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Editorial Board Advisory Board
Minarwan Prof. Yahdi Zaim Chief Editor Quaternary Geology Bangkok, Thailand Institute of Technology, Bandung E-mail: [email protected] Prof. R. P. Koesoemadinata Herman Darman Emeritus Professor Deputy Chief Editor Institute of Technology, Bandung Shell International EP Kuala Lumpur, Malaysia Ir. Wartono Rahardjo E-mail: [email protected] University of Gajah Mada, Yogyakarta, Indonesia
Fatrial Bahesti Dr. Ukat Sukanta PT. Pertamina E&P ENI Indonesia NAD-North Sumatra Assets rd Standard Chartered Building 23 Floor Mohammad Syaiful Jl Prof Dr Satrio No 164, Jakarta 12950 - Indonesia Exploration Think Tank Indonesia E-mail: [email protected]
F. Hasan Sidi Wayan Heru Young Woodside, Perth, Australia University Link coordinator Legian Kaja, Kuta, Bali 80361, Indonesia E-mail: [email protected] Prof. Dr. Harry Doust Faculty of Earth and Life Sciences, Vrije Universiteit Visitasi Femant De Boelelaan 1085 1081 HV Amsterdam, The Netherlands Treasurer E-mails: [email protected]; Pertamina Hulu Energi [email protected] Kwarnas Building 6th Floor Jl. Medan Merdeka Timur No.6, Jakarta 10110 E-mail: [email protected] Dr. J.T. (Han) van Gorsel 6516 Minola St., HOUSTON, TX 77007, USA Rahmat Utomo www.vangorselslist.com E-mail: [email protected] Bangkok, Thailand E-mail: [email protected] Dr. T.J.A. Reijers Farid Ferdian Geo-Training & Travel Gevelakkers 11, 9465TV Anderen, The Netherlands Saka Energi Indonesia E-mail: [email protected] Jakarta, Indonesia E-mail: [email protected] Dr. Andy Wight formerly IIAPCO-Maxus-Repsol, latterly consultant Guest Editors for Mitra Energy Ltd, KL E-mail: [email protected] Dr. Susilohadi
Pusat Penelitian dan Pengembangan Geologi Kelautan, (Marine Geological Institute) Bandung, Indonesia
Dr. Udrekh Al Hanif BPPT (Agency for the Assessment and Application of Technology) Jakarta, Indonesia Cover Photograph:
A 3D model of Indonesian seafloor, taken from the proceedings of a scientific meeting to commemorate the 10th anniversary of the French-Indonesian cooperation in oceanography (1993).
• 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.
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Berita Sedimentologi
A sedimentological Journal of the Indonesia Sedimentologists Forum (FOSI), a commission of the Indonesian Association of Geologist (IAGI)
From the Editor Dear readers, particular theme. In this issue, we therefore he knows the geology of present you 2 full articles on the region pretty well. He replaces Welcome to the first volume of seismic stratigraphy and heat Dr. Peter Barber, who has been Berita Sedimentologi in 2015! flow estimation from bottom very helpful to FOSI in the past. simulating reflectors of gas On behalf of FOSI, I would like to Berita Sedimentologi publications hydrates; an extended abstract on express our gratitude and thanks in 2015 are dedicated to topics integrated multibeam, drop core to both Drs. Andy Wight and related to Marine Geology of and seismic interpretation of Peter Barber. Indonesia and are supported by North Banggai-Sula seafloor and Dr. Susilohadi of Marine a short article on marine We continue to seek high quality Geological Institute (Pusat expeditions in Indonesia during articles to be included in Berita Penelitian dan Pengembangan the Colonial years. Sedimentologi, so please contact Geologi Kelautan) and Dr. Udrekh one of the editors if you are Al Hanif of Agency for Assessment We also welcome Dr. Andy Wight interested to contribute to our and Application of Technology who recently agreed to become society. In the meantime, we hope (Badan Pengkajian dan one of our International you enjoy reading this volume. Penerapan Teknologi) as guest Reviewers. Dr. Wight is a highly editors. This volume, Berita experienced Petroleum Geologist Chief Editor Sedimentologi No. 32, will be the who has spent most of his Minarwan first of 3 volumes on the professional career in SE Asia,
Regards, Minarwan Chief Editor
INSIDE THIS ISSUE
Book Review : The SE Asian : History and Plio-Pleistocene Seismic Stratigraphy of Tectonic of the Australian-Asia the Java Sea between Bawean Island and 5 Collision, editor: Robert Hall et J.A. 56 East Java – S. Susilohadi and T.A. Soeprapto Reijers
Merits and Shortcomings of Heat Flow Book Review - Biodiversity, Estimates from Bottom Simulating Biogeography and Nature Conservation 17 Reflectors – Minarwan and R. Utomo in Wallacea and New Guinea (Volume 1), 58 Edited by D. Telnov, Ph.D. – H. Darman Frontier Exploration Using an Integrated Approach of Seafloor Multibeam, Drop Core and Seismic Interpretation – A Study 27 Case from North Banggai Sula – F. Ferdian
Marine Expeditions in Indonesia during the Colonial Years – H. Darman 30
Call for paper BS #33 –
to be published in August 2015
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About FOSI
he forum was founded in FOSI has close international team. IAGI office in Jakarta will T 1995 as the Indonesian relations with the Society of help if necessary. Sedimentologists Forum Sedimentary Geology (SEPM) and (FOSI). This organization is a the International Association of communication 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 APRIL 2015
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Plio-Pleistocene Seismic Stratigraphy of the Java Sea between Bawean Island and East Java
Susilohadi Susilohadi and Tjoek Azis Soeprapto Pusat Penelitian dan Pengembangan Geologi Kelautan, (Marine Geological Institute), Bandung, Indonesia
Corresponding author: Jalan Dr. Junjunan 236, Bandung-40174, Indonesia; Tel.:+62-22-603-2020; Fax:+62-22-601-7887; E-mail address: [email protected] (S.Susilohadi)
ABSTRACT
The southeast Java Sea forms a submerged part of the Sunda Shelf and lies on a relatively stable continental shelf, which reached its final form during the Quaternary. Marine geological investigations in this area have mostly been carried out as part of regional studies on the Sunda Shelf. Detailed studies, particularly for younger sequences, are lacking and, as a result, the neo-tectonics and response of the shelf area to extreme sea level fluctuations during Plio-Quaternary times are poorly known.
A set of high resolution reflection seismic profiles totalling some 3750 line km has been studied. All data were acquired by the Marine Geological Institute of Indonesia, which ran the survey in the southeast Java Sea in 1989-1990. The data show that the Late Tertiary sedimentation in the study area partly occurred in half graben basins, mostly bounded by northeastward trending faults which may be related to the regional suture belts running from central Java to south Kalimantan. Towards Pliocene time, the sedimentation occurred in east-trending synclinal basins, which indicate the dominance of a northward tectonic compressional stress. This continued until the Early Pleistocene, as indicated by some local thickening of the Early Pleistocene deposits. Since then, further basin development appears to have ceased, and a tectonically stable condition may have been reached. Quaternary sedimentation gradually changed the basin morphology into a relatively flat plain characterised by multiple erosional features resulting from extreme sea level fluctuations.
Keywords: Seismic Stratigraphy, Pliocene, Pleistocene, Java Sea.
INTRODUCTION reflections, particularly in the area where surficial reflections are strong. The southeast Java Sea forms the submerged part of the Sunda Shelf and lies on a relatively stable REGIONAL GEOLOGY continental shelf (Figure 1). Marine geological investigations in the southeast Java Sea have Based on regional geophysical data, Ben-Avraham mostly been carried out as part of regional studies and Emery (1973) noted that Tertiary sedimentation on the Sunda Shelf (e.g. Emery et al., 1972; Voris, in the southeast Java Sea occurred in basins which 2000; Ben-Avraham & Emery, 1973). Detailed and were bounded mostly by northeastward trending published studies, particularly for the Plio- faults (Figure 1). Many of these structures are half Pleistocene periods, are rare, although such studies grabens that formed on the pre-Tertiary shelf are necessary in order to understand the tectonic (Kenyon, 1977; Bishop, 1980). These major features and response of the shelf area to extreme sea level were interpreted by Ben-Avraham and Emery (1973) fluctuations during these times. as resulting from past interaction between the Eurasian and Indian-Australian lithospheric plates, The present study discusses the sedimentary facies the principal ridges probably representing part of an distribution, chronology and the related tectonism island arc system that was active during the Late in the southeast Java Sea during the Late Tertiary Cretaceous-earliest Tertiary (Bishop, 1980). Such and Quaternary. The discussion relies heavily on an island arc complex has been deduced from the sparker single channel seismic data (Figure 2), occurrence of pre-Tertiary ophiolites cropping out in which have been interpreted by applying the Central Java and in Southeast Kalimantan (van sequence stratigraphic concepts developed by Vail Bemmelen, 1949) possibly representing a previous et al. (1977) and Posamentier and Vail (1988). subduction complex (Katili, 1989). However, this study lacks reliable age determinations, as well as other published The Karimunjawa Arch is the dominant ridge in the geological studies. In addition, problems inherent eastern Java Sea. It extends into the offshore area from the equipment include: (1) the limited of southern Kalimantan as a broad positive feature penetration, (2) and the presence of strong multiple (Bishop, 1980).
