weathering and the mobility of phosphorus in the catchments and forefields of the rhone and oberaar glaciers central switzerland implications for the global phosphorus cycle on glacial interglacial timescales abstract in this study we evaluate the dynamics of the biophile element phosphorus p in the catchment and proglacial areas of the rhone and oberaar glaciers central switzerland we analysed erosion and dissolution rates of p containing minerals in the subglacial environment by sampling water and suspended sediment in glacier outlets during three ablation and two accumulation seasons we also quantified biogeochemical weathering rates of detrital p in proglacial sedimentary deposits using two chronosequences of samples of fresh suspended material obtained from the oberaar and rhone water outlets little ice age lia moraines and younger dryas yd tills in each catchment subglacial p weathering is mainly a physical process and detrital p represents more than 99 of the precipitation corrected total p denudation flux 234 and 540 kg km 2 yr 1 for the rhone and oberaar catchments respectively the calculated detrital p flux rates are three to almost five times higher than the world average flux the precipitation corrected soluble reactive p srp flux corresponds to 1 88 1 99 kg km 2 yr 1 rhone and 2 12 2 44 kg km 2 yr 1 oberaar respectively these fluxes are comparable to those of tropical rivers draining transport limited tectonically inactive weathering areas in order to evaluate the efficiency of detrital p weathering in the rhone and oberaar proglacial areas we systematically graded apatite grains extracted from the chronosequence in each catchment relative to weathering induced changes in their surface morphologies grades 1 4 fresh apatite grains are heavily indented and dissolution rounded grade 1 lia grains from two 0 10 cm deep moraine samples show extensive dissolution etching similar to surface grains from the yd profile mean grades 2 7 3 5 and 3 5 respectively in these proglacial deposits the weathering front deepens progressively as a function of time due to biocorrosion in the evolving acidic pedosphere with mechanical indentations on grains acting as sites of preferential dissolution we also measured iron bound organic and detrital p concentrations in the chronosequence and show that organic and iron bound p has almost completely replaced detrital p in the top layers of the yd profiles detrital p weathering rates are calculated as 310 and 280 kg km 2 yr 1 for lia moraines and 10 kg km 2 yr 1 for yd tills during the first 300 years of glacial sediment exposure p dissolution rates are shown to be approximately 70 times higher than the mean global dissolved p flux from ice free continents after 11 6 kyr the flux is 2 5 times the global mean these data strengthen the argument for substantial changes in the global dissolved p flux on glacial interglacial timescales a crude extrapolation from the data described here suggests that the global dissolved p flux may increase by 40 45 during the first few hundred years of a deglaciation phase

a whiff of oxygen before the great oxidation event high resolution chemostratigraphy reveals an episode of enrichment of the redox sensitive transition metals molybdenum and rhenium in the late archean mount mcrae shale in western australia correlations with organic carbon indicate that these metals were derived from contemporaneous seawater rhenium osmium geochronology demonstrates that the enrichment is a primary sedimentary feature dating to 2501 8 million years ago ma molybdenum and rhenium were probably supplied to archean oceans by oxidative weathering of crustal sulfide minerals these findings point to the presence of small amounts of o 2 in the environment more than 50 million years before the start of the great oxidation event

contemporary changes in sediment yield in an alpine mountain basin due to afforestation the upper drome in france abstract the baurieres plain within the upper drome river basin was used to reconstruct recent changes in sediment supply in relation to changes in land use within an alpine catchment a considerable body of archival information is available furthermore the plain acts as a natural sediment trap and the reach basin interaction has not been disrupted by human activity based on archival data channel geometry measurements dendrogeomorphological and radionuclide analysis cs137 and unsupported pb210 the trends in channel change and sediment supply over the past two centuries are assessed and their causes are interpreted dendrogeomorphology and radionuclide profiles show that the floodplain is characterised by a decrease in sedimentation rate in the 1960s the ex pb210 profiles also suggest a spatial modification of the relative contribution in sediment supply of the catchment bedload yields are estimated to be at least 26 m3 km 2 year 1 between 1928 and 1996 based on an estimate of storage over a channel length of 11 5 km archival data concerning bedload removal from traps yields an estimate of 25 6 m3 km 2 year 1 between 1993 and 2001 these two values are very comparable suggesting no major modification in bedload transport within the reach during the 20th century if the bedload supply has not strongly decreased in the studied reach during this period the bedload sources have changed the volume of sediment stored in the beaurieres area between 1928 and 1996 corresponds to at least 40 of the sediment delivered by channel degradation from an upstream alluvial reach both changes in floodplain sedimentation as well as changes in bedload and suspended contributions from catchment sources are interpreted as responses to land use but also flow regime hillslope sediment production strongly decreased due to planned hillslope afforestation and torrent regulation at the end of the 19th century and spontaneous hillslope afforestation resulting from grazing decline mainly in the two decades following world war ii the observed change in suspended sediment supply which occurred around 1960 1965 has a clear synchronicity with spontaneous catchment afforestation following world war ii after this period a decrease in sediment supply a change in source but also a decrease in peak flow were observed changes in run off are complex and cannot be caused with only land use change flood hydrographs underwent peak decreases and duration increases through the 20th century because of increase in water retention capacity of the forested catchment in addition flood seasonality has changed with september and october flood events being much less frequent in the last part of the 20th century

lichenometric application to historical and subrecent dynamics and sediment transport of a corsican stream figarella river france abstract lichenometry has been applied to blocks canyon walls and terrace deposits a growth curve specific to corsica was made based on information obtained from tombstones old monuments from the genoese occupation of corsica and roman megaliths this allowed us to create a curve going as far back as 2000 years the curve is similar to those developed in mediterranean environments cevennes and eastern pyrenees but is very different from those developed in alpine and arctic regions lichens present on boulders of the bedload allow the time at which the boulders were laid down to be determined the lichenometric study of the figarella shows firstly that there is high stream competence blocks approximately 100 cm wide are moved during the 5 year flood recent important flood events were identified in 1973 and 1869 these correspond well with historical sources other older and much more important floods were also identified this analysis has allowed us to extend the specific streampower curves proposed by costa geol soc am bull 94 1983 986 and williams geogr ann 65a 1983 227 to blocks of more than 2 m wide lichens present on the canyon walls and on terrace sides in the plain allowed the last main incision phase to be dated to the little ice age aerial photograph analysis has shown that the present braided system in the lower course of the river is no longer active

palaeoflood and floodplain records from spain evidence for long term climate variability and environmental changes abstract palaeoflood chronologies from seven spanish river basins and floodplain aggradation chronologies from thirteen rivers are analysed these fluvial records were divided in to two sub sets namely atlantic 10 ka record and mediterranean 3 ka record river basins which represent distinct modern hydroclimatic conditions in atlantic basins floods result from intense widespread rainfalls associated with atlantic frontal systems transported by westerly airflow mediterranean river flooding is related to heavy rainfall induced by mesoscale convective systems mcss during autumn months evidence from radiocarbon dates in slackwater flood deposits shows six periods of flood clusters at 10 750 10 240 9550 9130 4820 4440 2865 2350 960 790 and 520 290 cal bp despite the different flood producing weather conditions in atlantic and mediterranean rivers the radiocarbon sample clusters overlap and indicate changes in large scale atmospheric circulation and climatic conditions in the iberian peninsula comparison with proxy records of mean temperature for the northern hemisphere demonstrates a relationship between the period of slackwater flood deposition and cold climatic phases e g the 2650 yr bp climatic event or ad 1590 1650 period of the little ice age radiocarbon dates from aggraded floodplain sediments were clustered at 2710 2320 2000 1830 and 910 500 cal bp the first cluster period is in phase with the timing of slackwater deposition whereas the third 910 500 cal bp occurs in between two periods of increased flood frequency as indicated by the palaeoflood and documentary flood records it is argued that the 910 500 cal bp floodplain aggradation period reflects the first post roman evidence of environmental change related to generalised land use changes at the catchment scale which produced high sediment load transported to overbank areas during high flows

sensitivity persistence and resolution of the geomorphological record of valley floor floods in an alpine glacier fed catchment leirdalen jotunheimen southern norway coarse grained flood deposits including 52 discrete berms bars terraces splays and sheets were investigated along a 6 6 km stretch of the leira river in a catchment containing several alpine glaciers these landforms were mapped characterized in terms of clast size and reconstructed hydrological parameters and dated using several techniques with differing temporal range and resolution high resolution lichenometric dating indicated that 60 65 of the deposits date from the 20th century whereas 5 7 are 300 600 years old in contrast low resolution schmidt hammer exposure age dating shd indicated that 85 of deposits have an age 500 years whereas 13 5 are older deposits with age estimates of 1000 6000 years simple indicators of soil development and vegetation succession demonstrated extensive recent disturbance of most surfaces by floods optically stimulated luminescence osl and radiocarbon dating of fine grained flood layers and buried palaeosols confirmed the existence of flood deposits

