Denudation of the continental shelf between Britain and France at the glacial–interglacial timescale

Claire L Mellett,David M Hodgson,Andrew J Plater,Barbara Mauz,Ian Selby,Andreas Lang

doi:10.1016/j.geomorph.2013.03.030

Claire L Mellett, David M Hodgson + Show 4 more

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https://doi.org/10.1016/j.geomorph.2013.03.030

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Abstract

The erosional morphology preserved at the sea bed in the eastern English Channel dominantly records denudation of the continental shelf by fluvial processes over multiple glacial–interglacial sea-level cycles rather than by catastrophic flooding through the Straits of Dover during the mid-Quaternary. Here, through the integration of multibeam bathymetry and shallow sub-bottom 2D seismic reflection profiles calibrated with vibrocore records, the first stratigraphic model of erosion and deposition on the eastern English Channel continental shelf is presented. Published Optical Stimulated Luminescence (OSL) and 14C ages were used to chronometrically constrain the stratigraphy and allow correlation of the continental shelf record with major climatic/sea-level periods. Five major erosion surfaces overlain by discrete sediment packages have been identified. The continental shelf in the eastern English Channel preserves a record of processes operating from Marine Isotope Stage (MIS) 6 to MIS 1. Planar and channelised erosion surfaces were formed by fluvial incision during lowstands or relative sea-level fall. The depth and lateral extent of incision was partly conditioned by underlying geology (rock type and tectonic structure), climatic conditions and changes in water and sediment discharge coupled to ice sheet dynamics and the drainage configuration of major rivers in Northwest Europe. Evidence for major erosion during or prior to MIS 6 is preserved. Fluvial sediments of MIS 2 age were identified within the Northern Palaeovalley, providing insights into the scale of erosion by normal fluvial regimes. Seismic and sedimentary facies indicate that deposition predominantly occurred during transgression when accommodation was created in palaeovalleys to allow discrete sediment bodies to form. Sediment reworking over multiple sea-level cycles (Saalian–Eemian–early Weichselian) by fluvial, coastal and marine processes created a multi-lateral, multi-storey succession of palaeovalley-fills that are preserved as a strath terrace. The data presented here reveal a composite erosional and depositional record that has undergone a high degree of reworking over multiple sea-level cycles leading to the preferential preservation of sediments associated with the most recent glacial–interglacial period.

Highlights

Significant changes in relative sea level repeatedly submerge and expose shallow continental shelves making them susceptible to erosion, reworking and deposition, by sedimentary processes operating in terrestrial, marine, and transitional environments
The data presented in this paper provide a framework to reconstruct the Middle to Late Pleistocene palaeogeographic configuration in the eastern English Channel (Fig. 13)
The landscape preserved on the present-day sea bed of the eastern English Channel is a record of the sedimentary processes that operated over glacial–interglacial sea-level cycles from Marine Isotope Stage (MIS) 6 to MIS 1

Summary

Introduction

Significant changes in relative sea level repeatedly submerge and expose shallow continental shelves making them susceptible to erosion, reworking and deposition, by sedimentary processes operating in terrestrial, marine, and transitional environments. The preservation of ancient landscapes on the sea bed of the continental shelf provides archives of palaeoenvironmental change (Fedje and Josenhans, 2000; Fitch et al, 2005; Gaffney et al, 2007; Kelley et al, 2010; Hijma et al, 2012), commonly from time periods poorly represented on land (Mellett et al, 2012a). These drowned landscapes are ideal for examining the interactions between sedimentary processes. Reorganisation of drainage basins and funnelling of freshwater discharge through the English Channel during cold stages as a consequence of breaching of the Straits of Dover (Gibbard et al, 1988; Bridgland et al, 1993; Bridgland and D'Olier, 1995; Gibbard, 1995; Busschers et al, 2007, 2008), may have contributed to destabilisation of the Atlantic thermohaline circulation (Menot et al, 2006; Gibbard, 2007; Toucanne et al, 2009b, 2010)

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