mum mm m m: W mm mm mica Wilton NMM- Mom 951 . ~ + MATERIAL “ IN BACK OF BOOK ,~ 111’ ‘ 43A: ‘1‘ This is to certify that the thesis entitled "A Quantitative Analysis of Silurian Sediments in the Michigan Basin" presented by Wilton Newton Lielhorn has been accepted towards fulfillment of the requirements for Master of Science degree in Geology and Geography 2m < ‘ v /\_J . /' Valli/(2‘74“ ’1‘. ! Major professdr / Date No £41.30, /9 sv 0-169 A QUANTITATIVE ANALYSIS OF SILURIAN SEDIMENTS IN THE MICHIGAN BASIN BY WILTON NEWTON MELHORN 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 MASTER OF SCIENCE Department of Geology and Geography 1951 THESS: 2633MB ACKNOWLEDGMENTS The author wishes to express appreciation to Dr. B. T. Sandefur, who first aroused the writer's interest in sedimenta- tion studies of a quantitative nature and pointed out their pos- sible economic applications. Dr. Sandefur also gave freely of his time and assistance in conduction of the preliminary experi- ments which are culminated in this paper. Thanks are due to Mr. George Strait of the Michigan Geological Survey, who aided in selection of samples for analy- sis and assisted in choosing of formational markers. Dr. W. A. Kelly gave valuable suggestions concerning Silurian stratigraphy. Dr. S. G. Bergquist edited the manuscript, and Mr. J. B. Long aided in sample analysis and offered constructive suggestions on and criticisms of laboratory techniques. Special thanks are due the writer's mother, Mrs. Pau- line Melhorn, for assistance in preparation of the facies maps. TABLE OF CON TEN TS .Page INTRODUCTION . . . . . . . . . . . . . . 1 History of Lithofacies Investigations . . . . . . 1 Statement of the Problem . . . . . . . . . 4 Location of Wells and Selection of Samples . . . 6 LABORATORY PROCEDURE . . . . . . . . . 14 Sample Cutting . . . . . . . . . . . . . 14 Sample Splitting . . . . . . . . . . . . . 15 Removal of Soluble Salts . . . . . . . . . . 15 Removal of Acid Soluble Compounds . . . . . . 16 Washing After Acid Treatment . . . . . . . . 18 Wet Sieving . . . . L. . . . . . . . . . 18 Pipetting . . . . . . . . . . . . . . . 19 List of Laboratory Equipment . . . . . . . . 21 Error in Sampling and Treatment . . . . . . 22 Summary of Laboratory Procedures . . . . . . 23 Results of Quantitative Analysis . . . . . . . 2.4 LITHOFACIES..............29 Definition of Facies . . . . . . . . . . . 29 Lithotopes and Lithofacies . . . Lithologic Ratios The Lithologic A5pect Triangle LITHOFACIES MAPS Construction . . . . Facies Maps . . . . . . SEDIMENTARY FACIES AND TECTONICS . Interpretation and Synthesis of Facies Analysis Sedimentary Tectonics . . . .. . . Intracratonic Basins Lithologic Associations in Intracratonic Basins LITHOFACIES MAPS AND APPLIED PROBLEMS Interpretation and Value of Facies Maps Properties of Contour-type Facies Maps CONCLUSIONS............ REFERENCES . . . . . . . iv Page 29 30 31 34 34 37 38 38 39 41 42 44 44 45 47 56 LIST OF FIGURES FIGURE Page 1. Generalized stratigraphic divisions of Michigan............. 9 Z. Clastic ratio and sand-shale ratio super- imposed on percentage triangle . . . . . 32 3. Use of the lithologic triangle as a scatter-diagram . . . . , . . . . . . 35 4. Clastic ratio and sand-shale ratio super- imposed on percentage triangle . . . . . 36 5. Regional structure of the Michigan Basin and adjacent areas . . . . . . . 51 LIST OF MAPS I. Base map of Michigan showing location of wells used in Silurian facies investigations . . . . . . . . . II. Clastic ratios . . . . . . . . . III. Sand—shale ratios . . . . . . . IV} lEvaporfie rafios . . . . . . . . . V.Isopachmap.......... Page pocket pocket pocket pocket LIST OF TABLES TABLE Page 1. List of wells used in Silurian facies inve stigation . . . . . . . . . . . 1 1 2. Statistical summary of quantitative analysis . . . . . . . . . . . . . 25 3. Statistical properties of 32 wells . . . . . 28 IN TROD UC TION History of Lithofacies Investigations In the present search for new petroleum reserves, the emphasis on discovery of stratigraphic traps has given steady impetus and increasing importance to studies in sedimentation. Changes in sedimentary facies suitable for the accumulation of oil have focused attention on methods of exploration applicable to this type of trap. The characteristics of sediments partly control the localization of lenses or traps. Methods of quan— titative sedimentation afford one means of attacking this prob- lem, because they furnish a more complete picture of sedimen- tary characters and processes than might otherwise be possible. As Moody (1) recently stated, The lateral variations of sedimentary rocks are now of fundamental concern to the practical, front—line explora- tion geologist. Quantitative petrographic data of regional scope might lift our exploration petrography above its pres- ent "sand-shale-lime" level. Can anyone say that this would not be a profitable accomplishment? In the past two decades, many techniques for the quan- titative measurement of sedimentary attributes have been devel- oped, and a large amount of theoretical knowledge has been made available for application to practical geological problems. Many writers, notably Knopf (2), Twenhofel (3), Trask (4), Pet- tijohn (5), and Levorsen (6) have discussed the place of sedi- mentation in geology, and have found that the use of quantita- tive data is increasing in the field of applied sedimentation. Particle properties, such as size, shape, roundness, surface texture, mineral composition, and orientation have been investigated and quantified by various authors. These proper- ties are, however, all reflected to a greater or lesser degree in the term "lithologic characteristics"; and in turn, the sum total of the lithologic characteristics of a sedimentary rock is its ”lithofacies" which may be represented by constructing a lithofacies map. Krumbein (7) has defined a lithofacies map as "an areal representation of sedimentary rock characteris- tics for a stratigraphic interval.” Lithofacies maps are based on the dominant lithologic characteristics in a certain geological section, which may be either a surface exposure or a subsurface interval. Ver Wiebe (8) in 1930 first recognized the value of contrasting clastic and non-Clastic components in the section. In 1945 Krumbein (9) initially suggested use of a map as a method of numerical representation to depict the percentages of various lithologies. Later Read and Wood (10) published a contour-type map based on the ratio of clastic to non-Clastic components. More re- cently Sloss, Krumbein, and Dapples (7) have advanced the idea of construction of lithofacies maps based on the so-called "litho- logic triangle." An expansion of this idea is found in a later paper by Krumbein (11), and a summary of this and other meth— ods of construction of lithofacies maps have been described in the most recent publication of Krumbein and 81035 (12). The preparation of any lithofacies map depends on a knowledge of the thickness and character of the sediments in the geological section under investigation. Work by the previ- ously mentioned authors (chiefly Krumbein and 51055) was based on data gathered mostly from measured outcrops or exposed sections of considerable vertical extent, and the results ex- pressed in terms of percentage thicknesses of elastic or non- clastic rocks. Only where exposures were not present were well records used to fill in gaps in the general pattern of the lithofacies map. Rittenhouse and Cather (13, 14) did attempt a textural (size) analysis of Paleozoic sandstones and sandy limestones, using both well and outcrop samples from a restricted 4 geographical area. Their analytical procedure involved treat- ing of the samples with hot hydrochloric acid and subsequently washing the samples to remove sand and silt. The percentages of sand and silt were then calculated separately on a basis of 100 per cent. However, their main concern was with the grade sizes of sand grains, and no emphasis was placed on the rela- tive proportions of soluble salts or carbonates, which occurred either as separate particles or as a sand-grain cement. Statement