IRIDIUM AND DINOCYSTS AT THE CRETACEOUS-TERTIARY BOUNDARY ON SEYMOUR-ISLAND, ANTARCTICA - IMPLICATIONS FOR THE K-T EVENT

A single iridium anomaly (40 times background concentration), correlat ed with the Cretaceous-Tertiary (K-T) boundary, is present within an i nterval of unconsolidated glauconitic silty sands in a marine clastic sequence on Seymour Island, Antarctic Peninsula. Dinocysts provide the basis for biostratigraphic identification of a 20-30 cm K-T transitio nal interval; calcareous microfossils have not been preserved in the g lauconitic beds. Dinocysts also record an earliest Danian transgressiv e event 10 cm above the transition interval. The Ir spike is near the base of the dinocyst transition interval and 30 cm below the flooding horizon. The Seymour Island site, located at a high latitude (63-degre es-S) at the end of the Cretaceous, provides no compelling evidence fo r mass extinction at the K-T boundary.