RESPONSE OF COLD SEEP PALEOCOMMUNITIES TO OCEANIC ANOXIC EVENT 2 IN THE WESTERN INTERIOR SEAWAY

Paleotemperature estimates across the Cenomanian-Turonian (C-T) boundary are amongst the highest of the Phanerozoic and coincide with Oceanic Anoxic Event 2 (OAE2; 94 Ma), a globally recognized event associated with massive organic carbon burial and faunal turnover. Strata deposited in the North American Western Interior Seaway (WIS) preserve a near continuous record of biotic responses and ecosystem change across this event. During OAE2, the southwestern margin of the WIS was the site of widespread cold seep activity. Although the paleontology of the C-T interval in the WIS has been well studied, the response of seep communities has not been investigated, hindering our ability to fully understand the spectrum of processes driving patterns of species distribution, survivorship, and extinction across OAE2. Here, we test the hypothesis that seep ecosystems responded differently to OAE2 using macroinvertebrate abundance, richness, and functional diversity from seep and non-seep deposits. We studied four seep localities from the Tropic Shale in Kane County, UT. Additional macroinvertebrate occurrence data from three correlative non-seep sites in UT, AZ, and CO were obtained from the Paleobiology Database. We correlated our sections to the Smoky Hollow #1 Core (SH#1) to utilize existing chemostratigraphic data, providing a high-resolution record of changing redox conditions across the C-T in our study area. Preliminary data suggest seep and non-seep communities were comparable in terms of taxonomic and functional diversity during early OAE2, though abundance is highest in UT. Pulses of increased anoxia appear to correlate to decreases in infaunal suspension feeders and increases in chemosymbiotic bivalves. During peak OAE2, benthic infauna abundance and diversity is greatly reduced at all localities, though seep carbonates are consistently fossiliferous. Ammonite abundance and richness declines and appear restricted to western margin sites, though abundance is highest at seeps; this supports previous studies’ interpretations of seeps as a preferred ammonite habitat in the WIS. Our preliminary data lead us to propose that seeps had an unrecognized role in shaping faunal distribution patterns during OAE2 in the WIS, and possibly, served as refuges during other environmental perturbations across time and space.