The BGS Lexicon of Named Rock Units — Result Details

Monadh Dubh Sandstone Formation

Computer Code: MODS Preferred Map Code: MoDS
Status Code: Pending Upgrade
Age range: Triassic Period (T) — Triassic Period (T)
Lithological Description: The Monadh Dubh sandstone Formation consists of 4 members, but was shown as one unit on the 50k maps. From the base these members are Shellesder, A'Mharagach, Sgaorishal and Allt Dubh. The base of the unit lies directly on the Torridonian and comprises coarse, continental-derived conglomerates. Gradually the succession fines upwards and the top 25m (two members) are dominated by fine sand and lacustrine carbonate rocks with ostracods.
Definition of Lower Boundary: Direct, unconformable contact on Torridonian sandstones.
Definition of Upper Boundary: Jurassic transgression - change from continental derived sediments - not seen?
Thickness: 82m+
Geographical Limits: Isle of Rum
Parent Unit: New Red Sandstone Supergroup (NRS)
Previous Name(s): none recorded or not applicable
Alternative Name(s): none recorded or not applicable
Reference Section  Monadh Dubh, northwest Rum. Emeleus, 1997. 
Emeleus, C H. 1997. Geology of Rum and the adjacent islands. Memoir (sheet) of the Geological Survey of Great Britain (Scotland) (60). (The Stationery Office for the British Geological Survey.) 171pp. 
Steel, R J. 1974. New Red Sandstone piedmont and floodplain sedimentation in the Hebridean province, Scotland. Journal of Sedimentary Petrology, Vol.44, 336-357. 
1:50K maps on which the lithostratigraphical unit is found, and map code used: