Ground Penetrating Radar (GPR) Measurements - Rim Wall and Ejecta Blanket - Saarlouis (Saarland, Germany) Impact Crater
The poster is a critical discussion of an article by Kenkmann et al. (GSA Bulletin, 2022). In the article, the Wyoming crater strewn field is declared to be a field of impact secondary craters from an unidentified primary crater. Our poster rejects this interpretation as consistently methodologically problematic to absolutely untenable. Many of the small craters analyzed by Kenkmann et al. do not have an independent position according to our own analyses, but are rather to be regarded as inner peak rings of much larger impact craters, especially with respect to their morphological high position. As primary structures recognized by us, the Wyoming craters show an amazing parallel to the important Holocene impact crater strewn field of the Chiemgau impact in Germany.
Introduction: ln 2022, an article was published in the GSA Bulletin  claiming that a secondary crater field of a major impact structure has been detected for the first time in the state of Wyoming in the United States, as has long been known from the Moon, other planets, and their moons. 31 craters are confirmed by shock effects, and more than 60 are considered possible craters. Here we discuss the article and disapprove of the arguments for a secondary cra-tering. The secondary-cratering model : Two findings are highlighted as evidence: the axial directions of elongated craters within four separately occurring clusters of craters. The elongated axis directions span four acute-angled corridors that overlap at a distance of roughly 200 km, where they are thought to mark the presumed primary crater from which projectiles were launched along the corridors to create the secondary craters. The landing of these projectiles after ballistic trajectory are then supposed to have produced the elliptical to ovoid asymmetric shapes of the secondary craters. In the intersection region of the three corridors, there should exist a significant negative gravity anomaly of a hypothesized primary impact crater measuring perhaps 50 km. Third, it is argued that such a large Wyoming strewn field, measuring close to 90 km, could never be attributed to a primary impact according to theoretical modeling and considerations. Failure of the secondary-cratering model: From the text of the article and the Supplementary Material, we deduce that the argument of asymmetry of the crater axes must be rejected. Of the 31 craters classified and measured as proven, 15 have an eccentricity e = 1, that is, they are circular. With an e ≤ 1.2, 19 of 31, well over half, are also practically round. Of 23 crater measurements in cluster SM, 11 have an e = 1, meaning they are round, and with e ≤ 1.2, 14, more than half, are also practically circular. In the WR and PCR clusters, only 2 and only one crater, respectively , were measured, but trajectory triangle corridors were constructed for the intersection of the assumed primary crater.-The suspected primary crater at the intersection of the above trajectory corridors is based also on a negative free-air gravity anomaly. The use of the free-air anomaly instead of the correct Bouguer anomaly makes the statement about a primary crater there completely worthless.-That the extension of the Wyming strewn field of about 90 km excludes a primary impact formation is based on rather old model calculations and ignores several actually existing larger primary terrestrial crater strewn fields, which the article does not list. Discussion and conclusion: The elongation of the postulated secondary craters (but only for roughly half) as assumed "signpost" to the primary crater remains without significance, because such an asymmetry can arise in both cases: at the impact of the projectiles of a previously disintegrated asteroid or comet, or at the impact of the ejecta launched from a primary crater. Elongated craters may be also the result of overlapping double craters suggesting only an apparent impact direction.-A secondary crater field logically requires a primary large impact crater. Such a primary crater does not exist so far, neither morphologically nor geologically. The negative gravity free-air anomaly (which is not shown in the article) is a fundamental methodological mistake, because geophysically relevant is the Bouguer anomaly. At the location of the free-air anomalies described in  the map of the Bouguer anomalies does not show any special feature suggesting a large impact structure there. It is not clear to us why the Bouguer map was ignored, as it is used in worldwide impact research.-The claim that a crater strewn field as extensive as Wyoming's would not be consistent with a primary impact ignores reality. The claim is supposedly supported by a 20 years old model calculation  and by a comparison with the small strewn fields from the densely clustered fields of Morasko, Odessa, Wabar, Henbury, Sikhote Alin, Kaalijärv, and Macha, but is contradicted by the three larger impact strewn fields of Campo del Cielo , Bajada del Diablo (very likely) [4, and ref. therein], and Chiemgau [5, and ref. therein; 6], which are best described in the literature but are not mentioned in  with a single word. We also miss in  the reference to the Carolina Bays probable true secondary crater field of the suspected YDB impact . A comparison of the Wyoming field with the Chiemgau impact field of similar extent but with far more than 100 craters in an elliptical scattering field shows  that practically all features of the Wyoming craters described in  occur in almost identical formation in the Chiemgau craters.-We conclude that the Wyoming secondary crater field is a fiction and not supported by anything. Nowhere is there any robust evidence for the existence of an associated primary crater.
