reservoir compartmentalization an introduction reservoir compartmentalization the segregation of a petroleum accumulation into a number of individual fluid pressure compartments occurs when flow is prevented across sealed boundaries in the reservoir these boundaries are caused by a variety of geological and fluid dynamic factors but there are two basic types static seals that are completely sealed and capable of withholding trapping petroleum columns over geological time and dynamic seals that are low to very low permeability flow baffles that reduce petroleum crossflow to infinitesimally slow rates the latter allow fluids and pressures to equilibrate across a boundary over geological time scales but act as seals over production time scales because they prevent crossflow at normal production rates such that fluid contacts saturations and pressures progressively segregate into dynamic compartments thus reservoir compartmentalization impacts the volume of moveable produceable oil or gas that might be connected to any given well drilled in a field which restricts the volume of reserves that can be booked for that field booking of reserves is tightly regulated by government authorities because it is a key measure used by stock analysts and investors to value an oil company this places reservoir compartmentalization studies and the predictive science and technology applied to them at the heart of company valuation unexpected compartmentalization can also seriously impact the profitability of a field with more data acquisition more study more wells more time being required to produce less oil and gas than was originally anticipated in extreme cases this might even lead to early field abandonment however unexpected or misunderstood reservoir compartmentalization has been an industrywide experience for over 30 years and it is clear that there is great value in learning from past often expensive mistakes e g smith 2008 this learning process has often driven developments in geoscience engineering and related technology enabling operating companies to identify and predict new untapped volumes in old fields make general improvements to field management e g gainski et al wonham et al and apply this knowledge to other similar but lessmature fields in their portfolio reservoir compartmentalization is therefore a major uncertainty that should be accurately assessed during the appraisal of petroleum reservoirs in order to avoid unexpected compartmentalization at the production stage in the past few decades there have been major advances in data detection and surveillance methods and our geoscience and reservoir engineering approaches however reservoir compartmentalization can still be underestimated during field appraisal and can still give surprises that force a re think of the field development and production plan e g smith 2008 this is not necessarily a defect in the science or technology but rather it may also be a result of ineffectual data appraisal or discipline integration within subsurface workflows thus it is not unusual for subsurface teams to place too much emphasis on one aspect of the evidence or to make early assumptions that bias data acquisition analyses and interpretations later on for example fisher jolley 2007 point out that non existent faults or improbable fault seal capacities might be invoked to explain variable petroleum contacts and dynamic fluid pressure behaviour when an alternative or combination of factors or other unrelated explanations might be more appropriate for the data e g hydrodynamic tilting of petroleum contacts tozer borthwick research initiatives and collaborations between oil companies service groups and academic institutions vary considerably in scope and content and there is often a creative tension between the competitive advantages motivations and knowledge gaps perceived by the sponsoring companies and their research partners in addition to this the scientific insights that can be gained from the

uranium distribution as a proxy for basin scale fluid flow in distributive fluvial systems we infer system scale fluid flow in the late jurassic salt wash fluvial succession sw usa by plotting uranium deposit distribution against sedimentological data using uranium distribution as a proxy for subsurface fluid flow more than 90 of uranium deposits in the salt wash occur where sandstone forms 40 55 and sand rich channel belts form 20 50 of the succession which coincides with changes in channel belt connectivity and gross scale architecture the paucity of uranium below these cut off values suggests that fluid flow is related directly to predictable downstream fining and facies variations in distributive fluvial systems supplementary material a summary table of location data key trends and the amalgamation ratio method is available at https doi org 10 6084 m9 figshare c 2849581

tibetan tectonic evolution inferred from spatial and temporal variations in post collisional magmatism cenozoic magmatism on the tibetan plateau shows systematic variations in space and time that must be considered in models concerning tibetan tectonic evolution after the india asia collision which started in the early tertiary and terminated the gangdese arc magmatism in the lhasa terrane made of the southern tibetan plateau widespread potassium rich lavas and subordinate sodium rich basalts were generated from f50 to 30 ma in the qiangtang terrane of northern tibet subsequent post collisional magmatism migrated southwards producing ultrapotassic and adakitic lavas coevally between f26 and 10 ma in the lhasa terrane then potassic volcanism was renewed to the north and has become extensive and semicontinuous since f13 ma in the western qiangtang and songpan ganze terranes such spatial temporal variations enable us to elaborate a geodynamic evolution model which depicts when and how the indian continental lithospheric mantle started thrusting under asia by involving rollback and breakoff of the subducted neo tethyan slab followed by removal of the thickened lhasa lithospheric root we propose that only after the lithospheric removal which occurred at f26 ma could the indian mantle lithosphere have commenced its northward underthrusting and henceforth served as a pivotal control to the himalayan tibetan orogenesis consequently the tibetan plateau is suggested to have risen diachronously from south to north whereas the southern part of the plateau may have been created and maintained since the late oligocene the northern plateau would have not attained its present day elevation and size until the mid miocene when the lower part of the western qiangtang and songpan ganze lithospheres began to founder owing to the push of the underthrust indian mantle lithosphere d 2004 elsevier b v all rights reserved

weakly coupled lithospheric extension in southern tibet a b s t r a c t west east extension is a prominent tectonic feature of southern and central tibet despite ongoing north south n s convergence between india and eurasia knowledge of deep structure beneath the n s trending rifts is key to evaluating models proposed for their origin including gravitational collapse oblique convergence along the arcuate plate boundary and mantle upwelling we model direct s and moho reflected sspmp phases at teleseismic distances to constrain variations in crustal thickness across the major rifts crossed by a 900 km long w e broadband array in the lhasa terrane crustal thicknesses are 70 80 km however moho depth decreases by 10 km within a horizontal distance of 100 km west of the yadong gulu rift ygr and nyainquentanghla mountains nqtl this moho uplift taken with deep extensional focal mechanisms and reduced seismic velocity in the upper mantle suggests that asthenospheric upwelling has significantly contributed to the pattern of extension across the ygr and nqtl the 100 km separation between surface rift and moho uplift is likely enabled by partial decoupling across a ductile middle crust 2015 the authors published by elsevier b v this is an open access article under the cc by nc nd license http creativecommons org licenses by nc nd 4 0

