effects of experimental leaching on rbsr and kar isotopic systems and ree contents of diagenetic illite leaching with 1 n hcl 1 n nh4cl acetone humic acid extracts cation exchange resin and nh4 edta have negligible effects on the rb sr and k ar systems of different size fractions 0 4 and 0 8 2 m of a 1m diagenetic illite none of these treatments including the 1 n hcl treatment induced preferential removal of radiogenic 87sr and 40ar from mineral structures however the 1 n hcl treatment removed significant amounts of sr and ree as compared to the treatments by nh4 edta and cation exchange resin however much of these hcl derived elements resided in non clay minerals such as carbonate and fe oxide phases the k ar and rb sr ages of the samples were not affected by the hcl treatment any more than by the nh4 edta or the cation exchange resin because of potential loss of solid material during elutriation of differentially treated samples the hcl treatment is preferred over other methods allowing sufficient controls on the isotopic and mass balances between the leachate and the corresponding residue of an untreated sample for rb sr isotopic dating purposes of clay minerals from sedimentary and metasedimentary rocks leaching experiments give information about the ambient environment of crystallization analysis of both the leachate and residue under carefully controlled conditions is recommended

sr nd isotopic geochemistry of holocene sediments from the south yellow sea implications for provenance and monsoon variability abstract elemental geochemical and sr nd isotopic signatures are used to decipher terrigenous sediments provenances and transport mechanisms in the south yellow sea during the holocene 87sr 86sr ratios in the chinese and korean riverine sediments overlap each other whereas end values of korean riverine sediments are generally less radiogenic in comparison to the changjiang and huanghe moreover end values of these two large rivers appear unaffected by mineral sorting and are relative stable during the holocene we propose a three endmembers i e the changjiang the huanghe and korean rivers mixing model to explain sediment provenances in the central yellow sea mud cysm mixing calculations show that the huanghe is the major sediment contributor to the cysm before 8 ka thousand years before 1950 ce whereas the changjiang has become the predominant sediment source after 8 ka holocene changes in riverine sediment supplies to the cysm are closely related to the oceanic circulation monsoon climate and drainage changes after examining several hypotheses to explain the variations in 87sr 86sr ratios of core ysc 1 during the past 8 kyr we tentatively attribute that to changes in the erosion patterns of the changjiang basin this in turn is associated with the asynchronous evolution of monsoon precipitation in the upper indian summer monsoon and middle lower changjiang east asian summer monsoon therefore our results highlight significant influences of monsoon climate on erosion patterns within the changjiang catchment at millennial timescales

identification et distribution des grandes masses d eau dans les mers du labrador et d irminger the main deep water masses present at the time of the css hudson cruises in labrador and irminger seas in june 1990 and october november 1991 have been identified using characteristic temperatures t and salinities s the purpose of this study was to establish the transfer functions between micropaleontological assemblages of top sediments and thermohaline characteristics of water masses the water mass at the top of the labrador sea labrador sea water lsw is formed after intense movements of winter convection in the first 900 m depth of the water column below that depth the lsw parameters reach a double minimum s 34 80 and t 2 9 c only the sediments located on the continental slopes of greenland and labrador between depths of 500 and 1500 m are in contact with the lsw below the lsw the superior fraction of the north east atlantic deep water neadw1 is characterized by a temperature maximum 3 3 c and as such is distinguishable from the inferior fraction neadw2 the latter is ch

sr and nd isotopes as tracers of north atlantic lithic particles paleoclimatic implications sr and nd isotopic compositions have been measured on the lithic fraction of last climatic cycle sediments from the north atlantic 40 n 60 n in order to identify the origins of the particles from the reconstruction of their transport pathways we deduce the mechanisms that explain their distributions the main source regions are the canadian shield mostly the area of baffin bay and western greenland the scandinavian shield the european region british isles and bay of biscay and iceland we observe a significant glacial interglacial contrast characterized by a dominant icelandic input via near bottom transport by north atlantic deep water nadw during the interglacials and a largely continent derived contribution of surface transported ice rafted detritus ird during the glacial period during the last glacial period the heinrich events abrupt massive discharges of ird originated not only from the laurentide ice sheet as heretofore envisioned but also from other sources three other major north atlantic ice sheets fennoscandian british isles and icelandic probably surged simultaneously discharging ice and ird into the north atlantic as opposed to theories implying a unique laurentide origin gwiazda et al 1995 driven by an internal mechanism mcayeal 1993 we confirm that the icelandic and the fennoscandian ice sheets also surged as recently proposed by other authors and we here also distinguish a possible detrital contribution from the british isles ice sheet this pan north atlantic phenomenon thus requires a common regional external forcing

clay supplies in the central indian basin since the late miocene climatic or tectonic control abstract mineralogical x ray diffraction differential thermal analysis geochemical microprobe inductively coupled plasma icp atomic emission spectrometry icp mass spectrometry and sr nd isotopic analyses have been carried out on the clay size fraction of late miocene to pleistocene sediments from the central indian basin the samples were taken from five giant cores recovered between 1 and 10 s on a transect along 80 e the clay assemblages are homogeneous and characterized by an alternation of illite and smectite rich levels most of the clays are detrital and were derived from a unique source the weathering of the indo gangetic plain supplied most of the eroded material temporal clay mineralogical fluctuations in the depositional basin reflect environmental changes in the provenance on the basis of spectral analyses of a mineralogical parameter peak height ratios the fluctuating smectite illite clay sedimentation is controlled by periodic late miocene climatic changes during the late pliocene an irregular probably tectonic control appeared

provenance and climate change inferred from sr nd pb isotopes of late quaternary sediments in the huanghe yellow river delta china we present a provenance study of core zk2 from the huanghe yellow river delta in order to assess the impacts of climate change on the sediment supplies during the last glacial interglacial cycle facies analysis and sequence stratigraphy methods are used to construct the age model sr isotopic compositions of zk2 range from 0 716389 to 0 723884 with 87sr 86sr increased with decreasing grain size nd and pb isotopic compositions display two large major excursions during marine oxygen isotope stages mis 2 and 4 with less radiogenic end and lower 208pb 204pb 207pb 204pb and 206pb 204pb values during these periods these excursions have been explained in terms of changes in the mixing proportion of sediments from the loess plateau and ordos plateau resulting from east asian monsoon intensity variations the weak summer monsoon precipitation resulted in decreased erosion of loess plateau during mis 2 4 and the middle of mis 3 meanwhile both the intensified east asian winter monsoon and the southward expansions of mu us desert significantly enhanced the eolian sand entering the huanghe therefore our results highlight the impact of monsoon variability on erosion patterns in the huanghe basin

nd and sr isotope compositions of different phases of surface sediments in the south pacific extraction of seawater signatures boundary exchange and detrital dust provenance the radiogenic isotope composition of neodymium nd and strontium sr are useful tools to investigate present and past oceanic circulation or input of terrigenous material we present nd and sr isotope compositions extracted from different sedimentary phases including early diagenetic fe mn coatings unclean foraminiferal shells fossil fish teeth and detritus of marine surface sediments core tops covering the entire midlatitude south pacific comparison of detrital nd isotope compositions to deep water values from the same locations suggests that boundary exchange has little influence on the nd isotope composition of western south pacific seawater concentrations of rare earth elements ree and al ca ratios of unclean planktonic foraminifera suggest that this phase is a reliable recorder of seawater nd isotope composition the signatures obtained from fish teeth and nondecarbonated leachates of bulk sediment fe mn oxyhydroxide coatings also agree with unclean foraminifera direct comparison of nd isotope compositions extracted using these methods with seawater nd isotope compositions is complicated by the low accumulation rates yielding radiocarbon ages of up to 24 kyr thus mixing the signal of different ocean circulation modes this suggests that different past seawater nd isotope compositions have been integrated in authigenic sediments from regions with low sedimentation rates combined detrital nd and sr isotope signatures indicate a dominant role of the westerly winds transporting lithogenic material from south new zealand and southeastern australia to the open south pacific the proportion of this material decreases toward the east where supply from the andes increases and contributions from antarctica cannot be ruled out

final stages in the collapse of the laurentide ice sheet hudson strait canada nwt 14c ams dates seismics stratigraphy and magnetic susceptibility logs hudson strait is a key element in the history of ice sheet ocean interactions during the deglaciation of the laurentide ice sheet data from over 30 giant piston cores supplemented by ca 40 14c ams dates on foraminifers and shells from sites within and adjacent to hudson strait are used to describe the timing and sediment processes associated with the final complex phases of deglaciation in hudson strait each core is placed in a regional seismic architectural context through examination of deep tow huntec profiles most cores sample a thin postglacial unit and extend several meters into glacial marine sediment mainly silty clays 14c dates on cores from the adjacent shelf indicate that deglaciation occurred by 13 ka we have not been unable to confirm that hudson strait was ice free by 11 12 ka although this is a probable scenario whole core magnetic susceptibility wcms data are used as the primary signature of changes in the style of sedimentation and provenance and to correlate between cores wcms indicates that there is a regional differentiation in the ms signal associated with bedrock provenance changes in contribution of detrital carbonate and style of sedimentation one low wcms event is present in cores from both the western and eastern basins it dates from 8 0 ka and provides an important regional stratigraphic marker probably associated with the final deglaciation of hudson bay and hudson strait sediment from a southerly source ungava bay continued to be contributed into the 900 m deep eastern basin of hudson strait 8 and 7 ka and thick postglacial sequences were piled within ungava bay between 6 and 7 ka

