geochemical characteristics of the eolian deposits in southern china and their implications for provenance and weathering intensity abstract the loess paleosol sequences in the middle lower reaches of the yantgze river are valuable geological records of quaternary environments that bear information about climate change for the subtropical zone of southern china type sections containing eolian deposits in this region mostly include the upper loess soil sequence referred to as xiashu loess formation the middle vermiculated red soil vrs and the underlying fluvial deposits or bedrock in this study xiashu loess paleosol formed in the xiashu loess and the vrs samples from xuancheng xc and jiujiang jj sections were analyzed for their elemental major and trace elements and isotopic sm nd geochemistry and compared with pleistocene loess and paleosol samples from the chinese loess plateau clp in northern china the results show an overall similarity in geochemical characteristics between the southern china loess and the average ucc indicating that the dust materials were derived from well mixed sedimentary protoliths which had undergone numerous upper crustal recycling processes in comparison with the loess of northern china the eolian deposits in southern china have higher tio2 zr hf and lower ba concentrations higher tio2 al2o3 u pb th pb and lower ba rb zr hf eu eu ce yb eu yb ratios and lower end 0 values with relatively greater range these features coincide with the complicated source rock compositions in the middle lower yangtze river which suggests local sources for the eolian deposits in this region the eolian deposits in southern china have experienced the intermediate k removal weathering stage ca sr na mg and k are the main mobile elements in the weathering process in comparison with the xiashu loess formation the vrs has greater depletion of na mg k and mn indicating a stronger weathering intensity or perhaps a longer period of weathering

holocene climate changes in the monsoon arid transition reflected by carbon concentration in daihai lake of inner mongolia two sediment cores recovered in the central part of daihai lake in north central china were analysed at 2 to 4 cm intervals for total inorganic and organic carbon tic and toc concentrations the tic concentration is inferred to reflect temperatures over the lake region and an increase in the tic concentration implies an increase in the temperature toc concentration is considered to reflect the precipitation in the lake basin and higher toc concentrations denote more precipitations thus ams 14c time series of the tic and toc records of daihai lake sediments uncovers a detailed history of changes in temperature and precipitation in north central china during the last c 12 000 yr the holocene an epoch of postglacial warmth started c 11 500 cal yr bp and can be subdivided into three stages the early c 11 500 8100 cal yr bp middle c 8100 3300 cal yr bp and the late holocene c 3300 0 cal yr bp the climate was warm and dry during the early holocene warm and wet during the middle holoce

preliminary comparison of diagenetic stratiform copper mineralization from redstone nw territories canada and kamoto shaban copperbelt zaire recent studies of stratiform copper mineralization in the redstone copperbelt of the nw territories canada indicate analogies with sediments of modern intertidal and supratidal environments textural analyses show that mineralization occurred in microbial laminated carbonate units during diagenesis following initial enrichment of the carbonates in iron sulphides and evaporitic sulphates similar features have been described for the dolomitic beds hosting the well known kamoto ores of the shaban copperbelt the present work gives a brief comparison of the redstone and shaban host rocks and their mineralization similarities include the interpreted shallow marine red bed sequence and the presence of stromatolitic and microbial laminated structures in the carbonates however the shaban host rocks are more magnesian than those at redstone and silicification in shaba surpasses the more normal diagenetic silification seen at redstone the copper copper iron and iron sulphides of redstone and shaba exhibit similar peneconcordant arrays across their respective basal carbonate horizons but cobalt is important only in the shaban mineralization a more detailed comparison of host rocks and mineralization in these two copperbelts is currently in progress

a semi quantitative method for the reconstruction of eustatic sea level history from seismic profiles and its application to the southern south china sea abstract a quantitative model is proposed to estimate the magnitude of eustatic sea level fluctuations on the basis of definitions of relative and eustatic sea level in this model factors such as erosion sedimentation compaction basement tectonic and loading subsidence and paleo bathymetry are considered to estimate incremental changes in eustatic sea level we developed methods to solve for the variables involved in the model on the basis of interpretation of seismic profiles we reconstructed the onlap offlap points removed by erosion by fitting the effective thickness in areas without erosion with a piecewise defined function and extrapolating this function to zero thickness we used decompaction and backstripping algorithms to remove the effect of compaction and to calculate loading subsidence of the basement regional data however are needed to estimate the paleo water depths and the tectonic subsidence for this reason our methodology is considered semi qualitative as an application of this model an eustatic sea level curve since the pliocene 5 33 my was deduced from interpretation of our high resolution seismic data from the northern sunda shelf south china sea scs on this curve 36 fourth order sea level cycles were recognized with periods ranging from 0 08 to 0 29 my the curve matches well with the smoothed deep sea stable oxygen isotope curves from benthic foraminifera

long term cooling drying record of north china since the middle pleistocene from geochemical evidence of a 150 m deep drill core beijing plain china the quaternary strata in north china primarily consist of fluvial sediments which react strongly to east asian monsoon circulation however the records of the quaternary climate change history in terms of these fluvial sedimentations were limited which impeded understanding the east asian monsoon evolution in north china thus a 150 m deep drill core was collected from changping in the beijing plain to reconstruct the quaternary palaeoenvironmental changes the core was chronologically well constrained using palaeomagnetic and thermoluminescence dating the magnetostratigraphic result indicated that the brunhes matuyama boundary is at 134 2 m 0 78 ma and the age at the bottom of the core is 1 07 ma the thermoluminescence tl dating of the upper sand at similar to 2 m was 10 4 ka the chemical weathering history since the middle pleistocene in beijing plain was reconstructed by using geochemical proxies including selected major element pairs chemical index of alteration and al2o3 cao na2o k2o diagrams the cia value of the changping core ranged from 50 3 to 69 4 average 59 2 which indicated that the sediment has experienced incipient to intermediate chemical weathering during the middle pleistocene the result of a cn k figure shows a high plagioclase to k feldspar ratio in the source which would be indicative of a granodiorite gd source from jundu mountains north of the beijing plain all the geochemical results revealed a long term gradual decrease of weathering since the middle pleistocene which implied a long term increasing aridification cooling in the beijing plain c 2014 elsevier ltd and inqua all rights reserved

