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KROPS CHOT A THESIS Submitted to the School of Graduate Studies of Michigan State College of Agriculture and Applied Science in partial fulfillment of the requirements for the degree of MAS TER OF SCIENCE Department of Geology and Geography 1953 A CKNOW LE DG M EN TS The author wishes to express his most sincere thanks to Dr. B. T. Sandefur. It was his constant encouragement, helpful sugges~ tions, and unfailing interest that aided in the completion of this in- Vestigation. Dr. Sandefur was more than generous with his time in helping compile and edit the final manuscript. The writer greatly appreciates the critical and constructive editing of the manuscript by Dr. S. G. Bergquist. Sincere thanks are also due to Dr. W. A. Kelly for his v‘aluaole suggestions concerning the interpretation of the lithofacies maps. Dr. Justin Zinn and Dr. J. W. Trow were very considerate in offering suggestions regarding the disaggregation of the carbonaceous shale. Messrs. R. M. Acker, Robert M. Ives, and Burton Brown of the Michigan Geological Survey generously assisted the author in obtain- ing the highly selective wells required for this study. TABLE OF ”55 L... CON TEN TS INTRODUCTION ............................... History of Investigation of the Michigan Basin ........ Facies Analysis ..... . . ...................... Mississippian Stratigraphy . ‘. . . . Requirements for Well Selection S ele ction of Wells ........................... LABORATORY PROCEDURE . ..................... Method of S ampling ............... . .......... Removal of Water-Soluble Salts Removal of Acid-Soluble Salts Dis aggregation ........ . ...................... Dispe rs ion ................ . ................ Pipetting.......... ..................... Required Laboratory Equipment . .............. . . . Possibility of Erroneous Data 16 17 18 20 23 24 26 28 28 Results of Laboratory Analysis .................. ILLUSTRATION OF LITHOLOGIC VARIATION .......... Lithologic Ratios ............................ Construction of Facies Maps ........ . ........... INTERPRETATION OF FACIES MAPS . .............. Methods of Interpretation ...................... Errors Involved in Interpretation ................. Interpretations .............................. REGIONAL TECTONICS ......................... Structural Relations of the Michigan Basin .......... Structural Interpretations in Relation to Tectonics ..... Tectonic Aspect ............................. CONCLUSIONS ................................ REFERENCES ................................ LIST OF TABLES AND FIGURES TABLE I. Lithology and Thickness of Mississippian Formations ........ . .............. II. Well Descriptions ................... III. Summary of Quantitative Analysis ....... IV. Lithologic Ratios ................... FIGURE I. Relations between isopachs and facies lines 13 30 31 3 '1' LIST'CH? NLAPS MAP 1. Areal extent of Mississippian and Pennsylvanian deposits within the Michigan basin .............. 2. Locations of wells used for facies analysis ........ 3. Clastic ratios ................... . ...... 4. Sand—shale ratios ........................ 5. Evaporite ratios ...... . .................. 6. Isopach.rnap ........................... 7. Inferred tectonic map during the Mississippian period ................................ Page 10 ll pocket pocket pocket pocket 54 INTRODUCTION History of Investigation of the Michigan Basin Inferring accurately the detailed structure of an unexposed. geologic area has long been the setting for intensive investigation. The Michigan basin, extensively covered by glacial deposits, is such an area. In certain places these deposits attain a maximum thickness of nearly 1,300 feet. Michigan'slower peninsula is so thoroughly covered by this mantle that only occasionally is the bed— rock exposed. These outcrops have shown the bedrock surface to be concentric rings of Paleozoic sediments, which are Pennsylvanian at the center, and regress through Mississippian, Devonian, and Silu— rian, to Ordovician and Cambrian at the outer margin. These layers of sediments would be analogous to a set of six progressively larger watch glasses stacked together; the largest, representing the Cambrian, at the bottom, and the smallest, the Pennsylvanian, at the top. King (1951) stated that: Drilling in the Michigan basin reveals that nearly all formations from Cambrian to Mississippian thicken progressively toward its center, indicating that it was a persistent negative region subjected to long-continued subsidence. The rate of thickening varies from one unit to another, and the center of greatest subsidence shifted position slightly from time to time. The center of the basin conforms approximately with the center of Michigan's lower peninsula. The outcrop pattern is elliptical in outline, with the major axis trending northwest—southeast. According to Pirtle (1932), the structure is bounded by the Wisconsin arch on the west, and by two diverging limbs of the Cin~ cinnati arch, the Kankakee arch to the southwest, and the Findlay arch to the southeast. A. continuation of the Findlay arch, the so- called Algonquin arch in Ontario, forms the eastern boundary, and the complex pre-Cambrian rocks form a barrier to the north. Evidence of minor irregularities within the basinal structure is illustrated in a report by R. A. Smith {1912), in the statement: The formations constituting the Michigan Basin are locally gently folded and, in some cases, slightly faulted. So far as known, the folds occur mainly near the margin of the Southern Peninsula and in Western Ontario. He found northwest—trending folds south and also northwest of Detroit, opposed by possible northeast—trending ridges in the southwestern part of the state. West of Petoskey, near the tip of the peninsula, a folded structure was aligned nearly north—south. This evidence was oL-tained by reconnaissance mapping, and information from the few wells drilled up to that time. Pirtle (1932) stated that the major intrabasinal structures oc- curred in the southeastern part of the state, and were rather sharp, elongated ridges striking to the northwest; also, that minor folds in the southwestern part of the state trended to the northeast. lie felt that these minor uplifts may possibly have been domes on the major ridges. Indication was also given of circular regional highs in the northern part of the state. Pirtle obtained his information from structural contours drawn on the top of the Trenton limestone of Middle Ordovician. Information for the structural contour map was enhanced by the increase in well drilling throughout the state. Ne'wcombe (1933) published the first thorough report on the sediments and structures of the basin. Both structural contour and isopach maps were used to aid in depicting the basin's internal struc- ture. According to Newcombe: The northwest—southeast folding seems to be the most pronounced and widespread in the eastern, southeastern, and cen— tral portions of the southern peninsula. The north-south flexures are present locally in the southern part of the State, but they seem to be more prominent in the north central part. He also'stated that: Northeast-southwest folds occur in the southwestern part of the State, and apparently these constitute broad, gentle flexures compared with sharper ones in central Michigan. Facies Analysis In addition to the structural contour and isopach methods of interpreting structure, Sloss, Krumbein, and Dapples (1949) have used the stratigraphic and sedimentary analysis approach. Their conclu- sions stem from a map portrayal of lateral variations of rock char- acter within a certain stratigraphic interval. These variations, called facies, were defined by Moore (1949) as ”areally segregated parts of differing nature belonging to any genetically related body of sedimen- tary deposits.H -Moore (1949) continued, then, that lithofacies would be ”groups of strata demonstrably different in lithologic aspect from laterally equivalent rocks.H Biofacies are laterally equivalent biotic assemblages differing in their biologic aspect. A third variation, tectofacies, was proposed by 51055, Krum— bein, and Dapples (1949): “A tectofacies is a group of strata of dif~ ferent tectonic aspect from laterally equivalent strata.” A tectofacies analysis would be useful in determining the gen- eral tectonic environment in a large geologic structure, while the lithofacies, and biofacies analysis would give minor variations in sedimentary environment within the structure. Krumbein and 51055 (1951) stated that, l'In the average case, lithofacies and biofacies maps of the same interval express similar trends and limits.” Purpose It is the purpose of this study to attempt to define the struc— tures within the Michigan basin by lithofacies analysis. The writer feels that by quantitatively analyzing a well-defined rock system, a broad, but accurate, portrayal of the tectonic environ- ment during that period of deposition may be determined. The Mississippian system was chosen for this study, as the complete section has been penetrated by several thousand wells. It is hoped that the lithofacies maps resulting from this analysis may add evidence to already determined structures, and possibly indicate features which have not been found through earlier research. SAMPLE SELECTION AND DISTRIBUTION Mis s is s ippian S tratig raphy The Mississippian system consists of ten formations, the lith— ology and thickness of which are shown in Table I. Some controversy has arisen as to the boundaries at the base and top of the system. To assure sampling of the same interval throughout the state, spe- cific, and distinct boundaries had to be selected. The top of the Bayport limestone was chosen for the upper limit, as this differs markedly from the unconformably overlying Parma sandstone of Pennsylvanian age. In certain areas, where the Parma is missing, the Saginaw formation tops the Bayport. Generally the Saginaw consists of a gray, shaly sandstone that is easily distin- guished from the Bayport. The base of the black Antrim shale was selected for the lower limit. This usually contrasted sharply with the underlying gray Trav— erse limestone of Devonian age. It was stated by Baltrusaitis et a1. (1948) that: The Devonian-Mississippian boundary has been placed at different positions in the Antrim-Ellsworth sequence by various workers but generally the upper part of the Antrim is considered Mississippian in age. TABLE I LITHOLOGY AND THICKNESS OF MISSISSIPPIAN FORMATIONS We 5 te rn Michigan Easte rn Michigan F0 rtnation Avg. Avg. Lithology Thick— Lithology Thick- ness ness Bayport Buff, dense lime- 100' Buff, dense dolo- 75' stone and dolomite, mite, some chert some chert and and shale. sand. Michigan Brown and gray 70' Gray shale and 60' dolomite, some sand, some dolo- sand and gypsum. mite, lime, and gypsum. Upper Gray, medium to 190' Gray, medium to 140' Marshall coarse grained coarse grained sandstone, dolo- sandstone, in rnitic in part. part dolomitic. Lower Red to gray, fine 120' Red to gray, fine 70' Marshall grained sandstone, grained sandstone, dolomitic in part. in part dolomitic. Coldwate-r Gray, flaky, Inica- 900' Light gray flaky 1000' ceous shale, dolo- shale, micaceous mite lenses near and dolomitic in base. ' part. Sunbury Black, hard shale, 15' Black, hard shale, 25' some limestone. minor glauconite. Ellsworth Dark, greenish 330' 0 shale, dolomitic and pyritiferous in part. TABLE I (Continue (1) we 5 te rn Mic hig an Eas te rn Michigan Formation Avg. Avg. Lithology Thick— Lithology Thick- ness ness Berea '0 Light gray, mica— 150' ceous sandstone, some shale. Bedford 0 Gray shale, some 40' dolomite. Antrim Black to brown, 220' Black to brown, 350' carbonaceous , and pyritiferous , hard shale. carbonaceous , and pyritiferous, hard shale. Requirements for Well Selection The cable-tool and rotary—tool methods of drilling were com- pared by Krumbein and $1055 (1951). They stated that, "cable-tool samples are relatively pure with a minor amount of material knocked off uncased portions of the bore by the passage of tools and bailer.” To contrast this they found that, "rotary samples taken for a given drilled interval contain not only cuttings from the strata represented but also fragments from any horizon drilled below the lowest casing point." Therefore, the first requirement for this study was to use samples taken from cable-tool wells. A second requirement was that the wells be sampled at rela- tively short intervals, say 5 or 10 feet, and that this sampling be continued throughout the complete Mississippian section. The avail— ability of these samples also had to be taken into consideration. The third factor was that the wells be properly spaced to give sufficient control for accurate results. Near the outer margin of the lower peninsula, the upper Mis- sissippian formations have been removed by erosion. This erosion .has occurred, to a certain extent, on the entire surface of the system; but the area presently covered by the Pennsylvanian sediments has been truncated to a definitely minor extent. Wells for analysis were selected within this area, as they alone would give the true picture of sedimentation during Mississippian time. Map 1 shows the areal extent of Mississippian and Pennsylvanian deposits within the Michigan basin. Selection of Wells Map 2 shows the locations of the wells used for this analy— sis. MICHIGAN W 1 Anal um; 01’ I1:- “cuppa.“ and Pon- uylvunu «poem within the “Chi“ min. 5cm: 29g 9 . 20 40 mus 20 o 20 40 trif- (o-plld I Dtm by Mm I). Mold. Ikl. ST“ (011..., Dart. of Tool. l Bug. is 01 h-____ I'— 1 -..__-___1_ _ ....... i ........ - 1% i ' 0 1 -o 1 1 ‘_ ,_._.1. 1 .——--- .._——-' ,- 74“. 43‘ - 42. O" .I‘ filth. sun (all... "on I7’ If (numb! 1951 I-I MICHIGAN L .... HP 2 __ __ __ - _. ~ , 1 Location. of wells 0 7 ’ "34 1—11 o 1 and for taciu only-1- 1 . o1 —---1__1 ' ,1 ______________ r :1 1----—-—-' , “-1- - 0 . 1 ' . 1 1 1 43° . g. _.___1..-——--~--:——' ____.-1 1 _ _1-_-.1 1 1 , T 1 1 a ‘ 0? s 5 . .9)“ 1k . 1. 1 ‘ 8' ___'1 ‘1 1 ___..- ...}...T- ------ "I _ '/’ ' 1 SCALE I L. ........ 1’“. ‘1 ~2'1—‘ 20 9 . 29 4‘0 1’ , I k - 4— loz- Mlfis— 1 1 ' 20 o 20 40 1 z, 1 __,1‘-___ <0 ‘M. ...... J..——---—1"" I} \______u (0-le I [Inn by Mac a. hull: ’0 lkh. St'm (oIIogc, Dori. of Tel. 8 Bug. - IO. 0" '7' 0" 06° '5' ‘3' list. Sm. (alloy. Pm: (ontlgh I951 I-I 12 With the exception of Lake County, all wells selected for this study were drilled with cable tools. For each well, a complete set of samples was obtained from the Michigan Geological Survey. To get an accurate picture, one well was selected from nearly every county within the area of Pennsylvanian cover. Table II lists the wells plotted on Map 2. Included in this table are the permit number, operator, and location for each well. Also included is the distance from the top of the Bayport to the bot- tom of the Antrim, which gives the total thickness of the Mississip— pian s e ction. TABLE II 13 WELL DES CRIP TIONS Depth Well Permit, Operator, Farm Land £2.05; Topt No County, and Township Description 0 ypor to Base of Antrim 1 4808, C. P. Hutton, Straszewski 24—Tl9N—R3E OF; 1766' #1, Arenac Co. Adams Twp. 2 7086, L. c. MacGregor, Euclid l7-—Tl4N-R5# SC; 1885.. 2.4: , .1.) Club #1, Bay Co. Bangor Twp. 3 10724, Freeman Oil, Gleason 35-T17N-R4+ 6/\/ 2150' 3'11?" 