Turbidite systems influenced by structurally induced topography in the multi-sourced Welsh Basin
The latest Ordovician and lower Silurian fill of the Welsh Basin contains a range (in terms of scale, sediment texture, stratigraphic architecture and supply configuration) of deep-water depositional systems that record the influence of basin-floor topography on sediment distribution patterns. Systems supplied from the eastern basin margin at a time of broadly rising relative sea-level are interpreted to have initially filled an inboard base of slope depression lying above a tilted basement fault block (Cerig Gwynion Grits System). An opposing slope is thought to have caused deflection of turbidity currents to run parallel with the strike of the slope. Following this fill phase, a channel-fed lobe system (Caban-Ystrad Meurig System) extended further basinwards. After flooding of the eastern basin margin, voluminous, texturally immature axial systems, supplied from the southern basin margin, developed. These systems exhibit evidence for deflection of flows to run parallel to tectonically induced slopes and probable local flow reflections in areas of obliquity between bounding slopes and incident flows. The architecture of the lateral-slope to basin-axis profile has been plausibly modelled using a geometric forward model with a low-gradient lower basin slope and basinward higher aggradation rates and sand percentage.
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This publication reflects a growing appreciation of the extent to which turbidite depositional system development is fundamentally affected by basin-floor topography. In the many turbidite and turbidite hydrocarbon reservoirs, depositional patterns have been moderately to strongly confined by pre-existing slopes; thus ‘submarine fans’ may be far from fan-shaped where constrained by significant bathymetric features. This volume examines aspects of sediment dispersal and accumulation in deep-water systems where sea-floor topography has exerted a decisive control on deposition, and explores the associated controls on hydrocarbon reservoir architecture and heterogeneity.
The papers presented here offer a global perspective, which is wide-ranging in terms of approach as well as location, including contrasting reviews and case studies of outcrop, subsurface, modern and experimental systems. This book will be of use both to academic geologists and to geoscience professionals in industry dealing with characterization and modelling of deep-water clastic reservoirs.