Berita Sedimentologi SUMATERA

RReevviiieeww oofff ttthhee PPaalllaaeeoozzooiiicc SStttrraatttiiiggrraapphhyy oofff ttthhee LLaannggkkaawwiii IIsslllaannddss,,, MMaalllaayyssiiiaa ppaaggee 55

AA FFiiieellldd TTrriiipp tttoo ttthhee SSyynn---RRiiifffttt PPeetttrroollleeuumm SSyyssttteemmss oofff CCeenntttrraalll SSuummaattteerraa ppaaggee 1188

SStttuuddeennttt aarrtttiiicclllee::: EEccoonnoommiiicc vvss FFrraacctttuurreedd BBaasseemmeennttt::: AA CCaassee SStttuuddyy fffrroomm NNoorrttthh SSuummaatttrraa BBaassiiinn ppaaggee 2211

Published by

The Indonesian Sedimentologists Forum (FOSI) The Sedimentology Commission - The Indonesian Association of Geologists (IAGI)

Number 27 –August 2013 Page 1 of 31

Berita Sedimentologi SUMATERA

Editorial Board Advisory Board

Herman Darman Prof. Yahdi Zaim Chief Editor Quaternary Geology Shell International Exploration and Production B.V. Institute of Technology, Bandung P.O. Box 162, 2501 AN, The Hague – The Netherlands Fax: +31-70 377 4978 Prof. R. P. Koesoemadinata E-mail: [email protected] Emeritus Professor Institute of Technology, Bandung Minarwan Deputy Chief Editor Wartono Rahardjo Mubadala Petroleum (Thailand) Ltd. University of Gajah Mada, Yogyakarta, Indonesia st 31 Floor, Shinawatra Tower 3, 1010 Viphavadi Rangsit Rd. Ukat Sukanta Chatuchak, Bangkok 10900, Thailand ENI Indonesia E-mail: [email protected]

Mohammad Syaiful Fuad Ahmadin Nasution Exploration Think Tank Indonesia Total E&P Indonesie Jl. Yos Sudarso, Balikpapan 76123 E-mail: [email protected] F. Hasan Sidi Woodside, Perth, Australia Fatrial Bahesti PT. Pertamina E&P NAD-North Sumatra Assets Prof. Dr. Harry Doust Standard Chartered Building 23rd Floor Faculty of Earth and Life Sciences, Vrije Universiteit Jl Prof Dr Satrio No 164, Jakarta 12950 - Indonesia De Boelelaan 1085 E-mail: [email protected] 1081 HV Amsterdam, The Netherlands E-mails: [email protected]; Wayan Heru Young [email protected] University Link coordinator Legian Kaja, Kuta, Bali 80361, Indonesia Dr. J.T. (Han) van Gorsel E-mail: [email protected] 6516 Minola St., HOUSTON, TX 77007, USA www.vangorselslist.com Visitasi Femant E-mail: [email protected] Treasurer Pertamina Hulu Energi Dr. T.J.A. Reijers Kwarnas Building 6th Floor Geo-Training & Travel Jl. Medan Merdeka Timur No.6, Jakarta 10110 Gevelakkers 11, 9465TV Anderen, The Netherlands E-mail: [email protected] E-mail: [email protected]

Rahmat Utomo Peter M. Barber PhD Mubadala Petroleum (Thailand) Ltd. Principal Sequence Stratigrapher 31st Floor, Shinawatra Tower 3, 1010 Viphavadi Isis Petroleum Consultants P/L Rangsit Rd. 47 Colin Street, West Perth, Western Australia 6005 Chatuchak, Bangkok 10900, Thailand E-mail: [email protected] E-mail: [email protected]

Cover Photograph:

The contact of Sawahlunto Formation (dark color at the bottom part) and Sawahtambang Formation (bright color) outcrop near Sawahlunto city – West Sumatera. Taken in June 2012.

Photo courtesy of Kirandra Ferari and Peri Raudatul Akmal from IAGI Riau. • Published 3 times a year by the Indonesian Sedimentologists Forum (Forum Sedimentologiwan Indonesia, FOSI), a commission of the Indonesian Association of Geologists (Ikatan Ahli Geologi Indonesia, IAGI). • Cover topics related to sedimentary geology, includes their depositional processes, deformation, minerals, basin fill, etc.

Number 27 –August 2013 Page 2 of 31

Berita Sedimentologi SUMATERA

Berita Sedimentologi

A sedimentological Journal of the Indonesia Sedimentologists Forum (FOSI), a commission of the Indonesian Association of Geologist (IAGI)

From the Editor Welcome to Berita Sedimentologi prepared by Andrew Carnell and a Invitations have been sent out to number 27! student article on fractured potential contributors to seek basement in the Malacca Strait by articles for both volumes. We We’re very pleased to deliver Ignatius Primadi. hope to get enough responses for another volume of Berita future publications and in the Sedimentologi to you. In this 27th Lee Chai Peng submitted an meantime, we hope you will edition of Berita Sedimentologi, article on stratigraphy of the benefit from the current edition of we received 5 articles, including 2 Langkawi Island, Malaysia; and a Berita Sedimentologi. See you articles from students to show group of students from again in November. our commitment to engage their Diponegoro University in Central interest in publishing their work Java wrote a short article on Warm Regards, on sedimentology/stratigraphy. depositional environment analysis of Kali Banyumeneng (Demak, Berita Sedimentologi No. 27 Central Java). focuses on Sumatra island however only three articles will We would like to remind you of discuss about Sumatra, while the our plan for near future rest of them are on other areas. publication themes as follow: The articles on Sumatra include a • BS#28 Borneo: to be published short communication on late in November 2013 synrift turbidite systems in the • BS#29 SE Asia Biostratigraphy Minarwan North Sumatra Basin written by to be published in early 2014 Deputy Chief Editor Lawrence (Trey) Meckel, a field trip report to Central Sumatra

INSIDE THIS ISSUE

Book Review : The SE Asian Getway: History and Tectonic of the Australian- Review of the Palaeozoic Stratigraphy of Student article Asia Collision, editor: Robert Hall et al – T.J.A. Reijers the Langkawi Islands, Malaysia – Lee Chai 5 Economic vs Fractured Basement: A Case 21 56 Peng Study from North Sumatra Basin – Ignatius Primadi

Short communication Student article Book Review - Biodiversity, Late Syn-Rift Turbidite Systems in the 15 Depositional Environment Analysis of Kali 26 Biogeography and Nature Conservation 58 North Sumatra Basin – Lawrence D. Meckel, Banyumeneng, Mranggen, Kabupaten in Wallacea and New Guinea (Volume 1), III Demak – Samuel R.N. Simorangkir et al. Edited by D. Telnov, Ph.D. – H. Darman

A Field Trip to the Syn-Rift Petroleum System of Central Sumatera – Andrew 18 Carnell et al.

Call for paper BS #28 – focus in Borneo to be published in November 2013

Number 27 –August 2013 Page 3 of 31

Berita Sedimentologi SUMATERA

About FOSI

he forum was founded in FOSI has close international team. IAGI office in Jakarta will 1995 as the Indonesian relations with the Society of help if necessary. TSedimentologists Forum Sedimentary Geology (SEPM) and (FOSI). This organization is a the International Association of commu-nication and discussion Sedimentologists (IAS). forum for geologists, especially for Fellowship is open to those those dealing with sedimentology holding a recognized degree in and sedimentary geology in geology or a cognate subject and Indonesia. non-graduates who have at least two years relevant experience. The forum was accepted as the sedimentological commission of FOSI has organized 2 the Indonesian Association of international conferences in 1999 The official website of FOSI is: Geologists (IAGI) in 1996. About and 2001, attended by more than 300 members were registered in 150 inter-national participants. 1999, including industrial and http://www.iagi.or.id/fosi/ academic fellows, as well as Most of FOSI administrative work students. will be handled by the editorial

FOSI Membership

Any person who has a background in geoscience and/or is engaged in the practising or teaching of geoscience or its related business may apply for general membership. As the organization has just been restarted, we use LinkedIn (www.linkedin.com) as the main data base platform. We realize that it is not the ideal solution, and we may look for other alternative in the near future. Having said that, for the current situation, LinkedIn is fit for purpose. International members and students are welcome to join the organization.