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Figure 1. Location of the study area and the generalized Tertiary basement configuration according to Kenyon (1977). Superimposed on the Java Sea is Molengraaff river system of the last glacial period,which has been deduced from the first Snellius expedition (Molengraaff, 1921; Kuenen, 1950).
It is capped by the Karimunjawa Islands on which during the survey relied mostly on GPS navigation pre-Tertiary quartzite and phyllitic shale, cut by system, and by the time the acquisition was basic dykes, and probable Quaternary fissure- conducted, the horizontal accuracy was not less eruptive sheets crop out. This arch is separated by than 100m. The profiles were mostly oriented north- the narrow, northeast trending Muria Basin (West south and spaced 5 to 10 km apart. Florence Deep) from the Bawean Arch. The Bawean Arch is characterised by alkaline volcanism of the Stratigraphic control for calibration of the seismic latest Neogene or Quaternary and steeply dipping data was provided by six petroleum exploratory Miocene marine strata (van Bemmelen, 1949). wells, JS1-1, JS2-1, JS3-1, JS8-1, JS10-1 and JS16-1. However, these data cannot provide a DATA reliable stratigraphic timing resolution as the biostratigraphic and lithofacies analyses done were The data base for this study is drawn from seismic based on well cuttings which were commonly profiles of about 3750 line km in the Java Sea sampled every 30 ft penetration. Even so, they have (Figure 2). All geophysical data were obtained from narrowed the age estimation of the stratigraphic the Marine Geological Institute of Indonesia which time markers. ran the survey in 1989/1990. The seismic system used is a single channel 600 Joule sparker system, SEISMIC STRATIGRAPHY fired every 1 second. These setting have allowed of about 400 milliseconds penetration below the Seismic analysis indicates that the Late Tertiary seabed. The seismic signals were not tape recorded, and Quaternary sediments in the study area can be but were directly band pass filtered (200-2000 Hz) subdivided into three major seismic units. These and graphically recorded in analog format during units correspond to the Miocene, Pliocene and the survey. Due to this technique, no further data Quaternary and are referred to as Units 1, 2 and 3 processing was carried out. The ship positions respectively.
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Figure 2. Tracklines of single channel sparker seismic records used in this study superimposed on the bathymetric map of the study area. Thicker lines are parts of seismic lines presented in this paper for discussion. Dots in the Java Sea represent the oil exploration wells.
Unit 1 consists of two subunits: 2a and 2b, with subunit This Miocene unit can only be observed on the 2a forming the major part of the sequence. structurally high areas, such as near the Bawean Correlation between the seismic and the and Karimunjawa Arches, and on Madura Island. micropalaeontological data from some petroleum The age of Unit 1 is confirmed by well data of JS8-1 exploratory wells confirmed that this unit developed and JS3-1. The internal seismic reflection patterns during the Pliocene. The top boundary of Unit 2 is and areal distribution are poorly defined, an erosional surface marking extensive subaerial particularly because of the limited penetration of exposure in the study area. Based on reflection the seismic system used and strong multiple configuration patterns, the sediment sources of reflections. The lower boundary is unidentifiable, these subunits were mainly the Karimunjawa and but the upper boundary is a regional unconformity Bawean Arches in the western half of the study as shown by a pronounced erosional surface on the area. In the eastern half, the deposits were sourced structurally high areas (Figures 3, 4, 5 and 6). On from both the Bawean Arch and Madura Island, but most of seismic sections, Unit 1 is characterised by the distribution was complicated by the a medium amplitude, continuous parallel- development of folds. subparallel reflection pattern of possibly interbedded sandstone and mudstone (Figures 3, 4 On the stable area, such as on the Karimunjawa and 5). The sections acquired near the Arch, the Pliocene unit was thinly deposited on top Karimunjawa and Bawean Arches suggest that the of the Miocene unit which suggests that the lower part of Unit 1 is probably equivalent to the subsidence rate on the arch was very low. The Miocene strata exposed on these islands, which are seismic characters are mainly form a strong characterised by the occurrence of limonitic amplitude parallel reflection pattern (Figure 3) sandstone, interbedded with lignite, marl and which is often associated with mounded forms of crystalline limestone (Bemmelen, 1949). A mounded possibly reefal limestone. In the areas where the structure characterised by low amplitude of internal depositional slope was high, such as near the reflectors is observed on the top of Unit 1, and margins of the Muria Trough, the East Bawean probably represent a highstand reef (Figure 6). Trough and the growing Madura Island, the deposition of the lower part of Unit 2 may be divided Unit 2 into two main systems tracts: the lowstand and Unit 2 is relatively thick and was deposited highstand systems tracts (Figures 5 and 6). following sea level fall at the end of the Miocene. It
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subsidence and low
Seismic line JA from east of the Karimunjawa Islands which comprises a stable area of the
.
3
Figure Figure Karimunjawa Arch. Pliocene and Quaternary slope.depositional units are thin and nearly flat due to slow
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Pliocene. of end the by lessened may which subsidence, of
Seismic Seismic line JD which represents southeast margin of the Bawean Arch. A thicker succession of the
.
4
Figure Figure The wedge sequence. upward of shoaling a indicative amplitudes, reflection parallel stronger shows units Miocene increase southward a indicates 2 Unit shaped
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reef in deposition the Late Miocene. The complex pronounced prograding on the flank of
Seismic line JCN from southwestern slope of the Bawean Arch. The arch was exposed subaerially subaerially exposed The was arch Arch. Bawean of the slope from southwestern JCN line Seismic
.
5
Figure Figure highstand following the arch represents the major lowstand. level highstand sea glacial deposition last the from in result may 3d subunit the Pliocene. A major channel observed on top of
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The continuous growth of the island has resulted of resulted has growth island the The continuous
Seismic line JI from northern flank of Madura flank of Island. from JI line Madura northern Seismic
.
6
Figure Figure in of a progradation northward the pronounced and lowstand systems in highstand tracts the Pliocene and Early area. study the in Java of coast northern the towards extend may conditions Such Quaternary.
