y I LIBRARY 'LllJ‘LL‘QI‘WHUJ‘IIM M 9% Unijrirsit‘y This is to certify that the thesis entitled FAULT PATTERNS IN SOUTHEASTERN MICHIGAN presented by Jeanne Ann Fisher has been accepted towards fulfillment of the requirements for Masters degree in Geology Date February 27, 1981 0-7639 1 .. Mm i lair-fix- «(199 W ' 9 2w 0492221 I . “p (138 ”37 ‘ 4 v‘. 62/ III! / M“ £7 (1 LATE KEWEENAWAN — foundering shallow marine protoceanic basin IHERMOTECIUNIC JACOBSVILLE FLUVIAL-DELTAI SEA LEVEL VOLCANlc-CLASTIC ssauaucs g MARINE FACIES c TRANSGRESSIVE MARINE SHORELINE :1 . . ‘ %u.i. ..,,.,. ~I- - """ .'~'-51w- E==€==z ' . .. .... .~.- - - e . :V p | 1 Fig. 10. Keweenawan rifting and associated igneous activity (Fowler and Kuenzi, 1978). 21 .. “95' r T -90' T r -es° I II I I I I I I I . I , I i I -. MIDCONTINENT GRAVITY HIGH *50‘ “‘5‘ +40' Fig. 11. 1973)- .r .... I, ---- HYPOTHETICAL TRANSFORM FAULTS V I-—+.-.om or GRAVITY HIGH NORMAL? '\ TO smxe I . ’~‘\ —4 I ' a, \- ‘f? I rmT' 'V'w' l ;I l I 1' l I J L .900 ~85“ Midcontinent gravity high (Chase and Gilmer, 22 that the trend of the Michigan arm of this triple junction was controlled by pre—existing lines of weakness in the Precambrian basement. The integration of gravity and magnetic maps with structure and isopach maps can be used to establish the character of deep basement structure in Michigan. Earthquake epicenters were plotted to show where deep basement seismic activity may correspond with known fault locations, or indicate the locations of faults not yet mapped (Fig. 12). These epicenters may yield clues con— cerning the location of unmapped faults, or they may reinforce the location of known faults. This evidence of present day earthquake activity emphasizes the periodic reactivation of movement along these old fault trends. In summary, it is prOposed that the basement rock of Michigan exhibits a faulting pattern which had its genesis early during the Precambrian. This pattern is a product of ancient deformation. Once these lines of weakness were developed, they remained unchanged throughout the geologic history of the region. Subsequent deformation, regardless of the direction from which it originated, resulted in shearing and slipping of fault blocks, and vertical move- ments along these pre—existing lines of weakness. This pattern of ancient breakage is what controls structure in southeastern Michigan, and probably the basin as a whole. The nature of this pattern should be expressed in the trends of faults, folds, and possibly the orientation of 23 / \ / 0!: l872 om \\ l9l8 II o l967 \ I ’ \ N I ‘\\' fbfi?3y I: was 0 l883 / o |899 Om I947 O 6 I! I. all” ==x== Fig. 12. Earthquake epicenters and faults in southeastern Michigan. Modified Mercalli scale intensities greater than III are shown (Consumers Power, 1978). 24 the Mid-Michigan gravity high, transecting Michigan's Lower Peninsula. Structure maps are used to delineate structural trends, and.is0pach maps are used to determine times when movement has occurred along faults. Three cross-sections were made and included in Appendix A that illustrate the change in elevation across the Bowling Green Fault, the Lucas—Monroe Monocline, the Howell Anticline, and the Sanilac fault. Elevations were taken from the Dundee structure map, which is the structure map with the greatest control. Ultimately this information may contribute toward a more complete understanding of the genesis of the Michigan Basin, and the structures in Phanerozoic sediments within it. Error Analysis There are basically two procedures in the preparation of data for this study which allow for the introduction of error. First, the correlation of formation tops may vary between investigators. The pinpointing of a top is usually accurate within two to five feet. Poorly recorded or printed logs, on which the graph is obscured, may intro- duce larger errors. Formation tops may be inaccurate where boreholes have been deviated somewhat, or whip-stocked. In most cases, slanted boreholes (which would exaggerate thicknesses and the depth of formations) are compensated for after deviation surveys are run. Some minor error is introduced regardless, as few wells are perfectly vertical. Secondly, contouring is an individual interpretation of a 25 rock surface or thickness. In areas where control is sparse, interpretations by two different researchers can be very different. These are the factors which can introduce variability into the data, and its interpretation. The maps have the densest control, and therefore, the greatest accuracy in St. Clair and Macomb Counties where extensive drilling has been done in the area of the Niagaran reef trend. Good control exists in Hillsdale and Jackson Counties where the southeastern portion of the Albion-Scipio field is located, and along the axes of the Lucas—Monroe Monocline and Howell Anticline. Control is sparse in and around the Detroit MetrOpolitan area, and in Genesee, Lapeer, and Oakland Counties. Control is absent on the Dundee and A-2 carbonate maps, where these formations suborOp in Monroe and Wayne Counties. Previous Work The prominent structural trends in Michigan have long been recognized, and many theories offered for their origin. Early studies based on maps drawn with significantly less data than is available today have become somewhat dated; yet have provided a broad foundation for subsequent work. Robinson (1923) prOposed that the structural elements observed in the Michigan Basin were folds resulting from vertically acting forces rather than compressional ones. He described five fold-types that could be formed in this manner: domes (genetically related to batholiths and laccoliths), radial linear folds, concentric terrace folds, 26 linear terrace folds, and monoclinal folds related to deep- seated faulting. Of these types, radial linear folds (Fig. 13) as well as concentric and linear terrace folds, may account for smaller features seen in structure maps of sedimentary formations. These fold types, which according to Robinson, are the result of intermittent subsidence and downwarping, are probably not responsible for the major, well-defined structural trends that dominate the south— eastern Michigan Basin. This is also the opinion of Pirtle (1932) who says these trends were not formed as a result of settling. Pirtle (1932) sought to explain structure in the basin in relation to the positive areas surrounding it. He believed the Wisconsin, Kankakee, and Cincinnatian arches to have played a role in the depositional and structural history of the Michigan Basin. He states that the basin had a Precambrian origin and that the structures within are "controlled by trends of folding or lines of structural weakness which originated in the basement rock". Citing the oblong trend of the basin, more evident in the older formations, he suggests the basin formed as a geosyncline paralleling a mountain range, the remnant of which is seen today as the Wisconsin Arch. These Precambrian mountains eroded to their igneous and metamorphosed core, shedding sediment into the Michigan Basin. Pirtle recognized the dominant northwest-southeast trends in the basin, as well as weaker subordinate trends running southwest—northeast. 