integrated gravity and seismic interpretation of duplex structures and imbricate thrust systems in the southeastern pyrenees ne spain abstract combined surface subsurface and gravity data were used to determine the deep structure of the thrust belt in the southeastern pyrenees the ripolles and la garrotxa areas are part of the cardona oil exploration permit hydrocarbons pervade the concession with numerous oil seeps abandoned oil wells and gas or condensate are in these two wells associated with the overthrust belt the source rocks the armancies formation upper cuisian lower lutetian consist of alternating layers of organic rich shales and thin limestones this formation outcrops in the cadi thrust sheet in the ripolles area the cadi unit overlies the serrat unit with a hanging wall ramp geometry as deduced from the serrat 1 well the structure of the garrotxa area is more complex it consists of a duplex structure folded by antiformal stack structures with basement rocks in their cores the northern boundary of these antiformal stacks represents an inversion of pre existent extensional faults the basement rocks involved in the structure represent shortcuts formed in the footwall of the extensional faults a negative anomaly is shown in these antiformal stacks these anomalies are interpreted as a combination of salt accumulation evaporites and sedimentary rocks under the antiformal stacks in the serrat 1 well the serrat unit is made up of a thick middle eocene evaporitic sequence but the gravity and seismic data evidence the presence of non evaporitic sedimentary rocks in the northern part of the serrat unit these sediments correspond to the footwall of the cadi series so the probable existence of the armancies formation in the serrat unit is a very good target for oil prospecting the existence of the previous extensional faults only in the garrotxa area determines the difference in the deep structure between the ripolles and garrotxa areas

moist hadley circulation possible role of wave convection coupling in aquaplanet experiments abstractaquaplanet simulations for a given sea surface temperature sst are conducted to elucidate possible roles of transient variability in the hadley circulation and the intertropical convergence zone itcz their roles are best illustrated with globally uniform ssts for such ssts an itcz and a hadley circulation that are nearly equatorially symmetric emerge spontaneously their strength varies over a wide range from being faint to climatologically significant depending on a tunable parameter of the model s cumulus parameterization in some cases asymmetric hadley circulations formed along with long lived tropical cyclones the tunable parameter affects the transient variability of tropical precipitation in the runs in which well defined near symmetric itczs formed tropical precipitation exhibited clear signatures of convectively coupled equatorial waves the waves can explain the concentration of precipitation to the equatorial region which induces the hadley circulation also the meridional st

a physical explanation of the relation between flank uplifts and the breakup unconformity at rifted continental margins rift flank uplifts and the breakup or postrift unconformity are characteristic features of many rifted passive or atlantic type continental margins but are not predicted as primary features of simple lithospheric stretching models the explanations that have been proposed for their origin remain controversial either because they call upon special circumstances or because they are difficult to test plane strain finite element models are used in this paper to explore the dynamics of lithospheric necking during rifting and rupture the results agree with the conceptual interpretation that uplift of the rift boundaries to form flank mountains and uplift of the basin responsible for the breakup unconformity are related consequences of regional isostatic compensation of mass that is redistributed during the necking and rupture phases although the amplitudes of these uplifts depend on the model parameter values the relations between and relative signs of these two effects appear to be fundamental the explanation we propose may have been missed in recent studies because there has been a tendency to concentrate on kinematic stretching models which assume local isostatic equilibrium through out the rifting process such an approach is predicated on the assumption that the lithosphere has an insignificant strength or flexural rigidity during extension which is not true if our explanation is correct

rheological stratification of the lithosphere abstract the rheology of the lithosphere is estimated on the basis of pore pressure dependent frictional failure in the brittle regime and power law steady state creep in the ductile regime different petrological models of the continental and oceanic lithosphere combined with different geotherms and thicknesses are used to generate models covering a variety of geodynamic situations results show that the depth dependence of lithospheric rheology varies with the tectonic province and that in many instances the continental lithosphere has one at the bottom of the crust or two the previous one plus another at mid crustal levels soft ductile layers sandwiched between brittle layers the depth distribution of geophysical parameters seismicity seismic wave velocity and electrical conductivity matches the theological predictions well the lithospheric rheological profiles are used to analyze observed variations in the structural style of deformed continental margin and oceanic terranes in the southeastern canadian cordillera the large scale characteristics of the system show a satisfactory agreement with the inferred rheological structure sub horizontal decollements should be the rule rather than the exception where the lithospheric rheology is strongly stratified

stresses in the lithosphere and sedimentary basin formation abstract seven fundamental questions on the relationship of lithospheric stresses and sedimentary basin origin and evolution are posed and elaborated these are 1 1 how is the evolution of sedimentary basins tied to lithospheric dynamics 2 2 what are the sources of stress that lead to formation of sedimentary basins 3 3 how does the interaction between internally and externally applied stresses affect the formation and evolution of sedimentary basins 4 4 how do space and time variations of rheology and pore pressure affect stress transmission strain vertical motions and stratigraphy during basin evolution 5 5 what factors influence spatial and temporal variations of rheology in and around different kinds of sedimentary basins 6 6 what is the role of magmatism in basin formation and what deep seated processes does it reflect 7 7 what is the relationship between basin evolution thermal history and fluid flow these fundamental questions can be investigated by developing fully dynamic models of processes at the basin and sub basin scale models must incorporate or honour basin history and plate reconstructions the intregration of structural and sedimentological data direct observations of the physical state and the synthesis of geological and geophysical data including tectono dynamic stratigraphy petrological and geochemical data and geophysical data gravity magnetics heat flow deep and shallow seismics a number of type basins in passive margin foreland rift and strike slip tectonic settings suitable for modelling studies elucidating the fundamental questions are identified

why the itcz is mostly north of the equator abstract although the distribution of sunshine is symmetrical about the equator the earth s climate is not climatic asymmetries are prominent in the eastern tropical pacific and atlantic oceans where the regions of maximum sea surface temperature convective cloud cover and rainfall are north of the equator this is the result of two sets of factors interactions between the ocean and atmosphere that are capable of converting symmetry into asymmetry and the geometries of the continents that determine in which longitudes the interactions are effective and in which hemisphere the warmest waters and the intertropical convergence zone are located the ocean atmosphere interactions are most effective where the thermocline is shallow because the winds can readily affect sea surface temperatures in such regions the thermocline happens to shoal in the eastern equatorial pacific and atlantic but not in the eastern indian ocean because easterly trade winds prevail over the tropical atlantic and pacific wher

