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

strain partitioning in the transition area between oblique subduction and continental collision hikurangi margin new zealand spatial differences in late quaternary structural style and deformation rates indicate a complex pattern of strain partitioning within the transition area from oblique subduction beneath southern north island to oblique continental collision in northern south island new zealand the late quaternary structure of the offshore southern hikurangi margin is determined here using seismic reflection profiles mr1 side scan sonar swath images em12dual multibeam swath bathymetry and backscatter images and sediment core and dredge samples where oblique 50 subduction of the oceanic hikurangi plateau is occurring beneath southern wairarapa region the steep dissected upper margin consists of a wedge of rocks that are being deformed by strike slip and reverse faults beneath the lower margin an accretionary wedge of quaternary age has developed rapidly by frontal accretion of a thick succession of turbidites on the pacific plate estimates of late quaternary geological strain rates have been made on two margin perpendicular transects across southern north island and the offshore margin to budget the predicted nuvel 1a plate motion more than 33 55 of the total plate motion is expressed in the offshore part of the upper plate above the subduction detachment in the central hikurangi margin between 40 s and 41 s this offshore deformation could potentially include margin parallel fault slip of up to 14 15 mm yr across the upper plate strain is partitioned into zones of folding and thrust faulting and possibly more than one zone of strike slip faulting but the partitioning may be incomplete with oblique slip thrusting an important component of the deformation the wide distribution of deformation within the upper plate partially reflects strong coupling between the subducting oceanic plateau and the leading edge of the overriding plate this coupling increases toward the southwest where the continental part of the subduction zone beneath marlborough may now be inactive or very strongly coupled toward the southwest the transpressive deformation style of the upper wairarapa margin continues into the upper marlborough margin and onshore into the strike slip marlborough fault system of northern south island in contrast the accretionary wedge narrows to the southwest and terminates in southeastern cook strait approximately above the transition from subducted oceanic crust to subducted continental crust of the pacific plate farther southwest beneath the lower marlborough margin low strain folding and thrust faulting is occurring but the style of deformation is not typical of the accretionary wedge this shortening results either from a small amount of subduction slip beneath marlborough and or from contractional strain partitioned to the southeast of the continental transpression zone whereas the initial onset of continental collision occurs in marlborough the surface expression of deformation of the pacific plate occurs south of 42 30 s normal faulting of the northwestern margin of the continental chatham rise possibly reflects flexural extension of the pacific plate crust at the southern end of the subduction zone whereas folding and thrust faulting of the north canterbury coastal region results from nw se contraction of the delaminated upper crust entering the southern alps collision zone

the position of paleopedology in geosciences and agricultural sciences abstract paleopedology is a relatively young science with roots in various older geosciences at present it suffers from a lack of clear definitions and fundamental principles nevertheless it has considerable potential for applications in stratigraphy paleontology sedimentology archeology paleoclimatology seismology geomorphology soil classification and agriculture consequently it could play a major coordinating role in soil science especially in contributing to a natural strongly genetic system of soil classification we suggest that such a system with emphasis on development of soil properties in relation to current and past environmental factors would be of greater value in all these subjects than the current systems designed principally for agricultural interpretation

wedge geometry mechanical strength and interseismic coupling of the hikurangi subduction thrust new zealand the hikurangi subduction thrust interface east coast north island new zealand exhibits along strike variations in seismic style the southern segment is interseismically locked while the plate boundary thrust slips aseismically in the north the geometry of the offshore accretionary prism is also heterogeneous changing from small to large taper angle fault dip plus surface slope from south to north along strike variations in accretionary prism geometry generally reflect changes in coulomb wedge critical taper angle such variations are controlled by the relative strengths of the subduction megathrust and the wedge material in the southern hikurangi margin the small taper angle indicates a relatively weak subduction thrust interface where strong interseismic locking is inferred in the northern margin high taper angle reflects a strong shallow decollement relative to the south thus based on critical coulomb wedge theory the shallow megathrust appears relatively weak in the locked segment and stronger in weakly coupled regions

landward and seaward directed thrusting accompanying the onset of subduction beneath new zealand a short 5 m y episode of deformation accompanied the onset of the present phase of subduction beneath northern and eastern new zealand in the earliest miocene at many places along the continental margin the structures produced were dominated by subhorizontal thrust sheets with tens of kilometres of displacement thrusting was directed both landward with or without involvement of the upper part of the downgoing plate and seaward the structures are different in style from those typical of active trench slopes which are predominantly seaward directed imbricate thrusts and associated folds the structures show that delamination of the downgoing plate occurred at some places and suggest that a high degree of coupling between upper and lower plates occurred at others

role of the shale tectonics on the evolution of the eastern venezuelan cenozoic thrust and fold belt this paper presents a structural and stratigraphic analysis of the foreland fold belt of the eastern venezuelan basin and the main conclusions about shale tectonic mechanisms in the area the deformation of the foreland fold belt has been investigated analyzing the growth strata architecture preserved on the structure fold limbs three contractional episodes are proposed for the eastern venezuelan basin 1 oligocene to middle miocene 2 late miocene to pliocene and 3 pleistocene the first episode produced contractional listric faults inside the shale and long displacement blind thrusts in the underlying cretaceous units the second episode produced the deformation of the cenozoic strata into overlapping east west trending convex northward anticlines that covers more than 200 kilometers in length and 40 kilometers wide break through normal faults product of a high sedimentary load that overcomes contraction and the formation of short displacement blind thrusts in the underlying cretaceous units the last episode is related to an oblique compression and the formation of high angle extensional faults with dextral movement and nw se strike the role of the shale tectonics in the evolution implies that shale deforms in two stages 1 folding and 2 normal faulting of the crest of the anticline break through normal faulting folding controlled the sediment distribution during most of the neogene strata while the normal faulting of the anticlines represent basin potential for hydrocarbon the best potential hydrocarbon plays in the basin are related to oblique collision restricted basins and controlled by break through normal faults and the presence of nw se strike faults that connect the hc source with the reservoirs results from this research imply that the role of sedimentation is fundamental for the overburden sand distribution and tectonic constrain of the folds

