structural and rheological features of the western liaoning metamorphic core complex corridor indications for late mesozoic extension of the eastern north china craton abstract the xingcheng taili ductile shear zone and yiwulushan metamorphic core complex formed during crustal extension of the eastern north china craton the ene trending xingchegn taili sinistral ductile shear zone developed along the margins of the western liaoning metamorphic core complex corridor within upper greenschist to lower amphibolite facies grade metamorphic conditions shearing was associated with two different ductile deformation events in the yiwulushan metamorphic core complex i e 1 an earlier dextral shearing and 2 later sinistral shearing the earlier dextral ductile shear zone is mainly characterized by simple shear dominated general shear with l s and ls tectonites under upper greenschist to lower amphibolite facies conditions the orientation and fabrics of l s tectonites indicate that the later ductile deformation consists of almost equally simple and pure shear and constrains a low middle temperature sinistral shear within upper greenschist facies grade conditions the estimation of rock rheological parameters from dynamically recrystallized grain sizes of quartz indicates that the high temperature shear zone has formed under lower stress conditions and higher strain rates while opposite features exist in the lower temperature shear zone the initiation of deformation of the western liaoning metamorphic core complex corridor might have started between 136 ma and 120 ma and its termination time was at ca 100 ma the ne ene strike slip ductile deformation in the western liaoning metamorphic core complex corridor within the eastern block of the north china craton was resulted from roll back of the subducting pacific plate beneath the north china craton along the eastern asian margin during early cretaceous times

large scale dynamics of sandy coastlines diffusivity and instability 1 the dynamics of small amplitude perturbations of an otherwise rectilinear coastline due to the wave driven alongshore sediment transport is examined at large time and length scales years and kilometers a linear stability analysis is performed by using an extended one line shoreline model with two main improvements 1 the curvature of the coastline features is accounted for and 2 the coastline features are assumed to extend offshore as a bathymetric perturbation up to a finite distance for high incidence angles instability is found in accordance with ashton et al 2001 however it is seen that instability is inhibited by high waves with long periods and gently sloping shorefaces so that in this case the coastline may be stable for any angle similarly there is no instability if the bathymetric perturbation is confined very close to the coast it is found that the traditional linearized one line model larson et al 1987 tends to overpredict the coastline diffusivity the overprediction is small for the conditions leading to a stable coastline and for moderate incidence angles but can be very dramatic for the conditions favoring instability an interesting finding is that high angle waves instability has a dominant wavelength at the linear regime which is in the order of 4 15 km one to two orders of magnitude larger than the length scale of surf zone rhythmic features intriguingly this is roughly the same range of the wavelength of some observed shoreline sand waves and in particular those observed along the dutch coast a model application to this coast is presented

jurassic earliest cretaceous tectonostratigraphic evolution of the erlian basin northeast china records of polyphase intracontinental deformation in northeast asia abstract the erlian basin is an important part of the late mesozoic extensional basin system in northeast asia the basin contains thick jurassic lower cretaceous rocks and provides excellent opportunities to understand intracontinental deformation in northeast asia during the late mesozoic however the jurassic early cretaceous evolution of the basin and associated driving mechanisms remain disputed based on 13 new zircon u pb ages for the jurassic lowest cretaceous strata in the erlian basin the correlation of jurassic lowest cretaceous strata between the erlian basin and the yan shan is reestablished and a high precision chronostratigraphic framework is presented the aqitu qiha formations are ascribed to the aalenian early bathonian ca 174 167 ma the xing anling group to the oxfordian early kimmeridgian ca 163 153 ma the hugejiletu formation to the tithonian early valanginian ca 151 139 ma and the aershan formation to the valanginian ca 138 ma combined with seismic reflection profiles the jurassic earliest cretaceous tectonostratigraphic evolution of the erlian basin is reconstructed and five major phases of deformation are revealed these deformation phases include aalenian early bathonian initial extension late bathonian callovian compression oxfordian early kimmeridgian extension late kimmeridgian earliest valanginian compression and valanginian extension integrated with geological evidences from peripheral regions of the erlian basin potential driving mechanisms related to far field tectonic events along asian margins are suggested for each of these deformation phases

nearshore oblique sand bars 1 the coupling between hydrodynamics and the evolving topography in the surf zone has been theoretically examined for oblique wave incidence it is shown that positive feedback can lead to the initial growth of several types of rhythmic systems of sand bars the bars can be down current oriented or up current oriented which means that the offshore end of the bar is shifted down current or up current with respect to the shore attachment in the limit of strong current compared to wave orbital motion very oblique down current oriented b ars are obtained with a spacing of several times the surf zone width when wave orbital motions are dominant systems of up current oriented bars and crescentic down current oriented bars appear with spacings of the order of the surf zone width the latter feature consists of alternating shoals and troughs at both sides of the break line with the inner shoals being bar shaped and oblique to the coast the growth e folding time of the bars ranges from a few hours to a few days and it is favored by constant wave conditions the range of model parameters leading to growth corresponds to intermediate beach states in between the fully dissipative and the fully reflective situations preliminary comparison with field observations shows qualitative agreement

further paleomagnetic results from the 155 ma tiaojishan formation yanshan belt north china and their implications for the tectonic evolution of the mongol okhotsk suture abstract a new paleomagnetic study on well dated 155 ma volcanic rocks of the tiaojishan formation fm in the northern margin of the north china block ncb has been carried out a total of 194 samples were collected from 26 sites in the yanshan belt areas of luanping beipiao and shouwangfen all samples were subjected to stepwise thermal demagnetization after removal of a recent geomagnetic field viscous component a stable high temperature component htc was isolated the inclinations of our new data are significantly steeper than those previously published from the tiaojishan fm in the chengde area pei et al 2011 tectonophysics 510 370 380 our analyses demonstrate that the paleomagnetic directions obtained from each sampled area were strongly biased by paleosecular variation psv but the psv can be averaged out by combining all the virtual geomagnetic poles vgps from the tiaojishan fm in the region the mean pole at 69 6 n 203 0 e a95 5 6 passes a reversal test and regional tilting test at 95 confidence and is thus considered as a primary paleomagnetic record this newly determined pole of the tiaojishan fm is consistent with available late jurassic poles from red beds in the southern part of the ncb but they are incompatible with coeval poles of siberia and the reference pole of eurasia indicating that convergence between siberia and the ncb had not yet ended by 155 ma our calculation shows a 1600 km latitudinal plate movement and crustal shortening between the siberia and ncb after 155 ma in addition no significant vertical axis rotation was found either between our sampled areas or between the yanshan belt and the major part of the ncb after 155 ma

a morphological stability analysis for a long straight barred coast a morphological stability analysis is carried out for a long straight coast with a longshore bar the situation with oblique wave incidence and a wave driven longshore current is considered the flow and sediment transport are described by a numerical modelling system the models comprise i a wave model with depth refraction shoaling and wave breaking ii a depth integrated model for wave driven currents and iii a sediment transport model for the bed load transport and the suspended load transport in combined waves and current the direction of the sediment transport is taken to be parallel to the depth integrated mean current velocity neglecting the effects of a bed slope and secondary currents an instability is found to develop around the bar crest the instability is periodic in the alongshore direction and tends to form rip channels and to steepen the offshore face of the bar between the rip channels the alongshore wave length of the most unstable perturbation is determined for different combinations of the wave conditions and the geometry of the profile

the goonumbla porphyry copper deposits new south wales significant porphyry copper gold deposits have been discovered at goonumbla near parkes in central new south wales australia exploratory drilling to date has defined a resource in excess of 250 million metric tons of mineralization with mean grades of 0 70 percent cu and 0 28 g metric ton au this mineralization is contained within the three largest deposits of nine so far located all of which occur toward the top of a calc alkaline volcanic pile of middle silurian age the host volcanics range from trachyte to andesite in composition and have been deposited in the central part of what is believed to have been a large collapse caldera vertical pipelike bodies of vein and disseminated bornite chalcopyrite and chalcocite mineralization are associated with small irregular quartz monzonite porphyry intrusions these porphyries have been derived as late stage quartz rich differentiates of a more mafic monzonitic magma and have migrated upward along and close to the contacts of larger earlier mafic intrusions pervasive pink k feldspar flooding of the volcanics with lesser development of secondary biotite is indicative of the intense potassic alteration which has accompanied the deposition of sulfides quartz vein stockwork systems are invariably developed at or near the porphyry andesite contacts and contain above average abundances of copper gold and silver the mineralizing hydrothermal solutions were low in sulfur content with the result that pyrite is almost totally absent from the central parts of the mineral bodies subsequent oxidation and secondary enrichment although present have not played an important role in the ore forming process bed rock geochemical sampling for copper and gold supported by ground magnetic and induced polarization surveys have proven to be the most effective exploration methods for detecting the soil covered mineralization the goonumbla deposits are high level volcanic to subvolcanic examples of the porphyry copper type and have been formed in a continental margin arc environment in the eastern side of the bogan gate trough

