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Abstract

Abstract The model of island-arc sedimentary environments proposed by Dickinson also applies to the Cretaceous volcaniclastic formations of Jamaica. Coarse volcaniclastic units with ash flows, lava flows, agglomerates, and laharic breccias belong to the central facies developed near active volcanic vent centers. Finer grained, bedded volcaniclastic units associated with shales and some limestone units are placed in the dispersal facies, representing distance from or quiescence of vent centers. The Cretaceous succession in central Jamaica contains more units typical of the central facies; westward, the sequence grades mainly into the dispersal facies, indicating increasing distance from the vent centers. Coral-rudist limestones, which occur dominantly in the dispersal facies, are characterized by mainly rudist frameworks associated with four coral assemblages, which either surround, encrust, or are interstitial to rudists. The assemblages are (1) Paracycloseris-Trochoseris-Actinacis assemblage, (2) Multicolumnastrea-Astrocoenia-Actinacis assemblage, (3) Multicolumn-astrea-Actinacis-Dictuophyllia-Dichocoenia assemblage, and (4) Dichocoenia trechmanni assemblage.

These coral-rudist limestone units are interpreted as very shallow-water shelf structures, unre-sistant to wave action, which developed at the beginning of transgression or toward the end of regression; these periods alternated with phases of volcanic activity. The complexity, diversity, and abundance of coral-rudist frameworks increased during Cretaceous time, apparently in conjunction with decreasing volcanism and increasing arc-shelf area.

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