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Two- and three-dimensional (2D and 3D) seismic stratigraphic interpretation, palaeobathymetric analysis from benthic foraminifera, and 2D forward tectonic modelling are combined to understand the genetic significance of prominent seismic discontinuity surfaces typically mapped as ?sequence boundaries? and ?flooding surfaces?, and their intervening sequences. Integration of these data has allowed interpretation of the Tertiary, heterozoan (i.e., non-photozoan) carbonate-dominated succession detailing the evolution of five prograding clinoformal sequences (2-5 m.y. duration), and 19 sub-sequences (<0.5-1 m.y. duration), along the Rankin Trend. Variations in accommodation space as modelled across the Dampier Sub-basin using 2D kinematic and flexural modelling are the combined result of synrift and postrift thermal subsidence, inversion and eustatic variations. The major observations and implications of this study are: ? Onlap onto the clinoform front of primary mappable surfaces is submarine with minimum estimated palaeo-water depths > 100 m at the shelf edge. Exposure surfaces identified in the middle Miocene are seismically less prominent, with potential karstification identified 6-8 km inboard of shelf edges. ? Systems tracts could not be consistently identified in the progradation-dominated succession. Lowstand basin-floor fans/aprons and transgressive systems tracts are largely absent on the seismic scale, resulting in downlap directly onto sequence boundaries. ? Linear, 30-80 km along strike, two-dimensional mapped sequences, are the integration of local sedimentary lobes up to 10 km in diameter. ? Canyon development may be controlled by inclination on gully failure walls rather than variations in sea level. Gully initiation is coincident with the mid-Miocene climatic Optimum. However, once established, erosion paths are maintained and enlarged by downslope sediment flows, derived from headward failure, regardless of proposed sea-level variations. ? The magnitude of inversion-related uplift is small, reaching a maximum of ~50-70 m at anticlinal crests focussed along the Rankin, Madeleine and Rosemary trends. Although this is of a similar scale to postulated eustatic variations that increase or decrease accommodation space across the entire margin, unconformities and onlap discontinuity surfaces related to these inversion structures are areally restricted.

Seismic sequence analysis across the Northern Carnarvon basin of the northwest Australian margin has been combined with a kinematic and flexural model for the deformation of the lithosphere and palaeobathymetric analysis of benthic foraminifera to define the history, distribution and magnitude of inversion within the Dampier Sub-basin during the Cretaceous and Tertiary. The large palaeo-water depths (>1000 m) developed across the outer margin in the late Oligocene-Miocene questions the results from earlier well-based backstripping studies. This accommodation was created by a combination of thermal subsidence engendered primarily by Tithonian-Valanginian extension and continental break-up and sediment loading associated with the progradation of Neogene clinoforms. Discrete inversion events characterize the Santonian, late early Miocene, middle Miocene, late Miocene, latest Miocene, and Plio-Pleistocene of the Northern Carnarvon basin. Compression-induced inversion creates and destroys accommodation space at different spatial wavelengths compared with thermal subsidence, sediment loading and eustatic variations and thus can be spatially separated. While brittle deformation in the upper crust results in relatively short-wavelength uplift, the flexural response to this tectonic loading produces a longer-wavelength regional subsidence adjacent to the inversion anticline. In general, the flexural component is negligible. Inversion tends to be focused along pre-existing rift fault systems. However, the spatial distribution of inversion varied through time, with Cretaceous inversion concentrated along the northeast-southwest oriented Rankin, Madeleine, and Rosemary trends while the locus of Miocene inversion was located ~20 km northwest of the Rosemary Trend. Clearly, different fault zones were involved in the inversion process at different times. We surmise that intraplate stresses generated from the readjustment of the Indo-Australian plate were a possible mechanism for Santonian inversion. Tertiary inversion, interpreted to have commenced in the middle Miocene (~17 Ma), continued to occur through to the Plio-Pleistocene. The onset and continued compression is interpreted to be related to the Australian/Indonesian continent-continent collision. Total shortening of the lithosphere during the Santonian and Tertiary was modelled to be 2.6 and 0.16 km, respectively.

A new sequence stratigraphic framework has been developed for the Otway Basin based on the interpretation and integration of offshore wells, key onshore wells, new biostratigraphic results and a regional grid of 2D seismic data. In the new tectonostratigraphic framework, seven major basin phases and their eight component supersequences are recognised as follows: 1) Tithonian?-Barremian rifting of the Crayfish Supersequence 2) Aptian-Albian post-rift deposition of the Eumeralla Supersequence 3) mid-Cretaceous compression and inversion 4) Late Cretaceous rifting of the Shipwreck and Sherbrook Supersequences 5) latest Maastrichtian to Middle Eocene basin reorganisation and early thermal subsidence of the Wangerrip Supersequence 6) local inversion and thermal subsidence of the Nirranda Supersequence (Middle Eocene to Early Oligocene) followed by thermal subsidence and progressive compression of the Heytesbury Supersequence (Late Oligocene to Late Miocene) leading to Late Miocene uplift and erosion and 7) Plio-Pleistocene deposition of the Whalers Bluff Supersequence. Basin phases are distinguished by their different tectonic driving mechanisms as the primary control on the creation of accommodation space. The supersequences are bounded by regional unconformities and define major episodes of sedimentation within each basin phase. Supersequences are related to second-order transgressive-regressive cycles within the basin and are regionally mappable. The new sequence stratigraphic framework is then used as the basis for correlation to deep-water regions where well-control is limited or absent. The framework is also used to help place existing, complex, facies-dependent lithostratigraphic schemes into depositional and petroleum systems context.

