morphodynamic evolution of the orb river languedoc france evidence of eustatic tectonic and climatic controls this study aims to reconstruct the cenozoic and pleistocene morphodynamic evolution of the orb a mediterranean river which crosses all the structural units of the south massif central border a geomorphological and sedimentological analysis of detrital deposits was carried out as a basis for correlating the different formations and reconstructing the palaeodrainage heavy minerals were used to reconstruct the main sedimentary palaeochannels since the messinian the successive orb longitudinal profiles show anomalies which can be caused by structure and by interactions between fluvial dynamics and tectonics evidence of volcanic heavy minerals on the faugeres mountains and in the upper pliocene deposits of the languedocian piedmont demonstrates that a north south flow took place during the upper pliocene nevertheless a palaeo orb existed at the place of the present course when the basaltic lava flows were spreading but headward erosion did not reach them until the upper pleistocene because the orb middle and high terraces do not contain volcanic minerals sourced from the escandorgue the successive orb longitudinal profiles show that headward erosion due to pleistocene low sea levels does not reach beyond beziers and that a tectonic hinge has functioned near the shoreline the non lithologic knickpoints are explained by the montagne noire and avant monts uplift up until the pleistocene a progressive continental uplift is necessary to explain the orb terraces staircase in the beziers district and the fluctuations of incision from upstream to downstream are due to laterally differential movements which are isostatic effects of thick regressive deposits on the gulf of lion shelf during the cold periods copyright 2008 john wiley sons ltd

palaeoenvironmental significance of rounded pyrite in siliciclastic sequences of the late archaean witwatersrand basin oxygen deficient atmosphere or hydrothermal alteration petrographic and sulphur isotope studies support the long held contention that rounded grains of pyrite in siliciclastic sequences of the late archaean witwatersrand supergroup originated as placer grains the grains areconcentrated at sites where detrital heavy minerals are abundant within quartz pebble conglomerates and quartzose sandstones depositional sites with abundant pyrite are 1 within the matrix of bar type clast supported conglomerates 2 on scoured or winnowed surfaces and 3 on stratification planes the grains are internally compact or porous with truncation of internal structure at outer margins indicating fragmentation and rounding of pyritic source rocks during erosion and sediment transport a large range in textures reflects source rock lithologies with known varieties linked to sedimentary hosted diagenetic pyrite volcanic hosted massive sulphide deposits and hydrothermal pyrite laser ablation sulphur isotope analysis of pyrite reveals a broader range in 3 4 s values 5 3 to 6 7 than that of previously reported conventional bulk grain analyses 1 to 4 rounded pyrite from the steyn reef has significant variation in 3 4 s values 4 7 to 6 7 that establishes heterogeneous sulphur compositions with even adjacent grains having diverse isotopic signatures the heterogeneity supports a placer origin for rounded pyrite euhedral pyrite and pyrite overgrowths which are undoubtedly authigenic have restricted 3 4 s values 0 5 to 2 5 are chemically distinct from rounded pyrite and are probably the products of metamorphism or hydrothermal alteration the placer origin of rounded pyrite indicates that pyrite was a stable heavy mineral during erosion and transport in the early atmosphere its distribution in three sequences witwatersrand supergroup ventersdorp contact reef and black reef and in other sequences not linked to witwatersrand type au u ore deposits implies deposition of redox sensitive detrital heavy minerals during the late archaean consequently rounded grains of detrital pyrite are strong indicators of an oxygen poor atmosphere while not confirming a placer origin for gold in witwatersrand au u ore deposits the palaeoenvironmental significance of rounded pyrite negates its link to hydrothermal mineralization

the 13c12c ratios of siderite and organic matter of a modern metalliferous hydrothermal sediment and their implications for banded iron formations abstract a hydrothermal ferruginous sediment precipitated by the activity of the microaerophilic chemolithotrophic bacterium galionella ferruginea has been sampled in a bay of nea kameni island santorini greece due to high fugacity of carbon dioxide precipitation of siderite also occurred the 13c value pdb was determined to be 6 5 in the siderite and 26 8 in the organic matter of mainly microbiological origin the enrichment of isotopically light carbon in carbonates of banded iron formations 13 c 10 has recently been discussed in literature the dilution of these marine carbonates by isotopically light carbon is suggested to have resulted from bacterial oxidation of reduced organic carbon during early diagenesis it is further suggested that fe iii in the newly precipitated sediment served as electron acceptor during oxidation in a hydrothermal model for the origin of banded iron formations this is consistent with the data presented here it is therefore postulated from the results presented that the reduced organic carbon in banded iron formations originates from microaerophilic chemolithotrophic bacteria

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

sulfur isotopic studies of archean slate and graywacke from northern minnesota evidence for the existence of sulfate reducing bacteria abstract sulfur isotopic studies of pyrite from metasediments in the 2 6 byr old deer lake green stone sequence minnesota have been conducted in order to evaluate the possible importance of sulfate reducing bacteria in sulfide formation pyrite occurs as ovules up to 2 cm in diameter within graphitic slates and as fine disseminations in metagraywacke units sem studies indicate the pyrite is framboidal in morphology 34 s values of pyrite from the deer lake sediments range from 2 3 to 11 1 with a peak at 2 isotopic data are consistent with either high temperature inorganic reduction of circulating seawater sulfate or low temperature bacterial reduction however the lack of sulfide bands or massive occurrences in the sediments the restriction of pyrite mineralization to the sediments and the absence of evidence for hot spring activity suggest that a diagenetic origin of pyrite is more feasible sulfide in such an environment would be produced principally by the action of sulfate reducing bacteria results of the study are in agreement with those of goodwin et al 1976 who suggest that dissimilatory sulfate reduction was operative in the archean ocean some 2 75 byr ago

the fluvial system research perspectives of its past and present dynamics and controls abstract during the conference the fluvial system past and present dynamics and controls held at the department of geography of bonn university from 16 to 22 of may 2005 the participants organised in 12 international organisations working in the fluvial environment were asked about their opinions about the main aspects to be considered for sustainable progress in future research projects the individual comments can be grouped by the following headlines integration and application of experiences considering system analytical approaches considering effects of climate and global change interdisciplinary work regarding extreme events and their frequencies and quantification of human impact detailed explanations and selected references of previous studies initially considering the mentioned aspects are given as a review

spatio temporally variable response of fluvial systems to late pleistocene climate change a case study from central germany abstract the change of the earth s climate and anthropogenic forcing challenge catchment management as the deliberate use of the fluvial system s natural resources depends to some extent on the predictability of the system s variable sensitivity to external impacts the alluvial history of the wetter valley in central germany provides an example of the occurrence of a spatio temporally variable catchment sensitivity to the late pleistocene climate change empirical models that are based on sediment flux controls such as sediment supply transport capacity and gradient serve to explain differential floodplain construction during the early younger dryas the large scale basin upland morphology caused localised divergent cooling impacts and vegetation changes which generated reach scale variable sediment transport system states in the wetter valley the spatial arrangement of reach scale variable response is ascribed to the tectonically driven morphological configuration of the wetter catchment the crucial amplification of differential floodplain construction can be assigned to the spatially variable availability of a surplus of laacher see tephra particles in manner of a pulsed sediment input the ubiquitous tephra cover was previously deposited by the laacher see volcano event in the upper allerod thus the reach scale variable response during the early younger dryas can be deemed to have been climatically triggered but superimposed by an internally driven specific upstream catchment response the documented processes of late quaternary alluviation in the wetter valley imply the need for whole catchment approaches the latter are a prerequisite to reveal the occurrence and causalities of variable fluvial response in relation to external impacts that interact with internal morphological controls this is seen to be crucial to achieve an improved predictability of future environmental change in fluvial landscapes

post saalian transformation of dry valleys in eastern europe an example from ne poland the studies were conducted in a dry valley in ne poland they were aimed at determining the origin of this structure and tracing the processes that have shaped the dry valley in a time span of about 130 ka the research included detailed geological mapping including piercing of a number of boreholes and electrical resistivity tomography ert surveys the obtained material was pollen analysed osl dated and the grain size distribution and the morphoscopy of sand quartz grains were investigated additionally the organic matter om content was determined based on the obtained results it was concluded that the structure currently occupied by sediments of the dry valley was formed during the warta stadial of the odranian glaciation saalian mis 6 as a glacial tunnel valley small probably isolated depressions functioned in the dry valley bottom after the ice sheet retreat the sediments record a full succession of climate oscillations from the eemian interglacial mis 5e pollen zones e1 to e7 through the early vistulian mis 5a 5d to mis 4 in the early vistulian the depressions functioned as lakes or got shallower and were replaced by peat bogs depending on the climate conditions during mis 4 the bottom of the dry valley was subjected to erosion as a result of concentrated water flow this caused draining of the existing depressions and their incorporation within the flow probably during mis 3 solifluction was activated on the slopes of the dry valley during lgm permafrost aggradation occurred in the study area recorded by two generations of epigenetic sand wedges and development of aeolian processes in contrast to analogous processes within the european sand belt the latter processes acted for a short time and only locally the final record are holocene soils it seems that the analysed valley is a good example of palaeoenvironmental conditions in eastern europe

process based modelling of fluvial system response to rapid climate change ii application to the river maas the netherlands during the last glacial interglacial transition a comprehensive process based numerical model of catchment hydrology and alluvial channel dynamics is applied to the evolution of the river maas during the last glacial interglacial transition palaeo climatological reconstructions based on a number of climatic and environmental proxies are combined with atmospheric circulation model predictions to yield continuous time series for temperature precipitation and vegetation cover for the period of 14 9 c 14 kyr bp these climatic data are used as input for the numerical model predictions are made for discharge statistics hillslope erosion potential river channel sediment transport channel pattern and incision potential these predictions are compared with reconstructed fluvial dynamics of the maas during this time period we find that the major fluvial morphodynamical events can be explained by our model as a result of climate change induced affects however relatively high precipitation amounts during gs 1 must be applied in order to correctly predict floodplain wide incision during this period we further show by means of a number of sensitivity analyses that the uncertainty in the adopted climate reconstructions do not have a large impact on modelled morphodynamics c 2003 elsevier science ltd all rights reserved

geomorphic signal of active faulting at the northern edge of lut block insights on the kinematic scenario of central iran recent works documented neogene to quaternary dextral strike slip tectonics along the kuh e sarhangi and kuh e faghan intraplate strike slip faults at the northern edge of the lut block of central iran previously thought to be dominated by sinistral strike slip deformation this work focuses on the evidence of quaternary activity of one of these fault systems in order to provide new spatiotemporal constraints on their role in the active regional kinematic scenario through geomorphological and structural investigation integrated with optically stimulated luminescence dating of three generations of alluvial fans and fluvial terraces at 53 25 and 6 ka this study documents i the topographic inheritance of the long term myr punctuated history of fault nucleation propagation and exhumation along the northern edge of lut block ii the tectonic control on drainage network evolution pediment formation fluvial terraces and alluvial fan architecture iii the minimum holocene age of quaternary dextral strike slip faulting and iv the evidence of late quaternary fault related uplift localized along the different fault strands the documented spatial and temporal constraints on the active dextral strike slip tectonics at the northern edge of lut block provide new insights on the kinematic model for active faulting in central iran which has been reinterpreted in an escape tectonic scenario

further sulfur and carbon isotope studies of late archean iron formations of the canadian shield and the rise of sulfate reducing bacteria sulfur and carbon contents and isotope ratios are reported for five archean iron formations helen nakina and finlayson lumby and bending lake areas distributed across 850 km of the canadian shield all 2 7 ga old a 34s profile through a complete stratigraphic column oxide facies excluded of the helen iron formation shows a 34s range of 30 2 mean 34s value of 2 5 and a standard deviation i of 7 3 in sharp contrast to the sulfide and siderite facies the oxide facies in the column shows a uniform 34s value close to zero the 34s values obtained for the other four iron formations are again wide ranging highly variable in the sulfide and pyrite siderite facies but uniform and close to zero for the oxide facies the carbon in the oxide siderite chert facies has 13c values of 2 3 to 1 1 in the range of phanerozoic marine carbonates however the carbonates in the graphite rich sulfide facies have 13c values as low as 7 6 the mixing of reduced carbon with marine carbonate is suggested to explain the light carbonate values the reduced carbon associated with the light carbonate is also relatively light at up to 13corg 33 5 but is in the range of other precambrian values distal high temperature abiogenic sulfate reduction as a source of highly fractionated sulfides in the archean iron formations is ruled out on the basis of both isotopic and geologic evidence it is concluded that only the bacterial reduction of sulfate at low temperatures could produce the wide ranging highly variable 34s values exhibited by these sulfides over large areas

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

multiple climatic cycles imprinted on regional uplift controlled fluvial terraces in the lower yalong river and anning river se tibetan plateau abstract the development of fluvial systems on the southeastern margin of the tibetan plateau is linked to significant and rapid late cenozoic uplift the relatively complete fluvial terrace sequence preserved along the yalong river valley and that of its tributary the anning river provides an excellent archive for studying the development of terraces in rapidly uplifting mountainous areas this study reveals that terrace development is predominantly controlled by multiscale climate cycles and long term uplift as shown by terrace dating sedimentary characteristics and incision rates at least six alluvial terrace units were identified in 20 transverse sections through the terraces along about a 600 km length of river and were dated using electron spin resonance esr and optically stimulated luminescence osl the climatostratigraphic positions of the terrace deposits and their respective age constraints suggest that fluvial aggradation was concentrated during marine isotope stages mis 32 22 18 4 2 and the younger dryas yd and that incision occurred during the succeeding cold to warm transitions the changes in fluvial style marked by terraces 6 5 and 4 predominantly occurred in synchrony with the 100 ka milankovitch climate cycles while terraces 3 and 2 were controlled by the obliquity driven 41 ka climate cycles finally the aggradation of terrace t1 occurred in response to the yd stadial during the intervening time between 0 72 and 0 063 ma terraces either did not form or were not preserved which may suggest that uplift rates varied through time and influenced terrace formation preservation the progressive valley incision recorded by these fluvial terraces cannot be entirely explained by climate cycling alone temporal and spatial variations in incision rates indicate that the continuing long term incision has been driven by uplift the temporal distribution of the incision rates reveals two rapidly uplifting stages in the southeastern tibetan plateau including an accelerated uplift that has been taking place since 0 06 ma the spatial distributions of differing incision rates reflect the geomorphological response to crustal shortening and differential uplift in this region

linking morphology across the glaciofluvial interface a 10be supported chronology of glacier advances and terrace formation in the garonne river northern pyrenees france abstract the garonne river drains an important part of the northern pyrenees and its northern foreland we investigated the middle reaches of the garonne river establishing a detailed morphogenetic profile of its foreland terrace staircase and the preserved palaeoglacier margins we particularly focussed on the glaciofluvial interface linking also genetically the fluvial sediment archives in the foreland with the terminal glacial basin upstream of the pyrenees mountain front using cosmogenic nuclide 10be analyses two terrace exposures have been dated including a prominent fluvioglacial outwash fan at the foreland transition we identified three terminal margins of late pleistocene glacier advances the prominent garonne staircase consists of three major terrace complexes comprising eight individual terrace levels results indicate a young age of the lower terrace complex of the garonne staircase mis 4 2 the morphogenetic relationships and the new 10be exposure age constraints suggest that during the last glaciation wurmian the garonne glacier reached its maximum extent at the north pyrenean mountain front apparently already during mis 4 two different ice margins were associated with mis 2 indicating close to maximum ice extent during early mis 2 lgm and relatively stationary ice recession in the late mis 2 the extensive garonne terrace complexes formed under cold climate conditions and were abandoned by incision during major glacial interglacial transitions during warm cold climate transitions lateral erosion caused the reworking of previously abandoned palaeofloodplains the long term quaternary incision of the garonne and other north pyrenean rivers indicates that the proximal aquitaine foreland basin experienced uplift however non uniform lateral course migrations and valley asymmetries of the north pyrenean piedmont rivers indicate that uplift magnitude is variable with maximum amounts in the centre of the molasse fan of lannemezan rivers on the western part of the fan were tilted toward the west whereas rivers in the eastern part like the garonne were tilted to the east

resolving time space histories of late cenozoic bedrock incision along the upper colorado river usa abstract the upper colorado river basin drains the western slope of the rocky mountains province of north america and hosts a rich record of fluvial terraces and volcanic deposits that provide an archive of bedrock river incision since the late miocene here we present new geochronology from fluvial deposits and associated volcanic units using multiple methods luminescence cosmogenic burial 40ar 39ar basalt and detrital sanidine and u pb detrital zircon to reconstruct a detailed record of bedrock incision in the upper colorado river over timescales ranging from miocene to late pleistocene late miocene ca 11 8 ma basalt flows perched 800 1700 m above the colorado river and the oldest known ancestral colorado river deposits preserved beneath basalt flows on grand mesa provide the basis for average long term 107 yr incision rates rates range from 110 160 m ma between grand junction downstream and glenwood canyon upstream with rates decreasing upvalley intermediate scale 105 106 yr incision rates are 200 320 m m y over the past 1 3 ma and these rates are faster than the average over the past 8 11 ma short term

petrological and stable isotope studies of carbonate and sulfide minerals from the gunflint formation ontario evidence for the origin of early proterozoic iron formation abstract the 1 9 ga gunflint formation in the thunder bay district of ontario principally comprises iron formation overlain by an iron poor limestone dolostone member the upper limestone member rocks are virtually unmetamorphosed retaining primary textures except locally around diabase sills the gunflint presents an opportunity to study both unmetamorphosed and metamorphosed iron formation and to study the changes from iron rich to iron poor sedimentation of the carbonate minerals in iron rich units siderite formed at or near the sediment water interface with ankerite and calcite forming later during diagenesis and during metamorphism around sills heaviest 13c values of siderite and of dolomite in the upper limestone member are consistently near 0 throughout the stratigraphic section indicating that marine bicarbonate was the source of carbon a spread of values between 0 and 7 for unmetamorphosed rocks is the result of the incorporation of oxidized organic matter during diagenesis whereas 13c values more negative than 7 are the result of metamorphism the heaviest 18o values from unmetamorphosed rocks 5 3 pdb for siderite 6 1 for ankerite and 6 7 for calcite are considered to represent the original marine composition lighter values to 17 represent isotopic exchange reactions with pore fluids at higher temperatures and or isotopic exchange with 18o depleted meteoric water low s c ratios and a relatively narrow range of positive 34s values in pyrite throughout most of the formation are consistent with bacterial sulphate reduction of seawater containing sulphate at a significantly lower concentration than the modern ocean locally higher sulfide contents and a wider range of 34s values were the product of the introduction of sulfur after deposition it is proposed that the gunflint formation was deposited in a stratified water column with anoxic bottom water the depositional basin had restricted communication with the open ocean and was affected by distal volcanism hydrothermal activity associated with the volcanism provided a large source of dissolved iron and possibly silica which helped buffer o2 and sulphate in water to low levels low concentrations of sulphate limited the generation of h2s that would otherwise have restricted the solubility of iron during periods of increased hydrothermal activity the anoxic oxic water boundary moved upwards permitting transport of iron to the shallow shelf where it was precipitated as siderite iron hydroxides iron silicates or pyrite depending on physico chemical conditions the transition to the overlying limestone marks a decrease in hydrothermal activity with a contraction of the redox boundary

stable isotope geochemistry of early protezozoic carbonate concretions in the animikie group of the lake superior region evidence for anaerobic bacterial processes abstract thirteen carbonate concretions from the rove thomson and gunflint formations of the early proterozoic 2 0 ga animikie group in the lake superior region were analyzed for variations in carbon and oxygen isotopes the isotope data of ferroan dolomite concretions from the rove formation yield trends comparable to the isotope systematics displayed by authigenic carbonate in modern organic rich marine burial environments the isotope systematics of the ferroan dolomite concretions suggest that carbonate initially precipitated in a zone of bacterial methane production and later at greater burial depths in a zone of thermal decarboxylation recrystallization of calcite concretions in the rove and thomson formations has homogenized the oxygen isotopic composition however because the carbon system was apparently rock dominated the primary 13c signateres have been preserved calcite concretions from the rove formation display a strong correlation between 13c weight percent carbonate and position in the concretion the data suggest that these concretions formed progressively during burial in the zone of bacterial sulfate reduction sulfur isotopic analysis of pyrite disseminated in the concretions yield high positive 34s values isotopic data for the pyrite and the host concretion are consistent with models that suggest that high positive 34s values of early proterozic pyrite result from bacterial reduction of a limited supply of seawater sulfate the isotopic composition of concretions in the gunflint formation suggest early formation in a system open with respect to seawater bicarbonate the detailed isotopic study of precambrian carbonate concretions is a useful approach for investigating precambrian organic matter diagenesis and the evolution of bacteria

fluvial response to late quaternary climate changes western india we review here the fluvial response to late quaternary climatic changes in the semi arid regions of western india i e the thar desert and its margins and maharashtra the rivers in the thar desert show a spectrum of environments from gravel bedload braided to ephemeral sand bed streams to sheet flows and sheet floods while those in the thar margin and maharashtra show dominantly two modes i e braided and meandering rivers the streams became defunct and aeolian sands were deposited during periods of relatively greater aridity in the thar desert and its margins incisions occurred during the wet phases in ois 1 it is inferred that changes in the monsoon precipitation led to relative changes in the discharge and sediment supply which were routed through those in the vegetation cover and played a key role in determining the fluvial style an inter comparison of the late quaternary alluvial deposits in the semi arid regions of western india suggests a continuum of fluvial environments interrelated through a precipitation gradient further a global comparison indicates that the response of semi arid western indian rivers was synchronous with the rivers in other climatic settings

climate forcing of fluvial system development an evolution of ideas starting from traditional ideas on the climatic steering of fluvial system dynamics it appears that there are different kinds of climatic influences on system dynamics they vary from direct climatic forcing like peak precipitation to indirect like permafrost and partial forcing like vegetation vegetation or its absence and not directly climate is considered as the main cause of fluvial incision or deposition during temperate or cold periods however other external factors than climate and non climatic factors such as local basin characteristics like subsoil lithology and relief express their effects on the fluvial systems by their role in the energy balance of the river catchment finally internal factors in fluvial system evolution like thresholds and response time should not be neglected

reflection of the glacial interglacial cycle in the evolution of the vistula river basin poland a variety of factors has controlled the evolution of the vistula river valley they include climatically induced changes of the river runoff and sediment load glacial advances and rapid variations of the base level as well as the influence of the tectonic factor the first order climatic cycles are reflected in separate terrace fills the second order fluctuations may be represented by separate cuts and fills by the change of the facies or by the change in the granulometric composition the analysis of the changes in the longitudinal profile helped to discover a great variety of different valley reaches and a general tendency to smooth the long profile during the quaternary