modelling the formation of shoreface connected sand ridges on storm dominated inner shelves a morphodynamic model is developed and analysed to gain fundamental understanding of the basic physical mechanisms responsible for the characteristics of shorefaceconnected sand ridges observed in some coastal seas these alongshore rhythmic bed forms have a horizontal lengthscale of order 5 km and are related to the mean current along the coast the seaward ends of their crests are shifted upstream with respect to where they are attached to the shoreface the model is based on the two dimensional shallow water equations and assumes that the sediment transport only takes place during storms the flux consists of a suspended load part and a bed load part and accounts for the eects of spatially non uniform wave stirring as well as for the preferred downslope movement of sediment the basic state of this model represents a steady longshore current driven by wind and a pressure gradient the dynamics of small perturbations to this state are controlled by a physical mechanism which is related to the transverse bottom slope this causes a seaward deflection of the current over the ridges and the loss of sediment carrying capacity of the flow into deeper water the orientation spacing and shape of the modelled ridges agree well with eld observations suspended load transport and spatially non uniform wave stirring are necessary in order to obtain correct e folding timescales and migration speeds the ridge growth is only due to suspended load transport whereas the migration is controlled by bed load transport

morphologic properties derived from a simple cross shore sediment transport model this paper builds on the now classical discussions by bowen 1980 and bailard 1981 on the applicability and implications of bagnold s 1963 sediment transport model to nearshore profile modeling we focus on the morphologic implications of both the strengths and weaknesses of bagnold s model isolating the transport terms that are well predicted i e mean flow terms from those that are not well predicted i e transport due to correlations between flow and sediment load we factor bagnold s model into a dimensional transport magnitude and a nondimensional term the nondimensional term describes the relative importance of transport due to undertow gravity and correlations between flow and sediment load the transport magnitude largely determines the response time of nearshore profiles for typical nearshore environments this response time was estimated to vary as a function of incident rms wave height hrms from 500 years hrms 0 5 m to 2 years hrms 3 m the relative importance of competing transport mechanisms is shown to depend strongly on the relative wave height defined as the ratio of the rms wave height to the local depth simplified nearshore transport parameterizations that are a function of this variable were derived and were interrogated for the existence and form of equilibrium profiles several differences from previously computed equilibrium profiles were noted first because the relative wave height saturates in natural surf zones equilibrium profiles converge to a relatively flat profile near the shoreline second under some situations a seaward sloping equilibrium profile may not exist third the long response times combined with unknown stability of an equilibrium profile make it difficult to assess the physical connection between theoretical equilibrium profiles and profiles observed in nature

formation and migration of transverse bars along a tidal sandy coast deduced from multi temporal lidar datasets a field of long crested transverse bars was monitored from a 2 5 year series of topographic lidar surveys in the vicinity of a tidal inlet on the macrotidal mean spring tidal range 7 to 12 m west coast of cotentin normandy france the bar field the alongshore extent of which is about 1 8 km is composed of a total of 8 bars with lengths varying from 320 m to 1300 m and mean heights comprised between 0 5 m and 2 5 m bar cross sections are variable between bars and for a single bar and also over time the surveys show a consistent northward migration of the bars at a mean rate of about 2 m month but the rate is larger in winter than in summer the lidar observations show that the tidal inlet located at the southern limit of the bar field where the bars start forming comprises a large sediment platform that acts as a source of sand for the bars the ebb jet debouching from the inlet is deflected northward by the ambient strong shore parallel tidal currents in this large tide range setting and this may be the primary mechanism leading to the emplacement of the bars smaller wave formed swash bars that further feed the development of these large transverse bars have also been observed monitoring of bar migration in the course of six consecutive spring tides with fair weather conditions showed that strong spring tidal currents are sufficient to drive bar mobility in the absence of waves storm wave resuspension of sand is thus expected to enhance bar mobility rates as shown by the higher rates of winter bar migration compared to the summer rates the ebb jet explains the slower bar migration rates at the vicinity of the inlet these rates increasing with distance northward of the inlet as the tidal currents become unimpeded the main difference between these macrotidal transverse bars and their counterparts in microtidal settings resides in these strong tidal currents that are the essential driver of bar migration unlike the wave driven migration of microtidal bars the large tidal range in conjunction with storm wave activity also induces longshore and seasonal variability in bar morphology the transverse bars of normandy appear to be inscribed in a sand circulation system involving the west cotentin coast the large ebb tidal delta from which they are formed and the central cotentin embayment where they are ultimately incorporated into the nearshore sand pool longer term field hydrodynamic monitoring and modelling will be required in order to further elucidate the mode of formation of these transverse bars

40ar 39ar dating of ignimbrite from inner mongolia northeastern china indicates a post middle jurassic age for the overlying daohugou bed the ar 40 ar 39 step heating analyses of k feldspar derived from the ignimbrite in inner mongolia china indicates that they were formed at 159 8 0 8 ma which provides a maximum age for the overlying fossil bearing lacustrine deposits daohugou bed this result favors a post middle jurassic late jurassic or younger rather than the middle jurassic age for the daohugou bed such a result is generally consistent with vertebrate biostratigraphic evidence providing a maximum known age for the first appearance of several major animal groups such as cryptobranchidae of urodela salamanders and maniraptora birds and their closest dinosaurian relatives

tidal induced large scale regular bed form patterns in a three dimensional shallow water model the three dimensional model presented in this paper is used to study how tidal currents form wave like bottom patterns inclusion of vertical flow structure turns out to be necessary to describe the formation or absence of all known large scale regular bottom features the tide and topography are treated as a coupled system and the potential free instabilities in this system are investigated a linear stability analysis is used to study the dynamics of bed forms this yields information on the role of physical mechanisms such information cannot be obtained by direct numerical nonlinear simulation the basic state represents a horizontal elliptical flow veering in vertical direction over a flat bottom it is shown that in such a system modes can grow which have characteristics of both tidal sand banks and sand waves the model predictions are compared with observations and show good agreement

a mechanism for the generation of wave driven rhythmic patterns in the surf zone the coupling between topographic irregularities and wave driven mean water motion in the surf zone is examined this coupling occurs because the topographic perturbations produce excess gradients in the wave radiation stress that cause a steady circulation this circulation in turn creates a sediment transport pattern that can reinforce the bottom disturbance and may thereby lead to the growth of large scale bed forms to investigate this coupling mechanism the linearized stability problem with an originally plane sloping beach and normal wave incidence is solved in two different cases first the breaking line is considered to be fixed and second the perturbations in water depth that produce a displacement of the breaker line are accounted for the first case shows that the basic topography can be unstable with respect to two different modes a giant cusp pattern with shore attached transverse bars that extend across the whole surf zone and a crescentic pattern with alternate shoals and pools at both sides of the breaking line showing a mirroring effect in the second case the varying breaker line may have a strong influence on the circulation this is clear for the giant cusp topography whose growth is totally inhibited in contrast the morphology and the growth of the crescentic pattern remains almost unchanged

