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ANATOMY OF YOUNG METEORITE CRATERS IN A SOFT TARGET (CHIEMGAU IMPACT STREWN FIELD, SE GERMANY) FROM GROUND PENETRATING RADAR (GPR) MEASUREMENTS

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ANATOMY OF YOUNG METEORITE CRATERS IN A SOFT TARGET (CHIEMGAU IMPACT
STREWN FIELD, SE GERMANY) FROM GROUND PENETRATING RADAR (GPR) MEASUREMENTS.
J. Poßekel1, K. Ernstson2 .1Geophysik Poßekel Mülheim, Germany, jens.possekel@cityweb.de 2Faculty of Philoso-
phy I, University of Würzburg, D-97074 Würzburg, Germany, kernstson@ernstson.de
Introduction: GPR is a widely used geophysical
method for the exploration of near-surface structures
and has also been successfully used in the investigation
of some meteorite impact structures. In the larger cra-
ters investigated (Bosumtwi, Barringer, Mistastin, [1-
3]), the depths of the crater floors can hardly be
reached even at very low antenna frequencies (e.g. 25
MHz at Bosumtwi), so that the measurements are usu-
ally limited to the marginal areas and their geological
structures (ejecta, layer deformations). The situation is
different with smaller craters (e.g. Haviland crater [4])
or with small structures for which an impact is dis-
cussed [5, 6]. We report here on a program of GPR
measurements over some craters of different size in the
soft Quaternary target of the Chiemgau impact strewn
field in southeast Bavaria (Germany).
Fig. 1. Location map for the GPR measurements over
craters (red circles) within the roughly elliptically
encircled Chiemgau meteorite impact strewn field.
The Chiemgau impact event: In a roughly ellipti-
cally shaped strewn field (Fig. 1) more than 100 most-
ly rimmed craters with diameters between a few meters
and a few 100 meters occur. Apart from the craters and
their distinct morphology as revealed from precise
Digital Terrain Model analyses (DGM 1; 1 m x 1 m
grid, vertical resolution 0.2 m; see e.g., Fig. 2) [7], the
impact strewn field shows all and abundant evidence
of impact signature as is required within the impact
research community (impact melt rocks, impact glass-
es, strong shock metamorphism like PDFs and diaplec-
tic glass - quartz and feldspar, shatter cones, geophysi-
cal anomalies, and meteoritic matter [8, 9, and refer-
ences therein]). The event happened in the Bronze
Age/Iron Age as revealed from impact catastrophe
layers and their archeological inventory [9].
Field work: So far, a total of seven craters of the
Chiemgau strewn field have been investigated with
GPR (Fig. 1), whereby two further smaller craters
accompanying the large Lake Tüttensee crater have
also been included in the measurements. A larger pro-
gram was dedicated to this Lake Tüttensee crater, and
a parallel campaign was carried out by a research team
from the Czech Republic with special, very low-
frequency equipments, which will be reported on sepa-
rately. The measurements reported here used different
antenna systems with 200, 300 and 400 MHz.
Results: From the amount of data collected so far
we select typical radargrams for the #004 Emmerting,
Aiching, Punzenpoint, Lake Tüttensee and Eglsee
craters (Fig. 2).
Fig. 2. Chiemgau impact craters for GPR measure-
ments. Surface 3D images are from the Digital Terrain
Model (in Germany: DGM 1). Note the strong exag-
geration. Meter specifications are rim wall diameters.
#004 Emmerting is the early and so far best inves-
tigated small crater. It is characterized by an impres-
sive impact inventory with extreme temperature and
pressure effects (melt rocks, shock effects PDF, dia-
plectic glass). Until today its exact formation has not
been clarified, since the extreme temperature effects on
the rocks, >1,500°C, within a 20 m measuring halo
cannot be attributed to the impact of a projectile, but
suggest a near-surface heavy impact explosion [8]. The
strong radar reflections (Fig. 3), which are good with a
drill core in the center of the crater that has proven
horizons of extreme sintering of the subsurface, fit well
with this assumption.
Fig. 3. Radargram across the #004 crater; see text.
(25 MHz center frequency with modulated 200 MHz;
data from P. Kalenda and R. Tengler).
Aiching: The semi crater Aiching appears punched
into the embankment of the Inn river valley, and the
data of the DGM 1 show its unmistakable contours of a
50 m diameter crater with a ring wall (Fig. 2). The
radargram in Fig. 4 reveals in beautiful resolution the
structure of the crater below its second half eroded and
1204.pdf50th Lunar and Planetary Science Conference 2019 (LPI Contrib. No. 2132)
leveled by the Inn river, which allows an exemplary
reconstruction of the formation of a meteorite crater
with the diameter of some decameters in a soft target.
