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The distribution of megablocks in the Ries crater, Germany: Remote sensing, field investigation, and statistical analyses
Author(s) -
Sturm Sebastian,
Kenkmann Thomas,
Willmes Malte,
Pösges Gisela,
Hiesinger Harald
Publication year - 2015
Publication title -
meteoritics and planetary science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.09
H-Index - 100
eISSN - 1945-5100
pISSN - 1086-9379
DOI - 10.1111/maps.12408
Subject(s) - impact crater , ejecta , geology , breccia , sedimentary rock , impact structure , clastic rock , geomorphology , petrology , geochemistry , mineralogy , astrobiology , physics , quantum mechanics , supernova
The Ries crater is a well‐preserved, complex impact crater that has been extensively used in the study of impact crater formation processes across the solar system. However, its geologic structure, especially the megablock zone, still poses questions regarding crater formation mechanics. The megablock zone, located between the inner crystalline ring and outer, morphologic crater rim, consists of allochthonous crystalline and sedimentary blocks, Bunte Breccia deposits, patches of suevite, and parautochthonous sedimentary blocks that slumped into the crater during crater modification. Our remote sensing detection method in combination with a shallow drilling campaign and geoelectric measurements at two selected megablocks proved successful in finding new megablock structures (>25 m mean diameter) within the upper approximately 1.5 m of the subsurface in the megablock zone. We analyzed 1777 megablocks of the megablock zone, 81 of which are new discoveries. In our statistical analysis, we also included 2318 ejecta blocks >25 m beyond the crater rim. Parautochthonous megablocks show an increase in total area and size toward the final crater rim. The sizes of allochthonous megablocks generally decrease with increasing radial range, but inside the megablock zone, the coverage with postimpact sediments obscures this trend. The size‐frequency distribution of all megablocks obeys a power‐law distribution with an exponent between approximately −1.7 and −2.3. We estimated a total volume of 95 km 3 of Bunte Breccia and 47 km 3 of megablocks. Ejecta volume calculations and a palinspastic restoration of the extension within the megablock zone indicate that the transient cavity diameter was probably 14–15 km.