27 c ..I..‘ a . . ‘ 5 O I I ”..‘ . - GAD. . I ‘ f' A n \. I.‘ Ii 5 v flirty .' OItO’A ! "Ar-nu Fig. 13 . 1923). Radial fold pattern (after Robinson, 28 These lesser trends are evident in southwest corner and in the center of the basin. He concluded that folds were formed where horizontal forces caused movement along fractures in the basement which had been formed by vertical forces early in the history of the basin. One of the most intense periods of horizontal stress occurred near the end of Middle Mississippian time. Newcombe (1933) was the first to endeavor to synthesize all available information into a superb series of maps and a comprehensive report of the geology of the Michigan Basin in his Michigan Geological Survey publication, "Oil and Gas Fields of Michigan". This study, for its time, was an excellent account which is still sought for its clear presentation, predictions, and hypotheses, many of which have been proven accurate by new data from the thousands of wells drilled since it was written. For example, Newcombe's structure map of the Traverse formation is still valid. Among his hypotheses is the suggestion that the Lake Superior Basin is a rift valley that connects with the Michigan Basin--an idea long before its time and later supported by geophysical surveys conducted by Hinze in 1963. Newcombe considered the basin to have originated during the Precambrian, and that structure was related to zones of weakness that developed in basement rock in Keweenawan time. Downwarping of blocks in the basement came about due to a change in direction of tangential forces transmitted horizontally through "deep-seated 29 rocks", i.e., forces originating from events as distant as the Appalachian orogeny. He believed the major stresses which created the synclinal basin to have been exerted primarily from the northeast prior to Keweenawan time, but that the basin's present character and shape were not developed until later. Lockett (194?), like Pirtle, favored a relationship with surrounding positive areas as a cause for the forma- tion of the basin and the structures within it. He suggests that where the Wisconsin and Kankakee Arches lie today was once a mountain range comparable to the Alps or the Rockies. As this range eroded, a substantial sediment load collected in the surrounding low areas, and caused them to sink. The mountains were eroded to their core prior to the Paleozoic, but the deep roots of the mountains kept the areas positive. This was possibly an effect of isostatic rebound as well. Lockett argues that the northwest-southeast trends in the southeast corner of the basin formed during subsidence as fractures paralleling positive areas to the northeast and southwest. The sediment load then caused differential downwarping and step-faulting to occur toward the center of the oblong basin. Neither Pirtle nor Lockett take into account the lack of geosynclinal-type sediments in the Michigan Basin. There is a conspicuous lack of coarse conglomerate that should exist if the erosion of the Wisconsin range was to have initiated the subsidence of the basin. 3O Cohee (1944-19u8) prepared an excellent series of maps on the Michigan Basin, including structure maps, is0pach maps, and numerous cross-sections based on outcrOps and the well data available at the time. This work is summarized in a 1958 publication by Cohee and Landes. In this article they acknowledge the dominant northwest-southeast trend, noting that no dominant trend exists specifically in the southwest area of the basin. They stress that comparison of various structural horizons over the Howell Anticline reveal a lateral movement of its axis. The contour axis on the Dundee is 1 % miles west of the axis as it appears on the Niagaran. Cohee and Landes consider the basin to have begun subsidence in the Late Silurian, with inter- mittent folding occurring throughout the Paleozoic, and the major folding to have taken place in Late Mississippian time. Hinze (1963) examined the regional structure of the Michigan Basin from gravity and magnetic maps made from observation points covering the entire Southern Peninsula of Michigan. Observation stations were established at the corners of townships and at areas of special interest throughout the basin. The resulting gravity and magnetic maps are representative of geological conditions primarily in the Precambrian basement rock. An anomalous gravity and magnetic high transects the basin from the northwest to the southeast, which at least in southeastern Michigan can be seen to parallel structure. The causative mass 31 for this anomaly is suggested to be basic rock in the base- ment complex of the late Precambrian, possibly of Keweenawan age. This suggests a relationship between the Lake Superior basin, and the Michigan Basin. As the form and magnitude of this major gravity and magnetic anomaly is similar to the anomalous Mid-Continent gravity high, the Michigan anomaly may be an extension of this feature. In later papers, Hinze and Merritt (1969) and Hinze, gt El- (1975), it is suggested that the anomalous area delineates a rift arm. This arm was part of a triple junction, according to Halls (1978), the other two arms of which are represented by the Mid-Continent gravity high, and an area with a weakly develOped positive gravity anomaly, trending north- east from the eastern end of Lake Superior. If rifting was initiated, mafic material may have welled up along the faults of the rift valley, filling the graben. When rifting aborted, the denser rock remained to produce an unusually high gravity and magnetic anomaly. Ells (1969) summarized all previous work done in the Michigan Basin. Basing his structural analysis on his own maps, and those of Cohee (1944-1948), he discusses the basin's origin and framework, focusing on the Howell Anti— cline. He declines to place a major fault along this dominant feature, but instead suggests it is formed by a series of minor faults. In an area he designates as the Washtenaw Anticlinorium, he postulates the existence of three major fault blocks which have moved relative to one 32 another in a vertical manner (Fig. 14). This he says is the cause of structure in the southeast; and may be the key to structure in the basin as a whole. Fisher (1969), in an examination of the early Paleozoic history of the basin, demonstrated with iSOpach maps that the Michigan Basin began as an embryonic basin during Cambrian time, evolving into a true basin of its present shape and size in the Ordovician, with significant sub- sidence in the Mohawkian and the Cincinnatian. The Algonquin Arch was intermittently positive during the Early and Middle Ordovician (Sanford, 1961), but by Cincinnatian time (Late Ordovician), it was no longer a positive feature capable of influencing patterns of sedimentation. The basin at this time was relatively shallow, with a center