elemental compositions and monazite age patterns of core sediments in the changjiang delta implications for sediment provenance and development history of the changjiang river core from a continuous borehole in the changjiang delta to a depth of 318 7 m dated back to the pliocene 3 58 ma and was selected for geochemical measurements and determinations of th u pb ages of monazite in order to investigate the changing sediment provenance and development history of the changjiang river geochemical proxies including fractionation parameters of rare earth elements cerium and europium anomalies and elemental ratios cr th nb co and th co suggest that the pliocene and quaternary sediments have remarkably different provenances six peak ages of monazite grains dated at 25 50 200 200 400 400 550 800 1000 and 1800 2000 ma are consistent with the main tectonic and magmatic events in the yangtze craton the data imply that the pliocene sediments were mostly derived from proximal and more silicic sources whereas the quaternary sediments were sourced from distal and more basic provenances including the emeishan basalt province in the upper changjiang valley we propose that during the pliocene the paleo changjiang or its eastern equivalent was a locally small river draining today s lower changjiang valley whereas during the early pleistocene not later than 1 18 ma it changed its drainage pattern and developed into a large river that originated from the eastern tibetan plateau this time matches well with many previous studies based upon geomorphologic geographic and tectonic observations in the jinshajiang valley and the three gorges

dating loess up to 800 ka by thermoluminescence thermoluminescence tl ages agreeing with expected ages have been obtained for 13 loess samples spanning the age range from 20 to 800 ka our samples are from alaska and north island new zealand and are unusual in tl dating studies of loess older than 80 100 ka by having independent age assignments that are generally well constrained from ages of associated tephra beds with the polymineral fine silt sized 4 11 m grains the partial bleach tl technique yielded expected ages up to about 350 ka whereas the total bleach method gave accurate ages in the range 100 to 800 ka thus the much disputed upper age limit of 100 150 ka for the tl dating of loess now appears to be sample and worker dependent rather than a global property of the tl signals in the tl dominant feldspars

release of heavy metals during weathering of the lower cambrian black shales in western hunan china weathering of heavy metal enriched black shales may be one of the most important sources of environmental contamination in areas where black shales are distributed heavy metal release during weathering of the lower cambrian black shales lcbs in western hunan china was investigated using traditional geochemical methods and the icp ms analytical technique concentrations of 16 heavy metals 8 trace elements and p were measured for samples from selected weathering profiles at the taiping vanadium ore mine tp the matian phosphorous ore mine mt and taojiang stone coal mine tj the results show that the bedrock at these three profiles is enriched with sc v cr co ni cu zn pb th u mo cd sb tl and p based on mass balance calculation the percentages of heavy metals released in loss relative to immobile element nb were estimated the results show significant rates of release during weathering of v cr co ni cu zn u mo cd sn sb and tl for the tp profile sc cr mn co ni cu zn pb th cd and sn for the mt profile and sc mn co ni zn th cd sn and tl for the tj profile among these heavy metals co ni zn cd and sn show very similar features of release from each of the three weathering profiles the heavy metals released during weathering may affect the environment especially topsoil and surface waters and are possibly related to an observed high incidence of endemic diseases in the area

quaternary surface processes indicated by the magnetic fabric of undisturbed reworked and fine layered loess in hungary abstract statistical analytical methods were applied to classify the magnetic fabric of samples from different hungarian loess profiles a previous study of the anisotropy of magnetic susceptibility ams of hungarian loess suggested that typical wind blown or undisturbed and redeposited loess were well differentiated by known statistical methods the analyses of new samples require a review of previous results and the terms like typical wind blown reworked and redeposited loess the type of magnetic fabric of fine layered loess is classified by a new mathematical method in ams study of loess hierarchical cluster analysis the following quaternary surface processes were revealed by characteristics of the magnetic fabric of hungarian loess the primary magnetic fabric preserves the possible transport or accumulation direction of dust direction of maximum susceptibility ne sw axis and the structure of the fabric was affected by compaction in the case of loess the deviation of the inclination from vertical indicates the accumulation of dust on a sloping surface the secondary magnetic fabric fabric of the material after reworking or redeposition of loess shows the magnetic fabric characteristics of reworked or redeposited material scattered values of the principal susceptibilities indicate the effect of bioturbation redeposition fine layered loess samples is indicated by the alignment of the direction of maximum and intermediate susceptibilities on a stereographic plot and the degree of alignment possibly indicates the energy of the surface process lower or higher degree of energy connected to different kind of surface process can produce different kind of magnetic fabric the magnetic mineralogy of the pilot samples is determined by isothermal remanent magnetisation irm measurements no differences between loess samples with different sedimentary structure could be shown the dominant phase in the magnetic fabric that determined the magnetic character of samples was magnetite maghemite

paleoclimatic forcing of magnetic susceptibility variations in alaskan loess during the late quaternary visual matches and statistical tests suggest correlations between marine isotope curves retrodictive solar insolation at lat 65 n and magnetic susceptibility profiles through late quaternary age alaskan loess sections the susceptibility changes largely appear to reflect variability in magnetite content due to climatically controlled changes in wind intensity and competence magnetic susceptibility profiles through massive loess can provide stratigraphic context for intercalated paleosols and tephras a prominent paleosol correlated with marine isotope stage 5 occurs several metres above the old crow ash in loess sections indicating that this important tephra is older than suggested by thermoluminescence dates and may have been deposited ca 215 25 ka

separation of local signals from the regional paleomonsoon record of the chinese loess plateau a rock magnetic approach we propose a method based on thermal unblocking of low temperature saturation remanent magnetization for a quantitative estimation of the superparamagnetic cullity 1972 fraction size d 30 nm of magnetite produced by pedogenesis in the chinese loess plateau liu 1988 we applied this method to the proxy climatic records of the last 130 ka from two sites 250 km apart but separated by the mountain range liupan shan xifeng to the east 35 7 n 107 6 e and baicaoyuan to the west 36 2 n 105 0 e currently have humid and arid microclimates respectively as expected the superparamagnetic fraction increases during known warm temperature intervals at each site furthermore the more humid site clearly has higher overall superparamagnetic fractions during most of the last 130 ka however during the period 5 to 10 ka ago the relative humidity at both sites was the same within experimental errors bulk grain size evidence confirms the magnetic data and we suggest that the present easterly summer monsoon in china came from a more southerly direction during this time to flow parallel to liupan shan resulting in very similar summer humidity at xifeng and baicaoyuan

major and trace element geochemistry in zeekoevlei south africa a lacustrine record of present and past processes this study reports a multi parameter geochemcial investigation in water and sediments of a shallow hyper eutrophic urban freshwater coastal lake zeekoevlei in south africa zeekoevlei receives it

