Cenozoic Carbonate Systems of Australasia. William A. Morgan, Annette George, Paul M. (Mitch) Harris, Julie A.Kupecz and J.F. (Rick) Sarg, Editors

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2 Cenozoic Carbonate Systems of Australasia William A. Morgan, Annette George, Paul M. (Mitch) Harris, Julie A.Kupecz and J.F. (Rick) Sarg, Editors CONTENTS Introduction Cenozoic Carbonate Systems of Australasia Introduction and Perspectives WILLIAM A. MORGAN, ANNETTE D. GEORGE, PAUL M. (MITCH) HARRIS, JULIE A. KUPECZ, AND J.F. (RICK) SARG Southeast Asian Carbonate Systems Tectonic Influences on SE Asian Carbonate Systems and their Reservoir Development MOYRA E.J. WILSON AND ROBERT HALL Equatorial Carbonate Depositional Systems of Indonesia ROBERT K. PARK, PAUL D. CREVELLO, AND WAHYOE HANTORO Seismic Characterization of Large-Scale Platform-Margin Collapse along the Zhujiang Carbonate Platform (Miocene) of the South China Sea, based on Miocene Outcrop Analogs from Mut Basin, Turkey XAVIER JANSON, GREGOR P EBERLI, ANTHONY J. LOMANDO, AND FLORENCE BONNAFFÉ The Impact of Postdepositional Processes on Reservoir Properties: Two Case Studies of Tertiary Carbonate Buildup Gas Fields in Southeast Asia (Malampaya and E11) GEORG WARRLICH, CONXITA TABERNER, WENCHE ASYEE, BEN STEPHENSON, MATEU ESTEBAN, MARIA BOYA-FERRERO, ANNA DOMBROWSKI, AND JAN-HENK VAN KANIJNENBURG Controlling Factors of a Miocene Carbonate Platform: Implications for Platform Architecture and Off-Platform Reservoirs (Luconia Province, Malaysia) VALENTINA ZAMPETTI Sequence Stratigraphy and Growth of Shelfal Carbonates in a Deltaic Province, Kutai Basin, Offshore East Kalimantan, Indonesia ARTHUR SALLER, SENA W. REKSALEGORA, AND PHILLIP BASSANT Seismic Stratigraphy and Geomorphology of Oligocene to Miocene Carbonate Buildups Offshore Madura, Indonesia H.W. POSAMENTIER, PRISCILLA LAURIN, ALEX WARMATH, MEIRINCE PURNAMA, AND DEDAN DRAJAT Australian Region Carbonate Systems Controls on Morphology and Growth History of Coral Reefs of Australia s Western Margin LINDSAY B. COLLINS Timing of Changes in Sea-Level and Currents along Miocene Platforms on the Marion Plateau GREGOR P. EBERLI, FLAVIO S. ANSELMETTI, ALEXANDRA R. ISERN, AND HEIKE DELIUS Neogene Lithofacies Evolution on a Small Carbonate Platform in the Loyalty Basin, Maré, New Caledonia DONALD F. MCNEILL AND ANDRZEJ PISERA

3 TECTONIC INFLUENCES ON SE ASIAN CARBONATE SYSTEMS AND THEIR RESERVOIR DEVELOPMENT MOYRA E.J. WILSON Department of Applied Geology, Curtin University, GPO Box U1987, Perth, WA 6845, Australia. E mail: m.wilson@curtin.edu.au ROBERT HALL SE Asia Research Group, Department of Earth Sciences, Royal Holloway University of London, Egham, Surrey, TW20 OEX, UK ABSTRACT: SE Asian carbonate formations have been reviewed with the aim of understanding the influence of tectonics on their development and reservoir potential through the Cenozoic. Regional tectonics, via plate movements, extensional basin formation, and uplift, was the dominant control on the location of carbonate deposits. These processes controlled the movement of shallow marine areas into the tropics, together with their emergence and disappearance. Although; 70% of the 250 shallow marine carbonate formations in SE Asia were initiated as attached features, 90% of economic hydrocarbon discoveries are in carbonate strata developed over antecedent topography, of which more than 75% were isolated platforms. Faulted highs influenced the siting of nearly two thirds of carbonates developed over antecedent topography. Around a third of carbonate units formed in intra and interarc areas; however, economic reservoirs are mainly in backarc and rift margin settings (; 40% each). Carbonate edifices show evidence of syntectonic sedimentation through: (1) fault margin collapse and resedimentation, (2) fault segmentation of platforms, (3) tilted strata and differential generation of accommodation space, and (4) modification of internal sequence character and facies distribution. The demise of many platforms, particularly those forming economic reservoirs, was influenced by tectonic subsidence, often in combination with eustatic sea level rise and environmental perturbations. Fractures, if open or widened by dissolution, enhance reservoir quality. However, fracturing may also result in compartmentalization of reservoirs through formation of fault gouge, or fault leakage via compromised seal integrity. This study will help in reservoir prediction in complex tectonic regions as the petroleum industry focuses on further exploration and development of economically important carbonate reservoirs.

