Weald Basin

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Section across southern England showing the inverted nature of the Weald Basin

The Weald Basin (

Wealden Anticline. The rock strata contain hydrocarbon
deposits which have yielded coal, oil and gas.

Formation

Geologic map of southeast England and the region around the English Channel, showing the Weald-Artois anticline and therefore the modern day form of the Weald Basin in its regional context

The Weald Basin's formation commenced during the

Variscan Orogeny, with the land now occupied by the Weald Basin being a low external fold belt to the main orogeny, which was located within the present day English Channel.[2] The remnants of the mountain belt can be seen today in Devon and Cornwall in what is known as the Cornubian Massif. Unlike in Devon and Cornwall the deformation caused little or no metamorphism.[2]

The mountain belt collapsed soon after the orogeny, leading to the former northward thrusts to be reactivated as normal faults, and led to the formation of the Weald basin, which developed as an extension of the considerably larger Wessex Basin .

London-Brabant Massif, but it is not clear whether this reflects a syn-rift origin for these rocks.[4] The Weald basin gently subsided throughout the Jurassic, Cretaceous and Early Tertiary leading to a thick succession of sedimentary rocks being deposited. During the Early Jurassic a north and east shallowing mud-dominated shelf developed.[4]

Basin reactivation

Cross-sectional diagram of eroded layers of geological anticline with locations of towns indicated
Geological section from north to south of the Wealden Anticline, note the unsymmetrical lower Cretaceous/Jurassic sediments in the core of the anticline. The diagram has undergone extensive vertical exaggeration

As a result of the Alpine orogeny the basin was squeezed between the basement to

Wealden Anticline and the Channel High, are superimposed upon earlier, Mesozoic basins, (the Weald and Channel basins). This nearly exact superimposition of compressional features upon underlying formerly extensional features exemplifies perfectly the principles of structural inversion across a large and well defined geologic feature.[5]
The overall uplift produced by the Tertiary inversion in the eastern Wealden basin has been estimated to be as much as 1525 m; which as a result of the large amount of Mesozoic sediments does not reveal the underlying Paleozoic basement.[2] Utilising estimations of the original thickness of Chalk (400–460 m) and other Mesozoic strata indicate a complex fold structure which, in the event it was not eroded during uplift, attained a crestal elevation of 1400 m over what is today Ashdown Forest.[6] However it is likely that erosion kept pace with uplift, resulting in large quantities of sediment supply to the North Sea and the English Channel

Economic resources

Coal seams were discovered when test boring for an early proposal for a Channel Tunnel at Dover in 1890.[7] This led to the development of four deep mines in the Kent Coalfield in the early 20th century. The Weald Basin has yielded significant quantities of gypsum from Jurassic Purbeck beds and a number of brickworks exploit the lower Cretaceous clays.

The inversion of the Weald Basin throughout the late Cretaceous and early Tertiary resulted in the formation of the Wealden Anticline and a number of smaller anticlines within the larger structure. The discovery in 1897 of

hydraulic fracturing developing in southeast England centred on Balcombe where an exploratory well was planned and the Balcombe drilling protest was in progress.[13][14]

A BGS/

Department for Energy and Climate Change (DECC) report from May 2014 suggest that there is the possibility for the extraction of light tight oil (LTO) in Weald Basin and the average figure of 4.4 billion barrels (700 million cubic metres) is suggested. The overall range of estimations is from 2.2 to 8.6 billion barrels (350 to 1,370 million cubic metres). The data is said to have a "high degree of uncertainty", and the amount that could be produced is unknown, and could be zero.[15]

See also

References

  1. ^ Gibbons, Wes (1981). The Weald, Rocks and Fossils Field Guide. Unwin Paperbacks. p. 115.
  2. ^
    doi:10.1144/gsl.sp.1990.055.01.19
    . Retrieved 26 September 2010.
  3. doi:10.1144/gsl.sp.2002.196.01.06
    . Retrieved 26 September 2010.
  4. ^
    doi:10.1016/S0040-1951(03)00289-0
    .
  5. doi:10.1144/gsjgs.150.2.0311
    .
  6. doi:10.1144/GSL.SP.1999.162.01.03. Retrieved 27 September 2010.{{cite journal}}: CS1 maint: multiple names: authors list (link
    )
  7. ^ "Housing". Coalfields Heritage Initiative Kent. Dover: Dover District Council. Retrieved 24 July 2013.
  8. doi:10.1144/gsl.jgs.1898.054.01-04.39
    .
  9. doi:10.1144/gsl.sp.1998.133.01.03
    . Retrieved 27 September 2010.
  10. ^ "Minerals, Waste and County Development Planning Applications, Decisions and Appeals". Surrey County Council. 8 August 2011. Retrieved 3 September 2013.
  11. ^ "Oil and gas well discoveries since 1983". London: The National Archives. 17 December 2012. Archived from the original on 17 December 2012. Retrieved 3 September 2013.
  12. ^ "Mineral Planning Factsheet - Onshore Oil and Gas". British Geological survey. March 2011. pp. 4, 10. Retrieved 30 June 2013.
  13. ^ Stanley Reed (May 24, 2013). "British Villagers, Fearing Fracking, Protest Plan for Drilling". The New York Times. Retrieved May 25, 2013.
  14. ^ Geoffrey Lean (June 28, 2013). "Fracking faces tough foes in leafy Sussex Shale gas and oil may hold the key to Britain's energy troubles – but not if grassroots protesters have their way". The Telegraph. Archived from the original on July 2, 2013. Retrieved June 29, 2013.
  15. ^ Andrews, I. J. (2014). The Jurassic shales of the Weald Basin: geology and shale oil and shale gas resource estimation (PDF) (Report). London, UK: British Geological Survey for Department of Energy and Climate Change. Retrieved 16 October 2014.
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