Cloford Quarry

Also within

Somerset County

Condition (Natural England)

Geology & landscape

Geological Feature: Fissure · Mining / Industrial: Quarry · Geological Period: Carboniferous, Jurassic, Triassic · Rock Type: Carboniferous Limestone, Limestone

Landscape processes: Karst

Description

Area, 39.92 ha. 98.64 ac. Description Cloford Quarry is important for the exposures of sediments of Triassic and Jurassic age which occur in major fissures within the Carboniferous Limestone. No other site in Britain shows such a variety and abundance of sediment infilled fissures of this age. The main part of the quarry exposes massively bedded Carboniferous Limestone, laid down beneath the sea some 350 million years ago. Later earth movements caused these rocks to be uplifted, folded, faulted and eroded, before becoming part of the land surface during Triassic times, some 230 million years ago. The Triassic environment was a desert. Towards the end of the Triassic the area was inundated by a rising sea which persisted into the Jurassic, some 205 million years ago. During this period fissures, created by the uplift, folding and faulting of the Carboniferous Limestone, periodically opened and closed. During each opening phase sediments collapsed into the fissures from the overlying sea bed progressively infilling them. In many fissures this process has been repeated on a number of occasions at widely differing times. Consequently the sediments filling the fissures become younger from the walls inwards producing vertical rather than horizontal stratification. The fissure infills contain a variety of fossils and provide important evidence on the geological history of the Mendip area over a long period of geological time. Deposits of Rhaetic, Hettangian, Sinemurian, Pliensbachian, Toarcian and Bathonian age have so far been identified in fissures. The upper surface of the Carboniferous Limestone has been reduced to a planar surface by marine erosion during early Jurassic times and horizontally bedded limestones of the Inferior Oolite rest upon the tilted Carboniferous Limestone; the surface also contains large number of borings made into it by bivalved molluscs living in the Jurassic seas.