.fsz' -' 1. ——_———v—— - ”bag as .-" _-. ‘ ' ‘ ‘ "‘ ""“‘ ' "-‘ “ "‘ ""‘ ‘ " ’ “""'“9”o ownafl‘flflf‘WOu moi-3.7-vafifimflflqfl‘w “fl '0‘x':.3 .' .- - . .. '. CARBONATE FACIES OF THE MDDLE BROOVECMN MSCHEGAN'BASSN ' Thesis for the Degree of M. S. WCHEGAN STATE UWERSITY RICHARD EUGENE NEWHART 1975 ‘ BINDING IV “OAS 8: SOIS’ BOOK BllllERY LIBRARY BINDERS r! ‘ (llllcflm‘ Inlllll "I III I!!!” NH HI 111111 11111111" U 111’ 3 1293 10351 6 111 ' “V ’ 7") 1‘13? 53"“, ‘ . I - fl ,\ u :I"q‘[ fl’-6+”¢ .\ . W 4.: 1 u, a. ABSTRACT CARBONATE FACIES OF THE MIDDLE ORDOVICIAN MICHIGAN BASIN by Richard Eugene Newhart Trenton-Black River oil traps are elusive owing to their undetectability by either geophysical or subsurface means. Production exists only where the limestone is dolo- mitized; however, dolomite occurrence does not insure pro- duction. A carbonate lithofacies separation benefits future Trenton-Black River exploration. Both regional and local dolomite are found in Michigan with both types differing considerably as to age and origin. Oil production comes from local linear structures with dolomitization believed to have resulted from magnesium-rich artesian waters ascending fracture systems. Damming effects by the overlying impervious shale causes the waters to spread, or ”mushroom" along permeable zones in the beds thus creating dolomite concentration invariably near the Trenton top. Absence of upper dolomite concentrations in an area suggests a lack of dolomitizing conditions thereby casting considerable doubt as to the promise of Ordovician oil en- trapment in the vicinity. A large regional dolomite facies exists along the western edge of Southern Michigan. A Dorag model likely best explains this regional dolomite but an evaporation- reflux model should not be ignored. Future Trenton-Black River oil strikes appear more likely to occur to the north and south away from the region- al dolomite influence. The undertaking of more detailed lithologic variation studies to the north and south similar to this will aid in the prediction of Ordovician oil. The "thumb" and unexplored central areas of the state, where basinal depths are greatest, must be considered low poten- tial owing to the virtual lack of dolomite shown in the few deep tests of that area. ii CARBONATE FACIES OF THE MIDDLE ORDOVICIAN MICHIGAN BASIN by Richard Eugene Newhart A THESIS Submitted to Michigan State University in partial fulfillment of the requirements for the degree of MASTER OF SCIENCE Department of Geology 1976 ACKNOWLEDGMENTS This study was carried out under the general super- vision of Dr. C. E. Prouty, Chairman of the Guidance. Committee. His devotion of time and energy is much appreciated. Thanks are extended also to Dr. James H. Fisher and Dr. Robert S. Carmichael, other members of the Committee, for their helpful suggestions and review of the thesis text and illustrations. Also, I am indebted to the Michigan Geological Survey, especially Mike Bricker and Ron Elowski, who provided me with many of the well samples. Many thanks are extended to Chris Gruesbeck, who typed the thesis from barely legible c0pies and also for minimal pay. Foremost thanks must go to my wife, Sue, who provided a constant inspiration and an occasional push toward the completion of my work. She suffered late hours and many lonely nights so that I could complete the study on schedule. iii TABLE OF CONTENTS ABSTRACT ACKNOWLEDGMENTS TABLE OF CONTENTS LIST OF FIGURES INTRODUCTION General Statement Purpose Method and Materials Previous Work DOLOMITIZATION CONCEPTS "Structural" Dolomite "Stratigraphic" Dolomite GENERAL DESCRIPTION OF UNITS TRENTON-UPPER 50 FEET Lithologic Description From Samples Map Interpretation Application of "Structural" Dolomite Theories Mechanisms for Ascending Groundwater MAIN BODY OF TRENTON AND BLACK RIVER Lithologic Description From Samples Map Interpretation Application of "Stratigraphic" Dolomite Models ECONOMIC IMPLICATIONS CONCLUSIONS RECOMMENDATIONS FOR FUTURE STUDY BIBLIOGRAPHY APPENDIX iv 13 15 15 16 23 26 30 3O 33 34 38 40 42 43 46 1. 2a. 2b. 3. 4. 5. 6. 7. 8. 9. 10. 11. LIST OF FIGURES Lithology of the Trenton-Black River Evaporation-Reflux Dolomitization Dorag Dolomitization Dolomite Percent - Upper 50 feet of Trenton Middle Ordovician Oil and Gas Fields of Michigan Major Structural Trends in the Michigan Basin Generalized Cross Section of "Structural" Dol- omitization Structure Contour Map of Trenton Limestone Stratigraphic Cross Section Through Regional Facies Boundary Dolomite Percent - Main Body of Trenton-Black River Proposed Barrier System Well Location Index Map INTRODUCTION General Statement The Middle Ordovician carbonates of Michigan have long been a producer of petroleum and their importance as a pet- roleum reservoir has grown throughout the years. Produc- tion ranges from scattered and Spotty to very prolific as evidenced by the Albion-Scipio Field of the southern part of Michigan. Oil production from this trend, classified as a giant oil field, amounts to a cumulative total exceed- ing 100,000,000 barrels of oil. The Middle Ordovician (Trenton and Black River forma- tions) production exists only where the limestone has been epigenetically altered to dolomite thus creating secondary porosity. The presence of dolomite however does not always insure production. Lithology varies in the Trenton and Black River from predominantly limestone in the center of the Michigan Basin to predominantly dolomite along the western flank with scattered linear patches of dolomite elsewhere. It is hoped that a lithofacies plot of the variation will yield new information that may prove condu- cive to future oil and gas operations in this carbonate section. Purpose This study will attempt to discover, plot, and contour the lithologic variations present in the Middle Ordovician carbonates. The data will be analyzed in the light of cer— tain existing theories on the origin of dolomite with atten- tion to any inferences that might suggest their modifica- tion or suggestions of alternative theories. Cohee (1948) performed a similar study on the Middle Ordovician lithology, constructing a map which delineated the occurrence of dolomite in what is generally considered a limestone section. This study was not quantitative but did yield a general view on dolomite occurrence. Lack of Middle Ordovician well control was a severe hindrance to Cohee, his study being restricted mainly to the southeastf ern portion of Southern Michigan with a few scattered wells to the southwest, west, and far north. Discovery of the Albion-Scipio trend in 1956 resulted in numerous Trenton and Black River tests in this and other areas of Southern Michigan. Some new wells also were drilled in the central and western portions of the state. An update of Cohee's original study occurred in 1960 to include additional well control (Burgess, 1960). This study undertakes the further updating and the detailing of dolomite occurrence not shown in the Cohee (1948) and Burgess (1960) studies. Two types of dolomite, ”stratigraphic" and "structur- al", are to be anticipated in the Middle Ordovician car- bonates on the basis of Cohee's earlier work and occurrences \ \\\\\\‘ \\ \ \ \ \\ ‘0 \ CD Dolomite and Limestone SSSSS experienced in the Albion-Scipio-type linear oil fields. Both are lithologically similar but differ as to origin. This study attempts to separate and classify dolomite of the Trenton and Black River using two main criteria: 1) Areal and vertical extent of the dolomite body (geometry of the body). 