Indentify Sungai Batu Ancient River by Magnetic Method

Indentify Sungai Batu Ancient River by
Magnetic Method
Dr. Rosli Saad
Senior Lecturer
Geophysics Section, School of Physics, 11800 Universiti Sains Malaysia, Penang,
Malaysia; e-mail:[email protected]
Dr. Mokhtar Saidin
Professor
Centre for Global Archeological Research Malaysia, 11800 Universiti Sains
Malaysia, Penang, Malaysia
e-mail:[email protected]
A. Fauzi
Postgraduate Student, Geophysics Section, School of Physics, 11800 Universiti
Sains Malaysia, Penang, Malaysia
Department of Geophysics Engineering, Faculty of Engineering, Syiah Kuala
University, Banda Aceh – Indonesia
e-mail: [email protected]
H. Tarmizi
Postgraduate Student, Geophysics Section, School of Physics, 11800 Universiti
Sains Malaysia, Penang, Malaysia
Department of Geophysics Engineering, Faculty of Engineering, Syiah Kuala
University, Banda Aceh – Indonesia
e-mail: [email protected]
ABSTRACT
Magnetic survey was conducted at Sungai Batu area, with the aim of identify an ancient river boundary
in a non destructive manner. The survey performed using G-856 proton precession magnetometer; the
magnetic data was processed by utilizing Microsoft Excels and Surfer8 software. Magnetic residual
value of <0 nT indicated as marine alluvium and >0 nT indicated as original land. The ancient river
was indicated by marine alluvium and flows from north-west to east.
KEYWORDS:
Marine alluvium, Ancient River, Original land, Magnetic residual map
INTRODUCTION
There are many historical sites in Lembah Bujang, Kedah. These make archaeologists classified
the historical sites into few categories such as abundant relics of antiquity, ancient structures and iron
foundries (Norhidayahti, 2012). Geophysics plays an important role in a process of finding evidences
of case prior to excavation. Magnetic method is one of the geophysical method apply in searching an
archaeological evidences of study site.
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Sungai Batu is located in Lembah Bujang district. The study site is along a main road from
Sungai Petani to Merbok. Sungai Batu is the richest archaeological site. Archaeological produce
important discoveries, including ancient structures and iron smelting area. Lembah Bujang district
was previously thought to have developed from around 4th century, new dates of around 110
common era for Sungai Batu have been confirmed by several overseas laboratories. Today some of
Kedah’s archaeological sites are located in the interior, a factor that points to modifications of the
physical environment because of coastal sedimentation and changes in the course of rivers. A study
need to be conducted about the nature of international trade in this sea-oriented region and its
relationship to surrounding ports with which it was linked by maritime and overland routes (Stephen
and Barbara, 2011).
GENERAL GEOLOGY
Sungai Batu is located in Lembah Bujang district and situated between Sungai Petani and Gunung
Jerai (Figure 1). The mid-south of Kedah was recorded as marine area in first and second century.
Since the sea level was rise, the area change to be landed area in years 1400 (Wheatley, 1961). The
soil types of the area are sandy clay covered with fine sand. The sediment was transported from the
river and being settled around this area. The sea level rises, the settled area turn to be landed area
(Jane, 1990). The geomorphology of the study area was flat landed fill with oil palm and rubber tree.
There are few small rivers and swamp at the eastern part of the area.
THEORY OF MAGNETIC SURVEY
Magnetic survey measure an intensity of the earth’s magnetic field which the ambient magnetic
fields caused by the minerals that are present in the ground. From these measurements, the magnitude
and orientation of the earth’s magnetic field of the subsurface can be estimated. Magnetic field at
Earth’s surface depends on field generated in Earth’s core, magnetic mineral content of surface
materials, and remnant magnetization of surface rocks. The physical parameter of magnetic survey is
magnetic susceptibility, ĸ. Magnetic signatures depend on magnetite content (Burger, 1992), which
tends to be low in most sediment and in many rocks constituting basement. A body placed in a
magnetic field acquires a magnetization, J which if small, it is proportional to the field, H.
J = κH
The susceptibility κ is very small for most natural materials and can be either negative for
diamagnetism or positive for paramagnetism. Rock susceptibility almost always directly related to the
percentage of magnetite present.
