Metropolitan Borough of Gateshead Geodiversity Audit July 2019 Hulam Tufa barrages at Lilycrook Burn Consulting Version control Version Date Author Notes 0.1 25 June 2019 Alistair Bowden First draft 0.2 19 July 2019 Alistair Bowden Second draft based on a meeting on 8 July and emails since 2 Contents 1 Introduction 4 1.1 What is a Geodiversity Audit? 4 1.2 A brief introduction to geological time 4 1.3 Brief overview of the area 5 2 Basement geology 9 3 Solid geology: Carboniferous Coal Measures 12 3.1 The Lower and Middle Coal Measures 15 3.2 Depositional environments 16 4 Superficial geology: Quaternary drift and landforms 20 4.1 Landscape and bedrock 20 4.2 Ice sheet advance 23 4.3 Ice sheet stagnation and retreat 24 4.4 Post-glacial superficial deposits 27 5 Human impact on the landscape 29 6 Recommendations 31 7 Glossary 32 8 References 33 3 1. Introduction In 2019, Hulam Consulting was commissioned by the Metropolitan Borough of Gateshead to produce a Geodiversity Audit of the Borough as part of the evidence base to support the Making Spaces for Growing Places Local Plan Document (Metropolitan Borough of Gateshead, 2018). The geodiversity of the Metropolitan Borough of Gateshead (the Borough) has had a huge impact not just on the Borough but also wider afield. The mineral wealth of the North East of England, in particular coal and metal ores, has driven the industrial development of the region and has contributed much to the prosperity of Great Britain as a whole. By far the most significant natural resource was coal. The Northumberland and Durham Coalfield was one of Britain’s earliest worked coalfields. Coal mining in the region reached its heyday at the end of the 19th and beginning of the 20th centuries. The depletion of reserves combined with other economic and social factors has seen the industry decline in importance to the point that all deep mining has finished in the region, and coal production is now restricted to a handful of opencast sites. This decline has also had huge knock-on effects for the local workforce as well as the fortunes of the Borough. Within the Borough, the production of iron, quarrying and the extraction of sand and gravel has also diminished/ceased. Much of the traces of the industrial and mining landscapes have been reclaimed and re-landscaped, whilst the leisure and tourist industries have shown significant growth, often utilising the surviving industrial heritage of the area, for example the Derwent Walk Country Park. 1.1 What is a Geodiversity Audit? Geodiversity has been defined as “the link between people, landscape and their culture: it is the variety of geological environments, phenomena and processes that make those landscapes, rocks, minerals, fossils and soils which provide the framework for life on earth” (Stanley, 2001) Geodiversity underpins much of what gives an area its unique character, from the building stone or clay that makes the bricks that contribute to the local architecture, to the natural resources which have provided employment and influenced the cultural heritage of the local community, to the biodiversity of the green spaces and rural areas. The aim of this report is to provide an introduction to the geological make-up of the Metropolitan Borough of Gateshead, provide a brief description of the key geological assets and outline the influence geology has had on land-use within the Borough. It concludes with recommendations for further investigation/survey to identify and potentially designate (e.g. local geological site) geological assets considered to be of sub-regional (County), regional and/or national importance. 1.2 A brief introduction to geological time The Earth formed around 4,500 million years ago, but most of the rocks found in Britain were formed in the last 600 million years. This is also the part of the geological record where fossils enable geologists to categorise the rock record into periods of geological time, from the Cambrian period through to the Quaternary period (Figure 1). All the rocks underlying the Borough are of the Westphalian Stage of the Carboniferous period, also known as the Carboniferous Coal Measures and date from around 304-318 million years ago. Smeared over this bedrock is a layer of drift deposits of clay and sand and gravels, of varying thicknesses, deposited during the ice ages of the Quaternary period. 