Indonesian Journal on Geoscience Vol. 1 No. 1 April 2014: 21-34 INDONESIAN JOURNAL ON GEOSCIENCE Geological Agency Ministry of Energy and Mineral Resources Journal homepage: h�p://ijog.bgl.esdm.go.id ISSN 2355-9314 (Print), e-ISSN 2355-9306 (Online) Limestone Microfacies of Baturaja Formation along Air Rambangnia Traverse, South OKU, South Sumatra Sigit Maryanto Centre for Geological Survey, Geological Agency Jln. Diponegoro No. 57 Bandung - 40122 Manuscript received: February 14, 2012, revised: March 18, 2013, approved: April 1, 2014 Corresponding Author: [email protected] Abstract - Limestones of the Baturaja Formation occur at Air Rambangnia traverse, South Ogan Komering Ulu, South Sumatra, and they are used as objects for microfacies studies. The microfacies studies are based on a detailed petro- graphic analysis of thirty four limestone samples, taken from the traverse. Four types of the limestones are identified such as wackestone, packstone, grainstone, and floatstone. At least five microfacies form the limestone succesion of the Baturaja Formation. They are interpreted as sedimentary facies of very restricted bay and pond, back reef local slope, slope and shelf edge, winnowed platform edge sand, and reef flank facies. Keywords: Baturaja, limestone, petrography, microfacies, sedimentary facies Introduction The researched location was along Air Ram- bangnia River, in between Baturaja and Muaradua The term microfacies was first put forward by towns, administratively belonging to the area Brown (1943; in Flugel, 1982). It is defined as of South Ogan Komering Ulu (OKU) Regency, extensively discrete paleontology and sedimen- South Sumatra Province (Figure 1). The carbon- tology aspects, that can be grouped based on the ate rocks from Baturaja Formation are well found type and number of components in petrographic along the Air Rambangnia traverse. This article thin section and polished sample examination. was written with the aim to study the environment Thereby, microfacies identifies environment of and deposition mechanism of those limestones deposition based on petrography data (Maryanto, based on petrography data in relation to the divi- 2005 and 2008). Based on the type and number of sion of limestone microfacies. components, Flugel (1982) divides microfacies of limestone into twenty-four types according to the former division of facies zone by Wilson (1975). Methodology Wilson and Rosen (1998) stated that carbonate platform in the western part of Indonesia has ap- In order to achieve the study purpose, the peared since the Late Oligocene. Bishop (2000a) research method includes field data collection concluded that the IJOGEarly Miocene of Baturaja and laboratory analysis. Field data collection is Formation consists of carbonate platform sedi- a systematical rock sampling, which is based on ments having totally thickness of 60 - 120 m. the results obtained by making detailed strati- Bishop (2000b) divided Baturaja Formation into graphic column along Air Rambangnia traverse. two lithostratigraphic units based on deposition, Laboratory work was done by quantitatively i.e. clastic sedimentary facies and limestone or petrographic analysis with point-counter for as carbonate rock facies. many as 300 counts (Maryanto, 2007a). Important IJOG/JGI (Jurnal Geologi Indonesia) - Acredited by LIPI No. 547/AU2/P2MI-LIPI/06/2013, valid 21 June 2013 - 21 June 2016 21 Indonesian Journal on Geoscience, Vol. 1 No. 1 April 2014: 21-34 o o o o o 102 E 103 Muarabulan 104 105 106 E o o 02 S 02 S Sungailiat JAMBI Bangko SOUTH SUMATRA BANGKA BELITUNG PROVINCE Pangkalpinang Sarolangun 03o 03o Sekayu PALEMBANG bangka Strait Lubuklinggau Argamakmur Kayuagung Prabumulih Curup Muaraenim o Bengkulu o 04 S Lahat 04 S Pagaralam HINDIA OCEANBENGKULU Baturaja Martapura Menggala Manna N LAMPUNG Muaradua Kotabumi 0 100 Km Investigated Traverse o o 102o E 103 104 105 o E Figure 1. Location map of South Sumatra Province and the investigated traverse at Air Rambangnia River. aspects of petrography to be identified include: consisting of granite, andesite-basalt, metasedi- 1. the proportion of major components, such as ment, mélange, and metamorphic rocks. Uncon- carbonate grains, terrigenous grains, matrix, formable overlying the basement rocks there are neomorphism materials, cement, and rock several Tertiary Formations of Kikim, Talangakar, porosities Baturaja, Gumai, Airbenakat, Muaraenim, Ranau, 2. identification of the characters of each com- Kasai, and Alluvium (Gafoer et al., 1986, 1993; ponents, Figure 2). Limestone of the Baturaja Formation 3. texture of rocks that include fabric, sorting, in general was deposited in the back-reef environ- grain size, and shapes. The classification is ment behind the edge of the basin during the Early