discussion on a new upper paleogene to neogene stratigraphy for sarawak and labuan in northwestern borneo paleogeography of the eastern sundaland margin abstract important new work is presented by the authors on radiometrically dating the bukit piring intrusion and associated arip volcanics as well as confirmation that widespread outcrops of oligocene and miocene clastic formations share a common sediment provenance this valuable contribution is weakened by a poorly researched stratigraphic model that conflicts with much published work the importance of good micropalaeontology is stressed in this review as without this tool the essential dimension of time is lost and facies determinations are less reliable these inputs are two of the three two components along with space that make stratigraphy a testable science under walther s law

late quaternary deltaic and carbonate sedimentation in the gulf of papua foreland basin response to sea level change abstract the rivers that drain the wet mountainous island of new guinea discharge about 1 5 billion tonnes yr of sediments into the adjacent seas including the foreland basin between new guinea and australia despite this huge sediment input there appears to have been only limited deposition in the gulf of papua during the holocene postglacial rise in sea level seismic and core data indicate that the transgressive systems tract in the gulf of papua is thin and patchy it is confined to regions within and north of an incised east west trending shelf valley system of the possible explanations for the absence of a significant transgressive systems tract inland storage and along and off shelf transport of the sediment are of greatest significance reef growth up to the latitude of the east west trending incised valley system in the southern gulf of papua is considered to have been facilitated by a northward flowing coastal boundary current the coral sea coastal current this current now sweeps turbid brackish waters and terrigenous sediments discharged by the rivers northwards away from the reefs an observed northward offset in transgressive sediments in relation to the axis of the shelf valleys suggests that such a northward flowing shelf current operated during the late pleistocene and early holocene the northern limit of the great barrier reef could thus be controlled by the balance between fluvial sediment supply and northward advection of suspended sediment by the coral sea coastal current this current may also be imp rtant in maintaining a supply of clear water to the eastern gulf of papua thus enabling photosynthesis and the flourishing of calcareous algae halimeda bioherms or biostromes at depths of up to 100 m over much of the middle and outer shelf directly offshore of the modern fly delta these carbonate sediments represent the exposed maximum flooding surface and condensed section modern highstand delta deposits have begun to prograde over this layer on the inner shelf

cenozoic deformation of the tarim plate and the implications for mountain building in the tibetan plateau and the tian shan 1 the tarim basin in nw china developed as a complex foreland basin in the cenozoic in association with mountain building in the tibetan plateau to the south and the tian shan orogen to the north we reconstructed the cenozoic deformation history of the tarim basement by backstripping the sedimentary rocks two dimensional and three dimensional finite element models are then used to simulate the flexural deformation of the tarim basement in response to the sedimentary loads and additional tectonic loads associated with overthrusting of the surrounding mountain belts the results suggest that uplift of both the western kunlun shan and the tian shan orogens started during or before oligocene since the miocene mountain building accelerated in the western kunlun shan but showed segmented development in the tian shan the results also indicate reduced tectonic load along the altyn tagh fault since late miocene consistent with geological and geophysical evidence of the fault cutting the entire lithosphere and migrating southward during its cause of the cenozoic evolution

anatomy of the buried burdekin river channel across the great barrier reef shelf how does a major river operate on a tropical mixed siliciclastic carbonate margin during sea level lowstand abstract a large palaeochannel on the northeastern australian continental shelf has been imaged by a series of shallow seismic reflection profiles the buried channel forms an important pleistocene route of the burdekin river and extends almost continuously for 160 km from the present coast to the outermost reef the channel floor profile steps across the shelf with alternating segments of gentle gradient flats and steeper gradient ramps channel sinuosity as interpreted from seismic records varies among segments between 1 and 1 72 with no consistent relationship between sinuosity and gradient the lower and upper parts of the channel fill have different geometry and reflection character suggesting channel excavation and initial filling occurred during a different regime than final filling in one section of the shelf about the 50 m isobath the channel is difficult to define and appears to have wandered significantly either because it has been modified by shoreface erosion ca 10 5 ka or because the river encountered a change in topography in front of karstified reefs as the channel passes between the numerous outer shelf reefs in water depths of 70 80 m it becomes progressively smaller conspicuously underfilled and absent entirely over the outermost 10 km of the shelf no discrete lowstand river mouth could be recognised on the present shelf edge the elevations of flat segments on the channel floor profile show considerable similarity to published elevations of stillstands or brief rises in sea level attained during the long term drawdown associated with the last glacial cycle 125 20 ka and are interpreted to have formed during this stepwise drop in sea level channels were cut and partially filled during the fall and lowstand and then backfilled during the holocene transgression the ancestral channel of the burdekin river therefore preserves a rare insight into the stratigraphic record of falling sea level during the last glacial

what matters for flow and recovery in carbonate gas reservoirs insights from the mature central luconia province offshore sarawak malaysia miocene carbonate reservoirs in central luconia offshore sarawak malaysia have been delivering gas for over 30 yr in this paper learnings from that period of production are used to understand the key drivers affecting flow during production and recovery optimization in existing fields as well as development decisions for new discoveries the large data set generated over more than 40 yr was analyzed in a consistent manner through a holistic database constrained by a stratigraphic framework to allow reservoir units to be compared like for like integrated knowledge base ikb concept carbonate reservoir heterogeneities impacting flow are grouped into horizontal heterogeneities argillaceous flooding layers and exposure related karst and vertical heterogeneities large scale architectural elements found especially along platform margins both types of heterogeneities control water ingress during production and influence the recovery mechanism argillaceous flooding layers can act as baffles holding back water rise during production or can form pressure compartments long lived fault bounded reef margins carbonate shoals islands and karsts can be vertical conduits for aquifer inflow platform shape and architecture impact column height and hence recovery efficiency additional drivers impacting recovery were found to be gas column height aquifer size and permeability pressure connection to neighboring fields and field development concepts all drivers identified impact decisions throughout the field life e g well count and design intervention capabilities evaluation and mitigation of early water breakthrough reservoir management selecting enhanced recovery methods and abandonment pressure the ikb allowed to derive big rules on what matters for flow which were used to decide on development strategies for greenfields in central luconia the presented outcomes can be extrapolated to comparable carbonate systems whereas the ikb approach can be adapted and applied to other mature basins and reservoir types where equally vast and historic data sets are awaiting to be used in the current era of digitalization

