| Computer Code: |
CMSL |
Preferred Map Code: |
notEntered |
| Status Code: |
Full, without ratification |
| Age range: |
Givetian Age (DV)
— Frasnian Age (DR) |
| Lithological Description: |
Silvery grey, calcareous slates that are commonly silty, with thin (< 0.3 m) grey fine-grained sandstones. Three distintive limestone beds occur within the sequence: Jenny Start Limestone (towards the base; 2 m to 10.5 m thick with an oolitic texture), Combe Martin Beach Limestone (towards the middle; 1.34 m thick - a ferruginous limestone with pyrite) and the David's Stone Limestone (towards the top; 9 m thick, comprising of two beds separated by slates, with locally abundant corals at Broadstrand Beach [SS 5318 4797]. The top 5 m of the basal slates contain bands and lenses of detrital limestone up to 25 mm thick with crinoid debris. |
| Definition of Lower Boundary: |
10 m above the top of the Holey Limestone (a lateral equivalent of Holwill's (1964) Rillage Limestone). Below the boundary, rocks assigned to the underlying Lester Slates-and-Sandstones, are sandstones and siltstones with abundant Chondrites; the rocks at the base of the Combe Martin Slates are silvery grey, calcareous slates that are commonly silty, with thin (< 0.3 m) grey fine-grained sandstones. Chondrites are less common in the Combe Martin Slates than in the underlying Lester Slates and Sandstones. |
| Definition of Upper Boundary: |
Located 30 m above the top of the David's Stone Limestone (two beds of limestone separated by slates identified at [SS 5703 4742]); the boundary is distinguished by a change from limestones (below) to thickly-bedded sandstone (above) in the Combe Martin Slates. |
| Thickness: |
120 m. |
| Geographical Limits: |
Outcrop band of variable width trending approximately north-west to south-east from NE of Ilfracombe to 1.5 km north of Simonsbath [SS 7740 3930]. |
| Parent Unit: |
Ilfracombe Slates Formation (IFS)
|
| Previous Name(s): |
Middle Ilfracombe Beds
(MILFR)
|
| Alternative Name(s): |
none recorded or not applicable
|
| Stratotypes: |
| Type Area |
Combe Martin Bay. |
| Reference(s): |
| Edmonds, E A, Whittaker, A, and Williams, B J. 1985. Geology of the country around Ilfracombe and Barnstaple. Memoir of the British Geological Survey, Sheets 277 and 293 (England and Wales). |
| Evans, J W. 1922. The geological structure of the country round Combe Martin. Proceedings of the Geologists' Association, Vol.33, 201-228. |
| Edmonds, E A, Williams, B J and Taylor, R T. 1979. Geology of Bideford and Lundy Island. Memoir of the Geological Survey of Great Britain, Sheets 292 with 275, 276, 291, and part of 308 (England and Wales). |
| Evans J W and Stubblefield C J, 1929. Handbook of the geology of Great Britain. (London: Thomas Murby & Co.) |
| Holwill F J W. 1964. The coral fauna from the Ilfracombe Beds of north Devon. Proceedings of Ussher Society, Vol. 1, 00. 126-129. |
| Holwill F J W, House M R, Lane R, Gauss G A, Hendriks E M L and Dearman W R. 1969. Summer (1966) field meeting in Devon and Cornwall. Proceedings of the Geologists Association, Vol. 80, pp 43-62. |
| 1:50K maps on which the lithostratigraphical unit is found, and map code used: |
|
E277
|
