geomorphic evolution and genesis of laterites around the east coast of madras tamil nadu india abstract laterites and lateritic soils red soils of the east coast especially around madras tamil nadu have been formed in different geomorphic conditions and on various geological deposits they occur as caprocks over recent alluvium upper gondwana sandstones and shales and precambrian basement rocks the laterite profiles studied around madras are generally 2 to 5 m thick and exposed 5 to 45 km inland from the present day shoreline detailed analysis micromorphological and chemical and the bore hole litho log data reveal that lateritisation was not continuous but occurred in phases lateritisation could have taken place in humid to sub humid conditions with a rich source of iron in the parent rock and sediment and efficient internal drainage geoarchaeological investigations and quaternary stratigraphical studies date the lateritic crust surface to the early late neogene neotectonics have played a vital role in shaping the present landscape

influence of periatlantic climates and paleoclimates on the distribution and mineralogical composition of bauxites and ferricretes

formation and evolution of lateritic profiles in the middle amazon basin insights from radiation induced defects in kaolinite abstract the content of radiation induced defects rids in kaolinite samples originating from lateritic soils and continental detritic sediments of the middle amazon basin brazil is investigated using electron paramagnetic resonance the paleodose registered by kaolinites ranges from 80 to 900 kgy present day dose rates of radiation determined from the whole rock u and th content range between 4000 and 40 000 mgy ka in most samples u and th concentrations are correlated suggesting that u has not been remobilized by lateritization this observation is consistent with the fact that 80 of the total u content is incorporated in resistant minerals such as zircon and ti oxides the heterogeneous distribution of u observed by induced fission tracks mapping makes it possible to neglect the radiation contribution of the u decay chains in the dose rate calculation the interpretation of the measured content of rids in kaolinite is then performed using the calculated present day dose rate and assuming equilibrium in the radioactive decay chains for the sedimentary samples the amount of rids is broadly correlated to the dose rate and provides apparent absolute ages older than 20 ma the rid contents in kaolinites from the lateritic soils provide apparent ages ranging from 10 to 6 ma the high rid content of these lateritic kaolinites shows that their chemical isotopic and crystallographic properties are not representative of present day weathering conditions models assuming the dynamical equilibrium of kaolinites with local physical chemical conditions prevailing in lateritic soils are thus questionable alternatively our findings bring strong support for the use of the isotopic composition of kaolinites to decipher continental paleo climates

petrological differentiation patterns and geomorphic distribution of ferricretes in central africa geomorphic distribution and petrological differentiation patterns of ferricretes widespread on landsurfaces were studied in the dembia zemio area southeastern central african republic four types of ferricretes are distributed on high plateaux hillslopes and low plateaux the main contrast corresponds to the differentiation between ferricretes of high plateaux rich in poorly hydrated minerals hematite and kaolinite and those covering hillslopes and low plateaux richer in hydrated minerals goethite and gibbsite a principal component analysis of geochemical and mineralogical data was used to characterize the main differentiation patterns of ferricretes in relation with their petrographic facies and the geomorphic features of the landscape the distribution of secondary minerals and their relationships to trace elements within and between the ferricrete types reflects differences in weathering and erosion processes our results document that the petrological patterns and the distribution of ferricretes are related to geomorphic features depending on hydroclimatic variations that govern the landscape evolution of many tropical shields

inductively mapping expert derived soil landscape units within dambo wetland catenae using multispectral and topographic data abstract constructing a cost effective and detailed digital soil map of africa will require the extensive utilization of both legacy soil data and legacy soil landscape knowledge which in africa is primarily available from reconnaissance scale catena or association maps and related studies we evaluated a hybrid approach for disaggregating reconnaissance scale soil maps rapid and inexpensive delineation of representative soil landscape units in the field using expert knowledge followed by the use of inductive empirical and correlative modeling techniques to map these landscape units our 2214 km 2 study area located in central uganda consisted predominantly of catenae that terminate in seasonal valley floor wetlands called dambos a type of landscape that can be found throughout the african continent for model training and validation we identified four landscape classes in the field using published expert knowledge well drained uplands red soils sloping dambo wetland margins gradient 2 frequently inundated dambo bottoms hummocky microtopography and flat dambo floors default using binary decision trees bdt with multispectral and topographic remote sensing covariates we created a 20 m resolution map of these four classes multispectral inputs included reflectance values vegetation indices and spectral mixture modeling fractions from systeme pour l observacion de la terre spot 4 satellite images acquired in december 2006 and february 2007 topographic inputs consisted of a digital elevation model dem from shuttle radar topography mission srtm data slope and 20 relative elevation layers calculated using moving windows of various sizes decision rules were based upon the following input variables the normalized difference vegetation index ndvi the normalized difference infrared index ndii the shortwave infrared swir reflectance northing slope and two relative elevation layers the overall classification accuracy of 75 5 and kappa coefficient of 0 67 suggest that a combination of multispectral topographic and spatial data may be used to reliably classify landscape classes for dambo terminated catenae at 59 of the 2214 km 2 study area the upland class was by far the most abundant with margins at 21 floors at 12 and bottoms at 8 a statistical analysis of soil property data from a small catchment located within the study area showed significant class differences in soil texture color organic carbon soc base saturation ph effective cation exchange capacity ecec and clay mineralogy though detailed soil maps are rare in africa reconnaissance soil maps can be inexpensively disaggregated to provide a valuable starting point for digital soil mapping

rheological properties of water ice applications to satellites of the outer planets 1 abstract the icy moons of the outer solar system have not been quiescent bodies in part because many have a substantial water component and have experienced significant internal heating we can begin to understand the thermal evolution of the moons and the rate of viscous relaxation of surface topography because we now have good constraints on how ice in several of its polymorphic forms flows under deviatoric stress at planetary conditions details of laboratory derived flow laws for pure polycrystalline ice are reviewed in detail one of the more important questions at hand is the role of ice grain size grain size may be a dynamic quantity within the icy moons and it may or may not significantly affect rheology one recent beneficiary of revelations about grain size sensitive flow is the calculation of the rheological structure of europa s outer ice shell which may be no thicker than 20 km

vertical distribution of trace elements in laterite soil suriname abstract the vertical distribution of 20 elements in a 12 5 m thick laterite profile from suriname south america has been investigated using neutron activation analysis atomic absorption spectrometry and x ray fluorescence the mineralogical composition was quantitatively determined from calculations based on results from x ray diffraction thermal gravimetric methods and from the data obtained for major elements using x ray fluorescence the most characteristic change observed in the mineralogy with depth is the increase in kaolinite relative to gibbsite a considerable fractionation with depth is found for different trace elements the enrichment of the lanthanoids la and ce at 3 4 m below surface and of sm and eu at 10 12 5 m depth demonstrates that the distribution of elements despite the similarity in chemical properties is seriously affected by weathering processes the laterite soil samples were also separated in al and fe rich fractions using naoh these separation experiments demonstrated that the trace elements are mainly associated with the fe rich red mud fraction of the laterite soil

timing of water plume eruptions on enceladus explained by interior viscosity structure water plume eruptions on saturn s icy moon enceladus are delayed relative to the peak tidal stresses simulations suggest the delay can be explained by the moon s interior structure and the presence of a subsurface ocean at the south pole of saturn s icy moon enceladus eruptions of water vapour and ice emanate from warm tectonic ridges1 2 3 4 observations in the infrared5 and visible6 spectra have shown an orbital modulation of the plume brightness which suggests that the eruption activity is influenced by tidal forces however the observed activity seems to be delayed by several hours with respect to predictions based on simple tidal models6 7 here we simulate the viscoelastic tidal response of enceladus with a full three dimensional numerical model8 9 and show that the delay in eruption activity may be a natural consequence of the viscosity structure in the south polar region and the size of the putative subsurface ocean by systematically comparing simulations of variations in normal stress along faults with plume brightness data we show that the observed activity is reproduced for two classes of interior models with contrasting thermal histories a low viscosity convective region above a polar sea extending about 45 60 from the south pole at a depth below the surface as small as 30 km or a convecting ice shell of 60 70 km in thickness above a global ocean our analysis further shows that the eruption activity is controlled by the average normal stress applied across the cracks thus providing a constraint on the eruption mechanism

chemical processes affecting the mobility of major minor and trace elements during weathering of granitic rocks abstract the behaviour of 38 major and trace elements as well as changes in the mineralogy have been examined in 10 weathering profiles developing on some portuguese granitic rocks element mobilities are calculated from geochemical data normalized with respect to ti in the fresh parent rock chemical elements are divided into two groups immobile and mobile on the basis of their geochemical distribution during weathering elements that are immobile during weathering are zr hf fe al th nb sc and the ree very mobile are ca na p k sr ba rb mg and si mobile elements are derived mainly from leachable minerals such as feldspars micas and apatites whereas immobile elements are either concentrated in resistate phases or strongly adsorbed by secondary minerals the geochemical behaviour of mn cr v fe and ce is very dependent on redox conditions redox transformations of these elements can be used to set limits on the oxidation state of a weathering suite the ree are mobilized or fractionated during late stages of weathering but not during moderate stages of weathering this fractionation is caused by selective leaching of rocks composed of both stable and unstable minerals containing ree