carbonate evaporite siliciclastic transitions in quaternary rift sediments of the northwestern red sea abstract the quaternary and recent coastal environments of the egyptian red sea and gulf of suez are characterized by rapid lateral variations carbonates evaporites and siliciclastic sediments exist in close proximity although the climate is exceptionally dry the numerous wadis draining high hinterland relief deliver important quantities of coarse clastics to coastal environments during the rare periods of flash flooding however because this efficient supply is sporadic coastal waters are contaminated for short catastrophic periods which are followed by a rapid return to clear water carbonate sedimentation the warm arid conditions on the other hand favour both carbonate reef production and evaporite mineral precipitation rapid lateral transitions between continental siliciclastic and marine carbonate facies are favoured by a particular morphology closely related to the active distensional tectonic setting within the red sea rift block faulting which began in the early miocene and continues today has resulted in numerous subparallel grabens and horsts situated between the onshore basement relief and the coast the structural depressions grabens tend to trap much of the episodic siliciclastic input favouring permanent carbonate production in the nearby littoral environments

present day stress field of southeast asia article i nfo it is now well established that ridge push forces provide a major control on the plate scale stress field in most of the earth s tectonic plates however the sunda plate that comprises much of southeast asia is one of only two plates not bounded by a major spreading centre and thus provides an opportunity to evaluate other forces that control the intraplate stress field the cenozoic tectonic evolution of the sunda plate is usually considered to be controlled by escape tectonics associated with india eurasia collision however the sunda plate is bounded by a poorly understood and complex range of convergent and strike slip zones and little is known about the effect of these other plate boundaries on the intraplate stress field in the region we compile the first extensive stress dataset for southeast asia containing 275 a d quality 177 a c horizontal stress orientations consisting of 72 stress indicators from earthquakes located mostly on the periphery of the plate 202 stress indicators from breakouts and drilling induced fractures and one hydraulic fracture test within 14 provinces in the plate interior this data reveals that a variable stress pattern exists throughout southeast asia that is largely inconsistent with the sunda plate s approximately ese absolute motion direction the present day maximum horizontal stress in thailand vietnam and the malay basin is predominately north south consistent with the radiating stress patterns arising from the eastern himalayan syntaxis however the present day maximum horizontal stress is primarily oriented nw se in borneo a direction that may reflect plate boundary forces or topographic stresses exerted by the central borneo highlands furthermore the south and central sumatra basins exhibit a ne sw maximum horizontal stress direction that is perpendicular to the indo australian subduction front hence the plate scale stress field in southeast asia appears to be controlled by a combination of himalayan orogeny related deformation forces related to subduction primarily trench suction and collision and intraplate sources of stress such as topography and basin geometry

architecture and growth history of a miocene carbonate platform from 3d seismic reflection data luconia province offshore sarawak malaysia using 3d seismic reflection data and wireline logs we reconstruct in detail the architecture and growth history of a miocene carbonate platform in the luconia province offshore sarawak malaysia platform growth started in the late oligocene to early miocene by coalescence of isolated patch reefs the growth history includes phases of progradation backstepping and occasional collapsing of platform flanks guided by syndepositional faulting the most pronounced seismic reflections in the platform correspond to flooding events thin transgressive systems tracts subaerial exposure preceding the flooding could be demonstrated in only one case platform growth was terminated by gradual submergence drowning indicated by smooth concentric seismic reflectors forming a convex mound

wings mushrooms and christmas trees the carbonate seismic geomorphology of central luconia miocene present offshore sarawak northwest borneo central luconia is a geological province of the sarawak basin offshore northwest borneo characterized by extensive development of miocene to holocene carbonate buildups the buildups are up to 2 km 1 mi thick and reveal complex seismic geomorphologies including out building in building carbonate siliciclastic intercalations and coalescence of neighboring carbonate bodies intermittent carbonate and siliciclastic deposition is interpreted to have been governed by frequently oscillating sea level and variable siliciclastic input location of the buildups with respect to deltaic facies and the seismic expressions of marginal carbonate strata locally known as wings are used here to classify carbonate seismic geomorphologies buildups encompassed by deltaic topsets are said to reside onshelf and are flanked by marginal carbonate deposits conformable with the onlapping siliciclastics and interpreted as thin carbonate platforms deposited in situ over prominent erosional unconformities and flooding surfaces such marginal facies are described on the basis of their appearance as open wings in contrast buildups downlapped by prodelta foresets or bottomsets or those draped by pelagic sediments are said to reside offshelf and are characterized by high relief steeply dipping marginal carbonate strata discordant with respect to the relatively flat lying platform carbonates as well as the onlapping siliciclastics these marginal strata have an appearance of closed wings and are interpreted as slope aprons composed of carbonate material derived from the productive platform tops and deposited off platform in deeper water carbonate geometries range from contracting upward pinnacles to expanding upward platforms in onshelf settings whereas buildups located offshelf have mostly contracting upward or aggrading morphologies buildups deposited onshelf have generally maintained a similar height of depositional slopes as they evolved reflecting rates of background siliciclastic deposition approximating those of carbonate growth in contrast depositional slopes of offshelf buildups have become progressively higher owing to limited siliciclastic input observations presented here on carbonate geomorphology and adjacent siliciclastic stratigraphy provide important clues for the understanding of the geology of the province because carbonates and siliciclastics intercalate frequently siliciclastic biostratigraphy can be used to precisely date and correlate geographically remote carbonate reservoir intervals and intrareservoir depositional and diagenetic events such as marine transgressive or exposure surfaces or karst networks conversely basin paleobathymetry can be measured by the size of carbonate clinoforms and the thickness of buildups established over flooded siliciclastic surfaces deposition of low relief carbonate platforms over siliciclastic substrates indicates shallow marine conditions as opposed to the prevalent notion of kilometer scale paleobathymetry these interpretations have important implications for understanding of the sedimentology and lithology of the ambient basinal siliciclastics with fundamental applications to hydrocarbon exploration

sea level changes shoreline journeys and the seismic stratigraphy of central luconia miocene present offshore sarawak nw borneo abstract central luconia is a geological province of the sarawak basin offshore nw borneo characterised by extensive development of miocene to recent carbonate build ups in the subsurface many of these build ups are reservoirs for hydrocarbons this study focuses on shelf wide stratigraphic architecture from which implications are drawn for the stratigraphic sealing potential of the deltaic clastics a stratigraphic model is proposed whereby clastic sediments surrounding the carbonate build ups are interpreted as stacked low relief deltas deposited in response to high frequency oscillation of the sea level the deltas are shown to have frequently prograded beyond carbonate build ups as a result of interaction between eustacy and deposition deltaic topsets are juxtaposed against carbonate build ups providing migration routes for hydrocarbons most of the carbonate reservoirs are consequently underfilled with hydrocarbon columns limited to the youngest onlapping stratigraphic sequence