generation and nonlinear evolution of shore oblique transverse sand bars the coupling between topography waves and currents in the surf zone may self organize to produce the formation of shore transverse or shore oblique sand bars on an otherwise alongshore uniform beach in the absence of shore parallel bars this has been shown by previous studies of linear stability analysis but is now extended to the finite amplitude regime to this end a nonlinear model coupling wave transformation and breaking a shallow water equations solver sediment transport and bed updating is developed the sediment flux consists of a stirring factor multiplied by the depth averaged current plus a downslope correction it is found that the cross shore profile of the ratio of stirring factor to water depth together with the wave incidence angle primarily determine the shape and the type of bars either transverse or oblique to the shore in the latter case they can open an acute angle against the current up current oriented or with the current down current oriented at the initial stages of development both the intensity of the instability which is responsible for the formation of the bars and the damping due to downslope transport grow at a similar rate with bar amplitude the former being somewhat stronger as bars keep on growing their finite amplitude shape either enhances downslope transport or weakens the instability mechanism so that an equilibrium between both opposing tendencies occurs leading to a final saturated amplitude the overall shape of the saturated bars in plan view is similar to that of the small amplitude ones however the final spacings may be up to a factor of 2 larger and final celerities can also be about a factor of 2 smaller or larger in the case of alongshore migrating bars the asymmetry of the longshore sections the lee being steeper than the stoss is well reproduced complex dynamics with merging and splitting of individual bars sometimes occur finally in the case of shore normal incidence the rip currents in the troughs between the bars are jet like while the onshore return flow is wider and weaker as is observed in nature

analysis of observed two and three dimensional nearshore bar behaviour abstract shore parallel sandbar systems often exhibit considerable quasi regular alongshore variations such as crescentic plan shapes therefore morphological change in such systems commonly consists of two and three dimensional variability the former is related to overall on offshore bar migration whereas the latter is induced by the horizontal amplitude growth migration or length scale change of the quasi regular topography in this paper we used a six week data set of bathymetric surveys and video images of breaking induced foam to quantify short term days weeks two and three dimensional variability in the bar crest position of the double barred beach at egmond aan zee netherlands the alongshore uniform response was computed as the mean of each bar crest line whereas the alongshore non uniform behaviour was characterised by the amplitude around each mean a more sophisticated description of the inner bar data set was provided by complex empirical orthogonal function ceof analysis the first complex mode containing about 85 of the variance in the data set corresponded to the amplitude growth and longshore migration of an approximately 600 m long alongshore non uniformity the longshore migration rate varied between 0 and 150 m day and was found to be well related to the longshore component of the offshore wave energy flux the second complex mode explained about 10 of the variance and largely described the alongshore averaged cross shore bar migration the ceof results suggest that short term variability in bar crest position is largely due to changes in the quasi regular topography and not to alongshore uniform on offshore oriented behaviour

taxonomic diversity stratigraphic range and exceptional preservation of juro cretaceous salamanders from northern china since the late 1990s eight localities in volcanic shale rich lacustrine deposits of middle jurassic through early cretaceous age in northern china western liaoning province northern hebei province and southern inner mongolia have yielded thousands of exceptionally well preserved salamander specimens with 10 species published and several new taxa yet to be named and described the fossil samples from northern china represent the most species diverse individually abundant and exquisitely preserved salamander fossil assemblage known from the mesozoic era the stratigraphic range of the fossil record covers a geologic time span of roughly 40 45 million years from the middle jurassic bathonian through the early cretaceous aptian in contrast to the well known stem group salamanders karaurus and kokartus from the middle to late jurassic of middle asia the chinese record contains the earliest known crown group salamanders including jurassic representatives of both cryptobranchoidea and salamandroid

metallogenic setting and ore genetic model for the beiya porphyry skarn polymetallic au orefield western yunnan china abstract the beiya in western yunnan china is a world class porphyry skarn polymetallic au orefield that is currently being explored and constitutes the topic of this paper the beiya orefield is a composite mineral system with a distinct zoning surrounding the causative intrusions for instance the wandongshan the largest deposit in the beiya orefield exhibits a zoning with 1 porphyry au fe cu orebodies in the cupolas to the intrusions 2 au fe cu skarn orebodies along contact zones between the alkaline porphyritic intrusions and triassic limestone country rocks and 3 distal stratiform pb zn ag au epithermal orebodies subsequent au and cu bearing quartz ankerite veins and barren calcite veins overprint the earlier magmatic hydrothermal zoned ore system the hypogene orebodies were weathered to form supergene au ores at shallow levels which were historically termed laterite gold deposits the 2000 km nwn striking jinshajiang ailaoshan metallogenic province located in the three river region of western yunnan western sichuan and eastern tibet hosts numerous world class porphyry and skarn cu mo au ores associated with alkaline porphyry emplacement the beiya polymetallic au orefield a representative example of these ore types is located close to the triassic ailaoshan songma suture to the east and formed during eocene oligocene intraplate extension the distal stratiform pb zn ag au orebodies are hosted by bedding or detachment faults based on exploration data and previous research and combined with our detailed field investigation and further studies in the beiya area we propose a new and comprehensive porphyry skarn epithermal deposit model the model explains the geological setting ore characteristics metallogenic zoning and ore forming processes of the deposits in the beiya area it provides useful insights for further mineral exploration in the jinshajiang ailaoshan province for porphyry and skarn cu mo au ore systems associated with alkaline magmatism and may also be applied to other metallogenic provinces within similar continental arc settings

the statistics and kinematics of transverse sand bars on an open coast abstract ten years 1987 1996 of time exposure video images of the nearshore region at duck nc were used to study transverse sand bars bathymetric features of intermediate length scales 10 200 m oriented oblique or perpendicular to the shoreline these transverse sand bars extend seaward from both the shoreline trough transverse bars and the shore parallel sand bar offshore transverse bars transverse bars had not previously been observed in an energetic coastal environment such as that at duck and their dynamics and role in nearshore processes is unknown frequency of occurrence statistics and length scales of the transverse bars were calculated using the video images trough and offshore transverse bars appeared a mean of 39 and 73 days per year respectively the offshore bars were found to be much larger features than the trough bars with mean wavelengths alongshore spacing between consecutive crests of 79 and 172 m for trough and offshore bars respectively both the trough and offshore bars were found to persist for periods of days to months the alongshore movement of the bars was measured and compared to estimates of surf zone longshore currents which were calculated from wave height and wave angle data both sets of bars were observed to move at rates up to 40 m day at times both trough and offshore bars were observed shifting in the same direction as the current was flowing and at other times both sets of bars remained stationary even under relatively strong longshore currents trough bars were also observed moving against the current an hypothesis proposed by barcilon and lau 1973 j geophys res 78 15 2656 2664 that the transverse bars were created as a sea bed instability under longshore currents was tested by comparing the magnitude of estimated surf zone longshore currents with times of formation or presence of transverse bars there was no evidence to suggest that the bars were formed by this simple longshore current instability mechanism instead it is plausible that the combined effects of waves and currents may drive the formation of these features

mechanisms for linear sandbank formation and maintenance in relation to dynamical oceanographic observations abstract theories associated with flow in the vicinity of headlands and sandbanks together with proposed mechanisms for sandbank formation and maintenance are reviewed to exemplify water and sand movement around a sandbank on a tidally dominated shelf tidal currents in the vicinity of a headland associated linear sandbank are described these data are integrated with sedimentological information on bedforms and grain size distributions the sandbank under detailed investigation the scarweather sands is located along the northern coastline of the bristol channel uk which is an area susceptible to high energy inputs the maximum spring tidal range here is around 10m and a 6000km fetch is available for storm wave approach from the atlantic ocean but the area is 460km from the shelf break detailed observations are presented from 11 long term current meter stations located within 10km of the sandbank currents are described in terms of residual water circulation shallow water harmonics and tidal ellipse characteristics bedload transport paths are inferred from the distribution of bedforms grain size and m2 m4 tidal current interactions transport vectors are predicted from near bed current meter observations combined with empirically derived formulae it is demonstrated that water circulation and sand transport paths form part of a clockwise eddy system around the sandbank mechanisms controlling the location and the characteristics of this particular sandbank are shown to be explicable in terms of a combination of models for sandbank formation and maintenance the results of the present study are thought to be applicable directly to headland associated sandbanks elsewhere it is shown on the basis of theoretical considerations that the pattern of residual water movement and possibly sand transport around this sandbank could be extended to continental shelves on a global basis

