sedimentary facies and radiocarbon dates of the nam dinh 1 core from the song hong red river delta vietnam abstract the song hong red river delta which is located on the western coast of the gulf of bac bo gulf of tonkin in the south china sea is characterized by three morphological systems that are clearly distinguished spatially fluvial tidal and wave dominated we obtained a 70 m long core of sediments the nam dinh 1 core from the central part of the delta in 1999 this paper presents the first detailed description of sedimentary facies with high resolution radiocarbon dating for the latest pleistocene holocene sediments of the song hong delta the core sediments were divided into three units on the basis of the sediment facies in ascending order unit 1 fluvial sediments consisting of fining upward gravels to clay unit 2 coarsening upward marine clay to shelly sand and unit 3 coarsening upward marine clay and laminated sand twenty one radiocarbon dates showed that the core succession was deposited after the last glacial maximum lgm the ages were 15 11 cal kyr bp for unit 1 11 9 cal kyr bp for unit 2 and 8 0 cal kyr bp for unit 3 these data indicate that sediments were deposited in transgressive fluvial estuarine to regressive deltaic environments formed in the central delta plain of the song hong after the lgm in response to sea level changes

formation and tectonic evolution of the cretaceous jurassic muslim bagh ophiolitic complex pakistan implications for the composite tectonic setting of ophiolites the muslim bagh ophiolitic complex balochistan pakistan is comprised of an upper and lower nappe and represents one of a number of ophiolites in this region which mark the boundary between the indian and eurasian plates these ophiolites were obducted onto the indian continental margin around the late cretaceous prior to the main collision between the indian and eurasian plates the upper nappe contains mantle sequence rocks with numerous isolated gabbro plutons which we show are fed by dolerite dykes each pluton has a transitional dunite rich zone at its base and new geochemical data suggest a similar mantle source region for both the plutons and dykes in contrast the lower nappe consists of pillow basalts deep marine sediments and a me lange of ophiolitic rocks the rocks of the upper nappe have a geochemical signature consistent with formation in an island arc environment whereas the basalts of the lower nappe contain no subduction component and are most likely to have formed at a mid ocean ridge the basalts and sediments of the lower nappe have been intruded by oceanic alkaline igneous rocks during the northward drift of the indian plate the two nappes of the muslim bagh ophiolitic complex are thus distinctively different in terms of their age lithology and tectonic setting the recognition of composite ophiolites such as this has an important bearing on the identification and interpretation of ophiolites where the plate tectonic setting is less well resolved

evaluation of recent tectonomagmatic discrimination diagrams and their application to the origin of basic magmas in southern mexico and central america discrimination diagrams to decipher tectonic settings have been in use for nearly 40 years although old diagrams have been extensively used the recent ones based on discriminant functions of ratio variables with or without log transformation proposed during 2004 2010 for the discrimination of four tectonic settings of island arc continental rift ocean island and mid ocean ridge were newly evaluated to show their high success rates of 57 3 100 and 58 5 100 for major element and immobile element based diagrams respectively for the continental arc of the andes evaluated for its similarity to island arc these four sets of diagrams showed success rates of 62 1 83 8 these four sets of five diagrams per set were therefore used to infer tectonic setting of the mexican volcanic belt mvb los tuxtlas volcanic field ltvf and central american volcanic arc cava using this approach the mvb especially its western central and eastern parts and the ltvf of southern mexico show a dominantly continental rift setting and the cava shows an arc setting the west central part of the mvb is consistent with dual tectonics of arc and rift these results confirm the application of an unusual mantle upwelling rift model for the mexican on land volcanism whereas the conventional plate tectonic subduction model seems to be applicable for the cava from guatemala to north western costa rica

a coupled hydrodynamic modeling system for phailin cyclone in the bay of bengal abstract east coast of india is characterized by low to medium topography and an extensive network of major estuaries bays mangrove creeks rivers and tidal inlets that permit inland flooding during tropical cyclones a coupled wave surge hydrodynamic modeling system adcirc swan is implemented to simulate storm surge still water level elevation and wave induced setup associated with phailin a very severe cyclonic storm that made landfall in the odisha state east coast of india during october 2013 the coupled model provides a realistic description on the dynamic interaction of tides wind waves and currents which is critical for operational needs the study assesses the role of wave induced setup on the net water level elevation using time varying wave radiation stress that is dynamically updated in the coupled model run numerical experiments are carried out for both storm surge alone and coupled mode versions dependent upon complex bathymetry and coastal geometry inclusion of wave induced setup in coupled runs results in an additional 23 36 increase of peak surge relative to an uncoupled surge tide simulation the significant wave height from coupled model also shows an excellent match with observed wave heights from a wave rider buoy located off the odisha coast the comparison of surge residuals between model and observation also exhibits a good match the study highlights the importance of having a coupled wave hydrodynamic model for operational needs in the north indian ocean