tropical cooling at the last glacial maximum and extratropical ocean ventilation1 1 the ncar csm is used to simulate the climate at last glacial maximum the csm simulates a tropical sst cooling of 2 1 c it is shown that about half of this tropical cooling is associated with the upper ocean circulation especially the ventilation of thermocline and intermediate waters from the mid high latitude south pacific

interhemispheric thermal gradient and tropical pacific climate 1 we explore the impact of interhemispheric thermal gradients forcing on the tropical pacific ocean atmosphere climate in an intermediate coupled model the equatorial zonal sea surface temperature sst gradient strengthens with an increased northward interhemispheric thermal gradient the increase arising from earlier onset and later retreat of the seasonal cold tongue and intensification during the peak cold season when the mean interhemispheric thermal gradient is reversed the central equatorial pacific sst annual cycle abruptly reverses in phase with its cold season in mar may rather than sep nov while startling this response is consistent with a prevailing hypothesis that ties the cold tongue sst annual cycle phase to the hemispheric mean asymmetry of the intertropical convergence zone el nino southern oscillation activity is also sensitive to the interhemispheric thermal gradient with peak activity occurring when the mean gradient is small reducing rapidly as the mean gradient increases in either direction

cross seasonal influence of the december february southern hemisphere annular mode on march may meridional circulation and precipitation abstractnew evidence suggests that interannual variability in zonal mean meridional circulation and precipitation can be partially attributed to the southern hemisphere annular mode sam the dominant mode of climate variability in the southern hemisphere sh extratropics a cross seasonal correlation exists between the december february djf sam and march may mam zonal mean meridional circulation and precipitation this correlation is not confined to the sh it also extends to the northern hemisphere nh subtropics when the preceding djf sam is positive counterclockwise and clockwise meridional cells accompanied by less and more precipitation occur alternately between the sh middle latitudes and nh subtropics in mam in particular less precipitation occurs in the sh middle latitudes the sh tropics and the nh subtropics but more precipitation occurs in the sh subtropics and the nh tropics a framework is built to explain the cross seasonal impact of sam related sst anomalies evidence indic

the last 2 myr of accretionary wedge construction in the central hikurangi margin north island new zealand insights from structural modeling three depth converted and geologically interpreted seismic profiles provide a clear image of the offshore outer accretionary wedge associated with oblique subduction of the pacific plate beneath the central hikurangi margin plio quaternary turbidites deposited over the pelagic cover sequence of the hikurangi plateau have been accreted to the margin by imbrication along e verging thrust faults that propagated up section from the plate boundary decollement growth stratigraphy of piggy back basins and thrusting of progressively younger horizons trace the eastward advance of the leading thrust front over c 60 km in the last 2 myr moderate internal shortening of fault bounded blocks typically 4 8 km wide reflects rapid creation of thrust faults with some early formed faults undergoing out of sequence reactivation to maintain critical wedge taper multi stage structural restorations show that forward progression of shortening involves 1 initial development of a c 10 25 km wide proto thrust zone comprising conjugate sets of moderately to steeply dipping low displacement c 10 100 m reverse faults and 2 growth of thrust faults that exploit some of the early proto thrust faults and propagate up section with progressive break through of folds localized above the fault tips the youngest still unbreached folds deform the present day seafloor progressive retro deformations show that macroscopic thrust faults and folds account for less than 50 of the margin perpendicular shortening imposed by plate convergence arguably significant fractions of the missing components can be attributed to meso and microscopic scale layer parallel shortening within the wedge in the proto thrust zones and in the outer decollement zone this article is protected by copyright all rights reserved

rates and mechanics of rapid frontal accretion along the very obliquely convergent southern hikurangi margin new zealand analysis of seismic reflection profiles swath bathymetry side scan sonar imagery and sediment samples reveal the three dimensional structure morphology and stratigraphic evolution of the central to southern hikurangi margin accretionary wedge which is developing in response to thick trench fill sediment and oblique convergence between the australian and pacific plates a seismic stratigraphy of the trench fill turbidites and frontal part of the wedge is constrained by seismic correlations to an already established stratigraphic succession nearby by coccolith and foraminifera biostratigraphy of three core and dredge samples and by estimates of stratigraphic thicknesses and rates of accumulation of compacted sediment structural and stratigraphic analyses of the frontal part of the wedge yield quantitative data on the timing of inception of thrust faults and folds on the growth and mechanics of frontal accretion under variable convergence obliquity and on the amounts and rates of horizontal shortening the data place constraints on the partitioning of geological strain across the entire southern hikurangi margin the principal deformation front at the toe of the wedge is discontinuous and represented by right stepping thrust faulted and folded ridges up to 1 km high which develop initially from discontinuous protothrusts in the central part of the margin near 41 s where the convergence obliquity is 50 orthogonal convergence rate is slow 27 mm yr and about 75 of the total 4 km of sediment on the pacific plate is accreted frontally the seismically resolvable structures within 30 km of the deformation front accommodate about 6 km of horizontal shortening at least 80 of this shortening has occurred within the last 0 4 0 1 m y at an average rate of 12 3 mm yr this rate indicates that the frontal 30 km of the wedge accounts for about 33 55 of the predicted orthogonal contraction across the entire plate boundary zone despite plate convergence obliquity of 50 rapid frontal accretion has occurred during the late quaternary with the principal deformation front migrating seaward up to 50 km within the last 0 5 m y i e at a rate of 100 km m y the structural response to this accretion rate has been a reduction in wedge taper and consequently internal deformation behind the present deformation front near the southwestern termination of the wedge where there is an along the margin transition to continental transpressional tectonics the convergence obliquity increases to 56 and the orthogonal convergence rate decreases to 22 mm yr the wedge narrows to 13 km and is characterized simply by two frontal backthrusts and landward verging folds these structures have accommodated not more than 0 5 km of horizontal shortening at a rate of 1 mm yr which represents 5 of the predicted orthogonal shortening across the entire plate boundary in southern north island the landward vergent structural domain may represent a transition zone from rapid frontal accretion associated with low basal friction and high pore pressure ratio in the central part of the margin to the northern south island region where the upper and lower plates are locked or at least very strongly coupled

