rare earth element geochemistry in soils developed in different geological settings of cuba abstract the increased exploitation of rare earth elements rees over the past few decades and the disposal of various products containing these elements have prompted numerous environmental studies and the need to establish regulatory guidelines we determined the concentration of rees in topsoil samples of 33 soil profiles collected from areas of different geological settings in cuba the average ree concentrations revealed the following chemical abundances in decreasing order ce nd la pr sm er yb dy tb lu ho gd eu tm the significant variation in ree levels reflects the geological diversity of cuba the highest ree concentrations were observed in typic rhodudalf and rhodic eutrodox which are derived from hard limestone in contrast the lowest ree concentrations were detected in the typic kandiustalf which originated from mica schist the lower light ree lree contents in cuban soils compared with soils from other countries is related to the low abundance of felsic rocks on the island we also observed a strong positive correlation between rees and some major elements in soils this finding implies that the distribution of rees in soils is partly governed by phosphates and aluminosilicates the low fractionation between lrees and heavy rees is likely related to the predominance of soils developed from carbonates this finding was also supported by the low lan smn and gdn ybn ratios and principal component analysis the spatial distribution of rees normalized to upper continental crust coupled with univariate and multivariate statistical techniques indicated that parent materials control the prevalence of rees in cuban soils the data presented here represent the first national wide survey of rees in cuban soils

a three dimensional surface velocity field for the mississippi delta implications for coastal restoration and flood potential accurate estimates of the current rate of subsidence in the mississippi delta southern united states provide a context for planning of wetland restoration and predictions of storm surge flooding we present a comprehensive three dimensional surface velocity field for the mississippi delta based on a network of 36 high precision continuous gps stations we show that while the majority of the delta is relatively stable the southern portion continues to experience high rates of subsidence 5 6 mm yr 1 our data are consistent with long term tide gauge records at grand isle louisiana and several stations in florida the current rate of relative sea level rise combined effect of land subsidence and sea level rise along parts of the coastal delta is 8 9 mm yr 1 most tide gauge stations have recorded sea level rise acceleration after a d 1970 these data have implications for land reclamation and wetland restoration in the region parts of the delta may not be viable in the long term

holocene vegetation and land use changes in response to climatic changes in the forelands of the southwestern alps italy the holocene sediment of lago piccolo di avigliana piedmont italy 356 m a s l was dated by 14 c and analysed for pollen to reconstruct the vegetation history of the area the early and mid holocene pollen record shows environmental responses to centennial scale climatic changes as evidenced by independent palaeoclimatic proxies when human impact was low or negligible con tinental mixed oak forests decreased at ca 9300 bc in response to the early holocene preboreal cli matic oscillation abies alba expanded in two phases probably in response to higher moisture availability at ca 6000 and ca 4000 bc while fagus expanded later possibly in response to a cli matic change at 3300 bc during and after the bronze age five distinct phases of intensified land use were detected the near synchroneity with the land use phases detected in wetter regions in northern and southern switzerland points to a common forcing factor in spite of cultural differences increasing minerogenic input to the lake since 1000 bc coincided with late bronze iron age technical innovations and probably indicate soil erosion as a consequence of deforestation in the lake catchment the highest values for cultural indicators occurred at 700 450 and at 300 50 bc coinciding with periods of high solar activity inferred from 14 c this suggests that iron age land use was enhanced by high solar activity while re occupation of partly abandoned areas after crises in earlier periods match better with the grip stable isotope record on the basis of our data and comparison with independent palaeoclimatic proxies we suggest that precipitation variation was much more important than tem perature oscillations in driving vegetation and societal changes throughout the holocene copyright 2006 john wiley sons ltd

acid drainage at the inactive santa lucia mine western cuba natural attenuation of arsenic barium and lead and geochemical behavior of rare earth elements abstract a detailed geochemical study was conducted at the inactive zn pb mine of santa lucia in western cuba the studied mine wastes are characterized by high total concentrations of potentially toxic elements pte with average values of 17 4 fe 5 47 ba 2 27 pb 0 83 zn 1724 mg kg as and 811 mg kg cu oxidation of sulfide minerals in mine waste dumps and in the open pit produces acid mine effluents ph 2 5 2 6 enriched in dissolved so 4 2 up to 6754 mg l fe up to 4620 mg l and zn up to 2090 mg l low ph values 2 5 2 8 and high dissolved concentrations of the same pte were found in surface waters up to 1500 m downstream from the mine nevertheless concentrations of as ba and pb in acid mine effluents and impacted surface waters are relatively low 0 01 0 3 mg l as 0 002 0 03 mg l ba and 0 3 4 3 mg l pb analysis by x ray diffraction and electron microscopy revealed the occurrence of lead bearing barite and beudantite and the more common solid phases reported elsewhere in similar environments including fe oxyhydroxides jarosite anglesite and plumbojarosite because the reported solubilities for barite and beudantite are very low under acidic conditions these minerals may serve as the most important control in the mobility of as ba and pb in contrast fe oxyhydroxides are relatively soluble under acidic conditions and therefore they may have a less significant role in pte on site immobilization mine wastes and stream sediments show a light ree lree and middle ree mree enrichment relative to heavy ree hree in contrast acid mine effluents and surface waters are enriched in hree relative to lree these results suggest that the lree released during the oxidation of sulfides are captured by secondary weathering minerals while the mree are removed from the altered rocks the low concentrations of lree in acid stream water suggest that these elements can be retained in the sediments more strongly than hree and mree one possible explanation for the sharp decrease in dissolved lree might be their retention by low solubility secondary minerals such as anglesite barite and jarosite

uranium and rare earth elements in co2 rich waters from vals les bains france abstract waters from springs at vals les bains result from the mixing of a co2 rich highly mineralized water with dilute shallow subsurface water total content of dissolved species vary from 5 mmol 1 to 100 mmol 1 for many elements mixing of these waters is non linear non conservative and further water rock reactions take place the ph is controlled by co2 outgassing redox conditions are controlled by both the iron hydroxide siderite buffer and the introduction of oxygen with shallow subsurface waters among the major elements concentrations of ca mg mn fe are related to mixing co2 outgassing and carbonate precipitation uranium shows a complex behaviour controlled by carbonate complexing redox conditions mixing of waters and leaching from the rocks the 234 u 238 u activity ratio is near secular equilibrium in the more dilute waters dissolved rare earth element ree patterns are almost flat with a slight negative eu anomaly in the concentrated waters heavy rare earth elements gd yb hree are strongly enriched relative to light rare earth elements ce eu lree we relate the enrichment in hree to water chemistry and to complexing with carbonate species

