| Computer Code: |
GUP |
Preferred Map Code: |
notEntered |
| Status Code: |
Full |
| Age range: |
Famennian Age (DA)
— Famennian Age (DA) |
| Lithological Description: |
The formation comprises two coarsening-upwards sequences of red mudstones passing up into clean, well-sorted sandstones.
The lower sequence (the Lower Sandstone Member) consists of thick, lenticular and tabular sandstones and pebbly sandstones which coarsen and thicken upwards. It shows an upward change from thin multistorey sandstones in a background of red mudstones and siltstones to thicker single-storey sandstones and eventually into stacked, pebbly sandstone-based fining-upwards units. It is only present in the southernmost outcrops at Freshwater West, where it is 55 m thick and crops out in the cliffs and foreshore [SR 8876 9885].
The upper sequence (the Stackpole Sandstone Member) comprises a lower mudstone-rich heterolithic facies association and an upper trough cross-bedded and parallel-laminated sandstone association. It ranges from 6 m in thickness in the north near the Ritec Fault to 68 m in the south. |
| Definition of Lower Boundary: |
The lower boundary overlies the regional Acadian unconformity. The formation rests unconformably on the underlying Lower Devonian Ridgeway Conglomerate Formation, overstepping it eastwards to lie on the Milford Haven Subgroup. The Lower Sandstone Member is unconformably overlain by the Stackpole Sandstone Member. The latter oversteps both the Lower Sandstone Member and the Ridgeway Conglomerate Formation to extend eastwards across the entire Pembroke Peninsula, resting directly on the Freshwater West Formation in the east, as for example on Caldey Island. |
| Definition of Upper Boundary: |
The upper boundary is disconformable in northern exposures, where an erosion surface at the top of the formation is cut in texturally mature trough-cross-bedded and parallel laminated sublitharenites and is overlain by immature pebbly red lithic sandstones and conglomerates rich in volcanic debris and calcrete-rich mudstones that form the base of the West Angle Formation. In the south, there is a transitional upper boundary, with interdigitation of the mature and immature facies. |
| Thickness: |
From 61 m to 123 m. |
| Geographical Limits: |
Extends across the Pembroke Peninula from West Angle Bay to Caldey Island. |
| Parent Unit: |
Skrinkle Sandstones Subgroup (SES)
|
| Previous Name(s): |
none recorded or not applicable
|
| Alternative Name(s): |
none recorded or not applicable
|
| Stratotypes: |
| Type Section |
Stackpole Quay [SR 994 958] (Barclay et al., 2015). |
| Reference Section |
West Angle Bay [SR 850 032] (Barclay et al., 2015). |
| Reference Section |
Freshwater West [SR 886 987] (Barclay et al., 2015). |
| Reference Section |
Skrinkle Haven [SS 083 974] (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. |
| Marshall, J D. 1977. Sedimentology of the Skrinkle Sandstones Group (Devonian–Carboniferous), south-west Dyfed. Unpublished Ph.D thesis, University of Bristol. |
| Marshall, J D. 2000. Fault-bounded basin-fill: fluvial response to tectonic controls in the Skrinkle Sandstones of SW Pembrokeshire, Wales. In: Friend, P F and Williams, B P J. 2000 (eds). New Perspectives on the Old Red Sandstone. Special Publication, Geological Society, London, 180, 401-416. |
| Marshall, J D. 2000. Sedimentology of a Devonian fault-bounded braidplain and lacustrine fill in the lower part of the Skrinkle Sandstones, Dyfed, Wales. Sedimentology, 47, 325-42. |
| 1:50K maps on which the lithostratigraphical unit is found, and map code used: |
| none recorded or not applicable |
