first cycle quartz arenites in the orinoco river basin venezuela and colombia modern first cycle quartz arenites are forming in the orinoco drainage basin by at least two distinct mechanisms common to both mechanisms is an environment of intense chemical weathering and extended time over which weathering can occur in the llanos andean foreland basin extended time is provided by temporary storage of orogenically derived sediments on extensive alluvial plains in lowland portions of the guayana shield long soil mineral residence times are produced by very low erosion and transport rates resulting from low relief and tectonic quiescence both weathering intensity and the duration of weathering are important in the modification of sand composition first cycle quartz arenites are produced in diverse tectonic settings and cannot be used by themselves to infer paleotectonic settings of ancient sequences furthermore although tectonic setting is of great importance in determining sand composition modifications during transport and deposition can overprint the effects of the tecto

influence of the yangtze river and grain size on the spatial variations of heavy metals and organic carbon in the east china sea continental shelf sediments abstract bulk heavy metal fe mn zn cu pb cd al organic carbon and carbonate concentrations grain sizes and c13 of the organic carbon distributions were studied in sediments collected throughout the east china sea continental shelf and the yangtze river delta the results demonstrated that terrigenous sediments from the yangtze river is a dominating factor controlling the spatial variations of heavy metals and organic carbon concentrations on the east china sea continental shelf in addition grain size and recent anthropogenic influences are also major factors modifying the spatial and vertical variations of heavy metals large spatial variations with a band type distribution of heavy metals grain size organic carbon and carbonate were observed higher concentrations of heavy metal and light c13 of the organic carbon were found primarily in the deltaic and inner shelf sediments the band type distribution generally followed the coastline with little variations in the north south direction away from the delta and inner shelf west east direction most heavy metal concentrations decreased rapidly with the exception of cd where high concentrations of cd were also found in the carbonate rich shelf break sediments coarse grained relict sediments and biogenic carbonate are two primary diluting agents for the fine grained aluminosilicate sediments from the yangtze river with high concentrations of heavy metals unusually high concentrations of cu pb and cd showed both spatially and vertically that more pollution prevention measures are needed in the yangtze river drainage basin in order to prevent further heavy metal pollution of the east china sea inner continental shelf

erosional response of south china to arc rifting and monsoonal strengthening a record from the south china sea abstract ocean drilling program sampling of the distal passive margin of south china at sites 1147 and 1148 has yielded clay rich hemipelagic sediments dating to 32 ma oligocene just prior to the onset of seafloor spreading in the south china sea the location of the drill sites offshore the pearl river suggests that this river or its predecessor may have been the source of the sediment in the basin which accounts for only 1 8 of the total neogene sediment in the asian marginal seas a mean erosion depth of 1 km over the current pearl river drainage basin is sufficient to account for the sediment volume on the margin two dimensional backstripping of across margin seismic profiles shows that sedimentation rates peaked during the middle miocene 11 16 ma and the pleistocene since 1 8 ma nd isotopic analysis of clays yielded nd values of 7 7 to 11 0 consistent with the south china block being the major source of sediment more positive nd values during and shortly after rifting compared to later sedimentation reflect preferential erosion at that time of more juvenile continental arc rocks exposed along the margin as the drainage basin developed and erosion shifted from within the rift to the continental interior nd values became more negative a rapid change in the clay mineralogy from smectite dominated to illite dominated at 15 5 ma synchronous with middle miocene rapid sedimentation mostly reflects a change to a wetter more erosive climate evidence that the elevation of the tibetan plateau and erosion in the western himalaya both peaked close to this time supports the suggestion that the asian monsoon became much more intense at that time much earlier than the 8 5 ma age commonly accepted

distribution of rare earth elements in surface sediments of the western gulf of thailand constraints from sedimentology and mineralogy abstract to understand the modern sedimentation and land sea interaction processes in the asian margin seas we analyze rare earth element contents ree i e la ce pr nd sm eu gd tb dy ho er tm yb lu and grain sizes detrital minerals from 158 surface sediment samples collected from the western gulf of thailand got the results reveal that the ree contents ranged from 25 42 g g to 201 21 g g with an average value of 137 21 g g and that the got is characterized by higher accumulations of lree relative to hree together with negative eu anomalies based on the spatial distribution characteristics of ree contents ce and eu the western got can be classified into three geochemical provinces the province i covers the northern and northwestern coastal zones of the got including the entire upper got its coarse size fraction and distribution pattern of hornblende and quartz dominated minerals caused ree contents to be the lowest and these sediments were mainly derived from the rivers around the upper got including the chao praya river and the kea klong river the province ii is located in the central got and has the highest ree concentrations due to finer sediment composition and higher contents of zircon authigenic pyrite and biogenetic limestone the province ii has two accumulation centers around samui island and koh chang island with ree spatial distribution influenced by the seasonal setting and mixed derived from multiple provenances around the got the province is located in the lower got close to malaysia the sediment type in this region is similar to that of province i except for different detrital mineral compositions especially the presence of siderite that is responsible for higher ree contents the sediments in this region exhibits similar distribution patterns to those of terrestrial materials from the malaysian peninsula such as that from the kelantan river the transportation processes of sediments in this region are mainly controlled by the coastal current