periglacial fluvial systems in northwest europe during marine isotope stages 4 and 3 comparison of fluvial successions in river valleys dating from marine isotope mi stages 4 and 3 in a west east transect from britain to poland shows the spatial and temporal variation in palaeohydrological characteristics of northwest european river valleys during these stages mi stage 4 has been a period of deep fluvial incision following this erosion most valleys were filled during mi stage 3 with successions of gravelly river deposits britain or sand silt peat successions northwest european lowlands the sedimentology of the deposits suggests strong discharge variations caused by a nival discharge regime with pronounced spring snowmelt discharges the mi stage 3 climate oscillations generally cannot be traced in the fluvial record an incision phase of hengelo interstadial age has been found in the netherlands but similar incision phases related to other warming events have not been proved convincingly the restricted reaction of the river systems is caused by the absence of geomorphologically effective vegetation changes and relatively minor variations in precipitation during mi stage 3 over longer time scales silt and peat beds gradually decrease in the younger post hengelo upton warren part of mi stage 3 corresponding with evidence of aeolian activity and permafrost this is related to the longer duration of the stadials in this part of mi stage 3

the middle pleistocene fluvial sequence at uichteritz central germany chronological framework paleoenvironmental history and early human presence during mis 11 abstract the site of uichteritz saxony anhalt germany is a quaternary gravel quarry hosting several middle pleistocene fluvial units of the saale river this fluvial archive contains detailed information on 1 the timing of middle pleistocene fluvial aggradation and erosion periods in the region 2 the driving forces for those alternations as well as 3 early human presence indicated by the presence of lower paleolithic stone artefacts here we establish a luminescence based numerical chronology at uichteritz additionally geophysical sedimentological and micromorphological analyses were applied to obtain information on depositional and post depositional processes of the fluvial sequence our results point to several fluvial aggradation periods between ca 420 and 180 ka a first fluvial unit was deposited during the late elsterian period followed by formation of a luvisol during mis 11 and its fluvial reworking at the transition from mis 11 to mis 10 and or during early mis 10 these mis 10 11 deposits with an age of about 400 ka also contain reworked lower paleolithic stone artefacts that document the initial appearance of humans in northwestern central europe during mis 11 after a period of fluvial incision during mis 10 which was accompanied by a change in the course of the saale river several stacked fluvial sequences of the saalian main terrace smt formed between mis 8 and mis 6 mainly during cold climatic periods our age estimates confirm the correlation of the elsterian ice advances with mis 12 and the saalian ice advances with later mis 6

quantifying fluvial non linearity and finding self organized criticality insights from simulations of river basin evolution abstract a numerical study was undertaken to investigate non linearity and the potential for self organized criticality soc in the evolution of river basins twenty three simulations were carried out using the authors caesar landscape evolution model in which the magnitude of storm events variability of storm events sediment heterogeneity sources of sediment supply and catchment morphology are systematically varied to evaluate their importance as possible drivers for non linear behavior and soc temporal fluctuations in simulated sediment yield show notable non linear behavior storm magnitude and occurrence of landslides appear to have little impact on variability of the sediment yield when compared to the impacts of sediment heterogeneity rainfall variability and catchment morphology particularly it appears that the non linearity of sediment yields results from the manner in which the catchment processes the variable rainfall rather than just the rainfall variability itself the variations in sediment yield show a power law magnitude frequency distribution which is a possible but inconclusive indicator of soc however several other more qualitative arguments can be made to support the case for soc in these simulations specifically we identify the nature of the critical state and suggest two cascade mechanisms by which the system can organize itself around this critical state combined these arguments indicate that simulated evolution of river basins indeed exhibits soc at least with respect to sediment yield the critical state appears to be an indicator of the connectivity of the drainage network thus the simulations indicate that unlike traditional soc systems the critical state of the system can vary in time as sudden changes in drainage network connectivity may result in sudden changes in the soc behavior of the system

sulfur and carbon isotopes in archean banded iron formations implications for sulfur sources abstract sulfur isotope ratios of pyrite from two late archean banded iron formations were used to constrain possible sources of sulfur the iron formations studied were the temagami iron formation which hosts the sherman mine near temagami and the boston iron formation including the adams mine south of kirkland lake both in ontario in both cases algomantype oxide facies magnetite chert ores predominate the sulfur studies were supplemented by limited carbon isotopic data for the sherman mine iron formation in the sherman mine occurs on both limbs of a regional synformal structure each iron formation unit caps a thick calc alkaline andesite dominated volcanic sequence with one band hosted in sedimentary rocks of turbidite origin the adams mine includes four major iron formation bands interbedded with mafic and ultramafic volcanic rocks and greywacke of turbidite origin the sulfur isotope statistics for averages of pyrites from these three units are sherman mine volcanic hosted suite 34 s 1 7 4 6 n 14 sherman mine sediment hosted suite 34 s 1 4 1 6 n 43 and adams mine 34 s 1 8 2 9 n 17 these averages differ by from juvenile sulfur and together with their limited dispersions suggest a predominantly unfractionated source of sulfur it is argued that this sulfur has been derived from the associated volcanic piles most of the pyrite occurs as disseminated grains in oxide facies iron formation and interbedded clastic sediments a distinctive nodular pyrite in the sherman mine sediment hosted suite occurs in cherty graphitic sulfide facies iron formation while the sulfur isotopic properties of this subset 34 s 0 0 0 8 are not suggestive of biogenic sulfur the geological setting and carbon isotopic compositions of associated graphite 13 c 34 imply that anaerobic bacterial processes were active in this reducing environment the apparent lack of biogenic sulfide is rationalized by models suggesting that archean marine basins differed from phanerozoic analogues in various parameters which influence sulfur isotopic characteristics it is argued that biogenic sulfide is probably a significant component of the sulfur in sherman mine nodular pyrite

changing river styles in response to weichselian climate changes in the vecht valley eastern netherlands abstract in the vecht valley eastern netherlands distinct changes in fluvial style and erosional phases took place from the middle part pleniglacial of the last glacial to the holocene a low energetic laterally inactive river changed around 41 ka into a higher energetic river accompanied by a distinct erosional phase even higher energetic conditions occurred during the late pleniglacial when a braided river was active fluvial activity diminished in the vecht valley towards the end of the late pleniglacial as aeolian processes became much more dominant the river became confined to a much more narrow flood plain where it incised at the onset of the late glacial deposits of two kinds of river types can be recognized in the late glacial low energetic probably meandering and braided the vecht became and remained meandering during the holocene the observed fluvial changes and erosional phases are most likely the result of climatically induced changes in the water sediment discharge ratio several distinct climate changes occurred since the middle pleniglacial some of them not all are reflected by changes in fluvial styles the response of vegetation to climate changes appears to be an important factor as it determined bank and soil stability and therefore sediment supply but also evapotranspiration rates which influenced discharge characteristics a model explaining the fluvial response to climate change is presented and discussed by the example from the vecht river incision took place at the onset of a cooler period when the discharge increased before the vegetation cover was destroyed incision also occurred as a response to warmer climate conditions but with a time lag depending on the time needed to establish a vegetation cover dense enough to decrease sediment supply and increase evapotranspiration rates

climate and related controls on interglacial fluvial sedimentation in lowland britain lewin john gibbard p l 2002 climate and related controls on interglacial fluvial sedimentation in lowland britain sedimentary geology 151 3 4 pp 187 210 rae2008

late quaternary linkage of sedimentary records to three astronomical rhythms and the asian monsoon inferred from a coastal borehole in the south bohai sea china abstract the bohai sea was formed by subsidence during the cenozoic some 2000 3000 m of fluvial lacustrine and marine sediments has been deposited in this basin previous studies focused mainly on the transgression history with little examination of orbital variation in relation to other areas within the asian monsoon domain here we present the late quaternary results of a new borehole in the south bohai sea optically stimulated luminescence and radiocarbon dating which provide concordant age estimates were employed to generate an initial chronology for the borehole after refining the chronology through astronomical tuning the results showed that 1 the grain size variation represents asian monsoon intensity which was dominated by both solar insolation major and global ice volume minor forcing 2 the magnetic susceptibility indicates river incision processes which were sensitive to orbital tilt with influence from solar insolation 3 the vegetation coverage responded to global ice volume coupled obliquity changes and that 4 neither external nor internal factors could dominate the paleoenvironmental evolution on orbital timescales in an independent way and they are both integrated in a complex pattern we conclude that three different astronomical rhythms have affected coastal evolution and that the sedimentary records in the south bohai sea china result from the nonlinear interaction and the complex response to driving processes

assessing tectonic and climatic controls for late quaternary fluvial terraces in guide jianzha and xunhua basins along the yellow river on the northeastern tibetan plateau abstract this study focused on well preserved fluvial terrace sequences that span the past 100 ka in the guide jianzha and xunhua basins along the yellow river that drained the northeastern tibetan plateau new geomorphic stratigraphic sedimentologic and chronologic data from twelve depositional sequences within terraces yielded better constraints on rates of incision degradational and aggradational phases for the yellow river age control was established by sixteen osl ages on quartz grains from fluvial sediments three fluvial aggradational phases were identified between 100 and 80 ka 53 and 40 ka and 21 and 12 ka associated with terrace levels respectively at 120 to 95 61 to 45 and 25 to 15 m above river level these aggradational phases reflect multiple processes including enhanced fluvial discharge sediment availability with glaciation deglaciation and increased monsoonal precipitation the initiation of fluvial degradation was linked to mega floods released from landslide dammed lakes at ca 76 38 and 16 ka though these changes may also reflect variations in sediment load discharge relations with climate change the apparent net incision rate is 1 13 0 11 mm yr for the past 100 ka and is consistent with late cenozoic tectonic uplift rates 0 5 2 mm yr and recent gps based rates the fluvial dynamics of the upper reach of the yellow river was variably controlled by climate induced changes in discharge sediment load relations on stadial to interstadial timescales episodic mega floods from the breach of landslide dams and with net incision in the past 100 ka in response to tectonic uplift of the tibetan plateau

river response to variations of periglacial climate in mid latitude europe abstract the last glaciation was characterised by considerable changes in climate many european river basins reacted to these changes by initial incision and subsequent pattern change earlier research explained this by the time lag of vegetation development after a climatic change which considerably affected the sediment load however since some river basins react differently or do not react at all this model needs to be refined this paper deals with the fluvial evolution of several rivers in northern and central europe during the last glaciation and two of them the weise elster river in the leipzig area and the spree river in the niederlausitz germany are discussed in more detail the vegetation cover on the floodplain in combination with the presence of frozen ground which affects the discharge characteristics largely determines the river type nevertheless when the sequences are compared not only synchronous changes in fluvial development may be observed but also distinct differences in fluvial development by analysing the different rivers in their varying geomorphological settings it appears that grain size basin configuration and catchment size are important parameters also which can determine whether a threshold is exceeded or not

isotopic composition of disseminated sulfur in precambrian sedimentary rocks abstract isotopic analyses of trace sulfur in precambrian carbonates and clastic sedimentary rocks support the results of previous studies which have shown that 34s measurements of archean sedimentary sulfur cluster mostly around mantle like values and that a significant overall dispersion of 34 s 32 s ratios commenced at about 2 7 ga ago the outstanding feature of the proterozoic record is the predominance of heavy 34ssulfide values mostly in excess of 0 cdm consideration of these data in combination with the sparse 534s record for proterozoic sulfates suggests that 34ssulfide sulfide may have been smaller than was the case during the phanerozoic a possible scenario that is compatible with the above data is based on a proposition that the terrestrial exogenic sulfur cycle evolved in a tripartite manner in the archean it was coupled to and controlled by the magmatic endogenic cycle the proterozoic for the most part represents a transitional stage into a phanerozoic like exogenic cycle the latter essentially decoupled from its endogenic counterpart and its redox balance maintained and mediated by the biosphere the indication that the mean combined 34s of proterozoic sulfate and sulfide may have significantly exceeded the phanerozoic mean value of 2 cdm is enigmatic and poses problems for balance considerations

microbial dolomite precipitation using sulfate reducing and halophilic bacteria results from qinghai lake tibetan plateau nw china past studies have revealed the important roles of certain types of microbes in precipitating dolomite in coastal hypersaline lakes and lagoons and marine sediments however it is still poorly known if other types of microbes can precipitate dolomite in low salinity lakes without any marine influence the objective of this study was therefore to expand the microbial dolomite precipitation model by investigating the origin of dolomite in the sediments of qinghai lake an inland slightly saline lake salinity 12 5 g l on the tibetan plateau nw china this objective was accomplished via an integrated approach combining geochemical investigations of natural dolomite present in the lake sediments with laboratory precipitation experiments a 5 m sediment core was collected and pore water chemistry was analyzed calculation of saturation index indicated that dolomite was oversaturated in sediment pore water sub spherical grains of dolomite with abundant pores and microstructures similar to microbially precipitated dolomite were found in the sediments suggesting a biogenic origin dolomite precipitation experiments were set up in the laboratory to simulate the natural conditions of the qinghai lake dolomite was precipitated using sulfate reducing bacterium srb desulfotomaculum ruminis and aerobic halophilic bacterium halomonas marina present in the qinghai lake sediments aqueous geochemistry and mineral characterization data collectively suggest that dolomite precipitation was accomplished via increase of ph and alkalinity to overcome the kinetic inhibitors and exopolymeric substances eps and cell walls as possible nucleation sites these results expand the current microbial dolomite precipitation model and have implications for dolomite formation in slightly saline inland lake environments

sulfur isotopes in early proterozoic volcanogenic massive sulfide deposits new data from arizona and implications for ocean chemistry the 34s range of sulfides from early proterozoic volcanogenic massive sulfides of arizona is narrow 129 out of 133 measurements lying within a range of 2 8 to 3 2 other early proterozoic and archean deposits of comparable type and mineralogy have similar s isotope characteristics these deposits unlike phanerozoic analogues do not appear to have incorporated reduced sulfur derived from marine sulfate early proterozoic oceans are known to have contained sulfate in this paper it is a major tenet that sulfate was confined to an upper water layer it is proposed that most volcanogenic massive sulfide hydrothermal systems prior to 1 7 ga were recharged with sulfate free water from an anoxic lower layer and in general discharged into reducing environments rare deposits with exceptional mineralogy or s isotope compositions may reflect hydrothermal recharge from the oxidized upper layer or deposition from fluids discharging into and mixing with the upper water layer

lateglacial changes in river morphologies of northwestern europe an example of a smooth response to climate forcing cher river france climatic oscillations occurring during the pleniglacial and lateglacial periods are generally associated with several changes in fluvial morphology and processes this study investigated two reaches of the cher river basin noyers sur cher and thenioux regarding morphological adjustments during the lateglacial period and the early holocene transitions from the pleniglacial to the lateglacial and from the lateglacial to the early holocene ca 14 700 11 500 cal bp are considered as interesting study cases because it consists of rapid and abrupt climate oscillations generally clearly recorded in current floodplains the sites studied are located in the cher river floodplain which is one of the main tributaries of the loire river several investigations have been conducted in the main valley but few of them specifically focused on geomorphological evolutions of medium sized catchments such as tributaries of the loire river therefore we examined this specific period through investigations recently conducted in the middle valley of the cher river this study aimed to 1 provide a geomorphological approach to fluvial adjustments during the lateglacial from cases located in lowland areas of a medium sized basin and 2 analyse the spatio temporal variability of fluvial responses assessment of geomorphological trajectories of the two reaches studied highlights that fluvial metamorphosis occurring during the lateglacial and early holocene seems to be characterised by lateral readjustments and a low signal of morphological instability shallow incision and aggradation processes slow and progressive change in channel morphology this observation is enhanced by the comparison with known geomorphological evolution patterns of adjacent basins the intrinsic components of the cher basin such as slope and valley width were considered as explanatory factors for the lack of morphogenetic processes in addition the geographical location of the reaches studied may also have led to a moderated expression of climate forcing indeed the elevation as well as the north south and east west gradients may contribute to the low level of geomorphological adjustments in response to these climatic oscillations this gradient could also have support this the fluvial response because of the weakly developed loess cover which may have limited the fine sediment supply and the aggradation of the valley bottom

interpreting drivers of change in fluvial archives of the western mediterranean a critical view abstract fluvial archives in particular late glacial to holocene floodplain records may provide valuable information regarding past environmental conditions and stages of landscape evolution in view of the high significance of floodplain dynamics for the development of entire landscapes the number of studies that have been performed on floodplain sediments remains comparatively low especially regarding the western mediterranean region however one of the reasons could be seen in the high complexity and diversity of processes and factors that control and influence fluvial activity that often hampers a straightforward interpretation of floodplain dynamics therefore a basic demand on fluvial archive research is to address the complexity of the factors that control the characteristics of fluvial sequences in order to provide a robust basis for their interpretation as a starting point for discussion this paper aims to give an overview of fluvial dynamic patterns in the western mediterranean for the last 15 ka in order to examine their relevance for palaeoenvironmental reconstructions the basis for this is provided by previous investigations on four different river systems in spain and northern africa the results of which are herein synthesized in order to propose a regional late pleistocene and holocene fluvial history for the western mediterranean realm basic results are related to alluvial floodplain deposits and visible features within them such as alluvial soils incision marks and aggradation phenomena since fluvial systems are open systems we discuss our findings against the background of different influencing factors that could modify fluvial architecture and may restrict palaeoenvironmental reconstructions a more comprehensive interpretation focuses on signals that are common to each of the studied river systems in this respect we critically discuss the customary nature of cumulative probability functions for the identification of regional flooding episodes and point out the benefits of a stratigraphy supported approach for characterizing regional floodplain dynamics finally three alluvial soil formation periods were found in all settings a first phase after 15 ka ending with the younger dryas event a second one from 7 to 5 ka with a break between 6 5 and 5 5 ka and a third phase between 3 and 2 ka these soil formation periods were interrupted and framed by fluvial dynamic phases accompanied by channel aggradation floodplain deposition floodplain erosion and or river incision in particular after 5 ka around 1 6 and at 1 ka and during the little ice age lia floodplain aggradation affected river systems in iberia and northern africa as well a cautious assessment of these results and extensive comparisons with secondary archive information prompts us to relate the aggradation periods with climate forcing by means of a supra regional aridification that effected large areas of the western mediterranean in contrast the three mentioned soil formation periods can be linked with landscape stability most probably triggered by favorable climate conditions in the western mediterranean apart from these large scale patterns we discuss the reliability of information emerging from floodplain records against the background of individualistic river behavior and self organization regarding future work we want to emphasize the great potential of yet rarely applied system oriented approaches that also attach importance to sub catchment dynamics as a link between catchment slopes and the main river floodplain

last glacial interglacial cycle in the evolution of river valleys in southern and central poland abstract the last glacial interglacial cycle is represented usually by several cuts and fills which have formed 2 3 terrace steps from the last cold stage and by two or more fills of lateglacial holocene age their number depends on the size of the river valley and the position in the longitudinal profile the sequence of changes reflects shorter stadial interstadial climatic fluctuations generally aggradation dominates during the cooler phases of the vistulian and during the interpleniglacial the most distinct erosional phases occurred during the change from a more oceanic to a more continental climate before the maximum extension of the ice sheet 25 20 ka bp and during the upper pleniglacial lateglacial transition 15 13 ka bp the second phase coincides with the rapid downcutting in the lower course of the main vistula valley which had been blocked earlier by the scandinavian ice sheet in the holocene aggradation prevailed accelerated by anthropogenic soil erosion it was only in the mountain foreland that shorter lived hydrological changes resulted in well expressed several cuts and fills

multiple sulfur isotopes and the evolution of earth s surface sulfur cycle abstract the distribution of sulfur isotopes in geological materials reveals information about earth history and biogeochemical processes research during the last several decades has used sulfur isotope geochemistry as a tool to better understand microbial processes harrison and thode 1958 kaplan 1975 monster et al 1979 peck 1959 peck 1962 rees 1973 and sediment diagenesis berner 1969 berner 1982 canfield et al 1993b earth historians also realized this potential as there exists a rich record of environmental change within the sedimentary records canfield and teske 1996 claypool et al 1980 goodwin et al 1976 habicht et al 2002 kah et al 2004 monster et al 1979 shen et al 2001 strauss 1993 thode and goodwin 1983 these applications have championed the use of the two most abundant sulfur isotopes 32s and 34s and provide a rich introduction to what the sulfur isotope record has to offer see canfield 2004 canfield and raiswell 1999 within the last decade this information has been supplemented by new data derived from the less abundant isotopes 33s and 36s the measurement of all four stable sulfur isotopes multiple sulfur isotope geochemistry has expanded our understanding of biological evolution and activity atmospheric chemistry and transport crustal recycling and many more fields related to earth surface processes see farquhar and wing 2003 here i present a review of recent works in multiple sulfur isotope geochemistry with a focus on results that inform our understanding of biogeochemical processes and earth surface evolution

carbon and sulfur isotopes in precambrian sediments from the canadian shield carbon and sulfur isotope ratios have been determined for more than 200 samples of precambrian graphitic and sulfidic metasediments from the superior and churchill provinces of canada the sediments were deposited in small sedimentary basins related to various canadian greenstone belts the age of the archean samples is approximately 2 7 ga the proterozoic samples about 1 8 ga the archean organic material shows c isotope values between 47 and 15 vs pdb the proterozoic metasediments show a smaller range with 13c between 30 and 17 a few carbonate samples yielded c isotopic compositions between 5 9 and 4 7 associated iron sulfides have 34s values ranging from 6 to 8 which are consistent with isotopic fractionation effects either by inorganic or bacterial reactions in the sedimentary sulfur cycle the great variability of organic c isotopic composition especially in the late archean although affected by extensive postdepositional alteration might indicate differences in the environmental conditions and or the organic content of these sedimentary basins some extremely 13c depleted organic carbon values support a global occurrence of environments likely dominated by methanotrophic organisms at the end of the archean

iron framboids in the hydrocarbon related middle devonian hollard mound of the anti atlas mountain range in morocco evidence of potential microbial biosignatures iron framboids in the context of a middle devonian hydrocarbon seep conical mound anti atlas morocco have been thoroughly investigated through a combination of techniques including optical and high resolution scanning electron microscopy x ray diffraction energy dispersive x ray spectroscopy raman microscopy and time of flight secondary ion mass spectroscopy framboids occur embedded in laminated carbonates of the mound and are precipitated along the veins that crosscut it and served as the conduits for channeled reduced hydrocarbon rich fluids the morphology structure and composition of the framboids contribute to the reconstruction of the complex interplay between the advected fluids and the associated biological and or abiological processes a comparison of our dataset with that from modern framboids formed under similar conditions indicates that the fe rich framboids represent replaced primary pyrite framboids produced as a consequence of bacterial sulfate reduction and the anaerobic oxidation of methane

