The Mimbral outcrop in northeastern Mexico represents nearly continuous sedimentation across the Cretaceous/Tertiary (K/T) transition. The K/T boundary is present in a 4 cm clay layer and 3 mm red layer above the top of a channel-fill deposit. The 60 m wide and 3 m high channel-fill deposit is of latest Maastrichtian age (A. mayaroensis Zone). It consists off aunally, lithologically and mineralogically distinct units that appear to represent a series of gravity flows related to the latest Maastrichtian sea-level lowstand. The biotic effects of the K/T boundary event were not catastrophic for planktic foraminiferal faunas at Mimbral, NE Mexico. Although 2/3 of the species disappeared at or below the K/T boundary, the effect on the overall foraminiferal population was small (<17%) because only rare, already endangered taxa disappeared. These taxa were specialized tropical and subtropical forms intolerant of environmental changes. The dominant taxa (>83%) consist of cosmopolitan forms tolerant of wide ranging environmental conditions. These survived the K/T boundary event without any sudden changes in their relative abundance. Their terminal decline about 100,000 years after the K/T boundary appears to be related to competition from the evolving Tertiary fauna. The limited biotic effects observed across the K/T boundary at Mimbral are consistent with other low latitude sections, and indicate that if a bolide impact occurred in the Caribbean, the biologic consequences were not as catastrophic as generally assumed even within a radius of 2000 miles.  PDF