GEOLOGY OF THE PENGKALAN HULU-BETONG TRANSECT ...

Figure 18: Stratigraphic sequence of the Sri Paen formation (Psp) in the Transect area.
The upper part of the formation is well exposed in the vicinity of Ban Na Kaset. The
other localities are found along road-cut outcrops from Khok Chang to Ban To village.
The fining upward sequence is approximately 150 – 200 m thick:
i) The lower portion consists predominantly of fining upward cycles of thickbedded,
greenish grey to dark grey shale, mudstone to siltstone (80%) intercalated
with thin- to moderate-bedded pale greenish grey to yellowish brown, fine- to
medium-grained, laminated, lithic, arkosic and quartzitic sandstones (20%) in the
bottom part. At Ban Na Kaset succession in the eastern part of Bang Lang National
Park, the rocks contain abundant brachiopods and a few bivalves (Figure 21).
ii) The middle portion, 40 m thick, is composed of sharp, parallel, wellbedded,
very thin- to thin-bedded, grey to dark grey colour, laminated silicified shale,
sandstone, and grey to milky grey ribbon chert with radiolarian assemblage (Figure
22). The sequence is overlain by thick-bedded siltstone to shale with argillaceous
limestone lenses.
iii) The upper portion is composed predominantly of thin- to thickbedded,
grey to greenish grey shale and siltstone (50%) intercalated with thickbedded
reddish brown to light grey, fine- to medium-grained, arkosic sandstone in
the middle part of the sequence.
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