climatic and morphological controls on diachronous postglacial lake and river valley evolution in the area of last glaciation northern poland abstract the wda river valley in northern poland is a polygenetic valley located in a former subglacial meltwater channel that after ice sheet retreat hosted separate and then interconnected lake basins subsequently replaced by a river in one part of the river system an abandoned lateglacial valley is found this dry valley is a unique feature in the area located within the limit of the scandinavian ice sheet during the last glaciation in the central european lowland we investigated lacustrine and fluvial sediments and landforms in the valley and applied palynological analysis combined with radiocarbon dating to reconstruct the valley evolution from the early period of river inception in the lateglacial through the formation of lakes during the pleistocene holocene transition up to the establishment of a modern river system in the early holocene three coeval processes were identified 1 formation of lake basins in the subglacial channel connected by a river 2 erosion of the river bed between the lakes and 3 sediment deposition at the mouths of the channels in the lake basins first generating delta fans and eventually filling the lakes entirely the valley formation was associated with diachronous melting of dead ice blocks buried in the subglacial channel controlled by the capacity of the hydrological system to evacuate the meltwater most of the lake basins in the study area were formed during the bolling allerod period but one section of the subglacial channel not affected by thermokarst processes survived protected by dead ice blocks throughout the entire lateglacial accelerated dead ice decay at the beginning of the holocene triggered widespread lowering of the base level which caused lake disappearance and the formation of the modern river system the processes reconstructed in the central section of the wda river indicate a highly dynamic and diachronous river valley development during the lateglacial and early holocene whereby the valley formation was interwoven with the formation of lake basins within the valley triggered by melting of dead ice blocks in the substratum

two sulphur isotope provinces deduced from ores in the mount isa eastern succession australia the sulphur isotopic characteristics of ore deposits in the australian mount isa eastern succession are not well known unlike those of the western succession in this study new detailed analyses are provided for recently discovered eastern succession mineralisation such as the starra and osborne bif hosted cu au ores the dugald river sediment hosted pb zn prospect and four vein hosted cloncurry style cu au deposits hampden mt elliot swan mt cobalt and the answer mine all of the deposits of the eastern succession have 34ssulphide between 8 and 9 regardless of their genesis empirically a moderate 34s range averaging close to 0 characterises starra style cu au and pegmont pb zn bif ores whereas shear and vein style cu mineralisation populations are tighter and do not average close to 0 this is a particularly surprising result for dugald river where a larger isotopic variation more typical of stratiform sediment hosted pb zn ores in the region might have been expected by comparison western succession stratiform pb zn and vein style cu deposits span a huge range of 15 to 51 large sulphur isotope ranges typify sulphate evaporite or organic sulphur rich sedimentary successions the lack of such variation in the eastern succession in turn suggests that primary evaporite sequences there were halite dominated but sulphate poor and or contained only limited volumes of organic sulphur rich sediment eastern succession sequences were therefore less likely hosts for giant stratiform pb zn deposits because of their paucity of sulphur although local sulphur sources permitted small deposits such as dugald river to develop sedimentary conditions were more favourable for the development of sulphur poor synsedimentary hydrothermal systems such as starra osborne and pegmont although sulphur isotope evidence is equivocal about the origin of these epigenetic deposits close to the williams batholith mt dore hampden owe their clustering around 0 to their granitic fluid source

an integrated field and numerical modelling study of controls on late quaternary fluvial landscape development tabernas southeast spain the variability of quaternary landforms preserved in the tabernas basin of southeast se spain raises numerous questions concerning the roles of external forcing mechanisms e g tectonics and or climate and internal landscape properties e g lithological controls in the evolution of the basin wide fluvial system over late quaternary timescales in this study we apply the fluver2 numerical model to investigate the significance of these landscape controls upon patterns of landscape evolution we highlight the complications of generating realistic input datasets for use in the modelling of long term landscape evolution e g discharge and runoff datasets model outputs are compared to extensive field mapping of fluvial terraces their sedimentary architecture and optically stimulated luminescence dating results of the terraces the results demonstrate the significance of non linear rates of flexural tectonic uplift towards the west of the tabernas basin which have controlled base levels throughout the quaternary and promoted the formation of a series of diverging fluvial terraces our numerical model results further highlight the importance of climate cycles upon river terrace formation basin wide aggradation events were modelled during the transition from marine isotope stage mis 6 to 5 and the last glacial maximum lgm as supported by field evidence this aggradational pattern supports the regional hypothesis of terrace formation during global glacial cycles and cold to warm stage transitions and supports the use of sea surface temperature climate proxy data in the modelling exercise the availability of sediments derived from the surrounding hillslopes and adjacent alluvial fans explains the generation of substantial terrace aggradations copyright 2015 john wiley sons ltd

multiple sulfur and carbon isotope composition of sediments from the belingwe greenstone belt zimbabwe a biogenic methane regulation on mass independent fractionation of sulfur during the neoarchean abstract to explore the linkage between mass independent sulfur isotope fractionation mif s and 13corg excursions during the neoarchean as well as the contemporary redox state and biogeochemical cycling of carbon and sulfur we report the results of a detailed carbon and multiple sulfur 34s 33s 36s isotopic study of the 2 7 ga manjeri and 2 65 ga cheshire formations of the ngezi group belingwe greenstone belt zimbabwe multiple sulfur isotope data show non zero 33s and 36s values for sediments older than 2 4 ga i e prior to the great oxidation event goe indicating mif s thought to be associated with low atmospheric oxygen concentration however in several 2 7 2 5 ga neoarchean localities small scale variations in mif s signal magnitude seem to correlate with negative excursion in 13corg possibly reflecting a global connection between the relative reaction rate of different mif s source reaction and sulfur exit channels and the biogenic flux of methane into the atmosphere during periods of localized microbiologically mediated shallow surface water oxygenation the manjeri formation black shales studied here display a wide range of 13corg between 35 4 and 16 2 average of 30 3 6 0 1 while the cheshire formation shales have 13corg between 47 7 and 35 1 average 41 3 3 1 the 34s values of sedimentary sulfides from manjeri formation vary between 15 15 and 2 37 average 1 71 4 76 1 showing very small and mostly negative 33s values varying from 0 58 to 0 87 average 0 02 0 43 1 cheshire formation black shale sulfide samples measured in this study have 34s values ranging from 2 11 to 2 39 average 0 25 1 08 1 and near zero and solely positive 33s anomalies between 0 14 and 1 17 average 0 56 0 29 1 moreover 36s 33s in the two formations are comparable with a slope of 1 38 manjeri formation and 1 67 cheshire formation respectively this differs from the archean reference line i e 0 9 the sulfur and carbon isotopic signatures recorded here likely reflect different environmental conditions and or ecosystems within the sampled cheshire and manjeri formations paleofacies the differences in carbon isotopes in different sedimentological facies are interpreted as recording different metabolic pathways including photosynthesis methanogenesis and methanotrophy low 13corg values in the cheshire formation black shales suggest a strong influence of methanotrophy likely preceded by bacterial methanogenesis while the large range of manjeri formation 34s may record bacterial sulfate reduction the c and multiple s isotopic variations recorded here may imply different patterns of c and s fractionation perhaps dependent on variations in the biogenic egress of methane to the atmosphere

microbial fixation of methane carbon at 2 7 ga was an anaerobic mechanism possible 1 in earth s history the most extreme episode of 13c depletion in sedimentary organic matter occurred about 2 7 billion years ago this isotopic excursion is widely interpreted as resulting from increased burial of organic carbon derived from microbial fixation of 13c depleted methane modern microbial physiologies involve either oxygen or sulfate as electron acceptors in such processes until now the isotopic signal has been exclusively assigned to growth of aerobic methanotrophic bacteria and consequently interpreted as an indication for the presence of molecular oxygen in late archaean surface environments the alternative anaerobic pathway involving sulfate as the electron acceptor was dismissed because this process has been considered inefficient in producing biomass sufficient to account for significant fractions of 13c depleted carbon in some archaean rocks calculations based on recent findings at two modern sites now show however that anaerobic processes could account for the archaean signal

the role of permafrost and seasonal frost in the hydrology of northern wetlands in north america abstract wetlands are a common landscape feature in the arctic subarctic and north temperate zones of north america in all three zones the occurrnce of seasonal frost results in similar surface water processes in the early spring for example surface ice and snow generally melt before the soil frost thaws causing melt water to flow into depressions over the land surface and at times across low topographic divides however evapotranspiration and ground water movement differ among the three climatic zones because they are more affected by permafrost than seasonal frost the water source for plants in the arctic is restricted to the small volume of subsurface water lying above the permafrost although this is also true in the subarctic where permafrost exists where it does not plants may receive and possibly reflect more regional ground water sources where permafrost exists the interaction of wetlands with subsurface water is largely restricted to shallow local flow systems but where permafrost is absent in parts of the subarctic and all of the temperature zone wetlands may have a complex interaction with ground water flow systems of all magnitudes

quantification of quaternary vertical movements in the central pannonian basin a review of chronologic data along the danube river hungary abstract this study aims at a new quantification of neotectonic deformation of the central part of the pannonian basin we use terrace levels and associated travertine as well as speleothem data along the danube river to quantify its incision rate and thus estimate the amount and rate of uplift at the axis of the hungarian mountain range hmr several terrace levels and other geomorphic features along the danube river are indicative for quaternary uplift of the axial part of the emerging hungarian mountain range while the correlative terraces are at considerable height at the axis of the hmr the terraces are gradually dipping below the basin fill of the adjacent lowlands the correlation of the terrace segments is difficult because of their poor preservation small size and variable height the geomorphologic horizons indicate gradual incision of the river throughout the quaternary during simultaneous deformation however no reliable chronological data have been available so far to quantify landscape forming processes such as uplift incision or erosion rates a reconsideration of existing published data for three consecutive segments of the danube valley yields incision rates between 0 14 and 0 41 mm year for the last 360 ky with the highest value for the area of the danube bend accordingly the middle to late quaternary uplift rate of the axial zone of the hmr exceeded significantly that of the marginal areas these rates represent an approximation as some quantitative data are still controversial our results suggest that formation of the danube terraces is result of river incision triggered by the uplift of the hmr and modified by periodic climate changes

paleomorphological and botanical evolution of small lowland valleys a case study of the mark valley in northern belgium abstract the sequence of fluvial activity in the lowland rivers is investigated by the case study of the mark valley at least five erosion sedimentation cycles from the middle pleistocene up to now are recognized in a detailed geological cross section made by handborings the organic accumulations of the holocene floodplain and a deep late glacial incision are pollenanalytically investigated they allow the reconstruction of the vegetational history and paleoecological evolution of the mark valley from the alerod to the atlantic the valley form and sedimentary environment at each cycle explain the morphology of the valley

fluvial connectivity and climate a comparison of channel pattern and process in two climatically contrasting fluvial sedimentary systems in south africa abstract the aim of this research was to investigate the dynamics of valley formation sediment delivery and channel pattern in two climatically contrasting fluvial sedimentary systems in south africa each system comprised a network of headwater valley fills and floodplains underlain by sedimentary karoo supergroup rocks that are intersected by resistant dolerite dykes and sills the seekoei river floodplain and gordonville valley fill site in the great karoo however experience less than half the annual precipitation of the nsonge river floodplain and hlatikhulu valley fill in the kwazulu natal drakensberg foothills furthermore rainfall is more variable in the karoo despite climatic differences headwater valley fills were geomorphically similar in contrast floodplains in the two regions were vastly different even when the same downstream control a resistant dolerite intrusion crossing the drainage line was considered upstream of a dolerite dyke the nsonge river is highly sinuous and located in a wide floodplain that has been carved by lateral planation of the underlying bedrock in comparison the seekoei river located upstream of a dolerite sill is discontinuous and characterized by floodouts and avulsing distributaries that undergo periods of bedrock incision followed by infilling it is likely that this disparity is caused by the inability of infrequent unsustained flows to develop meanders and thus adjust the channel planform to changes in discharge sediment load and valley slope flow variability thus exercises a strong control on channel pattern and causes floodouts in headwater settings and the semi arid karoo floodplain as a result sediment transport in the seekoei river is likely to be episodic and net retention of sediment in the semi arid floodplain is greater than in the sub humid nsonge river floodplain where sediment depth is limited

