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UE DATE DUE PLACE |N RETURN BOX to TO AVOID FINES return on DATE DUE DATE D i usu Is An Aflirmative ActionlEqual opportunity Institution THE LOWER ORDOVICIAN OF THE SOUTHERN MICHIGAN BASIN- HYDROCARBON POTENTIAL By John R. Nelson A THESIS Submitted to Michigan State University in partial fulfillment of the requirements for the degree of MASTER OF SCIENCE Department of Geological Sciences 1989 56mm) ABSTRACT THE LOWER ORDOVICIAN OF THE SOUTHERN MICHIGAN BASIN- HYDROCARBON POTENTIAL By John R. Nelson Lower Ordovician hydrocarbon exploration in the southern Michigan Basin has not been extensive due to lack of outcrop, deep-well data, and problems with Middle/Lower Ordovician nomenclature and lithostratigraphic correlations to the central Michigan Basin. Analysis of published data, structure maps, isopach maps, well-log data, core data, and petrographic data suggest Laj; hydrocarbon potential may exist in the southern Michigan Basin.x The massive shallow-water Prairie du Chien carbonates are extensively eroded on the basin margins yet possibly are entirely preserved under transgressive marine St. Peter clastics in the central basin area. Both structural and stratigraphic traps exist in the southern Michigan Basin but may be difficult to explore for. Hydrocarbon migration distances may be variable. Favorable porosity and reservoir potential may be found in association with viable traps, but will likely be limited in extent. Lower Ordovician hydrocarbons have been discovered in the southern Michigan Basin and surrounding areas but accumulations are generally small. Three possible hydrocarbon sources including the Precambrian Nonesuch Shale, the upper Prairie du Chien, and the Middle Ordovician Utica Shale may be found within the 'dry gas and oil windows’ in the southern Michigan Basin, respectively. ACKNOWLEDGEMENTS I would like to offer a multitude of thanks to my M.S. adviser, Chip Prouty, who took me on as his last student and patiently allowed me the freedom to work at my own pace and to do things in my own way. The wealth of knowledge he shared, his committment to his profession, and his sincere willingness to help his students in any way he could, will always be remembered by me and I'm sure by his many students before me as well. I would also like to thank my other committee members, Jim Trow and Mike Velbel. I would like to make acknowledgements to the oil companies that contributed to my project; Shell Oil Co. and Amoco Production Company for financial support, Steve Sinclair and Area O&G Co. for providing access to cores critical to my study, and Mobil Oil Corp. for giving me numerous opportunities to work for them and develop my professional background and for providing materials and facilities to conduct research at times. I am grateful to Bill Harrison at Western Michigan University whose unselfish sharing of ideas and information was a tremendous help to me. A special thanks goes to the State of Michigan, Dept. of Natural Resources, Geological Survey Division geologists, Randy Milstein, Bob Rezka, and Ron Elowski for their patience and cooperation during the countless hours collecting data there. The time I spent at Michigan State was very rewarding and I must acknowledge the many professors who put up with me and from whom I learned a great deal. A special thanks goes to Duncan Sibley i for reviewing my petrographic data and Mike Velbel for use of his photomicrograph set-up. It is to my many friends from over the years that I owe the most. Much of my success I attribute to them. Without their support and encouragement I may never have accomplished as much as I did. I'd like to especially thank Tim Flood (who typed part of my thesis), Kim Elias, Bill Sack, and Jorge Coppen, whose company as housemates l dearly miss; to Jerry Grantham for being like a brother to me; to Keith (Frank) Hill for many enjoyable boondoggles; to Mike (Savoir) Serafini, John (Josepie) Gillespie and Phildo Knapp for the many laughs we shared; to Alison (diploid mutant dildonic zeroid) Dohe for never giving up on me or letting me give up on myself; to Bob Pauken for being the best boss I could ever have; to Bill Stuart, Gene Hill and Bob Hiseler from Mobil Oil Co. whom graciously helped me out at times; to Mary and Kevin Kirkeby for typing a big part of my thesis; to Kurt Stepnitz for preparing quality slides for my defense presentation and to all my other friends as well. I would like to remember my grandparents, whose kindness, love, and dedication to their careers, community and each other were an inspiration to me. I also thank my mother for the many years of laundry she did without a complaint. And last but not least, I acknowledge my most loyal companion thru this whole grueling nightmare....my dog, Deke. 11 TABLE OF CONTENTS LIST OF FIGURES LIST OF TABLES LIST OF PLATES INTRODUCTION General . Area of Study . Purpose, Scope of Study and Objectives . . Methods . Previous Work . Sources of Error . MICHIGAN BASIN STRUCTURE. Introduction . Precambrian Regional Structural History Cambro/Ordovician Regional Structural History Origin of the Michigan Basin General Structure of the Michigan Basin . Major Structures within the Michigan Basin PRAIRIE DU CHIEN STRATIGRAPHY/SEDIMENTOLOGY. . . Regional Stratigraphy Michigan Basin Stratigraphy . . Lower Ordovician Depositional History/Paleogeography. Paleoenvironments. Prairie du Chien Facies . 111 TABLE OF CONTENTS (continued) PRAIRIE DU CHIEN LlTHOLOGY/PETROLOGY. . . . . . . . . . 80 Introduction . . . . . . . . . . . . . . . .. . . . 80 General lithology . . . . . . . . . . . . . . . . . 80 Textures. . . . . . . . . . . . .. . . . . . . . .81 Fossil and Trace Fossil Occurences . . . . . . . . . . 82 Sedimentation Structures . . . . . . . . . . . . . . . 84 Accessory Minerals. . . . . . . . . . . . . . . . . 84 Hydrocarbon Occurrences . . . . . . .. . . . . . . . 86 Cements . . . . . . . . . . . . . . . . . . . . . 87 Porosity......................88 Diagenetic History. . . . . . . . . . . . . . . . . 93 HYDROCARBON POTENTIAUPETROLEUM GEOLOGY OF THE PDC. . . 96 Hydrocarbon Generation. . . . . . . . . . . . . . . 96 Hydrocarbon Occurrences. . . . . . . . . . . . . . 100 PDC Hydrocarbon Trapping Mechanisms. . . . . . . . . . 102 Porosity Trends/Reservoir Potential . . . . . . . . . 107 Exploration Methods. . . . . . . . . . . . . . . . 109 SUMMARY Overall evaluation of the hydrocarbon potential for the Lower Ordovician of the southern Michigan Basin. . . . . . . . 113 REFERENCES/BIBLIOGRAPHY . . . . . . . . . . . . . . 114 APPENDIX A. Well-Core Data . . . . . . . . . . . . . . 124 APPENDIX B. PdC Structure Contour Maps by County. . . . .. 183 iv Figure 1. Figure 2. Figure 3. Figure 4. Figure 5. Figure 6. Figure 7. Figure 8. Figure 9. Figure 10. Figure 11. Figure 12. Figure 13. Figure 14. Figure 15. LIST OF FIGURES Stratigraphic section showing productive zones and dominant Iithologies of the Lower Ordovician. Study area . Stratigraphic interval pertaining to this study Michigan oil and gas fields, 1980. A compilation of major axial trends gleaned from maps of specific times in the Michigan Basin. The azimiths of several randomly selected, linear producing oil fields plotted in a ”rose" . . . Mid-continent rift trend and geology from eastern Lake Superior through lower peninsula of Michig Keewanawan rifting and associated igneous activity . Paleogeography during early Paleozoic time. Phanerozoic tectonic cycles in Appalachian Orogen. . . . . Structure contour map of Prairie du Chien Group. Isopach map of the Prairie du Chien formation Isopach map of Trenton Group . Isopach map of Black River Group. Structure contour map of the Prairie du Chien formation within the study area . V .17 18 19 22 .23 .24 .26 .30 .31 .32 .33 .34 Figure 16. Figure 17. Figure 18. Figure 19. Figure 20. LIST OF FIGURES (continued) Structure contour map of the Prairie du Chien formation. . Isopach map of the Prairie du Chien formation. Generalized St. Peter formation Iithofacies map. Major structural elements of the Basin and Arches Province. Middle Ordovician (permeability pinchout) play; example- Dover area . Figure 21A- Computer-based study of the stress field in the B Michigan Basin based on Iineament analysis Figure 22. Figure 23. Figure 24. Figure 25. Figure 26. Figure 27. Comparison of ”roses“ of LANDSAT imagery lineaments (A) and master joints from outcrop (B) . Lower-Middle Ordovician correlation in the Midwest Basin and Arches province. Map showing the thickness of Shakopee Dolomite in Indiana. . Map showing the geology at the unconformity at the top of the Sauk Sequence before the onset of Chazyan deposition. Generalized section across Ohio, Indiana, and Illinois assuming a horizontal datum on the unconformity surface at the top of the Sauk Sequence Index map of PdC well locations used for gamma- ray log correlations Vi .35 .36 .38 .39 .41 43... .44 45 .47 .50 .51 .51 .63 LIST OF FIGURES (continued) Figure 28. South to north cross-section A - 1. . . . . . . . . 64 Figure 29. South to north cross-section J - P . . . . . . . . 65 Figure 30. South to north cross-section Q - T . . . . . . . . 66 Figure 31. South to north cross-section U - W . . . . . . . . 67 Figure 32. South to north cross-section X - ZZ . . . . . . . . 68 Figure 33. Cross-section AA - V . . . . . . . . . . . . . . 69 Figure 34. West to east cross-section F - Z . . . . . . . . . 70 Figure 35. First and second order global cycles of relative change in sea level during Phanerozoic time. . . . . 74 Figure 36. Diagrammatic model of Lower Ordovician carbonates and lower Middle Ordovician clastics deposition. . . 76 Figure 37. (a) Structure contour map of central and northern parts of Albion-Scipio trend contoured on top of Trenton formation which directly overlies productive interval. (b) Plot of main axial trace of sag. . . . . 104 Figure 38. Cross-section across Albion-Scipio trend showing distribution of carbonate rock types in productive Middle Ordovician Trenton-Black River sequence. . . 104 Figure 39. Structure and development of the Washtenaw anticlinorium...............106 Figure 40 Index map showing locations of cores used in this study....................125 vii Table 1 . Table 2. Table 3. Table 4. Table 5. Table 6. LIST OF TABLES Well data summaries for walls which have produced hydrocarbons from the Prairie du Chien in the southern lower peninsula of Michigan. . . . . . . . . . . 4 Development of Middle and Lower Ordovician nomenclature and correlations in the Michigan Basin from1970to1988. . . . . . . . . . . . . . .54 Wells used in gamma-ray log correlations. . . . . . 60 PdC completions in the central Michigan Basin which had some initial production. . . . . . . . . . . .103 Listofcores used inthestudy . . . . . . . . . 124 Legend for abbreviations and symbols for appendix . 127 viii Plate 1. Plate 2. Plate 3. Plate 4. Plate 5. Plate 6. Plate 7. LIST OF PLATES A. PdC FM (3408.5'). Oolite fabrics including radial and concentric banded types. B. PdC FM (3408. 5'). Chart replaced oolites and pore lining cement . . . . . . . . . . . 134 PdC FM (4483.8'). Pore filling and replacement pyrite along a fracture within a finely crystalline replacement dolomite. . . . . . . . . . . . . 145 A. St. Peter Ss (3726.4'). Quartz arenite with authigenic chlorite/calcite cement lining the pore walls. B. St. Peter 85 (3726.4'). Same photo as above with uncrossed nichols showing pore geometries . . . 