HOW DOES SUBMARINE GROUNDWATER DISCHARGE AFFECT PALEOTEMPERATURE CALCULATIONS? A CASE STUDY FROM DEVONIAN ISLAND ARCS IN THE CENTRAL ASIAN OROGENIC BELT.

The Frasnian-Famennian (F-F) mass extinction during the Late Devonian period (372 Ma) is one of the most severe extinction events in Earth’s history. Although rapid climate change has been suggested as a cause, uncertainty remains about the ocean paleotemperatures associated with this extinction event. Paleotemperatures in marine environments can be inferred from δ¹⁸O isotope values in fossils using mineral-water oxygen isotope fractionation, but there are relative few study sites in open-ocean paleoenvironments at the F-F boundary, except for the volcanic island arcs of the Central Asian Orogenic Belt (CAOB). One of the challenges in determining paleotemperatures in near-shore, high-porosity island arc environments is accounting for submarine groundwater discharge, which can artificially inflate paleotemperatures derived from δ¹⁸O calcite-water fractionation. Paleozoic hydrogeologic conditions of the CAOB study sites were simulated using the island of Montserrat as a modern-day analog of a volcanic island arc environment, and a 2D submarine groundwater discharge model was developed using SUTRA. δ¹⁸O_water values were estimated using a salinity mixing model derived from SUTRA modeling, and δ¹⁸O_calcite was calculated using a temperature range from 5-45°C. Nearshore δ¹⁸O_calcite values are expected to range from 23.4 to 32.0‰ VSMOW (-7 to 1‰ VPDB) when affected by submarine groundwater discharge.