tropical zonal momentum balance in the ncep reanalyses the seasonal cycle of the zonal mean zonal momentum balance in the tropics is investigated using ncep reanalysis data it is found that the climatological stationary waves in the tropical upper troposphere which are dominated by the equatorial rossby wave response to tropical heating produce an equatorward eddy flux of westerly momentum in the equatorial belt the resulting westerly acceleration in the tropical upper troposphere is balanced by the advection of easterly momentum associated with the cross equatorial mean meridional circulation the eddy momentum fluxes and the cross equatorial flow both tend to be strongest during the monsoon seasons when the maximum diabatic heating is off the equator and weakest during april may the season of strongest equatorial symmetry of the heating the upper level rossby wave pattern exhibits a surprising degree of equatorial symmetry and follows a similar seasonal progression solutions of the nonlinear shallow water wave equation also show a predominantly equatorially symmetric response to a heat source centered off the equator

low temperature hydrothermal maturation of organic matter in sediments from the atlantis ii deep red sea abstract hydrocarbons and bulk organic matter of two sediment cores no 84 and 126 chain 61 cruise located within the atlantis ii deep have been analyzed although the brines overlying the coring areas were reported to be sterile microbial inputs and minor terrestrial sources represent the major sedimentary organic material this input is derived from the upper water column above the brines both steroid and triterpenoid hydrocarbons show that extensive acid catalyzed reactions are occurring in the sediments in comparison with other hydrothermal guaymas basin or intrusive systems cape verde rise the atlantis ii deep exhibits a lower degree of thermal maturation this is easily deduced from the elemental composition of the kerogens and the absence of polynuclear aromatic hydrocarbons of a pyrolytic origin in the bitumen the lack of carbon number preference among the n alkanes suggests especially in the case of the long chain homologs that the organic matter of atlantis ii deep sediments has undergone some degree of catagenesis however the yields of hydrocarbons are much lower than those observed in other hydrothermal areas the effect of lower temperature and poor source rock characteristics appear to be responsible for the differences

what are the sources of mechanical damping in matsuno gill type models the matsuno gill model has been widely used to study the tropical large scale circulations and atmosphere ocean interactions however a common critique of this model is that it requires a strong equivalent linear mechanical damping to get realistic wind response and it is unclear what could provide such a strong damping above the boundary layer this study evaluates the sources and strength of equivalent linear mechanical damping in the walker circulation by calculating the zonal momentum budget using 15 yr 1979 93 of daily global reanalysis data two different reanalyses ncep ncar and 15 yr ecmwf re analysis era 15 give qualitatively similar results for all major terms including the budget residual whose structure is consistent with its interpretation as eddy momentum flux convergence by convective momentum transport cmt the walker circulation is characterized by two distinct regions a deep convection region over the indo pacific warm pool and a shallow convection region over the eastern pacific cold tongue these two regions are separated by a strong upper tropospheric ridge and a strong lower tropospheric trough in the central pacific the resultant pressure gradient forces on both sides require strong approximately 5 10 days damping to balance them because coriolis force near the equator is too small to provide the balance in the deep convection region the damping is provided by cmt and advection together in both the upper and lower troposphere in the shallow convection region on the other hand the damping is provided mainly by advection in the upper troposphere and by cmt in the lower troposphere in other words the upperlevel tropical easterly jet and the low level trade wind are both braked by cmt these results support the use of strong damping in the matsuno gill type models but suggest that the damping rate is spatially inhomogeneous and the cmt related damping increases with the strength of convection implications for gcm s simulation of tropical mean climate are discussed

parameterization of the vertical transport of momentum by cumulus clouds part i theory abstract a scheme is developed to parameterize the vertical transport of momentum by cumulus clouds in which the effect of a cloud induced pressure field is included in addition a new form for momentum exchange between clouds and their environment is used the scheme incorporates a simple cloud model which includes both updraft and downdraft and specifies the cloud dynamic fields to enable us to determine the mean pressure gradient force across the clouds it is shown that in a typical environment with vertical wind shear the pressure gradient force is along the direction of the wind shear the equation governing cloud mean momentum together with the diagnostic equation for cloud induced pressure field is solved by iteration to evaluate quantitatively the horizontal pressure gradient force across the cloud and determine the cloud mean momentum application of the parameterization scheme to gate convective events will be presented in part ii of this paper

intersections of remanence small circles new tools to improve data processing and interpretation in palaeomagnetism summary intersections of remanence small circles are increasingly used in palaeomagnetism to determine the palaeofield direction from synfolding remanences the approach small circle intersection sci method presupposes that remanence small circles from sites tilted to different directions intersect in a common point which is assumed to represent the palaeofield direction the sci method is not restricted to synfolding remanences it can be applied also to derive the palaeofield direction from pre folding remanences in addition to tilt correction and as a cross check for fold tests however the sci method has specific requirements and does not work in all cases the suitability of data sets and reliability of palaeofield estimates have to be assessed carefully and always against the background of local geology this paper examines the occurrence and distribution of sci as a tool of judgement first a data set is most suitable and a palaeofield estimate by sci most reliable when most of the theoretically possible intersections are realized and in addition clearly grouping in a narrow region second the small circles that greatly determine the result of sci are identified by the highest number of intersections they have with the others these criteria allow a systematic investigation of sci estimates upon stability and dependencies moreover scis can be an indicator of irregular unexpected tectonic settings when the intersections disperse strongly although significant bedding strike differences are given relative rotations or other unexpected displacements are likely to have occurred if so the sci estimate will be invalid and probably biased however also fisher mean calculation and most fold tests will be affected in this case the scis can help to separate the data into subsets valid for fisher statistics and sci methods the other possibility is to use tentative reconstructions to infer the true sequence of tilts and rotations and correct the data adequately

experiments on tropical circulation with a simple moist model a simple model of the circulation of the tropical atmosphere is constructed where the circulation is determined entirely by the sea surface temperature s s t pattern or rather by a forcing field which is closely related to s s t it is an equatorial beta plane model with an assumed simple baroclinic vertical structure the moisture and precipitation fields are allowed to evolve freely so there are feedbacks between the latent heating which contributes to driving the motion and the low level velocity field which produces the moisture convergence required to generate precipitation experiments with idealized pacific s s t distributions produce qualitatively realistic precipitation patterns for january a patch in the west pacific over the equator and july a zonal strip north of the equator analytic solutions for zonally symmetric flow are given to illustrate the basic dynamics and to study the parameter dependence of the precipitation an analysis of zonal variations shows that a good simplifying approximation for this component is to neglect rayleigh friction while retaining newtonian cooling the effect of changing the zonal contrast in the prescribed forcing is to gradually alter the circulation from hadley like to walker like the model suggests that along the equator a relatively small contrast is needed to break a zonal band of precipitation

dynamics and thermodynamics of a warming event in a coupled tropical atmosphere ocean model abstract a simple coupled ocean atmosphere model similar to that of zebiak and cane is used to examine the dynamic and thermodynamic processes associated with el nino southern oscillation enso the model is run for 300 years the interannual variability which results is regular with a period of either 3 or 4 years quantized by the annual cycle the amplitude 1 5 m s 1 wind and 2 c sst anomalies period and structure of the interannual variability compare well with observations the model warm event is initiated in the spring prior to the event peak and is well described as an instability of the coupled system during instability growth the sea surface temperature sst anomaly is primarily generated by vertical upwelling processes the sst anomaly can be approximately described by the expression t t kth t where t is the sst anomaly t time h the upper layer thickness pycnocline perturbation and an effective damping time which includes heat loss to the atmosphere kt parameterizes

