origin of maghaemite in chinese loess deposits aeolian or pedogenic maghaemite and magnetite common ferrimagnetic minerals in surficial soils have physical properties which are similar except for the thermal instability of the former utilising this exception a study of thermomagnetic properties has been made to systematically separate these two magnetic components in loess and palaeosol samples from the upper parts of the luochuan section of the central chinese loess plateau this investigation has shown that although maghaemite thermally unstable component occurs in greater amounts in palaeosols ms 0 0187 am2 kg 1 1 1 than in loess units ms 0 0156 am2 kg 1 1 1 in relative terms its contribution to the ferrimagnetic component of magnetisation is higher in the loess units ms 32 2 2 0 than the soils ms 23 5 3 7 such an observation suggests that much of the maghaemite component originates in the aeolian source area with some addition of pedogenic maghaemite occurring in the palaeosols

40ar 39ar dating of supergene mn oxides from the zunyi mn deposit guizhou plateau sw china implications for chemical weathering and paleoclimatic evolution since the late miocene 40ar 39ar laser incremental heating analyses of potassium bearing mn oxides from a weathering profile at the zunyi manganese deposit northern guizhou plateau sw china were applied to constrain the timing and rate of chemical weathering in critical zone and to provide insights into paleoclimatic conditions under which the weathering profile and associated mn oxides formed eighteen mn oxide grains from nine samples at three sites in saprolite zone of a single weathering profile yield well defined plateau or pseudo plateau ages ranging from 13 1 0 3 to 0 1 0 4 ma 2 the mn oxide ages are progressively younger toward lower elevations 13 1 0 3 to 11 0 1 8 ma at 951 m 3 69 0 07 to 2 16 0 16 ma at 922 m 1 3 0 2 ma at 914 m yielding an average weathering front propagation rate at 3 3 m ma for the past 13 1 ma the calculated weathering front propagation rate corresponds to a chemical denudation rate of 4 6 0 2 t km2 yr which is consistent with values deduced from mass balance calculation for suspended and dissolved loads of river discharge across the guizhou plateau the mn oxide 40ar 39ar ages suggest that humid climate conducive to intense weathering has prevailed over the guizhou plateau at least since the late miocene the climatic conditions inferred from the weathering geochronology are consistent with the continuous sedimentary and paleontological records from many cenozoic basins over the guizhou plateau confirming that supergene mn oxides can serve as a paleoclimate proxy for the past climatic condition the present 40ar 39ar dating results when combined with previous geochronological data of weathering profiles in the yunnan guizhou plateau and coastal areas of south china document progressively intensive erosion toward areas proximal to the eastern margin of the tibet plateau

the mesoscale and microscale structure and organization of clouds and precipitation in midlatitude cyclones viii a model for the seeder feeder process in warm frontal rainbands abstract previous field studies have indicated that warm frontal rainbands form when ice particles from a seeder cloud grow as they fall through a lower level feeder cloud in this paper we present results from a parameterized numerical model of the growth processes that can lead to the enhancement of precipitation in a seeder feeder type situation the model is applied to two types of warm frontal rainbands in the first type 1 situation the vertical air motions are typical of those associated with slow widespread lifting in the vicinity of warm fronts in the second type 2 situation the vertical air motions are stronger and more characteristic of the mesoscale the model simulations show that in the type 1 situations the growth of the seed ice crystals within the feeder zone is due to vapor deposition the feeder zone in this case is slightly sub saturated with respect to water due to the presence of the seed crystals in regions where the feeder zone is not seeded from aloft snow cryst

potbellies wasp waists and superparamagnetism in magnetic hysteresis because the response of a magnetic substance to an applied field depends strongly on the physical properties of the material much can be learned by monitoring that response through what is known as a magnetic hysteresis loop the measurements are rapid and quickly becoming part of the standard set of tools supporting paleomagnetic research yet the interpretation of hysteresis loops is not simple it has become apparent that although classic single domain pseudo single domain and multidomain loops described in textbooks occur in natural samples loops are frequently distorted having constricted middles wasp waisted loops or spreading middles and slouching shoulders potbellies such complicated loops are often interpreted in oversimplified ways leading to erroneous conclusions the physics of the problem have been understood for nearly half a century yet numerical simulations appropriate to geological materials are almost unavailable in this paper we discuss results of numerical simulations using the simplest of systems the single domain superparamagnetic sd sp system examination of the synthetic hysteresis loops leads to the following observations 1 wasp waisting and potbellies can easily be generated from populations of sd and sp grains 2 wasp waisting requires an sp contribution that saturates quickly resulting in a steep initial slope and potbellies require low initial slopes the sp contribution approaching saturation at higher fields the approach to saturation is dependent on volume hence the cube of grain diameter therefore there is a very strong dependence of hysteresis loop shape on the assumed threshold size 3 we were unable to generate potbellies using an sp sd threshold size as large as 30 nm and wasp waists cannot be generated using a threshold size as small as 8 nm the occurrence of both potbellies and wasp waists in natural samples is consistent with a room temperature threshold size of some 15 nm 5 4 simulations using a threshold size of 15 20 nm with populations dominated by sp grain sizes that is with a small number of sd grains produce synthetic hysteresis loops consistent with measured hysteresis loops and transmission electron microscopic observations from submarine basaltic glass 5 simulations and measurements using two populations with distinct coercivity spectra can also generate wasp waisted loops a relatively straightforward analysis of the resulting loops can distinguish the latter case from wasp waisting resulting from sp sd behavior

the improve 1 storm of 1 2 february 2001 part i development of a forward tilted cold front and a warm occlusion abstract analysis of observations and the fifth generation pennsylvania state university national center for atmospheric research psu ncar mesoscale model mm5 are used to study the development of a forward tilted cold front off the coast of washington state the vertical velocity associated with the cold front produced a wide cold frontal rainband in the early stage of development the midtropospheric baroclinic zone or upper cold front moved forward with time over the warm sector to produce a structure similar to a split front the movement of the upper cold front was due to horizontal transport and frontogenetical propagation the frontogenetical propagation was produced by a combination of tilting and diabatic frontogenesis which resulted in a negative positive couplet of frontogenesis straddling the baroclinic zone the lower tropospheric cold front eventually caught up with the warm front to form a classical warm occlusion in the initial occluding process the converging frontal zones tilted i

correlation and interpretation of paleosols and loess across european russia and asia over the last interglacial glacial cycle abstract loess paleosol sequences of the last interglacial glacial cycle are correlated from european russia to central siberia and the chinese loess plateau during cold periods represented by marine oxygen isotope stages ois 2 and 4 loess deposition dominated in the russian plain and the loess plateau in central siberia loess deposition took place also but five to seven thin weakly developed paleosols are identified in both stages ois 3 in the chinese loess plateau near yangchang consists of a loess bed that is flanked by two weakly developed paleosols at kurtak siberia ois 3 is represented by two distinct stacked paleosols with no loess bed separating the paleosols in the russian plain ois 3 consists of a single possibly welded paleosol representing upper and lower stage 3 climates brunisols and chernozems dominate the profiles in china and siberia whereas regosols luvisols and chernozems are evident in the northern and southern russian plain respectively ois 5 is represented in china and the russian plain by pedo complexes in a series of welded soils whereas in contrast the kurtak site consists of six paleosols with interbedded loess the paleosols consist largely of brunisols and chernozems although the three areas examined have different climates geographical settings and loess source areas they all had similar climate changes during the last interglacial glacial cycle

