on salinity regimes and the vertical structure of residual flows in narrow tidal estuaries abstract an examination is made of the circulation in narrow estuaries subject to a predominant tidal forcing velocity structures are derived separately for residual flow components associated with a river flow b wind stress c a well mixed longitudinal density gradient and d a fully stratified saline wedge dimensionless parameters are introduced to indicate the magnitude of each component and these parameters are evaluated for 9 major estuaries thereby revealing their sensitivity to each component for a channel of constant breadth and depth formulae are deduced for the length of saline intrusion l comparisons with observed data show that such formulae may be used with confidence to predict changes in l arising from variations in river flow tidal range or channel depths the level of stratification is shown to be related to a product of two parameters one associated with velocity structure and a second involving the square of the flow ratio u u i e residual velocity amplitude of the tidal velocity this relationship provides a simple classification system for estuarine stratification which can be used to indicate the sensitivity of any particular estuary to changing conditions

terrestrial and marine extinction at the triassic jurassic boundary synchronized with major carbon cycle perturbation a link to initiation of massive volcanism mass extinction at the triassic jurassic tr j boundary occurred about the same time 200 ma as one of the largest volcanic eruptive events known that which characterized the central atlantic magmatic province organic carbon isotope data from the uk and greenland demonstrate that changes in flora and fauna from terrestrial and marine environments occurred synchronously with a light carbon isotope excursion and that this happened earlier than the tr j boundary marked by ammonites in the uk the results also point toward synchronicity between extinctions and eruption of the first central atlantic magmatic province lavas suggesting a causal link between loss of taxa and the very earliest eruptive phases the initial isotopic excursion potentially provides a widely correlatable marker for the base of the jurassic a temporary return to heavier values followed but relatively light carbon dominated the shallow oceanic and atmospheric reservoirs for at least 600 k y

long term cycles of triassic climate change a new δ18o record from conodont apatite jat and isw gratefully acknowledge financial support from the australian research council dp1096252 mr is grateful for financial support from progetto d ateneo 2009 cpda090175 09 and 2012 cpda 121100 and prin 2008 2008bef5z7 005

sudden productivity collapse associated with the triassic jurassic boundary mass extinction the end triassic mass extinction is one of the five most catastrophic in phanerozoic earth history here we report carbon isotope evidence of a pronounced productivity collapse at the boundary coincident with a sudden extinction among marine plankton from stratigraphic sections on the queen charlotte islands british columbia canada this signal is similar to though smaller than the carbon isotope excursions associated with the permian triassic and cretaceous tertiary events

how tides and river flows determine estuarine bathymetries abstract for strongly tidal funnel shaped estuaries we examine how tides and river flows determine size and shape we also consider how long it takes for bathymetric adjustment both to determine whether present day bathymetry reflects prevailing forcing and how rapidly changes might occur under future forcing scenarios starting with the assumption of a synchronous estuary i e where the sea surface slope resulting from the axial gradient in phase of tidal elevation significantly exceeds the gradient in tidal amplitude an expression is derived for the slope of the sea bed thence by integration we derive expressions for the axial depth profile and estuarine length l as a function of and d the prescribed depth at the mouth calculated values of l are broadly consistent with observations the synchronous estuary approach enables a number of dynamical parameters to be directly calculated and conveniently illustrated as functions of and d namely current amplitude u ratio of friction to inertia terms estuarine length stratification saline intrusion length flushing time mean suspended sediment concentration and sediment in fill times four separate derivations for the length of saline intrusion li all indicate a dependency on d 2 f u u o uo is the residual river flow velocity and f is the bed friction coefficient likely bathymetries for mixed estuaries can be delineated by mapping against and d the conditions li l however the length of saline intrusion in a funnel shaped estuary is also sensitive to axial location observations suggest that this location corresponds to a minimum in landward intrusion of salt by combining the derived expressions for l and li with this latter criterion an expression is derived relating di the depth at the centre of the intrusion to the corresponding value of uo this expression indicates uo is always close to 1 cm s 1 as commonly observed converting from uo to river flow q provides a morphological expression linking estuarine depth to q with a small dependence on side slope gradients these dynamical solutions are coupled with further generalised theory related to depth and time mean suspended sediment concentrations as functions of and d then by assuming the transport of fine marine sediments approximates that of a dissolved tracer the rate of estuarine supply can be determined by combining these derived mean concentrations with estimates of flushing time ft based on li by further assuming that all such sediments are deposited minimum times for these deposition rates to in fill estuaries are determined these times range from a decade for the shortest shallowest estuaries to upwards of millennia in longer deeper estuaries with smaller tidal ranges