of the Problem In the Michigan basin, where outcrops of any rock type are infrequent, a different approach to lithologic determination is mandatory. Fortunately some 17,000 wells have been drilled in Michigan in the search for oil and gas, and of this great number, a small percentage, perhaps 100 wells in all, have penetrated part or all of the Silurian formations and reached the underlying Ordovician rocks. Initially it was thought that a study of the driller's logs of these wells would be sufficient to establish the general lithologic character of Silurian sedi- ments in the basin; but on further inspection it was discovered that these records were inadequate, frequently incomplete, and 5 sometimes even entirely incorrect as to the types of sediments encountered in the course of drilling operations. The idea was then conceived of analyzing in quantitative fashion the actual sample cuttings from selected wells, and to construct lithofa- cies maps from the resultant statistics. The present report is based on an investigation conducted along these lines. The writer believes that a complete quantitative analysis of well samples for use in the preparation and interpretation of lithofacies maps is the key to a new approach to sedimen- tary research, and may in time assume economic significance in the prospecting for new petroleum reserves in Michigan. The individual who pioneers in a new field of investiga- tion often fails to consider every possible aspect of his prob- lem. This report is admittedly broad in scope, and it is hoped that the reader will give more consideration to the value of the theory involved than to the immediate results. As more deep drilling takes place in the Michigan basin, detailed lithofacies studies on a county or areal basis may become practical. Re- finements in laboratory techniques and improvements in the procurement of well samples will also allow for greater ana- lytical accuracy. 1 .K'Eiilii lawfu-Bhk'nfllgufi “. . Liv U innit .. Location of Wells and Selection of Samples The wells selected for study are shown on Map I. It will be noted that there is a pronounced clustering of wells around the margins of the basin leaving a considerable blank area in the center. This is simply because no wells are avail- able in mid-basin, where drilling depths of 8,000 feet or more would be required to penetrate even the uppermost Silurian formations. No oil tests in mid-basin have been carried deep- er than Devonian strata. Therefore, considerable leeway exists for future modifications in the lithofacies analysis as shown in Maps II to V inclusive. Where possible, an attempt was made to utilize at least one well from each county. Frequently only one well per county was available, and only in the southeastern and southwestern portions of the state was any real selectivity between wells possible. In all, 32 wells distributed over 28 counties were used. Six other wells were studied and discarded, either be- cause too large a percentage of the total section was missing or because removal of the amount of bottled sample requisite to this study would not leave a remainder sufficient for future use. MICHIGAN DEPARTMENT OF CONSERVATION GEOLOGICAL SURVEY DIVISION SCALE H II! I N .6 .0 Map I. Base map showing location of 0 wells used in Silu- rian facies inves- tigations. 9* a” L ’4 K E s u P E R ’ 0 R - \ DOMINION OF CANADA J éx. g I IMROUETH ‘, LUCE ‘ ALGER SCHOOLCRAFT “WE” DICKINSON ACKINAC - {00M ‘ ‘. (”ANA/[L 0 I . o . a D 0 TOWCMY l‘ . DO I?" V) 0 D «I! * 9 s .#-- o EUUET 7 Y" ° ’- / 95‘“ 4° 3 + }' ‘- ° Pncsouc ISLE 6‘ [Q' )9; 3 CHARLEVOIX . .' 'I | (I // Bag 3 'fimm orscoo lo” musing 9 . t ,I § LEELAW e / f " .' V BEN GRAND KALKASKA CRAWFORD oscoDA ALCDNA ZIE I Q, TRAVERSE I I" \ = '. ,t Amour Ntxroao MISSAUKECROSCOMMON 069:3! it?) n 0 2 .’/ b T I ARENAC , , \ MASON LAKE osccoLA CLARE DLADwIN t 6" / § 6““. HURON H BAY 9P I OCEANA utcosu ISABELLA IIIDLAND '7 I NEWAYGO A I ‘5 TUSCOL sANILAc LL) MONICALM GRATIOT 5‘5“” I‘ I *I KENT 28 GENESEE LAPEER SAINT1 . '- 0 IDNIA CLINTON WE CLMR ‘I 027 r* ‘ 9 uAcouD \' I ‘2' ° Va" OAKLAND . ALLEDAN BARRY EAION INDNAII LI GSTON 20 8 LA“ ' 'I . . I St CLAR ( VA UREN '26 9'8 ‘ V AALAIAAzoD CALHOUN . 1A6 KSON NASNTENAw WAYN ' n CANADA 0 .|2 . . o / 35““ CASS 350 BRANCH HILLSDALE LENAIIIEE uDNno: x " 0—..2—3. L25 5.JO_SEPH L _.. .‘9 '3 ,'/ L A KE IC—CC— .-. ER IE INDIANA :u—H OHIO 8 Before sample cuts were made from each well, the sam- ples were studied and checked against the records of driller's logs obtained from the Michigan Geological Survey. Sample tops were picked for the various formations and these tops frequently differed from tops as selected by the drillers. It may be appropriate to mention that one of the greatest diffi- culties in-a study of this nature occurs at this point. The se- lection of formational tops and marker beds in the Silurian are still a matter of controversy among practicing geologists in Michigan, and undoubtedly the selection of limits for the Si- lurian section as set by the writer would, in certain wells, meet with considerable objection; Therefore the limits as selected for the purpose of sample analysis must be considered as some- what arbitrary. Figure l is an abbreviated Michigan stratigraphic col- umn. It will be noted that the Bass Island group is now classed as Silurian, but the formations and members of this group are hard to differentiate on a basis of lithology from the overlying Detroit River group and Bois Blane formation of Devonian age, especially where the Sylvania sandstone is absent or has been replaced by shale or dolomite. Baltrusaitis (15) describes both omalo oooHIoom oowlomm ooonmu ooovtom ovmlom ooofilo ommlo oovHIomH mpfilo omlo oomloofi mmvdxowfirfi .nmmEuflz mo maowmffip oEdmanwuum poufiwuodoO A ousmwh occamvnmm mfiegov .ocgmogwd ongm me: .0350. 3.3? . oaopm we: . ofiEOHoQ ofluprgqm .vfimam .ofifiofiop .fidm ofiEBoQ phone .ofigoqofl oumaofiop .osgmpamm Dippiancm .fimm 6:03.29”: .vugofioq ongmofihq uncommon: .ofimam Bonn .ocopmogfld HmoaoguwaH nauflohdw Gdflnoij deHnEmU dmwxhdno houom .am ashram xomfimtnofinoufi Gmuogopuo A8sotzfimsmfiéaofiaflfi . . amnmcfiofiu Anonywunuv Aofiowmqmtuoaxooq Infiusov cmuewmnz caisim mnflmm 9.8de mmwm uamfim mfiom diagram Maxim fiohufl Gmflno>oQ monasQIEG muewom 20m omhv>muH :mwmmwmmwmmfiz downwargmgmvnm :msouofidonudu Icahn“: unoccumwgm mdouU .nofimghoh mofiuom .Egmtwm 10 the Detroit River and Bass Island groups as occurring charac- teristically in the form of gray, buff, or brown crystalline do- lomites. Anhydrite may be found in both groups in certain sections of the state. For purposes of this study, where the Salina salt is present, either the first salt (”F" unit) or gray shale (”G" unit) immediately overlying the salt was used as the top of the measured section. In part of the Southern Pe- ninsula, the salt beds are absent, and again selection of the Salina top is difficult. Sample study showed that frequently a gray shale member underlies the brown dolomite, and the de- cision was made to use this marker as representing the top of the Salina group. The separation between the Cataract formation and the underlying Richmond and Utica shales of Ordovician age is made with more facility and assurance. The Cataract contains dolo- mite (Manitoulin member) and a considerable amount of varie- gated red, greenish-gray and purple shale, while the Richmond is almost uniformly a light gray shale and the Utica a dark gray or black shale. Table 1 lists the wells shown on Map I. It gives the formational tops as found in each well, an asterisk indicating 1‘)! "d ‘ _v'- .H;‘.\-'-I- _M'I"”'\. 11 Table 1. List of Wells Used in Silurian Facies Investigation Well Cable Detroit Sylva- Bass , Niag— , or , _ Salina Clinton No. River ma Island ara Rotary 1 C 605 1400 1680 2062 4115 4115(?) 2 R 1245 2150 2435 2839 4155 3 C 640(?) 1415 1665* 2781 4 C 2000 2345 2565 2960 4195 5 C 2038 2575 2885 3600 3615(?) 6 C 3030 3590 3615 4115 5526 7 R 3079 3810(?) 4810 5480 8270 8353(?) 8 C 2030 2465(7) 2585 3200* 3410 9 C 2643 3140 3408 3566 4764 4914 10 R 2876 3942 5117 5393 8547 11 C 2074 2528 3096 3432 5466 12 C 1180(?) 