153 A. St. Peter Ss. (3748.5'). A subarkosic sandstone with authigenic microcrystalline quartz as a possible pore filling cement. B. PdC FM (4337.2'). Pyrite crystals associated with organic rich laminae and solution seams. . . . . 154 A. PdC Fm (4342.5'). An equant, medium-crystalline mozaic of replacement dolomite with fair intercrystalline porosity. B. PdC FM (4344.9'). A finely crystalline dolomite exhibiting vugular porosity which may be fossil (?) moldic..................163 A. Glenwood FM (4466.4'). A calcite cemented, quartz sandy, fossiliforous wackestone containing crinoids, gastropods, and phosphatic skeletons of brachiopods and/or trilobites. B. PdC FM (4470.9'). An intraclast composed of silica replacedooids...............170 A. PdC FM (4470.9'). Silica replaced ooids. B. PdC FM (4480.7'). Possible oil staining in microvugs 171 ix LIST OF PLATES (continued) Plate 8. A. PdC FM (44855). A caliche-like, ferruginous duracrust. B. PdC FM (4489. 5'). A medium to fine—grained quartz arenite interbed. . . . 174 Plate 9 A. PdC FM (4397.5’). Silica replaced micritic limestone with preserved gypsum/anhydrite crystals. B. PdC FM (4397. 5'). Large epigenetic, saddle-dolomite crystal in a silicified micrite. . . . . . . . 182 INTRODUCTION General Hydrocarbon exploration in the northern two thirds of Lower Michigan has increased since the discovery of hydrocarbons in the Cambro-Ordovician within the deeper portions of the Michigan Basin. The discovery of gas at the Dart-Edwards 7-36 well in Missaukee County in 1981 stimulated new interest and ideas, not only for hydrocarbon exploration but also for a better understanding of the historical development of the Michigan Basin. Excitement over the new exploration play dwindled in the years directly following the initial discovery as a result of poor success in follow-up drilling. More recent success has stimulated the drilling of numerous deep tests in the northern counties of the Lower Peninsula. The deep wells in the Michigan Basin prompted both explorationists and researchers to take a new look at the stratigraphic and structural relations throughout the Basin. As data from deep drilling become more available, geologists are realizing that the geologic history of the Michigan Basin may be more complex than previously understood. The Cambro-Ordovician and Middle/Lower Ordovician boundary is being traced deeper into the basin where gas condensate and oil have been discovered at depths previously thought to be well within the dry gas‘window', causing explorationists to question previously proposed geothermal gradients and burial histories for the deep basin. Probing for yet deeper hydrocarbon reserves continues. Most production from the "massive sands” of the "Prairie du Chien” of the northern part of southern Michigan (now generally correlated with the younger St. Peter Sandstone. (See chapter on Michigan Basin Stratigraphy.) has been limited to structural traps. Porosity within the sandstone Iithofacies is often the controlling factor between a productive well and a dry hole. Many of the discoveries have occurred in structures at Cambro-Ordovician depths below shallower structures with known production (Traverse and Dundee) such as the Falmouth field, the Pinconning field, the Reed City field ,and the Kawkawlin field. The emphasis on exploration has been directed primarily at the massive Ordovician sands in the northern counties of the Lower Peninsula. Some explorationists may be exploring for stratigraphic traps along the carbonate/sandstone transition zone across the lower middle section of the State, however no major discoveries with this type of play concept have yet been made. Lower Ordovician exploration in the southern Lower Peninsula has not been extensive. However, significant hydrocarbon potential may lay hidden within the Lower Ordovician in southern Michigan. This investigation will look into the hydrocarbon potential of the Lower Ordovician of the southern Michigan Basin and try to assess what factors may be controlling it. Much of the Cambro-Lower Ordovician in the southern part of the Michigan Basin is poorly understood because: 1) Relatively few wells have been drilled thru the entire Prairie du Chien section; 2) The number of complete well descriptions and complete sections of core 3 are few; 3) The Lower Peninsula lacks outcrops; 4) Some lateral facies changes may occur; and, 5) Stratigraphic terminology between the southern ”Prairie du Chien" carbonates and the northern ”Prairie du Chien“ sands is incomplete and not agreed upon by previous workers. No wells are currently producing from the Prairie du Chien Group in the southern Michigan Basin. Oil from the Prairie du Chien Group in the southern Lower Peninsula has been produced in the past from only three wells; the Zaremba no. 1 (Jackson County), Young no. 1 (Hillsdale County), and the Selders no.1-36 (Lenawee County) (Fig.1, Table 1). Production from these three wells came from the zone lying directly below the Post-Knox 'Unconformity" (actually a disconformity). Based on their on-trend location in relation to the fault-related Albion-Scipio oil field, it appears likely that oil production from the Zaremba and Young wells was also linked to fault- associated porosity development. Porosity traps of a stratigraphic nature may also exist in the Prairie du Chien sandstone units where abrupt changes in lithology occur from sandstone to carbonate, updip out of the basin. The discOvery of the Stoney Point Field, which offsets the Albion-Scipio trend, has also brought renewed interest in the potential of Ordovician plays in Michigan's southern Lower Peninsula. Although Prairie du Chien rocks have not yielded large amounts of hydrocarbons in the southern tier of counties, the potential for additional production from this interval still exists. Little work, however, has been published on what factors control the development of Prairie du Chien reservoirs. A synthesis of .mmm_.uuxuuum ”uuucc. .cmuuu>onuo uusoq us» no mofiooHozuaa ucmcusoo 0cm mecca o>fiuocooum mcwzonm c0wuomm cwzccumwucuum .P musmfim PEI-03.9!- .II-on... I - II .2 Q pd! mmmmgtt .............?....fi 10.83. m '23-: 3 5...! I I... 3.8 12.3. 00.0-4 to." r 10.10 3‘ 0.5.03“ Goon = u n [lit-IF 30:30.8 air: £38 933: 34a- gal- on.—- 3.33. 3.3.: :o ..3- 3n 3: 32 3.3.3 03.» 03.. 5: iii :32...— .n 2 9:5» ... 3.3.: :o .23 N3; 32 3: 3.323 .36 a2; .38 233 a :3 232:: .~ 3 339.3 .x snow...“ :9 .23 «3.3 no: 33 3323 nan; 3n; .3 J... 5.5 339:. .— . so..uaoo.. e...uae.g. e...u=eo.. mam os..u .... ».. .... ....u . a....uo. ..ans. 33259 a... no .3.» at: so so.» ... 3 3:8 2. 532.3 a 3.38 :3 .cmmunouz mo casmcwcom nozoa :uonusom on» :« AP .mam. Guano so ofiuacum one Eouu mconumuoun>n couscoua c>en zoazz maams MOM meannessm muco Haoz .F mqm--———-. = 5 3 , ' 4 ‘3‘ '.‘ “ a: 3 i am \ ..r V-‘.‘ ‘.‘.e: “:‘ no tree 0 a a \. f \ ‘:‘:“_‘ f ‘ 7 a I“. “ ‘ ‘ ,. 0‘ ‘ d ‘. ‘ a") 1". '3 ‘3", k z 3 I fi‘“ .‘ -‘ x, 4- : ‘ ‘ 3‘4 ‘.‘ ‘ M Q _—_ > 0 sun..- in g ’-_ -.- _-‘ .- ... or not 0 z . S 3 M W o "m ° 0 8 g 3 Ocean I’I ‘ r 0 ---?-r-?-—- it toe-lacuna 3” 1” ° 33 ... ...... m ‘::§“:§:§:§“:§:3-‘:§:§ ... .. o . m 10 no e ‘ z a; is w M .- 1. "g o 5 g ‘9 la Clo- A. tn & E 8 s .. i ‘ . m m 0 I- “ 3 PRECAMBRIAN ' ‘ ant-en ' uni-e - ”we —_-. Wm ‘ once-eon ' ten-ee- ° ...-II- 7 “a” W tattflnutmmul. can‘m InmecvMMw.aw~.w.le.euu—nm. mumtmmnfl Figure 3. Stratigraphic interval pertaining to this study. (After Harrison et a1, 1988) 9 hydrocarbons; and, 4) Petroleum geology, which includes trapping mechanisms, reservoir potential, porosity trends, and exploration methods. The overall objectives for this study include the following- (1) To aquire, assimilate, and summarize all published written data that would relate to the petroleum potential of the Michigan Basin. (2) To aquire all well data for the Middle and Lower Ordovician in the study area and prepare structure maps, isopach maps, and cross- sections for the counties within the study area. (3) To examine, describe, sample, and prepare thin-sections from well cores in the study area and conduct a petrographic analysis for a) correlation/comparison to well log data; b) lithostratigraphy; c) clues to facies and depositional environments; d) reservoir properties; a) diagenetic history; and f) possible all shows. (4) To resolve some of the Middle/Lower Ordovician nomenclature problems and correlation problems between the central and southern portions of the Michigan Basin. (5) To relate all geological parameters to the overall petroleum potential for the Lower Ordovician in the southern Michigan Basin. The research will hopefully contribute to both exploration and geology through the completed work, the assimilation of numerous ideas and concepts, and also in the questions that are raised that must be left for future testing. Mamas 10 Several types of data were collected and/or studied for this investigation. Well data in various forms were used extensively because of the subsurface nature of the project and include: 1) Data from over 1700 drillers reports which were used to obtain well depths, formation tops, some lithologic information, and production data. These data were used for construction of structure contour maps, isopach maps, St. Peter Sand distribution maps, and for locating wells with oil shows in the Lower Ordovician; 2) Electric logs for selected wells were gathered and used for checking discrepancies on the drillers reports, for constructing cross sections, for lithology, and for porosity data. Gamma-ray logs were used for correlations. Lithodensity logs were studied for lithologic and porosity information, if they were available for a well; 3) Six Prairie du Chien cores were available and described, photographed, and sampled at Atlantic Richfield Corporation's core warehouse in Dallas, Texas. The cores were described for lithology, grain or crystal size, visual porosity, sedimentary structures, and evidence of oil staining. The distribution of the cores over the study area and the core data are included in appendix A; 4) Selected samples from the described Prairie du Chien cores were thin sectioned for petrographic study. Eighty-four thin sections were prepared and examined in detail. Descriptions were made using a combination of Dunham (1962) and Folk (1959) rock classification schemes in an effort to best describe the composition and textural variations observed . Lithology, diagenetic history, cement types, porosity types, and presence of any oil staining were noted for each sample. The sample descriptions can be found in Appendix B; 5) Samples and 11 sample descriptions of Prairie du Chien well cuttings from ten wells were studied at Northern Michigan Exploration Company (NOMECO) in Jackson, Michigan. These data were not used for interpretation because of suspected errors in sample interval depths and compositions. 