palaeostress analysis of the northern nijar and southern vera basins constraints for the neogene displacement history of major strike slip faults in the betic cordilleras se spain this paper presents the results of a detailed structural analysis of the northern nijar and southern vera basins with special emphasis on the evolution of the regional stress field and the associated timing of movement of the serrata gafarillos and palomares strike slip fault zones these major fault zones control the neogene deformation of the se internal betic cordilleras in spain detailed stress analysis on neogene sediments of the vera and nijar basins shows a strike slip regime with nw se oriented subhorizontal maximum principal stress 1 during tortonian and earliest messinian times under the influence of this stress field dextral displacement along the n090e trending gafarillos fault zone resulted in deformation of the sediments of the southern sorbas and northeastern nijar basins during the early messinian a clock wise rotation of the stress field occurred stress analysis in rocks with late early messinian up to quaternary ages in the nijar and vera basins indicates a strike slip regime with n s oriented subhorizontal maximum principal stress 1 under the influence of this stress field the main activity along the n010e striking palomares strike slip fault zone took place resulting in deformation of the neogene sediments of the southeastern vera basin and culminating in a maximum sinistral displacement of more than 20 km at the same time the stress field was not suitably oriented to exert a large shear component on the gafarillos fault zone which activity ended after the earliest messinian fault and outcrop patterns of syntectonic neogene sediments in the vera basin show that displacement along the palomares fault zone decreased at the end of the middle miocene although minor displacement phases may still have occurred during the late miocene and possibly even pliocene from the middle miocene onward deformation in the nijar basin was controlled by sinistral displacement along the n040e trending serrata strike slip fault zone

geodynamic models of crustal scale episodic tectonic accretion and underplating in subduction zones we investigate the dynamics of crustal scale episodic accretion at convergent margins using a finite element model of subduction the numerical model incorporates effects from flexure subduction loading and large scale variations in material properties the model is used to assess the influence of these parameters on the discrete transfer of units from the lower to the upper plate during subduction the primary controls investigated are spatial variations in density material strength and thickness of material layers these controls correspond to natural examples where episodic accretion results from the thermal structure of subducting lithosphere giving rise to areas of thermally activated ductile creep attempted subduction of small crustal blocks density frictional and or ductile strength variations interaction between well attached basement blocks and overlying detachable sediments and spatial changes in thickness of sediment and crust in the experiments accretion of small continental terranes within a model subduction zone can cause crustal scale fold nappes and shear zones to develop with accompanying tectonic underplating and or frontal accretion the model results may provide insight into real cases of episodic accretion for example the emplacement of the upper penninic nappe stack of the central alps

tertiary tectonic evolution of the external south carpathians and the adjacent moesian platform romania depth interpreted seismic sections of the getic depression foredeep paleostress indicator data and analysis of outcrop to regional scale structures are integrated to derive the tectonic evolution of the south carpathians moesian platform area following late cretaceous and older orogenic phases the south carpathians moesian platform area underwent strike slip deformation with ne sw oriented compression and nw se tension in paleogene to early burdigalian times tensional deformation is recorded which led to the opening of wsw ene to e w trending extensional basins in the late burdigalian ne sw oriented contraction took over causing the oblique inversion of preexisting extensional structures during sarmatian times nw se and slightly younger n s trending compression caused the activation of mainly nw se dextral strike slip faults and in the frontal areas south directed thrusting the nw se direction of extension determined for paleogene to early burdigalian times is hardly compatible with presently accepted models of substantially continuous dextral wrenching between the intra carpathians units to the north of the south carpathians and the moesian platform to the south in contrast we have demonstrated dextral transpressive to transtensional movements within an e w trending corridor from the late burdigalian to late sarmatian which are compatible with available models

tectonic variation in the dniepr donets basin from automated modelling of backstripped subsidence curves abstract the multiphase rift evolution of the dniepr donets dd basin is analysed by 1d backstripping and tectonic modelling of 66 stratigraphic sections mostly from well data distributed throughout the basin the backstripping results illustrate strong temporal and lateral variations in tectonic subsidence it is minor during an inceptive pre rift phase givetian early frasnian 380 8 370 ma and does not show clear spatial correlations within the dd basin framework the main rift phase frasnian famennian 370 362 5 ma corresponds to an acceleration in subsidence rates with tectonic subsidence up to 1500 m along the basin axis displaying a slight increase from the northwest to the southeast strong lateral variations perpendicular to the basin axis reflect the effects of major basin border faults a rift phase in the visean 345 340 ma is characterised by relatively minor subsidence up to about 500 m except for some wells in the southeast following a stage of extremely low rates of deposition in the earliest carboniferous the end of this rift phase can be taken to mark the onset of convex subsidence patterns in the later carboniferous and permian typical in shape of post rift thermal subsidence but significantly increasing in magnitude from northwest to southeast in the basin this trend shows no one to one relationship with late devonian syn rift subsidence the tectonic subsidence curves have been modelled using lithospheric stretching assumptions allowing different stretching factors for the crustal and sub crustal lithosphere and the incorporation of finite and multiple stretching phases a numerical technique was developed that automatically finds best fit stretching parameters for part or all of the tectonic subsidence data given the specification of onset and duration of the various rifting events maps of the 1d modelling results display intrabasinal variations in terms of timing and magnitude of rifting the results indicate that the observed spatial and temporal variations of tectonic subsidence in the dd basin specifically the increasing ratio of carboniferous to late devonian subsidence from northwest to southeast cannot be explained by either a uniform or depth dependent stretching model adopting only a single frasnian famennian rift phase a two phase model in which a significant part of carboniferous tectonic subsidence is related to visean rift activity strongly dominated by sub crustal lithospheric attenuation provides a satisfactory fit to the data although the tectonic implications of such a model are not easily reconcilable by independent constraints a semi quantitative investigation of the possible role of withdrawal of underlying devonian salt during the carboniferous to produce additional post devonian rift phase sediment accommodation space suggests that the effects of such a mechanism could be significant but that they are unlikely to preclude the necessity of the visean rifting event to explain the carboniferous basin evolution

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

flexural expression of european continental lithosphere under the western outer carpathians we present the results of an analysis of the flexural down bending of the european lithosphere under the western outer carpathians for a grid of five profiles with a lateral spacing of about 100 km crossing the carpathians and its foreland seismic sections including two deep seismic reflection lines and numerous wells allowed us to quantify the flexural curvature of the lithosphere in addition gravity data are used to obtain independent constraints two evolutionary scenarios involving subduction underthrusting of passive margin and a phase change in the lower crust are investigated in a context of relatively flat moho under the area furthermore recent uplift expressing itself in erosional features observed along the distal margin of the foredeep is quantified the generally modest bouguer gravity anomaly points to nonisostatic processes causing this uplift steeply dipping basement under the carpathians to about 10 km depth at the location of the pieniny klippen belt is explained by relatively weak lithosphere which is expressed in the predicted low values of effective elastic thickness of 16 km decreasing locally to 3 km the low strength of the european lithosphere in this region is probably caused by mechanical weakening controlled by partial yielding due to high flexural curvature the weakest parts of the lithosphere along the profiles corresponding to low effective elastic thicknesses are concentrated in the areas of maximum bending predicted flexural bending stresses as a function of bending moment and effective elastic thickness increase dramatically under the outer zone of the carpathian belt explaining reactivations of older basement structures in these regions

