Revista de la Asociación Geológica Argentina

Nueva edad U-Pb de la Formación Cerro Barcino (Cretácico), Patagonia: implicancias estratigráficas y paleosísmicas

2024-07-31T12:48:26+00:00

Presentamos una nueva edad U-Pb de cristalización/depositación de la Formación Cerro Barcino (Grupo Chubut) del Cretácico, basada en una muestra volcaniclástica colectada cerca de la localidad Alto de Las Plumas. La muestra proviene de una sucesión aluvial previamente asignada al Miembro Las Plumas (Cenomaniano), que incluye sismitas interpretadas como el resultado de paleosismos probablemente relacionados con el movimiento a lo largo de una falla normal cercana. La datación U-Pb del circón por LA-ICP-MS arroja una edad de cristalización/depositación de 116,7 ± 0,75 Ma (2σ). Esta nueva edad sugiere que el intervalo estratigráfico puede corresponder con mayor precisión al Miembro Cerro Castaño (Aptiano), y que la actividad sísmica asociada responsable de las sismitas probablemente tuvo lugar durante el Aptiano y no durante el Cenomaniano.

ANTONIO INTROCASO

2025-08-05T22:57:54+00:00

MIGUEL J. HALLER

2025-08-05T23:04:45+00:00

Characterization of seismic hazard indicators and tsunamigenic potential in the Scotia region and Antarctic Peninsula

2024-06-06T13:47:10+00:00

The objective of this work is to evaluate seismic hazard indicators for the Scotia region and northern tip of the Antarctic Peninsula: predominantly marine geotectonic area, where intense seismic activity occurs adjacent to the antarctic continent.

In the first instance, seismicity from years 1970 to 2023 (inclusive) was characterized through its temporal occurrence, spatial distribution and radiated seismic energy. The different areas of cortical deformation associated with seismicity were characterized, establishing their greater or lesser potential for each of them.

Likewise, as a contributing factor to the seismic hazard in the region, the marine areas with the greatest tsunamigenic potential were determined. To this end, through numerical simulation based on the theory of propagation of gravitational waves in fluid media, dynamic indicators that characterize the temporal and spatial evolution of the tsunami phenomenon in the Antarctic and sub-Antarctic marine area were estimated.

Based on the analysis of seismic hazard indicators, a division into seismotectonic zones was developed according to the degree of potential seismic hazard.

With regard to seismic risk, the location with the highest risk are the South Orkney Islands, where the Argentine year-round Antarctic facility base Orcadas is located. In decreasing order of vulnerability, the South Shetland Islands represent the second seismic risk area, housing permanent Antarctic bases in its archipelago. The South Sandwich Islands region does not hold year-round human settlements, therefore, although it would constitute the area of greatest seismic hazard in the region, it does not usually pose a local seismic risk.

Análisis de facies y ambientes deposicionales del sector sur del Salar de Pocitos, Salta, Argentina

2025-02-04T13:54:13+00:00

El Salar de Pocitos (Puna Austral) es una cuenca endorreica con una orientación norte–sur que abarca una superficie de 405 km². En su sector sur, limitado por las Formaciones Coquena y Tolillar, el Complejo Básico Ojo de Colorados y el Grupo Pastos Grandes, se encuentran depósitos clásticos y evaporíticos que alojan salmueras ricas en litio. Este estudio se propone caracterizar sedimentológicamente el relleno de la cuenca para interpretar el marco estratigráfico, los ambientes deposicionales y su evolución sedimentaria. Se analizaron testigos corona de cuatro perforaciones, identificándose trece facies sedimentarias y realizándose un estudio de procedencia de areniscas. A partir de columnas tipo Selley se facilitaron correlaciones e interpretaciones ambientales. En el suroeste predominan areniscas finas con arcilitas, carbonatos y halita, mientras que en el sureste son comunes brechas, limolitas y halitas cristalinas. Hacia el depocentro, se observan brechas, areniscas finas, limolitas, carbonatos, yeso y halita. En el extremo norte, los depósitos incluyen bancos gruesos de areniscas finas a gruesas y halita, intercalados con arcilitas y limolitas, frecuentemente coronados por minerales sulfatados. Los resultados indican una sedimentación típica de sistemas playa-lake, compuesta por abanicos aluviales, sistemas fluviales efímeros y lagos salinos someros, característicos de cuencas endorreicas en ambientes áridos.

Geology of the western coast of Bahía Aguirre (Península Mitre), southeastern Tierra del Fuego, Argentina.