the quaternary geology of the labrador shelf the regional distribution of glacial and postglacial sediments on the labrador shelf was mapped by medium and high resolution seismics and shows a succession of tills that extend to the continental shelf edge at approximately 600 m the uppermost of these tills is less laterally extensive and does not occur on the labrador shelf bank tops in water depths less than 160 m we infer that the last glacial episode was less extensive than the preceding ones glaciomarine stratified silts and postglacial muds are found overlying the upper till in the deep basins that separate the banks the upper till glaciomarine silts and postglacial muds are interpreted to constitute one complete deglacial cycle radiocarbon age determination suggests this deglacial sequence began at approximately 20 000 years bp on the northernmost labrador shelf and hudson strait seismic evidence indicates a late glacial readvance locally deposited a till that overlies the glaciomarine sediments associated with the last glacial advance

postglacial emergence of ungava peninsula and its relationship to glacial history a series of 178 radiocarbon dates of late glacial and postglacial age from raised marine terraces on the hudson strait hudson bay and ungava bay coasts permit a new synthesis of deglaciation h

isotope stratigraphy sedimentation rates deep circulation and carbonate events in the labrador sea during the last 200 ka high resolution stable isotope and accelerator mass spectrometry 14c measurements in 25 box and piston cores from the labrador sea allow the reconstruction of major paleoceanographical changes during the last 200 ka in this basin and also document the links between the interior of the laurentide ice sheet and the north atlantic ocean during this interval two deep circulation regimes are indicated by contrasting sedimentation rates on the slopes i the modern situation is characterized by a gyre of the north atlantic deep water nadw components into the basin which is responsible for the high energy western boundary undercurrent this regime also prevailed during the former true interglacials and possibly during shorter warm intervals e g bolling allerod ii a more frequent nadw free situation during glacial and interstadial intervals is marked by the presence of a vertically homogeneous water mass in the basin sedimentological records also indicate that carbonate events i e pulses of

postdepositional sm nd fractionation in sandstones implications for neodymium isotope stratigraphy abstract sandstone reservoirs from the norwegian continental shelf commonly show varying degrees of postdepositional fractionation of sm nd ratio apparently due to preferential incorporation of sm in the crystal lattice of diagenetic apatite based on data from leaching experiments an apatite mineral separate and petrography it is proposed that fractionation occurred mainly during closed system burial diagenesis as phosphate deposited on the sea floor recrystallized to apatite and incorporated rare earth elements ree from the surrounding rock matrix as a result the sm nd model age parameter in general contains two components of information a the true crustal age of the sediment and b a secondary component of sm nd fractionation which can be either negligible or dominant it is difficult to separate these components and thus correct for component b even in data showing no obvious signs of postdepositional fractionation model ages may be variably disturbed by subordinate amounts of diagenetic alteration however the isotope ratio 143nd 144nd is expected to be relatively resistant to alteration by secondary sm nd fractionation and should therefore be used rather than model age as the principal correlation parameter in stratigraphic studies in this way nd isotope stratigraphy can still be used as a valuable and unique tool for studies of provenance and correlation even in strata showing strong sm nd fractionation effects strongly sm nd fractionated horizons recognized by bulk rock sm nd ratios 0 23 may also be useful for stratigraphic correlation but it is clear that their occurrence reflects special depositional conditions rather than shifts in sediment provenance

the high supply current dominated continental margin of southeastern south america during the late quaternary the continental margin off the la plata estuary se south america is characterized by high fluvial sediment supply and strong ocean currents high resolution sediment acoustic data combined with sedimentary facies analysis ams 14c ages and neodymium isotopic data allowed us to reconstruct late quaternary sedimentary dynamics in relation to the two major sediment sources the la plata estuary and the argentine margin sediments from these two provinces show completely different dispersal patterns we show that the northward trending la plata paleo valley was the sole transit path for the huge volumes of fluvial material during lower sea levels in contrast material from the argentine margin sector was transported northwards by the strong current system despite the large sediment volumes supplied by both sources wide parts of the shelf were characterized by either persistent non deposition or local short term depocenter formation the location and formation history of these depocenters were primarily controlled by the interplay of sea level with current strength and local morphology the high sediment supply was of secondary importance to the stratigraphic construction though locally resulting in high sedimentation rates thus the shelf system off the la plata estuary can be considered as a hydrodynamic controlled end member

cryosphere ocean interactions at the margin of the laurentide ice sheet during the younger dryas chron se baffin shelf northwest territories cores hu82 034 057 and hu84 035 008 resolution basin se baffin shelf contain 200 and 450 cm respectively of sediment that spans the younger dryas chron in both cores the interval is bracketed by 14c dates on foraminifera or molluscs these sites were close to the margin of the late wisconsin foxe ice sheet as it flowed toward the labrador sea prior to 11 ka both cores record moderate to high accumulations of foraminifera relatively high del 18o values in planktonic foraminifera and low values of detrital carbonate the diatom and percent opal records imply occasional seasonally open water conditions during part of the younger dryas chron both the diatom and opal analyses imply a shutoff of biogenic silica production suggesting surface water conditions affected by increased sea ice and or reduced nutrients in addition the younger dryas interval is marked by an increase in coarse sand and detrital carbonate a decrease in total organic carbon and foraminifera and high rates of sediment accumulation the inferred environment during the younger dryas is ice proximal in hu82 034 057 the foraminifera and other data suggest a change in conditions during the middle part of the younger dryas chron

changes in the western boundary undercurrent outflow since the last glacial maximum from smectite illite ratios in deep labrador sea sediments high resolution mineralogical studies were performed on late glacial and deglacial sediments from two deep piston cores from the labrador sea located at the inlet sw greenland rise and outlet labrador rise of the western boundary undercurrent wbuc gyre at the two sites smectites transported from the eastern iceland and irminger basins by the wbuc are observed clay mineral changes are used as proxies for the paleointensity reconstruction of the wbuc on the greenland rise a clay mineral index smectite illite s i ratio is defined a s i ratio of 1 characterized the last glacial maximum it increased after 17 ka and reached a maximum value of 4 during the early holocene the mineralogical changes are gradual and do not show any reversal during the younger dryas this pattern which is confirmed by first order estimations of smectite and illite fluxes suggests gradually increasing sedimentary fluxes and wbuc intensity since the last glacial maximum a peak in the velocity of the wbuc at 9 ka as recorded by clay assemblages is consistent with other regional studies based on pollen foraminifera or grain size measurements a massive dilution of smectites by illite and chlorite s i 3 occurs at 8 5 ka it corresponds to a period of rapid sediment accumulation and reflects an intensified illite rich detrital supply by meltwaters from the southern greenland ice margin on the labrador rise the smectite content varies between 20 and 60 with no obvious trend through time the mineralogical composition is strongly influenced by ice rafted deposition and by the abundance of fast deposit units cf heinrich layers in the north atlantic which contain abundant detrital carbonates spilled over from the north west atlantic mid ocean channel in such layers smectites are present but are diluted by the addition of illites chlorites and kaolinites this provides evidence for a discrete and continuous wbuc supply of fine particles from the irminger and iceland basins as far as the southeastern part of the labrador basin early deglacial smectite rich layers up to 60 are also observed at this site they indicate an increase in the outflow of the wbuc at 13 5 ka bolling allerod as previously reported from grain size or foraminiferal assemblage studies

impact of melting of the laurentide ice sheet on sediments from the upper continental slope off southeastern canada evidence from sm nd isotopesthis article is one of a series of papers published in this special issue on the theme polar climate stability network we present new sm nd isotope data for sediments from a core located on the continental slope of the st pierre bank of canada s east coast the nd analyses indicate that the sediments were derived from two principal sources the north american shield that yields an average early proterozoic isotopic signature and a younger proterozoic signature attributed to appalachian crustal sources the appalachian sourced sediments predominated during the last glacial maximum lgm and were associated with low sedimentation rates 30 cm ka with the exception of a strong north american shield signature present in a detrital carbonate layer that corresponds to heinrich layer 1 h1 the dominance of the appalachian signature decreased subsequent to h1 the appalachian signatures closely follow the distribution of sediments interpreted as locally derived glacial tills while the north american shield signatures follow the distribution of hemipelagic mud that was likely deposited by the labrador current the nd data a

a simulation model of morphological vegetation and sediment changes in ephemeral streams a model to simulate channel changes in ephemeral river channels and to test the effects of hydrological changes due to climate change and sol or land use change was developed under the auspices of the eu funded medalus programme mediterranean desertification and land use the model changism channel change gis simulation model is designed to simulate the effect of channel flow events and of climate conditions on morphology sediment and vegetation through sequences of events and conditions over periods of up to several decades the modelling is based on cellular automata but with calculations for water and sediment continuity process rules have both deterministic and stochastic elements an important feature of the model is that it incorporates feedback elements between each event the main aim of the model is to indicate the likely outcomes of events and combinations of conditions it is linked to gis for both input and output the modelling is based on a channel reach and state is input as gis layers of morphology dem sediment and vegetation cover and state other initial conditions of soil moisture groundwater level and overall gradient are input parameters for processes are read from tables and can be easily changed for successive runs of the model the bases for decisions on process specifications are discussed in this paper initial tests of the operation and sensitivity of the model were made on idealized reaches the model was then tested using data from monitored sites in se spain simulations using clearwater flow worked well but initial simulations using events with sediment loads showed some tendency for excess deposition further tests and modifications are taking place overall the model is one of the most sophisticated that simulates the interaction of flows with sediment and vegetation and the outcomes in terms of erosion deposition morphology sediment cover vegetation cover and plant survival over periods of up to 30 years for the scale of a channel reach copyright 2005 john wiley sons ltd

