new insight into east asian tectonism since the late mesozoic inferred from erratic inversions of nw trending faulting within the bohai bay basin abstract the stress state and its dynamic background of east asia especially that during the late mesozoic remain controversial we analyze the structural evolution of the bohai bay basin bbb and it relationship with the regional tectonic history of east asia in particular we focus on the central bbb nw trending faults that have received little attention due to their inconspicuous structural features here we show that the erratic inversion of these nw trending faults records episodic crustal deformation that is crucial for better understanding the regional tectonism we find that these faults experienced alternating phases of shortening stretching and shearing deformation they initiated as reverse faults during the late triassic and reversed to normal faults during the early cretaceous the pre existing faults determined the development of nw trending basins which are synchronous with the peak destruction period of the north china craton ncc the late cretaceous marks a stage of regional shortening without magmatism which we propose to reflect a previously unrecognized period of flat slab subduction of the izanagi plate during the early paleogene 65 40 ma the reactivation of the nw trending faults likely due to the rollback of the oceanic slab caused intensive rifting of the basin during the late paleogene 40 23 ma they transformed to transtensional faulting due to the north south oblique stretching from the parallel dextral strike slip bounding faults from neogene the basin entering its post rift stage was characterized by the conjugate ne and nw trending strike slip fault systems likely in response to e w regional compression

long term change in tidal dynamics and its cause in the pearl river delta china abstract this paper focuses on identifying changes in the tidal range and the duration of the flood tide in the pearl river delta region china mann kendall test and regression methods are employed to verify the existence of trends in the annual tidal range and duration series from the 1950s to 2005 at 17 stations in the 3 major tributaries of the delta the research results indicate that generally there is an increasing trend in the tidal range and flood tide duration at most of the stations in the channel network moreover the more upstream the location of the station the more obvious the change in trend is and these increasing trends are all significant at the stations in the upper part of the delta specifically the tidal range at shilong station in the east river has increased abruptly since the middle of the 1980s such that the mean level of post 1990 data is approximately three times that for pre 1985 most stations near the mouth of the estuary show significant downward trends in the tidal range and flood tide duration results of the intersection point of the mann kendall test curves for these pearl river delta stations appear mostly in 1980s 1990s indicating that a noticeable change point occurs during this period human activities in the pearl river delta reached their peak during the 1980s among these large scale and long term sand excavation modified the hydrodynamic regime dramatically in a way that increased the water depth and lowered the level of the riverbed leading to an increased tidal prism and upstream movement of the tidal limit land reclamation is also likely to have had a relatively large effect on the tidal range and flood tide duration at stations near to the estuary mouth changes in other factors such as freshwater flow and sea level rise seem to be of relatively minor importance it is noteworthy that in a dry season the tidal dynamics are greatly enhanced and has resulted in strong saltwater intrusion into the estuary in recent years

imaging a crustal low velocity layer using reflected seismic waves from the 2014 earthquake swarm at long valley caldera california the magmatic system roof

recent morphological changes in the mekong and bassac river channels mekong delta the marked impact of river bed mining and implications for delta destabilisation abstract the mekong delta in vietnam is the world s third largest delta densely populated the delta has been significantly armoured with engineering works and dykes to protect populations and infrastructure from storms and shrimp farms from saltwater intrusion considerable development pressures in vietnam and in the upstream countries have resulted in the construction of several dams in china and in important channel bed aggregate extractions especially in cambodia the effects of these developments impact the delta dynamics in various ways in this study changes in the channel morphology of the mekong proper and the bassac the two main distributaries in the 250 km long deltaic reach from the cambodian border to the coast were analysed using channel depth data for 1998 and 2008 the channels display important and irregular bed changes over the 10 year comparison period including significant incision and expansion and deepening of numerous pools the mean depth of both channels increased by more than 1 3 m both channels also showed correlative significant bed material losses respectively 90 million m 3 in the mekong and 110 million m 3 in the bassac over the 10 year period these important losses over a relatively short period and weak correlations between bed incision and hydraulic parameters suggest that the marked morphological changes are not in equilibrium with flow and sediment entrainment conditions and are therefore not related to changes in river hydrology we claim that aggregate extraction currently practised on a very large scale in the mekong delta channels and upstream of the delta is the main cause of these recent morphological changes these changes are deemed to contribute actively to rampant bank erosion in the delta as well as to erosion of the mekong delta shoreline other contributory activities include the numerous dykes and embankments the role of existing dams in bed losses remains unclear in the absence of reliable data on the mekong sediment load future large scale hydropower dam development on the lower mekong main stem will have cumulative effects with aggregate extraction leading to increased morphological changes that will further impact the delta especially in terms of sediment supply and coastal erosion

the effect of barriers on the tidal range in estuaries numerical simulations of the shallow water equations are used to study the effect of topographic barriers on the tidal range in estuaries the results show that the nonlinear advection terms in the momentum equations play very little role and that the interaction between the tide and the topographic barriers is mostly due to friction the simulations employ a quadratic bottom friction law in which the usual drag coefficient is enhanced to parameterize the energy loss due to the generation of small scale waves

holocene relative sea level changes and coastal vegetation history at kentra moss argyll northwest scotland abstract a late holocene fall in relative sea level in northwest scotland from ca 1 3mm yr 1 to ca 1 0 mm yr 1 is interpreted from lithostratigraphic biostratigraphic chronostratigraphic and numerical analyses of fossil tidal marsh and acidic peat bog communities elevated by isostatic uplift pollen diatom and stratigraphic data from contemporary depositional environments are used to define the indicative range 0 2 m and reference water level mean high water of spring tides or highest astronomical tide of thirteen dated sea level index points no holocene intertidal sediments are recorded above 7 7 m od and all sea level index points are younger than ca 4 kyr b p in parts of kentra moss beyond the limit of holocene intertidal clastic sedimentation raised bog communities were established by at least 8 3 kyr b p these age and altitude parameters differ from those interpolated for the main postglacial shoreline but support a regional model in which isostatic uplift continues at present in the kentra moss area

