IMPACT CRITERIA for the Chiemgau impact event and meteorite crater strewn field

When is a meteorite crater a meteorite crater?

macha
Image courtesy Google Earth

There are people believing this to be the case when a crater under discussion is accepted by a committee to be included in an official database like the Earth impact database of the New Brunswick university in Canada. There are other people being convinced a meteorite crater is a meteorite crater when there is clear scientific evidence for such an origin and who doubt that acommittee is qualified to decide on results of scientific research. This is the reason why different impact databases are revealing quite different numbers of established terrestrial meteorite craters (impact structures). Disregarding this fine distinction, there are quite a few criteria (e.g., morphological, geological, geophysical, mineralogic-petrographical, geochemical) as a base for the evaluation of a meteorite crater, and some of them are regarded as in proof of impact. In other words and to say it simpler: Having mapped basaltic rocks in the field, one will be convinced there is volcanism, and having mapped rocks displaying shock-metamorphic effects, one will be convinced there is a nearby impact site.

 

Impact criteria – compelling and less compelling – as compiled by Norton, O.R. (2002): The Cambridge Encyclopedia of Meteorites. – Cambridge University Press, pp. 291-299, and French, B.M. (1998): Traces of Catastrophe. A Handbook of Shock-Metamorphic Effects in Terrestrial Meteorite Impact Structures. Lunar and Planetary Institute, pp. 97-99 (download as a pdf file here), and others, are:

1. Morphology

Circular structures in general; depressions with raised rims or/and central uplifts; multi-ring structures: less meaningful because many other geological structures may show circular symmetries, and true impact structures may strongly deviate from such a shape.

2. Geophysical anomalies

Many impact structures  are closely related with characteristic gravity and magnetic anomalies, but reversely, measured anomalies in general don’t allow to deduce an impact event. Seismic reflection surveys may reveal the characteristic layering of buried impact structures.

3. Geologic evidence

Regularly found in and around impact structures: strong deformations, folding, faulting, fracturing; polymictic and monomictic breccias and dike breccias, megabreccias; high-pressure/short-term deformations of clasts in a soft matrix; rocks looking like volcanic or magmatic rocks; layers of exotic material.

4. High-temperature evidence

Melt rocks, natural glasses, breccias with melt rock fragments and glasses

5. High-pressure evidence – shock metamorphism

Planar deformation features (PDFs) in quartz, feldspar and other minerals, planar fractures (PFs) in quartz, diaplectic quartz and feldspar crystals, diaplectic glass; multiple sets of intense kink banding in mica, multiple sets of microtwinning in calcite. Kink banding in mica and PFs in quartz are also known from very strong tectonic deformation.

6. Shatter cones

 

Steinheim shatter cone Sudbury shatter cone

Shatter cones, here in limestone from the Steinheim Basin impact structure and in an quartz-arenite from the Sudbury impact structure, are characteristic shock-induced conical fracture planes in all types of hard rocks. Shatter-cone fracture planes show typical “horse-tail” fracture markings.

7. Special evidence

Occurrence of micro and/or nano-diamonds; accretionary lapilli, various kinds of spherules. – Spherules may be anthropogenic.

8. Meteorite fragments

In larger meteorite craters in most cases completely absent because of vaporization of the projectile upon impact. Microscopic geochemical signature of the impactor is possible. Meteorite fragments are in general found in and around young small craters. In the Macha crater strewn field (Yacutia), however, the largest particles assumed to be meteoritic are 1.2 mm-sized only.

9. Direct observation (historical record)

Apart from the observation of meteorite showers (e.g., Sikhote Alin) impacts to have formed a meteorite crater have not been passed on. Geomyths may be interpreted as document of observed impacts.

 

According to current understanding, points 5. shock metamorphism, 6. shatter cones, 8. meteorite fragments, and 9. direct observation are each one by itself accepted as a confirmation of an impact event.

The criteria 1. – 9. applied to
the Chiemgau crater strewn field

1. Morphology – yes

Numerous circularly shaped craters with raised rims

rimmed crater no. 004

The 11 m-diameter crater no. 004 in the Chiemgau impact strewn field. Note the distinct raised rim.

2. Geophysical anomalies – yes

– Gravity negative anomaly of the Lake Tüttensee crater surrounded by a conspicuous zone of relatively positive anomalies

– A distinct horizon of strongly enhanced soil magnetic susceptibility in the strewn field.

