GEOLOGY OF THE PENGKALAN HULU-BETONG TRANSECT ...

the banks of small rivers and streams. However, only indeterminable plant fragments and
traces of radiolarian tests were found along the security road to Bukit Kobeh,
UpperPerak.
The age of this unit is determined solely by a lithostratigraphic correlation with the
fossiliferous succession exposed in the Kuala Nerang area where Carboniferous age had
been assigned to this rock unit. In the Kuala Nerang and Sintok areas, fossil assemblages
of Bivalve Posidonomya sp., trilobites, ammonites, brachiopods, crinoids, gastropods and
plant remains had been found at Bukit Tunjang, Sintok, Kedah, to the west outside of the
Transect area. Further to the west of Sintok, Basir Jasin and Zaiton Harun (2001) reported
the occurrence of Albailella indensis-rota Assemblage Zone (radiolaria) in chert
representing the lower part of Kubang Pasu Formation at Bukit Binjal, Kedah. This
confirms that the age of the Kubang Pasu Formation (Ckp) is Late Tournaisian (Early
Carboniferous).
In Thailand, many microfossil assemblages i.e. radiolarians and conodonts were found
in chert and siliceous beds, in Yala Province. Sashida et al. (2000) reported the
occurrence of Eutactinia varispina, E. vulgaris, Astroentactinia multispinosa,
Spongentactinia sp. and Triaenospaera sp. The Early Carboniferous radiolarians
discovered from the chert lenses intercalated with sandstone and siltstone-dominated
sequence at Ban Wang Yai, 12 km east of Na Thawi District and Ban Kabang of Kabang
District, Yala Province; are indicative of the Early Carboniferous age of Tournaisian
stage. Based on fossils reported found in the adjacent areas to the Transect, it is
concluded that the age of the Kubang Pasu/Yaha Formation (Ckp/yh) is Carboniferous.
Depositional environment
The greywacky sandstone intercalated with thick- to very thick-bedded grey shale
beds, followed by thick-bedded to massive, well-sorted quartzitic sandstone with graded
bedding and cross lamination may represent a near shore environment of deposition,
probably in either intertidal or upper subtidal zones. The occurrence of plant fossil
fragments within the shale and fine-grained sandstone indicates that the environment of
deposition may be a shallow marine environment. The poorly sorted metaconglomerate is
interpreted as reworked conglomerate previously deposited in the shelf environment and
then redeposited in the deeper environment together with the arenaceous and argillaceous
materials. The presence of chert and siliceous shale may be due to the increasing supply
of silica derived from the siliceous rocks of the Kroh formation/Betong Formation
(SDkr/bt).
3.1.3 The Ratburi Group (P)
Javanaphet (1969) and Bunopas (1981) described the Permian clastic and carbonate
sequences in the western and southern parts of Thailand and introduced the term Ratburi
Group. It is named after Ratburi Province where they were first studied and good rock
outcrops were available.
In this Transect area, the Ratburi Group (P) is conformably underlain by the clastic
sequence of the Yaha Formation (Cyh). The group can be lithologically subdivided into
two formations: the Sri Paen (Psp) and Tham Krachaeng (Pkc) formations.
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