analysis of ordinary chondrites using powder x ray diffraction 2 applications to ordinary chondrite parent body processes abstract we evaluate the chemical and physical conditions of metamorphism in ordinary chondrite parent bodies using x ray diffraction xrd measured modal mineral abundances and geochemical analyses of 48 type 4 6 ordinary chondrites several observations indicate that oxidation may have occurred during progressive metamorphism of equilibrated chondrites including systematic changes with petrologic type in xrd derived olivine and low ca pyroxene abundances increasing ratios of mgo mgo feo in olivine and pyroxene mean ni fe and co fe ratios in bulk metal with increasing metamorphic grade and linear fe addition trends in molar fe mn and fe mg plots an aqueous fluid likely incorporated as hydrous silicates and distributed homogeneously throughout the parent body was responsible for oxidation based on mass balance calculations a minimum of 0 3 0 4 wt h2o reacted with metal to produce oxidized fe prior to oxidation the parent body underwent a period of reduction as evidenced by the unequilibrated chondrites unlike olivine and pyroxene average plagioclase abundances do not show any systematic changes with increasing petrologic type based on this observation and a comparison of modal and normative plagioclase abundances we suggest that plagioclase completely crystallized from glass by type 4 temperature conditions in the h and l chondrites and by type 5 in the ll chondrites because the validity of using the plagioclase thermometer to determine peak temperatures rests on the assumption that plagioclase continued to crystallize through type 6 conditions we suggest that temperatures calculated using pyroxene goethermometry provide more accurate estimates of the peak temperatures reached in ordinary chondrite parent bodies

an amoeboid olivine inclusion aoi in ck3 nwa 1559 comparison to aois in cv3 allende and the origin of aois in ck and cv chondrites an amoeboid olivine inclusion in ck3 nwa 1559 0 54 1 3 mm consists of a diopside rich interior approximately 35 vol and an olivine rich rim approximately 65 vol it is the first aoi to be described in ck chondrites the apparent paucity of these inclusions is due to extensive parent body recrystallization the aoi interior contains irregular 3 15 m sized al bearing diopside grains approximately 70 vol 2 20 m sized pores approximately 30 vol and traces of approximately 2 m plagioclase grains the 75 160 m thick rim contains 20 130 m sized ferroan olivine grains some with 120o triple junctions a few coarse 25 50 m sized patches of plagioclase with 2 18 m thick diopside rinds occur in several places just beneath the rim the occurrence of olivine rims around aoi 1 and around many aois in cv3 allende suggests that ck and cv aois formed by the acquisition of porous forsteritic rims around fine grained rimless cais that consisted of diopside anorthite melilite and spinel individual aois in carbonaceous chondrites may have formed after transient heating events melted their olivine rims as well as portions of the underlying interiors in aoi 1 coarse plagioclase grains with diopside rinds crystallized immediately below the olivine rim secondary parent body alteration transformed forsterite in the rims of cv and ck aois into more ferroan olivine some of the abundant pores in the interior of aoi 1 may have formed during aqueous alteration after fine grained melilite and anorthite were leached out chondrite groups with large chondrules tend to have large aois aois that formed in dust rich nebular regions where cv and ck chondrites later accreted tend to be larger than aois from less dusty regions

oxygen isotopic compositions and origins of calcium aluminum rich inclusions and chondrules primary minerals in calcium aluminum rich inclusions cais al rich and ferromagnesian chondrules in each chondrite group have 18o values that typically range from 50 to 5 0 neglecting effects due to minor mass fractionations the oxygen isotopic data for each chondrite group and for micrometeorites define lines on the three isotope plot with slopes of 1 01 0 06 and intercepts of 2 1 this suggests that the same kind of nebular process produced the 16o variations among chondrules and cais in all groups chemical and isotopic properties of some cais and chondrules strongly suggest that they formed from solar nebula condensates this is incompatible with the existing two component model for oxygen isotopes in which chondrules and cais were derived from heated and melted 16o rich presolar dust that exchanged oxygen with 16o poor nebular gas some fun cais inclusions with isotope anomalies due to fractionation and unknown nuclear effects have chemical and isotopic compositions indicating they are evaporative residues of presolar material which is incompatible with 16o fractionation during mass independent gas phase reactions in the solar nebula there is only one plausible reason why solar nebula condensates and evaporative residues of presolar materials are both enriched in 16o condensation must have occurred in a nebular region where the oxygen was largely derived from evaporated 16o rich dust a simple model suggests that dust was enriched or gas was depleted relative to cosmic proportions by factors of 10 to 50 prior to condensation for most cais and factors of 1 5 for chondrule precursor material we infer that dust gas fractionation prior to evaporation and condensation was more important in establishing the oxygen isotopic composition of cais and chondrules than any subsequent exchange with nebular gases dust gas fractionation may have occurred near the inner edge of the disk where nebular gases accreted into the protosun and shu and colleagues suggest that cais formed

characterising three dimensional anisotropic spatial correlation of soil properties through in situ test results proper characterisations of soil properties and their variations are pivotal to the geotechnical design process although multiple in situ soil tests are routinely specified and performed in geotec

16 o rich melilite in co3 0 chondrites possible formation of common 16 o poor melilite by aqueous alteration a problem of long standing is the origin of the high 17o 17o 0 52 18o values of melilite in the refractory inclusions of carbonaceous chondrites the spinel and usually also the diopside in the inclusions have primitive 17o 20 but in the widely studied cv3 chondrite allende the melilite commonly has a 17o of about 4 2 recent studies of oxygen diffusion coefficients in melilite and spinel have shown that the traditional model for altering the melilite diffusive exchange with the gas in the solar nebula cannot occur under plausible nebular scenarios because of increasing evidence for aqueous alteration of allende and other carbonaceous chondrites we tested the hypothesis that melilite alteration might occur during aqueous alteration by studying melilite in co chondrites showing variable degrees of alteration our results show that almost all melilite in co3 2 kainsaz and co3 3 ornans has 17o 15 whereas in co3 0 colony and inclusions in co3 0 yamato 81020 studied by itoh et al 2000 17o in the melilite is 20 with the exception of one unusual inclusion that has undergone two melting episodes we suggest that the o isotopic composition of the melilite is reset by dissolution of the primitive melilite and reprecipitation in the presence of h2o having a high 17o value similar to that inferred from studies of cv magnetite choi et al 1997 choi et al 2000 although alteration of melilite can produce phases such as nepheline andradite and hedenbergite it appears that depending on the composition of the microenvironment melilite present in a high energy state because of fine grain size dislocations other defects can dissolve and reprecipitate with an o isotopic composition intermediate between the initial composition and that of the h2o a possible implication of our study is that the slope 0 9 arrays observed in the minerals of refractory inclusions of many carbonaceous chondrites could be mainly the result of aqueous alteration

microfabric analysis of mn carbonate laminae deposition and mn sulfide formation in the gotland deep baltic sea the manganese carbonate deposits of the anoxic littorina sediments of the gotland deep have been commonly related to the periodic renewal of deep water by inflowing saline water from the north sea the use of scanning electron microscopy based techniques allows identification of small scale sedimentary and geochemical features associated with mn carbonate laminae which has significant implications for models of mn carbonate formation varves occurring in the littorina sequence contain up to four laminae that may be placed in a seasonal cycle and kutnahorite laminae occur within varves only as a winter early spring deposit this kutnahorite laminae seasonality is in agreement with the seasonal distribution of major baltic inflow events recorded in historical records and a direct causal link between inflows and kutnahorite deposition is implied benthic foraminifera tests are found to be heavily encrusted in kutnahorite implying that benthic recolonization during oxidation events occurs concurrently with kutnahorite formation the relatively common occurrence of small 50 to 100 m hexagonal mn sulfide pseudomorphs associated with 13 of kutnahorite laminae studied is reported in gotland deep sediments for the first time although mn sulfide crystals are not usually preserved in the sediment the discovery of mn sulfide pseudomorphs suggests that initial formation of mn sulfide in the gotland deep may occur much more commonly during the process of kutnahorite formation than previous reports of mn sulfide occurrence have implied

oxygen isotopes in r chondrite magnetite and olivine links between r chondrites and ordinary chondrites ion microprobe studies yield 17o 17o 0 52 18o values in magnetite from the rumurti chondrite rc pca91241 which is paired with pca91002 of 3 1 to 3 9 slightly higher than that in o from whole rock r samples despite 17o values in whole rock rcs that are much by ca 1 6 higher than in whole rock ll chondrites the 17o in r magnetite is much lower by ca 2 than the values 4 to 7 from ll3 semarkona and ngawi choi et al 1998 the 18o values in pca magnetite 15 to 10 are the lowest known in meteorites well below the range in semarkona 4 to 9 on a 17o 18o diagram both magnetite data sets form linear arrays with slopes of ca 0 7 indicating mixing of o from different isotopic reservoirs the slopes and intercepts of the two arrays are similar enough to permit them to be segments of a single array this suggests that in rcs and ll chondrites magnetite formed from the same raw materials by the same processes probably by aqueous alteration of metal in an asteroidal setting we observed 17o values in olivines and pyroxene from rcs ranging from 1 2 to 2 9 and 18o from 1 4 to 9 1 these compositions scatter in the same general range observed in chondrules from ordinary chondrites the similarity in the o isotopic composition of minerals that preserve a record of formation in the solar nebula supports a model in which rcs formed from nebular components similar to those in h chondrites but with a matrix chondrule ratio several times higher in the rcs and with more extensive aqueous alteration in the rcs than in known h chondrites we postulate that the matrix in r chondrites has 17o higher than whole rock values we suggest that the original 17o value of h2o in the rc body was similar to that incorporated into the ordinary chondrites previously estimated by choi et al 1998 to be ca 7 in the ll parent body

determination of efficient sampling locations in geotechnical site characterization using information entropy and bayesian compressive sampling site characterization is indispensable in geotechnical engineering practice and measurements on soil properties are performed through in situ tests laboratory tests or other methods however due

oxygen isotope studies of carbonaceous chondrites abstract the carbonaceous chondrites display the widest range of oxygen isotopic composition of any meteorite group as a consequence of the interaction of primordial isotopic reservoirs in the solar nebula these isotopic variations can be used to identify the reservoirs and to determine conditions and loci of their interactions we present a comprehensive set of whole rock analyses of cv co ck cm cr ch and ci chondrites as well as selected components of some of these meteorites a simple model is developed which describes the isotopic behavior during parent body aqueous alteration processes the process of thermal dehydration also produces a recognizable effect in the oxygen isotopic composition

the oxygen isotope record in murchison and other carbonaceous chondrites the ranges of 18o and 17o in components of the murchison c2 chondrite exceed those in all other meteorites analyzed previous authors have proposed that c2 chondrites are the products of aqueous alteration of anhydrous silicates a model is presented to determine whether the isotopic variations can be understood in terms of such alteration processes the minimum number two of initial isotopic reservoirs is assumed two major stages of reservoir interaction are required one at high temperature to produce the16o mixing line observed for the anhydrous minerals and another at low temperature to produce the matrix minerals the isotopic compositions severely constrain the conditions of the low temperature process requiring temperatures 44 extension of the model to the data on c1 chondrites requires aqueous alteration in a warmer wetter environment

