Footnotes
[1]
Spallation is a well-known process in fracture mechanics as well as in impact cratering and has been investigated theoretically and experimentally by many researchers. Unfortunately, it is less well known that spallation can also be observed in nature as an actually existing geologic phenomenon in and around impact structures.
Spallation takes place when a compressive shock pulse impinges on a free surface or boundary of material with reduced impedance (= the product of density and sound velocity) where it is reflected as a rarefaction pulse. The reflected tensile stresses may produce widely open tensile fractures and may lead to the detachment of a spall or series of spalls.
Here, in addition to Fig. 25, we show a cobble from the rim of the Tüttensee crater exhibiting a prominent spallation fracture strongly reminding of the experimentally shocked ARMCO iron in Fig. 26.
More about impact spallation can be read here:
http://www.impact-structures.com/Archiv/archiv.html (Impact spallation in nature and experiment)
and here:
http://www.impact-structures.com/spain/shocked/spallation.htm .
[2]
Several of the larger craters in the Chiemgau strewnfield, e.g. the Tüttensee crater, are commonly interpreted as dead-ice moraines. Dead-ice depressions originate from the melting of buried glaciers involving the sinking of moraine material and, in general, do not exhibit a ringed wall. In rare cases, dead-ice depressions may be surrounded by hilly moraines arranged to roughly form a ring pattern. The pattern is usually explained by differential melting rates in the center and in the periphery of the buried glacier.
The wall around the lake Tüttensee crater is to a large extent composed of heavily fractured and deformed clasts (see Figs. 19 - 23) typical of impact ejecta and not at all compatible with a ring formation of a dead-ice depression.
[3]
A short description of each of the crater strewnfields is given by P. Hodge:
Hodge, P. (1994): Meteor craters and impact structures. Cambridge University Press, 124 pp.
More information can be found here:
Kaalijarvi:
http://gisp.gi.alaska.edu/craterbase/kaalijarvi.htm
Morasko:
http://gisp.gi.alaska.edu/craterbase/morasko.htm
http://www.inyourpocket.com/poland/poznan/en/feature?id=55559
Sikhote Alin:
http://www.alaska.net/~meteor/SAinfo.htm
Henbury:
http://www.marssociety.org.au/jnt-db/Australia-NT_S-Henbury.html
Campo del Cielo:
http://gisp.gi.alaska.edu/craterbase/campo.htm
http://www.fcaglp.unlp.edu.ar/~sixto/arqueo/w-6-ing.htm - an article on: Meteorites of Campo del Cielo: Impact on the indian culture
Wabar:
http://volcanoes.usgs.gov/jwynn/3wabar.html
http://www.saudiaramcoworld.com/issue/198606/the.wabar.meteorite.htm
Gibeon:
http://www.alaska.net/~meteor/GNinfo.htm
[4]
In the Ries impact structure (Nördlinger Ries), Bavaria's "big" meteorite crater, deformations like rotated fractures and bread-cut-to-slices features are abundantly exhibited by clasts from the Bunte breccia ejecta.
Characteristically deformed clasts from the ejecta of the Ries impact structure.
For comparison: Characteristically deformed clasts from the Puerto Mínguez impact ejecta (Spain) and from the rim of the Tüttensee crater (to the right).
The clasts shown here have in common that they were embedded in a soft matrix excluding a long-lasting, e.g. tectonic, deformation process. Instead, the deformations are considered diagnostic of short-term impact deformation under high confining pressure.
A more comprehensive discussion of these high-pressure/short-term impact deformations is found also here:
http://www.impact-structures.com/spain/ptominguez.htm
[5]
Comparison of the grit brecciation shown in Fig. 18 with a similar monomictic movement breccia from the Ries impact structure (Nördlinger Ries):
Ries impact structure Chiemgau crater
Monomictic movement breccias are well-known to be exposed in and around impact structures. They may be related with giant rock falls and may in rare instances occur along tectonic fault zones. The observation of this grit brecciation in the Chiemgau craters is a strong clue to their impact nature. Evidently, an origin from Alpidic tectonics and a subsequent transport of the heavily fragmented clast can be excluded.
More about monomictic movement breccias can be read here:
http://www.impact-structures.com/breccia/monomictic.htm
[6]
For each crater a data sheet has been drawn up including location (village/town, field-name, field and/or topographic map, satellite imagery and/or aerial photograph, ground photograph, GPS coordinates), size, phenomenology, underground properties, geology, and special features (degree of destruction, possible risk of destruction, etc).
