Paleomagnestism of the Santa Victoria Group in the Mojotoro Range, Salta: Contributions to the paleogeographic position of Pampia in Early Paleozoic

Sedimentologic magnetofabric paleomagnetic studies were carried out on the early Ordovician La Pedrera Formation (Santa Victoria Group) in the Mojotoro Range Salta province. These studies aim at contributing to a better knowledge on the paleogeographic position of the Pampia block in the Early Paleozoic in relation to the Gondwana supercontinent. Oriented samples were collected from 12 sites distributed in three localities. These outcrops consist of middle to proximal shelf deposits of mainly quarzitic composition. Studies on the anisotropy of magnetic susceptibility (AMS) suggest a depositional fabric in one of these localities meanwhile some tectonic influence cannot be ruled out in the magnetic fabric found in the other two. The paleomagnetic analysis permitted to determine a characteristic magnetic remanence carried by hematite at all twelve sites. From the virtual geomagnetic poles computed at each site a paleomagnetic pole was obtained for the Santa Victoria Group at these localities which is located at 340,4°E 38,3°N A95=8,8°. This pole position suggests that any of the three localities underwent significant tectonic rotations due to the Andean orogeny or pre-vious tectonic events. However, it presents a somewhat lower than expected paleolatitude in comparison to coeval reference poles for Gondwana. Studies of oriented isothermal remanent magnetization suggest that this difference should not be due to inclination errors. On the other hand, the paleomagnetic pole for the Santa Victoria Group disagrees with those previously obtained for the middle to upper Cambrian Mesón Group and the lowermost Ordovician Santa Rosita Formation, to the north of our study localities but still in the same region. These discrepancies can be explained either by the presence of Andean local tectonic rotations around vertical axes in the localities to the north of our study zone or by considering that the hypothetical displacement of Pampia along the Río de la Plata craton margin was already over, or nearly so, by the Early Ordovician

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

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 the Late Triassic to Early Jurassic times as a continental rift basin in the context of a widespread extensional stage that affected western Gondwana andculminated with the break-up of the supercontinent.The Atuel depocenter is located in the northern sector of the Neuquén basin. Synrift and sag units are represented by Upper Triassic to Lower Jurassic siliciclastic marine and continental sedimentary rocks including the oldest marine deposits of the basin, of Late Triassic age. The depocenter infill hasbeen 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, and to evaluate the main controlling factors of thesynrift 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 anoblique rift setting, which generated a bimodal distribution of NNW- and WNW-striking major normal faults. 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 both activity of the larger faults, and to strain partitioning inside the Atueldepocenter.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 that an important basin reorganization by the Toarcian, probably related to the initiation of the sag stage in this depocenter.Fil: Bechis, Florencia. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte. Instituto de Investigaciones en Diversidad Cultural y Procesos de Cambio. Universidad Nacional de Río Negro. Instituto de Investigaciones en Diversidad Cultural y Procesos de Cambio; ArgentinaFil: Giambiagi, Laura Beatriz. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mendoza. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales. Museo de Historia Natural de San Rafael - Ianigla | Provincia de Mendoza. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales. Museo de Historia Natural de San Rafael - Ianigla | Universidad Nacional de Cuyo. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales. Museo de Historia Natural de San Rafael - Ianigla; ArgentinaFil: Tunik, Maisa Andrea. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte. Instituto de Investigación en Paleobiología y Geología; ArgentinaFil: Suriano, Julieta. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mendoza. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales. Museo de Historia Natural de San Rafael - Ianigla | Provincia de Mendoza. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales. Museo de Historia Natural de San Rafael - Ianigla | Universidad Nacional de Cuyo. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales. Museo de Historia Natural de San Rafael - Ianigla; ArgentinaFil: Lanés, Silvia. Cape Town; SudáfricaFil: Mescua, Jose Francisco. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mendoza. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales. Museo de Historia Natural de San Rafael - Ianigla | Provincia de Mendoza. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales. Museo de Historia Natural de San Rafael - Ianigla | Universidad Nacional de Cuyo. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales. Museo de Historia Natural de San Rafael - Ianigla; Argentina. Universidad Nacional de Cuyo; Argentin