the geographical distribution and palaeo ecology of selenopemphix undulata sp nov a new late quaternary dinoflagellate cyst from the pacific ocean abstract detailed palynological studies in the northeast ne pacific strait of georgia bc canada southeast se pacific and northwest pacific dongdo bay south korea resulted in the recognition of the new dinoflagellate cyst species selenopemphix undulata sp nov this species is restricted to cool temperate to sub polar climate zones where it is found in highest relative abundances in highly productive non to reduced upwelling regions with an annual mean sea surface temperature asst below 16 c and an annual mean sea surface salinity asss between 20 and 35 psu those observations are in agreement with the late quaternary fossil records from santa barbara basin odp 893 34 n and offshore chile odp 1233 41 s where this species thrived during the last glacial this period was characterised by high nutrient availability and the absence of species favouring upwelling conditions the indirect dependence of s undulata sp nov abundances on nutrient availability during reduced or non upwelling periods is expressed by the synchronous fluctuations with diatom abundances since the distribution and growth rates of the latter are directly related with the availability of macronutrients in the surface waters

the oxygen isotopic composition of olivine and pyroxene from ci chondrites the ci chondrites are taken to represent average solar system material based on the similarity of their elemental compositions to that of the solar photosphere however their oxygen isotope geochemistry is dominated by secondary minerals that formed during aqueous alteration on the ci parent body precursors to this alteration namely olivine and pyroxene are extremely rare in ci chondrites precluding previous measurements of their oxygen isotopic composition we report ion microprobe analyses of oxygen isotopes in single olivine and pyroxene grains separated from ci chondrites orgueil and ivuna the ci chondrite olivine and pyroxene grains most likely represent liberated chondrule phenocrysts based on petrographic chemical and isotopic evidence consistent with crystallization from a melt the oxygen isotope data form an array that falls nearly along the carbonaceous chondrite 16o mixing line with 18o values ranging from 9 3 to 12 3 o and 17o from 11 3 o to 7 8 o consistent with nebular processes being the source of the oxygen isotopic compositions the degree of 16o enrichment in orgueil olivines is negatively correlated with feo content but the exact nature and timing of the process that introduced this variation remains unknown the pyroxene oxygen isotopic compositions are similar to those of olivines with 5 mol fayalite the oxygen isotopic analyses of the olivine and pyroxene in ci chondrites have been used to revise previous models for the isotopic evolution of ci materials our data require more complete gas solid equilibration in the nebula and constrain the initial aqueous fluids on the ci parent body to have lower 17o values than previously postulated the refined model indicates that the temperature of aqueous activity on the ci parent body was no higher than 50 c and the fluid rock ratio was significantly less than previously estimated even prior to alteration and formation of secondary minerals the ci chondrites were the most 16o depleted carbonaceous chondrites and thus the solids originally contained in the ci chondrites are the most equilibrated nebular materials represented in the carbonaceous chondrites the data suggest the oxygen isotopic composition of average solar system to be approximately equivalent to average terrestrial oxygen as recorded in the compositions of terrestrial and lunar basalts

spatial correlation length of normalized cone data in sand case study in the north of denmark the main topic of this study is to assess the anisotropic spatial correlation lengths of a sand layer deposit based on cone penetration testing with pore pressure measurement cptu data spatial c

chondrules in the lew85332 ungrouped carbonaceous chondrite fractionation processes in the solar nebula abstract we studied 14 chondrules separated from lew85332 an ungrouped type 3 carbonaceous chondrite related to cr chondrites 23 elements were determined by neutron activation and the chondrules were characterized petrographically oxygen isotopic compositions were determined by r n clayton and t k mayeda for seven chondrules chondrule abundance ratios tend to form one of two distinct patterns in low feo chondrules refractory lithophile patterns are flat i e unfractionated siderophile abundances are high and show a small decrease with increasing volatility although high feo chondrules also have flat refractory lithophile abundance patterns siderophile abundances are highly fractionated refractory ir is very low and fe is very high relative to other siderophiles we suggest that the low feo chondrules in lew85332 formed early in nebular history when metal was intimately mixed with silicates in the chondrule precursors and that the viscosity of the liquid solid mix was too high to permit expulsion of the metal by centrifugal action their porphyritic structures are consistent with incomplete melting which would result in relatively high viscosities when the high feo chondrules formed somewhat later much of the fe was oxidized and the melting of precursors was more extensive feo and other oxidized siderophiles were retained in the silicate liquid and metal was lost possibly expelled from low viscosity chondrule melts the o isotopic compositions of the chondrules form a linear array of slope 0 93 0 05 on a three isotope diagram parallel to the carbonaceous chondrite anhydrous minerals ccam line and a cr chondrule array but offset from the latter by 1 in 18 o some or all of this offset may reflect incorporation of o from antarctic water during weathering chondrule 17 o values correlate positively with feo possibly indicating that the 17 o of the nebular gas composition increased with time the chemical and o isotopic data suggest a temporal sequence extending from early low feo to late high feo chondrules

microscale oxygen isotopic exchange and magnetite formation in the ningqiang anomalous carbonaceous chondrite we report in situ measurements of o isotopic compositions of magnetite olivine and pyroxene in chondrules of the ningqiang anomalous carbonaceous chondrite the petrographic setting of ningqiang magnetite is similar to those in oxidized cv chondrites such as allende where magnetite is found together with ni rich metal and sulfide in opaque assemblages in chondrules both magnetite and silicate oxygen data fall close to the carbonaceous chondrite anhydrous mineral line with relatively large ranges in 18o in magnetite 4 9 to 4 2 and in silicates 15 2 to 4 5 magnetite and silicates are not in o isotopic equilibrium the weighted average 17o 17o 0 52 18o values of magnetite are 1 7 to 3 6 higher than those of the silicates in the same chondrules the petrological characteristics and o isotopic disequilibrium between magnetite and silicates suggest the formation of ningqiang magnetite by the oxidation of preexisting metal grains by an aqueous fluid during parent body alteration the weighted average 17o of 3 3 0 3 is the lowest magnetite value measured in unequilibrated chondrites and there is a positive correlation between 17o values of magnetite and silicates in each chondrule these observations indicate that during aqueous alteration in the ningqiang parent asteroid the water rock ratio was relatively low and o isotopic exchange between the fluid and chondrule silicates occurred on the scale of individual chondrules

oxygen isotopic composition and chemical correlations in meteorites and the terrestrial planets recent models attempting to explain non mass dependent oxygen isotopic anomalies in meteorites and planets posit that they may have originated within the gas phase of the solar nebula which suggests the potential for correlations of non mass dependent oxygen isotopic anomalies with other chemical fractionations generated during cooling and condensation of the nebula we have examined three specific issues possible correlations of 17o with i oxidation state ii bulk chondrite chemistry and iii bulk planetary properties isolated grains and chondrules from several carbonaceous chondrite groups exhibit good to weak positive correlations between 17o and olivine fayalite content and whole rock ureilite samples show a positive correlation of 17o with olivine fayalite content these are consistent with oxidation of fe metal by 17o 18o enriched oxygen in the precursor materials that formed these objects in contrast oxygen isotopic and major element compositions of ferromagnesian phases in ordinary chondrite chondrules and in bulk chondrites do not show a correlation thus there is no compelling evidence that oxidation of nebular materials was tightly linked to gas species carrying anomalous o using average chondrite group compositions we demonstrate that significant negative correlations of refractory lithophile element mg and refractory siderophile element ni with 17o exist refractory inclusions cais and aoas are modally rare in many chondrite types that exhibit substantial range in 17o thus the refractory component in these chondrites must occur in a crypto component e g material dissolved in chondrule melts during chondrule formation significant positive correlations of moderately volatile elements mg with 17o are not simply explained by incomplete mixing of 16o enriched refractory grains but are broadly consistent with nebula based mechanisms of non mass dependent oxygen isotope fractionation the estimated compositions of the primitive mantles of the earth mars and 4 vesta have some compositional redox and isotopic properties that vary with heliocentric distance however 17o does not vary monotonically in this sequence indicating a decoupling of planetary o isotopic composition from other compositional characteristics

relationship among o mg isotopes and the petrography of two spinel bearing compound chondrules the petrological properties and o and al mg isotopic compositions of two spinel bearing chondrules from the allende cv chondrite were investigated using scanning electron microscopy and secondary ion mass spectrometry a coarse spinel grain in a barred olivine bo chondrule is less enriched in 16o 17o 5 17o 17o 0 52 18o whereas smaller spinel grains in a plagioclase rich chondrule member of a compound chondrule are extremely 16o rich 17o 17 and the spinels have a strongly serrated character the petrological features and 16o enrichments of the spinels in the plagioclase rich chondrule indicate that spinels originating in coarse grained ca al rich inclusions cais were incorporated into chondrule precursors and survived the chondrule forming event the degree of 16o excesses among minerals within each chondrule is correlated to the crystallization sequences this evidence suggests that the o isotopic variation among minerals may have resulted from incomplete exchange of o isotopes between 16o rich chondrule melt and 16o poor nebular gas aqueous alteration also has changed the o isotope compositions in the mesostasis the feldspathic mesostasis in the bo chondrule shows a disturbed mg al isochron indicating that the bo chondrule experienced secondary alteration while plagioclase in the plagioclase rich chondrule member of the compound chondrule shows slight 26mg excesses corresponding to 26al 27al 0 4 6 4 0 2 10 6 nepheline formed by secondary alteration shows no detectable excess the al mg isotopic system of these chondrules was disturbed by aqueous alteration and thermal metamorphism on the allende parent body

evidence in co3 0 chondrules for a drift in the o isotopic composition of the solar nebula several recent studies have shown that materials such as magnetite that formed in asteroids tend to have higher 17o 17o 0 52 x 18o values than those recorded in unaltered chondrules other recent studies have shown that in sets of chondrules from carbonaceous chondrites 17o tends to increase as the feo contents of the silicates increase we report a comparison of the o isotopic composition of olivine phenocrysts in low feo fa1 type i and high feo fa15 type ii porphyritic chondrules in the highly primitive co3 0 chondrite yamato 81020 in agreement with a similar study of chondrules in co3 0 alh a77307 by jones et al 2000 17o tends to increase with increasing feo we find that 17o values are resolved but only marginally between the two sets of olivine phenocrysts in two of the high feo chondrules the difference between 17o of the late formed high feo phenocryst olivine and those in the low feo cores of relict grains is well resolved although one of the relicts is interpreted to be a partly melted amoeboid olivine inclusion by yurimoto and wasson 2002 it appears that during much of the chondrule forming period there was a small upward drift in the 17o of nebular solids and that relict cores preserve the record of a different and earlier nebular environment

