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The Fraser River Delta (FRD) is a large sedimentary system and home to Metro Vancouver, situated within the unceded territories of several First Nations. This review provides an overview of the geological evolution of the FRD, connecting hydrodynamic processes with sedimentary deposits across its diverse environments, from the river to the delta slope. The study emphasizes the implications of sedimentation and delta evolution for natural hazards and coastal/delta management, pinpointing knowledge gaps. Comprising four main zones—river, delta plain, tidal flats, and delta slope—the FRD is subject to several natural hazards, including subsidence, flooding, earthquakes, liquefaction, and tsunamis. The delta plain, bordering the Fraser River's distributary channels, hosts tidal marshes and flats, including both active and abandoned areas. Active tidal flats like Roberts Bank and Sturgeon Bank receive sediment directly from the Fraser River, while abandoned tidal flats, like those at Boundary Bay and Mud Bay, no longer receive sediment. The tidal flats transition into the delta slope, characterized by sand in the south and mud in the north of the Main Channel. The FRD's susceptibility to hazards necessitates protective measures, with approximately 250 km of dykes shielding the delta plain from river floods and storm surges. Subsidence amplifies the impact of rising sea levels. Earthquakes in the region can induce tsunamis, submarine slope failures, and liquefaction of delta sediments, emphasizing the importance of incorporating sedimentation patterns and delta evolution into management strategies for sustainable urban development, habitat restoration, and coastal defence initiatives. [ABSTRACT FROM AUTHOR]

The Fraser River Delta exhibits distinct asymmetry in the sedimentological and neoichnological characteristics of the updrift (south) and downdrift (north) sides of the main distributary channel in water depths below storm-wave base. The asymmetry is the result of net northward tidal flow. Tides erode sediments across the updrift delta front, whereas the downdrift delta front is an area of net deposition. A submarine channel prevents sand eroded from the updrift delta front from reaching the downdrift delta. The updrift delta front and updrift upper prodelta are composed of sand or heterolithic sand and mud that show a low density of burrowing (Bioturbation Index 0 to 3) and are dominated by simple traces. The downdrift delta front and prodelta, and the updrift lower prodelta are composed of homogeneous muds with significantly higher bioturbation intensities (Bioturbation Index 3 to 6), and a more diverse suite of traces akin to Cruziana Ichnofacies. Using the Fraser River Delta as an archetype and comparing the Fraser to the Amazon River Delta, a preliminary model for deep-water (below storm-wave base: ca 20 m) asymmetrical deltas is proposed. Firstly, deep-water asymmetrical deltas are recognized from sediments deposited below storm-wave base. At these depths, tidal and ocean currents are more likely to impact sediment transport, but wave processes are less effective as a sediment transport mechanism. Sediments deposited below storm-wave base in deep-water asymmetrical deltas will display the following: (i) the updrift delta front will be coarser-grained (for example, sand-dominated or heterolithic sand and mud), than the downdrift delta front (for example, mud-dominated); and (ii) the updrift delta front should show low-diversity suites of simple burrows. Depending on sedimentation rates, the downdrift delta front and prodelta may show either high diversity suites of traces that are dominated by both complex and simple burrows (low sedimentation rates) or low density and diversity suites akin to the updrift delta front (high sedimentation rates). [ABSTRACT FROM AUTHOR]

Abstract: The Fraser River delta front exhibits asymmetry with respect to its neoichnological, biological, and sedimentological characteristics on opposing sides of the main distributary channel, as well as the submarine canyon seaward of the channel. This phenomenon is attributed to asymmetric tidal flow, wherein there is a net northward tidal flow along the delta front. The southern delta front lying updrift of the Main Channel, is primarily composed of sandy beds and bedsets that exhibit low bioturbation intensities (BI 0–3) and limited biodiversity (H` 0.9–1.4). Tracemakers in the updrift delta front predominantly consist of polychaetes and bivalves that produce suites dominated by simple vertical and horizontal traces attributable to the Skolithos Ichnofacies. The suites consist of traces comparable to Thalassinoides, Planolites, Skolithos, rare Conichnus, and Cylindrichnus. The northern delta front lying downdrift of the Main Channel, and the prodelta consist of muddy beds and bedsets that display high bioturbation intensities (BI 3–6) and diverse infaunal populations (H` 1.4–2.3). Polychaetes, bivalves, and echinoderms comprise the main tracemakers, and these infauna produce complex and robust ichnological suites typical of the Cruziana Ichnofacies. The downdrift delta front and prodelta trace assemblage includes traces comparable to Skolithos, Planolites, Thalassinoides, Artichnus, Palaeophycus, Conichnus, Asterosoma, Rosselia, Cylindrichnus, Gyrolithes, Teichichnus, Phycosiphon, Arenicolites, Polykladichnus, and Scolicia. The spatial distribution (area and volume) of biogenically induced sediment disruption indicates that the updrift delta front is significantly less bioturbated than its downdrift counterpart. Additionally, the prodelta does not exhibit evidence of asymmetry with respect to its neoichnological character; all spatial variability is recorded in delta front positions. [Copyright &y& Elsevier]

Abstract: Three anomalous events (AEs) were recorded off the Fraser River, Canada during the freshet of 2008, and are ascribed to quasi-continuous gravity flows. These flows transport warm, low-salinity Fraser River waters to the upper delta front of the Fraser delta to at least 50m water depth. All flows occurred during the freshet and spring ebbing tide, and were characterized by deposition of fine-grained sand and silt beds with likely high-water contents. These sediments were susceptible to resuspension by the subsequent flood-tide current, producing very high near bed suspended sediment concentrations (SSC) with enough excess density to generate hyper-concentrated flows. Our observations show that these episodic events result from the combination of high river discharge, high SSC, and strong tides, and therefore, are likely to occur on the delta fronts of other large tide-dominated and tide-influenced rivers. In shallow-water basins (< 50m water depth), these tide-supported gravity flows can affect sediment deposition on both the delta front and prodelta. [Copyright &y& Elsevier]