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The Patagonian Andean foreland system includes several intermountain basins filled with a Miocene non-marine record deposited under syn-tectonic conditions related to the Andean uplift and a regional climate change triggered by a rain shadow effect. Many of those basins, such as the Collón Cura basin in Neuquén Province, Argentina, present a well-preserved fluvial record (i.e. the Limay Chico Member of the Caleufú Formation). Sedimentological and palaeomagnetic studies have allowed the interpretation of coeval transverse distributary fan and axial mixed-load fluvial systems deposited between 10.6 ± 0.2 and 12.8 Ma. The basin infill arrangement shows that, while the axial mixed-load fluvial system exhibits an aggradational stacking pattern, the transverse distributary fluvial fan system denotes three different orders of stratigraphic patterns: (i) large-scale progradation of the transverse fluvial fan system over a time scale of 106 year; (ii) intermediate-scale progradational-retrogradational transverse intra-basinal fluvial fan episodes over a time scale of 105 year; and (iii) small-scale transverse lobe progradation over a time scale of 105-104 year. These patterns were interpreted as transverse sediment flux variations triggered by variable external forcings. To decouple those forcings, we estimated the Collón Cura basin equilibrium time at 3-5 × 105 year and compared it with the time scale over which different external forcings varied in the Patagonian Andean and foreland regions during Miocene times. Large-scale progradation is linked to an increase in sediment flux triggered by a long-term tectonically driven exhumation forcing associated with the Miocene Patagonian Andean contractional phase. Intermediate-scale progradational-retrogradational episodes are linked to variations in sediment flux due to a mid-term tectonic forcing associated with the western fault system activity. The small-scale fan lobe progradation is related to increases in sediment flux triggered by indistinguishable short-term autogenic processes and/or high-frequency tectonic and climatic forcings. This contribution shows the applicability and limitations of the basin equilibrium time concept to decouple external forcings from the geological record, considering their magnitude, nature and time scale, as well as the basin characteristics. [ABSTRACT FROM AUTHOR]

With the aim to better understand the timing and geological evolution of the late Cenozoic stratigraphic record of the onshore, western Valdés Basin in northeast Chubut province (Patagonia, Argentina), we perform sedimentological, stratigraphic, and zircon U–Pb geochronologic analyses. The study includes the terrestrial Early Miocene Trelew Member of the Sarmiento Formation, the shallow marine Early Miocene Gaiman Formation, the shallow marine to estuarine Late Miocene Puerto Madryn Formation, and the Plesitocene fluvial conglomerates of the Rodados Patagónicos. Based on our data set, together with the recognition of relevant stratigraphic surfaces, we divide the succession into stratigraphically bounded units and define three cycles of sedimentation. The Lower Cycle rests on top of Surface 1, which comprise a long hiatus including the entire Oligocene Epoch. This cycle is in turn divided into two subunits separated by the transgressive, ravinement Surface 2. The Lower Cycle is separated from the overlying Middle Cycle (=Puerto Madryn Formation) by the flat and regionally extensive Surface 3. Finally, the latter is separated from the Upper Cycle (=Rodados Patagónicos) by Surface 4, a complex surface at the base of gravel deposits forming several terrace levels. Maximum depositional ages calculated from 10 zircon U–Pb samples indicate the succession between surface 1 and 4 extends from 21.5 to 2.7 Ma (Aquitanian-Piacenzian). The Lower Cycle is restricted to the 21.5–16 Ma interval (Aquitanian-Burdigalian); the Middle Cycle between 12 and 2.7 Ma (latest Serravalian-Piacenzian), with most of the new and previous ages clustering in the Tortonian; whereas the Upper Cycle is restricted to the Pleistocene. Although most of the analyzed sediments show fresh volcanic glass particles, older zircon ages are dominant, representing detrital components with a dominant peak of Permian-aged grains, with subordinated Devonian, Jurassic, Cretaceous, and Paleogene peaks. We interpret the analyzed succession as a condensed section compared to the offshore Valdés Basin depocenter area. Sedimentation in the study area was controlled by periods of slow subsidence, probably related to thermal subsidence and sediment compaction in the depocenter. Two main sources of sediments for the analyzed succession are envisaged: one represented by explosive volcanism located either in the Andes or in the North Patagonian Massif, the other through erosion of older rocks surrounding the North Patagonian Massif where late Paleozoic plutonic rocks are abundant. Particularly for the Middle and Upper cycles, an increase in Mesozoic contribution suggests erosion from sediments of the Cañadón Asfalto Basin. The new ages and stratigraphic analyses here reported are of major relevance for the integration of the onshore and offshore stratigraphies of the Valdés Basin which is key to connect the geologic evolution of the Andean and passive margin areas of southern South America. They are also of major relevance for the calibration of fossil communities, particularly for the abundant and diverse marine vertebrates preserved in the Burdigalian Gaiman Formation. • Zircon U–Pb ages and stratigraphic descriptions are provided for Neogene strata. • Results indicate three Neogene depositional cycles in the onshore Valdés Basin. • The Gaiman Formation is isotopically dated for the first time. • Late Paleozoic zircons are dominant, puzzling the provenance interpretations. [ABSTRACT FROM AUTHOR]

