the deep water fold and thrust belt offshore nw borneo gravity driven versus basement driven shortening the deep water region offshore nw borneo is an active fold and thrust belt that hosts a signifi cant number of proven hydrocarbon accumulations in the past two mechanisms have been discussed as primary control for neogene to holocene folding and thrusting in this deep water province 1 basement driven crustal shortening and 2 gravity related delta tectonics in this study new balanced interpretations of regional crustal scale depth migrated twodimensional 2 d multichannel seismicrefl ection profi les are presented that provide for the fi rst time quantitative data on tectonic shortening throughout the entire deep water fold and thrust belt of nw borneo we use our tectonic restorations to compare the amount of deep water shortening on the nw borneo slope to the amount of extension across the nw borneo shelf a key result of this balancing study is the observation that pliocene to holocene gravity driven shortening decreases from south to north while the total amount of shortening increases slightly to the north consequently the amount of purely basement driven compression along nw borneo is strongly inferred to increase toward the north because most of the shortening is late pliocene and younger we interpret the tectonic shortening to be ongoing

seismic and geologic characteristics of drowning events on carbonate platforms carbonate platform drowning events are recorded in upper jurassic lower cretaceous carbonates of the baltimore canyon area offshore united states east coast and lower miocene carbonates of the pearl river mouth basin offshore people s republic of china cursory examination of seismic data from both areas would indicate that the platforms fit the classic definition of a drowning unconformity however detailed lithologic and paleontologic data indicate that the depositional erosional hiatuses vary widely in each area from 0 25 m y in the baltimore canyon area to a condensed section with no hiatus in the pearl river mouth basin the sedimentary sequence produced during drowning the drowning sequence in both areas is gradational with underlying shallow platform carbo ates and in some places overlying deeper marine limestones and shales the generalized facies models proposed for drowning events suggest that they may appear as instantaneous or gradual changes in geologic and seismic data however high resolution seismic data across the baltimore canyon and pearl river mouth basins show that some drowning sequences may be masked on conventionally processed seismic sections because of this resolution problem a distinction should be made between seismically and geologically defined unconformity surfaces the geologic characteristics of drowning events on carbonate platforms include a gradational lower and sometimes upper contact chemical sedimentation glauconite phosphate open marine shelf sediments and a variable hiatus at the upper boundary late growth shelf margin reefs also can be a diagnostic feature of drowned platforms seismic characteristics include horizontal to sub horizontal basinal marine onlap basin parallel reflector continuity above the carbonate sequence boundary and downlap of later highstand units evidence from platforms adjacent to continental margins baltimore canyon indicates that drowning occurs in a step wise fashion advancing more or less symmetrically across the platform from shelf to nearshore environments data from isolated open ocean atolls pearl river mouth basin indicate that they respond differently to drowning showing an asymmetric decrease in shallow platform environments as drowning occurs proper recognition by a geoscientist of the seismic and geologic characteristics of drowning events can lead to better reservoir and seal estimates and the correct reconstruction of the depositional tectonic and eustatic histories of an area

global marine gravity from retracked geosat and ers 1 altimetry ridge segmentation versus spreading rate 1 three approaches are used to reduce the error in the satellite derived marine gravity anomalies first we have retracked the raw waveforms from the ers 1 and geosat gm missions resulting in improvements in range precision of 40 and 27 respectively second we have used the recently published egm2008 global gravity model as a reference field to provide a seamless gravity transition from land to ocean third we have used a biharmonic spline interpolation method to construct residual vertical deflection grids comparisons between shipboard gravity and the global gravity grid show errors ranging from 2 0 mgal in the gulf of mexico to 4 0 mgal in areas with rugged seafloor topography the largest errors of up to 20 mgal occur on the crests of narrow large seamounts the global spreading ridges are well resolved and show variations in ridge axis morphology and segmentation with spreading rate for rates less than about 60 mm a the typical ridge segment is 50 80 km long while it increases dramatically at higher rates 100 1000 km this transition spreading rate of 60 mm a also marks the transition from axial valley to axial high we speculate that a single mechanism controls both transitions candidates include both lithospheric and asthenospheric processes

kinematics of cenozoic extension on the south china sea continental margin and its implications for the tectonic evolution of the region abstract in the northern south china sea several large sedimentary basins developed during the cenozoic characterized by episodic rifting clockwise rotation of the rifts an eastward aging breakup unconformity and intensifying crustal extension to the east these features may be summarized by a scissors model the maximum rifting occurred north of the maximum thermal subsidence which was in turn north of the seafloor opening in contrast the nansha microcontinent south of the south china sea basin was dominated by compressional deformation during the cenozoic extension was of subordinate significance and manifested mainly by block faulting and tilting in the late early oligocene maximum tilting occurred in the southern part of the nansha microcontinent at distance from the deep sea basin of the south china sea the asymmetric development of extensional structures around the south china sea basin may be explained by the simple shear model proposed by wernicke 1981 the tectonic development of the south china sea was the consequence of various interactions of three major plates and may be summarized into three stages with dominating influences of respectively the retreat of the west pacific subduction zone in the late cretaceous the hard collision and impinging of india to tibet since the late eocene and the fast northward subduction of the indian ocean australian plate since the late early miocene

