The BGS Lexicon of Named Rock Units — Result Details

Halkyn Formation [Obsolete Name And Code: See Revision Data]

Computer Code: HAF Preferred Map Code: notEntered
Status Code: Index Level
Age range: Namurian Stage (CN) — Namurian Stage (CN)
Lithological Description: Comprises Cefn-y-Fedw Sandstone at base (quartzose sandstone), replaced laterally by chert and mudstone in the type area; overlain by the Holywell Shales (grey and black mudstone with subsidiary sandstones) and Gwespyr Sandstone (feldspathic sandstone).
Definition of Lower Boundary: Base of Cefn-y-Fedw Sandstone (member) where present; overlies Minera Formation (limestone with interbedded sandstones). In type area, at base of Pentre Chert (member), unconformably overlies Cefn Mawr Limestone Formation.
Definition of Upper Boundary: Top of Gwespyr Sandstone (member).
Thickness: 250 - 350 metres.
Geographical Limits: Flintshire Coalfield, North Wales.
Parent Unit: Not Entered (?)
Previous Name(s): none recorded or not applicable
Alternative Name(s): none recorded or not applicable
Type Section  Bryn Mawr Quarry, Pentre Halkyn, Clwyd. 
Campbell, S D G, and Hains, B A. 1988. Deeside (North Wales) thematic geological mapping. British Geological Survey Technical Report, WA/88/2. p.78-79. 
1:50K maps on which the lithostratigraphical unit is found, and map code used: