Paleotopography, paleohydroclimate, or both? Unraveling terrestrial stable isotopic records through multi-proxy methods

Abstract:

All authigenic mineral and organic molecule stable isotopic proxies are complicated by the fact that meteoric-derived waters evaporate. As a consequence, it can be difficult to distinguish changes in paleotopography from changes in paleohydrology/climate across a given stratigraphic interval. Yet, what on the surface appears as a problem can instead be viewed as an opportunity: integrated paleotopographic-hydroclimatic reconstructions using multi-proxy methods. Using a combination of modern isotope hydrology data, evaporation experiment results, Quaternary authigenic mineral records, and both high-resolution and low-resolution Neogene proxy records, we show that the effects of evaporation on stable isotopic proxies follow quantitative empirical patterns that result from well known kinetic/disequilibrium fractionation. Results from the western U.S. cordillera and the New Zealand Southern Alps suggest that laminated lacustrine carbonates preserved in the geological record are particularly attractive archives of paleohydrology and local water balance. When combined with other proxies and atmospheric circulation/climate models, such high-resolution ‘snap-shots’ of paleohydroclimatic conditions facilitate a more complete and integrated understanding of the coupled evolution of topography and hydroclimate over tectonic time scales in these two highly debated orogenic systems.