the formation of turbidity maximum zones by minor axis tidal straining in regions of freshwater influence abstractthis study investigates the influence of tidal straining in the generation of turbidity maximum zones tmz which are observed to extend for tens of kilometers along some shallow open coa

superimposed tectono metamorphic episodes of jurassic and eocene age in the jadeite uplift myanmar as revealed by 40ar 39ar dating abstract the myanmar jadeite uplift forms an important link between the indo burma range and the tagaung myitkyina belt two contrasting ages of jurassic 152 4 1 5 ma of glaucophane from blueschist and eocene 44 8 1 1 and 45 0 1 3 ma of phengitic muscovites from quartz schists in the uplift were yielded using 40 ar 39 ar dating the jurassic age of the glaucophane even older than the forming age of the jadeitite from recent relevant literatures and for the reason of possible excess argon involved is interpreted as the lower limit of the subduction age previous studies correlated this subduction with the woyla intra oceanic arc or the incertus arc to the west the eocene ages of phengitic muscovites are interpreted as the time of an intra continental shearing deformation event against the timing of hp lt metamorphism as previously suggested combined with other studies it is suggested that the tagaung myitkyina belt and the indo burma range belonged to a single belt which has been separated by the sagaing fault leaving the jadeite uplift straddling along the fault between the belt and the range we propose a rapid exhumation model for the myanmar jadeitite at 45 ma coeval with onset of the sagaing fault

palaeomagnetism and 40ar 39ar age from a cretaceous volcanic sequence inner mongolia china implications for the field variation during the cretaceous normal superchron abstract an integrated palaeomagnetic and 40ar 39ar dating study was carried out on an early cretaceous volcanic lava sequence from the suhongtu section inner mongolia to determine the field behavior within the cretaceous normal superchron cns 40ar 39ar ages were obtained from 12 lava flows indicating that the studied lava was formed around 114 1 0 3 ma for the lower interval and 110 6 0 1 ma for the upper interval rock magnetic experiments and electron microprobe analyses indicate that the primary fe ti oxides are the main magnetic carriers all lava flows carry normal palaeomagnetic directions which can be grouped into 31 units by an f test with a fisher mean characteristic remanent magnetization chrm of d i 12 8 58 6 95 2 3 the corresponding palaeomagnetic pole is located at 80 3 n and 200 3 e a95 3 2 k 64 4 which is indistinguishable at the 95 confidence level from the eurasia pole derived from the apparent polar wander path for the early cretaceous using a modified thellier palaeointensity method with stringent acceptance criteria we obtained two time series of palaeointensity records from 15 independent palaeomagnetic units total 136 samples the virtual dipole moment vdm values varied from 2 53 1022 am2 to 9 92 1022 am2 the mean vdms for the upper and lower intervals are 5 38 2 06 1022 am2 and 4 61 2 67 1022 am2 respectively the observed time series of palaeointensity together with the previously available data for the cns suggest that magnetic field strength during the cns fluctuated significantly with time

diversity and evolution of the confuciusornithidae evidence from a new 131 million year old specimen from the huajiying formation in ne china gn is supported by a pg scholarship studentship from the alumni foundation university of bristol uk jml is supported by the spanish mineco project cgl 2013 42643 innovative team program of the beijing academy of science and technology the beijing millions of talents project in the new century the national natural science foundation of china no 41602006 and thebeijing natural science foundation no 5174032 provided funding for this research

paleomagnetic and geochronological constraints on the post collisional northward convergence of the southwest tian shan nw china a combined paleomagnetic and geochronological study is reported of paleogene basalt lavas and an intercalated red bed succession comprising a minimum of 14 basalt flows and 10 red bed horizons in the tuoyun basin of the southwest tian shan range china two basalt matrix samples yield 40 ar 39 ar isochron ages of 58 5f1 3 ma 2r mswd 0 9 and 60 4f1 3 ma 2r mswd 1 7 these compare well with a previously published k ar dilution age of 61 7f2 3 ma for comparable paleogene basalts and confirm that the younger pulse of magmatism in this basin is represented by both intrusive and extrusive activity demagnetization and component analysis identify a stable characteristic remanence chrm with predominantly reversed polarity following removal of secondary remanence by peak demagnetization steps below 250 350 8c or 5 mt rock magnetic analysis identifies pseudo single domain magnetite or titanomagnetite as carriers the stable chrm passes a fold test it was probably acquired at the time of lava emplacement results from the bulk of the collection imply that paleomagnetic data from the upper and lower 115 ma basalt series in the tuoyun basin are not distinguishable at the 95 significance level and indicate that this tectonic domain remained essentially stationary with respect to the earth s spin axis for 50 ma prior to onset of the india asia collision in early eocene times it is therefore probable that no paleomagnetically detectable crustal shortening occurred in the southwest tian shan prior to collision paleomagnetic data sets from the tuoyun basin also show that little or no paleolatitude difference is present between the tian shan and the reference latitude of eurasia at 60 ma this supports previous evidence suggesting that central asian blocks in the vicinity of the tian shan are unlikely to have experienced appreciable northward convergence relative to eurasia since onset of the india asia collision and initiation of the himalaya d 2005 elsevier b v all rights reserved

age of the barremian aptian boundary and onset of the cretaceous normal superchron abstract the age assigned to the boundary of the barremian and aptian stages remains one of the most poorly constrained post pangean stratigraphic boundaries the lack of a global boundary stratotype section and point gssp for the stage boundary has hampered efforts to calibrate the absolute age of the cretaceous period in the geological time scale the current definition of the barremian aptian boundary also approximates the onset of magnetic polarity chron m0r the end of this chron denotes the start of the cretaceous normal polarity superchron that is of fundamental importance for plate reconstructions currently there is up to 5 discrepancy in the age estimates of the barremian aptian boundary ca 126 121 ma and the start of the cretaceous normal superchron here we review available geochronological information from the late barremian and early aptian stages collected from the pacific ocean china california the ontong java nui large igneous province and the high arctic large igneous province by utilizing only robust geochronological data including u pb and recalibrated 40ar 39ar ages from sites with magnetic polarity information and or paleontological constraints we calculate a best estimate of between 123 8 and 121 8 ma for the barremian aptian boundary and the onset of chron m0r at 2 confidence using estimates of the duration of chron m0r 0 49 0 10 myr 2 we conservatively compute the start of the cretaceous normal superchron to between 123 4 and 121 2 ma 2 using an age of 83 07 0 15 ma 2 for the end of the cretaceous normal superchron the duration of the superchron is also constrained to between 38 0 and 40 5 myr 2 these age ranges for the barremian aptian boundary the onset of the cretaceous normal superchron and the duration of the superchron currently provide the best estimates until a gssp is formally ratified

detrital zircon u pb age constraints on cretaceous sedimentary rocks of lingshan island and implications for tectonic evolution of eastern shandong north china abstract in order to clarify sedimentary environment and tectonic history of the sulu orogenic belt we date zircons from four sandstones and one interbedded rhyolite collected on lingshan island in east shandong north china u pb age distributions of detrital zircon populations from the newly named lingshandao formation resemble that of overlying fluvial sedimentary rocks age distributions exhibit four main populations of paleoproterozoic 2 5 2 3 ga mesoproterozoic 2 1 1 9 ga neoproterozoic 850 700 ma and early cretaceous 138 121 ma age accompanied by sporadic occurrences of archean paleozoic and early mesozoic aged grains data indicate a depositional age of 121 ma for the lingshandao formation which constrains the maximum depositional age of overlying fluvial sedimentary rocks the lingshandao formation thus more likely correlates to the uppermost laiyang group of the jiaolai basin proterozoic age populations indicate a mixture of material derived from the north china ncb and yangtze block yzb basement along with protolith material from the hp uhp metamorphic units of the sulu orogenic belt proterozoic age populations differ from those of the roughly coeval jiaolai basin which represents a terrestrial depositional environment to the north of the sulu terrane the yzb appears to be a significant source of detrital zircons consistent with field observations