indepth iii seismic data from surface observations to deep crustal processes in tibet 1 during the summer of 1998 active source seismic data were collected along a transect running 400 km nnw sse across the central tibetan plateau as the third phase of project indepth international deep profiling of tibet and the himalaya the transect extends northward from the central lhasa block across the jurassic bangong nujiang suture bns at 89 5 e to the central qiangtang block a seismic velocity model for the transect to 25 km depth produced by inversion of p wave first arrivals on 3000 traces shows 1 a 50 km wide region of low velocity at least 5 less than surrounding velocities extending to the base of the model at the bns 2 sedimentary cover for the southern qiangtang block that is 3 5 km thick 3 a distinct interface between sedimentary cover and qiangtang basement or underplated jurassic melange in the central qiangtang block and 4 evidence that the bangoin granite extends to a depth of at least 15 km the bns has little geophysical signature and appears unrelated to the 5 km northward shallowing of the moho which is associated with the bns in central tibet geophysical data along the main indepth iii transect show little evidence for widespread crustal fluids in contrast to the seismic bright spots found in southern tibet and to magnetotelluric evidence of fluid accumulations in eastern tibet a comparison between the global average and tibetan velocity depth functions offers constraints for models of plateau uplift and crustal thickening taken together with the weak geophysical signature of the bns these velocity depth functions suggest that convergence has been accommodated largely through pure shear thickening accompanied by removal of lower crustal material by lateral escape likely via ductile flow although we cannot resolve the details we believe lateral lower crustal flow has overprinted or destroyed evidence in the deep crust for the earlier assembly of tibet as a series of accreted terranes

receiver function imaging of crustal suture steep subduction and mantle wedge in the eastern india tibet continental collision zone abstract to understand the along strike variation of crustal deformation and tectonic processes in the india tibet continental collision zone we deployed a linear array of broadband seismic stations along 92 e to image lithospheric structure our receiver function cross section reveals a prominent negative converter dipping 20 north from 10 55 km depth below sea level almost through the whole crust beneath the southern lhasa terrane we interpret it to be a manifestation of the yarlung zangbo suture zone yzs separating the continental crust of the indian and eurasian plates this implies the hypothesized channel flows of indian middle crust extruding southwards from tibet are limited at this longitude to the southernmost portion of the lhasa terrane a positive converter consistent with previous suggestions of eclogite formation is seen about 10 15 km above the moho and continuing 50 km north of the 20 dipping yzs converter we image this positive converter continuously from 60 km south of the surface trace of the yzs to the vicinity of the jiali fault supporting the interpretation of sub horizontal underplating of tibetan crust by indian crust to 31 n at 85 e on the hi climb transect however we also show a negative mantle converter sub parallel to the crustal yzs converter from the northern limit of the underplating indian lower crust to at least 140 km depth that we interpret as the base of tibetan lithosphere overlying an asthenospheric mantle wedge based on the lithospheric structure observed in this and other studies we infer that indian mantle lithosphere currently detaches from indian lower crust at the mantle suture that is nearly 50 km south of the surface trace of the yzs at 92 e south of the mantle suture suggested by indepth transect beneath the surface trace of the yzs at 90 e and far south of the mantle suture suggested to be at the 31 n northern limit of underthrusting indian lower crust suggested by hi climb transect at 85 e a change from underplating in the west to steep subduction in the east can reconcile all these observations

continent ocean transition at the western barents sea svalbard continental margin the change in crustal type at the western barents sea svalbard margin takes place over a narrow zone related to primary rift and shear structures reflecting the stepwise opening of the greenland sea regionally the margin is composed of two large shear zones and a central rifted margin segment local transtension and transpression at the plate boundary caused the early cenozoic tectonism in svalbard and the western barents sea and might explain the prominent marginal gravity and velocity anomalies

seismic imaging of the downwelling indian lithosphere beneath central tibet a tomographic image of the upper mantle beneath central tibet from indepth data has revealed a subvertical high velocity zone from 100 to 400 kilometers depth located approximately south of the bangong nujiang suture we interpret this zone to be downwelling indian mantle lithosphere this additional lithosphere would account for the total amount of shortening in the himalayas and tibet a consequence of this downwelling would be a deficit of asthenosphere which should be balanced by an upwelling counterflow and thus could explain the presence of warm mantle beneath north central tibet

wave field continuation and decomposition for passive seismic imaging under deep unconsolidated sediments abstract the coastal plains of the central and eastern united states contain deep sections of unconsolidated to poorly consolidated sediments these sediments mask deeper crustal and upper mantle converted phases in teleseismic receiver functions through large amplitude near surface reverberations thick sediments also amplify ambient noise levels to generally reduce data signal to noise ratios removing shallow sediment wave propagation effects is critical for imaging deep lithospheric structures a propagator matrix formalism is used to downward continue the wave field for teleseismic p waves into the midcrust and then to separate the upgoing s wave field from the total teleseismic response of the p wave to expose deep sp conversions this method requires that the earth model from the surface to the reference depth be known teleseismic p wave data for the memphis tennessee station mph are analyzed using a reference station deconvolution technique to produce vertical and radial p wave transfer functions these transfer functions are modeled using a simple model parameterization for sediment structure through grid inversion the inverted earth model is incorporated into the wave field continuation and decomposition technique to estimate the upgoing s wave field at 10 km depth in the crust moho and possible deeper ps conversions are identified with this process

geological controls on seismic sequence resolution a seismic sequence analysis of the canterbury basin eastern south island of new zealand has illustrated the roles of subsidence sediment supply and current activity as controls on sequence resolution and architecture during basin evolution the rates of sediment supply and subsidence determine the background depositional regime transgressive or regressive and effectively determine the frequency response of the continental margin sedimentary section to input signals with a broad range of frequencies including eustasy a regressive progradational depositional regime and minimal current erosion favor the preservation of high frequency sequences particularly at fourth order level under less favorable conditions the record of sequences is incomplete or ambiguous such frequency response characteristics must be considered when inverting sequence records to derive the frequency of the input cyclicity and when making global comparisons of regional sequence stratigraphic studies clastic basins with simple subsidence histories and uniform or increasing rates of sediment supply develop from a transgressive phase characterized by ramplike major sequence boundaries to a mature progradational shelf phase with clinoform sequences and optimum sequence resolution the mature phase constitutes the preferred setting for sequence stratigraphic analyses