2025-03-28T14:56:07+00:00

New field data from the western coast of Bahía Aguirre in southeastern Tierra del Fuego provide the basis for characterizing five volcanic, volcaniclastic, and sedimentary facies of the Lemaire Complex (Middle Jurassic–Berriasian), as well as a mylonitic rock developed on granite of unknown age, and sedimentary facies of the Beauvoir Formation (Lower Cretaceous), previously assigned either to the Lemaire Complex or the Yahgan Formation. The results of this study refine previous geological maps and introduce new information on the facies of the Lemaire Complex, including the first description of carbonate rocks within the unit. A detailed structural
analysis reveals a deformation sequence comprising an initial stage of ductile deformation contemporaneous with low-grade metamorphism,
overprinted by a later, more brittle deformation marked by thrust faulting. Both deformation stages are consistent with the known Late Cretaceous–Paleogene tectonic evolution of the Fuegian region.

Structural anatomy and deformation phases of the Silva Range, San Bernardo fold belt (Golfo San Jorge Basin, Argentine Patagonia).

2025-04-14T22:06:13+00:00

The Golfo San Jorge Basin (Argentina) plays a leading role in the construction of structural models for extra-Andean Central Patagonia. Notably, the Silva range represents a paradigmatic positive tectonic inversion fold, which reveals the complex tectonic evolution
of this region. Its tectonostratigraphic architecture in both the forelimb and backlimb defines a pre-inversion succession for the Castillo Formation (Albian). Furthermore, the deposits of the Bajo Barreal Formation substantiate a Late Cretaceous (post-Coniacian) extensional phase. This phase generated secondary sedimentary cover faults, oriented obliquely to transversely, relative to the main NNE-trending Sierra Silva basement fault. This three-dimensional distribution of normal faults conditioned the positive tectonic inversion that gave rise to the current morphostructure. Here, the shortening combines along-strike variations in the degree of inversion with partitioned deformation. The northern extremity of the Silva range is delineated by the NW-trending Cerro Chenques fault. This fault exhibits oblique inversion, characterized by inhomogeneous sinistral lateral displacement and localized compression, which respond to the inherited fabric and an antidilational curvature. The results of this study improve the understanding of the phases and dynamics of Cretaceous-Cenozoic deformation in the Patagonian broken foreland. From an applied perspective, the Silva range can be used
as a structural analogue for comprehending hydrocarbon traps within the San Bernardo fold belt. The anatomical and evolutionary complexity of the Silva Range makes it a globally significant reference case for oblique positive tectonic inversion.

Geophysical data for critical mineral prospecting in Estancia Valle Daza, La Pampa

2024-11-28T20:41:44+00:00

A geophysical survey was conducted in the Estancia Valle Daza, Utracán Department, La Pampa Province, within a 5 × 4 km area of mining interest due to the presence of critical minerals, including monazite and metagabbros with nickel anomalies. The study involved gravimetry, magnetometry, gamma-ray spectrometry, and electrical self-potential methods and represents a continuation of previous regional geophysical investigations. Residual gravity data revealed three gravimetric highs, spatially associated with bipolar magnetic
anomalies reaching up to 300 nT. The largest of these anomalies is oval-shaped, with a major axis of approximately 2 km. These gravimetric and magnetic features are interpreted as responses to mafic rocks, either sub-outcropping or located at shallow depths
within the crystalline basement of the study area. Gamma-ray spectrometry identified two zones with equivalent uranium contents of up to 10 ppm, comparable to the levels recorded in granitic mylonites rich in monazite from this sector. Additionally, the self-potential method was applied along a shear zone characterized by granitic mylonites containing monazite, providing further insight into the area's subsurface features. The results of this integrated geophysical approach highlight the value of combining multiple methods to
enhance critical mineral prospecting in Estancia Valle Daza.

Agates from the Uruguay River: Distribution, Abundance, and Characterization.

2025-06-27T20:52:39+00:00

This study evaluates the potential of agates found within the Plio-Pleistocene deposits of Entre Ríos Province (Argentina) for use as ornamental stones. A total of 19 sediment samples were collected from quarry pits and natural outcrops along the Uruguay River and analyzed through grain size distribution and petrographic techniques. The studied gravels exhibit a near-Gaussian size distribution, with an average grain size of 25 mm, corresponding to coarse pebbles. The coarser fractions (>32 mm), including very coarse pebbles and cobbles - those most suitable for lapidary purposes - are most abundant between the towns of Santa Ana and Concordia. Agates (both whole and fragmented) constitute approximately 28% of the total gravel analyzed, although only 4.6% exhibit the quality and size necessary to justify commercial lapidary work. This corresponds to a grade of 60kg/m3, which increases significantly in stockpiles from deposits exploited for construction purposes, where gravel smaller than 50 mm has been removed. Petrographically, the most
common agates display concentric banding of chalcedony with one or two generations of crystalline quartz. Horizontally banded agates are less frequent, while spherulitic varieties are rare.