The BGS Lexicon of Named Rock Units — Result Details

Highworth Limestone Member

Computer Code: HWLS Preferred Map Code: HwL
Status Code: Pending Upgrade
Age range: Oxfordian Age (JO) — Oxfordian Age (JO)
Lithological Description: Bedded shelly ooidal limestone, locally sandy or pisoidal, with thin interbedded calcareous mudstones. Commonly has a basal mudstone chert and sandstone pebble conglomerate, and coralliferous limestones are developed in the Highway area.
Definition of Lower Boundary: Base is either: (in east) sharp change up from medium- to coarse-grained sand/sandstone of Beckley Sand Member into shelly ooidal limestone with basal conglomerate, or a non-sequence with interbedded yellowish silty and clayey fine quartz sand with sandstone "doggers" and sandy mudstone (Hazelbury Bryan Formation) overlain by shelly ooidal limestone with local conglomerate (Highworth Limestone Member).
Definition of Upper Boundary: Top is marked by upward change from shelly ooidal limestone of the Highworth Limestone Member into cross-bedded fissile sandy ooidal limestone or calcareous mudstone (Pusey Flags Member), where present, or variably sandy grey to brown mudstone (Highworth Clay Member). Contact might be erosional.
Thickness: 2 to 3m in type area, 2.6m at Lamb and Flag Quarry, thins laterally, 0.3m at Wooton Bassett.
Geographical Limits: North Wiltshire to southwest Oxfordshire. Best developed in the area of Highworth; wedges out eastwards near Garford; thins out westwards to zero near Blunsdon. May be thinly represented at Spirt Hill, near Calne, Wiltshire.
Parent Unit: Kingston Formation (KTON)
Previous Name(s): Lower Coral Rag (-973)
Pebble Bed + Pisolite + Lower Trigonia Bed + Upper Trigonia Bed + Urchin Marls (-974)
Alternative Name(s): none recorded or not applicable
Stratotypes:
Reference Section  Lamb and Flag Quarry, Kingston Bagpuize, Oxfordshire. About 0.5m of the upper part of the Member is exposed. Wright in Wright and Cox, 2001. 
Reference(s):
Arkell, W J. 1941a. Map of the Corallian Beds around Highworth, Wiltshire. Proceedings of the Geologists' Association, Vol.52, 79-109. 
Arkell, W J. 1951. The geology of the Corallian ridge between Wootton Bassett and Lyneham, Wiltshire. Wiltshire Archaeological and Natural History Magazine, Vol.54, 1-18. 
Arkell, W J. 1939. Map of the Corallian Beds between Marcham and Faringdon, Berkshire. Proceedings of the Geologists' Association, Vol.50, 487-509. 
Wright, J K, and Cox, B M. 2001. British Upper Jurassic Stratigraphy (Oxfordian to Kimmeridgian). Geological Conservation Review Series. No. 21. (Peterborough: Joint Nature Conservation Committee/Chapman and Hall.) 
1:50K maps on which the lithostratigraphical unit is found, and map code used:
E253 E252