relict olivine chondrule recycling and the evolution of nebular oxygen reservoirs chondrules often contain relict olivine grains that did not crystallize in situ providing opportunities to decipher how chondrule components evolved we studied olivine in the sahara 97210 ll3 2 wells ll3 3 and chainpur ll3 4 chondrites using sem empa and sims techniques oxygen isotopes were analyzed in 16 objects from all three meteorites and trace elements were analyzed in sahara 97210 and chainpur two groups of olivine are identified based on oxygen isotope compositions one group is enriched in 16 o 17 o 8t o 4 and falls close to the ccam mixing line it includes forsterite and mg rich olivine present as relict grains in type ii ferrous chondrules and the forsteritic cores of some isolated grains these low 17 o grains are poor in mno 0 2 wt and are usually enriched in cao 0 3 0 65 wt the other group is less enriched in 16 o 17 o 3t o 4 it includes normal non relict ferrous olivine in type ii chondrules normal non relict mg rich olivine in type i magnesian chondrules dusty olivine relict grains in type i chondrules and mg rich olivine relicts in a type ii and a type i chondrule these high 17 o grains have variable cao 0 0 95 wt and mno 0 0 45 wt contents with the more calcic and mn poor compositions associated with forsteritic olivine trace element data show that forsteritic olivine grains in both oxygen groups are similarly enriched in refractory elements al sc y ca ti v and depleted in volatile elements cr mn p rb sometimes k and na compared to normal ferrous olivine suggesting that variations in chemical composition reflect the extent of thermal processing greater for magnesian olivine the data are consistent with a model in which nebular reservoirs became less enriched in 16 o with time an earlier episode of chondrule formation produced type i chondrules and isolated forsterites in carbonaceous chondrites and forsteritic grains that were incorporated into ordinary chondrites as relict grains in chondrules and as isolated grains later episodes of chondrule formation produced both type i and type ii chondrules in ordinary chondrites under a variety of thermal and redox conditions 2007 elsevier b v all rights reserved

integrated micropaleontological study of the messinian diatomaceous deposits of the monferrato arc piedmont basin nw italy new insights into the paleoceanographic evolution of the northernmost mediterranean region abstract the upper miocene diatom bearing section of pecetto di valenza piedmont nw italy represents a unique site for reconstructing the paleoceanographic processes that occurred before the onset of the messinian salinity crisis in the northernmost mediterranean basin the combined analysis of foraminifera calcareous nannofossils diatoms and other siliceous microfossils observed in the marly and diatomaceous sediments allowed us to define four main evolutionary stages of the biogenic sedimentation each stage was typified by specific water column and seafloor conditions tentatively correlated to the precession insolation variability in particular the variation of the benthic assemblages allowed us to distinguish two stages in the evolution of the diatomaceous deposition which would be otherwise impossible from the lithology the accumulation of the diatomaceous sediments was likely controlled by the interplay between riverine runoff water column stratification and convective mixing rather than with upwelling and seafloor anoxia as inferred for the western and eastern sectors of the mediterranean

rare earth element geochemistry of laminated diatom mats from tropical west pacific evidence for more reducing bottomwaters and higher primary productivity during the last glacial maximum rare earth elements ree along with selected major and trace elements were measured in laminated ethmodiscus rex diatom mats and associated sediments diatomaceous clay and pelagic clay in two sediment cores collected from the parece vela basin of the eastern philippine sea ree distributions are characterized by strong enrichment of middle ree mree and heavy ree hree over light ree lree and slight enrichment of mree over hree this distribution pattern suggests that ree compositions of the laminated e rex diatom mats were not the product of e rex blooms an inference also supported by the fact that ti normalized ree concentrations are not clearly different from those in the diatomaceous clay and pelagic clay comparison of ree patterns with the vertical distribution of authigenic phases in the sediment indicates that lree were dominantly associated with detrital materials whereas mree and hree were selectively enriched by mn oxyhydroxides and authigenic phosphates in the pelagic clay a weak negative ce anomaly cannot be linked to oxic depositional conditions but instead is attributed to the retention of a negative ce anomaly associated with authigenic phosphates in the laminated e rex diatom mats a weak positive ce anomaly is consistent with depositional sulfidic anoxic conditions and is interpreted to represent enhanced scavenging of reduced aqueous ce3 by barite in a strongly reducing environment moreover variably negative to positive ce anomalies in the diatomaceous clay may reflect the concurrent operation of the two processes controlling ce accumulation in the laminated e rex diatom mats and pelagic clay the study cores show a ubiquitous positive eu anomaly owing to the presence of volcanic materials the smaller eu anomaly in the laminated e rex diatom mats and diatomaceous clay relative to that in the pelagic clay may be attributed to the release of reduced eu2 from mineral phases to the sediment pore water under strongly reducing conditions previous studies have shown that the advection of lower circumpolar water lcpw strengthened during the last glacial maximum lgm which should have resulted in better ventilation of the deep eastern philippine sea evidence presented here for more reducing bottomwater conditions during the laminated e rex diatom mats formation implicates elevated primary productivity and enhanced organic sinking fluxes as primary controls on redox changes in the eastern philippine sea during the lgm enhanced primary productivity and more reducing bottomwaters during the laminated e rex diatom mats deposition resulted in a larger respired carbon pool in the deep eastern philippine sea which may have been part of a larger scale modulation of atmospheric co2 variation during pleistocene glacial interglacial cycles by deep ocean carbon storage c 2011 elsevier b v all rights reserved

oxygen isotopes in magnetite and fayalite in cv chondrites kaba and mokoia we report in situ measurements of o isotopic compositions of magnetite and primary and secondary olivine in the highly unequilibrated oxidized cv chondrites kaba and mokoia in both meteorites the magnetite and the secondary olivine fayalite fa90 100 have o isotopic compositions near the terrestrial fractionation tf line the mean 17o 17o 0 52 18o value is about 1 in contrast the compositions of nearby primary chondrule low feo olivines fa1 2 are well below the tf line 17o values range from 3 to 9 krot et al 1998 summarized evidence indicating that the secondary phases in these chondrites formed by aqueous alteration in an asteroidal setting the compositions of magnetite and fayalite in kaba and mokoia imply that the o isotopic composition of the oxidant was near or somewhat above the tf line in mokoia the fayalite and magnetite differ in 18o by 20 whereas these same materials in kaba have virtually identical compositions the difference between mokoia magnetite and fayalite may indicate formation in isotopic equilibrium in a water rich environment at low temperatures 300 k in contrast the similar compositions of these phases in kaba may indicate formation of the fayalite by replacement of preexisting magnetite in dry environment with the o coming entirely from the precursor magnetite and silica the 17o of the oxidant incorporated into the cv parent body as phyllosilicates or h2o appears to have been much 7 8 lower than that in that incorporated into the ll parent body choi et al 1998 which suggests that the o isotopic composition of the nebular gas was spatially or temporally variable

physical properties of chondrules in different chondrite groups implications for multiple melting events in dusty environments chondrite groups cv ck cr with large average chondrule sizes have low proportions of rp plus c chondrules high proportions of enveloping compound chondrules high proportions of chondrules with thick igneous rims and relatively low proportions of type i chondrules containing sulfide in contrast chondrite groups cm co oc r eh el with smaller average chondrule sizes have the opposite properties equilibrated ck chondrites have plagioclase with relatively low na equilibrated oc r eh and el chondrites have more sodic plagioclase enveloping compound chondrules and chondrules with igneous rims formed during a remelting event after the primary chondrule was incorporated into a dustball repeated episodes of remelting after chondrules were surrounded by dust would tend to produce large chondrules rp and c chondrules formed by complete melting of their precursor assemblages remelting of rp and c chondrules surrounded by dust would tend to produce porphyritic chondrules as small dust particles mixed with the melt providing nuclei for crystallizing phenocrysts this process would tend to diminish the numbers of rp and c chondrules correlations among these chondrule physical properties suggest that chondrite groups with large chondrules were typically surrounded by thick dust rich mantles that formed in locally dusty nebular environments chondrules that were surrounded by thick dust mantles tended to cool more slowly because heat could not quickly radiate away slow cooling led to enhanced migration of sulfide to chondrule surfaces and more extensive sulfide evaporation these chondrules also lost na the plagioclase that formed from equilibrated ck chondrites was thus depleted in na

drastic change in the late pliocene subarctic pacific diatom community associated with the onset of the northern hemisphere glaciation abstract to date there is scarcely clear understanding of the detailed responses of the subarctic pacific phytoplankton communities to the significant climate transition across the initiation of the northern hemisphere glaciation nhg approximately 2 7 million years ago we present more highly resolved evidence of the rapid and drastic change in the phytoplankton biosphere using diatom as a tracer of environmental changes and based on quantitative assemblage analysis of two marine cores from oceanic regions of the north pacific subarctic gyre in the late pliocene subarctic pacific coscinodiscus marginatus and neodenticula kamtschatica were widely dominant but the flora rapidly and drastically shifted to one rich in neodenticula complex n koizumii n seminae at the onset of nhg perhaps due to intense changes in paleoceanographic conditions such as cooling and or a collapse of the previously nutrient regime in the region we also suggest that vertical pumping of biogenic matter by diatoms may have been more efficient in this region earlier than the onset of nhg after the nhg intensification the major primary productivity role in the subarctic pacific shifted from the c marginatus rich flora to the neodenticula complex the drastic decrease of biogenic opaline accumulation reportedly associated with the initiation of nhg would have resulted from not only a decrease of primary production but also from the change in diatom assemblages and consequent effects on their principal role in export flux

anomalous south atlantic lithologies confirm global scale of unusual mid pleistocene climate excursion abstract carbonate rich nannofossil oozes are the typical sediments deposited under the low productivity regime of the subtropical gyre in the south atlantic surface productivity has remained virtually constant during the late pleistocene schmiedl and mackensen palaeogeogr palaeoclimatol palaeoecol 130 1997 43 80 increasing slightly only during the most extreme glacial periods recently the puzzling occurrence of thick monospecific diatom layers ethmodiscus rex has been reported within the carbonaceous sequences of two sediment cores in the south atlantic gyre schmieder et al earth planet sci lett 179 2000 539 549 the layers dated 544 534 ka are isochronous and record a period of increased organic carbon flux above them at 530 524 ka unusually high carbonate contents are recorded this double feature of anomalous lithologies is unique in the sediment record of the last 1500 kyr and can be related to the terminal event of the mid pleistocene climate transition mpt the mpt is characterized by reduced thermohaline circulation and stronger carbonate dissolution schmieder et al earth planet sci lett 179 2000 539 549 reduced circulation and a more stratified water column may have trapped nutrients in deep nitrate pools and may have fostered favorable conditions for the development of deep dwelling populations of e rex the onset of more turbid conditions led to the rapid settling of diatom populations subsequently introduced nutrients to the surface layer and improved calcite preservation thus creating a biogenic silica carbonate double peak the carbonate peak is synchronous with an unusual mid pleistocene sapropel observed in the mediterranean which is attributed to a massive odd monsoon over central africa rossignol strick et al nature 392 1998 269 272 since summer insolation was relatively low during this time the formation of this thick sapropel cannot be explained in terms of current understanding of astronomical forcing rossignol strick et al nature 392 1998 269 272 a non linear response to a 400 kyr low frequency climatic cycle as discussed for the mediterranean sapropel is not confirmed by data from our south atlantic core records

