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Authigenic calcian dolomite is a common but rarely abundant (≤20%) component of Neogene deep-water (475-2,767 m) carbonates peripheral to the Florida-Bahamas Platform. Dolomite concentrations as high as 57% of the carbonate fraction occur in the Miocene of west Florida, however, and as much as 86% dolomite has been found in a hardground from the Bahamas.

Dolomite occurs principally as pore-filling euhedral rhombs (5–20 μm) that precipitated in situ, as well as by replacement of calcite at disconformities. Stable isotope ratios (oxygen and carbon) suggest dolomite precipitation from deep, cold, seawater-derived fluids, and trace-element (Sr) concentrations suggest strontium-rich aragonitic(?) precursors. Preliminary 87Sr/86Sr data suggest substantial lag times for dolomite precipitation and contamination by "old" strontium.

Because of the high diagenetic potential of periplatform carbonates, Bahamian deep-water dolomites appear to be a natural consequence of shallow subsurface (<60 m) burial diagenesis. In contrast, carbonate ramp slope sediments from west Florida, which have a much lower initial diagenetic potential, are punctuated by discrete concentrations of authigenic dolomite, which may represent paleoceanographically controlled dolomite "events." Overall, our data indicate that deep-water dolomite has had little difficulty in precipitating from normal marine-derived fluids.

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