AN IKVESTIGATION 0F DIMENSIONAL GRAIN ORIENTATION IN A SANDSTONE by man. ALBEW SCHMIDT A El LQSIS Submitted in partial fulfillment of the requirements for the degree of Master of Science in Michipan State University East Lansing, Michigan 1958 AN INVESIIGATION OF DIMENSIONAL GRAIN ORIENTATION IN A SANDSTONE by EARL ALBERT scsxlom ABSTRACT This paper deals with the dimensional orientation of individual quartz sand grains studied on the bedding surfaces of a sandstone in rough sections prepared from field oriented samples. The positions of the long dimensions and the face poles to the maximum projection areas of the particles were deter- mined with a simplified three-axis universal stage. The cor- relation coefficient aave a statistical measure of the degree of preferred orientation in the long dimension diagrams. This test was also applied to the quartz optic-axis diavrams prepared from thin sections of two of the samples. A definite preferred shape orientation was found, al- though the orientation of the quartz optic-axes was not sta- tistically significant. The dimensional fabrics were of value in the interpretation of the local current direction at the time of final deposition of the sediment. A size sorting analysis was conducted in an attempt to correlate the degree of sorting and the statistical meas- ure of the grain—shape orientation. No obvious relationship was found between the two coefficients. ii I Jr .b:: :,. _ _ __ . A r w W 'ff- v-o r.'./,:.‘. \Jli"L-J LDVVI‘."_)‘ JD mt ine writer would like to express his sincere appre- ciation to Dr. J. W. Trow for his many helpful suggestions and criticisms offered throughout the preparation of this paper. Grateful acknowledgmen: is also due to Dr. B. T. Sandefur and to Dr. J. A. Kelly for the assistance and ad- vice rendered during the writinn of the final manuscript. H. H H. Fae DIST or NIGUWES . . . . . . . . . . . . . . . . . . v INTRODUCTIOK . . . . . . . . . . . . . . . . . . . . 1 PU? OSE . . . . . . . . . . . . . . . . . . . . . . it SIM-11311.83 o o o o o o o o o o o o o .0 o o o o o o o o I: R C C10. 1 P171") {1 t S e o o o o o o o o o o o o o o o o o 5 LOC 51 tiOI’l o o o o o o o o o o o e o o o o o e o 5 Preparation . . . . . . . . . . . . . . . . . . 7 METHODS OF AEALYSIS . . . . . . . . . . . . . . . . 10 Plotting of points . . . . . . . . . . . . . . lO Grain-shape orientation . . . . . . . . . . . . 11 Optic-axis orientation ... . . . . . . . . . . l3 Sievinp . . . . . . . . . . . . . . . . . . . 1} Correlation coefficient . . . . . . . . . . . . ll JOJSIDEYAEIOK O; DAKA . . . . . . . . . . . . . . . 19 General . . . . . . . . . . . . . . . . . . . . l9 Cross-bedded samples . . . . . . . . . . . . . l9 Horizontally-bedded samples . . . . . . . . . . 26 Grain-shape, OptiC-axis comparisons . . . . . . 3S Orientation, sorting comparisons . . . . . . . 39 cc CnUSIOTS . . . . . . . . . . . . . . . . . . .‘. an LIST‘ OT." EISiprfim‘ICES o o o o o o o o o o o o o o o o 0 [#5 iv Figure l. 2. ll. 12. 13. 1h. lg. 1' lb. 20. Outcrop area location map . . . . . . . . . Section of the cliff sampled at Point aux Barques . . . . . . . . . . . . . . . Relationship of the m.n.a. and the l.d. ‘v in grain—snaps definition . . . . . . . . Relationship of the m.p.a. and the l.d. in equal-area projection on the lower hemisphere. . . . . . . . . . . . . . . . Frequency table for the computation of the correlation coefficient . . . . . . . . . Computation of the correlation coefficient Grain-shape fabrics for s mple 7 . . . . . Grain-shape fabrics for sample 6 . . . . . Grain-shape fabrics for sample 2 . . . . . H C O Grain-shape fabrics for sample Grain-shape fabrics for sample 3 . . . . . Grain-shape fabrics for sample h . . . . . Grain-shape fabrics for sample h . . . . . Grain—shape fabrics for sample 6 . . . . . Grain-shape fabrics for sample 5 . . . . . 4.: Quartz Optic-axis fabric for sample Quartz optic-axis fabric for sample 2 . . . Sorting cumulative curves for samples 1’ 2’ 3, and LI.- 0 O 0 C O O O C 0 O O O O Sorting cumulative curves for samples 5, 6, 7’ and 8 o o o o o o o e o o o o o The correlation coefficianzvalues plotted versus the sorting values . . . . . . . . V Page 12 12 U) (3.