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

growth of a thrust fault array in space and time an example from the deep water niger delta abstract the temporal and spatial evolution of thrust fault arrays is currently poorly understood and marine fold and thrust belts at the toe of passive margin gravitational systems imaged by commercial 3d seismic reflection datasets afford a unique opportunity to investigate this problem in three dimensions using an extensive 3d seismic data set and age data the total cumulative strain shortening and interval strain rates have been calculated for 11 thrust related folds mapped in the toe thrust region of the southern lobe of the niger delta for the first time the sequence of thrust nucleation propagation and linkage through time at a scale of 10 s km both along and across strike is documented short thrust segments had nucleated throughout the entire study area by 15 ma they then grew largely by lateral growth and linkage increasing the fault trace length and generating asymmetric strain distance plots for the first 50 of their history thereafter growth continued by shortening with minimal along strike increase in fault length changes in shortening distance data between adjacent structures across strike suggest that the change in growth mode occurred once the thrusts had linked in 3d through the common underlying detachment over the entire thrust array the strain rate varies through time starting slowly

characteristics of repeated detached miocene pliocene tectonic inversion events in a large delta province on an active margin brunei darussalam borneo abstract the baram delta province evolved during the middle miocene to present day from a foreland basin to a shelf margin episodic folding events affected the region causing uplift of the hinterland delta progradation and inversion of gravity related faults existing models place the n s and ne sw trending folds in a strike slip transpressional setting new geological mapping and re interpretation of existing data suggest the region is better understood as the development of a west verging thrust belt in a middle miocene foreland basin filled by sandstones and shales of the belait and setap formations with key major folds jerudong and belait anticlines belait syncline forming during the middle miocene as fault bend and fault propagation folds the deformation style is complicated by the predominantly shaley middle miocene pliocene setap formation becoming thicker and more overpressured from south to north onshore where the setap formation is thin or absent the belait formation is attached to the underlying lower miocene and older sequences offshore and in a narrow onshore strip the overpressured setap formation causes deformation in the beltait formation to be detached from the underlying cretaceous tertiary accretionary prism basement the detached style exhibits considerable structural complexity including lift off folds growth faults shale diapirs and pipes onshore thrust and inversion features are dominantly n s trending and began activity in the middle miocene deformation is probably associated with an e w maximum horizontal stress direction in the late miocene around 7 5 ma watters et al 1999 ne sw striking inversion folds developed located mostly over early counter regional faults and associated reactive diapirs folds verge towards the nw when underlain by counter regional faults and towards the s or se when underlain by regional faults folds and diapirs along n s trends were also reactivated continuation of this deformation into the pliocene is largely confined to the offshore area onshore the n s structures no detachment were not reactivated during the pliocene

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

differential deformation of gravity driven deep water fold and thrust belts along the passive continental margin of east africa and their impact on petroleum migration and accumulation abstract passive margin deep water fold and thrus belts dwftbs have been the focus of a number of studies in recent decades because many oil and gas fields have been discovered in traps associated with them nevertheless the impact of dwftbs on petroleum plays remains unclear in this study we developed models for petroleum migration and accumulation in the offshore rovuma basin and lamu basin dwftbs located along the passive continental margin of east africa based on an integrated analysis of seismic geochemical and geological data using available high quality seismic data in the depth domain we were able to quantify the evolution of thrust anticline growth by applying the area depth strain ads method our results indicate that the offshore lamu basin dwftb was active from the late cretaceous period to the early miocene period while the offshore rovuma basin dwftb has been active from the oligocene period geochemical parameters and basin modeling show that widespread lower jurassic mudstone is the dominant source of petroleum resources with peaks of oil and gas generation in the cretaceous and cenozoic periods respectively based on this we suggest that the traps within the offshore lamu basin dwftb contain oil generated from lower jurassic sources that migrated along faults and accumulated during the late cretaceous period and gas generated from the same sources during the cenozoic period conversely there is an insufficient amount of oil in the offshore rovuma basin dwftb owing to the absence of oil migration pathways or traps as a result of the dwftb s more recent formation from the oligocene period

effects of mass waste events on thrust wedges analogue experiments and application to the makran accretionary wedge 1 olistostromes cover large portions of active thrust wedges like makran gulf of cadiz and offshore borneo olistostrome emplacement by submarine mass flow represents an instantaneous and massive mass redistribution that may influence thrust wedge mechanics different scenarios are experimentally tested they show that the postolistostrome wedge development depends on the thickness and extent of the added load these results are discussed after the example of the iranian makran wedge situated between the arabian and eurasian plates mass redistribution caused by a late miocene mass flow may explain a change in deformation style from intense folding and thrusting to gentle folding and eventually a jump of thrust imbrication toward the frontal offshore part of this active accretionary wedge

relationship between structural style overpressures and modern stress baram delta province northwest borneo christopher k morley mark tingay and richard hillis australian school of petroleum university of adelaide adelaide australia rosalind king

thrust tectonics along the north western continental margin of sabah borneo widely accepted plate tectonic models suggest that an inactive subduction zone lies along the north west continental margin of sabah in contrast interpretation of reflection seismic data acquired by bgr shows an autochthonous continental terrane comprising an oligocene to early miocene carbonate platform being progressively overthrust by an allochthonous rock complex progressive compression resulted in the development of four structural zones imbricated thrust sheets zone iii two thrust sheet systems one on top of the other zone iv a complex zone with multiphase deformation zone v and piercement ridges zone vi

