Environmental reconstructions of a late devensian terrace sequence. Some preliminary findings

Abstract

Facies analysis of Severn Main terrace sediments at Eardington, Shropshire is instructive in determining aspects of the sedimentary environment at a 'proximal' location in the terrace. Evaluation of the structural and directional properties of the gravels indicates that the terrace is a composite feature comprising two units. The lower unit is notable for the widespread Occurrence of large sandy facies, a near absence of massive gravel facies, and the presence of large, locally derived, lithoclasts in excess of 1 m in diameter. Facies associations observed indicate the existence of in-channel bars and large channels with bedforms at the dune-plane bed transition. The directional properties of the unit indicate flows parallel to the main valley axis and although the unit is unlike previously reported examples it is interpreted as being the product of a proximal low sinuosity environment. The upper unit is composed mainly of multistorey, coarse, massive gravel units with limited interbedded sand facies. Fabric analysis indicates progradation of the unit from the west. The facies sequence is similar to those encompassed by facies models proposed for proximal alluvial fan deposits and therefore, on structural and directional grounds, the upper unit is interpreted as an alluvial fan deposit which prograded into the main Severn valley from the adjacent Mor Brook tributary. The implications of the composite nature of the terrace at this point are considered both in terms of terrace correlation and palaeohyrological estimation.

New insights into the Quaternary evolution of the Bristol Channel, UK

“…Subsequent investigation of the Severn Estuary by Williams () further elaborated the evolution of the valley, and most recently dating of the pre‐Late Pleistocene terrace deposits was presented by Maddy et al . () and Maddy () and their sedimentation was discussed by Dawson (, ). Here the river's Late Pleistocene history, based upon the investigation from Worcester to the estuary at Gloucester, is summarized for comparison and interpretation of the form and development of the Bristol Channel.…”

“…Subsequently research by Beckinsale and Richardson (1964) presented a revised and elaborated model following the emergence of new evidence on the river's development. Subsequent investigation of the Severn Estuary by Williams (1968) further elaborated the evolution of the valley, and most recently dating of the pre-Late Pleistocene terrace deposits was presented by Maddy et al (1995) and Maddy (1999) and their sedimentation was discussed by Dawson (1985Dawson ( , 1989 Worcester to the estuary at Gloucester, is summarized for comparison and interpretation of the form and development of the Bristol Channel.…”

Quaternary river terraces in England: Forms, sediments and processes

“…Features suggest that the bulk of deposits accumulated in braided-river environments (e.g. Corner, 1975;Bryant, 1983a, b;Dawson, 1985;Gibbard, 1985Gibbard, , 1994Dawson and Bryant, 1987;Allen and Gibbard, 1993;Maddy et al, 1998;Lewis et al, 2001;Briant et al, 2008). The consistent association with climatic indicators such as icewedge casts, solifluction deposits, frozen block transport and cryoturbation structures suggest deposition under a predominantly periglacial regime.…”