Subsurface architecture of fluvial-deltaic deposits in high- and low-accommodation settings

Combined seismic and well interpretation methods can be used to elucidate detail of the subsurface architecture of fluvial and fluvio-deltaic deposits. Observations made from wireline and core logs, including facies and analysing the relative proportions of architectural elements and facies associations indicative of depositional sub-environments, can be used to interpret patterns of cyclicity, changes in local accommodation conditions, and periods of increased seasonal, tidal and marine influence. Horizon slices, taken from 3D seismic volumes aid in the visualisation of laterally discontinuous, often thinly-bedded, fluvial deposits. Seismic facies, when combined with core and wireline log facies, can be interpreted as a series of ‘seismic elements’. The relative proportions of seismic elements mapped out on horizon slices allows the interpretation of depositional environments and accommodation setting; allowing the distinction between fluvial and deltaic settings. A number of data conditioning and seismic interpretation techniques can be used to enhance the visualisation of channelized and non-channelized fluvio-deltaic deposits in the subsurface. Frequency decomposition (and the making of colour-blended volumes) allows the visualisation of the detail of channel belt deposits such as channel belt migration and lateral accretion deposits. Allogenic processes, particularly base-level (buttress) rise and fall have been shown to exert a control on the overall stacking pattern of the studied fluvio-deltaic deposits, whereas autogenic processes are interpreted as the major control on the local arrangement and architecture of channel belt and overbank deposits. The first study in this thesis uses the Upper Permian Rangal Coal Measures, a large-scale fluvial system, which accumulated in a foreland basin setting in the Bowen Basin, Queensland, Australia. The study investigates the architecture and connectivity of splay and distributary channels. The second study uses the Late Triassic Mungaroo Formation, a Mississippi-scale fluvio-deltaic system with a fluvially-dominated, tidally-influenced delta, which accumulated in the Northern Carnarvon Basin, Northwest Shelf, Australia. The study investigates different seismic interpretation techniques and investigates the relative control on fluvio-deltaic deposition of allogenic and autogenic processes.