Discussion of alternate models
An origin other than from the impact of cosmic material has been discussed for both the craters and the peculiar matter. Neither volcanism nor tectonics is known for the region under discussion and for the Holocene geological time of the phenomenon. Moreover, the craters are found randomly distributed over areas of quite different surface geology. Deep-seated dissolution and collapse processes like karstification may account for those depressions lacking a ring wall but can be excluded for all the craters exhibiting such a wall.
Assemblages of apparently man-made depressions with a similar morphological signature are well known from other regions in Germany (German terms “Mardellen”, “Mare” [Weber 1909, Stechele 1911]), and they have been reported also for regions in Belgium, Luxembourg and France (Van Werveke 1903; Barth & Löffler 1998, Barth 1996, Löhr 1985, 1986, Barth et al. 1996, Ginkel 1995, Wichmann 1903, and others).
A clear and unambiguous explanation of origin and purposes is so far lacking. Apart from geological causes, exploitation of earth materials (gravel, loam, ores), use as reservoirs, charcoal piles, production of quicklime, glassworks and housing estates have been proposed. Obviously, in some cases a multiple use can be assumed. On the other hand and as far as we know, an origin of the crater fields from meteorite impact has so far not been considered.
Within two of the smaller craters in the strewnfield, anthropogenic objects have been sampled (Bavarian Archaeological Survey) without, however, any hint to an excavation of the craters by man. It goes without saying that already existing craters could have served for special purposes.
Moreover, in the Chiemgau strewnfield area, an interpretation of the craters as the result of human activities presents basic difficulties. Lots of the depressions are located midst of arable land speaking against exploitation and housing purposes. Apart from the craters filled with water, water reservoirs can in most cases be excluded because of the high permeability of the Quaternary gravel layers, and sealing by loam has never been observed in the depressions.
On cursory inspection, some of the craters show similarities with funnel-shaped pits well known from medieval limonite mining and smelting (e.g., Wolf 1986, Frei 1965/66). Some 40 km north of the Burghausen-Marktl strewnfield near Kelheim and Painten, these pits have diameters between 1 and 5 m, and related charcoal piles may amount to the size of 10 m diameter. The observations, however, don’t explain the considerable number of much larger craters having diameters between 10 m and 400 m. Moreover, shafts have never be shown to exist and other man-made constructions in and outside the craters either. We also mention the complete absence of blocks of slag with charcoal imprints typically associated with smelting processes (Bielenin 1977). While regularly the magnetic signature of smelting activities (kilns, charcoal piles) is considerable (Bielenin 1977), the only faint magnetic anomalies in the strewnfield craters (see above) do not speak in favor of an anthropogenic origin. To the contrary, archaeological finds in and outside the craters are remarkably scarce. Neither oral nor written reports have ever mentioned mining and smelting activities related with the craters and depressions.
The observation of the heavy rock fracturing related with the craters implying evidence of strong dynamic deformation (e.g., spallation features – see Macroscopic deformations) may suggest explosion cratering from artillery fire or extensive bombing during World Wars One and Two. However, no metallic bomb splinters and no chemical matter from explosives have ever been found in the strewnfield. No aerial photographs typically taken from bombed areas in World War Two do exist. Even the giant World War One mortars (Lusar 2001) or the so-called “Grand Slam” or “Earthquake” bombs in World War Two produced craters not exceeding 66 m and 43 m, respectively (Battlefield Guide 2000). Moreover, neither eyewitness accounts nor archives have ever reported of any bombardment or artillery fire. Taking into account the 120-year age of lots of trees from within many craters (pers. comm. Altötting forestry office), their formation in World War One or later has to be excluded anyway.
In summary, for the most part of the craters under discussion a man-made origin can practically be excluded, and in rare cases, the proverbial exception that proves the rule may apply.
The peculiar matter
Opposed to the hypothesis of cosmic matter obviously related with the craters, an origin from industrial and local smelting processes or/and fertilizer application has to be taken into consideration. From the above discussion of the crater formation we conclude that simple iron smelting to produce the slag-like matter does not apply to the observations. Moreover, it lacks high fayalite, wuestite and FeO contents to be expected in material from ordinary kilns (Bielenin 1977, Wolf 1986, Sperl 1981).
In nature, the ferrosilicides Fe3Si (gupeiite) and Fe5Si3 (xifengite) are extremely rare, and only a few individual finds have been reported (Jambor et al. 2002, Rudashevskii 1995). The reason is that ferrosilicides can form only in an extremely reducing, oxygen-poor milieu that normally does not exist on earth. A small PGE-deposit related with an ultrabasic intrusion in the Urals near Nizhne Tagil is an exception where the occurrence of gupeiite has been reported.
