calculations on the thermal conditions around a salt diapir temperature modeling around the vejrum salt structure in denmark shows that the heat flow near the top is twice the regional heat flow the temperature in the vicinity of the top of the diapir is thus anomalously high overlying permeable formations could therefore be attractive for geothermal energy exploitation a negative temperature anomaly of 20 c is calculated around the root of the salt body comparisons between calculated and measured temperatures are used to test the model it is shown that measurements of heat flow or temperature gradients in wells penetrating the region of groundwater circulation could be used in identification of salt diapirs

relating petroleum system and play development to basin evolution west african south atlantic basins abstract sedimentary basins can be classified according to their structural genesis and evolutionary history and the latter can be linked to petroleum system and play development we propose an approach in which we use the established concepts in a new way breaking basins down into their natural basin cycle division then defining the characteristics of each basin cycle including the type of petroleum systems and plays they may contain and comparing them with similar basin cycles in other basins thereby providing a means to learn through a greater population of perhaps not immediately obvious analogues furthermore we introduce the use of the trajectory plot as a new tool in such an analysis this methodology has been applied to the west african south atlantic marginal basins between cameroon and angola and we demonstrate that the similar tectonostratigraphic evolution of the individual basins along this margin has led to the development of similar types of petroleum systems and play level s consequently we can make analogue comparisons among these basins in order to evaluate and predict the presence of potential yet undiscovered hydrocarbon accumulations in less well explored parts of the margin

thin skinned extensional tectonics on a salt detachment northern kwanza basin angola abstract thin skinned extension on a salt detachment of a style known as raft tectonics characterizes deformation of the late aptian to recent section in the northern kwanza basin angola large rafts and intervening grabens are interpreted to have developed as a result of gravity gliding increased dip and gravity spreading asymmetrical loading of a sedimentary wedge major raft movement occurred primarily from the middle tertiary but some deformation appears to have started as early as late cenomanian or early turonian times individual grabens measure up to 70 km in length 15 km in width and nearly 3 km in depth and show switching polarities in the sense of thickening of the tertiary sedimentary infill graben geometries were controlled by syndepositional extension and the local availability of salt from the data examined which includes both seismic and well data the grabens appear to become younger from east to west reflecting basinward progression of the deformation as the age relationships could be related to insufficient sampling of strata deposited in complex sedimentation patterns they may have no relevance to the timing of the deformation the diachronous deformation is therefore speculative extension in the northern kwanza basin is estimated at 60 the outermost raft is translated 55 km westwards in addition to the extensional structures compressional folds thrust faults and salt structures mark the toe of the gravity gliding and spreading system all of the rafts lie within the african portion of the aptian salt basin on rifted continental crust and they are generally unrelated to structures below the salt biostratigraphy and lithostratigraphy indicate that the grabens formed on the shelf and upper slope from the middle eocene associated compressional features developed near the slope rise the unusual expression of raft tectonics is attributed to a combination of 1 the presence of a salt layer 2 a stable basement configuration that allowed quiescent accumulation of the raft sequence and 3 an increase in basin dip and sediment supply

performance of miniature piezocones in thinly layered soils two piezocones with cross sectional areas of 1 cm2 and 5 cm2 and a variety of pore pressure filters were driven at the standard rate of 20 mm s into models of thinly layered soil and pore pressu

role of salt in restraining the maturation of subsalt source rocks abstract the presence of salt within a sedimentary basin can potentially modify its temperature distribution and history in particular the positive thermal anomaly associated with the top of salt domes has attracted considerable attention in the past the role of the lesser appreciated negative thermal anomaly associated with the base of salt domes in modifying the maturation history of subsalt source rocks is explored the finite element method was used to model the transient and steady state conductive temperature perturbations induced by salt layers domes and pillows the results indicate that the modification of the thermal regime due to evolving salt domes may significantly affect the maturation level of source rocks in the vicinity of the domes modelling the temperature structure of various salt structures has shown that in general the refraction of heat flow induces a dipole shaped temperature anomaly a positive anomaly located towards the top of the salt structure and a negative anomaly located towards its base these dipole anomalies can be strongly asymmetrical the degree of asymmetry depending on the shape of the salt structure and the proximity of the top of the salt structure to the surface of the basin however when the salt structure reaches the surface the dipole shaped temperature anomaly collapses to a monopole below the salt structure all sediments independent of their depth and lithology are colder relative to a section with no salt similarly salt domes that reach the surface very efficiently drain the heat from below and from the side of the dome these negative thermal anomalies may extend for a considerable depth beneath the base of the salt dome and may reach values of 85 c locally because of the large contrast in thermal conductivity between the highly porous sediments and salt at lower temperatures the efficiency of a salt dome to channel heat increases the closer the salt dome is to the surface these results indicate that deep sedimentary basins containing salt are more prospective than basins without salt and or salt diapirism in addition to the structural traps associated with salt tectonics salt domes and tongues connected to their source dissipate heat more efficiently and thus keep deeper regions of the basin relatively colder and potentially within the oil window for a longer time this cooling effect is maximized when the top of the salt dome remains close to the surface of the sedimentary basin for a significant period of time and may be especially important for continental margins such as brazil and offshore west africa where most of the source rocks lie beneath extensive evaporite deposits in contrast it was found that for the gulf of mexico basin pre and early tertiary salt diapirism and sheet emplacement may have caused significant delays in the maturation of subsalt source rocks in the deeper regions of the gulf basin but the maturation is likely to be relatively insensitive to the late miocene pliocene stage of salt mobilization because the time interval has been too short

upper plate magma poor rifted margins stratigraphic architecture and structural evolution abstract although it is generally accepted that many distal magma poor rifted margins are asymmetric and can be divided into lower and upper plate margins little is known about the details of how and when this asymmetry evolves and how upper and lower plate margins can be distinguished this is due to the fact that most papers focused on the so called lower plate margins while the upper plate margins remained less well understood mainly due to the lack of public accessible drill hole data the aim of this paper is to provide a first order description of the global architecture and stratigraphic evolution of an upper plate magma poor rifted margin in order to provide such a template we focused on 2 seismic sections the ion 1000 line east indian margin and the screech 2 line newfoundland margin and describe key km scale outcrops from the fossil european margin exposed in the western central alps all of which document classical upper plate margins based on these data we show that upper plate magma poor rifted margins can be characterized by a staircase type architecture with terraces t 1 t 2 t 3 and ramps r 1 r 2 that result as a consequence of an evolution through a coupling exhumation and breakup stage we also defined key stratigraphic levels that we try to link with the evolution of the margin which enables us to link the tectonic evolution with the creation of accommodation space and formation of the staircase architecture that characterizes the upper plate margin from these observations we develop a conceptual model for the evolution of upper plate margins and discuss the applicability of this model for different strain rates rates of subsidence and sedimentation rates

