The English Channel (La Manche): evolution, oceanography and sediment dynamics - a synthesis

Abstract

The English Channel is a shallow epicontinental sea, linking the Atlantic Ocean and the North Sea It is an excellent example of a tidally dominated shallow marine system, with limited sediment sources and extensive reworking of a relatively thin sediment cover It is bordered and floored by a range of rock types, ranging from Palaeozoic to Tertiary in age It has a variety of coastlines. including. cliffs. rills, estuaries and coastal sediment accumulations, ranging from gravel and sand beaches with aeolian dunes to broad intertidal flats The sediment is supplied by (i) rivets, with the French side of the system dominating the fluviatile sediment supply. (ii) erosion of cliffs and wave-cut platforms. which again is more important along the French coast. (iii) reworking of the sea floor, (iv) the breakdown of benthonic skeletal-debris, which is particularly important in the WSW towards the open ocean. and (v) sonic input (mainly of biogenic planktonic origin) from the At Ocean The system loses fine-grained sediment to the Atlantic Ocean in the WSW and the North Sea to the ENE and as a result of estuarine infilling Anthropoaenic changes are caused mainly by large-scale dredging of coarser-grained material for the construction industry. and within some of the estuaries (e g in the west of England) are the dumping sites of mining waste The area is dominated by strong tidal currents and by waves that originate mainly from the WSW and which only affect the shallow water areas during storms The central area of the Channel is covered by coarse-grained material since the finer fractions have been scoured away by the tidal action. this has been identified as a `bedload parting zone' Wide areas are covered by sand-sized sediments. fashioned into a variety of bed forms ripples. sandwaves, longitudinal bed-forms and sandbanks. Fine-grained sediments are confined to coastal embayments. rias, estuaries and open-coast intertidal flats A thin superficial blanket of Holocene sediment covers an important unconformity whose final development occurred during and succeeding the Flandrian Transgression If this is preserved. It will form an interesting sequence of deposits where the facies distribution is dominated by oceanographic processes and not merely by water depth and proximity to the coastline