characteristics of a surface buoyant jet tidal outflow from leschenault estuary in winter forms an unsteady surface buoyant jet in koombana bay on each outgoing tide as the water moves away from the exit channel and spreads radially over the bay it assumes a plumelike nature the mean features of this buoyant outflow such as the plume shape frontal celerity internal circulation and the bulk entrainment were measured in an intensive field program these features are shown to compare favorably with results from previous laboratory investigations and predictions from a simple inertia buoyancy force balance which includes entrainment at the front the stability of the plume frontal region was examined and it is shown that subfronts were present but their behavior cannot be explained by reference to previous work

high precision 40ar 39ar age for the jehol biota abstract abundant fossils of the terrestrial jehol biota including plants insects dinosaurs birds mammals and freshwater invertebrates were discovered from the yixian formation and the overlying jiufotang formation in inner mongolia hebei province and liaoning province northeastern china because of the exceptional preservation of fossils the jehol biota is one of the most important mesozoic lagerstatten and is referred to as a mesozoic pompeii the jehol biota has provided a rare opportunity to address questions about the origin of birds the evolution of feathers and flight the early diversification of angiosperms and the timing of placental mammal radiation six tuff samples and two basalt samples collected from the tuchengzi the yixian and the jiufotang formations near the classic outcrops in western liaoning ne china yielded high precision 40 ar 39 ar ages we obtain an age of 129 7 0 5 ma for a basaltic lava from the bottom of the yixian formation and an age of 122 1 0 3 ma for a tuff from the lowermost part of the overlying jiufotang formation our age results provide an age calibration of the whole yixian formation and show that the whole formation was deposited entirely within early cretaceous time over an interval of 7 ma

on the response of a buoyant plume to downwelling favorable wind stress here the responseof a coastallytrappedbuoyantplume to downwelling favorablewind forcingis explored using a simplified two dimensional numerical model and a prognostic theory for the resulting width depth and density anomaly and along shelf transport of the plume consistent with the numerical simulations the analytical model shows that the wind causes mixing of the plume water and that the forced cross shelf circulation can also generate significant deepening and surface narrowing as well as increased along shelf transport the response is due to a combination of the purely advective process that leads to the steepeningof the isopycnals and the entrainment of ambient water into the plume the advective component depends on the initial plume geometry plumes that have a large fraction of their total width in contact with the bottom bottom trapped suffer relatively small depth and width changes compared to plumes that have a large fraction of their total width detached from the bottom surface trapped key theoretical parameters are wg wa theratioofthewidthoftheplumedetachedfromthebottomtothewidthoftheplumein contactwith it and the ratio of the wind generated mixed layer de to the initial plume depth hp which determines the amountofwaterinitiallyentrainedintotheplume themodelresultsalsoshowthatthecross shelfcirculation can be strongly influenced by the wind driven response in combination with the geostrophic shear of the plume the continuous entrainment into the plume as well as transient events is also discussed

on boundary value problems of the ideal fluid thermocline abstract recent developments of ideal fluid thermocline models are briefly reviewed using density coordinates boundary value problems are formulated for the ideal fluid thermocline with continuous stratification ekman pumping and surface density are specified as the upper boundary conditions no flow is permitted through the ocean s eastern boundary nor its bottom each water column is divided into three parts i e the stagnant abyssal water with specified stratification the unventilated thermocline with its potential vorticity specified and the ventilated thermocline with its potential vorticity determined by a global dynamic balance the unventilated thermocline is further divided into the shallow and deep parts potential vorticity is specified a priori for the latter however for the former potential vorticity has to be chosen in the process of calculating the solution so as to make the solution self consistent numerical integration of the ideal fluid thermocline equations is reduced to repea

multiple controls on rift basin sedimentation in volcanic settings insights from the anatomy of a small early cretaceous basin in the yanshan belt northern north china this paper deals with a small continental rift basin in a volcanic setting and tries to decipher potential controls on its synrift sedimentation the luanping basin which is a well exposed early cretaceous rift basin in the yanshan belt on the northern periphery of the north china block was chosen as a case study we show that extensive and vigorous volcanism took place just prior to the onset of basin formation and continued into a synrift period basin fills consist predominantly of lacustrine fan delta braid delta and volcaniclastic deposits lacustrine facies are composed mostly of deep lake deposits that appear to have been established soon after basin initiation fan delta systems developed along two high angle border faults the master northern hongqi fault and the secondary western xiaobaiqi fault fan delta fronts were built up primarily by gravelly and sandy debrites and turbidites braid delta deposits are restricted to the eastern corner of the basin and are characterized by an aggregation of braid plain conglomeratic deposits underwater extrusions of magma and pyroclastic flows are inferred from the presence of volcanic breccias ignimbrites andesitic pillows and peperites which are enclosed by host lacustrine deposits deep lake and fan delta systems persisted throughout the synrift period indicating a rapid subsidence rate with both adequate sediment and water supply the high angle border faults are thought to have played a critical role in creating large accommodation space and simultaneous displacements of the hongqi and xiaobaiqi faults led to the localization of a major depocenter in the western part of the basin one dimensional backstripping analysis of three stratigraphic sections shows that the luanping basin experienced marked synrift tectonic subsidence up to 2 km at a subsidence rate close to 0 2 mm yr 1 we propose that the high rate of basin subsidence might have been caused mainly by left lateral transtensional faulting and was enhanced by the superposition of basement downsag induced by underlying magma withdrawal a predominance of volcanic particles in both debrites and sandstones suggests that source areas were erodible volcanic edifices a humid paleoclimate is inferred which not only provided enough water supply but also promoted weathering of volcanic rocks in source areas thus maintaining both the deep lake environment and sediment influx we conclude that relatively small and isolated rift basins in volcanic settings can experience both rapid subsidence and receive thick lacustrine deposits if they are under the combined control of favorable structure climate and magmatism the model proposed here is believed to be applicable to other rift basins in similar volcano tectonic settings

acoustic transmission in the cold eddy in the southern east china sea 1 an acoustic transmission experiment with the hydrological observation was carried out in the southern east china sea ecs in summer 2003 the experiment site was located at a northwestern position of a cold eddy the comb structure of multipath signals a feature of the acoustic transmission in the typical shallow water with thermocline is received by the receiver positioned in the mixed layer the formation of the comb structure is explained with the normal modes in a depth mode number space combined with modal group velocities gvs the cold eddy has influence on the mode patterns and the modal gvs and the multipath structure of received signals

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

dates and rates in ancient lakes 40ar 39ar evidence for an early cretaceous age for the jehol group northeast china the correlation of freshwater sediments in small fault bound basins in liaoning province northeast china known as the jehol or rehe group has been a subject of debate for many years with biochronological estimates ranging from late jurassic to the cretaceous periods we have applied the laser ar 40 ar 39 technique to volcanic intercalations and lacustrine sediments from the yixian formation at the base of the jehol group minerals and whole rock chips from the upper parts of the yixian formation give concordant ages with a mean of 121 1 0 2 ma 1 sigma ages for samples near the base of the yixian formation give 121 4 0 6 and 122 9 0 3 ma and appear to be synchronous or only slightly older than the top of the formation integrated ages of 122 ma for glaucony from the lacustrine sediments lying stratigraphically between the upper and lower parts of the yixian are in very good agreement with the absolute age framework provided by the volcanic units such disseminated facies of this clay show promise for directly dating lacustrine sediments all of the above ar 40 ar 39 dates provide an absolute calibration of the yixian formation and show that the whole formation was deposited entirely within early cretaceous time over an interval of no more than 2 3 ma

the age of the dinosaur bearing sediments at tebch inner mongolia people s republic of china the coarsening upward clastic sequence at tebch inner mongolia china containing the dinosaur psittacosaurus mongoliensis comprises the remains of a fluviolacustrine system deposited in an extensional tectonic setting the presence of asteropollis sp cf asteropollis trichotomosulcatus singh singh 1983 in conjunction with the absence of tricolpate pollen indicates a barremian or possibly early aptian age the overlying tebch basalt dated by the 40ar 39ar laser step heating method yields a mid aptian age of 110 0 52 ma this chronology supports the argument that the juifotang formation of the jehe group in western liaoning is early cretaceous with the jurassic cretaceous boundary very low within or below the base of the jehe group our data also suggest that the berriasian hauterivian neocomian age suggested for the one known russian locality that has yielded p mongoliensis shestakovskaya svita at gorno altayaskaya avtonomnaya oblast may be excessively old