1420 1490 2085* 2225 2470 13 C 115(?) 178 365* 955 1150 14 C 937 1650 1817 2331 3970 4117(?) 15 C 65 205 741 1135 16 C 1260 2140 3735 3835(?) 17 C 930 1170 1405 1646 2960 3057 18 C 215 495 620 990 2240 19 C 1220* 1345* 1465* 1760* 2025* 20 C 1418 1641 1650 1735 2293 21 R 2180 2590(?) 3070(7) 3700(7) 3820(?) 22 C 950 1073* 1463 23 C 630 765 870 960 24 R 1800 2230* 2845 25 C 826 1005* 1154 26 C 1575 1706 1923 2080 2337* 2590 27 C 2187 2624 3000 3820(?) 28 C 2524 2865 2956 3515 4522 4565 . 29 c 1940 219o(?) 2220 2600* 3280 3233(7) 30 C 1157 1325* 1337* 1777 31 C 1315 1939(?) none 2056* 2077* 32 C 1160 1275* 1395* 1625 12 Table 1 (Continued) Cabot Mani- Cincin— Tren— Total 2:1 Ele— Year Head toulin natian ton Depth tion vation Drilled 4445 4575(7) 4925 5145 5665 2863 803' 1936 5050 5235 5754 6150 2396 738' 1943 3707 3848 4440 4650 2183 822' 1949 4615 4685 4825 5000 5280 1865 591' 1928 3820 3845 3975 4315 4754 1090 636' 1931 6160 6385 6674 2045 830' 1935 8446 8584 9400 10447 3104 599' 1941 3650 3675 3770 4263 4405 570 864' 1929 5080 5250 5752 6599 1684 908' 1943 8829 8848(7) 8932 9779 11021 3539 903' 1948 5640* (stopped in Cataract) 5702 624' 1946 2610 2960 3269 4060 875 834' 1940 1330 1985 2091 965 682' 1940 4299 4575 4983 5958 2244 914' 1935 1155 1220 1269 1895 2910 1064 592' 1949 3870 (stopped in Cataract) 3960 729' -—-—- 3090 3152 3205 5692 1559 818' 1945 2355 2440 2490 3065 4050 1500 612' 1915 2040* 2308* 2905* 7 843 1061' 1948 2408 2517 2843 2848 782 662' 1950 3930 4487 5116 860 857' 1942 1721 1808* 2045 2711 735 667' 1939 1270 1345 1676 1832 475 746' 1948 3215* 3515* 3948 4286 1285 1031' 1941 1525 1558 1945 2029 553 855' 1929 2677 2780 3117 3209 700 857' 1948 3924 4550 5200 924’ 758' 1945 4624* 4913 5325 5575 1398 679' 1937 3325(7) 3560 3783 4006 960 634' 1939 2021(?) 2330 2595 2693 993 886' 1941 2263* 2420* 2578* 2721 364- 771' 1938 2150(2) 2220(?) 2255 2420 , 2523 860 772' 1930 13 formation tops as picked by the writer after study of the sam- ples. The “total thickness" column at the right of the table was used in drawing the isopach map (Map V) and represents the thickness of the "measured section." Wells 11 and 16, which did not penetrate the entire Cataract formation, were not employed in constructing the isopach map, but were used in preparation of the lithofacies maps because of their value as key wells in areas where no other control points were avail- able. LABORATORY PROCEDURE Sample Cutting The selected wells were numbered from 1 to 32 inclu- sive. Samples preserved on file at the Michigan Geological Survey offices are contained in glass vials, each vial when full holding seven to eight grams of sample, and 25 vials compris- ing one tray of samples. It was decided that removal of a one gram sample from each of the vials would permit construction of a composite sample large enough for quantitative analysis, yet at the same time not detract from the future value of the remaining sample. The sample in each vial ordinarily repre- sents the ”drilling screw" which is usually a 5 or 10 foot vertical interval. A portion of the sample from each vial was poured onto the pan of a chemical balance until one gram of sample was obtained. All the individual one gram samples from each well were poured together into a composite sample and placed in a 400 m1. beaker of predetermined weight. The beaker and contained sample could then be weighed and recorded 15 to the closest 0.005 gram. A total of 5,457 one gram samples were taken to form the composite samples for the 32 wells. Sample Splitting In cases where the total weight of the composite sample was less than 100 grams, the entire sample was used in analy- sis. Composites of more than 100 grams weight were split in the Jones sample splitter. A one-half or two-thirds split usu- ally gave a sample of suitable workable weight for analysis. The remainder of the composite sample was saved in glass jars as "seed" for other studies. Removal of Soluble Salts Each composite test sample contained in a beaker of known weight was covered with tap water which had been heated to boiling over a Bunsen flame. The sample was stirred with a glass rod during addition of the water. Weigner (16) has shown that if appreciable amounts of salts are present in sedi— ments, procedures such as boiling increase the agitation of the particles and thus increase the number of collisions between them, thereby aiding in dispersion. 16 The sample was allowed to boil on an electric plate for one hour, the water decanted, and the process repeated until the soluble salts (probably mostly chlorides of sodium, mag- nesium and calcium) were removed. Crystalline silver nitrate was used to test for degree of salt removal; this compound has a high order of sensitivity to chlorides and forms a milky pre- cipitate in their presence. As an extremely accurate test was not deemed necessary, the usual procedure involving preparation of a solution of the silver nitrate was not used. When the re- action of a single crystal of silver nitrate in the decanted water from the sample was no greater than that given in a test tube filled with tap water, the significant percentage of the salts was considered to be removed. The test sample and beaker were dried and weighed, and the weight in grams of salt lost by water immersion computed by taking the difference between the weights before and after boiling. Removal of Acid Soluble Compounds The dried sample was treated at least three times with hydrochloric acid to remove the soluble carbonates, which occurred l7 mostly as calcium carbonate and magnesium carbonate; minor amounts of gypsum and anhydrite (SO anions) and ferric chlo- 4 rides and carbonates will also slowly dissolve in hot acid. In the first two treatments a 50 per cent solution of .hydrochloric acid was used. In the third stage of treatment, a 100 per cent acid solution was employed. A few samples required more than three treatments to effect carbonate removal; nine samples gave no reaction to the third treatment. Experiment showed that gentle heating promoted acid action, but boiling of the treated samples was undesirable because of the danger of overflow foaming or cementation of the sample to the beaker if the fluid level was allowed to fall too low. After each treatment, the sample was permitted to settle and the supernatant fluid de- canted before the addition of new acid. Though some carbon- ate in the form of dolomite probably remained even after con- centrated acid treatment, this would constitute a relatively minor percentage of the total carbonate present in the original test sample . 18 Washing After Acid Treatment After final acid treatment, the sample was subjected to several washings in clear water. One or two drops of sodium oxalate added to the suspension after each addition of water fa- cilitated rapid settling of the suspended particles. During each washing, the water was tested with a strip of blue litmus paper to determine whether all acid had been removed; if any significant amount remained in the wash water, the litmus would turn pink. The acid-free sample was then decanted, oven dried and reweighed. The weight of removed carbonates was computed by taking the difference between the preacid and postacid weights. Wet Sieving The next step was to remove grains of sand size or larger from the dried residue. Using Wentworth's system of classification, in which one-sixteenth mm. is taken as the di- vision between grains of sand size and silt size, the remain- ing sample was again wetted and the resulting suspension poured through a 230 mesh Tyler sieve, which is designed to separate sand size grains from particles of smaller diameter. The 19 residue collected on the sieve was washed with a stream of water, and the liquid passing through the sieve caught in a flat—bottomed pan. Gentle shaking of the sieve or light brush- ing with the fingertips aided in passing grains less than one- sixteenth mm. in diameter through the sieve. The liquid col- lected in the pan was then poured into a 1,000 cc. graduated cylinder. During washing, care must be taken so that the total volume of the suspension remains less than 1,000 cc. That