Feature: Kuala Lumpur Karstic Limestones

This time around, i-Geology diverts its attention from Miri to Kuala Lumpur for a while. We'll be looking into the karstic features of Kuala Lumpur limestone. As what we have learnt in Geology 102 (it came out in last semester's exam question too!) karst is  is a geological formation shaped by the dissolution of a layer or layers of soluble bedrock, usually carbonate rock such as limestone or dolomite. 

Kuala Lumpur Limestone is well known for its highly erratic karstic features. With the exception of Batu Caves, exposures of Kuala Lumpur Limestone are mainly found in  tin mining areas.

Geology of Kuala Lumpur Area 

Figure 1: Geological section through KL. (Tan Siow Meng)

Published geological maps of Kuala Lumpur area show that Kuala Lumpur Limestone Formation dominates the majority area of KL. A geological section  through KL is shown in Fig. 1. The limestone is estimated to be about 1,850m thick, overlying graphitic  schist known as Hawthornden Schist. The top of the sequence is Kenny Hill formation which occupies the heartland of KL including areas at KLCC and Bukit Bintang. 

According to Gobbett & Hutchison (1973),  Kuala Lumpur Limestone is “Upper Silurian marble, finely crystalline grey to cream,  thickly bedded, variably dolomitic rock. Banded marble, saccharoidal dolomite, and pure calcitic limestone also occur”.

Karstic Features -- Development of Karsts  

Figure 2: Development of karsts

Karst topography in limestone is formed by a chemical dissolution process when groundwater  circulates through the limestone as illustrated in Fig. 2. Carbon dioxide from the atmosphere is fixed or converted in the soil in an aqueous state and combined with rainnwater to form carbonic  acid, which readily dissolves carbonate rocks. Karstic features develop from a self-accelerating process of water flow along well-defined pathways such as bedding planes, joints and faults

Jalan Cheras/Jalan Chan Sow Lin?

On a flat limestone terrain, steep depressions can occur. Such a feature was encountered in a deep excavation at a site near the junction of Jalan Cheras/Jalan Chan Sow Lin.  The depression was about 27m deep. Potholes as shown in Fig. 8 were exposed at an excavation site near Kg. Pandan Roundabout. The biggest pothole measured 11m in diameter and 8m deep. Another pothole was suspected 150m away as detected by boreholes supplemented by Mackintosh probing tests. The potholes at Sg. Besi Tin Mines observed by Ayob (1965) were 10m in diameter  and 25m deep. Similar features are described as ‘well like holes’ by Yeap (1986). Their sizes vary from  30m to 200m in diameter! 

Like limestone in other parts of the world, erratic karst topography commonly found in Kuala Lumpur Limestone is formed by a chemical dissolution process. The dissolution of limestone is a very slow process compared to human life span.  

The karsts consist of deep dissections, potholes, steep depressions and solution channels, resulting in erratic limestone rock bedrock profile that posts great uncertainties and challenges in foundation construction.

And this is where the role of a geologist is needed! 

Reference: Karstic Features of Kuala Lumpur Limestone. TAN Siow Meng, Simon, Committee Member, Geotechnical Engineering Technical Division