Cone of rays in opalinus clay concretions of the Steinheim Basin(Baden-Württemberg) | Strahlenkegel in opalinuston-konkretionen des Steinheimer Beckens (Baden-Württemberg)

The ~3.8 km wide Steinheim Basin (Baden-Württemberg, SW Germany), is formed in a sequence of Triassic to Upper Jurassic sedimentary rocks that support the karstified plateau of the eastern Swabian Alb. It is a well-preserved complex impact structure with a prominent central uplift. Shatter cones from the Steinheim Basin count among the most typically developed shatter cones so far known from terrestrial impact structures and were first described in 1905. In addition to the widely known, well-developed shatter cones in Upper Jurassic limestones of the crater rim domain and the central uplift, shatter cones were also noted in the Middle Jurassic "Eisensandstein" sandstones at the flanks of the central uplift. Recently, we discovered shatter cones in concretionary claystone nodules of the underlying Middle Jurassic "Opalinuston" Formation that was temporarily accessible during water catchment works at the top of the central uplift (Steinhirt). The Steinheim shatter cones are highly variable in their lithologic and structural properties, with well-defined individual or nested cones running either in one main or opposite directions, as well as cones arranged in a "sun-like" pattern radiating outward around concretionary cores within the "Opalinuston" nodules. Our observations suggest that, at least at Steinheim, shock-wave scattering and shatter-cone formation were not dominated by the general impact geometry as commonly stated, but governed by local, micro- to meso-scale target rock effects (e.g. rock inhomogeneities or local impedance). In particular, the "Opalinuston" shatter cones indicate that even comparatively soft clayey lithologies may be conductive to shock waves. © 2013 E. Schweizerbart'sche Verlagsbuchhandlung, Stuttgart, Germany.