2) Mode of origin. A close correspondence of the two classification schemes for each dolomitic body should result as the form of a dolomite body is believed to relate directly to its origin. An attempt to apply preexisting models on dolomitiza- tion of Middle Ordovician rocks is also included within this study. This includes appliCation of "structural" dolomitization models (Landes, 1946; and Tinklepaugh, 1957) as well as "stratigraphic" dolomitization models. Among the more important "stratigraphic" models include the application of an evaporation-reflux (Bonaire) type model or the more recent Dorag dolomitization model (Badiozamani, 1973). Method and Materials Data for this study were acquired by the examination of well cuttings from selected wells throughout the state. The sample libraries of both Michigan State University and the Michigan Geological Survey provided adequate cov- erage of the Basin. Middle Ordovician well control varies widely from hundreds per county in Jackson, Hillsdale, and Calhoun Counties to one per county in many northcentral Michigan counties. Eighteen northcentral counties yielded no Ordovician tests at all. Wells chosen were those which produced a uniform scatter of the state. This was possible in the townships from TSN south to the Michigan state line. Lack of well control severely hampered a uniform distri- bution along the western and northern portions of the lower peninsula. While gaining the uniform scatter, wells from major known Middle Ordovician oil fields (Albion-Scipio, Northville, Deerfield, and Reading) were also examined. Examination of cuttings employed the use of a reflec— ted light binocular microscope possessing a magnification range of 7X to 40X. All acid testing of samples used cold dilute hydrochloric acid with a distilled water to acid ratio of 7:1. Lithologic determination resulted from guidelines discussed in "Examination of Well Cuttings" (Quarterly of the Colorado School of Mines, v. 46, no. 4, 1951). Cautionary procedures must be employed in the exam- ination of well samples. This caution is necessitated by very severe contamination of samples, as seen in some wells, resulting from cavings. Other workers (Tinklepaugh, 1957) attempted to produce guidelines stating when samples were too contaminated to be of value. Careful study of the samples is necessitated by this contamination problem. Previous Work A number of studies within the Basin have been di— rected at such major problems as: 1) age of the Basin, 2) downwarping mechanism, 3) the origin of intrabasinal structural features, and 4) the role of the surrounding frame structures in Basin history. Among these are such classical works as Newcombe (1932), Pirtle (1932), and Lockett (1947). More recent studies of rather general coverage of the Basin were produced by the Michigan Basin Geological Society (Stonehouse, 1969). Studies pertaining to the Ordovician of the Michigan Basin are limited. Hussey (1950) examined Trenton and Black River outcrops in the Escanaba-Stonington area of Northern Michigan. Nurmi (1972) studied the Upper Ordovician (Cincinnatian) of the Michigan subsurface. Seyler (1974) made a structure and isopach study of the Middle Ordovician subsurface. Ordovician studies in areas adjacent to Michigan include Rooney (1966) in northern Indiana, Buschbach (1964) in northeastern Illinois, and Calvert (1974) in Ohio. Studies of dolomitization in the Ordovician of Mich- igan are mostly that of the afore mentioned work of Cohee (1948) and Burgess (1960) which dealt mostly with "stra- tigraphic" dolomite distribution. Kirschke (1962) made a qualitative, and Hamil (1961) a quantitative study of the limestone-dolomite relations of the Lower Middle Ordovician and Lower Ordovician of the Peterson-Howard well of the Albion-Scipio field. Bishop (1967) considered Black River- Trenton dolomitization in the Albion-Scipio field. The relationship of dolomitization to structure ("structural" dolomite) was studied by Jodry (1954), Tinklepaugh (1957), Young (1955), and Egleston (1958). Though treating Middle Devonian carbonates, these studies add information on secondary dolomitizing processes in oil field structures which may be suggestive of these processes in Ordovician structures. The classic study by Landes (1946) concerning secondary dolomitization likely served as a stimulus to the above studies. DOLOMITIZATION CONCEPTS Studies on dolomite occurrence in or surrounding the Michigan Basin as well as elsewhere have brought forward several theories that should be considered herein as a possible model or models. Both "structural" and "strati- graphic? dolomite models have been theorized upon and an attempt of model application to Michigan's Middle Ordovician dolomite will be made. "Structural" Dolomite The term "structural" dolomite is referred to herein as secondary, clearly epigenetic, dolomite occurring in linear trends in Michigan and in which solution has generated porosity. Lateral lithologic transition from pure dolomite to pure limestone is quite sudden. Origin of the linear dolomite is attributed to movement of mag- nesium rich groundwater along existing fractures present in the brittle carbonates. Comparison, to be discussed later, of the major north- west structural trend present in Michigan and the linear dolomitic streaks yields a close relationship. Alteration forming the "structural" dolomite had to occur long after original limestone deposition and consolidation as most structural features in Michigan are assigned a post Devon- ian age. Ells (1962), however, assigned a possible post Early Silurian to Devonian age for dolomitization along the Albion-Scipio trend. Earlier workers have postulated the magnesium-rich waters ascended fracture systems and became dammed by an impervious seal above. Notably, Landes (1946) applied this model to dolomitization of the Trenton limestone in the giant Lima-Indiana oil field of northern Ohio. In the same study, Landes assigned an ascending groundwater theory to the Devonian carbonate Deep River pool of Arenac County, Michigan. Landes, however, was careful to note that although all secondary local porosity results from the replacement process, the major porosity stems from solution in excess of reprecipitation during alteration - as Opposed to molecular volume reduction. Source for the dOlomitizing fluids is believed artesian in nature from outcrops along the major positive elements flanking the Michigan Basin. High magnesium concentrations in the groundwater were generated by its movement through older regional dolomites. Tinklepaugh (1957) also ascribed an ascending ground— water hypothesis for alteration found in the Coldwater, Sherman, and Fork Fields in central Michigan. High Mg/Ca ratios taken from well cuttings corresponded with major structural highs. Also believed was that the degree of lateral dolomitization away from the structural feature relates directly to primary porosity and permeability of the limestone along bedding planes. 