interpolation and stratification of multilayer soil property profile from sparse measurements using machine learning methods abstract identification of subsurface stratification and characterization of spatially varying soil properties profiles in multiple soil layers are indispensable in geotechnical site investigation subsurface soils are often stratified first through visual inspection of soil samples obtained from boreholes or soil behavior type index from cone penetration tests then the soil property profile within each layer is characterized via interpolation of the data points measured within the corresponding layer although this stratification first procedure is commonly used in engineering practice it is difficult to apply when measured data points within each layer are sparse and limited e g only a few data points within each layer a scenario often encountered in geotechnical site characterization when the number of measurements within each layer is small it is difficult to properly interpolate spatially varying soil property profiles in each layer to address this difficulty and increase the number of data points for enabling proper interpolation an interpolation first procedure is proposed which utilizes measurements from all layers as input for interpolation followed by soil stratification using the interpolation results the proposed procedure includes two key elements 1 a bayesian supervised learning method for interpolation of non stationary data from multiple layers and 2 an unsupervised machine learning method e g clustering for soil stratification an index is also proposed to determine when the proposed method is beneficial and performs better than the stratification first procedure in engineering geology practice both numerical and real life data are used to illustrate the proposed method

paleoecological significance of laminated diatomaceous oozes during the middle to late pleistocene north atlantic ocean iodp site u1304 abstract we examined diatom assemblages in a series of remarkable laminated diatomaceous ooze ldo horizons in the marine sediments from integrated ocean drilling program iodp site u1304 to reconstruct the middle to late pleistocene paleoceanographic evolution of the northern north atlantic ocean four confirmed diatom biohorizons combined with calcareous nannofossil and paleomagnetic stratigraphies established the chronological framework for the material the planktonic araphid needle like species thalassiothrix longissima was the greatest contributor to the ldo facies from the results of a principal component analysis using the percent abundances of 65 significant p 5 diatom taxa except for tx longissima which was extremely dominant in almost all horizons observed we identified two principal component pc axes taxa probably associated with the stratigraphic distribution of the major zonal marker neodenticula seminae ranging from 1 26 to 0 84 ma in this ocean loaded on pc1 with a high value pc2 was related to the ocean surface temperature the stratigraphic variability of the pc2 score indicated that switching between warm and cold water assemblages occurred concurrently with ldo deposition or extreme tx longissima dominance episodes in several horizons particularly after 0 84 ma suggesting that the subarctic convergence sac oceanic front passed over site u1304 during pleistocene glacial interglacial cycles our floral evidence supports the model of nearly monospecific ldo formation caused by the enhanced physical accumulation of particular diatoms such as tx longissima on the other hand nd seminae which probably contributes to spring phytoplankton blooms in the modern ocean was present only between 1 26 and 0 84 ma in this area thus we infer that the main contributor of export flux in the regional annual primary production cycle would have shifted drastically from one of a spring phytoplankton bloom leader nd seminae to minor but mass dump assemblages tx longissima etc in the mid pleistocene

migration of the antarctic polar front through the mid pleistocene transition evidence and climatic implications abstract the antarctic polar front is an important biogeochemical divider in the southern ocean laminated diatom mat deposits record episodes of massive flux of the diatom thalassiothrix antarctica beneath the antarctic polar front and provide a marker for tracking the migration of the front through time ocean drilling program sites 1091 1093 and 1094 are the only deep piston cored record hitherto sampled from the sediments of the circumpolar biogenic opal belt mapping of diatom mat deposits between these sites indicates a glacial interglacial front migration of up to 6 degrees of latitude in the early mid pleistocene the mid pleistocene transition marks a stepwise minimum 7 northward migration of the locus of the polar front sustained for about 450 kyr until an abrupt southward return to a locus similar to its modern position and further south than any mid pleistocene locus this interval from a 900 ka event that saw major cooling of the oceans and a 13c minimum through to the 424 ka mid brunhes event at termination v is also seemingly characterised by 1 sustained decreased carbonate in the sub tropical south atlantic 2 reduced strength of antarctic deep meridional circulation 3 lower interglacial temperatures and lower interglacial atmospheric co2 levels by some 30 per mil than those of the last 400 kyr evidencing less complete deglaciation this evidence is consistent with a prolonged period lasting 450 kyr of only partial ventilation of the deep ocean during interglacials and suggests that the mechanisms highlighted by recent hypotheses linking mid latitude atmospheric conditions to the extent of deep ocean ventilation and carbon sequestration over glacial interglacial cycles are likely in operation during the longer time scale characteristic of the mid pleistocene transition the cooling that initiated the 900 ka event may have been driven by minima in insolation amplitude related to eccentricity modulation of precession that also affected low latitude climates as marked by threshold changes in the african monsoon system the major thresholds in earth system behaviour through the mid pleistocene transition were likely governed by an interplay of the 100 kyr and 400 kyr eccentricity modulation of precession

oxygen isotopic evolution of the solar nebula studies of the three oxygen isotopes in chondrite meteorites demonstrate that diverse o reservoirs characterized by their 17o values were present in the solar nebula the discovery that some chondritic materials have o isotopic compositions that cannot be explained by mass dependent fractionation of an initially well mixed reservoir has important implications for the history of the solar nebula on a plot of 17o versus 18o or 17o 16o versus 18o 16o terrestrial samples with the main exception of stratospheric ozone fall along a single line the terrestrial fractionation or tf line having a slope 0 52 an indication that the parental reservoir was homogenized a convenient measure of o isotopic heterogeneity is the deviation from the tf line 17o 17o 0 52 18o a popular model to explain the evolution of chondritic oxygen compositions during nebular and asteroidal aqueous alteration processes calls for the nebula to have formed from solids having 18o 40 and 17o 41 17o 20 and a gas having a composition roughly estimated to be 18o 30 and 17o 24 17o 9 this model encounters serious difficulties when examined in detail in particular it cannot readily account for the o isotopic compositions of both chondrules and refractory inclusions from individual chondrite groups or for the differences between groups particularly in the compositions of chondrules magnetite fe3o4 is a key phase for o isotope studies because during its formation by the oxidation of ferrous metal or fes all o comes from the oxidant probably h2o it appears that most and possibly nearly all magnetite formed during aqueous alteration processes that occurred in asteroids in all chondrite groups studied to date 17o of the magnetite is greater than or equal to that of the chondrule silicates if the h2o originated in the ambient local nebula then at the time of accretion the 17o of the nebular gas was generally higher than that of the solids an alternative view is that the heterogeneity in the o isotopic composition of chondrites indicates that the nebula formed from diverse batches of presolar materials the precise o isotopic composition of the mix varying during the accretion history of the nebula the large compositional gaps between groups suggest that agglomeration of nebular dust to form chondrites did not proceed at a constant rate but that periods with turbulence levels low enough to allow agglomeration were punctuated by periods of high turbulence during which the composition of the inner nebula sampled by chondrites changed appreciably

oxygen isotope studies of ordinary chondrites several stages in the evolution of ordinary chondritic meteorites are recorded in the oxygen isotopic composition of the meteorites and their separable components chondrules fragments clasts and matrix the whole rock isotopic compositions reflect the iron group of the meteorite h l or ll isotopic uniformity of h3 to h6 and l3 to l6 are consistent with closed system metamorphism within each parent body ll3 chondrites differ slightly from ll4 to ll6 implying a small degree of opensystem aqueous alteration and carbon reduction on the scale of individual chondrules the meteorites are isotopically heterogeneous allowing recognition of the solar nebular processes of chondrule formation chondrules for all classes of ordinary chondrites are derived from a common population which was separate from the population of chondrules in carbonaceous or enstatite chondrites chondrules define an isotopic mixing line dominated by exchange between 16o rich and 16o poor reservoirs the oxygen isotopic compositions of chondrites serve as fingerprints for identification of genetic association with other meteorite types achondrites and iron and for recognition of source materials in meteoritic breccias

initial 26al 27al in carbonaceous chondrite chondrules too little 26al to melt asteroids we report 26mg excesses correlated with al mg ratios in five chondrules from the primitive co3 0 chondrite yamato 81020 that yield a mean initial 26al 27al ratio of only 3 8 0 7 10 6 about half that of ordinary chondrite oc chondrules even if asteroids formed immediately after chondrule formation this ratio and the mean al content of co chondrites is only capable of raising the temperature of a well insulated co asteroid to 940 k which is more than 560 k too low to produce differentiation the same ratio combined with the higher al content of cv chondrites results in a cv asteroid temperature of 1100 k we calculate that the mean initial 26al 27al ratio of about 7 4 10 6 found in ll chondrules is only able to produce small amounts of melting too little to produce differentiation these results cast serious doubt on the viability of 26al as the heat source responsible for asteroid differentiation inclusion of 60fe raises temperatures about 160 k but this increment is not enough to cause differentiation even of an ll chondrite asteroid

oxygen diffusion in an fe rich basalt melt abstract the self diffusion of oxygen has been measured in an feti basalt melt at one atmosphere from 1320 1500 c under different oxygen fugacities diffusivities were determined by measuring isotopic exchange between spheres of melt and flowing oxygen in a vertical tube furnace the oxidation state of the melt was varied by performing experiments in either o2 or co2 gas the diffusion data for experiments in both gases can be fit to the equation d 1 4 10 exp 60 7 10 3 rt cm 2 s the observed self diffusivities for oxygen in the basalt melt are one to two orders of magnitude lower than published chemical diffusivities at one atmosphere diffusivities in basalt melt at each temperature in o2 and co2 gas are similar within experimental error 0 2 log d units at the 1 level and indicate that oxygen self diffusion is insensitive to the oxidation state of fe in natural basalt melts the redox independence of oxygen self diffusion observed in this study suggests that oxygen transport in natural magmas will not be significantly affected by changes in their redox state caused by degassing and or crystallization

oxygen isotopic compositions of low feo relicts in high feo host chondrules in acfer 094 a type 3 0 carbonaceous chondrite closely related to cm with one exception the low feo relict olivine grains within high feo porphyritic chondrules in the type 3 0 acfer 094 carbonaceous chondrite have 17o 17o 0 52 18o values that are substantially more negative than those of the high feo olivine host materials these results are similar to observations made earlier on chondrules in co3 0 chondrites and are consistent with two independent models 1 nebular solids evolved from low feo low 17o compositions towards high feo more positive 17o compositions and 2 the range of compositions resulted from the mixing of two independently formed components the two models predict different trajectories on a 17o vs log fe mg olivine diagram but our sample set has too few values at intermediate fe mg ratios to yield a definitive answer published data showing that acfer 094 has higher volatile contents than co chondrites suggest a closer link to cm chondrites this is consistent with the high modal matrix abundance in acfer 094 49 vol acfer 094 may be an unaltered cm chondrite or an exceptionally matrix rich co chondrite chondrules in acfer 094 and in co and cm carbonaceous chondrites appear to sample the same population textural differences between acfer 094 and cm chondrites are largely attributable to the high degree of hydrothermal alteration that the cm chondrites experienced in an asteroidal setting

