Revista de la Asociación Geológica Argentina

The basaltic dykes of the quebrada de Tres Cerritos, sierra de Mojotoro, Cordillera Oriental Argentina, Salta

Pamela Aparicio Gonzalez — 2024-06-05

The petrographic, mineralogical and geochemical characteristics of basaltic dikes that intrude the shales of the Floresta Formation (Tremadocian) in a profile of the Tres Cerritos quebrada of the sierra de Mojotoro, Cordillera Oriental Argentina, are described. These are olivinic basalts with phaneritic texture in macroscopic samples with microporphiric and intergranular textures composed of plagioclase, olivine, titanian augite, biotite, analcime ± apatite ± opaque minerals. They present a selective deuteric and hydrotermal alterations, with olivine replaced by talc and calcite. Besides, these rocks have a complex association of secondary minerals that include: chlorite ± veremiculite ± interlayered biotite/smectite ± interlayered biotite/vermiculite ± interlayered chlorite/smectite. Geochemically, they are classified as alkaline basalts consistent with intraplate OIB (Ocean Island Basalts) type signature. Contents of Rare Earth Elements (REE) normalized to chondrite show a relative enrichment in light rare earths elements (LREE) in relation to the heavy rare earths elements (HREE). A continental intraplate tectonic setting is suggested for the formation of these basaltic dykes although there are no reliable isotopic ages that allow them to be correlated with other basic rocks in the region

Geology and geochronology of cabo Blanco, Santa Cruz, Patagonia

Maximiliano Naipauer — 2024-06-05

Cabo Blanco is located on the Atlantic coast, at the southern end of Golfo San Jorge (47°12' LS). The cape exposes rocks that were first identified by Darwin as quartzites comparable to those currently included in the Bahía Fox Formation of the Malvinas Islands. This correlation was followed by several authors who worked in the area up to the present. However, other authors interpreted these rocks as volcanic and included them within the Jurassic volcanism of extra-Andean Patagonia. In order to confirm the age of the possible Paleozoic quartzitic rocks, a field reconnaissance and a geochronological study were carried out. The zircons analyzed by U-Pb from two samples showed an age of 182.47 ± 2.01 Ma and 174.60 ± 2.46 Ma. According to the geological and geochronological study carried out, the occurrence of Paleozoic metamorphic and/or sedimentary rocks at Cabo Blanco as mentioned by different authors since the 19th century are discarded. The interpretations that the outcropping rocks at Cabo Blanco are of volcanic and sedimentary origin and of Jurassic age included within the Chon Aike magmatic province are confirmed.

The faulting of the Colombian Frente Llanero: a review of thin-skinned vs. thick-skinned interpretations based on Anderson's Law and analog models

Eduardo Rossello — 2024-06-05

The Frente Llanero of the Eastern Cordillera of Colombia exhibits a great remaining hydrocarbon potential based on the interpretation of exploratory objectives essentially controlled by the morphology of its various tectonic traps. These structures recognized on surface and subsurface suffered the effects of Andean transpressional inversion of normal faulting associated with the accommodation of Mesozoic depocenters. Based on limited surface and subsurface information, the balanced cross sections are the widely used technique for interpretation based mainly on subhorizontal faulting placed subparallel to compression. Basic mechanics and geometric principles are simplified to facilitate their making. These include considering the involved sequences as perfectly tabular with uniform deformation responses, despite their heterogeneous lithologies with different rheologies. Additionally, the spatial relationships between the dominant stress field and the fractures (joints and faults) established by Anderson's Law are not contemplated. Furthermore, multiple evolution sequences with inversions or transcurrent components are not allowed since the previous discontinuities of the underlying basement located in a preferred orientation for their reactivation are not considered. This paper summarizes the main tectonic characteristics of the Colombian Frente Llanero, and structural aspects of faulting based on analog models, mechanical principles of deformation, the influence of pre-existing discontinuities, and the postulates and limitations of analog modeling concepts are discussed. In this way, alternative and less subjective tectonic interpretations are proposed to study the exploratory potential of the hydrocarbon resources of the Colombian Frente Llanero and similar tectonic regions.

Contributions for an integrated water management system: an hydro-morphological study using multifrequency satellite data in the upper Colorado catchment, Argentina

Romina Solorza — 2024-06-05

The Colorado River catchment has its origin in the Andes Mountains, flows through the country for more than 1.200 km and drains into the Atlantic Ocean. Several uses of water depend on its path throughout the entire basin. For these reasons, it is essential to know the dynamics of the hydrometeorological variables during the melting season. This paper exposes a comprehensive methodology to monitor these variables, focusing on the upper basin, where one of the contribution sub-basins is located: Valle Hermoso. The use of satellite data from different sources is proposed: optical (MODIS, Landsat 5, 8 and 9, Sentinel 2), radar (Sentinel 1 and SAOCOM), digital terrain models and in situ measurements, are used to retrieve main snow variables and hydrological parameters. Main objectives are: to map the total snow-covered area, estimate the snow melting and analyze spatially and temporally the relationship of snow accumulation and melting process. In this study, the use of the big data processing platform Google Earth Engine (GEE) is used to calculate spatial and temporal dynamics of the studied variables.

