NORTH WEST JAVA BASIN

NORTH WEST JAVA BASIN

A. BRIEF REGIONAL GEOLOGICAL REVIEWS

The North West Java Basin has been known as the main hydrocarbon province in the Pertamina DOH JBB area, Cirebon. This basin is located between the Sunda Shelf in the North, the Perlipatan - Bogor Line in the South, the Appointment of Karimun Jawa in the East and the Seribu Island Exposure in the West. The North West Java Basin is influenced by the North-South block faulting system. North-South faults divide the basin into graben or several sub-basins, namely Jatibarang, Pasir Putih, Ciputat, Rangkas Bitung and some basement heights, such as Arjawinangun, Cilamaya, Pamanukan, Kandanghaur-Waled, Rengasdengklok and Tangerang. Based on the stratigraphy and its structural patterns, and its location in the pattern of subduction arc from time to time, it turns out that the West Java basin has experienced several times of sedimentation and tectonic phases since the Eocene to the present (Martodjojo, 2002).

 

Location of the West Java Basin (Northwest Java Basin)

B. TEKTONOSTRATIGRAPHY AND GEOLOGICAL STRUCTURE

The North West Java Basin consists of two areas, namely offshore in the North and onshore in the South (Darman and Sidi, 2000). The entire area is dominated by extensional faults with very little compressional structure. The basin is dominated by rifts which are associated with faults which form several deposited structures, including the main depositors, namely the Arjuna Sub-Basin and the Jatibarang Sub-Basin, as well as other deposers such as: Ciputat Sub-Basin, Pasirputih Sub-Basin. The depositors are dominated by Tertiary sequences with a thickness exceeding 5500 m.

The important structures in the basin consist of various elevation areas that are associated with broken anticlines and high blocks (horst block), folds on the part that descends on the main fault, keystone folding and hits the bedrock height. The compressional structure only occurs at the beginning of the formation of the first rift which is relatively northwest-southeast in the Paleogene period. This fault will be active again in the Oligocene. Tectonics of West Java are divided into three tectonic phases starting from Pre-Tertiary to Plio-Pliostosen.

 

The tectonic phase is as follows:

1. First Tectonic

In the Late Tertiary Cretaceous, North West Java can be classified as 'Fore Arc Basin' with structural orientations ranging from Cileutuh, Bogor Sub-Basin, Jatibarang, Muriah Basin and West Florence Basin which indicate control of the 'Meratus Trend'. The Paleogene (Eocene-Oligocene) Period is known as the Extensional Rifting Paleogene. In this period a horizontal shear fault occurred in the main Sundanese krataon due to the Indian Plate collision with the Eurasian Plate. These faults initiated the formation of Tertiary basins in Western Indonesia and formed the North West Java Basin as a pull apart basin.

This extension of tectonics forms half gnraben systems and is the first phase of rifting (Rifting I: fill phase). The sediment deposited on rifting I is called synrift sediment I. The initial rifting basin was formed during fragmentation, rotation and movement of the Sundanese palace. Two trends of normal fault caused by the development of rifting-I (early fill) trending N 60o W - N 40o W and almost N - S are known as the Sunda fault pattern. During this time lacustrin and volcanic deposits formed from the Jatibarang Formation which covered the low lows that existed. This sedimentation process continues with the discovery of the Talangakar Formation transition deposits. This system is then terminated with the carbonate deposited in the Baturaja Formation.

2. Second tectonic

The second tectonic phase occurs at the beginning of Neogen (Oligo-Miocene) and is known as Neogen Compressional Wrenching. It is characterized by the formation of shear faults due to the compressive force of the collision of the Indian Plate. Most of the fault shifts are reactive to normal faults formed in the Paleogene period.

A new subduction route was formed in southern Java. The Early Miocene volcanic pathway is currently located off the southern coast of Java. This row of volcanoes produces submarine volcanic deposits which are now known as "old andesite" which are spread along the southern part of Java. This tectonic pattern is called the Javanese Tectonic Pattern which changes the old tectonic pattern that happened previously to be trending east-west and produces an upward fault system, starting from the south (Ciletuh) moving north. This fault pattern is in accordance with the upward fault system behind the arc or known as the "thrust fold belt system".

3. Last Tectonics

The final tectonic phase that occurs is in the Pliocene - Pleistocene, where there is a process of compression again and forming structural traps in the form of rising faults on the southern path of the North West Java Basin. The upward faults formed are the faults rising in Pasirjadi and the faults rising in Subang, whereas in the northern path of the North West Java Basin a downward fault is formed in the form of a downward fault Pamanukan. As a result of the structural trap, the process of hydrocarbon migration occurs again.

 

(Physiographic transverse incision of the basin and volcanic arc of West Java)

C. REGIONAL STRATIGRAPHY

(StratigraphyTable of North West Java Basin )

The general stratigraphy of North West Java from old to young is as follows:

1. Basement rock

Bsement rocks are andesitic and basaltic igneous rocks that are Middle Cretaceous to Upper Cretaceous and Pre-Tertiary metamorphic rocks (Sinclair, et.al, 1995). Environment Deposition is a surface with the rest of weathered tropical vegetation (Koesoemadinata, 1980).

2. Jatibarang Formation

This unit is an early synrift deposit, mainly found in the central and eastern part of the North West Java Basin. In the western part of this basin, there is not much (very thin) appearance of the Jatibarang Formation. This formation consists of tuffs, breccia, agglomerates, and base conglomerates. This formation is deposited in fluvial facies. The age of this formation is from the Late Eocene to the Early Oligocene. In some places in this formation oil and gas are found in tuff fractures (Budiyani, et al., 1991).

