The BGS Lexicon of Named Rock Units — Result Details

Combe Downs Member

Computer Code: CODS Preferred Map Code: notEntered
Status Code: Pending Upgrade
Age range: Famennian Age (DA) — Tournaisian Stage (CT)
Lithological Description: Pale to mid grey to pale brown, ochreous-weathered or purple mottled, very fine- to fine-grained, locally micaceous sandstone interbedded with purplish grey, pale brown, pink or red-brown, finely micaceous siltstone, mid grey, purple-grey and red-brown mudstone and thin limestone beds. The limestone beds, to 0.1m thick, are typically soft and comprise mid grey, sparry calcarenite with abundant shelly material. Limestone and sandstone interbeds on the centimetre-scale are locally seen. Sandstone beds are typically 30cm thick, but in places coalesce to form thicker sandstone packages to 60cm thick. Sandstone and siltstone beds are commonly thinly planar laminated or cross laminated, locally massive. Mudstone beds range from thinly laminated or thinly bedded to massive. Crinoid ossicles and intact stems and brachiopod valves are locally common in all lithologies.
Definition of Lower Boundary: The base is taken where the base of the lowermost bed of sandstone or siltstone of the Combe Downs Member rests conformably upon pale to mid grey or purplish grey mudstone of the Pilton Mudstone Formation.
Definition of Upper Boundary: The top is taken where the top of the uppermost bed of sandstone and siltstone is conformably overlain by silvery pale greenish grey fissile mudstone of the Pilton Mudstone Formation.
Thickness: c.200m, but difficult to determine due to folding and faulting.
Geographical Limits: Mapped from east of Shillingford [SS 993 244] to west of Bathealton [ST 068 249] on the Tiverton Sheet (310). Expected to occur more extensively on the southern part of the Dulverton Sheet (294), where a type locality might be found, leading to a more suitable name for the Member.
Parent Unit: Pilton Mudstone Formation (PLT)
Previous Name(s): none recorded or not applicable
Alternative Name(s): none recorded or not applicable
Stratotypes:
Reference Section  Disused quarry in two levels, with a continuous section of 23m thickness. The base and top of the Member are not seen. 
Reference(s):
none recorded or not applicable
1:50K maps on which the lithostratigraphical unit is found, and map code used:
E310