An Evolutionary Model of the Near-shore Tinjar and Balingian Provinces, Sarawak, Malaysia

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International Journal of Petroleum and Geoscience Engineering (IJPGE) 2 (1): ISSN 2289-4713 Academic Research Online Publisher Research paper An Evolutionary Model of the Near-shore Tinjar and

1 International Journal of Petroleum and Geoscience Engineering (IJPGE) 2 (1): ISSN Academic Research Online Publisher Research paper An Evolutionary Model of the Near-shore Tinjar and Balingian Provinces, Sarawak, Malaysia M. J. Mathew a,*, N. A. Siddiqui a,b, David Menier a a Department of Petroleum Geosciences, Universiti Teknologi PETRONAS, Perak, Malaysia b NED University of Engineering and Technology, Karachi, Pakistan * Corresponding author. Tel.: ; address: manoj_mathew7@yahoo.com A b s t r a c t Keywords: Tectonic evolution, Balancing and restoration, Cross section, Subduction, Wedge, Piggyback basin. Accepted: 12March 2014 The tectonic evolution of a basin can hold vital information regarding the variations and changes in depositional environments. Sarawak basin has undergone strong tectonic activity in its past. In this study, a model has been proposed for the evolution of Tinjar and Balingian provinces in Sarawak, East Malaysia in order to throw light on tectonic events that was responsible for basin development. The model was developed by balancing and restoration of cross sections obtained from published interpreted seismic profiles. The model takes into account the subduction of proto-south China Sea oceanic crust beneath the Borneo plate during Middle Eocene to Middle Miocene. The resulting model depicts older sequences (T1S and T2S) were accreted on to Borneo continental plate as a wedge and younger sequences (T3S) as piggyback basins. Due to structural complexity and variability of the region, each tectonostratigraphic province of Sarawak should be analysed individually as the proposed model corresponds only to two provinces of Sarawak. Academic Research Online Publisher. All rights reserved. 1. Introduction A sequence is a relatively conformable succession of genetically related strata, bounded by unconformities or their correlative conformities [1]. The Sarawak basin consists of seven identified sequences and eight sedimentary cycle boundaries. The cycles and their cycle boundaries in the Sarawak basin are most likely controlled by eustatic sea level changes [2]. Approximate ages of the top of each sequence are shown in table 1 (ages of T6S and T7S unknown). Tectonic evolution of the basin can hold vital information regarding the variations & changes in depositional environments of each of these sequences. Sarawak basin is believed to be one that has undergone strong tectonic activity in its past. Various scholarly works and analysis pertaining to the evolution of the basin have been carried out previously.

2 Previous works had suggested the evolution of Sarawak basin commenced when the Luconia block collided with Borneo leading to the closure of the Rajang Sea in the Late Eocene time [3]. It was also proposed that the basin had a strike-slip origin during Oligocene time based on structural styles and subsidence history [4]. Concluded works saw the introduction of the NW Borneo geosyncline theory stating the origin as an elongated basin filled with intercalations of volcanic rocks and sediments. Due to sediment loading the basin floor subsided and subsequently strong deformation of the sediments takes places by orogenic forces. Granite emplacement at the lower sediments occurs due to metamorphosis [5]. Tectonic evolution of NW Borneo region was illustrated previously as a result of subduction, during Oligocene, of the South China Sea plate beneath the Borneo continental plate [6]. In the present study, a model has been proposed for the evolution of near shore regions of Tinjar and Balingian provinces by restoring cross sections obtained from interpreted seismic profiles and data obtained from published literature. Table 1: Approximate ages of sequences [7] Sequence Top T5S Top T4S Top T3S Top T2S Top T1S Age in Ma 5.3 (Early Pliocene) 11 (Late Miocene) 18 (Early Miocene) 22.5 (Early Miocene) 37 (Late Eocene) 2. Geologic Setting of Sarawak Basin The Sarawak basin is one of the most prolific hydrocarbon producing basins within the geologically complex Southeast Asia. The geological complexity with regard to evolution of the basin has prompted many previous scholarly works yielding various models. The basin forms the southern margin of Oligocene-Recent South China Sea basin and evidences suggest it has undergone phases of rifting and sea-floor spreading in the South China Sea marginal basin [8] and [9]. Sarawak basin is situated onshore and near coast regions with the tectonic discontinuity, the West Baram Line (~115 E), East of Miri, separating it from the Sabah basin, to the western extend of the Malaysian province Sarawak (~110 E) and offshore for approximately 400km (~7 N) [10]. The basin extends westward into Indonesia as the East Natuna basin. 82 P a g e

Fig. 1: Tinjar and Balingian Provinces (modified after [11] The Sarawak basin is broadly sub divided into seven tectonostratigraphic provinces based on structural styles and sedimentation history.