interpretation of cone penetration test data in layered soils using cavity expansion analysis cavity expansion theory plays an important role in many geotechnical engineering problems including the cone penetration test cpt one of the challenges of interpreting cpt data is the delineation of interfaces between soil layers and the identification of distinct thin layers a process which relies on an in depth understanding of the relationship between penetrometer readings and soil properties in this paper analytical cavity expansion solutions in two concentric regions of soil are applied to the interpretation of cpt data with a specific focus on the layered effects during penetration the solutions provide a large strain analysis of cavity expansion in two concentric regions for dilatant elastic perfectly plastic material the analysis of cpt data in two layered soils highlights the effect of respective soil properties strength stiffness on cpt measurements within the influence zones around the two soil interface results show good comparisons with numerical results and elastic solutions a simple superposition method of the two layered analytical approach is applied to the analysis of penetration in multilayered soils a good comparison with field data and numerical results is obtained it is illustrated that the proposed parameters effectively capture the influence of respective soil properties in the thin layer analysis it is also shown that results based on this analysis have better agreement with numerical results compared with elastic solutions

effect of plastic viscous layering and strain softening on mode selection during lithospheric extension 1 factors controlling the selection of deformation modes during continental extension are investigated using analytical and numerical methods we view the lithosphere as a laminate and examine a simple system with a uniform plastic layer overlying a uniform linear viscous layer the rate of energy dissipation is analyzed for pure shear ps symmetric plug sp and asymmetric plug ap extension modes and the analysis reveals that the primary control is the relative rate of dissipation in the two layers a basic difference is that the plastic layer yield strength is independent of the strain rate whereas the viscous stress depends on strain rate therefore dissipation scales linearly and quadratically with extension velocity for these respective layers when other parameters e g extension velocity and properties are held constant minimum dissipation predicts that the modes ap sp and ps will be selected in this order with increasing viscosity of the lower layer transition viscosities between modes t1 and t2 are 4 1021 pa s and 8 1022 pa s respectively for our parameters values numerical models confirm the analysis results inferred mode controls and order of mode selection when strain softening of the plastic layer occurs during extension implications for lithosphere that acts as a bonded plastic viscous laminate include the following 1 asymmetric extension ap mode is preferred when the extension rate and or effective viscosity is low or the viscous region temperature is high 2 symmetric sp mode extension is preferred for intermediate combinations of parameters and 3 overall pure shear ps mode may occur for opposite end member parameter combinations

pile and penetrometer end bearing resistance in two layered soil profiles the paper examines the influence of soil strength and stiffness on the end resistance mobilised by a cone or displacement pile in a two layered soil profile i e strong soil overlying or underlying weak soil the investigation involved a series of numerical analyses that idealise pile cone penetration assuming the spherical cavity expansion analogue it is shown how the end resistance mobilised by a penetrometer in a dense sand i e strong soil varies with the number of penetrometer diameters d from a weak soil assumed here to be either a loose sand or soft clay and depends on the ratio of the steady state penetration resistances of the strong and weak layers the penetrometer resistance in the weak soil is not affected by an adjacent strong layer at penetrations greater than 2d a design procedure based on a numerical parametric study is proposed and this is subsequently shown to compare well with centrifuge test data and with previous numerical research

time and temperature in petroleum formation application of lopatin s method to petroleum exploration n v lopatin in the soviet union has developed a method for taking both time and temperature into account as factors in thermal maturation of kerogen lopatin s time temperature index of maturity tti values correlate with the thermal regimes corresponding to generation and preservation of hydrocarbons because such information is potentially of great interest for oil exploration a calibration and evaluation have been made of lopatin s method within the limitations of the data presently available the following statements can be made 1 the rate of the chemical reactions involved in thermal maturation of organic material appears to double with every 10 c 18 f rise in temperature 2 threshold values of lopatin s time temperature index of maturity tti are 15 onset of oil generation 75 peak oil generation 160 end oil generation 500 40 oil preservation deadline 1 000 50 oil preservation deadline 1 500 wet gas preservation deadline 65 000 dry gas preservation deadline 3 tti values calculated from lopatin reconstructions consistently agree with other maturation parameters commonly used by petroleum geochemists potential applications of lopatin s method for oil exploration include timing of oil generation calculation of volume of hydrocarbons generated within a basin and determination of economic deadlines

volcanic margin formation and mesozoic rift propagators in the cuvier abyssal plain off western australia the western margin of australia is characterized by synrift and postrift magmatism which is not well understood a joint interpretation of magnetic anomaly satellite gravity anomaly and seismic data from the cuvier abyssal plain and margin shows that the breakup between india and australia started circa 136 ma m14 and was followed by two rift propagation events which transferred portions of the indian plate to the australian plate post breakup magmatism continued with the emplacement of the wallaby and zenith plateaus 17 18 km thick at their centers along a transform margin two narrow magmatic edifices adjacent to the wallaby plateau sonne and sonja ridges represent an extinct ridge and a pseudofault respectively they formed by excess volcanism probably by lateral migration of buoyant melt along upside down crustal drainage channels from the melt source underneath the wallaby plateau in a mantle plume scenario a small plume 400 km diameter located underneath the rift could have locally uplifted the bernier platform and exmouth sub basin in the early cretaceous and left a track consistent with the azimuth of the wallaby and zenith plateaus in this case ridge plume interaction would have caused two consecutive ridge propagation events towards the plume while the ridge moved away from the hotspot the abrupt end of the hotspot track west of the zenith plateau would be a consequence of the accelerating south eastward motion of the spreading ridge relative to the mantle after 120 ma leaving the mantle plume underneath the indian plate an alternative nonmantle plume scenario is based on the observation that between breakup and chron m0 120 ma the ocean crust in the southern cuvier abyssal plain was formed while the spreading ridge abutted indian continental crust small scale convection may have been initiated during rifting in the early cretaceous and maintained until the wallaby zenith ridge transform intersection passed by the eastern edge of indian continental crust at chron m0

a precise worldwide correlation of early ordovician graptolite sequences fourteen early ordovician tremadoc llandeilo graptolite sequences from around the world are precisely infrazonally correlated based on the stratigraphic ranges of 130 species and species groups the composite standard sequence css of graptolites has been determined from the six best regional sequences by a nonparametric graphic correlation two data sets were selected one comprised first appearance events of 103 taxa the other first and last appearance events of 45 taxa the results of the two runs accord well and reveal respectively 66 and 73 successive bioevents in early ordovician time event spacing averages 0 7 0 8 ma and enables fine subdivision correlation and homotaxial testing for diachroneity the strong correlation between each of the six regional sequences and the css indicates the high level of accordance among graptolite successions around the world

extensional tectonics in the jeanne d arc basin offshore newfoundland implications for the timing of break up between grand banks and iberia