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The transgressive systems tract on most of the sea level fluctuation. Because these subunits have a seismic lines studied is absent or unidentified, similar seismic character and do not represent thick probably due to a rapid sea level rise which did not deposits, lateral correlation is difficult and tends to permit formation of a seismically resolvable be speculative. But they can be grouped into five transgressive unit. subunits, 3a to 3e, based on the occurrence of widespread unconformities on top of each unit. In the western part of the study area, the upper These unconformities are commonly associated with part of Unit 2 is recognised as a thin prograding rather deep and wide fluvial channelling. complex downlapping onto the erosional surface at the top of Unit 2a (Figure 7). This erosional surface a. Subunits 3a and 3b should be correlated with a lowstand of sea level The subunits 3a and 3b were deposited during the and the prograding complex with the highstand Early Pleistocene, based on their stratigraphic deposits. On the flank of Madura Island a thicker position overlying Pliocene Unit 2. A stratigraphic unit was deposited, which may be resolved into subdivision between these subunits in the western lowstand and highstand deposits (Figure 6). part of the study area is rather speculative, but clear differentiation can be made in the areas near Figure 9 shows palaeogeographic maps during the the Java and Madura Islands due to the higher lowstand period of subunit 2a. These maps indicate subsidence rate and the occurrence of a relatively that the Pliocene basin in the western half of the large sea level fall at the end of subunit 3a study area was still influenced by the normal fault deposition (Figures 6 and 7). Seismic features, such movement of the half graben system in the Muria as rapid basinward thinning (Figure 6) and Trough. The occurrence of the deepest basin and pronounced anticlines (Figure 7) indicate that their accumulation of the thickest Pliocene sediments in distribution was influenced by local structural this trough (particularly along the normal faults) development. There, subunit 3a can be further has further suggested probable faster subsidence subdivided into subunits 3a-1 and 3a-2 based on and sedimentation rates. In the eastern half of the the occurrence of an internal erosional surface area, the influence of the previous structural (Figure 7). The thickness of subunit 3a-1 reaches configuration (Figure 3) is not obvious. The Pliocene 100 msec TWT (about 75 m) in the deepest portion structural development (east-west trending folds) of the basin, and it gradually thins toward the basin had more influence on the sedimentation margin. The maximum thickness of subunit 3a-2 is particularly in the area between Java and Bawean about 60 msec TWT (about 45 m). The thickness Islands and near the Madura Island, as indicated by variation is mainly due to local subsidence, post the trends of basin morphology and the Pliocene depositional erosion and a gradual thinning sediment accumulation (Figure 8). because of the rising of the basin margin. Subunit 3a-2 onlaps on subunit 3a-1 on the southern Unit 3 margin, and on Unit 2 when subunit 3a-1 wedges Unit 3 was deposited following a sea level fall which out. The seismic character of these subunits is exposed the whole study area at the end of the similar, a subparallel reflection pattern with Pliocene. The seismic characters and sedimentation medium amplitude and medium continuity which patterns of Unit 3 differ significantly from those of suggests deposition in a shallow marine the preceding Unit 2. They appear to be strongly environment (Sangree & Widmier, 1977). To the influenced by extreme and rapid sea level north of Madura Island a local deepening occurred fluctuations. Such fluctuations during the (Fig. 6), and subunits 3a-1 and 3a-2 are Quaternary have been demonstrated by many characterised by northward prograding clinoform workers through the oxygen isotope records of deep deposits, indicating that the sediments were derived sea cores, which they have related with the from the growing Madura Island. Subunits 3a-1 and orbitally-induced fluctuations of global ice volume. 3a-2 may be regarded as the units responsible for These glacio-eustatic sea level fluctuations are the flatness of this area. particularly apparent since 0.97 Ma (Harland et al., 1989) with a relatively constant period. The global The subunit 3b was deposited on a flat surface and sea level falls may have reached 130 m below has an extensive coverage although its thickness is present level during the glacial maximum (Bloom et less than 35 msec TWT (26 m). Seismically, this al., 1974; Chappell & Shackleton, 1986; Fairbanks, subunit is characterised by a similar appearance to 1989). subunits 3a-1 and 3a-2, and probably was deposited in a similar environment. The upper part The present seismic study identified five main tends to show subparallel to hummocky patterns Quaternary seismic subunits in the area. These with variable amplitude which indicates a shoaling subunits are characterised mostly by parallel to (regression) of the unit before finally being exposed subparallel reflection patterns or are reflection free. subaerially. Each of them ended with channel cut and fill along their upper part and are interpreted to represent b. Subunits 3c, 3d and 3e marine deposition and fluvial channelling Subunits 3c and 3d can further be subdivided into respectively. In some areas the thickness of these three (3c-1, 3c-2 and 3c-3) and two (3d-1 and 3d-2) subunits appears to be similar, which may indicate respectively. constant subsidence rates combined with periods of
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W and direction of are lateral distributions controlled the Late -
Seismic Seismic line JCS from the north of east Java which represents an area with high subsidence and Early Quaternary subunits. Quaternary Early
. 7
Figure rates. lie observed Local structures depositional in an E and Pliocene
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y Pliocene),
Palaeogeographic map during of the systems 2a Subunit deposition tract Palaeogeographic lowstand (Earl
.
8
Figure Figure Miocene. top at TWT) mSec. (in contours structure time the on plotted
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These subdivisions can only be recognised in a respectively. Because the average water depth in the limited area where the subsidence and study area is about 60 m, the fluvial channelling sedimentation rates were relatively high, such as in may be correlated with the major sea level lows the area just north of Java (Figure 7). during the Quaternary. The bases of subunits 3e, 3d and 3c are tentatively correlated with the glacial Subunits 3c-1 and 3c-2 are similar in seismic periods during oxygen isotope stages 2, 6 and 16 of character, showing a medium amplitude, Harland et al. (1989) respectively, while subunits 3a subparallel reflection pattern which probably and 3b represent earlier periods. During the glacial represents a shallow marine environment. Subunit periods the Sunda Shelf became widely exposed, 3c-3 is reflection free, indicating most probably and river systems such as the Molengraaff river homogeneous mudstone. Subunit 3d is extensively (Molengraaff, 1921; Kuenen, 1950; Voris, 2000) distributed and in some areas is characterised by may have developed in the last glacial period. an almost reflection free character suggesting a nearly homogeneous deposit probably of mudstone. ACKNOWLEDGEMENTS In the western part, subunits 3d-1 and 3d-2are very thin to absent, which indicates a low depositional The authors wish to thank the Head of the Marine rate. Geological Institute of Indonesia for permission to use the data. This paper is part of the first author’s Subunit 3e consists of a single reflection-free PhD thesis supervised by Dr. Leonie Jones, Prof. sequence of possibly homogeneous mudstone. The Colin Murray-Wallace and Prof. Brian G. Jones. maximum thickness in the basinal area is about 30 Therefore, their supervision, support and msec TWT (about 22 m) with a little variation on the contribution are greatly acknowledged. western part of the study area. On some parts to the north of Madura Island this subunit is too thin REFERENCES to be identified, but locally thick deposits of up to 25 msec TWT (about 19 m) occur in a limited area, Aziz, S., Sutrisno, Y. Noya, and K. Brata, 1993, particularly near the river mouths on the northern Geology of the Tanjungbumi and Pamekasan coast of Java. The fluvial channelling at the base of Quadrangle, Jawa: Bandung, Geological subunit 3e in some areas is very pronounced Research and Development Centre, p. 11. (Figure 6). Its occurrence can be related to the last Aziz, S., S. Hardjoprawiro, and A. Mangga, 1993, glacial period, during the oxygen isotope stage 6, Geological map of the Bawean and when the sea level was -130 m below present level Masalembo Quadrangle, Java.: Geological (Chappell & Shackleton, 1986). Research and Development Centre. Ben-Avraham, Z. and K. O. Emery, 1973, Structural DISCUSSION AND CONCLUSION framework of Sunda Shelf: American Association of Petroleum Geologists Bulletin, The Miocene basin configuration of the study area v. 57, no. 12, p. 2323-2366. is poorly known, but it is suspected that the basin Bishop, W. F., 1980, Structure, stratigraphy and development was still strongly influenced by the hydrocarbons offshore southern Kalimantan, northeast-trending structures related to the Indonesia: American Association of Petroleum basement configuration. These structures are half Geologists Bulletin, v. 64, no 1, p. 37-59. grabens and have been the major control for the Bloom, A.L., W. S. Broecker, J. M. A. Chappell, R. Early Tertiary sedimentation. Although some K. Matthews, and K. J. Mesolella, 1974, elements of these structures were still active until Quaternary sea level fluctuations on a the Pleistocene, their effectiveness in controlling the tectonic coast: New 230Th/234U dates from the sedimentation during the post-Miocene was Huon Peninsula, New Guinea: Quaternary diminished. The Pliocene sedimentation, in general, Research, v. 4, p. 185-205. occurred in E-W trending synclinal basins which Chappell, J., and N. J. Shackleton, 1986, Oxygen indicate the dominance of the northward tectonic isotopes and sea level: Nature 324, p. 137- compressional stress. This continued until the Early 140. Pleistocene, as is indicated by some local thickening Emery, K.O., E. Uchupi, J. Sunderland, H. L. of the Early Pleistocene deposits. Since then, Uktolseja, and E. M. Young, 1972, Geological further basin development appears to have ceased, structure and some water characteristics of and a tectonically stable condition may have been the Java Sea and adjacent continental shelf: reached. United Nation ECAFE-CCOP Technical Bulletin, v. 6, p. 197-223. The Quaternary units, which are represented by Harland, W.B., R. L. Armstrong, A. V. Cox, L. E. nine thin subunits, tend to be distributed widely Craig, A. G. Smith, and D. G. Smith, 1989, A because of deposition on a relatively flat lying area. Geologic Time Scale 1989: Cambridge, The seismic characters are very similar, comprising Cambridge University Press, 263 p. subparallel reflection or almost reflection free Kenyon, C.S., 1977, Distribution and morphology of patterns at the bottom which represent marine Early Miocene reefs, East Java Sea: deposits, topped by extensive fluvial channelling. Indonesian Petroleum Association, This repetitive succession is thought to represent Proceeding of the 6th Annual Convention highstand and lowstand periods of sea level May 1977, p. 215-223.