10 Prouty (1976) indicated in an oral presentation that dolomitization is apt to be most marked where the inter- section of fractures occurs and that cross—structures are common occurrences in producing fields. Proposed cross- faulting interpreted from Mg/Ca ratio maps by Egleston (1958), Young (1955), and Tinklepaugh (1957) display high Mg/Ca ratios. The zone of cross-fracturing may or may not correspond with a subsurface structural high but areas where trends intersect do display a high Mg/Ca ratio. It is therefore plausible to expect maximum dolomitization corresponding to areas of maximum fracturing. "Stratigraphic" Dolomite The term "stratigraphic" dolomite as used herein refers to a dolomite facies whose distribution (geometry) follows a stratigraphic unit. An evaporation-reflux or Bonaire- type model (Deffeyes, 1965) has long been assigned to the regional Middle Ordovician dolomitic facies trending along the Wisconsin Arch. Evaporation-reflux necessitates mag- nesium-rich groundwater moving through a carbonate body. Entrapped lagoonal sea water evaporates, thus increasing the dissolved Mg/Ca ratio. This is a result of the dis- solved Ca concentration decreasing during evaporite for- mation. .Dense magnesium-rich hypersaline brines then flow down into the limestone dolomitizing as they move. Exposure of Middle Ordovician carbonate terrain along a positive arch allows the possibility for this process. 11 Badiozamani (1973) offers an alternative model, termed Dorag, for the Middle Ordovician carbonates in the area of the Wisconsin Arch. Exposure of carbonate terrain is also necessitated but evaporation in trapped shoreline features is not. Magnesium concentrations in sea water are great but the kinetics of the reaction prohibits a pure precipi- tation of magnesium carbonate. In Dorag dolomitization, magnesium replacement for calcium proceeds in the zone of mixing between saline formational water and fresh ground- water generated by rainfall along the outcrop. This brackish zone becomes the site of dolomitization causing the areal and vertical extent of alteration to depend upon fluctuations in sea level. Primarily, this study attempts to test these models of dolomitization in the light of new data collected for this study. 12 SUPRATIDAL \ DOLOMITE OCEAN LIMESTONE Figure 2a. Evaporation - Reflux Dolomitization (after Deffeyes, 1965) Figure 2b. Dorag Dolomitization (after Badiozamani, 1973) GENERAL DESCRIPTION OF UNITS Earlier workers have noted the lithologic variation among the Trenton and Black River carbonates for some time. The previously mentioned study of Cohee (1948) produced a good general description of the section: "The Trenton and Black River rocks generally consist of brown and gray crystalline lime- stone and dolomite which occur in different proportions in different areas. These rocks are entirely dolomite in eastern Wisconsin, northeastern Illinois, and northwestern Indiana. Along the Kankakee and Findlay Archesanuiaround the margin of the Michigan Basin they are dolomite and limestone. In much of the central part of the Michigan Basin these rocks are all limestone. The rocks are entirely limestone east of the Findlay Arch in eastern Ohio and west of the La Salle Anticline in Illinois. The occurrence of dolomite and limestone along the major anticlinal axes indicates a secondary origin for the dolomite with dolomitization in part related to folding." Generally, the Black River Formation tends to be more lith- ographic than the above Trenton which is commonly coarsely crystalline to finely crystalline. Regionally present is a high argillaceous content in what otherwise appears to be the purest of limestones. Considerable residues remain after complete effervescence of the samples. Dolomite zones, where present, are invariably brown and possess highly crystalline characteristics often helpful in sight identification of the dolomite. There may be a relation- ship between this crystallinity and size of the grains after drilling as the cuttings often are of sand or silt size. Shale partings and even shaley zones are not 13 14 uncommon as evidenced by outcrop data (Hussey, 1950), core descriptions, and radiation logs. The calcareous content of these shales is high. Selected wells have encountered additional lithologic variations such as occasional anhy- drite, quartz sandstone lenses, metabentonite, and the presence of cherty zones. Most of these smaller variations (other than metabentonites) relate to primary environmental conditions and are not traceable on a regional scale. According to earlier studies and preliminary sample examination, "structural" dolomite, where present, tends to concentrate in the upper portion of the Trenton forma- tion, directly below the contact with the overlying Utica shale. This study, therefore, separates the Trenton-Black River into two subdivisions vertically. Lithofacies plots for the upper 50 feet of the Trenton and the main body of the Trenton and Black River formations resulted. The arbi- trary figure of 50 feet was selected because "structural" dolomitization rarely extended deeper than 50 feet below the Trenton top. In other instances, the complete section of Trenton-Black River was dolomitized. Consequently, "structural" dolomitization can be generally described as either complete alteration of the Middle Ordovician section or confined only to the upper Trenton. This observation lends preliminary support to the ascending groundwater hypothesis for dolomitization. TRENTON-UPPER 5 0 FEET Lithologic Description From Samples Sample examination shows the Trenton top, in the southern portion of the state, as predominantly tan to dark brown highly crystalline dolomite. The thickness of this dolomitic zone is highly variable from location to location in this area but is invariably present to some degree. Grading downwards from pure dolomite is a zone of brown