impact of inversion tectonics on hydrocarbon entrapment in the baggara basin western sudan abstract the baggara basin of sudan is an ene wsw trending basin located within the west and central africa rift system wcars and nw of the muglad basin the trend of the baggara basin is similar to other basins in eastern chad where oil has been discovered since there are no published studies for the baggara basin the present paper represents an addition to the geology of eastern extension of the wcars in sudan the 2d seismic data interpretation sheds light on the development and evolution of key regional and local structures of the basin the baggara basin is characterized by graben geometry with two boundary faults characterized by dextral strike slip movement and a depocenter at the central part the interpretation reveals the presence of two types of structures within the baggara basin inversion tectonics restricted to the larger basin bounding faults in the western part and en echelon faults in the central part the timing of inversion tectonics is during the eocene and it is related to a brief major compressional event due to the collision of the african and eurasian plates although the inversion created a four way dip closed anticline structure this anticline postdated the initial migration from the source rock accordingly the anticline structural is unsuccessful for hydrocarbon entrapment

stationary rossby wave propagation in a baroclinic atmosphere observational studies of teleconnections in both soisticial seasons have suggested various patterns of behaviour linked mainly to westerly jets and equatorial westerlies these have been interpreted using barotropic rossby wave theory and simulated using stationary forcing in barotropic models linearized about 300 hpa flows in this paper the relevant propagation behaviour is investigated using a baroclinic model with three dimensional climatological basic states time integrations are performed using localized thermal forcing as a wavemaker the propagation results are qualitatively very similar to those obtained with the barotropic model though there are quantitative differences the westerly jets still act as strong waveguides the shorter wavelengths and smaller wave activity speeds found with the baroclinic model are generally in better agreement with observation propagation into and from the upper tropospheric equatorial westerlies in the east pacific propagation across north america and propagation from europe across the arabian gulf are all found the extent to which upper tropospheric westerlies reach towards the equator influences the propagation into those regions barotropic models can only represent such behaviour if the basic state reflects the near equatorial upper tropospheric zonal wind structure

why do baroclinic waves tilt poleward with height theoretical and modeling studies of nongeostrophic effects in baroclinic waves predict that baroclinic waves should tilt poleward with height with a larger tilt in total meridional wind than in geostrophic quantities regression analysis of ncep ncar reanalysis 6 hourly data demonstrates that observed baroclinic waves do indeed tilt poleward with height although the observed tilt is smaller than predicted by previous studies the meridional ageostrophic wind enhances the poleward tilt of meridional wind perturbations despite being smaller in amplitude than the meridional geostrophic wind by a factor of 5 an improved estimate of the structure of the meridional ageostrophic wind in baroclinic waves is calculated assuming force balance several important terms in this estimate have been left out of previous estimates of the meridional ageostrophic wind three terms in the improved estimate produce nearly all of the poleward tilt of the meridional wind 1 the advection of geostrophic zonal wind perturbations by the mean zonal wind 2 the convergence of the eddy momentum flux and 3 the effect of friction the poleward tilt with height of baroclinic waves explains why upper level storm tracks tend to occur poleward of near surface baroclinic regions and may play a role in the midwinter suppression of the pacific storm track

causes of reduced north atlantic storm activity in a cam3 simulation of the last glacial maximum abstract the aim of this paper is to determine how an atmosphere with enhanced mean state baroclinity can support weaker baroclinic wave activity than an atmosphere with weak mean state baroclinity as a case study a last glacial maximum lgm model simulation previously documented to have reduced baroclinic storm activity relative to the modern day climate simulated by the same model despite having an enhanced midlatitude temperature gradient is considered several candidate mechanisms are evaluated to explain this apparent paradox a linear stability analysis is first performed on the jet in the modern day and the lgm simulation the latter has relatively strong barotropic velocity shear it was found that the lgm mean state is more unstable to baroclinic disturbances than the modern day mean state although the three dimensional jet structure does stabilize the lgm jet relative to the eady growth rate next feature tracking was used to assess the storm track seeding and temporal growth of distur

interannual and decadal modulations recently observed in the pacific storm track activity and east asian winter monsoon abstract interannual variability of the north pacific storm track observed over 17 recent winters is documented the local storm track activity is measured by a meridional flux of sensible heat associated with the lower tropospheric subweekly fluctuations the interannual variability in the heat flux over the northwestern nw pacific is found to be strongest in midwinter the first empirical orthogonal function of the interannual variability in midwinter captures the decadal tendency toward the enhanced storm track activity in midwinter over the nw pacific in association with the decadal weakening of the east asian winter monsoon siberian high and the aleutian low that occurred in the late 1980s the most marked signature of this enhancement is that the midwinter minimum in the storm track activity which had been apparent in the early to mid 1980s almost disappeared afterward as opposed to linear theory of baroclinic instability the enhanced activity occurred despite the weakening of the pacific j

pacific north american teleconnection controls on precipitation isotope ratios across the contiguous united states large scale climate teleconnections such as the pacific north american pna pattern strongly influence atmospheric processes and continental climate here we show that precipitation 18o values in the contiguous united states are correlated with an index of the pna pattern the 18o pna relationship varies across the study region and exhibits two prominent modes with positive correlation in the western usa and negative correlation in the east this spatial pattern appears not to reflect variation in local climate variables but rather primarily reflects differences in atmospheric circulation and moisture sources associated with pna our results suggest that strong antiphase variation in paired paleo water 18o proxy records from regions characterized by the two modes of 18o pna correlation especially in the midwest and southwestern usa may provide a robust basis for reconstruction of past variation in the pna pattern

present day crustal deformation and geodetic strain in the vicinity of dholavira harappan civilization site kachchh western part of the indian plate abstract to understand the geodynamics in the vicinity of dholavira a harappan civilization site hcs in kachchh western india gps data from 2009 to 2015 were processed and analyzed tectonically this part of northern kachchh is in the influence of island belt fault ibf and allah bund fault abf and is seismically one of the most active intra plate regions of india the motion with respect to indian plate is used for the estimation of deformation and strain rate while fault associated slip rate has been estimated by inverse modeling of observed site motions the analysis reveals that the abf deforms with an average rate of 1 8 mm yr however the segmented ibf has a maximum deformation rate of 2 9 mm yr towards the pachham island and minimum towards the khadir island the computation discloses a maximum seismic moment m0 of 2 1 1024 dyne cm in this part which corresponds to an earthquake of mw 6 0 the calculated maximum strain of 0 04 micro strain year is low but significant in the intra plate region the postseismic deformation after the mw 7 7 2001 bhuj earthquake is estimated to be low in this part the reverse along with strike slip motion of faults builds up stress in the area and accumulating more strain

early cretaceous rifts of western and central africa an overview abstract the structure and evolution of early cretaceous rift basins in western and central africa are described two stages of rift development and fracturing have been identified 1 from neocomian to early aptian roughly e w and nw trending troughs upper benue n cameroon s chad sudan etc opened in response to a submeridian extensional regime in central africa while in western africa the n s trending transsaharian fault zone acted as a sinistral wrench 2 from middle aptian to late albian large northwest trending troughs e niger sudan sirte etc opened in response to a northeast extensional regime while the central african fault zone from benue to sudan exhibited strike slip movements generating pull apart basins these rift and fracture systems delimit three large blocks within the african plate a western block an arabian nubian block and an austral block the arabian nubian block tends to separate from the two other blocks migrating towards the north during the first stage of basin development and then towards the ne during the second stage the opening of the atlantic ocean was the dominant driving force for the western and austral blocks while the arabian nubian block probably moved in response to the opening of the indian ocean and to the evolution of the tethyan margin