4 Figure 1 Geological periods (left) and main rock units from Northern England (right) (Stone et al., 2010, p. 4, Table 1) 1.3 Brief overview of the area The Borough is dominated by the conurbation of Gateshead with significant urban development along the Tyne and Team valleys (Figure 2). Many of the older developments close to the Tyne, such as Ryton and Crawcrook, Winlaton, Whickham and Gateshead tended to be built upon the sandstone ridges with newer development filling in the topographically lower areas. Elsewhere, development is more discrete, often focussed around a colliery, for example Clara Vale or Marley Hill, or brickworks, for example Kibblesworth. The Borough forms part of the catchment of the River Tyne, indeed the river forms the northern boundary to the Borough. Throughout most of its length the river is characterised by broad alluvial and terrace flats however below Dunston, the valley becomes narrower. Stanley Burn forms part 5 of the Western boundary to the Borough, entering the Tyne just opposite Wylam. A small stream, Barlow Burn, rises above Coalburns and flows northwest to enter the Tyne between Ryton and Winlaton. A major tributary of the Tyne, the River Derwent also flows north-westwards through the Borough and enters the Tyne at Blaydon. Finally, the River Team flows through the broad but pronounced Team Valley, which runs north past Birtley to join the Tyne, between Dunston and Gateshead. The hills are generally flat topped, capped by a relatively thick layer of sandstone. The west of the Borough is dominated by a series of ridges running broadly NE/SW, following a line of thick sandstones, and separated from each other by watercourses of varying magnitudes. The rocks underlying the Borough are a series of repeating cycles of mudstone, siltstone and sandstone, sometimes including coals and iron rich bands within the mudstones, which all belong to the Lower and Middle Coal Measures (Figure 3). The mudstones are relatively soft rocks and easily eroded and the sandstones are relatively harder and more resistant to erosion. The rocks in the Borough dip gently towards the SE so that the oldest rocks can be found towards the west of the Borough and in the base of valleys and the youngest towards the east and to the tops of hills. The drift deposits cover a significant part of the Borough, thickest in the valleys and thinning towards the tops of the hills, so that some hilltops are drift-free. 6 Figure 2. Topographic map of the Metropolitan Borough of Gateshead. 7 Figure 3. Summary bedrock geology map. 8 2. Basement geology The Borough is dissected by a major flaw in the Earth’s crust, the surface expression of which today is the Ninety Fathom Fault which strikes east-north-east. To understand the story behind this fault, we need to go back a long way in time and to a very different part of the Earth’s surface. Back in the Early Ordovician, approximately 480 million years ago, the area of the Earth’s crust containing current day ‘England’ was approximately 500 South of the Equator and the area of the Earth’s crust containing current day ‘Scotland’ was between the Tropic of Capricorn and the Equator (Figure 4a). ‘England’ and ‘Scotland’ were both sited on two enormous land masses which were separated by the Iapetus Ocean. Progressively during the Ordovician and Silurian periods, the two land masses migrated towards each other, closing the ocean and subsequently pushing into each other to form the Appalachian-Scottish-Scandinavian mountain chain (Figure 4b-c). Eventually, by the Permian, the enormous supercontinent Pangaea was formed, during which the Magnesian Limestone of South Tyneside, Sunderland and Durham was deposited (Figure 4d). Figure 4. Palaeogeographic reconstructions showing ‘England’ separated from ‘Scotland’ by the Iapetus Ocean which closed between the Early Ordovician and the Late Silurian and the northward migration of this portion of the Earth’s crust from the Tropic of Capricorn north to its current location (Stone et al., 2010, p. 8, Figure 3). 9 The collision of these two areas of the Earth’s crust was a cataclysmic affair. As the two continents collided, there was a widespread phase of deformation and mountain building, volcanism and the emplacement of granites beneath the Lake District, Dumfries & Galloway, the Cheviots and the North Pennines. The Weardale Granite is concealed underground beneath and to the southwest of the Borough (Figure 6). Using geophysics we can tell a lot about what is going on deep underground. For example, by measuring small variations in the strength of the Earth’s magnetic field or the force of gravity, we can deduce something about the rocks underground and predict where granites are concealed (Bott & Masson Smith, 1957; Kimbell et al., 2010). The Weardale Granite was proved in 1960-61 when a borehole was drilled in Rookhope (Dunham, et al.,1965). Of particular interest, in the Borough, is the hemispherical protrusion from the Weardale Granite in its NE corner named the Rowlands Gill Cupola (Figure 5). This is a high point on the top surface of the Weardale Granite which lies broadly beneath Rowlands Gill. It is not exposed at the surface – the top of the granite in this area is thought to be around 1km deep – but its presence guides major faults in the Gateshead area which were a significant factor in the deposition of Carboniferous coal bearing sediments in the area.