4 EQUATORIAL CARBONATE DEPOSITIONAL SYSTEMS OF INDONESIA ROBERT K. PARK Kodeco Energy Co. Ltd, Indonesia Stock Exchange Building, Twr.1 24th Fl., Jl. Jend. Sudirman kav 52, Jakarta e mail: park.rk.sm@attglobal.net PAUL D. CREVELLO BPC Limited, 28 Cumberland St., Nassau N 1991, The Bahamas e mail: p.crevello@bpcplc.com AND WAHYOE HANTORO Puslit Geoteknologi LIPI, Jl Sangkuriang, Gedung 70 Bandung 40135, Kota Bandung, Indonesia. e mail: hantoro@geotek.lipi.go.id ABSTRACT: The fundamental processes and controls on carbonate deposition are well established. These include: water depth, temperature, salinity, clarity, and an abundance of sunlight, all of which control rates of growth among the biota while wave and current energy ensure a steady supply of nutrients. The aragonite dominated systems of the tropical latitudes gave way to calcite dominance in higher latitudes. Mud rich tidal flat sequences characterize the Bahamian and Persian Gulf settings, while mud free systems dominate the higher energy settings of the Great Barrier Reef and coolerwater environments. With the inclusion of recently documented Lophelia reef mounds in deep arctic waters, together with studies of deep water pelagic limestones, the globalization of carbonates was nearly complete almost. One part of the global distribution pattern remains understudied and underappreciated, namely the equatorial belt. In old mariner terminology this latitudinal belt is known as the doldrums, notorious for its unpredictable calms and seasonal monsoon shifts in the wind and surface currents. In recent years, the Indonesia Philippines archipelago has received particular attention from oceanographers and climatologists in recognition and growing awareness of the role of El Nino Southern Oscillation (ENSO) and the Indonesian Throughflow (ITF) and its relation to upwelling and changes in seasurface temperature (SST), resulting in widespread reef death throughout the region. The archipelago straddles the equator and lies squarely within this equatorial belt. Average sea water temperatures are ~ o C, and salinities are much lower than normal, ~, 32 34%. These values test the tolerance limits of many reef community members, hence their susceptibility to El Niño events. Collision tectonics has defined the structural style, geography, and hydrography of the archipelago since the earliest Tertiary and has profoundly influenced modern and Cenozoic depositional systems. Shifts in relative sea level are frequent and often dramatic, affecting not only depositional patterns but also diagenesis, with repeated subaerial and flooding events. The symmetry of the seasonal shifts introduces a bimodal pattern while the energy of the system reduces mud accumulation on the shallow platforms. Nearshore fringing reefs are limited by the high clastic discharge associated with high rainfall and landform topography. Coastal plains are clastic dominated, with mangrove swamp peats replacing the microbial mats that typify large tracts of the Bahamian and Persian Gulf platform settings. Thus, the region offers an excellent opportunity to study modern and ancient carbonate systems under this particular climatic and, perhaps just as importantly, tectonic setting. That almost half of Indonesia s hydrocarbon reserves and production derive from these same Cenozoic carbonates provides additional reason for further study.

