IPA11-SG-034

PROCEEDINGS, INDONESIAN PETROLEUM ASSOCIATION Thirty-Fifth Annual Convention & Exhibition, May 2011

PETROLOGY AND PROVENANCE OF SANDSTONE FROM MESOZOIC SEQUENCE

SOE-KAPAN BLOCK, WEST TIMOR, NTT.

Didi Aulia* Samson H Sinaga*

Radi Adiarsa* Farouqi Al’ayubie*

Ida B. Arindra* Fajri Nikmata* Ivan Rodelian*

ABSTRACT Tectonic conditions and drainage in West Timor provide an excellent natural laboratory to study the composition and formation of central Timor Basin. As we know, Banda Arc is part of palleotimor island, the collision and subduction between palleotimor and the Australian Plate during Late cretaceous-Eocene formed Timor Island. For that condition, the Mutis complex is product of tectonic evolution (mélange). During the Eocene, Timor experienced subduction with reactivation of the old fault, forming a mélange zone sub-play. This reactivated subduction from Pliocene until recent resulted in a mélange zone called the Bobonaro Complex. Field samples were collected and thin sections prepared for petrography analysis including Pettijohn chart and Dickinson and Suczek (1979) ternary diagram (Q-F-L, Qm-F-Lt, Qm-P-K) in order to interpret the potential provenance for each formation. Samples were collected from two formations, five samples from Bisane Formation (Permian), with rich quartz (45-57%), (9-13%) feldspar and (9-19%) lithic fragment and nine samples from Aitutu Formation (Triassic), rich quartz (31-72%), (9-39%) feldspar and (5-21%) lithic fragment. Most likely potential provenance for each formation is recycled orogen and the influence of regional tectonics. Petrography analysis of Bisane and Aitutu Formation samples show characteristic sandstone type Arenite, pursuant to classification of Pettijohn (1975). Tectonic provenance of the sandstones is from recycled Orogen, meaning, from uplifted foreland fold-thrust belt; and the source rock from

acid to moderately igneous rock, and high grade metamorphism, such as; granite, gneiss, granidiorite and diorite originating from Mutis High Complex. This undergraduate thesis and research is sponsored by PT. Niko Asia Ltd. Keyword: Petrology, Source, Provenance INTRODUCTION Work in sedimentary petrology, geochemistry, and geomorphology has led to a better understanding of relative abundance of detritus controlled by climatic transport related to tectonic factors (Dickinson and Suczek, 1979). This paper presents a method of identification of sedimentary provenance from sandstone in Soe-Kapan Block, West Timor. Timor Island, located in the southern Banda Arc in eastern Indonesia forms part of the present-day collision zone between the northwestern margin of Australia and the southeast Asian island arc. Timor is the location of numerous oil and gas seeps and high-quality hydrocarbon source rocks (Charlton, 2002). The complex Timor collisions have affected the stratigraphy across the island. These collisions resulted in exposure of hydrocarbon source rocks and reservoirs making them potentially biodegradaded. Although biodegradation has destroyed the petroleum system onshore Timor, it is estimated that potential oil accumulations exist offshore. The tectonic history of Timor is complex and has been the subject of considerable attention. There areseveral theories attempting to explain the tectonic and formational history of Timor. Three main structural models with numerous variations in detail have been proposed for Timor, which for brevity are

