illite neoformation in plagioclase during weathering evidence from semi arid northeast brazil illite minerals in soils and weathered rocks are usually interpreted as secondary clays derived from the transformation of primary rock forming minerals with similar properties e g muscovite or as direct products of hydrothermal alteration after feldspar i e sericite with the help of detailed investigations involving x ray diffraction scanning electron microscopy and x ray element mapping this study testifies to the neoformation of illite inside plagioclase feldspar crystals after their partial dissolution in the weathering zone of luvisols in semi arid northeast brazil our results thus reveal that meteoric weathering can produce illite not only from mica i e by a transformation process but also within non alkali feldspar by a neoformation process at least under the semi arid conditions that have long prevailed in the study area given that illite in weathering mantles has recurrently been attributed often by default to hydrothermal processes results shown here provide new focus to an alternative pathway of illite formation primarily controlled by climate

chemical weathering indices applied to weathering profiles developed on heterogeneous felsic metamorphic parent rocks abstract chemical weathering indices are commonly used for characterizing weathering profiles by incorporating bulk major element oxide chemistry into a single metric for each sample generally on homogeneous parent rocks weathering indices change systematically with depth however the weathering of heterogeneous metamorphic rocks confounds the relationship between weathering index and depth in this paper we evaluate previously defined chemical weathering indices for their suitability in characterizing weathering profiles developed on felsic heterogeneous metasedimentary bedrock from coweeta hydrologic laboratory north carolina usa among the weathering indices evaluated here the weathering index of parker wip is the most appropriate for application to weathering profiles on heterogeneous and homogeneous parent rock because the wip includes only the highly mobile alkali and alkaline earth elements in its formulation it yields values that differ greatly from those of the parent rock in addition the wip allows for aluminum mobility unlike other weathering indices these characteristics combine to make the weathering index of parker the most applicable index for studying the weathering of heterogeneous metasedimentary rocks however the wip should be applied judiciously as alkali and alkaline earth metals may be readily depleted during weathering in addition to reflecting weathering the chemical index of alteration cia chemical index of weathering ciw plagioclase index of alteration pia and vogt s residual index v may be sensitive to subtle geochemical changes such as hydrothermal alteration along a fault and or alteration at the water table weathering indices that include iron in their calculations were not included in this study because they do not distinguish between ferric and ferrous iron the oxidation state and distribution of iron in a weathering profile is influenced by the proportion of oxidation states in the pre weathered metamorphic rock and interaction with groundwater during weathering

stereo topography of the south polar region of mars volatile inventory and mars polar lander landing site viking stereo images and topographic maps reveal that the south polar layered deposits of mars are topographically complex and morphologically distinct from the north polar layered deposits the dominant feature is a 500 km wide topographic dome that rises 3 km above the surrounding plains this dome underlies the residual ice cap but is at least 50 larger in area erosional scarps and terraces indicate that this dome was once more extensive and has undergone erosional retreat adjacent to the dome layered deposits form a vast plateau 1 1 5 km high extending 1000 km beyond and to one side of the residual south polar cap this plateau is relatively flat at kilometer scales although it is cut in places by troughs and depressions which have locally steep scarps up to 2 km high and sloping up to roughly 10 contiguously flat kilometer scale regions the size of the mars polar lander mpl landing ellipse are present these are in the form of plateaus 100 300 km wide and 1 2 km high one of the largest of these plateaus has been proposed as a landing site for the mars polar lander mpl the volume associated with the south polar layered deposits may be comparable to those of the layered deposits at the north pole although this doubles the current probable inventory of surface ice on mars it still falls far short of accounting for the inferred volume of water on mars in the past

stepped surfaces and palaeolandforms in the northern brazilian nordeste constraints on models of morphotectonic evolution abstract from the parnaiba basin to the borborema plateau northeastern brazil the crystalline and sedimentary highlands and plains of the huge jaguaribe piranhas amphitheatre are intersected seawards by offset elements of a marginal scarp which overlooks coastal lowlands along the equatorial atlantic transform margin its stepped surfaces are classically related to regional uplift induced by the break up of the gondwana supercontinent supposed to have triggered the formation until the plio pleistocene of successively younger planation surfaces below a culminating cretaceous surface a reinterpretation of this topography combined with analyses of palaeolandforms surface deposits drainage anomalies and structural controls on landforms is used to obtain ages for significant features of the stepped patterns and to propose a morphostratigraphic scheme for the whole area it is shown that the regional morphology is widely controlled by structures formed during early cretaceous continental rifting and later aptian oceanic opening exhumed pre cenomanian palaeolandforms planation surfaces residual cretaceous fault scarps are identified this study points out the value of the morphostructural approach for revisiting classical problems of geomorphology such as the meaning of stepped landforms identification of palaeosurfaces of cretaceous age at various levels and the age and origin of planation surfaces its results are considered as constraining elements for a further tentative reconstruction of the morphotectonic evolution of this margin

factors controlling sediment yield from small intensively cultivated catchments in a temperate humid climate abstract data on sediment yield from 26 small cultivated catchments 10 10 000 ha in central belgium were collected based on sedimentation rates in small flood retention ponds area specific sediment yield varies from 0 4 to 20 6 t ha 1 year 1 for catchments ranging from 7 to 4873 ha various catchment properties were analysed in order to understand this large variation in sediment yield catchment area alone explains 64 of the observed variance in area specific sediment yield although no other parameter could explain more it is concluded that catchment area is not a valid parameter to link with sediment yield overall catchment geomorphology e g presented by the hypsometric integral is much more important in controlling sediment yield the lack of data however made this not very clear a multiple regression model including three morphological catchment properties is a valuable tool to predict total sediment yield t year 1 from catchments in central belgium this model has an efficiency of 0 81 furthermore it was concluded that the within catchment spatial distribution of parameters for instance slope steepness is very important but difficult to obtain one single representative value the use of spatially distributed erosion and sediment delivery models is therefore necessary accurate sediment yield data like the one presented in this study however are needed to validate these models