ubiquitous low feo relict grains in type ii chondrules and limited overgrowths on phenocrysts following the final melting event type ii porphyritic chondrules commonly contain several large 40 m olivine phenocrysts furnace based cooling rates based on the assumption that these phenocrysts grew in a single stage melting cooling event yield chondrule cooling rate estimates of 0 01 1 k s 1 because other evidence indicates much higher cooling rates we examined type ii chondrules in the co3 0 chondrites that have experienced only minimal parent body alteration we discovered three kinds of evidence indicating that only minor 4 10 m olivine growth occurred after the final melting event 1 nearly all 90 type ii chondrules in co3 0 chondrites contain low feo relict grains overgrowths on these relicts are narrow in the range of 2 12 m 2 most type ii chondrules contain some feo rich olivine grains with decurved surfaces and acute angles between faces indicating that the grains are fragments from an earlier generation of chondrules the limited overgrowth thicknesses following the last melting event are too thin to disguise the shard like nature of these grains 3 most type ii chondrules contain many small 40 m high feo phenocrysts are relicts from earlier generations of chondrules and that cooling rates after the last melting event were much more rapid than indicated by models based on a single melting event these observations are thus inconsistent with the classic igneous model of formation of type ii porphyritic chondrules by near total melting of a precursor mix followed by olivine nucleation on a very limited number of nuclei say 10 and by growth to produce the large phenocrysts during a period of monotonic and roughly linear cooling our observations that recycled chondrule materials constitute a large component of the phenocrysts of type ii chondrules also imply that this kind of chondrule formed relatively late during the chondrule forming period

the interstellar dust as a precursor of ca al rich inclusions in carbonaceous chondrites abstract 1 the observed anomalies in meteoritic oxygen isotope compositions are not due to an incomplete mixing of several dust or gas plus dust components in the solar nebula if they were other elements would display similar anomalies the fun inclusions in allende appear to be exceptions to this premise 2 the anomalies must therefore stem from differing degrees of incomplete exchange of oxygen isotopes between the primordial gas and dust components of the nebula the dust is more likely to have been the 16 o enriched component 3 since the isotopic difference between dust and gas probably could not have been preserved if the dust was ever completely vaporized in the nebula the ca al rich inclusions cai s in carbonaceous chondrites are unlikely to be condensates but instead are distillation residues 4 if so the observed depletion of super refractory elements in the group ii cai s cannot have been accomplished by fractional condensation in the solar nebula 5 then this depletion and a number of other properties of the components of primitive meteoritic material must be relics of pre solar system fractionations among different populations of interstellar dust grains

the upper miocene diatomaceous sediments of the northernmost mediterranean region a lamina scale investigation of an overlooked palaeoceanographic archive

bayesian identification of soil strata in london clay identification of soil strata in the london clay formation lcf is of practical significance as it allows geotechnical property data within the same soil strata to be compared or used effectively the soil strata in lcf are generally determined based on their lithological characters and fossil contents with which geotechnical engineers are less familiar to assist geotechnical engineers in identifying the soil strata in lcf this paper aims to develop bayesian approaches to identification of soil strata in lcf using water content data equations are derived for the proposed bayesian approaches and the approaches are illustrated using a water content profile at st james s park london the proposed bayesian approaches are shown to correctly identify the soil strata in lcf in addition a sensitivity study is performed to explore the effect of data quantity i e both the measurement interval and number of measurements at the same depth in a water content profile and provide guidance on the water conten

the messinian diatomite deposition in the mediterranean region and its relationships to the global silica cycle abstract diatomites constitute a widely represented lithology in the messinian sections of the circum mediterranean neogene marginal basins although traditionally interpreted as genuine evidence of the gradually restricted conditions that characterized the mediterranean just before the messinian salinity crisis their coeval occurrence with a global intensification of the opaline production in the world oceans late miocene early pliocene biogenic bloom suggests that an integrative analysis of the origins of these sediments is necessary a comprehensive analysis of the geological and paleontological records suggests that the synergistic intervention of abiotic tectonic and climate reconfigurations and biotic expansion of grass dominated opal rich biomes controlling factors may have promoted a remarkable enhancement of silica flux from continents to oceans which in turn can explain the opaline burst that occurred during the late miocene at both the global and mediterranean scale the finely laminated pattern and the rich fossil content of diatomaceous deposits that are usually considered to be byproducts of anoxic conditions are briefly discussed some studies seem to indicate that instead of anoxia the aggregation and sedimentation of diatom tests may play a critical role in these processes the lower messinian diatomites of the mediterranean region are generally interbedded with organic rich sediments sapropels clearly attesting prolonged precessionally controlled periods of basin stratification and bottom water anoxia or hypoxia a causal relationship between sapropel and diatomite deposition in the mediterranean is proposed considering the possible interplay between stratification adapted diatoms and anaerobic bacteria and their respective role in influencing the marine silica cycle

oxygen isotopic compositions of relict and host grains in chondrules in the yamato 81020 co3 0 chondrite we report the oxygen isotope compositions of relict and host olivine grains in six high feo porphyritic olivine chondrules in one of the most primitive carbonaceous chondrites co3 0 yamato 81020 because the relict grains predate the host phenocrysts microscale in situ analyses of o isotope compositions can help assess the degree of heterogeneity among chondrule precursors and constrain the nebular processes that caused these isotopic differences in five of six chondrules studied the 17o 17o 0 52 18o compositions of host phenocrysts are higher than those in low feo relict grains the one exception is for a chondrule with a moderately high feo relict both the fayalite compositions as well as the o isotope data support the view that the low feo relict grains formed in a previous generation of low feo porphyritic chondrules that were subsequently fragmented it appears that most low feo porphyritic chondrules formed earlier than most high feo porphyritic chondrules although there were probably some low feo chondrules that formed during the period when most high feo chondrules were forming

on the occurrence of the giant diatom ethmodiscus rex in an 80 ka record from a deep sea core southeast of sumatra indonesia implications for tropical palaeoceanography environmental changes recognised in a 80 ka record obtained from a deep sea core taken at a water depth of 2542 m offshore southeast sumatra conclusively indicate for the first time that blooms of the giant diatom ethmodiscus rex occurred in the indian ocean during the last glacial period with the largest numbers coinciding with the last glacial maximum previous occurrences of e rex in both the indian and the western pacific oceans could not be dated due to the paucity of foraminifers and contamination by diagenetic carbonate found in association with the diatoms we use a reliable n 18 o record to date the core the interpretation of terrigenous clays and trace metals in the core sediments together with carbon isotopes measured on planktic foraminifers suggests that conditions that favoured the diatomaceous blooms were a combination of changes in hydrological regime in the region caused by a substantial increase in salinity near the surface and coinciding with a rise in nitrate levels near the surface no major upwelling was recorded during glacial times during the glacial period the indonesian archipelago as other tropical regions was much drier thus preventing a low salinity cap to occur at the surface of the oceans in contrast with the holocene in addition monsoonal winds were absent thus permitting the ocean to be permanently stratified with high levels of silica and nutrients near the surface the glacial mode of productivity represented by the blooms of e rex added considerable amounts of biogenic silica to the sediment but is not reflected by classic productivity proxies like biogenic barium therefore we have to distinguish between a classic productivity mode as observed in the photic zone today and a glacial deep productivity dominated by e rex which may have utilised nutrients from a wider depth range 9 2002 elsevier science b v all rights reserved

el nino southern oscillation variability from the late cretaceous marca shale of california changes in the possible behavior of el nino southern oscillation enso with global warming have provoked interest in records of enso from past greenhouse climate states the latest cretaceous laminated marca shale of california permits a seasonal scale reconstruction of water column flux events and hence interannual paleoclimate variability the annual flux cycle resembles that of the modern gulf of california with diatoms characteristic of spring upwelling blooms followed by silt and clay and is consistent with the existence of a paleo north american monsoon that brought input of terrigenous sediment during summer storms and precipitation runoff variation is also indicated in the extent of water column oxygenation by differences in lamina preservation time series analysis of interannual variability in terrigenous sediment and diatom flux and in the degree of bioturbation indicates strong periodicities in the quasi biennial 2 1 2 8 yr and low frequency 4 1 6 3 yr bands both characteristic of enso forcing as well as decadal frequencies this evidence for robust late cretaceous enso variability does not support the theory of a permanent el nino in the sense of a continual el nino like state in periods of warmer climate

oxygen isotopes in separated components of ci and cm meteorites oxygen isotopic compositions have been determined for whole rock and separated components from the ci chondrites alais ivuna and orgueil and from the atypical cm chondrites bells and essebi the composition of ci matrix is in agreement with previous measurements and is systematically different from that of cm matrix probably due to warmer and wetter conditions of aqueous alteration for ci matrix although bells matrix is like that of other cm chondrites the matrix of essebi falls in the ci field essebi also contains abundant magnetite like cis and unlike other cms the isotopic compositions of magnetite in alais ivuna orgueil and essebi define a trend with 17o of 1 3 to 1 8 distinctly out of isotopic equilibrium with the phyllosilicates in each meteorite the magnetite serves as an isotopic tracer for the fluid which brought about aqueous alteration and oxidation and thus provides additional evidence for a gaseous reservoir in the solar nebula which was more 16o depleted than the earth

stable isotopes and the noncarbonaceous derivation of ureilites in common with nearly all differentiated planetary materials abstract the abundant diverse ureilite meteorites are peridotitic asteroidal mantle restites that have remarkably high bulk carbon contents average 3 wt and have long been linked to the so called carbonaceous chondrites although this term is potentially misleading because the high petrologic type carbonaceous chondrites are if anything c poor compared to ordinary chondrites ureilite oxygen isotopic compositions i e diversely negative ccam like 17o viewed in isolation have long been viewed as confirming the carbonaceous chondritic derivation hypothesis however a very different picture emerges through analysis of a compilation of recently published high precision isotopic data for chromium titanium and nickel for ureilites and various other planetary materials ureilites have lower e62ni and far lower e50ti and e54cr than any known variety of carbonaceous chondrite on a plot of e50ti vs e54cr and similarly 17o vs e54cr ureilite compositions cluster far from and in a direction approximately orthogonal to a trend internal to the carbonaceous chondrites and the carbonaceous chondrites are separated by a wide margin from all other planetary materials i conclude that notwithstanding the impressive resemblance to carbonaceous chondrites in terms of diversely negative 17o the ureilite precursors accreted from preponderantly noncarbonaceous sensu stricto materials despite total depletion of basaltic matter the ureilites retain moderate pyroxene olivine ratios which is an expected outcome from simple partial melting of moderate sio2 feo mgo noncarbonaceous chondritic material but would imply an additional process of major reduction of feo if the precursor material were carbonaceous chondritic the striking bimodality of planetary materials on the e50ti vs e54cr and 17o vs e54cr diagrams may be an extreme manifestation of the effects of episodic accretion of early solids in the protoplanetary nebula however an alternative admittedly speculative explanation is that the bimodality corresponds to a division between materials that originally accreted in the outer solar system carbonaceous and materials that accreted in the inner solar system noncarbonaceous including the ureilites

interpretation of soil property profile from limited measurement data a compressive sampling perspective variation of soil properties with depth i e the soil property profile is a key input in geotechnical design and analysis and it is determined during geotechnical site characterization determi