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

geochemical composition of the last deglacial lacustrine sediments in east tibet and implications for provenance weathering and earthquake events abstract identifying and understanding the respective influence of climate and tectonic processes becomes a frontier topic in tectonically active mountain ranges in the eastern tibetan plateau earthquake occurred frequently and usually led to formation of many dammed lakes in this study a last deglacial section of lacustrine sediments at xinmocun in eastern tibet is selected for conventional x ray fluorescence xrf and scanning xrf sxrf elemental analysis the high correlation of major and trace element abundances between the xinmocun lacustrine samples and the loess soil samples from the chinese loess plateau clp supports the previous view of the eolian origin of the xinmocun lacustrine sediments analysis of major element abundances ratios and trace element ratios indicates that the dust provenance of the xinmocun lacustrine sediments is different from that of the clp and is similar to that of the loess at ganzi and hongyuan nearby the study area the significant variations of most geochemical elements and their close coupling with grain size variations cannot be reasonably explained by the changes in transport dynamics of eolian dust and is possibly caused by the intermittent changes in available dust provenance frequent earthquakes triggered abundant landslides and provided large amounts of dust for the study area accordingly in the 16 m fraction of the xinmocun grain size record many element abundances and their ratios such as sio2 al2o3 tio2 al2o3 cao al2o3 sr al2o3 rb sr and na2o al2o3 can be regarded as sensitive indicators of earthquake events in the tectonically active regions sxrf measurements at the u channel surface can provide some cost effective indicators of seismic events such as si al ti al ca al sr al zr rb and rb sr significant variations in most element abundances and their ratios of the xinmocun lacustrine sediments correlate closely with those of its grain size record they all show no increasing or decreasing trends with time these suggest that tectonic activities characterized by seismic events possibly had a major role on the landscape erosion in the eastern tibetan plateau while the climatic influence seems minor

a 20 ma pollen record of east asian summer monsoon evolution from guyuan ningxia china abstract pollen analysis was conducted on the fluviolacustrine sediments from the east side of the liupan mountains a relatively monsoon sensitive region and provided for the first time a continuous evolutionary history of vegetation and climate in east china during the neogene the pollen record spanning the last 20 ma indicates that the vegetation and thus east asian summer monsoon evolution can be divided into three stages 20 13 14 25 ma 14 25 11 35 ma and 11 35 0 08 ma in spite of general dominance of steppe throughout the neogene during the period 20 13 14 25 ma the pollen assemblage was characterized by high abundance of artemisia and small amounts of temperate to subtropical deciduous broad leafed trees such as juglans carya quercus and betula suggesting that the east asian summer monsoon was generally strong the interval from 14 25 to 11 35 ma was marked by a significant decline in the east asian summer monsoon as indicated by artemisia gradually replaced by humulus and halophytic chenopodiaceae nitraria and ephedra also reached high values in this period since 11 35 ma ago percentages of halophytes dominated by chenopodiaceae and tamaricaceae maintained a high mean value of about 40 revealing a weak intensity of east asian summer monsoon the general weakening of the monsoon circulation during the neogene and the significant monsoon decline during the late middle miocene in particular might link with the global cooling trend probably through two mechanisms cooling and ice sheet expansion over the polar region caused an increase in meridional temperature gradients leading to the southward retreat of the monsoon circulation the global cooling may have also reduced the amount of water vapor held in the atmosphere and led to both additional cooling and further weakening of the east asian summer monsoon the cause for a short lived resumption during the period 1 0 0 8 ma is under investigation

geological setting of zambian emerald deposits abstract the kafubu emerald deposits occur within rocks of the muva supergroup which form the youngest part of pre katangan basement immediately southwest of the well known copperbelt of zambia within the muva supergroup are persistent bands of talc chlorite amphibole tremolite actinolite magnetite schist which are intruded by pegmatites these pegmatites are believed to be related to neighbouring granitoids which originated or were rejuvenated during early stages of pan african orogeny pegmatites occur as feldspar quartz muscovite bodies or as minor quartz tourmaline veins contact aureoles of the pegmatitic veins with the ultramafic schists are usually altered to phlogopite biotite tourmaline aggregates and the minor veins are often concordant to the foliation of the country rocks the emeralds are found in the contact zones and sometimes within the quartz tourmaline veins the emerald fields are considered comparable in quantity and quality of material to the well known colombian fields but their lithological setting differs considerably striking similarities were found between the zambian occurrences and those of south africa and zimbabwe

magnetostratigraphy and grain size record of the xijiadian fluviolacustrine sediments in east china and its implied stepwise enhancement of the westerly circulation during the eocene period in order to reveal the eocene westerlies evolution history 1053 paleomagnetic samples were collected and thermally demagnetized for the fluviolacustrine sediments at xijiadian hubei province east china fourteen normal and 14 reversed polarity zones are recognized for the section correlation of the resultant magnetic polarity column to the geomagnetic polarity time scale suggests that the section was generally continuous and spanned 56 4 37 1 ma with respect to the stable eurasian continent variations in magnetic declination of the section indicate no significant rotations supporting the earlier view that the south china block has experienced no significant rotation relative to eurasia since the late cretaceous provenance analysis suggests that the dominant fine sediments red beds of the xijiadian section were transported by wind into the study area grain size measurements indicate that the 20 m fraction and clay in the study area decreased from 56 4 to 50 7 ma and stepwise increased during 50 7 37 3 ma implying that the westerly circulation in the northern hemisphere weakened during 56 4 50 7 ma and stepwise strengthened during 50 7 37 3 ma in contrast the 20 63 m fraction mainly from nearby dust sources of the study area generally increased during 56 4 50 7 ma and stepwise decreased from 50 7 to 37 3 ma implying aridity in the study area strengthened during 56 4 50 7 ma and stepwise mitigated from 50 7 to 37 3 ma changes in global temperature during the eocene period probably played the primary role on evolutions of the westerly circulation in the northern hemisphere and of the arid conditions in the study area

