from partial to full strain partitioning along the indo burmese hyper oblique subduction abstract the andaman nicobar trench and its onshore prolongation the indo burmese wedge is the least studied segment of the india australia subduction new offshore geological and geophysical data have recently been collected along the burma scarp during a marine survey conducted with the r v marion dufresne andaman cruise swath bathymetric mapping combined with shallow and deep seismic show that the dominant active tectonics is dextral strike slip faulting accompanied by various amounts of shortening the southern portion of the burma scarp is transpressive north andaman islands the central portion is pure strike slip on nne oriented segments southern myanmar the northern portion shows sedimentary wedge growth along nw segments both onshore and offshore arakan yoma prism further north the wedge bends to the west while dextral shear faults more or less parallel to the sagaing fault develop within the internal part of the wedge and elongated ns folds form in its external part abutting onto the shillong plateau we propose a simple kinematic model involving evolution from partial to full partitioning from south to north along the west burma scarp wbs and we test it quantitatively using the most recent geodetic results in the south half of the 3 5 cm year of india motion is taken at the trench itself the other half being accommodated onto a single shear fault the sagaing fault in myanmar in the north where the bangladesh fold system developed dextral strike slip faults are activated within the arakan yoma belt and at the accretionary prism backstop contact resulting in full partitioning there faults accommodating the oblique component of motion of india are progressively migrating in space from far field faults andaman sagaing to near trench faults arakan yoma belt and trench itself the burma sliver being buttressed by the eastern himalayas this kinematic extends back to 4 ma which is the time of initiation of the last pulse of oceanic accretion in the andaman basin

transmission electron microscopy of ejecta from the xvith century eruption of the soufriere guadeloupe microscopic evidence for magma mixing abstract pyroclastic products of the xvith century eruption of the soufriere of guadeloupe were examined in transmission electron microscopy features smaller than one micrometer inside the pyroxene and plagioclase phenocrysts were analyzed and provided information to constrain the mechanism and the chronology of the eruption the observations support a mechanism of triggering by injection of a hot andesitic magma into a chamber containing partly differentiated dacitic magma the analysis of the dusty zones in plagioclase phenocrysts suggests that the basic magma was about 200 c hotter than the resident magma the eruption probably had a very low chlorine yield and ended with a pyroclastic flow contemporaneous with the emplacement of the present dome

large scale sediment underplating in the makran accretionary prism southwest pakistan field relations in the emergent part of the makran accretionary prism show that a mid miocene to early pliocene slope and shelf sedimentary sequence was deposited directly on abyssal plain turbidites without any detectable stratigraphic or structural discordance sedimentological evidence for rapid shoaling however indicates that the underlying sediment column was tectonically thickened by a factor of between two and three during this period this can be explained by large scale underthrusting and underplating of sediment a mode of accretion that is also favored by mass balance considerations the visible deformation in the coastal makran occurred when the region was 70 100 km north of the contemporary prism front

salt tectonics in two convergent margin basins of the cyprus arc northeastern mediterranean abstract seismic reflection profiles from the adana cilicia and iskenderun latakia basin complexes in the ne mediterranean sea show the presence of linked extensional contractional fault systems detached at the base of the messinian evaporites the extensional domain is developed within the thick proximal part of the plio quaternary delta succession in the inner part of each basin it is characterized by imbricate fans of listric normal faults which delineate turtle anticlines and their intervening syncline the faults sole into the gently southwest dipping detachment surface in the inner basins salt is largely evacuated toward the outer basins but remnants occur as rollers in the footwalls of the listric extensional faults and small subdued pillows beneath turtle anticlines the narrow synclines between the two turtle back growth anticlines record a more complicated history of rise and fall of the salt related to switch in vergence of the extensional fault fan a large salt wall is developed at the toe of the delta complex in both basins two wide peripheral sinks are present within the plio quaternary units on both flanks of the salt wall locally small segments of salt welds are present near the base of the salt wall the contractional domain is characterized by a relatively thin plio quaternary cover overlying a relatively uniform 500 800 ms thick salt substrate a series of salt cored growth folds are commonly associated with thrusts of variable vergence the halokinetic structures in the cilicia and latakia basins display a remarkable resemblance to detached and linked systems of extensional and contractional fault fans documented in classical salt provinces on passive margins the study area also resembles scaled experiments which document synchronous development of extensional and contractional fault systems detached in a ductile substrate however a number of differences also exist which may arise from several factors including the nature of ductility contrast between the ductile portion of the evaporite layer and the supra salt succession the thickness ratio of overburden to evaporite unit and the rate of progradation and the nature of sediment distribution during the evolution of the delta complex the special aspect of these associations of linked gravity driven extensional and contractional salt structures is that they are developed as a self contained system wholly situated within a plio quaternary transtensional basin

