Identification of the late Homerian Mulde Excursion at the base of the Salina Group (Michigan Basin,USA) |
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| Authors: | Nicholas B Sullivan Patrick I McLaughlin Poul Emsbo James E Barrick Wayne R Premo |
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| Affiliation: | 1. Wisconsin Geological and Natural History Survey, Madison, WI, USA;2. Chemostrat Inc., Houston, TX, USA;3. Indiana Geological Survey, Indiana University, Bloomington, IN, USA;4. US Geological Survey, Federal Center, Denver, CO, USA;5. Department of Geosciences, Texas Tech University, Lubbock, TX, USA |
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| Abstract: | Constraining the age of strata is a fundamental source of uncertainty in the study of sedimentary rocks, particularly in restricted basins that generally lack index fossils. An illustrative example of this is the evaporite‐bearing Salina Group in the Michigan Basin. Our integrated study of facies, paleontology, and stable isotope geochemistry from the base of the Salina Group in Wisconsin addresses long‐standing chronostratigraphic uncertainty surrounding these units. Conodont samples from the basal boundary interval (Racine‐Waubakee formation contact) produced non‐diagnostic ‘disaster’ and ‘recovery’ faunas typical of both the Mulde (Homerian) and Lau (Ludfordian) events. Strontium isotope analysis (87Sr/86Sr) of these conodonts from five horizons just below the boundary yield values between 0.70844 and 0.70850 confirming a Homerian age. Multiple carbon isotope profiles through this interval confirm the presence of a 2.5–3‰ positive excursion. Cumulatively these data constrain the base of the Salina Group in Wisconsin to the Mulde Excursion interval (late Homerian). This integrated study provides a sound initial step towards a deeper understanding of the processes of Silurian evaporite formation in the Michigan Basin. |
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| Keywords: | Carbon Isotopes Conodonts Salina Silurian strontium Isotopes Wenlock |
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