Pre-European settlement paleoenvironments along the lower Saint-Charles River, Québec City (Canada)

Abstract

Geographical and high-resolution paleoecological data from a stratigraphic section recovered at the Intendant's Palace archeological site (PDI) were used to reconstruct the environmental setting that existed when Europeans first started to settle in Québec City's Lower Town. The reconstruction covers the period from 1310–520 cal BP to the permanent establishment of Europeans at the turn of the 17th century. Evidence of human settlement at PDI has been found on floodplain deposits overlying marine sands associated with the Mitis transgression (1975 cal BP) at 4–4.5 m above sea level. A second site (Chateauguay: CHAT) approximately 3 km upstream and at a higher elevation (18.8 m) enabled a paleoenvironmental reconstruction from the middle Holocene (6850 cal BP) to 490 cal BP. A 14C date on a waterworn white cedar (Thuja occidentalis) tree trunk at the bottom of the CHAT section provided an age of 4690 cal BP, an indication that the site was likely inundated during an exceptional hydrological event (storm or high tide) associated with the mid- Holocene Laurentian transgression (6600–4450 cal BP). Fluvial environments, corresponding to low energy sedimentary conditions, and wetlands along the lower Saint-Charles River were reconstructed from 66 and 33 taxa collected at the PDI and CHAT sites, respectively. Macrofossil assemblages at both sites indicate that the composition of the late Holocene plant communities was largely influenced by the local topography and proximity to the river bank. The CHAT site was first characterized by the presence of nearby mesophytic forest communities (Pinus strobus, Sambucus, Aralia). During the late Holocene, plant communities formed a mosaic that reflected both well- and poorly drained conditions (Betula alleghaniensis and Juglans cinerea on low ridges; Picea mariana, Larix laricina, and Thuja in depressions). At PDI, 2 episodes of sand deposition alternated with 2 episodes of organic accumulation (Thuja, Alnus, Picea) in less than 2000 y.