a source to sink perspective of the waipaoa river margin abstract a fundamental goal of the earth science community is to understand how perturbations on earth s surface are preserved in the stratigraphic record recent source to sink s2s studies of the waipaoa sedimentary system wss new zealand are synthesized herein to provide a holistic perspective of the processes that generate transport and preserve sedimentary strata and organic carbon on the waipaoa margin in the late quaternary rapid uplift associated with subduction processes and weak sedimentary units have conspired to generate rapid rates of incision and erosion in the waipaoa catchment since the last glacial maximum lgm we show that although much of the sediment exported offshore during this time interval originated from valley excavation a substantial portion emanated from hillslopes mostly through deep seated landslide and earthflow processes that were vigorous during periods of rapid fluvial incision just prior to the pleistocene holocene transition lacustrine sediments deposited in naturally dammed 7 ky old lake tutira provide a record of holocene environmental controls on upper catchment sedimentation in the wss with 1400 storms identified storm frequency is modulated by the waxing and waning of atmospheric teleconnections between the tropics and antarctica furthermore clear long term changes in sediment yield are evident from the lake tutira record following human settlement as conversion to pasture is accompanied by a 3 fold increase in the long term lake sediment accumulation rate whereas there is ample evidence that waipaoa river flood deposits are routinely deposited offshore in the sheltered confines of poverty bay over the longer term waves and currents subsequently resuspend and transport these deposits both landward sandy fraction and seaward finer fraction thus the timing of sediment supply to areas of net sediment accumulation is more often driven by wave events that are not associated with river flooding therefore we conclude that asynchronicity of river sediment delivery and of wave resuspension in most instances precludes the direct preservation of flood events in the stratigraphic record of the waipaoa shelf over the longer term the sediment package preserved on the shelf and slope since the lgm can be explained in large measure by sequence stratigraphic models forced by varying sea level and ongoing tectonic deformation of the margin as sea level rose sediment supply to the slope was reduced by about a factor of 5 due to shelf trapping despite this reduction turbidites are found at similar frequency throughout the lgm present as the dominant trigger appears to be subduction earthquakes with large ones having a return interval of about 200 100 years sediment budget exercises that consider both modern river discharge versus centennial accumulation rates and post lgm terrestrial production versus offshore isopachs mass balances indicate that about half of the total sediment production from the waipaoa escapes the study area moreover a coupled sediment transport hydrodynamic model and observations of textural trends on the shelf indicate that a large fraction of the sediment is carried outside the study area along the shelf to the northeast by the river plume or by combined current wave activity therefore we conclude that the wss is an open system with sediment escape from the present day through the lgm the organic matter associated with sediment as it moves from upland source to marine sink is a product of particle history and provides a record of materials that have cycled over timescales of days to millions of years the ubiquity of fossil organic carbon oc in both the terrestrial and marine realms of the waipaoa attests both to the chronic nature of its source crumbling mudstones further destabilized by land use and its biogeochemical recalcitrance modern oc persists by virtue of its continual production along the s2s transit and is buried and preserved within the adjacent marine depocenters the waipaoa contrasts with dispersal systems on wide energetic shelves e g the amazon and fly rivers where sediment is extensively refluxed in oxygenated overlying water resulting in the biogeochemical incineration of particulate oc the waipaoa like other small mountainous rivers on active margins exhibits a high riverine oc preservation efficiency 50 in its marine depocenters because of the relatively rapid event driven accumulation of sediment

distribution of clay minerals in surface sediments of the western gulf of thailand sources and transport patterns abstract a high density sampling program during two joint china thailand scientific cruises in 2011 2012 included collection of 152 gravity box cores in the gulf of thailand got samples from the top 5 cm of each core were analyzed by x ray diffraction for clay mineral content several systemic analytical approaches were applied to examine the distribution pattern and the constraint factors of clay minerals in the surface sediments of the western got the clay minerals mainly comprise illite kaolinite chlorite and smectite having the average weight percent distributions of 50 34 14 and 2 respectively based on the spatial distribution characteristics and statistical results the study area can be classified into three provinces province i contains high concentrations of smectite and covers the northern got sediments in this province are mainly from rivers discharging into the upper got especially the chao phraya and mae klong rivers sediments in province ii are characterized by higher values of illite located in the central got where fine sediments are contributed by the mekong river and from the south china sea province in the coastal regions of southwestern got close to malaysia exhibits a clay mineral assemblage with complex distribution patterns and may contain terrestrial materials from the mae klong river as well as re suspended sediments results of integrative analysis also demonstrate that the hydrodynamic environment in the study area especially the seasonal various circumfluence and eddies play an important role in the spatial distribution and dispersal of clay fraction in sediments

