Computer Science
Scientific paper
Nov 1994
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1994gecoa..58.5083s&link_type=abstract
Geochimica et Cosmochimica Acta, vol. 58, Issue 22, pp.5083-5090
Computer Science
6
Scientific paper
The nature of the impactor for the Nördlinger Ries has, so far, remained elusive. Suggestions have been made for a chondritic or an aubritic proctile but all studies had difficulties to establish beyond doubt the meteoritic parental material. The majority of the Ries samples so far analyzed derived from the present surface, which may have lead to some bias. Therefore, we analyzed fifty-five drill core samples from the research borehole Nördlingen 1973 to characterize the indigenous Ir concentrations of the target rocks and to search for any enrichments of Pt group elements in the suevite and the so-called Graded Unit. We found that ultramafic rocks in the crystalline basement at a depth of 826 m--far below the current crater bottom--contain up to 0.5 ng/g Ir, the highest concentrations ever measured in the target rocks. These rocks comprise about 8% of the crystalline basement, and thus, form a substantial indigenous source of Pt group elements. Taking this into account, one has to consider Ir concentrations of up to about 0.060 ng/g as indigenous, although the median concentration is 0.013 ng/g, close to earlier estimates. Our results show that there is no indication of unequivocal extraterrestrial contamination in the cored materials of the crater ejecta. It is surprising that this also holds for the current crater bottom and the Graded Unit, which have previously been suspected to contain meteoritic contamination. It seems that a chondritic projectile can be ruled out, but a clear geochemical association of any of the known meteorite types with the Ries bolide is not possible.
Pernicka Ernst
Schmidt Gerhard
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