usually described as the Imbricate, Overthrust and Rebound models (Charlton, et al., 1991). Exposures were described that consist of: 1) Permian to Neogene sediments that reflect the tectonic history of Gondwana and the Northwest Australian margin, 2) Cretaceous through Neogene sediments believed to represent an overthrusted volcanic forearc basin and 3) a syn-orogenic Plio-Plistocene deposit that reflects rapid collision-related uplift (Sawyer, et al.1993). Sandstone petrology has an important function in hydrocarbon exploration and reservoir characterization. From Dickinson and Suczek (1979), ternary diagram is a tool for determination of tectonic environment of the sandstone deposit. Specifically, this paper addresses the following questions: (1) What is the composition of sandstone from Mesozoic sequence in the study area? (2) What provenance domains can be distinguished by sandstone composition? SOE-KAPAN BLOCK STRATIGRAPHY (MESOZOIC) Field samples are from Bisane and Aitutu Formations along Noil Baki, Nifu Fatutupu villages, and Noil Nisnoni, Leloboko and Lilana Villages. The stratigraphic sequence used herein isbased on Rosidi, H.M.D., et.al, (1996). And Audley-Charles (1968). Bisane Formation The lower Bisane comprises monotonous layers of dark grey shale with purplish siltstone, reddish, generally calcareous sandstone with slate intercalations. Chloritized lava intercalations are also found. There are lesser amounts of shale and more sandstone in the upper section. Limestone and sandy shale are intercalated. Sandstones comprise grayish quartz with individual layers up to 20 cm thick, greywacke, micaceous sandstone, or greenish, medium grained carbonaceous sandstone. Carbonaceous sandstone may attain a thickness of 10 m. The thickness of the limestone intercalation is 50 cm or less. The best exposure of this unit which has been adopted as type locality may be observed along the bank of Noil (river) Bisane, a tributary of Noil Sitoto at the west side of Nuaf Kekneno. A comparable unit in East Timor has been subdivided into two formations, Atahoc and Cribas Formations (Audley-Charles, 1968). Previous investigators included this unit in the lower part of “Kekeno seie” or the “Flysch facies” (Warner, 1913; Molengraff, 1913, 1914, 1915). Fossils are scarce, only

fragments of Brachiopoda, crinoids, and some coral were found in the sandy sshale or siltstone intercalations. A trilobite fragment was found in a limestone intercalation at Noil Besasi; in the Buimanuk river Atomodesma sp was encountered. De Roever (1940) reported Permian cephalopods in the grey limestone intercalation in Tunsif River. The thickness of the formation is estimated at roughly 1.000 meters. (Appendix) Aitutu Formation The lower Aitutu Formation comprises interbedded varicolored (red, brown, grey, greenish) siltstone with marl and limestone. Quartz sandstone, micaceous sandstone, chert and crystalline limestone layers are intercalated. The upper section comprises alternating white to yellowish calcilutite with veinlets and grey shale. Calcilutite constitutes the greater part. The formation’s most extensive and best exposure in West Timor is at Nuaf Kekneno. Due to its complicated structure, the thickness is difficult to determine; however, it is estimated to be at least 1.000 meters thick. Based on abundant Halobia sp, chiefly in the reddish brown siltstone outcrop at the Mota Merak and in the Kekneno Mts., this formation is assigned to Upper Triassic. This unit is the “Kekneno Serie” of pre-war Dutch scientists (Simons, 1940). The name Aitutu Formation follows Audley-Charles (1968,) designation of a comparable unit in East Timor (Appendix). METHODS Modal analysis of petrographic composition constitutes the basis for our subsequent sandstone classification and provenance analysis. Macroscopic field descriptions were followed by thin section preparation of selected sandstones and petrographic study using a polarizing microscope. Modal sandstone composition from the Mesozoic sequence (Perm Bisane and Trias Aitutu) in Soe-Kapan Block, follows the Dickinson and Suczek method (Dickinson and Suczek, 1979). Fourteen samples were analysed with assigned grains < 0.03 mm to matrix, following Pettijohn et.al. (1987). Table 1 summarizes the recognized grain types and their definitions (Appendix). Ternary diagram with quartz-feldspar-lithic fragments (Q-F-L) end members typically illustrate sandstone classification based on framework composition and matrix proposition. Subsidiary diagrams focus on subsets of these three principal

components. Provenance is at its most effective by using a combination of several ternary diagrams rather than relying on a single diagram because combinations of specific end members discriminate between different grain properties. The standard combination was used for this work, after Dickinson and Suczek (1979), including Q-F-L, Qm-F-Lt and Qm-P-K diagrams (Appendix). The Q-F-L plot describes relative grain stability and weathering processes of three end members. Therefore, this diagram may indicate the provenance ratio in tectonic and source rock (Appendix). The Qm-F-Lt plot includes the polycristalline quartz and chert fragment (Qp) in the total lithic fragment (Lt) end member. This diagram takes into account the source rock ratio and tectonic location of the sandstone (Appendix). The Qm-P-K plot excludes the total lithic fragment (Lt) and proportionate feldspar in potassium feldspar (K) and plagioclase (P). This plot may differentiate between potentialpotential source rock, continental-derived, K-rich source rock versus P-rich sources of magmatic arc (Appendix). RESULTS Grain categories of sandy material The following paragraph briefly describes the major grain components of Bisane and Aitutu Formation sandstones. Results of thin section point count are listed in the Appendix. - Quartz