palaeoproterozoic evaporites in fennoscandia implications for seawater sulphate the rise of atmospheric oxygen and local amplification of the δ13c excursion this paper addresses global oxygenation and establishment of a marine sulphate reservoir in the palaeoproterozoic we report syn depositional marine anhydrite containing pseudomorphs after ca sulphates as widespread throughout the tulomozero formation in the se fennoscandian shield implying that surface waters were oxidized and a large so42 marine reservoir was developed as early as 2100 ma the ca sulphates and associated magnesite and halite precipitated syn depositionally from oxidized evolved and modified seawater in coastal playa sabkha and intertidal flat settings sr 87 sr 86 and delta 13 c of associated c 13 rich stromatolitic dolostones were environmentally controlled with the highest ratios occurring in playa and sabkha carbonates the results imply that the palaeoproterozoic delta 13 c carb excursion was amplified by 8 by local environmental factors and calls into question many observations of putative delta 13 c global signals reported previously from similar palaeoproterozoic evaporitic dolostones the local environmental amplification can explain a large regional and intercontinental delta 13 c discrepancy observed in synchronous carbonates

global nature of the paleoproterozoic lomagundi carbon isotope excursion a review of occurrences in brazil india and uruguay abstract positive carbon isotope excursion is reported from paleoproterozoic carbonates of the aravalli supergroup northwestern india the minas supergroup brazil and new sections of the paso severino formation uruguay the 2 42 ga gandarela formation minas gerais brazil contains red carbonate facies bif grading into dolostones and limestones and yielding 13 c values ranging from 1 6 to 0 4 v pdb the positive c isotope excursion up to 11 v pdb in marine shallow water carbonates in india and brazil jhamarkotra formation in northwestern india and cercadinho and fecho do funil formations in minas gerais state brazil is comparable to that observed in 2 22 2 1 ga carbonate successions worldwide that were deposited during the lomagundi excursion in uruguay 13 c values up to 11 6 v pdb in the deep water paso severino formation of the piedra alta terrane are compatible with deposition at ca 2 15 ga as indicated by the 2146 7 ma u pb age of dacites occurring at the top of the unit negative 13 c values are also present in carbonates of the paso severino formation but an origin related to organic matter remineralization cannot be ruled out thin carbonate beds in the rio itapicuru greenstone belt bahia state brazil are associated as in the paso severino formation with deep water black shales and have carbon isotope values up to 9 v pdb high metamorphic grade carbonates of the jacurici terrane in the medrado ipueira area bahia brazil have carbon isotope values up to 6 9 v pdb consistent with their minimum age of 2085 5 ma inferred from the intrusive contact with and the age of the medrado norite no evidence was found in india brazil or uruguay for paleoproterozoic glacial events recognized in the 2 45 2 22 ga sedimentary successions worldwide unconformities between the gandarela and cercadinho formations in brazil and the banded gneissic complex and the lower aravalli supergroup in india might explain the absence of glacial record compositional and isotopic data presented here for studied paleoproterozoic carbonate successions allow their integration into the global record of the paleoproterozoic evolution as well as correlation with other successions of similar age the study highlights the global nature of the lomagundi excursion furthermore it indicates that the lomagundi excursion is recorded in both shallow water aravalli and minas supergroups and deep water carbonates paso severino formation and rio itapicuru greenstone belt negating a significant impact of stromatolite productivity and hypersaline conditions on carbon isotope values of carbonates deposited in shallow water open marine and isolated basins

redox state of the archean atmosphere evidence from detrital heavy minerals in ca 3250 2750 ma sandstones from the pilbara craton australia the presence of detrital uraninite and pyrite in fluvial placers of the witwatersrand basin south africa has been used to infer low levels of atmospheric oxygen during the archean 2500 ma however recent studies advocate a hydrothermal origin for these minerals thereby limiting their value as constraints on the composition of the early atmosphere in contrast ca 3250 2750 ma fluvial siliciclastic sediments from the pilbara craton in australia have never undergone significant hydrothermal alteration and their heavy minerals are of unequivocal detrital origin these heavy minerals include the redox sensitive phases pyrite uraninite and gersdorffite along with more inert zircon rutile chromite and monazite locally siderite is a major constituent to 90 of the heavy mineral population with grains displaying evidence for several episodes of erosion rounding and subsequent authigenic overgrowth detrital siderite is very rare in post archean sandstones largely due to its instability in oxidizing environments however its frequent survival of prolonged transport in well mixed and therefore well aerated archean river waters that contained little organic matter strongly implies that the contemporary atmosphere was indeed much less oxidizing than at present moreover concentrations of reduced sulfur species must have been very low in surface fluids for siderite to survive repeated transportation events without pyritization

the value of lichenometry and historical archives in assessing the incision of submediterranean rivers from the little ice age in the ardeche and upper loire france the geomorphologic impact of the little ice age lia was determined on two french mediterranean rivers the upper ardeche and the upper loire in order to evaluate the impact of the lia on the hydrology of these rivers two historical flood chronicles were made from historical sources the lia can be divided in three phases of high activity 1530 1700 1750 1810 1840 1910 a geomorphologic study of the two rivers shows that incision is the principle process at work in the 20th century in order to date the low terraces and bedforms present in both valleys lichenometry was used rhizocarpon geographicum allowed the main features on the bottom of the valley to be dated using two growth curves made for the two studied areas in the ardeche lichenometric dating showed a progressive evacuation of the inherited alluvial stock the oldest lichens found on the foodplain and the outcrops indicate that incision began between the second half of the 17th century and the end of the 18th century in the mid little ice age incision stopped on the bedrock in the second half of the 19th century in the loire the narrowness of the gorge did not allow sediment to be stored during the first half of the lia very old lichens 1000 yr of age are present on the bedrock close to the bed however at a number of locations the valley slightly widens allowing sediment that was transiting through the gorge to be stored the geomorphologic features that characterise these basins clearly show a hydrosedimentary behaviour different before and after the beginning of the 20th century

coal weathering and the geochemical carbon cycle abstract the weathering rate of sedimentary organic matter in the continental surficial environment is poorly constrained despite its importance to the geochemical carbon cycle during this weathering complete oxidation to carbon dioxide is normally assumed but there is little proof that this actually occurs knowledge of the rate and mechanisms of sedimentary organic matter weathering is important because it is one of the major controls on atmospheric oxygen level through geologic time we have determined the aqueous oxidation rates of pyrite free bituminous coal at 24 and 50 c by using a dual cell flow through method coal was used as an example of sedimentary organic matter because of the difficulty in obtaining pyrite free kerogen for laboratory study the aqueous oxidation rate obtained in the present study for air saturated water 270 m o2 was found to be on the order of 2 10 12 mol o2 m2 s at 25 c which is fast compared to other geologic processes such as tectonic uplift and exposure through erosion the reaction order with respect to oxygen level is 0 5 on a several thousand hour time scale for both 24 and 50 c experiments activation energies determined under 24 and 50 c conditions were 40 kj mol o2 indicating that the oxidation reaction is surface reaction controlled the oxygen consumption rate obtained in this study is two to three orders of magnitude smaller than that for pyrite oxidation in water but still rapid on a geologic time scale aqueous coal oxidation results in the formation of dissolved co2 dissolved organic carbon doc and solid oxidation products which are all quantitatively significant reaction products

evidence for paleoproterozoic cap carbonates in north america the early paleoproterozoic snowy pass supergroup of the medicine bow mountains and sierra madre wyoming usa and huronian supergroup ontario canada were deposited along the present day southern flank of the wyoming and superior cratons whereas three discrete levels of glacial diamictite are developed in both successions carbonate strata are known only directly above the middle diamictite vagner and bottle creek formations in medicine bow mountains and sierra madre respectively and espanola formation in southern ontario in these thick correlative siliciclastics dominated strata the carbonates from each succession record negative 13 c values 4 0 to 0 8 v pdb and attenuated carbon isotopic difference between organic and inorganic phases oxygen in carbonates is strongly depleted in 18 o suggesting exchange with hot fluids which is consistent with pervasive recrystallization of carbonates and remobilization of elements however the stratigraphic coherence of carbon isotopic compositions and the general lack of correlation between 13 c and either 18 o values or trace element concentrations supports a primary origin for 13 c depleted carbonates which are interpreted here to reflect anomalous oceanic compositions the intimate association of thick carbonate units containing abundant carbonate debris flows with immediately underlying glacial strata indicates that chemical precipitation resulted from a rapid flux of carbonate alkalinity onto ocean margins during post glacial transgression although these early paleoproterozoic carbonates are similar to neoproterozoic cap dolomites in stratigraphic position and carbon isotopic compositions the older post glacial accumulations begin with limestone and lack many of the sedimentary structures typical of neoproterozoic deposits furthermore it is not understood why carbonates only occur above the middle of the three glacial horizons whereas these deposits are ubiquitous above neoproterozoic diamictites the differences might reflect lower overall carbonate saturation in early paleoproterozoic oceans which contrasts sharply with archean and later paleoproterozoic intervals and higher siliciclastic inputs in rift environments which shut down carbonate deposition geological and geochemical indicators suggest a stepwise increase in atmospheric oxygen across the paleoproterozoic glacial epoch the tempo and mode of atmospheric oxygen rise has significant consequences for the abundance of the important greenhouse gases ch4 and co2 and hence for oceanic acidity if we accept that atmospheric oxidation of methane to carbon

characterization and quantification of holocene colluvial and alluvial sediments in the valdaine region southern france this study presents a holocene sediment budget for the valdaine region located at the edge of the southern french pre alps holocene colluvial and alluvial deposition are quantified based on existing and new field data average sediment thickness values were calculated for different landscape units and available chronological data were used to make a time differentiated sediment budget total holocene colluvial deposition in the valdaine 334 km2 amounts 167 106 m3 while alluvial deposition in the roubion and jabron catchments in total 610 km2 including their catchment upstream the valdaine amounts 177 106 m3 especially colluvial deposition is high 0 75 106 g m2 compared with other catchments three major deposition periods 8500 2000 bc 700 bc ad 800 and ad 1200 2000 and two periods of relative hillslope stability with local fluvial incision 2000 700 bc and ad 800 1200 set the framework for a time differentiated sediment budget results show that depositional phases relate to intense

