composition of middle late eocene salt lakes in the jintan basin of eastern china evidence of marine transgressions abstract abundant continental salt deposits were formed in salt basins in eastern china around the cretaceous tertiary periods however whether these evaporites had a marine or non marine origin remains controversial the jintan basin is located between south china and north china and has a series of very thick relatively pure salt deposits such that data from the salt deposits in the jintan basin could provide new evidence of marine transgression the large scale of these salt deposits implies the supplies of marine transgression primary fluid inclusions in the halite deposits of the jintan basin have recorded the composition of the evaporated salt lake water the br contents in halite range from 2 to 16 ppm and clearly higher than inland non marine salt deposits in the yunying depression jianghan basin south china the 37cl values of marine salt deposits across different geological eras range from 1 to 1 the 37cl values from halite in the jintan basin range from 0 66 to 0 23 close to zero indicating a possible marine origin our analyses from fluid inclusions in halite show k varies from 0 7 to 15 8 g l mg from 1 1 to 3 1 g l sulfate ion from 3 7 to 27 7 g l in the samples the composition of fluid inclusions in halite from a sample in the lower part of the halite section in the jintan basin is very similar to marine seawater on janecke diagram the 34s of anhydrite deposits 26 32 to 26 51 are also very similar to contemporary seawater thus the evidence indicates the jintan basin was supplied sporadically by marine transgressions

sedimentation in the northern gulf of california after cessation of the colorado river discharge abstract the almost total elimination of sediment supply from the colorado river has produced a condition of sediment starvation in the entire northern gulf of california ngc textural and mineralogical analyses of 114 surface sediment samples collected in the area show that this situation has promoted alternate sediment sources to become more important in supplying and controlling the compositional characteristics of the sediments in the region by applying multivariate data analyses using q f ratios as well as heavy mineral and clay mineral content of samples four sedimentary provinces are identified colorado river delta province crdp concepcion river province ccrp transitional province tp and baja sonora province bsp the crdp dominates the regional distribution of sediments being mainly confined to the western side of the ngc the sediment source for this province is the deltaic structure of the colorado river sediment recycling through resuspension and reworking of the colorado delta and the shallow shelf of the upper gulf of california ugc is an important agent for supplying sediments to the ngc the ccrp reflects the mineralogical association of concepcion river while the tp contains a mineral association that is similar to crdp and ccrp but with intermediate values to these provinces this situation suggests that tp is a mixing zone between these two neighboring provinces the higher abundance of zircon and garnet in tp also suggests a clear contribution of sediment sources from the sonora desert in nw mexico clay mineral composition of these sediments indicates a greater abundance of smectite and chlorite relative to previous studies being mainly derived from eolian dust carried from the desert region of nw mexico and sw usa although eolian supply of fine grained sediments is important in the ngc colorado river delta sediments are still the largest single source of sediments to the region eolian supply of fine grained sediments is however more dominant in the southern half and along the eastern margin of the ngc the dispersion of sediments in the ngc is consistently cross basinal with a series of transport cells that follow a cyclonic circulation four depocenters were identified located all on the western side of the ngc and mainly associated to the deep basins the major effect that damming of the colorado river has had on the sedimentology of the area is that sediment dispersion is now cross basinal instead of long basinal this situation indicates that sediment dispersion at present is mainly controlled by oceanic forcing instead of fluvial processes as it was in the past

does neoproterozoic nam co formation in northwest vietnam belong to south china or indochina abstract the nam co belt is located to the northeast of song ma fault in northwestern vietnam the nature of the precambrian basement rocks in this area and its tectonic attribute have still been controversial in this study zircon u pb hf isotopic compositions and whole rock geochemical compositions of meta sedimentary rocks from the nam co formation in this belt have been integrated to reveal the components and tectonic setting of the formation of the basement rocks in the nam co belt zircon u pb dating results show that the nam co formation is of middle late neoproterozoic age the lower nam co formation probably formed between 821 and 726 ma and the upper formation was deposited later than 726 721 ma the sedimentary rocks from the lower and upper nam co formations are characterized by numerous neoproterozoic 900 800 ma detrital materials but the upper part contains more meso to paleoproterozoic sediments than the lower part detrital zircon age distribution and hf isotope compositions of the nam co formation are similar to those of neoproterozoic sedimentary rocks in the southern yangtze block both zircon u pb hf isotopic and whole rock geochemical data suggest that the source materials of the neoproterozoic nam co formation were dominated by felsic rocks with minor mafic materials and the detrital materials were mainly derived from the jiangnan orogenic belt in the southern yangtze block with minor contribution from the panxi belt in the western yangtze block ailaoshan song hong and phan si pan belts the lower nam co formation contains more sediments derived from the panxi belt than the upper part the middle late neoproterozoic nam co formation probably was deposited in a continental extensional basin and the sedimentation environment in later period

insights into marls from optical and back scattered electron petrography an example from the outer carpathians poland abstract this paper is a study of grain provenance depositional processes and the relationship of those processes to composition and diagenesis of fine grained rocks based on high resolution petrography the marly successions deposited in siliciclastic flysch and related to the paleotectonics of the northern domain of the tethys ocean outer carpathian basin were examined the following marls were studied upper jurassic marls from the vendryn formation goleszow marls upper cretaceous siliceous fucoid wegierka weglowka frydek jasienica and egocina marls eocene cko budzow zembrzyce and leluchow marls and oligocene sub cergowa and grybow marls these marls are products of the redeposition of shelf sediments into deeper parts of the basin knowledge of their diagenetic history can contribute to the evaluation of the petroleum potential of the polish outer carpathians thin section analysis by optical and electron back scattered microscopy fesem bse highlights the similarity of all these marls with respect to composition grain size sedimentary features and diagenetic changes they differ only in the quantitative proportion of constituents the relative extent of key microfacies and diagenetic effects the diagenetic modifications recognized in the rocks studied are characteristic of the processes operating in the sedimentary environment and during burial diagenesis thin section petrography of the marls reveals fine mostly silt size siliciclastic material and bioclasts supported by matrix siliciclastic particles comprise mostly quartz micas feldspars glauconitic nodules and lithoclasts calcareous and siliceous bioclasts mostly microfossils foram and sponge spicules and a few radiolarians and diatoms and coccospheres are variably preserved they may occur as calcite silica and clay pseudomorphs additional components include peloids and stringers of brown organic matter millimeter scale fabric analysis provides detailed insight into the processes of transport and deposition five microfacies are identified parallel laminated wavy and lenticular laminated homogeneous exhibiting preferred orientation of elongated components bioturbated and bioclast bearing the range of microfacies suggests that the marl sediment was deposited while currents were active the depositional settings identified range from traction reworking by bottom currents supply by nepheloid flow indistinctly bounded laminae possible eolian input laminae a few grains thick and biogenic reworking of sediments back scattered electron images reveal that the matrix consists of coccolithophorid remains with varying abundances of clay silica and carbonate cements five varieties of matrix are distinguished 1 carbonate clay silica bearing 2 carbonate clay supported 3 carbonate silica supported 4 clay silica supported and 5 clay dominated clay appears as rosette and lamellar aggregates silica as nanoquartz microspheres clusters coatings quartz overgrowths and occasionally opal ct as lepispheres and aggregates moss like in appearance and calcite as overgrown coccoliths pseudomicrite micrite and microspar pyrite framboids are present in some samples intrabiotic and intergranular cements are developed also present are partially dissolved coccolith placoliths silica and clay replaced micarb and grains similar in appearance to volcanic glass shards that now consist of calcite and quartz bioclasts may have been a source for calcite and silica cements volcanic glass may have been a source for authigenic silica and clay minerals this is suggested by the close spatial juxtaposition of silica microspheres and authigenic clay cauliflower like aggregates the authigenic origin of the clay in these marls is also suggested by the presence of overgrown coccoliths because recrystallization of shields is reduced when clay is present so that the overgrowths must have been formed in an environment where clay minerals were scarce initially despite diagenetic changes the presence of pyroclasts is still recognizable there are quartz crystal chips shard shaped grains volcanic rock fragments and minerals biotite apatite zircon the marls studied could be described as impure fine grained detrital limestones chalky in type with evidence of redeposition and possible volcanic ash input the marl depositional system within the outer carpathian basin was associated with tectonic movements which initiated chalk type facies and this was particularly widespread in the upper cretaceous and paleocene