occurrences of early cretaceous fossil woods in china implications for paleoclimates article i nfo the chinese early cretaceous flora was divided phytogeographically into the northern floristic province and the southern floristic province the temperate wet vegetations and tropic subtropic xeric vegetations were proposed to represent the two different vegetation types about 52 species of fossil woods belonging to cycadophytes 2 species ginkgoales 1 species and coniferales 49 species have been discovered in the two floristic provinces mainly from the northeast china the biodiversity and anatomical characteristics espe cially the growth ring feature analysis of fossil woods indicated climatic conditions with seasonal variation in both the northern and southern floristic provinces during the early cretaceous it suggests that a tropic to sub tropic semi arid climate might dominate over southern china while warm or temperate and wet climate prevailed in northern china during the early cretaceous the wood evidence is in accordance with that of the leaf fossils collected from the corresponding formations of the early cretaceous in china

triassic monsoonal climate and its signature in ladinian carnian carbonate platforms southern alps italy abstract paleoclimatic general circulation models suggest the existence of a monsoonal climate during the permo triassic over wide parts of the megacontinent pangea and its adjacent oceans this paper discusses how ladinian carnian sedimentary successions outcropping in the southern alps record the signature of this climate sedimentological associations of tepees capped by terra rossa paleokarst braided fluvial sediments capped by caliche soils and evaporite beds alternating with clay rich delta deposits all indicate that net precipitation values changed substantially over short geological time scales early diagenetic features including episodes of dissolution in stratigraphies of meteoric calcite cements corrosion and hematitization of siliciclastic detritus prior to deposition early eu edral tectosilicate cementation and dolomitization from evaporation concentrated seawater record frequently changing paleohydrological conditions sedimentological and early diagenetic data recording highly variable seemingly conflicting paleoclimate information can best be attributed to fluctuations in net precipitation intensities controlled by monsoonal climate ranging from seasons to 106 yr d18o values in early meteoric cements 5 2 to 6 4 reflect the presence of strongly depleted meteoric waters which are not compatible with the southern alps paleolatitude or paleotopography in the triassic and can be directly related to precipitation intensities associated with a monsoonal climate strong precipitation could have also resulted in decreased surface water salinities and depleted d18o in surface waters d18o time series from marine rocks and early meteoric cements indicate a trend from middle triassic values generally deplet d with respect to the expected marine signature to less depleted late triassic values this is interpreted to represent an unusually wet episode high net precipitation transitionally grading in the late triassic into a relatively add period or low net precipitation despite the fact that several factors controlled the intensity of monsoonal precipitation the effects of its variations through time are evident at different time scales in the middle and upper triassic record of the southern alps

new record of fossil wood xenoxylon from the late triassic in the sichuan basin southern china and its paleoclimatic implications abstract fossil wood is one of the significant proxies for terrestrial paleoclimate and paleogeographical reconstruction in earth history abundant and diversified mesozoic fossil woods are well recorded in china however triassic fossil wood is very scarce here we report a new fossil wood from the late triassic xujiahe formation norian to rhaetian in guangyuan of northern sichuan basin southwestern china the fossil wood material consists of two well preserved specimens yielding secondary xylem with distinct growth rings bordered pits on the radial tracheid walls are mostly contiguous biseriate alternate locally uniseriate and strongly flattened cross fields show a large window like pore this anatomy is typical for the important fossil wood morphogenus xenoxylon gothan and based on a novel combination of radial and cross field pitting type and ray height a new species xenoxylon guangyuanense sp nov is recognized the finding of this new fossil wood taxon contributes to a better understanding of the yet poorly documented xenoxylon early radiation during the late triassic as well as of the origin of x meisteri group a peculiar endemic group which diversified in far east asia from the triassic to the early cretaceous xenoxylon is a paleobiogeographically significant genus being bound to cooler and or wetter climates of northern hemisphere throughout its late triassic late cretaceous range the occurrence of xenoxylon in the sichuan basin of southern china may indicate a short term cooling event sandwiched within a period during which warm and wet climate conditions largely prevailed over lower latitude regions of the northern hemisphere such a cooling event in the sichuan basin which was located at a low paleolatitude on the eastern rim of tethys may be in accordance in time with the temperature decline event in norian rhaetian boundary uncovered by oxygen isotope 18 o record in italy of the western rim of tethys