portion of the sample remaining on the sieve was re- turned to the original beaker, dried and weighed. This "sand fraction" was then rebottled in glass vials with a view towards later studies of heavy minerals. Pipetting The method of elutriation used in this experiment is essentially that suggested by Robinson (17). Elutriation by the pipette method is particularly applicable to the silts and clays, though it may be used for fine and medium grained sands. The suspension washed through the sieve and into the graduated cyl- inder should receive the addition of enough plain water to bring the total volume to 1,000 cc. The liquid suspension in the 20 graduate was then thoroughly mixed by running forced air through a rubber tubing dropped to the bottom of the graduate. After three minutes of agitation the tube was removed and the solution permitted to settle for a period of two hours and three minutes. No dispersing agent was used during the pi- petting process. The pipette method is based on the principle that, in a dilute suspension, the particles fall as individuals according to size. By allowing all grains having a given velocity to settle below a certain level, a sample taken at that level at some critical time will contain the full concentration of all material having a lesser velocity. Stokes' Law (18) states that a sphere will sink in a liquid at a velocity directly proportional to the square of the diameter and the difference in density of the sphere and the liquid, and inversely proportional to the abso- lute viscosity of the liquid. Since the particles are not spheres it must be assumed that particles with equal diameters will settle with the same velocity. Therefore, given the settling velocities of particles with various diameters, the time which the particles take to settle a given distance may be determined. By taking samples at the determined time intervals, the samples 21 will include the wanted sizes and exclude the unwanted sizes. The period of two hours and three minutes has been computed as the critical time required for all particles of silt size to sink below a 10 cm. level, leaving the clay particles above that level. Immediately on completion of the settling period, using a 20 cc. pipette, a sample was removed from the graduate and drained into a 50 ml. beaker of known weight. This was oven dried and reweighed. The weight of the evaporite in the beaker represents the weight of the clay in 20 cc. of suspension, which, when multiplied by 50, gives the‘weight of the clay size parti- cles in the entire 1,000 cc. graduated cylinder. The remainder of the sediment in the graduate was taken to represent the weight in grams of the silt fraction. List of Laboratory Equipment The equipment needed for sample analysis includes the following: composite sample of known weight 230 mesh Tyler sieve chemical balance and weights to 0.005 gram graduated cylinder, 1,000 cc. glass stirring rod p-dy—Jp—OFIH 22 lengths l/4-inch rubber tubing pipette, 20 cc. beaker, 400 ml. beaker, 50 m1. electric oven Bunsen burner Flat-bottomed pans NI-‘l—‘F-iI-‘l-‘N Error in Sampling and Treatment Prewashing of the samples during drilling, sacking, and bottling has undoubtedly removed much of the clay and silt. The remaining subsand size grains remain as siltstone aggre- gates or shale fragments. It is necessary, therefore, to assume that the amount of fines lost has occurred on the same percent- age basis in each well. As a greater proportion of fine grained sediment is probably lost during rotary drilling than in cable tool operations, cable tool samples were used where possible, but a few rotary well samples had to be used for purposes of control. Minor errors may also enter when, in changing the sam- ple from one container to another, some of the fine material is floated away in the air as dust. Some fines may also be 10 s t during de cantation. 23 Summary of Laboratory Procedures The following summary may be useful to those wishing to duplicate the techniques described in the foregoing sections: 1. Weigh out a one gram sample from each vial. Make a composite sample population for each well from the individual one gram samples. Divide the composite into a workable portion using the Jones sample splitter. The weight of the work- able portion will vary with the number of samples and thickness of the measured section, but to facilitate analysis composite samples should, after splitting, approximate 100 grams. Weigh a clean empty 400 m1. beaker to the nearest 0.005 gram. Pour the composite sample into the beaker, add boiling water, and continue to heat on an electric hot plate until about half of the water evaporates. Decant the remainder of the water, and repeat the process until reaction of the decanted fluid to silver nitrate is not more than the reaction in ordinary tap water. After final decantation, dry and weigh the sample to determine the weight loss of soluble salts. Add a 50 per cent solution of hydrochloric acid to the sample, slowly, in order to minimize the danger of overflow by excessive effervescence. Continue this treatment, increasing the acid concentration, until effervescence ceases. A gently heated 100 per cent acid solution in the final stage of treatment should remove most of the remaining less soluble carbonates. To be most effective, decantation of the supernatant liquid is made after each stage in treat- ment. 24 7. After final acidization, continue to wash the sample with plain water until a blue litmus test shows it to be acid free. Dry the residue and reweigh to deter- mine the amount of carbonate loss. 8. Wash the dried residue through a 230 mesh Tyler sieve into a flat-bottomed pan, keeping the volume of suspension passing through the sieve less than 1,000 cc. 9. Dry, weigh and bottle the material retained on the Tyler sieve. This is the sand fraction from the com- posite sample. 10. Pour the suspension in the pan into a 1,000 cc. grad- uated cylinder, adding any necessary amount of water to bring the level to exactly 1,000 cc. 11. Agitate the suspension for three minutes and then allow to settle for two hours and three minutes. Pi- pette a 20 cc. sample from a depth of 10 cm. in the graduated cylinder. 12. Drain the pipette into a 50 ml. beaker of known weight. Dry in oven and reweigh. This weight, multiplied by 50, represents the weight of the clay fraction in the graduate. The sum of the clay and sand fractions subtracted from the total sample weight before wet sieving will give the weight of the silt fraction. Results of Quantitative Analysis A statistical summary of quantitative analysis of the 32 wells made in accordance with the foregoing procedures, is con- tained in Table 2. The data for each well in this table were used in computing the various lithologic ratios as summarized Well Number 1 10 11 13 1h 15 16 Permit,0perator,Farm, County and Township 2960,0.W.Teater,Nevins#l, Alpena Co. Long Rapids Tp. 1000h,0hio 0i1,0hamber1ain #1,Antrim Co. Central Lake Tp. 1&936,Rooseve1t 0i1,0rmsbee #l,0heboygan Co. Ellis Tp. 1h,huggles & Radamaoher, Fee #2h,flanistee Co. Filer Tp. 309,Mus:egon 011,H.Heinz#5, Muskegon Co. Muskegon Tp. h11,Newaygo Oil, Bates #1, Newaygo 00. Sherman Tp. 5hhl,Gu1f Oil, Bateson #1, Bay 00. Monitor Tp. h29,Wittmer 011,21pha Port- 1and#1,Eaton Co.Bellevue Tp. 10011,W.H.001vin, Glaser #l,Ingham.co. Wheatfield Tp. 12898,0hio 011,Reinhardt #1, OgemaW'Co.West Branch Tp. 1183h,Pure Oil,Stap1eton #1, Huron.Co. Rubicon Tp. 7598,Voorhees Drlg., Gove #1,Lenawoe 00. Clinton Tp. 7870,N.J.Berston, Heath #1, Lenawee Co. Deerfield Tp. 2179,Ta1bot 0i1,McPherson #1,Livingston Co.Howe11 Tp. 13867,F.T.Canon,Campau #1, Monroe Co.Frenehtown Tp. -—~—,Michigan Pet.,Richard- son#2, St.01air Co.,Grant Tp. Table 2 0 Land Survey Description 18~T32N=R6E lh~T31N€RSW 1~T3AN4R2W 12wT21N~Rl7W 8~T10N4R16W 12—T13N4813W 2~T14N~R4E 28~T1N4R6W lbw T3N~R1E 35-T22N4R2E 22-T17N4R15E 8- T5S€RAE 13— T7S~R5E 35* TBN-RAE 12- T6SéR9E 27— T8N-R16E Sample at., (Grams) 120.575 72.905 93.585 104.675 117.515 96.005 112.065 52.670 101.070 93.915 86.810 101.155 106.430 139.595 97.070 95.285 Solubles(Grams) A8.l95 13.000 10.100 27.910 37.9h0 37.820 28.990 