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Research Article
ScienceAsia 29 (2003): 307-317 |doi: 10.2306/scienceasia1513-1874.2003.29.307
Fluctuation of Depositional Environment
in the Bang Mark Coal Deposit, Krabi Mine,
Southern Thailand: Stable Isotope Implication
Bantita Udomkana,*, Benjavun Ratanasthiena, Katsumi Takayasub, William S Fyfec,
Shin-ichi Satob, Wittaya Kandharosaa, Pitsanu Wongpornchaia and Minoru Kusakabed
ABSTRACT: The isotopic composition of organic sulfate-sulfur and pyrite in coal from the Bang Mark coal
deposit in the Krabi mine, southern Thailand, was analyzed to determine the depositional environment of the
coal. High-sulfur content in coal has
 34S values that range from +1.6 to +9.8%o. Organic sulfur in coal has
34S values that vary narrowly from –1.4 to +4.7 %o. The
34S values of pyrite range from –3.0 to +1.4 %o.
The
34S values indicate that most of the sulfur in pyrite and coal was derived from a magmatic or hydrothermal
source. This sulfur was associated with organic matter during or after deposition. This also suggested that the
source of sulfur could have come from hydrothermal mineralization surrounding the area. Twenty-four fossil
shell specimens of Viviparus sp., Melanoides sp., and Mya arenaria were analyzed for their content of isotopic
13C and
18O. The
13C in these shells have negative values that range from –5.9 to –0.1 %o and average –
2.9  2.8%o. The
18O in these shells has a wider range of negative values, ranging from –11.7 to –2.9%o. It
averages –8.1 5.2%o. The
13C and
18O values indicate freshwater shells in the lower sequence and brackish
water shells in the upper sequence. Therefore, the depositional environment of the Bang Mark coal deposit based on stable isotopic study was dominated by freshwater in the beginning and later became brackish water
as a result of marine invasion under warmer conditions in a tropical region.
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a Department of Geological Sciences, Faculty of Science, Chiang Mai University, Chiang Mai 50200 Thailand.
b Research Center for Coastal Lagoon Environments, Shimane University, Matsue 690-8504 Japan.
c Department of Earth Sciences, University of Western Ontario, London, Ontario, Canada, N6A 5B8.
d Institute for Study of the Earth’s Interior, Okayama University, Misasa, Tottori-ken 682-0193 Japan.
* Corresponding author, Email: bantita_u@yahoo.com
Received 11 Feb 2003, Accepted 28 Aug 2003
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