The Loess and Coversands of Northern France and Southern England
Résumé
Loess and coversands are widespread on either side of the English Channel. In southern England, loess is generally thin and discontinuous, but locally reaches thickness of about 4 m in east Kent. Coversands occur mainly in areas well north of the Channel, such as parts of East Anglia and the southern side of the Bristol Channel. Most of the loess and coversand deposits in southern England date from the Late Devensian cold stage (marine oxygen isotope stage (MOIS) 2), but there are also a few localised patches of older (mainly MOIS 6 and 12) loess, which are the dissected remnants of originally more extensive covers. In France loess is widespread and locally very thick (up to 12 m), especially in northern and northeastern France. In Normandy and in the Somme basin some long records indicate that accumulation began at the end of the Lower Pleistocene, at about 900 ka. Nevertheless the main accumulations of typical calcareous loess are related to the Upper Weichselian and Upper Saalian stages (MOIS 2 and end of MOIS 3 and MOIS 6). Indeed, before about 160–170 ka, loess deposition was generally restricted to special sediment traps such as fluvial and marine terraces exposed to the east or northeast. These older deposits are characterised by more sandy facies derived from local fluvial sources (mainly by northwest to north‐northwest winds). Coversands occur locally along the coast of the Mont Saint‐Michel bay, and over the northern part of the Seine estuary near Le Havre. The main differences in thickness and extent of the loess deposits between southern England and northern France are linked to their location in relation to the source areas (Channel and North Sea), to ice sheets, and to the main wind directions (northwest to north‐northwest in France and western England but northeast in eastern England).