6) Various forms of published data including Bouguer anomaly gravity maps, magnetic anomaly maps, LAN DSAT data, thermal maturation data, scout tickets, and seismic data were studied and included in the text where appropriate; and 7) Personal communication with numerous individuals, both in private industry and in academia, provided much helpful information during this project. W The literature dealing with Lower Ordovician in the southern part of the Michigan Basin is not extensive, especially with regard to hydrocarbon exploration potential. Some work dealing with future potential and factors relevent to hydrocarbon exploration has been done for the Cambro-Ordovician of the northern Michigan Basin, but similar detailed studies extending toward the southern portion of the basin have not been done as yet. One of the earliest workers to study the Cambro-Ordovician of the Michigan Basin was Cohee (1945, 1946, 1948). Cohee (1948) made regional correlations to areas outside the Michigan Basin. He was the first worker to recognize the standard Wisconsin Prairie du Chien Group and formation subdivisions; the Oneota Dolomite, New Richmond Sandstone, and Shakopee Dolomite, in ascending order in 12 the Michigan Basin subsurface. This research served as an important contribution and formed the basis for stratigraphic nomenclature that is still in use today. As more deep well data from the Michigan Basin became available the feasibility of more detailed studies of Cambro-Ordovician stratigraphy became apparent. Ells (1967) used gamma ray logs and similar Iithologies between wells to construct cross-sections of Cambro-Ordovician strata between Michigans Upper and Lower Peninsulas. Much of Ells work was based on the previous work of Cohee. A more recent regional study of the Lower Ordovician in the Lower Peninsula of Michigan was conducted by Syrjamaki (1977). The lithology and distribution of the Prairie du Chien Group was delineated using well samples and correlations of Gamma-Ray logs. Syrjamaki divided the Oneota Member of the Prairie du Chien into a lower sandy dolomite unit and an upper argillaceous dolomite unit. The other two Prairie du Chien members were combined into the Shakopee-New Richmond interval because of difficulty recognizing the individual units. Syrjamaki speculated on possible hydrocarbon potential within the Lower Ordovician of Southern Michigan. He suggested the most likely occurrence would be: 1) porosity traps associated with faulted structures, 2) stratigraphic traps along the Post-Knox Unconformity where overlain by impervious Glenwood Shale; and 3) wedge outs along the margins of the basin. Bricker et al. (1983) constructed cross-sections of the Michigan Basin using the most current mechanical logs to correlate the upper Cambrian and Lower Ordovician. 13 Zwicker (1983) concluded future hydrocarbon occurrences would depend on favorable porosity trends as well as structural highs. These conclusions were based on over 200 well logs analyzed for the distribution of Cambro-Ordovician sandstones in the northern Lower Peninsula. Rohr (1985) believed the "massive sand” of the central Michigan Basin to be an accumulation of several distinct Iithofacies of the New Richmond sandstone member of the Prairie du Chien including lagoonal, near-shore, offshore, and barrier-bar facies. Rohr also suggested porosity in Prairie du Chien sandstones was entirely retained depositional porosity that escaped silica cementation. Fisher and Barratt (1985) named the massive sand found below the Glenwood in the central basin the 'Bruggers" and the underlying Lower Ordovician carbonate the ”Foster formation”. Based on the examination of numerous cores in conjunction with wireline logs Harrison (1987, 1988) suggests several facies occur within the thick sand sequence of the central basin and offers a time-stratigraphic depositional model correlating the Middle and Lower Ordovician units from areas surrounding the Michigan Basin to units within the Michigan Basin. Harrison (1987) also relates reservoir potential to the diagenetic history of the various sandstone Iithofacies found within the St. Peter sandstone in the central basin. Brady and DeHaas (1988) offer two new formation names; the Umlor formation for a traceable unit found at the base of the Prairie du Chien (Oneota member) and the Goodwell formation for what is now considered the lower Glenwood sequence. These formations 14 were derived from electric log picks which were believed continuous and mappable within the Michigan Basin in hopes to provide a better correlation framework, better structural and stratigraphic control, and to standardize some of the stratigraphic nomenclature problems that exist within the intervals. Use of the names has not gained wide acceptance as yet. Wm: There are several methods or types of data used in this study that may allow for the introduction of error. They are: 1) Drillers log data- This type of data was used for making structure contour maps. Some inconsistencies in picking formation tops may occur using this type of data. However, those wells which appeared anomalous were checked by using gamma-ray logs. 2) Well cuttings- These data were observed for lithologic studies but not included in the overall interpretations because of poor control on formation elevations and contamination by caving from overlying formations into the cutting samples. 3) Correlations of formation tops- Locating tops is probably accurate to within five or ten feet. Poorly printed logs or slanted and deviated boreholes may lead to greater errors in determining the true vertical depth to formation tops. 4) Contouring- Hand contouring of geologic maps is very objective on the part of the geologist constructing the map. Interpretations may differ significantly especially in areas of poor well control. 15 Error can be significant in those counties where few PDC wells have been drilled. Such areas should be scrutinized with an open mind. 5) Structural interpretation- Difficulties can arise where stratigraphic boundaries are altered by erosion or differential compaction, such as observed along the Post-Knox Unconformity on top of the PDC. Such uncomformable areas are difficult to interpret structurally, especially where well control is poor and/or deep wells do not fully penetrate the section making the construction of isopach maps useless. Very few wells are drilled below the Prairie du Chien. Isopach control has been used whenever possible for aiding structural interpretation. MICHIGAN BASIN STRUCTURE Winn The hydrocarbon potential of an area should be based not only on the structural geology of the exploration target, in this case the Prairie du Chien, but also on the structural style and the mechanisms responsible for the observed structure in the area. The structural nature of the basement rocks may have influenced the type of structures and trapping mechanisms found in the overlying strata of the Michigan Basin. Structural Iineations can be seen where the oil and gas fields have a general northwestward trend (Fig. 4). This alignment is similar to part of the major trend of gravity anomalies of Hinze and Merritt (1969). However, Prouty (1983) has shown (Fig.5,6) that intrabasin folds (shear folds formed by shear faults) have almost any azimuth but tend to concentrate in eight clusters. I The basement structural configuration and composition underlying the Paleozoic section of the Michigan Basin is not well understood or documented. To gain an understanding of the possible structural style of the basement rocks, and the relationships to Michigan Basin structures, an understanding of the tectonic history prior and up to the proposed origin of the Michigan Basin is necessary. The structural style of the basement rocks in the Michigan Basin is believed to be quite complex as a result of the culmination of various tectonic episodes. 16 (a w} 17 I'll!!!“ II “III“ “Sun! “In!“ mm "TIMI MICHIGAN OIL AND GAS FIELDS, 1973 “...-awn”. .. ...-..- n.—--......-..-..4 ma... . =15»- V m 9Q.-. Q ...a n. V“.- 18 '0 a“! no“ «(no eat-I- -- - Figure 5. A compilation of major axial trends gleaned from maps of specific times in the Michigan Basin. These folds are believed to be shear folds formed by wrenching tectonics. (Prouty,1983) 19 $4 6 I \ \ 7 23 33 e \ O I) I‘ ) O \‘ I ’v \ 3 e 9 9 O \ 3 e’ e 6 3‘: y \‘wfi a? I e, a; 9 ~ . ., a ~‘%~ ,,” 0w ’ 0 ~ av 10 O 0 9 ~ u n _ 2 8C) BC) '70 ‘ 70 6 D 6 0 5 O 5 O 4 o 4 0 3 O 3 0 IO 15 If) I. m. "enem- an; onset- 87! 18. Stony ute- m "' ‘.'.” faulte- ”t 19. leynolde-lflnfleld. neln trell- 32H: 2. Antenn- NE; ems mne- “If .crose-treno- 49E 3. Move". ne’er trend- Ofll: cm:- 20. Penn-our. nun trendo. "I: cross- feult- 23E: en echelon told» 23! trell- 46E 0. Deep liver- can 21. Heyleno. nun trend- 0!: cross- 5. anconnlngo 34: ""‘° " 22. Fill-ore. uh trend. 50': cm:- 7- ‘°"”“"" ‘“ 23. Coldneter- 23c; sou: u.s; 79:; 8. lonllng Green foul! systeo- ISU ; 21! 9. Santer- ISU 24. Austin. neln trend- av: cross-trend to. Ile- eomn- 45v 5 ‘5‘ 2 . lecosu Late. Iain trend- 64H: "' ”flw" 15' ems-trend- 49E '2' W‘ ‘5' 26. Sheridan. nun trend- 45!: cm:- 13. Dover- “If trend- 4’! 14. Albion-Scipio. neln trend- ZJI: en 27. Shea-en. neln "mo 45!: cm: echelon feults- “If: you. cme- fund» 30!; ll-S; 70E """ 3“ ze. Gil-ore. neln treno- 12v: cross- 15. Looensoort ”309' feuIt- 26! trend- 8)! 16. North Men» I“ 29. Fort. neln trend- 66H; cross- 17. Tekonslu- 25: "’"'" ‘°‘ ‘9‘ Figure 6. producing oil fields plotted in a The azimuths of several randomly selected, linear structures are anticlinal flexures; trend, for example) are faults only. There is a tendency toward clustering the azimuths of the producing structures but the considerable diversity of their azimuths is also noticeabl e . (Prouty, 1983) "rose". Most of the some (Albion-Scipio 20 E I'B'IS 111' The Michigan Basin may represent a major region of continental rifting that evolved during the early Precambrian history of the North American craton. The behavior of the deep crust over a large area of the North American craton at that time may give clues to the origin of the Michigan basin and the deep structural styles found in it. Three major orogenic periods occurred during the Precambrian in Michigan and the surrounding craton according to Rudman et al. (1965). These include from oldest to youngest; 1) the 2500 my. old Kenoran orogeny of the Superior Province; 2) the 1700 my. old Hudsonian orogeny of the Southern Province; and 3) The Grenville orogeny of the Grenville Province which reached a maximum intensity about 1000 my ago. The Grenville Province and related northeast-southwest trending Grenville front separate the Archean basement in the north from the younger rocks, with isotope dates of 1000 my, to the south. The Grenville front disappears under Lake Huron and is interpreted to continue into the midwest (Cambray, 1979) The Grenville front may mark the boundary of ancient metamorphic terrains of mobile belts which bordered the proto North American craton. Similar terrains are observed around cratonic blocks in Southern and Eastern Africa forming zones of 21 weakness. These zones may develop intracratonic rift systems depending on the global tectonic stress system (Nelson, 1986). Outstanding hydrocarbon potential has been demonstrated in similar rifts such as the Central and East African rifts. The first tectonic event in the Great Lakes area may have been Keweenawan age. Cambray (1979) states the three arms of a rift system developed with one arm parallel to the Mid-continent gravity high, another parallel to the mid-Michigan gravity high, and a third being a failed arm running north to Lake Nipigon. This appears to be a typical rrr triple junction. A rift of this nature running north- south through Michigan could have substantial impact on the later development and origin of the Michigan Basin. The linear anomaly known as the mid-continent gravity high has been established by Thiel (1956), who showed the positive part of the anomaly originates from dense basalt flows of Keweenawan age and that parallel negative anomalies result from a contrast of low density Keweenawan sediments. The linear positive anomaly in Michigan may be rift related and genetically similar to the mid- continent gravity high (Hinze,1963). Magnetic data in Michigan also show the existence of similar linear features. Deep crustal seismic reflection profiling conducted by COCORP (Consortium For Continental Reflection Profiling) near the center of the Michigan Basin (Fig. 7) has outlined the structure of a Precambrian trough previously outlined by Hinze (1963) from gravity and magnetics data (Brown, 1981). The seismic data support the structure of a paleorift probably closely related to the Keweenawan 22 rifting event (Fig. 8) associated with the midcontinent geophysical anomaly. Vander Voo and Watts (1979) discuss a single deep test (Sparks,Eckelbarger, and Whightsil no. 1-18) on the mid-Michigan gravity high which recovered Keweenawan metaspilites interbedded with the thick Precambrian redbeds. An embryonic form of the Michigan Basin may have been present as early as Cambrian time. ...