The Rimouski shelf is a smooth-surfaced, gently sloping platform which gives way to the north to a steep, sometimes irregular margin of the Laurentian Trough. The surficial sediments are sandy and change rapidly over short distances particularly in areas close to the shore. A zone of well-sorted medium sands, littered in places with gravel, and surrounded by bands of finer, more poorly sorted sediment occupies the western half of the shelf. The central part of the shelf is also banded but fine-grained sediment is more abundant. Sand deposits reappear on the eastern edge of the study area, while uniform muds occur over the slope. These surface deposits are thin and appear to be related to modern shelf currents, ice rafting from the shore, and local sources of mud. Below the surface the deposits become more sandy and are often in sharp contact with a dense clay. The latter is correlated with the Goldthwait Sea clays of 9–12000 years BP. Available information suggests that the Goldthwait Sea regression continued past the present shorelines to permit the emplacement of the sandy deposits and then transgressed once more to about the present sea level during the last 9000 years.

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