mineralization and element redistribution in the chah gheib ni laterite ore zone bavanat zagros belt iran abstract nickel laterites are supergene deposits derived from the weathering of serpentinized ultramafic rocks and they commonly accounts for over 70 of world land based ni resources serpentinized ultramafic rocks outcrop extensively in iran as result of collision between afro arabian and iranian micro plate during the late cretaceous two ni bearing laterite belts developed on the ultramafic rocks of the neyriz ophiolite have been recently discovered in the bavanat region south iran the chah gheib deposit as the biggest ni bearing laterite in the bavanat area hosts a total estimated reserve mineralization of about 102 000 tons of ore at 0 92 ni and 180 000 tons at 1 63 cr this study focuses on elemental fractionation and mineralogical control of major trace and rare earth elements in a selected profile from the chah gheib ni laterite in order to assess the conditions of ore formation and its paleo environmental significance four distinct horizons including saprolite lower limonite upper limonite and lateritic duricrust have been recognized from the bottom to the top of the studied profile iron oxy hydroxides are the dominant phases found in the laterite profile overall fe and other first raw transition metals i e cr ni v co cu and zn show abundances higher than those of the bedrock the main fe and cr carriers in the laterite deposit are fe oxy hydroxides and chromite respectively although authigenic ni and cr bearing palygorskite is also common throughout the profile elemental mobility estimated using th as immobile element showed that the major oxides are largely depleted with the exception of fe2o3 and cao among trace elements cr is the element resulting strongly enriched in those levels where large chromite crystals occurs while v co ni and zn are enriched only in some levels of the upper limonite horizon and in the lateritic duricrust likely as adsorbed cations onto iron oxy hydroxides and as a consequence of an alkaline ph environment alkaline ph conditions can also explain the cu depletion observed throughout the profile such a condition during lateritization appears further supported by both the occurrence of carbonates and palygorskite and by the distribution of the ba sr ratio carbonates and palygorskite as well as secondary quartz require dry climate to form and alternating wet dry climate may allow lateritization this study suggests that the chah gheib laterite formed in a subtropical climate possibly during the late cretaceous late paleocene period in a roughly 25 35 latitude range promoting si and mg mobilization during the wet season and carbonates quartz and mg rich silicate precipitation during the drier periods

the implications of tides on the mimas ocean hypothesis we investigate whether a present day global ocean within mimas is compatible with the lack of tectonic activity on its surface by computing tidal stresses for ocean bearing interior structure models derived from observed librations we find that for the suite of compatible rheological models peak surface tidal stresses caused by mimas high eccentricity would range from a factor of two smaller to an order of magnitude larger than those on tidally active europa thermal stresses from a freezing ocean or a past higher eccentricity would enhance present day tidal stresses exceeding the magnitudes associated with europa s ubiquitous tidally driven fractures and in some cases the failure strength of ice in laboratory studies therefore in order for mimas to have an ocean its ice shell cannot fail at the stress values implied for europa furthermore if mimas ocean is freezing out the ice shell must also be able to withstand thermal stresses that could be an order of magnitude higher than the failure strength of laboratory ice samples in light of these challenges we consider an ocean free mimas to be the most straightforward model best supported by our tidal stress analysis

robust geochemical indices for redox and weathering on a granitic laterite landscape in central uganda abstract most geochemical studies of laterite formation have been based on detailed examinations of a small number of hopefully representative profiles due to spatial variability in bedrock composition and geomorphic processes that sort materials by size density and other properties experimental designs developed for the geochemical analysis of single soil profiles are of limited use in landscape investigations in this study of a laterite landscape on a granitic rock in uganda we used element concentrations from neutron activation analysis naa to develop a suite of robust geochemical indices for landscape scale analysis of weathering and oxidation reduction redox processes in laterite formation to capture k feldspar weathering the k hf ratio served as a good proxy for feldspar zircon mineral ratios while k na ratios indexed feldspar concentration to quartz using principal components analysis we derived an index of rare earth elements ree leaching relative to th and an index of heavy to light ree hree lree fractionation we used the fe sc ratio to ascertain the absolute redox vs relative weathering fe accumulation in laterite formation with absolute fe accumulation also associated with lower fe as ratios mn ce ba nodules and concretions were identified by characteristically high ce values with individual ce values as high as 5000 g g 1 the relatively large amounts of k feldspar k avg is 4000 g g 1 and low degree of hree lree fractionation suggest that this landscape is weathered less than generally assumed the fe and mn derived indices highlight the important role of oxidation reduction processes in iron accumulation overall our findings suggest that the current ferricrete mantled hilltops were formerly located on a lower poorly drained part of the landscape

rhenium and osmium isotope and elemental behaviour accompanying laterite formation in the deccan region of india this study presents major trace element and re os isotope data for two laterite profiles from the deccan region in india the first profile from bidar developed upon deccan basalt itself the second from goa formed on an archean greywacke both profiles show the typical changes in mineralogy and chemistry accompanying laterite formation from little altered parent rock at depth to altered saprolite depleted in mobile elements to a highly altered si depleted fe rich laterite capped by an iron rich crust at the surface rhenium and os concentrations show a systematic enrichment with increasing degree of alteration where the highest concentrations are found in the fe rich laterite crust the level of os enrichment is greater than that of re and as a consequence 187re 188os ratios are lower in the laterite than the parent rock with time this leads to the development of 187os 188os ratios that are also less radiogenic than the parent rock and this relationship holds irrespective of rock type or age or the time of laterite formation the marked enrichment of both re and os and the patterns of change above and below the paleowatertable indicates that both elements are highly mobile high eh and low ph conditions facilitate re and os dissolution and redistribution occurs via groundwaters whereas with increasing ph higher in the profile both elements are scavenged out of solution and precipitate either as pge rich alloys or are strongly partitioned into oxides or oxyhydroxides nevertheless the isotope and elemental data for both profiles suggests that at least some of the re and os must be externally derived either from aeolian deposition or from the lateral movement of solute laden groundwaters given the high levels of os in laterites their extensive geographical coverage of the continents and their active role in the surface water cycle it seems likely that they will exert a significant influence on the continental flux of os to the oceans that will in turn be sensitive to tectonic or climatic change

implications of nonsynchronous rotation on the deformational history and ice shell properties in the south polar terrain of enceladus abstract numerous studies of the south polar region of saturn s moon enceladus have focused on the four main fractures the tiger stripes their associated water plume and the effects of diurnal tidal stresses on these fractures however due to their small magnitude 10 100 kpa diurnal stresses alone are unable to completely explain the initial formation of the tiger stripes and the many additional fractures in the region we suggest nonsynchronous rotation nsr stresses induced by a freely rotating ice shell over a global ocean are large enough to overcome the tensile strength of the ice shell and initiate fracturing on enceladus using the tidal stress calculation program satstressgui we demonstrate the dependence of the magnitude of the nsr stress on the thickness of the ice shell particularly the brittle outer layer of the ice shell we suggest the brittle layer in the south polar region is 2 4 km thick whereas in the more northern regions it is 6 8 km the difference is most likely due to the elevated energy flux at the south pole compared to the regions to the north resulting in a warmer and thinner ice shell in the south polar region the thinner ice around the south pole permits nsr tensile stresses of 5 mpa enough to fracture the ice however the thicker ice to the north reduces the nsr stress to less than 2 mpa making fracturing less likely the difference in ice shell thickness and resultant nsr stress can help explain the activity in the south but relative quiescence in the north our modeled nsr stress magnitudes and orientations suggests a nsr period on the order of 1 myr and advocate that the tiger stripes have rotated 45 clockwise about the south pole since their initial formation in response to nsr of the ice shell if the ice shell is rotating at a constant rate the tiger stripes would thus be up to 100 000 years old an apparent decreasing angular separation between consecutive fracture sets that formed in the south polar region suggests an ice shell that has weakened in strength over the course of its recent geologic history this could be a result of increased heating thinning of the ice shell or a combination of the two as the ice shell thinned the nsr stresses were enhanced making fracturing more likely after a smaller amount of nsr compared to the previous fracturing episode

