ORGANIC MOLECULAR RECORDS OF PALEOELEVATION: APPLICATIONS, UNCERTAINTIES AND PITFALLS

Organic molecular biomarkers are an important tool for understanding past environments, ecosystems, and topography. In particular, the hydrogen isotopic composition of organic biomarkers has been shown to be an important new proxy for the hydrogen isotopic composition of precipitation, which can be related to elevation through models of Rayleigh distillation of precipitation during orographic rainout. Biomarkers provide a unique record of past conditions because they are commonly preserved over geologic time without isotopic exchange and often abundant in depositional settings where there are few other available materials that can be used as a proxy for precipitation isotopes or temperature. Despite the utility of organic biomarkers in stable isotope paleoaltimetry, factors such as variations in ecosystems with space or time, uncertainties in the hypsometry of organic matter production and transport, and changes in moisture availability and the timing of production of plant waxes can impact the uncertainties associated with using the hydrogen isotopes of biomarkers as a record of precipitation δD. This talk will examine the controls of C and H isotope discrimination in modern plant materials, how these relate to elevation, uncertainty associated with organic molecular paleoelevation reconstruction, and how biomarker isotope records can be coupled with organic molecular records of temperature to better constrain paleoelevation. Modern calibrations will be applied to paleoelevation reconstructions of the Sierra Nevada and western North American Cordillera to examine the applications, uncertainties and pitfalls of organic molecular paleoelevation reconstruction.