modelling river history and evolution over the last few decades a suite of numerical models has been developed for studying river history and evolution that is almost as diverse as the subject of river history itself a distinction can be made between landscape evolution models lems alluvial architecture models meander models cellular models and computational fluid dynamics models although these models share some similarities there also are notable differences between them which make them more or less suitable for simulating particular aspects of river history and evolution lems embrace entire drainage basins at the price of detail alluvial architecture models simulate sedimentary facies but oversimplify flow characteristics and computational fluid dynamics models have to assume a fixed channel form while all these models have helped us to predict erosion and depositional processes as well as fluvial landscape evolution some areas of prediction are likely to remain limited and short term owing to the often nonlinear response of fluvial systems nevertheless progress in model algorithms computing and field data capture will lead to greater integration between these approaches and thus the ability to interpret river history more comprehensively

the holocene sedimentary regime in the northern mid atlantic ridge region the holocene 10 000 yr b p mid atlantic ridge sedimentary regime between 45 n and 65 n has been investigated by examination of sediments from 70 cores smectite chlorite and quartz 87sr 86sr isotopes and ree have been used as conservative tracers to provide source identification and to calculate accumulation rates the entire holocene sedimentary regime in this part of the atlantic can be attributed to particle fluxes from two sources the icelandic and north american systems two main transport mechanisms are identified 1 particles derived from the icelandic system have been transported southwards as far as 45 n by bottom currents 2 material coming from north america is mainly transported by the aeolian regime at 45 n the windborn accumulation rate is estimated to be 0 5 g cm 2 kyr 1 which is identical to the accumulation rate of bottom advected material from iceland finally a diagnostic model for the north atlantic sedimentary regime is proposed

depositional provinces dispersal and origin of terrigenous sediments along the se south american continental margin abstract continental margin sediments of se south america originate from various terrestrial sources each conveying specific magnetic and element signatures here we aim to identify the sources and transport characteristics of shelf and slope sediments deposited between east brazil and patagonia 20 48 s using enviromagnetic major element and grain size data a set of five source indicative parameters i e fd arm irm s0 3t sirm fe and fe k of 25 surface samples 16 1805 m water depth was analyzed by fuzzy c means clustering and non linear mapping to depict and unmix sediment province characteristics this multivariate approach yields three regionally coherent sediment provinces with petrologically and climatically distinct source regions the southernmost province is entirely restricted to the slope off the argentinean pampas and has been identified as relict andean sourced sands with coarse unaltered magnetite the direct transport to the slope was enabled by rio colorado and rio negro meltwaters during glacial and deglacial phases of low sea level the adjacent shelf province consists of coastal loessoidal sands highest hematite and goethite proportions delivered from the argentinean pampas by wave erosion and westerly winds the northernmost province includes the plata mudbelt and rio grande cone it contains tropically weathered clayey silts from the la plata drainage basin with pronounced proportions of fine magnetite which were distributed up to 24 s by the brazilian coastal current and admixed to coarser relict sediments of pampean loessoidal origin grain size analyses of all samples showed that sediment fractionation during transport and deposition had little impact on magnetic and element source characteristics this study corroborates the high potential of the chosen approach to access sediment origin in regions with contrasting sediment sources complex transport dynamics and large grain size variability

a pseudo genetic model of coarse braided river deposits a new method is proposed to produce three dimensional facies models of braided river aquifers based on analog data the algorithm consists of two steps the first step involves building the main geological units the production of the principal inner structures of the aquifer is achieved by stacking multiple point statistics simulations of successive topographies thus mimicking the major successive flooding events responsible for the erosion and deposition of sediments the second step of the algorithm consists of generating fine scale heterogeneity within the main geological units these smaller scale structures are generated by mimicking the trough filling process occurring in braided rivers the imitation of the physical processes relies on the local topography and on a local approximation of the flow this produces realistic cross stratified sediments comparable to what can be observed in outcrops the three main input parameters of the algorithm offer control over the proportions the continuity and the dimensions of the deposits calibration of these parameters does not require invasive field measurements and can rely partly on analog data

abrupt increase in greenland snow accumulation at the end of the younger dryas event the warming at the end of the last glaciation was characterized by a series of abrupt returns to glacial climate the best known of which is the younger dryas event1 despite much study of the causes of this event and the mechanisms by which it ended many questions remain unresolved1 oxygen isotope data from greenland ice cores2 4 suggest that the younger dryas ended abruptly over a period of about 50 years dust concentrations2 4 in these cores show an even more rapid transition 20 years this extremely short timescale places severe constraints on the mechanisms underlying the transition but dust concentrations can reflect subtle changes in atmospheric circulation which need not be associated with a large change in climate here we present results from a new greenland ice core gisp2 showing that snow accumulation doubled rapidly from the younger dryas event to the subsequent preboreal interval possibly in one to three years we also find that the accumulation rate change from the oldest dryas to the bo11ing allerod warm period was large and abrupt the extreme rapidity of these changes in a variable that directly represents regional climate implies that the events at the end of the last glaciation may have been responses to some kind of threshold or trigger in the north atlantic climate system

detrital sr nd isotopes sediment provenances and depositional processes in the laxmi basin of the arabian sea during the last 800 ka 87sr 86sr ratios and end values of detrital particles at international ocean discovery program iodp site u1456 in the laxmi basin of the arabian sea were measured to trace changes in sediment provenance over glacial interglacial cycles based on the correlation of planktonic foraminiferal globigerinoides ruber 18o fluctuations with the lr04 stack of benthic foraminifera 18o values combined with shipboard biostratigraphic and palaeomagnetic data the studied interval spans 1 2 ma over the past 800 ka 87sr 86sr values ranged from 0 711 to 0 726 while end values ranged between 12 5 and 7 3 in the detrital particles by comparing 87sr 86sr ratios and end values of the possible sources of river sediments with our data we found that sediments in the laxmi basin were influenced to various degrees by proportions of at least three sediment sources i e tapi river narmada river and indus river the indus river might be a more important contributor to glacial sediments although 87sr 86sr ratios and end values varied quasi cyclically this pattern did not correspond precisely to the glacial interglacial cycles in particular low magnetic susceptibility low ms intervals coinciding with pelagic carbonates were characterized by low 87sr 86sr ratios and high end values whereas high ms intervals matching turbidite deposits showed high 87sr 86sr ratios and low end values thus this study reveals that differences in the depositional processes between glacial and interglacial periods governed by changes in sea level and monsoon activity are an important factor in deciding 87sr 86sr ratios and end values of the detrital fraction in the indus fan of the arabian sea

clay minerals and sr nd isotopes of the sediments along the western margin of india and their implication for sediment provenance mineralogy and sr nd isotopic composition of the 2 m fraction of the holocene and late pleistocene sediments from 12 gravity cores collected along the western margin of india were used to delineate the provenance and understand the response of isotopes with respect to the source rock composition holocene sediments show distinct clay mineral associations representing three major sources illite chlorite rich sediments from the indus smectite dominated sediments from the deccan traps and kaolinite and smectite enriched sediments from gneissic rocks the mixing of indus derived sediment with the deccan traps derived sediment or the deccan traps derived sediment with gneissic rock derived sediment occurs in the deeper water cores sr isotopes are very sensitive to weathering and laterization weathering does not influence nd isotopes the 87sr 86sr ratios of the holocene sediments in shallow water cores are higher and fluctuated widely than those in deeper water cores nd correlates well with the clay mineral associations indicating source rock composition or mixing of source sediments kaolinite enriched sediments coupled with high sr ratios and low nd on the sw margin of india suggest intense chemical weathering in the hinterland the influence of the sediment from the ganges brahmaputra transported by the bay of bengal waters during the ne monsoon surface current or sw monsoon underwater current on the composition of the sediments of the sw indian margin is insignificant the late pleistocene sediments reflect a decrease of hydrolytic processes resulting in decrease of smectite and sr isotopic ratio clay minerals and nd values suggest that the provenance and transport pathways of the late pleistocene sediments are the same as those of the holocene for each region

wind variability over the northern indian ocean during the past 4 million years insights from coarse aeolian dust iodp exp 359 site u1467 maldives abstract the lithogenic fraction of carbonate drift sediments from iodp exp 359 site u1467 maldives provides a unique record of atmospheric dust transport over the northern indian ocean during the past 4 myr grain size data provide proxies for dust flux controlled by source area aridity as well as wind transport capacity wind speed entrainment and long range transport of dust in the medium to coarse silt size range is linked to the strength of the arabian shamal winds and the occurrence of convective storms which prolong dust transport dust flux and the size of dust particles increased between 4 0 and 3 3 ma corresponding to the closure of the indonesian seaway and the intensification of the south asian monsoon there is no clear trend in dust flux between 3 3 and 1 6 ma whereas wind transport capacity decreased between 1 6 ma and the recent dust flux increased and shows higher variability especially during the last 500 kyr transport capacity increased between 1 2 and 0 5 ma and slightly decreased since then frequency analysis shows that dust transport varies on orbital timescales with eccentricity control being the most prominent 400 kyr throughout the record 100 kyr between 2 0 and 1 3 ma and since 1 0 ma higher frequency cycles obliquity and precession are more pronounced in wind transport capacity than in the amount of dust this indicates that the amount of coarse dust in sediments from the maldives as a far field site is more prone to changes in transport mechanisms than to changes in dust source area aridity

north american origin of pink white layers at the mendeleev ridge arctic ocean new insights from lead and neodymium isotope composition of detrital sediment component abstract dolomite rich layers of distinct pinkish colour are used as lithostratigraphic markers in the amerasian basin of the arctic ocean however origin of dolomite in these sediment units has not been studied in detail in this study lead pb and neodymium nd isotope composition of detrital clay size fraction from different lithofacies were investigated in core ps72 340 5 recovered at the eastern flank of the mendeleev ridge prior to the geochemical analyses grain size distribution was analyzed in order to minimize the grain size effect on the provenance signature for provenance discrimination results of isotope measurements were compared with marine surface sediment data and values for the circum arctic subaerial provinces late quaternary sediment supply variability was analyzed using the mixing model constrained by two tracers 207pb 206pb and end variations of sediment isotopic composition are inferred to result from mixing of volcanic and plutonic components usage of pb isotopic ratios alone does not allow distinction between these two types of sources results confirm that over the last estimated ca 200 ka dolomite rich pink layers at the mendeleev ridge were deposited during events probably associated with intensified iceberg transport from north america in general however sedimentation was mostly controlled by terrigenous input from the chukchi and east siberian seas whereas sediment supply from the laptev sea area remained less important and relatively constant at the studied location

