The BGS Lexicon of Named Rock Units — Result Details

Aller Gravel Formation

Computer Code: AGR Preferred Map Code: notEntered
Status Code: Full
Age range: Eocene Epoch (GE) — Eocene Epoch (GE)
Lithological Description: Seen as 10-20cm-thick beds of lenticular-bedded abraded flint and chert gravels, with subordinate red-mottled silts and clays, coarse, angular, flinty gravelly clayey sand, with some cross-bedded coarse sand, lenticles of white clayey sand and reddish brown coarse sand. Locally finer-grained, more distinctly bedded flint gravels overlie the coarse gravels. The unit is interpreted to have been deposited by braided streams; the source is postulated to have been the Dartmoor highlands (Selwood and others, 1984; Cope et al., 1992), The constituents of the gravel vary locally, and may contain some or all of the following: flint, quartz and tourmaline rock, Greensand chert, Lower Carboniferous chert, Upper Carboniferous sandstone, white rounded clay clasts, vein quartz, dark grey hornfels and tuff.
Definition of Lower Boundary: Rests unconformably on Upper Greensand, where the contact is marked by an unconformable transition from pale green to pale brown sand with some glauconitic bands, iron staining with local chert from the Upper Greensand, to the overlying deposits of Aller Gravels. At Wolborough [SX 8535 7034], Aller Gravel has a faulted or unconformable contact with Upper Devonian Slates; here the contact is recognised by an abrupt change from the lithology of the Aller Gravel to coarse, locally dolomitised, limestones with red mudstone layers of the East Ogwell Limestone.
Definition of Upper Boundary: The Aller Gravels are locally overlain by the Palaeogene clays and sands of the Bovey Formation, indeed the Sandygate Borehole [SX 8672 7507] passes through this contact. In this location, the overlying Lappathorn Member of the Bovey Formation is comprised of siliceous clays, sands and silts with pink, red and brown iron staining; these are all underlain by flint gravels that are thought to represent the Aller Gravel.
Thickness: To 25m
Geographical Limits: Sands Copse, Kingsteignton, Milber, Wolborough and Kingskerswell, south Devon.
Parent Unit: Not Applicable (-)
Previous Name(s): Bovey Beds (-3157)
Tertiary Deposits (-633)
Aller Gravel (-1305)
Alternative Name(s): none recorded or not applicable
Stratotypes:
Partial Type Section  The Royal Aller Vale Quarry [SX 877 693], between Penn Inn and Kingskerswell. Faces in the quarry show about 25m of abraded flint gravel with subordinate silt and clay beds and lenses. Neither the top nor the base of the formation is visible. Selwood, E B and others, 1984. 
Reference(s):
Selwood, E B, Edwards, R A, Simpson, S, Chesher, J A, Hamblin, R J O, Henson, M R, Riddolls, B W and Waters, R A. 1984. Geology of the countryside around Newton Abbot. Memoir of the British Geological Survey, Sheet 339 (England and Wales). 
Vachell, E T. 1963. Fifth report on geology. Report and Transactions of the Devonshire Association for the advancement of science. 
Hamblin, R J O. 1974. On the correlation of the Haldon and Aller gravels, south Devon. Proceedings of the Ussher Society, Vol.3, 103-110. 
Cope, J W C, Ingham, J K, and Rawson, P F. 1992. Atlas of palaeogeography and lithofacies. Geological Society Memoir, No.13. 
Edwards, R A, 1973. The Aller Gravels: Lower Tertiary Braided River Deposits in South Devon. Proceedings of the Ussher Society, Vol.2, p.608-616. 
De La Beche, H T, 1939. Report on the geology of Cornwall, Devon and west Somerset. Memoir of the Geolgoical Survey. 
Edwards, R A. 1976. Tertiary sediments and structure of the Bovey Basin, south Devon. Proceedings of the Geologists' Association, Vol.87, 1-26. 
Edwards, R A. 1970. The geology of the Bovey Basin. Unpublished PhD thesis, University of Exeter. 
Ussher, W A E, 1913. Geology of the country around Newton Abbot. Memoir of the British Geological Survey, Sheet 339. (England and Wales). 
1:50K maps on which the lithostratigraphical unit is found, and map code used:
E339