paleomagnetic and geochronological study of the halaqiaola basalts southern margin of the altai mountains northern xinjiang constraints on neotectonic convergent patterns north of tibet 1 a combined geochronological and paleomagnetic study is reported from miocene basalts from halaqiaola and paleocene to eocene red beds from fuyun at the southern altai mountains northern xinjiang three new 40ar 39ar ages determined by fresh matrix from the halaqiaola basalts collectively confirm the presence of cenozoic magmatic activity in the northern xinjiang alternating field and thermal demagnetization identify stable characteristic remanences with single reversed polarity in the basalts and red beds rock magnetic analysis identifies pseudosingle domain titanomagnetites as carriers of remanence in the basalts paleomagnetic results from the fuyun red beds indicate that inclination shallowing is present in this rock facies as also found in previous red bed studies from central asia in contrast the time averaged paleomagnetic direction from the basalts shows that no paleomagnetically discernible northward convergence has occurred north of junggar since early miocene times analysis of available cretaceous and cenozoic paleomagnetic data from volcanic rocks in central asia shows that neogene and quaternary paleolatitudes are statistically concordant with predicted values from eurasian references suggesting that no significant northward convergence has occurred north of tibet during the last 20 myr cretaceous and paleogene paleolatitudes lie 5 6 7 south of predicted values from the eurasian path and suggest that neotectonic convergence of the order of several hundred kilometers has occurred north of the southwest tian shan it is possible that neotectonic northward convergence north of tibet will prove to be paleomagnetically undetectable but more data are required to confirm this

40ar 39ar dating and preliminary paleointensity determination on a single lava flow from chifeng inner mongolia abstract a precise 40ar 39ar age and paleointensity data for the cretaceous lava flow from chifeng southern inner mongolia northeastern china are presented in this study detailed rock magnetic investigations including the variation of magnetization with temperature low temperature susceptibility and hysteresis loops show that pseudo single domain psd grain size high ti titanomagnetite is the main magnetic mineral in the studied lava flow both the microwave and double heating thellier techniques were used to determine the paleointensity yielding mean flow paleointensities of 15 6 3 2 t and 23 9 8 0 t respectively however the paleointensity results using the microwave technique are of higher quality mean q 12 for microwave compared to q 2 for thellier and yield higher internal consistency for the flow mean 21 standard deviation about the mean for microwave compared to 34 for thellier the microwave paleointensity result 15 6 3 2 t is therefore deemed the more reliable estimate for the paleointensity of the niutoushan lava flow 40ar 39ar age determination on the lava flow is 106 42 0 48 ma 2 relative to ga 1550 biotite 98 79 0 96 ma combining our 40ar 39ar dating and paleointensity results with other published paleointensity data suggests that the intensity of the earth s magnetic field during the middle cretaceous normal superchron cns was weak but variable throughout the whole cns

isolated dinosaur teeth from the lower cretaceous shahai and fuxin formations of northeastern china abstract isolated dinosaur teeth recovered from seven localities near fuxin western liaoning province northeastern china are described they come from sediments belonging to the shahai and fuxin formations considered to be aptian to albian in age seven taxa have been recognized they include the oviraptorosaur incisivosaurus dromaeosaurid theropods euhelopus like sauropods as well as indeterminate nodosaurid ankylosaurid iguanodontoid and basal neoceratopsian ornithischians the shahai and fuxin dinosaur faunas show the persistence of some jehol biota taxa such as the highly specialised incisivosaurus basal titanosauriform sauropods basal neoceratopsians and some dromaeosaurids and the addition of more derived iguanodontoids and ankylosaurians the persistence of some dinosaurs of the jehol biota into the shahai and fuxin formations suggests a long term stability of liaoning terrestrial environments during the early cretaceous despite sampling bias and the rather small sample that must be taken into account teeth abundances show a significant compositional difference between the localities of the shahai and fuxin formations neoceratopsian teeth representing one third of dinosaur tooth remains in the shahai formation whereas they are totally absent in the fuxin formation ankylosaur teeth in contrast represent 3 of total remains in the shahai formation whereas they seem to be the only herbivorous dinosaurs in the fuxin formation with 40 of the total number of teeth the rest being theropod dinosaur teeth although a difference in micro environmental conditions between shahai and fuxin localities may at least partly explain such pattern the unusual and unbalanced faunal composition of fuxin localities remains enigmatic and will need further field collecting in order to be clarified

semidiurnal switching of stratification in the region of freshwater influence of the rhine observations in the rhine region of freshwater influence rofi system in the north sea show evidence of large semidiurnal oscillations in stability superimposed on a mean stratification occurring throughout the stratified region at times of reduced mixing the amplitude of this semidiurnal variation is of the same order as the mean stability and frequently results in conditions being mixed or nearly mixed once per tide it is deduced that this semidiurnal variation results primarily from cross shore tidal straining which interacts with the density gradient to induce stratification this conceptual picture of the contributing processes has been tested in a one dimensional point model forced by the observed slopes and the local density gradients the model exhibits the same qualitative behavior as the observations produces oscillations in stratification of the amplitude observed and confirms the critical role of cross shore tidal straining the large cross shore shear nder stratified conditions is identified with the changes in ellipse configuration which are observed between mixed and stratified conditions the occurrence of semidiurnal variations in stability in the rhine rofi is thus inferred to be a consequence of the development of mean stability whenever the horizontal density gradients relax in conditions of low stirring

the chinese pompeii death and destruction of dinosaurs in the early cretaceous of lujiatun ne china the lujiatun unit yixian formation yields some of the most spectacular vertebrate fossils of the jehol group lower cretaceous of ne china specimens are preserved both articulated and three dimensional unlike the majority of jehol fossils which are near two dimensional compression fossils the site has been referred to as the chinese pompeii because the dinosaurs and other animals were assumed to have been killed and buried by hot airborne volcanic debris and ash in a single event this has yet to be confirmed field and laboratory evidence for the sedimentological context of the fossils from the lujiatun unit is described in detail and used to assess whether the fossil remains correspond to a single depositional event and whether this event was the direct result of volcanic activity fossils of the lujiatun unit occur in several horizons of volcaniclastic sediments that represent multiple depositional events petrological analysis shows that the fossil bearing sediments were remobilised and deposited by water the lujiatun dinosaurs and other fossils were therefore not killed by a single airborne volcanic ash but in multiple flood events with a high load of volcaniclastic debris

palaeointensity just at the onset of the cretaceous normal superchron abstract a combined palaeomagnetic and geochronologic study has been conducted on a basaltic lava sequence of five flows at jianchang in liaoning province northeastern china radiometric 40 ar 39 ar dating indicates that the volcanism occurred at about 119 ma within the marine anomaly c34n in cretaceous normal superchron cns rock magnetic investigations show that pseudo single domain psd or a mixture of single domain and multi domain grain titanium poor titanomagnetite is dominant in the studied lava flows both stepwise thermal and alternating field demagnetizations isolate the well defined normal characteristic remanent magnetization chrm in five independent lava flows with a mean direction of d i 11 1 57 2 95 5 7 palaeointensity was determined using the coe modified thellier method with systematic partial thermoremanent magnetization ptrm checks all together 61 samples from 286 samples with positive ptrm and tail checks yield palaeointensities ranging between 10 1 and 73 6 t to further check the effects of thermal alteration on the palaeointensity results a new ratio m rs 480 c m rs 25 c where m rs 25 c and m rs 480 c are the room temperature saturation isothermal remanent magnetizations for the raw sample and the product after a 480 c thermal treatment respectively is proposed results show that the ratio changes significantly even for those samples with positive ptrm check we further put forward that palaeointensity results are acceptable with ratio between 0 9 and 1 1 with this new criteria 17 samples show consistent palaeointensity results with an average of 20 0 3 2 t this value corresponds to the virtual dipole magnetic moments vdm of 3 5 0 6 10 22 am 2 which is about half of the value of present field this finding combined with other available results suggests that magnetic field of the earth just at the onset of the cns is characterized by a weak palaeointensity

