MICROFACIES OF LOWER JONGGRANGAN FORMATION AT BRAJAN SECTION, BANJARARUM, KULON PROGO, INDONESIA

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1 MICROFACIES OF LOWER JONGGRANGAN FORMATION AT BRAJAN SECTION, BANJARARUM, KULON PROGO, INDONESIA Setyo PAMBUDI1,2*, Vijaya ISNANIAWARDHANI1, WINANTRIS1, Adjat SUDRADJAT1 1 2 Faculty of Geological Engineering, Padjadjaran University, Bandung Department of Geological Engineering, Sekolah Tinggi Teknologi Nasional (STTNAS) Yogyakarta, *Corresponding author: pambudisetyo@yahoo.com ABSTRACT The Jonggrangan Formation is one of the carbonate rock units of West Progo Hill exposed in Brajan, Banjararum, West Progo. The aim of this study is determining the environment and depositional mechanism of the lower Jonggrangan Formation at Brajan, Banjararum, West Progo. Petrographic analysis was used to find out the standard of microfacies while paleontological analysis have been done to determine the age and sedimentary environment. Based on stratigraphic measurement section at Brajan area, the lower Jonggrangan Formation is generally dominated by limestones, sandy limestone and intercalation of calcareous sandstone. Results of petrographic analysis show that the type of rocks are floatstone, packstone, sandy lime packstone, sandy lime wackestone and calcareous lithic arenite. The results of standard microfacies analysis show that the rocks have been deposited on the foreslope (SMF5 / FZ4), deep shelf margin (SMF5 / FZ3) and open sea shelf (SMF9 / FZ2) environments. Paleontological data indicates that sedimentary rocks deposited during the Early Miocene to lower Middle Miocene (N5 - N9) in inner middle neritic environment. Keywords: Microfacies, Jonggrangan Formation, limestone, Brajan. INTRODUCTION The Kulon Progo Hills have been extensively researched by several geologists from Indonesia and abroad (Table 1). The experts who have conducted the researchs are Marks (1957), Bemmelen (1949), Darwin Kadar (1976, 1981), Suyanto & Roskamil (1975), Rahardjo, et al (1977), Harsono & Purnamaningsih (1981), Suroso et al (1986), Harsono & Riyanto (1987) and Soeria - Atmadja, et al (1991). Jonggrangan Formation is composed of reef limestone, always in high altitude, overlain unconformably on Old Andesit Formation. The study of microfacies limestone aims to determine the environment and the depositional mechanism of the lower Jonggrangan Formation in Brajan area. The research was conducted in Brajan, Banjararum, Kalibawang, Kulon Progo District, Yogyakarta (Figure 1). 268

2 LITERATURE REVIEW The Kulon Progo Hills are an elongated dome-shaped ridges in the northeast-southwest direction (Bemmelen, 1949). Stratigraphy from previous researchers can be concluded that the regional stratigraphy of Kulon Progo Hills from old to young namely: Nanggulan Formation, Old Andesite Formation, Jonggrangan Formation, Sentolo Formation and Alluvium Depositions (Table 1). The Nanggulan Formation (Middle Late Eocene) is composed by sandstones, upwardly transformed into alternating sandstones and lignite-containing clay. The top of the Nanggulan Formation consists of the marl and carbonate sandstones called as the Seputih Member. The Old Andesite Formation (Oligocene) is composed of volcanic breccia, lava, lapilli breccia, lapilli tuff and sandstone, deposited unconformably on Nanggulan Formation. The Jonggrangan Formation (Early Miocene - Late Miocene) is composed by a tuffaceous marl, a carbonate sandstone with lignite inserts that upward turn into a layered limestone and a coral boulder that forms a reef. This formation is unconformable on Old Andesite Formation. The Sentolo Formation (Early Miocene - Pliocene) is composed of limestone, sandstone, fine tuffaceous marl with abundant foraminifera fossils content. The Sentolo formation is unconformable on Old Andesite Formation. While for Alluvium Deposits, Rahardjo (1977) said the Yogyakarta Formation, composed by Merapi volcano rocks and alluvial sediment of the river that is still ongoing until now. This unit is overlay unconformably on the older rock units. Figure 1. Location of research area. 269

