Tectono-Stratigraphic Evolution of the Atuel Depocenter During the Late Triassic to Early Jurassic Rift Stage, Neuquén Basin, West-Central Argentina

BECHIS, F.; GIAMBIAGI, L.B.; TUNIK, M.; SURIANO, J.; LANÉS, S.; MESCUA, J.F.

Opening and Closure of the Neuquén Basin in the Southern Andes

Springer

Año: 2020; p. 23 - 52

The Neuquén Basin presents an almost continuous record from the Late Triassic until the Paleocene, making it an excellent case study of the most relevant tectonic stages of southern South America during the Mesozoic. It was initiated in Late Triassic to Early Jurassic times as a continental rift basin in the context of a widespread extensional stage that affected western Gondwana and culminated with the break-up of the supercontinent. The Atuel depocenter is located in the northern sector of the Neuquén Basin. Its synrift and sag units are represented by Upper Triassic to Lower Jurassic siliciclastic marine and continental sedimentary rocks including the oldestmarine deposits of the basin, of Late Triassic age. The depocenter infill has been deformed and exhumed during the Andean orogeny, being presently exposed in the northern sector of the Malargüe fold and thrust belt. In this review, we have integrated a large set of stratigraphic, sedimentologic, geochronologic, and structural data in order to unravel the tectono-sedimentary evolution of the Atuel depocenter andto evaluate the main controlling factors of the synrift stage. We analyzed data from the synrift units, such as facies and thickness distribution, sandstone provenance, detrital zircon geochronology data, kinematic data from outcrop-scale normal faults, angular and progressive unconformities, and subsurface information. Reactivation of preexisting NNW-striking anisotropies under a regional NNE extension resulted in an oblique rift setting, which generated a bimodal distribution of NNW- and WNWstriking major normal faults. Reduced strain and stress tensors obtained from the kinematic and dynamic analysis of structural data show a complex heterogeneity that we interpreted as a result of local stress permutations due to the activity of the larger faults and to strain partitioning inside the Atuel depocenter. Sedimentologic and petrographic data revealed a complex evolution with strong lateral variations of the depositional environments during the synrift phase, which lasted from Rhaetian to Pliensbachian times.We identified several stages that were controlled by processes of initiation, propagation, growth, linkage, and deactivation of new and reactivated faults along the depocenter evolution, in combination with sea-level changes related to global eustatic variations. Sandstone provenance data suggest an important basin reorganization by the Toarcian, probably related to the initiation of the sag stage in this depocenter.