KUTAI BASIN, BORNEO

KUTAI BASIN, BORNEO

REGIONAL GEOLOGY

The Kutai Basin is limited by the Paternoster platform, Barito Basin, and the Meratus Mountains to the south, with the Schwaner Block to the southwest, then Mangkalihat Tinggian to the north - northeast, and the Central Kalimantan Mountains (Moss and Chambers, 1999) to the west and north

  

Regional Kutai Basin

The Kutai Basin has a complex history (Moss et al., 1997), and is the only Indonesian basin that has evolved from the internal rifting fracture / foreland basin to marginal-sag. Most of the initial products fill the Kutai Basin have been reversed and exposed ( Satyana et al., 1999), in the Middle Miocene to the Late Miocene as a result of Micro Continent collision / block collisions.

From this event it caused the removal of basins, changes in the anticline axis and surface erosion that controls sedimentation in the Mahakam Delta. The Mahakam Delta is formed at the mouth of the Mahakam river on the east coast of the island of Borneo. With its coastline oriented towards NE-SW and limited by the Makassar Strait, the strait separates the islands of Borneo and Sulawesi.

REGIONAL STRATIGRAPHY

Stratigraphy Kutai Basin

 

Satyana et all, 1999 in the 2001 Outline of the Geology of Indonesia conducted a study and compiled the stratigraphy of the Kutai Basin from old to young as follows:

1) Beriun Formation

The Beriun Formation consists of claystone, alternating sandstones and limestones. Beriun Formation Middle Eocene - Late Eocene and deposited in fluviatyl to litoral environments.

2) Atan Formation

Above the Formation Beriun is deposited at the Atan Formation which is the result of settling after a decrease in basins and precipitation in the Beriun Formation. The Atan Formation consists of quartz limestones and sandstones. Atan Formation is in the Early Oligocene.

3) Angry Formation

The Angry Formation was arranged in harmony above the Atan Formation. The Marah Formation consists of claystone, quartz sandstone and limestone in the late Oligocene.

4) Pamaluan Formation

Precipitated during Early Miocene to Late Miocene in neritic environments, with characteristics of claystone lithology, shale, limestone, siltstone and quartz sandstone inserts. This formation is deposited in the delta to litoral environment.

5) Bebulu Formation

Precipitated during Early Miocene to Middle Miocene in neritic environments. The lithology characteristic of the Bebulu Formation is limestone.

6) Pulubalang Formation

The Pulubalang Formation is deposited in harmony above the Pamaluan Formation, consisting of alternating silt sand with a thin slate of sandstone and claystone. The age of this formation is Middle Miocene and deposited in the sub-litoral environment, sometimes influenced by marine influx. This formation has a relationship with the Bebulu Formation which is composed of sandstone limestones with shale

7) Balikpapan Formation

The Balikpapan Formation is deposited in harmony above the Pulubalang Formation. This formation consists of alternating between claystone and sandstone with coal inserts and limestones at the bottom. Drilling data that has been carried out in the Kutai Basin proves that the Balikpapan Formation was deposited with a delta system, in plain delta to delta front. The age of this formation is Middle Miocene - Late Miocene.

8) Kampungbaru Formation

The Kampung Baru Formation is Mio-Pliosen, located above the Balikpapan Formation, consisting of alternating sandstones, claystone and coal with thin limestone slabs as marine influx. This formation depositional environment is delta.

9) Mahakam Formation

The Mahakam Formation was formed during the Pleistocene - now. The deposition process is still going on until now, with lithological characteristics of loose material from clay to fine sand.

REGIONAL GEOLOGICAL STRUCTURE

Like some basins in other Southeast Asia, half grabens were formed during the Eocene as a result of extensional or regional expansion phases (Allen and Chambers, 1998). This expansion is a manifestation of the Indian Continent sub plate collision with the Asian Continent plate which spurred expansion along the strike-slip fault series with the northwest-southeast direction (NW-SE) which was the reactivation of the previous structure, the Adang-Lupar fault and the Mangka fault.

This basin begins to fill transgressive sediment deposits during the Late Eocene to the Oligocene. Then it was followed by a regressive sequence at the time of the Early Miocene which was the initiation of the current Mahakam Delta complex. The Mahakam Delta propagation process increased very significantly in the Middle Miocene, when the elevation of Kuching in the West was raised and the first inversion occurred. The progress is still ongoing today. The second invasion occurred during the Mio-Pliocene period, when the Sula-Banggai plate crashed into Sulawesi and produced a mega shear Palu-Koro.

The formation and development of the main structures that control the sub-Lower Kutai Basin are closely related to the Second Inversion tectonic process, namely geological structures with a northeast-southwest (NNE-SSW) direction pattern. According to Allen and Chambers, (1998) this pattern can be seen in the general structure revealed in the current Kutai Basin, namely in the form of recommended fault lines and anticline / anticlinorium complexes.

Another structural development is the northwest-lateral alignment pattern (NW-SE), in the form of normal faults which are manifestations of the pre-formed main force release. These faults are mainly in the northern part of the basin, cutting sediments of Middle Miocene and other older parts.

 Surface Geology Map of Kutai Area

Tectonic Setting Kutai Basin

The tectonic order of the Kutai basin can be summarized as follows:

• Early Synrift (Paleocene to Early Eocene): This stage of sediment consists of alluvial sediments filling the NE-SW and NNE-SSW topography resulting from rifting trends in the overland Kutai Basin. They overwrite in the late Cretaceous compression basement to the beginning of the Tertiary in the sea in the sequence.
• End of Synrift (Middle to Late Eocene): During this period, a large transgression occurred in the Kutai Basin, partly related to rifting in the Makassar Strait, and accumulated shale bathial sand inserts.
• Early Postrift (Oligocene to Early Miocene): During this period, bathial conditions continued to dominate and several thousand meters were dominated by accumulated shale. In the shallow structural area the carbonate platform develops
• End of Postrift (Middle Miocene to Quaternary): From the Middle Miocene and so on the sequences of progressaded deltas have grown steadily into the sea in the Makassar Strait, forming a sequence of Mahakam Delta, which is the main part of the hydrocarbon carrier in the basin. Various types of delta deposits on - and offshore develop in the formations of Balikpapan and Kampungbaru, including also deep sea slope facies and basin facies. And there are also excellent host rocks and reservoirs with interbedded sealing shale. After this period, a large erosion process occurred in the Kutai synrift sequence.

Reference:

• Yahoo.com
• Google.com
• Wikipedia.com
• http://www.academia.edu/7302602/Laporan_Proposal_Eksplorasi_Batubara_di_Cekungan_Kutai_Balikpapan_Kalimantan_Timur_-_Johan_Edwart