titanium isotopic anomalies in chondrules from carbonaceous chondrites abstract isotopic analyses of ti from chondrules of carbonaceous chondrites reveal that ti anomalies are present anomalies are detected only at 50ti for a suite of eight allende chondrules four give well resolved anomalies which range from a 50ti deficit of two units to a 50ti excess of nine units no clear link is evident between the structure or composition of the chondrules and the ti anomalies however the chondrule with by far the largest ti isotopic anomaly is also al rich yet the absence of a strict correlation between the ca al ti contents and the ti anomalies together with the similarity of the 50ti excess for the one chondrule to that of most ca al rich inclusions cais indicate that the relation between degree of refractory enrichment and the magnitude of ti isotopic anomalies is not a simple one single chondrules from murchison kaidun and kakangari all fail to exhibit a well resolved anomaly although in the latter two the single analysis of each precludes resolving anomalies of less than three units these observations support the view that the ti isotopic diversity in chondrules is an inherited feature from their precursor assemblages of dust models which envision similar precursors for both chondrules and matrix are consistent with the ti isotopic data but at least two distinct solid matter reservoirs are required for the allende chondrules alone which underscores the diversity in the nebular dust these ti anomalies also caution that more than one dust isotopic component may be necessary to account fully for the oxygen isotopic variations in chondrules the ti anomalies in chondrules argue strongly against models which ascribe the ti anomalies in cais to unique features of their evolution instead heterogeneities were more common in the nebular dust

molybdenum isotopic evidence for the origin of chondrules and a distinct genetic heritage of carbonaceous and non carbonaceous meteorites abstract nucleosynthetic isotope anomalies are powerful tracers to determine the provenance of meteorites and their components and to identify genetic links between these materials here we show that chondrules and matrix separated from the allende cv3 chondrite have complementary nucleosynthetic mo isotope anomalies these anomalies result from the enrichment of a presolar carrier enriched in s process mo into the matrix and the corresponding depletion of this carrier in the chondrules this carrier most likely is a metal and so the uneven distribution of presolar material probably results from metal silicate fractionation during chondrule formation the mo isotope anomalies correlate with those reported for w isotopes on the same samples in an earlier study suggesting that the isotope variations for both mo and w are caused by the heterogeneous distribution of the same carrier the isotopic complementary of chondrules and matrix indicates that both components are genetically linked and formed together from one common reservoir of solar nebula dust as such the isotopic data require that most chondrules formed in the solar nebula and are not a product of protoplanetary impacts allende chondrules and matrix together with bulk carbonaceous chondrites and some iron meteorites groups iid iiif and ivb show uniform excesses in 92 mo 95 mo and 97 mo that result from the addition of supernova material to the solar nebula region in which these carbonaceous meteorites formed non carbonaceous meteorites enstatite and ordinary chondrites as well as most iron meteorites do not contain this material demonstrating that two distinct mo isotope reservoirs co existed in the early solar nebula that remained spatially separated for several million years this separation was most likely achieved through the formation of the gas giants which cleared the disk between the inner and outer solar system regions parental to the non carbonaceous and carbonaceous meteorites the mo isotope dichotomy of meteorites provides a new means to determine the provenance of meteoritic and planetary materials and to assess genetic links between chondrites and differentiated meteorites

postglacial marine diatom record of the palmer deep antarctic peninsula odp leg 178 site 1098 2 diatom assemblages 1 the distribution of late pleistocene to holocene diatom assemblages from ocean drilling program odp leg 178 site 1098 palmer deep is described and compared using multivariate statistical methods cluster analysis and analysis of variance five assemblages are identified from site 1098 which are correlated with the climatic zones identified previously in the palmer deep domack et al 2001 a thalassiosira diatom assemblage characterizes the deglaciation phase 13 2 11 0 ka and was deposited during glacial retreat at the end of the regional last glacial maximum a well preserved rhizosolenia assemblage was deposited during a climatic reversal 11 0 9 0 ka and indicates periods of seasonally open water with diatom blooms an open water fragilariopsis kerguelensis assemblage characterizes the mid holocene climatic optimum 9 0 3 7 ka in the neoglacial late holocene 3 7 ka climatic cooling increased sea ice cover and increased wind are inferred from a cocconeis assemblage during the climatic optimum neoglacial transition 4 4 1 8 ka laminae characterized by corethron criophilum were preserved it is uncertain whether the laminae represent short lived interannual bloom events with high settling rates or have been deposited over longer time periods

the deep sea microfossil record of macroevolutionary change in plankton and its study the deep sea planktonic microfossil record foraminifera coccolithophores diatoms radiolaria and dinoflagellates provides a unique resource for palaeobiology despite some geographical gaps due to poor regional preservation and intermittant time intervals lost to erosion most time periods for each cenozoic planktonic biogeographical province are preserved vast numbers of specimens and numerous deep sea cores provide abundant material and the opportunity to tightly integrate macroevolutionary and palaeoenvironmental data current documentation of this record is mixed catalogues for foraminifera and coccolithophores offer nearly complete species level clade histories but taxonomy for siliceous microfossils is incomplete published occurrence data is primarily stratigraphic and covers only a fraction of the total preserved diversity age models for some sections are excellent accuracy c 100 kya but for many other sections are still poor taxonomic errors age model errors and reworking displace fossil occurrences in time complicating palaeobiological analysis with additional taxonomic work careful collection of whole fauna floral assemblage occurrence data improved age models and the development of better data filtering and analysis tools to deal with data outliers the deep sea microfossil record can deliver its promise of providing the most complete detailed record of macroevolutionary change available to science

diatom mats in gulf of california sediments implications for the paleoenvironmental interpretation of laminated sediments and silica burial preservation of laminations in hemipelagic and pelagic sediments is routinely attributed to reduced oxygen conditions that inhibited benthic activity as such the degree of preservation of laminae is used commonly as a paleo oxygenation indicator recent evidence from deep sea pelagic sediments in the eastern equatorial pacific and north atlantic however demonstrates that preservation of laminae may occur by rapid deposition of ungrazed thalassiothrix longissima diatom mats that overwhelm the benthos in otherwise oxic bottom waters here we report that similar diatom mat laminae are common in hemipelagic sediments of the guaymas basin in the gulf of california have aided preservation of the laminated sediment sequence and have also enhanced opal burial examples of diatom mats influencing sediment preservation are also described from the northern california margin and from the miocene monterey formation southern california thus even in classical settings of laminated sediment occurrence caution needs to be taken in correlating degree of lamina preservation with paleo oxygen levels such studies must be underpinned by detailed microfabric and micropaleontological analyses

carbide magnetite assemblages in type 3 ordinary chondrites abundant carbide magnetite assemblages occur in matrix chondrules and chondrule rims in several h3 l3 and ll3 chondrites carbides cohenite fe ni 3c and haxonite fe ni 23c6 show compositional variations between different meteorites and appreciable ranges within meteorites carbides in h chondrites have lower co contents 0 0 6 wt than those in l and ll chondrites 0 3 1 2 wt metal associated with carbides and magnetite consists of high ni 50 70 wt taenite and in l and ll chondrites co rich up to 35 wt kamacite minor element contents of troilite and magnetite are very low textural observations indicate that carbide magnetite assemblages formed by replacement of metal sulfide nodules the high co contents of residual kamacite in association with carbides indicates that co is not incorporated into carbides i e fe co is much higher in the carbides than in kamacite because ni in carbides and magnetite is low the ni contents of residual taenite tend to be high ni rich sulfides were found only in ll3 chondrites possibly indicating their more extensive oxidation and or aqueous alteration we suggest that carbide magnetite assemblages in type 3 ordinary chondrites formed as the result of hydrothermal alteration of metallic fe in metal troilite nodules by a coh bearing fluid on their parent bodies this alteration resulted in carbidization of feni metal probably by co gas e g 15 fe s 4 co g fe3c s fe3o4 s or 3 fe s 2 co g fe3c s co2 g and oxidation probably by h2o gas e g 3fe s 4h2o g fe3o4 s 4h2 g the coh bearing fluids which were possibly released during metamorphism and transported through zones of high permeability may have been derived from ices adsorbed gases or hydrated minerals the co may be the result of the reaction of carbon compounds e g hydrocarbons with water vapor or magnetite

magnetite in the unequilibrated ck chondrites implications for metamorphism and new insights into the relationship between the cv and ck chondrites bulk isotopic and elemental compositions of cv and ck chondrites have led to the suggestion that both originate from the same asteroid it has been argued that magnetite compositions also support this model however magnetite has been studied almost exclusively in the equilibrated type 4 6 cks magnetite in seven unequilibrated cks analyzed here is enriched in mgo tio2 and al2o3 relative to the equilibrated cks suggesting that magnetite compositions are affected by metamorphism magnetite in cks is compositionally distinct from cvs particularly in abundances of cr2o3 nio and tio2 although there are minor similarities between cv and equilibrated ck chondrite magnetite this is contrary to what we would expect if the cvs and cks represent a single metamorphic sequence cv magnetite should resemble ck3 magnetite as both were metamorphosed to type 3 conditions oxygen fugacities and temperatures of cvox and ck chondrites are also difficult to reconcile using existing cv ck parent body models mineral chemistries which eliminate issues of bulk sample heterogeneity provide a reliable alternative to techniques that involve a small amount of sample material cv and ck chondrite magnetite has distinct compositional differences that cannot be explained by metamorphism

silica diagenesis porosity evolution and mechanical behavior in siliceous mudstones mowry shale cretaceous rocky mountains u s a quartz in mudstones of the mowry shale cretaceous rocky mountain region takes several forms extrabasinal detrital silt some with transported overgrowths replacement of skeletal debris minor overgrowth on detrital quartz and replaced radiolaria pore filling in the intragranular pores of allochems and authigenic microquartz that is dispersed through the clay size matrix the matrix dispersed microquartz has cl character similar to the overgrowths with which it is intergrown supporting the interpretation that it is authigenic and pore filling radiolaria are widely observed in these mudrocks but are poorly preserved by partial mineral replacement quartz dolomite calcite pyrite we interpret dissolved radiolaria and possibly now cryptic diatoms as the likely source of silica for the overgrowths and microquartz through a reaction pathway that entailed the formation of opal ct lepispheres that subsequently recrystallized to microquartz a newly devised variation of the igv intergranular volume concept a parameter igvm is applied for partitioning the causes of porosity decline in mudstones all of the samples examined contain authigenic microquartz which averages around 40 of the rock volume the large volume of microquartz together with the volumes of surviving intergranular pores and pore filling solid hydrocarbon constrain the porosity to around 50 at the time of initial lepisphere formation despite the exceptional abundance of cement overall porosity decline is compaction dominated the presence of significant volumes of cement has implications for mechanical rock properties in the mowry shale which is expected to manifest brittle behavior where cements are most prominently developed