1 #1, Clare Co. Grant Twp. 4 3728, Prima on, Fitzpatrick 10-T8N—R4wo/‘x’ 1885' «,1. #1, Clinton Co. Lebanon Twp. 5 27,67, Burris and Keeler, Moon ll—T2N—R4W 17,4; 1800' 1. “- #1, Eaton Co. Eaton Twp. 6 9669, A. L. Williams, Totten ll-T9N-R7E 1901' 5'" #1, Genesee Co. Thetford Twp. 7 7625, Sun 011, State-Gladwin l—Tl9N-R1W 19871 9 «r #A-l, Gladwin Co. Gladwin Twp. 8 3589, Carter on, McConkey 23—T11N-R2W .2004l 1- '“ ‘. #1, Gratiot Co. Emerson Twp. 9 10011, W. H. Colvin, Glaser #1 l4-T3N-R1E 18731 ’ Ingham Co. Wheatfield Twp. 10 3154, Terry-Dale-Mich., Tow lZ-T6N-R7W 1917l #1, Ionia Co. Berlin Twp. 14 TABLE II (Continued) Depth Well Permit, Operator, Farm, Land {:0}? Fopt No. County, and Township Description 0 aypor to Base of Antrim 3757 11 8751, Leonard and Rowrner, 20—T13N—R3W 21971 Whitney #1, Isabella Co. Coe Twp. . -- 1" 12 7453, Amer. Drill., Linkfield 8—T7N-R10W 1826' 0' 3 1 #1, Kent Co. Ada Twp. . ‘V 13 12885, Glavin Oil, Estates #1, 2-T18N-R11W 2140' 4 7 S Lake Co. Pinora Twp. 14 10038, J. T. Norris, Stowe #1 9-TZN-R3E 1594I 82f Livingston Co. Iosco Twp. 15 2811, Goll €2.15 31., Ruetz #1 l7-Tl4N-R7W 2282' 37"" Mecosta Co. Wheatland Twp. 16 6156, C. w. Teater, Dougherty lS—‘I‘l3N—R1E 2195' /7%’ #1, Midland Co. Mt. Haley Twp. 17 8467, w. Heintz, McCoy #1, 2-T21N-R6W 2300' 2 /1 Missaukee Co. Clam Union ’1 Twp. 18 2876, Sidney—Montcalm, Madison 33—T10N—R7W 1939' L1 #1, Montcalm Co. Sidney Twp. 19 4820, Gulf, Walker #1, New- 25-T13N-R13W 1922l [/3311 aygo Co. Sherman Twp. 20 6361, Sun on, Richardson #1 23-T18N-R9W 2138' ;,. Osceola Co. Cedar Twp. M TABLE II (Continued) 15 ‘— Depth Well Permit, Operator, Farm, Land firolrgn Topt No County, and Township Description 0 aypor to Base of Antrim 21 8212, E. Hilliard, State #1 19-T21N-R3W 23051 26(1'3 Roscommon Co., Rosco. Twp. 1 22 4511, Weber on, Uebler #1 9-TllN-R6E 1954' 11:31,, Saginaw Co. Frankenmuth Twp. ' 23 2098, J. F. Hurley, Van Pelt 35-T8N-R2E 1832' [7 #1, Shiawassee Co. Rush Twp. 24 2315, w. F. Wiechers, Gray 8—TlZN—R8E 20181 ,5}? #1, Tuscola Co. Juniata Twp. 25 8906, c. w. Teater, McNitt 2105' #1, Wexford Co. Harding Twp. 22.. TZZN-R9W LABORATORY PROCEDURE Method of Sampling Samples for each well, obtained from the Michigan Geological Survey, consisted of eight to ten trays, each containing about twenty- five vials. Each vial contained the sample taken for the interval drilled, usually 5 to 10 feet. Wentworth (1926) stated that to analyze mechanically, material of sand size or less, about 125 grams are necessary. Selecting a l-gram sample for every 20 feet, in a well averaging 2,000 feet, would result in a composite sample of 100 grams. This, of course, would vary with the thickness of the section, but would still approach the figure set by Wentworth. Each vial usually contains 8 to 10 grams of sample. There— fore, withdrawing one-quarter to one-half a gram per vial would not detract from the sample's value. A clean 400—milliliter beaker was weighed and labeled for each well. Each vial was sampled, according to the interval it rep- resented, and weighed to 0.005 gram. These small samples were poured into their proper beakers, until a composite sample representing 17 the entire well was obtained. The accuracy of sampling was checked 7 by weighing the filled beaker and subtracting the weight of the beaker. This amount should then be equal to the number of feet sampled, mul— tiplied by the amount of sample taken per foot (0.05 gram). In all cases the error was found to be less than 1% grams, and in most cases it was less than 1 gram. It is felt that this error was of insignificant magnitude to cause any serious misinterpretation of the results. Removal of Water-Soluble Salts Before attempting any method of dispersion or disaggregation Prior to mechanical analysis, the sample must be free of foreign electrolytes. When the sample is immersed in water, the electrolytes tend to lower the potential of the particles, resulting in coagulation. Weigner (1927) found that by boiling a water-immersed sample con- taining these electrolytes, the ionic particles went into solution, and could be removed by siphoning or filtering. For this analysis each well was treated with about 200 milli— liters of tap water, and boiled for an hour. Ten milliliters of clear solution was then withdrawn, and the salinity checked by adding a 18 small crystal of silver nitrate. If the precipitate formed was more dense than that observed with tap water, another treatment was nec- essary. Prior to additional treatment, the beaker was allowed to stand until all material had settled. The salt solution was then siphoned off, and more clear water was added. In most cases, three treatments served to remove the water- soluble salts. The remaining sample was then filtered and washed several times with warm water. An oven was used to dry the sam— ples before they were returned to their original beaker. The amount of water-soluble salt removed was found by subtracting the weight of the treated sample and beaker from that of the original sample and beaker. Account had to be taken for the fine material left on the filter paper. This was usually about 0.07 gram, and was determined by weighing the paper before and after use. This fine residue was added to the clay fraction obtained by pipetting. Removal of Acid—Soluble Salts Limestone, dolomite, and minor amounts of gypsum were now the only remaining nonclastic materials. Each sample was treated several times with hydrochloric acid. For the first treatment, a 25 per cent solution was added 19 slowly to the sample. Care was taken that no fine material was lost in the resulting effervescence. After the addition of acid, the sample was intermittently stirred until all reaction ceased. Several hours of settling were required before the supernatant liquid was siphoned. Similarly, a second treatment of 50 per cent and a third treatment of 100 per cent acid were employed. After the efferves- cence of the third treatment had ceased, the beaker was placed in a warm sand bath and heated for thirty to sixty minutes. This heating removed the less soluble dolomite, and possibly small amounts of gypsum and anhydrite. The warm liquid was kept below the boiling point, as boiling would possibly give rise to such undesirable effects as overflow or cementation. After cooling and settling, the excess acid was siphoned off; the remaining sample was then filtered, and washed several times. This washing was continued until the filtrate affected no change on blue litmus paper. The residue was then dried in a warm oven and returned to its original beaker. The difference in weight from that of the previous test was then the acid-soluble material. Again the change in weight of the filter paper was added to that of the clay. Although some gypsum and anhydrite probably remained after these treatments, they represent only a small fraction of the complete Mis sis sippian system . 20 Dis aggregation The most difficult and time-consuming problem in this study consisted of the disaggregation of the Antrim shale. As previously mentioned, this shale is cemented with bituminous material, which forms an extremely hard mass. Krumbein and Pettijolm (1938) defined disaggreagation as "the breaking-down of aggregates into smaller clusters or into individual grains." Concerning fine-grained sediments, these authors stated that: Because of the difficulty of determining in all cases the effect of various agents on the extremely small particles, it has been considered safest to avoid the more rigorous methods used with coarse sediments and in general to avoid the use of harsh chemicals. In addition to the actual chemical changes which may accompany drastic treatment, there is the factor that the clay minerals may be so thoroughly coagulated that they cannot be dispersed without considerable effort. Some of the disaggregating techniques attempted in this study are as follows: 1. A sample of Antrim shale was allowed to soak in a 0.01 N. sodium oxalate solution for one to two weeks, during which time it was stirred at least twice daily (Krumbein, 1933). After the first week, the beaker was heated daily for one-half hour. This caused no apparent change in the Antrim mass. 21 2. Use of the "Malted milk mixer" method of disaggregation U1 formulated by Bouyoucos (1936), for use on soils, again failed. Thi apparatus consists of the common metal "milk-shake" cannister, con«- taining three long wire baffles, and an electric motor, which rotates a propeller-shaped paddle. The material from the treatment above was poured in the cannister and agitated for thirty minutes. Only breakage, and not disaggregation resulted. 