Comparison of four meteorite penetration funnels in the Campo del Cielo crater field, Argentina

Abstract

Abstract-More craters may be discovered in the future, but as it is currently known, the Campo del Cielo crater field is 18 km long by 4 km at its widest point. Such a distribution of craters suggests that the parent meteoroid entered and traversed the atmosphere at a very low angle relative to horizontal. The crater field contains at least 20 small craters produced by the larger fragments of the parent meteoroid. Four of these are explosion analog craters and the rest are penetration funnels. During four field seasons, we have constructed topographic and magnetic maps of four of the penetration funnels as found, and then dug trenches across them to learn their original structures and recover meteorites preserved within them. Structures of these penetration funnels indicate very low angles of impact, i.e., 9-16°relative to horizontal. This supports the idea that the parent meteoroid traversed the atmosphere at a low angle. Data given here for the four penetration funnels include projectile masses, lengths, widths, depths, and estimates of impact angles and azimuths. One of the penetration funnels described here (No. 6) can almost be classified as an explosion analog crater.

Campo del Cielo modeling and comparison with observations: I. Atmospheric entry of the iron meteoroid

“…For comparison, the Sikhote‐Alin in Siberia is 1.2 km long, the Kaalijarv in Estonia is 1 km long, and Henbury in Australia is 0.7 km long (Passey & Melosh, 1980). Another interesting characteristic of CdC is that a lot of depressions found within the strewn field are not impact craters but penetration funnels (Vesconi et al., 2011). So far, 24 impact structures have been identified including four impact craters and 20 penetration funnels (Cassidy & Renard, 1996; Vesconi et al., 2011; Wright, personal communication); many meteorites with a total mass of ~140 t have also been found within this area.…”

“…It can then be found as a meteorite lying on the ground (Passey & Melosh, 1980). An impactor that reaches the Earth's surface at a higher velocity, but low enough to survive the impact as an intact body, creates a cavity, a so‐called penetration funnel (Kadono, 1999; Vesconi et al., 2011). A hypervelocity impact, in which the projectile fractures at impact (maybe even melts or vaporizes), forms an impact crater (Melosh, 1989).…”

The Archaeology of Cosmic Impact: Lessons from Two Mid-Holocene Argentine Case Studies

“…This portion of the Gran Chaco is semi-arid, hot, very flat, and covered equally by savanna, scrub, and dense thorn forests. The crater field contains at least 20 small, generally elongated impact craters within a northeast-trending ellipse (N61.5°E), 4 km wide and 19.2 km long (Cassidy et al 1965;Cassidy and Renard 1996;Liberman et al 2002;Wright et al 2007;Vesconi et al 2011). The impact infall angle was quite shallow, calculated at less than 10°from the horizontal.…”

“…Craters 1-4, the four largest and least elongated, were formed by ground explosions spread along a 6-km line (Wright et al 2007;Vesconi et al 2011). Fifteen of the 16 smaller craters do not exhibit evidence of explosive impact but instead are meteorite penetration funnels.…”

“…Crater 6, while having the general characteristics of a penetration funnel, is notably different from the other three excavated penetration funnels in not containing a carpet of fallback breccia and in having a smaller percentage of the impactor fragment survive the impact, both suggestive of explosion. The range of crater types at Campo del Cielo from hypervelocity explosion craters to non-hypervelocity penetration funnels serve as a reminder that an impact event is not necessarily uniform and can exhibit a continuum of energies and products (Vesconi et al 2011).…”