PLEISTOCENE SEA-LEVEL HISTORY OF FLORIDA: THE CASE FOR SMALL-SCALE VARIATION

A preliminary correlation of Florida's Plio-Pleistocene shell beds with third-order coastal onlap cycles of an existing sequence stratigraphic model for the Salisbury and Albemarle embayments of Virginia and North Carolina was published by Zullo and Harris (1992); the Floridian Bermont fauna was assigned to the third-order cycle 3.9. The seemingly homogeneous nature of Florida's Plio-Pleistocene shell beds is problematic when applied to the sequence stratigraphic model; however, by combining lithologic observations, taxonomic data, and sequence stratigraphic principles it is possible to analyze the discontinuous nature of sea-level change in Florida during the Pleistocene.

Stratigraphically continuous bulk samples were collected, sieved, and sorted for their macroinvertebrate fauna. Special attention was given to a five-meter sequence of near-shore shell beds containing Pleistocene Bermont fauna in the Longan Lakes Quarry near Naples, Florida. A striking feature of the Longan Lakes sequence is the pronounced, karstified biosparite beds which delineate the boundaries between a set of fining- and coarsening-upwards sequences. These sequences are poorly-sorted fine clayey sands that contain a diverse molluscan assemblage; these deposits appear to have been solely deposited in a subaqueous environment. The biosparite beds are fossiliferous consolidated sands that have been subaerially exposed, lithified, and subsequently karstified. Because the South Florida Peninsula does not appear to be significantly affected by rebound or uplift, the repetitive nature of marine beds and subaerially exposed beds indicates that sea-level during this portion of the Pleistocene fluctuated to produce cyclothem-type deposits. The cyclical nature of the sequence allows for further refinement of Florida's sequence stratigraphic model and the Pleistocene sea-level curve. Comparison of assemblage data for each of the shelly beds located between the biosparite beds further indicates that sea-level changes had no substantial impact on faunal distributions and other paleoenvironmental factors.