roll convection within an arctic cold air outbreak interpretation of in situ aircraft measurements and spaceborne sar imagery by a three dimensional atmospheric model abstract atmospheric roll convection within an arctic cold air outbreak was observed over the greenland sea during the arktis 1993 experiment on 24 march 1993 by in situ aircraft measurements and synthetic aperture radar sar imagery from the first european remote sensing satellite ers 1 inside a boundary layer heated from below two kinds of rolls were observed one aligned parallel and the other perpendicular to the mean wind direction the wind parallel rolls occupied the entire boundary layer whereas the wind perpendicular rolls were confined to a region around the top of the boundary layer where a strong vertical shear in the downstream wind component was observed a three dimensional numerical model has been applied to simulate the observed convective pattern it is shown that the model does not reproduce the observed pattern when using a height constant geostrophic wind profile however when adjusting the vertical wind profile to the one measured from the aircraft the model reproduces buoya

coupled ice ocean dynamics in the marginal ice zones upwelling downwelling and eddy generation this study is aimed at modeling mesoscale processes such as upwelling downwelling and ice edge eddies in the marginal ice zones a two dimensional coupled ice ocean model is used for the study the ice model is coupled to the reduced gravity ocean model through interfacial stresses the parameters of the ocean model were chosen so that the dynamics would be nonlinear the model was tested by studying the dynamics of upwelling winds parallel to the ice edge with the ice on the right produce upwelling because the air ice momentum flux is much greater than air ocean momentum flux thus the ekman transport is greater under the ice than in the open water the stability of the upwelling and downwelling jets is discussed the downwelling jet is found to be far more unstable than the upwelling jet because the upwelling jet is stabilized by the divergence a constant wind field exerted on a varying ice cover will generate vorticity leading to enhanced upwelling downwelling regions i e wind forced vortices steepening and strengthening of vortices are provided by the nonlinear terms when forcing is time varying the advection terms will also redistribute the vorticity the wind reversals will separate the vortices from the ice edge so that the upwelling enhancements are pushed to the open ocean and the downwelling enhancements are pushed underneath the ice

geochronology geochemistry and tectonic evolution of the western and central cordilleras of colombia abstract autochthonous rocks of the pre cretaceous continental margin of nw south america the tahami terrane are juxtaposed against a series of para autochthonous rock units that assembled during the early cretaceous allochthonous oceanic crust of the caribbean large igneous province collided with and accreted onto the margin during the late cretaceous we present the first regional scale dataset of zircon u pb la icp ms ages for intrusive and metamorphic rocks of the autochthonous tahami terrane early cretaceous igneous para autochthonous rocks and accreted oceanic crust the u pb zircon data are complemented by multiphase 40ar 39ar crystallization and cooling ages the geochronological data are combined with whole rock major oxide trace element and ree data acquired from the same units to constrain the tectonic origin of the rock units and terranes exposed in the western cordillera cauca patia valley and the central cordillera of colombia the tahami terrane includes lower paleozoic orthogneisses 440 ma that may have erupted during the active margin stage of the rheic ocean basement gneisses were intruded by permian continental arc granites during the final assembly of pangea triassic sedimentary rocks were subsequently deposited in rift basins and partially melted during high t metamorphism associated with rifting of western pangea during 240 220 ma continental arc magmatism during 180 145 ma is preserved along the whole length of the central cordillera and was followed by an early cretaceous out board step of the arc axis and the inception of the quebradagrande arc that fringed the continental margin back stepping of the arc axis may have been caused by the collision of buoyant seamounts which were coeval with plateau rocks exposed in the nicoya peninsular of costa rica rapid westward drift of south america closed the quebradagrande basin in the late aptian and caused medium high p t metamorphic rocks of the arquia complex to exhume and obduct onto the continental margin subduction beneath hot spot derived rocks of the caribbean plateau 100 92 ma formed an intra oceanic arc 92 75 ma which collectively comprise the late cretaceous caribbean large igneous province the remnant ocean basin located between south america and the caribbean large igneous province was partly consumed via continental subduction forming the large antioquia batholith the caribbean large igneous province collided and accreted to south america during 75 70 ma along the cauca almaguer fault resulting in the cessation of both arcs and the paleocene onset of subduction beneath the accreted oceanic crust

geochemical assessment and petroleum systems in the sinu san jacinto basin northwestern colombia abstract the sinu san jacinto basin ssjb onshore and offshore has abundant oil and gas manifestations evidencing the existence of various petroleum systems the onshore oils can be separated into at least two families the first one oil family i is derived from source rocks deposited in anoxic marine platform and the other one oil family ii is derived from source rocks deposited in deltaic marine environment with high input of terrestrial organic matter also there are heavy biodegrated oil seeps as well as oil seeps possibly derived from others organic facies a troublesome to classify with the available data regarding source rock correlations cansona formation bitumens exhibit good correlation with the oil family i and cienaga de oro formation extracts exhibit some correlation with oils from the oil family ii there are also some oils seeps onshore and offshore on which there is no conclusive information about its origin about the gases their isotopic and molecular composition indicate that some are biogenic and others thermogenic as well as others are mixtures biogenic thermogenic onshore and offshore ssjb were recognized three 3 kitchens or pods of generation with oil generation and expulsion determined by geochemical modeling at depths greater than 12000 feet associated with each one of the three kitchens have been postulated the petroleum systems cansona san cayetano and cienaga de oro cienaga de oro additionally in the southern onshore pod could be postulated a speculative petroleum system the precansona precansona petroleum system

a coupled ice ocean mixed layer model of the marginal ice zone responding to wind forcing a free drifting thermodynamic sea ice model is coupled with a continuously stratified ocean model whose vertical mixing coefficients are determined by a turbulent closure scheme the system has variability in the cross ice edge direction while two dimensionality along ice edge homogeneity is assumed the model is initially motionless and has no horizontal variability in ocean interior whereas ice covers only a half portion a uniform wind stress is imposed suddenly to drive the coupled system the surface mixed layer is developed as time increases i e a top few tens of meters are well mixed in a day with an initial water temperature above a freezing point the fresh mixed layer forms in the ice covered portion a wind driven ice velocity is oriented to the right from the wind direction a wind with the ice to the right left looking downstream produces upwelling downwelling under the ice edge caused by a difference in ekman transport an off ice on ice wind advects the ice toward the open water ice covered area and makes the ice edge sharper gentler owing partially to faster movement in the region with higher ice concentration in the off ice wind case the mixed layer near the ice edge is shallower under development so that a melt rate is smaller than that estimated by a prescribed depth mixed layer an inertio internal gravity wave is generated by a transient variability in surface stress associated with a moving ice edge most significantly in the case of the off ice wind and enhances sharpness of the ice edge

a geosat altimeter wind speed algorithm and a method for altimeter wind speed algorithm development a geosat altimeter wind speed algorithm is derived by cross calibrating geosat and seasat altimeter estimates of the normalized radar cross section 0 and modifying an existing seasat altimeter wind speed model function to obtain a model function appropriate for geosat observations it is argued that the 0 distribution measured by an altimeter is relatively stable over a sufficiently large geographical region and a long enough time period systematic differences between 0 estimates from two altimeters can therefore be identified based on comparisons of their 0 histograms any such systematic differences can then be corrected using independent 0 estimates when this method is applied to the geosat and seasat altimeters a systematic difference between the two 0 histograms is shown to be consistent with differences between seasat altimeter and nadir seasat scatterometer estimates of 0 deduced independently by a previous study this supports the conclusions that 1 the 0 distribution is stable and 2 the seasat altimeter estimates of 0 were miscalibrated after modifying the existing seasat altimeter wind speed algorithm to account for this apparent 0 error the resulting geosat estimates of wind speed agree with high quality buoy observations to within an rms difference of less than 2 m s

tectono sedimentary analysis of a complex extensional neogene basin formed on thrust faulted northern apennines hinterland radicofani basin italy abstract large nw se oriented neogene quaternary structural depressions up to about 200 km long and 25 km wide have developed on the western side hinterland of the northern apennines over thrust substrate the depressions are now for the most part laterally bounded by normal faults and are longitudinally separated into basins by transfer zones a debate exists in the literature as to whether these basins have developed as half graben under a predominantly extensional regime since late miocene or as thrust top basins under a predominantly compressional regime that has continued until the pleistocene the radicofani basin is one of the best preserved basins it developed mainly during the late miocene early pliocene in the southern half of the siena radicofani structural depression and is now bounded on the east by normal faults that transect a thrust anticline nose in the substrate to the north by a substrate high or transfer zone and to the south and west by quaternary igneous volcanic edifices the basin experienced variable differential tectonic and associated sedimentation along linking normal boundary faults along its eastern margin it shows the development of thick 600 m alluvial fans that developed in relay areas between boundary faults and transverse faults and transfer zones well exposed sections generally show upward transitions from conglomeratic alluvial fans to shoreface sandstone to offshore mudstones locally the transition is marked by deltas primarily characterised by thick gravelly sandy stacked cross sets the thicker sandy gravel to gravelly sand cross sets 5 8 m thick are interpreted as gilbert type deltas interstratified thinner 0 5 1 m thick generally openwork gravelly strata are part of delta topset assemblages and probably represent prograding fluvial bars tectonic movements provided the accommodation space for the total 2700 m thick basin fill sea level fluctuations that led to the repeated development of the cross sets may also have been influenced by climatic or eustatic changes possibly related to the effects of early antarctic glaciations some features of the radicofani basin can be found in both extensional and compressional basins however the position of the basin in the mountain chain and the development of alluvial fans fandeltas and associated deposits along the main boundary fault combined with structural evidence from seismic lines show that during the early pliocene this basin best conforms to existing models of half graben