FOSI Group Member as of AUGUST 2013

Number 27 –August 2013 Page 4 of 31

Berita Sedimentologi SUMATERA

Review of the Palaeozoic Stratigraphy of the Langkawi Islands, Malaysia

Lee Chai Peng University of Malaya, Kuala Lumpur Corresponding Author: [email protected]

INTRODUCTION outcrops due to numerous recent development projects on the islands. A helpful compilation of The Langkawi group of 99 islands off the published and unpublished geological researches northwest coast of Malaysian Peninsula is located on Langkawi was compiled by Sarman et al. some 30 km off the coast of Perlis and 112 km (1997). north of Penang. These islands are a paradise for geologists, including some of the best and most The spectacular geological heritage of the islands interesting exposures of Palaeozoic sedimentary heralded the formation of the Langkawi rocks in Malaysia, ranging in age from Cambrian Geoforestpark by the Kedah State Government, to Permian. These consist of both clastics and Malaysia in May 2006 to preserve and display its carbonates, deposited within a range of unique geological features. The Geoforestpark was depositional and palaeoclimatic conditions ranging endorsed by the United Nations Educational, from shallow marine shoreface to turbidites with Scientific and Cultural Organization (UNESCO) dropstones. In addition, these sedimentary rocks under the Global Network of National Geoparks in had been intruded by younger Mesozoic granites June 2007 (Leman et al., 2007). with considerable contact metamorphic effects. REGIONAL GEOLOGICAL SETTING Since the initial publication of the Geological Map of Langkawi and the subsequent Geology and Langkawi is located within the Northwestern Mineral Resources Memoir 17 on the States of Domain of the Western Belt of Peninsular Malaysia Perlis, North Kedah and the Langkawi Islands, (Figure 1) which is an integral part of Sundaland, both by Jones (1966, 1981) many more recent the SE Asian extension of the Eurasian plate. studies had been carried out. These studies were particularly facilitated by the creation of new

Figure 1. Location map of Langkawi Islands. The three belts and northwestern domain within the Western Belt are after Lee

(2009). Sumatra map is after

Darman & Sidi (2000).

Bentong- Raub suture

Number 27 –August 2013 Page 5 of 31

Berita Sedimentologi SUMATERA

The Paleozoic sedimentary rocks of Langkawi are Basin, have been affected by Neogene block mostly shallow-marine shelf type deposits that faulting caused by back arc extension associated extend within a broad linear belt from South with the continuous northwards push of the China, through Burma, Thailand, and northwest Australian Plate under the Eurasian Plate (Raj et Peninsular Malaysia into northern Sumatra. These al., 2009). sediments form part of the Sibumasu Block which broke away from northwestern Australia at the STRATIGRAPHY OF LANGKAWI northern edge of Gondwanaland, to subsequently collide with the Indochina or East Malaya block The Palaeozoic sedimentary rocks in Langkawi are along the Bentong-Raub Suture during the traditionally subdivided into four formations Triassic (Metcalfe, 2000; Hutchison, 2009a). The (Jones, 1981), although newer more detailed above-mentioned Northwestern Domain is part of stratigraphic subdivisions have been proposed the Patani Metamorphic Terrane related to this (Cocks et al. 2004; Meor and Lee, 2004; Lee, plate tectonic suturing episode. 2009). These units are, from the oldest to the youngest, the Machinchang, Setul, Singa and Cenozoic uplift of the Langkawi chain of islands is Chuping Formations. Their geographical related to the peripheral effects of later Neogene distribution and stratigraphic relationships are collision of India with Tibet creating the Himalayas given in Figures 2, 3 and Figure 4, respectively. as well extrusion of Sundaland to the southeast They are mostly shallow marine shelf type deposits (Tapponier et al., 1982). In addition, the Langkawi and are discussed as follows: islands, being geographically located on the northern cratonic margin of the North Sumatra

Figure 2. Revised stratigraphy of Palaeozoic rocks up to the Singa Formation in the Northwestern Zone of

Peninsular Malaysia (after Lee, 2009).

Number 27 –August 2013 Page 6 of 31

Berita Sedimentologi SUMATERA

Figure 3. Geological map of Langkawi Islands showing distribution of the various rock formations in the islands (after Leman et al., 2007). Common stops on field trip are numbered in circles.

1. Machinchang Formation interbeds of conglomerates, phyllitic slates and tuffs exposed in the northwestern corner of The Machinchang Formation type locality is Langkawi. It has been divided into three members derived from the conspicuous long serrated (Figure 6) according to Lee (2006) with a coarser quartzite ridge of five peaks aptly called Gunung sandy middle member sandwiched between two Machinchang or Mat Chinchang meaning finer grained members. The overall depositional “chopped-up mountain” (Figures 5a & 5b). environment is that of a high-destructive, wave- dominated delta which had built over an offshore This formation is composed of a thick succession shelf deposit to produce a series of barrier-beach of predominantly arenaceous rocks with minor sands cut by small channels (Lee, 2006).

Number 27 –August 2013 Page 7 of 31

Berita Sedimentologi SUMATERA

Figure 4. Stratigraphy and major events in geological history of Langkawi islands (after Leman et al., 2007).

a b

Figure 5. a) “Chopped up” Machinchang Range view from the south; b) Machinchang Formation deltaic sandstone beds in western limb of anticline dipping steeply into Malacca Strait.

In the Machinchang area these rocks spectacularly 1983). The base of the formation is not exposed outcrop as an asymmetrical anticline with a and the oldest part of the formation is the pelitic relatively undisturbed western limb that dips and rocks exposed in the core of the Machinchang plunge into the waters of the Straits of Malacca Anticline at Teluk Datai. The top of the formation (Figure 5b). Up section occurs a gentler more has several thin calcareous horizons before dome-like eastern limb that probably had been passing conformably up into the succeeding Setul uplifted by underlying Mesozoic granite (Lee, Formation limestone near Teluk Sabong.

Number 27 –August 2013 Page 8 of 31

Berita Sedimentologi SUMATERA

Figure 6. Stratigraphy of the Machinchang Formation (after Lee, 2006).