tracking repeated subduction of the hikurangi plateau beneath new zealand abstract the hikurangi plateau has been subducted beneath new zealand twice firstly at ca 100 ma during n s convergence with gondwana and currently during e w convergence between the pacific and australian plates here we use a nationwide 3 d seismic velocity model derived from seismic tomography studies and seismicity relocated with this model to determine the location of the subducted western and southern edges of the plateau in the hikurangi subduction zone in the north island and northern south island we identify the western edge in the 37 140 km depth range based on the distribution of seismic velocities in the top of the subducted pacific plate changes in the thickness of the dipping seismic zone and steepening of the subducted plate downdip of the buoyant plateau in the central south island where the hikurangi plateau is subducting for a second time the plateau dips less steeply its southern edge is well defined by the collision of the delaminated lower crust of the plateau with the northern fiordland subduction zone where it bends the younger subducted australian plate to vertical the hikurangi plateau was originally rifted from the ontong java plateau and the subducted portions of the hikurangi plateau identified here fill a gap in reconstructions of this large igneous province

structure of a growing accretionary prism hikurangi margin new zealand the hikurangi margin of eastern north island new zealand represents the feather edge of the indian plate at its convergent boundary with the subducting pacific plate a migrated seismic reflection profile across this margin clearly displays the structural evolution of an accretionary prism a 25 km wide band of protothrusts is delineated between the toe of the slope and a converging seamount this illustrates an early stage in the seaward propagation of a deformation front landward tilted trench slope basins are separated by ridges that have clearly defined thrusts which appear to sole out at a decollement the decollement continues at an angle of only 3 beneath the 150 km wide margin to a depth of 14 km near the coast where it coincides with an onshore zone of high seismicity

synconvergent ductile flow in variable strength continental crust numerical models with application to the western grenville orogen 1 we present results from numerical models for a convergent orogen with laterally variable lower crustal strength representing a simplified orogenic system in which a strong craton flanked by progressively weaker terranes collides with another continent with progressive convergence crustal thickening and thermal relaxation lower crust becomes decoupled from upper and middle crust forming a ductile orogenic infrastructure beneath a stronger superstructure collision with strong external crust results in uplift and expulsion of ductile nappes from the orogenic core creating allochthonous terranes overlying a lower crustal indentor the extent of transport and exhumation of lower crustal nappes over the indentor reflects the amount of convergence and the erosion rate the western grenville orogen displays across strike variations in age tectonic history and protolith association suggesting a systematic variation in precollision crustal strength the laurentian craton margin and accreted terranes were variably reworked at synorogenic depths of 25 35 km during the ottawan orogeny deformation propagated from younger monocyclic rocks in the southeast into older polycyclic rocks flanking the craton on the northwest a comparison between numerical model results and crustal scale cross sections from the georgian bay and montreal val d or transects shows close correspondence between crustal structure and model geometry this indicates that the models produce geologically realistic results and provides a context for interpreting the tectonic evolution of the western grenville orogen contrasts between the results of homogeneous channel flow models and the present ductile nappe models suggest that the effects of different styles of ductile flow can be distinguished in the geologic record

current controlled sediment deposition from the shelf to the deep ocean the cenozoic evolution of circulation through the sw pacific gateway the circulation of cold deep water is one of the controlling factors of the earth s climate forty percent of this water enters the world ocean through the southwest pacific as a deep western boundary current dwbc flowing northwards at bathyal to abyssal depths east of the new zealand microcontinent south of latitude 50 s the dwbc is intimately linked with the antarctic circumpolar current acc which is the prominent force for the shallow water circulation the pacific dwbc is presently the largest single contributor of deep ocean water and deciphering its evolution is of fundamental importance to understanding ocean and climate history and global ocean hydrography the evolution of the dwbc system and of related circum antarctic currents has taken place since 30 25 ma when plate movements created the first oceanic gaps south of australia and south america the stratigraphic record preserved in sediment drifts of the southwest pacific in eastern new zealand is the best available for deciphering the neogene history of southern ocean water masses and of the circulation of the acc dwbc and their precursor systems major current activity commenced on the new zealand margin in the late eocene or early oligocene hoiho drift early acc and was widespread by the mid late oligocene marshall paraconformity and weka pass limestone drift acc during the neogene the eastern south island continental shelf built seawards by accretion at its outer edge of large miocene current drifts up to tens of kilometres long and hundreds of metres thick canterbury drifts also commencing in the mid cenozoic but in depths 2000 m the dwbc emplaced large deep water sediment drifts rates of drift deposition accelerated considerably in the late neogene when climatic change and particularly glacial sea level falls caused the delivery of large volumes of turbiditic sediment into the path of the dwbc via the bounty and hikurangi channels

the lithospheric geodynamics of plate boundary transpression in new zealand initiating and emplacing subduction along the hikurangi margin and the tectonic evolution of the alpine fault system abstract in contrast to the normal wilson cycle sequence of subduction leading to continental collision and associated mountain building the evolution of the new zealand plate boundary in the neogene reflects the converse initially a period of continental convergence that is followed by the emplacement of subduction plate reconstructions allow us to place limits on the location and timing of the continental convergence and subduction zones and the migration of the transition between the two plate boundary regimes relative plate motions and reconstructions since the early to mid miocene require significant continental convergence in advance of the emplacement of the southward migrating hikurangi subduction a sequence of tectonism seen in the present plate boundary geography of hikurangi subduction beneath north island and convergence in the southern alps along the alpine fault in contrast to a transition from subduction to continental convergence where the leading edge of the upper plate is relatively thin and deformable the transition from a continental convergent regime with its associated crustal and lithospheric thickening to subduction of oceanic lithosphere requires substantial thinning removal of upper plate continental lithosphere to make room for the slab the simple structure of the wadati benioff zone seen in the present day geometry of the subducting pacific plate beneath north island indicates that this lithospheric adjustment occurs quickly associated with this rapid lithospheric thinning is the development of a series of ephemeral basins younging to the south that straddle the migrating slab edge based on this association between localized vertical tectonics and slab emplacement the tectonic history of these basins records the effects of lithospheric delamination driven by the southward migrating leading edge of the subducting pacific slab although the new zealand plate boundary is often described as simply two subduction zones linked by the transpressive alpine fault in actuality the present is merely a snapshot view of an ongoing and complex evolution from convergence to subduction

