A report submitted in fulfilment of the requirements for the degree of Bachelor of Applied Science (Geoscience) with Honours

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(1)By. RAIHANA AMIRA BINTI RAMLI. A report submitted in fulfilment of the requirements for the degree of Bachelor of Applied Science (Geoscience) with Honours. FACULTY OF EARTH SCIENCE UNIVERSITY MALAYSIA KELANTAN 2018. 0. FYP FSB. Geology of Cawas and the Demarcation of Groundwater Potential Zone Using 1D Electrical Resistivity Method in Tancep, Gunung Kidul, Yogyakarta.

(2) “I hereby declare that I have read this thesis and in our opinion this thesis is sufficient in terms of scope and quality for the award of the degree of Bachelor of Applied Science (Geoscience) with Honors”. Signature. : ___________________________. Name of Supervisor : ___________________________. Date. : ___________________________. i. FYP FSB. APPROVAL.

(3) I declare that this thesis entitled “Geology of Cawas and the Demarcation of Groundwater Potential Zone Using 1D Electrical Resistivity Method in Tancep, Gunung Kidul, Yogyakarta” is the result of my own research except as cited in the references. The thesis has not been accepted for any degree and is not concurrently submitted in candidature of any other degree.. Signature. : ___________________________. Name. : ___________________________. Date. : ___________________________. ii. FYP FSB. DECLARATION.

(4) First and foremost, my deepest love to my beloved parents, Ramli b. Senin and Rahayu binti Ma‟inn for their everlasting inspiration advise motivation and affection. A big thanks to them for always supporting me in every terms especially financially. Second of all, to my supervisor, Dr. Mohammad Muqtada Ali Khan, for his encouragement in this thesis, corrected my research and also keep me motivated, as well as being patiently advises and guidelines through the process until the end of my thesis writing. Not to forget my beloved lecturers, Mr. IR Arham Muchtar Bahar, the other lecturers that have been there to guide and helping me throughout this thesis aside from their work to teach and me everything that I should know and learn. A special thanks to my supervisor, Mr. Agus Hendratno and my examiner, Dr. rer. nat. Arifudin Idrus for guiding me during my mobility programme in Universitas Gadjah Mada (UGM) . I would like to express my gratitude also to staffs and students of UGM for helping me throughout the mobility programme. Last but not least, I would like to say thanks my fellow friends (Team Bayat) that have helped, guide and support me, during my mapping processes in Yogyakarta.. iii. FYP FSB. ACKNOWLEDGEMENT.

(5) The study area located in a region of Yogyakarta which is Cawas, Klaten and the specification took place in Tancep, Gunung Kidul. The study area is a complex area which consists of 3 types of rocks in an area and has seven lithology which are schist-phyllite, nummulitic limestone, tuffaceous sandstone, volcanic clastic sandstone, sandstone interbedded with siltstone, diorite and also crystalline limestone. The objectives of this research are to produce a geological map of the study area with scale 1:25000 and to demarcate the groundwater potential zone in Tancep, Gunung Kidul. The specification area was chosen because it has lack of groundwater well that needed by the community for daily activities. This research is important in demarcating groundwater potential zone for new groundwater resources. In order to satisfy the objectives, method such as geological mapping, geomorphological investigation, data collection and data processing must be conducted. For the demarcation of the groundwater potential zone, the 1D electrical resistivity method (ERI) or vertical electrical sounding (VES) method were conducted using Schlumberger array arrangement. The results that were interpreted were there are two potential groundwater sources in the study area. The lithology and groundwater sources were determined by correlating the result with regional geology of the area and also by using the resistivity chart. This research will give significant to people around study area for the community as it can accommodate demand for new groundwater resources. Keywords: Yogyakarta; geological map; groundwater; vertical electrical sounding; resistivity. iv. FYP FSB. Abtract.

(6) Kawasan kajian yang terletak di Cawas, Klaten yang termasuk di dalam wilayah Yogyakarta manakala spesifikasinya terletak di Tancep, Gunung Kidul. Kawasan kajian adalah kawasan yang kompleks yang terdiri daripada 3 jenis batu di suatu kawasan dan mempunyai tujuh litologi iaitu skisfilit, batu kapur nummulit, batu pasir tuff, batu pasir klastik gunung berapi, batu pasir berselang seli dengan batuan lanau, diorit dan batu kapur kristal. Objektif kajian ini adalah untuk menghasilkan peta geologi kawasan kajian dengan skala 1: 25000 dan untuk menanda zon potensi air tanah di Tancep, Gunung Kidul. Kawasan spesifikasi telah dipilih kerana kekurangan air bawah tanah yang diperlukan oleh masyarakat untuk kegiatan harian. Penyelidikan ini adalah penting untuk mengkaji zon potensi air bawah tanah untuk sumber air bawah tanah baru. Untuk memenuhi tujuan, kaedah seperti pemetaan geologi, penyiasatan geomorfologi, pengumpulan data dan pemprosesan data mesti dijalankan. Untuk penandaan zon potensi air bawah tanah, kaedah resistensi elektrik 1D (ERI) atau Vertical Electrical Sounding (VES) dilakukan dengan menggunakan susunan elektrode Schlumberger. Hasil yang ditafsirkan ada dua sumber air tanah yang berpotensi di kawasan kajian. Sumber litologi dan air bawah tanah ditentukan dengan mengaitkan hasil dengan geologi serantau di kawasan tersebut dan juga dengan menggunakan carta resistiviti. Penyelidikan ini akan memberi manfaat kepada orang ramai di sekitar kawasan kajian untuk komuniti kerana ia dapat menampung permintaan untuk sumber air bawah tanah baru. Kata Kunci: Yogyakarta; peta geologi; air bawah tanah; vertical electrical sounding; resistivity. v. FYP FSB. Abstrak.

(7) PAGE APPPROVAL. I. DECLARATION. Ii. ACKNOWLEDGEMENT. Iii. ABSTRACT. iv. TABLE OF CONTENTS. vi. LIST OF TABLES. x. LIST OF FIGURE. xi. CHAPTER 1 INTRODUCTION 1.1. General Background. 1. 1.2. Problem Statement. 2. 1.3. Objective. 3. 1.4. Scope of Study. 3. 1.5. Significance of Study. 4. 1.6. Study Area. 4. 1.6.1. Location. 4. 1.6.2. Road Connection. 7. 1.6.3. Demography. 7. 1.6.4. Climate. 7. vi. FYP FSB. TABLE OF CONTENTS.

(8) Landuse. 9. CHAPTER 2 LITERATURE REVIEW 2.1. Introduction. 10. 2.2. Regional Geology. 10. 2.3. Stratigraphy. 13. 2.3.1. Metamorphic Unit. 15. 2.3.2. Wungkal-Gamping Formation. 15. 2.3.3. Nampurejo Pillow Lava and Kebo-Butak Formation. 15. 2.3.4. Quarternary Alluvium. 16. 2.4. Structural Geology. 16. 2.5. Historical Geology. 18. 2.6. Research Specification. 18. 2.6.1. Groundwater Potential Using Electrical Resistivity. 18. 2.6.2. Common Type of Array Used in ERI. 20. 2.6.3. Resistivity and Conductivity of Various Rock Type. 23. 2.6.4. Previous Study of Groundwater Potential using ERI. 25. CHAPTER 3 MATERIALS AND METHOD 3.1. Introduction. 27. 3.2. Materials and Equipment. 29. 3.3. Methodology. 34. vii. FYP FSB. 1.6.5.

(9) Preparation/ Preliminary Studies. 34. 3.3.2. Preparation of Base Map. 34. 3.3.3. Geological Mapping. 33. 3.3.4. Laboratory Work. 37. 3.3.5. Data Processing and Interpretation. 38. CHAPTER 4 4.1. 4.2. GENERAL GEOLOGY. Introduction. 39. 4.1.1. Accessibility in the Study Area. 39. 4.1.2. Settlement and Vegetation. 39. 4.1.3. Traverses and Observation. 41. Geomorphology. 42. 4.2.1. Topography. 42. 4.2.3. Drainage Pattern. 45. 4.2.4. Weathering. 48. 4.3. Lithostratigraphy. 51. 4.4. Structural Geology. 80. 4.4.1. Joint Analysis. 80. 4.4.2. Fault Structure. 83. 4.4.5. Folding Structure. 85. 4.5. Historical Geology. CHAPTER 5. 87. DEMARCATION OF GROUNDWATER POTENTIAL ZONE USING ELECTRICAL. viii. FYP FSB. 3.3.1.