6.530 17.665 51.615 33.505 .100 .830 35.295 .215 38.455 Statistical Summary of Quantitative Analysis 51.795 £6.575 54.900 54.655 63.970 42.9h5 51.565 Al.030 Ah.170 30.975 32.8h0 60 9 L560 47.670 60.985 52.865 3h.110 ‘Weight Loss,Water'Weight Loss,ACid Sand Frac- Solubles(Grams) tion(Grams) 7.605 3.735 13.895 7.205 4.175 h.l95 15.985 0475 18.005 3.385 3.645 25.h75 36.020 16.860 28.515 6.210 Silt Frac- Clay'Fracm tion(Grams) tion(Grams) 11.480 1.500 9.135 .500 13.690 1.000 1h.305 .600 10.880 .550 10.195 .850 26.025 1.500 b.235 .400 19.980 1.250 7.220. .700 15.720 1.100 1h.270 .850 21.010 .900 25.455 1.000 14.525 .950 1h.810 1.700 25 Totals (Grams) 120.575 93.585 104.675 117.515 96.005 112.065 52.670 101.070 93.915 101.155 106.530 139.595 97.070 95.285 Well Number 17 18 19 21 22 23 24 25 26 27 28 29 30 31 32 Permit,0perator,Farm, County and Township 11361,W.H.Golvin,Meinzingm er#1,Washtenaw CO.Superior Tp. ~~~~H.R.Ford‘Well,Dearhorn Wayne Co. Dearborn Tp. 12307,Hugh Rogers,Zeiter #1, Hillsdale 00. Camden Tp. 15327,N.L.Stevens,3tarbakck #1,A11egan Co. Lee Tp. 9618,8un Oil Co, Mead #1 Barry Co. Rutland Tp. 6126,8prenger Bros.,Herwig #1,Berrien 00. Benton Tp. 13779,Norman Nelson,Speckine #1,Berrien Co. Buchanan Tp. 9261, Conoco Oil, Turner#l, Calhoun 00. Albion Tp. 579,B1air & Miller,Know1ton #1,Cass Co. Milton Tp. 13h83,Chas.L.Hook, Fee #1, Kalamazoo Co. Oshtemo Tp. 11540,Smith Pet.Co.,Sherk #1,Kent Co. Caledonia Tp. 3090,J.E.F1anigan, Croft #1,Kent Co. Vergennes Tp. 5689,Voorhees Drlg.,Reible #1,0ttawa Co.Grand Haven Tp. 7823,0ra Avery,Dunnworth#1, St.Joseph Co. Lockport Tp. 5229,Whitehill-Drury,Ament & webster#l,Van Buren 00., Bangor Tp. 119,wolverine Oil,V0ught #3, Van Buren Co. Decatur Tp. Land Survey Description 12m T2S~R7E 22m T2S~R10E T8SéRhW 1? 29 T1N~R15W I 10 T3N€R9W 10 TAS~R18W 32 T7S-R18W 15m TBSmRhW 2a T8SéR16W 31w T28~812W 21— T5N-R10W 35w T7N€R9W 36~ T7N€Rl6W 13- T6SnR11W 35. TZS—R16W 32- ThS-thw Table 2. (Continued) ' 26 Sample Wt., 'Weight Loss,Water'Weight Loss,Acid Sand Frac- Silt Frees Clay Frac~ Totals (Grams) Solubles(0rams) Solubles(Grams) tion(Grams) tion(Grams) tion(Grams) (Grams) 118.910 36.805 55.810 11.300 13.705 1.250 118.910 120.300 68.135 £6.825 7.880 16.060 1.A00 120.300 98.185 .790 87.375 6.670 4.850 .500 98.185 105.400 2.100 57.225 27.870 17.305 .900 105.600 68.250 .895 h0.620 16.755 9.080 .900 68.250 79.360 1.320 13.330 20.895 12.965 .850 79.360 75.315 1.920 h8.875 lh.h50 9.670 .600 75.315 99.250 .720 57.320 31.700 18.860 .650 99.250 75.375 19330 48.640 16.365 8.710 .350 75.375 73.920 2.340 h6.690 14.670 11.620 .600 73.920 67.280 22.820 37.065 3.530 3.615 .450 67.280 107.075 47.995 45.545 1.680 11.105 .750 107.075 80.225 2.225 56.315 12.115 10.790 .750 80.225 91.540 1.185 h5.685 25.185 18.785 .600 91.540 38.380 .515 30.485 1.770 5.180 .600 38.380 103.685 1.670 6h.7h0 23.565 13.310 .h00 103.685 27 in Table 3. The processes used in computing these ratios are described under the heading "Lithologic Ratios” in the following section. 28 Table 3. Statistical properties of 32 wells, computed by pro- cedures contained in the text, and summarized from Table 2. Well Clastic ratio Sand-shale ratio Evaporite ratio 1 .206 .586 .931 2 .224 .388 .279 3 .440 .946 .184 4 .268 .483 .571 5 .153 .365 .593 6 .189 .380 .881 7 .617 .531 .697 8 .108 .102 .159 9 .635 .848 .399 10 .137 .426 1.666 11 .309 .217 1.020 12 .670 1.685 .002 13 1.194 1.644 .017 14 .453 .635 .579 15 .829 1.843 .004 16 .313 .376 1.127 17 .283 .756 .660 18 .256 .451 1.028 19 .114 .873 .009 20 .777 1.531 .038 21 .644 1.678 .022 22 .777 1.513 .031 23 .483 1.435 .039 24 1.066 1.625 .015 25 .508 1.804 .027 26 .572 1.200 .052 27 .123 .913 .616 28 .252 .142 1.050 29 .419 1.053 .041 30 .949 1.299 .026 31 .237 .317 .018 32 .561 1.719 .026 LITHOFACIES Definitions of Facies According to Moore (21), "facies are areally segregated parts of differing nature belonging to any genetically related body of sedimentary deposits.” He emphasizes that facies are "variants or aspects of stratigraphic units having mutually ex- clusive space distribution," and clarifies the relationship be- tween lithofacies and lithotopes. Sloss, Krumbein and Dapples (11) believe facies may be considered as the resultant of any set of factors which permit an areal differentiation of varying aspects of a stratigraphic unit. Lithotope s and Lithofacie 5 Wells (22) has established the term "lithotope," mean- ing "rock environment," to include all the environmentally sig- nificant characteristics of a sedimentary deposit from which environmental conditions may be interpreted. Each recogniz- able rock environment in a succession is a lithotope. 30 ”Lithofacies" are groups of strata demonstrably differ- ent in lithologic aspect from laterally equivalent rocks, the as- pect being controlled by the lithotopes of which the lithofacies are composed. Thus a lithofacies may contain a number of lithotopes, the designation of the lithofacies being derived from the gross aspect of the lithology (ll). Lithologic Ratios The over-all lithologic character, or gross aspect, of a measured subsurface section may be determined by grouping the rocks into Clastic components (conglomerate, siltstone, sand- stone, shale) and non-Clastic components (limestone, dolomite, evaporites), and then be used in development of a lithofacies map. Table 2 expresses the amount, by weight, of evaporites, limestone-dolomite, sand, silt and clay (shale) in a composite sample taken from the measured section of a number of wells. The weight of each of these components can be converted into a. percentage of the total weight. The percentages of the clas- tics are then added together and divided by the sum of the per- centages of the non-clastics. The resulting decimal number is the "Clastic ratio." This may be augmented by a "Sand-shale 31 ratio," which is the ratio of sandstone and conglomerate to siltstone and shale in the section, regardless of the amount of non-Clastics present. The two ratios may be expressed as fol- lows: Conglomerate + Sandstone + Shale Clastic ratio = , , , Limestone + Dolomite + Evaporite Conglomerate + Sandstone d- h l t' = San s a e ra 10 Siltstone + Shale The Lithologic Aspect Triangle Clastic ratio and sand-shale ratio aspects of lithology can be referred to a triangle diagram (Fig. 2) on which both appear as parameters. A discussion of the fundamentals of construction of the lithologic triangle may be found in ”Stra- tigraphy and Sedimentation" (12). Each corner of the triangle represents 100 per cent of the non-clastics, sand, and shale respectively. Thus, for example, 100 per cent non-clastics at the triangle apex represents a Clastic ratio of zero, while the base line directly opposite represents a Clastic ratio of infin- ity. Intermediate values can be plotted at points between these extremes. In similar fashion the base line of the triangle rep- resents a sand-shale ratio ranging from zero to infinity. 32 NON—CLASTICS 1/4 1 /z CLASTIC RATIO 1 12 1 2 SAND SAN D-SHALE RATIO SHALE Figure 2. Clastic ratio and sand—shale ratio super- imposed on percentage triangle. The pat- terns illustrate nine statistical groupings of lithology. 33 In most instances, Clastic ratio, sand-shale ratio, and lithologic triangle form the basis for mapping nonspecific lithofacies. However, each of the end-member corners of the basic triangle either is subdivisible into other ratios or capable of expansion into other triangles. In this problem it is useful to differentiate the non-Clastics by application of an "Evaporite ratio," which is the ratio between evaporites and carbonates in the measured section. Thus: Evaporites Limestone + Dolomite Evaporite ratio = LITHOFACIES MAPS Construction Plotted on a base map, the values of the elastic ratio and sand-shale ratio may be contoured. Krumbein (7) super- posed these contoured ratios on an isopach base map, but the expression of so many features on one map makes it cumber- some and difficult to interpret. ' Therefore, in this report the isopach map is prepared on a base separate from that of the ratio maps. Since the lithologic triangle as set up by Krumbein (Fig. 2) is subdivided geometrically into nine types of lithol- ogy, the values obtained for the various ratios in each well determine its place relative to the network of lithofacies lines. The 32 wells are thus shown as a scatter-diagram (Fig. 3). The values used in construction of the triangle which limit the nine lithologic associations statistically are designated by different colors (Fig. 4). General stratigraphic procedure is used herein, the colors changing from yellow in the sand- dominated section to green in the shale-dominated section and NON—CLASTI CS 35 0 1/4 0.:. z“. ', 1/2 1, ' CLASTIC RATIO 0 . 