development of equatorial delta front patch reefs during the neogene borneo abstract miocene patch reefs formed in turbid waters associated with high siliciclastic input at the seaward margin of the equatorial mahakam delta in eastern borneo se asia patch reefs were initiated on unstable substrates on localized low relief bathymetric highs associated with delta front channels or distributary mouthbars in the process of abandonment patch reefs developed only in shallow waters formed low relief buildups lacked rigid frameworks and had gently sloping margins although the biodiversity of the patch reefs may be comparable with that of clear water systems all the organisms present were adapted to turbid water areas associated with siliciclastic and sometimes nutrient influx the patch reefs were transient features and their demise was influenced by increased siliciclastic and nutrient input perhaps at times associated with deepening carbonate production and bioherm or patch reef development can occur in turbid water delta front areas as localized or more regionally extensive units during any phases of eustatic sea level however development and preservation of turbid water carbonates is most likely during relative transgression or perhaps late lowstand periods this is in contrast with common highstand carbonates from clear water shelves where nearly pure carbonates interdigitate with siliciclastics it is the interplay between factors such as tectonics eustasy delta lobe switching shelf currents and amount and size fraction of siliciclastic influx that ultimately controlled carbonate development and preservation

development of a pliocene mixed carbonate siliciclastic reef limon costa rica the miocene to pleistocene limon group of costa rica is a mixed carbonate siliciclastic succession that formed in association with the emergence of the central american isthmus our study focuses on a lower late pliocene reef unit the newly excavated contact cut which is located at the contact between the siliciclastic sediments of the rio banano formation and the mixed reefal and coral bearing deposits and siliciclastic sediments of the quebrada chocolate formation the siliciclastic sediments were deposited in a thick deltaic setting sourced by erosion of the cordillera de talamanca deposits of the limon group preserve a sequence of progressively shallowing near shore sediments that were exposed by uplift during the early to middle pleistocene the contact cut outcrop shows the first reef sequence in the stratigraphic sequence and thus illustrates the reestablishment of caribbean coral reef predominance in the neogene it shows extensive reef growth during a rise in sea level and a slight progradation during the succeeding sea level highstand three stages of reef evolution are recognized based on faunal diversity the contact cut reef complex is comparable to the time equivalent reef of the las islas roadcut situated west of limon which shows a rapid burial of the corals by siliciclastics both reefs document a distinct facies diversification during the final stages of the closing of the central american seaway the reefs developed in an environment stressed by siliciclastic input which ultimately caused a decrease in coral diversity and abundance followed by a temporary demise of the reefs the biotic composition of the patch reefs that occurred during the sea level rise las islas and contact cut did not differ from the reefs that developed during the final highstand in sea level the reefs of the overlying moin formation limon group differences in the position on the shelf relative to the source of the siliciclastics might have been the cause for the different response to the rise in sea level of the transgressive reefs with a very fast give up scenario for las islas reef and a catch up followed by a give up phase for contact cut reef

from cyclothems to sequences the record of eustasy and climate on an icehouse epeiric platform pennsylvanian permian north american midcontinent the stratigraphic succession of the north american midcontinent contains a high resolution 100 000 year record of sea level and climate change spanning the pennsylvanian permian boundary outcrop based sequence stratigraphic analysis on the upper wabaunsee admire and lower council grove groups in kansas and nebraska reveals a hierarchy of fifty one fifth order meter scale cycles grouped into five fourth order composite sequences fifth order cycles are bounded by subaerial unconformities in nearshore settings and correlative conformities in offshore settings and are therefore very thin depositional sequences lowstand systems tracts observed only in nearshore deposits are expressed as sandy incised valley fills in these meter scale cycles transgressive systems tracts which are dominated by carbonate deposition include coastal evaporites indicating arid climatic conditions highstand systems tracts which are dominated by siliciclastic deposition include thin but persistent coals in muddy coastal successions indicating humid climatic conditions paleosols at sequence boundaries evolve from vertic to calcic indicating climate change from relatively humid to relatively arid conditions during subaerial exposure this indicates that relatively arid climate coincided with eustatic lows while relatively humid climate coincided with eustatic highs on this low latitude platform composite sequences are bounded by subaerial angular unconformities and display a transgressive regressive stacking pattern of meter scale cycles the high resolution stratigraphic record of the midcontinent helps constrain the rate and magnitude of environmental change in ancient icehouse conditions and can serve as a baseline of environmental change for comparison with other coeval successions

evolution of late oligocene early miocene attached and isolated carbonate platforms in a volcanic ridge context maldives type yadana field offshore myanmar this study investigates the stratigraphic evolution of the late oligocene early miocene carbonate platforms of the yadana area offshore myanmar well data regional 2d and local 3d seismic surveys allow the identification of three shallow water carbonate platforms yadana 3df and 3de showing various morphologic and stratigraphic patterns influenced by the presence of a paleohigh the identification of seven seismic sequences in the yadana area constrains the stratigraphic evolution in three stages 1 development of aggrading attached and isolated platforms during the chattian 2 a period of platform emersion during the oligocene miocene transition 3 drowning of the smaller buildup 3de associated with km scale backstepping on the large platforms 3df and yadana during the aquitanian the aquitanian marks the onset of renewed volcanic activity associated with the development of fringing carbonate reefs during the burdigalian the rapid similar to 6 my development of these wide similar to 5 70 km and thick similar to 300 850 m carbonate platforms has been mainly controlled by the subsidence however the results highlight a strong overprint of eustatic fluctuations on the rates of change in accommodation and hence on the stratigraphic architecture of the carbonate platforms based on an alternative model for the cenozoic geodynamic evolution of the yadana area our results suggest that the platforms developed on a volcanic ridge of hotspot origin located in the indian ocean and not on a volcanic arc subduction jump processes are interpreted to have played a key role in the demise of all platforms by drastically changing the paleoenvironmental conditions during the early miocene and led to the present day location of the yadana ridge in a back arc setting the carbonate platforms from the yadana area are thus a representative example of the interplay between global mechanisms and local paleoenvironmental parameters on carbonate platform initiation growth and demise c 2017 elsevier ltd all rights reserved