menai strait fault system an early caledonian terrane boundary in north wales a steep fault system runs parallel to the menai strait which separates anglesey from the mainland of north wales the menai strait fault system is interpreted as a major terrane boundary along which terrane docking took place during the late precambrian or earliest cambrian the evidence is based on 1 marked geologic dissimilarities exhibited by the pre late early cambrian basement to these terranes and 2 the existence of early major ductile shear zones within the fault system rocks as varied as blueschists low grade melange and shallow level granitic complexes were juxtaposed along these steep shear zones prior to the eruption of ash flow tuffs and deposition of upper lower cambrian marine sediments in the welsh basin since the amalgamation of the anglesey area with the avalonian terrane then a part of gondwana frequent phanerozoic reactivation of the resulting composite terrane boundary has been restricted to mostly dip slip fault movements

distribution and origin of lead in stream sediments from small agricultural catchments draining miocene molassic deposits sw france total pb concentrations and isotopic composition were determined in stream bed sediments and bedrock from 29 small agricultural or forested catchments in the gascogne area sw france the contribution of pb from various natural and anthropogenic sources was investigated in this rural area which is very weakly impacted by industrial or urban emissions environmental parameters in catchments importance of forest cover organic matter and oxide content in sediments were considered a combination of geochemical enrichment calculation sequential extraction and isotopic investigations was performed to constrain the origin of pb and the distribution of anthropogenic pb in sediments most of the sediments have low total pb content compared to other agricultural regions more impacted by industrial or urban emissions the results indicated a moderate but significant pb enrichment particularly for catchments draining forested areas this enrichment was positively related to organic c content in sediment and catchment forest cover whereas in entirely cultivated catchments it was related to fe oxide content an average anthropogenic end member was determined using pb isotopes and was supposed to be representative of background atmospheric pb pollution with a weak influence of pb from recent gasoline and local fertiliser spreading the amount of anthropogenic pb pbanthr in sediments estimated using a geochemical approach mean 63 7 20 4 was higher than that estimated using an isotopic approach mean 36 6 17 8 but the same trend was observed among the samples except for low anthropogenic contributions the distribution of pbanthr in sediments from weakly forested catchments indicated a strong affinity for carbonates and fe oxides amorphous fe oxides became preferential trapping compounds as soon as pb enrichment increased and carbonate content decreased finally in cultivated catchments organic c was not a main trapping component for pbanthr in sediments

a palaeomagnetic and mineral magnetic study of the loess sequence at liujiapo xian china employing an average vertical sampling interval of 20 cm oriented samples were collected from 26 m of the loess section at liujiapo near xian china in order to refine the existing magnetostratigraphic record palaeomagnetic results reveal two short reversed polarity subzones within a profile of predominantly normally magnetised sediments an interpretation that is at variance with previous results from this section and from other studies of chinese loess investigation of sediment mineral magnetic properties indicates a close correspondence between down section variations in intensity of magnetisation susceptibility and saturation isothermal journal of quaternary science remanence sirm and lithology the ratios irm 100mt sirm and sirm susceptibility appear to be particularly sensitive indicators of the degree of soil development and hence of palaeoclimate

rock magnetic proxies of climate change in the loess palaeosol sequences of the western loess plateau of china summary results of the first detailed study of the climate proxy record in the loess palaeosol sequence at xining one of the few palaeoclimate sites in the currently arid western loess plateau of china illustrate the importance of making many types of rockmagnetic measurements other than susceptibility a multiparameter approach yielded confirmation that here as elsewhere in the loess plateau the susceptibility enhancement in palaeosols was caused primarily by ultrafine magnetite and maghaemite nevertheless magnetic enhancement was caused not exclusively by changes in relative grain size but also by variations in concentration and mineralogy of the magnetic fraction the effects of concentration variations were removed through normalization of susceptibility and anhysteretic remanence with saturation magnetization and saturation remanence respectively the resulting signal was ascribed more confidently to variation in magnetic grain size which in turn was interpreted as a better proxy of pedogenesis than simple susceptibility variations in magnetic mineralogy were also determined to constrain interpretations further the data were then used to discuss climate history at xining finally results from xining were compared with other western sites and contrasted with eastern sites in summary 1 data is presented from a new loess plateau site which also appears to yield a global climate signal 2 a demonstration is made of a more rock magnetically robust way to separate concentration composition and grain size controls on susceptibility and other magnetic parameters and 3 models are provided for inter regional comparisons of palaeoclimate proxy records

magnetic mineral assemblages in soils and paleosols as the basis for paleoprecipitation proxies a review of magnetic methods and challenges abstract magnetic iron oxide minerals principally magnetite maghemite hematite and goethite are formed in well drained soils in response to a suite of physical chemical and biological factors despite a wide range of complexity in the pedogenic processes that lead to magnetic mineral formation dissolution and transformation there are well documented empirical relationships between various magnetic mineral assemblages in soils with environmental and climatic conditions recently there has been an increase in the number of quantitative magnetic paleoprecipitation proxies that have been developed and there is great potential for magnetic methods to be used in the geologic record to develop reconstructions of past climates magnetic paleoprecipitation proxies have been widely utilized in quaternary or younger loess paleosol systems however they have yet to be utilized in the pre quaternary fossil record future studies of magnetic mineralogy of soils and paleosols should aim to explore non loessic modern soils and pre quaternary paleosols with more focus on understanding the interaction between magnetic mineral assemblages and soil moisture applications of existing and novel magnetic paleoprecipitation proxies in the fossil record should prove to be a valuable resource for paleoclimatologists

spatial variations in paleowind direction during the last glacial period in north china reconstructed from variations in the anisotropy of magnetic susceptibility of loess deposits abstract anisotropy of magnetic susceptibility ams of chinese loess is considered to be an effective tool for determining paleowind direction however the relationship between ams and the paleowind direction is still a matter of debate this study reports the results of ams measurements of chinese loess deposited during the last glacial period on slopes of varying slope angles and orientations the sites are located on the chinese loess plateau in west qinling and on the eastern margin of qilian mountain the results show that within the same region magnetic lineations are clustered along similar orientations despite differences in slope exposure and slope angle but that different regions exhibit different directions of magnetic lineation these results suggest that the alignment of the magnetic grains during deposition of the eolian deposits was determined by air circulation rather than by water flow on the surface of the slopes and therefore that the ams of chinese loess can be used to determine paleowind directions in addition our results indicate that the ams of chinese loess is determined mainly by the patterns of regional surface wind flow that occurred during dust accumulation rather than by the uniform pattern of large scale atmospheric circulation in addition since wind direction is influenced significantly by regional topography the ams of chinese loess may have the potential to detect significant changes in past regional topography

the chinese loess in xifeng ii a study of anisotropy of magnetic susceptibility of loess from xifeng summary measurements of specimens from the loess profile of xifeng gansu province china all show original magnetic fabric for sediments i e nearly horizontal foliation and the commonly oblate magnitude ellipsoid the degree of anisotropy always shows a strong correlation with the foliation f rather than with the lineation l specimens from wind blown loess redeposited water lain loess and red clay show their own distribution areas respectively in a diagram of l versus f magnetic fabric provides evidence for the suggestion that the red clay like the overlying wind blown loess is aeolian in origin the data points from the red clay all falling within the distribution area of the wind blown loess data points the magnetic fabric measured from present day palaeosols may still represent the features of the parent loess although the orientation of fabric has been slightly weakened through pedogenesis as shown in the present study