—Tn 101 Fan 1: Q 1.10 Royals Paul: a..%‘ Wren . ,/. § .‘ ... 3° 0’}-.. ‘ ,' . ."3’5/ Kowoonomv Faun Figure 7. Mid-continent rift trend and geology from eastern Lake Superior through lower peninsula of Michigan. Projection of Keweenawan geology under Lake Superior shown by hatched pattern. Note location of COCORP line and McClure well. Sources of this interpretation: Hinze et al (1966,1975), Gray et al (1973), and Fowler and Kuenzi (1978). (After Dickas, 1986). 23 EARLY KEWEENAWAN - continental doming. rift valley stage IIFT VALLEY /—mome vuLcAmc: 4" _..~__:::: ‘.- er - "_.__ ALLIVIAL VAR: —- 4 ,7 IAFIC IIIES I on' I e Illl MIDDLE KEWEENAWAN - thermotectanic volcanic-dominated pmtocaamc basnn rennet uu vetcmcs' 'CIARIC crust Infill PC IETASIIIIERIAIV IOCIS PIEBIORT CLASTICS ALLUVIAL FANS I - luvoun: voumcs mum I noon \ sour» nus: VOLCAI’ICS - ‘ - . -- ‘ c ' “ To“ V03.) 1 ‘\\\,"”//I ' I II I l"/%& LATE KEWEENAWAN - laundering shallow marine protoceanic basir fuse-entrant: m “V“ meme-cum: flaunt: ‘ “u" "an TIAISGIESSIVI IAIIIE SNOIELIRI ‘ --.;f ;;i‘ . 3 - IACOISVILLI ILUVIAL-DELTAIE Figure 8. Keewanawan rifting and associated igneous 1978) activity,(Fowler and Kuenzi, 24 Figure 9. Paleogeography during early Paleozoic time. A) Late Cambrian (550-540 million years ago). B) Middle Ordo- vician (490—475 million years ago). C) Middle Ordovician, view of earth rotated 180°from the view of B. (After Bambach et al, 1980.) Black dot locates the Michigan Basin. 25 Eliil” B" ISI | ”'.' All continents are believed to have been dispersed and distributed around the equator by Late Cambrian time.(Fig. 9A) This is based on paleomagnetic and paleoclimatic data by Bambach et al. (1980). During the Paleozoic, Michigan was part of a large continent, Laurentia, which was composed of North America, Greenland, Scotland, and the Chukotski Peninsula of Eastern Russia.(fig. 9B,90) By the end of the Paleozoic most of the continental blocks were grouped together to form the supercontinent of Pangea. The tectonism during the Paleozoic that was related to the formation of Pangea, and later its break-up, may have controlled the structural configuration and structural development of the basement, Precambrian strata, and Paleozoic strata within the Michigan Basin. Tectonism along strike of the Mid- Michigan gravity anomaly may have been reactivated before and continued up to, the late Paleozoic to provide short wavelength folding and normal faulting (Hinze and Merritt, 1969). Stewart (1981) believed the stratigraphic and mechanical history of the Michigan Basin to be ultimately tied to the history of the Appalachian Mountains which began with the Taconic orogeny in early Ordovician times (Fig. 10). Prouty (1983) considers that episodic stresses conforming with Paleozoic orogenic periods in the Appalachians were carried northward in basement rocks setting shear fault patterns which developed the shear folds within the Michigan Basin. '.‘“ I‘m OCT." ...“ ..-- --.... ..-.. ..__.T_.._.-- '0“ (“Vent-one noon... ICIOIOOC (...-(I'Ol m nnnnnnn D on. COCCOOCV'OC Goons-o. — “'0 .3: 2:12.11".- -. 1:“;‘:-‘°. -' - z- r.) amt-7' [ untrue -'-uouca usoucoo .Houucoo Hamz ucmmmuoou moon xomam .moum >©zum msu cfinufiz ceauoEHOH :oflnu so ofiuwmum may no one McCucoo musuoouum .m. cosmos OOOOOO ooooooooooooooooooo QDOCO 29:0 :0 Nazca. vbzluzla lb‘b. 8(9.80.8 35 cannon—e “no.” Wee-mo. m . ..."...- eeuA-noen . . ----mwmmm “0"“ ‘.'- Figure 16. Structure contour map of the Prairie du Chien formation. Contour interval is 500 feet. 36 O I “I!” é Figure 17. Isopach map of the Prairie du Chien formation. Well symbols indicate wells that penetrated the entire PdC section. Contour interval is 100 feet. 37 carbonates was taking place on the Basin flanks. Rapid subsidence appears to have occurred during the marine transgression in early St. Peter time, keeping pace with St. Peter marine clastic deposition . This concept is neither entirely consistent with Fisher (1969) nor with Catacosinos (1972) but suggests that subsidence was occurring during Lower to Middle Ordovician time (late Canadian, early White Rockian). E ISII [ll II'I' B' The Michigan structural basin is centered symmetrically within the Lower Peninsula of Michigan and extends into Ontario, Ohio, Indiana, and Illinois. Precambrian outcrops bound the Basin to the north, the Wisconsin Arch bounds the west side, the Algonquin Arch is the boundary to the east, the Findlay Arch to the southeast and the Kankakee Arch to the southwest (Fig. 19). The basin is roughly circular with the deepest part of the depocenter containing in excess of 16,000 feet of sediments. Howell (1988) suggests the smooth, semi-circular shape of the Michigan Basin is the result of long term elastic flexural response of the lithosphere to a load in the center of the basin. The response may be related to a Precambrian thermal event (Nunn, 1981 and Nunn et al, 1984) The structural style of the Michigan Basin is probably quite complex. A broad curvilinear pattern of faulting is revealed on structural maps of the Canadian Shield (Fisher,1969). Western Ontario, in the region of the Grenville front, is marked by a 38 . ...—4r-——- I I l I I I ’ i ' l ' Y ‘1‘ ' '. i l l . { L 0...... U." 0' TR. ”If-I... “....”H'V _.‘ h ‘ . ,_l i I | I ~ - tnewoneee eouu anemones-- no «neonate» I TRIM.“ I...“ I'."TII IAGOIO PRO”... uncnoov 0' OT.'CTII OAM'AL '.'DTIOAt MARIN. PACIII IT. "TI. I“... CAI. PAC... I 0 ' .—- o I TIA-.mOOI'I CNAIQII. "LL I fl '03”... ITA 7' 0.0V OIIOIMIZII OT. "TO. I. LOTWRGIIO I” . .I'I: ”NO. OGMI: a IV: ”I. .. “L... Figure 18. Generalized St. Peter formation Iithofacies map. 39 . -. ”w‘..~-- “mm-”h Mae-oatmeal- \ _+_ Von-On!”- —-.-—'oonooiee-~ono W Gun Home. Dore Ive-n Moe Inn-o...“ eve-.000! “I...“ .0. '0. booed-me cove-nee See needed-ecu. “wade-u-“ uuum-Iw .0. l~ Figure 19. Major structural elements of the Basin and Arches Province. (After Fisher, 1969) 4O dominantly NE-SW structural grain with a NW-SE cross pattern within the igneous and metamorphic complex of the Canadian shield according to Paris (1977). Paris also noted the shield is marked by an E-W pattern to the east and north of the Upper Peninsula of Michigan as well as southern Wisconsin and southeast Ontario. Continuation of these structural patterns of the surrounding areas beneath the Michigan Basin would result in a complex structural style within the basement rocks. Sanford et al. (1985) performed reconstruction of Paleozoic depositional and tectonic processes along the eastern rim of the Michigan Basin in Ontario, and immediately adjacent regions of the Canadian Shield. This work, supported by satellite imagery studies indicated that basement uplift during and subsequent to Paleozoic time was transmitted through the crust by vertical rotation (tilting) of fault-bounded megablocks. The reconstructions Sanford et al. (1985) created further indicated that all the oil and gas fields discovered to date in Ontario are directly related to vertical fault- block movement that appear to be coincident with major tectonic events in the Appalachian orogen (Fig. 20). This finding not only has important application as a hydrocarbon tool in Southwestern Ontario but also may have application elsewhere in the Michigan Basin. 41 “HIST" I OOLOITONI E ooiomruuo zone emu nee-em ’ nvonocnnnone ——8——. Figure 20. Middle Ordovician (permeability pinchout) play; example- Dover area. (Sanford et al, 1985) 11' SI I 'II' II ll'l' 8' Three major structural features are observed in Southeastern Michigan according to Fisher (1981) and include; 1) the Howell Anticline; 2) the Lucas-Monroe Monocline; and 3) the Sanilac County Monocline. These structural features all trend northwest-southeast and are normaly faulted and steeply downthrown to the southwest. The origin of the structures may have been Precambrian with later development and movement occurring with various orogenies. These features are parallel to the southeastern rim of the mid-Michigan gravity and magnetic anomaly and suggest that pre-existing basement fabric has controlled their development and were created by tectonic events outside the basin (Fisher, 1981). This pattern of 42 basement fractures controls the 1 structures of southeastern Michigan, and probably the basement as a whole. At least three axial troughs representing graben structures are recognizable from subsurface Devonian structures in the central Michigan Basin with the prominent half-graben structures more pronounced at depth than the shallower Devonian structures according to Davies (1988). Davies claims several graben bounding normal faults are listric at depth, rooted deep in the crust, and have curved envelopes. The axial troughs exhibit classic zig-zag shear faults as the result of compressional wedging within the graben structures. These zig-zag faults may propogate across flanking normal faults segmenting the graben structures which may provide significant petroleum traps along the axis of deep structures (Davies,1988). Prouty (1983) suggests episodic lateral stresses, from the east- southeast probably resulting from Taconic, Acadian and Alleghenian Orogenies, show simple shear mechanics that could account for the fault patterns and fault-fold associations seen in the Michigan Basin (Fig. 21). Prouty (1978) mapped hundreds of Iineaments using LANDSAT imagery from the Piedmont of Pennsylvania across the Appalachians, Central Lowlands, the Michigan Basin and into eastern Iowa. The Iineaments involve Precambrian (but are not likely of that age) and Paleozoic rocks, and show little or no directional changes related to rock type, topography, or existing structures, apparently behaving as vertical faults,but of strike-slip mode. Those showing some vertical offset are believed lowered by dissolution of salts and or carbonates. 43 .Amme .susoumv mamanmu ca iamme Ammawcw mmmcdv one «0 mmoummp mDOHum> :uH3 mpfiocwou mausfifium mmona Amuaomm umonmv muzmsmccfia eh30¢a .uoo...o..o. 44 q Modo'hcd offer HardingQG‘u) (Fr- I51. znd Harmonics (A1" ° Figure 21 B Counter—based study of the stress field in the Michigan Basin based on Iineament analysis. Comparison of the second harmonic of a Fourier series (A) and the application of simple wrench tectonics carbined schematically with a strain ellipsoid (B). Both diagrams assume circles to start with and the development of ellipsoids by the second harmonic level. (A) oanpares closely with the elliptical shape, relative axial dimensions and orientation of the Michigan Basin. The optimum expression of the stress field based on the approximate 2000 lineaments of the Fourier series is shown at the 17th harmonic level. Source of the stress(es) was calculated to be from the 81 5°13 direction. (Prouty, 1983) 45 Figure 22. Comparison of "roses" of LANDSAT imagery Iineaments (A) and master joints from outcrop (B) . Numbers on periphery are average degrees of azimuth for each cluster of Iineaments or master joints. Occasional strays have been eliminated as "noise". The clusters represent principal shear directions. (Prouty, 1983) 46 Frequency analysis of the azimuths by Prouty (1983) (Fig. 22a) indicates cluster tendencies whose comparable orientations suggest a common overprint of the entire area, including the Michigan Basin. Figure 22b shows major fractures whose azimuths were measured in available outcrops and quarries in and surrounding the Michigan Basin. The clustering of the fractures fits the Iineament clusters, strongly suggesting that Iineaments and shear faults are in effect the same and their strike-slip movement developed the shear folds. 