The BGS Lexicon of Named Rock Units — Result Details

Arden Sandstone Formation

Computer Code: AS Preferred Map Code: AS
Status Code: Full
Age range: Carnian Age (TC) — Carnian Age (TC)
Lithological Description: Heterolithic, consisting of grey, green and purple mudstones interbedded with paler grey-green to buff coloured siltstones and fine- to medium-grained, varicoloured green, brown, buff, mauve sandstones; beds of conglomerate occur locally. Laminated and thinly interbedded sediments are commonly extensively bioturbated and show structures indicative of thixotropic deformation. The siltstones and finer sandstones show small-scale ripple drift cross bedding; thicker sandstone beds show trough and planar cross bedding. The proportion of fine to coarse clastics varies laterally within the Formation. The thicker sandstone units, composed of several individual beds, have a lenticular geometry and occupy the inferred former courses of fluvial distributary channels in a deltaic or estuarine environment. Less arenaceous, mudstone and siltstone-dominated successions occupy intervening interdistributary areas. The Arden Sandstone Formation is differentiated from the reddish-brown, blocky weathering mudstones of adjacent formations by its predominantly greenish grey colour, the presence of a significant, though often subordinate, proportion of sandstone, and the predominance of finely laminated lithologies throughout.
Definition of Lower Boundary: Placed at a rapid upward transition from the red mudstones or siltstones of the Sidmouth Mudstone Formation to the dominantly grey or green, partly or largely arenaceous beds of the Arden Sandstone Formation. Conformable in all areas. At outcrop, the boundary is typically marked by a change from the reddish-brown clayey soils of the Sidmouth Mudstone Formation to the grey, slightly sandy clay soils of the overlying Arden Sandstone Formation. Where the latter forms a marked cuesta feature, the boundary typically lies at a slight concave break in the scarp slope.
Definition of Upper Boundary: Placed at the base of the predominantly red mudstones and siltstones of the Branscombe Mudstone Formation where they rest on the interbedded dark grey-green siltstones and pale grey sandstones of the underlying Arden Sandstone Formation; the boundary is abrupt or a rapid, interbedded transition. At outcrop, the boundary is typically marked by a change from the grey, slightly sandy clay soils of the Arden Sandstone Formation to the reddish-brown clayey soils of the Branscombe Mudstone Formation. Where the Arden Sandstone forms a marked cuesta feature, the boundary lies at the down-dip limit of the dip slope.
Thickness: Typically 7m to 8m in the Warwickshire area near the type section, with a maximum of 20m in the Stowell Park Borehole [SP01SE/1, SP 0835 1176, Green and Melville, 1956] and a minimum, regionally, of 2 to 3m.
Geographical Limits: The outcrop of the Formation is traceable nearly continuously from Gloucestershire northward through Worcestershire and eastwards through Warwickshire into Leicestershire and Nottinghamshire. Less continuous outcrop is mapped in Somerset and east Devon. At subcrop, the Formation is proved in several cored and geophysically logged boreholes in the subsurface in the Central Midlands (Worcester and Knowle basins), East Midlands , and in southern England (Wessex Basin). It is not recognised in the Cheshire Basin and other basins farther northwest, though thin sandstones in the upper part of the Wilkesley Halite (Poole and Whiteman, 1966), might represent the Formation in the Cheshire Basin. At depth in Dorset and Somerset the Formation passes laterally into halite (Gallois, 2001).
Parent Unit: Mercia Mudstone Group (MMG)
Alternative Name(s): BUTCOMBE SANDSTONE
Reference Section  Shrewley Quarry and Canal section 
Reference Section  Road cutting near Blackford Hill, Henley in Arden, Warwickshire. 
Reference Section  Twyning Borehole. (Complete sequence stored in collection at BGS Keyworth). Borehole No. SO83NE/5. Depth range 310.51 to 315.0 metres 
Type Section  Canal cutting at Shrewley, Warwickshire, showing the full thickness (about 9m) of the Formation. 
Reference Section  Canal cutting, Rowington, Warwickshire. 
