Uisdean Nicholson - From the Nadir to Silverpit Crater: using 3D seismic to test impact origin, dynamics and hazards

Impact cratering is the dominant geological process shaping all solid planetary bodies in the Solar System and forms an important geological hazard on Earth. The 1908 Tunguska airblast, which flattened a forest over 2000 km², and the recent close call of Asteroid 2024 YR4 highlight the potential dangers posed by even small-scale collisions. However, impacts with Earth’s surface have never been observed in historic timescales, and our understanding of crater formation processes is particularly limited when it comes to larger (>3 km) "complex" craters. This talk focuses on the recent discovery and confirmation of impact origin of two mid-sized complex craters that represent a once per ~100 ky hazard.

Nadir Crater is an exceptionally well-preserved impact structure situated ~400 km offshore Guinea, West Africa. The crater was identified by chance from a single 2D seismic profile across the Guinea Plateau, that revealed a concave-up crater floor, a distinct central uplift and annular moat surrounded by normal faults, all consistent with a complex crater. Intriguingly, the crater floor was interpreted to be near K-Pg in age, leading to the possibility that this could be genetically related to the Chicxulub impact event (Nicholson et al., 2022).

Serendipity struck again in 2022, when we found out that a seismic company had acquired a new 3D seismic survey directly across the structure. These data (Nicholson et al., 2024) revealed the crater architecture in unprecedented detail, allowing us to reconstruct crater kinematics during the crater modification stage, and to observe evidence of the cascade of environmental consequences that ensued, including liquefaction, tsunami resurge and landslides.

Silverpit Crater was discovered in the North Sea in the early 2000s, but an impact origin was disputed over the subsequent decades. At a famous geological society debate in 2008, the consensus was that this was not an impact structure. However, new 3D seismic data acquired for carbon capture and storage in the early 2020s led to our re-assessment of an impact origin. In combination with petrographic analysis and impact modelling, we demonstrated unequivocally that this is an impact crater– the first such structure in the UK. The new seismic also reveal intriguing evidence for large-scale, catastrophic devolatilzation and the first clear evidence of secondary craters by ballistic ejection of target material.

3D seismic data has been critical to the enhanced imaging of these structures, providing crucial constraints on crater kinematics and impact modelling, as well as visually impressive data for public dissemination of scientific results. With Nadir Crater now scheduled to be drilled by IODP³ in 2027, we anticipate that these craters will continue to provide an important contribution to our understanding of planetary impacts for many years to come.