The diversification of rocks in Langkawi is impressive: from tropical karst limestones and cold water silt and mudstones, to massive sandstones, all which showcase a complete history of the Palaeozoic Era! Moreover, these rocks have then been intruded by large amounts of igneous rock, which drastically changed the terrain and geological formations.
The Machinchang Formation, found in the northwestern region of Langkawi, is a unique mountain enviroment dominated by barren rocky peaks and vertical cliffs made from yellowish, moderate-to-thickly bedded sandstone, interspersed with hints of interbedded dark-to-light gray shale and mudstone. This rock assemblage forms not only the oldest rock formation in Langkawi, but in the whole of Malaysia, with the Cambrian Machinchang Formation estimated at 550-490 million years old, and consisting of deltaic to shallow marine deposits which showcase a changing enviornment, with sea levels rising towards the end of the formations’ deposition.
The Machinchang Formation is host to excellent sedimentary structures including various types of cross-beds, ripple marks, load stuctures and many more. They also exhibit various types of trace fossils (ancient burrows, footprints or tracks) as well as body fossils (remnant body parts of animals or plants).
The Setul Formation is mainly found on the eastern portion of the Langkawi archipelago, but with features conformable with the Machinchang Formation near Kubang Badak in the northwest. The Setul Formation is the oldest carbonate rock formation in Malaysia and the region, forming 490-370 million years ago and showcasing the deposition of predominantly carbonate particles with small amounts of eroded rock fragments deposited in a shallow sea environment, creating limestone, sandstone and shale. The Setul Formation split into five sections: the Basal Limestone Member, Lower Limestone Member, Lower Detrital Member, Upper Limestone Member and the Upper Detrital Member, of which the first four can be seen in Teluk Mempelam. However the Setul Formation’s appearance above the younger Singa and Chuping Formations is unusual, and was only understood with the discovery of the large Kisap Thrust Fault, which uplifted the Setul Formation to dominate the eastern coast of Langkawi, allowing erosion and dissolution to create the magnificent karstic formations seen today.
The Setul Formation is host to some exemplary karstic formations with the formation of sea-notches, sea caves, sea arches, sea stacks and pinnacles with the appearance of magnificent caves with stalactites, stalagmites and tunnels.
The Singa Formation sits paraconformably (deposited on top of each other; however, significant time has passed between deposition) above the Setul Formation and is dominated by thickly bedded to massive, dark grey to black siltstone and mudstone which often contain sporadically distributed clasts of various sizes, shapes and origins within a fine grained rock mass. The clasts have been interpreted as dropstones of glacial origin and suggest the formation took place within a drastically colder and shallower environment than what was seen during the deposition of the Setul Formation. The Singa Formation is dated as beginning in the late Devonian (350 million years ago), and continuing deposition until the early Permian (290 million years ago). Throughout this time you can see variations in the intermittent deposists of sands, which evidence short-term rising and falling sea-levels, before a steady increase towards the end of the formation’s deposition, exhibited by the appearance of limestone lenses.
The Singa Formation is home to multiple unqiue features, the most noteworthy of which is the appearance of the one billion year old trondhjemite granite on Pulau Tepor. There are also other features found within the formation as seen in Sungai Itau and Batu Asah, where one can find brachiopod fossils indicative of cold water temperatures of the Gondwanaland seas.
The Chuping Formation is composed of thinly bedded dark grey bioclastic limestone which dominates the lower member of the formation and is believed to be deposited 290 to 250 million years ago. From a distance one could mistake the Chuping Formation for the Setul Formation, as they exhibit similar karstic formations and are found next to one another due to the Kisap thrust fault uplifting the older Setul Formation to the same level. The Chuping Formation has undergone metamorphism, which has transformed the limestone to marble and has removed many of its fossils and sedimentary structures. However, areas which haven’t undergone metamorphism are filled with fossils like fusulinids, brachiopods, bivalves, gastropods, corals, bryozoans and algae, which are used to date the formation.
The Chuping Formation, due to its metamorphism to marble, is heavily fractured, which has caused dolinas or collapsed caves, the most famous being Tasik Dayang Bunting, which is the largest lake in Langkawi. Within the less metamorphosed sections, like Pulau Jong, the limestones are rich in fossils such as foraminifera, molluscs, brachiopods, echinoderms, rugose corals and bryozoa.
Gunung Raya Granite
The granitic suites in Langkawi are found to be large and small igneous stocks (intrusions that are no bigger than 100 sq km) and are believed to be late Triassic in age, which suggests that emplacement of the granite took place almost concurrently with the region’s major tin-bearing granites. The dating of the granite is made by the observation that the granitic stocks follow major fault directions which suggests that the faults precede the granite intrusion.
The granite is predominantly made of porphyritic granites (large crystals in a compact groundmass) with some coarse- and fine-grained equigranular granites with rare dykes (small vertical intrusions) and sills (small horizontal intrusions) forming large pegmatite crystals.
The topography of Langkawi is dominated by the hard granites with both Bukit Sawak and Gunung Raya two of the islands hills/mountains consisting of granite.
Due to the long cooling time and porphytic texture there are areas in Langkawi where you can see crystals within the rocks as well as sills which have been folded in Pulau Tuba. Also due to the way that granite is eroded it has caused amazing features like the magnificent Telaga Tujuh Waterfall and Teluk Yu Granite Tors.