WIDER IMPLICATIONS AND FUTURE RESEARCH

The research presented in this thesis, whilst somewhat specific to the English Channel, has contributed to knowledge of landscape evolution in continental shelf environments, over glacial-interglacial cycles. More specifically, the research has uncovered a history of sedimentary processes, and by chronometrically constraining phases of deposition, it has been possible to couple process-response to major climate and sea-level cycles, and resolve higher frequency, more localised controls on landscape development. Using the stratigraphic framework presented in this thesis, the imprint of different sedimentary processes on the continental shelf, i.e. erosion or deposition, has been examined. Further, the persistence of landscapes, and preservation potential of erosional and depositional records, in a shelf setting over multiple sea-level cycles, has been addressed. Overall, the research has demonstrated the complexity and multi-phase character of continental shelf systems using a Quaternary example, thus confirming why shelf environments are so poorly represented in sequence stratigraphic models (e.g. Catuneanu, 2006). Given the range of allocyclic and autocyclic controls on continental shelf evolution operating over relatively short timescales (103 yrs), it may not be possible to develop a universal

Page| 143 stratigraphic model for the continental shelf environment. However, the research presented in this thesis can be used to provide a conceptual model of sedimentary processes operating on the continental shelf, and more importantly the archives these processes may or may not leave behind, which is fundamental for the study of sedimentology and drowned landscape evolution.

The chronometrically constrained stratigraphic model presented in this thesis was used as a framework to reconstruct palaeogeographic configuration of the eastern English Channel over the last ~200 ka. This has vastly improved understanding of Quaternary history of the English Channel and provided a basis to start addressing questions surrounding the timing and mechanism of breaching at the Straits of Dover. The research did not find any direct evidence to support either of the hypotheses currently under debate (e.g. Smith, 1985; Gupta et al., 2007; Busschers et al., 2008). However, a minimum age for breaching, determined using OSL, was established, and evidence for non catastrophic evolution of the palaeovalley complex was revealed. This research highlighted the fragmentary nature of sedimentary archives on the continental shelf and the difficulties in using them resolve sedimentary process-response at timescales >100 ka. It has been demonstrated that sedimentary archives preserved at the continental shelf edge break can document changes in climate, sea-level and major drainage configurations (e.g. Toucanne et al., 2009a). Therefore, rather than searching the continental shelf, i.e. an area of sediment bypass, for answers to ongoing debates, future research should focus on exploring the depositional records at the shelf margin (e.g. Eynaud et al., 2007).

It has been demonstrated that over shorter timescales (103 yrs), continental shelves have the potential to provide a wealth of information about landscape response to climate and sea-level change. The drowned barrier complex at Hastings Bank is a rare example where coastal facies are preserved during transgression. The fact that such a landscape exists, raises questions about current understanding of coastal response to rapid relative sea-level rise (e.g. Fitzgerald et al., 2008) and preservation potential of coastal facies in the rock record (e.g. Storms and Swift, 2003). The research presented in this thesis started to examine the controls on barrier behaviour during relative sea-level rise. OSL ages suggest that the barrier developed under rapid rates of sea-level rise, possibly associated with the 8.2 ka climatic event, during the early Holocene. However, the results also demonstrated that local conditions such as inherited topography played a significant role in determining barrier behaviour. This highlights the need to investigate the relative contribution of

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external (e.g. rate of sea-level rise and sediment supply) and internal factors (e.g. morphodynamics) on coastal landscape development further. Hastings Bank has the potential to provide chronometrically constrained geological data for testing numerical models of coastal landscape response to relative sea-level rise (e.g. Storms et al., 2002). This can be achived by obtaining multiple dates to provide a spatially and temporally constrained framework for the interpretation of landscape evolution (e.g. Roberts and Plater, 2007). Furthermore, by establishing a link between the Hastings Bank and Dungeness, it will be possible to assess spatial, as well as temporal evolution of gravel dominated coastal systems as a means to better understand their behaviour in response to future projections of climate and sea-level change.

Finally, the first attempt at dating a variety of drowned landscapes using OSL was carried out as part of this research – an approach that is essential for interpreting the sedimentary and morphological evidence preserved on continental shelves. The methodological approach presented in this thesis can be used as a guide by others to extracting sediment from drowned landscapes for dating using OSL. There are questions surrounding the reliability of some ages produced which needs to be investigated further. This can be achieved by improving precision and accuracy of the OSL dating technique (e.g. Bailey, 2004). Alternatively, the reliability of ages could be tested using an independent chronometric tool such as 14C dating. However, the data presented in this thesis demonstrate that organic sediments are rare in continental shelf settings and there is a high likelihood of reworking an incorporation of old carbon. Therefore, there is a need to explore the application of other dating techniques to drowned landscapes if we are to fully assess the reliability of OSL ages. OSL dating proved suitable in resolving the timing of depositional events on the continental shelf. However, one of the major limitations of the research carried out in this thesis was the inability to date erosion events. This is a common problem across a range of landscapes. In terrestrial systems it is being tackled using cosmogenic radionuclide dating (e.g. Cockburn and Summerfield, 2004) and thermochronometry (e.g. Binnie et al., 2008). The suitability of these techniques in dating drowned landscapes needs to be tested.

There is still a great deal to be resolved in unravelling the channel networks preserved in the eastern English Channel. This may be achieved using 3D seismic data. However, given the complexity of drainage networks and the multi-phase development of the fluvial system, this may not be possible. The influence of basement topography and underlying

Page| 145 land-level movements has not been fully examined in this thesis. This can be developed in the future by establishing a link between the palaeovalleys of the eastern English Channel and major drainage networks in Northwest Europe, i.e. the Thames and Rhine.

The emerging archaeological and palaeoenvironmental evidence from shelf seas (e.g. Doggerland) highlights the potential for the work presented in this thesis to be applied in the study of past human-environment interactions, exploring how different cultures and ways of living may have emerged in relation to the drowning of occupied landscapes. Indeed, the ongoing testing of ‘Noah’s Flood’ as a marine incursion in other parts of the world is likely to have wider material to draw on in relation to the unexpected and permanent drowning of settled land.

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