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

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.

Streamlined islands and the English Channel megaflood hypothesis

“…In places, particularly in the Weald and Hampshire Basin sections, the seafloor has 494 significant unconsolidated sediment. Published OSL and 14C ages of this material range between ~180 ka 495 and 5 ka and hence records deposition during the past two glacial cycles (Mellett et al, 2013). Indeed we 496 believe that once formed, the entire bedrock-carved channel system was probably fully infilled with fluvial 497 sediments during low sea-level stands.…”

North Sea palaeogeographical reconstructions for the last 1 Ma

“…Gupta et al, 2007;Gibbard, 2007;Mellett et al, 2013). Spillage of vast volumes of accumulated meltwater from proglacial lakes carved out the later sea strait and left the enigmatic scars still visible on the English Channel floor today (Belt, 1874;Gibbard, 1988).…”

Fault activity in the epicentral area of the 1580 Dover Strait (Pas-de-Calais) earthquake (northwestern Europe)

“…This structure also traverses two significant Quaternary features situated in the centre of the Dover Strait (Figs 3 and 4): a broad palaeochannel known as the Lobourg Channel and a complex sediment-filled palaeobasin network known as the 'Fosse Dangeard' (see Destombes et al 1975;James et al 2002). Elsewhere Quaternary sedimentary features are mainly limited to a number of major (stable) and minor (mobile) Holocene sandbanks (Mellet et al 2013) separated by areas with thin or absent sedimentary cover (see James et al 2002). Recent tectonic movements affecting the latter features will not be preserved for long due to the dynamic conditions this area has been subjected to during the Holocene, with strong sediment reworking, erosion and sediment starvation (e.g.…”