The BGS Lexicon of Named Rock Units — Result Details

Beacon Limestone Formation

Computer Code: BNLS Preferred Map Code: BnL
Status Code: Full
Age range: Pliensbachian Age (JE) — Toarcian Age (JT)
Lithological Description: Limestone, ferruginous-ooidal in lower part, nodular in upper part; conglomeratic in parts; variably grey, pink, reddish-brown and brown in colour. Includes Eype Mouth Limestone Member (above) and Marlstone Member (below).
Definition of Lower Boundary: Non-sequential; downward change from ferruginous, conglomeratic limestone to argillaceous, silty or sandy beds of the Dyrham Formation.
Definition of Upper Boundary: Base of sands of the Bridport Sand Formation.
Thickness: Up to 5m; typically less than 1.5m
Geographical Limits: Wessex Basin (including Central Somerset Basin) and Mendips-Radstock Shelf area, ie. Dorset coast to approximately Chipping Sodbury.
Parent Unit: Lias Group (LI)
Previous Name(s): Watton Bed (-1370)
Junction Bed [Obsolete Name And Code: Use BNLS] (JB)
Junction Bed and Marlstone [Rock Bed] (-2629)
Alternative Name(s): none recorded or not applicable
Stratotypes:
Reference Section  British Geological Survey Winterborne Kingston Borehole, Winterborne Kingston, Dorset (SY89NW/1) 1114.60-1117.89m depth. Ivimey-Cook, H C, 1982; Rhys, G H, Lott, G K and Calver, M A, 1982. See also Cox, B M, et al, 1999 for additional reference sections. 
Type Area  Dorset and east Somerset. 
Type Section  Cliff exposure beneath Thorncombe Beacon. Callomon, J H and Cope, J C W, 1995; Hesselbo, S P and Jenkyns, H C, 1995. 
Reference(s):
Callomon, J H and Cope, J C W. 1995. The Jurassic geology of Dorset. 51-103 in Taylor, P D (Editor), Field Geology of the British Jurassic. (Bath: The Geological Society.) 
Rhys, G H, Lott, G K, and Calver, M A. 1982. The Winterborne Kingston borehole, Dorset, England. Report of the Institute of Geological Sciences, No.81/3. 
Cox, B M, Sumbler, M G and Ivimey-Cook, H C, 1999. A Formational framework for the Lower Jurassic of England and Wales (Onshore Area). British Geological Survey Research Report No. RR/99/01. 
Hesselbo, S P and Jenkyns, H C A, 1995. A comparison of the Hettangian to Bajocian successions of Dorset and Yorkshire. 105-150 in Taylor, P D (Editor). Field geology of the British Jurassic (London Geological Society). 
Ivimey-Cook, H C, 1982. Biostratigraphy of the Lower Jurassic and Upper Triassic (Rhaetian rocks of the Winterborne Kingston borehole, Dorset). Report of the Institute of Geological Sciences, No.81/3, 97-106. 
1:50K maps on which the lithostratigraphical unit is found, and map code used:
E311 E327 E264 E265 E281 E341 E342 E343