Sarawak Geology Overview

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Questions and Answers

In the north zone, the Lambir Formation is overlain by the ______ Formation.

Miri

The Tatau-Mersing Line represents a major ______ between the Belaga, Mulu, and Kelalan formations and the overlying sediments.

unconformity

The Belaga Formation consists of thick shale-sandstone turbidite sequences deposited upon ______ crust during the Late Cretaceous.

oceanic

The Rajang Group includes deformed rocks that are part of the Rajang ______-Thrust Belt.

Fold Signup and view all the answers

The Liang Formation consists of a succession of clay and sand with abundant ______ and some tuff.

lignite Signup and view all the answers

Sarawak can be divided into three tectonostratigraphic ______ according to their geological history.

zones Signup and view all the answers

The Kuching Zone is believed to be the peripheral part of the continental basement of ______.

Borneo Signup and view all the answers

Oldest rocks in the region are believed to be phyllites and schists of the Kerait ______ and Tuang Formation.

Schist Signup and view all the answers

The Sibu zone is essentially formed by Upper Cretaceous to Upper ______ deepwater sediments of the Rajang Group.

Eocene Signup and view all the answers

The sediments of the Rajang Group have been deformed into a fold and thrust ______ referred to as the Rajang Fold-Thrust Belt.

Belt Signup and view all the answers

Miri Zone is underlain by Upper Eocene to ______ strata.

Recent Signup and view all the answers

The Sarawak Orogeny caused low-grade metamorphism and strong folding characterized by steep ______ of the Rajang Group.

dips Signup and view all the answers

Sedimentary rock formation in Miri Zone include Tatau Formation, Nyalau Formation, and ______ Formation.

Setap Signup and view all the answers

The ______ Formation is characterized by a thick sequence of sandstone, pebbly sandstone, fossiliferous mudstone with abundant coal and lignite.

Balingian Signup and view all the answers

The Tatau Formation consists of Middle Eocene to Oligocene clastic sediments approximately ______ thick.

2500m Signup and view all the answers

The ______ Member of the Tatau Formation is exposed in the Tatau area at Ransi Hill and Tutong Hill.

Ransi Signup and view all the answers

The Nyalau Formation has a thickness of ______.

5000m Signup and view all the answers

The Buan Formation is predominantly ______.

shaly Signup and view all the answers

The Setap Shale consists of a thick extensive succession of ______ with subordinate thin sandstone beds.

shale Signup and view all the answers

The Sibuti Formation is found in central and ______ Sarawak.

north Signup and view all the answers

The lower contact of the Tatau Formation with the underlying ______ Formation is an angular unconformity.

Belaga Signup and view all the answers

The Balaga turbidite was formed as a result of being compressed, uplifted, and sheared when the Sundaland and ______ blocks collided.

Luconia Signup and view all the answers

The boundary between the Sibu Zone and the Kuching Zone is known as the ______ Line.

Lupar Signup and view all the answers

The Lubok Antu ______ comprises blocks of various rocks including chert, sandstones, and limestone.

Melange Signup and view all the answers

The flysch-like deep sea sediments are part of the ______ Formation.

Lupar Signup and view all the answers

The Kuching Zone is located to the southwestern part of ______.

Sarawak Signup and view all the answers

The oldest rocks in the West Borneo Basement are Middle-Upper Carboniferous to Permian ______, hornfels, and metaquartzites.

mica-schist Signup and view all the answers

Cretaceous granitoids intrude the Cretaceous and ______ rocks.

older Signup and view all the answers

The rocks in the Kuching Zone above are overlain unconformably by mixed terrestrial – marine siliclastic rocks of Late ______ to Middle Miocene.

Cretaceous Signup and view all the answers

Intrusion by Middle Jurassic to Late Cretaceous plutonic suites comprises quartz diorite, tonalite, granite, some gabbro, diorite, and ______ with K-Ar ages (75-115 Ma).

norite Signup and view all the answers

The West Borneo Basement is separated by the Rajang Sea from the ______ which was the southern edge of the Luconia Microcontinent.

Miri Zone Signup and view all the answers

The collision of the Luconia Block with the West Borneo Basement during Late Mesozoic to Early ______ led to the uplifting of deep sea sediments.

Cenozoic Signup and view all the answers

Before the advent of plate tectonic theory, tectonic evolution of Sarawak was interpreted in the context of the ______ theory.

geosynclinal Signup and view all the answers

Deepwater turbiditic rocks in the Sibu zone were interpreted as '______ deposits.'

eugeosynclinal Signup and view all the answers

West Borneo Basement may have been contiguous with the East Malaya Block, which is part of the ______ craton.