geochemical evidence of windblown origin of the late cenozoic lacustrine sediments in beijing and implications for weathering and climate change abstract the origin of lacustrine sediments in the middle latitudes of asia remains controversial in this study we conducted major and trace element analyses on 86 lacustrine samples from the x5 core in beijing to determine their origin and provenance the results indicate that their abundances all varied in relatively narrow ranges similar to those of the samples in the chinese loess plateau clp a high correlation of major and trace element abundances exists between our lacustrine samples and the clp samples ucc normalized major and trace element abundances also have a similar pattern between the lacustrine and the clp samples with the exception of a few elements with high solubility such as mg in the ternary diagrams of a cn k la th sc and zr 10 th sc and the correlation maps of major trace elements and their ratios four groups of the x5 lacustrine samples with different sedimentation stages 3 16 2 7 ma 2 7 1 8 ma 1 8 0 9 ma and 0 9 0 ma overlap well with each other and with the clp samples indicating that the x5 lacustrine samples are likely of windblown origin and possibly shared common unchanged dust source regions with the clp since the late pliocene this interpretation is supported by the overlap of the lacustrine samples from beijing with the clp samples in the correlation maps of ms vs sorting ms vs skewness ms vs kurtosis and kurtosis vs skewness analysis of the frequency and cumulative frequency curves indicates that the x5 lacustrine sediments were dominantly transported by the winter monsoon and the westerly circulation given more scattered distributions of different elemental ratios and grain size parameters of the x5 core lacustrine sediments compared to those of the clp samples local dust particles must have contributed occasionally which deserves further investigation in the future several chemical ratios such as rb sr na 2 o al 2 o 3 cao al 2 o 3 and chemical index of alteration cia were calculated for the lacustrine samples in beijing comparison of these ratios variations with those of the sea level of the south china sea and the global benthic 18 o record indicates that na 2 o al 2 o 3 and cia can be regarded as sensitive indicators of chemical weathering of lacustrine dust sediments in the mid latitudes of northern hemisphere

variation of rb sr ratios in the loess paleosol sequences of central china during the last 130 000 years and their implications for monsoon paleoclimatology abstract rb sr and magnetic susceptibility have been measured in the last interglacial glacial loess profiles at luochuan and huanxian central china a high degree of similarity between the parameters in both profiles suggests that variations of rb sr ratios in the sequence can be regarded as an indicator of east asian summer monsoon strength matching the rb sr record with the specmap 18o curve suggests that the rb sr ratio responds sensitively to changes of the east asian monsoon induced by global ice volume variation

rare earth elements of aeolian deposits in northern china and their implications for determining the provenance of dust storms in beijing this paper contributes to a better understanding of the source of dust storms in northern china and the relationship between these sources and other aeolian sediments in this region sediment samples in potential source areas were collected from the hunshandake sandy land heaven desert the loess deposits of the bashang area the mountainous basins and valleys north of beijing and from the badain jaran desert and hulunbaier sandy land fig 1 dust samples were collected in beijing during two dust storms in march 2002 and april 2006 the laboratory methods used in this study included measurements of abundance of trace elements in particular the rare earth elements rees mineral assemblages and grain size the ree contents eu and ce anomalies show clear differences between various deposits provenance is considered to be the key factor influencing ree patterns in the study areas the ree abundances and patterns indicate that the aeolian sand north of beijing such as in the heaven desert is mainly of local origin rather than from desert encroachment from the north the mineral grains carried in dust storms however are highly mixed and may come partly from local sources but mainly from distant desert regions in western china

bimodal grain size distribution of chinese loess and its palaeoclimatic implications grain size analysis indicates that chinese loess generally shows a bimodal distribution with a coarse and a fine component the coarse component comprising the main part of the loess has pronounced kurtosis and is well sorted which is interpreted to be the product of dust storms generated by low altitude northwesterly winds its grain size reflects the strength of the low altitude circulation in the dust seasons of the year and its percentage provides an indicator of the source area aridity and the frequency of dust storms conversely the fine component has a wide grain size range and is poorly sorted sedimentary illustrations based on the grain size distribution characteristics of bulk samples and of detrital quartz suggest that the fine component probably represents the background dust load of the atmosphere and is mainly transported by high altitude westerly airstreams its grain size provides an estimate of the westerly air stream intensity the coarse and fine components of a loess sample can be mathematically separated by fitting a designated mathematical distribution function to the measured grain size data and this procedure constitutes an approach for reconstructing the palaeowind system of northern china c 2003 elsevier b v all rights reserved

zircon u pb and biotite 40ar 39ar geochronology from the anzan emerald deposit in zambia abstract the kafubu emerald area in zambia is an important producer of gemstone quality emeralds the country rocks include carbonatization altered rock and emerald hosting biotite chlorite schist from the anzan emerald deposit in the kafubu area zambia the technique of la mc icp ms is used to perform chronology measurements of the country rock and emerald hosting rock which belong to muva supergroup yielding zircon u pb concordia ages of 1966 12 ma in carbonatization altered rock and 1853 58 ma and 1344 30 ma in biotite chlorite schist meanwhile dating of biotite chlorite schist using the biotite 40 ar 39 ar method has obtained the plateau age of t 578 3 2 6 ma isochron age of 577 5 3 0 ma and reverse isochron age of 577 4 3 0 ma thus we have redefined the age of muva supergroup in the copperbelt province in zambia to be older than or equal to 1966 12 ma and found that the ore bodies in the anzan emerald deposit underwent three phases of metamorphism at 1853 58 ma 1344 ma 30 and 578 3 2 6 ma and finally accomplished the emerald mineralization the age of the anzan emerald deposit is earlier than the kagem 452 1 16 ma and the kamakanga emerald deposits 447 8 6 ma

impacts of post depositional processes on rapid monsoon signals recorded by the last glacial loess deposits of northern china abstract rapid east asian monsoon oscillations recorded by chinese loess are thought to be dynamically linked to north atlantic climate however few efforts have been made to assess the effects of post depositional processes e g surface mixing and pedogenesis on loess paleoclimatic records here a detailed optically stimulated luminescence dating of a thick loess sequence from the western loess plateau is presented offering a reliable chronology for last glacial deposits magnetic susceptibility and mean grain size records from three loess paleosol sequences along a northwest southeast transect are investigated to evaluate impacts of post depositional processes on these loess based proxy records our results indicate that 1 loess sequences developed within the flat tableland of the central and western loess plateau are nearly continuous during the last glaciation and 2 post depositional processes have distinct impacts on rapid monsoon signals recorded in loess sequences from different regions in the central loess plateau rapid monsoon signals have been attenuated to various degrees depending on the sedimentation rate and pedogenic intensity in the northwestern loess plateau however due to high sedimentation rate and relatively weak pedogenesis high resolution grain size oscillations reliably record rapid monsoon changes and can be well correlated to rapid climate changes recorded in the greenland ice core and hulu cave stalagmite

