Podcast
Questions and Answers
Which rock type is associated with both basalt and spilite?
Which rock type is associated with both basalt and spilite?
What formations lie unconformably on the basement rock of Mesozoic age?
What formations lie unconformably on the basement rock of Mesozoic age?
What geological feature is characterized by granitic and metamorphic rocks in Sabah?
What geological feature is characterized by granitic and metamorphic rocks in Sabah?
The Kudat Formation is primarily characterized by what type of sediments?
The Kudat Formation is primarily characterized by what type of sediments?
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Which formations are primarily found in the dominant geological unit of Sabah?
Which formations are primarily found in the dominant geological unit of Sabah?
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Which formation consists of shallow water deposits including sandstones and limestones?
Which formation consists of shallow water deposits including sandstones and limestones?
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What was a significant geological event that created the Top-Crocker unconformity in Sabah?
What was a significant geological event that created the Top-Crocker unconformity in Sabah?
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What age are the sediments of the Timohing Formation?
What age are the sediments of the Timohing Formation?
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Which rock types are predominantly found in the sedimentary rocks of Western and North Sabah?
Which rock types are predominantly found in the sedimentary rocks of Western and North Sabah?
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The Crocker Formation is characterized by which type of sedimentary structures?
The Crocker Formation is characterized by which type of sedimentary structures?
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What geological feature is divided into a lower sandstone unit and an upper shale unit?
What geological feature is divided into a lower sandstone unit and an upper shale unit?
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What age range does the oldest dated sedimentary rock in Sabah belong to?
What age range does the oldest dated sedimentary rock in Sabah belong to?
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What type of rocks were formed during Miocene-Pliocene times?
What type of rocks were formed during Miocene-Pliocene times?
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Which rock type is NOT mentioned as part of the igneous rocks in Sabah?
Which rock type is NOT mentioned as part of the igneous rocks in Sabah?
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What geological process is thought to have controlled the development of the basin in Western and Northern Sabah?
What geological process is thought to have controlled the development of the basin in Western and Northern Sabah?
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What type of sedimentary rocks are closely associated with basaltic/spilitic type of igneous rocks in Sabah?
What type of sedimentary rocks are closely associated with basaltic/spilitic type of igneous rocks in Sabah?
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What geological feature is considered one of the largest mélange terranes in the world?
What geological feature is considered one of the largest mélange terranes in the world?
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What primarily composes the lithology of the mélange units in Eastern Sabah?
What primarily composes the lithology of the mélange units in Eastern Sabah?
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What caused the formation of olistostrome deposits in Eastern Sabah?
What caused the formation of olistostrome deposits in Eastern Sabah?
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During which geological period did the uplift of olistostrome deposits and older rock units occur in Eastern Sabah?
During which geological period did the uplift of olistostrome deposits and older rock units occur in Eastern Sabah?
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What does the older igneous and metamorphic rocks in eastern Sabah indicate about its geological history?
What does the older igneous and metamorphic rocks in eastern Sabah indicate about its geological history?
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Which formations are represented in the Northern Tarakan Sub-basin?
Which formations are represented in the Northern Tarakan Sub-basin?
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What significant tectonic event affected the units in Eastern Sabah during the late Middle to early Late Miocene?
What significant tectonic event affected the units in Eastern Sabah during the late Middle to early Late Miocene?
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What types of deposits are predominantly found in the Sandakan Sub-basin?
What types of deposits are predominantly found in the Sandakan Sub-basin?
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What is the significance of the NW Borneo Trend in Sabah's tectonic evolution?
What is the significance of the NW Borneo Trend in Sabah's tectonic evolution?
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Which of the following describes the Late Miocene tectonic event in Sabah?
Which of the following describes the Late Miocene tectonic event in Sabah?
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What does the term 'Base Miocene Unconformity' refer to?
What does the term 'Base Miocene Unconformity' refer to?
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What impact did the collision of the Cagayan Arc and Palawan micro-continental block have on Sabah?
What impact did the collision of the Cagayan Arc and Palawan micro-continental block have on Sabah?
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What type of rock predominates in the coastal areas mentioned in the sedimentation remnant?
What type of rock predominates in the coastal areas mentioned in the sedimentation remnant?
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Which tectonic event is associated with a change from deepwater to shallow deltaic environments?
Which tectonic event is associated with a change from deepwater to shallow deltaic environments?
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What geological feature is suggested to lie beneath the ophiolite based on gravity data interpretation?
What geological feature is suggested to lie beneath the ophiolite based on gravity data interpretation?
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What is the primary composition of the Sebahat, Ganduman, and Togopi formations?
What is the primary composition of the Sebahat, Ganduman, and Togopi formations?
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What major tectonic event is associated with the Early Miocene deformation?
What major tectonic event is associated with the Early Miocene deformation?
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What change in depositional environment followed the Early Miocene deformation?
What change in depositional environment followed the Early Miocene deformation?
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What does the Gomantong Limestone Formation primarily signify in terms of geographic uplift?
What does the Gomantong Limestone Formation primarily signify in terms of geographic uplift?
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What sedimentary feature marks the end of the Early Miocene deformation?
What sedimentary feature marks the end of the Early Miocene deformation?
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How thick is the cumulative sedimentary layer that resulted from continued subsidence during the Middle Miocene?
How thick is the cumulative sedimentary layer that resulted from continued subsidence during the Middle Miocene?
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What is the significance of the Base Miocene Unconformity?
What is the significance of the Base Miocene Unconformity?
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What geological evidence is associated with the Late Early Miocene to Middle Miocene in terms of sediment deposition?
What geological evidence is associated with the Late Early Miocene to Middle Miocene in terms of sediment deposition?
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In which direction does the Gomantong Limestone outcrop in Sabah?
In which direction does the Gomantong Limestone outcrop in Sabah?
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Where is the Malay Basin located?
Where is the Malay Basin located?
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When did petroleum exploration in the Malay Basin begin?
