variations in monsoonal rainfall over the last 21 kyr inferred from sedimentary organic matter in tung yuan pond southern taiwan abstract changes in paleorainfall intensity linked to the strength of the east asian ea summer monsoon since 21 cal kyr bp are inferred from the organic matter contents of a 15 m sediment core from tung yuan pond in southern taiwan high total organic carbon total nitrogen toc tn values in association with increased toc content suggest that more soil derived material containing terrestrial organic matter om was delivered to the lake during periods of increased runoff associated with extensive precipitation that resulted from intensified summer monsoons whereas low values indicate om possessing a dominant algal origin during weakened summer monsoons rainfall intensity in terms of the proportion of terrestrial om was high in four periods the last deglaciation 17 2 to 12 2 ka the early holocene 10 6 to 8 6 ka the middle holocene thermal optimum 7 7 to 5 ka and the late holocene 4 2 to 2 ka whereas it was low in the intervening time periods high toc tn values coincide with peak values of summer insolation and thus the strongest ea summer monsoon during the early and middle holocene small drops in these ratios correspond to increasing and decreasing solar radiation in the deglacial period and the late holocene respectively the four intervals with low toc tn ratios as well as episodic drops of the ratios during the deglaciation and the early and late holocene are concordant with the late last glacial 21 to 17 2 ka the oldest 14 8 ka the older 13 3 ka and the younger dryas 13 to 11 5 ka the 8 2 cold event 8 6 7 7 ka and a late holocene cold event 5 4 2 ka and suggest a weakened ea summer monsoon during these times moreover high frequency hydrological variability occurred during the early holocene heavy rainfall persisted during the middle holocene and precipitation intensity generally diminished after 5 ka the tung yuan pond sediment record indicates that the toc tn ratio can be used as a paleorainfall intensity proxy to trace variations in the ea summer monsoon strength in other small lakes

implications of the carbonaceous chondrite mn cr isochron for the formation of early refractory planetesimals and chondrules abstract an excellent 53 mn 53 cr isochron for bulk ci cm co cv cb and ungrouped c3 chondrites seems to suggest that each carbonaceous chondrite group acquired its mn cr ratio 4568 1 myr ago this age is indistinguishable from the age of ca al rich inclusions cais which is considered to be the start of the solar system t 0 however carbonaceous chondrites were not assembled until at least 1 5 5 myr after t 0 to judge by the 207 pb 206 pb and 26 al 26 mg ages of the chondrules within them and by the fact that they were not melted by heat from the decay of 26 al presumably therefore these meteorites inherited their bulk mn cr isochron from precursor materials which experienced mn cr fractionation at t 0 as a possible physical mechanism for how the isochron was established initially and later inherited by the carbonaceous chondrites we propose the rapid formation at t 0 of planetesimals that were variably depleted in moderately volatile elements and hence had variably low mn cr the planetesimals and the undepleted high mn cr primitive dust from which they were made shared the same initial e 53 cr and therefore evolved on an isochron we suggest that later impact disruption of the planetesimals produced dusty debris which became mixed in various proportions with unprocessed high mn cr dust before accreting to the carbonaceous chondrite parent bodies with mixing in a closed system the isochron was unchanged we infer that some debris rich material was converted to chondrules prior to accretion the chondrules could have been formed by flash melting of the mixed dust or could instead have been made directly by the impact splashing of molten planetesimals or by condensation from impact generated vapor plumes

dynamic crystallization of chondrule melts of porphyritic and radial pyroxene composition abstract dynamic crystallization experiments in which heterogeneous nucleation is an important variable have been completed on four melts of chondrule composition compositions were chosen to best represent chondrules with porphyritic pyroxene and radial pyroxene textures experimental results show that heterogeneous nucleation is essential for the formation of porphyritic textures without preexisting nuclei too much supercooling is established before crystallization is initiated and the textures are more likely to be dendritic or radial in the near total absence of nuclei radial textures can form at cooling rates as slow as 5 c hr in this study by varying the heterogeneous nucleation conditions and having a melt in which the appropriate phases are stable or metastable analogs to most of the recognized chondrule textures can be produced in a single melt composition olivine inclusions in pyroxene can form readily during an experiment from a starting material which did not initially contain olivine crystals thus care must be taken in the assumption that olivine inclusions in pyroxene represent preexisting crystals

low concentration of heavy metals in the yangtze estuarine sediments china a diluting setting abstract an examination of the spatial and temporal distribution of 17 major heavy metals i e fe zn ni mg co mn etc was made in the yangtze estuarine sediments revealed by a number of vibrocores taken from the different sediment zones including delta front prodelta and delta shelf transition the results obtained from the numerous core samples which were also measured for pb 210 and cs 137 show that 1 the silty clay comprising the prodelta facies serves as a depositional sink attracting high concentrations of heavy metals delivered from the river mouth 2 after being normalized to aluminum as a proxy for grain size most heavy metals presented in the prodelta facies have lower concentrations than in the other adjacent sediment zones 3 also after normalization concentrations of most heavy metals in the vibrocore sediments tend to increase up core and 4 sedimentation rates in the study area range from 2 0 to 6 0 cm a hence the vibrocores contain a sedimentary record of metal deposition covering more than 50 years it has previously been assumed that sediments off the river mouth were heavily polluted due to industrialization of the shanghai metropolitan area which peaked about 50 years ago however the low concentrations of heavy metals in the study area before and after normalization do not support this assumption the yangtze estuary is characterized largely by the tremendous runoff and unpolluted sediments derived from the upper drainage basin to constitute a unique diluted setting in which the dispersal behavior of heavy metals from the adjacent industrialized coast is influenced substantially as a result the heavy metals in the study area are obviously lower than those previously determined along the coast

crystal morphologies in pillow basalts implications for mid ocean ridge processes abstract we present the results of a detailed petrological study of a sparsely phyric basalt mapco ch98 dr11 dredged along the mid atlantic ridge 30 41 n the sample contains microphenocrysts of olivine that display four different rapid growth morphologies comparison of these morphologies with those obtained in dynamic crystallization experiments allows us to constrain the thermal history of the sample the dendritic morphology swallowtail chain and lattice olivine is directly related to the final quenching during magma seawater interaction in contrast the three other morphologies namely the complex polyhedral crystal the closed hopper and the complex swallowtail morphology result from several cycles of cooling heating corresponding to a maximum degree of undercooling of 20 25 c during crystal growth these thermal variations occurred before eruption and are interpreted to be the result of turbulent convection in a small magmatic body beneath the ridge the results suggest that the mid atlantic ridge is underlain by a mush zone that releases batches of liquid during tectonic segregation aphyric basalts are emitted during eruptions controlled by the tectonic activity whereas phyric basalts correspond to small fractions of magma from the mush zone mobilized by reinjections of primitive magmas

contribution of icing ablation to streamflow in a discontinuous permafrost area icings present in many small streams in the discontinuous permafrost environment alter the seasonal water balance by redistributing a component of flow from the winter to the spring icing ablation continues to contribute to streamflow after the disappearance of the snowpack and constitutes an additional source of runoff the temporal variability and significance of icing ablation to streamflow were examined with a combined water balance and isotope study in a tributary of manners creek northwest territories icing accounted for 20 of the surface water available for melt over the spring study period icing ablation accounted for 6 of total streamflow while the total surface water flux provided 8 shallow subsurface flow which consisted of infiltrated snow meltwater and premelt groundwater contributed the most to streamflow at the end of the melt period icing ablation was the only source of surface runoff to the stream and was similar in magnitude to the estimated evapotranspiration loss compa

normalizing xrf scanner data a cautionary note on the interpretation of high resolution records from organic rich lakes x ray fluorescence xrf scanning of unlithified untreated sediment cores is becoming an increasingly common method used to obtain paleoproxy data from lake records xrf scanning is fast and delivers high resolution records of relative variations in the elemental composition of the sediment however lake sediments display extreme variations in their organic matter content which can vary from just a few percent to well over 50 as xrf scanners are largely insensitive to organic material in the sediment increasing levels of organic material effectively dilute those components that can be measured such as the lithogenic material the closed sum effect consequently in sediments with large variations in organic material the measured variations in an element will to a large extent mirror the changes in organic material it is therefore necessary to normalize the elements in the lithogenic component of the sediment against a conservative element to allow changes in the input of the elements to be addressed in this study we show that al which is the lightest element that can be measured using the itrax xrf scanner can be used to effectively normalize the elements of the lithogenic fraction of the sediment against variations in organic content we also show that care must be taken when choosing resolution and exposure time to ensure optimal output from the measurements

the ti al molar ratio as a new proxy for tracing sediment transportation processes and its application in aeolian events and sea level change in east asia abstract ti al molar ratios of sediments in various sedimentary environments are used to explain sediment transportation from source regions to sink areas samples were collected from outcrops soils fluvial lake and marine sediment environments initial ti al molar ratios of sediments are controlled by those of parent soils or rocks these ratios tend to decline gradually as a result of heavy mineral gravity fractionation during transportation sedimentary ti al molar ratios in sink areas such as lakes and pelagic environments are lower than those in source regions in this study for the changjiang river huanghe river and kaoping river ti al molar ratios decline considerably from downstream to estuary environments additionally well sorted aeolian sands have extremely low ti al molar ratios in northern china the ti al molar ratios of aerosol particles found in taiwan and the east china sea show reduced ratios as a result of asia dust storm episodes furthermore lower ti al molar ratios in deep ocean sediments were discovered by tracing the distribution of sedimentary ti al molar ratios in the south china sea when sea levels dropped during glacial periods the river estuary was closer to deep marine areas and carried more terrestrial sediments into deep marine environments the closer estuary with relatively higher ti al ratio would lead increase of ti al molar ratios in deep sea sediments in this study ti al molar ratio is promoted as a new proxy to help with understanding changes in sedimentary environments

