nd and sr isotopic variations in chinese eolian deposits during the past 8 ma implications for provenance change a record of changes in nd and sr isotopic composition of the eolian deposits from the central loess plateau has been determined for the past 8 ma the isotopic records of the silicate fraction of the quaternary and tertiary eolian deposits allow interpreting the interplay between the sr isotopic variations in the eolian deposits and the late cenozoic tectonic and climatic changes the results indicate that the temporal variations of nd and sr isotopes show remarkable changes around the beginning of the quaternary the lower values of the 143 nd 144 nd and the decreasing trend of the 87 sr 86 sr ratios after 2 58 ma ago are attributed to the additions of relatively younger crust materials in response to the climatic cooling and the late cenozoic uplift induced glacial grinding in the high orogenic belts in central asia in this context the substantial changes in climate and tectonics have modified dust sources significantly and the quaternary loess forming processes are preferentially sampling relatively younger and high relief crust materials than that of the tertiary red clay d 2005 elsevier b v all rights reserved

the weathering of micrometeorites from the transantarctic mountains abstract micrometeorites are cosmic dust particles recovered from the earth s surface that dominate the influx of extraterrestrial material accreting to our planet this paper provides the first in depth study of the weathering of micrometeorites within the antarctic environment that will allow primary and secondary features to be distinguished it is based on the analysis of 366 particles from larkman nunatak and 25 from the transantarctic mountain collection several important morphological categories of weathering effects were identified 1 irregular and faceted cavities 2 surface etch pits 3 infilled cavities 4 replaced silicate phases and 5 hydrated and replaced metal these features indicate that congruent dissolution of silicate phases in particular olivine is important in generating new pore space within particles comparison of the preservation of glass and olivine also indicates preferential dissolution of olivine by acidic solutions during low temperature aqueous alteration precipitation of new hydrous phases within cavities in particular ferrihydrite and jarosite results in pseudomorph textures within heavily altered particles glass in contrast is altered to palagonite gels and shows a sequential replacement indicative of varying water to rock ratios metal is variably replaced by fe oxyhydroxides and results in decreases in ni fe ratio in contrast sulphides within metal are largely preserved magnetite an essential component of micrometeorites formed during atmospheric entry is least altered by interaction with the terrestrial environment the extent of weathering in the studied micrometeorites is sensitive to differences in their primary mineralogy and varies significantly with particle type despite these differences we propose a weathering scale for micrometeorites based on both their degree of terrestrial alteration and the level of encrustation by secondary phases the compositions and textures of weathering products however suggest open system behaviour and variable water to rock ratios that imply climatic variation over the lifetime of the micrometeorite deposits

the classification of micrometeorites due to their small size the mineralogical and chemical properties of micrometeorites mms are not representative of their parent bodies on the centimeter to meter scales that are used to define parent body groups through the petrological study of meteorites identifying which groups of mm are derived from the same type of parent body is problematic and requires particles to be rigorously grouped on the basis of mineralogical textural and chemical properties that reflect the fundamental genetic differences between meteorite parent bodies albeit with minimal bias towards preconceived genetic models specifically the interpretation of mms requires a rigorous and meaningful classification scheme at present the classification of mms is however at best ambiguous a unified petrological chemical classification scheme is proposed in the current study and is based on observations of several thousand mms collected from antarctic ice

the stable isotopic composition of modern soil carbonate and its relationship to climate the oxygen isotopic composition of modern soil carbonate is well correlated with the isotopic composition of local meteoric water the carbon isotopic cycle for co 2 in soils can be described in terms of the proportion of biomass using the c 4 photosynthetic pathway and the co 2 respiration rate of the soil at low soil respiration rates significant atmospheric co 2 mixing can occur in general the carbon isotopic composition of soil carbonate is related to the proportion of c 4 biomass present in soil but soils that freeze to the depth of carbonate formation often have a significant atmospheric component this suggests that freezing of the soil solution should be considered as another important mechanism for soil carbonate formation because of these relationships the isotopic composition of soil carbonate may be a paleoclimatic and paleoecologic indicator in cases in which diagenetic alteration has not occurred

has the washington oregon coast range moved northward paleomagnetic studies on middle and early tertiary rocks from the coast range consistently find inclinations that are a few degrees shallower than predicted by reference poles for the craton rocks of very similar age and lithology in the cascade range and elsewhere in washington and oregon do not show this effect this suggests that the coast range has moved northward several hundred kilometres relative to stable north america this movement could have been accomplished in a few million years prior to accretion of the coast range to the continent by passive transport aboard the kula and or farallon plates alternatively northward displacement could reflect dextral strike slip faulting in the north american borderland probably both mechanisms contributed

oxygen isotope record of paleorainwater in authigenic carbonates of chinese loess paleosol sequences and its paleoclimatic significance abstract oxygen isotopic compositions of rhizoconcretions and land snail shells were measured to reconstruct the 18o profiles of paleorainwater 18op for well dated loess paleosols in luochuan china to assess the paleoclimatic significance of 18op factors that control the spatial and temporal 18o variations of rainwater in east asian monsoon regions were investigated modern records indicate that the spatial 18o variations of modern rainwater 18om are closely related to near surface temperature t and the amount of precipitation p in order to separate the effects of t and p on the 18om a linear relationship between 18om t and the natural logarithm of p is established by multiple regressing analyses 18 o m 1 070 0 326 t 2 041 ln p the 18o of paleorainwater over the past 130 ka in luochuan area is calculated by the modern spatial 18o t p relationship using estimated t and p from other paleoclimate records the calculated 18o match well to those reconstructed from the authigenic carbonates which implies that the spatial and temporal 18o variations of rainwater in east asian monsoon regions have similar 18o t p relationships and the authigenic carbonates in chinese loess paleosol sequences can serve as valid records of 18op as an application of the 18o t p relationship p variation in the past 130 ka in luochuan was evaluated the reconstructed p is in good agreement with other studies using different approaches our results suggest higher precipitation in marine isotope stages 1 3 and 5 reflecting intense summer monsoon influences during these periods of time

geochemistry of the pliocene red clay formation in the chinese loess plateau and implications for its origin source provenance and paleoclimate change abstract recent field observations and sedimentological studies suggest the eolian origin of the late tertiary red clay formation underlying the pleistocene loess soil sequence in the loess plateau thereby extending the wind blown record from 2 6 ma down to 7 0 ma in north central china to address the source provenance of the red clay major and trace element concentrations were analyzed on the samples from a north south loess transect of the loess plateau and a red clay section at jiaxian results show that there is a good agreement of both major and trace element compositions between the last glacial interglacial loess soil units and the jiaxian red clay record the ree distribution patterns of the loess soil and red clay samples are remarkably similar in shape with enriched lree and fairly flat hree profiles and clear negative eu anomaly the geochemical features of the red clay are also identical to those of upper continental crust these chemical characteristics provide further evidence for eolian sedimentation of the red clay from the relations both between na2o al2o3 and k2o al2o3 ratios and between u pb and th pb ratios the eolian loess and red clay materials must have been subject to thorough sedimentary differentiation and moderate chemical weathering in the source area the chemical similarity between soil unit s1 and the red clay implies that such an environment as occurred in the last interglacial period may have already formed in northwestern china during the late tertiary comparison of down section variations in elemental ratios with field observations of pedogenic development of the red clay suggests that cao al2o3 sr rb and sr ba are more sensitive to climate changes than magnetic susceptibility and can be used to reconstruct the climate history of the late cenozoic

micrometer and nanometer sized platinum group nuggets in micrometeorites from deep sea sediments of the indian ocean abstract we examined 378 micrometeorites collected from deep sea sediments of the indian ocean of which 175 180 and 23 are i type s type and g type respectively of the 175 i type spherules 13 contained platinum group element nuggets pgns the nuggets occur in two distinct sizes and have distinctly different elemental compositions micrometer m sized nuggets that are 3 m contain dominantly ir os and ru iridium platinum group element or ipge and sub m or nanometer sized 1 m nuggets which contain dominantly pt rh and pd palladium pge or ppge the m sized nuggets are found only one per spherule in the cross section observed and are usually found at the edge of the spherule by contrast there are hundreds of nanometer sized nuggets distributed dominantly in the magnetite phases of the spherules and rarely in the wustite phases both the nugget types are found as separate entities in the same spherule and apparently nugget formation is a common phenomenon among i type micrometeorites however the m sized nuggets are seen in fewer specimens 2 5 of the observed i type spherules in all we analyzed four nuggets of m size and 213 nanometer sized nuggets from 13 i type spherules for platinum group elements chemically the m sized pgns contain chondritic ratios of os ir but are depleted in the more volatile pge pt rh and pd relative to chondritic ratios on the other hand the nanometer sized nuggets contain dominantly pt and rh importantly the refractory pges are conspicuous by their absence in these nanometer nuggets palladium the most volatile pge is highly depleted 1 1 with respect to chondritic ratios in the m sized pgns and is observed in only 17 of 213 nanometer nuggets with concentrations that are just above the detection limit 0 2 distinct fractionation of the pge into ipge ir os ru and ppge seems to take place during the short span of atmospheric entry these observations suggest several implications 1 the observation of fractionated pge in an fe ni system gives rise to the possibility that earth s core could contain fractionated pge 2 the present data support the processes suggested for the fractionated pge patterns observed in the ejecta of ancient meteorite impacts 3 meteoric metals released in the troposphere could contain fractionated pgns in large numbers

