Investigating Te and other volatile trace elements in sediments as proxies for flood basalt volcanism

Linking the timing and eruption rate of flood basalt volcanism with the sedimentary record is critical to understanding how large volcanic events cause environmental change during periods of mass extinction. We investigated the trace elements Te, Re, Cd, As, Sb, Tl which are highly enriched in volcanic gas relative to crustal rocks, as potential proxies for past volcanism. We analysed sediments from the Permian-Triassic, Pliensbachian-Toarcian and Cretaceous-Paleogene boundaries where mass extinction events have been linked to Siberian, Karoo-Ferrar and Deccan flood basalt volcanism respectively.

At the P/Tr boundary at Spitsbergen, Te concentrations and Te/Th ratios increase by a factor of 10 together with Hg at the Late Permian Extinction level, and decrease gradually over 300-400 kyr into the Griesbachian. Two Lower Jurassic sections (Portugal, France) show similar enrichments in Te during and after the Toarcian Oceanic Anoxic Event, and at the Pl/To boundary. Late Maastrichtian and early Danian sediments at Elles (Tunisia) record several peaks in Te/Th below and above the K/Pg boundary, possibly corresponding to 100 kyr pulses of Deccan volcanism, and a ‘spike’ due to extra-terrestrial Te in the K/Pg boundary clay.

Te/Th does not appear to vary systematically with sediment lithology, or with changes in environmental conditions. We suggest that the Te enrichments are volcanic in origin, and together with Hg and Hg/TOC ratios, may be used as a proxy for the intensity of volcanic activity. In contrast, Cd, Tl and Re concentrations in sediments from these sections are at least partly influenced by environmental factors.