Quartz constitutes the highest proportion in all sandstones samples. Monocrystalline quartz grains are subrounded to subangular, With moderate to good sorting. More than 63% of monocrystalline quartz grains show non-undulatory extinction, but for some samples, they have undulatory extinction. The proportion of polycrystalline quartz grains is generally lower than that of monocrystalline quartz. Some samples have fine or coarse grained cherts.

- Feldspar Feldspar is subangular to subrounded and commonly fine grained. The orthoclase and plagioclase is the mostly feldspar in samples, and microcline in one sample. Clasbad twinning and albit is common for each sandstone sample.

- Lithic Fragment Lithic fragments in samples from sediment, igneous and metamorphic rock: for sediment fragment is present in most samples, the

metamorphic is more than igneous. The rock fragments are andesite, diorite, carbonate, sandstone, chert, schist and philyte.

- Accessory minerals Muscovite and chlorite are common accessory minerals in sandstones, in fine size. Pyroxene, amphibole, iron oxide, calcite are also present.

- Matrix The matrix from Bisane and Aitutu Formations are commonly the same, they are composed of clay mineral with some showing carbonates, and ranges between 6-14%, but one is 21%.

- Cement Quartz, calcite and clay cementation are common within the Bisane and Aitutu Formations. Calcite is the most common cement although none is observed in the studied samples.

Provenance analysis The study relied on QFL, QmFLt and QmPK ternary diagrams after Dickinson and Suczek, (1979) and paleo-current indicators to potential provenance (Appendix). However, the mineralogical composition of the sediments is also influenced by the size of outcrop, potential source rock and tectonic environment. Potential source rock for this sandstone can be determined from mineralogy and characteristicsof quartz, feldspar, lithic fragments and accessory minerals. Bisane Formation is assigned to Late Permian and Aitutu Formation is assigned to Triassic (Audley-Charles, 1968). Fourteen study samples comprise quartz with little matrix of clay and carbonate, the presentation of quartz between 31-72%, with dominantly monocristalline quartz (49-63%), no vacuola, but for one sample, non-undulatory extinction is present. The angular shape and thin, indicated the source rock came from plutonic igneous rock (Pettijohn, 1975). Some eldspar is present 11-39%, with orthoclase and plagioclase. Orthoclase is common in plutonic igneous rock and metamorphic medium-high grades, such as granite, diorite, gneiss and schist (Pettijohn, 1975 and Boggs 1992). Qm-P-K diagrams shows the source rock came from plutonic continental rock. Muscovite and chlorite is present in some samples, indicating the source rock for this formation came from metamorphics such as gneiss and schist (Setia Graha D, 1987 and Boggs 1992). So far source rocks for this formation are plutonic igneous rocks such granite and diorite, and also metamorphic rocks such gneiss and schist.

