early and late holocene paleoenvironmental reconstruction of the pearl river estuary south china sea using foraminiferal assemblages and stable carbon isotopes abstract proxy reconstructions of estuarine evolution provide perspectives on regional to global environmental changes including relative sea level changes climatic changes and agricultural developments here we present a new benthic foraminiferal record along with 13c and c n and lithological data from a sediment core in the pearl river estuary lingding bay adjacent to the south china sea the core has relatively thick holocene sediments 40 m due to its location in the paleo valley of the pearl river the lithologic and foraminiferal record reveal an evolution in paleoenvironment from fluvial inner estuary to middle estuary between 11300 and 8100 cal a bp in response to rapid sea level rise 13c and c n data indicate high freshwater discharge from 10500 to 8100 cal a bp driven by a strong asian monsoon the middle holocene 8100 3300 cal a bp sediment is absent in the core due to subaqueous erosion resulting from the unique geomorphology of the pearl river delta in the late holocene from 3300 cal a bp to the present the lithology and foraminiferal assemblages suggest a further evolution from outer estuary middle estuary channel to middle estuary shoal resulting from deltaic progradation under stable relative sea levels in the last 2000 years 13c and c n values reveal the intensive development of agriculture coupled with the reduction of freshwater input derived from a weakening asian monsoon

holocene sea level change and the emergence of neolithic seafaring in the fuzhou basin fujian china abstract neolithic seafaring across the taiwan strait began approximately 5000 years ago and involved open sea voyages over distances of at least 130 km rapid sea level rise preceded the emergence of open sea voyaging but the possible role of environmental change as a stimulus for the development of seafaring is poorly understood we investigate this problem by presenting a record of holocene sea level change and coastal transformation based on sediment cores obtained from the fuzhou basin on the coast of fujian china the cores are located in direct proximity to archaeological sites of the tanshishan neolithic culture 5000 4300 cal bp which is significant for its similarity to the earliest neolithic cultures of taiwan multiple lines of evidence record the early holocene inundation of the fuzhou basin around 9000 cal bp the mid holocene sea level highstand and the final holocene marine transgression this final transition is precisely documented with ams dates showing the change occurred close to 1900 cal bp our paleogeographic reconstruction shows that a large estuary filled the fuzhou basin during the mid holocene tanshishan and zhuangbianshan two of the major fuzhou basin neolithic sites are located today on hills nearly 80 km from the modern coastline however when the sites were settled around 5500 5000 cal bp the marine transgression had transformed these hills into islands in the upper estuary we suggest that the neolithic era estuary setting together with the lack of land suitable for rice paddy agriculture inhibited intensive food production but favored a maritime orientation and the development of seafaring

late quaternary environmental changes in the pearl river mouth region china abstract this study presents findings concerning late quaternary environmental changes in the pearl river mouth region china based on the study of over 300 boreholes out of these 35 boreholes are selected for the reconstruction of transects across the deltaic plain and estuary 39 radiocarbon dates obtained from these boreholes are used to help define the chronology of stratigraphic units present including two terrestrial units t1 and t2 and two marine units m1 and m2 diatom assemblages are studied in 6 boreholes revealing similarities and differences between the two marine units before the area was inundated by the last interglacial sea mis 5 an older terrestrial unit of sand and gravel t2 was laid down in a number of palaeo valleys during the last interglacial period an older marine unit of silt and clay m2 was laid down which was subsequently subaerially exposed when sea level regressed during the last glacial period mis 4 2 causing the uppermost section to be weathered during the same period a younger terrestrial unit of sand and gravel t1 was deposited along palaeo river channels around the early holocene before 8 2 cal ka bp the postglacial rise in sea level initiated a new phase of sedimentation in the outer part of the estuary characterised by the high percentages of marine diatoms in the sediments in the early holocene strong monsoon freshwater discharge resulted in sedimentation of a fine sand layer in the inner part of the estuary after 8 2 cal ka bp rapid rises in sea level caused widespread marine inundation and sedimentation the diatom data suggest that the relative sea level associated with the m2 and m1 units were both at similar levels because the m2 unit is typically recorded at altitudes of 15 m and 20 m below the present sea level this is likely to be a result of long term subsidence although numerical dating of the pre m1 units has not been made in the present study the chronology of these units can be inferred from uranium series ages and optically stimulated luminescence dating obtained from the adjacent coastal waters of hong kong the t1 unit has yielded ages of about 30 0 cal ka bp while the m2 unit has yielded ages about 130 0 cal ka bp confirming their mis 4 2 and mis 5 ages respectively

origin of groundwater salinity and hydrogeochemical processes in the confined quaternary aquifer of the pearl river delta china summary the pearl river delta prd located in the coastal area of south china contains a large confined quaternary aquifer this aquifer has been identified to have high concentrations of total dissolved solids ranging from 1 g l in the inland area to 26 8 g l near the southeast shoreline this work aims to investigate the origin of groundwater salinity and the major hydrogeochemical processes controlling the groundwater evolution in the confined basal aquifer of the prd a total of 40 boreholes were drilled in the prd during 2007 2009 and groundwater samples were collected for major ion ca 2 mg 2 na k nh 4 cl so 2 4 and hco 3 and isotope d 18 o d 2 h 3 h d 13 c and 14 c analyses these analyses demonstrate that groundwater in the confined basal aquifer is recharged by local rainwater and seawater and seawater is the major salinity source for groundwater the contribution of seawater varies from less than 1 in the inland areas to 74 near the shoreline so 2 4 reduction and methanogenesis occur in this reducing confined aquifer the results of ion exchange show that mg 2 exchanges mainly with the nh 4 ion which is derived from the mineralization of sedimentary organic matter ion exchange between na

alluvial channel geometry theory and applications the downstream hydraulic geometry of alluvial channels in terms of bank full width average flow depth mean flow velocity and friction slope is examined from a three dimensional stability analysis of noncohesive particles under two dimensional flows four governing equations flow rate resistance to flow secondary flow and particle mobility are solved to analytically define the downstream hydraulic geometry of noncohesive alluvial channels as a function of water discharge sediment size shields number and streamline deviation angle the exponents of hydraulic geometry relationships change with relative submergence four exponent diagrams illustrate the good agreement with several empirical regime equations found in the literature the analytical formulations were tested with a comprehensive data set consisting of 835 field channels and 45 laboratory channels the data set covers a wide range of flow conditions from meandering to braided sand bed and gravel bed rivers with flow depths and channe

worldwide initiation of holocene marine deltas by deceleration of sea level rise radiocarbon dated deltaic sequences of holocene age from different parts of the world began to accumulate within a restricted time range from about 8500 to 6500 years ago evaluation of major delta processes indicates that deceleration in sea level rise was the key factor in holocene delta formation within many deltas there is as much as a 2000 year age range between basal deposits in seaward and landward cores this age difference records the progressive landward migration of near mean sea level depositional environments during the lower to mid holocene establishment of a chronostratigraphic framework for holocene delta development provides a fundamental global baseline for distinguishing sea level change from vertical land motion by tectonism and isostasy and for evaluating rates of future marine incursion into low lying deltas

effect of grade control structures at various stages of their destruction on bed sediments and local channel parameters abstract grade control structures gcss represent the typical management of torrential streams preventing massive bed erosion and bedload transport the original and present geometric and sedimentary parameters of 18 gcss at various stages of their destruction since the 1970s were evaluated to determine the relationship between the former and present day components of the managed mohelnice river the western carpathians czech republic the latest changes in the gcs geometry related scour holes and bed surface grain size of sedimentary wedges were caused by the 2010 flood event of 20 50 r i discharge no relationship exists between the bed surface grain sizes and the present water drop or the present equilibrium channel slope of the sedimentary wedge a significant downstream coarsening of the largest grain size percentile represented by d 95 is detected through the sequence of gcss also statistically insignificant trends in downstream coarsening were observed for d 16 d 50 and d 84 grain sizes however the investigated sequence is still passable for grain diameters up to 200 mm during high magnitude floods similar to the 2010 event as documented by the development of a confluent gravel bar downstream of the sequence bedload transport simulations provide the highest bedload transport rates for the initial stage of the uppermost studied channel reach without the presence of gcss 30 000 kg min 1 for q 50 grade control structures reconstruction in the 1970s significantly decreased transport rates 2000 kg min 1 for q 50 owing to the erosion of gcs crests and an increase in related equilibrium channel slope damage on gcss can lead to an increase in bedload transport intensity 13 000 kg min 1 for q 50 significant linear relationships exist among the present parameters of the scour holes length of scour hole maximum scour depth and horizontal distance between the point of maximum depth and the gcs crest a statistical significant power relationship exists between the parameters of maximum scour hole depth and the present drop height showing adjustments of maximum scours to the present stage of gcss and the last flood event

flow characteristics of large eruption triggered debris flows at snow clad volcanoes constraints for debris flow models abstract theoretical modelling is not yet adequate to predict the behavior of debris flows which can be an extremely hazardous hydrologic process commonly associated with volcanic eruptions particularly at snow clad stratovolcanoes to provide a realistic basis for modelling the behavior of large 1000 m3 s debris flows this paper summarizes kinematic volumetric and hydraulic characteristics of ten large historic volcanic debris flows from four different volcanoes although debris flows larger than these are known to have occurred in the past the ten summarized here define a practical upper range in magnitude of more typical flows to be considered for future hazard prediction peak flow velocities of the ten debris flows studied were indirectly measured to be between about 5 and 20 m s on gradients of 0 005 to 0 25 m m but locally they were as great as 40 m s hydraulic average depths were as great as 25 m but were more commonly between 5 and 15 m in channels up to 400 m wide computed peak discharges volumetric flow rates were as high as 105 m3 s and total volumes were as much as 108 m3 total flow volumes increased by as much as four times in relatively steep channels as eroded sediment was incorporated into the debris flows flows generally achieved supercritical flow and deposited minimal volumes of sediment on gradients steeper than 0 02 m m subcritical flow and active deposition predominated on gradients less than 0 01 m m although flows travelled tens of kilometers on such low gradients while laying down deposits total distances travelled as debris flows were as far as 120 km