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Kuenen, P.H., 1950, Marine Geology: New York, Sumenep Quadrangle, Jawa: Bandung, John Wiley and Son, p. 551. Geological Research and Development Manur, H., R. Barraclough, 1994, Structural Centre, p.16. control on hydrocarbon habitat in the Susilohadi, 1995, Late Tertiary and Quaternary Bawean area, East Java Sea: Indonesian Geology of the East Java Basin, Indonesia.: Petroleum Association, Proceedings of the PhD thesis, unpublished, The University of 23th Annual Convention, October 1994, p. Wollongong, Australia. 129-144. Vail P. R., 1987, Seismic stratigraphy interpretation Molengraaff, G.A.F., 1921, Modern deep-sea using sequence stratigraphy. In Bally, A.W. research in the east Indian archipelago: (ed.). Atlas of Seismic Stratigraphy, vol. 1, p. Geological Journal, v. 57, p. 95-121. 1-14. Tulsa, American Association of Posamentier, H.W. and P. R. Vail, 1988, Eustatic Petroleum Geologists. controls on clastic deposition II - sequence Vail, P. R., R. M. Mitchum Jr., R. G. Todd, J. M. and system tract models. In Wilgus, C.K., Widmier, S. Thompson III, J. B. Sangree, J. Posamentier, H.W., Ross, C.A. and Kendall, N. Bubb, and W. G. Hatlelid, 1977, Seismic C.G., (eds). Sea-Level Changes: An Integrated stratigraphy and global changes of sea level. Approach, p. 125-154. Society of Economic In Payton, C.E., (ed.). Seismic Stratigraphy - Paleontologists and Mineralogists, Special Application to Hydrocarbon Exploration, p. Publication No. 42. 49-212. American Association of Petroleum Sangree, J.B. and J. M. Widmier, 1977, Seismic Geologists, Memoir 26. stratigraphy and global changes of sea level, Van Bemmelen, R.W., 1949, The Geology of part 9: seismic interpretation of clastic Indonesia: vol. 1. The Hague, Martinus depositional facies. In Payton, C.E., (ed.). Nijhoff, p. 732. Seismic Stratigraphy - Application to Voris, H.K., 2000, Maps of Pleistocene sea levels in Hydrocarbon Exploration, p. 165-184. Southeast Asia: shorelines, river systems American Association of Petroleum and time durations: Journal of Geologists, Memoir 26. Biogeography, v. 27, p. 1153–1167. Situmorang, R. L., D. A. Agustianto, and M. Suparman, 1992, Geology of the Waru-
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Merits and Shortcomings of Heat Flow Estimates from Bottom Simulating Reflectors
Minarwan and Rahmat Utomo Mubadala Petroleum (Thailand) Ltd, Bangkok, Thailand
Corresponding author: [email protected]
ABSTRACT
The presence of gas hydrates in deep marine sediments and their Bottom Simulating Reflectors (BSRs) on seismic lines can be used to estimate present-day surface heat flow. Despite its limited accuracy, the estimated heat flow is still useful as an input in thermal maturity modeling of a frontier basin.
BSRs commonly occur at several hundred meters below the seafloor, in low latitudes generally in areas with water depth greater than about 700-1000m. They run parallel to the sea floor and may cross-cut lithological boundaries. They represent a phase boundary between a gas-hydrates-stable zone and underlying free gas- and water-saturated sediments. Since the depth of the hydrate- free gas phase change is a function of temperature, depth (pressure) and gas composition for a given gas composition (assuming hydrostatic pressure and mainly methane gas), the temperature gradient between seafloor and the BSR can be calculated from its depth. The temperature gradient can then be converted into heat flow, provided that thermal conductivity of the sediment is known.
Keywords: heat flow, gas hydrates, bottom-simulating reflectors.
INTRODUCTION 2006), Gulf of Cadiz, Spain (León et al., 2009), Simeulue fore-arc basin, Indonesia (Lutz et al., Modeling source rock maturity in a basin requires 2011) and the Andaman Sea (Shankar and Riedel, reliable thermal calibration, ideally by using 2013; Shankar et al., 2014). vitrinite reflectance data or other maturity indicators. It is also important to calibrate the Despite its usefulness, calculated heat flow from present-day heat flow or geothermal gradient used BSRs can be inaccurate and show some disparities in the modeling against the present-day thermal with measured heat flow as reported by Kaul et al. condition, which can be done by using (2000) and He et al. (2009). This paper reviews temperature gradient data from wells or direct heat advantages and shortcomings of BSR heat flow flow measurements. If vitrinite reflectance or other based on personal experience and some published thermal indicators are not available, then the materials. We present the methods to derive heat minimum pre-requisite would be to find the flow from BSRs, within the context of Indonesian present-day geothermal gradient and/or heat flow sea waters, and provide suggestions on how to use data in order to predict the current level of thermal them as inputs in thermal maturity modeling. We maturity. As a temperature model forms an will also review potential errors associated with important part of source rock maturity modeling, parameter assumption and theoretical errors as maximum efforts have to be made in order to get shown by previous publications. the most representative temperature input. GAS HYDRATES AND BOTTOM In a frontier deepwater basin with a good coverage SIMULATING REFLECTION (BSR) of seismic data and where gas hydrates are present, heat flow can be estimated by deriving Gas hydrates are ice-like crystalline solids formed temperature of the phase change in relation to the from water and gases (mostly CH4) under low gas hydrate system. The method for estimating temperature and moderate to high pressure heat flow from marine gas hydrates was introduced conditions. They can be present in an area where by Yamano et al. (1982) and to date, it has been abundant supply of methane exists in the system. applied in many regions including Sebakor Sea, Their stability is controlled by methane solubility Irian Jaya, Indonesia (Hardjono et al., 1998), (the required minimum methane concentration) Kerala-Konkan, India (Shankar et al., 2004), and a three-phase equilibrium curve of CH4- Caribbean offshore Colombia (López and Ojeda, hydrates-water (e.g. Kvenvolden, 1988; Davie et 2006), offshore Southwest Taiwan (Shyu et al., al., 2004—Figure 1).
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Figure 1. P-T diagram of gas hydrate stability Figure 2. Gas hydrate stability zone in marine based on a three-phase equilibrium curve (after environment is located between sediment-water
Davie et al., 2004). Solid squares are P-T at the interface and the intersection of geothermal
gradient and the CH4-hydrates-water equilibrium base of natural GHSZ drilled by Ocean Drilling curve (Dickens and Quinby-Hunt, 1997). Graphic is Program, which show good correlation with experimental three-phase P-T curve (sea water). from Davie et al. (2004).