rare earth element and mineralogic changes in holocene soil and stream sediment a case study in the wet mountains colorado u s a size fractions of soil and stream sediment developed on plutonic metamorphic or mixed plutonic metamorphic sources in the wet mountains colorado have been analyzed for ree rare earth elements and mineralogy the clay sized fractions 0 5 m and 0 5 2 m or 2 m have ree contents that are similar to more enriched than the source eu sm ratios that are similar to the source and la lu ratios that are higher than their corresponding source the 0 5 m fractions have lower ree contents than the corresponding 0 5 2 m fraction in every stream sediment for example unweathered san isabel batholith near the sampled stream sediment contains ree 511 712 ppm and eusmratio 0 17 0 19 and lalu cn 9 8 10 3 the corresponding 0 5 and 0 5 2 m fractions of sediment formed from san isabel batholith are enriched in the ree ree 1135 and 2225 ppm respec are slightly lower in eu sm ratios 0 16 and 0 14 respec and are higher in la lu ratios 12 2 and 16 3 respec than the unweathered rocks the silts have lree light ree contents and eu sm ratios very similar to the source due to similar mineralogy but silts have hree heavy ree contents higher than the source due to high zircon for example silt sized fractions in stream sediment draining the san isabel batholith contain ree 808 ppm eusmratio 0 18 and lalu cn 7 4 in contrast the sands contain lower ree contents similar to higher eu sm ratios and lower la lu ratios than the corresponding source due to depletion in heavy minerals concentrated in the ree and containing lower eu sm ratios relative to quartz and feldspar depleted in the ree and containing higher eu sm ratios for example the sand fraction from stream sediment from the san isabel batholith has ree 206 ppm eusmratio 0 17 and lalu cn 5 6 small variations of accessory minerals concentrated in the ree like allanite or sphene may cause drastic variation in ree content in the sand fraction clays and silts derived only from the plutonic rocks have higher ree and similar to lower eu sm ratios than corresponding fractions derived only from migmatites e g ree of silt fractions from migmatites 224 ppm and from plutons 375 808 ppm eu sm ratios from migmatites 0 17 and from plutons 0 11 0 18 the ree content and the eu sm ratio of clays and silts derived from migmatites are much more similar to the average of mcps mid continent platform sediment than corresponding fractions derived from the plutons mcps has ree 192 ppm eusm 0 19 lalu 8 0 the eusm ratio of sands derived from plutons and migmatite are lower to mostly higher than the mcps the ree content of sands from plutons are not necessarily higher than the mcps due to variation in heavy minerals like allanite or sphene concentrated in the ree sediments derived from mixed sources have ree contents in fine fractions that may not necessarily reflect the ree content of the nearest source for example 0 5 2 m and silt fractions developed on the san isabel batholith with a migmatite upstream have the high ree content of the batholith ree in 0 5 2 m fraction 1100 ppm silt 573 ppm while the corresponding 0 5 m fraction has the very low ree content of the migmatites ree 110 ppm these results suggest fine grained material near the source may sample a much larger area than coarser material near the source thus analysis of fine grained sediment associated with coarse grained material near the source may give a much different impression of the source than would determination of the source using classic petrographic examination of the sand or gravels

erosion and accretion processes in a muddy dissipative coast the chao phraya river delta thailand seasonal variation in seabed elevation in the muddy intertidal zone of the chao phraya river delta an area of serious coastal erosion for 40 years was assessed using information on waves and tides predicted by numerical simulations the study area is under the influence of the southeast asian monsoon climate and lies in the innermost part of a sheltered gulf across which a low gradient slope has developed observations aimed at evaluating the effectiveness of a prototype breakwater on mitigating coastal erosion indicated that the seasonal variation in the seabed elevation typically about 30 cm was caused primarily by seasonal changes in wave direction and height the breakwater seems to have contributed to a net rise in the seabed level at sites behind the structure seabed erosion was most apparent during the northeast monsoon when waves are weak erosion under this low wave energy state was attributed to the combined effect of wave breaking and the low tidal level a difference in the observed seabed accretion rate between the transitional intermonsoon period and the succeeding southwest monsoon period was attributed to the direction of the wave energy flux offshore sediments seem to have been supplied efficiently to the study area by waves during the transitional period another potential cause of seabed erosion and accretion during the wet southwest monsoon season was the discharge of water and sediments from local canals associated with intense tropical rainfall this discharge seems to be linked to land use in the coastal area the results of this study show the importance of monitoring across shore sediment transport for better understanding of coastal erosion processes copyright 2010 john wiley sons ltd

