ARCHITECTURE AND EVOLUTION OF TIDAL POINT BARS: INFLUENCE OF THE HYDRODYNAMIC PROCESSES ON THE SEDIMENTARY RECORD

Point bars, forming in meandering channels, are areas of high sediment deposition. In tidal environments, point bars have a distinct evolution and heterogeneous distribution of muds and sands, compared to those forming in purely fluvial systems. Although the sedimentation processes and hydrodynamic conditions controlling the development of fluvial point bars are well documented and understood, studies of bar development in tidally-influenced channels are scarce. Tidal point bars, however, are common features occurring on a range of scales in most backbarrier and estuarine systems, for example, tidal point bars with lengths over 3.5 km are observed at meander bends in tidal channels of the Ganges-Brahmaputra delta, and may represent economically important subsurface hydrocarbon reservoirs, for example, the fluvial-estuarine point bars of the McMurray Formation, in northeastern Alberta, Canada. These features are equally important geomorphic features in terms of source-to-sink sediment pathways, and sediment supply to proximal wetlands. In order to examine the evolution of these systems and to address the uncertainties in connectivity and continuity of that type of reservoir, we need to understand the variation in tidal asymmetry contribute to the evolution of tidal point bars and the development of their internal architecture. Therefore, 6 modern tidal point bars, located along the Georgia coast and distributed across a gradient of tidal to fluvial-influence, were selected for investigation. Sedimentological analysis of 32 vibracores extracted from the bars show changes in lithology, grain size, bioturbation and presence of rhythmic sets of Inclined Heterolithic Stratification (IHS). The site with highest river-influence, in the zone of bed load convergence and turbidity maximum, was found to be muddier with thick massive beds of clay intercalated with beds of fine to medium sand, while the bars situated in tidally-dominated meanders, in the zones controlled by the preferential pathways of the bi-directional flows, are comprised of thin layers of silt intercalated with finer sands, presenting a more complex and heterogeneous architecture due to a higher percentage of IHS and bi-directional bedforms.