Its isotope fractionation is linked to water temperature and its isotope ratios from a variety of sources have been widely used to reconstruct paleoclimate. Oxygen isotope in calcium carbonates has become the most widely applied as geothermometer for estimating ancient ocean temperatures. The most successful applications of isotope paleoclimatology have been the study of foraminifera from deep-sea sediments. For instance, Shackleton and Kennett (1975) have established the Cenozoic paleotemperature history based on analyzing oxygen isotope composition of both planktonic and benthic foraminifera in the Antarctic region. Since the variations in the 18O/16O ratio in marine fossil records are global, the oxygen isotope stratigraphy has been used for chronological correlation.