Revista de la Asociación Geológica Argentina

Nora M. Sabattini (1941-2021)

2022-08-25T19:49:48+00:00

Buenos Aires dunes reservations in relation to the sea level reversal

2022-02-01T04:16:49+00:00

Buenos Aires coastal barriers originated by the Holocene fluctuation of the sea level. The fine sand abundance and the onshore winds constructed the Eastern Barrier while at the south dunes climbed to old cliffs. The increase in Precipitation and the afforestation transformed sand dune fields into resort villages, and later to cities devoted to the “sun and beach” tourism. Notwithstanding that, hydrogeologic water reserves always limited some localities. The urban sprawl led to implement urban cities that were limited to the widths of these barriers. Dune forestation led to beach unbalances, that increased triggered by extratropical storms arriving from the southeast. Sand mining from the beaches was forbidden (law 8758/77). Urban growth caused the proposal of buffer areas (statement 8912/77) and to promote reserves to compensate the urban expansion along the coast (statement 3202/06). During the eighties and nineties some coastal counties promote foredune fixation with fences (locally called “enquinchados”) constructed by branches, but without a proper sand management. Today, foredune retreat is 1 m/year averaged, although at some counties it could be higher caused by some activities (stormwater patterns, coastal defences, bathing facilities). Considering the present forecasts of a higher sea level (0.4-0.8 m for year 2100) and the increase in the frequency and intensity of extratropical storms, it is clear that these dune problems would be worse. In this sense, new initiatives and management policies should be planned.

Hydrodynamics, hydrochemistry and occurrence of uranium in the Ituzaingó and Salto Chico Aquifers, Entre Ríos Province

2022-05-30T13:39:25+00:00

Ituzaingó, Salto Chico and Ubajay Aquifers are the most important hydrogeological units in the Chaco-paranaense region because they are among the most productive, provide high quality fresh water and supply agriculture, industry and human consumption. From the hydrodynamic analysis at piezometric level, a network of groundwater flow was defined ―the groundwater divide―. The hydraulic head does not exceed 60 masl; therefore, potential fluvial recharge processes may be proposed with more extensive and deeper groundwater flows. This would increase the water-rock contact time, which would impact on salinity. A large extension of the Aquifer region has groundwater showing a salinity level lower than 2000 mg/l, even in the western areas, where the Salto Chico and Ubajay Aquifers rarely exceed 1000 mg/l. There sodium bicarbonate facies predominate; followed by the calcium bicarbonate facies, which are almost at the same level as the sodium chloride-sulfate ones. From a regional perspective, the average value of nitrates is close to 10 mg/l; there is a low concentration of arsenic (0.1 - 0.2 mg/l) and iron (0.2 - 0.4 mg/l), which are only present punctually. Uranium has been detected as a trace, showing a regional distribution and average values of 25 μg/l (3 μg/l minimum and 101μg/l maximum), so it can be considered almost a minority species. The positive and significant correlations of uranium with other components are TDS (0.62), SO42- (0.61) and Na+ (0.64). They coincide in their regional distribution ―center-north of the province of Entre Rios― in a clear association of hydrodynamic and hydrochemical processes.

Characterization and structural evolution of the Auca Mahuida volcanic field, Neuquén.

2022-04-12T19:27:00+00:00

By means of the analysis of topographic data and volcanic rock thicknesses, it was possible to prove that the Auca Mahuida volcanic field lies on a domed structure of similar diameter. The absence of the Malargüe Group (Campanian-Danian) below most of this massif, along with the presence of an erosive angular unconformity which separates the Cretaceous layers of the Neuquén Group from the Quaternary volcanic rocks, are a sign that this dome was raised and partially eroded before the Pleistocene volcanic activity. It is probable that this structure is due to a thermal uplift caused by the emplacement of magma chambers in depth and shallower igneous intrusive bodies during the Pliocene-Pleistocene. Furthermore, the presence of a slight regional slope towards the east-northeast was recognized in the study area, which explains the exiguous topographic asymmetry of the Auca Mahuida shield volcano and the larger spread of the basaltic flows on its eastern flank.

Multiple tectonic reactivations of the Cachi fault system at the eastern edge of the southern Luracatao valley, Calchaquíes valleys, northwestern Argentina

2022-05-12T22:24:03+00:00

The Luracatao valley (boundary between Calchaquí valleys and Puna) is flanked to the east by sierra de Cachi and cumbres de la Laguna mountain ranges, delimited by first-order structures called here as Cachi fault system, from east to west: eastern fault, central fault and western fault. These faults have N-S orientation dipping to the east. The eastern main fault corresponds to a normal cretaceous fault that bounded the Brealito-Molinos half-graben to the west. Central and western faults, interpreted as splays of the eastern fault, would have originated as cretaceous normal faults with multiple tectonic inversion-reactivation processes during the Andean orogeny. The basement heterogeneities have controlled the location of new structures during the Mesozoic and Cenozoic, through strong parallelism between the basement foliations and faults. In this study, we present new field data that help us to reconstruct this structures system evolution, which has been described in previous works as a unique master fault (Cachi fault) with a localized splay, and these document multiple reactivation stages from Eocene.

Structural evolution of the Quebrada del Toro Basin: Influence of pre-cretaceous structures on the Andean fold-and-thrust belt in the Argentinian Eastern Cordillera

2022-07-13T22:29:55+00:00

The superimposition of the tectonic events recorded in the Argentinian Eastern Cordillera conditioned the current structural style. In the Quebrada del Toro Basin (Salta province), coinciding with the central section of the Calama-Olacapato-Toro lineament (COT), pre-cretaceous structures are recognized that would have favored the development of inverse structures during Andean tectonics. We present new structural, stratigraphic and sedimentological data which allowed an integral analysis through the generation of balanced geological sections, deformation restorations and 2D forward modeling. At least two deformation events were identified: the first, during the upper Tremadocian, corresponds to the Tumbaya extensional phase expressed through two NNW-SSE striking and ENE dipping normal synsedimentary faults (de la Cruz and Pascha). The second deformation event, of compressive nature, would have begun during the middle Eocene, with the generation of large-scale folds related to relatively shallow Gólgota thrust and their subsequent transport by two high angle reverse faults (Gólgota and Lampazar) with deeper detachment. In this sense, Paleozoic structures controlled the location and western vergence of the Gólgota thrust in the study area, a caracteristic that reinforces the hypothesis about the preponderant influence of Ordovician normal faults on western vergence thrusts.