wind induced mesoscale features in a coupled ice ocean system a quasi geostrophic mesoscale eddy resolving model is coupled with free drifting sea ice to examine mesoscale oceanic structures which are induced by wind forcing on a nonuniform ice distribution and redistribution of sea ice initial concentration of sea ice has anomalies on the motionless ocean and the sea ice is suddenly forced by a wind stress differences in ekman transport between the high low concentration area and the surrounding area generate dipole eddylike features in the ocean with anticyclonic and cyclonic eddies on the right left and left right respectively looking in the downwind direction redistribution of ice by the ocean circulation continues after the wind ceases forming arch or hammer head shapes of ice anomalies interactions with the other anomalies can produce various shapes which could lead to misinterpretation of ocean flow field it is suggested that to detect ocean flow field in an ice covered area not near the ice edge trajectories should be used instead of shapes of ice cover

mesoscale variations in surface stress heat fluxes and drag coefficient in the marginal ice zone during the 1983 marginal ice zone experiment a series of turbulence and mean meteorological measurements were made from an instrumented aircraft during the 1983 marginal ice zone experiment in the greenland sea in july 1983 using the inertial dissipation method estimates of the surface fluxes of momentum sensible heat and latent heat have been obtained for five transects across the marginal ice zone miz the total heat flux was found to be about 30 w m 2 over the ocean and near zero over the ice the 10 m neutral drag coefficient went from an average of 1 3 10 3 over the ocean to 3 3 10 3 over the pack ice a total distance of about 160 km most of the change occurred in a region about 60 km wide in sea breeze conditions the surface stress was reduced about a factor of 2 in the miz center by stability effects

observation of tropical cyclones by high resolution scatterometry unprecedented views of surface wind fields in tropical cyclones hereafter tcs are provided by the european remote sensing satellite ers c band scatterometer scatterometer measurements at c band are able to penetrate convective storms clouds observing the surface wind fields with good accuracy however the resolution of the measurements 50x50 km 2 limits the interpretation of the scatterometer signals in such mesoscale events the strong gradients of the surface wind existing at scales of a few kms are smoothed in the measured features such as the intensity and location of the wind maxima and the position of the center beyond the ers systems the scatterometers on board the adeos and metop satellites designed by the jet propulsion laboratory and by the european space agency respectively will be able to produce measurements of the backscattering coefficient at about 25x25 km 2 resolution a few sets of ers 1 orbits sampling tc events were produced with an experimental 25x25 km 2 resolution enhancing the resolution by a factor of 2 allows location of the wind maxima and minima in a tc with a much better accuracy than at 50 km resolution in addition a better resolution reduces the geophysical noise variability of wind speed within the cell and effect of rain that dominates the radiometric noise and hence improves the definition of the backscattering measurements a comprehensive analysis of the backscattering measurements in the case of high winds and high sea states obtained within tcs is proposed in order to refine the interpretation of the wind vector derived from a backscattering model that is currently only calibrated up to moderate winds 20 m s in neutral conditions observations of the topex poseidon dual frequency altimeter are also used for that purpose patterns of the surface winds in tcs are described and characteristic features concerning asymmetries in the maximum winds and in the divergence field are discussed

sequence stratigraphy in active extensional basins implications for the interpretation of ancient basin fills abstract systematic variations in sequences their component units and their stacking patterns exist within rift basins these variations can be related to displacement gradients associated with the large scale 12 50 km segmentation of normal fault zones which control accommodation sediment supply and basin physiography sediment supply is also strongly influenced by the nature of pre rift drainage networks and variations in bedrock lithology high rates of hangingwall subsidence close to the centre of normal fault segments may cancel out the effects of glacio eustatic sea level fall so that accommodation development is normally characterized by the continual addition of new space the resulting sequences lack type 1 sequence boundaries and lowstand systems tracts and stack into aggradational sequence sets the adjacent footwall is subject to uplift which may lead to subaerial exposure and incision generating a composite type 1 sequence boundary away from the fault zone and near segment boundaries slip rates are much lower and hence relative sea level change is dominated by eustasy here falls in relative sea level are important resulting in type 1 sequences sequence stacking patterns reflect not only eustasy and local fault controlled subsidence but also the interaction of these with adjacent uplifting footwalls and or regional uplift tectonic influence on sequence development will be more pronounced during greenhouse times than icehouse times

to establish a sequence stratigraphy in lacustrine rift basin a 3d seismic case study from paleogene baxian sag in bohai bay basin china abstract the varied range usually corresponds to different levels of sequence boundaries in the lacustrine basin the correspondence between the unconformity of the paleogene and the sequence boundaries are studied in this article based on an integrated analysis of 3d seismic reflections wire logs and cores fifteen third order sequence boundaries are identified and the paleogene of baxian sag can be divided into one first order sequence 3 s order sequences and fourteen third order sequences four types of sequence architectures are identified fault slope break type fault bench slope break type weak fault slope bend slope type fault steep slope gentle slope type we try to set ideas and processes suitable for the study of the sequence of lacustrine rift basins it is believed that the sequence boundaries and orders in the continental fault lacustrine basin are comprehensive responses to tectonic activities and time the tectonic activity is not only the main contributor to the accommodation but also control the difference of spatial and temporal inheritance characteristics and fault spatial combination thus controlling the combination of the depositional systems under the sequence frame and adjust the spatial dispersion characteristics of the sediment therefore the sequence stratigraphic units of the lacustrine rift basin are highly consistent with tectonic evolution stratigraphic and sedimentary cycles

validating a scatterometer wind algorithm for ers 1 sar the ocean surface wind field is observed from space operationally using scatterometry the european space agency s esas ers 1 satellite scatterometer routinely produces a wind product that is assimilated into forecast models scatterometry cannot give accurate wind estimates close to land however because the field of view of a spaceborne scatterometer is on the order of 50 km side lobe contamination due to the large contrast in backscatter between land and water compounds the problem synthetic aperture radar sar can provide wind speed and direction estimates on a finer scale so that high resolution wind fields can be constructed near shore an algorithm has been developed that uses the spectral expression of wind in sar imagery to estimate wind direction and calibrated backscatter to estimate wind strength three versions based on c band scatterometer algorithms are evaluated for accuracy in potential operational use algorithm estimates are compared with wind measurements from buoys in the gulf of alaska bering strait and off the pacific northwest coast by using a data set of 61 near coincident buoy and ers 1 sar observations representative figures for the accuracy of the algorithm are spl plusmn 2 m s for wind speed and spl plusmn 37 spl deg for wind direction at a 25 km spatial resolution

early cenozoic two phase extension and late cenozoic thermal subsidence and inversion of the bohai basin northern china abstract the bohai basin is one of a family of early cenozoic extensional basins that lie along the eastern margin of asia from russia to vietnam initial extension was probably triggered by subduction roll back of the oceanic pacific plate from the asian continent there were two phases in the bohai basin s rift history the earlier paleocene early eocene phase resulted in the deposition of the kongdian formation and the fourth lowest member of the shahejie formation in a series of elongate half grabens these half grabens have master faults with a nne ssw orientation secondary normal faults are typically clockwise oblique to the master faults indicating a component of dextral transtension deposition was focused in the west and south of the present basin these rocks are mainly alluvial fan and fluvial red beds the architecture of the basin underwent an important change at ca 43 45 ma middle eocene beginning with the deposition of the third member of the shahejie formation in part these sediments were deposited in the same half grabens as the kongdian formation but the bozhong depression in the central part of the basin originated at this time and became the major depocentre the bozhong depression superficially resembles a pull apart basin it formed when continued transtension of the earlier tertiary fault systems to the east and west created an extensional overlap between them during this phase the basin as a whole had a geometry with elements typical of both pull apart and transtensional basins regional extension in many east asian basins ended at the end of the oligocene probably because of the onset of transpression within eastern asia caused by the collision of australia with the philippine sea plate dextral transpression caused minor inversion of some of the earlier normal faults in bohai but as a whole the basin began to subside in a post rift phase of thermal subsidence that has lasted until the present day

an insight into the bucaramanga nest abstract we used the local seismicity for the period of 1993 to 2001 in the northeast of colombia to show the existence of two slabs in the north and south of the bucaramanga nest the northern slab has a dip angle of about 25 and the southern slab has a 50 dip angle while the dip in the bucaramanga nest is about 29 in order to explain the nature of the bucaramanga nest we proposed the scenario of collision between these two slabs using a 3d finite element model fem we show that collision can concentrate modify and perturb the stress field the active process of dehydration embrittlement at intermediate depths and the concentrated stress field in the collision zone may explain the high rate of seismic activity inside the bucaramanga nest the perturbed and modified stress field resulting from the simultaneous effect of collision between two subducted slabs and subduction of the lithosphere under its own weight can explain the variation in the focal mechanism of micro earthquakes and the complexity in the source of the moderate size earthquakes in the bucaramanga nest