paleodepositional conditions in the orca basin as inferred from organic matter and trace metal contents abstract the orca basin located in the gulf of mexico is a highly stratified basin that collects sedimentary particles of clastic origin supplied by the mississippi river and of biogenic origin marine surface productivity the strong pycnocline induces anoxic bottom conditions that are expected to be favorable to organic matter om accumulation and prone to enrichment of sediments in redox sensitive trace metals here we report on om and trace metal contents in the upper 750 cm below sea floor cmbsf of core md02 2552 mostly holocene and deposited under permanently stratified bottom conditions the organic content is dominated by marine derived amorphous om contrary to expectations sedimentary om in the basin is highly degraded probably due to a long residence time of organic particles at the basin s basin s halocline at 2240 m also unexpected is the limited sedimentary enrichment of redox sensitive trace metals we suggest that the non enrichment in u and v could be explained by the so called basin reservoir effect that is limited metal availability because of low rates of water renewal in a strongly restricted subpycnoclinal water mass the non enrichment in cu could have the same cause plus the fact that the relatively degraded om may not readily form organometallic complexes however a marked enrichment is observed for mo and a moderate one for ni and cr which could be accounted for by sporadic presence of h 2 s in bottom waters such occurrences of h 2 s would not be sufficient to promote a detectable fes to fes 2 conversion but they would induce the capture of mo in the form of thiomolybdate and accessorily ni cr as ni cro 4 complexes

kinematics of orocline tightening in the core of an arc paleomagnetic analysis of the ponga unit cantabrian arc northern spain 1 paleomagnetic and structural analyses of the western european variscan belt wevb suggest that the most viable kinematic model for variscan deformation in northern iberia is oroclinal bending of an originally linear belt in a two stage tectonic history this history represents two regional compression phases e w in the late carboniferous and n s in the permian both in present day coordinates which resulted in the refolding about steeply plunging axes of initially north south trending thrusts and folds in the hinge zone and oroclinal tightening due to vertical axis rotation of the belt s limbs however the orocline model has yet to be critically tested in the wevb s core this study reports new paleomagnetic rock magnetic and structural data from the inner core of the wevb in order to test opposing kinematic models for the well documented fault and fold interference structures formed by late stage variscan deformation and to better understand the overall development of the wevb arc map scale structural features within the wevb core have a highly sinuous geometry characterized by transverse and thrust parallel fold systems formed by fault bend folding over footwall ramps the intersections of these two fold systems produce steeply plunging interference folds which are best exposed in the ponga thrust unit a total of 67 paleomagnetic sites were collected in the barcaliente formation of the ponga unit with emphasis placed on detailed spatial coverage of individual structural domains a multicomponent paleomagnetic remanence was measured which is interpreted to be composed of two components a low unblocking temperature recent viscous magnetization and a high unblocking temperature ancient magnetization that was acquired in the latest stephanian to early permian after initial d1 thrusting and folding bur prior to major secondary rotation rock magnetic experiments show that the characteristic remanence magnetization is carried by secondary authigenic pseudosingle domain magnetite these paleomagnetic results are used to determine the kinematics and geometry of postmagnetization deformation by restoring in situ magnetic vectors back to a defined reference direction on the basis of the restored ponga unit geometry the steeply plunging interference folds found in the wevb core are best described by a combination of secondary buckling of frontal ramp parallel hanging wall anticlines and modification of d1 lateral oblique ramps as frontal ramps during late stage north south shortening this combination of structural modification of the inner core of the wevb was necessary to accommodate oroclinal bending during the final amalgamation of pangea in the late paleozoic

interannual variability in a tropical atmosphere ocean model influence of the basic state ocean geometry and nonlinearity abstract the behavior of a tropical coupled atmosphere ocean model is analyzed for a range of different background states and ocean geometries the model is essentially that of cane and zebiak for the tropical pacific except only temporally constant background states are considered here for realistic background states and ocean geometry the model solutions feature oscillations of period of 3 5 yr by comparing the full model solution with a linearized version of the model it is shown that the basic mechanism of the oscillation is contained within linear theory a simple linear analog model is derived that describes the nature of the interannual variability in the coupled tropical atmosphere ocean system the analog model highlights the properties that produce coupled atmosphere ocean instability in the eastern ocean basin and the equatorial wave dynamics in the western ocean basin that are responsible for a delayed negative feedback into this instability growth the growth rate of the local instabil

sulfur and organic carbon contents in sediment cores from the tyro and orca basins abstract the tyro and orca basins are two small deep water euxinic depressions in the eastern mediterranean and the northern gulf of mexico respectively anoxic bottom waters are known to be nearly saturated with nacl sediment accumulation in the basins has been complicated by episodic slumping and or redeposition analyses of sediment total reduced sulfur and organic carbon and resulting s c ratios are used to test the feasibility of using these parameters as indicators for the mode of sediment deposition in the basins sediments originally deposited in the basin are as expected enriched in sulfur and carbon content as compared to sediments that originated from areas beyond the limit of the anoxic brine pool and were redeposited later inside the basin however values of the s c ratios of these primarily deposited sediments are less than those of sediments of redeposited origin and indicate a low rate of sulfide conversion during bacterial sulfate reduction this inconsistency is interpreted to be due to the high salinity basin waters inhibiting the overall activity of sulfate reducers and their associated heterotrophic microorganism communities and or the reactivity of initially deposited organic matter this study also demonstrates that variations of sulfur and carbon contents and their s c ratios together can be used as a geochemical tool to delineate the origin of sediments accumulated in hypersaline euxinic basins however the feasibility of the s c method requires a further check as to whether the rate of sulfate reduction could have been constrained even in environments of normal salinity

palaeomagnetic evidence for rotations and deformation in the nogueras zone central southern pyrenees spain a multicomponent palaeomagnetic remanence from the lower triassic buntsandstein redbeds of the central southern pyrenees has been interpreted as being composed of three components a low blocking temperature recent viscous magnetization l an intermediate blocking temperature eocene remagnetization i and a high blocking temperature lower triassic remanence h these palaeomagnetic results can be used in conjunction with structural evidence to identify poles of rotation during the development of the nogueras zone antiformal stack poles from individual sites reflect local deformation and folding including vertical rotation due to shearing between adjacent thrust sheets the i component was sometimes acquired syn tectonically during thrust motion and can be used to define intermediate stages of structural development results from sites located on a single thrust sheet no 7 indicate that it rotated by 45 clockwise during emplacement this is reflected in an easterly increase in displacement estimated from the construction of balanced cross sections thrust sheets appear to have been pinned close to the present day location of pont de suert during the later stages of structural development the arcuate path of thrust sheet motions and the potential movements in and out of cross section can lead to over and under estimates of minimum displacement when using line length cross section balancing techniques

uranium geochemistry of orca basin orca basin an anoxic brine filled depression at a depth of 2200 m in the northwestern gulf of mexico continental slope has been studied with respect to its uranium geochemistry uranium concentration profiles for four cores from within the basin were determined by delayed neutron counting uranium concentrations ranged from 2 1 to 4 1 ppm on a salt free and carbonate corrected basis the highest uranium concentrations were associated with the lowest percentage and 13c organic carbon values for comparison cores frm the brine filled suakin and atlantis ii deeps both in the red sea were also analyzed uranium concentrations ranged from 1 2 to 2 6 ppm in the suakin deep and from 8 0 to 11 0 ppm in the atlantis ii deep no significant correlation was found between uranium concentrations and organic carbon concentrations and 13c values for these cores although anoxic conditions are necessary for significant uranium uptake by non carbonate marine sediments other factors such as dilution by rapidly depositing materials and uranium supply via mixing and diffusion across density gradients may be as important in determining uranium concentrations in hypersaline basin sediments