distribution of magnetic properties of surface sediment and its implications on sediment provenance and transport in pearl river estuary abstract this study examines the magnetic properties of surface sediments and their implications on sediment provenance and transport in the lingding bay ldb which is the largest bay of pearl river estuary in china the concentration of magnetic and high coercivity minerals exhibits a low high low distribution pattern in the north middle south direction the western ldb is mainly covered by finer magnetic mineral particles whereas the eastern ldb is dominated by coarser particles three surface sediment provenances i e three groups are identified according to magnetic properties and particle size groups i and iii have terrestrial sources from the east river and west north river respectively whereas group ii is from a marine source in the adjacent sea the distribution of these three sediment provenances and their magnetic properties indicate that surface sediments are transported towards the southern direction with a sediment sink that occurs in the outer ldb as further confirmed by the grain size trend analysis results the main sediment depocenter moves southward because of human interventions the results further suggest that the ratio of saturation isothermal remanent magnetization to magnetic susceptibility sirm may be used as an indicator for distinguishing marine and terrestrial provenances and the s ratio s 100 may be employed as an indicator of sediment transport our findings demonstrate that sediment magnetic diagnosis provides an efficient approach to trace sediment provenance and transport and thereafter monitors the sediment process impacted by human intervention in estuaries worldwide

wave equation multiple imaging wemi swimming between the flags abstract deghosting dual sensor streamer seismic data requires separation of the total recorded wavefield into upgoing and downgoing components during seismic preprocessing imaging of multiples exploits the wavefield separation process by using the downgoing wavefield at each receiver location as a virtual source multiple imaging has been shown to effectively remove shallow acquisition related artifacts commonly seen on wide tow marine seismic surveys and improve imaging quality of the shallow overburden acquisition design factors imaging condition and cross talk noise are the main factors that determine the effectiveness of separated wavefield imaging swim of dual sensor streamer data swim is a common nontrademarked acronym used in the literature to describe multiple imaging of separated wavefields sampled from dual sensor streamer data in a field trial acquisition design did not allow for proper sampling of the total wavefield with the result that multiple imaging did not prove to be as rob

new insights into the hydrothermal evolution of skarn deposits a case study of the dongzhongla pb zn deposit in tibet sw china abstract revealing hydrothermal evolution from the early quartz sulfide to the late fluorite carbonate sulfide stages of skarn sulfide deposits is significant for understanding their ore formation processes but the detailed studies are rare in this study we choose the dongzhongla skarn pb zn deposit 0 38 mt pb zn located in central lhasa tibet as a case study and present detailed ore deposit geology and dataset of in situ chemical compositions of quartz in situ pb isotopic ratios of galena sulfur isotopic compositions of sulfides and c o isotopic compositions of hydrothermal calcite and wall rocks to address this issue there are two types of hydrothermal quartz in the early stage 1 the early phase euhedral quartz qz1 crosscut by quartz sulfide veins and 2 the late phase subhedral quartz qz2 coexisting with sulfides titaniq thermometer of qz1 and qz2 limits the two phases with a temperature range of 336 427 c mean 373 c and 357 461 c mean 386 c respectively the decreasing al concentrations of qz1 from core to rim suggest that magmatic fluids mixed with acidic meteoric water prevented the precipitation of sulfides during the early phase the increasing al and decreasing sulfur concentrations of qz2 indicate that the increasing ph values of hydrothermal fluids made principal sulfides precipitate during the late phase in addition fluid inclusions and c o isotopic studies reveal that the late stage minerals were deposited from low salinity

unravelling the causes of tidal asymmetry in deltas abstract tidal asymmetry in deltas is caused by both the intrinsic asymmetry resulting from the combination of astronomical tides and by nonlinear tidal interactions that occur in shallow water the relative importance of these sources of tidal asymmetry in delta channel networks have remained poorly studied partly due to the limitations of classical harmonic analysis ha in hindcasting nonstationary tides the pearl river delta prd is a multichannel system with rapidly changing bathymetry subject to severe human interventions this work applies a nonstationary harmonic model ns tide to hydrological data from 15 stations in the prd spanning the period 1961 2012 the spatiotemporal variation of multiple sources of tidal asymmetry is quantified by a skewness metric revealing how similar or dissimilar the development of alternative sources of tidal asymmetry develop in the delta subject to study a relative sensitivity coefficient rsc is introduced to decompose the contribution of tidal amplitude variations to multiple tidal asymmetries analytical results show the development of tides becoming gradually more asymmetric as they propagate into delta channel networks and how this depends on the river flow variation in the orientation of tidal asymmetries induced by different combinations of tidal constituents leads to a complex pattern of the overall tidal asymmetry in the prd our results show that tidal asymmetry in deltas can be significantly dependent on the river flow

prestack waveform inversion of three dimensional seismic data an example from the rock springs uplift wyoming usa abstractapplying seismic inversion to estimate subsurface elastic earth properties for reservoir characterization is a challenge in exploration seismology in recent years waveform based seismic inversions have gained popularity but due to high computational costs their applications are limited and amplitude variation with offset angle inversion is still the current state of the art we have developed a genetic algorithm based prestack seismic waveform inversion methodology by parallelizing at multiple levels and assuming a locally 1d structure such that forward computation of wave equation synthetics is computationally efficient this method is capable of inverting 3d prestack seismic data on parallel computers applying this inversion to a real prestack seismic data volume from the rock springs uplift rsu located in wyoming usa we determined that our method is capable of inverting the data in a reasonable runtime and producing much higher quality results than amplitude variation with offset ang