physical and chemical weathering rates and co2 consumption in a tropical lateritic environment the upper niger basin the chemical composition of niger river water measured bimonthly at bamako mali during the period 1990 1992 provides an estimate of present weathering rates in the upper niger basin the dominant weathering process is kaolinite formation monosiallitization however seasonal variations promote gibbsite formation in the rainy season september and smectite development in the dry season may the results show that lateritic profiles continue to develop even during very dry episodes the rate of profile development calculated as the difference between the chemical weathering rate at the base of the soil profile and mechanical erosion rate at the soil surface is about 1 3 to 3 7 m myr a comparison between 43 river basins of the world shows that for similar runoff the co2 flux consumed by silicate weathering is about two times lower in lateritic areas than in nonlateritic zones

the characterization of steady state in earth surface systems findings from the gradient modelling of an indian climosequence abstract gradient modelling of a steep ecocline in south india has highlighted a suite of landscape units which appear to be entirely ordained by a simple water balance index this univariate climofunction is reflected in vegetation landform weathering and soil patterns although the vegetation successions are the most spectacular consistent pedogeomorphological trends were identified at several embedded scales of reality at the microscopic scale the existence of illite rich saprolite situated between the kaolinite dominated and smectite dominated core areas of the climosequence so far a missing mineralogical link only predicted by geochemical theory was effectively verified by field evidence at the megascopic scale the variation in topographic texture from polyconvex to polyconcave land systems via a convexo concave transition zone also suggests a strong relationship between hydroclimatic budgets and landforms such an exceptional environmental cabinet is well suited to reexamining other benchmark climosequences of the tropics and to readdressing the debated theories of climatic geomorphology by a discussion on the applicability of climax and steady state to tropical landforms

discharge and suspended sediment patterns in a small mountainous watershed with widely distributed rock fragments summary understanding and quantifying sediment loads is important in watersheds with highly erodible materials which will eventually cause environmental and ecological problems within this context suspended sediment ss transport and its temporal dynamics were studied in a small mountainous watershed with sloping lands containing rock fragments in subtropical china soils containing rock fragments with many macro pores have a high permeability rate over a 7 year period the mean runoff coefficient of this watershed was 0 65 overall 30 flood events were monitored and accounted for 95 5 27 3 17 1 of the total ss load precipitation and total discharge respectively over a 5 year period the presence of rock fragments in soils can affect soil loss when comparing the soil loss in the studied watershed with that of other watersheds under similar climatic conditions rock fragments negatively affect soil loss however an extreme event occurred on 14 august 1990 and the sediment load exhibited a phenomenon called small deposits towards lump withdrawal which resulted in a soil loss of 20 499 t 4 6 times the mean yearly soil loss this event exhausted most of the ss s stored by the rock fragments on the slope and channel following this event the mean ss concentration ssc of the 11 events was 1 05 kg m 3 and the mean ssc of the 18 previous events was 1 75 kg m 3 twelve variables were separated using the classical hydrograph separation method partial least squares regression plsr was used to determine the highly co related variables of the discharge the results indicated that plsr could explain runoff well the relationship between discharge and ssc was highly scattered during 24 flood events three types of hysteresis loops were observed clockwise 17 events figure eight 3 events and complex 4 events

lightning as a geomorphic agent on mountain summits evidence from southern africa abstract the presence of angular bedrock derived debris on mountain summits worldwide has usually been associated with present or past periglacial frost shattering thermal fracturing and other climatically mediated weathering processes climatic inferences are commonly made based on such geomorphological evidence even if frost shattering and other processes are unlikely under present climatic conditions this paper questions this assumed genetic link between present past climate and production of angular bedrock derived debris by describing the geomorphological impacts of lightning strikes on exposed mountain summits using examples from the high drakensberg of eastern lesotho southern africa the impacts of lightning strikes are described which include the generation of angular fractured bedrock derived debris these impacts are identified in the field based on clear and unambiguous criteria that can be used to distinguish between lightning induced weathering processes and those processes associated with more typical alpine weathering this paper argues that lightning strikes are an important geomorphic agent of in particular low latitude mountain summits and that to make uncritical climatic inferences based on the presence of frost shattered debris on mountain summits is wholly erroneous

observations of the north polar region of mars from the mars orbiter laser altimeter elevations from the mars orbiter laser altimeter mola have been used to construct a precise topographic map of the martian north polar region the northern ice cap has a maximum elevation of 3 kilometers above its surroundings but lies within a 5 kilometer deep hemispheric depression that is contiguous with the area into which most outflow channels emptied polar cap topography displays evidence of modification by ablation flow and wind and is consistent with a primarily h2o composition correlation of topography with images suggests that the cap was more spatially extensive in the past the cap volume of 1 2 3 10 6 to 1 7 3 10 6 cubic kilometers is about half that of the greenland ice cap clouds observed over the polar cap are likely composed of co 2 that condensed out of the atmosphere during northern hemisphere winter many clouds exhibit dynamical structure likely caused by the interaction of propagating wave fronts with surface topography

above the weathering front contrasting approaches to the study and classification of weathered mantle abstract weathered mantle comprises the materials above bedrock and below the soil it can vary in thickness from millimeters to hundreds of meters depending primarily on climate and parent material study of the weathered mantle comes within the realms of four disciplines geology geomorphology soil science and civil engineering each of which uses a different approach to describe and classify the material the approaches of engineers geomorphologists and geologists are contrasted and compared using example papers from the published literature soil scientists rarely study the weathering profile as such and instead concentrate upon soil forming processes and spatial distribution primarily in the solum engineers including engineering geologists study the stability and durability of the weathered mantle and the strength of the materials using sophisticated procedures to classify weathered materials but their approach tends to be one dimensional furthermore they believe that the study of mineralogy and chemistry is not useful geomorphologists deal with weathering in terms of process how the weathered mantle is formed and with respect to landform evolution using a spatial approach geologists tend to ignore the weathered mantle because it is not bedrock or to study its mineralogy and or chemistry in the laboratory i recommend that the approaches of the various disciplines be integrated geomorphologists and geologists should consider using engineering weathering classifications and geologists should adopt a spatial perspective to weathering as should engineers and engineering geologists

