No abstract

No abstract

Five supersequences have been revealed by a regional sequence stratigraphic study conducted in the Albian (109 Ma) to Recent section of the Exmouth-Barrow passive margin. The interpretation utilises a new sequence stratigraphic model developed for mixed siliciclasticcarbonate lithofacies. A high degree of resolution is brought to the study by identification of 37 regional sequence boundaries controlled by biostratigraphic, wireline and seismic data. Ditch cutting analysis, integrated into the new chronostratigraphic framework, provided detailed lithofacies maps.The five supersequences, named the Gallic, Senonian, Palaeogene, Middle Neogene and Pliocene, are based upon regional lowstand, transgressive and highstand phases. The Gallic Supersequence (late Tithonian–latest Cenomanian) represents a marine incursion of siliciclastic sediments coincident with the rifting and accelerated movement of India away from Australia. A Senonian Supersequence (latest Cenomanian–middle Maastrichtian) truncates the previous supersequence with incised canyons developed on the outer shelf. The evolution of the Senonian section corresponds to the Australian separation from Antarctica and the first appearance of carbonates.The Palaeogene Supersequence (middle Maastrichtian– late Early Miocene) dominates much of the Tertiary and is identified by a basinward shift of facies following a Maastrichtian–Paleocene sea level fall. Enhanced subsidence on the outer shelf during the Eocene created a forced transgression with carbonate mudstonesiltstone deposition. A highstand during the Oligocene– Early Miocene formed the distinctive prograding carbonate shelf recognised throughout the North West Shelf.A Middle Neogene Supersequence (late Early Miocene– Early Pliocene) is identified by an erosive base and the development of a thin lowstand fan on the outer shelf. The supersequence is largely characterised by backstepping reefs following a Middle Miocene transgression. A Late Miocene eustatic stillstand restricted reef development to the inner shelf, generating coarsegrained carbonate progrades from highstand-shedding. The final Pliocene Supersequence (Pliocene–Recent) was initiated by a eustatic fall during the Early Pliocene and was followed by the development of a transgressive, aggrading shelf.

No abstract

No abstract

A successful approach to basin analysis requires the broad-scale reconstruction of the three dimensional depositional systems in relation to concurrent structural development of the basin. The Gidgealpa-Merrimelia-lnnamincka (GMI) Trend is a prominent, asymmetric, mildly compressional anticlinal trend located in the Late Carboniferous to Triassic Cooper Basin. Its northwest flank is controlled by high angle thrust faults which were reactivated repeatedly throughout geological time. The present study addresses both the structural style and depositional character of the GMI Trend, focusing on selected areas. It is an integrated approach utilising wire-line logs, seismic interpretation, isopach and structural maps and detailed palynology. This approach has produced a detailed chronostratigraphic subdivision of the Permo-Triassic sequence, particularly the Patchawarra Formation, which points to evidence of synsedimentary tectonics. Evidence from crestal unconformities suggests that the GMI Trend was uplifted during at least four distinct structural episodes. These phases of uplift result from the rejuvenation of pre-Permian faults. Regional investigation of chronostratigraphic units incorporating palynological information, clearly demonstrates the palaeogeography and the presence of internal unconformities within the Patchawarra Formation. Subsurface distribution of hydrocarbon pools and improved definition of areas of prospectivity relate to the episodic uplifts. Although known hydrocarbon reserves have largely accumulated in structural traps, additional potential exploration targets in the Permian sequence exist in stratigraphic, combination, pinchout and downflank fault traps as well as onlap plays along the mid flank areas of the GMI Trend.

No abstract

The northeast-trending Nappamerri Syncline and its flanking high to the southeast, the Murteree-Nappacoongee (NM) Trend, show structural development throughout the deposition of the Permo-Triassic Cooper Basin sequences. Pre-existing topography, such as around Moomba, influenced early depositional patterns within the area. Rates of sedimentation were influenced by the rate of uplift of source areas around the basin, largely as a consequence of buckling. Periods of active tectonism resulted in non-deposition and stripping of sediments from uplifted blocks while deposition continued in deeper areas. Hangingwall blocks, pushed up along reverse faults, strongly influenced the areas of sedimentation and the facies being deposited. This is particularly evident along the NM Trend. Phases of uplift were immediately followed by increased sedimentation where fluvial deposition dominated. The effect of displacement along the northwest-trending basement lineaments was to subdivide the northeast trends into compartments which contain similar facies within each time slice. Adjacent compartments may display different facies and different tectonic histories. An inversion episode, particularly evident in the Big Lake/Moomba area, resulted in a reversal of the depocentre and was related to phases of Sakmarian compression.Facies distribution and sandstone percentage maps of the chronostratigraphic units of the Patchawarra Formation suggest that a northeast-trending major channel system entered this part of basin along the NW edge of the Murteree area.