Ocean acidification and biocalcification crisis at the Triassic-Jurassic boundary

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Causes for the Triassic-Jurassic boundary mass-extinction event (Tr-J; 199.6 Ma) remain poorly understood. One popular extinction scenario envisions a role for the massive release of volatiles (CO2, SO2) from the outflow of voluminous amounts of flood basalt. Evidence for a role of flood basalt volcanism in Tr-J extinctions include: (1) a rapid four-fold rise in pCO2, documented by plant leaf stomata, (2) simultaneous, large negative carbon isotope excursions in carbonate and organic carbon pools and (3) gradual, rather than catastrophic, extinctions and turnover in many groups of marine and terrestrial biota. In analogy with the predicted impact of anthropogenic CO2 emissions on ocean chemistry, it can be hypothesized that a major consequence of a rapid and significant increase in pCO2 is the acidification of the surface ocean (pH decrease) and hence a decrease in carbonate saturation ([CO3 2 ] decrease), leading to a biocalcification crisis. Indeed, shallow marine carbonate-producing organisms, such as hermatypic scleractinian corals, bivalves and coccolithophorids, show some of the highest extinction rates during the latest Rhaetian, and reef building was disrupted worldwide for several million years after the Tr-J boundary. Furthermore, the Early Jurassic appears to mark a brief interlude of extensive calcite deposition in shallow marine settings during a time of predominant Aragonite Seas. In response to a halt in biogenic carbonate production, increased alkalinity may have been mediated by abiogenic carbonate precipitation in the form of widespread deposition of calcite ooids, low-magnesium calcite marine cements and/or microbially in the form of extensive micritic precipitates and microbialites. The aim of this research project is to find sedimentological and geochemical evidence for this hypothesized biocalcification crisis by studying in detail Tr-J boundary sections along the northern and southern margins of the Tethys in the Southern Alps, Lessini Mountains and Carpathian Mountains. The gathered results will serve as a pilot study for the further development of future research projects.