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Evidence for multi-phase rifting in the North Falklands Basin

Abstract The post-Gondwanide basin development of the North Falklands Shelf has been evaluated using seismic sequence stratigraphy to determine the structural and stratigraphic evolution of the region. Two areally distinct post-Gondwanide basin systems (megasequences) are identified on the North Falklands Shelf, each with an independent structural and stratigraphic history. This contrasts with published models which interpret all basin areas to have been initiated in the early-mid Jurassic. Megasequence I is developed in a series of northwest and subsidiary north and east trending half-graben, and typically shows sedimentary growth into faults indicating an active rifting environment. Pervasive small-scale synthetic faulting is largely non-rotational, suggesting that it represents later deformation. No post-rift sediments associated with this phase of extension are identified. Comparisons with seismic geometries of other basins in the region, based on a restored plate model, indicate that Megasequence I represents part of a widespread mid-late Jurassic rifting event, ultimately leading to the opening of the Rocas Verdes (oceanic) Basin. Megasequence I is cross-cut by a north trending half-graben system which represents a failed arm of the South Atlantic Rift. The sedimentary fill of this basin, Megasequence II, can be subdivided into two units. The lower unit locally demonstrates sedimentary growth into the main eastern bounding fault of the half-graben and is thought to represent the synrift phase of Atlantic extension. Within the upper unit of Megasequence II there is no evidence of fault-controlled sediment growth into the main easterly bounding fault and the overall geometry is indicative of passive fill of pre-existing topography, supporting a post-rift origin for this section. Similar seismic geometries are observed in parts of the North Atlantic Rift System and the northern North Sea. In particular, the North Shetland Basin has a Permo-Triassic to late Jurassic rift and post-rift section. Renewed extension in the early Cretaceous resulted in break-up and domino faulting, with the generation of high relief fault blocks. The intervening lows were sites of deposition for onlapping deepwater sediments.