A single iridium anomaly (40 times background concentration), correlated with the Cretaceous-Tertiary (K-T) boundary, is present within an interval 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 transitional interval; calcareous microfossils have not been preserved in the glauconitic beds. Dinocysts also record an earliest Danian transgressive 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°S) at the end of the Cretaceous, provides no compelling evidence for mass extinction at the K-T boundary.