold p o r o s ity w ere r e d i s t r i b u t e d as i n t e r c r y s t a l l i n e and m icrovuggy p o r o s ity (S ch m id t, 1965, f i g . 2 0 - 2 ) . 3) Nonporous d o lo m ite h av in g a m a rb le - lik e te x tu r e made up o f t i g h t in t e r lo c k i n g medium to c o a rs e a n h e d ra l d o lo m ite c r y s t a l s was o b serv ed n e a r f a u l t s . S tr a in d u rin g o v e r th r u s t f a u l t i n g was th o u g h t by Schmidt (1965, f i g . 2 1-2) to be re s p o n s ib le f o r th e t e x t u r e . In a d is c u s s io n o f t r a c e elem ent and s t a b l e is o to p i c g e o c h e m istry o f d o lo m ite s Land (1980) p o in ts o u t t h a t neomorphism o f a d o lo m ite o r a p ro to d o lo m ite may a f f e c t th e prim ary d o lo m ite ch e m istry ( s e e a ls o Land e t a l . , 1 9 7 5 ). Such a r e a c tio n would not n e c e s s a r i ly be c lo se d w ith r e s p e c t to is o to p e s o r tr a c e e le m e n ts. T h e re fo re , i f r e c r y s t a l l i z a t i o n has ta k e n p la c e th e is o to p e and tr a c e elem ent s ig n a tu r e o f an a n c ie n t ro ck may n o t r e f l e c t th e co m p o sitio n o f th e o r i g i n a l sed im en t. F in e g ra in e d x e n o to p ic d o lo m ite from th e Upper Knox c a rb o n a te s (C am bro-O rdovician) T ennessee a r e th o u g h t to be th e r e s u l t o f a g g ra d in g neomorphism o f a f i n e r g ra in e d d o lo m ite formed i n an i n t r a t i d a l to s u p r a t i d a l environm ent (C hurnet e t a l . , 1 9 8 2 ). Low Na and Sr c o n c e n tr a tio n s and n e a r s to ic h io m e try o f th e s e d o lo m ite s a r e a t t r i b u t e d by th e a u th o rs to neomorphism in th e p re se n c e o f f r e s h w a te r. T em perature R e la te d O rig in o f X enotopic D olom ite X enotopic te x tu r e in d o lo m ite may be r e l a t e d to th e te m p e ra tu re a t which th e p r e - e x i s t in g lim e sto n e was d o lo m itiz e d . Some ev id en ce e x i s t s in th e l i t e r a t u r e to s u p p o rt t h i s h y p o th e s is . Land (1967) d o lo m itiz e d a fragm ent o f th e P elecypod A rgina sp . i n a calciu m and magnesium c h lo r id e s o lu tio n w ith in th e d o lo m ite s t a b i l i t y ran g e a t 300°C in a h y d ro th erm al bomb f o r 22 h o u rs . The a r a g o n ite s h e l l fragm ent became p a r t i a l l y r e p la c e d by x e n o to p ic d o lo m ite . D olom ite, form ing d ik e s and pods in th e Wyman F o rm atio n , i s i n t e r p r e te d a s a rep la cem e n t o f lim e s to n e (Z en g er, 1 976). This rep lacem en t p ro b ab ly to o k p la c e under low g rad e m etam orphic c o n d itio n s and seems to have r e s u l t e d in a x e n o to p ic te x tu r e ( s e e 6 Z enger, 1976, f i g . 5 ). Radke and M athis (1980) i n f e r r e d a hig h te m p e ra tu re o r i g i n (60°-150°C ) fo r sa d d le d o lo m ite s . A sso ciated w ith p o re f i l l i n g s a d d le cem ents one o f te n o b se rv e s u n d u lo se sa d d le d o lo m ite s (x e n o to p ic d o lo m ite s) as a rep lacem en t phase (Radke and M ath is, 1980, fig . 8 ). A h ig h te m p e ra tu re (50°-130°C ) o r i g i n f o r u n d u lo se f e r r o a n d o lo m ite cem ents found in M is s is s ip p ia n c a rb o n a te s o f th e I l l i n o i s B asin was a ls o fav o red by C hoquette (1 9 7 0 ). Zenger (1980) s u g g e s ts t h a t h ig h te m p e ra tu re r e c r y s t a l l i z a t i o n a n d /o r rep la cem e n t may have produced c o a rs e , u n d u lo se x e n o to p ic d o lo m ite in th e L i t t l e F a ll s D olostone (Upper C am brian), e a s t - c e n t r a l New Y ork. S e v e ra l f l u i d in c lu s io n a n a ly se s s u p p o rte d by 5^-®0 v a lu e s in d i c a te te m p e ra tu re s > 80°C d u rin g th e fo rm a tio n o f th e s e d o lo m ite s . F a ir c h i ld (1980) d e s c rib e d un d u lo se d o lo m ite from th e P recam brian o f S co tlan d which he a t t r i b u t e s to h ig h te m p e ra tu re (150°-200°C ) r e c r y s t a l l i z a t i o n and rep la c e m e n t. The d if f e r e n c e betw een th e id i o t o p i c (e u h e d ra l rhombs) and x e n o to p ic (a n h e d ra l c r y s t a l s w ith i r r e g u l a r g r a in b o u n d a rie s) rep lacem en t te x tu r e s may be th e te m p e ra tu re a t w hich d o lo m itiz a tio n to o k p la c e ; h ig h te m p e ra tu re s pro d u cin g x en o to p ic te x tu r e and low te m p e ra tu re s p ro ducing i d i o to p ic t e x t u r e . N.A. D olom ite from B o n aire, r e p la c e s a r a g o n ite and h ig h magnesium c a l c i t e (HMC) w ith an i d i o t o p i c (rhom bic) h a b i t . O ther Q u atern ary d o lo m ite s from around th e hdr i d a ls o re p la c e s u b s t r a te calcium ca rb o n a te w ith e u h e d ra l to su b h e d ra l c r y s t a l s (S c h la n g e r, 1957; U l i n g e t a l . , 1965; B u chbinder, 1979; McKenzie, 1981; and S ib le y , in p r e s s , and many o t h e r s ) . In a l l o f th e s e c a s e s , i t i s d o u b tfu l th a t d o lo m itiz a tio n to o k p la c e a t h ig h e r th a n n e a r s u r f a c e te m p e ra tu re s . EFFECTS OF TEMPERATURE ON CRYSTAL GROWTH - THEORY The te m p e ra tu re a t which c r y s t a l s grow can a f f e c t th e mode o f grow th ( B r ic e , 1973; L ew is, 1975; K ir k p a tr ic k , 1981) and u ltim a te ly th e te x tu r e o f a m osaic o f th e s e c r y s t a l s . A s t a t i s t i c a l m ech an ical model f o r th e s u r f a c e s t r u c t u r e and k i n e t i c s o f grow th o f c r y s t a l s grow ing from a m e lt i s g iv e n by Jack so n (1958a and 1958b). J a c k s o n 's work i s summarized a s fo llo w s : The change in f r e e energy (AFS) o f a growing c r y s t a l s u r f a c e i s d iv id e d in to fo u r com ponents: 1) th e energy g ain ed by th e a d d i tio n o f atoms on th e c r y s t a l s u r f a c e , 2) th e energy g ain ed because some o f th e atoms added to th e s u rfa c e w i l l be a d ja c e n t to one a n o th e r , 3) th e en tro p y d if f e r e n c e between th e c r y s t a l fa c e and th e phase in w hich i t i s g row ing, 4) th e e n tro p y g ain ed by th e random arrangem ent of atoms on th e c r y s t a l s u r f a c e . I f te m p e ra tu re i s a t th e m e ltin g p o in t (te m p e ra tu re a t e q u ilib riu m so T = Tg ) th e above can be e x p re sse d a s : AF /NkT s e = a N (1-N )/N 2 - ln[N /(N -N ) J - (N /N )ln[(N -N )/N J a a a a a eq . 1 where N i s th e number o f s i t e s on th e c r y s t a l fa c e a v a i la b l e f o r o c c u p a tio n , and Na i s th e number o f s in g le atoms (m o lecu les o r io n s ) added to th e s u r f a c e . The term i s a roughness p aram eter d e riv e d from th e r e l a t i o n s h i p a= (L/kTe )(N0 /v ) =A S/k(N 0 /v ) L eq. 2 en erg y needed to ta k e an atom from th e c r y s t a l and put i t in to th e phase in which th e c r y s t a l 8 i s g row ing, [L a te n t h e a t o r e n th a lp y o f fo rm a tio n o f th e vapor p h a se , l i q u i d phase o r l a t e n t h e a t o f d i s s o l u t i o n (L ew is, 197)5).] AS th e change i n e n tro p y betw een th e c r y s t a l and th e phase in which i t i s grow ing, k Te N0 /v B o ltzm an 's c o n s ta n t e q u ilib r iu m te m p e ra tu re . th e f r a c t i o n o f th e t o t a l number o f n e a r e s t n e ig h b o rs i n a p la n e p a r a l l e l to th e fa c e u n d er c o n s id e r a tio n to th e t o t a l number o f p o s s ib le n e a r e s t n e ig h b o rs . [The f r a c t i o n o f th e t o t a l b in d in g en erg y p e r atom o p e r a tin g in th e p la n e o f th e s u r f a c e ( K ir k p a tr ic k , 1 9 8 1 ).] This w i l l f a l l betw een 0 .5 and 1. The ro u g h n ess p a ra m e te r, a, i s d i r e c t l y p r o p o r tio n a l to L and in v e r s e l y p r o p o r tio n a l to Te . As th e te m p e ra tu re o f th e r e a c tio n i n c r e a s e s , a becomes s m a lle r . F ig u re 3 shows th e r e l a t i o n s h i p in e q u a tio n 1 g r a p h ic a ll y . C urves a r e drawn f o r v a rio u s v a lu e s o f a. F or any a l e s s th a n 2 th e r e i s a minimum a t Na /N = 0 .5 on th e h o r iz o n t a l s c a le (1 /2 o f th e p o s s ib le s u r f a c e s i t e s a r e f i l l e d ) . F re e en erg y ( th e v e r t i c a l s c a le ) t h e r e f o r e has a minimum v a lu e when 1 /2 o f th e s i t e s a r e f i l l e d . As th e p r o b a b i l i t y o f th e fo rm a tio n o f c l u s t e r s o f atoms on th e h a l f f i l l e d s u r f a c e i s la r g e , new la y e r s may s t a r t to form b e fo re th e i n i t i a l la y e r i s f i l l e d . This w i l l r e s u l t in random a d d itio n o f atoms on an a to m ic a lly rough c r y s t a l s u r f a c e and r a p id c o n tin u o u s gro w th . T his ty p e o f grow th w i l l produce n o n fa c e te d c r y s t a l s as opposed to c r y s t a l s w ith w e ll dev elo p ed 9 1.0 111 uj ui 0.3 “ “ cm - . 0.5 OCCUPIED FRACTION OF SURFACE SITES Figure 3. Relative surface free energy as a function of the fraction of surface sites on a crystal face which are occupied; a depends on the crystal face, th<£ type of crystal and the phase from which the crystal is growing (from Jackson, 1958a). 10 c r y s t a l fa c e s (J a c k so n , 1 958). A m osaic o f n o n fa c e te d c r y s t a l s produces th e in te r lo c k in g a n h e d ra l g r a in m osacis such as o b serv ed in m e tal c a s tin g s ( a l l m e ta ls grow from t h e i r m e lts a t 1 9 5 8 )). a <2 (Jack so n , M osaics o f euhedra can o n ly be produced i f c r y s t a l fa c e s develop d u rin g th e grow th o f th e c r y s t a l s . At any a>2 t h e r e a r e t w Na 53 0. Na = 0 .5 . minima, one n ear Na = N and one n ear The maximum, o r h ig h e s t f r e e energy c o n f ig u r a tio n , i s a t Thus new atoms must be added one la y e r a t a tim e as p a r t i a l f i l l i n g o f a new la y e r i s e n e r g e tic a lly u n fa v o ra b le . Growth i s , th e r e f o r e , d i f f i c u l t and p ro ceed s by u se o f s u r f a c e im p e r f e c tio n s , such a s screw d i s l o c a t i o n s , as d e s c rib e d by B urton and C abrera (1949) and F rank (1 9 4 9 ). Under th e s e c o n d itio n s c r y s t a l fa c e s w i l l d ev elo p d u rin g grow th and m osaics o f e u h e d ra l and su b h e d ra l c r y s t a l s w i l l form . T his i s th e case when a m a te r ia l such as s a l o l i s s o l i d i f i e d from a m e lt (J a c k so n , 19 5 8 a). At a= 2 a t r a n s i t i o n between a rough and a smooth c r y s t a l s u r f a c e i s a t ta in e d . T his o c c u rs a t a s p e c i f i c te m p e ra tu re f o r a s p e c i f i c c r y s t a l f a c e . Below t h i s " c r i t i c a l roughening te m p e ra tu re " (CRT) a w i l l be g r e a t e r th a n 2 and th e c r y s t a l s u r f a c e w i l l be smooth. Above CRT a w i l l be l e s s th a n 2 and th e s u r f a c e w i l l be ro u g h . Temkin (1966) a r r iv e d a t s im i la r c o n c lu sio n s a s Jack so n (1958a and 1958b) u s in g a m u l ti- l a y e r mean f i e l d model. T his model does not g iv e a CRT; r a t h e r , a s te m p e ra tu re in c r e a s e s th e c r y s t a l fa c e becomes co n tin u o u s ly ro u g h e r. E x p erim en tal ev id en ce in d i c a te s t h a t th e CRT f o r c r y s t a l s growing from a m elt a r e s l i g h t l y h ig h e r th a n p r e d ic te d (Jack so n and G ilm er, 1 9 7 6 ). T his may be because o f low w e t t a b i l i t y (h ig h 11 ' i n t e r f a c l a l te n s io n ) o f th e c r y s t a l fa c e which has th e e f f e c t o f I n c r e a s in g th e r e a l a o v e r th e t h e o r e t i c a l l y p r e d ic te d t h e o r e t i c a l l y p r e d ic te d a. The assumes a h ig h w e t t a b i l i t y o f c r y s t a l f a c e s and, th e r e f o r e , th e t h e o r e t i c a l e s tim a te s o f i n t e r f a c l a l f r e e energy (AFS) may be low ( Z e l l and M u ta fts c h ie n , 1 9 7 2 ). The CRT o f c r y s t a l s grow ing from th e vap o r phase has been found e x p e rim e n ta lly to be low er th a n p r e d ic te d by a f a c t o r o f two. T his phenomenon i s n o t w e ll u n d ersto o d b u t may be due to th e m o b ility o f th e atoms added to th e s u rfa c e o f th e c r y s t a l (Jack so n and G ilm er, 1976 and Jack so n and H i l l e r , 1977). Replacem ent o f a calcium c a rb o n a te by d o lo m ite in v o lv e s a d i s s o l u t i o n r e p r e c i p i t a t i o n mechanism w ith an aqueous phase ( B a th u r s t, 1976 and K atz and M atthew s, 1 9 7 7 ). T h e re fo re , any a p p l ic a t io n o f th e above d is c u s s e d p r in c i p le s o f c r y s t a l grow th to d o lo m itiz a tio n must in v o lv e grow th o f d o lo m ite c r y s t a l s from a s o lu ti o n . J a c k s o n 's (1958a and 1958b) model can t h e o r e t i c a l l y be a p p lie d to grow th o f c r y s t a l s from s o lu ti o n (Bennema, 1974; Lew is, 1 975). S e v e ra l s tu d ie s ap p ly J a c k s o n 's (1958a) model to c r y s t a l grow th from s o lu tio n f o r exam ple: Veronkov and Chernov (1967) c a lc u la te d t h a t th e c r i t i c a l roug h en in g te m p e ra tu re i s dependent on th e c o n c e n tr a tio n o f th e s o lu ti o n ; th e more c o n c e n tra te d th e s o lu tio n th e low er th e CRT. A com puter s im u la tio n model developed by Bennema and Van d er Eerden (1977) i s u sed to c a l c u l a t e J a c k s o n 's (1958a) a f o r o r g a n ic c r y s t a l s grow ing in o r g a n ic and aqueous s o lv e n ts . C o rre c tio n s a re made f o r w e t t a b i l i t y and th e problem t h a t l a t e n t h e a t o f d i s s o l u t i o n i s n o t a c c u r a te ly known when s o l i d p a r t i c l e s a r e d is s o lv e d in 12 s a tu r a t e d s o lu ti o n s . Among th e d i f f i c u l t i e s in c a l c u la tin g th e CRT f o r a c a rb o n a te m in e ra l i s o b ta in in g a l a t e n t h e a t v a lu e a t s a t u r a t i o n ( e q u ilib r iu m ) . T h is i s n o t known f o r many s u b s ta n c e s , in c lu d in g d o lo m ite , and i s co m p lica ted by th e la r g e h y d ra tio n e n e rg ie s a s s o c ia te d w ith th e calciu m and magnesium io n s . A lso , because d o lo m ite does n o t form sim p le monoatomic c r y s t a l s in th e c u b ic sy stem , i t i s d i f f i c u l t to q u a n t i t a t i v e l y ap p ly J a c k s o n 's (1958a) m odel, (to st t h e o r e t i c a l work has been done on sim p le monatomic c u b ic c r y s t a l s u sin g com puter s im u la tio n te c h n iq u e s . A lthough th e sim p le model f o r c r y s t a l grow th must a p p ly to complex c r y s t a l s , many c o m p lic a tin g f a c t o r s make an a c c u r a te p r e d ic tio n o f th e CRT d i f f i c u l t (K.A. Jack so n , w r itt e n com m unication, 1 981). The model i s , how ever, o f c o n s id e ra b le u se i n q u a l i t a t i v e l y u n d e rs ta n d in g c r y s t a l grow th and m orphologies ( K ir k p a tr ic k , 1981). SAMPLES USED IN STUDY The T ren to n and G alena D olom ites The T ren to n F orm ation (M iddle O rd o v ic ia n ), M ichigan and G alena Group (M iddle O rd o v ic ia n ), W isco n sin , n o r th e r n I l l i n o i s and e a s te r n Iowa were chosen f o r t h i s stu d y b eca u se : 1) th e y have a wide ran g e o f d o lo m ite te x tu r e s ra n g in g from x e n o to p ic to i d i o t o p i c , 2) t h e i r g e o lo g ic h is to r y in c lu d e s deep b u r i a l in th e case o f th e T ren to n Form ation and e p ig e n e tic h y d ro th erm al a c t i v i t y in th e case o f both th e T ren to n F orm ation and th e G alena G roup, 3) th e a v a i l a b i l i t y o f enough sample c o n tr o l to conduct th e s tu d y . The lim e sto n e f a c i e s o f th e T ren to n Form ation a r e composed 13 p r im a r ily o f un ifo rm b io m ic r ite s which were d e p o s ite d below wave b ase in a low energy open m arine en v iro n m en t. There i s no ev id en ce o f r e e f developm ent in th e T renton and i t i s b e lie v e d to be p a r t o f a sh allo w m arine s h e lf complex (A rd re y , 1 9 7 8 ). Three b a s ic f a c i e s o f d o lo m ite e x i s t in th e T ren to n F orm ation o f th e M ichigan B asin ( f i g . 4 ) . These a r e 1) th e cap d o lo m ite in v o lv in g th e u p p er 50 f e e t o f th e fo rm a tio n , 2) e p ig e n e tic d o lo m itiz a tio n a s s o c ia te d w ith f r a c t u r i n g , in c lu d in g th e n o r th e a s t to so uthw est tre n d in g A lbion S cip io and N o r th v ille o i l f i e l d s , and 3) r e g io n a l d o lo m itiz a tio n in th e so u th w e ste rn p a r t o f M ichigan (S tew ard , 1957; Shaw, 1975; N ew hart, 1976; A rd rey , 1978; T a y lo r, 1982). The lim e s to n e f a c i e s o f th e G alena Group a r e composed o f b io m ic r ite s and a few b i o s p a r i t e s t h a t were d e p o s ite d on a s t a b l e , u n ifo rm , low energy se a b o ttom , in most c a se s below wave base (D elgado, 1979 and w r itt e n com m unication, 1 980). Badiozamani (1972 and 1973) p o s tu la te d a dorag o r m ixing zone model f o r r e g io n a l d o lo m ite s d u rin g th e u p l i f t o f th e W isconsin A rch. D olom ite i s lo c a liz e d along th e c r e s t o f th e a rc h becoming lim e sto n e tow ard th e f la n k s o f th e a rc h (B adiozom ani, 1973). The G alena Group was s u b je c te d to an e p ig e n e tic h y d ro th erm al ev en t r e s u l t i n g in th e emplacement o f th e s u l f i d e o re s o f th e Upper M is s is s ip p i V a lle y Z in c -le a d D i s t r i c t ( f i g . 5) (Heyl e t a l . , 1 9 5 9 ). The te m p e ra tu re s o f emplacement o f th e s e o r e s a r e e s tim a te d , by f l u i d in c lu s io n s tu d ie s to have ranged from 80 to 120°C (B a ile y and Cameron, 1 951), to 227°C (McLimans, 1977 and H. L. B arn es, p e rs o n a l com m unication, 1 9 8 2 ). H a ll and Friedm an (1969) c o rro b o ra te th e s e te m p e ra tu re s w ith s t a b l e oxygen is o to p e s (5*®0 SHOW =' 20 f o r d o lo m ite s a s s o c ia te d w ith o r e s ) . 14 HS 5 ' •i Jbion-Scipio kField Northville Field W2 Regional dolom ite 0 10 20m llea E xtent of cap dolom ite • L ocation of core Figure 4. Distribution of Trenton Formation facies in the Michigan Basin. Based on map by Taylor (1982) . IOWA E xtent of su lfid e m ineralization •3 0 S 20 33 •16 • is • WISCONSIN ILLINOIS Collecting Locality Figure 5. 20 mi, Upper Mississippi Valley Zinc-lead District. 16 The Hueco D olom ite and D o lo m ltic M arble A d o lo m itiz e d f a c i e s o f th e Hueco L im estone (W olfcam p), was in tr u d e d by a T e r t ia r y s y e n it e and gabbro s to c k (Kuehn, 1969) in M arble Canyon, C u lb e rts o n C ounty, T ex as. The d o lo m ite was r e c r y s t a l l i z e d in and n e a r a c o n ta c t m etam orphic a u r e o le ra n g in g i n w id th from 150 to 300 f t . ( f i g . 6) (K ing, 1965; B rid g e , 1 9 6 6 ). Near th e in t r u s i o n th e d o lo m ite a l t e r e d to a b le ach ed b r u c i t e - c a l c i t e m arb le w hich i s c u r r e n t ly b ein g q u a r r ie d f o r d e c o r a tiv e s to n e . S ix ty - f i v e sam ples w ere c o l le c t e d from m assiv e d o lo m ite and lim e s to n e s on th e e a s t s id e o f th e M arble Canyon in t r u s i o n ( f i g . 6 ). The sam ples were c o l l e c t e d a t d is ta n c e s ra n g in g from im m ediately a d ja c e n t to th e i n t r u s i o n to 1200 f t . away. C enozoic D olom ites D olom ites o f th e S eroe Domi F orm ation ( P lio c e n e ) , B o n aire and A ruba, N e th e rla n d s A n t i l l e s (s e e S ib le y , 1980) w ere used f o r com parison w ith a n c ie n t and s y n th e t ic d o lo m ite s and u se in h y d ro th erm al bomb e x p e rim e n ts . The P lio c e n e d o lo m ite s w ere n ev er s u b je c te d to o th e r th a n s u r f a c e te m p e ra tu re s . Samples o f r e c e n t s u p r a t i d a l c r u s t s c o n ta in in g a s much a s 60% d o lo m ite (a s d eterm in e d w ith x - r a y a n a ly s is and SEM) w ere o b ta in e d from Andros I s la n d . These sam ples w ere a ls o u sed f o r com parison w ith a n c ie n t and s y n th e t ic d o lo m ite s and in h y d ro th erm al bomb r e c r y s t a l l i z a t i o n e x p e rim e n ts. METHODS The sam ples c o l le c t e d from th e T ren to n F orm atio n (130 sam ples shown on f i g . 4 ) , G alena Group (130 sam ples shown on f i g . 5) and 17 ^ r n m ir n Pb /if f p p g L J § S /ffiss# ' fo :y ::y !;W ' f ^ 7 \ c ^ n ¥ ^ !? V -' ■' r . r i g v ,'••,’.•if ' N/ N fe%vi ' ' >fri£|k VA'.'.V-VA V ' \ , ^ \(n] s / /s . V fe \ ' /* % W * '' Dh 1 »«*,'.■••"•■•I l A / s ' ' Wk W W ' ii:i:-:! :\ Vi.,,«i,,).,,» A ' N_ v V&$#1 v / w / / m \ ^ ' N s ' f e 0 I*. H v Scale w1000 md ft. Lithologies I Alluvium '^ w m . - ' ' Ph Pb" YW&.vS V •< *•■/*••••i. / ' ' ' '* ''~X ' i p t T ortiary Intruaivas ' vfelil Iasi s' • '* * ,Ni f-. .'V;'■ 'A / f e f e ' ' VVv-'.-V /SvA . ■ * ■ ■•.''* A ' ^ •1 4 s. / * ' N ' / ' v. ^ V / i n 0 0 * t sI ' / ' . .‘ ‘..• '• I v U J p M atam o rp h ic s Bona Springs Formation H uaeo F o rm atio n Sections Collected A S am p la s B C TEXAS °Marbla Canyon Figure 6. D E F Marble Canyon, Culberson County, Texas. Geologic map based on King (1965) and Bridge (1966). 1 -5 6 -1 5 1 6 -4 6 47-51 52 53-61 18 Hueco Lim estone (65 sam ples shown on f i g . 