convergence and downwelling at a river plume front abstract the small scale structure of the circulation and hydrography at the frontal boundary of the connecticut river plume in long island sound has been resolved using a novel combination of instruments a towed acoustic doppler current profiler adcp and a rigid array of current meters and conductivity temperature sensors observations were made during the latter half of the eastward ebb tide when the river plume was well established and the front was moving to the west at approximately 0 3 m s 1 two across front transects revealed a horizontal convergence rate in the across front velocity components at 0 6 m of 0 05 0 1 s 1 this was associated with a salt induced horizontal density gradient of 10 2 kg m4 observations obtained during a period in which the towed adcp was caught in the zone of maximum surface convergence showed significant downwelling with a near surface maximum of 0 2 m s 1 vertical velocities of this magnitude are consistent with observed magnitudes of the convergence rate at 0 6

new chronostratigraphic constraints on the yixian formation with implications for the jehol biota abstract the fossils of the cretaceous jehol biota exhibit excellent preservation and extraordinary diversity terrestrial fossils including plants insects dinosaurs birds mammals and freshwater invertebrates have been discovered from the dabeigou yixian and jiufotang formations and correlative strata in central and east asia significant specimens have been recovered from the yixian formation of inner mongolia hebei province western liaoning province of ne china the yixian formation is generally divided from bottom to top into the lujiatun unit lower lava unit jianshangou unit upper lava unit dawangzhangzi unit and jingangshan unit however previously reported age data obtained through a range of methods and applied to different units of the yixian formation do not consistently integrate with the yixian s commonly accepted stratigraphic interpretation here we summarize previous age data for the yixian formation and recalibrate previously reported 40ar 39ar ages by using new age interpretations for the same standard i e fcs 28 294 we also present new high precision 40ar 39ar ages of 125 8 1 0 ma and 126 0 0 8 ma for two basaltic samples from the lujiatun unit a unit of previously uncertain age the new age data and re calibrated published data indicate that the lujiatun unit was deposited contemporaneously with the jianshangou unit the widely accepted stratigraphic column for the yixian formation therefore requires reinterpretation our study provides significant clues for reconstructing sedimentary environment for the fossil rich yixian deposits and allows to constrain evolutionary rates for early mammals primitive birds and feathered dinosaurs

stable isotope chemostratigraphy in lacustrine strata of the xiagou formation gansu province nw china two sections from early cretaceous lacustrine strata of the xiagou formation from the changma basin in gansu province china are correlated based on their carbon isotopic compositions of bulk sedimentary organic matter and carbonate as well as carbonate oxygen isotopic compositions the samples were collected from fossiliferous strata which contain well preserved cretaceous bird remains the sections are primarily correlated based on a two step increase in dcorg with an overall magnitude of c 12 5 the stratigraphic variations in carbon isotopes within the two lacustrine sections are correlated with global carbon isotope variations c3 c7 based on marine carbon isotope records this correlation places the xiagou lacustrine strata in this locality within the early aptian stage specifically the selli equivalent which is associated with ocean anoxic event 1a the lower cretaceous record of positive and negative dc excursions in organic carbon and carbonate carbon has been well documented menegatti et al 1998 bralower et al 1999 in marine strata based on the relationship between carbon reservoirs in the ocean atmosphere system variations of dc from organic carbon and carbonate in continental sediments have been used to correlate the continental chemostratigraphic record of these excursions with those in the marine record grocke et al 1999 heimhofer et al 2003 ludvigson et al 2010 this can be particularly useful in sedimentary sequences which may have limited means for chronostratigraphic constraints abundant exposures of lower cretaceous continental strata occur in gansu province china fig 1 and contain well preserved flora and fauna including the remains of dinosaurs birds and flowering plants tang et al 2001 you et al 2005 2006 2010 ji et al 2011 although palaeontological research in these regions has advanced detailed stratigraphic relationships and correlations between sites and between local basins are still uncertain palaeoenvironmental and palaeoclimatological interpretations are dependent on more accurately defining the stratigraphic succession and timing of these continental deposits this study focuses on the xiagou formation in the locally named changma basin in the northwestern part of gansu province fig 1 which has produced a number of well preserved early bird fossils and is known to be early cretaceous in age based on biostratigraphy of purported equivalent strata in the region see section background from bojar a v melinte dobrinescu m c smit j eds 2013 isotopic studies in cretaceous research geological society london special publications 382 http dx doi org 10 1144 sp382 1 the geological society of london 2013 publishing disclaimer www geolsoc org uk pub ethics at university of kansas on may 24 2013 http sp lyellcollection org downloaded from

oxygen deficiency in lake sihetun formation of the lower cretaceous liaoning fossillagerstatte china the redox state of lake sihetun represented by the lower cretaceous yixian formation western liaoning china is evaluated to understand the formation of this konservat lagerstatte lake evolution is subdivided into four phases of which phases 2 and 3 exhibit excellent fossil preservation exceptional preservation and mass mortality events within phase 2 were previously attributed to synsedimentary volcanism and oxygen deficiency however the volcanic trigger for mass mortality events remains enigmatic and distinction between anoxia and dysoxia has not been put forward so far to resolve the redox state of the lake during phase 2 5394 diameters of pyrite framboid pseudomorphs in 29 thin sections from three localities have been measured framboid size distributions reveal that lake sihetun was governed by dysoxic bottom waters with spells of anoxia recording pronounced environmental stress hence holomictic eutrophic conditions were episodically replaced by meromictic interludes spatial variations in redox state were common and oxic conditions were detected in two of the three studied localities concentrated iron sulphide layers resulted from biofilms at the lake floor or the development of microenvironments around organic remains which preserved highly reactive organic compounds in contrast sediments of phase 3 record oxic conditions and an entirely holomictic lake

new 40ar 39ar dating results from the shanwang basin eastern china constraints on the age of the shanwang formation and associated biota abstract the fluvio lacustrine sequence of the shanwang basin eastern china preserves a rich and important terrestrial fossil fauna and flora the exceptional preservation of these fossils reveals the dynamics of ancient mammalian ecosystems and plant biology however the timing of this sedimentary sequence has been the subject of debate for decades here we contribute to this debate by presenting the detailed results of 40 ar 39 ar analysis of the basalts above below and within the shanwang formation these dates place stringent constraints on the age of shanwang formation and associated biota 40 ar 39 ar ages obtained from basalts of the niushan and yaoshan formations which underlie and overlie the shanwang formation are 21 0 2 5 ma 2 full external error and 17 3 1 5 ma 2 full external error respectively the 40 ar 39 ar age of the basalt in the shanwang formation is 17 18 ma given the age constraints of the basalts of the yaoshan and shanwang formations the age of the shanwang biota is estimated to be ca 17 ma late burdigalian of the early miocene indicating that the deposition of this fauna coincided with the onset of the mid miocene climatic optimum the results provide new age constraints on the shanwang mammal fauna and independently support interpretations that this fauna can be assigned to chronozone mn4 and correlated with middle orleanian of the european land mammal age and to late hemingfordian of the north american land mammal age biological diversity of the shanwang formation could reflect the global scale mid miocene climatic optimum

