Two impact craters at Emmerting, Germany: field documentation and geophysics

New research of two craters at Emmerting (No. 4 and No. 5), Germany, is presented. This paper should be the first part of two papers concerning presumed impact craters at Emmerting. The second paper will be about mineralogical/petrological, temperature and stress analyses. The enstatite-dominated meteoritic material, found in the crater No. 4 [Procházka et al., 2022; Procházka, 2023], is the subject of a separate detailed research. High-temperature effects and extreme deformation are significant in both craters. This deformation is explained with the effects of pressure wave(s) and later decompression in a target dominated by large but unconsolidated pebbles. Mutual collisions and secondary projectiles were documented. While most pebbles in the Crater No. 4 were thermally affected, the fine-grained fraction of the filling is poor in such material. It follows that small particles were volatilized and/or blown away during crater formation, or transported away later (e.g., by groundwater). Gamma-ray spectrometry has indicated that the walls of Crater No. 4 are significantly enriched in major natural radionuclides of Th, K and partly U, while the crater interior is depleted in these elements which are concentrated mainly in fine-grained fractions. This suggests a selective removal and volatilization of fine-grained material during the crater formation. The georadar measurements at both craters show that crater rims (walls) were partly pushed from below and partly heaped up from above with material that came from the crater interior. Georadar detected a compact body below the crater floor which is supported by results of resistivity measurements. A set of geophysical, geochemical, microscopic and mineralogical measurements proved that the craters at Emmerting are of impact origin. Extreme high temperature (HT) conditions inside the crater and small diameter of both craters indicate possible existence of very small meteoroids that are able to penetrate Earth´s atmosphere with high impact velocity (more than 30 km/s). This fact should challenge current models of bolide penetration through atmosphere.