Number 27 –August 2013 Page 9 of 31

Berita Sedimentologi SUMATERA

Interesting trace fossils including Dictyodora (Lee, Langgun. The formation has been estimated to be 1980) and sedimentary structures such as various about 1500 m thick and was raised to group types of cross-beddings, convolute bedding and status in Cocks et al. (2005) and Lee (2009). load casts can be seen in the upper parts of the formation at Pasir Tengkorak and Pulau Jemurok. The Setul Formation is made up of predominantly Palaeocurrent studies on the abundant cross- dark coloured shelfal limestone with minor black beddings found in the formation gave a detrital bands. It is largely metamorphosed on the predominantly westward downcurrent direction. main island but good fossiliferous outcrops of the limestone are present in the vicinity of Pulau The Machinchang Formation is poorly fossiliferous Langgun. The impure limestone contains a rich and only poorly preserved fragments of trilobites fauna of fossils such as gastropods, bivalves, and brachiopods had been found at Tg. Buta and nautiloids, brachiopods, trilobites, crinoids and Pulau Jemurok. Better preserved fossilized saukid stromatolites while the hardened black mudstones trilobites and orthid brachiopods are found on have preserved graptolites, tentaculitids and Tarutao Island just 5 km north of Langkawi in trilobites. Thailand which give a Late Cambrian to Early Ordovician age to the uppermost part of the The unusual scyphocrinoid, probably Machinchang Formation. This is confirmed by Camarocrinus (Figure 7), with its calcareous fission track studies on zircon crystals which give floating lobolith has been discovered (Lee, 2005) an age of 555±37 Ma. from the top part of the Upper Setul limestone at Teluk Mempelam on Pulau Langgun. It is Acid volcanics or tuffs also occur as thin, fine restricted in age to the uppermost Pridolian- grained, pale green layers in the Machinchang lowermost Lochkovian (Late Silurian to Early Formation indicative of acid volcanism during Devonian) and enables correlation with similar Cambrian times. limestones in Myanmar (Ayeko Aung, pers comm. 2010). Microfossils such as conodonts and 2. Setul Formation ostracods are also found in these limestones.

The Setul Formation ranges in age from Early 3. Rebanggun Beds Ordovician to Early Devonian. It is divisible into a Lower Setul Formation of Ordovician age, The quartzitic sandstones and red to grey occurring below the Lower Detrital Band on Pulau mudstones known as the Rebanggun Beds outcrop Langgun and a Silurian to Devonian Upper Setul on Pulau Rebak Besar and Pulau Rebak Kecil and Formation above this band (Figure 4). The top of have been grouped together with similar beds the formation is represented by the Upper Detrital found above the Setul Formation at Pulau Band, a largely arenaceous unit with minor Langgun. argillaceous beds at Teluk Mempelam on Pulau

Figure 7. Upper Setul limestone bed with scyphocrinoid loboliths at Teluk Mempelam,

Pulau Langgun, northeast Langkawi.

Number 27 –August 2013 Page 10 of 31

Berita Sedimentologi SUMATERA

Correlation with better exposed sequences in Perlis (Visėan) based on Macrobole and its stratigraphic has placed the Langgun Redbeds higher up instead position above Late Touraisian chert beds. These of at the base of the transitional unit (Lee, 2009) to fossiliferous mudstones and associated sandstones the Singa / Kubang Pasu Formations. Fossils in that are pebbly in places were deposited in a quiet this unit are sparse and consist of small prodelta environment with occasional turbiditic ambocoeliid brachiopods, Posidonomya (Posidonia) input. These redbeds are quite widespread and bivalves and the trilobite Macrobole kedahensis. correlatable with the Khao Chunong Formation in The age of the unit is probably Early Carboniferous south Thailand. (Sakhmarian) age (Waterhouse,1982; Leman, 4. Singa Formation 2003). Other associated fossils are bryozoa, bivalves, gastropods, corals and crinoid stems. The Singa Formation is best exposed in the Sandstone beds are few and often calcareous. southwestern part of Langkawi. The basal contact with the Rebanggun Beds is unexposed and the The formation can be correlated with similar top is gradational into the overlying Chuping glacial marine diamictites found in the Mergui, Formation limestone that is exposed on Pulau Martaban and Lebyin Groups of Myanmar, the Singa Kecil. Kaeng Krachan Formation of the Phuket Group in Thailand and the Bohorok Formation of Sumatra. The age of the formation is probably Carboniferous to Early Permian. The Singa Formation, named 5. Chuping Limestone after Pulau Singa Besar, is a clastic unit typified by crudely laminated, dark grey, poorly sorted The Chuping Limestone is a unit of thickly bedded mudstones with scattered dropstone horizons. The to massive, light coloured limestone (Figure 9) that dropstones range in size from granules to boulders sits conformably above the Singa Formation in the (Figure 8) and are mainly composed of sandstone southeastern part of the island. It can be easily with subordinate limestone, vein quartz, granitic, distinguished from the more clayey and darker volcanic and metamorphic rocks. coloured Setul limestone.

They have been interpreted as glacial marine The Chuping limestone is fossiliferous in its basal dropstones derived from peri-Gondwana margin ice part with fusulines, brachiopods, bivalves, sheets during the Carboniferous (Stauffer & gastropods, corals, bryozoans and algae ranging Mantajit, 1981; Stauffer & Lee, 1986). Fossils are from a late Early Permian or early Middle Permian only common in its uppermost section but burrows age in Langkawi to the Triassic on the mainland and soft sediment deformation structures can be (Metcalfe, 1990). Chert nodules are common at its found in some parts. Long paired vertical burrows base in Pulau Singa Besar. The once famous exceeding a meter in length are found on Pulau Langkawi marble is a white saccharoidal Tepor. The brachiopods found in the uppermost ornamental stone quarried from metamorphosed part of the formation associated with dropstone equivalents of this limestone in southeastern horizons at Kilim, Batu Asah and Pulau Singa Langkawi and Pulau Dayang Bunting. Besar are “cool-water” forms of Permian

Figure 8. Glacial marine dropstones in pebbly mudstone horizon in Singa Formation at Pulau Ular.

Number 27 –August 201 3 Page 11 of 31

Berita Sedimentologi SUMATERA

Figure 9. White coloured marble of Chuping Formation behind former Kedah Marble factory near Kisap.

Figure 10. Tourmaline-quartz vein in Langkawi granite block.

Mesozoic Igneous Rocks Late Cretaceous in age while the smaller pluton in Pulau Tuba is Late Triassic in age. The granites Two granitic bodies are found in the islands. The are petrographically similar and hard to Raya and Tuba granites cover some 113 km2 of the distinguish in the field. Both are porphyritic biotite islands. The huge Gunung Raya massif which rises granites with tourmaline clots and veins (Figure to 878 m forms the highest part of the island. It is 10).