onset of subduction as the cause of rapid pliocene quaternary subsidence in the south caspian basin backstripping a representative stratigraphic column from the northwest of the south caspian basin shows that 2 4 km of tectonic subsidence has occurred since ca 5 5 ma at 1 5 10 times the rate recorded in typical foreland basins roughly half the basin s sedimentary thickness of 20 km has accumulated in this time while the upper part of the succession has begun to deform by buckle folding the south caspian basement appears to be either thick oceanic crust or thinned high velocity continental crust seismicity and gravity data indicate that the basement is in the initial stages of subduction under the middle caspian region to the north we propose that basement subduction began ca 5 5 ma to create the major pliocene quaternary subsidence subduction may have been triggered by a regional reorganization in the arabia eurasia collision at that time possibly following the construction of the turkish iranian plateau

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

internal deformation and compaction of the makran accretionary wedge the makran accretionary wedge is one of the largest on earth a 7 km thick column of sands and quartzolithic turbidites are incorporated into this wedge in a series of deformed thrust sheets we present the results of prestack depth migration and focusing error analysis migration velocity analysis performed on a profile across the makran wedge the depth section shows the deformation style of the accreted sediments and the migration velocities allow us to estimate porosity variations in the sediments the thrust sheets show evidence of fault propagation folding with a long wavelength of deformation 12 km and secondary thrusting in the kink bands of the folds such that the central part of each thrust sheet is elevated to form an additional ridge this deformation style and the 15 steep surface slope of the first ridge suggest a high degree of consolidation porosities were calculated from the seismic migration velocities and the ratio of fluid pressure to lithostatic pressure was estimated for 5 locations along the profile rather than being undercompacted and overpressured as in most accretionary wedges the sedimentary input is normally compacted exponential porosity decay throughout almost the whole wedge however a slight increase in porosity and at depth with respect to the normal compaction curve indicates that the turbiditic sequence might be overpressured landward of the deformation front

mass accumulation rates in asia during the cenozoic summary this work establishes estimates of mass accumulation rates in 18 mostly offshore sedimentary basins in asia since the beginning of the cenozoic 66 ma the estimates were derived from isopach maps cross sections and drill holes or stratigraphic columns assuming regional similarity of the strata average solid phase volumes and accumulation rates were calculated for nine epochs approximately corresponding to geological periods palaeocene 66 58 ma eocene 58 37 ma oligocene 37 30 and 30 24 ma miocene 24 17 17 11 and 11 5 ma pliocene 5 2 ma and quaternary 2 0 ma these rates shed new light on the geological history of asia since the onset of the collision of india with asia 50 ma the overall average accumulation rates curve for asian sedimentary basins since the beginning of the tertiary shows an exponential form with slow accumulation rates less than 0 5 106 km3 myr 1 until the beginning of the oligocene more than 15 myr after the onset of the collision from the oligocene onwards rates increase quickly in an exponential manner reaching their maximum values in the quaternary more than 1 5 106 km3 myr 1 from these observations we suggest that extrusion and crustal shortening are complementary processes that have been successively dominant throughout the india eurasia collision history at smaller scales one may distinguish between independent histories at the subcontinental and basin scales this permits a comparison of the relative importance of tectonic and climatic erosion processes affecting the different mountain belts of asia during the cenozoic

