Late Eocene sea surface temperatures

Abstract

Isotopic temperatures from Late Eocene (35±0.5Ma) Crassostrea gigantissima(Finch, 1824) agree well with a steady Middle to Late Eocene cooling trend seen in previously published isotope data from mollusks and benthic foraminifera. Oysters were collected from along the Savannah River at Griffins Landing in Burke County Georgia to address paleotemperatures during the Late Eocene. Specimens underwent sclerochronological analysis by high resolution microdrilling for carbon and oxygen isotope content. Prior to drilling, cathodoluminescence as well as thin section petrography was performed to assure pristine material. Results from 177 δ18Ocalcite analyses from the left valves of three shells range from -2.45‰ to 0.57‰ (PDB), and suggest average annual temperature of ~19ºC and an average annual range of ~15º to 23ºC. Compared to modern Georgia Coast temperatures, Late Eocene climate was similar during winter and 2ºC - 8ºC cooler during summer. Data also show agreement with 35Ma temperatures from the Gulf Coastal Plain.