6) were made in to s ta n d a rd p e tro g r a p h ic t h i n s e c t i o n s . Some o f th e s y n th e tic d o lo m ite s were made in to t h i n s e c tio n s t h a t were p o lis h e d to l e s s th a n 10 pm th ic k n e s s . Samples were s ta in e d f o r c a l c i t e w ith a l i z e r i n e re d S an d , in some c a s e s , s ta in e d f o r ir o n w ith p o tassiu m f e r r o c y a n id e . S e le c te d t h i n s e c tio n s were p o lis h e d and examined fo r catho d o lu m in escen ce u s in g a N u clid e C orp. model ELM-2A Lum inoscope, 12 to 14 kV (DC), 40 to 50 ma, 0 .5 to 1 cm d ia m ete r beam, co ld cath o d e gun, heliu m g a s , 150 m i l l i t o r r . Samples in c lu d in g th e C enozoic d o lo m ite s and s y n th e tic d o lo m ite s were a ls o examined u s in g IS1 Super I I I and JEOL 35C scan n in g e l e c tr o n m icro sco p es equipped w ith tu n g s te n fila m e n t guns a t 15 to 35 KV. The JEOL 35C was a ls o equ ip p ed w ith a d u a l a n u la r p h o to lith o g r a p h ic d is c b a c k s c a tte r e d e l e c tr o n d e t e c t o r . Some o f th e s y n th e tic d o lo m ite s were examined u s in g an ARL e l e c tr o n m icro p ro b e. Samples were gold o r carbo n co a te d f o r ex am in atio n w ith SEM and carbon co ated f o r m icro p ro b e. Only f r e s h f r a c t u r e o r p o lis h e d s u r f a c e s were exam ined. Samples c o l le c t e d from th e G alena Group and th e d o lo m itiz e d Hueco Lim estone were an aly zed f o r s t a b l e carbon and oxygen is o to p e s ( a t th e U n iv e r s ity o f M ichigan S ta b le Is o to p e L a b o ra to ry ). The sam ples were cru sh ed to a f i n e powder and c lean ed in an a c e to n e s o n ic b a th . Some o f th e sam ples were b o ile d in a s o lu tio n o f disodium EDTA to remove c a l c i t e . A ll o f th e sam ples were examined w ith x -ra y d i f f r a c t i o n to make s u re t h a t d o lo m ite was th e o n ly c a rb o n a te p r e s e n t. S to ic h io m e try and o r d e r in g o f s y n th e tic and n a t u r a l c a rb o n a te s were d eterm in ed u s in g a G en eral E l e c t r i c x -ra y d if f r a c to m e t e r , CuK 19 r a d i a t i o n , Ni f i l t e r , 1° e x i t s l i t and 0 .1 ° and 0 .0 5 ° s c a t t e r s l i t s . Samples were ground to l e s s th a n 10 h a l i t e s ta n d a rd f o r a n a l y s i s . m and mixed w ith a f l u o r i t e o r S to ic h io m e te ry was d eterm in ed from th e p o s itio n o f th e (104) d o lo m ite r e f l e c t i o n o f th e sample r e l a t i v e to th e s ta n d a rd (s e e Lumsden and Chimahusky, 1 980). O rdering in d o lo m ite s was q u a l i t a t i v e l y d eterm in ed by o b s e rv in g th e shape and h e ig h t o f th e (0 0 6 ), (015) and (012) r e f l e c t i o n s r e l a t i v e to th e (110) r e f l e c t i o n (s e e G raf and G o ld sm ith , 1 9 5 6 ). The h y d ro th erm al ex p erim en ts were c a r r i e d o u t u sin g two s t a i n l e s s s t e e l bombs o f 1 8 .5 and 6 .6 m l. c a p a c ity c lo se d copper g a s k e ts (A ppendix 1 ) . Noble m e ta l l i n e r s w ith were n o t used co ld in th e ex p erim en ts as i t seemed u n lik e ly t h a t s t a i n l e s s s t e e l would co n tam in a te th e ex p erim en ts a t th e modest te m p e ra tu re s and p r e s s u r e s u se d . M icroprobe a n a ly s is o f some bomb p ro d u c ts showed ir o n p re s e n t o n ly i n t r a c e amounts ( l e s s th a n 0.1% ). R eac tan t f l u i d s were p re p a re d u sin g s to c k aqueous s o lu tio n s o f 1 and 2 m olar CaCl2 and M gC^. S k e le ta l and sed im en tary c a rb o n a te sam ples were broken in to frag m e n ts w eighing l e s s th a n 0 .0 2 g in o rd e r to e f f e c t a more com plete r e a c tio n w ith th e su rro u n d in g s o lu ti o n . The h y d ro th erm al ex p erim en ts were c a r r i e d o u t in a L indberg H ev i-d u ty m u ffle fu rn a c e and a Sybran Thermolyne 2000 f u r n a c e . T em peratures u sed w ere 250°C and 300°C a t p r e s s u r e s o f 39 and 85 a tm ., r e s p e c t i v e l y . ta b le s . P re s s u re s were c a lc u la te d from s ta n d a rd steam Optimum Mg/Ca r a t i o s and c o n c e n tr a tio n s were found e m p ir ic a lly u s in g p u b lish e d phase diagram s (R osenberg and H o llan d , 1964) f o r maximum d o lo m ite p r o d u c tio n . In th e ex p erim en ts in v o lv in g a r a g o n ite m oH usk frag m en ts d o lo m ite u s u a lly formed as a r e a c tio n rim 20 around th e fragm ent w ith a c e n te r o f in v e r te d c a l c i t e . * T h e re fo re , a b a la n c e had to be e s ta b l is h e d between frag m en ts t h a t were too la r g e (p ro d u cin g a sm all amount o f d o lo m ite in p ro p o rtio n to c a l c i t e ) and th o s e too sm all fo r co n v en ien t l i g h t m icroscope and SEM e x am in atio n . This fragm ent s iz e was found to be between 1 and 3 mm in d ia m e te r. No d i f f i c u l t y was en co u n tered in d o lo m itiz in g h ig h magnesium c a l c i t e (HMC) c o r a l l i n e a l g a l o r e c h in o id fra g m e n ts . In a l l o f th e s e ex p erim en ts 100% d o lo m ite was produced w ith o u t a low magnesium c a l c i t e (LMC) p h a se . In d iv id u a l d o lo m ite c r y s t a l s produced in th e s e ex p erim en ts were too sm all to be o b serv ed w ith l i g h t m icro sco p e. RESULTS Proposed C l a s s i f i c a t i o n System f o r D olom ite T ex tu res D uring th e co u rse o f t h i s stu d y i t became o b v io u s t h a t a t e x t u r a l c l a s s i f i c a t i o n o f d o lo m ite s would have to be developed in in o rd e r to c o n s is te n tly d is ti n g u is h between th e d o lo m ite s b eing s tu d ie d . The te x tu r e o f a ro ck i s a d e riv e d p ro p e rty d eterm in ed by th e i n t e r r e l a t i o n s h i p o f fo u r o f th e fundam ental p r o p e r tie s o f th e g r a in s : 1) s i z e , 2) sh a p e , 3) o r i e n t a t i o n , and 4) p ack in g (se e B l a t t , e t a l . , 1 9 8 0 ). T ex tu re in d o lo m ite i s h e re d e fin e d a s th e r e la tio n s h ip s betw een in d iv id u a l d o lo m ite c r y s t a l s ( i . e . , g r a i n s ) . The a s p e c ts o f th e o r i g i n o f d o lo m ite c r y s t a l s t h a t a r e o f most * In f u r th e r h y d ro th erm al ex p erim en ts o f t h i s ty p e , c a r r ie d o u t by Sue B u llen ( p e rs o n a l com m unication, 1 9 8 2 ), i t was found th a t i f th e a r a g o n ite s h e l l fragm ent was f i r s t o x id iz e d in hydrogen p e ro x id e o r c h lo rin e b le a c h , to remove o rg a n ic m a tte r , com plete d o lo m itiz a tio n o c c u rre d when th e sample was r e a c te d in a bomb. 21 im p o rtan ce i n d is c u s s in g d o lo m ite t e x t u r a l c l a s s i f i c a t i o n s a r e d e n s ity o f n u c le a tio n and grow th mechanisms o f th e c r y s t a l s . These a s p e c ts c o n tr o l th e fu n d am en tal p r o p e r ti e s o f g r a in s iz e and g r a in shape r e s p e c t i v e l y . Friedm an (1965) p ro p o sed a t e x t u r a l c l a s s i f i c a t i o n f o r c r y s t a l l i n e s e d im e n ta ry ro c k s (T ab le 1) w hich was s p e c i f i c a l l y a p p lie d to d o lo m ite s by Friedm an and S an d ers (1 9 6 7 ). T h is c l a s s i f i c a t i o n system re c o g n iz e s th e im p o rtan ce o f c r y s t a l sh ap e ( c r y s t a l te x tu r e ) and r e l a t i v e s iz e and o r i e n t a t i o n o f g r a in s ( c r y s t a l f a b r i c ) a s c o n t r i b u ti n g f a c t o r s to th e o v e r a l l t e x t u r e o f th e ro c k . F rie d m a n 's (1965) t e x t u r a l c l a s s i f i c a t i o n system was found to be in a d e q u a te f o r t h i s stu d y b ecau se i t does n o t d i f f e r e n t i a t e betw een x e n o to p ic te x t u r e s w ith sm ooth, s t r a i g h t compromise b o u n d a rie s and th o s e w ith curved o r i r r e g u l a r i n t e r g r a i n b o u n d a rie s . T h is d i s t i n c t i o n may have c o n s id e r a b le g e n e tic im p o rta n c e . The pro p o sed c l a s s i f i c a t i o n sy stem which was used in t h i s stu d y ( f i g . 7) was d e sig n e d to d i s t i n g u i s h d o lo m ite s on th e b a s is o f c r y s t a l m orphology and g r a in b o u n d a rie s a s opposed to c r y s t a l s i z e . T h e re fo re , th e o v e r r id in g f a c t o r in how a d o lo m ite w i l l be c l a s s i f i e d i s th e mechanism o f c r y s t a l grow th r a t h e r th a n d e n s ity o f n u c le a tio n . A b in o m ial sy stem i s used to c l a s s i f y d o lo m ite . The d o lo m ite i s i n i t i a l l y c a te g o r iz e d a s i d i o t o p i c i f th e g r a in s have s t r a i g h t , compromise b o u n d a rie s and te n d to be rhom bic i n sh ap e; o r x e n o to p ic te x tu r e i f th e g r a in s have m o stly i r r e g u l a r i n t e r g r a i n b o u n d a rie s and te n d to n o t be rhom bic in sh ap e. H y p id io to p ic te x tu r e o f Friedm an (1965) i s c o n s id e re d to be i d i o t o p i c under t h i s sy stem . T able 1. D olom ite T e x tu re s and F a b ric s (from Friedm an, 1965 and Friedm an and S a n d e rs , 1 9 6 7 ). C r y s ta l T e x tu re 1) I n d iv id u a l C r y s ta l (a ) e u h e d ra l (b ) s u b h e d ra l (c ) a n h e d ra l 2) M a jo rity o f c r y s t a l s i n ro ck as a whole (a ) id io to p ic (b ) h y p id io to p ic ( c ) x e n o to p ic C r y s ta l F a b ric s 1 ) E q u ig ra n u la r 2) I n e q u ig r a n u la r ( a ) P o r p h y r o to p ic -la r g e d o lo m ite c r y s t a l s i n a m a trix o f sm a ll c r y s t a l s (b ) P o i k i l o t o p i c - l a r g e d o lo m ite c r y s t a l s in a m a trix o f sm all c r y s t a l s o f a d i f f e r e n t m in e ra l Idiotopic Dolomite- Rhombic shaped euhedral to subhedral grains (idiotopic and hypidiotopic of Friedman (1965)) Idiotopic-E (Euhedral), almost all grains are euhedral rhombs, grain supported with intergranular area filled by another mineral or comprised of porosity (sucrose texture). Idiotopic-S (Subhedral), subhedral to anhedral grains with low porosity or intergranular matrix, straight intergrain boundaries, and grains commonly have preserved crystal face junctions. Xenotopic Dolomite- Non-rhombic usually anhedral grains (xenotopic of Friedman (1965) and saddle dolomites). Xenotopic-A (Anhedral), tightly packed anhedral grains with mostly curved, lobate, serrated, indistinct, or otherwise irregular intergrain boundaries. Preserved crystal face junctions are rare and grains often have undulose extinction under cross polarized light. Xenotopic-C(Cement), pore lining saddle­ shaped or baroque dolomite crystals characterized by scimitar-like terminations and sweeping extinction when observed in thin section. Idiotopic-C (Cement), dolomite euhedra lining large pores, vugs, or patches of another mineral such as gypsum or calcite. Idiotopic-P (Poikilotopic), Floating euhedra of dolomite in a limestone matrix. Matrix supported rather than grain supported. Figure 7. Xenotopic-P (Poikilotopic), single anhedral grains or patches of anhedral grains of dolomite, usually having undulose extinction under cross polarized light, floating in a limestone matrix. Proposed dolomite textural classification. 24 F u rth e r re fin e m e n t In c l a s s i f i c a t i o n i s made by adding s u b c a te g o r ie s w ith in th e two d o lo m ite ty p e s . Id io to p ic -G (e u h e d ra l) c o n ta in s th o s e d o lo m ite s made up o f lo o s e ly packed, w ell-fo rm ed d o lo m ite rhombs. The ro c k must be g r a in su p p o rte d . The in t e r g r a n u la r a r e a may be f i l l e d w ith a n o th e r m in e ra l such as c a l c i t e o r p o r o s ity a s in th e c a se o f s u c ro se d o lo m ite . I d io to p ic - S (s u b h e d ra l) d o lo m ite s a r e th o s e r e f e r r e d to as h y p id io to p ic by Friedm an (1965) and may in c lu d e some o f F ried m an 's (1965) x e n o to p ic d o lo m ite s . These low p o r o s ity d o lo m ite s a r e c h a r a c te r iz e d by s t r a i g h t compromise b o u n d a rie s and a la r g e number o f p re se rv e d c r y s t a l fa c e ju n c tio n s . D olom ites t h a t l i n e p o re sp ace w ith te rm in a tio n s p r o je c tin g in to th e open po re o r vug a r e r e f e r r e d to as id io to p ic - C (cem ent) d o lo m ite s . Such d o lo m ite s may be produced by grow th o f d o lo m ite cement around th e edges o f th e p o re . A lte r n a te l y , p a r t i a l rep lacem en t o f a calciu m c a rb o n a te a llo ch em , such as a f o s s i l fra g m e n t, by im pin g in g d o lo m ite rhombs around i t s edge; fo llo w ed by th e d i s s o l u t i o n o f th e allo ch em would r e s u l t in a po re lin e d by d o lo m ite rhom bs. In many c a s e s i t m ight be d i f f i c u l t to d is ti n g u is h w hether th e id io to p ic - C d o lo m ite i s o f cem en ta tio n o r rep lacem en t o r i g i n . F ree f l o a t i n g rhombs in a lim e sto n e m a trix a re c l a s s i f i e d as id i o to p ic - P ( p o i k i l o t o p i c ) . These a r e d is tin g u is h e d from id io to p ic - A d o lo m ite in t h a t th e y a r e m a trix su p p o rte d . (The term s "m atrix " o r " g ra in " su p p o rte d a r e n o t meant to im ply a c l a s t i c o r i g i n f o r th e s e d o lo m ite s .) Friedm an (1965) u se s th e " c r y s t a l f a b r ic " term p o ik i lo to p i c to d e s c r ib e id i o to p ic - P t e x t u r e . D olom ites w ith low p o r o s ity , a n h e d ra l g r a in s and m o stly cu rv ed , l o b a te , s e r r a t e d , i n d i s t i n c t , o r o th e rw is e i r r e g u l a r i n t e r g r a i n 25 b o u n d arie s a r e c l a s s i f i e d a s x en o to p ic-A (a n h e d ra l) d o lo m ite . These d o lo m ite s a r e s im i la r in ap p earan ce to a c a l c i t e pseu d o sp ar and d o lo m itic m a rb le. In a d d itio n to th e i r r e g u l a r i n t e r g r a i n b o u n d arie s x en o to p ic-A d o lo m ite o f te n has a la r g e number o f in c lu s io n s (o b serv ed w ith SEM a s "Swiss ch eese" s t r u c t u r e (K atz and M atthews, 1 977)) which g iv e s them a d i r t y ap p earan ce in t h i n s e c tio n . X enotopic-A d o lo m ite u s u a lly d is p la y s u n d u lo se e x t i n c t i o n under c ro s s p o la r s . Replacem ent s a d d le d o lo m ite g r a in s (Radke and M a th is, 1980) a r e c l a s s i f i e d as x en o to p ic-A a s w e ll as th e low g rad e m etam orphic d o lo m ite s d e s c rib e d by Zenger (1 9 7 1 ). X enotoplc-A te x tu r e i s a ls o c l a s s i f i e d as x e n o to p ic by Friedm an (1965) a lth o u g h he d id n o t d i f f e r e n t i a t e d from some d e n se , nonporous d o lo m ite s h e re c l a s s i f i e d as id io to p ic - B . X enotopic-C (cem ent) d o lo m ite s a r e non-rhom bic pore and vug l i n i n g d o lo m ite s . These can be sa d d le d o lo m ite s o r in r a r e in s ta n c e s th e d i s t o r t e d o c ta h e d r a l c r y s t a l fo rm , [0001] and [4 0 4 1 ], o f d o lo m ite . S addle d o lo m ite s a r e b e s t re c o g n iz e d in t h i n s e c tio n by t h e i r sw eeping e x t i n c t i o n and by t h e i r lo n g curved edges le a d in g to p o in te d te r m in a tio n s , re m in is c e n t o f th e P e r s ia n s c im ita r . The l a s t c a te g o r y , x e n o to p ic -P ( p o ik i lo to p i c ) t e x t u r e , a r e " p o ik ilo to p ic " f a b r i c s made up o f d o lo m ite anhedra r e p la c in g p re c u rs o r c a rb o n a te s (s e e f i g u r e , Z enger, 1982). B ecause, w ith o u t s t a i n i n g , x e n o to p ic -P d o lo m ite i s n e a r ly im p o ssib le to d is ti n g u is h from s c a t t e r e d p a tc h e s o f p seu d o sp ar o r m icro sp ar in a lim e s to n e , i t i s p o s s ib le th a t t h i s d o lo m ite te x tu r e i s q u ite common b u t has n o t o f t e n been re c o g n iz e d . A d i f f i c u l t and g e n e t i c a l l y im p o rta n t d i s t i n c t i o n th a t o f te n must be made i s between d ense id i o to p ic - S d o lo m ite ( h y p id io to p ic and 26 sometimes x e n o to p ic o£ Friedm an (19 6 5 )) and x en o to p ic-A d o lo m ite . T ab le 2 l i s t s some o f th e q u a l i t a t i v e d if f e r e n c e s between th e s e te x tu r e s in t h i n s e c ti o n . The d i f f e r e n t i a t i o n between id io to p ic - S and x en o to p ic-A te x tu r e can be made q u a n t i t a t i v e l y by p o in t c o u n tin g th e numbr o f g r a in s TABLE 2 - Q u a lita tiv e d if f e r e n c e s between id io to p ic - B and x en o to p ic-A te x tu r e s in d o lo m ite . Id io to p ic - S 1. Most i n t e r g r a i n b o u n d aries a r e smooth and s t r a i g h t . 2. C ry s ta ls ten d to m a in ta in a rhom bic sh a p e . Angles formed by th e ju n c tio n o f c r y s t a l fa c e s a r e o f te n p re se rv e d as compromise b o u n d arie s w ith n e ig h b o rin g c r y s t a l s . 3. C r y s ta ls a r e r a r e l y un d u lo se under c ro sse d p o la rs X enotopic-A 1. I n te r g r a in b o u n d arie s a r e u s u a lly i r r e g u l a r . 2. C ry s ta ls do n o t te n d to have rhom bic sh ap e; c r y s t a l fa c e ju n c tio n s a r e n o t o f te n p re se rv e d by compromise b o u n d arie s w ith n e ig h b o rin g c r y s t a l s . 3. C r y s ta ls u s u a lly have u n d u lo se e x t in c ti o n . 27 F ig u re 8 . " C ry s ta l fa c e ju n c tio n s " (a rro w s) p re se rv e d by s t r a i g h t compromise b o u n d a rie s . T his sample o f d o lo m tie i s from th e P lio c e n e o f B o n aire, N.A. s c a le b ar =* 0 .0 5 mm. P a r t i a l l y c ro sse d p o la r s , 28 Figure 9 How a "crystal face junction" forms. Crystals A and B meet at point b at time 1 (T^) as shown, and continue to grow at constant rates, represented by T 2 and Tg• At Tg straight compromise boundaries exist forming angle abc and preserving the crystal face junction of crystal B at point b. 29 where compromise b o u n d arie s p re s e rv e a ju n c tio n between two c r y s t a l fa c e s o f th e same g r a in ( c r y s t a l fa c e ju n c tio n ) . F ig u re 8 shows such compromise b o u n d arie s and f ig u r e 9 i l l u s t r a t e s how th e s e b o u n d aries a r e form ed. T able 3 l i s t s th e c r i t e r i a f o r re c o g n iz in g t h i s r e l a t i o n s h i p which were used in p o in t c o u n tin g . Counts o f 100 to 300 g r a in s each were made f o r a number o f i d i o to p ic and x e n o to p ic d o lo m ite s used in t h i s s tu d y ; th e r e s u l t s o f th e s e co u n ts a r e shown i n t a b l e 4 . Samples which were q u a l i t a t i v e l y re c o g n iz e d as id i o to p ic - S d o lo m ite s c o n s is te n tly have a s i g n i f i c a n t l y h ig h e r number o f c r y s t a l fa c e ju n c tio n s p re se rv e d th a n x en o to p ic-A d o lo m ite . T h e re fo re , t h i s ap p e a rs to be a u s e f u l q u a n t i t a t i v e method o f d is tin g u is h in g between id io to p ic - S and x en o to p ic-A d o lo m ite te x t u r e s . The d iv id in g l i n e betw een th e two t e x t u r a l ty p e s i s p ro b ab ly w here p re s e rv e d . 30% o f th e g r a in s have c r y s t a l fa c e ju n c tio n s Above t h i s number th e d o lo m ite i s id i o to p ic and below , i t i s x e n o to p ic . The m a jo r ity o f th e p e tro g ra p h ic d e s c r ip tio n s fo r t h i s stu d y were done u sin g th e q u a l i t a t i v e system o f c l a s s i f i c a t i o n because most o f th e sam ples very o b v io u s ly f e l l in to one c a te g o ry o r a n o th e r. E x p erim en tal R e s u lts T h e 'r e s u l ts o f s e le c te d h y d ro th erm al ex p erim en ts a r e shown in T able 5 and Appendix 2. The amount o f o r d e rin g and th e s to ic h io m e try o f th e d o lo m ite produced was a f u n c tio n o f bo th th e te m p e ra tu re o f th e r e a c tio n and th e amount o f tim e th e r e a c tio n was a llo w ed . At 250°C a s h o r t r e a c tio n (23 h r s . ) produced s l i g h t l y d is o rd e re d calcium e n ric h e d d o lo m ite (o r p ro to d o lo m ite ). I f th e r e a c tio n was lo n g e r 30 T ab le 3 - C r i t e r i a f o r re c o g n iz in g a p re se rv e d rhombic c r y s t a l fa c e ju n c tio n in a compromise boundary. 1. The rhom bic c r y s t a l fa c e ju n c tio n must be in c o n ta c t w ith a n e ig h b o rin g d o lo m ite g r a in and ap p e a rs to make a " b i t e ” in to t h a t g r a in . T his in c lu d e s g r a in s where th e rhombic c r y s t a l fa c e ju n c tio n o v e r la p s th e n e ig h b o rin g g r a in . 2. There i s no o b s e rv a b le p o r o s ity o r o th e r n o n -d o lo m ite m in e ra ls n e ig h b o rin g th e g r a in b ein g c o u n ted . 3. A ngles la r g e r th a n 160° sh o u ld n o t be counted and c a re sh o u ld be ta k e n n o t to count a r c u a te b o u n d a rie s . 4. The tv» s t r a i g h t edges form ing th e i n t e r f a c e must cover a p e rim e te r o f a t l e a s t 1 /2 th e lo n g e s t d ia m e te r o f th e g r a in b ein g co u n ted . The edges may be in c o n ta c t w ith more th a n one g r a in as lo n g a s th e y c o n ta c t a s in g le g r a in where th e y j o i n , i . e . t r i p l e b o u n d arie s can n o t be co u n ted . Table 4. Point counting results for dolomite classification. Sample T e x tu r a l Type G rain s i z e A B C M arble Canyon, Hueco d o lo m ite I d io to p ic - S 0 .0 5 - 0 .2 mm 55 45 200 M arble Canyon, d o lo m ite m arb le X enotopic-A 0 .1 - 0 .4 mm 11 89 200 G alena d o lo m ite l o c a l i t y 20 I d io to p ic - S 0 .0 1 - 0 .1 mm 55 45 300 G alen a d o lo m ite l o c a l i t y 19 X enotopic-A 0 .1 - 0 .5 mm 24 76 300 T re n to n D olom ite Core £1 X enotopic-A 0 .3 - 0 .1 mm 18 82 100 T re n to n D olom ite Core L12 X enotopic-A 0 .1 - 0 .7 mm 27 73 150 P le io c e n e d o lo m ite , B o n a ire , N.A. I d io to p ic - S 0 .0 1 - 0 .1 mm 43 57 100 P le io c e n e d o lo m ite , B o n a ire , N.A. I d io to p ic - S 0 .0 1 - 0 .1 mm 45 55 100 Key: A - P e rc e n t o f g r a in s w ith c r y s t a l fa c e ju n c t i o n . B - P e rc e n t o f g r a in s w ith o u t c r y s t a l f a c e j u n c t i o n . C - T o ta l number o f g r a in s co u n te d . T ab le 5 . No. 1 E x p erim en tal R e s u lts S o lid r e a c t a n t s S o lid P ro d u c ts Mg C alc. G o n io llth o n o r d e r e d d o lo m ite Time (h rs) 98 *• 3 120 250 300 4 Mg C a lc . E ch ln o ld o rd e re d d o lo m ite 168 5 Mg C a lc . G o n io lith o n c a lc ite 335 •• 6 a r a g o n ite Strom bus c a lc ite t r a c e d o lo m ite 9 a r a g o n ite Area .2 4 1 m olar .04 00 N3 1516 300 .05 136 300 .15 23 8 10 300 F lu id Mg/Mg+Ca* (Mg/CaCl2 ) 2 m o lar .2 5 839 2 7 Temp.