temporal and spatial trends of precipitation and river flow in the yangtze river basin 1961 2000 the suspected impact of climate warming on precipitation distribution is examined in the yangtze river basin daily precipitation data for 147 meteorological stations from 1961 2000 and monthly discharge data for three stations in the basin have been analyzed for temporal and spatial trends the methods used include the mann kendall test and simple regression analysis the results show 1 a significant positive trend in summer precipitation at many stations especially for june and july with the summer precipitation maxima in the middle and lower yangtze river basin in the 1990s 2 a positive trend in rainstorm frequency that is the main contributor to increased summer precipitation in the basin and 3 a significant positive trend in flood discharges in the middle and lower basin related to the spatial patterns and temporal trends of both precipitation and individual rainstorms in the last 40 years the rainstorms have aggravated floods in the middle and lower yangtze river basin in recent decades the observed trends in precipitation and rainstorms are possibly caused by variations of atmospheric circulation weakened summer monsoon under climate warming

recent morphological changes of the yellow river huanghe submerged delta causes and environmental implications abstract the yellow river huanghe submerged delta yrsd has been under the threat of erosion and retreat during the anthropocene due to dramatic climatic and anthropogenic changes in the yellow river basin the analysis of field data shows that over the period of 1977 2005 the changes in climate decrease in precipitation and increase in air temperature and human interventions increase in water diversion projects throughout the watershed have resulted in the sharp reductions of river flow and sediment discharges into the bohai sea consequently over the decadal timescale morphological evolution of the yrsd has gone through three stages i e rapid accumulation 5 77 10 8 m 3 year in 1977 1985 moderate accumulation 3 80 10 8 m 3 year in 1986 1995 and slow accumulation 0 91 10 8 m 3 year in 1996 2005 climatic change within the catchment characterized by the rapid increase of air temperature contributed significantly to the transitions from the rapid accumulation to the moderate accumulation and to the subsequent slow accumulation the decadal morphological changes of the yrsd also show peculiar deposition erosion characteristics over the medium timescale under river input reduction within the three decades the patterns of the main sedimentary body exhibit irregular ellipses with the long axis parallel to the 5 or 10 m isobaths and short axis perpendicular to the isobaths the depocentres of the yrsd are located between the 10 and 15 m isobaths close to the respective river mouths with a high vertical accretion rate of 1 20 m year the time series data of annual volumetric change of the yrsd and river sediment load from 1977 to 2005 further demonstrate significant linear positive relationships between deltaic geomorphic change and fluvial input over shorter timescales annual and 3 year the critical sediment discharges for maintaining the deposition erosion equilibrium state of the yrsd over the annual and 3 year timescales are found to be 1 79 10 8 t year and 1 29 10 8 t year respectively the analysis from the latest hydrological data 2006 2015 suggests that over the decadal timescale the evolution state of the yrsd currently has transitioned from constructive to destructive due to the weakened fluvial input moreover there exists a close quantitative link between the progradation of the yellow river subaerial delta yrad and the yrsd over the five year timescale indicating that every 1 10 8 m 3 year increase of the yrsd s yearly volumetric change will result in a 3 28 km 2 year increase of the yrad s yearly land accretion area and the yrad will reach the extension retreat balance state when yearly morphological change of the yrsd is at 0 73 10 8 m 3 year

overview and classification of wavefield seismic imaging methods the literature and seismic processing practice overflow with a diversity of wave equation migration methods so what makes wave equation migration a wave equation migration what is the commonality of these methods and how do they differ this article provides a framework for understanding different wave equation migration methods

destruction of the north china craton in the mesozoic the north china craton ncc was originally formed by the amalgamation of the eastern and western blocks along an orogenic belt at 1 9 ga after cratonization the ncc was essentially stable until

geodynamic evolution of flat slab subduction of paleo pacific plate constraints from jurassic adakitic lavas in the hailar basin ne china

the holocene record of loch etive western scotland influence of catchment and relative sea level changes abstract two sediment cores from inner loch etive a deep fjord basin on the west coast of scotland reveal a continuous sediment sequence spanning the last 10 000 yr benthic foraminiferal assemblages indicate that marine conditions prevailed in loch etive throughout the holocene however changes in sediment grain size composition and magnetic susceptibility suggest that the strength and frequency of deep water renewal events has varied through time this exchange with coastal water is controlled mainly by relative sea level changes influencing sill depth and the influx of freshwater to the loch the very early holocene sediments are well sorted coarse silt fine sands with a diverse assemblage of calcareous foraminifera indicating frequent renewal of bottom waters during this period immediately following the withdrawal of younger dryas glaciers denudation rates were high in the catchment area the period 9 7 ky bp during which relative sea level rose in this part of w scotland is characterised by highly variable environments the grain size data indicate an enhanced transport of sandy bed load material from the bonawe sill region to the basin deep during the mid holocene relative sea level high 8 9 m higher than present high relative sea levels at this time would explain the occurrence of frequent vigorous deep water renewal events and an increased tidal current regime in the loch the late holocene record is characterised by an upward fining of sediment grain size disappearance of calcareous benthic foraminifera and increasing organic content suggesting a development towards a more restricted fjordic circulation in response to the progressive lowering of relative sea level a sudden acceleration in this late holocene trend took place during the last millennium during which time human land use and deforestation have influenced the sediment and organic material flux to loch etive it appears that average holocene sediment accumulation rates in the bonawe deep were about 0 01 0 03 g cm 2 yr 1 which is far below modern estimates for the site this can be explained by vigorous bottom current activity during much of the holocene leading to a low net depositional rate