to gray aphanitic to coarsely crystalline limestone with an abundance of crystalline dolomite present. Also present is extensive white secondary rhombohedral calcite and dol- omite. Extending downward, the lithology becomes predom- inantly finely crystalline or micritic limestone with a few scattered dolomitic chips possibly assignable to formational cavings. This transitional scheme is consistent throughout the southern counties of Michigan but variability in the rate of transition exists from well to well. Transition usually occurs between 10 and 50 feet of the Trenton top unless the whole section is dolomitized. In the southwest counties (Van Buren, Cass, and Ber- rien) and north along the western edge of Michigan, the upper Trenton is greatly influenced by the presence of "stratigraphic" dolomite, thus creating very high dolomite percentages. Examination of the Upper 50 feet map (Figure 3) 15 16 indicates the dolomite trend to be more regionally dis- tributed as opposed to the isolated linear trends in the southern counties. To the north, near the Cheyboygan County area, a transitional linear dolomite pattern similar to that found in the south is present. A major departure from the verti- cal dolomite to limestone transitional pattern of southern counties stems from the fact that the Trenton-Utica contact is very gradational. The samples grade downward from the slightly dolomitic Utica Shale, to a slightly calcareous shale, highly argillaceous limestone, and finally to rela- tively clean limestone. This transition occurs over an approximate span of 30 feet. Where upper Trenton dolomite occurs,the beds are also highly argillaceous. This shaley top occurs in all wells in the northern portion of the state and is especially evident in the McClure-State Beaver Island #1 well of T38N-R10W - 27. These transi- tion beds place doubt on the occurrence of a regional Post Trenton disconformity, at least in this area (Rooney, 1966). Map Interpretation Examination of the Upper 50 feet map (Figure 3) reveals a consPicuous absence of dolomite in the sparsely drilled central portion of Southern Michigan. Of more interest, however, is the virtually pure limestone Trenton top found in the "thumb" area of Michigan, which also possesses the LAKE 5K CLAIR CANADA LAN! ERIE Contour Interval — 10% For linear trends, contour interval has been altered to 30%, for clarity. Figire 3. Dolomite Percent — Upper 50 feet of Trenton 18 greatest thickness of Trenton and Black River rocks. (The "thumb" is referred to as the peninsular area of Michigan southeast of Saginaw Bay which would include Huron, Tuscola, Sanilac, and Lapeer Counties). Sample examination revealed finely crystalline to lithographic limestone for virtually the entire section with minute percentages of dolomite scattered throughout. A cursory examination concerning dolomite occurrence of the "thumb" well scatter in compar- ison to a comparable scatter in the southern part of Mich- igan implies but does not prove dissimilarity with respect to the epigenetic history of the two regions. Figure 3 also exhibits linear patches in the south with a corresponding lithology of 100% dolomite surrounded by wells with lesser percentages of dolomite for the upper Trenton. For the sake of clarity, not all contour lines are drawn for these linear trends. The lateral lithologic transition is so sharp that an analogous situation would be the topographic contouring of a cliff face. Some of these highly dolomitic zones readily correspond to existing Trenton oil fields. This becomes especially evident in the nearly 100% dolomitic streaks of southwest Jackson County and northwest Wayne County. These two zones correspond to the linear Albion-Scipio and Northville Fields. High dolo- mitic percentages also present themselves in the Deerfield Field (T68 - R6E), Reading Field (T7S - R4W), and the Medina Field (T88 - RlE). Although the producing area of these three lesser fields may not appear elongate in nature, the fields do border on possible structural elements. 19 -L14~+4—14- Llll If. Gill. Llll I'll Figure 4. Middle Ordovician Oil and Gas Fields of Michigan (compiled from Annual Stastical Summary 22, 1975) 20 .6’ C £1 lll' 'SSIP'IAI CI Old-nu on. .- NVOIIII Alm- —.. Inn". —..- m — monu- kuoo —. .6...'“ -- '8WI I'AC‘ ww "C'l‘ It"!!! —— - “‘1 i in . \ """""" i "X. ' /’ 0Q (0" . “CI". Al ' 1 . q H1 g“):- ‘ fitti‘t’ii-‘vi’o‘ifi'fi A1": __'—" i \* \ | "\, .1. | ’ ’1: Taxi-7.17; H‘Qfir ‘ "“7"???“ I —-ia'ouT 43‘0“}... ' ' | ' j N A O ' IL'II‘ “tin-A ‘ \ S / —W— "O 11* / . ’ s I C h ° 1 Figure 5. Major Structural Trends in the Michigan Basin (compiled by Prouty, 1971) 21 Also present in the south are some very high dolomite percentage areas which never produced hydrocarbons (TSS - R7E and T78 - R7W). These areas are most probably linear in nature based upon the regional structural trends of the state. These areas, therefore, underwent the dolomitization needed for porosity development but hydrocarbon accumulation never occurred. Doubtless, other known dolomitic streaks not included in this regional study exist which did not undergo oil accumulation. Possible explanation for these nonproductive high dolo- mite streaks could stem from Landes (1946) who was quick to mention that porosity sufficiently effective for oil produc- tion present in "structural" dolomite is not due to molecu- lar volume reduction alone, but solution activity during dolomitization exceeding the reprecipitation of dolomite, thus creating vugular porosity. If solution approximately equals reprecipitation, sufficient secondary porosities will not exist thus hindering the possibility for petro- leum accumulation. More recently, Stieglitz (1973) has observed Sparry white dolomite plugging void space in the Upper Trenton dolomites of northern Ohio and also found minor evidence of the same process in the Albion-Scipio Field. In the case of the Albion-Scipio Field, the degree of mineral infilling obviously did not preclude oil production. If the degree of infilling is major, however, then oil accumulation might be precluded. 22 A recently completed study of Middle Ordovician struc- ture and iSOpach from geophysical well logs (Seyler, 1974) prOposed a possible wrench fault with a northwest trend present in Cheyboygan and surrounding counties (Figure 3). Presence of this faulting would be further supported if large Trenton and Black River dolomite percentages were present. The Upper 50 feet map does indeed demonstrate dolomite percentages as high as 95% (T37N - R4W - 35) in the area. This dolomitic occurrence, therefore, does support Seyler's contention of faulting. 