ree geochemistry of recent clastic sediments from the kaveri floodplains southern india implication to source area weathering and sedimentary processes abstract the kaveri river drains through archean gneissic and charnockitic terranes in south india the rare earth element ree chemistry of the floodplain sediments along with their major and trace element composition in different size fractions are discussed we observe a strong coherence between ree and tio2 contents in the sediments which is suggestive of strong control by titanite or its weathered products on the ree chemistry ree concentrations also show a general increase with decreasing size of bulk sediments different size fractions and of light and heavy mineral fractions this suggests the presence of ree in the fe oxy hydroxide surface coatings on clastic grains formed by the weathering of hornblende and titanite in the granodioritic to dioritic protoliths we also interpret the data as showing that ree patterns of clastic sediments notably eu anomaly are affected by the degree of source rock weathering as well as by the fluvial processes of sorting and mineral differentiation therefore for provenance study sediments having all granulometric grades such as the floodplain sediments are preferable because they most closely represent the source particularly when the source region suffered little chemical weathering in the present case the sediments were derived from the high standing hills of archean charnockites because of their recent uplift and physical denudation

geochemical and nd isotope composition of detrital sediments on the north margin of the south china sea provenance and tectonic implications a major re organization of regional drainages in eastern tibet and southwestern china took place in the cenozoic as deformation from the growing himalayas and tibetan plateau affected an increasingly wider area the effects of these changes on the regional sediment routing systems is not well constrained this study examines the geochemical and nd signatures of sedimentary rocks from the ying qiong and nanxiong basins on the northern margin of the south china sea to constrain and identify any significant changes in sediment source upper cretaceous to lower eocene sedimentary rocks in the nanxiong basin show higher th sc la sc th cr and th co ratios and lower eu eu ratios than paas post archaean australian shale which indicates that palaeozoic sedimentary rocks of the south china block were the main basin sediment source in contrast oligocene to pleistocene sedimentary rocks of the ying qiong basin show an abrupt change in these trace element ratios between 16ae3 and 10ae4 ma indicating a mid miocene shift in provenance end values from the ying qiong basin range 11ae 1t o 2ae1 reinforce this with pre 13ae8 ma sedimentary rocks having average end of 5ae6 range 2ae 1t o 7ae4 and post 13ae8 ma sedimentary rocks having average end of 9ae3 range 8ae 7t o 11ae1 during the oligocene the centre of rifting transferred south and basins on the north margin of the south china sea experienced rapid subsidence further uplift and erosion then exposed mesozoic and cenozoic granites that supplied large amounts of granitic detritus especially to the ying qiong basin then a change occurred at ca 13 ma resulting in less input from local sources i e the fault blocks formed by mesozoic cenozoic tectonics and magmatism to an increasing contribution of older continental material mostly from indochina to the west of the south

apparent magnetic polarity reversals due to remagnetization resulting from late diagenetic growth of greigite from siderite summary a mixed polarity zone representing alternations between remagnetized and non remagnetized strata has been documented within the lower few metres of the crp 1 core ross sea antarctica detailed rock magnetic investigation of this interval indicates that the normal polarity remagnetization is carried by magnetostatically interacting single domain particles of a ferrimagnetic iron sulphide mineral while the reversed polarity magnetization of non remagnetized strata is carried by magnetite with a broad range of grain sizes and negligible magnetostatic interactions scanning electron microscope observations of polished sections indicate that the ferrimagnetic iron sulphide mineral is greigite fe3s4 based on microtextural relationships it is not possible to determine the relative timing of formation for much of the greigite however a significant proportion of the greigite has grown on the surface of authigenic siderite feco3 grains that occur as microconcretions and as cement surrounding detrital matrix grains in such cases microtextural relationships indicate that siderite post dates early diagenetic pyrite and that greigite post dates the siderite siderite usually forms in environments with abundant dissolved iron and carbonate but without dissolved pore water h2s this set of geochemical conditions occurs in methanic settings below the sulphate reduction zone in which early diagenetic pyrite forms we interpret the observed remagnetization of the lower part of the crp 1 core as due to a late diagenetic pore water migration event where abundant iron on the surface of siderite grains reacted with fluids containing limited dissolved sulphide thereby causing precipitation of greigite the distribution of siderite and associated greigite in the lower part of the crp 1 core is patchy which accounts for the apparent alternation of polarities this study is part of a growing catalogue of remagnetizations involving greigite which suggests that occurrences of greigite should be treated with caution in palaeomagnetic and environmental magnetic studies

