Jurassic: Pangaea break-up and birth of the Atlantic Ocean

Crustal extension across the Triassic–Jurassic boundary at c. 201 Ma marked the beginning of the break-up of the Pangaea super- continent, leading to the formation of shallow-marine basins and the opening of ocean gateways. In NW Europe the Jurassic Period is characterized by extension between the Laurentian, Baltic and Ava- lonian shields to form a series of fault-bounded sedimentary basins that ultimately culminated in seafloor spreading and the creation of the North Atlantic Ocean. These rift basins formed between Europe and North America/Greenland with variable links to the Tethyan and Arctic oceans. Throughout, the Scottish mainland, together with the Orkney and Shetland islands and the Central North Sea High, formed a divide in the evolving North Atlantic rift system (Fig. 12.1). This separates an eastern ‘Arctic’ branch of North Sea basins, which extends southwards towards Denmark and central Europe, from a western ‘Atlantic’ branch, which trends through the Inner Hebrides to the Rockall Basin and basins west of Ireland, and ultimately south towards Portugal and NW Africa. Doré et al. (1999) and Roberts et al. (1999) suggested that the Arctic and proto- Atlantic rift systems remained separate until at least the Late Jurassic or even Mid-Cretaceous, with only earlier fragmentary and discon- tinuous connections. In contrast, a number of authors (Ziegler 1992; Coward et al. 2003; Pharaoh et al. 2010) consider that a fully con- nected rift system developed much earlier, from the Permian onwards. Jurassic sediments in these rift basins subsequently pro- vided key source and reservoir rocks that developed significant hydrocarbon resources.