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.

Impact of anthropogenic subsidence on relative sea-level rise in the Fraser River delta

“…The Holocene part of the Fraser delta was built during the past 10 ka, after the retreat of the Cordilleran Ice Sheet (Clague et al, 1998), and currently is near sea level (Fig. 1).…”

“…Depth to Tertiary bedrock beneath the delta varies between 200 and 1000 m (Britton et al, 1995). Thus, significant variations in present-day vertical motions are expected, given the variations in lithology, deposition history, and thickness of the Quaternary units (Clague et al, 1998). In addition, the Tertiary bedrock surface may be deforming regionally in response to earthquake-cycle loading of the Cascadia subduction zone and postglacial rebound.…”

Seasonal Controls On the Development And Character of Inclined Heterolithic Stratification In A Tide-Influenced, Fluvially Dominated Channel: Fraser River, Canada

“…2.1). The last glacial period in the region, the Fraser Glaciation, began 25-30 ka, and ended with glacial retreat 11-13 ka (end of the Pleistocene Epoch; Clague et al, 1998) …”

Site period estimations in the Fraser River delta using microtremor measurements - experimental and analytical studies

“…These sediments overlie Pleistocene sediments, which in turn overlie the Tertiary bedrock. Amplification potential varies greatly over the delta as the thickness of the Holocene sediments is extremely variable and the bedrock surface beneath the delta is highly irregular [3,4]. The largest ground accelerations during two past earthquakes were recorded near the edge of the delta rather than on the thickest sediments [5].…”