Search for: All records

The Miocene Climatic Optimum (MCO; ~17–14 Ma) is one of Earth’s most recent protracted warming events and serves as an analog to anthropogenic climate change. Constraining the land surface response to the MCO is critical for paleoclimate model validation and for predictions of future climatic response. However, nonmarine records across the MCO interval are limited. The hinterland and foreland basins of the southern Central Andes in Argentina preserve stratigraphic records across the MCO. These continental deposits record the onset of dune fields at >30 Ma to ~19 Ma, with widespread eolian deposition at ~22–17 Ma. We document a regional change from eolian dune fields to fluvial and lacustrine conditions at ~18–15 Ma, broadly coincident with the MCO, over ~1000 km along-strike, in localities that would have occupied both high and low elevation positions and from different tectono-morphic settings. These paleoenvironmental changes are corroborated by new climate model simulations which show increased seasonality and precipitation along the eastern flank of the southern Central Andes during the MCO. Our results support a shift from arid to more humid and seasonal conditions during the MCO in the southern Central Andes, likely driven by intensification of the South American monsoon 

Abstract Lithospheric foundering is an important mechanism of crustal deformation and recycling, basin subsidence, and surface uplift in orogenic systems. The Arizaro Basin, in the Puna region of NW Argentina, is a place where foundering was proposed to have taken place during the late Miocene. The Arizaro Basin has been described as a “bobber” basin produced by Miocene lithospheric foundering. The geometry, sedimentology, deformation, and paleoelevation history of the Arizaro Basin and surrounding arc suggest dynamic processes associated with lithospheric removal. Although analogue and numerical models support this hypothesis, the history of crustal thickness in response to lithospheric removal remains unconstrained. Here, we used a novel approach exploiting the geochemistry of detrital zircons from volcanic ashes intercalated within the Arizaro Basin stratigraphy to reconstruct the paleocrustal thickness of the neighboring magmatic sources throughout the Cenozoic. Our data indicate that the sources of volcanism for the Arizaro Basin were characterized by relatively thick crust (~53 km) since ca. 36 Ma. Thickening between ca. 20 and 13 Ma and thinning after ca. 13 Ma are consistent with formation and subsequent removal of a crustal root under the nearby arc and Aguas Calientes caldera. 

The modern topography within the Laramide region consists of high-relief ranges and high-elevation low-relief (HELR) surfaces separated by intraforeland basins. However, the timing and development of this topography within the type-locality of the Wyoming Laramide province is poorly understood. Previous models suggest that the modern topography is a young feature that was acquired after Laramide tectonism, post-Laramide burial, and basin evacuation; however, evidence of such a progression is sparse. We present low-temperature-thermochronological data from two Laramide uplifts in Wyoming, the Wind River and Bighorn Ranges, which document an early record of Laramide exhumation, subsequent reheating, and significant cooling after 10 Ma. Our results indicate that the Laramide ranges were buried by post-Laramide Cenozoic basin fill, creating a low-relief topography by the early Miocene that was reduced due to late Miocene regional incision and basin evacuation. We suggest that HELR surfaces experienced further relief reduction from Pleistocene glaciation.