Number 27 –August 2013 Page 12 of 31

Berita Sedimentologi SUMATERA

Large K-feldspar phenocrysts and spherical quartz Hutchison, C.S., 2009 a, Bentong-Raub Suture. In: phenocrysts are common. Alignment of the large Hutchison, C.S. and Tan, D. N. K. (eds.) Geology K-feldspar crystals is common at the margins of of Peninsular Malaysia: Univ. Malaya & the plutons. The Raya Granite appears to be the Geological Society of Malaysia. p. 43-53. most southerly body of a belt of Late Cretaceous Hutchison, C.S., 2009 b, Tectonic Evolution. In: granite extending from west Thailand. Hutchison, C.S. and Tan, D. N. K. (eds.) Geology of Peninsular Malaysia: Univ. Malaya & Metamorphic Rocks Geological Society of Malaysia. p. 309-330. Jennings, J. R. and Lee, C. P., 1985, Preliminary Langkawi occurs within the Patani Metamorphic note on the occurrence of Carboniferous-age Terrane which trends northwest from mainland coals and in situ plant fossils in Eastern Kedah (Khoo, 1984) Rocks older than mid- Peninsular Malaysia: Geological Society Permian within this terrane have suffered severe Malaysia Newsletter, 11 (3), p. 117-121. deformation and low grade regional metamorphism Jones, C.R., 1981, Geology and mineral resources related to the collision of the Sibumasu micro-pl ate of Perlis, North Kedah and the Langkawi with Indochina Rocks of the Machinchang, Setul Islands: Geological Survey Malaysia District and the Singa Formations have developed at least Memoir, 17, 275 pp. (includes a detailed one set of low angle cleavages. geological map of Langkawi). Mohammed, K., Ali C.A., and Leman, M. S., 2007, These rocks occur as slates, phyllites, quartzites Ancient Higher Sea Level. I n : Mohd Shafeea and fine grained marbles where unaffected by later Leman, Kamarulzaman Abdul Ghani, Ibrahim contact metamorphism while rocks adjacent to the Komoo & Norhayati Ahmad (eds). Langkawi granites have recrystallized to mica schists, coarse Geopark : LESTARI, Universiti Kebangsaan grained marbles and tough metaquartzites. Small Malaysia. 113 pp. bodies of skarn have developed at the contacts Khoo, T.T., 1982, Pulau Puchong – a possible new between the igneous intrusions and some of the Setul limestone in the Langkawi area, Kedah: limestones. Malaysian Journal of Science, 7, p.103-111. Khoo, T.T., 1984, The terrane of the Patani CONCLUSIONS Metamorphics: Geological Society Malaysia Bulletin, 17, p. 79-95. Langkawi plays an important role in the Khoo, T.T., and Tan, B.K., 1983, Geological palaeogeographic reconstruction of the evolution of Peninsular Malaysia: Proceedings of northwestern part of Peninsular Malaya. the Workshop on Stratigraphic Correlation of Thailand and Malaysia, Geological Societies of The discovery of Lower Permian (Sakmarian) cool- Thailand and Malaysia. Vol. 1, p. 253-290. water shelly fauna particularly brachiopods in the Kimura, T., and Jones, C.R., 1967, Geological Singa Formation (Waterhouse,1982; Leman, 2003; structures in the northern and southern parts Shi et al., 1997) in addition to glacial marine of the Langkawi islands, northwest Malaya: dropstones (Stauffer & Mantajit, 1981; Stauffer & Geology and Palaeontology of Southeast Asia, 3, Lee, 1986) has enabled correlation with similar p.123-134. deposits in the Canning Basin of Australia Koopmans, B. N., 1965, Structural evidence for a (Hutchison, 2009b). This establishes the Palaeozoic orogeny in northwest Malaya: connection of Langkawi to Gondwana in pre-Late Geological Magazine, 102, p. 501-520. 34th IGC Permian times, when it formed part of the Excursion MY-1 18 Sibumasu microcontinent. Lee, C. P., 1980, A comparison of the supposed graptolites of the Tarutao Formation, Ko Sibumasu subsequently drifted north into lower Tarutao, with Dictyodora trace fossils found in palaeo-latitudes and eventually collided with the the Machinchang Formation, Pulau Jemurok, warmer climate provinces of the Indochina Block of Langkawi: Geological Society Malaysia Cathaysia, along the Bentong-Raub Suture of Newsletter, 6 (3), p. 69-74. Peninsular Malaysia during the Late Triassic. Lee. C. P., 1983, Stratigraphy of the Tarutao and Machinchang Formation: Proceedings of the SELECTED REFERENCES Workshop on Stratigraphic Correlation of Thailand and Malaysia, Geological Societies of Cocks, L. R. M., Fortey, R. A. and Lee, C. P., 2005, Thailand and Malaysia. Vol.1, p. 20-38. A review of Lower and Middle Palaeozoic Lee, C. P., 2005, Discovery of plate-type biostratigraphy in west peninsular Malaysia and scyphocrinoid loboliths in the uppermost southern Thailand in its context within the Pridolian lowermost Lochkovian Upper Setul Sibumasu Terrane: Journal of Asian Earth limestone of Peninsular Malaysia: Geological Sciences, 24. p. 703-717. Journal, 40, p. 331-342. Hutchison, C.S., 1973, Tectonic evolution of Lee, C. P., 2006, The Cambrian of Malaysia: Sundaland: a Phanerozoic synthesis: Geological Palaeoworld,15. p.242-255. Society Malaysia Bulletin, 6, p. 61-68. Lee, C. P., 2009, Palaeozoic Stratigraphy. In: Hutchison, C.S. and Tan, D. N. K. (eds.) Geology

Number 27 –August 2013 Page 13 of 31

Berita Sedimentologi SUMATERA

of Peninsular Malaysia: Univ. Malaya & Peninsular Malaysia: Univ. Malaya & Geological Geological Society of Malaysia. p. 55-86. Society of Malaysia. p.249-269. Raj, J. K., Tan, D. N. K, and Wan Hasiah Abdullah, Raj, J.K, Tan, D.N.K, and Wan Hasiah Abdullah. 2009, Cenozoic Stratigraphy. I n : Hutchison, C. 2009, Cenozoic Stratigraphy. I n : Hutchison, C.S S., and Tan, D. N. K. (eds.) Geology of & Tan, D. N. K. (eds.) Geology of Peninsular Peninsular Malaysia: Univ. Malaya & Geological Malaysia: Univ. Malaya & Geological Society of Society of Malaysia. p. 133-173. Malaysia. p. 133-173. Sarman, M., Komoo I., and Desa. K.M., 1997, Shi, G. R., Leman M. S.,and Tan, B.K., 1997, Early Status Permuliharaan Sumber Geologi Di Permian Brachiopods from the Singa Formation Malaysia: I n Ibrahim Komoo,Mohd Shafeea of Langkawi Island, Northwestern Peninsular Leman, Kadderi Md Desa & Ibrahim Abdullah Malaysia: Biostratigraphical and (eds.) Warisan Geologi Malaysia (Geological Biogeographical Implications. In: Phisit Heritage of Malaysia): LESTARI UKM, p.13-46. Dheeradilok & others (eds): Proceedings of the Meor, H. H., and Lee, C. P., 2005, The Devonian- International Conference on Stratigraphy and Lower Carboniferous succession in Northwest Tectonic Evolution of Southeast Asia and South Peninsular Malaysia: Journal of Asian Earth Pacific, p. 67-72. Sciences, 24. p. 719-738. Stauffer P. H., and Lee, C. P., 1986, Late Paleozoic Metcalfe, I., 1990, Stratigraphic and tectonic glacial marine facies in Southeast Asia and its implications of Triassic conodonts from implications: GEOSEA V Proceedings Vol. II, northwest Peninsular Malaysia: Geological Geological Society Malaysia Bulletin, 20, p. 363- Magazine, 127, p. 567-578. 397 Metcalfe, I., 2000, The Bentong-Raub suture zone: Stauffer, P.H., and Snelling, N. J., 1977, A Journal of Asian Earth Sciences, 18, p. 691- Precambrian trondhjemite boulder in Palaeozoic 712. mudstones of NW Malaya: Geological Magazine, Leman.M.S., 2003, An Early Permian (Early 114, p. 479-482. Sakmarian) brachiopod fauna from the Sungai Tan, B.K., 1981, On the supposed existence of the Itau Quarry and its relationship to other Early Kisap Thrust in the Langkawi Islands, Permian brachiopod horizons in Langkawi, northwest Peninsular Malaysia: Geological Malaysia: Geological Society Malysia Bulletin, Society Malysia Bulletin, 14, p. 127-133. 46, p. 155-160. Tapponier, P., Peltzer, G., Le Dain, A.Y., Armijo, R., Leman, M.S., Komoo, I., Mohamed, K.R., Ali C., and Cobbold, P., 1982, Propagating extrusion and Tanot Unjah. T., 2007, Geology and tectonics in Asia, new insights from simple Geoheritage. I n : Mohd Shafeea Leman, experiments with plasticene: Geology, 10, Kamarulzaman Abdul Ghani, Ibrahim Komoo & p.611-616. Norhayati Ahmad (eds). Langkawi Geopark: Tjia, H.J., 1993, The Kisap Thrust in the Kampung LESTARI , Universiti Kebangsaan Malaysia, p. Kilim area, Pulau Langkawi: Geological Society 43-86. Malaysia Newsletter, 19, p. 247-250. Leman, M.S., Ghani, K.A., Komoo I., and Ahmad Wakita, K., and Metcalfe, I., 2005, Ocean plate N., (eds). 2007. Langkawi Geopark: LESTARI , stratigraphy in East and Southeast Asia: Universiti Kebangsaan Malaysia. 113 pp. Journal of asian Earth Scioences, 24, p. 679- Shuib. M. K., 2009, Major Faults. I n : Hutchison, 702. C.S., and Tan, D. N. K. (eds.) Geology of Waterhouse, J.B., 1982, An early Permian cool- water fauna from pebbly mudstones in South Thailand: Geological Magazine, 119, p. 337-354.

