1. No category

Chapter 2: General Geology and Tectonic Setting
2.1 TECTONIC EVOLUTION AND BASIN DEVELOPMENT IN SABAH
The tectonic evolution of Sabah provides an overview of basin
development. The summary below was compiled from various studies (e.g.
Tongkul 1991; Tan and Lamy, 1990; Balaguru and Nicholas, 2003, Balaguru,
2006a, Balaguru, 2006b, ISIS (2005)).
Through this study, the regional palinspastic reconstruction by Tongkul
(1991) and ISIS (2005) was adopted as a series of model diagrams that
describe the regional plate tectonic evolution of Sabah. According to Tongkul
(1991), the diverse and complex structures in the Sabah resulted from at least 5
episodes of deformation which began in the early Cretaceous (Figure 2.1).
However, the Neogene Eastern Sabah Basin was probably initiated in the late
Eocene and undergone an episodic structural evolution in response to the plate
collision and extension with subsequent sedimentation (Noad, 2003). Focussing
on the Dent Group sediments in the Dent Peninsula, Ismail Che Mat Zin (1994)
reported that three major tectonic events (early Miocene, late Miocene and late
Pliocene). The following palinspastic reconstructions illustrated in Figures 2.1 to
Figure 2.8 show the tectonic evolution.
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11
Chapter 2: General Geology and Tectonic Setting
Early Cretaceous to Early Eocene (~42.5 ma) – Fig. 2.1
The Cretaceous - Eocene oceanic crust that was floored the Celebes
Sea is believed to be the oldest rocks in Sabah (Hutchison, 1989). During Early
Eocene, southeastward subduction of the proto South China Sea oceanic
lithosphere under the northwestern end of the Celebes Sea floor making up the
deformation and uplifting of the oceanic basement.
The major compressional tectonic trending NE-SW (Mid Eocene to early
Miocene) caused the deformation and imbrications of the oceanic basement as
can be seen in the Lubok Antu Melange, Lupar Valley of Sarawak (Tan, 1982)
and its continuation in Eastern Sabah Ophiolitic Mélange of the Chert-Spilite
Formation and Crystalline Basement (Leong, 1974). These events also
deformed and gradually uplifted the overlying Eocene to early Miocene
sediments in the western area (Balaguru, 2006a). The break up of Celebes
Sea, at the same time, has developed the SE Pacific margin accretionary
complex on Cretaceous oceanic crust and deposited deep marine sediments.
Balaguru (2006b) reported that the late Eocene deformation controlled
development of an elongate basin trending approximately NE-SW in Sabah.
The late Eocene appears to be a period of continued deposition of deep marine
turbidites. The basin was segmented by uplifted basement and was filled later
by shallow water facies on the relatively uplifted side of the basin (part of the
Kudat, Labang, Temburong and Kulapis Formations), while deep water
sediment was deposited in the centre of the basin (Crocker, Trusmadi, Sapulut,
Kudat, Labang, Kulapis and Temburong Formations) (Tongkul, 1991).
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Chapter 2: General Geology and Tectonic Setting
Figure 2.1. Schematic NW-SE sequential cross-sections show geological
evolution of Sabah (after Tongkul, 1991).
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13
Chapter 2: General Geology and Tectonic Setting
II. Oligocene – Early Miocene (~42.5 to 20.5 ma) – Fig. 2.2 to Fig. 2.3
Active opening of the South China Sea Basin in NW-SE and N-S
directions during the Middle Oligocene to Middle Miocene caused further
subduction and narrowing of the Sulu Sea basin. As a result, Mid Eocene to
Early Miocene sediments were compressed into a NE-SW trending fold-thrust
belt in the western part of Sabah and NW-SE in the northern and eastern part
of Sabah (Tongkul, 1991).
