GEOLOGY OF THE PENGKALAN HULU-BETONG TRANSECT ...

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may be concluded that the age of the Kroh formation/Betong Formation (SDkr/bt) is
ranging from Early Silurian to Devonian.
In Thailand, many fossil assemblages, i.e. Tentaculites elegans and Tentaculites sp.
occur in light pink shale strata and limestone lenses. Conodonts assemblage found in
chert beds indicate the age of rock sequence is Devonian. However, the discovery of
graptolite in light pink shale suggests the age of the succession is possibly Silurian-
Devonian. Therefore, the succession of the Kroh formation/Betong Formation (SDkr/bt)
can be dated as Silurian-Devonian age.
Depositional environment
The widely spread argillaceous facies with considerable amount of carbonaceous
content suggests that the deposition of this rock unit occurred in the euxinic marine
environment. Fine-grained materials indicate long distance transportation and the
deposition took place in a quite and undisturbed environment. The absence of benthos
fossils and bioturbation indicates that the deposition occurred in deep marine
environment. The calcareous facies and arenaceous facies with subordinate conglomerate
might be deposited in the continental shelf, the relatively shallower part of the
depositional basin.
3.1.2 The Kubang Pasu/Yaha Formation (Ckp/yh)
In Malaysia, The Kubang Pasu Formation (Ckp) is conformably underlain by the Kroh
formation (SDkr) and it is conformably overlain by the Gerik formation (Pgk). The term
Kubang Pasu Formation was introduced by Jones (1981) for a sequence of thick
sandstone and thin shale in the Kedah and Perlis areas in northwest peninsular Malaysia.
The stratigraphic name was taken after the Kubang Pasu District, Kedah where he first
discovered the good outcrops of this rock unit. The same lithological unit is observed to
extend eastwards into the Transect area.
In Thailand, the Yaha Formation (Cyh) is conformably underlain by the Betong
Formation. The term Yaha Formation was introduced by Nakapadungrat et al. (1988) to
describe a sequence of thick Carboniferous clastic sequence in the Sadao-Yala area. It is
named after Yaha District, where geological information was first studied and good
outcrops were available.
Distribution
In Malaysia, the Kubang Pasu/Yaha Formation (Ckp/yh) is well exposed in the northeast
Kedah State, and in UpperPerak State in the central part of the Transect area. The rock
exposures in northeast Kedah can only be observed along the streams i.e. Sungai Teliang
which located in the remote and forested area (Figure 12). The only access to that area is
by boat via Muda Lake, a man-made lake for the paddy field irrigation in Kedah State,
then preceed to continue the traverse by foot. In UpperPerak, good outcrops can be easily
observed along the border security road parallel to the Malaysia-Thailand border on the
Malaysian side known as FELDA Nenering area, Pengkalan Hulu, Perak. The Kubang
Pasu/Yaha Formation (Ckp/yh) underlies most of the Kerunai Malay Reserve area,
extending from the Bukit Kobeh (Khao Ko Be) area along the Malaysia-Thailand border
in the north to the Padang Sembai-Kubang Gondang area in the south. It is also well
exposed along the East-West Highway up to Banding Island, northeast Perak where this
rock unit is locally metamorphosed to metasandstone, phyllite and schist. Minor