the effect of observed ice conditions on the drag coefficient in the summer east greenland sea marginal ice zone the summer east greenland sea marginal ice zone is a region characterized by extreme horizontal variations of surface roughness characteristics the surface drag coefficient is found to be correlated with these roughness characteristics in particular ice concentration and ice floe roughness and size the estimates of wind stress and wind speed yield neutral drag coefficients cdn with standard deviations of 2 3 0 8 10 3 for areas with less than 40 ice concentration and 4 0 1 1 10 3 for ice concentrations greater than 70 much of the variation in cdn for a given ice concentration is explained by differences in ice floe size and roughness very small concentrated rough floes that have been affected by wave action produce twice as much wind stress cdn 4 2 0 7 10 3 as relatively large flat floes cdn 2 1 0 6 10 3 and 4 times as much as typical open ocean for a given wind speed and stability the drag coefficients in this region are higher than other marginal ice zones probably a result of the presence of large amounts of multiyear ice floes that extend higher above the ocean surface and create more drag than first year floes

mesoscale eddies in the fram strait marginal ice zone during the 1983 and 1984 marginal ice zone experiments during the summer marginal ice zone experiment in fram strait in 1983 and 1984 fourteen mesoscale eddies in both deep and shallow water were studied between 78 o and 81on sampling combined satellite and aircraft remote sensing observations conductivity temperature depth observations drift of surface and subsurface floats and current meter measurements typical scales of these eddies were 20 40 km rotation was mainly cyclonic with a maximum speed in several cases subsurface of up to 40 cm s observations further suggest that the eddy lifetime was at least 20 to 30 days five generation sources are suggested for these eddies several of the eddies were topographically trapped while others primarily formed by combined baroclinic and barotropic instability moved as much as 10 15 km d with the mean current the vorticity balance in the nontrapped eddies is dominated by the stretching of isopycnals accompanied by a change in the radial shear in the most completely observed eddy south of 79on the available potential energy exceeded the kinetic energy by a factor of 2 quantitative estimates suggest that the abundance of these eddies enhances the ice edge melt up to 1 2 km d

tectonic implications of tomographic images of subducted lithosphere beneath northwestern south america we used seismic tomography to investigate the complex structure of the upper mantle below northwestern south america images of slab structure not delineated by previous seismicity studies help us to refine existing tectonic models of subducted caribbean pacific lithosphere beneath the study area beneath western venezuela and colombia we distinguish two slabs a maracaibo and a redefined bucaramanga slab the maracaibo slab coinciding with most of the bucaramanga slab previously defined by w d pennington dips in a direction of 150 at an angle of 17 to a depth of 275 km and correlates to the subducted late cretaceous oceanic plateau of the caribbean plate farther south a second slab dips at an angle of 50 in a direction of 125 to a depth of at least 500 km and correlates to the subducted oceanic crust of the nazca plate and the downdip extension of the panama island arc we refer to this slab as the redefined bucaramanga slab because it is different from the bucaramanga slab segment defined by pennington the area of the south american plate overriding both slabs is characterized by the absence of an active volcanic arc an anomalously wide topographically uplifted and tectonically active area and the northward escape of the maracaibo block along active strike slip faults in support of earlier studies we attribute this to the underthrusting of the caribbean oceanic plateau our shallowly dipping maracaibo slab along the base of the south american lithosphere and to the recent collision of the panama island arc rafted in on more steeply dipping crust of the nazca plate our redefined bucaramanga slab

migration velocity analysis based on common shot depth migration applied to the seismic data of the caribbean oceanic plateau summary in areas where the geology is characterized by strong vertical and lateral velocity gradients pre stack depth migration will produce the optimum subsurface image an accurate velocity model is required for an accurate pre stack depth migration we developed a velocity analysis based on recursive pre stack depth migration that gives better results than the traditional cmp velocity analysis when applied to data over the caribbean oceanic plateau first the shot records are migrated with a series of constant velocities for each identified geological layer the velocity that best flattens the event in common receiver gathers crg is picked a large number of velocity analyses are run along the seismic line in order to define the reflector geometry for each layer we obtain the depth and interval velocity in order to make a model down to that depth this model is then used as the input for the next layer velocity analysis finally when all the layers have been picked the entire line is depth migrated with the derived model the migration algorithm used is a common shot kirchhoff technique which uses the ray tracing method of vidale 1988 to compute the traveltimes needed to determine the operator shape we applied this migration velocity analysis technique to seismic profiles of the casis cruise to define the deep structure of the caribbean oceanic plateau we imaged a 2500 m deep reflection sub b beneath the top of the plateau b horizon which defines the top of a 4500 4700 m s 1 layer the images obtained with this method will help to define odp sites that will provide information about geochemical and petrological variations of the volcanic basement

vertical tectonics at a continental crust oceanic plateau plate boundary zone fission track thermochronology of the sierra nevada de santa marta colombia 1 the topographically prominent sierra nevada de santa marta forms part of a faulted block of continental crust located along the northern boundary of the south american plate hosts the highest elevation in the world 5 75 km whose local base is at sea level and juxtaposes oceanic plateau rocks of the caribbean plate quantification of the amount and timing of exhumation constrains interpretations of the history of the plate boundary and the driving forces of rock uplift along the active margin the sierra nevada province of the southernmost sierra nevada de santa marta exhumed at elevated rates 0 2 km my during 65 58 ma in response to the collision of the caribbean plateau with northwestern south america a second pulse of exhumation 0 32 km my during 50 40 ma was driven by underthrusting of the caribbean plate beneath northern south america subsequent exhumation at 40 25 ma 0 15 km my is recorded proximal to the santa marta bucaramanga fault more northerly regions of the sierra nevada province exhumed rapidly during 26 29 ma 0 7 km my further northward the santa marta province exhumed at elevated rates during 30 25 ma and 25 16 ma the highest exhumation rates within the sierra nevada de santa marta progressed toward the northwest via the propagation of nw verging thrusts exhumation is not recorded after 16 ma which is unexpected given the high elevation and high erosive power of the climate implying that rock and surface uplift that gave rise to the current topography was very recent i e 1 ma and there has been insufficient time to expose the fossil apatite partial annealing zone

seismic stratigraphy and structure of the caribbean igneous province multichannel seismic reflection profiles reveal the tectonic and stratigraphic complexity of the caribbean province a smooth reflector b forms the top of widespread cretaceous volcanic flows drilled during dsdp leg 15 and odp leg 165 in addition we also show other seismic evidence of volcanism sills and dipping horizons the southern parts of the venezuela and colombia basins are underlain by rough basement that shows many characteristics of oceanic crust several thick volcanic plateaus separated by deep basins with thin crust comprise the caribbean volcanic province in the venezuela basin only normal oceanic crust is present but in other basins this crust is underlain by underplated volcanic material the crust of the venezuela basin is less than 5 km thick and was probably formed in the pacific during the jurassic refraction data indicate that a thin layer 2v is formed by original oceanic crust overlain by a thin volcanic layer an intra basement reflection sub b marks the top of original oceanic crust that is sandwiched between an upper volcanic layer and lower underplated material this underplated layer forms a very thick layer 3v beneath the beata and nicaragua volcanic plateaus the upper part of layer 3v is gabbroic and outcrops on the beata ridge the thickening occurs mainly in the high velocity lower part of layer 3v and is attributed to the presence of magnesian rocks picrites or ultramafic cumulates a highly reflective horizon r is located at the top of this layer we present a model where the galapagos plume is 2500 km wide but has narrow heads that formed the caribbean volcanic plateaus separated by deep basins the caribbean igneous province is compared to similar volcanic features in the indian ocean kerguelen plateau and in the western pacific ocean ontong java plateau nauru and pigafetta basins the thick plateaus of the caribbean province resemble the kerguelen and ontong java plateaus whereas the deep basins present some similarities with the nauru and pigafetta basins the caribbean igneous province is younger 90 75 ma than the indian and pacific plateaus 110 130 ma however several geological evidences from land and geophysical offshore observations indicate that the onset of volcanic activity in the caribbean province could be as old as 115 ma

long term erosion and exhumation of the altiplano antioqueno northern andes colombia from apatite u th he thermochronology abstract the antioqueno plateau ap in the northern cordillera central colombia is the largest high elevation erosional surface in the northern andes apatite u th he thermochronometry ahe of samples collected from two elevation profiles spanning 2 km of exhumed crustal sections reveal the long term erosional exhumation of the ap sample profiles exhibit ahe ages that increase with elevation from ca 22 ma 760 m at the bottom of regional scarps to ca 49 ma 2350 m on top of the ap a marked inflection point in age versus elevation data at ca 25 ma defines the bottom of the exhumed post oligocene he partial retention zone he prz elevation invariant ages below ca 25 ma record the onset of rapid exhumation and surface uplift of the ap that led to river incision a subtle change in slope within the he prz ca 41 ma is interpreted as a less intense exhumation related cooling episode these two exhumation pulses coincide with the proto andina and pre andina orogenic phases previously proposed for the colombian andes and are synchronous with tectonically driven exhumation events reported for the peruvian bolivian and argentinean andes and for some orogenic systems in the caribbean the pulses are correlated with variations in the rates of convergence between nazca farallon and south america documented for the middle eocene and the late oligocene suggesting continental scale controls on uplift and denudation throughout the andean range ahe data provide an average erosion rate of 0 04 mm yr for the last 25 million years erosion rates during the exhumation pulses were in the order of 0 2 0 4 mm yr similarity between ahe profiles indicates the whole ap was uplifted and exhumed as a coherent structural block corroborating previous structural evidence for the rigidity and coherence of this crustal block in the northern andes our results are in agreement with tectonostratigraphic data in the magdalena and cauca basins and with proposed scenarios for paleogeographic evolution in the northern andes

