Influence of Sediment Cohesion on Deltaic Morphodynamics and Stratigraphy Over Basin‐Filling Time Scales

• Published in: Journal of geophysical research. Earth surface 2017-10, Vol.122 (10), p.1808-1826
• Main Authors: Li, Qi, Matthew Benson, W., Harlan, Margaret, Robichaux, Patrick, Sha, Xiaoyu, Xu, Kehui, Straub, Kyle M.
• Format: Article
• Language: English
• Subjects: Channeling; Channels; Cohesion; delta; Environmental history; Fluvial deposits; Fluvial sediments; Geomorphology; Marine environment; Mobility; morphodynamics; Numerical experiments; Pumping; River channels; Rivers; Sand; Sediment; sediment cohesion; Sediment transport; Segregation; Spatial distribution; Stochasticity; Stratigraphy; Surface dynamics; Suspended sediments; Transport processes
• ISSN: 2169-9003; 2169-9011
• DOI: 10.1002/2017JF004216

Results from physical and numerical experiments suggest that sediment cohesion influences deltaic morphodynamics by promoting the development and maintenance of channels. As a result, cohesion is thought to increase the magnitude and time scales of internally generated (autogenic) processes and the dimensions of their stratigraphic products. We test these hypotheses by examining the surface processes and stratigraphic products from a suite of physical experiments where the influence of cohesion is isolated over temporal and spatial scales important for basin filling. Given the stochastic nature of autogenic sediment transport processes, we develop and employ a range of statistical tools and metrics. We observe that (1) an increase in sediment cohesion decreases lateral channel mobility and thus increases the time necessary to regrade deltaic surfaces; (2) enhanced channelization, due to sediment cohesion, increases the time necessary for the deposits of autogenic processes to average together and produce stratigraphic products with shapes set by the generation of regional accommodation; (3) cohesion promotes the transport of suspended sediment to terrestrial overbank and marine environments, which decreases the volume of channel, relative to overbank and marine deposits in the stratigraphic record. This increase in overbank and marine deposition changes the spatial distribution of sand in stratigraphy, with higher cohesion linked to enhanced segregation of fine particles from coarse sand in the experimental deposits. Combined, these results illustrate how the cohesion of sediment is fundamental in setting autogenic spatial and temporal scales and needs to be considered when inverting stratigraphic architecture for paleo‐environmental history. Key Points An increase in sediment cohesion promotes the development of deep and narrow channels and reduces lateral mobility The decrease in the mobility of sediment transport systems increases depositional persistence Cohesion aids the pumping of fine sand into deep marine and increases segregation between coarse sand and fine grains in the stratigraphy Plain Language Summary Sediment cohesion, which is mainly controlled by grain size and vegetation, promotes channelization on delta tops and increases the magnitude and time scales of internally generated processes, such as rapid changes of a river's couse. In this study, we use a suite of physical experiments to examine how sediment cohesion affects deltaic morpholo