structure of the eastern cordillera of colombia implications for trap styles and regional tectonics the northwest margin of south america has undergone multiple phases of compressional deformation beginning in the late cretaceous and culminating in the pliocene pleistocene the latest phases miocene to pleistocene of this deformation created the eastern cordillera of colombia compressional structures in the eastern cordillera formed traps that have petroleum exploration potential these are generally in the form of fault bend and fault propagation folds containing top sealed reservoir and mature source rocks trap delineation although difficult to achieve because of the poor seismic quality obtained in the region can be accomplished by supplementing the seismic data with geometric analysis of surficial structures the eastern cordillera is asymmetrical with the dominant tectonic transport direction towards the east west directed thrust faults are localized along the western flank of the eastern cordillera and are interpreted to be back thrusts splaying off a deep mid crustal detachment a regional retrodeformable cross section across the eastern cordillera shows that basement detached deformation of late miocene to pliocene age was followed by pliocene to holocene uplift of the cordillera on high angle basement involved reverse faults these two structural styles were superimposed on preexisting jurassic and lower cretaceous grabens whose normal faults were partially inverted during the later stages of compressional deformation a palinspastic restoration of this regional cross section indicates that approximately 150 km of shortening 40 shortening has occurred 105 km eastward directed towards the llanos basin and 45 km westward directed towards the middle magdalena basin this calculated shortening is very close to that calculated by summing microplate motions for the northwest corner of south america shortening in the sedimentary cover rocks exceeds that in the basement rocks by about three times this shortening can be regionally balanced with a gently dipping mid crustal detachment that extends beneath the middle magdalena basin and central cordillera and which roots in the benioff zone beneath the western cordillera the presence of a mid crustal detachment as postulated here provides a mechanism to transmit the shortening from the convergent plate margin in the pacific to the andean foreland and is interpreted to have provided the structural link between the three ranges of the colombian andes the detachment also provides a mechanism to explain the imbalance of shortening seen between eastern cordillera basement and the overlying strata and implies that the western and central colombian andes have been tectonically transported eastwards a distance of at least 150 km

climate dynamics along the arid northern coast of chile the 1997 1998 dinamica del clima de la region de antofagasta diclima experiment 1 the diclima field experiment was designed to test and quantify the hypothesis of an afternoon enhancement of the coastal subsidence in the extremely arid northern chile because of solar heating over the west slope of the andes ten day campaigns near antofagasta 23 s were carried out in january 1997 july 1997 and january 1998 significant diurnal cycles in temperature mixing ratio and wind from about 1000 to 4000 m above sea level were observed this layer was decoupled from the marine boundary layer circulation below by the subsidence inversion when its base was under the average height of the coastal mountain range the solar heating cycle over the andes and associated circulation resulted in a mean afternoon zonal divergence above the subsidence inversion base of about 30 10 6 s 1 exceeding by a factor of 5 typical subtropical west coast divergences the corresponding early morning convergence was particularly intense during the austral winter experiment in spite of the very strong el nino conditions that prevailed during the july 1997 and january 1998 experiments the overwhelming control that radiation exerts on the daily cycles of the atmospheric circulation over the west slope of the andes seems to guarantee the general validity of the results

coastal lows along the subtropical west coast of south america mean structure and evolution the typical conditions of the eastern boundary of the subtropical anticyclone e g well defined marine boundary layer mbl equatorward low level flow that prevail along the mountainous west coast of subtropical south america are frequently disrupted by shallow warm core low pressure cells with alongshore and crossshore scales of 1000 and 500 km respectively these so called coastal lows cls occur up to five times per month in all seasons although they are better defined from fall to spring marked weather changes along the coast and farther inland are associated with the transition from pressure drop to pressure rise the mean structure and evolution of cls is documented in this work using a compositing analysis of 57 episodes selected from hourly pressure observations at a coastal station at 30 8s during the austral winters of 1991 1993 and 1994 and concurrent measurements from a regional research network of nine automatic weather stations ncep ncar reanalysis fields and high resolution visible satellite imagery coastal lows tend to develop as a migratory surface anticyclone approaches southern chile at about 408s producing a poleward oriented pressure gradient and geostrophically balanced offshore component in the low level wind at subtropical latitudes the transition from negative to positive geopotential anomalies occurs around 850 hpa enhanced mid and lowlevel subsidence near the coast and downslope flow over the coastal range and andes mountains leads to the replacement of the cool marine air by adiabatically warmed air lowering the surface pressure at the coast and offshore as the midlatitude ridge moves to the east of the andes the alongshore pressure gradient reverts back and the easterly wind ceases to act the recovery of the surface pressure toward mean values occurs as the cool cloud topped mbl returns to the subtropical coast although the pressure rise can be attenuated by midlatitude troughing the return of the mbl resembles a kelvin wave propagating along the coast from northern chile where the mbl eventually thickened into subtropical latitudes in about a day

blocking in the southern hemisphere abstract the focus of this paper is on the frequency and spatial distributions of blocking and persistent anomalies of geopotential height over the southern hemisphere the analysis is based upon daily height fields at 1000 and 500 mb for both summer and winter histogram frequency distributions of height anomalies and maps of the skewness and kurtosis have been computed blocking events are objectively defined by requiring a large positive anomaly to exist for 5 days or more composite flow and anomaly fields for several cases are presented and examined in detail the geographical distribution of the frequency of lame amplitude 150 gpm anomalies at 500 mb that persist for only 1 3 days is very similar to that of the high frequency band 2 8 day period variances that identity the storm tracks in the southern hemisphere the primary location for blocking in the southern hemisphere is in the new zealand sector and blocking occurs through a local enhancement of the climatological split in the mean westerli

paleostress reconstructions and geodynamics of the baikal region central asia part 2 cenozoic rifting abstract investigations on the kinematics of rift opening and the associated stress field present a renewed interest since it has recently been shown that the control of the origin and evolution of sedimentary basins depends to a large extent on the interplay between lithospheric strength and applied stresses it appears that changes of stress field with time are an important factor that either controls or results from the rifting process the object of this paper is to study the changes of fault kinematics and paleostress field with time in the baikal rift system during the cenozoic reduced paleostress tensors were determined by inversion from fault slip data measured in the central part of the rift and its southwestern termination between 1991 and 1995 results show that the stress field varies as well in time as in space two major paleostress stages are determined corresponding broadly to the classical stages of rift evolution late oligocene early pliocene and late pliocene quaternary the first paleostress stage is related to the rift initiation and the second to the major stage of rift development similarities between the recent paleostress field and the present day stress field inverted from focal mechanisms indicate that the second paleostress stage is still active therefore we propose to use proto rift for the late oligocene early pliocene stage and active rift for the late pliocene quaternary stage of rift development during the proto rift stage the stress field was characterized by a compressional to strike slip regime a progressive change from transpression to transtension is suspected for the central part of the rift baikal and barguzin basins during this period in the western termination of the rift sayan massif tunka depression a strongly compressional stress field with oblique thrusting kinematics is well constrained in the late miocene early pliocene interval the active rift stage was initiated by a marked change in fault kinematics and stress regime in the late pliocene in the central part of the rift the stress regime changed into pure extension while in the southwestern extremity it changed into pure strike slip fault kinematics suggests that rifting was initiated by an extrusion mechanism due to the interaction of far field compressional stress on a mechanically heterogeneous crust with the southwards pointing wedge of the siberian craton acting as a passive indentor the cenozoic time space evolution of the stress field is believed to reflect the increasing influence of locally generated buoyancy extensional stresses associated with density anomalies of the lithosphere on intraplate stresses generated by the india eurasia convergence and the west pacific subduction

foehn event triggered by an atmospheric river underlies record setting temperature along continental antarctica fondap conicyt chile 15110009 cr2 scientific committee on antarctic research scar university of wisconsin madison antarctic meteorological research center for the data set data display and information nsf grant ant 1535632 nlhpc

