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Kuala Nyalau and Tanjung Similajau Recce Trip

26 Feb 2008

Kuala Nyalau – Tg. Similajau: Geology & Natural History

What can ring more true than MNS's very own mantra for many years "You don't love what you don''t know!" ... a few of us on the recce trip admitted their discovery of a new muse. Love is in the air ...

An extensive swath of the coastal area between Kuala Niah and Kuala Tatau (south of Bintulu) is underlain by the Nyalau Formation. The Oligocene to Early Miocene age Nyalau Formation consists of a thick succession of sandstones and shales, estimated to be about 5km in thickness. During the time of Nyalau deposition, isolated coral reefs were growing in the surrounding shelf. The remains of these reefs include the Melinau Limestone in Mulu and the Subis Limestone at Niah.

The upper part of the Nyalau Formation is exposed along the coast between Tg. Similajau and Kuala Nyalau. In this area, the Nyalau Formation consists of mainly hard, calcareous sandstones with minor interbeds of silty sandstones and shales. At Kuala Nyalau, the calcareous sandstone beds, exposed in a small area north of the river mouth, dip gently to the NE, extending from the edge of the beach to the low tide mark. These calcareous sandstones are characterized by numerous orthogonal joints, which weathered into a very distinctive block like patterns. Another interesting feature is the karst-like weathering effects in part of outcrops. Larger foraminifera are common in the outcrop at Kuala Nyalau, and one particular bed is composed nearly entirely of closely packed nummulites (large, coin-shaped foraminifera). The weathering and erosion of the calcareous shells of the nummulites leave a distinctive pattern of cavities in the outcrop.

Further to the southwest at Tg. Similajau, the rocky shores are made up of mostly fine-grained sandstones and calcareous sandstones of the Nyalau Formation. These hard, resistive sandstones form extensive wave cut platforms and low cliffs that extend southward through Similajau National Park. The rocky shores here are broken by short stretches of sandy beaches, with mostly coarse, well rounded quartz grains, giving the beaches here its distinctive golden colour. These quartz grains are derived from the weathering and erosion of the Nyalau Formation.

The costal habitat between Kuala Nyalau and Tg. Similajau, comprising mostly kerangas forest, has been degraded by logging and agriculture, especially conversion to oil palm plantation. The newly launched SALCO (a 40:60 joint venture between Cahya Mata Sarawak and Rio Tinto Aluminium), with its planned heavy industries, will no doubt further bring enormous changes the surrounding environment and remaining habitats.

Many interesting plants can still be observed in the scrublands and degraded kerangas forests, including pitchers plants and orchids. Two species of pitcher plants (Nepenthes rafflesiana and Nepenthes gracilis) and an unindetified ground orchid with beautiful white, lightly scented, flowers were observed along the Kuala Nyalau gravel road. At Kuala Nyalau, a large specimen of the common seashore tree, Calophllum inophyllum, with a long, twisted trunk nearly 2 m in diameter, is seen leaning out to sea at the rocky shore. This tree, locally called bintangor laut or Borneo mahogany, is estimated to be at least 150 years old based on its large trunk. Nearby on a rocky ledge, a large cluster of another unidentified orchid, with attractive brownish-green flowers on long hanging spikes, is observed.

On the beaches at both Kuala Nyalau and Tg. Similajau, the shells of several species of gastropods are found, including Atilia ocellata, Trochus radiatus and Neritidae species. Extensive live oyster beds, growing on rocky outcrops at the low tide mark, are observed along the rocky shores SW of the river mouth at Kuala Nyalau. It appears that the local inhabitants have not exploited these oyster beds. Though once common, these native oysters are fast disappearing from many similar habitats in Sarawak due to pollution and over-harvesting. Higher along the tide marks are numerous colonies of a small gastropods, an identified Turbinidae species.


CL and NA MNSMiri, 23-February-2008.

 

References:

Liechti, P. 1960. The geology of Sarawak, Brunei and the Western part of North Borneo. Bulletin Geological Survey Department, British Territories in Borneo, 3. 360 pp.

Wilford, G.E. 1961. The geology and mineral resources of, Brunei and adjacent parts of Sarawak, with descriptions of Seria and Miri Oilfileds. Memoir 10, Geological Survey Department, British Territories in Borneo. 319 pp.

Clarke, C. 1997. Nepenthes of Borneo. Natural History Publications. 207 pp.

Hazebroek, H.P. and Abang Morshidi, A.K 2000. National Parks of Sarawak. Natural History Publications. 474 pp.

Wee, Y.C. 2003. Tropical trees and shrubs, a selection for urban plantings. Sun Tree Publishing Ltd. 393 pp.

Some initial snaps made on the recce trip:


Orthogonal joints of foraminifera-rich rock formation, Kuala Nyalau.


Living native oyster beds, Kuala Nyalau.


Karst-like erosional patterns in calcareous bioclastic beds, Kuala Nyalau.


A tree on the beach, Tanjong Similajau.


Exposed intertwined tree roots, Tanjung Similajau.


Rock exposed during low tide, Tanjung Similajau.


Rendition of the "Rio Tinto Coast" by MNS Miri Branch members:

Kong Lih-Shan
Dominique Dodge-Wan
Charlie Lee
Nazeri Abghani

MNS Miri in conjunction with PhotoMalaysia and Miri Flickr community will be organising a few group photography outing to the area as part of our effort to bring the coast to the public at large via publicised images made of the area.

Please email mnsmiri@yahoo.com if you're keen to find out more or wish to participate.







 

 


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