mechanical restoration of gravity instabilities in the brunei margin n w borneo in offshore brunei the baram delta displays pliocene to recent gravitational deformations on top of the overpressured setap shales we use the limit analysis implemented in slamtec to constrain their kinematics and propose first order values of compatible pore pressures using the critical coulomb wedge theory we confirm that extreme overpressure are needed to account for the gravitational deformations currently observed in the delta slamtec simulations quantify the role of the migration of the deltaic system on the deformations and suggest that this overpressure has existed since the initiation of the gravity driven system an inverse analysis is performed to identify the fluid overpressure and sedimentation pattern that best reproduces the forward structural model this inverse approach validates the proposed kinematics since we can reproduce quantities describing the structural style with overpressure coherent with the present day observations it points out the existence of key events explaining the structural interpretations which leads to propose new kinematic models enriched with compatible pore pressure and sedimentation rates this mechanical study highlights how mechanical modelling helps design a cross section with an appropriate kinematics based on mechanical solutions and discuss on the basis of objective mechanical criteria the ranges of pore pressure consistent with a prescribed structural evolution

crustal evolution of the hercynian belt of western europe evidence from lower crustal granulitic xenoliths french massif central abstract granulite facies lower crustal xenoliths scavenged by the tertiary basaltic pipes of bournac and roche pointue massif central france have been analysed for major and trace elements and radiogenic sr nd isotope ratios they display wide variations in major elements rare earth elements and isotopes 87 sr 86 sr 0 7041 0 7216 nd 11 9 to 1 5 which tend to correlate with the three different rock types encountered basic and acidic meta igneous and metasediments the basic liquids are of calc alkaline affinity and cumulates are abundant there is a gap in silica content between the basic and acid meta igneous xenoliths the isotopic compositions suggest mixing of old pre existing continental crust represented by the metasediments and mantle derived basic melts which represent juvenile addition to the crust during the hercynian orogeny the basic meta igneous rocks have been contaminated during their emplacement into the crust whereas the surrounding metasediments have suffered partial fusion and contamination by the same liquid producing the hercynian granitoids which have nd and sr initial ratios identical to those of the lower crustal xenoliths the residue from melting may be represented by the acid meta igneous rocks some of which have positive eu anomalies these results indicate that an important basaltic underplating event occurred during the evolution of hercynian orogenic belt although the exact timing of the underplating requires further constraint

formation of accretionary prisms influenced by sediment subduction and supplied by sediments from adjacent continents mechanical models are used to investigate the formation of accretionary prisms and related basins fed by sediments supplied from adjacent continents and subjected to sediment subduction results show that prisms forming under the infl uence of a hinterland sediment fl ux exhibit markedly different characteristics compared to classic critical wedges with identical mechanical properties forming by frontal accretion of a preexisting layer the main differences are reduced surface slopes increased spacing between thrusts widespread wedgetop basins and the presence of buried structures these differences are explained by the ability of continuous sedimentation to reduce differential stresses in the wedge leading to stable supercritical geometries thus in regions of active sedimentation wedge geometries cannot be explained solely in terms of relative strengths of the wedge and its decollement as is the case for critical wedges results also show that variations in the relative rates of sediment supply e g linked to climate changes and sediment subduction may lead to pulsed growth and decline of wedges though time as has been evidenced for some natural wedges thus rather than viewing compressive plate margins as accretionary versus erosive the dominant mode may repeatedly switch back and forth through time in response to variations in relative rates of sediment supply and sediment subduction

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

deep water niger delta fold and thrust belt modeled as a critical taper wedge the influence of elevated basal fluid pressure on structural styles we use critical taper wedge mechanics theory to show that the niger delta toe thrust system deforms above a very weak basal detachment induced by high pore fluid pressure the niger delta exhibits similar rock properties but an anomalously low taper sum of the bathymetric slope and dip of the basal detachment compared with most orogenic fold belts this low taper implies that the niger delta has a very weak basal detachment which we interpret to reflect elevated pore fluid pressure 0 90 within the akata formation a prodelta marine shale that contains the basal detachment horizon the weak basal detachment zone has a significant influence on the structural styles in the deep water niger delta fold belts the overpressured and thereby weak akata shales ductilely deform within the cores of anticlines and in the hanging walls of toe thrust structures leading to the development of shear fault bend folds and detachment anticlines that form the main structural trap types in the deep water fold belts moreover the low taper shape leads to the widespread development of backthrust zones as well as the presence of large relatively undeformed regions that separate the deep water fold and thrust belts this study expands the use of critical taper wedge mechanics concepts to passive margin settings while documenting the influence of elevated basal fluid pressures on the structure and tectonics of the deep water niger delta

carbonate platforms in wedge top basins an example from the gunung mulu national park northern sarawak malaysia abstract the melinau carbonate platform initiated during the mid eocene on a rotating slice of the rajang accretionary prism the differential sedimentary loading enhanced a rotation of the mobile substratum and created an elongated asymmetrical wedge top basin the extensional southern margin of the basin consists of a 2100 2200 m thick section of eocene to oligocene carbonates these thin laterally towards the northern margin of the basin where a carbonate factory was active on a postulated underlying thrust backstepping and dismemberment of the carbonate system started during the latest oligocene and deep marine sedimentation became prevalent over the entire region during the early miocene

present day stress and neotectonic provinces of the baram delta and deep water fold thrust belt abstract we present the first present day stress orientation measurements across a delta and deep water delta toe fold thrust belt stress and neotectonic data for nw borneo reveal three discrete neotectonic provinces an inverted inner shelf province where present day maximum horizontal stress h is oriented margin normal an extensional delta top province h is margin parallel and a compressional delta toe province h is margin normal we interpret the delta top and delta toe data to reflect that compression in the fold thrust belt is coupled to delta top extension and that the inverted inner shelf province reflects the location of this system on an active margin

noncohesive critical coulomb wedges an exact solution active fold and thrust belts or submarine accretionary complexes can be modeled as critically tapered wedges of material on the verge of coulomb failure everywhere overlying a basal decollement where frictional sliding is occurring ignoring cohesion the four strength parameters needed to describe a critical coulomb wedge are its internal and basal coefficients of friction and b and its internal and basal hubbert rubey fluid pressure ratios and b an exact relation between surface slope and basal dip of a noncohesive critical wedge with uniform properties is derived the state of stress within such a wedge has the same orientation everywhere and is constant if is and vice versa a coefficient of internal friction 1 1 is consistent with the known surface slope basal dip and pore fluid pressures in the active fold and thrust belt of western taiwan assuming that byerlee s law b 0 85 is valid on the base the wide variety of tectonic styles observed to occur along convergent margins including subduction erosion active accretion subduction without accretion and even extension and normal faulting may be controlled by relatively small spatial or temporal variations in either b or b