comment on barckhausen et al 2014 evolution of the south china sea revised ages for breakup and seafloor spreading abstract we re examined the cessation of the south china sea seafloor spreading by using radioactive dating and fossil assemblage of the eto and the te derived age the youngest available age for the fragment of the south china sea is 15 ma and is more consistent with those suggested by previous studies moreover recent iodp expedition preliminary results suggested that the hemipelagic claystone layer stratigraphically bounded by igneous sequences of massive lava flow rock is early miocene in age therefore the previous interpretations are more inclusive than those provided by barckhasen et al 2014 and indicate that a slow spreading ridge was more plausible to have occurred during the seafloor spreading of the south china sea

what are the spratly islands abstract seismic records combined with dredged samples and a core indicate that the spratly islands of the dangerous ground province are constructed of presently active carbonate build ups known to extend back continuously at least to the pleistocene and presumed to have initiated in the miocene most likely upon the crests of sea floor cuestas that trend north east south west parallel to the sea floor spreading magnetic anomalies of the contiguous abyssal plain of the southern part of the south china sea the cuestas range from spectacular to subdued constructed of triassic and cretaceous strata and no older rocks have been identified from dredges the cuesta axes plunge towards the south west away from the islands suggesting that the reefs began colonising their more elevated parts but the timing is uncertain the highest seismically recorded cuesta crest is in 440 m of water and the islands and reefs are generally closely surrounded by water deeper than 1500 m since the so called mid miocene unconformity mmu the region has been undergoing post rift thermal subsidence however the nearby seismic lines show no evidence of drowned carbonate reefs it is suggested that the coral algal reefs colonised the crests of the most elevated cuestas that have maintained stability as shown by the 165 m core of one reef indicating periodic exposure with caliche horizons deepening water has protected the build ups from extinction by post rift draping strata in contrast to the central luconia province and the build ups have been able to keep up with regional thermal subsidence the dredged mesozoic strata indicate that the dangerous ground is not exotic and should be interpreted as an integral part of the pre rift sundaland continent that included south china vietnam peninsular malaysia western sarawak and possibly part of sabah igneous and metamorphic samples have been dredged although individual spot k ar dates cannot be accepted at face value such rocks can also be interpreted as an integral part of sundaland post mmu dredged samples are predominantly deep water calcareous mudstones typified by the draping strata of the ocean drilling program odp site 1143 cored from recent to late miocene

carbonate platform growth and demise offshore central vietnam effects of early miocene transgression and subsequent onshore uplift abstract miocene carbonate platforms cover a large part of the central vietnamese south china sea margin early carbonate deposition took place on two regional platforms separated by a narrow depression developed along the trace of the east vietnam boundary fault zone west of the east vietnam boundary fault zone the tuy hoa carbonate platform fringes the continental margin between da nang and nha trang here platform growth initiated during the early miocene and continued until middle miocene time when regional uplift led to subaerial exposure termination of platform growth and karstification east of the fault zone the triton carbonate platform was also initiated during the early miocene carbonate growth thrived during early and part of middle miocene time and a thick clean lower and middle miocene carbonate succession cover the triton horst and the qui nhon ridge during the middle miocene partial drowning resulted in the split up of the triton carbonate platform repeated partial drowning events throughout the middle and late miocene resulted in westwards retreat of platform growth and eventual platform drowning and termination of carbonate deposition modern carbonate growth continues on isolated platforms hosting the paracel islands farther seawards the onset of widespread carbonate deposition largely reflects the early miocene transgression of the area linked with early post rift subsidence and the opening of the south china sea the mid neogene shift in carbonate deposition is interpreted as a consequence of regional uplift and denudation of central and south indochina starting during middle miocene time when the tuy hoa carbonate platform became subaerially exposed stressed carbonate growth conditions on the triton carbonate platform probably resulted from increased inorganic nutrient input derived from the uplifted mainland possibly enhanced by deteriorated climatic conditions and rapid sea level fluctuations promoting platform drowning

the temporal and spatial distribution of volcanism in the south china sea region cenozoic magmatism in the south china sea the associated continental margins coastal south china and indochina is reviewed volcanism contemporaneous with rifting and sea floor spreading in the south china sea was very weak in the margins and adjacent areas there was only very limited magmatic activity most probably after the cessation of sea floor spreading the south china sea has non volcanic margins large basement relief caused by extension formed major basins and a continental oceanic transitional zone in the northern margin reflects high crustal rigidity during rifting and drifting the paucity of a magma supply and presence of rigid fault blocks are unfavorable to the mantle flow model previously proposed to account for the opening of the south china sea which was supposedly linked to the escape of indochina induced by indo eurasia collision c 2005 published by elsevier ltd

seismic sequence analysis and reservoir potential of drowned miocene carbonate platforms in the madura strait east java indonesia seismic analysis of four miocene carbonate buildups the porong ke 11c kd 11e and bd buildups in the madura strait region indonesia shows that they are constructed of four seismic units 1 4 all the buildups are located atop an east west trending oligocene fault block which through its uplift favored the deposition and aggradation of shoal water carbonates aggradation platform narrowing and backstepping of leeward reefs into the upper parts of individual buildups typify the growth profiles adjacent off buildup sedimentary rocks deposited at the same time as the buildups show clear horizontal onlap relationships in combination these observations imply that all the platforms were drowned the uppermost parts unit 4 of each of four major drowned buildups in the trend have been drilled to test for the presence of hydrocarbons an analysis of the drilling results in combination with our seismic analysis shows that those buildups that have relatively high levels of hydrocarbons have suitable trap configurations but lack seal integrity for example compactionally induced strain and gravitational gliding created leaky collapse graben faults extensional structures atop some buildups porong ke 11c which allowed hydrocarbons to drain likewise the updip inclination of some potential seal beds facilitated leakage ke 11e in terms of potential targets in similar drowned buildups in the region higher priority should be given to targets that 1 show evidence of ongoing platform backstepping and so called give up reef growth profiles associated with incipient drowning 2 contain all four seismic units units 1 4 in the buildup 3 lack an extensional collapse graben over the crest of the drowned structure and 4 demonstrate bed inclinations in the sealing beds that indicate likely closure over the crest of the buildup begin page 214

tectonic stratigraphic division and blind fold structures in nansha waters south china sea extensive multiple channel reflection seismic data have been collected in the nansha spratley islands waters the southern margin of the south china sea stratigraphic correlation is shown with focus on a comprehensive geophysixcal survey line run front offshore nw sabah to offshore se vietnam according to the varying tectono stratigraphy from southeast to northwest five tectonic belts can be determined i e the palawan borneo nappe nansha trough nanwei liyue compressive belt zheng he extensional belt and the circum southwest subbasin belt in the palawan borneo nappe neogene quaternary deposits were highly upthrust northwestwards resulting in a series of moderately to tightly folded anticlines separated by open synclines the nansha trough was a narrow deep water belt filled with thick undisturbed neogene quaternary deposits the nanwei liyue compressive bell was dominated by strongly folded paleo anticlines overlain by an undeformed sedimentary cap with a pronounced hiatus of paleogene sediments the zheng he extensional belt consisted of a rugged topography and paleogene half grabens bounded by listic faults the major extensional faults were reactivated to cut through the overlying neogene quaternary deposits over the circum southwest subbasin belt neogene quaternary deposits draped on the largely subsided fault blocks related to the late oligocene mid miocene seafloor spreading based on the regional stratigraphic correlation the prominent paleo anticlines found within the nanwei liyue compressive belt are deduced to consist of mainly mesozoic marine sediments that were compressed in the late mesozoic era therefore the nansha microcontinent block is shown to be a collision complex assembled during late mesozoic era c 2004 elsevier ltd all rights reserved

basement control on flexural profiles and the distribution of foreland facies the dwyka group of the karoo basin south africa flexural partitioning of a foreland system into foredeep forebulge and backbulge is the result of the interplay of lithospheric deflection under orogenic loading flexural tectonics and the structure of the underlying basement flexural tectonics is commonly invoked as the sole control on flexural profiles which are modeled as dampened sine curves with wavelengths and magnitudes controlled by a number of physical parameters of the lithosphere and the applied loads basement tectonics is shown here to be an equally important control on the scale and shape of flexural provinces by controlling the location of flexural hinge lines and the tilt directions within the foreland system the case study for this paper shows that basement heterogeneity coupled with the selective reactivation of major crustal faults may lead to distortion of the ideal flexural profile by modifying the wavelength and shape of individual flexural provinces

marginal basin evolution the southern south china sea abstract the southern south china sea is divided into contrasting morphology by the west baram line to the west is the sundaland extinct passive margin in which rifting began in the eocene 46 ma and ceased at 19 21 ma anomaly 6 where sea floor spreading began much later than along the shelf of china the break up hiatus lasted 3 5 ma marked by the mid miocene unconformity also preserved on land sarawak the post rift strata date from 16 ma and drape over the rifted topography to the east is a convergent margin that became a collision zone in the middle miocene the sunda shelf is of uniform 30 km thickness except in localised deep basins and extends to a water depth of 200 m the continental slope is narrow the continental rise dangerous grounds is covered by water ranging from 500 m to 3 5 km depth at the continent ocean transition its width ranges from 170 to 330 km the rajang delta extends over the shelf and continental slope its post rift sediments drape over the rifted proximal topography of the dangerous grounds to the east the drape is thinner and has not completely buried the rifted topography the cuestas appear to have supported the carbonate build up infrastructures of the spratly islands whose slopes rise abruptly from a sea floor of 2 3 km depth the sabah and brunei margin is a collision zone that was formerly convergent the on land geology indicates a mesozoic ophiolitic basement the main collision feature is the western cordillera constructed mainly of sandy eocene to lower miocene turbidites predominantly oligocene to lower miocene in the west crocker 32 18 ma uplifted episodically throughout the upper miocene and pliocene 14 8 ma the 2 km deep northwest borneo trough may be a relict of the convergence phase but could also be a collisional foredeep the oil prolific baram delta resulting from uplift and erosion of the western cordillera has built out as far as the northwest borneo trough it is suggested that the passive margin continental rise dangerous grounds has been underthrust beneath sabah to cause uplift of the western cordillera the west baram line accordingly abruptly separates the collision zone from the western extinct passive margin and is a now extinct major right lateral transform fault