3. A recent method of disaggregation that has resulted in some success was that of immersing the shale in gasoline for sev— eral days, and then pouring off that liquid and adding water. Ideally, the water should enter the -small interstices formed by the gasoline, and soften the rock. This method was also unsuccessful. 4. Krumbein and Pettijohn (1938) suggested the use of an organic solvent such as ether, acetone, benzol, or gasoline. These, again, had no effect on the shale. 5. It was felt that in order to remove the carbonaceous ma- terial, some oxidizing agent was needed. Hydrogen peroxide failed in this process, but a solution of 10 milliliters of nitric acid, 1 niil- liliter of sulfuric acid, and l milliliter of perchloric acid, added to 1 gram of the shale, attained a reasonable amount of success. After adding the concentrated acids in the above-mentioned order, the 22 mixture was heated until the nitric acid was driven off as nitrogen dioxide, and the perchloric acid emitted as a white vapor. This left a clean gray residue, within the clear sulfuric acid. The acid was removed by filtering, and the residue was washed and dried. Al- though the material was completely disaggregated, it can be seen that this process is contrary to the ideas of Krumbein and Pettijohn (1938) concerning the use of harsh chemicals. As no other method succeeded, it was decided that the acid method must be used. To prevent the precipitation of calcium sul- phate, it is essential that the acid mixture be kept in the same pro- portion. A treatment using three times the original prescribed amount of each acid was used on each of the well samples. This succeeded in only partially disaggregating each of the samples. The method was stopped at this point, for it was felt that further treatment would tend to seriously harm the clay minerals. Nearly all of the particles of shale remaining were large, and the removal of these was accom— plished, as will be later described in this chapter. Another reason for discontinuing this process was the large amount of time consumed. In order to find what per cent of the Antrim shale was silt and what per cent was clay, the acid test was run on a 40—gram 23 sample of that shale. By pipette analysis (explained later), it was determined that about 15 per cent of the Antrim was clay, while the remaining 85 per cent was silt. This is only a rough approximation and would probably vary over the state. Several disaggregating agents containing Antrim shale were set aside when the data for this paper were completed. Time pro— hibited their use for this problem, but one of the methods, that of soaking the shale for five weeks in concentrated hydrochloric acid, appears to be quite successful. The resulting shale was fairly soft and plastic to the touch, and with the proper dispersive chemicals could probably be completely disaggregated. Dispersion Prior to sieving and pipetting, the fine clay particles must be dispersed. In their normal state, these electrically charged flakes tend to coagulate and form small aggregates. In order to remove this electrical charge, a peptizer must be added. This raises the potential of the particles, which hinders coagulation. Krumbein. and Pettijohn (1938) found that a 0.01 N. sodium oxalate solution was most effective for this purpose. This solution was prepared by adding 0.67 gram of sodium oxalate to 1 liter of water. 24 S ieving Before attempting to remove the sand-size particles, 300 mil- liliters of sodium oxalate solution was added to the residue. This was then washed through a 230—mesh Tyler sieve, which is designed to separate sand-size grains from particles of smaller diameter. This sieve conforms to Wentworth's (1922) division for distinguishing between sand and silt. The residue passing through the sieve was caught in a flat-bottomed pan. Washing the sieve was continued until all silt and clay particles were removed. This washing was also done with the sodium oxalate solution, in order to minimize coagulation. It is essential to keep the amount of liquid used in this process below 1,000 milliliters. This muddy suspension in the pan was then poured into a 1,000-milliliter graduated cylinder, and saved for later pipette analysis. The residue remaining on the sieve consisted of sand and shale lumps. To free the sand from these lumps, two treatments were re- quired. First, the residue was dried and poured on the ZO-mesh Tyler sieve. It was felt that using this sieve should allow passage of all particles of sand size. Actually, according to Wentworth's (1922) classification, this is not the division between sand and gravel, but 25 microscopic examination showed no sand particles left on the screen. The sieve, covered at the top and bottom, was placed in the "Ro—Tap" shaker for seven minutes. All the materials remaining on the screen after this agitation were lumps of Antrim shale; therefore, this amount was added to the shale component. A large funnel, with a short piece of rubber tubing attached to the end and closed with a wire Clamp, was then filled with a mix- ture of bromoform and alcohol. This mixture was at a density be— tween the specific gravity of the quartz sand and the shale. That mixture was prepared by adding a large chunk of Antrim shale and a piece of quartz to bromoform and diluting with alcohol until the heavier quartz sank. The sand and shale passed through the 20—mesh sieve was poured into this funnel, and time was allowed for the sand to settle to the bottom. The clamp was then released, and quickly replaced, allowing the sand and some liquid to flow into another funnel contain- ing a filter paper. The sand was washed, allowed to dry, and then weighed. This weight represented the sand fraction present for that particular well. The material remaining in the bromoform was poured on another filter paper, dried, and weighed. Its weight was recorded with that of the shale fraction. 26 From both of the above cases, the amount of shale aggregates usually totaled about 10 grams per well. This weight was then sub- divided into 15 per cent clay and 85 per cent silt, and was recorded as such. It is again stated that this is only an approximation of the clay and silt percentage in the Antrim shale. Pipetting The pipette method of separating fine elastic particles was devised by Robinson (1922). Theoretically, the method is based on the determination of the density of a suspension of particles after a certain time and at a particular depth. These particles, along with some_dispersing agent, were placed in a 1,000 cubic centimeter grad- uated cylinder filled with water. After two hours and three minutes, Krumbein and Pettijohn (1938) found that the particles settling accord- ing to Stoke's Law, to a depth of 10 centimeters, will consist of only ClaY-Size material. The limiting diameter between Particles of clay and silt size, according to Wentworth (1922), is 1/256 millimeter; clay is the smaller. F03: this study, the fine material in suspension after the siev— ing PrOCess was poured into a 1,000 cubic centimeter graduated cyl- inder. If the liquid did not reach the 1,000 cubic centimeter mark, 27 enough of the 0.01 sodium oxalate solution was added to attain that volume. The material was mixed by lowering a rubber hose, connected to an air outlet, to the bottom of the cylinder. Air was then injected until the material was dispersed throughout the liquid. This process usually took five minutes. Caution had to be taken to prevent the bubbling air from splattering. Two hours and three minutes after the rubber tube was withdrawn, a 20 cubic centimeter pipette was inserted to a depth of 10 centimeters, and exactly 20 cubic centi— meters of the suspension was withdrawn. This was oven-dried in a 50-milliliter beaker of predetermined weight. The weight of the fine material represented one—fiftieth of the clay in the cylinder. As 0.67 gram of sodium oxalate was present in the graduate, one—fiftieth of that, or 0.013 gram, was subtracted from the weight of the residue dried in the small beaker. The remaining weight was then multiplied by 50 to obtain the amount of clay present. The total amount of clay in the entire well was found by adding the residue from the two filtrations, and the approximated amount from the undisaggregated shale to that of the pipette analysis. The silt fraction was determined by subtracting the nonclastics, sand and clay, from the weight of the original sample. This figure 28 should be correct within about 2 per cent, as insignificant amounts of pyrite and gypsum remained. These materials represented only a very small percentage of the total sample. Re quired Labo rato ry Equipment For a quantitative analysis of a well sample by this method, the following laboratory equipment is necessary: 400~ml. beaker. 