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  • We combine two- and three-dimensional seismic stratigraphic interpretation with paleobathymetric analysis from benthic foraminifera to understand the genetic significance of prominent seismic discontinuity surfaces typically mapped as "sequence boundaries" and "flooding surfaces" in the late Paleogene-early Neogene Northern Carnarvon Basin. The progradational succession, dominated by heterozoan carbonate sediments, is divided into five northwest-prograding clinoformal sequences and 19 sub-sequences. Clinoform fronts progress from smooth to highly dissected, with intense gullying apparent only after the mid Miocene optimum. Once initiated, gullies become the focus for sediment distribution across the front. Bottomsets remain relatively sediment-starved without the development of aprons on the lower slope and basin. Small-scale variability suggests heterogeneous sediment dispersal through the slope conduits. Along-strike sediment transport superimposed on progradation changes from south-directed in the late Oligocene to north-directed in the late mid-Miocene suggesting a major reorganization of circulation in the southeastern Indian Ocean. Prominent seismic discontinuity surfaces represent both intervals of shallow paleo-water depth and flooding of the shelf. Partial exposure of the shelf indicated by karst morphology is coeval with middle to outer neritic paleo-water depths on the outer shelf. Rather than build to sea-level, progradation occurs with shelf paleo-water depths at the clinoform rollover >100 m. Therefore, in the Northern Carnarvon Basin onlap onto the clinoform front is not coastal and the sensitivity of the clinoforms to sea-level changes is muted.

  • Multibeam sonar mapping, drill cores and underwater video data have confirmed the existence of a previously unknown reef province in the Gulf of Carpentaria, Australia. Seven reefs, comprised of coral limestone that support living corals have been mapped so far and as many as 50 other reefs may exist in the region. U/Th ages show that reef growth commenced shortly after limestone pedestals were submerged by rising sea level around 10.5 kyr BP, making them the oldest reefs known in Australia. Reef growth persisted for ~2.0 kyr but it had ceased at most locations by ~8.0 kyr BP. Measurements of reef growth rates (0.95 to 4 m kyr-1), indicate that the reefs were unable to keep pace with contemporaneous rapid sea level rise (>10 m kyr-1), which is consistent with a 'give up' reef growth history. Core samples from reef platforms demonstrate that Pleistocene limestone is exposed in depths of 27 and 30 m below present mean sea level. These depths represent regionally significant phases of reef growth during a prolonged sea level still stand. We conclude that the reefs are therefore mostly relict features, whose major phase of growth and development relates to an earlier, pre-Holocene sea level stillstand.

  • The mapping of seabed environments is fundamental to successful fisheries management and environmental monitoring, however, there is an emerging need to better characterise habitats based upon appropriate physical parameters. In this study, relationships between seabed geomorphology and the distribution of benthic habitats were examined using multibeam sonar, underwater video, predicted wave energy, and sediment data for Esperance Bay, part of the Recherche Archipelago. This shallow (<50 m), high energy, biogenic sediment dominated environment is located in temperate southwestern Australia. Exposure to wave energy appears to determine the distribution of unconsolidated substrate, and is the most useful regional scale predictor of rhodolith and seagrass habitats. Although they are intermittently smothered by mobile sediments, limestone reefs provide habitat for a wide range of sessile organisms, even in very high wave exposure environments. The distribution of rhodolith beds is related to poorly sorted sediments that contain high gravel, mud, and CaCO3 percentages. Our results reveal that in the Recherche Archipelago, wave abrasion coupled with localised sediment transport and accumulation play a major role in increasing the diversity of inner shelf benthic habitats. This highlights the value of assessing geomorphic processes in order to better understand the distribution and structure of benthic habitats.

  • The submarine Kenn Plateau has an area of about 140,000 km² and lies 500 km east of central Queensland beyond the Marion Plateau. It is one of several thinned continental fragments lying east of Australia that were once part of Australia, and it originally fitted south of the Marion Plateau as far south as Brisbane. It is cut into smaller blocks by east and northeast trending faults, with thinly sedimented basement highs separated by basins containing several kilometres of sediment. In the Cretaceous, it was probably underlain by rocks of the New England Fold Belt on which were stacked Late Triassic to Late Cretaceous basins. Late Cretaceous stretching and breakup was followed by Paleocene drifting, and the Kenn Plateau moved away to the northeast, rotating 45 degrees clockwise and leaving the Tasman Basin oceanic basalts behind. During these processes, siliciclastic sediments poured into the basins from the mainland and from locally eroding highs, but this sequence was terminated by a regional Late Paleocene to Early Eocene unconformity. Rift volcanics are common on the northern plateau. Radiolarian chalks were widely deposited until biosiliceous sedimentation ended with the regional Late Eocene to Early Oligocene unconformity, and warming surface waters led to younger chalk deposition. Some seismic profiles show the Middle to Late Eocene compression so well exemplified in the New Caledonian obduction to the east. Hotspots formed two volcanic chains as the plateau moved northward: the Oligocene Tasmantid chain in the west, and the Neogene Lord Howe chain in the east. As the volcanoes subsided they were fringed by reefs, some of which have persisted until the present day, whereas other reefs have not kept up with subsidence so guyots formed. The plateau has subsided 2000 m or more since breakup and is now subject solely to pelagic carbonate sedimentation.

  • This movie describes the main findings of two Geoscience Australia surveys to the Gulf of Carpentaria in 2003 (survey 238) and 2005 (survey 276). The story relates to the discovery of submerged coral reefs across the southern Gulf and how they were identified using new multibeam sonar technology. The age of the reefs was determined using drill-core samples collected from the reefs, and measured by the Uranium/Thorium method at the Australian National University. The submerged reefs in the Gulf were not known to exist prior to this study and their discovery adds a new coral reef province to be managed and protected as part of Australia's marine zone.