III. Early Miocene to Middle Miocene (20.5-15.5 ma) – Fig. 2.4 to Fig. 2.5
In Early Miocene, deformation took place after the South China Sea
microcontinent collided with the Palawan Arc and North Borneo. This is the
Sabah Orogeny and resulted in Base Miocene Unconformity (22Ma-20Ma)
(Hutchinson, 1996). During this period, major tectonic event took place with
major uplift and erosion which led to the formation of mélange. Patches of
Gomantong limestone, of Burdigalian age formed on structural highs during the
uplifting events. Similar to the eastern part, the opening of the Sulu Sea in early
– middle Miocene (~20–19Ma) is thought to have fragmented the NW-SE
trending thrust and fold belt, which subsequently shed the blocks to form the
chaotic deposits in Eastern Sabah. This event resulted in regional extension
and subsidence and initiated the rift basin (Balaguru and Nicholas, 2003). The
continual extension of the oceanic Sulu Sea tectonic plate resulted in formation
of horst and graben structures, combined with the NW-SE fold and thrust belts
in the older sediments, in the offshore area. These events likely controlled most
deposition Miocene sediment (Balaguru, 2006a).
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14
Chapter 2: General Geology and Tectonic Setting
The deposition of the broken Melange Formation was followed by a
change in depositional environment from deep water to a shallow deltaic setting
(Balaguru, 2001). The rift basin became depocentre for the deltaic-shallow
marine deposition of the Tanjong Formation in the east of Sabah (Balaguru,
2006b). The consequences of the N-S compression were probably subduction
towards the southeast, accompanied by volcanic activity in the eastern part of
Sabah which marked by thick deposits of early – middle Miocene pyroclastic
rocks, widely distributed in the Sulu Sea (Tongkul, 1993). This rock is similar to
the volcaniclastic sediments of the Libung and Tungku Formations in the
eastern Dent Peninsula.
The Andaman Sea broke up during ~19.0Ma to 15.5 ma giving rise to
Sulu Sea back-arc basin development and axial fluviodeltaic to shallow marine
and deep marine basin fill to the North (Balaguru, 2006b). Major uplifting during
Early Miocene has resulted in deformation and truncation of the Segama Group
sediments. Subsequent erosion occurs and depositing the sediment of older
Sebahat Formation in the offshore Kinabatangan area (Ismail Che Mat Zin,
1994). The erosional surface that overlies Dent Group sediments angularly is
interpreted as a regional unconformity. Balaguru (2006b) interpreted and
referred to this unconformity as the Deep Regional Unconformity (DRU, 15.5
Ma) in Sabah. Rangin (1991), in the different location reported the collision of
Cagayan Arc and Palawan micro continental block in Middle Miocene had
caused the Middle Miocene Unconformity (MMU).
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15
Chapter 2: General Geology and Tectonic Setting
A
Dangerous
Dangerous Grounds,
Reed
Grounds,
Reed bank
bank ?
(Southern
?
(Southern China)
China)
'Rajan
Sea
'Rajang
Sea'
Sapulu
g , East
'
Sapulut
, East
Crocker,
Trusma
t
Crocker,
Trusmadi
di
Continent
Continental
crus
al
tcrust Petrona
Modified
Oceanic
Oceanic crust
crust
0
100
0
Km100 Km
A
’
A’
A
Volcanic
ophiolite
Volcanic
arc,ophiolites
Cher -Chert
Spilit - Spilite
arc,
s
t
e
v
v + v
2004
from
Modified fromsPetronas. 2004.
A’
Adapted from Balaguru 2001, Hall 2002,
Figure 2.2. Palinspastic reconstruction of the Mid Eocene (~42.5 ma) - Celebes
Sea break-up and development of the SE Pacific margin accretionary complex
on Cretaceous oceanic crust; likely deep marine sedimentation (ISIS, 2005).
Rajan and
gFol - Thrust
Crocker
up'
d 'po -Belts,
u /
Laban &
p oslivers
Kulapi
F
f b b
g
s
m
A
0
A’
v
v
v
v
v
v v
v
A
Dent volcanics and
volcaniclastics
100 Km
Modified from Petronas 2004.
A’
Adapted from Balaguru 2001, Hall
2002,
Figure 2.3. Palinspastic reconstruction of the Middle Eocene to early Miocene
(~42.5 to 20.5 ma) - The South China Sea “break-up” and the development of
fore-arc basin and accretionary wedge; likely deep marine turbidite deposition
(ISIS, 2005).