50-rnl. .beaker 230-mesh Tyler sieve 20-mesh Tyler sieve chemical balance and weights 1,000—cc. graduated cylinder 20-cc. pipette 4-foot length of rubber tubing electric hot plate and sand bath electric oven glass stirring rod flat-bottomed pan a "Ro-Tap" sieve agitator 15-cm. diameter fine filter paper HHHHHHHHHHHH Possibility of Erroneous Data It can be seen that, in the withdrawal and subsequent drying of samples taken from a well, a considerable amount of fine material may be lost. In the laboratory, more of these fine particles may be carried away as dust or removed in the siphoning process. This may account for the relatively small percentage of clay present in 29 each. well. It is felt that the possible error resulting from this loss may have been balanced by the similar treatment of each composite sample. The pyrite present in the Antrim shale constituted a very minor percentage. The larger crystals were removed during the sampling, and probably many of the smaller ones were dissolved with the addition of nitric acid. Carbonaceous cement removed by the perchloric acid treatment was also considered negligible. It is noted that, in the final analysis, all of the unclassified material would fall into the silt category. This may tend to reduce the error, for the silt is a constituent of shale, and the shale probably contained most of the unclassified material present in this study. Results of Laboratory Analysis Table III represents the statistical summary of the quantitative analysis of the twenty-five wells. The lithologic ratios represented in Table IV were computed from these data according to the relation- ships presented in the following chapter. \ 30 TABLE III SUMMARY OF QUANTITATIVE ANALYSIS A. e11 s ample “:16 r Sid Sand Silt Clay 10. Weight 0 Fraction Fraction Fraction ubles ubles 1‘ A 9,. 21".: ‘1." mo 1‘51 ”fl. 1 88.18g. .80g. 18.81g. 9.333. 40.75g. 18.49g. 2 93.87 1.11 19.21 “ 15.48 » 43.344 14.73 I47? 3 107.82 1.31 32.28 14.29 40.69 19.25 4 92.97 .51 21.59 9.58 45.82 15.41 5 88.74 .49 18.68 12.00 38.17%"; 19.42 6 94.05 .39 15.35%" 21.77 43.14 13.40 7 99.23 1.22 25.81 7.53 e 42.26 22.41 8 101.53 .78 24.75 a 16.58 40.41 -- '- 19.01 9 92.03 .66 16.61 14.62 44.27 15.87 10 95.32 1.26 22.92 11.01 369.32 23.81 11 109.11 1.28 32.37 10.09 47.82 17.55 12 91.83 .83 23.35 16.33 31.29 20.03 13 107.04 .80 31.06 13.68 47.74 13.76 14 77.32 .28 14.431 " '- 10.62 40.54 11.45 15 113.36 1.64 29.26 15.45 41.74 25.27 16 109.48 1.06 28.56 17.32 48.20 14.44 17 114.17 1.47 37.49 9.80 36.65 28.76 18 95.29 .99 24.30 8.71 41.00 20.29 19 95.63 1.52 26.71 10.19 35.60 21.61 20 105.70 1.43 32.40 10.72 52.77 8.22 21 111.73 2.14 37.50 7.73 34.37 29.99 22 95.47 .99 18.21 20.60 42.15 13.52 23 89.15 .85 14.53 23.81 37.05 12.91 24 99.53 .52 17.50 15.40 49.16 16.95 25 103.68 1.43 37.98 12.59 39.75 11.93 .rf TABLE IV LI TI IOLOG IC RATIOS Well Clas tic Sand-Shale Evapo rite No . R atio R atio R atio l 3.49 0.157 0.043 2 3.62 .266 .057 3 2.21 .238 .056 4 3.19 .157 .026 5 3.63 .209 .026 6 4.97 .385 .026 7 2.67 .116 .047 8 2.98 .279 .032 9 4.33 .243 .040 10 2.94 .183 .055 11 2.24 .154 .040 12 2.80 .318 .035 13 2.36 .222 .026 14 4.25 .204 .019 15 2.67 .230 .056 16 2.70 .276 .037 17 1.93 .150 .039 18 2.76 .142 .041 19 2.38 .178 .057 20 2.12 .176 .044 21 1.81 .120 .057 22 3.97 .369 .055 23 4.80 .476 .058 24 4.52 .233 .030 25 1.63 0.243 0.038 ILLUSTRATION OF LITIIOLOGIC VARIATION Lithologic Ratios Although the concept of facies maps has been recognized for as long as fifty years, the recent availability of many subsurface data has increased their usage manyfold. Krumbein and Sloss (1951) stated that the expression of nu- merical data, such as those obtained from this study, may be achieved by: A quantitative approach in which each lithologic component is given a value according to the thickness of stratigraphic sec— tion in which it is represented. Then, the relationship between any two lithotopes in a stratigraphic interval at a given point may be expressed as a ratio. The most fundamental lithologic ratio is the elastic ratio, which is represented by this formula: Conglomerate + Sandstone + Shale Limestone + Dolomite + Evaporite Clastic Ratio = A lithologic unit consisting entirely of sandstone would be represented by a Clastic ratio of infinity, whereas that of an entire unit of lime- stone would be zero. A second method of illustrating variations of rock character is the sand-shale ratio, which is expressed as follows: 33 Conglome rate + S ands tone d-h1 Reti = san sac d O Silt+ Clay A third ratio, frequently used to illustrate variation within the nonclastics, is the evaporite ratio: Evapo rites Limes tone + Dolomite Evaporite Ratio == Although gypsum would ordinarily be classified as an evaporite, it was not considered as such in this lithologic ratio. Gypsum, because of its low degree of solubility in water, could not be removed by the treatments used in this study. The exclusion of that material from this category should have little effect, for only a small amount is present in the Mississippian ‘system. As was stated earlier, Newcombe (1933) felt that most of the salt deposited in the Mississippian system of Michigan was removed by subsequent solution. If this is the case, a map illustrating the evaporite ratio probably would not conform with the other lithologic ratio maps. If the map does conform with the others, it may indi-- cate that certain saline members have been preserved at their depo— sitional site. The three lithologic ratios, determined for each of the twenty- five well examined in this study, are shown in Table IV. These 34 ratios were found by substituting the proper numerical data, listed in Table III, into the three lithologic ratio formulas. Construction of Facies Maps In order to construct a facies map representing variations within a certain lithologic ratio, the ratios were first plotted at their respective positions on a base map. Contour lines of equal ratio value were then constructed. As the facies ratio variation is geo- metric, the contour interval is usually plotted geometrically, but Krumbein (1952) stated that, "this practice is not an essential part of the method." The ratios computed in this study showed little variation; therefore, they were contoured with an arithmetic rather than a geometric interval. Krumbein (1948) suggested that on each lithofacies map, there be superposed an isopach map of the time stratigraphic interval. As this would present a rather congested map, each ratio map was drawn on semitransparent tracing paper, while the isopach map was con- structed on opaque paper. To aid in interpreting the data, one or more of the lithologic ratio maps may be placed over the isopach during examination. 