Fig. 4. Radargram across the hidden half of the
Aiching semi crater in the Inn river valley. 300 MHz.
Punzenpoint was conspicuous as a flat depression
in the Quaternary gravel subsoil but had become a
candidate for an impact genesis only after a data analy-
sis of the DGM 1. In the DGM 1, but only in this high
resolution, it becomes clear that it is a walled doublet
structure in which a smaller, 50 m measuring crater has
dug itself into the ring wall of the larger, 120 m meas-
uring circular structure, i.e. a tiny time later (Fig. 2,
upper right). An ice age formation (e.g. a dead-ice
hole) could therefore be ruled out, and the most recent
GPR measurements (Fig. 5) have definitely excluded
such a formation and taught a meteorite impact as the
most plausible explanation.
Fig. 5. Radargram crossing the Punzenpoint doublet
crater. 300 MHz.
Fig. 6. Radargram (data superposition of 25 MHz and
200 MHz antennae; 25 MHz data from P. Kalenda and
R. Tengler) across the Lake Tüttensee crater rim wall.
Lake Tüttensee: From the very beginning there
was a fierce dispute between the local and regional
authoritative geologists on the one hand (proponents of
the textbook dead-ice formation) and the impact re-
searchers on the other hand (as advocates of a meteor-
ite crater) about the origin of the 600 m-diameter Lake
Tüttensee depression. For years, extensive geological-
geophysical-mineralogical-petrographic impact find-
ings [8, 9] have been permanently ignored by the ice
age geologists without ever having presented their own
evidence. The latest brilliant results of the GPR meas-
urements (Fig. 6) should also cause basic problems to
explain the structure of the crater as a dead-ice depres-
sion. Note the distinct imbricate layering reflecting the
excavation and ejection in the impact cratering pro-
cess. The top horizontal layering is interpreted as a
deposit from the Lake Chiemsee impact tsunami [10]
that finally overrun the crater.
Eglsee: The impact nature of the Eglsee crater,
which has a comparable size as the famous Barringer
(Arizona) crater (Fig. 2), was originally suspected by a
group of astronomers after having visited the
Chiemgau impact strewn field and then studied a satel-
lite imagery. Their suggestion fell into oblivion and
was reanimated by the study of the now available Digi-
tal Terrain Model, a subsequent gravity survey, geo-
logical field work, and the here presented GPR cam-
paign (Fig. 7).
Fig. 7. Radargram (300 MHz) across the ejecta curtain
of the Eglsee crater, which connects to the ring wall.
Conclusion: The here presented results of the GPR
measurements over meteorite impact craters of various
size in the young soft target of the Chiemgau impact
strewn field exemplify the enormous potential of this
high-resolution geophysical tool of underground explo-
ration, which may lead to a much better understanding
of impact cratering processes even on remote planetary
bodies. This knowledge adds to the conviction that a
combination of GPR and high-resolution DTM data
may also help to identify new meteorite craters (or
dismiss their impact origin), apart from the often
overworked mineralogical expertise.
References: [1] Boateng, C.D. et al. (2012) IJSRA,
1, 47-61. [2] Russel, P.S. et al. (2013) JGR Planets,
118, 1915-1933. [3] Beauchamp, M. et al. (2011) 42th
LPSC, Abstract #2147. [4] Click, K. et al. (2007) GSA,
39.3, pp. 71 (abstract). [5] Spooner, I. et al. (2009)
Met. Planet. Sci., 44, 1193-1202. [6] Heggy, E. &
Paillou, P. (2006) Geophys. Res. Let., 33, L05202, 4 p.
[7] Ernstson, K. (2017) http://www.impact-
structures.com/wp-content/uploads/2017/01/DGM-1-
final.pdf, (accessed 25/12/18) [8] Ernstson, K. et al.
(2010) J. Siberian Federal Univ., Engin. & Techn., 1,
72-103. [9] Rappenglück, M.A. et al. (2017) Z. Ano-
malistik, 17, 235-260. [10] Ernstson, K. (2016) 47th
LPSC, Abstract #1263.
