The BGS Lexicon of Named Rock Units — Result Details

Boyne Hollow Chert Member

Computer Code: BHC Preferred Map Code: BHC
Status Code: Full
Age range: Albian Age (KA) — Albian Age (KA)
Lithological Description: Glauconitic sand and sandstone with regularly developed nodular and tabular beds of chert. Interbedded chert beds and nodules, up to 0.4m thick.
Definition of Lower Boundary: The lower boundary is placed generally at the base of loose shelly and phosphatic sands resting on the "Ragstone" at the top of the Shaftesbury Sandstone Member. Elsewhere, where the Ragstone is absent, the boundary is placed at the base of the first chert bed or more commonly at an erosive contact between glauconitic sands a short distance below the first chert bed.
Definition of Upper Boundary: The upper boundary was originally defined by surveyors as "above the highest bed of chert". It is best defined as the top of the highest few metres of the Boyne Hollow Chert Member frequently lacking in chert, which in boreholes and sections is more precisely defined by the base of the glauconitic, marl-rich, fossiliferous phosphatic nodule bed at the base of the overlying Melbury Sandstone Member (basal Chalk Group).
Thickness: Between 0 and 15m (6.3m+ at the type locality). Variable over the Mid-Dorset Swell (Drummond, 1970).
Geographical Limits: In its type area it is seen from Compton Abbas [ST 870 185] northwards across the Shaftesbury sheet (313), and then across the Wincanton sheet (297). Further mapping has extended its distribution into the whole of Dorset and Wiltshire including 1:50 000 scale sheets 281 (Frome); 282 (Devizes, western part only); 298 (Salisbury); 314 (Ringwood); 341 and 342 (West Fleet and Weymouth).
Parent Unit: Upper Greensand Formation (UGS)
Previous Name(s): Chert Beds [Obsolete Name and Code: Use BHC, PECH, COH, SHWK, WHCH] (*642)
Alternative Name(s): none recorded or not applicable
Stratotypes:
Type Section  Old quarry, 110m at 295 degrees from Mayo Farm, Shaftesbury on northeast side of Boyne Hollow. Section now obscured, but recorded by Jukes-Browne and Hill, 1900, p.160. 
Reference(s):
Jukes-Browne, A J and Hill, W. 1900. The Cretaceous Rocks of Britain. 1. Gault and Upper Greensand. Memoir of the Geological Survey of Great Britain. 
Bristow, C R, Barton, C M, Freshney, E C, Wood, C J, Evans, D J, Cox, B M, Ivimey-Cook, H C, and Taylor, R T. 1995. Geology of the country around Shaftesbury. Memoir of the British Geological Survey, Sheet 313 (England and Wales). 
Bristow, C R, 1989. Geology of the East Stour - Shaftesbury district (Dorset) British Geological Survey Technical Report WA/89/58. 
Drummond, P U O. 1970. The Mid-Dorset Swell. Evidence of Albian-Cenomanian Movements in Wessex. Proceedings of the Geologists' Association, Vol.81, 679-714. 
1:50K maps on which the lithostratigraphical unit is found, and map code used:
E281 E282 E297 E298 E313 E314 E327 E341 E342 E343