an energetics total load sediment transport model for a plane sloping beach bagnold s energetics based total load sediment transport model for streams is used as a basis for the development of a total load model of time varying sediment transport over a plane sloping bed in both the bedload and suspended load the transport rate vectors are found to be composed of a velocity induced component directed parallel to the instantaneous velocity vector and a gravity induced component directed down slope the model is applied to idealized surfzone conditions leading to estimates of the local longshore and onshore offshore sediment transport rates as well as the equilibrium beach slope as a function of the local wave and current conditions the model is combined with a nonlinear longshore current model and spatially integrated to obtain predictions of the total longshore transport rate as a function of the incident wave conditions the results support the general form of the wave power equation except that the wave power coefficient is no longer constant but is instead a complex function of the incident wave and beach characteristics

self organization mechanisms for the formation of nearshore crescentic and transverse sand bars the formation and development of transverse and crescentic sand bars in the coastal marine environment has been investigated by means of a nonlinear numerical model based on the shallow water equations and on a simplified sediment transport parameterization by assuming normally approaching waves and a saturated surf zone rhythmic patterns develop from a planar slope where random perturbations of small amplitude have been superimposed two types of bedforms appear one is a crescentic bar pattern centred around the breakpoint and the other herein modelled for the first time is a transverse bar pattern the feedback mechanism related to the formation and development of the patterns can be explained by coupling the water and sediment conservation equations basically the waves stir up the sediment and keep it in suspension with a certain cross shore distribution of depth averaged concentration then a current flowing with against the gradient of sediment concentration produces erosion deposition it is shown that inside the surf zone these currents may occur due to the wave refraction and to the redistribution of wave breaking produced by the growing bedforms numerical simulations have been performed in order to understand the sensitivity of the pattern formation to the parameterization and to relate the hydro morphodynamic input conditions to which of the patterns develops it is suggested that crescentic bar growth would be favoured by high energy conditions and fine sediment while transverse bars would grow for milder waves and coarser sediment in intermediate conditions mixed patterns may occur

double bar beach dynamics on the high energy meso macrotidal french aquitanian coast a review the french aquitanian coast is an approximately 250 km long straight low coast exposed to high energy conditions in a mesomacrotidal setting offshore wave conditions are seasonally modulated predominantly with a wnw incidence with offshore significant wave height likely to reach 10 m during winter truc vert beach representative of most of the aquitanian coast beaches commonly exhibitstwodistinctsandbarsystems theinnerbarcangothroughallthestateswithintheintermediateclassificationandusuallyexhibitsa tansversebarandripmorphology afterafewweeksoflowerenergyconditionsduringsummer theinnerbarcommonlybecomesalow tideterracewithameanwavelengthof400mandameansoutherlymigrationrateofabout2 3m day crescenticbarshavebeenreported in the literature in nontidal to microtidal settings long term persistent crescentic patterns are however exhibited at a narrow range of wavelength mean of 700m by the outer bar at the meso macrotidal truc vert beach most of the time the outer bar is inactive and stagnates as offshore waves ofhsn3 m are required to induce a significant morphological change the crescent shape varies from a symmetric shape to a strongly asymmetric shape likely to be the result of a long period of nw wave conditions a strong and rarely observed elsewhere morphological coupling between the inner and outer bars can sometimes be observed and may be the result of the combined effectsof the initial presence of a well developed outer crescentic bar and a long period of shore normal low energy conditions a synthesis of all the data available on the area combined with observations on other environments leads to a truc vert beach state model ranging from a modal double bar configuration to an occasional triple bar configuration this work also identifies knowledge gaps to be explored by further numerical and field studies in tidal double sandbar environments 2007 elsevier b v all rights reserved

high precision 40ar 39ar age constraints on the basal lanqi formation and its implications for the origin of angiosperm plants abstract abundant mesozoic terrestrial fossils were discovered in the haifanggou formation and the overlying lanqi formation in northeastern china the recent discovery of schmeissneria sinensis from the haifanggou formation provides evidence that the origin of angiosperms could be much earlier than previously believed 92 taxa of plant fossils from the lanqi formation provide unique opportunities to understand the floral evolution and its diversification in the mesozoic here we present robust high precision 40ar 39ar data of 160 7 0 4 ma and 158 7 0 6 ma for two tuffs from the lowest part of the lanqi formation near the main outcrop of floral fossils in beipiao city liaoning china our age results indicate the whole lanqi formation was deposited in the late jurassic consequently the underlying haifanggou formation and schmeissneria sinensis are at least middle jurassic in age besides its importance for floral evolution our high precision age results for the basal lanqi formation indicate the paleoenvironment in the north margin of the north china craton was dry and hot in the late jurassic moreover the new age data for the basal lanqi formation suggest that the unearthed fossils from the haifanggou formation and lanqi formation should be equivalent to the daohugou biota in inner mongolia china

high resolution palaeoecological and taphonomic analysis of early cretaceous lake biota western liaoning ne china abstract the faunal content of eighteen bedding planes within the jianshangou unit of the lower cretaceous yixian formation of western liaoning has been analysed in detail in order to understand the environmental and taphonomic framework of this famous lacustrine fossillagerstatte the bedding planes were excavated within a 3 m thick section which is composed of laminated mudstones graded sandstones and mudstones and horizontally stratified structureless sandstones and tuffs all investigated bedding planes occur within the laminated mudstone facies and contain elements of the so called jehol biota in particular the conchostracan eosestheria ovata the ephemerid nymph hexagenites trisetalis and the crustacean liaoningogriphus quadripartitus these three faunal elements occur in high abundance originally possessed chitinous skeletons and are preserved as compressed faintly mineralized coats or in the case of eosestheria still possess organic material the specimens do no represent exuviae but body fossils the fossils can be grouped into three low diversity associations each characterized by one of the three taxa the plan view orientation of the taxa is invariably random and size frequency histograms are bimodal or polymodal this indicates that the fauna is autochthonous and that the histograms reflect several recruitment phases apparently the faunal elements suffered seasonal mass mortality caused by anoxic conditions which became established in the lake during the summer months increased humidity during the winter led to mixing of the lake waters re establishment of oxic conditions and to deposition of a thin film of sediment such environmental conditions were episodically interrupted by flash floods and volcanic ash falls which may have been responsible for the preservation of the more spectacular elements of the jehol biota such as birds and feathered dinosaurs

the spatial and temporal variability of sand bar morphology the spatial and temporal variability of nearshore sand bar morphology is quantified using a unique data set spanning 2 years the data consist of daily time exposure images of incident wave breaking on an open coast sandy beach which may be used to infer bar morphology lippmann and holman 1989 the morphology in each image is classified into an eight state morphologic scheme in which bars are uniquely defined by four independent criteria the most frequently observed morphologies are the longshore periodic rhythmic bars observed in 68 of the data linear bars occur under highest wave conditions h s 1 78 m and are unstable mean residence time 2 days shore attached rhythmic bars are the most stable mean residence time 11 days and generally form 5 16 days following peak wave events non rhythmic three dimensional bars are very transient mean residence time 3 days eighty seven percent of transitions to lower bar types defined in text occurred one state at a time supporting our selection of the ordering of states and suggesting the suitability of a sequential morphology model transitions to higher states occurred under rising wave energy and were evenly spread among the possible higher states with more substantial changes in morphology resulting from larger wave increases this suggests that up state erosional transitions based on offshore bar migration are better described by an equilibrium model where response is better correlated with incident wave energy than with preceding morphological state time exposure images were also digitized to yield quantitative estimates of bar crest location as a function of longshore distance principal component analysis was used to decompose bar position into two dimensional linear and three dimensional longshore variable components cross shore linear bar position ranges 50 m about the 2 year mean 27 m standard deviation and dominates bar variability 74 6 three dimensional bar structure accounts for 14 of the variance 12 m standard deviation changes in incident wave height precede cross shore bar migration by less than 1 day changes in longshore variability are inversely correlated to changing wave conditions with bar morphology becoming linear rapidly during storms on time scales of less than 1 day evolution to significantly three dimensional structure typically occurs over 5 7 days following peak wave events