using laterally compatible cross sections to infer fault growth and linkage models in foreland thrust belts abstract we investigate changes in shortening displacement and fold geometry to understand the detailed along strike structural variation within fold thrust belts and infer thrust growth and linkage mechanisms field observations from the vercors in se france are used to characterise deformation style in the region parallel cross sections are constructed analysed and used to create shortening and thrust displacement profiles from the northern to southern vercors sections show changes in structural style and shortening accommodation from thrust dominated in the north to fold dominated in the south the total shortening distance in the vercors does not change significantly along strike 3400 4650 m however displacements along individual thrust zones do vary significantly and displacement profiles show a range in displacement gradients 16 107 m km despite relatively simple shortening patterns in the vercors sections show a more complex 3d internal structure of the fold thrust belt thrust displacements and geometries suggest both large scale thrust zones and small scale thrusts are soft linked transferring displacement along strike through transfer zones short soft linked thrust segments indicate an intermediate stage of thrust growth and linkage well documented for normal fault systems which form prior to the formation of thrust branches and hard linked displacement transfer

strain partitioning between structural domains in the forearc of the hikurangi subduction zone new zealand the pacific plate obliquely converges with the australian plate at latitude 39 50 s along the hikurangi margin off the east coast of the north island of new zealand an extensive and youthful subaerially exposed forearc on the east coast of the north island in the hawke s bay area provides the opportunity to document contemporaneous forearc deformation in this obliquely convergent margin setting geologic mapping and analysis of strain at both mesoscale and megascale indicates that strain is partitioning into domains of extension contraction and strike slip the domains are elongate and trend parallel to the margin measurements of net shortening and transcurrent slip in the forearc show that the obliquely convergent motion is transferred across the plate interface deformation rates calculated for the past 1 2 m y for structures in all six forearc domains account for 50 70 of the margin parallel motion required by pacific australian plate convergence and about 6 of the plate motion perpendicular to the plate boundary at the surface in the forearc this obliquely convergent motion is manifest not by transpressional faults but rather by paired structural domains that consist of a strike slip fault zone and an accompanying contractional fault and fold zone on the trenchward side there are two such transcurrent faulting and contraction couplets one where the backstop daylights at the arcward edge of the forearc and another couplet trenchward of a relatively undisturbed forearc basin the small amount of shortening relative to strike slip in the onshore part of the forearc suggests that shortening perpendicular to the plate boundary may be concentrated offshore and that most of the component of plate motion perpendicular to the plate boundary may be accommodated by slip along the subduction zone megathrust

oblique back arc rifting of taupo volcanic zone new zealand taupo volcanic zone tvz is a back arc rift innorth island new zealand its geometry andkinematics are investigated using shaded reliefimages field examination of faults and offset streamchannels the results show that tvz trends nne is 250 km long by hikurangi margin in the north island of new zealand 20 km wide and consists of fivesegments extension is principally manifest as steeplydipping 60 90 normal faults parallel to tvz these in the last 300 kyr have experienced acomponent of dextral shear tvz is therefore anoblique back arc rift the dextral shear is 37 of thetotal displacement which for previously estimatedspreadingrates 7mm yr correspondsto 2 6mm yr thisvalueissimilartopreviousestimatesofthedextralshear from the back arc to the forearc domains in thenorthisland distributeddextralshearacrosstvzthussuggests that strain partitioning across the plateboundary at latitudes of tvz is less significant thanpreviously thought

influence of syntectonic sedimentation on thrust wedges in analogue models scaled analogue sandbox models have been used to simulate the growth of coulomb thrust wedges that include syntectonic sedimentation during thrusting increases in the syncontractional sedimentation rate dramatically change the shape of the coulomb thrust wedge decreasing the number of thrust slices the internal shortening and the critical taper of the wedge thrust trajectories change from ramp flat to sigmoidal with increased syncontractional sedimentation the analogue models show many similarities to thrust fault geometries in accretionary prisms and foreland fold and thrust belts in which thrust slices prograded into basins with active sedimentation

fast teleconnections to the tropical atlantic sector from atlantic thermohaline adjustment 1 we examine the first decade of adjustment of the north atlantic climate following an abrupt freshening of the high north atlantic and resulting slowdown of the atlantic meridional overturning circulation amoc in a coupled model with reference to previously proposed teleconnection mechanisms after an initial ocean driven cooling at the subtropical subpolar gyre boundary subsequent equatorward progression is dominated by an atmosphere surface ocean mechanism driving evaporative cooling in the tropical north atlantic and resulting in an anomalous southward itcz displacement by year 2 the tropical cooling is countered by fast ocean baroclinic adjustment to the reduced overturning that increases the volume of tropical surface waters as well as ocean circulation changes to the increased northeasterly trades however it is the atmosphere surface ocean teleconnection that explains the hemispheric asymmetric nature of the tropical atlantic surface climate impact to amoc slowdown underlining its crucial importance in high to low latitude teleconnections