Tüttensee gravity anomaly

Gravity survey (Bouguer residual anomaly) of the Lake Tüttensee cratersoil magnetic susceptibility

Anomalous soil magnetic susceptibility profile near the Lake Tüttensee crater

3. Geologic evidence – yes, multiple

Tüttensee breccia

Multicolored polymictic impact breccia from the Lake Tüttensee crater ejecta layer.coherent clasts

Highly fractured however coherent carbonate and silicate clasts from the Lake Tüttensee crater ejecta layer: evidence of high-pressure/short-term deformation.squeezed cobble

Highly fractured and squeezed however coherent quartzite cobble from the Lake Tüttensee crater rim wall: evidence of high-pressure/short-term deformationStöttham exotic layer

The Stöttham exotic impact layer (arrow)

4. High-temperature evidence – yes

Tüttensee impact melt rock

Pumice-like impact melt rock from the Lake Tüttensee crater.welded cobbles

Two glass-coated cobbles welded by cindery glass from crater no. 004melt rock

Sawed surface of a silicate cobble from crater no. 004. Extremely vesicular and fissured rock where, except for quartz, all minerals are more or less transformed to glass giving the dark color to the rock. The widely open fissures may result from shock spallation.

5. Shock metamorphism – yes

PDFs, Tüttensee PDFs, Popigai

“Toasted” quartz with multiple sets of PDFs in quartz; photomicrograph, crossed polarizers, quartzite clast from the Lake Tüttensee crater rim wall. “Toasted” quartz is a common feature in shocked grains and is explained by tiny fluid inclusions. – For comparison to the right: toasted quartz with PDFs from the Popigai impact structure, Russia

.PDFs, crater 004

Two sets of planar deformation features (PDFs) in quartz; photomicrograph, crossed polarizers, 1.5 mm field width; quartzite clast from the Chiemgau impact 004 crater. The slightly curved PDFs must not irritate: Although there are authors, e.g. Reimold & Koeberl (2000), who claim bent PDFs are of non-impact origin, the example of the Popigai bent PDFs in the above image and many other examples from various impact structures show the verdict of Reimold & Koeberl is not tenable

.shocked plagioclase

Twin lamellae and multiple sets of PDFs in feldspar. Photomicrograph, crossed polarizers; impact melt rock from the Lake Tüttensee crater.

6. Shatter cones – yes

shatter cone Tüttensee

Two shatter cones in counter position in a fine-grained sandstone from the Lake Tüttensee crater.

7. Special evidence  – yes

Nanodiamonds – yes  

Article

Rösler W., Hoffmann V., Raeymaekers, B., Schryvers, D. and Popp, J. (2005) Diamonds in carbon spherules –evidence for a cosmic impact? (http://www.lpi.usra.edu/meetings/metsoc2005/pdf/5114.pdf; 7.5.2006).

Accretionary lapilli – yes

Lapillo Chiemgau Lapillo Chiemgau2

Accretionary lapilli (to the right with a fragmental metallic core) from the Chiemgau impact strewn field. Lapilli diameters about 4 – 5 mm. Accretionary lapilli are normally known from volcanism but have been shown to occur also in impact structures where they have been formed in the impact explosion cloud.

Spherules – yes

glass spherule

2 mm-diameter broken vesicular glass spherule; Stöttham impact layer.carbon spherules

Carbon spherules from various sites in the Chiemgau impact strewn field. Also see Yang, Z.Q. et al., 2008: TEM and Raman characterization of diamond micro- and nanostructures in carbon spherules from upper soils. – Diamond and Related Materials 17/6: 937-943.

8. Meteorite fragments – probably yes

Exotic material like iron silicides gupeiite and xifengite, carbides like titanium carbide and silicon carbide moissanite strongly point to extraterrestrial origin.

SEM image of moissanite crystals in iron silicide matrix. Sample from the Chiemgau meteorite crater strewn field.

gupeiite suessite

Comparison of analyses of Chiemgau gupeiite and meteoritic suessite

9. Direct observation (historical record) – possibly yes

Rubens_Fall_of_Phaeton

Peter Paul Rubens: The fall of Phaeton, National Gallery of Art, Washington.

 

Article

Rappenglück, B. and Rappenglück, M., 2006: Does the myth of Phaethon reflect an impact? – Revising the fall of Phaethon and considering a possible relation to the Chiemgau Impact. – Mediterranean Archaeology and Archaeometry 6/3 (2006), 101-109.

