Abstract A thick, calcareous, clastic megabed of late Maastrichtian age has been known for sometime in western and central Cuba. This megabed was formed in association with the bolide impact at Chicxulub, Yucatán, at the K/T boundary, andiscomposed of a lower gravity-flow unit and an upper homogenite unit. The lower gravity-flow unit is dominantly composed of calcirudite that was formed because of collapses of the Yucatán, Cuban, and Bahamian platform margins and subsequent accumulation in the lower slope to basin margin environment. The gravity flow probably was triggered by a seismic wave induced by the impact, although a ballistic flow may have triggered collapse in the case of proximal sites (Yucatán margin). The upper homogenite unit is composed of massive and normally graded calcarenite to calcilutite that was formed as a result of large tsunamis associated with the impact and deposited in wider areas in the deeper part of Paleo-western Caribbean basin. Slight grain-size oscillations in this unit probably reflect the influence of repeated tsunamis. The large tsunamis were generated either by the movement of water into and out of the crater cavity or by the large-scale slope failure on the eastern margin of the Yucatán platform. In upper slope to shelf environments, gravity-flow deposits and homogenite are absent, and a thin sandstone complex influenced by repeating tsunami waves was deposited.

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