rapid flooding of the sunda shelf a late glacial sea level record the increase in sea level from the last glacial maximum has been derived from a siliciclastic system on the tectonically stable sunda shelf in southeast asia the time from 21 to 14 thousand calendar years before the present has been poorly covered in other records the record generally confirms sea level reconstructions from coral reefs the rise of sea level during meltwater pulse 1a was as much as 16 meters within 300 years 14 6 to 14 3 thousand years ago

impact of relative sea level and rapid climate changes on the architecture and lithofacies of the holocene rhone subaqueous delta western mediterranean sea abstract the modern rhone delta in the gulf of lions nw mediterranean is a typical wave dominated delta that developed after the stabilization of relative sea level following the last deglacial sea level rise similar to most other deltas worldwide it displays several stacked parasequences and lobes that reflect the complex interaction between accommodation sediment supply and autogenic processes on the architecture of a wave dominated delta the interpretation of a large set of newly acquired very high resolution seismic and sedimentological data well constrained by 14c dates provides a refined three dimensional image of the detailed architecture seismic bounding surfaces sedimentary facies of the rhone subaqueous delta and allows us to propose a scenario for delta evolution during the last deglaciation and holocene the subaqueous delta consists of parasequence like depositional wedges a few metres to 20 30 m in thickness these wedges first back stepped inland toward the nw in response to combined global sea level rise and overall westward oceanic circulation at a time when sediment supply could not keep pace with rapid absolute eustatic sea level rise at the younger dryas preboreal transition more rapid sea level rise led to the formation of a major flooding surface equivalent to a wave ravinement surface after stabilization of global sea level in the mid holocene accommodation became the leading factor in controlling delta architecture an eastward shift of depocentres occurred probably favoured by higher subsidence rate within the thick messinian rhone valley fill the transition between transgressive backstepping geometry and regressive prograding geometry para sequences resulted in creation of a maximum flooding surface mfs that differs from a classical mfs described in the literature it consists of a coarse grained interval incorporating reworked shoreface material within a silty clay matrix this distinct lithofacies results from condensation erosion which appears as an important process even within supply dominated deltaic systems due to avulsion of distributaries the age of the mfs varies along strike between ca 7 8 and 5 6 kyr cal bp in relation to the position of depocentres and climatically controlled sediment supply the last rapid climate change of the holocene the little ice age 1250 1850 ad had a distinct stratigraphic influence on the architecture and lithofacies of the rhone subaqueous delta through the progradation of two deltaic lobes in response to changes in sediment supply linked to rapid climate changes and to anthropic factors the rhone delta evolved from wave dominated to fluvial dominated and then wave dominated again

a reevaluation of tectonic discrimination diagrams and a new probabilistic approach using large geochemical databases moving beyond binary and ternary plots 1 statistically rigorous confidence intervals calculated from analyses of basaltic volcanic samples obtained from two large geochemical databases petdb and georoc demonstrate that published binary and ternary discrimination diagrams seldom correctly classify samples from mid ocean ridges island arcs and ocean islands with better than 60 accuracy the confidence intervals provide a measure of certainty that was previously absent from these diagrams allowing for a more robust analysis of results a new probabilistic method for geochemical discrimination is developed using the geochemical databases the new method is n dimensional and uses a priori data to construct probability distribution functions from which a posteriori probabilities are generated tests of the new method demonstrate single analysis classification success rates for volcanic rocks from island arcs to be 83 from ocean islands to be 75 and from mid ocean ridges to be 76

tectonic setting of the bela ophiolites southern pakistan abstract the bela ophiolites consist of a 3 5 km thick sequence of basaltic pillow lava inter flow sedimentary rocks chert argillite limestone and diabase gabbro sills debris of serpentinite up to kilometer sized blocks serpentinite carbonate breccia and less commonly of basalt gabbro peridotite pelagic limestone and their metamorphic equivalents occur throughout the ophiolite sequence and may form extensive horizons the age of the ophiolites as indicated by pelagic microfauna is aptian early maestrichtian the lava flows belong to a spilite keratophyre basaltic andesite suite of tholeiites enriched in fe tio 2 and other trace elements the lava flows although similar to the e type morb differ in details such as la ta ratio ranges 9 62 18 04 for the bela lavas versus 10 15 for the morb the diabase gabbro sills are similar to the associated lava flows however due to their relative enrichment in certain elements e g fe ti hf th and ta etc they may represent more fractionated late melts a comparison of the stratigraphic and structural features of the bela ophiolites with modern oceanic environments reveals that these ophiolites probably originated in a large oceanic fracture zone leaky transform this is based on lithotectonic features such as the common occurrence of debris of foliated serpentinite and serpentinite carbonate breccia bearing rocks in the ophiolite sequence and on geodynamic considerations the fracture zone ancestral to the bela ophiolites probably acted as a boundary between the indian and the neo tethys plates during the cretaceous analogous to the present day owen fracture zone which separates the indian and the arabian plates this ancestral fracture zone was destroyed when transform movement gave way to oblique convergence culminating in the ophiolite obduction in paleocene early eocene time the ophiolite obduction on the west indian continental margin was preceded by alkaline wpb type volcanism which is represented by the porali basalts the bibai lavas and the deccan basalts

