Testing the English Channel megaflood hypothesis by establishing the stratigraphy, sedimentology and chronology of shelf incision

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Recent high-resolution acoustic profiling investigations in the English Channel have identified a distinctive geomorphology that is interpreted to have formed by multiple extreme subaerial discharge events by which the underlying bedrock was incised (Gibbard, 2007; Gupta et al., 2007). Evidence of at least two catastrophic releases from a proglacial lake located in the southern North Sea includes anabranching bedrock channels and terraces, with basal scours and lineations, separated by streamlined islands. Currently, the timing of these megafloods is tied loosely to glacial maxima, thus the first major excavation is estimated around 425 ka, and a reactivation event during a subsequent period of significant glaciation before 180 ka. It is postulated that these floods impacted on the morphology of the English Channel and routeing of Quaternary drainages, hindered faunal migration, influenced water temperature and salinity and, hence, climate in the Atlantic region. The proposed studentship aims to address this present shortcoming in our understanding of the evolution of the English Channel by providing a chronology based on trapped charge dating techniques for the oldest sedimentary record preserved within the incised drainage system and for the overbank deposits laid down during the events. Available seismic and sonar data, calibrated to detailed facies analysis of extensive borehole data (BGS archive and Hanson datasets) will establish a stratigraphic framework for site selection and the strategic collection of new datasets and samples. To establish the chronology of erosional and depositional events a multi-technique approach will be employed: dosimetric dating techniques for the timing of channel-fill and overbank sediment deposition, and granulometric and micro- and macro-palaeontology to derive palaeoenvironmental information. Optical dating will be used for the younger sequences and electron spin resonance (ESR) dating will be used for the older sequences. In addition, deposits from marine incursions will provide minimum ages for incisional events. This chronological and palaeoenvironmental data will prove valuable in assessing the degree of re-activation and incision with respect to relative sea-level history and the known extent of glaciation. Collation and re-analysis of extensive geophysical, stratigraphical and palaeoenvironmental information from the wider southern approaches region will provide the basis for assessing the potential location of the associated deposits of material excavated and transported by the megafloods. These deposits may reside beyond the shelf-edge if timing is coincident with low sea-level stand, but might be located on the outer shelf if flooding was during shelf transgression. This requires the age data to be tied to the established record of relative sea-level, drainage pattern and channel infilling during the Pleistocene and will reveal the environmental constraints on the ponding of western European river discharge in the southern North Sea and its catastrophic release. Research aims: 1. Obtain the ages of fluvial channel incision and the ages of overlying marine sediments in the English Channel using dosimetric dating techniques; 2. Construct a history of channel excavation and fill events for the English Channel coast by integrating chronological, stratigraphical, sedimentological, morphological, palaeoenvironmental and relative sea-level data, with which to test the hypothesis of megaflood events; 3. Provide a model of Pleistocene evolution for the English Channel, focussing on the environmental conditions conducive to catastrophic flooding versus incision due to relative sea-level fall, and therefore the timing of shelf incision and location of sediments resulting from catastrophic drainage. 4. Investigate the linkage between meltwater pulses into the NE Atlantic and the climate system.