boron occurrence in halite and boron isotope geochemistry of halite in the qarhan salt lake western china abstract previous studies have investigated boron b isotope composition of salt lake brines in the qaidam basin western china however the research on b isotope geochemistry of halite from a sediment core in a typical sedimentary basin has been very limited in this study a 102 m long drill core isl1a was recovered from qarhan salt lake in eastern qaidam basin forty three halite samples from upper 44 0 m in isl1a were collected and analyzed for chemical compositions k na ca 2 mg 2 cl so 4 2 sr 2 and b 3 and b isotopes in order to investigate their relationships and b isotope fractionation between halite and brines in the qarhan salt lake the results show that 1 more b 3 and mg 2 values in halite are low concentrations and more concentrated and low b 3 concentrations have a strong correlation with low mg 2 in halite which imply that they might be the same source 2 low mg 2 values in halite from isl1a have a similar trend with m mg 2 molarity of fluid inclusion brines from two sediment cores east to isl1a about 50 km in the study area suggesting that low b 3 and mg 2 concentrations should derive from fluid inclusions in halite based on x ray diffraction results in isl1a that no borate and small amount of magnesium salts were deposited 3 11 b values of halite in isl1a range from 0 35 to 5 84 which are in the range of those of river water and brines 1 0 to 9 6 and almost overlapped with those of brines 2 9 to 7 5 in the qarhan salt lake these results suggest that no or minor b isotope fractionation between halite and brine occurred

the devonian vertebrates placodermi sarcopterygii from central vietnam and their bearing on the devonian palaeogeography of southeast asia abstract new vertebrate remains are described from the terrigenous facies of the givetian dong tho formation in quang binh province central vietnam they are referred to three placoderm groups the antiarchi arthrodira and acanthothoraci and to a sarcopterygian the antiarchs are represented by a new form vukhuclepis lyhoaensis n g n sp which is regarded here as closely related to the yunnanolepididae an endemic group from the lower devonian of the south china block additional material of the phlyctaeniid arthrodire lyhoalepis duckhoai tong dzuy thanh janvier and doan nh t truong is described the sarcopterygian is regarded here as a dipnomorph and may be closely related to the lower middle devonian youngolepididae of the south china block this material confirms the close ties between the indochina and south china blocks as early as the middle devonian

zircon u pb ages and geochemistry of granitoids in the truong son terrane vietnam tectonic and metallogenic implications abstract truong son terrane one of the most important tectonic and metallogenic terranes in indochina block is composed of many volcano plutonic complexes reported here is geochronological and geochemical data obtained from six different volcano plutonic complexes the new data reveals that the granite from the hai van complex is 438 ma in age and shows collision related geochemical characteristics whereas another five samples from five volcano plutonic complexes present consistent emplacement and crystallization ages ranging from 261 to 242 ma dien bien granodiorite phia bioc monzogranite and dong trau rhyolite display typical subduction related calc alkaline affinity e g depletion in nb ta and ti and enrichment in rb and la while monzogranite from song ma complex displays collision related shoshoniteseries and granites from bengiang queson complex are related to post collision calc alkaline series based on these observations in combination with the previous published geochronological data we propose that at least four major stages of magmatic activities occurred during the paleozoic and the early mesozoic through the truong son terrane ordovician silurian 420 470 ma late carboniferous early permian 280 300 ma late permian to mid triassic 245 270 ma and middle late triassic 200 245 ma these magmatic activities are not only attributed to the tethyan song ma ocean southwestward subduction but also related to paleo tamky phuoc son oceanic bidirectional subduction synthesized with regional metallogenic data we identified three metallogenic epochs 1 late carboniferous early permian 280 300 ma arc magmatic hydrothermal cu au fe polymetallic metallogenic system related to the tamky phuoc son ocean north dipping subduction 2 late permian middle triassic 245 280 ma arc magmatic hydrothermal cu au fe and orogenic w sn au polymetallic metallogenic system which linked to both paleo tethyan song ma ocean south dipping subduction and tamky phuoc son ocean closure 3 middle to late triassic 200 245 ma syn collisional magmatic epithermal fe au w sn and post collisional or orogenic au system

compositional evolution of siliciclastic sediments recording the tectonic stability of a pericratonic rift mesozoic kutch basin western india abstract this study presents a combined petrographical and geochemical investigation to track the compositional changes in the mesozoic sedimentary record during the evolution of the pericratonic rift basin of kutch the mesozoic sequence of the proven petroliferous basin of kutch representing 3000 m thick siliciclastic and carbonate deposition within a time frame of 70 ma consists of jhurio jhumara jhuran and bhuj formations in ascending order of succession the dominance of arkosic sandstones and the abundance of zircon and monazite indicate predominantly felsic source rocks the concentration of individual trace elements such as th sc zr v ni and ratios like th sc cr v y ni th co la sc support the predominantly felsic source rock the lree enrichment and the negative eu anomaly corroborate the predominantly felsic source however concentrations of v ni and ti reveal the mafic input in older stratigraphic units while gdn ybn indicates dominant post archean source across the mesozoic succession younger stratigraphic units reveal contributions from the archean rocks from nagar parkar and aravalli highland regions the cia values suggest intermediate to intense weathering while the icv data record a shift from immature sediments in the older formations to mature and recycled types in the younger formations the high value of zr sc as well a high content of hf reflects the addition of zircon by recycling or by erosional unroofing of older continental rocks major oxide sio2 na2o and k2o and trace elements la th and hf bear the passive margin setting for the kutch basin during the mesozoic the decrease in feldspar content in sandstones increase in the concentration of zr and hf in shale and a decrease in values of icv from older to younger stratigraphic units corresponds to the compositional evolution related to increased stability of the kutch basin during the transition from early syn rift to post rift

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

neoproterozoic to early triassic tectono stratigraphic evolution of indochina and adjacent areas a review with new data the neoproterozoic to early triassic tectono stratigraphic evolution of indochina and adjacent areas can be divided into six mega episodes 1 the neoproterozoic early cambrian mega episode was characterized by shallow marine environment in the sino vietnam composite terrane meanwhile the different blocks of the indochina composite terranes were still separated by branches of the proto tethys sino vietnam and part of indochina amalgamated along the proto song ma suture by the end of the early cambrian 2 during the middle cambrian early ordovician mega episode shallow shelf carbonate deposition prevailed north of the proto song ma suture with associated strata containing a rich benthic fauna this contrasts with deep marine and volcanic arc setting in the south of the proto song ma suture 3 the middle ordovician silurian mega episode was characterized by subduction of the tam ky phuoc son ocean beneath the viet lao terrane in the north and the kon tum terrane in the south this was followed by a collisional orogeny that sutured the kon tum terrane with the viet lao and viet cambodia terranes along the tam ky phuoc son suture the hypothetic po ko and chu sinh sutures are discussed the collision led to an intra continental orogeny in the sino vietnam composite terrane by the end of the mega episode a unified sino vietnam indochina super terrane was established during the latest silurian early devonian benthic fauna and flora of the sino vietnam and indochina composite terranes shared cathaysian affinity 4 the devonian tournaisian mega episode was characterized by an early middle devonian transgression and a late devonian earliest carboniferous regression except for parts of northern indochina where deep marine conditions remained 5 during the visean middle permian the song ma ocean reopenned in the north of indochina meanwhile in the west a volcano plutonic belt formed due to eastward subduction of the paleo tethys under the indochina composite terrane 6 the late permian early triassic mega episode was characterized by emeishan mantle plume related continental rifting and the indosinian orogeny resulting from resuturing of the indochina and sino vietnam composite terranes along the song ma suture

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

geochemistry of archean shales from the pilbara supergroup western australia archean clastic sedimentary rocks are well exposed in the pilbara block of western australia shales from turbidites in the gorge creek group ca 3 4 ae and shales from the whim creek group ca 2 7 ae have been examined the gorge creek group samples characterized by muscovite quartzchlorite mineralogy are enriched in incompatible elements k th u lree by factors of about two when compared to younger archean shales from the yilgarn block alkali and alkaline earth elements are depleted in a systematic fashion according to size when compared with an estimate of archean upper crust abundances this depletion is less notable in the whim creek group such a pattern indicates the source of these rocks underwent a rather severe episode of weathering the gorge creek group also has fairly high b content 85 29 ppm which may indicate normal marine conditions during deposition rare earth element ree patterns for the pilbara samples are characterized by light ree enrichment lanybn 7 5 and no or very slight eu depletion eueu 0 82 0 99 a source comprised of about 80 felsic igneous rocks without large negative eu anomalies felsic volcanics tonalites trondhjemites and 20 mafic ultramafic volcanics is indicated by the trace element data very high abundances of cr and ni cannot be explained by any reasonable provenance model and a secondary enrichment process is called for