morphological indicators of structural control relative sea level fluctuations and platform drowning on present day and miocene carbonate platforms abstract the morphology of carbonate platforms may be influenced by tectonic activity and eustatic variations 3d seismic data and satellite imagery are used in order to investigate the morphological similarities between present day carbonates platforms east of borneo island and miocene carbonate platforms of the south china sea the morphological similarities exhibit platform fragmentation that could be caused by subtle faulting sufficient to drown reef rims platform contraction which is a result of back stepping of the reef margin during a relative sea level rise and polygonal patterns in internal lagoons described as mesh reefs in modern platforms and possibly interpreted as karst in miocene platforms vertical movements may trigger the formation of new geomorphological conditions that modify the distribution of coral growth with respect to the new hydrodynamic conditions in space and time these movements uplift and tilting reduce and localize the space necessary for the coral ecosystem explaining the contraction leading to drowning of parts of and ultimately the whole platform

the structural evolution of folds in a deepwater fold and thrust belt a case study from the sabah continental margin offshore nw borneo se asia abstract the deepwater fold and thrust belt offshore sabah nw borneo is located on a continental margin that hosts a number of proven hydrocarbon accumulations reprocessed and depth migrated regional 2d seismic data reveal the occurrence of a wide range of compressional syn depositional deformation features including large scale thrust faults and prominent thrust hangingwall anticlines this paper focuses on the documentation and detailed description of the style of deepwater folds and the associated stratal patterns within a study area of ca 3000 km 2 offshore sabah nw borneo this region exhibits a variety of fold systems including 1 anticlines with large interlimb angles that exhibit no seafloor expression 2 anticlines with medium interlimb angles seafloor relief and a faulted anticline crest 3 anticlines with small to medium interlimb angles a seafloor expression and flanks associated with slides and slumps and finally 4 anticlines with small interlimb angles that are commonly buried by a thick sedimentary overburden and in places modified by superimposed syn sedimentary deltaic normal faults if analysed section per section perpendicular to the strike of the fold and thrust belt the widest anticlines occur in the most seaward parts of the fold belt near the present day thrust front whereas the narrower anticlines are located further landward however if viewed along the strike of the deepwater fold belt there are significant variations in the geometry of laterally corresponding contemporaneously developing fold systems to explain these differences factors such as rock inhomogeneities in the deformation wedge variable surface slope irregular basement topography differential sediment input or the presence or absence of subsurface gas hydrates need to be taken into account these factors vary significantly within the studied system and are therefore difficult to generalise and transfer to other submarine fold and thrust belts

development and controlling factors of miocene carbonate platform in the nam con son basin southwestern south china sea miocene carbonate platforms are located on intrabasinal structural highs and along the southern margin of the nam con son basin also referred to as the wanan basin by chinese southwestern south china sea these isolated platforms together cover a gross area of over 25 000 km 2 we map the platforms reconstruct their evolution and evaluate the controls on platform growth and demise within the regional geological setting using available seismic and well data the platforms initiated in the late early miocene and reached their widest extent during the middle miocene the platform margins were controlled by synsedimentary faults associated with carbonate slope failure deposits and or reef talus the platforms formed as isolated platform platform growth history involves six phases start up second start up keep up exposure renewal and drowning phases quantitative analysis of the basin evolution indicates that tectonism eustasy the supply of both terrigenous sediment and nutrients were the dominant controls on platform development and demise c 2013 elsevier ltd all rights reserved

seismic stratigraphy and tectonic structure from a composite multi channel seismic profile across the entire dangerous grounds south china sea abstract we interpret a more than 500 km long composite multi channel seismic reflection profile across the entire dangerous grounds the south china sea five tectonostratigraphic units are determined together with seven sequence boundaries detailed analysis of extensional features based on measurements of fault heaves revealed two major phases of extension separated by a distinct unconformity which likely correspond with the beginning of sea floor spreading in the south china sea early extension occurred during continental rifting late cretaceous early oligocene and resulted in formation of half grabens and rotated blocks controlled by a deeply rooted detachment system extension continued in our study area during the drifting phase of the east subbasin of the south china sea late oligocene early miocene until the subsequent opening of the southwest subbasin at about 25 ma but its intensity decreased markedly thereafter deeply rooted detachment systems evolved possibly during this second phase of extension at the continent ocean transition area from a coincidence of the lowermost reflections and moho depth as derived from gravity inversion we tentatively interpret the flattened part of this detachment system as the crust mantle boundary it is suggested that the dangerous grounds reflect a magma poor rift system at the initial stage of mantle unroofing we suggest that a widespread carbonate platform developed across the dangerous grounds concurrent with the period of seafloor spreading in the southwest subbasin of the south china sea fault related stretching factors f along the line show discrepancies with the whole crustal stretching factors c the continental crust of the dangerous grounds may have experienced nonuniform thinning

upper mississippian lower carboniferous carbonate stratigraphy and syndepositional faulting reveal likely ouachita flexural forebulge effects eastern kentucky u s a abstract stratigraphic analysis of late middle to early late mississippian early carboniferous late meramecian early chesterian carbonates in east central and northeastern kentucky u s a shows six unconformity bound sequences the earliest late meramecian st louis sequence shows a relatively uniform distribution and a typical eastward appalachian gradient along the ene trending outcrop belt on the western margin of the appalachian basin however abrupt uplift and exposure of deeper water st louis deposits indicated by erosional thinning and well developed exposure features at the meramecian chesterian transition signal inception of regional early chesterian uplift that intensively altered the nature and distribution of the five overlying early chesterian carbonate sequences uplift was related to the syndepositional reactivation of wnw trending basement faults that broke up the st louis platform and generated a mosaic like distribution of the overlying five sequences due to structurally related erosional incision and paleoslope change to the southwest these early chesterian events coincide with a major phase of northeast directed ouachita orogeny on the southern margin of laurussia and concomitant forebulge migration to the ene modeling of regional stress distribution as well as timing and location during bulge migration strongly indicate that a migrating ouachita bulge reactivated basement structures and generated the noted stratigraphic anomalies in eastern kentucky and nearby areas the likelihood of low amplitude flexural waves like the ouachita bulge migrating across areas where they were not previously considered has major implications for understanding structural stratigraphic and eustatic anomalies in supposedly stable cratonic areas far removed from active tectonism

paleoclimatic controls on sedimentation diagenesis and reservoir quality lessons from miocene carbonates miocene carbonates worldwide were deposited in a wide range of paleogeographic and tectonic settings and form important reservoirs in several regions the reservoir quality of these carbonates appears to have been primarily controlled by the prevailing paleoclimate which exerted a major control on both the depositional patterns and diagenetic pathways two end members are discussed here 1 humid oceanic tropical subtropical settings and 2 arid land locked temperate subtropical settings in humid oceanic tropical subtropical settings e g miocene of southeast asia a warming trend paralleled by generally rising sea level allowed thick coral reefs and skeletal banks to develop most of which are seismically resolvable these carbonates typically represent several stages or cycles of development largely third order separated by discontinuities in platform growth with episodic subaerial exposure development of economic reservoirs is mainly related to relative sea level falls and associated meteoric diagenesis trends and patterns of reservoir distribution can be predicted within a sequence stratigraphic framework basal transgressive carbonates are mostly tight because of their relatively fine grained textures intense compaction and isolation from meteoric water influence best reservoir quality is commonly developed beneath subaerial unconformities in highstand buildups where effects of meteoric water leaching and karstification are most intense in contrast in arid land locked subtropical temperate settings unfavorable environmental conditions caused by periodically increased salinity and probably relatively low temperature restricted the full growth of carbonate buildups as a result relatively thin and narrow fringing coral reefs with small poorly developed lagoons in rhodalgal ramps are the most common facies type in the upper miocene of the mediterranean and the middle miocene of the gulf of suez and red sea whereas the lower miocene of the middle east is characterized by low energy shallow shelfal and lagoonal carbonates under arid climatic conditions recharge of fresh groundwaters is limited thus minimizing meteoric dissolution and cementation during subaerial exposure instead sea level fall and lowstand ommonly resulted in extensive evaporitic conditions hypersaline brines originated within evaporitic basins or lagoons were the main cause of the pervasive dolomitization leaching of metastable skeletal grains and generation of moldic vuggy and intercrystalline porosity often associated with these arid land locked carbonates is the widespread anhydrite cement that precipitated over a wide range of burial depths porosity distribution in these carbonates thus depends not only on the original depositional fabrics but more importantly on the degree to which the porosity occluding anhydrite cement was dissolved or the low permeability carbonates were fractured these miocene examples illustrate the contrasting diagenetic patterns and reservoir styles controlled by paleoclimatic and paleoceanographic trends and demonstrate the importance of the often overlooked hypersaline diagenesis in arid land locked subtropical temperate settings the development of exploration and production strategies for carbonates that were deposited in different climatic settings should acknowledge and use these fundamentally different styles of diagenesis and reservoir characteristics

