Silvia N. Césaria, Carlos O. Limarino,Sergio Marenssi, Patricia L. Ciccioli, Fanny C. Bello, Luis C. Ferreira, Leonardo R. Scarlatta & Richard Friedman
2 022
Palynology
Palynology is one of the most useful tools for constructing biostratigraphic charts in the late Paleozoic basins of South America, but the lack of radiometric ages often makes it difficult to establish the precise age of the biozones. This paper focuses on two points: (i) the description of new Argentinian palynological assemblages referred to the Lueckisporites/Weylandites (LW) Biozone and (ii) the application of a new isotopic age that enables more confident large-scale correlations with the neighboring Paraná Basin of Brazil. The palynofloras were recovered from the upper part of the De La Cuesta Formation that crops out in the retroarc basin of the Paganzo Basin, more specifically obtained from mudstones intercalated with limestones, cherts, and tuffs interpreted as being deposited in a shallow water body. The assemblages are characterized by an abundance of bi-taeniate pollen grains of the Lueckisporites complex and multitaeniate pollen grains such as Lunatisporites, Protohaploxypinus, Striatopodocarpidites, Tornopollenites, and Vittatina. Colpate pollen grains are also represented by Marsupipollenites and Pakhapites. A U-Pb CA-ID-TIMS age of 278.84 ± 0.22 Ma, obtained from a tuff level interstratified with the fossiliferous strata, allows the age of the LW Biozone in the Paganzo Basin to be constrained for the first time and the adjustment of the record Lueckisporites virkkiae in Gondwana. Moreover, this date enables precise correlations with other basins, such as the San Rafael Basin (Yacimiento Los Reyunos Formation) in Argentina and the Brazilian Paraná Basin (Iratí Formation).
Jorge G. Lozano, Yasmin S. Gutierrez, Donaldo M. Bran, Emanuele Lodolo, María E. Cerredo, Alejandro Tassone, Juan F. Vilas
2 022
Geological Journal
Lago Roca is a NE–SW elongated lacustrine body located to the south of Lago Argentino, the largest lake of the UNESCO ‘Los Glaciares’ National Park. An extensive high-resolution seismic survey carried out within the Lago Roca, integrated with geological information gathered in the area, have allowed to produce: (a) a complete bathymetric map of the lake; (b) a basement topography map and a structural map; and (c) an analysis of the geometry, distribution, and thickness of the sedimentary infill. Two sub-basins were recognized in Lago Roca, separated by a central basement high that shows a pop-up structure. The northern and southern margins of the lake basement are bounded by NE–SW trending strike-slip faults that constitute subsidiary faults strands of the regional structural lineament known as the ‘Lago Argentino transfer fault’. The shallow, low magnitude seismicity recorded in the area supports the interpretation that this fault segment is active at the present. The relative motion along the fault led to the deformation of the sedimentary infill of the lake, which was also affected by several subsidiary normal faults oriented parallel to the Lago Argentino transfer fault. Data show the peculiar asymmetry in the sedimentary filling of Lago Roca, typical of those of pull-apart basins generated along transform margins. A simplified model for the evolution of Lago Roca is also here proposed, based on the analysed data and the regional tectonic background.
Las Segundas Jornadas Argentinas de Geoturismo se realizarán los días 21 al 23 de abril del 2023 en la localidad de Sierras Bayas, partido de Olavarría, Provincia de Buenos Aires en oportunidad de celebrarse el Día de la Tierra. Las mismas son continuación de las realizadas los días 19 y 20 de abril del 2019, realizadas ese año en coincidencia con la celebración del Día Latinoamericano del Geoturismo. Las medidas preventivas asociadas a la pandemia de COVID19 interrumpieron su continuidad en los años siguientes, pero las condiciones sanitarias actuales nos permiten, afortunadamente, poder convocar nuevamente al evento, que se desarrollará en forma exclusivamente presencial.
J.P. Ormazabal, J.I. Isola, F.I. Palma, J.G. Lozano, F. D. Esteban, M.M. Menichetti, E. Lodolo, A.A. Tassone
2 020
Journal of South American Earth Sciences Volume 103, November 2020, 102708
In this study, we examine the external part of the Magallanes-Malvinas Fold and Thrust Belt in offshore areas, including a portion in Tierra del Fuego onshore, in southern South America. Our investigations focus on the interaction between a thin-skinned fold and thrust belt and the basement in that deformation, considering pre-existing structures acting as stress risers and localizing a possible tectonic inversion. The data is composed of around 14,000 km of 2-D multichannel seismic lines and three exploratory wells, used to analyse the anticlines of the fold and thrust belt in the area. The strike of these folds progressively evolves from NW-SE trending in western onshore regions, to WSW-ENE trending in eastern offshore areas. The fold and thrust belt shows a buttressing effect against the Río Chico Arch. The most shortening is seen in the apex of the Río Chico Arch around 67° W, in the coast of Tierra del Fuego, and gradually decreases eastwards in offshore regions. A connection between basement-involved faults and folds offshore is inferred from the analysis of the Géminis and Ciclón anticlines, developed during the N–S last compressional stage of deformation in the late Oligocene/early Miocene. The Géminis anticline is a fault propagation fold with a total shortening of 205 m with a piggyback basin developed over its backlimb. The location and ENE-WSW strike-direction of the fold have been controlled by a basement-involved fault. The Ciclón anticline is a subtle fold trending WNW-ESE developed as a result of the slight tectonic inversion of a negative flower structure.