conditions for hydrofracture and the fluid permeability of accretionary wedges abstract the dewatering of fine grained sediment piles in accretionary wedges is controlled by zones of active deformation episodic hydrofracture in these zones enhances permeability enabling fluid flow to be faster than the speed of underthrusting here i investigate the mechanics of simultaneous shear failure and hydrofracture in muddy rocks as a function of the faulting mode the physical properties of model rock types are chosen to represent uncemented mud or cherty marly mudstones that have undergone significant diagenesis during thrust faulting hydrofracture always requires pore fluid pressures in excess of the lithostatic load whereas shallow level wrenching or normal faulting permits hydrofracture at hydrostatic pressures significantly lower than lithostatic load all three faulting modes are expected to occur in an accretionary wedge attempting to dynamically maintain its critical taper the model computations indicate that in the upper 80 120 m of a section of soft mudstone hydrofracture inevitably accompanies wrench or normal faulting hard mudstones inevitably hydrofracture to depths of up to 1400 m during normal faulting these differences in mechanical behaviour have profound consequences for fluid venting capabilities of accretionary wedges they influence hydrocarbon trapping and play a role in the localisation of mud diapirs and mud volcanism

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

plate tectonic evolution of the southern margin of eurasia in the mesozoic and cenozoic abstract thirteen time interval maps were constructed which depict the triassic to neogene plate tectonic configuration paleogeography and general lithofacies of the southern margin of eurasia the aim of this paper is to provide an outline of the geodynamic evolution and position of the major tectonic elements of the area within a global framework the hercynian orogeny was completed by the collision of gondwana and laurussia whereas the tethys ocean formed the embayment between the eurasian and gondwanian branches of pangea during late triassic early jurassic times several microplates were sutured to the eurasian margin closing the paleotethys ocean a jurassic cretaceous north dipping subduction boundary was developed along this new continental margin south of the pontides transcaucasus and iranian plates the subduction zone trench pulling effect caused rifting creating the back arc basin of the greater caucasus proto south caspian sea which achieved its maximum width during the late cretaceous in the western tethys separation of eurasia from gondwana resulted in the formation of the ligurian penninic pieniny magura ocean alpine tethys as an extension of middle atlantic system and a part of the pangean breakup tectonic system during late jurassic early cretaceous times the outer carpathian rift developed the opening of the western black sea occurred by rifting and drifting of the western central pontides away from the moesian and scythian platforms of eurasia during the early cretaceous cenomanian the latest cretaceous paleogene was the time of the closure of the ligurian pieniny ocean adria alcapa terranes continued their northward movement during eocene early miocene times their oblique collision with the north european plate led to the development of the accretionary wedge of the outer carpathians and its foreland basin the formation of the west carpathian thrusts was completed by the miocene the thrust front was still propagating eastwards in the eastern carpathians during the late cretaceous the lesser caucasus sanandaj sirjan and makran plates were sutured to the iranian afghanistan plates in the caucasus caspian sea area a north dipping subduction zone jumped during paleogene to the scythian turan platform the shatski terrane moved northward closing the greater caucasus basin and opening the eastern black sea the south caspian underwent reorganization during oligocene neogene times the southwestern part of the south caspian basin was reopened while the northwestern part was gradually reduced in size the collision of india and the lut plate with eurasia caused the deformation of central asia and created a system of nw se wrench faults the remnants of jurassic cretaceous back arc systems oceanic and attenuated crust as well as tertiary oceanic and attenuated crust were locked between adjacent continental plates and orogenic systems