influence of parent sediments on the concentration of heavy metals in urban and suburban soils in turku finland the purpose of this study was to examine the influence of parent sediment material on soil geochemistry and to locate possible pollution sources in the area of turku town in southwestern finland the study area is glaciated terrain and subsurface samples were chosen to represent five different parent sediment materials glacial till glaciofluvial or littoral sand clay peat and marine mud elemental concentrations of surface 100 samples and background soil 50 samples were analysed by icp aes al ba ca co cr cu fe k mg mn na ni p s sr ti v and by graphite furnace aas as cd mo se loss on ignition was determined as an indicator of organic matter analytical results were examined using multivariate statistical methods the results indicate that the studied soils are not heavily contaminated there were only few sample sites with elevated heavy metal concentrations high pb concentrations were observed along main traffic routes and also in places where there has been small scale use of antifouling paints however concentrations of heavy metals in topsoil were in general significantly lower than those measured in large cities elsewhere the parent material strongly affects the geochemical character of the soils clays naturally have a significantly higher concentration of heavy metals than sands or till material this is also reflected in concentrations in organic topsoil when assessing target levels for polluted soil the primary sediment appears to be a more important factor than the amount of organic matter

chemical weathering of volcanic rocks at the island of pantelleria italy information from soil profile and soil solution investigations abstract concentrations of major minor and trace elements were determined in soil profiles and soil solutions from the island of pantelleria sicily channel to evaluate the weathering extent of soils evolved on trachytic and pantelleritic rocks and the aqueous transport of elements by their soil solutions the chemical index of alteration cia indicates a low to moderate degree of weathering consistently the mineralogical and geochemical imprints of the parent rocks are generally preserved the chemical weathering appears to be incongruent owing to primary minerals and glass dissolving to a variable degree while secondary minerals have formed based on the calculated saturation state of primary and secondary minerals with respect to the soil solutions and on mineralogical observations olivine and pyroxene are unstable and dissolving whereas magnetite and hematite are stable the main weathering products are amorphous phases such as ferrihydrite amorphous aluminium hydroxide and silica clay mineral formation appears to be incipient and mainly limited to kaolinite and smectite although for some soil profiles a hydrothermal origin is suggested for these minerals chemical characteristics of soil solutions and elemental mobility are controlled by the element source and water rock interaction

rare earth elements absorption patterns in grapevine vitis vinifera l cultivated in carbonate terrains south eastern sicily italy vitis vinifera l vineyards grown on carbonate soil hyblean plateau se sicily have been characterized in terms of rare earth elements rees distribution results highlighted that the absorption of rees by plants depends on the composition of the underlying soil which in this case derives from limestone parent rock allowing us to recognize the area of origin indeed even slight differences in rees content in soils may affect the absorption pattern of each grapevine cultivar importantly the various parts of the plants showed differences in rees absorption such rees fractionation is particularly evident in the leaf and juice samples in general the uptake and concentrations of rees in plant tissues may be related to many factors such as geographical climatic and lithological features this is also pointed out by the statistical investigation which took into account either the grapevine variety or each part of the plant by taking into consideration both the grape variety and the type of soil the present multi elemental approach aims to provide a useful geochemical tool for assessing the geographical origin of the production area of wine

elevation and accretion dynamics at historical plots in the biloxi marshes mississippi delta abstract the objectives of this study were to examine changes in accretion and elevation change over periods of up to 15 years for the biloxi marsh complex bmc in southeastern louisiana part of the mississippi deltaic plain identify factors affecting accretionary dynamics and put these findings in the context of ongoing restoration we present elevation and accretion data from surface elevation table set and feldspar marker horizon sites first established in 2003 the sites were clustered in two areas east and west in the central bmc on the eastern edge of the mississippi delta accretion markers were used in conjunction with elevation measurements to calculate shallow subsidence these data were analyzed along with similar data from nearby coastwide reference monitoring system crms sites located around the periphery of the bmc elevation decreased at the western sites by 0 35 0 13 cm yr and increased at the eastern and crms sites by 0 40 0 03 cm yr and 0 72 0 09 cm yr respectively the rate of accretion was similar at the western 0 49 0 14 cm yr and eastern 0 64 0 07 cm yr sites and over twice as much 1 30 0 11 cm yr at the crms sites shallow subsidence calculated as the difference between vertical accretion and surface elevation change was 0 76 0 49 cm yr at the western sites 0 23 0 06 cm yr at the eastern sites and 0 58 0 11 cm yr at the crms sites these trends are consistent with the observation that sediment is brought in from chandeleur sound to the east and is attenuated as deposition occurs across the landscape from east to west and that levee flank depressions associated with bayou la loutre an abandoned mississippi river distributary ridge are causing locally high subsidence in the western region without intervention these localized areas of the western region will be submerged within the next several decades at current rates of elevation loss and eustatic sea level rise while the eastern sites and the wetlands on the periphery of the bmc are likely to keep pace with sea level rise well into the second half of this century these results demonstrate the importance of accurate knowledge of both subsidence and accretionary dynamics in determining coastal wetland sustainability and restoration approaches

coexistence of allophane gibbsite kaolinite and hydroxy al interlayered 2 1 clay minerals in a perudic andosol allophane and halloysite are the most common secondary aluminosilicate minerals in andosols developed in pyroclasts in humid tropical areas we studied the composition and the charge properties of the clays extracted from the weathered b horizon of a perhydrated andosol developed in andesitic ash in guadeloupe french west indies by selective dissolution x ray diffraction xrd thermal analysis and characterization of ion exchange properties the bw horizon contained weatherable minerals and exhibited an allophane content of 25 its clay fraction contained gibbsite allophane kaolinite and hydroxy al interlayered 2 1 clay minerals the occurrence of gibbsite allophane and kaolinite was linked with intense leaching of silica after oxalate dissolution of allophane the cation exchange capacity cec was 11 8 cmol c kg 1 clay i e a typical value for low activity clays subsequent citrate treatment completely dissolved gibbsite but partly extracted al interlayers from the hydroxy al interlayered phase this extraction led to a 5 6 fold increase of the cation exchange capacity 62 3 cmol c kg 1 clay and a 2 3 fold increase in k selectivity the 2 1 clay minerals involved a combination or continuum of high charge beidellite and vermiculite from our data we believe that the 2 1 clay minerals first acted as a sink for aluminium and might have expressed an anti gibbsitic effect after substantial al interlayering of 2 1 clay minerals mimicking low activity clay gibbsite might have formed in a second stage c 2003 elsevier science b v all rights reserved

