This study presents compelling evidence for a diverse and abundant seabed community which has developed over the course of the Holocene beneath the Amery Ice Shelf in East Antarctica. Fossil analysis of a 47 cm long sediment core reveals a rich modern fauna, dominated by filter feeders (sponges and bryozoans), with an abundant infauna predominantly of polychaetes. The down-core assemblage reveals a succession in the colonisation of this site. The lower portion of the core (prior to ~9600 yr BP) is completely devoid of preserved fauna. The first colonisers of the site after this time were the mobile benthic organisms. Their occurrence in the core is matched by the first appearance of planktonic taxa, indicating a retreat of the ice shelf following the last glaciation to within sufficient distance to advect planktonic particles via bottom currents. The benthic infauna and filter feeders emerged during the peak abundance of the planktonic organisms, indicating their dependence on this advected food supply which is brought via bottom currents flowing from the open shelf waters of Prydz Bay. Understanding patterns of species succession in this environment has important implications for determining the potential significance of future global change. The collapse of Antarctic ice shelves, as has happened in recent times, would significantly change the organic supply regime, and therefore the nature of these sub-ice shelf benthic communities.

The area northwest of Elura mine, northwest of Cobar, has diverse surficial materials reflecting a complex landscape history. This paper examines some of this history and its possible effects on surface geochemical sampling programs.

Beach ridges at Keppel Bay, central Queensland, Australia, preserve a record of sediment accumulation from the historical period back to middle Holocene times. The ridges comprise fine, well-sorted, feldspar-rich quartz sand that was eroded from the Fitzroy River catchment, deposited in Keppel Bay during floods of the Fitzroy River, and reworked onshore into beach and foredune deposits by the prevailing currents, waves and wind. These floods have an average recurrence interval of at least 7 yr and are induced by the passage of cyclones onshore into the large Fitzroy catchment. The youngest series of beach ridges sit sub-parallel to the modern beach and comprise six accretional units, each unit formed by a set of ridges and delineated by prominent swales. Optically stimulated luminescence (OSL) ages of beach ridges in these units indicate they were deposited in periods of rapid progradation approximately 1500, 1000, 450 and 230 yr BP, when there was an enhanced supply of sediment to the beach from the Fitzroy River via Keppel Bay. Estimates of the mass of sediment stored in the beach-ridge strandplain show that it represents a significant sediment store, potentially trapping the equivalent of 79% of the estimated long-term (100 yr) average annual bedload of the Fitzroy River that is deposited in Keppel Bay. There has been a reduction in the rate of sediment accumulation in the strandplain since around 1000 yr BP, which is consistent with other coastal records in eastern Australia of a relatively wetter phase of climate in the late Holocene compared to the present. The youngest beach ridges (OSL ages < 100 yr BP) are tall relict foredunes that reflect a low rate of sediment accumulation. These ridges have a distinctive trace-element composition produced by a greater contribution from catchment areas with basaltic soils. The change in catchment provenance has likely been a consequence of erosion that followed clearing of native vegetation in these areas. Our findings demonstrate the important insights that beach-ridge deposits proximal to a river sediment source can provide into processes of sediment accumulation and the response to variations in climate in tropical coastal sedimentary systems.