When did petroleum exploration in the Malay Basin begin?
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What is the largest oil field in the Malay Basin?
What is the largest oil field in the Malay Basin?
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Which companies were awarded the first concessions in the Malay Basin?
Which companies were awarded the first concessions in the Malay Basin?
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The Malay Basin is considered one of the deepest continental extensional basins in Southeast Asia.
The Malay Basin is considered one of the deepest continental extensional basins in Southeast Asia.
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What are the primary types of hydrocarbons found in the Malay Basin?
What are the primary types of hydrocarbons found in the Malay Basin?
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The Malay Basin is known for major oil discoveries, including the fields of _____ and _____ B.
The Malay Basin is known for major oil discoveries, including the fields of _____ and _____ B.
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What geological feature separates the Malay Basin from the Penyu Basin?
What geological feature separates the Malay Basin from the Penyu Basin?
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Which of the following statements is true regarding the Malay Basin's geological history?
Which of the following statements is true regarding the Malay Basin's geological history?
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Match the following fields with their respective resource type:
Match the following fields with their respective resource type:
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What types of source rocks are found in the Malay Basin?
What types of source rocks are found in the Malay Basin?
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What type of traps are most common in the Malay Basin?
What type of traps are most common in the Malay Basin?
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Ultrabasic rocks such as ______ are closely associated with basalt.
Ultrabasic rocks such as ______ are closely associated with basalt.
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The ______ Formation is primarily characterized by interbedded carbonaceous sandstones and shales.
The ______ Formation is primarily characterized by interbedded carbonaceous sandstones and shales.
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The ______ Formation consists of deep-water flysch sediments found mostly in Western Sabah.
The ______ Formation consists of deep-water flysch sediments found mostly in Western Sabah.
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The Bongaya Formation is of ______ age and consists of shallow water deposits.
The Bongaya Formation is of ______ age and consists of shallow water deposits.
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The turbidites in the Crocker Formation are divided into a lower sandstone unit and an upper ______ unit.
The turbidites in the Crocker Formation are divided into a lower sandstone unit and an upper ______ unit.
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The sediments of the Timohing Formation are primarily of ______ to Pleistocene age.
The sediments of the Timohing Formation are primarily of ______ to Pleistocene age.
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The ______ Formation represents interbedded sediments characteristic of a shallow water environment in Northern Sabah.
The ______ Formation represents interbedded sediments characteristic of a shallow water environment in Northern Sabah.
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The oldest unit in Sabah consists of crystalline basement rocks, which are mainly ______ and metamorphic rocks.
The oldest unit in Sabah consists of crystalline basement rocks, which are mainly ______ and metamorphic rocks.
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The Crocker Range is characterized by a series of high-angle ______ faults.
The Crocker Range is characterized by a series of high-angle ______ faults.
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The Crocker and Trusmadi Formation are highly deformed sedimentary rocks from the ______ to early Miocene period.
The Crocker and Trusmadi Formation are highly deformed sedimentary rocks from the ______ to early Miocene period.
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The Sabah Orogeny created the early Miocene ______ unconformity.
The Sabah Orogeny created the early Miocene ______ unconformity.
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In Western and North Sabah, the sedimentary rocks mainly consist of sandstones and ______ with subordinate cherts.
In Western and North Sabah, the sedimentary rocks mainly consist of sandstones and ______ with subordinate cherts.
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The oldest dated sedimentary rocks in Sabah are radiolarian ______ of Early Cretaceous age.
The oldest dated sedimentary rocks in Sabah are radiolarian ______ of Early Cretaceous age.
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The formation of an elongate basin in Sabah is thought to have occurred during the ______ to Early Eocene.
The formation of an elongate basin in Sabah is thought to have occurred during the ______ to Early Eocene.
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The Rajang Group consists of Late Cretaceous to Eocene deep water mudstones and _____ sandstones.
The Rajang Group consists of Late Cretaceous to Eocene deep water mudstones and _____ sandstones.
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The sedimentary rocks of Western & North Sabah have undergone several episodes of ______.
The sedimentary rocks of Western & North Sabah have undergone several episodes of ______.
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The region has a variety of igneous rocks, including serpentinites, basalts, and ______.
The region has a variety of igneous rocks, including serpentinites, basalts, and ______.
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The uplift associated with the Rajang Group is referred to as the '______ orogeny'.
The uplift associated with the Rajang Group is referred to as the '______ orogeny'.
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The strongly deformed turbiditic Rajang Group is interpreted as a part of an ______ prism.
The strongly deformed turbiditic Rajang Group is interpreted as a part of an ______ prism.
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The formations that comprise the Rajang Group include the Sapulut, Trusmadi and East _____ formations.
The formations that comprise the Rajang Group include the Sapulut, Trusmadi and East _____ formations.
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An unconformity within the succession of Palaeogene turbidites between the ______ and Upper Eocene is inferred.
An unconformity within the succession of Palaeogene turbidites between the ______ and Upper Eocene is inferred.
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The contact at the unconformity is generally difficult to recognize in outcrop because of similarities in ______ either side of it.
The contact at the unconformity is generally difficult to recognize in outcrop because of similarities in ______ either side of it.
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The fold-thrust belt of the West Crocker Formation represents the _____ complex related to continued southeasterly subduction.
The fold-thrust belt of the West Crocker Formation represents the _____ complex related to continued southeasterly subduction.
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The ______ was a period of continued deposition of deep marine turbidites during the Palaeogene.
The ______ was a period of continued deposition of deep marine turbidites during the Palaeogene.
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The present outcrop pattern of the Miocene strata is the product of regional strike-slip and transpressional tectonics and ______ during the Late Miocene.
The present outcrop pattern of the Miocene strata is the product of regional strike-slip and transpressional tectonics and ______ during the Late Miocene.
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The Late Eocene tectonic deformation is characterized by ______ and thrusting of basement rock.
The Late Eocene tectonic deformation is characterized by ______ and thrusting of basement rock.
