| Computer Code: |
PYMB |
Preferred Map Code: |
notEntered |
| Status Code: |
Full |
| Age range: |
Lochkovian Age (DO)
— Lochkovian Age (DO) |
| Lithological Description: |
Conglomerates, sandstones and red siltstones, typically arranged in fining-upwards alluvial cycles; the siltstones commonly contain calcrete glaebules and grade up into well developed, massive limestone or dolostone calcretes.
Fluvial deposition in a broad south-east-trending meandering river belt.
Probably Lochkovian, but no diagnostic fossil evidence has yet been found. |
| Definition of Lower Boundary: |
The lower boundary is placed at an erosion surface that truncates 1.5 m of massive calcrete at the top of the underlying Traeth Bach Formation and is overlain by a 1.5 m-thick extraformational conglomerate on the south side of Traeth yr Ora at the base of the Porth-y-Mor Formation. Note that this is slightly above the boundary proposed by Allen (1965a) (Davies, 2005). |
| Definition of Upper Boundary: |
The upper boundary is placed at 477 m (1565 feet) from the base of the section measured by Allen (1965a), at the base of a thinner bedded sandstone/mudstone succession lacking intraformational conglomerates and thick cyclic units (the Traeth Lligwy Formation). |
| Thickness: |
311.5 m at the coast, perhaps thinning inland as a result of internal overlap. |
| Geographical Limits: |
Extends from Traeth yr Ora to south of Porth-y-Mor [SH 490 885 to 494 878] and inland to Llangefni. |
| Parent Unit: |
Dulas Bay Subgroup (DULB)
|
| Previous Name(s): |
none recorded or not applicable
|
| Alternative Name(s): |
none recorded or not applicable
|
| Stratotypes: |
| Type Section |
Cliffs north and south of Porth-y-Mor [SH 490 885 to 494 878]. |
| 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. 1965. The sedimentation and palaeogeography of the Old Red Sandstone of Anglesey, North Wales. Proceedings of the Yorkshire Geological Society, Vol. 35, 139-185. |
| Davies, J R. 2005. Porth-y-Mor. 221-228 in Barclay, W J, Browne, M A E, McMillan, A A, Pickett, E A, Stone, P, and Wilby, P R. 2005. The Old Red Sandstone of Great Britain. Geological Conservation Review Series, No. 31. |
| 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 |
