crustal structure seismic stratigraphy and rift processes of the continental margin off eastern canada ocean bottom seismic refraction results off nova scotia two crustal seismic refraction profiles were obtained on the continental margin of eastern canada these lines were located on the upper continental rise and on the outer continental shelf off nova

seasonal variations of sediment discharge from the yangtze river before and after impoundment of the three gorges dam abstract over the past decades 50 000 dams and reforestation on the yangtze river changjiang have had little impact on water discharge but have drastically altered annual and particularly seasonal sediment discharge before impoundment of the three gorges dam tgd in june 2003 annual sediment discharge had decreased by 60 and the hysteresis of seasonal rating curves in the upper reaches at yichang station had shifted from clockwise to counterclockwise in addition the river channel in middle lower reaches had changed from depositional to erosional in 2002 during the four years 2003 2006 after tgd impoundment 60 of sediment entering the three gorges reservoir was trapped primarily during the high discharge months june september although periodic sediment deposition continues downstream of the tgd during most months substantial erosion has occurred supplying 70 million tons per year mt y of channel derived sediment to the lower reaches of the river if sand extraction 40 mt y is taken into consideration the river channel loses a total of 110 mt y during the extreme drought year 2006 sediment discharge in the upper reaches drastically decreased to 9 mt only 2 of its 1950 1960s level because of decreased water discharge and tgd trapping in addition dongting lake in the middle reaches for the first time changed from trapping net sediment from the mainstem to supplying 14 mt net sediment to the mainstem severe channel erosion and drastic sediment decline have put considerable pressure on the yangtze coastal areas and east china sea

former carboniferous overburden in the northern appalachian basin a reconstruction based on vitrinite reflectance abstract elevated vitrinite reflectance values have been observed in the upper devonian west falls group of the northern new york appalachian basin in new york lopatin modeling suggests that the high thermal maturity of these and associated strata was caused by the presence of a devonian and carboniferous overburden that has subsequently been eroded from the northern appalachian basin devonian overburden reconstructed from extrapolation of stratigraphic data thickens from west 0 4 km to east 2 0 km across the field area in contrast carboniferous overburden reconstructed by lopatin modeling thins from west 2 0 3 4 km to east 0 7 1 2 km the inferred geometry of a northeasterly thinning wedge of sediment is compatible with the existing distribution of late paleozoic sediments in the appalachian basin and suggests the northern part of the basin experienced only moderate subsidence during carboniferous time

calculation of vitrinite reflectance from thermal histories a comparison of some methods vitrinite reflectance values ro calculated from commonly used methods are compared with respect to time invariant temperatures and constant heating rates two monofunctional methods one involving a time temperature index to vitrinite reflectance correlation tti ro and the other involving a log ro to depth correlation yield vitrinite reflectance values that are similar to those calculated by recently published arrhenius based methods such as easy ro the approximate agreement between these methods supports the perception that the easy ro algorithm is the most accurate method for the prediction of vitrinite reflectances throughout the range of organic maturity normally encountered however calibration of the e methods against vitrinite reflectance data from two basin sequences with well documented geologic histories indicates that although the easy ro method has wide applicability it slightly overestimates vitrinite reflectances in strata of low to medium maturity up to a ro value of 0 9 the two monofunctional methods may be more accurate for prediction of vitrinite reflectances in similar sequences of low maturity an older but previously widely accepted tti ro correlation consistently overestimates vitrinite reflectances with respect to other methods underestimation of paleogeothermal gradients in the original calibration of time temperature history to vitrinite reflectance may have introduced a systematic bias to the tti ro correlation used in this method also incorporation of tai thermal alteration index data and its conversion to ro equivalent values may have introduced inaccuracies

sediment transport on dissipative intermediate and reflective beaches abstract in this paper we review and synthesize field measurements of suspended sediment transport on the shoreface of dissipative intermediate and reflective beach states the morphodynamic beach state continuum was originally established in the 1970s but at the time only hydrodynamic processes and morphologies in these various states were described since the early 1980s when sensors capable of resolving suspended sediment concentration at intra wave time scale became available many studies have examined suspended sediment transport by waves and currents on the shoreface the synthesis of this work shows that the two end states in the morphodynamic continuum which are the dissipative and reflective states exhibit relatively small rates of cross shore sediment transport and weak gradients in that transport which both ensure that the nearshore morphology is relatively stable the intervening intermediate beach states typically exhibit prominent bar topographies and in these states strong morphodynamic feedbacks between hydrodynamic processes and morphology create locally large transport rates and sharp transport gradients which is the reason for the dynamic nature of these beach states transport processes driving sediment onshore and offshore within beach states are discussed as well as the transport processes responsible for state transitions

prediction of time dependent sediment suspension in the surf zone using artificial neural network abstract a predictive model of time dependent sediment suspension was developed with artificial neural network using velocity and integrated sediment concentration i e suspended load data observed from a large scale laboratory experiment under erosive and accretive beach conditions low frequency motion wave induced motion and turbulent kinetic energy per unit mass at lower 1 cm above the bed and upper 50 cm above the bed adv were used as inputs and suspended load near the bed was used as output to account for the history prior to sediment suspension five time steps corresponding to 2 s of data prior to sediment suspension were included in the inputs the artificial neural network model shows a predictive capability of the time dependent sediment suspension in the surf zone for both erosive and accretive conditions the correlation coefficient r between the measured and predicted suspended load reached up to r 0 79 at the bar crest in the accretive beach condition and typical average correlation coefficients over all subsets r were 0 53 over the bar crest the results from various input cases showed that turbulent kinetic energy near the bed is most important to predict the sediment suspension in the surf zone for both erosive and accretive conditions also the best predictive performance was shown at the bar crest supporting the hypothesis that turbulence induced by intense wave breaking at the bar crest is a dominant mechanism for sediment suspension outside the surf zone the wave induced motion was the highest contributing factor for the sediment suspension furthermore when the information from the upper adv was included as inputs the model improved the prediction capability by 40 at the bar trough in the erosive beach condition the increased prediction at this location may possibly be attributed to the effect of vertical shear motion in the low frequency range due to strong undertow from wave breaking

high resolution reconstruction of historical flood events in the changjiang river catchment based on geochemical and biomarker records abstract extreme hydrologic events such as floods have caused catastrophic losses to modern human society especially in highly developed coastal areas however high resolution reconstructions of extreme flood events are scarce due to a paucity of suitable proxies in marginal seas here we present a high resolution record of extreme flood events in the changjiang river catchment during the last 110 years using samples from the subaqueous delta of changjiang river estuary we used a multi proxy approach including sr nd isotopes zr rb ratio and biomarkers branched gdgts i e brgdgts and crenarchaeol and the ratio of the two as calculated by the bit index as proxies for the evolution of extreme floods in the changjiang river catchment rapid shifts in these proxies agreed with the timing of floods on the changjiang river we also tested the reliability of biomarker indices to reconstruct paleoflood events in this area the results indicated that the abundances of gdgts fluctuated in concert with historical floods cross spectral analyses revealed that historical floods in the changjiang river catchment were consistent with enso variance

on bar growth and decay during interannual net offshore migration abstract multiple bar systems often show a cyclic net offshore directed migration with return periods on the order of years generally a bar is generated near the shoreline grows in height and width while migrating offshore before finally decaying at the seaward limit of the surf zone based on a three year hindcast of a bar cycle at noordwijk netherlands and on additional synthetic runs using a wave averaged cross shore process model this study identifies the dominant mechanisms that govern the bar amplitude growth and decay during net interannual offshore migration the bar amplitude response is particularly sensitive to the water depth above the bar crest h xb and the angle of wave incidence these variables largely control the amount of waves breaking on the bar and the strength and cross shore distribution of the associated longshore current the longshore current has its maximum landward of the bar crest inducing additional stirring of sediment on the landward bar slope and trough the enhanced sediment concentration in the trough region shifts the cross shore transports peak landward of the bar crest forcing bar amplitude growth during offshore migration for increased h xb values wave breaking becomes less frequent consequently reducing the influence of the longshore current on sediment stirring therefore the resulting dominance of the cross shore current results in a sediment transport peak at the bar crest causing bar amplitude decay all four types of bar response viz all combinations of onshore offshore migration and bar amplitude growth decay can occur for a single wave height and wave period combination depending on h xb and additional hindcast runs in which the wave direction was assumed time invariant confirmed that h xb and largely control the transient bar amplitude response

analysis of the scale of errors in nearshore bathymetric data most studies of nearshore hydrodynamics sediment transport and morphology focus on bathymetric variability within a narrow band of spatial and temporal scales typically these studies rely on bathymetry estimates derived from field observations consisting of discrete samples in space and time with varying degrees of measurement error sampling limitations which result in aliasing and measurement errors can significantly contaminate variability at resolved scales and may lead to large errors in the representation of the scales of interest using a spectral analysis interpolation errors were analyzed for three different nearshore bathymetric data sets each of which targeted a different range of spatial scales bathymetric features that were unresolved or poorly resolved e g beach cusps introduced the potential for contamination in two of the data sets this contamination was significantly reduced using an appropriate scale controlled interpolation method leading to more accurate representations of the actual bathymetry an additional benefit of using scale controlled interpolation is that interpolation errors may be estimated independently of actual observations which allows one to design bathymetric sampling strategies that ensure that dominant scales are either resolved or largely removed finally interpolation errors corresponding to a particular sample design can be used to determine which interpolated values contribute usefully to a band limited analysis of bathymetric variability

frequency dependent cross shore suspended sediment transport 1 a non barred shoreface abstract the local time varying and time averaged suspended sediment transports across a marine non barred shoreface were obtained from field measurements of the near bed velocity and sediment concentration vectors using electromagnetic current meters and optical backscatterance suspended solids sensors co spectral analyses of velocity and sediment concentration revealed the contributions of waves of different frequencies to the total transport the transport attributable to quasi steady currents was determined from the product of the time averaged cross shore velocity and sediment concentration estimates of the local time integrated sediment volume flux total and net and the associated erosion or accretion were determined using depth of activity rods suspended sediment transport was associated with 1 local wind forced waves 2 swell 3 low frequency waves group bound long waves and 4 offshore directed mean currents undertow these transport components varied spatially and temporally in response to changes in the wave height to water depth ratio the local net oscillatory transport rate at wind wave and swell wave frequencies was directed onshore predominantly and increased as water depth decreased in association with wave shoaling the local mean sediment transport rate was predominantly offshore and dominated the net transport rate wherever wave induced components were weak relative to the mean currents under breaking waves the suspended sediment transport contribution associated with wind waves and swell waves was reduced as a result of dissipation the net suspended sediment transport rate exhibited a distinct vertical structure reflecting the balance at each elevation between the opposing mean and oscillatory components of transport the local time averaged total and net sediment volume flux and resulting erosion and accretion patterns support the hypothesis of a near balance in sediment flux for the complete storm event

the systematic contribution of transporting mechanisms to the cross shore sediment transport in water depths of 3 to 9 m the systematic contributions of short waves infragravity waves and mean flows to the cross shore sediment transport were studied with direct measurements of instantaneous near bed sediment concentrations and velocities as well as with an energetics based sediment transport model using measured time series of near bed cross shore flow as input the study was conducted at four cross shore positions in the multiple bar system of terschelling netherlands during three field campaigns each with a five week duration the data were collected in 3 to 9 m water depth during a wide range of conditions from low energy non breaking conditions to almost fully saturated breakers the height over depth ratio hs h was applied at all four measuring stations as a local conditional parameter all model predictions were grouped into hs h classes with a width of 0 02 to highlight the generality of the data the energetics approach predicted that the suspended load dominated over the bedload at all four stations both the sediment flux measurements as well as the model predictions showed that the largest contributors to the gross suspended sediment transport were made by the short waves and the undertow inducing an onshore and offshore transport respectively their contributions to the gross suspended transport were about 40 to 50 under surf zone conditions bound infragravity waves were observed and predicted to result in an offshore directed transport that was of subordinate magnitude compared to the observed and estimated magnitudes by the short waves and the undertow however as these transports almost cancelled out because of their about equal magnitude but opposite sign the suspended transport by bound infragravity waves may not be ignored and may rather paradoxically have a relatively large influence on the net suspended sediment transport hydrodynamical processes that do not seem to be of importance to the onshore and offshore sediment transport in 3 to 9 m water depth in the long run are mean flows under non breaking conditions and free infragravity motions a direct comparison between measured sediment fluxes and the model predictions suggests that simple energetics models are suitable for predicting cross shore sediment transport in 3 to 9 m water depth