local scouring at bed sills in a mountain river plima river italian alps the main characteristics of local scouring below 26 bed sills constituting a sequence of grade control structures in a mountain river plima river italian alps have been surveyed bed sills were built with concrete strengthened boulders and other loose boulders were placed in the river bed to enhance habitat diversity for fish the most likely formative water discharge is used to evaluate specific flow energy at each bed sill measured maximum scour depths are well predicted by an empirical equation developed through laboratory results showing an average relative error of 0 15

reply to comment by jianguo liu wen yan zhong chen han chen jun lu on holocene evolution in weathering and erosion patterns in the pearl river delta

effects of check dams on bed load transport and steep slope stream morphodynamics abstract check dams are transversal structures built across morphologically active streams in mountainous regions these structures have been used widely in torrent hazard mitigation for over 150 years thousands of them are regularly maintained by stream managers and torrent control services the stabilization role of these structures is well known i e they durably constrain the stream bed through the creation of vertical and planar fixed points what is not yet clear is to what extent check dams influence bed load transport how do peak solid discharge or flood transported volume change when check dams are added to a reach to address these questions long lasting small scale experiments were conducted in a 4 8 m long flume with either one three or no structures the results show that the addition of structures creates independent compartments in the bed level which have a strong influence on bed surface armouring and stream morphodynamics the consequence is that instantaneous transport intensities are unchanged but peak solid discharge occur more often and for shorter duration this results in the same total transported volume over the long term but reduced volume for a single transport event it reaffirms the observation of pioneering authors of the mid 19th and early 20th century who conceptualized the possible sediment transport regulation function of check dams in addition to stabilizing the stream bed check dams influence bed load transport through a buffering effect releasing frequently and in small doses what in their absence would be transported abruptly en masse during rare extreme events

effect of sill spacing and sediment size grading on scouring at grade control structures sequences of arti cial steps are sometimes used to reproduce the natural step pool morphology of high gradient streams the depth length and shape of the scour holes in gravel bed rivers can be predicted reasonably using recently developed formulae however the properties of the scour holes can sometimes be affected by the distance between structures this effect is called geometrical interference and leads to a reduction of the scour hole compared to its potential size geometrical interference may occur in sequences of arti cial steps in high gradient torrents where structures are sometimes built at distances of a few tens of metres apart but may also apply to natural step pool systems in this paper a series of tests have been conducted to determine the effect of bed sill spacing and sediment grading on the potential erosion by jets forming over the sills a new formula is derived applicable to high gradient streams slope 0 04 which can be applied to the special case of scour holes developed by interfering sills sediment size gradation not accounted for in previous formulae is found to have a signi cant effect on the scour dimensions and is included in the new predictive formula copyright 2004 john wiley sons ltd

offshore quaternary sediments and their engineering significance in hong kong yim w w s 1994 offshore quaternary sediments and their engineering significance in hong kong in e f j de mulder editor engineering geology of quaternary deposits eng geol 37 31 50 investigation works undertaken for coastal engineering projects in hong kong has provided abundant information on the quaternary sedimentary sequence beneath the sea floor although the significance of such information may not have been realized at the time of these projects valuable lessons have often been learnt afterwards some examples of the important engineering applications concerning offshore quaternary sediments include 1 the provision of information on water movement sediment transport and sedimentation rates during the holocene period 2 the identification of exploitable offshore sand and gravel resources 3 the interpretation of marine geophysical data through the availability of reliable borehole descriptions 4 the enhancement of engineering soil testing results and their interpretation 5 the prediction of rates of long term ground settlement in coastal land reclaimations 6 the selection of offshore sites for waste disposal 7 the reduction in cost of coastal engineering projects through choosing the most cost effective site 8 the provision of baseline data to assist environmental impact assessment a new geological model is proposed for the offshore quaternary sedimentary sequence of hong kong the engineering properties of the sediments are found to be closely related to the palaco environmental changes

evolution of the lian river coastal basin in response to quaternary marine transgressions in southeast china abstract the coastal basin deposit in the lian river plain is among the thickest quaternary sequences along the southeastern coast of china the clastic sediment accumulated in a variety of environmental settings including fluvial channel estuary coastal and marine conditions detailed investigation of lithofacies grain size distributions magnetic susceptibility microfossils and chronology of marine core cn01 compared with regional cores and combined with offshore seismic reflection profiles has allowed us to correlate the spatial stratigraphy in the inner and outer plain and the seismic units grain size distribution analysis of core cn 01 through compositional data analysis and multivariate statistics were applied to clastic sedimentary facies and sedimentary cycles results show that these methods are able to derive a robust proxy information for the depositional environment of the lian river plain we have also been able to reconstruct deltaic evolution in response to marine transgressions on the basis of dating results and chronostratigraphy the estimated age of the onset of deposition in the lian river coastal plain was more than 260 kyr bp three transgressive sedimentary cycles revealed in many regional cores support this age model detailed lithological and microfossil studies confirm that three marine m3 m2 and m1 and three terrestrial t3 t2 and t1 units can be distinguished spatial correlation between the inner plain outer plain typical cores characterized by marine transgression cycles and offshore seismic reflectors reveals coherent sedimentary sequences two major boundaries unconformity and erosion surfaces can be recognized in the seismic profiles and these correspond to weathered reddish and or variegated clay in the study core suggesting that quaternary sediment changes on the lian river plain were largely controlled by sea level variations and coastline shift during glacial interglacial cycles

improved estimates of glacier change rates at nevado coropuna ice cap peru accurate quantification of rates of glacier mass loss is critical for managing water resources and for assessing hazards at ice clad volcanoes especially in arid regions like southern peru in these regions glacier and snow melt are crucial dry season water resources in order to verify previously reported rates of ice area decline at nevado coropuna in peru which are anomalously rapid for tropical glaciers we measured changes in ice cap area using 259 landsat images acquired from 1980 to 2014 we find that coropuna ice cap is presently the most extensive ice mass in the tropics with an area of 44 1 km 2 and has been shrinking at an average area loss rate of 0 409 km 2 a 1 0 71 a 1 since 1980 our estimated rate of change is considerably lower than previous studies 1 4 km 2 a 1 or 2 43 a 1 but is consistent with other tropical regions such as the cordillera blanca located 850 km to the nw 0 68 a 1 thus if glacier recession continues at its present rate our results suggest that coropuna ice cap will likely continue to contribute to water supply for agricultural and domestic uses until 2120 which is nearly 100 years longer than previously predicted

scour downstream of grade control structures a theoretical investigation of local scour downstream of gradecontrol structures based on twodimensional jet diffusion and particle stability is experimentally verified turbulent jet diffusion red

sediment supply and local scouring at bed sills in high gradient streams 1 this paper presents the results of an experimental study about the pattern of local scouring generated at the toe of bed sills which are commonly built in steep gravel bed mountain streams the aim of this study is to evaluate the effect of upstream sediment supply on the scour depth and shape the experiments simulated conditions of a steady upstream sediment supply which had the same grain size composition as the sediment deposit placed on the bed of the flume the geometric characteristics of three scour holes developed under conditions of steady flow discharge and steady upstream sediment supply were measured during 48 different tests this provided a data set containing measurements of 144 scour holes three different sediment feed rates were used and tests were also performed with clear water conditions geometric interference between sills was not observed a natural river gravel with a limited grain size was used the collected data were analyzed using nondimensional groups developed in previous clear water studies it is shown that the imposed sediment transport does not require the introduction of new dimensionless parameters into existing scour depth and length prediction formula the effects of sediment feed are shown to be incorporated in the existing dimensionless parameters the new data set was used to recalibrate existing scour depth formula the influence of jet erosion on scour geometry is also discussed inspection of the data indicates a possible two stage behavior with the threshold between behaviors related to the ratio of the value of the morphological jump created at a scour hole and the flow specific energy at the bed sill

stratigraphy and paleoenvironmental changes in the yangtze delta during the late quaternary the yangtze delta area may be subdivided into paleo valley and paleointerfluves of the last glaciation the postglacial transgressive sedimentary cycle ptsc on the front zones of the paleointerfluves is composed of marsh nearshore and barrier lagoon shallow marine and nearshore tidal flat units with a basement in stiff clay the ptsc in back zones of the paleointerfluves consists of lacustrine marsh deposits the ptsc in the incised valley contains river channel floodplain estuary estuarine shallow marine and deltaic units with an erosional surface at its bottom the stiff clay and the erosional surface constitute the ptsc lower boundary the stiff clay consisting of a paleosol experienced deposition alternating with pedogenesis during the falling of sea level during 18o stage 3 ongoing pedogenesis in the sea level lowstand of 18o stage 2 and early diagenesis after paleointerfluve inundation by the sea level rise of 18o stage 1 the climate during the paleosol formation was temperate with more than 500 mm a 1 rainfall and frequently fluctuating groundwater the yangtze river incised its course during falling sea level of stage 3 and a huge incised valley was formed during the sea level lowstand stage 2 the filling of the incised valley took place during the postglacial sea level rise and delta formation occurred at a late stage of ptsc development

reasons for the low sedimentation and slow progradation in the pearl river delta southern china during the middle holocene abstract holocene sea level rise monsoonal discharge and human activity have been the main drivers for the evolutionary history of asian deltas in theory when sea level ceased to rise in around 7000 cal a bp deltas should have started to prograde seawards however previous studies revealed that the progradation of modern deltas was initially very slow and more importantly sediment accumulation within central deltaic basins was exceptionally low between 7000 and 4000 cal a bp in order to investigate the main reasons for such slow progradation and low sedimentation during the middle holocene this study reconstructed the sedimentary history of the head area of the pearl river delta the results show marine transgression from 9500 to 7500 cal a bp followed by marine regression starting from 7500 to 4000 cal a bp in response to sea level change during the latter period sedimentation was concentrated in the head area the amount of sediment entering the central basin was significantly reduced this limited amount of sediment was spread thinly across the wide deltaic basin a portion of it could have been transported out into the south china sea by the strong tidal currents resulting in an exceptionally low sedimentation in the central basin however in locations adjacent to former present islands locally supplied sediment helped sedimentation to continue from 7500 to 4000 cal a bp by about 4000 cal a bp the deltaic shoreline advanced into the central basin this period saw an increase of human activity that caused soil erosion and sediment supply leading to a marked increase in sedimentation rate active land reclamations also helped the acceleration of shoreline advance this sedimentary evolution model in the pearl river delta mirrors those of other deltas in the monsoonal asia

