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. Alth ough the pH of pore waters within peat swamps is usually relatively low (le ss than or equal to 3.5), providing geochemical conditions that would promo te 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. Durin g this time of exposure on the forest floor, catabolic (internal enzymatic) , fungal, bacterial and root degradation, as well as saprophagous scavengin g, act upon the least resistant parts to promote decay into hemic and sapri c macerals. It is unusual, then, to find well-preserved leaves in peats or coals. When such accumulations are encountered, either permineralized in co al balls or duripartically preserved in lignites, the bedded leaves general ly are spatially isolated. Several explanations have been proposed to accou nt for such fossil Lagerstatten that require temporal changes in accumulati on or degradation rates. Neither of these mechanisms is required to account for such accumulations. Bedded leaves, showing minimal evidence of subaeri al 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, Sar awak, East Malaysia. Evidence is provided to indicate that such accumulatio ns form within peat substrate depressions resulting from the displacement o f 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. (C) 199 9 Elsevier Science B.V. All rights reserved.