prediction of some weathering trends of plutonic and volcanic rocks based on thermodynamic and kinetic considerations abstract the exposed crust consists mainly of plagioclase 35 quartz 20 k feldspar 11 volcanic glass 12 biotite 8 and muscovite 5 quartz is a resistate thus feldspars and glass represent approximately 75 percent of the labile minerals the weathering characteristics of these constituents are summarized in the context of thermodynamic mass balance and kinetic considerations experimentally determined release rate constants were used to predict the proportions of ca na and k released by feldspars of plutonic rocks granites to gabbros to weathering solutions the chemical weathering trends of the weathered residues calculated from the kinetic data conform closely to the initial trends observed in some recent weathering profiles demonstrating the accuracy of the predictions since the weathering of feldspars is controlled by processes that should not change through geological time the relative release rates of ca na and k from the feldspars of granitic rocks can be calculated for future and past episodes of continental weathering experimentally determined release rate constants are not available for a wide range of volcanic glass compositions but the limited data indicate that compositional trends are predictable in weathering profiles developed on volcanic rocks the kinetic data available for rhyolitic glasses accurately predict the initial weathering trends observed in a recent rhyolite weathering profile

late proterozoic thrust tectonics high pressure metamorphism and uranium mineralization in the domes area lufilian arc northwestern zambia abstract the following main lithostratigraphic units have been distinguished in the domes area the kibaran basement complex composed of gneisses migmatites with amphibolite bands and metagranites is exposed in dome structures metamorphic features of kibaran age have been almost completely obliterated by extensive lufilian reactivation the post kibaran cover sequence is subdivided into the lower roan group consisting of well preserved quartzites with high mg content talc bearing extremely foliated schists intercalated with pseudo conglomerates of tectonic origin and the upper roan group including dolomitic marbles with rare stromatolites metapelites and a sequence of detrital metasediments with local volcano sedimentary components and interlayered banded ironstones the sediments of the lower roan group are interpreted as continental to lagoonal evaporitic deposits partly converted into the talc kyanite garnet assemblage characteristic of white schists the dolomites and metapelites of the upper roan group are attributed to a carbonate platform sequence progressively subsiding under terrigenous deposits whilst the detrital metasediments and bif may be interpreted as a basinal sequence probably deposited on oceanic crust grading laterally into marbles metagabbros and metabasalts are considered as remnants of an ocean floor type crustal unit probably related to small basins alkaline stocks of silurian age intruded the post kibaran cover significant ancestral tectonic discontinuities promoted the development of a nappe pile that underwent high pressure metamorphism during the lufilian orogeny and all lithostratigraphic units rb sr and k ar and u pb data indicate an age of 700 ma for the highest grade metamorphism and 500 ma for blocking of the k ar and rb sr system in micas corresponding to the time when the temperature dropped below 350 400 c and to an age of about 400 ma for the emplacement of hypabyssal syenitic bodies a first phase of crustal shortening by decoupling of basement and cover slices along shallow shear zones has been recognized fluid rich tectonic slabs of cover sediments were thus able to transport fluids into the anhydrous metamorphic basement or mafic units during the subsequent metamorphic re equilibration stage of high pressure pre existing thrusts horizons were converted into recrystallized mylonites due to uplift rocks were re equilibrated into assemblages compatible with lower pressures and slightly lower temperatures this stage occurs under a decompressional nearly adiabatic regime with pfluid plithostatic it is accompanied by metasomatic development of minerals activated by injection of hot fluids new or reactivated shear zones and mylonitic belts were the preferred conduits of fluids the most evident regional scale effect of these processes is the intense metasomatic scapolitization of formerly plagioclase rich lithologies uraninite mineralization can probably be assigned to the beginning of the decompressional stage a third regional deformation phase characterized by open folds and local foliation is not accompanied by significant growth of new minerals however pitchblende mineralization can be ascribed to this phase as late stage short range remobilization of previously existing deposits finally shallow alkaline massifs were emplaced when the level of the domes area now exposed was already subjected to exchange with meteoric circuits activated by residual geothermal gradients generally related to intrusions or rifting most of the superficial u showings with u oxidation products were probably generated during this relatively recent phase

geochemical evolution of archean shales from south africa i the swaziland and pongola supergroups abstract the fig tree group and moodies group part of the swaziland supergroup are exposed in the barberton mountain land and are 3 3 3 5 ga old shales from the fig tree group are characterized by variable rare earth element ree patterns with lan ybn 5 5 1 8 95 confidence and eu eu 0 97 0 18 shales from the moodies group have more fractionated ree patterns lan ybn 8 7 2 0 and less variable eu anomalies eu eu 0 92 0 02 both groups are characterized by very high abundances of cr and ni modelling of those trace elements which are relatively unfractionated during sedimentary processes ree th sc is consistent with the derivation of these sedimentary rocks from a mixture of the archean bimodal igneous suite mafic volcanics tonalites trondhjemites felsic volcanics with the moodies group requiring a larger percentage of the felsic end member the data for shales from the swaziland supergroup support models suggesting that the archean exposed crust was of more mafic composition than the post archean upper crust and that intracrustal melting was relatively unimportant in differentiating the archean crust the pongola supergroup is younger than the swaziland supergroup but older than 2 9 ga shales and mudstones from the nsuze and mozaan groups show ree characteristics intermediate between the older shales of the swaziland supergroup and typical post archean shales one quartzite sample from the witwatersrand supergroup ca 2 6 ga has a ree pattern virtually parallel to average post archean shales but with much lower abundances the change from typical archean to post archean sedimentary trace element patterns has been documented in early proterozoic successions from canada and australia this change has been related to a short interval of intense growth and chemical differentiation of the continental crust during the late archean 2 7 2 5 ga in southern africa this change appears to have taken place much earlier 3 2 2 9 ga but can be related to similar processes thus the period of crustal evolution related to the archean proterozoic boundary while virtually episodic regionally occurred over a protracted period world wide during the period ca 3 2 2 5 ga

