The geology of portion of the Precambrian Lower Glacial Sequence in the Mt. Shanahan area of the Mt. Painter region, South Australia

Abstract

An area in the Mt. Painter region was investigated, in which the lower portion of the Sturtian Lower Glacial Sequence overlies the Proterozoic crystalline basement, with pronounced unconformity. Sedimentation was initiated by subsidence in a large trough controlled by marginal faulting. A thick section of southward onlapping shallow marine Fitton Formation, showing evidence of ice­rafting of megaclasts in the upper two-thirds by shore or river ice, was mapped. This sequence passes transitionally upward into the glacial marine Bolla Bollana Formation. Regional metamorphism in the greenschist facies produced recrystallization of muddy matrices, quartz-arenites and arkoses. Tremolite-talc assemblages formed in dolomitic clasts and interbeds, and abundant scapolite porphyroblasts were produced in favourable units. A contact metasomatic zonation in metasedimentary amphibolites in the southwest is tentatively proposed. Folding on an east-vest trend, faulting and some shear dislocation at the basement-cover contact, are evident.