temporal and spatial correlations between changes in plate motions and the evolution of rifted basins in africa we present the results of a backstripping study incorporating over 200 wells in 14 different basins or groups of basins located on the african interior or continental margins these results presented as mean tectonic subsidence rates averaged over appropriate periods are compared with the opening histories and changes in plate motions of the atlantic and indian oceans and the tethys mediterranean area for seven time steps from the late jurassic until present the results indicate a temporal and spatial correlation between phases of rapid subsidence in african basins and changes in plate motions and therefore are promising in terms of applicability of large scale plate motions in the studies of paleo stresses in sedimentary basins especially at times of initial rifting and formation of subduction zones reactivation of the basins appears to be primarily controlled by the orientation of the basin and underlying basement structures with respect to the stress direction the basins are preferably formed within weaker zones mostly pan african shear zones and the distance from the active plate boundary to the weak zone plays a minor role in whether or not it will be reactivated the presence of three important hot spots which were active during the early stages of break up of gondwana may have been important in preweakening the lithosphere at their sites this may have played an additional role in the localization of the basin deformation

implementation of a non hydrostatic adaptive grid dynamics core in cam3 part ii dynamical influences on itcz behavior and tropical precipitation previous aqua planet simulations reported in the literature have shown the existence of both single and double inter tropical convergence zones itczs in this study horizontal grid resolution strongly affects itcz morphology as well as the amount of tropical precipitation through its influence on resolved dynamics the grid adaptation capability of our global model enables simulations that separate the influence of tropical and extra tropical dynamics on both the itcz and tropical precipitation the presence of single versus double itczs in our aqua planet simulations depends on the resolution of convectively coupled equatorial waves when the tropical resolution is sufficiently high to resolve prominent equatorial waves a double itcz occurs otherwise a single itcz occurs in contrast tropical resolution does not affect the magnitude of tropical precipitation in our aqua planet simulations instead the magnitude is sensitive to extra tropical resolution through its influence on the strength of baroclinic eddies and their forcing of the hadley circulation

a spontaneously generated tropical atmospheric general circulation abstract a series of idealized atmospheric general circulation model agcm experiments are presented these experiments examine whether and how atmospheric deep moist convection in the absence of meridional gradients in external forcing interacts with the large scale flow becoming spatially organized and yielding a coherent general circulation in a control simulation where the sst and the incident solar flux are prescribed to be independent of latitude longitude and time a well defined intertropical convergence zone itcz forms this result suggests that the interaction between convection and the rotation of the earth causes convection and a corresponding general circulation to organize the actual latitude that the itcz forms at however may be parameterization dependent in this control simulation the sst is not interactive and cannot respond to the spatial variations of the heat flux into the ocean that result from the organization of the circulation in order to examine the circulation tha

observation of a quasi 2 day wave during toga coare abstract detailed structure of the quasi 2 day oscillation observed in the active phase of the madden julian oscillations during the intensive observation period of tropical ocean and global atmosphere coupled ocean atmosphere response experiment toga coare iop was described a variety of observational platforms is used including high resolution gms infrared histogram rain rate estimate from toga and mit radar measurements upper air soundings and boundary layer profiler winds from the integrated sounding system and surface data from the imet buoy the quasi 2 day mode had a westward propagation speed of 12 15 day 1 a horizontal wavelength of 25 30 longitude a coupling with the westward propagating n 1 inertio gravity waves was hypothesized from the space time power spectral distribution of the cloud field the wind disturbance structure was consistent with the hypothesis the vertical wave structure had an eastward phase tilt with height below 175 hpa and vice versa above indicating the wav

improving trigger functions for convective parameterization schemes using goamazon observations abstractusing observations from the green ocean amazon goamazon field campaign this study aims to improve trigger functions of convection schemes results show that the cape generation rate dcape type triggers are the first tier and that the bechtold and heated condensation framework hcf triggers are a distant second tier the composite analysis reveals that the undilute dcape trigger underpredicts convection when there is bottom heavy upward motion but overpredicts convection with low level downward and upper level upward motions the empirical orthogonal function eof analysis on vertical velocity shows that eof1 62 65 exhibits upward motion throughout the troposphere and that eof2 28 05 has lower level upward motion and upper level downward motion both of them have close relationships with precipitation indicating the role of vertical velocity in triggering convection the skill sensitivity analysis shows that the inclusion of 700 hpa upward motion significantly enhances the undilute dc

sensitivity of itcz configuration to cumulus convective parameterizations on an aqua planet this paper examines the performances of various cumulus convective parameterization schemes in the tropical atmosphere using an aqua planet atmospheric general circulation model forced by zonally symmetric but latitudinally varying sea surface temperature sst and solar angle the intertropical convergence zone itcz is represented by intense precipitation the assigned control experiment with a specific sst distribution as designated by the aqua planet experiment yields a single itcz when zhang s scheme or manabe s scheme is employed whereas a double itcz occurs when tiedtke s scheme is used the key to the occurrence of a double itcz is latitudinal variation in evaporation within the boundary layer such variation is induced mainly by latitudinal variation in the zonal wind speed with the existence of a calm belt at the equator and a maximum wind speed located off the equator arising from the evaporation wind feedback ewf mechanism the latitudinal distribution of evaporation results in a decrease in the height of the lifting condensation level in areas off the equator and an increase at the equator the occurrence of a single itcz in zhang s scheme is attributed to the use of a convective available potential energy criterion by which convection occurs more readily at the equator as a result a precipitation maximum is maintained at the equator via a prevailing conditional instability of the second kind mechanism

