Synchroneity of the K-T oceanic mass extinction and meteorite impact: Blake Nose, western North Atlantic

A 10-cm-thick layer of green spherules occurs precisely at the biostratigra phic boundary between the Cretaceous and Paleogene (K-T boundary) at Ocean Drilling Program Site 1049 (lat 30 degrees 08'N, long 76 degrees 06'W), The spherulitic layer contains abundant rock fragments (chalk, limestone, dolo mite, chert, mica books, and schist) as well as shocked quartz, abundant la rge Cretaceous planktic foraminifera, and rounded clasts of clay as long as 4 mm interpreted as altered tektite glass probably derived from the Chicxu lub impact structure, Most of the Cretaceous foraminifera present above the spherule layer are not survivors since small specimens are conspicuously r are compared to large individuals. Instead, the Cretaceous taxa in Paleocen e sediments are thought to be reworked. The first Paleocene planktic forami nifera and calcareous nannofossil species are recorded immediately above th e spherule bed, the upper part of which contains an iridium anomaly. Hence, deposition of the impact ejecta exactly coincided with the biostratigraphi c K-T boundary and demonstrates that the impact event was synchronous with the evolutionary turnover in the oceans. These results are consistent with a reanalysis of the biostratigraphy of the K-T boundary stratotype, which a rgues that shallow-marine K-T boundary sections are not biostratigraphicall y more complete than deep-sea K-T boundary sites.