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The Early Miocene deformation is interpreted to mark a major tectonic event causing formation of the ______, major uplift and erosion.
The Early Miocene deformation is interpreted to mark a major tectonic event causing formation of the ______, major uplift and erosion.
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The Paleogene regional tectonic setting of Sabah seems to be very complex, with southeasterly subduction in the NW Borneo and extension in the SE in the ______ Sea.
The Paleogene regional tectonic setting of Sabah seems to be very complex, with southeasterly subduction in the NW Borneo and extension in the SE in the ______ Sea.
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The Kuamut Formation has been linked to sedimentation on the flanks of an ______ wedge in Late Oligocene times.
The Kuamut Formation has been linked to sedimentation on the flanks of an ______ wedge in Late Oligocene times.
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The Early Miocene deformation is interpreted to mark a major ______ event.
The Early Miocene deformation is interpreted to mark a major ______ event.
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The structural development in these areas is possibly related to propagation of deformation from Sulawesi towards NW ______.
The structural development in these areas is possibly related to propagation of deformation from Sulawesi towards NW ______.
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The Gomantong Limestone Formation contains clasts of the ______ Formation.
The Gomantong Limestone Formation contains clasts of the ______ Formation.
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Major uplift and final structural development in Sabah region is interpreted to be caused by transpressional movement during the ______ period.
Major uplift and final structural development in Sabah region is interpreted to be caused by transpressional movement during the ______ period.
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The absence of widespread synsedimentary deformation in the Tanjong Formation suggests it was deposited during a period of relative ______ quiescence.
The absence of widespread synsedimentary deformation in the Tanjong Formation suggests it was deposited during a period of relative ______ quiescence.
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Related to subduction and collision of the Dangerous Ground Continental Block to the NW Borneo, this event is referred to as the '______ Orogeny'.
Related to subduction and collision of the Dangerous Ground Continental Block to the NW Borneo, this event is referred to as the '______ Orogeny'.
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The Late Miocene strike-slip ______ is regionally significant and occurred at a similar time as important deformation in NE Kalimantan.
The Late Miocene strike-slip ______ is regionally significant and occurred at a similar time as important deformation in NE Kalimantan.
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Limestone outcrops in southern Sabah are correlated with the Early Miocene (Burdigalian) ______ Limestone Formation.
Limestone outcrops in southern Sabah are correlated with the Early Miocene (Burdigalian) ______ Limestone Formation.
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The cumulative thickness created by continued subsidence is at least ______ m.
The cumulative thickness created by continued subsidence is at least ______ m.
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The associated major uplift and erosion provided sediment supply to the deltaic to shallow marine Middle to Upper Miocene successions of the ______ and Tanjong Deltas.
The associated major uplift and erosion provided sediment supply to the deltaic to shallow marine Middle to Upper Miocene successions of the ______ and Tanjong Deltas.
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This change in depositional environment is also recognized offshore NW ______.
This change in depositional environment is also recognized offshore NW ______.
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Study Notes
Sabah's Geology
- Sabah's oldest unit is the Crystalline Basement composed of granitic and metamorphic rocks found in the Darvel Bay and Segama areas.
- The dominant unit is the Crocker and Trusmadi Formation, consisting of deep-water sandstones with minor shales and argillaceous beds.
- Crocker and Trusmadi formations are highly deformed, formed during the Eocene to early Miocene, and are interpreted as an accretionary prism.
- The Sabah Orogeny created the early Miocene Top-Crocker unconformity and was followed by the deposition of neritic and fluvial formations, preserved in eastern Sabah.
Western and Northern Sabah
- Western and Northern Sabah consists of sedimentary and igneous rocks ranging in age from the Early Cretaceous to the Pliocene.
- Rocks in the region have undergone several episodes of deformation. The earliest deformation uplifted the basement rock during the Late Cretaceous to Early Eocene.
- The deformation controlled the development of a N-S and E-W trending basin in Western and Northern Sabah, respectively, which filled with Middle Eocene to Early Miocene sediments.
- Sedimentary rocks are dominantly sandstones and shales with subordinate cherts, limestones, and conglomerates.
- Igneous rocks include serpentinites, basalts/spilites, agglomerates, gabbros, dolerites, andesites, granodiorites, and adamellites.
- Metamorphic rocks are mainly hornblende schists and gneisses.
- The oldest dated sedimentary rocks are radiolarian cherts of Early Cretaceous age.
- The association of rock types resembles an ophiolite series, interpreted to represent an oceanic crust of Mesozoic age.
- The Crocker and Trusmadi Formations are mostly deep-water flysch sediments characterized by rhythmic alternation of sandstone and shale beds.
- The Kudat Formation consists of shallow water sediments characterized by interbedded carbonaceous sandstones and shales with lenses of Eocene-Early Miocene biohermal limestones.
- The Bongaya Formation is comprised of shallow water deposits consisting of sandstones, shales, limestone, and conglomerates, lying unconformably on the basement rock, Crocker, and Kudat formations.
- Igneous rocks were formed during Miocene-Pliocene times, including both intrusives (Mt. Kinabalu plutonics) and extrusive (Sirar Island volcanics).
Crocker Formation
- The Crocker Formation is composed of turbidites, likely reaching a thickness of 1,000 meters, interbedded with sandstone and shale deposited in a deepwater basin (submarine fan).
- The Crocker Range runs NNE-SSW and is deformed by a series of high-angle reverse faults dipping south or south-east.
- Reverse faults likely formed during the Miocene, with soft shale layers acting as slip planes for the faults and deformation.
- The Tongkul is a division within the turbidites, separating the lower sandstone unit (several hundred meters thick) from the upper shale unit (about 100 meters thick).
Eastern Sabah
- Eastern Sabah is characterized by chaotically disrupted rock units spanning approximately 12,000 square kilometers, considered one of the largest mélange (olistostrome) terranes in the world.
- The lithology primarily consists of mud-matrix olistostrome and broken formations, which include tuff and tuffaceous layers.