understanding coastal morphodynamic patterns from depth averaged sediment concentration this review highlights the important role of the depth averaged sediment concentration dasc to understand the formation of a number of coastal morphodynamic features that have an alongshore rhythmic pattern beach cusps surf zone transverse and crescentic bars and shoreface connected sand ridges we present a formulation and methodology based on the knowledge of the dasc which equals the sediment load divided by the water depth that has been successfully used to understand the characteristics of these features these sand bodies relevant for coastal engineering and other disciplines are located in different parts of the coastal zone and are characterized by different spatial and temporal scales but the same technique can be used to understand them since the sand bodies occur in the presence of depth averaged currents the sediment transport approximately equals a sediment load times the current moreover it is assumed that waves essentially mobilize the sediment and the current increases this mobilization and advects the sediment in such conditions knowing the spatial distribution of the dasc and the depth averaged currents induced by the forcing waves wind and pressure gradients over the patterns allows inferring the convergence divergence of sediment transport deposition erosion occurs where the current flows from areas of high to low low to high values of dasc the formulation and methodology are especially useful to understand the positive feedback mechanisms between flow and morphology leading to the formation of those morphological features but the physical mechanisms for their migration their finite amplitude behavior and their decay can also be explored

late jurassic fluvial eolian deposits from the tianchihe formation ningwu jingle basin shanxi province china abstract eolian systems were widespread in china in the cretaceous however the reports of pre cretaceous eolian and its related systems are scarce which prohibits studying the construction accumulation and preservation of eolian systems as well as its allogenic and autogenic controlling factors in this paper we report on fluvial eolian successions from the late jurassic tianchihe formation in the ningwu jingle basin these successions represent the oldest reported inland fluvial eolian systems in china fourteen lithofacies types are recognized in the tianchihe formation and have been grouped into six facies associations including meandering fluvial channel levee and overbank in the lower part and eolian sandsheet eolian dune ephemeral fluvial channel and floodplain in the upper part the fluvial system comprises a series of wetting upward cycles which indicate humid climate culminating in high precipitation and shallow water table level eolian dune deposits composed of grainflow grainfall wind ripple strata and pin stripe laminations currently implies that all deposits types are internally bounded by reactivation surface and superimposition surface suggesting compound dunes or draas eolian sandsheet deposits consist dominantly of subcritical climbing translatent strata and pin stripe lamination the association of eolian dune and eolian sandsheet is development of a dry eolian system twelve drying upward cycles mainly composed of eolian sandsheet eolian dune successions and four wetting upward cycles consisting of eolian sandsheet dune ephemeral fluvial channel floodplain successions occur in the eolian system these repeated cycles likely reflect an evolving erg system directly controlled by sediment supply sediment availability and relative water table the vertical transition from fluvial to eolian systems indicate a local climatic oscillation from relatively humid to arid conditions which may be related with the uplift of the east china plateau in the late jurassic

revisiting of the yanshanian basins in western and northern beijing north china abstract we present new laser ablation inductively coupled plasma mass spectrometry la icp ms zircon u pb ages and provenance data for the yanshanian basins in western and northern beijing north china with the aims of demonstrating the relationship between basin evolution and yanshanian tectonism and constraining the late jurassic early cretaceous tectonic evolution of the region the inherited yanshanian basin in western beijing has a late jurassic early cretaceous tectonic history similar to that of typical yanshanian basins in the yanshan fold thrust belt yftb and it became inactive at 138 ma the qianjiadian basin qjb in northern beijing is only infilled by the sediments of the tuchengzi formation our new zircon u pb ages 160 156 ma for the pyroclastic and volcanic rocks of the tuchengzi formation suggest that formation of the qjb commenced at 160 ma consistent with the main episode of yanshanian tectonism the qjb developed in the footwall of the pingquan gubeikou thrust fault pgf and records the syn tectonic unroofing and erosion of the hanging wall of that fault it was later reformed by the post depositional qianjiadian thrust fault qjf along the western margin the formation and development of the qjb in northern beijing and the inherited yanshanian basin in western beijing were related to the yanshanian tectonism especially at ca 160 ma when the intense deformation and large scale magmatism occurred the tectonic transition from n s to nw se shortening is attributed to the northwest ward subduction of the paleo pacific plate and is constrained to 156 135 ma in the yftb and eastern china

modeling and analyzing observed transverse sand bars in the surf zone 1 a morphodynamic model has been applied to explain the characteristics of transverse sandbars observed in the inner surf zone of open beaches the model describes the feedback between waves rollers depth averaged currents and bed evolution so that self organized processes can develop the modeled bar characteristics i e wavelength 30 70 m crest orientation up current and the e folding growth time about 12 hr are in good agreement with those of observed transverse bars at noordwijk beach the netherlands but modeled migration speeds tens of meters per day turn out to be a factor 2 larger than those observed the wavelength increases with the distance between the shoreline and the peak of the longshore current and the migration speed is correlated with the maximum longshore current the model also explains why transverse bar formation at noordwijk occurs for obliquely incident waves of intermediate heights realistic positive feedback leading to formation of up current oriented bars like those observed is only obtained if a term related to the turbulence sediment resuspension created by the rollers is included in the transport formula in that case the depth averaged sediment concentration decreases seaward across the inner surf zone enhancing the convergence of sediment transport in the offshore directed flow perturbations that occur over the up current bars this offshore current deflection is mainly caused by frictional torques but the roller radiation stresses also play an important role

bar generating cross shore flow mechanisms on a beach random waves normally incident on a dissipative beach induce a variety of cross shore flows such as asymmetric oscillatory flow wave grouping induced long wave flow breaking induced turbulent flow and momentum decay induced undertow these flows are identified analyzed and hindcasted in a set of laboratory experiments with the aim of revealing the role of each of the flow mechanisms in the two dimensional case of bar generation on a beach

the first 40ar 39ar date from oxfordian ammonite calibrated volcanic layers bentonites as a tie point for the late jurassic eight volcanic ash layers linked to large explosive events caused by subduction related volcanism from the vardar ocean back arc interbedded with marine limestones and cherts have been identified in the rosso ammonitico veronese formation northeastern italy the thickest ash layer attributed to the gregoryceras transversarium ammonite biozone oxfordian stage yields a precise and reliable 40 ar 39 ar date of 156 1 0 89 ma which is in better agreement with gts2004 boundaries than with the current gts2012 this first biostratigraphically well constrained oxfordian date is proposed as a new radiometric tie point to improve the geologic time scale for the late jurassic where ammonite calibrated radiometric dates are particularly scarce

shear instabilities in the longshore current a comparison of observation and theory abstract low frequency 0 01 hz oscillations in the surf zone longshore current with wavelengths too small 300 m to be surface gravity waves were observed during the 1986 superduck experiment at duck north carolina the observations suggest that these oscillations are dynamically linked to the mean longshore current in the surf zone leading bowen and holman to propose that the observed oscillations are manifestations of a shear instability in the longshore current in this paper field data from both the superduck experiment a barred beach and the l980 nsts experiment at leadbetter beach santa barbara california a plane beach are used to compare quantitatively the model of bowen and holman which is extended to include the effects of dissipation due to bottom friction with observation observed frequency cyclic wavenumber f k spectra constructed from alongshore arrays of velocity measurements made in about 1 5 2 m of water in the trough of the bar at superduck and in about 1 m at nsts

continental humid and arid zones during the jurassic and cretaceous abstract the global distribution of climatically significant criteria is surveyed for six successive time intervals hettangian toarcian aalenian callovian oxfordian tithonian berriasian barremian aptian cenomanian and turonian maastrichtian the criteria are primarily mineralogical evaporites coals bauxites ironstones and kaolinite but include sedimentological and palaeontological aspects of facies e g aeolian sands fossil ferns and xerophytes fresh water invertebrates in early and mid jurassic times an arid zone can be distinguished in low to mid latitudes in western pangaea with humid zones elsewhere in the late jurassic this arid zone spread northwards to embrace much of southern eurasia there followed in the early cretaceous a sharp reversal to more humid conditions over a large area extending from the eastern margin of north america to the middle east a major consequence of which was the widespread replacement of carbonates by coarse siliciclastic facies by late cretaceous times humid conditions were well established also in north america and the south atlantic margins and the tropical arid zone had contracted to a minimum the 87 sr 86 sr ratio of marine carbonates provides an independent monitor of continental runoff which is related to a area and b extent of aridity changes in the ratio confirm that taking sea level stand into account the late cretaceous was appreciably more humid than the late jurassic these climatic changes are related primarily to the progressive breakup of pangaea in the late jurassic and cretaceous which together with sea level rise in the mid to late cretaceous caused a significant increase in maritime influence this implies that monsoonal winds probably had a major role in promoting higher precipitation rates a puzzle remains as to why there was a spread of aridity in the late jurassic finally some implications for terrestrial plant evolution are noted