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Chapter 2: General Geology and Tectonic Setting
Rajan and
gFol - Thrust
Crocker
up'
d 'po -Belts,
p oslivers
u /
f b b
A
A’
Chaoti
c
deposit
s
v
v
v
v
0
v
v
v
Den volcanic
t
s volcaniclastics
A
v
100 Km
A’
Adapted from Balaguru 2001, Hall
2002,
Figure 2.4. Palinspastic reconstruction of the Early Miocene (20.5 ma) - Sabah
Orogeny occurred when the South China Sea microcontinent collided with the
Palawan Arc and North Borneo; likely deep marine gravity slide and melange
deposition (ISIS, 2005).
A
A’
Neogene
sediments
(Sabah Basin)
A
v v v
v vv v v
v
+
0
D ent volcanics and
volcaniclastics
(Extensional basin)
100 Km
Mo difie d fro m Petron as 2004 .
SB305
SB305
SB305
SB305
A’
Adapted f rom Balaguru 2001, Hall 2002, Petronas 2004
Figure 2.5. Palinspastic reconstruction of the early Miocene to mid Miocene
(~19.0 to 15.5 ma) with Andaman Sea „breakup‟ giving rise to Sulu Sea backarc basin development and basin-fill “axial” fluviodeltaic to shallow marine and
deep marine sedimentation in the northern area (ISIS, 2005).
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17
Chapter 2: General Geology and Tectonic Setting
IV. Middle Miocene to Pliocene (~15.5 – 5.5 ma) – Fig. 2.6 to Fig. 2.7
The major uplift and erosion during early Miocene continued until the late
Miocene. During the Mid Miocene (~15.5 to13.0Ma), the continuation of the
Andaman Sea break up stopped the spreading of Sulu Sea. During this time,
the fluvio-deltaic and shallow marine sedimentation later continued in the
northeastern and southeastern part of Dent Peninsula (Balaguru, 2006a). This
tectonic event resulted in deposition of the Sebahat and Ganduman Formations
in the eastern part of the dent Peninsula as deltaic facies successions. In late
Miocene (~11.6 to 5.5 Ma), the accretionary prism widened to the north and the
sediment depocentre shifted to the southeast (Balaguru, 2006a).
V. Pliocene – Recent (~5.5 - 0 ma) – Fig. 2.8
The Pliocene to Recent tectonic event (~5.5 - 0 Ma) is referred to the
Meliau Orogeny, which created transpression in Celebes Sea and inversion and
wrenching in NE Borneo (Balaguru, 2006b). In the southern area, low rates of
paralic turbidite sedimentation occurred. Uplifting and erosional events during
late Pliocene resulted in deposition of the Togopi Formation (Ismail Che Mat
Zin, 1994).
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18
Chapter 2: General Geology and Tectonic Setting
A
A’
Neogene
sediments
(Sabah Basin)
+
0
Dent volcanicsand
volcaniclastics
(Extensional basin)
vv v
v
100 Km
Modified from Petronas 2004.
A’
Adapted from Balaguru 2001, Hall
2002,
Figure 2.6. Palinspastic reconstruction of the Middle Miocene (~15.5 – 13.0 ma)
- Andaman Sea break-up where Sulu Sea spreading ceased, but likely
continued axial fluvio-deltaic and shallow marine sedimentation (ISIS, 2005).
A
Neogen
Neogene
esediments
sediment
s
0
Kinabal
Kinabalu
u + +
+
+
Semporn
- Tawa
- Sul - Sulu
Semporna
- Tawau
A’
a
u volcanics
u
volcanic
Neogen
Neogene
Neogen
Neogene
sediment
e sediments s
sediment
e
sediments
v
s
v v
sv
vv
vv
v v
v vv
v
vv v + vvv v v + vv
v vv v +v v
+ + +
100 Km
Modified from Petronas 2004.
A
A’
Adapted from Balaguru 2001, Hall
2002,
Figure 2.7. Palinspastic reconstruction of the Late Miocene (~11.6 – 5.5 ma) The accretionary prism to the north widens and the sediment depocentre shifts
to the South-East and the Manalunan trough develops in South with slope
turbidite deposition (ISIS, 2005).
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Chapter 2: General Geology and Tectonic Setting
Semporna
A
Neogene
Kinabalu
sediments
Neogene
sediments
A’
Neogene
sediments
v
+
vv
0
- Tawau - Sulu
volcanics
+
v
v
v v v v v + vv v
v v +
+
100 Km
Modified fromPetronas 2004.
A
A’
Adapted from Balaguru 2001, Hall 2002, Petronas 2004
Figure 2.8. Palinspastic reconstruction of the Pliocene to Recent (~5.5 - 0 ma) The Meliau Orogeny creating transpression in Celebes Sea and inversion and
wrench in NE Borneo; likely low rates of paralic sedimentation in the North with
slope turbidite deposition in the south (ISIS, 2005).
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20
Chapter 2: General Geology and Tectonic Setting
2.2 STRATIGRAPHY AND DEPOSITIONAL SETTING IN THE DENT
PENINSULA
Sediments in the Dent Peninsula were deposited in fore-arc and back-arc
basin. These fore-arc and back-arc sediments were sub-divided into four types
based on tectonic setting, including fore-arc sediments, back-arc syn-rift
sediments, back-arc post rift sediments, and back-arc inversion sediments
(Petronas, 2007; Balaguru, 2006a & 2006b). This section summarizes
lithostratigraphy of the Dent Peninsula, relative to depositional environments
and tectonic setting as shown in Figure 2.9.
The first depositional setting is characterized by Paleogene to Neogene
sediments which were deposited in the forearc basin, and are underlain by
obducted accretionary wedge deposits. Kinabatangan Groups sediments are
assigned to this type and comprise three main formations, Kulapis, Labang and
Ayer. These sediments were deposited in bathyal to deep marine settings, with
ages ranging from middle Eocene to late early Miocene.
The second type is characterized by Neogene sediments, deposited in
the passive margin of the back-arc syn-rift. Segama Group marked to these
sediments and has been deposited in back-arc basin that developed related to
the Sulu Arc during early Miocene to middle Miocene. The late early Miocene to
early middle Miocene sediments are chratecterized by Libong Formation. This
formation consists of sub littoral-bathyal tuffs, slump breccia, boulder beds,
chert and pebbly mudstone which lie unconformable over Labang Formation
(Balaguru, 2006a). In Lahad Datu area, the Libong Formation sediments
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21
Chapter 2: General Geology and Tectonic Setting
unconformably overlie crystalline basement (Leong, 1974). The depositional
setting changes to shallow marine in the Tungku Formation which occured after
thrusting, faulting and uplift events (Noad, 1998). Tungku Formation consists of
pyroclastic rocks, including poorly sorted volcanic boulder conglomerate of the
Bagahak pyroclastic Member. The age of Tungku Formation is considered to
range from early middle Miocene to middle middle Miocene.
The post-rift sediments are characterized by the Dent Group which was
deposited in the back-arc. These sediments were deposited in a passive margin
basin. The mid-middle Miocene to early upper Miocene interval of Sebahat
Formation consists of large delta system prograding onto the shallow marine
shelf (Noad, 1998). These sublittoral-neritic clastic marine sediments crop out in
the eastern part of the Dent Peninsula. The thickness of the Sebahat Formation
is estimated to be up to 2300 meters along the western flank of the Sebahat
anticline. The unit is overlain by the early Upper Miocene to Early Pliocene
Ganduman Formation. Paralic sedimentation continued in the Ganduman
Formation, with sandy facies passing eastwards into a shaley facies,
demarcating the contemporaneous shelf edge (Ismail Che Mat Zin, 1994). The
estimated thickness of the Ganduman formation is about 1400 meters.
Finally, back-arc inversion resulted in depositional of shallow marine
calcareous sediments of Togopi Formation. After a phase of major uplift and
erosion in the early Pliocene, the limestone which mostly consists of loosely
cemented rubbly limestone, calcareous sandstone, claystones and marls was
deposited. This formation overlies the basal Pliocene unconformity with
maximum thickness of 600m. Abundant marine fossils are reported in this
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22
Chapter 2: General Geology and Tectonic Setting
calcareous shallow marine sediment (Haile and Wong, 1965). The sediments
formed a bedded succession with common channel features, but no clear
carbonate build-ups were observed. Hence, these sediments are interpreted as
having been deposited as transported carbonates (Ismail Che Mat Zin, 1994).
