EOCENE-OLIGOCENE LATITUDINAL CLIMATE GRADIENTS IN NORTH AMERICA INFERRED FROM STABLE ISOTOPE RATIOS IN PERISSODACTYL TOOTH ENAMEL

摘要: The Eocene-Oligocene transition (~ 34 Ma) was one of the most pronounced episodes of climate change of the Cenozoic. In order to investigate this episode of global climate cooling in North America, we analyzed the carbon and oxygen stable isotope composition of the carbonate component of 19 perissodactyl (horses and rhinos) tooth enamel samples from the Eocene-Oligocene rocks of the Cypress Hills Formation (southwestern Saskatchewan, Canada); we then compared the results with previously published data from the US Great Plains (Nebraska, South Dakota, and Wyoming).Average (±1σ) perissodactyl enamel δ 13 C values (vs. V-PDB) in the Eocene (-8.8±0.3‰) and Oligocene (-9.0±0.3‰) are indistinguishable, suggesting no major change in mean annual precipitation (MAP) in Saskatchewan across the transition. Average δ 13 C values in Saskatchewan are slightly higher than those in the US Great Plains, suggesting drier conditions at higher latitudes.