a data adaptive multiscale approach of finite frequency traveltime tomography with special reference to p and s wave data from central tibet 1 we discuss an innovation in traveltime tomography that combines wavelet based multiscale parameterization and finite frequency theory to solve two outstanding issues that inevitably arise from uneven source station distributions and from the three dimensional 3 d nature of wavefront healing how to objectively address the intrinsically multiscale nature of data coverage while simultaneously maintain model resolution at each scale level we apply the new integrated methodology to investigate 3 d variations of p and s wave speeds lnvp and lnvs beneath the himalayan tibetan orogen in particular we are able to constrain variations in the poisson s ratio via ln vp vs the formulation is naturally data adaptive resolving features at each scale only if the required data converge is available the very first long wavelength feature that emerges is a clear anomaly of high lnv that extends over more than 500 km beyond the northern edge of the lhasa terrane at places farther northward a strong negative anomaly underlies the region where recent volcanism occurs in northern tibet regions of negative ln vp vs delineate a slab like subhorizontal feature concentrated between depths of 100 250 km such characteristics are consistent with the notion that chemically refractory and therefore buoyant mantle lithosphere of the indian shield greater india has advanced subhorizontally northward far beyond the surficial bangong nujiang suture in the crust two isolated regions of low lnv each extending to depths near 100 km occur along the lunggar and the yadong gulu active rifts in southern tibet deep penetrating rifts imply that only a limited amount of horizontal displacement is being accommodated on subvertical structures

the upper cainozoic of the norwegian continental shelf correlated with the deep sea record of the norwegian sea and the north atlantic a stratigraphic framework has been developed for the cainozoic succession of the norwegian continental shelf and margin this framework is consistent for the entire margin from the central north sea to the barents sea and also facilitates a correlation with the deep sea record of the norwegian sea and north atlantic a local system mainly utilising planktonic and benthic foraminiferal assemblages and bolboforma species is developed it can be potentially used for regional stratigraphic syntheses using this framework a more precise and detailed identification and age assignments of cainozoic and in particular neogene strata can be performed several revisions of previous age assignments and a more detailed dating of the various sediment packages are presented the most complete neogene succession is recorded in the central north sea further north the succession is interrupted by an increasing number of hiati of increasing duration after a period of erosion in the late middle to early late miocene there is a marked increase in the influx of terrigenous sediment in the late miocene a period of transgression in the early pliocene resulted in strongly reduced rates of deposition and sediments of this age are preserved mainly in the central north sea a period of regression in earliest late pliocene probably resulted in erosion of most of the norwegian continental shelf with the exception of the deeper areas of the central and viking grabens this period was immediately followed in the later part of late pliocene by rapid deposition of glacially derived sediment prograding along the entire shelf in general pleistocene development is a continuation of the late pliocene evolution but is marked by more extensive erosion of the inner shelf this is inferred from the flat truncation of underlying prograding strata and the extensive build up of debris flow sediments within glacial fan depocentres the entire neogene development is closely related to the climatic evolution of high latitude regions surrounding the north atlantic and the norwegian greenland sea

discordant contrasts of p and s wave speeds across the 660 km discontinuity beneath tibet a case for hydrous remnant of sub continental lithosphere abstract using high resolution triplicate shear waveforms recorded by broadband seismic arrays we show that a corresponding anomaly of high s wave speed v s is absent where an anomaly of high p wave speed v p was recently recognized in the transition zone of the mantle tz beneath central tibet a likely cause of the discrepancy between anomalies in v p and v s is a minor amount of water in nominally anhydrous polymorphs of olivine prior to thickening by continent continent collision the tibetan mantle was part of a mantle wedge which has been hydrated during past episodes of subduction hydration of the sub continental lithospheric mantle sclm provides a natural mechanism to facilitate ductile deformation so rapid thickening of the sclm which would have been hindered by advection of cold materials can take place convective instability would then lead to removal and sinking of thickened cold sclm leaving a remnant in the tz detectable only in v p this interpretation not only is consistent with previous reconstruction of the sclm in tibet based on several types of independent data but also provides a new pathway for water to enter and be stored in the tz

quantification of a distributive fluvial system the salt wash dfs of the morrison formation sw u s a abstract recent analysis of modern aggradational continental sedimentary basins reveals that sedimentation patterns are dominated by distributive fluvial systems dfss the salt wash member of the late jurassic morrison formation has previously been described as a fan shaped fluvial system this study characterizes facies variations across the salt wash dfs to quantitatively test predicted trends in conceptual dfs models notable proximal to distal trends include a change in total thickness of the fluvial succession from 174 m to 40 m and an average grain size from coarse sand to silt while the percentage of sand decreased from 70 in the proximal region to 8 in the distal region the proportion of amalgamated channel belt deposits decreased from 67 to 0 while floodplain facies and lacustrine deposits increase 38 to 94 and 0 1 to 7 respectively a downstream decrease in average channel belt thickness 15 m to 3 8 m from thickest to thinnest and average story thickness 7 7 m to 2 3 m from thickest to thinnest is also recorded significant downstream changes in deposit architecture were also noted with proximal regions dominated by stacked channel belt deposits with a high degree of amalgamation distal deposits are dominated by floodplain muds and sheet sandstones and sparse ribbon channels with little to no amalgamation of channel deposits this study provides quantified information for an ancient dfss with the aim of providing a dataset that can be used for objective comparison between different dfss as well as providing numerical data to aid resource exploration and modelling efforts

