Influence of delta growth on paleo‐tidal flow: Fraser River delta, British Columbia—Part 1: Geological framework and evolution of the delta

Abstract

The delta of the Fraser River has been growing for the last 9000 years into the strongly tidal strait of Georgia (5 m tidal range), an estuary between Vancouver Island and the mainland of the province of British Columbia. As the delta grew, it had an impact on the tidal flows adjacent to its shores. The objective of this research was to model tidal flows at different stages of the delta's growth during the late Quaternary. This chronological analysis of tidal flows and delta growth was possible because of the number of published radiocarbon ages as well as the detailed knowledge of the surface geomorphology and subsurface geology of this delta that is now available.

Four major units form the lithostratigraphic sequence of the delta: Unit 1 is a silt with thin sand beds formed in a delta‐front environment; Unit 2 is a sand with increasing amounts of silt in the upper part of the unit, formed in the lower tidal flats; Unit 3 is an organic rich silt containing peat interbeds and the Mazama ash, formed from both tidal marsh and floodplain silts; Unit 4 is a peat.

Estimates of the present advance of the delta vary from 2.3 to 3.1 m a⁻¹. To extend this analysis of delta progradation, maps of the delta's shoreline at different stages from 9000 years ago to the present were produced.