Eastern England from the Tees to the Wash areas - North York Moors and adjoining area
This area lies towards the northern limit of the region and extends from Saltburn south to Filey along the coast, passing inland to include the Vale of Pickering, the Howardian, Hambleton and Cleveland Hills and the North York Moors National Park. Important settlements include Scarborough, Whitby, Pickering and Malton.
Sedimentary bedrock
Boreholes in the northern and eastern parts of this area allow the overall shape and thickness of the sedimentary bedrock layers to be generally well-understood to a depth of at least 1500 m. In the south, where geological faulting has resulted in a complicated arrangement of these rocks, and in the west, relatively few boreholes are available so the geological structure at depth is less well understood. The sequence of these sedimentary rocks extends to depths of over 5500 m. Layers within 1000 m of the ground surface are mainly mudstones, sandstones, limestones, ironstones, thin coal beds and layers of mineral salts.
The uppermost layers in this sequence were laid down between 200 and 145 million years ago (Jurassic) and include the mudstones, sandstones and limestones. These form the impressive sea cliffs in the north-east of the area (Plate P006771) that are famous for their fossils and ‘Whitby jet’, a minor gemstone derived from fossil wood which has been crushed under very high pressure. These layers generally tilt inwards towards the centre and east of the area. In common with rock layers of a similar age described from other parts of this region, the total thickness of these layers changes dramatically, passing from about 900 m in the central part of this area to 250 m or less in the south. Their thickness continues to decrease to less than 40 m beneath the northern part of the Yorkshire Wolds, across a complex series of geological faults. Across the northern, central and eastern parts of this area, these rocks have historically been mined for ironstone, ‘alum shale’ (alum is used in dying and tanning), a small amount of coal and jet. The deepest of the ironstone mining reached around 220 m below the ground surface. Some of the thicker layers of limestone and sandstone provide locally important aquifers.
The Permian and Triassic sedimentary layers, including the Sherwood Sandstone aquifer and the mudstones, limestones and mineral salt layers described in the areas to the west and south also extend beneath this area. These layers are tilted in a similar way to those above, reaching a maximum depth of around 1700 m in the east. The mineral salt layers in the sequence beneath the Sherwood Sandstone become much thicker in the north-east where they are mined at a depth of around 1200 m in the Boulby area and used to manufacture agricultural fertilisers and as rock salt. Natural gas is found in some of the limestone and sandstone layers, with production of gas at several localities in the area.
Rock layers of a similar age to the oldest sedimentary bedrock found elsewhere in the region are also present in this area and at the top include the Coal Measures. These rocks comprise sandstone, mudstone, limestone and thin coal beds. Some of the sandstone layers are known to contain natural gas.
In the north of the area, a narrow, vertical, sheet-like intrusion of once molten rock called the 'Cleveland Dyke' cuts across these sedimentary layers. Very little is known about the basement rocks in this part of the region as they lie at several kilometres depth and they have not been reached by any deep boreholes.