35 Maps 3, 4, and 5 are Clastic ratio, sand-shale ratio, and evap- orite ratio maps, respectively. Map 6 is the isopach map constructed from the twenty—five wells examined in this study. Thirty—five addi- tional well logs, selected from different counties within the state, were used to give additional control. IN'I‘ERPRETA'I‘ION OF FACIES MAPS Methods of Interpretation In a brief observation of a lithofacies map, an experienced observer could usually arrive at a general conclusion concerning the active sedimentary processes and environment in that area during deposition. A region of high sand content is indicative of shallow or near—shore deposition, and progressive changes in the primary lithologic aspect to shale, and then limestone, would usually indicate a deposition toward areas of deeper water. It can be seen that many variations of interpretation could result from such. a general criterion of classification. It was felt, therefore, that a more specific means of inferring environmental conditions during deposition was necessary. Krumbein (1952) recently prepared a classification in which six distinct patterns formed by isopach and lithofacies ratio lines may be used in interpreting specific sedimentary conditions. These relations are illustrated in Figure I. Concerning this classification, Krumbein stated: The linear subparallel pattern may occur under conditions where elastic sediments are spread over a subsiding area in de— creasing amount away from the source, so that the elastic ratio 37 Figure 1. menu; batman nowh- (solid) and ruin 1130.. (After Win, 1958) M M \ \ \ W V\ \ ulna uni: mm mm 38 lines tend to decrease as the isopachs increase because of in- creasing lime deposition. The curvilinear discordant pattern may arise when a local concentration of clastics is poured into a sub‘siding area, as in a delta. Here the clastic ratio lines may project farther into the basin than normally. The concen— tric ovate pattern is characteristic of evaporites in an intra— cratonic basin. The irregular spotty pattern occurs near the deteriorating edges of sheet sands, where the accumulation be- comes patchy or spotty. From the interpretation of patterns formed by contours of isopach and lithofacies maps the tectonic condition controlling deposi— tion may be inferred. Within an intracratonic basin, such as the Michigan basin, Krumbein (1952) found that three patterns predom— inate. A curvilinear-discordant pattern would likely be the result of a nearby orogenic souce. The concentric-ovate pattern could stem from either a nearby orogenic source, a nearby epeirogenic source, or a distant source. The discordant-ovate pattern is indicative of either a nearby epeirogenic source or a distant source. It is evident, then, that by studying the patterns formed by the isopach and lithofacies ratio lines, a general idea of the distance from the uplifted source to the site of deposition may be determined. 39 Errors Involved in Interpretation In taking a large stratigraphic unit, such as the Mississippian system, the possibility of overlooking minor irregularities is much greater than if a shorter timerrock unit was selected. Smaller ir- regularities may tend to balance each other and be completely hidden, but the broad persistent intrabasinal features should be magnified by a composite study. Postdepositional erosion may considerably alter the isopach and lithofacies maps. This would seriously hinder the interpretation of data concerning-that ration. On each of the maps drawn for this study a somewhat ovate line was drawn to show the areal extent of the Pennsylvanian sediments. Within this area, erosional forces acting upon the Mississippian formations were minor in comparison to those acting on the formations not presently covered by the Penn- sylvanian sediments. To make accurate inferences of the original sedimentary environment, only the contours falling within this Penn— sylvanian boundary were studied. Interpretations Each of the three lithofacies maps was interpreted separately, by superposing them on the isopach map. Structures were located 40 0, with reference to counties; therefore, it would be haflpful to keep the isopach map, which includes county names, in sight during this dis- cussion. The elastic ratio map. In the southeastern part of the state a rather sharp nose, high in clastics, trends to the northwest through Livingston, Genesee, Shiawassee, and Clinton Counties. The facies lines, at the most protuberant part of this nose, roughly parallel the isopach lines, but to the south in Jackson, Eaton, and Ingham Coun- ties they form a curvilinear-discordant pattern with the isopachs. With the exception of the discordance on the south side of the nose, the isopachs and facies lines form a concentric-ovate pattern around the tip and along the north side of the structure to Tuscola County. By applying Krubein's (1952) theory of the tectonic factors controlling deposition in an intracratonic basin, we find that a curi- linear-discordant pattern is usually the product of sedimentation from a nearby orogenic source. The concentric-ovate pattern is not only. indicative of a nearby orogenic or epeirogenic source, but possibly that the source was rather distant. The concentric—ovate pattern is usually found along the margins of a basin. In northern Bay and southern Arenac Counties, the facies lines again swing toward the center of the basin. This implies a broad 41 flat fold, which, near its western limit in Gladwin and Clare Counties, again nearly parallels the isopach contours. The structure has a distinct east-west trend, and near the eastern end a definite curvi- linear discordance with the isopachs is observed. This would indi-- cate that the source area was relatively near the eastern extension of the fold, although probably not as near as was the area which sup- plied the sediments for the structure in Genesee and Livingston Counties. Along the northern and western margins of the map, the iso— pachs and facies lines conform to the concentric-ovate pattern, indi— cating that the source area was quite distant. The Clastic ratio has decreased measurably, and a closure in the isopach contours indi— cates that the center of maximum deposition during Mississippian time was in northern Clare County. Erosion removed the evidence necessary to form a closure in the lithofacies lines, but this closure probably would have occurred in that same general area. A striking discordance may be seen in the western part of the state, where the facies lines take the form of a bifurcating flat nose, with a relatively high Clastic ratio to the south. This struc— ture strikes slightly east of north through Kent and Montcalm Coun— ties, then splits and trends to the northeast in western Mecosta 42 County and toward the northwest in Lake County. The 3.00 Clastic ratio line does not Conform with the general trend of the nose. This may indicate that the structure curved to the southwest through Kent and Allegan Counties. Another interesting trend is that of the isopach contours which form a minor protuberance to the northeast through Newaygo and Osceola Counties. This roughly parallels the eastern limb of the bifurcating nose. One possible explanation of these unusual patterns could be that two structures are superposed,'and may repre- sent an early, nearly northward-stretching fold, and later an uplift which strikes northeast. Although the isopachs do not indicate which was first, their parallelism with the facies lines of the northeast- trending structure hints that this structure was probably the more persistent. Following is a summary of the major structural trends deter- mined from the elastic ratio map: 1. A relatively strong high area in Livingston, Genesee, and Shiawassee Counties pointing to the northwest, with its source not too distant in the southeast. 