neodymium isotopes as tracers in marine sediments and aerosols north atlantic nd and sm concentrations and nd isotopic compositions were measured on the detrital fraction of deep sea surface sediments and on aerosols sampled over the north atlantic and mediterranean sea the data expressed asend 0 and as model ages ranged from 14 5 end 0 4 9 and from 0 01 to 2 21 ga respectively two areas where the sediments contain relatively less radiogenic nd are to the west off north africa and eastward of the canadian shield this distribution is consistent with other tracers in suggesting that a significant fraction of the sediments are derived from aeolian material transported by major wind systems saharan dust transported in the equatorial trade winds belt and north american soil material transported in the latitudes of the westerlies between these aeolian dominated belts along an axis from the azores to gibraltar and the mediterranean lies a zone of more radiogenicend 0 values in sediments and aerosols influenced by the recent volcanism of this region previously reported distributions of nd isotopes in bottom formed iron manganese crusts and coatings are similar to distributions of nd isotope values in detrital sediments and aerosols this suggests that the detrital fraction has undergone partial dissolution and desorption in the water column and or in the pore waters of near surface sediments and that a significant proportion of nd in the authigenic ferromanganese phases is derived from this source and may therefore not represent strictly dissolved seawater nd isotope ratios useful as watermass tracers

geochemical and nd isotope composition of detrital sediments on the north margin of the south china sea provenance and tectonic implications a major re organization of regional drainages in eastern tibet and southwestern china took place in the cenozoic as deformation from the growing himalayas and tibetan plateau affected an increasingly wider area the effects of these changes on the regional sediment routing systems is not well constrained this study examines the geochemical and nd signatures of sedimentary rocks from the ying qiong and nanxiong basins on the northern margin of the south china sea to constrain and identify any significant changes in sediment source upper cretaceous to lower eocene sedimentary rocks in the nanxiong basin show higher th sc la sc th cr and th co ratios and lower eu eu ratios than paas post archaean australian shale which indicates that palaeozoic sedimentary rocks of the south china block were the main basin sediment source in contrast oligocene to pleistocene sedimentary rocks of the ying qiong basin show an abrupt change in these trace element ratios between 16ae3 and 10ae4 ma indicating a mid miocene shift in provenance end values from the ying qiong basin range 11ae 1t o 2ae1 reinforce this with pre 13ae8 ma sedimentary rocks having average end of 5ae6 range 2ae 1t o 7ae4 and post 13ae8 ma sedimentary rocks having average end of 9ae3 range 8ae 7t o 11ae1 during the oligocene the centre of rifting transferred south and basins on the north margin of the south china sea experienced rapid subsidence further uplift and erosion then exposed mesozoic and cenozoic granites that supplied large amounts of granitic detritus especially to the ying qiong basin then a change occurred at ca 13 ma resulting in less input from local sources i e the fault blocks formed by mesozoic cenozoic tectonics and magmatism to an increasing contribution of older continental material mostly from indochina to the west of the south

distinct control mechanism of fine grained sediments from yellow river and kyushu supply in the northern okinawa trough since the last glacial high resolution multi proxy records including clay minerals and sr nd pb isotopes of the clay sized silicate fraction of sediments from iodp site u1429 in the northern okinawa trough provide reliable evidence for distinct control mechanism on fine grained sediments input from the yellow river and the southern japanese islands to the northern okinawa trough since 34 ka bp provenance analysis indicates that the sediments were mainly derived from the yellow river and the island of kyushu since the last glacial clay sized sediments transported from the yellow river to the study site were strongly influenced by sea level fluctuation during low sea level stage 34 14 ka bp the paleo yellow river mouth was positioned closer to the northern okinawa trough favoring large fluvial discharge or even direct input of detrital sediments which resulted about four times more flux of clay sized sediments supply to the study area as during the relatively high sea level stage 14 0 ka bp the input of kyushu derived clay sized sediments to the study site was mainly controlled by the kuroshio current and tsushima warm current intensity with increased input in phase with weakened kuroshio current tsushima warm current our study suggests that the kuroshio current was very likely flowed into the okinawa trough and thus influenced the fine grained sediment transport in the area throughout the last glacial and deglacial during 34 11 ka bp the kyushu clay sized sediment input was mainly controlled by the kuroshio current since 11 ka bp the occurrence of tsushima warm current became important in influencing the kyushu fine grained sediment input to the northern okinawa trough

temporal variations in 87sr 86sr and ɛnd in sediments of the southeastern arabian sea impact of monsoon and surface water circulation sr and nd isotopic composition of silicate fractions of sediments have been measured in two well dated gravity cores from the eastern arabian sea archiving a depositional history of 29 and 40 ka the 87 sr 86 sr and e nd in the northern core ss 3104g 12 8 n 71 7 e ranges from 0 71416 to 0 71840 and 8 8 to 12 8 these variations are limited compared to those in the southeastern core ss 3101g 6 0 n 74 0 e in which they vary from 0 71412 to 0 72069 and 9 0 to 15 2 respectively this suggests that the variation in the relative proportions of sediments supplied from different sources to the core ss 3104g are limited compared to core ss 3101g the 87 sr 86 sr and e nd profiles of ss 3101g exhibit two major excursions ca 9 ka and 20 ka coinciding with periods of holocene intensified monsoon phase imp and the last glacial maximum lgm respectively with more radiogenic 87 sr 86 sr and lower e nd during these periods these excursions have been explained in terms of changes in the erosion patterns in the source regions and surface circulation of the northern indian ocean resulting from monsoon intensity variations the intensification of north east ne monsoon and associated strengthening of the east indian coastal current in southwest direction during lgm transported sediments with higher 87 sr 86 sr and lower e nd from the western bay of bengal to the arabian sea in contrast enhanced south west sw monsoon at 9 ka facilitated the transport of sediments from the northern arabian sea particularly indus derived to the southeastern arabian sea this study thus highlights the impact of monsoon variability on erosion patterns and ocean surface currents on the dispersal of sediments in determining the sr and nd isotopic composition of sediments deposited in the eastern arabian sea during the last 40 ka

the provenance of sediments in the gulf of lions western mediterranean sea in this study we undertook a reconnaissance study of sediments provenance in the gulf of lions focusing over the last 16 ka we used geochemical and isotopic tracers to determine the source of sediments and give insight into the weathering conditions prevailing sediments samples were selected both onshore and offshore from the western eastern and central part of the gulf of lions we analyzed bulk sediments coarse and fine silt and clay fractions elemental and nd isotope compositions appeared to differ from one grain size fraction to another one these are interpreted in terms of zircon addition in the coarse silt fraction for the elemental concentrations and variable sources influences for the nd isotope compositions our results indicate that sediments in the gulf of lions mainly originated from the rhone river watershed although a contribution of saharan dust is seen in one sample influence of pyrenean small rivers is minor in these samples some sr isotope compositions shifts are interpreted as reflecting variable amounts of chemical weathering that are consistent with published paleoclimatic reconstructions

patterns of ice rafted detritus in the glacial north atlantic 40 55 n the observation by heinrich 1988 that during the last glacial period much of the input of ice rafted detritus to the north atlantic sediments may have occurred as a succession of catastrophic events rekindled interest on the history of the northern ice sheets over the last glacial period in this paper we present a rapid method to study the distribution of these events both in space and time using whole core low field magnetic susceptibility we report on approximately 20 cores covering the last 150 to 250 kyr well defined patterns of ice rafted detritus appear during periods of large continental ice sheet extent although these are not always associated within their maxima most of the events may be traced across the north atlantic ocean for the six most recent heinrich layers hl two distinct patterns exist hl1 hl2 hl4 hl5 are distributed along the northern boundary of the glacial polar front over most of the north atlantic between 40 and 50 n hl3 is more restricted to the central and eastern part of the northern atlantic the nd sr isotopic composition of the material constituting different heinrich events indicates the different provenance of the two patterns hl3 has a typical scandinavia arctic icelandic young crust signature and the others have a large component of northern quebec and northern west greenland old crust material these isotopic results obtained on core su 9008 from the north american basin are in agreement with the study by jantschik and huon 1992 who used k ar dating of silt and clay size fractions of an eastern basin core me 68 89 these data confirm the large spatial scale of these events and the enormous amount of ice rafted detritus they represent