stratigraphy and optically stimulated luminescence osl dating of a quaternary sequence along the dong nai river southern vietnam abstract the pre holocene cenozoic sequence outcrops in the terrestrial part of the eastern margin of the mekong basin however the stratigraphy of the sequence is still unclear its detailed stratigraphy and chronology were therefore studied along the dong nai river southern vietnam and the lithofacies and the relations among the formations were investigated from the outcrops the ages of the deposits were determined by using optically stimulated luminescence osl dating the ba mieu formation was deposited about 176 52 ka during marine isotope stage mis 7 6 the thu duc formation was deposited about 97 27 ka during mis 5 both the ba mieu and thu duc formations are composed of fluvial and tidally influenced coastal deposits the newly proposed nhon trach formation was originally an eolian blanket deposit but it has been partly reworked by fluvial processes the nhon trach formation was deposited about 10 9 4 7 ka in the last part of the pleistocene to the beginning of the holocene the osl ages for the ba mieu thu duc and nhon trach formations are younger than the ages previously assigned to these formations

geochemical and sr nd pb isotopic evidence for a combined assimilation and fractional crystallisation process for volcanic rocks from the huichapan caldera hidalgo mexico abstract this study reports new geochemical and sr nd pb isotopic data for miocene to quaternary basaltic to andesitic dacitic and rhyolitic volcanic rocks from the huichapan caldera located in the central part of the mexican volcanic belt mvb the initial sr and nd isotopic ratios except for one rhyolite range as follows 87sr 86sr 0 70357 0 70498 and 143nd 144nd 0 51265 0 51282 the sr nd pb isotopic ratios are generally similar to those for volcanic rocks from other areas of the central and eastern parts of the mvb the isotopic ratios of one older pre caldera rhyolite hp30 from the huichapan area particularly its high 87sr 86sr are significantly different from rhyolitic rocks from this and other areas of the mvb but are isotopically similar to some felsic rocks from the neighbouring geological province of sierra madre occidental smo implying an origin as a partial melt of the underlying crust the evolved andesitic to rhyolitic magmas could have originated from a basaltic magma through a combined assimilation and fractional crystallisation afc process different compositions representing lower crust lc and upper crust uc as well as a hypothetical crust similar to the source of high 87sr 86sr rhyolite hp30 were tested as plausible assimilants for the afc process the results show that the uc represented by granitic rocks from a nearby los humeros area or by cretaceous limestone l rocks outcropping in the northern part of the study area and the lc represented by granulitic xenoliths from a nearby san luis potosi slp area are not possible assimilants for huichapan magmas whereas a hypothetical crust ha similar in isotopic compositions to rhyolite hp30 could be considered a possible assimilant for the afc process chemical composition of assimilant ha although not well constrained at present was inferred under the assumption that hp30 type partial melts could be generated from its partial melting these data were then used to evaluate the proposed afc process to explain the evolution of the huichapan magmas

geochemical characteristics 40ar 39ar ages and original tectonic setting of the band e zeyarat dar anar ophiolite makran accretionary prism s e iran abstract the makran accretionary prism in southeastern iran contains extensive mesozoic zones of melange and large intact ophiolites representing remnants of the tethys oceanic crust that was subducted beneath eurasia to the north of the makran accretionary prism lies the jaz murian depression which is a subduction related back arc basin the band e zeyarat dar anar ophiolite is one of the ophiolite complexes it is located on the west side of the makran accretionary prism and jaz murian depression and is bounded by two major fault systems the principal rock units of this complex are a gabbro sequence which includes low and high level gabbros an extensive sheeted diabase dike sequence late intrusive rocks which consist largely of trondhjemites and diorites and volcanic rocks which are largely pillow basalts interbedded with pelagic sedimentary rocks including radiolarian chert chondrite and primitive mantle normalized incompatible trace element data and age corrected nd pb and sr isotopic data indicate that the band e zeyarat dar anar ophiolite was derived from a midocean ridge basalt like mantle source the isotopic data also reveal that the source for basalts was indian ocean type mantle based on the rare earth element ree data and small isotopic range all the rocks from the band e zeyarat dar anar ophiolite are cogenetic and were derived by fractionation from melts with a composition similar to average e morb fractionation was controlled by the removal of clinopyroxene hornblende and plagioclase three 40ar 39ar plateau ages of 140 7 2 2 142 9 3 5 and 141 7 1 0 ma and five previously published k ar ages ranging from 121 4 to 146 5 ma for the hornblende gabbros suggest that rocks from this ophiolite were formed during the late jurassic early cretaceous plate reconstructions suggest that the rocks of this complex appear to be approximately contemporaneous with the masirah ophiolite which has crystallization age of 150 ma like masirah the rocks from the band e zeyarat dar anar ophiolite complex represent southern tethyan ocean crust that was formed distinctly earlier than crust preserved in the 90 100 ma bitlis zagros ophiolites including the samail ophiolite

