The 3D Quaternary geology of the area around Thornton, Cheshire

This report summarises the superficial (Quaternary) geology of the area around Thornton Science Park at Thornton-Le-Moors in north Cheshire, with an emphasis on understanding the geological units in terms of potential fluid transport through them. The study utilised existing geological maps and borehole records to construct a 3D geological model of the superficial deposits, covering an area of 63km2. The Quaternary succession in the area is dominated by glacigenic sediments, comprising till (gravelly clay), glaciofluvial deposits (gravels and sands) and lesser amounts of glaciolacustrine clays and silts. The tills and glaciofluvial deposits are intercalated in some areas, with intervals of sand and gravel within the till modelled as lenses. The superficial deposits vary laterally and vertically across short distances, making extrapolation difficult in areas where borehole data are absent. Holocene sediments, comprising tidal flat deposits, peat and alluvium occupy the northern part of the study area forms a tract through the middle of the area. The northern part of the model covers the southern bank of the Mersey estuary where tidal flat deposits, dominated by silt and clay, are mapped/modelled with till underneath. A laterally persistent peat layer within the tidal flat deposits is modelled where proven in boreholes. The River Gowy runs south-north through the middle of the model area to join the Mersey at Stanlow Point. An arbitrary mapped line separates alluvium associated with the River Gowy from the Mersey estuary tidal flat deposits, with which they are transitional. A large area of peat is mapped/modelled at surface in a marshy area in the River Gowy floodplain. Boreholes prove that much of this peat is underlain by alluvium. Bedrock is mapped/modelled at surface in isolated patches, representing bedrock ‘highs’ where superficial deposits are locally absent. There may be other unproven zones of thin or absent superficial deposits in the area that could provide direct connectivity from the ground surface to the underlying Sherwood Sandstone Group bedrock