characterization of the magnetic fabric of rocks abstract an inextensive system of magnetic susceptibility anisotropy factors is suggested which is sufficient in the majority of practical applications for characterizing the magnetic fabric of rocks the system involves three newly devised factors the corrected anisotropy degree the shape factor and the difference shape factor the first of these characterizes the quantity of anisotropy somewhat better than the commonly used anisotropy degree the shape factor characterizes the quality of anisotropy i e the shape of the susceptibility ellipsoid in a convenient way its definition is based on a certain analogy between the anisotropy ellipsoid and the strain ellipsoid the difference shape factor can replace the shape factor when only the differences between the principal susceptibilities are given while the mean susceptibility is unknown

bed sediment associated trace metals in an urban stream oahu hawaii of the 117 stream and lake systems sampled nationwide fish from manoa stream on oahu hawaii have consistently shown the highest pb concentrations therefore a detailed study was conducted to examine total metal contents in bed sediments from a 5 8 km stretch of manoa stream a total of 123 samples 63 m were examined for 18 elements and 14 samples for 21 elements selected samples were also examined using different leach solutions to examine metal phase associations all trace metal data computations of enrichment ratios and the modified index of geoaccumulation point to mineralogical control for cr and ni minor anthropogenic contamination for ba cd cu hg and zn and a very strong contamination signal for pb maximum pb contents up to 1080 mg kg 1 were associated with anthropogenic material dumping in minor tributaries storm sewer sediments and sediments in the lower section of the basin proportionally pb had the highest non residual component of elements examined dominantly in the reducible phase associated with mn and amorphous fe oxyhydroxides the contamination signal was typically lowest in the undisturbed headwater reach of the basin above 5 1 km with significant increases throughout the residential and commercial institutional zones of the mid basin the spatial pattern of bed sediment contamination and evidence from storm sewer outlet sediments strongly indicates that pb and to a lesser degree some other metals is still being transported to the stream and the primary agent is soil erosion and transport of metals sorbed to sediments the primary source of sediment associated metals is considered to be the automobile though other minor sources can not be ruled out

loess and palaeoenvironment some results of a european joint programme of research in 1985 a programme of research on the sedimentology and diagenesis of the loess and loessic silts of western europe was initiated jointly by laboratories in leicester meudon caen milan cardiff and southampton involving a limited amount of comparative work on the loess from types sites in the loess plateau of central china preliminary results include the following 1 experimental procedures in particle size analysis clay sample preparation and microscopy have been standardised in all cooperating groups distinctive fabrics indicative of depositional mechanisms have been recognised 2 comparison of aeolian colluvial and alluvial silt by laser scanning and bulk magnetic susceptibility anisotropy methods appears to differentiate aeolian silt from loessic silts re deposited by slope processes and flowing water 3 the variability in the anisotropy of the limon a doublet facies has been assessed by image analysis of scanning electron microscopy sem and optical microscopy strong anisotropy has also been measured in thin section imagery of loess from normandy and poland as the product of freezing and thawing this is confirmed by scanning electron microscopy and by experimental freezing of some silts 4 the clay fabric and mineralogy in western european loess differ from those in chinese loess especially in the case of semi arid deposits 5 distribution of caco3 using thin sections and sem analysis has been determined for loess from normandy and the rh ne valley in france and for some chinese loess at saint vallier zones of caco3 concentration occur masking much of the original loess sedimentary skeleton which is a locally reworked loessic silt with some laminations despite considerable scatter the palaeomagnetic results indicate a reversed polarity throughout placing the whole saint vallier sequence in the matuyama chron these preliminary results suggest the existence of two different palaeoenvironments one typified by central china with arid glacials and humid interglacials and the other represented by western europe with generally high humidities there was stronger weathering and soil development and fewer freezing effects on the lossic succession in northern italy than in western littoral europe

tracing the transport of anthropogenic lead in the atmosphere and in soils using isotopic ratios the isotopic composition of lead in aerosols and soils in israel is used to characterize the sources of anthropogenic lead in the region to ascertain the isotopic composition of natural rock derived lead in specific areas and to determine rates of anthropogenic lead migration in soils the isotopic composition of lead currently emitted from cars in israel 206pb207pb 1 115 2 is controlled by alkyl lead produced in france and germany in addition to petrol lead two more sources of anthropogenic lead can be detected in sampled aerosols the first one has low concentrations of lead 4 ng m3 and 206pb207pb 1 157 and is most likely lead emitted in turkey that traveled across the eastern mediterranean basin the second type of aerosols contains a mixture of lead emitted in several countries including turkey greece and ukraine 206pb207pb value of 1 155 1 160 pb 20 30 ng m3 anthropogenic lead is more accessible for acid leaching than natural lead therefore it is more labile in the soil the isotopic composition of lead in the acid leached fraction of near road soil profiles record the histor of alkyl lead emission in the country based on changes in the isotopic composition of lead with soil depth it is estimated that anthropogenic lead migrates into the soil at approximately 0 5 cm y a soil profile from a relatively remote area is less contaminated by anthropogenic lead and displays a different distribution of lead isotopic values with depth the isotopic composition of lead suggests that natural lead in soils developed on carbonate bedrock is derived from clays either from the rock esidue the clay fraction in the carbonate bedrock or from airborne clay but not from lead released from the carbonate fraction in the rock

a comparison of geochemical information obtained from two fluvial bed sediment fractions a total of 121 bed sediment samples were collected from a 5 8 km stretch of manoa stream hawaii samples were physically partitioned into two grain size fractions 63 m and 63 125 m acid digested and analyzed by icp aes and faas non parametric matched pair statistical testing and correlation analysis were used to assess differences and strengths of association between the two fractions for al ba cu fe mn ni pb ti and zn results indicated statistically significant differences between fractions for all elements except mn concentrations were significantly greater in the 63 m fraction for al cu pb ti and zn while ba fe and ni were higher in the 63 125 m fraction though some elements had statistically significant differences between fractions al ba fe and zn percentage differences were in the range of analytical precision of the instrument and thus differences were not practically significant correlation analysis indicated strong positive associations for all elements between the two fractions p 0 0001 three contamination indices indicated similar degrees of pollution for each size fraction for four elements having an anthropogenic signal ba cu pb and zn the environmental information obtained from the 63 125 m fraction was essentially equivalent to that from the 63 m fraction in this system it is clear that both bed sediment fractions indicate anthropogenic enrichment of trace metals especially pb and further supports previous research that has found that aquatic sediments are critical median for tracing sources of pollution

