STRATIGRAPHIC CHANGES OF GEOCHEMICAL SIGNATURES OF THE CENOZOIC BALINGIAN COAL, SARAWAK, MALAYSIA.

Abstract The thick coal seams of the Cenozoic Balingian coals in the Liang Formation, Sarawak, Malaysia are of interest in the present work. Through this paper, the genesis of the environmental conditions of thick coal seams in relation to their ancient peat and paleomires were investigated in vertical profile. A total of 40 coal samples were prepared and characterised based on organic geochemical analysis. The TOC content range is 40.5 to 58.2 wt.%, and the HI values range from 43 to 441 mg HC/g TOC in the samples tested. Collectively, the analysed coal samples were characterised by mixed Type II-III kerogen and predominantly Type III kerogen and demonstrated the ability to produce substantial gas and some oil generation potential. The carbon/nitrogen ratio of over 20, notable odd-over-even predominance, high long chain C25–35 n-alkanes (mean 79%), moderate ratios of pristane/phytane (mean 1.37) and diterpenes (mean 1.06), moderate carbon preference index (CPI, mean 1.98), high Tm/Ts (mean 2.52), high C29 norhopane/ C30 hopane (mean 3.21) and high C29 steranes (mean 63%) of the studied coals indicate the dominance of terrestrial source inputs. The ratio of C27/C31 (0.06 – 3.64) may further indicates a decrease in woody vs. herbaceous input characterised the upward trend. Peat’s doming is a significant factor of lowered in ash, and sulphur. The mildly influenced of brackish water in the ombrogenous peat were observed by slightly increase of C27, C28 steranes and decrease of C29 steranes and slightly increase of sulphur content. The ancient peat and mires are subjected to ever-wet climates, however an alternance relatively wet and dry episodes were deduced from the variation of n-alkanes, pristane/phytane and diterpanes ratios. The biomarker signatures, furthermore, indicative of oxygen-deficient and water-saturated conditions in the precursor mires due to seasonal dry/wet climates by high and reduced rainfall during peat growth.