Cambering and valley bulging, periglacial solifluction and LateglacialColeoptera at Dowdeswell, near Cheltenham

Abstract

Engineering works at Dowdeswell Dam, Gloucestershire, where the River Chelt emerges from the Cotswold scarp, enabled investigation of some of the local Quaternary features. The log of the dam cut-off trench (1884) shows the presence of a hitherto unreported valley bulge. It is of the type known as a crumple, exhibiting two sharp anticlinal folds superimposed upon a much gentler valley anticline. The former bulge had, as usual, been eroded away by the river. A trial pit at the foot of the northern valley side showed 2.86 m of silty clay head over a thin Oolitic breccia resting on the eroded surface of the Charmouth Mudstone Formation. Resting on the breccia was a thin discontinuous layer of organic clay. This was found to contain 19 taxa of Coleoptera, of which 11 could be identified to species or species group. The assemblage indicates that cold conditions obtained, with an open, barren landscape and a mean annual air temperature of −3°C. The deposit is assigned to the Younger Dryas period. The head mantling the valley slopes, at least in the area of Trial Pit 1, was probably emplaced predominantly during this cold period. The valley bulging was much earlier, evidence from other sites indicating an age of about oxygen isotope Stage 12.