flexural uplift of rift flanks due to mechanical unloading of the lithosphere during extension we suggest that the uplift of rift flanks results from mechanical unloading of the lithosphere during extension and consequent isostatic rebound this mechanism is presented as an alternative to explanations for rift flank uplift involving thermal or dynamic processes and magmatic thickening of the crust our hypothesis is based on two critical concepts first the lithosphere retains finite mechanical strength or flexural rigidity during extension second isostatic rebound uplift of the lithosphere follows when the kinematics of extension produces a surface topographic depression that is deeper than the level to which the surface of the extended lithosphere would subside assuming local isostatic compensation we develop and analyze two kinematic models for instantaneous extension of the lithosphere to show that flexural rebound is a viable explanation for the uplift of rift flanks we first investigate the isostatic consequences of finite simple slip on an initially planar dipping normal fault cutting the entire lithosphere when the lithosphere retains flexural rigidity during extension the topography resulting from this model resembles a half graben and the footwall rift flank is flexurally uplifted this simple normal faulting model explains free air gravity anomalies and topography observed at rift flanks in oceanic lithosphere such as broken ridge in the eastern indian ocean the caroline ridges sorol trough in the western equatorial pacific and the coriolis trough behind the new hebrides island arc we then investigate a general kinematic model for lithospheric extension where simple slip on a surface of arbitrary shape is accompanied by pure shear extension in the upper and lower plates when the simple slip component is not zero or the distribution of pure shear in the upper and lower plates is not identical the surface of slip can be regarded as a detachment by simplification our general model accounts for pure shear extension of the lithosphere that is uniform with depth in this case detachments have no meaning in the geologic sense however the kinematics of depth independent pure shear may nevertheless be described in terms of a surface which we term a kinematic reference surface at some depth in the lithosphere we speculate that the depth of this surface may be rheologically controlled the magnitude of rift flank uplift by flexure depends critically on the depth of this reference surface in contrast if local isostasy is assumed when the lithosphere undergoes a given amount of depth independent pure shear the resulting topography will be the same regardless of how the kinematics of that extension are formulated the basin and rift flank topography and free air gravity anomaly over young continental rifts such as the rhine graben can be satisfied using our general extensional model with a small amount 5 km of extension along a listric shaped detachment soling into the crust mantle boundary because the flexural rebound mechanism explains the observed topography and gravity anomaly over both oceanic and continental extensional domains we suggest that rheological differences between the two lithospheric types may not be important in their overall response to extension

centrifuge modelling of cone penetration tests in layered soils penetration problems are important in many areas of geotechnical engineering such as the prediction of pile capacity and interpretation of in situ test data the cone penetration test is a proven method for evaluating soil properties yet relatively little research has been conducted to understand the effect of soil layering on penetrometer readings this paper focuses on the penetration of a probe within layered soils and investigates the layered soil effects on both penetration resistance and soil deformation a series of centrifuge tests was performed in layered configurations of silica sand with varying relative density in a 180 axisymmetric model container the tests allowed for the use of a half probe for observation of the induced soil deformation through a poly methyl methacrylate window as well as a full probe for measurement of penetration resistance within the central area of the container the variations of penetration resistance and soil deformation characteristics as they relate to penetr

effects of cone tip roughness in situ stress anisotropy and strength inhomogeneity on cpt data interpretation in layered marine clays numerical study abstract this paper explores the effects of cone tip roughness factor soil in situ stress ratio and strength non homogeneity on cone tip resistance in three layer clay deposits aiming at presenting a general cpt data interpretation framework to extract soil layered profiles and strengths large deformation finite element ldfe analysis has been carried out simulating continuous penetration of the standard cone penetrometer from the seabed surface with the consideration of cone tip roughness factor in situ stress ratio and soil strength non homogeneity within a practical range in the ldfe analyses a thin relatively stiff or soft clay layer was interbedded in a uniform or nc clay deposit with various strength ratios between two successive layers and thickness ratios of the thin layer to the cone diameter explored the results have shown that the noted factors have significant influence on net cone penetration resistance in stratified deposits these influences in the layered deposits were found to be similar in magnitude to those on the cone limiting resistance in a single clay layer leading to the resultant influence on a thin layer correction factor for cone penetration resistance minimal this was confirmed by the evidence of the evolving soil flow mechanisms around the cone tip therefore the design charts and formulas developed for a smooth cone in uniform three layer soils are applicable for delineating layer boundaries and interpreting the undrained shear strength of each identified layer for a partially rough cone in three layer non homogeneous clay deposits however the cone tip roughness factor was shown to have an influence in the layer boundary identification especially for the cone penetration from a stiff layer to a soft layer

bearing capacity and stiffness of embedded circular footings on stiff over soft clay abstractthis technical note presents results from a series of undrained load tests performed at model scale on circular embedded footings founded in a two layered stratigraphy comprising uniform s

continental lithospheric thinning and breakup in response to upwelling divergent mantle flow application to the woodlark newfoundland and iberia margins abstract depth uniform stretching is not the dominant deformation process for thinning continental lithosphere leading to breakup it cannot explain the observed depth dependent lithosphere stretching and mantle exhumation at rifted continental margins depth dependent lithosphere thinning in which stretching of the lower crust and lithosphere mantle greatly exceeds that of the upper crust has been observed at many non volcanic and volcanic rifted continental margins including conjugate margin pairs passive continental margins show a paucity of brittle deformation in the upper crust during continental lithosphere thinning leading to breakup and sea floor spreading initiation a new model of rifted continental margin formation has been developed that assumes that deformation and thinning of continental lithosphere leading to breakup occurs in response to an upwelling divergent flow field within continental lithosphere and asthenosphere and that this deformation evolves into sea floor spreading the new model successfully predicts depth dependent stretching of continental margin lithosphere for both non volcanic and volcanic margins and mantle exhumation at non volcanic margins both of which are observed but are not explained by existing depth uniform continental lithosphere stretching models the new model provides a balance of extensional strain supplies an explanation for the paucity of synrift brittle deformation and offers a simple transition from prebreakup lithosphere thinning to sea floor spreading the observed diversity of rifted continental margin structure and width of the ocean continent transition can be explained by variability in the form of the upwelling divergent flow field the new upwelling divergent flow model of continental lithosphere thinning leading to continental breakup successfully predicts the observed bathymetry and margin geometry for the most recent segment of sea floor spreading initiation in the woodlark basin in the western pacific and the observed bathymetry and free air gravity anomaly for the newfoundland and iberian margins

lower crustal extension across the northern carnarvon basin australia evidence for an eastward dipping detachment asymmetry and strain partitioning along conjugate margins are often explained in terms of detachment faults nevertheless cogent evidence for their existence remains limited furthermore even when inferred detachment faults are imaged seismically it is difficult to demonstrate that differential displacement has occurred across these surfaces we present tectonic and stratigraphic evidence from the northern carnarvon basin northwest australia that documents the existence of an intracrustal eastward dipping detachment by integrating sequence stratigraphy with kinematic and isostatic models of basin development we conclude that the northern carnarvon basin was formed as a consequence of four extension events 1 a broadly distributed late permian event 2 a predominantly localized rhaetian event responsible for the inception of the barrow and dampier subbasins 3 a localized callovian fault reactivation within the barrow dampier subbasins and 4 a tithonian valanginian event that generated large post valanginian regional subsidence across the northern carnarvon basin with only minor accompanying brittle deformation and erosional truncation the regional distribution and amplitude of the post valanginian subsidence are not consistent with the minor amounts of tithonian valanginian brittle upper crustal extension observed on the margin large portions of the platform were emergent or at very shallow water depths prior to the tithonian valanginian extension to match the distribution and magnitude of the post valanginian thermal type subsidence requires significant lower crustal and mantle extension across the northern carnarvon basin such a distribution of extension implies the existence of an eastward dipping intracrustal detachment having a ramp flat ramp geometry that effectively thinned the lower crust and lithospheric mantle the detachment breached the surface close to the position of the continent ocean boundary west of the exmouth plateau the flat component of the detachment occurred at midcrustal depths 15 km across the plateau and ramped beneath the australian continent lower crustal ductile extension provides a viable mechanism to generate large regional subsidence with little attendant brittle deformation which may explain the paradox that both sides of many conjugate margins appear to be the upper plate