siltation on a highly regulated estuarine system the magdalena river mouth case northwestern south america abstracts comparison of geo referred bathymetric datasets from 2000 to 2017 at different timescales allowed to analyze changes in the sedimentary balance and to determine patterns of morphological adjustment in the magdalena river south america the magdalena river has one of the highest sediment yields among the major rivers of the world in addition it is a laterally constrained river mouth due to a series of man made structures inhibiting its morphological response thus it provides an illustrative example to study siltation processes in a river mouth system where a low capacity of morphological response interacts with a high magnitude sediment transport regime the river mouth exhibited an overall slow pace deepening trend between 2000 and 2017 however it experienced cyclic shifts between erosive and siltation states both at interannual and intra annual scales the rates of erosion were 310 mm yr 1 on average during the erosional stages whereas sedimentation rates were 293 mm yr 1 on average during the sedimentation stages maximum rates of erosion and sedimentation were 1450 mm yr 1 and 2625 mm yr 1 respectively however intra annual rates of sedimentation erosion were of the same magnitude or larger compared with the interannual rates such high rates and the rapid changes in the sedimentary balance is the result of the cumulative effect of its limited morphological response capacity and its large suspended sediment load these rapid processes generate constraints and threats to navigation particularly at intra annual scales consequently innovative intervention proposals recognizing the rapid transitions and geomorphological adaptations are required for managing this type of river mouths

channel response to low water levels in the pearl river delta a multi decadal analysis abstract the pearl river delta is a composite delta with one of the densest channel networks in the world to analyze the internal erosion deposition characteristics of the net channel area this paper studies the upstream evolution characteristics using digital elevation model data from local channel sections we attempt to establish the relationship between the changes in low water level and erosion rate by using the accumulated data for the main stream and hydrological stations over the past 50 years including the distributions of flow and sediment at the top of the net channel area and the erosion deposition data of a typical channel section in fact the net channel area has been in a forced erosion state artificial sand excavation for a long time forcing the flow and sediment distributions at makou and sanshui stations to adjust from 1993 to the present although the incoming sedimentation is far less than the net erosion and there are similarities and differences in the sources of the incoming flow and sediment from the main stream the internal characteristics of the upper and lower reaches of the delta have not changed substantially they have always been stable slow deposition channels the forced undercutting is concentrated within width depth ratios of approximately 50 250 which still meets the evolution characteristics of the natural channel artificial sand excavation during the 1980s tended to enhance the characteristics however the sudden increase in the undercutting rate has forced chaotic changes in the low water level since 1990 and the sediment transport rate decreased sharply the phenomena of salt tides retrogression and retrogressive erosion generally happen the water level evolution in the net channel area is chaotic and continuous undercutting is still occurring

evolution of the intra coastal tidal range in the rhine meuse delta and flevo lagoon 5700 3000 yrs cal b c abstract the evolution of the coastal and intra coastal tidal range in the western netherlands during the period 5700 3000 yrs cal b c 6875 4400 yrs b p is considered by comparing one coastal mean high water curve and two local mean high water curves mhw with respect to three alternative relative mean sea level msl curves 1 the existing 1982 msl curve for the western and northern netherlands 2 a msl curve based on the oldest part of the 1982 msl curve and the youngest part of a recently published msl curve based on data from the east central coastal plain and 3 a hypothetical msl curve for the east central coastal area assuming crustal subsidence of 0 10 m 1000 yr relative to the 1982 msl curve with regard to coastal tidal range the first and third msl curve yield a similar result a minor increase in coastal tidal range between 5200 yrs cal b c 6200 yrs b p and 4200 yrs cal b c 5350 yrs b p the second msl curve gives an increase in coastal tidal range from an assumed value of 2 m by 5200 yrs cal b c 6200 yrs b p to ca 3 m by 4100 yrs cal b c 5300 yrs b p conflicting with existing model results intra coastal tidal damping was a widespread phenomenon and played an important role in the evolution of the coastal plain for the first and second msl curves tidal attenuation in the rhine meuse delta and the east central coastal sector begins around 5250 yrs cal b c 6275 yrs b p with the third msl curve the reduction of the tidal range starts is 500 years later the first and third msl curves result in complete tidal damping in the rhine meuse delta and the east central coastal area with the second msl curve the tidal range in the rhine meuse delta remains ca 1 3 m whereas in the east central area tidal reduction is complete in spite of these different results it is clear that the period 5300 4300 yrs cal b c ca 6375 5400 yrs b p was very important for the subsequent evolution of the west netherlands coastal plain given that a the relative msl rise slowed down from about 0 8 m 100 yr to 0 23 m 100 yr b the coastal tidal range increased possibly by as much as 1 m resulting in higher sediment input into the intra coastal area while c further landward transportation of sediment was hampered due to intra coastal tidal damping which reduced rates of local mhw rise tidal current velocities and accommodation space

subtidal flow reversal associated with sediment accretion in a delta channel in branching delta channel networks tides intrude into parallel river outlets causing complex tidal behavior the tidal motion can impact the division of river discharge over distributary channels under some circumstances the discharge averaged over a tidal cycle may even reverse drawing ocean water intox the delta such as observed in the yangtze delta the fly delta and the colorado delta here we study the flow reversal associated with sediment accumulation of a distributary channel in terms of tidal propagation and subtidal discharge dynamics by focusing on the yangtze delta the yangtze delta channel configuration represents a deep and wide main channel and a smaller side channel that has rapidly accreted over the past decades a new mechanism is presented which results in seawater transport across the shallow side channel posing a risk to freshwater availability the shallowest section in the side channel nearly acts as a tidal divide in this section the tide has the character of a standing wave which implies that stokes transport converges from opposite sides of the channel this leads to significant variation of the total water storage in the side channel and subtidal water levels in the side channel being elevated above that in the main channel the bulge of water that is stored during spring tide leaves the side channel toward neap tide explaining reversal of the tide averaged discharge and seawater intrusion when the river discharge is low

