INVESTIGATING THE LINKAGE OF INCREASING OXYGEN TO THE GREAT ORDOVICIAN BIODIVERSIFICATION EVENT USING GEOCHEMICAL FINGERPRINTS IN THE APPALACHIAN BASIN

The marine redox evolution in the Ordovician is highly dynamic which directly effects multiple biogeochemical event and cycles. The largest biodiversification event in the Paleozoic was the Great Ordovician Biodiversification Event (GOBE) and occurs prior to the first of the “Big 5” mass extinctions. The GOBE is a roughly threefold increase in family and twofold increase in genera diversity. One hypothesis for this biodiversification is an increased oxygenation within shelf environments however, to-date there has been little direct evidence supporting this idea. This study focuses on biogeochemical signatures that occur in the Middle-Late Ordovician that includes the GOBE and mid-Darriwilian carbon isotope excursion (MDICE) to address the spatial and temporal changes of ocean oxygenation.

This study focuses on paired stable carbon and sulfur isotopes to elucidate the causes and consequences of this diversification event in two different sections in Tennessee and Virginia. δ¹³C_carb have been analyzed from the Evan’s Ferry thrust sheet in Tennessee, while δ¹³C_org will be taken from the Paperville shale in Virginia which show the diagnostic trends from the time period; a roughly +3‰ excursion. In addition to carbon, this study uses sulfur isotopes (δ³⁴S) in the form of carbonate associated sulfate (δ³⁴S_CAS) and in pyrite (δ³⁴S_pyr). The δ¹³C can be used to track the global burial of organic matter while δ³⁴S is a proxy for oxygen dynamics, in particular ocean euxinia (anoxic and free H₂S) through the global burial of pyrite. In addition, the Paperville will be evaluated for trace metal systematics to test for a global expansion of reducing conditions which might limit the amount of available bio-essential trace metals. This study will test the hypothesis that portions of Ordovician ocean basins cycled from oxic to anoxic or euxinic conditions, and that these intervals of increased oxygenation are coincident with the GOBE. We expect this study will greatly improve the understanding marine oxygen dynamics during the Ordovician period and how the changing climate system affects the biogeochemical cycling of key elements and their impacts on the global biosphere. This will build a better framework to understand the links between the global redox state of the oceans biodiversification or extinction events.