origin of sio2 rich components in ordinary chondrites abstract silica rich objects are common minor components in ordinary chondrites oc occurring as fragments and as chondrules their typical paragenesis is orthopyroxene sio 2 with bulk sio 2 65 wt and occasionally with additional olivine and or spinel individual silica rich components src have previously been studied in various types of ocs although there is only one comprehensive study of these objects by brigham et al brigham c a murrell m t yabuki h ouyang z el goresy a 1986 silica bearing chondrules and clasts in ordinary chondrites geochim cosmochim acta 50 1655 1666 several different explanations of how srcs formed have been published the main question is how silica enrichment was achieved because ci chondritic atomic mg si ratio is 1 07 and as a consequence only olivine and pyroxene but no free silica should be stable there are two basic possibilities for the sio 2 enrichment 1 a redox mechanism or magmatic fractionation on the parent body and 2 fractional condensation or recycling of chondrule mesostasis in the solar nebula to better constrain the origin of these objects we measured major and rare earth elements in srcs of various types of ordinary chondrites and in addition we studied silica polymorphism in these objects using an in situ micro raman technique bulk chondrule compositions define mixing lines between the compositions of olivine and pyroxene the srcs extend these lines to an sio 2 end member in contrast magmatic trends grossly deviate from these mixing lines concentrations of cao al 2 o 3 and ree in the pyroxenes of the srcs are low 0 01 to 1 ci and the ci normalized ree patterns are virtually flat typical of bulk chondrules but untypical of magmatic trends we therefore conclude that sio 2 rich objects are not of magmatic origin they are the result of fractional condensation in the solar nebula the silica in srcs occurs mainly as tridymite and sometimes as cristobalite or in very rare cases as quartz some sio 2 phases yielded a yet unknown micro raman spectrum which we were unable to identify the often chondrule like shape of srcs as well as the presence of high temperature sio 2 polymorphs lead to the following model for the origin of srcs formation of sio 2 rich precursors in the solar nebula by fractional condensation reheating to temperatures between 1140 and 1968 k thereby forming the srcs probably during the chondrule forming process followed by rapid cooling

thermoluminescence and compositional zoning in the mesostasis of a semarkona group a1 chondrule and new insights into the chondrule forming process a large group a1 porphyritic olivine chondrule in the semarkona ll3 0 chondrite with induced thermoluminescence tl and compositional zoning in its mesostasis has been discovered the chondrule has ca rich and fe poor olivine cao 0 36 0 40 wt fa0 3 0 5 and its mesostasis is highly anorthite normative 52 5 wt the chondrule shows an intense induced tl peak at 300 c with a half width of 180 c the induced tl in the 40 440 c range increases monotonically by a factor of 6 from center to rim while sio2 na2o and mno increase by factors of 1 1 3 6 and 6 respectively the spectrum of the induced tl over the 200 350 c range i e a dominant peak at 570 nm with a half width of about 100 nm and the mn tl correlation suggest mn activated plagioclase is an important constituent of the refractory mesostases in group a1 chondrules the zoning may reflect fractional crystallization soret diffusion transport of volatiles into the chondrule by aqueous alteration a zoned precursor reduction of precursor dust aggregate or recondensation of volatiles lost during chondrule formation the first four possibilities seem unlikely explanations for the zoning of the mesostasis but both reduction of precursor dust aggregate and recondensation of volatiles seem to have played significant roles to the formation of the zoning reducing conditions at high temperatures are suggested to have prevailed during the formation of group a1 chondrules

reconstruction of environmental changes using a multi proxy approach in the ulleung basin sea of japan over the last 48 ka based on elemental geochemical data we reconstructed the sediment provenance surface productivity and bottom water redox conditions for the last 48 ka in the ulleung basin sea of japan and inferred the factors controlling them al2o3 tio2 ratio and chemical index of alteration cia suggest that sediment provenance changed during the glacial period 48 18 ka compared to the deglacial ca 18 11 ka and holocene mass accumulation rates of total organic carbon toc caco3 phosphorus cadmium and excess barium reveal low paleoproductivity during low sea stand during 18 11 ka productivity increased due to increasing inflow of nutrient rich water masses the oyashio and the east china sea coastal water in tandem with the rising sea level maximum productivity occurred during younger dryas and pre boreal periods when sea level was at 60 m and then gradually decreased as the tsushima warm current inflow kicked off at ca 9 3 ka consistent with other paleoredox proxies which reveal the presence of anoxic bottom water during ca 12 9 ka with the changes in paleoredox proxies and their ratios toc mo u mn c s ratio and uauthigenic and mo contents we hypothesized that the redox changes were mainly ventilation driven and were superimposed on the influence of circulation induced productivity changes the global climate and sea level changes on a millennial timescale play a major role in enhancing paleoproductivity and restrict bottom water advection subsequently driving the oxygenation of bottom water in the ulleung basin copyright 2012 john wiley sons ltd

a review on the provenance discrimination of sediments in the yellow sea the yellow sea has been extensively studied for the understanding of dispersal patterns and limits of sediments from neighboring countries including china and korea although sedimentological mineralogical and geochemical approaches have been tried to solve the problems especially including the identification of sediment sources in and around the yellow sea the published results are not enough for understanding them suggestions on sediment origins budgets sediment accumulation rates mineralogical and geochemical compositions are not coincident to each other and sometimes even controversial for example conflicts on the distribution patterns of smectite and calcium carbonate the provenance of the southeastern yellow sea mud and sedimentation rates in there the ratios of v al and mn al in korea and china river sediments the origin of ba and pb in sandy sediments of the northeastern yellow sea and so on various geochemical indicators from the literature for the provenance discrimination in the yellow sea are reviewed here in depth and corresponding discussions are described separately research topics for the future study also are suggested for the proper access to the understanding of the origin and dispersal patterns of the yellow sea sediments especially focusing on the geochemical approaches d 2003 elsevier science b v all rights reserved

correlated millennial scale changes in surface hydrography and terrigenous sediment yield inferred from last glacial marine deposits off northeastern brazil abstract the stable isotope composition of planktonic foraminifera correlates with evidence for pulses of terrigenous sediment in a sediment core from the upper continental slope off northeastern brazil stable oxygen isotope records of the planktonic foraminiferal speciesglobigerinoides sacculiferandglobigerinoides ruber pink reveal sub milankovitch changes in sea surface hydrography during the last 85 000 yr warming of the surface water coincided with terrigenous sedimentation pulses that are inferred from high xrf intensities of ti and fe and which suggest humid conditions in northeast brazil these tropical signals correlate with climatic oscillations recorded in greenland ice cores dansgaard oeschger cycles and in sediment cores from the north atlantic heinrich events trade winds may have caused changes in the north brazil current that altered heat and salt flux into the north atlantic thus affecting the growth and decay of the large glacial ice sheets

response of manganese in the ocean to the climatic cycles in the quaternary profiles of the 230th concentration in mn crusts from the central pacific ocean measured at extremely high depth resolution reveal that the growth rates of mn crusts are influenced by climate based on a constant flux model the sections of maximum 230th concentration correspond to periods of slow growth during glacial stages fast growth occurred during interglacial stages 1 5 and 7 probably due to a larger supply of mn oxides from the water column high resolution profiles of 230th and 10be in sediment cores from high biological productivity areas display radioisotope maxima in the interglacial stages and minima during glacial periods the ratio of the fluxes of 10be 230th being 4 the only exceptions are observed at 135 and 270 kyr b p where the ratio of the fluxes is as low as 0 1 to 0 3 we presume that this 230th anomaly reflects short periods of time at the end of glacials when precipitation of mno2 occurred this hypothesis is confirmed by peaks of mn observed in sediment cores mainly at the transitions from glacial to interglacial stages the standing crops of mn in these layers suggest release of mn2 from the sediments during glacial stages and buildup of mn in the water column to concentrations of up to 10 mol l

diagenesis of dissolved aluminum in organic rich estuarine sediments abstract the sedimentary geochemistry of dissolved al is complicated by a number of different reactions in this study we show that complexation by organic matter adsorption to fe oxyhydroxides and reaction with si in solution have important effects on the distribution of dissolved al in sediments in the absence of physical resuspension of sediment into overlying waters dissolved al is rapidly consumed at the sediment water interface and is subsequently released upon reduction of fe oxyhydroxides this release does not cause noticeable perturbations in dissolved al concentrations in sediments because of rapid consumption reactions which mask the true mobility of al results suggest that one of the consumption reactions may be due to formation of an fe al silicate the amount of authigenic aluminosilicate formed in estuarine sediments must be very small relative to the detrital component in the deep sea however the long residence time of fe oxyhydroxides at the sediment water interface with resulting greater accumulation of adsorbed al may explain the abundance of al in fe smectites reported from many different areas

mineralogical and geochemical investigations of sediment source region changes in the okinawa trough during the past 100 ka images core md012404 abstract we present a mineralogical and geochemical study of core md012404 retrieved from the central okinawa trough ot of the east china sea our studies reveal that the sediment sources of the core have been changed through time during the past 100 ka our mineralogical proxies indicate that the sediments source from the yangtze river correlates well sea level changes before 24 ka our ti al ratios otherwise indicate an increase of sediment supply from eastern taiwan after 26 ka the cooler climate of the last glacial maximum lgm 23 19 ka led to a reduction in fluvial sediments from the yangtze river however subsequent climate warming after 19 ka resulted in an abrupt increase in fluvial sediments after the lgm the kuroshio intrusion flow into the ot may have increased we also infer anomalous changes in eolian sources transported by winter monsoons during the lgm and at 80 ka based on an eolian mineralogical indicator feldspar we conclude that the sediment source of core md012404 is primarily of terrestrial origins but influenced by sea level changes and variations in the east asian monsoon