2. An east-west structure in Arenac, Bay, Gladwin, Midland, Clare, and Isabella Counties, with a source at a moderate distance to the e as t. 43 3. ‘ A bifurcating structure in Kent, Montcalm, Mecosta, Osceola, and Lake Counties, which trends to the north and splits toward the northwest and northeast. These structures may indicate two periods of uplift at a moderate to far distance in the southwest. The sand-shale ratio map. In all cases shown on this map the sand-shale ratio falls below 0.500, which shows a definite pre— dominance of fine, rather than coarse, elastic material. A northwest-trending, sharp, elongated, ridgelike structure is readily recognizable in Genesee and Shiawassee Counties. The litho— facies lines parallel the isopachs near the end of the ridge, but form a definite curvilinear—discordant pattern to the north and south. Sev- eral smaller ridges radiate from this structure. The one extending to the southwest through Clinton County does not transect the isopach contours. This, then, is a simple, relatively flat spur which probably received deposition similar to that of a delta deposit. The other two spurs, one trending to the northwest through Gratiot County, and the other north through Saginaw, Bay, and Arenac Counties, also transect few isopach lines. This would indicate a fan—type deposit, with the material transported from the high ridge, toward their outer limits. The only other distinct structure, shown by these lithofacies lines, is a broad, low, rectangular—shaped nose extending from Kent 44 County straight to the northeast through Montcalm, Mecosta, Isabella, and Clare Counties. This is flanked on the west by a narrow trough, represented by closely spaced lines of lower sand-shale ratio that extend straight to the southwest, then form a semicircle, and return to the north. On the east is a gently curving trough that nearly bi- sects the state. The remarkable characteristic of the area embracing the rec- tangular-shaped structure is that, in all places except in the trough to the east, the lithofacies lines are curvilinearally discordant with the isopach lines. This indicates the possibility of some nearby up- lift in the southwest, which, judging from the large amount of fine elastic material in the Mississippian system, may have been promi- nent for a long period. The only conformity of lithofacies and isopach lines found in conjunction with this structure is in Ionia and eastern Montcalm Counties. This conforms to the concentric ovate pattern, indicating normal basinal sedimentation. The predominant structures represented on the sand—shale ratio map are summarized below: 1. A ridge-like structure trending northwest through Genesee and Shiawassee Counties, which is indicative of a source a short distance to the east. 2. A rectangular nose striking northeast through Kent, Mont- calm, Mecosta, Isabella, and Clare Counties, indicating a nearby source originating in the southwest. 3. A minor basinal structure in Ionia and Montcalm Counties, with relatively high areas to the east and west. The evaporite ratio map. The striking feature of this map is the distinct concentric-ovate pattern formed between the lithofacies lines and the isopach contours. This was predicted in the quotation of Krumbein (1952) concerning patterns found in intracratonic basins. The oblong-ovate structure running from Newaygo, through Mecosta and Clare Counties, to Roscommon County follows, fairly well, the isopachs representing the center of deposition during Mis- sissippian time. An extension of this structure to Ionia County also conforms with the isopachs. An area low in evaporite content runs from Eaton County in a nearly straight line to Arenac County. This transects the isopach lines, indicating a possible high area existing for a relatively short time. In northern Shiawassee County another region of high evaporite content swings through eastern Saginaw County, and terminates in southern Bay County. Although this does coincide with the isopach 46 map fairly well, it does not appear to be one of the areas of deep or continued sedimentation. Following is a summary of the structures indicated by the lithofacies lines on the evaporite map: 1. An ovate trough extending from Newaygo to Roscommon County, which conforms with the isopachs, denoting the center of deposition. 2. A minor basinal structure in Ionia County, indicating an area of relatively deep sedimentation. 3. A linear trough extending from Shiawassee to Bay County, which indicates local subsidence along the basin's eastern edge. 4. A possible low fold extending from Eaton to Arenac County, inferred from the lack of evaporite material. R EGIONAL TE C TONICS Structural Relations of the Michigan Basin In early Ordovician time, prior to the deposition of the St. Peter sandstone, several upheavals occurred which later served to define the limits of the Michigan basin. The Cincinnati arch, straddling the Ohio-Indiana boundary, heaved upward. This arch split at its northern end, extending a ridge to the northwest, and a long folded structure to the northeast along the present Michigan—Ontario boundary. These structures are named the Kankakee and Findlay arches, respectively. According to Eardley (1951), the first uplift of the Wisconsin dome, in northeastern Wiscon— sin, occurred at that time. Subsequent erosion, during Ordovician and Silurian times, lowered these structures. At the close of the Silurian an uplift occurred along the Wis- consin arch and its extension into Northern Illinois (Eardley, 1951). Late Devonian deposition was interrupted by another uplift of the Cincinnati arch. Eardley stated that this did not noticeably affect the Kanlzakee and Findlay structures. He did indicate that the subsidence on each side of the Kankakee arch caused a break between 48 the Michigan basin and the Illinois-Indiana—Kentucky basin. King (1951) stated that subsidence, more than uplift, was probably responsible for the pre-Mississippian structures. The final regional diastrophism, before the beginning of the Appalachian orogeny, occurred in late Mississippian, at which time Eardley believed the Wisconsin dome, and the Kankakee, Findlay, and Cincinnati arches were strongly uplifted. With this picture in mind, let us examine the possible correla- tions of the facies maps with the regional structure during the Mis- sis sippian time. Structural Interpretations in Relation to Tectonics The intrabasinal structures indicated by this analysis vary to a certain extent, between the facies ratio maps. Less variation is likely to occur betvreen the elastic ratio and sand-shale ratio maps than between either of these and the evaporite map. The former maps would tend to magnify the uplifted features, while the evaporite map would depict the areas of final evaporation of the seas. The areas of evaporite concentration would generally be the original deep syn- clines within the basin. 