mobilization and redistribution of rees and thorium in a syenitic lateritic profile a mass balance study abstract ree th geochemistry and mineralogy have been studied in a lateritic profile derived from a syenite at akongo in sw cameroon ree and th mass balance calculations for the host rock minerals show that at least 70 of the lree s and 50 of the hrees are contained in allanite apatite titanite and epidote and at least 50 of the th is controlled by the same accessory minerals which represent about 2 wt of the unaltered syenite these accessory phases are destroyed during the first stages of weathering causing most of the rees and th to be rapidly released into the soil comparison of the variation in the zr ti and th content as a function of the apparent density of the different zones of the saprolite shows that th is the least mobile element the presence of secondary thorianite tho2 the etched surface on zircon grains and the presence of ti in secondary cerianite support this geochemical interpretation the concentration of thorium was therefore chosen as invariant relative to the concentration of the other elements especially the rees in mass balance calculations most of the rees are leached in the iron rich upper horizons loose nodular horizon iron crust and top of mottled clay horizon where the groundwater table moves saprolite and bottom of the mottled clay horizon the rees are fractionated and redistributed there is a juxtaposition of leached and accumulation zones with precipitation of lree aluminous hydrated phosphates this study supports the existence of two different cycles for the redistribution of elements in the soil 1 1 as dissolved ions in the saprolite horizon and 2 2 as individual particles in the upper part of the profile

lineament azimuths on europa implications for obliquity and non synchronous rotation abstract lineaments are thought to form as tensile cracks due to tidal stress which is driven mainly by europa s eccentric orbit however this model would not produce the wide range of lineament azimuths observed on europa unless the stress in a given region or the conditions for fault failure change over time in this work we test the ability of two mechanisms that would alter the stress field over time to account for the observed lineament azimuths non synchronous rotation and spin pole precession first we revisit previous analysis of lineaments and find that an underlying assumption used to predict their azimuths was inconsistently applied after revising these predictions we incorporate the effects of a non zero obliquity which has been shown to influence the formation of other tidal tectonic features we then expand our analysis to include the effects of the time variable phenomena spin pole precession and non synchronous rotation of the ice shell we also consider additional failure assumptions to those used in previous work on lineament azimuths we test our models against the azimuths of observed lineaments in the bright plains region of europa without obliquity we find that non synchronous rotation is insufficient to explain the wide range of azimuths observed in this region in the presence of obliquity we find that either spin pole precession or non synchronous rotation could produce wide variations in lineament azimuths however neither model can independently account for the observed distribution of azimuths in the bright plains region in fact a model in which all of the lineaments are assumed to form at random orientations outperforms the non synchronous rotation model in our statistical tests the model with the highest likelihood of producing the observations is one in which 45 of the lineaments formed as predicted in the precession model 55 formed at random orientations and older lineaments are less represented in the tectonic record given the relative timescales expected for spin pole precession and non synchronous rotation it makes sense that the signal of precession is more apparent in the tectonic record these results are in good agreement with assessments of strike slip faults modeling of both types of features indicates a large obliquity the same spin pole direction during the most recent epoch of tectonic activity a similar percentage of features that are not well explained by the tidal model and little evidence of non synchronous rotation

solid tidal friction above a liquid water reservoir as the origin of the south pole hotspot on enceladus abstract earth jupiter s moon io and saturn s tiny moon enceladus are the only solid objects in the solar system to be sufficiently geologically active for their internal heat to be detected by remote sensing interestingly the endogenic activity on enceladus is only located on a specific region at the south pole from which jets of water vapor and ice particles have been observed spencer j r and 9 colleagues 2006 science 311 1401 1405 porco c c and 24 colleagues 2006 science 311 1393 1401 the current polar location of the thermal anomaly can possibly be explained by diapir induced reorientation of the satellite nimmo f pappalardo r t 2006 nature 441 614 616 but the thermal anomaly triggering and the heat power required to sustain it over geological timescales remain problematic using a three dimensional viscoelastic numerical model simulating the response of enceladus to tidal forcing we explore the effect of a low viscosity anomaly in the ice shell localized to the south polar region on the tidal dissipation patterns we demonstrate that only interior models with a liquid water layer at depth can explain the observed magnitude of dissipation rate and its particular location at the south pole moreover we show that tidally induced heat must be generated over a relatively broad region in the southern hemisphere and it is then transferred toward the south pole where it is episodically released during relatively short resurfacing events as large tidal dissipation and internal melting cannot be induced in the south polar region in the absence of a pre existing liquid decoupling layer we propose that liquid water must have been present in the interior for a very long period of time and possibly since the satellite formation owing to the orbital equilibrium requirement meyer j wisdom j 2007 icarus 188 535 539 sustaining some liquid water at depth is impossible if heat is continuously emitted at a rate of 4 8 gw at the south pole based on that requirement we propose that the current thermal emission is not in equilibrium with the heat production and that the thermal emission rate is abnormally high at present time alternatively continuous dissipation at a rate of 1 2 gw in the ice shell at the south pole should be sufficient to induce internal melting and it could sustain a layer of liquid water at depth over geologic timescales

soil erosion history in central tanzania based on osl dating of colluvial and alluvial hillslope deposits abstract the irangi hills in kondoa district central tanzania are severely degraded by sheet rill and gully erosion using recently developed optically stimulated luminescence osl dating techniques and a detailed study of the hillslope stratigraphy and soils we have determined the sequence of events that gave rise to this highly degraded landscape two major colluvial deposits have been identified on the slopes the oldest colluvium gave osl deposition dates of 14 700 1600 14 200 1500 and 11 400 1300 years ago these dates coincide with the climatic change from dry to wet conditions which took place during the late pleistocene it is possible that the erosion and deposition of the old colluvium occurred as a response to this change this phase of erosion and deposition was followed by a long phase of stability and pedogenetic alteration of the old colluvium a phase of accelerated soil erosion began not later than 900 years ago as indicated by a dated alluvial fan the presence of which indicates that some deeper gullies already existed on upper pediment slopes at that time the second more recent colluvial deposit gave osl dates of 460 40 590 70 and 660 50 years a major period of gully formation and incision with subsequent fan development occurred sometime between 600 and 300 years ago the recent phase of erosion

the fracture of water ice ih a short overview this paper presents a short overview of the fracture of water ice ih topics include the ductile to brittle transition tensile and compressive strength compressive failure under multiaxial loading compressive failure modes and brittle failure on the geophysical scale arctic sea ice cover europa s icy crust emphasis is placed on the underlying physical mechanisms where appropriate comment is made on the formation of high latitude impact craters on mars

geological implications of a physical libration on enceladus given the non spherical shape of enceladus thomas et al 2007 the satellite will experience gravitational torques that will cause it to physically librate as it orbits saturn physical libration would produce a diurnal oscillation in the longitude of enceladus tidal bulge which could have a profound effect on the diurnal tidal stresses experienced by the surface of the satellite although cassini iss has placed an observational upper limit on the amplitude of enceladus libration smaller amplitudes can still have geologically significant consequences here we present the first detailed description of how physical libration affects tidal stresses and how those stresses might then affect geological processes including crack formation and propagation south polar eruption activity and tidal heating our goal is to provide a framework for testing the hypothesis that geologic features on enceladus are produced by tidal stresses from diurnal librations of the satellite

geochemical balance of lateritization processes and climatic signatures in weathering profiles overlain by ferricretes in central africa a simple geochemical balance of lateritization processes governing the development of several tens of meters of weathering profiles overlain by ferricretes is estimated on the basis of detailed mineralogical and geochemical data the lateritic weathering mantle of the haut mbomou area in central africa is composed of different weathering layers described from the base to the top of vertical profiles as a saprolite a mottled clay layer a soft nodular layer a soft ferricrete and a ferricrete in which kaolinite gibbsite goethite and hematite occur in various quantities incongruent dissolution of kaolinite leads to the formation of gibbsite in the upper saprolite whereas the hematite does not clearly replace the kaolinite according to an epigene process in the upper ferruginous layers of the profiles instead that kaolinite is also transformed into gibbsite according to an incongruent dissolution under hydrated and reducing conditions induced by a relatively humid climatic pattern the respective relations of the silica iron and aluminum balances and the al substitution rate of the hematite on the one hand and of rhg rhg 100 hematite hematite goethite and the kaolinite on the other hand to the consumption or the release of protons h permit differentiation of aggrading ferruginization and degradation processes operating in the different lateritic weathering profiles the al substitution rate of the fe oxyhydroxides varies according to the nature of lateritization processes e g saprolitic weathering and aggrading ferruginization vs degradation the observations and results indicate that the ferruginization process of the weathering materials of parent rocks is not a simple ongoing process as often thought this suggests that the actual lateritic weathering mantle of the haut mbomou area may result from different stages of weathering and erosion during climatic changes