granoblastic olivine aggregates in magnesian chondrules planetesimal fragments or thermally annealed solar nebula condensates abstract granoblastic olivine aggregates goa have been discovered in some type i magnesian chondrules within carbonaceous chondrites by libourel and krot libourel g krot a n 2007 evidence for the presence of planetesimal material among the precursors of magnesian chondrules of nebular origin earth planet sci lett 254 1 8 who proposed an origin from pre existing planetesimals amoeboid olivine aggregates aoa generally considered as aggregates of solar nebula condensates and found within similar carbonaceous chondrites display similar equilibrium texture though on a finer scale for these reasons we conducted experiments to determine if annealing of olivine required time scales appropriate to planetesimal or nebular heating pressed 88 4 was isothermally heated at temperatures ranging from 1350 1550 c for 1 100 h the 100 h runs yield olivine aggregates with well developed granoblastic texture at all temperatures manifest as a network of randomly oriented and sutured olivine grains with 120 triple junctions individual olivine grains are 4 6 sided and polygonal by 1450 c and equigranular texture is developed at high temperature 1500 1550 c melting of olivine commences at 1450 1500 c and aids in ripening and suturing grain coarsening and grain boundary migration textural equilibrium is clearly met at 1550 c a planetesimal origin cannot be ruled out however the experimental evidence reveals that granoblastic texture can be reproduced in an interval not inconsistent with heating times for nebular objects goa may have experienced higher degrees of thermal processing than the finer grained aoa if the precursors were the same grain coarsening would have to be accompanied by modification to bulk and isotopic compositions however the precursors could have been olivine condensates formed later than aoa annealing may have been a widespread process operating in the primordial solar nebula responsible for thermal processing and formation of goa prior to their incorporation into chondrules

chemical cycles in pliocene sapropel bearing and sapropel barren eastern mediterranean sediments abstract high resolution 3 4 cm investigations of major and minor elements were carried out on sediment cores from odp leg 160 sites 964 ionian basin 969 mediterranean ridge 967 and 966 northern slope and top of eratosthenes seamount south of cyprus at site 967 element al ratios display pronounced cyclic records that are related to astronomically forced climatic variations sediments from the top of eratosthenes seamount site 966 show a similar pattern to those from site 967 but they are more disturbed by bioturbation and also strongly influenced by long term variations in sediment dispersal sediments from site 969 display similar trends to those from site 964 i e they are characterized by higher mg al slightly higher k al and lower ti al ratios during sapropel formation higher ti al ratios at site 969 compared with sediments from site 964 may be explained by a westward transport of material from a source in the east where ti al ratios are highest sites 966 and 967 elevated mg al ratios at site 969 during sapropel intervals are due to river derived material transported through the kithira strait between peloponnesus and crete from the northwestern aegean sea which originates from ultramafic rocks a change in intermediate water currents current reversal during sapropel formation may explain the enhanced supply of mg rich and the relatively diminished supply of ti rich material we propose that during deposition of the reddish intervals at site 969 a change in circulation did not occur because a drastic decrease in ti al ratios is not evident in these sediments ba peaks indicative of former sapropels are not present ba enrichments in the same sapropel barren intervals at site 967 northern slope of eratosthenes seamount suggest that during such intervals the burn down process was more effective than during the sapropel bearing intervals mn contents in all investigated pliocene sediments correlate with the carbonate contents higher mn contents of the sapropel barren sediments suggest that during time intervals of sapropel formation either mn accumulation at the margins of the permanently oxic upper water column or mn export into the western mediterranean might have occured the latter could only be explained by sub or anoxic conditions in large parts of the water column

late quaternary climate changes in central africa as inferred from terrigenous input to the niger fan time series of terrigenous source elements al k ti zr from core geob4901 8 recovered from the deep sea fan of the niger river record variations in riverine sediment discharge over the past 245 000 yr although the flux rates of all the elements depend on physical erosion which is mainly controlled by the extent of vegetation coverage in central africa element al ratios reflect conditions for chemical weathering in the river basin maximum sediment input to the ocean occurs during cold and arid periods when precipitation intensity and associated freshwater runoff are reduced high carbonate contents during the same periods indicate that the sediment supply has a positive effect on river induced marine productivity in general variations in the terrestrial signals contain a strong precessional component in tune with changes in low latitude solar radiation however the terrestrial signal lags the insolation signal by several thousand years k al ti al and zr al records reveal that african monsoonal precipitation depends on high latitude forcing we attribute the shift between insolation cycle and river discharge to the frequently reported nonlinear response of african climate to primary orbital configurations which may be caused by a complex interaction of the secondary control parameters such as surface albedo and or thermohaline circulation

northeast monsoon variations during the holocene inferred from palaeochannels and active channels of the palar river basin southern peninsular india the present day palar river and its palaeochannel located in the southern peninsular india were investigated with a multidisciplinary approach the main aim of the study was to reconstruct the palaeoenvironment history of the palar river basin and to delineate the role of holocene fluctuations that played a major role in the geomorphological evolution of the region since the holocene period the results obtained based on sedimentary facies analysis supported by elemental concentrations and optically stimulated luminescence osl dates reveal distinct seven climatic phases since the past 10 ka phase 1 signifies a very high precipitation as attested by the low cwi with high rb sr ratio subsequent to phase 1 a decreasing trend in the northeast monsoon rainfall nemr is observed phase 2 phase 3 4 83 3 59 ka reflects a decrease in nemr further supported by low mn al mg al and chemical index of alteration cia values phase 4 3 59 ka is marked by high sand flux higher k al ti al rb sr and ba

sedimentary responses to the sea level and indian summer monsoon changes in the central bay of bengal since 40 ka abstract we present a sedimentary multi index comprehensive study on sediment core bob 56 collected from the central bay of bengal bob with an attempt to understand the sedimentary processes and their responses to sea level change and the indian summer monsoon ism since the last glacial period we revealed the temporal evolution of terrigenous input and provided a brief discussion of the implications of our sedimentary indexes for ocean productivity then we proposed a simple depositional model in the central bob since the last glacial period as indicated by the geochemistry mineralogy and physical indexes including linear sedimentary rate lsr ti ca rb sr and quartz calcite ratios the terrigenous input was higher during the last glacial period than during the holocene period and the sea level is suggested to be responsible for this significant distinction through the depositional center transition in the bob at the glacial interglacial scale similar terrigenous input patterns with solar radiation and precipitation before 18 ka indicated that the monsoon controlled these situations at precession related scales synchronous changes with records in the north atlantic ocean during the last deglaciation and early holocene suggested terrigenous input responses to the climate changes that also recorded by high latitude sedimentary system at millennial scales indicated by the element caco3 ba and sr authigenic accumulation rates the paleoproductivity in the central bob was at a roughly equivalent level during the last glacial period and the holocene period different terrestrial nutrient inputs and ism related ocean surface stratifications were suggested to be responsible for the level of paleoproductivity this study provides a brief understanding of the sedimentary response to the climate and emphasizes the different roles of the sea level and ism in the central bob

association between wave and current aided hyperpycnites and flooding surfaces in shelfal mudstones an integrated sedimentologic sequence stratigraphic and geochemical approach

textural evolution of polyhedral olivine experiencing rapid cooling rates dynamic crystallization experiments in the cao mgo al2o3 sio2 cmas system have been used to investigate the change in crystal shape when pre existing polyhedral olivine crystals are cooled rapidly 1 639 2 182 c h polyhedral olivines are crystallized initially in a first step using a slow cooling rate 2 c h then skeletal and dendritic overgrowths develop on the polyhedral crystals during a subsequent fast cooling event during this second episode small dendritic olivines also nucleate within the liquid phase observation of the experimental sample by optical microscopy shows that the polyhedral olivine shape progressively changes to a skeletal and then to a dendritic morphology in the following sequence polyhedral hopper polyhedral dendritic polyhedral this evolutional sequence is discussed in terms of changes in the crystal growth conditions during cooling and a general relation between these olivine dynamic crystallization experiments and the integrated model of crystal growth by sunagawa bull miner 104 81 87 1981 morphology of crystals terra scientific publishing company 1987 is proposed

dynamic crystallization of shock melts in allan hills 77005 implications for melt pocket formation in martian meteorites abstract a series of crystallization experiments have been performed on synthetic glasses matching the composition of a melt pocket found in allan hills alh 77005 in order to evaluate the heterogeneous nucleation potential of the melt and the effect of oxygen fugacity on crystallization the starting temperature of the experiments varied from superliquidus liquidus and subliquidus temperatures each run was then cooled at rates of 10 500 and 1000 c h at fmq the results of this study constrain the heating and cooling regime for a microporphyritic melt pocket within the melt pocket strong thermal gradients existed at the onset of crystallization giving rise to a heterogeneous distribution of nucleation sites resulting in gradational textures of olivine and chromite skeletal olivine in the melt pocket center crystallized from a melt containing few nuclei cooled at a fast rate nearer to the melt pocket margin elongate skeletal shapes progress to hopper and equant euhedral reflecting an increase in nuclei in the melt at the initiation of crystallization and growth at low degrees of supercooling cooling from post shock temperatures took place on the order of minutes an additional series of experiments were conducted for a melt temperature of 1510 c and a cooling rate of 500 c h at the fmq buffer as well as 1 and 2 log units above and below fmq variation in chromite stability in these experiments is reflected in crystal shapes and composition and place constraints on the oxygen fugacity of crystallization of the melt pocket we conclude that the oxygen fugacity of the melt pocket was set by the fe 3 fe 2 ratio imparted by melting of the host rock rather than external factors such as incorporation of co 2 rich martian atmosphere or melting and injection of oxidized surface e g regolith material comparison with previous crystallization experiments on melt pockets in martian basalts indicate that the predominance of dendritic crystal shapes reflects the likelihood that those melt pockets with lower liquidus temperatures will be more completely melted destroying most or all nuclei in the melt in this case crystal growth takes place at high degrees of supercooling yielding dendritic shapes it appears as though the melting process is just as important as cooling rate in determining the final texture of the melt pocket as this process controls elimination or preservation of nuclei at the onset of cooling and crystallization

