CONICET | Buscador de Institutos y Recursos Humanos

An impact origin has been proposed for the circular structures found in Bajada del Diablo, Patagonia,Argentina. Taking into account its extension and the number of impact structures, Bajada del Diablowould be the largest meteoritic impact area known on Earth, being an extremely interesting area forthe research of impact events and processes. Moreover, the global distribution of known impact structuresshows a surprising asymmetry. Particularly, South America has only seven described areas. It is evidentthat this situation is an artifact, highlighting the importance of intensifying the research in the leaststudied areas such as Argentina. Circular structures in Bajada del Diablo have been identified on two rocktypes: the Quiñelaf eruptive complex and Pampa Sastre Formation. In the first case, circular structures areplaced in olivine basalts. On the other hand, Pampa Sastre Formation (late Pliocene/early Pleistocene) correspondsto conglomerate layers with basalt clasts boulder and block in size in a coarse sandy matrix.With the aim of further the investigation of the proposed impact origin for these circular structures,we carried out detailed topographic, magnetic and electromagnetic ground surveys in two circular structures(??8?? and ??A??) found in Pampa Sastre conglomerates. Both circular structures are simple, bowlshapedwith rim diameters of 300 m and maximum depths of 10 m. They have been partially filled inby debris flows from the rims and wind-blown sands. Two preliminary magnetic profiles have also beencarried out in circular structure ??G?? found in Quiñelaf basalts. The magnetic anomalies show a circularpattern with a slightly negative and relatively flat signal in the circular structures? bases. Furthermorein the circular structures? rims, high-amplitude, conspicuous and localized (short wavelength) anomaliesare observed. Such large amplitude and short wavelength anomalies are not detected outside the circularstructures. For all used frequencies, the electromagnetic profiles show lower apparent electrical conductivitiesin the circular structures? base, while the rims present notably higher values. Curvature attributes,analytic signal, horizontal gradient and Euler solutions were calculated for the magnetic data. 2.5D magneticmodels were developed across the studied circular structures. Our results suggest that in the circularstructures? bases up to 12 m of Pampa Sastre conglomerate would have been removed. On thecontrary, the circular structures? rims exhibit high-amplitude, localized magnetic anomalies and higherapparent electrical conductivities, which would be related to the anomalous accumulation of basalt bouldersand blocks remanently magnetized. Such high-amplitude anomalies are not present outside the surveyedcircular structures. The geomorphological, geological and geophysical features of the studiedcircular structures can only be explained by means of an extra-terrestrial projectile impact. We concludethat, considering the results obtained to date, Bajada del Diablo should be envisaged as a focus of furtherresearch, which could provide novel information about impact events, associated processes and theirevidences. Particularly, the data produced in this study could represent one of the first documentedgeophysical signatures of the impact of a comet nucleus on Earth.