(10) KIDUL. 5.1. Introduction. 90. 5.2. Location Of The Survey Lines. 90. 5.3. Results And Interpretation. 93. 5.3.1. Survey Line 1. 95. 5.3.2. Survey Line 2. 100. 5.3.3. Survey Line 3. 106. 5.4. The Correlation Between The Resistivity Logs. CHAPTER 6. 112. CONCLUSION AND RECOMMENDATION. 114. REFERENCES. 116. ix. FYP FSB. RESISTIVITY METHOD OF TANCEP, GUNUNG.

(11) Table 3. 1: Materials that will be used during field mapping and lab analysis.. 29. Table 4. 1: Topographic unit based on mean elevation.. 43. Table 4. 2: Mineralogy description of schist.. 56. Table 4. 3: Mineralogy description of nummulitic limestone.. 60. Table 4. 4: Mineralogy description of tuffaceous sandstone.. 63. Table 4. 5: Mineralogy description of sandstone.. 65. Table 4. 6: Mineralogy description of diorite.. 74. Table 4. 7: Mineralogy description of crystalline limestone.. 78. Table 5. 1: Resistivity and estimated lithology and hydrogeology of the layers.. 96. Table 5. 2: Observed data of line 1.. 98. Table 5. 3: Result of data processing of Line 1.. 99. Table 5. 4: Observed data of Line 2.. 104. Table 5. 5: Result of data processing of Line 2.. 106. Table 5. 6: Observed data of Line 1.. 110. Table 5. 7: Interpretation result of Line 3.. 112. x. FYP FSB. LIST OF TABLES.

(12) Figure 1. 1: The location map of the study area.. 6. Figure 1. 2: The climate graph of Klaten.. 8. Figure 1. 3: Landuse map of study area.. 9. Figure 2. 1: Geography of Indonesia and surrounding regions showing present-day tectonic boundaries and volcanic activity. Indonesia is shaded green, and neighbouring countries are shaded in pale grey (Robert et al., 2009).. 11. Figure 2. 2: Zone classification of Java Island (Bemmelen, 1949).. 12. Figure 2. 3: Geological map of Jiwo Hills and Southern Mountain.. 13. Figure 2. 4: The stratigraphy of Southern Mountain (Surono, 2008).. 14. Figure 2. 5: Common types of array used. (a) Wenner array (b) Schlumberger array (c) Dipole-dipole array (d) Pole-dipole array (e) Pole-pole array. 21. Figure 2. 6: Summary of all types of array. (Source: Samouëlian et al., 2005). 23. Figure 2. 7: Range of resistivity value and conductivity value on different rock and materials.. 24. Figure 2. 8: Schlumberger Array. 25. Figure 2. 9: Cross section of VES points.. 26. Figure 3. 1: Flow chart of the research study.. 28. Figure 3. 2: The geological mapping process.. 34. Figure 4. 1: Vegetation map and settlement map of the study area.. 40. Figure 4. 2: The traverse map and sample location of the study area.. 41. Figure 4. 3: Topography Map of Study Area. (a) Panorama showing the hilly area of northern part of study area. (b) Hilly area of southern part of study area.. 44. Figure 4. 4: Drainage pattern types.. 45. Figure 4. 5: Dry drainage in the study area.. 46. Figure 4. 6: Type of drainage pattern found in the study area.. 47. Figure 4. 7: Biological weathering at schist with limestone outcrop.. 48. Figure 4. 8: Spheroidal weathering on diorite.. 49. Figure 4. 9: Physical weathering on phyllite rock.. 50. xi. FYP FSB. LIST OF FIGURE.

(13) 52. Figure 4. 11: Boundry of numulitic limestone and metamorphic rock unit.. 54. Figure 4. 12: Quartz vein alligned in the foliation of phyllite.. 54. Figure 4. 13: Graphite schist outcrop.. 55. Figure 4. 14: Hand sample of schist.. 55. Figure 4. 15: Thin section of schist under xpl (A) and ppl (B) with magnification of 10x10.. 56. Figure 4. 16: Nummulitic limestone unit in Watuprau area.. 58. Figure 4. 17: Hand sample of nummulitic limestone.. 59. Figure 4. 18: Thin section of nummulitic limestone under XPL (A) and PPL (B) under 4x 10 magnification.. 59. Figure 4. 19: Volcanic rock unit which comprises of tuff, lapilli and also sandstone included.. 61. Figure 4. 20: Hand specimen of tuffaceous sandstone.. 62. Figure 4. 21: Thin section of tuffaceous sandstone under XPL (A) and PPL (B) under magnification 4x10.. 62. Figure 4. 22: Outcrop of volcanic clastic sandstone.. 64. Figure 4. 23: Hand specimen of volcanic clastic sandstone rock.. 65. Figure 4. 24: Volcanic Sandstone under XPL (A) and PPL (B) with magnification 10x10.. 65. Figure 4. 25: Sandstone interbedded with siltstone.. 68. Figure 4. 26: Hand sample of sandstone interbedded with siltstone.. 69. Figure 4. 27: Thin section of sandstone interbedded with siltstone (a) under XPL (b) under PPL with magnification 10x10. 69. Figure 4. 28: Diorite rock unit in Gunung Pendul.. 73. Figure 4. 29: Hand sample of diorite.. 73. Figure 4. 30: Diorite under XPL (A) and PPL (B) with magnification 4x10.. 74. Figure 4. 31: (a) The outcrop of well- bedded limestone outcrop. (b) Hand sample of packstone taken from the lower part of the well- bedded limestone. (c) Hand sample of chalk from well- bedded limestone of Gunung Lanang.. 77. Figure 4. 32: Outcrop of limestone in Gunung Temas.. 77. Figure 4. 33: Hand sample of Gunung Temas well- bedded limestone (wackstone). 77 Figure 4. 34: wackstone under XPL (A) and PPL (B) with magnification 10x10.. 78. Figure 4. 35: Alluvium unit of study area.. 79. xii. FYP FSB. Figure 4. 10: Outcrop of schist unit..

(14) 81. Figure 4. 37: Geological map of the study area.. 82. Figure 4. 38: Rose diagram of the joint analysis.. 85. Figure 4. 39: Joint analysis site.. 85. Figure 4. 40: Reverse fault of bearing 85°NW. 86. Figure 4. 41: two type of fault in the outcrop „A‟ is a reverse fault showing hanging wall moving upward and footwall moving downward. While „B‟ is showing the normal fault.. 87. Figure 4. 42: Normal fault of bearing 115° SE.. 87. Figure 4. 43: Normal fault of bearing 145° SE.. 88. Figure 4. 44: Syncline folding at well-bedded limestone of Gunung Temas.. 88. Figure 4. 45: Anticline structure on well-bedded limestone.. 89. Figure 4. 46: Lithostratigraphy related to the study area by Surono (2008).. 90. Figure 5. 1: The location of the 1D resistivity lines.. 95. Figure 5. 2: Schlumberger configuration.. 97. Figure 5. 3: The preparation of Line 1. The direction of line 1 shows as „A‟ and „B‟ while „C‟ is the centre of the survey line.. 99. Figure 5. 4: Data Processing of Line 1.. 101. Figure 5. 5: Resistivity log of Line 1.. 102. Figure 5. 6: Surrounding of Line 2. The arrow „A‟ showing the direction of Line A while arrow „B‟ showing the direction of line B.. 105. Figure 5. 7: Data processing of Line 2.. 107. Figure 5. 8: Resistivity log of Line 2.. 108. Figure 5. 9: Preparation of Line 3. „A‟ arrow showing the direction of line A while „B‟ arrow showing the direction of line B.. 111. Figure 5. 10: Data processing of Line 3. 113. Figure 5. 11: Resistivity log of Line 3.. 113. Figure 5. 12: Correlation of the resistivity log.. 114. xiii. FYP FSB. Figure 4. 36: Lithostratigraphy of the study area..

(15) INTRODUCTION. 1.1. General Background General geology is the principles of physical geology and its application in. interpreting the earth processes. It covers the identification of earth materials and the interpretation of topographic and geologic maps. In specific terms, geology covers the study of the rocks, minerals, the structures of the Earth and the processes that created those structures (Balasubramanian, 2017). The earth processes which started million years ago usually will be interpreted by the geologist to reveal the earth history and formation. Geology is important in order to locate the natural resources for our daily uses such as oil and gas, groundwater and many more. Groundwater is the natural resources that are available beneath the surface of our earth. It formed when the water on the surface flows and seeps to the ground in an unconsolidated deposit which is called aquifer (Simlandy, 2015). Groundwater makes up more than one-fifth (22%) of Earth‟s total fresh water supply and is very important in our daily life. Groundwater supplies are the fundamental resources for people drinking, agriculture and even for the industry. In most of the country in the world, 80% of the drinking water source is groundwater. Groundwater can occur in the cracks or fractures that are present in the rock. The fractures and porous rock which is filled and saturated with water at a certain depths is usually termed as the water table (Waller, 2016). Groundwater also can. 1. FYP FSB. CHAPTER 1.