linear contributions of different time scales to teleconnectivity the contributions of different time scales to extratropical teleconnections are examined by applying empirical orthogonal functions and correlation analyses to reanalysis data it is shown that eddies with periods shorter than 10 days have no linear contribution to teleconnectivity instead synoptic variability follows wavelike patterns along the storm tracks interpreted as propagating baroclinic disturbances in agreement with preceding studies it is found that teleconnections such as the north atlantic oscillation nao and the pacific north america pna pattern occur only at low frequencies typically for periods more than 20 days low frequency potential vorticity variability is shown to follow patterns analogous to known teleconnections but with shapes that differ considerably from them it is concluded that the role if any of synoptic eddies in determining and forcing teleconnections needs to be sought in nonlinear interactions with the slower transients the present results demonstrate that daily variability of teleconnection indices cannot be interpreted in terms of the teleconnection patterns only the slow part of the variability

differential opening of the central and south atlantic oceans and the opening of the west african rift system abstract plate tectonic studies of the development of the central and south atlantic oceans using seasat and geosat altimeter and magnetic anomaly isochron data now provide quantitative models of seafloor spreading through time such models enable an initial assessment of the differential opening between these two oceanic basins to be determined the equatorial atlantic is an integral part of this oceanic rifting process allowing stresses arising from the differential opening to be dissipated into both the caribbean and africa along its northern and southern boundaries respectively the tectonic model for the west african rift system based on geological and geophysical studies shows a series of strike slip fault zones diverging into africa from the gulf of guinea and dissipating their shear movement into the development of extensional basins orientated perpendicular to these faults zones the development of the west african rift system was contemporaneous with the early opening of the south atlantic continued to develop well after the final breakup of south america from africa and did not cease until the late cretaceous when there was a major phase of basin inversion and deformation santonian 80 ma deformation across the benue trough nigeria is broadly contemporaneous with dextral shear reactivation of the central african fracture system which in turn resulted in renewed extension in the sudan basins during the late cretaceous and early tertiary this paper illustrates the close linkage in both time and space between the history of the african rift basins and the opening of the atlantic both exhibit distinct phases of evolution with the rift basins developing in direct response to the differential opening between the central and south atlantic in order to dissipate stresses generated by this opening the mesozoic tectonic model proposed is therefore one of an intimate interaction between oceanic and continental tectonics

effects of initial rift inversion over fold and thrust development in a cratonic far foreland setting abstract the effects of initial rift inversion over the geometry of a far foreland intracratonic fold and thrust belt are investigated a total of 25 seismic reflection lines and stratigraphic data from 9 wells are used in association to digital elevation and field geological data to investigate the geometric relationship between shallow thrust development and initial positive inversion of buried rift faults in a cratonic environment where inversion tectonics is not common the study case is conducted in the meeting region of the opposed verging brasilia and aracuai foreland fold and thrust neoproterozoic belts located in central brazil formed in the first stages of west gondwana amalgamation seismic reflection sections are used to map buried paleorift faults and trust ramps the best 5 sections are also interpreted in detail in terms of fold and thrust geometry and their relationship to the inverted rifts is analyzed they show high correlation between shallow fold and thrust geometry and the shortening of synrift strata caused by rift inversion results indicate that initial positive rift fault reactivation exerts a determinant control over the locus of thrust ramp nucleation by causing syn rift strata to overfold and drape fold the passive folding propagates upwards forming gentle folds in the decollement plane where thrust ramps tend to nucleate back thrust forethrust pairs tend to form over elevated horsts where higher topographic plateaus are preserved multiple thrusting and lower relief occur over buried rifts with multiple inverted faults strata over non rifted basement remain practically unaffected by thrusting and folding moreover the development of thrust salients and recesses are demonstrated to be conditioned by the morphology of buried rifts the study also contributes with a more precise mapping of the buried rift system and thrust system in the area and brings new insights about the structural evolution of the brasiliano pan africano orogeny affecting the sao francisco craton basement and covers

a pathway connecting the monsoonal heating to the rapid arctic ice melt abstractthis study provides a monsoonal link to the rapid arctic ice melt each year the planetary scale african asian monsoonal outflow near the tropopause carries a large anticyclonic gyre that has a longitudinal spread that occupies nearly half of the entire tropics in recent years the south asian summer monsoon has experienced increased rainfall over northwestern india and pakistan and it has also contributed to more intense local anticyclonic outflows from this region the western lobes of these intense upper high pressure areas carry outflows with large heat fluxes from the monsoon belt toward central asia and eventually to the region of the rapid ice melt of the canadian arctic in this study this spectacular pathway has been defined from airflow trajectories heat content and heat flux anomalies most of these show slow increasing trends in the last 20 years the monsoonal connection to the rapid arctic ice melt is a new contribution of this study this is shown from the passage of a vertical c

vertical structure and energetics of the western pacific teleconnection pattern abstractthe western pacific wp pattern characterized by north south dipolar anomalies in pressure over the far east and western north pacific is known as one of the dominant teleconnection patterns in the wintertime northern hemisphere composite analysis reveals that monthly height anomalies exhibit baroclinic structure with their phase lines tilting southwestward with height in the lower troposphere the anomalies can thus yield not only a poleward heat flux across the climatological thermal gradient across the strong pacific jet but also a westward heat flux across the climatological thermal gradient between the north pacific and the cooler asian continent the resultant baroclinic conversion of available potential energy ape from the climatological mean flow contributes most efficiently to the ape maintenance of the monthly wp pattern acting against strong thermal damping effects by anomalous heat exchanges with the underlying ocean and anomalous precipitation in the subtropics and by the effec

characteristics of wave packets in the upper troposphere part i northern hemisphere winter abstract gridded data produced by the ecmwf reanalysis project have been analyzed to document the properties of wave packets in the northern hemisphere winter midlatitude upper troposphere based on results from earlier investigations 300 hpa meridional wind variations were chosen for analysis wave packet envelopes were also defined by performing complex demodulation on the wind data the properties of the wave packets are mainly illustrated using time lagged one point correlation maps performed both on and wave packet envelopes the results show that over most regions in the northern hemisphere winter with the exception of the deep tropics and near the aleutian low medium scale waves dominant wavenumber 5 8 exhibit the characteristics of downstream development and occur within wave trains that propagate with eastward group velocities much faster than the phase speeds of individual phases of the waves their group velocity is highly correlated with the local time mean 200 400 hpa wind while the

coupled surface subsurface hydrologic model of a nuclear subsidence crater at the nevada test site a series of computer models describing overland flow ponding and infiltration was dynamically linked to simulate the movement of water during seepage beneath a nuclear subsidence feature the coupled surface subsurface hydrologic model contains a terrain analysis module an overland flow simulator using the kinematic wave equation and a numerical richards equation solver to simulate moisture migration within the vadose zone simulations resulted in successful approximations to measured surface and subsurface data the surface water overland flow component was able to reach an agreement between observed and simulated water levels following a precipitation event long term simulations underpredicted the volumetric water contents and depth of moisture fronts the flux darcian velocity at 10 m below the surface was temporally stable with a temporal mean value of 0 75 m year 1 which is in agreement with an earlier estimate of 0 60 m year 1 the mean flux at 5 m below the surface was 1 4 m year 1 long term simulations suggest that significant recharge does exist beneath surface collapse structures owing to periodic ponding

mid cretaceous inversion in the northern khorat plateau of lao pdr and thailand evidence is presented from the study area for the occurrence of a regional compressive tectonic event in the mid cretaceous aptian cenomanian this is tentatively attributed to the effects of a distant continent continent collision to the west pre existing structural trends were reactivated parallel to palaeo continental sutures to the northeast song ma and song da and west nan the event interrupted the latest jurassic to earliest palaeocene subsidence and continental sedimentation of the khorat plateau basin the primary effects are shown by seismic data to be regional tilting compressive folding reverse faulting and inversion of the basin subsidence pattern the data do not support the current view that such structuring was initiated during the tertiary however they do show that there was some reactivation of mid cretaceous structures during regional uplift in the tertiary this revision of timing of structuring suggests the hydrocarbon potential of the area may be greater than previously anticipated

transient electromagnetic investigations in a tectonic domain of the kachchh intraplate region western india a morphotectonic study of the kachchh mainland fault