sahke geophysical transect reveals crustal and subduction zone structure at the southern hikurangi margin new zealand 1 the seismic array hikurangi experiment sahke investigated the structure of the forearc and subduction plate boundary beneath the southern north island along a 350 km transect tomographic inversion of first arrival travel times was used to derive a well resolved 15 20 km deep p wave image of the crust the refracted phases and migrated reflection events image subducting slab geometry and crustal structure in the west australian plate moho depth decreases westward across the taranaki fault system from 35 to 28 30 km in the east subducted pacific plate oceanic crust is recognized to have a positive velocity gradient but becomes less distinct beneath the tararua ranges where the interface increases in dip at about 15 km depth from 15 this bend in the subducted plate is associated with vertical clusters in seismicity splay fault branching and low velocity high attenuation material that we interpret to be an underplated subduction sedimentary channel we infer that a step down in the decollement transfers slip on the plate interface at the top of a subduction channel to the oceanic crust and drives local uplift of the tararua ranges reflections from the wairarapa fault show that it is listric and soles into the top of underplated sediments which in turn abut the moho of the overriding plate at 32 km depth near the downdip end of the strongly locked zone the change in dip of the hikurangi subduction interface is spatially correlated with the transition from geodetically determined locked to unlocked areas of the plate interface

late cenozoic exhumation model of new zealand impacts from tectonics and climate abstract late cenozoic convergence between the australian and pacific plates has led to extensive crustal deformation and exhumation in new zealand over the past five decades the convergence associated exhumation history of the palaeozoic mesozoic new zealand basement has been studied using various thermochronometric techniques here we compile 992 published ages and invert them to estimate the temporal and spatial variation in exhumation rates since 25 ma which we then interpret with a plate tectonic reconstruction model the results reveal widespread increases in the exhumation rates at 6 4 ma a time correlated with accelerations in the relative plate motion the absolute increases in exhumation rates are however not uniformly distributed over new zealand since the plio pleistocene the inferred models suggest variable response of exhumation to global cooling in the non glaciated eastern north island the hikurangi subduction margin the million year average exhumation rates have remained relatively low 5 km myr have been observed in the collision zone of the central southern alps of south island where both tectonic deformation and precipitation rates are highest in fiordland the puysegur subduction margin despite the weak crustal deformation the exhumation rates have been high 0 5 3 km myr which we suggest is due to intensified glacial erosion our findings highlight the determining role of tectonics in setting up the regional exhumation pattern but both strong tectonic deformation and efficient erosion are required to maintain rapid exhumation rates the influence of climate on mountain erosion can only be distinguished in regions under slow to mediate exhumation

variation of the north atlantic subtropical high western ridge and its implication to southeastern us summer precipitation variations of the north atlantic subtropical high nash western ridge and their implication to the southeastern united states se us summer precipitation were analyzed for the years 1948 2007 the results show that the movement of the nash western ridge regulates both moisture transport and vertical motion over the se us especially in the last three decades during which the ridge moved westward towards the american continent when the nash western ridge is located southwest sw of its mean climate position excessive summer precipitation is observed due to an enhanced moisture transport in contrast when the western ridge is located in the northwest nw a precipitation deficit prevails as downward motion dominates the region composite analysis indicates that sw ridging results mainly from the nash center s intensification whereas nw ridging is likely caused by stationary wave propagation from the eastern pacific us western coast in recent decades both the sw and nw ridge positions have been observed to increase in frequency our results suggest that the increase in the sw ridging consistently follows the nash s intensification associated with anthropogenic forcing as projected by coupled climate models however the increased frequency of nw ridging tends to follow the positive pacific decadal oscillation pdo index thus the enhanced variability in the se us summer precipitation in recent decades might be a combined result of anthropogenic forcing and internal variability of the climate system results suggest that as anthropogenic forcing continues to increase the se us will experience more frequent wet summers and an increase in the frequency of dry summers during positive pdo phases

late cenozoic evolution and earthquake potential of an active listric thrust complex above the hikurangi subduction zone new zealand in the center of the frontal wedge of the hikurangi subduction zone new zealand mahia peninsula and its submarine continuation lachlan ridge are being uplifted and folded above an active landward dipping thrust fault complex that is 80 km long high quality marine seismic reflection profiles reveal complex deformation of a cretaceous to holocene sedimentary section and enable a detailed analysis of the stratigraphy structural evolution deformation rates and future earthquake potential the structural analysis is facilitated by uplifted marine terraces on mahia peninsula and by 14 submarine unconformities in the hanging wall sequence five of which are correlated across the eroded crest of lachlan ridge and into the footwall basin the ages of the unconformities are determined by seismic ties to an offshore exploration well onshore outcrops on the peninsula and seabed samples dated by pollen coccolith nannoflora and foraminifera biostratigraphy nine regional quaternary unconformities which developed in response to eustatic fluctuations in sea level and are not older than ca 1 ma are correlated with oxygen isotope stages in equatorial pacific ocean drilling project core 677 the ages of fault growth strata and progressive restorations of deformed stratigraphy indicate that lachlan ridge developed during three phases of deformation since subduction of the pacific plate commenced beneath the australian plate in the early miocene these include an initial phase of thrust faulting a subsequent phase dominated by extensional faulting and the current mainly pleistocene to holocene phase of structural inversion reactivated listric thrust faulting and folding early to middle miocene thrusts in the deeper core of the complex developed out of sequence by sequentially stepping up into the hanging wall section creating an imbricate fan with emerging thrust tips now buried within the forelimb basin in the middle miocene early pliocene listric extensional faults developed in the active thrust wedge possibly as a result of substantial relief on the subducted pacific plate and controlled the development of lachlan basin to the west of the ridge the principal active thrust is the lachlan fault a listric extensional detachment reactivated to accommodate thrust movement and consisting of at least three right stepping segments depth converted seismic profiles indicate that the fault dips westward at 15 20 6 8 km beneath the western flank of lachlan ridge and steepens to 55 70 or even steeper in the upper 1 2 km of section beneath the eastern flank syninversion pleistocene fault growth strata on both flanks of the associated anticline provide an exceptional record of progressive fold limb rotation resulting from the listric fault geometry a geometric analysis of the fault growth strata and deformed terraces was used to derive a maximum dip slip displacement rate of as fast as 3 0 6 5 mm yr the implied shortening rate of 2 6 6 3 mm yr represents 8 20 of the total 31 mm yr of orthogonal plate convergence across this part of the upper plate of the hikurangi subduction zone the top of the pre fault growth paleogene section reveals as much as 5 8 1 5 km of vertical separation in the north decreasing to 30 50 of this value in the south temporal 10 3 10 6 yr and spatial 10 3 10 4 m of strike length variations in vertical deformation rate have occurred during the past 1 m y maximum rates occurred in the holocene and middle quaternary a long term increase in vertical separation rate on all segments during the pleistocene largely reflects a change in thrust kinematics associated with structural inversion the relatively greater increase in uplift rate on the northern part of the fault during the past 1 m y could be related to the possibility that a subducted seamount lies 10 km beneath the peninsula estimates of earthquake source parameters incorporating paleoseismic uplift data from mahia peninsula indicate a potential moment magnitude of up to m w 7 6 8 0 for an earthquake that ruptures all three segments of the lachlan fault the average recurrence interval for such events is estimated to be 615 2333 yr which is consistent with a mean recurrence interval of 1062 yr for four late holocene earthquakes thus the uplift and folding of mahia peninsula and lachlan ridge results from coseismic displacements on a major listric thrust fault that ruptures the upper plate frequently in association with large magnitude earthquakes