the sediment delivery problem abstract the linking of on site rates of erosion and soil loss within a drainage basin to the sediment yield at the basin outlet and improved knowledge and representation of the associated processes of sediment delivery represent a major research need within the field of erosion and sedimentation and also an important scale problem in drainage basin studies this paper reviews the limitations of the sediment delivery ratio concept by considering the problems of temporal and spatial lumping and its blackbox nature some recent advances in our understanding of the sediment delivery system and its modelling are described and the lack of detailed empirical investigations is highlighted the significance of recent concern for the role of sediments in the transport of nutrients and contaminants to sediment delivery studies is introduced and the need for further work in this field is emphasised

soils and climatic geomorphology on the karnataka plateau peninsular india abstract as a result of extensive field reconnaissance in southern india a geographical traverse across the planation surface of the karnataka uplands which lie in the rainshadow of the western ghats was selected to assess the consequences of a steep rainfall gradient on soil and landform patterns the study of the traverse described in detail reveals a characteristic progression of soil type and wash divide form from the high rainfall to the semi arid end of the continuum and invites a critical reappraisal of classical notions in climatic geomorphology and the soil sciences the assumption that alternations of wet and dry climates are necessary to achieve planation is given special consideration and the often held belief that kaolinite minerals are diagnostic of humid palaeoclimates when found in a semi arid climate is challenged the findings for the indian traverse are set against the better known data for west africa where the rainfall range between the gulf of guinea and the sahel is comparable with that observed in the south western deccan differences outweighing similarities attention is drawn to the possibility that tectonic regime which also controls the degree of landscape stripping is a major key to understanding the climatic geography of soils the tread of planation surfaces and the shape of hillslopes from one region of the tropics to another

paleomagnetism applied to lateritic profiles to assess saprolite and duricrust formation processes the example of mont baduel profile french guiana abstract based on the fact that a chemical remanent magnetization crm can be acquired during the lateritization the paleomagnetic signal was used to interpret the succession of horizons from the weathering front to the top of the duricrust surface of a thick bauxitic profile in french guiana the 54 m thick profile is composed of a saprolite capped by a duricrust comprising successively a mottled zone a massive facies and a pisolitic facies at the top at the base of the saprolite the natural remanent magnetization nrm is composed of a superimposed magnetite and hematite contribution the magnetite showing an apparently inherited proterozoic direction within the profile the main magnetic carrier is hematite goethite does not provide any significant contribution five magnetic reversals have been identified within the saprolite and through comparing the reversal sequence with the reference geomagnetic polarity time scale gpts it has been possible to deduce the saprolitization rate thus the bruhnes matuyama 780 ka transition is observed at 8 8 m above the weathering front giving a 11 3 0 5 m ma saprolitization rate the duricrust is significantly divided into two levels within the massive facies the base of the duricrust shows paleomagnetic directions that fit with the present day situation whereas the upper part records directions of the south american apparent pole wander path apwp older than 10 ma the study shows that hematite precipitation was not uniform within the duricrust during lateritization and seems to preserve traces of successive and distinct lateritization phases thus the lower massive duricrust formed during a recent lateritization period whereas the upper duricrust has preserved a paleomagnetic signal of an older lateritization phase our duricrust paleomagnetic interpretation is supported by sem observations of changes in hematite morphology

the neoproterozoic brasiliano orogeny in northeast brazil 40ar39ar and petrostructural data from ceara abstract the borborema province in ne brazil comprises paleoproterozoic basement and its proterozoic cover that experienced a complex tectonometamorphic history during the brasiliano pan african orogeny in ceara four major domains separated by continental scale steeply dipping dextral shear zones have been identified 40 ar 39 ar step heating of mineral separates and laser probe fusion of single grains have been used in conjunction with petro structural observations to delineate the cooling tectonic history of these domains to the north of the senador pompeu shear zone spsz amphibole and biotite pairs from low pressure granulite belts exposed along the granja shear zone and spsz record plateau ages in the range 575 560 ma corresponding to cooling rates close to 20 c m y 40 ar 39 ar laser probe muscovite dates from the chaval augen gneiss point to a similar age for shearing responsible for the exhumation and fast cooling of the granulite belts a muscovite biotite pair from the central ceara high pressure nappes lying between the shear zones documents a lower cooling rate in the interval 534 525 ma related to the decompression and uplift of previously deelly buried rocks to the south of the spsz only moderate crustal thickening occurred within the various schist belts a distinct cooling pattern is indicated for these belts and the western patos shear zone attesting to a different crustal development 40 ar 39 ar dates of amphibole phlogopite muscovite and biotite range from 550 to 522 ma recording a postmetamorphic cooling rate of 6 9 c m y slower cooling rates of 3 4 c m y between amphibole and biotite closure ages in the range 540 500 ma are reported for the eastern part of the palos shear zone system the diachronous cooling recorded along this shear zone is interpreted to reflect the variations in thickness of the high temperature mylonitic belts earlier more rapid cooling occurred where the belts are narrow in the west late slower cooling occurred in wider zones to the east these thermochronological data reveal an age and cooling rate distribution at the scale of the borborema province that provides new constraints on the development of the brasiliano orogeny between 580 and 500 ma

surface runoff features on mars testing the carbon dioxide formation hypothesis 1 fresh gully like features on mars strongly suggest that fluid flowed on the surface in the recent past here we consider the possibility that co2 vapor supported flows formed the gullies we find that neither condensed co2 nor co2 clathrate hydrate are likely to accumulate in significant quantities in the martian crust in addition if condensed co2 were present under lithostatic pressures exposure to the atmosphere would produce features analogous to terrestrial pyroclastic flows not surface runoff finally the source volume of co2 required to support a flow excludes clustered or episodic gully formation therefore we conclude that co2 cannot have formed the gullies in light of these results liquid water flow remains the preferred formation mechanism for the recent surface runoff features