The following contributions (oral, poster) of the Chiemgau Impact Research Team (CIRT) were presented:

 

Michael A. Rappenglück & Kord Ernstson: The Chiemgau crater strewn field (Southeast Bavaria, Germany): Evidence of a Holocene large impact event

International Conference “100 years since Tunguska phenomenon: Past, present and future”. – June 26 – 28, 2008, Moscow (Russia)

Kord Ernstson & Michael A. Rappenglück: The Chiemgau crater strewn field: Evidence of a Holocene large impact event in Southeast Bavaria, Germany

International Scientific Conference “100 years of the Tunguska event”. – June 30 – July 6, 2008, Krasnoyarsk (Russia)

Barbara Rappenglück & Michael A. Rappenglück (for the Chiemgau Impact Research Team): The fall of Phaethon:  Is this a geomyth reflecting an impact in Bavaria during the Celtic period?

33rd International Geological Congress. Session: Myth and Geology. – August 5 – 14, 2008, Oslo (Norway)

 

The following contributions (oral, poster) of the Chiemgau Impact Research Team (CIRT) submitted and has been accepted for presentation:

Chiemgau Impact Research Team (CIRT): The Chiemgau Impact: An extraordinary case-study for the question of Holocene impacts and their cultural implications

SEAC (Société Européenne pour l’astronomie dans la culture) meeting (XVIth). – September 8-12, 2008, Granada (Spain)

Article: Myth of Phaethon

Barbara and Michael Rappenglück (2006): Does the myth of Phaethon reflect an impact? – Revising the fall of Phaethon and considering a possible relation to the Chiemgau Impact. – Mediterranean Archaeology and Archaeometry, Proceedings of the International Conference on Archaeoastronomy, SEAC 14th 2006, “Ancient watching of cosmic space and observation of astronomical phenomena”, Vol. 6, No. 3 (2006), 101-109.

Abstract. – In Greek mythology there exists one story that has repeatedly been interpreted to describe the fall of a celestial body: the story of Phaethon, who undertakes a disastrous drive with the sun-chariot of his father Helios. First, the article presents the arguments given by ancient authors for interpreting this story as the reflection of a natural phenomenon. Then details given in the old descriptions of Phaethon’s fall are compared with nowadays knowledge of impact phenomena. Furthermore the texts are examined for clues to the time and the location of the hypothesised impact. These considerations substantiate the suggestion that the myth of Phaethon reflects a concrete strike of a meteorite, the so-called Chiemgau Impact. That impact struck the south-east of Bavaria/Germany at some time during the Celtic period and left an extended crater-strewnfield of about 100 craters. A conspicuous intersection between the tradition of the Phaethon-story and the up to now known time-frame for the Chiemgau Impact gives new clues for dating the Chiemgau Impact to the time between 600 and 428 BC.

Articles on Lake Tüttensee proposed meteorite impact crater on www.chiemgau-impact.com

The Holocene Tüttensee meteorite impact crater in southeast Germany

Abstract | Article

Shock effects (shock metamorphism) in rocks from the impact layer at Lake Tüttensee (ejecta, Bunte breccia). In German with English abstract and Figure captions.   pdf

The Tüttensee Bunte breccia. In German with English abstract and Figure captions.   pdf

New evidence of an impact origin for Lake Tüttensee (Chiemgau impact event): An impact layer in near Lake test pits. In German with English abstract and Figure captions.  pdf Part 1      pdf  Part 2

A gravity survey near Grabenstätt: Impact hypothesis for the Tüttensee crater (Chiemgau impact event) strengthened. In German with English abstract and Figure captions.  article

Regmaglyptic cobbles from Lake Chiemsee: Evidence of meteorite impact-induced ablation features

Well known among people around Lake Chiemsee, peculiarly sculptured limestone cobbles (Figs. 1 – 4) found at the shore and offshore at the lake bottom attracted special attention when Lake Chiemsee got into the focus of the meteorite strewn field impact research. Although most people are considering the groove cobbles no more than a freak of nature, the work of organisms, especially of mussels has always been suggested.

Fig. 1. Typical conically shaped groove stone from the Lake Chiemsee shore – originally a Quaternary fluvio-glacial limestone cobble. Photo courtesy of H. Eberle.

Fig. 2. Various aspects of groove cobbles from Lake Chiemsee. Photos courtesy of H. Eberle and T. Schwaier.

Fig. 3. Big grooved limestone block from the Lake Chiemsee shore. Note the distinctly parallel, knife-edge ridges between the grooves (in the same orientation found all around the block) hardly compatible with the work of organisms.