Sundaland Signup and view all the answers

In the Middle Permian to Early Triassic, sedimentation was interrupted by the suturing of East Malaya to ______.

Cathaysia Signup and view all the answers

Widespread andesitic to basaltic lavas and pyroclastics were associated with the ______ Volcanics.

Serian Signup and view all the answers

Near the end of the Late Cretaceous period, sedimentation was characterized by deep marine turbidite from the ______ Formation.

Belaga Signup and view all the answers

Similar turbiditic rocks occur in the inner Baram-Tinjar area as Mulu and ______ formations.

Kelalan Signup and view all the answers

What is the primary difference between the Miri Formation and the Begrih Formation in terms of their depositional environments?

The Miri Formation is characterized primarily by argillaceous lower parts and sandstone dominance in the upper parts, while the Begrih Formation is mainly fluviatile and non-marine. Signup and view all the answers

What geological significance does the Tatau-Mersing Line hold in relation to the Sibu and Miri Zones?

The Tatau-Mersing Line represents a major unconformity, indicating a significant tectonic phase which deformed the deep marine rocks of the Rajang Fold-Thrust Belt. Signup and view all the answers

Explain the main components of the Rajang Group and their relationship with the Sibu Zone.

The Rajang Group consists of rocks that are intensely folded, thrust, and low-grade metamorphosed, underlying the Sibu Zone, which is primarily composed of Upper Cretaceous to Upper Eocene age rocks. Signup and view all the answers

What characteristics make the Belaga Formation unique in terms of its geological history?

The Belaga Formation consists of thick shale-sandstone turbidite sequences deposited upon oceanic crust and is noted for being highly deformed during the Late Cretaceous to Eocene period due to the Sarawak Orogeny. Signup and view all the answers

Describe the lithological features of the Liang Formation and its depositional environment.

The Liang Formation is characterized by a succession of clay and sand interspersed with abundant lignite and some tuff, reflecting a coastal plain to shallow marine environment. Signup and view all the answers

What tectonic event led to the formation of the Balaga turbidite?

The Balaga turbidite was formed by the compression, uplift, and shearing from the collision of the Sundaland and Luconia blocks. Signup and view all the answers

What does the Lupar Line represent in the geological context of Sarawak?

The Lupar Line represents the boundary between the Sibu Zone and the Kuching Zone. Signup and view all the answers

What type of rocks does the Lubok Antu Melange comprise?

The Lubok Antu Melange comprises blocks of chert, sandstones, shale, limestone, gabbro, basalt, and serpentinite. Signup and view all the answers

What is the geological age of the Lupar Formation based on foraminiferal evidence?

The foraminiferal evidence suggests that the Lupar Formation is of Upper Cretaceous age. Signup and view all the answers

What types of deposits are found in the Kuching Zone?

The Kuching Zone consists of Jurassic-Cretaceous shelf deposits, molasses, and related non-marine deposits. Signup and view all the answers

What are the oldest rock types found in the West Borneo Basement?

The oldest rocks in the West Borneo Basement are Middle-Upper Carboniferous to Permian mica-schist, hornfels, and metaquartzites. Signup and view all the answers

How is the rock sequence in the Kuching Zone characterized above the limestone?

The limestone is overlain unconformably by Jurassic-Cretaceous mainly siliclastic sequences. Signup and view all the answers

What geological events occurred as a result of the collision of the Luconia Block with the West Borneo Basement?

The collision led to the uplifting of deep sea sediments and influenced the tectonic evolution of the area. Signup and view all the answers

What lithofacies are present in the Ransi Member of the Tatau Formation?

The Ransi Member includes three lithofacies: thick-bedded coarse-grained conglomerate, thin to medium-bedded coarse-grained bioturbated sandstone, and medium-grained cross-bedded sandstone. Signup and view all the answers

How does the Nyalau Formation differ from the Buan Formation in terms of composition?

The Nyalau Formation predominantly consists of hard fine to medium grained sandstones and shale, while the Buan Formation is primarily shaly with thin beds of siltstone and fine to medium grained sandstone. Signup and view all the answers

What are the three tectonostratigraphic zones of Sarawak?

The three tectonostratigraphic zones of Sarawak are the Miri Zone, Sibu Zone, and Kuching Zone. Signup and view all the answers

What is the significance of the angular unconformity in the Tatau Formation?

The angular unconformity at the lower contact with the underlying Belaga Formation indicates a period of erosion or non-deposition before the Tatau Formation was laid down. Signup and view all the answers

What geological structures are formed in the Sibu Zone?