47 PRAIRIE DU CHIEN STRATIGRAPHY/SEDIMENTOLOGY B'ISII'I Regional stratigraphic nomenclature across the upper Mississippi Valley is fairly well accepted. This report will not discuss details of the regional stratigraphic correlates of the Prairie du Chien group. A summary of comparisons, history, and evolution of the regional correlates can be found in Syrjamaki(1977). Figure 23 summarizes the general nomenclature and regional correlations for the Upper Cambrian and Lower Ordovician in the upper Mississippi Valley. )- 3 gg§ 3 $05 $235.. )- Soloeap rumors 01mg; 2 UN 385m IF— . Joachim 7 corbonotee d_ “—W 2 8 ' 4 3 3?. PETER - U o 2 smosroue > ('.' l: = .. see c saw 0 x PRAIRIE < 9 on 5 CHIEN 9 Figure 23. ORDOVICIAN CORRELATION UPPER MIDWEST NORTHWEST sounrusr soumerm cams». 11.le MINNE§OTA msconsm mm" mm stenwooo GLENWOOO GLENWOOO v”, ; ' 31. PETER 51. Penn? “WWW '31: PETER ””5“" “”57“: Isa-unaware smosroné /Z Ix 53" Z ‘s 7 7 , ° \\ ?. ‘ er. PETER \ / smos'rou: -.g in?!“ mm»: mm: PRAIRIE a“ do: Pam: 4' cm“ (:ch cam 9"" (CARBONATESI Lower-Middle Ordovician correlation in the Midwest Basin and Arches province after: Ethington et al, 1986; Fagerlin, 1980; Golden, 1969; Norby et al,1986; Repetski,1973; Shaw, 1987; 48 Shaw et al, 1988; and work in progress, Shaw pers. comm. (taken from Harrison,1988) Widespread carbonate deposition characterized the Lower Ordovician across much of the eastern United States. Lower Ordovician carbonate Iithologies are found from the Appalachians to Missouri, north to Minnesota, Michigan, and northeast to New York. Both dolomite and limestone are found throughout its distribution with some structural control being responsible for Iithofacies variations such as reported by Prouty (1948) for Lower Ordovician carbonates in the Appalachian- Valley and Ridge Province and along the Adirondack Arch. Prouty (1948) demonstrated that dolomite is the predominate lithology to the west, northwest and north to Missouri, Wisconsin, and New York, respectively. To the southeast of the Adirondack Arch the Lower Ordovician consists of limestone facies. The general Lower Ordovician stratigraphic correlations as shown in Figure 23 are based on Iithologies that remain very similar through much of the area of distribution which further supports these stratigraphic correlations. Prouty (1948) and Butts (1940) describe the lithology of the Beekmantown Group of Virginia and Tennessee as a thick bedded, bluish gray, fine to medium crystalline dolomite. Brown, coarse chert is abundant. White chert is occasionally observed and appears similar to the white chert found in the Oneota dolomite of Wisconsin (Prouty, 1948). Siliceous oolites and oolitic chert are common in the Lower Beekmantown and may be similar to Prairie du Chien Iithologies observed in the Michigan Basin cores of this study. Thin limestone units and 49 sandstone stringers are observed in the Beekmantown which may be similar to the Prairie du Chien of Michigan and Wisconsin as well. The Beekmantown weathers to a light to dark brown color. Correlation from the southeastern edge of the Michigan Basin over the Findlay Arch into the Appalachian Basin is presented by Shearrow (1957) to aid the subsurface stratigrapher in understanding the terminology discrepencies that often exist at political boundaries. The Lower Ordovician Prairie du Chien Group, well developed in the upper Mississippi Valley, is not present in wells located in the northcentral part of Ohio according to Shearrow (1957). Shearrow has identified Lower Ordovician sediments in the southwestern portion of the state and believes these sediments also occur in southeastern Ohio. Calvert (1974) discussed the Findlay Arch as a basement-related topographic feature and its effects on Upper Cambrian and Lower Ordovician deposition. Calvert used isopach maps of the Upper Cambrian Copper Ridge dolomite and the Lower Ordovician Beekmantown dolomite to suggest paleodrainage to the south occurred at that time. The Prairie du Chien Group in Indiana according to Droste and Patton (1985) is composed of the Oneota dolomite below and the Shakopee dolomite above while ranging in thickness from its eroded limit in northern Indiana to about twelve hundred feet in southwestern Indiana (fig.24). Removal of all the Shakopee and significant amounts of Oneota occurred prior to Chazyan deposition (fig. 25). In Illinois the Prairie du Chien Group contains in ascending order the Gunter sandstone, Oneota dolomite, New Richmond 50 Map showing the thickness of Shakopee Dolomite in Indiana. Black tone indicates the area where sandstones of the Shakopee are prominent rocks in the lower Shakopee. Line pattern indicates the Dolomite lie directly below rocks of the Ancell Groupnand where they area where sandstones are prominant rocks in the Shakopee Dolomite below the top of the unit. Contour interval is 100 Feet. (Droste and Figure 24. Patton, 1985) 51 .mmm. .gouuma can mumoua soon. ..osmpc scheme-cam ..msap. nomnsomsm use emananz .Amsmp. mammmcmn.eoum mono enema Buzoumcmm umnsmEom me am... 9? 503388 scan—£6 mo ummco on... $.3qu mocwsoom xsmm may no no“. on”. um. 5250.385. on... an >ooaooo 05 @5305 mm: .mm 9303 .mmm. .cobumm cam mumouo. .mocmsvmm xsmm may «0 QR. man an mommusm 5250.385 on» so 538 Amoconfiuon m mcaesmmm mnocaHHH one .mcmnccH .030 mmouom :oHuowm Gong—3950 .mm whom: ....- ..z... E mum... wow .. . .oa . .o . .. a. ..mwm ”sexy .n....n....u... anew-...“.wm....u.m a ...... .mmwmnue not 0 . . e . . .....K. .50 mmmm.‘ .20.: .93 52 sandstone, and Shakopee dolomite. In northern Michigan it is the Oneota, New Richmond, and Shakopee. Droste and Patton (1985) show neither the Gunter nor the New Richmond being traceable any further into the state than northwest Indiana where post-Knox eroSion has removed the entire Prairie du Chien section. This is consistent with observations of the Prairie du Chien in the southern Michigan Basin from this study where the majority of the upper Prairie du Chien Group has been eroded. The New Richmond sandstone does not appear to be present in the southern Michigan Basin. The distribution may be associated with the proximity of paleohighs and basin bounding framework structures such as the Wisconsin Arch with localized deposition of the sandstone occurring during a slight regression at mid-Prairie du Chien time. In southwest Indiana the Knox is composed of the Potosi dolomite, the Oneota dolomite, the Shakopee dolomite, and the Everton dolomite (Droste and Patton, 1985). The Everton dolomite appears to represent the last episode of carbonate deposition prior to or contemporaneous with the major post-Knox marine transgression. The occurrence of the Everton dolomite may be found only in the deeper portions of basins which escaped erosion during post-Knox time. The Everton has not been described in the central Michigan Basin but this does not preclude its possible existence there. Droste and Patton (1985) indicate the regional thickness of the Knox Supergroup shows two directions of thickening from north- central Ohio. The Knox thickens into a depocenter in central Michigan and to the southwest into the Reelfoot area. Prairie du Chien Group Iithologies described by Droste and Patton (1985) for 53 Indiana and surrouding areas are similar to Iithologies found for the Prairie du Chien in this study. The Post-Knox Unconformity following the Lower Ordovician was the result of a worldwide erosion surface caused from eustatic drawdown of Ordovician seas. The Post-Knox Unconformity is characterized by extensive solution features, karsting, channeling and erosional relief of hundreds of feet in the underlying Ordovician carbonates in some areas. Cooper and Prouty (1948), Dapples (1955), Janssens (1973), Calvert (1974), Droste and Patton (1985), and Mai and Dott (1985) all report solution features, channels, or paleodrainages in Lower Ordovician carbonates that are filled with St.Peter or equivalent age clastics. This study has found similar features within the Prairie du Chien of the southern Michigan Basin. Il'l' E . SI I' I .Lower Ordovician stratigraphy in the Michigan Basin is fairly well established; however, recent works by Zwicker (1983), Rohr (1985), Fisher and Barratt (1985), Harrison (1987,1988), and Brady and Dehaas (1988) have been cause for some controversy regarding Middle and Lower Ordovician nomenclature in the central Michigan Basin (see Table 2). Since 1980, the thick Lower to Middle Ordovicician sandstone unit in the central basin has been referred to as the ”massive sand”, ”Jordan” sandstone, 'Bruggers formation”, ”St. Peter" sand, and "Prairie du Chien" sand. Outside the central basin area Lower Ordovician terminology is well accepted. The study area in this report overlies the transition zone between the stable Lower 54 COEdm .uz COEHm .uz COEHm .uz COEAm .uz COE«m .u: 388 new 888 :8 8:8 and 9:20 new 888 2mm €285 5388 2:538 23528 M m macoocoum 3505?“ 380:3.“— macoocoum cacao—Bum m. saggy“. defined—5.5 goddamn—Ebb. goddamn—Una 8:333 .um . Em x90. 3095 com um» mom iiiiiiiii w iiiiiiii gawmimmz m W. on xocx i~moaoxuzm 30a {‘1 . J. mummmam V38 .um 48: um o . l 1 III: cocoon b a pm 8958 .g 88:88 .a m @8530 009530 000358 00955.3 08358 M m. a 9.52 x83 #52 x88 , “92 x88 9.53 x83 “32 x88 coucob. :35»... C353. caucub. c3559 mod»: coda: nod»: mod»: coda: moms mama Hemp hp w th— page: amp—3m uoxogs «gmgm 858035 ...".me .umm .53: 3m 5qu 35:00 Emma H3328 canon enhance 5qu Hanan—mo .82 B 22 59¢ imam 53:02 93 :« 20330.38 can manganese—.8 cofiogoouo g 93 p.83: no ”Em—53960 .N am”. 55 00.50 .0: 00.50 .0: 0950 .u: 00.50 .02 0058 .u: 0.330 and 0.330 :00 0:30 :00 0.330 0mm 0:30 and 20300.8 zomnmmuo comnmoua 20800.5 £0000qu “mu m 3:00:95 3000:0050 3:00:05“ 3:00:95 300055 1 m 3030005009 5030008009 20200050; 20300950.“. 303009509 m m m 00 300:0 000:0 mu 000:0 u :0 M 0:05:03 302 0 0009320 \immmlirrmru: 0009.20 0003020 12.039350 twig“. llllll. I.) l§§ III III I m .3000 .00 0002530 A 0003030 .4 3030000 0003030 .A 0030.— m. . 1. 0003030 0003030 0003030 0003:30 0003030 m w 003m x030 00>; x030 003m x030 uwim x003 003m x003 m. 0000009 .5009? 000:0”? c0000; c0050.”. 003: 003: 003: 83: 003: damn ad ad“ Juan am . >003 013. >050 35. 30:00 a W095 002.53: .29— :000m 000 _ Emma ~93ch .20?