133 / 1971-01-01 00:00:00

Depositional Environment Of Tertiary Krabi Basin From Southern Thailand Using Coal Petrography

Abstract

The Bang Mark coal deposit is situated at the Krabi mine in the Tertiary Krabi basin, Southern Thailand. The Bang Mark coal quality is the low rank coal (ranges from lignite to sub-bituminous), which is about 7 to 20 meter thickness. The purpose of this paper is to provide a comprehensive study of the composition, character and depositional environment of coal seams from the Bang Mark coal deposit in the Krabi Basin by using coal petrography.
The results of coal petrography in the lower coal seam are completely dominated by a huminite group between 50 to 70 percent. The liptinite group ranges from 20 to 45 percent. There are very low inertinite content ranging from 0 to 5 percent. The upper coal seam, the huminite content ranges from 50 to 60 percent. The liptinite group is dominated in this coal seam ranging from 30 to 40 percent and the inertinite ranging from 0 to 3 percent. The huminte group (humotelinite and humodetrinite) indicated generally oxygen-deficient conditions in paralic coal deposit. The liptinite group (sporinite, cutinite, resinite, fluorinite, suberinite, alginite, liptodetrinite and exsudatinite) indicated the forest-swamp and lake environments. The coal deposits associated with alginate indicating a stagnant water. The sclerotinite is only shown in the inertinite group indicating the rare occurrences of wildfire during the accumulation of coal.
From the association of the liptinite group, the alginite in the both coal seams is dominated by Botryococcus sp. (alginite A) of Pila and Reinschia types, which is associated with the green algae in the swamp depositional environment. The variation of Reinschia, Pila algae could indicate a change of water quality. The sporinites mainly occurs in the coal seam that associated with a forest swamp environment, which embedded in a groundmass of liptodetrinite, coal and clay matrixes. The megaspores mainly occur in the upper coal seam, and the microspores occur in both lower and upper coal seams. The Nypa-type pollen and palm leaves (Sabilistis sp.) also have been found in the lower coal seam, which is the indicators of the tropical- mangrove-plant environment. The cutinite is dominated in this coal deposit, which is probably shown by the prickly end needle like that of Pinus sp., indicating the association of the temperate plants and probably higher-elevation plant assemblages. The cutinite and alginite association in the both coal seams are an indication of intermediate to shallow water depth. The suberinite are dominantly represented in both lower and upper coal seams that indicating the common occurrence of large tree trunks in a forest swamp environment
In conclusion, the lower part of the Bang Mark coal seam represents the fluctuation environment, dominating the fresh water and may have been influenced by slightly saline water. The coals shows the very high destruction of the plant materials as precursors to coal indicating the high water content in the deposits. It could be possible that the environment was a large salt marsh or coastal swamp beyond the intertidal mud flat. The water level gradually increasing and then stable standing water level in the upper portion of the lower coal seam, indicating by high content of the alginite. The upper part of coal seam represents a dominated fresh water with a stable water level and the upward dryness in the upper portion of this coal seam indicating by the increasing of terrestrial plants (suberinite), and it also shows the balance between the coal accumulation and accommodation space.