The Sibu Zone is characterized by the Upper Cretaceous to Upper Eocene deepwater sediments of the Rajang Group, which have been deformed into the Rajang Fold-Thrust Belt. Signup and view all the answers

Describe the type of environment the Sibuti Formation was deposited in.

The Sibuti Formation was deposited in an inner neritic and shallow environment, characterized by clay, shale, and subordinate siltstone and limestone. Signup and view all the answers

What types of rocks primarily underlie the Miri Zone?

The Miri Zone is underlain by Upper Eocene strata dominated by Oligocene-Miocene shallow marine shelf sediments deposited upon older continental crust. Signup and view all the answers

What are the primary characteristics of the Setap Shale?

The Setap Shale consists of a thick succession of grey shale and mudstone, with subordinate thin sandstone beds and several thin lenses of limestone. Signup and view all the answers

What is the significance of the Sarawak Orogeny?

The Sarawak Orogeny resulted in low-grade metamorphism and strong folding of the sediments, particularly in the Rajang Group. Signup and view all the answers

What is the total thickness of the Tatau Formation and why is it significant?

The Tatau Formation is approximately 2500 meters thick, which indicates substantial sediment accumulation over geological time. Signup and view all the answers

What types of formations make up the sedimentary rock formations in the Miri Zone?

The sedimentary rock formations in the Miri Zone include the Tatau Formation, Nyalau Formation, Setap Formation, Lupar Formation, Belaga Formation, and Buan Formation. Signup and view all the answers

What types of sedimentary structures are found in the Nyalau Formation?

The Nyalau Formation features cross-bedding and ripples indicative of energetic depositional conditions. Signup and view all the answers

What is the oldest geological formation in Sarawak?

The oldest geological formations in Sarawak are the phyllites and schists of the Kerait Schist and Tuang Formation, which are believed to be pre-Late Carboniferous. Signup and view all the answers

What rock types dominate the Balingian Formation and what does it indicate about its environment?

The Balingian Formation is dominated by sandstone, pebbly sandstone, and fossiliferous mudstone, indicating an environment conducive to coal and lignite deposition. Signup and view all the answers

What geological processes characterized the Miri Zone during the Late Eocene?

During the Late Eocene, the Miri Zone experienced sedimentation through shallow marine shelf deposits upon older continental crust. Signup and view all the answers

How did the deposition of the Rajang Group sediments occur?

The Rajang Group sediments were deposited as deepwater flysch during the Upper Cretaceous to Upper Eocene period. Signup and view all the answers

What major geological event led to the exposure of deep sea turbiditic sequences in the Belaga Formation?

The collision of the Luconia Block with the West Borneo Basement during the Late Mesozoic to Early Cenozoic. Signup and view all the answers

Explain the relationship between the West Borneo Basement and the East Malaya Block before the Late Cretaceous.

The West Borneo Basement may have been contiguous with the East Malaya Block, forming part of the Sundaland craton. Signup and view all the answers

How did the geological interpretation shift from geosynclinal theory to plate tectonic theory in Sarawak?

Geosynclinal concepts were replaced by plate tectonic theory due to advancements in understanding tectonic processes. Signup and view all the answers

What types of sediments characterize the Sibu Zone according to the geosynclinal theory?

The Sibu Zone was characterized by eugeosynclinal deposits, indicating deepwater turbiditic rocks. Signup and view all the answers

Describe the geological conditions that occurred during the Late Cretaceous period in Sarawak.

During the Late Cretaceous, deep marine turbidite sedimentation occurred in a remnant ocean basin associated with a subduction zone. Signup and view all the answers

What type of volcanic activity is associated with sedimentation during the Jurassic and Cretaceous periods?

Basic volcanism is associated with the marine sedimentation of the Bau Limestone and other formations. Signup and view all the answers

What was the impact of the Tethys Ocean's evolution on the tectonic development of Sarawak?

The breakup of Gondwanaland and evolution of the Tethys Ocean significantly influenced Sarawak's tectonic development. Signup and view all the answers

Identify the formations involved in the sedimentation during the Early to Mid-Cretaceous period.

Significant formations during this period include the Sadong Formation, Bau Limestone, and others associated with andesitic and basaltic lavas. Signup and view all the answers

What geological features are associated with the Miri Zone and West Borneo Basement?

The Miri Zone serves as the southern edge of the Luconia Microcontinent, while the West Borneo Basement contains plutonic suites. Signup and view all the answers

What role did sedimentation play during the Late Carboniferous to Early Permian period in the West Borneo Basement?