bathymetric evolution of the mersey estuary uk 1906 1997 causes and effects this paper examines how a continuous series of measurements and model studies have developed our understanding of the evolving interactions between tidal dynamics sediment regime and bathymetry of the mersey estuary among the most intensively monitored worldwide this includes familiar assessments of the capabilities of fine resolution 3 d models but is here extended to examine historical changes in tides sediments and estuarine bathymetries a century of bathymetric surveys indicates a net loss of estuarine volume of about 0 1 or 1 million cubic metres per year in contrast sea level rise of 1 2 mm a 1 represents only a 0 02 annual increase this relative stability persists in a highly dynamic regime with suspended sediment concentrations exceeding 2000 mg l 1 and spring tide fluxes of order 200 000 t detailed analyses of the bathymetric sequences indicate most significant changes occur in the upper estuary and in inter tidal zones a long period up to 63 years of tidal elevation records in the lower estuary shows almost no changes to the predominant m2 and s2 constituents the 3 d numerical model accurately reproduces both these elevation constituents and corresponding cross sectional distributions of currents simulation accuracies reduce upstream due to cumulative errors associated with relatively unstable bathymetries and increasing sensitivities to the bed stress coefficients impacts from increases in river flows of up to two or three times the long term mean value can only be detected in the upper estuary a detailed examination of sediment fluxes utilised a numerical simulation of conditions over a cross section in the narrows the 10 km by 1 5 km prismatic entrance channel the limited mobility of coarse sediments was contrasted with the near continuously suspended nature of the finest clay a sensible match between the net sedimentation rates indicated by the model and the net observed deposition rate was found to occur for silty sand corresponding directly with evidence from dredging records and from direct sampling while the model indicated sedimentation rates might increase by up to a factor of ten for much finer particles such occurrences are likely to be restricted by the limited availability of such material in the adjacent coastal zone the controlling mechanism for this import of fine sediments is via tidal pumping the nature of which depends critically on the phase lead of tidal currents relative to elevation however since this phase lead is determined by the large scale tidal energy balance of the estuary the conclusion is that stability of the overall tidal dynamics the associated sediment regime and bathymetry are likely to co exist and evolve slowly as indicated by the observed annual decrease in net volume suggestions are included for monitoring strategies in other estuaries to provide insight into such dynamics sediment bathymetry inter relationships

carbon and nitrogen isotope disturbances and an end norian late triassic extinction event major perturbations of organic carbon and nitrogen isotope ratios from a norian rhaetian late triassic boundary section in british columbia coincide with an extinction of the dominant deep water invertebrate fauna of the late triassic monotids and most ammonoids the carbon isotope excursion is attributed to the development of widespread oceanic stagnation that favored organic rich shale deposition the coincident nitrogen isotope excursion suggests that progressively more nitrate limited productivity forced a change to nitrogen fixing cyanobacteria populations as ocean stagnation created nutrient starved conditions the biotic crisis and geochemical events of the norian rhaetian boundary predate the latest rhaetian end triassic mass extinction thus the late triassic interval was marked by more than one extinction event

