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NEAR-GROUND AIRBURST CRATERING: PETROGRAPHIC AND GROUND PENETRATING RADAR (GPR) EVIDENCE FOR A POSSIBLY ENLARGED CHIEMGAU IMPACT EVENT (BAVARIA, SE GERMANY)

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NEAR-GROUND AIRBURST CRATERING: PETROGRAPHIC AND GROUND PENETRATING RADAR (GPR) EVIDENCE FOR A POSSIBLY ENLARGED CHIEMGAU IMPACT EVENT (BAVARIA, SE GERMANY)

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NEAR-GROUND AIRBURST CRATERING: PETROGRAPHIC AND GROUND PENETRATING RADAR
(GPR) EVIDENCE FOR A POSSIBLY ENLARGED CHIEMGAU IMPACT EVENT (BAVARIA, SE-
GERMANY). K. Ernstson1, J. Poßekel2 and M.A. Rappenglück3, 1University of Würzburg, 97074 Würzburg, Ger-
many (kernstson@ernstson.de), 2Geophysik Poßekel Mülheim, Germany, (jens.possekel@cityweb.de) 3Institute for
Interdisciplinary Studies, D-82205 Gilching, Germany (mr@infis.org).
Introduction: The asteroid impact near the Rus-
sian city of Chelyabinsk in 2013 was the largest air-
burst on Earth since the 1908 Tunguska event. Mean-
while, there are scientists who consider airburst as
much more dangerous for mankind than direct projec-
tile impacts to form meteorite craters [1]. In the geo-
logical past impact cratering accompanied by giant
airbursts must have hit Earth periodically, whereby the
term cratering refers to the fact that projectiles explod-
ing in the atmosphere may leave their traces also on
the ground to form shallow craters. Here we report on
effects of a suspected large airburst event, the traces of
which are documented by small craters, shock effects,
an extended superficial melt rock sheet and significant
evidence from GPR investigations.
Fig. 1. Location map for the Bach melt rock sheet near
Regensburg (green arrow and red arrow top right) and
the Chiemgau impact strewn field (blue). Lower:
Sketch of the exposure of the melt rock sheet.
The Regensburg/Bach melt rock sheet: In the
early new millennium, a ca. 500 m x 50 m sheet of
surficial melt rock granite with abundant glass for-
mation down to a depth of roughly 1 m (Fig. 3) ex-
posed along the highest point of the granite massif
above the Danube valley (Fig. 1) was discovered by a
local mineral collector, raised some interest of a geolo-
gist, initiated early unpublished mineralogical work
and practically fell into oblivion. Man-made and vol-
canic activities can be (and were) absolutely excluded,
and the phenomenon had obviously escaped geologic
mapping in the forest. In the absence of plausible an-
thropogenic or geological causes, a meteorite impact
event was soon considered, and since no impact crater
of some size was known far and wide, superficial melt-
ing of the granite by an airburst was discussed as a
possible explanation. An extensive surface glass for-
mation was considered in analogy to the formation of
the famous Libyan desert glass and to the Trinity nu-
clear weapons experiment and the formation of the
trinitite glass [2], and new petrographic analyses con-
firm an impact shock event as very likely cause for the
granite melting (Fig.2).
Fig. 2. A: 300 MHz GPR on top of the melt rock sheet.
B: Granitic vesicular melt rock. Photomicrographs, C:
Quartz grains in glass from the melt rock sheet,
crossed polarizers and plane light. D: Silica ballen
structures. E: PDF in quartz.
Shock effects in the melt rock sheet: In terms of
impact nomenclature the material of the melt rock
sheet may be considered impact melt rocks, in which
relics of granites coexist with a strongly vesicular glass
matrix (Fig. 2 B, C). The granite must obviously have
been heated to such a degree that only quartz grains
could survive (Fig. 2C). These quartz grains must have
experienced extreme shattering (Fig. 2C, insertion),
possibly from thermal shock. Shock effects like those
well-known in quartz from impact cratering are ob-
served throughout analyzed samples, and we state pla-
nar deformation features (PDF, Fig. 2E), open, tensile
shock spallation fractures and diaplectic glass passing
over to ballen structures (Fig. 2D).
The GPR measurements: An example of typical
GPR parameters like layering, thicknesses, their varia-
tions and changes of facies is shown in Fig. 3A. The$$
most remarkable feature however are strong radar re-
flections from a bowl-shaped structure within the oth-
erwise homogeneous granite tracing a segment of a
1231.pdf51st Lunar and Planetary Science Conference (2020)
perfect circle over nearly 50 m (Fig. 3B). The signal
polarity suggests a low-density, highly porous, air-
filled fissure produced by strong tensile forces. An
explanation other than a point source of compressive
stress (an explosion) some distance above ground, pro-
ducing a reflected rarefaction wave of equivalent ge-
ometry and reminding of the superficial impact crater-
ing interference zone [3], causes basic difficulties.
More bowl-shaped GPR reflectors along the melt rock
sheet (Fig. 4) indicate a basic connection and a com-
mon process of formation.
Fig. 3. A: Typical radargram from the melt rock sheet.
B: The bowl-shaped GPR reflector. Note that the ra-
dargram is a 2D section of a possibly much larger
structure.
Fig. 4. Bowl-shaped and irregular strong reflectors are
abundant in the melt rock sheet and below.
