Tellurium anomalies as signs of intensive volcanic activity around the Devonian-Carboniferous boundary in The South Tian-Shan (southern Uzbekistan)

The Latest Devonian Hangenberg Event (ca.359 Ma) was one of the largest crises of the biosphere. It was directly responsible for the extinction of about 50 % of marine genera mainly from the pelagic realm such as ammonoids, conodonts and placoderm fish. This extinction is linked to worldwide anoxia caused by global climate changes, but its direct cause remains unidentified and still a topic of many scientific studies. Recently discovered mercury spikes, detected at the the D/C boundary in many parts of the world, present convincing evidence of increased volcanic and hydrothermal activity. Newly, tellurium, along Hg anomalies, has been successfully used to confirm Siberian volcanism at the end of the Permian. Today, the global volcanic tellurium flux often shows greater enrichment in Te compared to other volatile elements like mercury, thallium, or bismuth. Therefore tellurium may prove to be a much more promising indicator of volcanism. There is a lot of data on the Hg chemostratigraphy at the crucial intervals during Phanerozoic. In contrast, our knowledge of tellurium cycles during critical intervals of mass extinctions, LIPs emplacements and biotic crises, is entirely lacking. To investigate this issue, we have examined a succession of deep-water, pelagic sedimentary rocks, encompassing the Devonian–Carboniferous boundary interval in the Novchomok section (southern Uzbekistan) using tellurium chemostratigraphy. Previous studies of this section at the Devonian-Carboniferous boundary, had detected the Hg and Hg/TOC anomalies in marly shales, marls, and carbonates, occurring independently of the facies changes, which imply a volcanic origins of those anomalies. Additionally, the presence of negative δ13Corg excursions reflects a massive release of isotopically light carbon from volcanogenic and thermogenic devolatilization. Our preliminary results of Te contents and Te/Th ratios at the Devonian–Carboniferous boundary in the Tian-Shan are promising. Here we report for the first time large anomalous Te spikes (with maximum values reaching 930 ppb) and an increase in Te/Th ratios, which closely correspond with Hg spikes and a negative shift in ẟ13Corg, and indicate that Te could be promising volcanic activity proxy in deep time intervals.