Eustatic and hydrodynamic controls on the architecture of a deep shelf sand bank (Celtic Sea)

The architecture of a tidal sand bank in the south-eastern Celtic Sea was e xamined using very high-resolution seismic surveys. The bank comprises four depositional units. The lowest unit 1 is characterized by gently dipping ( 1-8 degrees) strata that strike parallel to the length of the bank. Unit 1 is erosionally overlain by unit 2, which forms the bulk of the bank. This u nit consists of stacked sets of downcurrent-dipping (7-12 degrees) master b edding formed by climbing, sinuous-crested tidal dunes that are up to 20 m high. These deposits are locally incised by an anastomosed channel network. (unit 3) that may represent a buried swatchway system. The upper part of t he bank comprises wave-related deposits that are mainly preserved on the ba nk flanks (unit 4). The outer bank surface is erosional. The bank is believ ed to have formed during the last postglacial sea-level rise. The facies ev olution from unit 1 to unit 3 indicates an upward increase in tidal energy, mainly characterized by the thickening of dune cross-bed sets in unit 2. T he majority of bank growth is inferred to have occurred in water depths of the order of 60 m. This evolution was controlled by relative sea-level rise , which is likely to have caused an episode of tidal resonance with associa ted strong tidal currents that were responsible for the incision of the dee p, cross-cutting channels of unit 3. The transition to wave-dominated sedim entation in unit 4 is related to the decay of resonance with continued sea- level rise.