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

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

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

sedimentological and geomorphological imprints of holocene tsunamis in southwestern spain an approach to establish the recurrence period this paper reviews the sedimentological and geomorphological imprints of prehistoric and historical tsunamis in the four main estuaries of sw spain these imprints include beach erosion filling of intertidal channels deposition of bioclastic layers washover fans and reworked aeolian sheets and the breaching of spits and tombolos most of these imprints were caused by the 218 209 bc and ad 1755 tsunamis although evidence of other tsunamis has been identified in these two events effects on human populations were severe and diverse such as human loss of life changes in coastal settlements and international borders damage to port infrastructure or flooding of marsh and inhabited areas new radiocarbon reservoir data were included in order to obtain an approach to the recurrence period of these high energy events 700 1000 years in this area 2013 elsevier b v

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

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

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

late holocene evolution of the southwestern donana national park guadalquivir estuary sw spain a multivariate approach four phases are distinguished in the late holocene evolution of the southwestern donana national park sw spain based on a multidisciplinary analysis of the sediments present in drill cores in the oldest phase 2400 2500 cal yr bp a coastal lagoon the roman lacus ligustinus was recognized in the central part of this area partly closed by the donana spit and limited by fluvial levees the following phase 2400 2200 cal yr bp is characterized by high energy events which caused the breakthrough of the donana spit and the creation of new littoral strands in the inner areas in the third phase 2200 2050 cal yr bp this new outlet was closed coinciding with the progradation of the donana spit the last phase 2050 cal yr bp recent comprises three periods a an unstable period 2050 1950 cal yr bp with the deposit of cheniers over the previous levees b an infilling period with a diminution of the marine influence and c the appearance of temporary ponds between the emerged levees and cheniers

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

morphostratigraphy of an ebb tidal delta system associated with a large spit in the piedras estuary mouth huelva coast southwestern spain abstract the piedras estuary is one of the most significative estuarine systems on the mesotidal huelva coast in the northwestern portion of the cadix gulf the river mouth is presently an estuarine lagoon partially closed by a large spit constructed from an old barrier island system this estuary is in an advanced state of infilling and its tidal prism has decreased during the holocene causing instability and clogging of old inlets and transforming the barrier island chain into a spit sedimentation is controlled by the interaction of ebb tide currents and the prevailing sw waves the main sediment supply is provided by an intensive west to east longshore current transporting sand material from portuguese cliffs and the guadiana river tidal range is mesotidal 2 0 m and the mean significant wave height is 0 6 m with an average period of 3 6 s a boxcore study allowed five depositional facies to be distinguished in the piedras estuary mouth 1 main ebb channels 2 marginal flood channels 3 ebb tidal delta lobes 4 marginal levees and 5 curved spits the recent evolution studied in this area suggests a cyclic evolutionary model for the ebb tidal delta system the architectural facies relations shown by the vibracore boxcore study confirm that the apical growth of the spit occurred over the innermost of these ebb tidal deltas consequently the preserved sequence shows the ebb tidal delta facies under the spit facies

geomorphological record of extreme wave events during roman times in the guadalquivir estuary gulf of cadiz sw spain an archaeological and paleogeographical approach abstract analysis of the geological record has made it possible to delimit for the guadalquivir estuary the traces of extreme wave events ewes during the roman period in the iberian peninsula 218 bce to 476 ce the largest event occurred in the 2nd 3rd century ce it generated clearly visible erosive effects in the coastal barriers including washover fans and erosional scarps in the inner estuary however the effects were minor crevasse splays that broke levees and cheniers as well as a residual sedimentary lag the significant development of the spits protected the inner estuary from the marine incursion which only caused a water level rise with low regime waves correlation of the geomorphological and sedimentary marks left by this event with the archaeological and geological evidence of other events recognized elsewhere in the gulf of cadiz effectively argues for a tsunami as to the nature of the 2nd 3rd century ce event yet this and the other identified ewes in the guadalquivir estuary during the pre roman and the roman period all fit a model of paleogeographic evolution dominated by processes of coastal progradation and estuarine infilling radiocarbon dating geomorphological analysis and historical references fail to warrant the so called 218 209 bce atlantic tsunami as hypothesized in the received scientific literature in pre roman and roman times human occupation at the mouth of the guadalquivir river was strongly influenced by various geodynamic processes the location of the settlements being contingent upon dependable fast communication with the sea and above all upon adequate protection from ewes on the leeward side of spits progressive progradation of these coastal barriers combined with the gradual infilling of the estuary to make navigation to open sea increasingly difficult and eventually to result in the abandonment of settlements

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

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

acoustic profiling of suspended sediments in the marine bottom boundary layer an acoustic 3 mhz backscattering profilometer has been developed for study of sediment transport in the bottom boundary layer laboratory experiments indicate reasonable correlations between backscattering intensity and mass concentrations for well sorted fine to coarse quartz sands typical of those found in marine sediments departure of the calibration curves from their expected values is thought to be due to the non spherical shape of the quartz grains field experiments on the inner shelf using the profilometer combined with velocity profiles show individual profiles taken at 1 hz during erosion events are characterized by highly variable concentrations surface wave groups rather than individual waves appear to be correlated with groups of profiles with high concentrations extending 25 100 cm above bottom averaging produces smooth profiles which fit well log normal distributions predicted by steady flow suspended load theories

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

cheniers and chenier plains a general introduction abstract cheniers and chenier plains have been studied in many coastal regions throughout the world an inventory of the investigations currently being carried out is presented in this and accompanying papers cheniers and chenier plains are azonal features their distribution ranges from tropical to the subarctic regions and they show a variety of features progradational shorelines where mud accretion is temporarily interrupted favour the development of these features in addition to the concept of otvos and price who define cheniers and chenier plains as being formed exclusively in relation to littoral progradational environments it is suggested here that chenier formation in deltaic progradational environments should also be included genetically two types of cheniers can be distinguished depending on the origin of the related sediments cheniers developing due to wave winnowing of the muddy sediments and the subsequent concentration of the coarser particles to form a longshore bar or ridge which is driven shoreward and cheniers built by littoral drift in both cases they can be recognised by their sedimentary structures when cheniers arrive onshore they will migrate further landward due to washover processes under extreme hydrodynamical conditions e g spring tides storm surges etc to summarise the information concerning the episodic development of chenier plains in order to produce a or a few universal model s appears to be very difficult owing to the numerous factors that influence their formation these include river mouth shifting sealevel changes climatic changes storm frequency mortality of shellfish and bay geometry owing to this sensitivity to environmental changes during their formation cheniers are considered to be very important geomorphological features they provide a relatively accurate record of sealevel and environmental changes which can be dated with high resolution

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

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

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

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

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