Champlain Sea Paleoenvironments in the Quebec City area, 11300-9750 BP: the Saint-Nicolas site (Quebec).

Champlain Sea Paleoenvironments in the Quebec City area, 11 300-9750 BP, the Saint-Nicolas site (Quebec). At Saint-Nicolas, in the Quebec City Strait, tidal current sands of the Pleistocene-Holocene transition preserve an exceptional marine fossil fauna: 34 types of invertebrates in addition to the microfossils, three species of marine mammals, three species of seabirds and five species of fish, whose C-14 age varies between 10 060 and 9810 BP (delta(13)C = 0 parts per thousand). These sands are overlain by tidalites which correspond to the last phase of the Champlain Sea, until ca. 9750 BP. The lithological, geochemical, and paleontological data gathered in the area suggest that sedimentation took place in an archipelago which was located at the entrance of the Champlain Sea and was subjected to tides that reached levels on the order of 5 to 10 metres. The strong currents of the rising tide favored the late occurrence of salt water influx in the area. The archipelago protected the sedimentary units from erosion during ebb tide as well as from later fluvial erosion resulting from glacioisostatic rebound. Faunal diversity is associated with high marine productivity which is tied to the mixing of fresh and salt waters. The food web was composed of molluscs which were abundant at low tide, of fishes, walrus, seals, and birds that nested on the small rocky islands. This sedimentary and ecological system implies a stabilization of the relative sea level attributed to the early Holocene eustatic rise. The dissolved inorganic carbon effect in the Champlain Sea is assessed on the basis of a comparison of 14C ages obtained from marine shells and wood. Ages from marine shells (delta(13)C = 0 parts per thousand) are at least 350 y. older than stratigraphically equivalent wood ages (delta(13)C = 25 parts per thousand).