The BGS Lexicon of Named Rock Units — Result Details
Moor Cliffs Formation
| Computer Code: | MOCL | Preferred Map Code: | notEntered |
|---|---|---|---|
| Status Code: | Full | ||
| Age range: | Pridoli Epoch (SO) — Lochkovian Age (DO) | ||
| Lithological Description: | Red (mainly) and green mudstones and siltstones rich in calcrete nodules, subordinate very fine- to fine-grained sandstones, rare exotic extraformational and intraformational conglomerate and air fall tuffs, and thick well-developed calcretes at the top (Chapel Point Limestone Member). The airfall tuffs include the Pickard Bay, Rooks Cave and Townsend tuffs. Marriott and Wright (2004) and Williams and Hillier (2004) provide more recent sedimentological descriptions. There are two named units: the informally named Holdgate Sandstone of the Cleobury Mortimer-Abberley district (Mitchell et al., 1962) and the widely distributed Chapel Point Limestone Member. | ||
| Definition of Lower Boundary: | The formation lies conformably on grey/green fossiliferous sandstones and mudstones of the Freshwater East Formation at Freshwater East in Pembrokeshire (Dixon, 1921; Williams et al., 1982). In the Welsh Borderland the lower boundary is placed at the top of the Downton Castle Sandstone Formation, or at the top of the Temeside Mudstone Formation where it is present, the boundary being marked in both cases by the incoming of red mudrock facies. | ||
| Definition of Upper Boundary: | The upper boundary is placed at the sharp junction of the basal pebbly sandstone of the Conigar Pit Sandstone Member of the Freshwater West Formation, where it overlies the topmost calcrete of the Chapel Point Limestone Member at West Moor Cliff [SS 032 980] and at Manorbier [SS 046 978]. Outside south Pembrokeshire, the upper boundary is placed at the top of the Chapel Point Limestone Member (formerly Bishop's Frome Limestone Member), where the topmost mature calcrete of the member is overlain by more sandstone-dominated strata of the Freshwater West (formerly St Maughans) Formation. | ||
| Thickness: | From 120 to 371 m in the type area (Williams and Hillier, 2004); up to 800 to 1100 m in the Welsh Borderland. | ||
| Geographical Limits: | Widely distributed throughout Wales, the Welsh Borderland and the West Midlands. | ||
| Parent Unit: | Milford Haven Subgroup (MIH) | ||
| Previous Name(s): | Ledbury Formation
(LBY)
Raglan Mudstone Formation (RG) Sandy Haven Formation (SAHA) Thornbury Formation (THB) |
||
| Alternative Name(s): | none recorded or not applicable | ||
| Stratotypes: | |||
| Type Section | Cliff section of West Moor Cliff [SS 036 978] (Marriott and Wright, 2004). | ||
| Type Section | Cliff section of East Moor Cliff [SS 047 976] (Marriott and Wright, 2004). | ||
| Reference Section | M50 Motorway cutting section [SO 6685 2636] near Ross-on-Wye. The section is now poorly exposed, but the log by Allen and Dineley (1976) provides a good reference section for the formation in the Welsh Borderland (Barclay et al., 2015). | ||
| Reference(s): | |||
| Almond, J. 1983. The sedimentology of the earliest Lower Old Red Sandstone, south central Wales. Unpublished Ph.D. thesis, University of Bristol. | |||
| Lynas, B D T. 1987. Geological notes and local details for 1:10 000 sheet SO 28NE (Mainstone). (Keyworth, Nottingham: British Geological Survey.) | |||
| Marriott, S B, and Wright, V P. 2004. Mudrock deposition in an ancient dryland system: Moor Cliffs Formation, Lower Old Red Sandstone, south-west Wales, UK. Geological Journal, Vol. 39, 277–298. | |||
| Williams, B P J, and Hillier, R D. 2004. Variable alluvial sandstone architecture within the Lower Old Red Sandstone, Pembrokeshire, UK. Geological Journal, Vol. 39, 257-276. | |||
| Barclay, W J, Davies, J R, Hillier, R D, and Waters, R A. 2015. Lithostratigraphy of the Old Red Sandstone successions of the Anglo-Welsh Basin. British Geological Survey Research Report, RR/14/02. 96pp. | |||
| Allen, J R L, and Dineley, D L. 1976. The succession of the Lower Old Red Sandstone (Siluro-Devonian) along the Ross - Tewkesbury Spur Motorway (M50), Hereford and Worcester. Geological Journal, Vol. 11, 1-14. | |||
| Cave, R and Hains, B A. 2001. Geology of the country around Montgomery. Memoir of the British Geological Survey, Sheet 165 with part of 151 (Welshpool) (England and Wales). | |||
| Dixon, E E L. 1921. The Geology of the South Wales Coalfield, Part XIII , the country around Pembroke and Tenby, being an account of the region comprised in sheets 244 and 245. Memoir of the Geological Survey of Great Britain (HMSO). | |||
| Holland, C H, 1959. The Ludlovian and Downtonian rocks of the Knighton district, Radnorshire. Quarterly Journal of the Geological Society, London, Vol.114, 449-482. | |||
| Mitchell, G H, Pocock, R W, and Taylor, J H. 1962. Geology of the country around Droitwich, Abberley and Kidderminster. Memoir of the Geological Survey of Great Britain, Sheet 182 (England and Wales). | |||
| White, D E and Lawson, J D, 1989. The Pridoli Series in the Welsh Borderland and south central Wales. 131-141 in A global standard for the Silurian System. Holland, C H and Bassett, M G (editors) National Museum of Wales, Geological Series No. 9, Cardiff. | |||
| Williams, B P J. 1971. Sedimentary features of the Old Red Sandstone and Lower Limestone Shales of south Pembrokeshire, south of the Ritec Fault. In Bassett, D. A. and Bassett, M. G. Geological Excursions in South Wales and the Forest of Dean. The Geologists’ Association, South Wales Group, Cardiff, pp. 222-239. | |||
| Williams, B P J, Allen, J R L, and Marshall, J D. 1982. Old Red Sandstone facies of the Pembroke Peninsula, south of the Ritec Fault. 151–174 in Geological excursions in Dyfed, south-west Wales. Bassett, M G (editor). (Cardiff: National Museum of Wales.) | |||
| Waters, C N, Smith, K, Hopson, P M, Wilson, D, Bridge, D M, Carney, J N, Cooper, A H, Crofts, R G, Ellison, R A, Mathers, S J, Moorlock, B S P, Scrivener, R C, McMillan, A A, Ambrose, K, Barclay, W J, and Barron, A J M. 2007. Stratigraphical Chart of the United Kingdom: Southern Britain. British Geological Survey, 1 poster. | |||
| 1:50K maps on which the lithostratigraphical unit is found, and map code used: | |||
| none recorded or not applicable | |||