The BGS Lexicon of Named Rock Units — Result Details

Poole Formation

Computer Code: POOL Preferred Map Code: notEntered
Status Code: Full
Age range: Ypresian Age (GY) — Lutetian Age (GL)
Lithological Description: The Poole Formation comprises four stacked depositional sequences, each based by an erosion surface and comprising a lower sand unit and an upper clay unit (Bristow et al., 1991; Bristow, 1999). Sand units: These often have a basal pebble lag. They are medium- to coarse-grained, partly trough and planar cross-bedded, often with water-escape structures, and some thin and lenticular clays. They tend to coarsen westwards, with the development of gravels which include significant proportions of quartz pebbles and pebbles of Palaeozoic and Jurassic rocks (Reid 1896, 1899). Clay units: These comprise units of kaolinitic clay and silt (‘ball clay’ or ‘pipe clay’), often with varicoloured tops indicating pedogenic overprint, interbedded with organic-rich clays and laminated clays, often channel-filling. Kaolinitic clays tend to be dominant in the Wareham area and laminated clays in the Bournemouth-Poole area.
Definition of Lower Boundary: Clean, coarse-grained sands of the Poole Formation overlie bioturbated, micaeous clayey sands and clays of the London Clay. The Poole Formation thins to the north and east of Poole, with the overstep of progressively higher units onto the London Clay Formation (Bristow et al., 1991).
Definition of Upper Boundary: Generally at the erosional contact between the clays and silts of the Parkstone Clay Member and the overlying sands of the Branksome Sand Formation. in places the Branksome Sand Formation cuts down through the Parkstone Clay to rest on the sands of the Parkstone Sand Member.
Thickness: Generally 67-110 m but up to 160-180 m in the most expanded successions around Poole. The two units attributed to the Poole Formation (divided by 23 m of the Wittering Formation) at Alum Bay on the Isle of Wight have a combined thickness of about 48 m.
Geographical Limits: East Dorset and west Hampshire, throughout the western Hampshire Basin. Best developed in the Wareham and Poole areas. Represented at Alum Bay in western Isle of Wight.
Parent Unit: Bracklesham Group (BRB)
Previous Name(s): LOWER DIVISION
Alternative Name(s): none recorded or not applicable
Reference Section  Christchurch Borehole SZ29SW12. 
Type Area  Numerous small exposures and boreholes in the Wareham Basin that constitute the type sites for each of the named members. 
Reid, C. 1896. The Eocene deposits of Dorset. Quarterly Journal of the Geological Society of London, Vol. 52, 490-496. 
White, H J O. 1917. Geology of the country around Bournemouth (2nd edition). Memoir of the Geological Survey of Great Britain, Sheet 329 (England and Wales). 
Bristow, C R, Freshney, E C and Penn, I E. 1991. Geology of the country around Bournemouth. Memoir for 1:50 000 geological sheet 329 (England and Wales). HMSO, London. 
Curry, D, Adams, C G, Boulter, M C, Dilley, F C, Eames, F E, Funnell, B M and Wells, M K. 1978. A Correlation of Tertiary rocks in the British Isles. Geological Society of London Special Publication, Vol.12, 1-72. 
Edwards, R A, and Freshney, E C. 1987. Geology of the country around Southampton. British Geological Survey Memoir, Sheet 315 (England and Wales). 
Edwards, R A, and Freshney, E C. 1987. Lithostratigraphical classification of the Hampshire Basin Palaeogene deposits (Reading Formation to Headon Formation). Tertiary Research, Vol. 8, 43-73. 
Bristow, C R. 1999. The geology of the Wareham, Arne, Creech and Corfe Castle area, Dorset. British Geological Survey Technical Report, WA/99/43 (Keyworth, Nottingham). 
King, C. 2006. Paleogene and Neogene: uplift and a cooling climate. 395-427 in Geology of England and Wales. Brenchley, P J, and Rawson, P F (editors). (London: The Geological Society.) 
King, C. In press. A correlation of Tertiary rocks in the British Isle and adjacent areas. Special Report of the Geological Society of London, No.12. 
Plint, A G. 1983. Facies, environments and sedimentary cycles in the Middle Eocene, Bracklesham Formation of the Hampshire Basin: evidence for global sea-level changes? Sedimentology, Vol. 30, 625-653. 
Reid, C. 1899. The geology of the country around Dorchester. Memoir of the Geological Survey of Great Britain, Sheet 328 (England and Wales). 
1:50K maps on which the lithostratigraphical unit is found, and map code used:
E314 E329 E341 E342 E343