| Summary: | The evolution and structure of a dendritic peat deposit in the interior lowland of tropical Peninsular
Malaysia is investigated as a viable archive of paleoecological and paleoclimatological changes. The
project was initiated due to the lack of understanding fundamental processes of intermontane peat
accumulating systems mainly because previous studies have focused exclusively on coastal lowland
deposits. Peat stratigraphy, mineralogy, organic petrography and geochemistry are some methods
utilized in this study.
The modern depositional environment of the Tasek Bera Basin includes lowland dipterocarp forest,
swamp forest, Cyperaceae/Pandanaceae swamp and open water areas. Widespread peat deposition in
the basin started about 5300 years BP, when Holocene climate changes led to the evolution of a wetland
system. Peat accumulation progressively expanded by processes of terrestrialization of channels and
subbasins and paludification of the riparian part of the lowland forest zone. Stratigraphic facies can be
distinguished in the field and combined with the ash yield, which indicates rapid and cyclic changes of
frequency and magnitude of runoff events, demonstrating that hydrologic and in turn climate dynamics
dictate peat evolution.
Although tropical peat deposits are widespread, few classification systems exist that recognize the
distinctive characteristics specifically of tropical peats. A three-group field classification (fibric, hemic,
sapric) for organic soils based on texture and fiber content is proposed. In addition, a new classification
of organic soils based on loss of ignition and carbon content for geological, engineering, agricultural
and economical studies of tropical peatlands is developed. Peat is defined as having a loss of ignition
of 45 to 100 wt-%, muck 35 to 45 wt-%, organic-rich soils/sediments 20 to 35 wt-%, and mineral
soils/sediments 0 to 20 wt-%.
Abundant and unique Al-Si bioliths exist in the mire system of Tasek Bera. These Al- and Sihydroxides
and the opaline silica from diatoms and sponges represent a repository of Al and Si, which
may contribute to mineral transformation, neoformation and alteration processes during coalification of
the peat deposits. Most plant-essential nutrients are biocycled within the top 150 cm of the organic
deposits causing an upward migration of plant-essential elements, such as Mg, Ca, or P, during mire
evolution. Hence, incorrect paleoclimatic and paleodepositional interpretation may result from utilizing
geochemical data (e.g. normalization of elements with Al, interpretations of major element data) of
tropical peat deposits.
With burial, the deposits of Tasek Bera Basin would yield a dendritic sediment pattern of sandstone,
shale, carbonaceous shale and low to high ash coal, overlain by carbonaceous shale. Because of the
dendritic nature of the basin, coal seams would most likely have a similar pattern as the Carboniferous
coal deposits of the Black Warrior Basin in Alabama (USA). The peat deposits of southern Tasek Bera
reveal that thick, low-ash, low sulfur peat may originate in narrow tributary valleys with moderately
steep flank gradients. The deposits may be favorable precursors to dulling-upward coals, in that they
contain high wood and low-ash content at depth and medium wood and slightly increasing ash content
in the upper parts.
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