of deposi- tion in the Saginaw Bay Area. In the Early Silurian, the shallow basin accumulated a thin blanket of shales and carbonates, and by the Middle Silurian had developed a massive barrier reef around its margin. Isopachs of the Niagaran have been interpreted to indicate that these marginal reefs starved the interior of the basin, as a marked thinning is seen toward the center of the basin. The major sinking of the basin was during Salina time, when a thick accumulation of carbonates, evaporites, and shales appear in the column. Following deposition of the C-shale, there was a regression of the sea from the southeast platform in Michigan, which is accentuated by mum. -mju a o 59: zuumo 02338 ozuE I , 0.10 \ 05.8.2053 2-. ..II- I-. .Iflesfiz. us; 5.3 o. I l / \7,\\/,...7h/.L./l. «J ..le :08“; \ cites». .2:qu cotnEuu ... :cmad. o» 1.8.5.: arms . s 2...; ...... .898 o 0 a .3» 8.5.5305 n j — _ _ u — _ 8.5 8. co NA we 5 o nsomo 20;.me% MI... .10 0.0;. wIk ZO mmDOPZOo Esflposflaofipfiw smcopswmz ......2.._n . Hm o o >0 EMV'I NVSIHOIW .25.: 2......ch .13.):— azxu: .2 .. J... I owed .ma my ......r... 1 .EEE : ...... .335... r... 5. 1:5. :0er 2.. ... :3! ..f $.- Tb. .rEIofi...‘ :ZE .5. .... .5? ....» F4 run-e. u as! go 5.3 ...... a ...: .21? ...«ZI re. 5: Ir. to?! 3.... ..— .}...é ...... : ..c. r. o uowo 23.102.40.54 azukzmdl status 3‘ 3.0.5:... . 2.2503 .005 \ \ MAI mydDdu quimmdm . 1_ _ XUOJm Z < mofirm WQCKKDm zofiocw ZSUSOOKO v.59: . wad UJ¢UM OZ §3_KOZ_I_O”HZ< >>> do ._.2m...g_o_OI_m>mo 34 Pre-Devonian erosion, and extensive leaching of the Salina salts. Intermittent uplift during the Early Devonian created several major unconformities. Following this, the rate of sinking increased and is marked by a thick Middle and Upper Devonian sequence of carbonates and black shales. Fisher (1969) believes the structure of the Michigan Basin is controlled by a rectilinear pattern of faulting in the basement rock that changes direction regionally along broad curving trends. Such a pattern can be seen in tectonic maps of the Canadian Shield (Fig. 15). Intermittent movement along these faults throughout the Paleozoic formed both the northwest-southeast trends that dominate the basin structure, and the weaker northeast-southwest trends. Brigham (1971) used computer contoured maps of various units and structural horizons in a study of southwest Ontario and southeast Michigan. This work includes a general review of the history, structure, and stratigraphy of that area. Nurmi (1972), in a regional study of the Ordovician in Michigan, subdivided the Cincinnatian formation into six units. The oldest of these, the Utica shale has long been accepted as a distinct unit. Nurmi found that the Upper Cincinnatian could be divided into five additional units that are recognizable throughout the state. Although they do not have a common thickening pattern individually, is0pached together as a unit, a center of deposition appears 35 )pN - . HURON“) per. 2'\ ‘ ‘2 \ “MN-m“ f \ I / \ , I .3/ / E S \ ouch e EF‘E/ '. ‘ DU“ ,. W‘an . LP} \ Scale 1:5,000.000 . . " . ) ’ “\3"// a 88 - 84” 5‘ Fig. 15. Rectilinear pattern of faulting in the Canadian Shield (Tectonic map of Canada, 1969). 36 north of Saginaw Bay. This was the typical center for deposition in the basin during Paleozoic time. Catacosinos (1973) studied the Cambrian units of Michigan in an attempt to solve problems of stratigraphy concerning the Cambrian-Ordovician boundary. In southwest Michigan, the Upper Cambrian Trempealeau is distinct from the Ordovician Prairie du Chien. Northward in the state, this separation is obscured and a thick sand deposit is encountered in the section, which has no counterpart to the south. This transition is one that is seen elsewhere in the central United States. The cause of this change has been recognized by stratigraphers as the shift from marine carbonate facies to thick near—shore sandstones produced by erosion from mountains of the Wisconsin High- land and the Canadian Shield. Catacosinos prOposed that in Michigan the terms Trempealeau and Prairie du Chien be drOpped and the term St. Lawrence substituted. This would avoid controversy that would arise in attempting to trace a formation boundary that is essentially lost in a transitional sequence. Seyler (1979) said that the basin in its present form began in Middle Ordovician time. He described the formation of the Albion-Scipio field and another structure in the northeast corner of the basin, as having been the result of wrench faulting during Trenton time. Mesolella (1974) published a regional study of the Niagaran and the pinnacle reefs associated with it, in 37 which he discusses the Lower Salina sequence as well. He presents an excellent set of maps of the carbonate and evaporite units deposited during Middle to Late Silurian time. Autra (1977), studying the same units as Mesolella, showed they were deposited during a period of rapid non-uniform subsidence of the basin, and suggested that the north half of the basin subsided 1,000 feet more than the south half during the same period of time. Lilienthal (1978) constructed a series of cross- sections in the basin, radiating from the Sparks deep test in Gratiot County. These cross-sections are the first to be based on geophysical well logs, and were used extensively for the correlation of formation t0ps in this study. STRATIGRAPHY Radiometric dating of crystalline material from three deep tests shows that the Precambrian basement rock which underlies the southeastern part of the Michigan Basin to be on the order of 0.9-1.0 billion years old. This correlates with metamorphic events associated with the Grenville Orogeny and also with Keweenawan rifting. The majority of the drill tests have encountered granite or granite gneiss, but the basement lithology is considered more varied (Hinze and Merritt, 1969). Geophysical surveys have yielded highly irregular gravity and magnetic responses possibly caused by the presence of mafic material. This is suggested to be the source of the Mid-Michigan gravity anomaly (Hinze and Merritt, 1969). The Phanerozoic sediments overlying the basement reach an estimated thick— ness of 15,000 feet. They range from Cambrian sandstones to Jurassic red beds. All periods, Cambrian through Pennsylvanian, are represented, as well as Jurassic. The sediments are largely a sequence of carbonates and shales, with lesser amounts of evaporites and sandstone (Brigham, 1971). The Trenton formation of Middle Ordovician age is composed of light-brown to brown and gray biolastic lime— stone of fine to medium crystallinity (Cohee, 1945), (Fisher, gt al., 1969). It also contains thin beds of black carbonaceous shale with associated nodules of black 38 39 chert. In the Southern Peninsula it ranges in thickness from 200 - 475 feet. The Trenton becomes more argillaceous in the northern portion of the Southern Peninsula, but in general throughout the basin the shales are more abundant near the base (Lilienthal, 1978). Dolomitization may occur in the section, but it is usually confined to the axes of major anticlines and to faults such as the Albion-Scipio. This illustrates the importance of the Trenton group as a major source of oil and gas in Michigan. The contact of the Trenton with the overlying Utica shale is perhaps the most easily recognizable and reliable marker on log curves, due to the sharp break from the highly radioactive Utica shale. The Utica shale is a uniformly gray to dark gray shale with minor amounts of greenish-gray and black shale in its upper portions (Lilienthal, 1978; Fisher, EI.