°C 43% o rd e re d d o lo m ite 57% c a l c i t e 239 73% o rd e re d d o lo m ite 27% c a l c i t e 334 ia 250 n 2 m olar .16 .30 .30 T ab le 5 . E x p erim en tal R e s u lts ( c o n tin u e d ) No. S o lid r e a c t a n t s S o lid P ro d u c ts 11 a r a g o n ite A rea 44% d is o r d e r e d d o lo m ite 56% c a l c i t e 12 a r a g o n ite A rea 13 Time (h rs) 23 Temp.°C 44% o r d e r e d d o lo m ite 56% c a l c i t e 979 300 43% o r d e r e d d o lo m ite 57% c a l c i t e 24 250 a r a g o n ite Strom bus c a lc ite 120 " 15 a r a g o n ite A rea c a lc ite 167 250 16 d is o r d e r e d d o lo ­ m ite and a r a g o n ite o rd e re d d o lo m ite 311 300 o r d e r e d d o lo m ite 120 18 n o n s to ic h io m e tr ic d o lo m itiz e d c o r a l­ l i n e a lg a e B onaire re c ry s ta lliz e d d o lo m ite 19 20 2184 120 d o lo m itiz e d mud B o n aire no change 720 2 m olar .23 .24 14 17 F lu id Mg/Mg+Ca* (Mg/CaCl2 ) 2 m olar .3 0 1 m olar M 2 m o lar 0 0 .25 34 th a n 1 week th e d o lo m ite a t ta in e d s to ic h io m e try and o r d e r in g . O rderin g and s to ic h io m e try were ach iev ed w ith in 24 h o u rs a t 300°C d u rin g rep lacem en t o f a r a g o n ite . There i s no ev id en ce from th e s e ex p erim en ts t h a t HMC ten d ed to produce more o rd e re d o r s to ic h io m e tr ic d o lo m ite th a n a r a g o n ite ; i t was j u s t d o lo m itiz e d more th o ro u g h ly . A rag o n ite to D olom ite and LMC: Fragm ents o f th e pelecypod Area pon d ero sa and th e g a stro p o d Strombus s p . were d o lo m itiz e d a t 250°C, 39 Atm. and 300°C, 85 Atm. In a l l c a se s an in te r lo c k in g x en o to p ic-A d o lo m ite te x tu r e re p la c e d th e a r a g o n ite s h e l l fragm ent ( f i g s . 10. 11 and 1 2 ). In t h i n s e c tio n th e d o lo m ite had un d u lo se e x t in c ti o n and v ery " d ir ty " ap p ea ran ce. SEM ex am in atio n showed v e ry i r r e g u l a r i n t e r g r a i n b o u n d arie s and a rough s u rfa c e te x tu r e w ith a "Swiss cheese" l i k e ap p earan ce caused by th e developm ent o f in c lu s io n s ( f i g . 1 2 ). C ry s ta l edges and cleav ag e fa c e s o f te n ap p eared curved ( f i g . 13) and in th e pore sp ace o f s e v e r a l sam p les, sa d d le d o lo m ite cem ents developed ( f i g . 1 4 ). The te x tu r e o f th e c a l c i t e produced by in v e rs io n o f a r a g o n ite was com prised o f in t e r lo c k i n g a n h e d ra l c r y s t a l s , as i n d o lo m ite te x tu r e s . The c a l c i t e s had sweeping e x t in c ti o n ( f i g . 15) and sometimes d is p la y e d f a s c i c u l a r te x tu r e c h a r a c t e r i s t i c o f neom orphic sp a rs. SEM re v e a le d rough s u r f a c e te x tu r e and v e ry i r r e g u l a r i n t e r g r a i n b o u n d arie s ( f i g . 1 6 ). In some c a se s th e c - a x is o r i e n t a t i o n o f th e o r i g i n a l a r a g o n ite in th e s h e l l fragm ents appeared to be m ain tain ed by th e c a l c i t e re p la c in g i t . 35 F ig u re 10. U n altered s k e l e t a l a r a g o n ite o f pelecypod A rea ponderosa SEM, s c a le b ar = 1 jim. 36 F ig u re 11 . A rea p o n d ero sa a f t e r a l t e r a t i o n to d o lo m ite (24 h r s . @ 300°C). Note u n d u lo se e x t in c ti o n in some o f th e g r a in s and th e i r r e g u l a r i n t e r g r a i n b o u n d a rie s. P a rtia lly c ro s s e d p o l a r s , s c a le b ar = 10 pm. F ig u re 12 • Area p o n d ero sa a l t e r e d to d o lo m ite (24 h rs @ 300°C). T his i s th e same sam ple as i n f i g . 11, n o te th e i r r e t u l a r i n t e r g r a i n b o u n d a rie s and "Sw iss ch eese" s tru c tu re . SEM, s c a le b ar = 10 pm. 37 F ig u re 11 Figure 12 38 F ig u re 13. A rea p o n d ero sa a l t e r e d to d o lo m ite (2 weeks @ 250°C ). Note th e curved edges o f c r y s t a l s (arro w s) in c e n te r o f fie ld . SEM, s c a le b a r = 10 pm. F ig u re 14. A rea pon d ero sa a l t e r e d to d o lo m ite (23 h r s . @ 250°G ), Note th e developm ent o f sa d d le shaped d o lo m ite c r y s t a l s (x en o to p ic-B t e x t u r e ) in th e po re sp ace ( c e n te r o f fie ld ). SEM, s c a le b ar = 0 . 1 pm. 39 Figure 14 40 F ig u re 15. Area pon d ero sa a l t e r e d to c a l c i t e (2 weeks @ 250°C ). P a r t i a l l y c ro s s e d p o la r s , s c a le b a r = 0 .1 jum. F ig u re 16. Area pon d ero sa a l t e r e d to c a l c i t e (1 week @ 250°C). SEM, s c a le b ar - 10 jutm. 41 F ig u re 15 ■>. . Figure 16 '“d i 42 HMC to Dolomite and LMC: Fragm ents o f th e c o r a l l i n e a lg a e G o n io lith o n s p . and th e e c h in o id Caenopedina s p . com prised o f HMC (25% and 13% MgC0 3 , r e s p e c t i v e l y , as d eterm in ed by x - r a y d i f f r a c t i o n ) were d o lo m itiz e d a t 300°C w ith r e a c tio n tim es from fo u r days to n in e w eeks. The HMC was c o n v e rte d to 100% w e ll o rd e re d d o lo m ite w ith 50% MgC03 to 49% MgC03 a s determ in ed by x - r a y d i f f r a c t i o n . The i n i t i a l HMC a l g a l and e c h in o id frag m en ts were composed o f c r y s t a l s too sm all to be re s o lv e d w ith th e SEM in s tru m e n ts a v a i la b l e ( f i g . 1 7 ). The in d iv id u a l c r y s t a l s produced by d o lo m itiz a tio n o f th e e c h in o id frag m en ts were a ls o n o t r e s o lv a b le u s in g SEM. The d o lo m ite d id m a in ta in th e C -ax is o r i e n t a t i o n o f th e p r e c u r s o r HMC c r y s t a l s i n th e e c h ln o id s becau se th e d o lo m itiz e d frag m en ts have u n it e x t in c ti o n . C r y s ta ls o f d o lo m ite produced from HMC a l g a l frag m en ts were ovo id shaped w ith i n d i s t i n c t , p o o rly developed c r y s t a l fa c e s ( f i g . 1 8 ). T h e ir av erag e s iz e was from 0 .2 5 to 1 .0 pm. . P ore f i l l i n g d o lo m ite s which sometimes grew in th e a l g a l c o n c e p tic a ls were com prised o f th e rhom bic (1011) c r y s t a l form w ith th e s te e p rhombic [4041] and b a s a l p in a c o id (0001) form s superim posed o v er i t ( f i g . 1 8 ). Experim ents were ru n to c o n v e rt HMC a l g a l frag m en ts to LMC. LMC c r y s t a l s t h a t r e p la c e d HMC a l g a l frag m en ts t e x t u r a l l y resem bled th e s y n th e tic d o lo m ite . The c r y s t a l s were o v o id shaped w ith p o o rly developed fa c e s ra n g in g in s iz e from ab o u t 1 /2 to 1 pm. C o n c e p tic a l f i l l i n g c a l c i t e c r y s t a l s had th e (2131) and (1011) forms ( f i g . 1 9 ). 43 F ig u re 17. HMC s k e l e t a l m a te r ia l from th e c o r a l l i n e a lg a e G o n io llth o n sp . SEM, s c a le b a r = 1 jtm. 44 F ig u re 18. G o n io lith o n s p . (HMC) a l t e r e d to d o lo m tie (60 days 0 300°C ). Note th e p o o rly developed (rounded) c r y s t a l f a c e s , th e developm ent o f [4041] and [0001] forms and curved i n t e r g r a i n b o u n d a rie s . These la r g e r euhedra ap p ear to have grown a s cem ents in to th e a g a l c o n c e p tic a ls s m a lle r c r y s t a l s r e p la c in g th e c e l l w a lls ap p ear to be a n h e d r a l. F ig u re 19. G o n io lith o n s p . SEM, s c a le b a r = 1 fim. (HMC) a l t e r e d to LMC (2 weeks 0 300°C). Note th e t e x t u r a l s i m i l a r i t y to th e d o lo m ite in F ig . 18. The la r g e pore l i n i n g c a l c i t e c r y s t a l s have th e (2131) and (1011) fo rm s. SEM, s c a le b a r = 1 m. 46 R e c r y s ta lli z a ti o n E xperim ents: Samples o f s u p r a ti d a l sedim ent from Andros I s la n d , Bahamas c o n ta in in g ab o u t 60% p o o rly o rd e re d n o n - s to ic h io m e tr ic d o lo m ite (40 mole % MgCOj) and ab o u t 40% a r a g o n ite were r e a c te d in d o lo m itiz in g s o lu tio n s a t 300°C f o r 5 and 13 d a y s . The u n a lte r e d s u p r a ti d a l sedim en t c o n ta in e d rhom bic (1011) d o lo m ite c r y s t a l s l e s s th a n 10 jim a c ro s s ( f i g . 2 0 ). and a r a g o n ite n e e d le s l e s s th a n 1 jim x 5 jjm. The sedim ent was u n c o n s o lid a te d and v ery p o ro u s. The p ro d u ct o f th e s e ex p erim en ts was 100% o rd e re d s to ic h io m e tr ic d o lo m ite . The te x tu r e produced by th e r e a c tio n was a porous m osaic o f d o lo m ite c r y s t a l s e x h ib itin g (1 0 1 1 ), (4041) and (0001) forms as i n th e HMC to d o lo m ite e x p e rim e n ts. The c r y s t a l s were s l i g h t l y la r g e r (on th e w hole) th a n th e i n i t i a l p ro to d o lo m ite s t a r t i n g m a te r ia l and ten d ed to be a n h e d ra l ( f i g . 2 1 ). The a r a g o n ite which was p re s e n t in th e i n i t i a l sedim ent was e n t i r e l y d o lo m itiz e d . In two e x p e rim e n ts, frag m en ts o f d o lo m itiz e d c o r a l l i n e a lg a e from B o n a ire , N.A. (o rd e re d w ith 46 mole'% MgC0 3 ) w ere r e a c te d in d o lo m itiz in g s o lu tio n s a t 300°C f o r 5 days and th r e e m onths. The s t a r t i n g m a te r ia l was com prised o f d o lo m ite rhombs (1011) m o stly l e s s th a n 2 fim a c ro s s f i l l i n g a l g a l c o n c e p tic a ls and f i n e r g ra in e d d o lo m ite re p la c in g th e c o n c e p tic a l w a lls ( f i g . 2 2 ). T his d o lo m ite i s c h a r a c te r iz e d by s t r a i g h t i n t e r g r a i n compromise b o u n d aries and w e ll formed rhombic c r y s t a l s . The p ro d u c ts o f th e s e r e a c tio n s were o rd e re d s to ic h io m e tr ic d o lo m ite in th e case o f th e 3 month experim ent and o rd e re d d o lo m ite w ith s to ic h io m e try ra n g in g from 50 mole % MgCOg to l e s s th a n 48 mole % MgCOj i n th e c a se o f th e 5 day ex p erim en t. The 47 F ig u re 20. U n a lte re d s u p r a ti d a l d o lo m ite from Andros I s la n d , Bahamas. T his d o lo m ite (o r pro to d o lo m ite ) i s p o o rly o rd e re d and c o n ta in s 40 mole % MgCOg). SEM, s c a le b a r » 1 jim. F ig u re 21. S u p r a tid a l n o n - s to ic h io m e tr ic d o lo m ite (p ro to d o lo m ite ) from Andros I s la n d , Bahamas r e c r y s t a l l i z e d to o r d e r e d , s to ic h io m e tr ic d o lo m ite (2 weeks @ 300dC). Note th a t most o f th e g r a in s ap p ear to be a n h e d ra l (arro w s) and n o te th e developm ent o f th e (4041) and (0001) form s. SGM, s c a le b a r = 1/im. 48 Figure 21 49 F ig u re 22. U n a lte re d d o lo m itiz e d c o r r a l l i n e a lg a e from B o n aire, N.A. Note th e w e ll formed d o lo m ite rhombs and s t r a i g h t i n t e r ­ g r a in b o u n d a rie s ( a rro w s ). Mast o f th e la r g e r c r y s t a l s a r e p ro b ab ly c o n c e p tic a l f i l l i n g cem ents. However, th e c e l l w a ll r e p la c in g c r y s t a l s , which a r e a t th e l i m i t o f th e r e s o lu t io n o f th e SEM, a ls o ap p ear to be e u h e d ra l. SEM, s c a le b a r = 1 fim. F ig u re 23. D o lom itized c o r a l l i n e a lg a e from B o n a ire , N.A. r e c r y s t a l l i z a t i o n (3 months @ 300°C ). curved i n t e r g r a i n b o u n d a rie s . a fte r Arrows show some SEN, s c a le b ar = 1 Jim. F ig u re 22 Figure 23 51 r e c r y s t a l l i z a t i o n te x tu r e s o f th e s e d o lo m ite s were s im ila r to th o se o f th e s u p r a ti d a l sedim ent exposed to th e same tr e a tm e n t. C r y s ta ls w ith th e (1 0 1 1 ), (4041) and (0001) forms p r e s e n t were pro d u ced . The a l g a l f a b r i c o f th e s t a r t i n g te x tu r e was e n t i r e l y o b l i t e r a t e d by re c ry s ta lliz a tio n . I n d iv id u a l c r y s t a l s were s l i g h t l y l a r g e r on th e av e ra g e th a n in th e s t a r t i n g m a te r ia l. They a ls o appeared s l i g h t l y ro u n d ed , c r y s t a l fa c e s p o o rly d e v e lo p e d , and in t e r g r a i n b o u n d aries te n d ed to be curved ( f i g . 2 3 ). A ttem pts to r e c r y s t a l l i z e n a t u r a l c o a rs e r g r a in (ab o u t 20 jam) n o n - s to ic h io m e tr ic (46 mole % MgCOj) , o rd e re d d o lo m ite w ith a r e a c tio n tim e o f two months showed no ev id en ce o f g r a in grow th o r o th e r t e x t u r a l change. S y n th e tic s to ic h io m e tr ic d o lo m ite ( g r a in s iz e l e s s th a n 1 jam) produced from c o r a l l i n e a lg a e ( f i g . 18) showed no ev id en ce o f c o n tin u in g g r a in grow th even w ith r e a c tio n tim es o f lo n g e r th a n 2 m onths. The f i n a l d o lo m ite te x tu r e a p p a re n tly d ev elo p s w ith in th e f i r s t 100 h o u rs o f r e a c tio n and no f u r th e r r e c r y s t a l l i z a t i o n (ag g rad in g neomorphism o r wet r e c r y s t a l l i z a t i o n ) seems to o c c u r. A ttem pts to r e c r y s t a l l i z e f in e g r a in LMC, which was s y n t h e t i c a l l y produced r e p la c in g HMC g o n io lith o n ( f i g . 1 9 ), a ls o met w ith f a i l u r e . R eac tio n tim es o f more th a n two months a t 300°C showed no t e x t u r a l d if f e r e n c e from th e sam ple produced in two weeks a t th e same te m p e ra tu re . P e tro g ra p h y , SEM and D is tr ib u t io n o f th e Hueco D olom ites The unmetamorphosed d o lo m ite f a c i e s o f th e Hueco Lim estone a t M arble Canyon, Texas c o n s is ts o f a f in e g ra in e d (0 .0 1 to 1 .5 mm, 52 m o stly above 0 .0 5 mm) id io to p ic - E and S d o lo m ite ( f i g s . 24 and 2 5 ). No s i g n i f i c a n t co m p o sitio n a l o r cath o d o lu m in escen t zoning was o b serv ed in t h i s d o lo m ite . The Hueco d o lo m ite has c o n s id e ra b le i n t e r c r y s t a l l i n e and f o s s i l mold p o r o s ity . Near h y drotherm al v e in s t h i s p o r o s ity i s sometimes f i l l e d by c o a rse g ra in e d c a l c i t e . O c c a s io n a lly f o s s i l f u s u lin i d s a r e r e p la c e d , w ith t h e i r i n t e r n a l s t r u c t u r e i n t a c t , by c h e r t . E ch in o id s a r e sometimes re p la c e d by s in g le d o lo m ite c r y s t a l s p re s e rv in g t h e i r u n it e x t in c ti o n , elsew h ere th e y a r e d is s o lv e d le a v in g f o s s i l m olds. Exam ination o f n earby and s t r a t i g r a p h i c a l l y e q u iv a le n t lim e s to n e s in d ic a te d t h a t th e d o lo m ite p ro b ab ly re p la c e d a f u s i l i n i d , e c h in o id b io m ic r ite . A th e rm a l g r a d ie n t i n r e l a t i o n to h o r iz o n ta l d is ta n c e from th e Marble Canyon in t r u s i o n was e s ta b l is h e d by B ridge (1 9 6 6 ). This g r a d ie n t was based on a stu d y o f m in e ra l assem blages in metamorphosed s i l i c e o u s lim e sto n e and d o lo m ite f a c i e s o f th e Hueco Lim estone and o v e rly in g Bone S p rin g F orm ation (Molfcamp) ( f i g . 2 6 ). The g r a d ie n t i s based on fo u r r e a c tio n s re c o g n iz e d by B ridge (1966) and p ro b ab ly f a l l alo n g a l i n e a r p o r tio n o f an e x p o n e n tia l curve d e s c rib e d by H. Jack so n (1 9 7 3 b ). A background te m p e ra tu re was n o t e s ta b lis h e d b u t i s assumed to be n e a r 100°C. II. Jack so n (1973b) determ ined th a t th e dom inant mode o f h e a t t r a n s f e r a t M arble Canyon was f l u i d flo w . T his, r e s u lt e d in r a p id h e a tin g follo w ed by slow c o o lin g o f th e co u n try ro c k . P e tro g ra p h ic ev id en ce o f r e c r y s t a l l i z a t i o n o f d o lo m ite was o b serv ed to b egin ab o u t 400 f t from th e i n t r u s i o n . The maximum te m p e ra tu re h ere was e s tim a te d to be between 250° and 300°C. The p a r t i a l l y r e c r y s t a l l i z e d d o lo m ite i s c h a r a c te r iz e d by f in e g r a in 53 F ig u re 24 . I d io to p ic - S d o lo m ite o f th e Hueco L im estone, M arble Canyon, T exas. P a r t i a l l y c ro sse d p o la r s , s c a le b a r * 0 . 1 mm. F ig u re 25 . I d io to p ic - S Hueco d o lo m ite (same sam ple a s in f i g . 2 4 ). The f l a t s u r f a c e s o f th e g r a in s p a r a l l e l to th e p la n e o f th e p h o tograph a r e compromise b o u n d arie s formed w ith g r a in s removed when th e sample was f r a c t u r e d . s c a le b ar = 10 jjm. SEM, Figure 25 55 T°C 100 200 300 400 •/C a l+ Q ■'Wo+COj 500 Dol=Par+ Cal+CO2 600 700 Di+Fo+Cal=3Mo+2C02 800 • Sp+2Mo-2Ma+Cal 900 0 100 200 ' 300 400 50 0 distance in feet Figure 26. Temperature gradient at Marble Canyon, based on the data of Bridge (1966). 600 56 (0 .0 5 to 0.1mm) id io to p ic - E and S d o lo m ite w ith p a tc h e s o f x en o to p ic-A d o lo m ite (0 .1 to 0 .2 mm). have un d u lo se e x t i n c t i o n . Some o f th e d o lo m ite an h ed ra The amount o f c o a rs e g ra in e d x en o to p ic-A d o lo m ite in c r e a s e s c lo s e r to th e i n t r u s i o n . Vugs up to 3 mm in d ia m e te r a r e o f te n f i l l e d by c o a rs e g ra in e d c a l c i t e ; som etim es one c a l c i t e c r y s t a l co m p letely f i l l i n g th e vug. The vugs a r e o f te n lin e d by id io to p ic - C d o lo m ite (0 .1 to 0 .2 mm) which has smooth rhombic te rm in a tio n s in c o n ta c t w ith th e vug f i l l i n g c a l c i t e b u t i r r e g u l a r g r a in b o u n d a rie s w ith n e ig h b o rin g d o lo m ite g r a in s ( f i g . 2 7 ). At a d is ta n c e o f about 300 f t . from th e in t r u s i o n r e c r y s t a l l i z a t i o n o f th e d o lo m ite i s com plete ( f i g . 2 8 ). At t h i s p o in t th e d o lo m ite te x tu r e i s e n t i r e l y x en o to p ic-A (0 .1 to 0 .4 mm) ex cep t f o r id io to p ic - C d o lo m ite around c a l c i t e f i l l e d v u g s. d o lo m ite an h ed ra o f te n have u n d u lo se e x t in c ti o n . The SEM r e v e a ls a n h e d ra l c r y s t a l s and i r r e g u l a r i n t e r g r a i n b o u n d arie s ( f i g . 2 9 ). Many o f th e g r a in s in t h i s and o th e r sam ples have f l a t s u rfa c e s s u b p a r a ll e l to th e p la n e o f th e SEM m ic ro g ra p h s. This i s due to c le a v in g when th e sam ple i s f r a c t u r e d f o r m ounting. N earer th a n 250 f t . from th e in t r u s i o n th e d o lo -m arb le has been b le ach ed by metamorphism and i s l i g h t g re y in hand specim en as opposed to d ark g rey in th e u n a lte r e d d o lo m ite . From ab o u t 140 f t . from th e in t r u s i o n th e d o lo m ite g ra d e s in to a w h ite b r u c i t e - c a l c i t e m arb le. This m arble was produced by in te n s e th e rm al metamorphism which a l t e r e d th e d o lo m ite to c a l c i t e and p e r i c l a s e . l a t e r a l t e r e d to b r u c i t e (B rid g e , 1 9 6 6 ). The p e r i c l a s e Some o f th e p e r ic la s e m arble a d ja c e n t to th e i n t r u s i o n to ab o u t '60 f t . away was re d o lo m itiz e d by l a t e h y d ro th erm al a c t i v i t y (B rid g e , 1 966). T his 57 F ig u re 27. Dolom ite c r y s t a l te rm in a tio n s (D) in a c a l c i t e f i l l e d vug (C) ( id io to p ic - C d o lo m ite ) . The d o lo m ite c r y s t a l s sh a re i r r e g u l a r b o u n d arie s w ith n e ig h b o rin g d o lo m ite g ra in s . T h is sam ple i s from th e r e c r y s t a l l i z e d m etam orphic f a c i e s o f th e Hueco d o lo m ite . c ro sse d p o la r s , s c a le b ar = 0 . 1 /jm. P a rtia lly 58 F ig u re 28. Hueco d o lo m ite m a rb le, c o lle c te d 120 f t . from th e M arble Canyon i n t r u s i o n . te x tu re . F ig u re 29. T his sample e x h ib its x en o to p ic-A P a r t i a l l y c ro s s e d p o la r s , s c a le b a r = 0 . 1 mm. Hueco d o lo m ite m arble (same sample as in f i g . 2 8 ). th e i r r e g u l a r i n t e r g r a i n b o u n d a rie s. Mote The f l a t s u rfa c e o f th e la r g e c r y s t a l in th e c e n t e r - r i g h t o f th e m icrograph i s p ro b ab ly a cleav ag e fa c e formed when th e sample was f r a c t u r e d f o r m ounting. SEM, s c a le b ar - 10 /tun. I 59 Figure 29 60 d o lo m ite I s a lso c h a r a c te r iz e d by a x en o to p ic-A te x tu r e made up o f d i r t y a p p ea rin g and sometimes u n d u lo se anhedra (0 .0 5 to 0.2mm). Aside from i t s p ro x im ity to th e in t r u s i o n t h i s d o lo m ite i s i n d i s t i n ­ g u is h a b le from th e r e c r y s t a l l i z e d d o lo m ite s ( f i g s . 30 and 3 1 ). P e tro g ra p h y , SEM and D is tr ib u t io n o f th e G alena D olom ites G en eralized p e tro g ra p h ic d e s c r ip t io n s o f G alena Group c o l le c t in g l o c a l i t i e s a r e g iv e n i n Appendix 3. The u n d o lo m itized p o r tio n s o f th e G alena Group in so u th w e ste rn W isconsin and e a s te r n Iowa a r e c h a r a c te r iz e d by b io m ic r ite s and some b i o s p a r i t e s . F o s s il c o n te n t o f th e s e lim e sto n e s in c lu d e frag m en ts o f e c h in o id s , b ry o zo a, b rach io p o d s and t r i l o b i t e s . The lim e s to n e s c o n ta in c h e r t n o d u les and some s l l i c i f i e d f o s s i l s a s w e ll as a sm a ll amount ( e s tim a te d to be l e s s th a n 1%) w e ll rounded q u a rtz and p o s s ib ly some f e ld s p a r san d . This sand c o n te n t i s common in th e d o lo m itiz e d as w ell as th e lim e sto n e f a c i e s o f th e G alena Group. D o lo m itiz a tio n co m p lete ly o b l i t e r a t e d th e i n i t i a l lim e sto n e f a b r ic s in most p la c e s . O ccasio n al s i l i c i f i e d f o s s i l s can be found in th e d o lo m ite and some o f th e vuggy p o r o s ity ap p e a rs to be f o s s i l m olds. I d io t o p ic d o lo m ite te x tu r e was o b serv ed a t a l l o f th e o u tc ro p s o f th e G alena Group th a t were sam pled. as: These d o lo m ite s were found 1) in d iv id u a l rhombs o f id io to p ic - P d o lo m ite (0 .0 1 to 0 .4 mm) r e p la c in g lim e sto n e m ic r ite ( f i g s . 32 and 3 3 ), 2) un ifo rm f in e g ra in e d id io to p ic - E and S d o lo m ite (0 .0 5 to 0.2mm) ( f i g s . 