seismic stratigraphy and subsidence analysis of the southern brazilian margin campos santos and pelotas basins abstract the campos santos and pelotas basins have been investigated in terms of 2d seismo stratigraphy and subsidence the processes controlling accommodation space e g eustacy subsidence sediment input and the evolution of the three basins are discussed depositional seismic sequences in the syn rift barremian to the drift holocene basin fill have been identified in addition the subsidence uplift history has been numerically modeled including i sediment flux ii sedimentary basin framework iii relation to plate tectonic reconfigurations and iv mechanism of crustal extension although the initial rift development of the three basins is very similar basin architecture sedimentary infill and distribution differ considerably during the syn rift sag to the drift basin stages after widespread late aptian early albian salt and carbonate deposition shelf retrogradation dominated in the campos basin whereas shelf progradation occurred in the santos basin in the tertiary these basin fill styles were reversed since the paleogene shelf progradation in the campos basin contrasts with overall retrogradation in the santos basin in contrast long term cretaceous paleogene shelf retrogradation and intense neogene progradation characterize the pelotas basin its specific basin fill and architecture mainly resulted from the absence of salt deposition and deformation these temporally and spatially varying successions were controlled by specific long term subsidence uplift trends onshore and offshore tectonism in the campos and santos basins affected the sediment flux history distribution of the main depocenters and occurrence of hydrocarbon stratigraphic structural traps this is highlighted by the exhumation and erosion of the serra do mar serra da mantiqueira and ponta grossa arch in the hinterland as well as salt tectonics in the offshore domain the pelotas basin was less affected by changes in structural regimes until the eocene when the andean orogeny caused uplift of the source areas flexural loading largely controlled its development and potential hydrocarbon traps are mainly stratigraphic

styles of rifting and fault spacing in numerical models of crustal extension extension of the earth s crust can result in differing styles of rifting such as horst and graben half graben metamorphic core complexes and areas of distributed crustal thinning faulting patterns can range from either being distributed to highly localized observations indicate that the factors controlling the extensional deformation symmetry and fault spacing include rheological aspects such as the yielding mechanism and strain softening and physical aspects such as initial heterogeneities and the strength of the lower crust compared to the upper crust time dependent numerical models of extension are presented which investigate the influence of the yielding mechanism lower crust strength strain weakening and initial heterogeneity in the crust have on a the style of rifting b fault spacing and c integrated strength in the upper crust models with an anisotropic yielding mechanism result in more realistic lithospheric strength profiles slip plane angle distributions and fault interaction than models with an isotropic yielding mechanism heterogeneity type and yielding mechanisms have the largest effect on the resulting symmetry of deformation whereas the amount of strain weakening has the greatest influence on asymmetry the likelihood of the metamorphic core complex mode occurring is primarily controlled by lower crust strength crustal thinning is encouraged by both low amounts of strain weakening and a strong lower crust lower crust viscosity exerts the primary control on whether the resulting deformation is distributed or localized the degree of strain weakening has the largest influence on the average strength of the upper crust and the slope of the strength profile in the upper crust

design of driven piles in sand estimation of the axial capacity of piles driven into sand involves considerable uncertainty and design rules are generally not consistent with the physical processes involved this paper reviews current understanding of the factors that determine the axial capacity of piles driven into sand and outlines a new framework for design which takes account of the physical processes is consistent with the existing database of load test results and is sufficiently flexible to permit refinement as new data become available it allows for the effects of confining stress on the frictional and compressibility characteristics of sand and hence on end bearing capacity in keeping with field observations shaft friction is assumed to degrade with driving of the pile past a particular location from an initial maximum value linked to the local end bearing capacity the resulting design approach is compared with field data and effects of factors such as the direction of loading are discussed l estimation de la resi

definition of the tremadoc series and the series of the ordovician system in britain the tremadoc series and series of the ordovician system are widely used in international correlations and this review explains and summarizes how the base of each of these series is recognized in britain no type section in which the base of any one of them is displayed has ever been selected and formally designated hence the basal horizon of each series is a matter of general understanding rather than precise definition this general understanding is of particular biozones or of assemblages of fossils and their relative ages the geographical separation between type sections of series and differences in facies complicate the understanding of relative ages of biozones brachiopod and trilobite faunas of the llandeilo caradoc and ashgill series have been studied in detail in recent years and biozones proposed these biozones have proved difficult or impossible to recognize outside their type areas in britain and brachiopod trilobite faunas of the tremadoc arenig and llanvirn series are likewise highly provincial thus for correlation within and outside britain attention has been focused on the standard graptolite biozones particularly since such conodont faunas as have been found have not proved useful yet there are problems associated with these standard biozones for example the tetragraptus approximatus biozone is unknown in wales or england the relationship between the base of the glyptograptus teretiusculus biozone and the earliest llandeilo shelly faunas requires clarification and at what level the base of the caradoc series may lie in the nemagraptus gracilis biozone is unknown thus to bring precision to definitions of ordovician series in britain the identification of continuous fossiliferous sequences that will serve as stratotypes is required such a section for the basal portion of the tremadoc series has recently been proposed systematic studies related to particular biozones are needed for example early caradoc and early ashgill brachiopods and graptolites of the didymograptus bifidus and glyptograptus teretiusculus biozones the stratigraphical ranges and abundances of species in particular sections require documentation so that the type of biozone assemblage acme concurrent range etc may be recognized such work could lead towards chronostratigraphy the provision of a standard stratigraphical scale in britain for the tremadoc series and ordovician series

pile end bearing capacity in crushable sands the occurrence and formation of crushable soils is a widespread phenomenon warm tropical seas give rise to deep deposits of biogenic skeletal sediments in coastal shelf areas or exposed granitic

rifted margin architecture and crustal rheology reviewing iberia newfoundland central south atlantic and south china sea abstract crustal rheology controls the style of rifting and ultimately the architecture of rifted margins here we review the formation of three magma poor margin pairs iberia newfoundland the central segment of the south atlantic rift and the south china sea by integrating observational data into a numerical forward modelling framework we utilise a 2d version of the finite element code slim3d which includes nonlinear temperature and stress dependent elasto visco plastic rheology and is able to reproduce a wide range of rift related deformation processes such as flexure lower crustal flow and faulting extension in cold strong or thin crust is accommodated by brittle faults and ductile shear zones that facilitate narrow rifts with asymmetric fault geometries hot weak or thick continental crust is dominated by ductile deformation and often extends symmetrically into a wide rift system this simple recipe provides the standard framework to understand initial rift geometry however it is insufficient to account for the dynamics of intermediate and late rift stages that shape the final margin architecture asymmetric conjugate margins where one side is wide and the other narrow can be formed via both wide and narrow rift styles which we reproduce with weak and strong crustal rheologies respectively exemplified by the iberia newfoundland conjugates and the central south atlantic we define three characteristic rift phases an initial phase of simultaneous faulting an intermediate phase of rift migration that involves sequential fault activity and finally the breakup phase crustal rheology plays an overarching role in governing the dynamics of these asymmetric margins we illustrate that weak rheologies generally prolong the phase of simultaneous faulting while rift migration is enabled by initial fault asymmetry as well as relatively weak crust formation of the predominantly symmetric and wide margins of the south china sea was controlled by extraordinarily weak crust that extended the phase of simultaneous faulting until breakup the weak crustal rheology of this region relates to the south china sea s pre rift history where plate convergence lead to crustal thickening and magmatic additions in a back arc regime shortly before the onset of rifting