anatomy of shelf deltas at the edge of a prograding eocene shelf margin spitsbergen although shelf edge deltas are well imaged seismic features of holocene and pleistocene shelf margins documented outcrop analogues of these important sand prone reservoirs are rare the facies and stratigraphic architecture of an outcropping shelf edge delta system in the eocene battfjellet formation spitsbergen is presented here as well as the implications of this delta system for the generation of sand prone shelf margin clinoforms the shelf edge deltas of the battfjellet formation on litledalsfjellet and hogsnyta produced a 3 5 15 km shelf edge attached slope apron 70 m of sandstones proximally tapering to zero on the lower slope the slope apron consists of distributary channel and mouth bar deposits in its shelf edge reaches passing downslope to slope channels chutes that fed turbiditic lobes and spillover sheets in the transgressive phase of the slope apron estuaries developed at the shelf edge and these also produced minor lobes on the slope the short headed mountainous rivers that drained the adjacent orogenic belt and fed the narrow shelf and the shelf edge position of the discharging deltas made an appropriate setting for the generation of hyperpycnal turbidity currents on the slope of the shelf margin the abundance of organic matter and of coal fragments in the slope turbidites is consistent with this notion evidence that many of the slope turbidites were generated by sustained turbidity currents that waxed then waned includes the presence of scour surfaces and thick intervals of plane parallel laminae within turbidite beds in the slope channels and thick spillover lobes with repetitive alternations of massive and flatlaminated intervals the examined shelf edge to slope system now preserved mainly below the shelf break and dominated by sediment gravity flow deposits has a threefold stratigraphic architecture a lower progradational part in which the clinoforms have a slight downward directed trajectory a thin aggradational zone and an upper part in which clinoforms backstep up onto the shelf edge a greatly increased density of erosional channels and chutes marks the regressive to transgressive turnaround within the slope apron and this zone becomes an angular unconformity up near the shelf edge this unconformity with both subaerial and subaqueous components is interpreted as a sequence boundary and developed by vigorous sand delivery and bypass across the shelf edge during the time interval of falling relative sea level the studied shelf margin clinoforms accreted mostly during falling stage sea level below the shelf edge but the outer shelf later became estuarine as sea level became re established above the shelf edge

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

clay clast aggregates in gouges new textural evidence for seismic faulting 1 spherical aggregates named clay clast aggregates ccas have been reported from recent investigations on retrieved clay bearing fault gouges from shallow depth seismogenic faults and rotary shear experiments conducted on clay bearing gouge at seismic slip rates the formation of ccas appears to be related to the shearing of a smectite rich granular material that expands and becomes fluidized we have conducted additional high velocity rotary shear experiments and low velocity double shear experiments we demonstrate that a critical temperature depending on dynamic pressure temperature conditions is needed for the formation of ccas this temperature corresponds to the phase transition of pore water from liquid to vapor or to critical which induced gouge pore fluid expansion and therefore a thermal pressurization of the fault a detailed examination by energy dispersive x ray spectrometry edx sem element mapping sem and transmission electron microscopy tem shows strong similar characteristics of experimental and natural ccas with a concentric well organized fabric of the cortex and reveals that their development may result from the combination of electrostatic and capillary forces in a critical reactive medium during the dynamic slip weakening accordingly the occurrence of ccas in natural clay rich fault gouges constitutes new unequivocal textural evidence for shallow depth thermal pressurization and consequently for past seismic faulting

assessing controls on isolated carbonate platform development in central luconia nw borneo from a regional 3d seismic facies and geomorphology investigation

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

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

the structural and sedimentological controls on the reoccupation of quaternary incised valleys belize southern lagoon a grid of high resolution single channel seismic data from the belize southern lagoon has documented the development of several generations of stacked late pleistocene 400 ka holocene incised valley fills a feedback mechanism between tectonics reefal buildups and incised valley location is apparent in the data incised valleys are recognized as medium to high amplitude reflections that truncate reflections produced by older strata on the seismic data the holocene valley fills in the belize southern lagoon contain three seismic facies units from bottom to top 1 a basal unit characterized by moderately high amplitude chaotic reflections or progradational patterns that downlap onto the valley floor 2 a middle unit characterized by continuous horizontal near transparent reflections that drape the basal unit and onlap the valley walls and 3 an upper unit that consists predominantly of transparent to low amplitude low angle downlapping reflections the middle and upper units are separated by an erosional surface based on core evidence and seismic facies analysis the basal middle and upper seismic and sedimentary facies units are interpreted as fluvial and carbonate sands estuarine muds and marine sands and muds respectively the erosional surface separating the upper and middle units is interpreted to be a ravinement surface that marks the transition from brackish estuarine conditions to open marine conditions faulting decreases and reefal buildups increase upsection the oldest valleys mimic structural trends and flow through areas currently occupied by extensive carbonate reefs rapid high amplitude late pleistocene sea level rises may have led to wides pread reef development creating a template that subsequent incisions reoccupation valleys followed regardless of structural trends the intimate relationship among tectonics sea level change carbonate reef buildups and incised valley reoccupation serves as a model for understanding ancient tropical mixed carbonate siliciclastic systems accelerator mass spectrometer 14c dates of sediment core samples marine gastropods marine mollusks barnacles worm tubes peat and oysters indicate all the sediment cored 1 4 m in this study is holocene in age between 4740 60 and 11 230 90 14c age this radiocarbon dating consistently links the erosional surface between the upper and middle units with the intersection of the regional sea level curve nonmarine marine boundary

present day stress orientation in brunei a snapshot of prograding tectonics in a tertiary delta the baram delta province of nw borneo is unusual when compared with most other tertiary deltas as it has built up upon an active margin hence structures observed in the baram delta province are the result of both margin parallel gravity driven deltaic tectonics and approximately margin normal transpressive tectonics associated with the active margin image and dipmeter logs have been examined for breakouts and drilling induced tensile fractures ditfs in 47 wells throughout brunei breakouts and ditfs observed in 19 wells suggest that the maximum horizontal stress is oriented margin normal nw se in the proximal parts of the basin and margin parallel ne sw in the outer shelf region the margin parallel outer shelf stress field is interpreted as a local deltaic stress field caused by the shape of the clastic wedge the margin normal maximum horizontal stress in the inner shelf is interpreted to reflect basement stresses associated with the active margin however the maximum horizontal stress in the inner shelf is approximately perpendicular to the strike of miocene pliocene normal growth faults suggesting that maximum horizontal stress in the inner shelf has rotated from margin parallel deltaic to margin normal basement associated over time hence approximately the same stress rotation has occurred over time in the inner shelf as is currently observed spatially from the outer to inner shelf the spatial and temporal stress rotations in brunei are thus interpreted to be the result of deltaic and basement associated tectonic regimes that are prograding basin wards the proximity of the active margin has resulted in progressive uplift and inversion of the hinterland that has forced the delta system to prograde rapidly the zone of active deltaic growth faulting and margin parallel maximum horizontal stress has shifted basin wards prograded as the delta system has rapidly prograded across the shelf after uplift and delta progradation the old growth faults of the inner shelf ceased being active and have then been successively reactivated by a similarly prograding margin normal inversion front

