Subsidence and sedimentation in semi-starved half-graben: a model based on North Sea data

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Abstract
By combining simple extensional fault-block geometries with overall tectonic subsidence curves generated by geodynamic mechanisms such as uniform lithospheric stretching, it is possible to generate forward tectono-stratigraphic models of basin evolution. Previous studies have used simplistic assumptions about sedimentation, e.g. that half-graben were filled to sea level or to the crests of their constituent fault blocks. A better appreciation of the range of possible natural geometries can be obtained by inputting subsidence and sedimentation histories derived by observation of a real sedimentary basin. The central North Sea is a well studied basin which in general terms can be explained by a simple model of uniform lithospheric stretching in the Late Jurassic, followed by thermal subsidence to the present day. Long-period departures from this model principally reflect the waning thermal effect of Permo-Triassic rifting, but short-period complications are shown to result primarily from variations in the externally controlled sediment input rate. Periods of sediment starvation permitted a substantial increase in water depth, and subsequent rapid sediment input resulted in episodes of load-driven subsidence. Three typical central North Sea subsidence histories have been combined with a simple model of domino faulting with a 10 km initial fault spacing. Contrasting depositional geometries, with or without the emergence of footwall islands, result from relatively subtle variations in sediment input rate within a small area which can reasonably be inferred to have had a consistent tectonic history.

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