40ar 39ar dating of lujiatun bed jehol group in liaoning northeastern china the lujiatun bed of the yixian formation is famous for its extraordinary preservation of three dimensional fossils and its implication for the most dramatic catastrophic mass mortality event in the jehol biota the precise age of the fossil bearing deposits however remains to be established ar 40 ar 39 step heating analyses on bulk k feldspars from the fossil bearing tuff gave a weighted mean age of 123 2 1 0 ma 2 sigma this date suggests the lujiatun bed was most likely deposited at about the same time as the jianshangou bed of the lower yixian formation representing a stage when the dinosaurs displayed the most significant radiation in the early cretaceous

structural and sedimentary evolution of the southern songliao basin northeast china and implications for hydrocarbon prospectivity the southern songliao basin manifests itself as a wide rift system that developed in northeast china from the late jurassic to early cretaceous individual basins in the system experienced marked rift subsidence but the postrift subsidence was insignificant in most of the basins contrasting strikingly with the tectonic subsidence history of the northern songliao basin two types of rift basins are defined according to whether the basins underwent prominent postrift subsidence type 1 basins are characterized by thick postrift accumulations type 2 basins although experiencing minor postrift subsidence represent most of the southern songliao basin and can be subdivided in accordance with bounding fault geometry and areal extent basins bounded by high angle faults type 2a basins bounded by low angle faults type 2b and basins with limited spatial area type 2c many rift basins are expressed as narrow belts in map view and are composed internally of several segments linked through different types of transfer zones depositional processes and facies architecture of the basins are controlled primarily by dips and migration of active bounding faults synrift depocenters occur close to high angle bounding faults and deep lake deposition commonly persists through much of the synrift subsidence lacustrine deposition can be enhanced by the backward or toward the footwall stepping of active bounding faults depocenters controlled by low angle bounding faults in contrast tend to shift basinward through time and deep lake facies commonly develop in the middle stage of rifting at the end of the cretaceous basin inversion was evident in type 1 basins such as the shiwu basin on the north but other basins appear to have mostly escaped the contractional deformation gravitational collapse of the previously thickened crust is considered the cause for the generation of the rift basins and lateral flow of the ductile lower crust may explain the significantly induced postrift subsidence of type 2 basins effective plays occur in basins bounded by high angle faults and therefore type 1 and type 2a basins are suggested to be the main targets of future oil exploration synrift source rock maturation might be partially attributed to the heating of early cretaceous magmatism because shallower burial alone could not elevate temperatures high enough for petroleum generation

timing of the jiufotang formation jehol group in liaoning northeastern china and its implications the timing of the jiufotang formation remains speculative despite recent progress in the study of the jehol biota in this paper we contribute to this topic with ar 40 ar 39 dating on k feldspar sanidine and orthoclase from tuffs interbedded within the fossil bearing shales of the jiufotang formation from the upper part of the jehol group in chaoyang liaoning northeastern china ar 40 39 ar step heating analyses of k feldspar and the shrimp u pb zircon data indicate that tuffs at the shangheshou section erupted at 120 3 0 7 million years ago this result confirms an aptian age for the jiufotang formation that was mainly based on biostratigraphic evidence it also places stringent controls on the age of the fossils from the formation providing a minimum age 120 ma for the four winged dinosaur microraptor and the seed eating bird jeholornis

the influence of wind forcing on the chesapeake bay buoyant coastal current observations of the buoyant coastal current that flows southward from chesapeake bay are used to describe how the thickness width and propagation speed vary in response to changes in the along shelf wind stress three basic regimes were observed depending on the strength of the wind for weak wind stresses from 0 02 to 0 02 pa the buoyant coastal current was relatively thin the front slope was not steep and the width was variable 1 20 km for moderate downwelling southward wind stresses 0 02 0 07 pa wind driven cross shelf advection steepened the front causing the plume to narrow and thicken for stronger downwelling wind stresses greater than 0 07 pa vertical mixing dominated bulk richardson numbers were approximately 0 25 isopycnals were nearly vertical and the plume front widened but the plume width did not change plume thickness and width were normalized by the theoretical plume scales in the absence of wind forcing normalized plume thickness increased linearly from 1 to 2 as downwelling wind stresses increased from 0 to 0 2 pa normalized plume widths were approximately 1 for downwelling wind stresses from 0 02 to 0 2 pa the observed along shelf propagation speed of the plume was roughly equal to the sum of the theoretical propagation speed and the wind driven along shelf flow

the influence of tide and wind on the propagation of fronts in a shallow river plume in this study we used field data and radar images to investigate the influence of winds and tides on the propagation of tidal plume fronts the measurements were collected in a shallow shelf region off the dutch coast 10 km north of the rhine river mouth and they clearly show the passage of distinct freshwater lenses and associated fronts at the surface that propagate all the way to the coastline these fronts are observed as a sudden drop in near surface salinity accompanied by high cross shore shear with onshore velocities at the surface we determined the arrival time to our measurement site frontal propagation speed and structure of the fronts by combining the in situ data and radar images frontal froude numbers show a wide range of values with an average of 0 44 our results show that fronts during spring tides are thinner more mixed and move faster relative to the ground during calm spring tides when compared to calm neap tides downwelling winds during spring tides result in thicker and faster fronts however the intrinsic frontal propagation speed indicates that the wind and tide control the frontal propagation mainly due to advection rather than by changing the frontal structure strong return currents in the near bed layer resulting from fast and thick fronts increase near bed turbulence and bed stresses these high stresses suggest that the passage of fronts in shallow coastal areas can initiate sediment resuspension and contribute to transport processes

cross shore transport of nearshore sediment by river plume frontal pumping we present a new mechanism for cross shore transport of fine sediment from the nearshore to the inner shelf resulting from the onshore propagation of river plume fronts onshore frontal propagation is observed in moorings and radar images which show that fronts penetrate onshore through the nearshore and surf zone almost to the waterline during frontal passage a two layer counterrotating velocity field characteristic of tidal straining is immediately set up generating a net offshore flow beneath the plume the seaward flow at depth carries with it high suspended sediment concentrations which appear to have been generated by wave resuspension in the nearshore region these observations describe a mechanism by which vertical density stratification can drive exchange of material between the nearshore region and the inner shelf to our knowledge these are the first observations of this frontal pumping mechanism which is expected to play an important role in sediment transport near river mouths

the appearance and duration of the jehol biota constraint from sims u pb zircon dating for the huajiying formation in northern china the lower cretaceous huajiying formation of the sichakou basin in northern hebei province northern china contains key vertebrate taxa of the early jehol biota e g protopteryx fengningensis archaeornithura meemannae peipiaosteus fengningensis and eoconfuciusornis zhengi this formation arguably documents the second oldest bird bearing horizon producing the oldest fossil records of the two major mesozoic avian groups enantiornithes and ornithuromorpha hence precisely determining the depositional ages of the huajiying formation would advance our understanding of the evolutionary history of the jehol biota here we present secondary ion mass spectrometry sims u pb zircon analysis results of eight interbedded tuff tuffaceous sandstone samples from the huajiying formation our findings combined with previous radiometric dates suggest that the oldest enantiornithine and ornithuromorph birds in the jehol biota are 129 131 ma and that the jehol biota most likely first appeared at 135 ma this expands the biota s temporal distribution from late valanginian to middle aptian with a time span of about 15 my

early cretaceous tectonostratigraphic evolution of the erlian basin ne china a record of late mesozoic intraplate deformation in east asia abstract the erlian basin is one of the largest intracontinental meso cenozoic basins in northeast china the basin is filled with extra thick cretaceous sediments and offers unique opportunities to untangle the late mesozoic intraplate deformation in east asia however despite decades of petroleum exploration in the basin the early cretaceous chronostratigraphy and structural evolution of the erlian basin have been poorly studied based on newly obtained zircon u pb geochronological data well lithological logs and seismic reflection profiles the present study carries out a detailed analysis of the tectonostratigraphic evolution of the erlian basin during the early cretaceous the depositional ages of the lower cretaceous strata in the basin are refined and the early cretaceous evolution of the basin is reestablished the lower aershan upper aershan lower tenggeer upper tenggeer and saihan formations are constrained to the middle valanginian ca 138 135 ma late valanginian ca 135 133 ma hauterivian early aptian ca 133 121 ma middle aptian ca 119 115 ma and latest aptian albian post ca 115 ma respectively the early cretaceous syn rift subsidence of the basin was intermittent rather than continuous and was punctuated by multiphase contractional deformation during the earliest cretaceous prior to ca 138 ma middle valanginian ca 135 ma latest valanginian ca 133 ma middle aptian ca 120 ma late aptian ca 115 ma and early late cretaceous boundary we tentatively attribute the extensional and contractional deformation in the erlian basin to a series of continental collisions along asian margins karakoram lhasa qiangtang collision kolyma omolon siberia collision siberia amuria collision chukotka kolyma omolon collision west philippines south china collision and okhotomorsk east asia collision

