Florida Geological Survey


taining subaerial exposure features occur immediately below this interval.

 Collophane, in the form of rounded peloids, was identified in thin section from the upper Oldsmar glauconitic interval in the South Beaches well (1,881-1,889 feet BLS). Phosphates such as collophane apparently form where phosphate-rich water upwells adjacent to shallow shelves or platforms that border deep marine basins (Friedman and Sanders, 1978). Collophane forms at the sediment-water interface under similar conditions to that of glauconite and consequently is common in glauconitic sediments.

 Pyrite occurs as subhedral to euhedral crystals in combination with glauconite. Pyrite crystals are commonly found within or form rims around glauconite peloids. Pyrite forms in organic, muddy sediments under reducing conditions (Miall, 1984) similar to those required for glauconitization which occurs at the oxidationreduction boundary (Odin and Fullagar, 1988).

 The origin of the clay is somewhat problematic given the apparent isolation of the carbonate platform from any potential siliciclastic source during this time. Possibly the clay is altered volcanic ash blown northward from erupting volcanoes associated with subduction along the Caribbean and North American plate boundary.

 The lower Oldsmar Formation is characterized by highly recrystallized, unfossiliferous dolostones. Original depositional textures that may have been present have been totally obliterated by dolomitization, making environmental interpretations impractical.

 Avon Park Formation

 A diversity of carbonate depositional environments are represented over the approximately 1,500 feet of vertical sequence that comprises the Avon Park Formation in Brevard County.


Sedimentary structures range from those indicative of low energy tidal flat to high energy shoaling conditions. Most environmental information for the Avon Park Formation is derived from limestones that have undergone low degrees of dolomitization. Much of the dolostone is highly recrystallized with poor preservation of primary textural features.

 A sequence of grainstone, packstone, and wackestone in the middle Avon Park Formation (approximately 200 feet below the "B" marker) contains sedimentary structures indicative of beach deposition. A complete vertical beach sequence from offshore at the base to shoreface and foreshore at the top (Benard et al., 1962) can be recognized. The best example of this sequence occurs in the Merritt Island well in the interval from 1,180 feet to 1,250 feet BLS. The lithofacies grades upward from a low-energy wackestone at the base to high-energy grainstones at the top (Appendix A5). High angle cross beds are common in grainstones and packstones. Some zones of coarse to gravelsized "lag" were noted at the base of cross-bedded strata. Allochemical grains are dominantly skeletal.

 The top of the beach sequence is capped by a peloidal grainstone (at 1,174 feet BLS) containing abundant tabular to spherical cavities known as "keystone vugs" which are commonly found in uppermost accretion beds of beach foreshore deposits (Dunham, 1970; Scholle et al., 1983). Keystone vugs are indicative of swash-zone deposition and represent cavities formed by trapped air bubbles that develop immediately above sediment which is flushed by onlapping wave action during daily tidal cycles (Scholle et al., 1983). The flushing action forces air out of the underlying sediment's intergranular pore space and upward into the overlying sediment where it can be preserved by early marine cementation (Scholle et al., 1983).

 Core below the keystone vug zone consists of peloidal grainstones and packstones much of