\ \ A) 1.2. A1“: I 3-? V SS I GA TI on c DIE-‘lfll‘uSIONAL "'T-ViAIlJ 031 313 Z’A‘I-Iom IN A 35310331323 INTRODUCTION A sand prain is generally a sliphtly elongate, irreg- ularly shaped particle. It tends to be deposited in a posi- tion controlled by the unequal surface area presented to the transportina medium. The study of this grain orientation in elastic sediments affords the petroloyist an important in- sinht into the depositional history of a sediment, particu- larly in reconstructing the environment to which the mater- ial was subjected at the time of final deposition, Dapples shad Rominaer (lQhS), state that: ...the arranpement of mineral grains in unmetamorphosed sediments appear to be least influenced by environments previous to the last and hence should provide one of the most reliable bases for interpretation of the ultimate depositional environment of a sediment. The analysis of elastic particle orientation is one of the most recent of the various methods employed in inter- Dreting sedimentary deposits. Much of the work that has been published deals with data obtained from studies relat- inr:to synthetically, or recent naturally, deposited uncon- SOlidated sands, the environment of which can be observed in action.or directly inferred. Krumbein (1939), and others have successfully devel- OFHMS techinques for observing and measuring the three dimen- 1 :0 “a? u 3 QV.. sional shape orientation of elastic particles that are large enough to be sampled singly. {rumbein, in his study of peb- bles taken from glacial and beach deposits, defines the longest axis and the maximum projection area as the dimen- sions necessary to determine uniquely the position of a peb- in space. Dapples and Rominger (l9h5), conducted a two dimen- sional study of sand grain outlines projected from the rough- ened plane of bedding: of artificially cemented, laboratory deposited, fluvial and eolian sands. They considered the least projection area and the larger end of the grain as be- in}? indicitive of current direction. The least projection area generally parallels the current and the larger and tends to be up current from the smaller. Griffiths and Rosenfield (1950), Griffiths (1952), and Curray (1956), used thin sections in their respective Works relating: to directional elongation of prains in sands and sandstones. A statistical correlation applied to mutu- ally perpendicular thin sections enabled Griffiths and ROsenfield to determine the inclination as well as a two di- menSional vector for the {tr-wins examined in their study re- latinfi’. orientation to directional permeability. A two-axis universal stage, used in conjunction with a binocular microscone, was constructed by Schwarzacher (19'31). This enabled him to observe both the strike and the plunge of a grain's long; dimension when viewed on the rouflh- ened surface of a sample slide. He was able to prepare fab- 1‘ ‘ (lukl‘... "0‘ ~¢v - ric diagrams of interpretive valie by plotting the elonga- tion vectors of grains from samples of experimentally de- posited sands. Rowland (l9h6), converted optic-axis diagrams to Krain-shape diagrams by applying the relationship he found to exist between the optic-axis and the grain-shape of clas- tic quartz. Ingerson and Hamish (l9h2), in a paper also dealing with prain-shape, optic-axis relationships found that quartz grain elonration is related to orirional shape and therefore not a constant for all sedimentary quartz par- ticles. PURPOSE It is the purpose of this investigation to measure use grain-shape orientation (defined by the long dimension and the maximum projection area) in some consolidated sand- stone samples. The above axial positions will be determined usinr a simplified three-axis universal stage devised and constructed by Smith (1952). flitn this he successfully pre- pared fabrie dia“rams from sand grain orientation in small naturally and experimentally deposited sedimentary features. If a wrain-shape orientation is found to exist an attempt will be made to determine the current direction at the time the sandstone was deposited. Heaascopic sedimentary features observed in the surface exposures and orientation diagrams prepared by other workers, from deposits with a known current direction, will be referred to for control in interpreting the diarrams presented here. a visual and statistical com- parison of the «rain-shape and the optic-axis orientation diarrams will be made in order to determine the relationship, if any, which exists between the two. A subsidiary study will also be carried out in an attempt to correlate the de- gree of orientation, measured statistically from the fabric dia r ms, with the rrain size sorting coefficient. The sort- inr will be determined by a sieve analysis Oi a representi- U tive portion of each sample considered. SAIuPL EL'S Any sandstone sampled for use in a basic investiya- tion of this type must outcrop extensively over a small area or be correlative over the short distances between the expo- Snres that do exist, and c ntain meyascopic sedimentary fea- + cures visible in the exposures which may indicate the local direction ofthe currents at the time of deposition. Location Specimens from the fine to med’um grained Port Austin- Point aux Barques sandstone of Huron County, Michigan, were selected for this study. The sanfistone, a member ofthe Mar- Shall formation (lower dississippian), acquired its name from the outcrops in the Flat Rock Point-Port Austin area and at Point aux Iarqaes (Nirure l). The names were used Separately until Kennett (lth), combined the location des- iinations, Port Austin and Point aux Earques in naming the Sandstone. He presented sufficient evidence in his paper to Support the stratasraphic correlation ofthe two outcrop lo- cations. Six field oriented samples were selected from an eighteen foot cliff on the shore of Lake Huron at Point aux Parques. ihe strata appear to be horizontal but a 1%0 dip to the south-west has been recorded elsewhere by other FLAT ROCK POINT POINT AUX BARQUES Port Austin e. 8 HUROl. COUNTY I L_-_-._-__-_-_ -_-_-_-_-__- “bl. E I o t IONIC. 7‘, LOhER 4g??? Haron County ///, PENINSULA °f OUTCROP AREA MICHIGAN LOCATION MAP -_-_-%-‘- Figure 1 I 1‘- W workers. Five ofthe above samples were taken in series from a vertical column on the cliff face. The exact vertic- al position of each sample is shown in Figure 2. The sixth was taken approximately one-hundred feet west of the series samples from a stratagraphic position exactly equal tothat of sample A. Fbreset beds denuded by the present wave action of Lake Huron are evident in the outcrop on the west shore of Flat Rock Point. The strike pattern of the foreset beds forms a series of concentric crescents, the arms of which before becoming covered, present an opening to the east approximately 300 feet across. The dip is into the convex Side ofthis feature indicating the location of a lower Miss- iSSippian beach. Two oriented samples here taken from one 4 n L at file oeds. fflflgparation Rough sections. Thin plates were separated from the oI‘iented field samples by forcinr a thin bladed knife into the sandstone blocks alone the wed/Jinn; planes. The slabs t1lus obtained were trimmed to an approximate one and one llalf'inch square Chip and cemented to a metal sample Slide. 3310 surface ofthe sanple slide was then linhtly brushed to cles that became loosened while pre- 1»!- ‘ 4HMnove any sand part Enarifif the mount. A red ink stain was applied tothe sur- -face of the chip. This was found to accentuate the shape Chitlines cf the individual grains. During the mounting Ill l f Horizontal scale 1": 3' Figure 2. Section of the cliff sampled at Point aux Barques. Numbered arrows indicate the exact vertical posi- tion of the samples. (xerat ion preat care res exercised in retaining the field ‘ :mientéation directions and in recoroinr them on the sample slides . 1“ Thin sections. To prevent possible rotation oi the sand grains while grinding it vas necessary to have tne smnples impregnated and thin sections made by a proffessional Inxnaarator. Further investigation or optic-axis orientation was rnevented by the high cost of such work. Disaggreration. A mortar and pestle served as the PIfiJnary means of disaf renatien. Grindins was avoided dur- in{; the process as a precaution against the possibility of flxlcturing the individual grains. flhe sandstone, in many 0f7 the samples, was quite friable and satisfactorily len i‘tself to this method, althouth all attempts with chemical (iisargregation met with little success. Microscopic exam- ination durinr the process revealed no fracturing or remain- ing agrregations of individual grains. MEiEUDS OF ANADISIS Plotting of points The grain-shape and quartz optic-axis diagrams pre- smsted in this paper are plotted on a horizontal plane “Wictlis the areal View of the inside of the lower half of a Stunere. All north-plunginw axes will therefore appear in l . . 11MB north half of the diagrams, south-plunging axes on the ‘um-..._.‘u._q,-_-— uu- 2.4g. ‘ e l r I l 31 '. SCilth half, and so on; face poles of the north-dipping planes Vflill appear in the south half of the diagrams, face poles of SCnith-dipping planes on the north half, and so on. Equal- aIVea polar co-ordinate paper vas used to represent the lxlwer hemiSpnere; this may be freely interchanged for a 'VSChmidt" net wnen it is necessary to plot only points and n0t planes. Contourinu and rotatixn oftzhe plorted data were aCCOmplished using the standard petrofabric techniques as described in Pairbairn (13hr). The lonr dimension (l.d.) and the maximum projection area (m.r.a.) fabrics are plotted cn separate diagrams for each sample studied. The l.d. fabric diaframs were pre- pare by contouring the differential densities of points representinm the intersections of the l.d.'s