The Pleistocene geology of the area north and west of Wolverhampton, Staffordshire, England

Abstract

Two hundred and fifty-two square kilometres of land north and west of Wolverhampton have been mapped on a scale of 1:10 560. This area includes a sequence at Four Ashes which has been designated the type section for the Devensian stage of the British Pleistocene. The last glacial advance into the West Midlands occurred during the Upper Devensian, some time after 30 500 years B.P., terminating along the 'Wolverhampton Line' marked by a pronounced thickening of the till sheet and a concentration of large erratics. The till at Four Ashes overlies a thin series of gravels which had at its base a restricted deposit of Ipswichian date and included many lenses of peat or organic silt ranging in age from ca. 70 000 B.P. to later than 30 500 B.P. (Lower and Middle Devensian) representing a period of fluctuating climate ranging from cool temperate to arctic continental in severity. During this period there was a considerable amount of erosion, resulting in the formation of the 'modern' landscape which has only been modified by glacial deposition and post-till periglacial activity. The earliest Pleistocene deposits found in the region are believed to be glacial outwash gravels, probably of late Anglian age which are overlain by Hoxnian Interglacial silts and clays. These early deposits occur beneath the till sheet of the last ice and extend for at least 10 km south of the Wolverhampton Line as eroded relics of a deep channel filling. Glacio-fluvial gravel sequences post-date the retreat of the Late Devensian ice and are concentrated along the principal drainage lines. Late-Glacial organic deposits indicate that the ice had retreated prior to 13 490 years B.P. in the Stafford region. A periglacial environment followed the retreat of the last ice (as evidenced by ice-wedge casts and ice-wedge polygons) and this is thought to have lasted until the climatic amelioration which started around 12 500 years B.P.