Warrington, G, Audley-Charles, M G, Elliott, R E, Evans, W B, Ivimey-Cook, H C, Kent, P E, Robinson, P L, Shotton, F W, and Taylor, F M. 1980. A correlation of the Triassic rocks in the British Isles. Special Report of the Geological Society of London, No.13. 
Old, R A, Hamblin, R J O, Ambrose, K and Warrington, G, 1991. Geology of the country around Redditch. Memoir of the British Geological Survey Sheet 183 (England and Wales). 
Murchison, R I and Strickland, H E. 1840. On the upper formations of the New Red Sandstone system in Gloucestershire, Worcestershire and Warwickshire. Transactions of the Geological Society of London, Series 2, Vol.5, 331-348. 
Phillips, J. 1848. The Malvern Hills, compared with the Palaeozoic districts of Abberley, Woolhope, May Hill, Tortworth and Usk. Memoir of the Geological Survey of the United Kingdom, Vol.2, Part 1, 1-330. 
Matley, C A. 1912. The Upper Keuper (or Arden) Sandstone Group and associated rocks of Warwickshire. Quarterly Journal of the Geological Society, London, Vol.68, 252-280. 
Brodie, P B. 1870. On the geology of Warwickshire. 34th Annual Report of the Warwickshire Natural History and Archaeological Society, 10-34. 
Gallois, R W, 2001. The lithostratigraphy of the Mercia Mudstone Group (mid to late Triassic) of the south Devon Coast. Geoscience in south-west England, Vol.10, 195-204. 
Charsley, T J, Rathbone, P A and Lowe, D J, 1990. Nottingham: A geological background for planning and development. British Geological Survey Technical Report WA/90/1. 
Elliott, R E 1961. The stratigraphy of the Keuper Series in southern Notinghamshire. Proceedings of the Yorkshire Geological Society, Vol.33, 197-231. 
Green, G W and Melville, R V, 1956. The stratigraphy of the Stowell Park Borehole (1949-1951). Bulletin of the Geological Survey of Great Britain, No.11, p.1-66. 
Green, G W and Welch F B A, 1965. The geology of the country around Wells and Chedder. Memoir of the Geological Survey of England and Wales, Sheet 280. 
Horwood, A R. 1913. The upper Trias of Leicestershire, Part 1. Geological Magazine, Vol.50, 21-32, 73-86, 109-121, 205-215. 
Howard, A S, Warrington, G, Carney, J N, Ambrose, K, Young, S R and Pharaoh, T C. In press. Geology of the country around Nottingham. Memoir of the British Geological Survey, Sheet 126 (England and Wales). 
Kellaway, G A and Welch, F B A, 1993. Geology of the Bristol district. Memoir of the British Geological Survey Special Sheet [England and Wales]. 
Plant, J. 1856. On the upper Keuper Sandstone (included in the New Red Marls) and its fossils at Leicester. Quarterly Journal of the Geological Society of London, Vol.12, 369-373. 
Poole, E G and Whiteman, A J. 1966. Geology of the country around Nantwich and Whitchurch. Memoir of the Geological Survey of Great Britain, Sheet 122 (England and Wales). 
Symonds, W S. 1855. Notice of fossils from the Keuper Sandstones of Pendock, Worcestershire. Quarterly Journal of the Geological Society of London, Vol.11, 450-451. 
Ussher, W A E. 1908. The geology of the Quantock Hills and of Taunton and Bridgewater. Memoir of the Geological Survey of Great Britain. 
Wills, L J, 1970. The Triassic succession in the central Midlands in its regional setting. Quarterly Journal of the Geological Society of London, Vol.126, 225-285. 
Wills, L J and Campbell Smith, W. 1913. Notes on the flora and fauna of the Upper Keuper Sandstones of Warwickshire and Worcestershire. Geological Magazine, Vol.50, 461-462. 
Howard, A S, Warrington, G, Ambrose, K, and Rees, J G. 2008. A formational framework for the Mercia Mudstone Group (Triassic) of England and Wales. British Geological Survey Research Report, RR/08/04. 
1:50K maps on which the lithostratigraphical unit is found, and map code used:
E216 E183 E184 E199 E326 E155 E156 E168 E182 E200 E234 E264 E280 E340