Palynofloral and organic characteristics of a Miocene bog-forest, Kalimantan, Indonesia

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Palynological investigations of a 20-m-thick Miocene lignite from southeastern Kalimantan, Indonesia, reveal that there are distinct vertical variations in palynofloral characteristics. Three palynofloral zones likely represent large-scale successional changes that were a product of long-term ecological and depositional changes within the original mire. All three zones are represented by palynofloras of both bog-forest and mangrove affinity. The abundance and diversity of these bog-forest palynofloras, accompanied by extremely low sulphur contents (<0.4%), suggests predominantly freshwater, terrestrial deposition. It is probable that the mangrove pollen is allochthonous and was transported into the mire by winds. Increasing relative abundances of mangrove pollen within the total palynofloral assemblage suggests encroachment of the mangrove swamp toward the bog-forest. Pollen common and abundant within all assemblages includes that of species of the genera Calophyllum, Melanorrhea and Dactylocladus. Overall, the vegetation that formed this Miocene lignite is virtually identical to the present-day peat-forming vegetation of Indonesia. Despite the vertical variations in vegetation within this Miocene lignite as deduced from palynology, coal petrographic investigations reveal that there is little variation in the organic characteristics within this seam. Petrographic analyses show that maceral assemblages are similar for most parts of this seam. Analyses of the plant-parts and matrix illustrate that these characteristics are similar for much of the seam, and that the composition and grain-size of organic components are wholly comparable to results of similar analyses from a Holocene mire. This suggests that degradation processes during the Miocene were similar to processes occurring in present-day Indonesian mires. It further suggests that these degradation processes have homogenized the organic characteristics within the lignite, despite original vegetational differences. © 1993.

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Organic Geochemistry

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