the incorporation of uranium into diagenetic phosphorite abstract the behavior of u during the diagenetic formation of marine phosphorite has been modelled the model examines a dissolution reprecipitation replacement of skeletal hydroxyapatite calcium carbonate and earlier generated francolite by francolite the amount of organic matter consumed relative to the mass of francolite formed the replacement reaction progress and the concentration of u in the replaced phases are the important parameters which dictate the concentration of u in the phosphate rock a partition coefficient between apatite and interstitial solution was calculated and is u f 0 57 natural phosphorites have been examined and are discussed in the light of the proposed model the u mass balance in a recent phosphorite is in good accord with theoretical predictions differences in u concentrations between sea floor phosphorites are explained either by the original variation in the organic matter distribution in the corresponding sediments and or by mineralogical differences caco3 vs hydroxyapatite therein senonian phosphate rocks which were formed via the francolite francolite transformation demonstrate that during that process the organic matter content in the sediment was approximately 50 the model supports the idea that phosphorite rock formation is a multistage process

effects of vertical wind shear on the cumulus transport of momentum observations and parameterization abstract dynamical effects of organized cumulus convection on its environment with vertical wind shear are studied analyses of the wind field and momentum budget residual for mesoscale convective systems observed during sesame and pre storm reveal systematic differences in the vertical transport of horizontal momentum between mesoscale convective complex mcc and squall line cases in the mcc a distinct minimum in wind speed appears over the area of intense convection and the momentum budget residual acts to decelerate the environmental wind and to reduce the upper level vertical shear therefore the inferred vertical transport of momentum in the mcc is downgradient in the upper layer on the other hand in the squall line there is no wind speed minimum and the upper level vertical shear of the line normall component of the environmental wind increases as convection develops thus the vertical transport of momentum normal to the squall line is upgradient in the upper layer although the transport of

stable carbon isotope ratio variations of organic matter in orca basin sediments abstract orca basin is a highly reducing basin on the slope of the gulf of mexico stable carbon isotope ratios and total organic carbon percentages were determined for two cores within the basin and one control core outside the basin the results show that the organic carbon content of the basin cores is consistently 2 3 times greater than that of the control core the pleistocene holocene boundary indicated by a break in the 13 c depth profile occurs at a greater sediment depth in the basin cores than in the control core a small sampling interval has made it possible to detect an unexplained fine structure in the 13 c profile not previously observed

postdepositional enrichment of uranium in sediment from the bering sea abstract deep sea sediments were collected from the northern north pacific and the bering sea and separated into hcl soluble and hcl insoluble fractions these sediments were analyzed for their uranium and thorium concentrations and 234 u 238 u activity ratios by alphaspectrometry the mean concentration of total uranium in the oxic northern north pacific sediment was relatively low 1 25 ppm and showed little variation with sediment depth the concentration of total uranium in the surface sediment of the bering sea basin was also low 0 85 ppm similar to those of the northern north pacific sediment but it was higher 2 36 ppm in the strongly reducing sediment below 40 cm this increase in uranium concentration with depth is ascribed to higher quantities of hcl soluble uranium it is suggested that uranium diffuses through interstitial water and is postdepositionally precipitated during early diagenesis in the subsurface reducing environment a postdepositional precipitation rate of uranium in the bering sea basin sediment was estimated to be 28 g cm 2 103 yr 1 in the reducing bering sea basin sediment the concentration of total uranium in the layers enriched in manganese carbonate was 1 68 ppm which was slightly less than that of the other normal deep layer this depletion of uranium may be due to dilution with volcanic material of coarser texture

fold interference structures in thrust systems abstract the accommodation problems associated with the generation of interference folds in thrust belts are examined there are several ways in which interference folds may grow in thrust systems such as moulding on to non planar ramps or via the interaction of non coaxial structures the geometries of interference folds from thrust belts in spain and pakistan are described and form the basis of an analog model the model is used to quantify the volume of rock which must be accommodated during the growth of these structures mechanisms which might solve the inherent space problem are discussed the simplest geometrical solution would involve a mechanism which caused thickening in the fold hinges but this was not observed in the field field evidence is used to construct a linked fold and fault model which reconciles the absence of thickening in the interference fold hinge with the volume of material which must be accounted for

the geochemistry of uranium and thorium in coastal marine sediments and sediment pore waters pore water profiles of uranium and thorium isotopes in the muddy sediments of buzzards bay ma permit an assessment of the effect of diagenetic redox reactions on the geochemical behavior of these elements uranium shows a pronounced minimum pore water concentration 1 2 dpm kg near the sediment water interface 0 3 cm which coincides with the pore water fe maximum u concentrations increase with depth to a broad maximum which is greater than the overlying seawater value then decrease laboratory sediment tank experiments maintained without macrofauna also show the near interface minimum and increase and sediment incubation experiments show removal of u from the pore water to a constant value by about 40 days the 234u238u activity ratio is equal to the seawater value in all samples oxidation state separations of pore water u in hcl solution using anion exchange demonstrate that u is present in the pore water as u vi the coincidence of the pore water uranium and fe maximum is consistent with the hypothesis of reduction of u vi to u iv and removal from solution at about the same depth or pe as fe is reduced increases in pore water u with depth appear to be related to release of authigenic seawater u vi to solution possibly as alkalinity and ph increase and organic matter with which the u is associated is oxidized lower concentrations at depth in the sediment column may be linked to increases of effective u reducing agents like hydrogen sulfide in the pore water or to the activities of macrofauna in contrast pore water profiles of the long lived th isotopes 232th and 230th show low activities 02 dpm kg and relatively little change with depth although values are greater than those in the overlying water solid phase activities are similarly constant with depth and the distribution may be controlled by a sorption equilibrium between pore water and the solid phase the short lived isotope 234th shows greatest pore water activities in the upper 5 cm and is present at virtually zero activities elsewhere in the sediment column the upper few centimeters of the sediment generally contain excess 234th scavenged from the overlying water column and distributed by bioturbation as well as pore water fe and mn profiles which show maxima indicating reduction and dissolution of fe and mn oxyhydroxides the pore water 234th profile can be explained by release of 234th from the solid phase as femn oxide surface coatings are reduced and dissolved

modeling tropical precipitation in a single column abstract a modified formulation of the traditional single column model for representing a limited area near the equator is proposed this formulation can also be considered a two column model in the limit as the area represented by one of the columns becomes very large compared to the other only a single column is explicitly modeled but its free tropospheric temperature rather than its mean vertical velocity is prescribed this allows the precipitation and vertical velocity to be true prognostic variables as in prior analytical theories of tropical precipitation two models developed by other authors are modified according to the proposed formulation the first is the intermediate atmospheric model of j d neelin and n zeng but with the horizontal connections between columns broken rendering it a set of disconnected column models the second is the column model of n o renno k a emanuel and p h stone in the first model the set of disconnected column models is run with a fixed temperature