magnetic properties and opaque mineralogy of drilled submarine intrusive rocks summary measurements of natural remanent magnetization nrm curie temperature ferrimagnetic and paramagnetic susceptibility saturation induced and remanent magnetizations coercive forces alternating field properties and viscous magnetization are reported for 50 submarine intrusive rocks drilled during legs 30 37 and 45 of dsdp the collection includes doleritic sill rocks fresh and serpentinized cumulate gabbros and serpentinized cumulate peridotites and serpentinized lherzolites believed to have originated in layers 2b 3b and 4 respectively magnetite with a curie temperature between 520 and 580 c is the principal magnetic mineral in all samples there is no indication of maghemitization or of metamorphism to greenschist facies or above the magnetite in the doleritic and cumulate gabbros is a product of deuteric alteration of titanomagnetite and pyroxene the stable nrm is a primary trm the magnetite in the serpentinized rocks is a secondary product of serpentinization the stable nrm is a crm in most rock types the magnetite is of single domain or pseudo single domain size and soft components of nrm are small the magnetite grain size in some of the doleritic gabbros is much coarser these rocks acquire large viscous magnetizations which however are readily removed by alternating field cleaning the cleaned nrms of legs 30 and 45 rocks have approximately dipole inclinations but the nrms of most of the mutually intruded leg 37 units have been dispersed by tectonic rotations the doleritic gabbros and the serpentinized peridotites have stable directionally coherent nrms 10 3emu cm 3 in intensity their counterparts in layers 2b and 3b 4 are likely contributors to oceanic magnetic anomalies layer 3b cumulate gabbros and tectonic serpentinites in the middle and upper crust are less likely anomaly sources

causes and implications of the middle rare earth element depletion in the eolian component of north pacific sediment abstract previous studies clearly demonstrate that the detrital fraction of central north pacific sediment is derived almost exclusively from wind born particles from the arid and semi arid regions in asia these conclusions are based in part on trajectories observed for westerly wind systems and on a grainsize distribution for central north pacific sediment which can only be explained by eolian transport these observations have been verified by comparing the mineralogy neodymium isotopic composition and trace element geochemistry of the sediment with its asian source region however recent geochemical investigations consistently highlight compositional differences exemplified by a mree middle rare earth element depletion and a lower th sc ratio in eolian material extracted from north pacific sediment when compared to bulk china loess the continental analog of the eolian material these geochemical differences persist even when the bulk loess is subjected to the same extraction procedure here we present experiments demonstrating that these compositional differences are caused by a combination of grainsize fractionation during transport and partial dissolution of ree and th bearing phosphatic phases during the extraction procedure two bulk loess samples from china were separated into several different grain size fractions and a split of each fraction was subjected to the extraction procedure commonly used to isolate terrigenous material from marine sediment all extracted and unextracted sample pairs were analyzed for p th sc fe la ce sm eu yb and lu the amount of p removed by the extraction procedure correlates well with both the observed mree depletion and the decrease in th sc and is most pronounced in the finest grained samples these correlations strongly suggest that the extraction procedure dissolves inorganic phosphate phases which are rich in mrees and th a comparison of the compositions of the 2 3 mm loess size fractions with central north pacific sediment shows that both of these materials are identical

microparticle content records of the dunde ice core and dust storms in northwestern china abstract dust storms are important atmospheric phenomenon in central asia particularly in the regions bordering deserts arid and semi arid regions dust storms occur quite often in northwestern china there are some research results about past dust storm events using historical archives in china however the archives used cover limited time and area microparticle concentrations in the dunde ice cap qilian mountain of northwestern china represent a continuous record of past dust storms comparison between dust rain frequency reconstructed from historical archives and the ice core record from the dunde ice cap demonstrate that the microparticle record in the dunde ice core is a good indicator of dust storms in northwest china according to the ice core records we can reconstruct the dust storm chronology for historical time during the past 700 years the dust content fluctuated with time and lower frequency variations existed although the linear trend increased over the past 700 years dust content was decreasing since the early 1700s during the little ice age it was slightly higher corresponding to the cold period

dust production and deposition in asia and the north pacific ocean over the past 12 myr the silicate fractions of recent pelagic sediments in the central north pacific ocean are dominated by eolian dust derived from central asia an 11 myr sedimentary record at odp sites 885 886 at 44 7 n 168 3 w allows the evaluation of how such dust and its sources have changed in response to late cenozoic climate and tectonics the extracted eolian fraction contains variable amounts 70 of clay minerals with subordinate quartz and plagioclase uniform nd isotopic compositions nd 8 6 to 10 5 and sm nd ratios 0 170 0 192 for most of the 11 myr record demonstrate a well mixed provenance in the basins north of the tibetan plateau and the gobi desert that was a source of dust long before the oldest preserved asian loess formed nd values of up to 6 5 for samples 2 9 ma indicate 35 wt admixture of a young kamchatka like volcanic arc component the coherence of pb and nd in the erosional cycle allows us to constrain the pb isotopic composition of asian loess devoid of anthropogenic contamination to 206pb 204pb 18 97 0 06 207pb 204pb 15 67 0 02 208pb 204pb 39 19 0 11 87sr 86sr 0 711 0 721 and rb sr ratios 0 39 1 1 vary with dust mineralogy and provide an age indication of 250 ma 40ar 39ar ages of six dust samples are uniform around 200 ma and match the k ar ages of modern dust deposited on hawaii these data reflect the weighted age average of illite formation changes from illite smectite with significant kaolinite to illite and chlorite rich kaolinite free assemblages since the late pliocene document changes in the intensity of chemical weathering in the source region such weathering evidently did not disturb the k ar systematics and only induced scatter in the rb sr data we propose that when smectite forms at the expense of illite k and ar are quantitatively lost from what becomes smectite but are quantitatively retained in adjacent illite layers 40ar 39ar age data therefore are insensitive to smectite formation during chemical weathering but date the diagenetic growth of illite the major k bearing phase in the dust over the past 12 myr the dust flux to the north pacific increased by more than an order of magnitude documenting a substantial drying of central asia this climatic change however did not alter the ultimate source of the dust and neoformational products of chemical weathering always remained subordinate to assemblages reworked by mechanical erosion in dust deposited in eastern asia and the pacific ocean

does δ13ccarb of the chinese loess indicate past c3 c4 abundance a review of research on stable carbon isotopes of the chinese loess current research on stable carbon isotopes of the chinese loess is reviewed the stable carbon isotopic composition of soil organic matter som 13corg of paleosols formed during interglacials is more positive than that within loess accumulated during glacials spatially it becomes progressively more negative from the eastern chinese loess plateau clp to the western however stable carbon isotopic composition of pedogenic carbonates 13ccarb from the same sequence produces an opposing trend both temporally and spatially and variation differs from expectations under conditions of equilibrium this indicates that 13ccarb in the chinese loess cannot be used to reconstruct the relative proportion of c3 c4 plants in past ecological communities furthermore use of 13ccarb to reconstruct the expansion of c4 plants in older tertiary red clay deposits is considered unreliable we believe 13ccarb may act as an indirect indicator of vegetation density following on changes in moisture supply controlled by the intensity of the asian summer monsoon but conclude that full understanding of the paleoclimatic significance of 13ccarb in the chinese loess and underlying tertiary red clay requires better understanding of modern isotopic processes

numbers types and compositions of an unbiased collection of cosmic spherules abstract abstract micrometeorites collected from the bottom of the south pole water well spww may represent a complete well preserved sample of the cosmic dust that accreted on earth from 1100 1500 a d we classified 1588 cosmic spherules in the size range 50 800 pm the collection has 41 barred olivine spherules 17 glass spheres 12 cryptocrystalline spherules 11 porphyritic olivine spherules 12 relic grain bearing spherules 3 scoriaceous spherules 2 i type spherules 1 ca al ti rich cat spherules and 1 g type spherules we also found bubbly glass spherules spherules with glass caps and ones with sulfide coatings particles that are absent from other collections a classification sequence of the stony spherules scoriaceous relic grain bearing porphyritic barred olivine cryptocrystalline glass and cat is consistent with progressive heating and evaporation of fe from chondritic materials the modem day accretion rate and size distribution measured at the spww can account for the stony spherules present in deep sea collection through preferential dissolution of glass and small stony spherules however weathering alone cannot account for the high accretion rate of i type spherules determined for two deep sea collections the spww collection provides data to constrain models of atmospheric entry heating and to assess the effects of terrestrial weathering

koronis asteroid dust within antarctic ice here i report the first discovery of large numbers of ordinary chondrite derived micro meteorites mms recovered from antarctic ice ordinary chondrite derived mms comprise 70 coarse grained igneous particles and are identified on the basis of their distribution of petrologic types accessory mineralogy and minor element compositions all of which are very similar to those of millimeter sized igneous objects known as chondrules from ordinary chondrites and largely distinct from those of other meteorite groups the majority of ordinary chondrite derived mms are unequilibrated materials however 15 are equilibrated indicating parent body metamorphism and have compositions consistent with both h high iron and l low iron chondrites the total abundance of ordinary chondrite derived mms of 18 is similar to predictions by numerical calculations for the abundance of dust generated by the recent breakup of the karin group asteroids of the koronis asteroid family suggesting that these asteroids are the main source of the particles these mms represent the first to be associated with a known asteroid and imply that the karin group progenitor asteroid was a rubble pile asteroid that sampled different depths within the original internally metamorphosed koronis parent body

loess sedimentation in tibet provenance processes and link with quaternary glaciations abstract well preserved loess deposits are found on the foothills of mountains along the middle reaches of the yarlung zangbo river in southern tibet optically stimulated luminescence osl dating is used to determine loess ages by applying the single aliquot regeneration technique geochemical mineralogical and granulometric measurements were carried out to allow a comparison between loess from tibet and the chinese loess plateau our results demonstrate that i the loess deposits have a basal age of 13 11 ka suggesting they accumulated after the last deglaciation ii loess in southern tibet has a glacial origin resulting from eolian sorting of glaciofluvial outwash deposits from braided river channels or alluvial fans by local near surface winds and iii the present loess in the interior of tibet has accumulated since the last deglaciation when increased monsoonal circulation provided an increased vegetation cover that was sufficient for trapping eolian silt the lack of full glacial loess is either due to minimal vegetation cover or possibly due to the erosion of loess as glaciofluvial outwash during the beginning of each interglacial such processes would have been repeated during each glacial interglacial cycle of the quaternary