isolation and water level fluctuations of lake kachishayoot northern quebec canada this study combines different methods including grain size macrofossil and pollen analyses to reconstruct paleogeographical and paleoclimatological conditions for periods before during and after the isolation of a small lake lake kachishayoot in northern quebec after the retreat of the laurentide ice sheet around 8000 14c yr b p the area was submerged by the tyrrell sea the transition from marine to lacustrine environment occurred about 5400 yr b p two major periods of water level fluctuations were inferred from organic and mineral sediments a high water level that occurred after 3200 yr b p and a low water level that started before 2200 yr b p our chronological data for the first period are consistent with those from nearby lac des pluviers and from other lakes in east central canada and in the northeastern united states during the low water level period however there is no evidence for minor fluctuations whereas other lakes in northern quebec and east central canada underwent several brief lowerings long term changes in atmospheric circulation caused by changing global boundary conditions likely explained long term water level fluctuations of lake kachishayoot

holocene climate changes in the mid high latitude monsoon margin reflected by the pollen record from hulun lake northeastern inner mongolia pollen assemblage data from a sediment core from hulun lake in northeastern inner mongolia describe the changes in the vegetation and climate of the east asian monsoon margin during the holocene dry steppe dominated the lake basin from ca 11 000 to 8000 cal yr bp suggesting a warm and dry climate grasses and birch forests expanded 8000 to 6400 cal yr bp implying a remarkable increase in the monsoon precipitation from 6400 to 4400 cal yr bp the climate became cooler and drier chenopodiaceae dominated the interval from 4400 to 3350 cal yr bp marking extremely dry condition artemisia recovered 3350 2050 cal yr bp denoting an amelioration of climatic conditions both temperature and precipitation decreased 2050 to 1000 cal yr bp as indicated by decreased artemisia and the development of pine forests during the last 1000 yr human activities might have had a significant influence on the environment of the lake region we suggest that the east asian summer monsoon did not become intensified until 8000 cal yr bp due to the existence of remnant ice sheets in the northern hemisphere changes in the monsoon precipitation on millennial to centennial scales would be related to ocean atmosphere interactions in the tropical pacific

last glacial climate instability documented by coarse grained sediments within the loess sequence at fanjiaping lanzhou china optically stimulated luminescence dating grain size analysis and magnetic susceptibility measurements were conducted on the fanjiaping loess section from the western chinese loess plateau the results confirm that last glacial high frequency climatic shifts were documented in mid latitude continental archives the grain size record indicated that coarse grained sediments with horizontal bedding and channel fill structures were only deposited in several short intervals equivalent to the beginning of marine oxygen isotope stage mis 4 and the early to middle mis 3 this probably implies brief rainfall intensification of the asian summer monsoon and its disappearance since the late mis 3 to mis 2 may have been a response to significant glacial cooling in the northern hemisphere previous investigations revealed high sea surface temperatures at high latitudes at the start of mis 4 and the early to middle mis 3 intensification of summer insolation in the northern hemisphere implying evident climate amelioration climate improvement favors boreal forest recovery enhancing both winter and summer air temperatures the resultant smaller equator polar temperature gradient probably helped the moisture laden summer monsoon to penetrate northward this study thus provides new significant information about the response of terrestrial loessic palaeoenvironments to millennial timescale climatic fluctuations during the last glacial period

refractory element mobility in volcanic soils refractory trace element concentrations in strongly weathered hawaiian soils ranging in age from 20 to 4100 ka are highly elevated over parent rock values due to extensive mass loss of more soluble major elements during pedogenesis nb and ta exhibit virtually no mobility soil nb ta ratios are within the range of fresh bedrock even when soil nb concentrations are residually enriched by a factor of 10 in contrast al zr and hf are depleted relative to nb in surface soil horizons but are enriched at depth clearly indicating mobility of these elements variations in th nb ratios in soil profiles indicate significant th mobility within the soil column however mass balance calculations require that accretion of th enriched asian dust has resulted in a net increase in th in some soils soils developed on a 150 ka rainfall gradient show that the mobility and loss of zr increase with mean annual precipitation

a pollen record of the mid pleistocene transition from beijing north china to reconstruct the history of climate and environment in east asia during the early pleistocene a palynofloral investigation was conducted on fluviolacustrine sediments in beijing north china the results indicate that herb and shrub taxa were dominant in most of the samples reflecting an open forest grassland covering the beijing region during much of the early pleistocene this vegetation generally declined during 1 68 1 25 ma and recovered in part during 1 25 0 96 ma from 0 96 ma conifers gradually replaced broad leaved trees shrubs and herbs after 0 65 ma the pollen abundance of conifers shrubs and herbs all increased significantly these vegetation changes took place in the context of long term global cooling during the late cenozoic a significant increase in antarctic ice volume at 1 25 1 20 ma and the resultant increased meridional temperature gradient in the southern ocean led to prominent anomalous warming in the tropics and increased heat moisture flow across the equator probably resulting in vegetation recovery in the study area to some extent during 1 25 0 96 ma from 0 96 ma the stepwise decline of vegetation cover in the study area especially after 0 65 ma was driven by further development of global cooling and increase in polar ice volume copyright 2013 john wiley sons ltd

tectonic evolution of the lufilian arc central africa copper belt during neoproterozoic pan african orogenesis abstract the lufilian arc of central africa also called katangan belt or copperbelt is a zone of low to highgrade metasedimentary and subsidiary igneous rocks of neoproterozoic age hosting highgrade cucou and pbzn mineralizations the lufilian arc is located between the congo and kalahari cratons and defines a structure which is convex to the north three major phases of deformation characterize the construction of the lufilian arc the first phase d1 called the kolwezian phase developed folds and thrust sheets with a northward transport direction d1 deformation occurred in the lufilian arc between ca 800 and 710 ma with a peak in the range 790 750 ma it is here correlated with the main deformation in the zambezi belt southward verging folds with the same trends as the d 1 structures were previously linked to a second tectonic event named kundelunguian phase of the lufilian orogeny we show in this paper that they are backfolds developed during d1 along katangan ramps and especially along the kibaran foreland the second phase d2 of the lufilian orogeny is the monwezi phase including several large leftlateral strikeslip faults which have been activated successively during this deformation phase the eastern block of the belt rotated clockwise giving the present day nwse trend of d1 structures in this part of the lufilian arc and generating its convex geometry the mwembeshi dislocation the major transcurrent shear zone separating the zambezi and lufilian arc was mostly active during the d2 deformation phase d2 deformation occurred between ca 690 and 540 ma such a long time interval is attributed to the migration of strikeslip faults developed sequentially from south to north and probably to a slow convergence velocity during the collision between the congo and kalahari cratons the third phase d3 of the lufilian orogeny is a late event called the chilatembo phase marked by structures transverse to the trends of the lufilian arc this deformation and the post d 2 uppermost kundelungu sequence ks3 plateaux group are younger than 540 ma and probably early paleozoic

