Insights into the Michigan Basin:

Salt Deposits, Impact Structure, Youngest Basin Bedrock, Glacial Geomorphology, Dune Complexes, and Coastal Bluff Stability

Edited by Robb Gillespie


This guidebook volume is a compilation of field excursions offered at the 47th annual meeting of the North-Central Section of the Geological Society of America, held in Kalamazoo, Michigan, May 2013. These field trips examine a wide range of geological time intervals and topics, from Silurian salt, to Cretaceous cosmic impact, to newly interpreted Mississippian–Pennsylvanian Michigan stratigraphy, to Quaternary glacial landscape formation, sand dune development, and present-day coastal bluff stability/erosion issues. Trips geographically range throughout southern Michigan and northern Indiana from Detroit, Michigan, in the east to the Kentland Quarry in Indiana to the west.

Early depositional events within the Michigan Basin are examined deep underground in the Detroit Salt Mine (trip leaders: W.B. Harrison III and E.Z. Manos [onsite leader]). This salt mine has been in operation for more than 100 years, and extends for miles beneath the city of Detroit.

Kentland Quarry, located in northwest Indiana, is the site of a Cretaceous-aged meteorite impact (trip leader: J.C. Weber). This site allows for surface examination of a similar style impact event that occurred in now buried Ordovician-age (Trenton) rocks located in Cass County, (southwest) Michigan.

Mississippian-aged fluvial deposits have been traditionally classified as the youngest bedrock exposed in Michigan. These rocks crop out in the center of the Michigan Basin near Grand Ledge, Michigan (trip leaders: N.B.H. Venable, D.A. Barnes, D.B. Westjohn, and P.J. Voice). Younger, more recently identified, Pennsylvanian rocks will be the subject of a related core workshop at the Michigan Geological Repository for Research and Education (MGRRE) in Kalamazoo (workshop leaders: S. Towne, W.B. Harrison, and D.B. Westjohn).

The regional, surficial geology of southwest Michigan is highlighted by three field trips. The first trip details the glacial landforms and sedimentary features formed by the differing dynamics of the Michigan and Saginaw lobes of the Laurentide Ice Sheet (trip leaders: A.E. Kehew, A.L. Kozlowski, B.C. Bird, and J.M. Esch). The two other trips follow along the Lake Michigan eastern shoreline and examine development of sand dune complexes (trip leader: E. Hansen) and present-day, coastal bluff stability and erosion issues (trip leaders: R.B. Chase and J.P. Selegean).

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    This field guide summarizes the main known and unknown aspects of the impact geology of the Kentland impact structure, and includes sections on results from recent research, evidence of impact, age of impact, and shock metamorphism. It is intended to lead visitors through the spectacular, three-dimensional outcrops in the central uplift of the structure, exposed in the Newton County Stone (Kentland) Quarry, western Indiana.

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    This annual meeting of the North-Central Section of the Geological Society of America provides an opportunity to visit a working underground salt mine on a field trip. The trip leaders will take a group into the Detroit Salt Mine, which is located approximately 1200 ft (364 m) deep beneath a portion of the city of Detroit, Michigan. This mine extracts salt through a room and pillar mining process from the Silurian Salina "F" Salt formation. Currently the mined salt is used primarily as crushed salt for ice control throughout the upper Midwest. The company is mining a 30-ft-thick seam of bedded halite. Thin beds of anhydrite and/or dolomite are occasionally interbedded with the high-purity halite.

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    Recent mapping in southwestern Michigan conducted through U.S. Geological Survey STATEMAP, EDMAP, and Great Lakes Geologic Mapping Coalition projects has produced new interpretations of the origin of the landforms and sediments of the Lake Michigan and Saginaw lobes of the Laurentide Ice Sheet and the dynamics of these lobes. The Lake Michigan lobe advanced southeastward into a proglacial lake at least as far east as the Kalamazoo moraine. During its advance, the lobe extensively deformed the lacustrine sediments it overrode. These structures will be discussed in several pits. When ice backed away from the Kalamazoo moraine, it formed a series of proglacial lakes, several of which were described for the first time in the studies upon which this guidebook is based. As the ice retreated, lowland areas between morainal uplands were utilized by meltwater drainage events, some of them probably catastrophic in nature.

    The Saginaw lobe stagnated over a broad marginal area as it retreated northeastward toward Saginaw Bay. The resulting stagnant marginal zone is coincident with the subcrop of the Marshall Sandstone. Enhanced basal drainage into the underlying sandstone may have played a role in the dynamics of the lobe. High-relief, supraglacial landforms such as hummocky topography and ice-walled lake plains overprint subglacial landforms in this region, which include large tunnel valleys with inset eskers. Better understanding of the glacial geology of this region is critical to economic development, management of water resources, and exploration for aggregates and other resources.

