Morphology, lateral migration, and internal structures of shoreface-connected ridges, Sable Island Bank, Nova Scotia, Canada

Abstract

An extensive complex of shoreface-connected ridges is present around Sable Island, near the outer edge of the Canadian east coast shelf. Two orders or ridges occur: the larger, first-order ridges are longer, wider, and higher than ridges along the east coast of the US, whereas the superimposed second-order ridges are smaller. All of the ridges converge eastward with the shoreface at angles up to 90/sup 0/. Sediment grain size becomes finer eastward over each ridge, the finest sediment occurring at the base of the eastern flank. Landward-facing, straight-crested megaripples and sandwaves are present in the troughs, whereas hummocky megaripples occur on the ridge crests. Eastward migration of the ridges will produce a 3-20-m-thick, upward-coarsening sequence that rests on an upward-fining basal lag. Cross-bedding predominates throughout the sequence, although the upper part may contain hummocky cross-stratification. The differences between the US and the Canadian ridges are due to a more intense storm climate and to obliquely onshore, rather than obliquely offshore, geostrophic flows in the Sable Island area; nevertheless, the sedimentological patterns over the ridges in both areas are similar. 17 references, 5 figures.