5 SEISMIC CHARACTERIZATION OF LARGE SCALE PLATFORM MARGIN COLLAPSE ALONG THE ZHUJIANG CARBONATE PLATFORM (MIOCENE) OF THE SOUTH CHINA SEA, BASED ON MIOCENE OUTCROP ANALOGS FROM MUT BASIN, TURKEY XAVIER JANSON Comparative Sedimentology Laboratory, RSMAS, University of Miami, Florida U.S.A. Present address: Bureau of Economic Geology, University of Texas at Austin, Texas U.S.A. GREGOR P. EBERLI Comparative Sedimentology Laboratory, RSMAS, University of Miami, Florida U.S.A. ANTHONY J. LOMANDO Chevron Business Development, Houston, TX U.S.A. AND FLORENCE BONNAFFÉ Comparative Sedimentology Laboratory, RSMAS, University of Miami, Florida U.S.A. Present address: Bureau of Economic Geology, University of Texas at Austin, TX U.S.A. ABSTRACT: Redeposition of carbonate sediment on all scales produces heterogeneous stratigraphic architecture along platform margin, slopes, toe of slope, and basin. Larger features, such as margin collapse or slumps, are visible on seismic sections, but their internal architecture is commonly beyond seismic resolution. Seismic data across the lower Miocene Zhujiang Platform margin in the subsurface of Pearl River Mouth Basin in the South China Sea show truncation of the margin associated with contorted and rotated reflections at the toe of slope and in the basin. This seismic facies occurs discontinuously along the margin in an area approximately 6 to 8 km wide paralleling the margin and 2 to 3 km wide in the dip direction. These seismic features are compared with similar geometries and bedding patterns observed in an analog Miocene platform margin that crops out in south central Turkey. There several slump scars truncate barrier margin deposits and are associated downslope with rotated and folded strata that are still connected to these detachment surfaces. The margin collapse observed in the outcrop allows interpretation of margin truncation and the contorted reflection package observed in the seismic as a largescale redeposited feature. The margin of the lower Miocene Zhujiang Platform displays multiple large scale slumping events distributed along strike. In the outcrop, large scale margin collapse internal architecture is made up of blocks of cemented margin material several tens of meters to a few of hundred meters wide. Using half time energy instantaneous seismic attributes reveals that large cemented blocks imaged as small energy anomalies on 2D seismic data might also exist within the margin collapse observed in Zhujiang Platform.

6 THE IMPACT OF POSTDEPOSITIONAL PROCESSES ON RESERVOIR PROPERTIES: TWO CASE STUDIES OF TERTIARY CARBONATE BUILDUP GAS FIELDS IN SOUTHEAST ASIA (MALAMPAYA AND E11) GEORG WARRLICH Petroleum Development Oman, P.O. Box 82, Muscat, 100, Sultanate of Oman e mail: gwarrlich@hotmail.com CONXITA TABERNER Shell Exploration and Production, Rijswijk, The Netherlands e mail: Conxita.Taberner@shell.com WENCHE ASYEE Shell Exploration and Production, Rijswijk, The Netherlands e mail: Wenche.Asyee@shell.com BEN STEPHENSON Shell Exploration and Production, Rijswijk, The Netherlands e mail: Ben.Stephenson@shell.com MATEU ESTEBAN Shell Exploration and Production, Rijswijk, The Netherlands e mail: carbonates@carbonates.com MARIA BOYA FERRERO Shell Exploration and Production, Rijswijk, The Netherlands e mail: Maria.Boyaferrero@shell.com ANNA DOMBROWSKI Shell Exploration and Production, Rijswijk, The Netherlands e mail: A.Dombrowski@shell.com AND JAN HENK VAN KONIJNENBURG Shell Exploration and Production, Rijswijk, The Netherlands e mail: J.J.VanKonijnenburg@shell.com ABSTRACT: This paper investigates the impact of diagenesis and tectonic deformation on the reservoir properties of two Tertiary gas bearing carbonate buildup reservoirs that formed in similar depositional environments: E11 of the Luconia Province, offshore Malaysia, and Malampaya, offshore the Philippines. Both buildups have comparable dimensions and ages, contain similar constituents and faunal assemblages, and comprise aggradational zones preceding final drowning. The aggradational zones overlie low porosity zones, which separate them from earlier shelf carbonates. The reservoir properties, however, were influenced very strongly by nondepositional reservoir modifying processes. The diagenetic histories were different for the two reservoirs: secondary porosity formation by early and late diagenetic processes was driven by dolomitization and late leaching in E11 and by exposure as well as burial related leaching in Malampaya. Low porosity zones in Malampaya are a result of meteoric diagenesis during exposure and late cementation, whereas in E11 they correspond to nonleached, argillaceous wackestones of

7 deeper water origin. Connected geobodies of either high or low porosity are the result of these processes and are visible on acoustic impedance volumes. They follow depositional trends or developed around faults: early diagenetic alterations were found to follow depositional trends; diagenetic overprints occurring in the burial realm can also exploit depositional patterns, but if the diagenetic fluids are guided by faults and fractures, the distribution and orientations of the faults appear be the overriding control. Diagenetic overprint also was found to result in porosity permeability relationships that are different from those of depositional rock fabrics. Significant postdepositional and syndepositional deformation is recognized only in Malampaya and led to increased fracture development in the low porosity zones, resulting in very good vertical connectivity across the low porosity layers. Absence of postdepositional deformation in E11 correlates with absence of conductive fractures and a vertical pressure barrier across the thickest low porosity zone. The sum of similar depositional processes and different reservoir modification processes led to overall alike reservoirs with low porosity and high porosity layering, but porosity distributions other than expected from depositional processes alone as well as different degrees of fracturing and dynamic behavior. In this study an improved understanding of the reservoir was found to result from an integrated approach combining all subsurface disciplines. Detailed investigations of the diagenesis incorporating petrography, stable isotopes and fluid inclusions were key to unravel the reservoir formation processes. Understanding those is critical to formulate conceptual geological models that can explain reservoir behavior, constrain the subsurface modeling uncertainties and rank modeled subsurface scenarios.

8 CONTROLLING FACTORS OF A MIOCENE CARBONATE PLATFORM: IMPLICATIONS FOR PLATFORM ARCHITECTURE AND OFF PLATFORM RESERVOIRS (LUCONIA PROVINCE, MALAYSIA) VALENTINA ZAMPETTI FALW, Vrije Universiteit, Amsterdam, 1081HV, Netherlands current address: Maersk Oil Qatar AS, Al Jazi Tower, P.O. Box 22050, Doha, Qatar e mail: Valentina.Zampetti@maerskoil.com ABSTRACT: A multidisciplinary approach was used to better reconstruct the architecture of a Miocene carbonate platform in the Luconia Province to provide a better understanding of the complexity of South East Asian Cenozoic carbonate systems and their controlling factors. Platform growth began in the Late Oligocene to Early Miocene by coalescence of isolated patch reefs, and includes phases of progradation, backstepping and occasional collapse of platform flanks terminated by gradual submergence (drowning). Geometry was controlled not only by the balance between the rate of accommodation space and carbonate production, but also extrinsic factors such faulting and ocean currents that strongly influenced platform architecture. A 2 D regional study of the carbonate platforms in the Luconia province indicates that asymmetry of the platform margins is largely related to ocean currents rather than wind shear over the platform top. The structural relief created by block tilting has determined the location of the initial carbonate buildup. However, the platform was strongly affected by active strike slip deformation during sedimentation that controls its shape and size. Syndepositional faulting has been interpreted to be responsible for the slope failure affecting the platform margins. Platform material is deposited as slide masses in the adjacent basin floor. Such deposits are likely to pass into debris flow and turbidites deposits, i.e. breccias and carbonate sands, and can extend many kilometers across the basin floor. Because slumping did not affect only the studied platform but also the adjacent buildups, debris tongues are likely to interfinger. Faults are also interpreted to have acted as conduits for deepseated fluids responsible for hydrothermal dissolution. The diagenetic history of the studied platform shows that much secondary porosity was created by dissolution during deep burial conditions, a process that may not be limited to the carbonate platforms but could also affect the slopes and intervening basins. Consequently, the carbonate slump, debris flow and turbiditic deposits on the lower slopes and basin floors may well contain significant secondary porosity. These porous bodies may onlap other platform slopes, terminate there and become enveloped in clay rich hemipelagic sediment. In addition, porous layers may establish fluid conduits between neighboring platforms if slides and turbidites from different platforms interfinger on the basin floor.