application of the stommel model to shallow mediterranean estuaries and their characterization during summer the basins of shallow estuaries in mediterranean climates are usually vertically mixed hypersaline and sometimes inverse in the sense of their densities being elevated above ocean values these estuaries are commonly controlled by heat and salt exchange with the ocean because of the compensating effect of estuarine heating the magnitude of the density inversion due to hypersalinity depends on the net surface buoyancy flux the surface heat and evaporative fluxes are functions of the estuarine temperature and so the estuarine state and its associated surface buoyancy flux depends on the strength of the ocean exchange processes a simple stommel model of a summer mediterranean estuary is presented here in which this exchange is controlled by density driven processes the stommel model has two possible stable stationary states and it is shown that the estuary can be characterized by four types of steady state they include the familiar classical and inverse estuaries plus a solution called quasi neutral in which the estuary is close to neutrality but just marginally inverse that is the net buoyancy flux is small and negative this quasi neutral solution resembles the steady state in tomales bay california in late summer and shows the characteristic high level of thermal compensation of the density inversion from hypersalinity it also has the observed very long flushing time which is responsible for some of the environmental fragility of this class of estuary this appears to be the first detailed confirmation of the applicability of the stommel model to estuaries the fourth type of estuarine state arises from the simultaneous existence of both stable states it is here called intermittent and contains both the classical and a quasi neutral stommel solution the type of estuarine state achieved by a narrow basin in autumn is highly dependent on its length and depth this produces extreme sensitivity to changes in basin geometry from human influences

saline intrusion in partially mixed estuaries abstract restricting interest to partially mixed estuaries earlier studies of tidally averaged linearised theories relating to the vertical structure of salinity and velocities accompanying saline intrusion are extended to take account of tidal straining and associated convective overturning the applicability of these theories is evaluated by reference to a single point numerical model in which the time varying cycle of depth averaged tidal current amplitude u and a temporally and vertically constant saline gradient sx are specified this model highlights the importance of convective overturning in counteracting unstable density structures introduced by tidal straining by omitting overturning in the model results agree closely with linearised theoretical derivations however incorporating overturning substantially increases tidally averaged surface to bed differences for both residual currents u and salinity s the vertical structure of tidal currents is a maximum and hence the effect of tidal straining in shallow macro tidal estuaries the propagation of tidal elevations and currents remains insensitive to saline intrusion in partially mixed estuaries the applicability of the model was evaluated by simulation of recent measurements by rippeth et al j phys oceanogr 31 2001 2458 to explore the generality of estuarine responses the model was run for a wide range of values of saline intrusion lengths l and water depths d additional sensitivity analyses were made for changes in u and bed stress coefficient k response frameworks are shown for u s potential energy anomaly work done by bed friction and internal shear rates and efficiency of saline mixing and ratios of relative mixing by diffusion to overturning by equating the rate of mixing associated with vertical diffusion with river flow q an expression for saline intrusion length l d 2 k u u o uo river flow velocity was derived this formulation agrees with an earlier derivation based on flume tests and showed reasonable agreement with observed values in six estuaries eight cases however in funnel shaped estuaries axial migration of the intrusion introduces major variations in d u and uo thereby complicating the application of the above expression for l moreover the time lag involved in the adjustment of l to changes in u and q may explain much of the complexity encountered in the observations

late triassic compositional changes of aeolian dusts in the pelagic panthalassa response to the continental climatic change abstract the carnian pluvial event cpe is considered as the drastic environmental change that occurred in the western tethys during the carnian late triassic although some studies have suggested that the cpe was a global event no studies have referred to pelagic environment related to the cpe to reveal the pelagic environment during the carnian x ray absorption fine structure xafs analysis was used to determine the iron fe species in chert samples collected from the ladinian carnian strata in the tamba mino ashio belt japan the x ray absorption near edge structure xanes analysis shows that all the red cherts contain hematite with a combination of clay minerals such as illite chlorite and smectite the existence of these minerals is identified using extended xafs exafs the xanes analysis of the green and the white cherts does not show any hematite signatures while the exafs analysis indicated increasing amounts of chlorite the stratigraphic change in the fe bearing compositions observed in this study can be divided into three stages i a stage where a relatively stable mineral composition chlorite illite hematite is observed in cherts deposited during the early carnian julian ii the abrupt change in mineral composition lack of chlorite and appearance of smectite observed in the middle area in the studied section and corresponding to the middle part of carnian late julian early tuvalian and iii the recovery of the previous stable mineral composition during the late carnian tuvalian these variations in the mineralogical composition of pelagic cherts can be interpreted to mean that the continental climate conditions changed during the carnian and different clay fractions were delivered to the pelagic region these data combined with the results of previous studies performed around the continental realm can be interpreted as follows i there was a relatively stable dry climate before the cpe ii there were increasing amounts of precipitation owing to the cpe and iii the climate returned to dry conditions similar to those prior to the cpe