temporal constraints on the paleoproterozoic lomagundi jatuli carbon isotopic event the paleoproterozoic lomagundi jatuli positive 13c excursion in sedimentary carbonates represents an event whose magnitude and duration is unique in earth history although precise absolute chronology of this event remains poorly constrained in northeastern fennoscandia an 1300 m thick sedimentary volcanic succession of the pechenga greenstone belt records decline of this isotopic excursion zircons from sedimentary rocks that occur within the decline have yielded 207pb 206pb dates at 2058 2 ma 6 ma including u decay constant uncertainties and provide the first maximum age constraint on the termination of the lomagundi jatuli event combined with existing constraints these data indicate an 140 m y interval characterized by 13c rich carbonate accumulation

multiple sulfur isotopes from paleoproterozoic huronian interglacial sediments and the rise of atmospheric oxygen mass dependently fractionated mdf sulfur isotopes in sedimentary sulfides and sulfates can provide information on the past activity of microbial metabolisms and serve as a proxy for the concentration of seawater sulfate in conjunction with these proxies mass independently fractionated mif sulfur isotopes can be used to track the rise of atmospheric oxygen the anoxic oxic transition of the surface environment in the paleoproterozoic has been constrained by mif sulfur in 2 47 ga sulfides from western australian banded iron formations and the absence of mif in diagenetic sulfides from 2 32 ga black shales in the transvaal supergroup south africa we report new multicollector ion microprobe data for individual sulfides from water lain sedimentary units in the 2 45 2 22 ga huronian supergroup ontario canada the authigenecity of sulfides in these units is interpreted on the basis of host lithology mode of distribution sulfide chemistry and mdf sulfur isotopes sulfides interpreted to have an authigenicsedimentary origin from the mckim fm have a range of 0 7 in 33 s values and those in the pecors fm preserve small magnitude mif 33 s values up to 0 88 which we propose represents the last remnants of an anoxic atmosphere high 34 s values up to 31 2 and near zero 33 s values in authigenic sulfides from the stratigraphically higher espanola and gordon lake fms suggest local variations of seawater sulfate concentrations and or 34 ssulfate consistent with increased atmospheric o2 levels mif sulfur is absent from the marine record after the second huronian glaciation which is analogous to the record of the transvaal supergroup where mif is absent from the upper part of the interglacial sequence our results suggest that the possible simultaneous demise of mif sulfur isotopes at these two localities may serve as a useful global geochemical marker to correlate paleoproterozoic supergroups we propose a new biogeochemical model where enhanced weathering rates during paleoproterozoic post glacial thawing served as a critical stimulus for interglacial blooms of oxygenic photosynthesis the demise of methane and ultimately to the irreversible rise in atmospheric oxygen

multiple palaeoproterozoic carbon burial episodes and excursions organic rich rocks averaging 2 5 total organic carbon and positive carbonate carbon isotope excursions view the mathml source and locally much higher i e the lomagundi jatuli event are hallmark features of palaeoproterozoic successions and are assumed to archive a global event of unique environmental conditions following the c 2 3 ga great oxidation event here we combine new and published geochronology that shows that the main palaeoproterozoic carbon burial episodes cbes preserved in russia gabon and australia were temporally discrete depositional events between c 2 10 and 1 85 ga in northwest russia we can also show that timing of the termination of the lomagundi jatuli event may have differed by up to 50 ma between localities and that ni mineralisation occurred at c 1920 ma further cbes have traits in common with mesozoic oceanic anoxic events oaes both are exceptionally organic rich relative to encasing strata associated with contemporaneous igneous activity and marked by organic carbon isotope profiles that exhibit a stepped decrease followed by a stabilisation period and recovery although cbe strata are thicker and of greater duration than oaes 100 s of metres versus metres 106 years versus 105 years their shared characteristics hint at a commonality of cause s and feedbacks this suggests that cbes represent processes that can be either basin specific or global in nature and a combination of circumstances that are not unique to the palaeoproterozoic our findings urge circumspection and re consideration of models that assume cbes are a deep time singularity

historical evolution of slope instability in the calore river basin southern italy abstract there is interest in knowing historical spatio temporal patterns of landslide activity however this is challenging to reconstruct because it is difficult to obtain detailed records for past landslide activity here we deal with hydro geomorphological signatures such as storms downpours floods snowmelt and mass movement to detect annual slope instability events asies over historical times in order to obtain asies for each year a monthly instability density index idi was used and then monthly values were summed up to obtain a yearly value classes of monthly idi varying between 0 no instability and 4 highest instability were determined from historical documents we present an application for the calore river basin southern italy using data from a 313 year long series 1701 2013 ce after 1880 ce the information becomes more valuable with directly observed landslide frequency by this cataloguing 129 asies were obtained their evolution shows slight instability during the 18th century uneven and greater slope instability occurred instead across the 19th century when an important phase of deforestation coincided with intensification of agricultural activities slope instability events continued during the 20th century but their causes are mainly related to anthropisation and the effects of recent climate change it was determined that stormy autumns until the 19th century and successive winter times with enhanced snowmelt may have driven the reactivation of widespread instability events we also found that mountainous and hilly terrains have an acute sensitivity to climate change

the weathering of sedimentary organic matter as a control on atmospheric o2 i analysis of a black shale to investigate the weathering of sedimentary organic matter and its role in regulating atmospheric oxygen a drill core of black shale from the new albany formation upper devonian clay city ky has been analyzed for total and organic carbon nitrogen phosphorus and sulfur and for porosity permeability and specific surface area the distribution of organic matter and pyrite in the shale has also been examined by means of electron photomicrography and element mapping element mapping indicates that shale organic matter is present mainly as 0 5 to 50 m discoidal clots and discontinuous laminae stringers and not as monomolecular coatings on clay grains loss of organic matter by oxidative weathering takes place across a reaction front where organic carbon content decreases sharply toward the land surface along with organic nitrogen and sulfur but not organic phosphorus which remains relatively constant over the same depth range accompanying the decrease in organic matter is an increase in porosity these results agree with earlier work on a single stratigraphic layer that found also that the oxygen content of the organic matter increases sharply toward the land surface across a similar carbon oxidation front pyrite in both the core and the layer was found to decrease toward the surface more continuously than organic matter and at intermediate depths is essentially absent in the presence of high levels of organic matter these results suggest that organic matter weathering in shales can be treated in terms of the reaction of organic matter with gaseous o2 and o2 dissolved in groundwater once a weathering profile is developed the inward or downward migrating o2 reacts first with modern soil organic matter and subsequently with low concentrations of remaining pyrite and ancient organic matter before reaching the front pyrite apparently reacts faster with o2 than does organic matter for a given local concentration of oxygen as evidenced by reduced pyrite concentrations accompanying high organic matter concentrations at the front upon further inward migration lower levels of o2 react with higher concentrations of pyrite and organic matter these data provide an important basis for the theoretical modeling of organic matter oxidation during weathering

paleoflood hydrology origin progress prospects from an origin in diverse studies of flood geomorphology and quaternary geology paleoflood hydrology emerged as a geophysical and an applied hydrological science during the 1970s and 1980s since acquiring its formal name in 1982 the most productive approach in paleoflood hydrology has become energy based inverse hydraulic modeling of discrete paleoflood events recorded in appropriate settings as slackwater deposits and other paleostage indicators swd psi or as various threshold indicators of non exceedence technological advances particularly in hydraulic modeling and geochronology were instrumental in moving the discipline to its present status the most recent advances include 1 new techniques for the accurate geochronology of flood sediments notably tams radiocarbon analyses and osl dating and 2 the phenomenal increase in computer power that allows complex hydraulic calculations to become feasible for routine studies from its initial demonstration in the southwestern united states swd psi paleoflood hydrology proved its widespread applicability to various landscape environments particularly important studies have been accomplished in australia china india israel south africa spain and thailand paleoflood hydrology has also generated its share of controversy in part because of the differing viewpoints and attitudes of the two scientific traditions from which it emerged quaternary geology geomorphology versus applied hydrologic hydraulic engineering nevertheless the future growth of the discipline is assured given the rapid pace of discoveries that it engenders indeed so many international studies exist that it is appropriate to pursue global syntheses to address interesting and timely questions of extreme flood phenomena in relation to global climatic change

reconstructing earth s surface oxidation across the archean proterozoic transition the archean proterozoic transition is characterized by the widespread deposition of organic rich shale sedimentary iron formation glacial diamictite and marine carbonates recording profound carbon isotope anomalies but notably lacks bedded evaporites all deposits refl ect environmental changes in oceanic and atmospheric redox states in part associated with earth s earliest ice ages time series data for multiple sulfur isotopes from carbonateassociated sulfate as well as sulfi des in sediments of the transvaal supergroup south africa capture the concomitant buildup of sulfate in the ocean and the loss of atmospheric massindependent sulfur isotope fractionation in phase with sulfur is the earliest recorded positive carbon isotope anomaly convincingly linking these environmental perturbations to the great oxidation event ca 2 3 ga

