Drowned landscapes of the eastern English Channel : records of Quaternary environmental change
Mellett, Claire Louise
PublisherUniversity of Liverpool
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The present-day seabed in the eastern English Channel is an erosional landscape dissected by a complicated network of palaeovalleys. The largest of these palaeovalleys has been interpreted as the product of catastrophic flooding though the Straits of Dover during the Mid Quaternary. Whilst the eastern English Channel is a valuable source of aggregates, little attention has been paid to the sedimentary record preserved on the continental shelf in terms of its ability to document landscape change throughout the Quaternary. This thesis aims to establish the first stratigraphic model of deposits preserved on the continental shelf in the eastern English Channel and chronometrically constrain the timing of deposition using Optical Stimulated Luminescence (OSL) dating. The model will be used as a framework to reconstruct landscape change and address questions regarding the preservation potential of sediments, and the imprint sedimentary processes have on the landscape, in continental shelf settings over glacial-interglacial cycles. The stratigraphic model was constructed through the integration of high resolution mutlibeam bathymetry, shallow sub-surface 2D seismic profiles, lithological information from vibrocores, and chronometric data obtained through OSL. A variety of drowned landscapes including terrestrial (fluvial and colluvial), coastal and shallow marine, were identified. These landscapes document palaeoenvironmental change on the continental shelf from MIS 6 to MIS 1. The fluvial landscape in the English Channel is dominated by multiple phases of lateral and vertical erosion, primarily in response to changes in sea level, but also as a result of reorganisation of drainage basins and variable discharges due to fluctuating ice margins. Exposure of the continental shelf during cold periods is documented in the form of remnant periglacial deposits and extensive palaeosols. The most volumetrically significant sediments preserved on the continental shelf were deposited in shallow marine and coastal settings. These sediments are typically restricted to palaeovalleys where accommodation created during relative sea-level rise enabled deposition. Elsewhere, sediments are preserved as relict coastal landforms, in particular, as part of an exceptionally rare drowned barrier complex at Hastings Bank. Over multiple sea-level cycles, sediments are recycled by fluvial and marine processes, with the most recent phase of deposition having the greatest preservation potential. Erosional processes have the greatest persistence in the landscape record. However, they create a composite record and distinguishing between different events without a correlative sediment package is problematic. The results presented in this thesis highlight the timing and nature of ‘normal’ sedimentary regimes in a continental shelf setting over multiple glacial-interglacial cycles. Further, they reveal evidence for erosion and deposition by fluvial processes in the Northern Palaeovalley during the last glacial period, thus contradicting an existing hypothesis that states the palaeovalley formed through catastrophic flooding.