coastal wind jets flowing into the tsushima strait and their effect on wind wave development abstract coastal wind jets that flow into the tsushima strait japan and their effects on wind waves are investigated using synthetic aperture radar sar images and altimeter derived wind and waves the coastal wind jets appear in 7 of 28 sar derived wind fields under the conditions of ambient southeasterly winds atmospheric conditions corresponding to the appearance of the coastal wind jets are examined by a high resolution atmospheric community model which indicates that stratified flows are influenced by the land topography and then pass through the strait forming low level jet flows sensitivity experiments reveal that easterly to southerly stratified flows are a necessary condition for a jet s formation and the degree of its enhancement is mostly controlled by the froude number of the upstream flows atmospheric conditions in which the sar observed the coastal jets meet the model derived necessary conditions which corroborate the validity of the model simulation and the jet s formation mechanism

tectonic and climatic control of paleogene sedimentation in the rhenodanubian flysch basin eastern alps austria abstract the paleocene to lowermost eocene formations of the rhenodanubian flysch were deposited in an abyssal environment at the continental rise to the south of the european plate the pattern of paleocurrents indicates a number of small distributary systems for the turbiditic material that entered the basin from the north and was deflected to the east and to the west heavy mineral assemblages in the turbidites suggest the erosion of medium grade metasediments in the danian and the progressive erosion of underlying metamorphic magmatic rocks in the thanetian and ypresian the most obvious sedimentary event is the breakdown in turbidite sedimentation during the late danian to the early thanetian remarkably this starvation of turbidites is associated with high values of chlorite in the clay mineral assemblages of interturbidite shales indicating increased mechanical erosion of the adjoining land areas tectonic uplift of these areas and associated block faulting and tilting is assumed to be responsible for this increase in erosion as well as for the synchronous cutting off of the basin from the source area of the turbidites this tectonic activity is related to the onset of the collision of the european and the adriatic plates a second major event documented in the paleogene record is the change from a predominantly siliciclastic system to a carbonate system in the latest thanetian associated with the global negative carbon isotope excursion cie in the upper part of calcareous nannozone np9 calcareous mudturbidites become the prevailing rock type eutrophication of surface waters is indicated by acmes of diatoms radiolaria and dinoflagellates at the level of the cie together with slightly increased values of kaolinite in the clay mineral assemblages of interturbidite shales this can be interpreted as a result of increased continental run off due to high precipitation rates in a humid climate the top of the increased kaolinite input is poorly constrained because of a very high input of smectite due to volcanic activity in sub zone np10a this igneous activity is assigned to the opening of the northern atlantic ocean and has no geodynamic relevance for the rhenodanubian basin

accommodation and supply a dual control on stratigraphic sequences abstract it is widely accepted that both eustatic and tectonically controlled regional changes of sea level have contributed to the record of stratigraphic sequences i suggest that environmental change be added as a third autonomous control sedimentologic principles clearly indicate that sequences and their systems tracts are controlled by the interplay of two rates the rate of change in accommodation space available for sedimentation and the rate of sediment supply sea level has direct control on accommodation but its influence on sediment supply is remote and easily overshadowed by environmental factors for instance the record of the most recent sea level rise is a transgressive systems tract where supply is low it is a prograding highstand systems tract in deltas where the supply is high examples of sequence boundaries generated by changes in sediment supply include tectonically driven shifts in sediment input into basins changes in ocean currents pulsating supply from failure of submarine slopes and drowning of carbonate platforms by environmental stress furthermore the stratigraphic sequences in fluviatile continental basins are physically removed from sea level induced changes in accommodation and must have formed by changes in the rate and pattern of supply subaerial exposure of marine sediments at the sequence boundary is a most important criterion for recognizing sea level cycles as opposed to supply cycles other criteria include downstepping of shelf breaks and characteristic patterns in the spacing of time lines within sequences some third order cycles ca 0 5 3 ma duration meet these criteria others do not cycle stacking patterns and the shifting facies belts on cratons indicate that many second and third order cycles lack pronounced exposure unconformities and represent gradual changes superimposed on more rapid shorter oscillations seismic data yield poor images of these gradational changes because they lack resolution seismic models of outcrops show that near the limits of resolution the seismic tool tends to portray rapid changes in facies and bed thickness i e lateral variations in supply as unconformities seismic unconformities do not necessarily correspond to unconformities in outcrop the succession of stratigraphic sequences is best considered a composite record of sea level and environmental change separating the various controls requires carefully planned experiments work on the oxygen isotope curve another proxy for sea level has set an example in this respect

tectonic evolution and mantle structure of the caribbean we investigate whether predictions of mantle structure from tectonic reconstructions are in agreement with a detailed tomographic image of seismic p wave velocity structure under the caribbean region in the upper mantle positive seismic anomalies are imaged under the lesser antilles and puerto rico these anomalies are interpreted as remnants of atlantic lithosphere subduction and confirm tectonic reconstructions that suggest at least 1100 km of convergence at the lesser antilles island arc during the past 45 myr the imaged lesser antilles slab consists of a northern and southern anomaly separated by a low velocity anomaly across most of the upper mantle which we interpret as the subducted north america south america plate boundary the southern edge of the imaged lesser antilles slab agrees with vertical tearing of south america lithosphere the northern lesser antilles slab is continuous with the puerto rico slab along the northeastern plate boundary this results in an amphitheater shaped slab and it is interpreted as westward subducting north america lithosphere that remained attached to the surface along the northeastern boundary of the caribbean plate at the muertos trough however material is imaged until a depth of only 100 km suggesting a small amount of subduction the location and length of the imaged south caribbean slab agrees with proposed subduction of caribbean lithosphere under the northern south america plate an anomaly related to proposed oligocene subduction at the nicaragua rise is absent in the tomographic model beneath panama a subduction window exists across the upper mantle which is related to the cessation of subduction of the nazca plate under panama since 9 5 ma and possibly the preceding subduction of the extinct cocos nazca spreading center in the lower mantle two large anomaly patterns are imaged the westernmost anomaly agrees with the subduction of farallon lithosphere the second lower mantle anomaly is found east of the farallon anomaly and is interpreted as a remnant of the late mesozoic subduction of north and south america oceanic lithosphere at the greater antilles aves ridge and leeward antilles the imaged mantle structure does not allow us to discriminate between an intra americas origin and a pacific origin of the caribbean plate key points tectonic reconstructions for the caribbean validated by seismic tomography cenozoic lesser antilles and mesozoic greater antilles subduction confirmed tomography gives insight into geodynamics of lesser antilles

gap winds and wakes sar observations and numerical simulations the nature of terrain induced gap winds and wakes in the atmosphere is examined using surface wind data from synthetic aperture radar sar and the shallow water equations the shallow water model is used to predict the types of wake jet wind patterns that might occur behind an idealized pair of bell shaped hills with a gap between them a regime diagram is constructed based on the width of the gap and the upstream froude number specific predictions of the model are found to compare moderately well with sar data from four examples of airflow near unimak island in the aleutian chain the model predicts the observed wakes and jets including jets that exceed the upstream speed theoretical analysis considers the relative importance of rising terrain and narrowing valley walls in the acceleration of gap winds wind speeds in the wake region are controlled by the bernoulli function and regional pressure gap winds therefore are streams of air that have avoided bernoulli loss over the terrain by passing through gaps the speed of gap winds can exceed the upstream speed only in ridgelike situations when the regional leeside pressure is lower than the upstream pressure

tearing and breaking off of subducted slabs as the result of collision of the panama arc indenter with northwestern south america we present two regional lithospheric cross sections that illustrate eastward and southeastward dipping subducted slabs to depths of 315 km beneath the surface of colombia in northwestern south america these cross sectional interpretations are based on relocated earthquake hypocentral solutions models supported on gravity and magnetic regional data and coda q q c tomography the method of tomographic imaging based on spatial inversion of the coda wave has advantages of providing information on the lateral variations of the anelastic properties and thermal structure of the lithospheric system mapping of earthquake defined benioff zones combined with tomographic imaging reveals the presence of an 240 km long east west striking slab tear named here the caldas tear the proposed caldas tear separates a zone of shallow 20 30 dipping southeastward subduction in the area of colombia adjacent to panama and the caribbean sea which is not associated with subduction related volcanism from an area of steeper 30 40 dipping slab adjacent to the eastern pacific ocean that is associated with an active north south chain of active arc volcanoes we propose that the caldas slab tear separating these two distinct subducted slabs originally formed as the southern boundary of the panama indenter an extinct island arc that began subducting beneath northwestern south america about 12 ma the area south of the panama indenter is miocene oceanic crust of the nazca plate which subducts eastward beneath northwestern south america at normal angles and melts to form a north south trending active volcanic arc in addition to the formation of the caldas tear we propose that impedance of the thicker crustal area of the panama arc indenter over the past 12 ma may have led to down dip break off of previously subducted oceanic crust that is marked by an extremely concentrated and active earthquake swarm of intermediate depth earthquakes beneath east central colombia

