Sulawesi Geological and Tectonic history in brief

It is widely accepted in geological literature that the Eastern Sulawesi Terrain is derived from a Gondwanaland fragment. Opinions differ as to the origin of the West Sulawesi Terrain. Older speculation tends to regard it as having once been part of Laurasia, along with the greater portion of Western Indonesia. More recently, authors such as Whitten have made the suggestion that it rifted in the Jurassic epoch from Gondwanaland. The account below is commensurate with Whitten’s opinion.

There is also some discussion as to the origin of Sulawesi’s northern arm. It is now generally regarded as part of the West Sulawesi Terrain/micro-plate but may once have existed separately.

Jurassic/200-250 million years BP

The Western Sulawesi Terrain (along with Thailand, Malaysia, Burma, Sumatra, etc.) rifted from Gondwanaland as a result of the opening up of a major east-west oceanic ridge that was located to the north of Australia. The Western Sulawesi Terrain, along with most of what was to become the Indonesian Archipelago, was at this time situated north of the ridge. The Eastern Sulawesi Terrain, and Banggai- Sula Terrain, were to the south of the ridge on the Indo-Australian plate margin, lying close to the land mass that was later to emerge as New Guinea.

Cretaceous 145-70 m y BP

With the continuing rotation of Australia in an anticlockwise direction, and general tectonic movement,the Eastern Sulawesi Terrain was carried north-westwards and started to subduct beneath the Western Sulawesi Terrain.

Palaeocene (70-60 m y BP) – Eocene (60-40 m y BP)

Subduction continued and volcanism in West Sulawesi commenced as the East Sulawesi Terrain was thrust towards West Sulawesi, at a speed of around 10 cm/year. Much of this energy dissipated as strata were uplifted, deformed and broken, and rocks metamorphosed. However, recent research suggests that the major units of Sulawesi were still quite far apart at the end of the Eocene, and much of the land that was eventually to become Sulawesi was still under water.

Oligocene 40-25 m y BP

The Banggai-Sula Terrain moved westward and the subduction of Eastern Sulawesi continued. Western Sulawesi had more or less reached its present position. By the mid-Oligocene, around 30 million years ago the main units formed a crescent shape with Eastern Sulawesi Terrain to the south, West Sulawesi just to the north with its axis running SW-NE and the area that was to become Sulawesi’s northern arm lying to the north east. By the end of the Oligocene the East Sulawesi Terrain had continued to move northwards and had collided with the West Sulawesi Terrain. However the large and small fragments which make up the northern arm was probably still separate. Hall diagrams tentatively suggests that at this time large areas of The West Sulawesi Terrain were still under water while much of the Eastern Terrain was above water.

Middle-Miocene 16.5-11 m y BP

The main terrains are finally unified. Rocks from Western Sulawesi partly override those of the Banggai-Sula. Volcanism became widespread over the Western Sulawesi Terrain, and patches of submarine volcanic activity occurred in the area where Lore Lindu NP is now situated.

From the Middle Miocene, through into the Pliocene, patches of mollase-type sediments were deposited across the main terrains.

Pliocene (10-1 m y BP)

Major granite intrusions occurred across the unified terrains. The plutonic Kambuno granite and gronodiorite, which underlies much of Lore Lindu NP, was formed in this period, at around 3 million years BP (Sukamto 1975). Uplifting, leading to the formation of current landform features, also occurred at this time. Sulawesi collided with Borneo in the late Pliocene – some 3 million years BP. The island has, at times, been very close to its larger neighbour during times of low sea level. It has also been suggested that while some monkeys arrived on Sulawesi from Borneo, animals such as the tarsier may have crossed from Sulawesi to Borneo, or vice versa, via island chains linking to the Philippines. The same may also be true of the anoa, which has as its closest relative, the tumaraw (Bubalus mindorensis), a species that is found in the Philippines.

Quaternary (Pleistocene 1 m y-10,000 y BP) and Holocene (10,000 y BP to present)

Sedimentary deposits were laid down along Sulawesi’s west coast, and lake deposits – clays silts, sands and gravels – built up in valleys. These formed horizontal beds within the Western Sulawesi Terrain, and now cover significant areas of Lore Lindu NP.

As little as 7000 years ago sea levels were approximately 180 m lower than present levels. At this time, the Makassar Straits would have been up to 2000 m deep in places, but exceedingly narrow. This raises speculation as to the extent to which species were able to cross over the divide. Species may have rafted across but it is generally accepted that there was never a dry land connection. Obviously the sea channel would not have presented an obstacle for some bird and mammal species. Amphibians, on the other hand, would have found the crossing more difficult, inhibited by the saline conditions.

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