Great Quarry, Swindon

Also within

Wiltshire County

Condition (Natural England)

Geology & landscape

Mining / Industrial: Quarry · Geological Period: Jurassic · Rock Type: Ironstone

Description

Description The section here includes the only exposure of Purbeck facies 'Swindon Series'. It has long been famous for the richness of its molluscan faunas from the marine Swindon roach. These beds, of Portlandian age, comprise a suite of sediments ranging in their depositional environment from freshwater and hypersaline lagoons to true marine shell beds and soil profiles. The site has been the subject of dozens of published accounts since the mid 19th century and is still the subject of active research. The channelled form and erosive pebbly bases which characterise the majority of the beds in this succession and the variety of environments exhibited make this by far the most complex Jurassic section in Britain. The north western exposures of the quarry include deposits of approximately one metre's depth, thought to be Wealden in age. Overlying Portlandian Swindon Flags, these putative Wealden beds comprise deposits of ferruginous sand, sandy ironstone and greenish clay. Their fauna Corbula ssp.? Neomiodon? Viviparus and serpulids appears to be of Purbeckian or pre Purbeckian age, a conclusion supported by the petrography of the clay's low kaolinite, etc. Some of the sand laminae, however, carry appreciable quantities of Cornubian detritus high tourmaline and tourmaline fine aggregates, etc possibly recycled from the Permo Trias through the Portland Beds. Other laminae contain mostly northern material low K feldspar, tourmaline, etc, kyanite > staurolite, higher microcline, plagioclase, garnet, sphene, etc, while mixtures and alternations of detritus from the west and north are additionally indicated. This is a key site for solving problems concerning the arrival date of Cornubian detritus and the relations of the Purbeck Wealden facies with their contemporary marine facies.