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Natural Resources Canada > Earth Sciences Sector > Priorities > Sustainable development of natural resources > Consolidating Canada's geoscience knowledge > Scotian Margin
Geology of the Scotian Margin Geologic overview
The evolution of the Scotian Margin is just the latest chapter in the long and complicated history of ocean closures and openings in this region. Atlantic Canada sits astride the eroded remnants of the Appalachian Orogen, which is comprised of several terranes and continental fragments brought together during closure of the Iapetus Ocean.
Mainland Nova Scotia is bisected by the Cobequid-Chedabucto fault system, which links the Bay of Fundy with Chedabucto Bay. South of this fault system lie metasedimentary rocks of the Meguma Terrane, and intruded rocks of the South Mountain batholith such as the granites seen at Peggy's Cove. North of the fault zone lie volcanic and sedimentary rocks of the Avalon Terrane, similar to those recognized in the southern parts of Newfoundland and New Brunswick.
Animation showing separation of African and North American plates and northward movement of Scotian Margin (yellow dot). Plate reconstructions from www.odsn.de based on work of Hay et al. (1999) |
During the initial break-up of Pangaea in the early Triassic, extension of the continental crust along the eastern margin of North America led to the formation of numerous elongate rift basins, including the Fundy and Orpheus Basins that developed along the re-activated plate boundary between the Meguma and Avalon terranes. As extension continued the locus of continental break-up shifted seaward to the location of the present-day continental margin. Small fault-bounded basins continued to form and deepen as the lithosphere stretched and thinned. Sands and muds from the eroding Appalachians were deposited in these basins, followed by thick deposits of salt that formed when shallow waters of the nearby Tethys Ocean extended into the region and periodically evaporated.
Paleogeography approximately 210 million years ago.
(Modified from figure from John Wade)
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Eventually, in the Early Jurassic the continent broke apart and the African plate started moving away from the North American plate. Magma that extruded at the spreading centre cooled to form oceanic crust, a process that continues today at the mid-Atlantic Ridge. The edges of the rift zone, no longer under extensional stress, began to cool and subside, forming broad depressions that incorporated the former small rift basins. Off Nova Scotia, sands and shales brought to the coast by river systems began filling the young Scotian Basin, with thickest accumulations at the large deltas which formed at the mouths of major drainage systems. Elsewhere, reefs developed parallel to the shoreline in the warm shallow seas.
Paleogeography approximately 150 million years ago.
(Modified from figure from John Wade)
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During the Cretaceous, the sediments brought to the coast by river systems became finer, predominantly silts and muds. Sea level rose but temperatures remained warm, allowing the deposition of marine sediments such as limestone and chalk on the Scotian Shelf.
Paleogeography approximately 135 million years ago.
(Modified from figure from John Wade)
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The ancestral Maritime region was mostly above sea level during the Tertiary and sediments eroded from the land were deposited offshore on the broad continental shelf. Falling sea levels and cooler temperatures led to a change in sediment type from the muds and limestone of the previous period to coarser material, predominantly sands.
Paleogeography approximately 30 million years ago.
(Modified from figure from John Wade)
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Today the Scotian Basin encompasses an area of over 300 000 square kilometres beneath the continental shelf and slope, and includes up to 20 km thickness of sedimentary rocks in its deepest areas south and east of Sable Island.
[Reference: Hay, W.W., DeConto, R., Wold, C.N., Wilson, K.M., Voigt, S., Schulz, M., Wold-Rossby, A., Dullo, W.-C., Ronov, A.B., Balukhovsky, A.N. and E. Soeding (1999): ALTERNATIVE GLOBAL CRETACEOUS PALEOGEOGRAPHY, in Barrera, E. and Johnson, C. (eds.), The Evolution of Cretaceous Ocean/Climate Systems, Geological Society of America Special Paper 332, pp. 1-47.]
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