[7]
Industrial titanium carbide (TiC) is usually produced from a mixture of titanium dioxide and carbon in an induction heater: TiO2 + 3 C = TiC + 2 CO (Weiland 1996). Since 1995, there is an additional process (IMTA, US Pat No. 5,417,952) that starts at TiO2 and C3H6.
[8]
Metallurgical studies of the properties of aluminium silicides (AlXSiY) und their industrial production have been performed in the last 20 - 30 years (Ejefor & Reddy 1997). There are hypoeutectic, eutectic and hypereutectic Al-Si systems (Teu = 577°C). As a rule, elements like Cu, Mg, Fe, Ni, Zn, and others are added in order to achieve the desirable material properties. Among the metallic matter from the Chiemgau strewnfield, a small piece of AlXSiY , probably corresponding with AlSi2 or AlSi3 of a hypereutectic Al-Si system, has been analyzed to yield no other elements oxygen included. Because of the purity of the Al-Si compound an origin from industrial production is highly improbable.
[9]
Ferrosilicides (FeSi, Fe2Si [hapkeite], and FeSi2) as new minerals have been detected in the lunar Dhofar 280 meteorite (Dh-280; Dhofar region, Oman, April 2001) (Anand et al. 2002, 2003). At grain sizes of 2-30 µm, they are embedded in a regolith breccia. More than 95 % of the rock is composed of Fe (66 %) and Si (31 %) with subordinate amounts of Ni (1 %), P and Cr. But enrichments of Ti (4.6 %) and P (15 %) have also been observed. The Fe-Si phases in Dh-280 are in proof of extremely reducing conditions on the Moon or on a planetoid. It is assumed that the reducing conditions are related with extremely high temperatures like in the process of formation of Fe-Si phases in fulgurite glass.
A mineral with a structure very similar to gupeiite - suessite, (Fe, Ni)3Si - is extremely rare in the North Haig ureilite type meteorite (Sleeper Camp, Australia, 30°26' S| 126° 13' E) (Keil et al. 1982) and NWA 1241 (Libya, 27° N| 16° E).
Gupeiite (Fe3Si) itself is contained in the FRO 90036 meteorite found in the Frontier Mountains (Antarctica, 72°59'27'' | 160°20'72'' E) (Wlotzka 1994).
[10]
The Yanshan meteorite having gupeite and xifengite as the main constituents is an individual find. The meteorite contains quite a few small iron spherules (0.1 - 0.5 mm diameter) composed of two or three shells of different phases. The inner shell is composed of Ni-Fe metal (kamacite and taenite) and the outermost shell of magnetite, wuestite and maghemite. On average, the analyses yield 84.8 % Fe, 0.8 % Ni, 14.1 % Si, 0.7 % Mn and traces of Cr, Cu, and Co. The low Ni content is striking. The core of the spherules predominantly contains cubic gupeiite (Fe3Si) and hexagonal xifengite (Fe5Si3) (Yu Zuxiang 1984). The spherules show wrinkled and scaly surfaces and aerodynamically shaped splash forms pointing to an extraterrestrial origin (Anthony et al. 1986). It is interesting to note that hongquiite, originally though to be TiO but now shown to be in fact TiC, is found to occur together with gupeiite in the core of the spherules (American Mineralogist 1986).
[11]
Glass-coated pebbles, cobbles and boulders can meanwhile be said to belong to the regular inventory of the impact strewnfield. They may be associated with craters but can also be sampled in the open field. In one case, a small glass-coated sandstone pebble was found to have been dug out by a mole. Below we show different aspects of the "glass stones".
A 10 kg glass-coated sandstone boulder found in the field near Vachendorf, 2.3 km southeast of the Tüttensee crater (southern part of the strewnfield).
Close-up of the glazed surface of the 10 kg boulder.
Broken glass-coated sandstone cobble found near Emmerting village (northern part of the strewnfield).
Glass is also filling the open fissures within the broken cobble and occurs along the bedding planes (the dark veins). Note the distinct fitting (arrows) along the sharp-edged fissures proving tensile (?spallation) fracturing.
Glass-coated sandstone pebble from a molehill.
Brownish glass coating a sandstone cobble.