a conceptual tectonostratigraphic model for seismic facies migrations in a fluvio lacustrine extensional basin one of the most fundamental differences between lacustrine basins and many marine basins is the stratigraphic response to differential tectonic subsidence because the water volume of a lake is finite tilting of the valley floor redistributes the lake water if the lake water level is below a hinge point fulcrum that experiences no net subsidence the lake shoreline is translated toward the site of subsidence and a deeper lake forms this tectonostratigraphic model for rift lake sedimentation is tested in a seismic and sequence stratigraphic study of deltaic and lacustrine deposits that accumulated in a cenozoic extensional basin beneath goshute valley nevada seismic sequences exhibit an internal cyclic stacking hierarchy of seismic reflections interpreted as the stratigraphic response of a lowstand paleolake to tectonism forced regression and subsequent lake level restoration transgressive and highstand systems tracts

linking late cretaceous to eocene tectonostratigraphy of the san jacinto fold belt of nw colombia with caribbean plateau collision and flat subduction collision with and subduction of an oceanic plateau is a rare and transient process that usually leaves an indirect imprint only through a tectono stratigraphic analysis of pre oligocene sequences in the san jacinto fold belt of northern colombia we show the late cretaceous to eocene tectonic evolution of northwestern south america upon collision and ongoing subduction with the caribbean plate we linked the deposition of four forearc basin sequences to specific collision subduction stages and related their bounding unconformities to major tectonic episodes the upper cretaceous cansona sequence was deposited in a marine forearc setting in which the caribbean plate was being subducted beneath northwestern south america producing contemporaneous magmatism in the present day lower magdalena valley basin coeval strike slip faulting by the romeral wrench fault system accommodated right lateral displacement due to oblique convergence in latest cretaceous times the caribbean plateau collided with south america marking a change to more terrestrially influenced marine environments characteristic of the upper paleocene to lower eocene san cayetano sequence also deposited in a forearc setting with an active volcanic arc a lower to middle eocene angular unconformity at the top of the san cayetano sequence the termination of the activity of the romeral fault system and the cessation of arc magmatism are interpreted to indicate the onset of low angle subduction of the thick and buoyant caribbean plateau beneath south america which occurred between 56 and 43 ma flat subduction of the plateau has continued to the present and would be the main cause of amagmatic post eocene deposition

the aerodynamic roughness of different types of sea ice the aerodynamic roughness for all major types of sea ice is specified on the basis of surface layer measurements from ship and ice floe platforms median neutral surface drag coefficients cdn 1000 for grease and nilas ice are 0 7 and 1 6 small medium large and fused pancake ice have cdn equal to 0 9 1 6 2 4 and 1 9 young ice cdn ranges from 2 3 to 3 1 very smooth first year or multiyear ice with no pressure ridges has cdn equal to 1 5 pack ice has median values of 2 0 and 2 2 for first year and multiyear ice marginal ice zone ice averages 3 1 and 3 4 first year multiyear if unaffected by wave action wave affected ice has cdn values of 4 2 and 4 6 first year multiyear extremely rough multiyear ice in intense shear or compaction regions has cdn equal to 8 0 open ocean areas within 100 km of an ice edge averaged 1 8 while ice free water downwind of ice with small or no waves is 1 4 these values can be adjusted if heat fluxes are present the accuracy of the cdn averages is estimated to be 20 or better

mesoscale wind measurements using recalibrated ers sar images the precision images pri of the synthetic aperture radars sar on board the european remote sensing satellites ers 1 and ers 2 are used to derive mesoscale wind fields over the ocean for calculation of the wind speed the c band model cmod4 is used which was originally developed by stoffelen and anderson 1993 for the european space agency esa to derive wind fields from measurements of the wind scatterometer scat in the case of the ers 1 2 sar the cmod4 is used to compute the wind speed from the normalized radar backscatter cross section nrcs and the incidence angle of the radar beam both computed from the sar pri data the third input variable is the wind direction which is estimated from the wind streaks in the images or from ground truth measurements the sar data are affected by a power loss caused by saturation of the analog to digital converter adc of the sar therefore the images have to be recalibrated errors in the derived wind speed are mainly due to adc saturation and uncertainties of the input wind direction these errors are estimated for various wind conditions mesoscale wind fields computed from ers 1 2 sar pri images taken between the shetland islands and the west coast of norway are compared to ground truth measurements and modeled wind fields from the german weather service dwd wind fields of the nonhydrostatic mesoscale model geesthacht simulation model of the atmosphere gesima are compared to the derived wind field of the ers 1 sar pri image at the island rugen in the baltic sea

oceanographic conditions in the marginal ice zone north of svalbard in early fall 1979 with an emphasis on mesoscale processes during september october 1979 the norwegian remote sensing experiment was carried out in the marginal ice zone north of svalbard convergence of the ice cover is correlated with along ice edge winds with the ice to the right while divergence occurs during office winds or calm conditions a wind driven ice edge jet is observed wind driven upwelling of the pycnocline of up to 7 m was present along the ice edge during a 10 to 15 m s easterly wind event the upwelling is due to ekman divergence at the ice edge caused by higher wind stress over ice than over open water the ice edge meanders with a scale of 20 40 km and sheds eddies with a scale of 5 to 15 km into the open water this scale is of the same order as the rossby radius of deformation eddies with the same scale are also seen in the conductivity temperature and depth observations conditions during the experiment were such that barotropic instabilities could have generated these eddies

syntectonic cenozoic sedimentation in the northern middle magdalena valley basin of colombia and implications for exhumation of the northern andes development of the colombian middle magdalena valley basin mmvb was determined by late cretaceous early eocene uplift of the central cordillera to the west and subsequent transferal of deformation to the eastern cordillera to the east these phases are separated in the tectono stratigraphic record by a major unconformity the middle magdalena valley unconformity mmvu paleocene coastal to alluvial facies underneath the mmvu were deposited in a foreland basin coupled to central cordillera kilometer scale uplift the middle eocene to neogene continental strata that onlap the mmvu document transformation of the mmvb into an interior basin due to eastern cordillera deformation recorded by growth strata in seismic lines and changing provenance and paleoflow patterns exhumation histories of the mmvb bounding ranges are further constrained by apatit fission track and vitrinite reflectance thermochronology and volcanic ash chronology this study indicates that the mmvb is fundamentally related to evolution of the entire andean margin of south america

thermohaline circulation in the arctic mediterranean seas the renewal of the deep north atlantic by the various overflows of the greenland scotland ridges is only one manifestation of the convective and mixing processes which occur in the various basins and shelf areas to the north the arctic ocean and the greenland iceland and norwegian seas collectively called the arctic mediterranean the traditional site of deep ventilation for these basins is the greenland sea but a growing body of evidence also points to the arctic ocean as a major source of deep water this deep water is relatively warm and saline and it appears to be a mixture of dense brine enriched shelf water with intermediate strata in the arctic ocean the deep water exits the arctic ocean along the greenland slope to mix with the greenland sea deep water conversely very cold low salinity deep water from the greenland sea enters the arctic ocean west of spitsbergen within the arctic ocean the lomonosov ridge excludes the greenland sea deep water from the canadian basin leaving the latter warm saline and rich in silica in general the entire deep water sphere of the arctic mediterranean is constrained by the greenland scotland ridges to circulate internally therefore it is certain of the intermediate waters formed in the greenland and iceland seas which ventilate the north atlantic these waters have a very short residence time in their formation areas and are therefore able to rapidly transmit surface induced signals into the deep north atlantic

comparison of sar derived wind speed with model predictions and ocean buoy measurements as part of the alaska synthetic aperture radar sar demonstration project in 1999 and 2000 wide swath radarsat sar imagery has been acquired on a regular basis in the gulf of alaska and the bering sea during 1998 and 1999 similar data were acquired off the east coast of the united states as part of the stormwatch project the radar cross section measurements from these images were combined with wind direction estimates from the navy operational global atmospheric prediction system model to produce high resolution maps of the surface wind speed for this study 2862 sar image frames were collected and examined averaged wind estimates from this data base have been systematically compared with corresponding wind speed estimates from buoy measurements and model predictions and very good agreement has been found the standard deviation between the buoy wind speed and the sar estimates is 1 76 m s details of the sar wind extraction procedure are discussed along with implications of the comparisons on the c band polarization ratio

tectono sequence stratigraphic analysis of the lower cretaceous abu gabra formation in the fula sub basin muglad basin southern sudan abstract the fula sub basin of the muglad basin of southern sudan is an active fault bounded basin with an area of approximately 3300 km 2 the lower cretaceous abu gabra formation formed during the first of three rifting cycles it can be subdivided into five 3rd order sequences named sqa sqe from bottom to top indicating five stages of tectonostratigraphy and tectonosedimentary evolution the spatial distribution and temporal evolution of clastic depositional systems are described in this paper based on integrated analysis of seismic core and well logging data in the abu gabra formation of the fula sub basin a variety of depositional systems are recognized namely fan delta braided delta delta sublacustrine fan and lacustrine system the fula sub basin has undergone a complex and phased rifting evolution and a high abundance of transfer zones developed causing the resulting distribution and architecture of both the sequence and depositional system to be controlled by various types of transfer zones the following three types of sequence architectures from northern to southern part of the fula sub basin have been identified simple dustpan shaped sequence architecture in the north transfer zone sequence stratigraphic architecture in the middle and graben shaped sequence architecture in the south the sequence architecture is under the control of the large scale central transfer zone and nine models are built to study the effect of at least three categories of small scale transfer zones on the depositional systems in the fula sub basin the small scale transfer zones play significant roles in basin fill primarily in controlling of the positions of deposit input points this study provides valuable insights into tectonic control of depositional systems and sequence architectures in a continental rift basin such as the fula sub basin