Number 27 –August 2013 Page 14 of 31

Berita Sedimentologi SUMATERA

Short communication Late Syn-Rift Turbidite Systems in the North Sumatra Basin

Lawrence D. Meckel, III Pexco Energy (Zaratex N. V.), Jakarta, Indonesia Corresponding Author: [email protected]

The North Sumatra Basin (NSB, Figure 1) in tectonic subsidence and a rise in eustatic sea level. Indonesia is one of the most prolific petroleum Water depths reached several hundred meters provinces in SE Asia. It has been affected by (bathyal paleobathymetries), and slope and basin- rifting, transtensional and transpressional shear, floor turbidite systems of the Bampo Formation and compression from the Paleogene to present (Figure 2) filled the newly-created accommodation day. This complex tectonic history has created space. Time-equivalent basement highs are numerous opportunities for petroleum exploration, characterized by unconformities or condensed, including an inverted deepwater turbidite play shallow marine deposits. (Figures 2 and 3) that has been relatively under- explored to date. Intra-formational, deep marine Bampo shales act as competent seals for individual turbidite sands During the late syn-rift stage of basin evolution (Figure 2). The shale-prone stratigraphy of the (Late Oligocene-Early Miocene), N-S to NE-SW stratigraphically younger Baong Formation acts as oriented half-grabens in the central and northern a regional seal, across which overpressures tend to part of the NSB (Figure 3) were subjected to rapid increase with depth (Figure 2). flooding, as a result of the complimentary effects of

Figure 1. Location map of study area (red box) in southern part of North Sumatra Basin relative to historical well database and existing oil (green) and gas (red) discoveries. Despite significant success in the onshore and on the shelf, fewer than 40 wells have been drilled in water depths greater than 100 m. Inset, upper right shows ultimate recoverable reserves (URR) for the 13 largest basins in SE Asia. Bubble size is scaled to UR. More than 6 billion barrels of oil equivalent have been discovered in the NSB. Inset, lower left, shows the creaming curve for the NSB. Note that exploration activity has been negligible in the past decade.

Number 27 –August 2013 Page 15 of 31

Berita Sedimentologi SUMATERA

Bampo Bampo Bampo Bampo

Bampo

Seal Reservoir/Trap Source

Figure 2. Stratigraphy and petroleum system elements of the North Sumatra Basin. Late syn-rift (Bampo) turbidites, highlighted by yellow arrows, are the subject of this paper.

Figure 3. Seismic section illustrating inverted syn-rift structure in the study area. Reservoir presence is demonstrated in regional wells. All wells have encountered hydrocarbon shows, although none is optimally placed to test the inverted syn-rift play.

During the late Miocene to Quaternary, dextral hydrocarbons in the Mergui Basin, the northern transpression on NW-SE oriented faults and N-S equivalent of the NSB, offshore Thailand. oriented compression formed a series of inverted structures, with potential hydrocarbon traps in 4- Bampo marine shales are the most probable way dip-closures at Parapat and Bampo levels source rocks (Figure 2). The Bampo source rock (Figure 3). These traps have not been tested in the has been typed to the gas-condensate at the super- Indonesian portion of the NSB, but contain giant Arun gas-condensate field.

Number 27 –August 2013 Page 16 of 31

Berita Sedimentologi SUMATERA

50 km N Increasing Topography Increasing Bathymetry

Basin Floor Figure 4. Simplified map of late syn -rift architecture, offshore North Sumatra Basin. Map is a smoothed grid of interpreted top Basin basement based on 2D and Floor 3D seismic, and is Continental Basin corrected to reflect Shelf Floor paleobathymetries inferred from well results (well locations not shown). Red Basin arrows indicate possible Basin Floor deepwater sediment Continental dispersal fairways. Floor Basin Shelf Subsequent tectonic Floor inversion of these sand- prone fairways creates an under-explored play concept in the basin.

It is a very lean source rock, with typical TOC values less than 1%, but has a demonstrated This wildcat inversion play has not been explored capacity to charge multi-TCF gas fields across the previously in the NSB because it only occurs in the NSB, so must be considered to be an ultra-prolific offshore part of the basin, where good-quality 3D - if not particularly spectacular - source rock. seismic data, only recently acquired, are necessary Older, syn-rift lacustrine shales, which could be to adequately characterize prospects. The play has liquid-prone, may also act as potential source high volumetric potential, and most aspects of the rocks (Figure 2). Their presence across the basin is petroleum system have been proven previously. much more speculative, though, and they have not The play concept is also relatively under-explored been definitively typed to any hydrocarbon elsewhere in southeast Asia, and opens accumulations. Migration is postulated to occur possibilities in other basins in the region (Figure from deep grabens, which thermal models show to 4). be in oil to post-mature temperature windows, up carrier beds and faults into closures.

Number 27 –August 2013 Page 17 of 31

Berita Sedimentologi SUMATERA

A Field Trip to the Syn-Rift Petroleum System of Central Sumatera

Andrew Carnell1, Chris Atkinson2 and Peter Butterworth3 1Shell Egypt 2Worldwide Petroleum Services 3BP Indonesia

In September 2012, a field trip was run by the Day 1 Basement and Regional Geology (SYN-RIFT) authors above into the Ombilin Basin of West Day 2 Source Rock (SYN-RIFT) Sumatra province to examine outcrop analogs of Day 3 Reservoirs (EARLY POST-RIFT) the syn-rift petroleum system of Central Sumatra Day 4 Syn-rift Reservoirs (SYN-RIFT) (Figure 1). This was organized by SEAPEX and AAPG as part of the AAPG International DAY 1 - BASEMENT AND REGIONAL Conference held in Singapore. The field trip started GEOLOGY and finished in Padang but was conducted in the Barisan mountains amidst the stunning scenery of The aim of the field trip stops on the first day was West Sumatra. to study the basement geology and to set the regional setting for the remainder of the field trip. Rift basin evolution is a key component of the Complex structural aspects were addressed, with petroleum systems of many Southeast Asian reference to the problems associated with basins (e.g. South Sumatra Basin, Sunda Basin). deciphering Oligocene rift related structures Syn-rift lacustrine mudstones are prolific oil prone subsequently modified by strike slip deformation source rocks and syn-rift and early post-rift and the Plio-Pleistocene Barisan mountain uplift. clastics sediments can provide excellent reservoir intervals. Rift petroleum systems are, however, Basement in the area is varied with metamorphic, geologically complex and hydrocarbon exploration igneous and sedimentary lithologies all exposed. within them requires a greater knowledge of the Basement sediments are both clastic and structures and sedimentological evolution of the carbonate in nature and range in age from Lower basin than is often the case elsewhere. Local Carboniferous to Triassic. Sediments are widely factors such as provenance and rift related metamorphosed. The igneous component to the tectonic activity can have a significant impact on basement is largely of an intrusive nature with the quality, quantity and distribution of source, granites dominant. Radiometric dating on a variety reservoir and seal. of exposures gives late Permian to early Miocene ages with most basement igneous activity The field trip was conducted over four days with occurring in the Mesozoic. each day concentrating on a separate aspect of the petroleum system as follows:

Figure 1. West Sumatra, showing location of principle outcrops visited. The Karbindo mine is in the highly fragmented Kiliran Sub-basin to the east. The Harau Canyon is on the north eastern margin of the Payakumbuh Basin.