fine sediment dynamics in the mekong river estuary vietnam field studies of fine sediment transport were carried out in the mekong river estuary vietnam in the high flow season of november 1993 in the freshwater region erosion and deposition of suspended sediment occurred at tidal frequency with a strong down river transport at a mean velocity of 1 m s 1and mean suspended solid concentration of about 250 mg l 1 also the suspended sediment was mostly fine silt and the clay fraction accounted for only 15 the suspended sediment was transported either as individual particles or agglomerated with organic detritus at the mouth of the estuary a salt wedge was present but was flushed out of the estuary at low tide flow reversal occurred across the pycnocline a turbidity maximum zone was present at the toe of the salt wedge at flood tide most of the suspended sediment was coagulated with little organic matter the bulk of the suspended sediment was exported to coastal waters but some sediment returned to the estuary in the salt wedge data for the low flow season are sparse but suggest that partially well mixed estuarine conditions prevail with salinity penetrating about 40 km inland carrying fine sediment up river to a turbidity maximum zone most of this sediment would have been deposited in shallow coastal waters in the previous high flow seasons the construction of large hydro electric dams further upstream on the mekong river may exacerbate siltation patterns in the estuary

bayesian geochemical discrimination of mafic volcanic rocks determining the original tectonic setting of volcanic rocks via their geochemical signature has been a long standing goal for petrologists however current visually based methods for geochemical discrimination afford only limited success we develop a probabilistic method for geochemical discrimination based upon statistics generated from geochemical databases and bayesian analysis this method incorporates elemental covariance accounts for data measurement and theoretical uncertainty and is not restricted in dimensionality of analysis which is inherent in visual systems of discrimination furthermore the method provides a direct way to discern statistical outliers whose inclusion would otherwise lead to lower discrimination accuracy tests of the approach yielded successful classification rates for single analyses of over 90 percent for volcanic arc basalts mid ocean ridge basalts and ocean island basalts

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

song hong red river delta evolution related to millennium scale holocene sea level changes abstract the song hong red river delta occurs on the northwest coast of the south china sea its evolution in response to holocene sea level changes was clarified on the basis of sedimentary facies and 14 radiocarbon dates from the 40 m long duy tien core from the delta plain and using previously reported geological geomorphological and archaeological data the delta prograded into the drowned valley as a result of early holocene inundation from 9 to 6 cal kyr bp as sea level rise decelerated the sea level highstand at 2 3 m from 6 to 4 cal kyr bp allowed widespread mangrove development on the delta plain and the formation of marine notches in the ha long bay and ninh binh areas during sea level lowering after 4 cal kyr bp the former delta plain emerged as a marine terrace and the delta changed into the present tide and wave influenced delta with accompanying beach ridges delta morphology depositional pattern and sedimentary facies are closely related to holocene sea level changes in particular falling sea level at 4 cal kyr bp had a major impact on the evolution of the song hong delta and is considered to be linked to climate changes

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

early growth stage of a large delta transformation from estuarine platform to deltaic progradational conditions the northeastern mekong river delta vietnam abstract the initial growth stage of a river delta can be defined either as the beginning geomorphologic expansion of the river dominated coastal lowland or as the starting basinward directed progradation of the geological stratigraphic delta body differentiating between these two perspectives is necessary for understanding the sensitive reaction of a deltaic system to dynamic changes in sea level and sediment availability the holocene evolution of the northeastern part of the mekong river delta southern vietnam offers a great chance to depict these two different definitions and relate them genetically to each other since the transition between an old abrasion platform inner delta and the continental shelf basin outer delta is well developed in this marginal part of the delta the early stage of delta growth taking place during transgression related inundation between 8 cal ka bp maximum flooding and 5 7 6 0 4 8 cal ka bp sea level highstand was characterized by tide and saltwater influenced nearshore conditions allowing extensive mangrove and tidal flat deposits to aggradate on the wide abrasion platform with the onset of regression around 4 8 cal ka bp the depositional center shifted immediately beyond the seaward margin of this estuarine platform and thus true deltaic progradation could develop leading to rapid construction of a delta body and in addition to subsidence tilting of the inner delta zone directly at the transition of these two deposystems remains of shore related deposits indicate the sudden breakdown of the estuarine platform conditions around 4 6 cal ka bp