constraints on europa s rotational dynamics from modeling of tidally driven fractures abstract cycloids arcuate features observed on europa s surface have been interpreted as tensile cracks that form in response to diurnal tidal stress caused by europa s orbital eccentricity stress from non synchronous rotation may also contribute to tidal stress and its influence on cycloid shapes has been investigated as well obliquity fast precession and physical libration would contribute to tidal stress but have often been neglected because they were expected to be negligibly small however more sophisticated analyses that include the influence of jupiter s other large satellites and the state of europa s interior indicate that perhaps these rotational parameters are large enough to alter the tidal stress field and the formation of tidally driven fractures we test tidal models that include obliquity fast precession stress due to non synchronous rotation and physical libration by comparing how well each model reproduces observed cycloids to do this we have designed and implemented an automated parameter searching algorithm that relies on a quantitative measure of fit quality which we use to identify the best fits to observed cycloids we then apply statistical techniques to determine the tidal model best supported by the data by incorporating obliquity fits to observed southern hemisphere cycloids improve and we can reproduce equatorial and equator crossing cycloids furthermore we find that obliquity plus physical libration is the tidal model best supported by the data with this model the obliquities range from 0 32 to 1 35 the libration amplitudes are 0 72 2 44 and the libration phases are 6 04 to 17 72 with one outlier at 84 5 the variability in obliquity is expected if europa s ice shell is mechanically decoupled from the interior and the libration amplitudes are plausible in the presence of a subsurface ocean indeed the presence of a decoupling ocean may result in feedbacks that cause all of these rotational parameters to become time variable

cerium anomalies in lateritic profiles the ree geochemistry and mineralogy have been studied in four lateritic profiles one derived from a syenite akongo sw cameroon the others being developed on a gneissic basement and located along a soil toposequence goyoum e cameroon there is a fractionation between lree and hree in the lateritic samples during weathering the weathered residual products being enriched in lree from la to eu and depleted in hree from gd to lu sampled waters are enriched in hree in relation to the syenite host rock a positive ce anomaly has been found systematically at the top of the saprolite beneath a zone of iron oxide accumulation in the laterite up to 2000 ppm ce may be present in the akongo profile cerianite ceo2 is present as very fine coatings in non ferruginous clayey domains primary ree bearing accessory minerals are weathered at the bottom of the profile specifically allanite and apatite are transformed into florencite and rhabdophane but these phases have no ce anomaly all the data are interpreted as the result of the following processes 1 1 ree leaching in a reducing environment 2 2 oxidation of ce3 to ce4 in an oxidizing environment 3 3 deposition of cerium as cerianite whereas the other ree remain in solution

rare earth element mineralogy and geochemistry in a laterite profile from madagascar abstract in this study rare earth element ree distribution has been investigated in a weathering profile from central madagascar combination of bulk rock geochemical data elements and isotopes with mineral characterization reveals a remarkable evolution of the ree abundances and ree minerals in the vertical weathering profile in the fresh tonalite bedrock ree y concentrations are typical of granitoids 299 363 ppm and the main ree minerals are allanite and chevkinite in the c horizon saprolite primary ree minerals disappear and rees are transported via fluid to precipitate rhabdophane group minerals in cracks and pores the presence of sulfate ligands produced by sulfide oxidation may be responsible for the ree speciation as suggested by the composition of the secondary ree minerals rhabdophane group minerals contain up to 9 wt so 3 and 7 wt cao indicating a mixture between rhabdophane sensu stricto ree po 4 h 2 o and tristamite ca u fe iii po 4 so 4 2h 2 o due to intense ca leaching rhabdophane disappears and al phosphates alunite jarosite group are found in the soil cerianite ce iv o 2 also precipitates in the b horizon of the soil mass transfer calculations based on immobile ti indicate significant ree leaching in a horizon with preferential leaching of the heavy ree rees accumulate partly in the b horizon the uniform nd isotope compositions and the constant proportion of immobile elements do not reveal external input in the b horizon total ree y reach 2194 ppm with high ce concentrations 1638 ppm 9 ce bedrock compared to other ree 3 4 ree bedrock tetravalent ce state is dominant in the b horizon and requires oxidizing conditions that likely account for the accumulation of redox sensitive elements in b horizon e g mn fe co under oxidizing conditions cerianite precipitation causes a ce fractionation from other trivalent ree in comparison to the ion adsorption clay of southern china preferential heavy ree enrichment was not observed in the weathering profile another remarkable peculiarity of the studied profile is the occurrence of gd 2 so 6 grains the discovery of this new mineral demonstrates that a natural process exists that that can fractionate ree to such an extent to produce a pure gadolinium end member mineral an understanding of such a mechanisms is crucial for the ree geochemistry of low temperature alteration processes as well as for the formation of ree ore deposits or industrial processing

the interior and orbital evolution of charon as preserved in its geologic record abstract pluto and its largest satellite charon currently orbit in a mutually synchronous state both bodies continuously show the same face to one another this orbital configuration is a natural end state for bodies that have undergone tidal dissipation in order to achieve this state both bodies would have experienced tidal heating and stress with the extent of tidal activity controlled by the orbital evolution of pluto and charon and by the interior structure and rheology of each body as the secondary charon would have experienced a larger tidal response than pluto which may have manifested as observable tectonism unfortunately there are few constraints on the interiors of pluto and charon in addition the pathway by which charon came to occupy its present orbital state is uncertain if charon s orbit experienced a high eccentricity phase as suggested by some orbital evolution models tidal effects would have likely been more significant therefore we determine the conditions under which charon could have experienced tidally driven geologic activity and the extent to which upcoming new horizons spacecraft observations could be used to constrain charon s internal structure and orbital evolution using plausible interior structure models that include an ocean layer we find that tidally driven tensile fractures would likely have formed on charon if its eccentricity were on the order of 0 01 especially if charon were orbiting closer to pluto than at present such fractures could display a variety of azimuths near the equator and near the poles with the range of azimuths in a given region dependent on longitude east west trending fractures should dominate at mid latitudes the fracture patterns we predict indicate that charon s surface geology could provide constraints on the thickness and viscosity of charon s ice shell at the time of fracture formation

the fate of chromium during tropical weathering a laterite profile from central madagascar abstract we performed a mineral geochemical and cr sr pb isotope study on a laterite profile developed on ca 540 ma old tonalitic bedrock in madagascar with special emphasis on the behavior of chromium during tropical weathering the observed strong depletions of ca si and p and enrichment of fe and al in the soil relative to bedrock and underlying saprolite are the characteristic features pertinent to laterites the enrichment of fe in topsoil horizon can be correlated with enrichment of p and the redox sensitive elements mn and cr and indicates redistribution of these elements related to oxidation reduction processes the slight scatter of 87sr 86sr and 206 207 208pb 204pb values in the profile is one consequence of such redistribution processes our results are compatible with a two stage process during alteration 1 an incipient alteration stage characterized mainly by a pervasive effective and complete loss of sulfides accompanied by patchy alteration constrained along fissures and cracks and 2 a main stage of soil formation actual laterization with loss of na k ca and si and accumulation of fe and mn relative to the unaltered bedrock this two stage evolution is also depicted by cr concentrations and 53cr values along the studied profile where the first incipient alteration stage caused a pronounced depletion of cr particularly hosted by sulfides and where the second alteration laterization led to redistribution and a small increase in cr concentration in the uppermost portions of the soil profile relative to stage one altered saprolite this gain in cr is accompanied by decreasing 53cr values and can be explained by partial immobilization possibly by adsorption coprecipitation on with fe oxy hydroxides of mobile cr iii during upward transport in the weathering profile the negatively fractionated 53cr values measured in the weathering profile relative to the unaltered tonalitic bedrock characterized by a high temperature magmatic inventory cr isotope signature are consistent with loss of a positively fractionated cr vi pool formed during weathering the predicted existence of a former positively fractionated and mobile chromium pool has been experimentally constrained in circumneutral and basic leachates of powdered tonalite bedrock where 53cr of 0 21 to 0 48 was measured our results show that mobilization of chromium is effective under highly oxidative conditions which in well drained sulfide bearing parent bedrocks potentially lead to both acid dissolution of sulfide hosted cr and redox promoted mobilization of cr vi from silicates during later stages of weathering under basic ph conditions

the formation of enceladus tiger stripe fractures from eccentricity tides abstract enceladus has a young tectonically active south polar region which is erupting material from a prominent set of fractures called tiger stripes no comparable activity is observed at the north pole which is heavily cratered with limited tectonism given the many lines of evidence supporting a global ocean under enceladus icy shell the reason for the dichotomy in geologic activity is unclear we model the formation of the tiger stripes as tidally driven fractures and examine the magnitudes of tidal stresses with different ice shell structures in order to explore whether and how tidal stress might explain enceladus distribution of tectonic activity we find that eccentricity driven tidal stresses would produce fractures of nearly identical orientations to the observed tiger stripe fractures and that a 10 km difference in ice shell thickness between the north and south poles can result in substantially different tidal stress magnitudes providing a natural explanation for the hemispheric dichotomy in tectonic activity on enceladus finally we synthesize these results with enceladus global geologic record to offer insight into the evolution of this enigmatic moon

solid liquid ree fractionation in the lateritic system of goyoum east cameroon the implication for the present dynamics of the soil covers of the humid tropical regions the ree th weathering geochemistry and mineralogy has been investigated in a lateritic soil cover in relation to the close hydrographical system at goyoum east cameroon the stutied area composed of gneissic hills covered by humid tropical forest belongs to the sanaga river basin and corresponds to a transition vegetation zone between rainforest and savannah a representative soil catena was taken as a reference zone close to the sanaga river the gneissic parent rock soil and groundwater samples have been cut off in pits in the lower part of the catena waters were also sampled both in brooks rich in organic matter and in the sanaga river all the waters were sampled seasonally during the rainy and dry periods the water rock interactions and the exportation of ree and th have been discussed as a function of the evolution of specific ratios considering th as the less mobile element during laterization variation of parent rock pr normalized ratios ln th pr vs depth show that the upper ferruginous horizons are depleted in ree while the basal saprolite presents accumulation zones which are differently located for ce and the other lrees the hrees are also depleted the la accumulations are located near the saprolite gneiss weathering front associated with negative ce anomalies ce ce 0 4 the ce accumulations inducing strong positive ce anomalies ce ce 4 are located in the upper saprolite beneath the ferruginous horizons all along the soil catena the secondary lree bearing minerals which reflect lree fractionation during incipient weathering of the gneiss are hydrous phosphates rhabdophane lreepo4 nh2o and cerianite ceo2 whose precipitation depends on the eh ph changes in the soil profiles on the other hand hree depletion is controlled by the dissolution of xenotime the major hree bearer in the parent gneiss in the 0 45 m filtered acidic groundwater ph 5 5 which have flooded the saprolite for a long residence time th contents are extremely low 0 th 10 ppt while lree contents are high 90 la 450 ppt in these filtered waters th seems to be strongly controlled by minerals i e thorianite which lead to its immobilization in the soil while lree remain in the soluble and or colloidal pools moreover the groundwaters show significant negative ce anomalies throughout the year 0 1 ce ce 0 4 the mobilization of lree except redox active ce results from the dissolution and or the mobilization in colloidal form of the secondary phosphates which may present major negative ce anomalies as indicated by the bulk soil analyses at the saprolite gneiss weathering front therefore the groundwaters have the signature of saprolitic materials we propose that the strong positive ce anomalies of the upper saprolite result from ancient weathering processes these processes would have led to much stronger ce iii ce iv dissolution reprecipitation conditions than those occurring at the present time in the saprolite in the 0 45 m filtered brook acidic blackwaters lree and th contents are high 100 th 400 ppt 400 la 1700 ppt in this organic matter rich environment lree and th are highly mobilized the colloial pool controls half of the whole lree th load the geochemical signature of these waters is independent of the gneissic parent rock and soil lree contents there is no ce anomaly this signature is similar to those of other organic rich rivers draining humid tropical ecosystems in the world in the 0 45 m filtered sanaga waters lree and th contents are lower than in the brooks 15 th 40 ppt 40 la 300 ppt these concentrations are dependent on the time and on the colloidal composition however 90 of these elements are mainly controlled by the suspended pool

stresses generated in cooling viscoelastic ice shells application to europa 1 a cooling viscoelastic ice shell overlying an ocean develops stresses due to two effects thermal contraction of the ice due to cooling and the expansion of the shell due to the ice water volume change the former effect generates near surface compression and deeper extension the second effect generates extension only in both cases stresses are smaller at depth due to viscous creep the resulting combined stresses are extensional except at shallow 1 km depths in thin ice shells for ice shells thicker than 45 km stresses are extensional throughout the extensional stresses exceed 10 mpa for shells thicker than 20 km and thus dominate all other likely sources of stress as long as shell cooling occurs the dominantly extensional nature of the stresses may help to explain the puzzling lack of compression observed on europa and other large icy satellites however after 100 myr of conductive cooling the maximum theoretical elastic strains for europa are 0 35 which are probably insufficient to explain the total amount of observed extension

ree fractionation and ce anomalies in weathered karoo dolerite abstract analyses of samples from a weathering profile on karoo dolerite allow elements to be divided into three groups depending on their behaviour si k na mg ca sr ba and v are mobilized and removed from weathered products fe al ti zr hf zn cu sc co and ni are immobile ree y and to a lesser extent cr are mobile and redistributed within the profile without a net loss of these elements from the profile large positive ce anomalies are developed in oxidized weathered products by preferential leaching of the other ree s negative ce anomalies and ree enrichment is a feature of less altered dolerite

ree fractionation during granite weathering and removal by waters and suspended loads sr and nd isotopic evidence very few studies deal with ree rare earth element mobility within the system soil soil solution streamwater in this article we try to characterize the fractionation and the migration of the ree in a granite derived soil system located in a small catchment of the vosges mountains icp ms and tims measurements were performed on both solid samples fresh granite soil and suspended load of the stream and waters soil solutions springwater and streamwater to determine their respective ree concentrations and sr and nd isotopic compositions the paas normalized ree pattern of the bedrock is characterized by a strong depletion in hree heavy ree and a negative eu anomaly 0 46 similarly the granite normalized ree distribution patterns of the soil samples show hree depletions that become more important with decreasing depth the correlative behavior between p2o5 th and ree with depth indicates that besides apatite other phosphate minerals such as monazite are the most important phases controlling the th and ree budget in the soil profile on the other hand at greater depth zircon seems to be another important mineral phase controlling especially the hree enrichment as shown by the positive relationship between zr content and the yb ho ratio different grain size fractions show similar ree distribution patterns and are only weakly fractionated compared with bulk soil sample however the finest fraction 0 20 m is more enriched in sr and ree suggesting a stronger concentration of ree carrying minerals in this fraction the suspended and dissolved load of the stream show as a whole an enrichment in hree if compared with the granite or with the different soil samples however compared with the uppermost soil samples the suspended load is significantly more enriched in hree its ree distribution pattern is more similar to that of the finest fraction of the deeper soil sample and to the fresh granite thus most probably the ree of the suspended load originated from a source with ree characteristics found in the deep soil horizons this source might have been situated in the uppermost soil profile which is actually ree depleted the weathering process can be compared with a leaching experiment where the waters correspond to the leachate and the soil to the residual phase of the granite the sr isotope data indicate that the suspended load originates from the finest soil fraction the sr and nd isotopic data of the suspended load suggest that it contains up to 3 sr and nd from apatite and up to 97 from feldspar most of the sr and nd in the waters originate from apatite leaching or dissolution

eruptions arising from tidally controlled periodic openings of rifts on enceladus the cassini flyby of 14 july 2005 revealed plumes of water vapour and ice associated with the tiger stripe features on the surface of saturn s icy moon enceladus since then the challenge has been to explain the nature of the plumes and the forces driving them two papers this week offer an explanation that accounts for both the plume characteristics and the presence of hot spots without the need to assume the existence of near surface liquid water a requirement of some previous models nimmo et al identify tidally driven lateral fault motions near the tiger stripes as the most likely drivers of heat and vapour production and hurford et al show that as enceladus orbits saturn the parent planet s tides make the satellite s ice flex this may cause the tiger stripes to open and close periodically exposing volatile gases and allowing them to be released plumes of gas have been seen near the south polar region of enceladus a small icy satellite of saturn and observations revealed large rifts in the crust informally called tiger stripes hurford et al report that during each orbit every portion of each tiger stripe rift spends about half the time in tension which allows the rift to open exposing volatiles and allowing eruptions plume activity is expected to vary periodically in 2005 plumes were detected near the south polar region of enceladus1 a small icy satellite of saturn observations of the south pole revealed large rifts in the crust informally called tiger stripes which exhibit higher temperatures than the surrounding terrain and are probably sources of the observed eruptions2 models of the ultimate interior source for the eruptions are under consideration1 3 4 5 other models of an expanding plume6 require eruptions from discrete sources as well as less voluminous eruptions from a more extended source to match the observations no physical mechanism that matches the observations has been identified to control these eruptions here we report a mechanism in which temporal variations in tidal stress open and close the tiger stripe rifts governing the timing of eruptions during each orbit every portion of each tiger stripe rift spends about half the time in tension which allows the rift to open exposing volatiles and allowing eruptions in a complementary process periodic shear stress along the rifts also generates heat along their lengths7 8 9 which has the capacity to enhance eruptions plume activity is expected to vary periodically affecting the injection of material into saturn s e ring10 and its formation evolution and structure moreover the stresses controlling eruptions imply that enceladus icy shell behaves as a thin elastic layer perhaps only a few tens of kilometres thick

