Bajada del Diablo impact crater-strewn field: The largest crater field in the Southern Hemisphere

摘要

Recent remote sensing analyses and field studies have shown that Bajada del Diablo, in Argentina, is a new crater-strewn field. Bajada del Diablo is located in a remote area of Chubut Province, Patagonia. This amazing strewn field contains more than 100 almost circular, crater-type structures with diameters ranging from 100 to 500 m in width and 30 to 50 m in depth. It is composed of three separated impact crater fields, which formed simultaneously. The impact was upon a Miocene basaltic plateau and Pliocene-Early Pleistocene pediments. The original crater field (60 km~2) was later eroded by Late Pleistocene fluvial processes; thus, three major, separate areas were defined. Due to the erosional processes that have affected the area, it is difficult to determine yet if the crater field has a classic elliptical distribution. Crater structures are similar in target rocks, although showing different response and morphology in relation to rock type. They are simple rings, bowl-shaped with raised rimrock. Basaltic boulders have been deposited as a ring-shaped pile and the ejecta are found toward the NE flanks. The craters present a hummocky bottom, with dry ponds and lakes in the center, but they do not show raised central peaks. The rocks within the craters have strong and stable magnetic signature. No meteorite fragments or other diagnostic landmarks have been found yet. The craters have been partially filled in by debris flows from the rim and windblown sands in recent times. The origin of these crater fields may be related to multiple fragmentation of one asteroid that broke up before impact, perhaps traveling across the space as a rubble pile. Alternatively, multiple collisions of comet fragments could explain the formation of these crater fields. Based on field geological and geomorphological data, the age of this event is estimated to be bracketed between Early Pleistocene and Late Pleistocene (i.e., 0.78-0.13 Ma ago).