The early diagenesis of recent marine carbonate sediments is pervasive and rapid in coastal ground-water systems characterized by the dynamic influx and mixing of meteoric and marine waters. In coastal areas subjected to high and continuous seaward fluxes of meteoric water, such as the eastern coast of Yucatan, extensive dissolution and removal of carbonate result simply from the physical mixing of meteoric and marine waters. However, comparative studies of coastal phreatic systems on St. Croix, Bermuda, and Jamaica demonstrate that where there is a marked seasonal variation in the influx of meteoric waters, carbonate dissolution and precipitation become progressively controlled by the in-situ production and loss of CO₂. In seasonally variable systems, rates of CO₂ production are controlled primarily by the availability of oxygen and the abundance and type of organic water episodically introduced into the pore waters and sediment. Rates of CO₂ loss are controlled by the dissolution of carbonate and by vertical mass transport resulting from the spatially and temporally variable processes of diffusion, dispersion, and hydraulic pumping.

A quantitative mass transport model has been developed to evaluate the diagenetic response of a vertical, magnesian

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calcite-aragonite sand sequence to temporal variations in rates of CO₂ production and loss. The model can be used to help predict the spatial distribution of zones of dissolution and cementation is various coastal marine carbonate sediments.

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