Continuous Deposits of the Ries Crater, Germany: Sedimentological and Micropaleontological Investigations of NASA Drill Core D

Abstract

NASA drill core D was taken about 25 km (2 crater radii) south of the center of the Ries crater in Southern Germany at 10^°27’02”E/48^°40’44”N. It penetrated 52.3 m of the “Bunte Breccia” continuous deposits of the Ries crater, and 2.7 m of autochthonous Tertiary “Obere Süßwassermolasse” sediments, terminating in Tertiary “Obere Meeres-molasse” sediments at a depth of 62.7 m. The Bunte Breccia consists of lithic fragments derived from the crater cavity (crystalline basement, Triassic and Jurassic sediments) and from local material outside the actual crater rim (Tertiary freshwater and marine sediments). These clasts are embedded in four different types of a fine-grained groundmass made up of sands and clays. More than 4500 clasts > 2 mm in the Bunte Breccia were assigned to their stratigraphic provenance. Clasts 2–28 mm consist predominantly of crater derived material, while clasts 28–200 mm and > 200 mm are dominated by lithologies derived from outside the crater cavity (local material). The population of crater derived clasts of all size fractions is dominated by lithic clasts from the uppermost strati-graphic levels. A comparison of grain size, heavy mineral, carbonate content, and micro-paleontological data of the groundmass with those of locally derived lithic clasts revealed that approximately 90 vol. % of the groundmass of the polymict breccia (grain size < 2 mm) consist of locally derived clastic sediments and only about 10 vol. % are crater derived. The breccia emplacement was a highly turbulent process which involved stripping of the local substrate as well as vertical and horizontal transport and intimate mixing of crater and locally derived materials. The high amount of locally derived material is predicted by the hypothesis of secondary cratering and associated mass wasting and is not compatible with a roll-and-glide mechanism of ejecta transport.