chemical denudation in the yellow river and its geomorphological implications abstract chemical denudation plays an important role in regulating atmospheric co2 balance and modulating global climate with weekly collected water samples at three stations on the yellow river mainstem from july 2011 to july 2012 we investigate its chemical denudation characteristics on the basis of water geochemistry and discuss the geomorphological implications because of limited atmospheric inputs into the yellow river chemical weathering is of first importance in affecting the chemical compositions of its water geochemistry as a result of extensive carbonates within the watershed carbonate dissolution is the major source of the dissolved solids accounting for 28 33 7 of the total dissolved solids tds in contrast silicate weathering contributes only 9 9 10 9 with a mean tds concentration of 639 mg l 1 the tds flux into the ocean is estimated at 16 mt yr 1 corresponding to a specific chemical denudation rate of 21 3 t km 2 yr 1 comparative analysis with physical erosion suggests the dominance of physical erosion over chemical weathering in providing riverine loads rapid removal by physical erosion may have restrained the chemical denudation processes rock weathering consumes on average 2 3 mt of atmospheric co2 during the one year long sampling campaign accounting for 0 22 0 31 of the global annual co2 consumption through chemical weathering of the co2 consumed 74 is caused by carbonate weathering and 26 by silicate weathering indicating the predominance of carbonate weathering in consuming atmospheric co2 within the watershed

tracking holocene glacial and high altitude alpine environments fluctuations from minerogenic and organic markers in proglacial lake sediments lake blanc huez western french alps holocene palaeoenvironmental evolution and glacial fluctuations at high altitude in the western french alps are reconstructed based on a multiproxy approach within lake blanc huez 2550 m a s l drainage basin the combination of seismic profiling 3 5 khz piston coring and radiocarbon dating in proglacial lacustrine sediments together with a detailed organic analysis of autochthonous and allochthonous supply allows documenting the evolution of glacier activity during the holocene over the last 9700 years the holocene lake record has a bimodal pattern whose transition is progressive and occurring between 5400 and 4700 cal bp during the early holocene the organic lacustrine facies reflects reduced glacial activity in the catchment this major glacial retreat seems to result from solar forcing and high summer insolation after 5400 cal bp lacustrine sedimentation is marked by the gradual increase both of minerogenic supply and soil erosion suggesting a progressive transition to wetter climatic conditions this climate change is synchronous both from the gradual decrease of summer insolation and the gradual reorganization of oceanic and atmospheric circulations characterizing the beginning of the neoglacial period both colder temperature and humid climate induced significant glacier advance since 4700 cal bp over this global trend three periods are particularly associated with higher runoff processes and higher soil erosion interpreted as wetter time intervals resulting from enhanced northern westerlies regimes across the north atlantic and western europe they are dated from 8700 to 7000 4700 to 2500 and 1200 to 200 cal bp these wetter phases drastically contrast with periods of reduced glacial activities dated from the early bronze age ca 3870 3770 cal bp the iron age ca 2220 2150 cal bp the roman period ca ad115 330 and the medieval warm period ca ad760 1160 in addition these dryer periods are associated with mining activities at high altitude

does planetary differentiation really fractionate iron isotopes the difference in the mean fe isotope composition of samples from the earth moon mars and vesta has been recently interpreted as tracking contrasted planetary accretion mechanisms f poitrasson a n halliday d c lee s levasseur n teutsch iron isotope differences between earth moon mars and vesta as possible records of contrasted accretion mechanisms earth planet sci lett 223 2004 253 266 using newly produced fe isotopic data on terrestrial and lunar samples pallasites eucrites and martian meteorites weyer et al s weyer a d anbar g p brey c munker k mezger a b woodland iron isotope fractionation during planetary differentiation earth planet sci lett 240 2005 251 264 reinterpreted these data as fingerprinting planetary differentiation in particular these authors suggested that partial melting in the terrestrial and lunar mantles produced melts isotopically heavy it is shown here that the inference of weyer et al s weyer a d anbar g p brey c munker k mezger a b woodland iron isotope fractionation during planetary differentiation earth planet sci lett 240 2005 251 264 is strongly biased by the sampling approach taken notably these authors used olivine in place of the host bulk peridotites 57fe signatures despite this mineral has been shown to be frequently isotopically lighter than coexisting phases and they analyzed lunar samples heavily affected chemically by the meteoritic bombardment a process known to alter fe isotope signatures their pallasite metal silicate fractionation data are also likely biased by the approach adopted to estimate the iron isotope composition of the different mineral phases in fact their conclusion of fe isotopic fractionation during basalt extraction from planetary mantles is invalidated by the observation that basaltic shergottites and eucrites have 57fe indistinguishable from those of chondrites therefore the heavier fe isotopic composition of the moon relative to the earth itself heavier than most chondrites and achondrites remains best explained by loss of light iron isotopes during the high temperature event accompanying the interplanetary impact that led to the formation of the moon f poitrasson a n halliday d c lee s levasseur n teutsch iron isotope differences between earth moon mars and vesta as possible records of contrasted accretion mechanisms earth planet sci lett 223 2004 253 266 f poitrasson s levasseur n teutsch significance of iron isotope mineral fractionation in pallasites and iron meteorites for the core mantle differentiation of terrestrial planets earth planet sci lett 234 2005 151 164

modeling of water rock interaction in the mackenzie basin competition between sulfuric and carbonic acids the chemical weathering of continental surfaces depends on many factors including lithology climate tectonics erosion soil or vegetation and also on the availability of acidity in the weathering zone in addition to atmospheric soil co2 sulfide oxidation may represent a significant source of protons for weathering reactions as shown previously for the rivers draining the mackenzie basin canada here a numerical model describing continental weathering reactions based on laboratory kinetic laws is coupled to a dynamic global vegetation model the b witch model in order to estimate the impact of sulfide oxidation on chemical weathering and associated atmospheric co2 consumption fluxes throughout the mackenzie river basin the model is first calibrated with available field data for the various sub basin of the mackenzie watershed and then a simulation is performed removing the contribution of sulfuric acid to the weathering system the main outcomes of the present study are that 1 the dissolved silica export is controlled by secondary minerals reactivity in soils and the calcium and magnesium fluxes are driven by the dissolution of calcite and dolomite 2 the atmospheric co2 consumption by weathering processes in the mackenzie river is limited accounting for only 24 of the total bicarbonate flux to the ocean confirming a previous study and suggesting that weathering processes in the mackenzie watershed acts as a source of carbon to the atmosphere at the geological timescale and 3 the presence of sulfide minerals within a river basin decreases the apparent net consumption of atmospheric co2 through chemical weathering we show that the actual production of sulfuric acid in the weathering zone of the mackenzie basin reduces the net atmospheric co2 consumption by about two compared to what the atmospheric co2 consumption should be in the absence of sulfide minerals sulfuric acid driven chemical weathering has thus to be considered at both short and long timescales when looking at the link between chemical weathering and the global carbon cycle

comments on the role of marine sediment burial as a repository for anthropogenic co2 in a recent letter to this journal smith and mackenzie 1991 emphasized the role of near shore environments such as bays and estuaries as being the principal locus for the enhanced burial of organic matter due to anthropogenically derived nutrient inputs to the oceans i commend them for this because of the relative lack of attention given to near shore environments by much of the biogeochemical and ocanographic community it is along continental margins and not in the pelagic ocean where most organic matter as well as most sediment is buried from an extensive review of the sediment literature i have shown berner 1982 that principal organic carbonburial on a global basis occurs in deltas and other continental margin environments a large proportion of the organic c may be of terrestrial origin although the average carbon content of the surficial portions of deltaic and continental shelf muds is only about 0 75 c the large mass of sediment carrying this small carbon percentage adds up to a very large burial rate the riverine flux of suspended sediment to the oceans has been estimated e g milliman and meade 1983 milliman and syvitski 1992 to be between 12 000 and 25 000 tg 102grams per year and most of this sediment is deposited at present on or near the continental shelves at 0 75 c this amounts to anannual carbon burial rate of 90 190 tg c burial rates in other environments such as offshore upwelling zones of high productivity or the vast pelagic realms of the oceans do not come close to matching these rates if one is to look for a locus for the burial of excess carbon from fossil fuel burning and deforestation the place to look is near the continents

inter mineral fe isotope variations in mantle derived rocks and implications for the fe geochemical cycle iron isotope and major and minor element compositions of coexisting olivine clinopyroxene and orthopyroxene from eight spinel peridotite mantle xenoliths olivine magnetite amphibole and biotite from four andesitic volcanic rocks and garnet and clinopyroxene from seven garnet peridotite and eclogites have been measured to evaluate if inter mineral fe isotope fractionation occurs in high temperature igneous and metamorphic minerals and if isotopic fractionation is related to equilibrium fe isotope partitioning or a result of open system behavior there is no measurable fractionation between silicate minerals and magnetite in andesitic volcanic rocks nor between olivine and orthopyroxene in spinel peridotite mantle xenoliths there are some inter mineral differences up to 0 2 in 56fe 54fe in the fe isotope composition of coexisting olivine and clinopyroxene in spinel peridotites the fe isotope fractionation observed between clinopyroxene and olivine appears to be a result of open system behavior based on a positive correlation between the 56feclinopyroxene olivine fractionation and the 56fe value of clinopyroxene and olivine there is also a significant difference in the isotopic compositions of garnet and clinopyroxene in garnet peridotites and eclogites where the average 56feclinopyroxene garnet fractionation is 0 32 0 07 for six of the seven samples the one sample that has a lower 56feclinopyroxene garnet fractionation of 0 08 has a low ca content in garnet which may reflect some crystal chemical control on fe isotope fractionation the fe isotope variability in mantle derived minerals is interpreted to reflect subduction of isotopically variable oceanic crust followed by transport through metasomatic fluids isotopic variability in the mantle might also occur during crystal fractionation of basaltic magmas within the mantle if garnet is a liquidus phase the isotopic variations in the mantle are apparently homogenized during melting processes producing homogenous fe isotope compositions during crust formation

a field study of the chemical weathering of ancient sedimentary organic matter weathering profiles developed on organic carbon rich black shales were studied to examine the loss and degradation of organic matter om during weathering and its role in the geochemical carbon cycle analysis of weathered shales reveals between 60 and nearly 100 total organic carbon toc loss in highly weathered samples relative to initial unweathered toc content pyrite loss coincides with or precedes organic carbon loss elemental analysis and flash pyrolysis gas chromatography py gc of kerogen concentrates indicate that there is little or no selective enrichment or depletion of norg containing sorg containing alkylaromatic branched alkyl or long chain n alkyl moieties in most profiles during weathering kerogen o c ratios consistently increase with toc and pyrite loss infrared spectroscopy ir reveals an increase in the relative abundance of c c and c o bonds relative to alkyl c h bonds in progressively weathered samples these results suggest a two component model for kerogen weathering largely non selective oxidation and hydration followed by cleavage dissolution of oxidized kerogen fragments the extent of weathering in a given outcrop is likely limited by a combination of the rate of physical erosion and exposure of the rock to oxidizing surface waters with om type composition playing a lesser role

iron isotope differences between earth moon mars and vesta as possible records of contrasted accretion mechanisms the iron isotope compositions of shergotty nakhla chassigny snc meteorites thought to come from mars eucrites and diogenites assumed to sample asteroid 4 vesta and rocks from the moon and earth have been measured using high precision plasma source mass spectrometry the means of eight samples from mars and nine samples from vesta are within error identical despite a range of rock types they are lighter by 0 1 in 57fe 54fe compared to the average of 13 terrestrial mantle derived rocks the latter value is identical within uncertainty with a previously published mean of 46 igneous rocks from the earth the average for 14 lunar basalts and highland plutonic rocks covering a broad spectrum of major element composition is heavier by 0 1 in 57fe 54fe relative to our estimate for the earth s mantle and therefore 0 2 heavier than the eucrites diogenites and snc meteorites however the data scatter somewhat and the apollo 15 green glass and apollo 17 orange glass are identical to samples from mars and vesta there is no clear relationship between petrological characteristics and fe isotope composition despite a wide spectrum of samples instead contrasted planetary isotopic signatures are clearly resolved statistically after evaluating alternative scenario it appears that the most plausible explanation for the heavier fe in the earth and moon is that both objects grew via processes that involved partial vaporisation leading to kinetic iron isotope fractionation followed by minor loss this is consistent with the theory in which the moon is thought to have originated from a giant impact between the proto earth and another planet combined with numerical simulations fe isotope data can offer the potential to provide constraints on the processes that occurred in planetary accretion

