The BGS Lexicon of Named Rock Units — Result Details

Dallas Psammite Formation

Computer Code: DAPS Preferred Map Code: TODU
Status Code: Full
Age range: Neoproterozoic Era (AZ) — Neoproterozoic Era (AZ)
Lithological Description: Pale grey, pink and white, flaggy to blocky, thin- to thick-bedded, siliceous and feldspathic psammite, locally with thin muscovite-rich beds and laminae. Subordinate quartzite beds common. Micaceous psammite and thin semipelite beds also present. Locally distinctive beds of interbanded psammitic and semipelitic gneiss, with quartz-feldspar augen and veins.
Definition of Lower Boundary: Passes downwards into more mixed psammites and semipelites, locally gneissose. Possibly locally shear zone boundary. Onlap of Upper Devonian sediments obscures lower contacts in parts.
Definition of Upper Boundary: Passes up with gradational contact up into the Knockando Quartzite Formation over much of its outcrop. Truncated to the north-east by the Rothes Fault, and North-east of this structure possibly equivalent to undefined psammite and quartzite units within the Grampian Group.
Thickness: Up to 3000m, and possibly thicker.
Geographical Limits: Stretches west from the Spey Valley around Rothes in an east-west swathe some 18 km wide at least as far as the Dorback Burn. Turns southwards and passes into the partly equivalent Nethybridge Psammite Formation. Overlain unconformably by Middle and Upper Devonian conglomerates and sandstones to the north. To the east truncated by the Rothes Fault, though possibly equivalent to some of the Grampian Group (undefined) psammites and quartzites farther east.
Parent Unit: Grampian Group (GRAM)
Previous Name(s): none recorded or not applicable
Alternative Name(s): none recorded or not applicable
Stratotypes:
Partial Type Section  Section along and adjacent to the Black Burn, between Whitetree Farm and Romach Loch, 2.5 km north-west of Dallas. [Stephenson et al, in prep.]. 
Reference Section  Section in the Burn of the Cowlatt, above Clune Lodge. [Stephenson et al, in prep]. 
Reference(s):
Stephenson, D, et al, in prep. The geology of the Knockando and Glenfiddich districts. Sheet explanation. Sheets 85W and 85E [Scotland]. British Geological Survey. 
1:50K maps on which the lithostratigraphical unit is found, and map code used:
S095 S085 S085 S075