architecture development and geological control of the xisha carbonate platforms northwestern south china sea newly acquired seismic data allow improved understanding of the architecture and evolution of isolated carbonate platforms on the continental slope of the northern south china sea the xisha carbonate platforms were initiated on a basement high the xisha uplift in the early miocene and have remained active up to the present their distribution is limited to pre existing localized fault bounded blocks within the xisha uplift so individual platforms were small in size at the beginning of the miocene however during the middle miocene the platform carbonate factories flourished across an extensive area with 55 900 km 2 the platforms began to backstep in response to a relative sea level rise in the late miocene platform edge reefs patch reefs pinnacle reefs atoll reefs and horseshoe reefs all developed on various platforms the distribution of platform carbonates shrank significantly during pliocene quaternary time to isolated carbonate platforms represented today by xuande atoll and yongle atoll tectonics and eustasy were the two main controls on platform development tectonics controlled both the initial topography for reef growth and the distribution of platforms including those that survived the drowning event associated with the late miocene rapid relative sea level rise eustasy controlled high frequency carbonate sequence development crown copyright c 2014 published by elsevier b v all rights reserved

methods for identification of isolated carbonate buildups from seismic reflection data isolated carbonate buildups icbs are commonly attractive exploration targets however identifying icbs based only on seismic data can be difficult for a variety of reasons these include poor quality two dimensional data and a basic similarity between icbs and other features such as volcanoes erosional remnants and tilted fault blocks to address these difficulties and develop reliable methods to identify icbs 234 seismic images were analyzed the images included proven icbs and other features such as folds volcanoes and basement highs which may appear similar to icbs when imaged in seismic data from this analysis 18 identification criteria were derived to distinguish icbs from non icb features these criteria can be grouped into four categories regional constraints analysis of basic seismic geometries analysis of geophysical details and finer scale seismic geometries systematically assessing the criteria is useful because it requires critical evaluation of the evidence present in the available data working from the large scale regional geology to the fine details of seismic response it is also useful to summarize the criteria as a numerical score to facilitate comparison between different examples and different classes of icbs and non icbs our analysis of scores of different classes of features suggests that the criteria do have some discriminatory power but significant challenges remain

orbital suppression of wind driven upwelling in the california current at 6 ka 1 marine records clearly show activity in the california current cc system to have been altered during the mid holocene however the specific nature of cc activity during this period remains ambiguous as proxies that suggest cooler than present sea surface temperatures co occur in mid holocene marine sediments with multiple proxies that suggest decreased coastal upwelling to test the sensitivity of wind driven upwelling in the cc to mid holocene orbital forcing we have employed a high resolution regional climate model rcm the seasonality of modern cc wind driven coastal upwelling simulated by the rcm is in strong agreement with observational data further we show that changes in the seasonality of solar insolation induced by mid holocene milankovitch forcing decrease early and peak season coastal upwelling in the cc along with increasing late season coastal upwelling these results are in agreement with several marine and terrestrial proxies suggesting that relative to present cc activity during the mid holocene was characterized by a longer and less vigorous upwelling season with decreased seasonal contrast

time constraints on the evolution of southern palawan island philippines from onshore and offshore correlation of miocene limestones abstract the link between the deformation of southern and central palawan island philippines and the deformation of the adjacent offshore wedge is investigated the wedge is a continuation of the palawan fold and thrust belt and bounds the borneo palawan trough to the dangerous grounds and to palawan island key parameters for the understanding of the formation and development of this wedge are two limestone formations the oligocene to middle miocene nido limestone and the upper miocene to lower pliocene tabon limestone the initiation of the thrust belt formation is constrained by the nido limestone which was deposited from shortly before the breakup of the eastern south china sea 35 ma until the early miocene age data available from wells offshore central palawan gives an age of early miocene close to the base of the nido limestone while cropping out onshore north palawan these limestones were overthrusted by the wedge in southern and central palawan seismic images show gently east dipping carbonates below the wedge the seismic data show that these limestones are only mildly affected by the wedge formation the end of the wedge development can be constrained by the tabon limestone with an age of 9 to 4 ma this limestone sequence overlies unconformably the offshore wedge a detailed biostratigraphic correlation of the tabon limestone along the southwest palawan shelf using well data combined with multichannel seismic data and investigations onshore southern and central palawan shows a time and space transgressive development of these limestones they are progressively younging towards the west we propose that the formation of the tabon limestone is directly linked with the development of the wedge that tectonically controls the formation of this carbonate platform this constrains the time for the final phase of the formation of the palawan thrust belt after the final compressional phase and wedge formation in the lower early pliocene the wedge underwent a phase of subsidence based upon the detailed correlation of these limestones we propose that the wedge did not form in the southern palawan area prior to 18 ma using the sealing tabon limestone as time constraint we suggest that the development of the wedge in the south palawan area started in the lower middle miocene 15 ma and continued developing towards the west until the upper late miocene to early pliocene 5 ma after the wedge propagation stopped the wedge front collapsed in several places due to gravitational sliding southern and central palawan were uplifted above sea level during a second phase of compression in the late pliocene onshore outcrops give indications to a working spleothem since 1 2 ma