late devensian and holocene records of relative sea level changes in northwest scotland and their implications for glacio hydro isostatic modelling raised tidal marshes and isolation basins lakes that were once connected to the sea in northwest scotland record changes in relative sea level following deglaciation during the late devensian to the present the kentra to arisaig area which was covered by relatively thick ice c 900 m at the last glacial maximum lgm shows a regression from a marine limit between 36 5 m od and 40 m od at c 15 9 kyr cal bp range 15 6 16 3 kyr cal bp through to an early holocene minimum a range of sites in the same area record a mid holocene maximum indicative of mean sea level c 6 5 m above present the maximum is not a well developed and short duration highstand as predicted by a number of models but is an extended period 8 0 5 0 kyr cal bp with sea level within c 1 m of the maximum sites to the north in kintail show no late devensian record because much of the area lies within the younger dryas ice limit the altitude of the mid holocene maximum in kintail is not well constrained but occurred 7 9 8 1 kyr cal bp further north sites on the applecross peninsula record a late devensian fall in sea level and a holocene maximum for mean sea level no higher than c 3 0 m above present in coigach the furthest north of the new sites and well outside the younger dryas ice limit there is no evidence recorded of late devensian sea levels above present the holocene maximum here was around c 2 5 m above present these observations of sea level change all standardised to change in mean sea level relative to present constrain the glacio hydroisostatic rebound model parameters earth models comprising three mantle layers with lateral viscosity and elastic parameters give a satisfactory description of rebound the parameters h lithosphere thickness 65 km g 6 upper mantle viscosity 4 1020 pa 14c seconds and g lower mantle viscosity 1022 pa 14c seconds give the best overall agreement but discrepancies between observations and predictions remain an increase of 10 in ice thickness north of the great glen compared to the previous optimum ice model provides good agreement for many sites but important discrepancies remain for the northern sites and indicate inadequacies in the model of the british ice sheet several alternative ice models are examined but the various combinations of earth and ice model illustrate the non uniqueness of the solution a combination of more extensive ice limits especially onto the hebridean shelf and west shetland shelf and some changes to ice thicknesses over the mainland should produce a better agreement but the spatial coverage of observations remains a limitation to producing a unique solution the characteristics of the holocene highstand age duration and amplitude at the di erent sites refutes the assumption that globally deglaciation ceased abruptly 7000 yr ago the observations are consistent with an ice model that includes c 3 m of melting over the last 7000 yr 2000 elsevier science ltd all rights reserved

nodal modulation of the lunar semidiurnal tide in the bay of fundy and gulf of maine observations numerical modeling and theoretical calculations show how the 18 6 year modulation of the main lunar semidiurnal tide in the bay of fundy and gulf of maine is reduced from its astronomical value of 3 7 percent to 2 4 percent by the effects of friction and resonance the agreement of the three approaches increases confidence in model predictions of widespread changes in the tidal regime resulting from development of tidal power

age and genesis of the neoarchean algoma type banded iron formations from the dengfeng greenstone belt southern north china craton geochronological geochemical and sm nd isotopic constraints abstract banded iron formations bifs are important for understanding the composition and redox condition of paleo oceans as well as the evolution of the precambrian crust the neoarchean dengfeng greenstone belt ca 2 54 2 50 ga in the southern north china craton ncc consists of metamorphosed igneous and sedimentary assemblages including some bifs here we present mineralogical geochronological geochemical and sm nd isotopic data of the dengfeng bifs for the first time to constrain their age origins and source characteristics and then discuss their paleo environmental implications the bifs are mainly associated with metabasaltic rocks and quartz rich schists and can be classified as algoma type bifs zircon u pb dating of quartz rich schists interbedded with the bifs coupled with ages of wall rock metabasites demonstrate that the dengfeng bifs formed at 2 53 2 51 ga most bif samples have high contents of sio2 and fe2o3t and extremely low contents of al2o3 tio2 and high field strength elements e g zr hf th u indicating that they are detrital free deposits in the post archean australia shale normalized multi element diagram the detritus free bif samples are characterized by depleted light rare earth elements positive la and y anomalies and suprachondritic y ho ratios resembling geochemical features of modern seawater the absence of negative ce anomaly indicates an anoxic condition positive eu anomalies and relatively high concentrations of transition metal elements suggest that high temperature hydrothermal fluids contributed to the source of bifs isotopically all bif samples have positive end t values 0 12 to 4 53 consistent with the range of those 0 10 to 4 31 of ca 2 66 2 50 ga dengfeng metabasites and ttg gneisses suggesting input of possible juvenile crustal fluxes the elemental and isotopic characteristics of the dengfeng bifs collectively suggest that they precipitated from anoxic seawater with various input of hydrothermal fluids and oceanic crust derived fluxes

human impact on floods and flood disasters on the yangtze river abstract in the middle reaches of the yangtze river the floods have become more and more frequent and the water level rises higher than before the damages are becoming ever more serious this is primarily a consequence of human activity in the river basin three aspects deserve particular attention first destruction of vegetation has led to soil erosion in the upper reaches in the past 30 years the forest cover has been reduced to half while the area exposed to severe erosion doubled in size in the long run this can be expected to increase flooding second land reclamation and siltation has reduced lake sizes this has resulted in decrease of the flood storage capacity third the construction of levees has caused flood levels to rise due to restricted flood discharge capacity establishment of the great jinjiang levee caused silting up of the riverbed and valley in the mid reaches of yangtze consequently the discharge capacity decreased to 60 000 68 000 m 3 s which is sufficient only for ordinary floods this article concludes that the deteriorating flood situation is the result of inappropriate human intervention in the natural environment it is suggested that the appropriate strategy should change from keeping the flood away to giving the flood way related tactics and strategies under consideration are briefly summarized