34 and 3 5 ), 3) c o a rs e g ra in e d (up to 0 .5 mm) id i o to p ic - E , S and C d o lo m ite s . most abundant o f th e s e were th e c o a rs e g ra in e d d o lo m ite s. Some o f t h i s c o a rse g ra in e d d o lo m ite has pronounced zoning and in th e more The 61 F ig u re 30 . D olom ite produced by h y d ro th erm al a l t e r a t i o n o f a p e r ic la s e m arb le; c o l le c t e d 30 f t . from th e M arble Canyon in tru s io n . Figure 31. P a r t i a l l y c ro sse d p o l a r s , s c a le b a r “ 0 .1 mm. D olom ite produced by h y d ro th erm al a l t e r a t i o n o f a p e r ic la s e m arble (same sample a s in f i g . 3 0 ). s c a le b a r = 0 .1 mm. SEM, 63 F ig u re 32. I d io to p ic - F d o lo m ite r e p la c in g lim e sto n e m i c r ite o f th e G alena Group ( l o c a l i t y 4 5 ) . Note th e p r e s e r v a tio n o f a c r y s t a l f a c e j u n c t i n where two la r g e rhombs ( c e n te r ) jo in . F ig u re 33. P lan e p o la riz e d l i g h t , s c a le b a r a 0 .1 mm. I d io to p ic - P d o lo m ite (d a rk ) r e p la c in g c a l c i t e m i c r it e ( l i g h t ) o f th e G alena Group (same sample as in F ig . 3 2 ). Note th e groove in th e la r g e rhomb (upper c e n te r ) c r e a te d by th e c r y s t a l fa c e ju n c tio n o f an a d jo in in g d o lo m ite c r y s t a l which was removed d u rin g f r a c t u r i n g o f th e sam ple. = 0 .1 mm. SEM b a c k s c a tte r e d e le c tr o n im age, s c a le b ar 65 F ig u re 34 . I d io to p ic - S G alena d o lo m ite from l o c a l i t y 20. Note th e s t r a i g h t i n t e r g r a i n b o u n d arie s and p re se rv e d c r y s t a l fa c e F ig u re 35 . j u n c tio n s . P a r tl y c ro sse d p o la r s , s c a le b a r = 0 .0 5 mm. I d io to p ic - S G alena d o lo m ite from l o c a l i t y 20. Note th e rhombic shape o f many o f th e g r a in s and r e l a t i v e l y s t r a i g h t i n t e r g r a i n b o u n d a rie s. T his sam ple i s from a w eathered ex p o su re and shows s ig n s o f d i s s o l u t i o n . s c a le bar = 0.0 5 mm. SEM, Figure 35 67 porous v a r i e t i e s , i n t e r c r y s t a l l i n e po re sp ace i s o f te n f i l l e d by brown to b la c k opaque m a te r ia l which c o a ts th e s u r f a c e o f th e c ry s ta ls . This i n t e r g r a n u la r m a te r ia l i s p ro b ab ly m o stly amorphous ir o n .hydroxide w ith some o rg a n ic m a te r ia l and ir o n s u l f i d e s ju d g in g from i t s c o lo rs in r e f l e c t e d l i g h t . S p h a le r ite was o b serv ed as in i n t e r g r a n u la r f i l i n g in a few sam p les. A c u rio u s a s p e c t o f some o f th e c o a rs e g ra in e d porous id io to p ic - E and C d o lo m ite i s t h a t i t te n d s to have undulose e x t i n c t i o n , and c lo s e ex am in atio n sometimes r e v e a ls s l i g h t l y curved c r y s t a l f a c e s ( f i g . 3 6 ). P o s s ib ly t h i s r e p r e s e n ts a t r a n s i t o n between i d i o t o p i c d o lo m ite and x en o to p ic-C o r sa d d le d o lo m ite . Undulose id i o t o p i c d o lo m ite i s found in a s s o c ia tio n w ith x en o to p ic-A d o lo m ite . SEM shows th e b a s ic rhombic shape o f th e c r y s t a l s making up th e i d i o t o p i c d o lo m ite s and th e r e l a t i v e l y s t r a i g h t compromise b o u n d arie s t h a t form between c r y s t a l s ( f i g s . 33 and 3 5 ) . The s u r f a c e s o f th e s e g r a in s ap p ear co rro d ed and somewhat p i t t e d ( f i g . 3 5 ). This i s pro b ab ly n o t due to c r y s t a l grow th b u t r a t h e r due to o u tc ro p w e a th e rin g . Mast o f th e G alena o u tc ro p s were m o d e ra tely to s tr o n g ly w eath ered making " fre s h " sam ples d i f f i c u l t to o b ta in . Because o f th e abundant in t e r g r a n u la r opaque m a te r ia l and w idesp read p atch y d i s t r i b u t i o n o f x e n o to p ic d o lo m ite ; w e ll developed unifo rm id io to p ic - S d o lo m ite s a r e r a r e in th e G alena Group. At l o c a l i t y 20 n e a r Mine P o in t, W isconsin th e c le a n e s t and most uniform f in e g ra in e d i d i o to p ic d o lo m ite s were fo u n d ; b u t even th e s e were a s s o c ia te d w ith some x en o to p ic-C d o lo m ite cement f i l l i n g f o s s i l m olds. X enotopic-A d o lo m ite s a r e o b serv ed in th e G alena F orm ation v a ry in g in s iz e from s c a t t e r e d p a tc h e s o f one to s e v e r a l c e n tim e te rs F ig u re 36. I d io to p ic - E G alena d o lo m ite from l o c a l i t y 28. th e c r y s t a l s have curved e d g e s. Some o f Note th e c le a r - r im , c lo u d y -c e n te r zoning and abundant i n t e r - c r y s t a l l i n e opaque m a te r ia l. mm. P lan e p o la r iz e d l i g h t , s c a le b ar = 0 .1 69 a c ro s s in s iz e mixed w ith id i o t o p i c d o lo m ite , to whole p o r tio n s o f o u tc ro p s composed e n t i r e l y o f x e n o to p ic t e x t u r e . No o u tc ro p s were sam pled t h a t a r e e n t i r e l y x e n o to p ic d o lo m ite ; how ever, a t l o c a l i t i e s 13, 15, 1 9 , 29 and 31 i t i s th e dom inant t e x t u r a l ty p e (Appendix 3 ) . At l o c a l i t y 45 j u s t so u th o f G u tten b u rg , Iowa, p atch es o f x en o to p ic-A d o lo m ite and some x e n o to p ic -P d o lo m ite r e p la c e a b io m ic r ite ( f i g s . 37 and 3 8 ). In t h i n s e c ti o n , th e x en o to p ic-A G alena d o lo m ite s a re c h a r a c te r iz e d by c u rv ed , i r r e g u l a r i n t e r g r a i n b o u n d a rie s, and th e g r a in s u s u a lly have u n d u lo se e x t in c ti o n under c ro sse d p o la rs ( f i g . 3 9 ). The x en o to p ic-A d o lo m ite g r a in s ran g e in s iz e from 0 .0 5 to 0 .4 mm, m o stly ab o u t 0.2mm. B a re ly , x e n o to p ic anhedra had c le a r - r im , cloudy c e n te r zo n in g ; how ever, t h i s k in d o f zoning was most o f te n found in th e c o a rs e g ra in e d id i o t o p i c d o lo m ite s . Both i d i o to p ic and x e n o to p ic G alena d o lo m ite s had th e same cath o d o lu m in escen t p ro p e rtie s . C ath o d o lu m in escen t zoning was n o t o b serv ed in th e G alena d o lo m ite s. At most lo c a tio n s x e n o to p ic te x tu r e s a r e a s s o c ia te d w ith some s t y l o l i t e s . Vuggy p o re sp ace in x e n o to p ic d o lo m ite s a r e u s u a lly li n e d w ith ld io to p ic - C d o lo m ite s . These g r a in s have rhom bic te rm in a tio n s where a d ja c e n t to p o re sp aces o r m a trix m a te r ia l b u t i r r e g u l a r b o u n d a rie s w ith n e ig h b o rin g d o lo m ite g r a i n s , j u s t a s d e s c rib e d in th e r e c r y s t a l l i z e d p o r tio n s o f th e Hueco d o lo m ite . SEM ex am in atio n o f x en o to p ic-A dolom tes from th e G alena Group show th e v e ry rough s u r f a c e te x tu r e o f th e g r a in s , i r r e g u l a r i n t e r g r a i n b o u n d aries and few rhom bic shaped g r a in s ( f i g s . 38 and 4 0 ). 70 F ig u re 37 . X enotopic-A G alena d o lo m ite from l o c a l i t y 45 w hich r e p la c e s a b io m ic r ite (n o t show n). The few rhomb shaped g r a in s may be from a p re c u rs o r id io to p ic -D d o lo m ite (a s in F ig . 32 which was c o lle c te d n e a rb y ). P a rtia lly c ro sse d p o l a r s , s c a le b ar = 0 .1 mm. Figure 38 . X enotopic-A G alena d o lo m ite (d a rk ) r e p la c in g c a l c i t e ( l i g h t ) from l o c a l i t y 45 (same sample as in F ig . 3 7 ). Note th e i r r e g u l a r i n t e r g r a i n b o u n d arie s as com prared to i d i o t o p i c d o lo m ite c o lle c te d a few f t . away ( F ig . 3 3 ). SEM b a c k s c a tte r e d e l e c tr o n im age, s c a le b a r = 10 pm. F ig u re 37 Figure 38 72 F ig u re 39 . X enotopic-A G alena d o lo m ite from l o c a l i t y 19. P a rtia lly c ro sse d p o la r s , s c a le b ar = 0 . 5 mm. F ig u re 40 . X enotopic-A G alena d o lo m ite from l o c a l i t y 19 (same sam ple as in F ig . 3 9 ). Note th e i r r e g u l a r i n t e r g r a i n b o u n d aries and "Swiss ch eese" s t r u c t u r e . SEM, s c a le b a r = 0 .1 mm. 74 Good exam ples o f x e n o to p lc d o lo m ite t e x tu r e were found th ro u g h o u t th e G alena Group in so u th w e ste rn W isco n sin . No a e r i a l o r s t r a t i g r a p h i c p a t te r n s o f t h i s d i s t r i b u t i o n were e s t a b l i s h e d . Such p a t t e r n s , how ever, may become a p p a re n t w ith more d e t a i l e d s tu d y . P e tro g ra p h y , SEM and D is tr ib u t io n o f th e T ren to n D olom ites G e n e ra liz e d p e tro g r a p h ic d e s c r ip t io n s o f th e T ren to n Form ation c o re s used in t h i s stu d y a r e found in Appendix 4. D olom ites o f th e T ren to n F orm ation o f th e M ichigan B asin re p la c e d b io m ic r ite s v ery s im i la r to th e lim e s to n e s o f th e G alena Group. F o s s il c o n te n t o f th e T ren to n lim e s to n e s c o n s is ts p r im a r ily o f b rach io p o d and e c h in o id frag m en ts and o c c a s io n a l b ry o zo an , g a stro p o d and t r i l o b i t e fra g m e n ts . F in e g ra in e d id io to p ic - S d o lo m ite s (0 .0 1 to 0 .1 mm) a r e found in th e "cap" o f th e T renton and in th e r e g io n a l T renton d o lo m ite in th e w e ste rn p a r t o f th e b a s in ( f i g . 4 ) . re p la c e d m i c r it e ( f i g . 4 1 ). T his d o lo m ite p r e f e r e n t i a l l y SEM shows th e rhom bic shape o f th e c r y s t a l s and t h e i r r e l a t i v e l y smooth i n t e r g r a i n b o u n d a rie s ( f i g . 4 2 ). Id io to p ic - P ( f l o a t i n g rhombs in m i c r it e ) can be found th ro u g h o u t th e lim e sto n e f a c i e s o f th e T ren to n F o rm atio n . X enotopic-A d o lo m ite i s th e p r i n c i p a l ty p e o f te x tu r e a s s o c ia te d w ith th e f r a c t u r e r e l a t e d d o lo m ite s ( f i g . 43) and i s a ls o found in th e " c a p ” , and th e w e ste rn r e g io n a l d o lo m ite s . S ty lo litiz a tio n sometimes g iv e s f i n e g ra in e d i d i o to p ic d o lo m ite o f th e "cap" and r e g io n a lly d o lo m itiz e d a r e a s a "cru sh ed " o r "ground-up" a p p e a ra n c e . In th e s e s t y l o l i t i z e d a re a s th e f o s s i l s were re p la c e d by c o a r s e , u ndulo se x en o to p ic-A d o lo m ite . This u n d u lo se x e n o to p lc d o lo m ite a ls o 75 F ig u re 41. I d io to p ic - S d o lo m ite r e p la c in g m i c r it e in th e "cap" o f th e T ren to n F orm ation (Br c o r e ) . r i g h t i s u n re p la c e d c a l c i t e . The f o s s i l in th e upper The d o lo m ite c o n ta in s abundant i n t e r c r y s t a l l i n e opaque m a te r ia l. P lan e p o la r iz e d l i g h t , s c a le b a r - 0 .1 mm. F ig u re 42. I d io to p ic - S d o lo m ite from th e "cap" o f th e T ren to n Form ation (same sample a s in F ig . 4 1 ). p re s e rv e d c r y s t a l fa c e ju n c tio n s . mm. Arrows show SEM, s c a le b ar = 0.05 77 F ig u re 43. X enotopic-A f r a c t u r e r e l a t e d d o lo m ite from th e T ren to n F orm ation (L12 c o r e ) . b a r = 0 .3 mm. P a r t i a l l y c ro sse d p o la r s , s c a le 78 re p la c e d Che rem ain in g m icriC e which had n o t p re v io u s ly been re p la c e d by th e f i n e g r a in id i o to p lc d o lo m ite . The f a b r ic o f th e p re c u rs o r b io m ic r lte i s , th e r e f o r e , p re s e rv e d in th e s e r o c k s ; th e f o s s i l s re p la c e d by c o a rs e g ra in e d x en o to p ic-A d o lo m ite and th e m ic r ite p r im a r ily by f in e g ra in e d id i o to p ic - S d o lo m ite ( f i g . 4 4 ). The f o s s i l r e p la c in g x en o to p ic-A d o lo m ite g r a in s ran g e in s iz e from 0 .1 to 0 .5 mm and have u n d u lo se e x t i n c t i o n . SGM ex am in atio n o f th e s e and o th e r x e n o to p ic d o lo m ite s in th e T ren to n F orm ation show t h e i r i r r e g u l a r i n t e r g r a i n b o u n d a rie s ( f i g . 4 5 ). X enotopic-A d o lo m ite t h a t d e s tr u c t iv e l y re p la c e d b io m ic r i tic lim e s to n e s o f th e T ren to n Form ation i s a s s o c ia te d w ith f r a c t u r e system s such as th e n o r th e a s t- s o u th w e s t tre n d in g A lbion S cip io and N o r th v ille f i e l d s , and w ith f r a c t u r i n g in r e g io n a l d o lo m ites in th e w e s te rn p a r t o f th e M ichigan B asin ( f i g . 4 3 ). In t h i n s e c tio n th e an h ed ra ran g e in s iz e from 0 .1 to 0 .8 mm; most o f th e g r a in s b eing n e a r 0 .5 mm and having u n d u lo se e x t in c ti o n . C athodolum inescent zoning was o b serv ed in some o f th e f r a c t u r e r e l a t e d x en o to p ic-A d o lo m ite s b u t n o t in th e t e x t u r a l l y s im ila r f o s s i l re p la c in g d o lo m ite s . There i s no o b serv ed t e x t u r a l o r g r a in s iz e v a r i a t i o n in th e f r a c t u r e - r e l a t e d x e n o to p ic-A d o lo m ite s t h a t would su g g est a d if f e r e n c e in n u c le a tio n o r grow th between th e g r a in s re p la c in g f o s s i l s and th o s e r e p la c in g m i c r i t e . In some sam ples g h o sts o f form er f o s s i l frag m en ts can be seen " f l o a t i n g 1 i n th e d o lo m ite w ith o u t a f f e c t i n g g r a in s iz e o r m orphology. In th e s e c a se s th e d o lo m ite re p la c e d th e p re c u rs o r b io m ic r lte w ith a uniform x en o to p ic-A te x t u r e , co m p letely o b l i t e r a t i n g th e o r i g i n a l lim esto n e f a b r i c . 79 F ig u re 44. D olom itized b io m ic r lte from th e "cap" o f th e T ren to n F orm ation (E l c o r e ) . The f o s s i l ( c e n te r ) i s re p la c e d by x en o to p ic-A d o lo m ite and th e m i c r ite m o stly by id io to p ic - S d o lo m ite , p re s e rv in g th e o r i g i n a l f a b r i c o f th e b io m ic r lte . P a r t i a l l y c ro sse d p o la r s , s c a le b a r ** 0 .5 mm. F ig u re 45. X enotopic-A d o lo m ite r e p la c in g a f o s s i l in th e "cap" o f th e T ren to n Form ation (same sample a s in F ig . 4 4 ). Arrows show g r a in b o u n d a rie s. SEM, s c a le b ar = 10 pm. 80 Figure 45 81 S e v e ra l s a l i e n t c h a r a c t e r i s t i c s a r e common to a l l o f th e c o a r s e , d e s tr u c t iv e x en o to p lc -A d o lo m ite s found in th e T ren to n : 1) They may r e p la c e th e lim e sto n e o v er a v e r t i c a l d is ta n c e o f s e v e r a l hundred f e e t , a s o b serv ed from com paring p e tro g r a p h ic d e s c r ip tio n s w ith c o re and gamma ra y - n e u tr o n lo g s from th e N o r th v ille f i e l d . However, th e r e seems to be v e ry l i t t l e l a t e r a l c o n tin u ity to th e s e d o lo m ite s as an o i l w e ll as n e a r as 0 .2 5 m ile s away may n o t e n co u n ter th e same d o lo m itiz e d s e c ti o n . [Compare, f o r exam ple, th e G l, E2 and Br c o re s in Appendix 4 and se e Shaw (1 9 7 4 , f i g . 1 0 ) ] . 2) They a r e o f te n a s s o c ia te d w ith f r a c t u r e and vuggy p o r o s ity lin e d w ith x en o to p ic-C (s a d d le ) d o lo m ite cement ( f i g . 46) and o f te n f i l l e d by a n h y d r ite . 3) In f i v e o f th e c o re s where th e s e d o lo m ite s were en co u n tered (L12, H i, W2, El and B r l, see f i g . 4 and Appendix 4 ) th e y were a s s o c ia te d w ith n o ta tio n s o f o i l o r gas shows in th e c o re d e s c r ip t io n s . F ra c tu re r e l a t e d d o lo m ite was a ls o o b serv ed in th e HS w e ll in S a n ila c C o ., M ichigan f o r which no d e s c r ip t io n s o r co m p letio n r e p o r ts were a v a i l a b l e , so i t i s n o t known i f t h i s d o lo m ite co n ta in e d h y d ro carb o n s. C oarse g ra in e d id io to p ic - E and S d o lo m ite s (0 .1 to 0 .5 mm) a r e o f te n a s s o c ia te d w ith th e d e s tr u c t iv e x en o to p ic-A d o lo m ites a s s o c ia te d w ith th e f r a c t u r i n g . These d o lo m ite s have un d u lo se e x t i n c t i o n and sometimes s l i g h t l y curved c r y s t a l f a c e s . They a r e p e tr o g r a p h ic a lly an alogous to th e s im i la r d o lo m ite te x tu r e s found in th e G alena group ( f i g . 3 6 ). A lso , l i k e t h e i r c o u n te r p a r ts in th e G alena Group, p o re space i s o f te n f i l l e d by opaque m a te r ia l and in d iv id u a l c r y s t a l s a r e o f te n co a te d by th e o p aq u es. F lo a tin g d o lo m ite an h ed ra o r x e n o to p ic -P d o lo m ite were o b serv ed i F ig u re 46. Saddle shaped x en o to p ic -C d o lo m ite growing in to f r a c t u r e p o r o s ity o f th e T ren to n F orm ation (E l c o r e ) . c ro sse d p o la r s , s c a le b a r *» 0 .5 mm. P a rtia lly 83 i n th e lim e sto n e f a c i e s and in a re a s o f p a r t i a l d o lo m itiz a tio n o f th e T ren to n F o rm atio n . The x en o to p ic-P d o lo m ite s ran g e in s iz e from 0 .0 5 to 0 .5 mmm and have u n d u lo se e x t in c ti o n a s do th e x en o to p ic-A d o lo m ite s . X enotopic-P d o lo m ite was o f te n o b serv ed p a r t i a l l y r e p la c in g f o s s i l s and m ic r ite i n a re a s t h a t a r e a ls o p a r t i a l l y re p la c e d by th e f in e g ra in e d id i o to p ic d o lo m ite ( f i g . 4 7 ). In t h i n s e c ti o n th e o n ly way x e n o to p ic -P d o lo m ite can be e a s i l y d is tin g u is h e d from c a l c i t e p seu d o sp ar, which a ls o r e p la c e s f o s s i l s and m i c r it e in th e T ren to n , i s w ith a s t a i n . In most o f th e c o re s in v e s t ig a t e d , th e x en o to p ic-P d o lo m ite s was found n e a r th e f r a c t u r e r e l a t e d d o lo m ite s ( f i g . 4 8 ). However, in th e JF1 co re in so u th w e ste rn Shiaw assee C o ., x en o to p ic -P and f in e g ra in e d id io to p ic - S and P d o lo m ite were a l l t h a t were o b serv ed . P o s s ib ly f r a c t u r e r e l a t e d d o lo m ite s a r e nearby b u t were n o t en co u n tered by t h i s c o re due to t h e i r lim ite d l a t e r a l e x t e n t. Summary o f th e O ccurrence o f X enotopic D olom ite Undulose X enotopic-A d o lo m ite was s y n th e s iz e d , a t 250°C and 300°C, from a r a g o n ite s h e l l fra g m e n ts. X enotopic-C ( s a d d le ) d o lo m ite cem ents were a lso s y n th e s iz e d in th e same e x p e rim e n ts. S y n th e sis o f d o lo m ite from HMC and r e c r y s t a l l i z a t i o n o f n o n s to ic h io m e trlc d o lo m ite produced d o lo m ite c r y s t a l s w ith p o o rly developed f a c e s . X enotopic-A d o lo m ite was o b serv ed in th e Hueco F orm ation a t M arble Canyon, Texas a s th e r e s u l t o f p ro g re s s iv e r e c r y s t a l l i z a t i o n o f an i d i o to p ic d o lo m ite n e a r an ig n eo u s in t r u s i o n . r e c r y s t a l l i z a t i o n o c c u rre d a t te m p e ra tu re s > 250°C. T his 84 F ig u re 4 7 . Anhedra o f x e n o to p ic -C d o lo m ite ( l i g h t ) p a r t i a l l y r e p la c in g a c a l c i t e b rach io p o d fragm ent ( s ta i n e d d ark ) in th e T ren to n Form ation "cap" (Br c o r e ) . Note th e f in e g ra in e d id i o t o p i c d o lo m ite r e p la c in g m i c r it e on th e low er le ft. F ig u re 4 8 . P lan e p o la r iz e d l i g h t , s c a le b a r = 0 .5 mm. X enotopic-C d o lo m ite ( l i g h t ) r e p la c in g lim e s to n e m i c r it e ( s ta in e d d a rk ) alo n g a f r a c t u r e i n th e T ren to n F orm ation (L12 c o r e ) . mm. P a r t i a l l y c ro s s e d p o la r s , s c a le b a r = 0 .1 85 I F ig u re 47 F ig u re 48 86 In th e G alena Group o f W isconsin and Iowa, x en o to p ic-A d o lo m ite s were s c a t t e r e d as p a tc h e s from s e v e r a l c e n tim e te rs to s e v e r a l m eters i n s iz e mixed w ith id i o t o p i c d o lo m ite . At one o u tc ro p x en o to p ic-A and C d o lo m ite was o b serv ed r e p la c in g b io m ic r ite . The x en o to p ic-A d o lo m ite s in th e G alena Group a r e sometimes a s s o c ia te d w ith sa d d le shaped x en o to p ic-C cem ents. In th e T ren to n F orm ation o f th e M ichigan B asin x en o to p ic-A d o lo m ite r e p la c e s f o s s i l s su rro u n d ed by s t y l o l i t i z e d f in e g r a in i d i o t o p i c d o lo m ite . T his r e l a t i o n s h i p i s o b serv ed most o f te n in th e "cap" and th e r e g io n a lly d o lo m itiz e d w e ste rn p o r tio n o f th e T ren to n F o rm atio n . D e s tr u c tiv e "whole rock" rep lacem en t o f th e T ren to n by x en o to p ic -A d o lo m ite i s a s s o c ia te d w ith f r a c t u r i n g in th e T renton F o rm atio n . These d o lo m ite s a r e found w ith x en o to p ic-C (s a d d le ) cem en ts, a n h y d r ite and p e tro le u m . F lo a tin g an h ed ra o f x en o to p ic-C d o lo m ite a r e found r e p la c in g f o s s i l s and m i c r ite in lim e sto n e s n e a r th e f r a c t u r e r e l a t e d d o lo m ite s. Mb x e n o to p ic d o lo m ite was found in th e P lio c e n e d o lo m ite s from th e N eth erlan d s A n til le s o r i n P le is to c e n e s u p r a t i d a l d o lo m ite s from Andros I s la n d . R e s u lts o f S ta b le Is o to p e A nalyses S ta b le oxygen and carbon is o to p e a n a ly s e s were made on 11 s e le c te d sam ples o f d o lo m ite from th e Hueco L im esto n e. t h e i r 8 ^ 0 and 8^ C v a lu e s r e l a t i v e to th e PDB s c a le . T able 6 shows The sam ples were s e le c te d a t i n t e r v a l s from 30 f t . from th e i n t r u s i o n to 1200 f t . from th e i n t r u s i o n . T able 6 a ls o shows th e maximum te m p e ra tu re which th e s e sam ples a r e e s tim a te d to have been s u b je c te d 87 T able 6 S ta b le Is o to p e V alues f o r Hueco D olom ites Sample Approxim ate D istan ce from I n tr u s io n Maximum Metamorphic T em perature ^g 5 0 13 ru o p er m il. 6 rUiJ p e r m il. MH52 1200 f t . * 100°C + 0.13 +4.95 MH18 820 f t . * 100°C +2.15 -1 .2 4 MH20 720 f t . * 100 ° C -0 .1 3 +5.22 MH24 660 f t . -v 100°C -0 .8 1 + 4.89 MH15 490 f t . 