- The broken formations are known variously as Kuamut, Garinono, Ayer, and Kalabakan formations.
- The olistostrome was formed by slumping into a deep marine basin.
- Explosive volcanism accompanied the olistostrome deposition, indicated by the presence of tuffaceous material in the Kuamut, Garinono, and especially the Ayer Formation in the Dent Peninsula.
Eastern Sabah - Continued
- Olistostrome deposits and older rock units were uplifted in the early Middle Miocene, with the uplifted Crystalline Basement and ophiolitic Chert-Spilite Formation acting as a barrier separating the NE Sabah Basin from the SE Sabah Basin.
- The formation of the Central Sabah Sub-basin (of the NE Sabah Basin) and Northern Tarakan Sub-basin (of the SE Sabah Basin) occurred.
- The Northern Tarakan Sub-basin is characterized by the Tanjong and Kapilit formations, mainly deltaic shallow marine clastics, exposed in circular, sub-circular, and synclinal basins.
Eastern Sabah - Continued
- The oldest rocks in Eastern Sabah are Mesozoic, located in the eastern part of Sabah (Semporna and Dent Peninsula), and include a basement complex formed of various types of igneous and metamorphic rocks.
- Volcanic activity began in the Early Miocene to Pleistocene in Semporna and Dent Peninsula.
- The occurrences of volcanic rocks in Semporna are believed to be a southwest onshore continuation of the Sulu Arc from Zamboanga, formed by the subduction of the Celebes Sea.
Eastern Sabah - Continued
- Volcanic activity in NE Sabah and SE Sabah is indicated by tuffaceous and volcanoclastics of the Segama Group of rocks in the Dent Peninsular and the Kalumpang Formation in the Semporna area.
- A tectonic event in the late Middle to early Late Miocene uplifted and eroded the Tanjong formation and equivalent units, resulting in a new cycle of deltaic to shallow marine sediment filling a new depocenter, the Sandakan Sub-basin in eastern Sabah.
- The Sandakan Sub-basin contains the Dent Groups of sediments, mainly clastics with minor carbonates, comprising the Sebahat, Ganduman, and Togopi formations.
Eastern Sabah - Continued
- Remnants of the younger sedimentation cycle in both NE Sabah and SE Sabah basins include the Sandakan Formation, Bongaya Fm, Simengaris Fm, Umas-Umas Fm, and Balung Formation.
- Plio-Pleistocene sediments are mainly limestones, calcareous sandstone, conglomerate, carbon shale, and are found in coastal areas.
- The Togopi and Wallace formations represent these Plio-Pleistocene sediments.
Tectonic Evolution of Sabah
- Sabah lies at the important junction between the Eurasian, Indo-Australian, Pacific, and Philippines Sea plates.
- Sabah occupies a central position between the Sulu, Celebes, and South China Seas.
- Sabah's main tectonic elements include a major fold-thrust belt trending northeast in the west (NW Borneo Trend) and bending east and southeast toward the north and eastern part (Sulu Trend) of Sabah.
- The arcuate belt consists of a deep-marine Eocene-Oligocene accretionary complex.
- The Early Miocene deformation marks a major tectonic event, causing the formation of mélanges, major uplift, and erosion that produced the Base Miocene Unconformity.
- Following the Early Miocene deformation was a change in depositional environment from deepwater to a shallow deltaic setting.
Tectonic Evolution - Continued
- NW-SE rifting of the Sulu Sea in the Late Early Miocene rejuvenated the Central Sabah Basin with regional extension and subsidence.
- The collision of the Cagayan Arc and Palawan micro-continental block in the Middle Miocene caused another Middle Miocene Unconformity, known as the Deep Regional Unconformity.
- A Late Miocene tectonic event resulted in major folding and uplift, correlated with the Shallow Regional Unconformity.
- The latest tectonic event was likely caused by strike-slip faulting and transpressional fault movement, which continued during the Pliocene to the present day.
Tectonic Evolution - Continued
- Pre-Cenozoic features include the presence of granitic and metamorphic rocks of possibly continental origin, associated with the ophiolitic complex.
- Gravity data suggests that normal continental basement lies beneath the ophiolite.
- Deformation continued for several million years, with the Gomantong Limestone forming on structural highs during relatively quiescent times in the Early Miocene.
- An unconformity separates the deformed and lithified melange unit from the less tectonised strata.
Early Miocene Deformation
- The Early Miocene deformation marks a major tectonic event, causing the formation of mélanges, major uplift, and erosion that produced the Base Miocene Unconformity.
- This deformation is related to the subduction and collision of the Dangerous Ground Continental Block to the NW Borneo, referred to as the "Sabah Orogeny."
- The Early Miocene deformation was followed by a change in depositional environment from deep-water to a shallow deltaic setting.
- Uplift and erosion provided sediment supply to the deltaic to shallow marine Middle to Upper Miocene successions of the Meligan and Tanjong Deltas.
Early Miocene Limestone Development
- Limestone outcrops in southern Sabah are correlated with the Early Miocene (Burdigalian) Gomantong Limestone Formation, which contains clasts of the Labang Formation.
- This suggests widespread uplift, followed by carbonate sedimentation throughout the central and eastern Sabah.
- This change in depositional environment is also recognized offshore NW Sabah.
- In eastern Sabah the Gomantong Limestone outcrops in an ENE-WSW-trending belt stretching at least 200 km, suggesting that this may have been a zone of uplift along which localized carbonate sedimentation occurred, isolated from any clastic sediment influx from the west.
Late Early Miocene to Middle Miocene Clastic Sedimentation
- The end of the early Miocene deformation is marked by the onset of Tanjong, Meligan, or Kudat Formation clastic deposition, the oldest dates for which are late Burdigalian.
- The absence of widespread synsedimentary deformation in the Tanjong Formation suggests that it was deposited during a period of relative tectonic quiescence, which lasted through the deposition of late Middle Miocene or younger strata.
