Non-diastrophic structures at Bredon Hill, Worcestershire

Abstract

B redon H ill is an outlier of the Cotswold Hills situated in the southern part of the Vale of Evesham. Essentially the hill is composed of argillaceous Lias sediments capped by Inferior Oolite limestones. A detailed six-inch geological survey in 1966–7, aided by the sinking of two cored boreholes and by photogeological studies, has enabled the effects of superficial mass movements to be assessed. Erosion of a thick, incompetent sequence of mudstones overlain by massive, competent limestones has led to the development of landslips, cambers and gulls. Several types of mass movement can be recognized, including slumping, mudflow and composite slip. Cambering is virtually restricted to the Inferior Oolite limestones which cap the hill and includes down-dip extension of the competent beds over the underlying mudstones. A type of hinged camber is also present. Gulls are well developed on the limestone dip-slope surface and have contributed considerably towards the down-dip extension of the beds. Wherever observed, the Inferior Oolite limestones are in a disturbed state, a feature which is attributed to the development of superficial structures under periglacial conditions. The Inferior Oolite surface presents a large catchment area for meteoric waters, and copious springs and water seepages break out at the limestone-mudstone junction in the south part of the hill. There is evidence for considerable sub-Inferior Oolite erosion, a process which would facilitate superficial mass movements. Evidence from gravels, which flank the hill, strongly suggests that many of the non-diastrophic structures were well developed by River Avon No. 2 Terrace times (38 000 ± 700), although later phases of instability are indicated by clayflow features which in places obscure older landslip and solifluxion deposits. There is much evidence that landslip movements have also taken place throughout historic times; eyewitness accounts are available over the last one hundred years or so.