9 SEQUENCE STRATIGRAPHY AND GROWTH OF SHELFAL CARBONATES IN A DELTAIC PROVINCE, KUTAI BASIN, OFFSHORE EAST KALIMANTAN, INDONESIA ARTHUR SALLER Chevron Energy Technology Company, 1400 Smith, Houston, Texas USA, asaller@chevron.com SENA W. REKSALEGORA Asia Pacific Exploration Consolidated, Indonesia Stock Exchange Building Tower 1, Level 28, Suite # 2802, Jl. Jend. Sudirman Kav , Jakarta 12190, Indonesia, senawr@yahoo.com AND PHILIP BASSANT Chevron Indonesia Company, Sentral Senayan I Office Tower, Jalan Asia Afrika No. 8, Jakarta 10270, Indonesia, Phil.bassant@chevron.com ABSTRACT: The Kutai Basin of East Kalimantan, Indonesia, has been dominated by deltaic deposition during the Neogene, but carbonate buildups are also common. Carbonate siliciclastic interactions were studied in 3D seismic and well data in the upper Pleistocene and uppermost Miocene to Pliocene, offshore north of the Mahakam delta. Upper Pleistocene carbonates accumulated over the siliciclastic shelf margins during ~ 110 kyr eustatic cycles. U Th dating supports deposition of ~ m of carbonate on the shelf margin during each of the last two eustatic cycles ( ka; ka). This sedimentation rate of m/100 kyr is higher than other documented carbonate systems for that length of time. Pleistocene shelf margin carbonates contain a lower transgressive ridge (TST) overlain by landward dipping clinoforms interpreted as the highstand systems tract (HST) and capped by subaerial exposure surfaces formed during falls of eustatic sea level. Coral rich packstone and grainstone dominate the upper Pleistocene shelf margin buildups, though partially dolomitized wackestones and siliciclastic mudstones are associated with maximum flooding surfaces. The uppermost Pleistocene shelf margin buildups are ~ 0.5 km wide and occur along a 50 km trend. Siliciclastic strata prograded across the inner and middle shelf during high and falling sea level. Uppermost Pleistocene buildups grew on siliciclastic strata on the middle shelf during the last eustatic sea level rise (after 18 ka). The middle shelf buildups are roughly circular to elongate in map view, vary from 5 km to less than 100 m across, are commonly m thick, and preferentially grew on the upthrown side of faults, though they are observed in many other places. Carbonates were deposited within two sequences in the uppermost Miocene and lower Pliocene. Shelf margin carbonate buildups grew above siliciclastic shelf margins during transgressions, and then those buildups were buried by basinward prograding siliciclastics during the following highstand. Mio Pliocene carbonate buildups on shelf margin are commonly 255 m thick, 5 km long, 1 km wide, and composed largely of bioclastic packstone and grainstone. The carbonate buildups are thicker with more relief and steeper margins to the north, away from the main influx of siliciclastics. High relief buildups to the north contain multiple stacked carbonate sequences that were not covered at earlier stages by siliciclastic mud, in contrast to thinner buildups in the south. Although porous, most of the Mio Pliocene shelf margin buildups are filled with water, probably because overlying downlapping siliciclastics do not provide a robust seal. Middle shelf buildups, equivalent in age to Mio Pliocene shelf margin carbonates, also grew during transgressions, but the middle shelf buildups are thinner (15 m) because they had less accommodation space, and because the middle shelf spent more time with siliciclastics deposition. Biostratigraphic dating suggests that one of these Mio Pliocene carbonate siliciclastic sequences is ~ 0.6 Myr in duration, resulting in a carbonate accumulation rate of ~ 425 m/myr.

