The BGS Lexicon of Named Rock Units — Result Details

Overwater Siltstone Formation

Computer Code: OV Preferred Map Code: OV
Status Code: Full
Age range: Caradoc Series (O4) — Caradoc Series (O4)
Lithological Description: Grey, laminated siltstones and tuffaceous fine-grained sandstones; channels of sedimentary breccia composed of platy siltstone clasts at base. Formation is intruded by sills of Eycott Volcanic Group age.
Definition of Lower Boundary: Unconformity with Skiddaw Group rocks below. (Angular discordance seen in places).
Definition of Upper Boundary: Overlain by conglomerate or by basaltic andesite and andesite lavas and sills forming main part of the Eycott Volcanic Group.
Thickness: c.8m at type section; up to 10m elsewhere; absent in some areas.
Geographical Limits: Limited to exposure of the base of the Eycott Volcanic Group. (Entirely within 1:50k Sheet 23, Cockermouth)
Parent Unit: Eycott Volcanic Group (EVG)
Previous Name(s): Overwater Formation (-4239)
Alternative Name(s): none recorded or not applicable
Stratotypes:
Type Section  Overwater Spillway, west of Chapelhouse Reservoir; between confluence of River Ellen and southern end of Chapelhouse Reservoir. 
Reference(s):
Millward, D, Carruthers, R M, Marriner, G F, Molyneux S G and Beddoe-Stephens, B. 1999. The Eycott Volcanic Group. British Geological Survey Technical Report, WA/99/68. 
Millward, D and Molyneaux, S G, 1992. Field and Biostratigraphic Evidence for an unconformity at the base of Eycott Volcanic Group in the Lake District. Geological Magazine, Vol.129/1, p.77-92. 
1:50K maps on which the lithostratigraphical unit is found, and map code used:
E023