GORONTALO BASIN - CELEBES

GORONTALO BASIN - CELEBES

Sulawesi Island is composed by four arms (arm): south arm, north arm, east arm, and southeast arm. In the South Arm there is a large city, Makassar. In North Arm there is Manado, on the East Arm there is Luwuk, and on the Southeast Arm there is Kendari. Kundig (1956) reports that the central part of the Togian is composed of andesite, and east by ofiolite (rock from the oceanic crust and upper mantle of the Earth). Please note that the East Arm of Sulawesi to the south of Togian is composed of ofiolite, the largest ofiolite mass in Indonesia. Because of that Silver et al (1983) once wrote that the Gorontalo Basin is a fore-arc basin with essentially oceanic / ofitic crust. But the mapping by Rusmana et al. (1982) found that the Togian Islands were almost entirely composed of tuffs (petrified volcanic ash) and sedimentary rocks of the Miocene-Pliocene age (between 7-5 million years). In South Sulawesi and West Sulawesi, there are believed to be pre-Tertiary microcontinents that infiltrate, Bone Bay which is very deep and open by the Makassar Strait open, there are also Enigma Bay / Gorontalo Basin, puzzles, and possibly storing microcontinents like in West Sulawesi from Australia.

Gorontalo Basin is located in Gorontalo Province, Central Sulawesi, extending east-west direction, covering an area of ​​34,320 km², at coordinates 120º5 '- 120º50' BT and 0º27 'LU - 1º24' LS. Basement rocks are Cretaceous, with sediment thickness between 500 - 2,000 m at a depth of 2,000 m.

 Location of Gorontalo Basin

This basin is geologically included in the suture basin. This basin is located in the northern region of Sulawesi flanked by the eastern arm of Sulawesi, composed of the East Sulawesi Ofiolite Complex rocks and thebred tertiary sedimentary rocks and the Sulawesi north arm compiled by Tertiary - Quaternary volcanic rocks (Lemigas, 2006).

Basin Type

The beginning of the formation of the Gorontalo basin was due to the fracturing and clockwise rotation of Sulawesi's northern arm in Neogen in about 5 Ma (Hamilton, 1979; Walpersdorf et al. 1997, 1998) or 3.5 Ma (Hinschberger et not active subduction to the southern Sea plate Sulawesi (LLS) (Jezek et al., 1981) is caused by collisions between the Sulawesi east arm arc and the Banggai-Sula micro continent. Another possibility is the opening of the back arc relative to subduction to the south from LLS and the North arm volcanic arc at the end of the Tertiary.

Walpersdorf et al., 1998 and Kadarusman, 2004, assume that the open axis of the Tomini-Gorontalo basin is northeast-southwest, while Hinschberger et al. (2005) in the opposite direction, namely northwest-southeast. The shape of the basin itself has no previous information whether in the form of graben, half-graben or other. Whereas with regard to its geographical position, it is likely that the dominant sediment source originates from the south (Figure 2.2). The Gorontalo Basin was formed due to block-faulting during a trip to the southeast of the East Sulawesi ofiolite complex during the micro-continental collision of Banggai-Sula (Figure 2.3). The basin is quickly filled by Quaternary-Late Late deposits up to 5000m thick (Hamilton, 1979).

Gorontalo Basin Formation Sketch

The main structure of the Gorontalo Basin is east-west, this basin appears in two parts based on bathymetric configuration:

1. To the west of Togan Island (Tomini Bay), it ranges from 1,000 - 2,000 m.
2. To the east of Togan Island, deeper into the Maluku Sea exceeds 3,000 m.

The configuration of this basin structure is generally similar to the Bone Basin, the middle part of which may be filled in the Middle Neogene - Late Neogen until now, in the position of the volcano-magmatic arc basin and the non-volcanic arc basin. Faults may be related to the graben formation that is present off the coast of Poso in the southwest part of Tomini Bay. Comparison of the main depression of the deepest part between Gorontalo and Togan Island is more than 3 s (TWT) above the bedrock acoustics. Indications of the bedrock height structure are only observed in the middle of the basin.

Regional tectonic reconstruction Hall's (2002) shows that the proto-Gorontalo basin is most likely a fore arc basin formed from the Middle Eocene to the Early Miocene, with arcs in the northern arm of Sulawesi.

Evolution of the Basin

The Gorontalo Basin is the result of the collision of the Australian Micro Plate with the Sunda Plate in the Mesozoic. Then followed by the Sunda strain as the Lhasa-Sikuleh Micro Plate which collided with Eurasia. In this period, dispersion of carbonate exposure was dispersed with several intrusions associated with the Oligocene - Middle Miocene volcanic process.

Carbon-Permian (Plate Configuration)

Research at this age is still very little, an explanation of the tectonic framework of Eastern Indonesia in this area is only supported by microplate configurations. Data from previous tectonic orders that are often used are the Southeast Halmahera tectonic model as a Tertiary-derived terrain (Hall, 2002 and Metcalf, 2002 in Jablonski et al., 2007).

Trias-Paleosen (Pre Break-up)

The thickness of the separate plates shows a complicated layer configuration, interpreted as the rest of the previous expansion. These layers are present along the northern boundary of the Gorontalo Basin. Block separation begins 205 jtl and then collides with the Sunda at the age of Cretaceous, then the ofiolite belt is trapped between these two plates. Offiolite exposed on land has been intruded by Granit Toboli aged 96.37 million (Hall, 2002 in Jablonski et al., 2007).

Middle-Eocene Early Eocene (Break-up Phase)

Following the Mangkalihat-Northwest Sulawesi collision with Northeast Sulawesi in the Cretaceous, the Lhasa-Sikeuleh Micro Plate collided with the Eurasian Plate in western Burma-Sumatra at 51.5 million (Rowley, 1996 in Jablonski et al., 2007). This causes a clockwise rotation of the Sundanese Mainland and a number of openings of tear rifts (Longley, 1997 in Jablonski et al., 2007) such as the opening of Bone Bay, opening of Tomini Bay / Gorontalo Basin, Sulawesi Sea subduction. Subduction that tilted towards the continent (roughly westward at that time) occurred many times and produced several magmatic and volcanic periods in western Sulawesi (Satyana, 2014).

During this period, a number of river deposits - deltas developed that could potentially contain hydrocarbons (oil prone). The Gorontalo Basin appears with two sub-basin depositors which are thought to be associated with the expansion of the Sulawesi back in the north and may also have a relationship with the Bone Basin in the south approaching the Palu Fault Zone.

Late Eocene - Upper Miocene

Significant period for Sulawesi, at this time there were collisions, collisions, docking of two Australian microcontinents towards Sulawesi from the southeast (Buton-Tukangbesi microcontinent) and from the east (Banggai-Sula microcontinent). In this period it is estimated that the main direction / polarity of the Sulawesi arcs for both magmatic arcs and subduction pathways from the convex to the ocean becomes concave towards the ocean (to the east at this time). The reversal of the polarity of the Sulawesi arcs is frontally due to the collision of the Banggai-Sula microcontinent which strikes it at the central point of Sulawesi, in the center, at the pivot point. The form of Sulawesi "K" is estimated to occur at this time. Sulawesi flips from convex to east to concave to the east. The reversal of the Sulawesi arcs occurs through the mass transfer of the Earth's crust called "rotation", the Southeast Arm rotates counterclockwise so that it opens to expand the Bone Bay to the west, the North Arm rotates clockwise so that it closes the Gorontalo Basin (Satyana, 2014).

 

Scheme of formation of "K" on Sulawesi Island

Upper Miocene - Resen

The finalization period for Sulawesi arc arcs and tectonic escape periods in Sulawesi. As theorized, following collisions, there will be a post-collision tectonic escape, then after the clash of Buton-Tukangbesi and the clash of Banggai-Sula, there was a tectonic escape in the form of large horizontal faults that fractured and shifted Sulawesi. These faults are generally eastward, namely towards the free oceanic edge at that time as tectonic escape theory. The faults in the landscape of Palu-Koro, Matano, Lawanopo, Kolaka, and Balantak occur through the mechanism of post-collision tectonic escape. Tectonic escape is also manifested in the form of cracks opening, extensional, in the collision area of ​​Banggai-Sula or Buton-Tukangbesi.

 

Post-docking tectonic model from Sulawesi

Basin Stratigraphy

Regional Stratigraphy

Based on the sheet geological map of Tilamuta (S. Bachri, et al., 1993) and the Kotamobagu sheet (T. Apandi, et al., 1997) from the Bandung Geological Research and Development Center, the basin stratigraphy is composed of rock formations as follows:

a. Surface Deposition

• Alwium (Qal), consisting of: loose sand, clay, silt, mud, gravel and gravel. These rock units occupy lowland areas, especially in the plains, river valleys and swamps. Disposal of these rock units is limited to watersheds (DAS) such as those located west of Lake Limboto.
• Lake sediments (Qpl), consisting of: clay stone, sandstone, and gravel. These rock units are generally dominated by clay stones that are brownish gray in color, locally contain plant residues and lignite, in some places there are fine grained to coarse sandstone, and gravel. Locally there are small-scale cross-sectional structures in the sandstones. Generally these rock units are still incompressible and are estimated to be Pliocene to Holocene. This distribution of rock units occupies the valley around Lake Limboto. The thickness of this rock unit reaches 94 meters and is lined by Diorite rocks (Trail, 1974).

b. Sediment and Volcanic Rock Unit

• Anombo Formation (Teot), consisting of: basal lava, andesite lava, volcanic breccia, with intermittent wake sandstones, green sandstones, siltstone, red limestone, gray limestone, and few thermal rocks. The age of these rock units is estimated to be Eocene to the Early Miocene. The rock units of this formation are found in the area around G. Tahupo (828 m) to the south.
• Dolokapa Formation (fmd), consisting of: wake sandstones, siltstone, mudstone, conglomerates, tuffs, tuff lapilli, agglomerates, volcanic breccia and andesitic lava to basalt. The age of this formation is estimated to be Middle Miocene to Early. Late Miocene with an "inner sublitoral" depositional environment with an estimated thickness of more than 2,000 meters. The distribution of rock units in this area occupies the central and northern parts of the Gorontalo region, namely to the north of the Limboto Basin (Paleleh area to around the Kuandang area).
• Bilungala Volcanic rocks (TMBV), consisting of: volcanic breccias, tuffs and lava. these rock units are thought to be Middle Miocene to the late Late Miocene with a thickness of more than 1,000 meters. The distribution of these rock units is in the eastern part of the Gorontalo region, in the Tolotio area to the east.
• Wobudu Breccia Unit (Tpwv), consisting of: volcanic breccias, agglomerates, tuffs, tuff lapilli, andesite lava and basal lava. This rock unit is thought to be of the Early Pliocene age with an estimated thickness of 1,000 to 1,500 meters. This rock unit is exposed in the northern part of the Limboto Basin, starting from the Paleleh Mountains to the west of Kuandang Bay.
• Pinogu Volcanic rocks (TQpv), consisting of: the intersection of agglomerates, tuffs and lava. This rock unit is estimated to be of Late Pliocene to Early Pliocene with a thickness of up to 250 meters, while its distribution is in the south of the Limboto Basin and the Teluk Kuandang area and in several places that form separate hills.
• Klastik limestone (TQI), consisting of: calcarenite, calcirudif and coral limestone. This rock unit is thought to be of Late Pliocene to Early Pliocene with a thickness of between 100 and 200 meters, while its distribution is in the west of Lake Limboto.
• Reef Limestone (QI), consisting of: coral limestone. The age of these rock units is estimated to be Late Pliocene until the Holocene reaches a thickness of 100 meters, while its distribution is in the area near the Limboto lake and the eastern coast of the east.

c. Breakthrough Rock Unit

• Diorite Bone (TMB), consisting of: diorite, quartz diorite, granodiorite and adamelit. These rock units are thought to be Middle Miocene to the early Late Miocene (Trail, 1974), and are found in the eastern part of the Gorontalo fault, also in the west of the fault in the north of the Limboto Basin (near Kuandang and Paleleh).
• Boliohuto diorite (Tmbo), consisting of: diorite and granodiorite These rock units are thought to be Middle Miocene to Late Miocene, and have a distribution in the area of ​​G. Boiiohuto.
• Rock Return Unit, consisting of: Andesite (Ta) and Basal (fb). These rock units break through rock units from the Tinombo Formation, Dolokapa, and Wobudu breccia, so that they are generally considered Miocene to Pliocene.

Reference:

• Jablonski, D., Priyono, P., Westlake, S., Larsen, O. A., 2007, Geology and Exploration Potential of the Gorontalo Basin, Central Indonesia-Eastern Extension of the North Makassar Basin?, Indonesian Pet. Assoc., 31st Annual Convention Proceeding.
• Puspita, S. D., Hall, R., Elders, C. F., 2005, Structural Styles of the Offshore West Sulawesi Fold Belt, North Makassar Straits, Indonesia, Indonesian Pet. Assoc., 30th Annual Convention Proceeding.
• Rangin, C., Silver E. A., 1990, Geological Setting of the Celebes and Sulu Seas, Proceedings of the Ocean Drilling Program, Initial Reports, Vol. 124.
• Silver, E. A., McCffrey, R., 1993, Ophiolit Emplacement by Collision Between the Sula Platform and the Sulawesi Island Arc, Indonesia, Journal of Geophysical Research, vol. 88, No. B11.
• http://awangsatyana.blogspot.com/2013/11/cekungan-gorontalo-teluk-tomini.html