THE CARBONATE ASSOCIATED SULFATE PROXY DURING THE GOBE: INVESTIGATING THE IMPACTS OF GLOBAL REDOX CHANGES ON SHALLOW MARINE ENVIRONMENTS DURING A TIME OF BIODIVERSIFICATION

Carbonate associated sulfate (CAS) is an important tool for understanding marine paleoenvironments. Although usually investigated in rocks formed in shallow marine settings, CAS changes are largely thought to reflect whole-ocean fluctuations in seawater sulfate. Most studies to date have used CAS to interpret anomalous oceanic conditions during times of high environmental stress such as Neoproterozoic glaciations, the Cambrian SPICE event, and the Permian-Triassic mass extinction. However, with few exceptions, CAS has not been widely used to investigate environmental conditions during times when marine animal life was flourishing.

In an effort to better understand the relationship between CAS dynamics in shallow marine settings during non-stressed intervals, we extracted CAS from rocks formed during the Great Ordovician Biodiversity Event (GOBE). We collected carbonate samples at 10m resolution from the Fillmore Formation of the Pogonip Group in Millard County, Utah, USA (C and G Sections of Hintze and Davis, 2003). Our results can be compared to CAS data from Thompson and Kah (2012), which indicate long-term deep-water anoxia.

Large (greater than 1m in height) stromatolite bioherms and patch reefs occur throughout the Fillmore sections. Occurrences of subtidal stromatolite bioherms in other strata, such as the Lower Triassic, have been interpreted to indicate anomalous seawater conditions. However, the presence of sponges in many of the stromatolitic buildups within our samples and a lack of lithologic indicators for anoxia suggest that anoxia was not prevalent during the deposition of these sediments. Our results will be used to investigate the interplay between deep-ocean anoxia (as indicated by CAS) and shallow-ocean environments which may only periodically have been exposed to anoxic conditions.