dynamical characterization of the fastex cyclogenesis cases summary a series of diagnostics based on the automatic tracking of cyclones is applied to the 25 life cycles captured during the fastex field experiment the tracking enables a setting of the various cases into a common frame of reference that moves with the system time filtering is used to further separate the events into a basic state and perturbations information is obtained on environmental properties such as strain or baroclinicity combining these diagnostics it is shown that instability mechanisms based on the existence of potential vorticity strips or the control of these instabilities by deformation may be involved in the initial genesis of a number of cases but do not seem to characterize specific types nor to determine a systematic behaviour on the other hand it is shown that rapid deepening phases leading eastern atlantic systems to their maximum amplitude happens suddenly and at the same time as crossing the jet stream even in the absence of a clear additional upper level feature for cold air systems development means meeting a diffluent zone this is unlike the american east coast systems that are associated with an exit entrance complex another remarkable feature is the generation of a frontal waveas a re sult of the parent vorticity maximum being apparently stretched and split this has occurred in 25 of cases a number of other properties of the fastex cases are shown such as several occurrences of large

mesozoic plate tectonic reconstructions of the central south atlantic ocean the role of the west and central african rift system abstract the mesozoic opening history of the central equatorial and south atlantic oceans is closely linked in time and space to the development of the cretaceous rift system in west and central africa geological and geophysical studies of the west and central african rift system indicate it to be dominated by a set of sinistral and dextral strike slip zones diverging from the gulf of guinea and terminating as extensional rift basins in niger and sudan plate tectonic studies of the opening history of the atlantic basins indicate four stages of development stage 1 the jurassic opening of the central atlantic stage 2 the early cretaceous 130 119 ma opening of the south atlantic with rifting propagating deep into africa via the benue trough stage 3 the opening of the equatorial atlantic 119 105 ma and stage 4 the linkage of these oceanic basins and development of a single opening mid oceanic rift system as seen today the west and central african rift system continued to develop until the end of the cretaceous i e into stage 4 when rifting was terminated by a compressional shear deformation event causing the folding of sediments in the benue trough and reactivation of the central african shear zone and extensional tectonics in the basins of southern sudan this event correlates with an important change in the relative opening of the atlantic basins during tertiary recent times the west african rift system has not been active however during this period domal uplift and volcanism have occurred in central cameroon and western sudan and a very active phase of volcanism has occurred within the last 10 ma along the present day cameroon volcanic line although these uplift and volcanic events indicate thermal processes in the upper mantle there is as yet no clear link between their development and plate tectonic processes

space time spectral analysis of the southern hemisphere daily 500 hpa geopotential height in this paper the authors use the ncep department of energy doe reanalysis 2 ncep2 data from 1979 to 2004 to expand the daily 500 hpa geopotential height in the southern hemisphere sh 908 208s into a double fourier series and analyze the temporal frequency characteristics of the expansion coefficients over various spatial scales for the daily series over the whole year the coefficient series of the extratropical mean heightischaracterizedbyasignificantlow frequency 10 30day variation forzonalwaveswith k l 5 1 5

horizontal structure of 500 mb height fluctuations with long intermediate and short time scales abstract maps of standard deviations and one point correlation maps based on twice daily data subjected to a variety of temporal filters are presented in order to document the horizontal structure of 500 mb height fluctuations with different time scales the filters have been chosen to isolate fluctuations with long time scales periods much longer than 30 days intermediate time scales 10 30 day periods and short time scales 2 5 6 day periods the one point correlation maps for long time scales resemble the teleconnection patterns described by wallace and cutzler these patterns are strongly regionally dependent with meridionally oriented dipole structures in the jet exit regions over the oceans indicative of strong fluctuations in the zonal wind for intermediate time scales the dominant patterns consist of more zonally oriented wave trains which originate in the jet entrance regions and cross the jet streams as they curve southeastward into the tropics another important distinction between th

revitalising exploration and re development of deep carbonate targets in the southern apennines thrust belt southern italy reappraising vintage data with modern approaches

patterns of wintertime jet stream variability and their relation to the storm tracks abstract a new approach is put forward for defining extratropical teleconnection patterns the zonal wind field at 250 hpa is analyzed separately in the north atlantic and north pacific ocean sectors during the winter season december march teleconnectivity of this field is found to be particularly strong eof analysis of the zonal wind field yields patterns that i are robust with respect to the range of frequencies included in the data ii relate clearly to the position of the climatological mean jets and iii are broadly consistent with their traditionally defined counterparts in terms of climatic impacts the patterns are characterized by a north south shifting or an extension retraction of the eddy driven jet in its exit region and similar changes at the entrance region of the subtropical jet the patterns also reflect the degree of separation between the subtropical and eddy driven jets atlantic eofs 1 and 2 are counterparts of the north atlantic oscillation nao and eastern atlantic patter

the late cretaceous tectonic evolution of the south china sea area an overview and new perspectives from 3d seismic reflection data abstract the late cretaceous is a significant geologic period in the south china sea area as it marks the tectonic transition from the early paleo pacific plate subduction to the subsequent cenozoic rifting related to the opening of the scs however the late cretaceous tectonic evolution of the south china sea area is yet to be clearly defined and it is at present largely debated in the literature in this paper mainly on the basis of 240 000 km2 newly acquired 3d seismic reflection data 94 industrial wells and existing u pb ages of basement granitoids we carried out an integrated interpretation mapping and analysis of the pre cenozoic 66 ma structures within the basement of the cenozoic rift basin in the northern south china sea area that can be crucial for a broad understanding of the late cretaceous tectonic evolution of this region results of this analysis suggest that three late cretaceous fault systems can be identified in the northern south china sea margin 1 the wnw striking thrust system 2 ene striking extensional fault system and 3 ene striking thrust system these three fault systems are considered to have developed in the late cretaceous since they are superimposed on the well dated late jurassic to early cretaceous 161 6 101 7 ma arc related granitoids that define most of the basement of the cenozoic rift basin within the study area this new structural evidence combined with a review of previous studies led us to propose a renewed multi phase geodynamic evolutionary model of the south china sea area during the late cretaceous the first tectonic event that can be recognized generated the wnw striking thrust system and is in this paper interpreted to have formed as a result of a sinistral transpressional event that took place in the south china sea area and adjacent areas around 100 ma at the early late cretaceous boundary this transpressional event was likely related to intense oblique convergence between the paleo pacific ocean plate and the eurasia plate the second tectonic phase that was identified in this paper 100 ma to 72 ma is defined by an extensional event that generated the largely ene striking extensional fault systems and associated basins which is interpreted to be related to the back arc extension that took place in this period in response to the slab roll back and high angle subduction of the paleo pacific plate this extensional phase eventually led to the opening of the proto south china sea on the se margin of the proto south china block and it should be distinguished from the cenozoic rifting phases that are related to the opening of the south china sea the third and last tectonic phase that was recognized in this paper is a compressional event that took place in the late stage of the late cretaceous 72 ma to 66 ma and was responsible for the development of the ene striking thrust system we suggest that this post subduction post yanshanian compressional event can be interpreted to have developed in response to process of ridge push related to the sea floor spreading of the proto south china sea

the influence of a reverse reactivated normal fault on natural fracture geometries and relative chronologies at castle cove otway basin abstract despite the ubiquity of normal faults that have undergone compressional inversion documentation of the structural history of natural fractures around these structures is limited in this paper we investigate the geometries and relative chronologies of natural fractures adjacent to a reverse reactivated normal fault the castle cove fault in the otway basin southeast australia local variations in strain resulted in greater deformation within the fault damage zone closer to the fault structural mapping within the damage zone reveals a complex tectonic history recording both regional and local perturbations in stress and a total of 11 fracture sets were identified with three sets geometrically related to the castle cove fault the remaining fracture sets formed in response to local stresses at castle cove rifting in the late cretaceous resulted in normal movement of the castle cove fault and associated rollover folding and the formation of the largest fracture set reverse reactivation of the fault and associated anticlinal folding occurred during late miocene to pliocene compression rollover folding may have provided structural traps if seals were not breached by fractures however anticlinal folding likely post dated the main episodes of hydrocarbon generation and migration in the region this study highlights the need to conduct careful reconstruction of the structural histories of fault zones that experienced complex reactivation histories when attempting to define off fault fluid flow properties

