4.8 The Bay of Fundy and the tides of climate change
1.2 The Bay of Fundy, a complex geology
The Fundy basin was formed as an aborted rift (an aulacogen) at the Triassic-Jurassic transition, 220 million years ago, during the breakup of the supercontinent Pangea in the same event that led to the separation of North-America from Africa and Europe and to the formation of the North Atlantic Ocean. It is part of a series of graben that formed along the eastern margin of North-America. The formation of the rift valley was accompanied by intense volcanic activity, so that the Fundy basin and its edges are covered by tholeitic basalt, a type of basalt formed by underwater volcanic eruption, almost 10 km thick, mixed with sedimentary rocks amassing over a 65 million year period, first from fluvial origin during a time of high discharge, since the area was located near the paleoequator, later from braided rivers, alluvial fan and eolian deposition during drier conditions when the Fundy basin was in the subtropical belt and transitioning to a lacustrine/playa environment in the late Triassic (Hubert and Mertz, 1980; Leleu and Hartley, 2009; Wade et al., 1996). On the eastern side of the Fundy basin, along the Annapolis valley in Nova Scotia, this basalt forms the North Mountain, with steep cliffs up to 30 meters high over the Bay of Fundy. There are also basalt cliffs on the western side of the Bay of Fundy, along the Grand Main fault, between Brier Island and the Minas Basin. A second deformation episode during the early Jurassic gave the Fundy basin its synclinal shape (Withjack et al., 1995). Subsequently, the Fundy basin was flooded by the Atlantic and gradually filled by marine sediments. On the upper reaches, the shore is constituted of softer substrates such as sandstone and shale, which under the influence of erosion result in wide sand and mud flats and salt marshes.