with the lower hemisphere. The che poles of the m.p.a.'s were also plot- ted on the lover hemisphere and the repcesentative points . Q10 . . . . were contoured. The data‘ys presented in the lolLOhing lO ll grain—shape fabric diagrams. The two axes (l.d. and the pole to the m.p.a.) are pamnuidicular to each other (Figure 3) although the plot of the sencond is not fixed with the location of the first. The only condition resulting from this perpendicular rela- tionshdp is that one axis must be normal to the plane con- tairiing the other (Figure h). It is possible then for the IflJDt of the l.d. of any particle to move alonf the arc forwned by the intersection between the plane of the m.p.a. atmi the surface of the lower hemisphere. Independent and Seflbarate plots for the l.d.'s of separate grains are there- IYDre possible even though the m.p.a.'s may occupy identical F<>sitions. The previous statement is also true if the axes r1Qtations are in terchamed . GPain-Shape orientation ¥ The simplified three-axis unive sal stage mounted under a LiJOCUlQP microscope provides an accurate means of Ineasurinp the azmiuths and the plunges of the axes in ques- tion. The stage consists of a movable transparent plastic hemisphere, calibrated in five decree parallels and merid- This "bowl" rests on a fixed circular plastic ring ians. to which four reference points are attached. The binocular microscope furnishes the Operator with a three dimensional View of the individual quartz grains. The l.d. and the m.p.a. are aligned with the cross hairs ofihe microsc0pe, their original positions in the n 12 -L T \+ l.d. 'm.p.a. Pole to m.p.8. # LFigure 3. Relationship of the m.p.a. and l.d. in grain- shape definition. J Plot of pole to Imepoao Plot 0 l.d. Plane of m.p.a. ~—__ii Ffigure h. Relationship of the m.p.a. and the l.d. in equal- area projection on the lower hemiSphere. 13 Imnuited rough sections are then determined by observing the posiixions of the apprOpriate reference points on the trans- parerit hemisphere. The plots of both the m.p.a. and the l.d. are obtained for each grain with a single setting of the rnovable hemisphere; therefore, the perpendicular rela- tfitmiship of the axes in space is maintained. Her 3 00mplete discussion of the construction and Opeliation or the stage, see Smith (l9fi2). Traverscs were run across the rough sections and CHIly'those firains which pasaed the intersection of the cross kfitirs were used. In a few cases it was impossible to deter- mixie successfully the orientation axes of particles. These IJPains vere omitted if eithev tne m.p.a. of the l.d. were Urideterminableo Optic-axis orientation A Leitz four axis universal stage mounted on a stand- ard petrcgraphic microscope was used to obtain the quartz c-axis orientation data from the thin sections. Only those grains which passed the intersection of the cross hairs dur- inr the traversing of the section were used. Single detri- tal quartz grains made up of apprefiates of small quartz crystals were infrequently encountered. These were disre- garded for it is impossible to obtain a single representa- tive orientation vector from such an aggrefate. Sievinp 11L Approximately 150 grams of the disa rregated mater- ial j?rom each sample was split from the original amount for the :sieve analysis. Number 10, 32, 60, 115, and 230 mesh siexres were used and the weight of the material in each graxie size was determined with a chemical balance. It was fOUIld that sufficient control for the cumulative curves ‘ \‘ Deemed on this analysis could be obtained from the size fac- A . o cicnqs used. Ccrrrelation coefficient .. Contouring 0: point diagrams enables a clearer dis- tSlinction to be drawn between areas in which points seen to {IPoup together and those areas in which relatively few if Shay points appear. The correlation coefficient (r) is used in this report as a measure or the degree of this preferred Orientation in the l.d. and c-axis diagrams. Chayes (l9h9), stated that the correlation method is in closer agreement with visual inspection than any of the other tests he dis- cussed. The "r" statistic measures the tendency for a grid square containing a certain number of points to be surround- ed by squares containing an equal number. If there is a tendency for these squares of equal density to lie closer together in some warts of the diagram than in others then the value of "r" will be significantly positive and the fab- ric may be said to have a preferred orientation. In practice a grid is drawn on tracing vellum by dividing a standard 10 centimeter equal-area net ("Schmidt" or polar co-ordinate) into 100 squares, 1.77 centimeters on a side. The grid is