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This study utilizes the magnetic susceptibility (MS) of sedimentary strata to correlate the Late Devonian Antrim Formation black shale and calcareous mudstone within the Michigan Basin as well as the Antrim with previously published MS profiles from contemporaneous, shale-dominated strata from the Illinois Basin. MS can be used as a proxy for changes in material composition, which is linked to paleoclimate-controlled sediment fluxes and depositional environments. In the Michigan Basin, MS profiles through the basin-margin State Chester Welch 18 and the more basinal Krocker 1-17 cores show that MS patterns correspond to lithostratigraphic units. For some of these units the MS patterns are similar among the cores, though not for all units. Preliminary interpretation is that MS patterns are a result of proximity to sediment source (Acadian Orogeny versus Transcontinental Arch) as well as intrabasinal early diagenetic processes (pyrite). Furthermore, the lithostratigraphic units in these cores may not be chronostratigraphically equivalent. This study also compares the Michigan Basin MS basinal profile (Krocker 1-17 core) with previously published data from the “Bullitt County Core” from Kentucky, in the southern Illinois Basin. Within a biostratigraphic framework, the Michigan and Illinois Basin cores appear to show similar MS patterns. This is possibly because sediment input to these two locations is primarily sourced from the Acadian Orogeny, and the depositional environment and therefore early diagenetic processes, are similar. Future work will combine mineralogical analysis with the MS profiles to decipher the source of magnetic susceptibility, currently hypothesized to be driven by ilmenite concentration.
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Preliminary geologic maps of Alpena County, Michigan
The purpose of this project is to produce multiple geologic maps of the Devonian-Mississippian strata in Alpena County, Michigan with a focus on delineating the members of the Antrim Shale. The resulting maps will be useful for resource assessment (aggregate and natural gas) and natural hazard assessment (sinkholes). Oil/gas and water well logs were analyzed for formation tops and bedrock elevation in order to construct four maps using ArcGIS Pro: bedrock, drift thickness, bedrock topography, and cross-sections. The well distribution provided an interesting difficulty in constraining the geology of Alpena County. The southern half of the county has an extensive subsurface dataset from Antrim gas wells which provided excellent constraints on bedrock elevations and formation tops. The northern half of the county by contrast has a paucity of hydrocarbon wells. Water wells provided constraints on the bedrock surface but the lack of detailed lithologic descriptions made interpreting the bedrock formations in this portion of the county challenging. Bedrock units form arcuate belts from northwest to southeast in Alpena County and range from the Lower Mississippian units in the far southwest (Bedford-Berea, Sunbury, and Coldwater formations) to Devonian units across the majority of the county (Traverse Group, “Squaw Bay Formation”, Antrim Shale, Ellsworth Shale). Pleistocene incision has carved significant paleovalleys on this bedrock surface, with valleys trending NE-SW in Alpena County. Glacial drift thickens to the south and southwest in Alpena County. The refined Alpena bedrock maps provide the community with a better assessment of where natural resources are present and the susceptibility of natural hazards in the area. Alpena historically has been a site of quarrying (limestone, shale) operations and hydrocarbon exploration. Carbonate-dominated intervals in the Traverse Group are susceptible to karsting and sinkholes are present in northeastern Alpena County. Understanding the risk of karsting assists in mitigating groundwater contamination risks from septic tanks and other sources of contamination.
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- Award ID(s):
- 2050697
- PAR ID:
- 10508882
- Publisher / Repository:
- Geological Society of America Abstracts with Programs
- Date Published:
- Volume:
- 56
- Issue:
- 3
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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The “Squaw Bay Formation,” a middle Devonian mixed carbonate-clastic unit located in the Michigan basin, was named almost 100 years ago by Warthin and Cooper (1935) for a single, poorly exposed outcropping of condensed strata. Since then the stratigraphic term has been used inconsistently in the subsurface where the unit is stratigraphically expanded, but should also be revised because it is a derogatory term for Native American Women. The goal of this study is to aid in the renaming process for this formation by determining its variability and defining boundaries. To accomplish this, the current research combines lithostratigraphy, paleoecology, and geochemical analyses of the Krocker 1-17, State Chester Welch 18, and Paxton Quarry cores to provide the background information needed to revise the formation. The “Squaw Bay Formation” in core is composed of predominantly argillaceous limestone and calcareous shale and is characterized by a crinoid and brachiopod fauna. Further lithologic analysis found that there are three main facies common in the studied cores; black shale with frequent pyrite nodules and silt laminae, calcareous fossiliferous shale, and a highly bioturbated calcareous shale with few fossils and pyrite nodules. The lower “Squaw Bay Formation” also contains zones of concentrated fossil debris, especially near the contact with the Traverse Limestone which is primarily a pyritized hardground. The studied formation also has an increasing black shale content up-section and a transitional contact with the overlying Antrim Shale. Future analysis of magnetic susceptibility, pXRF, and total organic carbon data will further illuminate the variability within the formation and characteristics of its boundaries with other stratigraphic units. Ultimately, the combination of lithostratigraphic, paleoecologic, and geochemical analysis of the Krocker 1-17, State Chester Welch 18, and Paxton Quarry cores will not only facilitate a better understanding of the “Squaw Bay Formation,” but also contribute to the process of revising and renaming the unit.more » « less
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