mesozoic diapirism in the pyrenean orogen salt tectonics on a transform plate boundary the mesozoic history of the pyrenean region was dominated by the opening of the north atlantic ocean and the left lateral movement of iberia relative to europe most deformation was tensional or transtensional but this style was interrupted by several short compressional events perhaps related to bends in the transform plate boundary or minor changes in plate movement directions these compressional events were recorded by deformation adjacent to and above salt structures which were the weakest parts of the system and so served as especially sensitive strain barometers the alternation of extension and shortening controlled the location and style of salt structures evaporites were initially deformed during the latest jurassic early cretaceous neocimmerian transpression which formed salt cored anticlines above west northwest east southeast trending basement faults transtension in the aptian albian caused salt domes to pierce to the surface at the intersections of these anticlines with reactivated northwest southeast and northeast southwest trending basement structures transtension was at least locally interrupted by brief periods of transpression at the aptian albian and albian cenomanian boundaries transpression shortened the diapirs causing rotation uplift and erosion of beds near the salt most diapirs were buried during the late cretaceous in some cases postburial hydrothermal circulation dissolved much of the halite causing the diapirs to sag and the basins to form in roof strata finally the entire region was shortened during the late cretaceous tertiary pyrenean orogeny which greatly distorted many of the preexisting geometries

quasi biweekly oscillation over the tibetan plateau and its link with the asian summer monsoon abstract intraseasonal variation isv is especially prominent and unique in the asian summer monsoon region in this work the dominant isv mode over the tibetan plateau tp in the summer monsoon season june august together with its structure and evolution is identified using station observations global precipitation climatology project precipitation data and era interim during 1979 2011 results indicate that quasi biweekly oscillation qbwo is the dominant mode of isv over the tp and is significant in terms of the circulation precipitation and diabatic heating fields in particular the qbwo is closely related to the onset and active break phases of the tp summer monsoon in most cases the qbwo originates from the equatorial western pacific and first propagates northwestward to the bay of bengal and northern india then northward to the southeastern tp and finally eastward to the east asian area showing a clockwise propagation pathway two main mechanisms are responsible for the northward

reconstructing sea level pressure variability via a feature tracking approach abstractthe aim of this paper is to quantify the contribution of synoptic transients to the full spectrum of space time variability of sea level pressure slp in middle latitudes in previous work by the authors it was shown that tracking cyclones and anticyclones in an idealized atmospheric model allows one to reconstruct a surprisingly large fraction of the model s variability including not only synoptic components but also its large scale low frequency component motivated by this result the authors performed tracking of cyclones and anticyclones and estimated cyclone and anticyclone size and geometry characteristics in the observed slp field using the 1948 2008 ncep ncar reanalysis dataset the reconstructed synoptic field was then produced via superimposing radially symmetrized eddies moving along their actual observed trajectories it was found that similar to earlier results for an idealized model the synoptic reconstruction so obtained accounts for a major fraction of the full observed slp v

inversion tectonics in central africa rift system evidence from the heglig field abstract the mesozoic cenozoic tectonic history of the muglad basin is dominated by extension and inversion tectonics but evidence of the inversion tectonics has not been well documented yet in some other rift basins of cars and wars the phase of the inversion tectonics is well documented by several authors this paper presents a structural study of the heglig field area located on the eastern flank of the muglad basin detailed 3d seismic interpretation allows a better understanding of the structural style of the heglig field the new structural analysis has shown that the heglig field has a complex structural framework reflected in the presence of a combination of two structural styles the extensional structure is influenced by inversion tectonics during the santonian time that creates four way dip anticline structure overprinted by the subsequent extensional movement that creates tilted fault block the presence of inversion tectonics has supported by different means including seismic reflection velocity and source rock maturity data the authors attributed the trapping of oil in the lower bentiu reservoir that requires a horizontal seal to the presence of the four way dip anticline structure created by the inversion tectonics the current interpretation of the heglig field 3d seismic data sheds new light on the development and evolution of a key structure in the muglad basin the results help to resolve long standing discussion concerning hydrocarbon accumulation of the lower part of bentiu formation that lacks horizontal sealing

afro eurasian intermediate frequency teleconnection and modulation by enso abstractthe afro eurasian intermediate frequency atmospheric teleconnection conveys meteorological signals zonally leads to various atmospheric variations and causes extreme events along its path

interannual variations and future change of wintertime extratropical cyclone activity over north america in ccsm3 climatology and interannual variations of wintertime extratropical cyclone frequency in ccsm3 twentieth century simulation are compared with the ncep ncar reanalysis during 1950 1999 ccsm3 can simulate the storm tracks reasonably well although the model produces slightly less cyclones at the beginning of the pacific and atlantic storm tracks and weaker poleward deflection over the pacific as in the reanalysis frequency of cyclones stronger than 980 hpa shows significant correlation with the pacific north america pna teleconnection pattern over the pacific region and with the north atlantic oscillation nao in the atlantic sector composite maps are constructed for opposite phases of el nino southern oscillation enso and the nao and all anomalous patterns coincide with observed one ccsm3 twenty first century a1b scenario realization indicates there is significant increase in the extratropical cyclone frequency on the us west coast and decrease in alaska meanwhile cyclone frequency increases from the great lakes region to quebec and decreases over the us east coast suggesting a possible northward shift of the atlantic storm tracks under the warmer climate the cyclone frequency anomalies are closely linked to changes in seasonal mean states of the upper troposphere zonal wind and baroclinicity in the lower troposphere due to lack of 6 hourly outputs we cannot apply the cyclone tracking algorithm to the other eight ccsm3 realizations based on the linkage between the mean state change and the cyclone frequency anomalies it is likely a common feature among the other ensemble members that cyclone activity is reduced on the east coast and in alaska as a result of global warming

push up inversion structures v fault bend reactivation anticlines along oblique thrust ramps examples from the apennines fold and thrust belt italy the study of inversion structures in fold and thrust belts that originated as extensional faults is valuable for the development of geometric and kinematic models that are helpful in unravelling the structural style and for detecting structural hydrocarbon traps we document push up inversion structures versus fault bend reactivation anticlines occurring along oblique thrust ramps by examining examples of buried apulian structures in the central southern apennines and outcropping thrust related folds in the central northern apennines of italy the different geometric features between push up inversion structures and fault bend reactivation anticlines are functionally controlled by the mechanical characteristics of the involved sedimentary multilayer the original architecture of the former extensional basin and the amount of thrust displacement the recognition of such inversion structures is important in understanding the anatomy and structural style of foreland fold and thrust belts in addition their identification is critical in interpreting the geometry and types of structural traps that may be expected along oblique thrust ramps this study reveals that push up inversion structures and fault bend reactivation anticlines could coexist along oblique thrust ramps within a curved thrust system and may be detected among analogous foreland thrust belts that include inherited extensional basins

daily scale planetary wave patterns and the modulation of cold season weather in the northern extratropics tropospheric planetary waves often linked to asymmetries in lower boundary forcing significantly modulate atmospheric blocking and storm track structures that are in turn linked to extreme surface weather events day to day variability in the planetary scale circulation taken as wavenumbers 1 to 5 in the daily 500 hpa geopotential heights and the associated impact on storm tracks and regional weather are studied for the period 1950 2005 six boreal cold season distinct planetary wave patterns are identified via hierarchical cluster analysis the first second and sixth patterns feature a prominent zonal wavenumber 1 structure while the fourth and fifth patterns resemble the negative and positive phases of northern annular mode respectively the second pattern represents an amplification of the climatological mean wave structure while the third pattern resembles the zonal wavenumber 3 pattern a multi taper spectral analysis of the daily projection indices indicates that the planetary wave patterns are primarily intraseasonal in nature the first sixth pattern combines the positive negative phase of the pacific north american teleconnection pattern and negative positive phase of the north atlantic oscillation inducing poleward equatorward shifts in the pacific storm track and a weakened strengthened atlantic storm track in contrast the fourth fifth pattern results in a simultaneous equatorward poleward displacement of both storm tracks extreme cold waves over the continental united states us are favored during occurrences of the fourth and sixth patterns during episodes of the first pattern increased rainfall prevails over much of the us while precipitation anomalies induced by the other patterns are more regional in nature

