The Origin and Development of Clay‐with‐flints and Associated Soil Horizons on the South Downs

Abstract

Clay-with-flints rests on remnants of the exhumed sub-Eocene surface, which is shown to be an important geomorphological feature of the West Sussex Downs. Mineralogical and other soil profile studies indicate that the deposit has developed by the action of cryoturbation and soil-forming processes on a thin cover of Reading Beds clay left on the sub-Eocene surface during the southward recession of a small Eocene escarpment. Two horizons corresponding to Claywith-flints sensu strict0 of Loveday (1962) are recognized. The basal horizon is composed partly of insoluble Chalk residue, but mainly of clay moved down from overlying horizons into the spaces left on dissolution of the Chalk at the junction of the Chalk with the base of the Clay-with-flints. The upper horizon ie composed of material from weathered remnants of Reading Beds clay, thoroughly mixed by cryoturbation with flints, other insoluble Chalk residue and clay from former basal horizons. The surface horizone of the soils often include additions of loess.Introduction THE term 'Clay-with-flints' has been used by various authors in different wa s and discussion of the literature is hindered by the lack of precise stiff brown and red cla containing unworn flints that lies on the Upper the Chalk, that it often contains uartz pebbles and fragments of sandbase. He distinguished mixed deposits of loam and sandy clay, which he termed 'Brick-earth', from Cla -with-flints, and noted that Clay-withwaste of Reading Beds sand and clay, gut suggested (1889) that the two could conveniently be ma ed together as Brick-earth bordered b de 22 'tions. Whitaker (Hull and Whitaker, 1861) first described it as a Chalk of southern Eng r and. He noted that the deposit often fills pipes in stone, and that a few inches of b 1 ack flinty clay commonly occur at its fits is commonly overlain by t K ese de osits, which he interpreted as the Clay-with-flints'. On t h e s e w Series Geolo deposits have subsequently been Many later workers attempted to within this broad mapping unit. Loveday (1958, 1962) summarized and discussed literature on Clay-with-flints; he restricted the use of the term 'Clay-with-flints' to a distinctive reddish highly tenacious clay that immediately overlies the Chalk and contains mainly nodular flints and broken portions thereof. He defined this as 'Clay-with-flints s m stricto' and described its characteristic roperties. natura e dissolution of the Chalk would produce a 'stony desert of angular flints', Wooldridge and Linton (1955, p. 55) and Wooldridge and Goldring (1953, p. I 17) assumed that 'true Clay-with-flints' is a residual In s ite of the assertions of Ju K es-Browne (1906) and Reid (1899) that

Distribution, petrology and mode of development of silcretes (sarsens and puddingstones) on the eastern South Downs, UK

“…However, the distribution of silcretes in the study area is largely peripheral to the present Lambeth Group outcrop. Similarly, silicification in association with a late Palaeogene or early Neogene erosion surface is not supported by distributional evidence, and, perhaps more critically, there is no evidence for a palaeosurface of this age in the eastern South Downs (Hodgson et al, 1967). Silicification at a later stage in the Cenozoic or even in the earlier Quaternary would, however, be in full accord with the observed distribution, since occurrences of silcretes at locations fringing the Lambeth Group suggests that these materials formed when the outcrop was more extensive.…”

“…Furthermore, the patchy distribution of sarsens in Clay-with-Flints and on the sub-Palaeogene surface (cf. Hodgson et al, 1967) is very difficult to explain when other displaced remnant materials, such as ferruginous sandstone fragments and glauconite-coated John Wiley & Sons, Ltd. Earth Surf. Process.…”

The geological history of the Isle of Wight: an overview of the ‘diamond in Britain's geological crown’

“…Part of the deposit has been re-mobilised in cold phases during the late Neogene and early Pleistocene and this has been described by others (Hodgson et al, 1967) as Clay-with-flints sensu lato. It shares many characteristics with Clay-with-flints sensu stricto but is found at levels adjacent to or below the sub-Palaeogene surface and the contained flints are predominantly angular rather than nodular.…”

“…The oldest deposit on the island is the ‗Angular Flint Gravel of the Downs' (White, 1921) that is essentially a local facies of the Clay-with-flints (Hodgson et al, 1967, and references therein) as seen on the mainland (the term Clay-with-flints will be applied to the new geological sheet). It is assumed to have a similar mode of formation over an extended period in the late Neogene and early Pleistocene, and, as a consequence, it was probably formed through a number of climatic phases.…”

“…It is assumed to have a similar mode of formation over an extended period in the late Neogene and early Pleistocene, and, as a consequence, it was probably formed through a number of climatic phases. The Claywith-flints sensu stricto (Hodgson et al, 1967) is a residual rubified stony clay deposit created by the modification of the original Palaeogene cover and progressive dissolution of the underlying Chalk. The basal surface of the deposit approximates to the sub-Palaeogene unconformity but this is much modified by dissolution of the underlying Chalk with karstic features in evidence in most exposures.…”