geochemical behaviour of ni cr cu zn and pb in an andosol cambisol climosequence on basaltic rocks in the french massif central abstract the objective of this study is to identify parameters influencing trace elements te vertical distributions in an andosol andic cambisol climosequence in order to understand processes involved in the current distribution of trace elements from basaltic rocks to associated soils six pedons developed on tertiary massive basaltic formations located at similar position in the hill slopes submitted to the same wet mountainous climate but under various microclimatic conditions altitude and annual rainfall were considered the six studied soils are andic and rich in organo metallic complexes two different and quantitative methods were used to compare the geochemical distributions of major and trace elements both being calculated with ti as invariant element isovolumetric mass balance and enrichment factors anthropogenic pedogenetic microclimatic inherited factors were discriminated anthropogenic influences are pointed out for k in two pedons and for pb in all studied sites distributions of other te are affected by discontinuities between underlying rocks and soil horizons zinc and cu distributions are controlled by organic matter whereas cr and ni distributions are influenced by pedogenetic processes results emphasize the relative trace element immobilization in andic soils under temperate climate

rare earth element behavior in soils and salt pan sediments of a semi arid granitic terrain in the western cape south africa the rare earth element ree contents of soils and pan sediments of the darling hills granitic terrain of southwestern south africa were determined to study the behavior of ree during weathering in a semi arid mediterranean climate the p rich stype bedrock granite has a middle ree mree enrichment relative to post archean australian sedimentary rocks paas that primarily reflects the ree content of feldspar and accessory apatite initial chemical weathering of the granite results in the loss of ree particularly ce eu and the heavy ree hree the enrichment of ree in soils relative to bedrock granite corresponds to clay mineral and amorphous fe oxide content in the case of the light ree lree and precipitation of pedogenic calcite in the case of the hree quartz sand dilutes the ree content and concentration of k feldspar produces positive eu anomalies cerium is rapidly precipitated during weathering and retained in clayey upper soil horizons as insoluble ceo2 most pan sediments have a bowl shaped ree pattern that is derived from the accumulation of eroded catchment soils modified by precipitation of evaporative carbonates ree enrichment particularly lree and the large negative ce anomaly of oxidized basal pan sediment relative to the bedrock granite suggest that ree entering the pan by groundwater flow are sorbed onto amorphous fe oxides in contrast goethite rich nodules from the pan have a low ree content and show hree enrichment relative to the granite precipitation of pedogenic calcite and evaporative pan carbonates greatly increases the retention of the hree in these semi arid soils diagenetic pan dolomite has a ree pattern similar to pedogenic and evaporative calcite but with a significantly lower ree content the ree patterns indicate that although most abundant in the bedrock granite the mree are least retained by soils during weathering the lree are generally retained by clayey and amorphous fe oxide rich soils and sediments whereas hree are retained by precipitation of soil and pan carbonates d 2003 elsevier b v all rights reserved

high precision measurements of wetland sediment elevation i recent improvements to the sedimentation erosion table abstract the sedimentation erosion table set developed by boumans and day 1993 is herein renamed the surface elevation table set to better reflect the conceptual view of the processes being measured the set was designed for making high resolution measurements of small scale changes in elevation of loose unconsolidated sediments in shallow water and mudflat habitats the set has undergone three major improvements to increase precision and so that it can be used to measure sediment elevation in vegetated wetlands as well as shallow water habitats the remote release sliding plate mechanism has been replaced with a single plate collars first 2 5 cm then 7 5 cm in length have been attached to the plate to reduce play in the placement of the measuring pins and the brass measuring pins have been replaced with fiberglass pins to reduce bending and consequent loss of precision under ideal laboratory conditions the 95 confidence limit for individual pin measurements averaged about 1 4 mm range 0 7 to 1 9 mm these modifications have resulted in a reduction of error by about 50

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

a method for measuring vertical accretion elevation and compaction of soft shallow water sediments high resolution measures of vertical accretion elevation and compaction of shallow water sediments are fundamental to understanding the processes that control elevation change and the mechanisms of progradation e g development of mudflats and intertidal wetlands in coastal systems yet measurements of elevation by traditional survey methods often are of low accuracy because of the compressible nature of the substrates nor do they provide measures of vertical accretion or sediment compaction this paper evaluates the use in shallow water systems of an approach designed to measure these variables in vegetated wetlands the approach employs simultaneous measures of elevation from temporary benchmarks using a sedimentation erosion table set and vertical accretion from marker horizons with sediment cores collected with a cryogenic coring apparatus the measures are made with a level of resolution sufficient to distinguish between the influence of surface and subsurface processes on elevation thus providing quantitative estimates of shallow subsidence the set marker horizon approach was evaluated on a developing splay created by an artificial crevasse of a distributary in the mississippi river delta the approach provided high resolution measures of vertical accretion 48 3 2 0 cm and elevation 36 7 1 6 cm over a 4 year period with the difference between the two indicating the amount of shallow subsidence in addition by laying new marker horizons in later years the approach provided rates not only of shallow subsidence 3 9 0 5 cm y 1 but also compaction of newly deposited sediments 2 1 0 6 cm y 1 and compaction of underlying sediments 1 8 0 20 cm y 1 over a two year period hence the set marker horizon approach has widespread applicability in both emergent wetland and shallow water environments for providing high resolution measures of the processes controlling elevation change

