SELECTED BY OCEAN ACIDIFICATION? EARLIEST JURASSIC BIVALVES OF NEVADA (USA)

Modern research of anthropogenic ocean acidification is relevant to Mesozoic paleoecology, particularly the interval of global carbon cycle changes that coincided with the Triassic – Jurassic mass extinction. Affecting both terrestrial and marine systems, this extinction interval has been characterized as the third largest ecological crash in earth history. Evidence for massive volcanism at the boundary has focused attention on proxies for atmospheric carbon, including studies of isotopic fractionation and shifts in plant morphology. Paleogeochemical models combine intense volcanic degassing (CO₂ and SO₂), chemical weathering, and seafloor CH₄ hydrate release to account for observed trends in the rock record. Global suspension of carbonate sedimentation at the boundary – previously interpreted as sea level fluctuation – supports the hypothesis that the latest Triassic ocean was less hospitable to biomineralization due to ocean acidification. Community-level changes in the fossil record reveal ecological responses to environmental change, and these responses are particularly extreme during intervals of mass extinction. Hypotheses about the effect of elevated marine pCO₂ on Triassic – Jurassic marine benthic communities have been tested and supported at the community level with Tethyan fauna. In this study, we discuss observations from the excellent benthic record of Panthalassic fauna in Nevada. Across the Triassic – Jurassic boundary at New York Canyon, a relatively diverse community of bivalves is replaced rapidly with a community of only two common reported components: mussels and pectinids. Previous studies suggested this benthic community change was evidence of local sea-level change, in lieu of direct sedimentological evidence. If the decrease in carbonate at the boundary in Nevada is interpreted to be part of the global pattern, then ocean acidification can be hypothesized in the region, as it is globally. Mussels might have been particularly equipped to succeed in an acidity crisis environment, according to modern analogues and modern marine biology. We further suggest that trends in the pelagic record (ammonoids) of New York Canyon are consistent with hypothesized consequences of ocean acidification.