diversity and origin of quartz cements in continental carbonates example from the lower cretaceous rift deposits of the south atlantic margin abstract silica precipitation in continental carbonates is a common process occurring during sedimentation and diagenesis the lower cretaceous rift deposits of the south atlantic equatorial margin which are intensively explored by petroleum companies provide good examples of such silicifications in carbonates exhibiting a wide diversity of petrographic habit of early to late quartz cements in order to understand the palaeoenvironmental and diagenetic conditions leading to this diversity we integrated detailed petrography of diagenetic sequences and quartz habit with 18oquartz measurements by sims of individual cements observed in samples from the offshore and onshore basins of the west african margin the petrographic description highlights the omnipresence of early fibrous microquartz cements exhibiting either length fast or length slow habit in addition to laminated microquartz and micro or mega quartz forms amongst the isotopic analysis the 18oquartz data show that length slow cements are generally strongly enriched in 18o 18oquartz ranging from 31 to 37 smow whereas length fast forms show less elevated values 25 c and

a mechanism to thin the continental lithosphere at magma poor margins crustal thinning where continental plates break apart can be accomplished by a system of conjugate concave downward faults instead of multiple normal faults through exhumation of mid crustal and mantle material where continental plates break apart slip along multiple normal faults provides the required space for the earth s crust to thin and subside1 after initial rifting however the displacement on normal faults observed at the sea floor seems not to match the inferred extension2 here we show that crustal thinning can be accomplished in such extensional environments by a system of conjugate concave downward faults instead of multiple normal faults our model predicts that these concave faults accumulate large amounts of extension and form a very thin crust 10 km by exhumation of mid crustal and mantle material this transitional crust is capped by sub horizontal detachment surfaces over distances exceeding 100 km with little visible deformation our rift model is based on numerical experiments constrained by geological and geophysical observations from the alpine tethys and iberia newfoundland margins3 4 5 6 7 8 9 furthermore we suggest that the observed transition from broadly distributed and symmetric extension to localized and asymmetric rifting is directly controlled by the existence of a strong gabbroic lower crust the presence of such lower crustal gabbros is well constrained for the alpine tethys system4 9 initial decoupling of upper crustal deformation from lower crustal and mantle deformation by progressive weakening of the middle crust is an essential requirement to reproduce the observed rift evolution this is achieved in our models by the formation of weak ductile shear zones

lateral response of piles in weak calcareous sandstone existing design methods for laterally loaded piles in soft rock have insufficient supporting case history data and consequently cannot be regarded as having a high level of reliability this paper addresses the shortage of experimental data by describing the results from four instrumented lateral load tests on drilled and grouted piles installed in weak calcareous sandstone the derived lateral load transfer p y curves are first compared with existing approaches for weak rock and cemented soils the paper then examines the potential of using cone penetration test cpt data directly for the design analysis of laterally loaded piles in weak rock it is shown that equivalent elastic moduli of the rock controlling values of qc at the test site are very similar to those controlling lateral pile response this finding is used to formulate a simple bilinear p y approximation of the lateral response that requires qc data and an estimate of the rock s effective stress strength parameters it is shown that such

exploration for lacustrine carbonate reservoirs insights from west africa production from lacustrine carbonate reservoirs some of which are giant fields makes them an important exploration target in many nonmarine rift basins chevron and its partners produce significant quantities of oil from pre salt lacustrine carbonate reservoirs offshore cabinda angola the toca carbonates are highly productive in two of the four fields discovered and developed to date these fields are distributed among three subbasins which have varied from connected to isolated at different times kambala field in the kambala subbasin is productive from two zones in the toca the lower zone is a dolomitized coated grain grainstone packstone shoal system with primary and secondary porosity the upper zone is an algal biolithite which has been hydrothermally dolomitized resulting in secondary vuggy and intercrystalline porosity malongo west field in the malongo subbasin also produces from the toca but here reservoir pore systems range from chalky microporosity dominated to vuggy karst related types this field has produced over 240 mmbo from these lacustrine carbonates and is still producing today both of these fields are trapped in different structural configurations of the rift basin fault blocks kambala field is located on the bounding fault side of a tilted fault block this structural configuration produced a perched platformmore during deposition which facilitated the accumulation of a thick carbonate sequence malongo west field is located on the open quotes ramp close quotes side of a major basement controlled high where synsedimentary faulting is less important these reservoirs share many similarities with their counterparts in the campos basin of brazil less

major controlling factors on hydrocarbon generation and leakage in south atlantic conjugate margins a comparative study of colorado orange campos and lower congo basins abstract we present a supra regional comparative study of the major internal and external factors controlling source rock sr maturation and hydrocarbon hc generation and leakage in two pairs of conjugate margins across the south atlantic the brazil campos basin angola lower congo basin margins located in the central segment and the argentina colorado basin south africa orange basin in the southern segment our approach is based on the analysis and integration of borehole data 1d numerical modeling 2d seismic reflection data and published reports coupling of modeling results sedimentation rate calculation and seal bypass system analysis reveal that 1 oil window is reached by syn rift srs in the southern segment during the early to late cretaceous when thermal subsidence is still active while in the central segment they reach it in late cretaceous neogene during a salt remobilization phase and 2 early hc generation from post rift srs in the southern segment and from all srs in the central segment appears to be controlled mainly by episodes of increased sedimentation rates the latter seems to be associated with the andes uplift history for the western south atlantic basins campos and colorado and to a possibly climate driven response for the eastern south atlantic basins orange and lower congo additionally we observe that the effect of volcanism on sr maturation in the southern segment is very local the comparison of cretaceous mass transport deposit mtd episodes with hc peak of generation and paleo leakage indicators in the southern segment revealed the possible causal effect that hc generation and leakage have over mtd development interestingly paleogene leakage indicators which were identified in the argentina south africa conjugate margins occur contemporaneously to low sedimentation rate periods nonetheless present day leakage indicators which were also identified in both pairs of conjugate margins might be related to seal failure events linked to eustatic sea level drops