seismic architecture of a miocene isolated carbonate platform and associated off platform strata central luconia province offshore malaysia abstract rather than being homogeneous and isotropic many isolated carbonate platforms in the geologic record include internal heterogeneity and complex geometric relations with off platform strata on their flanks to better understand stratal architecture of a miocene isolated platform central luconia offshore malaysia this study integrates core log and seismic data revealing stratal terminations and geometries that define several seismic stratigraphic units a thick in the basal seismic unit the initial deposits of the carbonate buildup is 4 5 km across this thick includes abrupt thinning to the west and east with onlap onto its flanks but continues outside of the survey area to the north and south above a mappable surface a less extensive 2 5 km seismic unit represents a backstepped isolated platform platform stage 1 across a pronounced normal fault on the east southeast margin of the platform occur marked isochron and seismic character changes with thicker carbonates on the downthrown western block the northern and western margins are not faulted a third seismic unit representing a smaller elongate the most marked stratigraphic theme within the isolated platform is the successive backsteps but the pattern is complicated by interactions with the basinal strata superposition and cross cutting relations document that isolated platform sourced flanking beds wings interfinger with basinal clinoforms wedges as defined by geometries on the margins and flanks of platform stages the platform evolution also was influenced markedly by syndepositional structural activity although structural trends changed from the initial buildup to later platform stages the results and comparison with other isolated platforms demonstrate the complex controls on carbonate platform growth and interactions with basinal siliciclastics

the late quaternary palaeogeography of mammal evolution in the indonesian archipelago abstract the quaternary faunal evolution for the indonesian archipelago reflects the unique relationship of each island with se asian mainland the recent sub faunas of sundaland kalimantan sumatra java and bali preserved broad connections with the se asian mainland during the latest glacial they are all balanced and show many mainland components alternatively wallacea sulawesi and the lesser sunda islands has always been geographically isolated from the mainland wallacea faunas thus remain unbalanced they lack large carnivores and endemic a significant turnover arrives throughout the region with pronounced global sea level recessions around 0 8 ma during the transition from early pleistocene ep to the middle pleistocene mp by way of comparison the palaeontological records of japan and taiwan also preserve this turnover with ep mp recessions bringing east asian mainland immigrants on java the earliest late pliocene to early pleistocene satir fauna indicates island conditions java became connected to the se asian mainland towards the end of the early pleistocene global cooling brought open woodlands on java an environment evidently preferred by homo erectus in the ci saat fauna and trinil h k fauna as ep mp sea level recessions created a wide corridor across the sunda shelf siwaliks and the se asian mainland terrestrial mammals invaded as is seen in the kedung brubus fauna the succeeding ngandong fauna maintains an open woodland character but shows some endemism homo erectus and stegodon trigonocephalus among others can be distinguished on a subspecies level the late pleistocene marks the earliest known tropical rainforest and the corresponding punung fauna is of chinese affinity with pongo hylobates and elephas maximus homo sapiens probably arrives at this point as well the youngest fossil faunas known from java are the still poorly known cipeundeuy fauna ca 30 ka and the holocene faunas from wajak and sampung while sulawesi and flores remained isolated throughout the quaternary only a limited number of terrestrial vertebrates arrived by crossing sea barriers endemic island faunas with pygmy elephantoids and giant tortoises were present during the early pleistocene ep mp sea level recessions allowed large to medium sized elephantoids to replace the dwarf species around the same time homo erectus appears on the island of flores modern faunas eventually replaced the middle pleistocene island faunas but the time frame has yet to be pinpointed sulawesi presents a unique case its current fauna holds no walanae representatives apart from the phalangers which must have come from the east the ancestors of all other large sulawesi land vertebrates fossil and extant reached the island by crossing the sunda sea as the south sulawesi fauna was stable until the middle pleistocene this area must have constituted a separate palaeo island some localized developments can be observed e g shortening of the metapodials in celebochoerus increasing hypsodonty in stegodon

gps velocity field for the tien shan and surrounding regions 1 measurements at 400 campaign style gps points and another 14 continuously recording stations in central asia define variations in their velocities both along and across the kyrgyz and neighboring parts of tien shan they show that at the longitude of kyrgyzstan the tarim basin converges with eurasia at 20 2 mm yr nearly two thirds of the total convergence rate between india and eurasia at this longitude this high rate suggests that the tien shan has grown into a major mountain range only late in the evolution of the india eurasia collision most of the convergence between tarim and eurasia within the upper crust of the tien shan presumably occurs by slip on faults on the edges of and within the belt but 1 3 mm yr of convergence is absorbed farther north at the dzungarian alatau and at a lower rate with the kazakh platform to the west the tarim basin is thrust beneath the tien shan at 4 7 mm yr with respect to eurasia the ferghana valley rotates counterclockwise at 0 7 myr 1 about an axis at the southwest end of the valley thus gps data place a bound of 4 mm yr on the rate of crustal shortening across the chatkal and neighboring ranges on the northwest margin of the ferghana valley and they limit the present day slip rate on the right lateral talas ferghana fault to less than 2 mm yr gps measurements corroborate geologic evidence indicating that the northern margin of the pamir overthrusts the alay valley and require a rate of at least 10 and possibly 15 mm yr

temporal constraints and pulsed late cenozoic deformation during the structural disruption of the active kashi foreland northwest china 1 in response to the ongoing indo asian collision structural deformation has encroached into the tian shan foreland in western china since the early miocene in order to reconstruct a detailed history of foreland deformation along the southern margin of the tian shan we have synthesized extensive mapping analysis of seismic sections magnetostratigraphy of the foreland fill and associated growth strata apatite fission track dating changes in sediment accumulation rates and geodetic surveys of deformed fluvial terraces across an area exceeding 6500 km2 that spans the kashi foreland in the northwestern tarim basin we use these data to place temporal constraints on individual structures that delineate at least 4 distinct stages of deformation stage 1 involved initial uplift of hinterland structures beginning at 20 25 ma stage 2 began at 16 3 ma when the basement involved deformation front stepped south to the kashi basin thrust that bounds the foredeep strata stage 3 occurred from 13 5 to 4 ma as the deformation front migrated south in episodic steps above thin skinned detachment and ramp flat folding finally stage 4 began after 4 ma with growth of the keketamu anticline followed by rapid southward migration of the deformation front to the atushi and then kashi detachment anticlines on the basis of the deformed tertiary strata and available seismic data calculations of the minimum magnitude of shortening yield totals ranging from 10 to 32 km since the early miocene of which 7 12 km occurred since 4 ma although average shortening rates since 16 3 ma were 0 8 1 3 mm a rates were faster from 16 3 to 13 5 ma 1 1 3 2 mm a after which they decreased to 0 5 mm a between 13 5 and 4 ma before increasing to 2 2 2 7 mm a after 4 ma similarly the rate of southward propagation of the deformation front was initially 3 7 mm a for the first 10 ma of basin development slowed to 1 5 mm a between 13 5 and 4 ma and increased to more than 10 mm a since 4 ma these changes in shortening and structural migration rates over time suggest that the loci of orogenic deformation shifted in and out of the foreland during the neogene surveyed stream terraces suggest that although most current deformation is located along the southern front of the foreland modest deformation and shortening continue in the hinterland structural style within the foreland has also changed over time from imbricate thrust faults with hanging wall folds along the northern margin to ramp flat faults and detachment folds along the southern margin where the basement rocks are previously deformed such as in the hinterland of the kashi foreland thick skinned fault ramps and related fault propagation folds dominate the structural style as syntectonic sedimentation within the foreland produced thick subhorizontal stratigraphy the structural style evolved to detachment and fault bend folding above these footwall flats within the neogene strata