east asian monsoon variation during the last 130 000 years evidence from the loess plateau of central china and lake biwa of japan abstract the loess paleosol sequence on the loess plateau of central china constitutes an excellent proxy record of variations in asian monsoon climate over the past 2 5 ma magnetic susceptibility of loess and paleosols has been used as a proxy indicator for summer monsoon intensity while the median diameter of quartz isolated from the loess and paleosols has been regarded as a proxy index of the strength of winter monsoon winds that were responsible for most of the dust transport the eolian quartz flux to lake biwa of central japan during the last 130 000 yr provides direct information on variations of the east asian winter monsoon whereas the fluvial quartz flux reflects significant changes in paleoprecipitation over the lake area the intervals of high eolian quartz flux values during marine oxygen isotope substages 5d and 5b and stages 4 and 2 correspond to the periods of large quartz median diameter values of the chinese loess and paleosols indicating strengthened winter monsoon winds whereas the intervals of high fluvial quartz flux values during isotope substages 5e 5c and 5a and stages 3 and 1 correlate to the periods of high magnetic susceptibility values of the chinese loess and paleosols suggesting increased summer monsoon intensity variations in winter monsoon strength indicated by the eolian quartz flux and quartz median diameter proxies bear a general inverse relation to those in summer monsoon intensity inferred from the fluvial quartz flux and magnetic susceptibility proxies

the origin of chondrules and chondrites debris from low velocity impacts between molten planetesimals we investigate the hypothesis that many chondrules are frozen droplets of spray from impact plumes launched when thin shelled largely molten planetesimals collided at low speed during accretion this scenario here dubbed splashing stems from evidence that such planetesimals intensely heated by 26al were abundant in the protoplanetary disk when chondrules were being formed approximately 2 myr after calcium aluminum rich inclusions cais and that chondrites far from sampling the earliest planetesimals are made from material that accreted later when 26al could no longer induce melting we show how splashing is reconcilable with many features of chondrules including their ages chemistry peak temperatures abundances sizes cooling rates indented shapes relict grains igneous rims and metal blebs and is also reconcilable with features that challenge the conventional view that chondrules are flash melted dust clumps particularly the high concentrations of na and feo in chondrules but also including chondrule diversity large phenocrysts macrochondrules scarcity of dust clumps and heating we speculate that type i feo poor chondrules come from planetesimals that accreted early in the reduced partially condensed hot inner nebula and that type ii feo rich chondrules come from planetesimals that accreted in a later or more distal cool nebular setting where incorporation of water ice with high 17o aided oxidation during heating we propose that multiple collisions and repeated re accretion of chondrules and other debris within restricted annular zones gave each chondrite group its distinctive properties and led to so called complementarity and metal depletion in chondrites we suggest that differentiated meteorites are numerically rare compared with chondrites because their initially plentiful molten parent bodies were mostly destroyed during chondrule formation

the huanghe and changjiang contribution to seasonal variability in terrigenous particulate load to the okinawa trough abstract terrigenous particulate load transported to the okinawa trough was examined using time series sediment trap samples collected in 1993 1994 at sst 1 29 21 6 n 128 13 5 e 1100 m water depth lateral transport through the bottom layer was important in transport of terrigenous particles from shelf to the trough flux reached a maximum in spring reflecting seasonal change although a short period of transport also occurred in the late summer unrelated with the general seasonal change mineralogical and chemical analyses revealed that contributions from sediment sources changed seasonally a changjiang yangtze river influence was relatively high during winter while the huanghe yellow river and or eolian derived sediment was enhanced in spring and late summer when the total flux also intensified

on the pseudomorphing of melt filled pores during the crystallization of migmatites pseudomorphs of melt filled pores recognized by their generally cuspate shape are used as diagnostic for the former presence of partial melt they are commonly observed in migmatites from the mid to deep crust although they occur in the smaller pores in migmatites from shallower levels 1 2 kbar the pseudomorphing of meltfilled pores is controlled by the kinetics of nucleation and is a consequence of the greater supersaturation required for nucleation in a small pore compared with a larger one we examine three migmatites in detail a contact metamorphosed cherty band from an iron formation an archaean regional granulite from an accretionary prism and an amphibolite facies sample from the roots of an archaean mountain chain the greater undercooling required for nucleation in progressively smaller pores is recorded by the composition of plagioclase pseudomorphs a study of dihedral angles at the corners of pseudomorphed pores demonstrates that melt solid textural equilibrium was probably attained only in the contact aureole the regional granulite preserves an almost unmodified reaction controlled melt distribution with little evidence for either melt solid textural equilibration or solid solid re equilibration whereas the reactioncontrolled melt distribution in the regional amphibolite facies example has been modified by a partial approach to solid solid textural equilibrium it is not clear whether the differences in dihedral angle population are due to differences in uplift and exhumation rates or due to the presence of h2o on grain boundaries

crystal growth in incongruently melting compositions programmed cooling experiments with diopside programmed cooling experiments using a synthetic diopside glass and constant cooling rates of from l0o to 300oc hr first crystallize forsterite and then with decreasing temperature clinopyroxene wollastonite the forsterite grows as hopper shaped crystals which then develop dendrites from external corners the morphological development can be qualitatively explained by a model involving di ffusion in the melt and interface attachment kinetics microprobe traverses across forsterite glass interfaces show that the magnitude of the mgo depletion in the melt near flat interface segments varies from 1 72 to 4 28 percent and increases with increasing run time for a given cooling rate and with increasing value of the product of the cooling rate times the run time for all cooling rates the results are in qualitative agreement with theoretical predictions near a particular crystal mgo depletion is least at corners and greatest in reentrants the clinopyroxene is more magnesian than diopside solid solution towards enstatite and grows as dendrites the wollastonite occurs between the clinopyroxene dendrite arms the clinopyroxene first appears at nominal undercoolings 1391 iou n of from l82o to 240 c depending on the cooling rate unlike other sets of programmed cooling experiments which show a continual increase in nominal undercooling with increasing cooling rate these experiments show a maximum in clinopyroxene undercooling at 50 c hr the undercooling is actually least for the 300oc hr runs introduction when crystals grow from a melt with a different composition at least two processes must be involved in the growth process the molecular attachment process occurring at the crystal melt interface and redistribution of chemical components in the melt in response to the selective removal of some of them by the crystal removal of the latent heat of crystallization from the crystal melt interface may be important if the growth rate is high traditional descriptions of the interaction of diffusion and crystal growth assume that the liquid and crystal compositions at the interface are the equilibrium compositions for the temperature at which growth is occuring e 9 elbaum 1959 such descriptions may not be satisfactory for silicates and other materials which grow by a layer spreading mechanism because these 0003 004x 8 l 0304 0223 02 00 materials require a finite supersaturation or undercooling really the same thing at the interface for growth to occur o hara et al 1968 hopper and uhlmann 1974 kirkpatrick 1975 this layerspreading growth mechanism also greatly affects the development of skeletal and dendritic crystal morphologies allowing fully faceted crystals to grow to a larger size than would be possible if interface kinetics were not important recent theoretical developments have shown how the effect of interface kinetics can be taken into account for both interface stability and the overall growth process this paper briefly reviews the recent theory presents the results of programmsd sssling experiments in which forsterite clinopyroxene and wollastonite grow from a synthetic stoichiometric diopside melt and uses the theory to interpret these results 223 kirkpatrick et al growth in incongruently melting compositions theory recent advances in crystal growth theory can help in the understanding of three major aspects of the experiments to be discussed here l the origin of the skeletal morphologies of the forsterite and clinopyroxene crystals 2 the time temperature position and cooling rate dependences of the liquid composition at the forsterite melt interface and 3 the variation in liquid composition away from the forsteriteliquid interface this section will briefly review these theoretical developments

scavenged excess aluminum and its relationship to bulk titanium in biogenic sediment from the central equatorial pacific ocean we present results from chemical analyses of al and ti in surface sediment sampled along two cross equator latitudinal transects at 135w and 140w in the central equatorial pacific ocean although traditionally both al and ti are considered to reside exclusively within terrigenous phases in marine sediment these sediments present extremely high al ti ratios that are several times that of average shale and other potential crustal sources a sharp maximum in al ti is observed slightly south of the equator where sedimentary bulk accumulation rate bar is also highest reflecting elevated productivity in the overlying water caused by surface water divergence bulk al ti decreases sharply away 2 latitude to near crustal values at 4 north and south the latitudinal profiles of al ti are entirely unrelated to the concentration of the biogenic components as well as to the absolute accumulation of al and ti these results indicate the presence of a significant scavenged component of al sourced directly from seawater during particle settling the data from the two transects analytically and oceanographically confirms our earlier work that was based on the single 135w transect calculations of alexcess indicate that the highest al ti ratios correspond to 50 of the total al being unsupported by the small amount of terrigenous phases present these results are consistent with previous and ongoing studies of biogenic sediment suspended particulate matter and sediment trap material quantitative use of al as an index of terrigenous material may therefore lead to an overestimation by a factor of two of the true terrigenous load in marine sediment sedimentary rock and settling particles because bulk al ti appears to respond to sedimentary bar which in biogenic regimes is linked to surface water productivity downcore records of al ti in biogenic sediment may track productivity changes through time such al ti proxy records may be applicable in sediment of all ages unlike radionuclide tracers which are limited by radioactive decay to use over the past hundreds of kyr

role of gas melt interaction during chondrule formation abstract it is generally believed that most chondrules formed in the protoplanetary disk by melting of fine grained solid precursor materials and that during these melting events chondrules behaved as closed systems both chemically and isotopically i e the observed range in chondrule bulk chemistry and modal mineralogy was entirely inherited from solid precursors that experienced melting to varying degrees followed by igneous crystallization accompanied by very limited if any evaporation recondensation our mineralogical and chemical study of magnesium rich porphyritic type i chondrules in primitive ordinary and carbonaceous chondrites revealed that chondrule glasses are not located on the subtraction lines of olivine or low ca pyroxene in appropriate phase diagrams indicating that type i chondrules do not obey closed system crystallization we suggest that gas melt interaction played a major role in evolution of mineralogy bulk chemical and isotopic compositions of type i chondrules chondrules are thus complex objects composed of an inherited solid component and a melt component that equilibrated with nebular gas suggesting that chondrules formed in regions with high ambient gas partial pressures as a result chondrule glasses melts are therefore thermochemical and isotopic sensors of the surrounding nebular gas in the chondrule forming regions of the protoplanetary disk and can be used for evaluating its physico chemical conditions

