Anisotropy of magnetic susceptibility (AMS) is a precise method to know the magnetic fabric and allows to know the spatial location of regional stresses in deformed areas. The relationship between the ellipsoid of AMS and its coaxiality with the ellipsoid of stress and deformation is known, where the minor axis of AMS (Kmin) coincides with the direction of the main stress σ1. From the measurement of magnetic susceptibility and the interpretation of the internal magnetic fabric of analogous sand models, an approximation can be made to the knowledge of the distribution of stress in deformation zones. Here we present the results of three analogues models with different magnetic mineralogies. They were performed with the objective of evaluating the magnetic susceptibility in different positions of the model and calculate the AMS ellipsoid and the relationship between the fabric obtained and the magnetic mineralogy, to compare which of the different mineralogies are the best to subsequent models.

This work focuses on the transition from the Las Leoneras to Lonco Trapial Formations, in the lower part of the Early Jurassic succession of the incipient rift phase of the Cañadon Asfalto Basin (western part of Chubut Province – Patagonia, Argentina). Twenty lithofacies have been identified and grouped into seven facies associations on the basis of field characteristics (sedimentological and lithological) and optical microscope analysis, from two localities representing proximal and distal locations in the basin. The spatial relationship between all the lithofacies provided a four‐dimensional reconstruction of the palaeoenvironmental evolution, showing how the original, clastic sedimentation in alluvial/fluvial and lake environments was modified by short‐lived volcanic events during three volcanic cycles, and how the environment reacted after the input of huge amounts of volcaniclastics. Progradation of small deltas and subaqueous lobes, retrogradation caused by rising lake levels, and frequent erosion of valleys were typical processes in this environment. When explosive volcanism began, the original tectono‐climatic control on sedimentation was replaced by the volcanic control, and the volcanically‐forced sedimentation broke the equilibrium among production, delivery and accumulation of sediments. The nature of the volcanic eruptions and the different propensity of volcanic lithofacies to produce particles of different size and types (lithics, crystals and glass) are also analyzed. The role of volcanism in the production and transport of great volumes of sediments across sedimentary systems needs to be carefully re‐examined, and the analysis on the variability in the composition of volcaniclastic deposits must take into account that volcaniclastic particle types may not simply reflect a linear deepening in the dissection of magmatic arcs through time but are often controlled by the style of the eruptions and the lithological variation of the volcanic products.

Although the subject “Oil and Gas” is not usually present in the Secondary School Curriculum, it is of interest to students due to its obvious relationships with everyday life, and has been selected to design a series of teaching resources. Not only natural sciences such as Geology, Biology and Chemistry are embedded in the formation and accumulation of petroleum, but also con-stant references to History, Geography and Technology are present when linking together its discovery, exploitation, industrial-ization and use. The materials being produced cover three categories: a reference text to be available in printed and PDF file versions, a portfolio of teaching resources and a website. The first two are described and exemplified. The portfolio also in-cludes examples of published materials, which contain conceptual errors proposing their use to explore misconceptions if used at the beginning of the presentation of the subject in class, or to identify levels of understanding if used at the end.

Lago Yehuin, a WNW-ESE elongated basin located in the outer fold-and-thrust belt of the Fuegian Andes, occupies a compartmented structural depression originated along a segment of the left-lateral Lago Deseado fault system. This paper describes the first geophysical survey performed within the lake. New acquired high-resolution single-channel seismic data, integrated with geological information in the surroundings of the Lago Yehuin, allowed to: (i) produce a complete bathymetric map of the lake, (ii) reconstruct the basement surface of the lake, and (iii) analyze the geometry, distribution, and thickness of the sedimentary infill. Two sub-basins were recognized within Lago Yehuin: A western sub-basin, 7.5 km long, with a maximum depth of 118 m; an eastern sub-basin, 7.2 km long with a maximum depth of 80 m. Both sub-basins are limited by a set of normal faults which overprint NE-verging thrusts. Three seismostratigraphic units have been identified in the seismic records: (1) a lower unit with wedged geometry interpreted as a mass flow deposits; (2) a thick (up to 120 m) intermediate unit of glacio-lacustrine nature and irregularly distributed in the Yehuin basin; (3) a thin (generally <10 m) upper lacustrine unit which drapes the entire basin. Lago Yehuin is considered a Neogene basin generated by strike-slip tectonics that was later affected by glacial and glacio-lacustrine deposition. Interpreted submerged ridge moraines within Lago Yehuin are correlated with onland moraine arcs built by the complete recessional paths of Fuego and Ewan ice lobes. A significant structural control is proposed not only for the formation of Lago Yehuin, but also for the general paths of the northern arms of the Fagnano palaeo-glacier.