diachronous onset and polyphase cooling of the taili yiwulushan metamorphic core complex corridor ne china and its relationships to the formation of adjacent extensional basins abstract the aim of the study to investigate the cooling and exhumation history of deep crustal rocks along the taili yiwulushan metamorphic core complex mcc corridor and correlate these with volcanic clastic deposition in the late jurassic to early cretaceous supra detachment fuxin yixian basin in the west and the mostly eocene liaohe basin in the east this corridor exposes low to medium grade metamorphic neoarchean rocks and late triassic late jurassic and early cretaceous granitic rocks which exhumed from the middle to shallow crustal levels new 40ar 39ar ages of muscovite biotite k feldspar and apatite u th sm he ages in combination with compiled published geochronological data from the granitic rocks constrain three major stages of cooling exhumation and deformation from late jurassic through early cretaceous to eocene interrupted by late cretaceous tectonic quiescence the onset of activity and exhumation and cooling is diachronous along the mcc corridor at taili in the south the main activity of the sinistral shear zone is constrained between 160 and 140 ma with major cooling from crystallization temperatures of granitoids from 700 750 c to 160 c first stage along the waziyu ductile detachment at the western border of the yiwulushan mcc major cooling and exhumation is bracketed between 130 ma and 100 ma second stage and thus indicates a northward progradation of deformation and exhumation activity however cooling ages as old as 159 ma along the eastern margin of the yiwulushan mcc indicate an earlier initiation of cooling and westward rolling hinge type propagation first stage late cretaceous and paleogene times are characterized by a tectonically quiet period with only minor cooling and exhumation stage three the fourth and final stage of exhumation and cooling to very low temperatures occurred during late paleocene to earliest eocene times and is associated with the transtensional or extensional opening of the liaohe basin

morphodynamic instabilities of planar beaches sensitivity to parameter values and process formulations the initial growth of bed perturbations on planar sloping beaches under the forcing of obliquely incident breaking waves is investigated using a state of the art numerical model this allows for a systematic investigation of the sensitivity of the spatial structures of the bed perturbations and their growth and migration rates to different model formulations and parameterizations if the sediment is only transported in the direction of the net current velocity and sediment stirring is taken proportional to the wave height squared growing up current oriented crescentic bars are found with a preferred spacing of 800 m and a down current migration rate of 10 m d 1 varying the angle of wave incidence drag coefficient and bed slope results in qualitatively similar growing bed forms using an engelund and hansen transport formula very oblique down current oriented bars are obtained that grow in time no preferred wavelength however is found using the bailard transport formula results in growing up current oriented bars with a preferred spacing smaller than 300 m for wave angles smaller than 7 when using either the engelund and hansen or bailard sediment transport formulation it is essential to take the transport in the direction of the wave orbital velocity into account in order to have growing bed perturbations

characteristics and dynamics of surfzone transverse finger bars 1 patches of transverse finger bars have been identified in the surf zone of noordwijk beach netherlands they consisted of three to nine elongated accumulations of sand attached to the low tide shoreline the bars extended up to 50 m into the inner surf zone had an oblique orientation with respect to the shore normal and were quasiregularly spaced in the alongshore direction we analyzed nearly 6 years of video data and observed a significant presence of finger bars 14 of the time with good data bars were visible on 193 days gathered in 44 events that persisted from 2 days to 2 months obliquely incident waves of intermediate and approximately constant height were dominant during finger bar presence shore normal incident or more energetic wave fields destroyed the bar patches the underlying bathymetry affected finger bar formation inner surfzone troughs with cross shore areas of 100 m2 and inner surfzone slopes of 0 02 were more conducive to their growth the mean alongshore wavelength of the finger bar patches was 39 m ranging from 21 to 75 m bar crests deviated up to 40 degrees from the shore normal against the alongshore current direction up current orientation and bar patches migrated at rates up to 22 m day in the direction of the alongshore current we used these observations to test existing theoretical self organization mechanisms for transverse bar formation the bed flow mechanism was the most viable explanation for the generation and persistence of noordwijk finger bars our observations were consistent with most of the predictions of two models that included this interaction but migration rates differed by 1 order of magnitude

first report of sauropod tracks from the upper jurassic tianchihe formation of guxian county shanxi province china abstract this paper presents the first report of sauropod tracks from the upper jurassic of shanxi province china dinosaur tracks appear concentrated in five trackways in different stratigraphic levels of the late jurassic tianchihe formation tracks are dominantly small and medium size sauropod tracks and are tentatively assigned to brontopodus based on preserved track morphology trackway pattern and statistical analysis the tianchihe formation in which the tracks appear shows a gradual change from meandering fluvial to sandy braided fluvial depositional systems developed in a seasonally arid environment comparisons of the evaluated speed of bipedal to quadruped trackways indicate that the slower walk more easily produces pes dominated overprints trackways in the guxian tracksite appear following different orientations suggesting that these trackways were produced by different sauropods at different times an unusual trackway following a curved pattern has been identified in the site and could represent a special locomotion character or a social behavior the presence of eolian deposits in central shanxi province could have acted as a paleogeographic and paleoenvironmental barrier for the dispersion of the yanliao biota that survived in northern hebei western liaoning and northestern shanxi province to the ordos basin during the late jurassic

mechanical anisotropy of columnar jointed basalts an example from the baihetan hydropower station china abstract columnar jointed basalts are characterized by a self organized joint network of discontinuities and pose a difficult challenge for geotechnical engineering design due to their inherent anisotropic nature we explore here the anisotropic characteristics of the columnar basalt formation in the chinese baihetan hydropower station including aspects of the geometrical rock structure deformation and strength anisotropy site investigations reveal that a typical cross section of the columnar basalt blocks is mainly quadrangular and pentagonal with an average edge length of 0 152 m three types of joints with different macro and micro characteristics form the columnar jointed rock mass and are identified by scanning electron microscopy in situ ultrasonic tests further confirm that the columnar basalt prisms exhibit transverse isotropy with the plane of isotropy perpendicular to the column axis as can also be observed in the field strength anisotropy is confirmed by point load and uniaxial compression tests the mechanical and anisotropic characteristics of baihetan s jointed basalt mass can be explained by its multi scale joints pattern by means of goodman s stiffness equation we find that the anisotropic coefficients obtained for its deformability and strength are similar for all testing methods employed including in situ p wave velocity point load tests and uniaxial compression tests this result confirms the strong anisotropic effect in these rock masses and facilitates an issue that must be considered when assigning input parameters for various classification and numerical analyses schemes

