New Mexico Geological Society Annual Spring Meeting — Abstracts

Ocean Anoxic Events (OAEs) are periods in time when the earth’s ocean basins became largely or entirely depleted of dissolved oxygen. These periods lasted several million years in some cases and have contributed to major die-offs such as the End-Permian Mass Extinction. The middle Cretaceous is characterized by a series of OAEs; however, the biotic impact of these events is unclear. Utilizing the Paleobiology Database (PBDB), we analyzed both species-level and generic-level global diversity of mollusks across the Bonarelli event (OAE2) at the Cenomanian-Turonian (C/T) stage boundary. In order to test whether survivorship across the OAE was influenced by paleoecological factors, diversity data was collected within the parameters of faunality (i.e., surface vs. burrowing lifestyle), mobility, and feeding strategy. Species and generic databases were sample-standardized, and diversity was statistically compared via a Mann-Whitney U. Significant (p<0.001) diversity losses and negative effect sizes (-1.669<E.S.<-0.358) were observed when comparing both total diversity, and across many paleoecological contexts with some exceptions. Diversity of epifaunal, semi-infaunal, stationary taxa, suspension feeders, chemosymbionts and omnivores did not significantly change (p>0.05) across the C/T boundary at the generic level. Preliminary analysis of the influence of paleoecological factors on extinction indicates that infaunal and actively mobile taxa were hit the hardest (E.S.= -1.669 and -1.408 respectively.) This contrasts to periods of gradual environmental change without anoxia such as the upper Campanian-Maastrichtian transition. Across this stage boundary, we find that there was a significant unilateral increase in total diversity at both the species- and generic level, with positive effect sizes (0.502<E.S.<4.908), as well as within all paleoecological categories. The few exceptions include omnivorous and carnivorous feeding strategies and nektonic lifestyle, which showed a loss in diversity (E.S.= -1.07). In contrast to previous research suggesting that OAE2 only caused minor impacts to global diversity patterns, these results support the Bonarelli Event as a significant driver of extinctions in Molluscan taxa.