LANGKAWI GEOLOGICAL FORMATION
Written by Super User. Posted in Shortcodes
This rocks formation have been named after the Machinchang range which formed in northwest of Langkawi Island. This formation can be found in the western part of Langkawi Island, from Pulau Jemuruk to Teluk Burau. The Machinchang Formation is the oldest sedimentary rock unit in Malaysia. The basal part of the formation is made up of pelitic rocks exposed in the core of the Machinchang Anticline at Teluk Datai, and the top of the formation exposed at Teluk Sabong.
- The Machinchang Formation consists principally of grey to red, coarse to medium- grained quartzite, arkose and subgreywacke, grey to black siltstone, shale and mudstone, with subordinate beds of conglomerate. Sedimentary structures such as cross-bedding, convolute bedding, gradded bedding, load casts and parallel lamination can be observed in the sandstone. The depositional environment for the Machinchang Formation is interpreted as a wave-dominated delta.
Fossil and Age :
- The Machinchang Formation is poorly fossiliferous. Organic remains are rare in the Machinchang Formation and limited to a few brachiopods, fragmentary trilobites and some trace fossils. However, in Tarutao Island of Thailand, the sequence of quartzite yields a relatively rich late Upper Cambrian trilobite- brachiopod fauna, which enabled the formation to be dated
Setul Formation is conformably overlying the Machinchang Formation, and the term Setul Formation has been given after the Setul Boundary Range, a limestone hills at the Malaysia-Thailand frontier. This formation was deposited in shallow marine environments. The Setul Formation can be observed on the eastern side of the Langkawi Island. An almost continuous belt of this formation can be traced from Tanjung Rhu in the north, Kilim, Kisap, Pulau Langgun, Pulau Timun, to Pulau Tuba and Pulau Dayang Bunting in the south. Strata of the detrital facies outcroped in Pulau Timun, Pulau Tuba, Pulau Dayang Bunting, Pulau Tanjung Dendang and Pulau Langgun.
- The Setul Formation composed dominantly of hard, brittle, dark- coloured, thick bedded limestone (or crystalline limestone), and the subordinate detrital facies includes well-bedded quartzitic sandstone, carbonaceous shale, slate and black chert. It is largely metamorphosed on the main island but good fossiliferous outcrops of limestone and detrital facies are present in Pulau Langgun and Pulau Tanjung Dendang.
Fossil and Age :
- The limestone and black mudstone facies of the Setul Formation contain a rich fauna such as gastropod, brachiopod, trilobite, graptolite and conodont. These fauna gave the formation a fairly precise age from the Lower Ordivician to Lower Devonian. Setul Formation can be divided in to four rock units.
- Lower Setul Limestone Lower - Upper Ordovisian
- Lower Detrital Member Lower Silurian (Llandovery)
- Upper Setul Limestone Upper Silurian
- Upper Detrital Member Lower Devonian
The name Singa Formation has been given after the Pulau Singa, where a thick succession of black siltstone and interbedded lighter coloured quartzite exposed. The Singa Formation is unconformably overlying the Setul Formation.
- The Singa Formation consists of arenaceous-argillaceous sequence, part of which has been metamorphosed due to the Gunung Raya granite intrusion. Massive black pebbly mudstone and interbedded shale-siltstone-sandstone are the two main litologic units found in the formation.
Sedimentary environment and paleogeography :
- The Singa Formation was deposited on a shallow marine shelf (partially influenced by glacier melting) which become deeper as a result of sea level change closely related to continental glaciation and interglacial melting. Based on litological and faunal evidences, it is very clear that the Langkawi islands were located very close to the Gondwana Supercontinent which has undergone global climatic changes from a cold regime during early Lower Permian To warmer conditions during Middle Permian.
Fossil and Age :
- Most of the fossils were found in thick shale, sandstone, calcareous sandstone and limestone consisting of brachiopods, bryozoa, crinoids, bivalves, gastropods and trace fossils. The fossil assemblage indicates an age of Lower Permian.
The name of the Chuping Formation is taken from Bukit Chuping, a prominent hill in Perlis. In Langkawi, the formation lies conformably on the Singa Formation, but it is faulted against the Setul Formation. The formation is composed characteristically of a pure, light-coloured, massive or thickly bedded limestone sequence of Late Permian to Triassic age. It can be easily distinguished from the dirty and dark coloured Setul Formation. The limestone of the Chuping Formation occurs on the west and north of Pulau Dayang Bunting and in the north and south Kg. Kisap of main island.
- The Chuping Formation consists of a fairly uniform deposit of massive or thickly bedded, white, crystalline limestone. Chert is common near the base of the succession. The basal limestone on Pulau Singa Kecil contains an abundance of irregular platy bodies of chert arranged parallel to the bedding.plane.
Fossil and Age :
- The Chuping limestone is fossiliferous in its basal part. Numerous fossils were recorded form the sequence of the Chuping Formation including conodonts, gastropods, brachiopods, bryozoa, foraminifera and corals. Paleontological evidence suggests that the formation ranges in age from late Early Permian to Middle or Late Triassic.
The Langkawi igneous bodies have been collectively named as the Gunung Raya Granite. The age of Langkawi granite has been dated as Late Triassic (~220 - 210 million years) hence the emplacement of Langkawi granite should have taken place almost concurrently with the region's major tin-bearing granites. Granites of Langkawi are predominantly made of porphyritic granites with some coarse- and fine-grained equigranular granites and rare dyke- and sill- forming pegmatite and aplite. The granites of Langkawi intrude several types of host rocks, transformed them into various types of metamorphic rocks, and bringing along with them some minerals such as tourmaline, ilmenite, zircon and garnet. In general, the topography of Langkawi granite is represented by broad conical hills with gently concave flanks. Near the shore, erosion on granitic top-soil has developed a beautiful landscape of submerged granite tors.