superimposed on the fabric diagram in (prestion and the number of points in each square is record- ed. Ench,square in turn is considered as a center and the ltnar adjacent squares are used as its neighbors. Squares uased as centers will in turn be used as neighbors and vice veyrsa. There are then 72 centers (The squares near the per- ipfiiery will not have a complete set of adjacent squares.) arid 280 neirhbor squares. The comparisons are then entered iri a frequency table such as the on presented here (fiigurc E3) illustratinf the "r" computation for the 300 optic-axes Efllotted from sample h. The entries are made such that (see Phigure S) of all tne squares containing 3 points, 19 of the nieighbors considered will contain 2 points, 2 neirhbors will CCHdtain 6 points, and so on. There will be 1? center squares CLMitaininn 3 points (65 § h = 17). The frequencies of either {”16 X.or the Y values summed in the table will be 266. These rRelationships enable the tabulated data to be checked before ark; calculations are UBLUU. The computations necessary to determine the correla- ‘Iion.coefiicient are carried out in the manner outlined in lfigure 6, using the values from the frequency table. It EShould be noted that the number of points plotted does not eriter into the computations. N is the number of comparisons lnade betweentshe center and neighbor squares. In order to comoensate for multiplication by zero, 16 Hopshm GOHpeEESm n m HOQShm honesuoau u 9 0mm: moH mam ems memH omHH Hmo msH oH xumx mmOH :m a: omH mmm dam wow :0 0H aux mean so :mm com OOOH NNOH mm» emm me wax NH mm me com mom mew meH me we ems: NNOH mmm. m e Hm Hm He me e: oH we omm mm emH NH 3 m H e mam om emm em. m H m s o sow ::H on: He :m H N s m m s m oomH cam mmo emH a: m m m 0H m OH 0H m : mmOH New owe esm as m m 0 mm oH o m m 030 eHm owe com N» H a HH om NH :H e m moH so zen mmH a: H m HH w mH : s H . 0H 0H em .em 0H m m n m is o ems he» xmw _xm m o m» memwmmmMA z m H o mpMWWoo A: madamm Seam weapoan moxw10Hon unease oom Soap bochpbo saucy ezmHOHmamoo zoee anrle with the supposed current direction. The direc- tixbnal arrozs, which were placed considering both the l.d. anti the m.p.a. fabrics, show an approximately eoual source dixeection for both samples even though the strike of the bed inas changed due to the different sample locations. The vectors indicate a curren from the south east. This dircc- F-— tion can only be roughly substantiated by the attitude of Use foreset beds. The cross b ds, although visible only in cross sec- ticmu at Point aux Barques, are of a tabular, herringbone ‘rl— natnire which indicates water-laid sediments from alonr the litrtoral zone (Shrock, lghh). The equal strataflraphic cor- reliation of tee two outcrop locations and the short distance betnueen them also tends to indicate a similarity in their onxrironments. The author therefore feels that the relation- :fiaips found between the fabrics of samples 7 and 8, and the manposed current direction, can be used as a control in in- terpreting the grain-shape fabrics of sample 2. Sample 2 (Figure 9), taken from a cross-bedded layer at Ebint aux Barques, does not show as well a develOped im- bPicate arrangement of the prains. The m.p.a. fabric indi- cates particles lyina in the plane of the foreset bed and a FTPeater concentration with a slight inclination into the ‘bad; althouyh the l.d. pattern contains a sinnle 6% maxima 1"Spresentinn grain imbrication in the supposed current di- I-"ection, a freater number here also seem to be inclined in- i Ham. | . I um: ..lu I. ..a l l. . . V l.d. fabric - '31; Contour interval N 2.u.6.8 :75 Cb m.p.a. fabric Sample 2 Figure 9. Grain-shape fabrics on the lower hemisphere. to 'the dip of the bed. These patterns can be explained by tie fact that the cuirreat on a beach moves in two directions - the incominr wasres or the wash, and the backwash. If the incoming cur- rerit is stronrer than the backwash then a pattern such as is feinad in Fieure 7 and 8 could be expected. Currents of equnal strenvth would result in flat lyinp particles, and a connea atively stronger backwash would result in fabric pat- ternis indicatinv rrair imbrication approximately opposite to 'that shown in Fifiures 7 and 8. Weak and somwhat isolated l.d. maxima representing Frwiins lyinr perpendicular to the current direction are ev- idcnit in Tirure 9 and appear to a lesser extent in the l.d. falyrics of the samples obtained from Flat Rock Point. Tfilose clusterings represent grains deposited in an unstable FNDsition. The particles probably rolled up and down the Slxspe of the foreset bed with the alternatinv wash and back- Vnish of the beach currents. The "rain-shape fabrics of sample 2 indicate that tile wa'es struck perpendicular to the shore line, causinr l3arallel wash and backwash curren a. An oblinue approach of tile raves would result in a non-parallel relationship of the Ifieversinc currents. This possibility does not seem to be Strbstantiated by the fabric of sample 2. The correlation coefficienhsfor tie samples compare f'lvorably in value and indicate a weak but definite pre- ferred orientation. V; i % Horiz ontalll-bedded samples The following grain-shape orientation diagrams rep- sterrt the samples taken from the horizontally bedded layers at Pk>int aux Barques. The fabric patterns discussed in con- juncrtion with.the cross-bedded samples are the main criteria used} here for the determination of the current directions. One-Qaundred sand grains were used in the preperation of each dirb‘ram. Any further plots only se med to reinforce the exixstinr maxima. This is in part supported by the higher anVraae correlation coefficient values for these samples in Ccnitrast to the cross-bedded ones. Samples 1 and 3 (Firures 10 and ll reSpectively) shuyw an almost identical confiourstion of l.d. fabrics. The inlbrication of the particles in sample 3 is somewhat less tfifni that in sauple 1. This is shown by the l.d. maxima of 1311% former bein“ located nearer the periphery or the up-cur- Iwfllt side, and by a rreater degree of Spread in the m.p.a. 3fabrdc of sample 3 parallel to the current flow. These l.d. patterns closely resemble th se obtained in; Schwarzacher (1951), from finely laminated sheet sands Vqlich had been artificially "eposited under conditions of "smooth phase" tranSport. Fine laminations are also present ill the sampled material. The close similarity between the fabwdcs of the syntheEically deposited sands and the sand- ‘3tone studied here indicates that a minimum amount of re- 27 fabric l.d. Contour interval 2.h.6.8 % fabric a. m. m Sample 1 Figure 10. Grain-shape fabrics on the lower hemiSphere. 28 N L ‘ V l.d. fabric 1" = 0.14.605“? Contourrinterval N 29149635 % m.p.a. fabric Sample 3 Figure 11. Grain-shape fabrics on the lower hemiSphere. R) \C orieentation due to compaction and settling has occured. This: is a fact that furnishes further control for the in- terqpretation of the grain-shape fabric dianrams. Sample 3 also shows a concentration of points repre- seriting grains lying with the l.d. perpendicular to tne cur- rerit direction. These are in the same relative position as true plots of grains discussed in sample 8 that were thought 'to show particles that had rolled with the current. The m413.a. fabric maxima of the sample also support the presence of‘ these particles with the elonfiation perpendicular to the onscrent flow. This arranrement is also represented in sam- 9143 1 by a few weak marina rouydly at ri hi angles to the StIflonper groupinas of the lone dimension concentrations. Two diaHrams (Figures 12 and 13) were prepared from Sample 14. The chips studied were taken from adjacent areas on_ the same nlane o“ beddin . The traverses fifin across the Secnond sample chip during the orientation Operation were perpendicular in relation to those rfin on the first. The Iwasulting contour patterns, although not identical, resemble 63E10h other favorably. The grouping of the l.d. maxima in tfile southern portion of the dianram would point to this lMaing the reneral up-current direction. The pattern of the Inop.a. maxima for each sample is slightly elongate parallel 1“) this assumed direction, but it also shows comparatively iAsolated carina at right angles to this elongation, again ihdicating; grains lLing perpendicular to the direction of Cniwent flow. 30 Contour interval 2.h.6.8 % m.p.a. fabric Sample h Figure 12. Grain-shape fabrics on the lower hemisphere. 31 l.d. fabric r : 0.u57*% Contouriinterval N 2.14.6,8 % m.p.a. fabric Sample h I-"‘:lgure 13. Grain-shape fabrics on the lower hemisphere. This comparison of diagrams from equal samples s a 'r-" gunssible means of gauging the error or bias in selecting ggwains for study on the roughened sample slide. It is pos- sileathat the contour patterns would tend to become identi- ca].'with the orientation of more grains per sample, although i1: is evident that diagrams of interpretive value can be prepared with the number used. Sample 6 (figure la), in both the configuration of the l.d. and the m.p.a. fabrics indicates a current direc- tion as shown. This vector differs considerally from that Of sample u even though both samples were obtained from ‘Separate but equal vertical positions in the same bed. This variation in careent direction over a stort distance (lould be justified by any feature inthe depositional envi- Zronment which had a modifyinq effect on local current flow. It is also quite probable that there is as wide a variation in) the local pattern of the depositional area here, as was -f0und at Flat Rock Point. This would also cause the sand {firain orientation pattern to vary widely over short distan- ees. Sample 5 (Figure 15) was obtained near the tOp of 'the same bed from which samples A and 6 were taken. The Cherrelation coefficient value indicates a weak although sig- rlificant orientation of the l.d. fabric. Definite maxima <>r both the l.d. and m.p.a. fabric are evident although they <30 not appear to form an interpretive pattern. The Opposite ‘ . . 