Mineral-Produced High-Pressure Striae and Clay Polish: Key Evidence for Nonballistic Transport of Ejecta from Ries Crater
E. C. T. CHAO 1
1 U.S. Geological Survey, National Center, Reston, Virginia 22092
Recently discovered mineral-produced, deeply incised striae and mirror-like polish on broken surfaces of limestone fragments from the sedimentary ejecta of the Ries impact crater of southern Germany are described. The striae and polish were produced under high confining pressures during high-velocity nonballistic transport of the ejecta mass within the time span of the cratering event (measured in terms of seconds). The striae on these fragments were produced by scouring by small mineral grains embedded in the surrounding clay matrix, and the polish was formed under the same condition, by movements of relatively fragment-free clay against the fragment surfaces. The occurrence of these striae and polish is key evidence for estimating the distribution and determining the relative importance of nonballistic and ballistic transport of ejecta from the shallow Ries stony meteorite impact crater.
Submitted on July 22, 1976
Revised on August 30, 1976
