Print this pageLow ash, low sulfur coal deposits are the most important economic coals worldwide and have exclusively been interpreted to be ombrotrophic and of lowland, coastal origin. New evidence from peat deposits of the Tasek Bera basin, Western Malaysia, reveals that thick low ash, low sulfur coal may also originate in intermontane narrow valleys with steep flank gradients.
Tasek Bera, situated in tropical Malaysia, is a dendritic, intermontane basin, 30 m above present sea level, with an average precipitation exceeding 2000 mm/a. The lowland hills are covered by dipterocarp rain forest. The swamp forest is dominated by species that include Pandanus artrocarpus, Macaranga puncticulata, Thoracostachyum sumatranum, Ficus sp., Cratoxylon arborescens, palmae and subordinate Eugenia sp.
Net peat accumulation began in Mid-Holocene time similar to other peat forming environments in SE-Asia. During the past 4500 years, 550 cm of low ash (< 5 wt-%), low sulfur (< 0.4 wt-%) woody peat was deposited in a narrow (400-700 m) elongate tributary (3 km) of the southern Tasek Bera swamp system. The deeply weathered bedrock of the lowland hills produces clay rich runoffs during heavy rainfalls throughout the year but no mineral matter extends more than 20 to 100 m into the marginal forest swamp. Restricted discharge and high acidity due to humic and fulvic acids are assumed to build up a chemical barrier for clay minerals leading to their flocculation and/or coagulation out of the black waters of the rheotrophic wetland tributary.
AAPG Search and Discovery Article #90925©1999 AAPG Foundation Grants-in-Aid