the role of sea level rise monsoonal discharge and the palaeo landscape in the early holocene evolution of the pearl river delta southern china abstract the early holocene history of the pearl river delta is reconstructed based on a series of sediment cores obtained from one of the main palaeo valleys in the basin sedimentary and microfossil diatom analyses combined with radiocarbon dating provide new evidence for the interactions between sea level rise antecedent topography and sedimentary discharge changes within the deltaic basin since the last glacial these new records show that river channels of last glacial age incised down to c 40 m into an older possibly mis5 age marine sequence which forms the floor of the deltaic basin and exists primarily at c 10 m 15 m below present mean sea level rapid postglacial sea level rise flooded the incised valleys by the beginning of the holocene and prior to c 9000 cal years bp marine inundation was largely confined within these incised valleys the confined available accommodation space of the incised valleys combined with strong monsoon driven freshwater high sediment discharge and a period of rapid rising sea level meant that sedimentation rates were exceptionally high towards c 8000 cal years bp as sea level rose to about 5 m marine inundation spilled out of the incised valleys and the sea flooded the whole deltaic basin as a result the mouth of the pearl river was forced to retreat to the apex of the deltaic basin water salinity within the basin increased markedly as the previously confined system dispersed across the basin and the sedimentation changed from fluvial dominated to tidal dominated sea level continued to rise albeit at a much reduced rate between 8000 and 7000 cal years bp and deltaic sedimentation was concentrated around the apex area of the basin during the last 7000 cal years bp the delta shoreline moved seawards and the sedimentary processes changed gradually from tidal dominated to fluvial dominated

hydrochemical reactions and origin of offshore relatively fresh pore water from core samples in hong kong summary the existence of relatively fresh pore water offshore has been well recognised over the globe but studies on the chemistry of the pore water from offshore geological formations are extremely limited this study aims to characterize the hydrochemistry of the submarine groundwater body in hong kong it looks into the major ion concentrations and the stable isotopic compositions of pore water extracted from core samples from an offshore 42 30 m vibrocore in the southwestern hong kong waters a minimum cl level of about one third of that in typical seawater was noted in the terrestrial sediments suggesting the presence of offshore relatively fresh water unexpectedly high nh 4 levels are attributed to organic matter decomposition in the terrestrial sediments the leaching of shells due to exposure of marine sediments at sea level low stands raises the mg 2 and ca 2 concentrations base exchange indices show weak cation exchange reactions in which na and k are released while mg 2 and ca 2 are adsorbed isotopic compositions of pore water reveal that the low salinity water is probably the relic water sequestered in fluvial systems during relative sea level low stands cores properly stored in a freezer for a long time has been used to study the pore water chemistry for the first time this study introduces an approach to correct the measured data by considering the possible evaporation effect during the transportation and storage of the samples corrections for evaporation were applied to the major ion concentrations and the stable isotopic compositions of pore water measured it is found that the corrections determined by the cl mass balance approach are more reliable the corrected measurements give more reasonable observations and hence allow sensible conclusions on the hydrochemical reactions and the origin of pore water

holocene sea level history of the northern coast of south china sea abstract this study has collected and analyzed seven sediment cores from the pearl river delta from which 16 new and high quality sea level index points are generated using a new approach this study has also re checked and re calibrated the previously published sea level data from china s southeast coast with corrections made for tectonic subsidence and sediment compaction factors these sea level data indicate a rise of relative sea level from 49 3 0 8 m to the present height between 10 500 and 7000 cal a bp this sea level history is similar to those recorded from other far field locations and ice volume equivalent sea level models the early to early middle holocene sea level history in the study area shows a phase of accelerated rise at a rate increasing rapidly from 16 4 6 1 mm a at 10 500 cal a bp to 33 0 7 1 mm a at 9500 cal a bp this phase was followed by a period of rapid decrease in the rate of sea level rise to 8 8 1 9 mm a at 8500 cal a bp and 1 7 1 3 mm a at 7500 cal a bp during the past 7000 years the relative sea level in the study area changed very little this new and complete history of holocene sea level change supports the following findings 1 no obvious higher than present sea level highstand in the holocene is found from the northern south china sea 2 certain proportion of the effects of the predicted glacial isostatic adjustment were cancelled out by the effects of the weak upper mantle viscosity in the study area 3 meltwater pulse 1b likely exists spanning into the early holocene 4 there are significant misfit between sea level data and glacial isostatic adjustment models and a revision to the existing ice melting history for the early holocene is possibly needed

holocene delta evolution and sediment flux of the pearl river southern china delta progradation and sediment flux of the pearl river delta prd southern china during the holocene are presented based on analyses of borehole data on the delta plain results indicate that the delta prograded into the drowned valley because of early holocene inundation from 9 to 6 cal ka bp as sea level rise decelerated the sea level reached its present level at about 6 cal ka bp and as a consequence a large portion of the drowned valley was covered by the estuary with more than 160 rock islands and platforms the scattered landmasses promoted active deposition and acted as deposition nuclei during deltaic evolution consequently apart from exhibiting a general tendency towards progression prd development occurred less regularly over time and space because of deposition around island boundaries during the last 2 ka mainly because of significantly increased human activities which have trapped sediments in the encircled tidal flats along the front of delta plains the shoreline has advanced rapidly estimated sediment fluxes for the three periods 9 6 6 2 and 2 0 cal ka bp based on the sediment volume analysis were 17 25 22 30 and 44 58 million t a 1 respectively copyright c 2016 john wiley sons ltd

stratigraphic sequence and episodes of the ancient huanghe delta along the southwestern bohai bay since the lgm abstract the sedimentary evolution of the ancient huanghe yellow river delta in china is not well documented due to frequent river avulsions and limited deep cores in this paper 22 cores with lengths of 20 m at the coastal plain along the southwestern bohai bay were used the sedimentary facies were determined by grain size and microfossil analysis and carbon 14 dating the strata in the study area since the last glacial maximum lgm are divided into lowstand system tract lst transgressive system tract tst highstand system tract hst and retrograding system tract rst the lst which formed during the lgm to 10 8 ka bp consists of hard mud layer and overlying interfluvial lowland and flood plain deposits the tst that formed during 10 8 8 5 ka bp mainly include coastal marsh onshore sand bars and filled incised valleys the hst that formed during 8 5 2 6 ka bp mainly includes flood plain river channel delta front mouth bar and prodelta the rst that formed after 2 6 ka bp mainly includes crevasse splay interfluvial lowlands and distributary channel about eight episodes of the ancient huanghe delta are observed during the holocene and the names of the deltas are given by corresponding location names of cheniers 1 during 10 8 8 5 ka bp around ys3 and np1 cores without formation of cheniers during the transgression 2 during 8 5 7 4 ka bp around ys1 ys4 and np3 cores the dongsun shuiyicheng delta 3 during 7 4 6 1 ka bp around ck1 core the mashanzi delta 4 during 6 9 5 7 ka bp around gz3 core the miaozhuang zhaizhuang delta 5 during 4 6 3 5 ka bp around ys4 core the wuditai delta 6 during 3 0 2 6 ka bp around hh4 and hh1 cores the qikou delta 7 during 2 6 1 9 ka bp around ys7 and np1 cores the nanpaihe delta and 8 during 1034 bc 1099 bc around wangzidao and dakouhe the wangzidao delta

long term morphodynamic evolution of the pearl river delta from the perspective of energy flux and dissipation changes abstract the pearl river delta prd is an extremely complex large scale estuary system in china in this study a long term process based morphodynamic model was developed to investigate the characteristics of variations in energy flux and dissipation and their evolution alongside the hydrodynamic and topographic evolution of the prd since the holocene transgression maximum the results show that the evolution of the dynamics and topography of the prd are largely influenced by the geological and geomorphological structures of the region energy flux and dissipation in the inner estuary exhibited a patchy distribution with areas of high energy flux appearing in deep troughs near headlands and in gorges containing bedrock islands and areas of relatively small energy flux appearing in the flow shadow zones of the islands tidal fluctuation confluence area and shoals corresponding to the energy flux distribution sediment accumulation also exhibited a high degree of spatial and temporal variability the evolution of the coastline of the prd is not driven from north to south or from the river outlet to the downstream area rather multiple deposition bodies simultaneously developed in the north and south without overlapping with the deposition of sediment in the estuary the isoamplitude lines of tidal waves were gradually extrapolated and the spatial distribution gradually shifted from the northwest to the southwest this indicates the mutual transformation between the estuarine river and tidal power and also reflects the development characteristics of the river system

a new regional mid holocene palaeoprecipitation signal of the asian summer monsoon the dongge cave speleothem 18o record which lies in the pearl river basin china has been interpreted as recording a regional decline in asian summer monsoon precipitation over the last 6 5 ka the same overall trend is seen in the bulk sedimentary organic 13corg record from a core in the pearl river estuary however the two records differ in detail and the regional nature of the dongge palaeoprecipitation signal has therefore been questioned our study re evaluates both records by constructing for the same estuarine core biomarker and compound specific 13c records which have better constrained terrestrial and marine end members than 13corg providing additional insights into the evolution of the asian summer monsoon the branched isoprenoidal tetraether bit index reflects the ratio of soil versus marine organic matter the bit record from the estuarine core co varies with the dongge cave 18o record suggesting the two share a common control which is likely to be driven by regional climate by contrast the sterols n alcohols and n fatty acid ratios show the same overall trend as dongge but parallel the 13corg record s variability between 6 5 and 2 ka indicating a partial decoupling between soil and land plant organic matter fluxes in the pearl river basin there is clear divergence between the biomarker and 13corg records from 2 ka to present analysis of the leaf wax 13c suggests that this results from an abrupt change in vegetation probably resulting from local anthropogenic cultivation two thousand years ago the basin scale of these estuarine records equates to up to 15 grid cells in typical earth system models used for simulating global climate this permits comparison of palaeoclimate model intercomparison project simulations of the mid holocene with spatially equivalent data relating to the summer asian monsoon for the first time