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

sedimentary facies diatom and foraminifer assemblages in a late pleistocene holocene incised valley sequence from the mekong river delta bentre province southern vietnam the bt2 core abstract a detailed description of sediment facies diatom mollusca and foraminifer assemblages and 14 c ages of the mekong river delta southern vietnam is presented in this paper a 71 m long core recovered in 1997 at the bentre province in the eastern part of the mekong river delta is divided into eight units and nine sediment facies on the basis of sedimentary properties diatom and foraminifer assemblages and 14 c ages these units show facies changes from transgression to regression in relation to the late pleistocene holocene sea level changes the postglacial transgression caused by a sea level rise led to infilling of the incised valley and formation of estuarine sediments and open bay muddy sediments in ascending order estuarine sediments consist of slightly oxidized yellowish grey silty sand and intercalated greenish grey and stiffly brownish grey sandy silt and silty clay the muddy facies 13 5 m thick is characterized by abundant marine planktonic diatoms and open sea foraminifers this facies indicates the maximum holocene marine influence was around 5300 cal yr bp at the bt2 site the regressive succession is composed of deltaic sediments from prodelta delta front sub to inter tidal flat and beach ridge in ascending order 14 c ages indicate that the delta front passed the core site at approximately 4000 3000 cal yr bp the coastal progradation rate was 17 18 m yr 1 during the 5300 3500 cal yr and decreased to 13 14 m yr 1 during the last 3500 cal yr

evaluation of arsenic sorption and mobility in stream sediment and hot spring deposit in three drainages of the tibetan plateau abstract enrichment of arsenic as in sediment 12 227 mg kg in the upstream tributaries of the indus and brahmaputra rivers originating from the tibetan plateau where hot springs were abundant has been found sandy sediment samples from the nu salween river lantsang mekong river and jinsha yangtze river also originating from the tibetan plateau were collected in july 2012 and were found to contain 6 8 mg kg to 30 5 mg kg as average17 3 6 5 mg kg n 12 deposits collected within 1 m of two hot springs in changdu tibet displayed significantly higher as levels 263 7 mg kg in ld 2 with 65 quartz and 101 8 mg kg in nud 1 with 82 calcite to evaluate the valence states of as and also the phases responsible for sorption x ray absorption spectroscopy xas was employed to analyze the two hot spring deposits and three river sediment samples coarse sand nud 6 as 14 6 mg kg fine sand nud 4 as 17 8 mg kg and silty sand ld 1 as 30 5 mg kg the x ray absorption near edge spectrum xanes data indicate that 70 of as from 3 samples in the nu salween river drainage nud 1 nud 4 and nud 6 is as v or arsenate with the rest being as 0 or as fe sulfides the proportion of as v is 90 for 2 samples in the lantsang mekong river drainage ld 1 and ld 2 linear combination fit of the iron extended x ray fine structure spectrum exafs show that 3 samples from the nu salween river contain 20 ferrihydrite and 10 goethite without any hematite being detected but 2 samples from the lantsang mekong river contain

tectonic discrimination of basalts with classification trees traditionally geochemical classification of basaltic rocks of unknown tectonic affinity has been performed by discrimination diagrams although easy to use this method is fairly inaccurate because it only uses bi or trivariate data furthermore many popular discrimination diagrams are statistically not very rigorous because the decision boundaries are drawn by eye and they ignore closure thus violating the rules of compositional data analysis classification trees approximate the data space by a stepwise constant function and are a more rigorous and potentially more effective way to determine tectonic affinity trees allow the simultaneous use of an unlimited number of geochemical features while still permitting visualization by an easy to use two dimensional graph two classification trees are presented for the discrimination of basalts of mid ocean ridge ocean island and island arc affinities the first tree uses 51 major minor and trace elements and isotopic ratios and should be used for the classification of fresh basalt samples a second tree only uses high field strength element analyses and isotopic ratios and can also be used for basalts that have undergone alteration the probability of successful classification is 89 for the first and 84 for the second tree as determined by 10 fold cross validation even though the trees presented in this paper use many geochemical features it is not a problem if some of these are missing in the unknown sample classification trees solve this problem with surrogate variables which give more or less the same decision as the primary variables the advantages of the classification tree approach over discrimination diagrams are illustrated by a comparative test on a sample dataset of known tectonic affinities although arguably better than discrimination diagrams classification trees are not perfect and the limitations of the method are illustrated on a published dataset of basalts from the pindos basin greece

mesophotic coral buildups in a prodelta setting late eocene southern pyrenees spain a mixed carbonate siliciclastic system lower priabonian coral bioherms and biostromes encased in prodelta marls clays occur in the ainsa jaca piggyback basin in the south central pyrenean zone detailed mapping of lithofacies and bounding surfaces onto photomosaics reveals the architecture of coral buildups coral lithosomes occur either isolated or amalgamated in larger buildups isolated lithosomes are 1 to 8 m thick and a few hundred metres wide clay content within coral colonies is significant stacked bioherms form low relief buildups commonly 20 to 30 m thick locally up to 50 m these bioherms are progressively younger to the west following progradation of the deltaic complex the lowermost skeletal rich beds consist of bryozoan floatstone with wackestone to packstone matrix in which planktonic foraminifera are abundant and light related organisms absent basal coral biostromes and the base of many bioherms consist of platy coral colonies floating in a fine grained matrix rich in branches of red algae corals with domal or massive shape locally mixed with branching corals and phaceloid coral colonies dominate buildup cores these corals are surrounded by matrix and lack organic framework the matrix consists of wackestone to packstone locally floatstone with conspicuous red algal and coral fragments along with bryozoans planktonic and benthonic foraminifera and locally sponges coral rudstone and skeletal packstone with wackestone to packstone matrix also occur as wedges abutting the buildup margins integrative analysis of rock textures skeletal components buildup anatomy and facies architecture clearly reveal that these coral buildups developed in a prodelta setting where shifting of delta lobes or rainfall cycles episodically resulted in water transparency that allowed zooxanthellate coral growth the bathymetric position of the buildups has been constrained from the light dependent communities and lithofacies distribution within the buildups the process product analysis used here reinforces the hypothesis that zooxanthellate corals thrived in mesophotic conditions at least during the late eocene and until the late miocene comparative analysis with some selected upper eocene coral buildups of the north mediterranean area show similarities in facies components and textures and suggest that they also grew in relatively low light mesophotic and low hydrodynamic conditions