150°C - 0 .6 6 + 5.29 MH27 480 f t . 150°C +0.33 + 4.67 M1LL1 400 f t . 240°C + 0.13 +3.99 -0 .2 8 +4.59 MH 9 340 f t . 325°C -1 .2 9 + 4 .8 4 MH 6 250 f t . 475°C -0 .8 2 +4.35 MH41 140 f t . 640°C -2 .5 8 + 4.35 MH 2 30 f t . 825°C -0 .1 8 +1.33 88 distance in feet approx. T^C 860 720 200 570 4 30 400 280 130 6 00 800 1000 1200 2 -1 0 1 2 5,80 per mil. (PDBI Figure 49. 18 6 0 values for Hueco dolomite plotted against temperature and distance from the intrusion. The two S 18 0 values plotted with open circles 13 had anomalous S C values and were not used to calculate r. 89 to d u rin g metamorphism. The te m p e ra tu re e s tim a te s a r e based on th e m in e ra l assem blage d a ta o f B ridge (1 9 6 6 ). F ig u re 49 p lo t s th e v a lu e s o b tin e d f o r th e Hueco d o lo m ite s r e l a t i v e to d is ta n c e from th e i n t r u s i o n and e s tim a te d maximum te m p e ra tu re . The lo w est fi^O v a lu e ( - 2 .5 8 p e r m i l .) was o b ta in e d f o r MH41 which was c o lle c te d 140 f t . from th e i n t r u s i o n (650°C ). T h is sam ple was r e c r y s t a l l i z e d in to a x en o to p ic-A d o lo m ite . The fil 80 v a lu e s in c re a s e w ith in c re a s in g d is ta n c e from th e i n t r u s i o n to ab o u t 400 f t . away. At t h i s p o in t and a t d is ta n c e s f u r t h e r away most o f th e v a lu e s a r e c lu s te r e d around a mean o f - 0 .1 2 p e r m il. The d is ta n c e o f 400 f t . from th e i n t r u s i o n c o in c id e s w ith th e f u r t h e s t d is ta n c e a t which r e c r y s t a l l i z a t i o n o f d o lo m ite i s p e tr o g r a p h ic a lly o b s e rv a b le in t h i n s e c ti o n . A ll b u t two o f th e sam ples had 6 ^ 0 v a lu e s c lu s te r e d around a mean v a lu e o f + 4 .7 2 p e r m il. w ith a h ig h o f + 5.29 and low o f + 3 .9 9 p e r m il. R e c r y s t a l l i z a t i o n had no e f f e c t on s ta b l e carbon is o to p e v a lu e s . Anomalous 6 ^ 0 and S^C v a lu e s were o b ta in e d f o r t m o f th e sam ples th a t were a n a ly s e d , MH2 and MH18 ( t a b l e 4 and f i g . 5 4 ). MH2 was c o lle c te d 30 f t . from th e i n t r u s i o n and i t s v a lu e s p ro b ab ly r e f l e c t th e l a t e r e d o lo m itiz a tio n o f p e r ic la s e m arble by magmatic w ater as re p o r te d by B ridge (1 9 6 6 ). The second anomalous v a lu e was f o r MH18 which was c o lle c te d from th e a l t e r a t i o n zone o f a h y d ro th erm al v e in . These two sam ples were s u b je c t to a more complex a l t e r a t i o n h is to r y th a n th e o th e r 9 sam ples which were s u b je c te d o n ly to metam orphic r e c r y s t a l l i z a t i o n . S ta b le is o to p e v a lu e s o b ta in e d f o r 21 d o lo m ite sam ples and 1 90 T ab le 7 . S ta b le is o to p e v a lu e s f o r th e G alena Group. The sam ples a r e grouped in to 11 p a i r s c o n ta in in g one x e n o to p ic and one i d i o to p ic d o lo m ite c o lle c te d in c lo s e p ro x im ity to one a n o th e r. Samples marked w ith an a s t e r i s k (* ) a r e l i s t e d in more th a n one p a i r . The s in g le lim e sto n e m ic r ite sample i s p a ire d w ith a d o lo m ite c o lle c te d form th e same l o c a l i t y . T ex tu re Lo catio n -S am p le 8180 8 13C 19-3 Id io to p ic - S X enotopic-A PDB -3 .4 4 -4 .3 7 PDB + 0.79 -0 .0 8 31-8 31-3 I d io to p ic - E and S X enotopic-A -4 .8 4 -5 .2 5 - 0 .0 2 -4 .0 7 33-3 34-2* Id io to p ic - S X enotopic-A -5 .1 8 -5 .4 5 -0 .7 5 -5 .2 2 34-1 34-2* I d io to p ic - E ( s l i g h t l y u n d u lo se) X enotopic-A -5 .0 6 -5 .4 5 +0.33 -5 .2 2 45-17 45-11 I d io to p ic - E and S X enotopic-A -3 .3 9 -5 .2 1 -0 .9 0 -0 .1 8 14-1 14-4 I d io to p ic - S X enotopic-A -3 .3 1 -3 .6 3 - 0 .2 0 -0 .0 9 15-1 15-2 30-1 3 0 - la uD 30-3 30-3a * I d io to p ic - E and S (zoned) X enotopic-A (unzoned) I d io to p ic - S X enotopic-A -2 .9 0 -6 .2 8 -5 .5 2 -5 .6 3 -0 .2 8 -0 .0 9 +0.31 -0 .0 4 Id io to p ic - E u n d u lo se w/some curved x l s . - 5 .9 0 X enotopic-A -5 .3 1 +0.16 -0 .3 4 30-3° Id io to p ic - S un d u lo se -5 .5 4 +0 .0 1 30-3 * c X enotopic-A -5 .3 1 -0 .3 4 28-3 28-5 50-1 50-1* Id io to p ic - E undulose w/some curved x l s .- 6 .3 2 X enotopic-B -3 .1 0 -4 .3 8 I d io to p ic - P -5 .6 8 Lim estone m ic r ite -0 .3 7 -0 .5 6 + 0.31 -0 .4 9 20-1 91 lim e s to n e sample from th e G alena Group a r e l i s t e d in t a b l e 6 . The d o lo m ite sam ples a r e grouped in to 11 p a i r s o f id i o to p ic d o lo m ite m atched w ith x e n o to p lc d o lo m ite . The two sam ples in each p a i r were c o lle c te d in c lo s e p ro x im ity to one a n o th e r. In a l l but two c a s e s , p a i r s were c o l le c t e d from th e same o u tc ro p an d , in two c a s e s , from th e same hand sam ple. Specimens were c a r e f u l ly examined in t h i n s e c tio n and o n ly re g io n s o f t e x t u r a l hom ogeneity were I s o la t e d f o r is o to p e a n a l y s i s . The 8^®0 and S ^ C v a lu e s r e p o r te d in t a b l e 7 a r e r e l a t i v e to th e PDB s c a le . In 8 o f th e p a i r s 8*®0 v a lu e s f o r th e xen o to p ic-A d o lo m ite w ere low er by an av era g e o f 0 .9 5 p e r m il. th a n th e matched id io to p ic - B d o lo m ite . In two o f th e p a i r s , an id io to p ic - E d o lo m ite had a lower 1*0 v a lu e th a n th e x e n o to p ic d o lo m ite . In b o th o f th e s e cases th e low er v a lu e s were f o r porous id io to p ic - A d o lo m ite s th a t have u n d u lo se e x t i n c t i o n and some curved c r y s t a l fa c e s ( f i g . 3 6 ). One id io to p ic - S d o lo m ite was found w ith a 8 ^ 0 v a lu e low er th a n i t s p a ire d x en o to p ic-A d o lo m ite . S ta b le carbon is o to p e v a lu e s ranged between 8 ^ C o f -5 .2 2 p e r m il. and + 0.79 p e r m il. N in eteen o f th e v a lu e s were between - 0 .9 0 and + 0 .7 9 p e r m il. w ith a mean o f - 0 .1 4 p e r m il. v a lu e s were anom alously low ( t a b l e 7 ) . Two o f th e No r e la tio n s h ip s were o b serv ed betw een d o lo m ite te x tu r e and s t a b l e carbon is o to p e v a lu e s . S ta b le carbon and oxygen is o to p e a n a ly se s were n o t o b ta in e d f o r d o lo m ite s o f th e T ren to n Form ation as p a r t o f t h i s s tu d y . However, oxygen is o to p e v a lu e s f o r th e T ren to n d o lo m ite were o b ta in e d by T ay lo r (1982 and p e rs o n a l com m unication, 1982) and w i l l be d is c u s s e d below . 92 X -ray D if f r a c t io n o f Hueco, G alena and T ren to n D olom ites S e le c te d sam ples o f id i o t o p i c and x e n o to p ic d o lo m ite from th e Hueco, G alena and T ren to n d o lo m ite s were a n a ly se d w ith x -ra y d iffra c tio n . The purpose was to see i f a d if f e r e n c e in o r d e r in g o r s to ic h io m e try e x is te d betw een x e n o to p ic and i d i o to p ic d o lo m ite s. A ll o f th e sam ples an a ly se d from th e Hueco and G alena d o lo m ite s proved to be s to ic h io m e tr ic , o rd e re d d o lo m ite r e g a r d le s s o f t e x t u r e . F ine g ra in e d id io to p ic - S d o lo m ite from th e "cap" o f th e T ren to n fo rm a tio n was c a lc u la te d to be e n ric h e d w ith calcium (54% CaCC^). In a d d i tio n , th e (006) and (110) r e f l e c t i o n s were broad and d i f f u s e and th e (015) r e f l e c t i o n n e a r ly n o n e x is te n t, in d i c a ti n g poor o r d e r in g . By c o n t r a s t , f r a c t u r e r e l a t e d x en o to p ic-A d o lo m ite sam ples c o lle c t e d from w ith in 5 f t ( i n one c a se from th e same hand sam ple) were s to ic h io m e tr ic and had w e ll dev elo p ed o r d e r in g r e f l e c t i o n s . The poor o r d e r in g and n o n sto ic h io m e try o f th e id i o t o p i c d o lo m ite in th e "cap" o f th e T renton i s p ro b a b ly due to i t s h ig h ir o n c o n te n t r e l a t i v e to th e x e n o to p ic f r a c t u r e r e l a t e d d o lo m ite . The d i s t r i b u t i o n and o r i g i n o f ir o n in th e T ren to n d o lo m ite s i s th o ro u g h ly d is c u s s e d by T ay lo r (1 9 8 2 ). DISCUSSION A p p lic a tio n o f C r y s ta l Growth Theory to C arbonate T ex tu re A rem ark ab le t e x t u r a l s i m i l a r i t y e x i s t s between x en o to p ic-A d o lo m ite s from th e T ren to n F o rm atio n , th e G alena Group, th e Hueco d o lo m itic m arbles and th e s y n th e t ic d o lo m ite s produced in th e la b o r a to r y by rep la cem e n t and r e c r y s t a l l i z a t i o n ( s e e , f o r exam ple, f i g s . 11, 28, 39 and 4 3 ) . These d o lo m ite s a re a l l c h a r a c te r iz e d by 93 a n h e d ra l c r y s t a l s w ith ro u g h , curved o r o th e rw is e i r r e g u l a r i n t e r g r a i n b o u n d arie s and undulose e x t in c ti o n under c ro s s e d p o la r s . The x en o to p ic -A d o lo m ite s have a s t r i k i n g l y d i f f e r e n t te x tu r e from C enozoic d o lo m ite s known to have formed a t n e a r s u r f a c e te m p e ra tu re ( f i g s . 8 , 20 and 22 ) and from id i o t o p i c d o lo m ite s found in a n c ie n t ro c k s ( s e e f o r example f i g s . 24, 34 and 4 1 ). I t i s h y p o th e siz e d t h a t th e x e n o to p ic te x tu r e o b serv ed in th e T ren to n and G alena d o lo m ite s formed above th e c r i t i c a l roughening te m p e ra tu re (CRT) i n acco rd an ce w ith J a c k s o n 's (1958a and 1958b) c r y s t a l grow th m odel. S y n th e tic d o lo m ite s and d o lo m itic m arb les were a ls o produced by c r y s t a l grow th above CRT, th e re b y cau sin g developm ent o f a te x tu r e s im ila r to th e sed im en tary r o c k s , even though th e y were exposed to h ig h e r te m p e ra tu re s th a n norm al f o r d ia g e n e tic c o n d itio n s . The o b s e r v a tio n o f a n h e d ra l g r a in m osaics such a s o b serv ed in x en o to p ic-A d o lo m ite i s c o n s is te n t w ith th e id e a t h a t th e s e c r y s t a l s formed by n o n -fa c e te d grow th above th e CRT. If w e ll developed c r y s t a l fa c e s do n o t form d u rin g grow th (se e f o r in s ta n c e f i g s . 47 and 48) th e n id i o t o p i c te x tu r e as d e fin e d h e re i s im p o s s ib le . E m p irica l e s tim a te s o f th e CRT f o r c r y s t a l fa c e s can be made by s tu d y in g c r y s t a l m o rphologies produced a t d i f f e r e n t te m p e ra tu re s in th e la b o r a to r y (Ja c k so n and M ille r , 1 9 7 7 ). In th e case o f d o lo m ite t h i s i s d i f f i c u l t b ecau se o f k i n e t i c problem s a s s o c ia te d w ith s y n th e s is o f d o lo m ite below 100°C (G a in e s , 1 9 8 0 ). T h e re fo re , com parisons must be made between n a t u r a l d o lo m ite produced n ear th e s u r f a c e and s y n th e tic and n a t u r a l d o lo m ite produced above 100°C. Because te m p e ra tu re s a few in c h e s below th e s u r f a c e i n P e r s ia n Gulf 94 sabkhas can re a c h a s h ig h as 50°C and d o lo m ite c r y s t a l s produced th e r e a r e e u h e d ra l ( I l l i n g a t a l . , 1965 and McKenzie, 1980, f i g s . 3 -7 ) t h i s i s ta k e n as a t e n t a t i v e low er te m p e ra tu re l i m i t . An upper l i m i t o f 100°C i s s u g g e ste d because t h i s i s about th e av erag e te m p e ra tu re o f th e le a d - z in c s u l f i d e emplacement in th e G alena Group (B a ile y and Cameron, 1951) and i s n e a r te m p e ra tu re e s tim a te s f o r f r a c t u r e r e l a t e d d o lo m ite s in th e T ren to n Form ation (Shaw, 1975; T a y lo r, 1 9 8 2 ). U ndoubtedly a la r g e r e g io n e x i s t s where th e CRT f o r d o lo m ite may r e s id e (betw een 50° and 100°C ). Change in th e CRT may be made by changing th e e n th a lp y f a c t o r (L) i n e q u a tio n 2 . In d o lo m ite , t h i s i s p o s s ib le by s u b s t i t u t i o n o f c a t i o n s , su ch as calciu m o r ir o n f o r magnesium. Such a s u b s t i t u t i o n may r e s u l t in a m in e ra l w ith a low er l a t e n t h e a t o f d is s o lu ti o n th a n s to ic h io m e tr ic d o lo m ite , in c r e a s in g th e ro u ghening f a c t o r and, th e r e b y , d e c re a s in g th e CRT. Some f e r r o a n d o lo m ite s and calciu m r i c h d o lo m ite s (p ro to d o lo m ite s ) may have a low er CRT th a n s to ic h io m e tr ic d o lo m ite . X enotopic a n k e r ite found in c o n c re tio n s from th e A ntrim S h ale (D ev o n ian ), M ichigan a r e p o s s ib ly o f low te m p e ra tu re (<50°C) o r i g i n (H athon, 1979). Dolom ite c r y s t a l s grow ing in to p o re space a r e o f te n o b serv ed in th e T ren to n and G alena d o lo m ite s to have c r y s t a l fa c e s even when th e y a r e c lo s e ly a s s o c ia te d w ith x e n o to p ic d o lo m ite and appear to have formed a t th e same tim e ( f i g . 3 6 ). Development o f c r y s t a l fa c e s a d ja c e n t to po re sp ace was a ls o o b serv ed in some o f th e s y n th e tic h y d ro th erm al d o lo m ite s ( f i g . 2 1 ). Lewis (1975) n o ted t h a t , e x p e r im e n ta lly , c r y s t a l s grown from s o lu tio n above CRT o f te n have w e ll dev elo p ed c r y s t a l f a c e s . He concluded t h a t " . . . in s o lu tio n 95 grow th o f p e r f e c t c r y s t a l p la n e s form becau se o f some a d d i tio n a l Impediment to t h e i r g row th, r e l a t e d to d e s o lv a tio n o r to th e a d s o r p tio n o f s o lv a n t" (L ew is, 1975, p . 3 3 ). This i s n o t in c o n s i s t e n t w ith th e model i f one c o n s id e rs t h a t in n e u t r a l to a l k a l i n e w ater th e d o lo m ite s u r f a c e ta k e s on a n e g a tiv e charge form ing a d if f u s e d o u b le la y e r between th e s u rfa c e and b u lk s o lu tio n (P a rk s , 1970, Stumm and Morgan, 1970, P r e d a li and C ases, 1 973). The c a t io n s , Mg^+ and Ca^+, a r e e l e c t r i c a l l y a t t r a c t e d to and c o n c e n tra te d n e a r th e s u r f a c e . In o r d e r to a t t a c h i t s e l f to th e grow ing c r y s t a l th e COj^- a n io n must lo o s e i t s h y d ra tin g w ater m o le c u le s, move from th e bu lk s o lu tio n th ro u g h th e d if f u s e double la y e r and overcome th e r e p e l l i n g f o rc e o f th e n e g a tiv e ly charged su rfa c e . The a v a i l a b i l i t y o f th e c a rb o n a te io n a t th e c r y s t a l s u rfa c e i s th e r e f o r e r a t e d e te rm in in g when th e d o lo m ite grows in to a b u lk s o lu tio n such a s an open po re s p a c e . This may p ro v id e th e impedim ent to gro w th , a llo w in g c r y s t a l fa c e s to d e v e lo p , as su g g e ste d by Lewis (1 9 7 5 ). In th e s u rfa c e dom inated t h i n f ilm o f s o lu tio n p r e s e n t between c r y s t a l s d u rin g a rep la cem e n t o r r e c r y s t a l l i z a t i n r e a c tio n , d ouble la y e r s o f th e d is s o lv in g and grow ing g r a in s o v e r la p . c o n c e n tr a tio n in th e t h i n f ilm i s rem oval from th e d is s o lv in g p h ase. The c o n tr o lle d by th e r a t e o f its Movement o f th e m a jo r ity o f th e a n io n from th e d is s o lv in g to th e growing g r a in i s r a p id and o c c u rs w ith o u t h aving to move i t (C C ^ - ) from th e bu lk s o lu tio n th ro u g h a d i f f u s e d o uble la y e r. In th e c a l c i t e to rep lacem en t r e a c tio n Mg2+ must d if f u s e th ro u g h th e t h i n film environm ent to th e s i t e o f a ttach m en t on th e grow ing d o lo m ite d o lo m ite 96 c ry s ta l. T his d if f u s io n i s r a p id r e l a t i v e to COj- ^ ( P in g it o r e , 1982) and does n o t impede d o lo m ite g row th. In th e d o lo m ite to d o lo m ite r e c r y s t a l l i z a t l n r e a c tio n a l l o f th e io n s a r e p ro v id ed by th e d is s o lv in g phase and a b u lk s o lu ti o n need n o t e x i s t . An a l t e r n a t e e x p la n a tio n f o r th e d if f e r e n c e betw een c r y s t a l grow th by t h i n film s o lu tio n s and b u lk s o lu tio n s in v o lv e s th e low er d i e l e c t r i c c o n s ta n t o f w ater in th e s u r f a c e environm ent (e= 7 8 .5 in b u lk s o l u t i o n , e =6 in s u r f a c e e n v iro n m en t). The low er d i e l e c t r i c c o n s ta n t i n s u r f a c e dom inated environm ents r e s u l t s in low er s o l u b i l i t i e s (M urray and D ill a r d , 1 9 7 9 ). In o th e r w ords,A G r and AHr a r e low er f o r th e d i s s o l u t i o n o f d o lo m ite in a s u rfa c e dom inated t h i n f ilm th a n d is s o lu ti o n i n a b u lk s o lu ti o n . The rough n ess p aram eter ( a ) would be c o rre sp o n d in g ly low er (s e e eq . 2 ) . T h e re fo re , CRT in a t h i n f ilm may be s i g n i f i c a n t l y low er th a n in a b u lk s o lu tio n a llo w in g n o n face ted c r y s t a l grow th a t low er te m p e ra tu re . Many o f th e undulose i d i o to p ic d o lo m ites in th e T ren to n Form ation and G alena Group, t h a t a r e a s s o c ia te d w ith x e n o to p ic d o lo m ite and a re presumed to be o f h ig h te m p e ra tu re o r i g i n , a re a s s o c ia te d w ith opaque m a te r ia l such a s h y d ro carb o n s. Ths opaque m a te r ia l i s very o f te n o b serv ed c o a tin g th e c r y s t a l s and f i l l i n g th e boundary la y e r s between g r a in s ( s e e , f o r exam ple, f i g . 3 6 ). The a s s o c ia t io n o f opaques w ith th e s e i d i o to p ic d o lo m ites s u g g e s ts th a t th e p re se n c e o f t h i s m a te r ia l m ight a ls o a c t a s an i n h i b i t o r , r e ta r d in g c r y s t a l g row th, th u s allo w in g c r y s t a l fa c e s to d ev elo p . One a s p e c t o f c a rb o n a te te x tu r e s t h a t i s e x p la in e d by t h i s model i s th e o b serv ed d if f e r e n c e between lim e sto n e and id i o to p ic d o lo m ite . 97 The form er i s u s u a lly composed o f a n h e d ra l c r y s t a l s w hereas th e l a t t e r o f e u h e d ra l rhom bic c r y s t a l s . The an h e d ra l m osaics o f c a l c i t e m icro sp ar and n eo sp ar produced by r e c r y s t a l l i z a t o n o r polym orphic in v e r s io n may be formed n e a r 25°C ( B a th u r s t, 1 9 7 6 ). These lim e sto n e te x tu r e s a r e s im ila r to x en o to p ic-A d o lo m ite an d , th e r e f o r e , a re presumed to be produced above th e CRT o f c a l c i t e . L ab o ra to ry grow th o f c a l c i t e from aqueous s o lu tio n s n e a r 25°C sometimes produce d e n d r i t i c c r y s t a l s (K ah le, w r itt e n and p e rs o n a l com m unication, 1 981). D e n d r itic c r y s t a l grow th o c c u rs above CRT (Ja c k so n , 1958a) and, th e r e f o r e , a CRT f o r c a l c i t e must e x i s t below 25°C. At n e a r s u rfa c e te m p e ra tu re s , t h e r e f o r e , c a l c i t e produces a n h e d ra l m osaics c h a r a c t e r i s t i c s o f neom orphic s p a rs w h ile d o lo m ite , grow ing below CRT a t 25°C, produces eu h ed ra w ith s t r a i g h t compromise b o u n d a rie s. When 4 th e te m p e ra tu re i s e le v a te d above th e CRT f o r d o lo m ite , x en o to p ic te x tu r e s im i la r to c a l c i t e n eo sp ar can d ev elo p . The s y n th e s is o f x en o to p ic-C ( s a d d le ) d o lo m ite a t 250°C ( f i g . 14) was an unex p ected bonus o f th e e x p e rim e n ta l s t u d i e s . Spry (1969) su g g e ste d t h a t th e curved fa c e s o f s a d d le dolom ie c r y s t a l s a r e caused by th e developm ent o f low an g le f a c e t s o r " v in c in a l f a c e s ." These fa c e s can d ev elo p becau se o f s im i la r bonding and s u r f a c e e n e rg ie s to th e (1011) f a c e s . Reeder and B arber (1982) a t t r i b u t e d d i s t o r t i o n in s a d d le shaped d o lo m ite c r y s t a l s to s u b p a r a ll e l s ta c k in g f a u l t s normal to th e rhom bic f a c e s . Radke and M athis (1980) su g g ested t h a t th e fo llo w in g c o n d itio n s m ight be f a v o r a b le to sa d d le d o lo m ite grow th: 1 ) te m p e ra tu re above 60°C, 2) p re se n c e o f i r o n , 3) s u lf id e - r e d u c ti o n c o n d itio n s and 4) p y r o e l e c t r i c e f f e c t s d u rin g f lu c t u a ti n g te m p e ra tu re c o n d itio n s . High te m p e ra tu re was th e o n ly one o f th e s e c o n d itio n s 98 t h a t e x is te d d u rin g h y d ro th erm al s y n th e s is o f sa d d le d o lo m ite . It can be presum ed, t h e r e f o r e , t h a t te m p e ra tu re i s p ro b ab ly im p o rta n t to th e developm ent o f sa d d le c r y s t a l s . I t i s n o t c le a r from t h i s stu d y what th e e x a c t r o l e o f te m p e ra tu re i s , o r i f and how c r y s t a l s u rfa c e morphology i s im p o rtan t to th e developm ent o f curved c r y s t a l fa c e s and th e grow th o f sa d d le -sh a p e d c r y s t a l s . The same kin d o f l a t t i c e d i s t o r t i o n t h a t produces sa d d le d o lo m ite may a ls o be r e s p o n s ib le f o r th e un d u lo se e x t in c ti o n o b serv ed in s y n th e t ic and many n a tu r a l x en o to p ic-A d o lo m ite s. X enotopic-C d o lo m ite cem ents produced a t 300°C, w ith developm ent o f (4041) and (0001) c r y s t a l form s superim posed on th e (1011) rhombic c r y s t a l form can be e x p la in e d by c r y s t a l grow th th e o ry . At 25°C th e ( 1011 ) fa c e s a r e underg o in g "smooth" g ro w th , o th e r t h e o r e t i c a l l y p o s s ib le fa c e s a r e "rough” and q u ic k ly grow th em selv es o u t o f e x is te n c e (se e B ric e , 1973, f i g . 