The Cacarajicara Formation of western Cuba is a more than 700-m-thick calcareous clastic sequence that contains shocked quartz throughout, and spherules. Three members are recognized. The lower member consists of limestone and chert boulders, and disconformably overlies Cretaceous deep-water turbidite. It is characterized by: (1) a grain-supported fabric with only a small amount of matrix, (2) 5-15 cm, well-sorted clasts and occasional boulders, (3) reversely graded, discoidal or rectangular boulders showing a preferred orientation, (4) abundant shallow- and deep-water carbonate clasts in a well-mixed fabric, (5) direct contact between adjacent clasts, and (6) hydrostatic deformation within a black clay matrix. This evidence suggests that the lower member was deposited under conditions of high-density and high-speed laminar flow. The middle member consists of upward graded, massive to well-bedded, homogeneous calcarenite. Unusual fluid-escape structures in the thick calcarenite suggest that this member formed by high-density turbidity suspension. The upper member consists of fine calcarenite mudstone; there is no evidence of bioturbation. We infer that it was deposited from a dilute, low-density suspension. On the basis of these criteria, the Cacarajicara Formation is interpreted to be a single hyperconcentrated flow that was formed by high-energy and high-speed concentrated flow. The south-southeast paleocurrent direction suggests that this high-energy flow originated on the Yucatan platform and was triggered by the Chicxulub impact.We propose that a gigantic flow deposit was induced by earthquake-generated collapse of the Yucatan platform margin owing to ballistic flow from the Chicxulub impact.
|ジャーナル||Special Paper of the Geological Society of America|
|出版ステータス||出版済み - 1月 1 2002|
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