calculation of organic maturation levels for offshore eastern canada implications for general application of lopatin s method recorded maximum bottom hole temperatures may vary significantly from true formation temperatures because of the effects of drilling fluid circulation a theoretical temperature correction technique was applied to log heading data to compute 191 static temperatures for 64 wells on the scotian shelf a linear regression performed on 140 computed temperatures produced an average geothermal gradient of 2 66 c 100 m correlation coefficient 0 97 a geothermal gradient map constructed from the corrected data shows that areas of thicker sediment accumulation are marked by high geothermal gradients e g abenaki sable subbasins whereas areas of shallow basement coincide with low gradients e g lahave platform canso ridge it is proposed that the major control on the distribution of scotian shelf geothermal gradients is the thermal conductivity of the sediments radiogenic heat production within the sediments and subsurface fluid movement probably contribute to a lesser extent within the basins higher

the impacts of the three gorges dam upon dynamic adjustment mode alterations in the jingjiang reach of the yangtze river china abstract dam operation profoundly modifies downstream flow sediment regimes resulting in a variety of geomorphologic responses without uniform laws the jingjiang reach of the middle yangtze river has undergone significant adjustment mode alterations with intensive channel erosion and major adjustment area changing from the bankfull channel to the medium flow channel at the time boundary of the three gorges dam tgd impoundment while these changes have received some attention little work has been undertaken to reveal the reason in this study based on 172 cross sections measured in the post flood period from 2003 to 2015 different river patterns longitude and reach averaged channel dimensions were assessed to reflect the channel adjustment characteristics of the jingjiang reach an index has been proposed to measure the cumulative water transport capacity of each discharge interval and to assess the relationship with reach scale medium flow channel dimensions the results indicate that the channel adjustment changes are directly driven by the alterations of flow duration and sediment transport capacity with the deficiency of floods medium flow channels respond quite well to small and medium discharges of under approximately 16 500 m3 s a discharge of 16 500 m3 s which can be regarded as a critical threshold corresponds to the average top levels of braided and meandering channel bars which are of morphological significance in constraining the passing flow in the medium flow channel small and medium discharges under the critical threshold associate with relatively larger reductions in sediment loads and hold increased geomorphic impacts qmjp eventually resulting in adjustment mode alterations the results present herein for the jingjiang reach of the yangtze river can provide a better understanding of dam operation and the corresponding impacts on downstream channel morphology

identification of intense intermittent coherent motions under shoaling and breaking waves laboratory measurements of the instantaneous horizontal and vertical turbulent velocities u and w induced by regular waves spilling on a rough impermeable slope were analyzed to elucidate the nature of turbulence generated in the bottom boundary layer and by wave breaking the analyses focused on the instantaneous turbulent events such as the absolute shear stress u w and turbulent kinetic energy k u 2 w 2 2 below trough level inside the surf zone the horizontal and vertical velocity records showed intense intermittent turbulent events that did not occur with the passing of each wave and the instantaneous quantities of and k could not be explained in terms of the phase averaged quantities the intermittent turbulent events extended into the bottom boundary layer inside the surf zone and in this region the infrequent but intense turbulence generated by wave breaking was an order of magnitude larger than the turbulence generated locally at the boundary two techniques were used to analyze the turbulent motions a quadrant analysis technique showed that although the large turbulent motions did not occur with each wave they were phase dependent near trough level and less so near the bottom a conditional sampling technique quantified the intensity and duration of the turbulent motions indicating that coherent events intense events occurred for 10 2 of the record and accounted for approximately 50 20 of the turbulent motion it is likely that the exactitude of these statistics will differ depending on breaker type nevertheless these statistics indicated that large turbulent motions are infrequent but contribute significantly to the turbulence intensity and possibly the suspension of bottom sediments

determination of geochronology and sedimentation rates of shallow lakes in the middle yangtze reaches using 210pb 137cs and spheroidal carbonaceous particles abstract accurate chronologies for recent sediments of shallow lakes in the yangtze floodplain are critical to calibrate proxy records for reconstructing environmental changes during the past century this study presents the results of detailed 210pb analysis from eight lake sediment cores collected from the middle yangtze reaches southeast china unsupported 210pb activities generally declined exponentially with mass depth in the eight cores the chronologies and sedimentation rates for the sediment cores were calculated using different 210pb based mathematical models the 137cs chronomarker i e the 1963 fallout peak and the spheroidal carbonaceous particle scp chronomarker i e the start of the rapid increase in 1970 ce were selected to validate the 210pb dating sedimentation rates derived from different models were validated using historical data including lake area arable land area sediment discharge and reservoir volume in the yangtze basin the scp corrected crs constant rate of supply model performs better than other models based on validation using historical documents in the yangtze basin the 137cs chronomarker might be erroneous due to catchment driven 137cs inputs from soil erosion and post depositional diffusion both scps and 137cs are susceptible to inputs from catchment soil erosion but scps show no apparent degradation and post depositional changes in lake sediments the scp profile provides a relatively reliable chronomarker which can be used for validating 210pb chronologies in these floodplain lakes generally sedimentation rates in the eight lakes were

geomorphologic changes in the lower pearl river delta 1850 2015 largely due to human activity abstract we use 165 years of navigational and bathymetric data and 60 years of sediment discharge data to document and explain geomorphic changes in the pearl river delta prd and its estuary which in recent years has experienced rapid urbanization and explosive economic growth a series of british and chinese navigation charts dating back to 1850 show that since then the prd has gained 1160 km2 of new land most of it reclaimed land derived from disposal of dredge spoils accordingly the prd estuary has decreased by 35 in ocean area and by 39 in water volume changes were most dramatic in the western part of the delta where the modaomen and huangmao seas decreased in ocean area by 62 and 39 respectively to the east upper lingding bay ldb decreased in ocean area by 36 in contrast the lower part of ldb decreased by only 3 in area although shoaling more by than 2 m some of which may come via influx of sediment from the south china sea since 1995 the rate of land accretion in the prd has declined to 40 of what it was over the previous 145 years and to

observations of turbulence within the surf and swash zone of a field scale sandy laboratory beach abstract current coastal evolution models generally lack the ability to accurately predict bed level change in shallow

intrawave sand suspension in the shoaling and surf zone of a field scale laboratory beach short wave sand transport in morphodynamic models is often based solely on the near bedwave orbital motion thereby neglec ting the e ect of ripple induced and surface induced turbulence onsand transport processes here sand stirring was studied using measurements of the wave orbital motion turbulence ripple characteristics and sand concentration collected on a eld scale laboratory beach underconditions ranging from irregular nonbreaking waves above vortex ripples to plunging waves and boresabove subdued bed forms turbulence and sand concentration were analyzed as individual events and ina wave phase averaged sense the frac tion of turbulence events related to suspension events is relativelyhigh 50 especially beneath plunging waves beneath nonbreaking waves with vortex ripples the sandconcentration close to the bed peaks right after the maximum positive wave orbital motion and shows amarked phase lag in the vertical although the peak in concentration at higher elevations does not shiftto beyond the positive to negative ow reversal under plunging waves concentration peaks beneaththe wavefront without any notable phase lags in the vertical in the inner surf zone bores the sandconcentration remains phase coupled to positive wave orbital motion but the concentration decreaseswith distance toward the shoreline on the whole our observations demonstrate that the wave drivensuspended load transport is onshore and largest beneath plunging waves while it is small and can alsobe o shore beneath shoaling waves to accurately predict wave driven sand transport in morphodynamicmodels the e ect of surface induced turbulence beneath plunging waves should thus be included

impacts of enso on multi scale variations in sediment discharge from the pearl river to the south china sea abstract sediment load delivered by rivers is an important terrestrial factor in the evolution and productivity of coastal ecosystems and coastal morphology as the strongest interannual climate signal the el nino southern oscillation enso is closely related to variations in the hydrological cycle at global and regional scales however the influence of enso on temporal variations in sediment discharge is poorly understood in this paper we examine periodic variations in sediment discharge to the south china sea from the pearl river since the 1950s using wavelet transform analysis wt furthermore we apply cross wavelet spectrum xwt and wavelet coherence wtc to investigate the linkages between enso and sediment variability the wt results revealed that periodic oscillations in sediment discharge in the pearl river occurred annually 1 yr before the 2000s interannually 2 8 yr from 1960 2002 and decadally 10 16 yr from 1975 1995 these periodic variations in the sediment load series had common spectrum power with the water discharge and precipitation series indicating an important climatic control the xwt and wtc results revealed significant impacts of enso on precipitation water discharge and sediment load at interannual time scales of 2 4 6 yr from 1960 2002 with a shift of patterns of enso on sediment variability after the 1970s in addition an in phase relation between sediment discharge and enso at time scales of 10 16 yr from 1975 1995 was detected indicating that variations at decadal scales could be related to other climatic teleconnections such as the pacific decadal oscillation compared with the spectrum structures of periodic variations in precipitation and water discharge and their relationship with enso there was a loss of energy in the sediment load at annual time scales after 2002 that can be attributed to dam construction in the river basin our study provides perspectives on the connections between enso and sediment variability at different time scales which is of practical and scientific importance for forecasting global hydrological processes and for river management

measurements of sheet flow transport in acceleration skewed oscillatory flow and comparison with practical formulations near bed oscillatory flows with acceleration skewness are characteristic of steep and breaking waves in shallow water in order to isolate the effects of acceleration skewness on sheet flow sand transport new experiments are carried out in the aberdeen oscillatory flow tunnel the experiments have produced a dataset of net transport rates for full scale oscillatory flows with varying degrees of acceleration skewness and three sand sizes the new data confirm previous research that net transport in acceleration skewed flow is non zero is always in the direction of the largest acceleration and increases with increasing acceleration skewness large transport rates for the fine sand conditions suggest that phase lag effects play an important role in augmenting positive net transport a comparison of the new experimental data with a number of practical sand transport formulations that incorporate acceleration skewness shows that none of the formulations performs well in predicting the measured net transport rates for both the fine and the coarser sands the new experimental data can be used to further develop practical sand transport formulations to better account for acceleration skewness

the scotian basin offshore nova scotia thermal history and provenance of sandstones from apatite fission track and 40ar 39ar data apatite fission track and 40ar 39ar age spectrum data from sandstone drill core minerals taken from depths of 2 5 km in nine wells from the scotian basin are presented and interpreted in terms of the thermal history of the basin and the provenance of its sediments the focus of the study is a comparison of the data from these thermochronometers with each other and with previously published vitrinite reflectance and aromatization isomerization a i reactions in biomarker compounds from the same or nearby wells apatite fission track ages are generally in agreement with expectations in that they trend to zero at a depth of 4 km corrected bottom hole temperature 120 c shallower lower present temperature samples are partially annealed the degree of partial annealing correlates closely with the degree of a i reactions both thermal indicators are activated over the temperature range 60 120 c samples from two wells mic mac j 77 and erie d 26 are anomalous they are more annealed than present formati

dynamic interpretation of organic matter maturation and evolution of oil generative window discussion two principal elements of the hydrocarbon generation model proposed by ejedawe and coker 1984 are as follows 1 organic matter maturation occurs in two phases the first phase corresponds to basinal subsidence with essentially constant burial rate and geothermal gradient therefore the oil generative window ogw is fixed in space the second phase is the postsubsidence phase when all materials remain at constant temperatures appropriate to their depths p 1028 and the ogw moves vertically upward through the static sedimentary fill and maturation is due to time effects p 1024 2 hydrocarbon generation begins with the lighter hydrocarbons or even thermogenic gas at the initial ogw at depth followed by progressively heavier hydrocarbons as the ogw moves vertically upward p 1024