late holocene sedimentary and environmental development of the northern mekong river delta vietnam abstract a sedimentological and palynological study of three sediment cores from the northern mekong river delta shows the regional sedimentary and environmental development since the mid holocene sea level highstand a sub to intertidal flat deposit of mid holocene age is recorded in the northernmost core shoreline deposits in all three cores show descending ages from n to s documenting 1 the early stages of the late holocene regression and 2 the subsequent delta progradation the delta plain successions vary from floodplain deposits with swamp like elements to natural levee sediments the uppermost sediments in all cores show human disturbance to varying degrees the most intense alteration is recorded in the northernmost core where the palynological signal together with a charcoal peak indicates the profound change of the environment during the modern land reclamation the sediments from at least one of the three presented cores do not show a true delta facies succession but rather estuary like features as also observed in records from southern cambodia this absence is probably due to lack of accommodation space during the initial phase of rapid delta progradation which impeded the development of true delta successions as shown in cores from the southern mekong river delta

systematic variation of sr nd and pb isotopes with time in lavas of mauritius reunion hotspot we report sr nd and pb isotopic compositions for the lavas of mauritius the second youngest volcanic island in the reunion hotspot the lavas of the older series 7 8 5 5 ma have identical isotopic compositions 87sr 86sr 0 70411 to 0 70422 143nd 144nd 0 512865 to 0 512854 and 206pb 204pb 19 016 to 19 041 to those of reunion where the center of volcanic activity is currently located the lavas of the intermediate series 3 5 1 9 ma and younger series 0 70 0 17 ma are shifted to lower sr isotopic compositions 0 70364 0 70394 with 143nd 144nd 0 512813 to 0 512948 and 206pb 204pb 18 794 to 18 984 the intermediate series lavas have similar trace element characteristics e g zr nb ba y to those of rodrigues in both cases requiring the involvement of an enriched mantle like component in the mantle source during the volcanic history of mauritius the magmas lost the principal isotopic characteristics of the reunion hotspot with time and became gradually imprinted with the isotopic signature of a shallower mantle source that produced the central indian ridge basalts

electrical resistivity tomography determines the spatial distribution of clay layer thickness and aquifer vulnerability kandal province cambodia despite being rich in water resources many areas of south east asia face difficulties in securing clean water supply this is particularly problematic in regions with a rapidly growing population in this study the spatial variability of the thickness of a clay layer controlling surface groundwater interactions that affect aquifer vulnerability was investigated using electrical resistivity tomography ert data were acquired along two transects showing significant differences in the imaged resistivities borehole samples were analyzed regarding particle density and composition and linked to their resistivity the obtained relationships were used to translate the field electrical resistivities into lithologies those revealed considerable variations in the thickness of the clay layer ranging from 0 m up to 25 m geochemical data highlighting zones of increased ingress of surface water into the groundwater confirmed areas of discontinuities in the clay layer which act as preferential flow paths the results may guide urban planning of the phnom penh city expansion in order to supply the growing population with safe water the presented approach of using geophysics to estimate groundwater availability accessibility and vulnerability is not only applicable to kandal province cambodia but also to many other areas of fast urbanization in south east asia and beyond

holocene variability of the kuroshio current in the okinawa trough northwestern pacific ocean abstract cores 255 and b 3gc from the southern and northern okinawa trough respectively were studied for determining the variability of the kuroshio current on centennial scales during the holocene based on detailed ams 14 c dates stable isotope and planktonic foraminiferal distribution the main flow of the kuroshio current was inferred to re enter the okinawa trough at 7 3 calendar cal kyr bp leading to abrupt changes in sedimentation rate remarkably increased abundance of the kuroshio current indicator pulleniatina obliquiloculata increased sea surface temperature sst and depth of thermocline dot during 4 6 2 7 cal kyr bp the abundance of p obliquiloculata sharply decreased corresponding to a decreases in sst and dot implying that the influence of the kuroshio current weakened at that time possibly as a result of the intensified winter monsoon significantly the kuroshio current proxies e g the difference in sst between the southern and northern okinawa trough display periodicities of 1500 yr and 700 800 yr ascribed to the second harmonic of the 1500 yr cycle in oceanic thermohaline circulation during the holocene the holocene events at 0 6 1 7 3 3 4 6 5 9 8 1 9 4 cal kyr bp in the okinawa trough appear to be the most recent manifestation of the millennial scale climate cycle recorded in the north atlantic arabian sea marine sediment cores and greenland ice cores suggesting global climatic tele connections