the north west borneo trough abstract the north west borneo trough is bordered along its south east margin by a melange wedge that has been the subject of disagreement with insufficient discussion offshore palawan it has been interpreted as an accretionary prism that has been preserved in place when subduction ceased in the middle miocene it is unconformably overlain by undeformed upper miocene to holocene draping strata farther south west along the trough the seismically identical melange wedge has been named a major thrust sheet system which was assumed to have been thrust as a nappe north westwards over the autochthonous dangerous grounds terrane of attenuated continental crust of the south china sea passive margin the accretionary prism model is the simplest resulting in interpretation of the north west borneo trough as a fossil trench subduction was halted by the rifted and attenuated continental crust arriving at the benioff zone choking subduction and causing isostatic uplift of the western cordillera of sabah the subduction system therefore became a collision zone resulting in the term foredeep in which case the actual trench position remains obscure and somewhere towards the south east but shown in unrestrained geological cartoons enigmas remain in the palawan area of the philippines the trough position is bathymetrically obscure in places and its given position makes it impossible to derive the calamian micro continent from continental asia as required from its stratigraphy in the south west the trough terminates abruptly at the west baram line the trough contains several spectacular edifices formerly suggested to be volcanoes or mud volcanoes but herein shown to be carbonate build ups that were drowned indicating that the trough subsided too fast for build up continuation whereas post rift thermal subsidence of the dangerous grounds was slower allowing the spratly islands build ups to continue active

late miocene pliocene deceleration of dextral slip between pamir and tarim implications for pamir orogenesis abstract the timing of the late cenozoic collision between the pamir salient and the tien shan as well as changes in the relative motion between the pamir and tarim are poorly constrained the northern margin of the pamir salient indented northward by 300 km during the late cenozoic accommodated by south dipping intracontinental subduction along the main pamir thrust mpt coupled to strike slip faults on the eastern flank of the orogen and both strike slip and thrust faults on the western margin the kashgar yecheng transfer system kyts is the main dextral slip shear zone separating tarim from the eastern pamir with an estimated cumulative offset of 280 km at an average late cenozoic dextral slip rate of 11 15 mm a cowgill 2010 in order to better constrain the slip history of the kyts we collected thermochronologic samples along the eastward flowing deeply incised antecedent tashkorgan yarkand river which crosses the fault system on the eastern flank of the orogen we present 29 new biotite 40 ar 39 ar ages apatite and zircon u th sm he ages and apatite fission track aft analysis combined with published muscovite and biotite 40 ar 39 ar and aft data to create a unique thermochronologic dataset in this poorly studied and remote region we constrain the timing of four major n trending faults the latter three are strands of the kyts the westernmost the kuke fault experienced significant dip slip west side up displacement between 12 and 6 ma to the east within the kyts our new thermochronologic data and geomorphic observations suggest that the kumtag and kusilaf dextral slip faults have been inactive since at least 3 5 ma long term incision rates across the aertashi dextral slip fault the easternmost strand of the kyts are compatible with slow horizontal slip rates of 1 7 5 3 mm a over the past 3 to 5 ma in summary these data show that the slip rate of the kyts decreased substantially during the late miocene or pliocene furthermore miocene present regional kinematic reconstructions suggest that this deceleration reflects the substantial increase of northward motion of tarim rather than a significant decrease of the northward velocity of the pamir

formation and fate of sedimentary depocentres on southeast asia s sunda shelf over the past sea level cycle and biogeographic implications abstract sea level variations are the major factor controlling sedimentation as well as the biogeographic patterns at continental margins over late quaternary times fluctuations on millennial time scales produce locally complex deposits in coasts and on shelves associated with short term influence on species development this article reviews the sedimentary and biogeographic history of the tropical siliciclastic sunda shelf as an end member of continental shelves regarding extreme width an enormous sediment supply and highest biodiversity in response to rapid sea level fluctuations we describe particular depositional segments as part of a genetic succession of zones from land to the deep sea based on literature data field observations and calculation of hydro isostatic adjustment effects on changing relative sea level these segments are characterized by individual sedimentary processes and deposits and by a specific potential for material storage and re mobilization long term regressive intervals led to overall sigmoidal promoting extremely thick and wide succeeding units in contrast rapid lateral shifts of defined depocentres over long distances took place in response to short term sea level fluctuations fully isolated small scale sediment bodies formed when sea level changed at exceptionally high rates as a result of the high availability of organic rich sediments mangrove and freshwater peats formed frequently over late quaternary times the appearance of thick massive and widespread peats is mainly linked to time intervals of a sea level rise at slow rates whilst organic matter appears much more dispersely in the sediments during episodes of rapidly changing sea level the preservation potential of the regressive units is generally high due to highest initial sediment supply stabilizing soil formation during exposure and rapid subsidence preservation of depositional elements from other periods is more exceptional and either restricted to local morphological depressions or to episodes of rapid sea level change besides complex channel incision an overall lowering of the sediment surface related to erosion as deep as 20 m or more over wide areas took place mainly during sea level lowering the final export of shelf material is documented by enormous mass wasting packages on the associated continental slope from a palaeogeographic perspective the rapid formation or disappearance of special habitat zones such as mangrove fringes and extended mud flats led to species establishment or truncation in distribution in addition the opening or closure of ocean passages as narrow bridges allowing limited species crossing or as fully colonized corridors had severe impact on eco fragmentation and the expansion or contraction of species independent of such particular conditions sea level changes have been too rapid over the past climatic cycle to allow full regeneration and mature development of coast related ecosystems

