The BGS Lexicon of Named Rock Units — Result Details
Milldale Limestone Formation
| Computer Code: | MI | Preferred Map Code: | Mi |
|---|---|---|---|
| Status Code: | Full | ||
| Age range: | Courceyan Substage (CF) — Asbian Substage (CR) | ||
| Lithological Description: | In the type area, comprises well-bedded mid-grey, crinoidal "biosparites" and dark grey cherty micrites of an inter-reef facies, passing vertically and laterally into knoll reef mud-mounds of poorly bedded grey micrite, which are locally partially or completely dolomitised. In the Loughborough area, comprises grey to buff, thin to thickly bedded, fine- to coarse-grained, locally pebbly dolostones, whereas altered tuff and vesicular basaltic lava are recorded in the Gun Hill Borehole (SJ96SE 18), [SJ9723 6182] between depths at 709 and 770.5m. | ||
| Definition of Lower Boundary: | Only seen in the Caldon Low Borehole, where fine-grained pale grey-white dolostones comprising the Rue Hill Dolomite, of Tournaisian age, pass up rapidly into a predominantly limestone sequence of the Milldale Limestone Formation, with the base of the Milldale Limestone Formation taken at the base of a 2cm-thick black fissile mudstone overlying 2.35m of very fine-grained dolostone. In the Hathern No.1 Hydrocarbon Borehole (SK52SW 3) [SK 5158 2416] limestones interpreted as the Milldale Limestone Formation are underlain by anhydrite, limestone and dolostone of the Hathern Anhydrite Formation. | ||
| Definition of Upper Boundary: | Seen as a rapid upward transition, from dark cherty micritic limestones to: a) grey coarsely bioclastic conglomeratic limestones of the Hopedale Limestone Formation; b) to thicker bedded, paler peloidal and crinoidal bioclastic limestone of the Ecton Limestone Formation; c) poorly sorted conglomerate of reef limestone pebbles at the base of the Kevin Limestone Formation; or d) a sharp discomformity at the base of dark to pale brown and grey calcareous mudstone and thinly bedded argillaceous limestones of the Widmerpool Formation. | ||
| Thickness: | From 305m in the type area, 470m in the Caldon Low Borehole (SK04NE 36) [SK 0804 4823], at least 380m at Breedon Hill, and 791.55m recorded in the Gun Hill Borehole (SJ96SE 18) [SJ 9723 6182], located 13km northwest of the Manifold Valley inlier. | ||
| Geographical Limits: | Staffordshire to Derbyshire, and at depth across northwestern Leicestershire. | ||
| Parent Unit: | Peak Limestone Group (PKLM) | ||
| Previous Name(s): | Weaver Beds [Obsolete Name And Code: Part Of MI]
(WVR)
Milldale Limestones [Obsolete Name and Code: Use MI] (-2323) |
||
| Alternative Name(s): | none recorded or not applicable | ||
| Stratotypes: | |||
| Reference Section | Breedon-on-the-Hill Quarry, which shows a Waulsortian mud-mound reef, of up to 100m thickness of unbedded dolostone, overlying about 280 m of well-bedded inter-reef facies. | ||
| Partial Type Section | Lower part: Caldon Low No.1 Borehole, from 2.59m to 280.6m, showing the lower boundary with the underlying Rue Hill Dolomite Formation. | ||
| Reference Section | Cloud Hill Quarry, new level; 4m level and 24m level (southern end of quarry) . Comprises 130m of well-bedded inter-reef facies with limestones, commonly bituminous clay, shaly mudstone and siltstone. The upper 61m comprises the Holly Bush Member. | ||
| Partial Type Section | Raven's Tor, Dovedale, exposes reef facies and lateral passage to inter-reef facies. | ||
| Partial Type Section | The bed of the River Manifold. | ||
| Partial Type Section | Top: Brownend Quarry, Waterhouses, which exposes the top 82.15m of the formation and the junction with the Hopedale Limestone Formation. | ||
| Partial Type Section | Disused railway cutting, displaying about 28.4m of discontinuously exposed strata below the knoll-reef at Thor's Cave, sections within the reef, and 49.02m of discontinuously exposed strata above the reef, passing up into rocks of the Ecton Limestone Formation. | ||
| Reference(s): | |||
| Aitkenhead, N, and Chisholm, J I. 1982. A standard nomenclature for the Dinantian formations of the Peak District of Derbshire and Staffordshire. Report of the Institute of Geological Sciences, No. 82/8. | |||
| Ambrose, K, and Carney, J N. 1997. Geology of the Breedon on the Hill area. British Geological Survey Technical Report WA/97/42. | |||
| Parkinson, D. 1949. The stratigraphy of the Dovedale area, Derbyshire. Staffordshire. Quarterly Journal of Geological Science, Vol.105, 265-294. | |||
| Chisholm, J I, Charsley, T J and Aitkenhead, N. 1988. Geology of the country around Ashbourne and Cheadle. Memoir of the British Geological Survey, Sheet 124 (England and Wales). | |||
| Aitkenhead, N, Chisholm, J I, and Stevenson, I P. 1985. Geology of the country around Buxton, Leek and Bakewell. Memoir of the British Geological Survey, England and Wales Sheet 111. | |||
| Carney, J N, Ambrose, K and Brandon, A. 2001. Geology of the country between Burton, Loughborough and Derby. Description of 1:50k Sheet 141 (England and Wales). | |||
| 1:50K maps on which the lithostratigraphical unit is found, and map code used: | |||
| E111 E141 E124 | |||