Impact ejecta horizon within late Precambrian shales, Adelaide Geosyncline, South Australia

Abstract

A solitary layer of shattered crustal rock fragments has been traced over a distance of 260 kilometers within folded 600-million-year-old Precambrian marine shales of the Adelaide Geosyncline, South Australia. The fragments consist entirely of acid to intermediate volcanks (approximately 1575 million years old) displaying shattered mineral grains, shock lamellae in quartz, and small shatter cones. Fragments reach 30 centimeters in diameter and show evidence of vertical fall emplacement. Available evidence points to derivation of the rock fragments from a distant hypervelocity impact into the Gawler Range Volcanics at Lake Acraman, approximately 300 kilometers west of the Adelaide Geosyncline. Show more