Academic literature on the topic 'Nelson Sub-basin'

The northwest-trending Otway Basin in southeast Australia formed during the separation of Australia and Antarctica between the latest Jurassic and the Early Cainozoic. A new, deep-seismic data set shows that the basin comprises two temporally and spatially overlapping rift components:the mainly Late Jurassic to mid-Cretaceous, east-west trending, inner Otway Basin—comprising the onshore basin and most of the continental shelf basin; andthe northwest–southeast to north–south trending depocentres beneath the outer shelf and continental slope, extending from eastern South Australia to the west coast of Tasmania, and a relatively minor and ill-defined sub-basin underlying the continental rise in water depths greater than about 4,500 m. This rift system was most active from the mid-Cretaceous to Palaeogene, and was strongly affected by sinistral strike-slip motion as Australia and Antarctica separated.The continental slope elements contain the bulk of the sediment volume in the basin. From northwest to southeast, these elements comprise the Beachport and Morum Sub-basins, the north-south trending Discovery Bay High, and the Nelson Sub-basin which appears to be structurally and stratigraphically continuous with the Sorell Basin off west Tasmania.The reflection character of the crust and upper mantle varies widely across the basin, and there is a strong correlation between that character and the basin configuration. It appears that accommodation space beneath the slope basin was created largely by extension and removal of most of the laminated deep continental crust.There is encouragement for hydrocarbon exploration in the deep-water basin. Firstly, there are indications of diagenesis related to fluid flow in and above the strongly faulted Cretaceous section in the Morum Sub-basin. As an Early Cretaceous petroleum system is already proven beneath the continental shelf, this suggests that the same system is also active in deep-water. Secondly, existing sample data suggest that a second, Late Cretaceous petroleum system could be active where any source rocks are sufficiently deeply buried; this condition would probably be met in the Nelson Sub-basin.

AbstractThe Nelson Field is located in Blocks 22/11, 22/6a, 22/7 and 22/12a in the UK Central North Sea. Nelson is a simple dip closed structure and is one of a series of Palaeocene Forties Sandstone Member oil accumulations situated on the Forties-Montrose High. The first exploration well on the prospect, 22/11-1, was drilled by Gulf Oil in 1967. Although hydrocarbon shows were encountered in a heterolithic section of Forties Sandstone Member, the well failed to flow on test and was abandoned. 3D seismic data were first acquired in 1985 and led to the discovery of Nelson in 1988 when the 22/11-5 well was drilled by Enterprise Oil plc. Following appraisal drilling, Nelson was granted production consent and the field came on-stream in February 1994. The hydrocarbon type is a light 40° API crude with a GOR of 555 SCF/BBL and is believed to be sourced from the East Forties Basin. The Nelson Field is developed from a 36 slot minimum facilities platform. Currently there are 23 platform producers, four sub-sea producers and four platform water injectors. Oil export is via the Forties Pipeline System and gas export is via the Fulmar Gas System. Oil originally in place is estimated at 790 million barrels of oil (MMBBL). Up to end-1999, the field had produced 261 MMBBL. Since the field was described by Whyatt et al. (1992), a further 28 wells have been drilled resulting in the collection of a considerable amount of new geological and geophysical data. This now includes a total of 6500 ft of Palaeocene core and 4D seismic data. This has enabled a more detailed understanding of the structure and sequence stratigraphy of the Nelson Field. This paper illustrates the importance of seismic mapping, high resolution biostratigraphy and sedimentology in developing the Nelson Field model.

Pindos foreland is a tertiary turbiditic basin fill trending parallel to the external Hellenides (Aubouin, 1959). The basin is bounded to the east by the Pindos thrust and to the west by the Ionian thrust. Apart of these two major thrusts, minor thrusts separate the basin into linear narrow sub-basins, trending also parallel to the basin axis. For the grain size statistical analysis 35 sandstone samples were collected from sandstone beds in three sections: Metsovo, Amphilochia and Palaiopyrgos. The thickness of the beds ranges from 8 to 25 cm, and comprise Ta, Tb and Te Bouma sequence subdivisions. The samples were smashed in small pieces and then they were disaggregated using acetic acid solution. Then the samples were washed with deionized water and prepared for sieve analysis. The results of the sieve analysis were plotted in grain size cumulative diagrams in order to estimate the statistical parameters. Sorting, skewness and kyrtosis were calculated and also the samples were plotted in CM, FM and LM diagrams (Passega, 1957; Passega, 1964) The palaeoflow velocity measurements were estimated using Komar's model (1985). The results of the above analysis provided the following conclusions: a) Sorting values are decreasing at the top of Metsovo and Palaiopyrgos sections indicating an increase of the sediments immaturity, b) The asymmetry values range from positive to very positive with a trend to increase at he top in the sections of Metsovo and Amphilochia, which shows a dominance of the coarser fraction in the selected samples, c) C-M, F-M, L-M affirms that the sediment was transported to the deeper parts of the basin by turbidity currents. Mean flow velocities at the time of deposition range between 1,86 and 26,59 cm/sec. These values are very much in agreement with those proposed for low-density turbidity currents (<25cm/sec) (Nelson and Nilsen, 1984). A similar velocity range is refereed also by Avramidis (1999) who studied the turbidites of the Middle Ionian zone. In Metsovo and Palaiopyrgos mean flow velocity values increase towards the top of the stratigraphy.