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    This field trip is an excursion to exposures of Pennsylvanian bedrock at Grand Ledge, Michigan, as a backdrop for interdisciplinary examination of the sedimentologic, stratigraphic, and hydrologic research conducted on these important bedrock aquifer units.

    The areal extent of Pennsylvanian rocks in the central Lower Peninsula of Michigan is ~28,490 km2. Pleistocene glacial deposits overlie these units throughout the state, but the drift is thin and locally absent along the Grand River Valley, in and around Grand Ledge, Michigan. The geology of the Pennsylvanian deposits is known almost entirely from subsurface research, although sparse outcrops occur near Parma and Jackson in Jackson County and at Grand Ledge in Eaton County. These outcrops, especially the ones at Grand Ledge, constitute the only exposures of coal-bearing strata in Michigan where visitors can see massive sandstone, shale, coal, and associated strata, and fine-grained, chaotic, riverbank-slump facies.

    The sections of the field trip will attempt to relate Grand Ledge area deposits to the Pennsylvanian section at the state and regional scale. First, general geologic and stratigraphic relations will be described on the basis of knowledge from the nearby cities of Lansing and Mason, where diamond drill cores and geophysical logs from extensively studied groundwater contamination sites are available. Lithologic and geophysical logs from these sites will be reviewed under the pavilion. Next, lithologic type sections of the Pennsylvanian material in outcrop will be observed and discussed. An example of core from a nearby industrial site will be studied under the pavilion during lunch, and a final trip to outcrop will be made to discuss stratigraphic relationships in an effort to bring into perspective the complexities of Pennsylvanian strata in the Michigan Basin.

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    Corresponding author:

    This field guide explores the geomorphology, ecology, contemporary processes, sedimentary structures, and geomorphic history of the large freshwater dune systems on the southeastern shore of Lake Michigan. Recent research studies on varying aspects of the dunes are highlighted at each stop. From north to south, these stops include P.J. Hoffmaster State Park near Muskegon, Michigan; Gilligan Lake and Green Mountain Beach southwest of Holland, Michigan; Saugatuck Dunes State Park and Saugatuck Harbor Natural Area, both near Saugatuck, Michigan; Warren Dunes State Park and Grand Mere State Park between the Indiana–Michigan border and Benton Harbor, Michigan; and Mount Baldy on the eastern edge of the Indiana Dunes National Lakeshore, Indiana. All of the complexes described are low perched transgressive dune complexes that are migrating inland over former lake plains or baymouth bars. Moving from the lake inland, the typical dune complex in this area consists of incipient foredunes, an established foredune ridge, a parabolic dune complex, and a back-dune ridge complex. All stages of ecological succession—beginning with a pioneer community dominated by beach grasses and ending with a mesic forest dominated by oak, maple, and beech—are typically present in the larger dune complexes. Like coastal dunes everywhere, surface changes in Lake Michigan dunes are driven by spatial gradients in sand flux, which, in turn, are determined by a complex interaction among wind, vegetation patterns, and preexisting topography. The patterns of surface change are modified by seasonal effects, with the majority of sand transport being associated with strong storms in the autumn, winter, and early spring. Sand can be temporarily stored in niveolian deposits during the winter, leading to oversteepened slopes, which collapse during the spring thaw. A variety of sedimentary bed forms and structures can be viewed in dunes along the southeastern shore of Lake Michigan, including wind ripples, lag deposits, raindrop impressions, adhesion ripples, adhesion warts, eolian turrets, sand pedestals, surface patches of fine-grained dark sand, pinstripes, paleosols, cross-bedding, climbing ripple lamination, niveolian deposits, and avalanche lobes. Most of these features are best seen immediately after strong storms in the autumn and winter. Remnants of older dune surfaces are exposed in a few places in back-dune ridge complexes; however, the current dune complexes are largely a product of events that occurred during and after the rise in lake levels to the Nipissing peak (ca. 4.5 ka). Broad fields of relatively low dunes developed during the drop in lake levels following the Nipissing peak. Beginning with the rise to the Algoma high lake level (ca. 3.2 ka), the lakeward edges of these fields were episodically reworked, forming the large parabolic dune complexes. A period of widespread dune stability resulted in the development of the Holland Paleosol, a particularly well-developed paleosol with Spodosol characteristics. Widespread dune growth and migration resumed prior to European settlement of the area and continue today.