(16) sedimentary rocks is based on the size of rock partials, their shapes and their sorting and cement degree. Usually, the higher the porosity and the permeability of a rock, the higher the potential of groundwater presents in the rock. In the present study, groundwater potential zone can be determined by using Electrical Resistivity Imaging (ERI) method. The ERI method maps the differences in the electrical properties of the subsurface if an electrical resistivity contrast exists between materials. It is highly dependent on the porosity and water content of the earth material where the greater the water content, the larger the electrical conductivity. For example, an accurate gradient boundary may be observed where a strong electrical contrast exists between a highly porous, low resistivity, water-filled aquifer regions and a less porous, less saturated, higher resistivity surrounding geology (Kelpie, 2017). Aquitards also generally act as electrical conductors as they often consist of water-trapped geological materials such as clay. These geological materials generally allow for an easier flow of electrical current.. 1.2. Problem Statement Cawas, Yogyakarta is believed that it has undergone a few changes due to the. earth dynamic properties. Some common process such as weathering processes will change the rocks whether it is based on physical, chemical or biological. Hazard processes such as landslides can change the study area in aspects of geomorphology or structure. Thus, a detailed geological map needs to be produced in order to add in the updated facts of the study area.. 2. FYP FSB. happen when there is pore surface at the soil or sedimentary rock. Porosity in.

(17) groundwater usage and management. Certain groundwater well in Cawas and the area near to it, the groundwater is low in quality and it is not a good drinking water resources. (Santosa, 2006). The new groundwater resources need to be searched as the demand getting high due lack of good quality groundwater resources. The determination of groundwater potential area for new sources of groundwater is important for different uses such as agriculture, drinking water, industries and others. Keeping in this view, the present research will be focused on the demarcation of groundwater potential zone.. 1.3. Objectives 1. To produce a geological map with scale 1:25,000 of the study area. 2. To determine the potential of groundwater locations by using vertical electrical sounding.. 1.4. Scope of Study The scope of study for Geology and the Demarcation of Groundwater Potential. Zone Using Resistivity Method of Cawas, Klaten, Yogyakarta Province, Indonesia come out with two scopes which are geological mapping and also a geophysical survey which is resistivity survey. The geological mapping needs to be done to produce a detail geological map with a scale of 1:25,000 of the study area. The geological mapping will cover the geomorphology, structural geology, drainage pattern and also lithology aspects. The specific method used is resistivity method to demarcate the potential zone of the groundwater.. 3. FYP FSB. The groundwater study is important in order to afford the planning of.

(18) Significant of study. This study is significant and important because it includes geological mapping which provides us with the information about the study area. Some of the important information includes lithology and stratigraphy of the study area. The important information can help another researcher for future studies. This research also will be useful to the community and society for the new sources of groundwater. Thus, the research will accommodate the demand for water sources that increases nowadays due to the agricultural, industrial and other activities. Lastly, this study will also significant to the developers and also planners for the development or urbanization processes. The geological or structural aspects of this research can help in engineering for a better development process.. 1.6. Study area The research area is located in the south of Central Java Island. Specifically, the. research area is in Cawas area and Gunung Kidul area and is included in Klaten district, Yogyakarta region. The size of the research area that was given is approximately 25km2.. 1.6.1. Location The research area located in Cawas area and Gunung Kidul area and is included. in Klaten district, Yogyakarta region. The northern part of the study area is 4. FYP FSB. 1.5.

(19) as Southern Mountain. The other part of study area are covered by alluvium area. The size of the research area that were given is approximately 25km2. The coordinate of the box is 7°45'26.82" S, 110°39'39.18" E. The second coordinate is 7°45'45.35" S and 110°42'23.00" E. The third coordinate of the study area is 7°48'30.62"S and 110°42'13.96"E. The fourth coordinate is 7°48'10.34" S and 110°39'30.28" E. The main river which is Dengkeng river is located on the north. The study area mainly is a flat area and the highest elevation is 200 m. the main town which is Cawas is located in the northeast of the study area. The main town can be accessed by Bayat-Cawas main road. Figure 1.1 below shows the location of the study area.. 5. FYP FSB. commonly called as East Jiwo Hills while the southern part of the study area is called.

(20) FYP FSB 6 Figure 1. 1: The location map of the study area..

(21) Road Connection/ Accessibility The main road connection of the study area from the base camp is Jalan Bayat-. Cawas located in the west of the study area. There are also a village area that has good cemented road and some small road connection. The study area is easily accessed by either car or motorcycle or other transportation.. Demography. 1.6.3. According to Statistics of Klaten Regency website, the population in Cawas on 2015 is approximate to be 10,334 people. It has land area cover with 36.1 km² and its density is 1,380/km².. 1.6.4. Climate and Rainfall Klaten district climate is classified as tropical. During most months of the year,. there is significant rainfall in Klaten. There is only a short dry season. Figure 1.2 below shows the climate graph of Klaten district in 2017. From the graph, January is the month that receives the highest rainfall. The pattern decreases until September. The rainfall increases again starting from October until December. The month of July, August and September receive the lowest amount of rainfall. As for the temperature of Klaten, at an average temperature of 26.5 °C, October is the hottest month of the year. In July, the average temperature is 24.8 °C. It is the lowest average temperature of the whole year.. 7. FYP FSB. 1.6.2.

(22) FYP FSB Figure 1. 2: The climate graph of Klaten (Source: climate-data.org). 1.5.5 Landuse Cawas is mainly an agriculture area. Almost 80 percent of Cawas area is covered by paddy field and it has some orchard or plantation area. According to website Statistics of Klaten regency in 2017, Cawas area of agriculture activity is approximately 2317 km2 and the non-agriculture area is about 1084 km2. The figure below shows the landuse map of Cawas sub-district.. 8.

(23) FYP FSB Figure 1. 3: Landuse map of study area.. 9.

(24) LITERATURE REVIEW. 2.1. Introduction Chapter 2 which is on literature review will discuss previous or preliminary. studies related to the research topic. This chapter will review the general geology, structural geology, stratigraphy and lithology, and geomorphology of Klaten area, Yogyakarta as the previous research conducted in the study area is limited. The review also basically will be related to the objectives, problem statements and also the methodology of this research.. 2.2. Regional Geology and Tectonic Setting Indonesia is a geologically complex region situated at the south-eastern edge of. the Eurasian continent. It is bordered by tectonically active zones characterized by intense seismicity and volcanism resulting from subduction. According to Robert et al., (2009), western Indonesia is largely underlain by continental crust, but in eastern Indonesia, there are more arcs and ophiolitic crust, and several young ocean basins. The Indonesian archipelago formed over the past 300 million years by reassembly of fragments rifted from the Gondwana supercontinent that arrived at the Eurasian subduction margin. The present-day geology of Indonesia is broadly the result of Cenozoic subduction and collision at this margin. Figure 2.1 below shows the present day tectonic setting of Indonesia.. 10. FYP FSB. CHAPTER 2.

(25) FYP FSB Figure 2. 1: Geography of Indonesia and surrounding regions showing present-day tectonic boundaries and volcanic activity. Indonesia is shaded green, and neighbouring countries are shaded in pale grey (Robert et al., 2009).. Java Island, Indonesia is located in the central of the Sunda Land because of the connection to Sunda Shelf-sea. Java Island has a cover area about 12,700 km2 and it is approximately 100 km long., The Java Island is divided into West Java, Central Java, East Java and the eastern spur of Java with Madura Strait and Madura Island. The division is made based on the characteristics of physiographic and also structural differences (Bemmelen, 1949). In geologic aspects, the Java belongs to tertiary mountain system around pre-Paleogene of Sunda Land. Bemmelen (1949), classify the central and also east part of Java Island into 5 zones which are Rembang zone, Randulblatung zone, Kendeng zone, Solo zone and also Southern Mountain zone. Figure 2.1 below shows the zones classification of central part and east part of Java Island:. 11.