a routine high precision method for lu hf isotope geochemistry and chronology a method for chemical separation of lu and hf from rock meteorite and mineral samples is described together with a much improved mass spectrometric running technique for hf this allows i geo and cosmochronology using the176lu 176hf decay scheme and ii geochemical studies of planetary processes in the earth and moon chemical yields for the three stage ion exchange column procedure average 90 for hf chemical blanks are 0 2 ng for lu and hf from 1 g of hf a total ion current of 0 5 10 11 ampere can be maintained for 3 5 h yielding 0 01 0 03 precision on the ratio176hf 177hf normalisation to179hf 177hf 0 7325 is used extensive results for the johnson matthey hf standard jmc 475 are presented and this sample is urged as an international mass spectrometric standard suitable aliquots prepared from a single batch of jmc 475 are available from denver lu hf analyses of the standard rocks bcr 1 and jb 1 are given the potential of the lu hf method in isotope geochemistry is assessed

wind vector retrieval using ers 1 synthetic aperture radar imagery an automated algorithm intended for operational use is developed and tested for estimating wind speed and direction using ers 1 sar imagery the wind direction comes from the orientation of low frequency linear signatures in the sar imagery that the authors believe are manifestations of roll vortices within the planetary boundary layer the wind direction thus has inherently a 180 spl deg ambiguity since only a single sar image is used wind speed is estimated by using a new algorithm that utilizes both the estimated wind direction and spl sigma sub 0 values to invert radar cross section models the authors show that 1 on average the direction of the roll vortices signatures is approximately 11 spl deg to the right of the surface wind direction and can be used to estimate the surface wind direction to within spl plusmn 19 spl deg and 2 utilizing these estimated wind directions from the sar imagery subsequently improves wind speed estimation generating errors of approximately spl plusmn 1 2 m s for ers 1 sar data collected during the norwegian continental shelf experiment in 1991

the influence of fault array evolution on synrift sedimentation patterns controls on deposition in the strathspey brent statfjord half graben northern north sea the dispersal and deposition of sediments in a rift basin are controlled by the sediment supply and the generation of accommodation space hence for the facies mosaic and depositional architecture of synrift sediments to be understood both these variables must be constrained subsurface data sets comprising three dimensional 3 d seismic and well data provide the opportunity to quantify the rates of sediment supply and accommodation generation for the duration of the extensional event and over an area of regional extent in this article we address the controls on synrift sedimentation through detailed analysis of a high resolution subsurface data set from the late jurassic northern north sea rift basin the sedimentation history in the study basin comprises four discrete stages intimately linked to the growth of the normal fault population the earliest stage of rifting is characterized by a distributed fault population comprising a large number of faults with low slip rates sediment supply outpaced tectonic subsidence at this time and rising eustatic sea level was the primary control on sedimentation as rifting progressed strain was localized onto a smaller number of active structures with higher displacement rates the basin developed a grabenlike geometry and the lateral propagation and linkage of fault strands controlled accommodation generation although the basin was flooded the rate of sediment supply remained high and largely kept pace with the rate of tectonic subsidence during the final two stages the fully linked half graben bounding fault was the only active structure in the basin the rate of sediment supply at this time was greatly exceeded by the rate of tectonic subsidence and the basin became underfilled significantly the final stage of the sedimentation history is characterized by large scale fault interactions that changed the fault controlled basin floor topography hence modified sediment dispersal and deposition we conclude that sediment dynamics and facies distribution in a rift can only be understood in the context of the coevally active fault population as the faults active at the close of a rift event are very different in location and character to those active during the initiation of rifting this further emphasizes the need to integrate structural sedimentary and stratigraphic studies in rift basins

tower based measurements of the ocean c band radar backscattering cross section continuous measurements of the c band normalized radar cross section nrcs at vertical vertical polarization as a function of wind speed and direction were carried out from a research platform in the north sea during a period of 11 months in 1984 the nrcss have been correlated with other environmental data routinely collected at the platform like air water temperature difference water temperature and ocean wave slope the wind speed exponent of the c band nrcs at 45 incidence angle was determined as 1 50 valid in the wind speed range 2 19 m s our data set shows that the c band nrcs depends strongly on the air sea temperature difference for example when the air sea temperature difference decreases from 5 c to 5 c the nrcs increases by 6 db at a wind speed of 8 9 m s and an incidence angle of 45 for stable air sea interfaces and low wind speeds the nrcs increases with increasing root mean square wave slope however no systematic dependence on water temperature was observed

guidelines for reporting zircon hf isotopic data by la mc icpms and potential pitfalls in the interpretation of these data invited technical paper high quality analytical data are essential for the development of sound scientific interpretations to ensure the quality of the data published in chemical geology a new type of contribution has been introduced the invited technical paper when a particular technical issue needing discussion or clarification is identified specialists in the technique will be invited to share their expertise as is true for all articles published in the journal these contributions will be subject to peer review before publication the first topic to be treated concerns in situ hf isotopic measurements in zircon by laser ablation inductively coupled plasma mass spectrometry this is an extremely powerful and promising technique that has been adopted by many laboratories throughout the world however if insufficient care is taken during analysis and data processing inaccurate results can be obtained notably because of the existence of very large isobaric interferences on the isotope of interest to address this issue we have asked christopher fisher jeffery vervoort and john hanchar to provide a set of guidelines that can be adopted to assure that reliable hf isotopic data are obtained by this technique abstract over the past decade the hf isotope composition of zircon as determined in situ by laser ablation multicollector inductively coupled plasma mass spectrometry la mc icpms has been applied increasingly to a wide range of geological problems and has proven to be a valuable analytical tool there has been no uniformity however in the reporting of in situ hf isotopic data and quite often reviewers and readers of papers are not provided with sufficient information to assess data quality the goal of this invited contribution is to provide the non specialist with a brief outline and explanation of what is required for proper presentation and documentation of in situ hf isotopic data from zircon including details of how the challenging large isobaric interference corrections have been made in addition we discuss a number of potential pitfalls vis a vis the assignment of the incorrect age to the measured hf isotope composition non specialists should be aware of these important issues when doing their own analyses and evaluating the analyses done by others

mantle flow beneath northwestern venezuela seismic evidence for a deep origin of the merida andes abstract we measured shear wave splitting from sks data recorded by the national seismic network of venezuela and a linear broadband passcal rice seismic array across the merida andes the linear array was installed in the second phase of the passive seismic component of the bolivar project to better understand the complicated regional tectonics in western venezuela using the method proposed by wolfe and silver 1998 sks waveforms from 2 to 36 earthquakes mostly from the tonga subduction zone were selected for each of the 23 stations in the region in order to do splitting analysis the fast polarization directions can be divided into 3 zones all in agreement with local gps data the first zone comprises the stations north of the dextral strike slip oca ancon fault these stations show the largest split times 1 6 3 2 s oriented in a roughly ew direction and are similar to splitting observations made further to the east along the strike slip plate boundary growdon et al 2009 we attribute this to trench parallel mantle flow that passes around the northwest corner of the subducting caribbean plate and along the northern edge of south america as proposed by russo and silver 1994 forming an eastward flow beneath the southern caribbean plate zone two is the merida andes with the right lateral bocono fault in the center where split orientations are at n45 e suggesting that the observed seismic anisotropy is likely caused by lithospheric deformation parallel to the bocono fault zone three is east of the bocono fault inside the barinas apure basin where the measured split times are smaller 0 8 s with an ew fast direction that is consistent with those observed at the guarico basin maturin basin and the guayana shield in the east and are interpreted as orientation with the motion of the continent

a model of the atmospheric boundary layer over the marginal ice zone a one layer primitive equation model is presented for the atmospheric boundary layer over the marginal ice zone miz the model simulates the slow rate of inversion growth and rate of warming of the boundary layer seaward of an ice edge for off ice winds observed on two cruises in the bering sea by the noaa r v surveyor the horizontal temperature gradient in the boundary layer caused by the oceanic heat flux seaward of an ice edge induced an increase in wind speed with a maximum increase of 8 at 50 km seaward of the edge at 100 km off ice a momentum balance is established between accelerative terms boundary layer baroclinity momentum entrainment synoptic scale scale pressure gradient and decelerative terms surface drag and the local pressure force resulting from inversion rise wind velocity in the boundary later over the miz during off ice winds is sensitive to changes in surface roughness when an miz is modeled as a smooth interior cd 2 10 3 and a 30 km wide rough marginal ice zone cd 3 8 10 3 with an unstable surface layer over the ocean the model shows a decrease in wind speed of 9 at the windward side of the miz and an 18 increase in wind speed from 5 km interior to the ice edge to 40 km seaward of the edge these results suggest an atmospheric mechanism for rafting at the windward side of the marginal ice zone divergence of the ice at the edge and ice band formation seaward of the edge

