Picture: Panorama of Keppel Container Terminal, Singapore. Photo: Kroisenbrunner. Wikimedia Commons.
Graham Leslie* and Rhian Kendall** explore the geology beneath one of the world’s fastest growing cities - Singapore.
The Republic of Singapore is a hugely vigorous and dynamic hub for global finance, commerce, and transport links, and is arguably one of the world’s most competitive countries. The only island city-state on the planet, and frequently cited as the most ‘technology-ready’ nation, Singapore is the world’s third-largest oil refining and trading centre, its second-busiest container port, largest oil-rig producer and a major hub for ship-repair services.
Picture: Marina Bay Gardens, Singapore – all on land reclaimed from the busy Singapore Strait
Looking to the future, Singapore today aspires to becoming a ‘smart’ nation – one that integrates transportation, utilities and service infrastructure with information communications technology (ICT), in order to facilitate the sustainable management of its societal assets.
Natural resources
The resulting demand on Singapore’s constrained land and natural resources is high. A growing population of over 5.6 million lives within an area of only 700km2, a population density of some 8264 people per km2 in an area approximately the same size as Anglesey (Ynys Môn) in North Wales!
Although half of Singapore’s land area comprises spectacular nature reserves, parks and gardens, natural outcrop is now extremely rare at surface; and so, getting to grips with Singapore’s geology is always challenging. Despite these challenges however, it is becoming increasingly clear that the story of Singapore’s geological evolution from Carboniferous times on, was diverse, often complex, and rapidly changing – at least on a geological timescale.
Picture: Outcrop is at a premium in heavily built-up Singapore.
Understanding that geological inheritance, and communicating its most significant characteristics to Singapore’s geological community, is vitally important to those responsible for fuelling and sustaining the country’s continued growth.
Taking a long-term view, the Singapore Government has already invested heavily and strategically in the creation of land and space, establishing an Economic Strategies Committee (ESC) in 2009. The Singapore Government is developing an underground master-plan and ‘land bank’, with a view to ensuring that underground and aboveground spaces are better integrated with surrounding developments and infrastructure.
All underground and other geological information that will benefit both private and public sector efforts in underground development has now been collated, and a subterranean land rights and valuation framework is being developed. The British Geological Survey (BGS) has been working with the Geological and Underground Projects Department in of the Building and Construction Authority (BCA) since 2012 to deliver this modern geological knowledge-base. This article tells the story (so far!) of the fascinating geology emerging from beneath the Asian Tiger City.
Picture: BGS has worked with BCA to revise the current stratigraphy of Singapore. The lithostratigraphical units of the new proposed stratigraphy framework have been developed to be consistent with International Commission on Stratigraphy (ICS) recommendations. Simplified Geological Map After Gillespie et al. (2014) and Goodenough et al. (2014)
Reclamation
Since the 1960s, land reclamation projects have increased Singapore's land area by almost 24% - to c. 720km2 in 2015. Its surface area is projected to grow by another 100km2 by 2030.
Singapore presently comprises 63 separate islands; some of these reclamation projects involve merging smaller islands to form larger, more functional islands (as has been done with Jurong Island in the south west). In still more ambitious plans, the subsurface is seen as an attractive development space for, among other things, basements, energy production and infrastructure, waste disposal and treatment, groundwater abstraction and water storage, transportation, industrial manufacturing, and logistics.
BISingapore lies at the southern end of Peninsular Malaysia, in a region dominated by the geological history of two continental fragments (Indochina-East Malaya and Sibumasu) that separated from the supercontinent of Gondwana during the Palaeozoic. These fragments are now joined together, along with rocks assigned to the Sukhothai Arc terrain, along the trace of the Bentong-Raub Suture Zone. Permian to mid-Triassic granitic and mafic intrusive rocks from that arc dominate central Singapore. In western and south-western Singapore a mid- to uppermost Triassic (to earliest Jurassic?) volcano-sedimentary succession was originally deposited in an active fore-arc basin as a shallow marine to terrestrial succession, broadly contemporaneous with the younger elements of the plutonic rocks of Singapore. After Metcalfe (2011) and Hall (2009).