1 O —— 2 —— 4 / / / \ X —\ 8 8 _ z 1 1/2 1/8 SAND SAND—SHALE RATIO SHALE Figure 3. Use of the lithOIOgic triangle as a scatter-diagram. The 32 wells are plotted relative to the lithofacies lines. Values of the various ratios determine the position of each well relative to the network of lines. SAND Figure 4. 36 NON—CLASTICS 1/4 1/2 CLASTIC RATIO SAND-SHALE RATIO SHALE Clastic ratio and sand—shale ratio super- imposed On percentage triangle. Same as Fig. 2 except statistical groupings are il-—. lustrated in color rather than in patterns. This coloration is used in the lithofacies maps. 37 blue in the limestone-dominated section. In accordance with the triangle, as constructed and colored, the lithofacies maps show the average statistical properties of the measured inter- val, so that it is possible to see at a glance whether sand, shale, or non-Clastics dominate in the particular section. Facies Maps Table 3 lists the Clastic ratio, sand-shale ratio, and evaporite ratio as computed for each well used in this study. Maps II and III are respectively Clastic ratio and sand-shale ratio maps drawn and colored in accordance with Figure 4. Map IV is an evaporite ratio map, and Map V is an isopach map of the measured Silurian section. SEDIMENTARY FACIES AND TECTONICS Interpretation and Synthesis of Facies Analysis One approach to a study of facies and their distribution patterns attempts a reconstruction of ancient source areas and depositional environments and their distribution in past geographic patterns. However, many attributes of ancient environments are not preserved and a strictly environmental approach is neces- sarily incomplete and may be dependent on difficultly substan- tiated inference. Lithofacies are subject to interpretation in respect to their dominant sedimentary environment. From a combination of environmental and tectonic data, a broad view of the paleo- geography of an area can be derived. The geographic recon- struction includes distribution of ancient lands and seas, of source areas and sites of deposition, the shifting pattern of environments, and the contemporaneous tectonic activity of the area during a particular time span of deposition. Studies of large stratigraphic units, such as the Silurian in the Michigan Basin, yield more or less broad aspects of paleogeography in 39 which a number of short-lived events and conditions may be obscured. A reduction in the vertical limits of the units stud- ied will change an over-all synthetic product into a more closely knit representation of actual conditions at any partic- ular time . Sedimentary Tec tonic s The term "tectonics“ refers to earth movements and rock structures in general. The multitude of information now available shows that a wide range of environmental conditions may occur. In sedimentary basins such as that in Michigan thick deposits with few. stratigraphic breaks imply nearly con— tinuous sedimentation and subsidence. Hence the very lack of discontinuity hinders facies analysis in a quantitative fashion. Schuchert (23) was the first to classify tectonic elements, especially geosynclines. A great number of concepts of tec- tonism have been advanced, and there are as many different terminologies applied as there are concepts. The term "cra- ton" is one of the more recent nomenclatural innovations to appear in print. Kay (24) defined the craton as ”the consoli- dated, relatively neutral area which comprises the main part 40 of the continent or of oceanic basins.‘l H. Stille in 1936 had used the term ”parageosyncline” to denote an area of subsi- dence within the craton itself, receiving thick sediments as compared to the cratonic areas intervening between themselves and the major geosynclines. Kay followed Stille in classifying geosynclines, but expanded the parageosynclines to include vary- ing types of subsidence within the craton. Among these types he lists the ”autogeosyncline" possessing the following charac- teristics: [1] isolated depositional area within a craton and [2] detritus gained from distant cratonic sources. The Michigan Basin is listed as a type example of an autogeosyncline. He also believed that the craton is not always a relatively stable and rigid mass, but displays local subsidence and uplift, giving rise to markedly greater thicknesses of sediment in the intra- cratonic basins. Krumbein and 51055 (12) imply that the Michigan Basin typifies a condition of rapid subsidence and slow deposition. Under such conditions, when the rate of subsidence exceeds the rate of sedimentation, bathyal or abyssal depths will be dominant; the detrital sediments will be fine—grained and the 41 deposition predominantly non-Clastic components. They further state: The Michigan Basin, during part of its history, was a subsiding basin without complementary uplift in nearby cratonic areas. There is no evidence in the sediments that bathyal or abyssal depths were attained, but the pres- ence of thick, non-Clastic sequences attests to the lack of appreciable land—derived debris. Intracratonic Basins These are Kay's intracratonic geosynclines, the term “basin” being appropriate for isolated, ovate areas. The basin lies within the craton and relatively distant from uplifted source areas of sediment. The sedimentary deposits may include fine clastics derived from distant sources, and abundant carbonates and associated evaporites. Kay considers the Michigan Basin to have been isolated during all or part of the Silurian. Krumbein and 51053 (12) show Michigan as a subsiding basin surrounded by a wide expanse of unstable shelf during Niagaran time. Whether this shelf was low-lying dry land or covered by a shallow sea is difficult to determine. Possibly dry land prevailed during the Salina interval. During Niagaran time there existed either dry land or a "barred basin” formed 42 by biohermal reefing in the shallow epicontinental seas on the surrounding shelf. Krynine (20) discusses the evolution of sediments in synclinal basins, stating that: First cycle carbonates and especially soluble salts are generally connected with low relief and weak tectonic activity and show strong affinities with shallow barred and semi-barred basins, frequently under arid conditions. . . . ”Normal" primary cherts produced by supersatura- tion of leached silica are related to very low relief, fre- quently under conditions approaching peneplanation. . . . A considerable amount of chert is present in the resi- dues from the wells used in this study. Lithologic Associations in Intracratonic Basins The idea of lithologic associations was derived from the principle that sedimentary properties are related to the tectonic intensity which prevails during their deposition. Krumbein, 51053 and Dapples (26) outlined the relation between sedimentary tectonics and sedimentary environments. The succeeding list of sedimentary attributes in intracratonic basins should therefore apply to the Michigan Basin, and appear on the lithofacies maps prepared for this study. 