determined according to Dunham (1962) de- Miocene (Maryanto, 2007b). Layered limestone veloped by Embry and Klovan (1971). can be observed directly along the Air Rambangnia Microfacies interpretation of the limestones traverse. The rocks are generally sloping ramps to from the Baturaja Formation along Air Rambang- the east (Figure 3), with the total thickness of about nia traverse is divided according to the standard 220 m, measurable reach including carbonate rocks classification of microfacies from Flugel (1982) from the Baturaja Formation of 196 m thick. and facies zone from Wilson (1975). As a compari- Volcanic rocks of the Kikim Formation are son, there are also references from many authors presented as a basement. It consists of volcanic that discuss microfacies and limestone depositional breccias, volcanic sandstone, mudstone, and environment, such as Andreeva (2008), Jones and conglomeratic sandstone, with andesite lava inser- Desrochers (1992), Kindler and Hearty (1996), tions. The Baturaja Formation limestone uncon- Read (1985), and TuckerIJOG and Wright (1990). formably overlies the Kikim Formation (Figure 4). The lower part of Baturaja Formation was initiated by the presence of grainstone containing Geological Review some pore-dissolving porosities. Furthermore, the rocks become developed onto layered wackestone- Regional geology in-between Baturaja and packstone that partially argillaceous with oriented Muaradua area is preceded by Pre-Tertiary rocks fossils of mollusks (Figure 5) and algae. Several 22 Limestone Microfacies of Baturaja Formation along Air Rambangnia Traverse, South OKU, South Sumatra (S. Maryanto) 1030 54’ E 1040 15’ E Qa Tma 0 Qtk Qhv N 0 04 06’S BATURAJA ka 04 06’S Sa Tmpm Air 0 10 Km Air Suban Besar Qtk SUMATERA Tma Tpok Batuiputih Tomt Tmb EXPLANATION: 15 Tmg 15 Tmb Qa Alluviumtu Tmg -ba atu 15 INDEX MAP Qv r BTuff Volcanic Unit i Laja Air A a Negerisindang Tmb mb Qhv Volcanic Unit Ta 12 Air 15 Qtk QTk Kasai Formation Penyandingan QUARTERNARY 10 QTr Ranau Formation Tomt 24 Tma Tma Tmpm Muaraenim Formation 17 Tpok 15 Tma Airbenakat Formation 13 Tmg Air Tebangka Qhv Tmg Gumai Formation Qhv Kungkilan Tmb Baturaja Formation 15Air LahatTmpm Tomt Talangakar Formation Tma Tpok Kikim Formation Tpok PALEOGENE MIOCENE Tpokc Cawang Mem. Kikim Fm. Pct Tomt Km MelangeA Complex i r L e Tmg Kjg Garba Formationng k Air Buluh Sundanaj KJgv Insu Mem. Garbaap Fm. Sagarakembang Air Tmb Kjgs KJgs Situlanglang Mem.Sukoraja Garba Fm. Kura-kura Qtk PRE-TERTIARY Kgr Garba Granite Negeriratu Pct Pct Tarap Formation Tpok Qtk Air Rambangnia Traverse Kjgv Tpok Kjgv Air Kiti Tmpm Tma Tmg Air Napalan Tmb Sabahlioh KJgs Qa Tpok Air Gilas Air Saman Qtk Kjg . Kgr Airbungin Tmpm Tmb Baturaja Air Rambangnia Qtk Pct Tanjungkurung Kgr Simpang Qtr Kgr Karangagung Kjgv Pct Tpokc Km Qtr A Umbulanmeliku 15 i Tpokc KJg Saungnaga r M Mehanggin Kgr a la Tmb u Tomt Qv Kotakarang Kjgv Qtr 10 10 Kgr Tmb Air Saka Tanjungbringin Tmb Qa 25 Tpokc 15 Negeriagung Tmg PCt Tma Qa Tomt Qv Air Kemu Air Komering Qtr MUARADUA Qa Tmpm Qtr Qa Tmb Kotamarga 17 Air Selabung Qa Qa Gedong Tmpm Qtr 0 Tmg 0 Tma Qtr Sukaraja Qtr Tmpm Umbulantelok 19 04 35’S 04 35’S 1030 54’E 1040 15’E Figure 2. Geological mapIJOG of Muaradua area, South Sumatra (Gafoer et al., 1993) and locations of Air Rambangnia traverse (Maryanto, 2007a and 2008). floatstone intercalations are found containing some The middle part of Baturaja Formation is coral skeletons. Stylobed is interlayering between composed of floatstone (Figure 6), of which later wackestone-packstone with marl ended the deposi- evolved into argillaceous wackestone. Interlayers tion of the lower part of Baturaja Formation. between floatstone with wackestone-packstone 23 Indonesian Journal on Geoscience, Vol. 1 No. 1 April 2014: 21-34 Kikim Formation Baturaja Formation Alluvium A B 196 m Section A - B Bedded wackestone sometimes argillaceous Argillaceous wackestone with Argillaceous wackestone-mudstone floatstone intercalations Argillaceous wackestone-mudstone with lot of concretions Argillaceous wackestone-mudstone Conglomeratic sandstone overlain Thick bedded floatstone SM326 by packstone Argillaceous wackestone-mudstone SM325B SM325A Volcanic breccia and Bedded floatstone with argillaceous SM324C sandstone with packstone-wackestone SM318B SM324B mudstone and Floatstone and wackestone SM318A 321 SM324A 320 sometimes argillaceous SM317B 8 0 lava intercalations 0 0 SM317A 322 S 04 25’ 08,5” S 04 25’ 10,0”, E 104 09’ 02,6” 319 10 324 12 0 0 SM316B 323 10 E 104 09’ 30,5” S 04 25’ 11,3” To Baturaja SM316A 325 0 Floatstone 318 326 E 104 08’ 40,0” 317 10 312 12 Carbonaceous 8 316 327 314 SM320A B 301 315 mudstone and 313 SM320B A sandstone SM321A SM321B Bedded wackestone-packstone 302 15 311 To Muaradua