Much disagreement over the interpretation of data bearing on various Cretaceous/Tertiary (K/T) extinction scenarios results from a failure to view these data within their appropriate stratigraphic context. Combined biostratigraphic and chronostratigraphic analyses of K/T boundary sequences have revealed systematic differences in patterns of sediment accumulation within continental-shelf and deep-sea depositional settings. Although virtually all deep-sea boundary sequences are marked by intervals of nondeposition or hiatus formation during the latest Cretaceous and earliest Tertiary, many continental shelf-slope sequences appear to be temporally complete over this same interval. This differential pattern of sediment accumulation can be related to the latest Maastrichtian-earliest Danian sea-level rise, during which deep-sea sediment- accumulation rates would be expected to drop as the locus of sediment deposition migrated across the continental shelf. Our data suggest that the abrupt shifts in carbon-isotope abundances, single-peak Ir anomalies, and apparently instantaneous mass extinctions of marine plankton—which are routinely reported from deep-sea K/T boundary sequences and used to support a causal relation between Late Cretaceous bolide impacts and K/T mass extinctions—may be artifacts of a temporally incomplete (or extremely condensed) deep-sea stratigraphic record.

This content is PDF only. Please click on the PDF icon to access.

First Page Preview

First page PDF preview
You do not currently have access to this article.