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The conjugate margins of Wilkes Land, Antarctica, and the Great Australian Bight (GAB) are amongst the least understood continental margins. Break up along the GAB-Wilkes Land part of the Australian-Antarctic margin commenced at approximately 83 Ma. Using recent stratigraphic interpretations developed for the GAB, we have established a sequence stratigraphy for the Wilkes Land margin that will, for the first time, allow for a unified study of the conjugate margins. By reconstructing the two margins to their positions prior to break up we were able to identify comparable packages on the Wilkes Land margin to those recognised on the GAB margin. Excluding the glacial sediments on the Antarctic margin, the sedimentary sequence along the Wilkes Land margin is very thin compared to the GAB margin, which has substantially more syn- and post-rift sediments. Despite the differences in thickness, the syn-rift sedimentary package on the Wilkes Land margin exhibits a similar style of extensional faulting and seismic character to its GAB margin counterpart. In comparison, post-rift sequences on the Wilkes Land margin are markedly different in geometry and seismic character from those found on the GAB margin. Isopach mapping shows substantial differences in the thickness of the post-breakup sediments, suggesting different sediment sources for the two margins. The Late Cretaceous Hammerhead Supersequence provides much of the post-rift thickness for the GAB margin as a result of large sediment influx into the basin. This supersequence is characterised by a thick progradational succession and was deposited in fluvio-deltaic and marine environments. The equivalent succession on the Wilkes Land margin has a different seismic character. It is thinner and aggradational, suggesting a distal marine environment of deposition.

Geoscience Australia is currently conducting a study under the National CO2 Infrastructure Plan (NCIP) to assess suitability of the Vlaming Sub-basin for CO2 storage. It involves characterisation of the potential seal, the Early Cretaceous South Perth Shale (SPS), by integrating seismic and well log interpretation into a sequence stratigraphic framework. The SPS, conventionally described as a regional seal deposited during a post-rift thermal subsidence phase, consists of a series of prograding units deposited in a deltaic to shallow marine setting. Mapping of the SPS has revealed differences in the geometries of progradational sequences between the northern and southern areas, related to the type and distance to the sediment source as well as the seafloor morphology. In the northern area, deltaic progradation and aggradation occurred over a flat topography between the two uplifted blocks. The succession is composed of prograding sequences commonly exhibiting sigmoidal to oblique geometries, prograding from the north-east to south-west. In the southern area the topography is more complex due to the presence of several paleotopographic highs associated with pre-existing structures. These sequences are sigmoidal to oblique in cross section. They were deposited in fan shaped lobes, successively infilling paleotopographic lows. Direction of the progradation is from southwest to northeast. The thickness of the SPS varies from 200 m between topographic highs to 700 m in the lows. Sedimentary facies are interpreted to vary from sandy delta front to muddy slope and prodelta deposits. These findings will be used in a 3D geological model for assessing CO2 storage potential.

Measured sections and sequence stratigraphic interpretations of the Upper McNamara and Fickling Groups, Queensland.

Paleoproterozoic-earliest Mesoproterozoic sequences in the Mount Isa region of northern Australia preserve a 200 Myr record of intracontinental rifting and consequent passive margin formation. Passive margin formation followed a switch in the extensional direction from ENE-WSW to NE-SW ca. 1740 Ma, and was accompanied by extensional unroofing of 1670 Ma magmatic rocks from mid-crustal depths. The resulting asymmetries in basin geometry and crustal architecture represent a first-order constraint on reconstructions of Rodinia that juxtapose Proterozoic eastern Australia against rocks of comparable age in western Laurentia.

A new tectonostratigraphic framework for the southern Bowen, Gunnedah and Surat basins in New South Wales is developed, based on the sequence stratigraphic and structural interpretation of regional reflection seismic data, and petroleum and stratigraphic wells. This framework provides an improved correlation between the Bowen and Gunnedah basins, and delineates the relationship between tectonic events, basin phases, and the development of depositional sequences. The Early Permian Cretaceous depositional history of the basins in this region was controlled by successive phases of tectonic subsidence driven by extension, thermal relaxation and lithospheric flexure, interrupted by periods of contraction and uplift. Early Permian extension was characterised by the eruption of volcanic rocks and the accumulation of dominantly lacustrine sediments, followed by the deposition of thick coal-conglomerate successions, particularly along the eastern margin of the basin. The succeeding thermal subsidence phase was quickly overwhelmed by flexural subsidence driven by foreland loading during the Early Late Permian, and the deposition of marine, deltaic and non-marine rocks. Late Permian contraction and uplift in the Gunnedah Basin was followed by the accumulation of non-marine Triassic rocks derived from the New England Orogen. A dominantly fluvial Middle Triassic succession is present across the entire region. Effects of the Middle Late Triassic contractional event that is evident throughout the Bowen Gunnedah Sydney basin system were concentrated along the basin-bounding Goondiwindi, Kelvin and Mooki faults and also adjacent to the Boggabri Ridge