Palynological studies of Triassic-Jurassic well sections in the Offshore North Perth Basin have helped to reveal a more complicated geological history than previously recognised. This work is part of a major Geoscience Australia project studying the geological history and petroleum prospectivity of the basin. Seismic and well log interpretations have been combined with the sedimentological data to develop a high resolution sequence stratigraphic framework. This work is heavily reliant on the palynological data to provide the necessary age control, palaeoenvironmental interpretations and well correlations. Abstract continues (no space in field).

The Darling Basin is a Late Silurian to Early Carboniferous feature occupying approximately 100 000 km2 of western New South Wales. In the area of the Pondie Range Trough, near the town of Wilcannia, it comprises up to 12 000 m of sediments, interpreted to have been deposited as syn-rift, thermal sag, and foreland basin phases of basin development, overlain by a veneer of Murray Basin and underlying infrabasin sediments.

The Perth Basin formed as part of an obliquely-oriented extensional rift system on Australia's southwestern margin during the Paleozoic to Mesozoic breakup of eastern Gondwana. The Houtman Sub-basin is situated in the offshore portion of the northern Perth Basin, located about 200 km northwest of Perth. It is an elongate, northwest-southeast trending depocentre containing up to 14 km of Early Triassic to Late Jurassic sedimentary strata. A detailed sequence stratigraphic study has been undertaken on the three wells in the Houtman Sub-basin: Gun Island 1, Houtman 1 and Charon 1. The purpose of this study was to investigate facies variations between the wells to gain a better understanding of potential source, reservoir and seal distribution and to assist regional palaeogeographic reconstructions of the Perth Basin. The study focussed on the Early-Late Jurassic succession comprising the Cattamarra Coal Measures, Cadda Formation and Yarragadee Formation. Wireline log character, cuttings, sidewall core and conventional core lithologies and palynological data were used to identify facies and paleoenvironments. Palynology for all wells has been reviewed, including new data collected by Geoscience Australia for Gun Island 1 and Charon 1. Facies stacking patterns were used to define systems tracts and subsequently ten third-order depositional sequences. Collectively these sequences define a larger scale, second-order (supersequence) transgressive-regressive cycle. The Cattamarra Sequence Set forms a regional transgression which culminates in an extensive marine maximum flooding event within the Cadda Sequence Set. These sequence sets are followed by the regressive highstand Yarragadee Sequence Set. The third-order sequences characterised in this study overprint this supersequence and control the local distribution of facies. The combined influence of these third- and second-order sequences on facies distribution has significant implications for the distribution of potential reservoirs and seals, particularly in the northern Houtman Sub-basin where well and seismic data are relatively sparse.

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.

The well folio package contains the combined data of 23 offshore wells in the northern Perth Basin, including the first published synthesis of data from fourteen new field wildcat wells drilled in this part of the basin since the Cliff Head 1 discovery (2001). Completed as part of the Australian Government's Offshore Energy Security Program, the well folio package will improve the assessment of petroleum prospectivity in the offshore Perth Basin. The well folio package consists of 23 composite well log plots, six well to well correlations and a new chronostratigraphic sequence framework and includes Geoscience Australia's revised Offshore Perth Basin Biozonation and Stratigraphy 2011 Chart 38 (Jones et al., 2011a). The well folio package summarises key stratigraphic, biostratigraphic and geochemical data and sequence interpretations for wells in the offshore northern Perth Basin from the Beagle and Turtle Dove ridges, Houtman and central Abrolhos sub-basins and the Wittecarra Terrace. Composite well log plots at 1:5000 scale summarise, in graphic form, the main stratigraphic features and hydrocarbon occurrences. The composite well logs also graphically summarise results from 120 new palynological samples and 244 new Rock-Eval pyrolysis/Total Organic Carbon (TOC), 85 new Vitrinite Reflectance (VR), 14 new FAMM maturity and compiled Grains with Oil Inclusions (GOITM) measurements. Compilations of new and open-file biostratigraphic and geochemical data are also included in digital spreadsheet formats. Data from the 23 offshore wells show that the main sedimentary succession in the offshore northern Perth Basin is Permian to Late Jurassic in age: two wells intersected a sandstone section of Late Cambrian to Early Ordovician age. Reviewed open-file biostratigraphic data, new biostratigraphic data and interpretations from these samples have been used in conjunction with well logs and lithological interpretations of cuttings, cores and side wall cores to define a new chronostratigraphic sequence framework for this part of the basin. Sequences and major maximum flooding surfaces are correlated between wells to show the spatial and temporal distribution of these sequences through the offshore northern Perth Basin.

No abstract available

The following abstract was written in order to facilitate the compilation of the Queensland four-mile geological sheets and the explanatory notes accompanying them. The area described covers the Springsure, Emerald, Jericho and partly the Tambo and Baralaba four-mile sheets.

No abstract available

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.