Pleistocene terrace sand, gravel, quaternary river deposits and coastal alluvium
are the youngest sediments mapped by Lim (1985).
LITHOLOGY
ONSHORE
LITHOSTRATIGRAPHY
FORMATION
EPOCH
DEPOSITIONAL
ENVIRONMENT
TECTONICSETTING
TOGOPI
LOWER COSTAL PLAIN
5.2 Ma
PLIOCENE
RESERVOIR HYDR
OCCU
ROCK
FINAL EXTENSION
TRANSPRESSION &
INVERSION
SHALLOW M ARINE
PLEISTOCENE
SOURCE
ROCK
TMU
GANDUMAN
Potential
UPPER
DENT GROUP
FAULTING & UPLIFT
BANGGAI SULA BLOCK
COLLISION
SHALLOW M ARINE
POST-INVERSION
LOWER COSTAL PLAIN
8.6 Ma
REGIONAL FOLDING
SRU & UPLIFT
HIGH PROGRADATION
PHILIPPINE BLOCKS
COLLISION
LOWER COSTAL PLAIN
15.5 Ma
LOWER COSTAL PLAIN
SHALLOW M ARINE
17.5 Ma
COLLISION
LIU
MARINE
19-20 Ma
AYER
DEEP MARINE
BMU
BATHYAL
SYN-RIFT
BLOCK & GROWTH
FAULTING
LIBUNG
1.REGRESSIVE
KINABATANGAN GP
LOWER
RAJANG
PALEOCENE
UPPER
CRETACEOUS
GROWT H FAULTING
MMU/ PALAWAN BLOCK &
UIU CAGAYAN ARC
TUNGKU
SUBSIDENCE
BACKARC EXTENSION
OF SULU SEA
REGIONAL FOLDING
FAULTING & UPLIFT
& EROSION
~22 Ma
DEEP MARINE
TURBIDITES
LABANG
KULAPIS
42.5 Ma
EOCENE
INVERSION & UPLIFT
MARINE
Potential
SEGAMA GROUP
MIDDLE
MIOCENE
AGGRADATION
OLGOCENE
POST-RIFT
MOD. PROGRADATION
Proven
SEBAHAT
EAST CROCKER
SAPULUT
TRUSMADI
CHERT SPILITE
BASEMENT
DEEP MARINE
TURBIDITES
DEEP MARINE
TURBIDITES
FOREARC
SETTING
REGIONAL FOLDING
FAULTING & UPLIFT
& EROSION
Figure 2.9. Lithostratigraphy of Dent Peninsula (modified after Balaguru, 2006a
& 2006b; Petronas, 2007).
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23
POSS
UNDI
HYDR
Chapter 2: General Geology and Tectonic Setting
2.3 GENERAL GEOLOGY OF THE DENT GROUP
General geology will discuss briefly on lithology distribution in Dent
Peninsula, relative to the Dent Group sediments. The geological map (Figure
2.10) shows the Dent Group occurs in the eastern part of the Dent Peninsula,
whereas the older Segama Group occurs in the western part. Generally, the
sediments are younging towards to the east. Most the major faults occur in the
Segama Group. A series of anticlinal fold axes, trending NEE, occur within the
Dent Group.
The geological cross section A-B-C in Figure 2.11 is a merged section of
an onshore geological cross section and a seismic section in the offshore (ISIS,
2005). The section shows that the Dent Group was deposited after or during
post-rifting periods, which indicated by the occurrence of faults, which
terminated at the base of Sebahat Formation. Structural patterns from the cross
section show the Dent Peninsula formed as an anticlinorium which can be
inferred from the geological map, whereas the synclinorium is marked by Tabin
Syncline. The anticlinorium surface known as Dent Anticlinorium has been
extensively eroded during the early Miocene to Pliocene (Ismail Che Mat Zin,
1994).