geochemistry of large river suspended sediments silicate weathering or recycling tracer this study focuses on the major and trace element composition of suspended sediments transported by the world s largest rivers its main purpose is to answer the following question is the degree of weathering of modern river borne particles consistent with the estimated river dissolved loads derived from silicate weathering in agreement with the well known mobility of elements during weathering of continental rocks we confirm that river sediments are systematically depleted in na k ba with respect to the upper continental crust for each of these mobile elements a systematics of weathering indexes of river borne solids is attempted a global consistency is found between all these indexes important variations in weathering intensities exist a clear dependence of weathering intensities with climate is observed for the rivers draining mostly lowlands however no global correlation exists between weathering intensities and climatic or relief parameters because the trend observed for lowlands is obscured by rivers draining orogenic zones an inverse correlation between weathering intensities and suspended sediment concentrations is observed showing that the regions having the highest rates of physical denudation produce the least weathered sediments finally chemical and physical weathering are compared through the use of a simple steady state model we show that the weathering intensities of large river suspended sediments can only be reconciled with the silicate derived dissolved load of rivers by admitting that most of the continental rocks submitted to weathering in large river basins have already suffered previous weathering cycles a simple graphical method is proposed for calculating the proportion of sedimentary recycling in large river basins finally even if orogenic zones produce weakly weathered sediments we emphasize the fact that silicate chemical weathering rates and hence co2 consumption rates by silicate weathering are greatly enhanced in mountains simply because the sediment yields in orogenic drainage basins are higher hence the parameters that control chemical weathering rates would be those that control physical denudation rates

geomorphic tectonic control of sediment discharge to the ocean the importance of small mountainous rivers analysis of data from 280 rivers discharging to the ocean indicates that sediment loads yields are a log linear function of basin area and maximum elevation of the river basin other factors controlling sediment discharge e g climate runoff appear to have secondary importance a notable exception is the influence of human activity climate and geology on the rivers draining southern asia and oceania sediment fluxes from small mountainous rivers many of which discharge directly onto active margins e g western south and north america and most high standing oceanic islands have been greatly underestimated in previous global sediment budgets perhaps by as much as a factor of three in contrast sediment fluxes to the ocean from large rivers nearly all of which discharge onto passive margins or marginal seas have been overestimated as some of the sediment load is subaerially sequestered in subsiding deltas before the proliferation of dam construction in the latter half of this century rivers

trace metal composition of and accumulation rates of sediments in the upper gulf of thailand sediment cores and grab samples were collected in the upper gulf of thailand to determine sedimentation rates and to determine if metal concentrations reflect anthropogenic inputs accumulation rates of sediments in the upper gulf measured using the 210pb method appear to vary from ca 4 to 11 mm yr 1 sediment budgets suggest that little of the sediment delivered to the upper gulf by the major rivers is ultimately transported to the lower gulf metal concentrations in upper gulf sediments appear to be dominantly controlled by natural inputs

pleistocene to holocene transition in the central basin of the gulf of thailand based on geoacoustic survey and radiocarbon ages abstract record of the last glacial maximum and postglacial sea level rise in the central gulf of thailand some 140 km offshore of the malay peninsula was studied along a nw striking section water depth 55 82 m below the present msl by means of geoacoustic surveys shallow gravity coring and radiocarbon dating the record comprises evidence of valley incision followed by estuarine to marine transgression which was interrupted by deltaic progradation the valley incision and delta formation are attributed to the kelantan river draining the malay peninsula the delta growth was halted at 10 4 cal kyr bp by transgressive ravinement followed by emplacement of a thin condensed mantle of modern marine muds such age is compatible with the fast but diachronous nature of this transgressive event that according to previous estimates began in the central sunda shelf at 11 11 5 cal kyr bp and reached the head of the thailand bay at 8 7 cal kyr bp the presence of deltaic deposits within postglacial transgressive systems tract is uncommon on extremely wide and accommodation dominated shelves such as the sunda shelf and is here interpreted to reflect a combination of decelerating sea level rise 13 10 cal kyr bp with increased precipitation and sediment yield coupled with the reactive nature of the kelantan river catchment

rare earth elements as provenance indicators in north australian estuarine and coastal marine sediments rare earth elements ree in three grain size fractions of clay dominated estuarine and coastal sediments from the north australian coastline have been investigated for use as potential provenance indicators comparisons of data based on instrumental neutron activation analysis and inductively coupled plasma mass spectrometry revealed that hf digestions of zircon bearing samples resulted in unsatisfactory recovery of ree instead a relatively simple fast and safe partial digestion using hclo4 hno3 was used to extract ree mainly from clay minerals while excluding extraction of ree from zircons a comparison with published data for primary rock units within river catchments showed that the main ree systematics has been preserved in downstream clay rich sediments analysis of variance of la gd paas la yb paas and eu eu paas ratios in five areas showed that the 63 m fraction possessed the greatest discriminating power all five areas could be distinguished from each other at highly significant levels based on one or more of these ratios

