BIOLOGICAL CONSEQUENCES OF CHICXULUB IMPACT ANGLE (Invited Presentation)

Schultz and D’Hondt (1996) proposed that geophysical signatures of the Chicxulub impact structure closely resemble asymmetries produced by oblique cratering experiments and observed on planetary surfaces. We interpreted these asymmetric signatures to suggest an impact trajectory from the southeast to the northwest at a 20–30° angle.

The oblique impact hypothesis has major implications for understanding the relationship between the Chicxulub impact and end-Cretaceous extinctions. First, the severity of global extinctions may have been strongly contingent on the angle of impact. Second, biotic consequences may have been most severe and catastrophic in the Northern Hemisphere, downrange of the impact. Geographic variation in the magnitude of Cretaceous-Paleogene (K-Pg) plant extinction and the earliest Paleocene “fern spike” are consistent with the proposed trajectory. Jiang and colleagues (2010) recently showed that the biogeography of K-Pg calcareous nannoplankton extinction is also consistent with the proposed trajectory.

For most categories of organisms, the biogeography of K-Pg extinction remains largely unknown. Closer examination of that variation will test the proposed consequences of impact angle. It may also greatly improve understanding of how geographic variation in extinction intensity shaped the recovery of biological diversity in the post-impact world.