carbon isotopes and the rise of atmospheric oxygen new data for the isotopic composition of carbon in carbonate sediments deposited between 2 6 and 1 6 ga indicate that the value of 13c in these sediments underwent a very large positive excursion between 2 22 and 2 06 ga a reassessment of the earlier 13c data for carbonate sediments shows that this excursion was probably worldwide and that it was preceded and followed by several hundred million years during which the 13c of carbonate sediments differed little from that of modern carbonates the large 13c excursion between 2 22 and 2 06 ga was probably related to an abnormally high rate of organic carbon deposition which generated an abnormally high rate of o2 production we estimate that the total excess o2 produced during the excursion was between 12 and 22 times the present atmospheric o2 inventory the 13c data therefore suggest that the o2 content of the atmosphere increased very significantly between 2 22 and 2 06 ga this inference is supported strongly by several other lines of evidence

causes of 20th century channel narrowing in mountain and piedmont rivers of southeastern france extensive channel narrowing in southeastern france provides an illustration of geomorphic response to land use changes the study region comprises a range of environments from large piedmont and intramountain gravel bed rivers to small mountain streams field measurements and analysis of historical data demonstrate two distinct periods of channel change from 1850 to 1950 channel narrowing is interpreted to be the result of a recovery process in response to widespread channel destabilization induced by major floods during the second half of the 19th century at the time the largely deforested basins were highly responsive to flooding whereas the recovery process was accelerated by floodplain and basin scale land use changes afforestation and torrential control works which in turn reduced sediment delivery and enabled vegetation development in channels from 1950 to 1970 channel narrowing accelerated in most of the studied rivers this recent phenomenon is considered as a human induced fluvial adjustment directly related to forest development on river margins and human abandonment of intensive floodplain land uses at the same time long profile degradation occurred as a result of long term bedload supply decrease in small mountain streams channel narrowing is mainly explained by channel incision which seems to progress from upstream where sediment sources are progressively stabilized by afforestation copyright 2002 john wiley sons ltd

rise in seawater sulphate concentration associated with the paleoproterozoic positive carbon isotope excursion evidence from sulphate evaporites in the 2 2 2 1 gyr shallow marine lucknow formation south africa past oceanic sulphate concentration is important for under standing how the oceansredox state responded to atmospheric oxygen levels the absence of extensive marine sulphate evaporites before 1 2 gyr probably reflects low seawater sulphate and or higher carbonate concentrations sulphate evaporites formed locally during the 2 22 2 06 gyr lomagundi positive d 13 c excursion however the 2 2 2 1 gyr lucknow formation south africa provides the first direct evidence for seawater sulphate precipitation on a carbonate platform with open ocean access and limited terrestrial input these marginal marine deposits contain evidence for evaporite molds pseudomorphs after selenite gypsum and solid inclusions of ca sulphate in quartz carbon and sulphur isotope data match the global record and indicate a marine source of the evaporitic brines the apparent precipitation of gypsum before halite requires 2 5 mm l 1 sulphate concentration higher than cur rent estimates for the paleoproterozoic during the lomagundi event which postdates the 2 32 gyr initial rise in atmospheric oxygen seawater sulphate concentration rose from archean values of 200 lm l 1 but dropped subsequently because of higher pyrite burial rates and a lower oceanic redox state

paleoproterozoic stark formation athapuscow basin northwest canada record of cratonic scale salinity crisis abstract the paleoproterozoic stark formation a thick breccia unit formed during the transition from marine to non marine foreland basin fill in the athapuscow basin northwest territories canada four types of breccia occur in the stark formation 1 bedded breccias at the base of the unit overlying the basinal facies of the underlying pethei group are interpreted as debris flows 2 massive chaotic breccias occur in the lower part of the stark formation throughout the basin and these are interpreted to be evaporite collapse breccias 3 siltstone and mudstone breccia occurs in the upper part of the stark formation and is also interpreted as evaporite collapse breccia though much less evaporite was involved in its formation than the underlying chaotic breccia and 4 laminar accretionary breccia consisting of laminar carbonate clasts commonly with flat bottoms and convex up upper surface geometries these clasts occur in lenticular pods and are interpreted to form in caves following dissolution of evaporites or carbonates the widespread presence and abundance of evaporite pseudomorphs especially halite in all breccia types the stratigraphic restriction of the stark formation and irregular filling above this unit indicates that all but the bedded breccia formed by the dissolution and collapse of evaporites chaotic breccia directly above underlying pethei group shallow water and deep water carbonates indicates the evaporates formed across the platform and adjacent deep basin foundered megaclasts up to 1 5 km long and 40 m thick in basinal settings suggest cumulative evaporite thicknesses on the order of a few tens to a few hundreds of meters carbonate clasts in all the breccias contain abundant wave ripples planar laminations stromatolites and ooids these structures along with a paucity of subaerial exposure features indicates nearly all carbonate deposition in the stark was subaqueous thus by inference the evaporites in the stark formation were also partially subaqueous displacive halite pseudomorphs are common throughout all facies in the stark formation silicified and dolomite filled halite pseudomorphs are common along the contact between the evaporite collapse breccia and underlying carbonate platform pethei group and surrounding large clasts in basinal settings silicified hopper crystal casts within deep water rhythmites of the uppermost pethei group indicate precipitation of halite over deep waters gypsum pseudomorphs are exceedingly rare and anhydrite pseudomorphs were not observed the dominance of halite features in this basin and two penecontemporaneous basins kilihigok basin and wopmay orogen surrounding the slave craton suggests that relative to the present day seawater at 1 9 to 1 8 ga was oversaturated with respect to calcium carbonate had higher hco3 concentration and possibly was depleted in so42 the dearth of extensive thick bedded marine gypsum in the archean and early paleoproterozoic can be explained by low atmospheric oxygen content prior to 2 ga in conjunction with increased carbonate saturation before 1 6 ga

flood alluviation and entrenchment holocene valley floor development and transformation in the british uplands the morphology sedimentary properties and sequence of recent coarse grained flood deposits and earlier holocene alluvial fills were investigated in thinhope burn a small 12 km2 catchment in the northern pennine uplands northern england twenty one large flood events are recorded by distinctive cobble boulder bars sheets and splays and boulder berms and lobes lichenometric analysis showed that all but one of these floods dated from the mid eighteenth century the timing of large floods between 1766 and 1960 corresponds with major hydroclimatic trends evident in northern britain and northwest europe over this period discharge estimates suggest that flood magnitudes have decreased since the mid eighteenth century channel and flood plain metamorphosis in late roman times and in the eighteenth century following major valley floor entrenchment locally as much as 8 m would appear to have been caused by increased runoff and flood magnitude this was linked to a shift to a wetter climate with flow augmented by iron age and roman woodland clearance and drainage of the catchment in more recent times results from this study suggest that current models of longer term holocene and pleistocene valley floor development in the british uplands may need to be re evaluated

geology and geochemistry of paleosols developed on the hekpoort basalt pretoria group south africa the hekpoort paleosols comprise a regional paleoweathering horizon developed on 2 224 0 021 ga basaltic andesite lavas at the top of the hekpoort formation of the pretoria group transvaal supergroup south africa in five separate profiles from outcrops along road cuts near waterval onder and the daspoort tunnel and in three drill cores from the bank break area bb3 bb8 and bb14 the top of the paleosol is a sericite rich zone the sericite zone grades downward into a chlorite rich zone in core bb8 and in the road cut at the daspoort tunnel we sampled the underlying or parent basaltic andesite into which the chlorite zone grades we did not obtain samples of the parent material at waterval onder and in cores bb3 and bb14 but chemical analyses indicate that the chlorite and sericite zones in these profiles derive from underlying lavas similar to the ones we sampled in core bb8 and at the daspoort tunnel the presence of apparent rip up clasts of the paleosol in the overlying ironstones of the strubenkop formation in the cores from bank break makes it very unlikely that most of the alteration was a result of interactions with hydrothermal fluids desiccation cracks at the top of the paleosol that were filled with sand during the deposition of the overlying sediments at waterval onder point to a subaerial weathering origin very little if any al ti zr v or cr moved a discernible distance during weathering of any of the five profiles the vertical distribution of fe mg mn ni and co indicates that these elements were largely removed from the top of the soil during weathering the overall abundance of these elements in each of the profiles indicates that a significant fraction of the complement lost from the top subsequently reprecipitated in the lower portion of the soil as constituents of an fe 2 rich smectite the loss of fe from the top of the soil during weathering of the hekpoort paleosols indicates that atmospheric p o 2 was less than 8 x 10 4 atm about 2 22 ga fe 2 rich smectite should only precipitate during soil formation if atmospheric p co 2 is less than or equal to 2 x 10 2 atm rye kuo and holland 1995 ca and na were largely lost during weathering some na was apparently added to the sericite zone in cores bb3 bb8 and bb14 after weathering all five profiles are enriched in k and rb and most are enriched in ba the distribution of these elements indicates that they all were added during post weathering hydrothermal metasomatism rb sr analysis of the paleosol at the daspoort tunnel indicates that metasomatism last affected that profile 1 925 0 032 ga macfarlane and holland 1991

