Quantifying particle aggregation in sediments

Sediments often occur as non-normal size distributions composed of discrete, partially aggregated particle populations. These populations reflect provenance, dispersal pathways and their depositional environments. Recent experimental laboratory studies describing mud flocculation in turbulent marine systems prompted this investigation of the potential of aggregates to record size-sensitive transport dynamics in a terrestrial fluvial system. Here, sediment-size distributions in their natural condition of particle–aggregate mixtures are analysed by parametric statistics. A practical and freely available decompositional approach is outlined and field tested, which allows sediment to be viewed in both its conventional particulate form and as its naturally occurring mixture of transport-stable aggregates and elementary particles. From a sequence of upward-fining slack water couplets in the Flinders Ranges, South Australia, it is demonstrated that the characteristics, provenance and depositional history of fine-grained sediments consisting of particle-aggregate mixtures can best be understood fully by quantifying aggregation.