on the seemingly incompatible parcel and globally integrated views of the energetics of triggered atmospheric deep convection over land the energetics of the diurnal cycle of atmospheric deep convection over land remain difficult to understand and simulate accurately with current cumulus parametrizations furthermore a proper formulation has remained elusive owing to seeming incompatibilities between on the one hand the parcel view of energetics which relies on such concepts as convective available potential energy cape and convective inhibition cin and on the other hand the globally integrated view which relies on such concepts as moist available energy mae reference states and energy conversion terms while the mae is intuitively the global counterpart of the parcel defined cape there seems to be no global analogue to the parcel defined concept of energy barrier attached to cin to gain insights into this issue a new cost function pe is introduced to quantify the amount of positive or negative energy required for a given sounding to undergo an arbitrary adiabatic rearrangement of mass and which encompasses both the parcel defined and global energy concepts as particular cases the function pe offers a complementary view of the stability and energy characteristics of atmospheric soundings whose local minima are naturally associated with the reference states of the system it is established that a mae is essentially equivalent to cape multiplied by a mass conversion factor mb which scales as the amount of convectively unstable boundary layer air using the available summer 1997 iop data from the arm sgp site mb is found to correlate with cape which suggests the existence of a functional relationship between cape and mae if further confirmed this result would considerably simplify the computation of mae b a global counterpart to the parcel defined concept of energy barrier can only be defined if the system considered admits several reference states and not one as is classically assumed in that case energy barriers naturally arise as the amount of energy required to switch from one reference state to another in the context of triggered deep convection there must be at least two reference states a shallow one which is the actual state or a slightly modified one if there is boundary layer cape and a deep one associated with the release of mae cape the energy barrier separating these two reference states naturally defines a generalized cin in the limited context of the above mentioned iop arm data it is further shown that c spatially averaged conditions exhibiting potential instability to deep convection may be associated with individual soundings having widely different stability characteristics including absolute stability potential instability and absolute instability this suggests that triggered deep convection may not necessarily be the result of a parcel s vertical kinetic energy exceeding its negative buoyancy but rather from the destruction of convective inhibition i e production of absolute instability in a local region d a few local soundings exhibit multiple reference states corresponding roughly to multiple levels of neutral buoyancy these may allow for convective clouds with cloud top heights significantly lower than those classically predicted by the undiluted ascent of a boundary layer air parcel up to its highest level of neutral buoyancy even in the absence of complex entrainment scenarios copyright 2004 royal meteorological society

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

geochemical characteristics of the miocene eolian deposits in china their provenance and climate implications 1 in the loess plateau in northern china the quaternary loess soil sequences the hipparion red earth of eolian origin red clay and the miocene loess soil sequences constitute a near continuous terrestrial record of paleoclimates for the past 22 ma in this study miocene loess and paleosol samples from qinan qa i were analyzed for their major trace and rare earth element chemistry and compared with the pliopleistocene samples from xifeng with emphasis on their provenance and paleoclimatic implications the results show similar geochemical signatures for the eolian deposits of different ages and they are also comparable to the average composition of the upper continental crust these suggest that the dust materials were all derived from well mixed sedimentary protoliths which had undergone numerous upper crustal recycling processes they also support the notion of broadly similar source areas and dust transporting trajectories for different periods since the early neogene the slightly higher k2o fe2o3 and mgo concentrations and loss on ignition values and the lower na2o content in the miocene loess samples compared to their quaternary counterparts are attributable to the finer grain size of the miocene loess associated with weaker dust carrying winds in comparison with some loess in europe and america with less extensive sources eolian deposits from northern china show higher cs and lower zr and hf content this is attributable to the sorting processes from remoter sources during transportation and could be regarded as an indication of the desert origin of the loess deposits miocene paleosol samples show higher chemical index of alteration values and lower cao mgo and na2o concentrations than does the intervening loess indicating stronger weathering of the paleosols however the moderate chemical weathering of the paleosol samples indicates a constant semiarid and subhumid climatic range in northern china since the early miocene components 9791 words 8 figures 3 tables

annually laminated lake sediments and environmental changes in bashang plateau north china abstract angulinuo lake is the biggest lake on the bashang plateau north china and is 47 6 km2 in area and 2 6 m in depth a core from the inner part of angulinuo lake was sliced and the sediment was observed by scanning electronic microscope sem annual laminations characterized by variable color and grain size were found and interpreted as recording the cyclic deposition of lacustrine clay and aeolian dust the results of chemical analysis of coarse grains conducted by sem edax and grain size analysis of modern aeolian dust in the ice on angulinuo lake support an aeolian origin for the light coarse layers image analysis technique was used to calculate the size and number of coarse grains in each layer the coarse grains were fractionated into four classes 42 m 14 42 m 14 4 2 m and 1 4 4 2 m in general the abundance of the four classes shows similar temporal variation patterns around angulinuo lake the winter monsoon is strong and transports aeolian dust into the lake when the winter monsoon is strong the size and amount of coarse grains are expected to increase we infer that the winter monsoon was weaker during 8430 5440 year bp and was unstable in the later part of this period from 5440 year bp the winter monsoon became stronger and then weaker from 3250 to 2490 year bp during 2490 1170 year bp the winter monsoon was slightly stronger but since 1170 year bp it has become weaker again the changes of the winter monsoon intensity recorded in the annual laminations in angulinuo lake sediments correspond well to environmental changes in north china and to changes in sea level during the same period periods of weaker winter monsoon correspond to times of higher sea levels while the periods of stronger winter monsoon correspond to the neoglaciation stage in china and the periods of lower sea levels