a simple theory for the fate of buoyant coastal discharges abstract a simple theory that predicts the vertical structure and offshore spreading of a localized buoyant inflow onto a continental shelf is formulated the theory is based on two competing mechanisms that move the buoyant fluid offshore 1 the radial spread of the lighter water over the ambient water being deflected by the coriolis force and producing an anticyclonic cyclostrophic plume and 2 offshore transport of buoyant water in the frictional bottom boundary layer that moves the entire plume offshore while maintaining contact with the bottom the surface expression of the cyclostrophic plume moves offshore a distance ys 2 3g h0 2i 2g h0 2i 1 2f where g is reduced gravity based on the inflow density anomaly h0 is the inflow depth i is the inflow velocity and f is the coriolis parameter the plume remains attached to the bottom to a depth given by hb 2l ih0f g 1 2 where l is the inflow width both scales are based solely on parameters of the buoyant inflow at its source there

alternation of back arc extension and compression in an overriding plate evidence from cretaceous structures in the western liaoning region eastern china the dynamic evolution in an overriding plate remains a controversial issue cretaceous structures in the western liaoning wl region of the eastern north china craton ncc an overriding plate bordering the pacific ocean provide insights into the dynamic evolution related to paleo pacific plate subduction we present structural and fault slip data from the jurassic cretaceous basins in the wl region together with previously published isotopic ages to constrain structural and stress field evolution during the cretaceous these data reveal four phases of deformation in the wl region tectonic shortening d1 at 137 136 ma extension d2 during 136 97 ma another shortening d3 at the beginning of the late cretaceous and relatively weak extension d4 during the late cretaceous inversions of the measured fault slip data yield nw se compression during d1 nw se extension during d2 nnw sse compression during d3 and n s extension during d4 deformation phases d1 and d3 correspond to shortening events b and c of the yanshan movement whereas d2 corresponds to the peak destruction of the ncc in a back arc extensional setting the structural evolution indicates that the back arc extension d2 of the early cretaceous started immediately after the brief shortening event d1 and ended with another shortening event d3 subsequently the back arc region underwent weak extension d4 during the late cretaceous a slab driven model could account for the tectonic evolution in the eastern ncc periodic changes in the kinematics of the subducting paleo pacific plate are responsible for the alternation of the back arc extension and compression in the overriding plate

the impact of storms and stratification on sediment transport in the rhine region of freshwater influence we present measurements of along and across shore sediment transport in a region of the dutch coast 10 km north of the rhine river mouth this section of the coast is characterized by strong vertical density stratification because it is within the midfield region of the rhine region of freshwater influence where processes typical of the far field such as tidal straining are modified by the passage of distinct freshwater lenses at the surface the experiment captured two storms and a wide range of wind wave tidal and stratification conditions we focus primarily on the mechanisms leading to cross shore sediment flux at a mooring location in 12 m of water which are responsible for the exchange of sediment between the nearshore and the inner shelf net transport during storms was directed offshore and influenced by cross shelf winds while net transport during spring tides was determined by the mean state of stratification tidal straining dominated during neap tides however cross shore transport was negligible due to small sediment concentrations the passage of freshwater lenses manifested as strong pulses of offshore transport primarily during spring tides we observe that both barotropic and baroclinic processes are relevant for cross shore transport at depth and since transport rates due to these competing processes were similar the net transport direction will be determined by the frequency and sequencing of these modes of transport based on our observations we find that wind and wave driven transport during storms tends move fine sediment offshore while calmer more stratified conditions move it back onshore

astrochronology for the early cretaceous jehol biota in northeastern china article i nfo the early cretaceous jehol biota in northeastern china provides an evolutionary window for feathered dinosaurs primitive birds insects and early flowering plants it also provides critical information for the bio diversity changes of the early cretaceous terrestrial ecosystem here we report a time series analysis for the 11 2 m thick fossil bearing lacustrine deposits at the sihetun section in western liaoning northeastern china on the basis of high resolution magnetic susceptibility ms and anhysteretic remanent magnetization arm measurements a hierarchy of sedimentary cycle bands of 120 260 cm 50 67 cm and 18 42 cm was recorded in the ms and arm series with available radioisotope age constraints from the same section sedimentary cycles of 120 260 cm 50 67 cm and 18 42 cm were interpreted as milankovitch cycles of short eccentricity 130 and 95 kyr obliquity 36 6 and 46 kyr and precession 22 1 20 9 and 18 kyr respectively the 100 kyr tuned floating astronomical time scale indicates that the duration of the 11 2 m thick section is 0 67 myr and the average depositional rate is 1 70 cm kyr the duration of the 1 8 m thick main fossil bearing interval that contains 8 beds of feathered dinosaur primitive bird fossils can be estimated as short as 150 kyr the results suggest that climate fluctuations manifested in paleobotanical sedimentological and geo chemical records of the yixian formation may have been controlled by orbital forcing during early cretaceous 2013 elsevier b v all rights reserved

particle resuspension in the columbia river plume near field 1 measurements of suspended sediment concentration velocity salinity and turbulent microscale shear in the near field region of the columbia river plume are used to investigate the mechanisms of sediment resuspension and entrainment into the plume an east west transect was occupied during spring and neap tide periods in august 2005 and may 2006 corresponding to low and high river discharge conditions respectively during the high discharge period the plume is decoupled from the bottom and fine sediment resuspended from the bottom does not leave the benthic boundary layer the primary modes of sediment transport associated with the plume are advection of sediment from the estuary and removal of sediment from the plume by gravitational settling and turbulent mixing in contrast the plume is much less stratified during low discharge conditions and large resuspension events are observed that entrained sediment through the water column and into the plume our measurements indicate that two factors control the magnitude and timing of sediment resuspension and entrainment the supply of fine sediment on the seabed and the relative influence of tidal turbulence compared with buoyancy input from the river the latter is quantified in terms of the estuary richardson number rie the magnitude of vertical turbulent sediment flux is correlated with rie during the low flow period when there is a sufficient supply of bottom sediment in the near field region such sediment resuspension may be an important mechanism for the delivery of bioavailable micronutrients to the plume during the summer

gravity current structure of the chesapeake bay outflow plume measurements made across the edge of the chesapeake bay outflow plume in september 1996 are examined for evidence of the frontal head structure expected for a buoyant gravity current shipboard acoustic doppler current profiler and hydrographic data from two distinct 2 hour long sets of frontal transects are analyzed one set of observations was acquired just south of the bay mouth near cape henry virginia during late flood tide in water depth of 8 m these measurements show a nearly steady frontal structure and a frontal head that is approximately 5 m deep and 20 m wide the second data set was acquired about 20 km southeast of the bay mouth where the plume bulges horizontally outward over the continental shelf these measurements show a 9 m deep frontal head in water depth of 18 m that ultimately dissipates during early flood tide in both sets of observations relative inflow of plume water into the frontal head is confined to a shallow surface layer estimated to be no more than about 2 m deep referenced to this layer frontal propagation is supercritical froude number greater than 1 also measured was an expected sinking motion of the order of 3 cm s along the front overall the results are consistent with previous measurements made across smaller buoyant plumes and in the laboratory and they are compatible with the use of fixed values of froude number and entrainment parameter in two layer plume models additional study of the plume front during ebb tide is recommended

observations at the tidal plume front of a high volume river outflow 1 we present shipboard observations of very strong convergence vertical velocities and mixing and near bed impacts associated with the leading edge front of the tidally pulsed columbia river plume with upwelling favorable winds and riverflow of 4900 m3s 1 the plume propagates as a buoyant gravity current with a rotary bore like vertical frontal circulation and downwelling as strong as 0 35 m s 1 in waters as deep as 65 m near bed currents intensify to as much as 1 0 m s 1 after frontal passage and are often associated with elevated acoustic backscatter mixing is locally strong with an eddy diffusivity of o 0 2 m2s 1 50 m behind the front and t s diagrams imply plume mixing with 10 m deep ocean water these observations indicate that the leading edge front of a surface advected plume can cause exchanges of a nutrients between cold subsurface shelf waters and the river plume and b nutrients and sediments across the sediment water interface