(26) FYP FSB Figure 2. 2: Zone classification of Java Island (Bemmelen, 1949).. The study area is located in southern part of the Central Java Island and it is part of the the Southern Mountain and also part of East Jiwo Hills. The Southern Mountains can be divided into a southern part, the limestone plateau with Karsttopography of the Gunung Sewu and a northern part which composed of mountain ranges (the Gunung Kidul or Baturagung Range, the Panggung Massif, the Plopoh Range, and the Kambengan Range). The southern and northern parts of the Southern Mountains are separated by the intermontane basins of Wonosari and Baturetno (Bemmelen, 1949). Jiwo Hills composed of Pre-Tertiary rocks and also Tertiary aged sediments which have Quarternary fluviovolcanic sediments surrounded the rocks and also sediments which derived from the Merapi. Jiwo Hills which has low elevation lower than 400 m above the sea level are divided into two which are West Jiwo and East Jiwo. The two Jiwo Hills are divided by an antecedent river namely as Dengkeng. 12.

(27) area.. Figure 2. 3: Geological map of Jiwo Hills and Southern Mountain.. 2.3. Stratigraphy The lithology of the study area is complex. It is composed of various kinds of. igneous, sedimentary, metamorphic and also volcanic rocks of Southern Mountain (Mulyaningsih, 2016). Most previous research state that Bayat is a mélange complex that constructed within a subduction zone. Kebo-Butak is one of the formations that form the Bayat field complex (Mulyaningsih, 2016). The regional stratigraphy based on according to some researchers (Surono et al., 1992) from the oldest to the youngest is the Cretaceous metamorphic unit, Eocene Gamping Formation, Oligocene Kebo and Butak Formation, Middle Miocene. 13. FYP FSB. River. Figure 2.3 shows the geological map of Jiwo hills and Southern Mountain.

(28) Jiwo hills and Southern Mountain area.. Figure 2. 4: The stratigraphy of Southern Mountain (Surono, 2008).. 14. FYP FSB. of Igneous intrusion and also Wonosari Formation. Figure 2.4 shows stratigraphy of.

(29) The metamorphic unit is the oldest rock unit in Southern Mountain area. It is deposited in between early Cretaceous to early Paleocene. The metamorphic unit consists of phyllite, schist and marble. Based on Surono et al., (1992) the metamorphic unit is overlain unconformably by Gamping- Wungkal Formation. The estimated age is based on a single fossil orbitolina found by Bothé, (1927). Among the three rock unit, phyllite is most widespread in weathered conditions (Salahuddin, 2014). According to Setiawan, et al., (2014), the metamorphic unit is interpreted to be involved in an ancient subduction of the lithospheric plate and the plates collision afterwards during its formation of the regional metamorphism.. Wungkal-Gamping Formation. 2.3.2. Wungkal-gamping formation generally consists of two members which are the Wungkal member and Gamping member. Wungkal member is on the upper of the formation and Gamping member is on the lower part. It is overlain unconformably of the metamorphic basement rock (Salahuddin, Guide Book of Geological Excursion, 2014). Gamping-Wungkal formation composed of rock unit sandstone, sandy marl, claystone and limestone lenses. According to research by Surono et al., (2006), Wungkal-Gamping formation age range from middle Eocene to late Eocene. This is proved by determination of the age of foraminifera fossils.. 2.3.3. Nampurejo Pillow Lava and Kebo-Butak Formation Based on Surono, (2009), Nampurejo pillow lava, Kebo formation and Butak. formation is a rock unit which is dominated by the rock unit from volcanic activities. 15. FYP FSB. Metamorphic Unit. 2.3.1.

(30) the oldest Oligocene ancient rock unit successively overlapped by the Kebo formation and Butak formation of the age late Oligocene-early Miocene. Magmatic activities take place during Kebo-Butak deposition, possibly in submarine volcanic setting, as indicated by some of the basaltic pillow lava fragment at the lower part of the formation (Husein and Sari, 2011). Sandstone, gravelly sandstone, siltstone, claystone, tuff and shale were discovered in the lower part of the formation. The upper part consists of polymict breccia, sandstone, pebbly sandstone, claystone, siltstone and shale while on the middle part has pebbly sandstone. 2.3.4. Quarternary Alluvium. The Graben of Yogyakarta and its surrounding flat area was filled with fluviovolcanic products from Young Merapi. The plain is filled with fluvio-volcanic materials that produced from age Pleistocene to recent in the Northern part of Mount Baturagung (Surono, 2009).. 2.4. Structural Geology. Java Island occupies an active margin of plates interaction between Eurasia continental plate and Indian oceanic plate, which have converged since Cretaceous. This explains why Java Island consist of both Eurasia continental crust and intermediate accreted terrane on its basement. (Awang, 2005) Many researchers have an opinion on the structural geology and plate collision of Java Island. This includes opinion from Hussein (2013), which stated that the southern mountain on Central Java was formed by the tectonic activity of fault. Awang (2005) also state that Central Java has some unique geologic-tectonic phenomena. One of this uniqueness includes its position on the transition of 16. FYP FSB. which spread to west-east on the northern slopes of the Mountains Baturagung. It is.

(31) that the Baturagung Range of the Southern Mountain is the result of extensional tectonics that formed from block faulting. According to Salahuddin et al., (2008) Tegalrejo thrust fault has an association with the formation of the Baturagung Range and also suggest that the range formed under a compressive tectonic regime. On the other hand, Husein (2013) concluded that because of the isostacy effect that origin from the subsidence of Kendeng Basin in early Pliocene, the Southern Mountain is uplifted. The sign of faulting also was found well developed in the south part. Southern Mountain has a very complex fault system. There is the strike-slip fault which also presents in the southern mountain in the direction of NE-SW as a sinistral strike-slip fault (Husein, 2013). There is also the presence of a shear fault. For example are Oyo fault and also the Opak fault which makes the western boundary of Southern Mountains sliding towards each other. Southern Mountain involves the intersection of two main structure patterns. The two main structure patterns are Meratus Pattern and Java Pattern. The Meratus Pattern fault was formed by the massive tectonic period experienced by the Southern Mountains (Prasetyadi, 2007). Meratus pattern is parallel to the subsurface structure of The Southern Mountain.. 17. FYP FSB. basement rocks from continental to accreted crusts. Some geologist has the opinion.

(32) The historical geology will basically discuss the formation of the study area together with its age. Historical geology of the Southern Mountain area started with a rift-basin formation which is the part of the frontal basin on a continental microplate during early Eocene. In the late Eocene until the early Miocene, the sea sediment of Gamping Formation exposed. The exposure then followed by the old Andesite volcanism deposition. This results in the Kebo-Butak, Formation. The carbonate sediment becomes dominant at the end of early Miocene by the deposition of Wonosari Formations and it is continuously dominant until early Pliocene. Then the Southern Mountain formation takes place and it is uplifted and inverted to become a land (Husein, 2013).. Research Specification. 2.6. The research specification is resistivity study on groundwater. The resistivity study can help in most of the geology sectors. For example is the groundwater exploration. The resistivity sections are correlated with ground interfaces such as soil and fill layers or soil-bedrock interfaces, to provide detailed information on subsurface ground conditions.. 2.6.1. Groundwater Potential using Electrical Resistivity Groundwater as well as springs can be found in various rocks, such as sand-. gravel sediments, sedimentary rocks in the form of limestone, or in volcanic sediments such as lava, breccia and lava sediments. Variation of the groundwater characteristic depends on the variation of morphology.. 18. FYP FSB. Historical Geology. 2.5.

(33) is based on the principle that the distribution of electrical potential in the ground around a current-carrying electrode depends on the electrical resistivity and distribution of the surrounding soils and rocks. The usual practice in the field is to apply an electrical direct current (DC) between two electrodes implanted in the ground and to measure the difference of potential between two additional electrodes that do not carry current. In some cases, the induced polarization (IP) method is used. An IP effect is created when the ionic current flow through the geology is changed into an electrical current flow at the surface of metallic minerals that are present and in contact with the charged ions in the fluid within the pore spaces. Through an inversion of the measured potential differences between recording electrodes for the ERI and IP methods, the apparent resistivity of the ground conditions can be estimated (Tasker, 2017). Mineral grains comprised of soils and rocks are essentially nonconductive, except in some exotic materials such as metallic ores, so the resistivity of soils and rocks is governed primarily by the amount of pore water, its resistivity, and the arrangement of the pores.. To the extent that differences of lithology are. accompanied by differences of resistivity, resistivity surveys can be useful in detecting bodies of anomalous materials or in estimating the depths of bedrock surfaces. In coarse, granular soils, the groundwater surface is generally marked by an abrupt change in water saturation and thus by a change of resistivity. In fine-grained soils, however, there may be no such resistivity change coinciding with a piezometric surface. Generally, since the resistivity of a soil or rock is controlled primarily by the pore water conditions, there are wide ranges in resistivity for any particular soil. 19. FYP FSB. According to Wightman et al., 2003 surface electrical resistivity surveying.