The fitting of a plane to data points is essential to the geosciences. However, it is recognized that the reliability of these best fit planes depends upon the point set distribution and geometry, evaluated in terms of the eigen‐based parameters derived from the moment of inertia analysis. Despite its significance, few studies have addressed the uncertainties of the analysis, which can adversely affect the reproduction of results one of the cornerstones of scientific endeavor. Aiming to contribute toward the neglected issue of the moment of inertia precision, we have developed a bootstrap resampling scheme to empirically discover the distribution of uncertainties in the orientation of best fit planes. Dispersion of the bootstrapped normal vectors to the best fit plane is regarded as a measure of precision, evaluated with the maximum angular distance from the optimal solution. This rationale was tested using Monte Carlo‐generated samples covering a comprehensive range of shape parameters to assess the dependence between eigen parameters and their inherent bias. Our results show that the oblateness of the point cloud is a robust parameter to assess the reliability of the best fit plane. Given this, the method was then applied to a publicly available lidar data set. We argue that georeferenced point clouds with an oblateness parameter greater than 3 and 1.5 may be placed at 95% confidence levels of 5° and 10°, respectively. We propose using these values as thresholds to obtain robust best fit planes, guaranteeing reproducible results for scientific research.

In this contribution we describe the textures and the mineralogy of eocene volcanic sequences from Bajada del Diablo and Marra-Có, Chubut province. They are composed of alkali basalt with three different sections. The two upper ones are characterized by the occurrence of secondary minerals among which amygdules filled by fibrous aggregates of natrolite are the most common ones. This species not only represents the last mineral precipitation but also the most important one. The alteration assemblages of primary minerals as well as the secondary assemblages, that fill each basalts’ cavities, suggest a very low-grade hydrothermal alteration with temperatures lower than 100°C and low silica activity.

“Identification of disequilibrium paragenesis by electron microprobe analysis of the andesitic facies of Trayén Niyeu Volcanites, Somún Curá plateau, Extra-andean Patagonia”. The Trayén Niyeu Volcanites TNV) represent an unusual miocene calc-alkaline magmatism related to the postshield stage of the Somún Curá Magmatic Province, of mainly alkaline nature. They develop a 650 km2 mesa at the north-western margin of the North Patagonian Massif, defining a back-arc to foreland transition zone. Textural and EMPA studies on TNV andesitic facies allowed us to establish that the equilibrium paragenesis with this liquid is of En78-80 and An43-52 composition, whereas individuals of composition An15-19 are not in equilibrium, developing a more calcic (An30-38) rim with spongy cellular texture of varying intensities. The growing of a boxy cellular texture rim on plagioclase and a clinopyroxene epitactic overgrowth on the orthopyroxene, probably result from the temperature drop associated to the dissolution and recrystallization of the sodic plagioclase. In this regard, TNV’s magmatic evolution must involve processes that account for the interaction of magmas of contrasting physicochemical properties, such as magma mixing by injection, chamber replenishment or convection.

This contribution considers that there is an increase of Galactic Cosmic Rays (GCR) in space due to the birth of a supernova near our solar system. This event would have started around 2.8 to 2.6 Ma and finished between 1.7 and 1.5 Ma with a peak around 2.2 Ma; a consequent increase of radiation input to Earth took place. This increase is favored by the weakening and even suspension of the Earth’s magnetic field during the reversion between the Gauss and Matuyama Chrones. All these factors generated a relative maximum of the GCR flux on the earth, which could act as trigger of the beginning of the first Quaternary glaciation and the appearance of the oscillations between warm and cold stages that characterized the Pleistocene.
Key words: Paleoclimate, galactic cosmic ray, geomagnetic field, Plio-Pleistocene boundary, supernova.