The Quaternary sediments of Banquereau, Scotian Shelf
The acoustic stratigraphy of Quaternary sediments on Banquereau, Scotian Shelf, interpreted from regional and site-survey seismic lines, is correlated with sedimentary units determined from undisturbed borehole samples. The informal litho-stratigraphic formations of the Quaternary sequence on the Scotian Shelf are subdivided into members and litho-chronozones diagnostic of depositional environments. A late Wisconsinan glacial advance, dated by C 14 analysis of shell material, took place ca. 18,000 to 26,000 yr B.P. It formed a widespread, gravel-rich unit barren of fauna and capped by an erosional surface. The unit occurs within stratified pro-glacial marine sediments known locally as the “Emerald silt formation.” The minimum stand of sea level, 110 m below present sea level, occurred ca. 14,000 yr B.P. and is confirmed by the presence of channel deposits at the top of the Pleistocene section. A marine transgression across Banquereau took place ca. 8,000 yr B.P. and is defined by a widespread erosion surface at the base of the Holocene section. This section, known locally as the “Sable Island sand and gravel formation,” comprises as much as 40 m of reworked sand which is divided into 3 members diagnostic of sand-ridge generation. Eastern Shoal, an offshore storm ridge situated on Banquereau, was formed during Holocene time, created by modern-day, storm-driven and tidal currents. The intensity of these currents is the result of water-mass acceleration over the shallow banks of the Scotian Shelf. Eastern Shoal appears to have moved 30 km across the continental shelf at a rate of ∼3–5 m/yr. The regional setting of this sand body is similar to that postulated for the Shannon and Tocito Sandstones of the Western Interior of the United States and shows that sand transport and large-scale ridge development can take place in a shelf-edge setting on present-day, storm-dominated continental shelves.