3 .3 ) . Once th e te m p e ra tu re i s r a is e d above CRT f o r th e (1011) f a c e s , grow th i n h i b i t i o n e f f e c t s as d is c u s s e d above b eg in to fa v o r th e developm ent o f th e (4 0 4 1 ), (0001) and (1011) fo rm s. Above 250°C th e s e fa c e s b eg in to d e v e lo p . The above e x p la n a tio n does n o t p re c lu d e th e developm ent o f th e (0001) and (4041) forms a t low er te m p e ra tu re . Naiman, e t a l . ( i n p r e s s ) d e s c r ib e p o ly h e d ra l d o lo m ite c r y s t a l s w ith developm ent o f th e (0 0 0 1 ), (4041) and o th e r fo rm s, from th e Perm ian o f West T exas. These c r y s t a l s ap p ear to have formed betw een 25° and 45°C and a r e a s s o c ia te d w ith h a l i t e . An e x te n s iv e s e a rc h o f th e l i t e r a t u r e by R. L. F o lk (p e rs o n a l com m unication, 1982) in d i c a te s th a t p erh ap s a l l n a t u r a l l y o c c u rrin g p o ly h e d ra l d o lo m ite c r y s t a l s a r e a s s o c ia te d w ith e v a p o r ite s . There seems to be l i t t l e in common between th e 99 c o n d itio n s d e s c rib e d by Naiman, e t a l . and th o s e o f th e h y d ro th erm al s y n th e s e s in t h i s stu d y ex ce p t f o r h ig h c h lo rid e c o n c e n tr a tio n s . However, o th e r e v a p o r ite (h ig h c h lo r id e ) r e l a t e d d o lo m ite s do n o t dev elo p th e (0001) o r (4041) forms ( s e e f o r example f i g . 20) and th e " p o ly h e d ra l" form s were s y n th e s iz e d o n ly a t 300°C n o t a t 250°C in d i c a ti n g a r e l a t i o n s h i p to te m p e ra tu re . T h e re fo re th e mechanism d is c u s s e d above may be s u f f i c i e n t to e x p la in th e h y d ro th erm al s y n th e s is o f th e u n u su al c r y s t a l fo rm s. At low er te m p e ra tu re s some chem ical s p e c ie s p r e s e n t i n c e r t a i n e v a p o r i tic s o lu tio n s may a c t to i n h i b i t grow th in th e (0 0 0 1 ), (4041) and o th e r c r y s t a l p la n e s a llo w in g th e s e fa c e s to form . This o c c u rs in o th e r c r y s t a l s , f o r in s ta n c e , h a l i t e w i l l d ev elo p o c ta h e d r a l fa c e s when L i+ i s added in sm a ll q u a n t i t i e s to a grow ing s o lu ti o n ( B r ic e , 1973). Neomorphism o f D olom ite T h e o r e tic a lly , a ch em ical d r iv e f o r neomorphism in c a rb o n a te s can be p ro v id ed by e i t h e r : 1 ) a phase change, i . e . , in v e rs io n from an u n s ta b le phase such as a r a g o n ite to a s t a b l e phase such as c a l c i t e o r n o n s to ic h io m e tr ic to s to ic h io m e tr ic d o lo m ite , 2 ) lo w erin g s u r f a c e e n e rg y , whereby a c o a rs e r g r a in s iz e i s e n e r g e tic a lly more fa v o ra b le th a n a f i n e g r a in s i z e , and 3) s t r a i n r e c r y s t a l l i z a t i o n (F o lk , 1965 and B a th u r s t, 1 9 7 6 ). In th e se d im en tary environm ent th e s e r e a c tio n s in v o lv e d i s s o l u t i o n and r e p r e c i p i t a t i o n in th e p re se n c e o f w ater (F o lk , 1 9 6 5 ). In th e c a se o f th e metamorphism o f th e Hueco d o lo m ite w a te r was th e po re f i l l i n g f l u i d d u rin g r e c r y s t a l l i z a t i o n (H. Ja c k so n , 1973a and 1973b). The r e s u l t s o f th e h y d ro th erm al bomb ex p erim en ts d em o n strated 100 t h a t s u r f a c e energy a lo n e i s n o t enough to r e c r y s t a l l i z e d o lo m ite a t th e te m p e ra tu re s and th e r e a c tio n tim es a llo w ed . F in e g ra in e d ( l e s s th a n ljim) s to ic h io m e tr ic * o rd e re d d o lo m ite ( f i g . 18) f a i l e d to show any s ig n o f in c re a s e d g r a in s i z e even a f t e r long r e a c tio n tim es a t 300°C. This d i f f i c u l t y in r e c r y s t a l l i z a t i o n a ls o proved to be tr u e f o r f i n e g r a in c a l c i t e s ( f i g . 1 9 ). Chai (1974) r e c r y s t a l l i z e d c a l c i t e in th e p re se n c e o f w ater a t 500°C and 2 k ilo b a r s o f p r e s s u r e . Much lo n g e r tim es a v a i la b l e i n n a tu r e may allo w r e c r y s t a l l i z a t i o n to o c c u r a t low er te m p e ra tu re s . O rdered, s to ic h io m e tr ic d o lo m ite a t M arble Canyon underw ent r e c r y s t a l l i z a t i o n a t te m p e ra tu re s in th e ran g e o f th o s e used in h y d ro th erm al bombs f o r t h i s s tu d y . The e x p e rim e n ta l r e c r y s t a l l i z a t i o n o f s u p r a ti d a l d o lo m ite and d o lo m itiz e d c o r a l l i n e a lg a e from Aruba, N.A. ( f i g s . 21 and 23) was most l i k e l y d riv e n by th e n o n s to ic h io m e try o f th e d o lo m ite s (Mg++/Ca++ + Mg'1-1" = 0 . 4 and 0 .4 6 r e s p e c t iv e l y ) and h ig h s u rf a c e en erg y caused by t h e i r sm all g r a in s i z e . C o arser g ra in e d (20 #tm) n o n s to ic h io m e tric d o lo m ite f a i l e d to r e c r y s t a l l i z e under s im i la r c o n d itio n s , p o s s ib ly due to th e s t a b i l i z i n g e f f e c t o f i t s low er s u r f a c e en e rg y . The s to ic h io m e try o f a n c ie n t d o lo m ite s was s tu d ie d by Lumsden and Chlmalusky (1 9 8 0 ). They found th e fo llo w in g two r e l a t i o n s h i p s : 1) s to ic h io m e tr ic d o lo m ite ten d ed to have a l a r g e r g r a in s iz e th a n n o n s to ic h io m e tric (calciu m e n ric h e d ) d o lo m ite ; and 2) s to ic h io m e tr ic d o lo m ite was more o f te n a s s o c ia te d w ith e v a p o r i tic d e p o s itio n a l enviro n m en ts th a n n o n s to ic h io m e tric d o lo m ite . The d o lo m ite s a s s o c ia te d w ith modern e v a p o r ite s e t t i n g s te n d to be v e ry f in e g ra in e d (<5 fim) and calciu m e n ric h e d (D effey es e t a l . , 1965; T ilin g 101 e t a l . , 1965; Shinn e t a l . , 1965; McKenzie, 1 981). Neomorphism may e x p la in t h i s a p p a re n t d isc re p a n c y between r e c e n t and a n c ie n t s u p r a t i d a l d o lo m ite s. The n o n s to ic h io m e try and h ig h s u r f a c e en erg y (due to sm all g r a in s iz e ) o f s u p r a ti d a l d o lo m ite s sh o u ld make them p a r t i c u l a r l y s u s c e p tib le to neom orphic r e c r y t a l l i z a t i o n . C o arser g ra in e d d o lo m ite formed in o th e r d ia g e n e tic s e t t i n g s may be more r e s i s t e n t to neomorphism. T h e re fo re , a n c ie n t s u p r a ti d a l d o lo m ite s a r e th o s e th a t have most l i k e l y undergone neomorphism. tim e th e y a t t a i n s to ic h io m e tr y . At th e same R e c r y s ta lliz e d d o lo m ite s r o u ld a ls o be more l i k e l y to have la r g e r g r a in s i z e s , on th e a v e ra g e , th a n u n r e c r y s ta lli z e d d o lo m ite s . X enotopic d o lo m ite te x tu r e sh o u ld o n ly r e s u l t from neomorphism i f i t o c c u rre d a t e le v a te d te m p e ra tu re s . R e c r y s ta lli z a ti o n o f n o n s to ic h io m e tric to s to ic h io m e tr ic d o lo m ite may o c c u r n e a r th e s u rfa c e a t n e a r 25°C p ro d u cin g an i d i o to p ic te x tu r e in acco rd an ce w ith c r y s t a l grow th th e o ry . As i t has been shown th a t h ig h te m p e ra tu re rep lacem en t o f lim e s to n e by d o lo m ite and h ig h te m p e ra tu re r e c r y s t a l l i z a t i o n o f d o lo m ite b o th can produce th e same te x t u r e , a problem e x i s t s in d i f f e r e n t i a t i n g te x tu r e s o f neom orphic o r i g i n from th o s e o f rep la cem e n t o r i g i n . A com parison o f d o lo m itic m arble o f rep lacem en t o r i g i n ( f i g s . 30 and 31) to d o lo m itic m arble o f r e c r y s t a l l i z a t i o n o r i g i n ( f i g s . 28 and 29) i l l u s t r a t e s t h i s p o in t. T h e o r e tic a lly , no d if f e r e n c e in c r y s t a l morphology i s to be ex p ected i f th e same grow th mechanisms produce b o th d o lo m ite s. What fo llo w s i s an a tte m p t to show how x e n o to p ic d o lo m ite produced by neomorphism may be d is tin g u is h e d from th a t produced by rep la cem e n t in t«o a n c ie n t d o lo m ite s . U n fo rtu n a te ly most o f th e 102 ev id en ce used I s e q u iv o c a l an d , t h e r e f o r e , c o n c lu sio n s drawn a r e open to q u e s tio n . The O rig in o f X enotopic D olom ite: G alena Group R egional d o lo m itiz a tlo n o f th e G alena Group p ro b ab ly o c c u rre d n e a r th e s u r f a c e d u rin g e a r ly d ia g e n e s is (B adiozam ani, 1972 and D elgado, w r itte n com m unication, 1 9 8 0 ). t o s t o f th e x e n o to p ic d o lo m ite s in th e G alena Group a r e in t e r p r e t e d as p ro b ab ly r e s u l t i n g from neomorphism o f th e s e e a r l y d o lo m ite s a t e le v a te d te m p e ra tu re s , p ro b ab ly d u rin g th e e p ig e n e tic ev en t a s s o c ia te d w ith s u l f i d e o re g e n e s is in t h i s a r e a . This i n t e r p r e t i o n i s based on th e r e s u l t s o f s t a b l e is o to p e s tu d ie s o f th e Hueco and G alena d o lo m ite s as w e ll as o th e r p e tro g ra p h ic e v id e n c e . S ta b le Is o to p e S tu d ie s : R e c r y s t a l l i z a t i o n o v er a te m p e ra tu re g r a d ie n t o f about 400°C a t M arble Canyon produced a 8^®0 d e p le tio n o f 2 .4 6 p e r m il. (T ab le 6 ). Assuming an ocean w ater com postion in an open system , homogeneous pore f l u i d c o n te n t, and u sin g Matthews and K atz d o lo m ite -w a te r f r a c t i o n a t i o n e q u a tio n , a d e p le tio n o f ab o u t 20 p e r m il. vrould be ex p ec ted f o r a 400°C te m p e ra tu re g r a d ie n t (M atthews and K atz, 1977). At M arble Canyon about 100 p o re volumes o f w ater a r e e s tim a te d to have moved th ro u g h th e c o u n try ro ck d u rin g metamorphism (H. Jack so n , 19 7 3 a). T h e re fo re , th e system th a t e x is te d d u rin g th e M arble Canyon m etam orphlc ev en t was ro c k p ro b ab ly dom inated and o n ly p a r t i a l l y open w ith r e s p e c t to f l u i d . The r e s t r i c t e d amount o f *®0 is o to p e in 103 th e system lim ite d th e e x te n t to w hich th e r e c r y s t a l l i z i n g d o lo m ite could f r a c t i o n a t e . R e c r y s ta lli z a ti o n in a c lo se d system w ith a sm all volume o f w ater w i l l th e r e f o r e r e s u l t in a sm all r e g a r d le s s o f te m p e ra tu re (Spooner e t a l . , 1977). G en e ra lly sm a ll d if f e r e n c e s in 5*®0 were o b serv ed between i d i o t o p i c and x e n o to p ic Galena d o lo m ite sam ples (av erag in g l e s s th a n 1 p er m i l .) w ith th e x e n o to p ic d o lo m ite s having more n e g a tiv e v a lu e s (T ab le 6 ) . This i s c o n s is te n t w ith a neomorphism ( r e c r y s t a l l i z a t i o n ) o r i g i n o f th e x e n o to p ic d o lo m ite s a t e le v a te d te m p e ra tu re i f a ro ck dom inated sy stem , a s a t M arble Canyon, i s presum ed. However, d o lo m ite has been o b serv ed to r e p la c e lim e s to n e , even a t h ig h te m p e ra tu re , r e t a i n i n g th e oxygen is o to p e s ig n a tu r e o f th e p re c u rs o r lim e s to n e ( E p s te in e t a l . , 1964; Friedm an and H a ll, 1 963). T h e re fo re , a lth o u g h a neom orphic o r i g i n o f some o f th e G alena d o lo m ite i s c o n s is te n t w ith th e oxygen is o to p e d a ta , a rep lacem en t o r i g i n a ls o f i t th e s e d a ta . had some o f th e lo w est Undulose id io to p ic - E d o lo m ite s ( f i g . 36) fil®0 v a lu e s (T ab le 7 ) . These a r e in a r e a s o f h ig h p o r o s ity and a r e i n t e r p r e t e d as having e q u i lib r a t e d in a system more open w ith r e s p e c t to th e h o t w a te r. showed t h e o r e t i c a l l y t h a t S v erjen sk y (1981) 0*® d e p le tio n o f c a rb o n a te s n ear o re b o d ie s in th e Upper M is s is s ip p i V alley z in c - le a d d i s t r i c t co u ld b e s t be e x p la in e d by in c re a s e d p o r o s ity n e a r th e o re b o d ie s r a th e r th a n h ig h e r te m p e ra tu re s . O ther Evidence f o r Neomorphism o f G alena D olom ites: Much o f th e x en o to p ic-A d o lo m ite in th e G alena Group i s p atch y i n d i s t r i b u t i o n mixed w ith id i o to p ic d o lo m ite t e x t u r e s . Some o f 104 th e s e id i o t o p i c d o lo m ite s may r e p r e s e n t th e p re c u rs o r d o lo m ite , p a r t i c u l a r l y th e ones t h a t a r e n o n -u n d u lo se, f i n e r g ra in e d th a n n earb y x e n o to p ic d o lo m ite a n d /o r zoned (com pare, f o r in s ta n c e , l o c a l i t i e s 19 and 20 i n Appendix 3 ) . The patch y d i s t r i b u t i o n o f th e x en o to p ic-A d o lo m ite s would be ex p ected in a p a r t i a l r e c r y s t a l l i z a t i o n o f an i d i o to p ic d o lo m ite . T his i s one o f th e p e tro g r a p h ic c r i t e r i a d is c u s s e d by B a th u rst (1976) as ev id en ce f o r neomorphism in lim e s to n e s . Neomorphism would be ex p ected to d e s tro y zoning in th e d o lo m ite b ein g r e c r y s t a l l i z e d . X enotopic d o lo m ite s in th e G alena Group a re r a r e l y zoned and when th e y a r e , do n o t have th e w e ll developed zoning o f th e i d i o t o p i c d o lo m ite s . P o s s ib le s u b tle changes i n chem ical c o n d itio n s d u rin g r e c r y s t a l l i z a t i o n can r e s u l t in a zoned x en o to p ic d o lo m ite ( F a i r c h i l d , 19 8 0 ); how ever, a r e c r y s t a l l i z a t i o n would no rm ally be ex p ected to have a hom ogenizing e f f e c t in a ch em ica lly c lo se d sy stem . I f a rep lacem en t r a t h e r th a n neom orphic o r ig i n fo r x en o to p ic d o lo m ite i n th e G alena Group i s p o s tu la te d , one i s face d w ith th e problem o f movement o f la r g e amounts o f Mg^+ . i t i s p o s s ib le to m o b iliz e Mg^+ Qn a lo c a l s c a le by p re s s u re s o lu tio n o f nearby d o lo m ite . This may have happened on a lo c a l s c a le in th e Galena Group; how ever, th e r e i s no ev id en ce o f p re s s u re s o lu tio n on th e s c a le n e c e ss a ry to produce th e volume o f x e n o to p ic d o lo m ite found in th e G alena Group. Mg2+ p o s s ib ly was in tro d u c e d d u rin g th e p e rio d o f h y d ro th erm al o r e g e n e s is . The p resen ce o f d o lo m ite cem ents a s s o c ia te d w ith o re s s u g g e s ts th a t th e o re f l u i d s were cap a b le o f 105 p rodu cin g d o lo m ite (B a ile y and Cameron, 1951; Heyl e t a l . , 1959; and H a ll and F riedm an, 1 9 6 9 ). However, th e volume o f x e n o to p ic d o lo m ite ( n e a r ly 1 /4 o f th e G alena Group i f sam pling f o r t h i s stu d y i s r e p r e s e n t a tiv e ) i n d i c a te s t h a t t h i s mechanism would be i n s u f f i c i e n t to tr a n s p o r t enough Mg^+ f o r w idespread e p ig e n e tic d o lo m itiz a tio n . T h e re fo re , th e b e s t e x p la n a tio n f o r most o f th e w id esp read x e n o to p ic te x tu r e in th e G alena Group i s t h a t i s r e s u lt e d from th e neomorphism o f a p r e - e x i s t in g d o lo m ite . ' The O rig in o f X enotopic D olom ite: T ren to n Form ation Mbst o f th e x e n o to p ic d o lo m ite in th e T ren to n Form ation o f th e M ichigan B asin p ro b ab ly formed d u rin g th e m ig ra tio n , alo n g f r a c t u r e s o f warm b r in e s a s s o c ia te d w ith one o r s e v e r a l e p ig e n e tic ev e n ts (Shaw, 1975; T a y lo r, 1 9 8 2 ). X enotopic-A d o lo m ite a s s o c ia te d w ith f r a c t u r i n g in th e T ren to n Form ation i s in t e r p r e te d a s p ro b ab ly b ein g o f h ig h te m p e ra tu re rep lacem en t o r i g i n . T h is i n t e r p r e t a t i o n i s su p p o rte d by th e fo llo w in g : 1) The b o d ie s o f x e n o to p ic d o lo m ite o f te n a r e o b serv ed to l a t e r a l l y and v e r t i c a l l y g rad e in to b i o m i c r i t i c lim e s to n e s (Shaw, 1975, f i g . 10) t h a t a r e p a r t i a l l y r e p la c e d by x e n o to p ic -P d o lo m ite ( f i g s . 47 and 4 8 ). This i n d i c a te s a d i r e c t rep la cem e n t o f b io m ic r ite by th e x e n o to p ic d o lo m ite r a t h e r th a n a r e c r y s t a l l i z a t i o n by a p re c u rs o r d o lo m ite . 2) No ev id en ce o f such a p re c u rs o r i s o b s e rv e d . The f r a c t u r e system s in th e M ichigan B asin o f f e r c o n d u its f o r in tr o d u c tio n o f Mg^+ r i c h , warm s o lu tio n s from deep er in th e b a s in a s su g g e ste d by Shaw (1 9 7 5 ). The lim ite d a r e a l e x te n t o f th e s e d o lo m ite s d im in ish e s th e problem o f moving enough Mg2+ to 106 acco m p lish th e d o lo m ltiz a tio n . F lu id in c lu s io n s tu d ie s by Shaw (1975) on pore f i l l i n g d o lo m ite s o f th e A lbion S cip io f i e l d in d ic a te d a te m p e ra tu re in e x c e ss o f 80°C d u rin g th e p r e c i p i t a t i o n o f th e s e d o lo m ite s . T a y lo r (1982) r e p o r te d 8180 v a lu e s a v era g in g - 8 .9 p e r m il. (PDB) f o r b u lk sam ples o f f r a c t u r e r e l a t e d T renton d o lo m ite from th e N o r th v il le , A lb io n -S c ip io , Reading and P en tw ater o i l f i e l d s . av e ra g e was based on 51 sam ples ra n g in g from to 8 180 = - 1 1 .4 p e r m il. T his = - 6 .9 p e r m il. Four v a lu e s f o r x en o to p ic-C (s a d d le ) d o lo m ite cements ranged between 8^80 = - 8 .8 and - 1 1 .2 p e r m il (PDB) and a v e ra g in g - 9 .8 p e r m il. Tem perature e s tim a te s were b ased on th e s e d o lo m ite cem ents because i t i s more l i k e l y t h a t th e y e q u i l i b r a t e d in a system open w ith r e s p e c t to w ater th a n th e b u lk sam p les. The te m p e ra tu re e s tim a te s ran g e between 50°C, assum ing O rd o v ic ia n se a w ater o f 8*80 = -5 p e r m i l . , to >80°C, assum ing o i l f i e l d b r in e o f fil8 0 = - 1 .4 p e r m il. (T a y lo r, 1 982). P o s s ib ly some neomorphism o f an e a r l i e r d o lo m ite o c c u rre d n e a r th e f r a c t u r e s d u rin g th e e p ig e n e tic a c t i v i t y . T his most l i k e l y would have o c c u rre d in a r e a s o f r e g io n a l d o lo m ltiz a tio n in th e w e ste rn p a r t o f th e M ichigan B asin ( f i g . 4 ) . No ev id en ce f o r t h i s was found, p o s s ib ly because o f a la c k o f c o n tr o l in t h i s a r e a . F o s s ils in b io m ic r ite s which a r e re p la c e d by x en o to p ic-A d o lo m ite and a r e su rro u n d ed by id i o t o p i c d o lo m ite ( f i g . 44) a re a ls o in t e r p r e t e d as rep lacem en t in o r i g i n . T h is r e l a t i o n s h i p i s found b o th i n th e "cap" and r e g io n a l d o lo m ite s o f th e T ren to n . The d o lo m ltiz a tio n o f th e s e b io m ic r ite s p o s s ib ly proceeded as fo llo w s : 1) The m i c r i t i c p o r tio n i s re p la c e d by f in e g ra in e d i d i o to p ic d o lo m ite 107 ( f i g . 4 1 ) , 2) f o s s i l s and u n re p la c e d m i c r it e a r e re p la c e d by x e n o to p ic d o lo m ite ( f i g . 47) presum ably a t h ig h e r te m p e ra tu re , f i n a l l y r e s u l t i n g i n 3) a d o lo m ite i n which th e o r i g i n a l b io m ic r ite f a b r i c i s p re s e rv e d ( f i g . 4 4 ). X enotopic-A d o lo m ite r e p la c in g f o s s i l s in two sam ples from th e T rento n "cap" in th e N o r th v ille o i l f i e l d ( f i g . 4) were found to have 6 ^ va l u e s 1 p e r m il. low er th a n t h a t o f th e su rro u n d in g id io to p ic - S d o lo m ite r e p la c in g m i c r it e (T a y lo r, p e rs o n a l com m unication, 1 9 8 2 ). G alena d o lo m ite s. A s im i la r r e l a t i o n s h i p was n o ted above in th e A c lo se d system can be p o s tu la te d d u rin g th e d o lo m ltiz a tio n o f th e f o s s i l s i f a lo c a l so u rce o f Mg^+ e x i s t e d . S t y l o l i t i z a t i o n o f th e f in e g r a in id i o t o p i c d o lo m ite su rro u n d in g th e d o lo m itiz e d f o s s i l s s u g g e s ts t h a t th e Mg^+ n e c e s s a ry f o r th e d o lo m ltiz a tio n o f th e f o s s i l s may, i n some c a s e s , have been d e riv e d l o c a lly by p r e s s u r e s o lu ti o n . S ig n ific a n c e and F u rth e r Study This stu d y a tte m p ts to d em o n strate th a t o b s e r v a tio n t h a t x en o to p ic d o lo m ite may be an im p o rta n t i n d i c a to r o f e p ig e n e tic d o lo m ltiz a tio n o f lim e sto n e o r neomorphism o f a p r e - e x i s t in g d o lo m ite . The te m p e ra tu re s p o s tu la te d f o r th e o r i g i n o f x e n o to p ic d o lo m ite (>50°C) c o in c id e w ith th o s e n e c e ss a ry f o r p etro leu m m a tu ra tio n and a s s o c ia te d w ith M is s is s ip p i V alle y Type s u l f i d e m in e r a liz a tio n . T h e re fo re , i d e n t i f i c a t i o n o f x e n o to p ic te x tu r e may be o f v a lu e as an e x p lo ra tio n t o o l when more p r e c is e p a le o te m p e ra tu re in d i c a to r s a re u n a v a ila b le . The low p o r o s ity o f th e x e n o to p ic d o lo m ite s examined in t h i s stu d y 108 s u g g e s t t h a t r e c r y s t a l l i z a t i o n o f d o lo m ite may have a d e tr im e n ta l e f f e c t on r e s e r v o ir q u a l i t y . F u rth e r l i n e s o f r e s e a r c h th a t may be o f i n t e r e s t a r e : 1) I n v e s ti g a tio n o f sabkha d o lo m ite s form ing n e a r 50°C to see i f th e y could be c h a r a c te r iz e d as x e n o to p ic . appro ach o r even be above CRT. The te m p e ra tu re s h e re may The u n eq u iv o cal d is c o v e ry o f low te m p e ra tu re (25°C) s to ic h io m e tr ic x en o to p ic-A d o lo m ite vrould p u t th e h ig h te m p e ra tu re h y p o th e sis in je o p a rd y . I d e a l ly , th e p la c e to lo o k f o r such d o lo m ite i s in u n a lte r e d p o s t-C re ta c e o u s ro ck s th a t have n o t been b u rie d d e e p ly . 