Carta Geológico-Económica de la República Argentina

Fil: Ploszkiewicz, Juan V. Ministerio de Economía. Secretaría de Minería. Dirección Nacional de Minería y Geología; Argentina

Synrift geometry of the Neuquén Basin in northeastern Neuquén Province, Argentina

A map of the principal grabens and half-grabens of the Neuquén Basin in the northeastern part of Neuquén Province, Argentina, was constructed based on twodimensional (2-D) and three-dimensional (3-D) seismic information. The synrift structure of the region is characterized by high angle NW-trending normal faults. Two populations can be distinguished: one with an azimuth of 140° and the other one with an azimuth of 105°. The principal half-grabens are accommodated by NEdipping normal faults. The principal NW-trending faults are less than 20 km long and are either crosscut by or terminate in transfer zones trending to the NE. The transfer zones are either faults or zones where the principal NW-trending faults loose slip or terminate. The principal normal faults were active until the deposition of the Lower Upper Jurassic Tordillo Formation. Subsequently, only a few faults related to differential subsidence over the half-grabens remained active. The typical structures of the region are smooth anticlines and synclines that affect the sag facies of Neuquén Basin. The anticlines developed over basement highs and the synclines over graben basins. The synclines are explained in this study as resulting from differential subsidence over the half-grabens. This differential subsidence could have been a continuous process that began in the synrift stage of the basin. A distinct element model was created to analyze the differential subsidence process and geometry. No evidence was found to support the hypothesis that tectonic inversion is an important process in this region. The main unconformities can be explained by the differential subsidence process.Fil: Cristallini, Ernesto Osvaldo. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Geociencias Básicas, Aplicadas y Ambientales de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Geociencias Básicas, Aplicadas y Ambientales de Buenos Aires; ArgentinaFil: Bottesi, Germán. Repsol YPF; ArgentinaFil: Gavarrino, Alejandro. Repsol YPF; ArgentinaFil: Rodríguez, Leonardo. Repsol YPF; ArgentinaFil: Tomezzoli, Renata Nela. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Geociencias Básicas, Aplicadas y Ambientales de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Geociencias Básicas, Aplicadas y Ambientales de Buenos Aires; ArgentinaFil: Comeron, Raúl. Repsol YPF; Argentin

Architecture and development of the alluvial sediments of the Upper Jurassic Tordillo Formation in the Cañada Ancha Valley, northern Neuquén Basin, Argentina

The Upper Jurassic Tordillo Formation at Cañada Ancha area, northern Neuquén Basin, Argentina, comprises a multi-stage suit of predominantly alluvial sediments that is heterolithic in nature. In that suit, several lithofacies, architectural elements, and bounding surfaces of different order have been identified and their lateral and vertical distribution characterized. This analysis allowed the differentiation of 3 main units (lower, middle and upper), 20 subunits (C-1 to C-20), and the characterization of their alluvial styles. The lower unit (which comprises subunits C-1 to C-4) is mainly formed by fine- to medium-grained sandstones, which become medium- to coarse-grained towards the top. These sandstones characterize settings ranging from floodplains with isolated, unconfined flows, to more complex, vertically stacked, multistorey sheet sandstones of braided fluvial systems. The middle unit (C-5 to C-10) is dominated by pale browngrey fine-to coarse-grained sands and medium size subangular to angular conglomerates, which reflect amalgamated complexes of sandstone sheets and downstream accretion macroforms. Remarkably, this alluvial sedimentation was episodically punctuated by volcaniclastic flows. The upper unit (C-11 to C-20) consists of finer sediments, mainly pink to white fine-to medium grained sandstones and red to green siltstones. Towards the top, bioturbation becomes important, and also the presence of volcanosedimentary flows is noticeable. Fluvial settings include braided sheet sandstones with waning flood deposits evolving to isolated high-sinuosity fluvial systems, with flash flood deposits. At the top of this unit, facies may suggest marine influence. Vertical changes in the fluvial style result from both climatic and tectonic controls. A semiarid to arid climate and the active tectonism linked to the eastward migration of the Andean volcanic arc determined major bounding surfaces, fluvial style evolution and the presence of the volcano-sedimentary deposits. Different stages of high and low subsidence rates has been deduced from the vertical stacking of sediments

Intraplate deformation in the Neuquén Embayment

The Neuquén Embayment, which developed along the eastern foothills of thesouthern Central Andes, has a complex history of intraplate deformation. The Paleozoicbasement fabrics exerted a major influence in Mesozoic and Cenozoic deformation.The most important feature is an E-W–striking fault system that is related to alate Paleozoic fabric and is associated with the Huincul basement high, which truncatesthe basin. This fabric is interpreted as being the result of the accretion of thePatagonia terrane with Gondwana during the Early Permian. Two-dimensional (2D)and three-dimensional (3D) seismic coverage and subsurface information identify differentsectors in the Neuquén Embayment that record alternating episodes of contractionand extension during the Jurassic and Cretaceous. The deformation historyeast of the thrust front of the Agrio fold-and-thrust belt is characterized by periods of1) transpression and almost orthogonal contraction to the continental margin, (2)extension, and (3) relative quiescence, which alternates in different sectors. The earliestshortening occurred in the Early Jurassic when the main stress was oriented inthe N-NW sector. The stress rotated to the northwest up to Valanginian times, when amore orthogonal orientation to the continental margin became dominant and prevailedafter the Cenomanian. After a period of quiescence in the Neuquén Embaymentassociated with very oblique subduction during the Paleogene, the finalcontractional deformation took place in the late Miocene, with a west-east orientationof the main stress, and was followed by Pliocene extension.The changing stress patterns correlate with differences in convergence vectorsbetween the Aluk, Farallon, and Nazca oceanic plates and the Gondwana or SouthAmerican continental plates. The Aluk stage from the Jurassic to the Valanginian wascharacterized by tectonic inversion that is shown by shortening and right-lateralstrike-slip structures that are concentrated in the Huincul system and more subtledeformation in the Chihuidos and Entre Lomas systems. The early Farallon stage wasdistinguished by reduced inversion and displacement in the Huincul system and ageneral retreat of deformation after the Valanginian. The change to late Farallonstage was characterized by a prominent tectonic inversion of the Entre Lomas system,which resulted from the inception of the formation of the Agrio fold-and-thrustbelt in the retroarc area. This belt developed during most of the Late Cretaceous,when the embayment showed a general quiescence. The Nazca stage was characterizedby the main episode of uplift, tectonic inversion of the older half-grabens, andimportant strike-slip faulting that was followed by local collapse of some structuresduring the Pliocene.Fil: Mosquera, Alfonso. Tecpetrol; ArgentinaFil: Ramos, Victor Alberto. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Estudios Andinos "Don Pablo Groeber". Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Estudios Andinos "Don Pablo Groeber"; Argentin