climatological features of cutoff low systems in the northern hemisphere this study presents the first multidecadal climatology of cutoff low systems in the northern hemisphere the climatology was constructed by using 41 yr 1958 98 of ncep ncar reanalysis data and identifying cutoff lows by means of an objective method based on imposing the three main physical characteristics of the conceptual model of cutoff low the 200 hpa geopotential minimum cutoff circulation and the specific structure of both equivalent thickness and thermal front parameter fields several results were confirmed and climatologically validated 1 the existence of three preferred areas of cutoff low occurrence the first one extends through southern europe and the eastern atlantic coast the second one is the eastern north pacific and the third one is the northern china siberian region extending to the northwestern pacific coast the european area is the most favored region 2 the known seasonal cycle with cutoff lows forming much more frequently in summer than in winter 3 the short lifetime of cutoff lows most cutoff lows lasted 2 3 days and very few lasted more than 5 days and 4 the mobility of the system with few cutoff lows being stationary furthermore the long study period has made it possible i to find a bimodal distribution in the geographical density of cutoff lows for the european sector in all the seasons with the exception of winter a summer displacement to the ocean in the american region and a summer extension to the continent in the asian region and ii to detect northward and westward motion especially in the transitions from the second to third day of occurrence and from the third to fourth day of occurrence the long term cutoff low database built in this study is appropriate to study the interannual variability of cutoff low occurrence and the links between cutoff lows and jet stream systems blocking or major modes of climate variability as well as the global importance of cutoff low in the stratosphere troposphere exchange mechanism which will be the focus of a subsequent paper

the effect of rift shoulder erosion on stratal patterns at passive margins implications for sequence stratigraphy abstract numerical modelling indicates that the erosion of uplifted rift flanks at passive margins has a profound effect on offshore stratigraphic patterns flexural uplift due to isostatic rebound in response to erosion extends far into the basin and causes uplift of the shelf as a result the contemporaneously deposited sedimentary wedge displays a characteristic offlap pattern when the rift shoulder is largely eroded onlap promoting mechanisms related to cooling of the lithosphere enable sediments to onlap onto the basin margin the initial offlapping and subsequent onlapping strata form one complete second order depositional sequence comprising a shelf margin transgressive and highstand systems tract the modelling inferences are in broad agreement with stratal patterns and basin geometries observed on the u s east coast the southeastern brazilian and southeastern australian passive margins and the transantarctic mountains ross sea shelf system the initial offlaps caused by erosion of rift shoulders have important implications for the deriviation of eustatic signals from coastal onlap patterns

relative importance of strain rate and rheology for the mode of continental extension summary both extension rate and rheology have been shown to influence the style of continental rifting so far their effect on the dynamics of extension has been discussed separately in the literature leading to diverging conclusions the rate of extension mostly affects the dynamics of rifting through the occurrence of syn rift cooling at low extension rates this cooling results in an increase of strength if the lithosphere has a temperature dependent rheology england 1983 first suggested that this effect will limit the amount of extension that an area may undergo kusznir park 1987 argued more generally that it will induce a widening of the rift and concluded that extension rate is the major control on wide versus narrow rifting later studies bassi 1991 bassi keen potter 1993 however have demonstrated the importance of rheological layering within the lithosphere for the mode of continental extension by showing that a plasticity dominated rheology will lead to rapid and narrow necking while a creep dominated rheology results in wider rifts and margins gravitational stresses arising from density anomalies due to lithosphere thinning also affect the style of rifting buck 1991 in this paper we examine the combined effect of these different parameters in order to reconcile earlier studies and assess the importance of syn rift cooling for the process of lithospheric necking the approach introduced in a previous study bassi 1991 uses a finite element technique to simulate extension of a vertical cross section of the lithosphere the effect of cooling on the necking pattern depends strongly on the rheology of the thinned lithosphere when it starts to cool if heat diffusion always induces strengthening and delays rupture in time it only modifies significantly the geometry of the rift when the upper mantle is weak and viscous in this case the locus of maximum strain rate migrates laterally once the central area starts to cool and harden as hypothesized by kusznir park 1987 eventually strain concentrates at the transition between deformed and undeformed lithosphere we predict that this pattern will induce asymmetric breakup and produce a very narrow margin and a wide uniformly thinned conjugate margin in all other cases i e when the upper mantle is initially in the low plasticity regime or if it reaches the yield stress during extension the rate of extension appears to have little effect on the rifting pattern

finite element modelling of tertiary paleostress fields in the eastern part of the tajo basin central spain three subsequent tertiary paleostress fields that are deduced from fault slip data for the eastern part of the tajo basin are analyzed by finite element studies the modelling results show that maximum horizontal stresses shmax are mainly controlled by the geometry of the model limits and the boundary conditions applied the models are used to test two hypotheses on the origin of the altomira range a local stress field responsible for its formation altomira can be modelled successfully by superposition in time and place of two major paleostress fields iberian and guadarrama stress trajectories have been modelled with respect to a homogeneous cover and heterogeneous basement to investigate the role of rheological contrasts between different basement blocks on the orientation of the stress field results of this kind of modelling suggest a mechanical decoupling between the cover and the basement especially for the altomira paleostress field

phanerozoic marine inundation of continents driven by dynamic topography above subducting slabs a spherical model of mantle flow constrained by the locations of trenches can be used to predict the dynamic topography of the earth s surface and hence the marine inundation of continents for past periods of high sea level the predicted geographical pattern of flooding correlates well with the geological record the high spatial correlation may result from increased plate velocities at these times leading to increased rates of subduction subsidence and inundation at convergent margins

jurassic la quinta formation in the sierra de perija northwestern venezuela geology and tectonic environment of red beds and volcanic rocks

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

lithospheric weakening during retroforeland basin formation tectonic evolution of the central south alpine foredeep beginning with the late cretaceous convergence between europe and adria caused the southward subduction of the european plate beneath adria contractional movements at high crustal levels were partly accommodated by southward thrusting southern alps causing flexure of the loaded adriatic plate and the formation of the late cretaceous to late miocene south alpine foredeep with respect to the alpine subduction system the south alpine foredeep is a retroforeland basin in the late paleogene dip values of the base foredeep varied between 3 and 5 the shallower dips were found along profiles crossing domains which had undergone extension during previous late triassic to middle jurassic rifting with ongoing convergence the base foredeep along the entire basin steepened and dip values in the tortonian are of about 7 8 the increase in dip goes hand in hand with an increase in the curvature of the loaded plate this suggests a progressive weakening of the flexed plate modeled effective elastic thickness te values derived from the analysis of plate curvatures decrease from 15 20 km in the late paleogene to 5 km in the tortonian preconvergence values obtained from modeling studies were even higher in the 24 27 km range a practically complete decoupling of the upper middle crust from its mantle substratum enabled the increase in curvature of the hinge zone the progressive weakening of the south alpine lithosphere around the bulge zone is correlated with the its upper plate position with respect to the alpine subduction system

