No Change in Plio–Pleistocene Ancestral Rio Grande Paleohydrology in Response to Regional Climate Change, Central and Southern New Mexico, USA

Fluvial cross-set heights from strata deposited by the Ancestral Rio Grande in central and southern New Mexico during Pliocene–Pleistocene time are used to reconstruct paleoflow depths for the Ancestral Rio Grande over a period of regional climate change. The results show a negligible change in flow depth between 5 Ma and 1.6 Ma despite an interpreted increase in temperature, aridity, and monsoon strength over this time period. Coefficients of variation (CV) for cross-set heights, a proxy for the flashiness of fluvial systems, show no substantial change from 5 Ma to 1.6 Ma. We suggest that the lack of change in flow depth and CV in response to regional climate change reflects either that the magnitude of climate change was not substantial enough to be recorded in the fluvial record or that the Ancestral Rio Grande was sufficiently hydrologically buffered such that changes in precipitation did not substantially affect flow depths or the flashiness of recorded flow.