Science & Technology: BUTON BASIN

BUTON BASIN

LOCATION MAP

The Buton Islands are located in the eastern part of Indonesia, precisely on the east coast of Southeast Sulawesi. Stratigraphy and island structure are distinguished from Southeast Sulawesi and the Muna Islands. But there are similarities between Buton and the adjacent islands in the Banda Arc, especially Timor, Seram, and Buru Island. Administratively, Buton Regency is located at 4.30º - 7.0º LS and 125º - 125º BT. The Buton Basin has the following limits:

North Side: Wawoni Island
South side: Flores Sea
West side: Muna Islands and Bone Bay
East: Banda Sea
Southeast: Tukangbesi Platform

REGIONAL PHYSIOGRAPHY

Based on the geomorphology of the physiology of the Buton region is divided into three parts, namely:

The southern part consists of hills and valleys with northeast trending with raised reef terraces and karst topography.
The Central part is dominated by mountainous ridges along the west coast, the sedimentary rocks are northeast.
The northern part is dominated by mountains on the seashore which have horseshoe-like shapes, the drainage pattern is directed towards the mangrove swamp in the lambele basin. In general, the existing mountains have a northwest-southeast direction that has low relief accompanied by raised coral reefs.

Map of the Buton Basin

REGIONAL TECTONIC

Buton is believed to consist of 2 separate and separate continental micro fragments. One is in the eastern part of Buton Island and the Ironman while the other is in the western part of Buton Island and Muna Island (Hamilton, 1979). Based on recent geological data and geophysical data, it has been shown that Buton consists of 3 different continental micro fragments that have a juxtapose relationship with the Buton region, Buton Island, Muna / SE Sulawesi, and Tukang Besi. This island stratigraphy indicates that each continuous micro fragment has a different paleogeographic position when Mesozoik and Paleogen (De Smet, 1991).

Like most Banda Arc islands, Buton is considered to be a fragment released from the Australian-New Guinea continent, mainly based on the correlation of similar Mesozoic fossils, pre-rift stratigraphy, and when rifts. Many similarities in tectonic history and stratigraphy support the similarities of the formation of Buru, Ceram, Banggai-Sula, and Timor (Audley-Charles et al., 1972; Price, 1976; Hamilton, 1979; Pilgram and Panggabean, 1984; Gerrard et al., 1988; Katili, 1989; De Smet et al., 1991).

The tectonic and stratigraphic history of most Banda Arc islands is characterized by several events. The pre-rift event was characterized by continental sediment deposition in half-graben, the rift event was characterized by lifting, erosion, and local volcanism, event drift was characterized by subsidence and sedimentation of open sea sediments, and a collagen-aged Neogen event. The basic difference between each island is only the time and duration of individual tectonic and stratigraphic events.

Buton sedimentation is controlled by 4 tectonic events:

1. Pre-Rift Perm until the End of the Trias. Deposition of continental sediments in half-graben, characterized by the presence of uplift, erosion, and local volcanism. There was a decrease and deposition of open sea sediments followed by neogen collision. In the aged layer of trias in igneous intrusion and indicates the beginning of rifting, the formation of extensional faults, and regional subsidence.

2. Rift-Drift End of the Trias to the Oligocene. The transition period towards the open sea environment with sedimentation on passive margins occurs in the middle to the end of the Jurassic result of deposition of orogenic syn clastics in the neogenous basin resulting from erosion and upward faults due to the removal of Triassic to Oligocene layers.

3. Syn and Post Orogenic early Miocene to Pliocene subduction, compression, and deformation until the mid-Miocene in the south resulted in the removal and erosion of syn orogenic clastic clans in the early Miocene region so that regional unconformity was formed. Collision from Buton-Muna Island did not affect the northern part of Buton Island until the mid-Miocene. In the late mid-Miocene to the end of the Miocene obduction occurred resulting in unconformity. After the mid-Miocene a major shear fault system (Kioko) occurred which absorbed sediments from two different environments. In five million years ago there was a change in deformation and structural force caused by the Buton subduction zone of Muna and Buton against the Ironman. Collision between Buton and Ironworker is recorded in the late Pliocene layer, this oblique collision produces strike-slip movement and dip-slip which results in local uplift and subsidence (Chamberlain et al., 1990; Fortuin et al., 1990) to date.

4. Resen Orogenic, south of Buton is now experiencing rapture while the north is decreasing (de Smet et al., 1989). Buton microcontinent is currently also experiencing transpressive strike-slip against the Iron and Muna microplate, the Buton plate moves northward. The orientation of the en-echelon wrench fault with the northeast orientation associated with the anticline in the Buton strait indicates that there is reactivation of the paleo suture zone, its main movement is synistral strike-slip.

GEOLOGICAL STRUCTURE

The geological structure is generally an anticline and syncline structure and several fault structures consisting of normal faults and faults, and horizontal faults. The structure of the anticlines is directed Southwest-Northeast to North-South. This structure almost affects the entire formation where it appears that all existing formations are folded with the slope angle of the rock layer in the eastern part is relatively steeper than in the western part. Horizontal faults are generally found in the southern part and intersect the Winto Formation, Tondo Formation, and Sampolakosa Formation. The direction of the horizontal fault is generally perpendicular to the fold axis that is Northwest-Southeast. While the normal fault is the structure formed most recently as a secondary fault structure.

Based on regional gravity data and the northeast-southwest orientation of the upheaval in the early Miocene age, it shows that the south of the island of Buton experienced a rotation of 450 clockwise. The time of rotation cannot be determined but is probably caused by compression in the mid-Miocene caused by collisions from Buton-Muna / SE Sulawesi. The fulcrum or rotation is in the eastern gian sea of Buton in Kulisusu Bay.