3 Fig. 1: Tinjar and Balingian Provinces (modified after [11] The Sarawak basin is broadly sub divided into seven tectonostratigraphic provinces based on structural styles and sedimentation history. They are SW Sarawak, Tatau, Balingian, Tinjar, Central Luconia, West Luconia and North Luconia. The northern parts of the basin comprises of the Luconia block. In the Southern parts, two wrench fault systems can be observed as a result of Luconia block collision along with a dextral system associated with the West Balingian Line. A sinistral system associated with strike-slip basement tectonics in East Balingian can also be observed [12]. The geology of Sarawak is recognized as belonging to two distinct provinces, corresponding to two main geographic regions, namely West Sarawak and Central-North Sarawak. West Sarawak is the part of the state South and West of the Lupar line. It forms part of the West Borneo Basement which extends into Sarawak from the south. Rocks of Palaeozoic and early Mesozoic ages in Sarawak are confined to this region. The oldest rocks in West Sarawak are considered to be pre-upper Carboniferous. Intrusive granitic rocks are confined mainly to this area. Faulting and folding are common but these are mostly localized. Central-North Sarawak is the part of the state North and East of the Lupar line. The geology of Central-North Sarawak is younger than that of West Sarawak. The oldest rocks known in this area is of Cretaceous age. Faulting and folding are common and appear to have affected all the rocks in the area except the Quaternary. 83 P a g e

4 a b c Fig. 2: a) Orientation of seismic lines used in study (modified after [4]), b) Interpreted cross section of Line 2 (L2) (modified by [4]), c) Interpreted cross section of Line 1 (L1), (modified by [4]). 84 P a g e

5 Sarawak basin consists of seven identified sequences and eight sedimentary cycle boundaries. The cycles and their cycle boundaries are most likely controlled by eustatic sea level changes. The age of the basin is Late Eocene to Recent age with onshore exposures that can be followed between Sibu and Miri and further Northeast into the Inboard Belt of the Sabah basin. The basement consists of pre- Oligocene rocks that are exposed to the south in the Rajang Fold-Thrust Belt which extends across Sarawak and Kalimantan, Indonesia [13] Area of Study Situated mainly onshore and a fragment nearshore, the Tinjar province is located between latitudes 2 25 N and 4 15 N and longitudes E and E. The province is separated from the offshore Balingian by the NE-SW to ENE-WSW Anau Nyalau Fault. The Balingian province flanked by the Central Luconia province to the North and Tinjar province to the South is mainly offshore. The location of study is nearshore Balingian and Tinjar province (Figure 1) [11] Seismic Profiles and Sequences The near shore reprocessed lines by Sarawak Shell, obtained in between the years and reprocessed in 1987 by Digicon has been interpreted by Zin Ismail Che Mat where five seismic sequences were identified. The orientation of the seismic lines and their interpreted cross section is shown in the figure below (Figure 2, a-c). A series of listric thrust faults due to compressional shortening and thickening of the crust along with fault propagated folding is observed in the sequences T1S, T2S and T3S suggesting strong tectonic activities during the Late Eocene to Middle Miocene. 3. Methodology The evolutionary model has been constructed by cross section balancing. Cross section balancing technique is a quantifying tool for geological structures [14]. Near shore sections have been interpreted and the resulting cross sections are used in the study. The balanced cross section can be tested for geological validity, structural balance and consistency of the internal geometry. Retrodeformation of the cross section is carried out in order to refine the subsurface faulting interpretation. 4. Results and Analysis The balanced and restored cross section (since both seismic lines show similar structures, only Line 1 was used) (Figure 3) is shown below and is based on the structural styles, geometry and geological validity. The proposed model encompasses the following stages. 85 P a g e

3: a) T4S has been deposited during the Middle Miocene period; b) The post uplift period showing faulting due to

6 a T1S- Middle Eocene to Early Oligocene sediments. b T2S- Early Oligocene to Early Miocene sediments. T3S- Early Miocene to Middle Miocene sediments. T4S- Middle Miocene sediments. c Fig. 3: a) T4S has been deposited during the Middle Miocene period; b) The post uplift period showing faulting due to uplift and after erosion of T3S, T2S and T1S; c) The pre uplift period showing possibility of T3S as a piggyback basin within an accretionary prism. 86 P a g e

4.1. Middle Eocene to Early Oligocene The Eocene period witnessed southward to South-Eastward subduction of the proto-south China Sea oceanic crust beneath Borneo

During subduction, the upper crustal sediments are scraped from the subducting plate and accreted against the overriding plate (Figure 4) [16]. Fig.