§l-: 1969). In southeast Michigan, some limestone stringers occur in the middle of the unit. The tOp of the Utica is not well defined. In many places it appears gradational into lighter gray shales, with a weaker radioactive response. It is quite variable in thickness, ranging from 200 - 400 feet in southeastern Michigan. It can be seen to thin anomalously in small localized areas of southeastern Wayne County. The Upper Cincinnatian Series is the uppermost sequence of Ordovician sediments. It is composed of red, green, and gray shales, argillaceous and fossiliferous limestone, and 4O dolomite. It ranges in thickness from 250 to nearly 600 feet in the Michigan Basin. Individual beds undergo facies changes in various portions of the depositional area. However, Nurmi (1972) and Lilienthal (1978) prove that with the use of gamma-ray logs, the series could be divided into six units, including the Utica shale, which are trace- able over a large part of the basin. A red shale in the uppermost zone of the Cincinnatian is sometimes identified as the Queenston shale, and gives a reliable tOp to the sequence. Where dolomite stringers occur instead, the tOp is more difficult to distinguish on logs and in samples. The A-2 carbonate of Salina age consists of gray to brown limestones and dolomites. Where it overlies the reef complex on the margin of the basin it is usually dolomite (Lilienthal, 1978). Within the A-2 carbonate, shale and anhydrite beds occur in the center of the basin, but these are poorly developed. The thickness of the A—2 carbonate averages 150 feet in the central basin area, but thins to 50-75 feet over the reef areas at the basin's margin. Where the A-2 carbonate has added to pinnacle reefs, it may thicken to as much as 275 feet. These anOmalous values are highly restricted in area, the largest pinnacle reef in Michigan being approximately 10 miles long, and three to four miles wide. The B-unit is predominantly a thick salt layer with interbedded shales, anhydrite, and dolomite toward the tOp. It is over 475 feet thick at the center of the basin, 41 but thins to 50 feet toward the southern reef complex as the lower salt pinches out (Lilienthal, 1978). Along the southeastern margin, the distribution of the B—unit becomes irregular, probably as a result of solution. Its generally low radioactive response makes it easily recognizable on log curves. The C-shale is a greenish-gray and partially dolomitic shale (Brigham, 1971) often containing anhydrite nodules (Fisher, gt g;., 1969). The C-shale is notable for its comparatively irregular thickness, ranging from 50-200 feet, its widespread occurrence, and its constant radioactive character. Some variations in thickness are found in a small area of southern Michigan where it thickens to approximately ZOO feet, and in extreme northern Michigan where it thins markedly (Lilienthal, 1978). Irregularities in its thickness are probably controlled by solution and or collapse of the underlying B-unit. The Dundee is a buff to brownish gray, fine to coarsely crystalline limestone. In much of the central basin, it is composed of limestone and dolomite with some anhydrite beds. In the extreme west and southwest areas, however, it is entirely dolomite (Lilienthal, 1978). Dolomite, when present, is generally found at the base of the formation. The Dundee in this study combines the Rogers City limestone with the Dundee limestone. The differentiation between these two formations are based on faunal succession and minor lithologic differences 42 (Lilienthal, 1978). The Dundee is found throughout the Southern Peninsula. It varies tremendously in thickness, from less than 40 feet in western Michigan, to as much as 475 feet in the area of Saginaw Bay. In southeastern Michigan it lies directly under the glacial drift, and can be seen in outcrOps along Mason Creek in Monroe County. According to Gardner (1974) the Dundee appears to be a shelf carbonate with dark fine-grained offshore facies deposited in a sea transgressing east to west. The Dundee has been the most prolific producer of oil and gas in Michigan. STRUCTURE Two major considerations in basin analysis are the nature of the force that caused the basin to subside, and the mechanism of deformation within the basin with attendant faulting and folding. Basin subsidence is a problem for which many theories have been advanced. For the Michigan Basin, no adequate explanation has been made that fits the known periods of subsidence as recorded by the sedimentary column. There are aspects of some subsidence models which may apply in part to what has occurred in the basin. Perhaps several of these events occurring in a concerted manner are responsible for phases of movement or deformation. Deep well tests and geOphysical surveys have yielded informa- tion on the character of the Precambrian basement. The structural trends in the southeastern corner of Michigan must be explained indirectly from the consideration of the well data available. Models of Basin Subsidence The factors to be considered in basin subsidence are: the location of the basin within the continental plate; the time of sinking; the depth, size and shape of the basin as well as structure within it and surrounding it. The continental interior of the United States can be divided into the stable interior and the foreland. In the stable interior, the Michigan, Illinois, and Williston basins began subsiding in their present size and shape during 43 44 Ordovician time (J. H. Fisher, personal communication). All three basins cease to subside in Pennsylvanian time. In contrast to this, the foreland basins have their strongest period of subsidence during the Pennsylvanian (e.g., Anadarko Basin, Denver Basin). The Anadarko Basin stabilizes by the middle of the Permian. The Denver Basin undergoes an additional subsiding phase during the Cretaceous. Thus, the pattern of subsidence for the basins is episodic, becoming younger from the shield margin outward. Some major influence must affect these regions or basins in a concerted sequence of subsidence and deformation (Sloss and Sleep, 1978). Pirtle (1932) and Lockett (1947) are proponents of the theory that the weight of sediments eroded from a high region and accumulating in a low region create sufficient force to initiate the downwarping that is the beginning of a basin structure. They favor this model for the origin of the Michigan Basin, stating that a tremendous sediment load was deposited in Michigan when the Precambrian