| Computer Code: |
DBIS |
Preferred Map Code: |
Isly |
| Status Code: |
Full |
| Age range: |
Neoproterozoic Era (AZ)
— Neoproterozoic Era (AZ) |
| Lithological Description: |
Diamictite ('Boulder Bed') with limestone clasts in its lower part and quartzite and granite clasts in upper part attains maximum thickness in Port Askaig area and on Garvellachs; overlying quartzite reaches 5km in thickness on Jura but is more usually 0.5 - 1km thick; dolomitic beds are locally developed near base of quartzite. In Ladder Hills area graded psammites and semipelites intervene between diamictite and quartzite. |
| Definition of Lower Boundary: |
Generally transitional over a few metres at base of tillite of Port Askaig (Schiehallion) Boulder Bed. |
| Definition of Upper Boundary: |
Abrupt transition from quartzite to graphitic pelite (Easdale) or mixed psammite, semipelite and pelite (Perthshire). |
| Thickness: |
Up to 5km |
| Geographical Limits: |
Connemara; North Mayo; Donegal; Islay, Jura, from Loch Rannoch to Glen Tilt, from near Spittal of Glen Shee via Upper Deeside, Donside and Ladder Hills to the coast between Sandend and Portsoy. |
| Parent Unit: |
Argyll Group (ARGY)
|
| Previous Name(s): |
Tillite (Banffshire) [Obsolete Name And Code: See DBIS, DBST, DBPT]
(DBBT)
|
| Alternative Name(s): |
none recorded or not applicable
|
| Stratotypes: |
| Type Area |
North-east Islay and Jura. (Spencer, A M, 1971. Anderton, R, 1976). |
| Reference(s): |
| Harris, A L and Pitcher, W S, 1975. The Dalradian Supergroup. "In" Harris, A L, Shackleton, R M, Watson, J, Downie, C, Harland, W B and Moorbath, S. A correlation of the Precambrian rocks in the British Isles. Geological Society Special Report, No.6. p.52-75. Scottish Academic Press, Edinburgh. |
| Anderton, R. 1977. The Dalradian rocks of Jura, Scottish Journal of Geology, Vol. 13, 135-142. |
| Harris, A L, Haselock, P J, Kennedy, M J and Mendum, J R, 1994. The Dalradian Supergroup in Scotland, Shetland and Ireland. 33-53 in Gibbons, W E and Harris, A L (editors). A revised correlation of Precambrian rocks in the British Isles. Special Report of the Geological Society, London, No.22. |
| Stephenson, D and Gould, D. 1995. British Regional Geology: the Grampian Highlands (4th edition). (London: HMSO for the British Geological Survey), 67-68. |
| Spencer, A M, 1971. Late Precambrian glaciation in Scotland. Memoir of the Geological Society of London, No.6. |
| Treagus, J E. 2001. Solid geology of the Schiehallion district. Memoir of the British Geological Survey, Sheet 55W (Scotland). |
| 1:50K maps on which the lithostratigraphical unit is found, and map code used: |
|
S019
S027
S028
S036
S055
S055
S056
S065
S065
S075
S075
S085
S086
S096
S028
S045
S045
S086
S096
|
