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BRITAIN'S OFFSHORE OIL & GAS

*Forces


The forces that created Britain's offshore oil and gas basins and their structures were related to global plate tectonics. Widespread basin formation occurred in the Permian period during the crustal subsidence that followed the Variscan folding. Often it simply added to pre-existing Devonian and Carboniferous basins of the Older Cover, and carried on into the Mesozoic and Tertiary Eras. Many of these superimposed basins seemed to be aligned along the dominant structural 'grain' in their basements (F20).

In the North Sea, the two main Permian basins running east-west are most likely related to the adjacent Variscan fold-belt (F24). Whether or not the Permian basin subsidence represents the earliest sign of the opening of the Atlantic Ocean is highly controversial, but by the middle of the Jurassic Period the opening was well under way. It advanced northwards in the Cretaceous Period and in the early Tertiary Period the North Atlantic rapidly opened out. During a crucial Jurassic and Cretaceous phase of widespread crustal tension, the crust around Britain rifted. Located over rising columns of hot mantle, these rifts ('failed arms') never became oceans but were the initial phase in the two-stage mechanism of basin formation. Tearing movements also produced local 'pull-apart' basins. Compressions originating in the plate collisions that produced the Alps caused uplift and erosion (inversion) of basin contents.

F24: Basin-forming forces acting on the British crust 285 million to 60 million years ago



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