High-resolution sequence stratigraphy of a mid-Cretaceous estuarine complex: the Woburn Sands of the Leighton Buzzard area, southern England

Abstract

Abstract The Woburn Sands Formation (Aptian-Albian) is a sand-rich, tide-dominated estuarine deposit up to 120 m thick, which is extensively exposed in the Leighton Buzzard area, southern England. Previous studies have interpreted the depositional processes and environments of these strata, but have not satisfactorily resolved their lithofacies complexity. Application of sequence stratigraphical methods and concepts has identified key surfaces (sequence boundaries, tidal and wave ravinement surfaces) which provide a useful framework for correlation of the succession and for understanding the complex facies architecture. Two regional-scale erosional surfaces identified in the succession are interpreted as erosional unconformities or sequence boundaries. These surfaces resulted from fluvial erosion during periods of relative sea-level fall, followed by extensive erosional modification by tidal currents during the early phases of relative sea-level rise. The depositional sequences defined by the erosional unconformities are dominated by the deposits of incised valleys. The valley-fills mainly comprise sand-dominated tidal current facies which occur as multistorey estuarine channel complexes. In the upper parts of the sequences thin, locally preserved units of shelf facies overlie wave ravinement surfaces. Over part of the study area the upper erosional unconformity erodes directly into the underlying incised valley-fill producing a composite sequence.