estimating shallow subsidence in microtidal salt marshes of the southeastern united states kaye and barghoorn revisited abstract simultaneous measurements of vertical accretion and change in surface elevation relative to a shallow 3 5 m subsurface datum were made in selected coastal salt marshes of louisiana florida and north carolina to quantitatively test kaye and barghoorn s contention that vertical accretion is not a good surrogate for surface elevation change because of autocompaction of the substrate rates of subsidence of the upper 3 5 m of marsh substrate were calculated for each marsh as the difference between vertical accretion and elevation change measured with feldspar marker horizons and a sedimentation erosion table surface elevation change was significantly lower than vertical accretion at each site after 2 years indicating a significant amount of shallow subsidence had occurred ranging from 0 45 to 4 90 cm the highest rate of shallow subsidence occurred in the mississippi delta results confirm kaye and barghoorn s contention that vertical accretion is not generally a good surrogate for elevation change because of processes occurring in the upper few meters of the substrate including not only compaction but also apparently shrink swell from water storage and or plant production decomposition at some sites indeed surface elevation change was completely decoupled from vertical accretion at the florida site the assumption of a 1 1 relationship between vertical accretion and surface elevation change is too simplistic a generalization of the complex interactions between accretionary and substrate processes consequently the potential for coastal marsh submergence should be expressed as an elevation deficit based on direct measures of surface elevation change rather than accretion deficits these findings also indicate the need for greater understanding of the influence of subsurface and small scale hydrologic processes on marsh surface elevation

a model of water and sediment balance as determinants of relative sea level rise in contemporary and future deltas abstract modern deltas are dependent on human mediated freshwater and sediment fluxes changes to these fluxes impact delta biogeophysical functioning and affect the long term sustainability of these landscapes for human and for natural systems here we present contemporary estimates of long term mean sediment balance and relative sea level rise across 46 global deltas we model scenarios of contemporary and future water resource management schemes and hydropower infrastructure in upstream river basins to explore how changing sediment fluxes impact relative sea level rise in delta systems model results show that contemporary sediment fluxes anthropogenic drivers of land subsidence and sea level rise result in delta relative sea level rise rates that average 6 8 mm y assessment of impacts of planned and under construction dams on relative sea level rise rates suggests increases on the order of 1 mm y in deltas with new upstream construction sediment fluxes are estimated to decrease by up to 60 in the danube and 21 in the ganges brahmaputra meghna if all currently planned dams are constructed reduced sediment retention on deltas caused by increased river channelization and management has a larger impact increasing relative sea level rise on average by nearly 2 mm y long term delta sustainability requires a more complete understanding of how geophysical and anthropogenic change impact delta geomorphology local and regional strategies for sustainable delta management that focus on local and regional drivers of change especially groundwater and hydrocarbon extraction and upstream dam construction can be highly impactful even in the context of global climate induced sea level rise

effect of i and s type granite parent material mineralogy and geochemistry on soil fertility a multivariate statistical and gis based approach abstract this study provides new insights into the effects of a parent material on inherent soil fertility we describe the mineralogy and geochemistry of i and s type granites and their effect on soil fertility under similar environmental conditions in borborema province ne brazil using standard mineralogical geochemical and soil analyses as well as multivariate analysis and geographic information system approaches we hypothesized that soils derived from i type granites will develop higher natural fertility than those derived from s type granites the mineralogy and chemistry of the two different granitic parent materials have a profound effect on soil fertility the s type and i type granites have different mineralogical compositions the s type granites have higher concentrations of silica and the i type granites contain larger concentrations of mafic and accessory minerals mainly amphibole and apatite geophysical field measurements show different magnetic susceptibilities for example the i type granites have substantial higher magnetic properties than the s type granites soils derived from the i type granites have higher natural fertility than soils derived from the s type granites principal component cluster and discriminant analyses 95 accuracy were effective tools to discriminate among soils developed from different granites spatial distribution maps are suitable soil fertility management tools to guide and support soil fertility management decisions for improved soil and crop specific fertilization these findings have wider implications in large parts of the tropics south america sub saharan africa india se and east asia and australia which are underlain by igneous and metamorphic rock types including s and i type granites and where effective management tools are needed to increase the nutrient use efficiencies for increased productivity of food fodder and energy crops

high precision measurements of wetland sediment elevation ii the rod surface elevation table abstract a new high precision device for measuring sediment elevation in emergent and shallow water wetland systems is described the rod surface elevation table rset is a balanced lightweight mechanical leveling device that attaches to both shallow 1 m in order to be stable the pipe is driven to refusal but typically to a depth shallower than the rod bench mark because of greater surface resistance of the pipe thus the rset makes it possible to partition change in sediment elevation over shallower e g the root zone and deeper depths of the sediment profile than is possible with the set the confidence intervals for the height of an individual pin measured by two different operators with the rset under laboratory conditions were 1 0 and 1 5 mm under field conditions confidence intervals for the measured height of an individual pin ranged from 1 3 mm in a mangrove forest up to 4 3 mm in a salt marsh

a new chemical index of weathering for metamorphic silicate rocks in tropical regions a study from sri lanka abstract weathered and fresh samples of metamorphic rocks from sri lanka were collected from various localities and analysed for major elements by xrf method rigaku kg x system japan the content of water was determined by the ignition method the xrf results obtained from these samples form the basis of a new index of chemical weathering particularly for sri lanka which is named the silica titania index and is calculated as follows silica titania index sio 2 tio 2 sio 2 tio 2 al 2 o 3 tio 2 sio 2 al 2 o 3 100 molecular proportions the index can be used to determine the degree of weathering in chemically weathered silicate rocks of other countries in tropical regions a triangular diagram plots the position of this index the point load strengths of fresh rocksand weathered rocks with different degrees of weathering were correlated with the values of this new chemical index the relative variation in strengths of fresh rocks and weathered rocks clearly indicates its suitability and usefulness for engineering geologists

climate dependent chemical weathering of volcanic soils in iceland abstract the major element mobility within soil profiles of brown to gleyic andosols that developed under diverse climatic conditions in iceland is assessed the volcanic soils were selected from areas with good monitoring of annual temperature and precipitation and the degree of weathering and elemental behavior is compared icelandic soils are subject to high fluxes of aeolian dust and at times to tephra ejecta from volcanic eruptions the source of dust input is assessed for each profile based on comparison of the chemical signatures found in the less weathered upper horizons with those of volcanic systems supplying material to source areas results show that tio 2 al 2 o 3 and fe 2 o 3 t and mno are the least mobile species and generally found enriched within more mature horizons the mobile base cations mgo cao and na 2 o are depleted in these horizons as a result of chemical weathering during pedogenesis soils developed in colder climatic conditions with mean annual temperature mat 1 c give values for the chemical index of weathering ciw of 37 45 that reflect only weak chemical weathering soils developed in milder climates mat 2 4 c are more strongly affected by weathering ciw 50 77 the parent material has ciw values of 37 temperature is demonstrated as the dominant variable exerting control on the extent of weathering with only minor mobilization following the incipient near surface weathering stage a robust linear relationship is found between ciw and model mat mat 0 21ciw 8 93 r 2 0 81 this climofunction can deliver proxy climate estimations from volcanic soils and paleosols of basaltic origin in cool to subarctic conditions 2 to 6 c