3 Table 1. Stratigraphy of Kulon Progo area according to some previous researchers. METHODS Petrographic testing of several rock samples was used to sharpen the analysis and interpretation of sedimentology aspects, particularly aspects of the microfacies of limestones. The classification of limestone types is based on the classification Dunham (1962), whereas non-carbonate rocks classification use Pettijohn s (1975). Paleontological analysis is used to determine the age and depositional environment of the rocks. Analysis of microfacies by Flugel (1982) and facial belt according to Wilson (1975). RESULT AND DISCUSSION Stratigraphic measurements in the Brajan, Banjararum, Kulonprogo regions are regionally included in the Old Andesite Formation and Jonggrangan Formation (Rahardjo et al, 1977). The Old Andesite Formation is composed of andesite breccia, overlain unconformably by Jonggrangan Formation, composed of limestones, sandy limestone and calcareous sandstones (Table 2). The results of the planktonic foraminifera analysis of Jonggrangan Formation in the Brajan region showed Early Miocene - early Middle Miocene (N5 - N9) age, ie the discovery of Globigerina binaiensis Koch, Globigerinoides trilobus (Reuss), Globigerinoides sacculiferus (Brady), Globigeinopides diminutus Bolli, Praeorbulina glomerosa Blow, Orbulina universa D'Orbigny. The results of the benthonic analysis showed that Jonggrangan Formation are deposited in the Inner Neritic Middle Neritic, ie the finding of Amphistegina lessonii D'Orbigny, Operculina complanata Defrance, Buccella parkerae Andrean, Anomalina colligera (Chapman & Parr), Nodosaria sp. Petrographic observations refer to Dunham (1962), Embry & Klovan (1971), the division of 270

4 microfasies according to Flugel (1982), which is the development of facial belts according to Wilson (1975). The observations from the bottom up in the example of SP-BRJ 01 showed floatstone type rock, in the example of SP-BRJ 02 showed rocks of the packstone type. Both rocks are deposited in the foreslope denoted by SMF5 / FZ4. In the example of SP-BRJ 04, SP-BRJ 06, SP-BRJ 07 rocks of sandy lime packestone, deposited in a deep shelf margin denoted by SMF5 / FZ3. At the top of the samples are SP-BRJ 10 and SP-BRJ 11 rocks of the sandy lime wackestone, deposited on open sea shelf denoted by SMF9 / FZ2. The intercalation of non-carbonate rock is calcareous lithic arenite as found in the example of SPBRJ 03, SP-BRJ 05, SP-BRJ 08 and SP-BRJ 09. The first tectonic phase that occurred in Kulon Progo Hill at Oligocene - Early Miocene was followed by active volcanic activity that produced three volcanous were Gajah, Ijo and Menoreh which have source of eruption in high altitude (Bemmelen, 1949). In the research area it is represented by andesite breccia of Old Andesite Formation. In the second tectonic phase of the Early Miocene there was subsidence of Kulon Progo area, causing the height area become the sea and deposited the reef limestone of Jonggrangan Formation. Thus, the stratigraphy in the Kulon Progo Hills shows that the Jonggrangan Formation is unconformably overlain on ride above the Old Andesite Formation. In the research area, sedimentation of limestone of Jonggrangan Formation much influenced by volcanism activities to form a sandy that is sandy lime packstone - sandy lime wackestone. CONCLUSION The Jonggrangan Formation in the Brajan, Banjararum, Kulon Progo region is composed of limestone, sandy limestone, and calcareous sandstone of Early - Middle (N5 - N9), deposited at the inner middle neritic, overlain unconformably on Old Andesite Formation, beginning the deposition of floatstone and packstone in foreslope environment (SMF5 / FZ4), then sedimented of sandy lime packstone in deep shelf margin (SMF5 / FZ3) environment. At the top is deposited sandy lime wackestone in open sea shelf (SMF9 / FZ2). The non-carbonate rock intercalation is calcareous lithic arenite. The deposition of Jonggrangan Formation was still influenced by volcanic activity. 271