impact of weathering on ree distribution in soil saprolite profiles developed on orthogneisses in borborema province ne brazil abstract rare earth elements rees are a group of elements from la to lu with high economic value and serve mainly as essential raw material for various high technology items this study explores mineral weathering and the geochemical evolution of regoliths quaternary period derived from orthogneisses late cretaceous period in four sites in borborema province ne brazil providing a new contribution to the understanding of the influence of soil and saprolite attributes on the distribution of rees in the regolith we used optical and electron microscopy to depict the weathering of minerals in the rock saprolite and soil microstructure focusing on the distribution of rees in the regolith depth 3 0 m we also determined the poorly and well crystallized iron oxide contents the clay fraction amount and the total organic carbon content to observe how these attributes influence the distribution of rees in the soil and saprolite the results allowed the classification of weathering for feldspars micas and other primary minerals into four stages based on their degree of alteration and the consequent influence on the geochemistry of the regoliths advancement of the weathering stages revealed the relative increases in fe and ti compared with ca mg na and k from the fresh rock up to the soil horizons and ilmenite and xenotime were the main sources of yb y co and p the patterns of signatures and anomalies were different for light lrees middle mrees and heavy rare earth elements hrees and for regoliths in different metamorphic complexes the lrees related well with the clay fraction amount the poorly crystallized iron oxides and the degree of weathering as estimated by the mineralogical index of alteration mia while the hrees related well with the total organic carbon toc in particular ce was strongly associated with mn oxides possibly due to simultaneous oxidative precipitation

spatial patterns of scale effect on specific sediment yield in the yangtze river basin abstract this paper examines the spatial variation of sediment yield in the yangtze basin in china a large basin with complex geology climate land use history and extensive sediment monitoring 287 stations with drainage area less than 10 000 km2 were used to study the scale effects of sediment yield in order to develop scale relations for regional sediment yield the whole study area was divided into eight sub basins relation between specific sediment yield and drainage basin area was built for each sub basin regional scaling relation was analyzed based on landforms geology lithology and land use of each sub basin three regional trends were identified in relation to the drainage area 1 a declining trend due to soil erosion on heavily cultivated steep land and the storage of sediment in floodplains 2 a flat trend due to mass movement on the upper reach and heavy agricultural disturbance on the middle and lower reaches and 3 an increasing trend due to downstream recruitment of sediment from land downstream where slope farming and deforestation occurred using these developed relations areally adjusted sediment yield maps were created over the entire yangtze basin

modeling the daily suspended sediment concentration in a hyperconcentrated river on the loess plateau china using the wavelet ann approach abstract the complexity of the relationship between suspended sediment concentration ssc and river discharge q remains a challenge for ssc prediction in hyperconcentrated rivers in this study the wavelet artificial neural network model wann was built to predict ssc in the kuye river a representative hyperconcentrated river in the middle yellow river catchments of china in the wann model the observed daily time series for q and ssc of 2193 days from 1967 to 1972 were decomposed into subseries at different scales using discrete wavelet analysis then the effective subseries were selected to construct q ssc inputs to the feed forward back propagation artificial neural network bp ann to predict ssc 1 day in advance the time resolution of the observed data the coefficient of determination r2 and root mean square error rmse were adopted to evaluate the model s performance the wann model showed higher prediction accuracy r2 0 846 and rmse 29 82 than the sediment rating curve src model r2 0 537 and rmse 55 40 or the ann model r2 0 664 and rmse 43 13 the wann model exhibited more robust performance than the src and ann models indicated by the appropriate values of error autocorrelation and input error correlation negative values of predicted ssc occurred in ann and in wann models by adjusting the negative values to zero the wann r2 was improved by 4 3 from 0 846 to 0 882 in general the results illustrate that the wann model better predicts ssc in a hyperconcentrated river setting with highly nonlinear and nonstationary time series

major element chemistry in the upper yangtze river a case study of the longchuanjiang river article water samples were collected twice per month over a two year period from the longchuanjiang river yunnan province china to understand monthly variations in major elements and solute fluxes as related to rock weatheringand associatedco2consumption rates solute concentrations were 5 times the medianof 65 mg l for global average total cationic exchange capacity tz

effects of sample size on the accuracy of geomorphological models abstract commonly the most costly part of geomorphological distribution modelling studies is gathering the data thus guidance for researchers concerning the quantity of field data needed would be extremely practical this paper scrutinises the relationship between the sample size the number of observations varied from 20 to 600 and the predictive ability of the generalized linear model glm generalized additive model gam generalized boosting method gbm and artificial neural network ann in two data settings i e independent and split sample approaches the study was performed using empirical data of periglacial processes from an area of 600 km2 in northernmost finland at grid resolutions of 1 ha 100 100 m and 25 ha 500 500 m a rather sharp increase in the predictive ability of the models was observed when the number of observations increased from 20 to 100 and the level of robust predictions was reached with 200 observations the result indicates that no more than a few hundred observations are needed in geomorphological distribution modelling at a medium scale resolution ca 0 01 1 km2

weathering geochronology by u th he dating of goethite nine samples of supergene goethite feooh from brazil and australia were selected to test the suitability of this mineral for u th he dating measured he ages ranged from 61 to 8 ma and were reproducible to better than a few percent despite very large variations in u and th in all samples with internal stratigraphy or independent age constraints the he ages corroborated the expected relationships these data demonstrate that internally consistent he ages can be obtained on goethite but do not prove quantitative 4he retention to assess possible diffusive he loss stepped heating experiments were performed on two goethite samples that were subjected to proton irradiation to produce a homogeneous distribution of spallogenic 3he the 3he release pattern indicates the presence of at least two diffusion domains one with high helium retentivity and the other with very low retentivity at earth surface conditions the low retentivity domain which accounts for 5 of 3he contains no natural 4he and may represent poorly crystalline or intergranular material which has lost all radiogenic 4he by diffusion in nature diffusive loss of 3he from the high retentivity domain is independent of the macroscopic dimensions of the analyzed polycrystalline aggregate so probably represents diffusion from individual micrometer size goethite crystals the 4he 3he evolution during the incremental heating experiments shows that the high retentivity domain has retained 90 95 of its radiogenic helium this degree of retentivity is in excellent agreement with that independently predicted from the helium diffusion coefficients extrapolated to earth surface temperature and held for the appropriate duration considering both the high and low retentivity domains these data indicate that one of the samples retained 90 of its radiogenic 4he over 47 5 ma and the other retained 86 over 12 3 ma thus while diffusive loss corrections to supergene goethite he ages are required these initial results indicate that the corrections are not extremely large and can be rigorously quantified using the proton irradiation 4he 3he method

