The BGS Lexicon of Named Rock Units — Result Details

Coire Daingean Semipelite Formation

Computer Code: DAIN Preferred Map Code: DAIN
Status Code: Full
Age range: Cryogenian Period (AC) — Cryogenian Period (AC)
Lithological Description: Formation comprises a lower calcareous semipelite unit succeeded by a massive schistose garnet-mica semipelite that constitutes the dominant lithology in the formation. The lower calcareous unit comprises 0 to 30m of calcareous garnet-mica schist and muscovite-quartz schist; extremely pitted weathering is conspicuous. The calcareous unit is succeeded by massive, poorly bedded garnet-mica schist and muscovite-quartz schist, poor in biotite but with abundant quartz sweats. Garnets are typically 1-2mm across, commonly chloritised and wrapped by muscovite. The unit is typically resistant to weathering and commonly forms brown-weathering cliffs 5 to 10m high.
Definition of Lower Boundary: Change from white-weathering pinkish-brown quartzose psammite and quartzite of the preceding Beinn a'Chaisteil Quartzite Formation.
Definition of Upper Boundary: Change to the alternating muscovite-rich semipelite, psammite and quartzite of the Beinn an Dothaidh Heterolithic Formation. A calcareous semipelite or calcsilicate-rock (c.5m thick) may be present at the base of the succeeding unit.
Thickness: Sections through the formation on Beinn a'Chaisteil and in Allt Coire an Lochain suggest of the order of 70m where not intensely folded. Contrast this with a thickness of at least 350m exposed in the back wall of Coire an Lochain on Beinn 'a Chreachain. In Coire Daingean the unit is 120 to 140m, again probably thickened by folding.
Geographical Limits: Recognized across northeastern parts of Sheet 46W (Crianlarich) west and north of Loch Lyon, also recognised northwest of Bridge Balgie Fault in upper Glen Lyon to Loch an Daimh in western part of Sheet 46E (Killin) and southwestern part of Sheet 54E (Loch Rannoch).
Parent Unit: Lochaber Subgroup (DALO)
Previous Name(s): none recorded or not applicable
Alternative Name(s): none recorded or not applicable
Reference Section  Coire Daingean, especially on eastern slopes below Beinn Achallader. Details will be included in Sheet Description for Sheet 46W (Crainlarich). Presently in draft BGS internal report: Leslie et al., Progress Report on the Geology of the Tyndrum area, 2003. 1:50k Sheet 46W (Crianlarich). 
Will be included in Sheet Description for Sheet 46W (Crianlarich) and 46E (Killin). 
1:50K maps on which the lithostratigraphical unit is found, and map code used:
none recorded or not applicable