Abstract
The middle Miocene Climatic Transition (MMCT) was a time when the global climate cooled and there was a broad reorganization of the hydrologic cycle in the southern hemisphere as Antarctic ice volume expanded. The effects of this global cooling on the Patagonian Andes have been historically challenging to disentangle from coeval tectonic growth of the Andes. The Paso del Sapo Basin (Chubut Province, Argentina) records the climatic and tectonic evolution of the northern Patagonian Andes during the middle Miocene. The basin hosts nearly equal 250 m of sediments deposited in an alluvial-fluvial system in the broken foreland of the main orogen. A sequence of volcanoclastic pedogenic sediments (La Pava Formation, nearly equal 15-14.6 Ma) grade into a palustrine-shallow lacustrine environment (Lower Collon Cura Formation, 14.6 - 12.8 Ma), and then back into a pedogenic-palustrine environment (Upper Collon Cura formation, 12.8 - 11.5 Ma). The transition from the La Pava Formation to the Lower Collon Cura Formation is hypothesized to have been tectonically controlled, whereas the transition from the Lower to Upper Collon Cura is hypothesized to have been climatically controlled. The sediments were sourced from the main Andean orogen and have abundant volcanic glass and detrital material suitable for paired stable isotope geochemistry and low temperature thermochronology. Here, we present volcanic glass stable isotope geochemistry (delta (super 2) H) and detrital thermochronology (dZHe) datasets through the La Pava and Collon Cura formations. For volcanic glass, we sampled tuff units at the base and top of the section, as well as paleosols throughout the section. To examine the influence of lithofacies, we also include samples from palustrine units in the middle of the section. We sampled medium to coarse grained fluvial channels throughout the section for detrital thermochronology. We qualitatively integrate these new proxy datasets with detailed sedimentology to examine the interplay of climate and tectonics in the northern Patagonian Andes through the middle Miocene Climatic Transition. In particular, the combination of detailed sedimentology with proxy data allow us to interrogate the mechanisms which caused shifts in depositional style across the basin, and allow us to interrogate how erosion in the main Andean orogen was influenced by the MMCT.