seismic images of crust and upper mantle beneath tibet evidence for eurasian plate subduction seismic data from central tibet have been combined to image the subsurface structure and understand the evolution of the collision of india and eurasia the 410 and 660 kilometer mantle discontinuities are sharply defined implying a lack of a subducting slab beneath the plateau the discontinuities appear slightly deeper beneath northern tibet implying that the average temperature of the mantle above the transition zone is about 300 c hotter in the north than in the south there is a prominent south dipping converter in the uppermost mantle beneath northern tibet that might represent the top of the eurasian mantle lithosphere underthrusting the northern margin of the plateau

mapping crustal structure beneath southern tibet seismic evidence for continental crustal underthrusting abstract receiver function imaging along a temporary seismic array antilope 2 reveals detailed information of the underthrusting of the indian crust in southern tibet the moho dips northward from 50 km to 80 km beneath the himalaya terrane and locally reaches 85 km beneath the indus yalung suture it remains at 80 km depth across the lhasa terrane and shallows to 70 km depth under the qiangtang terrane an intra crustal interface at 60 km beneath the lhasa terrane can be clearly followed southward through the main himalaya thrust and connects the main boundary thrust at the surface which represents the border of the indian crust that is underthrusting until south of the bangong nujiang suture a mid crustal low velocity zone is observed at depths of 14 30 km beneath the lhasa and himalaya terranes probably formed by partial melt and or aqueous fluids

post cretaceous uplift events on the voring continental margin the early tertiary voring margin off central norway records several distinct uplift events that have strongly influenced the deposition and composition of cenozoic sediments and may be linked with climatic change the events constitute two types uplift as a precursor to the opening of the norwegian greenland sea and subsequent intraplate deformation the late cretaceous paleocene dynamic uplift associated with the formation of the volcanic voring margin created a main western source area for the paleogene voring basin sediments the fennoscandian epeirogenic uplift which probably began in the late oligocene and continued through the pliocene was followed by glacial rebound deep erosion of the landmass left a huge late neogene sedimentary wedge along the margin and differential loading caused regional intrabasinal arching and local diapirism

undulating moho beneath a near uniform surface of central tibet abstract we present 805 reliable estimates of crustal thickness in central tibet revealing an undulating moho beneath a near uniform surface of the highest and the largest plateau in the world our results are derived from wide angle reflections of p waves from virtual seismic sources near seismographs virtual deep seismic sounding vdss the virtual sources are produced by large earthquakes well distributed in back azimuth and we also utilize obvious changes of measured arrival times as a function of ray parameter to constrain independently bulk thickness and p wave speed of the crust about 6 3 km s so there is little trade off between the two parameters additionally we consider effects of known heterogeneities in the upper mantle in regions surrounding the hi climb linear array there is an eastward trend in addition to the previously proposed northward trend of crustal thinning respectively these trends are approximately parallel and normal to the indian mantle front imf or the northern leading edge of underthrust lithospheric mantle of india deduced from a collection of additional geophysical evidence the moho near the imf also shows large 3 d variations in depths prompting us to propose that the leading edge of intact indian lower crust or the indian crustal front icf that accompanied the underthrusting indian lithospheric mantle beneath tibet lies along the zone of disturbed moho based on results from about a dozen permanent broadband seismographs of the china national seismic network more or less flat lying and thus presumably stable cratonic indian moho south of the icf apparently extends eastward for another 500 km to about 93 e

500 m of rapid base level rise along an inner passive margin seismic observations from the pliocene molo formation mid norway abstract the positions of late cenozoic coasts related base level changes and tectonic events are still an enigma along large parts of the north atlantic passive margin due to severe glacial erosion and inconclusive biostratigraphic ages periglacial paleo coastlines are best preserved along the mid norwegian margin from where we show the first 3d seismic images of a transgressive coastal delta lower molo formation that constrains the late cenozoic geological history well data 2d seismic sections and a 990 km 2 3d survey located above the froan basin and the draugen oil field are used to investigate the 60 km wide and 600 km long coast parallel molo formation we interpret the molo formation to be younger mainly pliocene than the kai formation mid and late miocene and propose a further subdivision of the molo formation into a lower largely transgressive and an upper highstand regressive unit a relative base level fall of several hundred meters is recorded at the onset of the miocene compression phase mid miocene simultaneously the mid miocene unconformity mmu developed and the syntectonic and lowstand kai formation was deposited to the west of the study area upon termination of the miocene compression phase a cumulative base level rise in the order of 500 m is interpreted the lower molo formation is interpreted as a coastal delta sequence and characterized by a sand rich parasequence set that exhibits a largely progradational motif the deposits record a stepped landward migration of the paleo coastline during the initial transgression locally the relative position of topset foreset rollovers and trajectory analysis document 90 m of the base level rise the upper molo formation is interpreted as a fluvial dominated wave influenced progradational shelf edge delta fluctuations in base level are interpreted to be largely tectonically driven

multi scale classification of fluvial architecture an example from the palaeocene eocene bighorn basin wyoming this work was supported by phase 2 of the fluvial systems research group bp bg chevron conocophillips and total mgms thanks the sao paulo research foundation fapesp 2014 13937 3 the authors also wish to thank numerous residents of the bighorn basin for their kind hospitality and access to land we also thank john howell for discussions on fluvial geometries and nomenclature and isobel buchanan and alistair swan for assistance in the field comments from reviewers andrew miall luca colombera and an anonymous reviewer greatly improved this manuscript

shear wave birefringence and current configuration of converging lithosphere under tibet article i nfo new data from west central tibet show that birefringence of s waves has two pronounced increases in magnitude toward the hinterland null birefringence persists to about 75 km north of the indus yarlung suture iys between the indian shield and the lhasa terrane of southern tibet a second rapid increase occurs about 100 km farther north of the bangong nujiang sutures between the lhasa terrane and the qiangtang terrane in central tibet the latter feature is consistently observed along three long transects that collectively span a lateral orogen parallel distance of about 600 km and is likely to mark the northern leading edge of sub horizontally advancing mantle lithosphere of the indian shield the greater india an interpretation consistent with the latest results of finite frequency tomography using both p and s wave travel times previous results of modeling gravity anomalies and a host of other seismic observations similarly complementary constraints indicate that the sudden onset of significant birefringence north of the iys is likely to be the southern termination of eurasian mantle lithosphere curiously the shortest of three transects showed null birefringence through much of the lhasa terrane a pattern inconsistent with those of he isotopes and gravity