spatial temporal relationships of mesozoic volcanic rocks in ne china constraints on tectonic overprinting and transformations between multiple tectonic regimes abstract la icp ms zircon u pb ages and geochemical data are presented for the mesozoic volcanic rocks in northeast china with the aim of determining the tectonic settings of the volcanism and constraining the timing of the overprinting and transformations between the paleo asian ocean mongol okhotsk and circum pacific tectonic regimes the new ages together with other available age data from the literature indicate that mesozoic volcanism in ne china can be subdivided into six episodes late triassic 228 201 ma early middle jurassic 190 173 ma middle late jurassic 166 155 ma early early cretaceous 145 138 ma late early cretaceous 133 106 ma and late cretaceous 97 88 ma the late triassic volcanic rocks occur in the lesser xing an zhangguangcai ranges where the volcanic rocks are bimodal and in the eastern heilongjiang jilin provinces where the volcanics are a type rhyolites implying that they formed in an extensional environment after the final closure of the paleo asian ocean the early middle jurassic 190 173 ma volcanic rocks both in the erguna massif and the eastern heilongjiang jilin provinces belong chemically to the calc alkaline series implying an active continental margin setting the volcanics in the erguna massif are related to the subduction of the mongol okhotsk oceanic plate beneath the massif and those in the eastern jilin heilongjiang provinces are related to the subduction of the paleo pacific plate beneath the eurasian continent the coeval bimodal volcanic rocks in the lesser xing an zhangguangcai ranges were probably formed under an extensional environment similar to a backarc setting of double direction subduction volcanic rocks of middle late jurassic 155 166 ma and early early cretaceous 145 138 ma age only occur in the great xing an range and the northern hebei and western liaoning provinces limited to the west of the songliao basin and they belong chemically to high k calc alkaline series and a type rhyolites respectively combined with the regional unconformity and thrust structures in the northern hebei and western liaoning provinces we conclude that these volcanics formed during a collapse or delamination of a thickened continental crust related to the evolution of the mongol okhotsk suture belt the late early cretaceous volcanic rocks widely distributed in ne china belong chemically to a low to medium k calc alkaline series in the eastern heilongjiang jilin provinces i e the eurasian continental margin and to a bimodal volcanic rock association within both the songliao basin and the great xing an range the volcanics in the eastern heilongjiang jilin provinces formed in an active continental margin setting related to the subduction of the paleo pacific plate beneath the eurasian continent and the bimodal volcanics formed under an extensional environment related either to a backarc setting or to delamination of a thickened crust or both late cretaceous volcanics limited to the eastern heilongjiang jilin provinces and the eastern north china craton ncc consist of calc alkaline rocks in the eastern heilongjiang jilin provinces and alkaline basalts in the eastern ncc suggesting that the former originated during subduction of the paleo pacific plate beneath the eurasian continent whereas the latter formed in an extensional environment similar to a backarc setting taking all this into account we conclude that 1 the transformation from the paleo asian ocean regime to the circum pacific tectonic regime happened during the late triassic to early jurassic 2 the effect of the mongol okhotsk suture belt on ne china was mainly in the early jurassic middle late jurassic and early early cretaceous and 3 the late early cretaceous and late cretaceous volcanics can be attributed to the subduction of the paleo pacific plate beneath the eurasian continent

quartz vein emplacement mechanisms at the e26 porphyry cu au deposit new south wales porphyry cu au mo deposits are characterized by numerous fracturing events brittle fracture of mineralized intrusions and the surrounding host rocks is a consequence of hydraulic breakage caused by the interplay of the changing physiochemical properties of magmatic fluids and or the local tectonic regime we have mapped more than 1 400 quartz sulfide vein sets at the ordovician endeavour 26 north e26 deposit central new south wales in order to constrain the processes influencing fracture development around small 200 m porphyritic intrusions veins from intermediate levels in the e26 deposit define complicated patterns within 10 m of the porphyritic intrusions whereas more systematic patterns occur up to 50 m from the intrusive contact the outer parts of the ore deposit are characterized by quartz veins with orientations of 340 and subordinate orthogonal sets of bisecting veins at 240 and 290 the data show a broad range of vein orientations that define a conical distribution around a vertical axis there is a rare subset of near horizontal veins that formed early relative to the main stage of ore bearing vein emplacement many quartz veins exhibit fault displacements at both micro and macroscopic scales and fabrics including serrate fractures slickenlines and asymmetric fiber trails the distribution of veins suggests that the dominant fracture array developed perpendicular to the direction of bulk finite extension but significant vein dilation also occurred in orientations with a component of shear strain we propose a physical model that combines intrusion driven hydraulic fracturing into a preexisting fracture mesh to help explain the observed vein patterns and to better link fracture development and vein emplacement hydraulically driven deformation was important locally at e26 contributing to the formation of the irregular fracture stockwork immediately adjacent to the small intrusive bodies the more predictable vein patterns that occur away from the porphyritic intrusions require part of the hydraulically driven extension to have reactivated the existing fracture mesh parts of this more systematic geometry including the occurrence of flat veins are probably related to the emplacement of larger 10 km diameter magma bodies adjacent to e26 with doming causing the subordinate fracture arrays including the gross conical distribution fluctuating fluid pressures combined with hydraulically driven extension caused dilation of preexisting and synmineralization fractures and superposition of veins with similar orientations vein patterns suggest that the regional stress state that existed prior to or synchronously with porphyry ore deposit formation strongly influenced vein orientation to within tens of meters away from the mineralizing intrusions fractures that localized ore in the e26 porphyry deposit developed in response to the infiltration of fluid batches including magma and magmatic hydrothermal fluids into a regional deformation environment

synchronous deformation and hydrothermal activity in the shear zone hosted high sulphidation au cu deposit at peak hill nsw australia altered and mineralised rocks at peak hill are confined to a 300 500 m wide north south striking steeply dipping shear zone that is flanked by the mingelo volcanics along its western side and cotton formation siltstones along its eastern side this shear zone is defined by extensive zones of cataclasite and strongly foliated micaceous schists in marked contrast to the largely undeformed nature of the adjacent rocks advanced argillic assemblages quartz kaolinite pyrite alunite illite occur throughout the core of the peak hill deposit propylitic assemblages including albite quartz interlayered chlorite smectite illite and ankerite and a narrow discontinuous zone of argillic quartz illite pyrite alteration are developed in the mingelo volcanics along the western side of the deposit propylitic argillic and advanced argillic assemblages are overprinted by an internally zoned phase of phyllosilicate alteration that grades inwards from a peripheral sericite clay chlorite assemblage through phyllic assemblages muscovite illite pyrite paragonite to a pyrophyllite pyrite diaspore andalusite altered core au cu mineralisation is hosted by barite pyrite veins that cut the advanced argillic assemblage but pre date the phyllosilicate dominated alteration native au lacking ag calaverite te rich tennantite tetrahedrite goldfieldite chalcopyrite covellite and chalcocite occur in the barite pyrite veins no ore bearing minerals were detected in any of the alteration assemblages the total gold content of the peak hill deposit is currently 720 k ounces and this includes 100 k ounces of unmined reserves within the shear zone phyllosilicate minerals are developed in strain shadows and partly define the stretching lineation associated with dip slip movement the zonation within the phyllosilicate assemblages mimics the geometry of bends in the shear zone and minor internal structures these textures indicate that the phyllosilicate alteration developed synchronous with movement on the shear zone earlier advanced argillic alteration and mineralisation are developed in rocks derived from both sides of the shear zone hydrothermal activity associated with the earlier advanced argillic alteration was therefore either synchronous with juxtaposition of these distinct rock units or occurred during a later phase of movement on the shear zone cross cutting fibrous textures in the auriferous barite pyrite veins indicate that repeated fracturing of the advanced argillic altered rocks accompanied development of successive generations of auriferous veins concentrations of auriferous veins are localised in steeply plunging shoots that are oriented parallel to the stretching lineation in the shear zone these features all indicate movement on the host shear zone accompanied each phase of hydrothermal activity in the peak hill deposit the location alteration zonation and distribution of mineralised veins within the deposit are intimately controlled by deformation on the host shear zone synchronous with hydrothermal activity the development of high sulphidation hydrothermal systems synchronous with deformation along brittle ductile shear zones is a predictable consequence of intrusive activity during deformation in areas characterised by a high geothermal gradient the close relationship between tectonism and hydrothermal activity indicates that these deposits are likely to be located in the vicinity of regional scale shear zones deposits are likely to be aligned parallel to the regional scale structural grain and restricted to areas of conspicuous deformation as is the case at peak hill and temora nsw aluminous alteration zones concentrated in the vicinity of regional scale structures in the carolina slate belt may be a further example of this style of hydrothermal activity

