CONTINENTAL PALEOCLIMATIC STUDY OF SOUTHERN ARGENTINA, 38MA TO THE PRESENT

Recent advances in isotope geochemistry have shown that the stable isotopes of oxygen preserved in the tooth enamel of mammals can be used to develop both modern and ancient climate records in various continents. Enamel isotope ratios are highly correlated with meteoric water compositions, which are in turn correlated with temperature and humidity. Through a wide range of modern mammalian studies a basic equation has been developed to relate d18O of phosphates in apatite to d18O of local precipitation: d18Op=m*d18Opt + c, where m and c depend upon the species studied. In this study the oxygen isotopes will be separated out of the phosphate component of apatite for climate estimates. The goal of the study is to develop a baseline climatic record for the southern continental hemisphere from 38Ma to the present, from which a temporal connection between the continental and marine climate records will be analyzed. The study site is the Sarmiento Formation of the Gran Baranca (S45*42’49", W68*44’16") in the Chubut Province, Argentina. Preliminary analysis shows that there are both seasonal and long time-scale changes throughout the record. The 38Ma teeth show an average d18O of 16.742 with respect to SMOW and a standard deviation of 0.42 (seasonality). The middle record (28-33Ma) maintains an average d18O=17.75 and a standard deviation of 0.63. The youngest teeth (11.8Ma) tested revert to a d18O of 16.07 but with a standard deviation of 0.623. The anticipated results will have important implications regarding the coupling of continental and marine climate in the Southern Hemisphere.