evolution of geochemistry and depositional settings of early palaeozoic siliciclastics of the barrandian tepla barrandian unit bohemian massif czech republic cambrian and ordovician middle devonian sequences of two successive early palaeozoic basins of the barrandian unconformably overlie cadomian basement in the bohemian massif nw interior tepla barrandian unit which is the easternmost peri gondwanan remnant within the variscides correlation of stratigraphy and geochemistry of the early palaeozoic siliciclastic rocks elucidated sediment provenances sandstones of the middle cambrian p ibram jince basin were derived from a cadomian neoproterozoic island arc the source area of the ordovician shallow marine siliciclastics of the successor prague basin is a dissected cadomian orogen late cambrian acid volcanics of the barrandian and cambrian meta granitoids emplaced in the w part of the tepla barrandian cadomian basement are also discernible in these sediments old sedimentary component increased during the ordovician early llandovery siliciclastic rocks show characteristics of an abruptly weakened supply of terrigenous material and an elevated proportion of synsedimentary basic volcanics as a result of silurian transgression emsian siliciclastics intercalated in the late silurian to early devonian limestone suite presumably comprise an addition of coeval basic ultrabasic volcaniclastics middle devonian flysch like siliciclastics indicate reappearance of cadomian source near the barrandian during early variscan convergences of armorican microplates that preceeded accretion of the tepla barrandian unit within the bohemian massif terrane mosaic

petrology and geochemistry of cretaceous sedimentary rocks of the monte soro unit sicily italy constraints on weathering diagenesis and provenance abstract the mineralogy and chemical compositions of shale and sandstone alternations of cretaceous age of the monte soro unit sicily have been determined the clay minerals in the shales are mostly illite and i rich mixed layer i s reflected by enrichment in al2o3 k2o and chemically similar elements the sandstones are subarkose to quartz arenite the shales and sandstones have upper crustal rare earth element patterns and except for k2o they are depleted in alkaline and alkaline earth elements as a result of intense weathering the sandstone and shale mineralogy suggests a diagenetic history in which the sediments were subjected to temperatures in excess of 100 c during which interaction between some minerals in the shales and sandstones took place thus diagenetic quartz cementation and feldspar alteration in the sandstones and smectite illitization in the shales occurred together with the shales being a sink for potassium and the sandstones a sink for silicon negative europium anomalies bet

quantitative provenance analysis of sediments review and outlook provenance analysis of sediments is aimed at reconstructing the parent rock assemblages of sediments and the climaticphysiographic conditions under which sediments formed inferring sediment provenance from the final product a basin fill is anything but straightforward because the detrital spectrum evolves as the sediment is transported along the pathway from source to basin successful provenance analysis requires that the nature and extent of compositional and textural modifications to the detrital spectrum be recognised if not quantified the history of quantification in sediment provenance studies is summarised and illustrated by tracking two fundamental ideas the concept of the sediment petrological province or petrofacies and the relation between sandstone composition and plate tectonic environment progress in sedimentary provenance analysis has been closely linked with advancements in measurement technology a brief survey of modern data acquisition tools illustrates the possibilities and limitations of modern provenance research an operational definition of quantitative provenance analysis qpa is presented in which the central role of mass balance is acknowledged extension of this definition to include quantitative predictions obtained by forward modelling computer simulation of sediment production as well as methodological improvements in data acquisition and processing is needed to cover likely future developments in qpa the contributions to the special issue quantitative provenance analysis of sediments illustrate the intrinsic multidisciplinarity and rapid expansion of qpa d 2004 elsevier b v all rights reserved

boron isotopic compositions of brine sediments and source water in da qaidam lake qinghai china abstract the isotopic compositions of boron in da qaidam lake quinghai have been determined by using the technique of thermal ionization mass spectrometry of cesium tetraborate the brines are enriched in 11b with an average 11b of 5 49 2 34 compared with those of lake sediments and boron minerals produced by the lake the apparent isotopic fractionation factors between brine and lake sediments as well as boron minerals are 0 988 0 001 and 0 986 0 001 respectively source water 11b values range from 11 72 to 16 69 depending on their origin

geochemical evaluation of the late paleocene and early eocene shales in siri canyon danish norwegian basin abstract late palaeocene to early eocene shales are widely distributed in siri canyon located in the danish norwegian basin geochemical study on the late paleocene early eocene shales has revealed a common provenance of intermediate rocks and the rogaland anorthosite complex located in the southwestern norway is supposed to provide the source materials the litho components of late paleocene shales were exposed to intermediate strong weathering and a decrease of weathering degree that probably accompanied with a shift to less oxic depositional environment was observed for the lower eocene shales the change could be related to continental rift that associated with the opening of north atlantic rifting zone at 56 ma spatially there is little elemental variability among the shales from different oil fields except distinct lower na contents in shales from the cecilie field the transformation of smectite to illite at greater deepth in cecilie filed may release more na which acts as an interlayer cation in the smectite

boron concentration and isotopic composition of halite from experiments and salt lakes in the qaidam basin abstract the concentration and isotopic abundance of boron in salt can be used to trace paleosalinities and depositional environments for marine and non marine evaporites however the mechanism of incorporating boron into halite during evaporation of salt lake brines is subject to dispute and there have been few studies of boron concentrations and isotopic compositions during this process due to the low boron concentration in halite a group of evaporation experiments from artificial solutions and salt lake brines have been analyzed in this study the results of boron concentration and isotopic analyses demonstrate that the boron in halite comes mainly from fluid inclusions with a lesser amount from coprecipitation the isotopic fractionation factors between the brine and halite are from 0 9857 to 1 0000 for the evaporation experiments and 0 9945 to 1 0009 for natural samples from the salt lake the 11b values of halite from the qaidam basin salt lakes vary from 4 7 to 25 8 compared to 4 7 to 31 4 in the salt lake brines these values are controlled by the boron isotopic composition of the boron sources ph values and na ca ratios in the salt lake brines the variation of boron isotopes in halite may be used to trace the hydrochemical evolution and paleoevaporation environment in salt lakes

early paleozoic or early middle triassic collision between the south china and indochina blocks the controversy resolved structural insights from the kon tum massif central vietnam abstract in central vietnam the kontum massif is subdivided from north to south into i kham duc ii ngoc linh iii kan nack complexes the kham duc complex consists of metapelite metapsammite paragneiss metagabbro amphibolite serpentinized ultramafic and orthogneiss blocks the southern part of this complex experienced an early paleozoic crustal melting event responsible for migmatites and anatectic granites the ngoc linh complex the largest one is formed by metatexite and granitoid enclosing blocks of eclogite high pressure hp granulite orthogneiss metagabbro amphibolite granodiorite and migmatite the kan nack complex is formed by migmatites with ultra high temperature u ht granulite charnockites and enderbites the three metamorphic complexes are intruded by per aluminous granite and subordinate mafic plutons in spite of local variations the foliation of the ngoc linh complex defines a bulk domal structure and the stretching lineation consistently trends nw se the nw se lineation is also observed in the tectonically overlying the kan nack complex the ngoc linh and kan nack complexes are interpreted here as parts of a metamorphic core complex mcc or ngoc linh mcc exhumed by a top to the nw detachment fault along the northern margin of the ngoc linh mcc upright folds with e w striking axes and e w stretching lineation deform the foliation these structures are developed in a transpressive regime coeval with the activity of plurikilometer scale dextral strike slip faults zircon and monazite u pb radiometric datings document a 250 240 ma age for the crustal melting and the top to the nw ductile shearing coeval with the formation of the ngoc linh mcc this extensional tectonics is followed by a dextral strike slip faulting at ca 240 230 ma before the emplacement of the two mica granitic plutons at ca 240 224 ma furthermore in the ngoc linh and kan nack complexes zircon and monazite yield u pb early paleozoic ages in the kham duc complex a ca 460 ma mp mt garnet biotite staurolite kyanite metamorphism followed by migmatites at ca 450 ma is also recognized the 420 400 ma age of the dai loc plutonic suite and the 450 425 ma age of the dien binh calc alkaline granodiorite document an early paleozoic event the early paleozoic mafic and ultramafic masses of the hiep duc complex are ophiolites included into a metasedimentary matrix thus the kham duc complex is interpreted as a tectonic melange formed during a collisional orogeny that subsequently underwent crustal melting giving rise to the migmatites a part of the early paleozoic rocks are enclosed as xenoliths in the triassic migmatite of the ngoc linh mcc these petrologic structural and chronological features allow us to propose the following geodynamic evolution for the kontum massif during the early paleozoic a continental collision which was accommodated by a north directed subduction of a southern block s vietnam or viet cambodia block below a northern block n vietnam or viet lao block occurred along the tam ky phuoc son suture during the early triassic at ca 250 245 ma the s vietnam block experienced a crustal melting giving rise to the ngoc linh mcc that reworked the early paleozoic orogen lastly during the middle triassic the dextral faulting superimposed upon the ngoc linh migmatite the geodynamic significance of the kontum massif is discussed in the general framework of indochina south china relationships the early paleozoic collision in vietnam is viewed as the driving force responsible for the development of the intracontinental orogeny of s china in order to account for the important heat flow required for the formation of uht metamorphic rocks a possible interaction between the scb indochina collision and the emeishan mantle plume is proposed

