Biomarker isotope and soil tetraether records of the paleotopographic and paleoenvironmental history of the SE margin of Tibet

Abstract:

Paleotopographic information is critical for evaluating geodynamic models and separating effects of climatic and tectonic change in sedimentary records. Compound-specific hydrogen isotopes of plant waxes and soil tetraethers provide a novel means of constraining changes in elevation through time for a diverse range of paleoenvironments. Recent stable isotopic data from paleosol and lacustrine carbonate from basins along the SE margin of the Tibetan plateau indicate carbonates formed from isotopically depleted waters. These are interpreted to reflect longstanding high topography with regional uplift contemporaneous with Paleogene faulting along the Alio Shan – Red River shear zone. Here, hydrogen isotopes of modern plant waxes and soil tetraether temperatures from modern soils in China’s Yunnan province are used to calibrate a multiproxy temperature and isotopic approach to evaluate the paleoelevation and paleoclimatic history of the SE margin of the Tibetan plateau. Modern organic molecular data are paired with plant wax hydrogen isotopes and tetraether temperatures from sediments along the SE plateau margin that date from Eocene to Pliocene to evaluate temperature and isotopic change that may be related to uplift. Organic molecular data show large temperature and isotopic gradients from the late Eocene to Pliocene. These data suggest longstanding high topography and minimal post-Miocene uplift due to lower crustal flow. However, stable isotopic and paleotemperature data must be reconciled with geomorphic evidence for post-Miocene changes in incision rates and model predictions of changing climate and isotopic lapse rates.