23 Application of "Structural" Dolomite Theories As before mentioned, most workers concur that the origin of "structural" dolomitization stems from ascending groundwaters up fracture systems. Theories on the origin of fracture trends in the Basin vary from worker to worker, but a general consensus supports structural formation re- sulting from movement along preexisting lines of weakness in the basement. The present writer believes movement originated as a result of basement instability possibly stemming from major Paleozoic tectonic disturbances along the eastern margin of North America. However, a common opinion exists that the lithosphere is not capable of trans- mitting stresses over long distances laterally and a more plausible explanation for instability is basinal subsidence. Either of these mechanisms for instability could provide the necessary movement along preexisting basement fractures. The consensus on ascending groundwater originates from the observation that "structural" dolomite in Middle Ordo- vician carbonates, tends to concentrate near the top. It is the opinion of this writer that where fractures pre- sent themselves, dolomitization usually will alter the entire section. Support for this is found in examination of the Albion-Scipio, and Northville Fields. These fields contain wells showing total dolomitization, with the lateral dolomite to limestone transition being extremely rapid and sharp, giving to the exception of the Upper 24 UTICA SHALE (impermeable) .pO' DOLOMITE ‘1 100' TRENTON .1- 200' 1. 300' BLACK RIVER. 1; 400' Figure 6. Generalized Cross Section of "Structural" Dolomitization Vertical Scale 1 in. = 100' 25 Trenton. Other comments upon this sharp transition exist in the literature (Bishop, 1967; and Harding, 1974). This writer proposes that wells portraying dolomite concentration alone at the Trenton t0p are slightly off structure. This process of upper dolomite concentration would be a lateral mushrooming or spreading of magnesium groundwaters out along bedding planes because of the dam- ming effect by the overlying impermeable Utica Shale. Prox- imity to structure, therefore, directly relates to the degree of upper Trenton dolomitization. It becomes possible then, even in the southern part of Michigan, to be so far removed from structure that dolomite occurrence will be minor as exemplified in T28 - R6W — 14 of Figure 3. The probability of "structural" dolomite occurrence in central Michigan is difficult to assess because of the lack of well control. Control in the "thumb" area is somewhat better but might be too thin to rule out the possibility of "structural" dolomite. However, the ab- sence of upper Trenton dolomite leads one to believe that dolomitization processes may not have existed in this area. Even the most poorly dolomitized well to the south yielded 15% dolomite, resulting from mushrooming magnesium waters. Either a lack of structures, which is doubtful (Lockett, 1947; Prouty, 1976) or a lack of magnesium waters exists for this area of the state. With this evidence, the "thumb" loses much of its promise as a future Ordovician producing area. 26 Mechanisms for Ascending Groundwaters The mechanism of groundwater ascension to the Middle Ordovician carbonates is problematical. Landes (1946) believed dolomitization of the Devonian Rogers City and Dundee Formations resulted from ascending groundwaters. These waters were believed of artesian origin from out- crops of Devonian strata flanking the Basin. The same artesian system conceivably could involve Trenton-Black River rocks as well. Another potential source might be the Lower Ordovician and Upper Cambrian dolomites. "Struc- tural" dolomite calls for groundwater circulation after fracturing. The age of fracturing involving Trenton-Black River rocks is conjectural, but is believed no older than Early Silurian by Ells (1962) in the Albion-Scipio area, and of post-Osage (Mississippian) age by Prouty (1972) for most faults involving major Basin structures. Difficulty arises demonstrating post-Trenton exposures along the southern frame structures in Ohio and Indiana that might have proved sources for the dolomitizing fluids. Otherwise, outcrops here could explain the "structural" dolomite abundance in southern Michigan. The Wisconsin Arch, on the other hand, evidenced outcr0ps exposed inter- mittantly throughout the Paleozoic. These outcrops to the west allow for dolomitizing waters to flow down bedding planes and subsequently ascend fracture systems present in the overlying Middle Ordovician carbonates. 27 An analogous situation may also exist along the Algonquin Arch which flanks the eastern rim of the Michigan Basin. Problems to a western or eastern water source arise from the distribution pattern of the "structural" dolomite (Figure 3). The "absence" of "structural" dolomite in the central and "thumb" areas yet the presence of such dolomite to the far south and north prompts attention. The central and "thumb" areas also coincide with the deepest parts of the Basin in Ordovician time (Fisher, 1969). A plausible explanation is that artesian pressures drove the groundwater only to depths where increasing for- mational pore pressures curtailed the flow. The dolomitiz- ing fluids may then proceed along lines of strike creating flow to the north and south. Preliminary support for this hypothesis arises in that the 10% and 20% isopleths on the Upper 50 Feet map roughly follow the strike of the Trenton rocks (Figures 3 and 7). Another possible mechanism for groundwater ascension employs the increasing lithostatic pressure from sediment loading and the confinement of trapped magnesium-rich waters. Increasing pore pressures in the sub-Trenton rocks (especially quartz sand zones in the Lower Ordovician and Upper Cambrian) will cause the formational fluids to seek an exit and fracture systems present in the overlying car- bonates could produce these channelways. 28 Figure 7. Structure Contour Map of Trenton Limestone (after Hinze and Merritt, 1969) Contour Interval - 200 ft. ‘3 '9 :3 1° 29 If this model is applicable, "structural" dolomite should be found all throughout the Basin with a possible concentration near the depocenter where sediments are thickest. This is highly contrary to the interpretation of the Upper 50 Feet map. Rebuttal could be offered on the negative conclusion that there is a lack of structures in the central and "thumb" areas; but existing general opinion presents this area, especially the "thumb", as replete with structural features (Lockett, 1947; Ells, 1969). On the other hand, the presence of such structures would not assure their role as open channelways for ascending waters. It becomes evident that the undertaking of additional study is needed to satisfy all the requisites of an ascen- ding water theory. MAIN BODY OF TRENTON AND BLACK RIVER Lithologic Description From Samples Sample examination shows the main body of the Trenton and Black River formations to be comprised essentially of .dolomite in the far southwestern corner of Michigan's lower peninsula (Figure 9). Eastward and northward from western Michigan, a decrease occurs in the dolomite percentage until near 100% limestone is encountered in parts of St. Joseph, Kalamazoo, Allegan, and Kent Counties. This decrease presents itself as intercalations of dolomite along the "stratigraphic" dolomite-limestone facies boun- dary (Figure 8). These intercalating lithosomal bodies are best evidenced in the well at T78 - R14W - 8 in Figure 8. Lithology of the "stratigraphic" facies is brown, highly crystalline dolomite which commonly drills up fine while the basinal limestone consists of gray to brown crystalline and aphanitic limestone with a tendency towards micritic textures in the Black River. Also, to the far north and south, linear patches of dark brown crystalline dolomite delineate "structural" dolomitization zones directly over fracture systems. 