mountains to the west in Wisconsin were eroded. The sediment load which accumulated in the Michigan Basin may have contri- buted to its sinking, but it is unlikely that these sediments have a provenance in Wisconsin. If material from a nearby mountain range was being deposited in the basin, it would be expected that a thick sequence of conglomerates would occur. There is no evidence for such an accumulation. Taking into consideration the 45 thin (1-2 feet) pebble layers in the McClure Beaver Island wells, these beds or layers are not of a magnitude to represent the erosion of a giant mountain range. It is probable that the major erosion of these ranges took place during the Precambrian and prior to the formation of the Michigan Basin. Pirtle and Lockett both suggest the possibility that the Michigan Basin is a geosyncline bordering the Wisconsin Mountains and that the basin folds are orogenic. Orogenic folds are asymmetric away from the major deforming force. Michigan Basin folds show no such pattern of eastward asymmetry. An additional problem in applying this mechanism to the formation of the Michigan Basin is that structural trends are best deveIOped in the center of the basin, appearing muted or even non—existent on the margins. It is difficult to conceive of an orogenic force which would deform the basin interior, but not the margins. Tectonic basins of the western foreland area such as the Powder River Basin and the Bighorn Basin exhibit intense deforma- tion around the margins, and basin centers that are virtually undeformed. The Michigan Basin shows the converse of this. Finally, there is no known orogenic force from the north- east or the southwest that could produce the observed dominant northwest-southeast trend of folding during Paleozoic time. Haxby, gt gt. (1976) prOposed a heating event, that originated in the mantle, and could have altered metastable 46 gabbroic rocks in the lower crust to eclogite. The eclo- gite being more dense, upon cooling, caused the basin to sink. This heavy material creates subsidence from beneath as Opposed to sedimentary loads pushing down from above. A problem with this theory is that a heating—cooling event should create a regular uninterrupted pattern of subsidence. Instead, the pattern of subsidence in the Michigan Basin is irregular. It sinks intermittently and at variable rates throughout the Paleozoic. No evidence of a high heat flow in the basin area has yet been found. Ge0physical Surveys The lack of deep test data in the Michigan has made the use of geophysical methods an important tool in deter- mining the lithology and structure for the Precambrian of Michigan. Rudman (1965) discussed the trend and signifi- cance of the Mid—Continent gravity high. This anomalous gravity high extends from Kansas through Nebraska, Iowa, and Minnesota, and terminates in the Keweenaw Peninsula in upper Michigan. These linear gravity highs are thought to be the result of dense mafic material rising along faults in the basement complex. Hinze (1963) shows an anomalous gravity and magnetic trend extending from the region of Traverse Bay into the southeastern corner of Michigan, transecting the Lower Peninsula. This trend dies out in southeastern Michigan or just across the boundary into Ontario. He suggests that the Mid-Continent and Mid-Michigan gravity highs are related. If forces 47 in the mantle began the development of a rift valley then Keweenawan basalts may have welled up along fractures and filled the graben with dense mafic rock. Supporting evidence for the existence of these faults comes from seismic lines made north-south and east-west through the Gratiot County, McClure-Sparks deep test (COCORP, Cornell University, 1978). The McClure-Sparks #1 deep test, Sec. 8, TION-RZW, cut a fairly typical section of the Paleozoic sedimentary column of Michigan, with the exception of a slight thick- ening of the lower Paleozoic formations. Below this, the well encountered 5,000 feet plus, of red beds of presumably Freda (Keweenawan) age (Van der Voo and Watts, 1978). The Mt. Simon sandstone (basal Upper Cambrian) thickens markedly in the well. This suggests that subsidence was continuing at a lesser rate during Mt. Simon time. Precambrian Tests of the Lower Peninsula of Michigan Of the 33 wells drilled to the Precambrian in the Lower Peninsula to date, only two encounter sedimentary units below the Mt. Simon (the McClure-Beaver Island #1, and McClure-Sparks #1). The 800+ feet of sediments encountered in the Beaver Island well are primarily coarse sandstone of an arkosic nature interbedded with thin beds of conglom- erate. Fowler and Kuenzi (1978) believe these sediments were eroded from a granitic terrain, and deposited by turbidity flows. They cite coarse red beds in the Sparks well as further proof of turbidite material and cite evidence for a Bouma sequence in the Sparks well. 48 The remainder of the wells in Michigan encounter, below the Mt. Simon, a relatively sharp Precambrian contact with, at best a few feet of granite wash overlying granite, granite gneiss, quartzite and occasionally schist. None of these wells encounters a red bed sequence like that found in the Sparks well. This may indicate that the Sparks well was in a structurally low area, possibly a rift in the Precambrian surface, which collected a red bed sequence. However, the Mobil-Messmore #1 well to the southeast, which was structurally high on the Precambrian, accumulated no such sequence. The Mobil-Messmore has a thin (abnormal for the area) section of Mt. Simon sandstone. Either this well is on a basement topographic high or a horst block, but either way this indicates that the graben dies out to the south as no red beds are present. The structural trends in the southeastern Michigan Basin are most likely controlled by many fault blocks which lie in a rectilinear pattern similar to that found in Canada to the north (Pirtle, 1932; Ells, 1969; and Fisher, 1969). This idea has been suggested by several researchers (see above) who agree on the mechanism, but disagree on the time the fault blocks formed, the orienta- tion of the stresses that deformed the basement initially and those which caused movement of these blocks in sub- sequent periods. When the igneous rock that forms the basement cooled, it formed a joint pattern. Deformation or major forces can also create a joint pattern. Subsequent 49 forces exerted on these blocks from any direction could cause vertical or horizontal movement along these planes of weakness. As these fault blocks were subjected to stresses from different directions, they could have moved up and down vertically or sheared by one another much as ice flows on a lake responding to wind action (Fig. 16). Some of the structure within a basin may be related to its subsidence. Robinson (1923), for example, explains radial folds as being due to subsidence. These are for the most part, very minor structural noses or crinkles in the sedimentary layers around the periphery of the basin in response to subsidence. The premise of this thesis is that none of the major trends in the Michigan Basin are of this origin; instead, structures seen in the Paleozoic sediments reflect movement on lines of pre-existing weakness during basin subsidence. Therefore, movement along faults during basin subsidence was responsible for the structures developed in Paleozoic sediments, but the fault pattern itself pre—dates basin subsidence, and was created by a different mechanism altogether. Many of the major structures present in interior basins have external origins. For example, the faulted Nemaha Arch which extends from Oklahoma City to Omaha, Nebraska, transects the old Salina Basin, but obviously was not created by Salina Basin tectonics. The LaSalle Anticline, which extends into the Illinois Basin, is a similar feature, in having originated in northern Illinois, outside the basin. This argues that some major Fig. 16. Vertical movement and horizontal shearing of basement blocks in response to regional stresses. 