GEOLOGY OF THE PENGKALAN HULU-BETONG TRANSECT ...

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The rocks display slightly developed S1 cleavage in the N-S direction, generally
dipping eastward, especially in the western and northern parts of the area. The succession
in the central part of the area generally shows both eastward and westward dipping, and
well developed N-S and NE-SW trending S1 cleavages (Figure 23). The total thickness of
the lower clastic Permian rocks in the section is exceeded 500 m.
Age and correlation
Based on many fossil assemblages i.e. bivalve and brachiopod in dark grey shale,
yellowish brown siltstone and dark grey argillaceous limestone lenses, and some
radiolarian assemblages in chert beds; the age of rock sequence is assigned as
Carboniferous to Permian. However, the stratigraphic sequence is conformably underlian
by the thick-bedded sandstone of the Carboniferous Yaha Formation. It is, therefore,
suggested that the Sri Paen formation (Psp) could be assigned as Early Permian age.
Figure 19: Photographs of the siliceous chert at the lower part of the Sri Paen formation
(Psp) at Amphoe Than To, Map Sheet (5221 III), grid reference 4677847,
Thailand.