weathering and sediment generation in the archean an integrated study of the evolution of siliciclastic sedimentary rocks of the 3 2ga moodies group barberton greenstone belt south africa abstract alluvial and braided fluvial deposits of the 3 2 ga moodies group in the barberton greenstone belt south africa are analyzed petrographically and geochemically to identify their source rocks provenance and assess the degree and type s of weathering required to produce the observed moodies sediment compositions conglomerate sandstone and shale data give somewhat differing pictures of provenance and weathering due to derivation from different components within the source terrane and size and compositional fractionation during transport the results suggest that shale geochemistry provides the most accurate estimate provenance although both rare earth element and trace element th sc zr cr and ti data must be used in combination to give the best results the source area for moodies group sediments was dominated by tonalite felsic volcanic rock komatiite basalt and granite based on mineralogical and major element divergence from estimated source area composition the moodies group sediments are remnants of an aggressive weathering environment labile materials such as komatiite basalt and coarse plagioclase grains decomposed almost entirely to clays and solutes and the chemical index of alteration for moodies shale is well above the global average an aggressive weathering environment in the archean may have been achieved by increased rainfall higher temperatures and or higher atmospheric p c o 2 more likely a combination of these conditions worked to offset the inhibitory weathering effects of a plant free environment

the south china block indochina collision where when and how this study uses new field observations and existing studies to shed new light on the origin and significance of two nw se striking orogens in nw and ne vietnam we conclude that the architecture of each belt is a stack of ne directed nappes formed either under deep ductile synmetamorphic conditions or under shallow depth in the sw and ne parts respectively the song ma zone and song chay ophiolitic melange represent two ophiolitic sutures however the late permian song da and babu mafic rocks are not ophiolites but intraplate basalts related to the emeishan plume a late triassic unconformity the 225 205 ma postorogenic plutonism and the 250 230 ma syntectonic metamorphism support an early to middle triassic age for these tectonic events both nw and ne belts are due to sw directed subduction with arc magmatism ocean closure and continental collision though two contemporary s dipping subduction zones might explain the structural evolution of the two belts a single convergent system offset by the tertiary red river fault is preferred as this s directed subduction better accounts for the late permian intraplate magmatism this scenario is discussed in the general geodynamic framework of se asia

redox stratification of an ancient lake in gale crater mars introduction the primary goal of nasa s curiosity rover mission is to explore and quantitatively assess a local region on mars surface as a potential habitat for past or present life a necessary component of that assessment involves an investigation of the surface chemical conditions and paleoclimate of ancient mars gale crater was selected as the landing site for curiosity it hosts a 5 km tall mountain of layered sedimentary rock the rocks of mount sharp preserve a long duration record of martian environmental conditions geological reconstructions from curiosity rover data have revealed an ancient habitable lake environment that was sustained for tens of thousands to tens of millions of years by rivers draining into the crater rationale we seek to constrain the chemical environment within the lake in gale crater as well as short and long term climate variations in and around gale crater we focus on fine grained sedimentary rocks that carry information about sediment provenance the environment of deposition the conversion of sediment to rock during burial i e lithification and the chemical conditions of later modification i e diagenesis these were investigated during the first 1300 martian solar days sols of rover operations in gale crater using bulk geochemical and mineralogical analysis techniques combined with high resolution color imagery at a variety of scales results two mudstone units have been recognized both deposited in lakes the sheepbed member of the yellowknife bay formation an older set of strata defining the base of the stratigraphic section and the murray formation of relatively younger age and positioned higher in the stratigraphic section the chemical index of alteration cia paleoclimate proxy increases by up to 10 to 20 cia units expressed in from the sheepbed member to the murray formation on the basis of mineralogy geochemistry textural properties and stratigraphic relationships the murray formation can be subdivided into two sedimentary associations or facies the hematite phyllosilicate hp facies and the magnetite silica ms facies the hp facies is characterized by abundant fe 3 oxides accompanied by phyllosilicates as well as indications of mn oxidation and trace metal concentration these properties are consistent with deposition in an oxidizing environment the ms facies is recognized by a near complete absence of pure fe 3 minerals and high concentrations of silica accompanied by magnetite consistent with deposition in an anoxic environment both facies were affected by a saline overprint after burial and lithification conclusion the observed variations in cia are consistent with modest short term fluctuations in the ancient climate between cold dry conditions and relatively warmer wetter conditions these changes occurred during the deposition of lake bed mudstones in an environment that was conducive to the presence of a long lived lake in gale crater we propose that the distinct properties of the two murray facies were developed as a result of i fractionation of river borne detritus into coarser denser materials in shallow water close to shore and finer lower density materials offshore in deeper water as a result of deceleration of river flow as it entered the lake and ii redox stratification of the lake water body caused by depth dependent variations in the concentration of atmospheric oxidants and dissolved groundwater derived solutes resulting in oxidizing conditions in shallow water and anoxia in deeper water the addition of saline minerals during a later phase of brine migration through the section records longer term changes in martian climate at gale crater perhaps driven by global atmospheric escape processes the recognition of redox stratification in the lake in gale crater adds new detail to our understanding of ancient martian aquatic environments previously reported detections of organic carbon compounds nitrogen phosphate minerals and fe and s minerals in a variety of redox states combined with the evidence presented here for relatively stable climate conditions and gradients in fluid oxidation state provide compelling evidence that all of the physical chemical and energetic conditions necessary to establish a habitable environment were present on mars between 3 8 billion and 3 1 billion years ago

evaporite minerals and geochemistry of the upper 400 m sediments in a core from the western qaidam basin tibet qaidam basin is a tectonically controlled depression on the northern margin of the tibetan plateau in 2008 a long core was drilled in the qahansilatu sub basin in the western qaidam basin the sediment layers in the upper 400 m alternate between evaporite mineral layers and carbonaceous clay layers the detailed mineralogical investigation focused on evaporite minerals including halite gypsum mirabilite thenardite glauberite eugsterite and bloedite gypsum and halite make up the majority of the evaporate minerals environmentally induced variations in the mineralogy and crystal habit of the sulfates have been extensively investigated gypsum has prismatic and pyramid habits such as disc pyramid stubby prismatic slender prismatic visible isolated gypsum and aggregates rosette radial and twins are mostly scattered in carbonaceous clay layers suggesting that secondary gypsum is well developed gypsum may be a precursor mineral of glauberite and thenardite is the precursor of bloedite as a metastable and rare mineral eugsterite does not appear in other tibetan areas it forms at the expense of pre existing gypsum or thenardite in the core at an experimental temperature of higher than room temperature the presence of eugsterite indicates a warm and or hot climate at its deposition time

modal and geochemical compositions of the lower silurian clastic rocks in north qilian nw china implications for provenance chemical weathering and tectonic setting abstract the north qilian orogenic belt records the transition from ordovician marine back arc basin to early devonian terrestrial molasse basin as the central qilian block was sutured to the north china craton the detrital framework and geochemical composition of lower silurian sedimentary rocks within the north qilian belt record the provenance tectonic setting and a variety of sedimentary processes that operated during transport from source to sink the petrological and geochemical characteristics of sandstones siltstones and shales in the western segment of the north qilian belt indicate a generally low degree of chemical weathering of source area s and limited sorting prior to deposition these characteristics suggest an active tectonic setting in contrast samples studied from the eastern part of the north qilian belt indicate low to moderate chemical weathering and low to moderate hydraulic sorting such characteristics imply a more stable tectonic setting geochemical data including eu eu ti nb th sc and co th ratios suggest contrasting source regions for the western and eastern segments of the north qilian belt sources in the west included basement rocks of the central qilian block and the north china craton in addition western sources may have included mafic rocks located within the north qilian arc in contrast data derived from eastern samples suggest a felsic provenance that probably formed part of the basement complex in the central qilian block and the north china craton overall detrital and geochemical data combined with the regional geology suggest a foreland basin setting that formed during collision of the central qilian block with the north china craton

from static to dynamic provenance analysis sedimentary petrology upgraded abstract the classical approach to sandstone petrology established in the golden years of plate tectonics and based on the axiom that detrital modes of sandstone suites primarily reflect the different tectonic settings of provenance terranes has represented a benchmark for decades the composition of sand and sandstone however simply provides us with a distorted image of the lithological structure of source terranes and gives us little clue whether they are allochthonous or autochthonous orogenic or anorogenic young or old what we may able to see reflected in detrital modes is the nature of source terranes continental arc oceanic and the tectonostratigraphic level reached by erosion in space and time the proposed new approach to the petrology of sand and sandstone 1 starts with a simple classification scheme circulated since the 1960s which is purely descriptive objective and free of ill defined ambiguous terms and 2 focuses on the nature and tectonostratigraphic level of source terranes further steps are essential to upgrade provenance analysis acquiring knowledge from modern settings is needed to properly identify and wherever possible correct for physical and chemical processes introducing environmental and diagenetic bias and thus address nature s complexities with adequate conceptual tools equally important is the integration of multiple techniques ideally including bulk sediment multi mineral and single mineral methods bulk sediment petrography remains the fundamental approach that allows us to capture the most precious source of direct provenance information represented by the mineralogy and texture of rock fragments bulk sediment geochemistry applicable also to silt and clay carried in suspension is a superior method to check for hydraulic sorting chemical weathering and fertility of detrital minerals in different sediment sources detrital geochronology thermochronology and isotope geochemistry reveal the diverse time structures of source rocks and have become necessary complementary techniques in modern provenance analysis inferences on geodynamic processes need independent geological information and come last but if tackled properly they can lead us much farther than the standard label obtained by using triangular diagrams uncritically as if they were infallible oracles