hydrocarbon generation a possible cause of elevated pore pressures in the osen roa thrust sheet norway abstract the osen roa thrust is very large 275 km wide in the thrust transport direction thin 1 4 km thick and internally shortened by 270 km over much of its extent the thrust sheet has moved over autochthonous or para autochthonous alum shales cambrian such a large and thin thrust sheet is difficult to move as a coherent unit high pore fluid pressures are commonly invoked to help explain such problems the alum shales are very rich in organic carbon 5 20 weight percent they are capable of generating large volumes of hydrocarbons which could have periodically caused elevated pore fluid pressures the first event that was likely to have buried the alum shales to oil generating depths was overthrusting during the caledonian orogeny consequently overpressuring in the alum shales due to hydrocarbon generation may help to explain the size of the osen roa thrust sheet

interaction between critical wedge geometry and sediment supply in a deep water fold belt the late miocene holocene deep water fold and thrust belt of offshore northwestern borneo displays one of the most acute angles recorded for a submarine critical taper wedge the very low surface 1 2 5 and basal detachment 2 5 dips require basal pore fluid pressures near lithostatic pressure for the wedge to propagate at such angles in the deep water environment sedimentary processes act against the wedge attaining critical taper in places of lower sedimentation rates the fold and thrust belt extends to the base of the slope and dips 1 5 2 5 in areas of the highest sedimentation rates baram delta the slope has a lower angle 1 and the slope continues beyond the limit of the fold and thrust belt slope morphology changes along the margin from concave up relatively low sedimentation rate low shortening rate to convex up relatively high sedimentation rate low shortening rate to stepped relatively low sedimentation rate high shortening rate

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

variation in geometries and displacement along thrust faults a quantitative analysis from sandbox models the present work combines theoretical analysis laboratory experiments and field examples together with quantitative analysis to understand displacement variation along fault surfaces with varying dip angle two sandbox experiments are described to quantitatively analyze the interactions between shortening and sedimentation during late stages of deformation the two models consisted of sand layers with single and two microbeads layer s within the sandpack sieved over horizontal frictional detachment the models demonstrate that the overlying sediment load bears a major role on kinematic of developing structures fault displacement varied along imbricate thrusts due to variation in fault dip angle in the listric geometry maximum displacement occurred in the up dip direction up section or near fault tip along the faults where fault dip angles were shallower and favourable for thrust displacement in contrast the displacement was limited in the down dip direction down section or near basal detachment where fault dip angles were steeper the variation in fault displacement with fault dip along the fault surfaces made it possible to establish an inverse relationship between the fault dip and related displacement values i e lower is the dip angle greater the displacement and vice versa despite the inherent limitations and assumptions of laboratory experiments application of results to natural examples sheds new light on the mechanics and geometry of thrust faults from the deep to shallow structural levels as well as structural patterns that could appear as anomalous at a first sight

distinguishing thrust sequences in gravity driven fold and thrust belts abstract piggyback or foreland propagating thrust sequences where younger thrusts develop in the footwalls of existing thrusts are generally assumed to be the typical order of thrust development in most orogenic settings however overstep or break back sequences where later thrusts develop above and in the hangingwalls of earlier thrusts may potentially form during cessation of movement in gravity driven mass transport deposits mtds in this study we provide a detailed outcrop based analysis of such an overstep thrust sequence developed in an mtd in the southern dead sea basin evidence that may be used to discriminate overstep thrusting from piggyback thrust sequences within the gravity driven fold and thrust belt includes upright folds and forethrusts that are cut by younger overlying thrusts backthrusts form ideal markers that are also clearly offset and cut by overlying younger forethrusts portions of the basal detachment to the thrust system are folded and locally imbricated in footwall synclines below forethrust ramps and these geometries also support an overstep sequence however new short cut basal detachments develop below these synclines indicating that movement continued on the basal detachment rather than it being abandoned as in classic overstep sequences further evidence for synchronous thrusting where movement on more than one thrust occurs at the same time is provided by displacement patterns on sequences of thrust ramp imbricates that systematically increases downslope towards the toe of the mtd older thrusts that initiate downslope in the broadly overstep sequence continue to move and therefore accrue greater displacements during synchronous thrusting our study provides a template to help distinguish different thrust sequences in both orogenic settings and gravity driven surficial systems with displacement patterns potentially being imaged in seismic sections across offshore mtds

comparison of fold thrust belts driven by plate convergence and gravitational failure abstract deepwater fold thrust belts ftbs are predominantly formed by the deformation of sedimentary sequences as a result of subduction of oceanic plates at active margins gravitational failure at passive margins or a combination of these two driving mechanisms at both types of margin a key question is is the ftb driven by gravitational failure basically the same as the ftb driven by plate convergence or are there fundamental differences to address this we reviewed ftb examples from different tectonic settings end members and hybrid systems in terms of geometry structure deformation shortening rate and tectonic process the energy source in gravity driven systems lies within the sedimentary material itself that is being deformed by updip extension and downdip contraction whereas in the plate convergence driven systems it lies outside the local sediment pile and within the broader undeformed crust and lithosphere the energy in gravity driven systems is resupplied by sediment input from large river deltas and therefore deformation tends to be episodic linked to episodes of major sediment input whereas in a system driven by plate motions the energy is resupplied by movement of a boundary upon which force is acting and tends to be stable and less episodic therefore the sedimentation plays an important role in the gravity driven deformation but a less important role in the plate convergence driven deformation in gravity driven systems it promotes upward propagation of normal faulting at upslope by increasing maximum principal stress but hinders upward propagation of thrusting i e mostly buried structures by increasing minimum principal stress at downslope while in plate convergence systems thrusts and folds tend to deform seafloor as a result of large compression with less effect from sedimentation despite the varying basal strength the observed thrust faults in both systems are mostly basinward verging in slight contrast to the theoretical model predication with homogeneous material implicating the control of likely variability of stratigraphic strength on thrust vergence the shortening rate across plate convergence driven systems is high several tens mm yr and continuous on a long timescale whereas across the gravity driven fold thrust belts it is generally slow several mm yr and more variable or even catastrophic through time despite overall seaward younging of thrusting fault activity differs slightly among different systems focused activity at the frontal structures of ftbs is more common at the plate convergence system while activity focused in the rear to middle of ftbs is more common in the gravity driven system plate convergence driven system is primarily limited by rate of plate motion i e the rate at which the plate is fed into the ftb whereas in gravity driven system the movement is limited resisted by the strength of sediments and detachment

