Chalk/Lias Group separation map

Area where aquifer and shale/clay are present	Yorkshire Lincolnshire Norfolk to Dorset Around the Weald Note that, for the purposes of drafting this separation map the maximum depth of the Chalk aquifer is taken to be 400 mbgl based on the recommendations in the UK TAG report. More information about this can be found in the methods section
Thickness of intervening strata	Yorkshire and Lincolnshire: up to 600 m, increasing north and south-eastwards Norfolk: 30 to 300 m, highest in north-west, decreasing southwards to about 100 m in Cambridgeshire and increasing again from Hertfordshire south westwards Southern England: from about 50 to 1750 m, thickest around the Weald, central Hampshire and Dorset and on Isle of Wight
	Northern part of Yorkshire: permeable Ravenscar Group; low permeability Oxford Clay Formation (clay); Osgodby Formation (clay); permeable Corallian Group (principal aquifer); low permeability Kimmeridge Clay Formation (clay); low permeability Ampthill Clay Formation (clay); low permeability Speeton Clay Formation; mixed permeability Lower Cretaceous sedimentary rocks East Yorkshire and Lincolnshire: permeable Great Oolite Group (principal aquifer); permeable Inferior Oolite Group (principal aquifer); low permeability Kellaways Formation (clay); Oxford Clay Formation (clay); low permeability Kimmeridge Clay Formation (clay); Ampthill Clay Formation (clay); permeable Spilsby Sandstone Formation (principal aquifer); permeable Lower Cretaceous sandstone; low permeability Wealden Group limestone; Lower Greensand Group (principal aquifer) Norfolk and Cambridgeshire: permeable Great Oolite Group (principal aquifer); permeable Inferior Oolite Group (principal aquifer); low permeability Kellaways Formation (clay); low permeability Oxford Clay Formation (clay); low permeability Kimmeridge Clay Formation (clay); low permeability Ampthill Clay Formation (clay); permeable Wealden Group sandstone; permeable Lower Greensand Group (principal aquifer); mixed permeability Gault Group (clay); Upper Greensand Formation Southern England including Oxfordshire and Buckinghamshire: permeable Great Oolite Group (principal aquifer); permeable Inferior Oolite Group (principal aquifer); low permeability Kellaways Formation (clay); Oxford Clay Formation (clay); permeable Corallian Group (principal aquifer); low permeability Kimmeridge Clay Formation (clay); low permeability Ampthill Clay Formation (clay); permeable Portland Goup; permeable Purbeck Group; low permeability Wealden Group; Lower Greensand Group (principal aquifer); mixed permeability Upper Greensand Formation; Gault Formation
Other major aquifers in the area	Yorkshire: Triassic sandstone; Magnesian limestone ( both below) Lincolnshire: Triassic sandstone; Magnesian limestone; Carboniferous limestone (all below) Norfolk and Cambridgeshire: Crag (above); Permian sandstone; Triassic sandstone; Magnesian limestone; Carboniferous limestone (all below) Southern England: Permian sandstone; Triassic sandstone; Magnesian limestone; Carboniferous limestone (all below)
Other shales or clays in the area	North Yorkshire: Bowland High Group; Craven Group (both below)
Aquifer map	Chalk principal aquifer
Shale/clay map	Lias Group shale/clay unit

cr-l — Crag/Lias Group separation map. BGS © UKRI.

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