apparent partial loss age spectra of neoarchean hornblende murmansk terrane kola peninsula russia the role of biotite inclusions revealed by 40ar 39ar laserprobe analysis metamorphic hornblende frequently yields spectra with progressively increasing 40ar 39ar age steps often interpreted as caused by partial resetting due to thermally activated radiogenic argon loss by solid state diffusion yet in many cases rising ca k ratio spectra for such samples imply the presence of minor inclusions of k contaminant minerals to avoid parts of grains with mineral inclusions or compositional zoning we drilled tiny discs from thin sections under a petrographic microscope laser step heating of drilled biotite free hornblende discs yielded flat age and ratio spectra in contrast furnace step heated hornblende separates from the same samples produced apparent loss age spectra moreover biotite free samples yielded flat spectra by laser and furnace dating consequently apparent loss spectra result from degassing of included substantially younger biotite before its hornblende host during laboratory step heating c 2640 ma hornblende ages constrain the murmansk terrane s cooling

toward age determination of the m0r barremian aptian boundary of the early cretaceous china most 973 program 2006cb701403 national natural science foundation of china 90714010 40573040 40634024 40221402 chinese academy of sciences kzcx3 sw 142

palaeomagnetism and 40ar 39ar age of a pliocene lava flow sequence in the lesser caucasus record of a clockwise rotation and analysis of palaeosecular variation summary a palaeomagnetic and rock magnetic investigation has been carried out on a pliocene lava flow sequence in the djavakheti highland in the central lesser caucasus in the republic of georgia in addition a 40 ar 39 ar dating and electronic microscopic studies were performed on samples of this sequence named the saro section which consists of 39 successive lava flows of doleritic basalts a characteristic magnetization could be isolated in all studied 39 flows yielding reverse polarity directions inall cases amean directiond 202 2 i 60 6 n 39 95 2 0 k 138 being obtained thermomagnetic experiments strong field versus temperature curves suggested low ti titanomagnetites and low curie temperature titanomagnetites with a rather high titanium content x 0 5 0 7 as the main carriers of remanence their domain structure is characterized by a mixture of single and multidomain grains 40 ar 39 ar dating yielded an age of 1 73 0 03 ma interpreted as the eruption age of the uppermost lava flow of the sequence analysis of palaeomagnetic results and radiometric data from the present and a previous study allows two different explanations about the time of emplacement of the section i the lower 36 flows of the sequence might have been emitted between the normal polarity reunion and olduvai chrons and the upper three flows after the olduvai chron with a long hiatus in volcanic activity of more than 150 kyr or ii the whole sequence has been emitted between 1 778 and 1 73 0 03 ma after the olduvai chron comparison of the palaeomagnetic results obtained in this study with the expected direction shows that while inclination values agree well declination shows an eastward deviation of 19 2 5 8 this discrepancy can be explained with a clockwise vertical axis rotation of the sequence which might have been produced by extensional structures with strike slip component which can be found in the study area virtual geomagnetic pole vgp scatter recorded in the sequence is somewhat lower than expected to analyse this behaviour vgp scatter of the sequence was first calculated with respect to the palaeomagnetic pole obtained from the fisher mean of all vgps then it was calculated with respect to the appropriate eurasian palaeomagnetic pole from vgps obtained after applying a 19 2 counter clockwise rotation of the sequence i e undoing the observed vertical axis rotation the observed scatter with both independent methods appeared to be very similar allowing the deduction that

the stratigraphy and paleoenvironment of a lycoptera bed site in eastern inner mongolia china correlation with the fossiliferous lower cretaceous strata in western liaoning abstract the stratigraphy and the fossil assemblage of a lower cretaceous lycoptera bed of the xinganling group in naketa arongqi area inner mongolia china are described and the paleoenvironment is discussed as it relates to the jehol biota the naketa fossil bed belongs to the lower part of volcanic sedimentary jiufengshan formation and preserves a typical eel eosestheria ephemeropsis trisetalis lycoptera davidi faunal assemblage which indicates a strong affiliation to the jehol biota of western liaoning china the fossil bed was deposited in a shallow to semi deep lacustrine setting with occurrence of oil shale facies and this is different from the lycoptera bed of the yixian formation and more similar to the overlying jiufotang formation in western liaoning a layer of volcanic tuffite within the fossil bed is dated as 121 6 0 47 ma using the zircon u pb isotopic dating method this age is contemporary with the age of the base of jehol biota producing jiufotang formation in western liaoning thereby supporting the biostratigraphic correlation however the genus lycoptera is almost entirely absent in western liaoning with only one species in the jiufotang formation where the dominant fish genus is jinanichthys therefore lycoptera in the great xing an mountain areas appears to have a longer record than in western liaoning which likely indicates that the fish fauna changed earlier in western liaoning and this observation supports the hypothesis that the yanliao area was the diversification center of some cretaceous new groups in ne asia preliminary analysis of the taphonomy and the geology indicates that the mass mortality of fish at the naketa site may not be related to volcanism additional taphonomic investigations would allow a better understanding of the early cretaceous aquatic paleoecology and paleoenvironment in the volcanic rifting regions the great xing an mountain area is a new opportunity for expanding the research on the jehol biota beyond the core localities in western liaoning

structure and dynamics of the columbia river tidal plume front 1 time dependent buoyant plumes form at the outflow of tidally dominated estuaries when estuary discharge velocity exceeds plume internal wave speed c a sharp front forms at the plume s leading edge that expands from the time dependent source using observations of the columbia river tidal plume from multiple tidal cycles we characterize time evolving plume structure and quantify front speed uf plume internal wave speed c front curvature and ultimate extent we identify three distinct stages of propagation 1 initially the plume is strongly influenced by shallow bathymetry near the river mouth 2 as the front advances offshore the plume detaches from the bottom and expands as a freely propagating gravity current with relatively constant uf c and frontal froude number f uf c ambient currents explain intracycle variability in uf and winds alter front shape variability in ambient stratification associated with previous cycles plume remnants leads to complex fronts and internal waves 3 finally the plume decelerates adjusts toward geostrophy and may radiate additional internal waves using a simple kinematic model we suggest that constant frontal propagation speed uf 0 9 0 1 m s during stage 2 is primarily controlled by linearly increasing volume flux from the columbia river mouth as this discharge rate subsides the plume expands as a fixed volume with decreasing front speed stage 3 the plume s final extent is controlled by the rossby radius which scales with a length based on the total volume discharged this provides an integral description of plume front evolution based on the time dependent estuary discharge

cruise observations of a cold core ring and β spiral on the east china sea continental shelf 1 cruise observations with ctds conductivity temperature depth profiler and a moored adcp acoustic doppler current profiler were carried out on the continental shelf of southern east china sea ecs in summer 2003 analyses of the cruise data reveal a low temperature belt sandwiched by warm waters on the shallow water side and on the continental slope side within the belt there are three cold centers with horizontal scales of 30 to 100 km distributed as a chain from the southwest to the northeast the upward protruding isotherms and spiral like daily averaged horizontal velocity structure indicate that the northeast cold center has all features of a mesoscale cold core ring estimated vertical velocity is of the order of 5 10 5 m s 1