rare earth and other trace and major elemental distribution in a pedogenic calcrete profile slimene ne tunisia a calcrete profile developed on the top of a calcareous consolidated dune located in a coastal area of ne tunisia semi arid climate was studied with the aim to investigate the behavior of the chemical elements rare earth elements ree and other trace and major elements during the processes associated with calcrete formation particularly dissolution and precipitation of carbonates in the vadose zone the profile shows a vertical sequence with clear zonations from the surface downwards a reddish soil at the land surface a nodular horizon a laminar structured level and the consolidated old dune chemical and mineralogical analyses of samples from all levels were performed by neutron activation analysis and x ray diffraction bulk samples and 2 m fraction detailed studies of iron speciation and iron minerals were done by mossbauer spectroscopy microfauna mineralogical and chemical variations in the slimene weathering profile point to a long term aerial exposure of the old dune in a semi arid carbonated environment leading to the development of a pedogenic calcrete profile the mineralogical variations with depth indicate carbonate dissolution at the surface and downward leaching of calcium secondary carbonates overgrow primary ones and precipitate as coating or concretions below minerals found in the upper levels correspond to original materials of the old dune and also weathering phases and atmospheric inputs phyllosilicates decrease while calcite and k feldspars increase with depth kaolinite was the only clay mineral found in the old dune illite and chlorite were also found in all samples with calcrete authigenic smectite formation occurs above the laminar structured calcrete due to restricted drainage conditions the most significant chemical variations associated with the calcrete formation are i enrichment of co u br and ree in calcrete ii depletion of middle ree in the upper levels particularly eu and enrichment of middle ree and heavy ree in calcrete and iii hf zr cr th cs ta ga rb and k appear to be retained in the upper levels where calcite has been dissolved here iron is more reduced fe3 occurs in iron oxides goethite and hematite and clay minerals the ratio goethite hematite appears to increase down the profile and fe2 is mainly present in clay minerals

geomechanical and geochemical changes during early stages of weathering of karamu basalt new zealand abstract variations in geochemical and geomechanical characteristics were measured through a basalt weathering sequence exposed at an abandoned quarry at karamu near hamilton new zealand geochemical measurements show that at the early stages of weathering fresh to slightly weathered reductions in the concentrations cao and mgo are rapid although they are not accompanied by major mineralogical change during later stages of weathering secondary clay minerals form following well described mineralogical changes fresh basalt is strong uniaxial compressive strength 262 mn m 2 point load index 5 59 with well developed closely spaced columnar jointing slightly weathered material is distinguished in the field only by slight discolouration along joint planes but laboratory tests show a dramatic loss of strength in slightly weathered rock point load index 0 41 cbr 43 a causal relationship between the loss of cations and loss of strength in the early stages of weathering is suggested this stage of weathering is diffusion controlled whereby cations are lost from the constituent primary minerals and replaced by h this process disrupts the lattice structure and causes a marked loss of strength implications are that slightly weathered rock which appears competent in the field is likely to have much lower strength and durability than assumed from field evidence

the ciw index a new chemical index of weathering abstract a new chemical index of weathering that can be applied to modern soils and precambrian paleosis is proposed ciw al2o3 the value of this index increases as the degree of weathering increases and the difference between ciw index values of the silicate parent rock and soil or sediment reflects the amount of weathering experienced by the weathered material

influence of chemical weathering on the composition of the continental crust insights from li and nd isotopes in bauxite profiles developed on columbia river basalts abstract mineralogical chemical and li and nd isotopic compositions of two drill cores 8 9 m deep through bauxites developed on the miocene columbia river basalts document the changes associated with basalt weathering provide insights into the processes involved and allow us to examine the overall influence of chemical weathering on juvenile basaltic crust gibbsite hematite kaolinite halloysite goethite and maghemite are the weathering products in the bauxites quartz is observed near the tops of the cores and its abundance decreases progressively with depth no quartz is observed below five meters depth in either core most major and trace elements including mobile and some immobile elements are severely depleted in the bauxites niobium is less mobile relative to the rare earth elements thus chemical weathering attenuates the negative nb anomaly in the continental crust li and nd are strongly depleted relative to fresh basalt and both increase systematically towards the surface in the quartz bearing samples while 7li and end values decrease systematically towards the surface in these same samples both li and nd were likely lost from the bauxites through leaching the systematic enrichment of li nd and quartz as well as the less radiogenic nd isotopic composition at the tops of both profiles reflects 20 60 wt addition of an eolian component to the soils the eolian dust is unlikely to have experienced significant post depositional weathering due to the relatively high li contents near the tops of the profiles and therefore the low 7li and end values suggest that the dust came from an old weathered region of the continent our results demonstrate that lithium isotopes are sensitive tracers of chemical weathering particularly in extreme weathering settings and support the hypothesis that chemical weathering influences the mass and composition of the continental crust

mineral weathering in trachydacitic derived soils and saprolites involving formation of embryonic halloysite and gibbsite at mt amiata central italy abstract mount amiata is a volcano that has been extinct for 200 ka it is located in southern tuscany central italy and is composed largely of trachydacitic rocks the soils of mt amiata show a dark carbon rich a horizon that overlies a slightly structured bw horizon or directly a very thick saprolite which at a depth of about 3 m still maintains some ellipsoidal cores of coherent material mineral weathering in two of these soils one under beech and the other under chestnut was studied in detail the mineralogy of the parent rock consists predominantly of volcanic glass with phenocrysts of feldspar principally k feldspar biotite and pyroxene the main weathering products are an embryonic form of halloysite and gibbsite while allophane is usually absent or occurs in minor amounts sem evidence indicates that the clay minerals form directly from the weathering of volcanic glass in an environment where si is preferentially depleted in relation to al in the saprolite an anomalous situation is observed where optically fresh ferromagnesian minerals are thickly coated by clay particles whereas the surfaces of the glass and feldspar grains are relatively much cleaner however the ferromagnesian minerals are also much more heavily colonised by fungal hyphae and it is proposed that this results in the preferential deposition or flocculation of colloidal suspensions which translocate from higher positions in the weathering profile