Los campos Matachines, localizados en la subcuenca de Girardot (cuenca del valle superior del Magdalena), presentan una morfología antiformal con su eje dispuesto en rumbo submeridianal que involucra secuencias tectosedimentarias multifásicas en las que pueden reconocerse geometrías de hemigraben asociadas con las secuencias mesozoicas que han sido reactivadas por al menos tres fases andinas. Las superficies de estratificación son planos mecánicamente activos contribuyentes de los flexodeslizamientos que genera el plegamiento de secuencias multilitológicas. En los campos Matachines, la estratificación contribuye a mejorar las características petrofísicas de sus reservorios al incorporar una importante participación de discontinuidades que complementan la conectividad de los fluidos. Así, desde sus posiciones subhorizontales se vincula con los planos de fracturas subverticales dispuestos preferencialmente en dirección ENE-WSW, generados por los esfuerzos compresionales horizontales. En particular, estos efectos se magnifican sobre el flanco occidental y charnelar de la estructura anticlinal, donde exhiben una mayor participación en la conectividad de los pozos productivos. En los reservorios considerados naturalmente fracturados, la correcta evaluación técnico-económica 4D de la calidad y disposición de las discontinuidades es fundamental para determinar las mejoras petrofísicas que determinan. En este sentido, muchas metodologías habitualmente aplicadas en el estudio de pozos a partir de núcleos o imágenes reconocen, además de distintos tipos de fracturas, la presencia de superficies de estratificación. Sin embargo, se las evalúa separadamente, lo que no incide estadísticamente en las consideraciones petrofísicas que contribuyenan evaluar su porosidad y permeabilidad. Se discuten los aspectos genéticos y morfológicos de las superficies de estratificación que contribuyen a aumentar la potencialidad petrofísica de los reservorios, cuyos valores primarios de permeabilidad y porosidad suelen ser limitados, para sostener expectativas económicas satisfactorias de ciertos recursos en actividades de exploración o producción de hidrocarburos.
The Matachines field, located in the Girardot subbasin, Upper Magdalena Valley (Valle Superior del Magdalena – VSM) basin, has a morphology characterized by antiforms arranged along a N–S axis. These antiforms involve multipha-se tectono-sedimentary sequences with half-graben geometries associated with Mesozoic sequences reactivated by at least three Andean phases. Bedding surfaces are mechanically active planes that contribute to the flexural slip that is generated by the folding of multilithologic sequences. In the Matachines field, the bedding planes help to improve the petrophysical characteristics of the reservoirs by incorporating a significant number of discontinuities, which comple-ment the fluid connectivity. Thus, the subhorizontal planes are linked to subvertical fractures preferentially arranged in the ENE–WSW direction, generated by horizontal compressive stress. In particular, these effects are magnified on the western flank and hinge zone of the anticline structure, where they contribute greatly to the connectivity of the production wells. In naturally fractured reservoirs, the correct 4D technical and economic evaluation of the quality and arrangement of discontinuities is essential to determine their actual contribution to improving the petrophysical properties of such reservoirs. Accordingly, many methods often used to study wells from core samples or images identify, along with different types of fractures, the presence of bedding surfa-ces, although they evaluate them separately, so they overlook petrophysical factors that affect the porosity and permeability of the wells. The present study discusses the genetic and morphological aspects of bedding surfaces that enhance the petrophysical potential of reservoirs, which usually have limited primary values of permeability and porosity, to meet the economic expectations of specific resources in hydrocarbon exploration and/or production activities.
Revista de la Asociación Geológica Argentina, Vol. 77 Núm. 3 (2020)
Rosselia socialis were studied in the Ordovician Áspero Formation, in order to explore their sedimentary and diagenetic fingerprint in the substrate. These trace fossils are found forming crowded Rosselia ichnofabrics, described for the first time in pre-Quaternary strata of Argentina. We identified three microstructures corresponding to the central shaft complex, the burrow lining and the host rock of a trace fossil assigned to a terebellid polychaete. The infill of the central shaft complex represents downwards advection of surficial deposits located close to the burrow opening: fine-grained fecal mounds, and sandy mounds and lag deposits of manipulated, non-ingested material. Abundant phylosillicates in the central shaft complex and burrow lining evidence mechanical selection of particles with high specific surface area by the tracemaker. The fine-grained composition and multilayered organically bound structure of the burrow lining generate an impermeable and reinforced burrow, which combined with crowding grants physical and chemical stability to its inhabitants. This is especially advantageous in the high energy environments with shifting substrates where crowded Rosselia ichnofabrics are typically found. The central shaft complex and burrow lining are enriched in secondary iron minerals with respect to the host rock. Mineralized bacterial structures in the burrow lining evidence biologically induced precipitation of iron oxides and possibly sulphides. This coupled with the distribution of iron minerals in the burrow lining and central shaft complex suggests the occurrence of early diagenetic processes of organic matter decomposition and precipitation of authigenic iron minerals in Rosselia burrows, as observed in modern terebellid polychaetes.
La anisotropía de susceptibilidad magnética (AMS) es un método preciso para conocer la fábrica magnética y permite conocer la ubicación espacial de los esfuerzos regionales en áreas deformadas. La relación entre el elipsoide de AMS y su coaxialidad con el elipsoide de esfuerzos y deformación es conocida, donde el eje menor de AMS (Kmin) coincide con la dirección del esfuerzo principal σ1. A partir de la medición de la susceptibilidad magnética y la interpretación de la fábrica magnética interna de modelos análogos de arena, se puede hacer una aproximación sobre la distribución de los esfuerzos en zonas de deformación. Aquí presentamos los resultados de tres modelos análogos con diferentes mineralogías magnéticas. Los modelos se realizaron con el objetivo de evaluar la susceptibilidad magnética en diferentes posiciones del modelo y calcular el elipsoide de AMS y la relación entre la fábrica magnética y la mineralogía magnética, para comparar cuáles de las diferentes mineralogías son las mejores para los modelos posteriores.
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.