stratigraphy and facies distribution of the utsira formation and the pliocene sequences in the northern north sea abstract the upper cenozoic deposits of the northern north sea have been analysed in order to establish a regional and detailed stratigraphy the utsira formation is subdivided into four log units and mapped and two main depocentres are outlined the lower part of the utsira formation consists of thick marine mounded sand bodies interpreted as overall stacked lowstand fan deposits while the upper part of the formation consists of more clayey silty intervals indicating increased relative sea level the succeeding progradational pliocene deposits are subdivided into 13 high frequency depositional sequences and are mapped the sequences are grouped into four composite sequences each of the four pliocene composite sequences is composed of one or two rather locally distributed prograding sequences lowstand sequence set succeeded by one or two more widely distributed aggrading prograding sequences transgressive highstand sequence set boundaries between the composite sequences are recorded as marked changes in distribution of depocentres and sequence architecture the regional uplift of scandinavia is believed to be the main control on sediment input feeding the succeeding general prograding pliocene sequences oscillations of the eustatic sea level punctuated the tectonically controlled progradation and affected variations in the accommodation space and thus created the high frequency sequences

mid cenozoic post breakup deformation in the passive margins bordering the norwegian greenland sea abstract since the initial breakup of the norwegian greenland sea in early eocene time chron 24b 53 7 ma the conjugate passive margins have been subject to compression extension magmatism and broad uplifts and subsidence mid to late cenozoic compressional doming basin inversion and reverse faulting occurred predominantly offshore within the rheologically weak deep cretaceous depocenters on the norwegian margin the domes seem to have formed primarily in middle eocene to early oligocene and in early miocene while doming in the faroes rockall region developed in late paleocene to early eocene oligocene and mid to late miocene we suggest that the main driving force was plume enhanced ridge push a testable working hypothesis is that discrete phases of compression were associated with periods of high plume flux in addition the oligocene chron 13 35 ma change in plate motion appears to have generated local shear adjustments along pre existing basement weaknesses forming compressional structures in the overlying sedimentary section this change in plate motion was first manifest by significant extension between the sw barents sea and the conjugate nne greenland margin and led to spreading along the knipovitch ridge mid cenozoic extension and magmatism also preceded the development of the kolbeinsey ridge the associated separation of the jan mayen microcontinent from east greenland must have been strongly influenced by the position of the iceland plume center in addition to the change in extension direction with respect to initial breakup of the norwegian greenland sea in early eocene time the mid cenozoic extension and magmatism is a post breakup phenomena widely spaced areas of neogene uplift occurred along all bordering margins these enigmatic uplifted areas acted as nucleation sites for growth of ice caps and initiated large glacial deposits that built out on the adjacent shelves

small 660 km seismic discontinuity beneath tibet implies resting ground for detached lithosphere 1 using seismic profiles comprising of high resolution triplicate waveforms across apertures of over 1 000 km we show that because of high p wave speed vp near the bottom of the mantle transition zone the contrast in vp across the 660 km discontinuity beneath central tibet is small only about 70 of that beneath the northern indian shield this subhorizontal anomaly of high vp is most likely a remnant of detached mantle lithosphere that recently sank to depth thus providing key evidence for a direct connection between continental collision near the surface and deep seated dynamics in the mantle

subduction of the indian lithosphere beneath the tibetan plateau and burma abstract subduction of the indian lithosphere under eurasia plays an important role in the tectonic evolution of the tibetan plateau and surrounding regions to improve our knowledge of pertinent mantle structures through tomographic imaging we combine p wave arrival time data from temporary arrays in tibet and stations of the chinese seismograph network with reprocessed data from the international seismological centre the new images reveal considerable spatial variations in mantle structure along the collision zone and the horizontal distance over which presumed continental indian lithosphere slides northward beneath the plateau decreases from west where it underlies the himalayas and the entire plateau to east where no indication is found for present day underthrusting beyond the himalayan block and indus tsangpo suture p wavespeed appears low in the shallow mantle beneath much of central and eastern tibet these observations suggest that indian lithosphere underlies only the southwestern part of the plateau and that the central and northeastern part is underlain by lithosphere of asian origin the continental parts of the indian plate that currently underthrust or subduct below the plateau appear generally detached from the oceanic slab fragments that subducted longer ago and that have been detected deeper in the mantle except perhaps in the central part of the collision zone 80 90 e this suggests that ongoing india eurasia collision must increasingly be driven by other forces such as subduction of the indian plate further west and east e g beneath indochina our images reveal structures associated with eastward subduction along the burmese arc southeast of the eastern himalayan syntaxis the tengchong volcanic complex in southwest china is marked by slow wave propagation to 150 km depth suggesting a causal link to subduction along the burmese arc the low velocities beneath the red river fault region extend to greater depth and may be related to upper mantle processes further southeast

continuous deformation of the tibetan plateau from global positioning system data global positioning system velocities from 553 control points within the tibetan plateau and on its margins show that the present day tectonics in the plateau is best described as deformation of a continuous medium at least when averaged over distances of 100 km deformation occurs throughout the plateau interior by ese wnw extension and slightly slower nne ssw shortening relative to eurasia material within the plateau interior moves roughly eastward with speeds that increase toward the east and then flows southward around the eastern end of the himalaya crustal thickening on the northeast ern and eastern margins of the plateau occurs over a zone 400 km wide and cannot be the result of elastic strain on a single major thrust fault shortening there accommodates much of india s penetration into eurasia a description in terms of movements of rigid blocks with elastic strain associated with slip on faults between them cannot match the velocity field