critical flow constrains flow hydraulics in mobile bed streams a new hypothesis a new hypothesis predicts that in mobile bed river channels interactions between the channel hydraulics and bed configuration prevent the froude number fr from exceeding 1 for more than short distances or periods of time flow conditions in many steep competent streams appear to be close to critical froude numbers of steep slope 0 01 sand bed streams with considerable freedom to adjust boundaries oscillate between 0 7 and 1 3 over 20 to 30 s cycles with an average of 1 0 at the channel thalweg criticalflow in these streams is maintained by the interaction between the mobile bed and free water surface at highfr which results in a cyclical pattern of creation and destruction of bed forms field observations support that a similar mechanism offlow bed form interaction constrains fr 1 in active bed braided gravel rivers step pool streams laboratory rills lahar runout channels and even some bedrock channels empirical and analytical results show that as slope increases competentflows tend to asymptotically approach criticalflow an assumption of criticalflow would dramatically simplify paleohydraulicflow reconstructions and modeling offlow hydraulics in high gradient streams

the development of late holocene coastal cooling in the northern south china sea abstract paired high resolution sea surface temperature sst records based on the long chain alkenone unsaturation index u 37 k were reconstructed to decipher the sst evolution over the past 8000 years and its possible driving mechanisms at the hong kong coastal region the two sst records derived from a sediment core in the pearl river estuary and an offshore core in the northern south china sea scs show different patterns of sst changes the coastal record shows relatively stable warm temperatures during the mid holocene 7 4 2 6 ka and substantial cooling 2 c thereafter the cooling was most pronounced in the past 0 6 ka likely associated with the little ice age lia the offshore record generally reveals a warming trend from 8 ka to 3 5 ka and relatively warm temperatures since then as a result the sst difference sst between the two sites increased over time suggesting that the sst gradient gradually developed in the northern scs the declining coastal sst with the increasing sst likely indicates and results from the intensified east asian winter monsoon since 7 ka especially during the late holocene consistent with previous terrestrial records revealing winter monsoon variability and modern observations sst between coastal and offshore sites could thus be used as an indicator of winter monsoon variability

causes of 20th century channel narrowing in mountain and piedmont rivers of southeastern france extensive channel narrowing in southeastern france provides an illustration of geomorphic response to land use changes the study region comprises a range of environments from large piedmont and intramountain gravel bed rivers to small mountain streams field measurements and analysis of historical data demonstrate two distinct periods of channel change from 1850 to 1950 channel narrowing is interpreted to be the result of a recovery process in response to widespread channel destabilization induced by major floods during the second half of the 19th century at the time the largely deforested basins were highly responsive to flooding whereas the recovery process was accelerated by floodplain and basin scale land use changes afforestation and torrential control works which in turn reduced sediment delivery and enabled vegetation development in channels from 1950 to 1970 channel narrowing accelerated in most of the studied rivers this recent phenomenon is considered as a human induced fluvial adjustment directly related to forest development on river margins and human abandonment of intensive floodplain land uses at the same time long profile degradation occurred as a result of long term bedload supply decrease in small mountain streams channel narrowing is mainly explained by channel incision which seems to progress from upstream where sediment sources are progressively stabilized by afforestation copyright 2002 john wiley sons ltd

sedimentary facies and holocene progradation rates of the changjiang yangtze delta china abstract the changjiang yangtze river one of the largest rivers in the world has formed a broad tide dominated delta at its mouth during the holocene sea level highstand three boreholes cm97 js98 and hq98 were obtained from the changjiang delta plain in 1997 1998 to clarify the characteristics of tide dominated delta sediments and architecture based on sediment composition and texture and faunal content core sediments were divided into six depositional units in ascending order they were interpreted as tidal sand ridge prodelta delta front subtidal to lower intertidal flat upper intertidal flat and surface soil deposits the deltaic sequence from the prodelta deposits to the delta front deposits showed an upward coarsening succession overlain by an upward fining succession from the uppermost part of the delta front deposits to the surface soil thinly interlaminated to thinly interbedded sand and mud sand mud couplets and bidirectional cross laminations in these deposits show that tide is the key factor affecting the formation of changjiang deltaic facies sediment facies and their succession combined with ams 14c dating revealed that isochron lines cross unit boundaries clearly and delta progradation has occurred since about 6000 to 7000 years bp when the rising sea level neared or reached its present position the average progradation rate of the delta front was approximately 50 km kyear over the last 5000 years the progradation rate however increased abruptly ca 2000 years bp going from 38 to 80 km kyear the possible causes for this active progradation could have been an increase in sediment production in the drainage basin due to widespread human interference and or decrease in deposition in the middle reaches related to the channel stability caused by human activity and climatic cooling after the mid holocene

early holocene initiation of the mekong river delta vietnam and the response to holocene sea level changes detected from dt1 core analyses abstract the early holocene initiation of the mekong river delta vietnam was investigated based on sedimentary facies microfossil analyses and radiocarbon dating of dt1 core taken from the upper delta plain the dt1 core 105 38 51 e 10 17 02 n elevation 2 m is 51 5 m long and located in fill of a buried incised valley this incised valley of the paleo mekong river formed during the last glacial maximum which is 20 30 km wide has been traced spatially from the cambodian border to the south china sea coast by compilation of existing core data the dt1 core records the history of the estuarine channel and delta systems of the mekong river during the early to middle holocene the sedimentary facies determined particularly from sedimentary structures diatom and foraminifera assemblages grain size variation and the accumulation rate clearly show an upward deepening succession in the lower part of the core from marsh or intertidal flat to subtidal inner bay facies and an overlying upward shallowing succession from prodelta to intertidal flat floodplain the boundary between the two successions indicating the maximum flooding surface occurred at approximately 8 0 ka at the time that the mekong river delta was initiated the delta initiation and sediment facies succession are closely linked to holocene sea level changes particularly a standstill from 8 0 to 7 5 ka after a rapid rise of sea level from 8 8 to 8 2 ka during the further sea level rise from 7 5 to 7 0 ka sediments aggraded forming topset sedimentary deposits

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

mid holocene sea level highstand along the southeast coast of china various sea level curves have been proposed for the coast of china in the past two decades these sea level curves indicate a complex history of holocene sea level and so the debate on whether or not a higher mid holocene sea level highstand exists in the coast of china has continued this paper aims to re examine the holocene sea level history for the low latitude part of the china coast between 18 n and 32 n by re assessing all the sea level data available from the east to south coasts and separating them according to geological settings in order to examine the influences of global and local factors the reconstructed sea level histories from different coastal sectors of the china coast reveal a certain degree of variability in the timing and height of mid holocene sea level highstand within large river deltas the mid holocene sea level highstand occurred earlier by almost 1000 years than that from other coastal sites the highstand from large river deltas appears also lower in altitude a few metres below the present day sea level due probably to the local factors of subsidence and sediment consolidation in geologically stable coastal sites the highstand is recorded at the same altitude as the present day sea level a 1 2 m higher highstand is found from sites where tectonic uplift is observed

sediment feed and recirculating flumes fundamental difference two standard modes of laboratory sediment transport flume operation are sediment feed and recirculating in the case of uniform sediment the final equilibriums achieved in the two modes are equivalent and independent of initial conditions even though the specified flow and sediment constraints differ when the sediment consists of a mixture of sizes however this symmetry breaks down in a sediment feed flume both the feed rate and size distribution are specified by the user and must be identical to those of the bed load at final equilibrium the final state thus becomes independent of initial conditions in a recirculating flume however the equilibrium size distribution of neither the bed load nor the bed surface material can be specified in advance as a result the final state depends on the initial conditions and can include the possibility of partial transport the equilibriums themselves are equivalent in that they obey the same laws of flow and sediment transport their ia priori n predictability however differs due to the difference in governing constraints when fractional transport is scaled by the bulk size distribution the two flume modes may produce very different transport relations even for the same sediment a consistent approach requires that the transport be scaled by the size distribution of the bed surface

numerical studies of vertical cl δ2h and δ18o profiles in the aquifer aquitard system in the pearl river delta china sedimentation may have a significant effect on the transport of solutes and environmental isotopes in sediment the depth profiles of the cl 2h and 18o in a borehole in the aquifer aquitard system in the pearl river delta prd china were obtained by centrifuging the core sediment samples a one dimensional model based on the sedimentation and sea level changes of the prd during the holocene was built to investigate numerically the transport mechanisms of cl 2h and 18o the sedimentation process was modelled as a moving boundary problem with the moving rate equal to the sedimentation rate the model was calibrated and the parameters were obtained by comparing simulated and measured data very good agreement between all the three observed profiles and the simulated ones demonstrates the reliability of the model and the parameters simulation results show that the shapes of the curves are controlled by the combination of sedimentation and upper boundary conditions diffusion solely is adequate to reconstruct the observed profiles which indicates that diffusion is the dominant vertical transport mechanism the effective diffusion coefficients of the aquitard and the aquifer equal to 5 0 10 11 and 2 0 10 10 m2 s respectively the results of this study will help in understanding the transport mechanisms of solutes and environmental tracers in deltas with geology and hydrogeology similar to the prd copyright 2015 john wiley sons ltd

stratigraphy and holocene evolution of the mud dominated chao phraya delta thailand abstract the central plain of thailand was formed over the last 8 7 kyr mainly by the deltaic processes of two major rivers the chao phraya and the mae klong the delta plain is the third largest delta plain in southeast asia after that of the mekong and the irrawaddy on the basis of sedimentological and paleontological analyses of samples from three boreholes and an open pit survey the evolution of the delta was clarified with high resolution 14 c dating after the maximum transgression at between 8 and 7 cal kyr bp the delta system migrated southward into the paleo gulf of ayutthaya a large mud shoal the sananivate mud shoal formed near the mouth of the paleo gulf between 7 and 3 cal kyr bp and facilitated its infilling as a result the delta has prograded rapidly particularly during the last 2 kyr deltaic sediment volume for the last 7 5 0 5 kyr shows that the average rate of sedimentation was 23 1 3 6 million t yr which is nearly the same as the present total sediment discharge from both rivers the comparatively wide delta plain relative to sediment discharge resulted from the stable sea level the shallow paleo gulf acting as a receiving basin and effective sediment trapping because of the mud shoal