sediment transport in oscillatory boundary layers in cases of rippled beds and sheet flow an experimental study was focused on the process of sediment transport in unsteady flow conditions due to wave action wave induced oscillatory flow conditions near the seabed were simulated at full scale 1 1 in a new large oscillating water tunnel two sets of experiments series a and b were carried out during series a bed forms and wave cycle averaged suspended sediment concentrations were measured under sinusoidal waves series b focused on measurement of the wave cycle averaged sediment transport rates under regular and random asymmetric oscillatory flows upper shoreface conditions and was aimed at the verification of quasi steady formulas for the description of cross shore sediment transport bedform dimensions appeared to decrease considerably under the influence of wave asymmetry and wave randomness only the measured ripple dimensions under asymmetric waves series b showed good agreement with nielsen s 1979 relations for most of the series b experiments the bed was plane sheet flow the net sediment transport was directed onshore and the measured transport rates showed a strong correlation with the velocity moment an empirical quasi steady transport model is proposed which is based on the new tunnel data and other existing data sets the limitations of the quasi steady model approach became clear in the rippled bed regime and through the presence of a consistent influence of the wave period in plane bed conditions in rippled bed conditions the suspended concentration profiles followed a negative exponential distribution for most of the experiments the measured concentration decay length showed a linear relation with the ripple height in plane bed sheet flow conditions the measured suspended concentration profiles followed a negative power function the power or concentration decay parameter was constant 2 1 for a wide range of velocity conditions it is suggested that the mobile bed sheet flow layer has a strong damping effect on the mixing of suspended sediments turbulence damping

geometry migration and evolution of wave orbital ripples at leo 15 observations of the temporal evolution of the geometric properties and migration of wave formed ripples are analyzed in terms of measured suspended sand profiles and water velocity measurements six weeks of bedform observations were taken at the sandy medium to coarse sized sand leo 15 site located on beach haven ridge during the late summer of 1995 with an autonomous rotary sidescan sonar during this period six tropical storms several of hurricane strength passed to the east of the study site ripples with wavelengths of up to 100 cm and with 15 cm amplitudes were observed the predominant ripples were found to be wave orbital scale ripples with ripple wavelengths equal to 3 4 of the wave orbital diameter although orbital diameters become larger than 130 cm during the maximum wave event it is unclear if a transition to non orbital scaling is occurring ripple migration is found to be directed primarily onshore at rates of up to 80 cm day suspended transport due to wave motions calculated by multiplying acoustic backscatter measurements of suspended sand concentrations by flow velocity measurements are unable to account for a sufficient amount of sand transport to force ripple migration and are in the opposite direction to ripple migration thus it is hypothesized that the onshore ripple migration is due to unobserved bedload transport or near bottom suspended transport bedload model calculations forced with measured wave velocities are able to predict the magnitude and direction of transport consistent with observed ripple migration rates sequences of ripple pattern temporal evolution are examined showing mechanisms for ripple directional change in response to changing wave direction as well as ripple wavelength adjustment and erosion due to changing wave orbital diameter and relative wave to current velocities

relationship of diagenetic chlorite rims to depositional facies in lower cretaceous reservoir sandstones of the scotian basin the relationship between diagenetic chlorite rims and depositional facies in deltaic strata of the lower cretaceous missisauga formation was investigated using a combination of electron microprobe bulk geochemistry and x ray diffraction data the succession studied comprises several stacked parasequences the delta progradational facies association includes i fluvial or distributary channel sandstones some with tidal influence ii thick bedded delta front graded beds of sandstone interpreted as resulting from fluvial hyperpycnal flow during floods and storms and iii more distal muddier delta front and prodeltaic facies the transgressive facies association includes lag conglomerate siderite cemented muddy sandstone and mudstone and bioclastic sandy limestone chlorite rims are absent in the fluvial facies and best developed in thick sandstones lacking mudstone baffles good quality chlorite rims are well correlated with ti in bulk geochemistry ti is a proxy for fe availability principally from the breakdown of abundant detrital ilmenite fetio3 under conditions of sea floor diagenesis the abrupt decrease in sedimentation rate at transgressive surfaces caused progressive shallowing of the sulphate depletion level and of the overlying eh controlled diagenetic zones resulting in conditions suitable for diagenetic formation of berthierine to migrate upwards through the packet of reservoir sandstones this early diagenetic berthierine suppressed silica cementation and later recrystallized to chlorite thick euhedral outer chlorite rims were precipitated from formation water in sandstone lacking muddy baffles on this chlorite substrate and inhibited late carbonate cementation this study thus shows that the preservation of porosity by chlorite rims is a two stage process rapidly deposited delta front turbidite facies create early diagenetic conditions that eventually lead to the formation of chlorite rims but the best quality chlorite rims are restricted to sandstones with high permeability during burial diagenesis

sediment rating parameters and their implications yangtze river china abstract this study examines the characteristics of sediment rating parameters recorded at various gauging stations in the yangtze basin in relation to their controls our findings indicate that the parameters are associated with river channel morphology of the selected reaches high b values 1 600 and low log a values 1 000 occur in the middle and lower yangtze river associated with meandering reaches over low gradients and can be taken to imply aggradation in these reaches with low stream power higher b values 0 900 1 600 and lower log a values 4 000 to 1 000 characterize the reaches between yichang and xinchang immediately below the three gorges these values indicate channel erosion and bed instability that result from changes in channel gradient from the upstream steep valley to downstream low slope flood plain settings differences in channel morphology accompany these changes confined v shaped valleys occur upstream and are replaced downstream by broad u shaped channels the middle and lower yangtze shows an apparent increase in channel instability over the past 40 years this inference is based on sediment rating parameters from various gauging stations that record increasing b values against decreasing log a values over that time analysis of the sediment load data also reveals a strong correlation between changes in sediment rating curve parameters and reduction of annual sediment budget 4 70 108 t to 3 50 108 t year from the 1950s to 1990s largely due to the damming of the yangtze and sediment load depletion through siltation in the dongting lake short term deviations from the general trends in the sediment rating parameters are related to hydroclimatic events extreme low b values and high log a values signify the major flood years while the reverse indicates drought events when compared with rivers from other climate settings it is evident that the wide range of values of the yangtze rating parameters reflects the huge discharge driven by the monsoon precipitation regime of eastern china

local human activities overwhelm decreased sediment supply from the changjiang river continued rapid accumulation in the hangzhou bay qiantang estuary system we investigate the morphological responses of the hangzhou bay china located immediately south of the changjiang estuary to the drastic reduction of the sediment load from the changjiang river and the large scale coastal embankment schemes over past decades the spatial patterns of deposition and erosion sediment volume changes and the hydrodynamic and sediment dynamic feedback were analyzed on the basis of historical bathymetric and hydrographic data the results show that the sedimentation rates in the bay have generally increased rather than decreased over the past decades despite bed erosion having occurred in the northern bay mouth this observation reveals that the influence of the reduction in the changjiang river sediment supply on the morphological evolution of hangzhou bay has to date been insignificant mainly due to the buffering effect of existing sediment in the outer changjiang estuary the morphological change is mainly related to the implementation process of the coastal embankment sediment accumulation induced by progressive seaward coastal embankment has resulted in seaward aggradation from the qiantang estuary towards hangzhou bay analysis of the annually averaged high and low tidal levels and durations of rising and falling tides reveals that flood dominance in the inner bay has been increased due to the coastal embankment and sediment accumulation the ratio between annually averaged rising tide and falling tide durations have decreased from 0 85 to 0 63 the tidal prism at the interface between the inner and outer bay has decreased by about 25 since the 1980s while the net landward sediment flux has been intensified to a certain extent which is responsible for the intensifying sedimentation in the inner bay the local human activities have overwhelm the decreased sediment from the changjiang river although the coastal embankment will cease in the near future the morphological response to human activities is expected to continue on for a longer time

construction and evolution of submerged deltaic bodies on the high energy se african coastline the interplay between relative sea level and antecedent controls abstract this paper investigates the interplay between allocyclic controls and antecedent topography in the evolution of submerged coastal landforms including a back stepped delta using high resolution tools we examine the wave dominated thukela shelf and define the major seismic units key features identified comprise incised valleys scoured into bedrock that have overspilled to form lagoons at depths of 50 m these are in turn overlain by two prograding and backstepped sandy delta systems at 40 m and 32 m depth respectively the deltas interfinger with muddy prodelta deposits and are truncated by the holocene ravinement overlain by the contemporary prodelta of the thukela river system a bedrock high separates two physically separate strato morphological zones landward a sediment stripped steep and shallow nearshore zone and seaward a gentle zone downdip where the deltaic accumulations are sited delta development was favoured during sea level stillstands at 40 m and 32 m respectively the step back of the deltas corresponds to sharp increases in the rate of sea level rise associated with meltwater pulses the overall gentle palaeo bathymetric gradient has moderated erosion associated with rising sea level preserving a sandy back stepping delta and a draping mud clinoform submerged delta positioning relates to underlying incised valleys suggesting a synchronous transgressive evolution of the drainage and the delta incised valley network positioning is further governed by late pliocene aged growth faults in the basement rocks the geological framework has acted as a recurring primary control to the geomorphic evolution of the area partitioning accommodation for sediment accumulation and moderating the efficiency of ravinement

response of the changjiang yangtze river water chemistry to the impoundment of three gorges dam during 2010 2011 abstract the environmental impact of three gorges dam tgd in the changjiang yangtze river is an important topic of concern for scientific communities and the public however the changes in river water chemistry in response to the dam construction remain poorly constrained this study presents the seasonal variability of all major cations and some anions in the lower changjiang during a full hydrological year from 2010 to 2011 the concentrations of all ions except for hco 3 are higher after the tgd operation than before p

terrestrial heat flow density estimates for the jeanne d arc basin offshore eastern canada corrected bottom hole temperatures from 35 wells together with measured and assumed rock thermal conductivities are used to estimate linear geothermal gradients and effective thermal conductivities in the jeanne d arc basin in offshore eastern canada heat flow density values calculated for each well location indicate that heat flow density is slightly higher in the deeper northern part of the basin than in the southern part it appears that the heat flow density distribution is affected by fluid motion within the sediments and not by heat generation or basement topography dehydration is suggested as the mechanism that produces the fluid flow pattern that influences the heat flow density distribution in the basin and a simple fluid flow model of the jeanne d arc basin is presented

an upper limit to palaeo heat flow theory and examples from the danish central graben abstract the surface heat flow yields a condensed expression of the subsurface thermal regime while the present heat flow can be measured as the product of thermal conductivity and temperature gradient resolution of the past surface heat flow variations calls for indirect methods such as the modelling of vitrinite reflectance and other organic maturity indicators which represent integrals of the past temperature history this paper argues that regarding the reflectance of vitrinite which is the most common maturity indicator the feature of the past thermal regime which can survive the effects of measuring and modelling uncertainties is the maximum temperature present or past how the maximum temperature was obtained is only rarely resolved given maximum temperature burial history thermal conductivity structure and surface temperature history the one dimensional steady state heat equation yields an approximate upper limit to the surface heat flow artificial examples show that the past heat flow may be similar to the maximum heat flow constraint when the past was significantly warmer than the present however this requires a delicate balancing of burial history and heat flow history to occur the thermal relaxation rate of the hot past must compensate for heating due to burial generally the past heat flow may be well below the maximum constraint examples from the central graben show that vitrinite reflectance samples of upper jurassic age constrain the maximum palaeo heat flow back to 150 ma this is due to the very rapid and significant sedimentation of upper jurassic sediments resulting in immediate deep burial of vitrinite the data of the present study are consistent with a early cretaceous heat flow elevated by about 20 30 above the present and with a heat flow throughout the cenzoic only marginally higher than the present however the data are also fully consistent with a time independent background heat flow history this illustrates the limits of resolution in palaeo thermal reconstruction based on vitrinite reflectance and temperature data the problem is one of finding the space of admissible solutions rather than one of finding a single solution