shesed a physically based distributed erosion and sediment yield component for the she hydrological modelling system abstract shesed is introduced as a physically based spatially distributed erosion and sediment yield component for the existing she hydrological modelling system for use at the catchment scale for hillslopes represented spatially by the she grid square network shesed simulates soil erosion by raindrop impact leaf drip and sheet overland flow without rilling and the transport of the eroded material by overland flow for channels the component simulates the erosion of bed material and the downstream transport of this material together with that supplied by overland flow in the channel sediment routing procedure it is assumed that the flow can carry any available load of fine sediments less than 0 062 mm in diameter but for coarser sediments the load is limited by the calculated capacity transport rate of the flow the channel component also allows for bed armouring application of shesed to rainfall induced sediment yield events at two agricultural catchments areas 5 1 and 6 4 ha in iowa shows generally good reproduction of the observed temporal variations in sediment yield application to a 3 3 km reach of the east fork river wyoming for a 37 day period shows good reproduction of observed sediment discharge magnitudes but some discrepancy in the timing of the simulated sediment discharge peak

late quaternary vegetational and climate dynamics in northeastern brazil inferences from marine core geob 3104 1 abstract late quaternary paleoenvironments from northeastern ne brazil have been studied by pollen analysis of marine sediment the studied core geob 3104 1 3 40 s 37 43 w 767 m b s l from the upper continental slope off ne brazil is 517 cm long and 42 000 14 c yr bp old chronological control was obtained by 12 radiocarbon ams dates from individuals of the foraminiferal species globigerinoides sacculifer modern pollen analogs were received from 15 river lake and forest soil surface samples from ne brazil marine pollen dates indicate the predominance of semi arid caatinga vegetation in ne brazil during the recorded period between 42 000 and 8500 14 c yr bp the increased fluvial input of terrigenous material with high concentrations of pollen and specially fern spores into the marine deposits about 40 000 33 000 and 24 000 14 c yr bp and between 15 500 and 11 800 14 c yr bp indicate short term periods of strong rainfall on the ne brazilian continent the expansion of mountain floodplain and gallery forests characterize the interval between 15 500 and 11 800 14 c yr bp as the wettest recorded period in ne brazil which allowed floristic exchanges between atlantic rain forest and amazonian rain forest and vice versa the paleodata from core geob 3104 1 confirm the in general dry pre last glacial maximum lgm and lgm conditions and the change to wet lateglacial environments in tropical south america the annual movement of the intertropical convergence zone over ne brazil the strong influence of the antarctic cold fronts and changes of the high pressure cell over the southern atlantic may explain the very wet lateglacial period in ne brazil the documented ne brazilian short term signals correlate with the documented dansgaard oeschger cycles and heinrich events from the northern hemisphere and suggest strong teleconnections

sediment yield variability in spain a quantitative and semiqualitative analysis using reservoir sedimentation rates an existing dataset of area specific sediment yield ssy for 60 catchments in spain that was retrieved from sediment deposition rates in reservoirs avendano salas c sanz montero e rayan c gomez montana 1997 sediment yield at spanish reservoirs and its relationship with the drainage basin area in proceedings of the 19th symposium of large dams florence 1997 icold international committee on large dams pp 863 874 reveals that catchment area alone explains only 17 of the variability in ssy in this study an attempt to explain the remaining variability in ssy was made using a quantitative and a semiqualitative approach for 22 catchments during a field survey the 22 selected catchments were characterised by topography vegetation cover lithology shape and the presence of gullies in the broad vicinity of the reservoir this information was used to develop a factorial scoring index model that provides a fairly accurate and reliable prediction of ssy a classical multiple regression model using climatic topographic and land use properties derived from regional datasets could not explain as much variance as the qualitative index model nor did it appear to be as reliable the same conclusion could be drawn when using the corine soil erosion risk map of southern europe the low prediction capability of the multiple regression models and the corine soil erosion risk map could be attributed mainly to the fact that these methods do not incorporate gully erosion and that the land cover data are not a good representation of soil cover both variables have been shown to be of great importance during the field surveys future assessments of ssy could be quickly and efficiently made using the proposed factorial scoring index model in comparison with other models which demand more data the index model offers an alternative prediction tool d 2002 elsevier science b v all rights reserved

forward modeling of ice topography on mars to infer basal shear stress conditions 1 understanding the history of ice caps on mars could reveal important information about martian geologic and climatic history to do this an ice reconstruction model is needed that operates over complex topography and can be constrained with a limited number of free parameters in this study we developed a threshold sliding model for ice cap morphology based on the classic model of nye later incorporated into the models of reeh and colleagues we have updated the nye reeh model with a new numerical algorithm although the model was originally developed to model perfectly plastic deformation it is applicable to any ice body that deforms when a threshold basal shear stress is exceeded the model requires three inputs a digital elevation model of bed topography a mask grid that defines the position of the ice terminus and a function defining the threshold basal shear stress to test the robustness of the model the morphology of the greenland ice sheet is reconstructed using an empirical equation between threshold basal shear stress and ice surface slope the model is then used to reconstruct the morphology of ice draping impact craters on the margins of the south polar layered deposits using an inferred constant basal shear stress of 0 6 bar for the majority of the examples this inferred basal shear stress value is almost 1 3 of the average basal shear stress calculated for the greenland ice sheet what causes this lower basal shear stress value on mars is unclear but could involve the strain weakening behavior of ice

spatial variations of soil weathering processes in a tropical mountain environment the baturite massif and its piedmont ceara ne brazil abstract strong spatial variations in soil weathering processes were identified in the uplands and piedmont zones of the baturite massif ceara ne brazil a medium elevation tropical mountain characterized by a steep ecocline between humid climate of the summit zone and semi arid conditions of the erosional piedmont with the combined help of field surveys and laboratory analyses involving micromorphological observations as well as geochemical and mineralogical investigations this study demonstrates a close spatial correlation between soil weathering processes and present day water balance wbi variations i in the humid massif wbi 500 mm y 1 monosiallitization is exclusive in soil and upper saprolite horizons and leads to the neoformation of 1 1 clay minerals well crystallized kaolinite with minor amounts of gibbsite ii in the subhumid peripheral area of the massif 50 1 monosiallitization coexists with bisiallitization in the soil profiles producing a mixture of 1 1 kaolinite and 2 1 illite clay minerals along with lower weathering intensity iii in the semiarid piedmont 0 1 bisiallitization becomes the dominant weathering pathway conducive to grus formation and fersiallitic pedogenesis with the most vulnerable primary minerals weathered into high charge 2 1 clay minerals smectite and illite given that soils and weathering mantles are integrators of average bioclimatic conditions that prevail at timescales of 1 to 10 myr the distribution of soil weathering signatures in the study area is probably reflective of inevitable long term quaternary to neogene climatic fluctuations around median values close to the present ones paleoclimatic legacies inherited from the paleogene lateritization event are rare because of the denudation pulse occurring in the late tertiary and favoring soil stripping to the paleoweathering front on the erosional piedmont