Planning
Geological and geotechnical understanding of Singapore’s sub-surface is critical to planning, design and construction of a future-proof city infrastructure. Very significant parts of that infrastructure will comprise enormous underground facilities, and land-scarce Singapore is already storing some of its military resources in this way.
The giant cavern facilities beneath Jurong Island entered service for oil storage in September 2014 (Pictured, left). This cavern complex lies some 150m below ground, delivering a storage capacity of 1.47 million m3 of liquid hydrocarbon - equivalent to some 580 Olympic-sized swimming pools. This capacity will double when the second phase of the work is completed.
In the last decade, the push to go underground has seen potential uses of cavern space as water reservoirs, power stations, port logistic systems, data centres, warehousing and storage all under consideration. The state-of-the-art underground MRT system for Singapore’s growing population continues to expand rapidly.
Bedrock is now preserved only sporadically at the modern metropolitan n surface. Most natural outcrop is confined to coastline and to disused quarries, many of which are now flooded or in varying stages of reclamation.
The present new study is only made possible because of a new and comprehensive ground investigation programme commissioned for the BCA. This includes acquiring drillcore from more than 100 boreholes. Each borehole is typically about 200m deep, extending from the ground surface to some 70m below the engineered floors of any anticipated cavern storage space designs - totalling approximately 13, 400m of new drillcore. Some 100km of new seismic reflection and refraction data have been acquired in a number of designated development areas; all these new data are having a very significant impact on current understanding of Singapore geology.
None of the geological record that emerges from beneath the modern Singapore cityscape is straightforward. Embedding robust geoscience knowledge in sub-surface planning will help ensure that the future decision-making process will be well informed and so improve urban resilience.
Singapore rocks
Singapore lies at the southern end of Peninsular Malaysia, in a region dominated by the geological history of two continental fragments (Indochina-East Malaya and Sibumasu) that separated from the supercontinent of Gondwana during the Palaeozoic. These fragments are now joined together, along with rocks assigned to the Sukhothai Arc terrain, along the trace of the Bentong-Raub Suture Zone (see map above).
Picture: Geological and geotechnical understanding of the Singapore sub-surface is critical to planning, design and construction of a future-proof city infrastructure.
Singapore’s oldest rocks are thought to be the siliciclastic sedimentary rocks of the Sajahat Formation, which crop out on the island of Pulau Tekong in north-eastern Singapore. Although the Formation’s age is not proven conclusively, these rocks have been thermally metamorphosed by the intrusion of granitic and associated mafic intrusive rocks of Permian to mid-Triassic age. The Central Singapore Granite and Gombak Norite plutons are a conspicuous feature on the geological map.
In western and south-western Singapore the Mid- to Upper Triassic (to earliest Jurassic?) volcano-sedimentary Jurong Formation (which has been assigned Group status in the BGS’s new proposed lithostratigraphical framework) was originally deposited in an active fore-arc basin as a shallow marine to terrestrial succession, broadly contemporaneous with the younger elements of the plutonic rocks. The sedimentary succession is punctuated by volcanogenic deposits that issued from the still-active arc; 240 million year-old tuffs are interlayered with Carnian/Norian fossil assemblages, all pointing to a mid- to late Triassic history.
Now folded, thrust and cleaved, these Jurong strata record deformation and low-grade metamorphism that resulted when the fore-arc sequence became accreted onto Mesozoic Indochina-East Malaya during collision and suturing with Sibumasu across the Bentong-Raub line.
Picture: Some of the c.13km of new core laid out for examination
During the earlier stages of that collision, and possibly as the subducting oceanic slab detached, the older inner fore-arc succession was buried beneath a 20 – 30Ma younger fluvial succession laden with volcanic, plutonic and metamorphic detritus. Gradually, that fluvial succession became more tidally dominated again, as relative sea-levels rose in the earliest Jurassic. Terminal collision of Sibumasu and SE Indochina- East Malaya (‘docking’) marked the end of deformation, focused in the Bentong-Raub suture zone. NE-vergent fold and thrust-belt deformation developed on the eastern side of the suture zone, affecting upper Triassic to earliest Jurassic strata.