(34) or lithology (Wightman et al., 2003).. 2.6.2. Common Type of Arrays Used in Electrical Resistivity Method Electrical and electromagnetic (EM) methods have been important in the. field of Applied Geophysics for many years, especially for shallow and near-surface investigations. Aizebeokhai et al., 2010 suggests that the types of arrays which are most commonly used in electrical resistivity imaging include Wenner array, Schlumberger array, dipole-dipole array, pole-pole array and also pole-dipole arrays. These arrays come with their corresponding geometric factors which are illustrated in the figure 2.5 below.. 20. FYP FSB. or rock type, and resistivity values cannot be directly interpreted in terms of soil type.

(35) FYP FSB Figure 2. 5: Common types of array used. (a) Wenner array (b) Schlumberger array (c) Dipole-dipole array (d) Pole-dipole array (e) Pole-pole array. The apparent resistivity values observed by the different array types over the same structure can be very different. The choice of a particular array depends on a number of factors, which include the geological structures to be delineated, heterogeneities of the subsurface, sensitivity of the resistivity meter, the background noise level and electromagnetic coupling. Other factors which are included are the sensitivity of the array to vertical and lateral variations in the resistivity of the subsurface, its depth of investigation, and the horizontal data coverage and signal strength of the array (Aizebeokhai et al., 2010). 21.

(36) vertical variations in the subsurface resistivity below the centre of the array but less sensitive to horizontal variations in the subsurface resistivity. The arrays can interpret moderate depths of investigation and generally strong signal strength which is inversely proportional to the geometric factor used in calculating the apparent resistivity values. The major weakness of these arrays is the relatively poor horizontal coverage with increased electrode spacing. Wenner array is perfect for surveys in a noisy site because of its high signal strength, but the limitation is the array is less sensitive to 3D structures (Dahlin & Loke, 1997). The dipole-dipole array can detect the resistivity variations below the electrodes in each dipole pair and is very sensitive to horizontal variations but it is not too sensitive to vertical variations in the subsurface. However dipole-dipole array is the most sensitive array to map 3D structure among the other arrays (Dahlin and Loke, 1997). The depth of investigation of the array depends on both the current electrode spacing, a, and the distance between the two dipoles and is generally shallower than that of Wenner array. However, the dipole-dipole array has better horizontal data coverage than Wenner array. The major disadvantage of this array is the decrease in signal strength with increasing distance between the dipole pair. The pole-dipole array has good horizontal coverage and higher signal strength compared with the dipole-dipole array. It is much less sensitive to telluric noise than the pole-pole array. For its weaknesses, the signal strength of the pole-dipole array is lower than that of Wenner and Schlumberger arrays and is very sensitive to vertical structures. For a pole-pole array, finding suitable locations for these electrodes so as to satisfy this theoretical requirement is often difficult. In addition to this limitation, the. 22. FYP FSB. Basically, the Wenner array and Schlumberger arrays are commonly sensitive to.

(37) degrading the quality of the observed data. However, the pole-pole array has the widest horizontal coverage and the deepest depth of investigation but the poorest resolution. The resolution of the pole-pole array is very poor as subsurface structures tend to be smeared out in the inversion model (Dahlin and Loke, 1997). If the electrode spacing is small and good horizontal coverage is desired, the pole-pole array is a reasonable choice. The figure 2.6 below shows the summary of the arrays:. Figure 2. 6: Summary of all types of array. (Source: Samouëlian et al., 2005). 2.6.3. Resistivity and Conductivity of Various Rock Type Fargier et al., 2014 in his research state that the resistivity determines how. materials resist or conduct to electricity. It strongly depends on the nature of the studied material, its water and clay contents. Other parameters like tortuosity or water salinity of soils are also of importance. The resistivity values of encountered materials such as in dykes spread in a large scale: few Ω.m (ohm meter) in clays, from few Ω.m to few hundreds Ω.m for silty soils and from few hundreds Ω.m to several thousand Ω.m in the sand, gravel and limestone. The figure 2.7 below shows the range of resistivity values of the main materials encountered in applied geophysics.. 23. FYP FSB. pole-pole array is highly susceptible to a large amount of telluric noise capable of.

(38) FYP FSB (Source:Palacky, 1991) Figure 2. 7: Range of resistivity value and conductivity value on different rock and materials.. Igneous rocks have a minor component of pore water. The substances with high resistivity are usually less permeable and less porous. Igneous and metamorphic rocks typically have high resistivity values. The resistivity of these rocks is greatly dependent on the degree of fracturing, and the percentage of the fractures filled with ground water. Thus a given rock type can have a large range of resistivity depending on whether it is wet or dry (Jones, 2007). Jones, 2007 also states that sedimentary rocks, which are usually more porous and have higher water content, normally have lower resistivity values compared to igneous and metamorphic rocks. The resistivity values are largely dependent on the porosity of the rocks, and the salinity of the contained water. The substances with low resistivity are highly permeable and porous to water. The resistivity of the subsurface depends on the presence of certain metallic ores, the temperature of the subsurface; geothermal energy, the presence of 24.

(39) Presence of contaminants, percentage of porosity and permeability. This resistivity survey method has some inherent limitations that affect the resolution and accuracy that may be expected from it. Like all methods using measurements of a potential field, the value of a measurement obtained at any location represents a weighted average of the effects produced over a large volume of material, with the nearby portions contributing most heavily. The materials contained in the ground itself might affect the reading of the terrameter. This tends to produce smooth curves, which do not lend themselves to high resolution for interpretations.. 2.6.4. Previous Study of Groundwater Potential Using ERI. Based on the previous study of Darsono et al., (2016), a geophysics survey by using resistivity method in Sambirejo and Kedawung subdistrict, Sragen regency, Indonesia has been done for identification of aquifer potential in those areas. The research is important in finding new sources of groundwater as the population in the study area increase and thus, this increase the demand for groundwater sources. The resistivity method is used with Schlumberger configuration. Figure 2.8 shows the Schlumberger array that used in the research.. (Source: Darsono et al., 2016) Figure 2. 8: Schlumberger Array 25. FYP FSB. archeological features, amount of groundwater present, amount of dissolved salts,.

(40) which is A-B section, C-D section, C-F section and E-A section. The result of each section is interpreted from the result of VES are shown in Figure 2.5 below. Based on this cross-section, it can provide delineation of the position, the thickness of the aquifer layer and layer which is not an aquifer (aquiclude).. Figure 2. 9: Cross section of VES points. The result from figure 2.9 above shows that in Sambirejo district, the aquifer layer consists of the clayey sand layer. In Kedawung district, the aquifer layers consist of clayey sand, sand, gravel sand, gravel and breccia. The entire study area can be classified as very good, good, moderate and poor for groundwater potential zones (Darsono et al., 2016).. 26. FYP FSB. A cross-section from several Vertical Electrical Sounding (VES) points.

(41) MATERIALS AND METHODOLOGIES. 3.1. Introduction This chapter will discuss the methodology and materials used in this research to. achieve the objectives. This chapter also explain what materials are used and how the research is conducted before and after geological mapping. In summary, the materials used in this research to smoothens the processes of this research are geological hammer, GPS, base map, handlens, measuring tape, compasses, HCl, sample bag, microscope, thin section machine, ERI instruments, and softwares. While the research processes are involving preliminary research study, preparation of base map, geological fieldwork including traversing, data collection for geomorphology, lithology and structural geology aspects. Other than that the methodology involving lab work which divided into two sections which are lab analysis and software application. After lab work, the research continue with data processing, data interpretation and lastly producing a complete geological map with scale 1:25000 and also writing of final report.. 27. FYP FSB. CHAPTER 3.

(42) FYP FSB. Preliminary studies: -Data collection from journal, thesis, books, etc.. Preparation of base map. Fieldwork. Geological fieldwork: -Traverse -Data collection for geomorphology, lithology, and structural geology.. -Rock sampling -Determination location for ERI. Lab work Lab analysis. Data processing. Software application:. -Thin section -ArcGIS -petrographic analysis. Data interpretation. Produce map with scale 1:25000. Final report. Figure 3. 1: Flow chart of the research study.. 28. -Progress Version 3.0 -CorelDraw.