geochemical and isotopic studies of aeolian sediments in china the sr and nd isotopic rare earth element ree and major element compositions together with mineral and grain size proportions are reported for aeolian loess deposits and desert sands from several chinese localities the study was carried out in order to examine regional variations in the isotopic and geochemical features of these aeolian sediments and to constrain the provenance of chinese loess samples include loesses from the tarim and junggar basins and desert sands from the taklimakan desert in north west china loess from the ordos area and desert sands from the tengger and mu us deserts in north central china as well as loess and desert sands from the naiman area north east china ree distributions show minimal variation among the chinese loess deposits whereas those for the desert sands show regional variations new isotopic data document a latitudinal variation in sr and nd isotopic features for the loesses and desert sands the naiman and junggar loesses have distinctly lower 87sr 86sr ratios and higher end 0 values than the loesses from the tarim basin the ordos area and the loess plateau among the desert sands the naiman samples have higher end 0 values than the taklimakan tengger and mu us samples isotopic data suggest that loesses of the loess plateau were supplied from the tarim basin loesses and taklimakan desert sand and that the naiman loesses were supplied from the junggar basin loesses the latitudinal variation in the loesses and desert sands may be partly explained by isotopic variations reported previously for moraines from the tianshan and west kunlun mountains which are possible sources for the loesses and desert sands these inferences on the provenance of the loesses and desert sands are consistent with the dust transport pattern over east asia

holocene east asian monsoonal precipitation pattern revealed by grain size distribution of core sediments of daihai lake in inner mongolia of north central china abstract two sediment cores recovered in the central part of daihai lake in north central china were analysed at 2 to 4 cm intervals for grain size distribution grain size distributions of the lake sediments are inferred to be a proxy for past changes in east asian monsoon precipitation such that greater silt size percentage and higher median grain size reflect increased monsoonal precipitation rates the grain size record of daihai lake sediments spanning the last ca 10 000 yr indicates that the monsoonal precipitation in the lake region can be divided into three stages the early middle and late holocene during the early holocene before ca 7900 cal yr bp the median grain size md and the silt fraction content were relatively low and constant suggesting relatively low precipitation over the lake region the middle holocene between ca 7900 and 3100 cal yr bp was marked by intensified and highly variable monsoonal precipitation as indicated by high and variable md values and silt contents of the lake sediments during this period average precipitation rate gradually increased from ca 7900 to 6900 cal yr bp displayed intense oscillations between ca 6900 and 4400 cal yr bp and exhibited a decreasing trend while fluctuating from ca 4400 to 3100 cal yr bp although generally high during the middle holocene both the md and the silt content assumed distinctly low values at the short intervals of ca 6500 6400 6000 5900 5700 5600 4400 4200 cal yr bp implying that monsoonal precipitation might have been significantly reduced during these intervals during the late holocene since ca 3100 cal yr bp grain size values suggest that precipitation decreased however during the late holocene relatively higher md values and silt contents occurring between ca 1700 to 1000 cal yr bp may denote an intensification of hydrological cycles in the lake area changes in the east asian monsoonal precipitation were not only directly linked with the changing seasonality of solar insolation resulting from progressive changes in the earth s orbital parameters but also may have been closely related to variations in the temperature and size of the western pacific warm pool in the intensity of the el nino southern oscillation and in the path and strength of the north equatorial current in the western pacific

basic magmatism and geotectonic evolution of the pan african belt in central africa evidence from the katangan and west congolian segments abstract in the west congolian and katangan pan african belts late proterozoic extensional tectonics related to the relaxation phase that followed the kibaran collision ca 1000 ma ago evolved to reach a mature rift stage characterized by the e morb from kimbungu bas zaire in the pan african west congolian belt and kibambale shaba zaire in the pan african katangan belt these mature rifts proto oceans closed during the pan african orogenic event in an embryonic collision between the kalahari craton to the south and the congo craton to the north this embryonic collisional belt differs from the classical ones in the lack of subduction and collision magmatic associations this difference is attributed to the limited extent of the collision slight crustal thickning and notably to the fact that it happened before the underthrust plate reached the minimum depth required to generate calc alkaline magmas through subduction

a geochemical study of loess and desert sand in northern china implications for continental crust weathering and composition abstract chemical compositional variations of desert sands and loess loess like deposits river deposits and saline lacustrine deposits collected mostly from the southern margin of the taklimakan desert china provide strong constraints on the chemical weathering processes of continental crust and also on the provenance compositions of these quaternary deposits constant but lower concentrations of al relative to the average upper continental crust ucc in these quaternary deposits could be attributed to chemical weathering of al rich minerals such as feldspar and mica and removal of clay minerals by wind and water large variations of mobile na ca mg and sr compared to relatively immobile al k and ba resulted from the chemical weathering of plagioclase and carbonate minerals salinization and carbonation of the arid lands most trace elements are not significantly fractionated their variations in absolute concentration are caused by the dilution of quartz evaporates and carbonate minerals variations in sn concentrations probably depend on relative contents of some heavy minerals high sr ba low th u k cs ratios of the saline lake deposits suggest differences in aqueous chemistry of these elements the occurrence of the m type tetrad effect a ree pattern with four convex curves of ree compositions found mainly in the river deposits is considered the result of water particle interaction during chemical weathering of crustal materials y ho ratios of these samples are significantly higher than those of chondrite and the ucc this suggests different chemical behavior of these two elements and possibly the enrichment of carbonate materials the low lree hree feature of the saline lake deposits can be interpreted as due to the different aqueous chemical behavior of the ree s however it can also be reasonably considered as the result of inheritance from their provenance since lree and lree hree variations may be related to the geological setting of the source according to some elements that are not significantly fractionated the average provenance composition of these quaternary deposits are probably characterized by enrichments of ni cr and v over fe higher la th lower la sc and th sc and lower ta w and nb w ratios compared with the ucc composition

