The formation of the Ries Crater, West Germany; evidence of atmospheric interactions during a larger cratering event

Early events during the formation of the Ries crater include ejection of moldavite tektites and deposition of the Bunte breccia outside of the uplifted inner crystalline ring of the crater. The restricted location of the moldavites may suggest an oblique impact at the Ries. The Bunte breccia ejecta was emplaced relatively cold and was probably a continuous ejecta blanket. Impact-melt-bearing breccias (suevite) were deposited inside the crater (crater suevite) and deposited on top of the Bunte breccia outside the crater (fallout suevite). The presence of aerodynamically shaped glass bombs in the fallout suevite indicates solidification during high-speed travel through the atmosphere, while the existence of fluid-drop chondrules and glass spherules in the fallout suevite and the upper sorted suevite within the crater indicates solidification of some of the melt in the absence of atmosphere or at low relative velocity to the atmosphere. Accretionary lapilli are also found in the upper sorted layer of the crater suevite, suggesting condensation of water vapor in a cloud over the center of the crater, similar to those produced by the rise of a nuclear fireball, or a Plinian eruption column. A thin, fine-grained layer at the base of the fallout suevite could be a lateral extension of the sorted crater suevite, or a depositional feature, similar to those seen in ignimbrite deposits. Following deposition of the suevite, formation of low-temperature (<100 degrees C) clays by hydrothermal alteration associated with cooling of the melt-bearing deposits is supported by recently obtained paleomagnetic data. Several of the features inferred for the Ries crater, such as an oblique impact, the cloud over the crater, and the ignimbrite-like depositional features may also have been present during larger events such as the Cretaceous/Tertiary boundary event.