LIPs Don’t Lie - Tellurium in Sediments as a Novel Proxy to Unravel the Link Between Flood Basalt Volcanism and Mass Extinctions

Large Igneous Provinces (LIPs) represent the largest volcanic structures on Earth and are mostly expressed as either subaerial continental flood basalts (CFBs) or submarine oceanic plateaus. In addition to their immense eruptive volumes of mostly basaltic rock, the main emplacement phases of LIPs is in general limited to less than 1 Myr. The the 5 biggest mass extinction events of Phanerozoic coincided in time with periods of LIP emplacement. Moreover, several smaller LIP events coincided with periods of climate change and biotic turnovers. A variety of magmatic and metamorphic processes have been proposed as catastrophe-driving mechanisms (i.e., emissions of CO2, SO2, toxic metals, release of thermogenic CH4, etc). However, the distinct rock records which either contain information about the magmatic volumes, volcanic rates, and chronology (volcanic rocks) or changes in the environment and biosphere (sediments) complicate tying cause and effect. Despite the temporal agreement, the role of LIPs in environmental changes has been discussed, mainly due to the fact that the paleo-environment did not exhibit the same response to every LIP event and for some extinction events other causes such as bolide impact have been proposed. Understanding the relationships between massive volcanism, environmental change, and extinction events is further hindered by difficulties in reconstructing volcanic stratigraphies and establishing geochronologic histories at a 100 - 10 kyr resolution, which is the timescale of many mass extinction events. A means of untangling the cause-and-effect relationship of large scale volcanism and environmental change is the use of geochemical proxies in sediments, recording volcanism during deposition. For the past decade sedimentary mercury (Hg) has emerged as the main geochemical proxy for flood basalt volcanism. However, due to the strong affinity of Hg for organic matter (OM), various second order processes influencing Hg in the natural environment, and analytical complexities, Hg studies have often showed to be inconsistent within individual extinction intervals. Although other sedimentary trace elements have been suggested as geochemical proxies for volcanism (e.g., Ni, Zn, Te), these potential proxies have found little application so far. Here, we investigate sedimentary tellurium (Te) as a novel and robust proxy to reconstruct CFB volcanism at the < 10 kyr scale. Te was shown to be among the most enriched trace elements in volcanic gas, contrasting with its otherwise exceptionally low natural abundance in the Earth’s crust. While the knowledge about Te in the natural environment is still riddled with gaps, it was shown to not be significantly affected by changes in paleoredox or -productivity, making it a potentially excellent geochemical proxy for volcanism recorded in sediments. We will present 3 works (2 of which are published in peer-reviewed journals), the first of which establishes the analytical methods needed to measure Te efficiently, before presenting 2 case studies, which demonstrate the ability of Te to reconstruct past periods of volcanism in the context of the Deccan Traps (∼66 Ma) and the North Atlantic Igneous Province (∼56 Ma; NAIP). First, we will present our analytical methods used to measure Te together with 45 other trace elements using dissolution single-quadrupole ICP-MS in a time- and cost-effective set up. We applied our method to international rock standards to verify our analyses and provide data for Deccan basalts and inter-trappean fossil soil horizons (red boles) to demonstrate the magmatic outgassing and sedimentary sequestration of Te. Furthermore, we measured glacial diamictite samples previously used to quantify the average chemical composition of the upper continental crust (UCC) and, thus, establish a robust average Te concentration for the UCC of 36.7 pbb. In a first case study, we will investigate a mostly complete sediment succession from Wadi Nukhul, Egypt of Late Maastrichtian to Early Eocene age and thus encompassing 2 LIP events (i.e., the Deccan Traps and the NAIP). We find enrichments in Te in the latest Maastrichtian and earliest Danian and in the Late Paleocene to Early Eocene, resulting from volcanic outgassing of the Deccan Traps and the NAIP respectively. While a first Te peak in the Late Maastrichtian coincides with Late Maastrichtian Warming Event (LMWE), a second, more intense peak which initiated approximately 100 kyr prior to the Cretaceous/Paleogene boundary (KPB) and reached its highest values 70 - 30 kyr before the KPB, is inferred to be related to eruptions of the voluminous Wai subgroup. We conclude that the Chicxulub impact did not trigger those eruptions as previously suggested and that Deccan volcanism may have had an amplifying effect on the KPB extinction. A following 6 Myr period of low Te during the Paleocene where no LIP volcanism occurred is followed by an increase in Te starting at 57.5 Ma and peaking at the Paleocene-Eocene boundary (PEB; 56 Ma) during the opening of the North Atlantic coinciding with the highest eruptive rates of the NAIP. We concluded that Te may be an additional proxy for volcanism of the Deccan Traps and NAIP. Our second case study focuses on the Paleocene-Eocene Thermal Maximum (PETM). We measured a total of 401 sediment samples from 3 different sites across the northern hemisphere and found an increase in Te concentrations and Te/Th ratios close to the onset of the PETM that remain high until the end of the main North Atlantic ash phase about 1 Myr later. The volcanic origin of these Te signals was supported by absence of correlations with trace elements controlled by changes in paleo-redox or -productivity. Calculated volcanic Te fluxes suggest increased volcanism in the latest Paleocene and early Eocene. This fits existing radiometric ages of the NAIP, which suggest that a more than 5 km thickness of lava in eastern Greenland and the Faroes was erupted within about 1 Myr between 56 to 55 Ma. While Te fluxes show similar trends across different sites, Hg concentrations and Hg/TOC ratios exhibit disparity between different PETM sites, suggesting the value of Te as an additional proxy for NAIP volcanism.