sea level rise and coastal marsh sustainability geological and ecological factors in the mississippi delta plain chronostratigraphic approaches to coastal geomorphology frequently include consideration of salt marsh deposits as indicators of past sea level positions continuous horizons of such deposits can be used to infer that salt marshes were keeping pace with local rates of relative sea level rise rslr rates of past accumulation estimated using dating techniques are then used to hindcast the rate of sea level rise in that area estimates of contemporary sea level rise rates are often derived from tide gauge records this approach allows identification of subdecadal variations in mean water level accumulation rates of both organic and inorganic sediments can also be derived at these time scales and studies from many coastal marshes demonstrate the episodic nature of inorganic sediment deposition the frequency and spacing of these events does not necessarily coincide with periods of increased local sea level in addition short term increases in sea level could result in marsh deterioration as soils become excessively waterlogged a conceptual model of changes in geomorphic and ecological processes contributing to marsh sustainability during the holocene has been developed for the mississippi delta plain mdp the survival of some marshes in this area despite high rates of subsidence indicates that the combined effect of organic and inorganic accumulation processes can be adequate to sustain coastal marshes in the face of sea level rise

fertiliser characterisation major trace and rare earth elements abstract in recent years there has been increasing concern regarding the chemical impact of agricultural activities on the environment so it is necessary to identify contaminants and or characterise the sources of contamination in this study a comprehensive chemical characterisation of 27 fertilisers of different types used in spain has been conducted major minor and trace elements were determined including rare earth elements results show that compound fertilisers used for fertigation or foliar application have low content of heavy metals whereas fertilisers used for basal and top dressing have the highest content of both ree and other heavy metals ree patterns of fertilisers have been determined in order for them to be used as tracers of fertilisers in future environmental studies furthermore in this work ree patterns of fertilisers are used as tracers of the source of phosphate in compound fertilisers distinguishing between phosphorite and carbonatite derived fertilisers fertilisers from carbonatites have higher contents of ree sr ba and th whereas fertilisers from phosphorites have higher contents of metals of environmental concern such as cd u and as and the sum of the heavy metals is higher some of the analysed fertilisers have cd concentrations that exceed maximum values established in some countries and can be expected to produce long term soil accumulation furthermore other elements such as u as and cr are 10 50 times higher in concentration than those of cd but there is no legislation regarding them therefore it is necessary to regulate fertiliser compositions in order to achieve environmental protection of soils and waters

basalt weathering and pedogenesis across an environmental gradient in the southern cascade range california usa abstract basalt rocks occupy substantial land area and play a significant role in global weathering patterns and biogeochemical cycling the objective of this research was to quantify climatic controls of weathering and pedogenic processes on basalt derived soils across an environmental gradient on the western slope of the casacade range of california usa we hypothesized that climate controls mineral neogenesis with cool moist conditions favoring formation of short range order sro materials and warm dry conditions favoring smectite crystalline fe oxyhydroxides and kaolins four pedons were sampled across an elevation gradient 250 2500 m having large variation in mean annual soil temperature 5 17 c and mean annual precipitation 750 1350 mm the soil mineral assemblage was characterized by x ray diffraction selective dissolution total elemental analysis and light microscopy the degree of weathering and mineral assemblage exhibited a clear threshold at the permanent winter snowline 1200 m maximum soil development was noted just below the snowline with soils dominated by kaolinite and dehydrated halloysite crystalline fe oxyhydroxides 48 kg m 2 extensive loss of cations chemical index of alteration cia 95 and clay accumulation 447 kg m 2 in contrast the high elevation snow dominated pedons displayed less intense weathering e g cia

mineralogy of some italian andosols with special reference to the origin of the clay fraction abstract the mineralogy of four italian andosols derived from volcanic material either oversaturated or undersaturated with respect to silica has been investigated by xrd em and ir the crystalline clay minerals in all four profiles are essentially similar consisting of abundant halloysite with moderate illite and 14a intergrade material minor kaolinite and occasional gibbsite the soils also contain large amounts of imogolite and proto imogolite allophane with the exception of illite all these clay minerals are believed to be of pedogenic origin halloysite occurs in the dehydrated form in the surface horizons but becomes progressively more hydrated with depth at depths of 1 4 m the clay fraction consists almost entirely of fully hydrated halloysite supporting the suggestion that halloysite forms best in a stagnant moisture regime where there is a depositional overburden acting as a silica source em observations show that the halloysite may have spherical morphology and may be intimately associated with gas vesicles in pumice grains where it probably forms by the transformation of allophanic material it seems likely that dehydrated halloysite slowly converts to poorly crystallized kaolinite in the upper horizons of these profiles the origin of the 2 1 minerals is more problematical illite is probably inherited from mica in the parent material but the 14a intergrade material is so poorly ordered that a pedogenic origin seems more likely than formation by inheritance or by transformation of pre existing 2 1 silicates

rare earth elements as reactive tracers of biogeochemical weathering in forested rhyolitic terrain article rareearthelements rees were evaluatedaspotentialtracers of biogeochemicalweathering atpedon hillslope and catchment scales in the jemez river basin critical zone observatory jrb czo valles caldera national pre serve nm usa we investigated time series of ree patterns in precipitation soil pore water groundwater and stream water and related these data to ree composition of soil rock and atmospheric dust ree signatures in stream waters are dynamic reflecting processes that occur along hydrologic flowpaths during transport to the stream including organic matter complexation primary and secondary mineral weathering water soil bedrock interaction and atmospheric deposition strong compositional similarities for the ree between soil waters and stream waters during the initial snowmelt are consistent with shallow subsurface flows to streams most bio