source variability of sediments in the shihmen reservoir northern taiwan sr isotopic evidence abstract high turbidity in water reservoirs during the monsoon season has caused serious problems for drinking water quality in taiwan in this study we collected stream waters and streambed sediments including bed loads and fresh landslide deposits in the dahan stream and analyzed 101 87 sr 86 sr ratios in different grain size fractions in the streambed sediments from the upper catchment and 3 sediment cores from the shihmen reservoir as well as dissolved major and trace elements in stream waters to identify possible changes of sediment sources in the reservoir the 87 sr 86 sr ratios in stream water and streambed sediments ranged from 0 71296 0 71349 and 0 71714 0 71843 respectively the large sr isotopic difference between the paired stream water and streambed sediments are evidence for disequilibrium water rock interaction in the weathering limited regions the sr isotopic compositions in bulk sediments and various grain size fractions showed no clear spatial variability however there is an interesting relationship between grain sizes and sr isotope ratios implying effects of mineral sorting during sediment transportation the illite crystallinity and the illite chemistry index of streambed sediment suggest moderate to strong chemical weathering in this regions the dissolved constituents in the dahan stream support that silicate weathering is the predominated controlled mechanism and only minor carbonate dissolution occurred near the central mountain range the 87 sr 86 sr ratios in the sediment cores suggest that modern reservoir sediment is mainly derived from the upper watershed composed of primarily oligocene sedimentary rocks however the sediment sources have changed significantly since the reservoir built 37 years ago the 87 sr 86 sr ratios were spread widely outside the present day observations in the dahan catchment the homogeneous distribution of 87 sr 86 sr in the upper reservoir cores reflected disturbance due to recent turbidity events within the reservoir these new chemical and isotopic data provide useful spatial and temporal information of weathering sources in a high denudation sub tropical mountainous watershed

nd isotopes in indian ocean sediments used as a tracer of supply to the ocean and circulation paths abstract neodynium isotopic compositions of eighteen sediments from the indian ocean were measured these quaternary marine sediments were collected in different physiographic provinces with samples being taken from the abyssal plain ridge submarine fan fracture zone and aseismic ridge environments the main results is that there are large areas in the indian ocean which are isotopically homogeneous although the results also enforce the idea that in marine sediments the continent derived material exerts an important control on the nd budget the northeastern part of the indian ocean is influenced by erosion of the indonesian arc the values between e 0 7 and e 0 8 observed in samples from the central indian ocean are nearly constant both in the eastern and western parts of the indian ocean this was interpreted as mixing between two major inputs firstly material coming from the erosion of the indian shield e 0 14 to 17 and secondly from the indonesian arc e 0 0 subsequently all the material is then homogenized by the oceanic circulation the western indian ocean values are more variable perhaps because of the proximity of old continental terrains i e southern africa and the influence of atlantic waters the highest value e 0 2 93 observed in the southern part of the indian ocean may be explained by the influence of the erosion of the crozet basaltic plateau indeed the two samples which exhibit positive nd isotopic values correspond geographically to the area of erosion of the crozet and possibly the kerguelen basaltic plateaus the location of the sample with the lowest isotopic value e 0 18 88 close to antarctica implies that this sediment might have included an old continental component of precambrian or even archaen age this result traces in the case of particle transport the circulation of water masses from antarctica to northern parts of the indian ocean which are known for their deep waters with the exception of the samples located near the crozet plateau where probable destruction of the plateau is occurring we do not observe any nd isotopic variations related to the specific physiographic location of any one sample consequently the nd isotopic variations are principally due to the pathways of water circulation and possibly winds over the indian ocean

deep circulation changes in the labrador sea since the last glacial maximum new constraints from sm nd data on sediments sm nd concentrations and nd isotopes were investigated in the fine fraction of two labrador sea cores to reconstruct the deep circulation patterns through changes in sedimentary supply since the last glacial stage three sources are involved the north american shield palaeozoic rocks from northeastern greenland and mid atlantic volcanism the variable input of these sources provides constraints on the relative sedimentary supply in conjunction with inception of deep currents during the last glacial stage a persistent but sluggish current occurred inside the labrador basin an increasing discharge of volcanic material driven by the north east atlantic deep water is documented since 14 3 kyr signaling the setup of a modern like deep circulation pattern throughout the labrador irminger and iceland basins during the last deglacial stage the isotopic record was punctually influenced by erosion processes related mainly to ice sheet instabilities especially 11 4 10 2 and 9 2 kyr ago

sr nd isotopic evidence of terrigenous flux variations in the bay of bengal implications of monsoons during the last 34 000 years 1 sr and nd isotopic compositions of a sediment core from the bay of bengal are used to constrain the provenance and transport pathways of their terrigenous component during the 3 to 34 14c kyr bp the results clearly demonstrate a distinctly different source for detrital fluxes on the ninetyeast ridge from that of distal and western fan sediments there is a systematic pattern of climate related variability in 87sr 86sr and nd o values at the studied location pulses of low 87sr 86sr higher radiogenic nd and high silt content occurring at 5 7 kyr intervals suggest significant changes in the detrital source increased supply of irrawaddy derived sediments appears to be the dominant source for these pulses our results support the hypothesis that rapid cold events of north atlantic heinrich events are characterized by the intensified northeast monsoon

nd and pb isotope signatures on the southeastern south american upper margin implications for sediment transport and source rocks abstract neodymium and lead isotope values in sediment samples were used to interpret sediment transport and source rocks on the southeastern south american upper margin the sediments of the argentinian margin exhibit an average nd value of 1 9 indicating the influence of the andean rocks as sediment sources sediments from the rio de la plata estuary show an average nd value of 9 6 which is similar to that of the southern brazilian upper margin finally sediments of southeastern brazil which are associated with the transport of the brazil current exhibit an average nd of 13 0 the pb isotope signatures also confirm the differentiation of source rocks in the sedimentation of the study area in addition pb isotopes helped to establish the extent of the influence of the rio de la plata on the sedimentation of the southern brazilian margin in terms of pb isotopes the sediments from the rio de la plata estuary and southern brazil are more radiogenic than those of southeastern brazil and the argentinian margin

sources of labrador sea sediments since the last glacial maximum inferred from nd pb isotopes pb isotopes have been measured in the clay size fraction of late glacial and holocene deep sea sediments recovered from two labrador sea piston cores that have been previously analyzed for nd isotopes the newly acquired pb isotopic data allow us to better constrain the different source areas that supplied clay size material during the last deglaciation until 8 6 kyr calendar ages nd pb data can be modeled mainly as a mixture between a precambrian crust and lower paleozoic material originating from the denudation of the pan african orogen the old material originates mainly from the archean lower proterozoic or both terranes of greenland and also probably corresponding terranes of labrador although minor input of other precambrian material is recorded in some detrital carbonate rich deglacial samples from orphan knoll the phanerozoic crustal end member consists of sediment material mainly originating from northwestern europe this source area is found to be the only significant source of young crustal material in early holocene sediments from the greenland rise no significant input from the mid atlantic volcanism is apparent this study puts further constraints on the deep circulation pattern during the last deglaciation it is concluded that at that time european phanerozoic material was carried from the norwegian sea through the wyville thompson ridge into the iceland basin by the north east atlantic deep water no evidence for an overflow is found either south of the iceland iceland scotland ridge or through the denmark strait

a 200 ka geomagnetic chronostratigraphy for the labrador sea indirect correlation of the sediment record to specmap abstract a chronostratigraphic framework for the last 200 ka based on relative variations of geomagnetic paleointensity has been derived for the labrador sea where 18o stratigraphies are compromised by lack of benthic foraminifera and environmental perturbations of the planktic record relative paleointensity records derived from three labrador sea piston cores are correlated to a recently developed 200 ka paleointensity composite sint 200 y guyodo j p valet earth planet sci lett 143 1996 23 36 the chronology for sint 200 was derived by correlating oxygen isotope stratigraphies from individual paleointensity records to the specmap chronostratigraphy the correlation of sint 200 to labrador sea paleointensity records allows the specmap chronology to be imported into the labrador sea although comparisons of the chronostratigraphy based on paleointensity correlations with those derived from ams 14c dates and 18o data indicate significant discrepancies support for the new chronostratigraphic framework is provided by 1 consistent correlation of labrador sea detrital layers to north atlantic heinrich layers 2 general consistency between planktic 18o values and the specmap reference curve and 3 feasible prediction for the age of ash layer 2 as the new chronostratigraphy is tied to specmap labrador sea sediment cores can now be directly compared with any specmap dated record

effects of sedimentary sorting on neodymium isotopes in deep sea turbidites the study of neodymium model ages of sedimentary rocks has added considerably to our understanding of crustal growth and evolution so far however the possible effects of various sedimentary processes on nd isotope distributions have not been fully evaluated here we present nd isotope data for a series of sand mud pairs in modern deep sea turbidites from different tectonic settings which show that sands and muds commonly have significantly different nd isotope compositions that in only some cases are associated with differences in sm nd ratio differences are as great as 7 ndunits corresponding to nd model ages that differ by up to 0 44 gyr and may be explained by separation or unmixing of components from different sources during sedimentary transport and sorting for one sample heavy mineral fraction ation may be indicated these results have implications for studies of nd model ages in sedimentary rocks and for the interpretation of provenance from sedimentary petrography and geochemistry

long term stability in the production of a nw mediterranean posidonia oceanica l delile meadow abstract long term changes in leaf net production of the seagrass posidonia oceanica l delile and in the irradiance arriving at the meadow canopy were investigated in a nw mediterranean meadow using a palaeoecological approach we conducted in situ shade experiments to find the relationships between the carbon stable isotope ratio 13c of plant tissues leaf net production and ambient irradiance the relationships were highly significant and fitted the michaelis menten equation and power functions these functions were used to reconstruct light and net production using the 13c of p oceanica detritus as a palaeoecological proxy along a 150 cm core of p oceanica matte a peat like deposit formed by this endemic seagrass species the 13c values of sheath detritus along the core i e the net leaf production showed a weak but significant decrease towards the present time r 0 308 p 0 02 probably as a result of 1 an increase in dic availability and or 2 a progressive change in the carbon isotopic signature of dic both of which are consistent with a rise in anthropogenic atmospheric co2 the canopy irradiance reconstructed for the last 1200 years showed a mean value of 128 e m 2 s 1 with a range of 12 5 280 e m 2 s 1 the reconstruction of the net leaf production for the same period yielded a mean value of 2 5 mg dw day 1 shoot 1 with a range of 2 0 2 7 mg dw day 1 shoot 1 both ranges are within the values reported in the literature for present day studies the absence of significant fluctuations or sudden changes through time suggests remarkable ecosystem stability during the last millennium