the terminology of structures in thrust belts abstract a review of structures and geometric relationships recognized in thrust belts is presented a thrust is defined as any contractional fault a corollary being that thrusts must cut up section in their transport direction flats are those portions of a thrust surface which were parallel to an arbitrary datum surface at the time of displacement and ramps are those portions of thrusts which cut across datum surfaces ramps are classified on the basis of their orientation relative to the thrust transport direction and whether they are cut offs in the hangingwall or footwall of the thrust lateral variations in the form of staircase trajectories are joined by oblique or lateral ramps which have a component of strike slip movement an array of thrusts which diverge in their transport direction may form by either of two propagation models these are termed piggy back propagation which is foreland directed and overstep propagation which is opposed to the thrust transport direction an array of thrust surfaces is termed an imbricate stack and should these surfaces anastamose upwards a duplex will result the fault bounded blocks are termed horses a duplex is bounded by a higher roof thrust and a lower floor thrust the intersection of any two thrust planes is termed a branch line thrusts can be classified on the basis of their relationship to asymmetric fold limbs which they cut a further classification arises from whether a particular thrust lies in the hangingwall or footwall of another one the movement of thrust sheets over corrugated surfaces or the local development of thrust structures beneath will fold higher thrust sheets these folds are termed culminations and their limbs are termed culmination walls accommodation of this folding may require movement on surfaces within the hangingwall of the active thrust these accommodation surfaces are termed hangingwall detachments and they need not root down into the active thrust this category of detachment includes dip slip hangingwall drop faults which are developed by differential uplift of duplex roofs and out of the syncline thrusts which develop from overtightened fold hinges back thrusts as well as forming as hangingwall detachments may also form due to layer parallel shortening above a sticking thrust or by rotation of the hangingwall above a ramp

biogenic hydrocarbon gases and sulfate reduction in the orca basin brine the composition of light hydrocarbon gases in the orca basin an anoxic hypersaline intraslope depression on the continental slope of the northern gulf of mexico indicates that both methane and ethane are biogenic in nature with a c1 c2 c3 ratio of 730 and a 13c of methane of 73 relative to the pdb standard the concentrations of methane 750 mm and ethane 1300 mm in the orca basin brine are higher than any other marine anoxic basin these high levels result not from high rates of productivity but from the long residence time of the brine in the basin due to its high stability toward mixing with overlying seawater 1 z 3 2m both methane and ethane show well mixed distributions in the brine these distributions probably result from convective mixing of the isohaline brine pool due to normal heat flow from the basin sediments methane and ethane maxima above the pycnocline at the brine seawater interface reflect in situ production and or consumption in the aerobic water column concurrent maxima in suspended particulate material distributions in this region suggest methane may be produced there in anaerobic microenvironments associated with the suspended matter reduced rates of anaerobic decomposition including sulfate reduction in the brine sediments are inferred from preserved sargassum fronds in the sediments vertical sulfate profiles in most cores and the sediment organic carbon content which is two to three times higher in sediments below the high salinity brine than in the normal gulf sediments nearby

conical folds and apparent rotations in paleomagnetism a case study in the southern pyrenees abstract the so called apparent rotation was defined as the angular deviation between a local paleomagnetic direction after the standard bedding correction and their corresponding paleomagnetic reference j geophys res 85 1980 3659 in this paper we make a theoretical exploration on this concept and we conclude that depending on the number sequence orientation and magnitude of the deformation axes that have affected to the rock volume the apparent rotation may be the addition of a vertical axis rotation plus a spurious rotation the later is an error whose origin is the inappropriate application of the bedding correction during the restoration which does not fit the reverse sequence of deformations then apparent rot s l spurious rot vertical axis rot conical folds are complex geometries that cannot be restored by using the bedding correction however appearance of apparent and spurious rotations has not been studied even though the presence of this kind of folds is very common in fold and thrust belts in this paper we show a way to restore these structures and its associated paleomagnetic data by means of forward modelling on a stereographic projection the modelling has to be based on a good characterization of the geometry fold axis orientation and understanding of the kinematics of the fold general modelling has also allowed us to predict the apparent rotation in conical synclines its magnitude depends on the semiapical angle and on the degree of development of the fold the sense of the rotation clockwise or counter clockwise will depend on the sense of rotation the fold axis the western external sierras provide an excellent case study of apparent rotations due to the presence of a conical fold in the footwall ebro foreland basin of the south pyrenean sole thrust in addition a vertical axis clockwise rotation up to 47 32 in average has been detected in the hagingwall an apparent rotation up to 28 20 in average is observed in the footwall of the structure when a simple bedding correction is used this deviation does not fit with the expected ebro basin direction reference and is caused by the effect of the riglos conical syncline developed by the flexure of the foot wall ramp of the south pyrenean sole thrust the forward modelling carried out considering the geometry and kinematics non significant rotations in the autochthonous foot wall of this structure predicts very well the paleomagnetic observations in the field geographic coordinates with angular departures of only 5 in average the only application of the bedding correction would introduce errors spurious rotations up to 21 12 in average related to the conical geometry that would not allow the differentiation of these distinct structural units

diagnosis of the surface momentum balance over the tropical pacific ocean abstract the purpose of this study is to evaluate the suitability of using linear drag as a proxy for surface friction in the observed climatological mean momentum balance over the tropical pacific ocean the linear drag parameterization of kinetic energy dissipation in the planetary boundary layer is widely used in simplified models of the tropical atmosphere and in numerous observational studies of the surface momentum balance climatological seasonal mean fields of sea level pressure and surface wind from the comprehensive ocean atmosphere data set are used to calculate the pressure gradient coriolis and acceleration terms in the momentum budget friction is derived as a residual it is found that when friction is parameterized as a linear dissipation of kinetic energy the damping time scale for the meridional wind is 2 3 times faster than the damping time for the zonal wind the preceding formulation fits the observations well especially in the trade wind regions it is suggested that the differ

pyritization of trace metals in anoxic marine sediments the pyritization of reactive trace elements in different anoxic marine sediments was investigated to determine the importance of factors such as h2s reactive fe pyrite content and salinity in controlling this process the areas studied included anoxic sulfidic sediments baffin bay a hypersaline coastal lagoon from texas and green canyon a hemipelagic oil seepage area anoxic nonsulfidic sediments with high sedimentation rates atchafalaya bay mississippi delta system hemipelagic anoxic nonsulfidic sediments with low sedimentation rates gulf of mexico shelf and slope and orca basin an euxinic hypersaline basin and organic rich marsh sediments atchafalaya bay results indicate that the degree of trace metal pyritization dtmp of all trace metals except cd increased with increasing degree of pyritization dop irrespective of the type of sedimentary environment involved however for as hg and mo the dtmpdop values were generally above the 1 1 ratio line whereas the transition metals co cu mn and ni displayed a close to linear increase in dtmp with dop and moderate incorporation into pyrite chromium and the class b metals pb and zn were also gradually incorporated into the pyrite phase but without reaching the dtmp levels exhibited by the transition metals cadmium was not incorporated to a significant extent these results are consistent with the chemical attributes of these different classes of trace elements availability of dissolved trace metals and organic matter content are apparently important factors controlling the incorporation of co cr cu and ni into pyrite in anoxicsulfidic fe poor and h2s rich environments

fold interference structures and coaptation folds abstract coaptation folds are bends in rock layers formed at the junctions of intersecting folds in a manner analogous to the line of junction between two intersecting cylinders they form purely as a geometric consequence of the fitting together of the fold forms and have no tectonic significance however the presence of unidentified coaptation folds may lead to misinterpretation of fold geometry and structural history interference patterns affected by coaptation folds are modified versions of ramsay s 1962 type 1 basin and dome patterns but form where the three dimensional shape of the interference structure is a convoluted conical shape rather than a simple conical shape