two unique weathering regimes in the changjiang and huanghe drainage basins geochemical evidence from river sediments the present research reconstructs the histories of chemical weathering in the drainage basins of the changjiang and huanghe based on the chemical compositions of the river sediments the silicate weathering of the changjiang basin is strong and naand ca silicate minerals are considerably dissolved while other silicate minerals are less attacked in comparison the huanghe basin is characterized by very weak silicate weathering and the weathering degree corresponds well with that of the loess which is the predominant source of the huanghe sediment overall the changjiang and huanghe basins constitute a consistent weathering spectrum from the early to intermediate stage the similarity of chemical compositions between upper continental crust and the huanghe sediments as well as the low degree of chemical weathering in the huanghe basin imply that the river sediments can be considered to be the representative of ucc and are suitable for studying the evolution of continental crust our observations indicate that climate is the predominant factor controlling silicate weathering in both river basins while controls by source rocks and relief are subordinate highly erosive river basins such as the huanghe produce poorly weathered materials which casts doubt on the idea that strong physical weathering naturally contributes much to chemical weathering differences in silicate weathering processes between the changjiang and huanghe basins may provide more constraints in estimating atmospheric co2 budget in china d 2003 elsevier b v all rights reserved

geochemistry of rare earth elements in the mainstream of the yangtze river china abstract water suspended matter and sediment samples were taken from 8 locations along the yangtze river in 1992 the concentration and speciation exchangeable bound to carbonates bound to fe mn oxides bound to organic matter and residual forms of rare earth elements la ce nd sm eu tb yb and lu were determined by instrumental neutron activation analysis inaa the contents of the soluble fraction of rees in the river are low and rees mainly reside in particulate form in the particles the chondrite normalized distribution patterns show significant lree enrichment and eu depletion while normalized to shales both sediments and suspended matter samples show relative lree enrichment and hree depletion rees are relatively enriched in fine grained fractions of the sediments the speciation characteristics of rees in the sediments and suspended matter are very similar the amount of the five forms follows the order residual bound to organic matter bound to fe mn oxides bound to carbonates exchangeable about 65 to 85 of rees in the particles exist in the residual form and the exchangeable form is very low high proportions of residual rees reveal that rees in sediments and suspended matter are controlled by their abundances in the earth s crust carbonate fe mn oxide and organic fractions of rees in sediments account for 2 4 6 9 5 2 11 1 and 7 3 14 0 of the total contents respectively they are similar to those in the suspended matter this shows that carbonates fe mn oxides and organic matter play important roles during the particle water interaction processes by normalization to shales the 3 forms of rees follow convex shapes according to atomic number with middle ree sm eu and tb enrichment while light ree and heavy ree are depleted

the estuarine geochemistry of rare earth elements and indium in the chao phraya river thailand abstract a new filtration method using a 0 04 m hollow fiber filter was applied to the river estuarine and coastal waters in the chao phraya estuary for geochemical investigation the filtered waters were analyzed for all the lanthanides y and in by using inductively coupled plasma mass spectrometry icpms the dissolved concentrations of rare earth elements rees are significantly lower than those reported previously for other rivers presumably because of effective removal of river colloids by the ultra filtration the variation of dissolved rees in the estuary is dependent on the season the light rees vary considerably in the low salinity s 3 show almost conservative trends being consistent with some of the previous works europium is strongly enriched in the river and estuarine waters compared to the south china sea waters thus the ree source of the chao phraya river must be fractionated and modified in entering to the south china sea dissolved in and ce in the high salinity s 20 25 zone of the estuary are lower than those of the offshore waters and therefore the dissolved flux of the chao phraya river cannot account for the higher concentrations of dissolved in and ce in the surface waters of the south china sea the negative ce anomaly is progressively developed with increasing salinity being consistent with continued oxidation of ce iii to ce iv in the estuary fractionation of the light to heavy rees seems to take place whereas the y ho fractionation is unclear in the estuarine mixing zone

rare earth elements in marine sediments and geochemical standards abstract a comparison was made of sediment dissolution methods used for analysis of rare earth elements ree and major elements fe al ti zr p dissolution by hf and lithium metaborate fusion were compared in seven geochemical standards and twenty marine sediments using hf dissolution of shelf and slope sediments this author previously observed that these marine sediments were significantly depleted in heavy ree hree relative to the crustal abundance i e shale this observation plus published ree compositions of river particles lead to the conclusion that the riverine input of particles to the oceans cannot be assumed to have the crustal abundance for ree comparisons of fusion total to hf dissolutions for marine sediments show that the latter method misses between 20 and 100 of the hree i e dy er yb lu and large percentages of zr in contrast fusion and hf dissolution yield similar concentrations for the light la ce nd and middle eu gd ree and other major elements the fusion data show that the marine sediments are more similar in ree composition to shales than previously reported by this author who underestimated the contribution of hf insoluble residues to the concentration of hree the heavy mineral zircon is the most likely cause of this observation zircons known to be enriched in hree were identified by x ray diffraction as a major component of the hf insoluble residues geochemical standards also have a significant but usually smaller fraction of their hree associated with hf insoluble phases these compositional differences have significance with respect to interpreting river inputs oceanic abundances and diagenesis of ree

