Concern about the impact of ocean acidification on organisms secreting high magnesium calcite skeletons has led to renewed interest in the mineralogy of these organisms. The identification of minerals making up the skeletons of tropical coralline algae, and in particular the determination of the Mg-content of calcite, is most commonly performed with X-ray diffraction. This method, based on XRD peak position, attracted criticism in the past because it produced Mg-contents that were in some cases lower compared to those based on chemical analyses of the bulk sample (in solution). The recent discovery of dolomite and magnesite in living coralline algae skeletons in addition to Mg-calcite explained this issue, and it is our goal in the present study to reinstate XRD as a reliable, quick and affordable method for the study of the mineral make-up of coralline algae species. In this paper we review the history of mineralogical analyses on tropical coralline algae and identify physical preparation methods that can affect results. We build on existing XRD methods to develop simple sampling and analytical methods to identify the presence of dolomite and magnesite, and numerically assess peak asymmetry that is caused by the overlapping reflections of calcite, dolomite and magnesite. These methods do not require specialist crystallographic knowledge or expensive or time consuming processes. The additional information our methods produce can be used to study intra-cellular calcification, and helps to rapidly assess and compare the mineral make-up of large numbers of samples. We conclude that XRD should be an integral part of any mineralogical analysis of coralline algae skeletons, which may be composed of not only Mg-calcite (Ca1.0-0.6Mg0-0.4CO3), but also dolomite (Ca0.5Mg0.5CO3), magnesite (MgCO3) and aragonite (CaCO3).

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.

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.

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.

High-CO2 gas fields serve as important analogues for understanding various processes related to CO2 injection and storage. The chemical signatures, both within the fluids and the solid phases, are especially useful for elucidating preferred gas migration pathways and also for assessing the relative importance of mineral dissolution and/or solution trapping efficiency. In this paper, we present a high resolution study focussed on the Gorgon gas field and associated Rankin trend gases on Australia's Northwest Shelf of Australia. The Gorgon field is characterized by a series of stacked reservoirs (Figure 1), and is therefore well placed to characterize CO2 migration, dissolution and reaction by looking at geochemical signatures in the different reservoirs. Hydrological data at the Gorgon field also suggests that many of the major faults possess very low transmissivities, which should prevent or limit mixing of reservoir fluids with different chemical imprints. The gas data we present here reveal correlatable trends for mole %-CO2 and --C CO2 both areally and vertically as observed by Edwards et al. (2007). We suggest that the observed relationships are imparted due to mineral carbonation reactions that occurred along the CO2 migration pathway. These results have important implications for carbon storage operations and suggest that under certain conditions mineral sequestration might occur over longer migration distances and on shorter timescales than previously thought.

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.

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.

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.

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.

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.