Bolide impact effects on the West Florida Platform, Gulf of Mexico: end Cretaceous and late Eocene

Abstract

This study documents seismic reflection evidence that two different bolide impacts significantly disrupted stratigraphic and depositional processes on the West Florida Platform (Gulf of Mexico). The first impact terminated the Late Cretaceous Epoch (Chicxulub impact, Mexico; ca. 66 Ma; end-Maastrichtian age). The second took place in the late Eocene (Chesapeake Bay impact, Virginia, USA, portion of the Chesapeake Bay; ca. 35 Ma; Priabonian age). Both impacts produced far-reaching seismic shaking and ground roll followed by an impact-generated tsunami, the effects of which are evident in the seismostratigraphic record. The Chicxulub seismic shaking caused collapse and shoreward retreat of the Florida Escarpment and widely disrupted (faulting, folding, slumping) normal flat-lying shelf beds. The associated tsunami currents redistributed these shelf deposits and mixed them together with collapse debris from the escarpment to form a thick wedge of sediments along the base of the escarpment. The Chesapeake Bay impact created a mounded sedimentary deposit near the outer edge of the late Eocene ramp slope. This deposit also has a bipartite origin. A lower layer is marked by en echelon faulting created in situ by seismic shaking, whereas an upper layer represents sediments redistributed from the late Eocene shelf and upper ramp slope by tsunami-driven bottom currents (debris flows, contour currents, slumps). This is the first report of seismic effects from the Chesapeake Bay impact in the Gulf of Mexico. These results further demonstrate that large-scale marine bolide impacts have widespread effects on the stratigraphic and depositional record of Earth.