wisconsinan late glacial environmental change on the southeast baffin shelf southeast baffin island and northern labrador the importance of the baffin labrador region is explained in terms of the channelling through this area of the mass flux of meltwater from the laurentide ice sheet and the probable effects of this on the thermohaline circulation of the north atlantic the chronology of glaciation and deglaciation in the region is summarised reference is made to recent marine records from the baffin shelf isotopic changes recorded in foraminiferal assemblages obtained from marine sediments in the baffin shelf labrador sea area indicate the timing and possible magnitude of meltwater fluxes during the period 14 0 11 0 ka bp

smnd signature of modern and late quaternary sediments from the northwest north atlantic implications for deep current changes since the last glacial maximum abstract nd isotopes and sm nd concentrations have been investigated in the clay size fraction of surface and late quaternary sediments of the northern north atlantic four sources of nd have been identified in the surface sediments 1 a radiogenic nd typical of the iceland volcanism 2 a pan african nd issued from eastern greenland 3 a variscan nd derived from the arctic ocean 4 an old unradiogenic nd related to the north american shield in the iceland and irminger basins the major sources of nd are the variscan nd derived from the arctic ocean and the iceland nd except in the western irminger basin where the pan african nd originating from eastern greenland is dominant and labels sedimentary supplies linked to the denmark strait overflow water nd derived from icelandic volcanism is never clearly dominant even on the reykjanes ridge and the nd derived from the american shield becomes dominant only in the labrador sea sediments lying in the pathway of the western boundary undercurrent have nd isotopic compositions which are shifted towards more radiogenic values indicating an input of material from the eastern basins carried by this deep current late quaternary sediments were cored from the southern greenland rise core 90 013 013 and eastern labrador rise orphan knoll core 91 045 094 in core 90 013 013 nd values during the last glacial maximum are as low as 20 but subsequently rose to 9 in the modern sediments indicating that the sedimentary material during the last glacial maximum was dominated by unradiogenic nd from the north american shield this may be related to a lesser outflow of the western boundary undercurrent in core 91 045 094 located along the labrador current trajectory a dominant supply of north american shield nd is recorded perhaps originating at least partially from the hudson strait the sm nd data are compatible with smectite vs illite studies at the same sites which suggest a continuous but more modest western boundary undercurrent supply during last glacial maximum

late glacial ice margins and deglacial chronology for southeastern baffin island and hudson strait eastern canadian arctic discussion the authors j a stravers g h miller and d s kaufman have provided an important synthesis of ongoing research bordering outer hudson strait their reconstruction proposes that on two occasions during the early holocene labrador sector ice crossed hudson strait to override parts of southeast baffin island their conclusion proposes that by 9900 bp the activity of foxe basin ice and the local ice caps had become subordinate to that of labrador ungava ice p 1015 so too had the hudson strait ice stream farther to the west if correct this reconstruction has considerable paleoclimatic and glaciological implications for the northeast laurentide ice sheet given its importance this hypothesis warrants further scrutiny especially the consideration of several alternative interpretations that arise from the data

holocene sea surface conditions in the north atlantic contrasted trends and regimes in the western and eastern sectors labrador sea vs iceland basin abstract two sediment cores from the labrador sea and one from the iceland basin were analysed in order to compare holocene sea surface conditions across the northern north atlantic 18o measurements on meso and epi planktonic foraminifera neogloboquadrina pachyderma left coiling and globigerina bulloides along with sea surface condition reconstructions using transfer functions based on dinoflagellate cyst assemblages were used to document thermohaline properties of the upper water column at the labrador sea sites a decreasing trend in sea surface temperature following an early holocene maximum is observed at the iceland basin site a hiatus between 13 and 8 ka bp prevents us from documenting the entire holocene but a stable to slightly decreasing trend is observed from 8 ka bp onwards sea surface salinity and potential density show little variation at the orphan knoll site in the labrador sea since 7 ka bp whereas they depict a decreasing trend at the two other sites since ca 8 ka bp this shift in values suggests a progressive enhancement of labrador sea water formation and a relative decrease in the nordic seas components of the north atlantic deep water i e denmark strait overflow water and norwegian sea overflow water discrepancies are also observed with regard to millennial frequency oscillations in sea surface conditions at the easternmost site they likely match previously documented cold water pulses in the north eastern atlantic whereas they do not show any clear pattern at the westernmost sites hence the western and eastern areas show different behaviours with respect to both long term and high frequency fluctuations

modelling of the construction of the rhone alluvial plain since 15 000 years bp a numerical model presented here develops a three dimensional image of alluvial media on an elementary scale significant for groundwater flow modelling the model was tested on the alluvial plain of the rhone river france on a scale of several kilometres and from geomorphological observations and dating reproduced the construction of this alluvial plain from 15 000 years bp to the present the history of the alluvial plain during the late glacial and holocene periods is summarized through most of this time the river rhone has maintained a braided pattern with the exception of two incising phases with a meander pattern the model does not use any physically based equations or water representation the main processes governing the construction of the plain are modelled by simple rules chosen according to geometrical or empirical laws taken from the literature or as modelling assumptions using multi agent concepts of distribution and interaction of elementary entities these sedimentary rules are applied to sediment entities or to conceptual erosion entities that simulate local deposition and erosion of sediments the sedimentation model reproduces the various climatic periods during which the sediments were deposited by simulating genetic periods and associated modelled processes for each period the model was constrained by quantitative field data such as altitude of ancient channels and deposits or thickness of sediments the general geometry of the alluvial deposits was satisfactorily reproduced during the simulation characteristic large scale features emerge despite the use of local rules the model results are discussed with reference to other approaches such as geostatistical or boolean models and the applicability of the model to other less documented alluvial plains is outlined

use of sedimentological information for geometric simulation of natural porous media structure a geometric simulation method was used to develop a three dimensional highly detailed synthetic representation of point bar sediments in the wabash river system geometric simulation methods in comparison to well known second order stochastic methods offer the advantage of being more closely related to depositional processes which are often similarly conceptualized i e described in terms of shapes of discrete bed forms trends in grain size and spatial relationships of defined geologic facies multiple scales of geometric variation were defined within a sedimentologically prescribed framework and shapes of discrete geometric elements were established at each scale the selected shapes were based on published field studies including sedimentological bed form studies and trench studies in active point bar sediments the parameterization of the shapes allowed for random variability of the shape descriptors discrete shapes were then generated and assimilated by computer hydraulic conductivity values were assigned to the discrete elements based on reports of observed variations in grain size and field measurements of hydraulic conductivity the synthetic model referred to as a numerical aquifer is being used as the basis for extensive numerical experimentation to study the relationship between natural spatial structure and subsurface flow and transport

reduced admixture of north atlantic deep water to the deep central south pacific during the last two glacial periods the south pacific is a sensitive location for the variability of the global oceanic thermohaline circulation given that deep waters from the atlantic ocean the southern ocean and the pacific basin are exchanged here we reconstruct the deep water circulation of the central south pacific for the last two glacial cycles from 240 000 years ago to the holocene based on radiogenic neodymium nd and lead pb isotope records complemented by benthic stable carbon data obtained from two sediment cores located on the flanks of the east pacific rise the records show small but consistent glacial interglacial changes in all three isotopic systems with interglacial average values of 5 8 and 18 757 for end and 206pb 204pb respectively whereas glacial averages are 5 3 and 18 744 comparison of this variability of circumpolar deep water cdw to previously published records along the pathway of the global thermohaline circulation is consistent with reduced admixture of north atlantic deep water to cdw during cold stages the absolute values and amplitudes of the benthic 13c variations are essentially indistinguishable from other records of the southern hemisphere and confirm that the low central south pacific sedimentation rates did not result in a significant reduction of the amplitude of any of the measured proxies in addition the combined detrital nd and strontium 87sr 86sr isotope signatures imply that australian and new zealand dust has remained the principal contributor of lithogenic material to the central south pacific

grain size and srnd isotopes as tracer of paleo bottom current strength northeast atlantic ocean abstract a crucial question in modern paleoceanographic research is how vigourous was the bottom current in the glacial north atlantic ocean distribution of sediment grain size can provide such information if the characteristics of the source functions are known the interest of this paper is to use the sr nd isotopic composition of lithic particles as a tracer of origin in order to determine possible changes in the source function over the last 185 kyr grain size distribution data are derived from a sediment core in the icelandic basin gardar drift the distribution pattern reveals a well sorted silt size modal size 20 m in the glacial deposits sr and nd isotopic composition measured on separate size fractions indicates a more constant local origin iceland for the silt fraction than for the fine fraction these data suggest that the increase in the silt fraction during glacial periods is related primarily to an increase in the bottom current strength rather than to changes in sediment supply i e ice rafting turbidity current the increase in vigour of the bottom current recorded during the isotopic stages 6 4 and the last post glacial periods could have been initiated by a southward shift of the zone of deep water formation in the northern part of the icelandic basin

riparian wetlands of the middle reach of the seine river france historical development investigation and present hydrologic functioning a case study along the middle reach of the seine river upstream from paris riparian wetlands that have been functioning for centuries first as a result of a succession of sedimentological hydrological processes and later of continuous management practices where the value of the wetlands has been acknowledged as well as their importance for the ecology here we present the results of a multidisciplinary research programme focused on this system with emphasis on its present hydrological functioning and on the tools used to understand and quantify it the major hydrological and geochemical processes that are active at present are reviewed but past processes are also described as well as the potential long term evolution of the system this study uses several innovative tools to investigate the wetlands and analyse them in space thermographic aerial survey and electromagnetic prospecting resulting in a map of clay layer thickness concerning the wetland hydrology water budgets established at different time scales several years one year a season illustrate the exchanges between the watershed the river and the wetland and water storage in the wetlands during flood events the results show how the upstream reservoirs built during the last 20 years presently control the preservation and functioning of downstream riparian wetlands monitoring and modelling of the hydrological functioning of one wetland site have made it possible to identify and quantify exchanges between the wetland especially in the unsaturated upper layer and its environment in situ measurements of denitrification rates in the wetland were used to make initial estimates of its nitrate elimination capacity

