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The Upper Greensand Formation is a Cretaceous formation of Albian to Cenomanian in age, found within the Wessex Basin and parts of the Weald Basin in southern England. [1] It overlies the Gault Clay and underlies the Chalk Group. It varies in thickness from zero to 75 m. It is predominantly a glauconitic fine-grained sandstone, locally becoming ...
Stratigraphically above the Lower Greensand Group is the Selborne Group which comprises a suite of mudstones, siltstones, sandstones and limestones laid down during the Albian age between 112 and 94 million years ago. It divides into an earlier Gault Formation and a later Upper Greensand Formation.
This sandy bank has been exposed by the River Wey as it cuts through the Upper Greensand stratum (mid Cretaceous) near Shalford. During the Early Cretaceous epoch (from about 145 to about 100 million years ago) Surrey alternated between a fresh-to-brackish water embayment depositing Hastings Beds and Weald Clay, comprising shales and mudstones that are often finely banded.
Overlying the Lower Greensand are the two formations which comprise the Selborne Group; the Albian age Gault Formation and the Upper Greensand Formation which extends from the Albian into the Cenomanian (c.100.5-94 Ma) thereby straddling the boundary with the Late Cretaceous epoch.
the Vale of Holmesdale formed from Gault Clay overlaid in the north with the upper layer greensand; the Greensand Ridge, formed from the lower layer of greensand, containing the source of the River Medway and its tributaries; the Low Weald, a Weald Clay valley; the sandstone High Weald. [3] [4] [5]
The geological map shows the High Weald in lime green (9a). The Low Weald, [18] the periphery of the Weald, is shown as darker green on the map (9), [19] and has an entirely different character. It is in effect the eroded outer edges of the High Weald, revealing a mixture of sandstone outcrops within the underlying clay.
On top of these clays is a non-contiguous layer of Upper Greensand above which lies a rolling bed of white chalk about 200 metres thick. In the Lower Chalk and in the lower region of the Middle Chalk there are abundant fossilized shell fragments, especially Inoceramus clams. In places these form the greater part of the rock but they decrease in ...
The formation is lithologically similar to the Ashdown Formation and comprises complex cyclic sequences of siltstones with sandstones and clays, typically fining upwards. In the western parts of the county the Tunbridge Wells Sands can be divided into three; the Lower Tunbridge Wells Sand, the Grinstead Clay, and the Upper Tunbridge Wells Sand.