BENGKULU BASIN

BENGKULU BASIN

The Bengkulu Basin is one of the forearc basins in Indonesia. Forearc basin means a basin that is positioned in front of the volcanic path (fore - arc; arc = volcanic path). But, we call it that based on its current geological position. Has the position been like that? Not necessarily, and this is what we must investigate. Publications from Howles (1986), Mulhadiono and Asikin (1989), Hall et al. (1993) and Yulihanto et al. (1995) —all of the good science proceedings to study about the Bengkulu Basin.

Based on various geological studies, it was agreed that the Barisan Mountains (in this case the volcanic arc) began to rise west of Sumatra in the Middle Miocene. The effect on the Bengkulu Basin is that before Central Misoen there was no Bengkulu forearc basin because at that time the arc itself did not exist.

That is what has been believed, namely that before the Middle Miocene, or Paleogene, the Bengkulu Basin was still the westernmost part of the South Sumatra Basin. Then in the period after the Middle Miocene or Neogen, after the Barisan Mountains rose, the Bengkulu Basin was separated from the South Sumatra Basin. From then on, the Bengkulu Basin became a forearc basin and the South Sumatra Basin became a backarc basin (behind the arc).

 

The history of the unification and separation of the Bengkulu Basin from the South Sumatra Basin can be studied from the Paleogene stratigraphy and the Neogen both of these basins. It can be observed that in Paleogene, the stratigraphy of the two basins is almost the same. Both of them developed a graben system in several places. In the Bengkulu Basin, there are Pagarjati Graben, Kedurang-Manna Graben, Ipuh Graben (at the same time in the South Sumatra Basin there were Jambi, Palembang, Lematang, and Kepahiang graben-graben). But after Neogen, the Bengkulu Basin entered a deeper basin than the South Sumatra Basin, evidenced by the development of massive carbonate reefs.

in the Upper Miocene which is almost the same age as Parigi carbonate in West Java (the operators who had worked in Bengkulu call it Parigi carbonate too). At the same time, more regressive sediments were deposited in the South Sumatra Basin (Air Benakat Formation / Lower Palembang and Muara Enim / Middle Palembang) because the basin was undergoing lift and inversion.

Tectonically, why is there a stratigraphic difference in Neogene in the Bengkulu Basin — the Bengkulu Basin in the sinking phase while the South Sumatra Basin is being lifted. Because in Neogen, the Bengkulu Basin became flanked by two large fault systems extending west of Sumatra, namely the Sumatra (Semangko) fault on land and the Mentawai Fault in the offshore region, a little to the east of Sumatra's outer arc islands (Simeulue-Enggano) . These two faults are dextral. The same slip (two strike-slip or duplex) shift properties will be trans-tensioned or open the area flanked by it. In this way all of the forearc basins in the west of Sumatra flanked by these two large faults were opened by a trans-tension pull apart which caused these basins to sink so that they had room to develop massive Neogen carbonate reefs as long as they were not too in.

In the northern forearc basins of Bengkulu (Mentawai, Sibolga, Meulaboh) also developed massive Neogen reefs due to the opening and sinking of these basins. And, in this petroleum world, reefs have been the targets of exploration drilling since the late 1960s. Unfortunately, until now no commercial reserves have been found, only biogenic gas and oil shows have been found (Dobson et al., 1998 and Yulihanto, 2000-IPA proceedings for information on Mentawai and Sibolga Basins).

The Bengkulu Basin is one of two forearc basins in Indonesia, which are mostly carried out by oil operators (the other is the Sibolga-Meulaboh Basin). Even though it has not succeeded in finding commercial oil or gas, it does not mean that these basins do not contain commercial oil and gas. Because, there are no targets for drilling in this region (a total of around 30 wells) that penetrate the Paleogene target with its graben system that has proven productive in the Central Sumatra and South Sumatra Basin.

Reference:

• Yahoo.com
• Google.com
• Wikipedia.com
• http://geologi.iagi.or.id/2009/03/22/cekungan-bengkulu/