43 Intracratonic basin associations are: An intracratonic basin develops when concentric sub- sidence at a point on the craton results in a circular or elliptical area with rates of subsidence varying from slight at the margin to moderate in the center of the basin. Intracratonic basins show greatest rate of deposition in the center, relatively slower at the margins. They may have open or restricted circulation. Occur- rence of evaporites is characteristic of intracratonic basins. The relation between rates of subsidence and of sedi- mentation is partly a matter of associated source areas. If adjacent uplifts are absent, subsidence may exceed deposition and non-clastics may dominate the section. If uplifts are nearby and active, elastic sediments may fill the basin. LITHOFACIES MAPS AND APPLIED PROBLEMS Interpretation and Value of Facies Maps The interpretation of facies maps designed to give an over-all picture, such as the ratio maps contained in this re- port, cannot show details on types or thicknesses of individual beds. Preparation of all specific aspects of facies variation would require an entire sequence of maps. The chief value of a regional study, such as this of Silurian sediments in the Mich- igan Basin, may lie only in its historical reconstruction of a major geological feature. In oil exploration, emphasis must be placed on all the possible relations between the specific and gross aspects. Among specific aspects could be included the study and preparation of maps showing the types and dis- tribution of heavy minerals, and the nature of the microfauna. It has occurred to the writer that a pursuit of studies along these lines would be of great complimentary value to the pres- ent report. The insoluble residues remaining from the current study were saved in glass vials, and could be used directly for heavy mineral studies. Microfossil studies could be made of N .. ”mall: xvi 1- (0.8.1.8 up 1.3.5.9, \ t 45 the samples from the same measured sections in the wells and biofacies maps constructed from the data obtained. Maps based on strictly numerical data, such as these ratio maps, are limited in interpretation. They do have an advantage over more qualitative maps in that lines of equal value on the maps are related to their neighboring lines by some constant quantity or ratio. On each map the lines are inversely proportional to the degree of slope, and the closeness of the linear spacing indicates the rapidity of facies changes. Properties of Contour-type Facies Maps Kay (27) has classified maps for stratigraphic and struc- tural studies. He contends that a map is geographic if it por- trays conditions at a single time, stratigraphic if it covers a span of time. When characteristics of sediments are converted to numbers, or ratios, they can be used to construct contour- type maps whose lines connect points of equal magnitude. These he calls "isopleth" maps, and the lines are referred to as "iso- liths.H The maps of this report cut across all groupings to some extent. Strictly speaking, they are both geographic and 46 stratigraphic. They are both isopleth and isolith maps, and the contour lines themselves can certainly be called isoliths. In a sense they are also isopach maps, inasmuch as they are con- toured through points of equal properties. CONCLUSIONS Can lithofacies maps be interpreted in terms of regional structure and tectonics? If we take a positive attitude and as- sume that such interpretations are possible, then an observa- tion of the lithofacies maps leads to some interesting conclu- sions. Maps 11 and III (Clastic ratio and Sand-shale ratio Maps respectively) can be studied almost as a unit. Their general degree of symmetry is quite remarkable. Cohee (28) has shown the center of the Michigan Basin during Niagaran time to be lo- cated in western Gladwin County. Other writers, including Eardley (19) have shown the approximate center of the early Paleozoic basins to be in the four-corner area where Clare, Gladwin, Midland and Isabella Counties meet. But both ratio maps prepared from evidence gathered in this study show the Silurian basin as wider, and elongated in a general northeast- southwest direction with the approximate center somewhat farther north and west, probably near the confluence of the Clare, Osceola and Missaukee County lines. Map V (Isopach Map) shows the greatest vertical thickness of Silurian sediments 48 (3,539 feet) in well 10 (Ogemaw County). However, there is no reason to believe, lacking evidence to the contrary, that any wells drilled to the west of well 10 would not encounter an equal or greater thickness of Silurian sediments. The Findlay arch, an extension of the Cincinnati arch, appears on both ratio maps. From southern Monroe County it seems to turn abruptly eastward into Ontario before again swinging northward. Wells 12 and 24 indicate either a flatten- ing and westward extension of the Findlay arch as far as Cal- houn County, or the presence of a cross-arch which bisected the Findlay feature and gradually died out to .the northwest. Though the ratios for well 24, a rotary well, may be too high, ratios for cable tool wells 9 and 14 tend to show that some fea- ture of this nature persisted throughout at least a part of the Silurian. Eardley states: In pre-Devonian time, the Michigan and Illinois- Indiana-Kentucky basins were continuous; but beginning in the Devonian, the Kankakee arch began to form, and the two basins became increasingly individualistic thereafter. The ratio maps show a deep trough containing non—elastic sediments swinging south by southeast from southern Eaton County through western Hillsdale and Calhoun counties, and 49 then southward into northeastern Indiana. But the wells in southwestern Michigan show that complimentary arch was pres- ent to the west of this trough, being especially prominent in Cass, St. Joseph, Van Buren and Kalamazoo Counties. Its in- fluence on sedimentary deposition must, at times, have prevailed as far north as southern Muskegon and Kent Counties. This ridge may have been either an offshoot from, or the forerunner of, the Kankakee arch. If Eardley is correct, the trough through Eaton, Calhoun, and Hillsdale Counties may have connected the Michigan and Indiana—Illinois Basins throughout middle Silurian time, disappearing prior to the deposition of the Salina salt. The writer wishes to suggest the name ”Battle Creek trough" for .this connection of the Michigan and Indiana-Illinois Basins. Along the northern borders of the Findlay and pre- Kankakee (7) arches there is a rapid change to the non-Clastic deposition in the central Michigan Basin. Another depositional trough of non-Clastic sediments paralleled the western flank of the Findlay arch through Sanilac, Lapeer, and eastern Oakland Counties. This trough will hereafter be referred to as the “East Michigan trough." In the Saginaw Bay area another ridge or arch, whose northeastward extent cannot be determined, 50 separated the East Michigan trough from the major basin in the central part of the state. In the northern part of the Southern Peninsula there is again a gradual transition from non-Clastic to Clastic sediments as progression is made toward the pre—Cambrian rocks of On- tario north of Lake Huron. Western Michigan seems to have been far distant from any land-derived sediment. There is only a gradual westward increase in elastic components progressing outward from the center of the basin. In general, it may be inferred that the Southern Penin- sula of Michigan was an area of oscillating shallow seas, with occasional emergences of dry land along the Findlay and pre- Kankakee (?) arches, so that Clastic deposition at times dom- inated. The central Part of the state remained as a subsiding basin of moderate depth, as did the East Michigan trough paral- leling the Findlay arch. The presence of non-Clastic deposition in these basins attests to the lack of appreciable land-derived debris. Map IV (Evaporite ratio Map) shows the thickest evap— orite sequence to be in Ogemaw County, but significant ratios of salt are present as far south as Kent, Ionia, and Clinton 51 .0230 uncommon was Gwmdm nmmEoQ/H 05 mo 03500.3...“ HNGmeom .m ousmfm .\ .w» (0.3,? s»... 13.; 414.. 7923.: ‘1‘. s L 207 , _¢Domm.2 1 a t .x. L . ._ \ a . u, .11. 11111 . . .J L a I. . . .2. 4 so _ . . , 0.10 M _ ...,m.o 3.: , . a . .7 / .. . _ ... , <30. ., .. L .1L . . .1). .11 L 42.30 \Q . 2 .l. . 1 .1... .b a 11. 0 .2. ill} 1 23.5.: . .22.: 0’s z.» ; -i 501. \ 590...... .