magnetism of loess palaeosol sequences recent developments abstract investigation of the global loess record primarily as a palaeoclimatic archive continues unabated one important aspect of this research effort is the determination of the magnetic properties of the loess itself and of the palaeosols developed within it in earlier work these have provided a record of major long term past climatic changes however recent studies are now revealing sub milankovitch signals with teleconnections from the chinese loess plateau clp to the greenland and antarctic ice caps as well as to climate related events in sediments recovered from the north atlantic these high resolution profiles cover to the last 130 000 years however progress is also being made in extending the record down below the loess sensu stricto of the clp into the so called red clay so that the aeolian record can now be carried back beyond 7 ma bp several authors have attempted to obtain quantitative estimates of palaeoprecipitation by comparing magnetic susceptibility of palaeosols with values for modern soils although the broad picture is qualitatively clear wetter interglacials dryer glacials the actual quantitative values provided by the various techniques differ significantly in the classic chinese sites palaeosols are always magnetically enhanced due to in situ pedogenic processes however evidence is now emerging to indicate that this is not the only magnetoclimatological model in cases such as siberia where wind vigour dominates over pedogenesis the opposite pattern is found with magnetic susceptibility minima in palaeosols this also occurs in situations where the sediments are water logged for significant amounts of time leading to gleying and concomitant loss of magnetic minerals the use of magnetic remanence as a geomagnetic polarity clock requires caution early interpretations were acceptable for establishing broad chronological control however recent scrutiny suggests that remanence lock in may be delayed by as much as 20 000 years furthermore synthetic magnetostratigraphies modelled on the basis of realistic sediment characteristics indicate that there are limits to the amount of geomagnetic detail likely to be resolved this seems to be the case for the blake event which manifests itself in a very variable way at different sites in the clp

recognition genesis and evolution of manganese ore deposits in southeastern china abstract manganese ore deposits are common in the falang formation of ladinian age middle triassic southeastern yunan china the deposits containing manganese oxide and manganese carbonate ores are not metamorphic in origin and they commonly contain bioclasts concentric ring structures are clearly observed in oolitic and pisolitic manganese ores an integrated approach using sedimentology and paleoenvironment analysis provides new insight into the genesis of these ores systematic research has been conducted on typical deposits dounan yanzijiao laowu tujichong using cathodoluminescence and scanning electron microscope techniques which allow elucidation of changes in laminated microtextures at the mm m scale preliminary results show that manganese enrichment in triassic deposits of this region may be related to microbial activity and mineralization was a consequence of bacterially mediated diagenetic reactions in addition findings of biodetritus in the manganese ore indicate that manganese ore is close to the redox level the concentration of manganese in solution and in precipitates in triassic is controlled by bacterial oxidation and redox conditions corresponding to sea level changes during the ladinian

mineralogy geochemistry and origin of mn in the high mn iron ores bahariya oasis egypt abstract although mn is one of the major impurities in the economic iron ores from the bahariya oasis information on its modes of occurrence and origin is lacking in previous studies high mn iron ores from el gedida and ghorabi nasser iron mines were subjected to detailed mineralogical geochemical and petrographic investigations using x ray diffraction xrd infrared absorption spectrometry ir raman spectroscopy x ray fluorescence xrf scanning electron microscopy sem and electron probe microanalyzer epma to clarify the modes of occurrence of mn in these deposits and its origin the results showed that the mno 2 contents range between 0 03 and 13 9 wt three mineralogical types have been identified for the mn in the high mn iron ores including 1 inclusions within the hematite and goethite and or mn accumulated on their active surfaces 2 coarse grained and crystalline pyrolusite and 3 fine grained cement like mn oxide and hydroxide minerals bixbyite cryptomelane aurorite romanechite manjiroite and pyrochroite between the fe bearing minerals the mn carbonate mineral rhodochrosite was detected only in the ghorabi nasser high mn iron ores since ir patterns of low mn and high mn samples are almost the same a combination of xrd analysis using non filtered fe k radiations and raman spectroscopy could be the best way to identify and distinguish between different mn minerals assuming that both fe and mn were derived from the same source the occurrence of high mn iron ores at the base of the stratigraphic section of the deposits overlain by the low mn iron ores indicated a supergene origin of the studied ores by descending solutions the predominance of mn oxide and hydroxide minerals in botryoidal shapes supports this interpretation the small grain size of mn bearing minerals as well as the features of microbial fossils such as spherical elliptical and filamentous shapes of the fe bearing minerals suggested a microbial origin of studied iron ores variations in the distribution and mineralogy types of mn in the iron ores of the bahariya oasis demanded detailed mineralogical and petrographic characterizations of the deposits before the beneficiation of high mn iron ores from the bahariya oasis as feedstock for the ironmaking industries in egypt by magnetizing reduction high mn contents especially in the ghorabi nasser iron ore and occurrence of mn as inclusions and or accumulated on the surface of the fe bearing minerals would suggest a possible utilization of the high mn iron ores to produce ferromanganese alloys

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

spatial variations of magnetic susceptibility of chinese loess for the last 600 kyr implications for monsoon evolution 1 we examine spatial variations in magnetic susceptibility ms over the loess plateau in china based on 50 sections in order to identify spatial changes in monsoon climate at key glacial interglacial and interstadial intervals for the last 600 kyr the results indicate strong coherence between ms variations during the interglacial periods and present day precipitation and temperature patterns this suggests that the strength of the summer monsoon had a dominant influence on the ms signals in soils through modulating pedogenic intensity the distribution of ms during glacial periods is characterized by weak s n gradients and rough w e zonal patterns indicating a negligible effect of the summer monsoon interstadial patterns are intermediate between the glacial and interglacial ones interglacial patterns for the last 600 kyr are essentially similar suggesting that the climate regime during these periods has not undergone significant changes and that the east asian summer monsoon has remained the main moisture carrier our estimates of the relative amplitudes of climate oscillations during these time slices are consistent with earlier paleoclimate studies these data associated with the available susceptibility based climofunctions may be used to estimate spatial changes of paleorainfall and paleotemperature for these key periods and hence to test climate models

influence of orbital parameters on pleistocene loess deposition in central alaska few long proxy climatic records are available from terrestrial locations the isotope records of pleistocene climate change found in marine cores reflect worldwide ice volume and temperature changes forced by variations in the earth s orbital geometry comparable terrestrial records are rare loess wind deposited silt is perhaps the closest terrestrial analogue to marine sediments in that both result from more or less continuous deposition of fine grained sediment here we examine the hypothesis that mag netic susceptibility variations through loess sections reflect climate forcing we statistically tested cross correlations between high precision orbitally tuned marine oxygen isotope curves recording the past 250 000 yr bp and magnetic susceptibility profiles through a thick loess section in central alaska highly significant p 0 0001 correlations indicate strong thick palaeosols formed in arctic loess during early parts of interglacial periods correspond ing to isotope stages 7 and 5 thinner soils formed during interstadial events corresponding to early stage 7 and stage 3 autocorrelation and time series analysis of the loess data show spectral peaks at 125 000 41 000 and 23 000 yr bp showing for the first time that terrestrial orbital periodicities influenced and are recorded in proxy climatic data from terrestrial aeolian deposits at high latitudes