relationships between pore pressure stresses and present day geodynamics in the scotian shelf offshore eastern canada a geomechanical study of the mesozoic and tertiary sediments beneath the scotian shelf shows that two major weak layers exist at depth the overpressured unit at 4000 m and the basal argo salt which is ductile and diapiric a consistent relationship is observed between the overpressures and the stress state in the basin first the smaller horizontal principal stress increases dramatically just above the onset of overpressuring and secondly borehole breakouts indicators of stress anisotropy decrease in abundance within the overpressured zone neither tectonic shear nor rapid burial can explain these observations however overpressuring by fluid generation will result in horizontal stress increase and eventually lead to an isotropic stress state compelling evidence is found for hydrocarbon generation being a key cause of overpressuring in the scotian shelf present day horizontal stress orientations in the sediments overlying the overpressured zone are aligned with contours of equal overpressure but not with the traces of tertiary listric normal faults or with the shelf edge this implies that contemporary stresses in these sediments are causally related to overpressuring the upward transmission of lithospheric plate movements and associated stress is unlikely because the ductile argo salt effectively detaches the sediments from basement instead the rocks of the scotian shelf are attempting to slide down the geomechanically weak overpressured zone in the directions indicated by the breakouts but they are prevented from doing so by the bowl shaped basement structure in the region

modeling cross shore sandbar behavior on the timescale of weeks we compare predictions of a coupled wave averaged cross shore waves currents bathymetric evolution model to observations of onshore and offshore nearshore sandbar migration the observations span a 10 and 44 day period with onshore offshore bar migration at duck north carolina and at hasaki kashima coast japan respectively a 3 5 month period of onshore bar migration at duck and a 22 day period of offshore bar migration at egmond netherlands with best fit parameter values the modeled temporal evolution of the cross shore bed profiles agrees well with the observations model skill defined as 1 minus the ratio of prediction to no change error variances ranges from 0 50 at egmond to 0 88 for the prolonged onshore bar migration at duck localized in time and space reductions in model skill coincide with alongshore variations in the observed morphology consistent with earlier observations simulated offshore bar migration takes place during storms when large waves break on the bar and is due to the feedback between waves undertow suspended sediment transport and the sandbar simulated onshore bar migration is predicted for energetic weakly to nonbreaking conditions and is due to the feedback between near bed wave skewness bedload transport and the sandbar with negligible to small effects of bound infragravity waves and near bed streaming under small waves and conditions when breaking and nonbreaking conditions alternate with the tide the sandbar is predicted to remain stationary the intersite differences in the optimum parameter values are at least partly induced by insensitivity to parameter variations parameter interdependence and errors in the offshore wave forcing

on the evolution of rifted continental margins comparison of models and observations for the nova scotian margin summary a model for the formation and evolution of rifted continental margins based on lithospheric extension during rifting and its thermal and mechanical consequences is proposed model predictions are then compared with geological and geophysical observations from a transect of the 185 ma old rifted margin off nova scotia through the scotian basin three kinematic models of the rifting process are discussed these are 1 the uniform extension model in which the amount of extension is uniform with depth but varies with position across the margin 2 the uniform extension and melt segregation model which has similar properties but also provides an explanation for the properties of the extended continental crust and its transition to oceanic crust by postulating that basaltic melt segregates from the asthenosphere and migrates to the crust and 3 the depth dependent extension model in which the first order consequences of rapidly changing rheological properties with depth in the lithosphere are included by decoupling the lithosphere into two zones with depth each of which undergoes differing amounts of extension these rift models predict the form of crustal and lithospheric thinning subsidence and temperature change once the amount of extension has been determined this is estimated from seismic measurements of present crustal thickness on the assumption that the crust had a uniform thickness equal to that currently measured in the adjacent continental region before rifting occurred rifting is also considered to occur instantaneously a time stepping thermo mechanical model is used to predict the cooling of rifted margin additional thermal contraction subsidence and its amplification by water and sediment loading thermal aspects are calculated using a finite difference model of time dependent conductive heat transport whereas regional isostatic response to loading is calculated by a finite element model the models are coupled because the temperature distribution is used to define a rheological lithosphere an elastic region with thickness that varies in time and space as the model evolves for flexural calculations in the mechanical model secondary coupling occurs through perturbations to the temperature field by sedimentary thermal blanketing and advection of heat during isostatic adjustment the model predictions of 1 sedimentary basin stratigraphy 2 moho position 3 free air gravity anomaly 4 age depth relations for deep exploratory wells and 5 subsidence and temperature histories agree well with observations from the scotian basin additional effects due to sedimentary and crustal radiogenic heat production lateral heat transport and the possible existence of a near surface brittle listric faulted region created during rifting are also considered it is concluded that a model in which rifting occurred by depth dependent extension and which includes a finite thickness for the rheological lithosphere radiogenic heat production in the sediments and crust and a brittle listric faulted crustal layer affords an accurate description of the first order processes that occur during rifting and evolution of this margin

fingerprinting suspended sediment sources in the catchment of the river ouse yorkshire uk statistically verified composite fingerprints and a multivariate mixing model have been employed to establish the main sources of the suspended sediment transported through the lower non tidal reaches of the river ouse and one of its main tributaries the river wharfe during the period 1994 1997 in the case of the suspended sediment samples collected from the river ouse the load weighted mean contributions from uncultivated topsoil cultivated topsoil and channel bank sources were estimated to be c 25 38 and 37 respectively while for the river wharfe these sources contributed c 70 4 and 23 respectively c 4 was derived from woodland topsoil suspended sediment samples collected during higher flows evidenced a greater contribution from channel banks than samples collected during lower flows source materials were also differentiated according to the three main geological source areas carboniferous permian and triassic and jurassic and their load weighted mean contributions were estimated to be c 24 41 and 35 for the river ouse and c 91 9 and 0 there are no jurassic rocks in this catchment for the river wharfe respectively when suspended sediment samples from tributary streams were used to characterize each geological source area the equivalent results for the river ouse were c 30 46 and 24 considering the three main tributaries that contribute to the river ouse the load weighted mean contributions from the rivers swale ure and nidd were estimated to be 82 15 and 3 respectively these values have been compared with estimates of the relative magnitude of the annual suspended sediment loads of these three rivers for the years 1995 and 1996 derived from continuous monitoring of discharge and turbidity differences between the two sets of results are ascribed to the different periods of record involved and to the timing of suspended sediment sampling relative to the overall storm hydrograph and thus the degree to which the available samples are representative of the overall suspended sediment flux although a number of limitations must be recognized the fingerprinting approach to source ascription is seen as providing valuable information regarding suspended sediment sources in the study catchments copyright 1999 john wiley sons ltd

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

diagenesis and anchimetamorphism in an overthrust belt external domain of the taconian orogen southern canadian applachians ii paleogeothermal gradients derived from maturation of different types of organic matter abstract 3hermal maturation patterns have been established for the external domain of taconian orogen of the southern quebec appalachians between quebec city and the u s border reflectance of three types of organic matter om measured in the same sample shows that graptolite reflectance r g is higher than pyrobitumen reflectance r b which in turn is higher than reflectance of amorphous organic matter r a r g r b and r a are converted to vitrinite equivalent reflectance from which maximum paleotemperatures were calculated inverted diagenesis is preserved in northwest part of the chaudiere nappe to the southeast original burial diagenetic grade was upgraded by later synorogenic heating in the st lawrence lowlands paleogeothermal gradients at maximum burial were 33 37 c km a gradual southwestward increase in maturation level suggests increasing post taconian burial depth from 4 6 to 6 7 km indicating an increasing thickness of eroded rocks from northeast to southwest along logan s line one of the most important contributions of this study is the proof that the acadian orogeny has affected the successor basin of the taconian orogeny in the st lawrence lowlands the thermal effect of the mid cretaceous intrusion of the monteregian hills on their country rocks is limited to one diameter or less of the intrusive body as shown by the narrow

sediment concentration and vertical mixing under breaking waves abstract field measurements of near bed sediment concentrations and sediment diffusivity in the breaker zone and in the inner surf zone of natural beaches were obtained using stacks of optical and fiber optical backscatter sensors under conditions with strongly plunging breakers as well as with spilling surf bores the field data suggest that significant differences exist between these wave types in terms of near bed sediment concentration levels and vertical mixing of sediment from the bed upward into the water column when plotting mean sediment concentration profiles in log c z space profiles are upward concave for spilling surf bores and sediment diffusivity increases approximately linearly upward from the bed for plunging waves however mean sediment concentration profiles are linear in a log c z plot indicating vertically constant sediment diffusivity this suggests that under surf bores sediment suspension from the bed occurs through diffusion processes while vertical mixing is mainly a convective process under plunging waves under surf bores sediment is largely confined to the lower layers of the water column while it is lifted to significantly higher elevations under plunging breakers

maturity studies and source rock potential in the southern sverdrup basin arctic canada abstract the purpose of the study is to better understand the relationship between organic matter optical properties and the presence of potentially large oil and gas accumulations in arctic canada the type and thermal maturity of the dispersed organic matter of the mesozoic formations in the southern sverdrup basin melville island have been studied using organic petrology and rock eval pyrolysis all types of organic matter are present in the strata of mesozoic age hydrogen rich liptinite is dominated by alginite botryococcus and tasmanites dinoflagellate cysts and amorphous fluorescing matrix sporinite cutinite resinite and liptodetrinite made up the lesser hydrogen rich exinite vitrinite reflectance in cretaceous sediments ranges from 0 36 to 0 65 ro in jurassic sediments it ranges from 0 40 to 1 0 ro and in the triassic from 0 45 to 1 30 ro showing an overall increase with depth of burial cretaceous sediments of the deer bay formation are thermally immature and contain organic matter of terrestrial origin the upper jurassic shales of the ringnes formation contain predominantly organic matter of liptinitic and exinitic origin with a considerable vitrinitic input at optimum maturation levels potential source beds of this formation would have a good hydrocarbon generating potential the hydrocarbon potential however would be limited to the generation of gases due to the leanness of the source rocks parts of the lower jurassic jameson bay formation are organic rich and contain a mixed exinitic vitrinitic organic matter botryococcus colonial algae but visible organic matter is dominated by high plant remains mainly spores the schei point group shales and siltstones contain organic matter of almost purely marine origin whereas the predominantly higher plant derived organic matter found in the deer bay jameson bay and partly in the ringnes formations have higher toc among the schei point group samples the cape richards and eden bay members of the hoyle bay formation are richer in toc 2 0 than the murray harbour formation cape caledonia member this may reflect differences in the level of maturity or in the depositional environment more anoxic conditions for the former regional variations in the level of thermal maturity of mesozoic sediments in sverdrup basin appear to be a function of burial depth the mesozoic formations thicken towards the basin centre nne direction reflecting the general pattern of increasing thermal maturity north of sabine peninsula however the regional thermal maturation pattern of the mesozoic is not solely a reflection of the present day geothermal gradient which indicates that anomalous zones of high geothermal gradient may have existed in the past at least since when the mesozoic sediments attained maximum burial depth the contour pattern of the regional variation of maturity at the base of numerous triassic formations is similar to that of the structural contours of the sverdrup basin indicating that present day maturation levels are largely controlled by basin subsidence

modeling suspended sediment discharge from the waipaoa river system new zealand the last 3000 years hydrotrend a hydrologic transport model is used to simulate the water and suspended sediment discharge of the waipaoa river system over the last 3 kyr a time period in which a well documented sequence of natural events and anthropogenic activities that profoundly impacted drainage basin processes occurred comparisons between observed and simulated data show that the model output replicates the frequency and distribution of flow events and the suspended sediment concentration discharge relationship and the long term trends in suspended sediment discharge are consistent with the sediment record preserved on the middle shelf water discharge tracks precipitation and average annual discharge may have been up to 20 higher and 6 lower at different times in the past suspended sediment discharge changed from 2 3 4 5 to 14 9 8 7 mt yr 1 during the anthropocene increasing by 140 after polynesian arrival by 350 after european colonization and by 660 after the catchment headwaters were deforested