response of the selle river to climatic modifications during the lateglacial and early holocene somme basin northern france abstract research on lateglacial sequences from the selle valley leads to an overview of its evolution in relation to climatic variations between the end of the weichselian upper pleniglacial and the beginning of the holocene the first major modification of the fluvial morphology is dated at the upper pleniglacial lateglacial transition 13 000 14 c yr bp at that time the response to climatic improvement and environmental modifications is marked by downcutting and evolution from a braided river to a transitional river pattern bolling infilling in the newly created channels after a short cold phase recorded in a thin calcareous bed at the top of the bolling peat attributed to the older dryas dr ii the allerod is characterized by the deposition of organic overbank silts within a large single channel meandering system in lower slope environments this period is also marked by slow rates of colluvial accumulation and by the development of upbuilding soils allerod soil on the other hand the end of the lateglacial is characterised by the infilling of the whole valley by fine calcareous overbank silts during the younger dryas cold phase overflow of a large single channel and lateral input of chalk mud a second major downcutting phase occurs at the beginning of the holocene at around 10 000 bp in parallel with another rapid climatic improvement and the renewed spread of vegetation from a general point of view the evolution of fluvial environments in the selle valley is comparable with many other river valleys in nw europe showing that fluvial systems react very quickly to climatic variations of short duration 1000 to 100 years finally in the upper selle river incision events occur clearly before the main modifications of the vegetal cover they are most likely linked to a rapid shift in the balance between water discharge and sediment supply caused by climate modifications shift to more temperate and oceanic conditions and the resulting environmental changes cessation in aeolian sedimentation strong reduction of slope processes permafrost disappearance and soil development

uranium bearing stratiform organic matter in paleoplacers of the lower huronian supergroup elliot lake blind river region canada the elliot lake blind river ontario paleoplacer deposits in the basal matineda formation lowermost member of the 2 25 2 45 ga old huronian supergroup contain organic matter chemically consistent with kerogen this substance is also referred to as thucholite uranium ores and some gold occur here and these minerals may be in close association with the kerogen two uraniferous and auriferous stratiform kerogens obtained from the denison mines limited s denison mine and rio algom limited s stanleigh mine have been analyzed by combined high vacuum pyrolysis gas chromatography mass spectrometry and by neutron activation the reflectances of these samples have also been determined related samples containing dispersed kerogen have been examined by backscattered scanning electron microscopy the polymer like matrix of the two stratiform kerogens consists of aromatic alkyl aromatic hydrocarbon and sulphur moieties and contains 20 and 32 uranium with gold abundances in the parts per billion range

sensitivity of weichselian fluvial systems to climate change nochten mine eastern germany abstract this paper aims to contribute to the understanding of fluvial system response to climate change during the last glacial interglacial cycle fluvial and aeolian successions have been studied in the opencast brown coal mine nochten in eastern germany an absolute chronology was established by luminescence and 14 c dating enabling to demonstrate the relations between depositional units and changes in sedimentary environment over time with regional climatic and vegetational changes it is concluded that the major climatic periods coinciding with the oxygen isotope stages are generally reflected in the fluvial sequence by distinct fluvial environments major climatic changes oxygen isotope stage boundaries have been preserved in the fluvial record as erosional bounding surfaces and by changes in fluvial style rapid climate changes like the middle pleniglacial dansgaard oeschger cycles are in general not reflected in the fluvial succession these cycles were too short or with too low amplitude to cause a strong vegetational response and related changes in water and sediment supply it is emphasized that also the preservation potential of short lived climatic warming events in high energy fluvial systems is low warming events may however have been preserved in lacustrine successions in former thermokarst lakes a strong cooling event at ca 40 ka leading to continuous permafrost conditions and changes in the water and sediment budget was reflected in the fluvial archive by a change from sandy anabranching to braided river conditions

channel changes in the jarama and tagus rivers central spain over the past 500 years abstract long term channel changes of the tagus and the jarama rivers in central spain were studied in relation to variations in hydroclimatic factors such as rainfall and flooding and also with respect to human activities undertaken in their valleys data were taken from historical 1580 1823 and topographical 1877 1988 maps as well as aerial photographs 1945 1999 the available hydroclimatic data consists of a series of monthly rainfall totals 1859 1994 and mean river flow values recorded at gauging stations 1911 1985 in addition a historical flood record 1550 1947 was produced from documentary sources some of the data was incorporated into a geographical information system gis to quantify the changes in the course of the rivers the results show there have been two distinct periods before and after human intervention in the river system which took place around 1950 during the earlier period 1550 1950 a correlation exists between climate frequency and magnitude of flooding and changes in fluvial geomorphology between 1860 and 1892 an increase in flood frequency and magnitude occurred which produced half of the cut offs recorded in the study area between 1823 and 1877 the meanders length l width w and radius of curvature rc of the tagus river have decreased since 1750 however those of the jarama reached their maximum values during flood periods both rivers have different geomorphological responses during flood events which can explain these different trends floods in the jarama not only led to the cut offs but also enlarged the channel size l w and rc in the second period 1956 present flow regulation via dams and gravel mining modified the system completely and impeded the natural development of these rivers

carbon isotope distribution in organic matter and siderite of a modern metalliferous hydrothermal sediment and possible implications for gold associated with banded iron formation abstract the carbon isotope distribution in organic matter and siderite has been determined in the metalliferous ferruginous sediments of santorini greece the sediments were precipitated by the microaerophilic chemolithotrophic bacterium galionella ferruginea from reduced hydrothermal solutions in siderites precipitated due to high co2 fugacity the 13 c 12 c isotope ratio pdb was 6 5 permil whereas the ratio was 26 8 permil in organic matter produced by the bacteria the common occurrence of isotopically light carbon 13c 10 permil pdb in carbonates of banded iron formations bif s was proposed some years ago to be the result of the dilution of carbon of marine carbonates by isotopically light carbon originally present in organic matter the explanation for this dilution would be that fe iii in newly precipitated oxide hydroxides served as an electron acceptor during oxidation of the organic carbon to carbonate the corresponding redistribution of some reduced carbon in the newly precipitated ferruginous sediment to carbonate minerals in the proportions found in some bif s has been modelled in the present study the isotopic shift to 13c 11 2 permil of the carbonate minerals of such a dilution by carbon of biological origin is close to the values observed in the geological record therefore organic matter appears to have been much more abundant during the early phases of bif development the association of gold and reduced organic carbon is well established in for instance the witwatersrand type conglomerates and some archaean bif s of hydrothermal origin this association may therefore make it worthwhile evaluating once again the role of organic activity in the deposition of bif s and their potential as a source of gold

environmental change and fluvial activity during the younger dryas in central germany abstract late pleistocene climatically induced environmental changes are reconstructed by applying a multidisciplinary approach on floodplain sediments of small to medium sized catchments in central germany radiocarbon dating pollen analysis and the presence of an accurately dated tephra layer allow the establishment of a reliable chronology the beginning of the younger dryas is marked by a change in fluvial activity that lasts for several hundred years during this period gravels and sands were deposited by a braided river system fluvial systems at this time were predominantly controlled by the climatic conditions of the surrounding uplands where the climatic deterioration led to a lowering of the forest limit and enhanced periglacial slope processes an open pine forest prevailed in the basin areas and no evidence of slope wash and solifluction was found the second part of the younger dryas is characterised by a meandering fluvial system and the deposition of overbank fines the rapid transition from younger dryas to preboreal coincides with an increase in organic deposition

a typology of pleistocene cold based rivers abstract a classification of periglacial rivers is proposed it is based on the generally valid laws relating the ratio of stream power to bed load with fluvial processes and morphology however river patterns may be modified by the special characteristics of the periglacial environment snowmelt especially in areas of continuous permafrost and river ice especially in zones of discontinuous permafrost determine the respective hydrological regimes the frozen state of the subsoil as well as the density of the vegetation cover contributes significantly to the bank cohesion and the sediment load of the rivers these specific periglacial characteristics have a complex influence on the thresholds in river activity resulting in a high diversity of periglacial river types

boundary conditions for damming of a large river by fallout during the 12 900 bp plinian laacher see eruption germany syn eruptive rhine damming ii abstract the rhine river germany the largest river in western europe was dammed by pyroclastic material multiple times during the major plinian laacher see eruption 12 900 bp dams formed both upstream and downstream of the broad tectonic lower neuwied basin lnb which interrupts the narrow rhine canyon here we document upstream damming of the rhine river at the entrance to the lnb close to the present city of koblenz due to overloading with tephra fall into the rhine and its major tributaries the moselle and the lahn the dam was formed repeatedly during rapid pumiceous tephra fall events and breached during breaks in eruptive activity causing extensive high energy flooding throughout the entire basin the ephemeral koblenz dams differed significantly from normal volcanically induced dams by consisting principally of washed together pumice clasts and some driftwood the porous nature of pumice and its ability to absorb water were crucial factors thus a large volume percentage of the tephra that had fallen into the rhine floated submerged within the upper part of the water column or swam at the surface moreover the absorption of the river water by the pumice clasts increased the sediment water ratio of the two phase flow considerably we here present a model of dam formation resembling the formation of ice jams we visualize the koblenz dams to have been elongate partly floating and partly grounded permeable plugs many kilometers long and rising no higher than the flood plain damming was most plausibly initiated in the lnb within the area of maximum tephra loading and propagated upstream in a chain reaction comparable to the formation of traffic jams a major dam was finally accumulated at the bottleneck entrance to the lnb a site combining several favorable conditions the upstream multi channel rhine was confined to a single channel change of flow direction by 125 extremely low gradient 0 19 starting already 24 km upstream of the bottleneck constant decrease of flow velocity over many kilometers towards the bottleneck and the moselle river largest tributary of the rhine within the lnb and an important conveyor of additional tephra masses entered the rhine only 700 m upstream of the bottleneck we assume that the koblenz dams could only have formed and been stabilized by an extremely long foot region that extended many kilometers downstream and that was possibly connected to one or several low rise secondary jams dams the backwater of lake brohl that was dammed by pyroclastic flows 7 km downstream of the lnb about halfway through the eruption extended further and further upstream into the lnb during the second plinian stage of the laacher see eruption and was probably a major factor contributing to the formation and large size of koblenz dam no 4 the koblenz dams were probably not completely sealed most of the time this way the major pre eruptive rhine channel received some water an equilibrium condition was established that enabled the dams to remain stable as long as tephra fell into the rhine relatively continuously

