Huish Colliery Quarry

Also within

Somerset County

Condition (Natural England)

Geology & landscape

Mining / Industrial: Coal Mine, Quarry · Geological Period: Jurassic

Description

Area, 0.8 ha. 2.1 ac. Description This is an important site in the study of the Lower Jurassic rocks of the Mendip area. Analysis of the assemblages of fossils which occur in the rocks seen here show that a large part of the Lower Jurassic 'Lias' rock sequence was removed by erosion during early Jurassic times, with the effect that the Lias sequence seen here is discontinuous, when compared with other Lias sites in the Mendip area. This enables geologists to develop a better understanding of the geological evolution of this part of southern England during early Jurassic times, some 195 million years ago. In early Jurassic times the area now occupied by the Mendip Hills stood up as an island area surrounded by a shallow sea. In this sea were laid down a series of marine sediments, mainly clays and limestones, with the thickest and most complete rock sequences accumulating further offshore and progressively thinner sequences being laid down close to shore. Detailed study of the sediments and fossils seen at Huish Colliery shows that a considerable part of the Lias sequence the whole of the unit known as the Sinemurian Stage and virtually all of the unit known as the Hettangian Stage is absent, due to erosion that took place not long after the sediments had been laid down. In detail, limestones of Pliensbachian age belonging to the jamesoni Zone rest directly upon shales and nodular limestones of basal Hettangian age the planorbis Zone. Other localities showing the effects of similar intro Liassic erosion occur in the Radstock area and a unified study of all these sites gives geologists a better understanding of the complex sequence of erosion and deposition which was occurring on the flanks of the Mendips in early Jurassic times. Huish Colliery Quarry stands out from other sites since it shows the most extreme example of pre jamesoni Zone erosion and is thus of great importance. Also notable is the fact that the jamesoni Zone limestones which occur here are much thicker and better developed than at any other comparable sites in the Mendips, and this juxtaposition of the biggest intro Liassic erosional break with the thickest sequence of post erosional sediments endows the site with considerable further interest for geologists.