morphotectonic evolution of rifted continental margins inferences from a coupled tectonic surface processes model and fission track thermochronology we use a numerical model to study the topographic evolution and erosional history of rifted continental margins the model combines a kinematic description of lithospheric extension tectonic model with a surface processes model that includes short range hillslope and long range fluvial transport the tectonic model predicts the evolution of the lithospheric temperature and strength elastic thickness distribution as well as the tectonic uplift through time this is input into the surface processes model which calculates the degradation of topography and associated isostatic rebound modeled denudation histories across the margin are used to predict apatite fission track age and length patterns modeling results indicate that depending on the adopted parameters an uplifted rift flank should degrade by erosion within 50 100 m y without significant retreat of the topographic elevation maximum the development of an escarpment system at rifted continental margins is in itself not an indication of tectonic rift flank uplift but results from the existence of a high elevation interior plateau erosional base level lowering as a consequence of rifting and regional isostatic response to erosion of the margin however apatite fission track thermochronology reveals that the areas seaward of the escarpment at a number of rifted margins have been exhumed from several kilometers depth such amounts of denudation cannot be accommodated with isostatic rebound alone and require additional tectonic uplift of the rift flanks modeling of apatite fission track patterns suggests that fission track thermochronology dates the onset of rapid erosion which coincides with the initiation of strong relief i e initiation of rifting fission track ages which are younger than the age of rifting thus cannot be unambiguously interpreted as excluding prerift uplift the timing of margin uplift can be established only by careful track length analysis and integration with regional stratigraphic data the model is applied to the saudi arabian red sea margin and the southeastern australian highlands where it is constrained by present day topography and apatite fission track data as well as seismic and gravity data for the saudi arabian red sea margin synrift regional plateau uplift with a magnitude of approximately 1 km is inferred possibly as a result of asthenospheric upwelling flexurally induced tectonic uplift of the rift flank with a magnitude of 2 km is superimposed on this regional uplift the relatively high elevation of the southeastern australian highlands their steep front and the relatively high amounts of erosion suggest that apart from mesozoic synrift flexural uplift tertiary rejuvenation of topography has occurred possibly as a result of renewed lithospheric thinning and underplating the low elevation of the australian interior would inhibit the evolution of a major escarpment in the absence of such renewed uplift

episodes of strong flow down the western slope of the subtropical andes nocturnal flows down the narrow andean valleys within the western slope of the subtropical andes central chile are episodically enhanced by easterly downslope winds that flow into the santiago basin over the radiatively cooled air above the surface local regional and large scale data have been used here to characterize the mean features of these episodes about 80 of easterly downslope flow episodes in austral winter are forced by a reversal in the sea level pressure gradient along the coast of south central chile when a midlatitude cold high migrates from southern chile eastward across the andes under midtroposphere sw winds associated with a warm ridge aloft under these circumstances low level easterly offshore flow sets in producing a compensating downslope flow that subsides over central chile the remaining cases are associated with prefrontal conditions under a midlatitude trough with nw winds aloft since in most of these cases the easterly low level flow occurs beneath westerly flow higher above these episodes classify as strong windward downslope flows within the andean valleys and canyons the near surface air experiences a sensible warming and drying at night and early morning during these episodes as the strong downvalley winds tend to destroy the surfacebased radiative inversion and mix down warmer air from aloft at the exit region of these valleys into the central basin these downslope flows in austral winter are not able to flush the cold air pool there hence dawn surface temperatures over the basin tend to be lower than average as clear skies and dry subsiding air aloft favor surface radiative cooling the resulting enhancement of the near surface static stability hampers the subsequent development of the mixed layer leading to severe air pollution events in santiago and other cities in central chile a comparative discussion on governing mechanisms with respect to apparently similar phenomena as gap flow and shallow foehn is included

a new multilayered model for intraplate stress induced differential subsidence of faulted lithosphere applied to rifted basins in plane horizontal stresses acting on predeformed lithosphere induce differential flexural vertical motions a high precision record of these motions can be found in the sedimentary record of rifted basins originally it was proposed that rifted basins experience flank uplift and basin center subsidence in response to a compressive change of in plane stress which agrees well with observed differential motions subsequently published models predicted that the vertical motions may be opposite because of the flexural state of the lithosphere induced by necking during extension however the total flexural and permanent geometry of the lithosphere underlying the rifted basin is the controlling parameter for the in plane stress caused vertical motions the largest part of this preexisting geometry is caused by faulting in the uppermost brittle part of the crust and ductile deformation in the underlying parts of the lithosphere we present a new multilayered model for stress induced differential subsidence taking into account the technically induced preexisting geometry of the lithosphere including faults in the upper crust as continental lithosphere may exhibit flexural decoupling due to a weak lower crustal layer the new multilayer in plane stress model discriminates the geometries of the separate competent layers at a basin wide scale the new model predicts that a compressive change of in plane force results in basin center subsidence and flank uplift confirming the original hypothesis compared to all previous models the new model requires a lower horizontal stress level change to explain observed differential vertical motions

dynamics of the low level jet off the west coast of subtropical south america the subtropical west coast of south america is under the influence of the southeast pacific anticyclone year round which induces persistent southerly winds along the coast of north central chile these winds often take the form of a low level coastal jet in many aspects similar to the coastal jet existing off the california coast extensive diagnostics of mesoscale model results for a case in october 2000 are used here to describe the mean momentum budget supporting the coastal jet the jet appears to occur when midlatitude synoptic conditions induce a northerly directed pressure gradient force along the coast of northcentral chile the very steep coastal terrain precludes the development of a significant easterly low level wind that would geostrophically balance the pressure gradient instead the meridional flow accelerates until turbulent friction in the marine boundary layer balances the meridional pressure gradient the resulting force balance is semigeostrophic with geostrophy valid only in the zonal cross shore direction at higher levels the topographic inhibition of the easterlies relaxes and a small easterly flow ensues which turns out to be very important in the temperature and stability budgets of the layer capping the marine boundary layer

mechanical aspects of sedimentary basin formation development of integrated models for lithospheric and surface processes different assumptions for the thermo mechanical properties of the lithosphere strongly affect predictions inferred from quantitative sedimentary basin modeling examples from various basins selected as natural laboratories illustrate the importance of incorporating a finite strength of the extending lithosphere in forward stratigraphic modeling of large scale basin stratigraphy current models can effectively couple erosion at uplifted rift shoulders of extensional basins with the basin fill architecture of the subsiding basin compartments modeling of the synrift strata integrates spatial scales characteristic for subbasins such as the oseberg field in the north sea with large scale lithospheric properties characterizing the bulk strength of extending lithosphere modeling of compressional basins in foreland fold and thrust belt settings can effectively link lithospheric flexure with surface processes scales pertinent to short term spatial and temporal variations in basin fill and basin deformation can now be addressed allowing the quantitative investigation of consequences of different modes of thrusting for basin fill geometry and facies characteristics

orogenic float of the venezuelan andes abstract the venezuelan or merida andes are a ne trending intracontinental orogen that started to rise from the middle miocene due to the e w far field convergence between the maracaibo block to the northwest and the guyana shield to the southeast oblique convergence is responsible for strain partitioning with thrusting along both foreland basins and right lateral strike slip faulting along the ne sw bocono fault cutting the venezuelan andes along strike the central part of the belt is also cut by the n s left lateral strike slip valera fault that connects the bocono fault both faults bounding the trujillo block that escapes towards the nne even though the regional geology of belt is well known its structure at depth remains a matter of debate our work based on the integration of geological and geophysical data aims to better constrain the deep geometry of faults and the tectonic evolution of the mountain belt we used the orogenic float model to construct two nw se trans andean crustal scale balanced sections the late neogene quaternary shortening varies from 40 km in the south to 30 km in the north across the trujillo block indicating that a quarter of the deformation seems to be absorbed by the tectonic escape process more importantly a major reorganization in the crust took place in the early pliocene it is characterized by the imbrication of the maracaibo crust into the guyana crust this resulted in the subduction of the guyana lower crust and the formation of a nw vergent basement thrust propagating upwards and surfacing along the las virtudes thrust rapid uplift of the northern flank of the belt subsequently occurred together with massive deposition of the plio quaternary coarse grained betijoque formation in the northwestern foreland basin

