| Computer Code: |
CHAP |
Preferred Map Code: |
notEntered |
| Status Code: |
Full |
| Age range: |
Pridoli Epoch (SO)
— Lochkovian Age (DO) |
| Lithological Description: |
Mudstone with an abundance of calcrete development in the form of massive limestones, tubules and large concretions, and interbedded intraformational calcrete-clast conglomerates at the type locality (Williams et al., 1982); elsewhere, it comprises similarly white, rubbly limestone, or a group of limestones, generally culminating in one or more thick, massive limestone(s) at or near the top of the member. |
| Definition of Lower Boundary: |
The lower boundary is gradational, and placed where red mudstones become increasingly calcretised and pass into the lowermost of a thick sequence of stacked calcrete horizons. |
| Definition of Upper Boundary: |
In south Pembrokeshire, the upper boundary is placed at the sharp, conformable junction of the basal sandstone of the Conigar Pit Sandstone Member of the Freshwater West Formation, where it overlies the topmost calcrete of the Chapel Point Limestone Member. Elsewhere, the upper boundary is placed at the sharp, conformable junction between the topmost, well developed calcrete of the member and the overlying sandstone at the base of the Freshwater West Formation. |
| Thickness: |
Thickness is variable, ranging from 5.7 m to over 30 m on Caldey Island. Elsewhere, it is up to about 12 m. |
| Geographical Limits: |
Restricted to south of the Ritec Fault in Pembrokeshire, but widespread elsewhere throughout south Wales, the Welsh Borderland and West Midlands. |
| Parent Unit: |
Moor Cliffs Formation (MOCL)
|
| Previous Name(s): |
none recorded or not applicable
|
| Alternative Name(s): |
none recorded or not applicable
|
| Stratotypes: |
| Reference Section |
Foreshore exposures and a gully wall of Little Furzenip headland [SR 8851 9939] at Freshwater West, where the member is 5.7 m thick (Allen et al., 1981a; Williams et al., 1982) |
| Reference Section |
Cliff exposures at King's Quoit [SS 0596 9733], Manorbier, where it is 10 to 15 m thick (Barclay, 2005b). |
| Reference Section |
A coastal section at Llansteffan, Carmarthenshire [SN 353 101-350 099] provides a magnificent development of six stacked, well developed calcretes totalling about 15 m (Allen, 1978a, Allen et al., 1981b, Barclay, 2005c). |
| Reference Section |
The M50 motorway provides a reference section in the Welsh Borderland [SO 6685 2636] (Allen and Dineley, 1976). Here, a 12 m-thick well developed rubbly calcrete caps a succession of mudstone/calcrete about 27 m thick. |
| Type Section |
Sea cliffs on Caldey Island, Pembrokeshire, where over 30 m of calcretes are magnificently exposed [SS 1435 9576] (Barclay et al., 2015). |
| Reference(s): |
| 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, Thomas, R G, and Williams, B P J. 1981. Field Meeting: the facies of the Lower Old Red Sandstone, north of Milford Haven, south-west Dyfed, Wales. Proceedings of the Geologists' Association, Vol. 92, 251-267. |
| Allen, J R L, Elliott, T, and Williams, B P J. 1981. Old Red Sandstone and Carboniferous fluvial sediments in South Wales. 1.1-1.39 in Field Guides to Modern and Ancient Fluvial Systems in Britain and Spain. Elliott, T (editor). Proceedings of the Second International Conference on Fluvial Sediments: Modern and Ancient Fluvial Systems: Sedimentology and Processes. University of Keele, UK, 21-25 September 1981. |
| 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. |
| Brandon, A. 1989. Geology of the country between Hereford and Leominster. Memoir for 1:50 000 Geological Sheet 198. |
| 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.) |
| Allen, J R L. 1978. Locality B11. Llanstephan, Dyfed. 79-82 in International Symposium on the Devonian System (PADS, 78) September 1978. A field guide to selected outcrop areas of the Devonian of Scotland, the Welsh Borderland and South Wales. Friend, P F, and Williams, B P J (editors). (London: The Palaeontological Association.) |
| Barclay, W J. 2005b. Freshwater East - Skrinkle Haven, Pembrokeshire. 301–308 in Barclay, W J, Browne, M A E, McMillan, A A, Pickett, E A, Stone, P, and Wilby, P R. The Old Red Sandstone of Great Britain. Geological Review Series, No. 31. (Peterborough: Joint Nature Conservation Committee.) |
| Barclay, W J. 2005c. Little Castle Head, Pembrokeshire. 284–286 in Barclay, W J, Browne, M A E, Mcmillan, A A, Pickett, E A, Stone, P, and Wilby, P R. The Old Red Sandstone of Great Britain. Geological Review Series, No. 31. (Peterborough: Joint Nature Conservation Committee.) |
| 1:50K maps on which the lithostratigraphical unit is found, and map code used: |
| none recorded or not applicable |
