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The mid-to-late pleistocene palaeoenvironments of the Gordano Valley, North Somerset

Bridle, Anne

Authors

Anne Bridle



Abstract

This study constitutes the first reconstruction of Pleistocene palaeoenvironmental change from the Gordano Valley, a low-lying valley marginal to the Severn Estuary in southwest England. The valley lies at the limit of Pleistocene glacial expansion and the threshold of terrestrial, marine and fluvial environments. An axial alignment opposite to that of the Severn Estuary provides a regionally unique preservational environment for valley floor Pleistocene sediments. These sediments potentially contain an important archive of palaeoenvironmental information yet they have received limited attention from previous researchers.
Data from 489 manual cores are used to determine the aerial extent, surface morphology and geometry of the uppermost minerogenic sediments. These reveal a patchwork of sands, silts and gravels with a hummocky surface topography and a central basin or channel. Stratigraphic, sedimentological and palaeontological analysis of eight percussion cores reveals thinly bedded, very poorly sorted gravel, silt and sand units with an altitude range of c. -2.5 to +3 m OD. Two units record abundant temperate freshwater and intertidal fossil material. Using a multi-faceted methodology, detailed analysis of relatively small volumes of material from core samples of the Gordano Valley’s minerogenic sediment archive has identified complex sequences of depositional and post-depositional environmental change. The sediments are characterised as representing a range of Pleistocene palaeohydrological environments interspersed with a number of periods of non-deposition, and involving a number of processes (aeolian, colluvial, pedogenetic, various fluvial, intertidal). Radiocarbon and optically stimulated luminescence dating and amino acid geochronology indicate Mid-to-Late Pleistocene deposition. A revised model of the Pleistocene Gordano Valley, presented here, suggests a landscape in which alluvial fans formed close to the valley margins and freshwater streams and interconnected pools which were open to tidal influence formed along the valley axis. The elevation of intertidal deposits appears to provide terrestrial validation for a low late-MIS 7 sea-level, in terms of known global sea-level, without recourse to a regional uplift model.
This thesis has demonstrated the potential to produce high-resolution reconstructions of environmental change from relatively small volumes of material, contributing an enhanced geochronology of landscape response to Mid-to-Late Pleistocene climate change in the Bristol Channel/Severn Estuary region that has wider national importance in the context of coastal lowlands.

Citation

Bridle, A. The mid-to-late pleistocene palaeoenvironments of the Gordano Valley, North Somerset. (Thesis). University of the West of England

Thesis Type Thesis
Publicly Available Date Nov 30, -0001
Keywords pleistocene, environmental reconstruction, palaeoenvironments

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Chapter 3 Quaternary environmental change in the Gordano Valley.pdf (3.2 Mb)
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Chapter 5 The aerial extent, surface morphology and geometry of the Gordano Valley Pleistocene minerogenic deposits.pdf (1.6 Mb)
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Chapter 6 The stratigraphy and sedimentology of the Gordano Valley Pleistocene minerogenic deposits.pdf (3.8 Mb)
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Chapter 7 Characterisation of the Pleistocene minerogenic sediments of the Gordano Valley.pdf (897 Kb)
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Chapter 9 The regional context of the Gordano Valley Pleistocene palaeoenvironments.pdf (221 Kb)
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Title page for Appendices to The Mid-to-Late Pleistocene Palaeoenvironments of the Gordano Valley, North Somerset.pdf (51 Kb)
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Appendix I Stratigraphic description of manual cores of Gordano Valley sediments.pdf (2.9 Mb)
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Appendix II Stratigraphic descriptions of percussion core sediments.pdf (369 Kb)
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Appendix III Particle size analysis data & particle size distribution histograms.pdf (1.6 Mb)
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Appendix IV Gravel analysis data for Gordano Valley sediments.pdf (737 Kb)
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