ENVIRONMENTAL CONTROLS ON ORGANIC CARBON PRODUCTIVITY IN THE MIDLAND BASIN

The Kasimovian (late Pennsylvanian) to early Roadian (middle Permian) is an interval of Earth history that can be studied for comparison to recent climate dynamics as it had relatively stable climatic conditions highlighted by significant glaciation. Vast dust deposits occurred and may have delivered more bioavailable iron to the oceans. Iron sourced by dust could have large implications for primary production, thus impacting pCO₂ through increased organic carbon (OC) burial. These mechanisms are important to constrain as they can reduce or magnify additional climate feedbacks. The δ¹³C record during this interval is relatively stable with a few minor and unexplored fluctuations of ~2 ‰ – suggesting comparably stable global OC burial even as peat/coal deposits declined into and through the Permian. Enhanced marine OC productivity can lead to increased carbon burial, potentially driving positive global δ¹³C excursions. For example, the Midland Basin in Texas represents a major Permian hydrocarbon source rock interval. Thus, there may be other substantial marine sinks of OC during this time, but global distributions are not well constrained. Resolving the potential mechanisms that may be driving local and global OC burial is imperative for understanding the Earth system feedbacks associated with ancient climate perturbations.

Here, we will constrain local and potentially global marine redox conditions using a multi-geochemical approach. Total OC contents and isotopes will constrain local and global burial of OC. Iron speciation and δ³⁴S will constrain local redox conditions – including anoxic, euxinic (anoxic and sulfidic water-column) – and pyrite burial. Redox-sensitive trace metals will be analyzed, and used in combination with Fe speciation, to interpret local and potentially global redox conditions. Lastly, thallium isotopes will be analyzed on anoxic to euxinic samples to track the global burial of manganese oxides, which is related to the global extent of oxic bottom waters for basins connected to the open ocean. The combination of these traditional and novel geochemical redox proxies can provide new context to interpret the local environment and may even provide information regarding the degree of restriction of the Midland Basin.