Secondary craters in impacts on moon, planets and their moons are a well known phenomenon, which has been investigated many times. In the article commented by us here, the authors report on a crater strewn field in the American state of Wyoming, which is interpreted as a field of secondary craters of a so far unknown larger primary impact structure and as a first on Earth. We compare the Wyoming crater strewn field with the Chiemgau impact crater strewn field in SE Germany and find that both have nearly identical characteristics of virtually all relevant features, in terms of geometries and petrography. We conclude that the alleged Wyoming secondary crater field is a fiction and the craters attributable to a primary impact. The alleged evidence is very poor to easily refuted. A primary crater does not exist to this day. The negative free-air gravity anomaly referred to, but not even shown, is invalid for this purpose. The Bouguer gravity map shows no indication of a possible large impact structure. Also unsuitable is the use of asymmetries with elongations of assumed secondary craters with a very questionable corridor intersection for the ejecta. Of 31 craters surveyed as proven, 15 are circular (eccentricity 1) and more than half (19) have an eccentricity ≤1.2. Circular and elongated craters are intermixed. The evaluated crater axes may just as well originate in a multiple primary impact. Elongated craters may also result from doublets of overlapping craters that are no longer fresh, as described by the authors themselves. In their paper, the authors do not show a Digital Terrain Model with contour lines for any of the surveyed craters, but only aerial photos blurred by vegetation. A verification of the crater measurements with the deduced eccentricities and strike directions is impossible. Not a single topographic profile over even a single crater in the strewn field is shown, either from DTM data or from an optical leveling, which could have been accomplished in an instant given the relatively small craters. Grave is the misconception that such a large crater field of 90 km length with three separate clusters is not possible according to 20 years old model calculations. A primary impact with multiple projectiles could perhaps be conceivable under rare circumstances, which are described by the authors as not relevant. The alleged impossibility of such a large primary strewn field with referring to the known small impact fields of Morasko, Odessa, Wabar, Henbury, Sikhote Alin, Kaalijärv, and Macha is contradicted by the three larger impact strewn fields of Campo del Cielo, Bajada del Diablo (very likely), and Chiemgau, which are best described in the literature but are not mentioned by Kenkmann et al. with a single word. The comparison of the Wyoming strewn field with the Chiemgau impact crater strewn field of about the same size here in the commentary article proves the scientifically clearly much greater significance of the Chiemgau impact, which must be considered as currently the largest and most significant Holocene impact despite the rejection and ignoring in some parts of the so-called impact community.
Impact cratering generally distinguishes between simple, bowl-shaped small craters and larger complex structures with a central peak and/or inner rings. In the modification stage of the latter, the transient crater is largely re-filled by centripetal movements particularly due to gravitational collapse of the crater rim. The transition from simple to complex craters is generally assumed to occur at about 1.5 - 4 km diameter of the final crater. Here we report on small craters, where in a modification stage the primary bowl has changed into a complex crater with internal peak or ring morphology seen on GPR profiles through the crater center. The Eglsee crater, which has a comparable size as the famous Barringer (Meteor) crater, belongs to the Chiemgau impact event (900-600 B.C.) and has a depth-to-diameter ration of roughly 1:70 comparable to much larger complex impact structures (like e.g. the Ries crater). The Eglsee crater complex nature of formation is underlined by GPR that reveals a buried ring-like mound below the otherwise flat crater interior. The nearby Riederting crater has a diameter of 250 m and, with a maximum depth of 5 m, is comparably shallow as the Eglsee crater and other complex craters. GPR through the flat basin shows a complexly sculptured wavy layering with a central depression several meters deep, which is surrounded by a steplike inner rim wall of roughly 60 m diameter. With a diameter of 60 m and a depth of about 10 m, the Aiching semi crater has indeed the typical bowl shape of a simple meteorite crater. The GPR on the flat crater floor however shows a very complex, wave-like layer structure and a central mound with a diameter of about 30 m, which reaches up to about 2 m below the crater floor in the center. We conclude from the GPR that in a soft target such as the unconsolidated, water-saturated Quaternary material in the strewn field of the Chiemgau impact, small craters may well have quite flat complex morphologies with central peak or ring-like mound in the subsurface. Similar to large complex craters, the partial collapse of the previously formed ring wall may have been effective in a modification stage.
