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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 ...
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.
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.
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 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.
The highest formation in the Group, the Wroxham Crag, contains over 10% of far-travelled lithologies, notably quartzite and vein quartz from the Midlands, igneous rocks from Wales, and chert from the Upper Greensand of southeastern England. This exotic rock component was introduced by rivers such as the Bytham River and Proto-Thames. [3] [4]
The Wealden Group is overlain by the Lower Greensand and the Gault Formation, consisting of the Gault and the Upper Greensand. [4] The rocks of the central part of the anticline include hard sandstones, and these form hills now called the High Weald.
Contact between two units of the lithostratigraphy of South England: the Chalk Group (left, white, upper unit) and the Greensand Formation (right, green, lower unit). Location: Lulworth Cove , near West Lulworth , Dorset , England.