| Computer Code: |
MCH |
Preferred Map Code: |
Mch |
| Status Code: |
Full |
| Age range: |
Arenig Series (OR)
— Arenig Series (OR) |
| Lithological Description: |
Well-bedded sandstone with mudstone interbeds. A thin phosphatic conglomerate horizon at the top. |
| Definition of Lower Boundary: |
Gradational contact taken at the base of the first prominent sandstone lying above muddy sandstones of the Penrhyn Du Member. |
| Definition of Upper Boundary: |
Sharply overlain by dark grey mudstones with sandstone and siltstone laminae of the Llanengan Formation. The boundary is taken at the top of a districtive phosphatic conglomerate bed within the Machroes Member. The contact may be a disconformity or non-sequence. |
| Thickness: |
<8m |
| Geographical Limits: |
Pwllheli area, northwest Wales. |
| Parent Unit: |
St Tudwal's Formation (STUD)
|
| Previous Name(s): |
Passage Beds [Obsolete Name and Code: Use BOOC, SGBK, CLGB, MCH, UND, YED, MYS]
(-3236)
|
| Alternative Name(s): |
none recorded or not applicable
|
| Stratotypes: |
| Type Section |
Machroes, in the Pwllheli area. |
| Reference(s): |
| Young, T P, Gibbons, W and McCarroll, D. 2002. Geology of the country around Pwllheli. Memoir of the British Geological Survey, Sheet 134 (England and Wales). |
| Nicholas, T C. 1915. Geology of the St Tudwal's Peninsula. Quarterly Journal of the Gelogical Society of London, Vol.71, 83-143. |
| 1:50K maps on which the lithostratigraphical unit is found, and map code used: |
|
E134
|
