Inorganic constituents from samples of a domed and lacustrine peat, Sumatra, Indonesia

Abstract

Two peat cores and one substrate core were collected from the Siak Kanan domed peat deposit in Riau Province, eastern Sumatra, Indonesia. The peat cores consisted of a 9.5-m core from the subaerial part of the domed peat and a 0.51-m core from the bottom of a lake located within the dome. Approximately 1.0 m of substrate material was obtained from a core from the bottom of the lake adjacent to the lacustrine peat core. Samples from selected intervals from the peat cores and from the underlying mineral substrate were low-temperature ashed and examined using light-optical, cathodoluminescent, and scanning electron microscopy, as well as by energy-dispersive X-ray analysis to chemically characterize the inorganic constituents. In addition, some of the ashed samples were analyzed by inductively coupled plasma-atomic emission spectroscopy and Fourier-transform infra-red spectrometry techniques.The low-temperature ash (LTA) of the peat samples is composed of discrete grains of biologic origin and volcanic eolian origin and aggregates of micrometer to submicrometer-sized particles that are largely artifacts of low-temperature ashing. Most of the aggregate material, which makes up approximately 90% of the LTA, probably results from reactions between organically bound cations and S and N which produce sulfate and nitrate compounds. All the Na, Ca, and Mg, and most of the K and the Al in the peat are concentrated in the aggregate fraction. The sulfate and the nitrate salts are readily soluble in water.Different suites of siliceous organisms that may have potential for environmental indicators are present in the lacustrine and domed peat intervals. In addition, rare but identifiable volcanic constituents are present in the samples of all the peat intervals. The volcanic constituents include glass shards, feldspars, zircons, and blue luminescent quartz. Most of the quartz grains from intervals of samples from the lake peat luminesce, however, in the orange plus blue range, which is indicative of a metamorphic origin. Phytoliths and siliceous organisms from samples of both the peats and the substrate intervals did not luminesce in the visible range, which is a characteristic of authigenic quartz and, apparently, biogenic silica. Biogenic silica grains, quartz grains, and other silicate minerals observed in the peat have etching features that may be caused by simple dissolution or interactions with multiple types of multiprotic organic acids. Dissolution and precipitation features are visible on quartz grains from the mineral substrate samples immediately below the peats.

Mineralogical and geochemical characterization of the Jurassic coal from Egypt

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Biogenic silica: a neglected component of the coupled global continental biogeochemical cycles of carbon and silicon

“…Chrysophyte microalgae are efficient competitors for nutrients, but are more restricted in distribution than diatoms or sponges. They are common in the cold, oligotrophic waters of Arctic and Antarctic lakes (Sandgren, 1988;Zeeb and Smol, 2001) as well as in some tropical swamps (Ruppert et al, 1993). Unlike diatoms, chrysophytes are relatively rare in alkaline, eutrophic waters, although exceptions exist.…”

Comparison of Radiocarbon Ages from Different Organic Fractions in Tropical Peat Cores: Insights from Kalimantan, Indonesia

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