oxygen isotopic constraints on the origin of mg rich olivines from chondritic meteorites chondrules are the major high temperature components of chondritic meteorites which accreted a few millions years after the oldest solids of the solar system the calcium aluminum rich inclusions were condensed from the nebula gas chondrules formed during brief heating events by incomplete melting of solid dust precursors in the protoplanetary disk petrographic compositional and isotopic arguments allowed the identification of metal bearing mg rich olivine aggregates among the precursors of magnesian type i chondrules two very different settings can be considered for the formation of these mg rich olivines either a nebular setting corresponding mostly to condensation evaporation processes in the nebular gas or a planetary setting corresponding mostly to differentiation processes in a planetesimal an ion microprobe survey of mg rich olivines of a set of type i chondrules and isolated olivines from unequilibrated ordinary chondrites and carbonaceous chondrites revealed the existence of several modes in the distribution of the 17o values and the presence of a large range of mass fractionation several within each mode the chemistry and the oxygen isotopic compositions indicate that mg rich olivines are unlikely to be of nebular origin i e solar nebula condensates but are more likely debris of broken differentiated planetesimals each of them being characterized by a given 17o mg rich olivines could have crystallized from magma ocean like environments on partially molten planetesimals undergoing metal silicate differentiation processes considering the very old age of chondrules mg rich olivine grains or aggregates might be considered as millimeter sized fragments from disrupted first generation differentiated planetesimals finally the finding of only a small number of discrete 17o modes for mg rich olivines grains or aggregates in a given chondrite suggests that these shattered fragments have not been efficiently mixed in the disk and or that chondrite formation occurred in the first vicinity of the breakup of these planetary bodies

crystallization kinetics in the system camgsi 2 o 6 caal 2 si 2 o 8 the delay in nucleation of diopside and anorthite the nucleation of diopside and anorthite is always delayed under supercooled conditions the delay in nucleation decreases with increasing degree of supercooling or increasing cooling rate with further increase in the degree of supercooling or the cooling rate the delay in anorthite nucleation increases for a given degree of supercooling the region of random nucleation of diopside is wider than that of anorthite steady state nucleation occurs for diopside and transient nucleation for anorthite modified journal abstract

influence of the intertropical convergence zone on the east asian monsoon a palaeoclimate record spanning the past 16 000 years with nearly annual time resolution has been obtained from lake huguang maar in china the magnetic properties and titanium content of the lake sediments are thought to reflect changes in the east asian winter monsoon strength thus providing a complement to palaeoclimate archives that record the strength of the rain bearing summer monsoon the records point to an anti correlation between winter and summer monsoon strength best explained by migration of the intertropical convergence zone itcz a belt of low pressure air at the equator interestingly the decline of china s tang dynasty and the mayan civilization broadly coincide with drought periods recorded in lake huguang maar and cariaco basin sediments respectively did major shifts in the position of the itcz catalyse simultaneous events in civilizations on opposite sides of the pacific ocean the asian australian monsoon is an important component of the earth s climate system that influences the societal and economic activity of roughly half the world s population the past strength of the rain bearing east asian summer monsoon can be reconstructed with archives such as cave deposits1 2 3 but the winter monsoon has no such signature in the hydrological cycle and has thus proved difficult to reconstruct here we present high resolution records of the magnetic properties and the titanium content of the sediments of lake huguang maar in coastal southeast china over the past 16 000 years which we use as proxies for the strength of the winter monsoon winds we find evidence for stronger winter monsoon winds before the bolling allerod warming during the younger dryas episode and during the middle and late holocene when cave stalagmites suggest weaker summer monsoons1 2 3 we conclude that this anticorrelation is best explained by migrations in the intertropical convergence zone similar migrations of the intertropical convergence zone have been observed in central america for the period ad 700 to 900 refs 4 6 suggesting global climatic changes at that time from the coincidence in timing we suggest that these migrations in the tropical rain belt could have contributed to the declines of both the tang dynasty in china and the classic maya in central america

late quaternary tectonic switching of siliciclastic provenance in the strike slip dominated foreland of the western carpathians upper morava basin bohemian massif abstract this study is focused on the lithology and provenance of late quaternary fluvial deposits of the upper morava basin a pull apart basin situated at the contact of the bohemian massif and western carpathians late cenozoic tectonic convergence between these two units caused differential subsidence along strike slip faults of the elbe odra zone leading to a distinct horst and graben morphology of the upper morava basin the pleistocene fluvial deposits are preserved in several terrace levels and partly buried under the present day floodplain of the morava river this study is based on four cores 11 25 m deep drilled in the floodplain of two major depocentres of the basin the lutin graben and the upper morava basin sensu stricto the drill cores were analysed for grain size pebble and heavy mineral composition chemical composition of detrital garnets bulk magnetic susceptibility sediment colour visible light spectral reflectance and bulk element geochemistry age interpretations are based on eight optically stimulated luminescence osl analyses the upper pleistocene sediments were deposited in a gravelly braided to transitional braided meandering river in both the upper morava basin s s and the lutin graben the oldest osl age is 161 5 ka corresponding to the late saalian between the end of the saalian and late weichselian glaciations the morava river abandoned the lutin graben for the upper morava basin s s where it flows up to the present day the pleistocene fluvial style contrasts with the present day meandering to anastomosing fluvial style of the morava river the pleistocene deposits were sourced from areas corresponding to the present day morava river catchment including crystalline units of the eastern bohemian massif and the moravo silesian carboniferous basin they also contain a considerable input from the bohemian cretaceous basin the composition of late weichselian deposits from the dub nad moravou core 34 53 3 42 ka and younger differs from the older fluvial deposits representing the other cores it indicates that a major provenance change occurred between the latest saalian and the late weichselian in the late weichselian the morava river started to recycle loess deposits which cover large areas of its catchment based on osl dating it may be assumed that the morava river turned from degrading between 92 6 8 03 and 34 53 3 42 ka to aggrading in style from 34 53 3 42 ka to the present day due to coeval tectonic movements in the umb which are indirectly indicated by present day seismicity geomorphic faults and palaeoseismic evidence both the tectonic context and fluvial deposition styles of the upper morava basin show similar features to the upper rhine graben of the alpine foreland

oxygen isotopic constraints on the origin of magnesian chondrules and on the gaseous reservoirs in the early solar system abstract we report in situ ion microprobe analyses of the oxygen isotopic composition of the major silicate phases olivine low ca pyroxene silica and mesostasis of 37 magnesian porphyritic type i chondrules from cv vigarano usnm 477 2 vigarano uh5 mokoia and efremovka and cr eet 92042 eet 92147 eet 87770 el djouf 001 mac 87320 and gra 95229 carbonaceous chondrites in spite of significant variations of the modal proportions of major mineral phases in cr and cv chondrules the same isotopic characteristics are observed i olivines are isotopically homogeneous at the level within a chondrule although they may vary significantly from one chondrule to another ii low ca pyroxenes are also isotopically homogeneous but systematically 16o depleted relative to olivines of the same chondrule and iii all chondrule minerals analyzed show 16o enrichments relative to the terrestrial mass fractionation line enrichments that decrease from olivine spinel to low ca pyroxene and to silica and mesostasis the observation that in most of the type i chondrules studied the coexisting olivine and pyroxene crystals and glassy mesostasis have different oxygen isotopic compositions implies that the olivine and pyroxene grains are not co magmatic and that the glassy mesostasis is not the parent liquid of the olivine the 18o and 17o values of pyroxene and olivine appear to be strongly correlated for all the studied cr and cv chondrules according to 18 o pyroxene 0 72 0 16 0 13 18 o olivine 1 21 0 54 0 79 17 o pyroxene 0 81 0 15 0 13 17 o olivine 0 60 1 00 0 95 these correlations are consistent with mass balance of oxygen isotopes calculated in the case of chondrule formation according to the following gas melt mineral reactions mg 2 sio 4 olivine sio 2 melt mg 2 si 2 o 6 pyroxene sio 2 melt sio gas 1 2 o 2 gas these equations imply that 2 3 of the oxygen incorporated by low ca pyroxene during its crystallization in the melt is derived from the dissolution of precursor olivine and 1 3 from the addition of chemical components such as sio from the nebular gas the composition of the nebular gaseous reservoir in which type i cr and cv chondrules formed is determined from the present data set to be 18o gas 3 6 1 and 17o gas 1 8 1 this isotopic composition is in excellent agreement with that of the gaseous reservoir previously inferred from the oxygen isotope systematics of bulk chondrules from various chondrite groups i e cv cr unequilibrated ordinary and eh thus the oxygen isotopic systematic strongly supports the idea that most of the olivines in type i chondrules are relict grains and that gas melt interaction played a major role in the formation of type i chondrules

a multiproxy lake record from inner mongolia displays a late holocene teleconnection between central asian and north atlantic climates in order to study how the holocene central asian climate is coupled to the global climate system a 4 24 m long lake core from western inner mongolia in china was studied using a multiproxy approach sedimentology and geochemical parameters such as gypsum and dolomite content presence of lakeshore sand changing to aeolian sand and changes in paleomagnetic properties bear witness to a trend toward a generally drier climate over the late holocene aridification is linked to the southward retreat of the northern boundary of the asian summer monsoon leaving central asia under the influence of the westerly belt the weakening of the asian summer monsoon in turn was caused by an orbitally driven decrease in summer insolation the weakening summer insolation also likely increased the intensity of the siberian high pressure system further promoting aridification of central asia on a shorter time scale the multiproxy record shows the climate to have been relatively dry during the medieval warm period ad 800 1100 with the ensuing humid environment at the end of this period gradually turning to become extremely dry ad 1100 1550 at the little ice age maximum switches in the north atlantic oscillation caused these changes through a teleconnection in the form of westerlies these westerlies provided most of central asia s moisture after the retreat of the asian summer monsoon the central asian climate therefore corresponds closely with late holocene european climate changes