2) Rapid c r y s t a l grow th may fa v o r th e developm ent o f in c lu s io n s a s compared to slow grow th (S p ry , 1 969). I t seems re a s o n a b le , th e r e f o r e , t h a t x e n o to p ic d o lo m ite s should have more in c lu s io n s th a n i d i o t o p i c d o lo m ite s i f th e y in d eed grew f a s t e r . A lthough th e x e n o to p ic d o lo m ite s i n t h i s stu d y had numerous in c lu s io n s so a p p a re n tly d id many o f th e id i o t o p i c d o lo m ite s . An a tte m p t sh o u ld be made to q u a n tif y th e r e l a t i v e number o f in c lu s io n s in x e n o to p ic and id i o to p ic d o lo m ite s. 3) The d o lo m ite c l a s s i f i c a t i o n system developed f o r t h i s stu d y proved q u ite u s e f u l in c a te g o r iz in g d o lo m ite te x tu r e s in th e rocks s tu d ie d . I t re m a in s, how ever, f o r t h i s c l a s s i f i c a t i o n system to be a p p lie d to a broad ran g e o f d o lo m ite s from a number o f s t r a t i g r a p h i c and g eo g rap h ic lo c a tio n s b e fo re i t can be u n iv e r s a l ly a p p lie d . CONCLUSIONS X enotopic d o lo m ite te x tu r e i s d e fin e d as a m osaic o f d o lo m ite an h ed ra w ith cu rv ed , i n t e r lo c k i n g , i r r e g u l a r in t e r g r a i n b o u n d a rie s. X enotopic d o lo m ite u s u a lly has u n d u lo se e x t in c ti o n and i s s im ila r in 109 ap p earan ce to neom orphic te x tu r e s o b serv ed in some lim e s to n e s . X enotopic d o lo m ite te x tu r e s were o b serv ed in th e G alena Group (O rd o v ic ia n ), W isconsin, th e T ren to n Form ation (O rd o v ic ia n ), M ichigan d o lo m ite m arble and h ig h te m p e ra tu re s y n th e tic d o lo m ite . X enotopic do lo m ite te x tu r e was n o t o b serv ed in any o f th e Cenozoic d o lo m ite s in v e s tig a te d in t h i s s tu d y . X enotopic d o lo m ite te x tu r e s c o n tr a s t w ith i d i o to p ic te x tu r e s t h a t a r e common i n Cenozoic as w e ll as a n c ie n t d o lo m ite s . I d io to p ic do lo m ite te x tu r e i s c h a r a c te r iz e d by m o stly e u h e d ra l to su b h e d ra l g r a in s and smooth, s t r a i g h t i n t e r g r a i n compromise b o u n d a rie s. A s t a t i s t i c a l m ech an ical model f o r c r y s t a l grow th proposed by Jack so n (1958a and 1958b) p r e d ic ts t h a t a t low te m p e ra tu re s c r y s t a l s grow by th e a d d itio n o f atoms la y e r by la y e r on a c r y s t a l f a c e . This k in d o f grow th r e q u ir e s s u r f a c e n u c le a tio n s i t e s , such as d is lo c a ti o n s and r e s u l t s in smooth c r y s t a l fa c e s and e u h e d ra l g r a in m o saics. Above a " c r i t i c a l roughening te m p e ra tu re " s u r f a c e n u c le a tio n does n o t r e q u ir e d is lo c a ti o n s and atoms a r e added randomly to th e c r y s t a l fa c e a s a rough s u rfa c e i s e n e r g e tic a ly more f a v o r a b le th a n a smooth s u r f a c e . T h is r e s u l t s in n o n -fa c e te d c r y s t a l s and can produce an in te r lo c k in g m osaic o f anhedra such as i s o b serv ed in x e n o to p ic d o lo m ite . I t i s h y p o th e sized t h a t a " c r i t i c a l roughening te m p e ra tu re " e x i s t s f o r d o lo m ite betw een 50°C and 100°C. X enotopic d o lo m ite te x tu r e s a r e produced by th e rep lacem en t o f lim e sto n e by d o lo m ite a n d /o r neom orphic r e c r y s t a l l i z a t i o n o f d o lo m ite a t e le v a te d te m p e ra tu re a f t e r b u r i a l . I d io t o p ic d o lo m ite s a r e produced below th e " c r i t i c a l roughening te m p e ra tu re " by n e a r s u r f a c e d o lo m ltiz a tio n p ro c e sse s. C a l c it e , in c o n tr a s t to d o lo m ite , has a " c r i t i c a l 110 roughening te m p e ra tu re " below 25°C, th u s a n h e d ra l g r a in t e x t u r e s , c h a r a c t e r i s t i c o f neom orphic lim e s to n e , can be produced d u rin g e a r ly d ia g e n e s is a t low te m p e ra tu re . S y n th e tic x en o to p ic d o lo m ite was produced in la b o r a to r y h y d ro th erm al bombs by d o lo m ltiz a tio n o f a r a g o n ite and c a l c i t e s k e l e t a l frag m en ts and by r e c r y s t a l l i z a t l o n o f n o n s to ic h lo m e tric Cenozoic d o lo m ite s . These s y n th e s e s were perform ed a t te m p e ra tu re s o f 250° and 300°C. X enotopic d o lo m ite r e s u lt e d from th e m etam orphic r e c r y s t a l l i z a t i o n o f id i o t o p i c d o lo m ite s in th e Hueco Lim estone (P erm ia n ), C u lb e rtso n C o ., T ex as, n e a r th e M arble Canyon in t r u s i o n . The r e c r y s t a l l i z a t i o n o c c u rre d a t te m p e ra tu re s ra n g in g from 250° to 600°C. L ate hy d ro th erm al d o lo m ltiz a tio n o f p e r i c l a s e - c a l c i t e m arble a d ja c e n t to th e i n t r u s i o n a lso had x e n o to p ic t e x t u r e . X enotopic d o lo m ite in th e G alena Group was produced by neomorphism o f a p r e - e x i s t in g i d i o to p ic d o lo m ite . This r e c r y s t a l l i z a t i o n p ro b ab ly o c c u rre d d u rin g th e emplacement o f th e Upper M is s is s ip p i V alley le a d - z in c s u lf id e s a t te m p e ra tu re s o f betw een 50°C and 120°C (B a ile y and Cameron, 1 9 5 1 ). S ta b le oxygen is o to p e d a ta f o r th e G alena d o lo m ite a r e c o n s is te n t w ith th e r e c r y s t a l l i z a t i o n model. X enotopic d o lo m ite in th e T ren to n Form ation was produced by rep lacem en t o f lim e sto n e a t e le v a te d te m p e ra tu re ; Most o f t h i s p ro b ab ly o c c u rre d d u rin g m ig ra tio n Mg2+ r i c h b r in e s along f r a c t u r e sy stem s. Minor rep lacem en t o f lim e sto n e p o s s ib ly o c c u rre d d u rin g p re s s u re s o lu tio n o f n earb y i d i o to p ic d o lo m ite s , which p ro v id ed a so u rce o f Mg^+ . Appendix 1 D esigns f o r H ydrotherm al Bombs Used in th e Experim ents 3 copper gasket S tainless S te e l H y d ro th e rm a l Bomb 6.4CC Capacity SCALE S tain less w ith steel IN INCHES h y d r o t h e r m a l bomb a n 1 8 . 5 ml c a p a c i t y . A seal ( d e s i g n by M orey, is effected 1953) by a c o p p e r w a s h e r a n d t h e s c r e w c a p i s made o f molybdnum s t e e l . Appendix 2 E x p erim en tal R e s u lts 113 1) High Magnesium Calcite to Dolomite U n a lte re d Sample: G o n lo lith o n s p . s k e l e t a l m a te r ia l, 25 mole p e rc e n t MgC03 F lu id C o n te n t: 2 M olar Mg/CaCl2 s o lu tio n R atio o f T o ta l C atio n s (sam ple and s o l u t i o n ) : Mg/Mg+Ca = .25 R eac tio n Time: 98 h r s . R e a c tio n T em p eratu re: 300°C P ro d u c t: 100% w e ll o rd e re d d o lo m ite , 49 mole p e rc e n t M ineralogy: MgC03 T e x tu re : Replacem ent by ovad shaped c r y s t a l s w ith in ­ d i s t i n c t f a c e s ( . 3 to .5 /im). A lg al c o n c e p tic le s som etim es f i l l e d w ith d o lo m ite cem ent; b a s a l te rm in a te d s te e p rhom bic form (4041) and (0001) superim posed onto normal rhombic form . 114 2) High Magnesium Calcite to Dolomite U n a lte re d Sample: G o n io lith o n s p . s k e l e t a l m a te r ia l, 25 mole p e rc e n t MgC03 F lu id C o n te n t: 2 Molar Mg/CaCl2 s o lu ti o n R atio o f T o ta l C atio n s (sam ple and s o l u t i o n ) : Mg/Mg+Ca * .25 R eac tio n Time: 839 h r s . R eac tio n T em p eratu re: 300°C P ro d u c t: 100% w e ll o rd e re d d o lo m ite , 50 mole p e rc e n t M ineralogy: MgC03 T ex tu re: Same a s in experim ent 1 115 3) High Magnesium Calclte to Dolomite U n a lte re d Sam ple: G o n lo llth o n s p . s k e l e t a l m a te r ia l, 25 mole p e rc e n t MgC03 F lu id C o n te n t; 2 M olar Mg/CaCl2 s o lu ti o n R atio o f T o ta l C atio n s (sam ple and s o l u t i o n ) : Mg/Mg+Ca = .25 R eac tio n Time: 120 h r s . R e a c tio n T em p eratu re: 250°C P ro d u c t: 100% w e ll o rd e re d d o lo m ite , 51 mole p e rc e n t M in eralo g y : MgC03 T e x tu re : Same as in exp erim en t 1 116 4) High Magnesium Calcite to Dolomite U n a lte re d Sample; E ch in o id s k e l e t a l m a te r ia l, 13 mole p e rc e n t MgC03 F lu id C o n te n t; 2 M olar Mg/CaCl2 s o lu ti o n R atio o f T o ta l C atio n s (sam ple and s o l u t i o n ) : Mg/Mg+Ca = ,239 R e a c tio n Time; 168 h r s . R e a c tio n T em p eratu re; 300°C P ro d u c t; 100% w e ll o rd e re d d o lo m ite , 50 mole p e rc e n t M in eralo g y : MgC03 T e x tu re : Pseudom orphic rep lacem en t o f HMC in c lu d in g p r e s e r v a tio n o f C -ax is o r i e n t a t i o n . I n d iv id u a l d o lo m ite c r y s t a l s too sm all to r e s o lv e w ith SEM. 117 5) High Magnesium Calcite to Low Magnesium Calcite U n a lte re d Sample: G o n io lith o n s p . s k e l e t a l m a te r ia l, 25 m ile p e rc e n t MgC03 F lu id C o n te n t: 1 M olar CaCl2 s o lu tio n R atio o f T o ta l C atio n s (sam ple and s o l u t i o n ) : Mg/Mg+Ca = .04 R eac tio n Time: 335 h r s . R eac tio n T em p eratu re: 300°C P ro d u c t: LMC, 4 mole p e rc e n t MgC03 M ineralogy: T ex tu re: Replacem ent te x tu r e s im ila r to exp erim en t 1 ( . 5 to 1 Jim). A lg al c o n c e p tic a ls f i l l e d w ith hexa­ g o n al s c a le n o h e d ra l c a l c i t e cem ent. 118 6) High Magnesium Calcite to Low Magnesium Calcite U n a lte re d Sample: G o n io lith o n s p . s k e l e t a l m a te r ia l, 25 m ile p e rc e n t MgCC>3 F lu id C o n te n t: 1 M olar CaCl2 s o lu tio n R atio o f T o ta l C a tio n s (sam ple and s o l u t i o n ) : Mg/Mg+Ca ■ .05 R e a c tio n Time: 1516 h r s . R eac tio n T em p eratu re: 300°C P ro d u c t: LMC, 4 mole p e rc e n t MgCOg M ineralogy: T e x tu re : Same as i n ex p erim en t 5 7) Aragonite to Dolomite Unaltered Samples F lu id C o n te n t: Strombus sp. shell fragments, aragonite 1 Molar Mg/CaCl2 s o lu ti o n R atio o f T o ta l C atio n s (sam ple and s o l u t i o n ) : Mg/Mg+Ca = .15 R e a c tio n Time: 136 h r s . R eac tio n T em p eratu re: 300°C P ro d u c t: LMC w ith t r a c e o f d o lo m ite . M ineralogy: T e x tu re : Not examined w ith SEM 120 8) Aragonite to Dolomite Unaltered Sample: F lu id C o n te n t: Strombus sp. shell fragments, aragonite 1 M alar Mg/CaCl2 s o lu ti o n R atio o f T o ta l C atio n s (sam ple and s o l u t i o n ) : Mg/Mg+Ca ■ .157 R eac tio n Time: 23 h r s . R eac tio n T em p eratu re: 300°C P ro d u c t: LMC w ith tr a c e o f d o lo m ite . M ineralogy: T e x tu re : Not examined w ith SGM 121 9) Aragonite to Dolomite Unaltered Sample: Strombus sp. shell fragments, aragonite F lu id C o n te n t: 2 M olar Mg/CaCl2 s o lu ti o n R atio o f T o ta l C atio n s (sam ple and s o l u t i o n ) : Hg/Mg+Ca » .30 R eac tio n Time: 239 h r s . R eac tio n T em p eratu re: 250°C P ro d u c t: 43% w e ll o rd e re d d o lo m ite (49 mole p e rc e n t M in eralo g y : MgC0 3 ) 57% c a l c i t e (2 mole p e rc e n t MgCOj) T e x tu re : I n te r lo c k in g m osaic o f d o lo m ite a n h e d ra , c h a ra c ­ t e r i s t i c o f x e n o to p ic t e x t u r e , in a r e a c tio n rim , around a c o re o f in v e r te d c a l c i t e a ls o w ith an in t e r lo c k i n g a n h e d ra l t e x t u r e , c h a r a c t e r i s t i c o f neom orphic s p a r . In th i n s e c tio n w ith a p o la r i z in g m icroscope th e a r a g o n ite i s re p la c e d by x e n o to p ic d o lo m ite w ith s tr o n g ly un d u lo se e x t i n c t i o n su rro u n d in g a co re o f neom orphic c a l c i t e s p a r w ith un d u lo se e x t in c ti o n and f a s c i c u l a r te x tu r e . 10) Aragonite to Dolomite U n a lte re d Sam ple; F lu id C o n te n t; A rea ponderosa s h e l l fra g m e n ts , a r a g o n ite 2 M olar Mg/CaCl2 s o lu ti o n R atio o f T o ta l C a tio n s (sam ple and s o l u t i o n ) : Mg/Mg+Ca ■ .298 R eac tio n Time: 334 h r s . R eac tio n T em p eratu re: 250°C P ro d u c t: 73% w e ll o rd e re d d o lo m ite (50 mole p e rc e n t M in eralo g y : MgCO-j) 27% c a l c i t e (4 mole p e rc e n t MgCOg) T e x tu re : The same as in ex p erim en t 9 . Some o f th e s m a lle r s h e l l frag m en ts ap p eared to have been e n t i r e l y re p la c e d by d o lo m ite w ith no c a l c i t e p r e s e n t. M icroprobe*: C a l c it e , CaO = 99.21% D olom ite, CaO = 48.55% MgO = .47% FeO =* .32%** MgO = 51.17% 8 FeO = .28% * M icroprobe r e s u l t s a r e th e av era g e v a lu e s fo r a t l e a s t fo u r peaks ta k e n from a t l e a s t t w lo c a tio n s on each sam ple. ** The ARL m icro p ro b e used c o n s is te n tly re a d s a few te n th s o f a p e rc e n t h ig h in i r o n , t h e r e f o r e th e a c tu a l ir o n c o n te n t i s p ro b ab ly l e s s th a n one te n th o f a p e r c e n t. 123 11) Aragonite to Dolomite Unaltered Sample: Area ponderosa shell fragments, aragonite F lu id C o n te n t: 2 M olar Mg/CaCl2 s o lu ti o n R a tio o f T o ta l C a tio n s (sam ple and s o l u t i o n ) : Mg/Mg+Ca “ .298 R eac tio n Time: 23 h r s . R eac tio n T em p eratu re: 250°C P ro d u c t: 44% d o lo m ite w ith r a t h e r d if f u s e o r d e rin g M ineralogy: p eaks (4 4 mole p e rc e n t MgCOj) 56% c a l c i t e (5 mole p e rc e n t MgCOj) T e x tu re : The same a s in ex p erim en t 9. Very w e ll dev elo p ed s a d d le d o lo m ite c r y s t a l s o b serv ed in some o f th e po re s p a c e . Thin s e c ti o n ex am in atio n o f th e p ro d u c ts o f ex p erim en ts 10 and 11 in d i c a te a s l i g h t l y la r g e r g r a in s iz e w ith lo n g e r cooking tim e s under th e same c o n d itio n . M icroprobe: C a lc ite D olom ite CaO = 98.21% CaO = 54.64% MgO - 1.53% MgO = 45.05% FeO = .26% % FeO = .3 1 I 124 12) Aragonite to Dolomite U n a lte re d Sample; F lu id C o n te n t: A rea p o n d ero sa s h e l l fra g m e n ts , a r a g o n ite 2 M olar Mg/CaCl2 s o lu tio n R atio o f T o ta l C atio n s (sam ple and s o l u t i o n ) : Mg/Mg+Ca = .23 R ea c tio n Time: 979 h r s . R e a c tio n T em p eratu re; 300°C P ro d u c t: 44% W ell o rd e re d d o lo m ite (50 mole p e rc e n t M in eralo g y : MgC03 ) 56% c a l c i t e (4 mole p e rc e n t MgC0 3 ) T e x tu re : The same a s i n experim ent 10. 125 13) Aragonite to Dolomite Unaltered Sample: Area ponderosa shell fragments, aragonite F lu id C o n te n t: 2 M olar Mg/CaCl2 s o lu ti o n R atio o f T o ta l C a tio n s (sam ple and s o l u t i o n ) : Mg/Mg+Ca ■ .24 R eac tio n Time: 24 h r s . R eac tio n T em p eratu re: 300°C P ro d u c t: 43% o rd e re d d o lo m ite (49 mole p e rc e n t M in eralo g y : MgC03 ) 57% c a l c i t e (3 mole p e rc e n t MgC03 ) T e x tu re : The same as i n exp erim en t 10. 126 14) Aragonite to Calcite U n a lte re d Sample; F lu id C o n te n t; Strombus s p . s h e l l fra g m e n ts, a r a g o n ite 1 Molar CaCl2 s o lu ti o n R atio o f T o ta l C atio n s (sam ple and s o l u t i o n ) : Mg/Mg+Ca - 0 R e a c tio n Time: 120 h r s . R ea c tio n T em p eratu re: 300°C P ro d u c t: 100% LMC M ineralogy: T e x tu re : I n te r lo c k in g m osaic o f c a l c i t e an h ed ra a p p a re n tly m a in ta in in g th e o r i g i n a l c - a x is o r i e n t a t i o n o f th e re p la c e d a r a g o n ite . produced in ex p erim en t 9. S im ila r to c a l c i t e 127 15) Aragonite to Calcite Unaltered Samplei Area ponderosa shell fragments, aragonite F lu id C o n te n t: 1 M olar CaCl2 s o lu tio n R atio o f T o ta l C atio n s (sam ple and s o l u t i o n ) : Mg/Mg+Ca ■ 0 R e a c tio n Time: 167 h r s . R e a c tio n T em p eratu re: 250°C P ro d u c t: 100% LMC M ineralogy: T e x tu re : I n te r lo c k in g m osaic o f c a l c i t e an h ed ra a p p a re n tly n o t m a in ta in in g th e o r i g i n a l c - a x is o r i e n t a t i o n o f th e re p la c e d a r a g o n ite . 128 16) Dolomite Recrystallization U n a lte re d Sample; S u p r a tid a l sedim ent from Andros I s la n d , Bahamas c o n ta in in g a r a g o n ite and p ro to d o lo m ite ; p o o rly o rd e re d w ith (015) r e f l e c t i o n a b s e n t, 41% MgC03 g r a in s i z e <3 F lu id C o n te n t; m 2 M olar Mg/CaCl2 s o lu tio n R atio o f T o ta l C atio n s (sam ple and s o l u t i o n ) : Mg/Mg+Ca = .246 R e a c tio n Time; 311 h r s . R ea c tio n T em p eratu re; 300°C P ro d u c t: 100% w e ll o rd e re d d o lo m ite , 50 mole p e rc e n t M ineralogy: MgC03 T e x tu re : A porous a g g re g a te o f b a s a l te rm in a te d s te e p rhomb c r y s t a l s [(4041) and (0001) form s] l e s s th a n 10 jjm. Where c r y s t a l s i n t e r f e r e w ith one a n o th e r, i r r e g u l a r i n t e r g r a i n b o u n d aries form c h a r a c t e r i s t i c o f x e n o to p ic d o lo m ite t e x t u r e . 129 17) Dolomite Recrystallization U n a lte re d Sample: S u p r a tid a l sedim ent from Andros I s la n d , Bahamas. Same sam ple as in experim ent 16. F lu id C o n te n t: 2 M olar Mg/CaCl2 s o lu ti o n R atio o f T o ta l C atio n s (sam ple and s o l u t i o n ) : Mg/Mg+Ca =* .25 R e a c tio n Time: 120 h r s . R e a c tio n T em p eratu re: 300°C P ro d u c t: 100% w e ll o rd e re d d o lo m ite , 50 mole p e rc e n t M in eralo g y : MgC03. T e x tu re : The same as in experim ent 16. 130 18) Dolomite Recrystallization U n a lte re d Sample: D o lo m itized c o r a l l i n e a lg a e from B o n a ire , N.A. Mg++/ Ca++ = .4 6 g r a in s i z e <3 m F lu id C o n te n t: 2 M olar Mg/CaCl2 s o lu ti o n R a tio o f T o ta l C atio n s (sam ple and s o l u t i o n ) : Mg/Mg+Ca = .25 R e a c tio n Time: 2184 h r s . R e a c tio n T em p eratu re: 300°C P ro d u c t: 100% o rd e re d d o lo m ite , 50 mole p e rc e n t M ineralogy: MgC03 T e x tu re : R e c r y s ta lliz e d w ith d e f i n i t e ev id en ce o f g r a in g ro w th . I n te r g r a in b o u n d arie s a r e cu rv ed . Development o f (4041) and (0001) c r y s t a l s forms ( b a s a l te rm in a tio n s and s te e p rhombic fo rm ). C r y s ta ls m ostly betw een 2 N ote: m and 5 m. Bomb f a i l u r e caused te rm in a tio n o f th e experim ent and o n ly a t r a c e o f f l u i d was re c o v e re d . 131 19) Dolomite Recrystallization U n a lte re d Sample: D o lom itized c o r a l l i n e alg a e from B o n a ire , N.A. Mg/Ca+Mg = .46 g r a in s iz e <3 F lu id C o n te n t; m 2 M olar Mg/CaCl2 s o lu tio n R a tio o f T o ta l C atio n s (sam ple and s o l u t i o n ) : Mg/Mg+Ca = .25 R e a c tio n Time: 120 h r s . R e a c tio n T em p eratu re: 300°C P ro d u c t: 100% o rd e re d d o lo m ite , x - r a y in d i c a te s 2 M ineralogy: phases o f d o lo m ite p r e s e n t; 50 mole p e rc e n t MgC03 and le s s th a n 48 mole p e rc e n t MgC0 3 « T ex tu re: R e c r y s ta lli z a ti o n as in experim ent 18. 132 20) Dolomite Recrystallization Attempt U n a lte re d Sample: D o lo m itized mud from B o n a ire , N.A. Mg++/Mg'H‘ + Ca++ = .4 6 g r a in s iz e F lu id C o n te n t: 20 m 2 M olar Mg/CaCl2 s o lu ti o n R atio o f T o ta l C atio n s (sam ple and s o l u t i o n ) : Mg/Mg+Ca ■ .25 R e a c tio n lim e : 720 h r s . R eac tio n T em p eratu re: 300°C P ro d u c t: Unchanged M in eralo g y : T e x tu re : Unchanged Appendix 3 P e tro g ra p h ic D e s c rip tio n s f o r th e G alena Group 133 The fo llo w in g a r e g e n e ra l p e tro g r a p h ic d e s c r ip t io n s o f th e G alena Group s e c tio n s which were sam pled. The d e s c r ip tio n s a r e based on t h i n s e c tio n d e s c r ip tio n s from th e 131 sam ples which were c o l le c t e d d u rin g S eptem ber, 1980. The 16 o u tc ro p s which were v i s i t e d a r e among th o s e d e s c rib e d by David Delgado f o r h i s Ph.D. d i s s e r t a t i o n a t th e U n iv e r s ity o f W isconsin. The num bering system u sed h e re f o r th e l o c a l i t i e s (o u tc ro p s ) i s t h a t o f David D elgado. L o c a lity 13 SW, NW, 10, IN, 4E, L a f a y e tte C o ., Wis. Road c u t , n o rth s id e o f highway N. 4 sam ples c o l le c t e d . Nonporous d o lo m ite s a r e alm ost e n t i r e l y x en o to p ic-A w ith un d u lo se e x t in c ti o n (0 .0 5 to 0 .3 mm) and unzoned. I d io to p ic - E d o lo m ite i s zoned 75% o f th e p o re sp ace i s f i l l e d by opaque n o n -c a rb o n a te m a trix . C ontain s abundant rounded q u a r tz ( f e ld s p a r ? ) sand g r a in s . L o c a lity 14 NE, NE, 9 , IN, 4E, L a fa y e tte C o ., Wis. Road c u t , b o th s id e s o f highway 11 6 sam ples c o lle c te d Nonporous x en o to p ic-A d o lo m ite about 0 .3 mm in p a tc h e s o f 1 to 2 cm. su rrou n d ed by id io to p ic - E and S d o lo m ite , zoned w ith cloudy c e n t e r - c l e a r rim . d o lo m ite . ch alced o n y . A few s t y l o l i t e s a r e p re s e n t in id i o to p ic Abundant rounded q u a r tz ( f e ld s p a r ) sand and some 134 Locality 15 C en ter l i n e ME, ME, 24, IN, IE , L a f a y e tte , C o ., Wis. R oadcut, b o th s id e s o f ro a d , County highway 1. 3 sam ples c o l le c t e d . X enotopic-A d o lo m ite p red o m in ates in a l l 3 sam ples ( 0 .1 - 0 .4 mm), i n a few sam ples i t ap p e a rs to th e zoned, b u t f o r th e most p a r t i t i s v e ry d i r t y and unzoned. P atc h es o f I d io to p ic - S d o lo m ite 0 .0 5 -0 .3 mm w ith good zoning and a few s t y l o l i t e s . Abundant rounded q u a rtz ( f e ld s p a r ? ) san d . L o c a lity 16 NW, NE, 14, IN, IE , L a f a y e tte C o ., Wis. Road c u t , n o r th s id e o f highway 11. 9 sam ples c o l le c t e d . X enotopic-A d o lo m ite ( 0 .1 - 0 .8 mm) i n s c a tt e r e d p a tc h e s and n e a r s t y l o l i t e s 1 to 2 cm a c ro s s in id io to p ic - E and S d o lo m ite (0 .1 to 0 .5 mm), id io to p ic - C d o lo m ite su rro u n d in g vuggy p o r o s ity ( f o s s i l m o ld s). A few h o r iz o n ta l s t y l o l i t e s a r e p r e s e n t. L o c a lity 19 N l/2 , SW, 1 6 , 4N, 2E, Iowa C o ., Wis. Road c u t , b o th s id e s o f U .S. 151. 10 sam ples c o l le c t e d . Dense nonporous d i r t y x en o to p ic-A d o lo m ite ( 0 .1 - 0 .5 mm) p red o m in ates w ith some x e n o to p ic -C (s a d d le )c e m e n ts (up to 1 m) in p o re sp a c e . Zoned id io to p ic - E and S d o lo m ite ( 0 .0 5 - 0 .3 mm) some w ith undulose e x t i n c t i o n in porous a r e a s . H o riz o n ta l s t y l o l i t e s a r e common in 135 x e n o to p ic d o lo m ite s , opaque m a te r ia l commonly c o a ts i d i o to p lc d o lo m ite c r y s t a l s . Vuggy p o r o s ity o f te n f i l l e d by opaque m a te r ia l a n d /o r ch alced o n y . Opaque to p a r t l y tr a n s l u c e n t m in e ra l f i l i n g some p o re space i s a p p a re n tly s p h a l e r i t e . L o c a lity 20 NE30, 6N, 2E, Iowa C o ., H is . Road c u t , b o th s id e s o f U .S. 151. 