annular modes in global daily surface pressure annular modes are patterns characterized by synchronous fluctuations in surface pressure of one sign over the polar caps and the opposite sign at lower latitudes the southern annular mode sam and northern annular mode nam also called the arctic oscillation patterns are the leading empirical orthogonal functions eofs of slowly varying hemispheric cold season sea level pressure anomalies deviations from climatology daily indices of the sam and nam are a measure of the similarity between surface pressure anomaly patterns and the annular modes here it is shown that the first two eof time series of daily global year round zonally averaged surface pressure are nearly identical to the sam and nam indices together they account for more than 57 of the daily variance of zonally averaged surface pressure the sam and nam patterns extend through the tropics well into the opposite hemispheres fluctuations of the sam and nam indices are accompanied by interhemispheric transfer of mass

the signature of the annular modes in the tropical troposphere the extratropical annular modes are coupled with a distinct pattern of climate anomalies that spans the circulation of the tropical troposphere the signature of the annular modes in the tropical troposphere exhibits a high degree of equatorial symmetry it is associated with upper tropospheric zonal wind anomalies centered about the equator midtropospheric temperature anomalies located 208n and 208s and opposing mean meridional circulation anomalies that span the subtropics of both hemispheres the linkages between the annular modes and the tropical circulation are only evident during the cold season months and are most robust in association with the northern hemisphere annular mode nam the coupling between the annular modes and the circulation of the tropical troposphere is consistent with forcing by waves originating at extratropical latitudes both annular modes are characterized by anomalies in the eddy momentum flux convergence at tropical latitudes that act to reinforce the changes in the tropical wind and temperature fields the most pronounced tropical anomalies lag indices of the annular modes by 2 weeks and are found over the eastern tropical pacific where climatological westerlies permit extratropical waves to propagate into the deep tropics the linkages between the nam and the tropical tropospheric circulation are

impact of synkinematic sedimentation on the geometry and dynamics of compressive growth structures insights from analogue modelling analogue sandbox models have been set up to study the impact of synkinematic deposits on the geometry and evolution of single thrusts and folds according to different sedimentation modes a slow or rapid sedimentation rate that is constant or changing in space and time and rheological profiles thin or thick sedimentary series with or without a basal decollement level a first series of experiments documents the influence of synkinematic deposits according to their sedimentation rate and the rheology of the prekinematic materials a second series investigates the influence of changes in the sedimentation rate through time a third one considers the influence of changes in the sedimentation rate in space all these experiments suggest that the geometry and evolution of single compressive growth structures vary according to the sedimentation rate the number and dip of their frontal thrust segments change with the ratio r between the sedimentation rate at the footwall of the faults and the uplift rate of their hanging wall the latter is then more or less uplifted depending on the dip of the thrusts as a result the overall structure has either a fault bend fold or a fault propagation fold geometry these rules are verified when the ratio r changes in space or through time in addition the rheological profile of the models also affects the geometry and evolution of compressive growth structures their structural style as well as the synsedimentary splitting and steepening of the associated thrusts varies according to the occurrence and strength of the brittle and ductile layers according to this modelling study the ratio r and its changes in space and time along with the rheology of the deformed materials are key parameters to better understand the geometrical and kinematical complexities of natural growth thrusts and folds and to improve their interpretation

submarine channel response to intrabasinal tectonics the influence of lateral tilt lateral tilting is a common deformation style in extensional basins its influence on subaerial channels is to a degree understood and may be significant controlling the style of channel development and the resultant sand body architecture growth faulting and lateral tilting in turbidite channel systems have been demonstrated from three dimensional seismic data but the resultant architecture of channels within these settings has not yet been documented in the carboniferous of northern england a sand rich slope channel developed within a basin undergoing late stage extension underwent progressive and unidirectional migration toward a topographic low on a laterally tilting block the resultant sandstone body is wedge shaped in cross section and composed dominantly of sigmoidal lateral accretion deposits the channel returned to an axial course before undergoing lateral migration in the same direction creating a multistory multilateral channel sandstone body the repeated unidirectional migration combined with evidence of syndepositional deformation suggests that active tectonism strongly influenced channel evolution and deposition a model of submarine channel evolution in extensional basins is presented in systems where large displacements occur the channel system may avulse creating isolated sand ribbons which are connected updip where the lateral dip is always more influential than the regional dip the system may pond in the hanging wall syncline the model is compared to a subsurface channel within the pliocene of the nile delta slope which was influenced by syndepositional fault movement application of the outcrop derived model allows some simple architectural interpretations to be made

variation in syn subduction sedimentation patterns from inner to outer portions of deep water fold and thrust belts examples from the hikurangi subduction margin of new zealand

