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Chiemite -a high PT carbon impactite from shock coalification/carbonization of impact target vegetation

Authors:

Abstract

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.
363
X. Минералогия астроблем и метеоритов
Chiemite — a high PT carbon impactite from shock coalification/carbonization
of impact target vegetation
K. Ernstson1, T. G. Shumilova2
1University of Würzburg, Würzburg, Germany; kernstson@ernstson.de
2IG FRC Komi SC UB RAS, Syktyvkar, Russia; shumilova@geo.komisc.ru
Introduction
Unusual carbonaceous matter in the form of
mostly centimetersized lumps and cobbles has
been sampled in the southeast Bavarian Alpine
Foreland, in the Czech Republic near Pardubice
and in the Saarland region near the French
border (Fig. 1). It is a highly porous blackish
material with a glassy luster on freshly crushed
surfaces (Fig. 2). The material is unknown from
any industrial or other anthropogenic processes
and thus appears to have a natural origin. Here
we report on results of a detailed analysis of this
strange matter pointing to a process of formation
in proposed meteorite impact events. From its
first discovery in the Bavarian Chiemgau impact
crater strewn field [1] the name chiemite gained
currency, and in particular these finds have
already been addressed earlier (references in [1])
before a more general occurrence in impact sites
became obvious [2, 3].
Material
Typical chiemite samples from the field are
shown in Fig. 3 as pure chiemite matter, where
the pseudomorphosis after wood sticks out, and in
compound with rock and organic matter. Under the
SEM the typical strongly porous texture is evident.
Physical properties are a low density mostly
<1 g/cm3, a significant electrical conductivity and in
some cases a moderate magnetic susceptibility and
remnant magnetization.
Methods (with a focus
on the Chiemgau impact chiemite):
Optical and atomic force microscopy, Xray flu
orescence spectroscopy, scanning and transmission
electron microscopy (SEM, TEM), highresolution
Raman spectroscopy, Xray diffraction and differen
tial thermal analysis, as well as δ13C and 14C radio
carbon isotopic data analysis.
Results
The most significant observations described in
[4] are tabulated in short as follows.
Fig. 3. Chiemite samples from the field. A: various shapes. B, C: chiemite
fragments pseudomorphic after pieces of branches. D: chiemite
breccialike intermeshed with a limestone cobble. E: chiemite crust
on a sandstone cobble. F: relatively fresh wood particle embedded in
chiemite [4]
Fig. 1. Location map for the three chiemite
sources in the Chiemgau, Saarland and Czech
impact strewn fields
Fig. 2. Freshly broken chiemite sample. Photo
width 6 cm
Modern Problems of Theoretical, Experimental, and Applied Mineralogy (Yushkin Readings 2020) -
Proceedings of Russian conference with international participation - Syktyvkar, Komi Republic, Russia
364
Юшкинские чтения — 2020
XRF: about 90 % carbon, remaining Si, Al and
Fe, subordinately S; traces of other elements.
SEM, microprobe: almost pure glasslike carbon
matrix contains finely dispersed micrometer and
submicrometersized inclusions with a complex
composition not known mineralogically.
XRD, XR synchrotron diffraction: Evidence of
nanocrystalline diamond and graphite.
TEM: Glasslike carbon structural features.
Crystalline carbyne and diamond matter with
different order level.
TEM and Raman: Polycrystalline fine grained
aggregates to polynanocrystalline diamond
aggregates and amorphous diamondlike carbon
exists. — αcarbyne and βcarbyne but not any
graphite were observed.
Raman spectroscopy: Submicrometersized
optically transparent substances are carbynelike
carbon or diamondlike carbon.
Carbon isotopes: Carbon δ13CPDB data show
values between –22.6 and –24.6 ‰ near to data of
C3 plants.
Radiocarbon data for two chiemite samples
are void of 14C corresponding to an age of > 48,000
years BP not compatible with the chiemite find
situation.
Discussion and conclusions
The fully amorphous chiemite matrix contains
diamond, amorphous diamondlike carbon and
monocrystalline carbyne inclusions. The strongly
porous texture requires an intense gas phase during
formation. — Carbyne formation needed very high
PT conditions of about 4—6 GPa and 2,500—
4,000 K. Probable carbon glass was formed at
temperatures as high as 3,800—4,000 K. — Organic
matter was involved in the formation process.
The lack of 14C requires an age > 48,000 years
(less probable) or isotope separation. Chiemite
does not correspond to any known natural earth
material. An industrial formation and an occurrence
from e.g. wildfires can reasonably be excluded. —
The chiemite components show similarities to
aftercoal meteorite impacts [5]. — We propose the
chiemite was formed by meteorite impact shock
having affected vegetation like wood and peat in
the impact target area, hence establishing a new
kind of impactite that originated from immediate