review of major shale dominated detachment and thrust characteristics in the diagenetic zone part ii rock mechanics and microscopic scale abstract characterising large shale thrust zone behaviour down to the diagenetic metamorphic boundary is both simple and complex the task in critical taper analogue and numerical models has been successfully approximated using simple material parameters yet the weakness of shales thrusts on a case by case basis show great variability in key factors across a wide range of scales understanding of these variables and their relationships to different tectonic settings is patchy due to the different objectives of workers studying the various systems e g seismic hazards hydrocarbon exploration structural geology research and the types of available geological and geophysical data early research recognized that megathrusts feature creeping and locked patches which may be described using the rate and state formalism in addition to temperature differential stress and strain rate key controlling factors on thrust weakness are mineralogy amount of weak phase present structure localization mechanisms grain size and shapes porosity permeability and pore fluid pressure the smectite illite transition has been a focus of seismic hazard research due to its coincidence with the top of the seismogenic zone while there may be a relationship other factors such as pore fluid pressure variations or structure localization are also important the critical taper model is a simple means of determining whether basic rock mechanics data e g frictional strength pore fluid pressure is appropriate for natural wedges for example aseismic basal detachments of gravity driven systems smaller critical taper wedges appear to retain higher pore fluid pressures along the basal detachment than seismogenic basal detachments higher critical taper wedges in many continental and deltaic fold and thrust belts high organic carbon content is a very important factor in shale weakness due to 1 the overall more ductile and well cleaved nature of the shale when organic content is high 2 the presence of high overpressures due to maturation of organic material and 3 metamorphism of carbon to low friction graphite this multifaceted influence of organic carbon content is just one example of the diversity of potential influences on shale thrust zone weakness which enable shales to be weak despite considerable lateral deposition related and vertical burial related changes in composition some key variations between different types of fold and thrust belt gravity driven accretionary prism andean himalayan type lie in systematic variations in clay mineralogy magnitudes and origins of overpressures seismic versus aseismic detachments and different structural localization mechanisms further research is required to explore the viability of such distinctions and their impact on structural styles

reprint of comparison of modern fluid distribution pressure and flow in sediments associated with anticlines growing in deepwater brunei and continental environments iran abstract differences in fluids origin creation of overpressure and migration are compared for end member neogene fold and thrust environments the deepwater region offshore brunei shale detachment and the onshore arid central basin of iran salt detachment variations in overpressure mechanism arise from a the availability of water trapped in pore space during early burial deepwater marine environment vs arid continental environment and b the depth temperature at which mechanical compaction becomes a secondary effect and chemical processes start to dominate overpressure development chemical reactions associated with smectite rich mud rocks in iran occur shallow 1900 m smectite to illite transformation causing load transfer related moderate overpressures whereas mechanical compaction and inflationary overpressures dominate smectite poor mud rocks offshore brunei the basal detachment in deepwater brunei generally lies below temperatures of about 150 c where chemical processes and metagenesis are inferred to drive overpressure development overall the deepwater brunei system is very water rich and multiple opportunities for overpressure generation and fluid leakage have occurred throughout the growth of the anticlines the result is a wide variety of fluid migration pathways and structures from deep to shallow levels particularly mud dykes sills laccoliths volcanoes and pipes fluid escape pipes crestal normal faults thrust faults and widespread inflationary type overpressure in the central basin the near surface environment is water limited mechanical and chemical compaction led to moderate overpressure development above the upper red formation evaporites only below thick early miocene evaporites have near lithostatic overpressures developed in carbonates and marls affected by a wide range of overpressure mechanisms fluid leakage episodes across the evaporites have either been very few or absent in most areas locations where leakage can episodically occur e g detaching thrusts deep normal faults salt welds are sparse however in both iran and brunei crestal normal faults play an important role in the transmission of fluids in the upper regions of folds

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

fluid generation and distribution in the highest sediment input accretionary margin the makran fluids in subduction zones can influence seismogenic behaviour and prism morphology the eastern makran subduction zone offshore pakistan has a very thick incoming sediment section of up to 7 5 km providing a large potential fluid source to the accretionary prism a hydrate related bottom simulating reflector bsr zones of high amplitude reflectivity seafloor seep sites and reflective thrust faults are present across the accretionary prism indicating the presence of fluids and suggesting active fluid migration high amplitude free gas zones and seep sites are primarily associated with anticlinal hinge traps and fluids here appear to be sourced from shallow biogenic sources and migrate to the seafloor along minor normal faults there are no observed seep sites associated with the surface expression of the wedge thrust faults potentially due to burial of the surface trace by failure of the steep thrust ridge slopes thrust fault reflectivity is restricted to the upper 3 km of sediment and the deeper decollement is non reflective we interpret that fluids and overpressure are not common in the deeper stratigraphic section thermal modelling of sediments at the deformation front suggests that the deeper sediment section is relatively dewatered and not currently contributing to fluid expulsion in the makran accretionary prism