sedimentary history of the western bohai coastal plain since the late pliocene implications on tectonic climatic and sea level changes abstract thick cenozoic deposits from the western bohai coastal plain a tectonic subsiding region provide the potential to study the relations between sedimentary environments and tectonic climatic and sea level changes however sedimentary history of this region extending to the whole quaternary as well as their links to tectonic climatic and sea level changes are still poorly understood mainly because of the lack of long term records with well constrained chronology in this study we present an integrated record based on sedimentology and proxies grain size and color reflectance of a 203 6 m core recovered from the western bohai coastal plain near tianjin the core was chronologically well constrained using paleomagnetic and optically stimulated luminescence dating methods the results show that from the late pliocene 3 3 ma to the late pleistocene 0 10 ma the study region was mainly dominated by fluvial setting and the extensive incursion of sea water into this region began during the last interglacial period 0 10 ma the sedimentology and the color index suggest that tectonic subsidence of the bohai basin during the plio quaternary must have played a significant role in controlling the sedimentary environments in this region the changes in base level because of sea level fluctuations during the quaternary influenced the fluvial development greatly and led to the alternations of coarse crevasse splay channel and finer floodplain deposits in the core sequence in addition climatic changes since the late pliocene also have had significant effects on the sedimentary settings in the bohai coastal plain by influencing the fluvial process with a series of mechanisms

u pb zircon geochronology of the selbaie cu zn ag au mine abitibi subprovince canada the selbaie mine is a large tonnage low grade cu zn ag au deposit with both stratiform and epithermal characteristics mineralization comprises lower grade disseminated zn ag ore and pyritic siliceous sinter of the a1 zone at the surface and higher grade cu zn ag au quartz sulfide lenses of the a2 zone below and transitional with the a1 zone and of the b zone 1 km to the west the copper rich quartz sulfide lenses comprise networks of subvertical quartz sulfide veins vein arrays and breccia they have irregular locally gradational boundaries and variable attitudes with dips from 25 o to 90os the mineralization is within a volcanic stratigraphic succession of heterolithic breccias and felsic and intermediate tuffs and flows which are cut by mafic and felsic intrusions and felsite dikes the felsic volcanic rocks and a tonalitic marginal phase from the adjacent brouillan pluton are calc alkalic and have geochemical signatures that support a cogenetic relationship the mineralization and mine stratigraphic succession are truncated by the brouillan faults a series of subparallel west directed predominantly brittle thrusts with the brouillan pluton on the upper plate above the mine stratigraphic succession galenas from stratiform and vein ore have uniform lead isotope compositions of 2o6pb 2o4pb 13 184 to 13 211 2o7pb 2o4pb 14s351 to 14 369 and 2ospb 2o4pb 33s039 to 33 100 with model values of 8 1 8 2 and model k values of 4 1 to 4 2 n 5 among the most primitive of abitibi volcanic associated massive sulfide depositss they have model ages that range from 2 71 to 2 68 ga a u pb zircon age of 2729 ma for a sericite altered calc alkalic quartz porphyry flow 150 m up section from stratiform mineralization closely approximates the age for this mineralization type a u pb zircon age for a felsite dike that cuts postore east west foliation is 2726 3 ma slightly younger but overlapping at the 20 level with the age for the quartz feldspar porphyry flow indicating that the copper rich quartz sulfide lenses are essentially coeval with the lower grade stratiform mineralization a sample of sheared chloritic granodiorite taken from one of the brouillan faults near the margin of the brouillan pluton has a complex zircon opulation six concordant anal ses of abraded multigrain fractions individual grains or grain tips 20 p 206 s

sulfur isotope variability in biogenic pyrite reflections of heterogeneous bacterial colonization the top 20 cm of sediments at active cold seeps in monterey bay coastal california contain framboidal pyrite that occurs as infillings and pseudomorphs of the chambers of the tests of foraminifera and rarely as irregularly shaped grains sulfur isotope compositions obtained with the ion microprobe show depletions in 34 s d 34 s 52 41 to 25 cdt and large variations both within and among these pyrite grains intergranular differences in d 34 s values in the same sediment are as large as 35 and intragranular zoning reaches 15 zoning is regular in some grains with systematic isotope changes from core to rim or from one foraminiferal chamber to another but irregular in others the regular zoning is consistent with an increase in 34 s through time backscattered electron imaging reveals three types of pyrite isolated framboids in a porous aggregation pf pyrite agglomerated framboids with cementing interstitial pyrite f 1i pyrite and recrystallized pyrite with isolated relicts of framboids rf pyrite in individual grains rf pyrite cores grade into f1i pyrite toward grain rims and f1i pyrite grades into pf pyrite at the grain edges these textures are consistent with a paragenetic sequence whereby framboids first agglomerate pf pyrite then cement f1i pyrite and finally recrystallize rf pyrite the d 34 s values of rf pyrite are generally lower than that of f1i pyrite if the paragenetic sequence is correct then this trend parallels the regular core rim isotopic zoning observed in some grains the implied increase in d 34 s with time is consistent with rayleigh fractionation of sulfur in a closed system bacteria are intimately involved in the production of pyrite from our samples and heterogeneous colonization by bacteria provides a simple explanation for the sulfur isotope heterogeneity among and within grains the foraminifera provide open space for colonization and local nutrients for bacterial growth whereas the cell walls of the bacteria may provide a local nucleation site for sulfides if so then initial colonization is reflected in lower d 34 s values whereas later bacterial emigration to other foraminifera chambers is indicated by higher d 34 s values

lacustrine fluvial interactions in australia s riverine plains climatic forcing of fluvial systems has been a pre occupation of geomorphological studies in australia since the 1940s in the riverine plain southeastern australia the stable tectonic setting and absence of glaciation have combined to produce sediment loads that are amongst the lowest in the world surficial sediments and landforms exceed 140 000 yr in age and geomorphological change recorded in the fluvial fluvio lacustrine and aeolian features have provided a well studied record of quaternary environmental change over the last glacial cycle the region includes the willandra lakes whose distinctive lunette lakes preserve a history of water level variations and ecological change that is the cornerstone of australian quaternary chronostratigraphy the lunette sediments also contain an ancient record of human occupation that includes the earliest human fossils yet found on the australian continent to date the lake level and palaeochannel records in the lachlan willandra system have not been fully integrated making it difficult to establish the regional significance of hydrological change here we compare the willandra lakes environmental record with the morphology and location of fluvial systems in the lower lachlan an ancient channel belt of the lachlan willandra creek acted as the main feeder channel to willandra lakes before channel avulsion caused the lakes to dry out in the late pleistocene electromagnetic surveys geomorphological and sedimentary evidence are used to reconstruct the evolution of the first new channel belt following the avulsion single grain optical dating of floodplain sediments indicates that sedimentation in the new middle billabong palaeochannel had commenced before 18 4 1 1 ka a second avulsion shifted its upper reaches to the location of the present lachlan river by 16 2 0 9 ka the timing of these events is consistent with palaeohydrological records reconstructed from willandra lakes and with the record of palaeochannels on the lachlan river upstream willandra lakes shows high inflows during the last glacial maximum 22 ka but their subsequent drying between 20 5 ka and 19 ka was caused by river avulsion rather than regional aridity this case study highlights the benefits of combining fluvial with lacustrine archives to build complementary records of hydrological change in lowland riverine plains

factors influencing periglacial fluvial morphology in the northern european russian tundra and taiga the influence of geology discharge regime slope vegetation type vegetation density and permafrost conditions on periglacial channel morphology has been investigated in the usa catchment northern european russia rivers are dominated by meandering or anabranching plan forms and rarely show braiding characteristics despite a nival discharge regime the presence of discontinuous permafrost and locally steep slopes the dense vegetation cover is an important factor in determining the meandering morphology as it inhibits the sediment supply and hence braided conditions differences in vegetation types taiga in the south tundra in the north have no effect on channel plan form copyright 2002 john wiley sons ltd

a carbon oxygen hydrogen and sulfur isotopic study of the gold mineralization at loulo mali abstract the isotopic compositions of oxygen hydrogen carbon and sulfur have been determined on silicate carbonate and sulfide samples from auriferous tourmalinized sandstone its footwall and hanging wall of birimian age 2 1 ga at loulo in mali the sandstones have undergone two phases of deformation the samples were taken from three different orebodies loulo 0 loulo 3 and p64 for loulo 0 18o values for vein quartz are consistently between 16 1 and 16 6 smow for oxygen with one exception at 11 6 the 18o values for detrital quartz grains from the tourmalinized sandstone are also 16 1 tourmaline has a high 18 o of 13 9 the 18o values for total rocks are also relatively homogeneous at 13 2 to 15 7 the lowest values 13 2 and 14 being those for the footwall samples dolomites from loulo 0 and p64 have 18o values between 15 1 and 19 5 smow for oxygen and 13c values of 13 5 to 2 0 pdb with the exception of one sample from the hanging wall which is of sedimentary origin 13 c 0 5 18 o 22 2 the sampled dolomites are in veinlets or veins or disseminated in rocks and were deposited by hydrothermal fluids the 34s values of samples from the three orebodies range between 6 0 and 12 9 cdt they fall into different groups according to location but pre and post schistosity sulfides within each group are indistinguishable the results are interpreted as indicating the existence of two hydrothermal systems enriched in 18o at different times one of these gave rise to tourmalinization silicification and dolomitization of the sandstone and the deposition of sulfides the high d values of the tourmalines in agreement with petrological data indicate that the fluid of this system was of marine origin the two phases of folding intervened between the activity of this hydrothermal system and the initiation of the second system which gave rise to the stockwork this fluid rich in 18o was possibly of metamorphic origin with a low water rock ratio it remobilized the pre schistosity sulfides concentrating them into post schistosity veins the partly remobilized silica and carbonates were deposited under temperature conditions such that their isotopic compositions were similar to those observed for the tourmalinized sandstone the vertical extent of this hydrothermal system is as yet poorly known it is very extensive horizontally and strongly pervasive in the tourmalinized sandstone but in the vertical sense appears to be confined to fractures in the footwall

river system evolution and environmental changes during the lateglacial in the paris basin france abstract lateglacial sequences from the paris basin floodplains provide a general overview of the valley s evolution related to climatic changes from the weichselian upper pleniglacial to the beginning of the holocene comparison between morphostratigraphical and palaeobiological data allows discussion of fluvial dynamics and related palaeoenvironmental conditions the upper pleniglacial oldest dryas transition remains poorly documented it is represented by sands and silts deposited by a braided channel network the bolling begins with a significant incision related to a meandering system which is followed by local organic and minerogenic deposition contemporaneous with vegetation development the older dryas is evident in several sequences the allerod appears more stable and the forest extension is accompanied by a thin soil formation on the banks the younger dryas is characterised by a strong infilling of the valleys by calcareous silts this last sharp event precedes a second major downcutting phase which takes place in the early postglacial and is followed by a decline in river flow and sediment supply this evolution reflects a broad regional pattern of fluvial response which illustrates its sensitivity to climatic change the study of various morphosedimentary contexts shows their influence on the fluvio dynamic record and bio proxies which complicates the detection of minor phases

climatically controlled terraces in uplifting mountain areas abstract terraces in tectonically active mountains and uplands record both tectonic uplift and rhythmic climatic variations the author discusses the question of how to distinguish the role of both tectonic and climatic factors in central europe with quaternary uplift of the order of 50 100 m climatically controlled terraces are well developed cold stage aggradation is recognised through the interfingering of periglacial alluvial slope and loess deposits erosional activity prevailed in transitional periods then follows a discussion of difficulties connected with the construction of timing and rate of tectonic uplift based on the depth of incision in the bedrock and on facies differentiation the examination of changes in longitudinal profiles of river valleys indicates that unrejuvenated upper valley courses cannot be used for the reconstruction of tectonic uplift finally the author presents several types of adaptation of tectonically determined downcutting and aggradation to quaternary climatic cyclicity