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Chapter 2: General Geology and Tectonic Setting
2.3.1 Sebahat Formation
The basal interval of the Dent Group comprises of sediment of Sebahat
Formation, which consist predominantly dark grey to black mudstone, with
subordinate marl, argillaceous sandstone and conglomerate (Haile and Wong,
1965). Noad (1998) described the main lithology of this formation as thick grey
mudstone beds, with thin well cemented and highly fossiliferous calcareous
horizons and rare siltstone beds. Results of the present study indicate Sebahat
Formation is dominated by mudstone with minor sandstone and siltstone. The
mudstones of Sebahat sediments are easily to be weathered and eroded. This
formation generally dips 20o-30o to the east. The age of Sebahat Formation
ranges from middle middle Miocene to early upper Miocene (Balaguru, 2006a).
2.3.2 Ganduman Formation
Noad (1998) carried out a detailed sedimentological study of the
Ganduman Formation and classified lithofacies. Generally, the Ganduman
Formation is divided into two parts which are Lower Ganduman and Upper
Ganduman Formations based on the sand content. The lower part is dominated
by sandstone whereas the upper part is interbedded with calcareous mudstone.
Khalid Ali (2004) described that the Ganduman Formation forms in two
sequences comprising on Upper Ganduman Formation (thick beds of
sandstone and thinner layer of mudstone) and Lower Ganduman Formation
(thick mudstone units and thinner sandstone beds). The average dips angle of
this formation ranges from 15o-20o to the east. According to Hutchinson (2005),
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25
Chapter 2: General Geology and Tectonic Setting
this formation is conformable upon the Sebahat Formation as onlapping
sequence as displayed in the offshore seismic section and unconformably
overlain by Togopi Formation. The age of Ganduman Formation is early upper
Miocene to early Pliocene (Balaguru, 2006a).
2.3.3 Togopi Formation
The Togopi Formation is dominated by fossiliferous limestone (Noad,
1998). Haile and Wong (1965) reported that this formation is comprised of
loosely cemented rubbly reef limestone, calcareous sandstone, clay and marl
with a general eastward dip of 3o-10o. Ismail Che Mat Zin (1994) reported that
most of the limestone was transported as a result of the Pleistocene erosional
event. The age of Togopi Formation ranges from late Pliocene to Pleistocene
(Haile and Wong, 1965).
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26
Chapter 2: General Geology and Tectonic Setting
Pulau
Tambisan
A
Dent
Heaven
Tg Labian
Sahabat
B
Tungku
C
LEGEND
SYNCLINE
ANTICLINE
FAULT
5km
Figure 2.10. Geological map of Dent Peninsula (modified after ISIS, 2005; Haile
and Wong, 1965).
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27
Chapter 2: General Geology and Tectonic Setting
B
A
ONSHORE
C
OFFSHORE
Figure 2.11.The merged of NW-SE onshore-offshore geological cross section with interpreted seismic section (after ISIS,
2005).
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28
Chapter 2: General Geology and Tectonic Setting
2.4 MAJOR STRUCTURAL ELEMENTS
Sabah has undergone at least five major episodes of deformation
associated with five main groups of rock units (Tongkul, 1991). A summary of
the structural evolution in Sabah was elaborated below as shown in Figure 2.12.
These structural episodes represent the regional scale structural evolution.
i.
Faulting, folding, metamorphism and local uplift of the oceanic basement
during the Early Cretaceous.
ii.
Imbrication and local uplift of the oceanic basement and associated
sediments (cherts, shales, sandstones and limestones) during Early
Eocene.
iii.
Imbrication of Eocene-Lower Miocene sediments and underlying
sediments during Late Oligocene to Middle Miocene produced the NESW and NW-SE fold and thrust belts in western and northern Sabah,
respectively.
iv.
NE-SW Normal faulting in eastern and central Sabah on basement rocks
and overlying younger sediments during the Early-Middle Miocene.
v.
Folding, faulting and uplift of the Neogene sediments and underlying
older rocks during the Late MiocenePliocene in southeastern and
western Sabah. Several NE-SW trending fold axes occur on the Late
Miocene-Pliocene clastic and volcaniclastic sediments in the Dent
Peninsula (Haile and Wong 1965). Similar trending folds also occur on
the Late Miocene-Pliocene.