50 51 structures in interior basins would still be present regard- less of whether or not these basins were present. Therefore, the mechanism for the formation of some major structures in basins is not necessarily related to basin subsidence. DATA ANALYSIS The location of faults in southeastern Michigan has been determined indirectly by examination of the structure and thickness of sedimentary units, as insufficient deep well coverage of the Precambrian makes mapping of the basement rock impracticable. It is prOposed that the convergence and abrupt change of direction of contour lines over a short distance indicates that a fault exists through such an area. Similar abrupt changes in the thickness of a rock unit may indicate the presence of a fault that was active at the time the unit was deposited. To reinforce trends surmised from structure and isopach maps, geOphysical surveys, seismic information, and earthquake epicenters have been utilized. It can be seen from the Dundee, A-2 carbonate, and Trenton structure maps that the region of southeastern Michigan forms a portion of a basin which centers on the Saginaw Bay area. Of the three structure maps, the Dundee (Plate 1) has the best well control, and so is used for the analysis of structural trends within the study area. Three major trends are seen in the Dundee. These are the Lucas-Monroe Monocline, the Howell Anticline, and a monocline in Sanilac and St. Clair Counties. The southeast end of the West Branch Anticline, a major feature north of Arenac County, is not discussed here as the greater part of the anticline 52 53 lies outside the study area. The Albion—Scipio trend is not evident in the Dundee. Three minor features are seen in the Dundee. These are an anticlinal nose in Lapeer County, an anticlinal nose in Sanilac County, and a wide syncline, south of Saginaw Bay. The placement of faults on a structure map is a subjective process, and may differ between workers. The structure maps are drawn entirely without faults so that the readers may make their own interpretations. The fault trend map (Plate 8) indicates the placement of faults in areas in which, in the opinion of the writer, the degree of merging of contours indicates faulting. Additional faults have been added to this map in areas where faults are surmised to exist based on borehole data and seismic surveys. Faults, determined in this manner, and not by this study, are indicated by dashed lines. The Lucas-Monroe Monocline (Fig. 17) trends approximately 20 to 400 west of north from Monroe County, nearly 70 miles. The west flank of the monocline appears steeper than the east. In the area of T1N, R2E, there is an elevation change in the Dundee of 700 feet over a distance of two miles. Directly Opposite on the east flank in T1N, R4E, the same elevation change occurs over a distance of 7 to 8 miles. The Lucas-Monroe feature has a well—defined axis, and exhibits a very strong nosing trend which more closely resembles anticlinal structure rather than that of a monocline. However, all of the literature to date describes 54 '3 nulu I Fig. 17. Fault trends in southeastern Michigan. Dashed lines indicate faults based on oil field studies (Merritt, 1968; Landes, 1948; Lundy, 1968b). 55 the Lucas—Monroe as a monocline, and the writer is following this convention. The northern part of the axis curves into a north-south pattern, almost intersecting the Howell Anticline. A narrow syncline separates the two positive features. The Howell Anticline is by far the most dominant linear feature in the Michigan Basin. It trends between 40 to 600 west of north and extends from Wayne to Clinton County, a distance of approximately 50 miles. The west flank of the Howell is very steep. In Livingston County elevation changes up to 1,000 feet occur with a distance of three miles. A monoclinal feature in Sanilac and St. Clair Counties trends slightly northwest for approximately 30 miles. This feature exhibits elevation changes of 500-600 feet across a distance of three miles--a dip half as steep as that along the west flank of the Howell Anticline. These three large scale features are considered by the author to have been faulted where the placement of contour lines indicate the steepest dip (Plate 8). All faults trend generally northwest-southeast, consistent with the regional trend of folds and domes in the study area. In northwestern Lapeer County, a smaller scale anti- clinal nose juts basinward along the -1,500 foot contour line. The feature is less linear than those previously described, but is slightly elongate in an east-west 56 direction. An anticlinal flexure in northern Sanilac County trends very slightly north of east, and noses into a small dome structure in Tuscola County. South of Saginaw Bay a large wedge-shaped syncline occurs which extends from western Sanilac County to Midland County. The syncline broadens westward, as far north as Bay County, and as far south as Shiawassee County. The axis of this syncline trends slightly north of east. On the whole, structure in the A-Z carbonate (Plate 2) reflects that of the Dundee. The dip along the flanks of the major trends, the Lucas-Monroe Monocline, the Howell Anticline, and the Sanilac County Monocline, steepens somewhat in the A-2 carbonate. This is to be expected as relief should become less subdued downward in the column. North of the —3,500 foot contour line, control for this horizon is very sparse. The elevations for wells that are known are honored, but where data is lacking, contours have been shaped to those on the Dundee. Control for the Trenton (Plate 3) is even more highly restricted than for the A-2 carbonate. Contours north of the —5,500 foot line honor the elevations from the few wells in this area, but these are primarily shaped to the structure of the Dundee. In most respects, the Trenton reflects trends seen in the Dundee and A-2 carbonate structure maps. A steepening of dip beyond that seen in the A-2 carbonate is not in evidence. Possibly this is an 57 effect of there being less control available