Transport, deposition and occurrence of charcoal in terrestrial and marine sediments: interpretation and use

Wildfire produces a range of pyrolysis products, including charcoal, whose size ranges from microns to millimeters and even centimeters. Charcoal may be lofted in to the atmosphere and carried on the wind or remain on the ground and be buried in situ or transported into a depositional environment. Microscopic (sub-millimeter) charcoal may be widely distributed by wind and even be found in oceanic sediments. However, macroscopic charcoal may float and be transported hundreds of kilometers in water to be deposited in a wide range of environments from continental to marine where it may dominate some organic matter assemblages. Experiments using settling and flume tanks and tumblers have indicated the role of charring temperature, size and nature of the plant organ burnt on the behavior of charcoal in water. Charcoal is found in sedimentary rocks from the late Silurian. From the late Devonian and Early Carboniferous charcoal becomes increasingly abundant implying the development of widespread fire systems. Charcoal (known as intertinite by petrographers) may represent a significant proportion of organic matter assemblages in some organic-rich shales, both marine and non-marine. Charcoal in coal may not only imply the occurrence of wildfire but quantitative studies imply an inter-play of changing climate and atmospheric oxygen. Macroscopic charcoal provides anatomical data on the plants leading to an understanding of fire-prone vegetation through time. Carbon isotopic studies of charcoal has led to the distinction of C3 and C4 plants and ultimately given rise to theories of the interaction of fire and the rise and spread of grasslands. Wildfire may be followed by extensive post-fire erosion leading to an increased deposition rate in environments far removed from that directly affected by the fire. Few sedimentologists have recognized this in the fossil record and it is likely to be more widespread than currently thought.