CONICET | Buscador de Institutos y Recursos Humanos

Climate changes related to orographic barrier uplift have been in the18 research spotlight over recent years. Several works have focused on the19 interactions between climatic and tectonic processes in order to20 understand the development of a rain shadow. Patagonia is an ideal21 region to analyze such interactions, since a Miocene climate change, from22 wetter to drier conditions, has mainly been associated with the Andean23 uplift. In this work, we analyze a succession of stacked paleosols24 recorded in a Miocene North Patagonian foreland basin in order to25 understand how the paleosol moisture regime relates to the atmospheric26 humidity changes caused by the uplift of the Patagonian Andes. Based on27 macromorphological, micromorphological and geochemical studies, and28 supported by a high-resolution chronostratigraphic scheme based on U?29 Pb geochronology and magnetostratigraphy, the paleosols were30 characterized with their corresponding mean annual paleoprecipitation31 (MAP) and mean annual temperature values. Alfisol-like paleosols were32 identified at the base of the foreland infill (15?14.6 Ma) with a MAP of 122933 ± 108 mm/yr. The Andisol-like paleosols recognized in the middle section34 of the sequence (14.6?12.75 Ma) exhibited a MAP of 1053 ± 108 mm/yr,35 whereas the Aridisol-like paleosols occurring in the upper section of the36 infill (12.75?11.5 Ma) presented a MAP of 677 ± 108 mm/yr. The Miocene37 mean annual temperatures determined (~11 ± 2.1 °C) were similar to the38 present-day values (11 °C). Based on the complete tectonic record of the39 Patagonian Andes, the observed decrease in MAP was assigned to therain shadow effect created by 40 the uplift of the North Patagonian Andes.41 Results indicate that although such a process started around 19 Ma, the42 rain shadow effect was not effectively recorded before ∽14.6 Ma.