CHICKEN OR EGG? THE LEGACY OF SCIENTIFIC OCEAN DRILLING IS TACKLING THE CLIMATE-TECTONIC DEBATE IN THE EARTH SCIENCES

The influence of climate-driven erosion on tectonic deformation and mountain building has been of foremost interest in earth sciences as plate tectonic theory has evolved in the past half century. Seminal work on addressing this debate came from observations of sedimentary volumes and records in the oceans that were interpreted as indicators of late Cenozoic climate-induced increases in mass removal from land. Yet, these conclusions have been questioned by observations of ocean chemistry and stratigraphic modeling that argue for no change in climatic weathering. Scientific ocean drilling has helped address this debate by quantifying cause and effect relationships between tectonics and climate, particularly in marine areas of rapid sedimentation, where the potential preservation and resolution of events is greatest. Terrigenous accumulation rates, driven by changing topographic relief and erosion, can be directly tied to a chronostratigraphy and to the proxy indicators of climate and unroofing history contained in the marine strata. Here we review the contributions that ocean drilling has made to advancing the science by highlighting results from drilling experiments that sampled the marine depocenters offshore of the Asian and American Cordilleran orogens. Results indicate that tectonics and climate both shape mass fluxes from orogens, with the relative importance varying in space and time. Onshore bedrock evidence exists of increased late Cenozic erosion. Mass fluxes from seismic reflection volumes constrained by ocean-drilling age control corroborate this for Pleistocene high latitude glaciated settings. The response is markedly different for pre-Pleistocene periods in Asian and Cordilleran orogens, where tectonic deformation appears to be the primary mechanism driving uplift and denudation as reflected in the marine record. Climate change appears to only affect the transfer of material from orogens to the ocean. Future scientific drilling targets should target recovery of terrestrial erosion proxies that can reconcile the onshore bedrock erosion record with the marine strata to untangle how or if climate signals ultimately propagate into marine sinks having a strong tectonic source signal.