Revista de la Asociación Geológica Argentina

New TT-OSL absolute ages in late cenozoic sediments from gualeguaychú southeast of Entre Ríos (Argentina).

Luiggina CAPPELLOTTO — 2025-12-15

This work presents two new ages determined by the Thermally Transferred and Optically Stimulated Luminescence (TT-OSL) method on quartz grains from a pedo-sedimentary profile located in the vicinity of the current Gualeguaychú Ecoparque (33°3’8.96’’ S, 58°31’40.00’’ W), former Irazusta quarry, southeast of Entre Ríos (Argentina). The two dated levels correspond to 590310 ± 33070 and 243300 ± 10970 years (Late Cenozoic). In particular, the sedimentological descriptions allowed for the identification of estuarine deposits which, associated with the age of 243300 ± 10970 years, would suggest their link to Marine Isotope Stage 7 (MIS 7).

Thermochronological modeling in Cretaceous-Cenozoic sequences from the northern sector of the Neuquén basin: contributions to the understanding of regional thermal evolution

cecilia wunderlin — 2025-12-15

This study presents new thermochronological data and models for the Cretaceous–Pliocene in the northern Neuquén Basin, Argentina. Samples were collected from the Huitrín, Rayoso, Diamante, Saldeño, Pircala, and Agua de la Piedra formations in the Arroyo Las Aucas section (eastern sector) and the Vega Grande and Vega de los Patos sections (western sector). Apatite (U–Th)/He (AHe; 4.7–53.3 Ma) and fission-track (AFT; 108–217 Ma) ages indicate partial to complete annealing. Thermochronological modeling reveals distinct thermal episodes in both sectors. In the western sector, heating is recorded during deposition of the Huitrín and Rayoso formations (Lower Cretaceous). AFT ages from the Rayoso Formation may alternatively reflect inheritance from volcanic sources or partial resetting, in which case maximum temperatures were reached either (1) during burial of the Diamante Formation, or (2) prior to the deposition of the Diamante Formation and related to a thermal anomaly. Subsequent thermal stability persisted until ~20 Ma, followed
by cooling associated with exhumation and deformation in the Malargüe fold-and-thrust belt. In the eastern sector, unreset AFT and AHe ages suggest thermal stability between ~60 and 40 Ma, followed by heating from ~20 Ma linked to deposition of the Agua de la Piedra Formation, and subsequent cooling (~13–10 Ma). These results highlight the complex interplay among sedimentation, heat flow, and tectonics along the northern margin of the Neuquén Basin.

Seismic swarm at Punta de Vacas, Frontal Cordillera of Mendoza: Analysis of the June–July 2019 seismic events.

Araceli Tamara Diaz Zapata — 2025-12-15

The northern sector of Mendoza Province is classified by the Instituto Nacional de Prevención Sísmica (INPRES) as one of the most seismically hazardous regions of Argentina. Nevertheless, the western margin of the Frontal Cordillera at the latitude of Mendoza City is generally characterized by low crustal seismicity and by the absence of structures with recognized neotectonic activity. Here we present a seismological analysis of a sequence of crustal earthquakes (Mw 2.7–3.9) reported by INPRES in the vicinity of Punta de Vacas (Frontal Cordillera
of Mendoza) between latitudes −32.7° and −32.9° and longitudes −69.7° and −70.0°, recorded during June–July 2019 after a 24-year
interval of very low seismicity in the area. These events were felt by residents of Las Cuevas, Punta de Vacas, Polvaredas, Uspallata, and even Mendoza City, raising concern particularly among the communities closest to the epicenters. Identifying seismogenic sources in this region is essential for assessing seismic hazard along National Route 7—an area of major logistical and touristic importance that connects Argentina and Chile through the Los Libertadores International Pass. Relocation of hypocenters and focal-mechanism determinations indicate that the recorded activity constitutes a seismic swarm aligned with the Las Vacas lineament, although its triggering mechanism remains unresolved.

