Turbidite systems influenced by structurally induced topography in the multi-sourced Welsh Basin

Abstract

Abstract 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.