mineralogical variation of sr nd isotopic and elemental compositions in loess and desert sand from the central loess plateau in china as a provenance tracer of wet and dry deposition in the northwestern pacific we determined sr and nd isotopic compositions and major trace and rare earth element ree compositions of evaporite and detrital minerals in loess and desert sand from the central loess plateau clp where 80 of the loess deposits in china are found the loess exhibited a narrow range of variation in 87sr 86sr 0 715 0 001 a sequential extraction experiment on the loess however showed that water and acetic acid hoac soluble minerals mainly halite and calcite hydrochloric acid hcl soluble minerals chlorite and phosphate and hcl insoluble minerals illite kaolinite smectite vermiculite feldspar and quartz have distinct 87sr 86sr ratios approximately 0 7111 0 0004 0 7141 0 0004 and 0 7195 0 0010 respectively the water and hoac soluble ratios were regionally uniform and were close to the 87sr 86sr value of river water from the huanghe yellow river and the maximum 87sr 86sr value of spring rainwater in japan suggesting selective solution of eolian halite and calcite into the chinese river water and into the japanese rainwater the mineralogical elemental and sr nd isotopic compositions of hcl soluble and insoluble minerals in the clp loess were different from those of the northern desert sand but were indistinguishable from those of its fine grained fraction supporting the view that the loess is composed of the fine grained fraction of desert sand that was transported to the southeast in the atmosphere the 87sr 86sr end and gd yb values of hcl insoluble minerals in the clp loess were almost identical to those of airborne dust soil minerals and deep sea sediments in the northwestern pacific considered to be of eolian origin suggesting dissolution of the loess evaporite minerals during atmospheric transportation these relationships demonstrate the usefulness of sr isotopes of water and hoac soluble minerals and sr and nd isotope ratios and ree compositions of acid insoluble minerals in loess as provenance markers for wet and dry deposition respectively

palaeoclimate interpretation of stable isotope data from lake sediment archives the isotope composition of authigenic and biogenic carbonates and diatom silica are commonly used as palaeoclimate proxies from lake sediments this article reviews the controls on the isotope composition of lacustrine skeletal and non skeletal deposits and illustrates how stable isotope studies contribute to an understanding of changes in temperature precipitation patterns evaporation and the carbon cycle it highlights the differences in the palaeoclimate potential of a wide range of lakes ranging from open to closed lake basins a large number of the case histories but not all are drawn from studies of temperate lakes from europe large closed lake systems in the tropics and elsewhere lose water predominantly through evaporation and contain sediments with variable and generally high 18o values fluctuations in the isotope composition of authigenic or biogenic minerals are mainly a function of long term changes in the precipitation evaporation ratio in contrast small open lakes which have a degree of through flow typically contain sediments with 18o values that vary by no more than a few these variations are generally ascribed to variations in temperature or the isotope composition of precipitation p from which either an annual or seasonally specific signal can be gained these types of lakes are common in northern europe and at high altitudes the interpretation of isotope data from a lacustrine succession requires a knowledge of the local processes that might control and modify the signal their effects need to be quantified and a robust calibration using the modern lake system is necessary to establish the relationship between the measured signal the isotopic composition of the host waters and climate

a global rain of micrometeorites following breakup of the l chondrite parent body evidence from solar wind implanted ne in fossil extraterrestrial chromite grains from china previous studies of limestone beds of mid ordovician age from both sweden and china show that the earth saw an at least two orders of magnitude increase in the influx of extraterrestrial material approximately 470 ma following the disruption of an l chondrite parent body in the asteroid belt recovered extraterrestrial material consists of fossil meteorites and sediment dispersed extraterrestrial chromite sec grains both with l chondritic origin ne isotope analysis of sec grains from one of the swedish limestone sections revealed that the vast majority of the grains were delivered to earth as micrometeorites in this study we extend the previous work both in time and geographically by measuring concentrations and isotopic ratios of ne in individual sec grains 60120 mu m in diameter from three different beds from a contemporary middle ordovician limestone section in china all of the chinese sec grains 44 in total contain surface implanted ne of fractionated solar wind composition implying that these grains were as in the case of the swedish sec grains delivered to earth as micrometeorites this gives further compelling evidence that the two to three orders of magnitude increase in the influx of micrometeoritic material following the breakup of the l chondrite parent body was indeed a global event the rain of micrometeorites prevailed for at least 2 myr the estimated time of the deposition of the topmost chinese bed after the breakup event less

effects of chemical weathering and sorting on the petrogenesis of siliciclastic sediments with implications for provenance studies the bulk chemical compositions mineralogy and mineral proportions of sands and muds of the mallacoota basin in southeastern australia reflect the composition of weathering profiles mantling source rocks rather than bedrock muds contain abundant clay minerals that are virtually absent from the source rocks but abundant in the weathering profiles sands are strongly enriched in quartz relative to source rocks even in the headwaters of the fluvial system demonstrating that feldspar destruction occurs by in situ chemical weathering within profiles and before detritus enters the fluvial system k feldspar is proportionally more abundant in fluvial sands than in source rocks because plagioclase is more rapidly destroyed than either quartz or k feldspar in weathering profiles subsequent erosion and sorting produce sands enriched in quartz with high k feldspar plagioclase ratios relative to source rocks the composition of plagioclase incorporated into the fluvial sands is also controlled by chemical weat

petrology and geochemistry of antarctic micrometeorites abstract the petrology and geochemistry of twentythree chondritic dust particles with masses of 1 47 g sizes 100 400 m were recovered from blue ice near cap prudhomme antarctica and studied by inaa asem empa and optical microscopy sample selection criteria were irregular shape and for a subsample black color with the aim of studying as many unmelted micrometeorites mms as possible of thirteen unmelted mms six were phyllosilicate dominated mms and seven were coarsegrained crystalline mms consisting mainly of olivine and pyroxene the remaining ten particles were largely melted and consisted of a foamy melt with variable amounts of relic phases scoriaceous mms thus of the black particles selected an astonishing portion 40 by number consisted of largely unmelted mms although unmelted most phyllosilicate mms have been thermally metamorphosed to a degree that most of the phyllosilicates were destroyed but not melted the original preterrestrial mineralogy is occasionally preserved and consists of serpentine like phyllosilicates with variable amounts of cronstedtite tochilinite like oxides olivine and pyroxene the crystalline mms consist of olivine low ca pyroxene tochilinite like oxides and occasional ni poor metal relics in scoriaceous mms consist of the same phases mineral compositions and the coexistence of phyllosilicates with anhydrous phases are typical of cm and cr type carbonaceous chondrites however the olivine pyroxene ratio 1 and the lack of carbonates sulfates and of very fe poor refractory element rich olivines and pyroxenes sets the mms apart from cm and cr chondrites the bulk chemistry of the phyllosilicate mms is similar to that of cm chondrites however several elements are either depleted ca ni s less commonly na mg and mn or enriched k fe as br rb sb and au in mms as compared to cm chondrites similar depletions and enrichments are also found in the scoriaceous mms we suggest that the depletions are probably due to terrestrial leaching of sulfates and carbonates from unmelted mms the overabundance of some elements may also be due to processes acting during atmospheric passage such as the recondensation of meteoric vapors in the high atmosphere most mms are coated by magnetite of platy or octahedral habit which is rich in mg al si mn and ni we interpret the magnetites to be products of recondensation processes in the high 90 km atmosphere which are therefore probably the first refractory aerominerals identified

lithoprobe southern vancouver island cenozoic subduction complex imaged by deep seismic reflections reply the lithoprobe seismic reflection project on vancouver island was designed to study the large scale structure of several accreted terranes exposed on the island and to determine the geometry and structural characteristics of the subducting juan de fuca plate in this paper we interpret two lithoprobe profiles from southernmost vancouver island that were shot across three important terrane bounding faults leech river san juan and survey mountain to determine their subsurface geometry and relationship to deeper structures associated with modem subduction the structure beneath the island can be divided into an upper crustal region consisting of several accreted terranes and a deeper region that represents a landward extension of the modern offshore subduction complex in the upper region the survey mountain and leech river faults are imaged as northeast dipping thrusts that separate wrangellia a large mesozoic paleozoic terrane from two smaller accreted terranes the leech river schist mesozoic rock

bathozonal tilt corrections to paleomagnetic data from mid cretaceous plutonic rocks examples from the omineca belt british columbia the skelly creek batholith 49 4 n 116 6 w 94 99ma and summit stock 49 1 n 117 0 w 102 ma are intruded into the southern omineca belt of southeastern british columbia bathozonal mineral assemblages from contact aureoles of these plutons and others of the same age indicate that post emplacement tilting of the purcell anticlinorium has probably not exceeded about 5 whereas the summit stock has been tilted 24 down to the west the skelly creek batholith has a mean direction of magnetization d i with respect to present horizontal 349 74 13 sites k 53 95 6 the mean direction of magnetization of the summit stock is 48 72 nine sites k 290 95 3 and after correction for a westerly dip of 24 the mean direction becomes 318 74 directions of the skelly creek batholith and tilt corrected direction from the summit stock are in agreement with the reference field for cratonic north america evidently this part of the eastern omineca belt was close to the margin of ancestral north america in mid cretaceous time essentially where it is today