magnetic indicator of global paleoclimate cycles in siberian loess paleosol sequences abstract the loess paleosol sequences of china siberia alaska and many other regions along with lake sediments and glaciers provide the only accurate paleoclimatic terrestrial records for intervals of thousands to hundreds of thousand years the frequency dependence fd of magnetic susceptibility ms in such sequences has become the leading parameter for analyzing climatic change and milankovitch astronomical periodicity in siberian sequences it is always higher in soil horizons than in loess the enhanced fd parameter in soils is associated with ferromagnetic minerals mostly magnetite produced during pedogenesis the ms and fd parameters of 670 samples from five sections in siberia are reported here inter section correlation is used to produce a combined fd time series for the studied sections chronological control is established by absolute dating and stratigraphic correlation spectral analysis of the fd time series reveals the presence of milankovitch signals at 100 kyr eccentricity 40 kyr obliquity and 23 kyr precession and demonstrates that siberian loess paleosol sequences are excellent continental recorders of long term paleoclimatic changes this suggests that the fd parameter can potentially be used more widely for evaluation of climate periodicity in loess paleosol sequences in other parts of the world

vertical structures of precipitation in cyclones crossing the oregon cascades abstract the vertical structure of radar echoes in extratropical cyclones moving over the oregon cascade mountains from the pacific ocean indicates characteristic precipitation processes in three basic storm sectors in the early sector of a cyclone a leading edge echo lee appears aloft and descends toward the surface updraft cells inferred from the vertically pointing doppler radial velocity are often absent or weak in the middle sector the radar echo consists of a thick vertically continuous layer extending from the mountainside up to a height of approximately 5 6 km that lasts for several hours when the middle sector passes over the windward slope of the cascades the vertical structure of the precipitation exhibits a double maximum echo dme one maximum is associated with the radar reflectivity bright band the second reflectivity maximum is located approximately 1 2 5 km above the bright band the secondary reflectivity maximum aloft does not appear until the middle sector passes over the wi

environmental magnetic study of a xeralf chronosequence in northwestern spain indications for pedogenesis article i nfo magnetic enhancement of a and b horizons during soil development is a common phenomenon to better understand the exact mechanism for the magnetic enhancement especially the mineral transformation pathways systematic rock magnetic studies were conducted on a xeralf chronosequence in northwestern spain a positive correlation was found between the average grain size and the concentration of pedogenic maghemite particles with the exception of some a horizons in which multiple factors seem to influence the nature and concentration of neoformed ferrimagnets it is argued that the interaction between the positively charged iron oxides and the anionic ligands present in the solution of these acidic soils plays an important role in this respect the time trends of the average grain size of pedogenic ferrimagnets and the strong correlation between the concentrations of hematite and maghemite in the magnetically enhanced horizons a and b are consistent with the hypothesis of a gradual formation of maghemite later converted into hematite via a precursor most likely ferrihydrite therefore this study provides strong evidence for the dynamic evolution of magnetic minerals upon pedogenesis

a composite analysis of winter season overrunning precipitation bands over the southern plains of the united states abstract this investigation presents an extensive analysis of precipitation bands associated with winter season over running events in the southern plains of the united states the primary motivation is an investigation of the relevance of conditional symmetric instability csi theory to overrunning precipitation events this is accomplished by means of a statistical composite study of events of differing degrees of bandedness using synoptic sounding and national weather service radar data the composite study shows that it is difficult to distinguish between the environments of banded and nonbanded cases on the basis of individually examined shear and buoyancy parameters some statistically significant differences do occur when shear and buoyancy effects are combined in an evaluation of csi with more strongly banded events showing greater instability

microphysical properties of convectively generated fall streaks within the stratiform comma head region of continental winter cyclones abstractthis paper presents analyses of the microphysical structure of comma head stratiform precipitation in 14 continental cyclones focusing on fall streaks of hydrometeors produced by cloud top convective generating cells data were obtained at temperatures between 4 and 45 c using in situ instrumentation and the w band university of wyoming cloud radar all operated aboard the national science foundation national center for atmospheric research c 130 analyses are presented first for a case study of one cyclone followed by statistical analyses of the full dataset using radar based objective classifications the statistical percentile number concentrations averaged 1 9 times larger within the fall streaks compared to the regions between them and the corresponding ice water content and median mass diameter values averaged 2 2 and 1 1 times larger ice phase conditions were predominant within the stratiform precipitation with deposition and aggregation the primary ice growth mechanisms no distinc

instability characteristics of radar derived mesoscale organization modes within cool season precipitation near portland oregon abstractthe instability characteristics associated with different radar derived mesoscale organization modes are examined using six cool seasons of operational scanning radar data near portland oregon and operational sounding data from salem oregon additionally several years of microwave rain radar ka band vertically pointing radar data from portland and merwin washington are used to characterize the nature and occurrence of generating cells and fall streaks the combination of a new metric convective stratiform intermittency with the classification of radar reflectivity maps into convective and stratiform precipitation types was applied to periods when the freezing level was 1 4 km altitude this method distinguishes periods with embedded convective within stratiform mesoscale organization from those that were mostly convective or mostly stratiform mesoscale organization occurs in a continuum of states with predominantly stratiform structure occurring most frequently generating cells in the s

characteristics and genesis of maghemite in chinese loess and paleosols mechanism for magnetic susceptibility enhancement in paleosols abstract morphological characteristics and microstructures of magnetic minerals extracted from chinese loess and paleosols were investigated using powder x ray diffraction xrd and high resolution transmission electron microscopy hrtem our results indicate that maghemite in loess paleosol sequences was transformed from magnetite through oxidation of magnetite maghemite transformed from eolian magnetite during chemical weathering has low angle grain boundaries among maghemite nano crystals some nano crystalline maghemites with nanoporous texture resulted from microbe induced precipitation of magnetite or transformation of poorly crystalline ferric fe oxy hydroxides in presence of fe reducing bacteria aggregates of euhedral maghemite nano crystals were transformed from magnetite magnetosomes both microbe induced nanoporous magnetite and microbe produced magnetite magnetosomes are directly related to microbial activities and pedogenesis of the paleosols it is proposed that the formation of nano crystalline maghemite with superparamagnetic property in paleosol results in the enhancement of magnetic susceptibility although the total amount weight percent of magnetic minerals in both paleosol and loess units is similar our results also show that nano crystalline and nanoporous magnetite grains prefer to transform into maghemite in semi arid soil environments instead of hematite although hematite is a thermodynamically stable phase this result also indicates that a decrease in crystal size will increase stability of maghemite it is also inferred that surface energy of maghemite is lower than that of hematite

dynamics of cloud top generating cells in winter cyclones part iii shear and convective organization abstractcloud top generating cells gcs are a common feature atop stratiform clouds within the comma head of winter cyclones the dynamics of cloud top gcs are investigated using very high resolution idealized wrf model simulations to examine the role of shear in modulating the structure and intensity of gcs simulations were run for the same combinations of radiative forcing and instability as in part ii of this series but with six different shear profiles ranging from 0 to 10 m s 1 km 1 within the layer encompassing the gcs the primary role of shear was to modulate the organization of gcs which organized as closed convective cells in simulations with radiative forcing and no shear in simulations with shear and radiative forcing gcs organized in linear streets parallel to the wind no gcs developed in the initially stable simulations with no radiative forcing in the initially unstable and neutral simulations with no radiative forcing or shear gcs were exceptionally weak with no clear organization

organization and structure of clouds and precipitation on the mid atlantic coast of the united states part ii the mesoscale and microscale structures of some frontal rainbands abstract the mesoscale and microscale structures of the clouds and precipitation associated with a frontal system on the mid atlantic coast of the united states are investigated using radar reflectivity and doppler velocity data surface mesonet conventional surface upper air and microphysical data the frontal structure showed similarities to a warm occlusion with code air advection aloft preceding cold air advection at lower levels six rainbands were observed in association with the frontal system all of these rainbands developed within the region of coverage of the nws wsr 57 radar at cape hatteras north carolina two were upper level features associated with a prefrontal surge of cold air and the main push of cold dry air aloft these rainbands were similar in structure to prefrontal surge and wide cold frontal rainbands respectively observed on the pacific northwest coast the microphysical and small mesoscale structures of the wide cold frontal rainband are examined three of the rainbands

geochemical studies on permian manganese deposits in guichi eastern china implications for their origin and formative environments abstract permian manganese ore deposits are widely distributed in southwestern and eastern china guichi permian manganese district in southern anhui province central eastern china is currently the most important manganese metal producers in eastern china manganese ores mno 18 2 45 4 wt in guichi region occur in calcareous argillaceous and siliceous mn bearing sequence of the permian gufeng formation in contrast to mn bearing rocks the ores have higher mn fe p sr more than 1500 ppm and ni contents 480 ppm higher mn fe 5 and lan cen 2 values and lower co ni

manganese mineralogy and diagenesis in the sedimentary rock record oxidation of manganese ii to manganese iii iv demands oxidants with very high redox potentials consequently manganese oxides are both excellent proxies for molecular oxygen and highly favorable electron acceptors when oxygen is absent the first of these features results in manganese enriched sedimentary rocks manganese deposits commonly mn ore deposits which generally correspond to the availability of molecular oxygen in earth surface environments and yet because manganese reduction is promoted by a variety of chemical species these ancient manganese deposits are often significantly more reduced than modern environmental manganese rich sediments we document the impacts of manganese reduction and the mineral phases that form stable manganese deposits from seven sedimentary examples spanning from modern surface environments to rocks over 2 billion years old integrating redox and coordination information from synchrotron x ray absorption spectroscopy and x ray microprobe imaging with scanning electron microscopy and energy and wavelength dispersive spectroscopy we find that unlike the mn iv dominated modern manganese deposits three manganese minerals dominate these representative ancient deposits kutnohorite camn co 3 2 rhodochrosite mnco 3 and braunite mn iii 6mn ii o 8sio 4 pairing these mineral and textural observations with previous studies of manganese geochemistry we develop a paragenetic model of post depositional manganese mineralization with kutnohorite and calcian rhodochrosite as the earliest diagenetic mineral phases rhodochrosite and braunite forming secondarily and later alteration forming mn silicates

manganese ores in tunisia genetic constraints from trace element geochemistry and mineralogy abstract northern and central tunisia hosts few small scale stratiform and stratabound mn deposits low to medium in grade mn

introduction to and classification of manganese deposits of china abstract manganese mn ore deposits are widely distributed in china and can be divided into six types based on origin and subsequent modifications 1 sedimentary 2 volcanic sedimentary 3 metamorphosed 4 hydrothermally modified 5 hydrothermal and 6 supergene sedimentary and supergene mn ore deposits are economically the most important mn ore deposits and ore bearing sequences are distributed temporally from the proterozoic through the quaternary but they principally are middle proterozoic sinian cambrian ordovician devonian carboniferous permian triassic and quaternary ages the largest mn metallogenic periods in china are sinian and devonian in contrast to the widespread proterozoic cretaceous and oligocene mn deposits found elsewhere in the world mn bearing stratigraphic successions in china can be divided into six types of lithologic associations 1 black shale series 2 chert mudstone limestone 3 carbonate 4 mudrock carbonate 5 volcanic sedimentary and 6 epeirogenic clastic rock types the most important mn metallogenic regions in china are 1 yanliao 2 border of hunan sichuan guizhou hubei provinces 3 southern shaanxi and northeastern sichuan 4 middle guizhou and eastern yunnan 5 southwestern guangxi 6 southeast yunnan 7 hunan guangxi guangdong fujian and 8 xinjiang the most striking characteristics of mn ore deposits in china are the wide distribution in geological ages and variety of compositional types of ores such as fe mn b mn p mn co mn ca mn ca mg mn among others the primary mn ores of china are mainly mn carbonates

magnetic properties of loess deposits in australia and their environmental significance abstract there are vast dry areas in australia but few loess sections have been reported mackenzie s waterholes creek mwc profile in new south wales was the deepest and first dated loess profile in this paper various measurements of magnetic parameters from mwc were carried out and comparison was made with those of luochuan profile which lies in the central chinese loess plateau clp the types of magnetic minerals are similar to the clp magnetite maghemite limonite and hematite however the magnetic properties of the australian aeolian sediment are quite different frequency dependent magnetic susceptibility fd is rather high while values of magnetic susceptibility are low the relative content of hard paramagnetic magnetic components is much higher than clp whereas the content of maghemite and hematite is much less furthermore hard magnetic minerals increase with depth while soft maghemite decrease with depth maghemite is more sensitive than magnetite under pedogenic condition of waterlogged environments it increases along with enhancement of magnetic susceptibility in luochuan section however decreases in mwc profile this very likely indicates that the pedogenesic processes in mwc took place under an environment in which maghemite magnetite were unstable the modern annual precipitation in the mwc area is 924 mm which is about 300 mm higher than that in luochuan that extra moisture may lead mwc to exceed the stable range for maghemite magnetite those minerals therefore were gradually converted to more stable goethite causing magnetic susceptibility to decrease fe and mn nodules are abundant in the lower part of section implying mildly reducing conditions that allowed fe and mn to be mobilised and enriched in near the oxidation front indicating that under waterlogged and reducing conditions wind blown maghemite magnetite were transformed to iron hydroxides such as goethite limonite or other paramagnetic minerals resulting in reduced magnetic susceptibility the susceptibility from most of the section shows a generally positive relationship to the loess particle size and seems to fit the alaskan wind vigor model however fe chemical weathering and movement in mwc suggests that the precondition for the wind vigor model cannot be satisfied and that the susceptibility variation can only be explained by pedogenesis

non magnetic indicators of pedogenesis related to loess magnetic enhancement and depletion examples from the czech republic and southern siberia abstract we carried out a multiparameter investigation for non magnetic proxies of the intensity of pedogenesis in loess paleosol sections from two different climate settings dolni v stonice central europe and krasnogorskoye southern siberia the work was performed in order to clarify the problem of two opposite scenarios of magnetic susceptibility ms patterns in these two profiles the chinese model with magnetically enhanced paleosols and the siberian alaskan model with magnetically depleted paleosols the age constraints on the krasnogorskoye section were inferred from an independent correlation with the well dated dolni v stonice section based on ms and sediment color cie l and with the ms log from lake baikal the pedologic description of the loess paleosol sections and their correlation was considerably improved by the use of vis spectral proxies cie l reflectance in the red band their weathering intensity can be effectively characterized by diffuse reflectance spectroscopy drs and geochemical cec and rb sr proxies whereas the ms is strongly dependent on the type of soil chernozems vs brown soils the geochemical proxies in particular cec proved to be relatively independent of the soil type these parameters are less affected by region specific conditions than the ms signal the non magnetic proxies indicate relatively dissimilar climatic trends at the two sites during the last glacial interglacial cycle a long distance correlation based solely on the ms signal can be adversely affected by switching between the chinese and the siberian alaskan magnetic modes this having been observed at the krasnogorskoye section in general no single universal proxy of weathering or pedogenesis intensity would be applicable across broad regions or considerable climatic gradients paleoclimatologic interpretations of large regions should always be based on a carefully designed multi proxy approach