experimental evidence for mobility of zr and other trace elements in soils a soxhlet extraction was carried out over a period of 27 d on a column comprising 3 cm of quartz overlain by 4 cm of soil from the b horizon and then 1 cm of soil from the a horizon of a granitic podzol major and trace elements were leached from the column and accumulated in a reservoir at the base of the column total loss of elements from the soil over the course of the experiment ranged from 0 002 to 1 wt with major elements and the light and heavy rare earth elements ree showing the largest percentage losses zirconium 0 002 and then al 0 008 showed the lowest percentage loss the light ree were leached out of the soil preferentially to the mid ree all elements showed accumulation by a factor of 2 to 11 in the quartz layers at the base of the column particularly in the upper first 1 cm of the quartz major elements were leached from the column at a rate of 0 02 to 0 59 mol h 1 whereas zr nd sm gd dy rb and sr were leached at the rate of 0 5 to 30 10 6 mol h 1 concentrations of other ree in the reservoir increased over the duration of the experiment but they were poorly correlated with time so leaching rates were not calculated normalization of the major element leaching rates to take into account the constant flushing of water through the column the average annual rainfall in the allt a mharcaidh catchment in scotland from where the soil was sampled and the cross sectional area of the soil in the column together with the temperature of the soil in the column 70 c compared with the average annual temperature of the allt a mharcaidh catchment 5 7 c gave major element release rates from the soil of 0 002 to 0 97 meq m 2 yr 1 depending on the choice of ea the dissolution activation energy which are generally less than those measured in the field of 0 1 to 40 9 meq m 2 yr 1 calculations showed that despite the redistribution and loss of zr from the column assumptions of zr mobility would have had a negligible effect on calculated element release rates of na ca fe and mg however significant underestimates of the release of k 5 ti 57 al 5 and si 10 as well as some trace elements e g nd 23 rb 54 sr 24 would have occurred concentrations of ca and sr leached from the column correlated well rsq 0 93 p 0 01 supporting the idea of the use of sr release as a proxy for ca release in weathering rate calculations the release rates and percentage loss of ree from the soil varied between elements indicating that ree distribution patterns of rocks and soils may not be preserved in drainage waters

geochemical and mineralogical behavior of ree th and u in the akongo lateritic profile sw cameroon abstract the ree u th geochemistry and mineralogy have been studied in a lateritic profile derived from a syenite akongo sw cameroon mass balance calculations have been done 1 in the syenite to determine the most important ree u th bearing minerals and 2 in the soil profile to understand the movement of these elements thorium has been used as an immobile element for these calculations the weathering of accessory minerals rich in ree and th of the syenite allanite apatite titanite and epidote has been especially studied in the saprolite several ree th secondary minerals florencite rhabdophane cerianite and thorianite important to explain the fractionation of ree in supergene environments have been found

unusually low rates of slip on the santa rosa range fault zone northern nevada the santa rosa range fault zone srrfz is one of the most topographically prominent normal fault systems in the northern basin and range province of the western united states it has been assigned high rates of vertical slip by others and has been identified as a possible site of the future extension of the central nevada seismic belt cnsb we use detailed trench mapping and luminescence dating to estimate displacements and timing of the last several large magnitude paleoearthquakes on the southern part of the srrfz at a trench site near orovada nevada coseismic vertical displacements ranged from 1 to 2 8 m for each of the last four events luminescence ages provide time limits for the last three events of 125 155 ka 90 108 ka and 11 16 ka these data yield recurrence intervals of 17 65 k y and 74 97 k y and an elapsed time of 11 16 k y since the youngest event slip rate determinations at the orovada site are complicated by multiple fault strands but rates calculated from a variety of data are surprisingly low 0 01 0 16 mm yr given the topographic prominence of the santa rosa range a lack of compelling patterns in a comparison of paleoseismic parameters indicate that the srrfz is no more likely a location for a large magnitude earthquake than previously identified seismic gaps or along faults that lie directly north of the cnsb

late quaternary environmental changes and the alluvial record in humid tropical environments abstract ice core and ocean drilling records now confirm the evidence from lakes rivers and mires concerning temperature depression in the humid tropics during the lgm by at least 5 c on land and this accords with the recent ccm1 model output there is less agreement about fluctuation in precipitation amount intensity and seasonality during the late quaternary pollen records remain indeterminate because of the absence of sites in lowland rainforest locations and a widespread hiatus in sedimentation spanning the lgm alluvial sediments have often been ignored by specialists from other disciplines but they also provide a valuable source of palaeoenvironmental information that reflects catchment wide conditions current evidence shows that prolonged sedimentation took place in stage 3 at sites in s america and se asia and this was followed by incision for up to 9 ka spanning the lgm streams either produced little sediment or were characterised by braided channels and sometimes fan deposits until the transition towards an interglacial mode took place after 12 700 bp 14 c in many places this transition was marked by large floods incision and deposition of coarse sediment but as the holocene climates stabilised and fluctuations of runoff reduced in amplitude so meandering rivers developed floodplains with thick overbank silts and clays these changes have regional and intercontinental patterns not everywhere identical in bracketing dates but demonstrating major changes to the fluvial systems as a result of profound changes to the hydrology of forested tropics during the last 60 ka

geochemistry and secular trends in the middle late permian karst bauxite deposits northwestern iran abstract this study focuses on the middle late permian bauxite deposits found within karstic depressions and sinkholes of carbonates of the ruteh and nessen formations northwestern iran data concerning five karst bauxite deposits each related to a different stratigraphic position within the bedrock were selected to address the chemical distribution and inter elemental relationships especially for critical elements factors that control bauxite formation and the parental affinity the analyzed samples mainly clayey bauxite and bauxitic clay are characterized by large compositional fluctuations involving both major and trace elements the major element composition is dominated by sio2 tio2 al2o3 and fe2o3 among the critical elements compositional fluctuations induce the occurrence of outliers for co nb ta lree and hree similar to other trace elements such as ba sr cr u and zr elemental mobility indicates that most of elements are generally depleted among the critical elements co is enriched only in several samples of the older deposits and ree are enriched in some samples of the younger deposits factor analysis suggests that due to the observed al ga covariance fairly acidic conditions were never attained during bauxitization and that detrital resistant minerals concentrated during a bauxitization stage promoting al ti accumulation furthermore the u co variance with low soluble elements nb ta and th suggests that u was mostly conservative during the formation of deposits cobalt co varies with cr and these elements accumulated during later bauxitization stages when the massive leaching of silica occurred the cia ciw and pia paleo weathering proxies indicate an upward weathering increase which suggests a trend toward more extreme weathering conditions in a wetter and warmer climate according to the permian global warming this is consistent with an upward increasing ba sr ratio and the inspection of the a cn k plot where the younger deposits fall close to the a k edge involving a clayey precursor requires a rainfall increase interestingly the upward trend toward a warmer and wetter climate was also coupled with paleo redox conditions promoting cerium oxidation as depicted by the ce ce values finally the eu anomaly and the sm nd ratio indicate that the studied bauxite deposits were mainly derived from a mafic protolith that formed in the middle late permian as a consequence of the volcanism that affected the entire iranian platform a cluster of karst bauxites however has eu eu values lower than the average standard deviation range of the mafic rocks suggesting a possible contribution of a more differentiated and less mafic protolith similarly the u th ratio at large supports the hypothesis of a mafic protolith for the middle late permian bauxite deposits although some samples show the u th values well above the average standard deviation range of the mafic rocks likely indicating that processes promoting the accumulation of resistant minerals with high u th ratios cannot be excluded this means that in this case the u th ratio does not necessarily reflect the protolith of karst bauxites and that more in general this proxy needs to be carefully interpreted when used to assess the parental affinity of residual rocks

distribution of rare earth elements and oxyhydroxide phases within a weathered felsic igneous profile in hong kong abstract variation in type and abundance of oxyhydroxide phases and the fractionation of rare earth elements ree within a weathered felsic pyroclastic profile in hong kong were investigated in order to assess the key factors and micro environmental conditions controlling their distribution during weathering at rock and mineral scales three types of oxyhydroxide phases fe mn and ce rich were recognized based on their most abundant elements the fe rich types appeared in all samples at different stages of weathering the mn rich types however were limited to samples at advanced stages of weathering while the ce rich types were found solely in samples from oxyhydroxide rich zones fractionation of ree likely started at the early stages of weathering but became evident only at the advanced stages characteristics of ree patterns especially the direction negative or positive and extent of ce anomalies correlated very well with the appearance and abundance of mn oxyhydroxides and were attributed to the co existence of distinct micro environmental conditions within the profile these conditions resulted from two major competing processes leaching and fixation and oxidation precipitation and reduction dissolution which operated simultaneously within the profile at any given stage of weathering