interpreting structural geometry in fold thrust belts why style matters abstract structural interpretation in fold thrust belts has become reliant on a few idealized geometric models i e fault bend fault propagation and detachment folding and their quantitative methods for section construction and validation we couple historical review with selected outcrops to show that there is a substantially greater range of solutions available for interpreting the geometry and evolution of thrust belt structures than implied by these idealized models examples are documented and lessons drawn from comparing structural interpretations developed in the foothills of the canadian rockies with those in the western alps both show a range of structural geometries with regional variations that reflect variations in the pre kinematic stratigraphic template locally fold thrust development can localize on pre existing structures thus consideration of the precursor geology is essential for structural interpretation using a case study from the papuan fold belt we show that even with seismic data assessing the role of basement in structural development can be uncertain the idealized models offer only a narrow range of possible geometries for constructing cross sections and developing structural understanding in fold thrust systems failure to consider alternatives and the inherent interpretation uncertainty has biased understanding of thrust systems leading in turn to over optimistic risk assessment and repeated drilling surprises

horizontal structure and seasonality of large scale circulations associated with submonthly tropical convection the relationship between deep tropical convection and large scale atmospheric circulation in the 6 30 day period range is examined regression relationships between filtered outgoing longwave radiation at various locations in the tropics and 200 and 850 mb circulation are mapped for the standard seasons and the spatial structure and seasonal dependence of the results are interpreted in view of the basic state circulation in regions where the convection is embedded in upper level easterlies anomalous equatorial easterly flow is typically present at 200 mb within and to the west of the convective signal along with patterns of meridional outflow into subtropical anticyclonic perturbations lagged relationships suggest that the convection is forcing the circulation in many of these cases the outflow and subtropical circulations are strongest into the winter hemisphere during the solstitial seasons with more symmetric signals about the equator seen in the equinoctial seasons the longitudinal positioning of the subtropical features with respect to the convection varies but is generally located due poleward or just to the east of the convection there tends to be a first baroclinic mode vertical structure to these circulations such that equatorial westerlies are present at 850 mb within the convection with closed circulations on either side of the equator resembling equatorial rossby modes especially common over the atlantic and pacific sectors as a contrast in regions located within upper level westerlies or along the margin of influence of upper westerly disturbances convection appears to be forced by upper level wave energy propagating into the deep tropics with the heating located in the upward motion region ahead of upper level troughs this occurs over the atlantic and eastern pacific sectors during northern winter and spring and over australia the south pacific and south america during southern summer when upper westerlies are at relatively low latitudes where they can interact with deep tropical convection the results confirm theoretical and modeling ideas that suggest that rossby wave energy is able to propagate into the deep tropics in regions where upper level westerlies exist in the tropics

subseasonal variations in warm season moisture transport and precipitation over the central and eastern united states abstract subseasonal variations in warm season may august precipitation over the central and eastern united states are shown to be strongly linked to variations in the moisture entering the continent from the gulf of mexico within a longitudinally confined channel referred to here as the texas corridor or tc these variations reflect the development of low level southerly wind maxima or jets on a number of different timescales in association with distinct subcontinental and larger scale phenomena on the diurnal timescale the tc moisture flux variations are tied to the development of the great plains low level jet the composite nighttime anomalies are characterized by a strong southerly moisture flux covering northeast mexico and the southern great plains and enhanced boundary layer convergence and precipitation over much of the upper great plains the strongest jets tend to be associated with an anomalous surface low over the great plains reflecting a predilection for periods when midlatitude

a general circulation model study of the atmospheric response to extratropical sst anomalies observed in 1950 79 abstract a 30 year experiment with an atmospheric general simulation model has been performed the lower boundary condition at all oceanic grid points between 38 s and 60 n has been prescribed to follow the observed month to month variation of the sea surface temperature sst field during the 1950 79 period much of the model diagnosis presented here pertains to the midlatitude atmospheric response to recurrent sst patterns in the north pacific and north atlantic in winter the principal modes of variability of the seasonally averaged 515 mb height and sst fields have been identified using rotated principal component rpc analysis the extrema of the first atmospheric mode reside over the north atlantic and eurasia whereas the second mode is associated with height anomalies in the north pacific north american sector cross correlation analysis reveals that these two atmospheric modes am linked to leading patterns of the sst field in the north atlantic and north pacific respectively it is also demonst

teleconnections and low frequency variability in idealized experiments with two storm tracks low frequency variability and teleconnection patterns induced by two storm tracks in idealized experiments depend on their zonal distance a separation of about 150 which resembles the northern hemisphere storm track distribution reveals teleconnection patterns which are similar to the pacific north american pna pattern and the north atlantic oscillation nao the nao like structure is associated with retrograde travelling rossby waves barotropic stream function tendencies show that the interaction of the stationary eddies with the low frequency flow and the high frequency eddies contribute to the amplification of the pattern its decay is due to their interaction with the zonal mean flow and the low frequency contribution to the divergence term the pna like pattern has a longer memory and is linked to a quasi stationary wave the stationary wave activity flux shows the dominating influence of baroclinic processes and the other storm track further upstream the correlation between the teleconnection indices is significant for storm track distances between 180 and 160 and vanishes between 150 and 130

rossby wave propagation into the tropics in two gfdl general circulation models during the northern winter the eastern pacific is characterized by upper level westerly flow extending from the equator into the midlatitudes of both hemispheres theoretical and simple modeling studies suggest that such a region should favor the penetration of rossby waves into the tropics from higher latitudes observational results by kiladis and weickmann using 200 mb data indicate that rossby waves do indeed propagate freely into the tropical eastern pacific during the northern winter from the asian jet exit region they also confirmed that cross equatorial dispersion of energy from the northern into the southern hemisphere occurs frequently the present study examines these interactions in climatological runs of two gfdl gcms the northern wintertime mean states of these models are characterized by a rather realistically simulated upper level westerly regime in the tropical pacific despite the relative weakness of the asian jet and wave activity with respect to observations propagation of rossby waves into the tropics is present in both models and these waves are strongly positively tilted as seen in the observations a momentum budget of the zonal wind and e vector diagnostics over the tropical pacific indicate that these transients are an important component of the momentum balance of the equatorial westerlies in both the observations and in the models

anatomy of synoptic eddy nao interaction through eddy structure decomposition abstracta method of eddy structure decomposition is proposed to detect how low frequency flow associated with the north atlantic oscillation nao organizes systematically synoptic eddy se activity to generate in phase and upstream feedbacks in this method a statistical eddy streamfunction ses field defined by the three point covariance of synoptic scale streamfunction is introduced to characterize spatiotemporal se flow structures the ses field is decomposed into basic and anomalous parts to represent the climatological se flow structure and its departure these two parts are used to calculate the basic and anomalous eddy velocity eddy vorticity and thus eddy vorticity flux fields in order to elucidate those two se feedbacks onto the nao this method is validated by the fact that the observed anomalous eddy vorticity flux field can be reproduced well by two linear terms the basic eddy velocity field multiplied by anomalous eddy vorticity field and the anomalous eddy velocity field multiplied

fault zone migration by footwall shortcut and recumbent folding along an inverted fault example from the mosha fault central alborz northern iran the mosha fault is a multiply inverted fault in the central alborz field observations and structural data from this fault show that a footwall shortcut is the major mode of response of this fault to contractional deformation although the mosha fault is a basement involved fault there is no evidence of involvement of basement along its footwall shortcuts at least in the study area footwall shortcuts along this fault vary in size from several hundreds of metres to tens of kilometres suggesting that a footwall shortcut can be scale independent it is proposed that footwall shortcuts can also occur as blind thrusts under fault related folds in the terrains near the major inverted faults similar cases also exist in other regions such as japan some large footwall shortcuts may be the causative fault of devastating earthquakes in the active inverted terrains such as the south central alborz incompetent layers acting as detachments may play an important role in the development of footwall shortcuts recu