formation and variability of a northerly itcz in a hybrid coupled agcm continental forcing and oceanic atmospheric feedback abstract despite the equatorial symmetry of the annual mean insolation the intertropical convergence zone itcz and the collocated band of high sea surface temperature sst assume perennial northern latitudes over the eastern pacific and atlantic an atmospheric general circulation model is coupled with an intermediate ocean model to study continental forcing and oceanic atmospheric interaction that act to break the equatorial symmetry the model reaches a statistically symmetric mean state under perfectly symmetric conditions with the continental coasts running along meridians when a bulge of landmass is added to the eastern continent north of the equator it initiates a coupled ocean atmosphere wave front that propagates westward across the ocean basin cooling the ocean surface and suppressing deep convection on and south of the equator as a result the itcz shifts into the northern hemisphere in contrast to this basinwide response little latitudinal asymmetry develops in the coupled model when

relation between salt diapirism and the tectonic history of the sverdrup basin arctic canada the sverdrup basin is a pericratonic sedimentary trough in northern canada containing up to 13 km of carboniferous to tertiary strata the basin formed by late paleozoic continental rifting and was subsequently affected by a series of alternating tectonic settings evaporite diapirs are well exposed at the present erosion level and occur mainly along the basin axis the diapiric source layer consists of about 400 m of anhydrite underlain by salt of unknown stratigraphic thickness deposited during the initial permo carboniferous synrift phase of basin subsidence large salt anhydrite diapirs rose into the sedimentary overburden when the overburden had reached a thickness of several kilometres they grew during a relatively long period of modest horizontal compression from the permo triassic to early cretaceous much smaller tabular anhydrite diapirs were rapidly emplaced during periods of high horizontal compression in the middle cretaceous when large flexural stresses were induced by sedimentary loadi

role of faults and layer interfaces on the spatial variation of stress regimes in basins inferences from numerical modelling abstract the spatial variation of the computed state of stress is studied in a series of numerically solved boundary value problems of basin scale deformation these numerical experiments illustrate simple situations of decollement tectonism under compression the study focuses on the local variation of the state of stress in a sedimentary overburden where major discontinuities such as large scale faults and layer interfaces are present the states of stress are computed using either the distinct element method or the finite element method classic elasto plasticity laws are used for the behaviour of the continuum and the discontinuities are modelled as coulomb contact surfaces a geologic interpretation of the numerical experiments is proposed to highlight the role played by major structural discontinuities in the local variations of the stress regime the models are two dimensional in space and assume plane strain but the full three dimensional stress strain constitutive relation is used therefore the stress regime variations can be represented by constructing the contour map of the wallace bott stress ratio this simple technique together with the construction of diagrams of principal stress magnitude across the model enables us to rapidly examine the stress field pattern and further discuss the deformation modes of faulting and fracturing which may take place at a small scale we have found that the local variations of the stress tensor are in good agreement with common geologic interpretation of brittle deformations in foreland and thrust systems we demonstrate how the presence of layer interface and the difference in mechanical properties of formation lithology may strongly affect the variation of stress in space this modelling approach has important issues when interpreting well tests to gain access to in situ stresses

the role of surface friction in tropical intraseasonal oscillation abstract the role of surface friction in the tropical intraseasonal oscillation or the madden julian oscillation mjo is investigated by comparing two 4 yr integrations with the goddard atmospheric general circulation model one with the original model design with one added feature to enhance the intensity of the mjo and the other is identical but with surface friction in the tropics replaced by its zonal mean value this comparison indicates that in the second experiment the mjo not only still exists but also exists with similar intensity the oft cited frictional wave cisk fwc interpretation for the origin of the mjo which emphasizes the role of frictionally induced convergence in the surface layer is reassessed in light of these experiments the possibility of the mjo in the second experiment being forced by the middle latitudes is excluded by a third experiment these experiments do not support one of the central ideas in fwc that surface friction plays an instability enhancing role

frequency distribution of daily itcz patterns over the western central pacific abstract this study attempts to explore a comprehensive and compact approach for delineating the multiscale and multivariate characteristics of the itcz over the western central pacific based on daily satellite observations of precipitation ssts and surface winds essentially six distinct itcz spatial patterns namely the north south equator double full and weak are identified according to the daily percentage coverage of deep convection within different latitudinal bands on and off the equator over the western central pacific the evolving structure of the itcz over the western central pacific is investigated with a focus on the transient statistical characteristics the relationship between these daily itcz patterns and ssts and near surface winds is also examined the north 37 south 24 and weak 24 itczs represent the three major itcz daily patterns over the western central pacific and combined they account for almost 85 of the total number of days within a 10 yr period the other

introduction to special issue on integrated basin studies ibs a european commission dgxii project this issue contains papers issued from the integrated basin studies project ibs which is part of a larger program of the european commission dgxii entitled geosciences ii the ibs project ec contract jou2 ct92 0110 originated in geosciences consultation meetings the first of them being held in strasbourg in june 1989 under the auspices of mr hubert curien former french minister for research and technology and the subsequent meeting being held in brussels these consultation meetings have resulted in the conclusion that a main axis of future research in geosciences should be the study of sedimentary basins upstream of industrial activities mainly the oil and gas industry but also water resources management the mining industry the storage of undesirable products and coastal engineering they also resulted in the conclusion that future research on sedimentary basins should fulfill two requirements integration of disciplines and modelling such a conclusion may now seem trivial but was not so generally accepted at that time in this spirit the ibs project was designed to provide the oil and gas industry with a new generation of models for basin formation basin evolution and basin fill architecture from basin scale to reservoir scale its main objectives are the linkage of crust thermomechanical behaviour to basin formation and deformation mechanics and the corresponding modelling the quantification of tectonic control on the sedimentary record and the analysis of compaction and mass and heat transfer the ibs strategy is to link subsurface data to field data and an important part of the project is devoted to thematic field studies in european sedimentary basins of different tectonic styles taken as natural laboratories basin research has gone through a rapid evolution during the last decade in particular through the development of new acquisition and processing methods for seismic data and advances in drilling technology modelling provides an important tool to analyse different aspects of basin formation processes and find their tectonic expression in the basin fill the need for 3 d modelling techniques and models capable of linking processes operating on basinwide to subbasin scales is increasingly recognized and a significant effort has been made in the ibs project to develop a new generation of basin formation models coping with these needs see also cloetingh et al 1993a van wees and cloetingh 1994 as many data required to test these models reside in industrial companies ibs has promoted a closer link between academic research and basin studies carried out by industry the participation of the petroleum industry has been vital in this project and ibs has been able to establish a well functioning system of cooperation that not only facilitated data access but most important guaranteed the suitability of the end products of the project this has led to an intensive exchange of modelling concepts and data sets between industry and academia the ibs project has also used extensively the international lithosphere program task force origin of sedimentary basins see cloetingh sassi and task force team 1994 cloetingh et al 1993a b 1994 to implement planning and to discuss preliminary results it also builds partly on joint research through the european commission tempus and peco programs on pannonian basin studies horvath 1993 van balen and cloetingh 1995 van balen et al 1995 horvath and cloetingh 1995 a stimulating aspect of the activity of the ibs group is the creation of a research network in the corresponding field of knowledge which comprises now 30 teams belonging to eight european countries england france germany hungary norway spain switzerland and the netherlands this demonstrates the capacity of the procedures used by the dgxii of the european community to formulate a really european research space phd students and young researchers form an important component of the research groups