petrographic and oxygen isotopic study of refractory forsterites from r chondrite dar al gani 013 r3 5 6 unequilibrated ordinary and carbonaceous chondrites we have conducted petrographic chemical and in situ oxygen isotopic studies of refractory forsterites from unequilibrated ordinary and carbonaceous chondrites as well as an unequilibrated r chondrite refractory forsterites occur in all types of unequilibrated chondrites and all have very similar chemical composition with low feo and high refractory lithophile element rle contents refractory forsterites are typically enriched in 16o relative to normal olivine independent of the bulk o isotope ratios of the parent meteorites analyses of refractory forsterites spread along a 17o mixing line with 17o ranging from 2 to 10 due to similarities in oxygen isotopes and chemical compositions we conclude that refractory forsterites of various types of chondrites come from a single common reservoir implications of this hypothesis for the chemical and o isotope evolution of silicates in the early solar nebular are discussed

granoblastic olivine aggregates as precursors of type i chondrules an experimental test abstract chondrule formation models involving precursors of granoblastic olivine aggregates goa of either planetesimal or nebular origin have recently been proposed we have therefore conducted chondrule simulation experiments using mixtures of 100 h thermally annealed goa and an en to test the viability of goa as predecessors of porphyritic olivine po chondrules isothermal runs of less than 5 min at 1350 1550 c result in goa disaggregation and fe mg exchange runs of 0 5 4 h show textures superficially similar to granular and po chondrules but with reversely zoned olivine charges isothermally heated at 1550 c for 1 and 4 h before being cooled at 10 and 100 c h undergo olivine crystallization and yield classical po textures although most evidence of origin from goa is erased the cores of normally zoned euhedral crystals are relict as phenocrysts in type i chondrules can be relict such chondrules could have experienced similar peak temperatures to those of type ii chondrules chondrules containing goa with olivine triple junctions resemble experimental charges heated for minutes at temperatures between 1350 and 1450 c and type i chondrules with subhedral to anhedral olivine plus goa relicts resemble charges heated at the same temperatures but for longer duration type i chondrules with a mass of granular olivine or irregular anhedral olivine grains in the center and much glass nearer the margin on the other hand require limited heating at high temperature 1550 c while type i chondrules with euhedral olivines resemble charges heated at 1550 c for 4 h the majority of type i chondrules in cv chondrites display evidence of derivation from goa many finer grained chondrules in cr and uoc on the other hand could not have been derived from such coarse grained precursors but could have formed from fine grained dustballs as stipulated in the standard paradigm thus both goa and dustballs represent viable chondrule precursors of coarser and finer grained type i po chondrules respectively

evidence for the presence of planetesimal material among the precursors of magnesian chondrules of nebular origin abstract chondrules are the major high temperature components of chondritic meteorites which are conventionally viewed as the samples from the very first generation of undifferentiated planetesimals growing evidences from long and short lived radionuclide chronologies indicate however that chondrite parent asteroids accreted after or contemporaneously with igneous activities on differentiated asteroids questioning the pristine nature of chondrites here we report a discovery of metal bearing olivine aggregates with granoblastic textures inside magnesian porphyritic type i chondrules from the cv carbonaceous chondrite vigarano formation of the granoblastic textures requires sintering and prolonged high temperature 1000 c annealing conditions which are not expected in the solar nebula during chondrule formation but could have been achieved on parent bodies of olivine rich differentiated or thermally metamorphosed meteorites the mineralogy and petrography of the metal olivine aggregates thus indicate that they are relict dunite like lithic fragments which resulted from fragmentation of such bodies the very old pb pb absolute ages and al mg relative model ages of bulk cv chondrules suggest that such planetesimals may have formed as early as the currently accepted age of the solar system 4567 2 0 6 ma

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

condensation of major elements during chondrule formation and its implication to the origin of chondrules abstract two glassy refractory al rich chondrules in semarkona ll3 0 the most primitive unequilibrated ordinary chondrite provide direct evidence for condensation of si and mg on melt droplets during cooling the chondrules are completely rounded rich in ca and al and poor in fe and alkalis they have extraordinarily abundant glass 70 80 vol with a subordinate amount of forsterite as the only crystalline phase that occurs mostly rimming the chondrule edge the groundmass glass is concentrically zoned in terms of si with an outward increase which is overlapped with local heterogeneity of mg and al induced by crystallization of forsterite the outward increase of si mostly compensated by al cannot be formed solely by crystallization of forsterite from a homogeneous melt in a closed system combined with skeletal or dendritic morphology and sector zoning of forsterite it is suggested that si condensed onto totally molten droplets initial melts accompanied by nucleation and rapid growth of forsterite with lowering temperature the initial melts the compositions of which were estimated from the ca contents of the first crystallized forsterite are very similar to type c cai but are notably poorer in mg and si than the bulk chondrules indicating condensation of mg in addition to si with an atomic ratio of mg si 3 2 the condensation after the nucleation of forsterite took place below 1300 c under cooling at 70 c h and amounted to 30 wt of the current chondrule this study suggests a model that a short time and local shock heating event induced melting of type c cai and concomitant evaporation of dusts ferromagnesian chondrules of earlier generation and their fragments to generate mg and si rich gas which condensed onto the melt droplets upon cooling accompanying condensation of type i chondrules

the impact of sediment provenance on barium based productivity estimates abstract biogenic barium in marine sediments has been suggested to be a reliable proxy of export productivity from the surface ocean and algorithms have been developed to link these properties however problems arise when the proposed algorithms are applied to predominantly terrigenous sediments a major source of error is incorrect estimates of the terrigenous ba al ratio in normative calculations of the amount of biogenic barium in the sediment compared to an often used global average ba al ratio much better results can be obtained by estimating the terrigenous ba al ratio from exponential regression of the ba al ratios of surface sediments obtained from continental slope transects this method has been applied to surface sediments from the chilean continental slope the calculated regional terrigenous ba al ratios could be verified with purely terrigenous samples from chilean rivers the resulting accumulation rates of biogenic barium on the chilean continental slope reliably reproduce the regional pattern of primary productivity in the southern peru chile current indicating the potential of biogenic barium as a useful paleo productivity proxy

climatically sensitive eolian and hemipelagic deposition in the cariaco basin venezuela over the past 578 000 years results from al ti and k al al ti and k al ratios in bulk sediment are used to interpret wind blown and hemipelagic sources of deposition to a 578 kyr record in the cariaco basin venezuela ocean drilling program site 1002 graphical and cross spectral analyses indicate that these ratios vary extremely closely with planktonic foraminiferal 18o with both ratios being significantly higher during interglacials and lower during glacials k al indicates that during glacials the lower sea level that results in relative basin isolation increases the relative proportion of kaolinite derived from local rivers draining the relatively humid venezuelan margin al ti decreases during glacials suggesting greater proportions of eolian rutile sourced from the northern sahara due to increased wind strength and or aridity this interpretation is consistent with previous studies of the chemistry and mineralogy of saharan derived eolian matter in the caribbean and with a mass balance determining the effect of changes in eolian rutile accumulation on the bulk sedimentary al ti ratio

origin of glass inclusions hosted in magnesian porphyritic olivines chondrules deciphering planetesimal compositions abstract glass inclusions occur in the most primitive magnesian porphyritic olivines of chondrules formed very early in the solar system and understanding their formation and preservation is crucial for explaining early solar system evolution several different and frequently opposed models have been proposed to explain the origin of these glass inclusions and their host olivines ranging from condensation processes in the nebula to crystallization products of chondrule melts however none of these models fully satisfy all the petrographic chemical and isotopic observations in this experimental work we show that the peculiar compositions of these inclusions that exhibit significant chemical disequilibrium between glass and host olivine result from the slow crystallization of metastable olivines from a magma the inhibition of plagioclase nucleation resulting in metastable olivine crystallization instead of the equilibrium assemblage anorthite clinopyroxene is a natural consequence of the high liquidus temperature of the magma this result implies a restricted compositional range for the parental magmas of these melt inclusions olivine phenocrysts inside type ia chondrules are thus interpreted as fragments of magmatic cumulates formed in magma ocean like environments on fully or partially molten planetesimals in a similar manner as for terrestrial rocks studies of melt inclusions giving information about the earliest magma oceans could open a new way of assessing the evolution of the earliest bodies of the solar system

a rb sr record of catchment weathering response to holocene climate change in inner mongolia variation in the rubidium to strontium rb sr ratio of the loess palaeosol sequences has been proposed to reflect the degree of pedogenesis and weathering in the northwestern region of china to characterize the rb sr ratio of the dissolved loads of a single catchment we analysed a 12 08 m sediment core from daihai lake in inner mongolia north china dating control was provided by 210pb 137cs and ams 14c sequential extraction experiments were conducted to investigate the concentrations of rb and sr on various chemical fractions in the lake sediments down core variation in the rb sr ratios provides a record of holocene weathering history from 9 to 3 5 ka bp accelerated chemical weathering was experienced throughout the daihai catchment under mainly warm and humid conditions and this reached a maximum at c 5 ka bp however weathering was reduced between c 8 25 and 7 90 ka bp which may reflect the global 8 2 ka cooling event after c 2 5 ka bp increased rb sr ratios with higher frequency of fluctuations indicate reduced weathering within the daihai catchment the highest rb sr ratios in the little ice age lake sediments indicate the weakest phase of holocene chemical weathering resulting from a marked reduction in sr flux into the basin the rb sr record also shows an enhancement of chemical weathering under today s climate but its intensity is less than that of the medieval warm period increased rb sr in lake sediment corresponding to reduced catchment weathering is in striking contrast to rb sr decrease in the glacial loess layers in the loess palaeosol sequence copyright 2005 john wiley sons ltd