holocene paleoclimatic reconstruction based on mud deposits on the inner shelf of the east china sea abstract we present a paleoclimatic reconstruction of the mid holocene by geochemical analysis of a sediment core mz01 retrieved from the mud area of the inner continental shelf of the east china sea ecs our results show that the downcore geochemical variations in the sediments of the core provide a link to historical climate changes relatively higher ratios of cia ba sr and a lower ratio of cao mgo coincide with major regional warm and humid climate episodes and vice versa therefore these geochemical indicators are useful in reconstructing the paleoclimate in eastern china using the geochemical records of core mz01 which are well constrained by ams 14c dating we found that from 8300 yr bp to 4200 yr bp the regional climate was moderately warm and humid and from 4200 yr bp to 2300 yr bp the climate was cool and dry with large fluctuations between cool dry 3700 yr bp 2850 yr bp and 2400 yr bp and warm wet 3250 yr bp and 2650 yr bp since 2300 yr bp our records indicate that the climate has gradually become warmer although a cold event centered at around 250 yr bp the little ice age lia interrupted this warming trend we also found significant 238 yr cycles in our cia records that imply a possible solar influence on the regional climate changes since the mid holocene

heavy metal and clay mineral analyses in the sediments of upper gulf of thailand and their implications on sedimentary provenance and dispersion pattern abstract forty eight sediment samples collected in the upper gulf of thailand ugot and its nearby rivers including the mae klong tha chin chao phraya and bang pakong were analyzed for grain size heavy metals cu pb zn cr and cd and clay minerals the results reveal that fine grained sediments with mz 1 than in other sampling areas meanwhile cd content is greater than 120 g kg 1 in sediments near the bang pakong river mouth and area between the tha chin and mae klong rivers mouth the concentrations of heavy metals are higher than background data and statistical analysis of geo accumulation index indicates that the study area is either unpolluted to moderately polluted or moderately polluted by heavy metals our results also verify that illite is the dominant clay mineral followed by kaolinite chlorite and smectite in terms of semi quantitative content smectite kaolinite can be used as an indicator to trace the riverine sediment in the study area which present a counterclockwise dispersion pattern of sediment from the chao phraya river

a comparison of geoid undulations for west central greenland the accuracy of a new local gravity field model geoid94a is examined at a site on the western greenland ice sheet the model developed by the danish national survey and cadastre incorporates several new gravity data sets including an extensive amount of airborne gravity data model derived geoid undulations were compared to independently determined undulations found by differencing the elevations from global positioning system controlled airborne laser altimetry and optical leveling surveys differences between the two sets of undulations were less than 6 cm rms the comparison improved 5 cm rms when geoid94a undulations were adjusted by local gravity observations also acquired at the site our comparisons demonstrate that geoid94a adequately models the long to intermediate wavelengths of the gravity field we conclude that geoid94a constitutes a reliable reference model for studies of greenland s gravity field

concentration distribution and assessment of heavy metals in sediments of mud area from inner continental shelf of the east china sea heavy metals cr cu zn cd pb hg and as grain size ph eh and total organic material tom and tn of 59 surficial sediments of mud area from the inner continental shelf of the east china sea have been analyzed the relations of the heavy metals to sediment composition ph reduction oxidation conditions and total organic materials were evaluated with multivariate statistics analysis and the hydrodynamic conditions such as coastal current and taiwan warm current are the other important controlling factors to the distribution of heavy metals sediment enrichment factors and potential ecological hazard index e text ri were used to assess the heavy metals accumulation the results indicate that moderate contamination of most heavy metals is prevalent and the contamination level in the estuary is rather high which is mainly from anthropogenic source compared with other areas in china the contaminant level of the study area is moderate

can seismic stratigraphy problems be solved using automated pattern analysis and recognition the problem four wells had been drilled in the four horses area of the powder river basin in weston county wyoming interpretation of well logs indicated that the sand content in the formation varied widely the key question in the development of the area was the locations of the boundaries between the different sand contents