a paleoweathering profile from griqualand west south africa evidence for a dramatic rise in atmospheric oxygen between 2 2 and 1 9 bybp a core drilled near wolhaarkop in griqualand west south africa intersected highly oxidized kuruman iron formation below red beds of the gamagara formation the lateral equivalents of the kuruman iron formation in this drill hole consist largely of siderite ankerite magnetite greenalite and quartz the oxidation of the kuruman iron formation in wol 2 occurred almost certainly during weathering prior to the deposition of the gamagara formation the date of this weathering episode is bracketed between about 2 2 and 1 9 bybp by the age of the ongeluk lavas in the transvaal sequence below the unconformity and by the age of the hartley lavas in the olifantshoek group above the unconformity the ratio of iron to sio2 in the several facies of the weathered kuruman iron formation in wol 2 is nearly the same as that in their unweathered equivalents since sio2 loss during weathering was almost certainly minor the similarity of the fe sio2 ratio in the weathered and unweathered bif indicates that nearly all the feo in the kuruman iron formation was oxidized and retained as feo3 during weathering such a high degree of iron retention is best explained by an o2 content of the atmosphere or 0 03 atm at the time of weathering such an o2 pressure is very much greater than that suggested by the composition of paleosols developed on basalt or 2 2 bybp but is consistent with the highly oxidized nature of the 1 85 by flin flon paleosol the new data suggest that po2 rose dramatically from about 1 percent pal present atmospheric level to or 15 percent pal between 2 2 and 1 9 bybp

chemostratigraphy of carbonates from the minas supergroup quadrilatero ferryifero iron quadrangle brazil a stratigraphic record of early proterozoic atmospheric biogeochemical and climactic change the ca 2 42 ga old gandarela formation overlies the finely laminated caue banded iron formation bif of the itabira group minas supergroup brazil and consists of red carbonate facies bif grading upsection into buff dolomites and limestones which are locally stromatolitic carbonates of the gandarela formation have 1 3 c values ranging narrowly from 1 6 to 0 4 permil versus pdb n 93 the cercadinho formation at the base of the overlying piracicaba group is a thick arenaceous succession with rare thin carbonates that have 1 3 c values ranging from 3 3 to 5 4 permil n 12 stromatolitic dolomites of the overlying fecho do funil formation have pb pb carbonate age 2 11 0 11 ga babinski and others 1995 that provide the minimum age for this unit and 1 3 c values ranging from 5 6 to 7 4 permil n 69 at present we find no evidence in brazil for the any of the three early paleoproterozoic glacial events recognized in 2 45 to 2 22 ga sedimentary successions in north america given the radiometric constraints however it is possible that geological and geochemical traces of these ice ages are missing along the unconformity between the gandarela and cercadinho formations if correct carbonates of the gandarela formation may provide a record of the carbon isotope composition of the seawater prior to any of the paleoproterozoic ice ages combined with other available 1 3 c data results from the gandarela formation suggest that seawater preceding the ice ages was not significantly enriched in 1 3 c on the other hand the carbon isotopic signature of the cercadinho carbonates and chemical composition of the cercadinho arenites are consistent with deposition after the end of the glacial epoch and likely during the early stage of ca 2 22 to 2 1 ga carbon isotope excursion the 1 3 c values of marine carbonates of the fecho do funil formation are consistent with carbon isotope record of contemporaneous carbonate successions worldwide providing additional evidence for a global biogeochemical anomaly at ca 2 22 to 2 1 ga these compositional and isotopic changes allow integration of the minas supergroup into the global record of the paleoproterozoic evolution as well as correlation with other successions of similar age

a critical look at iron paleoredox proxies new insights from modern euxinic marine basins enrichments in reactive iron occur under euxinic marine conditions that is where dissolved sulfide is present in the water column these enrichments result primarily from the export of remobilized iron from the oxic shelf which is scavenged from the euxinic water column during syngenetic pyrite formation and deposited in the underlying sediments strongly elevated ratios of highly reactive iron to total iron fehr fet and total iron to aluminum fet al and high degrees of pyritization dop are each products of this enrichment process these paleoredox proxies are among the most faithful recorders of ancient euxinia contrary to previous arguments iron enrichment is decoupled from biogenic sediment inputs but it does appear to be a uniquely euxinic phenomenon in other words we can rule out a major contribution from preferential physical transport of fehr rich detrital sediment to the deep basin which could also operate under oxic conditions furthermore enrichment via the shuttling of iron remobilized from oxic shelves appears to be limited by inefficient transport and trapping processes in deep oxic basins elevated fet al ratios in the euxinic sediments also cannot be a product of internal enhancement of the reactivity of the detrital iron pool without net fehr addition these conclusions are supported by observations in the modern black sea orca basin and effingham inlet fet al ratios are unambiguous recorders of paleoredox even in sediments that have experienced high degrees of metamorphic alteration however this study suggests that high siliciclastic accumulation rates can swamp the enrichment mechanism resulting in only intermediate dop values for euxinic sediments and fet al ratios that mimic the oxic shelf such dilution effects are well expressed in black sea basinal turbidites and rapidly accumulating muds on euxinic basin margins under conditions of persistent euxinia varying extents of fehr enrichment can illuminate spatial and temporal gradients in siliciclastic sedimentation the magnitude of enrichment is a function of the source shelf to sink ocean basin areal ratio suggesting that iron proxies can also record ocean scale paleoenvironmental properties through muted enrichments at times of very widespread euxinia for the first time manganese data are interpreted in light of the redox shuttle model as for the iron data the black sea orca basin and effingham inlet show enrichments in total manganese in the deep euxinic basin suggesting export from the suboxic porewaters of the oxic shelf and scavenging and burial in the basin the black sea data reveal iron and manganese enrichment across the broad deep euxinic basin suggesting efficient lateral transport and deep water mixing tied to the physical properties of the water column

detailed chronology of mid altitude fluvial system response to changing climate and societies at the end of the little ice age southwestern alps and cevennes france abstract over a historical timescale landscapes have been strongly affected by fluctuations in climate and by the impact of human societies this study examines the historical evolution of mid altitude fluvial systems in the western alps and cevennes se massif central in the context of marked climate and anthropogenic change at the end of the little ice age late 19th century this work contributes to the reconstruction of river paleodynamics by investigating the nature and chronology of geomorphological changes in upper river basins in order to produce a detailed reconstruction of hydromorphological changes we combined two approaches the study of historical archives and the use of bioindicators the dating of terraces using dendrochronology and of silt benches using lichenometry in order to reconstruct the evolution of the river channels the 19th century is a particularly propitious period for the study of surface dynamics because archives have preserved a wealth of qualitative and quantitative data concerning rivers economic statistics meteorological and hydrological observations illustrative documents descriptions by contemporary observers it is also a period for which reliable dating methods are available for detrital deposits in rivers the period provides new information on how the transition between the little ice age and current climate conditions affected the evolution of drainage basins and stream channels by highlighting a succession of phases in the erosive process e g the preparatory role of the drought of 1830 1838 in the erosion crisis of 1855 1870 and refining the chronology of events very early onset of riverbed incision the results highlight the effect of climate small hydroclimatic fluctuations amplified by strong anthropization on the rhythm of landscape change and on the relative stabilization of the landscape at the end of the 19th century in addition the synchronization of phenomena on the two sides of the rhone valley shows that these changes took place on a regional scale

oxidative forcing of global climate change a biogeochemical record across the oldest paleoproterozoic ice age in north america carbon isotope compositions of organic matter in fine grained siliciclastic units deposited above and below glacial diamictite at the base of the ca 2 45 2 22 ga huronian supergroup in ontario canada were studied to constrain relationships between profound fluctuations in the exogenic carbon cycle and dramatic climate changes at the beginning of the proterozoic eon in both drill core and outcrop sections the organic matter preserved in proximal lithofacies dominated by coarse grained sand and silt are enriched in 13 c relative to distal lithofacies dominated by argillites in the drill core sand dominated lithofacies of the mckim formation beneath the glacial diamictite of the ramsay lake formation have a narrow range of 13 c values 28 4 to 26 0 vpdb but organic matter in argillite dominated lithofacies of the outcrop section 40 km to the southeast is somewhat more 13 cdepleted with values ranging from 34 5 to 26 4 similarly sand dominated lithofacies of the pecors formation above the glacial diamictite in the drill core section with 13 c values of ca 28 are notably 13 c enriched relative to argillite dominated lithofacies which record values as low as 40 5 the sand dominated lithofacies of the pecors formation in the outcrop sections have 13 c compositions ranging from 34 4 to 27 9 the isotopic differences appear to be unrelated to organic carbon abundances so we suggest that these are controlled by environmental differences in proximal and distal settings the strong 13 cdepletion in the organic lean mckim and pecors argillites especially in the drill core section of the pecors formation is consistent with significant biological methane production and oxidative recycling by methanotrophs both before and after the ice age in shallow water environments stratified with respect to oxygen the rise of atmospheric oxygen and subsequent enhanced biogeochemical methane cycling in shallow water settings likely contributed to unstable climate conditions during the paleoproterozoic glacial epoch 2007 elsevier b v all rights reserved

water erosion in the southern french alps climatic and human mechanisms abstract a large number of studies have focused on water erosion in the southern alps because of its intensity and the high erodability affecting numerous outcrops in this region the aim of this paper is to determine the relations between natural and human factors on the one hand geomorphologic behaviour of hillslopes and fluvio torrential dynamics at two time scales geological and historical on the other hand this paper specially focuses on the recent weakening of torrential activity and its linkage with reforestation and rural desertion on the watersheds another objective is to compare these results with a rich mainly french scientific production on this theme experimental data on current erosion measurements and the analysis of its processes on the one hand and geomorphologic background of river beds and slopes are compared and analysed using archives and the present knowledge on historical climate it has been shown that the overexploitation of watersheds leads to an increase in soil loss in the number and intensity of floods in alpine valleys as well as to an enhancement of sediment transport however climatic changes during the holocene and during the past millennium have resulted in changes in morphological behaviour of the hillslopes upstream and of river beds downstream moreover a strong sedimentary deficit can be observed over the last three or four decades in all the alpine massifs the consequences of this sediment deficit are firstly an entrenchment of river beds which threatens bridges and embankments this recent trend is probably due to the excessive extraction of material in gravel pits and the sedimentation in the numerous dams built between 1920 and 1980 in the entire alpine range however the entrenchment appeared recently on non exploited rivers therefore the deficit is also due to the success of the natural and artificial reforestation and torrent correction since the end of 19th century