the amazon influenced muddy coast of south america a review of mud bank shoreline interactions the 1500 km long coast of south america between the amazon and the orinoco river mouths is the world s muddiest this is due to the huge suspended sediment discharge of the amazon river 106 754 tons yr 1 9 part of which is transported alongshore as mud banks mud bank formation is controlled by the physical oceanography of the continental shelf seaward of the amazon river mouth an initial seafloor storage area for much of the suspended sediment discharged from the river in this area rapid and sustained fluid mud concentration and trapping are associated with fresh water salt water interaction and estuarine front activity on the shelf due to the enormous amazon water discharge ca 173 000 m3 s 1 at obidos 900 km upstream of the mouth fluid mud is transported shoreward and then along the coasts of the guianas by a complex interaction of wave and tidal forcing and wind generated coastal currents the mud banks which may number up to 15 or more at any time are up to 5 m thick 10 to 60 km long and 20 to 30 km wide and each may contain the equivalent mass of the annual mud supply of the amazon as the banks migrate alongshore their interaction with waves results in complex and markedly fluctuating shorelines that are associated with space and time varying depositional bank phases and erosional inter bank phases bank zones are protected from wave attack as a result of wave energy dampening by mud and undergo significant albeit temporary coastal accretion accompanied by rapid mangrove colonization the dampening of waves in bank areas as they propagate onshore is accompanied by the shoreward recycling of mud commonly in the form of individual mud bars these bars progressively undergo desiccation and consolidation and thus constitute a major pathway for rapid and massive colonization by mangroves erosion by waves propagating across relatively mud deficient shoreface zones in inter bank areas can lead to muddy shoreline retreat rates of tens of metres to several kilometres over a few months to a few years accompanied by massive removal of mangroves notwithstanding the higher incident wave energy on inter bank shores inter bank shorefaces are permanently muddy due to the pervasive influence of the amazon muddy discharge inter bank and transitional bank to inter bank phases are associated with both periodic sandy chenier formation and extreme forms of rotation of rare headland bound sandy beaches the high mud supply from the amazon has been the overarching geological control on the quaternary evolution of the northeastern south american coast having led to the growth of a muddy shelf clinoform at the mouth of the amazon and more or less important progradation throughout this coast net progradation reflects an imbalance in favour of deposition during each mud bank inter bank cycle the high mud supply has presumably blanketed shelf sand deposited by smaller rivers during eustatic lowstand phases the shelf clinoform structure at the mouth of the amazon and the muddy coastal progradation throughout the coast of the guianas and into venezuela provide analogues of the geological record on muddy shorefaces

chemical weathering in the volcanic soils of isla santa cruz galapagos islands ecuador abstract forty three soils 130 horizons sampled by the geo pedological mission organized by the state university of gent belgium in 1962 on isla santa cruz galapagos islands were analysed in order to determine their degree of chemical evolution several weathering indices weathering index of parker wip chemical index of alteration cia chemical index of weathering ciw plagioclase index of alteration pia and silica titania index sti and multivariate statistical analysis principal components analysis based on chemical composition were used with the only exception of the sti the indices were highly correlated r 0 85 the highest wip and sti values 20 9 8 2 and 70 2 2 2 respectively were found for soils developed on basalt flows near the coast slightly lower values wip 16 8 5 1 and sti 61 3 4 were shown by brown soils developed from basaltic flows at elevations between 140 and 225 m a s l while the lowest values wip 9 5 and sti 47 6 8 representing the more weathered materials were found for soils located at the highest elevations 400 m a s l and mostly developed on pyroclastic materials tuff and tephra as the chemical composition of the geological material basalt and tephra is highly homogeneous the degree of weathering is likely to depend on climatic conditions controlled by altitude and orientation on the windward slopes of the island a gradient of increasing weathering is observed from the arid conditions predominant at the coast to elevations of 400 500 m a s l where much more humid conditions prevail principal component analysis on elemental composition also supported the interpretation that the degree of weathering first component and soil horizonation second component are both related to climatic conditions both the variation of the chemical indices and the principal components of the geochemical composition are related to the bioclimatic zones soils with the lowest degree of weathering are located in the arid coastal zone slightly higher intensity was found for soils located in the transition and scalesia zones while the most weathered soils appear in the brown zone compared to other volcanic soils studied in the literature soils from isla santa cruz are in the upper range of chemical weathering intensity only comparable to soils from azores islands and canary islands tenerife and la gomera developed on basalts under oceanic conditions

the weathering of basalt and relative mobilities of the major elements at belbex france abstract a basalt and its weathered profile have been analysed for major elements graphical examination shows al fe and ti to have been essentially immobile determining mobility sequences for this deposit is complicated by the long pedogenetic history of the area three different sequences are presented two for different stages of weathering integrated over time and one that reflects the weathering regime of the present day

the controls on the major and trace element evolution of shales siltstones and sandstones of ordovician to tertiary age in the wet mountains region colorado u s a a vertical section of shales siltstones and sandstones from ordovician to eocene age in a limited geographic area east of the wet mountains and sangre de cristo mountains in colorado have been analyzed for major elements and a variety of trace element concentrations including the ree in addition the petrography of the sandstones has been determined the quartz rich arenites contain considerably lower concentrations of most elements relative to coexisting shales or siltstones at the same outcrop the arkosic sandstones contain similar to lower concentrations of most elements compared to coexisting shales or siltstones in the same area accordingly the average concentrations of al2o3 fe2o3 mgo tio2 loi rb th co sc cr cs nb y and ree are significantly lower in all sandstones relative to all shales and siltstones the exceptions are sio2 na2o and ba concentrations and the eu eu lasc and thsc ratios as they are higher in the sandstones than the shales and siltstones there is no significant difference in the mno cao k2o and sr concentrations or the sollaco thco lani crth and lalucn ratios of the average sandstones relative to the shales and siltstones many of these differences may be related to the higher quartz and feldspar and lower clay mineral amounts in the sandstones than in the shales and siltstones for example average lasc thsc eueu and lalucn ratios of th arkosic sandstones tend to be higher than the coexisting shales and siltstones due to enrichment of the arkoses in feldspar relative to the other minerals e g eueu 0 82 0 19 in average arkoses in the trinidad vermejo raton poison canyon and cuchara formations eueu 0 63 0 19 in average shales and siltstones in the same formations in addition the elemental concentrations and ratios are more variable for most elements in the sandstones than the shales and siltstones this suggests that the shales are rapidly homogenized near the source the elemental fractionation in the arkosic sandstones due to enrichment of feldspar relative to other minerals suggests that they are poorer indicators of provenance that the associated shales whereas the more homogeneous elemental distributions in the shales and siltstones suggest that they may be better indicators of provenance than the sandstones nevertheless the elemental ratios that are most similar in the sandstones and in the shales and siltstones are consistent with their derivation from similar average intermediate to silicic source rocks

