Early Palaeozoic history of the upper Beardmore Glacier area: implications for a major Antarctic structural boundary within the Transantarctic Mountains

The central and western Transantarctic Mountains appear to be divided longitudinally by one or more terrane boundaries that separate two regions characterized by different Lower Palaeozoic successions. Re-examination of the upper Beardmore Glacier area and reinterpretation of its Early Palaeozoic stratigraphy emphasizes the strong similarity between it and the Byrd Group outcrops in the area between the Byrd and Nimrod glaciers. This similarity demonstrates that for several hundred kilometres the Cambrian succession of an inboard region is largely devoid of volcanic rocks but includes fossiliferous Lower Cambrian platformal limestones that are overlain unconformably by coarse basin-fill deposits. The latter probably include beds of Middle and perhaps early Late Cambrian age that were themselves deformed prior to the Devonian. Erratic blocks indicate that comparable successions may have been developed as far west as the Whichaway Nunataks. The inferred geological history of this part of the continental margin, which is commonly regarded as autochthonous, stands in contrast to that of more outboard regions where thick volcanic sequences occur in expanded stratigraphic sections that include shallow-marine Middle and Late Cambrian deposits. We consider that these regions, predominantly the Queen Maud and Theil mountains and the Neptune Range of the Pensacola Mountains, constitute one or more displaced crustal blocks. The boundary between them and the inboard sequence adjacent to the craton is probably a series of large strike-slip faults that may have been initiated during the Early Palaeozoic and have been active episodically since then.