The 1999 release of offshore petroleum exploration acreage in the Great Australian Bight and the acquisition of high quality seismic datasets covering the Bight and Duntroon Basins, have provided a timely opportunity to reassess the stratigraphic and tectonic evolution of the area. A sequence stratigraphic framework for the Great Australian Bight region has been developed based on the interpretation of exploration wells in the Bight and Duntroon basins and a grid of new and reprocessed seismic data in the Bight Basin. Previous formation-based nomenclature has emphasised lithostratigraphic correlations rather than the chronostratigraphic relationships. The new sequence framework underpins an analysis of play elements and petroleum systems and is helping to identify new exploration opportunities.Deposition in the Bight and Duntroon Basins commenced in the Late Jurassic during a period of lithospheric extension. Extensive half graben systems were filled with fluvial and lacustrine clastic sediments (Sea Lion and Minke supersequences). Potential source rocks within these supersequences are immature at Jerboa-1 in the Eyre Sub-basin, however higher maturities are expected within adjacent half graben and in the Ceduna and Recherche Sub-basins. The syn-rift successions are overlain by widespread Berriasian to Albian fluvio-lacustrine to marine sediments of the Southern Right and Bronze Whaler supersequences. The onlapping sag-fill geometry of these Early Cretaceous packages in the Eyre, Ceduna and inner Recherche Sub-basins suggests that they were deposited during a period of thermal subsidence.Accelerated subsidence commencing in the late Albian led to the deposition of the marine shales of the Blue Whale supersequence, followed by a period of gravity-controlled faulting and deformation in the Cenomanian. The White Pointer supersequence is characterised by growth strata associated with a series of listric faults that sole out in underlying ductile shales of the Blue Whale supersequence. Open marine conditions during the Turonian-Santonian (Tiger supersequence) were followed by the development of massive shelf margin delta complexes in the late Santonian-Maastrichtian (Hammerhead supersequence). The progradational to aggradational stratal geometries within the Hammerhead supersequence suggest initial high rates of sediment input that subsequently waned during this period. An overall transgressive phase of sedimentation in the Early Tertiary (Wobbegong supersequence) was followed by the establishment of open marine carbonate shelf conditions from the Early Eocene onward (Dugong supersequence). Organic geochemical studies show that the Bronze Whaler to White Pointer supersequences have good source rock potential in the relatively proximal facies intersected by existing petroleum exploration wells. Our sequence stratigraphic model predicts the likelihood of widespread late Aptian, Albian, Cenomanian-Santonian, and Campanian marine shales, which underpin four potential marine petroleum systems.
The Townsville Basin is an extensional sedimentary basin underlying the Townsville Trough, an east‐west‐trending bathymetric feature separating the Marion and Queensland Plateaus off northeastern Australia. With the exception of several Ocean Drilling Program holes which intersected Late Miocene to Holocene sediments, there is no direct control on the stratigraphy of the Townsville Basin. Thus, the timing of basin formation and the age of the sedimentary sequences can only be interpreted within a regional tectonostratigraphic context. The maximum sediment thickness in the basin is approximately 6.5 km [4.5 s two‐way time (twt)]. This fill can be subdivided into two main seismic megasequences of synrift and sag‐phase affinities. The synrift megasequence is of probable Cretaceous age and is restricted to fault‐controlled depocentres; it has a maximum thickness of 4 km (2 s twt). The sag‐phase megasequence is Tertiary in age and occurs as drape fill; it reaches a maximum thickness of 3.8 km (2.6 s twt). The two megasequences have been subdivided into regionally mappable sequences. The structural style of the Townsville Basin is characterised by a half‐graben morphology. The half‐grabens are bounded by major normal faults and typically contain a number of rotational blocks. Depth to basement, total sediment thickness, synrift isopach and gravity data all indicate that the basin is compartmentalised into distinct sub‐basins by major north‐northwest‐ to northwest‐trending transverse structural zones. These transverse structures are associated with distinct changes in structural trends and may represent major pre‐existing crustal‐scale basement structures. Local thickening of late synrift sediments in the opposite direction to that of early synrift sediments probably reflects at least two discrete extensional events during basin formation. A younger structuring event, which occurred during early sag‐phase sedimentation, was followed by multiple reactivation in the ?Late Miocene to Early Pliocene. The structural interpretation of the Townsville Basin indicates that it formed part of a complex rift system of probable Late Jurassic to Early Cretaceous age. This system formed as a result of oblique extension that utilised pre‐existing Palaeozoic structural trends. Comparison with interpreted structural trends of the adjacent Queensland Basin (Queensland Trough) supports the suggestion that the formation of both basins was independent of the tectonism related to sea‐floor spreading in the Tasman and Coral Sea Basins.
