The BGS Lexicon of Named Rock Units — Result Details

Ashton Mudstone Member

Computer Code: ANSH Preferred Map Code: notEntered
Status Code: Pending Upgrade
Age range: Brigantian Substage (CX) — Kinderscoutian Substage (CK)
Lithological Description: Greyish blue, rusty-weathering mudstones with scattered thin sooty goniatite-bearing mudstones. Scattered siltstones and sandstones (up to 7cm thick) form less than 10% of the Member. The sandstones are commonly medium-grained, quartzitic and feldspathic and thought to be derived from the south. Plant fragments are locally abundant.
Definition of Lower Boundary: The lower boundary is taken at the incoming of bluish grey micaceous mudstones with scattered thin sandstones and siltstones of the Ashton Mudstone Member above the fossiliferous interbedded cherts, limestones and mudstones (Posidonia Beds) of the Teign Chert Formation.
Definition of Upper Boundary: The upper boundary is taken at the gradational incoming of more abundant and relatively thicker sandstones of the overlying Crackington Formation above the mudstones with less than 10% sandstone of the Ashton Mudstone Member.
Thickness: 210-430m
Geographical Limits: Teign Valley (SX 84 84), and Exeter (SX 90 92) areas, south Devon. May extend westwards into the Okehampton area (SX 59 94), where it has previously been included in the Crackington Formation, but further investigation is needed.
Parent Unit: Dowhills Mudstone Formation (DHLS)
Previous Name(s): Ashton Shale Member (*260)
Ashton Shale Member (Of Crackington Formation) (-17)
Ashton Formation (-644)
Argillaceous Series (-1950)
Alternative Name(s): none recorded or not applicable
Stratotypes:
Partial Type Section  Road section, 230m south of Spara Bridge, Lower Ashton, middleTeign Valley, south Devon Section exhibits 2m of mudstones with plant fragments and thin black sooty beds with goniatites. 
Reference(s):
Chesher, J A, 1968. The succession and structure of the Middle Teign Valley. Proceedings of the Ussher Society, Vol.2, 15-17. 
Waters, C N, Brown, M A E, Dean, M T and Powell, J H. In press. Lithostratigraphical framework for Carboniferous successions of Great Britain (Onshore). British Geological Survey Research Report, RR/05/06. 
Morton, R D. 1958. The stratigraphy, structure and igneous rocks of the Central Teign Valley. Unpublished Ph.D. Thesis, University of Nottingham. 
Edwards, R A, Scrivener, R C, Barton, C M, Bristow, C R, Williams, B J, Goode, A J J, Cornwell, J D, Royles, C P, Self, S J, Warrington, G, Riley, N J, Turner, N, Jones, N S, Smith, S A, Marks, R J, Fortey, N J, Morton, R D, Strong, G E, Kemp, S J, Forster, A, Ault, L, Haslam, H W and Chesley, J T. 1999. Geology of the country around Exeter. Memoir of the British Geological Survey, Sheet 325 (England and Wales). 
1:50K maps on which the lithostratigraphical unit is found, and map code used:
E339