high resolution sea surface temperature records derived from foraminiferal mg ca ratios during the last 260 ka in the northern south china sea abstract high resolution sea surface temperatures sst derived from mg ca ratios of globeriginoides sacculifer at odp site 1144 were reported to reveal the sst changes during the last 260 ka in the northern south china sea scs the results indicate an average holocene sst of about 26 7 c about 3 6 c increase from lgm to the holocene and higher temperature during mis 5 5 than the holocene these agree well with other foraminifer mg ca and uk37 sst records in this region the mg ca records suggest warmer ssts during mis 3 in the northern scs compared with those in the eastern pacific strong east asian summer monsoon during mis 3 indicated by paleoclimate records from nearby continents may account for it step wise increases during terminations are shown in our sst record and the beginning of deglacial warming occurs at about 19 ka which precedes the change of oxygen isotopes suggesting a tropical driven forcing for the sst change in the northern scs this is further supported by a robust semi precessional cycle centering at 9 1 ka in the spectra of the sst record which is absent in that of the oxygen isotopes however tropical driven forcing seems not to be indicated in another mg ca sst record in the northern scs oppo d w and sun y b 2005 amplitude and timing of sea surface temperature change in the northern south china sea dynamic link to the east asian monsoon geology 33 10 785 788 the discrepancy may be caused by different post deposition dissolutions of foraminifer tests at these two sites details about the modification of foraminifer mg ca ratios after burial however are not well known in this region and further studies are needed

linking the acadian orogeny with organic rich black shale deposition evidence from the marcellus shale abstract the trace and rare earth elements ree analyses were conducted on samples collected from a 30 m core of the marcellus shale obtained from greene county southwestern pennsylvania our results suggest that organic matter enrichment trends in the marcellus shale can be directly linked with the acadian orogeny the acadian orogeny has been recognized as a main sediment source for the marcellus shale synthesis of tectonic history and recent ash bed geochronology reveals that deposition of the organic carbon rich or zone characterized by toc 4 located between 2393 m and 2406 5 m core depth in the studied marcellus shale core was coincident with tectonically active and magmatic quiescent period of the acadian orogeny ca 395 380 ma this time period also corresponds to the highest rate of mountain building in the acadian orogeny the light rare earth lree and selected trace elemental e g ta cs composition of the or zone sediments is similar to that of the bulk continental crust supporting the lack of magmatic activity in the source area i e acadian orogeny in contrast subsequent deposition of the organic carbon poor op sediments characterized by toc

localized shock melting in lherzolitic shergottite northwest africa 1950 comparison with allan hills 77005 the lherzolitic martian meteorite northwest africa nwa 1950 consists of two distinct zones 1 low ca pyroxene poikilically enclosing cumulate olivine fo70 75 and chromite and 2 areas interstitial to the oikocrysts comprised of maskelynite low and high ca pyroxene cumulate olivine fo68 71 and chromite shock metamorphic effects most likely associated with ejection from the martian subsurface by large scale impact include mechanical deformation of host rock olivine and pyroxene transformation of plagioclase to maskelynite and localized melting pockets and veins these shock effects indicate that nwa 1950 experienced an equilibration shock pressure of 35 45 gpa large millimeter size melt pockets have crystallized magnesian olivine fo78 87 and chromite embedded in an fe rich al poor basaltic to picro basaltic glass within the melt pockets strong thermal gradients minimum 1 c m existed at the onset of crystallization giving rise to a heterogeneous distribution of nucleation sites resulting in gradational textures of olivine and chromite dendritic and skeletal olivine crystallized in the melt pocket center has a nucleation density 1 0 x 10 3 crystals mm 2 that is two orders of magnitude lower than olivine euhedra near the melt margin 1 6 x 10 5 crystals mm 2 based on petrography and minor element abundances melt pocket formation occurred by in situ melting of host rock constituents by shock as opposed to melt injected into the lherzolitic target despite a common origin nwa 1950 is shocked to a lesser extent compared to allan hills alh 77005 45 55 gpa assuming ejection in a single shock event by spallation this places nwa 1950 near to alh 77005 but at a shallower depth within the martian subsurface extensive shock melt networks the interconnectivity between melt pockets and the ubiquitous presence of highly vesiculated plagioclase glass in alh 77005 suggests that this meteorite may be transitional between discreet shock melting and bulk rock melting

a magmatic origin for silica rich glass inclusions hosted in porphyritic magnesian olivines in chondrules an experimental study rare silica rich glass inclusions 69 sio2 82 wt are described within magnesian olivines of porphyritic type ia chondrules these glass inclusion compositions are clearly out of equilibrium with their host mg olivines and their presence within the olivines is generally attributed to an unclear secondary process such as a late interaction with nebular gases we performed dynamic crystallisation experiments that demonstrate that these si rich glass inclusions are actually magmatic in origin and were trapped inside olivines that crystallized slowly from a magma with a ci i e solar composition their silica rich compositions are the consequence of the small volumes of inclusions which inhibit the nucleation of secondary crystalline phase ca poor pyroxene but allow olivine to continue to crystallize metastably on the walls of the inclusions we suggest that si rich glass inclusions could be the only reliable relicts of what were the first magmas of the solar system exhibiting a ci i e non fractionated composition

cortex a shipboard xrf scanner for element analyses in split sediment cores abstract the cortex corescanner texel is a non destructive xrf system for the logging of split sediment cores it is a seaworthy instrument that remains active during heavy weather conditions the scanner produces reliable counts for k to sr highly correlated with concentrations measured with atomic absorption spectrometry aas the option to scan al si and elements heavier than sr is in preparation a core section of 1 m can be scanned at 2 cm intervals within an hour a maximum resolution of 1 mm can be achieved at present each region and sedimentary environment requires separate calibration in the nearby future the generator settings will be standardized which may result in the development of a standard calibration procedure because of the high resolution of its semi quantitative records the cortex is a useful tool for detailed time series analysis inter core correlation and shipboard analysis

late pleistocene and holocene aeolian dust deposition in north china and the northwest pacific ocean abstract rates of dust deposition in the north pacific and the central loess plateau of china show a poor correlation during the last 30 000 yr although in both cases the dust was derived from deserts in northern china loess accumulation rates were high at the time of the last glacial maximum while dust flux to the north pacific was low at this time maximum dust flux to the north pacific is recorded in the mid holocene but holocene rates of loess accumulation have been low these differences are shown to reflect the different nature of the wind conditions responsible for dust transport to the loess plateau and the north pacific dust transport responsible for formation of the loess occurred mainly in the lower 1 5 km of the atmosphere and was accomplished by cold low level northwesterly winds associated with cold waves emanating from the mongolian anticyclone at present such conditions occur quite frequently in winter but during the coldest phases of the pleistocene they probably also occurred in the spring and summer long range dust transport from northern china to the north pacific requires that the dust is lifted to high levels above 3 km where it can be incorporated into the strong mid latitude westerlies strong vertical motions of the atmosphere occur most frequently in the spring when the mongolian anticyclone begins to weaken and frontal depressions move across the deserts of northern china such frontal depressions were probably more frequent during the climatic optimum of the mid holocene and during previous interglacials changes in continental aridity have probably played a minor role in controlling the magnitude of the dust flux to the north pacific

strengthening of paleo typhoon and autumn rainfall in taiwan corresponding to the southern oscillation at late holocene the purpose of this study is to improve prehistoric knowledge of paleo typhoon and winter monsoon activity in the western north pacific after 8 cal ka bp we examine two sediment cores derived from lakes located to the south and north of the ilan plain in northeastern taiwan seasonal and typhoon rainfall data over the past several decades are collected for this study region we also use mineral indicators k rb ratios and grain size to estimate sediment sources intensity of chemical weathering and rainfall intensity the results show that the chemical weathering index k rb ratio of meihua lake indicates the continuing effects of autumn rainfall while coarse grain sizes of dahu lake sediments suggest increased intensity in typhoon rainfall grain size results reveal that increasing el nino southern oscillation intensity in the tropical pacific has intensified the activity of super typhoons in the western north pacific finally we find that frequent activity of super paleo typhoons occurred in taiwan during the la nina like state and the strengthening winter monsoon activity and higher sea surface temperature enhanced plentiful autumn rainfall in el nino like state after comparing our results with the paleo typhoon data in japan and south china we suggest that the tracks of super typhoon are mainly affected by variations in the warm pool and subtropical northwestern pacific high in the western pacific copyright 2012 john wiley sons ltd

microstructural evidence for complex formation histories of amoeboid olivine aggregates from the alha77307 co3 0 chondrite the microstructures and compositions of olivine and refractory components in six amoeboid olivine aggregates aoas in the allan hills a77307 co3 0 chondrite have been characterized in detail using the focused ion beam sample preparation technique with transmission electron microscopy in the aoas refractory components perovskite melilite spinel anorthite and al ti bearing diopside provide evidence of a high degree of textural and compositional heterogeneity suggesting that these phases have formed by disequilibrium gas solid condensation at high temperatures under highly dynamic conditions we infer different possible reactions of early condensed solid minerals perovskite and spinel with a nebular gas forming diopside with wide ranges of al and ti contents and or anorthite the progressive incomplete consumption of spinel in these reactions may have resulted in the cr enrichment in the remaining unreacted spinel in the aoas in contrast to the refractory components olivines in the aoas have equilibrated textures with 120 triple junctions indicating that the aoas were subjected to high temperature annealing after agglomeration of olivine and refractory components because the aoas consist of fine grained olivine grains with numerous pores the annealing is constrained by experimental data to have occurred for a short duration of the order of a few hours to tens of hours depending on the annealing temperature in comparison the effects of annealing on the refractory components are minimal probably due to pinning of grain boundaries in the multiphase assemblages that inhibited grain growth