Fig. 4. Pyramidally shaped groove stone. Note the geometrically orientated groves. Photo courtesy of H. Eberle.An impact-related formation came to the fore comparing the typical groove features with ablation features (regmaglypts) that meteorites may acquire when exposed to frictional heat on their passage through the Earth’s atmosphere. Moreover, an amazing similarity between the groove cobbles and regmaglyptic boulders from the Puerto Mínguez impact ejecta of the Spanish large Rubielos de la Cérida impact structure (Figs. 5, 6; also see the respective article: http://www.impact-structures.com/article%20text.pdf) exists. When we suggested that the cobble grooves were formed in the Chiemgau impact event as ablation features having developed by decarbonization and carbonate melting upon ejection and heating in a jet of super-heated volatiles, immediate reactions of local geologists ensued.

As later adopted by the local geologist Dr. Robert Darga, Dr. Robert Huber from the university of Bremen rejected the impact model of groove formation and instead seized again on the old explanation of the work of organisms, especially of bacteria and algae. He underlined his belief claiming that the same groove cobbles are a common feature in many lakes in the Alpine Forelands, Lake Constance included – see his blog contribution http://stratigraphynet.blogspot.com/2008_06_01_archive.html. We encourage you to read his remarks and to especially enlarge the photos in Dr. Huber’s blog comparing them with our photos from Figs. 1-4. It’s like comparing apples to oranges. And until today, Dr. Robert Huber fails to present groove cobbles like those shown in our figures from lakes other than Lake Chiemsee.

Of course, biogenic rock sculpture produced by organisms like, e.g., endolithic bacteria or piddocks is a well-known process, but once more, we must not compare apples to oranges, and obviously Dr. Huber has come to a deadlock.

There are very simple macroscopic observations proving the inorganic formation of the grooves. As shown in many of our photos, the grooved cobbles frequently exhibit distinct conical and pyramidal shape while the grooves, in most cases showing extremely sharp, knife-like edges, are geometrically related with the cones and pyramids. It’s exactly the same observation we are making with the regmaglyptic stones from the Rubielos de la Cérida impact ejecta (Figs. 5, 6). If the grooves were produced by organisms, these bacteria, algae and mussels must have had extraordinary intelligence, organization and communication capabilities to geometrically sculpture a large block as seen, e.g., in Fig. 3. Moreover, the identically grooved stones from the Spanish impact ejecta have never seen a lake, as can be read in more detail in the article referred to above.

In summary, a biogenic origin of the unmistakable, distinctly grooved cobbles from Lake Chiemsee has not any reasonable base. Instead, all features, the frequently conical and pyramidal orientations included, point to an erosion process initiating ablation due to decarbonization and melting.

Meanwhile, new finds of quite a few grooved cobbles (among them also grooved sandstones) substantiate the impact-related formation and, moreover, give highlighting insight into the unique process of deposition of the cobbles after having acquired their sculpture. We will report soon.

Fig. 5. Big grooved limestone clast embedded in the diamictic impact ejecta of the Rubielos de la Cérida impact structure in Spain. Note the pyramidal shape and the grooves diverging from the top of the pyramid.

Fig. 6. Regmaglyptic conically shaped limestone clast from the Puerto Mínguez ejecta of the Spanish large Rubielos de la Cérida impact structure. The clast that never saw any biogenic activities in a lake has remarkable similarity with the Lake Chiemsee groove stones.

An impact layer at Chieming-Stöttham


More than 30 excavation pits in the environs of Lake Tüttensee have encountered an impact layer that is suggested to be ejecta from the formation of Lake Tüttensee as a meteorite crater in the Chiemgau impact event [http://www.chiemgauimpact. com/artikel2.pdf]. Now, a very similar situation has been found with archeological excavations in the border area of Lake Chiemsee near Chieming-Stöttham. Undisturbed glacial drift with a fossil soil is overlain by a layer that must be interpreted as the result of a catastrophic event in the recent geological time. Like at Lake Tüttensee, the layer is composed of a multicolored mixture of deeply corroded rock fragments in a clayey matrix. Organic material like charcoal, teeth and bones as well as archeological objects are intermixed. This “catastrophe” horizon is overlain by a younger undisturbed occupation layer (Roman) and recent soil formation. Similar to Lake Tüttensee, the archeological finds and the geologic-archeological stratigraphy date the catastrophic event to have happened many thousand years after the end of the glacial period.

Fig. 1. The excavation pit and layering at Chieming-Stöttham exposing the “catastrophe”horizon (light, roughly in the middle of the image)

Fig. 2. Close-up of the impact catastrophe layer.

