Tyne and Wear
The geology of the Tyne and Wear area is relatively simple and is dominated by rocks from three main periods of geological time.
The high moorland between Teesdale and Weardale is underlain by Upper Carboniferous sediments.
The rocks slope gently to the south-east, so that the oldest occur in the north of the area and the youngest in the south. Newcastle and Tyneside are underlain by the mudstones, shales and coals of the Upper Carboniferous Coal Measures, while in the Sunderland area the marine limestones and evaporites of the Permian Magnesian Limestone form the solid geology.
The whole area was affected by glacial erosion and deposition during the Ice Age of the past two million years. As a result thick deposits of till, or boulder clay, deposited by the ice sheets cover the solid geology.
Carboniferous
Carboniferous rocks (345 – 280 million years old) dominate the underlying geology of the area to the north and north-west of Sunderland and comprise entirely the Upper Carboniferous Coal Measures. This varied sequence of shales, mudstones, sandstones and coal seams were deposited in the late Carboniferous (approximately 300 million years ago) in a coastal environment where large river deltas were building out into the shallow marine waters.
Continuing deposition over the millennia led to the further building out of the deltas and the formation of an extensive low-lying, swamps. The rocks of the Coal Measures show a repeated coal, sandstone and mudstone cycle which reflects relative changes in land and sea level. The coals represent the fossilised remains of swamp vegetation which grew as luxuriant forests on the deltas, while the mudstones were deposited under shallow marine conditions. The Coal Measures were heavily exploited by man until the gradual decline of the coal and steel industries from the 1930’s onwards.
Permian
Rocks of Permian age (290-248 million years ago) form the solid geology to the area running between Sunderland and Hartlepool on the coast and inland an escarpment that runs southwards from the west of Sunderland and down through Houghton-le-Spring. The sequence belongs to the Magnesian Limestone, although at its base is a unit of sandstones known as the ‘Yellow Sands’ which represent the remnants of Saharan-like desert sand dunes. The Yellow sands are overlain by a thin mudstone known as the Marl Slate and cream to buff coloured limestones; the Magnesian Limestone, within which there are beds of gypsum and anhydrite (collectively known as evaporites). These rocks were deposited in a relatively shallow landlocked sea, which extended from north east England to Poland, and has been named the Zechstein Sea. The estimated average temperature during the period was approximately 23°C.
Due to the landlocked nature of the sea and high temperatures the sea water gradually evaporated leaving behind salt deposits, that today are commercially worked to produce brine. Within the Magnesian Limestone the remains of fossil reefs (often including numerous fossil algae, bivalves, gastropods and bryozoans) which grew on the edge of the Zechstein Sea can be found. The cliff sections around Marsden Bay, Seaham and Blackhall Rocks provide excellent exposure through this sequence of rocks.
The unique chemistry of the Magnesian Limestone (the limestone is high in Magnesium carbonate, when compared with other limestones) gives rise to soil conditions which support an interesting combination of plants, with grassland species typical of the Chalk of southern England such as thyme and harebell occurring along with rare plants, such as thistle broomrape, which is not found away from the Magnesian limestone outcrop.
Quaternary
Over the last two million years the climate of Britain has varied tremendously with periods of temperate climate interrupted by repeated advances and retreats of glaciers and ice sheets. Collectively these periods have become known as the Ice Age (we are still in one of the temperate phases) and the actions of the ice sheets have been instrumental in forming the landscape we see today.
The whole of the north-east of England has been shaped by glacial erosion and deposition during the Quaternary. Ice sheets covered the area during the last two glacial periods, depositing thick sheets of boulder clay or till from the base of the ice over the land surface. Following melting of the last ice sheet, some 12,000 years ago, deposits of sand and gravel accumulated in the Wear Valley.
Temporary lakes also formed locally, in which deposits of fine silt and clay accumulated. Laminated clays of this sort have been extensively work for brick making in the Birtley area. Wind-blown sand, of post-glacial age, occurs on the low-lying coast south of the river Tyne at South Shields.
Glaciation also altered drainage patterns, by blocking the original route of the river Wear north, causing it to divert eastwards cutting a new channel through the Magnesian Limestone Plateau to flow into the North Sea at Sunderland. The abandoned course of the pre-glacial Wear is now occupied by the diminutive river Team in the Team valley at Gateshead.
Geological highlights:
The coast from Tynemouth to Seaton Sluice provides one of the best exposures of Coal Measures rocks in Great Britain. It includes outcrops of numerous coal seams, and several mudstone horizons yielding non-marine bivalves. Of particular importance are outcrops of sandstones within the rock sequence, which have been interpreted as braided river deposits. These contrast to the meandering river deposits which dominate the same rocks in the Pennines Coalfields to the south. Geologists suggest from this evidence that the Northumberland and Durham Coalfields formed in a more elevated area relative to the Pennines Coalfield, and was then probably rather further from the sea.
- The rocks platforms and cliffs cut into the Magnesian Limestone at Marsden Bay provide textbook examples of these erosional features. Local weaknesses in the Magnesian Limestone have been exploited by marine erosion processes leading to the formation of stacks, caves and arches. The best known of the stacks is Marsden Rock between South Shields and Sunderland. The speed of erosion along the coast is evidenced by the movement offshore of this rock. In the 1850s it was only about 10m from the cliff-line. Now it is about 100m. During the twentieth century a large arch formed at one end of the stack. This collapsed in 1998.
- Tunstall Hills, to the south of Sunderland, demonstrates the strong relationship between the Magnesian Limestone outcrop and the habitats that it supports. Geological interest centres upon numerous rock exposures which occur on the Maiden Paps, in disused quarries and in cuttings above the reclaimed Ryhope railway line. Gentle slopes on the Maiden Paps support species-rich Magnesian Limestone including species such as blue moor-grass, common rock-rose, perennial flax and locally uncommon plants such as frog orchid, autumn gentian and purple milk-vetch. The rock exposures of the Magnesian Limestone, in places, yield large numbers of fossils of the animals that inhabited the shallow water reefs including brachiopods, bivalves and snails which are so well preserved that they retain their original colour-banding.
- The Upper Carboniferous Coal Measures of the North-East have played a vital role in the industrial development of the area and Britain as a whole. It seems probable that the North East is the oldest intensive coal mining district in the country and evidence suggests that the Romans burned and excavated coal in the region. Exposed coal outcrops along the banks of the River Tyne, were of particular importance, as the river provided a means of transportation. The Tyne quickly developed into the major river for exporting coal to London and by the 13th century coal mining was well established, most notably at Whickham. Coal mining activity continued to increase in the sixteenth and seventeenth centuries with mining concentrated around Tyneside and the Washington area of Wearside. This production fuelled the birth of the railway and the development of the steam locomotive. Coal mining continued to grow throughout the later nineteenth and early twentieth century and brought about a tremendous increase in the population of the North East. The two world wars helped to boost the need for coal in industry, but in the later half of the twentieth century colliery closures began to increase. Closures continued throughout the eighties and nineties, and in 1994 the closure of the Wearmouth Colliery in Sunderland saw the end of the last remaining colliery in the Durham coalfield.
Local sites
The following localities represent, in part, the geology of this county. Each locality has a grid reference, a brief description of how to get there and a short summary of the geology you are likely to find. All the localities listed are openly accessible.
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