| Computer Code: |
BIES |
Preferred Map Code: |
notEntered |
| Status Code: |
Full |
| Age range: |
Devensian Stage (QD)
— Devensian Stage (QD) |
| Lithological Description: |
Dominantly yellow to pale brown and reddish yellow slightly clayey to slightly silty sand with local fine-grained gravels. The material is usually reddish brown and grey colour mottled as a result of near surface water processes. It is typically composed of moderately well sorted medium-grained quartz grains with minor bands of finer, coarser or pooly sorted material, including flint and chert. Thin beds (<5cm) of clayey sandy peat can occur within the unit. |
| Definition of Lower Boundary: |
The Bielby Sand Member rests mainly on the Pocklington Gravel Formation or the Hemingbrough Glaciolacustrine Formation. In places there is a thin peat bed at the base. The contact is commonly sharp but locally gradational, with an increase in clay, gravel and/or peat content. North of Bielby, an increase in gravel and peat content marks the lower boundary. |
| Definition of Upper Boundary: |
The upper surface of the Bielby Sand Member is usually eroded and overlain by younger alluvial and aeolian deposits. |
| Thickness: |
General thickness is between 1 and 2m, but it can exceed 6m in parts and may form elevated topographic features. |
| Geographical Limits: |
The Bielby Sand Member is known to extend along the eastern side of the Vale of York from the Escrick Moraine in the north to the Humber in the south. The deposit is part of a Late Devensian drainage system and forms some levee-like features, particularly around Melbourne. In some areas it is covered by younger deposits but has probably commonly been removed by later erosion. |
| Parent Unit: |
Breighton Sand Formation (BREI)
|
| Previous Name(s): |
Sand Of 25-Foot Drift Of The Vale Of York
(-698)
|
| Alternative Name(s): |
none recorded or not applicable
|
| Stratotypes: |
| Partial Type Section |
Coats Flat field from 0-300m north of Pinch Hall (north of Bielby). Several ditches expose 1 to 2m of the Bielby Sand Member. The deposit is colour-mottled and contains some clayey and organic layers. It is overlain by 0.4m of recent overbank deposits rests directly either on the Bielby Peat Bed or on the Pocklington Gravel Formation, and the contact is apparently erosional. |
| Reference(s): |
| 1:50k geological map of Selby (Sheet 71) (in prep): Selby Sheet Explantion (in prep). |
| British Geological Survey. 1983. Sheet 71 Selby solid and drift/compiled and drawn in the Leeds office of the Institute of Geological Sciences - Solid and drift ed. Provisional ed. |
| 1:50K maps on which the lithostratigraphical unit is found, and map code used: |
|
E071
|