the origin of sedimentary basins a status report from the task force of the international lithosphere program abstract better insights into the mechanisms of basin formation have a direct bearing on the predictive power of forward models for basin fill models that link flexure normal faulting and thrusting on a subbasin scale provide important constraints on the tectonic control of the sedimentary record enabling a quantitative comparsion with eustatic contributions to the basin architecture thus of special importance is the need to link processes with different spatial and temporal scales involved in the evolution of extensional and compressional basins by numerical modelling a new generation of basin modelling concepts and techniques is one of the main objectives of the task force origin of sedimentary basins of the international lithosphere program the focus of this work is on the quantification of the effects of the thermomechanical structure of the lithosphere and its interplay with regional and local stress changes other important developments include the step towards three dimensional modelling and the full integration of rapidly expanding fission track and other data sets to constrain vertical motions in basins as natural laboratories for the interactive testing and development of new basin modelling techniques a number of basins with high quality data from industry government and academia have been selected on the basis of specific testable problems

the role of the cloud radiative effect in the sensitivity of the intertropical convergence zone to convective mixing abstractstudies have shown that the location and structure of the simulated intertropical convergence zone itcz is sensitive to the treatment of sub gridscale convection and cloud radiation inter

the subsidence history of the northern hyblean plateau margin southeastern sicily abstract the southeastern corner of sicily is dominated by the hyblean plateau which is composed of carbonate rocks of triassic to miocene age the plateau forms part of the african foreland which collided during tertiary times with the calabrian arc giving rise to the maghrebian thrust belt the present study attempts to reconstruct the subsidence history of the northern hyblean plateau during the neogene climax of the plate collision this area has been a centre for widespread basaltic volcanic activity 8 1 ma and uplift at the close of the collisional events pliocene early pleistocene the area under consideration has been affected by subsidence and the progressive consumption of the northern margin of the hyblean plateau led to the development of the modern foredeep a quantitative analysis was done by one dimensional airy backstripping of seven deep wells located on this crucial part of the hyblean plateau the results of the analysis show that the subsidence history of the northern hyblean plateau area is characterized by four main phases similar to other domains in the central and eastern mediterranean basins these phases are a neotethyan rifting during late triassic early jurassic time b a slow thermal subsidence from early jurassic until late cretaceous time leading to the formation of a widespread mesozoic carbonate platform c compressional phase during late cretaceous palaeogene time which resulted in the formation of fold systems and d uplift and subsidence events during the middle tertiary which are probably the result of the continued collision of the european african plates after the early pleistocene unlike other terranes within the mediterranean an uplift occurred in the northern hyblean plateau following the upper miocene lower pleistocene massive volcanic activity this uplift is probably associated with the latest stages of thrusting along the frontal part of the maghrebian thrust belt

lateral variations in mechanical properties of the romanian external carpathians inferences of flexure and gravity modelling we present the results of two dimensional flexure and gravity modelling of the subsidence of the romanian carpathian foreland based on twenty profiles through the southern and eastern carpathians the narrow spacing of the grid of profiles allows us to investigate the lateral tectonic variations transverse to the belt but also along strike the topographic elevation of the romanian carpathian mountain belt is modest and the minimum in the bouguer gravity anomaly characteristic for flexural control of subsidence is located relatively far towards the foreland in respect to the mountain belt as the contribution of topographic loading to the evolution of the romanian carpathian foreland system is small a subduction underplating dominated tectonic regime controlled the nappes emplacement and basin shortening in the external flysch and molasse basins during the late tertiary the modelling results support the existence of important variations in effective elastic thicknesses te and plate boundary forces high flexural bending stresses in the western part of the southern carpathians can explain low te values whereas the increase of te to the east can be explained by changes in rheological properties of the moesian platform field observations indicate that variations in deflection along strike are probably also related to basement unregularities stress field rotations and strike slip movement along lateral ramps during the tertiary in the eastern carpathians the model results indicate a n s trend of lateral back stepping of the subduction system a distinct back step in the vicinity of the seismically active vrancea area supports the involvement of the e w crustal scale trotus fault which forms the transition from the east european platform to the scythian and moesian platforms development of a possible n s migration of plate boundary activity or slab detachment and successive intersection with the trotus fault can explain the large pliocene subsidence in the focsani depression and relative uplife of the east european platform north of the mentioned fault

the dynamics of idealized convection schemes and their effect on the zonally averaged tropical circulation in this paper the effect of a simple convection scheme on the zonally averaged tropical general circulation is examined within an idealized moist gcm to obtain broad classifications of the influence of convection on the tropics this is accomplished with a simplified convection scheme in the style of betts and miller the scheme is utilized in a moist gcm with simplified physical parameterizations gray radiation with zonally symmetric slab mixed layer ocean boundary conditions comparisons are made with simulations without a convection scheme i e with large scale condensation lsc only with the moist convective adjustment mca parameterization and with various formulations and parameter sets with a simplified betts miller sbm scheme with the control run using the sbm scheme the tropics become quieter and less dependent on horizontal resolution as compared with the lsc or mca simulations the hadley circulation mass transport is significantly reduced with the sbm scheme as is the itcz precipitation an important factor determining this behavior is the parameterization of shallow convection without shallow convection the convection scheme is largely ineffective at preventing convection from occurring at the grid scale the sensitivities to convection scheme parameters are also examined the simulations are remarkably insensitive to the convective relaxation time and only mildly sensitive to the relative humidity of the reference profile provided significant large scale condensation is not allowed to occur the changes in the zonally averaged tropical circulation that occur in all the simulations are understood based on the convective criteria of the schemes and the gross moist stability of the atmosphere

