The BGS Lexicon of Named Rock Units — Result Details

Sealyham Volcanic Formation

Computer Code: SVO Preferred Map Code: notEntered
Status Code: Pending Upgrade
Age range: Fennian Stage (OF) — Fennian Stage (OF)
Lithological Description: The lower part of the formation comprises green-grey, pillowed, andesitic or dacitic hyaloclastites (Bevins et al, 1992; cf. Thomas and Cox, 1924) The upper part of the Formation comprises rhyolitic tuffs.Geochemical investigations undertaken by Bevins et al (1992) confirm the calc-alkaline chemistry of these rocks, indicating that they are the continental-side products of island arc magmatism.
Definition of Lower Boundary: Gradational passage from shales of underlying Rosebush Formation. Boundary is drawn where volcanic rocks become dominant over shales.
Definition of Upper Boundary: Unconformable contact with the base of the Aber Mawr Shale Formation.
Thickness: 90 - 200m
Geographical Limits: none recorded or not applicable
Parent Unit: Not Entered (?)
Previous Name(s): Sealyham Volcanic Series (-2464)
Sealyham Volcanic Group (-1211)
Alternative Name(s): none recorded or not applicable
none recorded or not applicable
none recorded or not applicable
1:50K maps on which the lithostratigraphical unit is found, and map code used: