The BGS Lexicon of Named Rock Units — Result Details

Aston Limestone Formation

Computer Code: ASLS Preferred Map Code: AsL
Status Code: Full
Age range: Bajocian Age (JB) — Bajocian Age (JB)
Lithological Description: Grey and brown variously shelly, ooidal, sandy, shell-detrital and bioturbated limestones; rubbly in parts, with a median peloidal ooid-grainstone unit (Notgrove Member) well developed in places, and minor sandy and shell-detrital calcareous mudstone beds. The formation includes a bored hardground on top of the Notgrove Member. Shallow marine carbonate shelf. Mainly low energy conditions with carbonate mud deposition and terrigenous sediment influx, and a profuse shelly epifaunal biota. Higher energy conditions at times depositing coarser carbonate grains (ooids). Discites Zone to Sauzei Zone.
Definition of Lower Boundary: Disconformity: upward change from ooidal and peloidal limestone (Scottsquar Member: Birdlip Limestone Formation) or sand, mudstone and sandy limestone (Harford Member: Birdlip Limestone Formation) - the Bajocian Unconformity, into grey and brown variously shelly, ooidal, sandy, shell-detrital and bioturbated limestones. The basal beds commonly contain pebbles derived from the underlying rocks. Generally a hardground.
Definition of Upper Boundary: Disconformity, generally a hardground: grey and brown variously shelly, ooidal, sandy, shell-detrital and bioturbated limestones overlain by members of the Salperton Limestone Formation, i.e. very shelly and coarsely shell-detrital ooidal grainstone and packstone (Upper Trigonia Grit Member, where present) or rubbly, fine- to coarse-grained ooidal, peloidal and finely shell-detrital packstone to grainstone (Clypeus Grit Member) - the Vesulian Unconformity.
Thickness: Type section up to about 6.45 m. Maximum c.22 m (Cleeve Hill area).
Geographical Limits: North and mid-Cotswolds: west of Northleach, Cold Aston and Blockley, and northeast of Stroud, Gloucestershire. Present locally outside this area to the south of Cold Aston, and absent between Birdlip and Cirencester ('Birdlip Anticline') due to overstepping relationships resulting from differential subsidence (Barron et al., 1997, fig. 4; Sumbler et al., 2000).
Parent Unit: Inferior Oolite Group (INO)
Previous Name(s): Middle Inferior Oolite [Obsolete Name And Code: Use ASLS] (MINO)
Hartley Hill Formation [Obsolete Name and Code: Use ASLS] (-1958)
Alternative Name(s): none recorded or not applicable
Stratotypes:
Type Section  Harford railway cutting SSSI [SP 1360 2184 to 1404 2166], near Bourton-on-the-Water. 
Reference Section  Tumulus Railway Cutting, Chedworth Woods, Gloucestershire [SP 0507 1392 to 0500 1404]. 
Type Area  Cleeve Hill, Gloucestershire [SO 98 25 to 98 26]. 
Reference(s):
Sumbler, M G, Barron, A J M and Morigi, A N, 2000. Geology of the Cirencester district. Memoir of the British Geological Survey, Sheet 235 (England and Wales). 
Barron, A J M, Lott, G K, and Riding, J B. 2012. Stratigraphical framework for the Middle Jurassic strata of Great Britain and the adjoining continental shelf. British Geological Survey Research Report RR/11/06. 
Barron, A J M, Sumbler, M G and Morigi, A N, 1997. A revised lithostratigraphy for the Inferior Oolite Group (Middle Jurassic) of the Cotswolds, England. Proceedings of the Geologists' Association, Vol.108, 269-285. 
Buckman, S S, 1895. The Bajocian of the mid-Cotswolds. Quarterly Journal of the Geological Society of London, Vol.51, 388-445; 458-462. 
Waters, C N, Smith, K, Hopson, P M, Wilson, D, Bridge, D M, Carney, J N, Cooper, A H, Crofts, R G, Ellison, R A, Mathers, S J, Moorlock, B S P, Scrivener, R C, McMillan, A A, Ambrose, K, Barclay, W J, and Barron, A J M. 2007. Stratigraphical Chart of the United Kingdom: Southern Britain. British Geological Survey, 1 poster. 
Buckman, S S, 1897. Deposits of the Bajocian age in the northern Cotswolds: the Cleeve Hill Plateau. Quarterly Journal of the Geological Society of London, Vol.53, 607-629. 
Parsons, C F, 1980. Aspects of the statigraphy and ammonite faunas of the Aaenian-Bajocian stages in Great Britain. Unpublished PhD thesis, University of Keele. 
1:50K maps on which the lithostratigraphical unit is found, and map code used:
E234 E235 E217