paleoproductivity and paleoredox conditions during late pleistocene accumulation of laminated diatom mats in the tropical west pacific paleoproductivity and paleoredox conditions were reconstructed in a sediment core in the parece vela basin of the eastern philippine sea the core consists of three units from youngest to oldest 1 laminated diatom mats ldm formed by ethmodiscus rex during the last glacial maximum similar to 18 28 kyr b p 2 diatomaceous clay dc and 3 pelagic clay pc elevated levels of export productivity during ldm deposition are indicated by high values for excess ba opal content and toc ti ratios estimated rates of organic carbon degradation ca 98 opal mass accumulation average 1322 g m 2 yr 1 and corrected organic carbon flux average 248 g m 2 yr 1 are comparable to high productivity regions of the modem ocean the ldm is also characterized by moderate enrichment of redox sensitive elements such as u mo cd and zn highly s 34 depleted pyrite sulfur isotopic compositions indicating bacterial sulfate reduction in a sulfate unlimited system and c s fe systematics reflecting limitation of pyrite formation by organic matter rather than reactive fe availability these features suggest mainly suboxic conditions in bottom waters but development of sulfidic anoxic conditions at or close to the sediment water interface association of intensified anoxia with productivity maxima indicates that export production was a more important control on bottom water redox conditions than lateral ventilation the dc and pc accumulated under oxic to suboxic conditions our observations suggest that redox environments during deposition of laminated marine sediments are more complicated and varied than previously thought and thus the use of sediment lamination as an indicator of anoxic bottom water conditions must be approached cautiously c 2012 elsevier b v all rights reserved

planetary accretion oxygen isotopes and the central limit theorem the accumulation of presolar dust into increasingly larger aggregates such as calciumaluminum rich inclusions cais and chondrules asteroids and planets should result in a drastic reduction in the numerical spread in oxygen isotopic composition between bodies of similar size in accord with the central limit theorem observed variations in oxygen isotopic composition are many orders of magnitude larger than would be predicted by a simple random accumulation model that begins in a well mixed nebula no matter what size objects are used as the beginning or end points of the calculation this discrepancy implies either that some as yet unspecified but relatively long lived process acted on the solids in the solar nebula to increase the spread in oxygen isotopic composition during each and every stage of accumulation or that the nebula was heterogeneous at least in oxygen and maintained this heterogeneity throughout most of its nebular history depending on its origin large scale nebular heterogeneity could have significant consequences for many areas of cosmochemistry including the application of well known isotopic systems to the dating of nebular events and the prediction of bulk compositions of planetary bodies on the basis of a uniform cosmic abundance the evidence supports a scenario wherein the oxygen isotopic composition of nebular solids becomes progressively depleted in 16o with time due to chemical processing within the nebula rather than a scenario where 16o rich dust and other materials are injected into the nebula possibly causing its initial collapse

silica and pyroxene in iva irons possible formation of the iva magma by impact melting and reduction of l ll chondrite materials followed by crystallization and cooling abstract group iva is a large magmatic group of iron meteorites the mean 17o 17o 0 52 18o of the silicates is 1 2 similar to the highest values in l chondrites and the lowest values in ll chondrites 18o values are also in the l ll range this strongly suggests that iva irons formed by melting l ll parental material but the mean ni content of iva irons 83 mg g is much lower than that of a presumed l ll parent 170 mg g and the low ca pyroxene present in two iva meteorites is fs13 much lower than the fs20 29 values in l and ll chondrites thus formation from l ll precursors requires extensive addition of metallic fe probably produced by reduction of fes and feo group iva also has s ni ga ni and ge ni ratios that are much lower than those in l ll chondrites or any chondrite group that preserves nebular compositions implying loss of these volatile elements during asteroidal processing we suggest that these reduction and loss processes occurred near the surface of the asteroid during impact heating and resulted partly from reduction by c and partly from the thermal dissociation of fes and feo with loss of o and s the hot 1770 k low viscosity melt quickly moved through channels in the porous asteroid to form a core two members of the iva group sao joao nepomuceno hereafter sjn and steinbach contain moderate amounts of orthopyroxene and silica and minor amounts of low ca clinopyroxene even though sjn formed after 26 crystallization and steinbach formed after 77 crystallization of the iva core both could have originated within several tens of meters of the core mantle interface if 99 of the crystallization occurred from the center outwards two other members of the group gibeon and bishop canyon contain tabular tridymite which we infer to have initially formed as veins deposited from a cooling sio rich vapor the silicates were clearly introduced into iva irons after the initial magma crystallized because the iron crystals in sjn are typically about 5 cm across an order of magnitude smaller than in iva irons that do not contain massive silicates we infer that the metal was in the iron field when the silicates were injected the sjn and steinbach silicate compositions are near the low ca pyroxene silica eutectic compositions we suggest that a tectonic event produced a eutectic like liquid and injected it together with unmelted pyroxene grains into fissures in the solid metal core published estimates of iva metallographic cooling rates range from 20 to 3000 k ma leading to a hypothesized breakup of the core during a major impact followed by scrambling of the core and mantle debris haack h scott e r d love s g brearley a 1996 thermal histories of iva stony iron and iron meteorites evidence for asteroid fragmentation and reaccretion geochim cosmochim acta 60 3103 3113 this scrambling model is physically implausible and cannot explain the strong correlation of estimated cooling rates with metal composition previous workers concluded that the low ca clinopyroxene in sjn and steinbach formed from protopyroxene by quenching at a cooling rate of 1012 k ma and suggested that this also supported an impact scrambling model this implausible spike in cooling rate by a factor of 1010 can be avoided if the low ca clinopyroxene were formed by a late shock event that converted orthopyroxene to clinopyroxene followed by minimal growth in the clinopyroxene field probably because melt was also produced we suggest that metallographic cooling rate estimates e g based on island taenite giving similar values throughout the metal compositional range are more plausible and that the iva parent asteroid can be modeled by monotonic cooling followed by a high temperature impact event that introduced silicates into the metal and a low temperature impact event that partially converted orthopyroxene into low ca clinopyroxene

history of the south java current over the past 80 ka a sediment core located below the present south java current sjc was used to reconstruct paleoclimate and paleoceanography on the basis of biogenic and terrigenic proxy records the core spans the past 80 ka of environmental change and shows considerable contrasts from the glacial to the holocene presently the core site is situated beneath a seasonally varying low salinity tongue which is advected from the java sea via the sunda strait it carries terrigenous matter of a characteristic signature during the last glacial period stage 4 2 when sea level was lower than during the holocene the sunda strait was closed and the terrigenous supply from that source ceased as the core site is close to the equator our results indicate that atmospheric and oceanographic circulation was alternatively dominated by the northern hemisphere east asian monsoon system and the southern hemisphere australian monsoon system between 20 and 12 ka the australian se winter monsoon reached its maximum and intensified the westward flowing sjc increased mixing of the surface waters led to a slight rise in paleoproductivity a similar but much weaker situation prevailed from 74 to 70 ka during most of the glacial period from 70 to 20 ka strong northeasterly winds associated with the east asian winter monsoon intensified the indian monsoon current and the eastward flowing sjc and may have also carried dust across the equator to our core site during this glacial phase populations of the giant diatom ethmodiscus rex were thriving and may indicate a reduced deep and intermediate thermohaline circulation at the site the monsoonal system as we know it today with distinct dry and wet seasons may not have been active before v12 ka 2002 elsevier science b v all rights reserved

oxygen isotope heterogeneity in chondrules from the mokoia cv3 carbonaceous chondrite we report a study of the oxygen isotope ratios of chondrules and their constituent mineral grains from the mokoia oxidized cv3 chondrite bulk oxygen isotope ratios of 23 individual chondrules were determined by laser ablation fluorination and oxygen isotope ratios of individual grains mostly olivine were obtained in situ on polished mounts using secondary ion mass spectrometry sims our results can be compared with data obtained previously for the oxidized cv3 chondrite allende bulk oxygen isotope ratios of mokoia chondrules form an array on an oxygen three isotope plot that is subparallel to and slightly displaced from the ccam carbonaceous chondrite anhydrous minerals line the best fit line for all cv3 chondrite chondrules has a slope of 0 99 and is displaced significantly by 17o 2 5 from the young and russell slope one line for unaltered calcium aluminum rich inclusion cai minerals oxygen isotope ratios of many bulk cais also lie on the cv chondrule line which is the most relevant oxygen isotope array for most cv chondrite components bulk oxygen isotope ratios of most chondrules in mokoia have 18o values around 0 and olivine grains in these chondrules have similar oxygen isotope ratios to their bulk values in general it appears that chondrule mesostases have higher 18o values than olivines in the same chondrules our bulk chondrule data spread to lower 18o values than any ferromagnesian chondrules that have been measured previously two chondrules with the lowest bulk 18o values 7 5 and 11 7 contain olivine grains that display an extremely wide range of oxygen isotope ratios down to 17o 18o around 50 in one chondrule in these chondrules there are no apparent relict grains and essentially no relationships between olivine compositions which are homogeneous and oxygen isotopic compositions of individual grains heterogeneity of oxygen isotope ratios within these chondrules may be the result of incorporation of relict grains from objects such as amoeboid olivine aggregates followed by solid state chemical diffusion without concomitant oxygen equilibration alternatively oxygen isotope exchange between an 16o rich precursor and an 16o poor gas may have taken place during chondrule formation and these chondrules may represent partially equilibrated systems in which isotopic heterogeneities became frozen into the crystallizing olivine grains if this is the case we can infer that the earliest nebular solids from which chondrules formed had 17o and 18o values around 50 similar to those observed in refractory inclusions

varves in marine sediments a review the global compilation of reported marine varved sedimentary records throughout the quaternary contains 52 sites marine varve deposition and preservation typically depend on environmental and sedimentological conditions such as a sufficiently high sedimentation rate severe depletion of dissolved oxygen in bottom water to exclude bioturbation by macrobenthos and a seasonally varying sedimentary input to yield a recognizable rhythmic varve pattern additional oceanographic factors include the strength and depth range of the oxygen minimum zone omz and regional anthropogenic eutrophication from point sources such as large polluted rivers quaternary marine varves are not only found in those parts of the open ocean that comply with these conditions but also in fjords embayments and estuaries with thermohaline density stratification and nearshore marine lakes with strong hydrologic connections to ocean water this review critically describes settings and sedimentological characteristics of marine sites where varves have been reported broader applications of marine varve records are discussed for example in terms of radiocarbon calibration on high resolution time scales constraining paleoceanographic variability and global change teleconnections diagnosing factors affecting modern fish population dynamics based on past performance detailing biogeochemical cycles and deciphering complex factors influencing marine productivity varves in saline water bodies without hydrologic connection to the global ocean are not included in this review and instead pertain to the companion review on lacustrine varves where also general and fundamental principles of varve deposition classification and dating are covered zolitschka et al 2015 the postulated occurrence of varves in pre quaternary rocks is critically discussed in this review with representative examples in the case of non evaporitic laminations in fine grained ancient marine rocks such as banded iron formations and black shales laminations may not be varves but instead may have multiple alternative origins such as event beds or formation via bottom currents that transport and sort silt sized particles clay floccules and organic mineral aggregates in the form of migrating bedload ripples