the role of syntectonic sedimentation in the evolution of doubly vergent thrust wedges and foreland folds this paper shows the evolution of time constrained two dimensional scaled analogue models of doubly vergent thrust systems in the presence of syntectonic sedimentation two sets of experiments were considered 1 the addition of a syntectonic layer composed of a polymer and overlying sand in the prowedge and 2 the addition to the previous condition of a progradational sedimentary load results from the first set of experiments indicate that the foreland fold and thrust belt has a strong relationship with the competence of the syntectonic layers when the competence is low the deformation produces tight asymmetric detachment folds as the competence increases the fold and thrust belt shows break trough folds with longer and better defined foreland vergence results from the second set of experiments indicate that structural vergence is determined by the sense of progradation of the syntectonic layers and in the case of strong aggradation at the prowedge extension and reactive diapirism form contemporaneously with the contraction three end members are proposed for mountain front thrust systems formed in the presence of syntectonic polymer and sand sedimentation 1 outcropping fold and thrust belt sequence in the case of no syntectonic sedimentation 2 long displacement blind thrust sheets in the case of under filled basins and 3 short displacement blind thrust sheets in the case of over filled basins all results indicate that ductile units at the base of syntectonic layers increase the displacement of the underlying frontal thrusts at the prowedge and reduce the critical taper results also indicate that at very high sedimentary rates and hyper critical taper conditions the prowedge collapses conclusions drawn from this research may be applied as an analogue to foreland evolution and to evaluate hydrocarbon generation migration and entrapment in thrust belts in areas where seismic imaging is generally poor

extensional deformation across an active margin relations with subsidence uplift and rotations the hikurangi subduction new zealand on the basis of field studies in the forearc domain of the hikurangi subduction margin in the eastern north island of new zealand we analyze the evolution of the subduction since its onset 25 myr ago analyses of brittle deformation within this forearc domain have revealed evidence of extensional deformation contemporaneous with the subduction of the pacific plate beneath the north island the type and origin of extensional deformation during the development of the active margin are discussed the problem is crucial because this forearc domain was previously considered as having undergone almost continuous compression during the late cenozoic two distinct events of late cenozoic extensional deformation are identified the youngest one is quaternary in age it affects limited areas where important uplift prevails the orientation of extensional paleostress axes is perpendicular to that of uplift axes hence consistent with the classical hypothesis of gravitational collapse affecting the upper part of the margin of particular interest is the older extensional event middle late miocene in age it affected most of the forearc domain during a long time span that was also characterized by widespread margin subsidence some structures attributed to this event are syndepositional including rollover structures and there are mainly high angle normal faults that affect not only the miocene sediments but also the pre miocene basement the orientations of paleostress axes obtained by inversion of fault data sets are multiple after corrections taking into account the rotational history of the margin during the late cenozoic they are found to be generally consistent with two major trends because these extensional structures developed throughout a long period of the margin subsidence it is proposed that they reflect the process of tectonic erosion that affected the hikurangi active margin during the middle and late miocene between about 15 and 5 myr ago

tectonic and geological framework for gas hydrates and cold seeps on the hikurangi subduction margin new zealand the imbricated frontal wedge of the central hikurangi subduction margin is characteristic of wide ca 150 km poorly drained and over pressured low taper not vert similar 4 thrust systems associated with a relatively smooth subducting plate a thick trench sedimentary sequence not vert similar 3 4 km weak basal decollement and moderate convergence rate not vert similar 40 mm yr new seismic reflection and multibeam bathymetric data are used to interpret the regional tectonic structures and to establish the geological framework for gas hydrates and fluid seeps we discuss the stratigraphy of the subducting and accreting sequences characterize stratigraphically the location of the interplate decollement and describe the deformation of the upper plate thrust wedge together with its cover sequence of miocene to recent shelf and slope basin sediments we identify approximately the contact between an inner foundation of deforming late cretaceous and paleogene rocks in which widespread out of sequence thrusting occurs and a 65 70 km wide outer wedge of late cenozoic accreted turbidites although part of a seamount ridge is presently subducting beneath the deformation front at the widest part of the margin the morphology of the accretionary wedge indicates that frontal accretion there has been largely uninhibited for at least 1 2 myr this differs from the offshore hawkes bay sector of the margin to the north where a substantial seamount with up to 3 km of relief has been subducted beneath the lower margin resulting in uplift and complex deformation of the lower slope and a narrow 10 20 km active frontal wedge five areas with multiple fluid seep sites referred to informally as wairarapa uruti ridge omakere ridge rock garden and builders pencil typically lie in 700 1200 m water depth on the crests of thrust faulted anticlinal ridges along the mid slope uruti ridge sites also lie in close proximity to the eastern end of a major strike slip fault rock garden sites lie directly above a subducting seamount structural permeability is inferred to be important at all levels of the thrust system there is a clear relationship between the seeps and major seaward vergent thrust faults near the outer edge of the deforming cretaceous and paleogene inner foundation rocks this indicates that thrust faults are primary fluid conduits and that poor permeability of the cretaceous and paleogene inner foundation focuses fluid flow to its outer edge the sources of fluids expelling at active seep sites along the middle slope may include the inner parts of the thrust wedge and subducting sediments below the decollement within anticlinal ridges beneath the active seep sites there is a conspicuous break in the bottom simulating reflector bsr and commonly a seismically resolvable shallow fault network through which fluids and gas percolate to the seafloor no active fluid venting has yet been recognized over the frontal accretionary wedge but the presence of a widespread bsr an extensive protothrust zone 200 km by 20 km in the hikurangi trough and two unconfirmed sites of possible previous fluid expulsion suggest that the frontal wedge could be actively dewatering there are presently no constraints on the relative fluid flux between the frontal wedge and the active mid slope fluid seeps article outline