Deformation ended by about 195Ma and that terminal collision was followed by a long period of deeply penetrative weathering and erosion for c. 50 million years during the later Jurassic. No mid- to upper Jurassic strata are preserved.
Variably cemented Quaternary sands and gravels cover much of eastern Singapore Island. These are thought to have been deposited by braided river systems, flowing broadly southwards into the Straits of Singapore. They are known as ‘Old Alluvium’ in both Johor and Singapore (attributed to the Bedok Formation within the new proposed lithostratigraphical framework).
The youngest part of the succession comprises unconsolidated marine to terrestrial sediments of late Pleistocene to Holocene age, which are assigned to the Kallang Formation (also elevated to Group status in the BGS proposed lithostrat framework).
Pioneer
It is important though to acknowledge that our work did not start from nothing. One of the first geological maps for the whole island of Singapore was created by Dr Elizabeth Alexander and published in 1950. Frances Elizabeth Somerville Alexander (1908-1958) was a pioneering scientist (see this month’s second feature). She was awarded a PhD from Cambridge University in 1934 with a thesis on the main outcrop of the Aymestry Limestone (Silurian, Upper Ludlow Shales Group).
After her marriage the couple moved to Singapore in 1936, where they had a family of three children. Alexander worked for the Royal Navy on radio direction-finding, during which time she held the rank of Captain. She is, arguably, most well-known as the first female radio astronomer, discovering in 1945 the ‘Norfolk Island Effect’ - the connection between an increase in radio noise associated with the sun (solar radio emissions).
In 1942, with the threat of Japanese invasion looming, Alexander fled with her children to safety in New Zealand. Believing her husband to be dead (he was actually a prisoner of war at Changi), she remained there, and was appointed head of the Operations Research Section of the Radio Development Laboratory. After they were reunited, the couple returned to Singapore in 1947. Alexander became a geological consultant and in 1949 was appointed Geologist to the Government in Singapore.
Her main task was to make a survey of the islands resources of granite and other useful stone - one conclusion of which being that the island’s granite resources should last for 500 years. Alexander died in 1958, a few months short of her 50th birthday. Her contribution to geology and radio astronomy is extraordinary, considering her short life, detailed knowledge of two disciplines, and the traumatic circumstances in which she made it.
Our present work on Singapore’s subsurface geology (picture, left) rests on the pioneering work carried out by Alexander, often in the most difficult of circumstances. It is with a certain pride that by building on what she achieved, we are able to draw attention to this sadly neglected figure, whose daughter is currently engaged in writing her biography. The Asian Tiger City owes her a very great debt indeed.
Authors
*BGS Scotland, The Lyell Centre, Edinburgh EH14 4AP: E: [email protected]. **BGS Wales, Cardiff University, Main Building, Park Place, Cardiff CF10 3AT, Wales. Published with the permission of the Executive Director, British Geological Survey.
Further reading
- GILLESPIE, M. R. G., GOODENOUGH, K. M., KEARSEY, T., LESLIE, A. G., & PRICE, S. J. (2014). A Stratigraphical Guide for Singapore. (CR/13/046). Keyworth, Nottingham: British Geological Survey.
- GOODENOUGH, K. M., LESLIE, A. G., KEARSEY, T., PRICE, S. J., WOODS, M. A., GILLESPIE, M. R. and BOON, D. 2014. An Overview of the Geology of Singapore. Commissioned Report CR/13/037. Keyworth, Nottingham: British Geological Survey.
- HALL, R. 2009. The Eurasian SE Asian margin as a modern example of an accretionary orogen. 351-372 in Earth Accretionary Systems in Space and Time. CAWOOD, P. A. and KRONER, A. (editors). Geological Society Special Publication 318 (London: Geological Society of London).
- METCALFE, I. 2011. Palaeozoic-Mesozoic history of SE Asia. 7-35 in The SE Asian Gateway: History and Tectonics of the Australia-Asia Collision. HALL, R., COTTAM, M. A. and WILSON, M. E. J. (editors). Geological Society of London Special Publication 355 (London: Geological Society of London).