10 SEISMIC STRATIGRAPHY AND GEOMORPHOLOGY OF OLIGOCENE TO MIOCENE CARBONATE BUILDUPS OFFSHORE MADURA, INDONESIA H.W. POSAMENTIER Anadarko Petroleum Company, 1201 Lake Robbins Drive, The Woodlands, TX 77380, U.S.A. Present address: Chevron Energy Technology Company, 1500 Louisiana Street, Houston, TX 77002, U.S.A. e mail: henry.posamentier@chevron.com PRISCILLA LAURIN Anadarko Petroleum Company, 1201 Lake Robbins Drive, The Woodlands, TX 77380, U.S.A. Present address: Max Petroleum Plc, 9 Greenway Plaza, Suite 550, Houston, TX 77046, U.S.A. ALEX WARMATH Anadarko Petroleum Company, 1201 Lake Robbins Drive, The Woodlands, TX 77380, U.S.A. Present address: Greenfields Petroleum Corporation, 211 Highland Cross, Suite 227, Houston, TX 77073, U.S.A. MEIRINCE PURNAMA Anadarko Indonesia Company, One Pacific Place Building, Level 12, Suite , Jl. Jend. Sudirman, Kav 52 23, Jakarta, 12190, Indonesia AND DEDAN DRAJAT Anadarko Indonesia Company, One Pacific Place Building, Level 12, Suite , Jl. Jend. Sudirman, Kav 52 23, Jakarta, 12190, Indonesia ABSTRACT: A variety of carbonate landscapes have been imaged on 3D seismic data from the offshore area north of Madura Island, Indonesia. This paper is a case study based exclusively on seismic geomorphologic and seismic stratigraphic analyses. Carbonate buildups ranging from small patch reefs to platforms with outliers, and tide influenced elongate large patch reefs are observed within the Kujung 2, Kujung 1, and Wonocolo Formations. Clastic input characterized by low angle clinoforms from the north northwest and ubiquitous polygonal fracturing occurred between deposition of the Kujung 1 and the Wonocolo Formations. Subsequent to Wonocolo deposition, the basin gradually became subaerially exposed and was ultimately the site of densely spaced fluvial systems. The small patch reef buildups of the Kujung 2 range in size from less than 120 m up to 500 m in diameter. Across the platform these buildups are closely spaced, with less than 100 m separating isolated buildups. Each buildup is circular in plain view, with vertical relief of approximately m. Hundreds of these features are observed within the 3D seismic volume. Larger scale patch reefs of the Kujung 1 coalesced to form a northwest southeast trending platform. Individual buildups within the platform range from 600 m to 2 km in diameter and from 200 to 300 m in thickness. Smaller patch reefs ranging from 60 to 120 m in diameter are observed at the tops of these buildups. Large scale buildups form off the platform and can be up to 400 m thick with diameters from 1 to 6.5 km. The Kujung 1 reefs are circular to elliptical in planform. Anastamosing channels up to 200mdeep and 650mwide trend normal to the platform buildup and terminate at the buildup margin. The Woncolo carbonate buildups generally are larger than the Kujung buildups and are characterized by internal clinoform architecture. These buildups are circular to elliptical in planform and range in size from 4 to 10 km wide and up to 20 km in length. They are separated from each other by tidal channels km wide. The buildup tops are characterized by a complex network of channels, some up to 200 m wide.