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Study
Area
0
25
50 km
Figure 1: Geology map of Sungai Batu, Kedah (Geology Malaysia, 2004).
STUDY AREA
The study was carried out at Sungai Batu Lembah Bujang, Kedah, Malaysia. The location was
from 5.707172° N, 100.436010° E to 5.706726° N, 100.458335° E and 5.683586° N, 100.435914° E,
Vol. 20 [2015], Bund. 18
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to 5.683655° N, 100.458809° E (Figure 2). The study area is flat landed with secondary jungle mix
with rubber / oil palm estate. Towards north of the study area is Gunung Jerai.
Figure 2: Magnetic rover station at Sungai Batu, Kedah, Malaysia.
METHODOLOGY
Magnetic survey is base on mapping of localized variations Earth’s magnetic field caused by subsurface magnetic materials which range from naturally occurring magnetic minerals to man-made
ferrous objects. The survey was carried out using G- 856 portable proton magnetometer. This
equipment measure the total magnetic field intensity which is a scalar measurement of simply the
magnitude of Earth’s field vector in gammas or nanoTesla (nT). One base station (free from magnetic
disturbance) was set to auto function and taken for an interval of 1 minute to remove the diurnal
variation effects of the earth’s field from survey measurements. The magnetic data processed with
reductions such as diurnal correction before deduct with the base reading to get magnetic residual.
Magnetic residual graph is produced in Microsoft Excel in order to determine the optimum distance to
avoid cultural noise form ferrous object. Once corrections were done, the data were exported into a
grid file to Surfer8 software. After calculating a grid from xyz data in Surfer8, magnetic residual was
carried out to produce contour maps.
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RESULTS AND DISCUSSION
Figure 3 shows the residual magnetic contour map of the study area. Generally the magnetic
result interpreted as two main zones. The first zone was interpreted as alluvium/rock/clay with
magnetic residual value of >0 nT. The zone was saturated at the north and south part of the study
area. The second zone with magnetic residual value of <0 nT and interpreted as marine alluvium. The
marine alluvium flows from north-west to east of the study area. This area is suspected to be an
ancient river and the first zone was suspected to be as original land.
University
compound
5.704
5.702
5.700
Archeological
excavation sites
5.698
5.696
Housing Estate
5.694
5.692
5.690
5.688
5.686
5.684
100.436
100.440
100.444
100.448
100.452
100.456
nT
100
80
60
40
20
0
-20
-40
-60
-80
-100
-120
-140
-160
-180
-200
-220
-240
-260
-280
-300
-320
-340
-360
-380
-400
-420
Legend:
High Way
Road
Magnetic rover stationt
Figure 3: Magnetic residual map of Sungai Batu, Lembah Bujang, Kedah.
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CONCLUSION
Magnetic survey identifies marine alluvium with value of <0 nT and original land with value of
>0 nT. The marine alluvium indicates the ancient river which flow from north-west to east.
ACKNOWLEDGEMENTS
The authors thank the technical staffs of the geophysics laboratory and all geophysics
postgraduate students, School of Physics, Universiti Sains Malaysia for their assistance during the
data acquisition and Centre for Global Archaeological Research (CGAR), Universiti Sains Malaysia
for sponsoring the project
REFERENCES
1. Burger H.R. (1992), Exploration Geophysics of the Shallow Subsurface. Prentice-Hall.
Inc, Englewood Cliffs, New Jersey.
2. Geology map of Sungai Batu, Kedah (Geology Malaysia, 2004).
3. Jane, A. (1990), “Trade and site distribution in early historic-period Kedah geoarcheological historic and locational evidence”.
4. Norhidayahti Mohd. Muztaza, M. Mokhtar Saidin, Shyeh S.K. and Rosli Saad (2012),
“Locating and Mapping Archaeological Structure Using 2D Resistivity Method in
Jeniang, Kedah, Malaysia,” International Conference on Geological and Environmental
Sciences IPCBEE vol.3 6(2012) © (2012)IACSIT Press, Singapoore.
5. Stephen C. and Barbara W.A. (2011), Bujang Valley and Early Civilisations in Southeast
Asia. Department of National Heritage, Ministry of Information, Communicational and
Culture, Malaysia.
6. Wheatley, P. (1961), “The Golden Khersonese. Kuala Lumpur,” University of Malaya
Press.
© 2015 ejge