No abstract available

The recent drilling of ODP Leg 189 sheds new light on what happened as Gondwana broke up, Australia drifted northward from Antarctica, and the Tasmanian Gateway opened . The drifting contributed to the change in global climate from relatively warm early Cenozoic Greenhouse conditions to late Cenozoic Icehouse conditions. It isolated Antarctica from warm gyral surfacee currents from the north, and provided the critical deepwater conduits that eventually led to ocean conveyor circulation between the Atlantic and Pacific Oceans. One critical element in the global climate changes was the opening of the Tasmanian Gateway between Australia and Antarctica at ~33.5 Ma (Kennett, Houtz et al., 1975), which coincided with the onset of global cooling near the Eocene-Oligocene boundary. The other critical element was the opening of the Drake Passage between South America and Antarctica, which probably occurred somewhat later. Progressive cooling at high latitudes eventually formed major ice sheets, initially on Antarctica from ~33.5 Ma (Kennett, 1977; Miller et al., 1987), and later in the Northern Hemisphere from ~3 Ma (Shackleton and Opdyke, 1977; Ruddiman et al., 1989). High southern latitude development of glaciers triggered the formation of the cold deep ocean (psychrosphere) and intensified thermohaline circulation. The expansion of the Southern Ocean during the Cenozoic contributed to changes in the Earth's environmental system and in oceanic biogeographic patterns. Early DSDP drilling of the Tasmanian Gateway provided a basic framework of paleoenvironmental changes associated with the opening, but was inadequate to fully test the interrelationships of plate tectonics, circum-polar circulation and global climate. However, Kennett, Houtz et al. (1975) proposed that climatic cooling and an Antarctic ice sheet (cryosphere) developed as the Antarctic Circumpolar Current (ACC) progressively isolated Antarctica thermally. This current was initiated by the opening of the Tasmanian Gateway, and its history was a major focus of Leg 189. Leg 189 continuously cored sediments on foundered continental blocks (west Tasmanian margin, South Tasman Rise, East Tasman Plateau - Fig. 2), which were formerly part of the Tasmanian land bridge between Australia and Antarctica. The land bridge separated the Australo-Antarctic Gulf (AAG) in the west from the proto-Pacific Ocean to the east. The continuous coring has documented in detail what happened during the early and very slow separation of Australia and Antarctica from 75 Ma to 43 Ma, the fast separation between 43 Ma and 37 Ma while the land bridge still existed, the initial current break-through south of the South Tasman Rise (STR) from 37 to 33.5 Ma, and Australia's independent fast movement northward thereafter. This region with its always relatively shallow waters is one of the few places where well-preserved and almost complete Cenozoic marine sequences could be drilled in the Southern Ocean. Leg 189 exceeded our expectations in testing, refining and extending the above scenario, and will thus greatly improve the understanding of Southern Ocean evolution and its relationship with Antarctic climatic development during the last 70 m.y. (early results in Exon, Kennett, Malone et al., 2001). We have better documented the climatic and oceanographic consequences of the gateway opening during the transition from warm Eocene climates to cool Oligocene and Neogene climates. The sequences cored reflect the evolution of a tightly integrated and dynamically evolving system, involving the lithosphere, hydrosphere, atmosphere, cryosphere, and biosphere.

The sediments deposited beneath the floating ice shelves around the Antarctic margin provide important clues regarding the nature of sub-ice shelf circulation and the imprint of ice sheet dynamics and marine incursions on the sedimentary record. Understanding the nature of sedimentary deposits beneath ice shelves is important for reconstructing the icesheet history from shelf sediments. In addition, down core records from beneath ice shelves can be used to understand the past dynamics of the ice sheet. Six sediment cores have been collected from beneath the Amery Ice Shelf in East Antarctica, at distances from the ice edge of between 100 and 300 km. The sediment cores collected beneath this ice shelf provide a record of deglaciation on the Prydz Bay shelf following the last glaciation. Diatoms and other microfossils preserved in the cores reveal the occurrence and strength of marine incursions beneath the ice shelf, and indicate the varying marine influence between regions of the sub-ice shelf environment. Variations in diatom species also reveal changes in sea ice conditions in Prydz Bay during the deglaciation. Grain size analysis indicates the varying proximity to the grounding line through the deglaciation, and the timing of ice sheet retreat across the shelf based on 14C dating of the cores. Two of the cores contain evidence of cross-bedding towards the base of the core. These cross-beds most likely reflect tidal pumping at the base of the ice shelf at a time when these sites were close to the grounding line of the Lambert Glacier.

