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Twenty-Four. Stable Carbon and Oxygen Isotope Analysis of Marmot Cheek Teeth from the Pit Locality

orado, spans at least two glacial-interglacial cycles, the upper of which dates to somewhere between 780 and 900 Ka (Bell and Barnosky, 2000). The deposits probably correlate with parts of oxygen isotope stages 21 and 22, or, less likely, 19 and 20 (see figure 7.5). Recent work has demonstrated that carbon and oxygen isotope values found in the tooth enamel of large mammals (Equus and Cuvieronius; MacFadden, 2000) and small mammals (Thomomys and Geomys; Rogers and Wang, 2002) correlate well with the marine isotope record. This chapter reports isotopic signatures of marmot tooth enamel from stratigraphically superposed levels in the Pit in hopes of refining correlations and assessing vegetational change as indicated by diet. The carbon isotope values in the enamel of fossil teeth are useful in determining paleodiet because different photo-synthetic pathways impart different 13 C/ 12 C ratios to different plants, and these ratios are ultimately reflected in the animals that eat the plants Although postdepositional diagenesis can overprint carbon isotope values in bone (Schoeninger and DeNiro, 1982), tooth enamel is not prone to diagenetic alteration, and thus it reliably reflects isotope values derived from feeding (Quade et al. As a general guide, grazers are predominantly C 4 feeders, browsers are predominantly C 3 foragers, and intermediate and crassu-lacean acid metabolism (CAM) feeders utilize both C 3 and C 4 in modern ecosystems. In addition to their use in determining paleodiet, carbon isotope values fluctuate during glacial-interglacial cycles and so can be used for correlating the terrestrial and marine isotope records (Raymo et al., 1997; MacFadden, 2000). Oxygen isotope ratios in mammalian tooth enamel have been shown to reflect the isotopic ratio of ingested waters suggested that the oxygen isotope composition of teeth is dependent on the isotopic composition of the water ingested, the consistent fractionation of oxygen isotopes between the body water and the enamel, and the metabolism of the particular animal. If comparisons are made using the same species over time, the fractionation and metabolism effects should be the same for all samples. Therefore the tooth enamel oxygen isotope values should represent changes in the isotopic composition of the water, which is temperature dependent, and not changes in the metabolism or fractionation of the animals being sampled (Rozanski et al., 1992, 1993). Because oxygen isotope values of meteoric waters should be temperature dependent, this method should allow for discrimination between glacial stages (cold periods) and interglacial …