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THE SAARLOUIS SEMI CRATER STRUCTURE: NOTABLE INSIGHT INTO THE SAARLAND
(GERMANY) METEORITE IMPACT EVENT ACHIEVED K. Ernstson1, W. Müller2, A. Gawlik-Wagner3,
1Faculty of Philosophy I, University of Würzburg, D-97074 Würzburg, Germany (kernstson@ernstson.de),
2Diefflerstr. 217, 66809 Nalbach, Germany (edumueller@t-online.de), 3Antoniusweg 3, 86763 Dillingen, Germany
(andigawa@gmail.com).
Introduction: Some years ago finds of peculiar
samples by one of the authors (W.M.) initiated a few
analyses of glass fragments that were speaking in favor
of a Holocene possible meteorite impact site in the
Saarland region at Nalbach near the town of Saarlouis
[1, 2] (Fig. 1).
More finds of rocks and glasses with typical im-
pact features strengthened the impact hypothesis [3]
and initiated comprehensive new mineralogical anal-
yses at the university of Trier [4]. From thin-section
analyses strong shock metamorphism (shock-produced
melt, quartzite cobbles completely transferred to di-
aplectic glass, diaplectic sanidine, ballen structures
merging into cristobalite and tridymite, toasted quartz,
multiple sets of planar fractures and PDF in quartz,
strongly kinked mica, spallation fractures in quartz
grains) was established [5]. The strong shock meta-
morphism initially remained enigmatic because a relat-
ed impact crater was missing until W.M. could identify
a nearby rimmed 200 m-diameter crater, which in the
dense forest became fully obvious only by studying the
Digital Terrain Model [5]. Preliminary field work re-
vealed strongly fractured rocks and melt rocks sur-
rounding the crater up to larger distances, which were
interpreted as ejected material. Using impact scaling
laws an impactor to have produced this 200 m-
diameter crater may have had a size of the order of
only a few decameters. Hence, doubts were raised
whether such a relatively small impact was able to
produce these widespread highest shock levels. Here
we report on new findings by author A.G. and analyses
providing new insight into the so far described Saar-
land impact site.
Results. The Saarlouis semi crater. Not very often
a meteorite crater of some size is discovered within the
densely populated region of a town. This happened last
year when author A.G., a layman interested in impact
research, came across strange rocks completely ab-
normal in the region but strongly resembling a suevite
breccia known to him from the impact literature (Fig.
5). Rapidly he became aware that meteorite craters
need not necessarily be a round structure, if it was later
strongly overprinted by erosion and sedimentation, and
he established a structure that had always escaped the
attention of everybody, geographers and geologists
included, and that we now call the Saarlouis meteorite
semi crater (Fig. 2). The relic of a full crater is easily
understood from erosion and removal by the near Saar
river the valley of which is today reaching into the
semi bowl of the crater (Fig. 2). Originally seen in
Google Earth map only, the semi crater is clearly de-
lineated by high-resolution Digital Terrain Model
(DTM) data processing (Fig. 2). A random formation
of the semicircular edge of the valey can easily be ex-
cluded because upside the closely associated rim wall
geologically speaking doesn't make any sense. Moreo-
ver, delineating the rim wall crest along the semi crater
a nearly perfect circle is achieved (Fig. 2). Extrapolat-
ing the rim crest to a full circle, a diameter of 2.3 km
for the original Saarlouis crater results. Geologically,
the sharply countoured semi crater also portrays the
stratigraphy fixing the deposition of the Lower Terrace
as an upper limit for the age of the postulated event,
that is an impact in the Pleistocene or older.
Fig. 2. The Saarlouis semi crater: The rim wall
crest (+) is forming a segment of a nearly perfect 2.3
km-diameter circle. Fig. 3. Geological map; simplified
from [6].