provenance of loess material and formation of loess deposits on the chinese loess plateau abstract results of a multiple isotopic chemical and mineralogical analysis of loess from the three northwestern inland basins the junggar basin the tarim basin and the qaidam basin and the loess plateau region of china are summarized they suggest a qualification of the conventional views that the three northwestern basins were the important source areas of the loess plateau and that the sand deserts were the primary single source of the chinese loess it is argued that the gobi stony desert in southern mongolia and the adjoining gobi and sand deserts the badain jaran desert tengger desert ulan buh desert hobq desert and mu us desert in china rather than the three inland basins are the dominant source areas of the loess plateau however although these gobi and sand deserts are regarded as the main source regions they serve as dust and silt holding areas rather than dominant producers the mountain processes including glacial grinding frost weathering salt weathering tectonic processes and some fluvial comminution in the gobi altay mts hangayn mts and the qilian mts have played an important role in producing the vast amounts of loess sized material for forming the loess plateau

the textures and compositions of fine grained antarctic micrometeorites implications for comparisons with meteorites abstract micrometeorites recovered from the earth s surface constitute the most abundant interplanetary dust now falling to earth we studied eighty nine fine grained antarctic micrometeorites fg amms to evaluate their state of alteration and to identify the nature of their precursor materials fine grained amms are divided into melted and unmelted groups and subdivided on the basis of textures related to atmospheric entry heating the textures of melted particles reflect crystallisation after entry heating and those of unmelted amms broadly resemble cl cm and cr chondrite matrix the matrix compositions of the fg amms closely resemble those of cm2 chondrites matrices provide a more reliable comparison to meteorites than bulk compositions because components such as chondrules and cais are not present in representative proportions within individual amms divergences from cm like matrix compositions are generally minor and probably arose during entry heating by the dissociation of volatile bearing phases at subsolidus temperatures and evaporation and loss of immiscible metallic liquids at higher temperatures depletions in ni and mg relative to cm matrix are tentatively attributed to terrestrial weathering no conclusive evidence for contamination during atmospheric residence was observed contrary to theory textural evidence suggests that bow shocks and high thermal gradients existed during deceleration of micrometeoroids in the atmosphere

paleomagnetism of the tertiary clarno formation of central oregon and its significance for the tectonic history of the pacific northwest the clarno formation a mostly eocene and partly early oligocene sequence of andesitic lavas and volcaniclastic rocks is the oldest tertiary formation exposed in north central oregon remanent magnetization directions at 46 sites in the lavas provide a paleomagnetic pole at 84 n 278 e with a 95 confidence cone of 7 comparison of this pole with the north american reference pole for eocene time indicates that the clarno formation has rotated 16 clockwise with an uncertainty of 10 but has undergone no significant latitudinal displacement further comparison with paleomagnetic data from the miocene columbia river basalt group and steens basalt shows that large scale block rotations in the eastern columbia embayment ceased sometime between 38 m y and 15 m y a paleogeographic reconstruction for 38 m y is offered which is consistent with the observed rotation of the clarno and with the other paleomagnetic data from the pacific northwest which are briefly reviewed this reconstruction shows that it is possible to account for virtually all of the paleomagnetically indicated rotations in pre miocene tertiary rocks of the pacific northwest by an extensional tectonic model as a consequence only part of the rotations in the pre tertiary rocks of the eastern columbia embayment need to be the result of accretionary tectonics the initiation of magmatism in the eastern columbia embayment that is represented by the clarno formation itself may have been contemporaneous with the beginning of crustal extension in the pacific northwest

east asian monsoon variability between 15 000 and 2000 cal yr bp recorded in varved sediments of lake sihailongwan northeastern china long gang volcanic field a palaeohydrological reconstruction on decadal scale for the period 15000 2000 cal yr bp based on calculated net accumulation rates for biogenic silica f bsio2 and additional proxies sedimentol

paleomagnetism and counterclockwise tectonic rotation of the upper oligocene sooke formation southern vancouver island british columbia the age of the sooke formation on the southern coast of vancouver island british columbia canada has long been controversial prior paleomagnetic studies have produced a puzzling counterclockwise tectonic rotation on the underlying eocene volcanic basement rocks and no conclusive results on the sooke formation itself we took 21 samples in four sites in the fossiliferous portion of the sooke formation west of sooke bay from the mouth of muir creek to the mouth of sandcut creek after both alternating field af and thermal demagnetization the sooke formation produces a single component remanence held largely in magnetite which is entirely reversed and rotated counterclockwise by 35 12 this is consistent with earlier results and shows that the rotation is real and not due to tectonic tilting since the sooke formation in this region has almost no dip this rotational signature is also consistent with counterclockwise rotations obtained from the northeast tip of the olympic peninsula in the port

a new approach to stable isotope based paleoaltimetry implications for paleoaltimetry and paleohypsometry of the high himalaya since the late miocene the change in oxygen isotopic composition of precipitation is modeled using equilibrium fractionation during rayleigh distillation linked to the thermodynamics of atmospheric ascent and water vapor condensation the primary controllers of the vertical variation in isotopic composition with elevation are the low elevation temperature and relative humidity as these control the vertical distribution of condensation an empirical fit of precipitation versus model condensation based on alpine stations is derived this fit is represented in the model as the weighted mean composition of condensation within a 1000 m thick air parcel 1500 500 m above the ground surface and is used for all other regions comparison of model versus observed modern precipitation reveals a close fit particularly of more highly elevated sites comparison of modern waters in the himalayas and southern tibet with model predictions particularly as revealed by comparison of observed and predicted hypsometry provides additional support to the validity of the model finally application of this model to estimates of paleo waters in the himalayas and southern tibet reveals that this region had already achieved its present hypsometry by the late miocene about 10 ma ago fl 2001 published by elsevier science b v

late quaternary aeolian dust input variability on the chinese loess plateau inferences from unmixing of loess grain size records abstract the grain size distributions gsds of loess paleosol sequences may provide valuable information on provenance transport and paleoclimate variability and consequently a wide range of methods to extract genetic information from loess gsds has been proposed here it is shown that a genetically meaningful decomposition of a series of late quaternary loess grain size records extending across the chinese loess plateau can be accomplished with the end member modelling algorithm emma the unmixing results in conjunction with loess accumulation rate estimates reveal that two contrasting dust supply patterns were active over the loess plateau during the last glacial interglacial cycle i a background sedimentation pattern that was dominant during interglacial periods especially over the central and southern parts of the loess plateau is reflected by the constant flux of the fine grained loess component ii an episodic highly variable dust input pattern that was dominant during glacial periods throughout the loess plateau and noticeable during interglacial periods mainly over the northern loess plateau and almost disappearing over the southern loess plateau is reflected in the admixture of two coarse grained loess components a genetic interpretation and the paleoclimatic significance of the mixing model are provided by comparison of the modelled end members with modern dust samples in terms of their gsd and flux rates

the fusion crusts of stony meteorites implications for the atmospheric reprocessing of extraterrestrial materials fusion crusts develop on all meteorites during their passage through the atmosphere but have been little studied we have characterized the textures and compositions of the fusion crusts of 73 stony meteorites to identify the nature of meteorite ablation spheres mas and constrain the processes operating during the entry heating most chondrite fusion crusts are porphyritic and are dominated by olivine glass and accessory magnetite whereas those of the achondrites are mainly glassy chondrite fusion crusts contain sulphide droplets with high ni contents 55 wt the partially melted substrate of ordinary chondrites underlying the outer melted crusts are dominated by silicate glass and composite metal sulphide and cr bearing fe oxide droplets that form as coexisting immiscible liquids enstatite chondrite substrates contain cr and mn bearing sulphides the substrates of the carbonaceous chondrites comprise a sulphide enriched layer of matrix the compositions of melted crusts are similar to those of the bulk meteorite however differences from whole rock suggest that three main processes control their chemical evolution 1 the loss and reaction of immiscible fe rich liquids 2 mixing between substrate partial melts and bulk melts of the melted crust and 3 the loss of volatile components by evaporation and degassing data from fusion crusts suggest that mas produced at low altitude have compositions within the range of those of silicate dominated cosmic spherules that are formed by the melting dust particles meteorite ablation spheres produced at high altitude probably have compositions very different from bulk meteorite and will resemble cosmic spherules derived from coarse grained precursors

are post middle miocene tilts present in the southern coast belt of british columbia a case study of present earth s magnetic field overprints tectonic tilt is a possible explanation for the discordant cretaceous paleomagnetic poles obtained from intrusions in the coast belt of the canadian cordillera if tilting of these intrusions has taken place post cretaceous intrusions may have been similarly tilted paleomagnetism of the middle miocene rogers creek pluton 16 ma in the central southern coast belt was utilized to test the tilt hypothesis well grouped stable primary magnetizations have been isolated in 11 sites with both normal and reverse polarities the mean remanence component directed at d 000 7 i 67 9 95 3 9 paleolatitude 50 9 9 n paleopole 88 3 n 257 5 e a95 5 7 was likely acquired upon emplacement at 16 ma this direction agrees with the middle miocene reference direction d 357 i 68 calculated from the updated miocene 10 20 ma cratonic reference pole for north america this concordant result when combined with concordant data from other mid tertiary intrusions to the south defines a southern co

holocene loess sedimentation along the qilian shan china significance for understanding the processes and timing of loess deposition abstract we present optical ages for well preserved loess deposits along the qilian shan a 500 km long mountain belt forming the tectonically active northeastern margin of the tibetan plateau loess on tectonically controlled fill terraces along the shiyou and baiyong rivers was dated by applying the single aliquot regeneration sar technique to coarse grained 90 160 m quartz samples additional measurements on polymineralic fine grained 5 10 m samples were carried out to allow a comparison between various optical dating techniques currently in use the results demonstrate that i loess accumulation started between 13 and 11 ka b p continuing to the present ii mean loess accumulation rates range between 9 and 16 cm ka 1 and iii holocene loess is not restricted to certain sites only but is a prevalent phenomenon along the qilian shan mountain front the absence of loess deposits of late pleistocene age is a result of a combination of cold and dry climate conditions strong winds and the absence of a vegetation cover during the last glacial period only with the change to a warmer and moister climate at the onset of the holocene did a plant cover develop which acted as a dust trap thus initiating the formation of loess