direct correlation of the marine oxygen isotope record with the chinese loess plateau iron oxide and magnetic susceptibility records abstract monsoons are a major feature of global atmospheric circulation and derive heat and moisture from the oceans and transports much of that heat and moisture to nearby continents the east asian monsoon derives its heat and moisture from the eastern equatorial pacific and transfers it to southeast asia and the loess plateau of central china in order to examine the phasing of marine and terrestrial climatic events associated with this monsoon we have analyzed a core from the western pacific v21 146 downwind from the loess plateau iron oxides and magnetic susceptibility were analyzed because they have been used as loess plateau paleoclimate proxies comparison of temporal changes in both iron oxide and susceptibility signals in v21 146 to the well known luochuan loess section reveals an excellent correlation both in the timing and direction of the variations comparison of our loess plateau paleoclimatic proxies in v21 146 to previously published oxygen isotope data from this core suggests that through marine isotope stage mis 9 coincident with loess plateau interglacial soil level 3 s3 ocean temperature increases and the onset of monsoonal conditions on the loess plateau were synchronous however for mis 11 12 interglacial glacial s4 l5 changes in the ocean appear to significantly lead those on land and there is a lack of correlation between mis 13 and s5 these out of phase events may be a response to a reorganization of the ocean atmosphere system as indicated by changes in the 13c record it has previously been suggested that changes in eolian flux record eolian transport from the loess plateau but we find little correlation between eolian flux and our loess plateau proxies suggesting that some of the eolian sediments were derived from outside the loess plateau

surface convergence induced by cold fronts aloft and prefrontal surges abstract the magnitude of surface convergence produced by the movement of cold fronts aloft and prefrontal surges is derived by applying the linear divergence equation to observed surface pressure traces for pacific northwest warm occlusions and from a mesoscale model simulation of a warm occlusion like structure in the central united states convergence values of approximately 10 4 s 1 are found to be generated locally for periods of about 1 h yielding vertical displacements of 10 50 hpa it is hypothesized that such convergences should noticeably enhance condensation rates in the widespread lower stratiform clouds associated with warm occlusions and could be a key mechanism for the triggering of squall lines by cold fronts aloft in cyclones in the central united states

the occurrence of irregular ice particles in stratiform clouds abstract recent studies that have classified ice particles from airborne imaging probe data have concluded that the vast majority of ice particles in stratiform precipitation systems are of an irregular shape this conclusion stands in contrast to the findings from microscope observations of snow particles at the ground during the improvement of microphysical parameterization through observational verification experiment from november to december 2001 in the oregon cascade mountains improve 2 which show that most snow crystals either single crystals or the component crystals of snow aggregates are readily identified as regular types within established crystal classification systems this apparent contradiction is rectified by examining the definition of the term irregular as applied to ice particles and by considering limitations of different methods for observing ice particles it is concluded that the finding of the airborne probe based studies is a consequence of both limitations of the observin

the mesoscale and microscale structure and organization of clouds and precipitation in midlatitude cyclones iv vertical air motions and microphysical structures of prefrontal surge clouds and cold frontal clouds abstract the vertical air motions and microphysical structures of the clouds associated with two mesoscale precipitation systems in the pacific northwest are examined using rawinsonde aircraft and vertically pointing doppler radar data a rainband associated with a prefrontal surge of cold air aloft was found to consist of deep 3 4 km convective cells natural seeding by cirrostratus cloud spread ice crystals throughout the rainband all of the precipitation growth observed took place through ice phase processes much of the moisture necessary for precipitation growth entered the rainband at low levels in the form of vapor and condensate associated with widespread stratiform cloud a weakly organized cold frontal precipitation area was found to consist of snow trails originating from shallow 1 2 km convective cells in a seeder zone above 5 5 km altitude below this level the trails swept through a feeder zone which consisted of stratiform cloud downdrafts observed in one region of the feeder zon

characteristics of the devonian xialei manganese deposit guangxi zhuang autonomous region china abstract the xialei mn deposit occurs in the late devonian famenian wuzhishan formation and consists of three ore horizons composed of three ore types 1 mn carbonate 2 mn silicate mn carbonate and 3 mn oxide mn silicate mn carbonate ore beds consist of mn carbonates and associated rhodonite stilpnomelane actinolite chlorite mn epidote biotite and mn fe antigorite these minerals are mixed with each other and form thin beds bands pelletal and pisolitic grains and horizontal or wavy laminae abundant oolitic and pisolitic grains in mn ore beds show distinct boundaries and nuclei of mn carbonate and mn silicate minerals rarely clastic grains the ore deposit is divided into three zones 1 an inner zone composed of mn carbonate silicate and oxide minerals 2 a transitional zone consisting of mn carbonate and stilpnomelane and 3 an outer zone characterized by mn carbonate argillaceous limestone at the base of the ore beds has a mean 13 c pdb of about 0 0 indicating that the carbon was derived from seawater bicarbonate the 13 c pdb of mn carbonate ranges from 2 8 to 14 3 mean 7 1 indicating that the carbon was derived from both degradation of organic matter and seawater bicarbonate ores formed in a trough on a carbonate platform primary sedimentary mn carbonates precipitated from alkaline and negative eh waters in the diagenetic zone of sulfate reduction which occurred either during shallow burial or at the seafloor oolites and pisolites formed by sedimentary processes on the seafloor in places deposits were reworded and transported by gravity flow processes the region where these sedimentary diagenetic mn deposits formed was intruded by magma and hydrothermal fluids with dissolved metals leached from volcanic and sedimentary rocks ascended along fractures the mn silicate mn carbonate ore may have been produced by contact metamorphism of primary carbonate ore and metal sulfides deposited by hydrothermal fluids which overprinted the primary sedimentary ore

mesoscale circulations initiated by melting snow a linearized model is used to examine the dynamical effects of a mesoscale temperature perturbation in the lower troposphere the perturbation is a result of nonuniform cooling of the environment by melting snow an organized mesoscale thermal circulation develops with strong vertical motions in the interior outflow at low levels and a return flow at upper levels this circulation is similar to a sea breeze circulation but is forced by an elevated horizontal temperature gradient a possible application to the problem of observed enhanced precipitation regions near a rain snow boundary is considered

vertical cloud structure in a midlatitude cyclone from a 94 ghz radar abstract the vertical structure of clouds associated with a developing midlatitude cyclone was studied using a 94 ghz cloud radar accompanied by a host of other surface based instruments and rawinsondes a thickening cirrostratus deck was observed as the storm approached as the storm drew near low level moisture advection increased and a drizzle producing stratus deck quickly developed a rather lengthy period of light to occasionally moderate rain accompanied the passage of the storm when the storm pulled away to the northeast and the rain ended the character of the stratus deck changed markedly with no drizzle production evident other cloud features observed included generating cells and their resultant fallstreaks and an eye that apparently accompanied the passage of a negatively tilted upper level trough as evidenced by measurements from a 50 mhz wind profiler located near the cloud radar rawinsonde measurements showed that the cloud radar also traced the descent of the melting layer satel

