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The Ellsworth Formation is a Late Devonian gray-green silty shale found in the Michigan Basin. The relationship between the Ellsworth Formation and the underlying/interfingering Antrim Formation black shale is variable within the literature, and the delta that delivered this sediment to the basin is poorly constrained. This study aims to better understand the lithostratigraphic and chemostratigraphic variation of the Ellsworth among two drill cores: one located on the basin margin and the other more basinal. This work will help constrain the stratigraphic and paleoenvironmental aspects of the Ellsworth in different parts of the basin, providing a better understanding of Ellsworth delta construction. Elemental (pXRF) and mineralogical (XRD) analyses demonstrate a distinct difference between the cores. The Ellsworth Formation on the edge of the basin contains larger amounts of K-feldspar, quartz, and dolomite. In contrast, more basinal settings contained higher amounts of clay minerals as well as organic matter. Additionally, a high-resolution lithostratigraphic study of the basin-margin core was undertaken. Generalized linear models were used to measure lithologic trends throughout the Ellsworth Formation in this core, ultimately showing a coarsening upward sequence overprinting cyclical deposition of detrital sediments. Furthermore, sub-millimeter oscillating grain size variations were observed in cuttings at a microscopic scale. Together, these observations indicate that the sediment source for the Ellsworth Formation delta complex was likely to the modern day north-northwest, as suggested by previous studies, and that the delta deposits transitioned from shallower water feldspathic silty shale to organic-rich clay-dominated strata in basinal settings. Future work should focus on deciphering the causes of cyclicity observed at microscopic, centimeter, and decimeter scale. Ultimately, this study shows that there are distinct chemical and lithologic differences between the basin edge and central basin portions of the Ellsworth Formation, and these differences can be used to further understand the stratigraphy and paleoenvironmental history of the Michigan Basin.
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Magnetic susceptibility of the Late Devonian Antrim Shale of the Michigan Basin
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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- Award ID(s):
- 2050697
- PAR ID:
- 10508865
- 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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