7 4.1. Middle Eocene to Early Oligocene The Eocene period witnessed southward to South-Eastward subduction of the proto-south China Sea oceanic crust beneath Borneo continental plate [4], [6] and [15]. During subduction, the upper crustal sediments are scraped from the subducting plate and accreted against the overriding plate (Figure 4) [16]. Fig. 4: Subduction of proto-south China Sea oceanic crust below Borneo Late Oligocene to Early Miocene As subduction continued the sequence T2S was further combined atop on to the accreted T1S sediments forming an accretionary wedge (Figure 5). Fig. 5: T2S accreted along with T1S sediments as subduction continues. 87 P a g e

4.3. Early Miocene to Middle Miocene This time frame was eventful in the basin formation process. Deposition of T3S sediments commenced in the form of a piggyback basin (Figure 6).

8 4.3. Early Miocene to Middle Miocene This time frame was eventful in the basin formation process. Deposition of T3S sediments commenced in the form of a piggyback basin (Figure 6). At a plate convergence point, observations in the past from other basins, has shown the subducted lithosphere detaches from the lithosphere at the surface often after closing of an oceanic basin. Due to decrease in slab pull forces, a period of uplift of the surface occurs (Figure 7) [17]. Tectonic uplift of T3S sediments in the Southern and Southeastern parts of the study location is observed from distribution pattern and topography. This affected even the onshore area. The older sequences T2S and T1S were affected resulting in uplift and erosion of these sediments as well [4]. Fig. 6: Piggyback basin evolution with infill of T3S sediments Late Miocene to Pleistocene The younger sequences T4S and T5S were deposited atop the older three sequences and they do not bear any structural deformation and do not hold any significant exploration prospects. Subduction of oceanic lithosphere beneath NW Borneo, commenced between Paleocene and Middle Eocene, extended to Early Miocene has been documented by the previous scholars [18], [19], [20], [21], [22] and [23]. This tectonic process controlled the development of an elongated NE-SW trending basin [24]. Deposition of the thick sedimentary sequences in the Sarawak region coincides with the timing of subduction and basin by formation (Table 1). By the method of cross section restoration, the proposed model has attempted to throw light on the evolution of the near shore Tinjar and Balingian provinces as part of an accretionary wedge taking into account the subduction process. 88 P a g e

In this research, an evolutionary model for the nearshore Tinjar and Balingian provinces has been proposed using nearshore seismic lines and cross section balancing and restoration technique.

9 Uplift Slab detachment Fig. 7: Uplift of surface above slab detachment (modified after Buiter, 2000). 5. Conclusions Tectonism has played a crucial role in controlling the formation and development of the Sarawak basin which could also be deduced from the above results. In this research, an evolutionary model for the nearshore Tinjar and Balingian provinces has been proposed using nearshore seismic lines and cross section balancing and restoration technique. The resulting model depicts the subduction of proto-south China Sea oceanic crust beneath the Borneo plate during Eocene to Middle Miocene. The older sequences (T1S and T2S) are accreted on to the Borneo plate as a wedge and the formation of younger sequences (T3S) formed as piggyback basins. The sequences above T3S (T4S and younger) was deposited over the piggy back basin after the older sequences had subsided. Through the model, an attempt has been made to illustrate the course of formation of the nearshore areas of Tinjar and Balingian provinces. Even though, many works have been carried out in the past on the evolution of the Sarawak basin, in light of the current analysis and the known structural complexity & variability of the region, we recommend the evolution of each tectonic province within 89 P a g e

