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Original Article |
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K. Richards
Department of Earth Sciences, Parks Road, Oxford OX1 3PR, UK (e-mail: tony@earth.ox.ac.uk)
AFF Deceased. This paper was in review when W. S. McKerrow died on 12 June 2004. Many aspects of his wide-ranging interests are reflected in this study: geomorphology, stratigraphy and palaeontology, and geodynamics. It is hoped that this paper will stimulate increased communication between workers in these fields, in addition to providing a healthy debate on the tectonic evolution of the British landscape.
The Early Quaternary of south–central England is characterized by uplift, as is indicated by the river gravels that extend intermittently from Oxfordshire, through Northamptonshire, to Lincolnshire. The earliest of these gravels contain abundant quartz and quartzite clasts derived from Lower Triassic conglomerates in the West Midlands, but later deposits contain progressively larger amounts of locally derived Jurassic sediments. This compositional change is associated with the incision of the rivers that flowed eastwards from the West Midlands. Subsequently, the headwaters of some of these rivers were diverted towards the Bristol Channel and their suspended material was deposited on the outer parts of the UK continental shelf and slope. The area of incised drainage (Gloucestershire to Lincolnshire) did not extend to East Anglia (in the east) or to Somerset (in the west). Both these coastal regions contain several marine horizons showing that the area of uplift did not include the whole of southern England. The uplift cannot therefore be attributed to eustatic changes in sea level. The area of uplift is centred on the broad topographic depression of the English Midlands and corresponds approximately to the outcrop of thick (c. 1 km) Upper Triassic and Lower Jurassic mudrocks. We have used an Ordnance Survey 50 m x 50 m topographic ‘grid’ to estimate the amount of mudrocks that has been removed from the depression and 2D flexural unloading models to calculate the tectonic uplift that resulted, for various assumptions of the effective elastic thickness (which is determined by the flexural rigidity) of the lithosphere. The amount of material removed is in accord with what is known of the volume of Quaternary deposits offshore, and the uplift accounts for the incised plateau surfaces of the flanking Cotswold Hills and the high ground of Northamptonshire to the east, and the Forest of Dean and the hills of Herefordshire to the west.
Keywords: Quaternary, isostasy, flexure, landform evolution.
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  N.F. Lane, A.B. Watts, and A.R. Farrant An analysis of Cotswold topography: insights into the landscape response to denudational isostasy Journal of the Geological Society, 2008; 165: 85 - 103. [Abstract] [Full Text] [PDF]
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