characteristics of the double intertropical convergence zone over the tropical indian ocean 1 investigations on the double intertropical convergence zone ditcz over the indian ocean using the monthly mean surface wind divergence data obtained from scatterometers on board the ers 1 2 and quikscat satellites 1991 2005 and the monthly mean cloud amount obtained from the international satellite cloud climatology project 1988 1989 1998 2005 and the advanced very high resolution radiometer avhrr data 1996 2003 reveal that its frequency of occurrence is considerably larger than that reported earlier though the ditcz feature in this region is rather diffused compared to pacific the 14 year analysis of monthly mean surface wind divergence shows that ditcz structure is clearly discernible in april frequency of occurrence f 64 november f 73 and december f 60 in the 50 85 e longitude band over the tropical indian ocean though less frequent ditcz occur during other months also except the asian summer monsoon season most preferred latitudes of the north and south bands of ditcz are 6 n and 7 s respectively during november and december the ditcz structure is well manifested in the cloud amount also during november and december while it is less prominent in april a weak but clearly identifiable hemispherical asymmetry is observed in latitude of occurrence and amplitude of the ditcz bands since the sea surface temperature sst at the equatorial region over the indian ocean is nearly uniform the ditcz appears to be generated mainly by the atmospheric dynamics this provides a unique opportunity to investigate the structure of itcz created by the atmospheric dynamics alone which is one of the important problems in itcz dynamics

the role of rheology in extensional basin formation modelling the rheology of the lithosphere determines its deformation under given initial and boundary conditions this paper presents a critical discussion on how rheological properties are taken into account in extensional basin modelling since strength envelopes are often used in models we review the uncertainties in temperature and rheological parameters and assumptions in type of rheology and mode of deformation involved in their construction models of extensional basins are classified into three groups kinematic kinematic with rheological constraints and dynamic rheology enters kinematic models only implicitly in the assumption of an isostatic compensation mechanism we show that there is a critical level of necking that reconciles local isostasy with the finite strength of the lithosphere which requires a flexural response kinematic models with rheological constraints make use of strength envelopes to assess the initial lateral variations of lithospheric strength and its evolution with time at the site of extension dynamic models are the only ones to explicitly introduce rheological constitutive equations usually in plane strain or plane stress they usually however require the presence of an initial perturbation thickness variations pre existing faults thermal inhomogeneities rheological inhomogeneities the mechanical boundary conditions kinematic and dynamic and the thermal boundary conditions constant temperature or constant heat flux at the lower boundary of the lithosphere may result in negative positive feedbacks leading to cessation acceleration of extension we conclude that while kinematic models with rheological constraints if possible are very successful in accounting for the observed characteristics of sedimentary basins dynamic models are necessary to gain insight into the physical processes underlying basin formation and evolution

senonian basin inversion and rejuvenation of rifting in africa and arabia synthesis and implications to plate scale tectonics abstract the late paleozoic to tertiary stratigraphic record of much of the african plate reflects the effects of continental rifting and passive margin development several short lived but widespread and tectonically important compressional or wrench dominated events occurred however during the permian to recent evolution of africa we focus here on the best documented of these events which occurred during the late santonian at that time older sedimentary basins mostly ene wsw trending were folded and inverted including some basins along the tethyan margin from morocco to the syrian arc and the intraplate benue southern chad basins and the lugh mandera basin in oman ophiolites were obducted following the santonian tectonism an extensive phase of rifting occurred in central and north africa and northern arabia spanning from campanian to maastrichtian or paleocene times rejuvenation or acceleration of subsidence occurred in several basins located along the tethyan margin along the atlantic and indian ocean margins as well as within the intraplate domain rifting was sometimes accompanied by magmatic activity especially in offshore northern libya and along the indian ocean margin compressional deformations rejuvenated or developed by latest maastrichtian times along the tethyan margin and locally within the intraplate domain one of the most remarkable attributes of the santonian tectonic event which we consider representative of the major trans african stress field changes is the rapidity with which the change was reflected stratigraphically across north and central africa and its short duration the cause of the santonian compressional event is directly linked to the change in poles of rotation for the opening of the atlantic at 83 85 ma the end of the cretaceous normal magnetic quiet zone this was also synchronous with the obduction of ophiolites along the northeast margin of arabia oman the onset of separation between india and madagascar with formation of the mascarene oceanic basin and the development of the european alpine chain we interpret these phenomena as causally related aspects of a global tectonic event the santonian compressional event as well as the campanian maastrichtian rifting event and the end cretaceous compressional event illustrate the critical connection between intraplate tectonic histories and processes occurring at sometimes very distant plate boundaries

relationship between deeper lithospheric processes and near surface tectonics of sedimentary basins interactions between upper lithosphere deformation as manifested in the structure and evolution of sedimentary basins and lower lithospheric deformation presumably reflect large scale regional or global tectonic events we review the current state of knowledge regarding these interactions and suggest areas of research which may lead to an improvement in this knowledge understanding the development of sedimentary basins requires insight into the processes responsible both for basin subsidence and also for distribution and preservation of sediments within the basins while some classes of basins are better understood than others there remain significant gaps both in our ability to account for available data and also in the data available to test current models and develop new ones subsidence in some classes of basins can be related to lithospheric scale processes occurring as part of the overall plate tectonic paradigm for example it is widely accepted that passive margin basins subside as a result of lithospheric extension mckenzie 1978 and that foreland basins are flexural consequences of collision between a continent and outboard terranes beaumont 1981 on the other hand models for the origin of intracratonic forearc and trans tensional basins are essentially still at cartoon level involving processes that are difficult to quantify and evaluate in the following we review a number of fundamental questions of vital interest for understanding of the relationship between deeper lithospheric processes and near surface tectonics

