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The Atuel depocenter of the Neuquén basin originated as an Upper Triassic to Lower Jurassic rift system, later inverted during the Andean contractional deformation. In order to study the tectono-sedimentary evolution of this depocenter, we integrated a large set of stratigraphic, sedimentologic and structural data into a multidisciplinary approach. We used data from facies and thickness distribution of the synrift units, provenance studies on sandstones, palaeoslope and palaeocurrent field measurements, kinematic data from outcrop scale normal faults, and angular and progressive unconformities. Regarding its structural architecture, the Atuel depocenter has a NNW trend, showing a bimodal distribution of NNW and WNW major faults. The general orientation of this depocenter was controlled by the development of two first order faults of NNW trend and western hanging-wall, the La Manga and Alumbre faults. From kinematic indicators measured on outcrop-scale faults, we found a mean NE internal extension direction, which is oblique to the general trend of the sub-basin. Taking these particular characteristics into account, we interpreted the Atuel depocenter as an oblique rift system. The Upper Triassic to Lower Jurassic infill of the Atuel depocenter consists of siliciclastic marine and continental sedimentary rocks, grouped in the Arroyo Malo, El Freno, Puesto Araya and Tres Esquinas Formations. The Rhaetian to Early Sinemurian period was characterized by deposition of slope-type fan deltas in the western sector, while in the eastern sector a coeval braided fluvial system developed. By the end of Early Sinemurian period, an intermediate-type fan delta prograded over the slope-type fan deltas in the western sector, while in the eastern sector the fluvial systems increased their lateral migration. Later, during late Early Sinemurian to Toarcian times transgression of a marine shelf and a marked increase in the marine depositional area took place. We interpret the Rhaetian to Lower Sinemurian sediments as deposited during the synrift phase of the Atuel depocenter. The La Manga and Alumbre major faults controlled most of the basin subsidence, the distribution of the sedimentary environments and the drainage patterns during this stage. While the braided fluvial system characterizes the synrift infill in the hanging-wall of the La Manga fault, coetaneous deposits to the west of the Alumbre fault were deposited in the slope-type fan deltaic environment. The La Manga fault was the eastern border of the Atuel depocenter. To the east this fault, there is no record of Upper Triassic to Lower Jurassic synrift deposits neither in outcrops nor in wells, while more than 1,500 m of continental synrift deposits are registered in its hanging-wall. These fluvial deposits show outcrop scale normal faults and angular unconformities, indicating a syntectonic sedimentation. On the other hand, the Alumbre fault maintained a nearly fixed position of the coastal line from Hettangian to Early Sinemurian times, restricting the marine sedimentation to the western sector of the depocenter. Fan-deltaic deposits in the hanging-wall of the Alumbre fault show a marked cuneiform geometry, with strata thickening towards the structure. This synrift sequence also shows angular and progressive unconformities indicating a progressive eastward tilting of its hanging-wall. The decreasing accommodation observed by the end of the Early Sinemurian was previously related to the start of the sag phase. However, we observed outcrop scale faults affecting Pliensbachian sediments in the southeastern sector of the depocenter, suggesting that the extensional deformation continued for some more time, or that a second synrift stage took place. In this context, it will be necessary to review the tectonic setting during the Sinemurian to Toarcian marine transgression.

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