Legacy product - no abstract available

Legacy product - no abstract available

This Bulletin presents the results of a marine geological survey carried out by BMR in the Arafura Sea in 1969 as part of a program of regional geological reconnaissance mapping of the Australian continental shelf. It is a continuation of work in the Timor Sea and northwest shelf (van Andel, Veevers, 1967; Jones, 1968, 1970). The area surveyed is the northern Australian continental shelf between longitudes 130° and 136°E and between latitudes 8° and 12°S (Fig. 1), an area of about 240 000 km-. From 2 to 25 May the Japanese research submersible Yomiuri and its mothership, the converted deepsea tug Yamato, were made available. The major part of the survey lasted from 21 September to 6 December 1969, using the chartered oil-rig supply vessel San Pedro Sound as a platform.

Geoscience Australia has recently completed a marine survey in the offshore northern Perth Basin, off Western Australia (Jones et al., 2011b; Jones, 2011c, Upton and Jones, 2011). One of the principal aims of the survey was the collection of evidence for natural hydrocarbon seepage. The survey formed part of a regional reassessment of the basin's petroleum prospectivity in support of frontier exploration acreage Release Area W11-18. This reassessment was initiated under the Australian Government's Offshore Energy Security Program and formed part of Geoscience Australia's continuing efforts to identify a new offshore petroleum province. The offshore northern Perth Basin was identified as a basin with new frontier opportunities. New data demonstrated that proven onshore-nearshore petroleum system is also effective and widespread in the offshore (Jones et al., 2011a). Evidence for a Jurassic petroleum system was also demonstrated in the Release Area W11-18 (Jones et al., 2011a). The marine survey results provide additional support for the presence of an active petroleum system in the northern Perth Basin.

The Capel and Faust basins lie at water depths of 1,500-3,000 m 800 km east of Brisbane. Geoscience Australia began a petroleum prospectivity study of these remote frontier basins with the acquisition of 2D geophysical data (seismic reflection, refraction, gravity, magnetic, multi-beam bathymetry) across an area of 87,000 km2 during 2006/07. The approach mapped the complex distribution of sub-basins and determined sediment thickness through integration of traditional 2D time-domain seismic interpretation techniques with 3D mapping, visualisation and gravity modelling. Forward and inverse 3D gravity models were used to inform the seismic interpretation process and test the seismic basement pick. Gravity models had three sediment layers with inferred average densities of 1.85, 2.13, 2.31 t/m3 overlying a pre-rift basement of density 2.54 t/m3, itself considered to consist of older basin material evidently intruded by igneous rocks. Conversion of travel times of interpreted seismic horizons to depth domain was achieved using a quadratic function derived from ray-tracing forward modelling of refraction data supplemented by stacking interval velocities, and densities for gravity modelling were inferred from the same velocity models. These models suggest sediment of average velocity 3.5 km/s reaches a thickness exceeding 6 km in the northwest of the area, and for the first time mapped the extent and depth of sediment in these basins. The results of the study have confirmed that sediment thickness in the Capel and Faust basins is sufficient in places for potential petroleum generation.

Overall, the cruise met its objectives of studying rift and drift sedimentation, and obtaining cores for palaeo-oceanography. The east Tasmanian seismic program was completely successful. The planned sampling program was somewhat curtailed by bad weather, equipment failures and other factors. It was least successful off east Tasmania. A total of about 1300 km of 8-fold multichannel seismic data were acquired along 8 transects across the east Tasmanian margin. The quality of the seismic profiles was excellent, with good resolution and penetration, given the bad weather and the limitations of the acquisition system. The seismic source comprised 2 GI airguns (each 45/105 cu. in. capacity) giving a penetration of 2-2.5 s twt (2.5-3 km) in places. The seismic profiles indicate a structurally complex margin with rugged basement relief that includes large-scale horst/graben structures and volcanic intrusions. The sedimentary section on the continental slope is at least 1.5 s twt thick in some graben and includes Campanian-Paleocene early sag-phase deposits, which are 0.5-1.0 s twt thick. Regional compressive tectonism in the Late Paleocene-Early Eocene has produced widespread inversion (folding/faulting) in this succession. A wedge of Neogene shallow-water carbonates underlies the continental shelf. It shows seaward progradation and attains a maximum thickness of ~700 m beneath the shelf edge. Oceanic basement (?Campanian) adjacent to the margin lies at a depth of 7.0-7.5 s twt. The continental rise and Tasman Abyssal Plain in this zone are underlain by 1.5-2.0 s twt of post-breakup sedimentary section. The East Tasman Saddle is underlain by `transitional? basement and contains a sedimentary section of similar thickness. During the sampling program 58 of 86 stations were successful: 38 gravity cores (21 successful), 4 piston cores (3), 16 dredges (7) and 28 grabs (28). Total core recovery was 81.4 metres from the 16 successful cores taken in soft sediments, an average recovery of about 5 metres. The fairly low success rate with the gravity corer can be ascribed to problems with foram sand east of Tasmania, and shelly sand in Storm Bay. The low success rate with the dredge was related to the lightness of the gear. The deployment of the heavy piston corer for the first time on Franklin was successful. However, we did not attempt to piston core in deep water. East of Tasmania we recovered 8 gravity cores, and 7 dredge hauls. Deepwater dredging and coring were surprisingly unsuccessful. The upper slope stations, designed to sample older rocks, were reasonably successful. From these results and some existing information, general conclusions can be drawn about changes along the margin with increasing water depth. The shelf and upper slope wedge of Neogene, seaward-prograding sediments was sampled out to 1640 m. The sediments recovered include muddy sand, clayey sandstone with siliceous nodules, siliceous sandstone and calcarenite. The calcarenite is presumably part of the Middle Miocene shelf limestone sequence that is widespread off St Helens. Somewhat deeper on the upper slope, basement outcrops occur in steep slopes: granite, arkose, metasediments, conglomerate, quartz sandstone and gritty mudstone. The granites are probably from Devonian batholiths like those onshore up the east coast. Volcanic rocks and conglomerate form a basement block in deeper water on a ridge off northeast Tasmania at ~3750m. Deepwater outcrop ridges support manganese nodules and crusts. Nannofossil oozes cling to the slope, particularly in local basins, and are ubiquitous in deep water. The East Australian Current apparently winnows many of the oozes to form a blanket of foram sand.

