Late quaternary palaeovalley systems of the eastern English channel

Abstract

This thesis examines the Late Quaternary palaeoenvironmental history of the palaeovalley system located on the sea bed of the eastern English Channel. The work is based on an analysis of 500 km of high resolution seismic data, 189 boreholes, and an extensive grain size, microfossil and geochemical dataset. Within the study area arc two major palaeovalleys incised into Tertiary bedrock. They are on average 2 to 8 km wide and contain between 20 and 30 m of Late Quaternary sediments. Four Seismic Sequences are identified, separated by two sequence boundaries and one ravinement surface. Using an uplift-corrected eustatic sea level as a relative sea-level history for the study area, it is suggested that the palaeovalleys were cut at the transition from MOIS6 to 5e, and were infilled with transgressional shoreface sediments during the interval between MOIS5e and MOIS4. An upper seismic unit, also comprising marine sediment, developed following the Last Glacial Maximum as an extensive lag deposit. Comparison of this work with other records from the English Channel and other continental shelves demonstrate the pervasive importance of eustalic and tectonic controls in dctennining palaeovalley development. The major palaeovalleys of the English Channel probably originate from MOIS 12, created by the drainage of a large proglacial lake in the North Sea via the Strait of Dover. The palaeovalleys in the PhD study area post-date this initial phase of valley development, and were formed by a major гivег flowing through the region (presumably one or more the Thames, Rhine or Meuse). The results of this PhD demonstrate the high potential of continental shelf records as archives of Late Quaternary land-ocean interaction, as well as the benefits of close liaison between industry and academic stakeholders involved in offshore aggregate and palaeoemironmental exploration.