EVALUATING THE APPLICATION OF USING LASER-DIFFRACTION GRANULOMETRY TO DETERMINE PROCESS CONTROLS ON GRAIN SIZE DISTRIBUTIONS IN MODERN RIVERS AND SUBMARINE CHANNELS

Sieving and optical grain size analysis has been traditionally utilized to determine characteristic sediment distribution curves in various depositional environments. However, advances in laser-diffraction granulometry lead to new insights in sediment grain size analysis due to higher accuracy and reproducibility. This study presents a comprehensive sediment core analysis of characteristic grain size distributions from upstream to downstream in one modern fluvial and two modern submarine environments. We seek to determine (1) whether fluvial and submarine canyon systems display characteristic sediment grain size distributions; (2) what are the process controls on sediment grain size distributions in a fluvial vs. submarine system; and (3) whether our results on modern sediment grain size distributions can be utilized to interpret ancient channel origins as either fluvial or submarine. We hypothesize that (1) that sediment grain size distributions from modern fluvial systems are skewed to the > 100 micrometer particle size fraction with a multimodal distribution while modern submarine channel distributions show a unimodal distribution curve; (2) bedload transport is the dominant process control in fluvial systems, while turbidity flows dominate in submarine channel systems; and (3) that distinct sediment grain size distributions for modern fluvial and submarine canyon systems allow for the identification of channel origins in the ancient rock record.