geochemical variations in peoria loess of western iowa indicate paleowinds of midcontinental north america during last glaciation peoria loess deposited in western iowa during the last glacial maximum lgm shows distinct geochemical and particle size variations as a function of both depth and distance east of the missouri river geochemical and particle size data indicate that peoria loess in western iowa probably had two sources the missouri river valley and a source that lay to the west of the missouri river both sources indicate that lgm paleowinds in western iowa had a strong westerly component similar to interpretations of previous workers a compilation of loess studies in iowa and elsewhere indicates that westerly winds were dominant during loess transport over much of the midcontinent south of the laurentide ice sheet which is not in agreement with paleowinds simulated by atmospheric general circulation models agcms agcms consistently generate a glacial anticyclone with easterly or northeasterly winds over the laurentide ice sheet and the area to the south of it loess deposition in the midcontinent during the lgm may be a function of infrequent northwesterly winds that were unrelated to the presence of the glacial anticyclone

geomagnetic excursions recorded in chinese loess in the last 70 000 years detailed paleomagnetic investigations conducted on the malan loess l1 at a well dated section weinan in the chinese loess plateau revealed two distinct anomalous directional intervals adi accompanied by lower relative paleointensity rock magnetic properties and anisotropy of magnetic susceptibility ams of samples taken from sedimentary horizons carrying the anomalous directions are similar to those taken from outside the anomalous directional intervals thus the anomalous directions are interpreted as geomagnetic excursions based on 14c and tl data the excursions occurred at 27 1 26 0 and 46 8 37 4 kyr b p the ages are consistent with the ages assigned to the mono lake excursion mle and laschamp excursion le respectively the result indicates that the mle and le were independent geomagnetic excursions the morphology of le at this section suggests that the le might be an aborted geomagnetic reversal

paleowind directions from the magnetic fabric of loess profiles in central alaska abstract two parallel profiles of alternating loess and paleosol horizons from the halfway house site west of fairbanks in central alaska were evaluated in terms of their potential for preserving paleowind directions combined the profiles span specmap marine oxygen isotope stages 1 6 approximately the last 150 ka our analytical tools consisted of measuring the sample s anisotropy of magnetic susceptibility and characterizing the magnetic mineralogy by multiple approaches both primary eolian and secondary reworked magnetic fabrics are recognized along certain intervals of both profiles primary eolian fabrics display a horizontal magnetic foliation and a well defined magnetic lineation corresponding to the paleodirection of sediment transport and deposition a systematic change in transport direction is observed where long term prevailing winds appear to shift from a nw se to n s direction during glacial and interglacial periods respectively

influence of paleo trade winds on facies patterns of the cambrian shanganning carbonate platform north china abstract the shanganning carbonate platform scp of the north china craton ncc was located in the trade winds belt during the cambrian which influenced its facies development in recent years numerous drillcores have been recovered from these units but the depositional environments and facies architecture of this large 2 0 105 km2 carbonate platform system have not yet been reported in detail in this study we integrate sedimentological and magnetic fabric data collected from outcrops and drillcores in order to document variation in microfacies and facies associations within the scp to infer paleowind directions and constrain the paleogeographic location of the scp and to evaluate eolian controls on platform development this analysis documented numerous carbonate microfacies belonging to six fabric types mudstone wackestone packstone grainstone framestone and dolostone along with rarer siliciclastic sediments these microfacies belong to facies associations representing tidal flat open platform platform margin slope and deep basinal depositional environments anisotropy of magnetic susceptibility ams measurements yielded mean paleocurrent directions for the early middle and late cambrian of 114 63 and 83 30 from paleo north respectively that were relatively consistent for 12 out of 13 platform margin sites all vectors being corrected for a post cambrian 150 clockwise rotation of the ncc these wind orientations are consistent with the scp shifting from south of the paleo equator in the early cambrian to north of it by the middle cambrian paleo trade winds influenced facies patterns across the platform producing a distinct windward leeward zonation the windward margin is characterized by well sorted oolitic grainstone as well as favositids coral and dasycladacean algal sponge framestone and the leeward margin by poorly sorted oolitic wackestone grainstone and fine bioclastic sediments the present study is innovative in 1 integrating microfacies and ams analyses in order to establish paleowind patterns and influences on an ancient carbonate platform 2 documenting windward leeward variation in quantifiable sediment properties across the scp and 3 constraining the paleo hemispheric location of the ncc during the cambrian

major and trace elements of stream sediments from the lowermost amazon river geochemical results from river bottom sediments taken from the lowermost amazon river are presented bedload sediments were analyzed for 10 major and 38 minor elements mud bulk sediments exhibit a tendency to a slight enrichment in cr mn rb sr zr cs ba and hf pointing to the importance of these elements in the silt fraction generally cu zn rb cs ba and sn are clearly associated with clay minerals while y zr hf th and u are associated with heavy minerals the location of this area in an intensive chemical weathering environment results in the strong modification of sediment composition chemical weathering processes strongly modify original sediment composition and can be recognized apart from provenance processes on the basis of their geochemical signature discriminant analysis makes the detection of less marked differences in sediment characteristics possible thus improving the accuracy of distinctions between groups the amazon mouth and xingu mouth xm are discriminated principally by the textural maturity of their sediments the jari mouth jm shows highest co and fe2o3 contents despite similarities between the amazon north branch anb and amazon south branch asb the anb can be differentiated on the basis of its higher sr p2o5 and na2o contents the asb on the basis of its higher zn mno and cao contents and the estreitos de breves est based on its higher abundance of ni and cu higher contents in p2o5 fe and mn are related to laterite covers

transport direction of wisconsinan loess in southeastern minnesota a study of wisconsinan loess in part of southeastern minnesota confirms earlier suggestions that much of the loess in this region was not derived flora the floodplain of the mississippi river two wisconsinan loess units the peoria loess and roxana silt occur in the study area peoria loess 1 8 m thick fines systematically eastward from an abrupt western border toward the mississippi there are no apparent grain size trends away from other adjacent rivers peoria loess thickness generally decreases eastward but is highly variable probably because of differential erosion potential sources for this unit are pre wisconsinan sediments on the iowan erosion surface immediately west of the border of thick loess and wisconsinan glacial sources tens or hundreds of kilometers to the west the underlying roxana silt up to 1 m thick occurs only near the mississippi and fines away from that river the roxana silt deposit could reflect aggradation of the mississippi floodplain because of glacial activity upstream and does not have clear implications for upland vegetation near the study area by contrast transport of the peoria loess from distant glacial sources or wind erosion of upland surfaces closer to the loess deposit both imply extensive very sparsely vegetated surfaces west of the study area when the peoria loess accumulated