oblique stepwise rise and growth of the tibet plateau two end member models of how the high elevations in tibet formed are i continuous thickening and widespread viscous flow of the crust and mantle of the entire plateau and ii time dependent localized shear between coherent lithospheric blocks recent studies of cenozoic deformation magmatism and seismic structure lend support to the latter since india collided with asia 55 million years ago the rise of the high tibetan plateau likely occurred in three main steps by successive growth and uplift of 300 to 500 kilometer wide crustal thrust wedges the crust thickened while the mantle decoupled beneath gently dipping shear zones did not sediment infilling bathtub like of dammed intermontane basins formed flat high plains at each step the existence of magmatic belts younging northward implies that slabs of asian mantle subducted one after another under ranges north of the himalayas subduction was oblique and accompanied by extrusion along the left lateral strike slip faults that slice tibet s east side these mechanisms akin to plate tectonics hidden by thickening crust with slip partitioning account for the dominant growth of the tibet plateau toward the east and northeast

sedimentology architecture and depositional setting of the fluvial spireslack sandstone of the midland valley scotland insights from the spireslack surface coal mine

efficient calculation of differential seismograms for lithospheric receiver functions summary a new technique for computing differential seismograms for crustal and upper mantle response to a teleseismic wave receiver functions is developed using the matrix formalism of kennett the work was motivated by the difficulty of modelling teleseismic sv waves and has also proven useful for modelling teleseismic p waves this efficient method for calculating differential seismograms is based on three separate methods for computing synthetic seismograms two of the synthetic seismogram methods save intermediate results then the remaining synthetic seismogram algorithm uses the stored results in an efficient calculation of a new synthetic seismogram for a perturbed velocity model these developments have led to a faster for a 30 layer model a 90 per cent reduction in computation time and more accurate linearized inversion scheme for the determination of velocity models using teleseismic waves

about the lithospheric structure of central tibet based on seismic data from the indepth iii profile signals from 11 shots and 8 earthquakes and numerous teleseismic events were recorded along the 400 km seismic line indepth iii in central tibet and interpreted together with previous seismic and tectonic data the abnormal behavior of various mantle phases reveals a complex moho transition zone especially in the northern part of the line in the changtang block where the lower crust and the mantle show unusually low velocities a shingled appearance of pn and no low velocity layer in the upper crust the strong east west anisotropy in the changtang block is related to an easterly escape movement of the whole lithosphere facilitated by the warm and weak layers in the lower crust and the upper mantle bounded apparently by two prominent west east running fault zones

quaternary stratigraphy of the draugen area mid norwegian shelf abstract lithostratigraphic biostratigraphic and chronostratigraphic studies on a 130 m long core from haltenbanken mid norwegian shelf dr 88 30 shows sequences of short episodic glacigenic sedimentation and periods of more continuous marine sedimentation the sediment sequence is dated by palaeomagnetism as well as the amino acid and the strontium isotope methods back to ca 1 1 ma previous seismostratigraphic interpretations placed the regional pliocene pleistocene boundary at ca 90 m depth at the core site this level was dated to be of brunhes matuyama age the study area has been covered by grounded glaciers at least five times during the last 1 1 ma the first expansion of the scandinavian ice sheet was at ca 1 1 ma depositing a diamicton these sediments are overlain by a long sequence of normal marine sediments deposited during both glacial and interglacial conditions two interglacial periods from this sequence have been given an informal interglacial notation except for the glaciation at ca 1 1 ma the glacials during the early pleistocene which are identified in the core were relatively limited a transition to more extensive glaciations occurs in the early middle pleistocene during these more extensive glacial phases major erosion took place along the inner continental shelf this erosional phase resulted in overdeepening of the inner shelf which during the middle and late pleistocene influenced the depositional dynamics in the central and the outer part of the shelf in the study area the middle and late pleistocene periods are dominated by glacigenic sediments with only very thin interglacial sediments occasionally preserved one interglacial period from the middle pleistocene has been given an informal interglacial notation the core has been correlated to cores from the north sea basin on the basis of amino acid stratigraphy and palaeomagnetism the lithological and the foraminiferal stratigraphy indicates a synchronous appearance of the major lithological units and of the fauna assemblages in these areas

high frequency depositional sequences and stratal stacking patterns in lower pliocene coastal deltas mid norwegian continental shelf extensive deltaic and coastal progradation occurred along the mid norwegian continental shelf during the early pliocene thirty eight well developed high frequency fourth order sequences are identified within the deltaic complex on multifold seismic data the fourth order sequences are arranged in four oblique progradational and two sigmoid progradational sequence sets deposition of the high frequency sequences and their stacking patterns probably were in response to high frequency cycles of relative changes in sea level cycles produced by variable rates of subsidence and uplift superimposed on high frequency eustatic cycles within a lower frequency eustatic system the mixed aggrading prograding sequence sets are interpreted to represent increased space added accommodation rates and deposition within third order highstand systems tracts conversely the progradational sequence sets are interpreted to represent decreasing space added accommodation rates and deposition within the third order lowstand systems tracts the recognition of multiple sequence sets likely reflects the effect of long term relative fall in sea level tectonic uplift superim osed on high frequency eustatic cycles the terminal sequence boundaries of the sequence sets are formed by conjunction of third and fourth order falling inflection points on the relative sea level curve these sequence boundaries represent the timing of maximum subaerial erosion and may represent times of greatest potential for the deposition of reservoir sands

first multi scale finite frequency tomography illuminates 3 d anatomy of the tibetan plateau 1 with a new multi scale parameterization 3 d images from finite frequency seismic tomography including the very first images beneath central tibet from s waves reveal that regions of low electric resistivity in the crust previously observed along active rifts in southern tibet correlate well with regions of low p and s wave speeds v however such regions are not interconnected indicating that a prevailing south directed channel like crustal flow seems inactive or this popular geodynamic model needs modification in the upper mantle there is no clear indication of regional down welling between depths of 100 to 400 km instead a strong lateral boundary between high and low v extends up to 33 n marking the northern limit of sub horizontally advancing indian lithospheric mantle