Hydrogeology of the dune barriers of Buenos Aires: vulnerability to sea-level rise

Federico Isla — 2024-06-05

The sandy barriers of Buenos Aires have had an explosive urban growth once the dunes were afforested. The original bathing villages of Villa Gesell, Pinamar and Partido de la Costa are today being copied by counties where the water resources are limited and the Geomorphology conditions different. Several aquifers have been exploited with different successes. The well-known documented experiences from the Eastern Sandy Barrier (BMO) are considered, while some different experiences from the Southern Barrier (BMA) are also reported. The interface between the marine salt water and the fresh water is oblique at the BMO and is expected to migrate with the sea level rise. Instead, the interface between salt and fresh water is horizontal and conditioned to the nature of the rocks beneath. According to these trends in the land-use changes, the effects of the sea-level rise are forecasted.

Analysis of alluvial fans growth using topographic and empirical methods: National Route N° 150, San Juan, Argentina

Maria Yanina ESPER ANGILLIERI — 2024-06-05

The present study aims to estimate the growth rate of four alluvial fans from topographic information, by temporally comparing their surfaces and applying Gavrilovic's empirical method.

The selected sector includes a section of National Route 150 in the department of Iglesia, approximately 145 km north of the capital city of San Juan. This area is characterized by short-term heavy rainfall which triggers significant flows that transport large volumes of solid material (sediments of different granulometries, remains of vegetation and debris) and accumulate in the lower slopes, usually creating alluvial fans or supplying the already existing ones. The preliminary findings for four of the surveyed geoforms that are presented in this paper suggest that their volume has increased.

Geology of the Guaraní Aquifer System in the outcrop area of the Tacuarembó and Rivera formations (Norte Basin, Uruguay).

Gerardo Veroslavsky — 2024-06-05

The geology of the Tacuarembó and Rivera Formations, in the central-northern región of the Norte Basin (Uruguay) is described. Both units crop out along a wide, NE to NNE-trending belt and they constitute (along with the Itacumbú Formation which develops on the subsurface of the NW sector) the Guaraní Aquifer System (GAS), a regionally important aquifer unit. These units form part of a silicilastic sedimentary sucession, which crops out along 4,864 km², with relatively homogenous, esentially sandy lithologies, with a mean thickness between 80 and 100 m. Results of a 1:100.000 geological mapping including part of the adjacent basaltic region are presented. We provide and interpret fifteen lithological logs which are representative of the facies and facies associations, as well as five geological cross-sections including both surface and subsurface data. Moreover, we perform a structural analysis on the basis of digital elevation model and aerial photographs. The study area was divided in three morphostructural domains: North, Central and South, each one possessing distinct morphological, stratigraphical and structural features. Stratigraphic and structural features are analized and related to the SAG behavior, particularly aquifer compartmentalization through NW and NE fractures (both diaclases and faults) which are recognized in the study area. The new knowledge in the morphological and geological configuration of the central region of the Norte Basin is relevant to explain the hidrogeological behavior of the GAS in the outcropping area.

Carbon dioxide diffuse degassing and hydrothermal alteration in the soils of the Cerro Galán geothermal system (Catamarca, Puna Austral)

Antonella Massenzio — 2024-06-05

Cerro Galán, located in the Puna Austral, is a caldera formed during a Pleistocene-Holocene super-eruption. It is characterised by silicic volcanism, which could host a high potential geothermal system. However, this system has been little explored. The main objective of this paper is to contribute to the understanding of the geothermal system and to add new data to the geochemical conceptual model. The paper presents the first study of diffuse CO₂ degassing, temperature and hydrothermal ground disturbance of the three hydrothermal areas of the Cerro Galán caldera: La Colcha, Aguas Calientes and Piscinas Burbujeantes. A total of 148 CO₂ flux and soil temperature measurements were made. In addition, eight samples of precipitates and alteration clays were collected at the La Colcha and Piscinas Burbujeantes sites. CO₂ flux values ranged from 0 to 21.66 g/m²/d and temperature values from -5.2 to 35 ºC. Diffuse degassing structures were identified at La Colcha and Aguas Calientes in spatial relation to the thermal springs. We propose two sources of CO₂: a hydrothermal aquifer and one related to soil respiration. The diffuse degassing rate of hydrothermal CO₂ was 0.44 kg/day. The mineralogy of hydrothermal alteration was characterised by the presence of calcium carbonate, salts, clays, oxides and iron sulphides. Taken together, our results suggest a significant interaction of hydrothermal fluids with shallow water bodies during their ascent to the surface.