petrography and geochemistry of a 2000 2200 ma old hematitic paleo alteration profile on ongeluk basalt of the transvaal supergroup griqualand west south africa abstract a 4 m thick paleo alteration profile thought to represent one of the oldest known ferruginized hematitic paleoweathering zones is described from a depth of 720 m in a drill core on the farm drakenstein 263 some 20 km northwest of hotazel in griqualand west south africa the paleo alteration profile is developed on 2240 57 ma ongeluk basalt along the angular unconformity that separates transvaal strata from 2070 95 ma basal red beds of the olifantshoek group basaltic ongeluk lava was subjected to greenschist facies metamorphism represented by a mineral assemblage of fe pumpellyite chlorite albite and quartz before paleosol development the subsequent paleo alteration is characterized by concentration of fe2o3 in the form of hematite iron rich chlorite and abundant sericite the abundance of sericite results in a large excess of k2o relative to the amount of al2o3 that could have been derived from weathering of the parent basalt the origin of the excess potassium is problematical and could have been derived from basin water groundwater or metamorphic fluids field relationships favour introduction from basin water during deposition of overlying olifantshoek red beds elements such as sodium calcium and magnesium were leached from the alteration profile whereas ree became concentrated within it the most interesting aspect of the ree distribution is the preferred concentration of the lighter lanthanides la and nd in the middle part of the alteration profile relative to heavy ree and the development of a marked negative ce anomaly in the paleo weathered material hydrothermal vein alteration took place after deposition of the overlying olifantshoek red beds

assessment of channel changes due to long term bedload supply decrease roubion river france this paper presents the observations made in the watershed of the upper roubion river which drains a submediterranean mountainous environment and in two of its main tributaries the soubrion and bine creeks our aim was to analyze contemporary morphological and sedimentary changes in response to a progressive decrease in bedload supply this decrease is linked to an increase of forest cover in the watershed during the 20th century following rural depopulation and to a correlated decrease in peak flows several variables were systematically measured width slope bed level change sediment size along 23 km of river whereas dendrochronological data floodplain cross sections and estimated recurrence intervals of sediment entrainment based on critical shear stress calculations were also produced for specific sites to complete our analysis evidence of three major phenomena was obtained on both the roubion and its tributaries i bed degradation ii development of stable pavement in incised reaches and iii channel narrowing associated with the development of alluvial forest on recently abandoned portions of the pre existing active channel forest development began in the 1950s these three phenomena show positively covariant relationships that lead us to propose a descriptive model of mountain fluvial system adjustments to progressive decrease of bedload

formation and diagenesis of a sub huronian saprolith comparison with a modern weathering profile an early proterozoic paleosol that preserves archean granite protolith textures occurs beneath the lorrain formation in the early proterozoic huronian supergroup near ville marie quebec textural mineralogical and geochemical comparisons between this saprolith and a modern weathering profile developed on the devonian toorongo granodiorite in eastern australia indicate similarities that can be attributed to the effects of primary weathering reactions the comparison also reveals anomalous features at ville marie that are caused by diagenetic reactions between the weathered granite and meteoric waters k metasomatism in the form of sericite replacement of kandites is ubiquitous in the ville marie saprolith zone and is ascribed to reaction of low na k meteoric waters with the weathered profile as they moved along a relatively permeable unconformity surface earlier diagenetic reactions may have produced calcite alteration occurring in a thin zone at the base of the profile thought to represent the po

chemostratigraphy of the paleoproterozoic duitschland formation south africa implications for coupled climate change and carbon cycling the paleoproterozoic duitschland formation lies stratigraphically beneath the timeball hill formation which contains the only unequivocal glacial unit of this era in the transvaal basin south africa lithologic evidence in paleoproterozoic successions of north america however indicates the existence of three discrete and potentially global ice ages within this 300 my interval carbonates of the duitschland formation are significantly enriched in 13c up to 10 1 permil in the upper part of the succession above a notable sequence boundary in contrast the lower part of this unit contains carbonates with consistently negative 13c values trace and major element compositions of these carbonates as well as carbon isotopic compositions of coexisting organic matter support a primary origin for the markedly positive carbon isotope anomaly the stratigraphic constraints indicate that 13c enriched carbonates were deposited prior to paleoproterozoic glaciation in southern africa similar to carbonates stratigraphically beneath neoproterozoic glacial diamictites worldwide also mirroring the neoproterozoic record are strongly negative 13c values in cap carbonates atop glacial diamictites in paleoproterozoic strata of wyoming and ontario the litho and chemostratigraphic constraints indicate that the interval of negative carbon isotope values in well preserved carbonates of the lower duitschland formation may reflect a second paleoproterozoic ice age in the transvaal succession this interpretation is further supported by recently discovered bullet shaped clasts with striations in diamictite from the basal part of the succession thus the emerging temporal pattern of carbon isotope variations and glaciation in the paleoproterozoic has a close analogue to neoproterozoic events suggesting a coupling of climatic and biogeochemical changes at both ends of the eon

headwater valley response to climate and land use changes during the little ice age in the massif central yzeron basin france the geomorphological response of valley bottoms in eastern france to climatic fluctuations of the little ice age lia was investigated using sedimentological analysis together with optically stimulated luminescence osl and radiocarbon dating diachronic mapping of land use since the beginning of the nineteenth century was also carried out since a d 1500 the valley bottoms experienced three cycles of aggradation and subsequent incision each characterized by paired periods of high and low detritic activity while the impact of human activity on the aggradation of the alluvial plain is observed the vertical dynamics of the valley bottom deposits seemingly were also linked to the hydroclimatic fluctuations during the lia the sensitivity to these fluctuations was increased by human activity at the scale of the basin variations of the winter north atlantic oscillation nao and solar activity from the last five centuries correlate with wet and cold phases during which valley bottoms accumulated and dry and warm phases during which the streams incised into the valley floors this fluvial sensitivity to the meteorological conditions induced temporal variations in sedimentary supply originating from either direct input from remnants of periglacial alluvial sheets or local rocky outcrops and or from indirect input from the erosion of alluvial and colluvial deposits these two components combined with the sheet runoff over the ploughlands express the complex coupling between hillslopes and valley bottoms in the headwater catchments this caused a cascade shaped transit of the sediments characterized by alternating phases of storage and removal keywords little ice age headwater valley bottom deposits aggradation incision cycle osl and radiocarbon dating landscape history massif central

carbon isotope record for the onset of the lomagundi carbon isotope excursion in the great lakes area north america carbonate units of the chocolay group in the lake superior area usa and the gordon lake formation of the correlative upper huronian supergroup ontario canada were deposited after the last paleoproterozoic glacial event and an episode of intense chemical weathering the huronian supergroup contains at the base 2 45 ga volcanics and is intruded by the 2 22 ga nipissing diabase dykes and sills while the chocolay group is bracketed in age between 2 29 and 2 20 ga the lomagundi 2 22 2 1 ga carbon isotope excursion started after the paleoproterozoic glacial epoch and before a plume breakout event at 2 22 ga therefore the chocolay and upper huronian carbonates were deposited either before or during the onset of the lomagundi event notably thin carbonates of the basal gordon lake formation and thick carbonate succession of the kona dolomite in the northeastern exposures of the chocolay group record 13 c values as high as 9 5 versus v pdb similar to other successions deposited during the lomagundi event both units contain pseudomorphs and molds after sulfates this observation suggests that seawater sulfate contents rose dramatically in association with the onset of the lomagundi event and the rise of atmospheric oxygen carbonates in the western and southern exposures of the chocolay group randville and bad river dolomites and saunders formation previously assumed to be equivalent to the gordon lake formation and kona dolomite have carbon isotope values close to 0 based on basin analysis we infer that these carbonate units were deposited during a negative carbon isotope excursion after the lomagundi event started and are slightly younger than the kona dolomite and gordon lake formation this interpretation implies that the carbonate platform in the great lakes area transgressed to the west over shallow marine and fluvial deposits the negative carbon isotope excursion in the lake superior area might correspond to similar 13 c values of the mooidraai dolomite in the griqualand west basin south africa supporting correlation between paleoproterozoic successions of north america and south africa and the notion of three global glaciations in the paleoproterozoic era carbonates of the mille lacs group trout lake glen township and denham formations in minnesota have 13 c values ranging from 1 2 to 2 5 combined with geochronologic constraints these data suggest that these units were deposited after the lomagundi excursion and are related to the rifting event that led to development of the so far unrecognized 2 0 ga passive margin in the lake superior area 2006 elsevier b v all rights reserved

