Understanding fine-grained river-sediment dispersal on continental margins

Studies of fine-grained sediment dispersal in the marine environment have documented diversity in the behavior of depositional systems on continental margins with different oceanographic conditions and morphologies. Based on the pattern and nature of sediment accumulation for twenty-three case studies, we propose there are five basic types of dispersal systems, and these are related to river, wave, tide and margin characteristics. Data suggest that the type of dispersal system on any margin can be predicted with knowledge of sediment load, mean significant wave height, tidal range and continental-shelf width at a river mouth, and from these, a hierarchical decision tree is developed. Analysis of the dispersal-system type of more than 100 river mouths reveals that proximal-accumulation-dominated (PAD) and marine-dispersal-dominated (MDD) systems are most abundant. But, estuarine-accumulation-dominated (EAD) systems also are anticipated to be numerous globally. Research quantifying marine sediment dynamics in these system types is needed. Although less common, the size and nature of subaqueous-delta-clinoform (SDC) and canyon-captured (CC) systems also warrant future attention to their study. Strong correlations between physical characteristics (i.e., significant wave height and tidal range) and the depth and distance to the nearest maximum shelf depocenter provide evidence that in reality a continuum exists between the system types. The process-related partitioning of sediment in the five different types of marine dispersal systems has important implications for understanding the stratigraphic record and the cycling of carbon.