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): Milldale Limestones (-2323)
Weaver Beds [Obsolete Name And Code: Part Of MI] (WVR)
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  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  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  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. 
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). 
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. 
Ambrose, K and Carney, J N, 1997. Geology of the Breedon on the Hill area. British Geological Survey Technical Report WA/97/42. 
1:50K maps on which the lithostratigraphical unit is found, and map code used:
E111 E141 E124