Area: 0.15 hectares.
Description and Reasons for Notification:
This is a new site.
A Geological Conservation Review (GCR) site.
Crocadon Quarry is a small disused quarry lying about 300 metres south of Crocadon Farm, west of St Mellion in south-east Cornwall.
Exposures in the quarry contain crucial evidence of way-up and structural facing within the otherwise poorly exposed Tournasian to Namurian flysch deposits of south-east Cornwall. Across this part of the Variscides, these sequences are so poorly exposed that localities with an unambiguous structural context are rare and valuable.
Crocadon Quarry is the type locality for the Crocadon Formation, a sequence of thick-bedded grey-wacke turbidites, siltstones and shales of between 330 and 350 million years old. Structurally, the rocks form the inverted lower limb of the Blackdown Nappe. In this quarry, the sequence inversion is clearly demonstrable, and folds indicate that structurally, the nappe faces northward. Cleavage-bedding relationships also suggest a northward vergence, although this relationship is still a matter of scientific debate. The structural relationships exposed at Crocadon Quarry constitute important evidence in the piecing together an overall model – derived from several competing models – for the evolution of the Variscan Orogeny in this part of southeast Cornwall and southwest Devon.
Crocadon Quarry is of national significance for the understanding of the development of the Variscides in Britain.