In cold or deep marine environments, gas hydrates accumulation of methane hydrates in marine are stable between the sediment-water interface sediments. The most relevant points from their and the intersection of the geothermal gradient work regarding gas hydrate & BSR are: (1) the base with a CH4-hydrates-water equilibrium curve of the zone where actual gas hydrates occur is not (Dickens and Quinby-Hunt, 1997—Figure 2). always at the base of GHSZ, but rather lies at shallower depth than the base of the stability zone; Initial research on methane gas hydrates (2) If the BSR marks the top of the free gas zone, occurrence in marine sediments inferred that the then it will occur substantially deeper than the base of Gas Hydrates Stability Zone (GHSZ) or base of the stability zones in some settings and (3) Methane Hydrates Stability Zone (MHSZ), which the presence of methane within the pressure- represents the phase boundary from marine temperature stability field for methane gas sediments containing solid gas hydrates to those hydrates is not sufficient for gas hydrates to occur. containing only water and free gas, is frequently Gas hydrates “can only form if the mass fraction of imaged on seismic sections as a high amplitude methane dissolved in liquid exceeds methane reflection that mimics the seafloor and cross-cuts solubility in seawater and if the methane flux reflections of sedimentary layers. The reflection is exceeds a critical value corresponding to the rate of called a Bottom-Simulating Reflection (BSR) and it diffusive methane transport”. Figure 3 illustrates always shows reverse polarity from that of the the relationship between tops and bottoms of seafloor, due to the decrease in velocity and actual gas hydrate, hydrate stability zone and top density across the boundary (Yamano et al., 1982). of free gas according to the model developed by Xu The BSR is distinguishable from seafloor multiples & Ruppel (1999). as the multiples occur at twice the two-way time (TWT) between sea surface and seafloor. A BSR can ESTIMATING HEAT FLOW FROM THE BSR be present at depths of 100 to 1100 m below the seafloor (Collett, 2002) and the thickness of gas The commonly accepted method to estimate heat hydrates is usually 220–400 m (León et al., 2009). flow from gas hydrates requires the geothermal gradient from the seafloor to the base of the GHSZ Following Ocean Drilling Program (ODP) Leg 164 in (note: main assumption here is the BSR marks the late 1995, Xu and Ruppel (1999) developed a base of GHSZ and also the top free gas) and better analytical formula to explain evolution and thermal conductivity of the sediments where the
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Figure 3. Possible location of BSR and its relationship to the base of Gas Hydrate Stability Zone (GHSZ)/Methane Hydrate Stability Zone (MHSZ). BSRG1 is the estimated thermal gradient if the BSR
represents the base of Methane Hydrate Zone (this will give higher BSR heat flow than the measured
heat flow). BSRG2 is the estimated thermal gradient if the BSR represents the top of free gas zone (this will give lower BSR heat flow). Graphic is from He et al. (2009), based on the model developed by Xu & Ruppel (1999). gas hydrates are present. The geothermal gradient estimated by using seismic and bathymetric data. can be calculated if temperatures and depths of However, as the stability of the gas hydrate phase the BSR and the seafloor are known. The simplest is determined by temperature (T) and pressure (P), approach would be to relate temperature (T) and then another function [P=f(Z)] correlating P and Z depth (Z) at the base of the GHSZ as a function has to be known first. [T=f(Z)] because Z is the first variable that can be
The BSR heat flow is estimated by using the equals hydrostatic pressure (León et al., 2009) and following equation (e.g. Shankar and Riedel, 2013): therefore, P in Equation (1) can be calculated from this equation: Qbsr = 1000 x k x [(Tbsr - Tsea)/(Zbsr - Zsea)] (1) P = ρ x g x Zbsr (3) 2 where Qbsr is BSR heat flow (in mW/m ), k is the thermal conductivity of marine sediments (in where P is pressure at depth (MPa), ρ is density of 3 2 W/mK), Tbsr (K) is the temperature at the depth of water (kg/m ), g is gravity acceleration (9.81 m/s ) BSR (Zbsr) and Tsea is the temperature at the and Zbsr is depth of the BSR (m subsea). seafloor (Zsea). The density of seawater can be estimated by The temperature at the BSR (Tbsr) is estimated by assuming constant salinity and sea surface using the published empirical equation from temperature for practicality. The salinity and sea Dickens and Quinby-Hunt (1994), which relates surface temperature data can be taken from the pressure to temperature of methane hydrate World Ocean Atlas (2013), which can be accessed disassociation in a laboratory experiment by using online at US National Oceanic & Atmospheric seawater (salinity of 33.5 ppt). For any given Administration (NOAA) website. As an example, the pressure between 2.5–10 MPa, their experiment average salinity and surface temperature of shows that P and T follow this equation: Indonesian seawater are 33.5 ppt and 28.4 C, respectively (World Ocean Atlas, 2013). Using -3 -4 1/Tbsr = 3.79 x 10 – [2.83 x 10 x log(P)] (2) these numbers, the density of Indonesian seawater would be 1021.182 kg/m3 (Millero et al, 1980). If where Tbsr is temperature (K) and P is pressure this value is used in Equation (3) then the (MPa). equation becomes:
Assuming pore-waters are connected and there is P = 0.010017795 x Zbsr (4) no overpressure in the system, then pore pressure
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The Zbsr is calculated by converting Two-Way-Time (1990) suggested an empirical solution that gives (t) from seismic into depth. The depth conversion average thermal conductivity of sediments starting can be done by using the following steps from the sea floor as follows: (assuming constant seismic velocity in seawater of -4 -7 2 1500 m/s): k = 1.07 + (5.86 x 10 ) x Dbsr – (3.24 x 10 ) x Dbsr (10) Zbsr = Zsea + Dbsr (5) 1 Zsea = 1500 ( ⁄2 tsea) (6) where k is thermal conductivity of sediments (W/m K) and Dbsr is the thickness below the sea floor (m). Equations (7) and (8) are taken from Equations (1) This equation in general is consistent with & (2) of He et al. (2009), which were used to measured thermal conductivity in the Xisha estimate depth for the upper 1s seafloor sediments Trough (He et al., 2009). The measured thermal in the Xisha Trough and Northern South China conductivity of marine sediments actually can Sea. range pretty wide, for examples 1.1–1.8 W/m K (0– 3 m bsf) in the Makran accretionary prism, Dbsr = 982.576 (tbsr – tsea); if (tbsr – tsea) ≤ 0.5s (7) offshore Pakistan (Kaul et al., 2000) and 1.0–1.4 or W/m K (0–300 m bsf) in the Cascadia margin 2 Dbsr = 121.52 (tbsr – tsea) + 1269.1 (tbsr – tsea) – (Ganguly et al, 2000). However the average thermal 173.692; if 1s ≥ (tbsr – tsea) > 0.5s (8) conductivity of marine sediments can also be assumed to be approx. 1.2 W/m K (Davis et al., where Dbsr is thickness of the BSR (m from 1990) to 1.27 W/m K (Kaul et al., 2000). seafloor), tsea and tbsr are TWT of the sea floor and the BSR, respectively, from seismic datum (sea level) in seconds. ADVANTAGES AND SHORTCOMINGS
The Dbsr can also be estimated from depth Advantages conversion by using a constant interval velocity for In a frontier basin where no prior hydrocarbon the upper 1km of marine sediments. For examples, exploration activities have taken place and no Yamano et al. (1982) used 1.85±0.05 km/s in the present-day heat flow measurements are available, Nankai Trough, Japan; Davis et al. (1990) used BSR heat flow estimates are useful as a present- 2000 m/s in the Northern Cascadia margin; while day heat flow input in basin modeling. Having a in the Simeulue fore-arc basin the interval velocity favorable thermal maturity model of a basin would may range from 1900 m/s to 2200 m/s (Franke et support a decision of whether or not to explore for al., 2008). conventional hydrocarbon in a frontier area. The method is considerably less expensive and more After solving Equation (4), the calculated pressure practical than acquiring heat flow data directly can be used to solve Equation (2) and this gives through heat flow probes, because BSR can be the temperature of the BSR (Tbsr). The seafloor identified even from regional 2D seismic lines and temperature (Tsea in K) ideally should be taken calculations of heat flow values can be done from in situ measurement, however in the absence quickly by using publicly available parameter of CTD (Conductivity-Temperature-Depth) and assumptions. If BSR's occur in many regional Expandable Bathythermograph (XBT), Tsea can be seismic lines across a basin, then more heat flow estimated from the World Ocean Atlas (2013) values can be derived and variation of these values dataset, providing representative data points are can be taken into consideration to get appropriate available. Otherwise, another way to get seafloor thermal maturity model(s). temperature is by adopting an equation used by Shankar and Riedel (2013) in the Andaman Sea: Shortcomings As previously explained in the methodology to Tsea = 278.645 – (0.0002 x Zsea) (9) derive heat flow from the BSR, various levels of assumptions and simplification must be applied, The equation above was based on in situ due to either lack of data or naturally insufficient measurements and published data near Little empirical solution to constrain physical and Andaman Island, which is relatively close to chemical properties of the required input Indonesia region. It must be noted that seafloor parameters. The assumptions and simplifications temperature can be affected by deep current flow, may eventually lead to inaccurate BSR heat flow, therefore it is possible to get different temperatures which may show large variation and even from different measurements throughout the year. disparities to measured heat flow values. The seafloor temperatures generated by the two methods mentioned above can differ by approx. 1 Another limitation of using BSR to estimate heat C, hence creating some uncertainties on flow is related to the Tbsr-Pressure relationship estimated heat flow (see next section). (Equation 2) and the sea floor temperature (Equation 9) that are best-applied in the deepwater The last parameter to be estimated before setting (WD > 750m). Using these equations for calculating heat flow from the BSR is the thermal shallow water setting can give Tsea > Tbsr, hence conductivity (k) of marine sediments. Davis et al. giving negative heat flow values.
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BSR Heat Flow Variation northern Cascadia margin, Canada, the regional It is common to get a large variation of heat flow BSR heat flow increase towards the deformation when they are derived from the BSR in a basin. front, which is consistent with the trend shown by The following examples demonstrate how wide the heat flow probe, and locally, they are low over range can be: topographic highs and high over the flanks of the 36–90 mW/m2 (average 60.8 mW/m2) in one highs (Figure 4; Ganguly et al., 2000]. Similar Indonesian basin (unpublished) regional BSR heat flow behavior has also been 34.8–59.9 mW/m2 (average 47.7 mW/m2) in the seen by Kaul et al. (2000) in the Makran Sebakor Sea, Irian Jaya (Hardjono et al., 1998) accretionary prism offshore Pakistan. This large 32–80 mW/m2 in the Xisha Trough (He et al., variation of heat flow values could be controlled by 2009) active geological process such as proximity to 37–74 mW/m2 in the Simeulue fore-arc basin active deformation front and effects of rapid (Lutz et al., 2011), and sedimentation, but could also be due to poor 12–41.5 mW/m2 in the Andaman Sea (Shankar control of subsurface velocity variation. Local heat and Riedel, 2013). flow variation may be caused by dynamic effects such as upward migration of warm fluids along In some cases, heat flow variation follows both permeable faults and the displacement of isotherm regional and local trends. For example on the by thrust faulting (Ganguly et al., 2000).