creep of water ices at planetary conditions a compilation many constitutive laws for the flow of ice have been published since the advent of the voyager explorations of the outer solar system conflicting data have occasionally come from different laboratories and refinement of experimental techniques has led to the publication of laws that supersede earlier ones in addition there are unpublished data from ongoing research that also amend the constitutive laws here we compile the most current laboratory derived flow laws for water ice phases i ii iii v and vi and ice i mixtures with hard particulates the rheology of interest is mainly that of steady state and the conditions reviewed are the pressures and temperatures applicable to the surfaces and interiors of icy moons of the outer solar system advances in grain size dependent creep in ices i and ii as well as in phase transformations and metastability under differential stress are also included in this compilation at laboratory strain rates the several ice polymorphs are rheologically distinct in terms of their stress temperature and pressure dependencies but with the exception of ice iii have fairly similar strengths hard particulates strengthen ice i significantly only at high particulate volume fractions ice iii has the potential for significantly affecting mantle dynamics because it is much weaker than the other polymorphs and its region of stability which may extend metastably well into what is nominally the ice ii field is located near likely geotherms of large icy moons

predicting the terrestrial flux of sediment to the global ocean a planetary perspective a new model for predicting the long term flux of sediment from river basins to the coastal ocean is applied to a global data set of 340 river basins the model is based on relief basin area or averaged discharge and basin averaged temperature basinaveraged temperature is determined from basin location latitude longitude and the lapse rate across the basin relief hypsometric approximation the sediment flux model incorporates climate through basin temperature and hydrologic runoff solutions are provided for each of the major hemispheric climate regions polar temperate and tropic the model successfully predicts the pre anthropogenic flux of sediment to within the uncertainties associated with the global observations within a factor of two for 75 of rivers that range across five orders of magnitude in basin area and discharge most of the problem rivers are associated with low observational loads often smaller rivers where anthropogenic impacts are often magnified and temporal variability is high model predictions provide a baseline for researchers 1 to question the quality of observational data where available and disagreement is greatest 2 to examine a river basin for unusually large anthropogenic influences i e causes of erosion or causes of hinterland sediment retention and 3 to uncover secondary factors not addressed by our model lithology lakes the model provides a powerful tool to address the impact of paleo climate fluctuations warmer colder wetter drier on the impact of sediment flux to the coastal ocean d 2003 elsevier b v all rights reserved

effects of slope orientation on pedogenesis of altimontane soils from the brazilian semi arid region baturite massif ceara given the importance of climate conditions for the development of soils studies on climosequences are a valuable tool to predict the influence of climate change on weathering rates and on soil formation processes the baturite massif a humid enclave located in the brazilian semi arid region has unique characteristics that cause a disproportional distribution of rainfall the eastern and northern slopes receive more than 1 600 mm year of rainfall whereas the southern and western slopes have semi arid characteristics with rainfall of less than 600 mm year eight soil profiles were selected to investigate the influence of these distinct climates on soil formation to achieve this physical chemical morphological mineralogical and micromorphological data were determined and analyzed in the humid slope predominate soil processes include melanization brunification intense leaching acidification and alitization with intensified weathering in higher altitudes in contrast the environment in the dry slope favored the occurrence of soils with a higher base status high activity clays low al saturation and bisialitization processes coexisting with monosialitization mainly in the soils located at lower altitudes micromorphological data indicate that clay illuviation is not the main process responsible for the enrichment of clay in the subsurface horizons the contrasting environmental conditions with different mineralogical composition seem to be an important indicator of weathering intensity and pedoenvironmental conditions

mariner 9 observations of the south polar cap of mars evidence for residual co2 frost the first spacecraft observations of the south residual polar cap of mars were obtained by the mariner 9 orbiter during the martian southern summer season 1971 1972 analyses of viking orbiter observations obtained 3 mars years later have shown that residual carbon dioxide frost was present at the south polar cap in 1977 in this study mariner 9 infrared interferometer spectrometer spectra and television camera images are used in conjunction with multispectral thermal emission models to constrain the temperatures of dark bare ground and bright frost regions within the south residual cap the results provide strong evidence that carbon dioxide frost was present throughout the summer season despite the fact that the residual frost deposits observed by mariner 9 were less extensive than those observed by viking

sequential mineral transformation from kaolinite to fe illite in two brazilian mangrove soils abstract mangrove soils have peculiar chemical and physical conditions generated by the variable water salinity cyclic tidal changes and intense biological activity that produce complex clay suites in this study the crystal chemical characteristics of clay minerals from two mangrove soils were investigated in detail to further our understanding of the processes taking place the two brazilian mangroves are from zones of contrasting climatic type and continental sediment character 1 tropical wet climate area receiving highly weathered sediments braganca para state and 2 mild semiarid climate area supplied with a mixture of highly and moderately weathered sediments acarau ceara state the investigation of the 2 0 2 m and 4 ions abundant in the interstitial water superior fe rich illite contents in acarau mangrove compared to braganca mangrove are explained by high inputs of 2 1 clays from sediment source areas inland the above clay mineral reactions shed light on the role of clays and the interaction between minerals and biotic components in mangrove soils in addition these reactions may influence the cycle of major elements in coastal ecosystem surrounding mangroves

