The Gault Formation is a geological formation of stiff blue clay deposited in a calm, fairly deep-water marine environment during the Lower Cretaceous Period (Upper and Middle Albian). It is well exposed in the coastal cliffs at Copt Point in Folkestone, Kent, England, where it overlays the Lower Greensand formation, and underlies the Upper Greensand Formation.
The etymology of the name is uncertain and probably of local origin.
Distribution
It is found in exposure on the south side of the
North Downs and the north side of the
South Downs. It is also to be found beneath the
escarpment of the
Berkshire Downs, in the Vale of White Horse, in
Oxfordshire, England, and on the Isle of Wight where it is known as Blue Slipper.
Gault underlies the chalk beneath the
London Basin, generally overlying eroded rocks of
Jurassic and
Devonian age; lower gault is present only below the outer parts of the basin and is absent under central London. The Gault Formation represents a marine transgression following erosion of the Lower Greensand. It is subdivided into two sections, the Upper Gault and the Lower Gault. The Upper Gault
onto the Lower Gault. The Gault Formation thins across the
London Platform and then terminates against the Red Chalk just to the south of
The Wash in
East Anglia.
The Gault exposure at Copt Point, which is the type locality for the formation, is 40 m in thickness.
Uses
The clay has been used in several locations for making bricks, notably near
Dunton Green and near Wye in
Kent.
Gault often contains numerous phosphatic nodules, some thought to be coprolites, and may also contain sand as well as small grains of the mineral glauconite. Crystals of the mineral selenite are fairly common in places, as are nodules of pyrite.
Fossils
Gault yields abundant marine
, including
(such as
Hoplites,
Hamites,
Euhoplites,
Anahoplites, and
Dimorphoplites),
Belemnoidea (such as
Neohibolites),
Bivalvia (such as
Birostrina and
Pectinucula),
Gastropoda (such as
Anchura), solitary
,
fish remains (including
shark teeth), scattered
crinoid remains, and
(such as the
crab Notopocorystes). Terrestrial fossils that have been found at Gault include fossil wood, a dinosaur (
cf. Acanthopholis),
and
, including
Azhdarchoidea,
Ornithocheiridae, and the indeterminate
Pterodactyloidea "Pterodactylus"
daviesii.
Several pterosaur fossil remains from the overlying Cambridge Greensand may have been reworked from the underlying Gault.
See also
External links