10 Sarawak should be discreetly and prudently studied in order to understand how tectonics has played a major role in shaping the various vital parts of an extensive basin. Acknowledgments The author(s) would like to thank Prof. Dr. Manuel Pubellier, Dean of Faculty of Geosciences and Petroleum Engineering, for his timely advice & support and Universiti Teknologi PETRONAS for financial support. References [1] Mitchum, R. M.; P. R. Vail; S. Thompson III, Seismic stratigraphy and global changes of sea level, part 2: The depositional sequence as a basic unit for stratigraphic analysis. American Association of Petroleum Geologists 1977; 26: [2] Mat-Zin, I. C. and M. E. Tucker, An alternate stratigraphic scheme for the Sarawak basin. Journal of Asian Earth Sciences 1999; 17: [3] Hazebroek, H. P., D. N. K. Tan, Tertiary tectonic evolution of the NW Sabah continental margin, Proceedings of the Symposium on Tectonic Framework and Energy Resources of the Western margin of Pacific Basin. Bulletin of the Geological Society of Malaysia 1993; 33: [4] Mat-Zin, I. C, Tertiary tectonics and sedimentation history of the Sarawak basin, East Malaysia. PhD theses, Durham University 1996, Available at 277p. [5] Haile, N. S., Geosynclinal theory and the organizational pattern of the North-west Borneo Geosyncline. Geological Society of London 1969; 124: [6] James, D. M. D., The geology and hydrocarbon resources of Negara Brunei Darussalam. Regional geological setting, Muzium Brunei 1984; [7] Shell, Evaluation of block SK-5 by XSK evaluation team. Sarawak Shell report, (unpublished) [8] Mazlan M., C. L. Kim, R. Wong, The structure and stratigraphy of of Deepwater Sarawak, Malaysia: Implications for tectonic evolution. Journal of Asian Earth Sciences 2013; 76: [9] Holloway N. H., North Palawan block, Philippines Its relation to Asian mainland and role in evolution of South China Sea. American Association of Petroleum Geologists Bulletin 1982; 66: [10] King, R. C., Tingay, M. R. P., Hillis, R. R., Morley, C. K., Clark, J, Present-day stress orientations and tectonic provinces of the NW Borneo collisional margin. Journal of Geophysical Research 2010; 115: [11] Mazlan, M., Tinjar Province. The Petroleum Geology and resources of Malaysia 1999; 1(16): P a g e

11 [12] Mazlan Madon, Geological setting of Sarawak. The Petroleum Geology and Resources of Malaysia 1999; 1(12): [13] Madon, M.B.Hj., and P. Abolins, Balingian province, in K.M. Leong (ed). The Petroleum Geology and Resource of Malaysia 1999; [14] Shiguo, W., Ni Xianglong, G. Junhua, Balanced cross section for restoration of tectonic evolution in the Southwest Okinawa Trough. Journal of China University of Geosciences 2007; 18(1): [15] Sapin, F., Pubellier, M, Lahfid, A., Janots, D., Aubourg, C. and Ringenbach, J. C., Onshore record of the subduction of a crustal salient: example of the NW Borneo Wedge. Terra Nova 2011; 23(4): [16] Burbidge, D. and J. Braun, Dynamical Evolution of accretionary wedges and thrust belts. Geophysical Journal International 2002; 148(3): [17] Buiter, S. J. H., Surface deformation resulting from subduction and slab detachment. PhD theses, Universiteit Utrecht 2000; no. 191, 129p. [18] Lee, T. Y. and L. A. Laver, Cenozoic plate reconstructions of the South East Asia. Tectonophysics 1995; 251: [19] Hall, R., Cenozoic plate reconstructions of SE Asia. In: Hall R., Blundell D. J. (eds) Tectonic Evolution of Southeast Asia, Geological Society London Special Publications 1997; 106: [20] Murphy, R. W., SE Asia reconstruction with a non-rotating Borneo. Geological Society of Malaysia Bulletin 1998; 42: [21] Rangin, C., W. Spakman, M. Pubellier, H. Bijward, Tomographic and geological constraints on subduction along the eastern Sundaland continental margin, South-East Asia. Bulletin de la Société Geologique de France 1998; 170: [22] Morley, C. K., A tectonic model for the Tertiary evolution of strike slip faults and rift basins in SE Asia. Tectonophysics 2002; 347: [23] Cullen, A. B., Transverse segmentation of the Baram-Balabac Basin, NW Borneo: refining the model of Borneo s tectonic evolution. Petroleum Geoscience, GeoScience World 2010; 16(1): [24] Tongkul, F., Tectonic evolution of Sabah, Malaysia. In: G. Nichols, R. Hall (eds.), Proceedings of the orogenesis in Action Conference, London, Journal of Southeast Asian Earth Sciences 1991; 6: P a g e

The tectonic evolution history of Borneo is complicated and had been hotly debated

Chapter 2: General Geology & Structure 2.1 REGIONAL GEOLOGY The tectonic evolution history of Borneo is complicated and had been hotly debated by different geologists such as C.S. Hutchison (2005), and