genetic diversity of manganese deposition in the terrestrial geological record terrestrial manganese deposits formed by hydrothermal sedimentary and supergene processes ancient analogues of modern oceanic hydrothermal deposits formed in spreading centre and subduction related settings and those deposited from terrestrial hot springs are discussed sedimentary mn oxide deposits formed in shallow water at the margins of stratified oceans above the redoxcline during sea level changes mn carbonate deposits probably formed by diagenesis through mn oxyhydroxide reduction coupled with organic matter oxidation climatic variation and basin water stratification responsible for mn concentration were manifestations of atmospheric coz content prompted by tectonism supergene manganese enrichment in continental weathering profiles was mainly dictated by climate topography and drainage systems manganese deposits of diverse genetic types occur in the terrestrial geological record roy 1981 these were produced by direct hydro thermal activity sedimentary processes and continental weathering although the processes may be interrelated each involves distinct mechanisms that place the deposits into specific genetic types some of these processes are best understood in preset day depositional sites the ancient environments were determined by the intensity and style of tectonism volcanism and hydrothermal activity the composition of the atmosphere and the hydrosphere and the development of the biosphere which all varied with time it is my intention to unfold the total panorama of the environmental evolution during different time envelopes that produced a variety of manganese deposits in the past only major deposits and those providing distinctive evidence of their environment of deposition will be considered here

origin of manganese giants sea level change and anoxic oxic history inversely graded pisolites of manganese oxide in the mid cretaceous manganese giant at groote eylandt australia were deposited during a regional fall in sea level as indicated by their relationships to wave cut benches dissolved manganese was concentrated in relatively anoxic waters of the intracratonic basin during a marine transgression and precipitated as oxides and carbonates during a regression ore bodies ultimately formed by concentration of abundant particulate manganese by a tidal lag mechanism

rock magnetic record of the last glacial interglacial cycle from the kurtak loess section southern siberia summary detailed rock magnetic investigations grain size determination and x ray diffraction were carried out on loess and buried soils of the last glacial interglacial cycle from kurtak southern siberia the susceptibility and the sand fraction of 63 m fluctuate in parallel suggesting that the higher susceptibility values in the loess horizons are mainly associated with the coarse size fraction the frequency dependence of the magnetic susceptibility of the loess and buried soils is very low and uniform indicating the absence of superparamagnetic grains and negligible pedogenically induced enhancement of magnetic susceptibility the magnetic assemblage is dominated by multidomain like magnetite grains maghemite and haematite are also present in the buried soils and loess horizons goethite may have been formed from gleying or waterlogging processes under a cooler and more humid climate the coarse magnetite grains which contribute significantly to magnetic susceptibility are probably carried by valley winds and derived from local sources thus the coarser magnetite grains with higher susceptibility values in the loess horizons could mainly reflect stronger wind intensity during cold and semi arid conditions and the consequent ease with which dense magnetite particles can be transported the lower susceptibility values in the buried soil horizons are mainly caused by weaker wind intensity during interglacial and interstadial periods although post depositional processes associated with gleying modifications are also partially responsible for the observations

magnetoclimatology teleconnection between the siberian loess record and north atlantic heinrich events new environmental magnetic data from loess and paleosol successions in outcrops in the upper reaches of the ob river drainage southern siberia track the major climatic variations over the last glacial interglacial cycle profiles of magnetic susceptibility and alternating deposition of loess and soil formation events correspond to oxygen isotope stages 1 5 the magnetic susceptibility data in association with the stratigraphic succession confirm that the wind vigor magnetoclimatological model is a viable alternative to the classic pedogenic model interpretation of magnetic susceptibility data from loess paleosol successions must therefore consider eolian dynamics available source materials and transport directions in addition to pedogenic processes rapid magnetic fluctuations are also observed these are identified for the first time in siberian records as the signature of the abrupt cold pulses responsible for the heinrich layers in north atlantic marine sediments the data thus form a component of climatic teleconnections across the northern hemisphere allowing correlations to be made among 1 siberian magnetic susceptibility stratigraphy 2 data recorded from other loess paleosol successions in china european russia europe and north america 3 north atlantic ice rafted detritus and 4 sea surface temperatures derived from molecular stratigraphy of marine sediments off the northwest coast of africa

nanhuan manganese deposits within restricted basins of the southeastern yangtze platform china constraints from geological and geochemical evidence abstract the nanhuan manganese deposits in the southeastern yangtze platform occur in the black shale series in the lower part of the datangpo formation in order to constrain the genesis of the deposits a detailed study was undertaken that involved field observations major and trace element analyses organic carbon analyses and isotope analyses c o s the major findings are as follows 1 the ore bearing rock series morphology of the ore bodies and characteristics of ores in several deposits are similar the ore minerals are rhodochrosite and manganocalcite the gangue minerals are mainly quartz feldspar dolomite and illite minor apatite and bastnaesite occur in the manganese ores 2 the ores are enriched in ca and mg whereas they are depleted in si al k and ti compared to wall rocks the ores normalized to average post archean australian shale paas are enriched in co mo and sr the chondrite normalized rare earth element ree patterns for ores and wall rocks are between those of typical hydrogenous and hydrothermal type manganese deposits additionally the ores have positive ce anomalies with an average ce ce of 1 23 and positive eu anomalies with an average eu eu of 1 18 normalized to paas 3 the average content of organic carbon is 2 21 in the samples and the average organic carbon isotopic value 13cv pdb is 33 44 the average inorganic carbon isotopic value 13cv pdb of carbonates in gucheng is 3 07 while the values are similar in the other deposits with an average of 8 36 the oxygen isotopic compositions 18ov pdb are similar in different deposits with an average of 7 72 4 the sulfur isotopic values 34sv cdt of pyrite are very high and range from 37 9 to 62 6 average of 52 7 which suggests that the pyrite was formed in restricted basins where sulfate replenishment was limited the sulfate concentrations in the restricted basins were extremely low and enriched in 34s which resulted in the very high 34s values for the pyrite that formed in the manganese deposits therefore a terrigenous weathering origin for manganese can be excluded otherwise the sulfate would have been introduced into the basins together with terrigenous manganese which would have decreased the 34s values of pyrites the manganese which originated from hydrothermal processes was enriched in the restricted and anoxic basins and then it was oxidized to manganese oxyhydroxide in the overlying oxic waters whereby the products precipitated into the sediments the manganese oxyhydroxide in the sediment was then reduced to mn2 and released to the pore waters during the process of diagenesis some organic carbon was oxidized to co32 which made the depletion of 13c in manganese carbonates therefore we suggest that the nanhuan manganese deposits are hydrothermal sedimentary diagenetic type deposits

multiple origins and interpretations of the magnetic susceptibility signal in chinese wind blown sediments abstract in most chinese loess paleosol sequences high magnetic susceptibility values are found in the soil horizons with low values in the loess layers the susceptibility signal has been widely used as a proxy climatic indicator however both the causes and mechanisms which control susceptibility still remain controversial our recent studies challenge some earlier interpretations of the magnetic susceptibility signal in chinese wind blown sediments first the prevailing hypothesis of pedogenic origin cannot totally account for the susceptibility variations in many sections second in some cases the principal carrier of the magnetization seems not to be the ultrafine pedogenic minerals rather coarse lithogenic magnetic minerals derived from local sources can also contribute significantly to the susceptibility signal finally not all the chinese soils have higher susceptibility values than that of loess or sand layers opposite relationships do exist it is concluded that the source and causes of susceptibility may be different from site to site or even at different times at a given site any single hypothesis cannot completely account for the susceptibility variations in the chinese loess plateau and its surrounding regions besides the previous explanations of carbonate leaching pedogenic processes and organic decomposition the contribution of source materials to magnetic susceptibility must also be taken into account

aircraft observations of the origin and growth of very large snowflakes a new high volume precipitation probe capable of optically imaging particles up to about 5 cm was flown in a winter storm during the second canadian atlantic storms program casp ii dendritic crystals originating aloft in a region of weak convective instability were tracked and observed to aggregate into 4 5 cm snowflakes within an isothermal layer near 0 c the region containing the very large snowflakes was characterized by high radar reflectivities and rapid accumulation of snow at the surface

