Holocene evolution of the intermontane Tasek Bera peat deposit, Peninsular Malaysia : controls on composition and accumulation of a tropical freshwater peat deposit

• Main Author: Wuest, Raphael Andreas Josef
• Language: English
• Published: 2009
• Online Access: http://hdl.handle.net/2429/13871

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.