PALEOECOLOGY OF LATE-GLACIAL TERRESTRIAL DEPOSITS WITH IN SITU CONIFERS FROM THE SUBMERGED CONTINENTAL SHELF OF WESTERN CANADA AND ITS ARCHAEOLOGICAL IMPLICATIONS

Extensive portions of the continental shelf off the coast of British Columbia were subaerially exposed during Late Wisconsinan deglaciation due to lowering of relative sea level by as much as 150 m. It is likely that these ice-free lowlands served as a migration corridor for plants, animals and possibly humans. Paleoecological studies that reconstruct the nature and extent of the plant cover during this critical time are important for several reasons. In addition to determining local and regional vegetation dynamics, these studies describe potential sources of food, medicines, or fibres for early human migrants, and also provide proxy records of past climates. Until now, our understanding of the paleovegetation that grew on the emergent shelf during the late Pleistocene was based on only a few isolated samples from allochthonous plant fossils. We present the results of paleoecological analyses conducted at two sites on the submerged continental shelf where terrestrial surfaces with in situ conifers are preserved. The woody plant remains confirm that, during the latest period of subaerial exposure, terrestrial vegetation was well-established on the continental shelf. Microscopic identification of fossil wood, and analyses of pollen and plant macrofossils from the associated paleosols and overlying shallow pond sediments indicate that productive Pinus contorta-dominated communities with abundant Alnus crispa and ferns grew on the shelf adjacent to and on the Queen Charlotte Islands around 12,200 ¹⁴C yr B.P. Dwarf shrubs including Salix and Empetrum, and herbaceous plants such as Heracleum lanatum and Hippuris vulgaris were also important components of the shelf vegetation. Near northern Vancouver Island, mixed coniferous forests dominated by Pinus contorta with Picea, Tsuga spp., Alnus spp., and ferns occupied the shelf at 10,500 ¹⁴C yr B.P. Fossil pollen of Abronia latifolia indicates that beach vegetation grew along the ancient shoreline. Our analyses demonstrate that pollen analysis alone may be insufficient for paleoenvironmental reconstruction and should be accompanied by plant macrofossil analysis and fossil wood identification when possible, since both provide valuable and complementary paleoecological information.