'highs" at the ends of a NE-SW diagional represents a con- lode fabric 1" = O o 520535 Contour interval 2.14.6.6 5’?» m.p.a. fabric Sample 6 Figure la. Grain-shape fabrics on the lower hemisphere. 3h l.d. fabric I’ 3 00295-3“? Contour interval 2,u,6,8 €35 m.p.a. fabric Sample 5 Figure 15. Grain-shape fabrics on the loaer hemiSphere. ‘| 3 I .1»! ;. "'\ . I" "I 35 Cknitration o" grail long dimensions lying in the plane of tuediding. ihe isolated L fl contour closing in the SE quad- ]?811t shows a wash imbrication toward the SB and when con- sziciered with the diagional concentrations may be indicative (DI' a current direction. The m.p.a. fabric does not, how- exrery appear to support either of the perpendicular concen- tIvations in a manner which is of interpretive value. The densignation of an assumed current direction for the sample liass therefore been omitted. Gxuain-snase, optic-axis comparisons Figure 16 represents the plots of 300 quartz c-axes Olbtained from sample h. One-hundred determations from each 01‘ three mutually perpendicular thin-sections were combined irl the final diagram. One thin-section was taken in the FXLane of the bedding, the second at right angles to the Cklrrent direction (shown by the shape orientation diagram) arid the third parallel to this current direction or in the I3lane of imbrication. A definite lack of preferred orientation is evident 130th visually and statistically. ueak groups of max ma are Givident in the HE and Sb quadrants. These concentrations <30 not Marrant that an interpretation of the current direc- tion be dram-3n independenuwf the train-shape analysis for 'the sample. m, ine weak correlation that exists between the quartz c-axis and the l.d. fabrics is an indication that there is 36 ‘ ‘ ° mihaba ° ' Contour interval Sample 24. 1,2,3 % P I 000098 Figure 16. Quartz Optic-axis fabric on the lower hemisphere. _.,1 37 a peurallel relationship between the physical and Optical dhneamisi one of a major percentage of the quartz sand grains hi tlie sample. Previous studies have revealed that the angnilar relationship between these dimensions is determined mairily by the primary source of the material. Quartz grains in rnany metamorphic rocks tend to be elongate parallel to thca c-axis. This tendency is not as obvious in grains taken finam.igneous rocks. Elongation parallel tothe rhombohedral faxzes has also been note d in both igneous and metamorphic Pcmsks. Ingerson and Ramish (l9h2), discovered that quartz Efi?ain elongation parallel tothe optic-axis is not controled CT If ither cleavage or difler en tial abrasion durinr trans- 'pefficient (So was rscd to compute the values Sfiiown on the Figures. The construction of the cumulative Chirves and the location of the quartile valuesvmne accomp- ldished using the procedures outlined by Krumbein (1938). ihe sorting coefficient is a measure of the average Sipread of the grain size about its mean. It may therefore hO A.SEV nopoEwHQ moo. mNH. 0mm. oom. oo.H oo.m . . . . . . : oauEwm low flow OOH N00. MNH. omNo r p p com. oo.H oo.m b P m oHQEwm mo:.o mm.a 02L. ION so: .00 wow OOH A.ESV hopoEmHQ Nwo. mwa. 0mm. owm. ow.a ph.m moo. mma. 0mm. 0mm. oo.H oo.m . p . . . 0 wow M m. 10.4% H oHQEwm n+ IO 0% em:.o - a \ 0H.H . om .oe as Sorting cumulative curves for samples 1, 2, and u. 3: Figure 18 o bl 788V popoSwHQ Nwo. mwa. OMN. omm. om.a om.m w cagedm MN 0 0 HO II II '00 100 woo. mmH. omm. oom. oo.H oo.m b P p p b h OOH N OHQSam 5mm.) u n om.a u om VON OOH A.EEV hopoEmHQ an. mma. 0mm. 0mm. oo.a oo.N o oHQEwm ION 9M .osz .Oomw .bw OOH m oHQSdm U‘\ 700‘ HQ] 0 0 HO I" N O 0 Fa 3Figure 19. Sorting cumulative curves for samples 5, 6, 7, and 8. L2 .ftlrmish.clues to the nature of the environment in which the :nerterial was deposited. Geologic inferrences relating to (Bigfferent sorting values have been presented in the numer- omis papers and books dealing with the subject of sedimenta- tion. Figure 20 shows the plots of the "r" values versus ‘trie "So" values. It is obvious that a direct relationship dxbes not exist between the pairs of values, which indicates tliat each characteristic is independent of the other. This 1130K of correlation is reasonable considering that the de- zaositing agent varies in velocity over small changes in time Enid place, although the direction of flow may remain cons- tant. #3 111.11.11.11.