Number 27 –August 2013 Page 18 of 31

Berita Sedimentologi SUMATERA

Unfortunately it was not practical to visit all the differing types of basement have a variable basement lithologies present in the area, although influence on topography, tectonism, sediment a representative selection were examined. These supply and water chemistry. studied outcrops give a good indication of how Botrycoccus spp. rich assemblage. Deposition of DAY 2 – SOURCE ROCK the lower Brown Shale interval was in a shallow lake with a strongly stratified water column. The second day of the field trip was spent at the Karbindo Coal Mine, an open cast coal mine in The middle of the studied succession comprises which the Eocene Brown Shale is very well exposed beds of Goniobasis-like and Viviparus-like (Figure 2). This is a remarkable exposure since it is reworked gastropods. This interval weathers red one of the few places around the world where by and shows a slight reduction in organic content walking up through the mine it is possible to walk (TOC 2.58% - 5.94%) and source quality (HI 424- up through the evolution of a syn-rift lacustrine 547). Palynological data indicate a change in algal system. forms present with abundant Pediastrum spp recorded. This middle section of the Brown Shale The lowest exposures in the mine are a dark grey is interpreted to represent an overall shallowing to palaeosol in terrigenous mudstone (Figure 2). This a lacustrine margin setting where gastropod palaeosol is at least 25m thick (the base is not accumulations mark concentration by wave action. exposed) and represents slow sediment accumulation and subsidence. Any introduced sediment was fully reworked by pedogenetic processes so that no primary sedimentary structures remain. The palaeosol is overlain by a coal seam that varies in thickness from 5m to 18m along strike. At its base the coal is black hard and vitreous and represents peat accumulation in a slowly subsiding swamp. Towards the top of the coal are interbeds of dark brown algal rich coal that were deposited in standing water. Laterally these brown coals pass into agal-rich limestones which represent lacustrine margin carbonate accumulation. This upper part of the coal seam reflects continuing subsidence but at a rate where ephemeral lakes were able to develop. Coals show TOC and HI values of 36.71% - 71.77% and 237 - 350 respectively and are generally mostly gas Coal prone source rocks containing higher-plant material.

The coal seam is capped by a dark brown, highly organic rich (TOC 16.3% and HI 582), undercompacted shale of irregular thickness which is an excellent quality oil prone source rock with N algal organic matter predominant. This is Palaeosol interpreted to be the deposit of a shallow, algal rich lake and probably represents the very first development of continuous lacustrine conditions. 10 km

Overlying the carbonaceous shale are ~100m of Figure 2. The Karbindo Coal Mine. Palaeosols in

Brown Shale facies. In the Karbindo Coal mine the the foreground are overlain by coal, which in turn

Brown Shale is broadly divisible into three is overlain by a very thick section of lacustrine intervals, namely: a lower (approximately 40m Brown Shale. Note the light coloured limestone thick) highly fissile paper-laminated shale, a interbeds towards the top of the coal. The upper interval comprises dark brown, faintly middle (approximately 15m thick) gastropod-rich laminated, organic-rich brown shale, which in thin red weathering shale and an upper (approximately section is seen to be strongly bioturbated. TOC 50m thick) weakly laminated highly bioturbated (3.75%-8.44%) and HI (624-743) values are shale. At its base the brown shale is dark brown, exceptionally high and confirm the presence of oil finely laminated and fissile. The lowermost portion prone algal organic matter. Palynofacies analysis is strongly calcite replaced. Thin sharp–based reveals a Botrycoccus spp dominated assemblage. flood-related sandstones are locally developed and This interval represents a return to deeper become more frequent and thicker upwards. High lacustrine conditions. TOC (3.16%-8.91%) and HI (442-717) indicate an excellent quality oil prone source rock dominated by algal organic matter. Palynology reveals a

Number 27 –August 2013 Page 19 of 31

Berita Sedimentologi SUMATERA

The water column was strongly stratified but DAYS 3 AND 4 – RESERVOIRS sufficiently oxygenated to allow bioturbation to occur. Overall deposition of the Brown Shale The third and fourth days of the field trip sediments at Karbindo is interpreted to have taken concentrated on sandstone reservoirs in the syn- place in relatively shallow water where subtle and post-rift sequence and how their reservoir variations in the hydrological regime have resulted architecture is affected by local tectonic and in great differences in the rock record. provenance factors. In the Central Sumatra area, as with other syn-rift sections from Southeast Asia, there is considerable variation in sandstone thickness, lateral development and quality. Such sandstones are exposed in the Ombilin Basin and its environs where, unusually for Southeast Asia, there are numerous excellent quality exposures in river beds, cliffs, road cuts and coal mines (Figures 3 and 4). It is in the last mentioned that much of the third day is spent since in these mines exposures are extensive and allow for: • an appreciation of fluvial sandstone reservoir architecture, from isolated sand bodies surrounded by mudstones, to vertically and laterally stacked sandstone showing good three dimensional interconnection, • Allow for an interpretation of the evolution of fluvial systems such that conditions may become suitable for sandstone aggradation in vertical and lateral sense within the same overall sequence.

Although the greater part of the outcrops are fluviatile in nature and can be regarded as analogous to producing reservoirs elsewhere in Indonesia, turbidite and alluvial fan sediments were also examined. In the magnificent Harau canyon it is possible to cross over from basement to alluvial fan sediments and to walk up the alluvial fan observing how the sediments evolve with time. Figure 3. Allied Indo Coal Mine (Parambahan- Rasau Members, Sawahlunto Formation). Fluviatile sands are laterally discontinuous and separated by thick well developed palaeosols.

Figure 4. Sawahtambang Gorge (Sugar Member, Sawahtambang Formation). Sands are very well developed and show excellent lateral and vertical continuity.

Number 27 –August 2013 Page 20 of 31

Berita Sedimentologi SUMATERA

Student article Economic vs Fractured Basement: A Case Study from North Sumatra Basin

Ignatius Primadi Trisakti University, Jakarta, Indonesia Corresponding Author: [email protected]

ABSTRACT

North Sumatra basin developed during the Early Tertiary (Eocene-Oligocene) as a result of an oblique subduction of the Indian Oceanic Plate underneath the Sundaland continental block. The basin is comprised of Tertiary to Recent sediments that were deposited over Pre-Tertiary basement. Typically, in many places basement consists of complex igneous and metamorphic rocks, but it is different in the North Sumatra basin. Underneath this basin, there are carbonates (dolomites or limestones) and sandstones including the Eocene Tampur Formation that have been called economic basement. Economic basement refers to rocks that have no economic prospectivity whilst the formation is comprised of the sedimentary deposits. The term economic basement in the North Sumatra Basin should be reconsidered because some data shows porosity development in pores and fractures, therefore making them potential reservoir that can receive hydrocarbon charge from proven petroleum system in the basin.