global chemical erosion during the last glacial maximum and the present sensitivity to changes in lithology and hydrology geographically based calculations for 18 000 years ago 18 ka and today were made to examine the potential effects on terrestrial chemical erosion of changes in lithology and hydrology on glacial interglacial timescales runoff fields were derived from general circulation model predictions of precipitation minus evaporation then global lithologic maps were prepared so that empirical relationships for runoff versus bicarbonate flux for different rock types could be used to calculate global chemical erosion rates assuming that significant chemical erosion does not occur beneath ice sheets we find that chemical erosion in ice free areas at 18 ka was only slightly greater than today this result arises because the amount of land covered by ice sheets is roughly compensated for by exposed shelf areas and because there is little difference in global runoff the small 20 increase in the global chemical erosion rate during glacial conditions is due to exposure on the shelves of a relatively high proportion of carbonates which weather faster than average data on glacial interglacial movements of the calcite compensation depth ccd are inconclusive but seem to indicate little change whereas even a 20 increase in the riverine bicarbonate flux should cause an observable deepening if the ccd did not indeed change then our predicted increase in the bicarbonate flux from land during glaciations would have to be accommodated by other means such as increased carbonate productivity about half of the observed decrease in atmospheric pco2 at 18 ka could be explained if increased silicate chemical erosion accompanied increased total chemical erosion in ice free areas consideration of the maximum possible effect of meltwater at ice margins leads to an 80 increase in the global chemical erosion rate at 18 ka such an increase would lead to a larger and faster drop in atmospheric pco2 but also to an excessive deepening of the global ccd this scenario seems unrealistic our results are contrary to interpretations of a much higher silicate chemical erosion rate during glaciations based on recently published records of quaternary marine sr isotopic ratios therefore if these records are indeed globally representative and entirely due to increased silicate chemical erosion as opposed to changes in source areas or hydrothermal inputs then other factors such as a shift in the global weathering regime which we do not explicitly consider here may be involved sensitivity tests show that considering spatial heterogeneities in lithology and runoff leads to lower predictions of global chemical erosion rates than what one would obtain by considering only global averages in a non spatially resolved calculation

molecular 13c and 14c evidence for the allochthonous and ancient origin of c16c18 n alkanes in modern soils the heterogeneous isotopic composition of c3 and c4 plants can be used to to follow the fate of plant carbon into soil organic molecules thus after 23 years of cropping of maize c4 on a soil which was previously under c3 vegetation c25 c33 soil n alkanes are 13c enriched up to 9 relatively to the initial c3 soil reflecting the input of 13c enriched n alkanes from maize waxes in sharp contrast c16 c18 soil n alkanes do not show any significant 13c 12c variation over the same time interval this absence of isotopic variation along with consideration of their relative concentration absolute concentration and biodegradability demonstrate that these substances must represent a regular input from an external source evidence of a large contribution of an ancient source amounting to more than 65 of the alkane fraction is given by a 14c age of 8510 yrs bp moreover short chain n alkanes from soils diesel fuel diesel automobile exhaust and petroleum products exhibit similar distributions and 13c values these findings suggests that c16 c18 soil n alkanes represent a non point source pollution of ancient hydrocarbons either carried by aerosols or entering the soil via continuous hydrocarbon seepage from the deep sedimentary rocks of the paris basin

quantitative bedrock geology of the continents and large scale drainage regions we quantitatively analyze the area age distribution of sedimentary extrusive volcanic and endogenous plutonic and or metamorphic bedrock on the basis of data from the most recent digital geological map of the world at a scale of 1 25 000 000 the spatial resolution of the digital bedrock data averages 13 905 km2 per polygon comparison of certain regions of the world previously analyzed at higher spatial resolution with the low resolution world data reveals general consistency in the areal exposure of major rock types as well as a minor systematic bias toward older average bedrock ages in the global data set application of the global bedrock data to 19 large scale drainage regions and three large internally drained regions reveals considerable regional variability of earth s bedrock geology that is consistent with the dominant geotectonic setting of the respective drainage region

a 7000 year environmental history and soil erosion record inferred from the deep sediments of lake pavin massif central france a 14 m long sedimentary sequence core pav12 was collected in the deepest part of lake pavin a maar lake located in the french massif central the pav12 sedimentary sequence documents the lake s environmental evolution since its formation 7000 years ago the relationships between the catchment s vegetation cover erosion processes and changes in trophic status were shown using a multi proxy characterization of mineral and organic fractions supported by palynological data the record shows a succession of lithological units starting at the base with volcanoclastic material corresponding to the early stage of lake pavin the deposition of organic rich and diatomaceous sedimentary units above volcanoclastic material indicates an evolution toward a pristine lacustrine state the late holocene environmental history of this lake is marked by two tipping points reflecting major environmental disturbances at ca 4000 cal bp and after the deposition of erosive mass wasting deposits mwds at 1350 cal bp ce 600 and 650 cal bp ce 1300 the upper unit of core pav12 which corresponds to the past 700 years indicates that one of these mwds was likely the driving force behind a major limnological change marked by a shift in redox sensitive elements i e current meromictic lacustrine state the palynological diagram indicates a forested catchment where woodland clearances and agro pastoral activities have remained limited except over the last 700 years these findings suggest restricted human impact within the watershed compared to other regional archives the reconstruction of the lake pavin erosion record determined from titanium and red amorphous particle fluxes highlights phases of enhanced erosion at ca 6 5 5 5 4 1 3 8 3 5 2 8 2 6 1 6 1 4 cal kyr bp and during the little ice age lia a comparison between this erosion record palaeoenvironmental archives from western europe and palaeoclimatic data supports an atlantic signal driving precipitation patterns over lake pavin at centennial to millennial timescales the influence of local human activities even on a small scale cannot be completely discounted as their impact on erosional processes may be amplified in a steep catchment such as that found in lake pavin

using rock eval 6 pyrolysis for tracking fossil organic carbon in modern environments implications for the roles of erosion and weathering this work relates to the debate on the fossil organic carbon foc input in modern environments and its possible implication for the carbon cycle and suggests the use of rock eval 6 pyrolysis as a relevant tool for tracking foc in such environments considering that such a delivery is mainly due to supergene processes affecting the continental surface we studied organic matter in different reservoirs such as bedrocks alterites soils and rivers in two experimental catchments at draix alpes de haute provence france samples were subjected to geochemical rock eval 6 pyrolysis investigations and artificial bacterial degradations after comparing the geochemical fingerprint of samples geochemical markers of foc were defined and tracked in the different reservoirs our results confirm the contribution of foc in modern soils and rivers and display the various influences of weathering and erosional processes on the fate of foc during its exchange between these pools in addition the contrasting behaviour of these markers upon the supergene processes has also highlighted the refractory or labile characters of the fossil organic matter fom bedrock to river fluxes controlled by gully erosion are characterized by a qualitative and quantitative preservation of fom bedrock to alterite fluxes governed by chemical weathering are characterized by foc mineralization without qualitative changes in deeper alterites alterite to soils fluxes controlled by bio chemical weathering are characterized by strong foc mineralization and qualitative changes of fom thus weathering and erosional processes induce different fom evolution and affect the fate of foc towards the global carbon cycle in this study gully erosion would involve maintenance of an ancient sink for the global carbon cycle while bio chemical processes provide a source of co2 finally this study suggests that rock eval 6 pyrolysis can be considered as a relevant tool for tracking foc in modern environments copyright 2006 john wiley sons ltd

river fluxes to the sea from the oceanʼs 10be 9be ratio the ratio of the meteoric cosmogenic radionuclide 10be to the stable isotope 9be is proposed here to be a flux proxy of terrigenous input into the oceans the ocean s dissolved 10be 9be is set by 1 the flux of meteoric 10be produced in the atmosphere 2 the denudational flux of the rivers discharging into a given ocean basin 3 the fraction of 9be that is released from primary minerals during weathering meaning the 9be transported by rivers in either the dissolved form or adsorbed onto sedimentary particles and incorporated into secondary oxides and 4 the fraction of riverine 10be and 9be actually released into seawater using published 10be 9be data of rivers for which independent denudation rate estimates exist we first find that the global average fraction of 9be released during weathering into river waters and their particulate load is 20 and does not depend on denudation rate we then evaluate this quantitative proxy for terrigenous inputs by using published dissolved seawater be isotope data and a compilation of global river loads we find that the measured global average oceanic dissolved 10be 9be ratio of about 0 9 10 7 is satisfied by the mass balance if only about 6 of the dissolved and adsorbed riverine be is eventually released to the open ocean after escaping the coastal zone when we establish this mass balance for individual ocean basins good agreement results between 10be 9be ratios predicted from known river basin denudation rates and measured ocean 10be 9be ratios only in the south atlantic and the south pacific the 10be 9be ratio is dominated by advected be and in these basins the ratio is a proxy for ocean circulation as the seawater 10be 9be ratio is faithfully recorded in marine chemical precipitates the 10be 9be ratio extracted from authigenic sediments can now serve to estimate relative changes in terrigenous input into the oceans back through time on a global and on an ocean basin scale

exploration of driving mechanisms of equilibrium boron isotope fractionation in tourmaline group minerals and fluid a density functional theory study abstract the equilibrium boron isotope fractionations 3 4 11b tur fluid between tourmaline mineral groups and fluids at 0 5 gpa 600 1000 k are investigated using density functional theory calculations the first solvent shell controls boron isotope fractionation in solution where the values of both h3bo3 and b oh 4 decrease with increasing numbers of hydrogen bonds in supercritical fluids the weakening of hydrogen bonds and the diversity in configurations of hydrated boron species both contribute to variations in the vibrational frequencies the 1000ln tur fluid value increases with increasing mg fe mg ratios in the dravite schorl solid solution series this effect together with the crystallization sequence predicted from the gibbs free energies of tourmaline formation accounts well for the association of boron isotope and chemical zonation observed in zoned tourmaline grains the dependence of boron isotope fractionation on the b o bond length in tourmaline group minerals reflects the changes in relevant molar volumes caused by differences in the mass and charge of the atoms occupying the x y and z sites of tourmalines this study suggests that the chemical composition of the tourmaline plays an important role in controlling the boron isotope composition in tourmalines crystallized from hydrothermal systems

dissolved inorganic carbon in the xijiang river concentration and stable isotopic composition dissolved inorganic carbon dic is one the major products of chemical weathering of the land and it is also one of the most active components in the riverine carbon species concentration and stable isotopic composition of dic in the mainstream of the xijiang river xjr and its two tributaries the guijiang and hejiang rivers were investigated during a hydrological year and a massive flooding dic concentration of most selected sections of the xjr system varied from 750 to 2 400 m with an average of 1 630 390 m dic was significantly diluted in the massive flooding period the stable isotopic composition of dic 13cdic varied from 14 75 to 8 25 with an average of 11 19 1 18 from 17 22 to 10 65 with an average of 13 00 1 86 and from 15 94 to 9 71 with an average of 12 68 1 28 in the mainstream of the xjr the guijiang river and the hejiang river respectively this is jointly determined by the outcrop area of carbonate rocks and the properties of soil organic carbon within the catchments 13cdic is less negative in the dry season because of the increasing contribution from karst groundwater and more negative in the wet season because of the increasing contribution from surface soil water calcite was saturated sometimes at the mainstream sections of the xjr carbonate sourced dic contributes 10 32 43 95 with an average of about 27 69 6 03 of the riverine dic for the xjr the xjr exports about 4 27 1012 g of dic in the surveyed year of which about 83 occurred in the wet season

hydrochemistry of the narmada and tapti rivers india the chemistry of major ions and elements in narmada and tapti river water was studied based on the monitoring of the drainage basins for monsoon and post monsoon seasons in 2004 the results show the influence of rock weathering on the concentration of major ions in the surface water there is a significant contribution from the catchment geologies in the major constituents of water the total dissolved solids tds concentrations are reflecting the signature of weathering of rocks in the catchment areas in the narmada river hco 3 ca and mg are dominant ions whereas in the tapti river the ions dominating major compositions are hco 3 na and mg the high concentration of cl and so 4 2 is a signature of anthropogenic inputs in addition to the contribution of discharge from springs and or groundwater the high concentration of no 3 can exclusively be attributed to the anthropogenic activities the average concentration of dissolved silica being higher than the indian and world average is reflecting the contribution of silicate weathering the present study gives the silicate and carbonate weathering rates and the corresponding co consumption rates considering the contribution of carbonate rocks present in the selected river basins of the deccan basaltic province the mean silicate weathering rates during the investigation period for the narmada and tapti rivers show lower values but the corresponding mean co consumption rates give higher values compared with earlier estimated rates by dessert et al 2001 earth and planetary science letters 188 459 for the study period the mean carbonate weathering rates and the associated co consumption rates for the narmada and tapti rivers are 12 67 t km year and 7 32 t km year and 0 36 x 10 mol km year and 0 22 x 10 mol km year respectively