petrogenesis of uivfaq iron disko island greenland massive blocks of native iron and iron carbide weighing up to 22 tons have been found at uivfaq disko island western greenland the iron blocks are associated with tertiary basalts that erupted during rifting between greenland and baffin island early in the opening of the davis strait the iron is an asemblage of iron and iron carbide cohenite and various silicate sulphide and oxide inclusions containing highly reduced and iron rich phases including fayalite wustite troilite ulvospinel ilmenite ferriferous pigeonite and feo rich glass the chemistry and petrography of the inclusions are used to derive a paragenetic history for the uivfaq iron assemblage petrographic study of a massive uivfaq iron block shows that the block formed through accumulation of partly molten spherules of iron and cohenite 0 5 to 1 0 mm in diameter basaltic liquid was trapped by the accumulating metal spherules and reacted with the metal to form various highly reduced and iron enriched immiscible liquids these liquids solidified as inclusions in the iron mass various models are considered for the origin of the iron cohenite spherules at present a carbon reduction mechanism is preferred the association of graphite rich plagioclase spinel xenoliths thought to be derived from sediments with the iron masses suggests a genetic relation between the two we suggest that graphite was assimilated by mantle derived basaltic magma the carbon reduced iron oxide components of the basalt at a depth of 3 km or less and formed small immiscible droplets of high carbon iron carbon liquid these droplets were erupted with the magma the droplets settled and accumulated near or at the base of a flow or sill to form massive iron blocks

an experimental study of incongruent dissolution of caco3 under analogue glacial conditions this paper addresses the nature of incongruent dissolution of calcite in glacial settings using an experimental approach various caco 3 samples were comminuted using two contrasting techniques dry machine milling and hand grinding of an ice water mixture and dissolved to calcite saturation in both high pco 2 10 2 atm and low pco 2 10 3 5 atmospheric conditions ion yields of ca mg and sr were determined at the end of the experiments leachates displayed enhancement of mg ca and sr ca by a factor of 1 3 8 3 compared with bulk solid carbonate lower mg ca and sr ca ratios under higher pco 2 conditions reflect the percentage dissolution of the carbonate not the pco 2 per se the experimental results imply that reported natural incongruent dissolution is readily reproducible in the laboratory and is primarily dependent on the water rock ratio quantitative analysis of new and previous results suggests that the effect relates to the most reactive 0 15 0 25 of the sample equating volumetrically to the outer few lattice layers and it is interpreted as an anomalous leaching behaviour of calcite surfaces freshly exposed by crushing this phenomenon could serve as an index of the relative efficiencies of fragmenting and dissolutional processes in glacial environments

paleomagnetism of ocean layers 2 and 3 evidence from the metchosin complex vancouver island abstract the early eocene metchosin complex is an ophiolitic sequence and is the northernmost part of the crescent terrane it was underthrust beneath wrangellia later in the eocene directions of magnetization in sheeted diabase layer 2 and gabbroic intrusions layer 3 from the complex are internally consistent and both normal and reversed polarities are present mean directions irrespective of sign differ not only from the expected eocene palaeofield but also from one another these divergences have not therefore been caused by tectonic rotation of the metchosin complex as a whole but by variable tilting of bodies within the complex it is argued that these tilts probably were imposed during the emplacement of the metchosin complex adjacent to and beneath wrangellia the systematic clockwise rotations found further south in eocene rocks of the crescent terrane of washington and oregon do not occur the remanent magnetizations of the gabbros of layer 3 are commonly strong and stable these are the only rocks in the metchosin complex that had they been part of the present oceanic crust would be capable of contributing to marine magnetic anomalies the stable magnetization of diabase of layer 2 is too weak the dominant magnetization being a soft viscous remanence imposed by the present geomagnetic field the remanence of basalt lavas of layer 2 as previous work on the metchosin complex has shown is weak and scattered in direction

geochemical characterization of the luochuan loess paleosol sequence china and paleoclimatic implications abstract chemical major and trace element and isotopic sr nd analyses of the luochuan loess paleosol sequence in china were performed in order to examine the following problems 1 potential source heterogeneity 2 element behavior during pedogenesis 3 paleoclimatic implications and 4 the use of loess data to determine the average composition of the upper continental crust new results clearly indicate that rb sr u and ce abundances are severely depleted in paleosols relative to their parental loess the behavior of these elements is strongly controlled by the breakdown of primary minerals such as carbonate sr or by alteration processes in highly oxidizing environments ce and u the pattern of element variations through the upper section of the luochuan sequence mimics the magnetic susceptibility signal both in position and in intensity thus reinforcing the pedogenesic origin of the enhanced magnetic susceptibility in paleosols all loess samples display highly uniform ree patterns except for ce characterized by the upper continental crust ucc ratios la yb n 10 and eu eu 0 66 the paleosol ree patterns are similar to those of the loess with the same lree hree fractionation but they also show distinct and variable negative ce anomalies nd and sr isotopic compositions are rather uniform in both loess and paleosols and do not vary with stratigraphic position nd 10 5 to 9 2 87 sr 86 sr 0 715 to 0 719 the isotopic homogeneity in the luochuan sequence strongly suggests a uniform source region during the entire period of deposition since 800 ka ago to the present several conclusions may be drawn from the present study 1 1 no geochemical distinction can be made between loess layers l1 to l7 the sources and the dust storm trajectories must have been essendally the same for the last 800 ka 2 2 some elements e g ca rb sr u ce are strongly fractionated by pedogenesis between loess and paleosols ce mobility in soils is clearly demonstrated but the process responsible for this leaching is still poorly understood 3 3 systematic variations of element abundances and ratios between loess and paleosols can be used as chemical indicators for pedogenesic intensity and so for paleoclimatic change these chemical indicators serve a function similar to that of oxygen isotopes in deep sea sediments pelagic foraminifera or that of magnetic susceptibility in loess sequences they are different recorders of paleoclimatic change 4 4 the striking uniformity of ree patterns and la th ratios in the luochuan loess and paleosols as well as in loess worldwide is an excellent starting point for estimating the average composition of the upper continental crust

impact of tectonics on alluvial landforms in the hexi corridor northwest china abstract the hexi corridor is a cenozoic foreland basin system on the northeast margin of the qinghai tibet plateau the structure is characterised by reverse faults trending nnw or wnw rivers have been affected by sinistral offset by wnw trending faults and dextral offset by nnw trending faults the cenozoic sinistral offset reaches 24 km on the north front fault trending wnw of the qilian mountains on the northeast front fault trending nnw of the yumu mountains a bluff of the hei river terrace has been dextrally offset by 12 m with a rate of 1 2 m ka the vertical movement of the faults has caused the deformation of river terraces and controlled the distribution and migration of the alluvial fans three terraces of the hei river have been vertically dislocated 9 m 4 m and 2 m respectively by a reverse fault with uplift rates of 0 4 1 7 m ka two reverse faults have caused the older alluvial fans to be dissected and the younger fans to be deposited more towards the centre of the jiuquan basin the dislocation of terraces and the migration of alluvial fans suggests that tectonic activity was more intense around 160 and 40 ka bp

an urban collection of modern day large micrometeorites evidence for variations in the extraterrestrial dust flux through the quaternary we report the discovery of significant numbers 500 of large micrometeorites 100 m from rooftops in urban areas the identification of particles as micrometeorites is achieved on the basis of their compositions mineralogies and textures all particles are silicate dominated s type cosmic spherules with subspherical shapes that form by melting during atmospheric entry and consist of quench crystals of magnesian olivine relict crystals of forsterite and iron bearing olivine within glass four particles also contain ni rich metal sulfide beads bulk compositions are chondritic apart from depletions in the volatile moderately volatile and siderophile elements as observed in micrometeorites from other sources the reported particles are likely to have fallen on earth in the past 6 yr and thus represent the youngest large micrometeorites collected to date the relative abundance ratio of barred olivine to cryptocrystalline spherule types in the urban particles of 1 45 is shown to be higher than a quaternary average of 0 9 suggesting variations in the extraterrestrial dust flux over the past 800 k y changes in the entry velocities of dust caused by quasi periodic gravitational perturbation during transport to earth are suggested to be responsible variations in cosmic spherule abundance within the geologic column are thus unavoidable and can be a consequence of dust transport as well as major dust production events

depth trends in magnetic properties in an area of prolonged cold seawater drawdown in uppermost troodos type oceanic crust study of the oxide minerals and measurements of the magnetic properties of about 100 samples distributed over a 475 m continuous drill core section from the uppermost part of an extrusive sequence of the troodos cyprus ophiolite close to 35 02 n 33 11 e in the vicinity of malounda yields the following principal results 1 low temperature alteration is intense to a depth of 260 m below which it is relatively much subdued 2 saturation magnetization natural remanence intensity and initial susceptibility all increase continuously with depth throughout the section 3 curie temperature decreases with depth to 260 m below which a change in the style of the thermal decay of magnetization behaviour takes place 4 pillowed and massive flows differ in their magnetic properties the results are consistent with the downwards decrease in low temperature alteration also noted by k gillis from the distribution of secondary minerals the downwards variations in magnetic properties closely follow in both