Abstract As part of a program to improve the geological understanding and petroleum prospectivity of Australia's frontier offshore basins, Geoscience Australia has acquired new data and undertaken integrated geoscience studies of several poorly known or unexplored areas. Underpinned by these studies, new exploration opportunities have and will become available to explorers via an annual release of offshore acreage based on a system of competitive work program bids. Four exploration areas are available in the shallow water northern Arafura Basin (bids close 10th May 2007). A new geological framework study and a hydrocarbon seepage survey jointly provide strong evidence for an active Palaeozoic petroleum system in the undrilled northern portion of the basin. Deposition in the Arafura Basin commenced in the Neoproterozoic during a period of upper crustal extension that resulted in the formation of large NE-SW trending half graben. The overlying Palaeozoic section is more or less structurally conformable, despite long periods of non-deposition and erosion. Potential source rocks were deposited in the Middle Cambrian, Late Devonian and Late Carboniferous to Early Permian, in shallow-marine and deltaic environments. In comparison with the highly deformed Goulburn Graben to the south, the northern Arafura Basin has undergone only minor deformation, and previously identified exploration risks in the Goulburn Graben (timing of generation and expulsion, and reservoir quality) are reduced in the northern region. Evidence for hydrocarbon generation is provided by oil and gas shows and interstitial solid bitumens in wells in the Goulburn Graben, and SAR anomalies and shallow gas indications in sub-bottom profile, side-scan sonar and echosounder data in the northern Arafura Basin. Four shallow water offshore exploration areas are proposed for release in the Offshore Canning Basin in April 2007. The Offshore Canning Basin is a major northwest-trending, multi-phase, pericratonic basin of Early Ordovician- Carboniferous age, overlain by a northeast-trending Late Carboniferous- Cainozoic succession (part of the North West Shelf Westralian Superbasin). The release areas overlie the offshore extension of the Fitzroy Trough and Broome Platform which host several onshore oil and gas discoveries and minor oil production. The offshore Fitzroy Trough, also known as the Oobagooma Subbasin, comprises up to 5.5 km of Palaeozoic sediments and 4.5 km of Mesozoic- Cainozoic sediments. It contains only six wells, all drilled between 1970 and 1984. The older Palaeozoic section is poorly known offshore, but onshore contains proven Ordovician (Darawillian), Late Devonian (Frasnian) and Early Carboniferous (Tournaisian) source rocks that are likely to extend into the offshore area. Early Permian potential source rocks are also expected to be mature in offshore areas. Based on new biomarker analysis, multiple oil shows in the offshore Perindi-1 well correlate with onshore oils at Lloyd, Sundown and West Terrace, and are probably sourced from the Early Carboniferous Laurel Formation. Geoscience Australia conducted a hydrocarbon seepage survey of the region in 2006, and although active fluid escape pockmarks and fluid vents were identified, analysis of sediments recovered from the pockmarks show no evidence of thermogenic hydrocarbons. Acquisition of high-resolution aeromagnetic data is planned to support the release of these new