Bulletin of the Geological Society of Malaysia, Volume 43, Dec. 1999, pp. 229 – 249
1 Department of Earth and Ocean Sciences, The University of British Columbia, 6339 Stores Road, Vancouver, B.C. Canada, V6T 1 Z4
2Jabatan Geologi, Universiti Malaya, 50603 Kuala Lumpur, Malaysia
Abstract: Modern wetland environments represent the first step in production of peat deposits and are therefore precursors to coal seams. The characteristics of intermontane rheotrophic peat deposits are poorly constrained as modern analogues for coals but are critically important for understanding many deposits. Extensive organic rich sediments have developed in a closed drainage system in Tasik Bera, Pahang, West Malaysia. This thick, low- to high-ash, low-sulfur, low-nitrogen peat has accumulated in a dendritic drainage basin since the Mid-Holocene (for at least 4,500 years) and provides an excellent analogue for many Tertiary coals. Three distinctive ecological environments occur in Tasik Bera that give rise to spatial variations in peat composition: a) limnetic environment, dominated by algae and aquatic macrophyt (Utricularia flexuosa) deposits; b) littoral environment, dominated by sedges (Lepironia articulata) and woody shrubs (Pandanus heliocopus); and c) forest swamp dominated by trees and woody shrubs (Eugenia spp., Thoracostyachyum baucanum, Pandanus sp.). Detailed peat-depth transects and cores in the northern part of Tasik Bera model the vertical and lateral distribution of peat. Peat character is influenced by vegetation, topography, channel geometry and mineral matter input. Kaolinite and minor other clays with occasional laminae of fine silt (quartz rich) underlay organic rich deposits. Close to the northern outflow of the basin, adjacent the rivers Sungai Jelai and Sungai Bera, sand and silt form the base of the peat.
The Tasik Bera lake system was formed by damming by fluvial sediments of Sungai Bera, which restricted drainage and led to a high water table and to paludification (initial geogenic accumulation of organic matter) in the basin. Subsequently, due to low rates of decomposition and net peat accumulation, the basin progressively underwent terrestrialization. Arborescent organic rich deposits are widespread throughout the basin. The onset of the mire system in the Tasik Bera basin was dominated by swamp forest. South of Pos Iskandar, extensive forest swamp in three former tributaries, show highly humified (high CIN-ratio), woody, hemic to sapric peat up to 480 cm thick with intercalations of fine sand, silt and clay deposits towards the base. Open water and littoral vegetation yield fibric, hemic and sapric peat with an average thickness of 250 cm, dominate the northern part of Tasik Bera, up to the outflow into Sungai Bera. It is suggested that the upward vertical succession of decreasing woodiness and increasing lightness in color observed are comparable to features in Tertiary brown coals, i.e. color, texture, plant part composition.
The tropical freshwater peat deposits at Tasik Bera would yield a low sulfur, low to high ash thin banded stony coal seam of about 30 to 50 cm thick within a lateral extent of 250 to 350 km2.