The Quaternary Evolution of the Gordano Valley, North Somerset
The Quaternary Evolution of the Gordano Valley, North Somerset, UK. Thomas Charles Bernard Hill A thesis submitted in partial fulfilment of the requirements of the University of the West of England, Bristol for the degree of Doctor of Philosophy. Faculty of the Built Environment, University of the West of England, Bristol January 2006 Abstract The Gordano Valley is a low-lying valley positioned in close proximity to the Severn Estuary, in southwest England. Although its late Quaternary and Holocene sedimentary archive is extensive, the spatial and temporal evolution of the Gordano Valley has received only limited attention from previous researchers. In this study, stratigraphic analysis of the valley archive, combined with pollen, diatom and particle size analysis are utilised in a detailed reconstruction of the evolution of the Gordano Valley. Two contrasting depositional environments are present, separated by a sedimentary ridge traversing the width of the valley. A tentative mechanism is presented for the development of the ridge in response to periglacial hillslope erosion and deposition during the Devensian glacial period (c. 115,000-11,500 Cal. yrs BP). In contrast, the chronology and development of the two depositional environments is clearer. Detailed multiproxy analysis of the two sedimentary archives reveals the development of an enclosed lake basin headward of the ridge during the late glacial period (c. 18,000-15,000 Cal. yrs BP). Subsequent climatic amelioration in response to the transition from glacial to interglacial conditions resulted in the terrestrialisation of the lake at the onset of the BØlling/AllerØd interstadial, c. 15,000 Cal. yrs BP. A complete hydroseral succession sequence is present in the headward region of the valley, where the terrestrialised lake sequence developed into the fen peatland that is present today.
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