Qt-F-L and Qm-F-Lt diagrams from Dickinson and Suczek, 1979, shows the provenance of sandstone in this area came from Recycled Orogen (subzone Quartzose Recycled-Transitional Recycled), meaning the source areas were formed by collision of terranes that were once separate continental blocks or uplifted fold-thrust belts. The sediments or metasediments were uplifted by collision to the surface and formed the source area comprising sediments, metasediments, including plutonic even mélange. This type common sediment and metasediment fragments, are sandstones like quartz arenite, feldspathic arenite and abundant chert. (Boggs, 1992). In this case the potential provenance for this formation is Mutis Complex, formed since pre-Permian, in the time of Australian plate collision to paleo Timor, in Late Triassic, until the deposition of the Bisane and Aitutu Formations in shallow marine environment (Charlton, 2002). Six foresets of paleocurrents with indicators like flute casts, in Aitutu Formation, indicate a dominant Northwest to Southeast bidirectional transport direction. Regional geology setting in this area shows the Mutis Complex is the potential provenance, from Pre-Permian until Permian (Audley-Charles,1968), in western north until eastern north, comprising low-high grade metasediments and part igneous rock, such as schist, amphibolit, quartzite, gneiss, and granulite, diorite, granodiorite and diorite, in the Miomafo and Mutis Mountains. The Australian passive margin (during mesozoic) was another potential provenance. It is interpreted from this datathat the potential provenance is Mutis Complex for sediment subplay for Bisane and Aitutu formation. CONCLUSIONS Bisane and Aitutu Formation is characterized as commonly lithic arenite and sublithic arenite, but some samples included into quartz arenite sandstone. Provenance analysis of the Bisane Formation indicates a Recycled Orogen provenance with high quartz and metasediment rock fragments. With the source from acid-moderately plutonic rock or metamorphic rock from high grade-moderately from Mutis Complex. Provenance of the Aitutu Formation is indicated from analyses as Recyled Orogen with high quartz. Sediments sourced from Mutis Complex are high metasediment and acidic plutonic rock, such as granite, diorite, gneiss and schist. The palleotectonic environments indicate the study area is located along uplifted fold-thrust belt, during sedimentation.

ACKNOWLEDGEMENTS This study is part of Didi Aulia’s undergraduate thesis of Bachelor Degree in Padjadjaran University. Thanks to Dr. Ildrem Syafri and Dr. Yoga Adriana (Padjadjaran University) for their support. Special thanks to Niko Asia Ltd. for financial support, especially Mr. John, Mr. Farid and Mr. Phillips (Niko Asia Ltd.). REFERENCES Adams, MacKenzie & Guilford, 1984, Atlas of Sedimentary Rock Under Microscope, ELBS, UK Audley M.G - Charles 1968, The Geology of Portuguese Timor, Nurlington House, London. Boggs, Sam., 1992. Petrology of Sedimentary Rocks: Macmillan Publishing Company, Canada Charlton, T.R,. 2002. The Petroleum Potential Of West Timor: Proceedings Indonesian Petroleum Association 28. Dickinson W. R. dan Suzeck., C. A. 1979. Plate Tectonics and Sandstone Compositions. AAPG Bulletin V. 63 No. 12, 2164 – 2182 ESCAP., 2003. Geology and Mineral Resources of Timor-Leste., Journal Atlas of Mineral Resources of the Escap region vol 17. Folk, Robert L,. 1980. Petrology of Sedimentary Rock. Hemphill Publishing Company Austin, Texas Glazner, Allen.DR, http://Atlas of Igneous and Metamorphic Rocks, Minerals & Textures, University of North Carolina, UNC Hulka. C, Cornelius. U, Heubeck C Sandstone Petrology and Provenance of the Chaco Basin: record of foreland basin evolution and Adrian Uplift, Journal of Sedimentary Research. Harley B. Gerard M. Raymond M, 1972, Origin of Sedimentary Rocks, Prentice-Hall Inc Englewood Cliffs. New Jersey. Setia G.Doddy, 1987, Mineral dan batuan, NOVA Bandung. Sawyer, R.K., Sani K., and Brown, S., 1993. Stratigraphy and sedimentology of West Timor, Indonesia, Proceedings of the Indonesian Petroleum Association 22.

Mackenzie.W.S & Adams.A.E. Rock and Minerals in Thin Section, University of Manchester. UK Pettijohn F.J, Potter P.E, & Siever R, 1987. Sand and Sandstone second edition. Springer-Verlag, Newyork, Berlin, Heidelberg Pettijohn F.J 1975. Sedimentary Rocks, 628pp. Harper & Row, New York Rosidi, H.M.D., Tjokrosapoetro, S., Gafoer, S., 1996. Geological Map of Kupang-Atambua

Quadrangles Timor, Geological Research and Development Center. Sawyer, R.K., Sani K., and Brown, S., 1993. Stratigraphy and sedimentology of West Timor, Indonesia, Proceedings of the Indonesian Petroleum Association 22. Tucker, M.E., 1993, Sedimentary Rocks in the Field second edition. Department of Geological Sciences, University of Durban, UK

