Flow in the lower continental crust as a mechanism for the Quaternary uplift of south-east England: constraints from the Thames terrace record

Westaway, Rob; Maddy, Darrel; Bridgland, David R.

doi:10.1016/s0277-3791(01)00040-3

Cited by 156 publications

(222 citation statements)

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“…By not considering rates, these established techniques effectively allow these two problems to be traded off against each other, making it possible to say something quantitative about crustal deformation within the geological record without making too many untestable assumptions. In contrast, the modelling of detailed geomorphological records -of river and marine terrace sequences -that span much of the Quaternary provides control on rates of deformation and thus -as, for instance, Westaway et al (2002) and Westaway (2002b) have shown -on the viscosity of the lower continental crust in each study locality. One may thus anticipate that future studies on the same lines will gradually establish likely values for the lower-crustal viscosity in different geological settings, which will then be usable in modelling other aspects of crustal deformation.…”

Section: Introductionmentioning

confidence: 99%

“…The striking similarities between many long-term river terrace sequences (e.g., Westaway, 2002a) suggests that a common set of causal mechanisms is involved, and as many of these sequences occur in areas where active faulting in the brittle upper crust is unknown, the required surface uplift can only plausibly result from coupling between surface processes and lower-crustal flow. As Westaway (2001aWestaway ( , 2002b and Westaway et al (2002) have noted, the resulting uplift rates can contribute to constraining the viscosity of the lower continental crust.…”

Section: Introductionmentioning

confidence: 99%

“…The value of K is ~1.2xl0 -6 m 2 s" 1 for continental crust (e.g., Westaway, 2001a).Taking H as -30 km, t c can thus be estimated as ~2.4 Ma. Modelling studies (e.g., Westaway, 2001aWestaway, , 2002bWestaway et al, 2002) indicate that the transient response following a change in conditions becomes observable on a time scale of the order of ~t c /10 after the change. Such transient responses are thus evident on time scales of between a few hundred thousand years and a few million years after the change in conditions.…”

Section: Introductionmentioning

confidence: 99%

“…3). In south-east England, the Lower Thames flowed across a region that was subsiding in the Early Pleistocene but began uplifting at rates of up to ~0.09 mm a 1 in the Middle Pleistocene (e.g., Bridgland & Allen, 1996;Westaway et al, 2002). River terrace sequences that date from the Late Pliocene or earlier, notably of the Maas in the south-eastern Netherlands (e.g., Van den Berg, 1996;Van den Berg & Van Hoof, 2001;Westaway, 2001), also preserve evidence of an earlier increase in uplift rates, around 3 Ma.…”

Section: Introductionmentioning

confidence: 99%

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Geomorphological consequences of weak lower continental crust, and its significance for studies of uplift, landscape evolution, and the interpretation of river terrace sequences

Westaway¹

2002

Netherlands Journal of Geosciences

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Effects of flow in the lower continental crust have often been ignored in the geomorphological literature on the growth of topography during the Quaternary. However, the ability of the lower crust to flow in response to horizontal pressure gradients, caused by lateral variations in the depth of the base of the brittle upper crust, results in two mechanisms for the growth of topography, which can occur either separately or in combination. First, an increase in the rate of erosion in a region will result in a progressive reduction in the depth of the base of the brittle layer, which will drive inflow of lower crust to beneath the region, which will increase the crustal thickness and thus the altitude of the Earth's surface. It is important to note that this mechanism can increase the mean altitude of the Earth's surface, not just the altitude of summits formed of erosion-resistant rock or other features that are not eroding, which will rise faster than the surrounding eroding landscape. Second, repeated cyclic surface loading by ice sheets or fluctuations in global sea-level will cause net flow from areas of relatively cool lower crust to beneath areas of warmer crust. This process will thus usually result in net flow of lower crust from beneath offshore areas to beneath land areas, thinning the crust and increasing the bathymetry offshore but adding to the crustal thickness and so uplifting the land surface onshore. Although these two processes have different mechanisms, the time scale over which both operate is governed by the time required for heat diffusion, resulting from lower-crustal flow (which is concentrated near the Moho), to affect the position of the base of the brittle layer. As a result, the uplift responses for both processes can be very similar. This means that to resolve the physical cause of uplift at any locality requires knowledge of the regional conditions before uplift began, not just evidence (such as river terrace sequences) from during the course of uplift. This study illustrates the complexities and practical difficulties that can result from these issues, using case studies of localities that have been modelled in detail. It also points out that, although the ability to carry out quantitative calculations involving lower-crustal flow is new, the idea that such flow provides a general mechanism for the growth of topography was first suggested in the early 19th century, but was later abandoned -apparently mistakenly. An early Middle Pleistocene increase in uplift rates is widely-recognised from river terrace records, and typically marks a transition from broad valleys in areas of low relief to narrower, more deeply incised gorges. It is suggested that the isostatic response to cyclic surface loading, caused by the growth and decay of continental ice sheets and the associated sea-level fluctuations, is the main cause of this change, following the increase in scale of ice sheet development from oxygen isotope stage 22 (~0.9 Ma) onwards. The less well resolved earlier increase in upl...