Fe3Si and FeSi were analyzed in fulgurite glass from lightning into the ground (Heinrich 2001; also see Sheffer et al. 2003). The authors suggest short-term formation temperatures in excess of 1710°C, and they refer also to the reported rare occurrences of natural ferrosilicides in Russia which have partly been confirmed only, or which are related with meteorite falls. The type locality of xifengite is the Yanshan area, Hebei Province, China, where the mineral was identified in the Yanshan meteorite. Because of the extensive distribution in the Burghausen-Marktl region, lightnings to have produced the ferrosilicides can reasonably be excluded.
The first artificial production of ferrosilica by J.J. Berzelius is dated the year 1810 (Reller et al. 2000). In the early 20th century, the large-scale production of FeSi began (Reller et al. 2000), and today it is used in steel alloying.
Fe5Si3 (xifengite) has until today not been produced industrially in any notable extent, although its synthesis is possible and although its outstanding magnetic properties have become highly interesting. Only 1997, the production of xifengite (together with gupeite) from FeSi has been reported for the first time (Li et al. 1997). At the Hanyang university (Korea), research is being done on nanocrystalline Fe-Si alloys.
Only recently, traces of xifengite have been analyzed in a small drilling core from the wall of coke kiln in Norway.
Gupeiite is being synthesized since the late fifties of the 20th century. Gupeite powder can be ordered from Ospray Metals Ltd, UK. Research on gupeiite in a development stage is being done at the university of Wuhan (China) and at the university of Hanyang (Korea).
Inquiries at SKW Süddeutsche Kalkstickstoff-Werke:
Because of the possibility that ferrosilicides found in the strewnfield were deposited in larger quantities, knowingly or unwittingly, by the local industry, extensive inquiries were carried out especially at the SKW plant. Since 1945 there was a production of ferrosilicide FESI 75 composed of 20 % Fe, 75 % Si as well as 5 % Al and Ca. At present, FESI is being produced that is doped with Mg, Mn, Ba or other elements. Because of the enormous production costs, an accurate recycling is very important. Xifengite and gupeiite are completely unknown in the range of production and waste.
Titanium carbide (TiC)
In the terrestrial lithosphere, pure titanium carbide is hitherto unknown. Since the early thirties of the last century, its artificial production, however, is possible (communication Treibacher Industrie, Austria).
TiC is exceptional because of its remarkable high melting point of 3050 – 3230°C, its extreme hardness, and its resistance against corrosion and oxidation.
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.
Aluminium silicide (AlXSiY):
Like titanium carbide, pure aluminium silicides are no naturally occurring minerals, but they are industrially produced in the form of AlX=1SiY (communication UMEC, Ukraine). In the last two or three decades, properties and production technologies have intensely been studied (Ejifor & 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.
Summarizing and disregarding the FeSi and Fe3Si occurrences in fulgurites and the disputed and partly unconfirmed other rare occurrences of Fe5Si3, we note that ferrosilicides, titanium carbide and aluminium silicides are unknown as terrestrial minerals but may be produced industrially. Here, it is important to also mention the in most cases enormous technical expenditure, which explains that the large-scale industrial production did not start before the middle of the 20th century. Assumed the peculiar material from the Burghausen-Marktl area is industrial waste, then, with respect to simple FeSi, it could not have been produced before the beginning of the 20th century, with respect to TiC not before the early fifties of the last century, and with respect to Fe3Si and especially Fe5Si3 not before the end of the last century.
With regard to these time limits, an anthropogenic deposition of this extremely rare and valuable material in large quantities, over large areas and at depths of several decimeters beneath the soil is basically inexplicable. The assumption xifengite is a waste product of some completely unknown industrial activities is incompatible with the growing interest in this peculiar material against a background of possible economic importance. We furthermore remind of the fact that, with regard to the age of the trees, the xifengite deposits in the southern Bavarian crater strewnfield must be older than 120 years. At the end of the 19th century, however, human activities to produce such enormous quantities of xifengite are absolutely unknown.
Consequently, we are forced to present the following scenario: The peculiar material from the crater area originates from a modern high-tech industry that produced it in an expensive process in order to remove it, gone unnoticed by the public, to an area of at least 3,000 square kilometers, to depths of at least 20 cm below the soil, and to 1,200 m altitudes in the Alpine promontaries. We encourage the reader to assess the probability of such a scenario.
We may discuss the material to have precipitated from unknown sources, but the transport of the larger particles (several centimeters long) would have required strong winds, and it is inconceivable that this precipitation could have happened, escaped attention of the local population that well remembers the precipitation of, e.g., Sahara desert dust 25 years ago and of industrial dust from a defective filter some 40 years ago.
Finally, we asked some 50 farmers cultivating the fields and forests especially enriched in the strange material whether they used it for soil melioration or whether it is known to them at least. In unison they confirmed to have never seen those materials and, being aware of its extreme hardness, they said they would run the risk of damaging their farming machines.
At the final count we note that an anthropogenic origin of the peculiar material is beyond any reasonable argumentation. In combination with the crater assemblages for which we exclude an anthropogenic origin likewise, an extraterrestrial relation of the phenomenon is the simplest and most probable explanation.