vertical and horizontal structure is suspended sand concentrations and wave induced fluxes over bedforms abstract high resolution measurements of suspended sand concentrations have been made using a multi transducer acoustic back scatter sensor over both steep and flat bedforms under low energy swell conditions with weak currents present on a micro tidal beach in the southwest of england similar measurements were made over steep bedforms in a large scale laboratory wave basin using a wave record simulated from field data a detailed interpretation of the suspension process associated with steep vortex type ripples was made possible with knowledge of the position of the acoustic sensors relative to the bedform geometry analysis of time averaged wave ensemble averaged suspended sediment concentrations and velocity concentration phase angles indicates that the bedforms are an important control on the suspension patterns produced by wave induced flows steep asymmetric ripples under shoaling waves produces greater amounts of suspension than low steepness ripples due to the effects of vortex ejection associated with the steep ripples over rippled beds we find evidence for a significant phase couplined between the resuspended sediment and the bedforms in the near bed region

temporal distribution of suspended sediment transport in a mediterranean basin the lower tordera ne spain abstract suspended sediment dynamics are still imperfectly understood especially in areas of mediterranean climate with strong seasonal contrasts where few studies have been conducted the aim of this study is to analyze the variability in the suspended sediment load at different temporal scales within flood variability monthly seasonal and annual in the tordera river 894 km 2 located in northeastern spain suspended sediment samples were obtained during base flows q 3 5 m 3 s 1 and flood events q 3 5 m 3 s 1 the analysis of the variability in the suspended sediment is structured in two consecutive steps i the construction of statistical relations between suspended sediment concentrations c and discharge q and ii the application of those relations to assess the suspended sediment yield the results show that in a single event the sediment peak generally precedes the peak discharge following a clockwise hysteretic loop furthermore it was observed that the reduction in the suspended sediment concentrations in a sequence of events can be mainly associated with a phenomenon of sediment exhaustion the total amount of suspended sediment transported during a single flood is thus related to its duration and time during the year as well as to its magnitude at a seasonal scale the export of suspended sediment takes place in two phases i sediment preparation and ii sediment transfer and exhaustion during the latter phase the exhaustion of the sediment load is primarily related to the sequence of flood events at the annual scale the results show high inter annual variability according to the number of floods recorded yearly since almost all the suspended load is transported during those events

estimates of terrestrial heat flow in offshore eastern canada from available bottom hole temperatures and conductivities estimated from lithologic descriptions heat flow estimates are calculated for 72 sites on the canadian atlantic shelf the resulting data suggest a pattern of low heat flow 055 mw m2 within the paleozoic basins in proximity to land areas and generally intermediate heat flow 60 80 mw m2 along the outer half of the continental shelf higher heat flows 90 mw m2 are estimated along the shelf edge in some areas e g the southwestern scotian shelf and the eastern newfoundland and labrador shelves radioactive heat generation in sediments that thicken seawards probably does not account for the observed increase in heat flow the possibility that higher heat flows in some areas may arise because of fluid movement from depth is suggested various other causes for the high heat flows e g tectonic or magmatic activity are considered less likely

high resolution field measurements and numerical modelling of intra wave sediment suspension on plane beds under shoaling waves abstract intra wave sediment suspension is examined using high resolution field measurements and numerical hydrodynamic and sediment models within 120 mm of a plane seabed under natural asymmetric waves the detailed measurements of suspended sediment concentration at 5 mm vertical resolution and at 4 hz showed two or three entrainment bursts around peak flow under the wave crest and another at flow reversal during the decelerating phase at flow reversal the mixing length was found to be approximately double the value attained at peak flow under the crest to examine the cause of multiple suspension peaks and increased diffusion at flow reversal a numerical side view hydrodynamic model was developed to reproduce near bed wave induced orbital currents predicted currents at the bed and above the wave boundary layer were oppositely directed around flow reversal and this effect became more pronounced with increasing wave asymmetry when the predicted orbital currents and an enhanced eddy diffusivity during periods of oppositely directed flows were applied in a lagrangian numerical sediment transport model unprecedented and extremely close predictions of the measured instantaneous concentrations were obtained the numerical models were simplified to incorporate only the essential parameters and by simulating at short time scales empirical time averaged parameterisations were not required key factors in the sediment model were fall velocities of the full grain size distribution diffusion separation of entrainment from settlement and non constant but vertically uniform eddy diffusivity over the plane bed sediment convection by wave orbital vertical currents was found to have no significant influence on the results

observation of undertow and turbulence in a laboratory surf zone abstract undertow and turbulence in the surf zone have been studied in a wave flume for a spilling breaker and a plunging breaker fluid velocities across a 1 on 35 sloped false bottom were measured using a fiber optic laser doppler anemometer and wave decay and set up were measured using a capacitance wave gage the characteristics of mean flow and turbulence in spilling versus plunging breakers were studied the mean flow is the organized wave induced flow defined as the phase average of the instantaneous velocity while the turbulence is taken as the deviations from the phase average it was found that under the plunging breaker turbulence levels are much higher and vertical variations of undertow and turbulence intensity are much smaller in comparison with the spilling breaker it was also found that turbulent kinetic energy is transported seaward under the spilling breaker and landward under the plunging breaker by the mean flow the study indicates that there are fundamental differences in the dynamics of turbulence between spilling and plunging breakers which can be related to the processes of wave breaking and turbulence production it is suggested that the types of beach profile produced by storm and swell waves may be the results of different relationships between mean flow and turbulence in these waves

generation and migration of oil in the maturin subbasin eastern venezuelan basin abstract regional geochemical evaluation of the possible cretaceous and tertiary source rocks and oil oil and oil source rock correlation studies have identified the calcareous shales and limestones of the upper cretaceous querecual and san antonio formations of the guayuta group with amorphous marine type ii organic matter as the source rocks for oil in the maturin subbasin the deposition of the source rocks took place on a passive continental margin whilst the generation and migration of oil occurred in a foreland basin during miocene recent times the oils found in the northern part of the subbasin in different reservoirs cretaceous eocene oligocene miocene and pliocene formations are of mature marine type with or without bacterial alteration geochemical data indicate that some of these oils were mixed with the highly altered residue of a previously accumulated oil based on maturity and migration modelling it appears that the oils essentially migrated from active upper miocene recent kitchens in the cretaceous source rocks below the main thrusts the highly altered residue was formed during the upper miocene by the biodegradation of oil migrating during the middle and upper miocene large areas of mature to overmature cretaceous source rocks now exposed in the interior mountain front were in active oil kitchens during the lower and middle miocene before being involved in thrusting around 12 myr bp long distance 150 300 km southward lateral migration of oils during the middle miocene gave rise to the altered moderately mature marine oils in the shallow miocene stratigraphic reservoirs of cerro negro orinoco oil belt in the southern fringe of the subbasin

breaker turbulence and sediment suspension in the surf zone field measurements of fluid velocities and suspended sediment concentrations were used to investigate the relative role of coherent vortices related to wave breaking in suspended sediment dynamics the measurements were obtained from a barred intermediate type beach and the instrument rig was exposed to a range of wave types during the experiment including shoaling waves and both spilling and plunging breakers the time scale of the observed breaker vortices was 5 hz and thus in the frequency range of wave orbital motion coherent breaker vortices were separated from wave orbital motions and incoherent higher frequency turbulence using a threshold magnitude for the vertical velocity component plunging breakers displayed the largest root mean square rms and maximum vertical velocities the latter reaching approximately 1 m s 1 these measurements were made at an elevation of 0 15 m above the bed given the observed scale of the breaker vortices and the phase match between suspended sediment concentrations and fluid velocities the turbulence injected into the water column by the plunging breakers played a significant role in suspending bed sediment on the other hand the role of coherent vortex structures in suspending sediment under spilling breakers and shoaling waves is more limited rms vertical velocities under the spilling breakers and shoaling waves in this experiment were respectively a factor 2 and 4 smaller than for plunging breakers different phase relationships were observed between the horizontal fluid velocity and vortex induced sediment suspension for each of the wave types which may contribute to an explanation of net offshore and onshore sediment transport observed during episodes of beach erosion and recovery respectively

measurements of near bed intra wave sediment entrainment above vortex ripples 1 in general descriptions of suspended sediment transport beneath surface waves are based on the turbulent diffusion concept however it is recognised that this approach is questionable for the suspension of sediment when the seabed is rippled in this case at least if the ripples are sufficiently steep the entrainment process is likely to be well organised and associated with vortex formation and shedding from the ripples to investigate the entrainment process above ripples a study was carried out in a large scale wave flume facility utilising acoustic techniques visualisations of the intra wave sediment entrainment above vortex ripples have been generated the observations provide a detailed description of entrainment which is interpreted here in relation to the process of vortex formation and shedding it is anticipated that such measurements will contribute to the development of improved physical process models of sediment transport in the rippled bed regime

secular bathymetric variations of the north channel in the changjiang yangtze estuary china 1880 2013 causes and effects abstract as the interface between the fluvial upland system and the open coast global estuaries are facing serious challenges owing to various anthropogenic activities especially to the changjiang estuary since the establishment of the three gorges dam tgd currently the world s largest hydraulic structure and certain other local hydraulic engineering structures the changjiang estuary has experienced severe bathymetric variations it is urgent to analyze the estuarine morphological response to the basin wide disturbance to enable a better management of estuarine environments north channel nc the largest anabranched estuary in the changjiang estuary is the focus of this study based on the analysis of bathymetric data between 1880 and 2013 and related hydrological data we developed the first study on the centennial bathymetric variations of the nc it is found that the bathymetric changes of nc include two main modes with the first mode representing 64 of the nc variability which indicates observable deposition in the mouth bar and its outer side area lower reach the second mode representing 11 of the nc variability which further demonstrates channel deepening along the inner side of the mouth bar upper reach during 1970 2013 further recent erosion observed along the inner side of the mouth bar is caused by riverine sediment decrease especially in relation to tgd induced sediment trapping since 2003 while the deposition along the lower reach since 2003 can be explained by the landward sediment transport because of flood tide force strengthen under the joint action of tgd induced seasonal flood discharge decrease and land reclamation induced lower reach narrowing generally the upper and lower nc reach are respectively dominated by fluvial and tidal discharge however episodic extreme floods can completely alter the channel morphology by smoothing the entire channel the results presented herein for the nc enrich our understanding of bathymetric variations of the changjiang estuary in response to human activities which can be well applied to other estuaries subject to similar interferences

analysis of dune erosion processes in large scale flume experiments abstract large scale physical model tests were conducted with different wave periods to examine the physical processes driving dune erosion the model tests have been carried out in a flume 2dv with a sandy dune exposed to extreme surge and wave conditions van gent m r a van thiel de vries j s m coeveld e m de vroeg j h and van de graaff j 2008 large scale dune erosion tests to study the effect of wave periods coastal engineering doi 10 1016 j coastaleng 2008 04 003 detailed measurements in time and space of water pressure flow velocities and sediment concentrations were performed in the near shore area the data revealed that both short and long waves are important to inner surf hydrodynamics depth averaged flows are directed offshore and increase towards the shore line the corresponding mean sediment concentrations rise sharply towards the dune face up to 50 g l near the bed the strong increase in the mean sediment concentration towards the dune face correlates well with the maximum wave surface slope which in turn is coupled to both the pressure gradient and the near bed wave breaking induced turbulence analysis shows that the pressure gradient is only partially coupled to the flow acceleration suggesting that the latter cannot always be used as a proxy for the first weak correlation is obtained with the near bed flows related to the bed shear stress tests with a larger wave period resulted in a larger dune erosion volume during these tests more wave energy combined incident and infragravity waves reached the dune face but more importantly this wave energy is dissipated by fewer waves resulting in more intense wave breakers and steeper wave fronts it is therefore expected that the wave breaking induced near bed turbulence increases resulting in significantly higher o 100 mean sediment concentrations in addition the mean flow velocities are comparable yielding a substantially larger offshore directed sediment transport capacity this increase in offshore directed transport is only partially compensated by a concurrent increase in the wave related onshore transport capacity associated with intrawave processes resulting in a net increase in the dune erosion rate