spherulitic siderites in the holocene coastal deposits of korea eastern yellow sea elemental and isotopic composition and depositional environment abstract siderite concretions are recovered from both freshwater unit ii and tidal unit i deposits in the holocene macrotidal flat of kyunggi bay west coast of korea siderites from both units show a spherulitic and well rounded texture and well developed equant rhombs on the external surfaces the size of the concretions in unit ii 50 150 m in diameter is normally larger than that in unit i 10 20 m the siderites in unit ii are chemically pure and highly enriched in fe whereas those of unit i are relatively impure and distinctly zoned demarcating high mn up to 69 1 mol in the core and high fe up to 75 9 mol in the margin within siderites of unit i substitution for fe by ca and mg reaches up to 20 3 mol mean 15 1 mol and 16 1 mol mean 12 6 mol respectively bulk 18 o values 0 7 to 1 3 peedee belemnite pdb for siderites in unit i are relatively higher than those 7 1 to 0 5 pdb in unit ii regardless of units siderite 13 c values 21 3 to 11 2 pdb are persistently low indicating microbially mediated precipitation at shallow burial depth extensive mn ca and mg substitution coupled with enrichment of 18 o in the siderites of unit i seems to reflect marine influence during the holocene transgression the occurrence of early diagenetic siderites provides supporting evidence on the depositional environment marine vs non marine of the holocene muddy coastal deposits of korea eastern yellow sea

natural controls of fluvial denudation rates in major world drainage basins we present a new compilation of estimates of modern rates of mechanical and chemical denudation for externally drained basins exceeding 5 105 km2 in area these estimates are based on sediment and solute load data selected in order to represent natural rates as far as possible chemical denudation rates have been calculated by deducting the nondenudational component of solute load mechanical denudation rates range from 1 mm kyr 1 for the st lawrence and dnepr basins to 670 mm kyr 1 for the brahmaputra basin chemical denudation rates vary from 1 mm kyr 1 kolyma niger nile and rio grande basins to 27 mm kyr 1 chiang jiang basin the kolyma basin has the lowest 4 mm kyr 1 and the brahmaputra basin the highest overall rate of denudation 688 mm kyr 1 relationships between denudation rates and a range of morphometric hydrologic and climatic variables are investigated through correlation and regression analysis morphometric variables such as mean local relief are accurately calculated for large basins for the first time by using the national geophysical data center 10 minute topographic database variables expressing basin relief characteristics and runoff are found to be most strongly associated with both mechanical and chemical denudation rates with more than 60 of the variance in total denudation being accounted for by basin relief ratio and runoff basin area runoff variability and mean temperature however are only weakly associated with rates of denudation although direct comparisons cannot be made it appears that rates of basin denudation derived from present day mass flux estimates are not overall significantly different from estimates of long term rates based on sediment volume and thermochronologic data it therefore appears that the key factors identified as controlling denudation rates here are also applicable to the geological time spans relevant to the interaction between tectonic and denudational processes

large scale drainage capture and surface uplift in eastern tibet sw china before 24 ma inferred from sediments of the hanoi basin vietnam current models of drainage evolution suggest that the non dendritic patterns seen in rivers in se asia reflect progressive capture of headwaters away from the red river during and as a result of surface uplift of eastern asia mass balancing of eroded and deposited rock volumes demonstrates that the red river catchment must have been much larger in the past in addition the nd isotope composition of sediments from the hanoi basin vietnam interpreted as paleo red river sediments shows rapid change during the oligocene before similar to 24 ma we interpret this change to reflect large scale drainage capture away from the red river possibly involving loss of the middle yangtze river reorganization was triggered by regional tilting of the region towards the east this study constrains initial surface uplift in eastern tibet and southwestern china to be no later than 24 ma well before major surface uplift and gorge incision after 13 ma

rare earth elements in fine grained sediments of major rivers from the high standing island of taiwan thirty eight sediment samples from 15 primary rivers on taiwan were retrieved to characterize the rare earth element ree signature of fluvial fine sediment sources compared to the three large rivers on the chinese mainland distinct differences were observed in the ree contents upper continental crust normalized patterns and fractionation factors of the sediment samples the average ree concentrations of the taiwanese river sediments are higher than those of the changjiang and huanghe but lower than the zhujiang light rare earth elements lrees are enriched relative to heavy rare earth elements hrees with ratios from 7 48 to 13 03 we found that the variations in la lu ucc gd lu ucc and la yb ucc gd yb ucc are good proxies for tracing the source sediments of taiwanese and chinese rivers due to their distinguishable values our analyses indicate that the ree compositions of taiwanese river sediments were primarily determined by the properties of the bedrock and the intensity of chemical weathering in the drainage areas the relatively high relief and heavy rainfall also have caused the rees in the fluvial sediments from taiwan to be transported to the estuaries down rivers from the mountains and in turn delivered nearly coincidently to the adjacent seas by currents and waves our studies suggest that the ree patterns of the river sediments from taiwan are distinguishable from those from the other sources of sediments transported into the adjacent seas and therefore are useful proxies for tracing the provenances and dispersal patterns of sediments as well as paleoenvironmental changes in the marginal seas