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The Role of Variable Paleotopography and Upwelling on Deposition of Late Oligocene and Miocene Heterozoan-Large Benthic Foraminifera-Coral Sequences, Jamaica

Abstract

Late Oligocene-Miocene carbonate exposures along a 70 km transect from the south to north coast of Jamaica illustrate the importance of paleotopography and regional upwelling on the nature and distribution of facies and sequence stratigraphic architecture. In contrast to previous studies interpreting a broad S-N dipping ramp, paleotopographic reconstruction indicates the Cretaceous to Eocene substrate had variable paleotopography and that the Late Oligocene-Miocene carbonates were deposited on the flanks of substrate highs and dip up to a documented 8° in various directions away from highs. Facies are dominated by heterozoan (molluscs, echinoderm, bryozoans) and large benthic foraminifera (LBF) packstones and grainstones. Coral boundstones are locally present, occurring as isolated corals, small mounds and thickets. The only photozoan components in this tropical setting are corals, dominantly those tolerant of turbid- and cooler-water conditions (e.g. Porites sp., Montastraea sp.) and LBFs, many of which tolerate mesotrophic and cooler water conditions (e.g. Lepidocyclina, Sorites). The facies composition and stratigraphic architecture reflect adverse photic zone conditions, likely due to the well-documented upwelling in the Caribbean during this time. The grainy nature of the facies and variable paleotopography made the systems susceptible to reworking and transport. In general, substrate slopes >5° promoted bypass of sediments as sedimentary gravity flows. Substrate slopes <5° generally preserve in-place facies, consisting of heterozoan-LBF packstones grainstones and local in-place corals. Presence of abraded and non-abraded bioclasts, trough crossbedding, in-place Kuphus sp. and local corals and stromatolites indicate shallow subtidal environments with intermittent energy. These types of atypical tropical carbonate systems occur throughout the rock record and form significant reservoirs (e.g. Cenozoic reservoirs in the Caribbean and Indo-Pacific). In addition to forming ramps, it is increasingly being recognized that the systems can be composed of transported deposits in relation to paleotopography. This study provides insight and quantitative data on substrate slope gradients that promote in-place preservation of shallow-water facies, or bypass to deeper water. The results provide some predictive capability for understanding the nature of facies, facies distribution, and reservoir character in similar subsurface systems with variable paleotopography.