comparing results from two continental geochemical surveys to world soil composition and deriving predicted empirical global soil pegs2 reference values analytical data for 10 major oxides al2o3 cao fe2o3 k2o mgo mno na2o p2o5 sio2 and tio2 16 total trace elements as ba ce co cr ga nb ni pb rb sr th v y zn and zr 14 aqua regia extracted elements ag as bi cd ce co cs cu fe la li mn mo and pb loss on ignition loi and ph from 3526 soil samples from two continets australia and europe are presented and compared to 1 the composition of the upper continetal crust 2 published word soil awerage values and 3 data from other continetal scale soil surveys it cab be demonstrated that average upper continetal crust values do not provide reliable estimates for natural concentrations of elements in soil for many elements there exist substantial differences between published world aoil averages and the median concentrations observed on two continets direct comparison with other continetal datasets is hampered by the fact that often mean instead of the statistically more robust median is reported using a database of the worldwide disstribution of lithological units it can be demonstrated that lithology is a poor predictor of soil chemistry climate related processes such as glaciation and weathering are strong modifiers of the geochemical signature inherited from bedrock during pedogenesis to overcome existing shortcomings of predicted global or world soil geochemical reference values we propose preliminary empirical global soil reference values based on analytical results of a representative number of soil samples from two continets pegs2

weathering and the global carbon cycle geomorphological perspectives abstract the links between the weathering of silicate minerals the global carbon cycle and climate change are complex and involve a whole range of often inter related tectonic climatic geomorphological and biological factors silicate weathering rates are known to have varied through geological time and increasingly sophisticated models now link such variation to the long term carbon cycle and climate change in order to improve the modelling further one key research need is for more and better datasets on weathering and the factors that control it as a contribution to this we review the nature of the weathering carbon cycle system the sources of evidence used to understand it and the challenges that remain in quantifying the feedbacks between weathering and the global carbon cycle we propose that increased understanding of geomorphological diversity of landscapes and processes and especially the dynamic relationships between weathering and erosion will aid clearer portrayal of the links between weathering and the long term carbon cycle

extent and isotopic composition of fe and mo release from two pennsylvania shales in the presence of organic ligands and bacteria abstract isotopic fractionation of fe and mo during weathering could contribute toward the isotopic signatures of river and ocean waters to investigate weathering processes batch experiments were carried out at ph 6 under oxygenated conditions to investigate the influence of a nitrogen fixing soil bacterium and organic ligands on the extent and isotopic signature of fe and mo release from two pennsylvania shales with different mineralogies an olive to grey shale rose hill and a black shale marcellus results of these studies showed that fe and mo were mainly released from illite chlorite vermiculite and fe oxides in the rhs and from pyrite in the ms dissolution rates of the clays estimated from our batch experiments are broadly consistent with published estimates release of fe from both shales was only enhanced by the hydroxamate siderophore desferrioxamine b dfam in contrast none of the treatments enhanced release of mo furthermore release of this metal was measurable only for the black shale for both shales fe that was released in the presence of dfam was depleted in 56 fe as compared to the bulk rock in contrast leachate solutions were enriched in the heavier mo isotope as compared to the bulk marcellus in all experiments with and without organic ligands and the bacterium the isotopic fractionations in fe and mo are broadly consistent with previously reported fractionation effects during sorption onto precipitating fe mn oxides the observed mo isotope fractionation is also consistent with all published studies of rivers i e riverine mo is enriched in heavy mo isotopes the observed fe isotope fractionation is likewise consistent with published studies for some rivers i e riverine fe is sometimes depleted in 56 fe our experimental results are consistent with sorption of fe and mo onto fe oxyhydr oxides during weathering as a possible explanation for the isotopic signatures of these metals in many rivers

changes in the storage and sink of carbon dioxide in subsurface atmospheres controlled by climate driven processes the case of the ojo guarena karst system a comprehensive environmental monitoring program was conducted in the ojo guarena cave system spain one of the longest cave systems in europe to assess the magnitude of the spatiotemporal changes in carbon dioxide gas co2 in the cave soil atmosphere profile the key climate driven processes involved in gas exchange primarily gas diffusion and cave ventilation due to advective forces were characterized the spatial distributions of both processes were described through measurements of co2 and its carbon isotopic signal 13c co2 from exterior soil and cave air samples analyzed by cavity ring down spectroscopy crds the trigger mechanisms of air advection temperature or air density differences or barometric imbalances were controlled by continuous logging systems radon monitoring was also used to characterize the changing airflow that results in a predictable seasonal or daily pattern of co2 concentrations and its carbon isotopic signal large daily oscillations of co2 levels ranging from 680 to 1900 ppm day 1 on average were registered during the daily oscillations of the exterior air temperature around the cave air temperature these daily variations in co2 concentration were unobservable once the outside air temperature was continuously below the cave temperature and a prevailing advective renewal of cave air was established such that the daily averaged concentrations of co2 reached minimum values close to atmospheric background the daily pulses of co2 and other tracer gases such as radon 222rn were smoothed in the inner cave locations where fluctuation of both gases was primarily correlated with medium term changes in air pressure a pooled analysis of these data provided evidence that atmospheric air that is inhaled into dynamically ventilated caves can then return to the lower troposphere as co2 rich cave air

storage and release of fossil organic carbon related to weathering of sedimentary rocks abstract the biogeochemical carbon cycle which plays an undeniable role in global climate change is defined both by the size of carbon reservoirs such as the atmosphere biomass soil and bedrock and the exchange between them of various mineral and organic carbon forms among these carbon forms fossil organic carbon foc i e the ancient organic matter stored in sedimentary rocks is widely observed in modern environments but is not included in the supergene carbon budget using a digitized map of the world and an existing model of co 2 consumption associated with rock weathering we establish the global distribution of foc stored in the first meter of sedimentary rocks and a first estimation of annual foc delivery to the modern environment resulting from chemical weathering of these rocks results are given for the world s 40 major river basins and extended to the entire continental surface with a mean value of 1100 10 9 t mainly controlled by shale distribution the global foc stock is significant and comparable to that of soil organic carbon 1500 10 9 t the annual chemical delivery of foc estimated at 43 10 6 t yr 1 and controlled by the areal distribution of shales and runoff is of the same order of magnitude as the foc output flux to oceans chemical weathering of bedrock within the amazon basin produces one quarter of the total global flux of foc derived from chemical weathering and thus is expected to govern foc release on a global scale these results raise important questions concerning the role of foc in the modern carbon cycle as well as the origin and the budget of carbon in soils and rivers

continental erosion and large scale relief a worldwide investigation of continental erosion is carried out by the study of large drainage basins on the basis of hydrological data environmental factors and basin relief distribution inside each basin mean geochemical and mechanical denudation rates are defined a multicorrelation analysis shows that the mechanical denudation rates ds are uncorrelated with environmental factors and correlated with mean basin elevation h while chemical denudation rates dd are insensitive to relief but correlated with mean annual precipitation furthermore two linear relationships between h and ds are detected 1 ds m 10 yr 419 10 6 h m 0 245 with v explained variance 95 1 this law concerns basins related to orogenies younger than 250 ma the negative intercept is interpreted as a continental sedimentation rate of 245 m m y an alternative model in which one invokes a critical elevation separating erosion from sedimentation is equally successful and leads to lower sedimentation rates 60 110 m m y for both models one derives from the slope of the adjustments erosion time constants on the order of 2 5 m y 2 ds m 10 yr 61 10 6 h m with v 86 5 this law concerns basins related to older orogenies the null intercept suggests the lack of continental storage because of the more important dispersion of the data the erosion time constant is calculated separately for each basin it ranges from 15 to 360 m y the tectonic implications of these results are discussed in particular the short time constant 2 5 m y agrees with orogenic uplift rates on the order of 1 mm yr observed in active mountain chains

fe cycling in the shale hills critical zone observatory pennsylvania an analysis of biogeochemical weathering and fe isotope fractionation abstract during weathering fe in primary minerals is solubilized by ligands and or reduced by bacteria and released into soil porewaters such fe is then removed or reprecipitated in soils to understand these processes we analyzed fe chemistry and isotopic composition in regolith of the shale hills watershed a critical zone observatory in central pennsylvania overlying iron rich shale of the rose hill formation elemental concentrations were measured in soil from a well drained catena on a planar hillslope on the south side of the catchment based upon x ray diffraction and bulk elemental data loss of fe commences as clay begins to weather 15 cm below the depth of auger refusal more fe iii was present than fe ii in all soil samples from the ridge top to the valley floor both total and ferrous iron are depleted from the land surface of catena soils relative to the bedrock loss of ferrous fe is attributed mostly to abiotic or biotic oxidation loss of fe is most likely due to transport of micron sized particles that are not sampled by porous cup lysimeters but which are sampled in stream and ground waters the isotopic compositions 56 fe relative to irmm 014 of bulk fe and 0 5 n hcl extracted fe operationally designed to remove amorphous fe oxyhydr oxides range between 0 3 and 0 3 with 56 fe bulk extractable values between 0 2 and 0 4 throughout the soils along the catena 56 fe signatures of both bulk fe and hcl extracted fe become isotopically lighter as the extent of weathering proceeds the isotopic trends are attributed to one of two proposed mechanisms one mechanism involves fe fractionation during mobilization of fe from the parent material due to either fe reduction or ligand promoted dissolution the other mechanism involves fractionation during immobilization of fe oxyhydr oxides if the latter mechanism is true then shale which comprises one quarter of continental rocks could be an important source of isotopically heavy fe for rivers

the persistence of memory the fate of ancient sedimentary organic carbon in a modern sedimentary system the cycle of organic carbon burial and exhumation moderates atmospheric chemistry and global climate over geologic timescales the burial of organic carbon occurs predominantly at sea in association with clay sized particles derived from the erosion of uplifted continental rocks it follows that the history of the fine grained particles on land may bear on the nature of the organic carbon buried in this study the evolution of clay associated organic matter was followed from bedrock source to the seabed in the eel river sedimentary system of northern california using natural abundance 13c and 14c tracers approximately half of the fine grained organic carbon delivered to the shelf is derived from ancient sedimentary organic carbon found in the uplifted mesozoic tertiary franciscan complex of the watershed the short residence time of friable soils on steep hill slopes coupled with rapid sediment accumulation rates on the shelf slope act to preserve the ancient organic carbon a comparable quantity of modern organic carbon is added to particles in the watershed and on the shelf and slope the bimodal mixture of ancient and modern c in soils and sediments may be characteristic of many short mountainous rivers if the eel river chemistry is typical of such rivers more than 40 tg of ancient organic c may be delivered to the world s oceans each year a flux of that magnitude would have a significant influence on marine and global c cycles

palynofacies and geochemical analysis of the triassic yanchang formation ordos basin implications for hydrocarbon generation potential and the paleoenvironment of continental source rocks abstract the petroliferous basins that have formed in china since the mesozoic are characterized by non marine organic matter input a characteristic that is significantly different from that of marine organic sources the triassic yanchang formation in the ordos basin is a suite of typical intra continental lacustrine sediments that comprise the most important source rocks for the triassic oil reservoirs the yanchang formation is divided into ten subsections from top to bottom chan 1 to chan 10 three borehole successions in the southern ordos basin located in the huachi zhidan and yichuan areas cross the chan 4 5 to chan 10 subsections and have been studied using the palynofacies method combined with organic geochemistry data palynofacies analysis indicates that the sediments are rich in amorphous organic matter aom and phytoclasts the aom content in all of the samples positively correlated with the hydrogen index hi in contrast the transparent ligno cellulosic fragments tlf opaque particles op content are negatively correlated with the hi values additionally the gelified particles gp content has no linear correlation with the geochemistry data based on the quantitative composition of the particulate organic matter three palynofacies types are identified reflecting depositional settings in a distal dysoxic anoxic deep basin a shelf to basin transition zone and a proximal suboxic shelf the palynofacies total organic carbon toc and rock eval data together indicate that type i and ii kerogen are abundant in the d48 and w22 wells in the zhidan and yichuan areas respectively these kerogen types are uncommon in the l94 well in the huachi area which suggests low hydrocarbon generation potential in detail the chan 7 and chan 9 subsections of the three wells contain abundant type i and ii kerogen indicating that these layers are likely the two primary source rocks in the southern ordos basin