-- .11. .. oo.a om.a o:.a om.H om.H oa.a 11V . .... T ... Q .1: ._ $1. 4.1..“ ..m. u mx1h-n.h_...1m1n.s., . 11.1 ....1... J- .H. .1. 314.. . _ . : .:;:1 .H. .. 1;... .. ... 1 .r 1 . H 14...; l .«1 J . w . .71 11 1 ..11. 311. t .. .1. .. M .1. .1 .-. (1117))! ~. . .1 . .1 ..vllvl.3.-1| ... H. . .1. .1. 1. .. L. .1.. H. .4. .1 a 1+ .111 ”1. €in .. .1 it.» is .1. I. fill . h 1 .. 1... O1 .1 1 .1 -...14H..-» . .~. .....~.. . . c . ~. ...a~.v..>uivtoivp .....e»..e*. T.( ...t“. to 4 1. < «ll 44 1 l . . . . I . . ~ . . . . . IVIQO t» a O c. . . O uieie to L 1.. .0 7» OYA\ . . . . _ . - . ).Yv ~ 0 n .. 5.11 I. 7.19 v 79.. .8 7o felo . . olv...‘ as v .1 . . p . .1 .. . O. . . u 1~ v. A Io e.+|o vi...» .... .Ate Ifo‘eo ... T...o ‘6‘19 1. . .. . .. .. . - . . . .. ..-... .3- ...: -.1 .1. ......Li. . . - . . >u om. \. .u The correlation coefficient (r) values plotted versusthe sorting (30) values. F1 gure 20 . Sample numbers are shown adjacent to the respective points. :V‘ 1 1 .1 1. e = wt} 5.5. COgCLUSIONS The data presented in the preceding pages reveal the existence of a preferred dimensional grain orientation in the sandstone studied. The interpretations of the contoured .fabudc diagrams representing this orientation indicates hat a current direction can be established for the medium Of‘depcsition; although, due to wide local variation of tilese directions the information would be of little value .in.reyional studies when widely separated sample locations are used. A statistically insignificant Quartz optic—axis or- tientation vas found for the samples studied in thin section. liecause of the limited scope of the investigation little interpretive value was pieced on the results obtained. to obvious relationship was found to exist between the sorting and the degree of dimensional grain orientation, nwasured statistically. LIST or'RcfiszNCES 11321231912218. CURRAY, J. R. (1966) Dimensional grain orientation studies of recent coastal sands: Bull. Am. Assoc. Petrol. Geol., vol. 20, no. 10, pp. 2uhO-21E5. 'DAPPLES, E. 3., and RC"IN GE:C, J. E. (19h5) Orientation an- alysis oi' fine-{lained clastic sediments: Jour. of Geology, vol. 53, pp. Bub -2bl. GRIvMIlfiS, J. C., and liSEVPIELD, L. A. (l‘jSD) Prop ress in rneasurnent of grain orientation in Bradford san1: "he Penn- sylvania State College, Min. Ind. Exp. Sta., Bull. 3o, pp. 2J2-2Bbo GJI"11¥S: 3- C. (1952) A re.iev of dimensional orientation Of quartz grains in sediments: lhe Pennsylvania State 301- leee, Lin. Ind. Exo. Sta., full. Ao, pp, @7156, ( IIIu‘ JCS‘IL, I". 3., and XENIS‘JI, .... L. (19212) Ori tin of shapes of quartz said jrgius: Am. hineralo ist, vol. 27, no. 9, 0/. K1 UL EIR, b. C. (1939) Preferred orientation of pebbles in sedimentary deposits: dour. of Geoloyy, vol. b7, pp. 673- 706. LOZI. ‘IE‘1T, V. S. (194-3 ) Lis sissinnian Marsiall formation of Iiichiran: Bull. Am. Assoc. Petrol. Geol., vol. 32, no. u, pp. 6Z)l" {ICBO PCHLAYD, R. A. (19h6) Grain- -shape fa‘nrics of elastic quarts: Cool. Soc. America, Pulletin, vol. 77, pp. $47-56h. SCHLAY 5A3 "ER, W. (1961) Grain orientation in sands and sand- stones: Jour. Sed. Petrology, vol. 21, pp. 162-172. .S Iii, H. C. (1952) Sedimentary fabrics in unconsolidated s nds: (unpublished Lester's thesis, Dept. of Geology and (}eo raphy, Michigan State College). T“ nooks (JHAYES, F. (l9hé) Statistical analysis of three-dimensional pr \1‘1 pa. '3“) Structural pet- f"III-TV-I‘ic diar“ans: in EAIE*aigi 4 3-: Addison-Wesley T rolomv of deformed rocks, CamVridre, i PLIIliSI'linf CO. 3 Inc. TDIXON, a. J., and LAS.3E”, E. J. Jr. (1951) Introduction to statistical analysis, has York, he Grew-Hill Book Co., Inc. FAIPPAIRK, H. w. (l9h9) Structural petr010{y of deformed rocks, Cambridge, Lass., Addison-Lesley Pu1;1i shinb Co., Inc. JOHNSOE, D. h. (1919) snore processes and shoreline devel- Opment, New York, John ailey and Sons, Inc. 9) Manual of sed- I‘E'"“Nf' u. 3., arvi P'ZTTIJlLfi , F. G. 3 on-Century 30., imentarv petro Paphj; Kev fork, D. A031 1 r.‘ V .L ,' C)" l H 0 w v 7-; ‘1 ‘7‘? '7: '2‘ N ‘ r] :‘ .. ' . C. i. (1944) secuence in layered POCnS, L./.IJ-, 24c Grew-Hill Pook Cc., Inc. 1' . ’ 1 Net lorx, w fP”“1”097 L. H. (1970) Principles of sedimentation, New Efiark, Hc Graw—?111 Book Co., Inc. r0": ( V5“; uni» K9". ” $29.. s ,.‘ Ynhiii Juan—a Mai- Date Due Demco-293