The BGS Lexicon of Named Rock Units — Result Details

Ben Challum Quartzite Formation

Computer Code: CHAL Preferred Map Code: CHAL
Status Code: Full
Age range: Ediacaran Period (AD) — Ediacaran Period (AD)
Lithological Description: 5 to 10m-scale bedded/banded, pale brown quartzite to quartzose psammite with cm-scale schistose quartz, muscovite, +/- biotite semipelite interbeds. Approximately 70:30 psammite/quartzite to semipelite. Quartzite/quartzose psammite beds are thicker (20 to 40cm) in lower part (semipelite less than 3cm-thick layers and less than 20%) of the formation; hornblende schist layers (30 to 40cm thick) are conspicuous.
Definition of Lower Boundary: The change from calcareous "pitted" psammites and semipelites of underlying Ben Lawers Schist Formation appears sharp (in the Allt Challum section) with abrupt loss of any calcareous component and a decrease in the semipelite content, which is typically 50% or more in the Ben Lawers Schist Formation.
Definition of Upper Boundary: Transitional/gradational change upwards with increasing semipelite proportion into the Ben Lui Schist Formation. Upper limit taken where conspicuous quartzose psammite layers are <20%.
Thickness: c.20m
Geographical Limits: Occurs east of the Tyndrum Fault, across Beinn Chaorach, Ben Challum and into upper Glen Lochay, Sheet 46W. Always at the boundary between the Ben Lawers Schist Formation and Ben Lui Schist Formation.
Parent Unit: Crinan Subgroup (DBCN)
Previous Name(s): none recorded or not applicable
Alternative Name(s): none recorded or not applicable
Stratotypes:
Reference Section  Allt Challum, northern slopes of Ben Challum. 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). 
Reference(s):
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