Current knowledge of the Ordovician System in Antarctica

Abstract

Abstract Evidence of Early Ordovician deposition and intrusion in East Antarctica is best known from the Ross Orogen, postdating the 495–489 Ma Ross Orogeny. Here, c. 490–475 Ma granites (with related dykes and sills) of the Granite Harbour Intrusives represent roots of a continental margin arc. Detrital zircon grains in the upper Byrd Group (Central Transantarctic Mountains) are of comparable Early Ordovician age. Contemporaneous fossils are rare. In northern Victoria Land they include latest Cambrian to earliest Ordovician conodonts and microbrachiopods in allochthonous limestones of the Handler Formation (Robertson Bay Group) in the Robertson Bay Terrane, and probable Early Ordovician trace fossils in the Camp Ridge Quartzite of the Leap Year Group in the Bowers Terrane. In the Shackleton Range of Coats Land, West Antarctica, the Blaiklock Glacier Group contains a diverse ichnofossil fauna of probable Ordovician age associated with undescribed bivalved arthropods and segmented crustacea. The Swanson Formation of the Ross Province in Marie Byrd Land (correlated with the Robertson Bay Group of the Ross Orogen) is a turbiditic unit dominated by quartz-rich sandstones. Its Ordovician age is based on a post-depositional whole rock K–Ar metamorphic age of 448–444 Ma, with detrital zircon grains indicating a late Cambrian maximum depositional age.