Melt-bearing clastic deposits (suevites) at impact craters have traditionally been regarded as plume fallout deposits. We present new field, textural, and chemical evidence that the subcircular blanket of suevite at the type locality, the Ries impact crater, Germany, was emplaced by a radial, granular fluid-based particulate density current, analogous to those that form ignimbrites of volcanic origin. Newly mapped chemical zoning patterns in the blanket record the response of the current to changing topography during the earliest modification stages of impact crater formation. The eastern sector of the suevite blanket has a different high field strength element composition than the western sector. The crater-fill facies also shows vertical gradational zoning that records changes in the composition of suevite deposited with time. The lateral zoning is best explained by radial outflow of the density currents, but changes in the crater topography caused the flow directions of the melt-bearing density current to change (return flow). The later convergence of flow paths allowed more thorough mixing in the crater, and is recorded by the more uniform composition of the later deposited upper parts of the crater-fill suevite. Emplacement by density currents is indicated by (1) topography-influenced (ponded) thickness variations of the suevite sheet, (2) very poor sorting, (3) matrix support, (4) massive nature, (5) subtle coarse-tail grading, (6) abundant elutriation pipes, (7) abundance of broken and whole matrix-supported concentric-laminated accretionary lapilli in uppermost parts, and (8) an inverse-graded basal layer with low-angle cross-stratification. These are classic features of deposits from granular fluid-based density currents, such as ignimbrites deposited by pyroclastic density currents at explosive caldera volcanoes, but differ markedly from fallout deposits worldwide.

Carbonate carbon‐isotope values from the Permian–Triassic (P–T) boundary section at Seis/Siusi (Southern Alps, Italy) show a trend similar to that in numerous other P–T boundary sections worldwide. Values decrease from 3.2 ‰ (V‐PDB) in the upper Bellerophon Limestone Formation (Late Permian) to a minimum of –1.7 ‰ in the lower Mazzin Member. This minimum may represent the P–T boundary. The overall declining carbon‐isotope trend is interrupted by a ca. 1 ‰ positive excursion in the higher Tesero Oolite Horizon. This positive peak is located at a higher lithostratigraphic level than a comparable peak in the adjacent Pufels section, which suggests that the Tesero Oolite Horizon in the Seis section is stratigraphically slightly older than in the Pufels section, and this is also suggested by palaeomagnetic correlation. It is therefore concluded that the base of the Tesero Oolite Horizon does not reflect a synchronous “current event” but is slightly diachronous, a result that was previously shown by biostratigraphic correlation. Nevertheless, this suggestion should be verified by further detailed litho‐, magneto‐ and chemostratigraphic analysis of other P–T sections in the Southern Alps. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Impact melt‐bearing clastic deposits (suevites) are one of the most important records of the impact cratering process. A deeper understanding of their composition and formation is therefore essential. This study focuses on impact melt particles in suevite at Ries, Germany. Textures and chemical evidence indicate that the suevite contains three melt types that originate from different shock levels in the target. The most abundant melt type (“melt type 1”) represents well‐mixed whole‐rock melting of crystalline basement and includes incompletely mixed mafic melt schlieren (“melt type 1 mafic”). Polymineralic melt type 2 comprises mixes between monomineralic melt types 3 and melt type 1. Melt types 2 and 3 are located within melt type 1 as small patches or schlieren but also isolated within the suevite matrix. The main melt type 1 is heterogeneous with respect to trace elements, varying geographically around the crater: in the western sector, it has lower values in trace elements, e.g., Ba, Zr, Th, and Ce, than in the eastern sector. The west–east zoning likely reflects the heterogeneous nature of crystalline basement target rocks with lower trace element contents, e.g., Ba, Zr, Th, and Ce, in the west compared to the east. The chemical zoning pattern of suevite melt type 1 indicates that mixing during ejection and emplacement occurred only on a local (hundreds of meters) scale. The incomplete larger scale mixing indicated by the preservation of these local chemical signatures, and schlieren corroborate the assumption that mixing, ejection, and quenching were very rapid, short‐lived processes.