investigating the kinematics of local thrust sheet rotation in the limb of an orocline a paleomagnetic and structural analysis of the esla tectonic unit cantabrian asturian arc nw iberia the esla tectonic unit lies along the southern boundary of the cantabrian asturian arc a highly curved foreland fold thrust belt that was deformed during the final amalgamation of the pangea supercontinent previous structural and paleomagnetic analyses of the cantabrian asturian arc suggest a two stage tectonic history in which an originally linear belt was bent into its present configuration creating an orocline the esla tectonic unit is a particularly complex region due to the interaction of rotating thrust sheets from the southern limb of the arc and the southward directed thrusts of the picos de europa tectonic domain during late stage north south shortening and oroclinal bending these structural interactions resulted in intense modification of early phase thin skinned tectonic structures that were previously affected by a deeper out of sequence antiformal stack that passively deformed the early thrust stack a total of 75 paleomagnetic sites were collected from the portilla and santa lucia formations two carbonate passive margin reef platform units from the middle devonian similar to other regions of the cantabrian asturian arc esla unit samples carry a secondary remanent magnetization that was acquired after initial thrusting and folding of variscan deformation in the late carboniferous protracted deformation during late stage oroclinal bending caused reactivation of existing thrust sheets that include the esla and younger corniero and valbuena thrusts when combined with existing structural data and interpretations these data indicate that the present day sinuosity of the esla unit is the consequence of both secondary rotation of originally linear features in the western esla exposures e g frontal thrusts and secondary modification and tightening of originally curvilinear features in the eastern esla exposures e g hanging wall lateral oblique ramps differences in structural style between the esla and other tectonic units of the arc highlight the complex kinematics of oroclinal bending which at the orogen scale buckled an originally linear north south in present day coordinates trending cantabrian asturian thrust belt during the final stages of pangea amalgamation

permian palaeomagnetism of east kazakhstan and the amalgamation of eurasia summary most of kazakhstan belongs to the ural mongol belt the tectonic evolution of which is poorly understood as demonstrated by disparate tectonic models suggested thus far we undertook a palaeomagnetic study of upper permian basalts and andesites from two localities in east kazakhstan in order to evaluate the final stages of the evolution of this belt and eurasian amalgamation thermal demagnetization revealed a single pre tilting characteristic component of ubiquitously reversed polarity from all samples the mean declination of this remanence from one locality agrees rather well with the permian european palaeomeridian whereas that from the other is clockwise rotated by 28 8 the overall mean inclination of 49 4 differs by 9 7 4 2 from the reference inclination calculated for our localities from the eurasian mean pole for the 245 260 ma interval and is in agreement with 260 275 ma data we account for the observed pattern by either a slightly erroneous rock age lithologies are somewhat older than indicated by geological data or non dipole octopole components of the geomagnetic field because significant relative motion of the study area with respect to eurasia is not demonstrated we conclude that welding of kazakhstan europe and siberia was essentially completed by mid permian time

fold interference structures the influence of layer competence contrast using the geometrical properties of curved surfaces it can be predicted that the geometries of natural refolded folds should differ from the well known forms resulting from superposed shear folds if the sequence undergoing folding contains competent horizons the simple dome and basin patterns expected from kinematic considerations are incompatible with constant bed length folding isometric deformation isometric deformation requires that a flat sheet folds to give a surface consisting of points of zero gaussian curvature like for example the surfaces of cylindrical and conical folds we suggest that the coaptation folds recently recognized by stauffer 1988 are topologically necessary crumples on the flanks of domes and basins rather than bends at the intersection of two oblique intersecting folds and should be known as curvature accommodation folds

thermally driven motions in an equatorial β plane hadley and walker circulations during the winter monsoon abstract the linearized shallow water equatorial plane equation was solved for a subset of approximate solutions applicable to thermally driven large scale tropical circulation in particular the heat induced monsoon circulations during southeast asian northeasterly cold surges are investigated it was demonstrated that the response of the tropical atmosphere to a localized heat source consists of forced rossby waves propagating westward and kelvin waves eastward along the equator away from the region of forcing in general for any source sink distribution the heat induced motion can have the characteristics of a walker type 0 at the equator or a hadley type u 0 at the equator response or a combination of both depending on the latitudinal location of the forcing away from the equator a forcing corresponding to the sudden imposition of mass at the lower layer or equivalently in our model a rapid cooling of the lower troposphere produces a sudden local surface pressure rise and strong an

geochemical evidence for anoxic deep water in the arabian sea during the last glaciation various paleoceanographic studies have indicated that the deep ocean was probably depleted in dissolved oxygen during the last glacial period approximately 18 kyr b p delta sup 18 o stage 2 compared to present time however direct evidence of low oxygen content in the deep waters has been lacking here the authors report geochemical evidence of near anoxic conditions in the deep arabian sea during the entire last glacial cycle delta sup 18 o stages 2 3 and 4 anoxia is inferred from the concomitant enrichment of organic carbon and authigenic uranium in the glacial sections of a core from the deep eastern arabian sea the anoxic conditions during the last glacial period probably caused by a change in deep water circulation evidently enhanced preservation of organic matter and simultaneous removal of uranium from seawater 57 refs 3 figs 2 tabs

linear response of a stratified tropical atmosphere to convective forcing abstract the three dimensional response of the tropical atmosphere to an isolated heat source is investigated using a primitive equation model linearized about a resting basic state on an equatorial plane the model equations are solved by applying vertical and horizontal normal mode transforms the thermal forcing was chosen to simulate the convection which occurs over tropical south america during the southern hemisphere summer the vertical dependence of the forcing is such that the heating is zero at the top and bottom boundaries with a variable level of maximum beating the model results with steady forcing are compared with the average circulation over tropical south america for a 19 day period in the southern hemisphere summer of 1979 and it is shown that the model reproduces many aspects of the observed circulation the partition of the energy of the steady state response between the vertical modes is calculated and it is shown that the internal mode with an equivalent depth of 208 m is domina

a consistent model for the large scale steady surface atmospheric circulation in the tropics the authors present a new model of the tropical surface circulation forced by changes in sensible heat and evaporative flux anomalies that are associated with prescribed sea surface temperature anomalies the model is similar to the lindzen and nigam ln boundary layer model also driven by the above flux anomalies but here since the boundary layer is assumed well mixed and capped by an inversion the model reduces to a twolayer reduced gravity system furthermore the rate of exchange of mass across the boundary layer free atmosphere interface is dependent on the moisture budget in the boundary layer when moist convection is diagnosed to occur detrainment operates on the timescale associated with the life cycle of deep convection approximately eight hours otherwise the detrainment is assumed to be associated with the mixing out of the stable tropical boundary layer which has a timescale of about one day the model provides a diagnostic estimate of the anomalies in precipitation however it is assumed that the latent heat is released above the boundary layer and it drives a circulation that does not impact the boundary layer the authors discuss the derivations of the gill zebiak gz and lindzen nigam models and highlight some apparent inconsistencies between their derivation and the values of several of the parameters that are required for these models to achieve realistic solutions for the circulations then the new reduced gravity boundary model equations are rewritten in the form of the gz and ln models using realistic values for the parameters in the new model geometry it is shown that the constants combine in the rewritten equations to produce the physically doubtful constants in the gz and ln models hence the reason for the apparent success of these models

