AN IMPACT-RELATED, HIGH-ENERGY FLOW DEPOSIT FROM WESTERN CUBA

In resent years, the Chicxulub impact related several high energy flow deposite reported arong Yucat? platform (eg. Pope et al. Grajales-Nishimura et al., 2000, Kiyokawa et al., 2002). These sediments are identified as how strong flow occurred and influences around environments during the giant impact. Especially the Cacarajicara Formation in the Rosario belt of Western Cuba is a calcareous clastic sequence, more than 700 m thick, which contains shocked quartz throughout, and smectite and goethite spherules in its lower part. Three members are recognized: The lower member consists of cobbles (mainly limestone) and chert boulders, and it disconformably overlies Cretaceous deep-water rocks. Well-sorted clasts having little matrix suggest that the small fragments in this member have been washed away under high-pore pressure conditions. The reversely graded clasts, highly hydrostatically fractured grains, and evidence for high pore pressure suggest that the lower member was deposited under a high-density and high-speed laminar-flow condition. The middle member consists of upward-grading, massive to well-bedded, homogeneous calcarenite. Unusual fluid-escape structures in the thick calcarenite and well-stratified sequence suggest that this member formed by high-density turbidity suspension. The upper member consists of massive, fine calcarenite to limey mudstone without evidence of bioturbation. We infer that it was deposited from a dilute, low-density suspension. Based on these criteria, the Cacarajicara Formation is interpreted to be a single "hyper-concentrated flow", which was formed by a high-energy and high-speed concentrated flow. The SSE paleocurrent direction, evidenced by the imbrication of the boulders, suggests that this high-energy flow originated on the Yucat? platform and was triggered by the Chicxulub impact. The gigantic flow deposit was induced by earthquake-generated collapse of the Yucat? platform margin owing to ballistic flow from the Chicxulub impact.