Bierton Clay Pit SSSI

  Bucks County Council administration area: Aylesbury Vale District Council

Grid reference: SP 839 157

Area of site: 0.07 ha; 0.2 acres

Access, location and parking: 2 km NE of Aylesbury, off the A418. The site can be viewed from the footpath which runs along the southern end of the complex of small ponds. Actual access is from the eastern end where a main entrance will be found and parking is best in Barnett Way .

Site description: Disused clay pit, now flooded.

Geological interpretation: The succession spans the Kimmeridgian-Tithonian (Portlandian) boundary and includes an exposure of the basal Upper Lydite Bed of the Portland Sand. (Lydite is a distinctive shiny, black, cherty rock). This is a correlatable Bed across the area, but there are very few exposures and these are only temporary. The bed is a transgressive horizon, that is, it shows evidence for a rise in sea level after a period of non-deposition and erosion. This event left a pebble bed over a substantial gap in time (an unconformity). This site is therefore useful for stratigraphy.

Current and potential educational  use (geology, ecology, archaeology, industrial archaeology): No geological exposure is currently available, but could be potential future exposures if ponds are drained are new drainage channels or ditches are dug. Ecological interest only.

Conservation interest: The pit is flooded, no conservation is appropriate for geological interest from BEHG.

Threats to site (present and future): None at present.

Constraints (basic risk assessment): The pit is flooded and care should be taken if walking around the perimeter of the water.

Reference list/bibliography:

Ballance, P. F. 1963. The beds between the Kimmeridge and the Gault Clays in the Thame-Aylesbury area. Proc. Geol. Assoc. 74, 393-418.

Casey, R. 1967. The position of the Middle Volgian in the English Jurassic. Proc.Geol. Assoc. 78, 128-133.

Davies, A. M. 1934. A field meeting at Aylesbury. Proc. Geol. Assoc. 45, 104-6.

Davies, A. M. and Wilson, V. 1949. Field meeting in the north Chiltern Hills and Aylesbury District. Proc. Geol. Assoc. 60, 219-221.

Neaverson, E. 1925. The petrology of the Upper Kimmeridge Clay and Portland Sand in Dorset, Wiltshire Oxfordshire and Buckinghamshire. Proc. Geol. Assoc. 36, 240-256.

Oates, M. J. 1974. The stratigraphy and palaeoecology of the Hartwell Clay ( Upper Kimmeridgian ) of Aylesbury, Buckinghamshire. Proc. Geol. Assoc. 85,   367-375.

Wimbledon , W. A. 1980. Portlandian correlation chart. In: Cope, C. J. W (ed.) A correlation of Jurassic rocks in the British Isles . Part 2: Middle and Upper Jurassic. Spec. Rep. Geol. Soc. London. 15, 85-93.

Sylvester-Bradley, P. C. and Ford, T. D. (eds.) 1968. The geology of the East Midlands, Leicester University Press, 400 pp.

Recommendations: Note if new sections are dug for drainage, etc. Otherwise not suitable for group activities.