flow and form in rehabilitation of large river ecosystems an example from the lower missouri river abstract on large intensively engineered rivers like the lower missouri the template of the physical habitat is determined by the nearly independent interaction of channel form and flow regime we evaluated the interaction between flow and form by modeling four combinations of modern and historical channel form and modern and historical flow regimes the analysis used shallow slow water shallow water habitat swh defined as depths between 0 and 1 5 m and current velocities between 0 and 0 75 m s as an indicator of habitat that has been lost on many intensively engineered rivers and one that is thought to be especially important in rearing of young fishes two dimensional hydrodynamic models for modern and historical channels of the lower missouri river at hermann missouri indicate substantial differences between the two channels in total availability and spatial characteristics of swh in the modern channel swh is maximized at extremely low flows and in overbank flows whereas the historical channel had substantially more swh at all discharges and swh increased with increasing discharge the historical channel form produced 3 7 times the swh area of the modern channel regardless of flow regime the effect of flow regime is evident in increased within year swh variability with the natural flow regime including significant seasonal peaks of swh associated with spring flooding comparison with other reaches along the lower missouri river indicates that a channel form is the dominant control of the availability of habitat even in reaches where the hydrograph is more intensively altered and b rehabilitation projects that move toward the historical condition can be successful in increasing topographic diversity and thereby decreasing sensitivity of the availability of habitat to flow regime the relative efficacy of managing flow and form in creating swh is useful information toward achieving socially acceptable rehabilitation of the ecosystem in large river systems

sediment transport from the yangtze river china into the sea over the post three gorge dam period a discussion sediment loads from the yangtze river into the sea experienced a major increase in the late holocene when sand beaches along the deltaic coast changed into tidal flats sediment transport averaged about 472 million tons a year between the 1950s and the mid 1980s and decreased by 124 million tons a year after the mid 1980s followed by a dramatic drop since the closure of the three gorge dam tgd this paper discusses the major processes for the decline of sediment discharge since the 1950s and discusses the method for evaluating its future development over the post tgd period sediment loads in the post tgd period will be mainly determined by the major processes that may significantly contribute to the following three components i e 1 the sediment input from the upper basin into the three gorge reservoir tgr 2 the ratio of sediment export from the tgr relative to the input and 3 the amount of sediment recovery downstream the tgd restrained by available sediment sources an integrated evaluation shows that the annual sediment loads over the post tgd period will possibly vary from 1 12 to 1 32 million tons a year or less in ordinary years

late jurassic to early early cretaceous tectonic nature on the ne asian continental margin constraints from mesozoic accretionary complexes abstract it is widely accepted that subduction of the paleo pacific plate beneath eurasia began in the early mesozoic however the tectonic nature and processes of the ne asian continental margin in the late jurassic to early early cretaceous remain unclear in this contribution lithological provenance and metamorphic deformation data are used to constrain the formation of mesozoic accretionary complexes ac along the ne asian continental margin and determine the tectonic relationship between the ne asian continental margin and the paleo pacific plate in the late jurassic to early early cretaceous the mesozoic ac formed during the late jurassic including the raohe ac in ne china the khabarovsk samarka and taukha acs in the russian far east and the mino tamba ac in japan and early cretaceous including the shimanto ac in japan and the kiselevka manoma ac in the russian far east the jurassic ac underwent a complex evolution including the formation of seamounts middle late jurassic terrigenous clastic sedimentation adjacent to the trench collision of seamounts with eurasia northward migration of the ac early early cretaceous terrigenous clastic sedimentation a second period of accretion and final emplacement the earliest mesozoic ac arrived at the trench at ca 195 ma combined with the occurrence of early mesozoic calc alkaline igneous rocks along the ne asian continental margin we suggest that subduction of the paleo pacific plate beneath eurasia began in the early jurassic jurassic ac in japan was affected by a regional high p t metamorphic event at 160 ma which might have been related to subduction collision of seamounts with eurasia at the trench ages and hf isotopic compositions of detrital zircon grains from the middle upper jurassic and cretaceous ac sandstones together with paleontological and paleomagnetic data indicate that jurassic clastic sediments were sourced mainly from the south china block scb whereas the lower cretaceous sandstones were sourced from the eastern central asian orogenic belt caob the inferred northward migration of jurassic ac in the late jurassic to early early cretaceous indicates that the boundary between the ne asian continental margin and the paleo pacific plate was characterized by strike slip tectonics at this time likely due to a small angle of obliquity in the subduction of the paleo pacific plate beneath eurasia in the late early cretaceous westward subduction of the paleo pacific plate beneath eurasia resulted in the emplacement of the raohe and khabarovsk acs at 137 130 ma and the formation of acs in the russian far east and japan

geological control of the eastern great wall mountain basin relationships in the eastern north china craton abstract the e w trending yanshan belt an intraplate fold thrust belt located in the northern north china craton has experienced several episodes of mesozoic deformation which resulted in the widely distributed magmatism and mountain basin tectonics that completely re shaped the topography of the eastern north china craton the eastern part of the famous chinese great wall was built on the high range of the southeastern yanshan mountain belt juxta posed to the plain which directly relates to the bohai bay basin our study focuses on which tectonic processes created such mountain basin couple in mid late mesozoic times the u pb la icp ms dating of zircons yield ages of 114 to 201 ma for various granites and 115 to 116 ma for volcanic rocks from yixian and jiufotang fms the detrital zircons from the lower cretaceous sandstones yield four age groups of 2587 to 2460 ma 2222 to 1828 ma 297 to 190 ma and 187 to 100 ma which are all sourced from the qinglong and surrounding areas and indicating that the qinglong area started to uplift after the middle jurassic the qinglong area underwent multiple deformation by ne sw compression in the middle late jurassic times wnw ese compression in the late jurassic to early cretaceous ene wsw extension in the early cretaceous and nnw sse compression in the late cretaceous during the final stage of the yanshanian orogeny meanwhile widely distributed granite intrusions and emplacement of the upper jurassic lower cretaceous volcanic rocks indicate a large amount of magma input into the area the qinglong area with the great wall along its southern margin close to adjacent plain to the south was uplifted to form the qinglong highland and surrounding related basins by combination of the following three processes the multiple tectonic late jurassic and late cretaceous shortening processes related to yanshanian orogeny early cretaceous regional extension triggered by slab retreat of the paleo pacific ocean and inflation of large amount magma at depth during jurassic and early cretaceous