intraseasonal variations in the southern hemisphere circulation abstract intraseasonal variations in the southern hemisphere atmospheric circulation have been examined through the application of a 10 50 day bandpass filter to daily ecmwf analyses for 1980 88 variations on this time scale contribute more than 40 of the daily variance in 500 hpa geopotential over much of the middle and high latitudes of the southern hemisphere eof analysis of the unnormalized variance for all seasons shows that 49 of this variance can be explained by zonal wave trains centered on the south pacific and southern atlantic indian oceans a high latitude mode of global extent and a wavenumber 3 pattern at midlatitudes these modes are essentially equivalent barotropic but slope westward with height so that the patterns at 100 hpa typically lag those at 1000 hpa by around 1o longitude there appears to be little interaction with the low latitude circulation all of the leading modes propagate eastward but the most consistent movement is shown by the south pacific wave train represented

the asymmetric eddy background flow interaction in the north pacific storm track using a recently developed methodology namely the multiscale window transform mwt and the mwt based theory of canonical transfer and localized multiscale energetics analysis we investigate in an eddy following way the nonlinear eddy background flow interaction in the north pacific storm track based on the era40 reanalysis data from ecwmf it is found that more than 50 of the storms occur on the northern flank of the jet stream about 40 are around the jet center and very few less than 5 happen on the southern flank for storms near or to the north of the jet center their interaction with the background flow is asymmetric in latitude in higher latitudes strong downscale canonical available potential energy transfer happens especially in the middle troposphere which reduces the background baroclinicity and decelerates the jet in lower latitudes upscale canonical kinetic energy transfer intensifies at the jet center accelerating the jet and enhancing the middle level baroclinicity the resultant effect is that the jet strengthens but narrows leading to an anomalous dipolar pattern in the fields of background wind and baroclinicity for the storms on the southern side of the jet the baroclinic canonical transfer is rather weak on average the local interaction begins from about 3 days before a storm arrives at the site of observation achieves its maximum as the storm arrives and then weakens

the spring relationship between the pacific north american pattern and the north atlantic oscillation the pacific north american pattern pna and north atlantic oscillation nao are two dominant modes of low frequency variability in the northern hemisphere winter generally these two patterns are separable and uncorrelated in both space and time however dating back to the 1970s there have been studies which have linked the aleutian and icelandic low intensities and shown that a significant temporal correlation does on occasion occur each of these semi permanent low pressure systems is a part of the pna and nao patterns respectively and therefore given a link between the two semi permanent low pressure systems we explore whether a link between the pna and nao also appears recently studies have found such a link during the winters of certain decades the present study documents an observed relationship between the pna and nao which is consistently present during the spring and early summer this relationship is shown to be due to the fact that the pna and nao are spatially overlapping projections of the same pattern of variability given by the first eof of 500 hpa geopotential height both the pna and nao patterns correlate more strongly to the first eof s spatial pattern resembling the aleutian low icelandic low seesaw pattern than the rotated eof reof loading patterns used to compute their respective indices furthermore when the two patterns are correlated the effect of el nino on the northern hemisphere is separate from the pattern associated with the pna finally we examine a 21 year period in the winter for which the pna and nao are significantly correlated and find that the conclusions drawn from the spring hold true the results presented herein demonstrate that defining the pna and nao based upon typical loading patterns may not be the ideal approach especially given that the patterns are spatially similar and covary in time

interannual variability in north atlantic weather data analysis and a quasigeostrophic model abstractthis paper addresses the effect of interannual variability in jet stream orientation on weather systems over the north atlantic basin nab the observational analysis relies on 65 yr of ncep ncar reanalysis 1948 2012 the total daily kinetic energy of the geostrophic wind gtke is taken as a measure of storm activity over the north atlantic the nab is partitioned into four rectangular regions and the winter average of gtke is calculated for each quadrant the spatial gtke average over all four quadrants shows striking year to year variability and is strongly correlated with the north atlantic oscillation nao the gtke strength in the northeast quadrant is closely related to the diffluence angle of the jet stream in the northwest quadrant to gain insight into the relationship between the diffluence angle and its downstream impact a quasigeostrophic baroclinic model is used the results show that an initially zonal jet persists at its initial latitude over 30 days or longer while a tilted

carbonate platform to foreland basin revised stratigraphy of the table head group middle ordovician western newfoundland carbonates of the table head group and associated strata were deposited along the western margin of a foreland basin during initial stages of the taconian orogeny and record collapse and cannibalization of a long lived carbonate platform the stratigraphy of klappa opalinski and james is here revised to reflect better understanding of lithologic units within this complex tectono stratigraphic assemblage the table head group now contains only three formations the table point and table cove formations as originally defined and the cape cormorant formation redefined and restricted to western port au port peninsula black cove formation shales are removed from the table head distinctive conglomerates once placed in the cape cormorant are now recognized as separate units within the overlying flysch and called the daniel s harbour member the foreland basin developed in three stages 1 fragmentation uplift and erosion of the platform and subsequent deposition of shallow water limestones table point

long term equilibrium tides extreme equilibrium tides or hypertides are computed in a new equilibrium tidal model combining algorithms of a version of the chapront elp 2000 82 lunar theory with the ber78 milankovitch astronomical expansions for the rerent past a high correspondence exists between computed semidiurnal tide levels and a record of coastal flooding demonstrating that astronomical alignment is a potential influence on such flooding for the holocene and near future maximum tides demonstrate cyclic variations with peaks at near 5000 b p and 4000 a p on the late quaternary timescale variations in maximum equilibrium tide level display oscillations with periods of approximately 10 000 100 000 and 400 000 years because of precessional shifts in tidal maxima between vernal and autumnal equinoxes while flooding occurs under the combined effects of tides and storms via storm surges the most extensive flooding will occur with the coincidence of storms and the rarer hypertides and is thus primarily influenced by hypertides therefore we suggest that astronomical alignment s relationship to coastal flooding is probabilistic rather than deterministic data derived from this model are applicable to 1 archaeological and paleoclimatic coastal reconstructions 2 long term planning for example radioactive waste site selection 3 sealevel change and paleoestuarine studies or 4 ocean meteorological interactions

the amplitude asymmetry between synoptic cyclones and anticyclones implications for filtering methods in feature tracking abstract the background state is commonly removed from synoptic fields by use of either a spatial or temporal filter prior to the application of feature tracking commonly used spatial and temporal filters applied to sea level pressure data admit substantially different information to be included in the synoptic fields the spatial filter retains a time mean field that has comparable magnitude to a typical synoptic perturbation in contrast the temporal filter removes the entire time mean field the inclusion of the time mean spatially filtered field biases the feature tracking statistics toward large cyclone anticyclone magnitudes in the regions of climatological lows highs the resulting cyclone anticyclone magnitude asymmetries in each region are found to be inconsistent with the unfiltered data fields and merely result from the spurious inclusion of the time mean fields in the spatially filtered data the temporally filtered fields do not suffer from the same problem and produce modest cyclone

an analysis of a relatively rare case of continental blocking planetary and synoptic scale analyses of a relatively rare continental blocking event that occurred over north america during the spring of 1980 are undertaken to determine whether or not this event was different from its counterparts which occur over oceanic regions the planetary scale analysis demonstrates that during the spring season a ridge was located further inland over the north american continent and amplified with respect to climatology the position of this ridge may have been linked to a broad region of colder than normal sea surface temperatures found over the north central pacific during the spring season and much of the previous winter simple sutcliffe type and thermodynamic analyses of the accompanying lower tropospheric warm anomaly associated with the ridging show that lower tropospheric temperature advection and subsidence associated with anticyclonic vorticity advection by the time mean thermal wind produced much of the anomalous warmth a simple synoptic scale analysis was performed using both the zwack okossi zo equation and potential vorticity pv thinking approaches these complementary analyses demonstrated that synoptic scale cyclones were instrumental in the formation and maintenance and or intensification of this blocking event the pv analysis demonstrated that low pv air was swept polewards and then was advected over the blocking region sustaining the broad region of low potential vorticity associated with the block over north america the zo analysis showed that the advection of anticyclonic vorticity was the most important mechanism forcing geopotential height rises at 500 hpa over the block centre the region of low pv and zo height rises could be associated with the anticyclonic shear side of an upstream jet maximum typically found in association with developing and or intensifying blocking events thus negative pv advection correlated significantly with calculated zo height rises finally it is suggested that a favourable phase relationship between the upstream cyclones and the large scale ridge is necessary for block development or intensification