thermomechanical implications of sediment transport for the architecture and evolution of continental rifts and margins erosion and deposition redistribute mass as a continental rift evolves which modifies crustal loads and influences subsequent deformation surface processes therefore impact both the architecture and the evolution of passive margins here we use coupled numerical models to explore the interactions between the surface crust and lithosphere this interaction is primarily sensitive to the efficiency of the surface processes in transporting mass from source to sink if transport is efficient there are two possible outcomes 1 faulting within the zone of extension is longer lived and has larger offsets this implies a reduction of the number of faults and the width of the proximal domain 2 efficient transport of sediment leads to significant deposition and hence thermal blanketing this will induce a switch from brittle to ductile deformation of the upper crust in the distal domains the feedbacks between these two outcomes depend on the extension history the underlying lithospheric rheology and the influence of submarine deposition on sediment transport high erosion sedimentation during early faulting leads to abrupt crustal necking while intermediate syntectonic sedimentation rates over distal deep submarine hotter crust leads to unstructured wide distal domains in models where rheological conditions favor the formation of asymmetric conjugate margins only subaerial transport of sediments into the distal domains can increase conjugate symmetry by plastic localization these models suggest that passive margin architecture can be strongly shaped by the solid earth structure sea level and climatic conditions during breakup

symmetry vs asymmetry of a hyper thinned rift example of the mauleon basin western pyrenees france abstract the aim of this study is to unravel the tectono sedimentary evolution of a hyper thinned rift based on the example of the mauleon basin a basin filled by thick synrift deposits the integrated study combines field data detailed geological mapping and seismic interpretation the field study focuses on the iberian margin of the mauleon basin seismic interpretation and well calibration along a n s transect of the mauleon basin enable imaging the transition with the northern conjugate margin the synrift records are very different on either side of the basin the southern margin is composed of a proximal turbiditic s l siliciclastic system whereas the northern margin is characterized by a carbonate system extending from the platform to the basin we recognize the mauleon rift as an apparent symmetric hyper thinned rift related to a southward dipping albian detachment and a northward dipping cenomanian one two stages of continental crustal thinning are inferred to explain the development of the mauleon basin first a barremian to earliest albian ductile pure shear thinning phase responsible for the lower crustal thinning and the formation of a symmetric sag basin second an albian cenomanian simple shear thinning phase responsible for the onset of the southward dipping saint palais detachment faulting and for evolution to an asymmetric basin the iberian margin appears as an upper plate and the european one as a lower plate during albian time at early cenomanian time the basin was affected by structural changes of the margins resulting from shift in detachment direction interpreted as flip flop detachment tectonics

the geological development of the passive margins of the exmouth plateau off northwest australia abstract the exmouth plateau is a very large sunken continental block off australia s northwest shelf whose culmination lies 800 m below sea level it is elongated in a northeasterly direction and bounded by abyssal plains on three sides its broad tectonic framework is controlled by mesozoic rifting and transform faulting which accompanied the breakup of australia and greater india after which the plateau sank to bathyal depths the pre breakup sequence consists of more than 5000 m of palaeozoic and early mesozoic shallow marine to terrestrial detrital sediments the post breakup sequence consists of about 2000 m of late mesozoic and cainozoic marine sediments mainly carbonates the northern margin came into existence in the callovian 155 m y ago when a continental fragment separated from it and moved off to the northwest an early phase of rifting gave rise to triassic jurassic intermediate and acid volcanics 213 192 m y ago which overlie a thick triassic paralic sequence steady subsidence north of an east west hinge line allowed several thousand metres of early and middle jurassic carbonates and coal measures to accumulate before breakup breakup occurred along a series of rifted and sheared segments and the margin is further complicated by northeast trending callovian horsts and grabens the horsts were planed off in late jurassic and early cretaceous times and the whole margin was covered by a few hundred metres of late cretaceous and cainozoic pelagic carbonate as it sank steadily to its present average depth of 2000 2500 m the northeast trending western margin formed by rifting in the neocomian 120 125 m y ago as greater india moved off to the northwest callovian normal faults parallel the margin a thick triassic paralic sequence is unconformably overlain by thin late jurassic and younger marine sequences indicating that the area was high in the early and middle jurassic thin late cretaceous and cainozoic pelagic carbonates cover the margin which now lies more than 2000 m below sea level the northwest trending southern margin formed by shearing in the neocomian at the same time as the western margin it is cut by northeast trending normal faults which formed in the late triassic and callovian and is paralleled by neocomian and later normal faults a thick triassic paralic sequence is unconformably overlain by a thick late jurassic and neocomian delta suggesting that the area was high in the early and middle jurassic but a depocentre before and afterwards there was thermal uplift of more than 1000 m during the neocomian period of shearing and igneous intrusions buttressed the margin later normal faulting lowered the outermost margin and turned the uplift into a marginal anticline trending northwest the anticline had sunk beneath the sea by late in the cretaceous and thereafter this margin was covered by a thin sequence of pelagic carbonate which now lies beneath more than 1500 m of water

the influence of extension rate and crustal rheology on the evolution of passive margins from rifting to break up abstract extension rate and crustal strength are two important factors that influence the shape of initial rift basins and final passive margin architecture the extension rate will also affect crustal strength as the passive margin evolves therefore adding more complexity to the system we used thermomechanical numerical experiments to systematically explore the relationship of extension rate and initial crustal strength on final passive margin structure varying the initial amount of ductile crust from 33 to 70 and extension rates from 2 to 50 mm yr 1 results in passive margins of different widths shapes and evolution histories we find four distinct margin types type i narrow symmetric margins type ii wide symmetric margins type iii asymmetric margins and type iv rift jumping experiments with strong initial crust 33 ductile crust have crust mantle coupling of strain and produce narrow symmetric margins with high rift flank uplift type i margins ultraslow extension experiments 2 mm yr 1 undergo thermal cooling and produce wide symmetric margins with hyperextended crust type ii margins experiments with intermediate to fast extension rates 10 50 mm yr 1 and thick layers of ductile crust will produce initial rift basins that are symmetric but later rifting stages yield asymmetric conjugate margins with hyperextended domains 100 250 km wide type iii margins in special cases with intermediate extension rates and thick ductile crustal layers we observe a jump in rift location over 50 km and abandoned rifts with isolated crustal blocks type iv margins these results highlight how ductile crustal layers and extension rates influence passive margin formation during different stages of rifting

origin and diagenetic evolution of gypsum and microbialitic carbonates in the late sag of the namibe basin sw angola abstract ephemeral evaporitic conditions developed within the uppermost part of the transgressive late sag sequence in the namibe basin sw angola leading to the formation of extensive centimetre to metre thick sulphate bearing deposits and correlative microbialitic carbonates rich in pseudomorphs after evaporite crystals the onshore pre salt beds examined in this study are located up to 25 m underneath the major mid aptian evaporitic succession which is typified at the outcrop by gypsiferous bambata formation and in the subsurface by the halite dominated loeme formation carbonate evaporite cycles mostly occur at the top of metre thick regressive parasequences which progressively onlap and overstep landward the former faulted rift topography or fill major pre salt palaeo valleys the sulphate beds are made up of alabastrine gypsum associated with embedded botryoidal nodules dissolution related gypsum breccia and are cross cut by thin satin spar gypsum veins nodular and fine grained fabrics are interpreted as being diagenetic gypsum deposits resulting from the dissolution and recrystallisation of former depositional subaqueous sulphates whereas gypsum veins and breccia result from telogenetic processes the carbonates display a broader diversity of facies characterised by rapid lateral variations along strike thin dolomitic and calcitic bacterial mediated filamentous microbialitic boundstones enclose a broad variety of evaporite pseudomorphs and can pass laterally over a few metres into sulphate beds dissolution related depositional breccias are also common and indicate early dissolution of former evaporite layers embedded within the microbialites sulphate and carbonate units are interpreted as being concomitantly deposited along a tide dominated coastal supra to intertidal sabkha and constitute high frequency hypersaline precursor events prior to the accumulation of the giant saline mid aptian bambata and loeme formations petrographic and geochemical analyses reveal successive dissolution recrystallisation and cementation phases that occurred during burial uplift and exhumation implying a complex diagenetic evolution of both gypsum and carbonates influenced by pore fluids of diverse composition which distinctly varied from meso to telogenetic domains

