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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.
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