11 CONTROLS ON MORPHOLOGY AND GROWTH HISTORY OF CORAL REEFS OF AUSTRALIA S WESTERN MARGIN LINDSAY B. COLLINS Department of Applied Geology, Curtin University of Technology, GPO Box U1987, Perth Australia ABSTRACT: The western margin of Australia provides a regional latitudinal and climatic gradient from the macrotidal tropical north to the microtidal temperate south, modulated by the poleward flowing warm Leeuwin Current. Coral reef systems, discontinuously developed during the late Tertiary Quaternary, vary from fringing reefs to isolated reefs which rise from deep ramp settings. Quaternary evolution of the reef systems is being documented using regional mapping, seismic imaging, coring and U series dating. The well constrained sea level data from the Houtman Abrolhos carbonate platforms (at o S) have also been applied to the less known North West Shelf reefs. The Ningaloo fringing reef at o S records Holocene and last interglacial phases of reef growth in a tectonically stable environment. It overlies Tertiary carbonates of the Cape Range, which is flanked by uplifted Plio Pleistocene terraces and reefs. Scott Reef (at 14 o S) is a macrotidal, isolated reef which overlies a carbonate platform and a major gas discovery. Seismic profiles reveal a last interglacial (ca. 125,000 year) reef system, but reefs which apparently grew to sea level are 30 m below present sea level, indicating significant subsidence in the late Quaternary. Contemporary reefs grew during the Holocene in the accommodation space provided by subsidence and are up to 35 m thick. The Rowley Shoals (15 17 o S) comprise one of the most perfect morphological series of reefs known, and these emergent, annular reefs rise from depths of m. Seismic profiles suggest that late Quaternary subsidence has been an important control on reef growth, while differential subsidence has influenced reef morpho1ogy. Differential geomorphic and physical process settings, seismic stratigraphy, sealevel history, and subsidence are keys to patterns of reef growth which can be seen as responses to these controls.

12 TIMING OF CHANGES IN SEA LEVEL AND CURRENTS ALONG MIOCENE PLATFORMS ON THE MARION PLATEAU, AUSTRALIA GREGOR P. EBERLI Comparative Sedimentology Laboratory, University of Miami, 4600 Rickenbacker Causeway, Miami, FL 33149, U.S.A. e mail: geberli@rsmas.miami.edu FLAVIO S. ANSELMETTI Eawag, Swiss Federal Institute of Aquatic Science & Technology, Department of Surface Waters; Sedimentology Group, U berlandstrasse 133, CH 8600 Du bendorf, Switzerland e mail: flavio.anselmetti@eawag.ch ALEXANDRA R. ISERN Program Director for Antarctic Earth Sciences, National Science Foundation, 4201 Wilson Boulevard, Arlington, Virginia 22230, U.S.A. e mail: aisern@nsf.gov AND HEIKE DELIUS Task Geoscience Ltd. Exploration House, Aberdeen Science & Energy Park, Bridge of Don, Aberdeen, AB23 8GX, U.K. e mail: heike.delius@taskgeoscience.com ABSTRACT: The question of global synchroneity of sea level changes and their role in the formation of coeval unconformities on continental margins in different ocean basins remain major research topics in sequence stratigraphy. The Ocean Drilling Program (ODP) has addressed questions surrounding sea level in several drilling legs. One of these drilling efforts was ODP Leg 194, which drilled two platform to slope transects of the Miocene carbonate platforms on the Marion Plateau, situated just seaward from the Great Barrier Reef, NE Australia. The seismic and core information of this leg are used for an assessment of eustasy by determining the ages of seismic sequence boundaries on the Plateau and comparing them to sequence boundaries in the Atlantic. In addition, we evaluate the influence of current changes on the current swept Plateau and its effect on the sequence architecture and the drowning of these cool, subtropical carbonate sequences. The two platforms, Northern and Southern Marion Platforms, are built by cool, subtropical faunal assemblages and have an asymmetric geometry. Four previously defined megasequences (A D) are subdivided into 14 unconformity bounded sequences. The early to middle Miocene sequences are prograding and aggrading sequences that responded mostly to the fluctuating sea level. From the late middle Miocene onward, the sea level changes are coupled with increased activity of the southwardflowing East Australian Current. As a result, the sequences developed a characteristic mounded geometry in the basinal area where large drift deposits accumulated. Changes of current strength and position produced unconformities within the drift successions that are identified by downlap, onlap terminations