seismic geomorphology and evolution of early mid miocene isolated carbonate build ups in the timor sea north west shelf of australia abstract analysis of extensive 2d and 3d seismic data reveals the presence of about sixty isolated carbonate build ups icbs of early mid miocene age spreading over a wide area of the northwestern bonaparte basin individual build ups are 100 m thick with an average diameter of 3 km integration of full volume 3d seismic attribute analysis with extensive biostratigraphic and lithological data from exploration wells allows examining the evolution of icbs and their associated morphologies at high resolution the development of icbs took place above a seismically flat surface the stratigraphic architecture of the build ups typically consists of 1 mid burdigalian initiation tf1 cn2 2 lateral expansion during the late burdigalian cn3 and 3 backstepping and drowning during the langhian tf2 cn4 this is followed by sub aerial exposure that probably corresponds to a major sea level fall during the serravallian only small patch reefs pinnacles developed afterwards during the late miocene the observed growth phases of the icbs correlate with global sea level fluctuations and major changes in global climate and oceanography the role of local tectonics in the initiation and demise of these build ups appears as minimal growth of the northwestern bonaparte basin icbs is synchronous with the establishment of tropical carbonate factories elsewhere along the australia s north west shelf that suggest an acme of reef development during the early to middle miocene

bathymetric expression of the fitzroy river palaeochannel northeast australia response of a major river to sea level change on a semi rimmed mixed siliciclastic carbonate shelf abstract palaeo river channels record the response of alluvial and estuarine depositional environments to sea level change and are also important geological indicators of former subaerial unconformities earlier studies have characterised lowstand palaeochannels on the central great barrier reef gbr shelf of northeastern australia reporting channel entrenchment shelf aggradation and topographic control of rivers by the outer shelf reef barrier we report the bathymetric expression of a palaeochannel corresponding to the last glacial lowstand path of the fitzroy river a high sediment yield river in the southern gbr during regression and lowstand the fitzroy river palaeochannel entrenched into the low gradient middle shelf and may have begun to incise the steeper outer shelf between the exposed reef platforms the wide spacing of outer shelf reefs and the continuous seabed slope may have enabled the palaeo fitzroy to maintain connection with the lowstand shoreline without becoming trapped behind shelf edge reefs the palaeochannel now forms a prominent depression across the middle and outer shelf evidently the sloping inter reefal seabed of the southern gbr coupled with tidal processes and wave exposure has limited shelf aggradation since the transgression this finding provides evidence that modern bathymetry can reflect palaeochannel location on the gbr shelf our results offer new insights into the evolution of the southern gbr shelf and show that no single existing model is able to adequately explain the behaviour of lowstand palaeochannels on rimmed siliciclastic carbonate shelves

growth architecture faulting and karstification of a middle miocene carbonate platform luconia province offshore sarawak malaysia the mega platform is a 30 50 km large and 1 2 km thick middle miocene carbonate platform located in the luconia province offshore sarawak borneo the platform originated in the late early to early middle miocene on a regional fault bounded structural high first aggraded and then backstepped during a series of third order sea level fluctuations during the middle miocene tb2 32 6 the jintan platform termination with an area of 8 12 km is one of the prominent backsteps toward the top of the mega platform three dimensional 3 d seismic indicates that growth on jintan ceased relatively early with continued carbonate aggradation in adjacent smaller terminations m1 m1 east spectacular reservoir architecture and diagenesis are revealed by the seismic several transgressive aggradational and progradational cycles are overprinted by repeated karst events dissolution features and bank margin collapse are aligned to a deep seated regional fault system which periodically became reactivated during carbonate growth a large triangular shaped graben formed during one of the faulting periods but subsequently healed by a prograding reef margin sequences two alternative scenarios are presented to explain the ultimate demise of the platform the first proposes drowning resulting from a combination of subsidence and eustatic sea level rise the second evokes a much later drowning which was preceded by a long period of exposure resulting from a second order sea level fall and an initial decrease in subsidence caused by the onset of tectonism in borneo during the late miocene in any case following a hiatus of about 5 m y the platform was finally buried by deep marine siliciclastics that prograded into the basin from the large delta systems of northwest borneo recognition of growth architecture faulting and karstification is a key to exploiting the hydrocarbon reservoirs of the mega platform a 30 m thick low porosity and permeability layer shields the gas trapped in jintan from the underlying aquifer penetrated by only one well the extent of the layer and areas of breaching caused by faulting and karstification are identified on seismic interpretation of the seismic is critical to assessing whether and how the underlying aquifer is felt during reservoir depletion and whether there is pressure communication between adjacent reservoirs connected via the aquifer cores and logs from three wells provide ground truthing of reservoir architecture karst features and faulting derived from the interpretation of reflection and inversion seismic the interpretation is then imported into static and dynamic 3 d models to constrain reservoir properties predict dynamic behavior and guide optimum field development

siliciclastic influx and burial of the cenozoic carbonate system in the gulf of papua abstract an extensive carbonate system in the gulf of papua gop developed in the late oligocene middle miocene was buried by huge influx of siliciclastics originated from papua new guinea major episodes of siliciclastic influx in the carbonate system are related to tectonic activity in the fold and thrust belt during the oligocene peninsular orogeny late miocene central range orogeny and late pliocene renewed uplift and exhumation of peninsular region siliciclastics did not influence the carbonate deposition during the late oligocene middle miocene since they were accumulated in the aure trough proximal foreland basin protecting the carbonate system the most significant burial of the carbonate system started during the late miocene early pliocene in the result of the central range orogeny however the largest influx was related to the renewed uplift of the papuan peninsula during the early late pliocene the shelf edge prograded 150 km and formed more than 80 of the modern shelf this high siliciclastic influx was also enhanced by the mid pliocene global warmth period and intensified east asian monsoons at 3 6 2 9 ma although many publications exist on carbonate siliciclastic mixing in different depositional environments this study helps understand the carbonate siliciclastic interactions in space and time especially at basinal scale and during different intervals of the carbonate system burial by siliciclastic sediments

miocene pliocene exhumation along the west salton detachment fault southern california from u th he thermochronometry of apatite and zircon 1 the salton trough is the northernmost segment of the active gulf of california oblique rift system the main rift related structure in the western salton trough is the low angle west salton detachment fault wsdf footwall and hanging wall apatite and zircon u th he ages record a significant contrast in thermal history across the wsdf confirming pliocene normal slip along the fault apatite u th he ages record rapid exhumational cooling from 5 to 2 ma consistent with the timing of accelerated tectonic subsidence recorded in wsdf hanging wall sedimentary strata and consistent with the initiation age of dextral plate boundary slip on the southern san andreas fault in the salton trough our results indicate that the wsdf caused at least 2 3 4 km of exhumation and 8 10 km of approximately e directed horizontal extension since 5 ma slip rate of the wsdf at yaqui ridge was likely in the range of 2 3 5 km ma from 7 to 2 ma the wsdf may have been active well before 5 ma middle miocene apatite u th he ages from samples at high elevations have steep age elevation gradients and suggest that exhumation may have initiated by 12 ma about when subduction ceased along a large segment of the baja california margin and consistent with the age of onset of extension in northeastern baja california

