A mechanism to explain the preservation of leaf litter lenses in coals derived from raised mires

Leaves and other non-woody canopy parts are rarely preserved in coals. Although the pH of pore waters within peat swamps is usually relatively low (≤3.5), providing geochemical conditions that would promote preservation after burial, shed canopy parts may remain at the air–soil interface for periods of up to several months prior to burial by additional organic detritus. Leaf half-life in tropical forests has been reported to range from several weeks to months, depending upon species histology. During this time of exposure on the forest floor, catabolic (internal enzymatic), fungal, bacterial and root degradation, as well as saprophagous scavenging, act upon the least resistant parts to promote decay into hemic and sapric macerals. It is unusual, then, to find well-preserved leaves in peats or coals. When such accumulations are encountered, either permineralized in coal balls or duripartically preserved in lignites, the bedded leaves generally are spatially isolated. Several explanations have been proposed to account for such fossil Lagerstätten that require temporal changes in accumulation or degradation rates. Neither of these mechanisms is required to account for such accumulations. Bedded leaves, showing minimal evidence of subaerial exposure and degradation, have been recovered at depth from a vibracore taken 1 km into the interior of a peat swamp in the Rajang River delta, Sarawak, East Malaysia. Evidence is provided to indicate that such accumulations form within peat substrate depressions resulting from the displacement of rootstocks as trees either die and fall over, or are blown down in severe storms. These localized, acidic water-filled pools act as a natural buffer to the degradation of fallen canopy parts that accumulate therein.