ABSTRACT

The dominantly carbonate sediments within Florida Bay contain small percentages of insoluble silicate minerals, ranging in our samples from 1.25 to 14.91 percent by weight. Quartz, chlorite, and montmorillonite compose most of the silicate fraction, with very minor amounts of illite and kaolinite. Clay mineral distribution can be described by concentration gradients based on two end member assemblages: A chloritic assemblage dominates in the eastern part of the bay, but declines westward. In a reciprocal manner, a montmorillonitic assemblage dominates the western bay and declines eastward. The two clay mineral assemblages reflect different sources--chlorite from the Atlantic province, and montmorillonite from the Gulf of Mexico province. Shallow and subaerial carbonate mud banks and intervening basins inhibit mixing of waters bearing the two clay assemblages; this has caused the relatively rapid transition from one clay suite to another in the 30-40 mile span of Florida Bay. The clay mineral fractions of similar ancient carbonate reef trends would be expected to show analogous concentration gradients in the back-reef area.

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