Tuttensee (Chiemgau), Germany, southeastern Bavaria
Up to now, roughly 100 craters have been identified, measured and catalogued on the basis of topographic mapping, satellite imagery, systematic aerial photography, and time-consuming ground inspection (to be continued in the future). This documentation has established the scattering ellipse shown in Pic. 1. The size of the ellipse is given by a major axis of ca 58 km and a minor axis of ca 27 km. The strewnfield covers an area of about 1,200 km² between 47.8° to 48.4° N and 12.3° to 13.0° E. The craters are situated at altitudes ranging from 362 m to 560 m asl.
The diameter of the documented craters ranges between 3 m and several 100 m. Some of them are permanently filled with water. There is a large number of craters and depressions having diameters below 3 m. They have so far not been documented, and in many cases the origin of the smaller pits from meteorite impact may be questioned without closer inspection.
(Ernstson K., 2006).
The 400 m-diameter Lake Tuttensee in southeast Germany is the largest crater in the strewn field of meteorite craters that formed in the Holocene Chiemgau impact event possibly in the 6th or 5th century BC. The crater was excavated from a Quaternary target of predominantly moraine and fluvioglacial material and is surrounded by an 8 m-height rim wall and an extensive ejecta blanket. The up to 1 m thick ejecta layer is a polymictic breccia containing heavily fractured cobbles and boulders of Alpine lithologies and is rich in organic material like wood, charcoal, animal bones and teeth. Extremely corroded silicate and carbonate clasts in the breccia point to carbonate melting/decarbonization and/or dissolution by nitric acid. The ejecta layer has conserved an underlying fossil soil rich in organic material, too. A gravity survey reveals a zone of relatively positive anomalies around Lake Tuttensee interpreted by impact shock densification of the highly porous target rocks. Abundant, although moderate, shock metamorphism is observed to occur in clasts from the rim wall and the ejecta layer. An impact cratering process is able to explain all observed features that are completely inconsistent with a formation of Lake Tuttensee by glacial process.
Summary and the Tuttensee impact cratering process.
-- The Lake Tuttensee structure is surrounded by an originally continuous and closed rim wall.
-- The rim wall contains large quantities of strongly deformed pebbles, cobbles and boulders pointing to short-term/high-pressure load typical of impact cratering.
-- Clasts from the Tuttensee rim wall give clear evidence of shock metamorphism in the form of multiple sets of planar deformation features (PDFs) in quartz requiring shock pressures of the order of 10 GPa (100 kbar) or more.
-- The Tuttensee rim wall is surrounded by a blanket of a polymictic breccia in part similar to the Bunte breccia of the Nordlinger Ries impact structure. The Tuttensee Bunte breccia contains brecciated clasts exhibiting grit brecciation and mortar texture and the peculiarity that the clasts in spite of strongest smashing are encountered coherent in the clayey matrix. The breccia is rich in organic material like wood and charcoal, and it contains animal bones and teeth.
-- The breccia overlies a fossil soil also rich in organic material (wood, blades of excellently conserved reed, tufts of human or/and animal hair). Individual, frequently shattered but coherent clasts of competent rocks are observed to stick in the fossil soil horizon.
-- Clasts from the Bunte breccia layer show abundant although moderate shock metamorphism like PDFs in quartz, very strong kink-banding in mica and intense microtwinning in calcite.
-- Clasts of all lithologies (thus also silicate rocks like sandstones or amphibolites) from the Tuttensee Bunte breccia show an extremely deep-reaching corrosion to the point of residual rock skeletons.
-- The Tuttensee Bunte breccia is overlaid either by a fresh, probably Holocene gravel layer of completely untouched cobbles and recent soil formation, or immediately by recent soil.
-- Radiocarbon dating of organic material from the polymictic breccia (CEDAD 2006) proves that the breccia layer is younger than 2,500 BC and thus cannot have resulted from any glacial process.
Conclusions. Opposing the results of our Tuttensee research to the arguments of the critics of the proposed impact scenario, we conclude that there is ample evidence to establish Lake Tuttensee as a confirmed impact crater and that the counter-arguments based on a competing glacial origin are extremely poor only (Doppler & Geiss 2005, Schieber, written comm.) or simply lack any substance (Reimold et al. 2006).
The acceptance of lake Tuttensee as an authentic meteorite impact crater substantiates the proposed large crater strewn field (Rappengluck et al (2004) that is assumed to have formed in the Chiemgau impact event, and implies more credit for the work of those authors (Fehr et al. 2005 , Hoffmann et al. 2004 c, 2005 a, b, 2006 a, b, Rosler et al. 2005 a, b, 2006 a) who consider the numerous craterform structures in the northern part of the strewn field to be only possibly impact-related.
(The Chiemgau Impact Research Team (CIRT), 2006).