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    The Great Lakes coast contains numerous unstable bluffs underlain by heterogeneous glacial materials consisting of till, sand, and gravel layers, and lacustrine clays. Many of the bluffs are steeper than their equilibrium angles and typically move as slow earth slides or occasional rapid slumps. Such movements develop largely where interlayered sand and clay contain perched groundwater that acts to reduce effective stress during winter months when perched potentiometric surface elevations rise because water cannot discharge through frozen soil. Aerial photograph records dating back to 1938 show that bluffs recede in amphitheater-like depressions followed by "catch up" where headlands between amphitheaters are attacked by other forms of erosion. This bluff recession is particularly pronounced during stages of high lake levels.

    The erosion control experiment described herein has been designed to determine the manner in which groundwater activity influences the causes and mechanisms of mass wasting on the Great Lakes coasts. Three dewatering demonstration sites were selected, monitored electronically for virtually all movement and cause relationships, and dewatered to demonstrate a potential mitigation strategy other than construction of wave barriers.

    Erosion activity and dewatering effects were carefully monitored for three seasonal cycles. Results show that (1) dewatering greatly reduces ground displacements during winter months, and (2) bluff movements are almost perfectly timed to, or lag slightly after, the hours when potentiometric surfaces near the bluff face reach their highest elevations during freezing (greatest soil pore pressure) or their greatest rates of surficial discharge (soon after thaw).

    This field guide project was supported by grants from the U.S. Army Research Office, Terrestrial Sciences Program (Grant 3467-GS) from 1996 to 1999 and the U.S. Army Engineer Research and Development Center (ERDC) from 2000 to 2007, and 2012, through U.S. Senate Bill 227 (National Shoreline Erosion Control Development and Demonstration Program), with support from Western Michigan University (WMU). Additional personnel involved were Alan E. Kehew, Co-PIand, WMU graduate students William Montgomery, Rennie Kaunda, Mark Worrall, Gregory Young, William Bush, and Amanda Brotz. Well and monitoring instrument positions were chosen by R. Chase and designed by Ronald L. Erickson and James P. Selegean, U.S. Army Engineer District, Detroit, Michigan. Well constructions and instrument installations were done by STS Consultants, Chicago, Illinois. This huge project was very smoothly administered by M. Eileen Glynn and William R. Curtis, ERDC, Vicksburg, Mississippi.

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    Over 2000 linear feet of recently acquired conventional core and hundreds of well logs were analyzed to reevaluate regional, middle Carboniferous litho- and bio-stratigraphic relationships in the Michigan Basin, USA. The main objective of this workshop is to interpret the evolution of the Michigan Basin relative to other more extensively studied, North American cratonic interior basin successions in the Illinois and Appalachian basins. Stratigraphic relationships are evaluated in the Michigan, Bayport, and Saginaw formations on the basis of sedimentary lithofacies, contact relationships, and facies stacking patterns, in addition to new age determinations from several distinct pollen and spore assemblages. Core and well-log cross sections are presented to establish regional stratal geometry and corroborate stratigraphic relationships established in core studies. Biostratigraphic analysis has established the age range of these middle Carboniferous strata, which range from late Mississippian (Chesterian) through the early–middle Pennsylvanian (Morrowan and Atokan) North American stages, with no indication of significant hiatus relative to existing chronostratigraphic resolution. Significant soil horizons and incised valley-fill deposits found at the Mississippian-Pennsylvanian systemic boundary, however, are interpreted to represent the basal Absaroka sequence boundary.

    Significant variations in eustatic, climatic, and tectonic signals recorded in Carboniferous strata of the Michigan Basin are found to be in close agreement with regional geological relationships established in recent sequence stratigraphic and basin analysis studies conducted in adjacent cratonic interior basins. Shallow, mostly restricted marine, mixed clastic, carbonate, and evaporite strata of the Mississippian Michigan and Bayport formations are overlain by carbonaceous debris-rich, terrigenous clastics dominated marginal marine and terrestrial strata of the Pennsylvanian Saginaw Formation. These strata record the complex interplay among second and higher order eustatic changes, global climate variations, and the culmination of Appalachian orogenic activity along the eastern margin of North America during the middle Carboniferous. These geological factors resulted in the dramatic transition from carbonate-dominated, stable cratonic interior basin sedimentation during the Siluro-Devonian to siliciclastic-dominated strata in the latest Devonian through Carboniferous in the Michigan Basin.

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