provenance of the cretaceous eocene rajang group submarine fan sarawak malaysia from light and heavy mineral assemblages and u pb zircon geochronology abstract the rajang group sediments in central borneo form a very thick deep water sequence which was deposited in one of the world s largest ancient submarine fans in sarawak the lupar and belaga formations form the rajang group characterised by turbidites and large debris flows deposited in an interval of at least 30 ma between the late cretaceous maastrichtian and late middle eocene borneo is one of the few places in se asia where sediments of this age are preserved heavy mineral assemblages and detrital zircon u pb dating permit the rajang group to be divided into three units the schwaner mountains area in sw borneo and west borneo and the malay tin belt were the main source regions and the contribution from these source areas varied with time unit 1 of late cretaceous to early eocene age is characterised by zircon tourmaline dominated heavy mineral assemblages derived from both source areas unit 2 of early to middle eocene age has zircon dominated heavy mineral assemblages abundant cretaceous zircons and few precambrian zircons derived primarily from the schwaner mountains unit 3 of middle eocene age has zircon tourmaline dominated heavy mineral assemblages derived from both sources and reworked sedimentary rocks there was limited contemporaneous magmatism during deposition of the rajang group inconsistent with a subduction arc setting we suggest the rajang group was deposited north of the shelf edge formed by the lupar line which was a significant strike slip fault

evaluating the role of syn thrusting sedimentation and interaction with frictional detachment in the structural evolution of the sw tarim basin nw china insights from analogue modeling abstract the structural evolution of the fold and thrust belt in sw tarim basin nw china is poorly understood as the region is covered by thick pliocene quaternary conglomerate which significantly decreases the quality of seismic images we here improve the understanding of the thrust belt evolution with an investigation using analogue modeling on the deformation mechanism based on a case of real geological section in which we focus on the impact of syn thrusting sedimentation on the structural style and evolution the results show that syn thrusting sedimentation significantly increases the distance and rate of foreland propagation resulting in a much broader fold and thrust belt the modeling results also suggest that the fold and thrust belt exhibits different structural patterns under different syn thrusting sedimentary conditions in the case of thick syn thrusting sediments a frictional detachment layer of mudstone acts as decollement and the fold and thrust belt develops a duplex pattern in the hinterland in the case of thin syn thrusting deposits the belt develops a pop up structure with backthrusts in the foreland region which cut through the detachment layer the striking similarity between the model with thick syn thrusting sediments and the real geologic section implies that the overlying thick pliocene quaternary sediments play a major role in shaping the structure pattern in the fold and thrust belt of sw tarim basin

review of major shale dominated detachment and thrust characteristics in the diagenetic zone part i meso and macro scopic scale there is considerable variability in the thickness structure and macroscopic deformation style within shale prone major thrust zones which also impacts the structural style in the overlying and sometimes the underlying section the properties and percentages of clay minerals and percentages of organic material quartz and calcite affect fault zone weakness and behaviour the distribution of competent units within a shale prone zone can also significantly affect fault zone architecture even over short strike distance of 10s to 100s of metres other influences include high pore fluid pressures and associated veins deformation of the fault zone may disrupt the original principal displacement zones and force them to relocate including switching lithologies calcite veins can become concentrated locally in the fault zone and become a focus of fault zone weakness we still need many more descriptions of shale prone fault zones to understand the potential variations in thrust sheet structural style caused by differences in shale detachment characteristics the variations in structural style in the hanging walls of shale detachments are broad and range between the sledge runner style in many appalachian examples and the extensive closely spaced imbricate style of the osen roa detachment southern norway such contrasts are related to several factors including thrust sheet mechanical stratigraphy thickness of the overburden lateral continuity of the detachment detachment mechanical properties composition pore fluid pressures presence absence of higher level detachments and strain rate in many structural locations and at many scales shale prone sequences will pile up to produce over thickened masses cleavage duplexes s c fabrics duplexes imbricates pseudo duplexes and vein formation can all contribute to the thickening at nested scales a mixture of brittle and solution diffusion processes overall cause the affected unit to exhibit flow like characteristics while the broad principles are now well established considerable work remains to be done understanding the full range of structural geometries associated with shale detachments what factors regarding the nature of the detachments affect overlying structural styles rates of deformation and the controls on deformation mechanisms within the thrust zones

gravity driven deformation controlled by the migration of the delta front the plio pleistocene of the eastern niger delta abstract the occurrence in large shelf edge deltas of gravity driven deformation related to overpressured shales is now well documented in many natural examples in this paper we explored the implications of the migration of the delta front on the kinematics of gravity driven deformation in a case where the stratigraphic framework is detailed enough to discuss deformation kinematics and sedimentary supply at high temporal resolution 0 1 myr we determined the deformation for the last 4 myr at the scale of the whole eastern niger delta the upslope extensional domain showed ew asymmetric grabens the transitional domain displayed i deformation restricted to folding to the east and ii a thicker sedimentary wedge and a larger deformation accommodated by thrust related folds to the west the compressional front was a fold and thrust belt extensional deformation decreased in amount and rate over the plio pleistocene it also evolved significantly from distributed over the whole area to localized either to the western or eastern domains over that period the compressional deformation followed the same evolution i e the greater the extension the greater the compression in either time or space demonstrating the strong coupling between the extensional and compressional domains gravity deformation during the plio pleistocene was driven by the continental slope spanning the coastal plain to distal deposits over the oceanic crust about 2800 m of gravity potential the superimposition of the delta front migration area and the extensional domain show that the associated pressure gradient localized the extensional domain deformation was closely linked to migrations of the delta front and the sedimentary supply reaching the delta i the decrease in extension rate over the plio pleistocene is related to a decrease in sedimentary supply over the plio pleistocene and ii the spatial variations in extension intensity and rate are related to spatial variations of sedimentary supply

