A high-precision 40Ar/39Ar age for the Nördlinger Ries impact crater, Germany, and implications for the accurate dating of terrestrial impact events

Martin Schmieder, Trudi Kennedy, Fred Jourdan, Elmar Buchner, Wolf Uwe Reimold

Geochimica et Cosmochimica Acta
In Press, Accepted Manuscript, Available online 28 September 2017

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“40Ar/39Ar dating of specimens of moldavite, the formation of which is linked to the Ries impact in southern Germany, with a latest-generation ARGUS VI multi-collector mass spectrometer yielded three fully concordant plateau ages with a weighted mean age of 14.808 ± 0.021 Ma (± 0.038 Ma including all external uncertainties; 2σ; MSWD = 0.40, P = 0.67). This new best-estimate age for the Nördlinger Ries is in general agreement with previous 40Ar/39Ar results for moldavites, but constitutes a significantly improved precision with respect to the formation age of the distal Ries-produced tektites. Separates of impact glass from proximal Ries ejecta (suevite glass from three different surface outcrops) and partially melted feldspar particles from impact melt rock of the SUBO 18 Enkingen drill core failed to produce meaningful ages. These glasses show evidence for excess 40Ar introduction, which may have been incurred during interaction with hydrothermal fluids. Only partially reset 40Ar/39Ar could be determined for the feldspathic melt separates from the Enkingen core. The new 40Ar/39Ar results for the Ries impact structure constrain the duration of crater cooling, during the prevailing hydrothermal activity, to locally at least ∼60 kyr. With respect to the dating of terrestrial impact events, this paper briefly discusses a number of potential issues and effects that may be the cause for seemingly precise, but on a kyr-scale inaccurate, impact ages.”

Comment on “A high-precision 40Ar/39Ar age for the Nördlinger Ries impact crater, Germany, and implications for the accurate dating of terrestrial impact events” by Schmieder et al

(Geochimica et Cosmochimica Acta 220 (2018) 146-157

Alexander Rocholl, , Madelaine Böhme, H. Albert Gilg, Jean Pohl, Urs Schaltegger, Jan Wijbrans

Geochimica et Cosmochimica Acta
In Press, Accepted Manuscript, Available online 23 May 2018

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“Schmieder et al. (2018) suggest an impact age for the Ries crater in Southern Germany that is at odds with paleomagnetic systematics and thus geologically impossible, even within its external 2-sigma error. Paleomagnetic systematics allow for only two alternative impact ages that are both tightly constrained by orbital tuning. The relative differences to the Schmieder et al. (2018) age amount to 60 and 200 ka, respectively. Such time intervals are, however, highly significant with respect to the timing of climatic and environmental signals recorded in the Middle Miocene molasses sediments.”