climate of the supercontinent pangea numerous climate models predict that the geography of the supercontinent pangea was conducive to the establishment of a megamonsoonal circulation in general geologic evidence supports the hypothesis of a megamonsoon that reached maximum strength in the triassic pangea in the late carboniferous had widespread peat formation in what is now central and eastern north america and europe and relatively dry conditions on the colorado plateau the equatorial region of the continent became drier through the end of the carboniferous by the permian the equatorial region of pangea was dry and indicators of aridity and rainfall seasonality became more widespread wind directions from colorado plateau eolian sandstones are consistent with an increasing influence of monsoonal circulation at this time in the triassic climate in the colorado plateau region became relatively wet though still seasonal and the few eolian sandstones indicate a major shift in wind direction at that time in addition sedimentation

impacts of topography change on saltwater intrusion over the past decade in the changjiang estuary abstract saltwater intrusion in estuaries is mainly controlled by tides and river discharge as well as by topography and other factors the changjiang estuary has been seen a significant change in its topography from the data obtained in 2007 and 2017 in this study a well validated 3d numerical model was used to simulate and analyze the residual water and salt transport water diversion ratio wdr in bifurcated channels and water resources in the changjiang estuary in 2007 and 2017 the comparisons of the model results showed that due to the north branch becoming much shallower and narrower over the period from 2007 to 2017 the overall salinity in the north branch decreased and the intensity of saltwater spillover sso from the north branch into the south branch weakened in the north channel the simulated residual or net transection water flux ntwf and wdr decreased during spring tides resulting in increased saltwater intrusion during neap tides the saltwater intrusion was weakened despite the decreased ntwf and wdr because the water depth at the river mouth became shallower the changes of topography during that period also resulted in changes of dwr ntwf salt transport across the tidal flats and dykes in the north passage south passage and the south channel as well as overall dynamic mechanism the results indicated that the salinity at the water intakes of the three reservoirs in the estuary slightly decreased indicating that the time that reservoirs can take water from the estuary become longer in dry seasons in the scenario of complete silt up of the north branch the saltwater intrusion was weakened in the south branch because of the disappearance of the sso which was favorable for the utilization of freshwater resources but enhanced in the north channel north and south passages the overall influence from the topographic change over the period is that the saltwater intrusion is weakened in the north branch and enhanced during spring tides and weakened during neap tides in the north channel north and south passages sediment accretion in the north branch is favorable for utilization of freshwater resources

wood decay of xenoxylon yunnanensis feng sp nov from the middle jurassic of yunnan province china abstract a permineralised gymnosperm wood xenoxylon yunnanensis feng sp nov is described from the middle jurassic shaximiao formation in huize county yunnan province southwest china the pycnoxylic wood consists of thick walled tracheids and thin walled rays it is characterised by uniseriate contiguous compressed bordered pits on the radial walls of tracheids and one large simple pit in each cross field growth rings exhibit narrow latewood the mean sensitivity of analysis of 25 growth rings is 0 2 suggesting that a climate with abundant rainfall and weak seasonality could have prevailed in yunnan at least locally during the middle jurassic the outer portion of the wood is largely decayed and shows poorly preserved cells lacking details decayed tracheids displaying various features including removal of middle lamellae separations of secondary walls presence of thickened corners and appositions are recognised as cell reactions to fungal activity irregularly distributed micro cavities are formed by complete decomposition of tracheids and rays in the wood abundant fungal remains occurring in the wood generally consist of multiple branched hyphae these fungal hyphae are either confined to individual cell lumens or extend through adjacent cells although the probable reproductive structure and typical clamp connection are very rarely observed with few septate hyphae the affinities of these fungal hyphae are somewhat obscure nevertheless our study sheds light on the palaeoecology of middle jurassic terrestrial ecosystems of southwest china

