GEOLOGY OF THE PENGKALAN HULU-BETONG TRANSECT ...

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2. PREVIOUS WORKS AND GEOLOGIC SETTING
2.1 Previous Works
Systematic geological mapping on the scale of 1:63,360 covering the Transect area on
the Malaysian side had been intially carried out by the geologists of formerly Geological
Survey Department between 1957 to 1963, i.e. C.R. Jones and C.K. Burton in the Gerik
and Baling areas, respectively. Their works were later published as District Memoir 11
(Jones, 1970) and District Memoir 12 (Burton, 1970). Burton (1965 & 1970) informally
introduced the term Baling formation to designate a widespread sequence of graptolites
and Tentaculites bearing black shale, sub-mature arenites, calcareous shales, siltstone,
calcareous sandstone and limestone exposed in the Baling area, Kedah. The geographic
name of this formation has been taken after the name of the Baling town, east of Kedah
State. Burton (1965) assigned the age of the Baling formation as Early Silurian based on
graptolites found in this area. The term Baling formation was also adopted by Jones
(1968a) for pre-granite sedimentary rocks in the Gerik area. Later, Burton (1967 & 1972)
indicated the possibility of raising the status of Baling formation to Baling group.
In the Baling area, Burton (1970) recognised four principal lithofacies in the Baling
formation (now known as Baling group): argillaceous facies (mainly carbonaceous and
siliceous shales), with subordinate arenaceous, calc-silicate facies and minor calcareous
facies. Similar stratigraphic nomenclature was followed by Jones (1970) for the rock units
in the Gerik area, but with inclusion of a prominent pyroclastic facies (rhyolitic to
rhyodacitic tuffs) into the Baling formation. Jones (1973a) estimated the thickness of the
Baling group rock sequence is at least 2,700 m. Burton (1986) reviewed the Baling
formation and raised its stratigraphic rank to the Baling group. He divided the Baling
group into three units:
i) Kroh formation: composed of predominantly black argillites with minor
calcareous rocks.
ii) Grik tuff: composed of a thick sequence of pyroclastic rocks of rhyolitic to
rhyodacitic composition.
iii) Papulut quartzite: composed of arenites and limestone, and calc-silicate rocks.
Systematic geological mapping activity in the north Perak and north Kedah areas was
stopped for sometimes due to security reasons. However, systematic geological mapping
programme on the scale of 1:63,360 was later resumed in early nineties when problems
on security were settled. Mohd Badzran et al. mapped the Kerunai area (Sheet 19) during
the year 1991-1993, and Mohd Asbi et al. mapped part of the Gerik area (Sheet 31)
during the year 1994-1996. They adopted the stratigraphic rank of Baling formation as
proposed by Burton (1970) and Jones (1970). Abdullah Sulaiman and Mat Niza Abdul
Rahman mapped the Gubir area (Sheet 9 and parts of Sheets 2, 3 & 10) and the Baling
area (parts of Sheet 18) in 1995-1999 but they adopted the stratigraphical rank “Baling
group” as proposed by Burton (1986).
Mohd Badzran et al. (1993) noted the occurrence of two younger rock units in the
Kerunai area and assigned the two rock units as Kobeh sandstone (Triassic?) and
Nenering beds (late Tertiary–Pleistocene?). The term Kobeh sandstone was referred to the
sequence of areno-argillaceous rocks, assumed overlying uncomformably the Kroh
formation (SDkr). Exposures of this rock unit can be observed along the security road of
Malaysia-Thailand border in the Nenering area. The Nenering beds was introduced for
the semi-consolidated continental deposits, which is correlatable with the late Tertiary–
Pleistocene Lawin beds.