sar retrieved wind in polar regions comparison with in situ data and atmospheric model output european remote sensing ers satellites synthetic aperture radar sar wind retrievals using cmod ifr2 are for the first time retrieved in the marginal ice zone miz and in arctic coastal areas and compared with in situ observations from reseach vessels rvs and output from a high resolution atmospheric model the root mean squares rms of the comparisons were 1 6 m s sup 1 and 2 m s sup 1 respectively the spatial variation of the sar wind fields established a decrease in wind speed close to the ice edge for the late summer situations where the wind was along the ice edge with the ice to the left this decrease is believed to be due to changes in atmospheric stability possibly through development of an internal boundary layer caused by the cold ice cover and melt water lower wind speed near the ice edge is confirmed by the atmospheric model and the in situ observations furthermore good results are obtained from sar wind retrieval in leads when compared with model output during a cold air outbreak routine measurements in the miz are useful for estimating the wind stress and therefore sar may play an important role in this region finally the identification of a jet out from hinlopen strait in the svalbard region and low wind wakes along the coast in the sar retrieved wind field is confirmed by in situ observations as the rv moves through the region the jet is also confirmed by the atmospheric model which is able to reproduce the situation

katabatic wind fields in coastal areas studied by ers 1 synthetic aperture radar imagery and numerical modeling synthetic aperture radar sar images acquired over mediterranean coastal waters from the first european remote sensing satellite ers 1 showing sea surface manifestations of katabatic wind fields are presented in particular sea surface roughness patterns generated by katabatic winds blowing from 1800 in high mountains through a broad valley at the western coast of calabria southern italy into the gulf of gioia is investigated the ers 1 sar images show that their areal extent and shape vary strongly depending on the meteorological conditions the roughness pattern sometimes has the form of a mushroom an elongated tongue a broad blob or a narrow truncated band for one event september 8 1992 we have simulated the wind field at the sea surface by using a nonhydrostatic mesoscale atmospheric model and then compared it with the wind field derived from the ers 1 sar image by using the c band wind scatterometer model cmod4 the comparison shows that the atmospheric model reproduces quite well the mushroom like form of the wind field pattern while the wind speed is obtained somewhat lower than the one inferred from the sar image this study demonstrates that sar images acquired over coastal waters are well suited to study local wind fields in coastal areas and to test numerical models that describe local wind fields which extend from the coast onto the sea

lithosphere tearing at step faults response to edges of subduction zones abstract slab edges are a relatively common feature in plate tectonics two prominent examples are the northern end of the tonga subduction zone and the southern end of the new hebrides subduction zone near such horizontal terminations of subduction trenches ongoing tearing of oceanic lithosphere is a geometric consequence we refer to such kinks in the plate boundary as a subduction transform edge propagator or step other steps are the north and south ends of the lesser antilles trench the north end of the south sandwich trench the south end of the vrancea trench and both ends of the calabria trench volcanism near steps is distinct from typical arc volcanism in some cases slab edges appear to coincide with mantle plumes using 3d mechanical models we establish that step faults are stable plate tectonic features in most circumstances in the probably rare cases that the resistance to fault propagation is high slab break off will occur relative motion along the transform segment of the plate boundary often is non uniform and the step is not a transform plate boundary in the rigid plate tectonics sense of the phrase step propagation may result in substantial deformation rotation topography and sedimentary basins with a very specific time space evolution surface velocities are substantially affected by nearby steps

the geological history of northwestern south america from pangaea to the early collision of the caribbean large igneous province 290 75ma abstract northwestern south america preserves a record of the assembly of western pangaea its disassembly and initiation of the far western tethys wilson cycle subsequent pacific margin magmatism and ocean plateau continent interaction since the late cretaceous numerous models have been presented for various time slices although they are based on either spatially restricted datasets or dates that are inaccurate estimates of the time of crystallisation here we review a very large quantity of geochronological geochemical thermochronological sedimentological and palaeomagnetic data that collectively provide tight constraints for geological models these data have been collected over a trench pacific parallel distance of 1500 km colombia and ecuador and reveal important temporal trends in rifting and subduction the temporal framework for our model constraints are obtained from robust concordant zircon u pb ages of magmatic rocks during 290 75 ma the late cretaceous thermal history of the margin

a coupled ice ocean model of upwelling in the marginal ice zone a dynamical coupled ice ocean numerical model for the marginal ice zone miz is suggested and used to study upwelling dynamics in the miz the nonlinear sea ice model has a variable ice concentration and includes internal ice stress the model is forced by stresses on the air ocean and air ice surfaces the main coupling between the ice and the ocean is in the form of an interfacial stress on the ice ocean interface the ocean model is a linear reduced gravity model the wind stress exerted by the atmosphere on the ocean is proportional to the fraction of open water while the interfacial stress ice ocean is proportional to the concentration of ice a new mechanism for ice edge upwelling is suggested based on a geostrophic equilibrium solution for the sea ice medium the upwelling reported in previous models invoking a stationary ice cover is shown to be replaced by a weak downwelling due to the ice motion most of the upwelling dynamics can be understood by analysis of the divergence of the across ice edge upper ocean transport on the basis of numerical model an analytical model is suggested that reproduces most of the upwelling dynamics of the more complex numerical model

sequence stratigraphy sedimentary systems and petroleum plays in a low accommodation basin middle to upper members of the lower jurassic sangonghe formation central junggar basin northwestern china abstract the lower jurassic junggar basin is a low accommodation basin in northwestern china because of low subsidence rates and a warm wet climate deposits of the central subbasin of the junggar basin formed from fluvial deltaic shallow lake facies sequence stratigraphy and sedimentary systems of the lower jurassic members of the sangonghe formation j1s were evaluated by observing cores interpreting wireline logs and examining seismic profiles two third order sequences were recognized in the strata the distribution of the sedimentary systems in the systems tracts shows that tectonic movement paleorelief paleoclimate and changes in lake level controlled the architecture of individual sequences during the development of the lowstand systems tract lst the intense structural movement of the basin resulted in a significant fall in the water level in the lake accompanied by rapid accommodation decrease braided rivers and their deltaic systems were also developed in the central junggar basin sediments carried by braided rivers were deposited on upward slopes of the paleorelief and braid delta fronts were deposited on downward slopes during the transgressive systems tract tst the tectonic movement of the basin was quiescent and the climate was warm and humid lake levels rose and accommodation increased quickly shoal lines moved landward and shore to shallow lake deposits sublacustrine fans and deep lake facies were deposited in shallow to deep lake environments during the highstand systems tract hst the accommodation no longer increased but sediment supply continued far exceeding accommodation hst deposits slowly formed in shallow lake to meandering river delta front environments relatively low rates of structural subsidence and low accommodation resulted in coarse grained successions that were fining upward deposits were controlled by structural movement and paleorelief within the lst to tst deposits in the central subbasin fine to medium grained coarsening upward successions developed during the hst the sand bodies of braid delta fronts on the downward slopes of the paleorelief in the lst and the sublacustrine fans in the tst became reservoirs for hydrocarbon accumulation petroleum plays have only been found in the sangonghe formation j1s located on structural ridges that consist of sand bodies comprising these sequences favorable conditions for petroleum plays in hst1 lst2 occur where the sand bodies have been fractured by faults and sealed by denudation and pinch out lines then overlain by deep lake mudstone in tst2 the favorable condition of the sand bodies within tst2 occurs where isolated sand bodies have been fractured by faults

early subduction related orogeny in the northern andes turonian to eocene magmatic and provenance record in the santa marta massif and rancheria basin northern colombia terra nova 23 26 34 2011 abstract the timing of orogeny in the northern andes and the mechanism driving it are still debated we have studied the age composition and provenance of granitoids and sandstones of the santa marta massif and rancheria basin northern colombia to relate deep seated and surface tectonic processes attending the late cretaceous palaeogene history of the northern andes our results indicate the development of five tectonic episodes 1 collision of northwestern south america with a 92 80 ma caribbean arc 70 ma 2 late collisional to early subduction metamorphism and magmatism 65 ma 3 distal accumulation of a thick siliciclastic sequence 60 58 ma 4 renewed arc magmatism 58 50 ma and 5 magmatic quiescence and block uplift post 50 ma the first episodes are related to the onset of subduction and the last episode is related to shallow subduction and oblique convergence similar events in colombia and ecuador reveal that the late cretaceous eocene orogeny of the northern andes was influenced by the collision and subduction of the caribbean oceanic plate

coastal wind field retrievals from ers synthetic aperture radar images a unique series of european remote sensing satellite ers 1 and 2 c band synthetic aperture radar sar images was obtained off the southern coast of norway during the coast watch 95 experiment in september 1995 in this paper we carry out a systematic analysis of the mesoscale coastal wind field conditions expressed in the sar images four different categories of phenomena including windrows fetch limited seas wind fronts and oceanographic fronts are examined and discussed the quantitative retrievals of the wind field are based on examination of both the sar image backscatter characteristics and the spectral properties results are compared and validated against coincident ship and buoy data providing complementary and independent observations of the oceanographic and meteorological conditions