channel degradation and slope adjustment in steep streams controlled through bed sills general parallel and rotational degradation and the effect of bed sills are investigated with the aid of historical field data and laboratory experiments the case under consideration is a system of two tributaries and a main river in northeast spain characterized by its short length steepness and ephemeral nature the comparison of bed profiles since 1962 revealed an incision greater than 5 5 m the main causes of degradation are thought to be channelization width reduction and urban growth the equilibrium slopes with and without sills were obtained in 111 live bed flume tests it is demonstrated that the bed slope is milder with sills than without sills under the same flow and sediment rates the equations for the calculation of equilibrium slopes scaled to prototype are applied to the case study with good agreement copyright 2008 john wiley and sons ltd

glacial cover mapping 1987 1996 of the cordillera blanca peru using satellite imagery multitemporal glacier area mapping is a key element in accurately determining fresh water reserves as well as providing an indicator of climate change in peru the first glacier inventory was based on visual interpretation of aerial photos requiring several years of effort landsat thematic mapper satellite imagery on the other hand provides an increasingly employed alternative for the monitoring of changes in glacier area and in other glaciological parameters by means of normalized difference snow index ndsi computations on tm images an estimate of the glacierized area in cordillera blanca peru was carried out for 1987 643 63 km2 and 1996 600 61 km2 compared to an estimate of 721 km2 in 1970 it can be concluded that the glacier area has retreated in this massif by more than 15 in 25 years

pollen record in the northwestern continental shelf of the south china sea in the past 82 ka paleoenvironmental changes in the last glacial period abstract the northwestern continental shelf of the south china sea scs is in a geographic location that was sensitive to the global paleoenvironmental change during the last glacial period here we present a high resolution palynological record of core zbw 100 65 m in length from the continental shelf of the scs in the past 82 ka in contrast to results for the northern scs the core s pollen assemblage was dominated by arboreal trees between mis5a and mis1 even during the glacial period pollen provenance analyses indicated it was mainly from the drainage basin of the red river the yungui plateau and tibetan plateau between 66 and 64 ka the contribution of pinus fell while that of cyclobalanopsis and trilete spores increased indicating a drier and cooler climate conversely during mis3 the contributions of pinus and lowland trees were high indicating a warm and wet climate the sedimentary environment in core zbw alternated between coastal marine and river alluvial or shore facies a sedimentary hiatus between 42 and 13 ka coincided with a significant fall in sea levels seismic data indicate that the hainan paleo river delta hprd process occurred at the core site between 65 and 56 ka with extremely high rates of sediment deposition pollen data indicate the hprd process was coincided with a transition period from cooler and drier climate to warmer and wetter climate and lower sea levels to higher sea levels

the history and variability of the east asian paleomonsoon climate abstract changes in the east asian paleomonsoon reflect interactions between the global atmosphere ocean land and ice systems and are also an expression of their combined effect within the boundary conditions imposed by the east asian continent and solar radiation the history of the east asian monsoon is an alternation between dominance by the dry cold winter and warm humid summer monsoons high resolution eolian sequences preserved in the chinese loess plateau reveal that the east asian monsoon may have commenced at least 7 2 ma ago they also provide evidence indicating that the pulsed uplift of the tibetan plateau at about 3 4 and 7 2 ma may have played an important role in inducing climate change the palaeoclimatic records of the last glacial cycle show high frequency variability on time scales of 1000 year or even shorter and instability of the east asian paleomonsoon system the high frequency variability could be due to a non linear response to orbital forcing or a result of the coupling processes between different components of the global system cold air activity in northern high latitudes the trans equatorial air streams from the southern hemisphere and possibly enso may have played an important role in east asian monsoon variability the synchroneity of all the palaeoclimatic events along the polar equator polar pep transect is still an open question correlation of limited palaeoclimatic records for the last 30 kyr obtained from east asia and australia suggests that the trans equatorial air streams driven by the monsoon and trade winds may have had an influence on opposite hemispheres

modern fine grained sedimentation spatial variability and environmental controls on an inner pericontinental shelf hong kong abstract fine grained sediments in hong kong form part of an extensive cover that extends from nearshore locations to the mid continental shelf this featureless mud blanket is associated with sediment inputs from the pearl river and has generally been considered to be homogeneous in its characteristics however detailed sedimentological and geochemical analyses have revealed that the superficial deposits show systematic spatial variations that reflect contrasts in deposition between the pearl river estuary to the west and fully marine conditions to the east results indicate significant differences in particle size accumulation rates biogenic silica organic carbon content c n ratios and stable carbon and nitrogen isotopes that reflect location with respect to the pearl river delta calcium carbonate content varies widely tending to be higher close to land major controls over spatial variability include rainfall patterns and the supply of estuarine suspended particulate matter the effects of palaeotopography and modern water depth resuspension induced by monsoon winds and typhoons and human impacts on the sea floor

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

quaternary sea level change on the continental shelf of hong kong high resolution seismic reflection profiles and continuously sampled boreholes have been used to investigate the quaternary offshore sequence that overlies weathered bedrock in hong kong four formations have been recognized the lowermost chek lap kok formation comprises dominantly fluvial sand and mud much of which probably accumulated prior to 130 000 years bp during sea level lowstands of middle pleistocene oxygen isotope stage 6 age and earlier the upper surface of the chek lap kok formation is defined by a fluvial tidal entrenchment surface that is overlain by transgressive fine grained marine sediments of the sham wat formation these were deposited during the eemian interglacial stage 5c at a time when sea level was similar to that of today in southeastern hong kong waters a late weichselian stage 5c ravinement surface is overlain by submerged shoreface sands succeeded by a back stepping wedge of marine sediments that comprise the waglan formation fluvial tidal entrenchment of the top of this formation occurred prior to the deposition of the uppermost dominantly marine hang hau formation deposited during the late weichselian to holocene transgression the main phase of which is represented by a ravinement surface

holocene hydrological and sea surface temperature changes in the northern coast of the south china sea abstract in order to reconstruct the holocene environmental history of a coastal site in the northern south china sea this study analysed the organic carbon isotope ratios 13corg and alkenone unsaturation ratios uk 37 from a 36 5 m long sediment core drilled at seabed in the mouth region of the pearl river estuary and generated a coupled hydrological and temperature record this record reveals changes of monsoon induced sediment discharge and sea surface temperature of the holocene in four stages in stage i the site was under fluvial conditions prior to postglacial marine transgression stage ii saw an increase of sea surface temperature from c 23 0 c to 27 0 c associated with a strengthened summer monsoon from c 10 350 to 8900 cal years bp this was also a period of rapid sea level rise and marine transgression during which the sea inundated the palaeo incised channel i e the lower part of the t shape accommodation space created by the rising sea in these 1500 years fluvial discharge was strong and concentrated within the channel and the high sedimentation rate 11 8 mm year was very close to the rate of sea level rise in the subsequent 2000 years stage iii sea level continued to rise and the sea flooded the broad seabed above the palaeo incised channel resulted in fluvial discharge spreading thinly across the wide accommodation space and a much reduced sedimentation rate 1 8 mm year sea surface temperature in this stage reached 27 3 c initially but dropped sharply to 26 1 c towards c 8200 cal years bp the final stage covers the last 7000 years and the site was under a stable sea level sedimentation in this stage varied a little but averaged at 1 8 mm year whilst fluvial discharge and sea surface temperature didn t change much two short periods of hydrological and temperature change were observed which are related to the climatic cooling events of c 4200 cal years ago and the little ice age

late holocene flooding history of a tropical river in western india in response to southwest monsoon fluctuations a multi proxy study from lower narmada valley abstract a multi proxy study on the sediments from lower narmada valley western india records large flooding events and high sediment influx linked to southwest monsoon variations during late holocene on the basis of proxy data and chronology of preserved sediments three major environmental perturbations at 1809 1487 and 1187 cal bp have been identified that corroborate well with the regional fluctuations in southwest monsoon variability a phase of dominant marine influence between 2185 and 1809 cal bp is inferred based on the presence of marine palynomorphs mangrove pollen and amorphous organic matter and is coincident with the phase of weak monsoon in the region a transition from marine marsh environment to a phase of high fluvial influx occurred around 1809 cal bp the fluvial influence is inferred based on the replacement of amorphous organic matter with structured organic matter presence of fresh water algae decrease in the 13c values and dominance of kaolinite clay the fluvial regime stabilized between 1487 and 1187 cal bp as recorded in the overbank sediments palynomorphs and geochemical indices and sedimentation occurred under a highly oxidizing and high energy condition with long distance transport of sediments the later incision of the sediment sequence which post dates 1187 cal bp can be attributed to enhanced precipitation the response of the lower narmada valley to short term southwest monsoon fluctuations is manifest in the shifting deposition environments and a major role of terrestrial sediment influx variability is surmised leading to relative sea level variations in this part of the indian subcontinent a temporal and process based interplay between flooding periods and sediment discharge in river systems and tidal conditions is suggested for the tropical estuarine environments

postglacial sea level changes in the northern south china sea continental shelf evidence for a post 8200 calendar yr bp meltwater pulse abstract a postglacial sea level record reconstructed through the study of 25 cores and 10 grab samples obtained from the siliciclastic dominated northern south china sea continental shelf between hong kong and dongsha is presented the seven sedimentary facies recognized are 1 pleistocene overconsolidated mud facies affected by palaeosol development due to sub aerial exposure during the last glacial maximum lgm 2 bioclastic sandy gravel facies occurring at a present day seabed depth exceeding 120 m 3 lgm bioclastic beach dune sand facies at a present day seabed depth between 110 and 120 m 4 postglacial siliciclastic beach dune sand facies formed during at least two episodes of sea level stillstands at present day seabed depths between 80 and 90 m and 30 and 50 m respectively 5 postglacial transgressive sand facies of late pleistocene to early holocene age radiocarbon dating shows that this facies was deposited in two stages before and after the 8200 calendar yr bp cold event 6 postglacial sand and gravel dominated facies with acoustic turbidity at a present day seabed depth of about 50 m 7 postglacial mud facies based on the radiocarbon ages obtained from samples located above and below the holocene pleistocene hiatus in the two innermost shelf cores and large variations of atmospheric radiocarbon concentration found during the last glacial period in a submerged stalagmite from the bahamas beck et al 2001 science 292 2453 2458 ages exceeding 8200 calendar yr bp are likely to represent minimum values ages postdating this limit which are less affected by variations of atmospheric radiocarbon concentration indicate the presence of a post 8200 calendar yr bp cold event meltwater pulse caused by eustatic sea level rise from approximately 40 m below present to the present level by about 6000 calendar yr bp inaccuracies of the pre 8200 calendar yr bp radiocarbon ages may be attributed to large variations of atmospheric 14 c during the postglacial period with greenhouse gases released from the sub aerially exposed continental shelf probably accounting for a significant proportion

