| Computer Code: |
GACH |
Preferred Map Code: |
notEntered |
| Status Code: |
Full |
| Age range: |
Tonian Period (AT)
— Tonian Period (AT) |
| Lithological Description: |
Locally a 10-20 m thick garnetiferous semipelite unit at the base, followed by tabular trough cross-bedded psammite interbedded with garnetiferous semipelite in fining -upwards sequences. At the top of the formation is another c. 10-20 m thick garnetiferous semipelite with locally thin quartzite. |
| Definition of Lower Boundary: |
Conformably upon the remainder of the Altnaharra Psammite Formation (GLPS). Incoming of significant (>2 m) garnet-bearing semipelite layers. |
| Definition of Upper Boundary: |
Conformably overlain by the Glascarnoch Psammite Formation (GLPS). Boundary set above uppermost limit of thick (>2 m) garnet-bearing semipelite units. A discontinuous quartzite bed forms the very top of the Member in some outcrops. |
| Thickness: |
c. 500 (estimated maximum); thinner to SW and NE. |
| Geographical Limits: |
Northern Highlands: Central Ross-shire. |
| Parent Unit: |
Altnaharra Psammite Formation (ALPS)
|
| Previous Name(s): |
none recorded or not applicable
|
| Alternative Name(s): |
none recorded or not applicable
|
| Stratotypes: |
| Type Area |
North of Glen Achall: Meall Liath Choire to Cnoc Damh [NH 227 961 - NH 271 963]. |
| Reference(s): |
| Bonsor, H C, Strachan, R A, Prave, A, and Krabbendam, M. 2010. Fluvial braidplain to shallow marine transition in the early Neoproterozoic Morar Group, Fannich Mountains, northern Scotland. Precambrian Research 183, 791-804. |
| Krabbendam, M. 2021. A stratigraphic framework for the early Neoproterozoic successions of the Northern Highlands of Scotland. UK Stratigraphic Framework Series. British Geological Survey Open Report, OR/21/072. 86pp. |
| Krabbendam, M, Strachan, R A, Leslie, A G, Goodenough, K M and Bonsor, H C. 2011. The internal structure of the Moine Nappe Complex and the stratigraphy of the Morar Group in the Fannichs-Beinn Dearg area, NW Highlands. Scottish Journal of Geology, 47, 1-20. |
| 1:50K maps on which the lithostratigraphical unit is found, and map code used: |
|
S101
|
