GEOLOGY OF THE PENGKALAN HULU-BETONG TRANSECT ...

nomenclature of the Nenering beds (Qnn) and they are assigned as the Basal Gravel Beds
and Gravelly Sand Layers facies, respectively.
On the Thai side, the term Ai Yoe Boe Chang Gravel beds is proposed, to describe the
young sediments in small hills around the Betong township. It is named after Ai Yoe Boe
Chang village where good outcrops are exposed.
Distribution
In Malaysia, the Nenering beds/Ai Yoe Boe Chang Gravel beds (Qnn/ay) are well
exposed along the Kampung Ayer Panas-Kampung Lalang road and along the border
security road. The outcrops extend from Sungai Kuak, 3.5 km south of Kampung Ayer
Panas (7.5 km from Pengkalan Hulu town) to FELDA Nenering in the south, covering an
area of about 12 square kilometres. On the Thai side, these sediments, more than 20 m
thick, are well exposed at small hills around Betong District. Good exposures of this unit
are found along the road-cuts from the checkpoint at the Malaysia-Thailand border to Ai
Yoe Boe Chang-Suan Som village. Other outcrops can be observed along the road-cuts
from the border check point to Betong town and then to Ya Rom village, and also from
Ko Mo 7 to Chantharat villages.
Lithology
On the Malaysian side, the Nenering beds/Ai Yoe Boe Chang Gravel beds (Qnn/ay)
is made up essentially of semi-consolidated sediments i.e. sandy, muddy and
gravelly layers. The beds are characterised by gentle dips, and exhibits prominently
alternating bands of sandy, muddy, and gravelly layers (Figure 32). These gravelly
beds unconformably overlies the Silurian-Devonian Kroh formation/Betong
Formation (SDkr/bt).
A closer observation on the beds shows cross-bedding structures occur in the sandy
beds, and graded bedding in the gravel beds. These sediments also show significant
differences in clast sizes, from granule (2 mm x 2 mm) to pebble (20 mm x 20 mm), but
in some places they reach to boulder size. The clasts are made up essentially of vein
quartz, quartzite, sandstone, chert, conglomerate and subordinate amount of shale,
limestone, and granite with clast-supported as well as matrix-supported textures. Gravel
beds with larger clasts occur in the western part of the Nenering beds/Ai Yoe Boe Chang
Gravel beds (Qnn/ay). They appear to gradually decrease in size and abundant in a narrow
band overlying the sandy and muddy beds towards the east. Beyond that, the deposits are
essentially sandy and muddy up to its eastern extent, and coal-bearing beds were not
observed.
45