Quaternary stratigraphy and evolution of the Fraser delta

Abstract

The Fraser River delta is underlain by thick Quaternary sediments and Tertiary sedimentary rocks separated by an unconformity with up to 800 m of relief. Pleistocene sediments consist mainly of sand and silt deposited in proglacial glaciomarine environments during several glaciations. These glacial sediments are separated by nonglacial marine deposits or, more commonly, by unconformities. The Pleistocene sequence is overlain by sediments of the Holocene Fraser River delta across a surface with up to 300 m of relief. The delta deposits comprise bottomset, foreset, and topset units. The bottomset unit consists mainly of clayey silt. Silty and sandy foreset deposits overlie the bottomset unit, and are unconformably overlain by 10 to 30 m of distributary- channel sands. The channel sands, which constitute the lower part of the topset unit, grade upward into several metres of intertidal and floodplain silts, and peat. The delta started to form about 10 000 years ago, when the Fraser River advanced its floodplain beyond the Pleistocene uplands at New Westminster. About 6000 years ago, the locus of deposition shifted from southward into Boundary Bay to westward into the Strait of Georgia proper.