— 30 Emma Hmuucwo 0003 300000 503 Hmuucwu ...u.:oo. a mamas 56 Ordovician carbonate platform in the southern basin and the deep depocenter of the central basin area; therefore, the stratigraphic problems of the central basin will be partly addressed. Outcrop lithologic descriptions by various workers have divided the Prairie du Chien Group into three formations in ascending order; the Oneota dolomite, the New Richmond sandstone, and the Shakopee dolomite. It is not clear as to the extent of these formations within the subsurface of the Michigan Basin. Dixon (1961) reports finding New Richmond sand in a core taken in Delta County of the Upper Peninsula of Michigan. Syrjamaki (1977) combined the Shakopee- New Richmond into one interval due to difficulty in distinquishing between them on geophysical logs. This study does not recognize New Richmond in the southern Michigan Basin and considers the Prairie du Chien to consist only of the Shakopee and Oneota formations. The New Richmond sandstone may not be widespread throughout the Michigan Basin and most probably is deposited near the basin flanks in close proximity to paleohighs such as the Wisconsin Arch, Algonquin Arch, and the Canadian Shield (Harrison, 1987, pers. comm). Rohr (1985) interpreted the thick massive sands found in the central basin to be New Richmond equivalents in origin. He presents no evidence for the Post-Knox Unconformity in the central basin yet does not adequately account for the missing Shakopee dolomite section above the massive sands. Zwicker (1983) called the massive sand in the central basin the "Knox sandstone". Zwicker considered the sandstone to be early Ordovician. Lilienthal (1978) and Bricker (1988) considered the “massive sand” in the central Basin to be early Ordovician age and 57 the carbonate section underlying the sands to be Cambrian age. Ells(1966) produced a cross-section from northern Illinois to the Upper Peninsula of Michigan but experienced much difficulty in trying to correlate Lower Ordovician units of the basin margins to the central basin area. Lilienthal (1978) and other workers expressed difficulty in correlating Lower Ordovician units in the central basin as well. Harrison and Barnes (1988) used basic sequence stratigraphic concepts and comparison/correlation of well established stratigraphy in the upper Mississippi Valley outcrop belt to determine the stratigraphic sequences in the Michigan Basin. They found the Lower and Middle Ordovician strata in the Michigan Basin to be lithologically similar to the Prairie du Chien in Wisconsin but as young as Lower Whiterockian age. The Prairie du Chien in the southern Michigan Basin is bounded below by an unconformity on top of the Upper Cambrian middle to lower Trempealeau dolomites. The upper Trempealeau Jordan Sandstone may not be present across much of the southern basin within the study area. The top of the Prairie du Chien in the southern basin is bounded unconformably by the Glenwood Shale and in places by the St. Peter Sandstone which appears to fill channels and lows on the karsted and eroded Prairie du Chien surface. In the central basin area a complete Prairie du Chien section is believed to be present above the Upper Cambrian Trempealeau formation. A complete section of the Trempealeau may exist including the upper Jordan sandstone. The upper Prairie du Chien is probably bounded conformably by a eustatically cont-rolled S8 regressive to transgressive marine quartz sandstone depositional sequence with thin discontinuous beds dolomite, siltstone and shale (Harrison and Barnes, 1988) Between the central basin and the carbonate platform in the southern basin a transition zone may exist where the St. Peter transgressive marine clastic sequence pinches out, the Post-Knox Unconformity is evident, and erosion of the upper Prairie du Chien section occurs. Figure 26 illustrates the depositional formation of sequence boundaries in the Midwest Basin and Arches province. The two high stands would be represented by the Prairie du Chien, below; and the Trenton/Black River, above.. In this study the Foster formation of Fisher and Barratt (1985) is considered the upper-most Prairie du Chien or upper Shakopee interval. Most, if not all , of the Prairie du Chien in the study area has been eroded off ; therefore, Prairie du Chien cores used in the southern Basin may bear little resemblence to the Brazos State Foster core. However, by using the central basin core along with core segments in the southern basin from this study, a complete sequence of the Prairie du Chien Group may be obtainable. Wells with cored Prairie du Chien intervals have been included and indicated in the well correlations. The location of the wells can be found in Appendix A. In general , the lithology of the lower Shakopee is a gray to light brown finely crystalline dolomite, silty or argillaceous dolomite, containing minor amounts of oolitic chert, siltstone, and shale stringers. This lithology is similar to the Oneota which is a buff to brown heavily recrystallized dolomite with oolitic chert clasts, 59 nodular chert, glauconite, shale and sand stringers. A definite Iithologic contrast is often difficult to observe between the Shakopee and Oneota.in cores and cuttings. In outcrop the distinction is not so obscure. In core , the Oneota appears darker, mottled and more heavily recrystallized then the Shakopee, in general. In outcrop, the abundance of white chert is often used as a Iithologic parameter to separate the Oneota member from the Shakopee member. The amount of white chert could not be used as a reliable indicator for the core comparisons. Detailed Iithologic descriptions can be found in the Petrology/Lithology section of this report and in appendix A. Gamma-ray log correlations (Figs. 27-34) were based on log/core comparisons and careful comparison of gamma log signatures of the stratigraphic sequences of all the wells. Information for wells used in the correlations can be found in Table 3. Formation tops picked by the Michigan State, Dept. of Natural Resources, Geological Survey Division were not used due to considerable inconsistencies from well to well across the study area. This is most likely due to the variability of the Middle and Lower Ordovician lithology and thickness both north to south and east to west across the study area. The picks used in this study (upper PDC-lower PDC) do not indicate the true Shakopee-Oneota boundary but have been used as an arbitrary boundary and for correlation of Iithologic units. The Oneota(L.PDC unit) is represented by a low gamma ray zone below the Shakopee. This interval has been referred to as PdC and Trempealeau, Foster, and Umlor by Bricker and others (1983), Fisher and Barratt (1985), and Brady and Dehaas (1988), respectively. 60 TABLE 3 . Wells used in gan'ma-ray log correlations. (A) J.O. Mutch R.A. Rensel & A. Allen 1—13 PN- 33019 Branch County 813, T88, R6W TD- 4633', KB- 1019' (C) Consumers Power Co. Harvey Clark NO. 1 PN- 29969 Branch County 88, T58, R8W TD- 5475', KB- 889' (E) Kulka & Schmidt Markovich No. 1-5 PN- 40417 Calhoun County SS, T18, R7W TD- 6240', KB- 947 (G) McClure Oil Co. Hibbard No. 1 PN- 20732 Barry County 834, TZN, R9W TD- 4745', KB- 976' (I) Ohio N.W. Development Corp. Disposal No. 2-156 PN- ED 156 Kent County 83, TSN, R9W 'ID— 7820', KB- 831' (B) Atlantic Richfield Co. Riddle No. 1-20 PN- 37236 Branch County 820, TSS, R8w TD— 3660', KB- 878' (D) Trenton Pet.& McClure Oil Co. Bernloehr et al PN- 22352 Calhoun County 813, T38, R8W TD- 4739', KB- 952' (F) Battle Creek Gas Co. BD- No. 153 PN- ED 153 Barry County 814, T1N, R8W m- 6618', KB- 942' (H) Trenton Exploration Co . Tobias No. 23-11 PN- 40548 Barry County 811, T3N, R7W I'D-6487' , KB-948' (J) Houseknecht Oil Production Price-Strafford Unit No.1 PN-26500' Hillsdale County 820, T68, R4w TD— 4099', ICE-1062' TABLE 3.cont. (K) Atlantic Richfield Co. Stevens No. 1-35 PN-37302 Calhoun County 835, T38, RSW TD- 4700', KB- 1008' (M) Atlantic Richfield Co. Butler No. 1-12 PN- 37238 Calhoun County 812, T38, RSW TD- 4700', KB- 990' (O) Mobil Oil Corp. Gladys Kelly Unit No. 1 PN-29117 Eaton Co. 824, TZN, 33w TD- 6923', KB-870' (Q) Bell & Gault Drilling Co. H.J. Young No. 1 PN- 22536 Hillsdale County 811, T88, R1W TD- 3729', KB- 290' (S) A.E. Rovsek C. McFarlane No. 1 PN- 24840' Jackson County 835, T38, R3w TD— 5200', KB- 1078.8' (L) Atlantic Richfield Co. Dunn No. 1-14 PN- 37239 Calhoun Co. 814, T38, RSW 'ID- 4700', KB- 967' I (N) Earl Midlam Midlam No. 1 PN- 30468 Calhoun Co. 813, T18, RSW 'ID- 6000', KB- 968' (P) McClure Oil Co. Sparks, et al No. 1-8 PN- 29739' Gratiot County 88, T10N, R2W R Atlantic Richfield Co. Schumacher No. 1-24 PN- 37237 Jackson County 824, T48, 33w TD— 4700', KB-1137.8' (T) Mobil Oil Co. Reeve Unit No. 2 PN- 29672 Ingham County 836, TIN, RIW TD— 6300', KB- 977' TABLEJ3.cont. (U) Besko Petroleum Corp. Eva Allen No. 1-A PN- 26204 Washtenaw County 527, T48, R4E TD— 4037', DF- 864' (W) Terra Energy LTD. Phillips No. 1-2 PN-40438 Livingston County 82, T3N, R38 TD- 7454', KB 940' (Y) Good & Good Drilling Co. W.P. Schowacke No. 08-1 PN-24714 Washtenaw County 816, T48, RSE TD— 3830', DF- 864' (AA) Marathon Oil Co. Lloyd Cupp No. 1-11 PN- 31335 St. Joseph County 811, T68, mow TD- 5283', KB-892' (C13) N.R.M. Petroleum Corp. Copeland No. 1-1 PN- 34688 Branch County 81, T58, R6W TD- 4506', KB- 990' 62 W) New York Petromin Corp. Paul Widmayer No. 1 -A PN-28990 Washtenaw County 821, T38, R3E TD- 5241', KB- 980' (X) Gulf Oil Corp. Gilmore et al No. 1-15 PN- 31792 Lenawee County 815, T58, RSE TD- 3798', ICE-760' (2) Hunt Energy Corp. Worrell No. 1-28 PN- 34223 Washtenaw County 828, T18, R6E TD- 6325', KB- 942' (BB) Atlantic Richfield Co. Peck No. 1-16 PN— 38103 Branch County 816, T58, R7W TD- 3950', KB- 964' (22) Mobil Oil Corp. Howard J. Messmore No. 1. Pn- 27968 Livingston County 829, T3N, RSE TD- 7589', I mun-mm 1 Wlt ”it” ”I. "u ‘I . ‘ In" “'0 t Figure 31. South to north cross-section.U - W. Prairie du Chien formation.gamma log correlations. 68 W x v 2‘— W 6.. 0000mm“. manna“... ““3... IO... 4. M “A "on”. ° 0... \ I ‘— l-um "\ new «an um" um IA! L0. 11) ‘ mm m- — f j v ... . M «melon . :f‘ um gnu sea..- ) o \ 0' J.“ coo-unnwm “'7- num no can nu ) p‘. ' " "“°" “ .. mun"- -- , ,4 g. / um mas- _ ..." moons-u; so»: u out n " Figure 32. South to north cross-section X - 22. Prairie du Chien formation ganma log correlations . . 69 )4 .HN w . ”I! . . _ . . . l m . , . . Li H/» .“$>$\»J\Jviti.€‘w5)>_brwwl)(. . _ \— ifiézfi . . .x N F. )4 -1 5-21 h L \ _ . _ _ Gamma log correlations. Cross-section AA - V. Figure 33. 70 — fi 1 west F N 1' 2 But OA'YLI SO!!! “I ‘0. [Alt M ICON. OI. 6000. NI! IIIIO' CO” ...... “I. ”J IIIVI “.7 ...! DWI-L ”.108. ”-0.4" '.'...“ “-0001. ".8000. 000-0. 6. Ice-"II.- 60 I H I“. "I h- ". no I“ II-OIOI' loo" 1 “an. IO. 0 ... '0. 1 man. 10°.“ . “.0. u "flunk?“ UL ’ - [PETER F” ' a .II. Don-ano- m. — ”.10.”:. M W m. -7- mm- Wv— -~-- «on ma- - om II? 1.0. common. ' Figure 34. West to east cross-section F - Z. Prairie du Chien formation ganma log correlations . 