the structure and stratigraphy of deepwater sarawak malaysia implications for tectonic evolution abstract the structural stratigraphic history of the north luconia province sarawak deepwater area is related to the tectonic history of the south china sea the sarawak basin initiated as a foreland basin as a result of the collision of the luconia continental block with sarawak sarawak orogeny the foreland basin was later overridden by and buried under the prograding oligocene recent shelf slope system the basin had evolved through a deep foreland basin flysch phase during late eocene oligocene times followed by post oligocene molasse phase of shallow marine shelf progradation to present day seismic interpretation reveals a regional early miocene unconformity emu separating pre oligocene to miocene rifted basement from overlying undeformed upper miocene pliocene bathyal sediments seismic well data and subsidence analysis indicate that the emu was caused by relative uplift and predominantly submarine erosion between 19 and 17 ma ago the subsidence history suggests a rift like subsidence pattern probably with a foreland basin overprint during the last 10 ma modelling results indicate that the emu represents a major hiatus in the sedimentation history with an estimated 500 2600 m of missing section equivalent to a time gap of 8 10 ma the emu is known to extend over the entire nw borneo margin and is probably related to the sabah orogeny which marks the cessation of sea floor spreading in the south china sea and collision of dangerous grounds block with sabah gravity modelling indicates a thinned continental crust underneath the sarawak shelf and slope and supports the seismic and well data interpretation there is a probable presence of an overthrust wedge beneath the sarawak shelf which could be interpreted as a sliver of the rajang group accretionary prism alternatively magmatic underplating beneath the sarawak shelf could equally explain the free air gravity anomaly the sarawak basin was part of a remnant ocean basin that was closed by oblique collision along the nw borneo margin the closure started in the late eocene in sarawak and moved progressively northeastwards into sabah until the middle miocene the present day nw sabah margin may be a useful analogue for the oligocene miocene sarawak foreland basin

oligocene miocene carbonates and their role for constraining the rifting and collision history of the dangerous grounds south china sea abstract the attenuated continental crust of the dangerous grounds is located in the southeastern part of the south china sea it was affected by unconformities as identified by several authors cullen et al 2010 hinz and schluter 1985 hutchison 2010 hutchison and vijayan 2010 in the northeastern dangerous grounds a prominent reflector in seismic data is associated with the top of a widespread oligocene to early miocene 18 20 ma carbonate platform this reflector and the underlying carbonates can be used to constrain the timing of the unconformities and the rifting history of the dangerous grounds by carefully interpreting seismic reflection lines we trace the platform carbonates based upon their appearance in the seismic image this platform is continuous in the palawan borneo trough and gets patchy toward the dangerous grounds in the dangerous grounds the image of this key reflector changes and here it merely forms the top of a clastic layer carbonates remain abundant but mainly as isolated reefs that grew on top of tilted fault blocks in the southwestern dangerous grounds the prominent unconformity sealing the tectonic activity is known as the middle miocene unconformity this in fact is an early miocene unconformity which represents a sequence boundary in the borneo palawan trough and in various parts of the dangerous grounds while in other parts of the dangerous grounds it represents a major angular unconformity the unconformity characteristics supplemented with tentative ages indicate that luconia and the southern dangerous grounds were sub aerial during the early miocene while the reed bank the northern dangerous grounds and parts of the central dangerous grounds were mostly submerged except for some islands concentrated on the western edge of the borneo palawan trough this trough is interpreted as a foreland basin where the flexural forebulge provided shallow marine conditions that promoted reef growth as the carbonate deposition migrated from the borneo palawan trough toward the dangerous grounds we suggest that the flexural forebulge provided shallow water conditions for further reef growth on the eastern dangerous grounds

crustal structure north of the taiping island itu aba island southern margin of the south china sea abstract based on the multi channel seismic mcs and gravity data offshore north of taiping island itu aba island in the spratly islands nansha islands we revisited the crustal structures in the northern part of the southern margin of the southwest sw sub basin of the south china sea scs the mcs data suggest that the basement structural highs in the southwest margin of the scs are dominated by both fault blocks and volcanic basement structures that probably formed along with the basement faults the gravity modeling results reveal that these volcanic basement structures were probably associated with the high velocity or density lower crust hvdlc suggesting that the southern margin of the sw sub basin serves as an intermediate margin based on the tectonic features in the scs margins including 1 the transition between the magma poor margins of the northwest nw sub basin and intermediate margins of the east and sw sub basins 2 the cessation of the seafloor spreading in the nw sub basin being succeeded by a major ridge jump event which was very likely to reflect an active mantle upwelling event 3 the extensive distribution of the hvdlc beneath in the well investigated northern margin of the east sub basin and as explored in the sw sub basin in this study and 4 basement faulting and volcanism shown in this study that may be related to the hvdlc and hyper extension we proposed a conceptual model to interpret the origin of the hvdlc in the southern margin of the sw sub basin the margin of the scs basin was magma poor at the time it occurred an active mantle upwelling event caused by small scale mantle convection possibly related to the influence of the nascent hainan mantle plume was formed subsequently resulting in a southward ridge jump and the hvdlc beneath the current margins of the east and sw sub basins the east and sw sub basins continued to spread latitudinally dividing their hvdlcs as the margins separated accordingly afterwards the hyper extension in the distal margins may also be responsible for a crust weakening zone wherein the subsequent volcanic events could occur