1204.pdf50th Lunar and Planetary Science Conference 2019 (LPI Contrib. No. 2132)
... The small depressions at Emmerting and Grabenstätt-Kaltenbach (Bavaria, Germany) are located in the so-called Chiemgau Impact strewn field which, according to the proponents, contains more than 100 craters of Holocene age, formed most likely in the 1 st millennium B.C., perhaps at the end of the Bronze Age [Rappenglück et al., 2004;Ernstson, 2017, Possekel andErnstson, 2019]. The Chiemgau Impact strewn field would form an ellipse with small craters at NE and hypothetical large craters at SW. ...
... Ground penetrating radar (GPR) showed strong reflections from 2.7 to at least 7.5 m depth inside of the crater [Rösler et al., 2006], which has been attributed to "extreme sintering of the subsurface" [Possekel, Ernstson, 2019]. ...
... The most important body is the highly reflective layer(s) at a depth of 2 -5 m right below the crater. This body consists of compact and hard breccia (Poßekel and Ernstson 2019); even drilling with a diamond drill was problematic (see also Appendix 1, Fig. A2). A compact, melt-cemented rock mass (perhaps representing the original crater's floor) was also reached ca. ...
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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.
... 1,2 m depth). There the following peculiarities were found: thermo-plastically deformed rocks, partly fused and/or glazed at the rim wall, indicating complete heating of the rim wall (Rösler et al., 2006;; indications of temperatures close to 2000° C (Rösler et al., 2006); strong magnetic anomalies associated with the thermally altered wall material (Rösler et al., 2006); superparamagnetic nanoparticles in limestones (Prochazka and Kletetschka, 2016); carbon spherules containing nano-and microdiamonds (Rösler et al., 2006;Yang et al., 2008), partly together with iron silicides (Schryvers and Raeymakers, 2004) in the melt crust of cobbles (Rösler et al., 2006); Kamacite, indicating a meteorite fragment (Prochazka, 2023); GPR data pointing to massive physical changes of the underground and indicating that the morphology of the crater wall continues into a depth of several meters (Rösler et al., 2006;Poßekel and Ernstson, 2019;Ernstson and Poßekel, 2020); impact-diagnostic shock metamorphism in cobbles from this crater (Ernstson et al., 2010, Fig. 18 left;Rappenglück et al., 2010, Fig. 3). The synopsis of these findings strongly suggests that "the crater formation must have been accompanied by a discrete strong thermal event independent of impact shock" (Ernstson et al., 2010: 93). ...
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Anhand von sedimentologischen und geländemorphologischen Untersuchungen wird die Abschmelzgeschichte des südöstlichen Chiemsee-Gletschers beschrieben. Mit dem Trockenfallen der Bad Adelholzen-Erlstätter Rinne im Verlaufe des Spätwürm entwickelt sich aus dem Abschmelzen des Eislappens in der Grabenstätter Bucht eine sich ständig tiefer legende konzentrische Abfolge von zunächst peripheren Entwässerungsrinnen, wobei die ältesten Rinnen dieser Phase bei Chieming, die jüngeren dann entsprechend weiter im Süden, in die zentripetale Richtung umschwenken. Die Entstehung des Tüttensee-Komplexes ist im Kontext dieser Entwicklung zu sehen. Er ist das Ergebnis der glazifluvialen und glazilakustrinen Sedimentation im Einflussbereich des sukzessiven Eisabbaus in der Grabenstätter Bucht in Kombination mit einer Toteisbildung im Bereich des heutigen Tüttensees. Dafür sprechen die stufenartige Abfolge der beschriebenen peripheren Abflussrinnen mit ihren immer tiefer liegenden Abflussniveaus, die Höhengleichheit von drei dieser Rinnen mit den Tüttensee-Terrassen sowie die für die jeweilige Terrassenentstehung typische glazifluviale bzw. delta-artige Sedimentstruktur und -reife. Dieses Ergebnis stellt ein Korrektiv zur Hypothese des Chiemgau-Impakts dar, wonach der Tüttensee ein Impaktkrater sein soll. Da diese nun falsifizierte Annahme vor allem im deutschsprachigen Raum von zahlreichen Medien propagiert wird, ist der folgende Artikel auf Deutsch verfasst, um einer breiten Leserschaft zugänglich zu sein.
  • C D Boateng
References: [1] Boateng, C.D. et al. (2012) IJSRA, 1, 47-61. [2] Russel, P.S. et al. (2013) JGR Planets, 118, 1915-1933. [3] Beauchamp, M. et al. (2011) 42th
  • I Spooner
Spooner, I. et al. (2009) Met. Planet. Sci., 44, 1193-1202. [6] Heggy, E. & Paillou, P. (2006) Geophys. Res. Let., 33, L05202, 4 p.