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The AAPG/Datapages Combined Publications Database
Journal of Sedimentary Research (SEPM)
Recent Sediments of the St. Lawrence Middle Estuary
B. d'Anglejan, M. Brisebois
Little deposition takes place at the present in the St. Lawrence middle estuary. In the shallow marginal areas, broad unconformities under a thin cover of sandy muds reflect the dominance of erosional processes during the post-glacial emergence. Sands from nearby recessional moraines have been carried into the north channel troughs. Numerous sand dunes and ripples develop there. Over the central regions, a thin layer of inhomogeneous sandy sediments unconformably covers a deposit of massive grey muds, which seismic reflection data indicate to be possibly 15-30 meters thick resting over a well defined late glacial horizon. At the surface, the silt-to-clay ratio remains remarkably constant (about 3:1) in spite of highly variable proportions of sand, perhaps as a result of the continuous winnowing action of tidal currents which range between 10 cm/sec and 150 cm/sec near the bottom. In the underlying massive grey muds, X-ray radiographs reveal silty and less silty layers 2 to 3 cm thick. These muds were formed under a different sedimentation regime in which deposition from suspension must have been dominant.
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