Weathering response of a clastic source-to-sink system to extreme environmental perturbations: the Permian-Triassic transition on Finnmark Platform, Barents Sea

The eruption of the Siberian Traps at the Permian-Triassic transition significantly affected depositional environments world-wide. Known consequences are (I) extreme global warming, (II) increased soil-erosion, decreasing chemical weathering and aridification on the continents, (III) oceanic stagnation and acidification, and (IV) the most severe mass extinction on Earth. In the Southwestern Barents Sea, the record across the Permian transition is continuous at a cored site located close to the basin margin, making it possible to study the response of a relatively proximal source-to-sink system in terms of petrography, provenance, and sedimentary environments. The record consists of Upper Permian carbonates developed as an oxygenated carbonate platform, overlain by transitional dys- or anoxic, organic-rich shales and a Lower Triassic prograding siliciclastic turbidite-prodelta-delta system.

In this project we use these deposits to reconstruct the sediment source area and changes within the catchment area across the Permian-Triassic transition. From a dataset of >50 2D seismic lines and sampled sandstones from ~160 m stratigraphic cores, we have already found that the sediment supply rate increased by more than 100-fold, which vastly exceeds the world-wide trend of sediment supply increase across the Permian-Triassic transition (6–7-fold). This has led to several models that may explain the observed evolution, but in order to distinguish between these models, mudstone provenance and weathering proxies must also be investigated. Herein we focus on the Neodymium and Hafnium isotopic composition in the mudstones, and thus present insights into weathering processes. This will allow us to investigate the climatic component in the catchment across the transition. Our preliminary results show that the catchment in the Late Permian supplied mudstones with extreme (much more than observed in modern deposits) chemical weathering and a stable provenance from a small, nearshore catchment. Broadly coincident with the Permian Triassic Transition, mudstones show a provenance change consistent with increase in catchment area and a strong decrease in chemical weathering. This indicates that the increase in sediment supply from at the Permian-Triassic transition was not caused by sudden flushing of onshore weathered material stored in catchments during the Permian, nor can it be caused by increase in chemical weathering because of climate change. It appears that the observed changes are mainly a result of tectonic uplift and tilting of Northern Fennoscandia possibly due to onset of a new rifting episode in the Norwegian-Greenland Sea. The coincidence of this strong response to the Permian-Triassic transition could perhaps indicate that adjustments of the catchment to the new topographic setting was helped by the climate change.