palaeomagnetic analysis of plunging fold structures errors and a simple fold test abstract the conventional corrections for bedding dip in palaeomagnetic studies involve either untilting about strike or about some inclined axis the choice is usually governed by the perceived fold hinge orientation while it has been recognised that untilting bedding about strike can be erroneous if the beds lie within plunging fold structures there are several types of fold which have plunging hinges but whose limbs have rotated about horizontal axes examples are interference structures and forced folds restoration about inclined axes may be incorrect in these cases the angular errors imposed upon palaeomagnetic lineation data via the wrong choice of rotation axis during unfolding are calculated here and presented for lineations in any orientation which could be associated with an upright symmetrical fold this extends to palaeomagnetic data previous analyses which were relevant to bedding parallel lineations this numerical analysis highlights the influence of various parameters which describe fold geometry and relative lineation orientation upon the angular error imparted to lineation data by the wrong unfolding method the effect of each parameter is described and the interaction of the parameters in producing the final error is discussed structural and palaeomagnetic data are cited from two field examples of fold structures which illustrate the alternative kinematic histories both are from thin skinned thrust belts but the data show that one is a true plunging fold formed by rotation about its inclined hinge whereas the other is an interference structure produced by rotation of the limbs about non parallel horizontal axes since the angle between the palaeomagnetic lineations and the inclined fold hinge is equal on both limbs in the former type of structure but varies from limb to limb in the latter a simple test can be defined which uses palaeomagnetic lineation data to identify rotation axes and hence fold type this test can use pre or syn folding lineations and could be useful in areas of non coaxial folding

palaeomagnetic investigation on early middle triassic sediments of the north china block a new early triassic palaeopole and its tectonic implications summary palaeomagnetic and rock magnetic study is reported of early middle triassic terrestrial sediments from the jiaocheng and yushe areas shanxi province thermomagnetic analysis indicates that magnetite and haematite are the main magnetic carriers thermal demagnetization shows that the majority of early triassic specimens from the jiaocheng area contain an intermediate temperature component itc between 500 250 c and a high temperature component htc between 500 680 c the itc has a negative fold test and might be a cretaceous or recent overprint the htc contains both normal and reversed polarities with positive fold and c level reversal tests we interpret the htc as primary magnetization unfortunately we failed to isolate a meaningful mean direction from middle triassic rocks of the yushe area new early triassic palaeopole from the jiaocheng area confirms an 10 counter clockwise displacement of the taihang early triassic palaeopoles relative to their ordos counterparts this study thus suggests that the north china block ncb has generally behaved as rigid block since the early triassic but there might be an 9 counter clockwise rotation of the taihang terrane with respect to stable ncb in the late triassic the slight rotation of the taihang terrane does not bear significantly on what has been previously concluded concerning the mesozoic history of the ncb south china block scb collision however triassic palaeomagnetic data from stable ncb indicate that the east end of the ncb and scb did not undergo large convergence or significant opposite latitudinal displacement after the initial contact at the end of the late permian

two dimensional refold interference patterns abstract when a rock undergoes two generations of folding complex three dimensional refolded structures result if such a structure is then sectioned two dimensional interference patterns result these patterns have been discussed before but the incredible variety and complexities of these patterns can be shown only with a large number of diagrams using a computer simulation various refolded structures have been sliced at every unique 30 combination of strike and dip thirty sections per structure the characteristics of the patterns observed are discussed and recurring recognizable patterns are identified

margin parallel translation in the western pacific paleomagnetic evidence from an allochthonous terrane in japan abstract a new paleomagnetic study illustrates latitudinal translation of ribbon shaped continental fragments along the western margin of the pacific ocean though tectonic translations have long been recognized as prominent features in the eastern pacific margin i e north american cordillera we present new quantitative evidence for similar margin parallel motion through large scale strike slip faulting in the western pacific margin the kurosegawa terrane in southwest japan is an attenuated tectonic sliver and considered to be allochthonous with respect to the main part of southwest japan late triassic and early cretaceous sedimentary rocks from the terrane yielded paleolatitudes of 4 n and 18 n respectively based on paleomagnetic data of the kurosegawa terrane and plate reconstructions of east asia we suggest that the terrane was the easternmost element of the south china block at least from the late triassic to the early cretaceous the terrane was then translated 1500 km northward from the continental margin to its present position associated with sinistral strike slip movement along the east asian continental margin in mid to late cretaceous times the average displacement rate is calculated to be 7 cm yr and is comparable to rates reported for the eastern pacific margin

rotation velocity of a thrust a paleomagnetic study in the external sierras southern pyrenees abstract an accurate calibration of chronologic and geologic data biostratigraphic and magnetostratigraphic with gpts has been performed for the middle and upper eocene syntectonic deposits in the surrounding areas of the pico del aguila anticline south pyrenean external sierras this calibration shows a variable sedimentation rate that changes from 4 8 cm ka at the bottom to 34 cm ka at the top with a maximum of 58 6 cm ka in the upper part of the studied stratigraphic section and gives a fine and continuous chronologic frame to understand the rotational kinematics of the infrajacent thrust system at the same time a detailed paleomagnetic study has been carried out 14 sites and a total of 157 thermally demagnetised samples to know the amount of rotation in the area taking advantage the tape recording effect of the syntectonic materials these samples display a chrm between 250 and 400 c both polarities that agree very well with the sequence of magnetostratigraphic zones and consistency with the magnetic reference due to the decreasing value of the magnetic declination from 46 to 3 of the primary components checked by fold and reversal test the calibration has been useful to assign an absolute age to every rotation value from 40 32 to 37 05 ma a time versus rotation curve does not show significant differences of rotation between the flanks of the pico del aguila anticline less than 8 thus the clockwise rotations detected in the study area result from the kinematics of the imbricate basal thrust system which is also responsible for the development of detachment folds e g pico del aguila anticline in a time against rotation graph the simplest fit for the overall rotation values is given by a linear segment rotation velocity of 10 ma however the best fit is given by a segment of a parabolic curve this pattern implies that there were changes of the rotation velocities between 21 ma and 5 3 ma that in this segment of the external sierras were caused by an acceleration of the rotational movement between 9 ma2 and 5 5 ma2 the thrust sheet shows maximum values of at least 40 of clockwise rotation

seasonal migration of itcz precipitation across the equator why can t gcms simulate it 1 the secondary meridional circulation induced by convective momentum transport cmt within the ascending branch of the hadley circulation is a missing dynamical mechanism that can cause common failure of general circulation models gcms in simulating seasonal migration of the intertropical convergence zone itcz precipitation maximum across the equator this failure is manifested by the model bias that the precipitation peak remains north of the equator during november march the cmt induced secondary circulation characterized by strong downward motion along the equatorial belt and upward motion south and north of the belt tends to modify the meridional distribution of precipitation with the strongest impacts during boreal winter and spring a 20 year gcm simulation with the cmt parameterization successfully reproduces the observed seasonal migration of the itcz precipitation across the equator with the peaks near 8 n during boreal summer and near 8 s during boreal winter

parametrization of momentum transport by convection ii tests in single column and general circulation models diagnostics derived from cloud resolving model simulations in part i of this study relating to the vertical transport of horizontal momentum by convection are used to develop a parametrization of convective momentum transports for deep convection based upon the mass flux convection scheme discussed by gregory and rowntree the importance of cloud pressure gradients to the flow within the cloud is emphasised and a simple method of representing their effect is suggested the scheme is able to reproduce the fluxes derived from the cloud resolving model studies where cloud organization by the flow is unimportant inclusion of the parametrization in a version of the meteorological office unified model demonstrates that convective momentum transports play a large role in the momentum balance of the atmosphere generally simulation of the mean atmospheric circulation by the unified model is improved by the inclusion of such transports