southward migration of the intertropical convergence zone through the holocene titanium and iron concentration data from the anoxic cariaco basin off the venezuelan coast can be used to infer variations in the hydrological cycle over northern south america during the past 14 000 years with subdecadal resolution following a dry younger dryas a period of increased precipitation and riverine discharge occurred during the holocene thermal maximum since approximately 5400 years ago a trend toward drier conditions is evident from the data with high amplitude fluctuations and precipitation minima during the time interval 3800 to 2800 years ago and during the little ice age these regional changes in precipitation are best explained by shifts in the mean latitude of the atlantic intertropical convergence zone itcz potentially driven by pacific based climate variability the cariaco basin record exhibits strong correlations with climate records from distant regions including the high latitude northern hemisphere providing evidence for global teleconnections among regional climates

discrimination of geochemical compositions between the changjiang and the huanghe sediments and its application for the identification of sediment source in the jiangsu coastal plain china concentrations of 25 elements in the fine grained fraction 6 63 wm of bottom sediments of the changjiang and the huanghe were determined to characterize the geochemical compositions of each riverine origin most of the elements except for alkali and alkaline earth elements na ca sr and ba are highly enriched in the changjiang sediments compared to those in the huanghe sediments differences in source rocks and weathering mechanisms between the two drainage basins are the major factors controlling those compositional characteristics the provenance index of core sediments from the northern jiangsu coastal plain calculated with nine elements with distinct compositional differences between both river sediments indicates that the changjiang had prevailed in the coastal plain sedimentation during the early stage of holocene while the huanghe dominated over the area during the late holocene however neither of the signatures of the modern changjiang and huanghe derived sediments is remarkable in the present day coastal plain 5 2002 elsevier science b v all rights reserved

silicon isotopic compositions of chondrule silicates in carbonaceous chondrites and the formation of primordial solids in the accretion disk abstract we determined the silicon isotopic compositions of silicates olivine and low ca pyroxene in type i and type ii chondrules of the carbonaceous chondrites allende kaba nwa northwest africa 5958 and mil miller range 07342 type i chondrule silicates show large mass dependent si isotopic fractionations with 30 si values ranging from 7 to 2 6 whereas the 30 si values of type ii chondrule silicates are close to zero and vary by less than 2 when present mg rich relict olivine grains in type ii chondrules show larger si variations than their feo rich counterparts in type i chondrules low ca pyroxenes yield systematically lighter 30 si values than mg rich olivines our results show that type i chondrules are complex objects whose si isotopic compositions derived from their precursors and sio rich gas melt interactions this corroborates that type i chondrules are nebular products that formed under open system conditions our data also suggest that at least some type ii chondrules derived from their type i counterparts overall this demonstrates that recycling was common during the evolution of the protoplanetary disk

mass independent fractionation of oxygen isotopes in the mesostasis of a chondrule from the semarkona ll3 0 ordinary chondrite abstract a large chondrule from semarkona the most primitive ordinary chondrite known has been discovered to contain a record of mass transport during its formation in most respects it is a normal type i group a1 low feo chondrule that was produced by reduction and mass loss during the unidentified flash heating event that produced the chondrules the most abundant structural component in primitive meteorites we have previously measured elemental abundances and abundance profiles in this chondrule we here report oxygen isotope ratio abundances and ratio abundance profiles we have found that the mesostasis is zoned in oxygen isotope ratio with the center of the chondrule containing isotopically heavier oxygen than the outer regions the outer regions being volatile rich from the diffusion of volatiles into the chondrule during cooling the 17o values range from 2 0 to 9 9 while 18o range from 1 9 to 9 6 more importantly a plot of 17o against 18o has a slope of 1 1 0 2 1 and 0 88 0 10 1 when measured by two independent methods co variation of 17o with 18o that does not follow mass dependent fractionation has often been seen in primitive solar system materials and is usually ascribed to the mixing of different oxygen reservoirs we argue that petrographic and compositional data indicate that this chondrule was completely melted at the time of its formation so that relic grains could not have survived furthermore there is petrographic and compositional evidence that there was no aqueous alteration of this chondrule subsequent to its formation although it is possible to formulate a series of exchanges between the chondrule and external 16o rich and 16o poor reservoirs that may explain the detailed oxygen isotope systematics of this chondrule such a sequence of events looks very contrived we therefore hypothesize that reduction devolatilization and crystallization of the chondrule melt may have produced 16o rich olivines and 16o poor mesostasis plotting on a slope one line as part of the chondrule forming process in an analogous fashion to known chemical mass independent isotopic fractionation mechanisms during cooling volatiles and oxygen near the terrestrial line in oxygen isotope composition produced the outer zone of volatile rich and 16o rich mesostasis the chondrule therefore not only retains a record of considerable mass transport accompanying formation but also may indicate that the isotopes of oxygen underwent mass independent fractionation during the process

evidence for fractional condensation and reprocessing at high temperatures in ch chondrites we performed a detailed study of silica rich components src in the paired ch chondrites acfer 182 and 207 these srcs appear either as chondrules or fragments and they contribute 0 1 vol to the bulk meteorite they usually contain a silica and a silicate portion both portions are in most cases cryptocrystalline and have bulk sio2 concentrations between 65 and 85 wt the silicate generally has a pyroxene normative composition the silica often appears as blebs within the silicate matrix or vice versa if there are no blebs silica and silicate still form rounded interfaces the srcs are depleted in refractory elements like ca al and ti relative to ci a few src like objects are extremely rich in mn and show no depletion in refractory elements we conducted micro raman studies on the silica portions of the srcs to determine their structure and we identified several silica phases quartz cristobalite glass and a yet unidentified polymorph the silicate portion is glass when the silica is glass and crystalline when the silica is crystalline the low contents of al and ca make an igneous origin of the srcs very unlikely and the absence of metal excludes the formation by reduction of pyroxene we suggest instead a fractional condensation origin of the srcs from a si enriched gas after removal of gaseous mg by forsterite condensation additional evidence for fractional condensation is provided by a unique layered object with olivine in the core pyroxene and metal at the rim and silica at the outermost border these layers record the condensation sequence two chondrules were found with several percent of mn and high cr na and k contents providing further evidence for condensation from a fractionated gas the texture of the srcs and the occurrence of cristobalite and silica glass however require formation by liquid immiscibility at high temperatures above 1968 k and subsequent fast cooling therefore we propose a 2 stage model for the formation of srcs in ch chondrites 1 fractional condensation of forsterite enstatite and sio2 rich phases and 2 reheating of sio2 rich components to temperatures above 1968 k followed by rapid cooling all other phases identified in ch chondrites can be understood within the framework of this model thus the extremely unequilibrated ch chondrites provide a wealth of evidence for fractional condensation processes in the early solar nebula in metals meibom et al 1999 and in silicates

sea level and deep water temperature changes derived from benthic foraminifera isotopic records we show that robust regressions can be established between relative sea level rsl data and benthic foraminifera oxygen isotopic ratios from the north atlantic and equatorial pacific ocean over the last climatic cycle we then apply these regressions to long benthic isotopic records retrieved at one north atlantic and one equatorial pacific site to build a composite rsl curve as well as the associated confidence interval over the last four climatic cycles our proposed reconstruction of rsl is in good agreement with the sparse rsl data available prior to the last climatic cycle we compute bottom water temperature changes at the two sites and at one southern indian ocean site taking into account potential variations in north atlantic local deep water 18o our results indicate that a last glacial maximum lgm enrichment of the ocean mean oxygen isotopic ratio of 0 95 is the lowest value compatible with unfrozen deep waters in the southern indian ocean if local deep water 18o did not increase during glacials with respect to present such a value of the lgm mean ocean isotopic enrichment would impose a maximum decrease in local bottom water 18o at the north atlantic site of 0 30 during glacials

a developmental model of olivine morphology as a function of the cooling rate and the degree of undercooling we performed dynamic crystallization experiments in the cmas system at 1 atm to investigate the evolution of the morphology of forsterite crystals as a function of cooling rate and degree of undercooling in sections parallel to the 010 plane we observed the evolution of the forsterite morphology from tablets to hopper skeletal crystals and then to swallowtail shapes dendritic morphology for increased degree of undercooling the other shapes described in the literature can be interpreted as particular sections of those three shapes the onset of dendritic growth is due to a competition between the growth of the faces of the initial hopper crystal and dendrite overgrowths the forsterite dendrites are formed by a succession of units which look like hopper shapes this result has been tested by an additional set of experiments

silica bearing chondrules and clasts in ordinary chondrites unusual silica bearing chondrules and clasts have been observed in several unequilibrated ordinary chondrites there appear to be two distinct types i silica low ca pyroxene assemblages and ii silica fayalite intergrowths coexisting with low ca pyroxene only the former types are chondrules the bulk compositions of most of these objects can be expressed in terms of three components mgo feo and sio 2 since ca al and na are essentially trace elements secondary alteration has probably perturbed the fe mg ratios in most objects and produced ca rich pyroxenes in some type ii clasts but the silica low ca pyroxene and fayalite are hard to understand as other than primary phases such silica rich bulk compositions can be understood as an intermediate temperature condensate of a solar gas formed by the loss of refractory solid material by gas solid separation before the complete condensation of silicon alternatively the silicarich bulk compositions could have been formed by extreme reduction of normal chondritic olivine and orthopyroxene however the observed ca al depletion and the lack of ni poor metals are not explained by this model the fayalite bearing clasts can be explained by a relatively complex two stage process involving reduction followed by oxidation partial reduction of olivine in the presence of s produces mg rich pyroxene silica and fefes oxidation of metal and sulfide followed by reaction with silica forms fayalite an alternative is that the fayalite bearing clasts result from the decomposition of ferrosilite but this requires the production of metastable ferrosilite during shock or some other high pressure event the simplest unflawed alternative is that the fayalite bearing clasts result from the mixing of a partially molten silica fayalite liquid with mg rich pyroxene