erosion and sedimentation associated with the last sea level rise offshore hong kong south china sea abstract high resolution seismic data reveals an extensive planar seaward dipping reflector offshore south of hong kong this is interpreted as a ravinement surface created during the last transgression and is associated with ca 2 5 m of shoreface sand which is overlain by a 6 15 m thick sheet of prodelta marine shelf sediments on seismic profiles the shoreface sand is characterised by a chaotic reflector pattern and the sheet by low amplitude parallel flat or low angle continuous reflectors particle size data reveal a westward coarsening and decrease in sorting which reflects increasing proximity to the pearl river foraminiferal and diatom assemblages demonstrate the same overall westward shallowing trend with increase in inner shelf foraminifera and brackish planktonic diatom species a phase of early holocene shoreface sand and intertidal silt deposition in eastern and central areas culminated in a brief period of subaerial exposure this was succeeded by an extensive period of shelf and inner shelf deposition brought about by variation in balance between the rate of sea level rise and accommodation and the discharge and sediment supply from the pearl river

river response to channel regulation case study of the raba river carpathians poland processes induced by the channelization of the raba river in the present century are examined to illustrate the response of a gravel bed stream following narrowing and straightening of its channel up to 3 m of incision has occurred the change from a slow and relatively steady degradation in the lower reaches to separate degradation events in the higher reaches is attributed to the differential rate of headcut retreat and to the control exerted by mid channel bars upon the rate of river energy dissipation progressive outwashing of finer grains from bed material has followed the diminishing sediment yield of the basin and the increase in stream power the ensuing growth in mean grain size and changes in sediment fabric have increased boundary resistance to flow and reduced particle susceptibility to entrainment downstream magnification of peak discharges has become increasingly pronounced with the advancing incision the decrease in flood plain storage and self acceleration of flows passing the relatively deep and straight channel has caused flood waves to become progressively more flashy in nature an increase in channel depth and reduction in gradient caused by downward and backward erosion as well as bed material coarsening has promoted the re establishment of an equilibrium conversely flow velocity increases due to flow concentration in the deepened channel reduction in grain mobility allows the river to attain a new equilibrium at flow velocity and stream power levels higher than before the channelization numerous disadvantages of the applied regulation scheme and its failure to reduce flood hazard raise the question of its maintenance to be successful any regulation design must take into account changes in sediment supply and flood hydrographs resulting from the simultaneous alterations in basin management

coastal gia processes revealed by the early to middle holocene sea level history of east china abstract in order to examine relative sea level responses to the postglacial ice volume change and the glacio hydro isostatic adjustments gia this study investigated the inner part of the hangzhou bay east china a tectonically relatively stable far field location and reconstructed the early to middle holocene sea level history this investigation has established the elevational relationship between modern saltmarsh mudflat and tidal levels based on diatom analysis for sea level indicative meaning estimates produced 17 high quality sea level index points and simulated gia processes for the study site these results reveal that the relative sea level rose from 38 3 1 6 m in c 10 000 cal a bp to the present height by c 7000 cal a bp and the average rate of sea level rise decreased gradually from 19 6 2 6 mm a to 2 3 1 5 mm a during the 3000 years this period of sea level history was punctuated by two episodes of accelerated rise around 8200 and 7500 cal a bp the relative sea level rose to 0 8 1 4 m above msl by c 6500 cal a bp followed by a gradual fall back to the present height at 4500 cal a bp implying a different response to the potential additional ice melting between 7000 and 4000 cal a bp a comparison of the sea level histories between the inner and outer hangzhou bay indicates the coastal levering effect due to the marine inundation of the continental shelves a further comparison between sea level data from china and malay peninsula reveals different gia effects between the cathaysia yangtze blocks and the sundaland block

sedimentary evidence of late holocene human activity in the pearl river delta china this study examines the sedimentary evidence of human activities during the last 4000 years in the pearl river deltaic area the analyses are focused on indentifying agricultural signatures present in the sedimentary record and establishing the timing of a change from a simple rice based agriculture to a more advanced diverse agriculture the examination is based on modern sediment and plant samples and a sediment core collected from the deltaic area the analyses include particle size and diatom analysis to determine the environmental conditions that were associated with the period of human activities organic carbon isotope ratios and major metal elements reveal an expansion in commercial crop production and metal smelting in the pearl river delta area about 2000 years ago the input of organic matter from introduced sugarcane a c4 plant elevates the bulk organic carbon isotope values in the estuarine sediments above that represented by other common agricultural crops in the study area including rice banana and lotus which are all c3 plants the increase in bulk organic isotopic value coincides with the rise in the concentration of copper iron and lead in the sedimentary sequence suggesting a wider use of metal tools these results indicate that advanced agriculture started about 2000 years ago as an expansion in human population took place in the area this record also provides sedimentary evidence that help ascertain the timing and type of human activities that are linked to subsequent land reclamation on the deltaic plain resulting in rapid shoreline advancement in the last 2000 years copyright 2010 john wiley sons ltd

ultimate bed slope in calabrian streams upstream of check dams field study in this paper a number of proposed criteria are analyzed that predict the ultimate equilibrium bed slope in streams upstream of a check dam the analysis is based on a comprehensive data set that includes 132 reaches in streams located in southern italy the results of this study show that the procedures suggested by ferro et al and julien and wargadalam do not lead to satisfactory results better predictions of the ultimate bed slope are achieved using the criterion suggested by gessler which is based on the stochastic analysis of incipient motion in nonuniform bed material this analysis is based on a design discharge corresponding to a return period of 1 2 years and accounts for the armoring process at the bed surface the procedure allows an estimate of the equilibrium slope of a nonhomogeneous bed material

organic matter distribution in the modern sediments of the pearl river estuary we determined biomarker concentrations and distributions for surface sediments from 54 sites in the pearl river estuary china we focus on a suite of four biomarker based indicators for relative terrestrial to marine organic matter om source the branched isoprenoid tetraether bit index the ratio of high low molecular weight n alcohols c26 34 c16 18 c26 34 an analogous ratio for n fatty acids and the c29 steroids c29 steroids brassicasterol ratio all four exhibit the same terrestrial to marine transition seen in previous bulk 13c studies but with an abrupt decrease in the relative terrestrial contribution across the delta front to pro delta transition concentrations of terrestrially derived biomarkers show no systematic decrease across the transition instead the decrease in the proportion of terrestrial om is due to a decrease in the sedimentation rate and associated terrestrial om burial across the delta toe this suggests that diagenetic controls on the fate of terrestrial om such as increased biodegradation where sedimentation rate is low are subordinate to sedimentological processes biomarker derived temperature values are cooler than expected for the lower pearl river catchment suggesting that the dominant component of the terrestrial om is derived from the cooler upland regions of the catchment the dominance of input from more distal terrain with greater topographic relief is evidence for the importance of geomorphological control on terrigenous om transport collectively the results demonstrate the importance of sedimentological processes in the supply deposition and transport of terrestrial om

disturbance caused by bed sills on the slopes of steep streams live bed tests on steep bed slopes are run in a laboratory flume to investigate the slope of equilibrium the tests simulate a general degradation until a new equilibrium is reached subsequently different bed sill settings are tested as a countermeasure against degradation evidence is presented that in some cases the bed slope with sills is milder than the one without sills under the same flow and sediment rates this fact implies that the efficiency of the bed sill system to stop degradation decreases as the sills are placed closer together tests are on the verge of sheet flow and friction factors are heavily dependent on sediment transport reaches in uniform and gradually varied flow behave very differently bed profiles are not straight and grain size is linked to this fact other detailed information on testing equipment experimental program time development and local scour in a total number of 111 tests is given

the huanghe yellow river and changjiang yangtze river deltas a review on their characteristics evolution and sediment discharge during the holocene abstract today asian rivers play an important role in delivering sediment from the land to the oceans however past sediment discharge before human activities modified the landscape is not well known and is estimated to have been roughly one third to one half of the present level chinese rivers have been strongly influenced by human activities and their sediment discharge has changed over the last 6000 years for the study of the long term human impact on rivers and catchment basins chinese rivers provide excellent examples because continuous historical records are available here the characteristics evolution and sediment discharge during the holocene of the deltas of two large chinese rivers huanghe yellow river and changjiang yangtze river are summarized the huanghe and changjiang deltas are different with respect to coastal environments water and sediment discharge the pattern of development of the delta lobe thickness of holocene sediments and basal topography of the incised valleys formed during the last glacial period the huanghe delta is characterized by a high concentration of sediment huge sediment discharge thin holocene deltaic sediments a lateral delta lobe shift and a steep longitudinal profile in its lower reaches the changjiang delta is characterized by a large water discharge a large interseasonal water level change a tide dominated coastal environment continuous seaward progradation with isolated river mouth sand bodies thick holocene sediments and a deep incised valley formed during the last glacial period based on the sediment volume of prograding deltaic sediments over the last 6000 years the sediment discharge of huanghe 1000 years ago is estimated to have been 1 10 8 tons year 1 10 of the present level an abrupt increase occurred at ca 1000 years ago as a consequence of human activities on the loess plateau especially involving cultivation and deforestation moreover the estimated sediment load of huanghe at sanmenxia station prior to 1000 years was 2 7 4 0 10 8 tons year or about 20 15 25 of the present level our recent study estimated that the sediment discharge of changjiang before 2000 years bp was ca 2 4 10 8 tons year total sediment discharge of both rivers before 2000 years bp is estimated to have been 3 4 10 8 tons year or only about 20 of the present level moreover the total sediment load to the lower reaches is estimated to have been 5 6 10 8 tons year or one fourth the present level