71 Minor disconformities may be present in the section above and below the major Post-Knox Unconformity. A minor disconformity may exist between the Shakopee and Oneota formations and may be indicated by the higher gamma response below the upper PdC/lower PdC pick. The lower gamma response just above the pick may represent a New Richmond time-stratigraphic equivalent. The Oneota is believed to be uneroded and preserved in the basin center as well as most of the basin margin; therefore, an effort was made to maintain a somewhat uniform Oneota thickness for correlation purposes. The gamma log correlations clearly show the unconformable nature of the Post-Knox erosion surface across the carbonate platform. Channels filled with St. Peter eolian sands are indicated on wells T, C, and 88. A cored interval of the St. Peter sand was taken from the ARGO-Peck no.1-16 well (BB). The cored interval showed a clean, white, unfossiliferous, friable sandstone with frosted, well rounded, uniform-sized quartz grains of a possible eolian origin. See appendix A for detailed descriptions. These channel-fill sands can be seen on seimic sections and have a typical channel-fill type morphology with a steep side and a gradually sloped side, in profile (Sinclair, 1985, pers. comm.). The north-south gamma ray log profiles clearly show the structural and stratigraphic relations of the Prairie du Chien Group and the overlying St. Peter formation from the stable carbonate platform in the southern basin into what was the gradually subsiding central basin depocenter. An attempt was made to correlate the Prairie du Chien carbonates and the massive transgressive marine clastics of the central basin area to the Lower Ordovician carbonate 72 platform and St. Peter eolian clastics in the southern basin in order to understand the depositional history and to formulate a depositional model for the Lower Ordovician Prairie du Chien carbonates and the overlying sands within the study area and the Michigan Basin in general. The north-south gamma ray log profiles (figs. 28-32) , the Prairie du Chien structure contour map (fig. 16) and the Prairie du Chien isopach map (fig.17) show a definite deepening and thickening of the Prairie du Chien Group and overlying sandstone into the deep basin to the north. This author believes that the Post-Knox Unconformity is non- existent in the central basin area and that a complete section of the Prairie du Chien Group underlies the massive sand as indicated on profile well 'P" (Spark et. el. no. 1-8, Gratiot County). The overlying massive sand is considered a marine facies of the St. Peter formation. The origin of this facies will be discussed under Depositional History/Paleogeography. The St. Peter formation found on the carbonate platform in the southern basin is believed to be transgressive channel-fill eolian sands. The Lower Ordovician carbonates found in the southern basin are the lower and middle Prairie du Chien formation. The entire 400 to 500 feet of the upper Prairie du Chien have been eroded from the carbonate platform during Post-Knox time. Overlying the St. Peter marine clastics in the central basin and underlying the widespread Glenwood Shale is a lithologically heterogeneous sequence of starved basin sediments consisting of interbedded shales, argillaceous dolomite, siltstones, and 73 sandstones referred to by the Michigan State Geological Survey as the ”junk zone” or " zone of unconformities" (Bricker,et.el., 1983), and Goodwell unit (Brady and Dehaas,1988). This author prefers to use the term "Lower Glenwood” after Zwicker (1983), Rohr (1985) and Fisher and Barratt (1985). This unit is approximately one hundred and fifty feet thick in the central basin and is conformable with the St.Peter marine clastic sequence, below; and the Glenwood Shale, above (Harrison et al, 1988). The lower Glenwood is not present in the southern basin area where an unconformity (Post- Knox) is evident at the base of the Glenwood Shale. Deposition of this sequence occurred as a result of an initial rise in sea level in what was a fairly isolated basin northwest of Saginaw Bay. l DI" D 'I' ”'.' [El | A widespread regional open marine carbonate shelf existed at the beginning of Lower Ordovician deposition within the study area. The transition from Upper Cambrian Trempealeau formation to Lower Ordovician Prairie du Chien was a time of essentially continuous carbonate deposition within a transgressing sea. However, a regression occurred at'the Cambro-Ordovician boundary (Fig.35) evidenced by the increase in clastics within the upper Trempealeau Jordan and Lower Ordovician Oneota formations (Syrjamaki,1977). A minor disconformity may exist at these contacts. Carbonate deposition and the rise of sea level continued until the end of Oneota time. A lowering of sea level brought localized New 74 ofiououmcmnm 95.8.6 H93 mom 5 omcono 9338 no $35 3903 “mono 28mm can umuE .82 $8382 den. .2 933m / 25523me 25mm2OO¢O UJOO... 8&304 bh.IIOsI°0ID oTl‘l‘l‘ D0¢08300 8..b¢l..b o IIIIIII. Banana IOIIOOII IOIOCIIIII'IL IIhCI 09...... 3.... ....... [1| GOODS-J...- .3. ...-m... 2.04. ..(Cbzmo .0.b.¢40 ...-lldo ....- dd-‘ J O l l. 2...... s.‘ 2.0(0 2(0.20.3 8..20% Within the Arco-Riddle 1-20 well core, good vugular and fossil moldic porosity was observed in places. Fracture porosity was not extensive but was fair to good in places. Low to fair intraparticle and interparticle porosity within silicified oolitic packstones were observed. The Schumacher 1-24 well core contained good intergranular, vuggy and fracture porosity in places. Some low to fair microvugular porosity was observed in the dolomicrite portion of samples. This well core had up to twenty five feet of quartz sandy dolomite with thin stringers of sandstone. Porosity within the quartz arenites was reduced by quartz overgrowth cementation and clay pore linings, but was still fair to good in places. The Peck 1-16 well core had very good intergranular pore space within the quartz arenite sections of the core. Poor porosity was observed in the subarkose portion of the core because of chert cement and illite within the pore spaces. Good to excellent interparticle and intraparticle porosity were observed in silicified oolites of the Stevens 1-35 well core. Good fracture and fossil moldic porosity were observed in places. Good intercrystalline porosity was found within the medium to coarsely crystalline replacement dolomite, where it was found. 93 Porosity and pore textures in the Butler 1-12 well core were similar to the Stevens 1-35 well core. Fair porosity was found in vugular chert zones within the Dunn 1- 14 well core. Overall, the extent of porosity found within the Prairie du Chien cores was poor to fair, with the exception of the Peck 1-16 well core. Good porosity was found in each core but was not extensive throughout the core. Low porosity was generally found in zones of variable grainsize and lithology such as quartz silty, quartz sandy dolomudstones. The presence of clays usually results in lower porosity. The dolomicrites and dolomudstones were usually tight except where microvugs occurred. Good porosity in the cores was generally found in the coarsely crystalline dolomites, within silicified oolitic packstone/grainstones, within breccias, and along fracture zones. The Peck 1-16 sandstone core contained fair to good porosity throughout. Fluid migration and reservoir potential within the Prairie du Chien will probably be closely tied to the presence of fracture zones, oolitic facies zones, and quartz sandy sections of the Prairie du Chien. D' I' Ill The textural characteristics and the distribution of silica and dolomite types in the Prairie du Chien are strong evidence that they formed under different conditions and probably in different diagenetic environments; i.e. epigenetic vs. penecontemporaneous 94 dolomites. In some instances it appears as if diagenesis was the product of the original local depositional environment and not necessarily regionally extensive. The Prairie du Chien carbonates were deposited under shallow water, generally low energy, open marine conditions. Breccias were commonly observed and may be related to large-scale storm deposits, periodic subaerial exposure, or a result of the erosional Post-Knox Unconformity. As the early Ordovician seas regressed the carbonate platforms became subaerially exposed. An early phase of dolomitization may have occurred penecontemporaneously with deposition. This episode of dolomitization may be regional in extent. Taylor (1982) believed regional dolomites of the Middle Ordovician formed at or near the surface during early diagenesis. Similarly, Lower Ordovician Prairie du Chien regional penecontemporaneous dolomites may have formed under much the same conditions. Prouty (1948) discusses the penecontemporaneous origin for regional dolomites of the Chapultepec formation (PdC equivalent) as far southeast as the Tazewell Arch in Virginia and Tennessee. The distribution of the saddle or fracture filling epigenetic dolomite, along large and small scale fractures, faults, partings and bedding planes, requires that dolomitization of this type occurred after lithification of the Prairie du Chien. The usual coarse textured, large crystalline epigenetic dolomite is found replacing the usual fine-to-medium crystalline regional dolomites along faults and fractures, such as in the Albion-Scipio Field. Shaw (1975) suggests that the timing of epigenetic dolomitization, as found in the Albion- Scipio field, occurred sometime after Niagaran (Silurian) time. 95 Epigenetic dolomite of this type is believed to have possibly formed under elevated temperature conditions and may have been derived from hot brines migrating out of the deep basin, perhaps under artesian flow off the flanks of the frame structures, and rising along major shear faults and fractures as the Michigan Basin was subsiding (Prouty, 1988). The actual occurrence of saddle dolomite may be a separate phase of epigenetic dolomitization or a late stage development during the emplacement of epigenetic dolomite thru a continuous cycle of hydrothermal alteration. Silicification observed in the Prairie du Chien cores, where it has replaced dolomite, probably occurred prior to emplacement of the epigenetic fracture dolomite. Plate 9b in Appendix A shows a large epigenetic saddle dolomite crystal within a silicified fine grain carbonate. The source of silica may have been derived from dissolution of quartz sands and silts from the Prairie du Chien and Cambrian sediments or from overlying St. Peter sands upon burial. Migration of the silica-rich fluids along fracture zones most likely would result in localized silicification. This was not observed. It is suggested that silicification may have occurred -by either infiltration of silica and freshwater after post-Knox time or by vertical migration of silica-rich fluids derived from older sediments undergoing pressure solution as a result of compaction and bunaL 96 HYDROCARBON POTENTIAUPETROLEUM GEOLOGY OF THE PRAIRIE DU CHIEN WW Three possible sources of hydrocarbons exist that could be found in Prairie du Chien reservoirs. These sources may be found in Precambrian or Cambro-Ordovician strata. In the Precambrian, the Nonesuch Shale or its equivalent may be a possible source of hydrocarbon, within the Ordovician the Utica Shale is the most likely source rock. The upper Prairie du Chien section which may be fully preserved in the deep portion of the basin may be a viable source rock due to its algal rich nature (Harrison,1988, pers. comm.). McKirdy and Hahn (1982) believed most Precambrian organic rich sediments have crossed the threshold of intense hydrocarbon generation; yet suggest some sediments, such as the Nonesuch Shale, still lie within the ‘oil window‘ in places. They have found the many Precambrian sediments contain a complete range of hydrocarbons typical of unbiodegraded crude oil. Precambrian sediments in the Michigan Basin are now mostly found within the zone of thermal organic degradation. However, the Precambrian may have been a viable source in Lower Ordovician time. The timing of structural trap development in conjunction with hydrocarbon generation is critical. The Prairie du Chien in the study area may not have been buried deeply enough or involved in suitable hydrocarbon trapping structures when Precambrian sources were generating 97 hydrocarbons. The Precambrian along the basin flanks may