Welsh Basin ‘contourites’ reinterpreted as fine-grained turbidites: the Grogal Sandstones

Abstract

AbstractSince 1976 the Lower Silurian Grogal Sandstones of the Welsh Basin have been interpreted as contourites. Here we show that they are in fact fine-grained turbidites, frequently with pale-coloured oxidized top layers which enable distinction of individual event deposits. As reported previously, palaeocurrent directions derived from ripple cross-lamination are typically at a high angle, often close to perpendicular, to those measured from sole structures. The favoured explanation is that ripples migrated under transverse internal waves generated at an intrabasinal slope to the east. Evidence for the lateral confinement of the overlying Aberystwyth Grits by such a slope provides support for this explanation.