subduction history of the tethyan region derived from seismic tomography and tectonic reconstructions 1 in the mantle underneath the tethyan suture zone large volumes of positive velocity anomalies have been imaged by seismic tomography and interpreted as the present day signature of subducted tethyan lithosphere we investigate the mesozoic cenozoic subduction history of the region by integrating independent information from mantle tomography and tectonic reconstructions three different subduction scenarios for the tethyan oceanic lithosphere representative for the available tectonic reconstructions are used to predict the present thermally anomalous volumes associated with the lithospheric surface subducted since the late mesozoic next these predicted thermal volumes and their expected positions are compared to the relevant anomalous volumes derived from seismic tomographic images in this analysis we include among others the possible effects of ridge subduction and slab detachment after the cenozoic continental collisions absolute plate motion and slab thickening in the mantle our preferred subduction model comprises the opening of large back arc oceanic basins within the eurasian margin the model points to slab thickening by a factor of 3 in the mantle in which case the estimated volumes allow for active oceanic spreading 1 2 5 cm yr in the tethyan lithosphere during convergence our results further indicate the occurrence of early oligocene slab detachment underneath the northern zagros suture zone followed by both westward and eastward propagation of the slab tear and diachronous eocene to miocene slab detachment below the eastern to western himalayas free sinking rates of the detached material of 2 cm yr in the lower mantle provide the best fit between the tomographic mantle structure and our tethyan subduction model

structure and kinematics of the indo burmese wedge recent and fast growth of the outer wedge 1 the northern sunda subduction zone offshore burma and the associated indo burmese wedge mark the active eastern boundary of the burma platelet jammed between the india plate and the sunda plate the aim of this paper is to provide a structural and kinematics analysis of the indo burmese wedge based on seismic reflection geodetic and geological field data we found out that the indo burmese wedge is the place of diffuse strain partitioning right lateral shearing in the innermost part and e w shortening in the outermost part in the outer wedge thick skinned deformation overprints thin skinned deformation it can be explained by the required preservation of the critical taper after the fast westward propagation of the outer wedge above a very efficient clayey decollement layer the thick skinned deformation is here characterized by major right lateral strike slip faults the kaladan fault and the chittagong coastal fault and yet a typical internal deformation of the indo burmese wedge we suggest that the westward migration of internal right lateral shear deformation allows preservation of the strain partitioning ratios between internal n s trending right lateral shearing and external e w shortening some seismic lines show that the outer wedge deformation is not older than 2 ma its propagation could have been enhanced by the large amount of sediments filling up the sylhet flexural basin formed after the pliocene tectonic uplift of the shillong plateau

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

influence of overpressure on formation velocity evaluation of neogene strata from the eastern bengal basin bangladesh abstract interpretation of sonic log data of anticlinal structures from eastern bangladesh reveals significant variations of acoustic velocity of subsurface strata the amount of variation in velocity is 32 from miocene to pliocene stratigraphic units in titas and bakhrabad structure whereas 21 in rashidpur structure velocity fluctuations are influenced by the presence of gas bearing horizons with velocities of gas producing strata 3 7 lower than laterally equivalent strata at similar depth average velocities of miocene boka bil and bhuban formations are respectively 2630 and 3480 m s at titas structure 2820 and 3750 m s at bakhrabad and 3430 and 3843 m s at the rashidpur structure from the overall velocity depth distribution for a common depth range of 915 3000 m the titas bakhrabad and rashidpur structures show a gradual increase in velocity with depth in contrast the sitakund anticline in se bangladesh reveals a decrease in velocity with depth from 3000 to 4000 m probably due to the presence of overpressured mudrocks of the bhuban formation tectonic compression associated with the indo burmese plate convergence likely contributed the most toward formation of subsurface overpressure in the sitakund structure situated in the chittagong tripura fold belt of the eastern bengal basin bangladesh

a tectonic pulse in the makran accretionary prism recorded in iranian coastal sediments many recent studies of syndeformational sediments in a wide range of tectonic environments have improved our understanding of the development of individual or regional deformation structures here we report studies of growth strata that imply an unexpected tectonic history within part of the makran accretionary prism currently the largest on earth we interpret the lithostratigraphy and ichnofacies of plio pleistocene marine deposits logged along part of the makran coast in terms of their palaeoenvironments lateral trends in thickness and depositional facies of rock units and erosional surfaces among them are correlated and then related to displacements along syndepositional faults that are distinguishable from changes in global sea level past studies of accretionary prisms have emphasized thrusting at the deformation front offshore however at the shoreline we find episodes of deposition during subsidence as a result of oblique slip normal faulting alternating with episodes of erosion during uplift driven by oblique slip thrusting the absolute timing of these displacements is not yet known however faults above a deep zone of subcretion or underplating well behind the surficial deformation front have clearly undergone episodic reversals in throw that imply alternations in lateral shortening and extension

