Regional tectonics in relation to Permo-Carboniferous hydrocarbon potential, Southern North Sea Basin: Difference between revisions

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'''By K. W. Glennie Department of Geology & Petroleum Geology, University of Aberdeen, Aberdeen AB9 2UE'''
'''By K. W. Glennie Department of Geology & Petroleum Geology, University of Aberdeen, Aberdeen AB9 2UE'''

Revision as of 08:24, 27 July 2019

From: Carboniferous hydrocarbon resources: the southern North Sea and surrounding onshore areas, edited by J. D. Collinson, D. J. Evans, D. W. Holliday, N. S. Jones. Published as volume 7 in the Occasional Publications series of the Yorkshire Geological Society , Copyright Yorkshire Geological Society 2005.

By K. W. Glennie Department of Geology & Petroleum Geology, University of Aberdeen, Aberdeen AB9 2UE

From: Pages 1–12 of Carboniferous hydrocarbon resources: the southern North Sea and surrounding onshore areas, edited by J. D. Collinson, D. J. Evans, D. W. Holliday, N. S. Jones. Published as volume 7 in the Occasional Publications series of the Yorkshire Geological Society, © Yorkshire Geological Society 2005.

Summary

The tectonic development of the Southern North Sea Basin during the Permo-Carboniferous was the outcome of geological events that began in the Early Palaeozoic when Scotland–Greenland and England–Baltica were on opposite sides of the Iapetus Ocean, which lay within the Southern Hemisphere. Closure of the Iapetus Ocean, completed by the end of the Silurian, resulted in the formation of the Scottish and Scandinavian Caledonides, and associated Siluro-Devonian granite intrusions. Gondwana-derived Avalonia (Nova Scotia–England) drifted northwards across the Equator more rapidly than Laurentia–Baltica did. Closure of the more southerly Rheic Ocean began in the Viséan, eventually forming the Hercynian–Variscan Fold Belt across Appalachia and central Europe. The northward drift had a strong climatic influence on the sediment types deposited from the Devonian to the end-Permian. Reactivated structural relief inherited from the Caledonian orogeny controlled Early Carboniferous sedimentation. The Carboniferous sequence was deformed and truncated prior to deposition of the Late Permian Rotliegend reservoir rocks. Equatorial Carboniferous coals are probably the source all the gas found in the overlying Rotliegend desert sandstones of the Southern Permian Basin. The latest Permian Zechstein Sea transgressed the area via a young Viking–Central graben system. Post-Permian subsidence carried Coal Measures to depths and temperatures at which methane was generated. Gas in Late Westphalian–Stephanian red sandstones is capped by Rotliegend claystones and salts, and in Rotliegend reservoirs by Zechstein salt, which forms an almost perfect top seal.

Carboniferous coals provided much of the energy that drove the Industrial Revolution in Britain during the eighteenth and nineteenth centuries. Coals and associated carbonaceous shales are the source of major volumes of methane, especially in The Netherlands and beneath the Southern North Sea, which have been exploited only since the 1960s. These coal-bearing beds are distributed in an apparently simple west–east zone that, prior to the opening of the Atlantic Ocean, extended from the Appalachian Mountains of North America (e.g. Ziegler 1987, 1990, Calder 1998, Scott 1998), across South Wales (where many coals have been converted to anthracite), central England, the Midland Valley of Scotland, and beneath especially the Southern North Sea, The Netherlands, northern Germany and Poland to Russia. In detail, the depositional and structural history of the belt is relatively complex.

The Carboniferous rocks of the British Isles are underlain by older Palaeozoic marine sedimentary rocks, similar to those of the Welsh highlands and the Lake District and, locally, by Devonian sequences (mostly terrestrial). These rocks are the product of deposition in and around the Iapetus Ocean, and their deposition was associated with the relative movement of crustal plates that led, in the Late Silurian and Devonian, to the Caledonian orogeny and a more or less unified British Isles.