(43) Materials and also equipment that will be used in this research is required for both field mapping and lab analysis. The materials which will be used are shown in the table below:. Table 3. 1: Materials that will be used during field mapping and lab analysis.. Equipment/ tools Geological hammer. Uses. Pictures. The 2 types of the 1. 1. Tip- point hammer 2. Chisel head hammer. geological hammer are tip-point and chisel head hammer. It is used to break rocks in the field to be taken as samples.. Global Positioning. GPS is a device which. System (GPS). detects a position on the map by showing coordinate in longitude and latitude based on earth navigation system of the satellite.. Base map. The base map will be used as a preview of the study area and as a guide to plot the location.. 29. 2. FYP FSB. Materials/ Equipment. 3.2.

(44) FYP FSB. Hand lens. Hand lens usually is used to observe minerals in the rock sample that is too fine to look with naked eyes.. Measuring tape. The measuring tape is used to measure the length of the outcrop. It also can be used to measure the length of fracture such as joints for joint analysis.. Brunton compass. The compasses are used to determine the bearing of the outcrop. It also used in the measurement of the rocks such as strike and dip reading. Compass also act as a substitute for GPS in determining the position on the map.. 30. 1.

(45) The HCL will be used to. acid (HCl). distinguish between quartz and calcite mineral.. Sample bag. The sample bag is used to put the rock sample that was taken in the research area.. Microscope. The common microscope used is polarized microscope which is used to identify the rock composition and characterize rock textures and fabrics.. Thin section. The machine is used to. machine. cut and grind the rock sample to be analysed under the polarized microscope.. Software. The ArcGIS and. . Progress 3.0. CorelDraw software will. . ArcGIS. be used to digitize and. . CorelDraw. produced a geological map. The Progress 3.0. 31. FYP FSB. Dilute hydrochloric.

(46) interpret data of the ERI.. Electrical. The ERI instrument is. Resistivity Imaging. used to investigate. (ERI). variations of electrical. 2. 1. 1. Mc Ohm. resistance, by causing an. Model 2115. electrical current to flow. instrument. through the subsurface. with battery. using wires (electrodes). 2. Multicore. connected to the ground. 3. cables 3. Current Meter 4. Current electrode and. 4. potential electrode Walkie talkie. Use to communicate and give instructions in short distance.. 32. FYP FSB. software will be used to.

(47) Use to hit the electrode into the ground.. 3.3. Methodology Methodology basically explained the procedure and methods that was used and. conducted during the research. As a summary, the first methodology is preparation which involves base map preparation and also preliminary studies of the research. After the preparation step is the fieldwork and followed by lab work.. 3.3.1 Preparation/ Preliminary studies The preliminary studies method is a necessary method in the research proposal. It is the first step in research before starting fieldwork. The data collected from the previous studies was used to get additional information about the targeted study area. The preliminary studies were conducted by collecting information about the lithology, stratigraphy, geomorphology and structural geology data and also about the research specification. The source of preliminary studies can be from thesis, journal, books, article, website and others.. 3.3.2. Preparation of Base Map Next step that was done is the preparation. The preparation of base map was. done using software which is ArcGis version 10.2. In the base map information that was included is typically main road, main river and stream, main town in the study 33. FYP FSB. 2 hammer.

(48) using ArcGis 10.2 can give geomorphology information about the study area. Before going fieldwork, a geomorphology analysis must be done. This is because geomorphology analysis is important for location of lineament in the study area. The purpose of locating lineament is because the lineament is one of indicator of faulting that exists in study area. The fault can be a good evidence of historical geology of the study area and also how the study area form. Other than that, from the topography map that was produced, lithology interpretation needs to be made. The boundary of different lithology can be determined by differentiate the contour pattern. Usually high contour pattern indicate hard rock such as igneous and metamorphic rock while the low contour pattern indicated soft rock such as sedimentary rock. Furthermore, the location of the highest and the lowest elevation also was determined. This is to make the traversing plan smooth and to be well prepared for sufficient and good data collection during fieldwork. The highest locations and elevation also need to be determined for geomorphology analysis of the study area.. 3.3.3 Geological mapping. Figure 3. 2: The geological mapping process.. 34. FYP FSB. area and also contour line. The topographic map or base map that was produced.

(49) and the research specification. It was being done to collect variable amounts of field data. Geological mapping also is the process of making observations of geology and structure in the field and recording them on a base map. The information recorded must be factual and thorough based on objective examination of rocks and exposures. Three important things during geological mapping were traversing, sampling and data collection. For research specification purpose, the determination of location to run the ERI was also being made. First is traversing method. Traversing is a method of making an observation and recording information of outcrops along a path that will be taken during geological mapping. Traversing is important to collect all necessary data such as lithology, structural, geomorphology and stratigraphy aspects specifically. Second is sampling of rock. Sampling will be made for outcrops that were found in the research area. The sampling of rock was taken using the geological hammer and being kept in the sample bags. The sampling also labelled with the number of sample, date and the person who take the sample. It is important to take fresh rock samples. This is because petrographic analyses can easier being done for fresh rock sample and determination of rock type also will be easier. Third is data collection for geomorphology, lithology and structural aspects. For geomorphology aspects observation will be done in determination of type of landscape that present in study area. The other geomorphology aspects such as weathering also need to be taking in count. For the landscape, a panorama view will be taken by using camera. For structural geology aspects, important geological structures such as joint, bedding structure, folding and also faulting will be measured and recorded. Basically 35. FYP FSB. Geological mapping was conducted to investigate the geology of study area.

(50) strike and dip direction of the bedding is determined using right hand rule or left hand rule. The thumb pointing indicates where the strike directions while the other fingers pointing to indicated dip direction. For joint and other fracture, the orientation is measured for joint analysis and fault analysis. For lithology and also stratigraphy aspects, observation on outcrops will be made based on the colour, grain size, structure that is presence at the outcrop, type of rock and also name of rock. For specific observation such as mineral content, cleavage and others will be further to lab analysis for petrographic analysis by providing rock samples. For groundwater potential zone analysis aspects, the area in which ERI should be placed need to be determined. This is the purpose of doing observation first in the study area to determine the potential area for ERI analysis. Usually, the place with alluvium area and good recharge area will be chosen for ERI survey. The area with many joints and fracture also can be a good aquifer system. During fieldwork, all important information such as type of surrounding, type of rock, fracture system, existing well, and other information need to be note down for easier work of ERI. Next step would be ERI analysis. The ERI instrument such as ABEM Terrameter is used to investigate variations of electrical resistance, by causing an electrical current to flow through the subsurface using wires (electrodes) connected to the ground. The ERI data will be collected with a 41 electrode array on the surface with 2.5 meter spacing. This spacing generated a 100 meter long, straight line that imaged approximately 17 meters deep. During fieldwork, ERI survey line endpoint coordinates and start point coordinates will be collected using a GPS to support. 36. FYP FSB. the measurement that will be made on these structures will be using compasses. The.

(51) along the lines.. 3.3.4 Laboratory work Lab work involves the sample preparation. The sample preparation starts with rock cutting, sample grinding, glue the slide to the sample, sample slide‟s grinding, and lastly, add the coverslip. The lab work also involves petrographic analysis using a polarized microscope. The rock samples which are taken from the fieldwork are being cut into thin section using non-deformational diamond saw. The sample which have been cut to thin section will be grinded by hand or grinding machine until the sample. is. completely flat. After grinding processes, the sample will be glued to slide using epoxy or mounting medium. After the glue dried up, the thin section sampple is then being cut to thickness of approximately 2 mm. After all of these processes, the petrographic analysis can be done by analyzing mineral content, cleavage, mineral properties and other petrographic aspects. The type of rock and rock name can also be confirmed using petrographic analysis. Lab work also involves the use of software for geological map and also for the resistivity method. The CorelDraw and ArcGIS software are used to produce a detailed geological map with scale 1:25,000. The Produce 3.0 software is used to produce a 1D model of the subsurface from the apparent resistivity data which taken from ERI instruments.. 3.3.5. Data Processing and data interpretation. All the raw field data including the resistivity raw data is collected and processed. During the fieldwork, data such as geomorphology analysis, structural 37. FYP FSB. future acquisition of ERI data along the same lines along without placing markers.