and, locally, erosional truncation. These drift unconformities are observed along reflections that in the proximal position are onlap unconformities and sequence boundaries. The coeval nature of the two types of unconformities indicates that changes in sea level and currents occurred in concert. The interplay between sea level and currents also produced hardgrounds that record long hiatuses at sequence boundaries. The two most prominent sequences boundaries are drowning unconformities. An older one covers the top and flanks of the Northern Marion Platform, which drowned during the sea level rise at 11.1 Ma. The Southern Marion Platform survived this event only to drown at the end of the late Miocene at approximately 7 Ma. A thin and varied drowning succession documents that the platform was intermittently active in the Pliocene. The top of the drowning succession is still a hardground surface on the modern seafloor, whereas Pliocene to

13 Recent drift deposits overlie the hardgrounds on the slopes. It is likely that the combined effect of sea level rise and subsequent sweeping of the platform by strong currents prevented the re establishment of carbonate production on the bank and aided in the demise of the platforms. The timing of the sea level changes is assessed by determining the ages of the sequence boundaries based on revised age models relying on biostratigraphy and Sr isotope dates from cores at ODP Leg 194 drill sites. The age of each sequence boundary is remarkably similar at each site along the drilled transects. The age consistency along the seismic reflections corroborates the hypothesis that seismic reflections follow depositional surfaces and have chronostratigraphic significance. Furthermore, the timing of many Neogene sequence boundaries on the Marion Plateau (ODP Leg 194) coincides with the timing of sequence boundaries on the Queensland Plateau (ODP Leg 133) and along the Bahamas Transect (ODP Leg 166). The similar ages of the sequence boundaries and associated sealevel changes on the Pacific northeast Australian margin and the Atlantic Bahamian margin indicate a global synchroneity of third order sea level changes in the Neogene.

14 NEOGENE LITHOFACIES EVOLUTION ONA SMALL CARBONATE PLATFORM IN THE LOYALTY BASIN, MARÉ, NEW CALEDONIA DONALD F. MCNEILL Division of Marine Geology & Geophysics, Rosenstiel School of Marine and Atmospheric Science, University of Miami, 4600 Rickenbacker Causeway, Miami, Florida U.S.A e mail: dmcneill@rsmas.miami.edu AND ANDRZEJ PISERA Institute of Paleobiology, Polish Academy of Sciences, ul. Twarda 51/56, Warszawa, Poland e mail: apis@twarda.pan.pl ABSTRACT: The succession of biofacies recorded in a small carbonate platform (Maré, ~ 40 km diameter) in the Loyalty Islands, New Caledonia, is used to evaluate the geological and paleoenvironmental evolution of the platform. The depositional succession shows a distinct change in biotic assemblages across a subaerial discontinuity at the Miocene Pliocene boundary. This change from an underlying late Miocene fringing reef and rhodolith shelf built around the volcanic core, to a thin bed (~ 2 m) of early Pliocene foraminifera algal (foralgalith) macroids that forms the base of a massive coraldominated atoll. The rhodolith facies is dominated by coralline red algae, whereas the foralgaliths contain abundant sessile acervulinid foraminifera, some crusts of coral, and minor coralline red algae. This foralgalith macroid composition indicates initial deepening before a switch to coraldominated biota that formed the steep sided atoll rim. These new data and existing petrographic evidence suggests a sequence of marine cementation of the rhodoliths followed by subaerial exposure and shoreline erosion around the platform rim. Subsequently the platform was reflooded in the early Pliocene, partially drowned, and recovered with the deeper water foralgalith facies followed by the establishment of a massive coral atoll. This platform atoll evolution closely reflects eustatic sea level changes and local tectonic uplift related to lithospheric flexure. A switch to a coral dominated atoll in the Pliocene likely reflects a (global?) trend of decreased coralline red algae species richness, improved water quality, and the reestablishment of photic zone conditions more favorable to warm water carbonates. The combination of refined age control integrated with biotic changes provides sufficient sensitivity of the carbonate facies to record local tectonic changes, ecologic changes, and eustatic events. These results provide calibration of the lithofacies successions that may occur on small, tectonically active tropical Pacific platforms.