30 31 mumocsom mmflomm Hmsoflmmm smoouna cofiuomm mmouo ownmmumfiuwuum .m whomfim .room 1 1 I mzoemmsan :11: W11} I .uoov an: c0wumooq :oom As 3.3 u L M 33m Hmucouflom 1%! 3.00N .OOH " :H THMUW 0HOHHHO> 1A a: .. co wzoemmas M . H AMI. 1 on coucona mo mou mBHSOA 4 . b . P L Efiumw . . . q ..o 2.578 musing 3-33-3 3.321% 3.33.? SE WE /’—— LAKE SK CLAIR CANADA LAA’! (RI! Contour Interval — 1.0% o 5 .2 lamiloc =1=r= For linear trends, only the 50% and 90% isopleths are drawn, for clarity. Figure 9. Dolomite Percent — Main Body of Trenton and Black River Section 33 Map Interpretation Examination of the main body map, (Figure 9) displays the large dolomitic facies to the west plus the fairly wide transitional band from 100% dolomite to nearly 100% limestone. This map most accurately portrays the true distribution of the regional dolomite facies. Also visible on the main body map are major structural trends to the south and evidence of some main body dolomi- tization near Seyler's prOposed fault. In comparison to the Upper 50 Feet map, the areas surrounding the major structural trends are "cleaned up" or otherwise nearly devoid of dolomite throughout the main body. Only those areas in the proximity of the fracture zones are highly dolomitic. This "cleaning up" lends further support to the observations made earlier (Figure 6) that the mushrooming effect of lateral dolomitization is largely confined to the upper Trenton beds. Again, the extremely rapid lateral transition from pure dolomite to pure limestone becomes very evident as portrayed in the Albion-Scipio and Northville Fields. As before, some contour lines have been deleted from the map for the sake of clarity. A potentially problematic well exists in the McClure State Beaver Island #1 (T38N - R10W - 27). The high incidence of dolomite here could conceivably be attributed to either "stratigraphic" occurrence, or "structural" dol- omitization northwest along the linear trend in Charlevoix 34 County (Figure 3); or possibly an extension of Seyler's proposed fault in Cheboygan and Emmet Counties. It has been contoured as "stratigraphic" in origin mainly because the dolomite occurs in different zones within the Trenton- Black River. Application of "Stratigraphic" Dolomite Models The diagenetic origin for the "stratigraphic" dolomite could be explained by one of the two models discussed in detail in the Introduction. Both models necessitate exposure of the Middle Ordovician carbonates along the Wisconsin Arch to allow diagenetic alteration of the lime- stone. Each model offers good points of support for itself but at the same time possesses drawbacks as to application. An evaporation-reflux (Bonaire) method of dolomitiza- tion was long assigned to the origin of dolomite along the Wisconsin Arch area. Periodic supratidal Trenton exposures resulting from sea level fluctuations would produce dolomi- tizing fluids flowing down into, and towards the Michigan area (Figure 2a). This movement of water from the Arch towards Michigan could explain how dolomitization extends so far east. Movement, of the fluids because of density gradients, would follow zones of high primary permeability in the limestone. This would result in a lateral transi- tional series ranging from total dolomite, to intercalating dolomite and limestone layers, and finally to pure limestone eastward. 35 In support of evaporation-reflux the possibility of a large lagoon in western Michigan was suggested by Jodry (1957) as having existed during Traverse deposition. A western Michigan barrier (Figure 10) was postulated on the basis of facies changes in the Middle Devonian Traverse Group. Further support for a barrier stems from gravimetric data by Logue (1954) delineating anomalous gravity highs in areas which correspond closely to the Traverse facies changes. Proof of a Trenton or directly post Trenton bar- rier is not possible yielding to poor Ordovician well con— trol in western Michigan but a barrier, if present, could have isolated the area between Wisconsin and western Mich- igan allowing evaporation and thus an elevation of the Mg/Ca ratio in the lagoonal waters. A more recent study of the Wisconsin dolomite by Badiozamani (1973) disagrees with the evaporation-reflux model and pr0poses another mechanism for dolomitization, termed Dorag. Lengthy discussion of this model is included in the Introduction. Badiozamani, from outcrop examination, cited the lack of supratidal features (mud- cracks, ripple marks, and evaporites) significantly hindered application of an evaporation-reflux model to Wisconsin. Sample descriptions for wells of eastern Wisconsin strongly support Badiozamani's contention concerning the absence of evaporites. 36 '30 I; -+.- ‘T—J._._-+-+-L.—‘-+-!'—1'+-'_ 'E. . +“f‘1'f—+l - *~ +-T LII! I 7. CA A M All! I'll Figure 10. Proposed Barrier System (after Jodry, 1957) 37 During Dorag dolomitization, diagenesis occurs in the brackish zone of mixing waters. The location and size of the brackish water lens depends upon fluctuations of sea level in transgressive and regressive sequences. Therefore, spreading of the "stratigraphic" facies to western Michigan would depend solely upon large regressions allowing the brackish lens to extend far eastward. In this regard, evap- oration-reflux gains an advantage over the Dorag model in that the former offers a more direct mechanism for forcing dolomitizing fluids eastward. It is worthy to note that Badiozamani portrays the largest regression and therefore most widespread dolomiti- zation as occurring near the end of Galena Dolomite time, which is equivalent to the Trenton. This widespread "stra- tigraphic" lithosome aids in explaining why the 100% dolo- mite line on the Upper 50 Feet map extends farther eastward than the comparable line on the Main Body of Trenton-Black River map. This upper lithosome through its high