(52) to produce a geological map. The resistivity data is also being interpreted to identify the type of material in the subsurface. By using the reference from table of resistivity and conductivity value of rock, the result which are processed using Progress 3.0 software will be interpreted. For high potential of groundwater zone, the resistivity are usually low resistivity due to highly porous material and highly permeable. Final steps will be the complete geological map which produced at scale 1:25000 and the process of writing full report of the research.. 38. FYP FSB. analysis, and lithology and stratigraphy record need to be transferred and combined.

(53) FYP FSB. CHAPTER 4. GENERAL GEOLOGY. 4.1. INTRODUCTION This chapter will discuss about. general. geology which includes. geomorphology, stratigraphy, structural geology and also historical geology. This chapter covers the geological mapping part of the final year project. The chapter is a complete representation of all the landform and structure in the study area. This chapter also focuses on the geological history of area based on the analysis, interpretation and observation of the lithology, geomorphology, geological structure and also sedimentology data.. 4.1.1. Accessibility in the Study Area The study is well accessible from the main town which is Cawas and there. are many well cemented roads. The main road in the study area is Bayat-Cawas road which connected to the Cawas town. Only few parts of study area does not have pavement road mostly in the hilly area but still can be access by walking. 4.1.2. Settlement and Vegetation The study area is mostly covered by vegetation and also plantation which is. paddy field. Most of the alluvium area especially in the eastern part of the study area is paddy field. The western part of the study area is the settlement area and also some. 39.

(54) 40 Figure 4. 1: Vegetation map and settlement map of the study area.. FYP FSB. orchard present. Figure 4.1 below shows the landuse map of the study area with pictures of settlement and vegetation in the study area..

(55) Traverses and Observation Traversing is a method of making an observation and recording information. of outcrops along a path that will be taken during geological mapping. Traversing of the study area took about 2 weeks with 30 observation stations of the lithology and other aspects which is geomorphology, structural geology and others. Figure below shows the traverse map with the observation stations of the study area.. Figure 4. 2: The traverse map and sample location of the study area.. 41. FYP FSB. 4.1.3.

(56) GEOMORPHOLOGY Generally, geomorphology is the study of landform and nature that makes up. the landscape of an area. Geomorphology included mountain, valley, lake, rifts and also rivers. Geomorphology was concerned largely with erosion surface, the age, origin and also the processes that formed the landscape. Analysis of the structure of the study area such as lineament, joint, fault and others can give interpretation about the tectonic activities that had occurred before. There are few aspects of morphology that were observed during the geological mapping which is topography, vegetation, drainage pattern and weathering aspects.. 4.2.1 Topography Topography can be referred as the elevation and the relief of the earth surface and mostly used to describe the earth surface. It includes a variety of features and the landform of the area. The topography of the study area are varied due to the variable pattern of lithology distribution, physical and chemical properties of the rocks, structures present around the study area and also geomorphic processes such as weathering processes. There is hilly topography and mostly alluvium covered the area. On the northwest part of the study area, there are mostly hilly area with some of them are slightly steep with low elevation. The highest elevation is 212 metres above the sea level. The lowest elevation can be observed on alluvium area which is located mostly in eastern part of the study area. Most of the alluvium area is paddy field and also vegetation. Five broad topographic units can be distinguished based on differences in mean elevation as. 42. FYP FSB. 4.2.

(57) topography map of the study area.. Table 4. 1: Topographic unit based on mean elevation.. Topographic uniit. Low lying. Mean elevation (m. Rolling. Hilly. Mountaineous. 16-30 < 15 (not. above the sea. 31-75(not (not. found) level). Undulating. >301 (not 76-300. found). found). found). Based on the table 4.1 the study area composed of hilly area. Although all of the part of the study area is classified as hilly area, there is also plain area or alluvium area with elevation more than 90m above the sea level. The topography of the area can be influenced by the type of the lithology. For example, on the northwest part of the study area composed of mainly metamorphic rock and also igneous rock that is categorized as hard rock. Thus, the area in north western part consists of steep hill. The hard rock normally makes up high elevation because it is more resistant to weathering than the soft rock. The topography of the southwest area is less steep than the northwest part maybe because of the type of lithology is less resistant rock.. 43. FYP FSB. shown in table 4.1 below (Hutchinson & Tan, 2009) and figure 4.3 shows the.

(58) FYP FSB 44 (b) (a). Figure 4. 3: Topography Map of Study Area. (a) Panorama showing the hilly area of northern part of study area. (b) Hilly area of southern part of study area..

(59) Drainage Pattern Drainage pattern are controlled by some factors which are type of rock and. the location of the lithology at the land surface. For example, the resistivity of rocks and weakness of planes in rocks such as bedding plane, fault or joint can influence the shape of the drainage pattern. Other factors such as folding, precipitation and disintegration affect the formation of drainage pattern. The sort of drainage that was controlled by the slope or structure was dendritic, parallel, trellis, rectangular and reticulates as shown in figure 4.4. Some of the drainage had undergone changes due to human activities such as agricultural activities. There is also much drainage that was found dry due to drought season in Bayat. The water will flow from high elevation to low elevation such as the alluvium plain. Figure 4.5 shows the drainage that was found dry due to dry season.. (Source: Michael & Scott, 2018) Figure 4. 4: Drainage pattern types.. 45. FYP FSB. 4.2.3.

(60) The types of drainage that can be found in the study area are dendritic, parallel and also rectangular. The dendritic type can be found at the south western part of the study area in Gunung Kidul area. The parallel type can be found in north western part of the study area while the rectangular type can be found in the middle of the study area. Figure 4.6 shows the drainage pattern map of the study area.. 46. FYP FSB. Figure 4. 5: Dry drainage in the study area..

(61) FYP FSB. Parallel. Rectangular. Dendritic. Figure 4. 6: Type of drainage pattern found in the study area.. 47.

(62) Weathering Weathering is the process where rocks, soil and minerals are broken down. through contact with the Earth‟s atmosphere, waters and biological organisms. Weathering can either occur on the sites or also known as in situ weathering. In situ weathering occurs with little or no movement of the rocks and minerals, thus making it different with erosion which involves the movement of rocks and minerals by agents such as water, ice, snow, wind, waves and gravity. The three types of weathering are physical weathering, chemical weathering and biological weathering. Most of the weathering processes that occur in study area are biological weathering. Biological weathering is another type of weathering that causes by the presence of vegetation including root wedging that form on rock crack and fracture. Figure 4.7 shows biological weathering on metamorphic rock with limestone outcrop.. Figure 4. 7: Biological weathering at schist with limestone outcrop.. 48. FYP FSB. 4.2.4.

(63) outcrop. Both were affected by the action of biological weathering but schist is more weathered than the limestone. This might because of schist is the oldest rock formation on the study area. Schist undergoes weathering process longer compared to limestone which explains why schist is more weathered than the limestone. There is also presence of spheroidal weathering mostly on diorite rock in the study area. Spheroidal weathering is a form of chemical weathering that affects jointed bedrock and results in the formation of concentric or spherical layers of highly decayed rock within weathered bedrock that is known as saprolite. Figure 4.8 shows spheroidal weathering on diorite.. Figure 4. 8: Spheroidal weathering on diorite.. The spheroidal weathering causing the diorite rock becomes very brittle. The colour of the rock also turns to light brown and it is to observe minerals using naked eyes. 49. FYP FSB. The schist is in a very weathered condition compared to the limestone.

(64) weathering changes the physical properties of the rock but not the chemical composition. Physical weathering on the phyllite happens because of the plants roots which grow in the phyllite and causing the phyllite to have cracks. The process might also occur because of the thermal expansion of the rock which causing it to expand and contract and finally cracks.. Cracks. Figure 4. 9: Physical weathering on phyllite rock.. 50. FYP FSB. Figure 4.9 below an example of physical weathering on phyllite. Physical.

(65) Lithostratigraphy Lithostratigraphy focus on the study of rocks existed in the study area and. relates it with its age. This part of analysis was done via geological mapping and preliminary research that is by the help of literature review. In this part, we also manage to understand more on the ages and depositional environment of the rocks. It is very important to understand the lithology of the study area and identifying the lithological boundary in order to create a detail geological map.. 4.3.1. Units Explaination The areas around Watuprau, Bayat and also Gunung Kidul have a very. complex lithology. Areas around Watuprau in the northern part consist of schistphyllite unit, well-bedded limestone unit of Wonosari Formation, numulitic limestone, tuffaceous sandstone and also intrusion of igneous rocks which are diorite and andesite. Gunung Kidul areas in southern part consist of sandstone unit, tuff, lapilli, tuffaceous sandtone and alternation of sandstone and siltstone unit.. a). Schist-phyllite unit Schist-phyllite unit can be found on the northern and western part of the study. area. It is metamorphic rock with foliation structure. The schist-phyllite unit consist of schist, phyllite and also graphite schist. The alignment of mineral with the foliation can be seen clearly in the rock. The exposed outcrop of schist can be found near Watuprau Bukit Cinta striking to the west with less than 10° dip angle as shown in figure 4.10.. 51. FYP FSB. 4.3..

