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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.
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Lithological & geochemical analysis of the Middle to Upper Devonian Antrim Shale, Michigan Basin: insights into detrital input dynamics
The Middle to Upper Devonian is distinguished by global biotic events attributed to marine anoxia (black shale) and perturbations in the carbon cycle. While previous studies had documented these events in the North American Appalachian Basin, less attention has been directed toward discerning analogous global biotic occurrences within the neighboring Michigan Basin. This investigation aims to reconstruct the organic carbon isotopic composition of Middle to Upper Devonian sediments within the Antrim Shale, from the Krocker 1-17 and State Chester Welch 18 drill cores located in the north-central Michigan Basin. Since black shale organic matter (OM) is a combination of marine and terrestrial sources, the first step is to utilize elemental proxies for sedimentation to understand terrestrial OM input to the basin. Elemental analysis was performed on powdered core samples at approximately three-foot intervals across the (oldest to youngest) Norwood, Paxton, and Lachine members of the Antrim Shale. Initial pXRF analysis shows similar trends in sedimentation rate proxies between the two core locations, suggesting that basin-fill dynamics are spatially consistent. In the Norwood, Si%, Si/Al, and K% mostly correspond suggesting predominantly clay mineral deposition, though an anomalously high interval of Si%, Si/Al, and TOC (and low K%) is interpreted as high paleoproductivity and biogenic silica production (radiolarians). In the Paxton, all elemental proxies for sedimentation are relatively consistent through time, indicating minimal detrital flux changes. In the Lachine, the overall trend of increasing Si% and Si/Al and corresponding decreasing K and TOC suggests increased detrital input through time. These trends provide the necessary baseline for future work interpreting organic carbon isotopic data. A detailed understanding of local detrital fluxes into the Michigan Basin and potential terrestrial organic carbon input to marine settings is necessary to place the Michigan Basin carbon isotopic profile within the global framework. This study will provide valuable insights into deciphering global events within the stratigraphic succession of the Michigan Basin. The anticipated outcome is an enhanced understanding of the localized manifestations of Middle to Upper Devonian global events.
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- Award ID(s):
- 2050697
- PAR ID:
- 10508872
- 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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