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Visita técnica a sectores de la comuna de Lota, región del Biobío, afectados por remociones en masa durante el mes de julio de 2022
Get PDFRevisores: Monica Marin y Carolina Jara -- Informe Técnico17 p
Relationship between fissility, composition, rock fabric and reservoir properties in Vaca Muerta Formation (Neuquén Basin, Argentina) : From outcrop to subsurface core data
No full textThe fissility is the ability of some rocks to split along relatively smooth surfaces parallel to the bedding. This property observed mostly in fine-grained rocks is particularly expressed in outcrops, where rocks are subjected to weathering processes. Most authors associate the fissility to the abundance of clay minerals and their orientation parallel to the bedding. The horizontal fabric can be promoted by depositional conditions such as sediment composition, quantity of total organic carbon content (TOC) and depositional mechanisms, giving rise to a primary fissility. Alternatively, the alignment of platy minerals can be linked to the burial history of the rock, by processes such as mechanical compaction or secondary mineral growth, resulting in a secondary fissility. The present study aims to identify the main controls of fissility development at the micro- and macroscopic scale in rocks of the Vaca Muerta Formation exposed in the Cerro Mulichinco area and in a 121-meter-long core extracted from a well within the Neuquén Basin. In outcrops, fissility is related to fine-grained laminated facies with low carbonate content, revealing the strong control exerted by lithology. The TOC measurements allow establishing a positive correlation between organic matter content and fissility intensity. Moreover, the analysis of the transgressive-regressive cycles shows that fissility is higher around the maximum flooding surfaces. Regarding their mechanical characteristics, the different interfaces observed in core are classified into first and second-order, the last one including fissility planes. Some of these interfaces evolve from potential (partially open) to effective (totally open) discontinuities in response to changes of stress conditions during the core extraction and due to the stress relaxation through time: weeks (T1), months (T2) and years (T3) after extraction. The time evolution of the effective core discontinuities points out rock intervals that are variably broken and core segments that remain intact. The Drying Alcohol Discontinuities (DAD) methodology reveals potential discontinuities within apparently intact core segments. By using this technique, a 4-class index is established as a proxy for fissility degree. When integrated with geological, petrophysical and geomechanical data, this index enables characterizing the main mechanisms controlling rock fissility that express through discontinuities promoting the loss of competence of a rock. Consequently, this mechanical property is considered to influence the efficiency of hydraulic fracture in shale reservoir completion.pp.345-38
Nuevos sitios fosilíferos y evolución paleoambiental del Cenozoico tardío del suroeste de Córdoba, Argentina
No full textNuevos restos fósiles fueron hallados en secuencias sedimentarias neógenas y cuaternarias que afloranen las localidades de Alpa Corral y río San Bartolomé (departamento de Río Cuarto, provincia de Córdoba). Estos fueron asignados a Nopachtus cabrerai (Xenarthra, Cingulata, Glyptodontidae), Notiomastodon platensis (Proboscidea, Gomphotheriidae) y cf. Trigodon gaudryi (Notoungulata, Toxodontidae), y se identificaron trazas de la icnofacies deScoyenia como Taenidium barretti. Sobre la base de estos registros se concluye: 1. las especies Nopachtus cabrerai ycf. Trigodon gaudryi se registran por primera vez en la región de las Sierras Pampeanas y se suman al conjunto de taxones que indican una clara similitud faunística con la región Pampeana; 2. el inicio de la sedimentación neógena en la regiónde Alpa Corral (valle del río de Las Barrancas y río San Bartolomé) habría comenzado durante el Plioceno temprano(Edad Montehermosense); 3. el paleoambiente habría sido un sistema fluvial con canales meandriformes, intercaladoscon paleosuelos desarrollados en llanuras de inundación con depósitos de desborde o meandros abandonados; 4. elregistro paleontológico y sedimentario sugiere un diacronismo muy marcado en el inicio de la depositación neógena(con dirección oeste a este), entre el sector sur del valle de San Alberto (Mioceno tardío; Edad Huayqueriense), en laregión de Alpa Corral (Plioceno temprano; Edad Montehermosense), y el valle del río de La Cruz (Plioceno tardío;Edad Chapadmalalense).pp.94-12