present day stress orientations and tectonic provinces of the nw borneo collisional margin received 23 september 2009 revised 17 may 2010 accepted 9 june 2010 published 16 october 2010 1 borehole failure observed on image and dipmeter logs from 55 petroleum wells across the nw borneo collisional margin were used to determine maximum horizontal stress sh orientations combined with seismic and outcrop data they define seven tectonic provinces the baram delta deepwater fold thrust belt exhibits three tectonic provinces its inner shelf inverted province sh is nw se margin normal its outer shelf extension province sh is ne sw margin parallel and its slope to basin floor compression province sh is nw se margin normal in the inverted province sh reflects inversion of deltaic normal faults the sh orientations in the extension and compression provinces reflect deltaic gravitational tectonics the shale and minibasin provinces have been recognized in offshore sabah in the shale province sh is n010 e which aligns around the boundary of a massif of mobile shale currently no data are available to determine sh in the minibasin province in the balingian province sh is ese wnw reflecting ese absolute sunda plate motions due to the absence of a thick detachment seen elsewhere in nw borneo the central luconia province demonstrates poorly constrained and variable sh orientations these seven provinces result from the heterogeneous structural and stratigraphic development of the nw borneo margin and formed due to complex collisional tectonics and the varied distribution and thicknesses of stratigraphic packages

late cenozoic tectonic development of the intramontane alai valley pamir tien shan region central asia an example of intracontinental deformation due to the indo eurasia collision 1 the pamir indentor of the northwestern himalayan syntaxis is a first order feature demonstrating partly the northward extent of deformation due to the cenozoic indo eurasia collision the alai valley of kyrgyzstan at the northern end of the indentor is a strategically positioned e w trending intramontane basin that constrains the timing and extent of crustal deformation in this area of the collision zone to quantify the convergence accommodated across the alai valley during the late cenozoic we collected structural and stratigraphic field data reviewed existing soviet literature and analyzed migrated seismic reflection profiles to construct and restore two regional sections crosscutting the basin our study suggests that the development progressive closure and conversion of this formerly marine basin into a terrestrial intramontane basin result from two main deformation events 1 distributed north south contraction took place during the late oligocene early miocene accommodated one third to half of the total shortening and was followed by the formation of a regional erosion surface and 2 n s shortening resumed in the mid miocene and continues today during this second episode the thrust front migrated southward localized along the trans alai ranges and failed to reactivate earlier neogene structures horizontal shortening of about 35 across the alai valley implies relatively low strain rates and displacement rates of about 4 18 4 69 10 16 s 1 and 0 66 0 78 mm yr 1 respectively for the last 25 myr our study confirms other regional observations indicating that contractional deformation occurred far in the interior of the asian continent as early as the late oligocene

stratigraphic simulation of sedimentary basins concepts and calibration a two dimensional stratigraphic simulation program based on semiempirical algorithms has been successfully applied to clastic carbonate and mixed clastic carbonate depositional regimes the program may be used to predict reservoir distribution to constrain interpretations of well and seismic data to test exploration scenarios in frontier basins and to evaluate the fundamental controls on basin stratigraphy applications to seismic and well log data sets from main pass u s gulf coast offshore sarawak malaysia and the baltimore canyon u s east coast demonstrate that the program simulates stratigraphy on a basin wide scale as well as on the scale of individual prospects the main pass section is an offlapping sequence of neogene clastics the model simulates 17 m y of geologic history at a 200 000 yr resolution and reproduces gross basin geometry major sequence boundaries depth and location of nearshore marine sands intervals of sediment bypass into deep water shelf margin positions and paleobathymetry three neogene carbonate buildups of central luconia offshore sarawak malaysia were simulated using a sea level history optimized to reproduce the carbonate growth anatomy the model reproduced observed seismic reflection geometries and transgressive aggradational progradational retrogradational and subaerial exposure phases the program has also simulated jurassic pleistocene basin and stratigraphic sequence geometries and mixed clastic carbonate facies distribution along a 300 km regional dip line of the baltimore canyon trough modeled features of interest include a progradational middle jurassic carbonate margin punctuated by clastic deposition during sea level lowstands and a late jurassic early cretaceous aggradational carbonate margin culminating in the development and subsequent drowning of isolated carbonate buildups simulated bathymetries facies relations and subaerial exposure surfaces for the early cretaceous aggradation margin are consistent with detailed petrographic paleontologic and seismic stratigraphic interpretations

alpine orogenic evolution from subduction to collisional thermal overprint the 40ar 39ar age constraints from the valaisan ocean central alps 1 the investigated hp lt metasedimentary units of the valaisan and adjacent european domains occupy a key position in the alpine belt for understanding the transition from early subduction related hp lt metamorphism to collision related barrovian overprint and the evolution of mountain belts in general the timing of high pressure metamorphism subsequent retrogression and following barrow type overprint was studied by 40ar 39ar dating of biotite and several white mica generations that are well characterized in terms of mineral chemistry texture and associated mineral assemblages four distinct age populations of white mica record peak pressure conditions 42 40 ma and several stages of subsequent retrograde metamorphic evolution 36 25 ma biotite isotopic analyses yield consistent apparent ages that cluster around 18 16 ma for the barrow type thermal overprint the recorded isotopic data reveal a significant time gap in the order of some 20 ma between subduction related hp lt metamorphism and collision related barrovian overprint supporting the notion of a polymetamorphic evolution associated with a bimodal p t path

the vegetation and climate at the last glaciation on the emerged continental shelf of the south china sea studies on the dispersal mechanism and source areas of pollen from hemipelagic sediments recovered from the continental slopes of the south china sea scs reveal that vegetation existed on the exposed shelves at the last glacial maximum lgm and the latter part of the marine isotope stage 3 at the low sea level stand artemisiadominated grassland covered the northern continental shelf and tropical lowland rainforest and mangroves grew on the southern shelf sunda land consequently the climate in the northern scs must have been much colder and drier during the last glacial period compared to the present sunda land experienced only a marginally lower temperature but was not drier than today the enhanced contrast between the northern and southern parts of the scs in vegetation and climate during the lgm may be ascribed at least partly to the strengthening of winter monsoon during the last glacial period 2000 elsevier science b v all rights reserved

geometric attributes for seismic stratigraphic interpretation the application of sequence stratigraphy to seismic interpretation has proven to be fundamentally important in basin analysis it provides a framework for understanding strat igraphic evolution and is a key element in predicting the spatial distribution of reservoir seal and source rocks traditional methods of seismic se quence stratigraphy make use of observations such as stacking patterns seismic character of facies and their distribution to develop subsurface models we present a set of seismically derived geometric attributes that enhance and characterize these observations allowing a sequence stratigraphic framework to be developed in the earliest stages of interpretation