The BGS Lexicon of Named Rock Units — Result Details

Crewi Formation

Computer Code: CIF Preferred Map Code: notEntered
Status Code: Pending Upgrade
Age range: Llandovery Epoch (SL) — Llandovery Epoch (SL)
Lithological Description: Comprises banded mudstones and siltstones. Very minor sandstones. Banding is characteristically wide - 10-30cm +, is common. May reach 60cm. Turbiditic mudstones overlain by oxic or anoxic hemipelagite intervals. Graptolitic units may be present.
Definition of Lower Boundary: Taken to be at the base of a laterally traceable anoxic mudstone (graptolitic) horizon (7878 0050).
Definition of Upper Boundary: Not seen on Sheet 149.
Thickness: At least about 800m thick, top of formation not yet located.
Geographical Limits: Confined to southeast corner of Sheet 149, only present on Sheet SH70SE. Best exposed in base of River Crew.
Parent Unit: Not Entered (?)
Previous Name(s): none recorded or not applicable
Alternative Name(s): none recorded or not applicable
none recorded or not applicable
Scott, M M. 1990. Geological notes and local details for 1:10,000 Sheet SH70SE Llanwrin, part of 1:50,000 Sheet 149 Cadair Idris. 
1:50K maps on which the lithostratigraphical unit is found, and map code used: