n uplift in Patagonia: Insights from sedimentary record of the Ñirihuau Formation, Ñirihuau Basin Miocene.

SANTONJA, C.; SURIANO, J.; BECHIS, F.; BENAVENTE, C.A.; PASSALIA, M.G.

Workshop; Climate Workshop: Exploring New Directions in Miocene Earth System Connections; 2024

The Ñirihuau basin, located between 41° and 43° S, on the eastern side of the North Patagonian Andes, Argentina, exhibits a sequence of Oligocene to Miocene volcanic rocks (Ventana Formation) followed by Miocene volcaniclastic, clastic, and carbonatic rocks (Ñirihuau and Collón Curá formations). Based on U-Pb geochronological data, the Ñirihuau Formation’s continental deposits are constrained to the Early to Late Miocene (22-11 Ma). The lower section of the unit consists of synrift deposits while the middle section registers a transition to a foreland basin stage, associated with the advance of a fold and thrust belt to the west, represented by the upper section. The middle section consists of lacustrine facies deposited between ~15 and 13 Ma, coincident with the Middle Miocene Climatic Optimum, and holds particular interest because it contains carbonate beds that can provide information about the climate signature. This study aims to understand the paleoenvironmental and climatic conditions and discern the tectonic versus climate control during the deposition of the middle lacustrine section, and their relationship to Andean geodynamics, through a detailed facies, microfacies and geochemical analysis of carbonate beds, combined with a complete stratigraphic analysis, representing one of the first contributions of this kind from southern South America. Results suggests deposition occurred under temperate to warm and humid conditions, supported by the paleoflora registered on the middle and basal sections. Instead, the upper section’s flora indicates a westward retreat of taxa from humid climates, due to the rain shadow effect aridization, caused by the Miocene Andean uplift.