AGES OF PLIO-PLEISTOCENE FORMATIONS IN SOUTH FLORIDA BASED ON THE REVISED IUGS BOUNDARY AGE OF THE LOWER PLEISTOCENE

Addition of the Gelasian stage into the lower Pleistocene somewhat simplifies the ages of one classic formation in South Florida. Considerable debate has occurred over the past century regarding the age of the Caloosahatchee Formation. Based on various correlations of mollusks, foraminifera, strontium isotopes, and magnetic reversal data, the unit has been alternatively placed into either the Pleistocene or the Pliocene. More recent chronostratigraphic investigations (Missimer, 2002), have placed the Pliocene-Pleistocene boundary within the lower part of the formation. Based on the bulk of the age data available on the Caloosahatchee Formation, it does straddle the Calabrian and Gelasian stages and is now firmly constrained within the Pleistocene.

The age of the Pinecrest Member of the Tamiami Formation (?) is, however, unclear. Based on the current age data available, the age of this unit lies between 2 and 3 Ma, suggesting that the Pliocene-Pleistocene boundary lies within it. While the close relationship of the mollusk faunal assemblage between the lower Caloosahatchee and upper Pinecrest suggests the both are Pleistocene in age, the disconformity at the boundary between the Pinecrest and the Sand or Sandstone facies of the Tamiami Formation raises a question concerning the age constraint of the lower part of the unit within the Pliocene. The lower part of the unit containing abundant aragonitic shell material appears to occur within the C2An.1n chron, thereby making it Pliocene within the revised age the units. More detailed age data is required to further constrain the lowermost part of this unit. If the unit is constrained to the Pleistocene at its base or one of the disconformities, a redefinition of stratigraphic units may be appropriate with the definition of a new group, perhaps termed the Everglades group with a number of formations including the Fort Thompson (Tarantian and Ionian), Caloosahatchee (Calabrian-Gelasian), and the Pinecrest (Gelasian). The lowest current part of the Pinecrest would be included in the Tamiami Formation, which is currently constrained to The Placenzian stage.