devonian fish placodermi antiarcha from tra ban island bai tu long bay quang ninh province vietnam and the question of the age of the do son formation abstract remains of an asterolepis like antiarchan placoderm fish are reported from the top part of the sandstone series of the tra ban island quang ninh province vietnam which are referred to the do son formation this sandstone series is overlain by the well dated late givetian frasnian trang kenh formation which constrains the top part of the do son formation to the middle devonian and most probably the givetian as suggested by the presence of a large asterolepis like antiarch this would agree with the fish and plant assemblage previously recorded from the upper part of the do son formation at do son the question of the age of the base of the do son formation is raised by the discovery of late silurian or early lochkovian plant arthropod and fish remains at do son the do son formation now appears to be composed of two members late silurian or early lochkovian and givetian in age respectively recent field observations suggest that the two members are separated by an unconformity the meaning of the devonian terrigenous deposits in the eastern part of vietnam and south china is briefly discussed

heterogeneities and interconnections in groundwaters coupled b li and stable isotope variations in a large aquifer system eocene sand aquifer southwestern france abstract the study of stable isotope of the water molecule and elemental data for groundwater in the large eocene sand aquifer system of sw france showed that the 18 o values of groundwater fall in the range 5 6 to 10 6 vs smow with 2 h values varying between and 34 3 to 72 3 vs smow there is no relationship between 18 o and 2 h values and the salinity but the stable isotopes data plot on or near the global meteoric water line taken as a whole the enriched samples clearly correlate with present day recharge while the most depleted samples reflect an old recharge groundwaters in the present study display large ranges of both boron concentrations 7 to 2550 g l 1 and boron isotopic compositions the lowest 11 b value being close to 18 0 and the highest one near 36 2 the scatter of b concentrations and 11 b values reflects the different rock types contributing to the supply of dissolved boron carbonates evaporites and silicates as well as an input from rainwater and fractionation during water rock interaction with clay minerals lithium concentrations in groundwater also span a wide range 0 6 to 253 g l 1 as do the lithium isotopic signatures that range between 6 5 and 28 6 we can evidence there that the b isotopic compositions are controlled by water rock interactions while li and 7 li variations are also controlled by water rock interaction processes dissolution and formation of alteration minerals that can occur at different temperatures within the groundwater system

fish suggests continental connections between the indochina and south china blocks in middle devonian time a yunnanolepiform antiarch placoderm fish is recorded from the givetian dong tho formation of quang binh province central vietnam this and other fishes from the same locality occur in marginal marine detrital facies with plant remains and lingulid brachiopods that indicate a nearshore to deltaic environment yunnanolepiform antiarchs were hitherto known exclusively from the lower devonian of the south china block the new occurrence of this group well south of the song ma suture suggests close links between the indochina and south china blocks in middle devonian time the massive sandstone exposures of the dong tho formation may be a southern extension of the do son sandstone formation of the hai phong area which is located on the south china block

the major composition of a middle late eocene salt lake in the yunying depression of jianghan basin of middle china based on analyses of fluid inclusions in halite abstract during the cretaceous tertiary transition in eastern china abundant halites formed in non marine areas many continental salt deposits from inland salt lakes were formed in eastern china in faulted basins as a result of the northward movement and collision of the indo china plate with the eurasian plate including the bohai gulf basin however a marine transgression versus a non marine origin of these evaporites remains to be determined primary fluid inclusions trapped in halite deposits can directly record the composition of evaporated seawater or salt lake water such as those in the cretaceous halite in the khorat plateau laos and thailand area can resolve the origins of the evaporate deposits recent fluid inclusions data in the khorat plateau coincide with the predicted secular variation of seawater and are comparable to other fluid inclusions in cretaceous marine halite indicating these fluid inclusions are directly related to a marine transgression our analyses in this study shows that the average k mg2 and so 4 2 contents are 8 8 5 0 and 6 8 g l respectively in the primary fluid inclusions in halite of middle late eocene from the yunying depression of china these numbers are much less than those in the contemporary spanish primary fluid inclusions in halite precipitated from seawater 16 4 36 3 and 12 5 g l for k mg2 and so 4 2 respectively furthermore br contents of all fluid inclusion samples in halite from the yunying depression are lower than 2 ppm vs 55 58 ppm at the base of spanish contemporary marine halite and their 37cl values range from 0 11 to 2 94 vs 0 09 to 0 24 in sylvite of spanish deposit indicating that the compositions of the middle late eocene brines trapped in halite in the yunying depression of china are very different from those derived from the contemporary seawater and are considered to be resulted from evaporation of an inland saline lake water with little influence of seawater

the influence of sediment recycling and basement composition on evolution of mudrock chemistry in the southwestern united states this paper reports systematic changes in mudrock composition through time on a single con tinental cmstal block the changes reflect both sediment recycling processes and changes through time in the composition of crystalline material being added to the sedimentary system and are related to tectonic evolution as the block matures from a series of accreted arc terranes to a stable craton the major and trace element distributions reflect different aspects of the provenance of the mudrocks in this study major elements record sediment recycling processes as well as changing proportions of sedi mentary and first cycle source rocks with the exceptions of kzo which tends to increase and sioz and a o3 which show no trend most major oxides tend to decline in relative abundance in younger mud rocks patterns shown by the index of compositional variability fe03 kro naao cao mgo mno tiojialro and by k20 a1203 indicate that the major oxide trends are due to decreasing proportions of nonclay silicate minerals and a concomitant increase in the proportion of clay minerals probably due to decreasing input of first cycle detritus coupled with recycling of sedimentary material excursions from progressive trends marked by increases in mgo k20 and cao reflect episodes of large scale input of nonclay first cycle minerals from crystalline source rocks due to large scale basement uplift the chemistry of low solubility trace elements in contrast is not sensitive to recycling effects and reflects the composition of first cycle input incompatible elements are progressively enriched relative to compatible elements in younger mudrocks and values for chondrite normalised rare earth elements also increase in addition the eu anomaly becomes systematically more negative in younger samples these trends cmnot be explained by diagenetic or weathering processes and therefore indicate that the proportion of fnc tionated granitic first cycle detritus being added to the sedimentary system becomes greater with time these results confirm the importance of tectonic setting in controlling mudrock chemistry and also demonstrate that there is a dynamic relationship between the tectonic evolution of a continental block and the composition of its sedimentary mantle

stages of late paleozoic to early mesozoic magmatism in the song ma belt nw vietnam evidence from zircon u pb geochronology and hf isotope composition the song ma zone in nw vietnam bears important tectonic implications as a potential subduction corridor between the indochina and south china blocks on the basis of u pb ages the hf isotopic characteristics of zircons and the geochemical composition of granitoids a two stage magmatic evolution process of the song ma zone at 290 260 and 245 230 ma can be proposed isotopic analyses indicate magmatic contributions from neoproterozoic oceanic island basalt proterozoic continental crust and depleted mantle or juvenile lithosphere by combining geochronological and geochemical data from the granitoid rocks we suggest that the staged magmatic processes of song ma zone may be related to a long lasting period of ocean subduction ca 290 260 ma and subsequent syn post collisional evolution ca 245 230 ma

boron isotopic composition of marine and nonmarine evaporite borates abstract here we present the results of the boron isotopic analysis of borates from some well known marine and nonmarine evaporite deposits combining new analyses with analyses from the literature yields a mean 11 b value for nine marine evaporite borate analyses of 25 4 permil 11 b 10 b 4 15 0 02 and a mean for twenty five nonmarine evaporite borates of 7 10 permil 11 b 10 b 4 02 0 04 previous studies have shown that the boron isotopic composition of seawater 11 b 40 permil 11 b 10 b 4 20 is about four percent heavier than the boron isotopic composition of most crustal rocks and minerals we suggest that our results for marine and nonmarine evaporite borates reflect this difference thus it should be possible to use boron isotopic composition as a tracer for boron of marine evaporitic origin applications include borate bearing evaporite deposits and perhaps borate and or borosilicate bearing metamorphic rocks