still be within the ‘dry gas window'. Cambro-Ordovician structures along the basin flank may be likely reservoirs. Oils presumed to be Precambrian are found in the White Pine Copper Mine in Michigan's Upper Peninsula. The geochemical signature of the Precambrian oils is unique (McKirdy and Hahn, 1982). These Precambrian oils should be compared to oil and gas condensate found in the Prairie du Chien of the central and southern parts of the basin, to oils found in Cambro-Ordovician structures in Ontario, and to Cambro-Ordovician oils found near the fringe of the Michigan Basin, such as in the Lima- Findley oil field in Ohio. Powell et al. (1984) identified the hydrocarbon source in the Ordovician of Southwestern Ontario to be the Middle Ordovician Collingwood Member of the Utica shale. The Collingwood Member oil was correlated to the Cambro-Ordovician oils on the basis of distinctive geochemical characteristics between the oil fractions and the Collingwood kerogen (Powell et al., 1984). The Ordovician oils are believed to be fairly typical of oils derived from marine organic matter. Dally and Lilly (1985) using a thermal subsidence model from Nunn et al. (1984) suggest that Lower Ordovician and older sources would be completely within the ‘oil generation window' over the entire basin perimeter and well within the ‘gas window' in the central basin. In either event it is likely the Prairie du Chien oil could have been derived from underlying older (Cambrian) sources or were from younger Middle to Upper Ordovician sources which provide hydrocarbons from a structurally lower position into a 98 stratigraphically lower but structurally higher Prairie du Chien reservoir rocks higher along the basin flanks (Sryjamaki,1977) with vertical shear faults being possible avenues of migration (Prouty,1984). According to Hogarth (1985) the thermal history of the Michigan Basin has changed little since its inception. The model proposed by Hogarth (1985) using Middle Ordovician conodants as indicators of organic metamorphism, was in agreement with the geophysical model of the basin constructed by Nunn et al., (1984), but differed significantly from the thermal model of Cercone (1984). Hogarth (1985) found a paleogeothermal gradient of 23°Cle to be the best fit for the observed maturity in the northern and central sections of the basin. In the southern portion of the basin either an average gradient of 31°C/Km or additional overburden had to exist to account for the observed maturity of the Middle Ordovician conodants in the study. ‘ The regional movement of fluids through time could account for the maturity observed in the southern portion of the basin. Hitchon (1984) associates hydrocarbon accumulations and variations in paleogeothermal gradients to gravity-driven paleohydrologic conditions operating in the Alberta Basin of Canada. The paleohydrology of the Michigan Basin has not been studied. However, Bethke (1985) concluded gravity driven groundwaters moved in a south to north direction through the Illinois Basin, after modeling the paleohydrology. Bethke (1985) found that with gravity drive, heat flow is increased significantly in the northern Illinois Basin because of warm ascending fluids. A similar mechanism may have 99 occurred in the southern Michigan Basin. The formation of hydrothermal dolomite from ascending deep basinal brines along fractures in the Middle Ordovician ‘Trenton Formation' may be consistent with paleohydrogeological models in other areas. The ‘oil generative window' for the Middle Ordovician, based on the constraints of paleogeothermal gradients and burial history curves for the Michigan Basin, from Hogarth (1985) implies: 1) In the central basin the initial generation of oil began in the lower Ordovician section during Mississippian time and is now completed for all the Lower and Middle Ordovician sections, the base of the oil window being at 2.85 Km from the surface of the central Michigan burial history curves; 2) In the northern basin oil generation began in the Lower Ordovician during Mississippian time and is completed for a small section of the Lower Ordovician, the base of the ‘oil window' being 2.75 Km below the surface; 3) in the southern basin only the rocks of Ordovician age or older are capable of oil generation, the top of the ‘oil window' being 1 Km below the surface; and 4) evidence from southern Ontario suggests that the Ordovician section is intensely generating oil (Powell et al., 1984). The migration distance of hydrocarbons from potential source rocks to most reservoirs may be variable. Since source rocks are in close proximity to most reservoirs, only short lateral migration distances along intrastratal pathways are required (Bender, 1986). Long distance lateral, interstratigraphic migration of hydrocarbons out of the deep basin, where initial hydrocarbon generation began, to reservoirs along the flanks of the basin may have occurred. The vertical and lateral migration may have been facilitated by 100 numerous shear faults which penetrate the entire stratigraphic section within the basin (Prouty, 1987, pers. comm.). It has been suggested by Syrjamaki (1977) that oils found on the southern perimeter of the Michigan Basin, in Indiana and Ohio, may have migrated from the central basin. The paleohydrology of the Michigan Basin is not well understood but migration along major fracture trends may be possible and could explain interstratal migration across normally impervious stratigraphic sections. WW Hydrocarbons have been found in Cambrian and Ordovician strata of the Michigan Basin in Southwest Ontario and Southern Michigan. The Prairie du Chien of the southern Michigan Basin has thus far not yielded significant quantities of hydrocarbons. The production that has been obtained does signify that potential exists for additional production from this stratigraphic interval. However, PdC exploration has been substantial in the central portion of the Basin. A study conducted by Powell et al. (1984) indicates that in 1981, Ordovician and Cambrian Systems accounted for 2% and 13.2% of the oil production in Southern Ontario, respectively. Commercial production was found to occur in Cambrian dolomites and dolomitic sandstones along the southeast flank of the Algonquin Arch bordering the Appalachian Basin. Of the seven producing fields in 1981, one field was a fault trap while the remaining six fields were stratigraphic traps occurring on the updip truncated edges of Cambrian strata flanking the south side of the Algonquin Arch. Case 101 studies of these fields would be beneficial to exploration of similar trap scenarios in Southern Michigan. Powell et al. (1984) found that over 50% of the sedimentary volume of southern Ontario consists of Ordovician rocks, yet these rocks must lack suitable reservoirs as only small volumes of hydrocarbons have been found there. Of the six fields in operation in 1981, all production was found to occur in dolomitized zones associated with gently folded or faulted structures within the Middle Ordovician Trenton-Black River carbonate sequences. The production of hydrocarbons from the Prairie du Chien Group in the southern Lower Peninsula has been reported in three wells drilled in Jackson, Hillsdale and Lenawee counties between 1960 and 1982 (Bricker, 1982). Table 2 and Figure 1 show well data summaries for three wells and stratigraphic cross-sections showing the productive zones. All production to date in the southern Lower Peninsula has been located immediately below the widespread post- Knox unconformity (Bricker, 1982) which is found at the top of the Prairie du Chien Group. Additionally, shows of hydrocarbons in the Prairie du Chien have been reported or recorded on drillers logs for wells in the southern Basin. Prairie du Chien production in the northern Lower Peninsula has increased dramatically in recent years. Table 4 summarizes well data for PdC(?) completions in the northern Basin. The significant amounts of hydrocarbons being found in the deep portion of the Michigan Basin may signify potential for hydrocarbon entrapment of a stratigraphic nature where St.Peter marine clastic units coming updip out of the Basin interfinger with PdC carbonates. 102 EICIII | | 'lll' Trapping mechanisms for Prairie du Chien hydrocarbons in the southern Michigan Basin may be variable. Both structural and stratigraphic traps are possible. A widespread network of shear faults may be the main pathway system through which basinal fluids have been transported in the geologic past (Prouty,1976). Production from the Zaremba and Young wells (Table 1) are most likely fault related, based on their on-trend location with the fault- associated Albion-Scipio oil field. The Albion-Scipio trend extends 35 miles in a northwest-southeast direction across parts of Hillsdale, Jackson, and Calhoun counties in southern Michigan (Fig. 37,38). Oil and gas is produced from a dolomitized fracture zone in the Trenton and Black River formation of Middle Ordovician age (Ells, 1978). Strike-slip movements in the Michigan Basin are suggested by a unique sag which overlies and closely follows the productive fairway (Harding, 1974). Prouty (1976) demonstrates the Albion- Scipio field represents a model for a northwest set of fractures with left-lateral movements, in an en echelon arrangement, and with no apparent vertical structural offset. Most production in the Albion-Scipio trend comes from the Middle Ordovician Trenton-Black River section. Oil found in the Prairie du Chien section in relation to the Albion-Scipio trend may have come from vertical migration downward along fractures. Analysis of PdC oil in Lenawee County indicate a close) similarity to oil of the Trenton-Black River section (De Hass, 1979). 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(Harding, 1974) 105 Other examples of Albion-Scipio type fracture patterns and oil fields occur. At the Sussex-Meadow Creek field in the Powder River Basin of Wyoming, oil is trapped by an echelon normal faults which appear to be related to left slip on an east-west trending wrench fault. Most intracratonic basins exihibit some type of shear fault overprint. To date, no structure in Michigan comparable to the Albion-Scipio trend has been found. The Stoney Point field to the northeast of the Albion-Scipio field is the most recent comparable discovery, but is much less extensive. Hydrocarbon trapping mechanisms have been recognized for Cambrian reservoirs in Ontario where tilted fault-blocks that initially formed in early Ordovician became reactivated in Late Ordovician, Middle and Late Silurian, Devonian, and post-Devonian times, creating triangle shaped blocks uptilted to the north placing Cambrian sandstone and dolostone in juxtaposition to impervious limestones of middle Ordovician age (Sanford et al, 1985). Similar structural/stratigraphic traps may occur in Lower Ordovician strata on the Michigan Basin side of. the Algonquin Arch. The Washtenaw Anticlinorium which is a complex of horst and graben structures in southeastern lower Michigan might provide suitable structural traps at drilling depths on the order of 5000 feet(Fig.39). The Northville Field at the junction of Wayne, Oakland, and Washtenaw counties has been a prolific Trenton-Black River hydrocarbon producer. Production also comes from the shallower Devonian Dundee formation. Checkley (1968) notes that the Dundee production in the Northville field is offset to the production from the deeper zones. This pattern of structural offset is not 106 oozqocz a: om