stratig- raphic position thus might be mistaken for the upper Trenton "structural" dolomite, unless other factors are considered. Again, the Main Body map is the more accurate portrayal of the regional diagenetic facies boundary. Badiozamani's lack of supratidal or lagoonal features leads the present writer to accept the Dorag dolomitization model to account for the "stratigraphic" facies, although one cannot ignore totally the considerable support for evaporation-reflux. Future studies must take place before the question can be answered satisfactorily. ECONOMIC IMPLICATIONS Perhaps the foremost contribution of this study with respect to future oil production is that it has delineated areas where not to prOSpect for Trenton oil and gas. The sparsely drilled central Michigan area is relatively un- known but the slightly better well controlled "thumb" area contrasts so strikingly with the dolomitized area to the north and south that appreciable doubt is placed on the economic future of this area. Closer attention to criteria of faulting in oil fields developed in younger formations could brighten its petroleum potential however. Also expected to yield little oil and gas is the "stratigraphic" facies of western Michigan. "Stratigraphic" dolomitization predates the "structural" dolomitization. Later "structural" alteration would probably only serve to seal up any porosity left by the "stratigraphic" process. Also, since alteration is believed to be pre-consolidation for "stratigraphic" dolomite, any porosity created was probably since obliterated by sediment loading while capable of plastic yielding. This "stratigraphic" area mainly con- sisting of Berrien, Van Buren, Cass, and western Allegan counties should be considered a low potential area for Trenton oil. Based upon the results of this study, two areas appear more likely than others for future discoveries. As dis- cussed earlier, the lateral transition from dolomite to 38 39 limestone is so sudden that existing dry Trenton tests could lie in fairly close proximity to other Albion-Scipio type fields and show little evidence of it. The best ex- ploration technique for the highly drilled southern counties might be to determine and plot the dolomite percentage for all possible wells. Wells with a high dolomite content (90% or greater for the upper 50 feet and 25% or greater for the main body) might warrant offset wells in search for ad- jacent fracture zones. This method could prove successful for the southern counties as well control is so dense. How- ever, exploration for Trenton oil trends of the Albion-Scipio Field type is high risk. This risk stems from the field's resistance to geophysical prospecting and the rapid facies changes. The writer contends that this procedure represents the most promising next step for exploration of Ordovician oil accumulation in Michigan. This study also lends considerable support to Seyler's (1974) contention of faulting in Emmet, Cheboygan and Presque Isle Counties. Also the writer maps a linear trend in Charlevoix County (Figure 3) which may represent faulting. Well control is poor in comparison to that of southern Mich- igan. A dolomitic upper Trenton does present itself along these prOposed trends and becomes especially evident in the Emmet County well (T37N - R4W - 34). If the mushrooming hypothesis is valid, this well most probably lies in close proximity to a major fracture system. Unfortunately, no more can be told until additional wells yield more infor- mation. However, a good potential could exist for this area. CONCLUSIONS It would appear that the magnitude and form of a dol- omitic body directly relates to its mode of origin. Two distinct types of dolomite exist, classified on their origin as "structural" and "stratigraphic". They may be separated generally on their geometry in that "structural" dolomite is localized and linear, with the "stratigraphic" dolomite being more regional in extent. It is concluded from this study that two origins for the dolomite exist and that the origin of "stratigraphic" dolomite calls for an Ordovician age and the "structural" dolomite likely a mid-Paleozoic age. It is believed that dolomitizing fluids during "structural" dolomitization processes ascend fracture systems. Evidence for the ascending nature is provided by high concentrations of dolomite in the upper Trenton. A damming effect by the overlying impermeable shale results in a mushrooming or spreading of the fluids and therefore, dolomite accumulation near the Trenton-Utica contact. Approximate proximity to a fracture system can possibly be estimated by the dolomite percentage present. Proximity to a fracture system implies proximity to possible produc- tion so this could be a valuable tool in petroleum explor- ation. The groundwaters are believed to be ascending artesian waters from the Wisconsin Arch or possibly the Algonquin Arch 40 41 exposures of sub-Trenton beds. Sufficient research has not been performed to make definite statements concerning the driving mechanism of these ascending waters. The facies boundary separating the "stratigraphic" dolomite from the basinal limestone is not gradational but sharp and exhibits an intercalating character. Large beds of dolomite reach down off the Arch and extend out into the state of Michigan. The Dorag dolomitization theory applies very well to the Wisconsin dolomites but more de- tailed studies must occur before evaporation—reflux can be discounted altogether. It also appears that the future of Ordovician oil pro- duction is restricted to southern Michigan and the northern tip of the lower peninsula. Because of various circum- stances, other portions of the state possess low potential for Ordovician strikes. l) 2) 3) 4) 5) RECOMMENDATIONS FOR FUTURE STUDY Detailed work on the possible mechanism for groundwater ascension would be helpful in accounting for the lack of dolomite in the deeply buried rocks of the "thumb" area . Well sample and outcrop studies for Wisconsin and western Michigan may shed additional light on the Dorag versus Bonaire dolomitization controversy. A more detailed study of the southern "structural" dolo- mite area would aid in future oil and gas exploration. Detailed study of the lateral lithologic transition along known producing fields may aid in the prediction of future Middle Ordovician oil fields. A closer attention to fault patterns that may exist within the Basin could help in delimiting the more likely areas of linear trend develOpment. 