During this period, shallow marine sedimentation occurred, forming the Terbat Formation. Signup and view all the answers

Study Notes

Sarawak Geology

Sarawak is divided into three zones: Miri, Sibu and Kuching, which represent a decreasing stratigraphic age towards the east.
The oldest rocks in Sarawak are found in the Kuching Zone and are believed to be part of the West Borneo Basement.
The Miri Zone is underlain by Upper Eocene to Recent strata and dominated by Oligocene-Miocene shallow marine shelf sediments.
The Sibu Zone is formed by Upper Cretaceous to Upper Eocene deepwater sediments of the Rajang Group, which have been deformed into a fold and thrust belt called the Rajang Fold-Thrust Belt.

Miri Zone Formations

The Tatau Formation, Middle Eocene to Oligocene age, is approximately 2500m thick and consists of clastic sediments.
The Ransi Member, the oldest unit of the Tatau Formation, is exposed in the Tatau area and is made up of sandy conglomerate and sandstone with thin beds of shale.
The Buan Formation is predominantly shaly with thin beds of siltstone and sandstone.
The Nyalau Formation, Oligocene-Miocene age, is characterized by hard sandstone alternating with shale, coal beds, and burrows.
The Sibuti Formation consists of clay and shale with subordinate siltstone and limestone.
The Setap Shale is a thick sequence of shale with subordinate sandstone and limestone beds.
The Balingian Formation is a thick sequence of sandstone, pebbly sandstone, mudstone, and coal.
The Begrih Formation is mainly fluviatile and non-marine, containing abandoned channel deposits.

Sibu Zone Formations

The Belaga Formation, the oldest formation of the Rajang Group, consists of thick shale-sandstone turbidite sequences deposited upon oceanic crust.
The Lupar Line, a major fault zone, separates the Sibu Zone from the Kuching Zone.
The Lubok Antu Melange, located along the Lupar Line, comprises blocks of chert, sandstone, shale, limestone, and gabbro in a sheared clay matrix.
The Lupar Formation, located in the southwestern part of Sarawak, is composed of flysch-like deep sea sediments interbedded with pillow basalt.

Kuching Zone

The Kuching Zone is characterized by Paleozoic and Early Mesozoic rocks, including Jurassic-Cretaceous shelf deposits and non-marine deposits on the edge of the West Borneo Basement Complex .
The West Borneo Basement, the most southerly zone in Sarawak, is composed of Carboniferous-Permian basement rocks intruded by Cretaceous volcanic and plutonic rocks.

Tectonic Evolution

The tectonic evolution of Sarawak is related to the breakup of Gondwanaland and the evolution of the Tethys Ocean.
The Luconia microcontinent, located on the southern edge of the Miri Zone, collided with the West Borneo Basement during Late Mesozoic to Early Cenozoic.
The collision caused the uplift of the deep sea sediments of the Sibu Zone and exposed the deep sea turbiditic sequence of the Belaga Formation.

Introduction

Sarawak contains three tectonostratigraphic zones, each with its own geological history: Miri Zone, Sibu Zone and Kuching Zone.
The zones represent decreasing stratigraphic age towards the east.
The Kuching Zone is believed to be the peripheral part of the continental basement of Borneo, the West Borneo Basement and extends into Kalimantan, with Paleozoic and Mesozoic rocks.
Pre-Late Carboniferous rocks are believed to be phyllites and schists represented by the Kerait Schist and Tuang Formation.
These rocks are covered by thick succession of continental Tertiary strata.

Miri Zone

Northernmost zone, predominantly Upper Eocene strata.
Oligocene-Miocene shallow marine shelf sediments dominate the area, deposited on older continental crust.
Key sedimentary rock sequences include: Tatau, Nyalau, Setap, Lupar, Belaga and Buan Formations.
The Upper Cretaceous to Upper Eocene Rajang Group (flysch) forms the Sibu Zone and underlies the Miri zone.
The Sarawak Orogeny, characterized by low-grade metamorphism and strong folding with steep dips of the Rajang Group, impacted this zone.
Overlying formations (molasse) are less deformed and un-metamorphosed, except in localized shear zones.

Tatau Formation

Middle Eocene to Oligocene clastic sediments; approximately 2500m thick.
Oldest unit is the Ransi Member.
Found in the Tatau area, at Ransi Hill and Tutong Hill.
Composed of 20-30m moderately thick bedded (1-2m) sandy conglomerate and sandstone, with very thin bedded light to dark grey shale.
Consists of three lithofacies:
- Thick-bedded, coarse-grained conglomerate in the lower part.
- Thin to medium-bedded coarse-grained, bioturbated sandstone in the middle part.
- Medium-grained, cross-bedded sandstone in the upper part.
Lower contact with the underlying Belaga Formation is an angular unconformity, grading upward into the rest of the Tatau Formation.
Rest unconformably on the Belaga Formation.