5 Table 2. Jonggrangan Formation stratigraphic column in Brajan area. 272

6 ACKNOWLEDGEMENT The authors would like to thank the Chairman of STTNAS who has financed the research and Joint Conference in Japan. REFERENCES Bemmelen, R.W. van The Geology of Indonesia. Vol.1A. Netherland: Government Printing Office, Martinus Nijhoff, The Hague. 732 p. Dunham, R.J Classification of Carbonate Rocks According to Depositional Texture. Dalam Ham, W.W. Classification of Carbonate Rocks. AAPG Mem. p Harsono, P. dan Purnamaningsih, S Stratigraphy and Planktonic Foraminifera of the Eocene Oligocene Nanggulan Formation, Central Java. Geol. Res. Dev. Centre Paleontology Series. Bandung. No. 1, pp Hartono, H.G. dan Pambudi, S Gunung Api Purba Mujil, Kulonprogo, Yogyakarta: Suatu Bukti dan Pemikiran. Prosiding ReTII ke 10. Yogyakarta : STTNAS. Kadar, D Planktonic Foraminifera Biostratigraphy of the Sentolo Formation, Central Java, Indonesia. Proc. the first International Conggres on Pacific Neogene Stratigraphy. Bandung. Pringgoprawiro, H. & Riyanto, B Formasi Andesit Tua Suatu Revisi. Proc. PIT IAGI XVI. Bandung: IAGI. Martodjojo, S. dan Pulunggono, A Perubahan Tektonik Paleogen-Neogen Merupakan Peristiwa Tektonik Terpenting di Jawa. Prosiding Geologi dan Geotektonik Pulau Jawa sejak Akhir Mesozoik hingga Kuarter. Yogyakarta: Jurusan T. Geologi Fak. Teknik UGM. hal Pambudi, S., Sutarman, dan Budiadi, Ev Pola Sedimentasi Formasi Jonggrangan Sentolo di Gunung Kucir Gunung Dlanggung Barat, Kec. Samigaluh dan Kec. Kalibawang, Kab. Kulonprogo. Jurnal Teknologi Nasional, Vol. II No. 1. Yogyakarta :STTNAS. Pettijohn, F.L Sedimentary Rocks. 3rd. Ed. New York: Harper & Row Publ. 628 p. Postuma, J.A Manual of Planktonic Foraminifera. Amsterdam: Elsevier Publ. Co. 420 p. Rahardjo, W., Sukandarrumidi, & Rosidi, H.M.S Peta Geologi Lembar Yogyakarta. Skala 1 : Bandung: Direktorat Geologi. Soeria-Atmadja, R., Maory, R.C., Bellon, Pringgoprawiro, H., Polve, M., & Priadi, B The Tertiary Magmatic Belt in Java. Proc. of Symposium in the Dynamic of Subduction and Its Products. Yogyakarta: Puslitbang Geoteknologi-LIPI. p Sujanto, F. X., and Sumantri, Y. R Preliminary Study of Tertiery Depositional Patterns of Java. Proc. of IPA, 6th and Conv. Jakarta: IPA. pp Suroso, P., Achmad, R., & Sutanto Usulan Penyesuaian Tata Nama Litostratigrafi Kulon Progo, DIY. Proc. PIT XV IAGI. Yogyakarta: IAGI. h Suyanto, F.X. dan Roskamil The Geology and Hydrocarbon Aspect of the South Central Java. Proc. of Indonesion Association of Geologists. Bandung: IAGI. 273

The analysis of volcanic activity influences at the lower and middle part of Sentolo Formation, Kulon Progo using petrographic method

The analysis of volcanic activity influences at the lower and middle part of Sentolo Formation, Kulon Progo using petrographic method Tri Winarno 1,*, Jenian Marin 1, Ilham Hani Pratama 1, and Anis Kurniasih