seismic sequence stratigraphic analysis of the carbonate platform north offshore taiping island dangerous grounds south china sea abstract taiping island also known as itu aba is the largest natural terrestrial landmass in the south china sea and is centrally located using bathymetry and marine multi channel seismic data we explored the seismic stratigraphic features of the offshore and isolated carbonate platform north of taiping island the western flank of the carbonate platform is characterized by an intercalation between high amplitude and low amplitude reflections showing the landward and seaward migration of the platform foreslope deposits in addition there are two offshore carbonate build ups that are underlain by normal faults six sequence boundaries and five depositional sequences caused by eustatic sea level cycles are identified and correlated with the eustatic sea level change chart although the evolution of the seismic sequences is partly controlled by local tectonics the overall stacking pattern of the sedimentary strata in our study area reveals five third order cycles and one second order cycle which is in accordance with the eustatic sea level chart additionally the formations of the western taiping seamount group and the zhenghe daoming trough are preliminarily analyzed based on seismic data

dry climate near the western pacific warm pool pleistocene caliches of the nansha islands south china sea abstract the nansha spratly islands are located in the middle of the south china sea at about 10 n near the northwestern margin of the western pacific warm pool wpwp a borehole was drilled at an atoll at nansha and cores were taken the upper 165 4 m of the borehole consists entirely of limestone of reef facies and lagoon facies which had been influenced by extensive meteoric diagenesis petrographic and geochemical studies have identified at least four subaerial exposure surfaces ses in the pleistocene carbonate sequence these ses are thought to have resulted from global sea level changes and characterized by caliche formation when developed in limestone caliches typically form in areas where annual precipitation ranges from 500 mm up to about 1200 mm compared with 1800 2200 mm of annual rainfall of the present day nansha islands the nansha caliche therefore indicates the existence of several dry climate episodes during pleistocene sea level lowstands lower rainfall and higher evaporation during such dry conditions may explain the higher sea surface salinities reported elsewhere in the south china sea the nansha caliche may also indicate reduced extent of the wpwp and southerly shift of the intertropical convergence zone during major sea level lowstands

evolution of the south china sea revised ages for breakup and seafloor spreading abstract the continental breakup which gave way to the formation of the oceanic south china sea scs basin began in the latest cretaceous in the northeastern scs and propagated in southern and western direction over a long period of time possibly more than 40 m y the seafloor spreading history of the south china sea has been interpreted in different ways in the past and the debate over the correct timing of the major tectonic events continues we review the different models that have been published and present a revised interpretation of seafloor spreading anomalies based on three datasets with documented high quality which cover all of the scs but the northernmost and southernmost parts we can precisely date the onset of seafloor spreading in the central part of the scs at 32 ma after a ridge jump at 25 ma spreading also began in the southwestern sub basin and spreading ended at 20 5 ma in the entire basin followed by a phase of magmatic seamount formation mainly along the abandoned spreading ridge spreading rates vary from 56 mm yr in the early stages to 72 mm yr after the ridge jump to 80 mm yr in the southwestern sub basin we find indications for a stepwise propagation of the seafloor spreading from northeast to southwest in segments bounded by major fracture zones seafloor spreading ended abruptly probably because the subduction zone along the eastern and southern boundary of the scs of which today the manila trench remains was blocked by collision with a continental fragment possibly the northern part of palawan or a part of the dangerous grounds

drowning history of a miocene carbonate platform zhujiang formation south china sea abstract the identification and interpretation of drowning events in the geologic record can aid significantly to the reconstruction of the depositional tectonic and eustatic history of a study area and often improve reservoir and seal prediction in carbonate rocks the differentiation between drowned platforms showing a record of continuous deepening and those with a record of exposure followed by rapid deepening remains however problematic the zhujiang carbonate platform liuhua 11 1 field south china sea study shown here provides an example of an integrated approach combining high resolution geochemistry microfacies analyses and foraminiferal biostratigraphy in order to improve the reconstruction of environmental conditions prior during and after platform demise and drowning the zhujiang carbonate platform displays the following vertical succession of four facies types i skeletal grain facies with a miogypsinid lepidocyclinid dominated fauna deposited in a moderately deep heterostegina sp and spiroclypeids possibly capped by a subaerial exposure surface well rounded rhodoids representing a mesotrophic lagoon dominate the upper portions of the rhodoid facies iv pelagic marine shales of the hanjiang formation burying the carbonate platform after drowning this facies succession in combination with geochemical evidence suggests a deepening upward trend this trend might have been interrupted by transient subaerial exposure but no evidence for meteoric diagenesis was found at the drowning unconformity topping the carbonate platform instead microfacies analyses suggest that platform demise may be related to progressive changes in environmental conditions including increasing nutrient levels and or decreasing temperature up core towards the drowning unconformity these findings are of significance for those concerned with miocene carbonate factories and more specifically the demise of carbonate platforms in general