Characterization and distribution of adularia and other alteration minerals by X-ray diffraction analysis at the El Peñón Au-Ag epithermal deposit, northern Chile
No full textThe El Peñón low-sulfidation epithermal deposit, located in the Paleocene metallogenic belt in the Antofagasta region, northern Chile, consists of Au-Ag bearing veins and hydrothermal breccias hosted in volcanic rocks and surrounded by alteration haloes consisting of a series of minerals, such as adularia, carbonates and clay minerals. They are the result of metasomatism generated by the passage of reduced, and near neutral pH, hydrothermal fluids, that transported gold through structures and its interaction with the host rock. We investigated the spatial distribution of these minerals (mainly adularia) in the Aleste vein and its host rock, located in the northern part of the district, to establish their relationship with the Au-Ag ore and, thus, support the identification of new exploration targets. An X-ray diffraction technique to discriminate adularia from other K-feldspars in whole rock samples was developed by the detail study of the diffractogram patterns of an adularia standard. The study of an X-ray diffraction standard pattern allowed the recognition of this mineral by 4 secondary peaks. Our results indicated that adularia occurs in association with felsic volcanic rocks, and it is restricted in intermediate composition units. The spatial distribution of this mineral is correlated with the mineralized zones, being adularia semi-quantitative abundance in the range of 25 to 40% a good indicator of gold mineralization. Sericite and illite occur mainly where adularia is scarce or absent. The spatial distribution of these minerals showed the structural control in the evolution and flow path of the hydrothermal fluids toward the surface. Kaolinite is related to argillic alteration caused by steam-heated fluids, and the advanced argillic alteration associated with later supergene alteration. Chlorite usually is far from the mineralized areas; therefore, it could be a reliable indicator of the margins of the system. The characterization and spatial distribution pattern of the alteration minerals identified by the X-ray diffraction method in the veins of El Peñón deposit show the capability of this type of analyses in determining possible prospection targets.pp.185-20
Geología de las islas Robinson Crusoe y Santa Clara, región de Valparaíso
Get PDFContiene Anexos: Anexo I.Dataciones Radiométricas ; Anexo II.Localidades Fosilíferas ; Escala: 1:25.000 ; Coordenadas: 33,64°S / 78,84°O42 p
Evaluación de peligro de remoción en masa en ladera del estero Cudico, comuna de Panguipulli, Región de Los Ríos
No full textRevisores: Paola Ramirez y Carlos Johnson ; Informe Técnico21 p
Caracterización de remoción en masa por colapso de muro de contención en población Modelo, comuna de Puerto Montt, región de Los Lagos
No full textInforme Técnico INF-Los Lagos-10, 2022 -- Unidad Ejecutora: Oficina Técnica Puerto Varas14 p
Remociones en masa y activación de quebradas por eventos hidrometeorológicos, ocurridos en julio de 2022, región de Coquimbo
No full textRevisores: Mónica Marin D., Alejandro Alfaro S. y Carolina Jara I.-- Informe Técnico119 p
The first fossil record of a giant horsetail (Equisetum, Equisetaceae) is from the Miocene of Patagonia, Argentina
No full textA Miocene macroflora recovered from Ñirihuau Formation sediments exposed at Quebrada Vera site in northwesterern Patagonia, Argentina, is recorded and described for the first time. The assemblage is composed exclusively of free-sporing plants, mainly by Equisetum remains with subordinate occurrences of four fern morphotypes (represented by bi-, tri- and pinnate fronds). Equisetum imprints and molds include distinctive jointed stems with whorls of linear and basally fused leaves, numerous scars of lateral branches arranged in a radially symmetrical pattern situated at the nodes, and nodal diaphragms of up to 4 cm in diameter. The large size and regular branching of the stems link the fossils to the South American giant members of the genus and they probably represent a new fossil species. This is the first conclusive fossil record of a giant Equisetum worldwide, and consequently, it is biogeographically and evolutionarily relevant. The new findings attest that members of the giant horsetail clade were components of the Patagonian vegetation in the Miocene, implying that the age of the clade must predate that estimated from morphological and/or molecular data. The plant fossil assemblage represents part of a wetland community probably growing close to a riverside or lakeshore in coincidence with previous sedimentological estimates.pp.273-28