for this unit. Location of Faults The Lucas-Monroe axis exhibits a great deal of curva- ture. It begins in Michigan trending only about 100 west of north between Monroe and Lenawee Counties, then turns westward to 500 west of north for approximately 15 miles. In the northwest corner of Washtenaw County, it trends further westward, only to curve back in a northeast direc- tion, almost intersecting the Howell fault. This unusual pattern of curvature is confirmed by seismic information (J. H. Fisher, personal communication). This trend extends for approximately 70 miles in Michigan, but continues into Ohio as the Bowling Green fault. The offset is on the order of 500-700 feet over a distance of two miles—-a relatively steep angle. The Howell fault begins in northwestern Wayne County and trends roughly 50 to 700 west of north to northwestern Livingston County, a distance of approximately 40 miles. Contours on this structure suggested that it was comprised of at least three separate fault lines, the axes of which were slightly en echelon and offset by at the most, a mile or two. The Howell is an extremely high angle fault. An offset of 1,000 feet is seen within a distance of a half- mile. A monoclinal feature in north-central St. Clair and southcentral Sanilac Counties, trends 10 to 200 west of north, from T8N, R15E, to T11N, RluE, for a distance of 58 about 20 miles. This is a thrust fault, as indicated in the Humble-Hoppinthal borehole (Fig. 18). A fault, only four miles long, trending 30 to 400 west of north, straddles the boundary between Ingham and Jackson Counties near T18, R1W, but this is placed on the basis of changes in rock unit thickness, and is discussed later. Three faults are placed in Arenac County based on oil and gas field reports. These faults are based on oil and gas producing features, Fig. 19. The location of the Albion-Scipio trend is based on geOphysical data (Merritt, 1968). The upthrown and downthrown sides of the faults, as they are today, is determined by comparing the elevations on each side of the fault line (see Plate 8). All the faults with the exception of the smallest one on the Jackson-Ingham County boundary, are downthrown on the southwest side, and upthrown on the northeast side. In summary, the Dundee, A-2 carbonate, and Trenton structure maps indicate these formations dip regionally toward the center of the Michigan Basin. The dominant structural trends within this southeastern portion of the basin, as represented by faults, anticlines, synclines, monoclines, and domes is northwest-southeast. These trends are plotted and compared with the trend of the Mid-Michigan Anomaly in Figure 20. A high degree of parallelism can be seen to exist relative to this feature. 59 SCHLUMBERGER COMPANY WEI“ “MIN". ._ . ND. LHOPRIMHAL FIElO [REHOIII M. HICHIUN [OCAVION Jmefi will In . 1 mummi— COM'ANVW um... COUNTVJMJLAL "(l0 9' rm PEMII N0. 25.357 zllnv.: 759.6 ’1. Ab." hm. Dawn GROUND LEVEL I . 9 90" n g2: Jul 0! . Mai 06 0| 759- mm K. Fig. 18. Humble—Hoppinthal #1 showing repetition of the A—1 evaporite indicating a reverse fault. R4E ‘ o ‘5‘ ‘VJ Detroit} 2.& M 7/;— . . . t . \‘ ooi'l and Ca: Fields . (0009 River Field /V' ‘i’mo‘ . . . . _. 93 In!“ . § 19 ’ 8 -" \ \ :V \ \ T \ \ \ o \F \ \ ‘3 J “-5 Contours on top ‘of Rogers City limestone Scale Contour InlerOI IOfeel, datum sea level °0il well Traverse group — —- ———,Bell shale — limestone Diagrammatic Cross Section of Producing Area i: Shale -Zone of Porosity Fig. 19. Deep River field--dolomitization along a fault zone (Landes, 1958). if?“ _ _ _ _ _ __ - __ _ __1___ _____ o C I I. IN“ =l==l Fig. 20. Structural trends in southeastern Michigan relative to the Mid—Michigan gravity anomaly. 62 A weaker subordinate trend, northeast—southwest, is demon— strated by some structures in the study area. These are fewer in number, and of lesser magnitude and areal extent than the six features described here. The fault trends as determined by this study are summarized in Plate 8. Is0pach Analysis Is0pach maps can aid in determining the times during which movement occurred along faults. Is0pach trends have been combined for purposes of comparison in Plate 9. The salient features of this map are that anomalous thicknesses are associated with major structural trends, and with Niagaran reefs. Where anomalous thicknesses are not in evidence, it is assumed that no uplift or downwarping was occurring (other than basin subsidence). Where a unit thins adjacent to a fault, that area is considered to have been upthrown during the time of its deposition. Anomalous thickening is considered evidence for an area being down- thrown during the time of sediment deposition. In some places these trends of anomalous thickness relative to a fault Oppose each other in different units deposited during different periods. This is considered to be proof that an inversion of structure has occurred (Fig. 21). Movement of fault blocks along the Lucas—Monroe fault has not been consistent over time. The Utica shale (Plate 4) can be seen to thin anomalously along the northeast side of the fault. This indicates this side was upthrown in Utica time, similar to the position the fault is seen Fig. 21. Anomalous thicknesses of sediments across fault zones~—evidence of structural inversion. 63 6b in today. The Upper Cincinnatian, however, (Plate 5) thickens on the northeast side to a tremendous degree in the west half of Monroe County. This is evidence for an inversion of structure in this region, indicating that in Cincinnatian time the downthrown side was to the northeast. Farther north in Washtenaw County, the Cincinnatian thins on the same northeast side. This can be interpreted to indicate that the Lucas-Monroe is probably a series of faults, rather than one single continuous fault. Fault blocks may at different times move independent of one another. The B-unit thins along the southwestern side of the Lucas-Monroe fault. This could be a result of flowage caused by tectonic movement, an effect of deposition, or leaching of the salt across a positive area. The anomalous thin could possibly be reef controlled. If positive structure is the cause of thinning, then a structural inversion is indicated to have occurred between Cincinnatian and B-unit time, reversing the up and downthrown sides of the fault in that area. The C-shale (Plate 7) thins along the northeast side of the Lucas-Monroe in Washtenaw County, but an area of anomalously thick C-shale traverses the fault line, making an evaluation of the positioning of fault blocks vague. Along the Howell fault, the thinning of the Utica northeast of the fault line indicates that the up and downthrown sides of the fault were positioned as they are 65 today with the upthrown side to the northeast. An exception to this trend exists in central Livingston County where the orientation seems to have been the apposite. During Cincinnatian time, the general thickening of sediment on the northeast side indicates that structural inversion occurred. The fault blocks in central