Environmental units identification for sustainable management based on geological studies

María Agostina Grígolo — 2024-06-05

There are numerous world examples of cities founded on free soils, without previous studies of the physical environment, with the consequent appearance of problems related to its intrinsic characteristics. Detailed knowledge of the physical environment within the Territorial Planning, through geology, allows us to anticipate possible negative scenarios in the territory and generate measures to minimize them.

This paper presents the case study of the northern sector of the Tulum Valley fan, Angaco department. There are large tracts of uncultivated land, with potential for growth; Therefore, the territorial ordering of the area for future activities is considered of great relevance. The lack of land use planning has generated problems such as depleted and exploited soils due to bad practices, which lead to a decrease in annual crops, areas affected by desertification problems, flooding, contamination by urban solid waste, fires, liquefaction of soils, industrial activities such as quarries in areas of debris slides or between rural areas.

The objective of the work is to analyze the Quaternary geology of this region and define environmental units for the land-use planning. For this, geophysical measurements were used to delimit geological structures, geomorphological and hydrological mapping, and an inventory of natural hazards. Four units resulted, on which conditioning overloads were identified. A GIS was used as support, relationship evaluation matrices between activities supported by the soil, of environmental valuation. Finally, guidelines for the development of the territory are delivered.

Geochemical characterization of the Tai Pichín thermal area, Cuniputo Range, province of Córdoba

Isaac Elias Burgos — 2024-06-05

The thermal spring known as Tai Pichín is located in the Cuniputo range, Córdoba province, and has a spring temperature of 21 °C. This study presents the results of the geochemical and isotopic analysis of water samples, both from the Tai Pichín spring and from nearby surface water courses, which were used to characterize the fluids and develop a conceptual model for the geothermal system. The hydrothermal fluid has a Na+ - HCO3- composition and an estimated temperature of 87 °C at depth. This fluid would be hosted in the metamorphic basement of the La Falda Metamorphic Complex, and the main structures in the area would control its ascent. The isotopic data of water (δ18O y δ2H) suggest local meteoric recharge, with the Cuniputo range being the main recharge area. However, a more extensive circulation pathway is suggested, including the granite outcrop area of Capilla del Monte as a recharge zone. Meteoric water could reach depths of ~2 km, acquiring the estimated temperatures by geothermometers in a normal gradient area, thus establishing a possible heat source linked to the deep circulation of fluids through the structures. However, the existence of a shallower circulation circuit cannot be ruled out, where water attains high temperatures at depth due to radiogenic heat associated with the Capilla del Monte granite.

The Yacoraite Formation in the Espinazo del Diablo range and its importance in the stratigraphic analysis of the Cretaceous basin in northwestern Argentina

Ariadna Coppa Vigliocco — 2024-06-05

The Yacoraite Formation is a predominantly carbonate unit, unique for its lithological characteristics within the Cretaceous rift framework of northwestern Argentina. With an age between approximately 68,1 to 62,3 million years, it represents an interval during which epicontinental seas developed, genetically connected to the opening of the South Atlantic Ocean. With a maximum thickness of 300 m, it is composed of oolitic calcarenites, dolomites, calcareous sandstones, marls, and tuffs, standing out in Northwest Argentina as a key-stratigraphic interval within the Salta Group. In addition to its paleogeographic importance, it has exploratory interest, as it forms reservoirs and serves as source rock in the Olmedo sub-basin. Despite its renown, the Yacoraite Formation has issues in its original definition, and a recent study in the Espinazo del Diablo locality (Eastern Cordillera of Jujuy) allows for the definition of a parastratotype, where 5 distinctive members are separated. The lower calcareous member rests in clear erosive unconformity on the Lecho Formation eolianites and is characterized by the development of upward-coarsening cycles crowned by domal stromatolites. In contrast, the upper calcareous member, characterized by cycles of green shales and marls intercalated with tabular stromatolites, is truncated by another unconformity separating it from the overlying Mealla Formation, characterized by red fine-grained siliciclastic series. This profile located within the Tres Cruces sub-basin allows for a revision and reevaluation of its stratigraphy and significance.

Geochronology of the cerro La Grasa subvolcanic body: new evidence of Miocene magmatism in the Agrio fold and thrust belt, Neuquén

Fernando Lebinson — 2024-06-05

This contribution reports the first age of the subvolcanic bodies located in Cerro La Grasa, north of the Las Lajas town (Neuquén). These rocks are arranged along the core of an anticline, forming globular laccoliths that thin into sills towards the sides, interdigitated in the Mulichinco Formation. An age of 19.4 ±0.2 Ma (Miocene) was obtained using the U/Pb method, which allows these rocks to be distinguished from the Naunauco Andesitic Belt (Cretaceous-Paleogene) that extends along the Agrio fold and thrust belt.

Recent translational slide in the wet Andes of Argentina (37.22°S)

Maria Yanina ESPER ANGILLIERI — 2024-06-05

On August 1, 2023, provincial route 43 near the town of Chos Malal (Neuquén, Argentina), the main connection to the north of Neuquén, was completely blocked due to a translational landslide. Four people were injured.