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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 integration of geochemistry and sequence stratigraphic models in the study of shale formations is critical to the development of robust stratigraphic correlations and paleoenvironmental interpretations. The Middle and Upper Devonian Horn River Group is a prominent organic-rich shale sequence in northeastern British Columbia, Canada, and it also hosts major natural gas reserves. The availability of high-resolution geochemical data sets on five continuous cores and an independent core-based sequence stratigraphic framework provide new insights into the effects of relative sea-level changes on redox conditions, productivity, detrital flux, and organic matter enrichment patterns and their geographic variation. Sequence stratigraphic analysis documents three third-order transgressive-regressive cycles within the Horn River Group. Organic carbon content is typically enriched in transgressive systems tracts and depleted in regressive systems tracts. Correlations among total organic carbon (TOC) content and multiple geochemical proxies indicate that organic matter accumulation was controlled by redox conditions, bioproductivity, and detrital dilution, all of which were directly affected by relative sea-level fluctuations. Redox proxies are strongly correlated to TOC content, suggesting that redox conditions exerted a major control over organic carbon accumulation. Redox-sensitive traceelemental ratios and Corg-Fe-S relationships suggest that bottom water was less oxygenated during transgressions than regressions and in distal areas than in proximal parts of the basin. Productivity may have been linked to anoxia via mineralization of organic matter during periods of high productivity, resulting in water-column oxygen depletion. However, biogenic silica concentrations demonstrate enhanced productivity during transgressions, perhaps related to enhanced recycling of nutrients under anoxic conditions. Relative detrital sediment flux to the basin, as measured by aluminum and titanium concentrations, varied systematically as a function of relative sea level and paleogeographic position. Specifically, elevated detrital flux accompanied regressions and was greatest in proximal areas of the basin, resulting in dilution of organic matter concentration at these times in these regions of the basin. Our study demonstrates that relative sea-level fluctuations exerted substantial control on patterns of organic carbon enrichment. However, geochemical signatures of sea-level cycles vary with respect to paleogeographic location within the basin and are most obvious at intermediate locations and water depths, where sea-level falls brought chemoclines to the seabed and forced clastic sediments to the basin floor. [ABSTRACT FROM AUTHOR]

Organic matter (OM) accumulation in organic matter-rich mudstones, or black shales, is generally recognized to be controlled by combinations of bioproductivity, preservation, and dilution. However, specific triggers of OM deposition in these formations are commonly difficult to identify with geochemical proxies, in part because of feedbacks that cause geochemical proxies for these controls to vary synchronously. This apparent synchronicity is partly a function of sample spacing, commonly at decimeter to meter intervals, which may represent longer periods of time than is required for the development of feedbacks. Higher resolution data sets may be required to fully interpret OM accumulation.This study applies a novel combination of technologies to develop a high-resolution geochemical data set, integrating energy-dispersive X-ray fluorescence (EDXRF) and infrared imagery analyses, to record proxies for redox conditions, bioproductivity, and clastic and carbonate dilution in millimeter-resolution profiles of 133 core slabs from the Middle and Upper Devonian Horn River shale in the Western Canada Sedimentary Basin, which provides decadal-scale temporal resolution. A comparison to a more coarsely sampled data set from the same core results in substantially different interpretations of variations in bioproductivity, redox, and dilution proxies. Stratigraphic distributions of organic matter accumulation patterns (bioproductivity-control, siliciclastic/carbonate-dilution, and redox conditions-control) show that organic enrichment events were highly varied during deposition of the shale and were closely related to second- and third-order sea-level changes. High-resolution profiles indicate that bioproductivity was the predominant trigger for organic matter accumulation in a second-order highstand, particularly during deposition of third-order transgressive systems tracts. Organic matter accumulation was largely controlled by dilution from either carbonate or clastic sediments in a second-order lowstand. Bioproductivity-redox feedbacks developed on timescales of decades to centuries. [ABSTRACT FROM AUTHOR]