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Bucks Geology Group

Gault Clay

The Gault Clay Formation covered northern Europe during the Middle-Late Albian stage of the Early Cretaceous (around 105 to 95 million years ago). This was a time when the world was experiencing global warming, sea levels were rising rapidly, culminating with record high levels during the deposition of the Chalk. The base of the Gault Clay often directly overlies the eroded, unconformable surface of older sediments. In Buckinghamshire, borehole evidence shows that it sits directly on Upper to Middle Jurassic towards the south of the county. (Beneath London, the Gault Clay rests directly upon the old, Devonian, land surface. The Gault Clay is a grey clay, particularly fossiliferous near its base, but becoming more monotonous in its higher part. The sediment was probably derived from Jurassic Clay formations being eroded from low-lying surrounding land areas (such as the London Platform; the Armorican area - Devon, Cornwall; Northern England)

Fossil shells are often preserved in their original material, albeit very fragile and crushed as the clay has compressed. Others attracted a phosphatic cementation shortly after burial. These are now preserved as hard, fully 3-dimensional casts which are very robust. Some concentrations of phosphatic fossil casts occur in discrete bands and represent a time of ocean deepening, and the subsequent period when the sediment did not reach this offshore area of the sea-floor.

Early Cretaceous Strtigraphy Chart

The Gault Formation of Buckinghamshire Stratigraphy

In the early 20th Century the Gault clay was worked for it's phosphatic pebbles of 'coprolite beds'.

Hover cursor over photograph for label.

Typical block of pale grey Gault Clay with fossils. Pit N. of Tree Farm, Shenley, near Leighton Buzzard. Looking NW. Junction of Upper Gault and Lower Greensand. The photograph shows the cross-stratified silver-sands at the base of the stratified loamy succeeding beds trangressed by the Upper Gault.

Below are a number of fossils which you can expect to find within the Gault Clay Formation. Hover cursor over photograph to enlarge.


Bivalve, Birostrina sulcata, an Upper Gault Clay form, which is believed to have evolved from the 
concentrically-ribbed species, as some intermediate forms have been discovered. An artist impression of Belemnites swimming in the Cretaceous sea. This Scaphopod Mollusc, Dentalium, was a calcareous tube inhabited by a small animal with a filter 
feeding arm which could protrude from the shell.

Further reading suggestions:

Horton, A., 1995. Geology of the country around the Thame. Memoir for geological map 237.

Young, J.R., 2009. Fossils of the Gault Clay. The Palaeontological Association, London.

Images used with permission: © Copyright Buckinghamshire County Museum (Licence No. 44)

BGG Contact : Mike Palmer (

page last updated: 28th March 2024

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