Seismic risk zonation in the urban development of the Andorra Valley, Ushuaia, Tierra del Fuego (Argentina)

Violeta L. COMPAN — 2025-12-15

The city of Ushuaia is located within tectonic valleys at the southern end of the Andes Mountains, carved into schists, phyllites, and slates, whose landforms are associated with glacial processes that occurred during the Pleistocene. The urban area lies approximately 30 km south of the Magallanes-Fagnano Fault System, the main seismogenic source in Tierra del Fuego. The city has experienced significant population growth, leading to a large number of buildings that do not comply with the seismic resistance standards of the National Institute for Seismic Prevention (INPRES).
This study presents the seismic risk zoning and its components for the Valle de Andorra neighborhood, located northeast of the city, based on geological, geomorphological, and geophysical information, as well as on the assessment of buildings and their distribution, in order to determine the exposure and vulnerability of the population. The neighborhood is mainly built on moraines and glacilacustrine deposits, which have geotechnical characteristics that favor seismic wave amplification. Furthermore, houses in the peripheral areas are exposed to mass-wasting processes.

The results show that 89% of the neighborhood falls within moderate to high-risk zones, and public institutions such as schools, police stations, and health centers are located in high and very high-risk areas. This work highlights the importance of geological risk zoning in vulnerable populations and aims to present results that can be applied to local urban planning and methodologically replicated in other regions.

Morphosedimentary dynamics of the Salado River, hydroclimatic variability, and alterations caused by the dam at General Belgrano, Buenos Aires

Antonella MONTI — 2025-12-15

The flood risk along the banks of the Salado River represents a serious socio-environmental issue. Despite various measures being taken to mitigate this problem, the consequences during drought-typical phenomena of the Pampean region—have not been adequately addressed. This study examines the geomorphological and environmental changes that occurred in a stretch of the Salado River following the construction of two dams in the General Belgrano area. Two river sections were compared: one stagnant and the other natural, from which sediment and water samples were collected. In the stagnant section, a higher sedimentation rate was observed compared to the natural section, with the presence of muddy sediments (15 % sand), high organic matter content (11.42 % by weight), low compaction, and dark colors. Additionally, an anoxic environment was generated, with an ORP of 27 mV (reductive), high organic degradation, and a high degree of eutrophication. Alkaline pH values (9.28), a more than double increase in salinity (49.08 µS/cm), and higher temperature (32.84 °C) were recorded compared to the natural section. These negative impacts led to aquatic fauna mortality, significantly affecting local tourism. Core samples revealed the sedimentary and environmental changes in both river sections after the construction of the dams, reflected in alterations in sediment texture, color, and compaction. It is recommended to regulate water levels before potential droughts and to avoid discharging domestic effluents to prevent eutrophication of the system.

Carbon isotopes on pedogenic carbonates of the Fray Bentos Formation (late Oligocene-early Miocene): a geochemical approach for calculating atmospheric paleoCO2

Romina Sanci — 2025-12-15

In the context of modern climate change, constraining past atmospheric greenhouse gas concentrations and their paleoenvironmental settings is essential for improving predictions of future climate responses to elevated CO₂ levels. This contribution presents the first atmospheric paleo-CO₂ estimates derived from calcretes of the Fray Bentos Formation (late Oligocene–early Miocene) based
on the application of the pedogenic CO₂paleobarometry model. An 11-m-thick profile at Picada de Berget (Canelones Department, Uruguay) was analyzed and subdivided into ten units according to sedimentary discontinuities and field and laboratory observations. The succession consists of loess deposits and paleosols that, under semi-arid conditions, developed into calcretes dominated by
powdery and laminar pedogenic varieties. Stable-isotope analyses from seven calcrete horizons yield δ¹³C values between −10.2‰ and −8.3‰, δ¹³C of organic matter of approximately −25‰, and δ¹⁸O values ranging from −4.7‰ to −4.1‰. Using these data, we obtained reasonable paleo-CO² estimates for the late Oligocene–early Miocene, ranging from ~280 to 550 ppmv. These results fall within the range reported by independent proxies for this interval and support the potential of Fray Bentos calcretes as reliable archives for reconstructing atmospheric CO² concentration during the Paleogene–Neogene transition.