The BGS Lexicon of Named Rock Units — Result Details

Lower Matlock Lava Member

Computer Code: LRB Preferred Map Code: notEntered
Status Code: Full
Age range: Brigantian Substage (CX) — Brigantian Substage (CX)
Lithological Description: Dark green, grey or brown basalt lava with interbedded tuff and locally, in the Masson Hill (SK 286 587) - Bonsall area (SK 2758), interdigitations of limestone and tuffaceous limestone (Chisholm et al., 1983; Walters and Ineson, 1981). At Masson Hill three distinct lava flows are recognized, characterised by vesicular upper and lower surfaces, separated by tuff or decomposed clay (Walters and Ineson, 1981), with the lower two flows containing abundant marmorised limestone and angular basaltic fragments. Typically amygdaloidal towards the top of the lava flows and may include haematite veinlets. Locally, the lavas include vertical wedges of clay representing partial weathering of the basalt (Smith et al., 1967). In places the weathering of the basalt to a grey or brown clay is complete, although the presence of amygdales indicates origin as a lava.
Definition of Lower Boundary: Generally, the basalt lava of the Lower Matlock Lava Member rests upon thickly bedded limestones of the Monsal Dale Limestone Formation. At Hoptonwoodstone Quarry (SK 277 557) the basal c.3m comprises amygdaloidal basalt, thoroughly altered to grey and yellow clay, with lenses of pink limestone (Smith, 1967). The base of the lava, here, has been interpreted as a palaeokarstic surface with pits up to 10m deep filled by weathered blocks of lava, tuff and limestone in a clay matrix (Walters, 1981). South of Bonsall the formation thins markedly and around Golconda Mine (SK 249 551) a thin lava rests upon pale grey calcarenites of the Bee Low Limestone Formation.
Definition of Upper Boundary: Lavas and tuffs of the Lower Matlock Lava Member are overlain by thickly bedded limestones of the Monsal Dale Limestone Formation. At Hoptonwoodstone Quarry (SK 277 557) the uppermost 0.3m-thick bed of the Member comprises brecciated limestone in a matrix of clay with vestiges of amygdales (weathered basalt).
Thickness: Maximum of 99m at Masson Hill (SK 286 587); about 50m thick in boreholes north of Winster.
Geographical Limits: The Member has a poorly exposed outcrop from west of Gratton Dale (SK 198 604) to Masson Hill (SK 286 587) and the Bonsall area (SK 27 58). Present as inliers in the Derwent Valley at Matlock (SK 249 589) and Matlock Bath (SK 293 579). Also crops out around Aldwark (SK 23 57) in the Buxton district, where exposures are rare. From Aldwark the Member thins toward the west and south and cannot be traced beyond Minninglow Hill (SK 209 573), Curzon Lodge (SK 234 560) and Golconda Mine (SK 249 551).
Parent Unit: Monsal Dale Limestone Formation (MO)
Previous Name(s): Lower Matlock Lava (-375)
Matlock Lower Basalt (-1045)
Matlock Lower Lava (-1046)
Alternative Name(s): none recorded or not applicable
Reference Section  Via Gellia Valley, small quarry: 6.1m of dark green basalt with some amygdales in the upper 1.8m. Smith et al., 1967 
Reference Section  Hoptonwoodstone Quarry: Full thickness of 19.8m of basalt and clay (thoroughly weathered basalt). Smith et al., 1967. 
Walters, S G and Ineson, P R. 1981. A review of the distribution of and the correlation of igneous rocks in Derbyshire, England. Mercian Geologist, Vol. 8, 81-132. 
Chisholm J, Mitchell, M, Strank, A, Cox, F and Harrison D. 1983. A revision of the Asbian and Brigantian limestones of the area west of Matlock, Derbyshire. Report of the Institute of Geological Sciences, 83/10, 17-24. 
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. 
Smith, E G, Rhys, G H and Eden, R A. 1967. Geology of the country around Chesterfield, Matlock, and Mansfield. Memoir of the Geological Survey of Great Britain. England and Wales Sheet 112. 
1:50K maps on which the lithostratigraphical unit is found, and map code used:
E111 E112 E125