The BGS Lexicon of Named Rock Units — Result Details
Rodway Siltstone Formation
| Computer Code: | RSI | Preferred Map Code: | notEntered |
|---|---|---|---|
| Status Code: | Full | ||
| 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 Beds
(ROS)
Rodway Siltstones [Obsolete Name and Code: Use RSI] (-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): | |||
| 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). | |||
| Whittaker, A. 1975. Namurian strata near Cannington Park, Somerset. Geological Magazine, Vol.112, 325-326. | |||
| 1:50K maps on which the lithostratigraphical unit is found, and map code used: | |||
| E295 | |||