Multi-proxy paleosol evidence for a rain shadow effect linked to Miocene uplift of North Patagonian Andes

BUCHER, JOAQUIN; VARELA, AUGUSTO; D'ELIA, LEANDRO; BILMES, ANDRÉS; LÓPEZ, MANUEL; GARCÍA, MICAELA; FRANZESE, JUAN

GEOLOGICAL SOCIETY OF AMERICA BULLETIN

GEOLOGICAL SOC AMER, INC

Lugar: Boulder; Año: 2020

0016-7606

Climate changes related to orographic barrier uplift have been in the research spotlight over recent years. Several works have focused on the interactions between climatic and tectonic processes in order to understand the development of a rain shadow. Patagonia is an ideal region to analyze such interactions, since a Miocene climate change, from wetter to drier conditions, has mainly been associated with the Andean uplift. In this work, we analyze a succession of stacked paleosols recorded in a Miocene North Patagonian foreland basin in order to understand how the paleosol moisture regime relates to the atmospheric humidity changes caused by the uplift of the Patagonian Andes. Based on macromorphological, micromorphological and geochemical studies, and supported by a high-resolution chronostratigraphic scheme based on U?Pb geochronology and magnetostratigraphy, the paleosols were characterized with their corresponding mean annual paleoprecipitation (MAP) and mean annual temperature values. Alfisol-like paleosols were identified at the base of the foreland infill (15?14.6 Ma) with a MAP of 1229 ± 108 mm/yr. The Andisol-like paleosols recognized in the middle section of the sequence (14.6?12.75 Ma) exhibited a MAP of 1053 ± 108 mm/yr, whereas the Aridisol-like paleosols occurring in the upper section of the infill (12.75?11.5 Ma) presented a MAP of 677 ± 108 mm/yr. The Miocenemean annual temperatures determined (~11 ± 2.1 °C) were similar to the present-day values (11 °C). Based on the complete tectonic record of the Patagonian Andes, the observed decrease in MAP was assigned to the rain shadow effect created by 40 the uplift of the North Patagonian Andes. Results indicate that although such a process started around 19 Ma, the rain shadow effect was not effectively recorded before ∽14.6 Ma.