strain localization as a key to reconciling experimentally derived flow law data with dynamic models of continental collision published strength profiles predict strength discontinuities within and or at the base of continental crust during compression we use finite element models to investigate the effect of strength discontinuities on continental collision dynamics the style of deformation in model crust during continued subduction of underlying mantle lithosphere is controlled by 1 experimental flow law data 2 the crustal geotherm 3 strain localization by erosion 4 strain softening and other localization effects in the absence of erosion and other factors causing strain localization numerical models with typical geothermal gradients and frictional ductile rheologies predict diffuse crustal deformation with whole scale detachment of crust from mantle lithosphere this prediction is at odds with earlier model studies that only considered frictional crustal rheologies and showed asymmetric focused crustal deformation without localization model deformation is not consistent with that observed in small collisional orogens such as the swiss alps this suggests that strain localization by a combination of erosion and rheological effects such as strain softening must play a major role in focusing deformation and that strength profiles derived under constant strain rates and uniform material properties cannot be used to infer crustal strength during collision dynamics

palaeoecology palaeogeography and depositional environments of upper cretaceous rocks of western venezuela abstract the end of the early cretaceous in northern south america was marked by regional palaeoceanographic change in western venezuela this change was highlighted near the end of the albian by drowning of the maraca formation shallow water carbonate platform regional marine transgression continued during the cenomanian and turonian in western venezuela with drowning of the more southerly guayacan member capacho and escandalosa formations carbonate platform deposition of organic carbon rich intervals of the la luna and navay formations occurred unconformably on maraca formation and guayacan member shallow water carbonates and continued through the early santonian during this interval the maracaibo and barinas apure basins were characterized by low oxygen or anoxic bottom water conditions away from the basin margins deposition of organic carbon lean upper la luna and navay formation strata show that bottom water oxygen content increased from the late santonian through the end of the cretaceous the siliceous and phosphatic late santonian to early maastrichtian tres esquinas member and the glauconitic late campanian to early maastrichtian socuy member both of the la luna formation represent the final phase of la luna deposition in the maracaibo basin tectonic uplift in eastern colombia during the campanian and maastrichtian caused progradation of the colon mito juan and burguita formation deltas and eventual infilling of the maracaibo and barinas apure basins

climatological features of cutoff low systems in the southern hemisphere abstract this study presents the first multidecadal climatology of cutoff low systems in the northern hemisphere the climatology was constructed by using 41 yr 1958 98 of ncep ncar reanalysis data and identifying cutoff lows by means of an objective method based on imposing the three main physical characteristics of the conceptual model of cutoff low the 200 hpa geopotential minimum cutoff circulation and the specific structure of both equivalent thickness and thermal front parameter fields several results were confirmed and climatologically validated 1 the existence of three preferred areas of cutoff low occurrence the first one extends through southern europe and the eastern atlantic coast the second one is the eastern north pacific and the third one is the northern china siberian region extending to the northwestern pacific coast the european area is the most favored region 2 the known seasonal cycle with cutoff lows forming much more frequently in summer than in winter 3 the short

collision tectonics in the swiss alps insight from geodynamic modeling this paper compares results from two dimensional finite element dynamic modeling with the kinematic evolution of the swiss alps during the collision phase in particular we investigate the role of inherited lateral strength heterogeneities on orogenesis a number of first order characteristics are directly comparable at crustal scales in the models the entry of continental crust into the convergent margin marks the end of near perfect subduction accretion of material of the subducting plate to the upper plate creates an orogenic wedge on the incoming pro side and initiates a retroshear zone or model backthrust the addition of material to the upper plate builds a bivergent orogen heterogeneities in the pro crust focus shear and lead to the development of nappe structures the combined action of pro shear nappe stacking and retroshear backthrusting uplifts a plug between the two shear zones subsequent focusing of shear along the retroshear zone results in rotation of the plug and overlying units leading to crustal scale backfolds as observed in the swiss alps the model experiments predict features relevant to alpine dynamics including 1 similar crustal thicknesses and exhumation patterns to those observed in the swiss alps today for erosion rates comparable to natural ones 1 mm yr 1 2 continued accretion and subduction of upper crustal fragments allowing high pressure metamorphic conditions 3 tilting and exhumation of lower crust when a midcrustal weak zone is present and 4 shunting of material across the strong lower crustal wedge of the upper plate

local stress fields and intraplate deformation of iberia variations in spatial and temporal interplay of regional stress sources tertiary to present deformation in the interior of the iberian peninsula reflects spatial and temporal variations of the activity of the plate boundaries local deformation patterns observed in many of the numerous intraplate tertiary basins and their borders such as the madrid basin and the sierra de altomira are at first sight incompatible with the regional stress field under which they were formed we demonstrate however that they can be explained as the effect of several stress fields that acted on the iberian peninsula from earliest tertiary onward data on local deformation can constrain both magnitudes and directions of forces acting on the plate boundaries of iberia enabling us to estimate the relative importance of the different plate driving and deforming mechanisms providing further constraints on the tectonic evolution of iberia

four phase tectonostratigraphic development of the southern caribbean abstract although the stratigraphy of northern south america and the southern caribbean has been studied in detail in many areas a clear understanding of the sequence of tectonic events and their relation to regional stratigraphy has not been forthcoming since northern south america collided with southern north america in the late palaeozoic we identify four discrete tectonic phases from the stratigraphy of the area that is now the southern caribbean these phases derived from a synthesis of regional stratigraphy were 1 panama arc collistion with colombia in the late miocene early pliocene which drove a complex triangular wedge bounded by strike slip faults northward into the caribbean 2 right lateral strike slip faulting associated with post eocene eastern motion of the caribbean ocean floor into the gap between the separating americas 3 island arc development and collision associated with the entry of the present caribbean ocean floor an area of buoyant ocean crust into the gap between the separating americas and 4 continental rifting and passive margin development in the late jurassic early cretaceous associated with the separation of north and south america approximately along the palaeozoic suture zone overprinting of younger structures on inherited structures from previous phases is responsible for the overall complexity of the region

rheology predictions across the western carpathians bohemian massif and the pannonian basin implications for tectonic scenarios on the basis of extrapolation of failure criteria lithology and temperature models we predict the rheology of the lithosphere for several sections through the carpathians and surrounding regions our models show significant lateral variations in rheology for the different tectonic units with important implications for the tectonic evolution the theologically strong lithosphere of the polish platform area contrasts with the weak lithosphere of the pannonian basin indicating that the arcuate shape of the carpathian orogen is primarily caused by an inherited curvature of an ancient embayment in the foreland with the pannonian units passively filling the space the polish platform and the moesian platform exhibit a similar rheological anisotropy caused by nw se trending weakness zones paralleling the tornquist teisseyre zone this anisotropy was the main controlling factor on the behavior of the lithosphere in this area since cadomian times as documented by the geological evolution of the sudety mountains and the mesozoic polish trough including the late cretaceous alpine inversion and the neogene development of the carpathian foreland this rheological anisotropy appears to have a major controlling impact on the development of at least the eastern part of the european lithosphere rheology predictions for the bohemian massif support the idea that the rigid lithosphere of the bohemian massif governed the bending of the alpine carpathian transition zone expressed in the large scale wrench movements opening the vienna basin in the foreland area detachment levels are predicted for upper and lower crustal levels leading to a decoupling of crustal and subcrustal flexure in most areas comparison with basin formation models indicates that our predictions for effective elastic thickness eet are similar to those derived from flexural models for the foreland area also eet predictions from extensional basin models in the pannonian region yield values close to our findings