transport of riverine sediment from different outlets in the pearl river estuary during the wet season abstract riverine sediment is important for the development of river deltas and for carrying both nutrients and contaminants into estuaries and coasts previous studies of sediment transport have focused on single sourced estuaries and paid less attention to multi sourced estuaries estuaries with multiple river discharge sources in this study we used the coupled ocean atmosphere wave sediment transport coawst modeling system to study the sediment transport in the pearl river estuary pre where riverine sediments come from four different outlets during a typical wet season 2007 about 6 8 million tons of riverine sediments were discharged into the pre most of which were trapped in shoals during neap tides while about 11 8 by mass was transported out of the estuary during spring tides the proportions of the multi sourced sediments trapped in the pre or escaping from the estuary depended on the morphology of the estuary and the location of the outlets in relation to the estuarine morphology the distributions of different riverine sediments were mostly independent in neap tides but overlapped more in spring tides the seaward sediment transport was dominated by river freshwater discharge in the upper estuary and by tidal forcing in the lower channels while tides and winds controlled the sediment transport in the lower shoals this study aids our understanding of sediment transport processes in multi sourced estuaries and has implications for coastal environmental management

multi stage jurassic magmatism in the liaodong peninsula constraints on crustal evolution beneath the eastern north china craton abstract whole rock geochemical and in situ zircon u pb and hf o isotope compositions have been measured for the jurassic granitoids in the liaodong peninsula in order to investigate their genesis and reveal the jurassic crustal evolution of the eastern north china craton our new data combined with field and petrological observations indicate multi stage jurassic magmatism now represented by early to middle jurassic biotite granites and monzogranites and late jurassic two mica monzogranites the early to middle jurassic granitoids have relatively low sio2 contents 64 4 69 6 wt and k2o na2o ratios 0 4 1 0 adakitic characteristics with enriched lree and depleted hree contents high sr y ratios 52 189 positive eu and ba anomalies and negative nb and ta anomalies together with their highly negative zircon hf t 26 6 to 16 1 and mantle like 18o 4 6 to 6 3 values partial melting of a basaltic lower crust which formed at ca 2 5 ga can be proposed for the magma source of the early to middle jurassic granitoids these source rocks have not experienced significant water rock alteration after formation in contrary the late jurassic two mica granitoids exhibit relatively differentiated geochemical characteristics with high sio2 contents 72 wt and k2o na2o ratios and variable eu anomalies their parental magma was also enriched in lrees and depleted in hrees with high sr y 49 8 134 and la yb n 22 6 38 0 ratios the magmatic zircons have extremely negative hf t 37 5 to 19 6 and relatively high 18o 6 9 to 9 6 values indicating the involvement of an ancient crustal component with high 18o values such as metasedimentary rocks we propose therefore that the late jurassic two mica monzogranites originated from partial melting of reworked ancient crustal materials at the depth of lower crust and with the magma subsequently evolving as a result of plagioclase dominated fractional crystallization during early to middle jurassic westward subduction of the paleo pacific plate resulted in the partial melting of the mafic lower crust and the burial of ancient crustal materials in to deep crust while crustal stretching in late jurassic might account for the decompression melting of the ancient crustal source thus multi stage jurassic magmatism in the liaodong peninsula recorded a complex crustal evolution history which closely related to the westward subduction of the paleo pacific plate

assessment of flow paths and confluences for saltwater intrusion in a deltaic river network saltwater intrusion is a serious issue in estuarine deltas all over the world due to rapid urban sprawl and water shortage therefore detecting the major flow paths or locations at risk of saltwater intrusion in estuarine ecosystems is important for mitigating saltwater intrusion in this paper we introduce a centrality index the betweenness centrality bc to address this problem using the bc as the weighted attribute of the river network we identify the critical confluences for saltwater intrusion and detect the preferential flow paths for saltwater intrusion through the least cost path algorithm from a graph theory approach moreover we analyse the responses of the bc values of confluences calculated in the river network to salinity our results show that the major flow paths and critical confluences for saltwater intrusion in a deltaic river network can be represented by the least cost paths and the bc values of confluences respectively in addition a significant positive correlation between the bc values of confluences and salinity is determined in the pearl river delta changes in the salinity can produce significant variation in the bc values of confluences therefore freshwater can be diverted into these major flow paths and critical confluences to improve river network management under saltwater intrusion copyright 2015 john wiley sons ltd

sediment budget of the yangtze river the sediment budget is a method to study the distribution of sediment in different parts of a river basin this paper studies the sediment budget of the yangtze river by analyzing the data on soil erosion size distributions of sediment deposits sediment load and fluvial process a method to determine the sediment budget for the yangtze river is proposed in which the total soil erosion from the upstream reaches and tributaries is divided into two parts sediment load transported to the yichang station and sediment storage in the tributaries and gullies furthermore the sediment load is divided into three parts bed material load deposited in the middle and lower reaches for the fluvial process wash load transported to the estuary and sediment deposition in tongting lake the sediment transported into the estuary is further divided into two parts very fine sediment drifting to the ocean and sediment deposition in the estuary for land creation there is a large sediment demand for 1 the fluvial process to reach the minimum stream power in the middle and lower reaches 2 sediment mining for building material and 3 land creation in the estuary the riverbed profile in the middle and lower reaches is developing toward the equilibrium profile defined by the minimum stream power but the impoundment of the three gorges reservoir interrupts and modifies this fluvial process the annual sediment load in the yangtze river has reduced due to various human activities by about 100 x 10 6 t in the past 15 years thus there is a sediment shortage for land creation in the river mouth