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Geomorphological consequences of weak lower continental crust, and its significance for studies of uplift, landscape evolution, and the interpretation of river terrace sequences

Westaway¹

2002

Netherlands Journal of Geosciences

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“…The wide spread oc cur rence of si der it ic iron stones also con firms early diagenesis in the sed iments (Lake and Thurrell, 1974;Lake and Shephard-Thorn, 1987; Akinlotan, 2015). The geo ther mal gra di ent be neath the con ti nen tal crust of the United King dom is ~10°Ckm -1 (Rollin, 1995;Westaway et al, 2002). This geo ther mal gra di ent has pro duced in suf fi cient heat (~15-20°C) to drive any ma jor diagenetic al ter ation of the sed i ments or the trans for ma tion of smectite to illite-smectite in these for ma tions.…”

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confidence: 99%

Geochemical analysis for palaeoenvironmental interpretations – a case study of the English Wealden (Lower Cretaceous, south-east England)

Akinlotan

2016

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Geo chem i cal anal y sis for palaeoenvironmental in ter pre ta tionsa case study of the Eng lish Wealden (Lower Cre ta ceous, south-east Eng land)Oladapo AKINLOTAN 1, * 1 Uni ver sity of Brigh ton, School of En vi ron ment and Tech nol ogy, Lewes Road, Brigh ton, BN2 4GJ, UK Akinlotan, O., 2017. Geo chem i cal anal y sis for palaeoenvironmental in ter pre ta tions -a case study of the Eng lish Wealden (Lower Cre ta ceous, south-east Eng land). Geo log i cal Quar terly, 61 (1): 227-238, doi: 10.7306/gq.1328The el e men tal com po si tion of terrigenous sed i ments is ex tremely im por tant for in ter pret ing the depositional con di tions of sed i men tary bas ins es pe cially when tra di tional data are not avail able or in suf fi cient. For the first time in the pub lished lit er ature, the el e men tal com po si tion of the Lower Cre ta ceous Weald Ba sin (south-east Eng land) is pre sented via X-ray flu o rescence (XRF) and Spec tral Gamma-ray (SGR) meth ods. The con cen tra tions of Zr, Cr, Ni, Rb, and Sr in vary ing quan ti ties sug gest that the sed i ments may have been sourced from a sta ble craton while the en riched re dox-sen si tive el e ments such as Mo and Co con firm the pres ence of anoxic and re duc ing con di tions at the sites of de po si tion. The spec tral gamma-ray data show that the sand stone fa cies are more ra dio ac tive than the ad ja cent mudstone and shale and this trend is con sis tent with a fresh wa ter or i gin. The higher quan tity of tho rium in re la tion to ura nium in di cates hu mid and hot palaeoclimatic con ditions at the source ar eas that fa voured in tense weath er ing. The re sults of these anal y ses re in force the im por tance of the geo chem is try of sed i men tary rocks as use ful tools for un der stand ing the depositional con di tions of sed i men tary bas ins.Key words: el e men tal com po si tion, X-ray flu o res cence, spec tral gamma-ray, palaeoenvironments, Lower Cre ta ceous, south-east Eng land. INTRODUCTIONThe use of the geo chem i cal com po si tion of sed i men tary rocks for in ter pret ing palaeo-and depositional en vi ron ments is well-doc u mented (e.g., Alvarez and Roser, 2007;Pe-Piper et al., 2008;Ghasemi-Nejad et al., 2010;González-Álvarez and Kerrich, 2010; Eker et al., 2012;Garnit et al., 2012;Pi et al., 2014;Wójcik-Tabol, 2015). The el e men tal com po si tion of terrigenous sed i ments is ex tremely im por tant for in ter pret ing the depositional con di tions of sed i men tary bas ins and may be more use ful than ex pected when tra di tional data such as field ob ser va tions and palaeontological ex am i na tions are not available or in suf fi cient. The geo chem i cal com po si tion of terrigenous sed i men tary rocks is a func tion of tec tonic set ting, prov e nance, weath er ing, trans por ta tion and diagenesis (e.g., Bhatia and Crook, 1986; Alvarez and Roser, 2007;González-Álvarez and Kerrich, 2010). Many ma jor el e ments such as Fe, K, Ca, Ti and Mn in de creas ing or der of abun dance may be af fected by diagenesis or bi o log ...

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2012

An Introduction to Thermogeology: Ground Source Heating and Cooling

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Flow in the lower continental crust as a mechanism for the Quaternary uplift of south-east England: constraints from the Thames terrace record

Cited by 156 publications

References 108 publications

Geomorphological consequences of weak lower continental crust, and its significance for studies of uplift, landscape evolution, and the interpretation of river terrace sequences

Geomorphological consequences of weak lower continental crust, and its significance for studies of uplift, landscape evolution, and the interpretation of river terrace sequences

Geochemical analysis for palaeoenvironmental interpretations – a case study of the English Wealden (Lower Cretaceous, south-east England)

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