From the Tüttensee Bunte breccia

Repeatedly, the Tüttensee ejecta layer has served for the Weekly Images, which can be tracked in the Archives of this website. Now, we present several especially beautiful individual components after having released them from the clayey matrix of this polymictic breccia. As for the term “breccia”, we note that according to current

classification a breccia is a clastic sedimentary rock composed of angular clasts in a cementing matrix. The rounded clasts encountered in the Bunte breccia seem to contradict this definition, the case, however, is to be comprehended as follows: Upon impact in the area of the today’s Tüttensee, a conglomeratic rock composed of Alpine lithologies was shattered whereby components of the fragmentation could survive as rounded cobbles to become incorporated in the breccia. Correspondingly, well-rounded clasts can be found within the Bunte breccia ejecta of the Nördlinger Ries impact structure (e.g., the so-called Buchberg cobbles).

Image 1. Chiemgau impact ejecta: Strong corrosion of a limestone boulder.

The here presented cobbles and boulders from the Tüttensee Bunte breccia stand out to have still more experienced. We explain the deep-reaching corrosion and rock dissolution right up to skeletal formation by the action of high temperatures or/and the action of strong acid dissolution.

The voluminous boulder in Image 1 is a limestone that because of its peculiar sculpture can impossibly have come from the Alps as is (note, e.g., the roughly central fine pin). Obviously, a noticeable part of the rock has been removed, and that did not happen by fracture. Instead, we suggest high temperatures in the impact process being able to melt a limestone or, like in lime works, to decarbonize it. We also consider a dissolution by nitric acid that may be produced in the impact explosion cloud, as previously discussed here on our website. Both processes heat and acid need not be mutually exclusive.

Image 2. Chiemgau-impact ejecta: strong corrosion of a sandstone cobble.

Image 2 shows a sandstone component from the Bunte breccia already, joking,  called a saurian embryo. For the formation of this “sculpture” we can refer to the same processes of destruction. If the quartz grains of the sandstone are carbonate-cemented then on action of temperature and/or acid a deep-reaching corrosion starts. On decreasing temperature and acidity rock skeletons as shown may remain.

The same carbonate disintegration applies to the boulders shown in Images 3 and 4. The pervasively corroded limestone and dolostone, resp., exhibit sharp-edged sculptured ridges representing quartz dikelets that need significantly higher melting temperatures and are by far more acid resistant

Image 3. Chiemgau impact ejecta – strongly corroded limestone/dolostone from the Tüttensee excavation.

Image 4. Corroded limestone boulder from the Tüttensee ejecta.

We would like to once more point out that the drastic rock modifications shown here are observed with clasts that are constituent part of a rock, namely the Bunte breccia. Recently, geologists of the Bavarian Geological Survey (now Landesamt für Umwelt) have explained the deep-reaching skeletal corrosion of clasts from the impact layer by sour soils, which we don’t want to comment any further.

Image 5

The clast shown in Image 5 also originates from the Tüttensee impact layer. It was encountered at some 1.5 m depth at the base of the Bunte breccia pushed-in in the fossil soil horizon underneath. The boulder is a hard, dense quartzite and exhibits distinct abrasions all around. Not any striations can be observed on the surface of the rock, and the imprints cannot possibly have originated from glacial abrasion – in order to preclude respective objections by deniers of the Chiemgau impact. The directional imprints are smooth suggesting a plastic, if only short, behavior (like a pulp) of the quartzite material. Within the frame of our model that defines the Bunte breccia to be ejecta from the Tüttensee crater, the boulder underwent the excavation of the growing crater initiated by extreme shock pressures following the impact into the target of Alpine material. During this high-pressure phase, the boulder became plastically deformed by neighboring clasts was ejected and landed on the (at present fossil) soil at the base of the developing Bunte breccia ejecta horizon.

Bones and teeth from the impact layer (ejecta, Bunte breccia) at Lake Tüttensee (Chiemgau impact event).

In numerous excavation pits around Lake Tüttensee, a polymictic breccia layer has been encountered to be probably impact ejecta from the Tüttensee crater  ( http://chiemgau-impakt.de/ATT00007.pdf ). In a clayey matrix, the breccia contains multicolored rock fragments exhibiting shock-metamorphic effects (http://chiemgau-impakt.de/bdw3.pdf ), and is rich in organic material like wood and charcoal. Moreover, bones, bone fragments and teeth were found in the breccia from four excavation pits. Meantime, for two bones and two teeth a more accurate determination has been performed by Dr. M. Mäuser, director of the Naturkundemuseum (Museum of Natural History) in Bamberg.

Bone 1 (excavation 11; image 1) is a cattle’s second phalange (toe bone). Bone 2 (excavation pit 11, image 2) belongs to the left astragalus (talus bone of the ankle) of a deer, probably a red deer (possibly a fallow deer). Tooth 1 (excavation 25, image 3) is an upper-jaw molar of a goatish (Caprinae). Caprinae include sheep and chamois but also goats and the ibex (capricorn). The size of the molar speaks in favor of a sheep or an ibex. Tooth 2 (excavation 25, image 4) probably is a Caprinae milk premolar.