Fig. 4 conveys a further strong argument for the re-
ality of the impact event. In the map of the shaded re-
lief seven radial DMT profiles for topographical sec-
tions across the rim wall are plotted, and comparing
the shape of the semi crater and its rim wall with cross
sections of young bowl-shaped proven meteorite cra-
ters with diameters of roughly the same order an amaz-
ing similarity is evident.
Suevite. The rock having reminded A.G. of a sue-
vite had been excavated by a farmer on the plateau
1876.pdf49th Lunar and Planetary Science Conference 2018 (LPI Contrib. No. 2083)
immediately outside the rim wall being probably im-
pact ejecta. Macroscopically and from thin-section
analysis we are dealing with a polymictic breccia com-
posed of sharp-edged, in part vesicular rock fragments
in a finer-grained matrix of dominantly quartz, calcite
and rarely glass splinters.
Fig. 4. Map of shaded relief of the DTM and profiles
across the rim wall. For comparison other typical crater
profiles are shown.
The dark components prove to be basaltic andesite
both in a dense form and as vesicular melt rock, which
will in more detail be addressed later. The grading and
the adjustment of particles (nw - se) indicates flow
texture. Close-up shows vesicular melt rock particles
with metallic spherules (see the insertion in Fig. 5.)
Fig. 5. Cut face of suevite from the Saarlouis semi
crater (see text).
Preliminary SEM-EDS analyses of a few spherules
(Fig. 6) show an iron core with vermicular carbon in-
clusions embedded in basaltic andesite of the breccia
component. A host of more elements contribute, how-
ever in general at < 1 wt%.
With the verification of melt particles and shock ef-
fects (Fig. 7) and with regard to the common impactite
nomenclature the Saarlouis polymictic breccia can
reasonably be called a suevite impactite strongly sup-
portimg the hypothesis of a Saarlouis meteorite crater.
Target rocks. For the time being we avoid going
into details of the postulated impact cratering process
and the affected stratigraphy. The basaltic andesite
contributing to the suevite breccia is not exposed in the
Saarlouis vicinity but is closest exposed and exploited
10 km apart.
Fig. 6. Electron image of metallic spherules and EDS
layered image (see text).
Fig. 7. Moderate shock effects in the suevite breccia.
A: multiple sets of planar deformation features (PDF)
in feldspar, B: PDF in quartz.
Hence, the impact excavation should have met a so
far unknown basaltic andesite complex below the to-
day's crater floor in the Saar valley possibly at a depth
of several hundred meters. Interestingly, two big basal-
tic andesite "erratic" blocks have earlier been excavat-
ed from a purely loamy ground near the town of Nab-
ach 8 km apart without having ever understood the
process of emplacement. The now proposed Saarlouis
impact excavation and ejection could well have been
the source.
Conclusions: With the discovery of the 2.3 km-
diameter Saarlouis crater the earlier discussed Nalbach
impact event and its inexplicably widely disseminated
strongly shocked rocks [5] can be seen in a completely
new context. Together with the previously established
smaller crater near Nalbach (Fig. 8) a paired impact
within a distance of roughly 8 km and a related much
broader impact reach make perfect sense. However, the
geologically established age - Pleistocene or older -
makes an earlier suggested hypothetical relation with
the Chiemgau meteorite impact event [3] obsolete.
Acknowledgement: We thank Dr. M Hiltl for the
SEM-EDS analysis.
References: [1] Buchner, E. et al. (2011) 74th Ann.
Meteoritical Soc. Meeting, Abstract #5048. [2]
Schmieder, M. et al. (2011). 74th Ann. Meteoritical
Soc. Meeting. Abstract #5059. [3] Ernstson, K. et al.
(2013) Meteoritics & Planet. Sci., 48, s1, Abstract
#5058. [4] Berger, N. (2014) Diploma thesis, Universi-
ty of Trier. [5] Berger, N. et al. (2015) 46th LPSC,
Abstract [6] geoportal.saarland.de. - DTM data from
LVGL Saarland.
1876.pdf49th Lunar and Planetary Science Conference 2018 (LPI Contrib. No. 2083)