high precision u pb geochronology of the jurassic yanliao biota from jianchang western liaoning province china age constraints on the rise of feathered dinosaurs and eutherian mammals the yanliao biota of northeastern china comprises the oldest feathered dinosaurs transitional pterosaurs as well as the earliest eutherian mammals multituberculate mammals and new euharamiyidan species that are key elements of the mesozoic biotic record recent discovery of the yanliao biota in the daxishan section near the town of linglongta jianchang county in western liaoning province have greatly enhanced our knowledge of the transition from dinosaurs to birds primitive to derived pterosaurs and the early evolution of mammals nevertheless fundamental questions regarding the correlation of fossil bearing strata rates of dinosaur and mammalian evolution and their relationship to environmental change in deep time remain unresolved due to the paucity of precise and accurate temporal constraints these limitations underscore the importance of placing the rich fossil record of jianchang within a high resolution chronostratigraphic framework that has thus far been hampered by the relatively low precision of in situ radioisotopic dating techniques here we present high precision u pb zircon geochronology by the chemical abrasion isotope dilution thermal ionization mass spectrometry ca id tims from three interstratified ash beds previously dated by secondary ion mass spectrometry sims technique the results constrain the key fossil horizons of the daxishan section to an interval spanning 160 89 to 160 25 ma with 2 analytical uncertainties that range from 46 to 69 kyr these data place the yanliao biota from jianchang in the oxfordian stage of the late jurassic and mark the daxishan section as the site of earth s oldest precisely dated feathered dinosaurs and eutherian mammals

timing of the earliest known feathered dinosaurs and transitional pterosaurs older than the jehol biota abstract the early cretaceous jehol biota in china has produced numerous well preserved fossils of feathered theropods and early birds recent discoveries of feathered dinosaurs as well as transitional pterosaurs and a sexually mature individual of darwinopterus preserved together with an egg from the daohugou biota of an earlier age than the jehol biota in northeastern china have greatly enriched our knowledge of the transition from dinosaurs to birds and primitive to derived pterosaurs the age estimate of fossils or host strata however has proven to be contentious and varies widely from the middle jurassic to the early cretaceous here we report a shrimp u pb zircon date unambiguously associated with the fossil horizons and thus for the first time provide an age calibration for the earliest appearance of feathered dinosaurs and transitional pterosaurs date results indicate that the feathered dinosaurs of china were present more than 161 ma ago unquestionably older than archaeopteryx in germany and are the earliest known feathered dinosaurs in the world furthermore feathers appeared in ornithischians before 159 ma rather than late in the early cretaceous the known transitional pterosaurs first emerged before 161 ma the daohugou biota containing mammals primitive pterosaurs insects and plants in addition to the feathered dinosaurs was living in inner mongolia western liaoning and northern hebei in northeastern china during the middle jurassic

development of crescentic bars for a periodically perturbed initial bathymetry 1 the development of crescentic bed patterns starting from an undisturbed beach i e one only perturbed so as to simulate background noise and thereby initiate morphological development is compared with that starting from a beach where monochromatic and in some cases bichromatic bed patterns pre exist using a fully non linear model morfo55 a wide range of different lengthscales and amplitudes is investigated the findings suggest that the pre existence of crescentic bed forms can influence the subsequent morphological development of this beach significantly but that this development is related to the undisturbed beach development whether a pre existing bed form remains under certain forcing conditions depends on the position of the pre existing lengthscale along the undisturbed linear growth rate curve if the pre existing mode shows significant linear growth in the undisturbed scenario this pre existing lengthscale remains otherwise the pre existing mode will be replaced by a bed form with a lengthscale closer to the undisturbed fastest growing mode a pre existing lengthscale that is significantly longer than the undisturbed fastest growing mode will be replaced by a higher harmonic of the original lengthscale for shorter pre existing lengthscales this will be the linear fastest growing mode an increased amplitude of the pre existing bed form accelerates the development toward a new stable situation for small initial amplitudes the initial response of the system to pre existing bed forms could theoretically be described using linearized equations alone the migration rates of both the pre existing and newly arising modes correspond to the migration rate of these modes in the undisturbed scenario

rhythmic morphology in a microtidal low energy beach abstract observations of rythmic features along the inner side of the trabucador barrier beach are coupled to two numerical models to unravel the mechanisms of its formation the trabucador is a long 6 km narrow 125 m barrier and microtidal beach at the sw side of the ebro delta catalonia its inner side is a low energy beach with a sandy shallow terrace featuring an intricate alongshore rhythmic morphology sixteen aerial orthophotos from 1946 to 2014 have been analyzed and complemented with field observations from 1986 to present this morphology is dynamic but it is usually characterized by a long finger transverse bars lftb and b large scale shoreline undulations lssu the lftb are thin and elongated with a length of the order of their spacing they are intertidal and typically attach to the shoreline by a megacusp commonly opening an anti clockwise angle of 10 40 with the shore normal there can be many up to 90 with both the mean and the most frequent alongshore spacing in the range 15 25 m spectral analysis always shows peaks in this range and sometimes additional peaks in the range 30 65 m that correspond to the spacing between the largest bars with smaller bars in between the lssu typically have wavelengths in the range 150 250 m their apexes sometimes coincide with the shore attachment of the largest bars but not always numerical modelling shows that both features could emerge out of feedbacks between hydrodynamics and morphology during the sw wind events involving a deflection of the longshore current by the bars combined with the refractive wave focusing and b gradients in total alongshore sediment transport rate triggering the high angle wave instability

bars bumps and holes models for the generation of complex beach topography in shallow water any two waves of the same frequency are shown to produce complex patterns of drift velocity above the sea bed if the longshore components hi h of the wave numbers of the two waves are different these steady flow patterns exhibit a longshore periodicity of wave number hi h irrespective of whether the waves propagate in the same direction say hi he positive or in opposite directions he negative the interaction of two edge wave modes is examined in detail the drift velocities are calculated and a simple sediment transport model is used to predict the beach topography that would be in equilibrium with these flow patterns as expected crescentic sand bars are produced by the special case of standing edge waves hi h intriguingly for all other cases a combination of complex transverse bars plus meandering or straight offshore bars result patterns that are surprisingly reminiscent of many published descriptions of complex rhythmic topography the extension of the model to three or more waves produces topography that appears to be very irregular although the pattern should repeat over sufficiently long distances along the beach even with only three waves these distances may be very large compared to the scale of the bars

a review of mesozoic climates there is overwhelming evidence based on the distribution of distinctive sediments and fossils and oxygen isotope data that the climate of the mesozoic world was appreciably more equable than that of today with no polar ice caps but precise quantitative data are not available except for an episode of late cretaceous cooling there is no good documentation of any significant change in global temperature distributions through the era the distribution of coals and evaporites together with other criteria indicates a pattern of humid arid and zones appreciably different in important respects from that of today during the triassic and jurassic western pangaea in low to middle latitudes was largely arid but in the early cretaceous the lands on the margin of the newly opening central atlantic and western tethys experienced a humid climate by late cretaceous times arid zones had become very restricted in extent because of insufficient suitable data attempts at climatic modelling have had only modest success and only to a limited extent can the major long term changes in climate between the permian and the present be explained in terms of changing geography the most probable explanation of mesozoic equability is an increased atmospheric co 2 content a number of enigmas remain such as the existence of flourishing forests in polar palaeolatitudes whereas for the late cenozoic short term climatic changes can be related successfully to variations in the geometry and mechanics of the earth sun system there is a long way to go before comparable success can be claimed for the mesozoic

2500 year paleotempestological record of intense storms for the northern gulf of mexico united states abstract the northern gulf of mexico has been devastated by recent intense storms camille 1969 and katrina 2005 are two notable hurricanes that made landfall in nearly the same location in mississippi fully understanding the risks and processes associated with hurricane impacts are impeded by a short and fragmented instrumental record however paleotempestology has the potential to employ modern analogues from intense storms in this region to extend the hurricane record beyond pre observational time existing empirically based models can back calculate surge heights over coastal systems as a function of transport distance particle settling velocity and gravitational acceleration we collected sediment cores in a pond 3 and adjacent beach 1 in hancock county mississippi grain size loss on ignition and microfossil analyses were conducted on cores in the context of a bayesian statistical age model using 137cs and 14c dating using hurricane camille to calibrate the archive similar coarse grained deposits were identified and inverse sediment transport models calculated paleosurge intensities similar in magnitude to camille over the 2500 yr record our multi millennial annual average landfall probability 0 48 closely matches previously published studies from the gulf of mexico indicating that intense hurricanes have not varied over these timescales over centennial timescales active intervals occurred between 900 to 600 and 2200 to 1900 yr bp with relative quiescence between 1900 to 900 yr bp comparisons with other published sites support the notion that southerly shifts in the loop current may be responsible for the decline in activity around 600 yr bp