The BGS Lexicon of Named Rock Units — Result Details

Orrisdale Formation

Computer Code: ORRIS Preferred Map Code: notEntered
Status Code: Full
Age range: Devensian Stage (QD) — Devensian Stage (QD)
Lithological Description: Stratigraphically complex sequence of stratified coarse-grained diamictons, sands and gravels. It is dominated by material derived from offshore within the Irish Sea basin. The Formation includes tills that are thought to have been formed subglacially or by glaciomarine deposition, and some of sands and gravels show extensive flow folding.
Definition of Lower Boundary: Unconformably overlies the glacially tectonically deformed complex of diamictons, gravels and shelly sands of the Shellag Formation.
Definition of Upper Boundary: At the base of the stratigraphically complex sequence of laminated and massive muds with dropstones, gravel, sand and muddy diamicton comprising the Jurby Formation.
Thickness: Up to at least 60m
Geographical Limits: Northern part of the Isle of Man (50k Sheets 36 and possibly 46).
Parent Unit: Irish Sea Coast Glacigenic Subgroup (ISCG)
Previous Name(s): none recorded or not applicable
Alternative Name(s): none recorded or not applicable
Type Section  Coastal cliff section at Orrisdale Head, c.2km north of Kirk Michael, on the western side of the Isle of Man. Chadwick, R A, et al. 2001. 
Chadwick, R A, Jackson, D I, Barnes, R P, Kimbell, G S, Johnson, H, Chiverell, R C, Thomas, G S P, Jones, N S, Riley, N J, Pickett, E A, Young, B, Holliday, D W, Ball, D F, Molyneux, S G, Long, D, Power, G M and Roberts, D H. 2001. Geology of the Isle of Man and its offshore area. British Geological Survey Research Report, RR/01/06. 
Thomas, G S P. 1999. Northern England. 91-98 in Bowen, D Q (Editor), A revised correlation of Quaternary and Neogene 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: