⁴⁰Ar/³⁹Ar laser probe age determination confirms the Ries impact crater as the source of glass particles in Graupensand sediments (Grimmelfingen Formation, North Alpine Foreland Basin)

Abstract.

Mineralogical and chemical characteristics of reworked suevite material recovered from Graupensand deposits (Grimmelfingen Formation, North Alpine Foreland Basin, Middle Miocene) are identical to those recorded in Ries suevite. ⁴⁰Ar/³⁹Ar laser probe analyses of two glass particles from Graupensand components and of a glass fragment from the Ries suevite yielded ages ranging between 14.3 and 14.4 Ma, identical within analytical uncertainties. Hitherto, the Ries impact event was dated at 15 Ma (conventional K/Ar and ⁴⁰Ar/³⁹Ar methods) whereas the Graupensande have been placed into the Ottnangian (around 18.5 Ma), on the basis of mammal biostratigraphy. Small sample masses involved in laser probe technique allowed rigorous preselection of highly pure glass particles, thus reducing possible age determination errors through partly molten (or even unmolten) mineral fragments from the Variscan crystalline basement. Our results reconfirm previous statements considering the Graupensande as reworked products of the Ries impact ejecta blanket, thus placing the age of the Grimmelfingen Formation into the Badenian (of Middle Miocene) rather than into the Ottnangian (Early Miocene).