shock transformation of organic matter to high
rank carbon. — The impactite nature is underlined
by the occurrence of chiemite samples in three
established or proposed young impact strewn fields
(Fig. 1). The finds closely resembling each other up
to the enigmatic absence of 14C despite their evident
young ages, and a so far unknown isotope separation
in the impact process has to be assumed. — In all
three impact cases there is much evidence of big
airbursts, which initiated extremetemperature gas
jets impinging on the ground. The surviving of
fresh organic matter in the impactite under these
extreme conditions is important for astrobiological
aspects. — The prediction [5, 6] of more impact
diamonds from organic matter than hitherto
assumed is likewise underlined.
The authors thank Isaenko S. I., Ulyashev V. V.,
Makeev B. A., Rappenglück M. A., Veligzhanin A. A. for
help in the analytical studies and discussion.
References
1. Rappenglück, M. A., Rappenglück, B. & Ernstson.
K. Cosmic collision in prehistory. The Chiemgau
Impact: research in a Bavarian meteorite crater strewn
field // Zeitschrift für Anomalistik. 2017. V 17. P. 235—
260.
2. Ernstson, K., Müller, W., Neumair, A. The proposed
Nalbach (Saarland, Germany) impact site: is it a compan
ion to the Chiemgau (Southeast Bavaria, Germany) im
pact strewn field? // 2013. 76th Annual Meteoritical
Society Meeting, 5058.
3. Molnár, M., Ventura, K., Švanda, P., Štaffen, Z.,
Rappenglück, M. A., Ernstson, K. Chrudim Pardubice:
Evidence for a Young Meteorite Impact Strewn Field
in the Czech Republic // Lunar and Planetary Science
Conference XLVIII. 2017. 1920.
Fig. 4. Chiemite under the SEM. Chiemgau impact (A, B) [3], Saarland impact (C, D), Czech impact (E). Fossilized wooden
structure in C
365
X. Минералогия астроблем и метеоритов
4. Shumilova, T. G., Isaenko, S. I., Ulyashev, V. V., Makeev,
B. A., Rappenglück, M. A., Veligzhanin, A. A., Ernstson,
K. Enigmatic GlassLike Carbon from the Alpine Foreland,
Southeast Germany: A Natural Carbonization Process//
Acta Geologica Sinica. 2018. V. 92, P. 2179—2200.
5. Shumilova, T. G., Isaenko, S. I., Ulyashev, V. V.,
Kazakov, V. A., and Makeev, B. A. Aftercoal diamonds: an
enigmatic type of impact diamonds // Eur. J. Min. 2018.
V. 30. P. 61—76.
6. Shumilova, T. G., Ulyashev, V. V., Kazakov, V. A.,
Isaenko, S. I., Vasil`ev, E. A., Svetov, S. A., Chazhengina, Y.,
Kovalchuk, N. S. Karite diamond fossil: a new type of
natural diamond // Geoscience Frontiers, 2019. https://
doi.org/10.1016/j.gsf.2019.09.011
Artifact-in-impactite: a new kind of impact rock.
Evidence from the Chiemgau meteorite impact in southeast Germany
B. Rappenglück1, M. Hiltl2, K. Ernstson3
1Institute for Interdisciplinary Studies, D82205 Gilching, Germany; b.rappenglueck@infis.org
2Carl Zeiss Microscopy GmbH, D73447 Oberkochen; mhiltl@online.de
3University of Würzburg, 97074 Würzburg, Germany; kernstson@ernstson.de
Introduction
The Chiemgau impact (Fig. 1) as a meanwhile
established Holocene impact event has featured
quite a few exceptional observations in the last 15
years, which are summarized in [1, and referenc
es therein]. From the beginning of research it was
clear that a huge catastrophe in the Bronze Age or
Celtic era must have already affected densely pop
ulated regions, and in a routine archeological ex
cavation at Lake Chiemsee the worldwide unique
constellation was encountered that an impact ca
tastrophe layer was excavated sandwiched be
tween settlement layers of the Stone Age/Bronze
Age and the Roman Period (Fig. 1, 2) [2]. Among
the finds of ceramics, stone tools, bones and metal
artefacts also featured externally rather unsight
ly lumps, which were found by use of metal de
tectors and were addressed as «slag» by the ex
cavator. Here we report on specifically conducted
mineralogicalgeochemical investigations on 16
«slag» samples which have led to very remarkable
results.
Fig. 2. Inventory of the Stöttham archeological site (from left to right): diamictite of the catastrophic layer; archeological
finds; carbon, metallic and glass spherules; strongly corroded and fractured cobbles, metalrich «slag»
Fig. 1. Location map for the Stöttham archeological excavation (B) in the Chiemgau impact crater strewn field
... Such spherules were found embedded in the fusion crust of cobbles from a crater as well as a possible outfall in soils widespread over Europe Hoffmann et al. 2005Hoffmann et al. , 2006Yang et al., 2008). Abundant finds of glass-like carbon fragments with pumice texture, which has been given the name chiemite, contain the carbon allotropes diamond and carbyne in a largely amorphous matrix of more than 90 % carbon (Shumilova et al. 2018, Ernstson andShumilova 2020). A formation of a direct airburst shock transformation of the target vegetation (wood, peat) to carbon melt and vapor in the impact event is suggested. ...
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