on large scale circulations in convecting atmospheres the dominant thinking about the interaction between large scale atmospheric circulations and moist convection holds that convection acts as a heat source for the large scale circulations while the latter supply water vapour to the convection we show that this idea has led to fundamental misconceptions about this interaction and offer an alternative paradigm based on the idea that convection is nearly in statistical equilibrium with its environment according to the alternative paradigm the vertical temperature profile itself rather than the heating is controlled by the convection which ties the temperature directly to the subcloud layer entropy the understanding of large scale circulations in convecting atmospheres can therefore be regarded as a problem of understanding the distribution in space and time of the subcloud layer entropy we show that the subcloud layer entropy is controlled by the sea surface temperature the surface wind speed and the large scale vertical velocity in the convecting layer and demonstrate how the recognition of this control leads to a simple physically consistent view of large scale flows ranging from the hadley and walker circulations to the 30 50 day oscillation in particular we argue that the direct effect of convection on large scale circulations is to reduce by roughly an order of magnitude the effective static stability felt by such circulations and to damp all of them

single and double itcz in an aqua planet model with constant sea surface temperature and solar angle it has been known for more than a decade that an aqua planet model with a globally and temporally uniform sea surface temperature and solar isolation angle can generate intertropical convergence zones itcz employing such a model previous studies have shown that one of several means can be used to change between a single itcz over the equator and a double itcz straddling the equator these means include switching to a different cumulus parametrization scheme making changes within the cumulus parametrization scheme and changing other aspects of the model such as horizontal resolution here an interpretation of these findings is offered in an aqua planet model with globally and temporally uniform sea surface temperature and solar isolation angle the latitudinal location of an itcz is the latitude where a balance exists between two types of attraction both resulting from the earth s rotation the first attraction pulls the itcz towards the equator and is not sensitive to changes in model design it is directly related to the coriolis parameter which provides stability to the atmosphere the second ssattraction pulls the itcz poleward and is sensitive to changes in model design it is related to the convective circulation modified by the coriolis force a balance between the two types of attraction is reached either at the equator or more than 10 north and south of the equator depending on the shape and magnitude of the attractions a balance at the equator yields a single itcz over the equator whereas a balance north and south of the equator yields a double itcz straddling the equator

thermomechanical structure of european continental lithosphere constraints from rheological profiles and eet estimates summary the eet equivalent elastic thickness of the lithosphere is a measure of the integrated lithospheric strength it is directly related to the mechanical thickness and rheology of the crustal and mantle lithosphere we present a comparison of eet estimates and strength profiles based on the extrapolation of rock mechanics data for different parts of the european and eurasian continental lithosphere we discuss the temporal and spatial variations in the mechanical thickness and strength inferred from data for precambrian segments of europe s lithosphere variscan europe and the alpine collision belt this analysis demonstrates important spatial and temporal variations in lithospheric rigidity for orogenic belts and sedimentary basins in eastern and western europe and asian parts of eurasia the eet estimates based on synthetic rheological profiles constrained by newly available geophysical data are consistent with the estimates of eet derived from flexural studies of sedimentary basins forelands and orogenic belts these rheological profiles suggest weakening of the major parts of the european and eurasian continental lithosphere by decoupling of the crustal and upper mantle parts a comparison with the seismicity depth distribution for some selected sites suggests that the intra plate seismicity is essentially restricted to the upper crustal parts of europe s lithosphere providing additional support to the notion of the decoupled lithosphere the presence of intra plate stress fields can explain a significant part of the observed variations in eet estimates within individual thermotectonic age groups a comparison of wavelengths of crustal and lithospheric folding with observations shows these wavelengths to be consistent with estimates of eet inferred from the rheological response of basins and orogens at more moderate levels of intra plate stress

superposed deposits of thick coal on the eastern edge of the illinois basin and their association with underlying geologic features abstract comparison of maps produced from publicly available data drillers logs electrical logs and mine maps provides a basis for inferring a deep seated influence on the distribution of superposed deposits of thick coal 1 4 m in four middle pennsylvania desmoinesian series coal beds in three mining districts of west central indiana thick sandstone 18 m is common in areas between and around the mining districts but less than 3 percent of the study area consisting of 3200 km 2 is underlain by both thick coal and thick sandstone only thick sandstone associated with the survant coal member linton formation and informally referred to by us survant sandstone exists in all of the thin coal areas after comparison with published maps by other authors it is inferred that distribution of the survant sandstone which was deposited immediately after a long period of slow deposition associated with the colchester coal member linton formation may reflect topographic expression of long term subsidence associated with differential thinning of much deeper silurian strata 580 m below although the findings of this study provide the basis for a conceptual geologic model with a hypothetical structure that is amenable to statistical testing such analysis should be undertaken only after the data are analyzed for randomness spatial autocorrelation linearity and normality

on a tectonic mechanism for regional sealevel variations abstract no satisfactory tectonic explanations have yet been offered for the apparent sealevel fluctuations of about 1 cm 1000 years and a magnitude of up to a few hundred meters that have been proposed by vail et al 1 we propose a mechanism that does appear to be able to explain these changes if horizontal stresses of the order of a few kilobars occur in the lithosphere and if changes in these stress fields occur on geological time scales the proposed model is one of an interaction between these stresses and the deflections of the lithosphere caused by sedimentary loading apparent sealevel changes of up to 100 m can be produced at the flanks of the sedimentary basins by this interaction the mechanism is most effective for young margins that are subject to rapid sediment loading by its nature the tectonic model can explain contemporaneous fluctuations in apparent sealevel in neighbouring depositional environments in principle it implies the possibility of regional correlations in different basinal settings