new early jurassic tetrapod assemblages constrain triassic jurassic tetrapod extinction event the discovery of the first definitively correlated earliest jurassic 200 million years before present tetrapod assemblage fundy basin newark supergroup nova scotia allows reevaluation of the duration of the triassic jurassic tetrapod extinction event present are tritheledont and mammal like reptiles prosauropod theropod and ornithischian dinosaurs protosuchian and sphenosuchian crocodylomorphs sphenodontids and hybodont semionotid and palaeonisciform fishes all of the families are known from late triassic and jurassic strata from elsewhere however pollen and spore radiometric and geochemical correlation indicate an early hettangian age for these assemblages because all typical triassic forms are absent from these assemblages most triassic jurassic tetrapod extinctions occurred before this time and without the introduction of new families as was previously suggested by studies of marine invertebrates this pattern is consistent with a global extinction event at the triassic jurassic boundary the manicouagan impact structure of quebec provides dates broadly compatible with the triassic jurassic boundary and following the impact theory of mass extinctions may be implicated in the cause

residual circulation in shallow estuaries 2 weakly stratified and partially mixed narrow estuaries long wave theory is used herein to analyze circulation in weakly stratified and partially mixed estuaries unlike the highly stratified systems considered in part 1 the flows considered here have only a minimal tidal frequency internal wave component these estuaries may therefore be modeled as the sum of weakly interacting barotropic and baroclinic modes the dominant factors driving the residual flow are finite amplitude barotropic effects in weakly stratified estuaries and a combination of barotropic effects and steady horizontal density gradient forcing in partially mixed estuaries the dominant vertical exchange mechanism in the weakly stratified case is bottom boundary induced turbulence and that in partially mixed estuaries is believed to be random internal wave interactions a model of the columbia river estuary under weakly stratified conditions accurately predicts the observed residual velocity and salinity fields and the tidal amplitude at which a transition to a highly stratified state takes place the partially mixed state is unstable in the columbia river estuary because the tides and buoyancy input are both too strong

environment and ecology of east asian dinosaurs during the early cretaceous inferred from stable oxygen and carbon isotopes in apatite abstract during the cold late barremian early albian interval terrestrial environments in east asia were populated by rich and diverse vertebrate faunas characterized by a strong provincialism the latitudinal gradient of temperature and the existence of geographic barriers likely accounted for some aspects of this heterogeneous distribution of faunas other factors however such as local environmental conditions and interactions within vertebrate communities which could have influenced their distribution have not yet been fully identified and understood therefore new and published oxygen and carbon isotope compositions of apatite from chinese and thai reptiles dinosaurs crocodilians and turtles have been analyzed and interpreted in terms of ecology local air temperature and precipitation amounts differences in carbon and oxygen isotope compositions between various groups of sympatric plant eating dinosaurs sauropods ornithopods and ceratopsians indicate food resources partitioning among them most likely to avoid competition mid latitude environments where the jehol biota flourished were submitted to cool temperate climatic conditions with mean air temperature mat of 10 4 c and mean annual precipitations map of about 600 mm yr compatible with the existence of forest environments by contrast sub tropical regions characterized by mat of about 20 25 c were either submitted to high amounts of seasonal precipitations of about 1200 mm yr in thailand or to significant aridity map of about 400 mm yr in south china this difference in precipitation regime between thailand and south china may be attributed to the occurrence of the coastal cordillera extending along the east margin of the south china block these mountain ranges likely prevented humid air masses from the pacific to penetrate some parts of south china thus generating a rain shadow effect mosaic environments characterizing east asia during the late early cretaceous may have acted as a cradle for the origination of advanced dinosaur taxa that subsequently radiated over eurasia and north america during the late cretaceous

estimation of 3 d current fields near the rhine outflow from hf radar surface current data hf radar systems are designed to measure spatially variable sea surface currents a methodology was developed to complement these data with information about the current variability over the water column in a stratified shallow sea current profiles were estimated using a diagnostic model driven by surface current measurements from an hf radar system and by sea surface slopes derived from tide gauge data the structure of the model has a physical basis but its parameters were derived from an analysis of in situ current profile measurements application of the model to hf radar data from the scawvex rhine outflow experiment showed fair agreement with in situ current data as applications estimation and tidal analysis of current fields are demonstrated