impacts of large dams on downstream fluvial sedimentation an example of the three gorges dam tgd on the changjiang yangtze river summary under the influence of climate and human activities fluvial systems have natural ability to make adjustments so that the river hydrology sediment movement and channel morphology are in dynamic equilibrium taking the changjiang yangtze river for example in the early stages after the three gorges dam tgd began operational ten years ago the suspended sediment content ssc and fluxes in the middle and lower reaches of the river decreased noticeably at present they appear to be in a stable state on the decadal scale although the river runoff has not shown any trends the water level in the river decreased appreciably in time in the meantime channel down cutting along the thalweg almost existed throughout the river course the riverbed has turned from depositional before the dam construction to erosional afterwards in other words the riverbed had turned from being sediment sinks to sediment sources in the main channel of the changjiang between yichang and nanjing a distance of 1300 km the riverbed sedimentation mode displays strong intermediate and weak erosion depending on the closeness to the tgd

observations of turbulence within a natural surf zone abstract here the reynolds stresses u w and w where u and w are the cross shore alongshore and vertical turbulence velocities respectively and the angle brackets represent time averaging are used to diagnose turbulence dynamics beneath natural breaking surf zone waves the data were collected at truc vert beach france during a 12 day period in 1 3 m water depth with strong cross shore and alongshore currents under high energy wave conditions offshore significant wave heights ranged between 2 and 8 m the u w term is predominantly negative increases with the ratio of wave height hs to water depth h degree of wave breaking and decreases in magnitude toward the bed this supports the view that the cross shore shear stress is due to breaking induced vortices that transport high speed cross shore flow downward and disintegrate close to the bed the occasional positive sign of u w within the lower 15 20 of the water column indicates that sometimes surface generated turbule

measured radiogenic heat production in sediments from continental margin of eastern north america implications for petroleum generation measurements of radiogenic heat production are presented for most of the major sedimentary formations beneath the rifted continental margin off nova scotia canada the measurements were made on 32 samples from 14 deep exploratory wells drilled in the area the results show that heat production ranges from about 1 8 to 0 3 w m 3 and varies with lithology the effect of this radiogenic heat production is to increase the heat flow and the temperatures within the sediments by up to 15 and 30 6 f 17 c respectively these temperature changes will increase the rate of organic maturation so that for example oil generation should occur 10 to 30 ma earlier in jurassic sediments than if those sediments exhibited no heat production it is noted ho ever that other thermal properties of the sediments must be studied before predictions of organic maturation and the timing of oil generation can be considered reliable the results presented here show that radiogenic heat production in sediments is an important parameter in making reliable predictions of their thermal maturity and thus should be included in future studies of thermal models for sedimentary basins

geometry and dynamics of wave ripples in the nearshore zone of a coarse sandy beach 1 extensive measurements of ripple characteristics and dynamics along with associated suspended sediment fluxes and hydrodynamic conditions were made in the shoaling and surf zones of a macrotidal coarse grained beach at sennen cove cornwall england median grain diameter 0 69 mm suborbital vortex ripples were observed during the majority of the study period with height 5 cm and length 35 cm the scale and shape of the ripples did not vary significantly as the bed shear stress increased during wave shoaling and breaking however ripple migration rates onshore directed were strongly dependent on their location relative to the breakpoint increasing from 0 1 cm min 1 under shoaling waves to 2 cm min 1 in the outer surf zone during low energy conditions farther inside the surf zone ripples persisted but migration rates slowed probably owing to the presence of the offshore directed mean flow which impedes landward migration of the ripples under low wave conditions during which measured sediment fluxes peaked around the outer surf zone and decreased through the saturated surf zone bed form transport rates under shoaling waves were of the same magnitude as net suspended sediment fluxes but at least an order of magnitude smaller in the outer surf zone under high energy conditions during which suspended sediment fluxes in the surf zone were offshore directed owing to the presence of the seaward directed mean flow bed form transport rates were several orders of magnitude smaller than suspended fluxes

the variations of sediment transport patterns in the outer changjiang estuary and hangzhou bay over the last 30 years the research objective is to investigate the variations of sediment transport in outer changjiang estuary and adjacent hangzhou bay induced by the decline of changjiang river sediment discharge and massive land reclamation in the last three decades a synchronous hydrographic survey was conducted along two transects at the bay mouth and outer changjiang estuary respectively during the spring neap tides of january and july 2014 the results show that the suspended sediment grain size current velocity suspended sediment concentration ssc and the water and sediment fluxes varied with the tidal cycles quantitative correlations with the tidal range were found for ssc and fluxes these data have been compared with those at the same hydrographic stations in the summer and winter of the early 1980s along the outer changjiang estuary transect the sscs and sediment fluxes decreased in the winter but no apparent changes occurred in the summer the sscs in the northern hangzhou bay decreased in both summer and winter while the southern bay mouth has evolved from a low ssc region to a high ssc region the findings clarify that the ssc and sediment flux changes in this area have only an indirect connection to the dramatic riverine sediment decline because the sediment resuspension by the strong tidal currents provided a major source at the present stage the impact of the riverine sediment decline is insignificant for the ssc variation off the changjiang river mouth finally a sediment flux model is proposed to explain and predict the morphological evolution trends

observation of the sediment trapping during flood season in the deep water navigational channel of the changjiang estuary china abstract after the construction of the deep water navigational channel dnc in the north passage of the changjiang estuary siltation in the channel became severe during the flood season in the navigation channel to investigate the causes field observations of tidal current salinity and suspended sediment concentration ssc were conducted by 16 anchored boats in the navigation channel of north passage during spring tide in the flood season the across channel differences of salinity ssc and near bottom residual sediment transport at the high siltation area of the dnc were observed and analyzed the results show that the near bottom ssc presented a south to north decreasing trend during the flood tide at the lower reach of the north passage during the ebb tide a suspended sediment cloud of extremely high concentration was detected within the channel the observed longitudinal sediment trapping was not only shown as the turbidity maximum tm trapped within the moving salinity front but also as the longitudinal convergence of the residual sediment transport at the middle reach the mechanism for the longitudinal sediment trapping was due to the tidal asymmetry in mixing the observed lateral sediment trapping was prominent at the most severe siltation area of the dnc in the section 2 the lateral sediment trapping at the across channel section 2 was not only shown as the lateral transport of the sediments from the channel flanks during the flood slack but also as the lateral convergence of the residual sediment transport during the entire spring tidal cycle the mechanism for the lateral sediment trapping was dominated by the advective transport the lateral impact on the channel sediment trapping was not negligible in view of the depth mean lateral tidal straining on the water stratification the observed convergences of both the longitudinal and the lateral residual sediment transports were responsible for the severe channel siltation in the north passage

spatial temporal evolution of the eastern nanhui mudflat in the changjiang yangtze river estuary under intensified human activities abstract the eastern nanhui mudflat enm located in the southern flank of the changjiang yangtze river estuary plays a key role in storm protection defense against sea level rise and land resource provision for shanghai china s largest city recently there has been a great deal of concern for its evolutionary fate since a drastic reduction in the changjiang sediment discharge rate and an increased number of estuarine enclosures might negatively impact the environmental protection functions that this mudflat provides in this paper a novel method which employed the envelope lines of instantaneous shoreline positions identified in 436 landsat satellite images from 1975 to 2016 was used to demonstrate the evolution of the mudflat high and low tide lines in a detailed quantitative way our study reveals the southeast progradation rate of the mudflat doubled from 24 m yr in 713 1974 ce to 49 m yr in 1975 1995 ce probably due to the influence of the estuarine turbidity maximum zone shifting to the enm under the ample sediment input directly from the turbidity maximum zone the spatial evolution of the enm was governed predominantly by the changing morphology of the south passage due to the quick progradation of the enm which narrowed the south passage by pushing the south passage trumpet southeastward therefore the enm experienced rapid accretion during 1975 2016 the accretion rate of the high tide line increased 2 13 times due to vegetation and intertidal enclosures resulting in the rapid reduction of the intertidal area the area decreased from 97 km2 in 1976 to 66 km2 in 1995 mainly due to vegetation and continued decreasing to 12 km2 in 2006 due to the intertidal enclosures in contrast the accretion rate of the low tide line increased by 25 times due to subtidal enclosures and caused the intertidal area increased to 78 km2 in 2015 the almost disappeared intertidal zones in 2006 reappeared however this reappearance might be a temporary transitional state and once the subtidal enclosures are completed most of the intertidal zones will be replaced by enclosure land our study reveals that the drastic reduction in the changjiang sediment flow to the sea has not caused a decline in the enm in contrast the enm has experienced rapid accretion in the past 40 years resulting in the strengthening of its functional abilities to protect shanghai an unexpected outcome

implications of flow control by the three gorges dam on sediment and channel dynamics of the middle yangtze changjiang river china the impacts of a dam on the river downstream in terms of hydrology and morphology are determined by a complex mix of variables that includes the patterns of release of water through the dam and the characteristics of the downstream channel scour of the downstream channel is a common response because large dams cause a significant interruption to sediment continuity here we show that in the case of china9s three gorges dam on the yangtze river the outcome is complicated as is commonly the case in large rivers the downstream channel and floodplain system compose an area of long term sediment accumulation and unstable channels with seasonally contrasting erosion and deposition patterns related to the migrating seasonal monsoon rainfall zones in achieving one of the main purposes of this dam that of flood control in the middle and lower basins the pattern of flows released from the dam will closely resemble those seasonal flows that are responsible for channel instability in the middle catchment thus effectively making erosive conditions the most common during a year there is obviously concern about the ultimate impact of sediment storage in the dam on the dynamics of the delta and adjacent coast and we show that this depends on the trajectory and duration of the erosive responses in the middle yangtze basin in this particular case the outcome is of great significance to the well being of the densely populated riparian areas of the river

basin modeling meets rift analysis a numerical modeling study from the jeanne d arc basin offshore newfoundland canada abstract the jeanne d arc basin on the grand banks offshore newfoundland is a confined failed rift basin its initial development and burial history were controlled by crustal stretching and thinning this study provides a detailed analysis of the heat flow tectonic subsidence stretching factor maturation and temperature history based on 44 1d models and one full 4d space and time model in basin models the heat flow history is usually calculated from vitrinite reflectance vrr data however this causes uncertainties and reflects only the periods of sedimentation which where penetrated by wells therefore other methods should be used to reconstruct the early heat flow history not recorded by sediments in this study a discontinuous pure shear stretching model including radioactive heat production reflecting the timing and magnitude of stretching factors of crust and lithospheric mantle was applied to a 4d numerical model for the jeanne d arc basin it is the first time that this new technique is shown on a real case scenario and it gives new insights into the regional geodynamics results show that to understand the thermal evolution of the jeanne d arc sedimentary basin completely it is crucial to consider the triassic rift system this first rift generated the structural framework of the basin where most of the sediments were deposited the second extension in the cretaceous represents most likely an ultra slow extension phase with a heat impulse too weak to leave any thermal record this study demonstrates that the entire evolution of the jeanne d arc basin can be reconstructed assuming just one single triassic thermal rift additionally it shows the effects of a lateral heat transfer on the determination of stretching factors and thus on tectonic subsidence and the resulting heat flow history

