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Schencman L.J.,University of Buenos Aires | Leal P.R.,University of Buenos Aires | Perez D.J.,University of Buenos Aires | Perez D.J.,Institute Estudios Andinos Don Pablo Groeber IDEAN
Revista de la Asociacion Geologica Argentina

The aim of this paper is the characterization of a copper mineralization located in the Agrio fold and thrust belt (20 km to the west of Chos Malal, Neuquén Province). Analyzing the structures and textures that could be researched in the mineralizations and the bed rock, we deduced a hydrothermal origin for the deposit. We had determined two assemblages: a primary one of iron and copper sulphids, and a secondary one of oxides and hydroxides, with minor quantity of carbonates and silicates. The interaction with the bed rock is limited to a partial sericitic alteration, with subordinated amount of iron oxides and carbonates. In relation to the spatial distribution of the mineralization and the vein's geometry, we had determined that the main control of the deposit were subvertical structures. After a textural analysis of the mineralization we recognized three deformation events, which affected the bed rock and the ore deposit. The microthermometric studies made over carbonates from the latest stages of the mineralization process had showed a trap temperature of 95.4 °C as an average. Source

Kietzmann D.A.,Institute Estudios Andinos Don Pablo Groeber IDEAN | Kietzmann D.A.,University of Buenos Aires | Kietzmann D.A.,CONICET | Palma R.M.,Institute Estudios Andinos Don Pablo Groeber IDEAN | And 5 more authors.
Sedimentary Geology

Detailed sedimentological, sequence stratigraphical and cyclostratigraphical analyses have been made from four lower Tithonian-lower Valanginian sections of the Vaca Muerta Formation, exposed in the southern Mendoza area of the Neuquén Basin, Argentina. The Vaca Muerta Formation is characterized by decimetre-scale rhythmic alternations of marls, shales and limestones, and consists of five facies associations, which reflect different paleoenvironmental conditions: basin to restricted outer ramp, outer ramp, and middle ramp. Vertical organization within the Vaca Muerta Formation shows a well-ordered hierarchy of cycles, where elementary cycles, bundles and superbundles with frequencies within the Milankovitch band have been recognized. According to biostratigraphic data, elementary cycles have a periodicity of ~. 20 ky, which correlates with the precession cycle of Earth's axis. Spectral analysis based on series of cycle thickness allows us to identify frequencies of about 400 ky and 90-120 ky, which we interpret as the modulation of the precessional cycle by the Earth's orbital eccentricity. Cycles are probably driven by variations in carbonate exportation, as fluctuations in shallow-water carbonate production involve modifications in carbonate basinward exportation. Cyclostratigraphic data allowed us to build a floating orbital scale for the Tithonian-lower Valanginian interval in the Neuquén Basin. Correlation between studied sections allowed us to recognize a discontinuity between the Substeueroceras koeneni and Argentiniceras noduliferum ammonite zones in the Malargüe Anticline area. Orbital calibration of these sections is consistent with Riccardi's biostratigraphic scheme, wich place the Jurassic-Cretaceous boundary within the Substeueroceras koeneni ammonite Zone. On the other hand, the base of the Vaca Muerta Formation (Virgatosphinctes mendozanus ammonite Zone) would be probably placed in the base of the middle Tithonian rather than the lower Tithonian, which is also consistent with our preliminary palaeomagnetic data. © 2014 Elsevier B.V. Source

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