A GEOCHEMICAL INVESTIGATION OF THE EFFECTS OF DEEP OCEAN EUXINIA ON CONTINENTAL SHELF ENVIRONMENTS DURING THE GOBE: INSIGHTS FROM THE MIDDLE AND UPPER FILLMORE FORMATION, UTAH

The Great Ordovician Biodiversification Event (GOBE) was an exceptional radiation within the Paleozoic and Modern Evolutionary Faunas. It is likely that a combination of tectonic, ecological and climate-related factors contributed to the diversification event (e.g., Servais et al., 2009). In particular, continental shelf area during the Ordovician was the largest of the Phanerozoic (e.g., Servais et al., 2009). Despite the biodiversification in continental shelf settings, recent geochemical research has pointed to the existence of deep ocean euxinia during the GOBE (e.g., Thompson and Kah, 2012). While the exact link between the GOBE and the presence of deep ocean euxinia is unclear, geochemical approaches can shed light on this paradox.

For example, organic carbon (C_org) and total sulfur (S_total) abundances can be used as proxies for redox conditions in localized depositional environments. By examining these proxies from rocks formed in continental shelf settings, we can investigate the effects of deep ocean euxinia on shallow marine environments. In order to address this question, samples were collected at a resolution of 10m from the Lower Ordovician Fillmore Formation of Millard County, Utah (the H section of Hintze, 1973). C_org and S_total were measured on these samples using an ELTRA Carbon and Sulfur Determinator. The samples exhibited low C_org and low S_total abundances. C_org averaged 0.23 wt.% while S_total averaged 0.02 wt.%. The highest C_org measurement yielded 1.05 wt.% from a sample that contained 0.04 wt. % S_total. Although there are other factors to consider, the low abundances suggest a lack of anoxia in the majority of samples from this section. This data contributes to ongoing research investigating the relationship between deep ocean anoxia and biodiversification in shallow continental shelf environments.