During the late Neogene, the Lambert Glacier-Amery Ice Shelf drainage system flowed across Prydz Bay in an ice stream that reached the shelf edge and built a trough mouth fan on the upper continental slope. The adjacent banks saw mostly subglacial till deposition beneath slower-moving ice. The fan consists mostly of debris flow deposits derived from the melting out of subglacial debris at the grounding line at the continental shelf edge. Thick debris flow intervals are separated by thin mudstone horizons deposited when the ice had retreated from the shelf edge. Age control in ODP Site 1167 indicates that the bulk of the trough mouth fan was deposited prior to the Brunhes-Matuyama Boundary (780 ka) with as few as 3 debris flow intervals deposited since then. This stratigraphy indicates that extreme advances of the Lambert Glacier-Amery Ice Shelf system ceased during the mid Pleistocene. Possible causes for this change are progressive over-deepening of the inner shelf, a reduction in maximum ice volumes in the interior of the East Antarctic Ice Sheet caused by temperature change and a change in the interaction of Milanckovich cycles and the response time of the ice sheet.

This Geocat record is a CD of presentations delivered as part of the 4th Technical Advisory Group workshop for the Palaeovalley Groundwater Project. The workshop was held in Canberra at Geoscience Australia on 5 and 6 April 2011 and involved ~20 people including GA staff and invited guests from state government water resource and geological survey organisations in SA, NT and WA. The CD has been compiled as a record of the workshop and will be delivered to the workshop participants as a record of the event.

The Lower Darling Valley (LDV) Cenozoic sequence contains Paleogene and Neogene shallow marine and shoreline as well as fluvial and shoreline sediments overlain by Quaternary lacustrine, aeolian and fluvial units. Recent investigations in the LDV using multiple datasets have provided new insights into the nature of post-Blanchetown Clay Quaternary fluvial deposition which differs to the Mallee and Riverine Plain regions elsewhere in the Murray Basin. In the LDV Quaternary fluvial sequence, multiple scroll-plain tracts are incised into higher, older and more featureless floodplain terrain. Prior to this study, these were respectively correlated to the Coonambidgal and Shepparton Formations of the Riverine Plain in the eastern Murray Basin. These formations were originally associated with the subsequently discarded Prior Stream/Ancestral River chronosequence of different climatically controlled depositional styles. In contrast to that suggestion, we ascribe all LDV Quaternary fluvial deposition to lateral-migration depositional phases of one style, though with variable stream discharges and channel and meander-scroll dimensions. Successively higher overbank-mud deposition through time obscures scroll traces and provides the main ongoing morphologic difference. A new morphostratigraphic unit, the Menindee Formation, refers to mostly older and higher floodplain sediments, where scroll traces are obscured by overbank mud which continues to be deposited by the highest modern floods. Younger inset scroll-plain tracts, with visible scroll-plain traces, are still referred to as the Coonambidgal Formation. Another new stratigraphic unit, the Willotia beds, refers to even older fluvial sediments, now above modern floodplain levels and mostly covered by aeolian sediments.

Two sediment cores collected from beneath the Amery Ice Shelf, East Antarctica describe the physical sedimentation patterns beneath an existing major embayed ice shelf. The latest core, AM01b, was collected from a site of basal freezing, contrasting with the previous core AM02, collected from a site of basal melting. Both cores comprise Holocene siliceous muddy ooze (SMO) however AM01b recovered interbedded siliciclastic mud, sand and gravel with inclined bedding in its lower 27 cm. This interval indicates an episode of variable but strong current activity before SMO sedimentation became dominant. 14C ages corrected for old surface ages are consistent with previous dating of marine sediments in Prydz Bay however the basal age of the AM01b core of 28250 +/- 230 14C yr BP probably results from greater contamination by recycled organic matter. Lithology, 14C surface ages, absolute diatom abundance, and the diatom assemblage are used as indicators of sediment transport pathways beneath the ice shelf. The transport pathways suggested from these indicators do not correspond to previous models of the basal melt/freeze pattern. This indicates that the overturning baroclinic circulation beneath the Amery Ice Shelf (near-bed inflow - surface outflow) is a more important influence on basal melt/freeze and sediment distributions than the barotropic circulation that produces inflow in the east and outflow in the west of the ice front. Localised topographic (ice draft and bed elevation) variations are likely to play a dominant role in the resulting sub-ice-shelf melt and sediment distribution. The inflow of marine sediments in the Holocene section of AM01b, as shown by the abundance of marine diatoms and other planktonic organisms, supports a diverse filter feeder community beneath the ice shelf through the supply of suspended organic matter and oxygen.