temporal and spatial variations of mesozoic magmatism and deformation in the north china craton implications for lithospheric thinning and decratonization abstract mesozoic triassic cretaceous magmatic rocks and structural deformation are widely distributed in the north china craton ncc and are crucial to understanding the timing location and geodynamic mechanisms of lithospheric thinning and decratonization of the ncc our new geochronological geochemical and structural data combined with previously published results on mesozoic magmatic rocks and deformational structures in the ncc indicate a temporal and spatial migration of magmatism and deformation from its margins to its cratonal interior triassic and early jurassic igneous rocks are only distributed along the northern southern and eastern margins of the ncc in contrast cretaceous magmatic rocks are widely distributed in whole eastern and central parts of the ncc there is a younging trend for mesozoic magmatic rocks from the northern and eastern parts yanshan jiaodong peninsula and liaodong to the central part of the ncc taihangshan mesozoic deformation in the ncc exhibits a similar migration trend from craton margins to its inland areas triassic early jurassic deformation mainly occurred in the margins of the ncc and transformed from compression during the early middle triassic to extension during the late triassic to early jurassic in its northern margin middle late jurassic to earliest cretaceous deformation is widely distributed in the ncc and exhibited non unique contractional directions usually perpendicular to boundaries of the ncc and its ordos block indicating that it was likely controlled by multiple tectonic regimes during the middle late jurassic to earliest cretaceous early cretaceous deformation was characterized by near unique nw se extension that was likely controlled by unique geodynamic regime that probably related to the far field effect of cretaceous paleo pacific plate subduction the above mentioned temporal and spatial migrations of mesozoic magmatic rocks and deformation indicate that lithospheric thinning and decratonization of the ncc was diachronous and complex the lithospheric thinning and decratonization of the ncc initially started from its northern and eastern margins as a result of post collisional post orogenic lithospheric delamination during the middle late triassic and then spread to the interior of the craton during the late mesozoic interactions of the surrounding orogenesis and the small size of the ncc may have played important roles on its late mesozoic lithospheric thinning and decratonization

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

evolution of nonlinear internal waves in the east and south china seas synthetic aperture radar sar images from ers i have been used to study the characteristics of internal waves northeast and south of taiwan in the east china sea and east of hainan island in the south china sea rank ordered packets of internal solitons propagating shoreward from the edge of the continental shelf were observed in the sar images on the basis of the assumption of a semidiurnal tidal origin the wave speed can be estimated and is consistent with the internal wave theory by using the sar images and hydrographic data internal waves of elevation have been identified in shallow water by a thicker mixed layer as compared with the bottom layer on the continental shelf the generation mechanism includes the influences of the tide and the kuroshio intrusion across the continental shelf for the formations of elevation internal waves the effects of water depth on the evolution of solitons and wave packets are modeled by the nonlinear kortweg devries kdv type equation and linked to satellite image observations the numerical calculations of internal wave evolution on the continental shelf have been performed and compared with the sar observations for a case of depression waves in deep water the solitons first disintegrate into dispersive wave trains and then evolve to a packet of elevation waves in the shallow water area after they pass through a turning point of approximately equal layer depths that has been observed in the sar image and simulated by the numerical model the importance of the dissipation effect in the coastal area is also discussed and demonstrated

timing of the late jehol biota new geochronometric constraints from the jixi basin ne china abstract the jehol biota is a world famous early cretaceous terrestrial ecosystem in east asia and has revealed exceptionally well preserved fossils which provide significant insights into the origin and evolution of birds and feathers and the early diversifications of mammals and angiosperms after the long lived controversies over the timing of the biota varying from late jurassic to early cretaceous in last century the lifespan of the early middle jehol biota has been precisely dated from barremian to early aptian ca 131 120 ma by a series of recent radiometric analyses however few well constrained ages are available for the late jehol biota hindering our complete understanding of the evolutionary history of the terrestrial ecosystem alternating marine and non marine deposits of the chengzihe formation in eastern heilongjiang have yielded a non marine bivalve assemblage of the jehol biota basal angiosperms and cretaceous marine index bivalves which collectively offer crucial and indisputable clues against the prevailing jurassic time of the biota since 1990s here we present the first discovery of tephra layers from the chengzihe formation dated by zircon u pb geochronology as ca 116 111 ma providing the first quantitative age calibration for the early angiosperms and the jehol bivalve assemblage therefore we demonstrate that the duration of the jehol biota extends to late aptian early albian approximately 4 9 myr younger than the currently accepted age limits

a numerical technique to incorporate frontal boundaries in two dimensional layer models of ocean dynamics abstract this paper describes a novel numerical technique that exploits the method of bicharacteristics to allow small fronts to he included in numerical layer models of the ocean the approach treats a front as a free boundary and solves the interior problem using a standard finite difference scheme it employs a method based on the bicharacteristics of the equations to locate the boundary and enforce the boundary conditions the bicharacteristics for the nonlinear shallow water wave equations are derived and their application to the problem is outlined the method is demonstrated and evaluated by compared calculated approximate solutions first to the exact solution of a simple problem and second to a numerical solution of the more complicated problem of the radially symmetric discharge of a buoyant fluid into a stationary deep ambient fluid obtained using a simple alternative method the scheme is then successfully applied to investigate the effect of a uniform crossflow in the ambient fluid on the

determination of winter temperature patterns fronts and surface currents in the yellow sea and east china sea from satellite imagery abstract a detailed winter sea surface temperature sst pattern in the yellow sea and east china sea is derived from meteorological satellite thermal infrared images the isotherms in the pattern are calibrated by temperature measurements in situ the features of sst patterns are analyzed using images taken from a variety of satellites dmsp noaa 5 6 gms 1 and tiros n over the last 10 years the winter sst pattern has a sandwich structure which implies that two warm tongues sandwich one cold tongue this pattern starts forming at the end of november has formed by the end of january begins to decline at the end of february and disappears at the end of april in the sst patterns strong coastal fronts can be discerned they are the shandong peninsula coastal front the zhejiang fujian coastal front and the south korean coastal front based on the features of sst patterns and these fronts the winter surface currents are discussed

the 40ar 39ar dating of the early jehol biota from fengning hebei province northern china the bird fossil bearing deposits at the jiecaigou section correlative to the dabeigou formation in fengning hebei province northern china is well known for yielding a fossil assemblage representing the earliest evolutionary stage of the jehol biota the precise age of the fossil bearing deposits however is unknown the ar 40 ar 39 age spectrum obtained on bulk k feldspars from the tuff layer about 2 m below the bird fossil bearing layer gave a plateau age of 129 0 1 3 ma 2 sigma full external error and an isochron age of 132 3 4 5 ma 2 sigma full external error seventeen total fusion ar 40 ar 39 ages on k feldspars from the interbedded tuff about 6 m below the fossil bearing layer resulted in a weighted mean of 130 7 1 4 ma 2 sigma full external error these dates suggest an age of similar to 131 ma for the early jehol biota and combined with previous dating indicate that this biota lasted at least from 131 ma to 120 ma late hauterivian to aptian these dates also represent the earliest absolute age for known enantiornithine birds in the world

cyclostratigraphic analysis of magnetic records for orbital chronology of the lower cretaceous xiagou formation in linze northwestern china abstract in this study we report a tuned astronomical time scale for a sedimentary formation in early cretaceous the lower linze section located in the zhangye basin of the central hexi corridor northwestern china based on detailed field investigations we identified this sediment as the xiagou formation which is widely distributed in the region a thick prominent limestone layer crops out in the middle portion of the linze section and can be correlated to a similar limestone layer in the liupanshan group which has been dated via high resolution magnetostratigraphy this correlation places an age constraint of around 114 ma for the top of the underlying strata a total of 1245 samples were collected from the 474 m thick lower linze section for magnetic susceptibility measurements and cyclostratigraphic analysis spectral and continuous wavelet analyses were applied to the low frequency magnetic susceptibility series and the percentage frequency dependent magnetic susceptibility series as well as to specific subsections exhibiting visible rhythmic bedding a hierarchy of sedimentary cycles was identified with wavelengths of 21 5 37 0 m 7 5 9 5 m 2 1 4 4 m and 1 4 1 7 m the ratios between these lengths correspond well to the ratios between the durations of earth s orbital long eccentricity short eccentricity obliquity and precession cycles we interpret these sedimentary cycles to reflect the effects of orbital forcing on sedimentary processes using band pass filtering to specifically extract eccentricity cycles we established a tuned astronomical time scale for the xiagou formation in the lower linze section with a total duration of about 6 1 myr 114 1 ma to 120 2 ma based on this timescale the sedimentation rate of the xiagou formation is estimated to be in the range of 62 105 m myr with most intervals yielding rates in the 70 80 m myr range