Authigenic dolomite in Bahamian peri-platform slope sediment

Abstract

Authigenic, calcium-rich dolomite has been discovered in poorly consolidated lower Pliocene-upper Miocene carbonate slope sediments north of Little Bahama Bank. The dolomite was recovered from a 5.6-m-long piston core that penetrated a slide scar in 600 m of water. Below an unconformity at −105 cm, which extends from the late Pleistocene to about the Miocene/Pliocene boundary, X-ray diffraction data indicate only calcite (85%–99%) and dolomite (as much as 15%), and scanning electron microscopy observations indicate in situ precipitation of dolomite. Stable carbon-isotope data indicate a normal, open-marine source of carbon, and oxygen-isotope values are consistent with precipitation of both calcite and dolomite from deep, cold, open-marine waters. Trace-element data reveal that dolomitic sediments are depleted in Sr 2+ and Mg 2+ relative to nondolomitic upper Pleistocene oozes. Dolomitization occurred in a deep, open-marine diagenetic environment via “whole scale” dissolution of aragonite and magnesian calcite and reprecipitation of calcite and dolomite.