provenance of silt and clay within sandy deposits of the lithuanian coastal zone baltic sea abstract mineralogical analysis of the silt and clay fraction of sandy deposits of 37 surface samples and grain size data are used to interpret sediment sources acting in the se baltic sea along the lithuanian coast mineralogical composition was determined using x ray diffraction xrd methods grain size distribution was obtained by standard dry sieving and pipette techniques for identification of sources we combined known compositional information of possible sources with logical models for mineral combinations related to regional geological provinces and processes supported by results of correlation and factor principal component analyses between minerals grain size parameters and bathymetric features of the area the main sources supplying sediment into the area are 1 the sambian peninsula to the south 2 the nemunas river whose discharge passes through the curonian lagoon and 3 late pleistocene till erosion on the sea floor in the north and at the olando kepure shore cliffs the general pattern of spatial distribution related to the identified sources for the fine grained sediment fraction is interpreted as a shore parallel transport of suspended matter flowing northwards in the southeastern part of the baltic sea

diagenetic origin of quartz silt in mudstones and implications for silica cycling mudstone the most abundant sedimentary rock type1 composed primarily of clay or silt sized particles contains most of the quartz found in sedimentary rocks2 these quartz grains which are chemically and mechanically resistant and therefore preserve their characteristics well have long been considered to be derived from the continental crust1 here we analyse quartz silt from black shales in the eastern usa dating back to the late devonian period about 370 million years ago using backscattered electron and cathodoluminescence imaging and measure oxygen isotopes with an ion probe our results indicate that up to 100 of the quartz silt in our samples does not originate from the continental crust instead it appears to have precipitated early in diagenesis in algal cysts and other pore spaces3 with silica derived from the dissolution of opaline skeletons of planktonic organisms such as radiolaria and diatoms transformation of early diatoms into in situ quartz silt might explain the time gap between the earliest fossil occurrences of diatoms about 120 myr ago4 and molecular evidence for a much earlier appearance between 266 or even 500 myr ago5 6 moreover if many other mudstone successions show similarly high proportions of in situ precipitated rather than detrital quartz silt the sedimentary record in mudstones may have been misinterpreted in the past with consequences for our estimates of palaeoproductivity as well as our perceptions of the dynamics and magnitude of global biogeochemical cycling of silica

quantitative provenance of silt and clay within sandy deposits of the lithuanian coastal zone baltic sea abstract a quantitative provenance approach is developed and in this study applied for the silt and clay fractions of sandy coastal deposits mineralogical composition of 37 surface samples was determined by x ray diffraction xrd grain size distributions were obtained by standard dry sieving and pipette techniques the characterization of mineralogical provenance is based upon known compositional information of possible sources logical models for mineral combinations related to regional geological provinces and processes and geographical features of the documented mineral distribution in the area of investigation these interpretations are further supported by results of correlation and principal component analyses of mineral varieties grain size parameters and bathymetric features of the area partitioning of source contributions specific for each site of deposition is derived by solving simultaneous equations then the quantified mineral composition at the initial source is reconstructed in the se baltic sea along the lithuanian coast exemplifying this new methodology for quantification of sediment sources the main sources supplying sediment to the area are 1 sambian peninsula to the south erosion of pleistocene till and blue earth paleogene sediments supplying 33 of fine grained sediment on average 2 nemunas river the discharge of which passes through curonian lagoon and supplies an average 17 of the coastal fine sediments and 3 pleistocene till eroded on the sea floor in the north and at the olando kepur shore cliff and contributing an average of 50 of the sediment although we use the mineralogy within the environmentally important fine grained fraction this mathematically simple approach could be used with any other parameters characterizing the identified sources a quantification of the separate source contributions to each individual site of accumulation studied using the stable mineralogical components of the sediment archive offers a time integrated net effect reflection of the combined processes of an entire environmental system

geochronology and geochemistry of the paleoproterozoic yinyugou group in the southern north china craton implications for provenance and tectonic evolution abstract the paleoproterozoic yinyugou group in the southern north china craton is a littoral facies sedimentary sequence which is mainly composed of feldspar quartzites and mica schists with minor carbonate rocks u pb isotopic dating of detrital zircons bracket the depositional age of the yinyugou group at 2 43 2 30 ga chemical index of alteration cia values of most feldspar quartzite and schist samples are lower than 75 indicating generally weak to moderate source weathering conditions for the yinyugou rocks the majority of the studied yinyugou samples give a large range of index of compositional variability icv values of 0 93 2 59 revealing a chemically immature source which deposited in an active continental margin setting chondrite normalized ree patterns and discrimination diagrams involving la th hf co and sc reveal that the yinyugou group dominantly received detritus from felsic sources with minor contribution from mafic igneous rocks u pb ages of detrital zircons from the yinyugou group can be divided into two groups 2 90 2 40 ga and 3 50 3 20 ga with a predominant age peak at 2 50 ga the 3 50 3 20 ga detrital zircons have negative ehf t values ranging from 11 2 to 3 8 and old crustal model ages tdmc of 4246 to 3909 ma indicating a mature crustal source most 2 50 ga zircons show sub depleted mantle positive ehf t values and tdmc ages mainly ranging from 3 10 to 2 70 ga representing the time when juvenile materials were extracted from the depleted mantle taking all these data into account the yinyugou group was most likely deposited in a back arc setting in combination with previous studies on other paleoproterozoic volcanic sedimentary sequences and magmatic rocks in the ncc a cycle of subduction collision extension rift subduction processes is proposed to explain the tectonic evolution of the ncc during paleoproterozoic

llandovery lower silurian graptolites from the sepon mine truong son terrane central laos and their palaeogeographical significance abstract graptolites are described from the llandovery of the sepon mine area central laos part of the truong son terrane the palaeobiogeographical affinities of the rhuddanian graptolites are with peri gondwanan europe and arabia rather than equatorial regions such as south china and laurentia arctic canada a review of previous palaeontological research on the middle palaeozoic of the indochina terranes reveals an often contradictory picture with vertebrates suggesting close proximity of south china to the truong son terrane in the devonian and invertebrates and radiolarians providing evidence for a palaeogeographical barrier between the two graptolites from the mojiang area yunnan are typical of low latitude silurian faunas and suggest that this area simao or loei terrane was separate from the truong son terrane

boron isotopic compositions of corals seawater or diagenesis record abstract the first analyses of modern and fossil corals calcite free using a positive ion cs2bo2 tims technique and a chemical procedure for b extraction are reported the 11b for modern corals fluctuates between 23 3 and 25 5 the range of variation of fossil corals from the last interglacial period is greater from 23 5 to 27 3 and the lowest 11b corresponds to the corals close to last glacial maximum boron concentrations show a variation from 49 to 58 ppm in the recent corals and from 39 to 52 ppm in ancient corals for the ancient corals linear correlations are observed in both 11b vs b concentration and 11b vs 1 b plots but these correlations are not observed for modern corals two interpretations are presented to account for these observations and to test the potential of 11b for reconstructing paleo ocean ph the first interpretation assumes a thermodynamic partitioning of b between seawater and carbonates and shows that both boron isotopic compositions and concentrations can be used to calculate the ph of seawater in which corals grow for our data such a model requires that both the ph and the co2 of the deglacial ocean was lower than present day values the second interpretation is based on the correlation observed for ancient corals between boron isotopic compositions and 1 b we suggest that the measured boron isotopic compositions of ancient corals are caused by the mixing of a primary aragonite the coral skeleton and secondary aragonite precipitated from 10b enriched reef pore fluids the characteristics 11b and b concentrations of the diagenetic aragonite and the fluids from which it precipitates can be constrained if this proves correct only the non recrystallised parts of ancient corals can be used for paleo ph reconstructions these recrystallisation processes did not affect the 234u 238u ratios of the corals

mineralogical and chemical changes of soil and stream sediment formed by intense weathering of the danburg granite georgia u s a abstract a series of soil and stream sediments developed during intense weathering on the metaluminous danburg granite northeastern georgia u s a have been analyzed mineralogically and chemically the concentrations of ba na rb and cs in the silt and coarser fractions are controlled mainly by feldspars and biotite hf is controlled by zircon and the ree rare earth elements and th are largely controlled by sphene variations in feldspar sphene and zircon may produce small variations in eu sm and la lu ratios ferromagnesian minerals control ta fe co sc and cr concentrations the mineralogical and chemical composition of the danburg granite is more closely reflected in the silt than in the sand or gravel fractions of stream sediments in the silt the contents of rb ree th ta fe co and sc and the ratios of la sc th sc la co th co eu sm and la lu are similar to those in the unweathered granite in contrast these element contents or ratios in the sands and gravels are 0 05 3 the concentration in the unweathered granite ta and ba contents are an exception to the above the ta and ba contents of the sands and gravels are similar to those of the granite in the kaolinite halloysite clays the content of na is depleted relative to the source rb cs ba hf and ta are depleted or enriched in the clays relative to the source while the ree th fe co sc and cr are enriched the eu sm eu anomaly size and la lu ratios and the ree patterns of the clays are similar to those of the source thus the mineralogy and element contents of a siltstone developed from metaluminous granitic sources during intense weathering would be expected to be more similar to the source rock than the sandstones and conglomerates claystones should contain similar ree patterns and eu sm ratios as the source rock but such fine grained sediments might represent much larger areas of source rocks than the more locally derived sandstones or conglomerates

