The effects of the Chesapeake Bay impact on calcareous nannofossil assemblages: patterns from the Watkins School core, Newport News, Virginia (USA)

The goal of this study was to assess the effect that the Late Eocene Chesapeake Bay bolide impact had on local patterns of calcareous nannofossil species composition, richness and preservation. Although calcareous nannofossil assemblages have been described from a handful of coreholes drilled within the impact structure, this is the first study to examine the calcareous nannofossils from the Watkins School core , which was recovered along the outer rim of the crater. A detailed stratigraphic assessment of the calcareous nannofossil assemblages across the synimpact-postimpact boundary was performed to determine whether the impact produced any local extinction. The results obtained suggest that, despite its size, the Chesapeake Bay impact did not significantly affect the local calcareous nannoplankton community. Little or no change was documented across the synimpact-postimpact boundary in calcareous nannofossil species composition, richness or preservation quality. These findings do not support the existence of a calcareous nannofossil 'dead zone' in this particular core; however, the presence of impact-fractured calcareous nannofossils does attest to the tremendous pressures generated by the impact.