the role of inertial instability in determining the location and strength of near equatorial convection there are two major organized cloud configurations in the vicinity of the equator where there is a small cross equatorial surface pressure gradient convection is close to the equator and is generally tied to the location of the lowest sea level pressure slp and warmest sea surface temperature sst in agreement with arguments based upon simple thermodynamical considerations however when there is a substantial cross equatorial pressure gradient such as occurs in the monsoon regions organized convection appears off the equator in the summer hemisphere equatorward of the slp minimum and not necessarily collocated with the warmest ssts thus in this instance simple thermodynamical considerations alone cannot explain 2he location of the convection in this situation the zero absolute vorticity contour 0 also lies in the summer hemisphere therefore between the equator and the 0 contour is a region of locally anticyclonic absolute vorticity and an inertially unstable regime it is argued that the convection results from the low level divergence convergence doublet centred about the 0 contour which is the mitigating response to the inertial instability the associated latitude height secondary circulation should provide subsidence suppressed convection over the equator and rising motion enhanced convection to the north of the zero absolute vorticity contour signatures of the inertial instability predicted by theory are found in observations supporting the hypothesis wherever a strong cross equatorial pressure gradient exists the 0 contour bisects a maximum in the divergent wind field divergence is found equatorward of the zero contour and convergence on the poleward side latitude height cross sections show strong local meridional circulations with maximum rising motion on the poleward side of 0 as the regions where the rising motions occur are conditionally unstable there is deep convection and the vertical circulations extend throughout the troposphere it is noted that the intensity of the off equator convection is deeper and probably stronger than convection located at the equator this is probably because the convection associated with the inertial instability is more efficient necessary conditions for the location of near equatorial convection are listed arguments are presented whereby inertial instability is established as the cause rather than an effect of off equatorial convection these include an outline of the sequence of processes leading up to the convection the factors that limit the encroachment of the 0 contour into the summer hemisphere are discussed and an explanation for the existence of the low level westerly monsoon wind maximum is suggested the possible role played by the instability mechanism or the lack of it in coupled model simulations that produce seasonally migrating and or double itczs in the eastern pacific ocean is discussed finally it is proposed that the instability mechanism is important in the initiation of westward moving disturbances found in the eastern pacific and in determining active and break periods in the summer indian monsoon

breakdown and reformation of the intertropical convergence zone in a moist atmosphere abstract the effects of moisture on the intertropical convergence zone itcz over the eastern pacific on the synoptic time scale are investigated using an intermediate complexity atmospheric circulation model the quasi equilibrium tropical circulation model qtcm1 on an aquaplanet the dry simulation shows results consistent with those of simple dynamic models except that a slightly stronger heating rate is needed owing to different model designs in the moist simulations the most important result is the formation of a tail southwest of a vortex during and after the itcz breakdown this tail may extend zonally more than 60 longitude and last for more than two weeks in an idealized simulation in the eastern north pacific this phenomenon is often observed in cases that involve easterly waves in a sense the formation of the tail suggests a possible mechanism that forms an itcz efficiently this study shows that the surface convergent flow induced by a disturbance initializes a positive wind evapor

maintenance of the intertropical convergence zones and the large scale tropical circulation on a water covered earth abstract how the surface boundary heating sea surface temperature and cumulus adjustment process affect the location structure energetics and dynamics of the intertropical convergence zones itczs is investigated a series of experiments is performed with a general circulation model where the lower boundary is specified to be water at a fixed sea surface temperature sst an aqua planet all experiments are run using equinoctal insolation with no longitudinal variation in sst two different convective parameterization schemes kuo and moist convective adjustment and several different zonally symmetric sst distributions are used in these experiments the location of the itcz is found to be sensitive to the convective parameterization scheme and the sst distribution the model with the moist convective adjustment scheme produces an itcz over the tropical sst maximum even under conditions where the sst gradient is weak by contrast the model with the kuo convective parameterization is not as sensit

structural controls on sedimentary basin evolution introduction this volume contains a collection of papers on structural controls on sedimentary basin evolution presented at the sixth annual workshop of the international lithosphere program task force origin of sedimentary basins in sitges at the rim of the ebro basin september 1995 previous workshops of the ilp task force had been in rueil malmaison france 1990 in matrahaza hungary 1991 on the rim of the pannonian basin in sundvollen norway 1992 in the oslo graben in benevento italy 1993 in the southern apennines fold andthrust belt and in the dead sea rift of israel 1994 the task force also organized a number of sessions during the 1992 and 1996 european geophysical society and the 1993 and 1995 european union of geosciences conferences reports of these meetings have been published in a number of special volumes and papers cloetingh et al 1993a b 1994 1995a b 1996 stephenson 1993 stephenson et al 1996 a position paper cloetingh sassi and task force team 1994 published in m a r i n e a n d p e t r o l e u m geo logy has outlined the task force strategy to pursue the development of a new generation of basin models using natural laboratories with high quality data sets obtained through close partnership with industry the 7th task force workshop was held on the faroe islands northern atlantic in 1996 with the aim of examining the dynamics of rifting

tropical intraseasonal oscillation super cloud clusters and cumulus convection schemes abstract a new framework for interpreting the origin of the tropical intraseasonal oscillation tiso which avoids the speed and scale selection problems in the previous theories is proposed in this study in this interpretation tiso is viewed as an oscillation driven by an eastward moving convective region this convective region consists of one or more super cloud clusters originating in the indian ocean and terminating in mid pacific and is then followed by another convective region arising in the indian ocean in a period of 40 50 days additionally a formal analogy is pointed out between super cloud clusters and the middle latitude baroclinic wave packets this study includes a simulation of tiso in a 2d model to support our interpretation experiments were conducted with four different convection schemes the authors advocate that the successful simulation of tiso depends on the successful simulation of super cloud clusters which in turn depends on the successful simulation of the life cycle of

preferred latitudes of the intertropical convergence zone abstract the latitude preference of the intertropical convergence zone itcz is examined on the basis of observations theory and a modeling analysis observations show that convection is enhanced at latitudes of about 4 to 10 relative to the equator even in regions where the sea surface temperature sst is maximum on the equator both linear shallow water theory and a moist primitive equation model suggest a new explanation for the off equatorial latitude preference of the itcz that requires neither the existence of zonally propagating disturbances nor an off equatorial maximum in sst the shallow water theory indicates that a finite width zonally oriented midtropospheric heat source i e an itcz produces the greatest local low level convergence when placed a finite distance away from the equator this result suggests that an itcz is most likely to be supported via low level convergence of moist energy when located at these preferred latitudes away from the equator for a plausible range of

