Computer Code: |
PBTI |
Preferred Map Code: |
notEntered |
Status Code: |
Full |
Age range: |
Devensian Stage (QD)
— Devensian Stage (QD) |
Lithological Description: |
Reddish brown, matrix-supported diamicton with a notable proportion of clasts of Torridonian sandstone and, at the type section, blocks of the underlying organic sand and silt. Generally occurs as an interbedded and locally glacitectonically deformed sequence of shelly diamicton, silt, sand and gravel. |
Definition of Lower Boundary: |
Irregular, unconformable contact with underlying deposits of organic sand and silt belonging to the Mid-Devensian Tolsta Head Member of the Lewis Formation of Bowen (1999). |
Definition of Upper Boundary: |
Ground surface or unconformably overlain by glaciofluvial sand and gravel. |
Thickness: |
Up to 25m |
Geographical Limits: |
Northern Lewis, northeast of a prominent lateral moraine. |
Parent Unit: |
Western Isles Glacigenic Subgroup (WISG)
|
Previous Name(s): |
none recorded or not applicable
|
Alternative Name(s): |
Port Beag Member
|
Stratotypes: |
Type Section |
Cliff top section at Port Beag on the southern side of the Tolsta Head peninsula, Isle of Lewis. Gordon and Sutherland, 1993. |
Reference(s): |
Peacock, J D. 1991. Glacial deposits of the Hebridean region. 109-119 in Ehers, J, Gibbard, P L and Rose, J (editors), Glacial deposits in Great Britain and Ireland. (Rotterdam: Belkema.) |
Gordon, J E and Sutherland, D G. 1993. Tolsta Head, in Quaternary of Scotland (Geological conservation review series: 6) Gordon, J E and Sutherland, D G (editors). (London: Chapman and Hall). 423-425. |
Bowen, D Q. 1999. A revised correlation of Quaternary deposits in the British Isles. Geological Society Special Report, No. 23. |
1:50K maps on which the lithostratigraphical unit is found, and map code used: |
none recorded or not applicable |