petrology and geochemistry of rodrigues island indian ocean rodrigues island is composed of a differentiated series of transitional mildly alkaline olivine basalts the lavas contain phenocrysts of olivine fo88 68 plagioclase an73 50 together with a megacryst suite involving olivine plagioclase kaersutite clinopyroxene apatite magnetite and hercynite rich spinels troctolitic anorthositic gabbro xenoliths are widely dispersed throughout the lavas and are probably derived from the upper parts of an underlying layered complex the megacrysts may originate from coarse easily disaggregated differentiates near the top of this body modelling of major and trace element data suggests that the majority of chemical variation in the lavas results from up to 45 fractionation of olivine clinopyroxene plagioclase and magnetite at low pressures in the ratio 20 35 39 6 the clinopyroxene rich nature of this extract assemblage is significantly different to that of the xenoliths and suggests that clinopyroxene rich gabbros and or ultrabasic rocks may lie at greater depth sr and nd isotopic data 87sr 86sr 0 70357 070406 143nd 144nd 0 51283 0 51289 indicate a mantle source with relative lree depletion and emphasise an unusual degree of uniformity in indian ocean island sources a small group of lavas with strong hree enrichment suggest a garnet poor source for these while high overall al2o3 cao ratios imply high clinopyroxene garnet ratios in refractory residua

geochemistry of hydrothermally altered basaltic rocks from the southwest indian ridge near the rodriguez triple junction abstract petrographic and geochemical analyses of basaltic rocks dredged from the first segment of the southwest indian ridge near the rodriguez triple junction have been completed in order to investigate water rock interaction processes during mid ocean ridge mor hydrothermal alteration in the indian ocean in the study area we have successfully recovered a serial section of upper oceanic crust exposed along a steep rift valley wall which was uplifted and emplaced along a low angle normal fault on the basis of microscopic observation dredged samples are classified into three types fresh lavas low temperature altered rocks and high temperature altered rocks the fresh lavas have essentially the same chemical composition as typical n morb although lile and nb are slightly enriched and depleted respectively low temperature alteration brought about the enrichment of k2o rb and u due to the presence of k rich celadonite and u adsorption onto fe oxyhydroxide and clay minerals on the other hand chloritization albitization and addition of base metals by high temperature hydrothermal alteration result in enrichments of mno mgo na2o cu and zn and depletions of cao k2o cr co ni rb sr and ba in addition u enrichment is also observable in the high temperature altered rocks probably due to the decrease of uranite solubility in the reducing high temperature hydrothermal solution these petrological and geochemical features are comparable to those of the volcanic zone to transition zone rocks in the dsdp odp hole 504b indicating that our samples were recovered from the upper 1000 m section of the oceanic crust only the alteration minerals related to off axis alteration are absent in our samples dredged from near the spreading axis the similarity of alteration between our samples from the indian ocean and the hole 504b rocks from the pacific ocean suggests that mor hydrothermal systems are probably similar across all world oceans

sediment facies and late holocene progradation of the mekong river delta in bentre province southern vietnam an example of evolution from a tide dominated to a tide and wave dominated delta abstract the mekong river delta southern vietnam is a typical mixed tide and wave energy delta with a wide delta plain formed during the last 6 ka and is one of the largest deltas in the world three cores were taken from bentre province in the lower delta plain with the objective to describe the sediment facies and to clarify the changes from tide dominated to tide wave dominated delta of the mekong river delta during the late holocene three cores bt1 bt2 and bt3 were obtained in 1997 holocene sediments in bt1 and bt3 with thickness ranging from 10 to 20 m were mainly composed of deltaic sediments unconformably overlying the late pleistocene sediments the bt2 core however consisted of transgressive estuarine sediments covered by deltaic sediments infilling the paleo mekong river incised valley which is more than 70 m deep and was formed during the last glacial period the deltaic sediment facies and succession in the bt2 and bt3 cores taken from the outer delta plain with beach ridges were different from those of the bt1 core taken from the inland delta plain the bt2 and bt3 cores provide a good example of tide and wave dominated delta sediments and were characterized by a coarsening upward delta front facies covered by a fining upward subtidal to intertidal flat facies followed by a coarsening upward foreshore dune facies these changes from the inland delta plain to the beach ridge delta plain were accompanied by changes in progradation rates and subaqueous delta topography caused by increased wave influence