Livingston County also experienced inversion, as a reversal of the thickness trends prove. Anomalous thicknesses of the B-unit (Plate 6) are related to the Howell fault, as they are to the Lucas-Monroe, but the structural significance is similarly unclear. During the deposition of the C—shale in the Late Silurian, it appears that separate parts of the Howell fault were moving or had moved in Opposing directions relative to one another. The southeastern "third" of the fault was downthrown on the northeast where the shale thickens, while the northwestern "third" of the fault was upthrown on that side where the shale thins. This provides support for separating the Howell into at least three shorter faults, along which movement was not identical or synchronous. The Utica and the Cincinnatian thin over the Lapeer anticlinal nose. This indicates that either this area was positive during the Late Ordovician when these units were deposited, or that after the Utica was deposited, uplift began causing erosion of this shale, and prevented the even deposition of Cincinnatian sediment. By the time of the B-unit deposition, this area was no longer positive, 66 or had ceased to experience uplift. A marked contrast of thickness is seen in north central Jackson County during the deposition of the Utica shale, in Late Ordovician time. An anomalous thin area lies directly adjacent to an extremely anomalous thick area. This is evidently a growth fault, along which move- ment began as the Utica was being deposited. To the north- east downwarping created a low area into which the shale thickened. To the southwest, uplift caused the Utica to thin. Based on these changes in thickness, a northwest- southeast trending fault is indicated. The epicenters of earthquakes occurring in Michigan since 1872 bear no direct relationship to the faulting pattern as revealed in this study. Epicenters are plotted relative to faults in Fig. 12. The roman numerals indicate intensity on the Modified Mercalli Scale. None of the epicenters fall along a fault line. The only pattern to be discerned is that epicenters are concentrated in south and southeastern Michigan. The 1967 quake of intensity IV near Lansing could possibly be related to the Howell fault, as it lies just northwest along its trend. The only conclusion that can be made is that since 1872 no movement detectable by seismic instruments has occurred along the faults in southeastern Michigan. CONCLUSIONS Southeastern Michigan is dominated by three major structural features -- the Lucas-Monroe Monocline, the Howell Anticline, and the Sanilac County Monocline. All three of these structures are faulted on the southwest side, with the faults downthrown to the southwest. The axes of these and other folds, parallel the trend of the southeastern limb of the Mid-Michigan gravity and magnetic anomalies, which probably overlie a graben of Keweenawan age. These three major structures and the minor features associated with them are controlled by a combination of vertical movements of basement fault blocks, and a horizon- tal shearing force derived from tectonic events outside the basin and culminating at the end of Mississippian time. Structure in the Michigan Basin as a whole is controlled by a rectilinear pattern of faults and fractures in the Precambrian basement. This fracture pattern originated early in the Precambrian history of the region. Isopach map trends confirm that faulted structures were intermittently active during much of Paleozoic time. Alternating thick and thin trends occurring in different periods over the same area indicate that structural inver- sion of fault blocks has occurred. Since all of the four is0pached units chosen for this study show anomalous patterns of thickness in the faulted areas, it is a reasonable assumption that movements were occurring along 67 68 these faults throughout the Paleozoic. Variations in thick- ness of a stratigraphic unit along the same side of a fault indicate that movement was not uniform along the strike of these longer faults. The epicenters of recent earthquakes in Michigan are not located along known faults in southeastern Michigan. These are minor earthquakes (maximum VI on the modified Mercalli scale) and may be associated with lesser faults. The lack of conglomerate and arkose in the geologic column does not support the theory of basin origin which requires sinking under sedimentary loads derived from mountain ranges in either Wisconsin or the Cincinnati Arch area. The irregular pattern of subsidence in the Michigan Basin is not compatible with a single upper mantle-lower crust heating event. None of the present explanations of basin subsidence fits the observed pattern of formation thickening and fault movement observed in southeastern Michigan. Albion-Scipio, the only giant oil field in Michigan, produces from a dolomitized zone in the Ordovician, Trenton and Black River Formations. The linear nature of the field indicates a fault origin. The trend and spacing of faults described in this study may be an aid in exploring for fields of this type. APPENDIX A APPENDIX A Cross—Sections These three cross—sections (Fig. A-1) illustrate the structure and comparative magnitude of the major folds in southeastern Michigan, as seen on the Dundee. These folds exhibit limbs with dips of sufficient steepness to suggest they reflect faulting in basement rock. The displacement across these large features is probably the result of slippage along several roughly parallel faults rather than along only one. Multiple faults are shown diagrammatically in the cross-sections, their exact locations are unknown. It is known that the Sanilac Fault is probably a reverse fault. A geOphysical well log from Sanilac County (Fig. 18) records a repetition of section that may be the result of reverse faulting. The direction of the fault angle is not known, but is arbitrarily drawn for the purpose of illustrating the type of faulting present. The geographical positions of the cross-sections are illustrated in Figures A-2, A-3 and A-4. Cross-section A-A' of the Bowling Green Fault illustrates this features monoclinal character. The diSplacement along the fault at this location is 850 feet. It can be seen from cross-section B—B' of the Lucas-Monroe Monocline, and the Howell Anticline, that these are the two most prominent features in southeastern Michigan. The displacement along 69 7O SAN I LAC feet ‘8 Fig. A-le BOWLING GREEN f| FAuur I2 l8 miles Vertical exaggeration approx. X 63 Cross-sections. '5°°" FAULT -m0 ' O 6 l2 l8 miles a s' O P Sea level I I J -500- l | HOWELL (”II | | ANTICLINE a J I '3 “If : l r-IOOO I lf' If, LUCAS-MONROE l l "MONOCLINE' I 1 L 1 l o 6 :2 l8 24 30 36 A A' +500- 71 gélmifi 72 Fig. A-3. Location map, cross-section B-B'. 73 i W 2m); Fig. A-4. Location map, cross-section C-C'. 74 them is 650 feet and 1,300 feet, respectively. The Sanilac Fault in cross-section C-C' is a reverse fault, with a displacement of approximately 700 feet. 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