simulating hydrodynamics in a spring fed estuary using a three dimensional unstructured cartesian grid model abstract this paper presents an application of a three dimensional unstructured cartesian grid model chen 2011 to a real world case namely the crystal river kings bay system located on the gulf coast of the florida peninsula of the united states crystal river kings bay is a spring fed estuarine system which is believed to be the largest natural refuge in the united states for manatees during the coldest days in winter because of the existence of a large amount of discharge out of numerous spring vents at the bottom of kings bay the unstructured cartesian grid model was used to simulate hydrodynamics including salinity transport processes and thermodynamics in the estuary during a 34 month period from april 2007 to february 2010 although there are some unidentified uncertainties in quantifying flow rates from the spring vents and salinity variations in spring flows simulated water elevations salinities temperatures and cross sectional flux all match well or very well with measured real time field data this suggests that the unstructured cartesian grid model can adequately simulate hydrodynamics in a complex shallow water system such as crystal river kings bay and the numerical theory for the unstructured cartesian grid model works properly the successful simulation of hydrodynamics in the estuarine system also suggests that an empirical formula that relates the spring discharge with the water level in kings bay and the groundwater level measured in a nearby well is reasonable

peat forming materials and evolution of swamp sequences case analysis of a jurassic inland coal basin in china abstract a case analysis was conducted in the yima coal mine which is located in a jurassic inland basin located in the henan province of central china using data from palynological ecology plant residues coal petrography and some geochemical characteristics the plant community during this coal forming period and the precursors of the coal forming peat were determined the peat forming paleoenvironment and evolutionary sequences within the swamp were reconstructed according to the differences in the spore pollen complex of the coals in the yima mine seven kinds of palynofacies each characterized by predominant species occured within the relative beds seven different types of ecological characteristics are indicated the different stages are represented by the corresponding floral facies six diagnostic properties of the coal facies were determined by studying the petrographic characteristics of each coal and seven different kinds of ancient peat forming swamp paleoenvironments are indicated by the coal facies a genetic model of formation development and evolutionary sequences of the coal forming swamp in the jurassic of central china is proposed

oxygen isotopes of east asian dinosaurs reveal exceptionally cold early cretaceous climates early cretaceous vertebrate assemblages from east asia and particularly the jehol biota of northeastern china flourished during a period of highly debated climatic history while the unique characters of these continental faunas have been the subject of various speculations about their biogeographic history little attention has been paid to their possible climatic causes here we address this question using the oxygen isotope composition of apatite phosphate from various reptile remains recovered from china thailand and japan values indicate that cold terrestrial climates prevailed at least in this part of asia during the barremian early albian interval estimated mean air temperatures of about 10 4 c at midlatitudes 42 n correspond to present day cool temperate climatic conditions such low temperatures are in agreement with previous reports of cold marine temperatures during this part of the early cretaceous as well as with the widespread occurrence of the temperate fossil wood genus xenoxylon and the absence of thermophilic reptiles such as crocodilians in northeastern china the unique character of the jehol biota is thus not only the result of its evolutionary and biogeographical history but is also due to rather cold local climatic conditions linked to the paleolatitudinal position of northeastern china and global icehouse climates that prevailed during this part of the early cretaceous

a tethys wide mid carnian upper triassic carbonate productivity crisis evidence for the alpine reingraben event from spiti indian himalaya abstract a significant mid carnian lithological change from carbonatic to siliciclastic sedimentation is described from the spiti himalaya n india the recorded sudden increase of terrigenous influx occurs at the boundary from the chomule to the rama formation it is dated within the late lower carnian uppermost aonoides zone and isochronous all over the tethys himalaya bio and chemostratigraphic data point to a synchrony with changes in carbonate productivity known from on area of wide extent along the nw tethys the reingraben event of the northern calcareous alps austria defines a regional decline in carbonate productivity related to both a platform demise and enhanced siliciclastic input laminated shales found in a distal part of the spiti basin document the onset of anoxic conditions within the deeper shelf synchronous to the reingraben event in austria high resolution biostratigraphy and identical 13ccarb curves are therefore in support of a direct link between the change in spiti and the reingraben event our data combined with a comprehensive review of previously postulated scenarios regarding the reingraben event suggest linking of climatic change with siliciclastic input and a carbonate productivity crisis initiated by onset of a relatively humid megamonsoonal late lower carnian atmospheric system that affected both the southern and northwestern tethys and point to a supra regional trigger of the alpine reingraben event

