BARITO BASIN

BARITO BASIN

Tectonically the Barito Basin is located in the southeastern boundary of Schwanner Shield, South Kalimantan. This basin is bounded by Tinggian Meratus in the East and in the North part is separated from the Kutai Basin by the form of Adang Fault, to the South it still opens to the Java Sea, and to the West is limited by the Sunda Exposure.

The Barito Basin is an asymmetric basin, has a front basin (foredeep) at the easternmost part and is a platform on the western side. The Barito Basin began to form in the Late Cretaceous, after collisions between microcontinent Paternoster and Southwest Kalimantan (Metcalfe, 1996; Satyana, 1996).

At the Early Tertiary extensional deformation occurred as a result of convergent tectonics, and produced the Northeast - Southeast rifting pattern. Rifting was then the site of sedimentation of lacustrine and alluvial fan from the lower Tanjung Formation originating from the Horst region and filling the graben section, then followed by deposition of the upper Tanjung Formation in the transgression relationship.

At the beginning of the Oligocene, a lifting process occurs followed by deposition of the Lower Berai Formation which covers the upper Tanjung Formation in harmony in the regression relationship. In the Early Miocene it was followed by the deposition of massive limestone units of the Berai Formation.

During the middle Miocene a process of removal of the Meratus complex occurred which resulted in a simultaneous regression cycle with the deposition of the lower Warukin Formation, and in several places showed symptoms of local (hiatus) inconsistency between the upper Warukin Formation and the lower Warukin Formation.

This appointment continues until the Middle Miocene End which ultimately results in regional inconsistencies between the upper Warukin Formation and the Upper Miocene Dahor Formation - pliocene.

The last tectonic occurred at the time of Plio-Pliestosen, the entire area was raised, folded and broken. The structure axis is parallel to Tinggian Meratus. Upward faults are formed with a slope to the east, breaking tertiary rocks, especially the Tinggian Meratus areas.

Barito Basin Geology

STATIGRAFI

Barito Basin Stratigraphy, Kutai Basin, and Tarakan Basin. (Courtney, et al., 1991, op. Cit., Bachtiar, 2006).

The stratigraphic sequence of the Barito Basin from old to young are:

• Tanjung Formation (Eocene - Early Oligocene)

This formation is composed of sandstones, conglomerates, claystone, coal, and basalt. This formation is deposited in the neritic litoral environment.

• Berai Formation (Late Oligocene - Early Miocene)

The Berai Formation is composed of limestone interspersed with claystone / shale at the bottom, in the middle consists of massive limestone and at the top it repeats itself again into the intersection of limestone, shale, and sandstone. This formation is deposited in the middle lagoon-nile environment and covers in harmony the Tanjung Formation which is located at the bottom. Both the Berai Formation, and Tanjung have a thickness of 1100 m near the Cape.

• Warukin Formation (Lower Miocene - Middle Miocene)

The Warukin Formation is deposited on the Berai Formation and is covered in inconsistency by the Dahor Formation. Most have been exposed, especially along the western part of Tinggian Meratus, but in the Tanjung and Kambitin regions have eroded. Only to the south of Tanjung which is still below the surface.

This formation is divided into two members, namely the lower part of Warukin (clastic member), and the upper part of Warukin (coal member). The two members are distinguished based on their lithological arrangement.

Warukin the lower part (clastic member) in the form of nesting between marl or slime clay with thin sandstone inserts, and thin limestone at the bottom, while at the top is alternating sandstones, clays, and coal. The coal has a thickness of no more than 5 m, while the sandstone can reach a thickness of more than 30 m.

Warukin the upper part (coal member) with a maximum thickness of ± 500 meters, in the form of sandstone interbreeding, and claystone with coal inserts. The thickness of the coal seams reaches more than 40 m, while the sandstones are not very thick, usually containing fresh water. The Warukin formation is deposited in an innerneritic - deltaik environment and shows a regression phase.

• Dahor Formation (Upper Miocene - Pliocene)

This formation consists of alternating between sandstones, coal, conglomerates, and shales deposited in a litoral environment - supra litoral.

Reference:

• Bachtiar, A., 2006, Slide Kuliah Geologi Indonesia, Prodi Teknik Geologi, FITB-ITB
• Satyana, A.H., 2000, Kalimantan, An Outline of The Geology of Indonesia, Indonesian Association of Geologists, p.69-89.