2-D Resistivity Imaging of Buried Furnace at Sik, Kedah (Malaysia)
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2-D Resistivity Imaging of Buried Furnace at Sik, Kedah (Malaysia) Dr. M.M. Nordiana Lecturer at Geophysics Section, School of Physics, 11800 Universiti Sains Malaysia, Penang, Malaysia e-mail: [email protected] Dr. Rosli Saad Senior Lecturer at Geophysics Section, School of Physics, 11800 Universiti Sains Malaysia, Penang, Malaysia e-mail:[email protected] Dr. Mokhtar Saidin Professor at Centre for Global Archeological Research Malaysia, 11800 Universiti Sains Malaysia, Penang, Malaysia e-mail:[email protected] ABSTRACT 2-D resistivity imaging is non-destructive method that becomes important tools for the scientific investigation of archaeological study. Kedah area has recently shown a great potential of archaeological findings. The main objective of the present work is to locate the extension of the buried furnace in the area of Padang Cicak, Sik, Kedah (Malaysia) using 2-D resistivity survey for shallow investigations. Resistivity data were collected using Pole-Dipole array with 0.5 m electrode spacing. Afterwards, the resistivity data were processed with 2-D inversion resistivity (Res2Dinv) software which includes smoothness constrained. The results revealed high resistivity zones with < 15 Ωm at depth ranging from 0.-1.5 m at the study area. Base on the archaeological evidence, the lower resistivity values indicate the interest anomaly for archaeological excavation. KEYWORDS: 2-D Resistivity, Archaeology, Buried, Furnace, Kedah. INTRODUCTION The geophysical study was conducted at Kampong Padang Cicak, Sik Kedah. It involves 2-D resistivity imaging. The objective of the study is to identify the extension of the furnace found at the area. In an attempt to non-invasively assess the number and extent of the excavation structures, 2-D resistivity was applied at that archaeological area. Archaeogeophysics is the application of nondestructive geophysical methods and principles to archaeological settings. More specifically, archaeogeophysics involves the interpretation of geophysical signatures (anomalies) that may be due to buried archaeological sites and features. This paper provides preliminary study from Padang Cicak site in Sik, Kedah (Malaysia). THEORY OF RESISTIVITY The resistivity method basically measures the resistivity distribution of the subsurface materials. Table 1 shows the resistivity values of some of the typical rocks and soil materials - 17635 - Vol. 19 [2014], Bund. Z6 17636 (Keller and Frischknecht, 1996). Igneous and metamorphic rocks typically have high resistivity values. The resistivity of these rocks is mainly dependent on the degree of fracturing. Since the water table in Malaysia is generally shallow, the fractures are commonly filled with ground water. The greater the fracturing, the lower is the resistivity value of the rock. As an example, the resistivity of granite varies from 5000 Ωm in wet condition to 10,000 Ωm when it is dry. When these rocks are saturated with ground water, the resistivity values are low to moderate, from a few ohm-m to a less than a hundred Ωm. Soils above the water table are drier and have a higher resistivity value of several hundred to several thousand Ωm, while soils below the water table generally have resistivity values of less than 100 Ωm. Also clay has a significantly lower resistivity than sand. Table 1: Resistivity values of common rocks and soil materials in survey area. Material Resistivity (Ωm) Alluvium 10 to 800 Sand 60 to1000 Clay 1 to 100 Groundwater (fresh) 10 to 100 Sandstone 8 - 4 x 103 Shale 20 - 2 x 103 Limestone 50 – 4 x 103 Granite 5000 to 1,000,000 PREVIOUS STUDY Norhidayahti et al., 2012 conducted Ground Penetrating Radar (GPR) for excavation plan in Jeniang, Kedah (Malaysia). Archaeological features and information acquired from the geophysics data gives an advantage for archaeologist to plan for archaeological research framework especially in optimizing the excavation work. GPR was applied in detecting buried archaeological structure in Kampung Sungai Perahu, Jeniang, Kedah. The purpose of this application is to plan an excavation strategy due to the location of the site which is near to a local resident. GPR with 3-D interpretation managed to locate buried objects in KSP’12 study area. Excavation has been conducted based on the result obtained from 3-D GPR mapping. GPR successfully detected a possible ancient furnace or kiln located at L11-L13 with depth of 0.3 m, which is located almost the same distance with the existing furnace or kiln (surface finding). Besides, the result from this study may be used to detect similar archaeological findings for future research. Discoveries of archaeological structures in Jeniang were reported in 1990 and 1992. In 2010, USM Centre for Global Archaeological Research (CGAR), unearthed similar structures at two different locations in the district of Jeniang. Such findings have led to other discoveries, particularly from the survey conducted around the area of Kampung Sungai Perahu (KSP). There are two site in the village, named