fault zone evolution and its controls on ore grade distribution at the jian cha ling gold deposit western qinling region central china the jian cha ling gold deposit is sited in folded and faulted palaeoproterozoic rocks of the uplifted mian lue yang block adjacent to the mianlue suture zone within the west qinling mineral province along the northern margin of the south china craton early mesozoic gold mineralization at jian cha ling which has a pre mined resource of about 536 000 oz au is controlled by the so called f145 fault the fault is a generally steeply n dipping wnw trending deformation zone that is the result of dislocation along bedding planes early foliation and axial planar surfaces of regional folds the fault zone marks the contact between serpentinized lower greenschist facies dunites harzburgites and minor gabbroic units in the footwall and a metasedimentary sequence in the hanging wall that is dominated by metadolomite metalimestone and phyllitic schists brittle ductile deformation partitioning of strain along pre existing zones of weakness and the formation of intrashear zone lozenges contributed to the development of a complex fault zone geometry variations in both dip and strike of discrete dislocation surfaces related to oblique sinistral reverse movement along the f145 fault zone focussed auriferous hydrothermal fluids along three dominant structural orientations gold was preferentially deposited along shallowly nne dipping and shallowly to moderately nnw dipping fault segments and is also associated with shallowly wsw dipping dolomite dominated vein sets disseminated economic gold grades 4 g t au are restricted to the footwall ultramafic rocks to within about 5 to 10 m of the contact with the hanging wall gold is related to laminated realgar and orpiment bearing sheeted veins and hydrothermal breccias as well as slickolites and fault gouge gold bearing vein sets are located within the relatively undeformed ultramafic intrashear zone lozenges gold related alteration is dominated by extremely fine grained arsenic bearing sulphide minerals and dolomite with additional white mica and clay minerals the structural setting of the deposit combined with published data on the geological evolution of the west qinling mineral province suggest that the jian cha ling gold deposit developed in an uplifted basement block during the final phases of northward subduction and suturing of the south china craton with the south qinling orogen along the mianlue suture zone during the changeover from a compressional to transpressional tectonic regime in late triassic to middle jurassic times

evolution of a cold front encountering steep quasi 2d terrain coordinated aircraft observations on 8 9 december 2001 during improve 2 abstract research aircraft observations from the 8 9 december 2001 case of the second phase of the improvement of microphysical parameterization through operational verification experiment improve 2 describe the evolution of a wide cold frontal rainband wcfr during its eastward advance from the pacific coastline to a point 200 km inland over the cascade mountains of oregon this analysis has two objectives first to illustrate the rapid weakening of the circulation associated with a landfalling wcfr and the relationship of these changes to terrain induced airflow modifications and second to quantify the degree to which this weakening impacted cloud microphysical properties such as liquid water content ice particle concentrations and precipitation rate the kinematic structure of the wcfr is detailed using doppler radar observations from a noaa p 3 aircraft while some concomitant cloud microphysical properties are documented using flight level measurements from the university of washington convai

frontogenesis and symmetric stability in a major new england snowstorm abstract synoptic and doppler radar data are used to study the roles of large scale frontogenetical forcing and of moist symmetric instability in the new england snowstorm of 5 6 december 1981 associated with an explosively intensifying cyclone offshore radar reflectivity patterns showed a tendency toward banded structure particularly near the leading northwestern edge of the storm only a minor portion of the snowfall however was associated with this pronounced bandedness from a set of constant pressure analyses the frontogenetical forcing was measured from the variation along the temperature gradient of the geostrophic wind component in the direction of this gradient over southeastern new england maximum forcing found near 500 mb at the outset of the storm descended to the layer between 850 and 700 mb 24 h later magnitudes were 3 7 10 10 deg m 1 s 1 observed rates of strengthening of temperature gradient were less than half this value implying relative adiabatic cooling in the rising

comparison between datangpo type manganese ores and modern marine ferromanganese oxyhydroxide precipitates based on rare earth elements abstract datangpo type sedimentary manganese deposits which are located in northeastern guizhou province and its adjacent areas are mn carbonate type deposits hosted in black carbonaceous shale that represent a series of medium to large deposits containing a huge tonnage of reserves paas normalized rare earth element distribution patterns of manganese ores record hat shaped rey ree y plots characterized by pronounced middle rare earth element enrichment evident positive ce anomalies weak to strong positive eu anomalies and negligible negative y anomalies these rey geochemical characteristics are different from those of country rocks and record the processes and features of sedimentation and diagenesis manganese was precipitated as mn oxyhydroxide particles in oxidized water columns with the sorption of a certain amount of rare earth elements subsequently transforming from mn oxyhydroxides to rhodochrosite and redistributing rey in reducing alkaline pore water during early diagenesis a number of similarities can be observed through a comparison of datangpo type manganese ores and modern marine ferromanganese oxyhydroxide precipitates based on their rare earth elements the precipitation of datangpo type manganese ores is similar to that of hydrogenetic crusts and nodules based on their positive ce anomalies and relatively higher total rey concentrations however several differences also exist compared to hydrogenetic crusts and nodules datangpo type manganese ores record smaller positive ce anomalies lower total rey concentrations unobvious fractionation between y and ho and weak to strong positive eu anomalies these were caused by quicker sedimentary rates in the oxic water columns of the shallower basin after which pore water became strongly reducing and alkaline due to the degradation of organic matter in the early diagenetic stage in addition compared to typical deposits in the world datangpo type manganese ores are similar to hydrogenetic deposits and different than hydrothermal deposits all of these characteristics of manganese ores indicate that datangpo type manganese ores the principal metallogenic factors of which include oxidation conditions during deposition and reducing conditions during early diagenetic stages represent hydrogenetic deposits

the improve 1 storm of 1 2 february 2001 part ii cloud structures and the growth of precipitation abstract on 1 2 february 2001 a strong cyclonic storm system developed over the northeastern pacific ocean and moved onto the washington coast this storm was one of several that were documented during the first field phase of the improvement of microphysical parameterization through observational verification experiment improve in the 1 2 february case soundings and wind profiler measurements showed that a wide cold frontal rainband was coincident with the leading edge of an upper level cold front in a classical warm occlusion ground based radar observations revealed the presence of subbands within the wide cold frontal rainband and two layers of precipitation generating cells within this rainband one at 5 7 km msl and the other at 9 10 km msl the lower layer of generating cells produced fallstreaks that were traced from the cells down to the radar bright band at 2 km msl observations suggest a connection between the subbands and the lower layer of generating cells a research aircraft equipped

organization and structure of clouds and precipitation on the mid atlantic coast of theunited states part iii the evolution of a middle tropospheric cold front abstract the development of a complex middle tropospheric frontal structure the various weather associated with itsprogression across the united states and its role in the production of precipitation in the eastern third of theunited states are examined the frontal structure consisted of two features a middle tropospheric cold front associated with a strong 500mb short wave that moved eastward from the pacific ocean and a leeside warm front that formed in a northwardsloping zone of warm air advection associated with a trough in the lee of the rocky mountains the middletropospheric cold front overtook the leeside warm front to produce a warm occlusion like structure in the middletroposphere as this system progressed eastward across the united states precipitation from light rain to convectiveshowers occurred along the leading edge of the middle4ropospheric frontal zone well ahead of a decayingsurface trough this study highlights the importance of middle tropospheric frontal structures in the org