- Continued subsidence created a cumulative thickness of at least 6,000 meters.
Malay Basin Overview
- Located within the southern Gulf of Thailand, bordered by Vietnam and Malaysia
- Covers 80,000 km2, containing 14 km thick sediment deposits
- Extends northwestward towards Thailand's Pattani Trough and southeastward towards Indonesia's West Natuna Basin
- Petroleum exploration commenced in 1968, leading to numerous discoveries and production
Exploration History
- First concessions granted to Esso and Conoco in 1968
- Esso explored north of 5°N latitude, while Conoco focused on the southern region, encompassing the Penyu Basin
- Production-sharing contracts with oil companies initiated in 1974
- Esso drilled the first well, Tapis-1, in 1969, followed by Tapis-2 in 1974
- Tapis-1 discovered gas in sandstones, while Tapis-2 found oil
- Significant oil discoveries followed at Seligi and Bekok
- First oil production from Pulai and Tapis fields in 1978
- Seligi is the largest oil field in the basin, with over 550 MMSTB (Million Stock Tank Barrels) of Estimated Ultimate Recovery (EUR)
- Exploration continued with the discovery of Angsi, Besar, Palas, Guntong, Irong, Irong Barat, Semangkok, Tinggi, and Dulang fields
- By 1997, over 330 exploration wells had been drilled, leading to the identification of roughly 50 oil and 30 gas accumulations
Tectonic Framework
- Occupies a central position within Sundaland
- Recognized as one of the deepest continental extensional basins in the region
- Believed to have formed during the early Tertiary
- Separated from the Penyu Basin by the Tenggol Arch and the Pattani Basin by the Narathiwat High
- Exhibits an elongated NW-SE orientation, with a pre-Tertiary basement composed of metamorphic, igneous, and sedimentary rocks
- The basement is believed to represent an offshore continuation of the geology in eastern Peninsular Malaysia
- Bounded by relatively shallow basement areas: Terengganu Platform and Tenggol Arch to the southwest, Narathiwat High to the northwest, and Con Son Swell to the northeast
- Characterized by a complex rift system composed of numerous extensional grabens, interpreted from geophysical data due to significant depths
- Smaller grabens identified through seismic mapping on the west-central margin
- The pre-Tertiary basement shallows towards the southeast due to Late Middle Miocene tectonic deformation and uplift, which resulted in numerous compressional anticlines
- Origin of the Malay Basin is debated with various tectonic models proposed
- Tjia's (1999) triple junction model suggests that the Malay Basin, along with the Penyu and West Natuna basins, formed as failed rift arms of a triple junction above a Late Cretaceous thermal dome (mantle hot spot)
Tectonic Origin
- The triple junction model suggests the presence of a hot spot composed of a mantle plume, leading to the development of a "circular regional uplift" known as the Malay Dome
- Plate tectonic theory suggests T-shaped rift arms may spread outwards and produce ocean basins. In the case of the Malay Basin, Penyu, and West Natuna, the rift arms spread to form regional grabens radiating from the triple junction, becoming depocenters for sediment deposition
Stratigraphy
- Malay Basin strata are informally categorized into seismostratigraphic units known as Groups
- Groups are designated alphabetically, starting with A and progressing to M with increasing age
- Stratigraphic development is directly tied to the basin's structural evolution, occurring in three phases:
- A pre-Miocene extensional or synrift phase
- An Early to Middle Miocene thermal/tectonic subsidence phase
- A Late Miocene – Quaternary subsidence phase (representing a tectonically quiescent period)
Miocene Phase
- Represents the extensional development phase of the basin
- Subsidence is controlled by faulting, leading to deposition of thick synrift successions of alternating sand-dominated and shale-dominated fluviolacustrine sequences within isolated half-graben depocenters
- Groups M to K fill the extensional sub-basins, composed of deposits from braided streams, coastal plains, lacustrine deltas, and lakes
- Extensional faulting ceased during the Late Oligocene, but continued thermal subsidence resulted in the deposition of Groups L to D
- The basin likely reached sea level by Early Miocene times, indicated by the presence of coal-bearing strata in the succession
Early-Middle Miocene Phase
- Defined by thermal/tectonic subsidence, coupled with compressional deformation, which resulted in local inversion of half-grabens due to the reactivation of their bounding faults, and a major uplift in the southeastern part of the basin
- An unconformity truncates folded and uplifted strata as old as Group H in the southern part of the basin
- The unconformity is overlain by undeformed marine sediment of Groups A and B
Late Miocene – Quaternary Phase
- Characterized by gentle subsidence without significant tectonic activity
- Fully open marine conditions were established
- Groups A and B consist mainly of marine clays and silts deposited during an overall marine transgression in a nearshore to shallow marine environment
- Reconstruction of the Malay Basin's paleo-geographic development shows a progression from mainly non-marine (alluvial to coastal plain) environments during the Oligocene (Groups L and M), representing the synrift basin development phase, to increasingly marine environments (coastal fluviomarine to inner neritic) during the Miocene and later (Groups K to A/B)
- The Malay Basin acted as a narrow seaway or gulf receiving sediment from its northeastern and southwestern flanks
Hydrocarbon Occurrences
- The southern part of the basin contains most of the oil reserves, encompassing several giant fields such as Seligi and Tapis (both with EURs of almost 600 MMSTB)
- Hydrocarbons occur in reservoirs ranging from Group L to D, with Groups E, I, J, and K being the most prolific
- The basin can be broadly subdivided into a northern gas-prone province and a southern oil-prone province, although exceptions do exist
- On a regional scale, the geographic and stratigraphic distribution of oil and gas appears to be controlled by basin morphology
Hydrocarbon Occurrence Controls
- On a semi-regional scale, the main factors controlling oil and gas distribution include source rock quality and maturity, and the relative timing of generation and structuration
- Coal-rich source rocks are found in the north (primarily in Group I), while lacustrine source rocks are present in the south (Groups K, L, and M)
- The relative timing between structuration and hydrocarbon migration varies from south to north, with structures forming earlier in the south, allowing them to trap oil, whereas late structuration in the north resulted in more gas being trapped
Hydrocarbon Plays and Trap Styles
- Hydrocarbon occurrences in the Malay Basin can be categorized according to the structural style of the traps
- Main structural trap styles include:
- Compressional anticlines: Most prolific trap style, comprising E-W trending anticlines formed by inverted grabens. Located mainly along the central/axial part of the basin, formed during the basin inversion phase in the Middle Miocene (beginning of Group F times), often resulting from wrench movement associated with transpressional deformation of the underlying fault-bounded half-grabens. Notably observed in the southern part of the basin
- Fault dip closures
- Categorization of trap styles and hydrocarbon plays is based on structural features, geographic and stratigraphic distribution, and source-reservoir relationships
Compressional Anticlines
- Compressional anticlines in the south are typically oil-prone, while those in the north tend to be gas-prone
- Main reservoirs consist of shallow marine and fluvial sandstones of Group H, I, J, and K
- Structures are sealed by intra-group claystone and shale beds
- Hydrocarbons within these structures were sourced from interbedded carbonaceous shales and coals, primarily within Group 1
Compressional Anticlines: Central Part
- Compressional anticlines in the central part of the basin involve reservoirs mainly formed by shallow marine sandstones of Group D and E
- Seals are interbedded claystone and shale units within Group D and E
- Source rocks are deeply buried rocks in Group 1, migrating vertically through fault conduits
- Examples : Bintang, Lawit, Jerneh, Dulang, Sepat, Noring, Bujang, Ular, Tangga, Bergading, Inas
Compressional Anticlines: Southwestern Part
- The southwestern part represents a major gas trend near the Tenggol Fault, known as the Angsi-Duyong trend, which includes major gas discoveries of Angsi and Besar
- These are large compressional anticlines structurally similar to those in the main oil province to the north, underlain by synrift half-grabens controlled by normal faults
- Currently, only Duyong is in production
Tenggol Arch Plays
- The Tenggol Arch is a relatively shallow, flat, NW-trending pre-Tertiary basement segment that separates the Malay and Penyu basins
- Its northeastern boundary is marked by the Tenggol Fault, a significant normal fault zone with a maximum throw of roughly 2500 m
- The Tenggol Arch serves as a sediment source for the half-grabens located in the north
- Relatively featureless except for isolated basement mounds, some of which became structural closures when Tertiary sediments draped over them upon compaction
- The basement drapes form a unique trap style where oil has been discovered in a structure at Malong, located within Group J shallow marine sandstones
- Hydrocarbons at Malong are likely sourced from Group K or older lacustrine shales in the basin, migrating up-dip onto the Tenggol Arch, with interbedded shales providing the top seal
- The sedimentary succession on the Tenggol Arch is generally less than 1,500 m thick, suggesting potential rocks would be immature. Therefore, the Malong oil may have originated from deeper half-grabens located to the northeast of the Tenggol Fault
- The migration distance to the Malong structure is at most 10 km
- The Malong discovery raised interest in other basement structures along the arch, with assumptions that oil migrated over long distances (30-60 km) from the Malay Basin to fill these structures
- However, testing of some of these basement structures revealed they were dry, prompting a revision of the migration model
NE Ramp Margin Play
- 19 oil and 15 gas discoveries have been made on the northeastern flank of the Malay Basin
- Major trap styles include:
- Subtle stratigraphic/fault traps in Group I, J, and K, such as the Larut and Bunga Raya fields
- Faulted anticlinal traps in Group I, J, and K reservoirs, primarily found in the northeastern and eastern parts of the basin
- Lateral seal provided by sand-shale juxtaposition, with the top seal provided by interbedded shale
- Hydrocarbons are sourced from either in situ interbedded source beds or down-dip beds (Group K and L shales) via long-range migration
- Examples: Bunga Orkid, Bunga Kekwa, and Bunga Raya oilfields in the PM3 CAA area; Lerek, Pantai, Lumut, East Belumut, Larut, and Abu oilfields in PM5 and PM8
- Trap styles also include those formed by basement drapes, similar to those on the Tenggol Arch, such as the South Raya Field, where oil and gas have been found in Group I, J, and K reservoirs
- Stratigraphic channel plays, such as the Bindu discovery
- Stratigraphic pinch-out traps
- Onlap traps
Deep Reservoir Play
- This play involves reservoirs within or below the overpressured zone, believed to be present beneath existing discoveries / fields
- An example : The Bergading structure, a normal fault-bounded N-trending anticline located in the northern part of the basin near JDA
- Bergading-1 well found gas in Group B, D, and E
- The Bergading Deep-1 well was drilled to approximately 3,100 m, penetrating the overpressured zone in Group F
- Substantial amounts of gas and condensate were discovered in Group H and I reservoirs
Reservoir Rocks
- Hydrocarbons in the Malay Basin are found in sandstone reservoirs ranging from Group D to K
- The depositional environment of the sandstones varies according to stratigraphy
- In older groups (K, L, and M), reservoirs are formed, mainly by fluvial channels in a nonmarine-lacustrine setting
- In J and younger groups, sandstones are predominantly shoreface and subtidal shelf sands (especially in J) and fluvial-deltaic to estuarine channel complexes (I group and younger)
Source Rocks
- The abundance of oil and gas reserves in the Malay Basin points to the presence of effective source rocks
- Geochemical studies indicate two main depositional settings for source rocks: lacustrine and fluviodeltaic, with varying degrees of mixing between the two
-
Lacustrine source rocks:
- Consist of shales rich in algal components
- Occur in Oligocene/Early Miocene K, L, M, and pre-M/synrift groups
- Have only been penetrated at shallow depths on the flanks of the basin
-
Fluviodeltaic source rocks:
- Found mainly in the Lower-Middle Miocene I and E groups
- Predominantly located in coastal plain shales and coal/carbonaceous shales
- Encountered in the basin center
Natural Gases
- The Malay Basin is not solely an oil province but also contains several large gas accumulations
- Natural gas is estimated to comprise more than half of the basin's hydrocarbon reserves
- Total gas reserve in place is estimated to exceed 60 TSCF (Trillion Standard Cubic Feet)
- Significant gas reserves are found in the Jernih, Lawit, Duyong, and Seligi fields
- The largest gas accumulations occur primarily in reservoirs of Group D, E, I, and J
- In the northwestern part, gas is found in stratigraphically younger reservoirs while gas in the south occurs in older/deeper reservoirs
- Biogenic gas is largely confined to the eastern flank of the basin within Group H and older units
- Thermogenic gas, generated from source rocks, may be produced by kerogen decomposition or derived from the cracking of oils
Gas Stratigraphic Groupings
- Malay Basin gases can be classified into three stratigraphic groupings:
- Group E and younger rocks
- Group H and I gases
- Pre-Group I gases
Introduction
- The oldest rocks in Sabah are crystalline basement rocks, composed of granitic and metamorphic materials, located in the Darvel Bay and Segama areas, dating back to the Triassic–Jurassic period.
