DECODING DEVONIAN DYNAMICS: CARBON ISOTOPES FROM THE JEFFERSON FORMATION IN MONTANA

The Devonian Period was a dynamic interval in Earth's history marked by significant changes in the terrestrial biosphere and a shift to icehouse conditions. Using stable carbon isotopes to document perturbations to the global carbon cycle during this time, especially the regional expression of the isotopic record, can help us to better understand the connection between the biosphere and climate. For the Late Devonian of Montana, that record is preserved in the Jefferson Formation. However, the extensive dolomitization of the Jefferson Formation has led some to argue that the geochemistry of these rocks has been altered and cannot provide an accurate depiction of the ancient carbon cycle. To better understand the carbon isotopic record of the Jefferson Formation this study focused on the Baker Mountain section on the eastern flanks of the Beartooth Mountains in south central Montana. We measured and described 84.5 meters of strata and collected samples for geochemical and petrographic analysis. In total we present 178 carbonate carbon isotopic values, 27 organic carbon values, and total organic carbon (TOC) estimates paired with a detailed sedimentological framework for this section. Using this new dataset, we explore the relationship between depositional environment, sea level, dolomitization, and carbon isotopes.