piecewise tendency diagnosis of weather regime transitions abstract piecewise tendency diagnosis ptd is extended and employed to study the dynamics of weather regime transitions originally developed for adiabatic and inviscid quasigeostrophic flow on a beta plane ptd partitions local geopotential tendencies into a linear combination of dynamically meaningful source terms within a potential vorticity pv framework here ptd is amended to account for spherical geometry diabatic heating and ageostrophic processes and is then used to identify the primary mechanisms responsible for northern hemisphere weather regime transitions height tendency patterns obtained by summing the contributions of individual ptd forcing terms correspond very well to actual height tendencies composite ptd analyses reveal that linear pv advections provide the largest dynamical forcing for the weather regime development over the north pacific specifically linear baroclinic growth provides the primary forcing while barotropic deformation of pv anomalies provides a secondary contrib

a new variable threshold persistent anomaly index northern hemisphere anomalies in the era interim reanalysis abstractpersistent weather regimes characterized by anomalous temperature or precipitation are often associated with persistent anomalies pas in the tropospheric geopotential height field to ide

the structure of mountain fronts commonly the part of a mountain front which is visible at the surface consists of foreland dipping thrust belt rocks elevated above their regional structural position and overlain more or less conformably by molasse several explanations for their geometry are possible 1 major detachments exist within or beneath the molasse resulting in transport of the foreland basin examples of this geometry come from the swiss molasse plain the southern pyrenees and the mackenzie mountains of canada 2 displacement is lost on major backthrusts beneath the frontal monocline examples cited here are the rockies of alberta the sulaiman ranges of pakistan the mackenzies and the andes in peru 3 thrust sheets travelled over an old land surface and syntectonic molasse contemporaneously offlaps the topographic high of the thrust front this phenomenon occurs along the alpine thrust front in haute provence 4 the frontal fold represents deformation above a large scale thrust tip no unequivocal example of tip line strain at this scale has been recorded although this type of deformation may occur in the brooks range of alaska in many areas mountain fronts show a combination of these idealized geometries

structural inheritance in mountain belts an alpine apennine perspective abstract the geological structure of continental lithosphere shows complex variety that is inherited into orogenic belts and influences the localization and amplification of contractional structures during mountain building in the alpine apennine sector together with other sectors of the tethyan orogenic system the pre orogenic crustal template can include arrays of extensional faults other faults can form adjacent to the evolving mountain belt and subsequently become incorporated as the thrust belts migrate into their forelands while in some areas these inherited features may simply reactivate under inversion more commonly faults show complex partial reactivation structures in volumes of distributed strain faults may serve to nucleate large scale buckle folds for example along basement cover interfaces these different patterns of basement reactivation may reflect spatially varying strength depth profiles in continental lithosphere that are themselves inherited from spatially distinct geological histories even when not themselves reactivating basement faults can control deformation in the overlying sedimentary cover by offsetting otherwise regionally extensive detachment horizons the 3d form of thrust systems can be strongly compartmentalized by pre existing cross faults such as the oblique lineaments of the apennines on a large scale the distribution of pre existing faults and other weaknesses may affect the propensity for orogenic contraction in basement and therefore directly control larger scale tectonic processes in the central mediterranean the evolution of slab roll back and the related growth of overlying extensional basins e g tyrrhenian sea may be strongly modulated by the distribution of rift related weak zones in the adjacent continental crust the subduction of continental crust will strongly depend on the inherited structure of this crust specifically the distribution of deep crust of basic composition this develops relatively higher densities associated with eclogite metamorphism which act in turn to reduce the buoyancy of thickened continental crust that otherwise serves to inhibit further shortening investigating all these aspects from the scale of bulk crustal compositions to the geometry timing and strength of earlier fault zones preserved in orogenic belts requires the integration of substantial multidisciplinary geological data sets the extent to which continental orogenic belts represent the amplification of inherited geological heterogeneities as opposed to self ordered phenomena modulated by the syntectonic environment remains unclear

thick skinned tectonics and basement involved fold thrust belts insights from selected cenozoic orogens defining the structural style of fold thrust belts and understanding the controlling factors are necessary steps towards prediction of their long term and short term dynamics including seismic hazard and to assess their potential in terms of hydrocarbon exploration while the thin skinned structural style has long been a fashionable view for outer parts of orogens worldwide a wealth of new geological and geophysical studies has pointed out that a description in terms of thick skinned deformation is in many cases more appropriate this paper aims at providing a review of what we know about basement involved shortening in foreland fold thrust belts on the basis of the examination of selected cenozoic orogens after describing how structural interpretations of fold thrust belts have evolved through time this paper addresses how and the extent to which basement tectonics influence their geometry and their kinematics and emphasizes the key control exerted by lithosphere rheology including structural and thermal inheritance and local regional boundary conditions on the occurrence of thick skinned tectonics in the outer parts of orogens

basin development and inversion at the appalachian structural front port au port peninsula western newfoundland appalachians in the humber zone of the newfoundland appalachians cambro ordovician shelf and foreland basin successions are affected by middle ordovician taconian orogeny and devonian acadian orogeny deformation on port au port peninsula the presence of the late ordovician to late silurian long point clam bank succession allows these episodes to be separated the taconian foreland basin stratigraphy on port au port peninsula is highly variable on the west coast platform carbonates are overlain by megaconglomerates of the cape cormorant formation which record progressive exposure of 1 km of the platform succession the conglomerates are restricted to a narrow zone consistent with derivation from a fault scarp originally immediately west of the outcrops in palinspastic restoration farther east at victors brook the cape cormorant formation is absent but the overlying almost undeformed goose tickle group contains conglomerate derived both from the upper part of the platform succession and from the tacon

late jurassic half graben control on the siting and structure of hydrocarbon accumulations uk norwegian central graben abstract the late jurassic structure of the central graben is discussed both in terms of the extensional features developed at this time and their subsequent controls on younger inversion structures the regional kinematics of the north sea rift suggest that during the late jurassic the central graben opened approximately orthogonally to the main nnw sse fault trend within the basin some evidence that triassic extensional faults were reactivated at this time is seen towards the basin margins and a significant triassic extensional history is inferred the late jurassic basin comprises the axial c 100 km of the central graben s l the basin axis is offset progressively to the se by both transfer zones and discrete transfer faults footwall uplift of the basin margins during extension provided the source for the upper jurassic reservoir sands encountered by exploration drilling these sands were probably preferentially fed into the basin at transfer zones in the margins salt structures are ubiquitous within the central graben and their siting is everywhere controlled by the underlying fault block topography salt structures form preferentially towards the crests of half graben or buttressed against their boundary faults inversion structures in the norwegian sector reactivated with a reverse sense of displacement late jurassic extensional faults a model is proposed which shows the two main inversion structures feda graben norway tail end graben denmark to be detached on antithetic reverse faults riding in the salt these faults terminate at tip folds within major salt walls the geometry of the inversion structures can be understood only when considered together with the geometry of the underlying late jurassic half graben

the large scale modulation of subtropical cyclogenesis in the central and eastern pacific ocean abstract an analysis of the composite large scale circulation associated with periods of enhanced active or diminished inactive cyclogenesis in the subtropical central and eastern pacific ocean is presented composites were constructed using surface and tropospheric analyses from the ecmwf tropical ocean global atmosphere toga dataset for 10 northern hemisphere cool seasons 1986 96 active periods of subtropical cyclogenesis were defined to be periods in which two or more cyclones developed in close succession to each other while inactive periods were defined to be periods of at least 10 days duration during which no cyclones with a subtropical origin were present in the pacific basin the analysis revealed that the occurrence of subtropical cyclones in the central and eastern pacific ocean is strongly linked to the strength and location of the asian jet with active periods characterized by a weaker zonally retracted asian jet while inactive periods are characterized by a stronger zonally elon