the nature origin and accumulation of loess abstract loess can be defined simply as a terrestrial clastic sediment composed predominantly of silt size particles which is formed essentially by the accumulation of wind blown dust there are three fundamental requirements for its formation 1 a sustained source of dust 2 adequate wind energy to transport the dust and 3 a suitable accumulation site most loess has been modified to some degree by local reworking bioturbation and syn depositional weathering but a process of loessification is not necessary for a dust deposit to qualify as loess the terms primary loess and secondary loess have previously been used to described wind deposited loess and redeposited loess respectively but it is more accurate to describe material reworked and redeposited by non aeolian processes as loess derived colluvium or loess derived alluvium during the quaternary loess formed in three main situations 1 mid continental shield areas beyond the limits of ice sheets periglacial loess 2 on the margins of high mountain ranges perimontane loess and 3 on the semi arid margins of some lowland deserts peridesert loess peridesert loess is relatively poorly developed partly due to the limited efficiency of silt generating mechanisms in low land deserts compared with glaciation but also important is the tendency in arid areas for dust to be dispersed over a wide area and to be rapidly reworked after deposition particularly in areas which experience frequent climatic changes the remarkably thick loess of china and central asia results from an unusual combination of conditions which has persisted for much of the last 2 3 million years namely rapid uplift of the tibetan plateau and surrounding mountain ranges high rates of sediment production and supply to adjacent basins a strong northwesterly and westerly wind regime and the existence of effective dust traps downwind of the source regions

melted micrometeorites from antarctic ice with evidence for the separation of immiscible fe ni s liquids during entry heating we report the discovery of four large 50 m cosmic spherules css and a single scoriaceous micrometeorite smm that contain evidence for the separation of immiscible fe ni s liquids during atmospheric entry heating the particles contain segregated fe rich regions dominated by either ni s bearing fe oxides or iron sulphides and have textural relations that suggest these separated from the silicate portions of the particles as metallic liquids the oxides which may be hydrous are thought to result from alteration of metal and sulphide the compositions of the silicate portions of the css are equivalent to spherules without fe rich regions implying that metallic liquids are exsolved during the heating of most spherules but completely separate the single smm has a very different composition from other scoriaceous particles and the occurrence of an exsolved metallic liquid probably indicates extreme reduction during entry heating the pyrolysis of carbonaceous materials is the most likely explanation for reduction and suggests that the precursor material of this particle was unusually c rich this smm might be therefore an appropriate candidate for a large melted anhydrous or smectite interplanetary dust particle idp the exsolution of immiscible fe ni s liquids during entry heating will result in systematic changes in the compositions of the remaining silicate melt

on determining paleohorizontal and latitudinal shifts paleomagnetism of spences bridge group british columbia the spences bridge group of late albian age palynology and u pb zircon date of 104 5 ma is situated in the intermontane belt of the southern canadian cordillera zeolite grade andesite lavas and interbedded volcaniclastic rocks have been sampled through a thickness of about 2900 m sampling has been confined to localities whose bedding attitudes are well defined and to rocks that have not undergone internal deformation of the 27 sites studied 25 gave single component magnetizations with well grouped directions high coercivities and high unblocking temperatures applying corrections for geological tilt to all 25 sites yielded minimum dispersion after 65 untilting analysis indicates that this is a consequence of the interaction of two modes of behavior one exhibited by y magnetizations at 8 sites in which minimum dispersion occurs after 35 untilting and one x magnetizations at 17 sites in which minimum dispersion occurs after 100 correction actually the dispersion is essentially constant in the range 88 to 100 correction the y magnetizations are uninterpretable in terms of the paleofield because no estimate of paleohorizontal can be made because of their positive response to the tilt test the x magnetizations were acquired before tilting and it is argued that geologically determined bedding planes are good estimators of paleohorizontal at the time of remanence aquisition there may be errors because of paleoslope but arguments are presented for believing that these are small on this basis the best estimate of the mean direction of the paleofield in spences bridge time is estimated to be d i declination inclination 38 7 63 9 17 sites k 44 compared with k 11 in situ 95 5 4 with a paleopole at 64 4 n 321 0 e k 24 compared with k 5 in situ a95 7 5 when compared with the cratonic reference field for mid cretaceous time this pretilting magnetization indicates a clockwise rotation of the study area of 66 3 11 8 p 0 05 and an apparent displacement from the south of 15 5 7 1 1725 790 km when these and other data previously obtained from cretaceous rocks of the pacific northwest are compiled they show an increase in apparent displacement from east to west across the cordillera this result is discussed in terms of three hypotheses 1 no translation but systematic tilts of about 30 to the southwest 2 translation of a substantial part of the pacific northwest referred to as baja british columbia and is defined more exactly in the text by variable amounts up to more than 2000 km from the south together with clockwise rotations and 3 lesser translation of baja british columbia by about 1500 km combined with variable tilting predominantly to the south it is concluded that paleomagnetic data as they are presently known are consistent with hypotheses 2 and 3 but unless serious sources of error are present are not consistent with hypothesis 1 the most likely candidate for such errors is the uncertainty in estimating initial dip of beds paleoslope in volcanic rock units

active thrusting and folding in the qilian shan and decoupling between upper crust and mantle in northeastern tibet fieldwork south of the city of gaotai gansu province china shows that active shortening of surface sediments in the foothills of the yumu shan a large fore mountain of the qilian shan at the northeastern edge of tibet involves both overthrusting and flexural slip folding north of this mountain we found and mapped a prominent north facing thrust scarp that offsets a holocene fan sloping gently 3 4 to the north part of this scarp appears to be related to the m 7 5 180 a d earthquake that may have led to the demise of the han dynasty city of luo tuo chen in the hexi corridor a set of 10 100 150 m long profiles measured across this scarp 3 2 m high on the average can be made to fit the diffusion degraded morphology of a surface break related to the 180 a d event using a value of about 3 3 m 2 10 3 yr for the mass diffusivity of fanglomerates in this part of gansu province smaller mountain facing scarps on a terrace capped foothill result from bedding slip concurrent with active folding of underlying steeply northdipping plioquaternary sandstone and conglomerate beds holocene uplift rates along the yumu shan which is only one of the qilian shan ranges are estimated to be between 0 4 and 1 9 mm yr which implies that much of the mountain formed in the quaternary the periclinal structure of the plioquaternary envelope under which the paleozoic core of the yumu shan plunges towards the west suggests that the whole 3200 m high mountain is a basement ramp anticline mountains striking parallel to the yumu shan with similar structure and comparable or greater sizes north and south of the hexi corridor probably also correspond to recent crustal ramp anticlines this implies that the wide mountainous upper crustal wedge making the northeastern edge of the tibet qinghai plateau is detached from the underlying lower crust and upper mantle

loess stratigraphy in central china abstract the loess deposits in central china record world wide climate changes of the last 2 5 ma numerous climatic oscillations are marked by alternating loess and soil units with continuous coverage of the matuyama and brunhes epochs magnetic susceptibility of the deposits correlates closely with the oxygen isotope record of the deep sea sediments and provides an independent measure of climate and time the key marker bed of the chinese loess sequence is the paleosol s5 the time equivalent of the mid brunhes oxygen isotope stages 13 14 and 15 it marks a prolonged interval of warm humid climate lasting from approximately 615 to 470 thousand years ago several episodes of river downcutting coincide with deposition of the exceptionally thick loess units l1 oceanic oxygen isotope stages 2 to 4 l2 stage 6 l5 stage 12 l6 stage 16 l9 stage 22 l15 stage 38 about 1 15 ma and ws4 about 2 3 ma these erosional events are interpreted as a result of episodic uplift of the loess plateau the deposition of the earliest loess layers between 2 5 and 2 3 ma ago marks a first order shift from warm and humid environments toward harsh continental steppes comparable to those of the middle and late pleistocene little if any lithologic or paleontologic changes were noted within or above the olduvai magnetozone so that the proposed plio pleistocene boundary at approximately 1 65 ma has no lithostratigraphic and biostratigraphic representation in the chinese loess series comparison with the deep sea drilling program core 552a in the north atlantic and with the santerno river section near bologna shows that the occurrence of the earliest loess in china coincides with the timing of the first significant ice rafting in the north atlantic and with the appearance of cold water foraminifers in the marine deposits of northern italy an extension of the stage system of the oxygen isotope signal extended back to the gauss matuyama boundary is proposed

paleomagnetism and tectonics of the crescent formation northern olympic mountains washington a stable prefolding magnetization has been discovered in pillow basalts of the eocene lower crescent formation of the northern olympic mountains the curved outcrop pattern of the crescent formation has been the target of several unsuccessful studies to test for oroclinal bending the success of this study is due in part to the development of a small diameter electric core drill for sampling the fractured rims of basalt pillows thermal demagnetization produced stable endpoints by 580 c in 12 of the 34 sites sampled large within site scatter was common in the remaining sites among the accepted sites within site scatter was small and correction for bedding tilt significantly reduced the scatter between sites the mean paleomagnetic pole for newly sampled pillow basalts 86 4 north latitude 170 0 east longitude a95 16 5 is indistinguishable from the early to middle eocene pole expected for north america including previous results from sites in subaerial basalt of the upper crescent formation in and near the easterm olympic mountains results in a more regional paleomagnetic pole 80 7 north latitude 192 0 east longitude a95 8 0 n 46 that shows no significant rotation 0 8 14 4 or poleward displacement 3 6 8 5 analysis of the magnetic mineralogy suggests that the remanence is early probably primary the pole therefore should be valid for tectonic interpretation of the region a circular distribution of virtual geomagnetic poles after correction for bedding tilt supports the hypothesis that the northern crescent formation experienced deformation due to the rise in a domelike fashion of the sediments of the olympic core terrane erosion of a partial dome open to the west could have produced the curvature seen in the outcrop pattern of the crescent formation the lack of significant rotation of the northernmost coast ranges contrasts with the net clockwise rotation seen to the south the difference could be that irrotational northward translation paleomagnetically insignificant yet geologically important driven by oblique convergence was accommodated by the north south trending strike slip faults to the east of the olympic mountains

