AbstractIn this paper, we present an expansion of the model for marine ecosystem collapse at the Cretaceous‐Tertiary boundary presented by Brinkhuis and Zachariasse (1988). A long‐term sea‐level drop at the end of the Cretaceous culminated in a short‐term regressive pulse at K‐T time. Deep‐water production was curtailed, minimizing the vertical advection of nutrients and oxygen in the oceans. Consequently, a productivity crisis developed, which could only be survived by cosmopolitan shallow‐dwellers, and the Oxygen Minimum Zone (OMZ) expanded. No sustained Oceanic Anoxic Event followed the K‐T boundary event, since productivity had dropped to extremely low values. At K‐T time, however, the short‐term expansion of the OMZ, invoked by the combination of minimized oxygen advection and abrupt mass mortality, caused dysoxic conditions even to reach up to the shelves, as can be deduced from sedimentological, chemical and fau