Geology of Northumberland

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This article describes the geology of the historic county of Northumberland. It does not include that southeastern part of the historic county which has since 1974 formed a part of the metropolitan county of Tyne and Wear

The geology of Northumberland in northeast

Palaeogene dykes and sills and the whole is overlain by unconsolidated sediments from the last ice age and the post-glacial period.[1] The Whin Sill makes a significant impact on Northumberland's character and the former working of the Northumberland Coalfield significantly influenced the development of the county's economy. The county's geology contributes to a series of significant landscape features around which the Northumberland National Park
was designated.

Silurian

Rocks of the Gala Group outcrop near Berwick.

Wenlock epoch of the Silurian Period are assigned to the Riccarton Group and occupy an area either side of the border to the north of Byrness
.

Devonian

Old Red Sandstone

The late Devonian Stratheden Group is characterised by sandstones with subordinate siltstones and mudstones. A small area of these rocks straddles the border to the southwest of The Cheviot.

Igneous rocks

Rocks assigned to the Cheviot Volcanic Formation, itself within the Reston Group, straddle the border with Scotland. This thick pile (over 1000m) of andesitic lavas was erupted during the early Devonian. The sequence includes rhyolites, agglomerates and tuff.[2] The Cheviot Pluton is a mass of Devonian granite.

Carboniferous

Yoredale Group

The Inverclyde Group extends from to the Scottish border near Byrness. Rocks of the Border Group extend in a broken and faulted belt south from Berwick towards Alnwick then southwest via Rothbury then onward to the county boundary west of Kielder Water. Within the Border Group the Fell Sandstone Formation reaches up to 370m thickness and is locally prominent around Rothbury Forest where it also forms the Simonside Hills which reach a height of 440m at Tosson Hill.

The

South Tyne
.

Coal Measures

The sandstones, siltstones, mudstones and

coalfields
.

Permian

The

tholeiitic basalt of the Whin Sill was emplaced during early Permian times. As much as 215 cubic kilometres of quartz-dolerite may have been emplaced within lower Carboniferous bedrock in a sheet which extends to more than 4500 square kilometres of Northumberland and county Durham and which is typically 30m thick. A series of dyke sub-swarms is associated with the sill. Those within Northumberland are referred to as the Holy Island, High Green and St. Oswald's subswarms. The sill provides for characterful topography at Dunstanburgh, Bamburgh, Lindisfarne and neighbouring districts including the Farne Islands, offering several good sites for the construction of castles. Further south it provides the extended north-facing scarp on which the Roman emperor Hadrian had his eponymous wall
built.

Palaeogene

Numerous dykes of

Sunderland subswarm of broadly parallel dykes are recognised as likely emanating from the same source, the Mull igneous centre in the west of Scotland.[3]

Structure

Northumberland sits above the

Caledonian Orogeny. During Carboniferous times, the Northumberland basin occupied the ground between the Cheviot block to the north and the Alston Block
to the south.

Quaternary

Glacial legacy

The larger part of the county is mantled by glacial

glacio-fluvial deposits, is assigned to the Caledonia Glacigenic Group; within Northumberland, several different sub-groups are recognised according to the source of the material. North of the Cheviot massif, the till is assigned to the Borders Subgroup and to the south to the North Pennine Subgroup whilst that associated with the massif itself is classed as Cheviot Subgroup. Material originating from offshore (in terms of the present position of the coastline) is assigned to the North Sea Coast Subgroup, though the material along the coast from around Beadnell southwards is of mixed North Sea/Pennine provenance. The Pennine tills are generally dark grey reflecting the nature of the Carboniferous bedrock from which they largely originate.[4][5]

Blown sand

Much of the coast is backed by areas of blown sand, notably at Ross Links south of Lindisfarne, Druridge Bay, at Lynemouth and to the north and south of Blyth.

Raised beach

Raised beach deposits are recorded at Spittal, Berwick-upon-Tweed, at Lindisfarne and around Budle Bay and elsewhere.[6]

Peat

Large parts of Northumberland's uplands are blanketed by peat.

Alluvium

The floors of the main river valleys are formed by

River terraces are evident along the Tyne valley and three terraces are developed along that of the River Tweed
. Terraces are also developed along the course of the Till, Aln, Coquet, Font, Wansbeck and Breamish.

See also

Further reading

British Geological Survey 1:50,000 scale geological map series sheets (England and Wales) 1-10 & 12-15, 18-20 & 24-25 and accompanying memoirs.

References

  1. ^ British Geological Survey 1:625,000 scale geological map Bedrock Geology UK North 5th Edn. NERC 2007
  2. ^ "BGS Lexicon of Named Rock Units - Result Details". Bgs.ac.uk. Retrieved 17 February 2019.
  3. ^ Stone, P. et al 2010 British Regional Geology: Northern England (5th edn) (Keyworth, Nottingham: British Geological Survey),pp184-5
  4. ^ Stone, P. et al 2010 British Regional Geology: Northern England (5th edn) (Keyworth, Nottingham: British Geological Survey), pp212-3
  5. ^ British Geological Survey 1:625,000 scale geological map Quaternary Map of the United Kingdom South 1st Edn. 1977
  6. ^ BGS 1:50,000 scale geological map sheets (England and Wales series) sheet 1&2 Berwick-upon-Tweed and Norham & sheet 4 Holy Island
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