Geochemical evidence for volcanic activity prior to and enhanced terrestrial weathering during the paleocene eocene thermal maximum

Abstract

The Re-Os and major element geochemistry of an expanded gray shale sequence from the Central Basin in Spitsbergen, Svalbard Archipelago (Norway) over the Paleocene Eocene Thermal Maximum (PETM) is presented. The data suggest that a significant volcanic episode, as indicated primarily by a large drop in 187Os/188Os, occurred just prior to or coincident with the onset of the PETM. The distinct geochemistry of the inferred ash component is consistent with the geochemistry of contemporaneous ashes previously sampled in Denmark, and persists in the sedimentary record for ~8ka. Based on the substantial size of the 187Os/188Os decrease (δ187Os/188Os ~-0.23), the volcanic event must have involved widespread ash deposition in the local catchment. The terrestrially deposited ash weathered rapidly, shifting the 187Os/188Os of the basin water column to <0.5. Temporally, the volcanic event coincides with (or predates by a few thousand years) the onset of the PETM, suggesting northwest European shelf volcanism as the trigger for the PETM. As the planet warmed, both dissolved and detrital indicators of weathering indicate a <10ka pulse of more weathered material to the basin, shifting authigenic 187Os/188Os to more radiogenic values and depositing clastic materials with higher Chemical Index of Alteration and lower Na/Ti. Persistently anoxic sedimentary pore fluids, interpreted to reflect bottom water anoxia, initiated close to the onset of the PETM. Anoxic, mainly euxinic, conditions persisted for ~50ka, ending abruptly ~55.77Ma. Anoxia appears related to enhanced high-latitude hydrological cycling and consequent basinal stratification during the PETM. © 2013 Elsevier Ltd.