Figure 4. Local variation of BSR heat flow in the Cascadia Margin, Canada, showing low heat flow values on the topographic highs and high heat flow on the flank (Ganguly et al., 2000).
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Disparities between BSR and Measured Heat sediment types, therefore using a single thermal Flow conductivity for every calculation is not perfect. Disparities between BSR-derived and measured heat flow were reported by Kaul et al. (2000) in the The biggest uncertainty is the gas composition, Makran accretionary prism and He et al. (2009) in because the general assumption is that gas in the Xisha Trough, South China Sea. In the Makran hydrates is pure methane (CH4). León et al. (2009) accretionary prism, the BSR heat flow values are showed that if the gas is thermogenic (i.e. contains consistently higher than the measured heat flow C2 to C5), for any given depth between 2000 and by about 15 to 25 mW/m2. The discrepancies were 3000 m, the T at the base of the GHSZ will be 5 ºC attributed to high sedimentation rate and tectonic higher than that of biogenic methane hydrates, uplift that led to the upward migration of gas which means the estimated heat flow will be hotter hydrate stability zone (as gas hydrates are by approximately 29 to 35%. dissolved at the base of the GHSZ). Geological Phenomenon In the Xisha Trough, the BSR heat flow values are Examples of the geological phenomenon that can 32–80 mW/m2 and are significantly lower than the influence heat flow near the seafloor is the measured values of 83–112 mW/m2. He et al. thickening of sediment wedge towards the (2009) argued that the disparities are caused by coastline from the deformation front of a theoretical errors rather than parameter errors subduction zone (e.g. Northern Cascadia, Canada because the discrepancies are larger than a change and Makran accretionary prism, Pakistan) and in the input parameters would have contributed to. upward migration of warm fluid through They estimated that the parameter errors would permeable faults or due to rapid dewatering have affected the BSR heat flow by only less than process when sediments are compacting. Wang et 25%, while their calculations indicate al. (1993) modeled that heat reduction due to the discrepancies of up to 50% in some geological thickening of sediment wedge is more significant settings. than the heat increase caused by the upward- migrating fluid expulsion, which consequently Source of Error and Implications to BSR Heat significantly can depress the seafloor heat flow to Flow become lower than the deep lithospheric heat flow. Uncertainties in Input Parameter Assumptions The first source of errors in BSR heat flow Theoretical Errors estimation is due to uncertainties in input The model involving a critical value of methane parameter assumptions, particularly from flux to exceed methane solubility in seawater, subsurface velocity (for time-depth conversion), necessary for methane hydrates to form, was seafloor temperature, thermal conductivity and gas developed by Xu and Ruppel (1999) to explain composition. Tables 1 and 2 show the sensitivity of natural occurrence gas hydrates and its various input parameters changes to the estimated relationship to the BSRs on the Blake Ridge heat flow. Assuming all other parameters are (offshore southeast US). Their work demonstrates similar, an increase in the interval seismic velocity that the base of GHSZ (MHSZ) does not necessarily by 10% would increase the estimated heat flow by coincide with a BSR and in some geological around 8-9%, while a decrease of 10% would make settings the BSRs can represent the base of the the calculated heat flow lower by around 6–7% actual methane hydrates or the top of the free gas (Table 1). A variation in seafloor temperature of 1 zone. The meaning of ‘some geological settings’ ºC lower or higher would contribute to the increase here is those with different combination of water or decrease of estimated heat flow by ±6-10%, depth, regional heat flow and available mass respectively (Table 2, columns 2 & 3). fraction of methane. In some settings, if the BSR represents the base of methane hydrate zone A change in thermal conductivity by 0.1 W/mK (shallower than the base of the stability zone), then (Table 2, columns 4 and 5) correlates to a change the BSR heat flow will be higher than the regional in the estimated heat flow by ±8-9%. As the heat flow. However, if the BSR represents the top thermal conductivity may range from 1.0 to 1.4 of free gas zone, then the BSR heat flow will be W/m K for the first 300 m of sediments below the lower (see Figure 3). The latter case was proposed seafloor (Ganguly et al., 2000), then the estimated by He et al. (1999) as the reason for the much heat flow can vary by 18% colder for lower thermal lower BSR heat flow in the Xisha Trough, South conductivity and 15% hotter for higher thermal China Sea. The disparities were caused by an conductivity (Table 2, columns 6 and 7). At some oversimplification of the BSR as the base of the circumstances, when the TWT thickness between GHSZ (MHSZ) in every setting. This is a potential the BSR and the seafloor is within the range of error in the theoretical assumption of BSR heat 0.5–1.0 s, a thermal conductivity of 1.0 W/m K flow calculation and can only be solved when heat can lead to approximately 24% colder heat flow flow probes or direct drilling data are available. (Table 2, column 6 Case 2). The thermal conductivity may also vary spatially depending on
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against frequency and suitable range to identify where the heat values are concentrated; 2. Compare the results with published present-day heat flow at the surface of the Earth's crust (Global Heat Flow Database of the International Heat Flow Commission, Figure 5; Pollack et al., 1993), or for SE Asia and Indonesia region compare with the published heat flow data compilation from Smyth (2010). 3. Build low, expected and high case heat flow models that are sensible to present-day heat flow values as guided by global database and also tectonic setting of the basin. Currie and Hyndman (2006) observed that the typical heat flow for fore arc basins is approx. 40 mW/m2, while for Indonesian back arc basins it is 76±18 mW/m2.
CONCLUSIONS
The method of deriving heat flow from BSRs, despite not being new and highly accurate, is still useful to evaluate hydrocarbon potential of a frontier region. It can give significant input for making a quick decision in evaluating a new area with limited information. The method can be applied to any frontier basin where gas hydrates are present, providing the assumptions to derive the heat flow are appropriate to local conditions.
Input parameter assumptions are a source of uncertainties in estimating heat flow by using the BSR method. Parameters that are sensitive to the
resultant heat flow estimation include gas Table 1. Sensitivity of average seismic velocity composition (29-35%), thermal conductivity
changes to estimated BSR heat flow. The 'Base (±17%), depth conversion (±8%) and seafloor
case' Dbsr was calculated by using Equations (7) temperature (6-10% for 1 ºC change). In order to
& (8) for Case 1 and Case 2, respectively. The reduce uncertainties and to get a more accurate
Dbsr in other cases was calculated from assumed estimation, it is important to use real
measurements as much as possible, however when single seismic velocity in marine sediments. real data are not available, then care should be
taken when making assumptions for those four USING BSR HEAT FLOW IN THERMAL components. Another source of error is the MATURITY MODELLING possibly erroneous assumption of the BSR as the base of GHSZ (MHSZ) in all settings, leading to We suggest the following steps to capture disparities between BSR-derived and directly uncertainty generated by large variation of measured heat flow. This theoretical error can only calculated BSR heat flow when they are used as be solved when real measurements or drilling data inputs in a thermal maturity modeling: are available. 1. Apply a simple statistical analysis to get arithmetic mean and standard deviation. Check
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Table 2. Sensitivity of seafloor temperature and thermal conductivity changes to estimated BSR heat flow. Columns (6) and (7) are for assumed average thermal conductivity (see text for more explanation).
Figure 5. Present-day heat flow at the surface of the Earth's crust (Global Heat Flow Database of International Heat Flow Commission) as compiled by Pollack et al. (1993).