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

characteristics of suspended sediment and river discharge during the beginning of snowmelt in volcanically active mountainous environments abstract to better understand instream suspended sediment delivery and transformation processes we conducted field measurements and laboratory experiments to study the natural function of spatial and temporal variation sediment particles stable isotopes particle size and aspect ratio from tributary to mainstream flows of the sukhaya elizovskaya river catchment at the beginning of and during snowmelt the sukhaya elizovskaya river is located in the kamchatka peninsula of russia and is surrounded by active volcanic territory the study area has a range of hydrological features that determine the extreme amounts of washed sediments sediment transported to the river channels in volcanic mountainous terrain is believed to be strongly influenced by climate conditions particularly when heavy precipitation and warmer climate trigger mudflows in association with the melting snow the high porosity of the channel bottom material also leads to interactions with the surface water causing temporal variability in the daily fluctuations in water and sediment flow field measurements revealed that suspended sediment behaviour and fluxes decreased along the mainstream sukhaya elizovskaya river from inflows from a tributary catchment located in the volcanic mountain range in laboratory experiments water samples collected from tributaries were mixed with those from the mainstream flow of the sukhaya elizovskaya river to examine the cause of debris flow and characteristics of suspended sediment in the mainstream these findings and the geological conditions of the tributary catchments studied led us to conclude that halloysite minerals likely comprise the majority of suspended sediments and play a significant role in phosphate adsorption the experimental results were upscaled and verified using field measurements our results indicate that the characteristics of suspended sediment and river discharge in the sukhaya elizovskaya river can be attributed primarily to the beginning of snowmelt in volcanic tributaries of the lahar valley suggesting a significant hydrological contribution of volcanic catchments to instream suspended sediment transport daily fluctuations in discharge caused by snowmelt with debris flow were observed in this measurement period in which suspended sediment concentration is 10 mg l during nonflooding periods and 1400 mg l when flooding occurs the oxygen and hydrogen isotope measurements when compared with japan indicated that the kamchatka region water is relatively lightweight incorporating the effects of topography and the water from the beginning of the snowmelt is relatively lightweight when compared with water from the end of the snowmelt the trend line of isotopes from the beginning of the snowmelt was defined by a slope of 6 88 n 12 r 2 0 97 significantly less than that of isotopes from the snowmelt 8 72 the sediment particles collected during the snowmelt were round in shape caused by the extreme flows and high discharge the shape of the sediment particles collected at the beginning of the snowmelt assumed to be fresh samples from the hillslope was sharper caused by the relatively small discharge by moderate snowmelt finally the relationship between river discharge and suspended sediment concentration was indicated the results are compared with mountainous rivers of japan and malaysia a new diagram is proposed to describe the relationship between suspended sediment concentration and river discharge

human impact on land ocean sediment transfer by the world s rivers abstract land ocean transfer of sediment by rivers is a key pathway for material transfer on earth contemporary data on the sediment loads of rivers provide clear evidence of significant recent changes in the sediment fluxes of several rivers in response to human impact the key drivers of increased sediment loads include land clearance for agriculture and other facets of land surface disturbance including logging activity and mining although programmes for soil conservation and sediment control can result in reduced sediment loads the trapping of sediment by dams represents the dominant cause of reduced loads this influence is currently assuming increasing importance at the global scale any attempt to link these drivers to changes in the global land ocean sediment flux must take account of the aggregation and buffering effects that operate in larger basins which can cause damping and even removal of signals of increasing flux within the upstream basin and complicate the link between upstream and downstream response to human impact further work is required to provide a precise quantitative assessment of the human impact on global land ocean sediment fluxes and the net effect of increasing and decreasing fluxes particular attention must be paid to the temporal perspective and the variation of impact trajectories in different areas of the globe and for river basins of different sizes

flux and fate of yangtze river sediment delivered to the east china sea numerous cores and dating show the yangtze river has accumulated about 1 16 x 10 12 t sediment in its delta plain and proximal subaqueous delta during holocene high resolution seismic profiling and coring in the southern east china sea during 2003 and 2004 cruises has revealed an elongated similar to 800 km distal subaqueous mud wedge extending from the yangtze river mouth southward off the zhejiang and fujian coasts into the taiwan strait overlying what appears to be a transgressive sand layer this distal clinoform thins offshore from similar to 40 in thickness between the 20 and 30 m water depth to 1 2 in between 60 and 90 m water depth corresponding to an across shelf distance of less than 100 km total volume of this distal mud wedge is about 4 5 x 10 11 m 3 equivalent to similar to 5 4 x 10 11 t of sediment most of the sediment in this mud wedge comes from the yangtze river with some input presumably coming from local smaller rivers thus the total yangtze derived sediments accumulated in its deltaic system and east china sea inner shelf have amounted to about 1 7 x 10 12 t preliminary analyses suggest this longshore and across shelf transported clinoform mainly formed in the past 7000 yrs after postglacial sea level reached its mid holocene highstand and after re intensification of the chinese longshore current system sedimentation accumulation apparently increased around 2000 yrs bp reflecting the evolution of the yangtze estuary and increased land erosion due to human activities such as fanning and deforestation the southward flowing china coastal current the northward flowing taiwan warm current and the kuroshio current appear to have played critical roles in transporting and trapping most of yangtze derived materials in the inner shelf and hence preventing the sediment escape into the deep ocean c 2006 elsevier b v all rights reserved

decline in suspended sediment concentration delivered by the changjiang yangtze river into the east china sea between 1956 and 2013 abstract the temporal evolution of suspended sediment concentration ssc in a river debouching into the ocean provides vital insights into erosion processes in the watershed and dictates the evolution of the inner continental shelf while the delivery of sediment from rivers to the ocean has received special attention in the recent past few studies focused on the variability and dynamics of river ssc especially in the changjiang yangtze river china the longest river in asia here variations in ssc delivered by the changjiang river to the east china sea and possible causes of its variability were detected based on a long term time series of daily ssc and monthly water discharge measured at the datong gauging station the ssc data are further compared to a hydrological analysis of yearly precipitation covering the entire catchment the results indicate the presence of a decline in ssc in the period 1956 2013 which can be divided into three phases i high ssc 0 69 kg m3 in the wet season and low ssc 0 2 kg m3 in the dry season from 1956 to 1970 ii relative high ssc 0 58 kg m3 in the wet season and low ssc 0 15 kg m3 in the dry season from 1971 to 2002 and iii low ssc 0 19 kg m3 in the wet season and very low ssc 0 09 kg m3 in the dry season after 2002 these three periods have a mean yearly ssc values of 0 62 0 42 and 0 18 kg m3 respectively compared with 1956 1970 the slope of the rating curve between ssc and water discharge decreased respectively by 2 and 30 during the period 1971 2002 and 2002 2013 soil erosion dam construction and banks reinforcement along the changjiang river are the main causes of ssc variations fluctuations in water discharge are also controlling the ssc long term variations specifically from 1956 to 1970 the effect of soil erosion overrules that of dam impoundment which is likely responsible for the high ssc during the period 1970 2002 the influence of dam impoundment increases while that of soil erosion decreases which together produce a small reduction in ssc since 2002 the impact of soil erosion further decreases and large scale sediment trapping behind the three gorges dam is responsible for the occurrence of extremely low ssc the results presented herein for the changjiang river can inform a better management strategy of sediment resources and water quality for both the river and the coast our conclusions can be well applied to other rivers discharging in the ocean subject to similar human activities

hydrocarbon fluid inclusions in the argo salt offshore canadian atlantic margin1 fluid inclusions hosted in rock salt from the triassic argo formation in the canadian atlantic continental margin were studied to investigate the nature and origin of petroleum fluids in them incl

regional maturity as determined by organic petrography and geochemistry of the schei point group triassic in the western sverdrup basin canadian arctic archipelago abstract maturity and source rock potential of organic rich beds in the triassic schei point group in the sverdrup basin arctic canada have been investigated using reflected light microscopy and the results are compared with other maturity parameters determined geochemically i e rock eval and biomarker maturation parameters the samples evaluated belong to the eden bay member of the hoyle bay formation and contain a predominance of marine algal material in the form of tasmanales and dinoflagellates along with mixed terrestrial organics the rock matrix is dominantly carbonate with some shaly input indicating that the rocks were deposited in an iron poor highly euxinic environment with few exceptions there is good agreement between parameters determined using microscopy namely r o max and r gq and geochemical parameters t max hi dia c 27 dia c 27 reg c 27 steranes s s r c 29 steranes the ternary diagram showing the abundance of normalized c 27 c 28 and c 29 regular steranes indicates a mostly marine depositional environment for the schei point source rock this is confirmed by the abundance of marine fauna and flora in these samples analytical results from several different techniques indicate that the source rocks become more mature from the margin towards the axis of the sverdrup basin this is due in part to the increase in overburden of sediments in the axis of the basin also the high thermal conductivity of salt has strongly influenced the maturity of schei point source rocks over the crest of the salt cored structures i e well hazen f 54 and the proximity of salt has enhanced maturation levels at well rock point j 43 the sections investigated were also considered to have an excellent gas potential due to their higher than average toc content

a graphical method to study suspended sediment dynamics during flood events in the wadi sebdou nw algeria 1973 2004 small sub basins are numerous in mediterranean area and global sedimentary budgets cannot be obtained without a detailed understanding of the hydroclimatic processes that govern sediment fluxes in these small river systems in this study the shape of the relationship between sediment concentration c and water discharge q during flood events of a 31 years period 1973 2004 was analyzed at the outlet of the wadi sebdou basin 256 km2 in northwest algeria using a new graphical analysis method based on features of hysteresis loops each flood was decomposed as successive stages each of which being characterized by a sediment rating curve and used to quantify the contribution of diverse sediment sources within the basin seven common classes of hydrological events single valued and six hysteresis loops clockwise counter clockwise eight shaped single valued plus one loop either clockwise or counter clockwise and single valued plus at least two loops were explored sediment supply from locally derived sources or base load was high and reached 77 of total sediment yield for the study period and was attributed to weathering of bed material or gullies the remainder portion was derived from hill slopes re suspension of fresh fine deposits in the river bed or bank collapse the ratio of suspended sediment load derived from active sediment source varies considerably from one flood to another depending on many factors such as seasonality and antecedent type of flood the simpler floods were the most frequent ones but produced less sediment the most frequent floods were clockwise or anticlockwise 52 of floods but brought only 34 of the total sediment flux the 18 of the most complex floods single valued plus at least two loops produced more than 53 of the sediments mainly supplied by base load 84 intra annual variability was very high over 31 years the five biggest floods cumulated 64 of the total sediment flux and were of three classes the most complex floods being dominant the largest contribution occurred during one single 33 days long hydrological event with complex form which represented 26 of the total sediment flux apart from the five biggest flood events the base load represented 53 the biggest floods favour base load as compared to the smallest ones

thermal history of alberta deep basin comparative study of fluid inclusion and vitrinite reflectance data the thermal history of the alberta deep basin the gas saturated westernmost part of the western canadian sedimentary basin has been studied by analyzing aqueous and hydrocarbon fluid inclusions in diagenetic cements and comparing the results with coal maturity data results indicate that most of the diagenetic quartz druse precipitated from low salinity fluids 2 3 wt at a temperature of 170 195 c calcite cement precipitated after quartz druse during uplift and cooling at temperatures of 108 169 c inclusions rich in larger hydrocarbon molecules occur in cements that precipitated at 150 c whereas methane rich inclusions occur in cements that precipitated at 165 c or at lower temperatures after significant uplift and cooling of the b sin maximum burial temperatures tmb calculated from vitrinite reflectance data using the lopatin waples tti ro calibration are significantly lower 150 c than the temperature at which quartz druse precipitated in the same area 190 c an equation directly relating tmb and ro proposed by barker and pawlewicz in 1986 yields maximum burial temperatures 200 210 c only slightly higher than the fluid temperatures the results from this study suggest that hot fluids migrated updip along permeable conglomerates and bedding plane fractures to produce unexpectedly high geothermal gradients 38 c km in the western part of the study area the apparent restriction of hot fluids to the western part of the study area sugge ts that convective heat transfer by fluids may have operated on a scale of only tens of kilometers in lower cretaceous rocks of the alberta deep basin

source rock and seep oil maturity in dorset southern england abstract analysis of the steranes and triterpanes in the oil seeps of the dorset coast of southern england mupe bay osmington mills shows both the oils to derive from a similar mid late mature source rock measured maturity of the jurassic source rocks at outcrop are uniformally immature 0 3 0 5 r despite a history of mesozoic burial and tertiary inversion and uplift evidence from oil cemented sandstone clasts within oil stained lower cretaceous fluviatile channel sands at mupe bay suggests that oil was already seeping during the lower cretaceous detailed work comparing the extracts of the oil stained clasts and the surrounding oil stained sandstones shows the clasts to contain oil derived from a slightly but significantly less mature source rock this is consistent with lower maturity oil seeping first into the sand that was then incorporated as rip up or bank collapse clasts into the channel sand at a later stage with further source rock burial more mature oil entered the matrix sandstone locally calibrated time temperature thermal geohistory modelling can just simulate source rock maturities appropriate to the seep oils if paleo geothermal gradients and surface temperatures were locally higher in the jurassic than at the present day a volumetric balance between oil in place in the wytch farm field and the available area of source rock draining into the structure suggests that an anomalously thick and or organic rich rhaeto liassic section must have developed in the bournemouth bay basin and that cretaceous palaeo geothermal gradients were higher in this specific area

