The monsoonal Mitchell River delta and megafan shows minimal anthropogenic disturbance and thus provides a unique opportunity to examine the autogenic and allogenic controls on the evolution of deltas and fluvial megafans. Detailed mapping, vibracoring, trenching and topographic surveying were used to characterize the palaeodistributary channel belts on the megafan and the depositional elements that comprise the delta. Chronological analyses of these data facilitated the reconstruction of the megafan and delta evolution and enabled the identification of discrete periods of delta progradation within the last 6000 years. These results indicate that sediment distribution is controlled primarily by two types of avulsion: (1) delta avulsions, which are frequent (>16/1000 years), typically backwater-mediated and associated with local shifts in sedimentation loci; and (2) megafan avulsions, which are less frequent (>3/1000 years), but which are also associated with more significant shifts in depositional loci. These links between megafan and delta processes and geomorphology in the Mitchell River region were integrated to develop a new model of channel belt facies associated with fluvial (F), fluvial backwater-affected (FBW), fluvial-dominated, tide-influenced (Ft) and tide-dominated, fluvial-influenced (Tf) channels. This model enables improved predictions of channel belt composition in modern and ancient marginal-marine systems by providing sedimentological and ichnological criteria for distinguishing between channel types.
Supplementary material: Mitchell River region optically stimulated luminescence (OSL) dating methodology and results are available at https://doi.org/10.6084/m9.figshare.c.3280949
Figures & Tables
Paralic reservoirs reflect a range of depositional environments including deltas, shoreline-shelf systems and estuaries. They provide the backbone of production in many mature basins, and contribute significantly to global conventional hydrocarbon production. However, the range of environments, together with relative sea-level and sediment supply changes, result in significant variability in their stratigraphic architecture and sedimentological heterogeneity, which translates into complex patterns of reservoir distribution and production that are challenging to predict, optimize and manage.
This volume presents new research and developments in established approaches to the exploration and production of paralic reservoirs. The 13 papers in the volume are grouped into three thematic sections, which address: the sedimentological characterization of paralic reservoirs using subsurface data; lithological heterogeneity in paralic depositional systems arising from the influence of tidal currents; and paralic reservoir analogue studies of modern sediments and ancient outcrops. The volume demonstrates that heterogeneity in paralic reservoirs is increasingly well understood at all scales, but highlights gaps in our knowledge and areas of current research.