the petroleum potential of inversion anticlines in the banda arc the banda arc in eastern indonesia and newly independent timor leste east timor is the zone of collision between the northern margin of the australian continent and an oceanic island arc system bordering the eurasian plate structurally the banda forearc is a fold and thrust belt consisting of the imbricated outer edge of the australian continent overlain locally by fragments of the precollisional oceanic forearc the banda forearc is an established petroleum province in the island of seram but the remainder of the forearc has so far yielded no further exploration success despite close geological similarity to seram a major disincentive to exploration in the banda forearc has been a common perception of structural complexity this complexity may however have been overstated and this paper presents a simple structural model for the evolution of the banda forearc key to this model is the recognition of basement involved inversion structures in the deeper parts of the collision complex the inverted graben basins are filled with permianjurassic continental margin sequences including high quality source rocks of late triassicearly jurassic age and contemporaneous potential reservoir sequences sealed by middlelate jurassic shales these jurassic shales also act as an important decollement horizon separating shallow level structural complexity from a simpler structural style beneath characterized by large inversion anticlines the oseil field in seram may be located in such an inversion anticline and comparable prospective structures are identified elsewhere in the banda forearc particularly in timor and the tanimbar islands

behavior of one to two week summertime subtropical wind maxima over the south pacific during an enso cycle abstract the behavior of subtropical jet streaks over the australian south pacific region is investigated for four consecutive 6 month summer seasons november to april during the period 1985 89 the study is an extension of a recent one by ko and vincent hereafter referred to as kv in which jet streaks during the summer season of 1984 85 were examined ko and vincent found that the upper tropospheric zonal wind behaved in a quasi periodic manner with maxima recurring over the western south pacific at intervals between one and two weeks in the present study wind maxima are found to exhibit a 1 2 week periodic oscillation over the south pacific in all four years thus substantiating the finding by kv in addition a second set of jet streaks with a similar periodicity is found over the southern australian region it is also seen that the mean summertime position of the south pacific jet and its accompanying jet streaks are much farther cast during the el nino event of 1986 87 than they are in the

fault kinematics and localised inversion within the troms finnmark fault complex sw barents sea abstract the areas bounding the troms finnmark fault complex are affected by complex tectonic evolution in this work the history of fault growth reactivation and inversion of major faults in the troms finnmark fault complex and the ringvassoy loppa fault complex is interpreted from three dimensional seismic data structural maps and fault displacement plots our results reveal eight normal faults bounding rotated fault blocks in the troms finnmark fault complex both the throw depth and displacement distance plots show that the faults exhibit complex configurations of lateral and vertical segmentation with varied profiles some of the faults were reactivated by dip linkages during the late jurassic and exhibit polycyclic fault growth including radial syn sedimentary and hybrid propagation localised positive inversion is the main mechanism of fault reactivation occurring at the troms finnmark fault complex the observed structural styles include folds associated with extensional faults folded growth wedges and inverted depocentres localised inversion was intermittent with rifting during the middle jurassic early cretaceous at the boundaries of the troms finnmark fault complex to the finnmark platform additionally tectonic inversion was more intense at the boundaries of the two fault complexes affecting middle triassic to early cretaceous strata our study shows that localised folding is either a product of compressional forces or of lateral movements in the troms finnmark fault complex regional stresses due to the uplift in the loppa high and halokinesis in the tromso basin are likely additional causes of inversion in the troms finnmark fault complex

selkirk fan structure southeastern canadian cordillera tectonic wedging against an inherited basement ramp a revised cross section through the selkirk fan structure provides the basis for a new model for the middle jurassic tectonic evolution of the southern omineca belt canadian cordillera palinspastic restoration of this cross section shows that the southwest verging structures along the west flank of the selkirk fan structure formed as a result of tectonic wedging of distal north american strata clachnacudainn complex beneath more proximal north american strata and that the selkirk fan structure developed outboard from a crustal ramp dogtooth high inherited from late proterozoic early paleozoic rifting along the western margin of north america the first episode of mesozoic deformation in southeastern british columbia occurred between 187 and 173 ma and involved the northeastward juxtaposition of the intermontane superterrane over the outer part of the north american continental terrace wedge it resulted in deep burial 20 25 km of the outer margin of north america a crustal ramp localized along the western edge of the late proterozoic early paleozoic dogtooth high impeded the northeastward propagation of the orogenic wedge comprising the intermontane superterrane and the imbricate underlying northeast verging thrust sheets of north american supracrustal rocks tectonic wedging involving southwest verging deformation occurred within the orogenic wedge and the resulting crustal thickening established sufficient topography and gravitational potential to drive the propagation of the deformation eastward into the dogtooth range and the rocky mountains the southwest verging structures along the west flank of the selkirk fan developed between approximately 173 and 168 ma concurrent with synorogenic extension and 10 km of exhumation the initial subsidence of the foreland basin during kimmeridgian time ca 154 ma provides the first indication of tectonic loading and lithospheric flexure of the north american plate it is interpreted to mark the time at which the orogenic wedge overrode the crustal ramp of the dogtooth high and advanced onto relatively thick and rigid continental lithosphere the tectonic model proposed for the selkirk fan structure illustrates how the configuration of the rifted margin influenced the style of crustal thickening during subsequent compressional deformation

spatial and temporal characteristics of the wind forcing of the bering sea abstract the surface wind stress over the bering sea is estimated for the period 1946 90 from sea level pressure analyses empirical relationships between the geostrophic wind and the surface wind and a bulk aerodynamic formula the focus is on the propagation and variability of the stress and the curl of the stress as a function of frequency the stress at high frequencies 0 1 cpd is dominated by northward and eastward propagating disturbances with mean wavelengths of 2500 and 10 000 km respectively at periods of 10 100 days the mean propagation is near zero there are however significant interannual variations in the zonal propagation wind driven ocean transports estimated by the sverdrup method for the deep bering basin account for 6 sv or roughly one half of the observed transport within the western boundary current along the kamchatka peninsula a low pass filtered retaining periods greater than 18 months time series of the sverdrup transport exhibits a standard deviation of 25 of th

structural and tectonic evolution of the humber zone western newfoundland 1 implications of balanced cross sections through the appalachian structural front port au port peninsula the appalachian structural front in western newfoundland which is principally a submarine feature that comes ashore on port au port peninsula is interpreted to be a structural triangle zone or tectonic wedge rocks within the triangle zone which are therefore transported include the taconian middle ordovician humber arm allochthon taconian foreland clastic sediments and the cambro ordovician platform succession the transported clastic sediments and platformal rocks as well as structurally involved grenville crystalline basement exposed east of the peninsula compose the acadian siluro devonian port au port allochthon which carried the humber arm allochthon as a high structural slice acadian transport of tens of kilometers westward is suggested this interpretation contrasts markedly with the traditional and widely accepted interpretation of the taconian and acadian orogenies in western newfoundland here we reinforce our earlier arguments for an allochthonous interpretation by presenting a series of six closely spaced balanced cross sections across the port au port peninsula these sections illustrate our interpretation of complex and noncylindrical structures within the triangle zone as well as the envisioned structural linkage between exposures on port au port peninsula and the geometry of the triangle zone interpreted from offshore seismic data 23 km along strike to the northeast the southeast vergent tea cove thrust which formed an early upper detachment to the triangle zone is offset and overturned by the north northwest vergent round head thrust the round head thrust is interpreted to flatten into a second southeast vergent thrust the red brook detachment which formed a late upper detachment to the triangle zone some map scale structures are interpreted as fault bend folds above oblique ramps on the red brook detachment allochthonous crystalline basement within the triangle zone beneath its attached platformal cover is interpreted as a result of thrust reactivation of a preexisting basement cutting normal fault which may have formed during rifting of the early paleozoic iapetus ocean this interpretation is suggested by the stratigraphy and geometry of spatially restricted coarse conglomeratic units on port au port peninsula and is supported by the restored cross sections