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Discussion |
1 School of Ocean Sciences, College of Natural Sciences, Bangor University, Menai Bridge LL59 5AB, UK
2 Department of Zoology, University of Cambridge, Downing Street, Cambridge CB2 3EJ, UK
Lane et al. (2008) interestingly interpret the evolution of the Cotswold scarp and vale landscape in terms of lithospheric response to erosional unloading, ’denudational isostasy', and elastic plate flexure tectonics. They attribute up to 50% of the relief in the Cotswolds to erosional unloading and discuss viscoelastic plate models, which predict initial uplift rates as high as 8 m ka–1. They note that Late Anglian and early post-Anglian incision rates inferred from the Thames terrace sequence by Maddy & Bridgland (2000) are consistent with this high rate against a longer-term (last 2 Ma) slower uplift rate for southern England of 0.07–0.10 m ka–1. The data for this longer-term estimate are based on Bowen (1994), Maddy & Bridgland (2000) and our interpretation for uplift rates based on raised interglacial shorelines in central southern England (Preece et al. 1990). The rates invoked in this last study have since been supported by analysis of raised shoreline and fluvial terrace sequences over a wider region of central southern England (Westaway et al. 2006).
We would like to highlight here the paper by Gale et al. (1999), which was not cited by Lane et al. (2008) and which we feel adds significant new data to our understanding of long-term uplift rates in central southern England. Based on the contribution and distribution of derived lithoclast and fossil suites in the Selsey, Barton and Becton Formations in Whitecliff Bay, Isle of Wight, Gale et al. (1999) interpreted Mid–Late Eocene uplift of +500 m on the northern limb of the Sandown Pericline. This yields a mean Eocene uplift rate of 0.10 m ka–1, almost identical, and well within the range of possibilities, to that calculated by Preece et al. (1990) for uplift in the same area over the past 500 ka. As in the Lane et al. (2008) analysis, Preece et al. (1990) attributed this uplift to denudational isostasy, but Gale et al. (1999) highlighted continuing uplift of the Sandown Pericline. We are not qualified to comment on the competing structural explanations for the identified uplift, but if the consistent rate of uplift of 0.10 m ka–1 constrained during the Eocene and during the last 500 ka on the northern limb of the Sandown Pericline has been sustained over the entire period of the last c. 50 Ma, and not just within the Eocene and Pleistocene, then this indicates a total uplift of 5 km. This is an order of magnitude too high in relation to the ages of other uplifted Cenozoic sequences across southern England (compare Preece et al. 1990). This implies that the uplift must have been pulsed, as suggested by Lane et al. (2008) in their paper, and this has implications for studies of long-term landscape evolution over a wider region of southern England.
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References |
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 Top References |
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Bowen, D.Q. 1994. Late Cenozoic Wales and South West England, Proceedings of the Ussher Society 1994, 8 , 209–213.
Gale, A.S., Jeffrey, P.A., Huggett, J.M. & Connolly, P., 1999. Eocene inversion history of the Sandown Pericline, Isle of Wight, southern England, Journal of the Geological Society, London 1999, 156 , 327–339.
Lane, N.F., Watts, A.B. & Farrant, A.R., 2008. An analysis of Cotswold topography: insights into the landscape response to denudational isostasy, Journal of the Geological Society, London 2008, 165 , 85–103.
Maddy, D. & Bridgland, D.R., 2000. Accelerated uplift resulting from Anglian glacioisostatic rebound in the Middle Thames valley, UK? Evidence from the river terrace record, Quaternary Science Reviews 2000, 19 , 1581–1588.[CrossRef][Web of Science][GeoRef]
Preece, R.C., Scourse, J.D., Houghton, S., Knudsen, K.L. & Penney, D.N., 1990. The Pleistocene sea level and neotectonic history of the eastern Solent, southern England, Philosophical Transactions of the Royal Society of London, Series B 1990, 328 , 425–477.
Westaway, R., Bridgland, D. & White, M., 2006. The Quaternary uplift history of central southern England: evidence from the terraces of the Solent River system and nearby raised beaches, Quaternary Science Reviews 2006, 25 , 2212–2250.[CrossRef][Web of Science][GeoRef]
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