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

Abstract

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°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.

Post‐impact alteration of surficial suevites in Ries crater, Germany: Hydrothermal modification or weathering processes?

“…The outer zone of the structure is overlain by different types of proximal impactites (Engelhardt 1990): (1) Bunte Breccia; (2) polymict crystalline breccias; (3) surficial suevites; and (4) coherent impact melt rocks. Surficial suevites, up to 25-30 m thick can be found in a distance of 22 km from the crater centre (Newsom et al 1990;Engelhardt 1990).…”

“…Newsom et al 1986;Osinski et al 2004;Osinski 2005). It has been generally accepted that these clays formed by postimpact hydrothermal alteration of impact-generated glasses and/or finely comminuted crystalline basement material (Engelhardt 1972;Stähle 1972;Engelhardt and Graup 1984; Newsom et al 1986Newsom et al , 1990. The same was assumed for the origin of calcite in the Ries surficial suevites.…”

Supercomputer modeling of volcanic eruption dynamics

“…Field evidence suggests that ejecta emplacement from large events is strongly influenced by density current processes (Chao, 1976;Chao et al, 1978;Horz et al, 1983). For example, ejecta deposits around the Xes crater (Germany) share many common characteristics of pyroclastic flow deposits (Newsom et al, 1990). In addition to the lack of modeling studies of ejecta emplacement by flow, it appears that most field studies of large fragmental ejecta deposits were carried out 2-3 decades ago.…”

Magnetostratigraphy of the Cretaceous/Tertiary boundary and early Paleocene sedimentary sequence from the Chicxulub Impact Crater

“…2(b)) and the contact with the Tertiary carbonates is at 222.2 m deep. The lower breccias (carbonate-rich or bunte type, also described in the Ries crater, Stöffler, 1977;Hörz et al, 1983;Von Engelhardt, 1990;Newsom et al, 1990) in UNAM-7 lies at 348.4 m deep, with a thickness of 180 m (Fig. 2(b)).…”

“…Three boreholes sampled the impact lithologies (UNAM-5, UNAM-6 and UNAM-7), which are here used for the paleomagnetic and rock magnetic investigations. Two units are documented as impact lithologies, an upper breccia sequence (comparable to the suevitic and bunte breccias documented in the Ries crater, Von Engelhardt, 1990;Newsom et al, 1990). In UNAM-5 ( Fig.…”