estimation of s wave velocity structures in and around the sendai basin japan using array records of microtremors we conducted array measurements of microtremors at six sites in and around the sendai basin to estimate deep s wave velocity structures above the seismological bedrock pre tertiary bedrock after estimating phase velocities of microtremors in the frequency range from about 0 5 to 3 hz we succeeded to estimate the deep structures above the pre tertiary bedrock at four soil sites kata okin arah and myg15 and only the upper part just beneath the pliocene layer at the other soil site trma using a rayleigh wave inversion technique at trma and a rock site tama we roughly estimate the deep s wave velocity structures using empirical site amplification factors derived from strong motion records the deepest bedrock depth is 1 km and the shallowest depth is 200 m among these six sites the difference of the bedrock depth between the eastern side and the western side of an active thrust fault the nagamachi rifu line is only 120 m the difference of the bedrock depth between two sites in the east of the basin reaches about 500 m although any geological boundaries or buried faults have not been mapped since the deep s wave velocity structure of the sendai basin had been basically unknown we delineate it for the first time in this article using array measurement of microtremors

slope failure dynamics and impacts from seafloor and shallow sub seafloor geophysical data case studies from the costa project holocene and slightly pre holocene submarine landslide are found both in high latitude glacial dominated margins and in lower latitude river dominated margins this paper constitutes a major assessment on some of the best studied submarine instabilities in the world we review and update from original data and literature reports the current state of knowledge of storegga traenadjupet and finneidfjord slides from the mid norwegian margin afen slide from the faeroe shetland channel big 95 slide and central adriatic deformation belt cadeb from continental slope and inner continental shelf settings off the ebro and po rivers in the mediterranean sea canary slide west of the westernmost youngest canary islands and gebra slide off the northern tip of the antarctic peninsula in the southern hemisphere i e those studied in the continental slope stability costa project the investigated slides range in size from the gigantic 90 000 km2 and almost 3000 km3 storegga slide to the tiny 1 km2 and 0 001 km3 finneidfjord slide not only do individual submarine landslides rarely involve processes precisely fitting with pre established categories mostly based on subaerial research but also they display complex mechanical behaviors within the elastic and plastic fields individual events can involve simultaneous or successive vertical to translational movements including block detachment block gliding debris flow mud flow and turbidity currents the need for an in depth revision of the classification criteria and eventually for a new classification system based on the new imaging capabilities provided by modern techniques is more than obvious we suggest a new system which for the moment is restricted to debris flows and debris avalanches volume calculation methods are critically reviewed and the relations between some key geomorphic parameters are established for the selected slides the assumed volume missing from scar areas does not necessarily match the actual volume of sediment remobilised by an individual event since in situ sediment can be remoulded and eventually incorporated during the slide downslope journey cadeb a shore parallel prodelta detached from its source is the exception to the good correlation found between across slope width and alongslope length with slide area height drop measured from the headwall upper rim to its foot correlates with the debris deposit maximum thickness unless the slide moves into restricted areas which prevent farther forward expansion of the deposit such as gebra and big 95 in such cases over thickened deposits are found a particularly loose and fluid behavior can be deduced for slides showing an over thinned character such as the canary slide that traveled 600 km scar areas and slip planes have been investigated with particular emphasis although slide headwalls might present locally steep gradients up to 23 for storegga slide the slope gradients of both the failed segment margins and the main slip planes are very low max 2 and usually around 1 and less an exception is the finneidfjord slide 20 5 that occurred in 1996 because of a combination of climatic and anthropogenic factors leading to excess pore pressure and failure mechanically distinct low permeable clayey weak layers often correspond to slip planes beyond the slide headwall since not only formation of these weak layers but also sedimentation rates are climatically controlled we can state that slide pre conditioning is climatically driven too run out distances reflect the degree of disintegration of the failed mass of sediment the total volume of initially failed material and transport mechanisms including hydroplanning commonly specific run outs could be attributed to distinct elements such as cohesive blocks and looser matrix as nicely illustrated by the big 95 slide total run outs usually correspond to matrix run outs since the coarser elements tend to rest at shorter distances outrunner blocks are finally a very common feature proving the ability of those elements to glide over long distances with independence of the rest of the failed mass in addition to pre conditioning factors related to geological setting and sedimentation conditions a final trigger is required for submarine landslides to take place which is most often assumed to be an earthquake in high latitude margins earthquake magnitude intensification because of post glacial isostatic rebound has likely played a major role in triggering landslides although it cannot be totally ruled out there is little proof at least amongst the costa slides that gas hydrate destabilisation or other processes linked to the presence of shallow gas have acted as final triggers