quantitative geochemical approach to pedogenesis importance of parent material reduction volumetric expansion and eolian influx in lateritization abstract using mass balance techniques we test the prevalent view that laterite genesis is dominated by in situ residual enrichment during chemical weathering of bedrock through calculation of net mass fluxes through the laterite soils in mali west africa we show that residual enrichment by removal of mobile elements with a corresponding increase in bulk porosity and decrease in bulk density contributes only a very minor fraction of the enrichment of al fe si and au instead we demonstrate that the abundance of these elements is due to the influx and accumulation by selective retention of chemically mature detritus of local and foreign origin clearly evident in micromorphological infilling features at the same sample depths that accumulation reaches extreme values we show that volumetric expansion in excess of 200 has occurred locally we infer that these spatially coincidental zones of mass influx of rock forming metals fe al si and also au with dilational hyperstrains result from a mutually reinforcing mechanical interaction between material influx and the effects of subsurface deformational processes such as shrink swell cycles and root growth and decay we propose that with progressive infilling of available connected voids by illuvial microsedimentary deposits of insoluble resistate and neoformed minerals the capacity for the combined skeleton and plasma to remain isovulumetric is exceeded we speculate that the resultant space problem is relieved by upwards expansion towards the overlying free surface continued translocation and void infilling occur and are limited to the depth where the size of translocational particles is smaller than that of the connected voids consequently progressive hyperstrains accumulate above this critical depth by the long term influence of a proposed translocational wedge of chemically resistant minerals against which numerous generations of plant roots have exerted stresses eclectic surficial contaminants involved are continuously derived from above leaving no indication of a relict source region within the present soil profile from which they might have been extracted instead the source region is largely the existing regolith column itself which releases local material and in addition is supplemented by deposition of colluvial detritus shed nearby by escarpment retreat

microbial controls on phosphate and lanthanide distributions during granite weathering and soil formation abstract both microbial and geochemical factors control the form distribution and abundance of lanthanides during weathering and soil formation in a profile in the bemboka granodiorite from southern new south wales australia during the initial stages of weathering hydrous ce bearing lanthanide and lanthanide aluminum phosphates including rhabdophane and florencite crystallize on etched apatite surfaces throughout the profile however their fate depends greatly on their location within the profile in rocks weathered 5 6 m below the soil zone the lower profile secondary lanthanide phosphates persist long after all apatite has been dissolved however in rocks weathered within 2 m of the soil zone the upper profile secondary phosphates are dissolved and lanthanides other than ce are removed bacteria and fungal hyphae are localized on secondary phosphate surfaces suggesting that rhabdophane and florencite are solubilized in the upper profile due to organic complexation of dissolved lanthanides and or uptake of phosphate by cells in the soils defined by loss of granitic texture secondary phosphates are replaced by ce oxides lanthanides other than ce removed in solution from the upper profile precipitate as ce poor phosphates in the lower profile when the solubility product is exceeded due to high dissolved phosphate concentrations in proximity to apatite thus the upper profile is the source of lanthanides added to the lower profile in both the lower and upper weathered granite the degree to which weight based ce abundances increase with increasing weathering is consistent with ce immobility on the centimeter scale we attribute the very high weight based ce abundances up to 12 concentrations in fresh rock to extensive leaching and compaction during transformation of weathered rock to soil

cassini observes the active south pole of enceladus cassini has identified a geologically active province at the south pole of saturn s moon enceladus in images acquired by the imaging science subsystem iss this region is circumscribed by a chain of folded ridges and troughs at 55 s latitude the terrain southward of this boundary is distinguished by its albedo and color contrasts elevated temperatures extreme geologic youth and narrow tectonic rifts that exhibit coarse grained ice and coincide with the hottest temperatures measured in the region jets of fine icy particles that supply saturn s e ring emanate from this province carried aloft by water vapor probably venting from subsurface reservoirs of liquid water the shape of enceladus suggests a possible intense heating epoch in the past by capture into a 1 4 secondary spin orbit resonance

a fracture history on enceladus provides evidence for a global ocean 1 the region surrounding the south pole of saturn s moon enceladus shows a young pervasively fractured surface that emanates enough heat to be detected by the cassini spacecraft to explain the elevated heat and eruptive icy plumes originating from large cracks informally called tiger stripes in the surface many models implicitly assume a global liquid ocean beneath the surface here we show that the fracture patterns in the south polar terrain spt of enceladus are inconsistent with contemporary stress fields but instead formed in a temporally varying global stress field related to nonsynchronous rotation of a floating ice shell above a global liquid ocean this finding increase to at least three the number of outer planet satellites likely to possess a subsurface liquid water layer

geochemistry mineralogy and geochemical mass balance on major elements in two peat bog profiles jura mountains switzerland abstract the mineralogical and chemical composition of peats from two sphagnum bogs in the franches montagnes region jura mountains switzerland were compared the peats in the top 102 cm at etang de la gruere egr represent 2110 years of peat formation compared with 1730 years for the first 84 cm at tourbiere de genevez tge scandium was used as a conservative tracer to distinguish between the primary sources of major elements to the bogs atmospheric deposition of soil derived aerosols egr and tge physical incorporation of elements along with mineral matter from the underlying sediments tge and adsorption or complexation by the peat following diffusion from groundwater tge these results support previous findings which showed that the egr core 102 cm is exclusively ombrogenic compared with tge where the peats below approx 30 cm become predominantly minerogenic the modern rates of sc accumulation past 100 years are similar in the two cores 39 g m 2 a 1 at egr versus 52 g m 2 a 1 at tge however comparison with deeper sections of the egr core reveals that the present day rates of atmospheric sc deposition are nearly 3 times greater than the long term average rate reflecting the higher concentrations of soil derived atmospheric aerosols today the rates of sc accumulation in the tge core are slightly higher than at egr this reflects the incorporation of mineral matter from the underlying sediments in the deeper minerogenic peats at tge the long term rates of fe and ca accumulation are 5 and 7 times higher respectively than in the egr core these fluxes greatly exceed the difference in sc flux and cannot be explained by the differences in amount of mineral matter in the peats these enrichments require an independent explanation and are most likely the result of adsorption and or complexation of cationic ca and fe species diffusing from deeper layers in the profile the mineralogical composition of the ash is mainly quartz 60 90 with feldspar 5 15 and muscovite 5 15 although various other minerals 5 10 are commonly present biogenic si represents another important fraction of ash and is abundant 30 70 at discrete depths the vertical profiles showed no significant changes in mineralogy with depth assuming a constant composition of source materials the lack of progressive mineralogical change suggests that the fine grained silicates supplied by soil dust have not been measurably weathered during the past two millennia a number of peaks in fe sc are found in both cores above peaks in ash content and density these appear to correspond with temporal fluctuations in wet dry conditions accumulation of fe oxides during dry periods and leaching during wetter conditions

formation and transformation processes of iron duricrust systems in tropical humid environment abstract formation and transformation processes of iron duricrust developed under tropical humid conditions in the southeastern part of the central african republic have been investigated in terms of geomorphological petrological and geochemical pathways the study of five typical weathering profiles of the most extensive iron duricrust system now known in the world indicates that saprolitization and ferruginization are sequentially involved in such processes as reflected by kaolinite gibbsite and hematite goethite replacements alkali earths rare earths metals and elements belonging to chemically inert minerals segregate during saprolite and iron duricrust formation and degradation mass balance calculations performed on a typical weathering system enable us to quantify net mass element transfers deriving from lateritic weathering processes volumetric change collapse or dilation as well as al and ti clearly discriminate between the saprolitization and ferruginization processes saprolite development preserves the geochemical inheritance of parent rocks whereas ferruginization depletes it and mostly reflects through mineralogical pathways pedoclimatic conditions and global climatic changes the global iron duricrust system of the southern part of central africa derived from previous hematite rich crust and not from ancient bauxites as it is generally believed for iron crusts formed on west african shields

the use of duricrusts and topographic relationships in geomorphological correlation conclusions based in australian experience though there are many possible pitfalls duricrusted surfaces provide morphostratigraphic markers which are useful in preliminary extrapolation and correlation at the local and regional scales especially if other factors such as landscape evolution and topographic relationships are also considered particular reference is made to ferruginous and siliceous cappings close stratigraphic dating of the duricrusts allows regional differentiation but correlations are preferably intra rather than inter regional and are at best general and involve age ranges rather than narrow time frames problems broached include type of landscape development the relation of surface and duricrusts and the temporal equivalence of duricrust facies i e duricrusts of similar chemical tendencies but contrasted morphology the roles of duricrusts in relief inversion surface preservation and climatic interpretation are also mentioned