a review on the potentiality of rare earth elements to trace pedogenetic processes abstract this review aims at considering the use of rees to trace pedogenetic processes in order to quantify the respective contribution of the successive processes on pedogenesis we first consider the origins and contents of rees in soils to assess their natural occurrence and tackle the common data treatment used to interpret their concentrations we review subsequently the impact of the different pedogenetic processes on the fate of rees in soils from their release into a soil solution by primary mineral heavy minerals phosphates silicates and carbonates dissolution during weathering to their fixation on or into main ree bearing secondary minerals clay minerals fe mn oxides and carbonates then their mobilization by plant recycling and organic matter and finally the impact of argilluviation and redox processes on their fractionation we conclude that rees much more than other trace elements can interestingly trace the considered processes that are encountered in a large diversity of non polluted soils arising from diverse parent materials weathering generally fractionates rees and accounts for a significant part of the variation in the initial ree stock of the soils plant recycling induces a weak mobilization of rees and their accumulation in topsoil argilluviation can be traced using the mree enrichment and the eu anomaly of the clay minerals redox processes can be traced by the ce anomaly caused by the precipitation of cerium on mn oxides to use rees as tracers of pedogenetic processes we recommend to i precisely characterize the ree bearing minerals ii adapt the choice of reference s for normalization and iii perform mass balance calculations

statistical empirical index of chemical weathering in igneous rocks a new tool for evaluating the degree of weathering abstract chemical weathering indices are useful tools in characterizing weathering profiles and determining the extent of weathering however the predictive performance of the conventional indices is critically dependent on the composition of the unweathered parent rock to overcome this limitation the present paper introduces an alternative statistical empirical index of chemical weathering that is extracted by the principal component analysis pca of a large dataset derived from unweathered igneous rocks and their weathering profiles the pca analysis yields two principal components pc1 and pc2 which capture 39 23 and 35 17 of total variability respectively the extent of weathering is reflected by variation along pc1 primarily due to the loss of na 2 o and cao during weathering in contrast pc2 is the direction along which the projections of unweathered felsic intermediate and mafic igneous rocks appear to be best discriminated therefore pc1 and pc2 represent independent latent variables that correspond to the extent of weathering and the chemistry of the unweathered parent rock subsequently pc1 and pc2 were then mapped onto a ternary diagram mfw diagram the m and f vertices characterize mafic and felsic rock source respectively while the w vertex identifies the degree of weathering of these sources independent of the chemistry of the unweathered parent rock the w index has a number of significant properties that are not found in conventional weathering indices first the w index is sensitive to chemical changes that occur during weathering because it is based on eight major oxides whereas most conventional indices are defined by between two and four oxides second the w index provides robust results even for highly weathered sesquioxide rich samples third the w index is applicable to a wide range of felsic intermediate and mafic igneous rock types finally the mfw diagram is expected to facilitate provenance analysis of sedimentary rocks by identifying their weathering trends and thereby enabling a backward estimate of the composition of the unweathered source rock

the mississippi delta region past present and future the mississippi delta region of south louisiana houses a wealth of resources within a dynamic subsiding landscape foundations for the delta region reflect neogene evolution of the depocenter whereas details of the modern landscape reflect late pleistocene to holocene evolution of the alluvial deltaic plain the holocene delta plain was constructed by cyclical growth of deltaic headlands followed by avulsion and relocation of the fluvial sediment source abandoned headlands were then submerged and reworked while a new headland was created at the site of active fluvial sediment input historic period levees have decoupled the delta plain from its fluvial sediment source at the same time global sea level rise was accelerating which has accelerated delta plain submergence diversions of mississippi river water and sediment are necessary to achieve delta plain sustainability but upstream dams trap 50 of the total sediment load and there is not enough supply to keep pace with subsidence and accelerated

mineral neoformation in pore spaces during alteration and weathering of andesitic rocks in humid tropical indonesia abstract the morphology chemistry and mineralogy of minerals newly formed in voids products of weathering of andesitic rocks were studied using optical and submicroscopic techniques on thin sections combined with scanning electron microscopy sem energy dispersion x ray analysis edxra and x ray diffraction analysis on subsamples samples were taken from the core the outer core and the soft outer layers of weathered andesitic boulders in the cigudeg area west java about 75 km south of jakarta indonesia with udic moisture and isohyperthermic temperature regime the neoformed minerals observed in planar voids and cavities comprise 1 1 phyllosilicates goethite and gibbsite and juxtaposed coatings of halloysite mixed layer phyllosilicates goethite and gibbsite the mineral sequences observed confirm former studies on the groundmass of the boulder in the first weathering layer an absolute accumulation of gibbsite takes place further away from the core the gibbsite is redissolved and replaced by illuvial phyllosilicate clay the possibility of inheritance of the 2 1 layer silicates from a hydrothermal alteration is discussed the sharp boundaries in the juxtaposed coatings point to a stepwise sequential rather than a gradual evolution of the microenvironment

rare earth element trends and cerium uranium manganese associations in weathered rock from koongarra northern territory australia at koongarra australia three drill cores form the cahill schist formation containing u ore and regolith above it containing secondary u ore were studied to ascertain the distribution of rare earth elements rees and u the unaltered schist has a ree trend similar to the post archaean australian shale paas which is therefore used as a normalising standard unweathered rock from the zone of primary u mineralisation contained strong enrichment of the heavy rees and this pattern is retained during most of the weathering strongly bleached and very weathered shallow samples from this zone do not show enrichment of hrees in general however weathering appears to have little effect on the pattern of rees in the bulk rock at this site zones rich in mn oxy hydroxides occurring as coatings on fissure surfaces contain large concentrations of ce and u with a clear ce anomaly ce ce 3 8 the ce and u apparently occur together as microcrystalline oxides within 1 2 mu m diameter globules on mineral surfaces in the mn rich zones 46 refs 10 figs 2 tabs