Discussion on lithospheric flexure, uplift, and landscape evolution in south‐central England

Abstract

Scientific editing by Alex Maltman. J. C. W. Cope writes: The paper by Watts et al. contains interesting ideas on landscape evolution, but by concentrating their observations locally, and by overestimating post-Anglian erosion, they may have lost sight of more widespread effects that could have been major contributors to the features they describe, and thus their causative mechanisms may need re-examination. ⇓Cope (1994) suggested that uplift centred in the Irish Sea explained the loss of >2 km of Mesozoic cover there, explaining apatite fission track analyses from the eastern Irish Sea and northwestern England. The southeasterly regional dip of the Mesozoic outcrop of the English Midlands could be attributed to this uplift; although a mantle plume was suggested as the cause, the same effect could be attributed to mantle underplating. Substantial igneous activity is known around the Irish Sea region before the earliest Antrim basalts. The Fleetwood dyke, in the Eastern Irish Sea is dated at 65.5 Ma (⇓Arter & Fagin 1993) and similar ages are known from dykes in North Wales (⇓Evans et al. 1973). Pre-basalt dykes exist in Northern Ireland whence ⇓Simms (2000) records dykes cutting Chalk and truncated by the basal Palaeogene lavas. ⇓Cope’s (1994) reconstruction of the missing Mesozoic cover of the area from the Cheshire Basin southwards led him to suggest that the resultant average gradient imparted over the Midlands from the Cheshire Basin to the Chiltern scarp was 1: 87.5. What was incorrectly calculated from this figure by ⇓Cope (1994) was the angle of dip represented by that figure, which is 0.7° and not 2°. The former is close to that recorded by Watts et al. for the area of Oxfordshire they considered and this suggests that they may have overestimated the uplift caused by lithospheric flexuring. There may be …