A COMPARATIVE STUDY OF LATE MIOCENE-PLIOCENE PALEOENVIRONMENTAL CONDITIONS IN NW ARGENTINA: INSIGHTS FROM PALEOSOL PROXIES

High topographic relief in the central Andes has created a pronounced east-west climate gradient influencing ecological evolution through the Cenozoic. The late Miocene expansion of C₄ grasses in this area coincides with climate changes driven by Andean orogenic activity. This study explores late Miocene-Pliocene deposits of the Choromoro and Tucumán Basins in NW Argentina to understand the link between climate variation and vegetation dynamics by reconstructing paleoclimate and paleovegetation conditions. It uses paleosol geochemical composition and phytoliths preserved in paleosols from two geochronologically correlated formations to provide insights into the environmental changes during this interval. The Las Cañas Fm. studied along the Dulce River section in Tucumán Basin, consists of fine red sandstone with interbedded mudstones and paleosols. It was deposited in a fluvial environment during the Pliocene and correlated with the India Muerta Fm. from Tucumán and Choromoro Basins. The lower India Muerta Fm. is composed of fine to coarse sandstone and interbedded siltstone and paleosols, and was deposited in an ephemeral fluvial environment during the late Miocene. In contrast, the upper India Muerta Fm., composed of coarse sandstone or conglomerates and paleosols, was deposited in an established fluvial environment during the late Miocene–Pliocene. Paleovegetation reconstructions from these formations indicate a mixed forest-grassland ecosystem where forest and grass vegetation account for an average of 52% and 36% of the total vegetation, respectively. It also suggests a substantial rise in C₄ grasses throughout the studied interval, where C₄ vegetation from Las Canas Fm. ranges between 0 and 21%, while samples from the India Muerta Fm. vary between 0 and 20%. To understand the link between climate and vegetation changes, this study will also estimate mean annual precipitation, growing season precipitation, and mean annual temperature using paleosol geochemistry climofunctions. Our proxy-based paleoenvironmental reconstructions provide insights into regional climate patterns and their effect on ecology through a comparative analysis with basins located further northwest, which improves our understanding of the Cenozoic climate and ecological dynamics associated with Andean orogenic activities in the central Andean foreland basin.