Keywords: Economic Basement, Fractured Basement, North Sumatra Basin

INTRODUCTION North Sumatra Basin is one of several prolific basins in Sumatra, Indonesia. The basin was Basement and crystalline basement are defined as formed during Early Tertiary (Eocene-Oligocene) as the rocks underneath a sedimentary basin or those a result of an oblique subduction. The research covered by sedimentary rocks. Nowadays, they are area is located in Malacca Strait, approximately not merely the rocks which accommodate the 150km to the NNW of Medan, the capital city of sedimentary basins but also play a significant role North Sumatra Province (Figure 1). The pre- as hydrocarbon reservoirs in several countries Tertiary basement at this location was categorized including Indonesia. For example, in the Beruk as economic basement (Beicip, 1977 in Darman Northeast Field, Central Sumatra, which has and Sidi, 2000). Darman and Sidi (2000) described produced about 2 million barrels of oil and in the basement as being composed of sandstones, South Sumatra, where several gas fields are limestones, or dolomites which are dense and producing from the pre-Tertiary basement, fractured, without any metamorphic alteration. collectively have estimated reserves of about 5 TCF They are supposed to be less dense than igneous (Koning, 2007). Those basements are called or metamorphic basement, but they are difficult to fractured basement because they have fractures be traced and identified. The fact that the through which hydrocarbons flow. Another basement is fractured and possibly connected to a terminology for describing basement is by using proven petroleum system means that they can be the term economic basement. An economic prospective for hydrocarbon exploration. The main basement is defined as non-petroleum prospective objective of this study is to reconsider the sedimentary rocks that underlie a sedimentary basement of North Sumatra Basin as fractured basin. basement and not only economic basement based on data presented in this article.

Figure 1. Location of research area is shown by the red box (map from Google).

Number 27 –August 2013 Page 21 of 31

Berita Sedimentologi SUMATERA

DATA AVAILABILITY & SCOPE OF WORK cemented with calcite and quartz and show no reservoir potential. However, observation of core The primary data used in this study include plugs and even dating from these “basement” seismic and well data. The seismic data was shows that they are not easily recognized as interpreted and used in building a geological cross basement and distinguishing them from the section. The well data consist of wireline logs used Tampur Formation is difficult. in stratigraphic correlation and thin sections for describing lithology and pore characteristics and TAMPUR FORMATION estimating the porosity. Secondary data include published work on the region by previous authors The name Tampur Formation has been used for all such as Anderson et al. (1993), whose Pre-Oligocene carbonates in the North Sumatra lithostratigraphic subdivision has been used as a Basin (Collins et al. 1996), but is commonly viewed reference in this study (Figure 2). All of these data as Eocene in age (Caughey and Wahyudi 1994, are used to support interpretation for basement Ryacudu and Sjahbuddin 1994). However, the prospectivity. faunas on which this age is reportedly based have never been documented. Eocene Nummulites PRE-TERTIARY BASEMENT limestone is present in West Sumatra, in the Ombilin Basin. But, on the other hand, 'Basement' The Pre-Tertiary rocks in the North Sumatra Basin carbonate in the Singa Besar 1 well, just across consist of limestones and dolomites which underlie the Malaysian border in Malacca Straits, contains the Tertiary sediments. Previous authors suggested the Middle-Late Permian foraminifer Shanita and that within the Pre-Tertiary rocks, there are also other Permian fauna (Fontaine et al. 1992). sandstones, metasediments, tuffs, and granites. Drill cuttings from the study area reveal that these The Tampur formation was described by Ryacudu carbonates are typically wackestone-packstones, and Sjahbuddin (1994) as massive, partly bioclasts, skeletal packestones with fracture and biocalcarenites and calcilutites, common vuggy porosity ranging 5-10%. Porosity estimation dolarenites, chert nodules and basal limestone from well data reveals porosity range from 5 to conglomerates, that indicate deposits of an open 25%. Nevertheless, Caughey and Wahyudi (1993) marine sublittoral environment. reported that despite some of the Pre-Tertiary sedimentary rocks were fractured, they are tightly

Stratigraphic column of North Sumatra Basin (Anderson et al., 1993). Figure 2.

Number 27 –August 2013 Page 22 of 31

Berita Sedimentologi SUMATERA

0 1 mm.

Figure 3. Photo of thin sections in 5990’ interval of basement carbonates with interparticle and fracture porosity, totaling 10% in porosity.

From the reports of deep wells in the Aru and Bampo black shales and in the Meucampli Langkat areas, it consists of limestones, commonly Formation. fractured and dolomitised (Ryacudu and Sjahbuddin, 1994). Collins e t a l . (1996) also stated There are no specific permeability and porosity that drill cuttings f r o m t h e Tampur Formation data taken from Tampur Formation. However, from consist of mudstones, skeletal wackestones, cutting description of a well near Aru Bay-1, where intraclast, oolite packstones, and grainstones. 85 meters of thick, fractured dolomites that may These descriptions show a slightly similar correlate to the Tampur carbonates have been characteristic as those of the Pre-Tertiary drilled, the estimated secondary porosity is around basement rocks. 5-10% (Ryacudu and Sjahbuddin, 1996).

We may conclude that some of the basal INTERPRETATION limestones in the North Sumatra Basin are of well defined Pre-Tertiary (Permian) age, while Late Pre-Tertiary basement in the North Sumatra Basin Eocene limestones may be present as well, similar is difficult to be distinguished from Tampur to the thin foraminiferal carbonates outcropping in Formation, because it is comprised mainly of the southwestern part of the Central Sumatra wackestone-packstones. At 5990’ and deeper basin. If the Late Eocene age interpretation is the interval in a well (Figure 3), thin sections mostly correct one, this means that the Tampur show that the wacke-packstone is composed of sediments are related to syn-rift phase and most calcite and other minerals, with grains size of likely distinct from the fractured basement around 0.05-0.2mm, subangular-subrounded in carbonates (Collins et al, 1996). grain shape, grain supported and poorly supported, point contact. Matrix consists of SOURCE ROCK AND RESERVOIR carbonate. Cements consist of sparry calcite type. CONSIDERATION The rock contains interparticle and fracture types porosity totaling 10%. Another thin section also The Tampur Formation was deposited in an open shows moldic and vuggy porosity. With the marine shelf setting that generally is lean in integration of well and core porosity that ranges 5- organic matter and normally provides poor source 20%, the described characteristics are likely material for large scale hydrocarbon generation similar to those of Tampur carbonates. (Ryacudu and Sjahbuddin, 1994). This means younger sediments are the only possible source for From correlated seismic section (Figure 4) between hydrocarbon generation, such as organic-rich wells, it can be interpreted that the Tampur shales in the Belumai Formation, Baong Shales, Formation is laterally widely distributed. Structural and stratigraphic traps may exist in the

Number 27 –August 2013 Page 23 of 31

Berita Sedimentologi SUMATERA

Tampur Formation. Considering reef buildups makes them highly prospective for reservoir. The could occur along the shelf margin, the fractured shales of Lower Baong Formation could be the cap Tampur Formation located on the highs as seen on rock for the Tampur carbonates reservoir along Figure 4 and 5 might contain fair to good porosity with its entrapment. and permeability if they had been exposed. This

Figure 4. Seismic section of "A" to "E" Well.

Figure 5. Cross section of the study area, red circles indicating the possible accumulation of hydrocarbon for basement fractured. Red arrow indicating the migration pathway.