history of terrigenous sedimentation during the past 10 m y in the north atlantic odp legs 104 and 105 and dsdp leg 81 bulk sediment measurements and analyses of the input of 63 m terrigenous particles have enabled us to reconstruct the variability of sediment flux in the norwegian and the labrador seas as a function of paleoceanographic and paleoclimatic changes in both areas minor amounts of coarse terrigenous particles occur in sediments that were deposited between 9 5 and 7 0 ma the higher amounts are only documented in the norwegian sea around 5 7 5 4 ma variations in bulk sediment accumulation are related to a strengthening of denmark strait overflow which is closely connected with the production of norwegian sea deep water between 8 3 and 7 8 ma 6 9 and 6 1 ma and 5 3 and 4 2 ma in the labrador sea reduced bottom water activity coincided with the highest levels of organic carbon accumulation and an increase in bulk sediment accumulation and may correlate with the latest miocene messinian event in both the labrador sea and the norwegian sea a drastic increase in the amount of coarse terrigenous particles rock fragments and quartz started at around 4 0 ma recording a nearly simultaneous onset of large scale ice rafting this was ultimately caused by a deterioration in the northern hemisphere climate possibly related to the final closure of the isthmus of panama

braided rivers perspectives and problems progress towards a fuller understanding of the dynamics and deposits of braided rivers demands an interdisciplinary approach to a host of unresolved problems although many advances have been made within recent years in interpreting the mechanics of flow transport of sediment and sedimentary architecture of braided rivers many key issues remain to be addressed in particular several areas demand attention the mechanisms of braid bar initiation confluence diffluence dynamics the nature of sedimentary facies over a range of grain sizes and the influence of flow stage and aggradational regime upon the depositional architecture over a range of channel scales this paper focuses upon these issues and highlights several areas of fruitful future interdisciplinary collaboration 1993 the geological society

underplating in the himalaya tibet collision zone revealed by the hi climb experiment we studied the formation of the himalayan mountain range and the tibetan plateau by investigating their lithospheric structure using an 800 kilometer long densely spaced seismic array we have constructed an image of the crust and upper mantle beneath the himalayas and the southern tibetan plateau the image reveals in a continuous fashion the main himalayan thrust fault as it extends from a shallow depth under nepal to the mid crust under southern tibet indian crust can be traced to 31 n the crust mantle interface beneath tibet is anisotropic indicating shearing during its formation the dipping mantle fabric suggests that the indian mantle is subducting in a diffuse fashion along several evolving subparallel structures

glacigenic sediments on a passive continental margin as exemplified by the barents sea abstract reflection seismics data borehole data and gravity cores have been used to map the sedimentary facies of the epicontinental southwestern barents sea its continental margin and adjacent coastal areas an upper unconformity with a glacially eroded morphology extends over most of the continental shelf up to 300 m of stratiform glacigenic sediments overlie this unconformity these sediments can be grouped into seismic units which are separated by smooth or irregular erosional surfaces each sequence may be up to 150 m thick normally with a lateral extent of 100 300 km three dominant seismic signatures may be discerned semi transparent stratified and chaotic reflection patterns these sediments are partly glacifluvial in origin but on the whole they represent more or less tectonized glacimarine deposits the deeper troughs on the continental shelf contain an undeformed postglacial glacimarine marine trough fill the greatest thickness up to 1000 m of glacigenic sediments occurs at the shelf break and below the upper slope the depocentres are situated at trough mouth fans the sediments comprise several prograding sequences with a complex sigmoid oblique character indicating alternating upbuilding and depositional bypass erosion in the topset segment small and large scale slide scars are observed on the upper slope and debris lobes on the lower slope a marked progradation seems to have occurred during the plio pleistocene glacial periods this progradation also resulted in an unstable slope with various types of sediment gravity flows currents flowing along the slope were established during interglacials and gullying by cold dense shelf water and downslope transport occurred maximum net sedimentation rates are 0 2 m ka continental slope 0 4 m ka shelf break 0 1 m ka shelf stratiform diamictons 1 m ka shelf trough fills and 60 m ka fjord trough fills

large scale development of the mid norwegian margin during the last 3 million years abstract during the last c 2 7 my large quantities of glacially derived material were transported westwards from the norwegian mainland areas and inner shelf and deposited mainly as prograding sediment wedges into a basin of intermediate depth offshore mid norway the deposits are more than 1000 m thick in extensive areas and are defined as the naust formation in the haltenbanken traenabanken region the shelf edge migrated 100 150 km westwards the narrow more shelf was built out only in the order of 30 50 km mainly due to a steeper pre existing slope dipping towards a much deeper basin in this area the holocene storegga slide as well as older slides displaced slope sediments towards the deeper part of the basin in early naust time the most extensive progradation occurred in the northern area possibly due to the combined effect of land uplift and glaciations the importance of glaciations for the progradation of the more shelf and areas farther south increased through the pleistocene period the norwegian channel ice stream became very important during the last three glaciations and a thick succession of glacigenic debris flows was deposited on the north sea fan more than 400 m of sediments accumulated during the weichselian all the last three glaciations supplied glacial debris beyond the shelf edge the most extensive progradation in the north was in the skjoldryggen region particularly during the elsterian glaciation during ice free periods hemipelagic and contouritic sediments were deposited on the slope such sediments are most common in the storegga slide area where they hosted glide planes beneath the major slides

reconstruction of glaciation over the past 6 myr from ice borne deposits in the norwegian sea it is well known that a significant intensification of northern hemisphere glaciation occurred 2 5 myr ago in contrast to the much earlier onset 35 myr of glaciation in antarctica1 3 much less is known about the behaviour of the climate before 2 5 myr and it has remained unclear when sizeable glaciers first started to develop in the northern hemisphere here we deduce the history of high northern latitude glaciation over the past 6 myr from records of ice borne deposits in deep sea sediments of the norwegian sea we find that glaciers large enough to reach sea level were present in the norwegian sea area as early as 5 5 myr three million years before the intensification of glaciation at 2 5 myr fluctuations in ice volume can be deduced from the oxygen isotope record but this provides only a global average which may not reflect the history of ice sheet growth in specific regions from a comparison of the oxygen isotope records with the record of ice rafted material we derive an estimate of the relative contributions of southern and northern hemisphere glaciation to global variations in ice volume

