Development of the ground model for the Clay-with-flints Formation: adventures in geological boundaries

Abstract

The Clay-with-flints Formation crops out on the high chalk plateaux in southern England. Changes in terminology are summarized and distinctions from adjacent similar deposits (e.g. Valley Gravel) are detailed. A threefold division of the transition zone between the two deposits is proposed based on degree of disturbance. Relationships with parent materials are discussed through structural and spatial relationships, as shown on published maps and in memoirs. Dominant pedological processes involved in the formation of the Clay-with-flints Formation from the Lambeth Group are described. A twofold division between the two is proposed based on physical changes. In addition to geological and pedological information, the deposit was studied through ground investigation data from 60 km of motorway network, which covers the variation in the Paleocene deposits (Lambeth Group facies (Reading Formation to Woolwich Formation) and the increasing presence of Thanet Sand Formation along the North Downs, east of approximately Leatherhead). The resulting ground model requires detailed knowledge of the microstructures of the chalk, the facies variation of Paleocene and Pliocene deposits, and temperate climate pedological processes in the vadose zone. Future work to study the engineering properties reflecting the variation of both the Paleocene facies and the development of the vadose zone is summarized. Thematic collection: This article is part of the Ground models in engineering geology and hydrogeology collection available at: https://www.lyellcollection.org/cc/Ground-models-in-engineering-geology-and-hydrogeology