Because of the great distance to Lake Tüttensee, a formation of the Stöttham “catastrophe” horizon as ejecta from that crater can be excluded. Instead we propose another nearby impact, and there is some evidence that an impact into Lake Chiemsee was involved at least

Fig. 3. Another exposure in the area of the archeological excavation. Here, the roughly 2 m deep pit cutting through the “catastrophe” layer has not encountered the autochthonous ground moraine. In comparison with Fig. 1 the exposure shows the fluctuation of thickness and composition of the layer. Many of the dark components are intermixed charcoal.

A new geophysical campaign at Lake Tüttensee crater

Geophysical measurements play an important role in the research on meteorite craters (impact structures). The unusual pressures, temperatures and mass movements closely related to meteorite impact result in partly drastic changes of the physical properties of the target rocks. These changes correspond to characteristic geophysical anomalies, and many a crater buried deeply in the Earth’s crust have first been discovered by geophysical soundings.

In an earlier geophysical gravity survey at Lake Tüttensee, a peculiar ring of positive gravity anomalies was measured to have possibly resulted from a shock densification [article]. Now, we conducted a new campaign of geophysical measurements in the zone of impact ejecta that have been encountered in more than 30 excavation pits around Lake Tüttensee.

Fig. 1. Klaus Ebinger (to the left), owner of the EBINGER company, during the Tüttensee crater geophysical campaign.

 

 Fig. 2. Pulse electromagnetic (TEM) survey at Lake Tüttensee using the EBINGER UPEX 740 M Large Twin Loop equipment.

 

The geophysical survey comprised pulse (TEM) and frequency (FEM) electromagnetic soundings, and the primary objective was an area-wide investigation of the impact-related geological underground und its peculiarities so far only known from selective excavations around Lake Tüttensee.

The campaign was generously supported by the EBINGER company (Cologne) [Ebinger Prüf- und Ortungstechnik GmbH], a worldwide operating producer of high-tech search and detection equipment (Fig. 1). The EBINGER products are applied to various fields like unexploded ordnance (UXO) disposal both by sea and by land, safety engineering, environmental geophysics, industry and research, and in this particular case the EBINGER company in a three-day campaign (Fig. 2) supported at no charge the research of the Chiemgau Impact Research Team (CIRT).

From that campaign, Fig. 3 shows an example of processed pulse-electromagnetic (TEM) data sampled on an area of 150 x 100 m². The map exhibits conspicuous resistivity contours that, however, need further interpretation.

Fig. 3. Pulse-electromagnetic (TEM) resistivity mapping at Lake Tüttensee crater using EBINGER Large Loop equipment.

A peculiar prehistoric artifact in the Tüttensee impact ejecta (“Bunte Breccia”; Chiemgau Holocene impact event)

In the environs of the Tüttensee crater (Chiemgau Holocene impact event), a new campaign of geological and geophysical investigations has been performed also including new excavation pits (now totaling 37).

In the excavation pits, the stratigraphy well known from earlier excavations [http://www.chiemgau-impact.com/artikel2.pdf] has again been encountered (top down):

recent soil

layer of Tüttensee impact ejecta (“Bunte Breccia”)

fossil soil horizon

autochthonous ground (lacustrine clay)

The ejecta layer exhibits the well-known composition of crushed, yet abundantly coherent clasts and the frequently strongly corroded skeletal carbonate and silicate cobbles and boulders in a clayey matrix (Fig. 1).

Fig. 1. Typical, strongly wrecked cobbles from the Tüttensee impact layer in excavation pit No. 35. Together with these cobbles the quartzite artifact (Fig. 2) was recovered. As noted in previous articles, the sharp-edged fracturing can only have originated from impact deformation, and the extreme corrosion of the clasts can be explained by impact nitric-acid dissolution and/or carbonate decarbonization/melting.

 

As a peculiarity in the Bunte breccia ejecta layer of excavation pit No. 35, about 900 m east of Lake Tüttensee, a broken white quartzite boulder was recovered that

has clearly been elaborated by man (Figs. 2, 3). A funnel-shaped “picked” dent passes over into a drilled hole that breaks off midway through the boulder. A central rise at the base of the hole (Fig. 3) proves it was drilled with a hollow rod, possibly a hollow bone.

Fig. 2. The drilled quartzite boulder recovered from the Tüttensee impact ejecta layer.

 

Fig. 3. Close-up of the bore. The central rise at the base proves the use of a hollow rod, possibly a hollow bone.

 

It is well known that artifacts were produced from impactites and impact glasses, resp., (e.g., Elgygytgin impact structure [Gurov & Gozhic, 2006, Impact Cratering in the Earth’s History, in Russian], Libyan Desert glass, tektites). Here, in the Tüttensee case, obviously the first find of an artifact in an impact rock is documented.

The full article on this find can be clicked here.