Opaline and Al–Si phytoliths from a tropical mire system of West Malaysia: abundance, habit, elemental composition, preservation and significance

Abundant and unique opaline and Al–Si phytoliths and opaline bioliths have been discovered in Holocene peat deposits of tropical Tasek Bera in Peninsular Malaysia. These are secreted mainly by plants (higher plants and algae) and incorporated in the sediment cycle during the rapid biomass turnover. Many wetland plants have entire skeletons secreted. The study shows that differing plant parts of same species as well as same parts of differing plant species incorporate different amounts of elements. Whilst deciduous trees of the swamp forest have phytoliths enriched in Al, most phytoliths of palms, sedges and grasses of the littoral swamp are composed of opaline silica. Incorporation of Al and many other elements into relatively stable phytoliths is the result of high evapotranspiration rate and ample plant-available elements and can serve to detoxify the soil solution. Because of the abundance of such opaline and Al–Si structures, spongillid and algal remains in acid peat-accumulating environments, tropical peatlands represent repositories of Si and Al, which together with variable amounts of other elements could provide the prime material for silicate neoformation during later diagenetic processes. Neoformation of minerals from bioliths would explain the scarcity of biogenic remains in Carboniferous and Tertiary coal deposits. Furthermore, incorporation of major elements in phytoliths may limit the rate of leaching of these elements in an environment where biomass turnover is rapid, thus reducing the loss of nutrients and other plant-essential elements. Most nutrients of tropical peats are recycled by plants within the top 150 cm and an upward migration of plant-essential elements, such as Mg, Ca, or P, but also of Si and Al, occurs during peat accumulation. Such elemental cycling strongly influences the geochemical composition of the peats during mire evolution. Utilizing Al for normalization of major and minor elements of tropical peats for paleoclimatic and paleodepositional analyses may thus result in incorrect interpretations.