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.

Cool-water carbonate environments may be responsible for up to one third of the carbonate sediment produced on continental shelves, and are useful modern analogues for many geologically ancient deposits. The extensive southern margin of the Australian continent is recognised as the world's largest modern example of a high energy, cool-water carbonate depositional realm. A number of studies have suggested that Quaternary sediment production here is largely influenced by oceanography, and that wave abrasion strongly limits sediment accumulation. Therefore, in this region the outer-shelf, below the storm wave base, is thought to be the focus of sediment accumulation. The inner shelf is considered a zone of active sediment production due to the proliferation of carbonate secreting organisms, although few studies have investigated sediment production or accumulation in this energetic and dynamic environment. The Recherche Archipelago, which sits at the western margin of the Great Australian Bight (GAB), was examined to better understand Quaternary shelf evolution and the importance of this type of inner shelf as a carbonate 'factory'. Surficial sediments, video, multibeam sonar data, cores and shallow seismics were collected. The present seabed of the archipelago features extensive areas where flat-lying limestones sit over the often irregular granite basement. The Pleistocene erosional surface is overlain by a coarse bivalve and rhodolith dominated gravel lag. Significantly, there are extensive Holocene deposits, up to 7 m thick, throughout the archipelago, particularly in association with granite islands. These deposits comprise cross-bedded gravelly carbonate sands dominated by fragments of calcareous algae (rhodoliths), molluscs and bryozoans. In contrast, the inshore and coast is dominated by terrigenous sediment. Seismic profiles and preserved palaeo-shoreline features suggest that slow but episodic aggradation of marine sediment has occurred on the inner shelf over successive Quaternary sea level cycles, although there are also extensive areas of non-deposition. This accumulation is partly attributable to the sheltering effect of high-relief granitic outcrops and cementation of subaerially exposed carbonate sediments.

New 2D seismic data acquired in the Mentelle Basin by Geoscience Australia in 2008-09 has been used for a seismic facies study of the post-rift succession. The Mentelle Basin is a large deep to ultra deep-water, frontier basin located on Australia's southwestern margin about 200 km southwest of Perth. The study focused on the post-rift sequences deposited following the breakup between Australia and Greater India. Stratigraphic wells DSDP 258 and DSDP 264 provide age and lithological constraints on the upper portion of the post-rift succession down to mid-Albian strata. The depositional environment and lithology of the older sequences are based on analysis of the seismic facies, stratal geometries and comparisons to the age equivalent units in the south Perth Basin. Fourteen seismic facies were identified based on reflection continuity, amplitude and frequency, internal reflection configuration and external geometries. They range from high continuity, high amplitude, parallel sheet facies to low continuity, low amplitude, parallel, subparallel and chaotic sheet, wedge and basin fill facies. Channel and channel fill features are common in several facies along with a mounded facies (probably contourite) and its associated ponded turbidite fill. A progradational sigmoidal to oblique wedge facies occurs at several stratigraphic levels in the section. A chaotic mound facies, probably comprising debrite deposits, has a localised distribution.

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.

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.

The Coompana Project is a collaborative project between Geoscience Australia and the Geological Survey of South Australia, co-funded by Geoscience Australia’s Exploring for the Future Programme and the South Australian Government’s PACE Copper Initiative. The Coompana Project aims to provide new precompetitive geological, geophysical and geochemical data in the under-explored Coompana Province in South Australia. The pre-drilling geophysics program was undertaken to assist the drilling process by reducing the uncertainty associated with intersecting the targeted stratigraphy. Seismic data were acquired at eight proposed drilling sites for the Coompana Drilling Program in February 2017. Seismic data were collected using vertical and horizontal geophones. An accelerated weight-drop source was tested with metal and plastic strike plates. The plastic strike plate was preferred and used for all sites. P-wave reflection images were used to images subsurface layers and estimate bedrock depth at each drill site. Horizontal geophone data indicated S-wave data had higher resolution than the vertical geophone P-wave data, but initial testing did not provide good bedrock imaging. Fan shots can indicate zones of low velocity weathering at the near surface. Multichannel Analysis of Surface Waves provided near surface weathering profiles. Near surface weathering can be an indication of caves in this limestone environment. The S-wave shot records may indicate the presence of caves with S-wave signal degradation at cave locations, as S-waves do not travel through voids, not noticed at these sites. The seismic reflection method can be used to show subsurface variations and provide bedrock depth estimates, though the bedrock can be difficult to identify. The data is very noisy and data quality changes at different locations. Seismic data quality can be improved with a higher energy source.

As part of a study to investigate relative sea level history from the Tertiary North West Shelf of Australia, we descibe a seismically imaged. stratigraphic architectural element not previously associated with prograding carbonate clinoforms. a strike-oriented trough on an early mid0Miocene sequence boundary. This trough located on a shallowly dipping carbonate ramp, is recognized on both 2-D and 3-D seismic data by truncation, reflector interruption and amplitude variations. It is composed of three individual segments, each up to 500 m wide and 60 m deep, wide variable cross-sections. Their combined length, orthogonal to the progradation direction, is ~ 8 km. The trough occurs where there is a slight basinward increase in dip, and a facies change on the ramp from sand-sized calcarenite to clay-sized calcilutite. It has both a cross-cutting and sub-parallel relationship with underlying Paleogene faults reactivated within a Mesozoic basin-forming trend. The trough, does not conform to known drainage patterns, or contour current incisions mapped in similar environments elsewhere. We propose that this seismically mapped trough is karst topography that developed as a result of preferential dissolution focused by heterogeneities within the exposed carbonate ramp. Stable isotope analyses conducted on bulk carbonate samples ~ 2 km updip, suggest a mixed, marine to slightly meteoric origin for associated porewaters. Furthermore, the sequence boundary on which the the trough is developed is contemporaneous with recognized subaerial exposure surfaces to the northeast and southwest. The presence of such a karst feature indicates a minimum fall in relative sea level at this location of 80-160 m during the early mid-Miocene.

The Browse Basin is located in the southern Timor Sea region of Australia's North West Shelf and covers an area of ~140,000 km2. It was identified as containing potential Environmentally Suitable Sites for carbon dioxide (CO2) Injection (ESSCI) by the Australian Petroleum CRC's GEODISC program (1999-2003). A regional geological reconnaissance of Cenozoic sandstone and carbonate sequences in the Browse Basin was undertaken in 2007 to determine the potential storage and sealing capacity for geological storage of CO2, the results of which are presented in this report. Methods included the review of available literature and well-completion reports, lithological and mineral analysis of selected well cuttings and interpretation of the wire-line and seismic response of the Cenozoic section.

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.

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.