fingerprinting gondwana versus baltica provenance nd and sr isotopes in lower paleozoic clastic rocks of the malopolska and łysogory terranes southern poland abstract neodymium and strontium isotope compositions of clastic material in lower paleozoic rocks in addition to detrital zircon and mica geochronology and faunal data are used to constrain the geotectonic provenance of the malopolska and ysogory terranes in southern poland being characterized by markedly different geological histories during early paleozoic times malopolska and ysogory were most often interpreted as exotic terranes but their identity provenance and accretionary history are still being discussed this study presents the first systematic nd and sr isotope survey of the lower paleozoic siliciclastic rocks cambrian clastic rocks of malopolska differ in their nd and sr isotope compositions from those of ysogory the former are characterized by a wide range of the end 505 ma values from 11 7 to 5 7 sr isotope ratios from 0 712 to 0 767 and model ages t2dm predominantly younger than 1 9 ga whereas the end t values of the latter vary within a fairly narrow range of the end 505 ma from 11 0 to 8 3 sr isotope ratios from 0 722 to 0 754 and model ages are older than 1 9 ga new nd data combined with detrital zircon ages provide evidence that malopolska must have been supplied with clastic material from amazonian sources during cambrian times being also progressively sourced from the baltic svecofennian crust in the middle cambrian detritus recognized in ysogory has mostly been derived from the svecofennian basement of fennoscandia but it has also a small addition from cadomian sources all provenance and biogeographic data suggest that malopolska was situated close to the amazonian craton near the western end of the cadomian belt during the early cambrian and it was not until the late middle cambrian that malopolska collided with the baltica margin during the late cambrian ysogory occupied a position between baltica and the cadomian belt but it was probably not yet accreted to the baltic crust at that time

a field study of wave reflections from an exposed dissipative beach abstract this paper describes a field study of wave reflections from an exposed dissipative beach using only water surface elevation data from five wave height sensors many insights were gained into beach reflections and their detection a technique normally reserved for laboratory use was successfully applied to surf zone data to separate incident and reflected infragravity wave energy spectra the reflected wave energy was found to be significant for all wave periods greater than 20 seconds and often total for wave periods greater than 30 seconds the evidence was heavily weighted towards the observed reflected wave activity being essentially two dimensional with the influence of three dimensional edge waves being minimal other findings relate to the value of wave energy spectra computed from a single surf zone sensor the relevance of single slope approximations of beach profiles and the relationship between incident infragravity wave activity and the longer period swash excursions on a beach face

interglacial responses of the southern greenland ice sheet over the last 430 000 years determined using particle size specific magnetic and isotopic tracers abstract the past behavior of the greenland ice sheet can provide important insight into climatic thresholds that may initiate and drive major ice sheet retreat particle size specific magnetic and sr nd pb isotope records from eirik ridge sediments south of greenland track southern greenland ice sheet sgis erosional signatures over the past 430 ka by discriminating changes in sediment source and transport over the eirik ridge ground truthed magnetic and isotopic compositions of subglacial silt from south greenland s precambrian bedrock terranes constrain independent magnetic and isotopic estimates of eirik ridge silt provenance which in turn indicate that the southern greenland ice sheet sgis retreated within its present margin during three of the four previous interglaciations over the past 430 ka retreat of the sgis was extensive during the marine isotope stage mis 5e 9 and 11 interglaciations continuing unabated despite declining insolation during mis 5e and 9 with near complete deglaciation in mis 11 retreat of the sgis during mis 7 was minimal notwithstanding strong insolation forcing while holocene retreat slowed shortly after peak insolation the reconstruction of sgis retreat during the last five deglacial and interglacial periods suggests that a threshold for extensive sgis retreat exists between the insolation and co 2 states of the holocene and the mis 5e and 9 interglaciations with co 2 exerting a stronger control on sgis retreat than insolation our results also suggest that the extent and stability of the sgis in the holocene is anomalous in the context of late quaternary interglaciations

calibration of the c 14 timescale over the past 30 000 years using mass spectrometric u th ages from barbados corals uranium thorium ages obtained by mass spectrometry from corals raised off the island of barbados confirm the high precision of this technique over at least the past 30 000 years comparison of the u th ages with 14c ages obtained on the holocene samples shows that the u th ages are accurate because they accord with the dendrochronological calibration before 9 000 yr bp the 14c ages are systematically younger than the u th ages with a maximum difference of 3 500 yr at 20 000 yrbp the u th technique thus provides a way of calibrating the radiocarbon timescale beyond the range of dendrochronological calibration

strontium neodymium and lead isotope variations of authigenic and silicate sediment components from the late cenozoic arctic ocean implications for sediment provenance and the source of trace metals in seawater proven ance changes of silicate sediment deposited during the late cenozoic 5 0 ma on the alpha ridge central arctic ocean are determined from variations in strontium lead and neodymium isotope compositions whereas strontium and lead isotope compositions are relatively invariant from 5 to 1 7 ma end values start to increase at 3 ma subsequently s7sr 86sr and 2 6pb z 4pb ratios progressively increase and end values progressively decrease from 1 7 ma to the present day from these isotope variations three different endmember compositions for sediment source regions are defined the two endmember compositions defined by sediment that was deposited by sea ice from 5 to 1 7 ma are consistent with a significant component being derived from the east siberian shelf the progressive change in isotope compositions from 1 7 to 0 ma correlates with an increase in coarse detritus deposited by icebergs over this time period the isotope data are consistent with a progressive increase in the proportion of sediment that was deposited in the central arctic ocean since 1 7 ma having been derived from the northern canada or queen elizabeth island region changes in the strontium neodymium and lead isotope compositions of arctic seawater are determined by analyzing the oxide fractions of fe mn micronodules strontium isotope compositions of the microno dule oxide fractions are similar to published late cenozoic seawater data and indicate that 97 of the sr is seawater derived but minute contributions of sr from silicate detritus prohibit using the hydrogenous fractions for chronostratigraphic purposes neodymium and lead isotope compositions of the micronodule oxide fractions which reflect those of arctic seawater follow the isotope variations of the silicate components throughout the late cenozoic these relations indicate that river water can not be the primary source of rare earth elements and pb to the dissolved reservoir in arctic seawater and that ice rafted detritus by dissolution or exchange processes is an important source of trace elements to seawater in ice covered oceans copyright 1997 elsevier science ltd

neodymium isotopic variations in north pacific modern silicate sediment and the insignificance of detrital ree contributions to seawater the neodymium isotopic composition of the silicate fraction of holocene pelagic sediments from the north pacific define two provinces a central north pacific province characterized by unradiogenic and remarkably homogeneous end 10 2 0 5 and a narrow circum pacific marginal province characterized by more radiogenic and variable end 4 2 3 8 the silicate fraction in the central north pacific is exclusively eolian based on prevailing wind patterns meteorological data and neodymium isotopic data the only significant sediment source is chinese loess leaching experiments on chinese loess confirm that leachable nd is isotopically indistinguishable from bulk and residual silicate nd silicates in the circum north pacific marginal province comprise eolian loess volcanic ash and hemipelagic sediments derived from volcanic arcs a compilation of pacific seawater and mn nodule end data shows no clear spatial variation except for a general decrease from surface to deep waters from 3 to 4 and slightly lower end in bottom waters along the western north pacific due to the incursion of antarctic bottom water the relative homogeneity of bottom water end which contrasts sharply with the distinctive variation in sediment end plus the large difference between the average end of bottom waters and the central north pacific eolian silicates 4 vs 10 suggests that any contribution of ree to seawater from eolian materials is insignificant furthermore leaching of ree from eolian particles as they sink though the water column must be insignificant because nd in shallow waters is more radiogenic than nd in deeper waters that there is no contrast in the nd isotopic composition of bottom waters that overlie the central and marginal sediment provinces suggests that the ash and hemipelagic sediments derived from pacific rim volcanic arcs also contribute minimal ree to seawater the elimination of eolian ash and hemipelagic sediments leaves only near shore riverine particulates as a possibly significant particulate source of ree to seawater

using nd isotopes to understand the provenance of sedimentary rocks from a continental margin to a foreland basin in the neoproterozoic paraguay belt central brazil abstract the neoproterozoic paraguay belt pb in central south america includes a thick sequence of sedimentary rocks that were deposited and deformed along the southeastern margin of the amazonian craton the stratigraphy is divided into four major successions 1 a lower succession of fine grained sedimentary rocks in the cuiaba group 2 a glacial diamictite turbidite succession in the cuiaba group and puga formation 3 a carbonate succession in the araras group and 4 an upper succession composed of sandstones siltstones and arkoses in the alto paraguay group this sequence of sedimentary rocks represents a passive margin that was deformed during late neoproterozoic cambrian epoch we investigated the nd isotope signature of the sedimentary rocks while considering the different lithostratigraphic sequences and their geographic extent within the pb nd isotopic ratios and tdm model ages suggest a dominant continental source where are related to paleoproterozoic to mesoproterozoic rocks of the amazonian craton the nd isotopic compositions do not display a major contribution from the younger neoproterozoic juvenile magmatic arc terrane of the brasilia belt tdm model ages plotted against the stratigraphy show old tdm model ages of ca 2 3 1 5 ga and strongly negative nd t values of 11 to 6 revealing sedimentary changes in the source the changing nd t values are interpreted to be function of the erosion deposition ratio that occurred due to uplift during orogenic processes causing variations in the source area compared to the lower glacial and carbonate successions the upper siliciclastic succession shows lower nd isotopic ratios that is consistent with a source from the paraguay belt or another neoproterozoic continental source this can be accommodated by the change from an extensional continental margin to a compressional foreland basin setting this provenance study of the paraguay belt sedimentary rocks has important implications for the west gondwana collision history prior to its final amalgamation at the end of the neoproterozoic and beginning of the cambrian epoch

