Lower Palaeozoic rocks of the Ross Sea area and their significance in the Gondwana context

In the Ross Sea area fossiliferous Lower Palaeozoic sedimentary rocks mainly crop out in the central Transantarctic Mountains and in northern Victoria Land. In the former area, shallow marine Cambrian sediments, part of a semicontinuous belt deposited along the margin of the East Antarctic craton between the Ross and Weddell Seas, rest unconformably on strongly deformed Late Precambrian sediments. In the Queen Maud Mountains, Early to Middle Cambrian limestone and associated clastic sediments (Liv Group) are subordinate to silicic volcanic rocks up to 3000 m thick. Farther north, between the Byrd and Beardmore Glaciers, over 8000 m of Byrd Group are dominated by Early and ?Middle Cambrian archaeocyathine limestone. Deformation and metamorphism during the Late Cambrian Ross Orogeny were followed during the Early Ordovician by intrusion of granitic batholiths (Granite Harbour Intrusives). The Bowers Supergroup, faulted against flanking older sequences, includes all known Lower Palaeozoic sediments of northern Victoria Land. The Sledgers Group, consisting of at least 3000 m of Vendian to Early Cambrian flysch‐like sediments and basic volcanics, is overlain with inferred disconformity by the late Middle Cambrian to late Late Cambrian fossiliferous shallow marine Mariner Group (2000+ m). A marked unconformity separates these sediments from at least 3000 m of dominantly quartzose fluvial deposits forming the Leap Year Group, of probable latest Cambrian or Ordovician age. The Sledgers and Leap Year Groups and perhaps also the Mariner Group are inferred to have been deposited in an elongate northwest trending fault‐controlled basin (the Bowers Trough). The Ross Orogeny appears to have caused only low‐grade regional metamorphism and block faulting: limited radiometric evidence suggests a Silurian‐Devonian metamorphic event (Borchgrevink Orogeny?). Granitic rocks were intruded in the Early Ordovician (Granite Harbour Intrusives) and in the mid‐Devonian to Carboniferous (Admiralty Intrusives). The contrasting age, sedimentation, and tectonic and igneous activity in the two areas, imply separate but subparallel belts showing close similarity to belts with similar characteristics in southeast Australia. Possible Early Palaeozoic reassemblies of Australia!Antarctica are considered.