\ .... a \ .v w a. n1). .1. .. . \ 52 Counties, where the evaporite series abruptly disappears. The salt basin assumes the same general northeast-southwest con— figuration displayed by the other ratio maps. The East Mich- igan trough must have shifted farther eastward during the Sa- lina so as to lie in eastern Macomb and St. Clair Counties and beneath Lake St. Clair and Lake Huron. If the Findlay and pre-Kankakee (?) arches were joined as a broad unstable shelf, and the Battle Creek trough was closed, separation of the Michigan and Indiana-Illinois Basins was accomplished at the beginning of Salina deposition. The abrupt rise out of the salt basin in south-central Michigan tends to show that the subsiding basin of the central part of the state was being counteracted by a continuous slow rising of the unstable shelf area to the south. This rapid interplay and change from a predominant evaporite sequence to a sequence of another type may be sig- ‘i-ficant from an economic standpoint. Eardley (19) says: _ Significant units in the Michigan basin are the evap- I'gaéorite series of the Silurian and Devonian. . . . Porous olomites in these evaporite series are reservoir rocks ' Par oil and gas, and many oil fields have been developed -".%;._the basin. Very gentle folds or ”highs" ripple the ba- beds and take an irregular northwest-southeast direc- a, They have served to trap the oil. 53 More than 200 wells have been drilled into or through the Niagaran formation, and oil shows have been reported in at least 20 wells distributed over 13 counties. The only pro- ductive Niagaran field in Michigan is the Howell gas field in Livingston County, which produces from the lower basal Salina and the top 40 feet of the Lockport (Niagaran) dolomite (28). Boyd (28) states the structural high on top of the Niag- aran structure at Howell does not conform to the Dundee (mid- dle Devonian) high, but is about 1-1/2 miles to the southwest. Evans (29) reports similar conditions of structure in south- western Ontario where the Niagaran top is structurally high and the Devonian rocks are structurally low. The variation in thickness of the salt beds, dolomites, and shales of the rocks of the upper Silurian (Salina) account largely for the structural variation between the shallower beds and the top of the Niag- aran. Most of the deep Silurian oil tests have been drilled at or near the axes of known Devonian structures. Is there not reason to believe that this theory of exploration is in error? Perhaps facies analyses combined with detailed stratigraphic studies will open the way to another method' of location for 54 future Silurian Oil tests in Michigan. A statement by Krumbein (9) may be the key to a new line of thinking: Where rapid changes in sedimentary attributes re- sult in closer spacing of the lines, they may indicate that other features are changing rapidly also. In short, it may be the steeper slopes or the margins of the steeper slopes which may be significant in the search for sedimentary- stratigraphic oil. Moreover, these areas of rapid change may show typical closure, so that “attribute highs” instead of structural highs may afford the magic closed contour for sedimentary-stratigraphic exploration. The facies maps, and the interpretations therefrom, sat— isfy the criteria necessary for classification of Michigan as an intracratonic basin. The lithofacies maps of the Michigan Ba- sin during the Silurian display these characteristics: [1] Mich- igan is an elliptical basin with moderate subsidence in the cen- ter, slight subsidence at the margins; [2] the greatest deposition is in the center of the basin; [3] it shows evidence of both re- stricted and open circulation, and contains evaporites; and [4] shows evidence of slow and relatively minor adjacent uplifts, with subsidence exceeding deposition so that non-Clastic com- ponents dominate in the section. In conclusion, the writer wishes to reiterate that the lithofacies maps are subject to correction or change in light of new evidence gained from future drilling. If similar lithofacies 55 studies were made using well samples from northern Ohio, Indiana, and western Ontario, a broader regional picture would become available. The present interpretations of Silurian litho- facies and tectonics could then be modified in accordance with any new evidence gained through these studies. 10. REFERENCES Moody, C. L. (1951), Petroleum Geology, 1951, Am. Assoc. Petrol. Geol. Bull., v01. 35, pp. 1499-1504. Knopf, A. (1941), Petrology in Geology, 1888-1938, Geol. Soc. Am., 50th Anniversary Volume. Twenhofel, W. H. (1941), The Frontiers of Sedimentary Mineralogy and Petrology. Jour. Sed. Pet., vol. 11, pp. 53--63. Trask, P. D. (1941), Sedimentation in Geology, 18884938, Geol. Soc. Am., 50th Anniversary Volume. Pettijohn, F. J. (1942), Quantitative and Analytical Sedi- mentation, Nat. Research Council, Rept. of Comm. on Sedimentation, pp. 43-61. Levorsen, A. I. (1942), Report of a Conference on Sedi- mentation, Am. Assoc. Petrol. Geol., Tulsa. Krumbein, W. C. (1948), Lithofacies Maps and Regional Sedimentary-Stratigraphic Analysis, Am. Assoc. 23- trol. Geol. Bull., vol. 32, pp. 1909-1923. Ver Wiebe, W. A. (1930), Ancestral Rocky Mountains, Am. Assoc. Petrol. Geol. Bull., vol. 14, pp. 765-788. Krumbein, W. C. (1945), Recent Sedimentation and the Search for Petroleum, Am. Assoc. Petrol. Geol. Bull., vol. 29. PP. 1233—1261. Read, C. B., and G. H. Wood (1947), Distribution and Cor- relation of Pennsylvanian Rocks in Late Paleozoic Sedimentary Basins of Northern New Mexico, £2111. 9321., vol. 55, pp. 220-236. 11. 12. 13. 14. 15. 16. 17. 18. 19. 20. 57 81055, L. L., W. C. Krumbein, and E. C. Dapples (1949), Integrated Facies Analysis, Geol. Soc. Am., Mem. 39’ PP. 91-124. Krumbein, W. C., and L. L. 51055 (1951), Stratigraphy and Sedimentation, W. H. Freeman and Co., San Fran— cisco. Rittenhouse, G., and E. Cather (1946), The Texture of Mississippian, Upper Devonian, and Lower Pennsyl- vanian Sandstones in the Appalachian Basin, U. S. 133%. 9.1213121" Geol. Survey, Washington, mimeo- graphed. Rittenhouse, G., and E. Cather, The Texture of Paleozoic Sandstones and Sandy Limestones in the Appalachian Basin, U. S. Dept. o__f_ the _I_n_t., Geol. Survey, Wash- ington, mimeographed. Baltrusaitis, E. J., _e_E 31; (1948), A Summary of the Stra- tigraphy of the Southern Peninsula of Michigan, pp. 1-16, mimeographed. Wiegner, G. (1927), Method of Preparation of Soil Suspen- sion and Degree of Dispersion as Measured by the Wiegner-Gessner Apparatus, _S_p_i_l §_c_i_., vol. 23, pp. 377-390. Robinson, G. W. (1922), A New Method for the Mechanical Analysis of Soils and other Dispersions, Jour. Agr. _S__g:__i_., v01. 12, pp. 306-321. Stokes, G. G. (1851), On the Effect of the Internal Friction of Fluids on the Motion of Pendulums, Cambridge Philos. Soc. _'I_'_1:., vol. 9, pt. 2, pp. 48-57. Eardley, A. J. (1951), Structural Geology _o_f_ North America, Harper Bros., New York. Krynine, P. D. (1943), Diastrophism and the Evolution of Sedimentary Rocks, Am. Assoc. Petrol. Geol., Dis- tinguished Lecture Committee, mimeographed. 21. 22. 23. 24. 25. 26. 27. 28. 29. 58 Moore, R. C. (1949), The Meaning of Facies, Geol. Soc. Am., Mem. 39, pp. 1-34. Wells, .I. W. (1947), Provisional Paleoecological Analysis of the Devonian Rocks of the Columbus Region, Ohio Jour. Sci” vol. 47, pp. 119-126. Schuchert, ‘C. (1923), Sites and Nature of the North Ameri- can Geosynclines, Geol. Soc. Am. Bull., vol. 34, pp. 151-230. Kay, M. H. (1947), Geosynclinal Nomenclature and the Craton, Am. Assoc. Petrol. Geol. Bull., vol. 31, pp. 1289-1293. Dapples, E. C., W. C. Krumbein, and L. L. 51055 (1948), Tectonic Control of Lithologic Associations, Am. Assoc. Petrol. Geol. Bull., vol. 32, pp. 1924-1947. Krumbein, W. C., L. L. 51053, and E. C. Dapples (1949), Sedimentary Tectonics and Sedimentary Environ- ments, Am. Assoc. Petrol. Geol. Bull., vol. 33, pp. 1859-1891. Kay, M. H. (1945), Paleogeographic and Palinspastic Maps, Am. Assoc. Petrol. Geol. Bull., vol. 29, pp. 426-450. Cohee, G. V. (1948), Thickness and Lithology of Upper Ordovician and Lower and Middle Silurian Rocks in the Michigan Basin, H. S. Geol. Survey, Oil and Gas Invest., Prelim. Char? 33. Evans, C. (1944), Natural Gas Fields in Southwestern On- tario, Canadian Gas Jour., Oct., 1944. 1.1123 ‘53 11%314951 1’ "(,4 ', 4., '/‘J .5 .Jm'éi“: _.