tephrochronology of late cenozoic loess at fairbanks central alaska nineteen distinctive distal tephra beds from the gold hill loess in the fairbanks region central alaska are divided into two groups based on their color mineralogy glass shard morphology and the major and trace element composition of their glass shards this dichotomy in tephra composition is believed to reflect the two source regions namely the eastern aleutian arc alaska peninsula region and the wrangell volcanic field despite the fragmentary nature of the preserved loess record which contains many local unconformities these tephra beds can be used to link the numerous loess exposures in the fairbanks region in their proper time sequence establishing thereby a comprehensive reliable time stratigraphic framework because these distal tephra beds are related to large magnitude volcanic eruptions given the long distance to the nearest possible source vent they will also enable correlation of the late cenozoic sedimentary sequence at fairbanks to those of adjacent regions of alaska and the yukon tephra beds with bubble wall or chunky glass shards have been dated by the isothermal plateau fission track method results demonstrate that the gold hill loess spans a long interval of time from late pliocene time to the last interglacial about 125 ka however the age of the basal part of this formation is not well constrained due to the apparent absence of tephra beds paleomagnetic studies suggest that loess deposition in the fairbanks region began about 3 ma

re arrangement of atmospheric circulation at about 2 6 ma over northern china evidence from grain size records of loess palaeosol and red clay sequences abstract recent studies have shown that the red clay sequence underlying the quaternary loess of the chinese loess plateau is wind blown in origin continuous atmospheric dust deposition in the past 7 0 ma has been documented to address the wind system that transported the tertiary red clay two north south transects were studied in the chinese loess plateau one of the transects was designed to study spatial changes in grain size of the last glacial interglacial loess records and the other to observe particle changes of the tertiary red clay underlying the quaternary loess the loess transect consists of nine sections and the red clay transect of four sections analyses of closely spaced samples show that there is a strong southward decrease in grain size of both loess and palaeosol horizons of the late pleistocene which is consistent with the idea that the aeolian materials of the quaternary in the loess plateau are transported by the northerly winter monsoonal winds grain size distribution of the red clay sequences however does not show such a change from north to south along the red clay transect the particle size distribution is almost identical in the four sections suggesting that the winter monsoonal winds might have played a less important role in transporting the red clay material it is suggested that the red clay may have been transported by the westerlies from the dust source regions of northwestern china onto the loess plateau a remarkable re arrangement of atmospheric patterns at about 2 6 ma therefore has been recorded by the red clay loess shift it is speculated that this re arrangement of atmospheric patterns may have been caused by the onset of glaciation in the northern hemisphere

magnetic anisotropy of some phyllosilicates magnetic susceptibility anisotropy of susceptibility and hysteresis of single microcrystals of chlorite biotite phlogopite muscovite zinnwaldite and fuchsite were measured in low and high magnetic fields with an alternating gradient force magnetometer micromag their properties are sufficient to account for the low field susceptibility ams of most micaceous rocks nearly all samples show some ferromagnetic contribution at low fields due to inclusions of pseudosingle domain and multidomain magnetite the paramagnetic contribution isolated at high fields usually exceeds the ferromagnetic contribution the paramagnetic susceptibility is intrinsic to the silicate lattice and agrees with values predicted from chemical composition within the limits of error the minimum susceptibility is nearly parallel to c another axis is parallel to b and the third susceptibility usually the maximum is close to a the paramagnetic susceptibility has a disk shaped magnitude ellipsoid with strong anisotropy p 2 the ferromagnetic contributions at low fields have more variably shaped ellipsoids with greater eccentricity p 5 the silicate lattice does not constrain their orientation our technique cannot determine the principal axes of the ferromagnetic component however its principal values usually correspond with the paramagnetic principal susceptibilities in order of magnitude thus the combined paramagnetic ferromagnetic anisotropy recognised in routine studies of ams should faithfully represent the petrofabric of most micaceous rocks nevertheless nearly 10 of our samples have incompatible anisotropy ellipsoids for the silicate host and magnetite inclusions these yield a net inverse ams that does not correctly represent the orientation of the silicate lattice therefore some caution is necessary in petrofabric ams studies of micaceous rocks

the stratigraphy and setting of the precambrian rocks of the llangynog inlier dyfed south wales detailed mapping of the precambrian rocks of the llangynog inlier made possible by a series of new exposures has allowed the establishment for the first time of the 1100 m thick succession within the precambrian rocks of the area all boundaries of the precambrian rocks with younger strata in the area are either faults or unconformities some 350 400 m of rhyolitic lavas form the oldest rocks seen in the area they are extensively silicified and devitrified and show little of their original texture although flow banding is visible in some outcrops and the presence of perlitic and snowflake textures imply that originally they were glassy in part these lavas are succeeded by a varied succession dominated by volcaniclastic siltstones showing evidence of shallow water deposition and containing medusoids and trace fossils of ediacaran age interbedded in the sediments are basaltic lavas autobreccias and rare hyaloclastites displaying textural features characteristic of submarine eruption and rhyolitic pumiceous and shardic ash flow tuffs the name coomb volcanic formation is proposed for this succession within which are recognized two members a lower castell cogan rhyolite member succeeded by the coed cochion volcaniclastic member in association are varied intrusions comprising both dolerites and dacites a palaeoenvironmental model built on evidence of petrography palaeontology and sedimentology is that of shallow water to emergent volcanic islands

lead pb isotopes as a tracer of pb origin in yangtze river intertidal zone abstract in order to investigate the source of pb within the yangtze river intertidal zone studying pb isotope ratios is a likely approach because the ratios of these pb isotopes can be used to identify the natural or anthropogenic origin of pb in this study a total of 59 surface sediment samples 204 pb 206 pb 207 pb and 208 pb and found that the total pb concentrations varied from 18 3 to 44 1 mg kg 1 with an average concentration of 27 3 mg kg 1 the observed pb isotope ratios excluding one station near shanghai pudong airport which is significantly influenced by anthropogenic sources varied from 18 459 to 18 750 for 206 pb 204 pb 15 628 to 15 728 for 207 pb 204 pb and 38 715 to 39 213 for 208 pb 204 pb this study shows that pb found within the yangtze river intertidal zone sediments was mainly from the catchment in the yangtze river watershed significant pb pollution was not discerned in the yangtze river intertidal zone however pb contamination in some localized areas was suggested by pb enrichment factor ef