reconstruction of holocene monsoon history from the pearl river estuary southern china using diatoms and carbon isotope ratios this study employs a multiproxy approach in the reconstruction of holocene monsoon history from sedimentary sequences obtained from the pearl river estuary southern china a set of modern surface sediment samples were collected within and outside the estuary and a sediment core was obtained from the mouth of the estuary a range of modern environmental variables were recorded including water salinity summer winter and annual average and water depth the diatom results show a good relationship with water salinity with marine diatoms dominating the more distal samples from outside the main estuary and freshwater diatoms dominating the proximal samples influenced by higher freshwater flux this pattern is matched by the bulk organic carbon isotopes the isotope values vary between 21 1 0 3 0 for samples from the fully marine environment between 23 2 0 8 and 23 7 0 8 for samples from the mid to outer estuary brackish water environment and less than 24 7 1 3 for samples from the inner estuary close to the freshwater sources similarly the c n ratios vary from below 7 0 6 in the marine end members to over 14 8 3 0 in the freshwater end members both the diatom and carbon data from the sediment core reveal a significant increase in freshwater flux from 8500 cal yr bp resulting from the enhanced summer monsoon regime in early holocene the strength of freshwater flux reached its highest between 7500 and 6000 cal yr bp in the last 6000 years freshwater flux decreased towards present reflecting a gradual weakening of the summer monsoon

sedimentary responses to holocene sea level change in a shallow marine environment of southern china abstract this study has examined how the sedimentary processes in the prevalent non deltaic coastal marine environments along the southeast coast of china have responded to sea level change and other environmental drivers during the holocene three sediment cores collected from a shallow marine embayment of the lantau island hong kong on the northern coast of the south china sea were analyzed the results of particle size total organic carbon content organic carbon and nitrogen ratios organic carbon stable isotope ratios abundance of alkenones and radiocarbon dating of these cores have helped reconstruct the sedimentary history of this site this history shares the similarity in sedimentary processes within the deltaic environment for the early holocene because palaeo incised channels exist in both environments the first 1500 years of deposition involved rapid channel infill caused by the rapidly rising sea level and strong monsoon driven discharge this was followed by a period of decelerated sedimentation under strong marine influence as the sea flooded the wide accommodation space in the subsequent two millennia major differences between the two environmental settings occur in the past 7000 years vertical accretion was seen in the non deltaic coastal environment whilst lateral shoreline advance was the dominant process in the deltaic basin the progressively slowing down in sedimentation rate in the non deltaic site during the middle and late holocene was caused by the reduced monsoon discharge intensified disturbance from tropical cyclone activity and coastal currents

application of a diffusion erosion model to alluvial channels which degrade due to base level lowering the applicability of a diffusion erosion model that predicts transient longitudinal profiles of degrading alluvial channels has already been demonstrated in laboratory experiments and is here applied to some field examples by fitting simulated longitudinal profiles to measured ones for several streams with discharge 0 04 q5 680 m3s 1 diffusion erosion coefficients k were determined which are well correlated to discharge and drainage area headward knickpoint migration which results from base level lowering was also treated through the diffusion erosion model theoretically the distance of a knickpoint from the mouth of a tributary should be proportional to the square root of the time that elapsed since the base level was lowered field observations are in accordance with these theoretical considerations use of the model is discussed for prediction of erosion and for assessment of the age of alluvial fault scarps crossed by streams

dating of debris flow fan complexes from lantau island hong kong china the potential relationship between landslide activity and climate change five debris flow fan complexes bordering the coastal foothills of western lantau island hong kong have been the subject of a stratigraphic and dating study to explore the potential relationship between past periods of climate change and landslide activity luminescence osl ages from the fan complexes supported by a few calibrated radiocarbon 14c ages on duplicate samples suggest six main periods of accumulation 28 000 20 000 ka 14 500 10 500 ka 5800 5000 ka 4370 4230 ka 3560 3320 ka and 1350 1050 ka the younger periods 10 000 ka appear to be dominated by relatively thin 0 5 1 5 m units deposited mainly by debris flood events whereas the older periods are dominated by thicker 1 0 3 5 m units deposited by debris flow events we hypothesise that immediately prior to the last glacial maximum lgm i e 21 000 ka the climate was cool and dry upland areas were probably devoid of vegetation providing favourable conditions for sediment production in source areas these debris laden source areas are likely to have been mobilised during periodic rainstorm activity rapidly channelised over relatively short drainage courses and then deposited as thick sediment rich debris flow deposits along the coastal foothills during the early to middle holocene the climate was warmer and more humid pluvial conditions dominated forests occupied the upland source areas leading to possibly reduced sediment yields more frequent flash floods and deposition dominated by debris floods compared with recent studies on the weathering and erosion history of the pearl river delta our landslide age data are indicative of a potential link between increased landslide activity and intensification of the east asian monsoon during the early to middle holocene

comment on holocene evolution in weathering and erosion patterns in the pearl river delta by hu et al a recent paper hu et al 2013 reports holocene evolution in weathering and erosion patterns in the pearl river delta the paper concludes the modern pearl river is a poor proxy for understanding the typical erosional flux from southern china to the south china sea scs principally based on low smectite percentage in the modern river sediments but high smectite percentage in two cores through much of the holocene which may lead to misinterpretation of depositional environment in the deep sea basin from the scs in this comment we first point out that core locations determine sedimentary records in the pearl river delta second we show that high smectite percentage at both cores during the holocene was correlated with weathering of neighboring islands or even transported by coastal currents from nearby bays instead of sediment supply changes from south china via the pearl river we thus conclude that sediment flux of the pearl river remained relatively stable during the holocene and correlated parameters derived from the river sediments could be utilized to effectively trace sediment sources in deepwater environments from the northern scs

the history of water salinity in the pearl river estuary china during the late quaternary this research reconstructed the late quaternary salinity history of the pearl river estuary china from diatom records of four sedimentary cores the reconstruction was produced through the application of a diatom salinity transfer function developed based on 77 modern surface sediment samples collected across the estuary from shallow marine environment to deltaic distributaries the statistical analysis indicates that the majority of sediment samples from the cores has good modern analogues thus the reconstructions are reliable the reconstructed salinity history shows the older estuarine sequence formed during the last interglacial was deposited under similar salinity conditions to the younger estuarine sequence which was formed during the present interglacial further analysis into the younger estuarine sequence reveals the interplays between sea level monsoon driven freshwater discharge and deltaic shoreline movement key factors that have influenced water salinity in the estuary in particular a core from the delta plain shows the effects of sea level change and deltaic progradation while cores from the mouth region of the estuary reveal changes of monsoon driven freshwater discharge this study demonstrates the advantages of quantitative salinity reconstructions to improve the quality of reconstruction and allow direct comparison with other quantitative records and the instrumentally observed values of salinity copyright 2010 john wiley sons ltd

an evolutionary model for the holocene formation of the pearl river delta china this paper reconstructs the evolutionary history of the pearl river delta over the last 9000 years and investigates land sea interaction in a large deltaic complex which formed under the influence

causes of river bed degradation river bed degradation can proceed downstream as well as upstream depending upon the cause of degradation the causes of downstream progressing degradation are primarily related to changes in independent river channel variables such as increase in water discharge decrease in size of bed material and decrease in bed material discharge the causes of upstream progressing degradation are all related to an imposed increase in river slope which can occur as a result of natural river behavior or by man made changes study of various case histories indicates that river slopes are increased by lowering a base level by decreasing the length of a river or by removal of a control point case histories also show that downstream and upstream progressing degradation can act in combination along a river system downstream progressing degradation along the main stream of a river system can initiate upstream progressing degradation on a tributary

an inflection in the rate of early mid holocene eustatic sea level rise a new sea level curve from singapore this study presents a sea level curve from 9500 to 6500 cal bp for the farfield location of singapore on the sunda shelf in southeast asia the curve is based on more than 50 radiocarbon dates from elevations of 1 43 m to 15 09 m representing sea level index points in intertidal mangrove and shallow marine sediments deposited by sea level rise accompanying deglaciation the results indicate that mean sea level rose rapidly from around 17 m at 9500 cal bp to around 3 m by 8000 cal bp after this time the data suggest but do not unequivocally prove that the rate of sea rise slowed for a period of 300 500 years centred on 7700 cal bp shortly after the cessation of meltwater input to the oceans from the northern hemisphere renewed sea level rise amounting to 3 5 m began around 7400 cal bp and was complete by 7000 cal bp the existence of an inflection in the rate of sea level rise with a slow down centred on 7700 cal bp is broadly consistent with other available sea level curves over this interval and is supported by evidence of stable shorelines and delta initiation elsewhere at this time as well as evidence of comparatively rapid retreat of the west antarctic ice sheet beginning around 7500 cal bp stepped sea level rise occurring shortly after 7500 cal bp and also earlier during deglaciation may have served to focus significant post glacial episodes of human maritime coastal dispersal into comparatively narrow time intervals

late holocene depositional environments and coastal evolution of the mekong river delta southern vietnam abstract the mekong river delta in southern vietnam is a tide dominated delta and has been formed by the mekong river system the sediments are dominantly fine grained and were deposited in the receiving basin with slight inclination of pre existing deposits in the south china sea and gulf of thailand around 6000 to 5000 yr bp maximum holocene transgression occurred and seawaves surrounded uplands of the late pleistocene terrace basement rock and weathered land in the northern parts of the delta double notches were undercut by seawaves on the limestone hill in hatien at about 4 5 and 2 5 m above present sea level marine deposits prevailed throughout the delta during the highstand and regressions of relative sea level over the last 4550 yr bp delta progradation has produced a great flat plain of 62 520 km 2 this extremely fast progradation could be due to a very high sediment supply depositing in the slight inclination of the receiving basin b neotectonic movements and relative sea level changes c widespread mangrove forests playing an important role to enhance sediment accumulation former mangrove marshy deposits were significantly developed in the plain of reeds and longxuyen quadrangle mangrove marshes have also been developing well in the camau peninsula and present coastlines moreover regressions over the last 4550 yr bp have produced many distinct sets of relict beach ridges which are useful in distinguishing the former coastlines and evolutionary history of the delta