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

neogene history of the deep western boundary current at rekohu sediment drift southwest pacific odp site 1124 abstract odp site 1124 located 600 km east of the north island of new zealand records post middle oligocene variations in the pacific deep western boundary current dwbc and new zealand s climatic and tectonic evolution sediment parameters such as terrigenous grain size flux magnetic fabric and non depositional episodes are used to interpret dwbc intensity and antarctic climate interpretations of dwbc velocities indicate that the antarctic circumpolar current reached modern intensities at 23 ma as the tectonic seaways expanded completing the thermal isolation of antarctica periods of more intense bottom water formation are suggested by the presence of hiatuses formed under the dwbc at 22 5 17 6 16 5 15 and 14 11 ma the oldest interval of high current intensity occurs within a climatically warm period during which the intensity of thermohaline circulation around antarctica increased as a result of recent opening of circum antarctic gateways the younger hiatuses represent glacial periods on antarctica and major fluctuations in the east antarctic ice sheet whereas intervals around the hiatuses represent times of relative warmth but with continued current activity the period between 11 to 9 ma is characterized by conditions surrounding a high velocity dwbc around the time of the formation and stabilization of the west antarctic ice sheet the increased terrigenous input may result from either changing antarctic conditions or more direct sediment transport from new zealand the pacific dwbc did not exert a major influence on sedimentation at site 1124 from 9 ma to the present the late miocene to pleistocene sequence is more influenced by the climatic and tectonic history of new zealand despite the apparent potential for increased sediment supply to this site from changes in sediment channeling increasing rates of mountain uplift and volcanic activity terrigenous fluxes remain low and constant throughout this younger period

turbidite deposition in five miocene bathyal formations along an active plate margin north island new zealand with notes on styles of deposition at the margins of east coast bathyal basins abstract five miocene turbidite formations whakataki oldest greenhollows tanawa pakowhai waihoki youngest in northern wairarapa north island new zealand are described the whakataki formation widespread on the east coast of wairarapa formed at the onset of the kaikoura orogeny earliest miocene to recent on a deep sea plain whereas younger formations were deposited in a part of a long lived slope basin the tawhero basin situated between the greenhill anticline in the west and the tinui fault in the east the whakataki and the mud rich tanawa formations were probably largely fan deposited whereas the greenhollows pakowhai and waihoki formations are largely non fan deposited the mid miocene tanawa formation has turbidites which invariably lack sole structures even in areas close to the mouths of small submarine channels canyons i e in proximal locations and contains sandstone mudstone couplets usually with t b or t c basal this is thought to indicate that the formation was largely deposited from low velocity turbidity currents the early miocene greenhollows formation and the latest miocene waihoki formation are composed of couplets containing thick sandstone parts and they represent sheeted high density turbidity currents features recognised within miocene northern wairarapa deep sea turbidite formations are 1 fan and non fan styles of deposition 2 deposition from high or low velocity turbidity currents 3 thick turbidites having a sheet like distribution in three of the formations 4 deposition of turbidites at mid or upper bathyal depths 5 syndepositional deformation and 6 the small size of the basin in which the four youngest formations were deposited little sediment is deposited at the margin of slope basins where there is substantial syndepositional uplift whereas at the margins of turbidite basins formed in foreare areas there is thick massive upper bathyal slope deposited siltstone

temporal stability of deformation rates comparison of geological and geodetic observations hikurangi subduction margin new zealand abstract we examine how well contemporary horizontal velocity fields from global positioning system gps geodetic measurements describe long term deformation rates million year rates of extension shortening strike slip and vertical axis rotations are compared with modelling of gps velocities from the last 10 15 years in the hikurangi subduction margin new zealand within measurement uncertainties of mainly 50 the rates of deformation and vertical axis rotations for each time interval are usually indistinguishable the comparable deformation rates are consistent with the notion of near constant rates since 1 5 ma during this time oblique relative plate motion was partitioned with the majority 85 of margin normal motion accommodated on the plate interface and most 60 margin parallel motion by strike slip faulting and vertical axis rotations in the upper plate prior to 1 5 ma gps velocities cannot be reliably used to describe deformation and rotations of the hikurangi margin because at this time the taupo rift commenced opening the boundary between raukumara and wairoa rotational domains was abandoned and the rates of upper plate shortening increased the broad compatibility of gps and geological deformation and rotation rates since 1 5 ma suggests that the build up of contemporary elastic strains in the north island measured by gps is largely uniform for much of the duration of each seismic cycle the good agreement between the gps and geological deformation rates in the north island is consistent with the view that contemporary elastic strains will mainly be converted to permanent dip slip on the subduction thrust and to displacement on upper plate faults during future large magnitude earthquakes

neogene evolution of lower trench slope basins and wedge development in the central hikurangi subduction margin new zealand detailed analysis of the stratigraphic architecture and deformation of lower trench slope sedimentary basins permits the tectonic evolution of subduction margins to be constrained this study utilises offshore seismic reflection profiles and onshore outcrop data to examine the entire lower trench slope of the hikurangi subduction margin in the eastern north island new zealand our results constrain the main spatial and temporal changes of facies and sedimentary units since about 25 ma we demonstrate that the geometries and locations of miocene to quaternary sedimentary basins are controlled by tectonic activity and reflect stages of subduction wedge development four types of sedimentary basins have been recognized 1 flysch basins with local olistostromes at the front of seaward propagating thrust sheets 2 5 10 km wide turbidite rich trench slope basins between uplifting structural ridges i e anticlines associated with shortening within 100 km of the subduction front at the seafloor 3 30 40 km wide trench slope basins associated with an upslope increase in thrust and ridge spacing and 4 mixed siliciclastic carbonate shelves formed in association with margin uplift after filling of the wider 30 40 km trench slope basins the lateral and vertical successions of basin geometries and sedimentary infill are consistent with the overall progressive uplift of the subduction wedge formation of some of the wide trench slope basins may be accompanied by significant local subsidence and normal faulting synchronous with active shortening at the subduction front margin wide normal faulting during the middle late miocene may have formed due to upslope collapse related to tectonic erosion all of the basins studied contain major unconformities at their base and top with basin strata deposited over about 2 8 myr the short life span of these lower trench slope sedimentary basins is consistent with a succession of short paroxysmal tectonic episodes rather than continuous deformation for the duration of subduction stratigraphic discontinuities within basins e g facies changes and reversal of paleo currents also record short term tectonic events c 1 2 myr on the basin bounding structures and attest to the episodic nature of upper plate deformation in response to continuous subduction beneath the active margin