thick crust beneath the ordos plateau implications for instability of the north china craton abstract surrounded by seismicity and other manifestations of active deformation the ordos plateau or the western portion of the north china craton ncc is a uniquely stable terrane in asia results from virtual deep seismic sounding and crustal receiver functions suggests that the crust under the eastern ordos is thicker at least 60 km than expected from previous studies and from its modest elevation 1500 m above sea level receiver functions also reveal a pronounced elastic impedance contrast within the crust at 40 km depth which we interpret as the conrad discontinuity the presence of a 20 km thick layer of mafic lower crust between the conrad and moho discontinuities would maintain crustal isostasy the 1000 km long seismic profile from the ordos plateau in the west to the north china basin in the east reveals that crustal thickness changes by almost a factor of two across the active shanxi rift in central ncc over a distance of only about 100 km insofar the current configuration of the lithosphere under the ordos plateau might serve as a proxy for the initial condition prior to reactivation of the eastern part of ncc where a cratonic keel no longer seems to exist our results support the hypothesis that lower crust foundering was due to transformation of a thick mafic lower crust to a garnet rich assemblage possibly caused by hydration associated with subduction during and or before mid mesozoic times

sequence stratigraphy and marine to nonmarine facies architecture of foreland basin strata book cliffs utah u s a the desert member of the blackhawk formation and the castlegate sandstone in the book cliffs of utah and colorado were analyzed to develop a model of sequence stratigraphy and facies architecture in foreland basins stratal architecture of these rocks is controlled by two regionally extensive surfaces of incision and subaerial exposure interpreted as major sequence boundaries and at least six surfaces of incision and subaerial exposure with more limited lateral extent interpreted as minor sequence boundaries each sequence boundary is a regionally correlatable single surface major sequence boundaries can be traced from marine into proximal alluvial plain environments sequence boundaries have different physical expressions depending upon where in the basin they are observed strata beneath sequence boundaries are unrelated to strata above and time lines cannot be carried across these boundaries flooding surfaces called parasequence or parasequence set boundaries also exert an important control on facies architecture based on parasequence stacking patterns position of sequence boundaries and facies associations the desert member and castlegate sandstone have been divided into sequences with durations of 200 000 to 300 000 yr there are an order of magnitude more sequences in this interval than are predicted by the global sea level chart of haq et al 1988 the major sequences have been divided into the following systems tracts or sequence sets 1 grassy highstand sequence set below the desert sequence boundary named for the grassy member of the blackhawk formation 2 desert lowstand transgressive and highstand systems tracts between the desert and castlegate sequence boundaries 3 castlegate lowstand sequence set resting on the castlegate sequence boundary and 4 castlegate transgressive systems tract parasequence stacking patterns suggest that the grassy highstand sequence set and the desert highstand systems tract were deposited during a relative rise in baselevel the grassy highstand sequence set is punctuated by minor relative falls in baselevel both of these stratal units contain thick

tectonic development of the mid norway continental margin abstract the area reviewed covers the mid norway continental margin between latitudes 62 n and 68 n main structural elements as defined at the base cretaceous level are the trondelag platform underlying the inner shelf the more and voring basins located beneath the outer shelf and slope and the more platform and the outer voring plateau forming a base of slope trend of highs sediments contained in the mid norway basin range in age from late palaeozoic to cenozoic the basement was consolidated during the caledonian orogenic cycle devonian and early carboniferous wrench movements along the axis of the arctic north atlantic caledonides are thought to have preceded the namurian onset of crustal extension rifting processes were intermittently active for some 270 my until crustal separation between greenland and fennoscandia was achieved during the early eocene during the evolution of the norwegian greenland sea rift system a stepwise concentration of tectonic activities to its axial zone the area of subsequent continental separation is observed during the late palaeozoic to mid jurassic a broad zone was affected by tensional faulting during the late jurassic and cretaceous the trondelag platform was little affected by faulting whilst major rift systems in the more and voring basins subsided rapidly and their shoulders became concomitantly upwarped during the latest cretaceous and early palaeogene terminal rifting phase only the western more and voring basins were affected by intrusive and extrusive igneous activity following the early eocene crustal separation and the onset of sea floor spreading in the norwegian greenland sea the voring segment of the mid norway marginal basin subsided less rapidly than the more segment during the early and mid tertiary minor compressional deformations affected the voring basin and to a lesser degree the more basin tensional forces dominated the late palaeozoic to early cenozoic evolution of the mid norway basin and effected strain mainly in the area where the crust was weakened by the previous lateral displacements the lithosphere thinned progressively and the effects of the passively upwelling hot asthenospheric material became more pronounced massive dyke invasion of the thinned crust preceded its rupture

seismic properties of the central indian shield we use broadband seismic data at hyderabad to investigate average crustal properties of the central indian shield crustal receiver functions p to sv conversions based on data of excellent quality and azimuthal coverage show essentially no signal on the transverse component indicating laterally homogeneous structures near this station a joint analysis of receiver functions and the dispersion of fundamental mode rayleigh waves result in a simple model for the shear wave speed v s with a moderate gradient of 0 010 0 028 km sec km in the crust the moho is sharp with a contrast of approximately 0 7 km sec in v s across a small thickness of only 0 4 km measured from the middle of the moho region the crust is 30 34 km thick with an average v s of 3 58 0 10 km sec by modeling the timing and waveforms of sp and sspmp phases sv to p conversions we estimate the average crustal poisson9s ratio to be 0 26 0 01 this value is comparable to that found in the tanzanian craton which is also of archean age both values being somewhat lower than the global average of 0 29 0 02 for shield regions that include both proterozoic and archean crust a low poisson9s ratio and a slow v s in the crust indicate that on average archean crust beneath the central indian shield is intermediate to felsic in composition somewhat less mafic than globally averaged precambrian crust

lhasa block and bordering sutures a continuation of a 500 km moho traverse through tibet a north south wide angle fan profile through the yarlung zangbo suture across the lhasa block and through the bangong nujiang suture shows several significant and sharp changes in crustal thickness both sutures appear as vertical 20 km steps in the moho and may have been the loci for eastward strike slip motion of the tibetan lithosphere