Particle shape trends across experimental cohesive and non-cohesive sediment gravity flow deposits: Implications for particle fractionation and discrimination of depositional settings

Fractionation of particles in deep-water sediment gravity flows is an important factor in the resulting deposit and for discriminating sedimentary environments, but remains poorly understood. Quantitative characterization of particle shape was performed for more than ten-thousand particles of experimental gravity flow experiments (both of cohesive and non-cohesive nature) made using coal and kaolin particles. Eleven particle shape parameters were calculated and their distribution and trends within the experimental basin were evaluated. Results indicate the existence of non-normal distributions and observable correlations between particle shape parameters. Shape parameters such as circularity and roundness are dominant controls on shape variation. Strong correlations exist between mean shape parameters and along-flow distance from the source for particles in non-cohesive flow experiments. Important differences were observed between shape parameter distributions of particles sampled at different areas within the experimental basin, which can be grouped based on their depositional setting (proximal or distal) using multivariate statistical analysis, especially for the non-cohesive flow experiments. A tendency for more elongated and irregularly-shaped particles at the more distal and marginal areas of the studied experimental basin was observed and validated by previous field studies in real-world deep-marine deposits. Besides, fractionation of particles is less-pronounced in cohesive flows compared with non-cohesive ones suggesting the soundness of discrimination of depositional settings based solely on particle shape characteristics is strongly dependent on parent flow characteristics. Yet, results highlight the potential of particle shape analysis in revealing spatial particle shape trends due to hydrodynamic fractionation and discriminating different depositional settings within submarine fans. This methodology may be applied to seafloor and subsurface samples to help identify the flow process and depositional environment.