sediment trapping turbidity maxima and bathymetric stability in macrotidal estuaries 1 this paper examines how fine marine sediments are trapped in macrotidal estuaries and what processes coexist to maintain bathymetric stability an analytical emulator is constructed integrating explicit formulations for tidal and residual current structures together with sediment erosion suspension and deposition the emulator estimates suspended concentrations and net sediment fluxes and indicates the nature of their functional dependencies and corresponding sensitivities to tidal elevation amplitude or tidal current channel depth d bed friction coefficient f sediment size specifically settling velocity ws and river flow velocity ur associated scaling analyses reveal the relative impacts of terms representing tidal nonlinearities gravitational circulation and delayed settling using the emulator to determine conditions consistent with zero net flux of sediments or bathymetric stability we deduce ws f overall finer sediments are imported and coarser ones are exported with more imports extending to a coarser fraction on spring tides than on neaps the emulator indicates that the spring neap shifting of this coarse fine boundary corresponds to particle diameters between 30 and 50 m this constitutes selective sorting maintaining a widely distributed source of continuously resuspended material in a size range commonly observed by illustrating the acute sensitivity of sediment fluxes to the bed friction coefficient we anticipate feedback adjustments between suspended and surficial sediments factors governing the generation location and characteristics of turbidity maxima are indicated including dependence on d a direct link is shown between parameters that control sediment flux at a specific cross section and net upstream tidal energy dissipation

climatic and biotic change in the late triassic generally arid conditions that pervaded much of europe and north america during the late triassic were interrupted by a wet monsoonal climatic phase during middle and late carnian times extensive fluviatile sandstones deposited at this time throughout the region occur within a thick sequence of playa lake mudstones the sandstones occasionally contain kaolinite suggesting a humid climate an extreme 13 c depletion in a shallow marine sequence of this age in israel has been interpreted as evidence for an influx of freshwater a widespread change from carbonates to clastics in marine sequences at this time may also be climate related water course cave systems in limestone areas exposed during the late triassic indicate high levels of runoff during the middle and late carnian the marine invertebrate fauna shows a significant turnover at the end of the early carnian the terrestrial fauna and flora were relatively unaffected at this time but subsequently diversified prior to a major biotic turnover at the carnian norian boundary these periods of biotic change appear to be synchronous with the onset and cessation of a carnian humid phase the change to a monsoonal climate during this interval has been documented over more than 90 of longitude between 5 and 50 north of the triassic equator it may have been caused by rising atmospheric co 2 levels due to volcanism associated with the incipient dispersal of pangaea

relationships between tidal dynamics and bathymetry in strongly convergent estuaries abstract localized analytical solutions are derived for the propagation of a single predominant tidal constituent in estuaries with strongly convergent triangular cross sections the advective term is neglected and the friction term is linearized the solutions apply at any locality where the cross sectional shape remains sensibly congruent and the spatial gradient of tidal elevation amplitude is small i e synchronous then for specified tidal elevation amplitude and water depth d these solutions indicate values of tidal current amplitude u ratio of friction to inertial terms slope of the estuarine bed rate of energy dissipation and phase difference between and u illustrations of these results over a range of and d provide reference frameworks to assess observed conditions at any position in any estuary satisfying the criteria cited they may also indicate the range of parameters likely to be consistent with bathymetric equilibrium in dynamic sedimentary regimes the ratio of fr

new quantitative displacement criteria for slope deformation process from the onset of the accelerating creep to brittle rupture and final failure abstract two quantitative displacement criteria for slope deformation were deduced through the combination of a one dimensional renormalization group model and the strain softening constitutive model of geological materials the criteria can be used to understand the mechanical process from the onset of the accelerating creep on a slope through brittle rupture to the final failure and landslides the study showed that according to the first criterion the displacement ratio between the brittle rupture and the onset of the accelerating creep is approximately 1 48 which can be used to predict the brittle rupture of a slope with continuous progressive deformation the second displacement criterion shows that the displacement ratio between the final failure and the onset of the accelerating creep is approximately 2 59 which can be used to predict the occurrence of the ultimate disaster thus the critical displacement prior to the failure of the slope can be predicted using a time series of monitoring displacement data the methodology proposed in this study was validated using data from two well known landslides the vajont landslide in italy and the xintan landslide in china the results verify the applicability of this method