the distribution and behaviour of 230th and 231pa at an ocean margin baja california mexico uranium th and pa isotopes were measured in sediments collected by box core along a transect normal to the baja california continental margin six cores were analyzed ranging in depositional environment from manganese nodule bearing pelagic red clay to hemipelagic sediments displaying mn reduction in the upper 5 cm in the hemipelagic cores solid phase mn peaks due to diagenetic remobilization occur within the upper layers which are well mixed with respect to unsupported sup 230 th and sup 231 pa the fact that sup 230 th and sup 231 pa are not concentrated at the mn peaks suggests that little mobility of these nuclides occurs within the sediment column unsupported sup 230 th sup 231 pa activity ratios in the biomixed layer of the sediments range from 10 9 to 6 6 generally decreasing towards the inshore stations the flux of sup 230 th and sup 231 pa across the sediment water interface is almost in balance with the theoretical water column supply in the most distal core but rapidly increases inshore this evidence from the sediment column confirms that enhanced sup 230 th and sup 231 pa removal occurs at ocean margins and that sup 231 pa is removed from the water column to the sediments in preference to sup 230 th

formation of hematite in the euxinic orca basin northern gulf of mexico abstract the orca basin is a depression in the northern continental slope of the gulf of mexico which is partially filled with hypersaline anoxic brine pool sediment cores taken from this basin show millimeters to centimeters thick red layers within typical dark anoxic muds chemical and x ray mineralogical analyses reveal that the red laminae are invariably enriched in iron in the form of hematite they are formed primarily by interaction of ferrous iron in the brine with dissolved oxygen from overlying seawater during isolated incidences of enhanced mixing a cross the normally stable oxic anoxic boundary the presence of hematite red layers within generally anoxic sediment cores would complicate interpretation in the sedimentary record and limit the usefulness of hematite as an indicator for environment of deposition it also demonstrates that the close association of iron formation with interbedded sulphic shales observed in many proterozoic iron formations is practically feasible the processes associated with the formation of hematite in red layers might affect the extent and nature of organic matter eventually deposited in the basin as well a fact of considerable significance for petroleum source bed formation

paleomagnetic results in support of a model for the origin of the asturian arc abstract paleomagnetic directions have been determined at 17 cambrian and 28 carboniferous limestone sites distributed along the asturian arc of the hercynian fold belt in northwestern spain the stable vectors are carried by hematite in all cases and also by magnetite in some grey carboniferous limestones a secondary component of magnetization is usually removed well below 400 c and the higher temperature component is taken to be the characteristic direction the structure at each site was carefully evaluated in order to make optimum local tectonic corrections in addition the data must be corrected for rotations about a vertical axis to allow for a phase of radial folding superimposed on earlier structures the corrected paleomagnetic declinations are found to vary systematically along the arc of the fold belt consequently paleomagnetic data from the asturian arc should not be included in compilations used for the construction of a paleozoic apparent polar wander path the paleomagnetic data allow us to distinguish between different tectonic models for the evolution of the asturian arc a two stage model for the development of the present curvature is favored part of the curvature appears to be primary preceding the hercynian deformation the first stage of the model involved rotations of thrust sheets during their emplacement producing a more tightly curved arc than the original form in a second stage the development of radial folds further tightened the curvature of the arc both stages result in clockwise rotations in the north and anticlockwise rotations in the south

paleomagnetism of the santa fe group central brazil implications for the late paleozoic apparent polar wander path for south america 1 paleomagnetic and rockmagnetic data are reported for the floresta formation santa fe group of the sanfranciscana basin central brazil this formation represents the permo carboniferous glacial record of the basin and comprises the brocoto diamictites and flow diamictites brejo do arroz red sandstones and shales with dropstones and invertebrate trails and lavado red sandstones members which crop out near the cities of santa fe de minas and canabrava minas gerais state both brejo do arroz and lavado members were sampled in the vicinities of the two localities alternating field and thermal demagnetizations of 268 samples from 76 sites revealed reversed components of magnetization in all samples in accordance with the permo carboniferous reversed superchron the magnetic carriers are magnetite and hematite with both minerals exhibiting the same magnetization component suggesting a primary origin for the remanence we use the high quality paleomagnetic pole for the santa fe group 330 9 e 65 7 s n 60 95 4 1 k 21 in a revised late carboniferous to early triassic apparent polar wander path for south america on the basis of this result it is shown that an early permian pangea a type fit is possible if better determined paleomagnetic poles become available

distribution and origin of uranium in surficial sediments from the arabian sea abstract uranium data is reported for sediments from various physiographic tectonic provinces in the arabian sea the distribution pattern of u brings out various marine processes and environmental conditions prevalent in the area reducing environment of the owen basin hydrothermal exhalations from the carlsberg ridge bathymetric control of u geochemistry etc uranium seems to have four origins in different parts of the arabian sea hydrogenous hydrothermal biogenic and terrigenous

restoring paleomagnetic data in complex superposed folding settings the boltana anticline southern pyrenees abstract complex kinematic scenarios in fold and thrust belts often produce superposed and non coaxial folding interpretation of primary linear indicators must be based on a careful restoration to the undeformed stage following the reverse order of the deformation events therefore sequential restoration to the ancient coordinate system is of key importance to obtain reliable kinematic interpretations using paleomagnetic data in this paper a new paleomagnetic study in the western flank of the boltana anticline southern pyrenees illustrates a case study of a complex tectonic setting having superposed non coaxial folds the first stage of nw se folding linked to the oblique boltana anticline took place during lutetian times the second stage was linked to the vertical axis rotation and placed the boltana anticline in its present day n s configuration our data support a long lasting lutetian to priabonian period with main rotational activity during the bartonian priabonian other authors support a var coeval with anticlinal growth the third stage resulted in southwards tilting related to the emplacement of the n120e striking guarga basement thrust oligocene early miocene based on this deformational history a sequential restoration was applied and compared with the classic bedding correction at the site scale single bedding correction gives errors ranging between 31 and 31 in the estimation of vertical axis rotations at the locality scale in sites grouped in three folds from w to e arbella planillo and san felizes the bedding corrected data display rotation values in accordance with those found in the ainsa basin by other authors sequential restoration based on the afore mentioned evolution in three steps improves both some locality means and the internal consistency of the data therefore reasonably constrained sequential restoration becomes essential to reconstruct the actual history of superposed folding areas

a computed tomography approach for understanding 3d deformation patterns in complex folds abstract analog models are an important tool for understanding complexly folded and faulted geological structures in this paper we propose the use of x ray computed tomography to accurately reconstruct the geometry of analog models using an orthogonal reference system and to completely characterize deformation patterns within the modeled structure in 3d the rheology and radiological contrast of various different materials have been studied showing that eva sheets are a good choice to model buckling layers after considering various possibilities to define the reference system we opted to screen print two orthogonal sets of parallel lines on the surfaces using minium lead tetroxide the model was then built with gocad using a series of ct slices that can be closely spaced this kind of model allows us to reconstruct the volume distribution of strain ellipsoids and can be very accurate and useful to ascertain the orientation of folded lineations in complex structures as well as to characterize the expected deformation on the surfaces we have built a simple analog model inspired in the balzes anticline located in the external sierras southern pyrenees to illustrate the potential of the technique and to analyze the deformation patterns of this complex curved fold that has accommodated significant magnitudes of vertical axis rotation during its formation