summer monsoon intensity controls c4 c3 plant abundance during the last 35 ka in the chinese loess plateau carbon isotope evidence from bulk organic matter and individual leaf waxes the natural abundance of c3 and c4 plants is affected by multiple environmental factors including temperature moisture balance and atmospheric pco2 the relative importance of these factors is a subject of considerable debate and may vary in different natural ecosystems previous studies generally focus on single loess sequences in the chinese loess plateau and conflicting conclusions on c4 c3 have been reached when studying carbon isotope ratios in carbonate and organic matter in this paper we report a comprehensive carbon isotopic characterization of total organic carbon toc and individual higher plant leaf waxes from five loess sequences spanning the last 35 ka from the chinese loess plateau clp the five coring sites encompass large gradients of annual mean temperature 9 2 13 9 c and precipitation 402 673 mm allowing us to assess the controlling mechanisms on c4 c3 plant ratios glacial interglacial sequences provide carbon isotope data for comparison with other climatic and environmental proxies such as lithology and magnetic susceptibility our results demonstrate that increased c4 c3 ratios are positively correlated with higher temperature and increased summer rainfall which characterize stronger summer monsoon in all five sites we conclude c4 abundance increases from the last glacial to the holocene in response to greater monsoon activity and that the c4 expression is suppressed in the cold and drier intervals

combined irsl osl single aliquot regeneration sar equivalent dose de estimates from source proximal chinese loess tectono sedimentary systems are readily recognized in northeastern tibet and elsewhere but they have proved difficult to date via conventional absolute dating techniques in the qilian shan the application of cosmogenic methods is complicated by the presence of terrace blanketing loess deposits we have chosen to explore the potential of applying optical dating techniques to directly date the loess cover deposits to provide minimum ages for terrace abandonment events we focussed on a suite of six loess mantled terraces cut into an abandoned alluvial fan sequence which was uplifted by thrust faulting on the zhangye thrust fault east of the hei he river at its exit from the qilian shan application of single aliquot regeneration sar optical dating techniques provides a chronology of terrace age we employ a double sar procedure in which aliquots are subjected to both infrared lin 830 nm and blue lin 470 nm stimulation and two sets of de determinations are produced and assumed to relate predominantly to feldspathic and quartz fine grain populations respectively our de and age determinations are stratigraphically sensible and we do not observe a significant difference between irsland osl de estimates which has been the case in previous studies r 2003 published by elsevier science ltd

paleomagnetism of eocene rocks of the kelowna and castlegar areas british columbia studies in determining paleohorizontal the middle eocene marron volcanics mean age 52 2 ma of the kelowna outlier form the upper part of the hanging wall of the westerly dipping okanagan valley fault ovf in south central british columbia they overlie quesnellia the ovf is currently interpreted as the westernmost member of a network of low angle extension faults in the southern omenica belt the ovf was active in the middle eocene at much the same time that the marron volcanics were cooling relative to present horizontal the magnetizations are widely scattered fisher s precision parameter k 8 and after correction for bedding attitudes there is no significant improvement k 9 evidently some magnetizations were acquired before referred to as category 1 and others after category 2 tilting that is the horizontal plane at the time of magnetization sometimes did and sometimes did not coincide with the bedding plane partial unfolding experiments carried out on the two categories separately yield a precision comparable to t

holocene moisture evolution in arid central asia and its out of phase relationship with asian monsoon history we synthesize palaeoclimate records from the mid latitude arid asian region dominated today by the westerlies arid central asia aca to evaluate spatial and temporal patterns of moisture changes during the holocene sediment records from i i takes with reliable chronologies and robust proxies were selected to reconstruct moisture histories based on a five class ordinal wetness index with assigned scores from the driest to wettest periods at individual sites for 200 year time slices the proxies used in these records include pollen and diatom assemblages sediment lithology lake levels and geochemistry mainly isotope data the results of our synthesis show that aca as a whole experienced synchronous and coherent moisture changes during the holocene namely a dry early holocene a wetter less dry early to mid holocene and a moderately wet late holocene during the early holocene most of the lakes experienced very low water levels and even dried out before ca 8 ka 1 ka 1000cal a bp hence the effective moisture history in aca is out of phase with that in monsoonal asia as documented by numerous palaeoclimate records in monsoonal asia a strong summer monsoon and humid climate characterized the early holocene and a weakened summer monsoon and drier climate prevailed during the late holocene which were mainly controlled by changes in low latitude summer insolation in contrast we propose that the pattern of holocene effective moisture evolution in the westerly dominated aca was mainly determined by north atlantic sea surface temperatures ssts and high latitude air temperatures that affect the availability amount and transport of water vapor also topography of the tibetan plateau and adjacent asian highlands could have contributed to the intensification of dry climate in aca during the early holocene as a result of strengthening the subsidence of dry air masses associated with stronger uplift motion on the plateau by intense heating under a stronger summer insolation summer insolation might have played a key role in directly controlling moisture conditions in aca but only after the northern hemisphere ice sheets had disappeared in the mid and late holocene c 2007 elsevier ltd all rights reserved

geochemistry of the xining xifeng and jixian sections loess plateau of china eolian dust provenance and paleosol evolution during the last 140 ka abstract loess and paleosol samples from three distant sections xining xifeng jixian of the chinese loess plateau were analyzed for chemical and nd sr isotopic compositions in order to obtain information about the paleoclimatic variation during the last 140 ka these three sections represent three different climatic conditions from arid in the west xining to more humid in the east jixian across the loess plateau isotopic analyses show that all the three sections display a restricted range of 143 nd 144 nd ratios or e nd 10 0 5 indicating the dominance of relatively young and uniform upper crustal sources for the eolian dust the loess and paleosol samples have typical upper crustal 87 sr 86 sr ratios 0 714 0 718 and their variation can partly be attributed to different carbonate silicate ratios in the samples ree data from the three sections are indistinguishable from each other they show typical upper crust patterns characterized by la yb n 10 and eu eu 0 65 the high degree of chemical and isotopic homogeneity suggests that the dust source region must have undergone multiple recycling and thorough sedimentary mixing processes various chemical indicators have been used to monitor the pedogenetic intensity in these sections although results for the jixian section agree reasonably well with the known climatic conditions on the loess plateau the other two sections yield results not in agreement with some well accepted proxies like magnetic susceptibility or grain size distribution some chemical proxy indicators established in our previous work on the luochuan section such as the systematic u depletion and negative ce anomalies in ree patterns in soils are not clearly recorded in the present case the discrepancy between different climatic proxies could be related to the effective soil water budget temperature as well as the rate of development of each proxy

the sr and nd isotopic variations of the chinese loess plateau during the past 7 ma implications for the east asian winter monsoon and source areas of loess abstract 143 nd 144 nd and 87 sr 86 sr ratios of the acid insoluble residues of the red clay and overlying loess paleosols from the lingtai profile of the loess plateau china were investigated the results show that variations of the 87 sr 86 sr ratios of the lingtai profile can be divided into two stages from 7 ma b p to 2 5 ma b p the acid insoluble residues in the red clay rc formation are characterized by higher 87 sr 86 sr ratios with an average of 0 7230 from 2 5 ma b p to the present the acid insoluble residues in the wuchen loess wl4 ws1 lishi loess l15 s1 malan loess l1 and holocene loess s0 have relatively lower 87 sr 86 sr ratios and display an overall descending trend from 0 7223 at 2 5 ma b p to 0 7182 at the present among three possible interpretations for the variations of 87 sr 86 sr ratios of acid insoluble residues of the loess provenance change chemical weathering change or grain size distribution change only grain size distribution change provides a satisfactory interpretation this implies that the east asian winter monsoon strength was weak and relatively stable from 7 ma b p to 2 5 ma b p but became continuously enhanced from 2 5 ma b p to the present all the red clay and the overlying loess paleosols in the lingtai profile have generally identical e nd 0 implying that the source regions of these eolian deposits of the chinese loess plateau may be relatively stable and has not changed since 7 ma b p

nd and sr isotopic characteristics of chinese deserts implications for the provenances of asian dust silicate nd sr isotopes of the fine grained fractions of the 10 major deserts and sandy lands in north china and the loess in chinese loess plateau were systematically investigated wide ranges in nd sr isotopic compositions have been observed the results of the 7 0 b the deserts on the northern margin of tibetan plateau with end 0 ranging from 11 9 to 7 4 and c the deserts on the ordos plateau with the lowest end 0 11 5 the distribution of the threes isotopic regions is controlled by the tectonic setting in north china which implies that the materials of the deserts are derived from the locally eroded rocks from the surrounding mountains and the nd sr isotopic signatures of these deserts could be quit stable over the past million years on the sub tectonic time scales if there is any desert at those times the nd sr isotopic compositions of the loess are mostly close to those of the deserts in isotopic region b suggesting that the main source regions of the last glacial loess in the chinese loess plateau are badain jaran desert tengger desert and qaidam desert also the comparison between the nd sr isotopes of the 5 lm silicate fractions of the deserts and the ancient dust falls in the north pacific and greenland show that the asian end members of these dust falls are derived most from the deserts in the isotopic region b and less from those in the isotopic region c

paleomagnetism of the late cretaceous early tertiary north central montana alkalic province paleomagnetic results have been obtained from the late cretaceous early tertiary igneous complexes of the north central montana alkalic province data from 94 sites in eocene volcanic and intrusive rocks give a paleomagnetic pole located at 82 0 n 170 2 e a95 3 5 k 18 6 while 36 sites in paleocene intrusions yield a paleomagnetic pole at 81 8 n 181 4 e a95 5 4 k 20 2 these poles differ by only 1 6 and are not significantly different statistically the 130 site virtual geomagnetic poles show no significant elongation and suggest no significant apparent polar wander apw during the period of magnetization of the igneous centers postmagnetization structural complications in these rocks are minimal the presence of a single predominant polarity in these intrusive complexes reinforces the radiometric age data that suggest that igneous activity within individual centers was of short duration the northcentral montana data together with other early tertiary cretaceous and mid tertiary paleomagnetic results require modification of our earlier apw chronology diehl et al 1980 it now appears that apw relative to north america since the early cretaceous consists of a polar still stand during much of the cretaceous 120 75 m y b p a period of rapid movement in latest cretaceous time 75 65 m y b p and a period of slow polar movement thereafter the onset of this period of rapid apw correlates well with a major change in plate motions at 80 m y and the beginning of the laramide orogeny

