Sedimentary Infill and Stratigraphy
The London Basin is mainly filled with Palaeogene sediments. The lowest (oldest) unit is the Thanet Sand Formation (of Thanetian age, 56 – 58 million years old), which rests unconformable on top of the Chalk. It is composed dominantly of shallow marine sands. On top of the Thanet Sand Formation lies the Lambeth Group, which was deposited in a coastal plain and/or adjacent shallow sea water during the late Thanetian and early Ypresian ages. The Lambeth Group consists of the Upnor Formation, the Woolwich Formation and the Reading Formation.
The Lambeth Group is overlain by the Thames Group, which consists of two formations. From old to young these are the Harwich Formation and the Londen Clay Formation (famous for its fossils). They were deposited in shallow marine, estuarine or coastal plain (paralic) environments and were deposited during the Ypresian age (55.8 – 48.6 million years ago).
On top of the Lambeth Group is the Bracklesham Group, which consists of the Bagshot Formation, the Windlesham Formation and the Camberley Sand Formation. The Bracklesham Group is also composed of shallow marine (near-shore) and coastal facies rocks. It can be up to 140 meter thick and is of late Ypresian to Lutetian age.
Read more about this topic: London Basin