role of structural inheritance and salt tectonics in the formation of pseudosymmetric continental rifts on the european margin of the hyperextended mauleon basin early cretaceous arzacq and tartas basins abstract arzacq and tartas were two cretaceous basins developing in the bay of biscay as secondary depocentres in the larger aquitaine basin they belong to an albian rift system where recent studies have stressed the role of simple shear thinning on the genesis of regional asymmetric basins however the two basins differ from recent models in having a pseudo symmetric morphology here we address the early cretaceous tectono sedimentary evolution of the arzacq and tartas rift basins and the lithospheric processes associated with their genesis these basins did not suffer major brittle deformation during rifting stage but nevertheless record a major change in their configuration between the aptian and the albian the arzacq basin shifted from a symmetric to a slightly asymmetric configuration this change was controlled by gravity sliding of the pre rift sedimentary cover in the eastern arzacq basin moving its depocenter south and by salt diapirism in the western arzacq basin moving its depocenter north several inherited paleozoic structures were reactivated as transfer zones and appear to be responsible for this depocenter shift the emplacement of salt diapirs at same time regionally limiting gravity sliding the tartas basin maintained a symmetric regime throughout the early cretaceous except along the barlanes transfer zone where the lussagnet salt diapir originated two drivers of subsidence are thus envisaged in the arzacq basin a neocomian aptian crustal thinning stage followed by reactivation of paleozoic faults in albian time accompanied by salt diapirism and gravity cover sliding the mauleon north pyrenean basin and its north adjacent tartas and arzacq basins thus formed part of a series of rift basins that progressed in maturity southward from a simple sag basin tartas to a slightly asymmetric basin aborted detachment arzacq to a hyperthinned basin mauleon our results offer new insights on the role of 1 structural inheritance in partitioning extensional strain 2 transfer zones as able to influence the sedimentary record of basins during crustal thinning and 3 pre rift salt decollements as able to separate the structural styles of sub and supra salt successions

syn rift regional subsidence across the west african continental margin the role of lower plate ductile extension abstract new ostracode data from the west african margin indicate that the outer basin sediment wedge also termed the pre salt wedge and the pre salt sag basin is neocomian to aptian in age and is contemporaneous with syn rift deposits developed inboard of the atlantic hinge zone despite the fact that the outer basin sediment wedge is clearly a syn rift deposit it does not exhibit any of the diagnostic characteristics of brittle deformation such as the existence of normal faults and the faulting and rotation of crustal blocks such features are common between the atlantic and eastern hinges for the early stages of rifting between west africa and brazil which occurred as a series of extensional phases commencing in the berriasian and culminating in the late aptian to reconcile the concomitant development of fault controlled subsidence between the hinges and across the atlantic hinge zone and sag basin development seaward of the atlantic hinge zone requires that 1 extension seaward of the atlantic hinge is the result of strain partitioning between a relatively non deforming upper crust i e the upper plate and a ductile deforming lower crust and lithospheric mantle i e the lower plate during the second and third rift phases while 2 between the hinges early brittle deformation normal faulting progresses to ductile deformation in the third rift phase during the third rift phase lower plate ductile deformation across the entire region generated regional subsidence both seaward of the atlantic hinge and between the hinges with little attendant brittle deformation this extension style produced directly or indirectly a sequence of crucial events across the west african margin 1 the development of the pre chela unconformity as lake level dropped in the early aptian exposing the prograding deltas of the argilles vertes formation 2 the regional development of the chela unconformity and transgressive lag deposits of the chela formation in the mid aptian 3 the development of regionally extensive shallow water restricted marine conditions across the entire margin between west africa and brazil immediately prior to evaporite precipitation and 4 the development of significant post rift accommodation deposition of the late cretaceous paleogene and neogene formations in the same region previously characterized by minor syn rift faulting repeated dessication cycles allowing the precipitation of thick evaporites and negligible erosional truncation of earlier syn rift units previous workers have suggested that the loeme evaporites were formed as part of the rapid early post rift phase of basin subsidence as the region became inundated by sea water across the walvis ridge in this model it is difficult to develop the restrictive environments required to deposit the thick 1 km evaporites of the loeme formation and the equivalent ezanga and ibura evaporites of gabon and brazil respectively across the entire west african brazilian rift system the existence of shallow water environments across the entire region is not consistent with water depths determined from the relief of clinoform foresets existing immediately prior to evaporite deposition thus requiring tectonic uplift of the deep water regions these evaporites therefore appear to be part of the late stage syn rift sediment package and the break up unconformity if it exists separates the loeme evaporites below from the overlying albian carbonates a direct consequence of ductile extension is one of increased heat input accompanying the rift stage in those areas dominated by syn rift sag basin development the distribution and amplitude of the heat pulse is governed by the geometry of the mid crustal weak zone and the distribution and amplitude of the lower plate extension seaward of the atlantic hinge zone the maximum heat flow is predicted to be in excess of 200 mw m 2 whereas between the hinge zones the heat flow is significantly less and ranges between 20mw m 2 and 100 mw m 2 because sediment temperature is a function of thermal conductivity and thickness of sediment overburden the viability of syn rift sources and prospectivity of the deep water west african margin will to a large degree depend on the delicate interplay between the cooling of the extended lithosphere and subsequent burial of source rocks as a function of time

the great west african tertiary coastal uplift fact or fiction a perspective from the angolan divergent margin 1 we explore exhumation in the coastal kwanza basin by combining analyses of tertiary hiatuses and apatite fission tracks planktonic biozones show five major hiatuses in the oligo miocene and plio pleistocene between gaps oligo miocene strata accumulated under marine conditions a marine setting refutes the idea of a massively raised coastal plateau in the mid tertiary marine conditions continued until 5 ma fission track data suggest three thermal events 150 ma during rifting and volcanism 100 70 ma during shortening and volcanism and 20 10 ma during exhumation tertiary uplift was spatially highly variable for the kwanza basin we infer that tertiary uplift on the west african margin is indeed a fact but that estimates of uplift timing and size are unreliable when extrapolated to adjoining areas massive uplift 2000 4000 m of the precambrian craton had little structural effect in the outer basin instead minor uplifts on the shelf drove late tertiary deformation on the slope