The high-pressure, high-temperature carbon impactite of more than 90% carbon with inclusions of diamond and carbines, named after the Chiemgau impact crater strewn field, which must have been formed by direct shock carbonization of the target vegetation, has now been evidenced in the same formation in the impact areas of the Saarland and the Czech Republic.
A hitherto worldwide unique evidence of a new type of impactite contains particles of metallic bronze and iron artefacts in a strongly shocked polymictic impact breccia from an archaeological excavation in the crater strewn field of the Chiemgau impact, dating the impact to relatively precise 900-600 BC.
The finds of iron silicides composed, among others, of xifengite, gupeiite, hapkeite with inclusions of titanium carbide, khamrabaevite and moissanite, and CAIs, together with about 30 elements including uranium and REE, which have been regarded as extraterrestrial for about 15 years in the crater strewn field of the Chiemgau impact, have been enriched by an 8 kg find with analogous composition.
Spallation is a well-known process in technical fracture mechanics that describes the particularly destructive effect of dynamic tensile stresses as a result of reflected dynamic compressive stresses. In meteorite impacts, it is primarily reflected shock waves (rarefaction waves) that leave their mark in dimensions from mega to micro. We describe the investigation of quite unusual and so far geologically not understood layer deformations with geophysical ground penetrating radar (GPR) measurements and consider impact shock spallation as causal force.
Spallation is a well-known process in technical fracture mechanics. It describes strong tensile pulses, reflected from incident compression pulses at free surfaces, which can lead to decisive material damage due to the usually significantly lower tensile strength. In meteoric impacts with shock propagations, they play an important role in all dimensions, from mega to micro (Ernstson 2014). Early considerations led to the model of so-called spall plates (Melosh 1989), which describes near-surface platy rock bodies ejected at high speed during the formation of impact structures, a consequence of the spallation superposition of the propagating shock front with the rarefaction wave reflected at the free Earth surface. We describe known terrain observations (Ries impact event) of structurally very conspicuous impact layer deformations in Upper Jurassic limestones (Chao et al. 1978, Rutte 2003) , which so far cannot be explained geologically. GPR measurements show an extrapolation into the depth (8 m) and suggest that, based on the model of spall plates, shock spallation during the propagation of impact shock waves is the only reasonable explanation so far.-Very unusual GPR reflections are associated with a suggested impact airburst in Lower Bavaria. A 500 m x 50 m area of surficially melted granites shows narrow, circular curved, isolated reflection bands of high energy at apex depths down to a few meters. Conventional GPR interpretations and geologic considerations do not explain the observation. It is suggested that the GPR reflection traces an arcuate thin weak zone in the hard granite, caused by a rarefaction front of strong tensile stress propagating into the subsurface in response to an incident shock front. A specification of such a process in more detail is still pending, but shows how impressively GPR measurements can contribute to the clarification of near-surface impact processes (Poßekel & Ernstson 2019, Ernstson & Poßekel 2017). Plain Language Summary Spallation is a well-known process in technical fracture mechanics that describes the particularly destructive effect of dynamic tensile stresses as a result of reflected dynamic compressive stresses. In meteorite impacts, it is primarily reflected shock waves (rarefaction waves) that leave their mark in dimensions from mega to micro. We describe the investigation of quite unusual and so far geologically not understood layer deformations with geophysical ground penetrating radar (GPR) measurements and consider impact shock spallation as causal force.
Unusual carbonaceous matter, termed here chiemite, composed of more than 90% C from the Alpine Foreland at Lake Chiemsee in Bavaria, southeastern Germany has been investigated using optical and atomic force microscopy, X‐ray fluorescence spectroscopy, scanning and transmission electron microscopy, high‐resolution Raman spectroscopy, X‐ray diffraction and differential thermal analysis, as well as by δ13C and 14C radiocarbon isotopic data analysis. In the pumice‐like fragments, poorly ordered carbon matter co‐exists with high‐ordering monocrystalline α‐carbyne, and contains submicrometer‐sized inclusions of complex composition. Diamond and carbyne add to the peculiar mix of matter. The required very high temperatures and pressures for carbyne formation point to a shock event probably from the recently proposed Holocene Chiemgau meteorite impact. The carbon material is suggested to have largely formed from heavily shocked coal, vegetation like wood, and peat from the impact target area. The carbonization/coalification high PT process may be attributed to a strong shock that instantaneously caused the complete evaporation and loss of volatile matter and water, which nevertheless preserved the original cellular structure seen fossilized in many fragments. Relatively fresh wood encapsulated in the purported strongly shocked matter point to quenched carbon melt components possibly important for the discussion of survival of organic matter in meteorite impacts, implying an astrobiological relationship.