tectonic and climatic controls on the spatial distribution of denudation rates in northern chile 18 s to 23 s determined from cosmogenic nuclides in the arid region of northern chile the environmental conditions are favorable for measuring tectonic and climatic influences on catchment denudation rates in the absence of vegetation previous studies of denudation rates from cosmogenic 10be and 26al concentrations are limited to single drainages in this study we examine catchment to orogen scale spatial variation in denudation rates between 18 23 s in the coastal and western cordilleras of northern chile 10be and 26al data were obtained from 33 catchments to examine the relative roles of tectonics and climate on catchment averaged denudation rates at broader scales we examine whether denudation rates and orogen topography reflect the 3d plate geometry of the region cosmogenic nuclide derived denudation rates range from 0 4 0 5 to 20 6 1 5 m myr in the coastal cordillera and from 1 4 0 7 to 168 0 19 8 m myr in the western cordillera the controls on the denudation rates are evaluated using a statistical factor analysis of ten selected catchment parameters denudation rates indicate a strong linear relationship with channel steepness indices but insignificant correlations and covariation with mean annual precipitation rates drainage area stream order mean elevation mean local relief mean basin slope and analyzed grain size of the sampled sediments moreover denudation rates are better correlated with tectonic controls at catchment scale than orogen scale plate tectonics in the western and coastal cordillera

an integrated analysis of the march 2015 atacama floods in march 2015 unusual ocean and atmospheric conditions produced many years worth of rainfall in a 48 h period over northern chile s atacama desert one of earth s driest regions resulting in catastrophic flooding here we describe the hydrologic and geomorphic drivers of and responses to the 2015 atacama floods in the salado river we estimated a flood peak discharge of approximately 1000 m3 s which caused widespread damage and high sediment loads that were primarily derived from valley fill erosion hillslopes remained surprisingly intact despite their lack of vegetation in the coastal city of chanaral flooding of the salado river produced maximum water depths over 4 5 m meters thick mud deposition in buildings and along city streets and coastal erosion the atacama flooding has broad implications in the context of hazard reduction erosion of contaminated legacy mine tailings and the atacama s status as a terrestrial analog for mars

u pb la mc icp ms zircon geochronology and geochemistry from a postcollisional biotite granite of the baja guajira basin colombia implications for late cretaceous and neogene caribbean south american tectonics abstract u pb la mc icp ms zircon ages and whole rock geochemistry from a biotite granitoid recovered at 2 1 km depth from the rancheria 2 well in the baja guajira basin southern caribbean region reveal the existence of a ca 70 ma silicic plutonic event this granitoid intrudes ca 76 80 ma intraoceanic arc fragments and continental margin sediments that experienced continental subduction and collision since ca 76 ma the major compositional shift recorded by this granitoid including light rare earth element lree enrichment documentclass aastex usepackage amsbsy usepackage amsfonts usepackage amssymb usepackage bm usepackage mathrsfs usepackage pifont usepackage stmaryrd usepackage textcomp usepackage portland xspace usepackage amsmath amsxtra usepackage ot2 ot1 fontenc newcommand cyr renewcommand rmdefault wncyr renewcommand sfdefault wncyss renewcommand encodingdefault ot2 normalfont selectfont declaretextfontcommand textcyr cyr pagestyle empty decl

thermomechanical consequences of cretaceous continent continent collision in the eastern alps austria insights from two dimensional modeling we use two dimensional numerical modeling techniques to investigate the thermomechanical consequences of closure of the meliata hallstatt ocean and consequent cretaceous continent continent collision in the eastern alps austria in the modeling a lower plate position of the austro alpine aa continental block is adopted during collision with the upper juvavic silice block the thermal structure of the lithosphere was calculated for major aa tectonic units upper middle and lower austro alpine by integration of the transient heat flow equation along an approximately nw se cross section east of the tauern window indications of the rheological evolution of the aa were determined by calculating strength profiles at key stages of the cretaceous orogeny making use of the thermal modeling predictions combined with rock mechanics data cooling in the upper plate and lower greenschist facies metamorphism within footwall parts of the lower upper austro alpine ua plate related to se directed underthrusting of the ua beneath the upper juvavic silice block at circa 100 ma were predicted by the numerical model the observed pressure temperature path for deeply buried middle austro alpine ma upper crustal units and their subsequent isothermal exhumation are best reproduced assuming a pressure peak at 95 ma and exhumation rates ranging between 4 and 7 5 mm yr 1 from the modeling results we deduce that the temperature evolution during eclogite exhumation is primarily dependent on rates of tectonic movements and largely independent of the mode of exhumation thrusting versus erosion furthermore very rapid postmetamorphic exhumation of southern lower austro alpine la units is predicted in order to account for subsequent cooling this is constrained by 40ar 39ar data the cooling paths of ma and la rocks appear to be primarily controlled by their near surface positions at the end of the cretaceous rather than by other processes such as concurrent underthrusting upward advection of heat by rapid exhumation induced thermal weakening of the thickened crust the inferred weakness of the central parts of the orogenic system may play an important role during detachment related tectonic unroofing orogenic collapse and concomitant basin formation central alpine gosau basins

the great atacama flood of 2001 and its implications for andean hydrology in february 2001 widespread flooding occurred throughout the atacama desert of northern chile and southern peru it was particularly severe in the rio loa basin where roads and bridges were disrupted and the town of calama inundated the instantaneous peak flow in the rio salado a tributary of the rio loa reached 310 m3 s 1 an order of magnitude higher than any previously recorded event the flood is estimated to have a return period of 100 200 years and is shown to have been caused by intense long duration rainfall in the western cordillera associated with la nina the surface water response is typical of arid areas and highly dependent on antecedent conditions but is quite different in perennial and ephemeral catchments ephemeral flood flows suffer high transmission losses recharging phreatic aquifers perennial rivers have lower runoff coefficients but baseflow levels remained high after the event for several months due to bank storage rebound and interflow extremely high energies of 3000 w m 2 were generated by the floods in the cordillera becoming less in the precordillera and downstream erosion and sediment transport were consequently highest in the upper and middle reaches of the rivers with mixed erosion deposition in the lowest reach the new insights gained from the interpretation and quantification of this event have important implications for palaeoenvironmental analysis hazard management water resource evaluation and the palaeohydrological evolution of the andes copyright 2005 john wiley sons ltd

a diagnosis of a long lasting blocking event over the southeast pacific ocean abstract a long lasting blocking event occurred over the southeast pacific ocean near the west coast of south america from 29 july through 14 august 1986 this blocking happened in a recently found new region of blocking in the southeast pacific during the blocking event the transient eddies were forced to move to the north and south of the blocking this caused precipitation over south america to increase to the north of the blocking high and diminish over southern south america the blocking event is analyzed in detail and its impact on the winter general circulation is discussed change in amplitude of several wavenumbers and the zonal wind zero wavenumber suggest that the blocking event is essentially a local phenomenon since transient eddies are prevented from moving through the blocking high the variance of meridional wind is small however the variance of geopotential height is maximized because of the persistence of the block this signature of the blocking on the general circulation is simil

thermomechanical evolution of the south alpine rifted margin north italy constraints on the strength of passive continental margins abstract we have reconstructed the kinematic thermal and rheological evolution of the triassic cretaceous south alpine passive continental margin northern italy and estimated lateral strength variations associated with rifting rifting initially caused the formation of a roughly symmetrical ca 100 km wide graben located 150 200 km away from the future break up site 30 myr after the onset of rifting the rift axis shifted laterally and eventually led to oceanic crust formation the thermal evolution of the margin was first controlled by the waning of a thermal anomaly which was emplaced shortly before rifting and was cooling during the first extensional stages numerical modelling of rifting and drifting constrained by field data is used to trace thermal and rheological changes affecting the rifted margin the effects of the thermal anomaly are restricted to the first 10 20 myr of rifting subsequently isotherms are slightly affected by lithospheric thinning and show very little distortion after break up rheological modelling demonstrates that the south alpine lithosphere preserved substantial strength even shortly before break up and became stronger thereafter the modelling also shows that at break up and 100 myr later thinned domains of the margin are stronger than the less thinned ones

