The Neogene succession of the South Western Approaches, Great Britain

Abstract

The outer continental shelf in the South Western Approaches is underlain by an oceanward-dipping wedge of Neogene strata up to 400 m thick that is divisible into three units: (a) the early to mid-Miocene, parallel-bedded calcilutites of the Jones Formation, which rest with a marked eastward overstep on Palaeogene and Cretaceous strata; (b) the mid- to late Miocene Cockburn Formation, which consists of calcarenites fashioned into a series of linear tidal ridges that are separated locally by an unconformity from the underlying unit; (c) the Plio-Pleistocene Little Sole Formation, which sits with a planar unconformity on the Miocene strata and is divisible into a lower, wedge-like member, restricted to near the shelf edge, and an upper, more widespread, sheet-like member. Palaeo-bathymetric and seismo-stratigraphic evidence indicates that the shelf and adjacent land areas have suffered epeirogenic movement since the early Miocene.

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“…Predominantly mud and sandy muds (Fig. 5) were observed in water depths >500 m which is in agreement with other studies from the region (Cunningham et al, 2005, Evans, 1990and Evans and Hughes, 1984. Areas of rock cropping out at sea bed were observed in areas with slope angles >20° and only found in water depths >300 m corresponding to amphitheatre rims, slump headwalls and flute features located on the canyon flanks ( Fig.…”

“…The Jones Formation rests unconformably on Paleogene strata in the vicinity of the study area. This formation was deposited on a shelf with slightly deeper water depths than present day, with relatively uniform rates of deposition and low energy sea-bed currents (Evans and Hughes, 1984).…”

“…The alpine inversion event caused the seaward deposition of two prograding, deltaic wedges during the Miocene (the Jones and Cockburn formations), which downlap onto the unconformable surface of the Late Cretaceous Chalk. The present-day upper continental slope and outer continental slope is underlain by Pliocene to Pleistocene sediments (Little Sole Formation) that thin landward onto the outer continental shelf and oceanward below a depth of around 1500 m. Submarine canyons of the upper continental slope were incised during a number of episodic sea level low stands during Plio-Pleistocene times , Evans, 1990and Evans and Hughes, 1984. There is no evidence to suggest that canyon cutting is ongoing today although active retrogressive headwall erosion has occurred since the last glacial maximum (21 ka BP) (Cunningham et al, 2005, Evans, 1990, Evans and Hughes, 1984and Scourse et al, 2009.…”

“…Unit V is correlated with the early to mid-Miocene age Jones Formation that comprises progradational calcilutites with up to 25% sand-sized particles (Evans and Hughes, 1984). The Jones Formation rests unconformably on Paleogene strata in the vicinity of the study area.…”

“…7), this change is probably the result of an increase in hydrodynamics as discussed above. Evans and Hughes (1984) report that the Cockburn Formation has a thickness in excess of 150 m in the vicinity of the shelf break.…”