palaeopedogenesis of red palaeosols in yunnan plateau southwestern china pedogenical geochemical and mineralogical evidences and palaeoenvironmental implication abstract red palaeosol as an important archive of ancient pedoenvironments effectively reflects the palaeoenvironmental change and tectonic uplift history of the plateau four red palaeosol profiles were collected at 2200 to 2400 m elevations from the yunnan plateau yp to investigate the pedogenic features chemical weathering process and mineral assemblages of soils pedological geochemical and mineralogical techniques were used to understand the palaeopedogenic palaeoenvironmental change and landscape evolution of the plateau pedologically the red palaeosols were characterized by the dark red color a hue of 5yr or redder strong acidity ph 50 g kg 1 and clay 50 contents the red palaeosols were enriched with fe 2 o 3 al 2 o 3 and tio 2 with very low contents of cao mgo na 2 o and k 2 o and slightly low contents of si 2 o and mno chemical weathering indices such as cia cia al 2 o 3 al 2 o 3 cao na 2 o k 2 o 100 sa sa sio 2 al 2 o 3 saf saf sio 2 al 2 o 3 fe 2 o 3 and a cn k diagram al 2 o 3 cao na 2 o k 2 o indicated that the red palaeosols had experienced strong chemical weathering processes scanning electron microscopy analyses revealed that quartz grains of the red palaeosols were characterized by a number of deep dissolution pits and cracks on their surfaces the clay minerals of the red palaeosols were composed of kaolinite gibbsite hematite and vermiculite in the order of abundance pedogenical geochemical and clay mineralogical evidences revealed that the red palaeosols were developed by palaeopedogenic processes under tropical climatic environments the presence of highly weathered soils at an altitude of 2200 2400 m indicated the influence of tectonic uplift on the soil vertical distribution it is estimated that the red palaeosols had uplifted about 1600 2000 m since their initial formation palaeopedogenesis of red palaeosols provides new insight into the palaeoclimatic and palaeoenvironmental reconstruct and tectonic movement of yp

gneiss saprolite weathering and soil genesis along an east west regolith sequence ne brazil abstract the pressure to increase biomass production worldwide has pushed the boundaries of agricultural lands towards fragile soils this process is particularly intense in pernambuco state ne brazil pernambuco features a moisture gradient with soils developed from similar gneisses resistant structures within the rock influenced the internal movement and distribution of water consequently influencing regolith genesis this paper presents the mineralogical characteristics of three regolith profiles with shallow soils here assumed to be soils in which the top of the cr horizon is at a depth of 1 5 m or less along a transect at 8 s and discusses their weathering and pedogenetic processes samples were investigated via optical microscopy and scanning electron microscopy sem x ray diffraction xrd and total chemical analysis by inductively coupled plasma atomic emission spectrometry icp aes the presence of weathering resistant quartz veins and planes in the rock structure played a central role in controlling the water dynamics and the advancement of the weathering front therefore desilication was dominantly controlled by the pore network hence the weathering indexes did not differ appreciably among the climatic zones and both 1 1 and 2 1 type clays were found in all profiles although the amount of clay minerals that formed and the degree of dissolution of the primary minerals varied among the climate types from an agricultural perspective the thinness of these soil profiles and the presence of leucocratic layers are the main drawbacks of the regoliths whereas the capacity to supply plant nutrients via primary mineral dissolution near the root zone can be an advantage

weathering and pedogenesis in the sila grande massif calabria south italy from field scale to micromorphology abstract weathering and soil features in the upland landscapes developed on granitic terrains of the sila grande massif calabria south italy have been studied in this work the attempt to link field scale and micromorphological observations in order to better understand the main weathering processes and their controlling factors is revealed to be very powerful six soil profiles in the area around the cecita lake representative of different geomorphological units were characterised by field work optical microscopy and sem eds analysis a strong influence on weathering and pedogenesis by micro scale features of primary minerals and parent rock fabrics is shown key roles are played also by relief in the development and preservation or stripping of regolith soil mantles in relation to natural and man induced phenomena by time controlling rates and degree of development of the main weathering features by climate in terms of type and intensity of dominant processes

accumulation of sedimentary debris in the south polar region of mars and implications for climate history abstract stratigraphic units of the south polar region of mars were mapped relative chronology determined and detailed modeling of the observed crater populations was used to set absolute constraints on the age of emplacement of materials significant secular variation in the net debris accumulation rate over history is evident an episode of enhanced crater obliteration at about 3 7 ga ago lasting a few hundred ma is inferred for south polar cratered terrains a similar peak in low latitude obliteration rates suggests that the event may have been global in scale whether the debris is volcanic or aeolian in origin the event suggests a possible enhancement in atmospheric density at the time modeling results imply that cratered terrains poleward of 65 south latitude have subsequently experienced steady state net accumulation of material at a rate of about 0 1 km ga while equatorial cratered terrains have been retained in relatively pristine form fifteen craters of impact origin were discovered on the south polar layered terrain formerly thought to be almost devoid of craters their presence implies that the surface is at least a few 100 ma old and that the net accumulation rate is no more than 10 km ga if layer formation is modulated by periodic climatic effects either the period of oscillation is a few ma or longer or the layer deposition mechanism ceased operating at least several 100 ma ago

grus weathering mantles problems of interpretation abstract grus is an ill defined product of deep weathering of coarse grained rocks whose relationships to other weathering changes remain unclear this paper attempts to address this issue by reviewing a number of examples of coarse saprolites from a variety of climatic and topographic settings grus is the category of weathering mantle that possesses the following characteristics sand gravel 75 100 silt clay

climate and tectonic influences on continental erosion of tropical south america 0 13 ma is tectonic uplift or climate change the primary driving force behind continent scale erosion here we examine these two hypotheses for tropical south america by comparing a high resolution record of terrigenous sediment accumulation rates from the western tropical atlantic ocean with continental tectonic reconstructions and both low latitude and high latitude climate indices that span the past 13 m y over the full record terrigenous sedimentation rates most closely follow lowland aridity as recorded by abundance ratios of terrigenous oxide minerals an indication that basin integrated climate is an important control of erosion step like transitions in the flux and composition of terrigenous material near 8 and 4 5 ma however follow dated tectonic events which suggests progressive expansion of the drainage basin into less humid or less vegetated regions that were more prone to erosion on long time scales high latitude climate variability and sea level as recorded by 1 8 o do not closely track terrigenous sedimentation we conclude that regional climate change provides a mechanism for long term erosion of tropical south america tectonics plays a significant but secondary role in this area perhaps by shaping the drainage basin to include regions in which the climate is more favorable to erosion