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29
Chapter 2: General Geology and Tectonic Setting
Figure 2.12. Structural sketch map of Sabah from various sources showing
three main sets of faults (N-S wrench fault, NW-SE trending extension and
wrench, and NE-SW trending extension and wrench) and the bends of the foldthrust belt and similar pattern offshore (as quoted after Leong, 1994).
Recent studies on local structural trend in Dent Peninsula were carried
out by Ismail Che Mat Zin (1994) and Balaguru and Nicholas (2003). The major
structure formed in the Dent Peninsula is a series of NEE-SWW trending foldthrust belts (Figure 2.13). The series of anticlinal fold belts formed an
anticlinorium as interpreted having a parallel axis trending ENE (Ismail Che Mat
Zin, 1994). He also verified Tabin fault is a transpressive fault. Leong and Azlina
(1999) confirmed the anticlinorium axis trends NNE-SWW, based on
aeromagnetic data. The major thrust fault belt trends northeast in the west and
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Chapter 2: General Geology and Tectonic Setting
bending to the east and south east towards to the north and eastern part of
Sabah (Balaguru, 2006a).
Figure 2.13. Structural trend in the Dent Peninsula locally shows the position
and lateral extent of Tabin Fault (Ismail Che Mat Zin, 1994).
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Chapter 2: General Geology and Tectonic Setting
2.5 IGNEOUS AND VOLCANIC ACTIVITY
The Dent Peninsula was surrounded by the active plate tectonics which
resulting the occurrences of rifting, plate collision, subduction, and magmatism.
The Neogene volcanism occurs in three principal areas, with ages ranging from
Miocene to Pleistocene (Chiang, 2002). Igneous activity seems to have
occurred almost throughout the periods represented in the stratigraphic column.
However, it can be generally grouped into three main phases, summarized
below (Tongkul, 1991). Figure 2.14 shows the model of the subduction zone of
Southeast Sabah.
i.
The earliest phase is associated with the basement complex and
associated sediments, whereby intrusions and extrusions of acidicbasic-ultrabasic rocks occurred in the Darvel Bay region. Little is known
of the timing of this igneous activity. Leong (1974) suggested that the
intrusion and extrusion of the igneous rocks probably occurred during
pre-Triassic and continued until Cretaceous. Intermittent volcanic
activity also occurred after the main phase, and tuffaceous materials
occur in Eocene-Oligocene sediments (Collenette 1965, Leong 1974).
ii.
The second phase is associated with the extrusion of Early-Middle
Miocene volcanics and pyroclastics in the Dent Peninsula and Labuk
Valley (Kirk 1968, Rangin et al. 1990). The widespread occurrence of
tuffs and andesitic flows in the Dent Peninsula possibly indicates a
volcanic arc in that region. Hutchison (1989) has suggested that this
volcanic arc was probably related to southeastward subduction of the
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Chapter 2: General Geology and Tectonic Setting
South China Sea oceanic lithosphere in eastern Borneo, whereas
Rangin (1989) favoured a north-westward subduction of the Celebes
Sea oceanic lithosphere in eastern Sabah.
iii.
The third phase of igneous activity occurred during the Late Miocene to
Quaternary. This is represented by the intrusive and extrusive rocks
mainly found in the Semporna and Tawau region with minor
occurrence in western Sabah. The igneous rocks in the Semporna and
Tawau region probably represent the southwestward extension of the
Sulu volcanic arc resulting from the southeastward subduction along
the Sulu Trench (Hamilton, 1979).
Igneous and volcanic activity described above play an important role for
source rocks maturity. Heat sourced from volcanic and igneous activity convert
kerogen to hydrocarbon. These volcanic and igneous activities occur during
second phase and third phase could give a clue to determine a relative heat
flow values. This value is important to reconstruct paleo heat flow in basin
modelling during calibration and affects source rock maturity.
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Chapter 2: General Geology and Tectonic Setting
Figure 2.14. (A) Model of the subduction zone for the Miocene volcanic rocks of
SE Sabah. I to IV is an alternative models for melting in intra-plate settings
applicable to the Pliocene-Pleistocene volcanic rocks of SE Sabah (after
Chiang, 2002).
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