The BGS Lexicon of Named Rock Units — Result Details
Boscastle Formation
| Computer Code: | BOSC | Preferred Map Code: | notEntered |
|---|---|---|---|
| Status Code: | Full | ||
| Age range: | Visean Age (CV) — Chokierian Substage (CH) | ||
| Lithological Description: | Dark grey to black pyritous mudstones with thin laminated siltstones. Packets of thin- to thick-bedded grey fine- to coarse-grained quartzose sandstones punctuate the Formation. Adjacent to intertonguing contacts with the Buckator Formation, the sandstones are calcareous, locally shelly and locally accompanied by thick beds of bioclastic limestone and nodules of silicified limestone. The mudstones are locally burrowed. Rare thin beds of tuffaceous mudstone, and tuffs and lavas also occur. | ||
| Definition of Lower Boundary: | The lower boundary is not seen as it is tectonic. However, the Formation inter-tongues with the Buckator and Teign Chert formations. Lower boundaries with the Buckator Formation are taken at the gradational appearance of dark grey sandstones and mudstones of the Boscastle Formation above the green grey mudstones with thin calcareous siltstones and limestones of the underlying Buckator Formation. Only an upper boundary is seen with the Teign Chert Formation. | ||
| Definition of Upper Boundary: | The upper boundary is not seen as it is tectonic. However, the formation intertongues with the Buckator and Teign Chert formations. Upper boundaries with the Buckator Formation are taken at the gradational appearance of green grey mudstones with thin calcareous siltstones and limestones of the underlying Buckator Formation above the dark grey sandstones and mudstones of the Boscastle Formation. Upper boundaries with the Teign Chert Formation are taken at the incoming of silicified siltstones, mudstones and scattered chert beds of the Teign Chert Formation above the interbedded sandstones and mudstones of the Boscastle Formation. | ||
| Thickness: | Several hundred metres, but may be more or less due to the faulting, thrusting and folding. | ||
| Geographical Limits: | Between Boscastle (SX 95 91) and Lewanwick (SX 27 81), north Cornwall. | ||
| Parent Unit: | Teign Valley Group (TEVY) | ||
| Previous Name(s): | Crackington Formation
(CKF)
Boscastle Measures [Obsolete Name and Code: Use BOSC] (-4485) |
||
| Alternative Name(s): | none recorded or not applicable | ||
| Stratotypes: | |||
| Partial Type Section | Sea cliffs and crags on the south side of Boscastle Harbour. Section exposes the ?lower part of the Formation, which comprises mudstones with siltstones and packets of sandstones. Low angle faulting, folding and quartz veining are ubiquitous. At the western end of the section the formation overlies the Trambley Cove Formation tectonically. Selwood, E B, Stewart, I J and Thomas, J M, 1985. | ||
| Reference(s): | |||
| McKeown, M C, Edmonds, E A, Williams, M, Freshney, E C and Masson Smith, D J. 1973. Geology of the country around Boscastle and Holsworthy. Memoir of the British Geological Survey, sheets 322 and 323 (England and Wales). | |||
| Ashwin, D P. 1958. The coastal outcrop of the Culm Measures of south-west England. Abstracts of the Proceedings of the Conference of Geologists and Geomorphologists in south-west England, Vol. 2, 2-3. | |||
| Freshney, E C, McKeown, M C and Williams, M. 1972. Geology of the coast between Tintagel and Bude. Memoir of the Geological Survey of Great Britain, part of sheet 322 (England and Wales). | |||
| Selwood, E B, Stewart, I J and Thomas, J M. 1985. Upper Palaeozoic sediments and structure in north Cornwall - a reinterpretation. Proceedings of the Geologists' Association, Vol.96, 129-141. | |||
| 1:50K maps on which the lithostratigraphical unit is found, and map code used: | |||
| none recorded or not applicable | |||