mechanism of thin skinned detachment in the amazon fan assessing the importance of fluid overpressure and hydrocarbon generation abstract since about 10 ma a wedge of clastic sediment up to 10 km in thickness has accumulated near the mouth of the amazon river forming the amazon fan thin skinned extensional and contractional structures root into a common basal detachment hundreds of kilometers long extensional faults have formed landward of the prograding delta slope and contractional folds and faults have formed seaward of it by plan view restoration we show that extension and contraction balance we therefore infer that slope instability has provided the driving force for thin skinned deformation on seismic data the detachment appears as a sharp surface within late cretaceous strata however there is no evidence at that level for soft layers such as evaporites or muds abnormal fluid pressure provides a more reasonable mechanism for the detachment at depths of several thousand meters deep wells have encountered fluid overpressures amongst the possible causes of abnormal fluid pressures are compaction and hydrocarbon generation although compaction may have contributed to fluid overpressures encountered in wells we argue that hydrocarbon generation provides the best explanation for detachment in cretaceous rocks which were old and lithified when it occurred in particular the broadly triangular area of detachment coincides with an inferred pod of cenomanian turonian source rock which is interpreted to have been in the gas window during detached deformation we have developed new techniques of sandbox modelling to investigate the geometries of fault patterns produced by fluid flow through porous media for the amazon fan we have been able to reproduce the structural pattern on the assumption that fluid overpressures existed over a broadly triangular area beneath the detachment

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

liquefied vs stratified sediment mobilization processes insight from the south of the barbados accretionary prism this paper discusses the nature and origin of subsurface sediment mobilization processes in deep marine clay rich environments in the studied area of the southern barbados accretionary prism new geophysical acquisitions have emphasized the spectacular widespread development of mud volcanoes that are well developed along ramp anticlines and along sigmoidal rises with trends that are oblique to the axes of the main folds of the accretionary wedge on some active mud volcanoes heat flow measurements show high positive anomalies related to high fluxes of mud transfer the mobilized solid fraction expelled by the mud volcanoes does not originate from a unique source bed but from various formations pierced by the mud conduits and is driven by the water phase the area studied also exhibits trends of structures corresponding to sub circular massive local uplifts of deformed but well preserved stratified sediments turbidites and hemipelagics no piercing shale diapirs have been encountered in this area some of these local uplift structures are complicated by the development of collapses calderas and superimposed mud volcanoes mud volcanism corresponds fundamentally to fluid displacement water and gas whereas massive sedimentary uplift corresponds to large vertical displacements of stratified solid levels but for which the deep cause could be partly the intrusion of mud plugs both are dynamic phenomena controlled by the development of overpressure at depth contributing to sedimentary mobilizations

