Coastal Mixing Zone Dolomite, Forward Modeling, and Massive Dolomitization of Platform-Margin Carbonates

Abstract

ABSTRACT Dolomite of mixed-water origin occurs in three late Pleistocene raised reef terraces in southeastern Barbados, West Indies. Dolomite concentrations range from trace quantities to locally complete, with a general increase in dolomite percentage with increasing terrace age. Most of the dolomite is replacive, both mimetic and fabric selective, with limpid pore-lining dolomite cements common in the oldest terrace. Stratigraphic relationships suggest that mixing zone dolomitization occurred locally during three temporally separate sea level events. The rapidity of Quaternary glacio-eustasy constrains dolomitization to have occurred within about 5,000 yr in each terrace. Rapid, recurring dolomitization resulted from development of similar hydrologic and hydrochemical conditions during each ea level event. Barbados data are used as conceptual input for a computer-based forward model which simulates the development of thick, platform-margin sections of mixing zone dolomite through the interaction of sea level fluctuations, sedimentation, rapid recurring dolomitization, and subsidence. Sensitivity tests of the model indicate that the most important parameters for producing thick sections of platform-margin dolomite are: (1) dolomitization rate, (2) sea level still stand duration, and (3) rate of sea level change. Dolomite thus formed may provide nuclei for later burial dolomitization or may provide an intrabasinal magnesium source for stepwise stabilization of platform interior dolomites.