11 sam ples c o lle c t e d . Lower p a r t o f s e c tio n p red o m in an tly f i n e g ra in e d (ab o u t 0 .1 mm) id io to p ic - S d o lo m ite w ith sm all amounts o f u n d u lo se x en o to p ic-C d o lo m ite cement f i l i n g f o s s i l m olds. In upper p a r t o f th e s e c tio n d i r t y c o a r s e r g r a in i d i o to p ic - S d o lo m ite p red o m in ates (0 .0 5 to 0 .2 mm) w ith p a tc h e s and h o r iz o n ta l bands o f x en o to p ic-C d o lo m ite . id io to p ic - C d o lo m ite a s ( l a t e ? ) f r a c t u r e f i l l i n g . Some Vuggy and f r a c t u r e p o r o s ity f i l l e d by opaque m a te r ia l, c h e r t a n d /o r c a l c i t e . Rounded q u a rtz sand common in upper p a r t o f th e s e c tio n . L o c a lity 23 NE30, 6N, 2E, Iowa C o ., H is . Road c u t , so u th s id e o f U .S. 18 and q u a rry 0 .5 m i. n o rth o f highw ay. 9 sam ples c o l le c t e d . Id io to p ic - E and S d o lo m ite pred o m in ate (ab o u t .2 mm) w ith p a tc h e s (0 .1 mm - 1 cm) o f x en o to p ic -A d o lo m ite (0 .1 to 0 .4 mm). I n te r g r a n u la r p o r o s ity in i d i o to p ic d o lo m ite f i l l e d w ith brown opaque m a te r ia l. p r e s e n t. F o s s il mold p o r o s ity common and a few s t y l o l i t e s 136 Locality 28 W l/2, SW, NW, 33, 7N, 3E, Iowa C o ., Wis. Road c u t , b o th s id e s o f Highway 23. 5 sam p les. H o riz o n ta l bands and p a tc h e s o f x en o to p ic-A d o lo m ite (0 .1 to 0 .5 mmm) w ith la y e r s o f id io to p ic - S d o lo m ite (ab o u t 0 .1 mm) alo n g s t y l o l i t e s and c o a rs e r un d u lo se id io to p ic - E and S d o lo m ite (some w ith s l i g h t l y curved c r y s t a l ed g es) (0 .1 to 0 .5 mm) which p re d o m in a te s. One sample c o n s is te d e n t i r e l y o f c o a r s e , u n d u lo se x en o to p ic-A ( 0 .3 to 0 .6 mm). Vuggy p o r o s ity common, vuggy and in t e r g r a n u la r sp ace o f te n f i l l e d by r e d d is h brown opaque m a te r ia l o f te n c o a tin g d o lo m ite eu h ed ra. L o c a lity 29 C en ter N l i n e , 33, 7N, 3E Iowa C o ., Wic. Road c u t , bo th s id e s o f Highway 23 4 sam ples c o lle c te d X enotopic-A d o lo m ite pred o m in ates (0 .1 to 0 .4 mm) sometimes in t e r la y e r e d w ith id i o to p ic - S d o lo m ite (0 .0 5 to 0 .2 mm) some o f which a r e zoned. S t y l o l i t e s a r e p r e s e n t th ro u g h o u t s e c tio n ; vuggy p o r o s ity i s common, o f te n f i l l e d w ith opaque m a te r ia l. Bounded q u a rtz ( f e ld s p a r ? ) sand th ro u g h o u t. L o c a lity 30 NW, NE, 28, 7N, 3E, Iowa C o ., Wis. Boad c u t , b o th s id e s o f highway 23 9 sam ples c o lle c te d M ostly id io to p ic - E and S d o lo m ite (0 .0 5 to 0 .6 mm) w ith p atch es o f I 137 x en o to p ic-A d o lo m ite th ro u g h o u t (0 .1 to 0 .4 mm), e s p e c i a ll y in a r e a s w hich a r e p red o m in an tly f i n e r g r a in id io to p ic - S d o lo m ite . Vuggy p o r o s ity i s common as a r e o p aq u es, rounded sand g r a i n s , and f o s s i l s p re s e rv e d by c h e r t . A few s t y l o l i t e s a r e p r e s e n t. L o c a lity 31 NE10, 6N, SE Iowa C o ., Wis. Quarry on n o rth s id e o f highway 151. 8 sam ples c o lle c t e d . P red o m in an tely x en o to p ic-A d o lo m ite (0 .0 5 - 3 mm) w ith some vuggy p o r o s ity f i l l e d by id io to p ic - C d o lo m ite (0 .1 to 0 .5 mm) and b la c k (o rg a n ic ? ) opaque m a te r ia l. A few s t y l o l i t e s a r e p r e s e n t a s w e ll as v e r t i c a l f r a c t u r e s f i l l e d by b la c k o p aq u es. L o c a lity 33 SE, 1 , and NW, NE, 12, 2N 2W, G rant C o ., Wis. Koad c u t , n o rth s id e o f U .S. 151. 13 sam ples c o l le c t e d . M ostly id io to p ic - E and S d o lo m ite (0 .1 to 0 .6 mm) some zoned, and vug f i l l i n g id io to p ic - C d o lo m ite some o f w hich i s un d u lo se and a s s o c ia te d w ith vug f i l l i n g b la ck opaque m a te r ia l. A few p a tc h e s (1 -3 cm) o f un d u lo se x en o to p ic-A d o lo m ite were o b serv ed ( g r a in s about 0 .3 mm and unzoned) su rro u n d ed by id i o t o p i c d o lo m ite . S t y l o l i t e s appear to be common and vuggy p o r o s ity i s o f te n f i l l e d by c a l c i t e cem ent. sand g r a in s a r e common th ro u g h o u t th e s e c tio n . Bounded 138 Locality 34 S l/2 , NW and NE, NE, SW, 7 , 2N, 2W, G rant C o., Wis. 4 ro ad c u ts on e a s t s id e and 1 ro ad c u t on w est s id e U .S. 61. 5 sam ples c o lle c te d from 3 rd ro a d c u t on e a s t (w h ile fa c in g s o u th ) . M astly id i o to p ic - S d o lo m ite ( 0 .0 5 - 0 .4 mm) w ith p atch y x en o to p ic-A d o lo m ite (0 .1 to 0 .5 mm) a s a t l o c a l i t y 33. Vuggy p o r o s ity , s t y l o l i t e s , opaques and sand a s a t l o c a l i t y 33. L o c a lity 37 NW, SW, 31, 5N, 3W, G rant C o ., Wis. Road c u t on b o th s id e s o f County Highway V. 8 sam ples c o l le c t e d . Lim estone b io m ic r ite s and b io s p a r i te s w ith id io to p ic -D and p a tc h e s o f id io to p ic - E and S d o lo m ite r e p la c in g m i c r it e . S t y l o l i t e s common w ith some a s o c ia te d n e o sp a rs r e p la c in g m i c r it e . L o c a lity 45 E l/2 , SW, 28, 92N, 2W, C layton C o ., Iowa. Road c u t , w est s id e o f U.S 52 alo n g M is s is s ip p i R iv e r. 23 sam ples c o l le c t e d . B io m ic rite in te rb e d d e d w ith and p a r t i a l l y re p la c e d by id i o to p ic - E , S and P d o lo m ite ( 0 .0 5 - 0 .2 mm). A few p a tc h e s (1 -3 cm) o f x en o to p ic-A d o lo m ite (u n d u lo se and up to 0 .5 mm) r e p la c e b o th b io m ic r ite and id io to p ic - S d o lo m ite . S c a tte re d an h ed ra o f x e n o to p ic -P d o lo m ite a r e a ls o p re s e n t in some lim e s to n e s . S t y l o l i t e s a r e common, e s p e c i a ll y in a re a s t h a t a r e d o lo m itiz e d , d o lo m ite rhombs a r e commonly a s s o c ia te d w ith s t y l o l i t e s in lim e s to n e s . 139 Locality 50 NE, NE, 26 and SE23, 98N, 8W, W inneshiek C o ., Iowa. Goad c u t s , b o th s id e s o f highway 9 4 sam ples c o l le c t e d . B io m ic rite and b i o s p a r i t e w ith s c a t t e r e d rhombs o f id io to p ic - P d o lo m ite (0 .0 1 to 0 .1 mm). by id io to p ic - S d o lo m ite . In one specim en a warm t r a i l was r e p la c e d Sounded to su b an g u lar q u a rtz ( f e ld s p a r ? ) sand common th ro u g h o u t s e c ti o n . APPENDIX 4 P e tr o g r a p h ic D e s c rip tio n s f o r th e T ren to n F orm ation 140 The fo llo w in g a r e g e n e ra l p e tro g r a p h ic d e s c r ip tio n s o f th e T re n to n F orm ation c o re s s tu d ie d . The g e n e ra l d e s c r ip tio n s a r e based on 130 in d iv id u a l t h i n s e c t i n d e s c r ip tio n s and, where n o te d , an o i l company c o re d e s c r ip t io n s and d r i l l i n g lo g s . The num bering system used f o r th e T ren to n c o re s i s sim ply an a b b r e v ia tio n o f th e w e ll name and number. Depth i s g iv en in f e e t below k e l ly b u sh in g . In most o f th e s u b s u rfa c e re c o rd s ( lo g s , c o re o r sample d e s c r ip t io n s ) o f th e M ichigan B asin th e T ren to n F orm ation i s n o t d i f f e r e n t i a t e d from th e u n d e rly in g B lack R iver F o rm atio n , which i s l i t h o l o g i c a l l y s i m i l a r . In th e fo llo w in g d e s c r i p t i o n s , th e r e f o r e , b o th u n i t s a r e r e f e r r e d to a s "T ren to n F o rm a tio n .” 1. 2. HS (H ew ett-Shadd No. 1) P erm it Number: 30974 L o c a tio n : SW, Se, 20, 12N, 15# S a n ila c C o ., M ichigan F ie ld : none, Dry h o le E le v a tio n : Top o f T ren to n F o rm atio n : 6,370 f t . Number o f t h i n s e c t i o n s : 11, no co re d e s c r ip tio n a v a i la b l e Depth in F e e t 6392-6412 L ith o lo g y S parse b io m ic r ite w ith a few s t y l o l i t e s and id i o to p ic - P d o lo m ite and a few s c a tt e r e d p a tc h e s o f x e n o to p ic -P d o lo m ite . 6412-6452 B io m ic rite p a r t i a l l y re p la c e d by x e n o to p ic -P d o lo m ite , x en o to p ic-C d o lo m ite cem ents f i l l i n g vugs and f r a c t u r e s , and c o a rs e u n d u lo se id io to p ic - S d o lo m ite . 6452-6572 B io m ic rite w ith s c a tt e r e d p atc h e s o f f in e g r a in id io to p ic - S and id io to p ic - P d o lo m ite . 6512-6562 B io m ic rite w ith s c a tt e r e d f in e g r a in id i o to p ic - P d o lo m ite eu h ed ra and s c a tt e r e d x en o to p ic-P d o lo m ite euhedra some a p p a re n tly r e l a t e d to f r a c t u r e s f i l l e d w ith x en o to p ic-C d o lo m ite cem ent. E—1 (Evans PRoducts Co. No. 1) P erm it Number: 26075 L o c a tio n : SE, NE, 25, 15, 8E. Wayne C o ., M ichigan. 141 F ie ld : N o r th v ille E le v a tio n : 718 f e e t above se a le v e l (K .B .) Top o f T renton Form ation: 3651 f t . Number o f t h i n s e c tio n s : 31 Depth in F eet 3651-3656 L ith o lo g y F in e g r a in id io to p ic - S d o lo m ite (< 0 .1 mm), h ig h ly s t y l o l i t i z e d , r e p la c in g m i c r i t e . C oarser g ra in e d ( 0 .1 - 0 .5 mm) x en o to p ic-A d o lo m ite r e p la c in g f o s s i l s and p a tc h e s o f m i c r it e . Gore d e s c r ip t io n r e p o rte d b le e d in g o i l from v e r t i c a l f r a c t u r e s and h o r iz o n ta l p a r ti n g s . 3656-3658 D e s tr u c tiv e rep lacem en t by c o a rs e (0 .1 to 1 x en o to p ic-A d o lo m ite ( o b l i t e r a t i n g b io m ic r ite f a b r i c ) . Core d e s c r ip t io n re p o r te d b le e d in g o i l as above. 3659-3779 B io m ic rite w ith s c a tt e r e d euhedra o f f i n e g ra in id i o to p ic - P d o lo m ite (< 0 .1 mm) r e p la c in g m ic r ite s c a t t e r e d p a tc h e s o f x en o to p ic-A and P d o lo m ite re p la c in g m i c r it e and f o s s i l s . Some s t y l o l i t e s . 3779-3825 D e s tr u c tiv e rep lacem en t by c o a rs e x enotopic-A d o lo m ite ( 0 .2 to 1mm) and c o a rse u n d u lo se id io to p ic - E and S d o lo m ite a s s o c ia te d w ith opaque m a te r ia l. F in e r g r a in d o lo m ite n ear s y l o l i t e s . F r a c tu r e s f i l l e d w ith x en o to p ic-B (s a d d le ) d o lo m ite cem en ts, a n h y d rite and opaque m a te r ia l. Gore d e s c r ip t io n r e p o rte d gas shows. 3825-4028 Core d e s c r ip t io n r e p o r ts medium g r a in d o lo m ite , w ith s u c r o s ic , vuggy and f r a c t u r e p o r o s ity . F r a c tu r e s a r e o f te n lin e d w ith c o a r s e , w h ite d o lo m ite cem ents. The d o lo m ite s a r e in te rb e d d e d w ith f o s s i l i f e r o u s lim e s to n e s . This s e c tio n has numerous sh ale. p a r t i n g s . A n h y d rite , p y r i t e and o i l shows a re r e p o r te d a s s o c ia te d w ith th e d o lo m ite s. „ , 4028 Base o f c o re 4150 T.D. 3. E-2 (Evans P ro d u cts Co. No. 2) P erm it Number: 26100 L o c a tio n : N l/2 , NE, 25, I S , 8E Wayne C o ., M ichigan F ie ld : N o r th v ille E le v a tio n : 772 f e e t above se a le v e l (K .B .) Top o f T ren to n Form ation: 3678 f t . Number o f t h i n s e c tio n s : 10 Depth in f e e t 3678-3681 L ith o lo g y F in e g r a in id io to p ic - S d o lo m ite (< 0 .1 mm) w ith s t y l o l i t e s r e p la c in g m i c r it e . C oarse x en o to p ic-A 142 d o lo m ite (0 .2 to 0 .6 mm) r e p la c in g f o s s i l s and about a sm all amount o f th e m i c r i t e , p re s e rv in g b io m ic r ite f a b r i c . Some o f th e b io m ic r ite i s d e s tr u c t iv e l y re p la c e d ( o b l i t e r a t i n g b io m ic r ite f a b r i c ) by c o a rse x en o to p ic-A and u n d u lo se ld io to p ic -G and S d o lo m ite (up to 1 mm) w ith i n t e r c r y s t a l l i n e opaque m a te r ia l. Vuggy and v e r t i c a l f r a c t u r e p o r o s ity a r e f i l l e d by x en o to p ic-C (s a d d le ) d o lo m ite cement and a n h y d r ite . 3681-3693 M ostly b io m ic r ite w ith some s t y l o l i t e s p a r t l y re p la c e d by f i n e g r a in id i o to p ic - P d o lo m ite (0 .0 5 to 0 .2 mm) and s c a tt e r e d p a tc h e s o f x en o to p ic-A and P d o lo m ite (0 .1 to 0 .3 mm). 3693-4152 Gore d e s c r ip t io n r e p o r ts o n ly lim e s to n e , ta k e n . 4152-4285 Core d e s c r ip t io n r e p o r ts "mediumc r y s t a l l i n e ” d o lo m ite in te rb e d d e d w ith lim e s to n e . O il and gas shows in th e d o lo m ite . 4285 T. D. 4. no sam ples BR (B urroughs C o rp o ra tio n No. 1) P erm it Number: 25808 L o c a tio n : N l/2 , NW, NW, 25, IS , 8E F ie ld : N o r th v ille E le v a tio n : 725 f e e t above se a le v e l (K .B .) Top o f T ren to n F orm ation: 3651 f t . Number o f th i n s e c tio n s : 9 Depth i n f e e t 3651-3654 ............... L ith o lo g y F in e g r a in id io to p ic - S d o lo m ite (<0.1 mm) w ith . s t y l o l i t e s r e p la c in g m i c r i t e . F o s s ils p a r t i a l l y to w holely re p la c e d by x en o to p ic-A and P d o lo m ite (0 .1 to 0 .5 mm). Some d e s tr u c t iv e rep lacem en t ( o b l i t e r a t i n g b io m ic r ite f a b r ic ) by c o a rse g r a in x en o to p ic-A and u n d u lo se id io to p ic - E and S d o lo m ite . 3654-3660 B io m ic rite w ith f in e g r a in id io to p ic - S d o lo m ite (a s above) p a r t i a l l y r e p la c in g m i c r it e and s c a tt e r e d p a tc h e s o f x en o to p ic -P d o lo m ite r e p la c in g m ic r ite and f o s s i l s . 3660-4022 Core d e s c r ip t io n r e p o r ts in te rb e d d e d f in e l y c r y s t a l l i n e , f o s s i l i f e r o u s lim e s to n e s in te rb e d d e d w ith porous p e t r o l i f e r o u s d o lo m ite s (vuggy, f r a c t u r e and i n t e r c r y s t a l l i n e p o r o s ity ) . 4022 Base o f T ren to n c o re . 4264 T. D. 143 5. W2 (R o b ert and Dorothy W hitaker No. 2) P erm it Number: 28407 L o c a tio n : SW, NW, NE, 2 9 , 75, 4W F ie ld : Reading E le v a tio n : 1061 f e e t above se a le v e l (K .B .) Top o f T renton F orm ation: 3043 f t . Number o f t h i n s e c tio n s : 9 Depth i n f e e t 3043-3063 L ith o lo g y Gore d e s c r ip t io n r e p o r ts medium c r y s t a l l i n e , s l i g h t l y f o s s i l i f e r o u s d o lo m ite w ith a few s h a le p a r tin g s and tr a c e o f p y r i t e . 3063-3068 B io m ic rite lim e sto n e w ith f in e g r a in id io to p ic - P d o lo m ite (< 0 .1 mm) p a r t i a l l y r e p la c in g m i c r it e and p a tc h e s o f c o a r s e r x e n o to p ic -P d o lo m ite ( 0 .1 - 0 .5 mm) r e p la c in g b o th f o s s i l s and m i c r i t e . X enotopic d o lo m ite a p p e a rs more abundant n ear s t y l o l i t e s in th e lim e s to n e . 3068-3092 C oarse g r a in s l i g h t l y un d u lo se id io to p ic - E and S d o lo m ite (up to 0 .8 mm), many c r y s t a l s a r e m icely zoned, b la c k and brown opaque m a te r ia l f i l l i n g i n t e r c r y s t a l l i n e s p a c e , and c o a rs e g r a in x en o to p ic-A d o lo m ite (up to 0 .8 mm). S t y l o l i t e s a r e common and d o lo m ite n e a r them te n d s to be f i n e r g r a in , rhom bic and a s s o c ia te d w ith more opaque m a te r ia l th a n e lse w h e re . Gore d e s c r ip t io n r e p o r ts o i l shows in t h i s s e c tio n . 3092-3300 Core d e s c r ip t io n r e p o r ts f in e to c o a rse c r y s t a l l i n e d o lo m ite s w ith p in p o in t, i n t e r - c r y s t a l l i n e , vuggy and f r a c t u r e p o r o s ity , f r a c t u r e s f i l l e d by c o a rse d o lo m ite cem en ts. D olom ites in te rb e d d e d w ith d e n se , f i n e g r a in f o s s i l i f e r o u s lim e s to n e . 3308 T. D. 6. JF ( J e l i n e k - F e r r i s U n it No. 1) P erm it Number: 27907 L o c a tio n : SE, SE, NW, 5 , 5N, 2E Shiaw assee C o ., M ichigan F ie ld : None, on N o r th v ille -H o w e ll-F o w le rv llle tr e n d , Dry Hole E le v a tio n : 843 f e e t above se a le v e l (K .B .) Top o f T renton F orm ation: 6101 f t . Number o f t h i n s e c tio n s : 19 Depth in f e e t 6101-6164 L ith o lo g y B io m ic rite lim e sto n e w ith m ic r ite p a r t i a l l y re p la c e d by f i n e g r a in id io to p ic - P d o lo m ite and p a tc h e s o f id io to p ic - E and S d o lo m ite ( 0 .0 2 -0 .1 mm). F o s s ils and m i c r it e a r e p a r t i a l l y re p la c e d by p a tc h e s and in d iv id u a l an h ed ra o f x en o to p ic-P d o lo m ite (0 .0 5 0 .6 mm). S t y l o l i t e s a r e common in th e b io m ic r ite s , id io to p ic - C d o lo m ite s a re most common in and a d ja c e n t to th e s t y l o l i t e s . 144 6164-6190 No co re d e s c r ip t io n a v a i l a b l e . 6190 Base o f T ren to n c o re . 7056 T. D. 7. HI (Elmer M. Haab U n it NO. 1) P erm it Number: 19231 L o c a tio n : SW, SE, NW, 8 , 3S, 4E Washtenaw C o ., M ichigan F ie ld : Freedom F ie ld , Dry Hole E le v a tio n : 963 f e e t above se a le v e l (K .B .) Top o f T ren to n F orm ation: 3760 f t . Number o f t h i n s e c ti o n s : 9 Depth i n f e e t 3760-3771 L ith o lo g y C oarse g r a in x en o to p ic-A d o lo m ite ( 0 .2 - 0 .7 mm) c o n ta in in g g h o s ts o f e c h in o id f o s s i l s . F in e r g r a in id io to p ic - E and S d o lo m ite (< 0 .1 mm), w ith abundant i n t e r c r y s t a l l i n e opaque m a te r ia l, n e a r s t y l o l i t e s . Core d e s c r ip t io n r e p o r ts f r a c t u r e f i l l e d w ith c o a rse w h ite d o lo m ite cement and a n h y d r ite . 3771-3832 E c h in o id a l b io m ic r ite w ith f in e g r a in id io to p ic - D d o lo m ite r e p la c in g m i c r i t e , e s p e c i a ll y n e a r s t y l o l i t e s . C oarse g r a in x e n o to p ic -P d o lo m ite (up to 0 .5 mm) r e p la c in g m i c r it e and f o s s i l s . Some sam ples a r e up to 50% re p la c e d by d o lo m ite . F ra c tu re p o r o s ity i s li n e d by x en o to p ic-B (s a d d le ) d o lo m ite (up to 0 .5 mm) and f i l l e d w ith a n h y d r ite . Gore d e s c r ip t io n r e p o r ts in te rb e d d e d d o lo m ite and f o s s i l i f e r o u s lim e sto n e and shows o f o i l . 3832-4365 Gore d e s c r ip t io n r e p o r ts f o s s i l i f e r o u s lim e s to n e w ith one th i n bed o f d o lo m ite ( l 17" th ic k ) a t 3930. The lim e s to n e c o n ta in s s h a le p a r tin g s c h e r t n o d u les and o i l shows th ro u g h o u t. 4365-4408 Core d e s c r ip t io n r e p o r ts f in e to c o a rs e c r y s t a l l i n e d o lo m ite w ith v e r t i c a l f r a c t u r in g (som etim es f i l l e d w ith gypsum), vuggy, p in p o in t and i n t e r c r y s t a l l i n e p o r o s ity , and o i l shows th ro u g h o u t. 4408 Base o f T ren to n c o re . 4691 T. D. 8. L12 (Ja c k Lauber No. 12) P erm it number: 17549 L o c a tio n : C en ter SE, SE, 6 , 16N, 17W Oceana C o ., M ichigan F ie ld : P en tw ater F ie ld , deep t e s t , d ry h o le E le v a tio n : 684 f e e t above se a le v e l (K .B .) Top o f T ren to n F orm ation: 4947 f t . Number o f t h i n s e c tio n s : 32 145 Depth i n f e e t 4947-4996 L ith o lo g y F in e g ra in e d id io to p ic - S d o lo m ite (< 0 .1 mm), w ith numerous s t y l o l i t e s g iv in g i t a "ground-up" a p p e a ra n c e , r e p la in g m i c r it e . C oarse g ra in e d x e n o to p ic-A d o lo m ite ( . 2 - . 4 mm) r e p la c in g f o s s i l fra g m e n ts . Some a re a s o f d e s tr u c t iv e rep lacem en t ( o b l i t e r a t i n g b io m ic r ite f a b r i c ) by c o a rs e g ra in e d x en o to p ic-A (up to 0 .5 mm) d o lo m ite . B lack opaque m a te r ia l was o b serv ed in some sam ples su rro u n d in g c o a rs e (up to 0 .5 mm) u n d u lo se id io to p ic - E d o lo m ite . Saddle shaped x en o to p ic -C d o lo m ite cement o se rv e d as vug f i l l i n g s . 4996-5078 No co re ta k e n , d r i l l i n g lo g re c o rd s d ense f o s s i l i f e r o u s d o lo m ite s , d o lo m itic lim e s to n e s , tr a c e s o f gypsum, and o i l shows. 5078-5105 D olom ite a s in 4947-4996 s e c ti o n in c lu d in g c o a rs e , u n d u lo se id io to p ic - A d o lo m ite (up to 1 mm) co a te d w ith b la c k opaque m a te r ia l. A s e c tio n o f b io m ic r ite p a r t i a l l y re p la c e d by x e n o to p ic -P d o lo m ite was o b se rv e d a t 5 1 0 3 '. The co re d e s c r ip t io n n o te s b le e d in g o i l and gas th ro u g h o u t t h i s s e c tio n o f c o re . 5106-5109 B io m ic rite p a r t i a l l y re p la c e d by x e n o to p ic -P d o lo m ite (up to 0 .3 mm) and id i o to p ic - P d o lo m ite (< 0 .1 mm). 5109-5152 No c o re ta k e n , d r i l l i n g lo g re c o rd s d e n se , s h a le y lim e s to n e s and medium c r y s t a l l i n e d o lo m ite , some fo s s ilife ro u s . 5152-5202 M ostly c o a rs e g ra in e d x en o to p ic-A d o lo m ite (up to 1 mm) and id io to p ic - E and S d o lo m ite (up to 1 mm, u s u a lly co a te d by opaque m a te r ia l) d e s tr u c t iv e l y r e p la c in g b io m ic r i te s . A few a re a s o f f in e g ra in id i o to p ic - S d o lo m ite r e p la c in g m i c r ite and c o a rs e r x en o to p ic -A r e p la c in g f o s s i l s were o b se rv e d , p a r t i c u l a r l y in th e i n t e r v a l o f 5190-5201 a s s o c ia te d w ith u n re p la c e d b io m ic r i te . The c o re d e s c r ip t io n n o te s o i l shows th ro u g h o u t t h i s s e c tio n . 5202-5243 Gore d e s c r ip t io n r e c o rd s d e n se , s h a le y f in e c r y s t a l l i n g d o lo m ite . 5243 Base o f T ren to n c o re . 5382 T.D. BIBLIOGRAPHY 146 BIBLIOGRAPHY A rdrey, R. H ., 1978, D iag en esis o f th e M iddle O rd o v ician T ren to n F orm ation in so u th e rn M ichigan: u n p u b lish e d M.S. T h e s is , U n iv e rs ity o f M ichigan, 50 p . Badiozam ani, K ., 1972. 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