TABLE 1

GRAIN FRAMEWORK

Abbreviation Explanation Q Total quartz, including monocrystalline and polycrystallin quartz grains Qm Monocrystalline quartz Qp Polycrystalline quartz F Total feldspar, including potassic feldspar and plagioclase K Potassic feldspar

P Plagioclase

L Total lithic components, including sedimentary, metasedimentary and volcanic lithic components

Lt Total lithic components, including sedimentary, metasedimentary, volcanic lithic components, polycristalline quartz and chert.

TABLE 2

MINERALOGY COMPOSITIONS FROM BISANE FORMATION.

Sample code Mineralogy B91A B93B A85 B91B B91

Qm 38 49 47 36 36 Q Qp 10 8 10 11 15 P 4 6 4 6 11 F K-feldspar 9 4 7 3 5 Igneous 2 - 2 10 4 Sediment 6 3 8 5 6 L Metamorphic 8 6 5 4 4

Matrix 10 14 11 6 6 Cement 5 5 2 2 3 Pyroxene - 2 - - Muscovite 4 - - 1 2 Chlorite - - 4 1 - Iron oxide - 3 - - - Calcite fragment - - - 10 - Porosity primer/secondary 4/- -/- -/- 3/4 8/-

Rock name (Pettijohn, 1975)

Lithic Arenite

Sublthic Arenite

Lithic Arenite Lithic arenite Lithic

Arenite Total 100 100 100 100 100

TABLE 3

MINERALOGY COMPOSITIONS FROM AITUTU FORMATION

Sample code Mineralogy

B85B C94 B83TS B82 B83L A86 B84A B98 C92

Qm 18 26 22 26 36 35 63 45 34 Q Qp 24 13 9 23 9 10 9 11 19 P 5 8 15 4 6 3 2 7 3 F K-feldspar 9 15 24 10 8 11 14 12 6 Igneous 4 4 3 2 5 - 3 - - Sediment 14 11 8 6 11 8 6 - 8 L Metamorphic 4 7 4 2 3 4 - 5 6

Matrix 11 6 10 13 7 21 6 6 10 Cement 4 6 4 2 6 7 4 4 4 Muscovite 2 2 1 - - - 1 3 - Iron oxide - 2 - 3 - - - - 2 Clorite - - - 6 - - - - - Amphibole - - - 2 - - - - - calcite - - - - - 2 - - - Opax Minerals - - 1 - - 2 - - 1 Pyroxene - - - - - 2 - 2 1 Garnet - - - 1 - - - - - Porosity Primer/Secondary 5/- - - - 3/6 - - - 6/-

Rock Name (Pettijohn, 1975)

Lithic Arenite

Lithic Arenite

Arkose Arenite

Lithic Arenite

Lithic Arenite

Lithic Greywacke

Quartz Arenite

Subarkose Arenite

Lithic Arenite

Total 100 100 100 100 100 100 100 100 100

Figure 1 - Study area in Soe And Kapan Blocks West Timor

Figure 2 - Stratigraphy of study area Permian Bisane (Atahok-Cribas) and Triassic Aitutu (Pb- TRa)

(Source: Charlton, 2002) Mesozoic sandstone from Soe-Kapan Block (Sample Code: B 93 B; Formation: Bisane)

  // Nikol (Zoom 40x)    X‐ Nikol (Zoom 40x) 

                Figure 3 - Sublithic arenite fine grain, 0.02-0.6 mm sandstone (Pettijohn, 1975), with grey yellowish color,

subangular to subrounded grains, dominantly quartz. (Sample Code: C 94; Formation: Aitutu)     

      Figure 4 - Lithic arenite moderately sandstone, 0.2-0.9 mm, (Prttijohn,1975), with grey color, subangular to

subrounded grains, dominantly quartz with cement carbonate.

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Figure 4 - The Dickinson and Suczek, 1979, plot diagrams of mineralogy compositions. ( ) Bisane

Formation, ( ) Aitutu Formation