It is left to assumptions whether the animals perished on impact or whether the skeletons existed already and were smashed and intermixed in the impact breccia. Sheep and cattle may have been domestic animals

Shock effects (shock metamorphism) in rocks from the impact layer (ejecta, Bunte Breccia) at Lake Tüttensee

Quartz grains in mica gneiss from the Chiemgau impact Tüttensee ejecta layer – full of planar deformation features (PDFs).

Two sets of crossing kink bands in mica. Shock effect from the Chiemgau impact Tüttensee ejecta layer.

Numerous excavation pits have been performed in the surroundings of Lake Tüttensee that is proposed to have formed as a meteorite crater in the Chiemgau impact event. The excavation pits have revealed the existence of a more or less continuous ejecta blanket around the lake, and the peculiarities of the layer have already been described:http://www.chiemgau-impakt.de/ATT00007.pdfhttp://www.chiemgau-impakt.de/Seiten%201-10.pdf (part 1) and http://www.chiemgau-impakt.de/Seiten%2011-26.pdf (part 2). Now, samples (from crystalline and sedimentary Alpine cobbles) were selectively taken from this ejecta layer in order to systematically analyze them for shock effects, for the time being under the optical microscope only. The study of thin sections from 31 rock samples taken from 7 different excavations establishes a rich inventory of mineral deformations that with reasonable certainty or with great likeliness have originated from shock load. The photomicrographs (crossed polarizers) show planar deformation features (PDFs) in quartz from a mica quartzite (upper) and two sets of extremely closely spaced kink bands in biotite from a gneiss (lower). A more comprehensive report including 17 photomicrographs (in German with English abstract and figure captions) may be clicked HERE.

 

The Tüttensee “Bunte Breccia”

 Apart from the suevite the ejecta blanket of the Ries impact structure (Germany) is composed of the so-called Bunte (= multicolored) breccia (clast size < 25 m) and allochthonous megablocks (coherent clasts  > 25 m). The distinction has been made for mapping reasons but otherwise is arbitrary. The term “Bunte” refers to the many colors (black Jurassic claystones, white Malmian limestones, purple and greenish Keuper sandstones and claystones, various crystalline rocks) that on intensive mixture of the components cause the multicolored appearance of the breccia. New excavation pits at Lake Tüttensee (Chiemgau impact event) have encountered a “Bunte breccia” (the image shown here) very similar to its namesake of the Ries impact crater. The probable similar formation of the breccias (as impact ejecta) is especially evident when the Tüttensee breccia is compared with the small-grained clayey Ries breccia. A preliminary short report (in German with English abstract and figure captions) on the new excavation results may be clicked HERE.

On the Lake Tüttensee discussion:

Critics of the impact origin for the Lake Tüttensee crater (e.g., Doppler & Geiß 2005) argue that the strong deformations exhibited by the cobbles and boulders from the rim wall are the result of tectonic processes in the Alps and that the tectonically deformed clasts were transported and deposited in the region of the strewnfield. The impact advocates counter that such deformed cobbles and boulders would not have survived any transport over a distance of more than 50 m. Instead, they point to the typical features of a high-pressure/short-term process of deformation and to the fact that gravel pits outside the Lake Tüttensee area are void of these characteristically deformed rocks.

We have received a comment on this controversy by F. Claudin, geologist from Barcelona (Spain):

“We can compare the deformations observed in the Lake Tüttensee rim wall with the supposed deformations that must be present in other glacial moraines. In the Pyrenees, near Les Bordes de Llestui at the Clot and Malmarrui torrents, we can observe a glaciolacustrine-glacial complex. Neither in the clasts of the subglacial till nor in those of the supraglacial till, deformations as described for Lake Tüttensee can be seen. Only striae on the clasts are observed. The same observations can be made in the moraine deposits near Vilaller (Verge de Riupedrós, Sant Mamés, Sant Antoni), near the hospital of Vielha, or in the “Barranco de la runada” (near Senet). Glaciers may produce enough pressure to ensure striae deformations or fragmentation of clasts, but they are unable to produce short-term deformations under high confining pressure as seen in the photos of the Lake Tüttensee clasts. Typical aspects of the Pyrenees glacial deposits are shown down below the text.

The above-mentioned deposits have in more detail been described by

  • Bordonau, J (2000): Itinerario 3 (Vilaller, Hospital de Vielha, Valle de Llauset y Noguera Ribargozana), in Geopirineos, Monografias de Enseñanza de las Ciencias de la Tierra, Serie Itinerarios, nº 2.
  • Bordonau, J.; Pous, J., Queralt, P., Vilaplana, J.M. (1989) : Geometria y depósitos de las cubetas glaciolacustres del Pirineo. Estudios Geológicos, 45, 1-2: 71-79.
  • Bordonau, J., Vilaplana, J.M., Fontugne, M. (1993) : The glaciolacustrine complex of Llestui (Central South Pyrenees) : a key-locality for the chronology of the last glacial cycle in the Pyrenees. C.R. Acad. Sci. Paris, 316, série II: 807-813.
  • Vilaplana, J.M., Bordonau, J. (1989): Dynamique sédimentaire lacustre de marge glaciaire : le paléolac de Llestui (Noguera Ribagorçana, Versant Sud des Pyrénées), Bull. A.F.E.Q., 1989-4 : 219-224.”