sediment export by water from an agricultural catchment in the loam belt of central belgium abstract an agricultural drainage basin of 250 ha was selected in the belgian loam belt to evaluate sediment export by water water discharge was continuously measured at the outlet of the catchment and suspended sediment samples were taken proportional with discharge during rainfall events from these samples supended sediment concentration and grain size distribution were determined within the catchment regular surveys were conducted in order to obtain detailed data on vegetation cover soil surface parameters and erosion and sedimentation features important variations in sediment yield were detected at various time scales ranging from a year over a season to one event these variations could be linked with processes occurring within the catchment due to the development of a vegetation cover the suspended sediment concentrations were lower during the summer period than during the winter period for the same discharge the evolution in both suspended sediment concentration and grain size distribution during the winter period is explained by variations in the soil surface state of the fields as well as the development of a rill and gully network the positive hysteresis observed within a single event is explained by taking into account the distance between the sediment source and the catchment outlet and not by sediment flushing our analysis shows that the role of the main factors controlling the geomorphic response of such a catchment can be identified only if measurements at the outlet are complemented by detailed data on the conditions within the catchment catchment model calibration and validation are therefore impossible if this information is lacking

petroleum geochemistry of the midyan and jaizan basins of the red sea saudi arabia abstract during the 1960s petroleum exploration activities in the offshore red sea areas of saudi arabia tested gas and condensate reservoired in the miocene sands immediately below the mansiyah evaporites in the offshore midyan basin recent onshore exploration activity in the red sea has resulted in the discovery of accumulations of oil gas and condensate in the lower miocene maqna group in the midyan and jaizan basins as a result of this exploration success an effort to understand the origin of these hydrocarbons was initiated the two basins were assessed geochemically by addressing 1 the potential source rocks 2 the extent of the hydrocarbon kitchens and 3 characterization of the hydrocarbons the potential source rocks for the reservoired hydrocarbons are 1 the organic rich oil prone shales of the predominantly evaporitic mansiyah formation 2 the variable quality shales and carbonates of the magna group and 3 the moderately organic rich shales of the burqan and tayran groups the reservoired hydrocarbons were characterized by carbon isotopes gas chromatography mass spectrometry and gas chromatography and compared with the potential source rocks the results showed an acceptable match to the maqna and burqan organic rich units detailed burial history thermal modelling projects were undertaken to assess the hydrocarbon kitchens of both basins results for the midyan basin indicated that over large areas tayran and burqan sediments are oil to gas mature and may be sources for the gas and or condensate accumulations whereas the limited area of mature maqna sediments may be responsible for sourcing the black oil accumulations in the jaizan basin the maqna and burqan sediments range from high oil maturity to thermally spent due to high geothermal conditions and excessive burial the burial of the source rocks increases fairly rapidly from east to west in the jaizan basin

paleo heat flow of eastern canada s passive margins abstract tectonic subsidence rates derived from several wells in the labrador sea and offshore nova scotia and newfoundland were used to estimate the paleo heat flow along the margins of eastern canada if tectonic subsidence is caused by the cooling of the lithosphere only the transient component of the heat flow i e the heat flow in excess of background heat flow can be estimated directly from subsidence data for the nova scotia and the labrador sea margins the analysis shows that the transient component of the heat flow decreased markedly from 28 56 mw m 2 immediately after rifting to a present value between 7 and 14 mw m 2 depending on boundary conditions the analysis shows a distinctive difference between the evolution of the labrador sea and that of the northeastern newfoundland margin where it is estimated that the transient component of the heat flow exceeded 100 mw m 2 after rifting and dropped rapidly to very low values the study suggests that the subsidence of the newfoundland margin was not caused by cooling only but required an additional mechanism such as lower crustal phase transformations or continuing extension after continental breakup with ductile deformation in the lower crust and upper mantle the estimated transient heat flow was used to calculate the average present surface heat flow in eastern canada s margins which is the sum of heat flow from the mantle crustal heat production and the transient cooling of the lithosphere the calculated heat flow compares well with heat flow density data obtained from bottom hole temperature measurements

simulating high ebb currents in the north passage of the yangtze estuary using a vertical 1 d model abstract a strong maximum ebb current 3 m s in the upper water column was observed at station cs3 in the middle of the north passage of the yangtze river estuary during the wet season which was higher than either its upstream or downstream counterparts to better understand the mechanisms and factors causing the strong ebb current a vertical one dimensional 1 d model was used to conduct a diagnostic study the model used time series of observed tidal amplitudes vertical salinity and suspended sediment concentration ssc profiles to compute the density and turbulence two tunable parameters the tidal amplitude attenuation coefficient i e the phase lag and the background surface pressure gradient that represents the net pressure gradient induced by the freshwater discharge and baroclinic effect were used to determine the best match with the observed high velocity amplitudes in addition to the bottom roughness height three hypotheses of possible causes are tested 1 the large freshwater discharge 2 the bottom stratification effects which were caused by a possible high near bed suspended sediment gradient and 3 the unique location of the cs3 station that was influenced by local geometry the findings show that neither of the first two factors has much influence on the pronounced ebb velocities instead the energy loss caused by the change of channel geometry and a maximum convex bathymetry in the north passage of the yangtze river estuary are the main reasons behind the extremely high observed ebb current velocity profiles the high near bottom ssc and gradient located within 0 5 m above the bed only slightly alters the velocity profiles this 1 d model is convenient for testing a different hypothesis and for coupling with other selected variables to account for the floc size distributions in future studies

influence of live microbes on suspended sediment concentration in coastal ecosystem abstract microbes present in both fresh and saline water associate with suspended sediments by secrete extracellular polymeric substance to survive under stressful environmental conditions deposition of these bio contaminated sediments affects the bed ecosystem when re suspended they further affect water quality and health of both human as well as aquatic life in this study laboratory experiments are conducted in an annular flume to understand the interaction between suspended sediments attached with microbes biosediment and without microbes non biosediment at different mix ratios mr 0 1 0 25 0 75 0 50 0 50 and 1 0 and water salinity s 0 1 2 5 10 and 35 g l results show that rate of deposition increases with an increase in biosediment concentration for any water salinity and mix ratio in saline water presence of microbes on suspended sediments induces more deposition until water salinity of 5 g l and thereafter deposition reduces presence of 25 and 50 of biosediment in water increases deposition up to a critical salinity of 1 72 g l and 2 60 g l respectively suspended sediment particle size increases with an increase in biosediment concentration and decreases with an increase in water salinity fractal dimension results show that when salinity increases fragile non biosediment and dense biosediments are retained in suspension this study shows that presence of live microbes on suspended sediments affects their depositional behaviour

bedform contributions to cross shore sediment transport on a dissipative beach abstract field measurements of hydrodynamics suspended sediment transport rates and bedform sediment transport rates were made in the intertidal section of a dissipative sandy beach d50 0 26 mm slope 1 80 at perranporth uk pressure transducers acoustic doppler velocimeters optical backscatter sensors and an acoustic sand ripple profiler were deployed for 12 tides measuring in a range of wave heights from 0 5 to 2 2 m water depths from 1 to 6 m and in current strengths up to 0 4 m s data were analysed in terms of the distance to shore x normalised by the surf zone width xs and spanned the region 0 4 1 5 the fractional contribution of the shoreward directed bedform transport to the total absolute transport was up to 100 and occurred broadly in the region of the breakpoint 0 5

the effect of air bubbles on optical backscatter sensors the sensitivity of an optical backscatter sensor obs to bubbles is tested using a variety of bubble generating mechanisms that span the range of bubble sizes typically observed in surf zone studies over 1200 one minute runs were performed in a stirred test tank by altering the bubbler type water type air flow rate and sand or mud concentration the laboratory data shows a strong dependence of obs response to bubble size and concentration for sand or mud sediments the optical backscatter sensor voltage is increased by the presence of bubbles and smaller bubbles had a larger effect the effect was more pronounced in salt water than fresh water we conservatively report that obs output voltage is increased due to the presence of bubbles by 25 for the trials undertaken here in the cases performed in vigorously stirred salt and synthetic salt water bubbles were smaller than those measured under quiescent water conditions due to bubble shattering at the bubbler orifices and by the pumps used for stirring it was found in those cases that the bubble effect on obs was larger than the 25 reported here but the extension of this finding to a natural setting such as in the direct vicinity of the breakpoint or a bore is not known

flow tunnel measurements of velocities and sand flux in oscillatory sheet flow for well sorted and graded sands oscillatory flow tunnel measurements of velocities and fluxes for sands in oscillatory sheet flow conditions are presented the experiments involved a range of well sorted and graded sands in two asymmetric flows velocities were measured using an ultrasonic velocity profiler uvp capable of measuring deep within the sheet flow layer velocity profiles are found to be similar for the same flow but different sand beds and display expected features of oscillatory boundary layer flow the near bed velocity leads the main flow velocity by approximately 21 and a small offshore directed current is generated near the bed measures of the boundary layer thickness are in good agreement with those predicted using an equation formulated for the boundary layer thickness over fixed beds velocity data have been combined with concentration data to produce time dependent sand flux profiles covering the sheet flow and suspension regions there are fundamental differences in the transport processes of sands of different size and grading caused by unsteady effects which dominate in the case of fine sand and are largely absent in the case of coarse sand 1 time averaged flux is onshore directed positive in the case of coarse sand and is confined to a region immediately above the bed in contrast time averaged flux in the case of fine sand extends high above the bed is offshore directed negative in the sheet flow layer and becomes onshore directed in the suspension layer 2 net transport in the case of coarse sand is directed onshore as the percentage of fine sand in the bed increases offshore transport becomes increasingly dominant as the percentage of fine sand increases 3 net transport in the suspension layer is onshore while net transport in the sheet flow layer may be onshore or offshore depending on sand size and grading

thermal and isostatic consequences of simple shear extension of the continental lithosphere abstract quantitative results are presented for a model involving large scale simple shear of continental lithosphere the locally compensated finite element model includes the effects of sedimentation radiogenic heat production in the crust and sediments and finite rates of extension flexural effects during firting are examined using a simple shear model with a uniform initial elastic thickness the locally compensated model predicts that a breakup unconformity develops on the upper plate when extension occurs at typical plate tectonic velocities subsidence occurs as the upper and lower lithospheric plates separate extension creates the potential for large accumulations of sediment 20 km most of which is syn rift if sedimentation keeps pace with subsidence the effect of flexure is to modify the shape of the detachment surface and the uplift patterns on the flanks of the upper and lower plate sedimentary basins a model which incorporates flexure predicts significant uplift of the lower plate as it is unloaded by the upper plate during extension the wernicke simple shear model can be distinguished from its opposite end member the mckenzie pure shear model by the predicted asymmetry in thermal evolution higher predicted heat flux within the upper plate uplift subsidence histories and stratigraphic development of the upper and lower plates

submarine groundwater borne nutrients in a tropical bay maowei sea china and their impacts on the oyster aquaculture submarine groundwater discharge sgd has been recognized as an important pathway for nutrients into estuaries coasts and the adjacent seas in this study 222rn was used to estimate the sgd associated nutrient fluxes into an aquaculture area in a typical tropical bay maowei sea china the sgd into the maowei sea during june of 2016 was estimated to be 0 36 0 33 m d 1 and was associated with sgd derived dissolved inorganic nitrogen din dissolved inorganic phosphorus dip and dissolved silicon dsi fluxes mol d 1 of 4 5 5 5 106 5 3 9 1 104 and 9 4 9 3 106 respectively the sgd derived nutrients i e din dip and dsi were more than 1 9 0 9 and 3 6 times the amounts in the local river input and served as dominant sources in the nutrient budgets in the maowei sea moreover the n p ratios in the sgd around the maowei sea were high mean 64 and these ratios likely exceeded the environmental self purification capacity thereby enhancing the biomass and changing the phytoplankton community structure therefore sgd processes with derived nutrients may affect the biogeochemical cycles and marine ecological environment in the maowei sea furthermore the n p ratios 67 in oysters are very close to those in the sgd in the maowei sea this coincidence suggests that the high n p ratios in the sgd are likely to be one of the most important sources that support oyster aquaculture which might weaken the burden of water eutrophication in the maowei sea