chemostratigraphy of paleoproterozoic carbonate successions of the wyoming craton tectonic forcing of biogeochemical change the archean wyoming craton is flanked on the south and east by belts of paleoproterozoic supracrustal successions whose correlation is complicated by lack of geochronologic constraints and continuous outcrop however carbonate units in these successions may be correlated by integrating carbon isotope stratigraphy with lithostratigraphy the 10 km thick paleoproterozoic snowy pass supergroup in the medicine bow mountains was deposited on the present day southern flank of the wyoming craton it contains three discrete levels of glacial diamictite correlative with those in the huronian supergroup on the southern margin of the superior craton the nash fork formation of the upper snowy pass supergroup is significantly younger than the uppermost diamictite and was deposited after the end of the paleoproterozoic glacial epoch carbonates at the base of the nash fork formation record remarkable 13 cenrichment up to 28 v pdb whereas those from overlying members of the lower nash fork formation have d 13 c values between 6 and 8 carbonates from the upper nash fork formation above the carbonaceous shale have carbon isotope values ranging between 0 and 2 5 the transition from high carbon isotope values to those near 0 in the nash fork formation is similar to that at the end of the ca 2 2 2 1 ga carbon isotope excursion in fennoscandia this chemostratigraphic trend and deposition of bifs mn rich lithologies carbonaceous shales and phosphorites at the end of the global ca 2 2 2 1 ga carbon isotope excursion are likely related to ocean overturn associated with the final breakup of the kenorland supercontinent correlative carbonates from the slaughterhouse formation in the sierra madre wy and from the whalen group in the rawhide creek area in the hartville uplift wy have highly positive carbon isotope values in contrast carbonates from other exposures of the whalen group in the hartville uplift and all carbonate units in the black hills sd have carbon isotope values close to 0 combined with existing geochronologic and stratigraphic constraints these data suggest that the slaughterhouse formation and the succession exposed in the rawhide creek area of the hartville uplift are correlative with the lower and middle nash fork formation and were deposited during the ca 2 2 2 1 ga carbon isotope excursion the estes and roberts draw formations in the black hills and carbonates from other exposures in the hartville uplift postdate the ca 2 2 2 1 ga

comment on the night when the auroral and equatorial ionospheres converged by martinis c j baumgardner m mendillo j wroten a coster and l paxton intense oi 630 0 nm emission depletions were detected over mexico by an all sky imager during the main phase of the geomagnetic storm on 1 june 2013 minimum dst index 119 nt those emission depletions were interpreted to be associated with equatorial plasma bubbles martinis et al 2015 if bubbles were responsible for those middle latitude emission depletions they would have been extreme bubbles which extended over 40 magnetic latitudes and 7000 km in altitude at the magnetic equator however a few factors challenge this interpretation first the emission depletions detected over mexico showed westward drift whereas the equatorial ionosphere including bubbles drifted eastward on that night second the middle latitude emission depletions were tilted westward with respect to the geographic meridian but the westward tilt of bubbles was not identified third the growth of bubbles was not evident when the middle latitude emission depletions grew the westward tilt and westward propagation of the middle latitude emission depletions are consistent with the characteristics of medium scale traveling ionospheric disturbances mstids observed over the united states on that night thus the emission depletions over mexico can be interpreted to be the signature of mstids

chemical weathering in the foreland of a retreating glacier chemical denudation rates and strontium isotope ratios in streams vary substantially and systematically in the foreland of the retreating bench glacier in south central alaska to study weathering of young glacier sediments we sampled 12 streams draining a chronosequence of till and moraine soils derived from cretaceous metagraywacke metapelite bedrock both sediment age and vegetation cover increase with distance from the glacier cation denudation rates decline with increasing distance from the glacier whereas silica denudation rates increase carbonate dissolution and sulfide oxidation account for roughly 90 of the solute flux from the youngest sediments biotite alteration accounts for 5 11 of the solute flux its peak contribution is found in the glacier outlet stream silicate weathering is the dominant reaction only in the oldest sediments in a laboratory dissolution experiment using fresh glacial sediment carbonate dissolution dominated the solute flux during the first 700 hours paralleling the behavior of young sediments in the field in contrast to trends in the field the silica flux did not increase after the carbonate was exhausted from the reactor a possible reason for this difference is that establishment of vegetation causes an increase in silicate weathering the 87sr 86sr ratio in the glacier outlet stream is greater than that in proglacial streams and in bulk rock due to a greater contribution of biotite weathering in the outlet than in proglacial streams strontium isotope ratios decline with sediment exposure age in the proglacial streams and are consistent with a carbonate source because the dominant weathering reactions in the young sediments are of carbonate and sulfide rather than silicate minerals weathering at the glacier margin is not an important long term sink for atmospheric co2

decline in oceanic sulfate levels during the early mesoproterozoic abstract multiple sulfur isotope compositions 32 s 33 s 34 s and 36 s were analyzed for paired carbonate associated sulfate cas and disseminated pyrite py from the 1 6 ga gaoyuzhuang formation of the north china craton to reconstruct the history of sulfate levels in proterozoic oceans the 200 m thick study interval yielded relatively constant values for 34 s cas 13 0 1 8 34 s py 8 0 2 3 and 34 s cas py 5 as well as relatively constant 33 s 0 0 05 and 36 s 0 35 0 15 for both cas and pyrite limited variation in 34 s py and slightly lower 33 s of pyrite relative to cas suggest water column precipitation of pyrite limited fractionation of sulfur during microbial sulfate reduction as documented by 34 s cas py implies low seawater sulfate concentrations in the early mesoproterozoic ocean we quantitatively constrained paleo seawater so 4 2 using a novel modeling approach based on measured values of 34 s cas py and 34 s cas t max for the study unit 34 s cas py is 5 4 1 4 n 17 and 34 s cas t max is 6 8 34 myr 1 based on sedimentation rates of 30 150 m myr 1 these data indicate early mesoproterozoic seawater so 4 2 of p o 2 after great oxidation event i

geology and major and trace element chemistry of late archean weathering profiles in the fortescue group western australia implications for atmospheric po2 abstract we have identified two thick weathering profiles between flows of the mt roe basalt unit of the fortescue group in the pilbara area of western australia the age of weathering is constrained by u pb zircon dating to lie between 2765 and 2715 ma the profiles herein referred to as the mt roe 1 and 2 paleosols were mapped in detail for 1500 m and 760 m along strike respectively samples were collected along traverses across both profiles where they were well developed and well exposed the profiles which may be structurally offset parts of the same weathering horizon have well developed upper sericite zones 1 15 m thick these grade downward into chlorite rich zones which are chemically and physically heterogeneous the chlorite zones grade downward into unweathered basalts the mt roe 1 profile is overlain by 2 6 m of bedded probably lacustrine sediments these in turn are covered by succeeding lava flows evidence of a surficial origin for the paleosols includes mud cracks ripple marks and rip ups of the paleosol material in the post paleosol sediments soft sediment deformation and probable dewatering structures are present along the paleosol sediment contact the mt roe 2 profile is overlain directly by the succeeding lava flow with little or no intervening sediments some brecciation and pillowing is observed along the base of the overlying basalt flow in both cases probably due to emplacement of lava into a shallow lake or onto wet soil in the sericite zones of both profiles nearly all of the fe mn mg and zn and a substantial fraction of the ca pb na ni and si have been leached the chlorite zones have elevated fe pb ni and zn contents and appear to be repositories of elements lost from the sericite zone al ti zr and th were immobile in the mt roe 1 paleosol and are concentrated by factors of 2 5 2 6 over the unweathered basalt v u and cr were also nearly immobile major element and trace element data indicate that weathering took place under conditions of low atmospheric oxygen k is strongly enriched toward the upper contact of the sericite zone and was introduced during post weathering metasomatism together with rb and sr na and ca are also enriched near the top of each profile and small amounts of each may have been introduced during regional low grade metamorphism of the hamersley basin at 2168 10 ma

experimental study of igneous and sedimentary apatite dissolution control of ph distance from equilibrium and temperature on dissolution rates apatite dissolution experiments were conducted using both a fluidized bed and stirred tank reactor over a range of ph temperature solution saturation state and on non carbonated and carbonated apatite compositions igneous fluorapatite fap and sedimentary carbonate fluorapatite cfa respectively from 2 8 5 were not possible due to detection limits of the analytical techniques used in this study and the high insolubility of fap for the cfa compositions studied the dissolution rate decreased with increasing ph from 4 ph 7 during early stages of the dissolution reaction for both fap and cfa mineral components were released in non stoichiometric ratios with reacted solution ratios of dissolved ca p and ca f being greater than mineral stoichiometric ratios suggesting that ca was preferentially released compared to p and f from the mineral structure during the early stages of dissolution an increase in reacted solution ph accompanies this early elevated release of ca as the dissolution reaction proceeded to steady state dissolution became congruent when normalized to bet measured surface area fap dissolved faster from 4 ph 7 compared to cfa the apparent arrhenius activation energy ea of fap dissolution over the temperature range of 25 55 c at ph 3 0 i 0 1 and pco2 0 is 8 3 0 2 kcal mol 1 both the apparent exchange of solution h for solid bound ca at low ph in the early stage of dissolution and the ea of dissolution suggest a surface and not a diffusion controlled dissolution reaction for fap and cfa the degree of undersaturation of the solution gr with respect to fap was important in determining the dissolution rate at ph 3 0 i 0 1 and pco2 0 the dissolution rate of fap was 5 greater in the far from equilibrium region compared to the near equilibrium slope region a simple apatite weathering model incorporating the experimental results from this study was constructed and numerical calculations suggest that during the phanerozoic both the surface area of igneous rock available for weathering and the average global temperature were important factors in determining the p weathering flux from apatite dissolution it is possible that elevated global temperatures coupled with relatively high surface area of igneous rock during the early to mid paleozoic resulted in elevated p weathering fluxes which along with climatic evolutionary pressures of the neoproterozoic facilitated the radiation of multicellular organisms large scale phosphorite deposition and abundance of calcium phosphate shelled organisms during the early cambrian