Discussion: After the discovery of the melt rock
sheet near Bach and a presumed formation by an im-
pact airburst, a connection with the$ now$ established$
Chiemgau$ multiple$ impact$ event$ ([4,$ 5],$ and$ refer-
ences$ therein)$ with$ the$ 120$ -$ 130$ km$ distant$ crater$
strewn$field$(Fig.$1)$was$soon$seen,$because$the role of
strong airbursts in the Chiemgau impact in addition to
crater formation (Tüttensee crater, Chiemsee double
crater, etc.) became more and more evident. Consider-
ing effects of plasma formation and neutron radiation
obviously being well observed and discussed in the
crater strewn field, we moreover mention widespread
effects of extreme heating of the ground ([5, 6], and
references therein): Halos of strongly enhanced tem-
peratures (>1,500°C) around smaller craters are ob-
served, and anomalous distinct magnetic susceptibility
peaks measured over large areas at some depth in the
soil excluding industrial or geogenic origin could well
be explained by an impact remagnetization due to
strong temperature overprint. Unusually strongly mag-
netized limestone cobbles and boulders from some of
the smaller craters, containing superparamagnetic na-
noparticles, point to short-term high PT conditions. In
particular, the formation of the chiemite carbon impac-
tite containing diamonds and carbynes are reasonably
explained by instantaneous shock carbonization/coali-
fication of the target vegetation [6]. Hence, one or sev-
eral airbursts in the Chiemgau area could well explain
these observations, in particular with view to the low-
density disintegrated, loosely bound asteroid or disin-
tegrated comet proposed for the Chiemgau impact
event [4, 5].
Conclusions: While impact airbursts and their threat
to mankind are generally discussed for asteroids or
meteoroids exploding high in the atmosphere, we pre-
sent evidence that a larger dimensioned airburst was
triggered close to the earth's surface, whereby not only
noticeable craters were formed (Chiemgau impact), but
obviously strong shock could be produced without
crater formation (Bach). To our knowledge, no compa-
rable event has yet been proven on Earth. It also puts
into perspective the recent discussion about the for-
mation of the Libyan desert glass, for which an airburst
formation is once again ruled out in favor of a hitherto
not found impact crater, and the above-mentioned dan-
ger from airbursts is considered exaggerated [7]. This
view is contrasted by our now presented research.
While the Chiemgau impact is fairly well dated be-
tween 900 and 600 B.C. [8], no dating is available for
the melt rock sheet, although due to the low soil for-
mation and the freshness of the glasses, a very young
age is likely and a synchronous impact event must be
seriously considered. Otherwise, it must be assumed
that airbursts near the ground were much more fre-
quent than expected.
!!!!!References: [1] Boslough, M. (2015) Airburst
Modeling, https://www.osti.gov/servlets/purl/1328668.
[2] Hermes, R. and Strickfaden, W. (2005) Nuclear
Weapons J., 2, 2-7. [3] Melosh, H.J. (1989) Impact
cratering: A geologic process, New York (Oxford Uni-
versity Press). [4] Ernstson, K. et al. (2010) J. Siberian
Fed. Univ., Eng. Techn., 1, 72-103. [5] Rappenglück,
M.A. et al. (2017) Z. Anomalistik, 17, 235-260. [6]
Shumilova, T.G. et al. (2018) Acta Geologica Sinica
(Engl. Ed.), 92, 2179-2200. [7] Cavosie, A.J. and
Koeberl, C. (2019) Geology, 47, 609-612. [8] Rap-
penglück, B. et al. (2020) Nuncius Hamburgensis,
Wolfschmidt, G. (ed.), in press.
1231.pdf51st Lunar and Planetary Science Conference (2020)
Article
Full-text available
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.
Article
Full-text available
We use Schmieder and Kring's article to show how science still works within the so-called "impact community" and how scienti c data are manipulated and "rubber-stamped" by reviewers (here, e.g., C. Koeberl and G. Osinski). We accuse the authors of continuing to list the Azuara and Rubielos de la Cérida impact structures and one of the world's most prominent ejecta occurrences of the Pelarda Fm. in Spain 1 2 as non-existent in the compilation. The same applies to the spectacular Chiemgau impact in Germany, which has been proven by all impact criteria for several years. For the authors' dating list, we propose that the multiple impact of Azuara is included together with the crater chain of the Rubielos de la Cérida impact basin as a dated candidate for the third, so far undated impact markers in the Massignano outcrop in Italy.
Article
The mechanisms involved in the formation of impact craters are examined theoretically, reviewing the results of recent investigations. Topics addressed include crater morphology, stress waves in solids, the contact and compression stage, the excavation stage, and ejecta deposits. Consideration is given to the scaling of crater dimensions, the crater modification stage, multiring basins, cratered landscapes, atmospheric interactions, and the implications of impact cratering for planetary evolution. Extensive diagrams, graphs, tables, and images of typical craters are provided.
  • K Ernstson
Ernstson, K. et al. (2010) J. Siberian Fed. Univ., Eng. Techn., 1, 72-103. [5] Rappenglück, M.A. et al. (2017) Z. Anomalistik, 17, 235-260. [6]
Acta Geologica Sinica (Engl
  • T G Shumilova
Shumilova, T.G. et al. (2018) Acta Geologica Sinica (Engl. Ed.), 92, 2179-2200. [7] Cavosie, A.J. and Koeberl, C. (2019) Geology, 47, 609-612. [8] Rappenglück, B. et al. (2020) Nuncius Hamburgensis, Wolfschmidt, G. (ed.), in press.