exploration areas. The Mentelle Basin is a large, deep-water, unexplored basin in close proximity to the oil- and gas-producing Perth Basin on Australia's southwest margin. The basin formed near a triple junction between Australia, Antarctica and India during the breakup of eastern Gondwana in the Middle Jurassic to Early Cretaceous. In 2004- 2005 Geoscience Australia acquired 1450 km of regional 2D seismic data as well as sub-bottom profile, swath bathymetry, dredge samples and SAR data. This new data has been integrated with a regional tectonostratigraphic framework of the southern Perth and Mentelle basins to assess their petroleum prospectivity. Preliminary results indicate that the Mentelle Basin comprises several large depocentres with apparent extensional architecture and a total sediment thickness up to 9 km. The western, deep water (2000–3500 m), depocentre contains at least 6 km of inferred Middle-Late Jurassic to Early Cretaceous synrift sedimentary section. A series of smaller extensional depocentres in the shallower water (500–1500 m) eastern region contain at least 4 km of synrift sedimentary section. Source potential is interpreted to be similar to that of the southern Perth Basin where Jurassic and Berriasian coals, coaly mudstones and lacustrine shales have generated both oil and gas. Regional basin architecture favours eastward migration of hydrocarbons from western source kitchens updip into structural and stratigraphic traps in shallower water eastern areas. Geoscience Australia will acquire new long-cable seismic data, potential field data and seabed samples prior to the proposed inaugural release of exploration areas in this frontier basin. Presented at: 2007 South East Asia Petroleum Exploration Society (SEAPEX) Conference, Singapore, 2007
New geophysical data acquired by Geoscience Australia during the Southwest Margins 2D seismic survey in 2008-09 has been used to interpret the tectonic and depositional history of the Mentelle Basin. The Mentelle Basin is a large, potentially prospective frontier basin located between the Yallingup Shelf and the Naturaliste Plateau, offshore southwestern Australia. It comprises several intermediate water-depth (500?2000 m) depocentres in the east (eastern Mentelle Basin) and a large ultra deep-water (2000?4000 m) depocentre in the west (western Mentelle Basin). Interpretation of the new data suggests that initial rifting in the Mentelle Basin occurred in the Early Permian as part of the Perth Basin extensional system. This was followed by Late Permian to Early Jurassic thermal subsidence. Half graben with Permo-Triassic fill are mapped in the eastern Mentelle Basin. The main depositional phase in the western Mentelle Basin is interpreted to correlate with Mid-Jurassic to Early Cretaceous extension in the Perth Basin and on the southern margin. Structural interpretation of the new dataset indicates that in the northern part of the western Mentelle Basin, major structures are trending north? south, similar to the Perth Basin, whereas in the south most structures are trending northeast?southwest, which is consistent with the orientation of the extensional basins on the southern margin. The proximity of the southern margin rift system not only affected the structure of the Mentelle Basin but also resulted in major fault reactivation, inversion and margin collapse in the Eocene corresponding to the onset of fast spreading in the Southern Ocean.