Geoscience Australia Marine Survey 267 was undertaken aboard the Parmelia K, a 28 m pearling boat out of Broome. The survey departed Darwin on 3 March 2004 and terminated in Broome on 18 March 2004. The length of the survey was curtailed by unfavourable weather conditions associated with tropical cyclones Evan and Fay. The aim of the survey was to test and validate a range of techniques used in the detection/identification of natural hydrocarbon seepage. The Yampi Shelf in the northern North West Shelf was selected for the test bed as it is a known region of intense and widespread hydrocarbon seepage. One of the most significant findings of the survey was the direct observation of natural hydrocarbon seepage in the Timor Sea region of the North West Shelf, which has previously only been interpreted through remote sensing or automated water sampling techniques (sniffer). Seepage plumes were observed rising from pockmark fields or hard-grounds on the vessel's echosounder and the side-scan sonar. Gas bubbles with oily films were observed at the surface. Active seepage sites were detected in close associated with hydrocarbon related diagenetic zones (HRDZs) interpreted in 3D seismic coverage of the region. A towed fluorometer detected variations in the hydrocarbon concentration of the sea surface over the study areas. Seepage appeared to be most active in association with low-tide, and more suppressed during high tide. Multi-beam swath bathymetry of the study areas revealed channels between 2 and 20 m deep on the Yampi Shelf headland and in the vicinity of the major HRDZs. Tidal current directions measured by an acoustic doppler current profiler (ADCP) in the Yampi Shelf headland channels suggests that tidal shears over this headland may be giving a response on Synthetic Aperture Radar (SAR). Sediment samples were collected with a Smith-Macintyre Grab, a dredge and a gravity core, although coring was largely unsuccessful due to carbonate hard-grounds over the seepage sites. Grab and dredge samples suggest that the active seeps are zones of preferential macro-biotic distribution. Significant down-time was introduced through poorly functioning equipment and a lack of experience on behalf of the staff. This was primarily due to the fact that some of the equipment was leased from Seismic Asia Pacific Ltd. Therefore it is recommended for future surveys that an operator be supplied with leased equipment, or that the equipment is purchased by Geoscience Australia and staff are appropriately trained before the survey. It is also highly recommended that the survey have seismic acquisition capability, as the seismic data proved to be the best proxy for seepage site location.

This report contains the preliminary results of Geoscience Australia survey 266 to central Torres Strait. The survey was undertaken to investigate the seabed geomorphology and sedimentary processes in the vicinity of Turnagain Island and to infer the possible effects (if any) on the distribution, abundance and survival of seagrasses. The Turnagain Island region was chosen because it is a known site of recent widespread seagrass dieback. The present survey is the first of two by Geoscience Australia to be carried out in 2004 and is part of a larger field-based program managed by the Reef CRC aimed at identifying and quantifying the principal physical and biological processes operating in Torres Strait. The impetus for the program is the threat of widespread seagrass dieback and its effects on local dugong and turtle populations and the implications for indigenous islander communities.

This abstract describes the results of integrated potential firld modelling and deep-seismic interpretation from the Enderby Land and Wilkes Land margins of East Antarctica. The interpretation is based on data acquired under the Australian Antarctic and Southern Ocean Profiling Project.

Lord Howe Island is a volcanic island, rising to over 800 m, draped with Late Quaternary submarine and subaerial carbonate sediments. The island and neighbouring islets lie within a chain of seamounts and is presently at or close to the latitudinal limit to coral reef growth. Lord Howe Island and adjacent Balls Pyramid, composed of the basalts erupted around 6 million years ago, sit near the middle of broad shelves on separate peaks of one major volcanic edifice. The central part of the Lord Howe Island is covered by calcarenite that was deposited primarily as dunes (eolianite), but with isolated beach units. Uranium-series, amino acid racemisation, and thermoluminescence dating indicate that many of these were deposited during marine oxygen isotope stage 5. Eolianite units stratigraphically below the beach deposits are of penultimate interglacial, or in places perhaps older, age. Different suites of erosional landforms are associated with different lithologies. Towering plunging cliffs characterise the resistant Mount Lidgbird Basalt, in some cases fringed with large talus slopes. On less resistant lithologies or where nearshore topography means greater wave force as a result of waves breaking, there are shore platforms. Slumping cliffs abut broad erosional platforms on the poorly lithified calcarenite. A fringing reef on the western side of Lord Howe Island, the southernmost coral reef in the Pacific, is dominated by coral and coralline algae.Carbonate sediments veneering the shelf around the islands contain a more temperate biota. Located at the southern limit of reef-forming seas, but apparently having undergone erosion for much of its history outside of reef seas, Lord Howe Island provides insights into marine planation of volcanic islands close to what has been termed the Darwin Point. It represents the initial stages of fringing reef development on a volcanic island.