The spatial and temporal performance of an ensemble of five gridded climate datasets (precipitation) (North American Regional Reanalysis, European Centre for Medium-Range Weather Forecasts interim reanalysis, European Union Water and Global Change (WATCH) Watch Forcing data ERA-Interim, Global Forcing Data-Hydro, and The Australian National University spline interpolation) was evaluated towards quantifying gridded precipitation data ensemble uncertainty for hydrologic model input. Performance was evaluated over the Nelson–Churchill Watershed via comparison to two ground-based climate station datasets for year-to-year and season-to-season periods (1981–2010) at three spatial discretizations: distributed, sub-basin aggregation, and full watershed aggregation. All gridded datasets showed spatial performance variations, most notably in year-to-year total precipitation bias. Absolute minimum and maximum realizations were generated and assumed to represent total possible uncertainty bounds of the ensemble. Analyses showed that high magnitude precipitation events were often outside the uncertainty envelope; some increase in spatial aggregation, however, enveloped more observations. Results suggest that hydrologic models can reduce input uncertainty with some spatial aggregation, but begin to lose information as aggregation increases. Uncertainty bounds also revealed periods of elevated uncertainty. Assessing input ensemble bounds can be used to include high and low uncertainty periods in hydrologic model calibration and validation.

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Prominent growth faulting and sediment bypass influenced the thickness of Sherbrook Supersequence sediments south of the Mussel Fault Zone in the Voluta Trough. This study quantifies the geometry and kinematics of faults and sediment dispersal in the deep-water province of the Otway Basin, offshore Victoria. A 3D seismic reflection survey was used to investigate the geometries and origin of complex linked growth fault arrays present within the Upper Cretaceous Sherbrook Supersequence in the Voluta Trough area. Five horizons and 46 faults were mapped within the confines of the OS2-3D seismic reflection survey which encompasses a 773 km² area along the present-day shelf edge in the central Otway Basin, Victoria. The resulting geological framework consists of two NW striking listric hard-linked fault arrays, as well as two NNE striking fault arrays that are crosscut by the identified NW striking fault arrays. Isopach maps of four Upper Cretaceous stratal units indicate growth of all studied faults has controlled distribution of sediments temporally throughout the study area since the Turonian or earlier. Episodes of growth faulting created scoop shaped hanging-wall depocentres and caused SW-SE basinward thickening of stratal units. Isolated hanging-wall depocentres coalesced to form large combined depocentres in subsequent strata. Growth faults overlying basement faults underwent multiple separate phases of displacement and may have been activated preferentially. Cumulative displacement of major NW-SE striking fault arrays increases SE along strike, where growth strata reach thicknesses >1500 m. Lateral throw variations along strike of fault arrays imply fault arrays once consisted of individual faults that grew independently prior to linkage. Throw variations along depth of faults reveals up to 722 m of throw present within Turonian-Santonian and age strata, and suggests faults nucleated in response to an Upper Cretaceous phase of rifting proposed by previous studies of the Otway Basin. Differential compaction of sediment above basement-related topography may be an important factor influencing fault distribution within the study area.
Thesis (B.Sc.(Hons)) -- University of Adelaide, School of Physical Sciences, YEAR

It is almost impossible to overemphasize the importance of good chronological control to paleolimnology. Age control allows us to determine rates of processes and fluxes of materials, and to test hypotheses of linkage between archives and hypothesized external controls of those archives. Geologists differentiate between relative age versus absolute dating methods. Relative age determinations are based on the concepts of superposition (older sediments are on the bottom, in the absence of tectonic disturbance) and lithological correlation. In contrast, absolute dating methods are done without necessary reference to other analyses or locations, to produce an age determination (i.e., 100,000 yr before present). Some methods, such as paleomagnetics, amino acid racemization, and biostratigraphy, lie in a gray area between these two, providing absolute dates or age ranges in certain circumstances and relative age constraints in others. In this book, I will refer to the general study of both relative and absolute age determination as geochronology, and use the term geochronometry to refer to absolute dating. Lithological correlation involves matching similar lithologies between outcrop or core localities, allowing a network of age relationships to be established between various sites. This can be done at any scale, from within a lake to intercontinental, although lithostratigraphical correlations based on core or outcrop observations are most commonly useful only at a local, intrabasinal level. Correlation within basins is often achieved using reflection seismic stratigraphy. Depositional or unconformity surfaces can normally be recognized on seismic lines that extend over the scale of individual sub-basins to entire lakes (Nelson et al., 1994; Lezzar et al., 1996; Van Rensbergen et al., 1998). When dated cores are obtained or outcrops studied along these seismic lines, a correlation network can be established, with probable ages attached to specific seismic horizons. Intrabasinal correlation can also be done by correlating distinctive patterns of change in features such as magnetic intensity, patterns of stable isotopic change in sediments, or biostratigraphical markers, that may be consistent across a lake basin. Sometimes, relative correlations can be made between lakes.