Facies changes, volcanism, and mass extinction conundrum: the Permian-Triassic boundary across the Barents Sea Shelf

The most dramatic mass extinction the Earth has ever experienced occurred 252 million years ago, at the end of the Permian. It was likely triggered by the volcanic eruptions and magmatic intrusions associated with the Siberian Traps Large Igneous Province (LIP), leading to dramatic climatic changes, with consequences lasting well into the Early Triassic. Here, we present a summary of the findings from the study of several sedimentary successions distributed across the Barents Sea that spanned the End Permian Mass Extinction (EPME) and the Permian-Triassic boundary. The four studied successions included the renowned Festningen section in the outer part of Isfjorden, western Spitsbergen; the DD-1 core and the associated river section in Deltadalen, central Spitsbergen; a core drilled offshore Kvitøya in northern Svalbard, and a core drilled on the Horda Platform in the Barents Sea. Datasets of various research lines were collected from these sections including sedimentology, organic geochemistry, isotope, geochronology, XRF, mineralogy, ichnology, palaeontology, palynology and digital outcrop data. Historically, the Permian-Triassic boundary exposed today in Svalbard (and at various places across the High Arctic regions) was placed at the very prominent and abrupt facies change occurring between the siliceous mudstones or spiculites of the Kapp Starostin Formation, and the overlying soft, non-siliceous mudstones and siltstones of the Vardebukta and Vikinghøgda formations. The abruptness of this facies change, which also marks the demise of sponges, led to the belief that it represented a hiatus or a gap of several million years, with the uppermost Permian strata missing from the sedimentary record, while the mudstones of the Vardebukta and Vikinghøgda formations were definitely of Lower Triassic age, based on ammonoid biostratigraphy. Hindeodus parvus, the conodont that defines the base of the Triassic, was for the first time identified in Svalbard a few meters above the lithostratigraphic boundary, which is therefore of Upper Permian age. Additionally, our new data show that sedimentation was continuous across this lithostratigraphic boundary. This transition from the Kapp Starostin Formation to the Vardebukta and Vikinghøgda formations was accompanied by a major reorganisation/inversion of the basin(s), but its exact nature remains puzzling. Further, all measured sections record the EPME, which is associated with a 6-8 ‰ δ13CVPDB negative excursion, and measured between the lithostratigraphic and the Permian-Triassic boundaries. These negative isotopic excursions are found in close vicinity to several tephra layers that have been precisely dated at 252.13 ± 0.62 Ma, strongly suggesting a connection to the Siberian Traps LIP event. The mass extinction is also confirmed by the very rapid decreasing of trace fossil abundance and diversity, as anoxia spread across the water from proximal and shallow water to deeper settings. Geochemical and ichnological data indicate the occurrence of several anoxic pulses, intersected by very brief episodes of improved oxygenation levels. It took ca. 145 Kyr for life to recover after the extinction event, based on sedimentation rate calculations. Data also suggest that a shift towards more arid climatic conditions and increased eutrophication on land accompanied the EPME.