Remarks to results of Ground Penetrating Radar (GPR) measurements in four GKCF structures

Norbert Brügge


E. Heggy & P. Paillou -- Lunar and Planetary Science XXXVII (2006); 1264.pdf

"We report results from a field survey performed on a recently discovered impact field in the southwestern Egyptian desert, using a 270 MHz Ground-Penetrating Radar (GPR). Profiles across small-buried craters revealed a coherent sequence of tilted layers constituting the cratonic infill resulting from aeolian deposits. In the intercrater areas the radargram revealed a poorly defined subsurface stratigraphy and the presence of shallow structural elements associated with potential evidences of the consequences of the shock effects, i.e., faulting, fractures, and chaotic bedrock. The radarpenetration depth varied from 2 to 15 m, depending mainly on the amplitude of the volume and multiple scattering in the subsurface, caused by fractures and debris.

GPR Survey Setup and Results: We profiled four small buried craters where we crossed the investigated structures in orthogonal directions in 30-meters-long profiles. Our profiles confirmed the morphology of small buried craters partially outcropping at the surface. On the 30-m-long radar transect crossing the GKCF-28 crater, we can clearly distinguish the crater curvature, with its nearly flat bottom (due to the presence of breccias) being located 4 m deep, about one-tenth its diameter.
This typical ratio has been observed on all four of the small craters covered by the GPR study. The figures shows layered deposits (in yellow) in the crater filling.
A predominant feature on the radargram near the bottom of the crater is the fractured and brecciated bedrock that diffuses and scatters the radar signal, giving rise to the purple hyperbolic-like forms observed at 6 m depth. All four GPR profiles obtained for the buried craters revealed the same subsurface morphology: a perturbed hemispherical structure buried under sediments. Radar was unable to resolve any structure under the craters, due to the strong volume and multiple scattering in the bedrock."

My diagnosis: Since it has since been proven that all structures (cater-like or dykes) are of volcanic-tectonic origin, we can interpret the results of the GPR contrary, even in such an insignificant crater. The predominant feature on the radargram under the bottom of the crater is not fractured and brecciated bedrock. It is very likely a plug of a volcanically shaped breccia that was non-explosively uplifted. The edges of the crater are made of squetched bedrock, which also may contain parts of breccia.
A strange breccia found at two large craters consists of a more or less iron-rich mass, which apparently contains various fragments of basement and possibly from the earth's crust. Unfortunately, there are no detailed examinations, or it has not been published.