sequestration of atmospheric co2 in chrysotile mine tailings of the woodsreef asbestos mine australia quantitative mineralogy isotopic fingerprinting and carbonation rates since closure of the woodsreef asbestos mine located in the great serpentinite belt gsb new south wales australia extensive carbonate rich crusts have formed by recessive weathering of fine grained material on the surface of the tailings pile a relationship exists between the mode of carbonate occurrence the mineralogy and the isotopic fingerprint of carbonates from the tailings pile vertical carbonate crusts covering most of the tailings predominantly consist of the hydrated mg carbonate hydromagnesite mg5 co3 4 oh 2 4h2o which has precipitated from evaporating meteoric waters incorporating atmospheric co2 as reflected in high 18o 13c and f14c signatures respectively low and variable concentrations of magnesite dolomite and calcite represent bedrock carbonate which has formed during alteration of the serpentinite bedrock before mining and is characterised by moderately high 18o low 13c and f14c a signature typical for weathering derived magnesite deposits in the gsb the carbonate fraction of deep cement samples collected from 70 to 120 cm below the surface representing the bulk tailings material at depth predominantly consists of pyroaurite mg6fe2 co3 oh 16 4h2o and despite stable isotope signatures similar to bedrock contains significant radiocarbon this indicates that pyroaurite forming under different conditions as hydromagnesite may represent an additional trap for atmospheric co2 in the woodsreef mine tailings the distribution of carbonates and quartz together with the absence of isotopic mixing trends between bedrock carbonate and atmospheric derived carbonate strongly indicates that dissolution and re precipitation of bedrock carbonate is not a dominant process in the woodsreef tailings the cations for carbonate formation are instead derived from the dissolution of serpentine minerals lizardite and chrysotile and brucite the internal standard method and the reference intensity method have been used with x ray diffraction data to estimate the abundance of the two major carbonate minerals hydromagnesite and pyroaurite respectively considering the formation of hydromagnesite on the outer surface of the tailings pile alone or together with formation of pyroaurite within the tailings pile we conclude that between 1400 and 70 000 t of atmospheric co2 have been sequestered in the mine tailings since closure of the mine 29 a ago carbonation rates of 27 g c m 2 y 1 and 1330 g c m 2 y 1 are significantly higher than background rates of co2 uptake by chemical weathering and demonstrate the potential of passive carbonation of mine tailings as a cost and energy effective alternative for storage of co2 in carbonate minerals

the nature and origin of fissures in the east anglian coralline and red crags vertical or inclined planar fissures that may for the most part be classified as joints are commonly seen in exposures of both the coralline and red crag in east anglia measurements of fissure orientation reveal orthogonal patterns of alignment in both formations the field relations of the fissures to the host crag sediment suggest a tectonic rather than periglacial origin it is proposed that the fissure system is the product of early pleistocene tectonic flexuring in the area on the western margin of the subsiding southern north sea basin

erosion of deccan traps determined by river geochemistry impact on the global climate and the 87sr 86sr ratio of seawater abstract the impact of the deccan traps on chemical weathering and atmospheric co2 consumption on earth is evaluated based on the study of major elements strontium and 87sr 86sr isotopic ratios of the main rivers flowing through the traps using a numerical model which describes the coupled evolution of the chemical cycles of carbon alkalinity and strontium and allows one to compute the variations in atmospheric pco2 mean global temperature and the 87sr 86sr isotopic ratio of seawater in response to deccan trap emplacement the results suggest that the rate of chemical weathering of deccan traps 21 63 t km2 yr and associated atmospheric co2 consumption 0 58 2 54 106 mol c km2 yr are relatively high compared to those linked to other basaltic regions our results on the deccan and available data from other basaltic regions show that runoff and temperature are the two main parameters which control the rate of co2 consumption during weathering of basalts according to the relationship f r f c 0 exp ea r 1 t 1 298 where f is the specific co2 consumption rate mol km2 yr rf is runoff mm yr c0 is a constant 1764 mol l ea represents an apparent activation energy for basalt weathering with a value of 42 3 kj mol determined in the present study r is the gas constant and t is the absolute temperature k modelling results show that emplacement and weathering of deccan traps basalts played an important role in the geochemical cycles of carbon and strontium in particular the traps led to a change in weathering rate of both carbonates and silicates in carbonate deposition on seafloor in sr isotopic composition of the riverine flux and hence a change in marine sr isotopic composition as a result deccan traps emplacement was responsible for a strong increase of atmospheric pco2 by 1050 ppmv followed by a new steady state pco2 lower than that in pre deccan times by 57 ppmv implying that pre industrial atmospheric pco2 would have been 20 higher in the absence of deccan basalts pco2 evolution was accompanied by a rapid warming of 4 c followed after 1 myr by a global cooling of 0 55 c during the warming phase continental silicate weathering is increased globally since weathering of continental silicate rocks provides radiogenic sr to the ocean the model predicts a peak in the 87sr 86sr ratio of seawater following the deccan traps emplacement the amplitude and duration of this spike in the sr isotopic signal are comparable to those observed at the cretaceous tertiary boundary the results of this study demonstrate the important control exerted by the emplacement and weathering of large basaltic provinces on the geochemical and climatic changes on earth

review and update of the applications of organic petrology part 1 geological applications abstract organic petrology developed as coal petrology at the beginning of the 20th century dedicated mainly to the study of coals because of their utilization in industry coal petrology was then considered a branch of coal science later with the development of specialized nomenclature classification of coal components and the standardization and improvement of analytical microscopical methods this discipline expanded in interests and name becoming organic petrology organic petrology carries a broader context being as well a tool applied in the study of dispersed organic matter in sedimentary rocks due to its importance in exploration for fossil fuel resources at present organic petrology is a discipline widely recognized for its role in fundamental and applied research with respect to both coal utilization and in geosciences throughout the 20th century several important monographs have been published on the discipline of organic petrology including stach s textbook of coal petrology 1st edition 1935 2nd 1975 3rd 1982 updated as the more general organic petrology by taylor et al 1998 more recently the text applied coal petrology the role of petrology in coal utilization was published by suarez ruiz and crelling 2008 this review is the first in a two part review series that describes and updates the role of organic petrology in geosciences a second part complementing this one and focused on the applications of organic petrology to other scientific fields will follow

enhanced chemical weathering of rocks during the last glacial maximum a sink for atmospheric co2 abstract it has been proposed that increased rates of chemical weathering and the related drawdown of atmospheric co2 on the continents may have at least partly contributed to the low co2 concentrations during the last glacial maximum lgm variations in continental erosion could thus be one of the driving forces for the glacial interglacial climate cycles during quaternary times to test such an hypothesis a global carbon erosion model has been applied to a lgm scenario in order to determine the amount of co2 consumed by chemical rock weathering during that time in this model both the part of atmospheric co2 coming from silicate weathering and the part coming from carbonate weathering are distinguished the climatic conditions during lgm were reconstructed on the basis of the output files from a computer simulation with a general circulation model only the predicted changes in precipitation and temperature have been used whereas the changes in continental runoff were determined with an empirical method it is found that during the lgm the overall atmospheric co2 consumption may have been greater than today by about 20 mainly because of greater carbonate outcrop area related to the lower sea level on the shelves this does not however affect the atmospheric co2 consumption by silicate weathering which alone has the potential to alter atmospheric co2 on the long term silicate weathering and the concomitant atmospheric co2 consumption decreased together with a global decrease of continental runoff compared to present day both by about 10 nevertheless some uncertainty remains because the individual lithologies of the continental shelves as well as their behavior with respect to chemical weathering are probably not well enough known the values we present refer to the ice free continental area only but we tested also whether chemical weathering under the huge ice sheets could have been important for the global budget although glacial runoff was considerably increased during lgm weathering under the ice sheets seems to be of minor importance

the riverine silicon isotope composition of the amazon basin we present here the first large scale study of riverine silicon isotope signatures in the amazon basin the amazon and five of its main tributaries were studied at different seasons of the annual hydrological cycle the 30si signature of the dissolved silicon dsi exported to the estuary weighted for dsi flux for the period considered is estimated at 0 92 a river cross section shows the homogeneity of the amazon river regarding dsi concentration and isotope ratio the biogenic silica bsi concentration measured in surface water from all rivers is generally small compared to the dsi reservoir but large variations exist between rivers very low isotope signatures were measured in the upper rio negro 30si 0 05 0 06 which we explain both by an equilibrium between clay formation and dissolution and by gibbsite formation the si isotope fractionation in the andean tributaries and the amazon main stem can be explained by clay formation and follow either a rayleigh or a batch equilibrium fractionation model our results also suggest that the formation of 2 1 clays induces a fractionation factor similar to that of kaolinite formation

watershed control on the carbon loading of marine sedimentary particles abstract previous investigations of the factors governing organic carbon burial on continental margins have pointed toward the important apparently protective association of carbon with mineral particles these studies have also revealed dramatic transformations of carbon particle relationships at the land sea interface riverine particles in some settings lose a large portion of their loads of sorbed terrestrial carbon upon discharge to the ocean and gradually reload to similar levels with marine carbon the eel river in northern california and the adjacent continental shelf were selected as an ideal system to investigate the rates of these processes the river is episodically subject to large floods and the shelf stratigraphy preserves a record of the resultant large pulses of sediment and carbon input to the marine environment carbon isotopic carbon to nitrogen and carbon to surface area ratios of particles in flood deposits were expected to reflect the rapid unloading of terrestrial carbon from discharged particles whereas nonflood sediments that have accumulated at slower rates on the shelf were expected to carry higher loads of marine carbon our results indicate however that particles on the eel shelf have retained their loads of terrigenous carbon and that a significant portion of the particle sorbed carbon buried on the shelf is kerogen derived from the mesozoic tertiary franciscan complex we hypothesize that rates of uplift and mass wasting in the eel watershed and rates of particle delivery to and burial on the continental shelf are so rapid that kerogen is not completely oxidized and is recycled instead the loading of carbon on clay sized particles delivered to the shelf moreover is dependent on river discharge and may reflect the relative importance of different mass wasting processes during precipitation events of varying intensity the eel river system is likely to be representative of other small mountainous rivers and indicates that processes on land may play an important role in governing the amount and character of carbon being buried on the continental margins

holocene land use evolution and associated soil erosion in the french prealps inferred from lake paladru sediments and archaeological evidences a source to sink multi proxy approach has been performed within lake paladru 492 m a s l french prealps catchment and a six meter long sediment sequence retrieved from the central lacustrine basin the combination of minerogenic signal specific organic markers of autochthonous and allochthonous supply and archaeological data allows the reconstruction of a continuous record of past human disturbances over the last 10000 years the lacustrine sedimentation was dominated by autochthonous carbonates and the watershed was mostly forest covered however seven phases of higher accumulation rate soil erosion algal productivity and landscape disturbances have been identified and dated from 8400 7900 6000 4800 4500 3200 2700 2050 cal bp as well as ad 350 850 ad 1250 1850 and after ad 1970 before 5200 cal bp soil erosion is interpreted as resulting from climatic deterioration phases toward cooler and wetter conditions during the mid late holocene period erosion fluxes and landscape disturbances are always associated with prehistorical and historical human activities and amplified by climatic oscillations such changes in human land used led to increasing minerogenic supply and nutrients loading that affected lacustrine trophic levels especially during the last 1600 years in addition organic and molecular markers document previously unknown human settlements around lake paladru during the bronze and the iron ages

lower pleistocene dinoflagellate cyst foraminiferal and pollen assemblages in four boreholes in the southern north sea neogene and lower pleistocene stratigraphy in the southern north sea has been investigated in four i g s boreholes between east anglia and the netherlands the foraminifera of the red crag formation in borehole 81 51 are closely similar to upper pliocene assemblages in holland the overlying succession is clearly punctuated by unconformities in seismic profiles separating four early pleistocene formations in the boreholes and indicating intervals of significant stratigraphic hiatus offshore the westkapelle ground and smith s knoll formations correlate with thurnian and antian stage deposits in east anglia pollen spectra in the winterton shoal and yarmouth roads formations are similar to baventian and bramertonian assemblages in britain the autochthonous marine and allochthonous terrestrial microfauna and flora provide conflicting evidence of early pleistocene palaeoclimate the dinoflagellate cysts and foraminifera indicate that each formation was deposited in a warm temperate neritic environment the pollen record containing evidence of fluctuation between boreal and mixed coniferous deciduous regional forest cover suggests alternation between cool and warm temperate palaeoclimate

silicate rock weathering and atmospheric soil co2 uptake in the amazon basin estimated from river water geochemistry seasonal and spatial variations abstract using the data of the camrex project 1982 1984 on the water geochemistry of the amazon river and its main tributaries it was possible to assess the silicate rock weathering processes and the associated consumption of atmospheric soil co2 taking into account seasonal and spatial variations this study confirms the important role of the andes in the fluvial transport of dissolved and particulate material by the amazon and it shows for the first time that the silicate weathering rate and atmospheric soil co2 consumption are higher in the andes than in the rest of the amazon basin the seasonal variations exhibit the significant role of runoff as a major factor controlling silicate weathering processes and show that the chemical erosion rates vary greatly from low discharge to high discharge the average weathering rate estimated for the whole amazon basin 15 m my is comparable to other estimations made for other tropical equatorial environments a comparison between physical and chemical weathering rates of silicate rocks for the amazon basin and for each tributary basin show that in the andes and in the amazon trough the soil thicknesses are decreasing whereas in the shield the soil profiles are deepening

