The BGS Lexicon of Named Rock Units — Result Details

Rodway Siltstone Formation

Computer Code: RSI Preferred Map Code: notEntered
Status Code: Pending Upgrade
Age range: Marsdenian Substage (CZ) — Yeadonian Substage (CY)
Lithological Description: Dark grey, locally red, purple and green stained, micaceous siltstone with subordinate thin beds of pale grey or purple-stained, fine- to medium-grained, locally bioturbated sandstone. Near the base there are small-scale rhythmic cycles of sandstone, siltstone and black shale.
Definition of Lower Boundary: At the type locality the base of the formation is faulted against mid to pale grey oolitic limestone of the Pembroke Limestone Group. A non-tectonized base of the Formation has not been recorded at crop or in boreholes, suggesting that the formation was displaced to its current location above a low-angle lag fault, (Whittaker, 1975).
Definition of Upper Boundary: The grey siltstones of the Rodway Silstone Formation are overlain unconformably by red, yellow and buff mottled, fine- to medium-grained sandstone of the Otter Sandstone Formation (Sherwood Sandstone Group).
Thickness: More than 138m, with 138m exposed (top not seen) at the type locality.
Geographical Limits: The outcrop is restricted to the Rodway Inlier [ST 244 398] and Swang Farm Inlier [ST 231 392], located northwest of Cannington, Somerset. The Formation is also proved in boreholes to occur beneath the Sherwood Sandstone and Mercia Mudstone groups within the vicinity of the inliers.
Parent Unit: Marros Group (MARR)
Previous Name(s): Rodway Siltstones (-3650)
Rodway Beds (ROS)
Alternative Name(s): none recorded or not applicable
Stratotypes:
Partial Type Section  The Withiel Farm No.1 Borehole (ST23NW/6) [ST 2435 3981], near Cannington, Bridgwater, proved the thickest development of the formation from ground surface to 138.2m depth and records the base. Edwmonds and Williams, 1985. 
Reference(s):
Whittaker, A. 1975. Namurian strata near Cannington Park, Somerset. Geological Magazine, Vol.112, 325-326. 
Edmonds, E A and Williams, B J, 1985. Geology of the country around Taunton and the Quantock Hills. Memoir of the British Geological Survey, Sheet 295. (England and Wales). 
1:50K maps on which the lithostratigraphical unit is found, and map code used:
E295