The lithostratigraphy, biostratigraphy and hydrogeological significance of the mud springs at Templars Firs, Wootton Bassett, Wiltshire

The mud springs at Wootton Bassett have only come to public notice in the last ten years. Best known for their small, beautifully preserved, iridescent ammonites, they have excited much media interest. Despite this interest, the origin and driving mechanism of the mud springs has remained conjectural. Recent studies by the British Geological Survey have located additional mud springs about 1.5 km southwest of Templars Firs. However, the mud springs at Templars Firs are unique in bringing well-preserved, pyritized, fossils to the surface. Both sets of springs can now be placed in their true geological setting; they are sited along the axis of a syncline. Confined groundwater from the Coral Rag, passing up through c. 20 m of Ampthill Clay, is probably the force driving the mud springs. The clay particles tend to stay as a colloid suspension and do not easily separate out. This is thought to be due to a decrease in the ionic strength of the solution by the uptake of Ca2+ on to the clays and the release of Na2+ from the clays to solution.