  • With the increasing need to extend mineral exploration undercover, new approaches are required to better constrain concealed geology, thereby reducing exploration risk and search space. Hydrogeochemistry is an under-utilised tool that can identify subsurface geology and buried mineral system components, while also providing valuable insights into environmental baselines, energy systems and groundwater resources. With this aim, 238 water bores spanning seven geological provinces in the Northern Territory and Queensland were sampled and analysed for major cations and anions, trace elements, stable and radiogenic isotopes, organic species, and dissolved gases. Here, we demonstrate the utility of this dataset for identifying carbonate-rich aquifers and mineral system components therein. First, we use trends in major element ratios (Ca+Mg)/Cl– and SiO2/HCO–3, then strontium isotope ratios (87Sr/86Sr), to define subpopulations that reflect both spatial and compositional differences. We then apply mafic-to-felsic trace element ratios (V/Cs and Cu/Rb) to reveal elevated base metal concentrations near Lake Woods caused by water–rock interaction with dolerite intrusions. Correlated Sr concentrations between groundwater and surface sediments suggest that the geochemical evolution of these mediums in carbonate-dominated terrains is coupled. Our work develops an approach to guide mineral exploration undercover via the characterisation and differentiation of groundwaters from different aquifers, resulting in improved identification of geochemical anomalies. <b>Citation:</b> Schroder, I., de Caritat, P. and Wallace, L., 2020. The Northern Australia Hydrogeochemical Survey: aquifer lithologies, local backgrounds and undercover processes. In: Czarnota, K., Roach, I., Abbott, S., Haynes, M., Kositcin, N., Ray, A. and Slatter, E. (eds.) Exploring for the Future: Extended Abstracts, Geoscience Australia, Canberra, 1–4.

  • This record contains the preliminary results of Geoscience Australia marine survey 238 (SS04/2003) to southeast Gulf of Carpentaria. The survey was completed between 9 May and 10 June 2003 using Australia's national facility research vessel Southern Surveyor. The survey included Geoscience Australia and CSIRO and Marine and Atmospheric Research scientists.

  • Dense hydrocoral-sponge communities have been identified on the upper continental slope of George V Land, East Antarctica and declared Vulnerable Marine Ecosystems. Analysis of physical and biological datasets collected during the 2007/08 CEAMARC survey identified that the richest communities are found in the heads of canyons which receive Antarctic Bottom Water formed on the George V shelf, and the canyons harbouring rich benthos are also those that cut the shelf break. This led to several hypotheses regarding their distribution and three main factors were identified. These hypotheses were tested during a recent marine science voyage in January 2011 to the same region. Initial analysis of the new data supports the hypotheses regarding the physical controls on hydrocoral-sponge community distribution.

  • This study was undertaken as part of a program to collect baseline data from the seabed environments over the Van Diemen Rise, which comprises a series of carbonate platforms and banks in the eastern Joseph Bonaparte Gulf, northwest of Darwin. Samples were collected during a survey on board the RV Solander in August and September 2009. The state of saturation for the different carbonate minerals (aragonite, calcite, high-magnesium calcite) was calculated for each sampling site from the ratio of the ion activity product and the solubility product. The carbonate ion concentration used for the ion activity product was calculated from total alkalinity and pH. The solubility products of the carbonate minerals were derived from literature data, e.g. the solubility for high-magnesium calcite as a function of the mol% MgCO3 was based on experimental results by Plummer and Mackenzie (1974, American Journal of Science vol. 274, p. 61-83). The calculated average state of saturation was 1.4 (range: 0.8-1.9) for high-magnesium calcite, 4.2 (range: 3.4-4.6) for aragonite, and 6.4 (range: 5.1-6.8) for calcite. Values close to 1 suggest the mineral is in thermodynamic equilibrium with ambient water, which is the case for high-magnesium calcite. In contrast, aragonite and calcite are distinctively supersaturated. Given the near-equilibrium state of high-magnesium calcite, this mineral phase will likely be lost over a time scale of decades as ocean acidification progresses. This ongoing process will alter the sediment composition significantly given the high abundance of high-magnesium calcite. This study supports the concept of using high-magnesium calcite as an indicator for the progression of ocean acidification where surface sediments have been sampled and preserved over time.

  • Dolomite is a magnesium rich carbonate mineral abundant in ancient coral reef formations [1-3] yet very little is found forming in modern sedimentary environments. For over 150 years this conundrum has led to various theories being put forward about dolomite formation, however none have solved the so called `Dolomite Problem'[1]. It has generally been considered a post-depositional diagenetic process [2, 3], despite little experimental success at replicating dolomite formation in normal sea water conditions [4]. Here we show dolomite is in fact forming with living crustose coralline algae Hydrolithon onkodes, a species growing prolifically in coral reefs globally. Chemical micro-analysis of the coralline skeleton reveals that not only are the cell walls calcitised, but that the cell spaces are typically filled with magnesite, rimmed by dolomite, or both. Thus there are at least three mineral phases present (magnesium calcite, dolomite and magnesite) rather than one or two (magnesium calcite and brucite) as previously thought[5-7]. Both the magnesium calcite and dolomite phases comprise a continuum of magnesium to calcium compositions, whereas magnesite is near ideal composition. Using a mass balance approach we quantify potential dolomitisation of the coralline algae and can account for the total amount of dolomite found in a raised Pleistocene reef [2]. Our results are consistent with observed dolomites in coralline-algal rich environments in fossil reefs. This is the first time the presence of dolomite in living coralline algae has been confirmed.