- The Crocker and Trusmadi Formation is the dominant unit, comprised of deep-water sandstones, minor shales, and argillaceous beds.
- The Crocker and Trusmadi Formation is highly deformed and dates back to the Eocene to early Miocene period.
- The Crocker and Trusmadi Formation is interpreted as an accretionary prism formed during the subduction of the proto– South China Sea under Sabah.
- The Sabah Orogeny, a significant geological event, created the early Miocene Top-Crocker unconformity.
- The Sabah Orogeny was followed by the deposition of neritic and fluvial formations, preserved in eastern Sabah.
Western and North Sabah
- Western and North Sabah comprise mainly sedimentary and igneous rocks from the Early Cretaceous to the Pliocene period, with minor metamorphic rocks.
- The region experienced several periods of deformation:
- The earliest deformation event caused the deformation and uplift of the basement rock (chert-spilite formation) during the Late Cretaceous to Early Eocene period.
- The deformation controlled the development of an elongate basin trending N-S and E-W in Western and Northern Sabah respectively.
- The basin later became the site for the deposition of Middle Eocene to Early Miocene sediments of the Crocker, Trusmadi and Kudat formations.
Western and North Sabah - Sedimentary Rocks
- Western and North Sabah predominantly have sandstones and shales with minor cherts, limestones and conglomerates.
Western and North Sabah - Igneous Rocks
- Western and North Sabah also contain serpentinites, basalts/spilites, agglomerates, gabbros, dolerites, andesites, granodiorites, and adamellites.
Western and North Sabah - Metamorphic Rocks
- Western and North Sabah also contain primarily hornblende schists and gneisses
Western and North Sabah - Oldest Dated Rocks
- The oldest sedimentary rocks in Western and North Sabah are radiolarian cherts of the Early Cretaceous period.
- The cherts are closely associated with basaltic/spilitic-type basaltic igneous rocks, as well as basalt and spilite, ultrabasic rocks (serpentinites/peridotites), intrusive rocks (dolerites), and metamorphic rocks (hornblende schists and gneiss).
- This association of rock types, resembling an ophiolite series, is interpreted to represent an oceanic crust of Mesozoic age, forming the basement rock of the region.
- Lying unconformably on this basement rock are sedimentary rocks of Eocene to Early Miocene age.
Western and North Sabah - Crocker & Trusmadi Formation
- The Crocker and Trusmadi Formations are mostly found in Western Sabah.
- They predominantly comprise deep-water flysch sediments characterized by rhythmic alternation of sandstone and shale beds.
Western and North Sabah - Kudat Formation
- The Kudat Formation is found in Northern Sabah.
- It primarily consists of shallow water sediments.
- It is characterized by interbedded carbonaceous sandstones and shales with lenses of Eocene-Early Miocene biohermal limestones.
Western and North Sabah - Bongaya Formation
- The Bongaya Formation is primarily composed of shallow water deposits of sandstones, shales, limestone and conglomerates.
- It dates back to the Upper Miocene period.
- It lies unconformably on the basement rock, Crocker, and Kudat Formations in Northern Sabah.
- The Bongaya Formation is in turn overlain unconformably by shallow water sediments of the Timohing Formation of Pliocene -Pleistocene age on Balambangan Island.
Western and North Sabah - Igneous Rocks
- Igneous rocks, both intrusive (Mt.Kinabalu plutonics) and extrusive (Sirar Island volcanics) formed during Miocene-Pliocene times.
Crocker Formation
- The Crocker Formation comprises turbidites (up to 1,000 m thick).
- The turbidites consist of interbedded sandstone and shale deposited in a deepwater basin (submarine fan) during the latest Eocene (37 Ma) through to the earliest Miocene (21 Ma).
- The Crocker Range, running NNE to SSW, is deformed by a series of high-angle reverse faults dipping south or south-east.
- The reverse faults formed during the Miocene, and the soft shale layers served as slip planes for fault and deformation.
- The Tongkul structure divides the turbidites into the lower sandstone unit (several hundreds of metres thick) and the upper shale unit (about 100m thick).
- The lower sandstone unit comprises an alternation of thick grey sandstone beds and relatively thin shale beds.
Tectonic Evolution
- Most metamorphic rocks have a basic protolith (Hall and Wilson, 2000).
- Granitic rocks, of small volume (Hutchison et al., 2000), could represent arc plutonic rocks intruded into older ophiolitic basement.
Tectonic Evolution - Paleocene to Eocene Sedimentation
- The Rajang Group is a widespread association of Late Cretaceous to Eocene deep water mudstones and turbiditic sandstones, including the Sapulut, Trusmadi and East Crocker formations.
- The Rajang Group is believed to have been deposited in the large NE-SW trending Crocker Basin and is highly deformed with tight isoclinal folds and thrusts (Hutchison, 1996).