the influence of cross equatorial pressure gradients on the location of near equatorial convection tomas and webster note that in regions where there is a substantial cross equator surface pressure gradient there is locally anticyclonic absolute vorticity on the low pressure side of the equator and thus the flow in this region meets the parcel criterion for inertial instability they hypothesize that the atmospheric response to this absolute vorticity distribution is a convergence divergence doublet in the boundary layer the convergence centre results in strong convection and thus is very important in determining the strength and location of convection i e the intertropical convergence zones whereas the divergence centre results in suppressed convection in this work a zonally symmetric model of the boundary layer is developed to investigate this hypothesis further an analysis of a linearized version of the model indicates that although the observed flow in these regions meets the parcel criterion for instability it does not satisfy the linear stability criteria because of the stabilizing influence of dissipation and the finite vertical scale much greater shear than that observed is required for linear instability it is noted however that when the parcel criterion is met one of the nonlinear terms which was neglected in the linear analysis may have an important influence on the flow several experiments are performed integrating the full nonlinear model relaxing back to a pressure distribution having a cross equatorial gradient to test whether the observed vorticity wind and convergence distributions can be well simulated it is found that the simulations reach a steady state in which there is a region of locally anticyclonic absolute vorticity on the low pressure side of the equator this absolute vorticity distribution results in an anomalous acceleration of the meridional wind and a convergence divergence doublet similar to that observed by tomas and webster this response is explained as resulting from accelerations that act to bring the zonal flow out of geostrophic balance as it passes through the region of locally anticyclonic absolute vorticity the response of the meridional wind to the strength of the pressure gradient is quasi linear for small and somewhat larger values of forcing but between these values there is a range where the response is highly nonlinear i e large increases in the strength of the meridional wind result from small changes in the pressure gradient it is suggested that this nonlinear response may play a role in the observed sudden onset of the monsoon circulations the nonlinear model is also forced using pressure distributions taken from observations the resulting steady state simulated vorticity wind and convergence distributions closely match the observations for the cases of pressure distributions taken from the east pacific and east atlantic during july when forced using the pressure distribution from the indian ocean region during july the model produces an unrealistically strong meridional wind response some improvement is obtained by including the latitudinally dependent zonal pressure gradient force which is moderately strong in this region finally the model is forced using a pressure distribution taken from observations in the central pacific ocean during july in this case the cross equator pressure gradient is near zero

the role of pre existing faults in basin evolution constraints from 2d finite element and 3d flexure models the lithospheric driving forces which cause intraplate basin deformation are relatively constant over large areas consequently lateral variations in deformation and stress and strain concentrations seem to be primarily caused by pre existing heterogenities in the rheological signature of the continental lithosphere underlying the sedimentary basins in this paper we explore the weak character of upper crustal faults and their control on basin shape for a number of case studies on intraplate phanerozoic basin settings using a 2d finite element and a 3d flexure model of key importance is the integration of seismic data and field observations with the tectonic modelling allowing the investigation of deformation processes and their expressions on different scales operating on different levels of the lithosphere finite element models for sub basin scales incorporating weak upper crustal faults predict strong control of these weak zones on local stress distributions and subsequent deformation in agreement with observed deformation patterns slip along upper crustal faults control stress distribution and subsequent faulting in overlying sedimentary rocks the effect of weak upper crustal fault movements on basin wide regional upper crustal flexure is looked at in two case studies on 1 extensional tectonics in the lake tanganyika rift zone east africa and 2 compressional tectonics in the central system and tajo basin central spain both settings indicate that basement warpings are controlled by large amounts of slip along so called weak crustal scale border faults which are mostly planar adopting border fault displacements in the 3d flexure model the results indicate low effective elastic thickness eet values in a range of 3 7 km for induced basement deflection patterns in accordance with observations the low eet values most likely reflect a partly decoupling of upper crustal and subcrustal deformation facilitated by the weak lower crust and in agreement with standard rheological assumptions for phanerozoic lithosphere in contrast the inferred weakness of upper crustal faults relative to surrounding rock is not evident from uniform rheological assumptions however observations of reactivations of faults which are not preferably aligned with the stress field and reactivations of basin deformation on long time scales are in support of this feature

gravity evidence for an alpine buckling of the crust beneath the paris basin abstract the processing of the gravity data of the paris basin has enlightened the existence of crustal ridges these ridges correspond to the zones of different crustal thicknesses in plan view the ridges are concentric with the alpine orogen and were probably controlled by this tertiary alpine mountain building the thinned zones related with the mesozoic and pre mesozoic basins were already existing before the alpine deformations these are of limited size and clearly associated with the basins on a large scale two different domains have been recognized the first one corresponds with a zone where the crust is 37 km thick it is also the place where the tertiary depocentres developed the second one relates with a zone where the crust is 29 30 km thick it has been uplifted during the alpine orogeny these two observations suggest the existence of a tertiary lithospheric buckling beneath the paris basin

climatically driven sedimentary cycles in the late miocene sediments of the pannonian basin hungary abstract by detailed cycle analysis of marginal mostly delta plain facies successions of pannonian sediments the frequency of water level changes of the late miocene pannonian lake hungary can be identified cycle analysis is presented with the object of defining the orbital record preserved in the strata we use the bed thickness as input data for our cycle analysis statistical analysis revealed a slow upward increase of both the frequency and thickness of sand beds in the boreholes resulting from infilling of the lake by a basinward migration of the marginal facies cycles of different order were detected in the sediments the higher order cycles are very close to or are equivalent with the milankovitch climatic cycles 19 ka caused by precession 50 ka caused by obliquity and 400 ka is the longer period of eccentricity the longer 1 m y cycle is very poorly developed here it is probably the analogue of the 3rd order global climatic cycle cycle analysis suggests that one of the main controlling factors of the water level changes of the pannonian lake was high frequency climatic oscillations the long term climatic changes only had a faint impact on the sediments the record of the 3rd order water level changes is very subtle our results show that the water level changes followed the rhythm of that of the eustatic changes but being asynchronous to them i e at high sea level stage the pannonian lake level was low and vice versa