Preliminary Study of Determination Boundary Zone of Ancient River with Original Landform in Sungai Batu Muhammad Taqiuddin Zakaria Postgraduate Student, Geophysics Section, School of Physics, 11800 Universiti Sains Malaysia, Penang, Malaysia e-mail:
[email protected]
Dr. M.M. Nordiana Senior Lecturer, Geophysics Section, School of Physics, 11800 Universiti Sains Malaysia, Penang, Malaysia e-mail:
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Dr. Mokhtar Saidin Professor Centre for Global Archeological Research Malaysia, 11800 Universiti Sains Malaysia, Penang, Malaysia e-mail:
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Rose Nadia bt Abu Samah Postgraduate Student, Geophysics Section, School of Physics, 11800 Universiti Sains Malaysia, Penang, Malaysia e-mail:
[email protected]
ABSTRACT Magnetic is a non-destructive geophysical technique that measure the Earth's magnetic field at specific location. The application of magnetic method is widely used in archaeological purpose such as locating and planning archaeological sites. The objective of this survey is to identify the possible boundary between ancient oceanic or river area with original landform. Magnetic survey was conducted using proton magnetometer with interval of each magnetic station (rover) was 10 m spacing gridding. The magnetic data was processed by utilizing Microsoft excels and Surfer10 software which was displayed in a form of contouring and revealed possible boundary zone. The result of low magnetic value 0 nT from range of 0 nT to 350 nT indicated as an original landforms.
KEYWORDS: Magnetic, Archaeological
INTRODUCTION Sungai Batu area was located at Sungai Merbok district which is situated between Sungai Petani and Gunung Jerai. Sungai Batu are important in archaeological prospect and the previous history shows that Sungai Batu has been used since 500 BC as famous international entrepot. From the archaeological evidence of ancient structure and iron smelting area with supported data - 2849 -
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from geophysical method shows that Sungai Batu is the oldest civilization that has been recorded in Southeast Asia (Ramzul et al., 2015). The mid-south of Kedah was recorded as marine area in 1st to 2nd century. Rise in sea level changes the area to be landed area in years 1400 (Wheatly, 1961). The sediments include of rocks, soil, and mineral from weathering process was transported from the river and ocean to lower area and strongly influenced by the geology of the surrounding environments. The repeated process time to time with deposition and erosion factor changes the area become landed region. Changes in magnetic susceptibility also related to sea-level variations (Devleeschouwer 1999; Ellwood et al., 1999). Decrease in sea level will increase the erosion which tend to leads the higher magnetic susceptibility while rise in sea level decrease the magnetic susceptibility (Crick et al., 2001). Furthermore, climatic variations also influence the changes in magnetic susceptiblity. The sedimentation process in Sungai Batu region was control by the depositional process from the Sungai Merbok and Malacca Street. Terrigenous sediments from Gunung Jerai was transported by Sungai Merbok to lower region with high of turbidity current until it settled down due to gravity factor. Hydrogenous sediments from Malacca Street plays important role in deposition process of Sungai Batu. The sediments from Malacca Street are transported due to longshore drift from the tidal current to formed range of landforms. Geophysical survey was carried out in order to identify the boundary of ancient landform with oceanic region area of Sungai Batu which today are covered with landfill.
GENERAL GEOLOGY Sungai Batu are located in Bujang Valley (Lembah Bujang) along the road from the Sungai Petani to Merbok northwestern of Malaysia and located near Gunung Jerai and Sungai Merbok area. Most of the Sungai Merbok area is underlain by the Mahang formation especially in eastern and southern part (Habibah et a., 2004). This formation formed in Middle Ordovician to Early Devonian age (Bradford, 1970). The rock unit comprises shale, red slate, grey slate and black slate. This area experiencing a hot and humid climate during a year which leads the high chemical weathering to occurs which changes the shale become soil and laterite (Habibah and Wan, 2002). The main mineralogy of rocks are mica and chloride. Black slate contains an abundance of carbon and red slate consists of high iron oxide (Almashoor, 1974). Granite-pegmatite formed a stock of Gunung Jerai. Granitic intrusion cause the rocks of surroundings area become metamorphose to produce schist rocks (Bradford, 1970). The northern part of this study area located of Gunung Jerai which recorded as highest mountain in the valley of the rock cockerel made of schist rocks with a few layers of quartzite. The soil types of the study area are sandy clays with covered of fine sand grain. The geomorphology of this area was flat landed fill with palm and rubber tree and also covered with small stream, rivers and swamp area at eastern part of the study area (figure 1).
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Sungai Batu Area
Legend
Figure 1: Map of Sungai Batu area (Geological Map of Peninsular Malaysia, Minerals and Geoscience Department Malaysia. 8th Edition, 1985)
THEORY OF MAGNETIC METHOD Magnetic survey measures the magnitude and the orientation of the Earth's magnetic field intensity. The purpose of magnetic survey is to identify the subsurface geology on the basis of the anomalies in the earth's magnetic field due to magnetic properties of underlying rock (Keller, 1986). When a magnet undergo magnetization it will have a remanent that refer to magnetization left behind after an external magnetic field is removed. It also refer as magnetic memory in magnetic storage and source of information on the past Earth's field in paleomagnetism (Nurgaleiva, 2013). Induced magnetization depends on the magnetic susceptibility of the material and magnitude and direction of ambient magnetic field while remanent magnetization reflects the previous past of magnetic history of the material (William,2013). Table 1 shows the general magnetic susceptibility value in common rocks and ores. The magnetic properties of highly magnetic rocks tend to be extremely variable and their magnetization is not directly proportional to the applied field (Milsom, 2003).
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Table 1: Magnetic susceptibility in common rocks and ores Common rocks Slate Dolerite Greenstone Basalt Granulite Rhyolite Salt Gabbro Limestone Ores Hematite Magnetite Chromite Pyrrhotite Phyrite
0-0.002 0.01-0.15 0.0005-0.001 0.001-0.1 0.0001-0.05 0.00025-0.01 0.0-0.001 0.001-0.1 0.00001-0.0001
0.001-0.0001 0.1-20.0 0.0075-1.5 0.001-1.0 0.0001-0.005
Magnetic anomalies are produced by contrast in rock magnetism. This anomalies is a result from magnetization of a mineral. Table 2 shows general summary of type magnetization based on magnetic susceptibility.
Table 2: Types of magnetization Susceptibility Type Source k