of KSP 1 and KSP 2. Norhidayahti et al., 2012 focus on the resistivity study conducted in KSP 2. Preliminary research on the site does not rule out the possibility that the structure in Jeniang may have been a furnace or a kiln. The study attempts to identify the archaeological structures of Jeniang using 2-D resistivity method. The 2D inversion model resistivity shows initial description of anomalies possibly associated with archeological structures with low resistivity value of < 15 ohm-m at depth < 1.5 m. The visible upper part of archeological structure was located at 11.5 m to 12.5 m. However, the inversion model resistivity shows the distribution of low resistivity value of < 15 ohm-m at 10-13 m and decreasing towards Vol. 19 [2014], Bund. Z6 17637 last survey line. These low resistivity value indicated clay corresponding to the archeological structure which has made of clay known as cylindrical clay shaft. The results from the inversion model resistivity may be used to detect similar structures for future research. Lembah Bujang is one of the earliest entrepot and religious center in Malaysia available for archaeological and historical investigations. This archaeological site is situated between Gunung Jerai in the north and Muda River in the south, Kuala Muda, Kedah. Only little archaeological fieldwork in and around Malaysia has so far been carried out, thus delimiting our knowledge of the site and its role. In order to provide further data on the site, 2-D resistivity technique was carried out in an area of SB2ZZ. 2-D resistivity surveys facilate tracing of buried archaeological anomaly at the archaeological site of Sungai Batu, Lembah Bujang, Kedah (Malaysia). Resistivity surveys have been applied using Pole-dipole arrays with 15 survey lines. The resistivity data were processed with Res2Dinv software which includes smoothness constrained. The 2-D resistivity profiles obtained some high anomalies (up to 3500 ohm-m). The inversion results revealed that a rectangular gridding pattern and a dense anomaly existed at depth of 0-1 m. The on-site calibration at partly exhumed sites, such anomalies are interpreted as baked clay bricks. 2-D resistivity is very useful and efficient to determine the archaeological anomaly (Rosli, Nordiana and Mokhtar, 2014). Nordiana et al., 2014 conducted magnetic method at archaeological sites. Sungai Batu area has recently shown a great potential of archaeological findings. The main objective of the present work is to locate the buried archaeological remain of the area using magnetic survey for shallow investigations. The magnetic survey was performed using G-856 proton magnetometer and the spacing between stations was 1-2 m gridding. The magnetic data was processed by utilizing Microsoft excels and Surfer8 software which was displayed in a form of contouring and revealed high residual zones causing the magnetic anomalies. The results of high magnetic values (30-180 nT) indicated a distribution of the anomaly features within the study area. These anomaly features are detected according to the magnetic contrast (baked clay bricks) and the surrounding, mainly sandy clay. Magnetic method is powerful tool to obtain useful information about underground for archaeological prospecting. The first archaeogeophysical survey at the ancient site of Parion (Bigo-Canakale) is presented by Yunus and Mehmet, 2007. Resistivity data were collected along parallel profiles using Wenner-Schlumberger array with electrode spacing of 1 m. A 2-D least squares algorithm based on the smoothness-constrained technique inverted the apparent resistivity data. MATLAB based visualization tools displayed resistivity distribution of the subsurface in 3-D volume. These tools yield volumetric resistivity images by combining 2-D model resistivity sections. Thus, both the horizontal and vertical extent of the anomalous zones was displayed. This visualization technique revealed high resistivity zones at depths of 0.25-2.5 m at the investigation area. Taking into account archaeological evidence, these higher resistivity zones are the most promising locations for archaeological excavation. GENERAL GEOLOGY Sik is a major town and district in Kedah, Malaysia. It is located on the eastern part of the state, and is bordered by Padang Terap district to the northwest. Sik is famous for Muda River and part of Sungai Petani formation (Jane, 1990). Sungai Petani formation consisting shale, siltstone, sandstone, orthoquarzite and homologous with Mahang formation. The soil type of the study area is fine sandy clay (Figure 1). Vol. 19 [2014], Bund. Z6 17638 6° 20′ 6° 00′ 5° 45′ 5° 25′ 5° 05′ 4° 45′ 100°10′ 100°30′ 100°50′ 101°10′ scale 0 20 40 km Figure 1: Geology map of Sik, Kedah (Geological Map of Peninsular Malaysia. Minerals and Geoscience Department Malaysia. 8th Edition, 1985). STUDY AREA The study location was situated near river and resident places. Geomorphology of the study area is flat and planted with rubber tree. The location was on Kampong Padang Cicak with coordinate of 5°56'0.10"N; 100°40'42.66"E. 2-D resistivity imaging method was applied on the study area.