chemical mobilizations in laterites evidence from trace elements and 238u 234u 230th disequilibria geochemical and mineralogical investigations including measurements of major and trace elements sr isotope ratios and 238u 234u 230th activity ratios were made on an old african laterite to reconstruct its formation steps and assess recent chemical mobilization the present data support a scenario of discontinuous formation for the laterite with different bedrock weathering conditions during the formation of each unit rather than a scenario of continuous formation absolute accumulation of fe u and lanthanides in the uppermost ferruginous unit suggests an autochthonous origin of this iron cap by leaching of an older overlying profile present chemical distributions of lanthanides as well as of rb k ba and sr within the profile cannot be linked to the mineralogical distribution of both relictual primary and authigenic secondary phases complementary lanthanide patterns indicate that these elements were primarily accumulated in the uppermost ferruginous unit before further remobilization and accumulation in the underlying horizons these redistribution processes may be related to the chemical instability of the ferruginous cap the 238u 234u 230th disequilibria indicate that recent u mobilization occurs in the whole profile and that as for lanthanides there is a vertical redistribution of u from the uppermost ferruginous unit to the underlying horizons moreover these data show that both u losses and gains exist at each level of the profile a simple modeling of this double u mobilization process is proposed to interpret the 238u 234u 230th data differences in the mobilization and fractionation intensities of the u input and removal processes can account for the two evolution trends which distinguish the ferruginous unit from the underlying ones furthermore on the basis of this modeling the profile appears to be in a transient state because of recent changes in the u mobilization conditions which could correspond to major pleistocene climatic variations

glacialanterglacial record from intertropical africa high resolution pollen and carbon data at rusaka burundi abstract in northern intertropical africa many geological data have documented several abrupt climatic fluctuations taking place during the time of the last deglaciation one of them is an aridity event generally placed in the interval 11 000 10 000 bp and synchronous with the younger dryas cold episode of the temperate regions that has been explained by the influence of the atlantic ocean circulation on global climate in this paper we present high resolution 50 to 150 years studies of organic matter and pollen undertaken on a new core from the rusaka peat bog 3 26 south 29 37 east 2070 m altitude dated by the conventional l2 dates and the ams methods 18 dates obtained on bulk sediment and macroremains although the sediment at the bottom of the core was deposited during the last glacial period prior to 21 000 bp the dating provides a reliable chronology for the last 12 000 bp only several vegetational changes are documented in the interval 12 000 9000 bp but their chronological placement can only be achieved with a few years of uncertainties a great dispersion of ams dates is attributed to contamination by charcoal dated between 11 700 and 11 500 bp and to a possible age plateau at ca 10 000 bp therefore the results are preferably presented versus depth to keep synchronism in the stratigraphic placement of the successive events at rusaka increase in carbon storage c n ratio for terrestrial plants and tree cover began at ca 12 000 bp soon after the swamp had been established this date is in good agreement with a major increased hydrological balance well documented throughout the intertropical region the forest installation is progressive rather complex and seen as a two step process the first forest phase 11 700 bp to 10 600 bp is dominated by hagenia a montane taxon in good correspondance with previous records from other authors in east african mountains the second forest regeneration took place post 10 000 bp after a clearly reversed trend of tree cover from 10 600 to 10 000 bp ending with a short episode of minimum trees lasting no more than about 200 years but there is no indication of cooling whatsoever and the opening of the forest is better explained by increased aridity rather than normal pattern of forest succession this will remain a controversal interpretation among palynologists until high resolution pollen data can be obtained for the 13 000 bp and earlier period nevertheless the timing of the arid episode at rusaka is in good agreement with other evidence mentioned from highland and lowland pollen data a detailed comparison with 25 available pollen diagrams is limited by poor or inconsistent dating or low resolution of the pollen data nevertheless pollen from four of them document an arid event in good agreement with its timing at rusaka and high resolution isotopic results from two sites in equatorial lowlands and from the sahel this work shows that the arid younger dryas occurred at the same time both in lowlands and highlands and therefore was most likely a precipitation signal rather than a response to temperature decrease

tidal disruption of phobos as the cause of surface fractures phobos the innermost satellite of mars displays an extensive system of grooves that are mostly symmetric about its sub mars point phobos is steadily spiraling inward due to the tides it raises on mars lagging behind phobos orbital position and will suffer tidal disruption before colliding with mars in a few tens of millions of years we calculate the surface stress field of the deorbiting satellite and show that the first signs of tidal disruption are already present on its surface most of phobos prominent grooves have an excellent correlation with computed stress orientations the model requires a weak interior that has very low rigidity on the tidal evolution time scale overlain by an 10 100 m exterior shell that has elastic properties similar to lunar regolith as described by horvath et al 1980

intensive kaolinization during a lateritic weathering event in south west spain mineralogical and geochemical inferences from a relict paleosol abstract this study documents the mineralogical and geochemical record of a lateritic weathering event during the pliocene in south west spain the paleoweathering profile derived from arkosic sands and comprises a white sandy clayey saprolite a red mottled clay zone overlain by a thick soft layer and a ferruginous pisolitic hardcap partially dismantled by erosive processes kaolinite quartz and degraded k feldspars are the major minerals forming the saprolite along with al goethite mottled zone as well as gibbsite and boehmite soft layer while the pisolitic duricrust is essentially composed of quartz grains embedded in a matrix of fe oxy hydroxides hematite goethite and or maghemite besides quartz the phases most resistant to alteration were a variety of heavy minerals mostly titanium oxides that are present as minor impurities in the residual kaolin deposit the dominant weathering process of kaolinization is geochemically characterized by striking losses of na k ca mg and large ion lithophile elements rb sr cs ba and u because of the almost entirely breakdown of primary minerals mainly feldspars and 2 1 phyllosilicates the ti normalized distribution patterns of trace elements also reveals remobilization and redistribution processes within the profile involving high field strength elements classically regarded as immobile like zr and hf iron showed a contrasted behaviour with depletion in the saprolite zone and strong accumulation in the pisolitic duricrust various transition trace metals cr v sc th nb and ta remained relatively immobile during the weathering and were residually concentrated in the duricrust linked to the fe oxy hydroxides the geochemical and mineralogical evolution of the paleosol studied is consistent with a laterization process evolved under humid subtropical conditions and driven by morphodynamic and hydrodynamic factors gently sloping coastal area with fluctuating water table and rapid water percolation favourable for the development of a deeply kaolinized paleosurface

gravitational spreading bookshelf faulting and tectonic evolution of the south polar terrain of saturn s moon enceladus abstract despite a decade of intense research the mechanical origin of the tiger stripe fractures tsf and their geologic relationship to the hosting south polar terrain spt of enceladus remain poorly understood here we show via systematic photo geological mapping that the semi squared spt is bounded by right slip left slip extensional and contractional zones on its four edges discrete deformation along the edges in turn accommodates translation of the spt as a single sheet with its transport direction parallel to the regional topographic gradient this parallel relationship implies that the gradient of gravitational potential energy drove the spt motion in map view internal deformation of the spt is expressed by distributed right slip shear parallel to the spt transport direction the broad right slip shear across the whole spt was facilitated by left slip bookshelf faulting along the parallel tsf we suggest that the flow like tectonics to the first approximation across the spt on enceladus is best explained by the occurrence of a transient thermal event which allowed the release of gravitational potential energy via lateral viscous flow within the thermally weakened ice shell

effect of enceladus s rapid synchronous spin on interpretation of cassini gravity enceladus s degree 2 gravity determined by cassini is nominally nonhydrostatic to 3 j2 c22 3 38 3 63 as opposed to 10 3 iess et al 2014 interpret this in terms of a hydrostatic interior core and isostatic not hydrostatic floating ice shell enceladus s rapid 1 37 d synchronous spin and tide distorts its shape substantially though enough that the predicted hydrostatic j2 c22 is not 10 3 but closer to 3 25 this leads to the following revision to the internal picture of enceladus compared with iess et al 1 the satellite s core is somewhat smaller and slightly denser 190 km radius and 2450 kg m3 2 the compensation depth shell thickness of the global degree 2 ice shell is 50 km rather close to the base of the modeled ice water layer and 3 the compensation depth shell thickness beneath the south polar terrain from j3 remains shallower thinner at 30 km independent of but influenced by the degree 2 solution

zircon an immobile index in soils interpretation of any element s mobility in soils needs rigorous means of calculating losses or gains in relation to parent rock the first mass balance calculations were based on isoelement changes major elements during conversion of fresh rocks to weathered materials harrisson 1933 leneuf 1959 isovolumetric mass balance calculations were applied for the first t ime in 1955 to determine mass transfers in saprolite millot and bonifas 1955 since that time numerous works have been carried out on mass balance calculations in determining transfers during weathering brimhall and dietrich 1986 recently equations used to calculate volumetric changes and net mass gain or loss of mobile elements have been based on zirconium mostly from the mineral zircon the aim of the paper is to question the axiomatic immobility of zircon in soils and then to assess the limit of mass balance calculations in surficial weathering systems

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