The BGS Lexicon of Named Rock Units — Result Details

Barrow Hill Basaltic Vent

Computer Code: BWHL Preferred Map Code: BHC
Status Code: Full
Age range: Bolsovian Substage (CC) — Bolsovian Substage (CC)
Lithological Description: At Barrow Hill a basalt pipe is intruded within vent agglomerates and country-rock of the Etruria Formation. The vent agglomerate comprises fault-bounded blocks of volcanic breccia with clasts of Etruria Formation and Pennine Coal Measures mudstones, coal and rounded quartzite pebbles in a tuffaceous matrix. The basalt is also fault-bounded and contains abundant Pennine Coal Measures and Etruria Formation xenoliths up to 4.5 m diameter. The basalt is typically fine, microporphyritic, with labradorite microphenocrysts commonly clustered around serpentinized olivine or as flow-aligned laths. Groundmass comprises labradorite-andesine laths, augite, magnetite and interstitial analcime. At Tansey Green, the Etruria Formation includes volcaniclastic deposits associated with tuffisitic and agglomeratic dykes and pipes and alkaline basalt dykes. The bedded volcaniclastic sequence comprises 31 m of volcanic breccia, scoriaceous lapilli-tuff and tuffaceous mudstone and siltstone. The lapilli-tuff preserves conifer stems in growth position. An agglomerate pipe, up to 10 m in diameter, and a single alkaline basalt dyke (0.3 m width) are also present.
Definition of Lower Boundary: Basalt pipe and vent agglomerate are non-stratiform. Basalt is typically finer grained towards the contact, with abundant small xenoliths. Base of volcaniclastic deposits at Tansey Green comprises purple, red, brown and greenish grey mudstone of the Etruria Formation overlain with a sharp base by 0.6 m of scoriaceous lapilli-tuff, parallel-laminated with conifer stems in growth position.
Definition of Upper Boundary: Basalt pipe and vent agglomerate are non-stratiform. Top of volcaniclastic deposits at Tansey Green is not seen, faulted against Etruria Formation.
Thickness: Basalt pipe and vent agglomerate are non-stratiform and thickness is unknown. Volcaniclastic deposits at Tansey Green about 30 m seen.
Geographical Limits: The complex is exposed in two disused quarries at Barrow Hill [SO 917 896] and a disused clay pit at Tansey Green [SO 910 896], west of Dudley.The complex occurs within, and adjacent to, the W–E-trending Tansey Green Trough.
Parent Unit: Dudley Basaltic Sill-and-vent-swarm (DUDB)
Previous Name(s): none recorded or not applicable
Alternative Name(s): none recorded or not applicable
Partial Type Section  Upper part of main Barrow Hill quarry basalt pipe is seen intruding vent agglomerate. Described by Waters (2003). 
Reference Section  c. 30 m of poorly sorted volcaniclastic breccia with amygdaloidal basalt bombs and lithic fragments in a tuffaceous matrix, overlies 0.4 m of tuffaceous-mudstone and siltstone, green-grey and thinly laminated, in turn overlies 0.6 m of scoriaceous lapilli-tuff, parallel laminated with conifer stems in growth position. Described by Glover et al. (1993). 
Glover, B W, Powell, J H, and Waters, C N. 1993. Etruria Formation (Westphalian C) palaeoenvironments and volcanicity on the southern margins of the Pennine Basin, South Staffordshire, England. Journal of the Geological Society, London, Vol. 150, 737-750. 
Waters, C N. 2003. Carboniferous and Permian igneous rocks of central England and the Welsh Borderland. In: Carboniferous and Permian Igneous Rocks of Great Britain North of the Variscan Front. (editors Stephenson D, Loughlin S C, Millward D, Waters C N, and Williamson I T.), pp. 279-316, Geological Conservation Review Series, No. 27 (JNCC). 
1:50K maps on which the lithostratigraphical unit is found, and map code used: