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Geology of Singapore

General outlook

The geological history of Singapore is closely related to the geology of the Malayan Peninsula where three main south-north trending zones are distinguished, i.e. the Western, Central and Eastern Belts. These zones are marked by two major tectonic zones (Benton-Raub Suture Zone and Lebir Fault Zone), and their origin dates back to the Indosinian Orogeny which happened during the Triassic. Singapore lies on the extension of the Central and Eastern Belt. As a result the area to the west of the Bukit Timah Fault - crossing Lim Chu Kang, running along the western edge of the Bukit Timah towards Outram - is composed mainly of younger sedimentary rocks (Late Triassic to Present), while the predominant part to the east of it is built of metamorphic, intrusive and volcanic rocks of Palaeozoic to Late Triassic age. The Tertiary and Quaternary soft sediments are spread across both zones.

Formations in Singapore:

Late Pleistocene to Present

Residual soils: insitu product of chemical weathering of underlying rocks, up to 30 m thick, although occasionally thicker (even over 45 m).

Kallang Formation: consists of soft sediments and includes: the Reef Member (active coral reefs and calcareous sand), Littoral Member (coastal sand and gravel, beach, littoral and sand bank deposits), Transitional Member (organic mud found in river mouths and tidal flats, represents former mangrove swamp environment), Alluvial Member (valley fill consisting of gravel, sand, silt and peat) and the Marine Member (marine clay deposited during the Holocene sea-level high).

Tekong Formation (Holocene 5-6 ka): thin layer of sand and gravel (littoral and fluvial), occasionally mud and peaty mud (estuarine).

Late Tertiary (Pliocene) to Mid-Pleistocene: Old Alluvium: matrix supported gravelly sand, or poorly cemented sandstone-conglomerate (alluvial fan, fluvial to delta deposits). Formation is interpreted as alluvial fan and proximal braided river facies (Gupta et al. 1987), mostly found to the east of the Bukit Timah Fault.

Area west of the Bukit Timah Fault

Early to Mid Pleistocene: Huat Choe Formation: white kaolin clay with occasional quartz gravel (weathering profile). These deposits are up to 6 m thick and limited to a small area (200 by 400 metres) in south-western part of Singapore.

Late Tertiary, or Early Pleistocene: Fort Canning Boulder Bed, or Bouldery Clay (landslide deposit): sandstone boulders in stiff silty/sandy clay matrix, thickness of 30 to 90, at least 300-m-wide belt in southern part of Singapore. Landslides probably were caused by tectonic movements on normal faults during the Late Tertiary, or Early Pleistocene. Sandstone boulders were derived from the Jurong Formation. These deposits were covered by the Old Alluvium.

Late Triassic Jurong Formation (possibly to Early Jurassic, about 230 to 209.5 Ma., maybe younger?): considered molasse deposits (post-orogenic deposition) which filled half-graben formed by extensional tectonic movements which in the Late Triassic followed the Indosinian Orogeny (Oliver and Prave 2013). It consists of red beds: mudstones, siltstones, sandstones and conglomerates as well as occasional volcanic rocks (photo to the right).

Area east of the Bukit Timah Fault

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Late Triassic Dyke Rocks: intrusions within the Palaeozoic Formations and the Bukit Timah Granite considered as syntectonic, i.e. associated with Indosinian orogenic movements.

Early to Late Triassic (about 240 to 200 Ma) Bukit Timah Granite: consists of granite, adamelilite, granodiorite, norite-granite mixed rocks.

Late Palaeozoic (possibly Carboniferous, about 360 to 280 Ma): Volcanic rocks: Andesitic ashy tuff and agglomerate tuff related to volcanic arc located within the continental plate west of the Variscan subduction zone.

Early Paleozoic (probably):
Gombak Norite (probably about 450 to 360 Ma): gabro and norite with metasomatic changes close to the Bukit Timah Granite.
Sajahat Formation (probably about 500 to 450 Ma): quartzite, quartz sandstone and mudstone (originally shallow marine).

Literature

Gupta A., Rachman A., Wong Poh Poh Pitts J. 1987. The Old Alluvium of Singapore and the extinct drainage system of the South China Sea. Earth Surface Processes and Landforms 12
Hutchison C.S. 1964. A gabbro—granodiorite association in Singapore Island, Quarterly Journal Geological Society of London 120
Hutchison C.S. 1973. Tectonic Evolution of Sundaland: A Phanerozoic Synthesis, Geological Society of Malaysia, Bulletin
Lee K.W., Zhou Y., 2009. Geology of Singapore, Defence Science and Technology Agency, Singapore,
Lin S.C. 1991. The Biophysical Environment of Singapore, NUS Press
Oliver G., Prave A. 2013. Palaeogeography of Late Triassic red-beds in Singapore and the Indosinian orogeny. Journal of Asian Earth Science 76
Pitts J. 1984. A survey of engineering geology of Singapore, Geotechnical Engineering, Journal of Southeast Asian Geotechnical Society 15
Han K.K., Wong K.S. , Broms B.B., Yap L.P. 1993. The origin and properties of bouldery clay in Singapore, Geotechnical Engineering 24