- The Palaeogene was a period of continuous deep marine turbidite deposition.
- The strongly deformed turbiditic Rajang Group is interpreted as part of an accretionary prism related to southeasterly subduction of the proto-South China Sea in the NW Borneo.
Tectonic Evolution - Late Eocene Uplift
- An unconformity within the succession of Palaeogene turbidites between the Middle and Upper Eocene was inferred by Rangin et al. (1990), based on the reworking of nannofossils.
- Hutchison (1996) argued that the West Crocker Formation includes detritus from uplifted and eroded Rajang Group and East Crocker Formation rocks.
- Hutchison (1996) called this uplift the ‘Sarawak orogeny’ and suggested it was likely caused by collision along the northern Borneo margin.
- The unconformity is difficult to recognize in outcrop in Sabah due to similar lithologies and strong Neogene deformation.
- The contact is generally obscure.
Tectonic Evolution - Late Eocene - Miocene
- Uplifting and erosion of the Rajang Group accretionary complex supplied sediment to the Borneo trough to the NW and to the SE, where material was deposited in a deep water setting as the West Crocker, Labang and Kulapis formations.
- The fold-thrust belt of the West Crocker Formation, prominently exposed in western Sabah, represents the accretionary complex related to ongoing southeasterly subduction of the proto-South China Sea in NW Borneo.
- Deformation continued for several million years, with the Gomantong Limestone forming on structural highs during periods of relative tectonic quiescence in the Early Miocene.
- An unconformity separates the deformed and lithified melange unit of the Kuamut, Garinono, or Ayer formations from the less tectonised strata (Balaguru, 2001, 2003).
Tectonic Evolution - Early Miocene Deformation (22 – 20 Ma)
- The Early Miocene deformation is interpreted as a major tectonic event, responsible for the formation of mélanges, major uplift and erosion, which produced the Base Miocene Unconformity (BMU or Pre-DRU).
- This deformation is related to the subduction and collision of the Dangerous Ground Continental Block to the NW Borneo and is referred to as the ‘Sabah Orogeny’ (Hutchison, 1996).
- This was followed by a shift in depositional environment from deep-water to a shallow deltaic setting (Balaguru, 2001; Balaguru et al., 2003; Van Hattam, 2005).
- The associated major uplift and erosion provided sediment supply to the deltaic to shallow marine Middle to Upper Miocene successions of the Meligan and Tanjong Deltas.
Tectonic Evolution - Early Miocene Limestone Development
- Limestone outcrops in southern Sabah correlate with the Early Miocene (Burdigalian) Gomantong Limestone Formation, containing clasts of the Labang Formation (Noad, 1998).
- This indicates widespread uplift followed by carbonate sedimentation throughout central and eastern Sabah.
- This change in depositional environment is also observed offshore NW Sabah.
- In eastern Sabah, the Gomantong Limestone outcrops in an ENE-WSW-trending belt of at least 200 km, suggesting that this zone might have been a zone of uplift where localized carbonate sedimentation occurred, isolated from clastic sediment influx from the west.
Tectonic Evolution - Late Early Miocene to Middle Miocene Clastic Sedimentation
- The end of early Miocene deformation is marked by the onset of Tanjong, Meligan or Kudat Formation clastic deposition. The oldest dates for this deposition are late Burdigalian (18-16 Ma).
- The absence of widespread synsedimentary deformation in the Tanjong Formation suggests that it was deposited during a period of relative tectonic quiescence, which lasted through the deposition of late Middle Miocene (12-10 Ma) or younger strata.
- Continued subsidence created a cumulative thickness of at least 6,000 m.
- The present outcrop pattern of the Miocene strata is the product of regional strike-slip and transpressional tectonics and inversion during the Late Miocene (8.6 Ma) onwards and probably lasted until the latest Pliocene.
Tectonic Evolution - Late Miocene Deformation and Uplift
- The transpressional movement along the major strike-slip faults in the region provides a better explanation for the structural development in these areas and is likely linked to deformation propagation from Sulawesi towards NW Sabah.
- Late Pliocene strike-slip deformation is significant regionally and occurred at a similar time as important deformation in NE Kalimantan, Sulawesi and NW Sabah.
- This transpressional movement is interpreted as the cause of the major orogenic deformation, uplift and final structural development in the Sabah region, possibly continuing to present day.
Tectonic Evolution of Sabah
- Tectonic evolution in Sabah occurred since the Early Tertiary.
- The region has experienced several tectonic events, resulting in diverse structural trends and depositional frameworks in Sabah.
- At least three major episodes are linked to NW-SE compression, coinciding with the ongoing subduction of the proto-South China Sea during the Late Eocene, Early Miocene and Middle Miocene.
- Late Eocene tectonic deformation is characterized by folding and thrusting of basement rock and older paleogene sediments.
- The Paleogene regional tectonic setting of Sabah is complex, with southeasterly subduction in NW Borneo, and extension in the SE in the Celebes Sea and Makassar Strait.
- The Early Miocene deformation is interpreted as a major tectonic event, resulting in the formation of mélanges, major uplift and erosion which produced the Base Miocene Unconformity.
- This was followed by a change in depositional environment from deep-water to a shallow deltaic.
- The Kuamut Formation is linked to sedimentation on the flanks of an accretionary wedge during the Late Oligocene (Balaguru et al., 2003; Balaguru and Hall, 2009; Hall, 2013, Fig. 3), but as noted above this is actually an Early Miocene formation, and as Leong (1974) described in detail (op.cit., p. 180–183) it is an extensional mélange or olistostrome deposit.
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Description
Explore the fascinating geological formations of Sabah, focusing on the Crystalline Basement, Crocker and Trusmadi Formations, and the impacts of the Sabah Orogeny. This quiz covers different geological units and their historical significance from the Early Cretaceous to the Pliocene. Test your knowledge on sedimentary and igneous rocks as well as the deformations that have shaped the region.
