The Bajada del Diablo astrobleme-strewn field, central Patagonia Argentina: 2 Extending the exploration to surrounding areas

ACEVEDO, R.D; RABASSA, J.; PONCE, J.F.; MARTÍNEZ, O.; ORGEIRA, M.J.; PREZZI, C.; CORBELLA, H.; GONZÁLEZ GUILLOT, M.; ROCCA, M.; SUBÍAS PÉREZ, I.; VÁZQUEZ, C.

GEOMORPHOLOGY

ELSEVIER SCIENCE BV

Lugar: Amsterdam; Año: 2012 vol. 113 p. 1 - 14

0169-555X

The Bajada del Diablo astrobleme-strewn field is a huge domain of enigmatic circular structures located incentral Patagonia.Three more localities are herein described, adding to the first area studied so far. Taking into consideration thefour areas, a single, blurred crater dispersion ellipse has been identified. The four sectors now have been investigated,mapped, and georreferenced. Their circular structures, with a total of 185 (some of which are partiallyobliterated by erosion or sediment accumulation), were identified by remote sensing techniques, but manyhave been evaluated in situ and interpreted as impact craters. Moreover, two of the structures have been surveyedin detail in the field using a total station instrument.In addition to the previously known occurrence of circular structures on the Eruptive Complex Quiñelaf (Miocenebasalts), the Pampa Sastre Fm. (Pliocene conglomerates), and of the Pleistocene pediment gravels and sands, andthe geomorphological inferences that have suggested the extra-terrestrial origin of this event,we should nowaddthat the recurrent absence of the cited Pliocene stratigraphic unit at the bottomof the craters is found in thepediment gravel and sands. Its removal has been interpreted as directly related to the impact, according tothe magnetometric record of existing magnetic anomalies.Other preliminary observations on the collected samples (glass, breccias, and, most relevant, Fe-Ni-bearingspherules picked up within the impact zones) are herein discussed.Two hypotheses have been put forward about the nature of the possible impacting object that formed theseastroblemes which, fragmented into hundreds of pieces, hit the surface of the Earth most likely in middle Pleistocenetimes. One of these hypotheses is related to the impact of a disintegrated asteroid of the rubble pile type,whereas a second hypothesis refers to the collision of a split cometwith the Earth surface. The latter hypothesis isfavoured since no meteorite fragments have been found so far.