diffusive transport of water in porous fresh to altered mid ocean ridge basalts abstract studying diffusive transport in porous rocks is of fundamental importance in understanding a variety of geochemical processes including element transfer primary mineral dissolution kinetics and precipitation of secondary phases here we report new findings on the relationship between diffusive transport and textural characteristics of the pore systems on the example of mid oceanic ridge basalts having different degree of alteration but very similar bulk pore volume diffusion processes in porous basalts were studied in situ using h 2 o d 2 o exchange experiments the effective diffusion coefficients of water molecules increase systematically from 5 05 10 11 to 1 19 10 10 m 2 s for fresh and moderately altered basalts and from 2 40 10 11 to 6 72 10 11 m 2 s for completely altered basalt as temperature increases from 5 to 50 c the activation energy of the diffusion process increases from 12 29 0 71 kj mol for fresh and moderately altered basalts to 14 3 1 33 kj mol for completely altered basalt the results indicate that neither the bulk porosity nor the degree of alteration can be used as proxies for the efficiency of element transport during morb water interaction the formation of secondary phases that replace primary minerals and fill the pore space in the rock leads to the formation of tiny pores and phases with large specific surface area these factors might have a dominant control on the transport properties of altered basaltic rocks

recent climatic and anthropogenic imprints on lacustrine systems in the pyrenean mountains inferred from minerogenic and organic clastic supply vicdessos valley pyrenees france high resolution seismic profiling has been combined with geochemical analyses of both watershed samples and five lacustrine cores retrieved from two natural lacustrine basins of glacial origin lake majeur and lake sigriou 1630 m a s l and 1995 m a s l respectively eastern french pyrenees identifying specific minerogenic and organic markers of autochthonous and allochthonous supply data allow documenting past climatic and anthropogenic pressures over the past century the lacustrine sediment of lake majeur has been essentially composed of algae drastically contrasting with the natural sedimentary infill of the basin mainly resulting from soil erosion from the mid late holocene since ad 1907 the lake majeur has been used for hydroelectricity production human induced lake level regulations affecting up to 37 of the lacustrine surface have increased by fourfold the accumulation rate of the lake and favoured water enrichment rubidium abundance within the lacustrine sediments of the two lakes reflects the mid late holocene palaeohydrology after dam construction in ad 1907 greater quantities of rubidium found in lake majeur sedimentary infills indicate drier climatic periods such as from ad 1975 to ad 1982 during which water reservoirs were particularly in demand inversely before the dam was built rubidium fluctuations were correlated with wetter conditions and hydrological events were recorded as sandy layers deposited by canyon reactivation synchronous with european climatic deterioration phases we notably document that the mediaeval climate anomaly was interrupted by some humid periods dated c ad 940 ad 1080 ad 1100 and ad 1250 we also date the onset of the little ice age c ad 1360 and identify that this period was wetter after c ad 1500

heterogeneities of organic matter and its occurrence forms in mudrocks evidence from comparisons of palynofacies abstract mudrocks buried at different depths in a single well exhibiting different sedimentary environments and lithologies were collected from the dongying sag of the jiyang depression of eastern china to investigate the heterogeneities of organic matter om and its occurrence forms in this study both bulk rocks and their organo clay composites i e

a reactive transport model for marcellus shale weathering abstract shale formations account for 25 of the land surface globally and contribute a large proportion of the natural gas used in the united states one of the most productive shale gas formations is the marcellus a black shale that is rich in organic matter and pyrite as a first step toward understanding how marcellus shale interacts with water in the surface or deep subsurface we developed a reactive transport model to simulate shale weathering under ambient temperature and pressure conditions constrained by soil and water chemistry data the simulation was carried out for 10 000 years since deglaciation assuming bedrock weathering and soil genesis began after the last glacial maximum results indicate weathering was initiated by pyrite dissolution for the first 1000 years leading to low ph and enhanced dissolution of chlorite and precipitation of iron hydroxides after pyrite depletion chlorite dissolved slowly primarily facilitated by the presence of co2 and organic acids forming vermiculite as a secondary mineral a sensitivity analysis indicated that the most important controls on weathering include the presence of reactive gases co2 and o2 specific surface area and flow velocity of infiltrating meteoric water the soil chemistry and mineralogy data could not be reproduced without including the reactive gases for example pyrite remained in the soil even after 10 000 years if o2 was not continuously present in the soil column likewise chlorite remained abundant and porosity remained small if co2 was not present in the soil gas the field observations were only simulated successfully when the modeled specific surface areas of the reactive minerals were 1 3 orders of magnitude smaller than surface area values measured for powdered minerals small surface areas could be consistent with the lack of accessibility of some fluids to mineral surfaces due to surface coatings in addition some mineral surface is likely interacting only with equilibrated pore fluids an increase in the water infiltration rate enhanced weathering by removing dissolution products and maintaining far from equilibrium conditions we conclude from these observations that availability of reactive surface area and transport of h2o and gases are the most important factors affecting rates of marcellus shale weathering of the in the shallow subsurface this weathering study documents the utility of reactive transport modeling for complex subsurface processes such modelling could be extended to understand interactions between injected fluids and marcellus shale gas reservoirs at higher temperature pressure and salinity conditions

quantitative palynofacies analysis as a new tool to study transfers of fossil organic matter in recent terrestrial environments classical palynofacies method which consists in an organic concentrate microscopic qualitative observation after mineral phase dissolution is commonly used in order to study sedimentary organic matter in the present study we develop a new quantitative palynofacies method that allows organic particles mass concentrations to be determined in studied samples this method was developed to help quantify the input of fossil organic matter fom into modern environments as a result of sedimentary rocks weathering studied samples were collected from different pools like bedrocks weathering profiles soils and riverine particles in an experimental watershed le laval this watershed overlying callovo oxfordian marls 1 km in area is located near digne alpes de haute provence in france in addition to palynofacies techniques rock eval 6 pyrolysis and al2o3 content measurements inductively coupled plasma emission spectrometry were carried out on the samples obtained results show that this quantitative palynofacies method is suitable for fom studies in modern environments and fom particles are quantified in the different pools results also give evidence that fom alteration depends on the type of weathering but also on the kind of organic particles soil formation under vegetation resulting from the bio chemical weathering lead to fossil organic particles concentration losses that do not exceed 30 elsewhere mechanical weathering appears extremely fast and has no qualitative or quantitative influence on the observed fom particles which feeds directly into riverine stocks fom appears to be very resistant to weathering processes this highlights its occurrence into supergene pools and then into carbon cycle quantitative palynofacies analysis is a new method adapted to a such study but can also be applied to other palynological paleoenvironmental or archeological studies

considering lacustrine erosion records and the de ploey erosion model in an examination of mountain catchment erosion susceptibility and precipitation reconstruction reconstruction of paleo precipitation can provide an insight into past climate and precipitation de ploey et al 1995 presents a highly simplified erosion equation to consider precipitation and erosion susceptibility this empirical model allows estimation of total precipitation and erosion susceptibility across a range of catchment characteristics including catchment area slope elevation vegetation cover and when limited catchment or meteorological data is available the presented study tests the de ploey equation using dated lacustrine records of catchment soil deposition both spatially and temporally the objective is to examine the de ploey equation s ability and efficiency in reconstructing past long term precipitation using sedimentological parameters the erosion susceptibility factor is described as a black box value by de ploey et al 1995 this research unravels the erosion susceptibility variable identifying it to change spatially and temporally according to precipitation vegetation cover and composition the extent of tree establishment across the catchment total lacustrine deposition and geochemical signatures in the archive calculation of the erosion sustainability variable and it s use within the de ploey erosion equation illustrate a reconstruction of an indicative mean annual precipitation and erosion susceptibility change over the recent period 100 years

temperate meteoric diagenesis of pliocene skeletal carbonates from eastern england the crags of eastern england include marine skeletal carbonates which were deposited and lithified under temperate conditions the coralline crag pliocene in particular exhibits a variety of carbonate cement types which indicate exposure to meteoric groundwaters during a regressive episode the coralline crag has been divided into an upper division of dominantly well sorted skeletal calcarenites and calcirudites and a lower poorly sorted silty calcarenite division dogtooth spardcement and rudimentary syntaxial cement overgrowths on echinoderm fragments are characteristic of the sediments of the upper division which has undergone extensive aragonite dissolution this division is consequently relatively evenly cemented in the underlying sediments aragonite dissolution has not occurred and the sediments have remained largely uncemented with cement restricted to irregular patches where growth of intra and inter particle equant spar has effectively eliminated porosity in contrast with the upper leached sediments syntaxial echinoderm overgrowths show a greater development but only where interference from surrounding sediment and sparry cement was absent the elongate shape of the coralline crag outcrop may be the result of preferential cementation of the upper coarser well sorted calcarenites originally deposited as an elongate sediment body possibly as an offshore sandbank

annual fossil organic carbon delivery due to mechanical and chemical weathering of marly badlands areas a key issue in the study of the carbon cycle is constraining the stocks and fluxes in and between c reservoirs among these the role and importance of fossil organic carbon foc release by weathering of outcropping sedimentary rocks on continental surfaces is still debated and remains poorly constrained our work focuses on foc fluxes due to chemical and mechanical weathering of marls in two experimental watersheds with typical badlands geomorphology draix watersheds laval and moulin alpes de haute provence france organic matter from bedrock soil litter and riverine particles are characterized by rock eval 6 pyrolysis foc fluxes due to mechanical weathering are then estimated by monitoring the annual particulate solid exports at the outlets of the watersheds 1985 2005 period foc fluxes from chemical weathering were calculated using ca2 concentrations in dissolved loads year 2002 to assess the amount of foc released by the dissolution of the carbonate matrix results show that foc delivery is mainly driven by mechanical weathering with a yield ranging from 30 to 59 t km 2 yr 1 in the moulin 0 08 km2 and laval 0 86 km2 catchments respectively 1985 2005 average the release of foc attributed to chemical weathering was 2 2 to 4 2 t km 2 for the year 2002 these high foc fluxes from badlands are similar to those observed in tectonically active mountain catchments at a regional scale badland outcropping within the durance watershed does not exceed 0 25 in area of the rhone catchment but could annually deliver 12 000 t yr 1 of foc this flux could correspond to 27 of the total particulate organic carbon poc load exported by the rhone river to the mediterranean sea at a global scale our findings suggest that erosion of badlands may contribute significantly to the transfer of foc from continental surfaces to depositional environments copyright 2012 john wiley sons ltd

weathering indices as climate proxies a step forward based on congo and sw african river muds abstract despite the influence of other geological and geomorphological factors chemical weathering at the earth s surface is strongly controlled by climate thus a measure of weathering intensity determined from soils or sediments should provide information about the climatic conditions associated with their formation available geochemical and mineralogical data on modern fluvial and marine muds from different regions of southern africa and its atlantic continental margin are used to review the links between sediment composition and climatic properties together with the possible causes of variance although river muds may not be generated exclusively in a single sedimentary cycle and erosion and weathering processes do not necessarily take place in a spatially homogeneous way significant relationships between mineralogical and geochemical signatures of river mud and rainfall in the corresponding catchment area were recognised our study shows that the composition of clay is strongly influenced by climatically driven weathering whilst coarser mud fractions tend to be more affected by provenance grain size hydraulic sorting and recycling in the marine environment the climatic signal may be lost even in clay because of hydraulic fractionation authigenic mineral growth and mixing with foreign particles given the ubiquitous character of fluvial muds and the easy and non expensive methods available for separating and analysing clay fractions their geochemical fingerprints represent a most precious source of information concerning climate any geochemical parameter used as a regional proxy of climate however still requires that the diversity of geological geomorphological and biological factors that affect its value are cautiously considered

clay minerals of late pleistocene sites jonzac and les cottes sw france applications of x ray diffraction analyses to local paleoclimatic and paleoenvironmental reconstructions abstract the crystal chemical properties of clay minerals are closely dependent on the physicochemical conditions prevailing at the time when they formed in soils and weathered zones the degree of alteration of primary minerals and the composition of the secondary products are clearly linked to climate and plant cover in particular changes are rapid under temperate conditions which favor the development of thick soils but slow in cold contexts favoring thin and fragile soils in this paper the mineral composition of two pleistocene clay rich deposits is investigated in order to contribute to reconstructing paleoenvironmental changes jonzac charentes sw france and les cottes vienne sw france are two rock shelters with long archaeological sequences which include faunal remains and were recently radiometrically dated the decomposition of xrd patterns at each site allows identification of the principal mineral phases and semi quantitative estimation of their relative proportions the variation of these proportions is analyzed through indexes based on the relative intensities of the decomposed bands the clay fraction of both sites mostly results from the transformation of the minerals forming the sediments in the surrounding area of the rock shelter terrace including contributions from the hillside mineralogical clay data are compared with the faunal spectrum identified at both sites in order to discuss paleoenvironmental implications at jonzac during the quina mousterian period dated to mis4 the environment was cold and dry the dominant mineralogical phases are inherited from the rocks weak pedogenesis this is consistent with the faunal analysis data typical of the mis4 during the mousterian of acheulean tradition period dated to mis3 the mineralogical composition of the clay deposits changed significantly suggesting a less wet environment the aurignacian deposits dated to the end of mis3 early mis2 are rich in mixed layer minerals mlms which are produced by the hydrolysis processes in soils the climatic conditions probably became milder however because no faunal remains were found this evolution is uncertain the les cottes deposits dated between mis3 and early mis2 are mineralogically typical of a cold environment where soil reactions are not very active however some weak variations of the indexes suggest temporary temperate conditions during the les cottes interstadial and in the aurignacian the parallelism between mineral signature and paleontological evidence in recording relatively rapid variations between contrasted climates suggests that clay mineral assemblages from rock shelter deposits can be used to assess paleoclimatic and paleoenvironmental dynamics at a local scale