(66) FYP FSB Figure 4. 10: Outcrop of schist unit.. 52.

(67) the foliation structure is influenced by the process of regional metamorphism, with the pressure factor and temperature factor. This rock composed of fine-sized minerals (<1mm) with foliation structure, and the rock is textured. Based on the crystal form, it is lepidoblastic textured because the original minerals are in the form of sheets. There is also boundary of numulitic limestone and phyllite in the area (figure 4.11). The contact between nummulitic limestone and phyllite can be seen in figure below. The light brown colour is the outcrop of the phyllite which is very brittle and wethered while the nummulitic limestone has light grey colour. In the schist-phyllite unit, phyllite is the most dominant among the other rock unit. Some of the schist-phyllite, there are quartz vein aligned in between their foliation. Figure 4.12 shows the quartz vein structure which aligned in the foliation. Another unit of schist-phyllite is graphite schist. Graphite schist can be found near Gunung Gajah swimming pool striking to the south. Some of them are very brittle because of weathering. Graphite schist is grey in colour and it is very fine grained. Figure 4.13 shows the outcrop of graphite schist. Figure 4.14 shows the hand sample of schist rock. The schist has brownish grey colour with a clear schistose foliation. The texture of the rock is lapidioblastic. Some of the mineral can be seen with naked eyes such as quartz, mica and also feldspar. Schist is a type of metamorphic rock which undergoes regional metamorphism. Figure 4.15 shows the thin section image of shist.. 53. FYP FSB. This rock is a type of metamorphic rock that has a structure foliation, where.

(68) FYP FSB Figure 4. 11: Boundry of numulitic limestone and metamorphic rock unit.. Quartz vein. Figure 4. 12: Quartz vein alligned in the foliation of phyllite.. 54.

(69) FYP FSB Figure 4. 13: Graphite schist outcrop.. Figure 4. 14: Hand sample of schist.. 55.

(70) Gr Qz. Gr Fs. Mcz Mcz. Figure 4. 15: Thin section of schist under xpl (A) and ppl (B) with magnification of 10x10.. Table 4. 2: Mineralogy description of schist.. Mineralogy Description Composition of. Estimated. Minerals. Percentage (%). Description of Optical Mineralogy. PPL: Anhedral to subhedral with fibrous habit. It is colourless under PPL, has low relief and does not have pleochroism. XPL: the maximum interference is first Quartz (Qz). 30 order interference with grey and white colour. It has ununiformed and also has shadowy extinction which is fairly common in deformed rock.. Graphite Foliation. Do not shows change whether in PPL or 30. (Gr). XPL. Minerals look black regardless of. 56. FYP FSB. B. A.

(71) known as opaque mineral. PPL: Muscovite has small, good cleavage lines. It is colourless and possesses no pleochroism. Muscovite (Mcv). 20. XPL: In XPL, muscovite shows second order interference color against the minerals around it. The extinction is parallel to cleavage in all orientations. PPL: Euhedral to subhedral with good cleavage. It has high relief and possesses no pleochroism.. Plagioclase Feldspar 10. XPL:. The. plagioclase. feldspar. is. (Pl) anisotropic mineral. It shows interference in the first order black and also white. It has inclined extinction and also has twinning. Other mineral that can be found is biotite. The biotite has only one direction of Others. 10 cleavage. It has brownish colour and moderately high relief. Schist. Name of the rock. 57. FYP FSB. orientation of mineral or polarizer. It is also.

(72) Numulitic Limestone Unit The numulitic limestone unit outcrop is exposed on tourism site which is. Watuprau Bukit Cinta. It is also in the north western part of study area. There is obvious boundary between numulitic limestone and schist-phyllite unit from figure 4.11 above. Figure 4.16 shows the limestone outcrop in Watuprau area. It is a clastic sedimentary rock with blackish grey colour and has the grains of sand and silt-sized matrix. The grain shape is rounded grain with bad sorting. The limestone is grain supported and it is massive shaped rock. The rocks composed of carbonate minerals measuring silt and fossil nummilites sp. Figure 4.17 shows the rock sample of nummulitic limestone. The composition of nummulitic limestone composed of fragments Fossils nummulites sp. with grey colour, shaped flat with spaces (septa). From naked eyes observation, the matrix is composed of clay-brown, amorphous, orange-brown clay minerals with luster of soil.. Figure 4. 16: Nummulitic limestone unit in Watuprau area.. 58. FYP FSB. b).

(73) FYP FSB. Nummulites. Figure 4. 17: Hand sample of nummulitic limestone.. A. B. Qz. Nf Nf. mtx. mtx Qz. Figure 4. 18: Thin section of nummulitic limestone under XPL (A) and PPL (B) under 4x 10 magnification.. 59.

(74) Mineralogy Description Composition of. Estimated Percentage. Minerals. (%). Description of Optical Mineralogy. PPL: Anhedral to subhedral with fibrous habit. It is colourless under PPL, has low relief and does not have Quartz (Qz). 60. pleochroism. XPL: the maximum interference is first order interference with grey and white colour. Nummulite is a type of formaninifera which common in Eocene to Miocene. Nummulite fossils 20. marine rock. The nummulite fossils are. (Nf) the. age. indicator. of. nummulitic. limestone. The matrix of carbonate rocks consists Sparrite matrix. of coarser grained calcite crystals 15. (mtx). formed. during. diagenesis,. called. sparite. Other minerals include biotite and also some Others mineral. isotropic. mineral.. Isotropic. 5 mineral appear black but can transmit light in PPL.. Name of the rock. Nummulitic limestone 60. FYP FSB. Table 4. 3: Mineralogy description of nummulitic limestone..

(75) Tuffaceous sandstone unit Tuffaceous sandstone unit can be found in southern mountain area which is in. the south west of the study area. Some volcanic rock that was found is lapilli, tuff, tuffaceous sandstone and also some sandstone interbed in the tuffaceous sandstone. The volcanic rock unit is included in Kebo Formation. There is presence of faulting structure in this site. The type of fault found is reverse fault. The tuffaceous sandstone unit are interbedded with lapilli and also sandstone. There are thick bedding of tuffaceous sandstone and thin bedding of lapilli and sandstone in between the tuffaceous sandstone unit. The tuffaceous sandstone is fine grained with light colour. Some of the tuffaceous sandstone have slightly greenish colour which might contain some zeolite. Figure 4.18 shows the outcrop of tuffaceous sandstone unit. Figure 4.20 shows the rock sample from the outcrop above. The rock has a pale green colour and has lamination structure in the sample. It is very fine grained sand texture. The rock contains zeolite mineral which makes it colour slightly greenish. The rock is called as tuffaceous sandstone and it is a type of volcanic rock. Figure 4.21 shows the thin section of the tuffaceous sandstone.. Figure 4. 19: Volcanic rock unit which comprises of tuff, lapilli and also sandstone included.. 61. FYP FSB. c).

(76) FYP FSB Figure 4. 20: Hand specimen of tuffaceous sandstone.. A. B. zt. Is. Is. Qz bt. bt. Figure 4. 21: Thin section of tuffaceous sandstone under XPL (A) and PPL (B) under magnification 4x10.. 62.

(77) Mineralogy Description Estimated Composition of Minerals. Description of Optical Mineralogy Percentage (%) PPL: Anhedral to subhedral with fibrous habit. It is colourless under PPL, has low relief and does not have. Quartz (Qz). 40. pleochroism. XPL: the maximum interference is first order interference with grey and white colour. Isotropic mineral appear black but can transmit. Isotropic minerals (Is). light. in PPL but. it. is. 40 colourless. The isotropic mineral in the tuffaceous sandstone is volcanic ashes. PPL: The colour is brown to reddish brown with strong pleochroism. Biotite also has irregular grain and has moderately high relief. It also has only. Biotite (Bt). 10 one direction of cleavage. XPL: The interference is third to fourth order of interference colour. Biotite also has bird eye extinction. Natural zeolites form where volcanic. Zeolite (Zt). 10 rocks and ash layers react with alkaline. 63. FYP FSB. Table 4. 4: Mineralogy description of tuffaceous sandstone..