size dependent geochemical signatures of holocene loess deposits from the hexi corridor china well dated holocene loess sequences from uplifted river terraces at the northern margin of the tibetan plateau are characterised by their chemical grain size sr isotope and their oxygen and carbon isotope composition of the carbonate fractions prevailing wind directions suggest the source areas of the loess to be largely restricted to dry lands in northwest china and the deserts north to the hexi corridor e g badain jaran and tengger desert which receive fluvial input by rivers draining the qilian shan the dry lands of northwest china are one of the most important dust source areas globally local and conditions make the investigated loess sequences insensitive to element leaching the loess is characterised by a relatively narrow variation of sr 87 sr 86 0 7139 0 7164 the sr 87 sr 86 ratios of surface and carbonate bound sr are similar 0 7114 and 0 7111 and lower than those of silicate bound sr 63 2 mu m fractions similar to 0 7196 2 mu m fractions similar to 0 7247 since the clay fractions have higher caco3 contents than the silt fractions the isotopic contrast between the silicate debris of clay and silt size is camouflaged in the bulk compositions of these grain size fractions oxygen isotope and chemical compositions of clay and silt sized carbonate particles differ significantly silt sized loess carbonates formed authigenically and they are largely present as coatings of silicate grains whereas clay sized carbonate particles are of remote provenance and precipitated under evaporative conditions in line with further implications from the multi proxy study upward trends in the composition of the pedogenic carbonate document climate change to drier conditions after the mid holocene c 2009 elsevier ltd all rights reserved

diagenetically altered fossil micrometeorites suggest cosmic dust is common in the geological record abstract we report the discovery of fossil micrometeorites from late cretaceous chalk seventy six cosmic spherules were recovered from coniacian 87 1 ma sediments of the white chalk supergroup particles vary from pristine silicate and iron type spherules to pseudomorphic spherules consisting of either single phase recrystallized magnetite or fe silicide pristine spherules are readily identified as micrometeorites on the basis of their characteristic mineralogies textures and compositions both magnetite and silicide spherules contain dendritic crystals and spherical morphologies testifying to rapid crystallisation of high temperature iron rich metallic and oxide liquids these particles also contain spherical cavities representing weathering and removal of metal beads and irregular cavities representing vesicles formed by trapped gas during crystallization both features commonly found among modern antarctic iron type i type cosmic spherules on the basis of textural analysis the magnetite and fe silicide spherules are shown to be i type cosmic spherules that have experienced complete secondary replacement during diagenesis fossilization our results demonstrate that micrometeorites preserved in sedimentary rocks are affected by a suite of complex diagenetic processes which can result in disparate replacement minerals even within the same sequence of sedimentary beds as a result the identification of fossil micrometeorites requires careful observation of particle textures and comparisons with modern antarctic collections replaced micrometeorites imply that geochemical signatures the extraterrestrial dust are subject to diagenetic remobilisation that limits their stratigraphic resolution however this study demonstrates that fossil pseudomorphic micrometeorites can be recognised and are likely common within the geological record

asian aridity and the zonal westerlies late pleistocene and holocene record of eolian deposition in the northwest pacific ocean rea d k and leinen m 1988 asian aridity and the zonal westerlies late pleistocene and holocene record of eolian deposition in the northwest pacific ocean palaeogeogr palaeoclimatol palaeoecol 66 1 8 a 30 000 year record of eolian deposition in the northwestern pacific ocean provides a history of the aridity of the asian source region and information on the changing latitude and intensity of the zonal westerlies the position of the maximum in eolian flux to the deep sea remained unchanged at 38 to 40 n during this entire time period but the dust flux record of aridity is greatest 6000 years ago at the holocene climatic optimum eolian grainsize data indicate that the northern margin of the westerly jet stream retreated northward during the holocene to a poleward extreme at about 6000 years ago and then moved back toward the equator the change in wind intensity across this margin was continually reduced throughout the holocene these sorts of data enhance our understanding of the behavior of the atmosphere during times of climate change and can be used to test computer generated models of past climatic conditions

cometary dust in antarctic ice and snow past and present chondritic porous micrometeorites preserved on the earth s surface abstract chondritic porous interplanetary dust particles cp idps collected in the stratosphere are regarded as possibly being cometary dust and are therefore the most primitive solar system material that is currently available for analysis in laboratories in this paper we report the discovery of more than 40 chondritic porous micrometeorites cp mms in the surface snow and blue ice of antarctica which are indistinguishable from cp idps the cp mms are botryoidal aggregates composed mainly of sub micrometer sized constituents they contain two components that characterize them as cp idps enstatite whiskers and gems glass with embedded metal and sulfides enstatite whiskers appear as 2 o 6 rich high ca pyroxene roedderite k na 2 mg 5 si 12 o 30 and carbonaceous nanoglobules these components have previously been discovered in primitive solar system materials such as the cp idps matrices of primitive chondrites phyllosilicate rich mms ultracarbonaceous mms and cometary particles recovered from the 81p wild 2 comet the most outstanding feature of these cp mms is the presence of kosmochlor rich high ca pyroxene and roedderite which suggest that they have building blocks in common with cp idps and cometary dust particles and therefore suggest a possible cometary origin of both cp mms and cp idps it is therefore considered that cp mms are cp idps that have fallen to earth and have survived the terrestrial environment

variations in 87sr 86sr ratios of calcites in chinese loess a proxy for chemical weathering associated with the east asian summer monsoon abstract 87sr 86sr ratios of loess paleosol calcites of luochuan in china over the past 130 ka display a regular change with increasing trend of 87sr 86sr ratios in the following order loess calcite weakly pedogenetic paleosol calcite paleosol calcite pure secondary calcite the observed variations in the 87sr 86sr record of loess paleosol calcites correlate closely with the records of the magnetic susceptibility coarse grain fraction content in the same profile an et al chin sci bull 39 1994 182 184 and the specmap stacked 18o record of global ice volume imbrie et al in berger et al eds milankovitch and climate part i reidel boston 1984 pp 269 305 strata from the last glacial consist mostly of loesses and weakly developed paleosols and have lower 87sr 86sr ratios averaging 0 71079 paleosols which developed during the last interglacial have higher 87sr 86sr ratios averaging 0 71131 the four periods ca 125 110 98 90 80 75 and 9 5 ka b p of increased summer monsoonal rainfall coincide with the four peaks in 87sr 86sr values a series of 87sr 86sr high frequency high amplitude fluctuations is superimposed on the last glacial interglacial cycle over the past 130 ka occurring on millennium timescales with an average time span of about 3 ka during the last glacial the fluctuations of the 87sr 86sr ratios of the luochuan loess paleosol calcites lie in the range 0 71036 0 71176 for the past 130 ka the study shows that the sr isotopic system in loess paleosol calcites may therefore be an excellent proxy of chemical weathering on continents associated with the east asian summer monsoon

spatial and temporal variability in the stable isotope systematics of modern precipitation in china implications for paleoclimate reconstructions the stable isotopic composition of materials such as glacial ice tree rings lake sediments and speleothems from low to mid latitudes contains information about past changes in temperature t and precipitation amount p however the transfer functions which link 18op to changes in t or p d 18op dt and d 18op dp can exhibit significant temporal and spatial variability in these regions in areas affected by the southeast asian monsoon past variations in 18o and d of precipitation have been attributed to variations in monsoon intensity storm tracks and or variations in temperature proper interpretation of past 18op variations here requires an understanding of these complicated stable isotope systematics since temperature and precipitation are positively correlated in china and have opposite effects on 18op it is necessary to determine which of these effects is dominant for a specific region in order to perform even qualitative paleoclimate reconstructions here we evaluate the value of the transfer functions in modern precipitation to more accurately interpret the paleorecord the strength of these transfer functions in china is investigated using multiple regression analysis of data from 10 sites within the global network for isotopes in precipitation gnip 18op is modeled as a function of both temperature and precipitation the magnitude and signs of the transfer functions at any given site are closely related to the degree of summer monsoon influence 18op values at sites with intense summer monsoon precipitation are more dependent on the amount of precipitation than on temperature and therefore exhibit more negative values in the summer in contrast 18op values at sites that are unaffected by summer monsoon precipitation exhibit strong relationships between 18op and temperature the sites that are near the northern limit of the summer monsoon exhibit dependence on both temperature and amount of precipitation comparison with simple linear models 18op as a function of t or p and a geographic model 18op as a function of latitude and altitude shows that the multiple regression model is more successful at reproducing 18op values at sites that are strongly influenced by the summer monsoon the fact that the transfer function values are highly spatially variable and closely related to the degree of summer monsoon influence suggests that these values may also vary temporally since the southeast asian monsoon intensity is known to exhibit large variations on a number of timescales annual to glacial interglacial and the magnitude and sign of the transfer functions is related to monsoon intensity we suggest that as monsoon intensity changes the magnitude and possibly even the sign of the transfer functions may vary therefore quantitative paleoclimate reconstructions based on 18op variations may not be valid

metchosin igneous complex southern vancouver island ophiolite stratigraphy developed in an emergent island setting the metchosin igneous complex of southern vancouver island has three components gabbro stocks formerly sooke gabbro a newly recognized sheeted dike complex and a basaltic volcanic sequence formerly the metchosin volcanics the sheeted dikes occupy a position transitional between the gabbro stocks and submarine volcanics which they tie together in an ophiolitic pseudostratigraphy the submarine volcanics shoal upward and pass into subaerial sheet flows the complex formed in an area of regional extension as an emergent island