Dredging up Mawson: implications for the geology of coastal East Antarctica.

During the 1911–1914 Australasian Antarctic Expedition samples of bottom sediment were dredged from a wide sweep of coastline extending from the main base at Commonwealth Bay, to the western edge of the Shackleton Ice Shelf. An earlier study showed these sediments to contain palynomorphs recycled from eroding sedimentary sequences. High concentrations of Permian, Jurassic to Early Cretaceous, and Cenozoic microfossils were present in three regions of the continental shelf, namely, offshore from the Shackleton Ice Shelf, from Cape Carr and from close to the Mertz Glacier. The findings of the earlier study are re-evaluated in the light of new information concerning the bathymetry of sampled areas on the continental shelf, the sub-ice topography of ice shelves and the Antarctic interior, and of sedimentary processes controlling the movement of palynomorphs on the sea floor. Data from the vicinity of the Shackleton Ice Shelf raise the possibility of sourcing some recycled material through sub-ice connections with the deep Aurora Subglacial Basin of the interior. From the George V Basin, west of the Mertz Glacier, new echo-sounding data show the dredges collected lie mostly on the edge of a steep trough parallel to the coast. Previous suggestions that Jurassic to Cretaceous sequences there correlate with those of the Otway Basin on the Australian margin are corroborated by recent seismic reflection data showing thick rift and pre-rift sequences offshore from the Adélie and Wilkes coasts. The relationship of these sequences to putative Mesozoic sequences within the inland Wilkes Basin is uncertain. Limited studies suggest that recycled palynomorphs in continental shelf sediments may lie close to the sites of their original deposition

The stratigraphy of a Late Palaeozoic borehole section at Douglas River, eastern Tasmania: a synthesis of marine macro-invertebrate and palynological data

A section 236.8 m in thickness of Late Palaeozoic (Late Carboniferous-Permian) rocks of the Lower Parmeener Super-Group was encountered in a borehole at Douglas River, eastern Tasmania. Lithological, marine macro-invertebrate and palynological data are documented and collated. The section displays many similarities with sequences elsewhere in eastern and northeastern Tasmania, but is unusual in the development of rocks (including Tasmanites shale) as old as Early Tamarian. This occurrence may indicate a narrow, but significant east-west breaching of the land barrier which persisted throughout the Tamarian over most of eastern and northeastern Tasmania. Acritarch swarms coeval with sedimentation occur at intervals, whereas other acritarchs may be derived from earlier Palaeozoic rocks. The Tasmanian Late Permian palynofloras lack diversity and resemble those from the Transantarctic Mountains, Antarctica, rather than those from elsewhere in eastern Australia

Late Quaternary history of sedimentation on the Mac. Robertson shelf, East Antarctica: problems with 14C-dating of marine sediment cores

Stratigraphic information concerning the retreat of the Antarctic ice sheet from the continental shelf after the Last Glacial Maximum is reviewed and compared with new results from a shelf valley off Mac. Robertson Land, East Antarctica. Radiocarbon dates and detailed lithostratigraphic logs indicate that the onset of open-marine conditions over shallow shelfbanks (<200 m water depth) was achieved prior to 7000 yr BP and over deep (~l 000 m) middle to oliter shelf valleys, open-marine conditions were achieved prior to 5400 yr BP. Radiocarbon dating of bulk-organic carbon in some diatom oozes by the AMS method demonstrates problems of contamination. Jurassic pollen, spores and organic matter have been eroded and incorporated into Holocene diatom ooze, causing anomalously old 14C dates (e.g. one surface age of 7084 ± 86 yr BP was determined). This problem may arise at other locations around East Antarctica where older strata outcrop on the seafloor

First evidence for Wollemi Pine-type pollen (Dilwynites: Araucariaceae) in South America

We report the first fossil pollen from South America of the lineage that includes the recently discovered, extremely rare Australian Wollemi Pine, Wollemia nobilis (Araucariaceae). The grains are from the late Paleocene to early middle Eocene Ligorio Márquez Formation of Santa Cruz, Patagonia, Argentina, and are assigned to Dilwynites, the fossil pollen type that closely resembles the pollen of modern Wollemia and some species of its Australasian sister genus, Agathis. Dilwynites was formerly known only from Australia, New Zealand, and East Antarctica. The Patagonian Dilwynites occurs with several taxa of Podocarpaceae and a diverse range of cryptogams and angiosperms, but not Nothofagus. The fossils greatly extend the known geographic range of Dilwynites and provide important new evidence for the Antarctic region as an early Paleogene portal for biotic interchange between Australasia and South America.Mike Macphail, Raymond J. Carpenter, Ari Iglesias, Peter Wil