the process of formation of manganese carbonate deposits hosted in black shale series the two most important types of manganese deposits in china are sedimentary and supergene which account for 71 and 15 percent of the total manganese reserves respectively according to the host rock associations sedimentary manganese deposits can be classified into 1 a mud rock type 2 a black shale series type 3 a carbonate rock type and 4 a chert limestone mudstone type the black shale series type manganese deposits account for 48 percent of the total manganese reserves and are large or medium sized deposits the black shale series or dark colored sedimentary association consists of dark colored mudrock chert carbonate rocks rich in sulfides and organic matter c organic or 1 the term black shale series type manganese deposits is a general name for all manganese deposits hosted in black shale black chert black siliceous shale dark gray limestone etc black shale series type manganese deposits are distributed in 13 stratigraphic horizons from middle proteozoic to early triassic they can be divided into three subtypes 1 a black shale subtype 2 a black chert siliceous shale subtype and 3 a dark gray limestone subtype subtype 1 consists mainly of primary mn carbonate ores subtypes 2 and 3 consist mainly of mn containing limestones weathering and leaching processes can change the mn limestones into mn oxide ores which form large and high quality supergene deposits for example the mugui and dongxiangqiao deposits manganese carbonate ores hosted in the black shale series consist mainly of rhodochrosite calcio rhodochrosite kutnohorite manganocalcite mn containing calcite mn containing dolomite etc the ores are black dark gray light gray yellowish and pink in color and have banded laminated massive oolitic spotted and brecciated structures commonly changes in the ore bearing sequences show from bottom to top 1 black shale series 2 mn carbonate ore bed 3 light colored rocks this indicates that ore beds formed in the transition from reduced to slightly oxidized and from weakly alkaline to alkaline conditions the evolution of the ore bearing sequence indicates that manganese mineralization occurred during the early stage of regression the important mn carbonate deposits hosted in the black shale series resulted from three main processes during formation concentration in seawater precipitation from seawater and enrichment in the sediments anoxic conditions are a basic factor for manganese concentration in seawater a weak oxic and alkaline environment is favorable for mn carbonate precipitation and microbiological activities play an important role for early diagenetic enrichment of manganese in the deposits

characteristics and origin of the middle proterozoic dongshuichang chambersite deposit jixian tianjin china abstract the jixian type boron manganese b mn deposits include both chambersite and rhodochrosite deposits from which dongshuichang is economically the best chambersite deposit although the ore bodies of the region are relatively small they contain a rare b mn ore that is scientifically significant chambersite mn 3 b 7 o 13 cl is a rare mineral discovered as a mineral in 1957 and as an ore in 1971 at the dongshuichang deposit near jixian tianjin city the deposit forms a monocline with a southwest dip and covers an area of 2 km 2 in the mine area the gaoyuzhuang formation the upper member of the middle proterozoic changcheng system consists mainly of stromatolitic and muddy dolostone with b mn bearing siliceous shale and dark gray dolostone individual ore lenses range in length from 1 to 4 m with a mean thickness of 0 25 m the ores can be divided into high grade and low grade the former is composed of spindle and granular chambersite aggregates and the latter of spheroidal chambersite in dark gray micritic dolostone the center of spheroids is commonly composed of micritic and columnar chambersite dolomite clay minerals and organic matter around which columnar chambersite grew forming a sunflower shape the organic carbon content in high grade ores is 0 63 in low grade ores 0 83 and in overlying black siliceous shale 3 75 total rare earth element ree contents of two chambersite ore samples are 29 and 35 ppm whereas that of rhodochrosite ore is 22 ppm the chondrite normalized ree patterns of chambersite and rhodochrosite ores are similar with small negative ce and eu anomalies and a small positive gd anomaly the 13 c pdb values of two rhodochrosite ore samples are 4 3 and 7 3 indicating that the carbon source of mn carbonate minerals was mainly seawater bicarbonate with a small contribution from the degradation of organic carbon the source of the dongshuichang ore components was mainly submarine volcanic eruptions and a small amount from the weathering of pre proterozoic boron deposits the chambersite precipitated under conditions of high salinity high b mn and mg concentrations and weak alkalinity low oxygen conditions might be favorable for precipitation of chambersite

500 000 year paleomagnetic record from new zealand loess abstract a paleomagnetic record of secular variation has been obtained from a 17 4 m long core drilled from loess in north island new zealand three dated rhyolitic tephra occur in the loess core at depths of 1 5 3 4 and 13 0 m with ages of 22 500 42 000 and 370 000 years respectively the base of the core is estimated to be 500 000 years old which makes this the longest continuous loess sequence yet described from the southern hemisphere two periods of anomalously low inclination in the core are correlated with the mungo event ca 35 000 years ago and the emperor event ca 490 000 years ago the blake event ca 115 000 years ago is not recorded

ice crystal habits and growth processes in stratiform clouds with embedded convection examined through aircraft observation in northern china abstractice crystal habits and growth processes in two cases of stratiform clouds with embedded convection are investigated using data observed simultaneously from three aircraft on 18 april 2009 and 1 may 2009 as part of the beijing cloud experiment bce the results show that the majority of ice crystal habits found in the two cases at temperatures between 0 and 16 c included platelike needle column capped column dendrite and irregular a mixture of several ice crystal habits was identified in all of the clouds studied however the ice crystals recorded in the embedded convection regions contained more dendrites and possessed heavier riming degrees and the ice crystals identified in the stratiform clouds contained more hexagonal plate crystals both riming and aggregation processes played central roles in the broadening of particle size distributions psds and these processes were more active in embedded convection regions than in stratiform regions however riming was more prevalent in the

mineralogy and geochemistry of the proterozoic wafangzi ferromanganese deposit china in the proterozoic wafangzi deposit china sedimentary manganite ores are interstratified with red shale and silty limestone whereas sedimentary rhodochrosite ores are interbedded with organic rich black shale lateral change in mineralogy of the ores accompanying lateral changes in the host rocks demonstrates a classic example of facies variation in a zoned deposit the manganite ores show a distinct ce depletion reflecting a hydrothermal contribution in the seawater from which they precipitated absence of volcanics in the sequence suggests that the source of the hydrothermal input should be remote it is likely that manganite precipitated directly from seawater in these deposits above the redox interface whereas rhodochrosite was possibly early diagenetic formed in an anoxic environment manganite has been converted to braunite through a deoxidation dehydration reaction during late diagenesis both types of ores have been thermally metamorphosed at the contact with igneous intrusions four distinct mineral assemblages have been identified in the thermally metamorphosed ores which were produced as a result of variations in bulk compositions including volatiles of the premetamorphic ores in the final stage the ores have been affected by supergene processes to give rise to pyrolusite vernadite assemblages in the weathering zone

stable isotope chemical and mineral compositions of the middle proterozoic lijiaying mn deposit shaanxi province china abstract the lijiaying mn deposit located about 250 km southwest of xian is a high quality ore characterized by low p and fe contents and a mean mn content of about 23 the ore deposit occurs in shallow water marine sedimentary rocks of probable middle proterozoic age carbonate minerals in the ore deposit include kutnahorite calcite mn calcite and mg calcite carbon 0 4 to 4 0 and oxygen 3 7 to 12 9 isotopes show that with a few exceptions those carbonate minerals are not pristine low temperature marine precipitates all samples are depleted in rare earth elements rees relative to shale and have negative eu and positive ce anomalies on chondrite normalized plots the fe mn ratios of representative ore samples range from about 0 034 to