The beds between the Kimeridge and Gault Clays in the Thame—Aylesbury neighbourhood

Abstract

Some twenty square miles of the Thame Valley consist of Sandy Upper Kimeridge, Portland, Purbeck and Lower Cretaceous Beds. All the beds are thin and condensed. The Upper Kimeridgian Thame Sand passes laterally into silty Hartwell Clay; the Thame Sand is lenticular, and its base diachronous. Lateral variations of the lowest Portland beds, Glauconitic sand and Rubbly Limestone, are described, the two succeeding units of the Portland beds, the Crendon Sand and Creamy Limestone, being more uniform. The very thin Purbeck Beds have a wide outcrop. The unfossiliferous, ferruginous Lower Cretaceous Beds are divided into two formations; freshwater, mainly fine-grained, Wealden Beds which generally follow the Jurassic Beds conformably, overlain unconformably by coarse-grained marine Lower Greensand. North-south faulting, tilting and erosion took place in the Wealden-Lower Greensand interval. It is suggested that the Wealden Beds are more likely to be of Upper than Lower Wealden age, while the Lower Greensand is probably of Upper Aptian or lowest Albian age. Further erosion preceded the deposition of the Lower Gault Clay. Post-Gault east-west faults and warps, a sequence of river terraces 25, 50 and 100 feet above the River Thame, and late-glacial solifluxion deposits are described.