the instability of a south polar cap on mars composed of carbon dioxide abstract if the martian south polar cap were composed of solid carbon dioxide would it be sufficiently stable against collapse under its own weight this question is examined in the light of new experiments on the creep of solid carbon dioxide and new high resolution topographic mapping of the south polar cap the conclusion from a simple model is that with the strongest of three flow laws compatible with the measurements co 2 is strong enough to support a cap of this material with thickness about 1800 m for 10 7 years or more which is the age suggested by the cratering record however none of the three possible flow laws will allow a 3000 m cap the thickness suggested by stereogrammetry to survive for 10 7 years indicating that the south polar ice cap is probably not composed of pure co 2 ice

present weathering rates in a humid tropical watershed nsimi south cameroon the study of biogeochemical and hydrological cycles in small experimental watersheds on silicate rocks common for the temperate zone has not yet been widely applied to the tropics especially humid areas this paper presents an updated database for a six year period for the small experimental watershed of the mengong brook in the humid tropics nsimi south cameroon this watershed is developed on precambrian granitoids north congo shield and consists of two convexo concave lateritic hills surrounding a large flat swamp covered by hydromorphic soils rich in upward organic matter mineralogical and geochemical investigations were carried out in the protolith the saprolite the hillside lateritic soils and the swamp hydromorphic soils biomass chemical analyses were done for the representative species of the swamp vegetation the groundwater was analysed from the parent rock saprolite weathering front to the upper fringe in the hillside and swamp system the chemistry of the wet atmospheric and throughfall deposits and the mengong waters was monitored in the nsimi watershed the carbon transfer occurs primarily in an organic form and essentially as colloids produced by the slow biodegradation of the swamp organic matter these organic colloids contribute significantly to the mobilization and transfer of fe al zr ti and th in the uppermost first meter of the swamp regolith when the organic colloid content is low i e in the hillside groundwater th and zr concentrations are extremely low 3 pmol l icp ms detection limits strongly insoluble secondary thorianite tho 2 and primary zircon zrsio 4 crystals control their mobilization respectively this finding thus justifies the potential use of both these elements as inert elements for isoelement mass balance calculations pertaining to the hillside regolith chloride can not be used as a conservative tracer of hydrological processes and chemical weathering in this watershed biogenic recycling significantly influences the low cl input fluxes sodium is a good tracer of chemical weathering in the watershed the sodium solute flux corrected from cyclic salt input was used to assess the chemical weathering rate even though low 2 8 mm kyr the chemical weathering rate predominates over the mechanical weathering rate 1 9 mm kyr compared to the rio icacos watershed the most studied tropical site the chemical weathering fluxes of silica and sodium in the mengong are 16 and 40 times lower respectively this is not only related to the protective role of the regolith thick in both cases but also to differences in the hydrological functioning this is to be taken into account in the calculations of the carbon cycle balance for large surfaces like that of the tropical forest ecosystems on a stable shield at the global level

viscous relaxation of craters within the martian south polar layered deposits abstract the south polar layered deposits pld are of fundamental importance to martian climatology as they may comprise the largest reservoir of near surface water on mars the south pld exhibit relatively young crater retention surface ages which are widely attributed to recent resurfacing however we show that both constructional and destructional resurfacing mechanisms such as dust deposition and water ice sublimation respectively are inconsistent with the size depth and spatial distributions of south pld craters we demonstrate that another process viscous creep relaxation of dusty water ice is more compatible with the observed cratering of south pld surfaces the results of our finite element relaxation simulations suggest that despite their apparent youthfulness the pld have been stable for at least several hundred million and perhaps even over a billion years consequently our modeling implies that the time scales for the formation and preservation of the layers characteristic of the south and possibly north pld are much longer than generally assumed

suspended sediment flux modeling with artificial neural network an example of the longchuanjiang river in the upper yangtze catchment china artificial neural network ann was used to model the monthly suspended sediment flux in the longchuanjiang river the upper yangtze catchment china the suspended sediment flux was related to the average rainfall temperature rainfall intensity and water discharge it is demonstrated that ann is capable of modeling the monthly suspended sediment flux with fairly good accuracy when proper variables and their lag effect on the suspended sediment flux are used as inputs compared with multiple linear regression and power relation models ann can generate a better fit under the same data requirement in addition ann can provide more reasonable predictions for extremely high or low values because of the distributed information processing system and the nonlinear transformation involved compared with the anns that use the values of the dependent variable at previous time steps as inputs the anns established in this research with only climate variables have an advantage because it can be used to assess hydrological responses to climate change

the global topography of mars and implications for surface evolution elevations measured by the mars orbiter laser altimeter have yielded a high accuracy global map of the topography of mars dominant features include the low northern hemisphere the tharsis province and the hellas impact basin the northern hemisphere depression is primarily a long wavelength effect that has been shaped by an internal mechanism the topography of tharsis consists of two broad rises material excavated from hellas contributes to the high elevation of the southern hemisphere and to the scarp along the hemispheric boundary the present topography has three major drainage centers with the northern lowlands being the largest the two polar cap volumes yield an upper limit of the present surface water inventory of 3 2 to 4 7 million cubic kilometers

variations in sub tropical deep weathering profiles over the kowloon granite hong kong variations in the physical characteristics of the weathering profile over the kowloon granite in hong kong have been established using borehole records supported by field mapping there is a strong correlation between topography of the weathered profile base and the main structural trends linear zones of deep weathering have been preferentially eroded to create valleys which subsequently became sites of alluvial and colluvial accumulation variations in weathering patterns are primarily a function of the geometry and infilling of relict jointing which together determine local hydrogeology and hence intensity of weathering magnetic susceptibility is a reliable indicator of material weathering grade in the kowloon granite corestones are generally restricted to weathered profiles over topographically high areas the locations of which are controlled by regional joint spacing and orientation corestone bearing profiles are rare and more commonly deeply weathered granite without corestones passes abruptly into relatively fresh rock this has important implications for engineering ground models derived from borehole interpretation