geodynamics of the northern andes subductions and intracontinental deformation colombia new regional seismological data acquired in colombia during 1993 to 1996 and tectonic field data from the eastern cordillera ec permit a reexamination of the complex geodynamics of northwestern south america the effect of the accretion of the baudo panama oceanic arc which began 12 myr ago is highlighted in connection with mountain building in the ec the istmina and ibague faults in the south and the santa marta bucaramanga fault to the northeast limit an e se moving continental wedge progressive indentation of the wedge is absorbed along reverse faults located in the foothills of the cordilleras northward of 5 n and transpressive deformation in the santander massif crustal seismicity in colombia is accurately correlated with active faults showing neotectonic morphological evidences intermediate seismicity allows to identify a n ne trending subduction segment beneath the ec which plunges toward the e se this subduction is interpreted as a remnant of the paleo caribbean plateau pcp as suggested by geological and tomographic profiles the pcp shows a low angle subduction northward of 5 2 n and is limited southward by a major e w transpressive shear zone normal oceanic subduction of the nazca plate np ends abruptly at the southern limit of the baudo range northward the np subducts beneath the choco block overlapping the southern part of the pcp cenozoic shortening in the ec estimated from a balanced section is 120 km stress analysis of fault slip data in the ec northward of 4 n indicates an e se orientation of 1 in agreement with the pcp subduction direction northward near bucaramanga two stress solutions were observed 1 a late andean n80 e compression and 2 an early andean nw se compression

kinematic reconstruction of the caribbean region since the early jurassic abstract the caribbean oceanic crust was formed west of the north and south american continents probably from late jurassic through early cretaceous time its subsequent evolution has resulted from a complex tectonic history governed by the interplay of the north american south american and paleo pacific plates during its entire tectonic evolution the caribbean plate was largely surrounded by subduction and transform boundaries and the oceanic crust has been overlain by the caribbean large igneous province clip since 90 ma the consequent absence of passive margins and measurable marine magnetic anomalies hampers a quantitative integration into the global circuit of plate motions here we present an updated quantitatively described kinematic reconstruction of the caribbean region back to 200 ma integrated into the global plate circuit and implemented with gplates free software our reconstruction includes description of the tectonic units in terms of euler poles and finite rotation angles our analysis of caribbean tectonic evolution incorporates an extensive literature review to constrain the caribbean plate motion between the american continents we use a novel approach that takes structural geological observations rather than marine magnetic anomalies as prime input and uses regionally extensive metamorphic and magmatic phenomena such as the great arc of the caribbean the clip and the caribbean high pressure belt as correlation markers the resulting model restores the caribbean plate back along the cayman trough and major strike slip faults in guatemala offshore nicaragua offshore belize and along the northern andes towards its position of origin west of the north and south american continents in early cretaceous time we provide the paleomagnetic reference frame for the caribbean region by rotating the global apparent polar wander path into coordinates of the caribbean plate interior cuba and the chortis block we conclude that formation of the caribbean plate west of the north and south americas as a result of panthalassa pacific spreading leads to a much simpler plate kinematic scenario than proto caribbean atlantic spreading placing our reconstruction in the most recent mantle reference frames shows that the clip originated 2000 3000 km east of the modern galapagos hotspot and may not have been derived from the corresponding mantle plume finally our reconstruction suggests that most if not all modern subduction zones surrounding the caribbean plate initiated at transform faults two of these along the southern mexican and nw south american margins evolved diachronously as a result of migrating trench trench transform triple junctions

case study of a coastal jet at spitsbergen comparison of sar and model estimated wind a combination of in situ ship measurements synthetic aperture radar sar imagery and high resolution numerical modeling was used to investigate a mesoscale coastal jet radiating out from hinlopenstretet norway on 14 august 1996 in the meteorological analysis a light breeze and high static stability were found upstream of svalbard by studying results of numerical simulations in relation to the topography upstream stagnation flow splitting and downstream jets and wakes were identified in the hinlopenstretet area this flow pattern was confirmed by in situ ship measurements and the sar estimated wind through investigations of sensitivity simulations it was found that the low level jet mainly was a result of stratified flow around dynamically steep isolated topography while the channeling effect of hinlopenstretet had a minor influence in the core of the jet the velocity was increased by a factor of about 3 compared to the upstream velocity

the isotopic composition of yb and the precise and accurate determination of lu concentrations and lu hf ratios by isotope dilution using mc icpms 1 we report yb isotopic data for the purpose of accurately correcting measurements of lu and lu hf ratios during multicollector inductively coupled plasma mass spectrometer mc icpms analysis the yb isotopic ratios agree with recent results of chu et al 2002 and amelin and davis 2004 when corrected for mass fractionation to the same reference values protocols for lu measurement involving simultaneous subtraction of yb interference and application of a fractionation correction based on yb are described it is shown that lu concentrations and lu hf ratios determined by mc icpms using this methodology are more precise and potentially more accurate than results based on analysis of lu by thermal ionization mass spectrometry tims a number of mc icpms lu hf isotopic analyses of standard rocks and other geological samples previously analyzed by tims are presented these document reproducibility of lu hf within 0 2 where most discrepancies can be assigned to the unknown lu mass fractionation during tims analysis

permo triassic anatexis continental rifting and the disassembly of western pangaea crustal anatectites are frequently observed along ocean continent active margins although their origins are disputed with interpretations varying between rift related and collisional we report geochemical isotopic and geochronological data that define an 1500 km long belt of s type meta granites along the andes of colombia and ecuador which formed during 275 223 ma these are accompanied by amphibolitized tholeiitic basaltic dykes that yield concordant zircon u pb dates ranging between 240 and 223 ma a model is presented which places these rocks within a compressive permian arc setting that existed during the amalgamation of westernmost pangaea anatexis and mafic intrusion during 240 223 ma are interpreted to have occurred during continental rifting which culminated in the formation of oceanic crust and initiated the break up of western pangaea compression during 275 240 ma generated small volumes of crustal melting rifting during 240 225 ma was characterized by basaltic underplating the intrusion of tholeiitic basalts and a peak in crustal melting tholeiitic intrusions during 225 216 ma isotopically resemble depleted mantle and yield no evidence for contamination by continental crust and we assign this period to the onset of continental drift dissected ophiolitic sequences in northern colombia yield zircon u pb dates of 216 ma the permo triassic margin of ecuador and colombia exhibits close temporal faunal and geochemical similarities with various crustal blocks that form the basement to parts of mexico and thus these may represent the relict conjugate margin to nw gondwana the magmatic record of the early disassembly of pangaea spans 20 ma 240 216 ma and the duration of rifting and rift drift transition is similar to that documented in cretaceous tertiary rift settings such as the west iberia newfoundland conjugate margins and the taupo lau havre system where rifting and continental disassembly also occurred over periods lasting 20 ma

subduction in the southern caribbean images from finite frequency p wave tomography 1 the eastern boundary of the caribbean plate is marked by subduction of the atlantic under the lesser antilles the southeastern plate boundary is characterized by a strike slip margin while different configurations of subduction of the southwest caribbean under south america have been proposed we investigate the slab geometry in the upper mantle using multiple frequency teleseismic p wave tomography waveforms from p and pkpdf phases from 285 mb 5 0 events occurring at epicentral distances from 30 to 90 and greater than 150 were bandpass filtered and cross correlated to obtain up to three sets of delay times for each event the delay times were inverted using approximate first fresnel zone sensitivity kernels our results show the subducting atlantic slab as well as a second slab in the west of the study area that we interpret as a subducting fragment of the caribbean plate both slabs have steep dips where imaged and can be traced to depths greater than 600 km these results are consistent with transition zone boundary topography as determined by receiver function analysis the atlantic slab extends continent ward south of the plate bounding strike slip margin we interpret this extension as continental margin lithospheric mantle that is detaching from beneath south america and subducting along with the oceanic atlantic slab the steep subduction of the caribbean occurs 500 km landward from the trench implying an initial stage of shallow subduction as far to the east as the lake maracaibo merida andes region as has been inferred from intermediate depth seismicity

subduction of the eastern panama basin and seismotectonics of northwestern south america spreading along the cocos nazca plate boundary since the breakup of the farallon plate in the miocene has resulted in the formation of the panama basin and a complex interaction of plates in and near northwestern south america current plate boundaries have been defined and segments of subducted lithosphere identified through selection of hypocentral locations of earthquakes considering only well located events and through focal mechanism determinations the existence of relict plate boundaries bathymetric features and the panamanian isthmus has affected the subduction process of the nazca plate beneath south america and determined the present day configuration of the subducting lithospheric plate there is no single triple junction separating the caribbean south american and nazca plates instead the panamanian isthmus and surrounding areas are accommodating east west compression and a lesser degree of north south compression along a series of thrust faults striking nw to ne and the andean ranges of ecuador colombia and venezeula are moving as a block nne relative to the rest of the south american plates along a system of faults following the front of the eastern cordillera the subducted portions of the panama basin and old farallon plate have become segmented into three pieces recognized in this study from north to south they are 1 a bucaramanga segment continuous with the caribbean seafloor northwest of colombia 2 a cauca segment continuous with oceanic crust nazca plate currently being subducted beneath south america at the colombia ecuador trench and 3 an ecuador segment at the northern end of the subducted lithospheric plate which is dipping at a small angle to the east beneath northern peru the segmentation of the subducted plate can be explained by the buoyancy of bathymetric features which have been partially subducted