Number 27 –August 2013 Page 24 of 31

Berita Sedimentologi SUMATERA

CONCLUSION Caughey, Charles A., and Turcahyo W., 1994, Gas Reservoirs in the Lower Miocene Peutu Under certain circumstances, the presence of Formation, Aceh Timur, Sumatra: Indonesian carbonates in the North Sumatra Basin basement, Petroleum Association 22nd Annual Convention, whether Eocene Tampur Formation or older Pre- v.1, p.191-218. Tertiary constituents, suggest that the basement is Collins, J.F., Kristanto, A.S., Bon, J., and not an economic basement but fractured basement Caughey, C. A., 1996, Sequence Stratigraphic with potential to be reservoir. However, this study Framework of Oligocene and Miocene only covered a small portion of the basin and Carbonates, North Sumatra Basin, Indonesia: further work is required to prove the prospectivity 25th Silver Anniversary Convention Proceedings of the fractured basement. of Indonesian Petroleum Association, Vol.1, p.267-279. ACKNOWLEDGEMENT Darman, H., and Sidi, F. H. (eds.), 2000, An Outline of Geology of Indonesia: IAGI, Jakarta. The author gratefully acknowledges Mr. Taat Fontaine, H., Asiah, M.S., and Sanatul, S.H., Purwanto, as the main mentor of the author, for 1992, Pre-Tertiary limestones found at the his permission to release certain data and to bottom of wells drilled in Malacca Straits: CCOP publish this article. Newsl. 17, 4, p.12-17. Koning, T., 2007, Remember Basement in your Oil REFERENCES and Exploration: Examples of Producing Basement Reservoirs in Indonesia, Venezuela,

and USA: CSPG CSEG Convention 2007. Anderson, B.L., Bon, J., and Wahono, H. E., 1993, Ryacudu, R., and Sjahbuddin, E., 1994, Tampur Reassessment of the Miocene Stratigraphy, Formation, The Forgotten Objective in The Paleogeography and Petroleum Geochemistry of North Sumatra Basin: Indonesian Petroleum the Langsa Block in the Offshore North Association 23rd Annual Convention, v.1, p.160- Sumatra Basin: Indonesian Petroleum 179. Association 22nd Annual Convention, v.1, p.170-

189.

Number 27 –August 2013 Page 25 of 31

Berita Sedimentologi SUMATERA

Student article Depositional Environment Analysis of Kali Banyumeneng, Mranggen, Kabupaten Demak

Samuel R.N. Simorangkir, Fahmi Abdillah, Zul Hayuddin and Galang Virgiawan Geological Engineering Department, Diponegoro University, Semarang Corresponding Author: [email protected]

INTRODUCTION Previous work (e.g. van Bemmelen, 1949) shows Kali Banyumeneng is located in Mranggen, Demak that the study area consists of two (Central Java province). The studied outcrop is lithostratigraphic units called Kerek and Kalibeng located approximately 11.25 km to the SE of Formations. Kerek Formation consists of Semarang city and at the geographic coordinate of interbedded sandstones, claystones, and sandy 100° 28’ 59.65” E and 7° 02’ 43.45” S (Figure 1). limestones with observed sedimentary structures such as graded bedding, ripple mark and The study area is geologically located in Kendeng convolute. Kalibeng Formation is subdivided into Zone, which is also often referred as Kendeng lower and upper parts. The lower part of Kalibeng Mountains, an east-west trending anticlinorium in Formation consists of sandstones that shows the northern part of Java. The northern border of turbiditic nature. The upper part of Kalibeng the Kendeng Zone is Randublatung Depression, Formation is composed of breccias with fragments while the southern border comprises a line of formed by limestone. The Upper Kalibeng volcanoes called Solo Zone. Kendeng zone is a Formation also contains forams, molluscs, corals continuation of the Northern Mountains Serayu and algae and it shows a bedding structure. Zone that developed in Central Java. The Salatiga section of the Kendeng zone extends towards the Observations were carried out to determine the east to Mojokerto and plunges under the Brantas depositional environment model of Kali river. The continuation of these mountains can Banyumeneng area based on lithology, still be tracked under the Madura Strait. sedimentary structures and fossils.

Van Bemmelen (1949) subdivided Kendeng METHODOLOGY Mountains into 3 parts that consist of the western part, which lies between Mt. Ungaran and Solo The observation began with data collection in the (north Ngawi); the central part that lies between field. The field data collection was carried out with Solo and Jombang and the eastern part that stratigraphic section measurement followed by an extends from east Jombang to Brantas River Delta analysis to determine the depositional environment and continuously to Madura Bay. The study area of the outcrops. occurs in the western Kendeng Zone.

Figure 1. Location map of Kali Banyumeneng outcrop discussed in the article (Google Maps, 2013).

Number 27 –August 2013 Page 26 of 31

Berita Sedimentologi SUMATERA

Figure 2. Sedimentological description of Kali Banyumeneng outcrop (to be continued to the next page).

Number 27 –August 2013 Page 27 of 31

Berita Sedimentologi SUMATERA

Figure 2. Sedimentological description of Kali Banyumeneng outcrop.

Number 27 –August 2013 Page 28 of 31

Berita Sedimentologi SUMATERA

RESULTS

From the results of the 100 meter section measurement, it can be seen that the constituent lithologies are sandstones, limestones, and siltstones (Figures 2 & 3). Sandstones in this area are bright brown in color, with layering structure, and fine to medium in grain size, well sorted and calcareous. The limestone is characterized by gray colour, laminated structure, with coarser grain, poorly sorted, and composed of Pelecypoda macrofossil as well as foraminifera fossils. The siltstones in this outcrop are characterized by grayish brown color, no-sedimentary structure, with a silty grain size, well sorted and calcareous.

A

Figure 3. Interbedded of limestones and sandstones. Bed thickness increases towards the B upstream direction. Figure 4. Sedimentary structures in sandstone, (A) parallel bedding and (B) ripple marks. The sedimentary structures observed in the Kali Banyumeneng area include bedding, lamination, We have also identified the following foraminifera cross stratification, convolute, load casts, species from the outcrops: Globigerinoides hummocky and ripple marks found on sandstones immaturus, Globigerina venezuelana, Hastigerina (Figure 4). Hydrodynamic sedimentary structures acquilezeralis, Globigerinoides sicanus, Globigerina are indication of gravitational flow (Boggs, 1987). obligus, Globorotalia multicamerata, Globigerinoides In addition, the hummocky cross-stratification ruber, Globigerinoides diminutus, Globigerinoides indicate that the sequence was deposited under trilobus, Globorotalia obesa, Cassigerinella storm influence. Mudcracks and rainmarks are chipolensis, Globigerinoides primodius and also visible in younger sediments probably of Praerbulina glomerosa. These assemblages of Quaternary age. foraminifera species indicate sediments of most likely Middle Miocene age. ANALYSIS REFERENCES Based on our field observation, the Banyumeneng outcrops are interpreted as having deposited in Boggs, Sam Jr., 1987, Principles of Sedimentology shallow marine to deep water settings. This is and Stratigraphy: Merrill Publishing Company, indicated by the presence of sedimentary Columbia. structures exposed on the ground in the form of Staff Asisten Sedimentologi dan Stratigrafi, 2011, convolute (identifier slope areas) and the presence Panduan Praktikum Sedimentologi dan of Pelecypoda, which usually lives in shallow Stratigrafi: Teknik Geologi UNDIP, Semarang. marine setting. Other indications include Van Bemmelen, R., 1949, The Geology of Indonesia sedimentary structures such as hummocky cross- Volume 1A: Government Printing Office, The stratification that developed in the area, which Hague, Netherlands. have been described above.

Number 27 –August 2013 Page 29 of 31

Berita Sedimentologi SUMATERA

Number 27 –August 2013 Page 30 of 31

Berita Sedimentologi SUMATERA

Number 27 –August 2013 Page 31 of 31