structural styles and tectonic evolution of the seram trough indonesia abstract the seram trough is located in the northern part of the banda arc australian collision zone in eastern indonesia and is currently the site of contraction between the bird s head of new guinea and seram island it has been interpreted as a subduction trench an intra continental thrust zone and foredeep and a zone of strike slip faulting recently acquired 2d seismic lines clarify its tectonic evolution and relationship to the bird s head folding in the early pliocene formed an anticlinorium running from misool to the onin peninsula of irian jaya and produced a newly recognised angular unconformity the unconformity truncates sediments as old as middle jurassic and is an ancient topographic surface with significant relief it was later folded and now dips south towards the trough where it is covered by up to 3 km of sediments initial tilting of the unconformity surface was accompanied by deposition of a transgressive sequence which can be traced into the trough this is overlain by two sequences which prograde towards the trough these sequences show progressive rotation of the unconformity surface gravitational displacement of sediments into the trough and thrusting which continues to the present day contraction occurred in the trough after the early pliocene and is younger than the previously suggested late miocene age thrust faults in the trough deform sediments deposited above the unconformity and detach at the unconformity surface on seram thrust faults repeat mesozoic miocene sequences and probably detach at their contact with metamorphic basement the detachment surface must cut through the mesozoic miocene sequence between seram and the trough this work suggests the seram trough is not a subduction trench but a foredeep produced in response to loading by the developing fold and thrust belt of seram with an associated peripheral bulge to the north the seram trough is interpreted to be a very young zone of thrusting within the australian continental margin

quaternary sandy deposits and canyons on the venezuelan margin and south barbados accretionary prism abstract the geomorphological and tectonic setting distribution and origin of late quaternary sandy deposits on the southern termination of the barbados accretionary prism and the adjacent abyssal plain have been investigated using seabeam and 3 5 khz echosounding data and lithological and mineralogical analyses of 28 kullenberg cores quaternary sands on this prism are deposited in piggyback basins they are transported along three major canyons the morphology and trend of which are highly variable and which are tectonically controlled the narrow and relatively shallow canyon sections are in some ways like the major distributary channels of deep sea fans but they are true canyons in terms of the sedimentary processes taking place namely active erosion associated with the continuous uplift of tectonic structures and deposition of only slightly elevated sediment levees the sand is partly trapped on basin floors as flat sediment sheets composed of thinly and thickly bedded fine grained sandy turbidites high deposition rates occurred during the last period of low sea levels the sands originated from the orinoco trinidad shelf as inferred from geographical considerations and clay and heavy mineral provenance data predominently kaolinite illite hornblende and epidote sands of the abyssal plain settled on a deep sea fan system that trends north south parallel to the toe of the prism most of the sediments are introduced at the southern end of the system where they are delivered by the three major canyons which merge on the fan in a northward braided channel system this material consists of sandy turbidites that originated from the orinoco trinidad margin the grain size of the sands is similar to or coarser than the grain size of the prism sands sand components are identical and preclude supply from the amazon river the sedimentation rate during periods of low sea level seems to be lower a significant percentage of smectite in the clay fraction suggests that a minor part of the material may be derived from the demerara margin located closer to the main smectite source i e the amazon delta these results emphasize the difference between the sand distribution on active and passive margins

decollement depth versus accretionary prism dimension in the apennines and the barbados 1 along representative cross sections of the apennines and the northern barbados accretionary prisms we measured the area the decollement depth the angle a of the upper envelope and the angle b of the dip of the regional monocline the continental sections of the apennines accretionary prism have a deeper decollement than the oceanic sections of the northern barbados 6 10 km depth and 1 km depth respectively because the sediment pile is thinner on the incoming barbados plate and its denser oceanic structure is more easily subducted considering the frontal 50 km the apennines have an average cross sectional area of 500 km 2 and the northern barbados ridge of 100 km 2 the total area is a function of the depth of the decollement plane therefore at a given amount of subduction the deeper the decollement depth is the bigger the area of the wedge will result assuming negligible compaction and erosion as a consequence the larger area volume and higher elevation of the apennines with respect to the barbados is determined by the apenninic deeper decollement despite these differences the geometry of both decollements is in some cases comparable in particular close to the boundary between the crystalline crust and the sediment pile where the main density and strength contrasts are concentrated variations in depth of the decollement occur moving along strike in both accretionary prisms the geometry of the prisms is further controlled by the different values of a and b their sum and the distance of the accretionary prism relative to the subduction hinge index terms 8099 structural geology general or miscellaneous 8150 tectonophysics evolution of the earth plate boundary general 3040 8122 tectonophysics dynamics gravity and tectonics keywords decollement depth accretionary prism apennines barbados citation bigi s f lenci c doglioni j c moore e carminati and d scrocca decollement depth versus