ISOTOPIC RECONSTRUCTION OF PAST CONTINENTAL ENVIRONMENTS

Vertebrate fossils and continental sediments provide a rich record of variations in the isotopic composition of surface environments. To int erpret these records, a greater understanding of isotopic sources, as well as fractionations associated with animal physiology, soil geochem istry, and diagenesis, has been essential. Tooth enamel and fish otoli ths yield subannual records of surface environments, whereas soil mine rals may integrate signals over many thousands of years. Carbon isotop e variations in fossil vertebrates and soils record changes in the str ucture of vegetation and the isotope composition and concentration of atmospheric CO2. Oxygen isotope variations may be indirectly related t o climate, through reconstruction of the oxygen isotope composition of meteoric water, or directly related to temperature, through applicati on of oxygen isotope paleothermometry to soil minerals or otoliths. In Africa, nitrogen isotope variations show promise as a proxy for rainf all abundance, though the generality of this association elsewhere has not been demonstrated.