structural comparison of archetypal atlantic rifted margins a review of observations and concepts abstract in this study we compare three pairs of conjugate rifted margins that are often referred to as archetypes of rift systems despite numerous differences a remarkable first order structural similarity appears between the magma poor iberia newfoundland the magma rich mid norway east greenland and the sediment rich angola brazil rifted margins typical is the seaward arrangement of distinct domains proximal necking distal and outer that each present specific comparable structural characteristics our study also suggests that magma rich systems may go through a stage of hyper extension indicating that extreme crustal thinning does not preclude a magmatic breakup in this contribution we clarify the definition of a number of terms introduced recently in rifted margin studies we review the major features constitutive of these key referenced systems discuss their similarities and differences and examine how the related deformation modes develop in the life cycle of a rift that goes to seafloor spreading we conclude that the distinct domains observed in the margin architecture represent distinct stages in the evolution of rifted margin independently of their later evolution into magma poor or magma rich environments

complex rifted continental margins explained by dynamical models of depth dependent lithospheric extension observations from a number of rifted margins e g south atlantic salt basin mid norwegian margin exmouth plateau reveal wide regions of extremely attenuated crust and depositional environments that indicate depth dependent lithospheric extension although the one dimensional thermal kinematic consequences of depth dependent extension are understood no comprehensive process based explanation for the complex style of these margins exists here we present self consistent numerical models of passive margin formation that explain the depth dependent extension the width of the margin its characteristic tripartite nature and why such margins are prone to deposition of evaporites under appropriate climatic conditions some features that are important to reproducing the observed characteristics include decoupling between upper and lower parts of the lithosphere during stretching contrasting wide and narrow extensional styles above and below the decoupling level and progressive focusing of crustal extension toward the rift axis

rate effects on penetrometer resistance in kaolin this paper describes the results from a centrifuge investigation into the rate dependence of t bar and ball penetrometer resistance in kaolin four t bar diameters and two ball diameters were installed in kaolin with overconsolidation ratios of 1 2 and 5 at penetration velocities varying over five orders of magnitude the penetration resistances are compared with the properties of kaolin as measured in element tests to assist in the development of a framework that describes this resistance over the full velocity range consistent trends emerge when the soil viscosity is assumed to affect the penetration resistance in both the partially drained and undrained conditions enabling the dependence of the t bar and ball resistances on diameter velocity and soil characteristics to be quantified

ordovician graptolite biostratigraphy in the welsh basin a review ordovician graptolite biostratigraphy in wales is crude compared with that of the silurian and is in need of refinement especially by detailed collecting from suitable sections and consequent taxonomic work this has been done in parts of the arenig llandeilo and lower caradoc successions there is particular potential for subdivision of and improvement in the correlation of the llanvirn series and the gracilis linearis biozones but there is little prospect of much new and detailed information from the upper tremadoc or ashgill series

controls on the thermomechanical evolution of hyperextended lithosphere at magma poor rifted margins the example of espirito santo and the kwanza basins high quality long offset seismic data from many distal rifted margins show evidence for hyper extended 10 km thick crust direct observation of such domains is challenging as they lie at great water depth buried beneath thick sedimentary sequences and formed by rock assemblages that are hydrated and geophysically indistinguishable only a few drill holes have penetrated basement at ultradistal rifted margins these observations together with outcrops of preserved analogs exposed in collisional orogens suggest that the complex interaction of detachment faults rooted in a subhorizontal shear zone in the hyperextended crust or in the serpentinized mantle controls the formation of the ocean continent transition while depth dependent thinning controls the early phases of rifting conforming to classical rift models we still have a superficial understanding of how normal faults and subhorizontal shear zones form and evolve during rifting and lithospheric breakup here we develop a rheological parameterization to simulate the formation of and slip on large offset normal faults rooted in growing brittle to ductile shear zones the evolution of these structures leads to the creation of a hyperextended crust and eventually exhumed serpentinized mantle we also propose a simplified formulation to simulate magmatic underplating and seafloor spreading the resulting numerical models provide a self consistent picture for the evolution of magma poor rifted margins from initiation of rifting to seafloor spreading the model results are compared with first order observations of the kwanza and espirito santo conjugate margins in the south atlantic as well as of magma poor margins globally

depositional wedge cycles on evolving plate margin western and northwestern australia the barrow province lies at the transition between the western and northwestern rift domains of the australian continental margin as these domains evolved during the mesozoic five depositional wedge sequences developed in the eastern half of the province each sequence possesses distinct stratigraphic and sedimentological characteristics which differs from the others as a function of proximity direction and style of rift related diastrophism along the evolving margin the first depositional sequence developed during the triassic as part of a regional tethyan facing passive margin clastic wedge this event was followed during the early and middle jurassic by a second more provincial sequence in response to early syn rift fault related subsidence by the callovian a deep anastomosing rift complex had formed and deposition of the third late jurassic cycle was initially very localized confined by the new graben topography however stratigraphic continuity returned during post breakup subsidence of the northwestern margin as subregional depositional systems began to bury the fragmented borderland this cycle was terminated at the close of the jurassic in response to renewed rifting between western australia and greater india sediment stripped from t e uplifted rift shoulders fed the northerly prograding barrow delta system to form a fourth depositional sequence during the late jurassic early neocomian the final cycle commenced as greater india uncoupled from australia during the middle neocomian post breakup subsidence is reflected by a major regional transgression and the development of a second margin wide depositional wedge during the later cretaceous the close temporal and spatial relationship that exists between these cycles and the evolution of the western and northwestern australian continental margin emphasizes the importance of tectonic control upon sedimentation

interpretation of layer boundaries and shear strengths for soft stiff soft clays using cpt data ldfe analyses abstractthis paper describes a new approach for interpreting cone penetrometer data in soft stiff soft clay deposits the identification of layer boundaries and interpretation of shear strength profile were of particular interest the proposed approach was based on an extensive parametric study using large deformation finite element ldfe analyses with a standard cone penetrometer penetrated continuously from the soil surface the ldfe model has been validated against existing theoretical solutions and numerical results with good agreement obtained regardless of strength ratio between two successive layers the interface of soft stiff layers can be identified at 0 8d d is the cone diameter below the kink in penetration resistance curve in the top soft layer the interface of stiff soft layers can be demarked at 1 3d above the kink in the penetration resistance profile in the bottom soft layer the undrained shear strength of a soft clay layer can be interpreted using a single layer approach and the

science and empiricism in pile foundation design scientific approaches to pile design have advanced enormously in recent decades and yet still the most fundamental aspect of pile design that of estimating the axial capacity relies heavily upon empirical correlations improvements have been made in identifying the processes that occur within the critical zone of soil immediately surrounding the pile but quantification of the changes in stress and fabric is not straightforward this paper addresses the degree of confidence we can now place a on the conceptual and analytical frameworks for estimating pile capacity and b on the quantitative parameters required to achieve a design the discussion is restricted to driven piles in clays and siliceous sands with particular attention given to extrapolating from design approaches derived for closed ended piles of relatively small diameter to the large diameter open ended piles that are used routinely in the offshore industry from a practical viewpoint we need design approaches that minimise sensitivity

graptolites in british stratigraphy 697 taxa of planktonic graptolites are recorded and their stratigraphical ranges are given through 60 biozones and subzones in the ordovician and silurian strata of england wales and scotland in the first such stratigraphical compilation for great britain since the synthesis of elles wood 1901 1918