generation of the 105 100 ma dagze volcanic rocks in the north lhasa terrane by lower crustal melting at different temperature and depth implications for tectonic transition

seasonal changes in river tide dynamics in a highly human modified estuary modaomen estuary case study abstract many estuaries worldwide are subject to significant human interventions such as dam construction channel deepening and land reclamation however the impact of these interventions on the spatiotemporal river tide dynamics is insufficiently understood in this study we explored the seasonal changes in river tide dynamics in the modaomen estuary of the pearl river where a significant increase in tidal range by approximately 0 14 m on average was observed after substantive channel deepening mainly due to human induced sand excavations using the double mass curve approach with regard to the river discharge and the absolute value of tidal damping rate or residual water level slope we identified three stepwise phases i e 1960 1990 representing the pre human intervention period 1991 2000 representing the transitional period and 2001 2016 representing the post human intervention period corresponding to high to low residual water level slopes and qualitatively matched the river tide dynamics shift observed in the modaomen estuary it was shown that the increase in tidal range was primarily due to the reduction in residual water level slope and thus the weakening of the tidal damping effect caused by the channel deepening along the modaomen estuary with length of 124 km where the residual water level slope was decreased by 46 from the pre human period 1960 1990 to the post human period 2001 2016 while the absolute value of the tidal damping rate was decreased by 32 due to the overall impacts from human interventions based on the regression coefficients obtained from the double mass curve approach we showed that the river tide dynamics in terms of tidal damping rate and residual water level slope were more sensitive to human interventions during the dry season than during the wet season owing to the combined impacts of riverbed deepening and freshwater regulation by dam s operation the underlying mechanism could be primarily attributed to the considerable seasonal variation in the lateral storage area such as tidal flats or salt marshes the results also showed that larger freshwater discharge is required to alter the critical value of maximum tidal damping indicating the strongest damping effect along the channel owing to the increase in tidal range due to substantial riverbed deepening and hence significant increase in channel storage the method proposed in this study to quantify the overall impacts of human interventions on seasonal changes in river tide dynamics is particularly useful for setting scientific guidelines for sustainable water management and conservation planning for engineering works in the modaomen estuary and other estuaries with significant human interventions

dam impacts on the changjiang yangtze river sediment discharge to the sea the past 55 years and after the three gorges dam 1 in 5 recent years 2000 2004 the changjiang yangtze river has discharged past datong 600 km from the river mouth an average of 250 million tons mt of sediment per year a decrease of more than 40 since the 1950s and 1960s whereas water discharge at datong has increased slightly water and sediment discharge data from the upper middle and lower reaches of the river suggest that the reduction of the changjiang sediment load has occurred in two phases between 1950 and 2002 following the closure of the danjiangkou reservoir on the hanjiang tributary in 1968 and following the installation of numerous dams and water soil conservation works in the jialingjijang catchment after 1985 as the three gorges dam tgd started operating in 2003 the changjiang entered a third phase of sediment reduction with annual sediment loads at datong less than 200 mt yr upon completion of the three gorges dam tgd in 2009 the sediment load at datong will decrease to 210 mt yr for the first 20 years then will recover to 230 mt yr during 2030 2060 and will reach 310 mt yr during 2060 2110 from the sediment budget and sediment erosion data for the changjiang subaqueous delta it can be assumed that the delta will be eroded extensively during the first five decades after tgd operation and then will approach a balance during the next five decades as sediment discharging from tgd again increases

morphological change in the pearl river delta china morphological changes in the pearl river delta prd have been investigated using bathymetric charts underwater digital elevation models remote sensing data and geographic information systems water depths were extracted from digitized charts to explore the accretion erosion characteristics of three estuarine environments and to provide quantitative estimates of changes in sediment volumes multi temporal satellite images have been used in combination with topographical data to analyze the coastline changes prd has gained an abundant amount of sediment of almost 9 45 105 km3 above the 10 m isobath in the period roughly between 1970 and 2010 the average sedimentation rate was 3 15 104 km3 yr between 1976 and 2006 the coastline extended seaward by 579 2 m on average with a mean net extension rate of 19 3 m yr the results suggest that the prd experienced a major phase of accretion with net erosion only in some local zones coastline extension associated with major morphological changes has accelerated in recent decades changes in boundary conditions such as sea level rise seem to have relatively minor impacts on the dramatic changes in the morphology of the estuaries the seaward extension of the coastlines shows an increasing trend whereas the sediment supply from the delta displays a decreasing trend a detailed comparative analysis demonstrates that land reclamation in the prd is the most significant factor that progressively alters the delta morphology overwhelming the effects of subsidence and sediment supply

influence of river discharge and dredging on tidal wave propagation modaomen estuary case abstractdredging and flow reduction in the modaomen estuary in china have had a measurable impact on tidal propagation and damping this paper includes an assessment of the impacts of these human interventions through the use of a new analytical hydraulic model procedure the model calculates tidal propagation and damping as a function of bathymetry and river discharge through a simple iterative procedure with explicit analytical equations the results obtained are accurate and allow both an analysis of the historic development and a sensitivity analysis to assess the effect of possible further dredging and flow reduction particularly in the upper reaches of the estuary tidal damping and wave celerity are sensitive to dredging and flow reduction historic analysis shows that due to these activities since 1993 the tidal amplitude in the modaomen estuary has increased by more than 0 1 m while the travel time of the tidal wave has decreased by 30 min in the middle part of the estuary and up to 80 min in