The Mesozoic development of aseismic continental margins

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Abstract
Mesozoic basin development with in the North-west European Continental Shelf took place in belts peripheral to old Palaeozoic massifs. The area was dominated by vertical tectonic movements from the end of the Hercynian orogeny, and basin development along characterized by intermittent marginal faulting and graben formation dated as Permian, Triassic, and Lower, Middle and Upper Jurassic. On a world scale the Mesozoic basin development and the subsequent late-Mesozoic separation of the elements of the North Atlantic and Gondwanaland was the final episode of a long-continued subsidence, peripheral to ancient blocks defined during Palaeozoic times. Marine transgression on or close to the later sutures is recognized in the Lower Palaeozoic in eastern America, West Africa, South Africa and Western Australia. Faulted basin development along what were to become the world's Atlantic-type ('aseismic') margins became widespread by the Permian, and continued intermittently until the Middle Cretaceous. Widely around the world the long-established Mesozoic regime of synsedimentary graben formation and intermittent major faulting ended with an Aptian transgression, and was replaced by a regime of simple miogeosynclinal subsidence with prograding sedimentation which has continued to the present day. In Greenland and the Grand Banks of Canada, in Gabon and Australia, the history is strikingly similar to that of Northwest Europe, on what are now open ocean coasts. Thick earlier sediments are related to fault-controlled subsidences and rifts, a regime which was replaced worldwide within a very short period, by prograding basinal sedimentation in which faulting played a minor or very local role, and in which beds of Middle Cretaceous or somewhat earlier date transgress the planed-off structures of the previous regime. Although this relationship is not universal, there is a broad uniformity in the dating of the fundamental change in the style of aseismic marginal basins despite the different dates ascribed to opening of adjoining oceans. This requires a world-wide mechanism, not yet understood.

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