lead isotopes as tracers of pollutants in soils in order to gain insight into pb pollution of soils a pb isotope study was performed on soil profiles from selected sites in switzerland samples were analysed from the swiss national park where high pb contents have been observed despite the absence of obvious pollution sources other samples were taken in populated areas n of zurich where soil pollution was expected major goals of this study were 1 to distinguish anthropogenic from natural pollution by pb isotopic means 2 to determine the magnitude of pollution penetration 3 to assess the extent of pollution and 4 to identify the anthropogenic sources of pollution for major pollutants the pb isotopic compositions have been determined on samples collected between 1993 and 1995 fly ash from waste incinerators showed a constant isotopic composition 206pb 204pb 17 92 17 96 independent of the plant and sampling year in contrast samples representative for petrol pb displayed a larger spread 17 13 17 52 but generally had the least radiogenic composition among the pollutants sewage sludge showed an intermediate composition 17 74 17 88 aerosols as omnipresent pollutants had compositions 17 49 17 77 between car exhausts and fly ash from waste incineration reflecting their mixed nature for air fall deposition a mean pb isotopic composition 206pb 204pb 17 99 has been calculated for the 20th century taking into account the time dependent evolution of aerosols due to the pb isotopic contrast between unpolluted soil 206pb 204pb 18 8 and the anthropogenic contaminants pollution could be detected in all but one soil profile penetration of pollution reached to depths of between 20 and 30 cm calculated anthropogenic net pb inputs amounted to approximately 2 2 g m 2 in weakly polluted soils national park and reached values of 15 7 17 5 g m 2 in soils closely exposed to pollutants in soils with low anthropogenic pb inputs pollution could be explained by air fall deposition in stronger polluted soil profiles the pb isotopic composition of the pollutant did not allow us to clearly identify the pollution sources because of anthropogenic inputs from several sources

directional petrological characterisation of deep marine sandstones using grain fabric and permeability anisotropy methodologies theory application and suggestions for integration abstract different methods for quantifying preferred grain orientation or grain shape fabric in sandstones are reviewed and their value for the reconstruction of palaeocurrent direction and preferred direction of pore fluid flow is reassessed critically based on existing knowledge from literature and new grain fabric data it is shown that petrographic analysis has distinct merits because grain fabric can be determined with low equipment costs and population statistics are based on the orientation of individual grains several recommendations are given how to standardise procedures for acquisition of grain fabric through microscopy these recommendations include 1 the careful selection of cross section orientations to acquire apparent long grain axes that are representative of true long grain axes 2 the preferred measurement of the coarsest grains in cross section and 3 a new statistically founded method to select a subset of grains that is representative of the total population of grains in a sandstone sample magnetic techniques that use anisotropy of magnetic susceptibility ams as a proxy for grain orientation require specialised equipment and are more restricted in statistical evaluation but these methods benefit greatly from being able to measure a large number of grains in a three dimensional space in a short amount of time and with a lower sensitivity to user bias of the two magnetic techniques discussed in this paper the new enhanced ams method in which rock magnetic properties are enhanced by introducing magnetite into the pores and as precipitates on grain surfaces is regarded to be an improvement over the traditional natural ams method in which only the natural assemblage of magnetite particles present in the rock is analysed enhanced ams measures the preferred orientation of essentially all grains in a rock sample thus providing the shape fabric of a hydrodynamically more accurate representation of framework grains than natural ams through a small technical modification the enhanced ams method can be used to obtain a magnetic cast of the pore network of a rock sample so that the resulting ams is controlled by the shape anisotropy of the individual pores it is commonly assumed that long axes of sand grains in sedimentary deposits parallel the direction of the flows that formed the deposits this concept is challenged by a new systematic study of grain fabric in deep marine turbidites it indeed appears that grains in ripple cross laminated divisions of turbidites dominantly attain a preferred orientation parallel to the palaeoflow direction but grains in plane parallel laminated divisions have an additional flow perpendicular mode which suggests a contribution of rolling grain transport three different fabric modes occur in massive structureless sandstones and massive divisions in turbidites apart from flow aligned and flow perpendicular modes there is a statistically significant but hydrodynamically enigmatic flow oblique mode with an average azimuthal deviation of 40 this large variation of fabric types suggests that a similar variation exists in preferred paths of pore fluid flow within turbidites controlled to at least some degree by depositional process this is confirmed by independent laboratory measurements of permeability anisotropy on samples for which grain fabric data are available and thus defines grain fabric analysis as a viable alternative to traditional permeametry techniques

rock magnetism of remagnetized paleozoic carbonates low temperature behavior and susceptibility characteristics we have conducted a new set of rock magnetic experiments on samples of remagnetized paleozoic carbonates of eastern north america these experiments were designed to investigate the origin of the unusual hysteresis behavior of these rocks by evaluating 1 the importance of ferrimagnetic pyrrhotite as a remanence carrier and 2 the sources of low field susceptibility low temperature measurements of saturation isothermal remanent magnetization sirm indicate that the pyrrhotite magnetic transition at 32 k is absent in the trenton and onondaga limestones of new york this transition is observed but poorly expressed in the knox group of east tennessee room temperature sirms cooled to 10 k in zero field lose a small fraction of their intensity between 30 and 35 k samples from all three formations show a broad peak in irm intensity at about 200 k which is typical of pyrrhotite in the trenton and onondaga samples the ferrimagnetic component of low field susceptibility is significantly larger than the ratio mrs hcr and is thus probably due dominantly to magnetite in some of the knox samples the reverse is true suggesting an important pyrrhotite contribution for all of the samples the ferrimagnetic susceptibility normalized by the saturation magnetization is anomalously high about a factor of 5 or 10 higher than the typical value for magnetite we believe that this indicates a very substantial contribution from superparamagnetic particles strong frequency dependence of susceptibility and very high ratios of anhysteretic to saturation remanence confirm the importance of ultrafine particles spanning the superparamagnetic single domain boundary all three of these chemically remagnetized carbonates units exhibit the following properties which have not previously been found together for any rock or synthetic analog and which therefore appear to constitute a diagnostic set of rockmagnetic criteria for recognizing chemically remagnetized rocks mrs ms 0 89 hcr hc 0 6 k ms 50 m a arm sirm 20 ka mrs hcr 50

magnetic properties and magnetic fabrics of pleistocene loess palaeosol deposits along west central siberian transect and their palaeoclimatic implications

palaeowind directions and sources of detrital material archived in the roxolany loess section southern ukraine abstract measurements of the anisotropy of whole rock magnetic susceptibility ams and u pb ages of detrital zircons have been combined to define the palaeowind directions and sources of wind blown dust in the loess palaeosol key section at roxolany southern ukraine zircon dating has also been used to determine the age and provenance of the interbedded roxolany tephra the distribution of ams axes in the loess indicates that the prevailing wind during its accumulation blew from the north west the same as the mean present day summer wind direction measured in the nerby city of odessa the u pb isotopic ages of the detrital zircons mostly range between 0 25 and 2 ga with clusters at 0 28 0 32 0 45 0 58 1 0 and 1 5 ga single neoarchean grains ca 2 7 ga were also found these ages indicate that material from carpathian and podolian sources formed the roxolany loess this material initially was transported by the dniester river then was wind blown form the dniester liman and the lower dniester valley located nw of roxolany most of the pyroclastic zircons from the roxolany tephra gave ages of 470 840 ka with a peak between 500 and 750 ka this age range is consistent with their being derived from the ciomadul volcano in romania

petrological and geochemical variations within the tal y fan intrusion a study of element mobility during low grade metamorphism with implications for petrotectonic modelling