Buan Formation

Predominantly shaly.
Contains thin beds of siltstone and fine to medium grained sandstone.

Nyalau Formation

Oligocene-Miocene.
Hard fine to medium grained sandstones alternate with shale.
Overlies Buan Formation.
Coal beds are present.
Sandstones exhibit cross-bedding and ripples.
Burrows - Ophiomorpha are common.
Shallow marine to estuarine, shallow littoral to inner neritic environment.
Thickness 5000m.
Conformably overlain by Sibuti Formation in the east.
Interfingering with shaly Setap Shale in the northeast.

Sibuti Formation

Found in central and north Sarawak.
Composed of clay and shale with subordinate siltstone and limestone.
Inner neritic and shallow environment (presence of ripples).

Setap Shale

Thick, extensive, monotonous succession of shale with subordinate thin sandstone beds and a few thin lenses of limestone.
Lithologies include grey shale, mudstone, sandstone and a few limestone.
Inner neritic and shallow environment (presence of ripples).
Changes to very sandy Lambir Formation in north Sarawak.
Found in the Central zone also.
1600m thick.

Balingian Formation

Thick sequence of sandstone, pebbly sandstone, fossiliferous mudstone with abundant coal and lignite.
Estuarine to lagoonal environment.
In the Central zone, Balingian rests unconformably on Lambir Formation and is unconformably overlain by Begrih Formation.
In the north zone, Lambir Formation is overlain by Miri Formation.
Miri Formation - mainly argillaceous in the lower part, with sandstone dominance in the upper part.

Begrih Formation

Predominantly fluviatile and non-marine.
Contains abandoned channel deposits.
Conformably overlain by Liang Formation.
Liang Formation: succession of clay and sand with abundant lignite and some tuff.
Coastal plain to shallow marine environment.

Tatau-Mersing Line

Boundary between Miri Zone and Sibu Zone.
Structurally complex zone consisting of Palaeocene to Eocene ophiolitic rocks including spilite, basalt, tuff and radiolarian chert.
The line also represents a major unconformity between the Belaga, Mulu and Kelalan formations (Rajang Group) and the overlying Upper Eocene-Recent sediments of the Miri Zone.
The Late Eocene unconformity marks a major phase of tectonism that deformed the deep marine rocks of the Rajang Fold-Thrust Belt.
It represents a major thrust fault zone or terrane suture.

Sibu Zone

Rocks are predominantly Upper Cretaceous to Upper Eocene age.
Rocks of the Rajang Group underlie the Sibu Zone.
Lupar, Belaga and part of Danau Formation are part of the Rajang Group.
Rajang Group:
- Deformed into the Rajang Fold-Thrust Belt - rocks are intensely folded, thrust and low grade metamorphosed.

Belaga Formation

Thick shale-sandstone turbidite sequences deposited upon oceanic crust during the Late Cretaceous and ended in the Eocene by the Sarawak Orogeny.
The oldest formation at the base of the Rajang Group.
Highly deformed, steeply dipping.
Rocks were uplifted in Late to Middle Eocene time.
Surrounded by younger formations – Tatau and Nyalau Formations.

Belaga Turbidite

The formation of the Balaga turbidite was a result of compression, uplift and shearing when the Sundaland and Luconia blocks collided.
This collision led to the subduction of the Rajang Sea beneath the south Borneo Block which uplifted the Balaga Formation.

Lupar Line

Boundary between Sibu Zone and Kuching Zone.
Part of the southwestern boundary of the Rajang Group is faulted along the Lupar Line, juxtaposing the Rajang group rocks against a zone of Melange termed the Lubok Antu Melange.
The Rajang group is divided into Lupar and Belaga Formation by the Lupar Line.
Lubok Antu Melange: comprises of blocks of chert, sandstones, shale, limestone, gabbro, basalt and serpentinite in sheared, cleavely clay matrix.
Interpreted as a tectonic melange formed during the Eocene.
Lubok Antu Melange is overlain by the flysch-like deep sea sediments (Lupar Formation) that are interbedded with pillow basalt and intruded by gabbro.
Lupar Formation: Overlain by the basal member of the Balaga Formation. Foraminiferal evidence suggests an Upper Cretaceous age.