A Paleoecological Interpretation of the Caloosahatchee Formation, Using Stable Isotope Methods

Oxygen and carbon isotope analyses of four pelecypod species collected from the Pleistocene Caloosa-hatchee Formation of south Florida are presented. Based on these data and some knowledge of the ecological habitats of the species, a detailed interpretation of the paleoecology and paleogeography during Caloosahatchee time is given. The interpretation suggests that most of the Caloosahatchee Formation was deposited in very shallow restricted marine water that varied from brackish to hypersaline but maintained a high${\delta}O^{18}$composition. From geographic variations in 5018 it is suggested that the restriction in water circulation resulted from paleotopographic highs of Miocene-age rocks which at low sea-level stands acted as islands in the Caloosahatchee Sea. Periods of higher sea level, when such highs had very little effect on the circulation of sea water, are also noted. The carbon isotope data show large variations which are believed related to varying contributions of carbon from different sources to the dissolved bicarbonate-carbonate system at the site of shell growth.