Formation of a small impact structure discovered within the Agoudal meteorite strewn field, Morocco

Abstract

A relic impact structure was recognized within the strewn field of the Agoudal iron meteorite. The heavily eroded structure has preserved shatter cones in a limestone basement, and remnants of autochthonous and allochthonous breccias. Fragments of iron incorporated into the allochthonous breccia have a chemical composition (Ni = 5.16 wt%, Ir = 0.019 ppm) similar to that of the Agoudal meteorite, supporting a syngenetic origin of the strewn field and the impact structure. The total recovered mass of Agoudal meteorite fragments is estimated at approximately 500 kg. The estimated size of the SE–NW‐oriented strewn field is 6 × 2 km. Model calculations with minimal preatmospheric size show that a similar meteorite strewn field plus one small crater with observed shock effects could be formed by fragmentation of a meteoroid approximately 1.4 m in diameter with an impact angle of approximately 60° from the horizontal. However, the most probable is an impact of a larger, 3–4 m diameter meteoroid, resulting a strewn field with approximately 10 craters, 10–30 m in diameter each, plus numerous meteorite fragments. The calculated scattering area of meteorite shrapnel ejected from these impact craters could completely cover the observed strewn field of the Agoudal meteorite.

The Agoudal (High Atlas Mountains, Morocco) shatter cone conundrum: A recent meteorite fall onto the remnant of an impact site

“…This breccia likely corresponds to the one described by Lorenz et al. ()—at least the images presented by these authors strongly suggest this. The presence of shatter‐coned marl fragments within the breccia indicates that the breccia was deposited after shatter cone formation.…”

“…Therefore, the presence of meteorite fragments noted by Lorenz et al. () within this breccia does not necessarily imply a genetic link between the breccia and the meteorite fall, but meteorite fragments may have been incorporated and cemented in the superficial recent deposit.…”

“…() and Lorenz et al. () identified and described shatter cones at a single outcrop located 5 km southwest of Agoudal village (at N31°59′12.7″, W5°30′57.5″), in a bluish—when weathered beige—formation of marly limestone with oolitic limestones (Fig. , SC1).…”

“…A poorly sorted breccia was observed exclusively at or just below the surface within the shatter cone area (e.g., Lorenz et al. ). Our breccia samples (Fig.…”

“…; Lorenz et al. ). Following these discoveries, some writings in Moroccan newspapers suggested that two subcircular lakes termed Isli and Tislit, located some 25 km to the northwest of Agoudal village, could be impact craters.…”