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As the BSR heat flow results cover a wide range, it He, L., J. Wang, X. Xu, J. Liang, H. Wang, and G. is advisable to use statistical analysis prior to Zhang, 2009, Disparity between measured using the estimated heat flow as inputs in a and BSR heat flow in the Xisha Trough of thermal maturity modeling. It is also important to the South China Sea and its implications for compare the estimation results with the global the methane hydrate: J. Asian Earth heat flow database because the database has been Sciences, 34, p. 771–780. compiled from direct heat flow measurements. Kaul, N., A. Rosenberger, and H. Villinger, 2000, Comparison of measured and BSR-derived ACKNOWLEDGEMENTS heat flow values, Makran accretionary prism, Pakistan: Marine Geology, 164, p. We would like to thank Dr. J.T. van Gorsel and Dr. 37–51. Udrekh Al Hanif for their comments and Kvenvolden, K. A., 1988, Methane hydrate—a corrections that helped to improve this article. major reservoir of carbon in the shallow geosphere?: Chemical Geology, 71, p. 41–51. REFERENCES León, R., L. Somoza, C. J. Giménez-Moreno, C. J. Dabrio, G. Ercilla, D. Praeg, V. Díaz-del-Río, Collett, T. S., 2002, Energy resources potential of and M. Gómez-Delgado, 2009, A predictive natural gas hydrates: AAPG Bulletin, 86 numerical model for potential mapping of (11), p. 1971–1992. the gas hydrate stability zone in the Gulf of Currie, C. A. and R. D. Hyndman, 2006, The Cadiz: Marine and Petroleum Geology, 26, p. thermal structure of subduction zone back 1564–1579. arcs: J. Geophysical Research, 111, B08404, López, C. and G. Y. Ojeda, 2006, Heat flow in the doi:10.1029/2005JB004024, 22p.. Colombian Caribbean from the Bottom Davie, M. K., O. Y. Zatsepina, and B. A. Buffett, Simulating Reflector (BSR): Ciencia, 2004, Methane solubility in marine hydrates Tecnología & Futuro, 3 (2), p. 29–39. environments: Marine Geology, 203, p. 177– Lutz, R., C. Gaedicke, K. Berglar, S. Schloemer, D. 184. Franke, and Y. S. Djajadihardja, 2011, Davis, E. E., R. D. Hyndman, and H. Villinger, Petroleum systems of the Simeulue fore-arc 1990, Rates of fluid expulsion across the basin, offshore Sumatra, Indonesia: AAPG Northern Cascadia accretionary prism: Bulletin, 95 (9), p. 1589–1616. Constraints from new heat flow and Millero, F., C. Chen, A. Bradshaw, and K. multichannel seismic reflection data: J. Schleicher, 1980, A new high pressure Geophysical Research, 95 (B6), p. 8869– equation of state for seawater: Deep Sea 8889. Research, Part A, 27, p. 255-264 (water Dickens, G. R. and M. S. Quinby-Hunt, 1994, density equation was accessed at Methane hydrate stability in seawater: http://www.csgnetwork.com/water_density_ Geophysical Research Letters, 21 (19), p. calculator.html , on 10th of March, 2015). 2115–2118. Pollack, H. N., S. J. Hurter, and J. R. Johnson, Dickens, G. R. and M. S. Quinby-Hunt, 1997, 1993, Heat flow from the earth's interior: Methane hydrate stability in pore water: A Analysis of the global data set: Review of simple theoretical approach for geophysical Geophysics, 31 (3), p. 267–280. (Note: global applications: J. Geophysical Research, 102 heat flow database is also available at (B1), p. 773–783. http://www.heatflow.und.edu/ and the Franke, D., M. Schnabel, S. Ladage, D. R. Tappin, colour-coded world heat flow distribution is S. Neben, Y. S. Djajadihardja, C. Mueller, H. available at http://www.geophysik.rwth- Kopp, and C. Gaedicke, 2008, The great aachen.de/IHFC/heatflow.html) Sumatra-Andaman earthquakes: Imaging Shankar, U., N. K. Thakur, and S. I. Reddi, 2004, the boundary between the ruptures of the Estimation of geothermal gradients and heat great 2004 and 2005 earthquakes: Earth flow from Bottom Simulating Refelectors and Planetary Science Letters, 269, p. 118– along the Kerala-Konkan basin of Western 130. Continental Margin of India: Current Ganguly, N., G. D. Spence, N. R. Chapman, and R. Science, 87 (2), p. 250–253. D. Hyndman, 2000, Heat flow variations Shankar, U. and M. Riedel, 2013, Heat flow and from bottom simulating reflectors on the gas hydrate saturation estimates from Cascadia margin: Marine Geology, 164, p. Andaman Sea, India: Marine and Petroleum 53–68. Geology, 43, p. 434–449 Hardjono, T. S. Asikin, and J. Purnomo, 1998, Shankar, U., K. Sain, and M. Riedel, 2014, Heat flow estimation from seismic reflection Assessment of gas hydrate stability zone and anomalies in a frontier area of the Sebakor geothermal modeling of BSR in the Sea, Irian Jaya, Indonesia. In: J.L. Rau Andaman Sea: J. Asian Earth Sci.79, p. (Ed.): Proc. 33rd Session Co-ord. Committee 358-365. Coastal Offshore Geosci. Programmes East Shyu, C.T., Y. J. Chen, S. T. Chiang, and C. S. Liu, and SE Asia (CCOP), Shanghai 1996, 2, p. 2006, Heat flow measurements over Bottom 56–83. Simulating Reflectors, offshore southwestern
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Taiwan: Journal of Terrestrial Atmospheric World Ocean Atlas, 2013, and Oceanic Sciences, 17 (4), p. 845–869. http://www.nodc.noaa.gov/cgi- Smyth, H., 2010, SE Asia heatflow database: bin/OC5/SELECT/woaselect.pl accessed Accessed online on March 20, 2015 online on March 8, 2015. http://searg.rhul.ac.uk/current_research/h Xu, W. and C. Ruppel, 1999, Predicting the eatflow/index.html occurrence, distribution and evolution of Wang, K., R. D. Hyndman, and E. E. Davis, 1993, methane gas hydrate in porous marine Thermal effects of sediment thickening and sediments: J. Geophysical Research, 104 fluid expulsion in accretionary prisms: (B3), p. 5081–5095. Model and parameter analysis: J. Yamano, M., S. Uyeda, Y. Aoki, and T. H. Shipley, Geophysical Research, 98 (B6), p. 9975- 1982, Estimates of heat flow derived from 9984. gas hydrates: Geology, 10, p. 339–343.
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Berita Sedimentologi MARINE GEOLOGY OF INDONESIA
Frontier Exploration Using an Integrated Approach of Seafloor Multibeam, Drop Core and Seismic Interpretation – A Study Case from North Banggai Sula
Farid Ferdian Saka Energi Indonesia
Corresponding author: [email protected]
EXTENDED ABSTRACT
Figure 1. Regional Structures Map (After Ferdian, 2010 and Ferdian et al., 2010).
Exploration in frontier areas is always challenging energy received by the sonar after interactions with and has resulted in the development of various the sea floor and are used to infer seabed features new technologies including georeferenced, high and materials. Interpretation of these new dataset resolution seafloor multibeam bathymetry and combined with piston cores and seismic data have backscatter. The multibeam bathymetry data been conducted in the offshore of North Banggai provides sea floor depth information, while the Sula. This integrated approach has been termed as backscatter data records the amount of acoustic SeaSeepTM technology.
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Berita Sedimentologi MARINE GEOLOGY OF INDONESIA
Figure 2. Seafloor multibeam bathymetry (a) and backscatter (b) of the western portion of study area (After Ferdian, 2010).
Figure 3. Seafloor multibeam bathymetry and backscatter which corresponds with: 3a. Mounded feature interpreted as mud volcano; 3b. Subsea outcrop due to fault displacement.