fluid seepage variability across the external northern apennines italy structural controls with seismotectonic and geodynamic implications abstract the relations between fluid seeps and tectonic structures have been targeted in some key areas of the axial sector and partly at the edge of the exposed northern apennines pede apennine margin in the axial zone fluid seepage is dominated by methane venting which may occur in the form of dry seeps or associated with mineral springs surface venting is linked to the presence of foreland dipping normal faults or related to reservoirs localised at inactive anticlines the pede apennine margin is instead dominated by thrusting and mud volcanism the two different categories of fluid seepage appear strongly coupled to the dissimilar stress fields compressional or extensional operating in these sectors pressure data inferred from deep wells delineate an overall fluid pressure increase from the axial zone toward the pede apennine margin possibly as a result of the growth of tectonic compaction in this direction the increase of fluid pressure at the pede apennine margin is thus interpreted as the primary control on the transition from dry vents to mud volcanism the intimate association between seepage modes and distinct tectonic structures involves relevant consequences on fluid fault interactions and seismotectonics and also shows connections with processes dictating the internal deformation of evolving fold and thrust belts

re evaluation of mobile shale occurrences on seismic sections of the champion and baram deltas offshore brunei 3d seismic data in the baram and champion delta provinces offshore brunei show that regions thought to be occupied entirely by chaotic seismic data and conventionally interpreted as shale diapirs are regions of dimmed but coherent reflectivity such data indicate shale diapir masses are not present instead dimming can be attributed to sediment intrusive complexes overpressured fluids and gas clouds or processing artefacts in this way significant delta structures are masked on 2d seismic data which are important to interpret delta tectonic evolution the middle miocene recent champion and baram deltaic provinces are characterized by typical gravity tectonics related structures however being situated on an active margin they are also affected by episodic development of contractional structures which are located on older reactive shale bulges and result in inversion of motion on some growth faults the emplacement of shale pipes gas clouds and intrusive complexes is generally relatively late pliocene in comparison with the underlying reactive diapirs late miocene and their emplacement events may be separated in time by several million years late overpressured systems may be related to phases of pore fluid pressure increase during or following periods of inversion tectonics which resulted in phases of enhanced fluid migration in the basin where fluids were either expelled laterally oceanwards or vertically

crustal motion and block behaviour in se asia from gps measurements results acquired using global positioning system gps data taken over a large part of se asia indicate that sundaland i e indochina along with the western and central part of indonesia constitutes a stable tectonic block moving approximately east with respect to eurasia at a velocity of 12 3 mm yr 31 with respect to india and australia this block moves due south significant motion has not been detected along the northern boundary to south china i e along the red river fault whereas nearly 50 mm yr 31 of right lateral motion has to be accommodated between india and sundaland in the andaman burma region fl 2001 elsevier science b v all rights reserved

deepwater north west borneo hydrocarbon accumulation in an active fold and thrust belt in the deepwater acreage of north west borneo an active offshore fold and thrust belt hosts a number of proven hydrocarbon accumulations and promises to deliver considerable additional hydrocarbon volumes as a result of ongoing exploration campaigns typical trapping geometries observed in this neogene large scale linked fold and thrust belt are hanging wall anticlines foreland folds and ridges and sub thrust footwall cut offs commercial drilling targets lie within the deformed miocene and pliocene sediment pile and these have been charged with oil and gas from a petroleum system that is still active at the present day a major challenge here is to avoid drilling traps that have expelled their hydrocarbons during periods of active deformation and uplift in recent geological time studies of tectonic deformation phases are beginning to illuminate some key controls on trap formation and hydrocarbon retention history this paper focuses on providing an overview of the north west borneo deepwater fold and thrust belt and introduces some key issues and challenges for future hydrocarbon exploration in the region

wedge geometry and detachment strength in deepwater fold thrust belts deepwater fold thrust belts dwftbs have been classified into three groups according to the present day stress regime and tectonic setting near field stress driven dwftbs are usually associated with passive margins they are thin skinned gravitational deformation with thick salt or overpressured shale detachments dwftbs formed by far field stresses are primarily associated with continent convergent zones and active margins mixed near and far field stress driven dwftbs have aspects of both thin skinned and thick skinned tectonics detachment strength is the primary control on the first order wedge geometry of a dwftbs and is controlled by lithology and overpressure based on analysis of fault strength calculated from critical taper measurements it is found that detachments beneath different classes of dwftbs are not analogously weak near field stress driven dwftbs at passive margins generally have smaller wedge taper angles and weaker detachments far field stress driven and mixed near and far field stress driven dwftbs at continent convergent zones or active margins generally have larger wedge taper angles and stronger detachments differences in the way overpressures are generated and dissipated between the different types of dwftb are thought to be primarily responsible for the systematic variations in shale prone basal detachment weakness found in this study clear lithology related differences in dwftb critical taper are shown between shale higher taper and salt lower taper dominated basal detachments

the relationship between the instantaneous velocity field and the rate of moment release in the lithosphere summary instantaneous velocity gradients within the continental lithosphere are often related to the tectonic driving forces this relationship is direct if the forces are secular as for the case of loading of a locked section of a subduction interface by the downgoing plate if the forces are static as for the case of lateral variations in gravitational potential energy then velocity gradients can be produced only if the lithosphere has on average zero strength the static force model may be related to the long term velocity field but not the instantaneous velocity field typically measured geodetically over a period of several years because over short time intervals the upper lithosphere behaves elastically in order to describe both the short and long term behaviour of an elastic lithosphere viscoelastic asthenosphere system in a selfconsistent manner i construct a deformation model termed the expected interseismic velocity eiv model assuming that the lithosphere is populated with faults that rupture continually each with a definite mean recurrence time and that the earth is well approximated as a linear elastic viscoelastic coupled system i derive a simple relationship between the instantaneous velocity field and the average rate of moment release in the lithosphere examples with synthetic fault networks demonstrate that velocity gradients in actively deforming regions may to a large extent be the product of compounded viscoelastic relaxation from past earthquakes on hundreds of faults distributed over large 10 6 km 2 areas