magnetic fabrics in the basal ice of a surge type glacier 1 anisotropy of magnetic susceptibility ams has been shown to provide specific useful information regarding the kinematics of deformation within subglacially deformed sediments here we present results from debris rich basal glacier ice to examine deformation associated with glacier motion basal ice samples were collected from tunabreen a polythermal surge type glacier in svalbard the magnetic fabrics recorded show strong correlation with structures within the ice such as sheath folds and macroscopic stretching lineations thermomagnetic low temperature susceptibility varying field susceptibility and isothermal remanent magnetism acquisition experiments reveal that the debris rich basal ice samples have a susceptibility and anisotropy dominated by paramagnetic phases within the detrital sediment sediment grains entrained within the basal ice are inferred to have rotated into a preferential alignment during deformation associated with flow of the glacier an up glacier directed plunge of magnetic lineations and subtle deviation from bulk glacier flow at the margins highlight the importance of noncoaxial strain during surge propagation the results suggest that ams can be used as an ice petrofabric indicator for investigations of glacier deformation and interactions with the bed

cryptic post depositional reworking in aeolian sediments revealed by the anisotropy of magnetic susceptibility abstract our anisotropy of magnetic susceptibility ams investigation of the gold hill steps ghs2 and halfway house hh3 loess and paleosol profiles in central alaska confirms that post depositional reworking of loess at gold hill steps has taken place and of greater importance identifies the reworked depth intervals in ghs2 the majority of the loess below 7 80 m depth has been reworked the loess at the halfway house site is as stated in the literature a predominantly undisturbed aeolian deposit however we have identified two intervals that have been reworked in hh3 we infer from the depth variation of the ams orientation distribution at ghs2 that the presence of permafrost in the past was the dominant active mechanism producing the observed deformations permafrost loess behaved 1 as impermeable layers focusing and channeling flow most likely that of groundwater and 2 as rigid bodies undergoing rotations and lateral translations a modern analogue of focused flow by an impermeable layer is identified at hh3

lead isotopic systematics of major river sediments a new estimate of the pb isotopic composition of the upper continental crust abstract the lead isotopic composition of river sediments is reported in the present work for the earth s major river basins from old cratonic to young orogenic areas and from subarctic to tropical climates sediment samples from these large river basins provide a useful tool to calculate the average upper crustal composition because they are large scale integrated samples of the weathering products of the present day upper continental crust ucc two different and complementary calculations were done to estimate the average lead isotopic composition of the ucc the first based on the flux weighted average of particulate lead delivered by the rivers gave values of 19 07 15 74 and 39 35 for 206 pb 204 pb 207 pb 204 pb and 208 pb 204 pb ratios respectively to avoid over estimating the contribution of orogenic areas which produces a bias because the flux of particulate lead depends strongly on the physical erosion rate a second calculation was done by averaging with drainage areas of each river basin this gave values of 18 93 15 71 and 39 03 for 206 pb 204 pb 207 pb 204 pb and 208 pb 204 pb ratios respectively these direct calculations of the lead isotopic composition of the ucc are similar and are in agreement with previous estimates made using an indirect approach

a 3 m y record of pliocene pleistocene loess in interior alaska many distal tephra beds exist in the thick fossiliferous loess deposits near fairbanks interior alaska isothermal plateau fission track ages determined on glass shards from tephra beds in conjunction with tephrostratigraphic and magnetostratigraphic techniques indicate that loess deposition began in the late pliocene an antiquity previously unsuspected hence there is the opportunity now to reconstruct a detailed well dated record of environmental changes in interior alaska during the past 3 m y

paleoenvironmental significance of the magnetic fabrics in chinese loess paleosols since the last interglacial 130 ka abstract we compare new anisotropy of magnetic susceptibility ams data with previously determined paleoclimatically sensitive parameters for a loess profile at lingtai central loess plateau china to unravel factors that control loess ams magnetic lineations are clustered along ne sw and nw se orientations during cold and warm periods respectively which probably corresponded to paleowind directions of both winter and summer monsoons anomalously steep magnetic foliations coincidentally occur at the paleoclimatic stage boundaries indicating sediment disturbance lineation strength appears to be sensitive to millennial scale rapid paleoclimatic fluctuations generally the winter monsoon produces a lower degree of lineation than the summer monsoon furthermore by studying lineation subsets for the cold and warm periods we find that the cold interval lineation strengths co vary with grain size over the last 70 ka during the last interglacial about 74 128 ka the lineation and declination of the susceptibility maximum dec k max are sensitive to rapid fluctuations in winter and summer monsoons long term trends of magnetic foliation and anisotropy degree replicate grain size variations with superimposed short term peaks related to post depositional compaction as suggested by density the ams shape parameter t indicates oblate fabrics these new findings will not only improve our understandings of loess ams but also expand the possibilities of paleoclimatic studies in the chinese loess

geochemistry of trace metals and pb isotopes of sediments from the lowermost xiangjiang river hunan province p r china implications on sources of trace metals this paper reports a geochemical study of trace metals and pb isotopes of sediments from the lowermost xiangjiang river hunan province p r china trace metals ba bi sc v cr mn co ni cu zn mo cd sn sb pb tl th u zr hf nb and ta were analyzed using icp ms and pb isotopes of the bulk sediments were measured by mc icp ms the results show that trace metals cd bi sn sc cr mn co ni cu zn sb pb and tl are enriched in the sediments among these metals cd bi and sn are extremely highly enriched ef values 40 metals zn sn sb and pb significantly highly 5 ef 20 and metals sc cr mn co ni cu and tl moderately highly 2 ef 5 enriched in the river sediments all these metals however are moderately enriched in the lake sediments geochemical results of trace metals th sc co cr zr hf and la and pb isotopes suggest that metals in the river sediments are of multi sources including both natural and anthropogenic sources metals of the natural sources might be contributed mostly from weathering of the indosinian granites gr and palaeozoic sandstones pl and metals of anthropogenic sources were contributed from pb zn ore deposits distributed in upper river areas metals in the lake sediments consist of the anthropogenic proportions which were contributed from automobile exhausts and coal dusts thus heavy metal contamination for the river sediments is attributed to the exploitation and utilization e g mining smelting and refining of pb zn ore mineral resources in the upper river areas and this for the lake sediments was caused by automobile exhausts and coal combustion metals bi cd pb sn and sb have anthropogenic proportion of higher than 90 with natural contribution less than 10 metals mn and zn consist of anthropogenic proportion of 60 85 with natural proportion higher than 15 metals sc cr co cu tl th u and ta have anthropogenic proportion of 30 70 with natural contribution higher than 30 metals ba v and mo might be contributed mostly from natural process

continuous record of microparticle concentration and size distribution in the central greenland ngrip ice core during the last glacial period 1 a novel laser microparticle detector used in conjunction with continuous sample melting has provided a more than 1500 m long record of particle concentration and size distribution of the ngrip ice core covering continuously the period approximately from 9 5 100 kyr before present measurements were at 1 65 m depth resolution corresponding to approximately 35 200 yr particle concentration increased by a factor of 100 in the last glacial maximum lgm compared to the preboreal and sharp variations of concentration occurred synchronously with rapid changes in the 18o temperature proxy the lognormal mode of the volume distribution shows clear systematic variations with smaller modes during warmer climates and coarser modes during colder periods we find 1 7 m diameter during lgm and 1 3 m during the preboreal on timescales below several 100 years and the particle concentration exhibit a certain degree of independence present especially during warm periods when generally is more variable using highly simplifying considerations for atmospheric transport and deposition of particles we infer that 1 the observed changes of in the ice largely reflect changes in the size of airborne particles above the ice sheet and 2 changes of are indicative of changes in long range atmospheric transport time from the observed size changes we estimate shorter transit times by roughly 25 during lgm compared to the preboreal the associated particle concentration increase from more efficient long range transport is estimated to less than one order of magnitude

continuous late quaternary proxy climate records from loess in beringia abstract loess deposits in eastern beringia contain continuous proxy records of the effects of past climatic change on terrestrial landscapes at high latitudes variations of environmental magnetism and sedimentology of high latitude loess deposits indicate that the timing and pattern of responses to local variations in wind intensity storminess and pedogenesis in eastern beringia closely resemble the pattern of global climate change during the late quaternary deduced from studies of marine and ice core records the age of paleoclimatic fluctuations permafrost features volcanic ash horizons buried forest layers and paleosols and other features of the eastern beringian loess record can be determined using a variety of quaternary dating methods tephrochronologic correlations between the loess record and the glacial history of eastern beringia indicate the delta glaciation occurred during marine isotope stage 6 several other middle and late quaternary glaciations across eastern beringia can be tephrochronologically tied to the loess record and appear to have been in phase with episodes of global cooling recorded in deep sea records

geological and geochemical constraints on the genesis of the huachanggou gold deposit western qinling region central china the huachanggou gold deposit is located in lueyang county shaanxi province central china it is situated in the mian lue sutural zone in the western qinling orogen and controlled by a wnw striking ductile shear zone the ore deposit is developed in spilite limestone and phyllite in the middle lower devonian sanhekou group and the wall rocks show evidence of deformation pyrite is the main gold bearing mineral and the native gold is either visible or microscopic the huachanggou gold deposit is considered to be an orogenic gold deposit controlled by a ductile shear zone related to the indosinian qinling orogenic event the ores show a strong enrichment in au ag and as but exhibit a simple assemblage of au and ag that are strongly correlated together gold was deposited from a moderate to low salinity salt solution co2 hydrothermal fluid at medium temperature variations in s pb c and o isotopic composition indicate that the sulfur was derived from the reduction of seawater sulfate in the wall rocks the lead was derived mainly from the wall rocks the carbon was derived from the dissolution of marine carbonate the variations in h and o isotopic composition indicate that the ore forming fluids were derived originally from metamorphic fluid with meteoric water mixing in later stages au migrated mainly in the form of au hs 2 to form the deposit boiling of the fluid triggered the precipitation of the metal sulfides that contain the gold

millennial scale climatic change during the last interglacial period superparamagnetic sediment proxy from paleosol s1 western chinese loess plateau detailed magnetic analyses of samples from the jiuzhoutai well section on the western chinese loess plateau reveal high resolution signals of summer monsoon change the last interglacial period is represented here by the 8 meter thick s1 paleosol complex we have used low temperature remanence studies to analyze variations in the concentration of superparamagnetic sp grains which previous studies have shown to be largely of pedogenic origin the sp concentration interpreted as a proxy for the extent of pedogenesis shows millennial scale variations within s1 we conclude that the last interglacial period in asia was characterized by rapid climate fluctuations with at least one brief return to near glacial conditions in the middle of oxygen isotope substage 5e

a 37 000 year environmental magnetic record of aeolian dust deposition from burial lake arctic alaska abstract environmental magnetism and radiocarbon dating of burial lake sediments constrain the timing and magnitude of regional aeolian deposition for the noatak region of western arctic alaska for the last 37 000 years burial lake 68 43 n 159 17 w 21 5 m water depth is optimally located to monitor regional dust deposition because it is perched above local drainage and isolated from glacial processes cores collected in the summer of 2010 were studied through the application of magnetizations and progressive alternating field af demagnetization of u channel samples with additional data provided by computed tomography ct derived density hysteresis measurements isothermal remanent magnetization irm acquisition experiments organic carbon content biogenic silica physical grain size radiocarbon dating of wood seeds and plant macrofossils point source magnetic susceptibility and x ray fluorescence xrf with similar magnetic properties to regional alaskan loess deposits low coercivity highly magnetic material deposited during the late pleistocene contrasts with a high coercivity weakly magnetic component found throughout the record consistent with locally derived detritus the relative proportion of low coercivity to high coercivity magnetic material defined by the s ratios is used to reconstruct the regional input of dust to the basin over time a four fold decrease in the low coercivity component through the deglacial transition is interpreted to reflect diminished dust input to the region comparisons with potential sources of dust show that the timing of deposition in burial lake is largely consistent with general aridity lack of vegetative cover and increased windiness rather than glacial advances or retreats the influence from subaerial exposure of continental shelves cannot be ruled out as a significant far field source of dust to interior alaska during the last glacial maximum lgm but is unlikely to have been the sole source or to have contributed to increased dust in both the early and late holocene

reappraising the neoproterozoic east avalonian terranes of southern great britain abstract inliers of late neoproterozoic basement rocks exposed in southern great britain described in summary herein have been previously attributed to a series of terranes bounded by major crustal lineaments that form a dissected remnant of a single subduction complex together these terranes have been termed east avalonia and interpreted as correlative with west avalonia of the northern appalachian orogen a review of age and nd and o isotopic data shows an essentially ensialic complex with two broad overlapping divisions 1 the monian composite terrane of nw wales and fenland terrane of eastern england that are characterised by felsic intrusions at around 615 ma and have more evolved end t 7 5 to 2 5 older t dm 1868 ma to 1269 ma and generally more elevated 18 o up to 13 7 and 2 a more diverse assemblage represented by the cymru wrekin and charnwood terranes including more substantive volcano sedimentary successions and intrusions ranging in age between around 710 ma and 566 ma in which 615 ma magmatic rocks are not represented less evolved end t 2 5 to 3 5 younger t dm 1501 994 ma and lower 18 o 6 5 to 10 1 comparison with other neoproterozoic basement units throughout the northern appalachian orogen shows that both divisions from southern great britain have closer isotopic affinity with igneous components of ganderia which generally have evolved compositions interpreted to reflect an ensialic setting and the input of gondwanan cratonic source components they are mostly dissimilar from magmatic rocks of west avalonia which typically have less evolved compositions interpreted to reflect the contribution of juvenile mesoproterozoic source components