chondrules precursors and interactions with the nebular gas chondrule compositions suggest either ferroan precursors and evaporation or magnesian precursors and condensation type i chondrule precursors include granoblastic olivine aggregates planetary or nebular and fine grained dustball precursors in carbonaceous chondrites type i chondrule precursors were s free while type ii chondrules have higher fe mn than in ordinary chondrites many type ii chondrules contain diverse forsteritic relicts consistent with polymict dustball precursors the relationship between finer and coarser grained type i chondrules in ordinary chondrites suggests more evaporation from more highly melted chondrules fe metal in type i and na and s in type ii chondrules indicate high partial pressures in ambient gas as they are rapidly evaporated at canonical conditions the occurrence of metal sulfide or low ca pyroxene on chondrule rims suggests re condensation in semarkona type ii chondrules na rich olivine cores na poor melt inclusions and na rich mesostases suggest evaporation followed by recondensation type ii chondrules have correlated feo and mno consistent with condensation onto forsteritic precursors but with different ratios in carbonaceous chondrites and ordinary chondrites indicating different redox history the high partial pressures of lithophile elements require large dense clouds either clumps in the protoplanetary disk impact plumes or bow shocks around protoplanets in ordinary chondrites clusters of type i and type ii chondrules indicate high number densities and their similar oxygen isotopic compositions suggest recycling together in carbonaceous chondrites the much less abundant type ii chondrules were probably added late to batches of type i chondrules from different o isotopic reservoirs

high resolution migration history of the subtropical high trade wind system of the northeastern pacific during the last 55 years implications for glacial atmospheric reorganization 1 guaymas basin gulf of california is a restricted basin located under the present day wet dry subtropical divide 27 n and is ideally circumstanced for detecting variations in the north pacific subtropical high npsh trade wind system controlled by climate cell boundary displacement npsh midwinter location was the primary influence on timing and intensity of upwelling seasons in guaymas basin analysis of high resolution x ray fluoresence data and sediment fabric log from 75 laminated core md02 2517 2515 western guaymas basin reveals systematic changes in npsh behavior over the last 55 kyr bp southward displacement of the wet dry subtropical divide controlled upwelling related diatom productivity while sea level and regional rainfall controlled terrigenous supply the basin was oxic during the glacial and preservation was ensured by high burial rate due to the increased deposition of terrigenous sediment sediment fabric style number and or thickness of laminae plus color banding and homogeneous intervals changes systematically through the core and gives insights into the number of seasons occurring in guaymas basin and the occurrence and intensity of the upwelling season five millennial scale low flux events with close timing to heinrich events and ten decadal centennial scale low biogenic silica events occurring in the interval 33 16 5000 years before present kyr bp are interpreted as times of extreme aridity at 16 5 kyr bp a regime shift from terrigenous dominated oxic to evenly balanced biogenic terrigenous dysoxic conditions occurred although there was a further extreme arid event at 11 5 kyr bp 16 5 kyr bp was essentially the beginning of the interglacial

mineral equilibrium in fractionated nebular systems we investigated the equilibrium mineral assemblages in chemically fractionated nebular systems using a computer routine that finds the set of minerals and gases which minimizes the gibbs free energy of a system with stipulated elemental abundances diagrams are presented showing the equilibrium mineralogy as a function of temperature 400 2300 k for unfractionated solar material and five fractionated systems the fractionated systems were defined by mixing in various proportions the following four volatility components that solar material can be divided into refractory dust carbonaceous matter ices and h2 gas dust enrichment is seen to increase temperatures of condensation evaporation and the fe2 content of mafic minerals and to permit existence of stable melt phases enrichment of dust and organic matter produces mineral assemblages that are similar in many ways to those of enstatite chondrites but with mafic minerals that are far more reduced fe2 poor than those in primitive enstatite chondrites enrichment of dust organics and ices leads to highly ferrous mineralogies even at the highest temperatures but does not predict the stability of hydrous phases above 450 k

the compositional classification of chondrites vii the r chondrite group bulk compositional and petrographic data clearly define the new r rumuruti group of chondrites consisting of rumuruti the only fall alh85151 acfer 217 carlisle lakes dar al gani 013 pca91002 pca91241 y 75302 y 793575 and y 82002 compositional petrographic rare gas and 0 isotopic data strongly suggest that pca91002 and pca91241 are paired the yamato specimens are probably not paired the matrices of the known r chondrites have experienced similar minor degrees of metamorphism petrographic types are 3 8 3 9 with the exception of alh85151 3 6 all except carlisle lakes contain equilibrated r5 r6 clasts petrographically the r chondrites are characterized by a low chondrule matrix modal abundance ratio high states of oxidation reflected by abundant nio bearing olivine with fa37 40 relatively small chondrules mean apparent diameters of 400 abundant up to 11 wt sulfides mainly pyrrhotite and pentlandite and negligible amounts of metallic fe ni refractory lithophile abundances are 0 95 x cl intermediate between those in ordinary chondrites oc and ci chondrites abundances of the volatile elements se and zn are greatly enhanced relative to oc the r chondrites are clearly distinguished from other chondrite groups on the basis of al mn and zn mn abundance ratios the oxygen isotopic data plot roughly along a slope 12 line with whole rock 17o values higher than for any other chondrite group rumuruti acfer 217 alh85151 pca91002 and pca91241 have light dark structures and solar wind implanted rare gases indicating that they are regolith breccias the yamato specimens also have light dark structures and are inferred to be regolith breccias carlisle lakes lacks solar rare gases and is unbrecciated based on similarities in refractory lithophile abundances 00 95 x ci oxygen isotope compositions 17o 0 and refractory inclusion abundances 0 1 vol none have been reported the r chondrites probably belong to a noncarbonaceous superclan of chondrites that also includes ordinary and enstatite chondrites the high oxidation state high matrix chondrule modal abundance ratio relatively low abundance of droplet chondrules and high 17o composition suggest that the r chondrites formed at greater heliocentric distances than the oc

oxygen isotopes in chondrules and coarse grained chondrule rims from the allende meteorite abstract the oxygen isotopic compositions of porphyritic chondrules and coarse grained chondrule rims from the allende cv chondrite form a 16 o mixing trend situated near the carbonaceous chondrite anhydrous minerals ccam mixing line lying 0 1 0 7 higher in 17 o coarse grained rims are depleted in 16 o relative to their enclosed chondrules chondrules and rims exhibit significant correlations between their oxygen isotopic and chemical compositions objects rich in 16 o tend to have higher contents of refractory lithophiles and alkalies objects poor in 16 o tend to have higher contents of feo and volatile siderophiles cv chondrite matrix material is chemically and isotopically similar to some coarse grained chondrule rims previous work showed that o isotope data for cv barred olivine bo chondrules plot just below the terrestrial fractionation tf line near 18 o 4 well off the ccam line the allende data suggest that three solid precursor components are required to account for the o isotopic compositions of cv chondrules and rims 1 a high temperature refractory alkali and 16 o rich component perhaps near 18 o 40 17 o 42 relative to smow 2 a low temperature feo rich refractory and 16 o poor component lying near the ccam line perhaps near its intersection with the tf line at 18 o 10 and 3 an additional component required to explain the composition of bo chondrules

size scales over which ordinary chondrites and their parent asteroids are homogeneous in oxidation state and oxygen isotopic composition abstract literature data demonstrate that on a global asteroid wide scale plausibly on the order of 100 km ordinary chondrites oc have heterogeneous oxidation states and o isotopic compositions represented respectively by the mean olivine fa and bulk 17 o compositions of equilibrated samples samples analyzed here include a two h5 chondrite antarctic finds alha79046 and til 82415 that have the same cosmic ray exposure age 7 6 ma and were probably within 1 km of each other when they were excavated from the h chondrite parent body b different individual stones from the holbrook l ll6 fall that were probably within 1 m of each other when their parent meteoroid penetrated the earth s atmosphere and c drill cores from a large slab of the estacado h6 find located within a few tens of centimeters of each other our results indicate that oc are heterogeneous in their bulk oxidation state and o isotopic composition on 100 km size scales but homogeneous on meter decimeter and centimeter size scales on kilometer size scales oxidation state is heterogeneous but o isotopes appear to be homogeneous the asteroid wide heterogeneity in oxidation state and o isotopic composition was inherited from the solar nebula the homogeneity on small size scales was probably caused in part by fluid assisted metamorphism and mainly by impact gardening processes which are most effective at mixing target materials on scales of 1 m

a new model for the origin of type b and fluffy type a cais analogies to remelted compound chondrules abstract in the scenario developed here most types of calcium aluminum rich inclusions cais formed near the sun where they developed wark lovering rims before being transported by aerodynamic forces throughout the nebula the amount of ambient dust in the nebula varied with heliocentric distance peaking in the cv ck formation location literature data show that accretionary rims which occur outside the wark lovering rims around cais contain substantial 16o rich forsterite suggesting that at this time the ambient dust in the nebula consisted largely of 16o rich forsterite individual sub millimeter size compact type a cais each surrounded by a wark lovering rim collided in the cv ck region and stuck together in a manner similar to that of sibling compound chondrules the ctas were mixed with small amounts of 16o rich mafic dust and formed centimeter size compound objects large fluffy type a cais after experiencing minor melting in contrast to other types of cais centimeter size type b cais formed directly in the cv ck region after gehlenite rich compact type a cais collided and stuck together incorporated significant amounts of 16o rich forsteritic dust on the order of 10 15 and probably some anorthite and experienced extensive melting and partial evaporation enveloping compound chondrules formed in an analogous manner in those cases where appreciably higher amounts of 16o rich forsterite on the order of 25 and perhaps minor anorthite and pyroxene were incorporated into compound type a objects prior to melting centimeter size forsterite bearing type b cais b3 inclusions were produced type b1 inclusions formed from b2 inclusions that collided with and stuck to melilite rich compact type a cais and experienced high temperature processing

oxidation during metamorphism of the ordinary chondrites subtle but progressive changes in the compositions and relative abundances of olivine pyroxene and metal with increasing metamorphic grade in equilibrated types 4 6 ordinary chondrites indicate that these meteorites experienced oxidation of metallic fe during heating oxygen fugacities calculated from these mineral assemblages increase with petrologic type the hypothesis of oxidation during chondrite metamorphism differs from a commonly accepted idea that chondritic fe was reduced by graphite the mineralogies of unequilibrated type 3 chondrites do not conform to the progressions in equilibrated chondrites allowing the possibility that fe may first have been reduced through reaction with graphite at the onset of metamorphism although there are conflicting observations supporting both oxidation and reduction in these meteorites as temperatures increased to levels appropriate for types 4 6 chondrites the activity of graphite may have been lowered by its dissolution in taenite and in any case oxygen fugacities appear to have been well within the stability field of graphite precluding its reaction at these temperatures oxidation state was largely controlled by equilibrium between ferromagnesian silicates and metal oxygen fugacities calculated from chondrite mineral equilibria are 2 3 log units below previously reported intrinsic o2 measurements we propose that progressive oxidation during metamorphism was promoted by interaction with small amounts of an oxidizing vapor derived by heating ices originally accreted into the parent asteroids assuming that this vapor was pure h2o the watenrock weight ratio required to account for the observed oxidation of fe in h and l chondrites is very modest less than several per mil progressive oxidation in the metamorphic sequence resulted from different degrees of reaction with such a fluid possibly caused by temperature variations or evolution of the composition of the fluid as it permeated through the body the presence of even minor amounts of a vapor phase during metamorphism affects interpretations of the volatile trace element and oxygen isotopic fractionations observed in ordinary chondrites and inferred to have formed by nebular or parent body processes