Chalk/Lias separation map

Area where both aquifer and shale are present

Yorkshire, Lincolnshire, Norfolk to Dorset and 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 m below ground level based on the recommendations in the UK TAG report (UK TAG, 2011). 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 being 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.

Lithology of intervening strata

Northern part of Yorkshire: permeable Ravenscar Group, low permeability Oxford Clay and Osgodby Formations (clay), permeable Corallian (principal aquifer), low permeability Kimmeridge and Ampthill Clays (clay), low permeability Speeton Clay and mixed permeability Lower Cretaceous sediments.

East Yorkshire and Lincolnshire: permeable Oolites (principal aquifer), low permeability Kellaways and Oxford Clay (clay), low permeability Kimmeridge and Ampthill Clays (clay), permeable Spilsby Sandstone (principal aquifer), permeable Lower Cretaceous sandstone, low permeability Wealden limestone and Lower Greensand (principal aquifer).

Norfolk and Cambridgeshire: permeable Oolites (principal aquifer), low permeability Kellaways and Oxford Clay (clay), low permeability Kimmeridge and Ampthill clays (clay), permeable Wealden sandstones, permeable Lower Greensand (principal aquifer), mixed permeability Gault (clay) and Upper Greensand.

Southern England including Oxfordshire and Buckinghamshire: permeable Oolites (principal aquifer), low permeability Kellaways and Oxford Clay (clay), permeable Corallian (principal aquifer), low permeability Kimmeridge and Ampthill Clay (clay), permeable Portland, permeable Purbeck, low permeability Wealden, Lower Greensand (principal aquifer), mixed permeability Upper Greensand and Gault.

Other major aquifers in the area

Yorkshire: Triassic sandstones (below) and Magnesian limestone (below).

Lincolnshire: Triassic sandstones (below), Magnesian limestone (below) and Carboniferous Limestone (below).

Norfolk and Cambridgeshire: the Crag (above), Permian sandstones (below), Triassic sandstones (below), Magnesian limestone (below) and Carboniferous Limestone (below).

Southern England: Permian sandstones (below), Triassic sandstones (below), Magnesian limestone (below) and Carboniferous Limestone (below).

Other shales or clays in the area

Yorkshire and Lincolnshire: Bowland High and Craven Groups (below).

Norfolk to Dorset and around Weald: none.

Links to aquifer and shale/clay maps

View the map of the Chalk principal aquifer.

View the map of the Lias.

References

UK TAG. 2011. Defining and reporting on groundwater bodies. UK Technical Advisory Group on the Water Framework Directive, working paper V6.21/Mar/2011