extreme temperature and precipitation events in march 2015 in central and northern chile from 18 to 27 march 2015 northern central and southern chile experienced a series of extreme hydrometeorological events first the highest surface air temperature ever recorded in santiago with reliable records dating to 1877 36 8 c at quinta normal was measured at 15 47 local time on 20 march 2015 immediately following this high heat event an extreme precipitation event with damaging streamflows from precipitation totals greater than 45 mm occurred in the semiarid and hyperarid atacama regions finally concurrent with the heavy precipitation event extremely warm temperatures were recorded throughout southern chile these events were examined from a synoptic perspective with the goal of identifying forcing mechanisms and potential interaction between each analysis which provides operational context by which to identify and predict similar events in the future primary findings were as follows 1 record warm temperatures in central chile resulted from anomalous lower troposphere ridging and easterly downslope flow both of which developed in response to an anomalous midtroposphere ridge trough pattern 2 a cutoff low with anomalous heights near one standard deviation below normal slowly moved east and was steered ashore near 25 s by circulation around a very strong ridge anomalies more than 3 standard deviations above normal centered near 60 s 3 anomalously high precipitable water content 20 mm above climatological norms over the peruvian bight region was advected southward and eastward ahead of the cutoff low by low level northwesterly flow greatly enhancing observed precipitation over northern chile

devonian plants from colombia with discussion of their geological and palaeogeographical context plant fossils are described from the cuche formation eastern cordillera colombia in the area of floresta those identified as colpodexylon cf deatsii banks and cf archaeopteris sp suggest an earliest late devonian frasnian age for the formation these or similar taxa are also found in contemporaneous deposits in western venezuela and other elements of the venezuelan flora are found in a geographically intermediate locality all three devonian plant localities in the northwest of south america are within the colombian eastern cordillera and its northern extension the venezuelan perija range an area that has been integrated as a part of the so called eastern andean terrane or central andean province supposedly accreted to the autochthonous block of the guyana shield during the early jurassic or before although both invertebrates and plants from this terrane have strong affinities to north american and european assemblages and might be interpreted as implying a laurussian origin for the eastern andean terrane the evidence is not yet unequivocal with some authors postulating an in situ development of this province

intrabasinal thrust tectonic versus climate control on rhythmicities in the eocene south pyrenean tremp graus foreland basin inferences from forward modelling abstract small scale 10 m sedimentary cycles of alternating fine grained and coarse grained sediments occur in 40 60 m thick fan delta sequences in eocene deposits in the tremp graus foreland basin these deposits are investigated by means of numerical forward modelling of short term 10 100 kyr scale changes in sediment flux due to orbitally induced climate changes and related fluctuations in precipitation and vegetation de boer et al 1991 and as an alternative control intrabasinal fault activity we show that pulsating intrabasinal uplifting related to deep seated thrusting may serve as an alternative to climate induced fluctuations in sediment flux provided that thrusting is cyclic in the models faulting between the source area and the site of the rhythmic succession causes temporal intrabasinal uplift leading to contemporary erosion of the uplifted area and to a nearly instantaneous redistribution of sediment in a thin veneer across a wide area this reduces the effect of flexural subsidence due to fault activity so that major lateral facies shifts through time are absent while significant changes in sediment flux do occur the models also provide new insights into the dominant geodynamic mechanisms during deposition of the eocene sequence to explain the observed sediment thickness in the studied sequence either a sea level rise accompanied by relatively high transportation coefficients larger maximum erosion rates millimetres per year or orogenic wedge growth accompanied by smaller transportation coefficients lower maximum erosion rates tenths of millimetres per year has to be adopted in the case of the eustasy scenario it is predicted that the basin thins to the north in case of the orogenic wedge growth scenario a northward thickening of the basin fill is predicted unless a subsurface triangular fault zone is adopted

graben inversion in nature and experiments the inversion of crustal scale basement grabens is studied here through laboratory experiments on small scale models and available oil industry seismic lines from the southern north sea two basic configurations are considered first both the basement and the sedimentary cover are brittle and inversion does not involve any potential decollement between them second the basement and sedimentary cover are separated by a weak ductile layer e g salt which can allow decollement of the cover during both extension and later compression and inversion the second configuration is more complicated and can lead to a large variety of geological structures laboratory experiments were carried out on brittle ductile models built with sand to represent brittle layers basement and sedimentary cover and silicone putty to simulate the decollement layer between basement and cover a mechanically based classification of inversion structures is proposed the effects of some crucial parameters are investigated including obliquity between the direction of shortening and normal faults as well as strength profiles and the presence or absence of salt diapirs the experimental investigation leads to the following conclusions 1 the inversion of the graben by reactivation of normal faults implies that the angle between the direction of compression and the graben is less than 45 2 if there is a superficial decollement e g basement cover interface inversion initiates low dipping thrust faults in the cover localized at graben borders 3 salt diapirs or salt walls localized along the graben borders in the cover are preferential sites for the development of thrust faults and 4 when the cover is decoupled from the basement by a decollement layer inversion induced deformation in the cover which is partitioned between thrust faults along the graben borders and strike slip faults within the graben trending oblique to the graben borders experimental results are compared with field examples in particular from the southern north sea

sources of recent tectonic stress in the pannonian region inferences from finite element modelling summary we present the results of finite element modelling of the recent stress field in the pannonian basin and surrounding alpine orogenic belt our results show that the recent predominantly compressive stress regime in the alpine pannonian carpathian dinaric system is governed by distinct tectonic factors of great importance is the deformation of crustal blocks with diverent geometries and rigidities in an overall convergent setting associated with the africa europe collision the most important stress source appears to be the counterclockwise rotation of the adriatic microplate at the southwest boundary of the pannonian basin this plate tectonic unit has been interpreted as moving independently of both the european plate and the african plate additional boundary conditions active shortening and compression in the vrancea zone and the bohemian massif and the evect of the immobile moesian platform also significantly influence the modelling results the incorporation of additional stress sources such as crustal thickness variation and the presence of two main fault zones separating the primary tectonic units in the study area have only locally important evects but improve the fit between the calculated results and the observed stress pattern

the influence of a stratified rheology on the flexural response of the lithosphere to un loading by extensional faulting summary we present a two layered finite diverence model for the flexural response of the lithosphere to extensional faulting the model allows for three modes of flexure 1 fully coupled with the upper crust and mantle welded together by the lower crust 2 fully decoupled with the upper crust and mantle behaving as independent layers and 3 partly decoupled signifying that the response of the upper crust to small wavelength loads is superimposed on the response of the entire lithosphere to long wavelength loads which of these modes of flexure is to be expected depends on the rheology and especially the thermal state of the lithosphere coupled behaviour is related to a cold and strong lithosphere the baikal rift zone provides a typical example for this mode of flexure a fully decoupled lithosphere is an exceptional case related to anomalous high temperatures in the lower crust and is observed in the basin and range province the most common case is a partly decoupled lithosphere with the degree of decoupling depending on the thickness and viscosity of the lower crust this is inferred for example for the bay of biscay margin