the significance of large sediment supply active tectonism and eustasy on margin sequence development late quaternary stratigraphy and evolution of the ganges brahmaputra delta abstract borehole data from the ganges brahmaputra delta system unveil an intriguing late quaternary history controlled by immense sediment discharge tectonics and eustasy sea level first intersected a major portion of the lowstand surface 10 000 11 000 cal yr bp marking the onset of sediment trapping and delta growth despite rapid sea level rise 1 cm yr sediment load was sufficient to maintain relative shoreline stability during this time by 7000 cal yr bp accommodation was quickly infilled with slowed sea level rise leading to upstream channel migration and widespread dispersal of sands this forced coastal progradation along the western delta front where the ganges was situated and much of the river s fine grained discharge bypassed the subaerial delta and formed a prograding deltaic clinoform on the shelf concurrently brahmaputra sediments were sequestered to an inland tectonic basin thus starving the adjacent shoreline and leading to transgression along the eastern delta by 5000 cal yr bp the two rivers had migrated or changed course to discharge along the eastern delta shoreline which began to prograde into what is now the modern river mouth estuary present delta configuration appears to have developed by 3000 cal yr bp evolution of the tectonically active ganges brahmaputra g b system reveals important similarities and differences with other deltas overall facies succession follows that of basic models progressing from an alluvial valley to coastal marine delta front to a prograding subaerial delta plain however the timing thickness and controls of these deposits differ immense sediment discharge from the ganges and brahmaputra rivers allowed initial delta growth 2000 3000 yr earlier than the global average despite debouching onto a canyon incised high energy margin subsequently a thick 50 m transgressive systems tract was formed during the early holocene phase of delta aggradation contrasting with extensive shoreline retreat documented along most margins highstand progradation of coastal and shelf sequences ensued by the middle holocene but subsiding inland basins also favored accumulation of a thick to 40 m highstand sequence in the lower floodplains unlike many other delta systems subsidence in the subaerial g b delta is not dominated by compaction but rather by plate driven tectonic processes that generate rates up to 4 mm year overall the huge sediment load tectonic subsidence major seismic events and a nearshore canyon system have led to widespread sediment dispersal and sequence formation across the subaerial delta shelf and deep sea bengal fan throughout the late quaternary

when and where did india and asia collide timing of the collision between india and asia is the key boundary condition in all models for the evolution of the himalaya tibetan orogenic system thus it profoundly affects the interpretation of the rates of a multitude of associated geological processes ranging from tibetan plateau uplift through continental extrusion across eastern asia as well as our understanding of global climate change during the cenozoic although an abrupt slowdown in the rate of convergence between india and asia around 55 ma is widely regarded as indicating the beginning of the collision most of the effects attributed to this major tectonic episode do not occur until more than 20 ma later refined estimates of the relative positions of india and asia indicate that they were not close enough to one another to have collided at 55 ma on the basis of new field evidence from tibet and a reassessment of published data we suggest that continent continent collision began around the eocene oligocene boundary 34 ma and propose an alternative explanation for events at 55 ma

holocene evolution in weathering and erosion patterns in the pearl river delta sediments in the pearl river delta have the potential to record the weathering response of this river basin to climate change since 9 5 ka most notably weakening of the asian monsoon since the early holocene approximate to 8 ka cores from the pearl river delta show a clear temporal evolution of weathering intensity as measured by k al k rb and clay mineralogy that shows deposition of less weathered sediment at a time of weakening monsoon rainfall in the early mid holocene 6 0 2 5 ka this may reflect an immediate response to a less humid climate or more likely reduced reworking of older deposits from river terraces as the monsoon weakened human settlement of the pearl river basin may have had a major impact on landscape and erosion as a result of the establishment of widespread agriculture after around 2 5 ka weathering intensity sharply increased despite limited change in the monsoon but at a time when anthropogenic pollutants e g cu zn and pb increased and when the flora of the basin changed sr 87 sr 86 covaries with these other proxies but is also partly influenced by the presence of carbonate the sediments in the modern pearl river are even more weathered than the youngest material from the delta cores we infer that the spread of farming into the pearl river basin around 2 7 ka was followed by a widespread reworking of old weathered soils after 2 5 ka and large scale disruption of the river system that was advanced by 2 0 ka

a preliminary study on the offshore stratigraphy in hong kong and its hydrogeological implications offshore groundwater reserves commonly sequestered in relict fluvial systems have been reported globally in hong kong submarine terrestrial sediments are the evidence of local fluvial systems during glacial periods and they probably sequester relatively fresh water this study aims to locate these sand deposits an offshore vibrocore in the southwestern waters of hong kong was analysed for its geophysical and elemental properties in order to deduce the palaeoenvironment also marine seismic profiling was adopted at two selected sites to depict the distribution of sand and gravel deposits and to estimate the average thickness of these aquifer materials a four unit sequence was noted with increasing marine influence since 8 ka bp this agrees with the hypothesis that the offshore groundwater reserves are the relics of flow systems during glacial periods the extensive sand deposits in the study areas are often shielded by sufficiently thick marine clay against vertical salinisation allowing fresh groundwater to be preserved the average thickness of these aquifer materials is about 11 m at the study sites if these sand deposits are recharged through onshore outcrops the reserves may be a sustainable water resource

holocene delta evolution and sediment discharge of the mekong river southern vietnam abstract evolutionary changes delta progradation and sediment discharge of the mekong river delta southern vietnam during the late holocene are presented based on detailed analyses of samples from six boreholes on the lower delta plain sedimentological and chronostratigraphic analyses indicate clearly that the last 3 kyr were characterized by delta progradation under increasing wave influence southeastward sediment dispersal decreasing progradation rates beach ridge formation and steepening of the face of the delta front estimated sediment discharge of the mekong river for the last 3 kyr based on sediment volume analysis was 144 36 million t yr 1 on average or almost the same as the present level the constant rate of delta front migration and stable sediment discharge during the last 3 kyr indicate that a dramatic increase in sediment discharge owing to human activities as has been suggested for the yellow river watershed did not occur although southeast asian rivers have been considered candidates for such dramatic increases in discharge during the last 2 kyr the mekong river example although it is a typical large river of this region does not support this hypothesis therefore estimates of the millennial scale global pristine sediment flux to the oceans must be revised

radiocarbon dating chronologic framework and changes in accumulation rates of holocene estuarine sediments from chesapeake bay abstract rapidly accumulating holocene sediments in estuaries commonly are difficult to sample and date in chesapeake bay we obtained sediment cores as much as 20 m in length and used numerous radiocarbon ages measured by accelerator mass spectrometry methods to provide the first detailed chronologies of holocene sediment accumulation in the bay carbon in these sediments is a complex mixture of materials from a variety of sources analyses of different components of the sediments show that total organic carbon ages are largely unreliable because much of the carbon including coal has been transported to the bay from upstream sources and is older than sediments in which it was deposited mollusk shells clams oysters and foraminifera appear to give reliable results although reworking and burrowing are potential problems analyses of museum specimens collected alive before atmospheric nuclear testing suggest that the standard reservoir correction for marine samples is appropriate for middle to lower chesapeake bay the biogenic carbonate radiocarbon ages are compatible with 210pb and 137cs data and pollen stratigraphy from the same sites post settlement changes in sediment transport and accumulation is an important environmental issue in many estuaries including the chesapeake our data show that large variations in sediment mass accumulation rates occur among sites at shallow water sites local factors seem to control changes in accumulation rates with time our two relatively deep water sites in the axial channel of the bay have different long term average accumulation rates but the history of sediment accumulation at these sites appears to reflect overall conditions in the bay mass accumulation rates at the two deep water sites rapidly increased by about fourfold coincident with widespread land clearance for agriculture in the chesapeake watershed

holocene evolution of the song hong red river delta system northern vietnam abstract the song hong red river delta located on the western coast of the gulf of bac bo tonkin in the south china sea formed as a result of the song hong sediment discharge throughout the holocene the river s sedimentary basin upstream from the delta plain is not large the delta plain comprises emerged tidal mangrove flats formed during the sea level highstand at 2 3 m 6 4 cal kyr bp and a beach ridge strandplain with straight to lobate beach ridges on the landward and seaward sides of the delta plain respectively the delta affords us the opportunity to examine river mouth morphodynamics comprehensively in relation to sediment discharge and sea level changes in this paper we describe the holocene evolution of the song hong delta system and the river mouth morphodynamics on the basis of seven sediment cores each 30 70 m long taken from the delta plain during 1999 2001 and 101 radiocarbon dates obtained from the core sediments sediments from the seven cores consisting of incised valley fills since the last glacial maximum can be divided in ascending order into fluvial sediments composed of gravelly sand and mottled clay tide influenced estuarine sediments containing shell and wood fragments and deltaic sediments composed of tide influenced sand and mud deposits in which the contents of sand and wood fragments increase upward by applying sequence stratigraphic concepts a transgressive surface can be identified at the gravelly sand mottled clay boundary and the maximum flooding surface can be identified at the estuarine deltaic sediments boundary the lowstand systems tract transgressive systems tract and highstand systems tract record 15 15 9 and 9 0 cal kyr bp respectively during the past 9 kyr the majority of the sediment discharged by the song hong accumulated in the incised valley and enhanced progradation at the river mouth the river mouth prograded from the bay head toward the gulf and its morphology changed from funnel shaped 9 6 cal kyr bp to straight 6 2 cal kyr bp and finally to lobate 2 0 cal kyr bp the morphological change from a funnel shaped to straight coast is interpreted to have been closely related to a hydrologic regime shift from a tide dominated bay head setting to a wave influenced open coast setting the cessation of the sea level rise at 6 cal kyr bp may have played only a small role in the change of river mouth morphology because the progradation rate decelerated from 22 to 4 m yr instead of accelerating at that time the river mouth morphodynamic change from straight to lobate was largely caused by an increase in the song hong sediment discharge from 17 27 9 2 cal kyr bp to 49 million t yr 2 0 cal kyr bp as a result of anthropogenic deforestation along the upper reaches of the song hong