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 in which to analyze such interactions, since a Miocene climate change, from wetter to drier conditions, has mainly been associated with Andean uplift. In this work, we analyzed a succession of stacked paleosols recorded in a Miocene North Patagonian foreland basin in order to understand how the paleosol moisture regime related 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 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 Aridisollike paleosols occurring in the upper section of the infill (12.75-11.5 Ma) presented a MAP of 677 ± 108 mm/yr. The determined Miocene mean annual temperatures (11 ± 2.1 ℃) were similar to the present- day values (11 ℃). Based on the complete tectonic record of the Patagonian Andes, the observed decrease in MAP was assigned to the rain shadow effect created by the uplift of the North Patagonian Andes. Results indicate that although the process started around 19 Ma, the rain shadow effect was not effectively recorded before ca. 14.6 Ma. [ABSTRACT FROM AUTHOR]

Several segments of the Central and Southern Andes show deformation evidences located far away from the orogenic front. As a result, a landscape constituted by fault-blocks mountains and intermontane basins occurs. The spatial-temporal distribution of the deformation in these Broken Foreland Systems is still uncertain. Some works suggest that change in space and time of rock uplift along the structures is controlled mainly by older crustal discontinuities. However, other authors propose, a particular deformation pattern between the Andean and extra Andean regions, such as eastward-westward migration of the orogenic front related to subduction zone dynamics. In this work we analyse new structural, geomorphological and tectono-stratigraphical data together with previous chronological scheme (based on U-Pb and magnetostratigraphic ages) of one of the Patagonian Broken Foreland depocenters: the Paso del Sapo Basin. The results allow to perform the tectonostratigraphic evolution of the basin and constrain the timing of deformation in Paso del Sapo Basin at 15–11.5 Ma. Different tectonic structures were activated and de-activated in this time interval, while an older crustal discontinuity – the Río Chubut Medio fault, located at the eastern border of the basin – recorded a continuous tectonic activity throughout the entire evolution of the basin. These evidences show a synchronous tectonic activity for the Andean and extra-Andean Patagonian regions at those times. In addition, the presence of a climax deformation constrained to 15–14.6 Ma and the deceleration of the Río Chubut Medio Fault at 12.2 Ma could be related to eastward expansion and westward retraction of the orogenic front respectively. Therefore, our data indicate that both the presence and absence of a deformation pattern in extra-Andean regions should be considered to suggest alternative lithospheric-scale models. • We analyse morphostructural, tectono-stratigraphical and geochronological data in one Patagonian Broken Foreland basin. • The results allow to constrain the timing of deformation in Paso del Sapo Basin at 15–11.5 Ma. • Minor faults were activated and de-activated, but an older crustal heterogeneity had a continuous activity between 15-11.5 Ma. • These evidences show a synchronous tectonic activity for the Andean and extra-Andean Patagonian regions at those times. [ABSTRACT FROM AUTHOR]