3. Talang Akar Formation

The next syn rift phase is precipitated by Talang Akar Formation above the Jatibarang Formation. In the beginning fluvio-deltaic functioned to marine phaises. The lithology of this formation is preceded by the intersection of sandstone sediments with nonmarine flakes and is terminated by interrelationships between limestone, shale, and sandstones in marine facies. At the end of sedimentation, the Talang Akar Formation is characterized by the end of synrift sedimentation. This formation is expected to develop quite well in the Sukamandi area and its surroundings. The sedimentation of this formation occurs from the Oligocene to the Early Miocene.

4. Baturaja Formation

This formation is deposited in harmony above the Talang Akar Formation. Sedimentation of the Baturaja Formation which consists of limestones, both in the form of exposures and those that develop as a reef post-shifting phase buildup which regionally covers all clastic sediments of the Talang Akar Formation in the North West Java Basin. The development of reef limestones is generally found in high elevations. However, it is now known as an inner area. This formation was formed in the Early Miocene - Middle Miocene (mainly from the association of foraminifera). The formation environment of this formation is in shallow sea conditions, the water is quite clear, sunlight is present (especially from the abundance of foraminifera Spriroclypens Sp).

5. Upper Cibulakan Formation

This formation consists of alternating between shale with sandstones and limestone. Limestone in this unit is generally clastic and limestone reefs that develop locally. This limestone is known as the Mid Main Carbonate (MMC). This formation is deposited in Early Miocene-Late Miocene. This formation is divided into 3 Members, namely:

• Massive

This member is deposited incongruously above the Baturaja Formation. The lithology of this member is the intersection of claystone with sandstones which have a fine-medium grain size. In this massive hydrocarbon content is found, especially at the top. In addition there are fossils of planktonic foraminifera such as Globigerina trilobus, bentonic foraminifera such as Amphistegina (Arpandi and Patmosukismo, 1975).

• Play

The Main Member is deposited in harmony above the Massive Member. The constituent lithology is claystone interspersed with sandstones which have fine-medium grain size (glauconitic). At the beginning of its formation develops limestones and also the sand cage, where in this section the Main Member is divided again called the Mid Main Carbonat (Budiyani et al, 1991).

• Parigi

Pre Parigi members are deposited in harmony above the Main Member. The lithology is the intersection of limestone, dolomite, sandstone and siltstone. This member was formed in the Middle-Miocene Middle Miocene Late and was deposited in the Middle-Neritik Inner Environment (Arpandi & Patmosukismo, 1975), with shallow sea fauna and glauconitic sandstones present.

6. Parigi Formation

This formation is deposited in harmony above the Upper Cibulakan Formation. The constituent lithology is mostly clastic and reef limestones. The sedimentation of these limestones extends throughout the North West Java Basin. The depositional environment of this formation is the shallow-middle sea (Arpandi & Patmosukismo, 1975). The lower limit of the Parigi Formation is characterized by gradual changes from the mixed carbonic facies rocks of the Upper Cibulakan Formation to the carbonate rocks of the Parigi Formation. This formation was deposited in the Late Miocene-Pliocene Period.

7. Cisubuh Formation

This formation is deposited in harmony above the Parigi Formation. The constituent lithology is claystone interspersed with sandstones and side shales. The age of this formation is from Late Miocene to Pliocene - Pleistocene. Formations are deposited in shallow marine environments which are increasingly upward becoming litoral-parallic environments (Arpandi & Patmosukismo, 1975).

D. BASIN SEDIMENTATION

The initial period of sedimentation in the North West Java Basin begins at the Middle Eocene - Early Oligocene (transgression phase) which produces sedimentation of volcanic land - shallow sea from the Jatibarang Formation. At that time volcanism increased. This is related to the interaction between plates in the southern part of Java Island, as a result the unstable regions often experience tectonic activity. Volcanic materials from the east begin to be deposited.

The next period is the transgression phase that takes place during the Late Oligocene - Early Miocene which produces deltaic trangresive transition sediments to shallow seas which are equivalent to the Talang Akar Formation at the beginning of the period. The basin area consists of two different environments, the western part is paralic, while the eastern part is the shallow sea. Furthermore, volcanic activity diminishes so that the areas become somewhat stable, but the Ciputat basin children are still active. Then the seawater inundated the land which took place during the Early Miocene starting from the northwest and continuing to the southeast inundating several heights except the Tangerang high. From these heights the resulting clastic sediments are equivalent to the Talang Akar formation.

At the end of the early Miocene the basin area was relatively stable, and the western part of Pamanukan was a shallow platform, where the carbonate developed well so that it formed the equivalent of the Baturaja formation, while the eastern part was a deeper base. In the Middle Miocene, which is a regression phase, the North West Java Basin is deposited with shallow marine sediments from the Upper Cibulakan formation. The main sediment source from the Upper Cibulakan formation is thought to originate from the north-northwest direction. At the end of the Middle Miocene back away from a stable area, limestone developed well. This good development is due to very weak tectonic activity and the environment in the form of shallow seas. Late Miocene - Pliocene (regression phase) is the phase of formation of the Parigi and Cisubuh Formations. The condition of the basin area undergoes a slight change where the sea conditions diminish into the parallel environment.

In Pleistocene Period - Alluvium is marked for the removal of the main axis of Java. This appointment was also followed by increased volcanic activity and also followed by the formation of the main structure of Java. The removal of the main axis of Java ends suddenly, affecting sea conditions. The coarse grains are deposited incongruously above the Cisubuh Formation.

 

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• https://www.slideshare.net/RichardNetherwood/pet-geol-indonesia-55727765?from_action=save