Remarks to results of Ground Penetrating
Radar (GPR) measurements in four GKCF structures
SOUNDING CRATONIC FILL IN SMALL BURIED
CRATERS USING GROUND PENETRATING RADAR
E. Heggy & P. Paillou -- Lunar and Planetary Science XXXVII (2006);
"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.
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.