Ries impact crater sedimentary conglomerates: Sedimentary particle 'impact pre-processing', transport distances and provenance, and implications for Gale crater conglomerates, Mars

摘要: Abstract Terrestrial impact cratering events produce anomalous rock fragmentation and alteration, form sedimentary basins that are out of equilibrium with the local geomorphological environment. Assessement their initial deposits, crater erosion infilling, lacustrine environments biology can provide important insights into similar features on Mars. Here we report fluviodeltaic conglomerates associated 26 km diameter Miocene Ries structure (target: sediments overlying crystalline basement) respect to shock features, grain size distribution, roundness, potential parent rocks (provenance). The poorly sorted coarsening-upwards cycles a delta-mouth bar system, subangular subrounded pebbles derived from breccia deposits. Pebbles comprise wide range lithologies states ranging fresh solid intensively impact-fractured, friable rocks, including shatter cones. Shocked quartz grains, however, restricted sand fraction. latter observation points suevite as an additional, but subordinate source conglomerates. Granulometric analysis indicates that, in contrast being weathering bedrock, brecciation generated distribution (i.e., preprocessing). This concept “impact preprocessing” helped defne provenance, post-impact sedimentologic history sediment transport distances Post-impact fluvial leads outwash fine fractions prodelta subenvironment, increase roundness mean residual (i.e. hydraulic sorting). On basis characteristics ejecta deposits present-day locations occurrences breccias blocks northwestern segment analyzed, distance less than 3.5 km is for these impact-preprocessed Reconstruction composition primary layer composed solely had maximum 6.5 km, i.e., within closed basin structure. In traditional interpretations conglomerates, requiring long bedrock regions deposition ensure sufficient rounding sorting, sorting short explained by preprocessing enhanced susceptibility abrasion. Consequently, conglomeratic fragments craters, such Gale Mars, likely have been only few kilometers, nearby ejecta, most inner walls. crater-based model implies unusual represent immediate target material excavated event, rather transported laterally greater outside crater.