channel network morphology and sediment dynamics under alternating periglacial and temperate regimes a numerical simulation study the occurrence of permafrost in a highly permeable catchment has a profound effect on runoff generation the presence of permafrost effectively makes the subsoil impermeable therefore overland flow can be the dominant runoff generating process during periglacial conditions the absence of permafrost will promote subsurface drainage and therefore saturation excess overland flow can become the dominant runoff generating process during temperate conditions in this paper we present a numerical modelling study in which the effect of alternating climate related phases of permafrost and nonpermafrost on catchment hydrology and geomorphology is investigated special attention is given to the characteristics of the channel network being formed and the sediment yield from these catchments we find that channel networks expand under permafrost conditions and contract under nonpermafrost conditions a change from permafrost to nonpermafrost conditions is characterised by a decrease in sediment yield while a change towards permafrost conditions is marked by a peak in sediment yield this peak is explained by the build up of a reservoir of erodible sediment during the nonpermafrost phase the driving force behind this reservoir build up may be local base level change due to tectonic uplift or eustacy we present a number of experiments which show the details of this process the results are in line with existing reconstructions of climate and fluvial dynamics during the pleistocene in europe and offer a new explanation to these observations

iron and sulfur in the pre biologic ocean tentative geochemical cycles for the pre biologic earth are developed by comparing the relative fluxes of oxygen dissolved iron and sulfide to the atmosphere and ocean the flux of iron is found to exceed both the oxygen and the sulfide fluxes because of the insolubility of iron oxides and sulfides the implication is that dissolved iron was fairly abundant and that oxygen and sulfide were rare in the atmosphere and ocean sulfate produced by the oxidation of volcanogenic sulfur gases was the most abundant sulfur species in the ocean but its concentration was low by modern standards because of the absence of the river borne flux of dissolved sulfate produced by oxidative weathering of the continents these findings are consistent with the geologic record of the isotopic composition of sedimentary sulfates and sulfides except in restricted environments the sulfur metabolism of the earliest organisms probably involved oxidized sulfur species not sulfide

evidence for an intrabasinal source and multiple concentration processes in the formation of the carbon leader reef witwatersrand supergroup south africa laser ablation inductively coupled plasma mass spectrometer la icp ms trace element maps of pyrite and gold from the carbon leader reef in the witwatersrand basin provide new evidence that a significant proportion of the pyrite and gold was intrabasinal derived from the west rand group or equivalent shales stratigraphically below this reef rounded detrital pyrite grains in the carbon leader reef vary from compact to porous to sooty with similar textures and composition to diagenetic pyrites reported from sedimentary rocks in the west rand group detrital porous and sooty pyrites contain 0 4 to 11 3 ppm solid solution gold sulfur isotope 34s values from 17 to 16 and high levels of as and te plus a wide range of other trace elements in decreasing order ni co sb cr cu u pb bi mo zn and ag the sooty pyrite is the most au te and mo rich and is intergrown with alumino silicates and organic matter the detrital pyrite textures s isotopes and geochemistry resemble diagenetic pyrite developed under suboxic to anoxic bottom water conditions the laicp ms maps also show that the detrital pyrite grains have euhedral hydrothermal pyrite overgrowths containing micro inclusions of gold brannerite and ni as sulfides the pyrite overgrowths are also enriched in solid solution gold tellurium and other trace elements including in decreasing order as co ni cr cu mn pb bi and ag fractured and brecciated pyrite associated with brittle bedding parallel fracture zones in the carbon leader reef are also enriched in these elements due to alteration of pyrite surrounding the fractures laser icp ms pb isotope determinations on the cores of detrital pyrite indicate an age between 2750 and 2950 ma with hydrothermal overgrowths originating between 2100 and 2020 ma incorporating highly radiogenic pb this study demonstrates that both of the two competing theories for the origin of the witwatersrand gold reefs are likely to be correct we suggest that the hydrothermal event was widespread kilometer scale and involved basinal fluids that scavenged gold tellurium arsenic and trace elements co ni cr cu mn pb bi ag from gold bearing sedimentary units in the central rand group 2013 society of economic geologists inc

fluvial response to weichselian climate changes in the niederlausitz germany the last glacial shows large variations in climate which are reflected in the fluvial record in the niederlausitz eastern germany the entire sequence resembles the fluvial development in other river basins in northwestern europe which show contemporaneous changes in depositional style at the onset of a climatic change during the middle and the late pleniglacial permafrost conditions resulted in an episodic river discharge the presence or absence of vegetation in combination with such ephemeral stream conditions determined the type of river during each period a relatively well developed vegetation cover on the flood plains during the middle pleniglacial resulted in a low sediment yield in combination with the intermittent discharge this caused the development of an ephemeral anastomosing river system a river with stable channels and extensive sandy overbank areas the decline in vegetation cover at ca 28 ka bp caused an increase in sediment yield and peak discharges which resulted in the development of a sandy braided river in adjustment to these new conditions following the coldest period at around 20 ka precipitation was so low that fluvial activity was limited and aeolian deposition took place in the valley 1997 by john wiley sons ltd

fe c and o isotope compositions of banded iron formation carbonates demonstrate a major role for dissimilatory iron reduction in 2 5 ga marine environments abstract combined fe c and o isotope measurements of 2 5 ga banded iron formation bif carbonates from the kuruman iron formation and underlying bif and platform ca mg carbonates of the gamohaan formation south africa constrain the biologic and abiologic formation pathways in these extensive bif deposits vertical intervals of up to 100 m were sampled in three cores that cover a lateral extent of 250 km bif fe carbonates have significant fe isotope variability 56fe 1 to 1 and relatively low 13c down to 12 and 18o values 18o 21 in contrast gamohaan and stratigraphically equivalent campbellrand ca mg carbonates have near zero 13c values and higher 18o values these findings argue against siderite precipitation from seawater as the origin of bif fe rich carbonates instead the c o and fe isotope compositions of bif fe carbonates reflect authigenic pathways of formation in the sedimentary pile prior to lithification where microbial dissimilatory iron reduction dir was the major process that controlled the c o and fe isotope compositions of siderite isotope mass balance reactions indicate that the low 13c and low 18o values of bif siderite relative to those expected for precipitation from seawater reflect inheritance of c and o isotope compositions of precursor organic carbon and ferric hydroxide that were generated in the photic zone and deposited on the seafloor carbon fe isotope relations suggest that bif fe carbonates formed through two end member pathways low 13c low 56fe fe carbonates formed from remobilized low 56fe aqueous fe2 produced by partial dir of iron oxide whereas low 13c high 56fe fe carbonates formed by near complete dir of high 56fe iron oxides that were residual from prior partial dir an important observation is the common occurrence of iron oxide inclusions in the high 56fe siderite supporting a model where such compositions reflect dir in place in the soft sediment in contrast the isotopic composition of low fe carbonates in limestone dolomite may constitute a record of seawater environments although our petrographic studies indicate that the presence of pyrite in most low fe carbonates may influence the fe isotope compositions the combined fe c and o isotope data from kuruman bif carbonates indicate that bif siderites that have negative near zero or positive 56fe values may all record biological fe cycling where the range in 56fe values records differential fe mobilization via dir in the sediment prior to lithification our results demonstrate that the inventory of low 56fe marine sedimentary rocks of neoarchean to paleoproterozoic age although impressive in volume may represent only a minimum of the total inventory of fe that was cycled by bacteria

reconstruction of a pleistocene meandering river in east hungary by vhr seismic images and its climatic implications abstract the upper 20 30 m of the pleistocene alluvial sequence on the tisza river hungary is investigated by 200 km of vhr single channel seismic sections frequent internal configurations such as 1 bundles of inclined reflections 2 trough shaped converging and 3 horizontal parallel reflections are interpreted respectively as lateral accretion of point bars abandoned channel fills and floodplain deposits the series of 5 8 m thick inclined strata sets occurring at the same depth throughout the area suggest the presence of a meandering river dated to about 43 47 ka in the late pleistocene according to osl data newly recorded quasi 3d seismic profiles reveal that each 1 3 km long inclined series correlates with an individual point bar continuously migrating in the same direction small deviations in the direction of migration are caused by natural wandering of the meander bend morphometric parameters of point bars are used to calculate ancient channel parameters width and depth of 200 500 m and 5 8 m respectively values imply a channel forming discharge of q 400 900 m 3 s these results imply a greater amount of runoff and supply in the basin during mis3 compared to the present day long lasting meandering indicates the role of local factors and a different fluvial environment compared to the commonly anastomosing systems in nw europe our data support the thesis of the three axis drainage system for the basin new evidence is provided for the antecedent existence of a temporally active third trunk river in addition to the ancestors of danube and tisza rivers contrary to the present day two axis drainage pattern

timescales climate and river development abstract in the long term glacial interglacial sequences river development follows general climatic evolution however at the scale of one cold warm cycle it appears that the geomorphological effect of river activity is best expressed at times of climatic change such periods of pronounced fluvial action last only a short time in more detail the internal evolution in a drainage basin after a climatic event results in a delayed response of the morphology and sedimentation pattern finally on the shortest timescale local thresholds may play a decisive role in the reactions of river systems it is concluded that the relation between fluvial development and climate is not a simple one but is fundamentally dependant on the timescale

milankovitch scale multi proxy records from fluvial sediments of the last 2 6 ma pannonian basin hungary abstract the continuous cores of two nearly 500 m deep boreholes cutting pleistocene fluvial sequences in the eastern part of the pannonian basin hungary have been studied magnetostratigraphy indicates that the sediment sequences span the last 2 6 ma without significant hiatuses comparison of systematic variations in magnetic susceptibility with changes in grain size distribution revealed milankovitch scale cyclicity in sedimentation of 40 and 100 kyr cyclicity which also shows a correspondence with the 18o variations of the odp 677 site comparison of pollen and gastropod paleoecological data with the magnetic susceptibility proxies suggests that climate was a major allogenic control on the cyclicity zones of high magnetic susceptibility correspond closely with sandy and coarse silty parts of the borehole successions which largely coincide with pollen and molluscs indicating a warm climate on the contrary zones with low magnetic susceptibility correspond to silts and clays and in most cases coincide with cold climate indicator pollen and molluscs heavy mineral and xrd studies revealed that magnetic susceptibility reflects the absolute amount of detrital fe oxide minerals mostly magnetite variations in the amount of magnetite are related to changes in heavy mineral content which arise primarily from changes in sediment supply to the basin by rivers the depositional model for the pleistocene fluvial sediments suggests that sediment flux increased towards the basin during interglacials due to the increased discharge and transport capacity of the rivers while a decreased sediment supply to the distal parts of the basin occurred during glacials a delay between erosion and storage of weathering products near to the source area and subsequent transportation and re deposition of sediments in the basin interior setting is an important cause of this effect

influence of late glacial climate changes on sediment transport in the river werra thuringia germany abstract several sedimentary records of floodplain sediments in the werra valley and subcatchments have been analysed in order to investigate the influence of climate change on the sediment transport system in the sedimentary records of the subcatchments a marked change from minerogenic to organic sediments is visible about 14 6 ka b p according to palynological analyses this change occurs in a period with a remarkable rise in arboreal pollen percentages in addition a reverse change from organic to clastic sediments takes place shortly after 12 9 ka b p coincident with a decrease in arboreal pollen percentages during this period assuming that changes in vegetation cover are mainly caused by climate the variations in the sedimentary records are also attributed to these climatic oscillations in contrast to the subcatchments comparable changes in the sedimentary record are not detectable in the floodplain of the werra river this points to the conclusion that the influence of late glacial climate fluctuations on the sedimentary regime of a river with a relatively large and a more heterogeneous catchment seems less pronounced