Terra Nova, 24, 167–180, 2012 Abstract The rifting history of the magma‐poor conjugate margins of Australia and Antarctica is still a controversial issue. In this article, we present a model for lithosphere‐scale rifting and deformation history from initial Jurassic rifting to Late Cretaceous breakup for the conjugate Bight Basin–Terre Adélie section of the margin, based on the interpretation of two regional conjugate seismic profiles of the margins, and the construction of a lithosphere‐scale, balanced cross‐section, sequentially restored through time. The model scenario highlights the symmetric pattern of initial stretching resulting from pure shear at lithospheric‐scale accompanied by the development of four conjugate detachments and crustal half‐graben systems. This system progressively evolves to completely asymmetric shearing along a single south‐dipping detachment at the scale of the lithosphere. Antarctica plays the role of the upper plate and Australia, the lower plate. The detachment accounts for the exhumation of the mantle part of the Australian lithosphere, and the isolation of a crustal klippe separated from the margin by a serpentinized peridotite ridge. The total elongation amount of the Australian–Antarctic conjugate system reaches ∼473 km (178%). Elongation was partitioned through time: ∼189 and ∼284 km during symmetric and asymmetric stages respectively. During the symmetric stage, both margins underwent approximately the same degree of crustal stretching [∼105 km (75%) and ∼84 km (67%) for Australia and Antarctica respectively]. Again, both margins accommodated relatively the same elongation during the asymmetric stage: the Antarctic upper plate records an elongation amount of ∼284 km (88%) as crustal/mantle stretching, above the inferred low‐angle south‐dipping detachment zone, whereas the Australian lower plate underwent ∼270 km (206%) of elongation through mantle exhumation. Although the restoration process does not allow reconstruction of the precise geometry before deformation, we propose that the Jurassic early geometric evolution of the margins may have been controlled by the inherited structure or rheological heterogeneities of the continental crust; its later evolution is thought to relate to the mechanical evolution of the crustal and mantle material during exhumation, with a strong increase in localization of shear in the lower crust and mantle part of the Australian margin. The geometry of the rifted margins is comparable to other magma‐poor rifted margin such as the Newfoundland–Iberia margins or the exhumed Alpine Tethys margin exposed in the Central Alps.
The interpretation of two regional seismic reflection profiles and the construction of a balanced cross section through the southern Australian margin (Bight Basin) are designed to analyze the influence of the Australia‐Antarctica continental breakup process on the kinematic evolution of the Cretaceous Ceduna delta system. The data show that the structural architecture of this delta system consists of two stacked delta systems. The lower White Pointer delta system (Late Albian‐Santonian) is an unstable tectonic wedge, regionally detached seaward above Late Albian ductile shales. Sequential restoration suggests that the overall gravitational sliding behavior of the White Pointer delta wedge (∼45 km of seaward extension, i.e., ∼27%) is partially balanced by the tectonic denudation of the subcontinental mantle. We are able to estimate the horizontal stretching rate of the mantle exhumation between ∼2 and 5 km Ma −1 . The associated uplift of the distal part of the margin and associated flexural subsidence in the proximal part of the basin are partially responsible for the decrease of the gravitational sliding of the White Pointer delta system. Lithospheric failure occurs at ∼84 Ma through the rapid exhumation of the mantle. The upper Hammerhead delta system (Late Santonian‐Maastrichtian) forms a stable tectonic wedge developed during initial, slow seafloor spreading and sag basin evolution of the Australian side margin. Lateral variation of basin slope (related to the geometry of the underlying White Pointer delta wedge) is associated with distal raft tectonic structures sustained by high sedimentation rates. Finally, we propose a conceptual low‐angle detachment fault model for the evolution of the Australian‐Antarctic conjugate margins, in which the Antarctic margin corresponds to the upper plate and the Australian margin to the lower plate.
'/%3e%3c/defs%3e%3cpath fill='%23012169' d='M0 0h10080v5040H0z'/%3e%3cpath stroke='%23fff' stroke-width='.6' d='m0 0 6 3m0-3L0 3' clip-path='url(%23b)' transform='scale(840)'/%3e%3cpath stroke='%23e4002b' stroke-width='.4' d='m0 0 6 3m0-3L0 3' clip-path='url(%23c)' transform='scale(840)'/%3e%3cpath stroke='%23fff' stroke-width='840' d='M2520 0v2520M0 1260h5040'/%3e%3cpath stroke='%23e4002b' stroke-width='504' d='M2520 0v2520M0 1260h5040'/%3e%3cg fill='%23fff'%3e%3cuse xlink:href='%23d' x='2520' y='3780'/%3e%3cuse xlink:href='%23a' x='7560' y='4200'/%3e%3cuse xlink:href='%23a' x='6300' y='2205'/%3e%3cuse xlink:href='%23a' x='7560' y='840'/%3e%3cuse xlink:href='%23a' x='8680' y='1869'/%3e%3cuse xlink:href='%23e' x='8064' y='2730'/%3e%3c/g%3e%3c/svg%3e)
