Ejecta layer at the Cretaceous-Tertiary boundary, Bass River, New Jersey (Ocean Drilling Program Leg 174AX)

Abstract

A continuously cored borehole drilled at Bass River, New Jersey, recovered a Cretaceous-Tertiary (K-T) succession with a 6-cm-thick spherule layer immediately above the boundary. Below the spherule layer, the Cretaceous glauconitic clay is extensively burrowed and contains the uppermost Maastrichtian Micula prinsii calcareous nannofossil zone. Spherical impressions of spherules at the top of the Cretaceous indicate nearly instantaneous deposition of ejecta from the Chicxulub impact. The thickest ejecta layer shows clearly that a single impact occurred precisely at K-T boundary time. Above the spherule layer, the glauconitic clay contains the planktonic foraminiferal P0 and P-alpha Zones, indicating (1) a complete K-T succession and (2) continuous deposition interrupted only by fallout of the ejecta layer. Clay clasts within a 6 cm interval above the spherule layer contain Cretaceous microfossils and may be rip-up clasts from a tsunami or possibly a megastorm event. Extinction of the Cretaceous planktonic foraminifers and burrowing organisms occurs abruptly at the K-T boundary. Thus, the Bass River K-T succession unequivocally links the Chicxulub bolide impact to the mass extinctions at the end of the Mesozoic.