A sequence of events across the Cretaceous-Tertiary boundary

Abstract

The lithological and biological sequence of events across the Cretaceous-Tertiary (K/T), as developed in thick and complete landbased sections and termed the standard K/T event sequence, is also found in many DSDP cores from all over the globe.

Microtektite-like spherules have been found in almost every core or outcrop with an iridium anomaly, forming a worldwide strewnfield. These “microtektites” are an excellent indicator of the K/T boundary level.

The basal Paleocene “Globigerina” eugubina Zone is now established in all major ocean basins. The difference in faunas between the Pacific and Tethys/Atlantic Oceans may point to different recovery of the oldest Paleocene planktonic foraminiferal assemblages in different ocean basins. Planktonic foraminifera and nannoplankton apparently show a different extinction-recovery pattern at the K/T boundary which suggests that the nannoplankton underwent final extinction later recover later than planktonic foraminifera. These patterns may be important for the evaluation of the type and range of environmental stress resulting from the hypothesized impact(s) at the K/T boundary. Blocking of sunlight by the dust cloud still can account for the clear mass-mortality at the K/T boundary but seems less likely as explanation for the final nannoplankton extinction, as photosynthetic nannoplankton appear to survive 1000–10,000 years into the Tertiary.