The Holocene sediment sequence immediately seaward of the Florida Bay mud-bank complex consists of a thin (<0.25 m) skeletal-sand sheet and skeletal-sand banks as much as 2.0 m thick. This is in marked contrast to the myriad carbonate mud banks within the bay.

Sedimentologic, stratigraphic, and radiocarbon data suggest that the skeletal sands are partly the product of physical and biological degradation of precursor mud banks which existed at least 3500 yr B.P. During degradation of mud banks, most of the skeletal material is locally reworked, whereas mud is transported onshore (eastward) where it contributes to the buildup of younger constructional banks.

Active mud-bank destruction is presently occurring in a transitional zone between the transgressive sand sheet and accretionary mud-bank complex. In this zone, bank stratigraphy consists of a lower mud-bank core and upper skeletal sand or entirely of skeletal sand. The sands diminish toward the interior of the bay, whereas the basal mud-bank facies disappears to the west.

Continued sea-level rise at its present long-term rate of ∼4 cm/100 yr should be accompanied by a landward shift in the destructional zone and expansion of the transgressive sand sheet. Hence, it is hypothesized that much of the western Florida Bay mud-bank complex may ultimately be preserved as a thin skeletal-sand sheet and not as a muddy carbonate sequence as previously suggested. Paleoenvironmental reconstructions of Pliocene and Pleistocene transgressive sediment sequences from the south Florida peninsula support this hypothesis.

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