asymmetry in holocene river deltas patterns controls and stratigraphic effects abstract understanding controls on sediment distribution in river deltas is paramount to predicting facies relationships and stratal architecture most classifications of deltas have focused on subaerial plan morphology as a simplistic function of river tide and wave energy new work however is revealing the importance of subaqueous deposits and in particular shore parallel sediment redistribution in the shaping of delta planform delta asymmetry has emerged as an important characteristic reflective of patterns of alongshore sediment dispersal asymmetry has been described from onshore and offshore environments from several different types of modern deltas but aspects of asymmetry have not been fully documented and the degree to which these patterns are recorded in deltaic strata is not yet known this study is a comprehensive literature review of sediment distributions in modern deltas focusing on studies with high resolution geomorphic geophysical and geochronological datasets we reviewed 27 deltas using over 100 papers primarily from the past 15 20 years morphological facies and stratigraphic aspects were analyzed across the entire spectrum of deposits from the delta apex to the most distal muds of the prodelta we define quantifiable indices of asymmetry describing upcurrent vs downcurrent distribution of sediment volume sediment area sediment caliber and distributary channels most deltas are asymmetrical to some degree with respect to one or more of these parameters many deltas are increasingly skewed toward the downcurrent side from proximal to distal sub environments i e delta plain delta front prodelta some deltas are skewed toward the upcurrent side in one sub environment and toward the downcurrent side in another sub environment sand is preferentially deposited on the downcurrent side of most deltas but distributary channels tend to develop toward the upcurrent side the highest sand mud ratios are often on the upcurrent side in the lower delta plain but in the delta front these ratios are highest on the downcurrent side these complex patterns of asymmetry reflect different combinations of controls including discharge partitioning lobe abandonment and localized transgression plume deflection by coastal currents dominance of longshore current direction variable subsidence and other factors these processes may result in upcurrent downcurrent variations in clinoform geometry rates of progradation and stratal lapping relationships asymmetry has multiple aspects manifestations and controls even within a single delta but the long term preservation potential of these patterns likely varies depending on depositional setting and shoreline trajectory studies of ancient deltas will be better informed by recognizing the wide variety of controls on sediment distribution and avoiding the tendency toward a single model of delta asymmetry

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

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

do major oxide tectonic discrimination diagrams work evaluating new log ratio and discriminant analysis based diagrams with indian ocean mafic volcanics and asian ophiolites many geochemical diagrams exist that classify old volcanic terranes of ambiguous provenance into various modern plate tectonic settings with variable success recently proposed diagrams based on log ratios and linear discriminant analysis with large datasets of major oxides were tested here with data for ocean island arc and mid ocean ridge lavas from the indian ocean success rates are 45 100 with misclassifications potentially caused by alteration although alteration demonstrably need not cause misclassification the diagrams were further applied to some asian ophiolites representing tethyan and indian ocean crusts to see if the diagrams confirm their tectonic setting inferred from trace and isotopic data lower success rates 30 60 but 75 100 for specific suites are not surprising in view of the ubiquitous and complex alteration in ophiolites log ratio transformation and linear discriminant analysis appear to be powerful methods when discrimination diagrams are based on major oxide data alone

seawater alteration effects on 87sr86sr k rb cs ba and sr in oceanic igneous rocks abstract a study of low temperature alteration effects on three samples of tholeiitic basalts dredged from the gulf of california and a basalt sample drilled from the ne pacific has been described the analysis of core margin pairs for k rb cs ba and sr contents does not always show the consistent mobility pattern reported earlier namely cs rb k ba sr and ree leaching experiments conducted on these samples show normal 87 sr 86 sr ratios as determined on the leached samples when combined with the existing data the 87 sr 86 sr ratio from the gulf of california ranges from 0 70235 5 to 0 70280 6 averaging 0 7025 implying that these rocks have been derived from a source similar to that of the normal ocean ridge basalts

cycling of trace metals and rare earth elements ree in acid sulfate soils in the plain of reeds vietnam abstract trace metals and rare earth elements ree are subject to intensive chemical cycling in acid sulfate soils the oxidation of pyrite bearing deposits and the subsequent acidification mobilizes a variety of trace metals and ree in this study solid phase and pore water data of three cores from the plain of reeds in the mekong river delta vietnam were analyzed distinct authigenic enrichments of trace metals and ree were observed in the solid phase of these cores thermodynamic modeling was employed to elucidate the controls on trace metal and ree mobility and the governing factors for the formation of these authigenic enrichments the formation of ree enrichments in these settings is clearly controlled by ph and the availability of potent sorbents under suitable conditions trace metals such as e g zinc nickel and cobalt are likely bound as trace metal monosulfides in the enrichment zones the solid phase and pore water data and the results of a thermodynamic model suggest a possible sequential precipitation of trace metal sulfides however the incorporation of trace metals into iron sulfides cannot be ruled out in the case of lead and arsenic the formation of pb as jarosite proved to be a further major sink these insights provide a better understanding of the controls and governing factors for trace metal and ree mobility in acid sulfate soils and will therefore help to assess impacts on soil and water

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