boron isotope geochemistry of salt sediments from the dongtai salt lake in qaidam basin boron budget and sources abstract dongtai salt lake in qaidam basin contains abundant boron and lithium resources and has the highest reserve of lithium found in the world but the origin of these resources is highly controversial in this study we carried out a detailed study on chemical compositions and boron isotope characteristics of salt sediments collected from a drill core in the dongtai salt lake the evaporite carbonate and silicate phases of the sediments show 11 b values of 6 4 to 2 2 17 3 to 0 5 and 14 6 to 2 8 respectively which suggest a non marine origin for the salt lake the variation of 11 b vs k identified the evolution process of the salt lake the geochemical hydrochemical signatures and the reserve estimation of boron resources approved the dominant sources of saline resources containing abundant b k and li from the inflowing nalenggele river the boron isotopic fractionation factors between evaporite and brine i e evaporite brine vary from 0 9869 to 0 9955 and the linear variation of evaporite brine vs li mg molar ratios reflects the boron isotopic fractionation during crystallization of the salts the positive correlation between 11 b and b in the carbonate phase reflects the ph control on the incorporation of boron into the carbonates and the equilibrium isotope fractionation follows the rayleigh isotope fractionation rule in a closed system the variation of 11 b values in the silicate phase behaved as an oscillating pattern and the more negative shift of 11 b values corresponds to the mudstone strata deposited under warm humid climate conditions indicating the influence of intensive weathering

the changning menglian suture zone a segment of the major cathaysian gondwana divide in southeast asia abstract in southwest china the major cathaysian gondwana divide the palaeo tethyan suture is very well delineated by a narrow north south zone of oceanic siliceous sedimentary rocks and dismembered ophiolite complexes including probable remains of reef capped oceanic islands the location of this zone the changning menglian suture is not well appreciated in the english language literature probably because of the failure to recognise the approximately 600 400 km simao terrane which lies to the east of the suture many analyses mistakenly include the simao element in the sibumasu terrane thus placing a terrane of distinct cathaysian affinities on the gondwana side of the major palaeogeographic divide a measure of the size and time span of palaeo tethys is contained in the changning menglian suture zone sedimentary rocks deep marine cherts are dated between early devonian and middle permian and limestones interpreted as caps to seamounts extend the age range of the ocean to late permian these data agree with recent views of cathaysian elements rifting from gondwana in the silurian or devonian followed by a major rifting event on the north gondwana margin early in the permian subduction created an active continental margin on the western edge of the simao terrane throughout much of the triassic and the closure of this branch of palaeo tethys is marked by the cessation of this activity in the early late triassic

geochemical signature of provenance in sand size material in soils and stream sediments near the tobacco root batholith montana u s a abstract trace element geochemistry of sandstones are being used to determine provenance we have conducted preliminary and limited experiments to determine to what extent daughter sands retain the geochemical signature of parent rocks six sets of first order stream sediments soils from adjacent slopes and a variety of parent rocks were collected from southwestern montana u s a sampling in a low relief area ensured that climate and residence time of soils on slopes could be eliminated as variables sand size fractions of stream sediments and soils and the corresponding parent rocks granodiorite quartz monzonite granite gneiss biotite tonalite gneiss and amphibolite were analyzed for most major elements and selected trace elements petrologic modal analysis of the parent rocks and the 0 25 0 50 mm fraction of each sand was done to monitor major mineralogic control if any on chemical compositions of the samples our data show that the abundances of the si and al in sediments do not discriminate provenance abundances of ca mg fe and ti may broadly distinguish between sands derived from metamorphic and igneous source rocks at least in the area studied differences in abundances of the ba and th and the ratio of la lu between granitic tonalitic and amphibolitic parent rocks are preserved in the daughter sediments that we studied however the size of the eu anomaly in the ree patterns of different daughter sediments is not diagnostic of parent rocks abundances of co and sc distinguish between sediments derived from felsic and mafic rocks a better provenance discrimination is obtained if the ratios la sc th sc la co ba sc and ba co are used petrologic modal data show that mineral contents and chemical compositions of parent rocks are compatible with each other the chemical composition of the sands may be roughly correlated to the petrological modal data but the abundances of some minor and trace elements of sediments cannot be inferred from modal mineralogy this is expected because these elements may concentrate in accessory minerals and or may weather out into aqueous or clay mineral fractions it is also compatible with conclusions of previous studies that some of these elements do not reside in sand size fractions of siliciclastic sediments

paleotethyan evolution of the indochina block as deduced from granites in northern laos abstract the paleotethyan evolution of the southeast asia has become better understood in recent years questions remain however over the role of the dien bien phu suture zone in the evolution of the indochina block and whether the song ma suture represents the boundary between the indochina block and the south china block granitoid geochronological and geochemical data obtained in northern laos provide new information vis a vis these arguments zircon u pb ages together with whole rock trace and rare earth element data from 27 granitic rocks from five complexes allow us to conclude that these granites are typical of i type indosinian volcanic arc granites however the 234 256 ma i type granites mismatch the initiation age obtained from the ductile shear zone of the dien bien phu fault thus repudiating the existence of the dien bien phu suture zone this then implies that the qamdo simao and indochina blocks were united the geochemical and geochronological data further suggest that the main crust in the indochina block formed in the late paleoproterozoic to early mesoproterozoic much later than the archean crustal formation age identified east of the song ma suture moreover the 440 404 ma and 234 256 ma i type granites suggest that the boundary between indochina and south china should be the jinsha river suture song ma suture kontum massif instead of the jinsha river suture song chay suture finally the emeishan basalt and granite complexes both form part of the south china tectonic units subducting westward under the qamdo simao and indochina blocks

geochemistry of shales from the paleoproterozoic to neoproterozoic vindhyan supergroup implications on provenance tectonics and paleoweathering abstract major trace and rare earth element ree concentrations were measured for 88 shale samples from the paleoproterozoic to neoproterozoic vindhyan supergroup in central india the major and trace element data of the vindhyan shales are compared with north american shale composite upper crust mid oceanic ridge basalts and many other shale standards of archean proterozoic and phanerozoic age ree concentrations of the vindhyan shales are comparable to the upper continental crust various discriminant diagrams were used to reveal the inferred provenance tectonics and paleoweathering conditions a predominantly granitic source rock is inferred for the lower vindhyan shales whereas partial contribution from basaltic source is evident during deposition of the upper vindhyan shales existing paleocurrent data and the present geochemical investigations together suggest archean paleoproterozoic basement rocks exposed beyond the southern basin margin of the vindhyan outcrops as the possible source rocks the deposition of the vindhyan shales took place in an intracratonic basin where sediments were primarily derived from stable continental areas moderate climatic conditions are inferred during the deposition of the shales the upper vindhyan shales however reflect more intense weathering compared to the lower vindhyan shales which may be attributed to relative tectonic stability and more humid conditions during deposition of upper vindhyan shales

cyclic variations of sulfate and boron concentrations and isotopes in deep groundwaters in the aquitaine basin france abstract concentrations and isotope contents of major and trace elements are principal factors in determining the origin of the chemical composition of groundwater this paper focuses specifically on the use of sulfur and boron isotopes to characterize the origin of cyclic variations in the deep eocene aquifer in the aquitaine sedimentary basin southwest of france it is part of a multi layer system mainly composed of sands and sandstone deposits groundwater contained in this deep reservoir is known to present stable chemical compositions allowing its use for various purposes like drinking water geothermal energy thermal activity and agricultural irrigation however among the dozens of wells exploiting this aquifer and despite the reservoir s substantial depth variations in sulfate concentration have been identified in a limited area of the reservoir these fluctuations are cyclic and they seem to be correlated with water level variations due to gas storage activities nearby in the same aquifer regular water samplings and analyses of major and trace elements and their isotopes have identified that bore concentration variations are correlated with sulfate variations a geochemical modelling approach based on water mixes elucidates the causes of these variations in chemical composition especially the boron and sulfate concentrations and their respective 11b and 34sso4 values from these numerical results we identify that different sources explain the variations of boron concentration one part coming from the silicates alteration present in sub layers of the exploited aquifer and the other part coming from the evaporites alteration present in the underlying molasse unit these results also confirm the existence of mass and potentially water transfers between the different sub layers of the reservoir and with the underlying molasse aquitard implying new constraints for the future hydrogeologic modelling

