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

• Published in: Geomorphology (Amsterdam, Netherlands) Vol. 169-170; pp. 151 - 164
• Main Authors: Acevedo, R.D., Rabassa, J., Ponce, J.F., Martínez, O., Orgeira, M.J., Prezzi, C., Corbella, H., González-Guillot, M., Rocca, M., Subías, I., Vásquez, C.
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 01-10-2012
• Subjects: Argentina; Astrobleme-strewn field; Bajada del Diablo; geomorphology; glass; gravel; Patagonia; Pleistocene; remote sensing; Argentina; Argentina; Astrobleme-strewn field; Patagonia; Bajada del Diablo; Pleistocene
• ISSN: 0169-555X; 1872-695X
• DOI: 10.1016/j.geomorph.2012.04.020

The Bajada del Diablo astrobleme-strewn field is a huge domain of enigmatic circular structures located in central Patagonia.
Three more localities are herein described, adding to the first area studied so far. Taking into consideration the four 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 partially obliterated by erosion or sediment accumulation), were identified by remote sensing techniques, but many have been evaluated in situ and interpreted as impact craters. Moreover, two of the structures have been surveyed in detail in the field using a total station instrument.
In addition to the previously known occurrence of circular structures on the Eruptive Complex Quiñelaf (Miocene basalts), the Pampa Sastre Fm. (Pliocene conglomerates), and of the Pleistocene pediment gravels and sands, and the geomorphological inferences that have suggested the extra-terrestrial origin of this event, we should now add that the recurrent absence of the cited Pliocene stratigraphic unit at the bottom of the craters is found in the pediment gravel and sands. Its removal has been interpreted as directly related to the impact, according to the magnetometric record of existing magnetic anomalies.
Other preliminary observations on the collected samples (glass, breccias, and, most relevant, Fe-Ni-bearing spherules 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 these astroblemes which, fragmented into hundreds of pieces, hit the surface of the Earth most likely in middle Pleistocene times. 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 comet with the Earth surface. The latter hypothesis is favoured since no meteorite fragments have been found so far.
► We obtained geomorphological, geophysical and mineralogical data from craters. ► Evidence strongly supports a new large scale extraterrestrial impact event in Patagonia. ► The hypothesis of a split comet collision appears as the most reliable.