The BGS Lexicon of Named Rock Units — Result Details

Pocklington Gravel Formation

Computer Code: POCKG Preferred Map Code: notEntered
Status Code: Full
Age range: Devensian Stage (QD) — Devensian Stage (QD)
Lithological Description: Matrix to clast supported clayey sandy medium to coarse gravel. Clast composition is typically polymodal, domiated by chalk and flint. Average clast composition is 75% well-rounded chalk, 15% sub-angular flint, plus 10% accessory lithologies including ironstone and oolitic limestone. Clast composition varies in extreme cases to 100% chalk or 100% flint, increased flint content may be due in part to different dissolution of chalk clasts. Matrix material is characterized by reddish brown clayey sand to sandy clay with varying degrees of partially decomposed chalk.
Definition of Lower Boundary: Sandy gravel of the Pocklington Gravel Formation rests unconformably on Mesozoic bedrock with a sharp to variably disturbed (cryoturbated, soliflucted, reworked) basal content.
Definition of Upper Boundary: The upper contact with the Breighton Sand Formation is proved in auger holes to be relatively sharp with minor intercalation due to local reworking. Elsewhere, the Pocklington Gravel Formation is known to be overlain by alluvial, aeolian and artificial deposits with varying degrees of incision and disturbance.
Thickness: In excess of 1m (1.2m observed in temporary excavation [480417, 448013]).
Geographical Limits: The Pocklington Gravel Formation exists as a blanket deposit at the eastern limit of the Vale of York, The gravel is known to extend beneath the Breighton Sand Formation to the west of Bielby. To the north and south the gravel flanks the elevated ground into the York and Beverley areas.
Parent Unit: North Pennine Glacigenic Subgroup (NPEG)
Previous Name(s): Older Littoral Sand And Gravel (OLSG)
Alternative Name(s): none recorded or not applicable
Stratotypes:
Partial Type Section  Temporary section at Balk Field in foundation trench of housing development on southern edge of Pocklington, 375m southeast of cemetary. A composite vertical section in excess of 1m (upper and lower boundaries not represented) was logged. The section describes a matric supported sandy gravel, dominated by sub-rounded chalk and sub-angular flint fragments with minor rounded ironstone clasts. See revised 1:50k geological map of Selby (Sheet 71). 
Reference(s):
British Geological Survey, 1973. Sheet 71 Selby solid and drift/compiled and draw in Leeds Office of the Institute of Geological Sciences - Solid and drft ed. Provisional ed. 
1:50k geological map of Selby (Sheet 71) (in prep): Selby Sheet Explantion (in prep). 
1:50K maps on which the lithostratigraphical unit is found, and map code used:
none recorded or not applicable