geological evolution of seawater boron isotopic composition recorded in evaporites the abundance of boron isotopes in ancient marine carbonates can be used to estimate oceanic ph that reflects atmospheric co 2 levels this proxy requires that the boron isotopic composition of seawater at the time the carbonate has formed is known and thus the past changes in seawater chemistry here we report the boron isotopic composition of selected ancient marine halites and modern sea salts the signal interpreted as marine reveals a clear evolution of the boron isotopic composition of seawater to 8 variations over the cenozoic comparison between this reconstructed curve and the mg ca ratio reveals a high level of consistency that will help to better define oceanic geochemical cycles

geochemistry of mansar lake sediments jammu india implication for source area weathering provenance and tectonic setting abstract the sediment geochemistry including ree of surface and core samples from mansar lake along with mineralogical investigations have been carried out in order to understand the provenance source area weathering hydrolic sorting and tectonic setting of the basin the geochemical signatures preserved in these sediments have been exploited as proxies in order to delineate these different parameters the major element log values fe 2 o 3 k 2 o vs sio 2 al 2 o 3 and na 2 o k 2 o vs sio 2 al 2 o 3 demarcate a lithology remarkably similar to that exposed in the catchment area the chondrite normalized ree patterns of lake samples are similar to post archaean australian shale paas with lree enrichment a negative eu anomaly and almost flat hree pattern similar to a felsic and or cratonic sedimentary source however the la th sc plot of samples fall in a mixed sedimentary domain close to upper continental crust ucc and paas suggesting sedimentary source rocks for the mansar detritus it also indicates that these elements remained immobile during weathering and transportation the mineralogical characteristic rees and high field strength elements hfse together with the high percentage of metamorphic rock fragments in the siwalik sandstone support a metamorphic source for lower siwalik sediments a very weak positive correlation between zr and sio 2 poor negative correlation with al 2 o 3 negative correlation of la yb n and gd yb n ratios with sio 2 and positive correlation with al 2 o 3 suggest that zr does not dominantly control the ree distribution in mansar sediments the petrographic character and textural immaturity indicate a short distance transport for the detritus the distribution of elements in core samples reflect fractionation the higher zr th and zr yb ratios in coarse sediments and paas compared to finer grained detritus indicate sedimentary sorting plots of the geochemical data on tectonic discrimination diagrams suggest that the sediments derived from the lower siwalik were originated within a cratonic interior and later deposited along a passive margin basinal setting it therefore reveals lower siwalik depositional history

rare earth element geochemistry of australian paleozoic graywackes and mudrocks provenance and tectonic control abstract in the paleozoic graywackes of eastern australia there is an increase in the total abundance of rare earth elements ree a light to heavy ree ratio and a decrease in the chondrite normalized eu anomaly with the increase in sio2 al2o3 and k2o na2o ratios this is due to the change in the dominant source rocks from andesite to dacite to granite gneiss and sedimentary rocks similarly an increase in total ree and a decrease in eu anomaly is also seen in the associated mudrocks with the increase in total clay content this correlation in paleozoic sedimentary rocks suggests that the ree characteristics of terrigenous sedimentary rocks reflect the depositional tectonic setting of the basin the oceanic island arc type graywackes are characterised by their lower total ree abundance only slight enrichment of lree over hree and the absence of a negative eu anomaly on chondrite normalised plots the continental island arc type graywackes are discriminated by their higher ree abundance and la yb ratio the presence of a small negative eu anomaly on the chondrite normalised plots and the significant enrichment of eu compared to paas post archean average australian shale the sedimentary rocks deposited on andean type active continental margins passive margins platform and cratonic basins are all characterised by the high enrichment of lree over hree and the presence of a pronounced negative eu anomaly on chondrite normalised plots and can not be discriminated from each other by ree patterns alone

boron isotope geochemistry of australian salt lakes boron isotope geochemistry has been investigated in brines groundwaters and sediments from the modern australian salt lakes of victoria south australia and western australia by applying negative thermal ionization mass spectrometry techniques the geochemical history of the brines has been reconstructed by using 11b bcl and nacl ratios the victorian volcanic crater lakes of southeastern australia have water salinities of up to 60 g l molar nacl ratios 0 87 similar to the marine ratio molar bcl ratios of 2 9 10 4 to 4 9 10 4 and 11b values of 54 to 59 relative to nbs 951 the depletion of total b and the high positive 11b values relative to seawater bclratio 7 9 10 4 11b 39 are attributed to a marine cyclic salt origin together with adsorption processes in closed systems with low water sediment wr ratios in contrast salt lakes from south australia and western australia which are large shallow playas associated with halite gypsum and detrital clay minerals have interstitial and surface brines characterized by salinities of 80 to 280 g l molar nacl ratios of 0 85 to 1 molar bcl ratios of 4 10 6 to 4 10 4 and 11 values of 25 to 48 the 11 values of these brines are different from those of groundwaters from the great artesian basin 11 15 9 to 2 2 with high molar bcl ratios of 1 10 3 to 3 8 10 2 country rocks 11b 8 7 to 6 8 and modern detrital sediments present in these salt lakes 11b 3 2 to 12 3 the 11b values of these salt lakes overlap with those of surface and brackish waters 11b 28 to 35 and with the b isotopic composition of seawater 11b 39 both low molar nacl ratios 39 of some brines indicate interaction of the brines with detrital sediments within the salt lake systems 11 values 39 suggest mixing of brines of marine origin from which b was partly removed by adsorption with waters of terrestrial origin with low 11 values nacl ratios are used as indicators of the origin of the salts as well as of halite dissolution precipitation the 11 values and bcl ratios are sensitive to a marine or non marine origin adsorption of boron onto clays and the effective water sediment ratio at low wr ratios the preferential removal of 10b from the solution affects the bulk solution whereas at high wr ratios the 11 value of a solution is not affected by adsorption although the 11 value of borate minerals may be a discriminant of marine or non marine origin boron isotopes are less distinctive in evaporative environments where boron is not an abundant component and where water sediment interaction occurs

rare earth elements in the sedimentary cycle a pilot study of the first leg the effects of source rock composition and climate on the natural abundances of rare elements ree in the first leg of the sedimentary cycle are evaluated using a study with holocene fluvia sands the medium grained sand fraction of samples collected from first order streams exclusively draining granitic plutons in montana semi arid georgia humid and south carolina humid are analyzed it is found that the ree distribution patterns but not the total absolute abundances of the daughter sands are very similar despite compositional differences between parent plutons averages of the three areas are determined to have a la lu ratio of about 103 showing a depletion of heavy ree with respect to an average granite la lu 79 or the composition of north american shales la lu 55 however the eu sm ratio in sands from these areas is about 0 22 which is very close to this ratio in north american shales 0 21 although the overall ree distribution of these sands is not similar to that of the north american shales in any way it is concluded that the major rock type but neither its minor subdivisions nor the climate controls the ree distribution patterns in first cycle daughter sands although the total and the parent rock normalized abundances of ree in sands from humid areas are much lower than those in sands from arid areas

raman spectroscopy in heavy mineral studies abstract raman spectroscopy is an innovative tool with tremendous potential serving as a fun damental complement to a variety of provenance methods including heavy mineral analysis anddetrital geochronology because of its accuracy ef ciency and versatility the results of theraman technique are indispensable for fully reliable identi cation of heavy minerals in grainmounts or thin sections thorny long standing problems that cannot be solved con dently witha polarizing microscope alone such as the determination of opaque and altered heavy minerals of detrital grains as small as a few microns or of colourless crystals with uncertain orientationand rounded morphology can nally be addressed although the method can be highly automa tized the full ability and experience of the operator is required to combine raman data with theoptical information obtained under the microscope on the same grains which is essential for theef cient application of the method in provenance studies this article provides exemplaryramanspectrausefulforthecomparisonand determinationof over70 differentopaqueandtrans parent heavy mineral species commonly found in sediments conveying speci c information onthe genesis of their source rocks and thus is particularly useful in provenance diagnoses andpalaeotectonic reconstructions supplementary material detailed information on the lasers used and the origin of the analysedminerals is available at http www geolsoc org uk sup18615it is the scattering of light by atoms and moleculesthat gives us the light of the sky the blue colour ofthe deep sea and the delicate opalescence of largemasses of clear ice raman 1928 pp 368 369

provenance studies and mudrocks abstract provenance studies based on the mineralogy of sandstones seem to be falling rapidly into disrepute as a result of the increasing emphasis on the effects of diagenesis on the original detrital mineral composition feldspars in sandstones commonly are dissolved altered to clay minerals and albitized by widely occurring diagenetic processes accessory minerals all too frequently are confined in ancient sandstones to ztr mudrocks in contrast have the potential of greater preservation of feldspars and accessory minerals because of their lesser permeabilities few studies have attempted to use the nonclay mineralogy of mudrocks for provenance work and these few have had promising but mixed results mudrocks deserve more attention in provenance studies than they have received