The silver bullet - new evidence for a hypervelocity impact origin for the Silverpit Crater

An impact origin for the Silverpit Crater, on the UK continental shelf, has been contested over the last two decades, with a lack of a ‘silver bullet’ – traditionally petrographic evidence of shock metamorphism – to resolve the debate. Here we present new 3D seismic, petrographic and biostratigraphic data, and numerical impact simulations to test the impact hypothesis. The seismic data provide exceptional imaging of the entire structure for the first time, confirming the presence of a central uplift, annular moat, damage zone and numerous secondary craters on the contemporaneous seabed. The distribution of normal and reverse faults in the brim, and curved radial faults around the central uplift suggest a low-angle impact from the west. The pitted, flat-topped central uplift at the top chalk horizon may indicate significant devolatilization of chalk immediately following impact. Biostratigraphic data confirm that this event occurred during the middle Eocene, between 43-46 million years ago. Petrographic analysis from the reworked ejecta sequence in the nearby 43/25-1 well reveals two grains with shock lamellae, indicating shock pressures of ~10-13 GPa, consistent with results from our numerical models. This combination of evidence proves that the Silverpit structure is an exceptionally preserved hypervelocity impact structure.