onset of asian desertification by 22 myr ago inferred from loess deposits in china the initial desertification in the asian interior is thought to be one of the most prominent climate changes in the northern hemisphere during the cenozoic era1 2 3 4 but the dating of this transition is uncertain partly because desert sediments are usually scattered discontinuous and difficult to date here we report nearly continuous aeolian deposits covering the interval from 22 to 6 2 million years ago on the basis of palaeomagnetic measurements and fossil evidence a total of 231 visually definable aeolian layers occur as brownish loesses interbedded with reddish soils this new evidence indicates that large source areas of aeolian dust and energetic winter monsoon winds to transport the material must have existed in the interior of asia by the early miocene epoch at least 14 million years earlier than previously thought3 5 regional tectonic changes and ongoing global cooling are probable causes of these changes in aridity and circulation in asia

the paks loess paleosol sequence a record of chemical weathering and provenance for the last 800 ka in the mid carpathian basin abstract the paks loess paleosol sequence is one of the most important terrestrial records of middle and late pleistocene environmental changes in east central europe spanning the last ca 0 8 ma while geochemical proxies demonstrate a general decreasing chemical weathering trend over the last 0 8 ma in the carpathian basin mineralogy and derived indices reflect intensifying physical erosion in theory the observed chemical weathering trend can be accounted for both by enhanced input of relatively unweathered material and by climate deterioration during the quaternary as the proxies such as cia are not capable of distinguishing between pre and post depositional weathering enhanced physical erosion of the source areas driven by tectonism and resulting increased sedimentation of fresh mineral dust at the depositional site are demonstrated by increasing dolomite illite and chlorite contents and sme ill sme ill chl ratios from older to younger sediments in the profile together with increasing thickness of loess layers towards the youngest part of the sequence at the same time constant smectite contents 30 40 in paleosols appear to disprove progressive aridization of interglacials through time and suggest that the duration of pedogenesis played an important role in determining soil types further the increasing proportion of inherited phyllosilicates illite and chlorite would in theory raise the possibility that the decreasing values of chemical weathering indices are just artifacts of enhanced physical erosion and resulting increased dust deposition by a dilution effect the above findings highlight the fact that the general view on chemical weathering is oversimplistic as its equation includes two basic variables tectonism and time beyond climate and the interplay of these equally important factors will eventually determine its final value to get a better grasp of these processes needs further data more age control in loess profiles data on uplift in and around sedimentary basins and more sophisticated proxies as the mineralogical data presented here can be considered only semiquantitative regarding the provenance of sediments in the paks profile geochemical data demonstrate that felsic rocks dominated the source areas and there have been only very little variations in provenance over the last ca 0 8 ma significant contributions from mafic ultramafic rocks to the sediments can be ruled out as revealed by lower abundances of ferromagnesian trace elements the appearance of amphiboles and high dolomite contents suggest that loess material was at least partly sourced from local rocks and geochemical data reveal a genetic link between floodplain sediments and loess deposits

patterns of local and regional grain size distribution and their application to holocene climate reconstruction in semi arid inner mongolia china abstract the semi arid temperate steppe in northern central china is one of the main areas influenced by frequent dust and sand storms and is at the same time a primary source of dust from deteriorated grasslands thus the sediment grain size distribution of inland lakes in this region can be a particularly useful indicator of palaeoenvrionmental change the local pattern of grain size suggests that aeolian activity is the most important agent for sedimentation in the lake center in this region as strong northwesterly winds prevail for most of the year and the surface runoff is very weak meanwhile the regional pattern of topsoil grain size and its close association with mean annual precipitation map allows the establishment of a statistical model for palaeo moisture reconstruction from sediment grain size in this study we reconstructed a humidity time series based on the sediment grain size sequence from anguli nuur lake on the southern inner mongolian plateau in china and found that it coincides very closely with the c n ratio carbon to nitrogen ratio and other humidity indices revealed in previous studies of this temperate steppe region and from the 18 o values of stalagmite calcite in southern monsoon dominated china this close relationship suggests that climate change in the semi arid areas of asia is strongly influenced by the pacific summer monsoon and that it is reasonable to use sediment grain size as an indicator of humidity variability in the semi arid steppe region the reconstructed humidity increased during the early holocene and generally humid conditions lasted from about 10 400 until 7000 yr bp the period from around 7000 to 5200 yr bp was a transition phase from humid to semi arid conditions and the monsoon intensity of that time may have been at the threshold for a semi arid vegetation ecosystem finally since approximately 5200 yr bp to present the climate has become more arid with corresponding vegetation deterioration and strong aeolian activity

origin weathering and geochemical composition of loess in southwestern hungary abstract loess geochemistry generally reflects paleo weathering conditions and it can be used to determine the average composition of the upper continental crust ucc in this study major and trace element concentrations were analyzed on loess samples from southwestern hungary to determine the factors influencing their chemical compositions and to propose new average loess compositions all studied loess samples had nearly uniform chemical composition suggesting similar alteration history of these deposits chemical index of alteration values 58 69 suggested a weak to moderate degree of weathering in a felsic source area typical non steady state weathering conditions were shown on the al 2 o 3 cao na 2 o k 2 o patterns indicating active tectonism of the alpine carpathian system during the pleistocene whole rock element budgets were controlled by heavy minerals derived from a felsic magmatic or reworked sedimentary provenance geochemical parameters indicated that dust particles must have been recycled and well homogenized during fluvial and eolian transport processes

in situ u pb zircon dating using laser ablation multi ion counting icp ms high resolution in situ u pb zircon geochronology on zoned grains can obtain isotope signatures from multiple growth or thermal events we present a method using laser ablation multicollector inductively coupled plasma mass spectrometry la mc icp ms to overcome complications associated with intricately zoned zircon crystals through in situ sampling of zircon volumes as small as 12 m 25 m and 40 m in diameter by about 10 m in depth high precision u pb age of a series of zircon standard covering a wide age range of 30 to 1 065 ma was acquired using la mc icp ms the precision of measured pb u ratios in homogeneous zircon is about 2 2 resulting in routinely achieved precision of u pb ages obtained by external calibration of 1 2 or better all masses of interest can be simultaneously recorded with a multi ion counting system mic operating in static mode and the short ablation required to achieve such precision results in spatial resolution that is superior to comparable u pb zircon analyses by single collector icp ms the resulting present u pb age for five zircon reference samples and two geological samples show an excellent agreement with the previously reported id tims or shrimp data