a simple model of the climatology and variability of the low level wind field in the tropics abstract a simple model of the low level wind field in the entire tropics is presented the dynamics are the same as those within the familiar gill model i e linear steady state contained within a single vertical mode and damped by rayleigh friction convective atmospheric heating can occur if a lifted air parcel is buoyant relative to its surroundings and the heating is computed with reference to the cloud model of yanai et al radiative cooling is represented by a newtonian cooling to an equilibrium lapse rate the model is forced by surface temperature and humidity a qualitatively correct representation of the climatological flow is achieved the main differences between model and observations relate to the model s inability to reproduce the intensity and limited spatial scale of the convergence zones model simulations of anomalous circulations are subject to the same limitations problems related to the lack of an explicit boundary layer in the model the poor representation of radiation and

organic rich sediments in brine filled shaban and kebrit deeps northern red sea the element compositions si ca and al of up to 2 1 1 ka old sediments in about 10 in long cores from the southern basin of the shaban and kebrit deeps in the northern red sea allowed a classification of major sediment types in carbonate sands and muds and siliceous oozes a feooh enriched sediment horizon and a few samples with high zn values in the kebrit core indicate a hydrothermal origin probably near the brine sea water interface with subsequent transport of hydrothermal compounds into the deep sediments high organic carbon contents up to 8 4 are positively correlated with the ba concentrations which suggests that high bioproductivity and rapid deposition c 14 dating suggests a sedimentation rate near 70 cm ka led to the formation of sapropelic sediments between 11 8 and 13 6 ka younger dryas organic petrological observations showed that the sediment organic material largely consists of 20 gm sized roundish fecal pellets intimate mixtures of organic matter and inorganic constituents and bituminite terrestrial organic matter pollens of land plants fusinite etc is very rare in the sediment cores from both deeps organic geochemical investigations of kerogens and organic extracts show that a significant hydrothermal hydrocarbon production did not occur in near surface sediments of the shaban and kebrit deeps rock eval pyrolysis of kerogens characterised the organic matter to be of type ii quality the delta c 13 values of the kerogens from the most prominent sapropel in the shaban deep indicate an enrichment of c 12 rich nutrients in the water column during postglacial sapropel formation in the younger dryas the n alkane spectra are dominated by short chain lengths between n c 15 and n c 25 prevailing n c 15 to n c 25 alkanes in low mature sediments are indicative of algal and microbial source pristane phytane ratios are generally low i to similar to 1 which suggests that anoxic conditions prevailed within the anaerobic brine filled deeps for the whole time covered by the sediments this again indicates that sapropel formation was caused by high bioproductivity in the northern red sea rather than episodic stagnation with better preservation of the organic matter long chain alkenones and sterols are the dominating compounds of the lipid fraction cholesterol contents in the sediment cores reflect phases of eukaryotes production in the water column whereas the positive correlations of dinosterol with toc and the amounts of total extract suggests that the major organic carbon source in the northern red sea during postglacial high productivity stages were dinoflagellates another important carbon source however is indicated by the occurrence of 22 29 30 trisnorhopan 21 one tnh although the formation of tnh from its precursors is not fully understood this compound probably results from microbial degradation of intact bacteriohopanepolyols bhp which can be used as indicators for bacterial abundances and phyla tnh is most likely produced at the brine sea water interface where sedimenting organic matter accumulates and if the redoxcline corresponds to the density gradient the organic matter is subjected to efficient aerobic bacterial degradation processes however during high bioproductivity stage younger dryas the redoxcline was probably higher in the water column and thus a significant tnh production at the brine sea water interface did not occur at times of sapropel formation in the northern red sea deeps c 2007 elsevier b v all rights reserved

parametrization of momentum transport by convection i theory and cloud modelling results summary the theory of the mass flux approach to parametrization of convective momentum transport is presented a cloud resolving model is used to simulate momentum transport by ensembles of deep convective clouds in two very different regimes a mid latitude cold air outbreak and tropical convection forced by convergence idealized unidirectional wind profiles are used to simplify interpretation of the results diagnostics relevant to the parametrization problem are presented and it is shown that for both regimes the approximations inherent in the parametrization equations are reasonable the pressure gradients inside clouds play an important role in determining horizontal velocities in the clouds for the cold air outbreak with linear shear the results suggest that these pressure gradients are proportional to the shear and to the up downdraught mass fluxes sensitivity studies suggest that the results are not very sensitive to resolution or parametrization of subgrid scale processes giving some confidence that the results are reasonably accurate for the tropical case with a low level jet the pressure gradients change sign with the wind shear in part i1 of this paper these results will be used to develop and validate a mass flux parametrization of convective momentum transport which is tested in single column and global versions of the meteorological office unified model

systematic multiscale models for the tropics systematic multi scale perturbation theory is utilized to develop self consistent simplified model equations for the interaction across multiple spatial and or temporal scales in the tropics one of these models involves simplified equations for intraseasonal planetary equatorial synoptic scale dynamics ipesd this model includes the self consistent quasi linear interaction of synoptic scale generalized steady matsuno webster gill models with planetary scale dynamics of equatorial long waves these new models have the potential for providing self consistent prognostic and diagnostic models for the intraseasonal tropical oscillation other applications of the systematic approach reveal three different balanced weak temperature gradient wtg approximations for the tropics with different regimes of validity in space and time a synoptic equatorial scale wtg sewtg a mesoscale equatorial wtg mewtg which reduces to the classical models treated by others and a new seasonal planetary equatorial wtg spewtg both the spewtg and mewtg model equations have solutions with general vertical structure yet have the linearized dispersion relation of barotropic rossby waves thus these models can play an important role in theories for midlatitude connections with the tropics the models are derived both from the equatorial shallow water equations in a simplified context and also as distinguished limits from the compressible primitive equations in general

redox dynamics in the chesapeake bay the effect on sediment water uranium exchange the effect of seasonal variations in productivity and redox dynamics on the sediment water exchange of uranium was investigated on a twelve cruise time series in the chesapeake bay the deep waters of the bay undergo seasonal anoxia in response to high primary productivity and water column stratification from late spring to early fall dissolved oxygen was used to monitor water column redox conditions and dissolved iron manganese and sulfide were measured to monitor sediment redox conditions dissolved 238u was measured in the water column and sediment porewaters to monitor water column sediment exchange uranium incorporation in bay sediments results from two distinct processes productivity dependent scavenging from the water column and redox dependent cycling of uranium between sediments and bottomwater uranium is removed from surface waters of the bay by scavenging with biodetritus during periods of high primary productivity bottomwater and sediment redox conditions determine whether this particle bound uranium is buried or released to overlying water particulate uranium is released to bottomwaters and porewaters during the degradation of biodetritus and oxidation of authigenic uranium low oxygen in bottomwaters in the summer results in minimal exchange of uranium between the sediments and bottomwater due to the stability of reduced u iv high bottomwater oxygen concentrations associated with bay turnover in the fall results in release of authigenic uranium by oxidation to the soluble vi form enrichment of uranium in fall bottomwater suggests that authigenic uranium is very labile when exposed to oxic environmental conditions this process is enhanced by physical mixing when anoxic sediments are resuspended into the oxic bottomwaters