the co2 consumption potential during gray shale weathering insights from the evolution of carbon isotopes in the susquehanna shale hills critical zone observatory abstract shale covers about 25 of the land surface and is therefore an important rock type that consumes co 2 during weathering we evaluated the potential of gray shale to take up co 2 from the atmosphere by investigating the evolution of dissolved inorganic carbon dic concentrations and its carbon isotopic ratio 13 c dic along water flow paths in a well characterized critical zone observatory susquehanna shale hills catchment in this catchment chemical weathering in shallow soils is dominated by clay transformation as no carbonates are present and soil pore waters are characterized by low dic and ph in shallow soil porewaters the dic dominated by dissolved co 2 is in chemical and isotopic equilibrium with co 2 in the soil atmosphere where pco 2 varies seasonally to as high as 40 times that of the atmosphere the degradation of ancient organic matter is negligible in contributing to soil co 2 the chemistry of groundwater varies along different flowpaths as soil pore water recharges to the water table and then dissolves ankerite or secondary calcite under the valley floor weathering of carbonate leads to much higher concentrations of dic 2500 mol l and divalent cations ca 2 and mg 2 in groundwaters than soil waters the depth to the ankerite weathering front is hypothesized to be roughly coincident with the water table but it varies due to heterogeneities in the protolith composition groundwater chemistry therefore shows different saturation indices with respect to ankerite depending upon location along the valley the 13 c dic values of these groundwaters document mixing between the ankerite and soil co 2 the major element concentrations dic and 13 c dic in the first order stream incising the valley of the catchment are derived from groundwater and soil waters in proportions that vary both spatially and temporally the co 2 degassed slightly in the stream but little evidence of c isotopic equilibration with the atmosphere is observed due to the short length of the stream and short contact time with air the ankerite reaction front also lies close to the pyrite dissolution front pyrite oxidation in bedrock likely released sulfuric acid and played a minor role in the ankerite dissolution shifting groundwater 13 c dic slightly above the expected mixing values at the catchment scale the stream so 4 2 is also dominantly derived from wet deposition as stream has 34 s so4 values around 3 well within the range of acid deposition a mass balance calculation shows that silicate and ankerite dissolution of the rose hill shale at shale hills consumes co 2 at a rate of 44 and 42 48 mol m 2 ky 1 respectively while degradation of ancient organic matter releases co 2 at a rate of 1 3 mol m 2 ky 1 silicate dissolution at the shallow soils is facilitated by low ph and high soil pco 2 as ankerite dissolution and organic matter oxidation are shown to occur early during shale alteration co 2 consumption by shale weathering is thus limited by initiation of rock disintegration e g fractures and exposure of fresh surface area to infiltrating co 2 and o 2 rich water

modelling of atmospheric co2 consumption by chemical weathering of rocks application to the garonne congo and amazon basins modelling of atmospheric co consumption by chemical weathering of rocks application to the garonne congo and amazon basins

the iron isotope composition of enstatite meteorites implications for their origin and the metal sulfide fe isotopic fractionation factor abstract despite their unusual chemical composition it is often proposed that the enstatite chondrites represent a significant component of earth s building materials based on their terrestrial similarity for numerous isotope systems in order to investigate a possible genetic relationship between the fe isotope composition of enstatite chondrites and the earth we have analyzed 22 samples from different subgroups of the enstatite meteorites including eh and el chondrites aubrites main group and shallowater and the happy canyon impact melt we have also analyzed the fe isotopic compositions of separated magnetic and non magnetic phases from both enstatite chondrites and achondrites on average eh3 5 chondrites 56fe 0 003 0 042 2 standard deviation n 9 including previous literature data as well as el3 chondrites 56fe 0 030 0 038 2 sd n 2 have identical and homogeneous fe isotopic compositions indistinguishable from those of the carbonaceous chondrites and average terrestrial peridotite in contrast el6 chondrites display a larger range of isotopic compositions 0 180 enstatite achondrites aubrites also exhibit a relatively large range of fe isotope compositions all main group aubrites are enriched in the light fe isotopes 56fe 0 170 0 189 2 sd n 6 while shallowater is isotopically relatively heavy 56fe 0 045 0 101 2 sd n 4 number of chips we take this variation to suggest that the main group aubrite parent body formed a discreet heavy fe isotope enriched core whilst the shallowater meteorite is most likely from a different parent body where core and silicate material remixed this could be due to intensive impact induced shearing stress or the ultimate destruction of the shallowater parent body analysis of separated enstatite meteorite mineral phases show that the magnetic phase fe metal is systematically enriched in the heavier fe isotopes when compared to non magnetic phases fe hosted in troilite which agrees with previous experimental observations and theoretical calculations the difference between magnetic and non magnetic phases from enstatite achondrites provides an equilibrium metal sulfide fe isotopic fractionation factor of 56femetal troilite 56femetal 56fetroilite of 0 129 0 060 2 se at 1060 80 k which confirms the predictions of previous theoretical calculations

occurrence of fossil organic matter in modern environments optical geochemical and isotopic evidence abstract this study relates to the input and fate of fossil organic matter fom in the modern environment and focuses on two experimental watersheds overlying jurassic marls le laval and le brusquet 1 km2 in area located near digne alpes de haute provence france considering that fom delivery is mainly a result of different processes affecting sedimentary rocks bio chemical and mechanical weathering samples from different pools were collected bedrocks weathering profiles soils and riverine particles the samples were examined using complementary techniques optical palynofacies methods geochemical rock eval 6 pyrolysis c n ratio molecular gas chromatography mass spectrometry and isotopic stable c isotopic composition as a result fom markers were identified and tracked through the different pools the results highlight the contribution of fom which can be found in all the studied pools transfer of fom between bedrocks weathering profiles governed mainly by chemical weathering and bedrocks riverine particles governed mainly by mechanical weathering reveals any qualitative change weathering profiles soils transition governed by bio chemical weathering is characterized by alteration of the fom which is difficult to describe because fossil material is mixed with recent organic matter rom despite this latter point the study provides evidence for a relative resistance of fom to weathering processes and points to its contribution to the modern geosystem and the c cycle

the dynamics of si cycling during weathering in two small catchments in the black forest germany traced by si isotopes abstract silicon stable isotopes have emerged as a powerful proxy to investigate weathering because si uptake from solution by secondary minerals or by the vegetation causes significant shifts in the isotope composition in this study we determined the si isotope compositions of the principle si pools within two small catchments located on sandstone and paragneiss respectively in the temperate black forest germany at both settings clay formation is dominated by mineral transformation preserving largely the signature of parental minerals with 30si values of around 0 7 bulk soils rich in primary minerals are similar to bulk parental material with 30si values close to 0 4 topsoils are partly different because organic matter degradation has promoted intense weathering leading to 30si values as low as 1 0 water samples expose highly dynamic weathering processes in the soil zone 1 after spring snowmelt increased release of doc and high water fluxes trigger clay mineral dissolution which leads to 30si values down to 0 7 and 2 in course of the summer si uptake by the vegetation and secondary mineral formation drives dissolved si to typical positive 30si values up to 1 1 groundwater with 30si values of around 0 4 records steady processes in bedrock reflecting plagioclase weathering together with kaolinite precipitation an isotope mass balance approach reveals incongruent weathering conditions where denudation of si is largely driven by physical erosion erosion of phytoliths contributes 3 to 21 to the total si export flux which is in the same order as the dissolved si flux these results elucidate the si dynamics during weathering on catchments underlain of sedimentary origin prevailing on the earth surface and provide therefore valuable information to interpret the isotope signature of large river systems

terrestrial sedimentation and the carbon cycle coupling weathering and erosion to carbon burial this paper examines the linkages between the carbon cycle and sedimentary processes on land available data suggest that sedimentation on land can bury vast quantities of organic carbon roughly 1015 g c yr 1 to evaluate the relative roles of various classes of processes in the burial of carbon on land terrestrial sedimentation was modeled as a series of 864 scenarios each scenario represents a unique choice of intensities for seven classes of processes and two different global wetland distributions comparison was made with presumed preagricultural conditions the classes of processes were divided into two major component parts clastic sedimentation of soil derived carbon and organic sedimentation of autochthonous carbon for clastic sedimentation masses of sediment were considered for burial as reservoir sediment lake sediment and combined colluvium alluvium and aeolian deposits when the ensemble of models is examined the human induced burial of 0 6 1 5 1015 g yr 1 of carbon on land is entirely plausible this sink reaches its maximum strength between 30 and 50 n paddy lands stand out as a type of land use that warrants future study but the many faces of rice agriculture limit generalization in an extreme scenario paddy lands alone could be made to bury about 1 1015 g c yr 1 arguing that terrestrial sedimentation processes could be much of the sink for the so called missing carbon is reasonable such a hypothesis however requires major redesign of how the carbon cycle is modeled unlike ecosystem processes that are amenable to satellite monitoring and parallel modeling many aspects of terrestrial sedimentation are hidden from space

assessing the role of submarine groundwater discharge as a source of sr to the mediterranean sea abstract submarine groundwater discharge sgd has been identified as an important source of sr to the ocean and the sgd driven sr flux to the global ocean has been recently re evaluated beck et al 2013 however the uncertainty of this value is still high because of the uncertainties related to the determination of sgd flow rates and the paucity of 87 sr 86 sr data in sgd end members as carbonates have high sr concentrations and are subjected to intense heightened weathering they might significantly influence the sgd input of sr to the ocean here we present data on sr concentrations and 87 sr 86 sr ratios in three carbonate dominated sites of the western area of the mediterranean sea a semi enclosed basin characterized by abundant coastal carbonates the 87 sr 86 sr ratios in groundwater were lower compared to modern seawater 0 70916 as expected for areas dominated by carbonate lithologies concentrations of sr and 87 sr 86 sr ratios in groundwater showed conservative mixing in the studied subterranean estuaries by using sgd flow rates reported in the literature for the study areas a flow weighted fresh sgd end member characterized by a sr concentration of 27 30 m and a 87 sr 86 sr ratio of 0 707834 0 708020 was calculated for the eastern coast of the iberian peninsula integrating these sr data with literature data i e values of sr concentration and 87 sr 86 sr ratio from other lithologies as well as sgd flow rates we also calculated the fresh sgd driven sr flux to the entire mediterranean sea obtaining a value of 0 34 0 83 10 9 mol y 1 with a 87 sr 86 sr of 0 7081 0 7086 thus for the entire mediterranean basin sgd is globally a source of sr less radiogenic compared to seawater the sgd sr flux to the mediterranean sea represents 5 6 of the sgd sr flux to the global ocean and the mediterranean sgd end member has higher sr concentration 5 12 m than the global sgd end member 2 9 m this confirms the significant role of carbonate lithologies on sgd driven sr fluxes to seawater the fresh sgd driven sr flux to the mediterranean sea is about 20 50 of the riverine sr input and significantly higher than the input through atmospheric dust deposition therefore sgd should be considered as an important continental source of sr to the basin

iron isotope fractionation in the earth s lower mantle the two main iron bearing silicate phases in the mantle ferroperovskite and ferropericlase are expected to partition iron isotopes differently theoretical calculations suggest that the spin state of iron strongly influences the iron isotopic composition of ferropericlase whereas the iron isotopic composition of ferroperovskite is almost independent of spin state