flood frequency analysis on the ardeche river using french documentary sources from the last two centuries fitting statistical laws from a short time series does not give any guarantee of reliability on extreme flood estimation historical investigation through documentary sources can enlarge the record period this paper presents a case study on the ardeche river based on collaboration between historians archivists hydraulic engineers and hydrologists for a better assessment of the flood risk a list of historical flood levels from 1644 to the present has been drawn up and converted into discharge using hydraulic modelling a sensitivity analysis provides error intervals on discharge estimates taking into account uncertainties on water level roughness coefficient and channel geometry and the impact of a nonpermanent discharge or the backward effect a flood frequency analysis using systematic and nonsystematic data gives a practical example on how historical information can improve flood knowledge it reduces the sampling uncertainty and shows also a good agreement with a hydrometeorological approach gradex model

morphological changes in alpine rivers following the end of the little ice age abstract this work investigates the channel changes of alpine rivers from the end of the little ice age 1850s to the 1950s with the aim to determine the possible role of climatic variations occurred in this period before the onset of anthropic pressures i e dams check dams bank protections and gravel mining the research was conducted on 17 river catchments of south tyrol northern italy glaciated and unglaciated a multitemporal gis analysis approach was adopted to assess the morphological changes in terms of channel width and pattern from three different sources i austrian cadastral map 1858 ii maps from the italian institute of military geography 1917 1925 and iii two aerial photo sets taken in 1945 and 1954 the analysed river network a total of 480 km was subdivided into 162 morphologically homogeneous reaches 76 confined 81 partly confined and 5 unconfined with lengths ranging from 630 to 5500 m slope from 0 3 to 24 and drained area from 20 to 4000 km 2 the statistical relationships among morphological changes and reach and basin scale factors were analysed by univariate and multivariate methods and the relationships between width changes and 36 controlling factors were explored using principal component analysis the variability in width and morphological pattern changes were very pronounced between and within single rivers highlighting the value of such a large data set overall the analysed rivers varied their morphological pattern mostly exhibiting a shift from multithread transitional to single thread patterns but unchanged planform types were also common variations in channel width varied substantially among the analysed rivers which featured narrowing slightly prevailing and widening the least common as well as many cases of very limited changes channel width variations appear statistically although weakly related to some morphometric variables and significant differences emerge comparing glaciated vs unglaciated basins climate related variations glacier dynamics and channel disturbance frequency are argued to be the dominant factors that affected channel variations

fractionation between inorganic and organic carbon during the lomagundi 2 22 2 1 ga carbon isotope excursion article i nfo the lomagundi 2 22 2 1 ga positive carbon isotope excursion in shallow marine sedimentary carbonates has been associated with the rise in atmospheric oxygen but subsequent studies have demonstrated that the carbon isotope excursion was preceded by the rise in atmospheric oxygen the amount of oxygen released to the exosphere during the lomagundi excursion is constrained by the average global fractionation between inorganic and organic carbon which is poorly characterized because dissolved inorganic and organic carbon reservoirs were arguably larger in the paleoproterozoic ocean at a time of lower solar luminosity and lower ocean redox state decoupling between these two variables might be expected we determined carbon isotope values of carbonate and organic matter in carbonates and shales of the silverton formation south africa and in the correlative sengoma argillite formation near the border in botswana these units were deposited between 2 22 and 2 06 ga along the margin of the kaapvaal craton in an open marine deltaic setting and experienced lower greenschist facies metamorphism the prodelta to offshore marine shales are overlain by a subtidal carbonate sequence carbonates exhibit elevated 13 c values ranging from 8 3 to 11 2 vs vpdb consistent with deposition during the lomagundi positive excursion the total organic carbon toc contents range from 0 01 to 0 6 and 13 c values range from 24 8 to 13 9 thus the isotopic fractionation between organic and carbonate carbon was on average 30 3 2 8 n 32 in the shallow marine environment the underlying sengoma shales have highly variable toc contents 0 14 to 21 94 and 13 c values 33 7 to 20 8 with an average of 27 0 3 0 n 50 considering that the shales were also deposited during the lomagundi excursion and taking 13 c values of the overlying carbonates as representative of the 13 c value of dissolved inorganic carbon during shale deposition a carbon isotope fractionation as large as 37 appears to characterize the production of bulk organic matter in the deeper part of the pretoria basin at that time this enhanced fractionation relative to that observed in shallow water environments likely reflects heterotrophic secondary and chemotrophic productivity at and below a pronounced redoxcline consistent with the euxinic conditions inferred from independent evidence for the deeper part of the pretoria basin greater variability in organic carbon vs carbonate carbon isotopic values on the shallow marine carbonate platform suggests that the carbon cycling was dominated by a large dissolved inorganic carbon reservoir during the lomagundi excursion our study suggests that in contrast to the late neoproterozoic and phanerozoic when carbon isotope fractionation between carbonate and organic carbon in the open ocean was mostly controlled by primary producers in the paleoproterozoic redox stratified ocean heterotrophic and chemotrophic productivity overprinted a signal of primary productivity below the redoxcline this strong imprint of heterotrophic and chemotrophic productivity on organic carbon isotope records complicates the reconstruction of spatial patterns and secular trends in the 13 c values of dissolved inorganic carbon in the paleoproterozoic seawater

evolutionary trajectory of channel morphology and controlling factors in a large gravel bed river abstract interpretation of channel changes is not always straightforward since it requires a detailed reconstruction of the evolutionary trajectory of channel morphology a quantitative analysis of controlling factors and finally identification of links between evolutionary trajectories and controlling factors the aim of this paper is to explain channel adjustments and controlling factors in the tagliamento river a large gravel bed river in northeastern italy traditional methods for studying historical channel changes i e use of aerial photos topographic data were employed but numerical modelling turned out to be very useful for the quantification of bedload transport and for supporting interpretation of past changes and likely future channel evolution river channel underwent three main phases of adjustment over the last 200 years the first two phases from the end of the nineteenth century to the early 1990s were characterized by narrowing channel width decreased from 1250 to 540 m and incision about 1 m and the third phase from the 1990s to present day by widening from 540 to 600 m and slight aggradation about 0 2 m combining evolutionary trajectories of channel morphology and analysis of controlling factors we argue that the long term channel evolution of the tagliamento river was driven mainly by human intervention at the reach scale i e sediment mining and channelization changes in sediment supply in the catchment area had no or minor effects in the study reach the most recent changes i e widening and slight aggradation are explained as a response to past disturbances that have produced a remarkable change of channel geometry and an increase of unit stream power in the reach magnitude and frequency of formative discharges are a key driving factor of the intensity of recent changes while this was not the case during the previous phases of adjustment

oxygen overshoot and recovery during the early paleoproterozoic abstract during the lomagundi event ca 2 22 to 2 06 ga marine carbonates recorded the largest and longest uninterrupted positive carbon isotope excursion the earliest extensive marine sulfate evaporites were deposited and the average ferric iron to total iron expressed as fe 2 o 3 fe fe2o3 ratio of shales increased dramatically at the end of the lomagundi event the first economic sedimentary phosphorites were deposited and the carbon isotope values of marine carbonates returned to 0 vpdb thereafter marine sulfate evaporites and phosphorites again became scarce while the average fe 2 o 3 fe fe2o3 ratio of shales decreased to values intermediate between those of the archean and lomagundi age shales we propose that the large isotopic and chemical excursions during the lomagundi event were caused by a positive feedback between the rise of atmospheric o 2 the weathering of sulfides in the pre 2 3 ga continental crust and the flux of phosphate to the oceans cf holland 2002 the rise in the terrestrial phosphate flux led to an increase in the burial rate of organic carbon and a major transfer of oxygen from the carbon to the sulfur cycle the end of the lomagundi event was probably caused by a decrease in the terrestrial phosphate flux related to the weathering of low pyrite sediments that were deposited during the lomagundi event the rate of deposition of organic matter and the precipitation of sulfate evaporites decreased the isotopic and chemical excesses of the lomagundi event were eliminated and the ocean atmosphere system entered the period frequently called the boring billion

evolutionary trajectory of channel planforms in the middle garonne river toulouse sw france over a 130 year period contribution of mixed multiple factor analysis mfamix the purpose of this study is to propose a methodological essay for defining evolutionary trajectories of channel planforms and to examine the channel change in the middle garonne river southwest france over a 130 year period the study focuses on a reach of 90 km situated downstream from the city of toulouse a set of four historical maps 1868 1940s 1970s and 2000s is used to build a geomorphometric diachronic database data processing through mixed multiple factor analysis mfamix and hierarchical cluster analysis hca allows distinction between four homogeneous zones within the study reach depending on their evolutionary trajectories channel behavior in the upstream and median zones evolved as of the beginning of the study period narrowing of the fluvial area colonization by vegetation and removal of alluvial bars likely owing to punctual anthropogenic actions the downstream zone is characterized by stabilization of the channel and alluvial bar removal over the second half of the twentieth century coinciding with the campaign undertaken by french local authorities between 1960 and 1984 to protect river banks the role of accepted manuscript climate transition between the little ice age lia and the onset of the global warming period gw is also discussed results generally are consistent with the chronology established for most european rivers