42 BIBLIOGRAPHY Annual Statistical Summary 22, Michigan's Oil and Gas Fields, 1974: Michigan Department of Natural Resources, Geo- logical Survey Division. Badiozamani, K., 1973, The Dorag Dolomitization Model - Ap- plication to the Middle Ordovician of Wisconsin: Journal of Sedimentary Petrology, v. 43, no. 4, pp. 965- 984. Bishop, W. C., 1967, Study of the Albion-Scipio Field of Michigan: Unpublished Master's Thesis, Michgan State University. Burgess, R. J., 1960, Oil in Trenton Synclines: Oil and Gas Journal, v. 58, no. 33, pp. 124-130. Buschbach, T. C., 1964, Cambrian and Ordovician Strata of Northeastern Illinois: Illinois State Geol. Survey, Report of Investigations 218, 90 p. Calvert, T. C., 1974, Sub-Trenton Structure of Ohio: Am. Assoc. Petroleum Geologists Bull., v. 58, pp. 957-972. Cohee, G. V., 1948, Cambrian and Ordovician Rocks in the Michigan Basin and Adjoining Areas: Am. Assoc. Petroleum Geologists Bull., v. 32, pp. 1417-1448. Deffeyes, K. 8., 1965, Dolomitization of Recent and Plio- Pleistocene Sediments by Marine Evaporite Waters on Bonaire, Netherlands Antilles: Soc. of Economic Paleontologists and Mineralogists, Special Publication #13, pp. 71-88. Egleston, D. C., 1958, Relationship of the Magnesium/Calcium Ratio to the Structure of the Reynolds and Winfield Oil Fields Montcalm County, Michigan: Unpublished Master's Thesis, Michigan State University. Ekblaw, G. E., 1938, Kankakee Arch in Illinois: Geol. Soc. of America Bull., v. 49, pp. 1425—1430. Ells, G. D., 1969, Architecture of the Michigan Basin: Mich. Basin Geol. Soc. Annual Field Excursion, pp. 60-88. , 1962, Structures Associated with the Albion-Scipio Oil Field Trend: Michigan Dept. of Conservation, Geo— logical Survey Division. 43 44 Fettke, C. R., 1948, Subsurface Trenton and Sub-Trenton Rocks in Ohio, New York, Pennsylvania, and West Virginia: Am. Assoc. Petroleum Geologists Bull., v. 32, pp. 1457- 1492. Fisher, J. H., 1969, Early Paleozoic History of the Michigan Basin: Mich. Basin Geol. Soc. Annual Field Excursion, pp. 89-93. Green, D. A., 1957, Trenton Structure in Ohio, Indiana, and Northern Illinois: Am. Assoc. Petroleum Geologists, v. 41, pp. 627-642. Hamil, D. F., 1961, A Detailed Chemical Analysis for Calcium and Magnesium of the Sun Oil Company, Peterson-Howard Well #1 Core Sample: Unpublished Master's Thesis, Michigan State University. Harding, T. P., 1974, Petroleum Traps Associated with Wrench Faults: Am. Assoc. Petroleum Geologists Bull., v. 58, pp. 1290-1304. Hinze, W. J. and D. W. Merritt, 1969, Basement Rocks of the Southern Peninsula of Michigan: Mich. Basin Geol. Soc. Annual Field Excursion, pp. 28-59. Hussey, R. C., 1950, The Ordovician Rocks of the Escanaba- Stonington Area: Mich. Basin Geol. Soc. Annual Field Excursion, p. 24. Jodry, R. L., 1954, A Rapid Method for Determining the Magnesium/Calcium Ratios of Well Samples and Its Use as an Aid in Predicting Porosity in Calcareous For- mations: Unpublished Master's Thesis, Michigan State University. , 1957, Reflection of Possible Deep Structures by Traverse Group Facies Changes in Western Michigan: Am. Assoc. Petroleum Geologists Bull., v. 41, pp. 2677- 2694. Kirschke, W. H., 1962, A Petrographic Core Analysis of the Lower and Middle Ordovician Rocks, Pulaski Fields, Jackson County, Michigan: Unpublished Master's Thesis, Michigan State University. Landes, K. K., 1946, Porosity Through Dolomitization: Am. Assoc. Petroleum Geologists Bull., v. 30, pp. 305-318. 45 Lockett, J. R., 1947, Development of Structures in Basin Areas of Northeastern United States: Am. Assoc. Petroleum Geologists Bull., v. 31, pp. 429-446. Newcombe, R. B., 1932, Oil and Gas Fields of Michigan: Michigan Department of Conservation, Geological Survey Division. Nurmi, R. D., 1972, Upper Ordovician Stratigraphy of the Southern Peninsula, Unpublished Master's Thesis, Michigan State University. Pirtle, G. W., 1932, Michigan Structural Basin and Its Relationship to Surrounding Areas: Am. Assoc. Petroleum Geologists Bull., v. 16, pp. 145-152. Prouty, C. E., 1976, Michigan Basin - A Wrenching Defor- mation Model?: Abs. with Prog., Geol. Soc. of America, v. 8, no. 4, p. 505. , 1972, Michigan Basin Development and the Appalachian Foreland: XXIV Annual Session, International Geological Congress, Montreal, Canada, p. 72. Rooney, L. F., 1966, Evidence of Unconformity at Top of Trenton Limestone in Indiana and Adjacent States: Am. Assoc. Petroleum Geologists Bull., v. 50, pp. 533-, 546. Seyler, D. J., 1974, Middle Ordovician of the Michigan Basin: Unpublished Master's Thesis, Michigan State University. Stieglitz, R. D., 1975, Sparry White Dolomite and Porosity in Trenton Limestone (Middle Ordovician) of North- western Ohio: Am. Assoc. Petroleum Geologists Bull., v. 59, pp. 530-533. Stonehouse, H. B., 1969, The Precambrian Around and Under the Michigan Basin: Mich. Basin Geol. Soc. Annual Field Excursion, pp. 15-27 Tinklepaugh, B. M., 1957, A Chemical, Statistical, and Structural Analysis of Secondary Dolomitization in the Rogers City - Dundee Formation of the Central Michigan Basin: Unpublished Ph.D. Thesis, Michigan State University. Young, R. T., 1958, Relationship of the Magnesium/Calcium Ratio as Related to Structure in the Stoney Lake Oil Field, Michigan: Unpublished Master's Thesis, Mich- igan State University. APPENDIX Location Map and Well Listings Q9 _+__ Q8 T * 27 LE KACAWOD 0300 -1 | I LAKE $7.0LAIR CANADA LAKE ERIE O 6 I2 lemma :2: Figure 11. Well Location Index Map LOCATION 1N-2E-13 1N-5W—18 2N-7W—22 2N-9W-34 2N-12W—10 3N-1E-14 3N-4E-35 3N-9W-4 3N-13E-34 3N-16E-31 4N-7E-9 4N-7W-20 4N-15W—28 5N-2E-5 5N-3E-15 5N-15W-30 6N-12E-18 6N-16E-6 7N-9W-35 7N-12W-30 7N-16W-36 9N-8E-4 9N-13W-16 9N-15E-16 lON-16W-8 llN-14E-21 12N-13W-11 12N-17W-20 13N-1W—21 13N-11E-16 l3N-13W-12 14N-4E-2 15N-15E-26 l6N-16W-11 21N-17W—14 PERMIT NO. 22607 21769 21999 20732 23685 10011 2179 18526 22825 24961 22665 23572 21655 22379 23375 21529 22534 25024 3090 9166 5689 24079 537 25357 309 29157 13816 18666 23849 25609 411 5441 29191 22801 14 48 DOLOMITE % UPPER 50' DOLOMITE % MAIN BODY 26.9 53.3 LOCATION 23N-3E-28 24N-2E-28 24N-13W—8 29N-4W-2 30N-11W—6 31N-9E-5 32N-6E-l8 32N-8W—19 34N-2W—1 34N-5E-20 34N-7W-14 35N-2E-29 37N-4W—35 38N-10W-23 18-8E-7 18-8E-16 18-12W-32 15-14W-16 2S-1W-10 25-5E-28 2S-6W-14 3S-4W-15 3S-8W-13 4S-2E-9 4S-5E-14 4S-10W—11 4S-18W-10 SS-3W-4 SS-7E-22 SS-7W-l7 SS-15W-29 6S-2E-25 6S-2W-7 6S-6E-30 6S-11W-27 PERMIT NO. 28456 25099 24557 25873 22627 25690 2960 22639 14936 22638 29119 27199 28212 23435 12589 19421 789 28590 22483 19202 864 21432 22352 22017 23921 23004 6126 22201 23532 21968 23876 23751 21834 8449 21155 49 DOLOMITE % UPPER 50' 19.5 48.1 100.0 100.0 100.0 25.0 44.8 15.0 99.0 52.0 48.0 65.3 81.0 100.0 22.7 96.2 59.2 100.0 18.5 29.3 99.0 91.0 DOLOMITE % MAIN BODY A 50 DOLOMITE % DOLOMITE % LOCATION PERMIT NO. UPPER 50' MAIN BODY 6S-17W-14 23545 100.0 100.0 7S-4W-29 21856 93.0 94.9 7S-7W-10 21893 90.1 4.7 7S-9W-15 23389 53.0 8.3 7S-14W-8 23829 95.5 46.2 8S-1E-3 23276 97.1 14.8 8S-4E-18 16693 26.8 .2 8S-6E-31 23373 30.4 1.7 88-20W-8 6364 100.0 100.0 HICHIGQN STRTE UNIV. LIBRARIES l1 MN" I 1 312931035 6492