A latest Cretaceous hotspot and the southeasterly tilt of Britain

Abstract

The southeasterly regional dip of England and Wales is usually ascribed to Miocene movements. Loss of up to 2 km of cover from northern England, shown by apatite fission track analysis, has been related to uplift and erosion induced by a mantle hotspot, but its effects were far more widespread than considered hitherto. Outcrop patterns throughout much of England, Wales and eastern Ireland can be related to a hotspot beneath the Irish Sea. Uplift occurred within the late Maastrichtian and erosion continued into the late Palaeogene. After post-Oligocene down-faulting of the Irish sea, the modern drainage was initiated on the eroded surface. Unconformities provide the best means of dating orogenic movements; in some localities the time interval between the youngest rocks preserved beneath the unconformity and the oldest preserved above may be small enough to enable the dating of fold movements to be determined with some precision. Thus in southeastern Britain the major E-W structures of the Hampshire Basin, the Weald and the London Basin can be dated as Miocene, as rocks of Oligocene age are involved in the folding in the Hampshire Basin and Pliocene sands rest in erosional pockets of the Chalk of SE England. Because fold movements tend to affect large areas of the crust at discrete intervals of time, the southeasterly tilt of Britain, evident from the fact that a NW-SE transect from Anglesey to London crosses outcrops of rocks getting progressively younger from the Precambrian of Anglesey to the Tertiary of the London Basin, has

Episodic Cenozoic tectonism and the development of the NW European ‘passive’ continental margin

“…In contrast to the Neogene episodes, early Cenozoic uplift is not recorded in Denmark and affected a narrower area of Britain and Ireland (Japsen, 1997(Japsen, , 1998, corresponding to an elongate zone west of the present extent of the Chalk Group, up to 500 km wide and at least 1000 km long, extending from south of Ireland in the SW to the Moray Firth in the NE (Green, 2001;Green et al, 2002). Early concepts of an elongate domal uplift centred over the Irish Sea (Cope, 1994;White and Lovell, 1997; are not supported by later palaeo-thermal data, which indicate spatial variability in geothermal gradients, including up to Fig. 3.…”

Stagnant lid convection and the thermal subsidence of sedimentary basins with reference to Michigan

“…Provenance studies, however, might provide information on the detritus from accessible rocks on the basin flanks of the extent of pre-Mount Simon erosion. Irish Sea associated with the Iceland plume provides analogy; a radial system of drainage developed [Cope, 1994;Sleep, 2003]. This system of rivers, including the Thames, persists in the British Isles even though the center of the uplift is beveled by erosion into a shallow sea.…”

Early-Middle Pleistocene Beheading of the River Thames

“…A traditional view of river development in southern England and Wales (Ramsey, 1872;Linton, 1951), recently reiterated by Cope (1994Cope ( , 1995, is that some major English rivers, including the Thames, originated as consequent streams on a gently dipping Cretaceous Chalk cover extending westwards across all but the highest parts of Wales, if not the whole country. Following Davis' hypothesis it could be argued that gradual removal of the Chalk cover would have led to the exposure of underlying rocks of variable erodability and the development of subsequent streams, one of which, the River Severn, ultimately beheaded the Thames.…”