blocking over the south pacific and rossby wave propagation abstract atmospheric blocking events over the south pacific are investigated using a 39 yr record of 500 hpa height fields from the ncep ncar reanalysis dataset the analysis extends earlier work using a 16 yr record and confirms that the occurrence of blocking over the southeast pacific is strongly modulated by the enso cycle during austral spring and summer comparison of results at 500 hpa with the 300 hpa meridional wind component showed that blocking events are associated with large scale wave trains lying across the south pacific from the region of australia to southern south america similar wave trains are evident in both hemispheres in singular value decomposition analyses between 300 hpa meridional wind components and tropical pacific outgoing longwave radiation olr anomalies the hypothesis that the divergence associated with tropical olr anomalies forces an extratropical wave response that results in enhanced blocking over the southeast pacific was tested using a linearized barotropic vorti

dynamics of sediment subduction accretion at convergent margins short term modes long term deformation and tectonic implications a conceptual model is proposed for the short term operation of subduction accretion systems at convergent margins the operation is described in terms of the mass fluxes among the four system components namely the accretionary or prowedge wedge p an uplifted plug u a retrowedge r and the subduction zone the latter consists of a conduit c of slowly moving and deforming material and an underlying subduction channel where material moves and deforms more rapidly a broad range of convergent margin types can be accommodated within the conceptual model framework with differing short term modes that depend on which of the p u r c components that are active finite element geodynamical model experiments are used to investigate whether these modes are dynamically feasible these experiments determine excitation of modes under controls that include model entry and exit mass fluxes flexural loading by accreted material and slab pull forces boundary velocities corresponding to subduction and subduction zone advance retreat distribution thickness and density of accreted sediment and internal frictional properties of the coulomb sediments that all modes with the exception of p in which only a prowedge is created are seen in the models provides support for the concepts and allows conditions that favor particular modes to be recognized in addition the finite deformation predicted by the models is used to infer the long term tectonic styles associated with both single mode evolutions and those that exhibit mode switching a steady state mass balance can occur for modes 0 pure subduction p c i e where components p and c are active or other modes when the surface mass denudation plus the subduction flux balances accretion plus tectonic underplating the p c mode is favored by subduction zone retreat and or an increasing subduction load and creates an apparent landward dipping backstop p u c is predicted to be the most common mode and it creates an apparent seaward dipping backstop p u r c is an inefficient mode but is favored by easily detached retrocrust or sediment and or a decreasing subduction load

spatial and temporal relationships between compression strike slip and extension in the central venezuelan andes clues for plio quaternary tectonic escape abstract the geometry of tectonic structures attributed to the neogene quaternary time interval is described in the active setting of the venezuelan andes our methodology is based on the analysis of radar satellite and digital elevation model imagery complemented by structural fieldwork and the compilation of seismotectonic data to make a structural analysis on a regional scale radar images provide first class data for morphostructural analysis in areas of dense vegetation and frequent cloud covering like the venezuelan andes we focused our analysis in the burbusay rio momboy and bocono faults corner located in the central part of the belt we have described three stages of deformation during the neogene quaternary the first one mio pliocene in age is a nw se compression responsible for the uplift of the venezuelan andes the second tectonic stage corresponds to a strike slip regime of deformation marked by shearing along the bocono burbusay and valera faults which separates two triangular wedges in the larger trujillo block this strike slip faulting dominated compressional extensional tectonic regime allowed the trujillo crustal block to move towards the ne wrenching has therefore started at some point between the pliocene and the quaternary these two tectonic events are consistent with ongoing strain partitioning in the venezuelan andes the third stage corresponds to extensional deformation limited to the trujillo block and is still active today extension is associated with the motion of crustal blocks moving relative to each other probably above the upper lower crust boundary such extensional deformation can be understood considering that the crust extends and stretches at the same time as it moves towards the ne the combination of both horizontal lateral motion and extension is characteristic of a tectonic escape process the northeastward escape of the trujillo block which belongs to the larger north andes block occurs as a result of the combination of the nw se intracontinental convergence between the south american plate and the maracaibo block and the presence to the north of the caribbean oceanic plate considered as a free boundary we have showed that the kinematics of the caribbean plate offers not only a favorable environment but may also be considered as the driving force of the tectonic escape of the north andes block

palaeo elevation and effective elastic thickness evolution at mountain ranges inferences from flexural modelling in the eastern pyrenees and ebro basin abstract the results are presented of a two dimensional flexural modelling study of the lithosphere underlying the southern pyrenees and the ebro basin the modelling is based on a crustal scale balanced cross section along a profile through the north eastern part of the iberian plate two time slices of the structural evolutions of the mountain chain are modelled the present day configuration and the configuration at middle lutetian time 47 ma where important structural and sedimentological changes are observed the flexure model incorporates lateral variations in the effective elastic thickness eet of the lithosphere the present day deflection in the profile is simulated using boundary forces and a northward decreasing eet that varies from 30 to 11 km models for middle lutetian times indicate eet values of 26 18 km in the northern part of the profile assuming that the eet at the distal margin of the ebro basin has not significantly changed since middle lutetian times these higher values for the eet at middle lutetian times suggest that the effect of the cretaceous extensional phase on the present day flexural rigidity is small and therfore the inferred northward decreasing rigidity is predominantly related to the pyrenean collision flexural modelling provides also constraints for the palaeo elevation of the inner part of the chain including the assumption that the eet at the distal margin of the ebro basin has not significantly changed since middle lutetian times the model predicts a maximum palaeo elevation of 2000 m which is in agreement with geological observations concerning the relation between basin fill and palaeo elevation

effect of the andes cordillera on precipitation from a midlatitude cold front the effects of the andes cordillera the major mountain range in south america on precipitation patterns of baroclinic systems approaching from the southeast pacific remain largely unstudied this study focuses on a case in late may 2008 when an upper level trough and surface cold front produced widespread precipitation in central chile the primary goal was to analyze the physical mechanisms responsible for the structure and evolution of the precipitation weather research and forecasting wrf model simulations indicate that as an upper level trough approached central chile midtropospheric flow below 700 hpa was blocked by the high topography and deflected poleward in the form of a barrier jet this northerly jet had wind maxima in excess of 15 m s 21 was centered around 925 hpa and extended westward 200 km from the mountains it intersected the cold front which approached from the south near the coast thereby increasing convergence along the frontal surface slowing its equatorward progress and enhancing rainfall over central chile another separate region of heavy precipitation formed over the upwind slopes of the cordillera a trajectory analysis confirmed that the barrier jet moved low level parcels from their origin in the moist southeast pacific boundary layer to the coast when model topography was reduced to twenty percent of its original height the cold front advanced more rapidly to the northeast generated less precipitation in central chile between 338 and 368s and produced minimal orographic precipitation on the upwind andean slopes based on these findings the high topography appears responsible for not only orographic precipitation but also for substantially increasing precipitation totals over the central coast and valley

local and synoptic mechanisms causing southern california s santa ana winds the atmospheric conditions that lead to strong offshore surface winds in southern california commonly referred to as santa ana winds are investigated using the north american regional reanalysis and a 12 year 6 km resolution regional climate simulation of southern california we first construct an index to characterize santa ana events based on offshore wind strength this index is then used to identify the average synoptic conditions associated with santa ana events a high pressure anomaly over the great basin this pressure anomaly causes offshore geostrophic winds roughly perpendicular to the region s mountain ranges which in turn cause surface flow as the offshore momentum is transferred to the surface we find however that there are large variations in the synoptic conditions during santa ana conditions and that there are many days with strong offshore flow and weak synoptic forcing this is due to local thermodynamic forcing that also causes strong offshore surface flow a large temperature gradient between the cold desert surface and the warm ocean air at the same altitude creates an offshore pressure gradient at that altitude in turn causing katabatic like offshore flow in a thin layer near the surface we quantify the contribution of synoptic and local thermodynamic mechanisms using a bivariate linear regression model and find that unless synoptic conditions force strongly onshore winds the local thermodynamic forcing is the primary control on santa ana variability