global geologic maps are tectonic speedometers rates of rock cycling from area age frequencies relations among ages and present areas of exposure of volcanic sedimentary plutonic and metamorphic rock units lithosomes record a complex interplay between depths and rates of formation rates of subsequent tectonic subsidence and burial and or rates of uplift and erosion thus they potentially serve as efficient deep time geologic speedometers providing quantitative insight into rates of material transfer among the principal rock reservoirs processes central to the rock cycle areal extents of lithosomes exposed on all continents from two map sources geological survey of canada gsc and the food and agricultural organization fao of the united nations educational scientific and cultural organization unesco indicate that volcanic sedimentary plutonic and metamorphic rocks occupy 8 73 7 and 12 of global exposures respectively plots of area versus age of all mapped rock types display a power law relation where 6 5 of continental area is resurfaced with younger 10 volcanic 90 sedimentary units every million years and where areas of rock exposure decrease by 0 86 for each 1 increase in outcrop age r 2 0 90 area age relations for volcanic and sedimentary lithosomes are similar to the power law distribution defined by all rock units because 81 of mapped area consists of these two lithologies and reflect progressive decrease in amount of exposure with increasing age over the long term continental surfaces are blanketed by new volcanic rocks and sediments at rates of 1 5 and 12 1 10 6 km 2 ma respectively in contrast to power law distributed volcanic and sedimentary rocks that form at the earth9s surface age frequency distributions for plutonic and metamorphic rocks exhibit lognormal relations with modes at ca 154 and 697 ma respectively a dearth of younger exposures of plutonic and metamorphic rocks reflects the fact that these rock types form at depth and some duration of tectonism is therefore required for their exposure increasing modal ages from quaternary for volcanic and sedimentary successions to early mesozoic for intrusive rocks to neoproterozoic for metamorphic rocks demonstrate that greater amounts of geologic time are required for uplift to bring more deeply formed rocks to the earth9s surface the two different age frequency distributions observed for these major rock types a general power law age distribution for volcanic and sedimentary rocks and a lognormal distribution for plutonic and metamorphic rock ages reflect the interplay between depths of formation and mean rates of vertical tectonic displacement age frequency distributions for each of the major rock types are closely replicated by a model that presumes that individual crustal elements behave as a large population of random walks in geologic time and crustal depth and where the processes of surficial erosion associated with tectonic uplift serve to impose an absorbing boundary on this random walk space comparisons between model predicted age frequencies and those apparent in global map data suggest that mean rates of crustal subsidence and uplift are approximately equal in magnitude with mean rates of vertical tectonic diffusion of lithosomes from crustal depths of formation of about half a kilometer per million years rates of uplift and subsidence are strongly dependent on durations of tectonic dispersion lithosome ages however mean rates on the order of hundreds of meters per million years suggested by map age frequencies are the same as would be anticipated on the basis of hundreds of published rates of erosional uplift and exhumation determined by more conventional geochronometers this agreement suggests that geologic maps serve as effective deep time speedometers for the geologic rock cycle

modelling basalt weathering at elevated co2 concentrations implications for terminal to post magmatic rifting in the deccan traps kachchh india

determining contemporary stress directions from neotectonic joint systems a neotectonic joint is a crack which propagated in a tectonic stress field that has persisted with little or no change of orientation until the present day investigating neotectonic joints is of value because the approximate orientation of the contemporary stress field can be inferred from them although exposed neotectonic joints in the flat lying sedimentary rocks of some cratons are related to regional stress fields their initiation and propagation occurred close to the earth s surface for example neotectonic joints in the centre of the ebro basin n spain preferentially developed in a thin near surface channel sited within a sequence of weak miocene limestones underlying the upper levels of plateaux the ebro basin joints strike uniformly nnw sse throughout an area of at least 10000 km2 and they are parallel or subparallel to the direction of greatest horizontal stress extrapolated from in situ stress measurements and fault plane solutions of earthquakes 1 preamble this paper has three aims firstly to review the general attributes of exposed neotectonic joints secondly to demonstrate that in s england n france and the ebro basin spain the directions of greatest horizontal principal stress that were inferred from neotectonic joints are parallel to those determined later from geophysical observations and thirdly to discuss why neotectonic joints in the ebro basin are better developed in weak limestones cropping out in the upper parts of plateaux in this paper the word neotectonic is used to indicate that a fracture was propagated in a tectonic stress field that has persisted with little or no change of orientation until the present day hancock engelder 1989 a fracture is called a joint if at the scale of observation possible in the field it is barren and there is no measurable offset related to shear dilation or pressure solution because joints are the most abundant of non penetrative geological structures they are of great potential value for tracking the orientations of principal stress axes at the time of failure confidence in the value of joints as stress indicators is greatest where they are uniformly arranged throughout a large area of flat lying rocks

stable intermediate spin ferrous iron in lower mantle perovskite iron has the ability to adopt different electronic configurations and transitions in its spin state in the lower mantle can significantly influence mantle properties and dynamics experimental results for two lower mantle perovskite compositions show that the intermediate spin state of iron is stable throughout the bulk of the lower mantle

chemical weathering and co2 consumption in the xijiang river basin south china monthly samples of riverine water were collected and analyzed for the concentrations of major ions ca2 mg2 k na hco3 so42 cl no3 dissolved silicon and total dissolved solids tds at wuzhou hydrological station located between the middle and lower reaches of the xijiang river xjr from march 2005 to april 2006 more frequent sampling and analysis were carried out during the catastrophic flooding in june 2005 stoichiometric analysis was applied for tracing sources of major ions and estimating co2 consumption from the chemical weathering of rocks the results demonstrate that the chemical weathering of carbonate and silicate rocks within the drainage basin is the main source of the dissolved chemical substances in the xjr some 81 20 of the riverine cations originated from the chemical weathering processes induced by carbonic acid 11 32 by sulfuric acid and the other 7 48 from the dissolution of gypsum and precipitates of sea salts within the drainage basin the co2 flux consumed by the rock chemical weathering within the xjr basin is 2 37 x 10 11 mol y 1 of which 0 64 x 10 11 mol y 1 results from silicate rock chemical weathering and 1 73 x 10 11 mol y 1 results from carbonate rock chemical weathering the co2 consumption comprises 0 38 x 10 11 mol during the 9 d catastrophic flooding the co2 consumption from rock chemical weathering in humid subtropical zones regulates atmospheric co2 level and constitutes a significant part of the global carbon budget the carbon sink potential of rock chemical weathering processes in the humid subtropical zones deserves extra attention c 2008 elsevier b v all rights reserved

chemical weathering in the krishna basin and western ghats of the deccan traps india rates of basalt weathering and their controls rates of chemical and silicate weathering of the deccan trap basalts india have been determined through major ion measurements in the headwaters of the krishna and the bhima rivers their tributaries and the west flowing streams of the western ghats all of which flow almost entirely through the deccan basalts samples n 63 for this study were collected from 23 rivers during two consecutive monsoon seasons of 2001 and 2002 the total dissolved solid tds in the samples range from 27 to 640 mg l 1 the rivers draining the western ghats that flow through patches of cation deficient lateritic soils have lower tds average 74 mg l 1 whereas the bhima except at origin and its tributaries that seem to receive na cl and so4 from saline soils and anthropogenic inputs have values in excess of 170 mg l 1 many of the rivers sampled are supersaturated with respect to calcite the chemical weathering rates cwr of selected basins which exclude rivers supersaturated in calcite and which have high cl and so4 are in range of 3 to 60 t km 2 y 1 this yields an area weighted average cwr of 16 t km 2 y 1 for the deccan traps this is a factor of 2 lower than that reported for the narmada tapti wainganga ntw systems draining the more northern regions of the deccan the difference can be because of i natural variations in cwr among the different basins of the deccan ii selection of river basin for cwr calculation in this study and iii possible contribution of major ions from sources in addition to basalts to rivers of the northern deccan traps silicate weathering rates swr in the selected basins calculated using dissolved mg as an index varies between 3 to 60 t km 2 y 1 nearly identical to their cwr the ca mg and na mg in these rivers after correcting for rain input are quite similar to those in average basalts of the region suggesting near congruent release of ca mg and na from basalts to rivers comparison of calculated and measured silicate ca in these rivers indicates that at most 30 of ca can be of nonsilicate origin a likely source being carbonates in basalts and sediments the chemical and silicate weathering rates of the west flowing rivers of the deccan are 4 times higher than the east flowing rivers this difference is due to the correspondingly higher rainfall and runoff in the western region and thus reemphasises the dominant role of runoff in regulating weathering rates the silicon weathering rate swr in the krishna basin is 15 t km 2 y 1 within a factor of 2 to those in the yamuna bhagirathi and alaknanda basins of the himalaya suggesting that under favourable conditions intense physical weathering high runoff granites and the other silicates in the himalaya weather at rates similar to those of deccan basalts the co2 consumption rate for the deccan is deduced to be 3 6 105 moles km 2 y 1 based on the swr the rate though is two to three times lower than reported for the ntw rivers system it still reinforces the earlier findings that in general basalts weather more rapidly than other silicates and that they significantly influence the atmospheric co2 budget on long term scales

inventory of sedimentary organic matter in modern wetland marais vernier normandy france as source indicative tools to study holocene alluvial deposits lower seine valley france palynofacies analysis was developed for petroleum exploration but it is now commonly used to differentiate the major constituents of the sedimentary organic matter som in postglacial deposits our work aimed at studying the som distribution in a present wetland of the seine estuary vernier marsh in order to provide comparative elements to interpret the composition of som in the lower seine valley alluvial infilling in the vernier marsh the distribution of major constituents is heterogeneous thus for each depositional environment studied soils drainage ditches channels ponds the composition of som has been characterized by using two ternary diagrams amorphous om preserved phytoclasts transformed phytoclasts and opaque amorphous gelified particles op ap gp this approach allowed us to define four optical indices that can be used to estimate the relative abundances of principal organic fractions in mixed deposits based on the origin of som aquatic terrestrial its source areas vegetation soils river and controls of early diagenetic changes aerobic anaerobic conditions advanced oxidation amorphous om contents increase from terrestrial environments to fluvial deposits and evaluate the abundance of planktonic contribution preserved transformed phytoclasts ratio decreases from sites of production to those of deposition indicating the degree of degradation of terrestrial materials op contents allow one to define fluvial high values and palustrine low values environments gp ap ratio allows one to discern soil low values and plant high values supplied areas finally these optical compositional indices are measured in holocene deposits and used to complete palaeoenvironmental reconstructions

palynofacies as useful tool to study origins and transfers of particulate organic matter in recent terrestrial environments synopsis and prospects palynofacies analysis is based on transmitted light microscope study of organic constituents isolated and concentrated by acid and basic digestions published results of studies of present day terrestrial environments show that two complementary approaches successfully characterize particulate organic matter om from palynofacies analyses the first method is based on the identification and the quantification of some typical particles optical markers according to their origin i e aquatic or terrestrial their nature i e biogenic anthropogenic fossil and or their formation i e biodegradation combustion oxidation the second approach is based on the use of binary or ternary diagrams in order to define petrographical signatures from the relative proportions of significant organic constituents this approach can be used for tracking i changes in om composition during humification in soil profiles ii transport of reworked terrestrial particles iii diagenesis of peaty deposits or iv weathering of geological substratum the more advanced approach is based on the use of some predefined optical markers and their optical signatures to establish the relation between the om compositions palynofacies and their depositional environments in addition this kind of study aims to define a modern frame of reference that can be applied in paleoenvironmental reconstructions this paper combines a bibliographic review with previously unpublished data from palynofacies analyses the aim is to present some applied examples illustrating 1 the main approaches developed for characterization of the particulate om in surficial deposits and 2 the study of om transfers in terrestrial geosystems

the fate of river organic carbon in coastal areas a study in the rhone river delta using multiple isotopic delta c 13 delta c 14 and organic tracers a significant fraction of the global carbon flux to the ocean occurs in river dominated ocean margins riomar although large uncertainties remain in the cycle of organic matter om in these syste

intermediate spin ferrous iron in lowermost mantle post perovskite and perovskite the earth s lowermost mantle displays an important mineralogical transition from perovskite to post perovskite but the spin state of iron in these phases remains poorly known experimental results suggest that iron occurs in the intermediate spin state in both of these phases which implies that changes in physical properties of the lower mantle must be governed by factors other than spin transitions in iron

carbon isotope geochemistry of the santa clara river the santa clara river is a prototypical small mountainous river with a headwater height greater than 1000 m and a basin area smaller than 10 000 m 2 although individual small mountainous rivers export trivial amounts of sediment and carbon to the ocean as a group these rivers may export a major fraction as much as 50 of the total global river sediment flux milliman and syvitski 1992 making their geochemistry relevant the study of the ocean s carbon cycle in addition many small rivers export sediment in a few high flux events causing massive sporadic discharge of carbon onto coastal shelves discharge conditions very different from those of large rivers this class of rivers is an end member of the river ocean carbon exchange system opposite the earth s largest river the amazon the carbon mass and isotopic properties of the santa clara river are significantly different from previously studied large rivers during the 1997 1998 winter all santa clara carbon pools were old with flux weighted average l4c values of 428 76 for particulate organic carbon 73 31 for dissolved organic carbon and 644 58 for black carbon the age of exported carbon is primarily due to the deep erosion of old soils and not to inclusion of fossil fuel carbon additionally the 13c signatures of exported carbon pools were high relative to terrestrial carbon bearing a signature quite similar to marine carbon average particulate organic carbon poc 13c 22 2 0 8 the santa clara s estuary is small and drains onto the narrow eastern pacific coastal margin exporting this old soil organic matter directly into the ocean if the santa clara export patterns are representative of this class of rivers they may be a significant source of refractory terrestrial carbon to the ocean

