Substrates of the Strait of Georgia, British Columbia

The subtidal floor of the Strait of Georgia west of the Fraser River Delta and north to Texada Island is blanketed mainly by silt and clay derived from the Fraser River and from failed deposits at the delta front. On the western part of the Strait south of the delta to the San Juan and Orcas islands, sediments are mainly lag sand and gravel eroded from Pleistocene deposits by strong tidal currents. East of this area in a more sheltered embayed part of the Strait the seafloor is covered by silt and clay derived from local mainland streams and possibly from the Fraser River. North of southern Texada Island, influence of the Fraser River also has been minimal. Although bottoms of basins in this part of the Strait are blanketed by mud, coarser sediments are dominant elsewhere. Substrate materials in the northern Strait are products of wave and current reworking of Pleistocene deposits and deposition from local streams and rivers. The shoreline of the Strait is mainly rocky but includes sand and/or gravel beaches and deltaic tidal flats. Development of the intertidal zone has been controlled by Pleistocene glaciation, postglacial changes in sea level, local wave and current regimes, and sediment availability.