application of the ads method to predict a hidden basal detachment nw borneo fold and thrust belt abstract the nw borneo margin is characterized by a complex deepwater fold and thrust belt despite previous studies the definition of a univocal detachment level for folding and thrusting is still lacking the area depth strain ads method can be used to determine the location for a detachment in areas lacking data and to balance geological cross sections this study applies the ads method to the central part of the nw borneo fold and thrust belt to predict a structurally conclusive detachment level in an area lacking a seismic detachment reflection seismic interpretations were completed after the ads determination of the basal detachment providing input for a 2d sequential restoration that delivered values on shortening distribution and shortening rate the kinematic and mechanic analyses presented document that the central part of the nw borneo fold and thrust belt is affected by both near and far field stresses and that the far field crustal shortening component becomes more important northward this work demonstrates that the ads method can be effectively applied in fold thrust belt settings with limited information on the detachment supports in a quantitative way the tectonic and stratigraphic interpretation of seismic reflection data and provides a robust structural base for the restoration of balanced cross sections including the reconstruction of syn kinematically eroded stratigraphy

balancing deformation in nw borneo quantifying plate scale vs gravitational tectonics in a delta and deepwater fold thrust belt system abstract recent gps measurements demonstrate that nw borneo undergoes 4 6 mm of plate scale shortening a year which is not accommodated by plate scale structures the only geological structure in nw borneo described to accommodate on going shortening is the baram delta system located on the outer shelf to basin floor delta toe fold thrust belts are commonly thought to be caused by margin normal compressional stresses generated by margin parallel upslope gravitational extension the baram delta system is divided into three neotectonic provinces 1 an inactive onshore and inner shelf region of inversion superimposed on an older extensional deltaic province 2 an outer shelf region of present day deltaic extension and 3 a compressional delta toe however it is uncertain whether compression in the delta toe area is purely driven by gravity i e shortening is less than upslope extension or if there is a component of regional shortening involved which can only be demonstrated if shortening is greater than upslope extension in order to quantify the balance between the shortening related to the upslope gravitational extension and the shortening related to the regional geodynamic framework in the baram delta system we have used a geomechanical code based on the finite element method and conservation of mass and momentum dynel 2d this enabled us to reconstruct the tectonic evolution of the delta and to demonstrate for the first time that the total shortening observed in the delta toe does not balance against the active extension in the delta top with the system exhibiting 1 8 shortening overall or 2 0 km this additional shortening is therefore attributed to plate scale shortening across nw borneo produced by far field compression using a convergence rate of 4 mm y 1 demonstrated by gps measurements the delta toe has accommodated far field compression only in the last 0 5 my

structural and tectonic development of the indo burma ranges abstract the indo burma ranges form an enigmatic mountain belt with fragments of evidence for an early accretionary history jurassic jade belt hp lt metamorphism early cretaceous ophiolites highly deformed triassic turbidites pane chaung formation pcf kanpetlet schists it remains uncertain whether this early history involved collision of a microcontinent mt victoria land mvl unconformably sealed by aptian cenomanian limestones or can be explained entirely as an accretionary type ophiolite on the western margin of the west burma terrane wbt complex deformation in the deepwater triassic jurassic late cretaceous and paleogene deepwater sequences is replaced in the late eocene early oligocene by molasse deposition these events mark closure of the neo tethys ocean between india and the ibr wbt and the onset of major dextral translation 2000 km 40 ma recent between the coupled india ibr wbt region and sundaland in the late miocene recent major transpressional deformation affected the ibr and central basin of the wbt the late deformation events sedimentary depocentres and impinging thick crustal regions of the eastern himalayas and shillong plateau have all affected the overall shape wedge taper of the modern ibr with the wedge and retro wedge behaving anomalously compared with typical accretionary prisms all tectonic models proposed for the ibr wbt have weaknesses or ambiguities and there is considerable scope for future research to resolve the many outstanding tectonic metamorphic structural and sedimentary issues these are important tasks because the ibr is a key region for understanding the development of northern gondwana the himalayan orogeny and se asia as well as providing insights into the complex development of highly oblique collisional margins

contraction and extension in northern borneo driven by subduction rollback abstract during the paleogene the proto south china sea was subducted beneath northern borneo subduction ended with early miocene collision of the dangerous grounds reed bank north palawan block and the sabah cagayan arc much of northern borneo then became emergent forming the top crocker unconformity later in the early miocene subsidence resumed it is proposed that northward subduction of the celebes sea initiated formation of the sulu sea backarc basin followed by subduction rollback to the se this formed a volcanic arc which emerged briefly above sea level and collapsed in the middle miocene as rollback continued the sulu arc was active during middle and late miocene between sabah and the philippines rollback drove extension in northern borneo and palawan accompanied by elevation of mountains crustal melting and deformation offshore there were two important extensional episodes the first at about 16 ma is marked by the deep regional unconformity and the second at about 10 ma produced the shallow regional unconformity both episodes caused exhumation of deep crust probably on low angle detachments and were followed by granite magmatism the nw borneo palawan trough and offshore sabah fold and thrust belt are often interpreted as features resulting from collision regional compression or subduction however there is no seismicity dipping slab or volcanicity indicating subduction nor obvious causes of compression the trough developed after the middle miocene and is not the position of the paleogene trench nor the site of neogene subduction inboard of the trough is a thick sediment wedge composed of an external fold and thrust belt and internal extensional zone with structures broadly parallel to the trough the trough is interpreted as a flexural response to gravity driven deformation of the sediment wedge caused by uplift on land that resulted from extension with a contribution of deep crustal flow

crustal accretion in the manila trench accretionary wedge at the transition from subduction to mountain building in taiwan abstract new marine seismic reflection and coincident wide angle ocean bottom seismometer data acquired offshore taiwan provide high resolution constraints on the crustal structure of an incipient mountain belt during the earliest stage of arc continent collision the new seismic reflection image and travel time tomography velocity model show evidence for crust of the distal southern chinese continental margin being subducted eastward beneath the manila trench and underplated to the accretionary wedge before collision with the southern chinese continental shelf the distal margin crust consists of highly extended continental crust interspersed with volcanic bodies and a high velocity lower crustal layer of likely magmatic intrusions the distal margin crust is 10 14 km thick outboard of the trench but thins to 6 km thick beneath the lower slope of the manila trench accretionary wedge along the lower slope of the accretionary prism we image westward verging imbricate thrusts and folded strata up to 10 km thick a sharp decrease in bathymetry marks the transition from lower to upper slope where we observe a fast 6 0 km s seismic velocity anomaly at the base of the wedge that we interpret as structurally underplated crust from the distal continental margin our results support a model of arc continent collision in taiwan where the accretionary wedge is first thickened by structural underplating of distal margin crust prior to collision with the continental shelf the crustal rocks exposed throughout the central range in taiwan may be similarly derived from subducted and structurally underplated crust from the highly extended distal continental margin

