Controls on the Deposition of Charcoal: Implications for Sedimentary Accumulations of Fusain

Abstract

ABSTRACT The effects of formation temperature, particle size, water salinity, and composition of suspended clay and substrate on the sedimentation of charcoal under agitated conditions in a wave tank were studied in a series of experiments. The temperature of formation of charcoal has a strong effect on the rate at which charcoal becomes waterlogged. Examination of the microstructure of the chars formed at different temperatures shows that the formation of fractures within the wood affects the permeability and hence the rate of water penetration. Heating up to 300°C results in fusion of the cell walls, which inhibits water penetration and shows the rate of settling. At higher temperatures the cell walls progressively fracture, increasing the permeability, and the chars waterlog and settle aster. The settling rates and hence the distribution of charcoal in sedimentary deposits are therefore controlled by the temperatures reached in the fire that generated the material. This sorting related to temperature of charcoal formation has implications for the determination of the size of a paleowildfire from the volume of fusain in a sedimentary deposit. Salinity variations and the presence of a clay substrate were also shown to have a small effect on charcoal sedimentation rates.