Eastern England from the Tees to the Wash areas - Western Lowlands
This area covers the strip of generally low-lying ground that runs north−south along the western edge of the region, broadly adjacent to the River Trent in the south, and the Ouse, Swale and Tees in the north. Principal settlements include Newark, Goole, the eastern part of York and Teesside.
Sedimentary bedrock
A concentration of borehole information in the south of this area allows the shape and thickness of the bedrock layers to be well understood to at least 1500 m. Fewer boreholes in the north mean that the understanding in this part is much less certain. Bedrock layers within 1000 m of the ground surface include mudstones, sandstones, mineral salts, limestones, and coals. The total thickness of the sedimentary bedrock increases from around 1200 m in the south to over 6000 m in the north.
The youngest bedrock layers in this area (Permian and Triassic sediments) were laid down between 300 to 200 million years ago and form a more-or-less continuous belt that runs from Newark to Teesside. These layers are generally gently tilted towards the east and have a total thickness of up to 1000 m. These layers include the Sherwood Sandstone that ranges from about 120 m thick in the south to more than 350 m around York. This sandstone is porous and is used to provide large quantities of drinking water. Rocks which provide water in this way are referred to as aquifers and the Sherwood Sandstone is the second most important aquifer in England. Water in this layer flows between the individual sand grains and within fractures in the rock and is generally low in natural minerals such as calcium carbonate. In the south of the region, the layer above the Sherwood Sandstone is also a minor aquifer, however across the rest of the region the Sherwood Sandstone has a mudstone layer above that seals in the water. This layer, the Mercia Mudstone contains layers of gypsum that have been quarried to produce plaster in the south of the region (Plate P708326). Over most of the area, the layers beneath the Sherwood Sandstone form a sequence of red-brown mudstones, limestones, sandstones and mineral salts (including gypsum and rock-salt). This stack of (Permian) sediments reaches its maximum thickness of 350 m around Teesside and thins towards the south, dying out completely near Newark. The major limestone within this sequence, the Magnesian Limestone is an aquifer containing water that is naturally rich in dissolved salts, especially sulphates. Beneath these rocks lie older sedimentary layers (Carboniferous) that were laid down around 360 to 300 million years ago including sandstones, mudstones, limestones, locally important deposits of coal and a small amount of volcanic rock. Included within this sequence are the Carboniferous Limestone at the base and the Coal Measures at the top. These rocks come to the ground surface to the west and north of this region and are described in more detail in the corresponding accounts. Although these layers are generally tilted towards the east, they are far less continuous than the younger covering layers. Their extent is complicated by geological faulting and rapid changes in thickness, with areas where erosion removed parts of the layers before the overlying younger rocks were deposited.
The Coal Measures were deposited in relatively shallow seas, with vast quantities of sand and mud gradually building up to form large river deltas. When the tops of these deltas were exposed, massive swampy forests grew up and the vegetation from these forests was later buried and compressed to produce layers of coal. Deep mining in the west of the area has taken coal from layers at the top of this package in both Nottinghamshire and Yorkshire. Natural gas is found in some of the limestone and sandstone layers and is produced at several localities in Nottinghamshire and Lincolnshire. The underlying basement rocks are at least 1200 m below the ground surface throughout. They have not been reached by any boreholes in this area.