Geomorphology and stratigraphy of the nimrod glacier–beaumont bay region, Southern Victoria land, Antarctica

Abstract

An account is given of the geomorphology and stratigraphy of about 3,000 square miles of southern Victoria Land between the Nimrod Glacier and Beaumont Bay. The present topography has resulted largely from extensive late Cainozoic block faulting, modified by glacial erosion. Strongly folded basement rocks belong to two distinct groups. The older Beardmore Group is composed of thermally altered grey-wacke and argillite of late Precambrian to early Cambrian age, which have been extensively intruded by post-tectonic plutons predominantly of porphyritic microcline-biotite granite. The younger Byrd Group is distinguished by predominantly calcareous strata, which have been divided into two formations, the Shackleton and the Starshot. The Shackleton Limestone contains Archaeocyathids, and is therefore of Early to Middle Cambrian age. A type section for this formation is proposed. In several places it has been intruded by small stocks of gabbro, which have locally altered the limestone to marble. The Starshot Formation, consisting of shallow-water calcareous conglomerate, sandstone, and shale, together with interbedded rhyolite and trachvte flows, is believed to be contemporaneous with the Archaeocyathid limestones of the Shackleton Formation. In the western part of the region the peneplaned basement rocks are overlain by flat-lying sedimentary beds of the Beacon Group, which are extensively intruded by dolerite sills.