deepwater fold and thrust belt classification tectonics structure and hydrocarbon prospectivity a review abstract deepwater fold and thrust belts dwftbs are classified into near field stress driven type 1 systems confined to the sedimentary section and type 2 systems deformed by either far field stresses alone or mixed near and far field stresses dwftbs can occur at all stages of the wilson cycle up to early stage continent continent collision type 1 systems have either weak shale or salt detachments they occur predominantly on passive margins but can also be found in convergent related areas such as the mediterranean and n borneo examples include the niger and nile deltas the west coast of africa and the gulf of mexico type 2 systems are subdivided on a tectonic setting basis into continent convergence zones and active margin dwftbs continent convergence zones cover dwftbs developed during continent arc or continent continent collision and those in a deepwater intracontinental setting e g w sulawesi makassar straits active margins include accretionary prisms and transform margins the greatest variability in dwftb structural style occurs between salt and shale detachments and not between tectonic settings changes in fold amplitude and wavelength appear to be more related to thickness of the sedimentary section than to dwftb type in comparison with shale salt detachment dwftbs display a lower critical wedge taper more detachment folds long and episodic duration of deformation and more variation in vergence structures unique to salt include canopies and nappes accretionary prisms also standout from other dwftbs due to their relatively long continuous duration rapid offshore propagation of the thrust front and large amount of shortening in terms of petroleum systems many similar issues affect all dwftbs these include the oceanward decrease in heat flow offshore increase in age of mature source rock and causes of trap failure e g leaky oblique and frontal thrust faults breach of top seal by fluid pipes one major difference between type 1 and type 2 systems is reservoir rock high quality continent derived quartz rich sandstones are generally prevalent in type 1 systems more diagenetically reactive minerals derived from igneous and ophiolitic sources are commonly present in type 2 systems or many are simply poor in well developed turbidite sandstone units however some type 2 systems particularly those adjacent to active orogenic belts are partially sourced by high quality continent derived sandstones e g nw borneo s caspian sea columbus basin in some cases very high rates of deposition in accretionary prisms adjacent to orogenic belts coupled with uplift due to collision results in accretionary prism related fold belts that pass laterally from sub aerial to deepwater conditions e g s caspian sea indo burma ranges the six major hydrocarbon producing regions of dwftbs worldwide gulf of mexico niger delta nw borneo brazil west africa s caspian sea stand out as differing from most other dwftbs in certain fundamental ways particularly the very large volume of sediment deposited in the basins and or the great thickness and extent of salt or overpressured shale sdetachments

tectono stratigraphic terranes and detachment faulting of the south china sea and sulu sea abstract geoscientific data acquired from the south china sea and sulu sea areas by bgr since 1977 are compiled and interpreted as comprehensive data sets together with available information of commercial wells and drillsites of the ocean drilling program odp generalized stratigraphy and lithology are discussed and correlated with the interpreted seismic profiles on the basis of the stratigraphic and structural analysis 5 main tectono stratigraphic terranes are defined for the south china sea and 4 main terranes for the sulu sea respectively the dangerous grounds reed bank palawan nw borneo trough and palawan island represent terranes of continental origin which developed on the proto china margin by uniform sense low angle simple shearing within the crust in late cretaceous to early paleocene this rift was abandoned and a new westward propagating rift system developed north of the dangerous grounds reed bank area from the middle eocene to the oligocene early miocene together with seafloor spreading in the south china sea basin the leading edge of the southward drifting continental terranes collided with the late cretaceous to early eocene subduction complex of the northernmost terrane of the proto sulu sea continuous convergence of these terranes back arc spreading creating the se sulu sea terrane and the assumed anti clockwise rotation of borneo are responsible for the complex collision compression structures of the sulu sea terranes including the formation of splinters of oceanic crust major right lateral wrench systems are nnw sse running up to 500 km long and cut across most of the identified terranes wrenching presumably ceased 12 to 16 myr ago

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

growth faults above shale seismic scale outcrop analogues from the makran foreland sw pakistan abstract the southern makran fold thrust belt pakistan displays unique outcrop examples of well exposed kilometre scale listric growth faults that displace miocene age deltaic growth strata by several hundreds of metres to kilometers the largest growth faults are counter regional landward dipping bounding major clastic depocentres exposed over areas 1000 km 2 stratal offset along these faults can exceed 1 5 km fault zone thicknesses range between ca 100 and 400 m and average fault thickness displacement ratios are around 1 10 high resolution satellite data show in unprecedented detail the faults and the stratigraphic architecture of associated growth sequences which comprise kilometre scale progradational clinoforms thick mudstone units and basinwards wedging sandstone shale deposits the true vertical thickness of the syn kinematic record is in places up to 8 km making the outcrop examples equivalent to major growth faulted successions known from seismic data of large deltas and at least an order of magnitude larger than other outcrop examples a comparison of the makran outcrops with seismic reflection examples offshore nw borneo reveals distinct similarities in the gross depocentre geometries and internal architecture the key control for growth faulting is interpreted to result from sedimentary loading with rapid sedimentary progradation causing the development of rollover synclines by differential compaction and fluid expulsion and counter regional growth faults preferentially forming on the basinward side of these synclines the data and interpretations presented can be used to assess the key parameters that contribute to the development of growth faults and growth successions above shale reinforcing structural and stratigraphic observations from seismic interpretation and modelling studies in demonstrating their occurrence in exposure