ABSTRACT

Accretionary features (grain coatings, intragranular void fillings, internal and external cements) of Florida reef tract calcarenites are morphologically diverse, but are all products of non-skeletal submarine carbonate precipitation and lithification. Such features are most abundant in sands along the platform edge near the outer margin of the reef tract where flushing of sediment by ocean water is most intense and generally become less abundant on the back reef toward the Keys.

Accretionary features and lithified micritic aggregates (mostly fecal pellets) common in clean sands are rare in muddy calcarenites of the inner back reef. Presumably, even piecemeal cementation is inhibited in muddy environments, for two possible reasons: 1) The flux of dissolved carbonate to and within impermeable muddy sediments is relatively small, and 2) the muddy sediments are generally poorly aerated and relatively rich in organic matter; failure of oxidative decomposition of organic films on carbonate particles may prevent welding of groups of particles or the formation of overgrowths on particles.

Well-developed superficial ooids and clear microcrystalline cements essentially free of entrapped detrital micrite are found only near the platform edge, where water turbidity is low. A systematic change in abundance and type of accretionary phenomena, like that observed on the present Florida reef tract, may be a useful paleogeographic indicator.