In 2007, TGS-NOPEC with co-operation of Migas publications on the application of these new data has conducted Indodeep multi-client project which (e.g. Decker et al., 2009; Noble et al., 2009; Orange is comprised of acquiring seafloor multibeam et al., 2009; Riadini et al., 2009; Ferdian et al., bathymetry and backscatter, seafloor piston cores 2010; Rudyawan et al., 2011 etc.) have given a and regional 2D seismic survey across the frontier new understanding of the geology and hydrocarbon areas of Eastern Indonesia, including the study prospectivity of these frontier areas. One of the area presented here (Figure 1). Subsequent publications, entitled “Evolution and hydrocarbon
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Berita Sedimentologi MARINE GEOLOGY OF INDONESIA prospects of the North Banggai-Sula area: an tectonic evolution of the Bird’s Head, West application of Sea SeepTM technology for Papua, Indonesia: Indonesian Petroleum hydrocarbon exploration in underexplored areas” Association, Proceedings of the 33rd and was written by current author and published Convention and Exhibition. in the Proceedings of 2010 IPA Convention, is Ferdian, F., 2010, Evolution and hydrocarbon summarized here as this extended abstract. prospect of the North Banggai-Sula area: an application of Sea SeepTM technology for Interpretation of both seabed multibeam hydrocarbon exploration in underexplored bathymetry and 2D seismic lines has identified areas: Indonesian Petroleum Association, several new structures in the area (Figure 1). In Proceedings of the 34th Convention & the west, a dextral fault system is clearly identified Exhibition. which is thought to continue onshore to the Poh Ferdian, F., R. Hall, and I. Watkinson, 2010, Head of Sulawesi’s East Arm. In this Poh Head Structural re-evaluation of the north area, an abrupt elevation change with steep-sided Banggai-Sula, eastern Sulawesi: Indonesian topography most likely indicates a strike-slip fault. Petroleum Association, Proceedings of the Along the slope base of Banggai-Sula 34th Convention and Exhibition. Microcontinent (BSM) a series of relatively south- Garrard, R. A., J. B. Supandjono, and Surono, verging thrusts is identified. However, these 1988, The geology of the Banggai-Sula thrusts are not a single fault system such as the microcontinent, eastern Indonesia: so-called North Banggai-Sula fault that has been Indonesian Petroleum Association, published by many workers (Hamilton, 1978; Proceedings of 17th Annual Convention, p. Silver, 1981; Silver et al., 1983; Garrard et al., 23–52. 1988; Davies, 1990). These thrusts are actually Hamilton, W., 1978, Tectonic map of the formed by at least two different events: in the west Indonesian Region: U.S. Geological Survey it relates to the dextral fault system described Map G78156. above, while in the east it formed as a southward Noble, R., D. Orange, J. Decker, P. A. Teas, and P. continuation of the widespread south-verging Baillie, 2009, Oil and Gas Seeps in Deep thrust due to gravitational slide from the Central Marine Sea Floor Cores as Indicators of Molucca Sea Collision Zone. In the middle area Active Petroleum Systems in Indonesia: where these two structure systems met, a large Indonesian Petroleum Association, scale slip plane was formed at the seafloor. Proceedings of the 33rd Convention and Exhibition. Multibeam backscatter data show numbers of Orange, D., J. Decker, P. A. Teas, P. Baillie, and T. anomalously high backscatter areas across the Johnstone, 2009, Using SeaSeep Surveys to study area which correspond to locations of fault Identify and Sample Natural Hydrocarbon lineaments (Figure 2), mud volcanoes (Figure 3a), Seeps in Offshore Frontier Basins: authigenic carbonates and possibly outcrops Indonesian Petroleum Association, (Figure 3b) [Ferdian, 2010]. The well-positioned of Proceedings of the 33rd Convention and the piston cores deployed into these anomalies can Exhibition. give further insights on the sedimentology of the Riadini, P., A. C. Adyagharini, A. M. S. Nugraha, B. basin through subsequent geochemical analyses Sapiie, and P. A. Teas, 2009, Palinspastic performed by TDI Brooks. Seven core locations reconstruction of the Bird Head pop-up contain possible migrated liquid hydrocarbon (oil), structure as a new mechanism of the Sorong 5 locations of possible migrated thermogenic gas fault: Indonesian Petroleum Association, and another 5 locations of possible migrated both Proceedings of the 33rd Convention and oil and gas. Hydrocarbon charges from certain Exhibition. parts of this area show definite marine Silver, E. A., 1981, A New Tectonic Map of the characteristic (Noble et al., 2009) with the Molucca Sea and East Sulawesi, Indonesia Mesozoic marine shale (i.e. Buya Fm.) being the With Implications for Hydrocarbon Potential possible source rocks. and Metallogenesis. In: Barber, A. J. and Wiroyusujono, S. (Editors). The Geology and REFERENCES Tectonics of Eastern Indonesia: Geological Research and Development Centre – Special Davies, I. C., 1990, Geology and exploration review Publication No. 2 Pergamon Press. of the Tomori PSC, eastern Indonesia: Silver, E. A., R. McCaffrey, Y. Joyodiwiryo, and S. Indonesian Petroleum Association, Stevens, 1983, Ophiolite emplacement and Proceedings of the 19th Annual Convention, collision between the Sula platform and the p. 41–68. Sulawesi island arc, Indonesia: Journal of Decker, J., S. C. Bergman, P. A. Teas, P. Baillie, Geophysical Research, 88, p. 9419–9435. and D. L. Orange, 2009, Constraints on the
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Berita Sedimentologi MARINE GEOLOGY OF INDONESIA
Marine Expeditions in Indonesia during the Colonial Years
Prepared by Herman Darman based on 2005 publication by van Aken
Corresponding author: [email protected]
During the colonial years there was little support The Siboga expedition (1899-1900, Figures 1 and from the Netherlands government for non-applied 2) was executed with an adapted gunboat made scientific work. The colonies had to pay for available and paid for by the colonial government. themselves and had to be profitable for the It was very much biologically oriented (Figure 3), Netherlands; science was not considered to be a but useful oceanographical data were also good investment. Nevertheless, a number of collected. Some 238 depth soundings were added important oceanographic expeditions took place, to the 50 already measured, but few purely for example, the Siboga and Snellius expeditions. geological data were collected. Of interest is the Both were named after the ships that carried the fact that a female scientist, Mrs. Weber-Van Bosse scientists and both were paid for by the (Figure 4), specialist in algae, participated in the Netherlands government. The objective was to entire trip; she was probably the first woman in prove that the Dutch Indies were not only the best the history of oceanography to serve in such a role. governed, but also the scientifically most developed She also was the wife of the leader of the tropical colony. Moreover there were the Dutch expedition, the biologist Max Weber, but she fully who needed to consolidate colonial rule by showing earned her keep and published three monographs the flag over the whole archipelago. Germans, on the algae collected during the expedition. British, Americans and Japanese were encroaching Amongst other things she proved beyond doubt, on the Far East (New Guinea, Philippines, that coccoliths are of organic origin and belong to Malaysia and Taiwan) and in some ways the the algae (Weber-Van Bosse, 2000). She received expedition can be considered as ‘gunboat science’. an honorary doctorate from Utrecht University in Even so, vast amount of prime oceanographical, 1910, another first in history for a Dutch woman. hydrographical, biological and geological data were collected with state-of-the-art equipment.
Figure 1. The Siboga at sea (source: http://hydro-international.com & http://nl.wikipedia.org/wiki/Siboga-expeditie).
Figure 2. The Siboga expedition trips 1, 2 and 3. (source: van Aken, 2005). Number 32 – April 2015 Page 30 of 34
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The Snellius expedition (1929-1930, Figures 4, 5 and 6) focused on the physical and chemical oceanography of the deep basins of the East Indies and the geology of its coral reefs. Again the government provided the ship, this time built as a scientific vessel, named it after one of the greatest Dutch scientists Snel(lius) van Royen and paid for the expedition expenses. The expedition leader was P. M. van Riel, a retired naval officer, head of oceanography and maritime meteorology at the Royal Meteorological Institute of the Netherlands (Koninklijk Nederlands Meteorologisch Institut, KNMI). On board was also Philip Kuenen (Figure 4), who was to become an internationally renowned sedimentological and marine geologist at Groningen University. A total of 374 station soundings were recorded and over 500 bottom samples were collected during three trips. Regular shore parties were organized to visit the coral islands and to study their geology. The echo sounder was in nearly constant use, resulting in 33,000 measurements and this alone immensely improved our knowledge of these deep-sea tract.
Study of the vast amount of data collected by the expedition was greatly delayed, especially as far as the purely oceanographic data were concerned, but also the geological and biological data
Figure 3. Cover of a report from Siboga proved too much to be quickly dealt with. This is
Expedition, a collection of the Naturalist Museum, aptly demonstrated by the fact that, as late as
Leiden, the Netherlands (photo by H. Darman). 1978, an article was published on the foraminifers
from the Snellius expedition, as a final addition to
the already published 23 volumes of Snellius
reports (Figure 7).
Figure 4. Left: Anne Antoinette Weber-van Bosse (1852-1942); Source: Wikipedia (left); and Right: Philip H. Kuenen (1902- 1976); Source: http://resources.huygens. knaw.nl/bwn1880- 2000/lemmata/bwn5/kue nen).
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Figure 5. Snellius expedition 1929-1930 (1st trip) (Boekschoten. et al., 2012).
Figure 6. The Hr. Ms. Snellius ship at sea (Boekschoten. et al., 2012).
Figure 7. Example of a Snellius expedition report in the Naturalist Museum, Leiden, the Netherlands (Photo by H. Darman). REFERENCES
Boekschoten, B. et al., 2012, Dutch Earth http://hydro-international.com Sciences: Development and Impact, Royal http://nl.wikipedia.org/wiki/Siboga-expeditie Geological and Mining Society of the van Aken, H. M., 2005, Dutch oceanographic Netherlands, 1912-2012 Centenary Volume. research in Indonesia in colonial times: http://resources.huygens.knaw.nl/bwn1880- Oceanography 18(4), p. 30–41. 2000/lemmata/bwn5/kuenen)
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Berita Sedimentologi BIOSTRATIGRAPHY OF SE ASIA – PART 2
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