a reassessment of the iron isotope composition of the moon and its implications for the accretion and differentiation of terrestrial planets abstract the fe isotope composition of planetary bodies may provide constraints on their accretion modes and or differentiation processes but to do so the fe isotope systematics of key planetary reservoirs needs to be determined to investigate this for the moon we measured the fe isotope compositions for a suite of 33 bulk lunar mare basalts and highland rocks combined with published data a compendium of 73 different lunar bulk rocks reveals a statistically significant fe isotope difference between low ti and high ti mare basalts yielding average 57fe 0 127 0 012 2se n 27 and 57fe 0 274 0 020 2 se n 25 respectively relative to the irmm 14 isotopic reference material as lunar basalts are thought to reflect the fe isotope composition of their respective mantle sources the estimated relative proportion of the low ti and high ti source mantle suggests that the lunar upper mantle 57fe value should be close to 0 142 0 026 whilst the composition of highland rocks ferroan anorthosites and mg suite rocks should provide a more global view of the moon the calculation of the mean 57fe value of 15 available highland rock analyses yields 57fe 0 078 0 124 such a value is not defined precisely enough to be of critical use for comparative planetology ferroan anorthosites and mg suite rocks also give unresolvable means it appears that fe isotope heterogeneity among the lunar highland rocks is caused by non representatively too small sample aliquots of coarse grained rocks it can also be the result of mixed lithologies for some when the kinetic effect of olivine tending towards low 57fe and feldspar with predominantly high 57fe is cancelled a more precise 57fe value of 0 094 0 035 is calculated it is indistinguishable from the mean 57fe of impact melts and is also similar to the upper lunar mantle estimate obtained from mare basalts collectively this newly determined fe isotope composition of the bulk moon is indistinguishable from that of the earth and heavier than those reported for other planetary bodies this planetary isotope relationship is only observed for silicon given the currently available mass dependent stable isotope database because both iron and silicon reside in the earth s metallic core in significant quantities this may point to the involvement of metallic cores of the earth and moon in the interplanetary fe and si isotope fractionation rather than via high pressure metal silicate fractionation at the core mantle boundary this would more likely be achieved by partial vaporization of the liquid outer metallic core in the aftermath of a moon forming giant impact

new data on equilibrium iron isotope fractionation among sulfides constraints on mechanisms of sulfide formation in hydrothermal and igneous systems abstract fe s and cu reduced partition function ratios factors allow calculation of equilibrium isotope fractionation factors factors for chalcopyrite are calculated from experimental and theoretical partial phonon densities of state states kobayashi et al 2007 the fe factors for mackinawite are calculated from mossbauer spectroscopy data bertaut et al 1965 excellent agreement exists between fe factors for chalcopyrite calculated from the experimental and theoretical 57fe phonon densities of states supporting the reliability of the fe factors for chalcopyrite the 34s factor for chalcopyrite is consistent with experimental data on equilibrium sulfur isotope fractionation factors among sulfides and theoretical 34s factors except those recently calculated by a dft approach up to date experimental isotope exchange data on equilibrium fe isotope fractionation factors between minerals and aqueous fe were critically reevaluated in conjunction with fe factors for minerals and the following expressions for factors for aqueous fe2 and fe3 were obtained 10 3 ln fe aq 3 1 0063 10 6 t 2 t 273 k 10 3 ln fe aq 2 0 6537 10 6 t 2 t 273 k application of these new factors to fe and s isotope fractionation at seafloor hydrothermal conditions shows that chalcopyrite may precipitate in equilibrium with fe in hydrothermal fluids in contrast fe and s isotope compositions of pyrite are may not be controlled by isotope equilibration with fe in the hydrothermal fluid previously reported data on fe isotope fractionation between pyrite and chalcopyrite in intrusions in the grasberg igneous complex seem to be reasonable and are in general agreement with previous non isotopic estimates fe isotope fractionation between pyrite and chalcopyrite appear to reflect equilibrium in the intrusions of the grasberg igneous complex and fe isotopes may therefore be considered as a potential geothermometer the pyrite chalcopyrite fe isotope geothermometer however cannot be applied to the skarn facies of the grasberg complex where the initial fe isotope compositions may have been disturbed by subsequent processes related to skarn formation

worldwide distribution of continental rock lithology implications for the atmospheric soil co2 uptake by continental weathering and alkalinity river transport to the oceans 1 the silicate rock weathering followed by the formation of carbonate rocks in the ocean transfers co2 from the atmosphere to the lithosphere this co2 uptake plays a major role in the regulation of atmospheric co2 concentrations at the geologic timescale and is mainly controlled by the chemical properties of rocks this leads us to develop the first world lithological map with a grid resolution of 1 1 this paper analyzes the spatial distribution of the six main rock types by latitude continents and ocean drainage basins and for 49 large river basins coupling our digital map with the gem co2 model we have also calculated the amount of atmospheric soil co2 consumed by rock weathering and alkalinity river transport to the ocean among all silicate rocks shales and basalts appear to have a significant influence on the amount of co2 uptake by chemical weathering

the equation of state of a molten komatiite 2 application to komatiite petrogenesis and the hadean mantle new experimental data for the equation of state of a komatiitic liquid were used to model adiabatic melting in a peridotitic mantle if komatiites are formed by 30 partial melting of a peridotitic mantle then komatiites generated by adiabatic melting come from source regions that began their unmelted ascent in the lower transition zone 500 670 km or the lower mantle 670 km the great depth of incipient melting implied by this model suggests that komatiitic liquids may form in a pressure regime where they are denser than their coexisting crystals possibly the bulk mantle although komatiitic magmas are thought to separate from residual crystals in the mantle at a temperature 200 c greater than modem mid ocean ridge basalts morbs their ultimate sources are predicted to be diapirs that if adiabatically decompressed from initially solid mantle were more than 700 c hotter than the sources of morbs and were derived from great depth we also studied the evolution of an initially molten mantle i e a magma ocean our model considers the thermal structure of the magma ocean density constraints on crystal segregation and approximate phase relationships for a nominally chondritic mantle crystallization will begin at the core mantle boundary perovskite buoyancy at 70 gpa may lead to a compositionally stratified lower mantle with iron enriched magnesiowustite content increasing with depth large convective velocities in the magma ocean would prohibit crystal liquid fractionation by settling or flotation until quiescent boundary layers form such boundary layers could form when the crystal content of the magma reaches a critical value near 44 vol and in the late stages of crystallization around unmelted blocks of foundered protocrust matrix compaction and diapirism could also lead to fractionation effects the upper mantle could be depleted or enriched in perovskite components relative to the bulk mantle olivine neutral buoyancy may lead to the formation of a dunite septum in the upper mantle partitioning the ocean into upper and lower reservoirs but this septum must be permeable

the neodymium stable isotope composition of the silicate earth and chondrites abstract the non chondritic neodymium nd 142nd 144nd ratio of the silicate earth potentially provides a key constraint on the accretion and early evolution of the earth yet it is debated whether this offset is due to the earth being formed from material enriched in s process nd isotopes or results from an early differentiation process such as the segregation of a late sulfide matte during core formation collisional erosion or a some combination of these processes neodymium stable isotopes are potentially sensitive to early sulfide segregation into earth s core a process that cannot be resolved using their radiogenic counterparts this study presents the first comprehensive nd stable isotope data for chondritic meteorites and terrestrial rocks stable nd measurements were made using a double spike technique coupled with thermal ionisation mass spectrometry all three of the major classes of chondritic meteorites carbonaceous enstatite and ordinary chondrites have broadly similar isotopic compositions allowing calculation of a chondritic mean of 146 144nd 0 025 0 025 2 s d n 39 enstatite chondrites yield the most uniform stable isotope composition 146 144nd 26 ppm with considerably more variability observed within ordinary 146 144nd 72 ppm and carbonaceous meteorites 146 144nd 143 ppm terrestrial weathering nucleosynthetic variations and parent body thermal metamorphism appear to have little measurable effect on 146 144nd in chondrites the small variations observed between ordinary chondrite groups most likely reflect inherited compositional differences between parent bodies with the larger variations observed in carbonaceous chondrites being linked to varying modal proportions of calcium aluminium rich inclusions the terrestrial samples analysed here include rocks ranging from basaltic to rhyolitic in composition morb glasses and residual mantle lithologies all of these terrestrial rocks possess a broadly similar nd isotope composition giving an average composition for the bulk silicate earth of 146 144nd 0 022 0 034 n 30 in the samples here magmatic differentiation appears to only have an effect on stable nd in highly evolved magmas with heavier 146 144nd values observed in samples with 70 wt sio2 the average stable nd isotope composition of chondrites and the bulk silicate earth are indistinguishable at the 95 confidence level however mantle samples do possess variable stable nd isotope compositions 146 144nd 75 ppm with an average 146 144 nd value of 0 008 if these heavier values represent the true composition of pristine mantle then it is not possible to completely rule out some role for core formation in accounting for some of the offset between the mantle and chondrites overall these results indicate that the mismatch of 142nd between the earth and chondrites is best explained by a higher proportion of s process nd in the earth rather than partitioning into sulfide or s rich metal in the core

impact of atmospheric co2 levels on continental silicate weathering 1 anthropogenic sources are widely accepted as the dominant cause for the increase in atmospheric co2 concentrations since the beginning of the industrial revolution here we use the b witch model to quantify the impact of increased co2 concentrations on co2 consumption by weathering of continental surfaces b witch couples a dynamic biogeochemistry model lpj and a process based numerical model of continental weathering witch it allows simultaneous calculations of the different components of continental weathering fluxes terrestrial vegetation dynamics and carbon and water fluxes the co2 consumption rates are estimated at four different atmospheric co2 concentrations from 280 up to 1120 ppmv for 22 sites characterized by silicate lithologies basalt granite or sandstones the sensitivity to atmospheric co2 variations is explored while temperature and rainfall are held constant first we show that under 355 ppmv of atmospheric co2 b witch is able to reproduce the global pattern of weathering rates as a function of annual runoff mean annual temperature or latitude for silicate lithologies when atmospheric co2 increases evapotranspiration generally decreases due to progressive stomatal closure and the soil co2 pressure increases due to enhanced biospheric productivity as a result vertical drainage and soil acidity increase promoting co2 consumption by mineral weathering we calculate an increase of about 3 of the co2 consumption through silicate weathering mol ha 1 yr 1 for 100 ppmv rise in co2 importantly the sensitivity of the weathering system to the co2 rise is not uniform and heavily depends on the climatic lithologic pedologic and biospheric settings

carbon sinks in small sahelian lakes as an unexpected effect of land use changes since the 1960s saga gorou and dallol bosso sw niger for several decades global change has resulted in an increase in runoff in the sahelian belt provoking major changes in the quality and quantity of sediments transported by drainage networks one of the astonishing consequences is the establishment of numerous permanent lakes the origins of particulate organic matter om preserved within lacustrine sediments of three lakes were investigated by coupling optical observations palynofacies and bulk geochemistry rock eval 6 pyrolysis an initial estimate of particulate organic carbon oc stored in these lacustrine sediments was assessed soil organic matter som was sampled from the surface 0 10 cm of various land use and land cover areas and was characterized and compared with sedimentary organic matter our results reveal that lake tankalawal is subjected to high autochthonous organic sedimentation toc ranges between 3 0 and 10 0 wt while lakes bangou kirey and bi are characterized by weak sedimentation of non indigenous om originating from the soil erosion and shore vegetation toc 3 0 wt in sediments the effects of early diagenesis on the om induce not only a loss of labile and aquatic om but also a significant loss of terrestrial om which is supposed to be more resistant than its aquatic counterpart both the preservation of om in top sediments and the relative preservation of terrestrial om impact the oc storage in lakes indeed oc storage in lacustrine sediments lake bangou kirey was two to seven times higher than the oc storage in sahelian soils where greater contributions of terrestrial om to sedimentary om are associated with lower oc storage in lacustrine sediments for lakes bangou kirey and bi oc accumulation rates were also assessed due to the identification of a sedimentary limit corresponding to the establishment of permanent lakes dated earlier 1960s high oc fluxes were estimated and ranged between 104 and 213 g oc m 2 yr 1 compared with other oc accumulation rates for various african lakes these high values are similar to those calculated for reservoirs and are related to anthropogenic pressure soil textures favoring erosion and proper physical and chemical conditions for om preservation in sediments accordingly in these sahelian environments that are generally viewed as non efficient in storing oc we claim that global change could promote a new oc sink if other similar studies reinforce our assertion then regional c budgets should be revisited