The formation of tephra layers in peatlands: An experimental approach

Tephrochronology provides a valuable method of dating peat deposits but results may be compromised if tephra undergoes significant post-depositional movement. This study takes an experimental approach to investigate the processes of tephra taphonomy. Tephra was applied to peats and movement monitored over periods of up to 6 years. Experiments combined field studies on six British peatlands with rainfall simulation experiments in the laboratory. Tephra moved up to 15 cm down through the peat but the vast majority remained at the surface at time of deposition, forming a layer which accurately recorded the palaeo-surface. Tephra moved both down, by shards sinking through the peat, and up, with shards probably being moved by plant growth or with water table variability. The extent of tephra movement most likely depends on the density and porosity of the surface peat; there is no simple relationship with wetness. There is some indication that the extent of tephra movement depends on the tephra particle size but this will require further work to confirm. The taphonomy of tephra is an important issue which should be considered in all tephrochronology studies in peatlands.