49 The strongly positive structure in Livingston, Genesee, and Shiawassee Counties is shown on both the elastic and sand—shale maps. If this structure had a nearby orogenic source, as mentioned earlier, it is felt that the Findlay arch must fall in close proximity on the east. The time of uplift is one of. concern. If it occurred in late Mississippian, as indicated by Eardley (1951), the large Clastic ratio would not be expected; therefore, contrary to Eardley, it is felt-that this part of the Findlay arch may have been a strong positive area during most of the Mississippian period. This does not conform with the present structure recognized by Pirtle (1932) and Newcombe (1933). Structural contours drawn by Newcombe on the Berea sand show that the northwest-trending structure passes through Livingston and Shiawassee Counties, and does not include the southeast corner of Genesee County, as indicated on the lithofacies maps of this report. It is possible, then, that the facies contours show the actual center of the ridge farther to the north, and that a post-Mississippian period of folding and faulting caused the present structure to the southeast. Three spurs, shown on the sand—shale map as radiating from the Livingston structure, are not present on the other facies maps. These spurs probably lasted for a short period during Mississippian time. 50 The east-west structure, present in Arenac and Bay Counties, is shown only on the elastic ratio map. This structure may indicate a gentle warp in the basin floor which received more Clastic sedi~ ment than the surrounding area, but this undulation was still so gentle that no anomalous amount of coarse elastic material was deposited. It may be assumed, then, that the northern end of the Findlay arch underwent some uplift, and that this uplift and the one to the south may have been separated by a sag in the arch. An isopach map of the Marshall formation (Mississippian), drawn by I‘Jewcombe (1933), does not indicate a structure in northern Bay or southern Arenac Counties, but his isopach map of the Grand Rapids series (Bayport and Michigan formations) does indicate a structure similar to the one indicated on the Clastic map of this report. As shown by Eardley (1951), this uplift to the east probably did occur late in the Mississippian. A trough, transecting the state, is apparent on each of the three facies maps. The uplift immediately to the west of this trough trends to the northeast, and is evident only on the elastic and sand- shale maps. This structure, extending through Kent, Montcalm, Me— costa, and Isabella Counties, terminates in southern Clare County. The possibility that this was a relatively long, flat warp in the basin 51 is supported by two facts: First, the warp ends very near the center of maximum deposition in Clare County. A high structure would not be likely in such an area. Second, neither the elastic nor the sand—- shale ratio contours indicate anomalies comparable to those seen on the Livingston structure. This evidence indicates a source in the area of the Kankahee arch. The large amount of fine Clastic material indicates a warp of long duration extending from the arch. Possibly the area near the southern end of Lake Michigan was positive during most of the Mississippian. Newcombe (1933) referred to broad, gentle flexures trending to the northeast in southwestern Michigan. He found that the ter- mini of these structures were in northern Kent and western Mont- calm Counties. The structure indicated by the lithofacies maps aligns itself with Newcombe's flexure, but extends farther to the north. Pos- sibly post-Mississippian basinal subsidence erased the evidence New- combe needed to extend the structure he found. Near the western edge of the state, a conflict exists between the patterns formed by the contours of the sand-shale and Clastic ratio maps. The structure on the elastic map bifurcates north of Kent County, with one arm extending north through Lake County, and the other continuing northeast to Clare County. The sand-shale map 52 structure parallels the Kent—to—Clare flexure, but trends northeast through Lake and Wexford Counties. A small anomaly in that same area, shown on the evaporite ratio map, is similar to that of the sand-shale Inap. The coarse material found along the west side of the basin may have been derived from the uplifted Wisconsin arch. The com- plexity of the Clastic and sand-shale maps may indicate an overlap of sedimentation from the Wisconsin and Kankakee arches. Little mention was made of the evaporite map in the above discussion. By construcing this map, an attempt was made to deter- mine if any primary salt formation remained in the Mississippia system. Two of the three high-salt-ratio areas do coincide with the synclinal structures, but the third cuts directly across the Livingston ridge. This indicates that some secondary factor may have altered the original extent of the salt formations. Since the amount of evap— orite material found in this study was very small, it is felt that the evaporite ratio map is of little significance. Tectonic A spect The possible relationship between the basinal structures and those of the surrounding areas during Mississippian time are shown 53 on Map '2. The marked dissimilarity between the Devonian facies maps (Bruce B. Dice, personal communication), and those of this study indicate that a major uplift occurred either before or during deposition of the Mississippian system. The author feels that a major uplift in late Mississippian could not cause this contrast. Possibly the source of these elastic sediments was a rejuvenation of the Kankakee, Findlay, Cincinnati, and Wisconsin arches at the close of the Devonian. The marked change in sedimentation after the deposition of the Antrim and Coldwater shales may indicate two later movements along the rejuvenated structures. 54 5 il.’ _ ilk \ // s _ // ... /l.»/ V I I/ / Inferred tectonic up auras the tsunami“ ported. m7. CON CL US IONS Some of the structures found in this analysis do not coincide with the present known structures of the Michigan basin. It is prob- able that these early structures were removed by post—Mississippian erosion or diastrophism. Their presence during the deposition of the Mississippian system was extremely valuable in determining the tectonic activity of that interval. With similar analysis of the other rock systems or formations in the Michigan basin, we may, in the future, be able to draw a more exact tectonic history of the Paleozoic era. REFERENCES Baltrusaitis, E. J., et a1. (1948), A summary of the stratigraphy of the southern peninsula of Michigan, pp. 1-16, mimeographed. Bouyoucos, G. J. (1936), Directions for making mechanical analyses of soils by the hydrometer method, Soil Sci., vol. 42, pp. 225- 229. Eardley, A. J. (1951), Structural Geology of North America, Harper Bros., New York, pp. 12—35. King, P, B. (1951), The Tectonics of Middle North America, Prince- ton Univ. Press, New Jersey, pp. 39-41. Krumbein, W. C. (1933), The dispersion of fine—grained sediments for mechanical analysis, Jour. Sed. Petrology, vol. 3, pp. 121—135. Krumbein, W. C. (1948), Lithofacies maps and regional sedimentary—- stratigraphic analysis, A.m Assoc. Petrol. Geol. Bull., vol. 32, pp. 765—788. Krumbein, W. C. (1952), Principles of facies map interpretation, .1931. Sedg. Petrology, vol. 22, pp. 200—211. Krumbein, W. C., and F. J. Pettijohn (1938), Manual of Sedimentary Petrography, Appleton-Century-Crofts, New York. Krumbein, W. C., and L. L. Sloss (1951), Stratigraphy and Sedimenta~ tion, W. H. Freeman and Co., San Francisco. Moore, R. C. (1949), The meaning of facies, .Geol. Soc. Am_.,_Mem. 39. PP. 1—34. Newcombe, R. J. B. (1933), Oil and gas fields of Michigan, Mich. Geol. Survey Div., Pub. 38, Geol. Ser. 32, pp. 3—124, 205—210. Pirtle, G. W. (1932), Michigan structural basin and its relationship to surrounding areas, Am. Assoc. Petrol. Geol. Bull., vol. 16 pp. 145—152. 1 Robinson, G. W. (1922), A new method for the Mechanical. analysis of soils and other dispersions, Jour. Agr. Sci., vol. 12, pp. 306—326. Sloss, L. L., W. C. Krumbein, and E. C. Dapples (1949), Integrated facies analysis, Geol. Soc. Am., Mem. 39, pp. 91-124. Smith, R. A. (1912), The occurrence of oil and gas in Michigan, Mich. Geological and Biological Survey, Pub. 14, Geol. Ser. 11, pp. 19-32. Wentworth, C. K. (1922), A scale of grade and class terms for Clastic sediments, Jour. GeolggL vol. 30, pp. 377-392. Wentworth, C. K. (1926), Methods of mechanical analysis of sedi- ments, Univ. Iowa Studies in Nat. History, vol. 11, no. 11. Wiegner, G. (1927), Method of preparation of soil suspension and degree of dispersion as measured by the Wiegner-Gessner apparatus, Soil Sci., vol. 23, pp. 377-390 (translated by R. M. Barnette). EVAPOR ITE R A TIO OF MISSISSIPPIAN ratio evaporflc lsolith Interval : .005 ISOPACH OF MISSISSIPPIAN CONTOUR INTERVAL - 500' (ff u . fit Changes to ICC atISOO ’ holith Interval: .025 sand-shale ratio SAND‘SHALE RATIO OF MISSISSIPPIAN CLASTIC RATIO OF MISSISSIPPIAN tio I: .25 elastic ra Isolith Interva