ABSTRACT: Indices de fluctuations mineures du niveau marin relatif à l'Holocène Supérieur, à l'isle-verte, côte sud de l'estuaire du Saint-laurent, Québec. [Geomorphic observations on the tidal flat and the low terrace at Isle-Verte, south shore of the St. Lawrence estuary.].

CGRG Bibliography of Canadian Geomorphology
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Recent field work at Isle-Verte on the south shore of the lower St. Lawrence estuary provided evidence for minor relative sea-level fluctuations (RSL) during the second half of the Holocene. At this locality, the shore is characterized by a wide tidal flat, a low emerged terrace and a former cliff. The tidal flat and the substrate of the low terrace are an erosion surface cut into glacio-marine clay of the Goldthwait Sea, most likely during the Laurentian transgression. Also cut in marine clay, the former cliff belongs to the same event. A 14C date on Mya arenaria in growth position around a small boulder at the surface of the clay platform released an age of 4 ka providing a minimum age for the erosion surface. The low terrace at the foot of the former cliff is made of fine-grained sediments (silt and fine sand). The age of the inner section at 5-6 m a.s.l. (south side of the national road 132), which is locally covered by sand and gravel, is probably about 2 ka, which is the average age of the Mitis terrace on both shores of the St. Lawrence estuary. The outer section at 4-5 m a.s.l. is younger. At the outlet of Riviere Verte, a tidal flat deposit overlying fluvial gravel dated 1.4 to 1.6 ka was emplaced during a minor RSL (Â± 1 m) fluctuation which occurred during the last millenium. Two tidal flat deposit units underlying the modern high marsh were also built during the same period. Presently, a relative stability seems to characterize the shoreline at Isle-Verte.

Bibliography of Canadian Geomorphology