link between climate and catchment erosion in the himalaya during the late quaternary abstract few studies using geochemistry of sediments from plains and delta of the himalayan river system have reported contrasting results on the shift in erosion of different lithotectonic units across the strike of himalayan orogen in response to changes in the intensity of indian summer monsoon ism and glacial cover during the late quaternary here we present records of the 143nd 144nd end and 87sr 86sr ratios and 13c of sediment organic matter 13csom in bulk sediment samples from two 45 m long alluvial cores collected from a paleo sutlej channel in sirhind punjab at an upstream connection of a large river ghaggar hakra with present day sutlej river in nw india the isotopic variations are compared with the available proxy records that document changes in the ism and himalayan glacial extent significant covariation in down core profiles of end 14 1 to 22 2 and 87sr 86sr 0 72251 0 79456 reveals changing contributions of sediment derived from the higher and lesser himalaya end member sources in the catchment higher end and lower 87sr 86sr during early marine isotope stage mis 1 and late mis3 reflects increased contribution from the higher himalaya as a result of receding glacial cover as well as intense ism that penetrates into the interior of the higher himalaya during warm periods the 13csom varies from 28 5 to 21 3 and shows a 5 7 increase from colder mis2 to warmer early mis1 implying an increase in c4 plant abundance during the same period in response to intensification of the ism in the post last glacial maximum period these variations in sediment provenance and vegetation pattern thus highlight the pronounced influence of climate on distribution of erosion and vegetation types in the nw himalaya

modern sedimentary dynamics in the southwestern atlantic contouritic depositional system new insights from the uruguayan margin based on a geochemical approach abstract recent high resolution multidisciplinary studies have provided models of modern and ancient sedimentary processes along the uruguayan slope 34 s to 36 s a strategic location in the southwestern atlantic margin sam according to these models modern surface sedimentation is controlled by the transition between the subtropical shelf front and the brazil malvinas confluence bmc and presumably by the summer rio de la plata rdlp buoyant plume ancient sedimentary dynamics is reflected as the northernmost distribution of the contouritic terraces present in the argentinean margin reflecting the position of the bmc during glacial stages in this work the spatial correlation of previous evidence from modern surface facies and ancient geomorphological features sedimentation provides a sound framework in order to interpret novel information on the geochemical composition of surface sediments proxies for the origins of lithogenic nd al si and fe k and organic matter c n 13 c and 15 n previously calibrated for the sam and the elemental compositions al ti fe k mn ca p mg ba and si of surface sediments were used to test working hypotheses on sediment provenance surface productivity and the environmental control of elementary composition the distribution of surface sediments is correlated with regional geomorphology which includes contouritic terraces in the south and a progradational slope in the north this supports the idea of a strong morphological control on the modern sedimentary processes however the distribution and content of terrigenous biogenic and erosional elements together with the dominance of pampean patagonian sediments suggests that 1 the rdlp does not contribute with any lithogenic sediments to the slope and instead fertilizes open waters with contributions consisting of mixed marine organic matter 2 in the north the strong action of the bc and the re circulated aaiw below promotes redistribution of sediments from the shelf and upper slope towards the middle slope including sandy spillover slump transport and hemipelagic sedimentation re suspended from the continental shelf 3 with respect to glacial stages this across slope sedimentation was displaced southwards dominating even the northernmost distribution of contouritic terraces and 4 sedimentation related to contouritic features as modern depositional and erosional sedimentation was restricted to the south accompanying the distribution of the mc thus although the core hypothesis of the previous modern sedimentary model can be retained considerable improvements in our knowledge of the sediment dynamics in the sam have emerged from the present analysis of geochemical proxies

recirculating components to the deep boundary current of the northern north atlantic abstract the meridional overturning system of the north atlantic is conventionally thought of as transporting warm water 4 c to high latitudes and covd water to low latitudes the northern cold water sources for this system are dense overflow from the nordic seas and less dense water from the labrador sea lsw the overflow components are carried westward by a deep northern boundary current dnbc that is shown here actually to begin southeast of the overflow regions the dnbc lies along the southern side of a system of islands and submarine ridges that divides the nordic seas from the subpolar basins the overflows act to increase the transport of the dnbc and this transport is further increased through the entrainment of warm waters once inside the labrador sea the dnbc is joined by lsw before continuing south to low latitudes as a cold deep western boundary current dwbc however published transport estimates are larger than can be explained by warm water entrainment alone thus indicating entrainment also of recirculating cold components the subject of this paper their sources are shown to be the lsw and cold abyssal waters originating from the southern hemisphere the lsw is entrained downward into the denser part of the dnbc and laterally into the upper part of the dwbc whereas the cold abyssal waters are supplied by an eastern intensified northward flow in the eastern atlantic that serves as the initial source of the dnbc and by a similar northward flow in the western atlantic the meridional overturning system described includes recirculations and poleward transport of cold water in addition tothe components described by the conventional system the cold abyssal waters in both the eastern and western basins have relatively low levels of oxygen and high concentrations of silicate reflecting their southern origin but their influence in the northwestern atlantic is somewhat obscurred by strong recirculating cyclonic gyres in the newfoundland and labrador basins this influence is detected by a deep silicate maximum extending poleward from the mid latitude western atlantic through the two gyres with eastern concentration and recirculating back diluted toward the south in the dwbc within the respective basins such a maximum also extends northward through the irminger basin into the dnbc but there is an ambiguity as to whether this is a direct extension of the signal from the south in the western basin or if it comes from the mid latitude eastern basin by way of westward flow through the charlie gibbs fracture zone it is perhaps consequence of both estimates of the volume transports of the various recirculating cold components indicate that they supply about as much water to the deep boundary currents as do the combined cold water sources in the north

south greenland ice sheet collapse during marine isotope stage 11 varying levels of boreal summer insolation and associated earth system feedbacks led to differing climate and ice sheet states during late quaternary interglaciations in particular marine isotope stage mis 11 was an exceptionally long interglaciation and potentially had a global mean sea level 6 to 13 metres above the present level around 410 000 to 400 000 years ago implying substantial mass loss from the greenland ice sheet gis there are however no model simulations and only limited proxy data to constrain the magnitude of the gis response to climate change during this super interglacial thus confounding efforts to assess climate ice sheet threshold behaviour and associated sea level rise here we show that the south gis was drastically smaller during mis 11 than it is now with only a small residual ice dome over southernmost greenland we use the strontium neodymium lead isotopic composition of proglacial sediment discharged from south greenland to constrain the provenance of terrigenous silt deposited on the eirik drift a sedimentary deposit off the south greenland margin we identify a major reduction in sediment input derived from south greenland s precambrian bedrock terranes probably reflecting the cessation of subglacial erosion and sediment transport as a result of near complete deglaciation of south greenland comparison with ice sheet configurations from numerical models suggests that the gis lost about 4 5 to 6 metres of sea level equivalent volume during mis 11 this is evidence for late quaternary gis collapse after it crossed a climate ice sheet stability threshold that may have been no more than several degrees above pre industrial temperatures

braided rivers perspectives and problems progress towards a fuller understanding of the dynamics and deposits of braided rivers demands an interdisciplinary approach to a host of unresolved problems although many advances have been made within recent years in interpreting the mechanics of flow transport of sediment and sedimentary architecture of braided rivers many key issues remain to be addressed in particular several areas demand attention the mechanisms of braid bar initiation confluence diffluence dynamics the nature of sedimentary facies over a range of grain sizes and the influence of flow stage and aggradational regime upon the depositional architecture over a range of channel scales this paper focuses upon these issues and highlights several areas of fruitful future interdisciplinary collaboration 1993 the geological society

comparison of genesis and geostatistical methods for characterizing the heterogeneity of alluvial media groundwater flow and transport simulations abstract we describe a new method for generating the sediment heterogeneity of alluvial deposits based on a genesis model which mimics some of the hydraulic rules by which meandering or braided streams deposit or erode sediments the new model is described and compared with other approaches and is then applied to a 5 4 1 4 km 2 reach of the aube river upstream of paris the model is based on data obtained from a single cross section of the alluvial plain with 44 auger holes along the 1 4 km stretch of the plain as the model describes the sediment facies we assign to each facies an assumed hydraulic conductivity flow and transport simulations are then made with the commonly used code modflow in order to compare the results with simulations based on other descriptions of heterogeneous media we then use classical geostatistical tools indicator simulations to generate alternative images of the same medium based on the same initial data and the same assumptions on the hydraulic conductivity of each facies finally an equivalent uniform medium obtained through permeability upscaling is also generated comparing these three approaches on the basis of the flow and transport results we show the intrinsic capacity of the new model to generate more realistic flow and transport processes in heterogeneous alluvial media where permeability barriers and buried channels dominate the spatial distribution of heterogeneities

fluvial responses to climate and sea level change a review and look forward summary fluvial landforms and deposits provide one of the most readily studied quaternary continental records and alluvial strata represent an important component in most ancient continental interior and continental margin successions moreover studies of the long term dynamics of fluvial systems and their responses to external or allogenic controls can play important roles in research concerning both global change and sequence stratigraphy as well as in studies of the dynamic interactions between tectonic activity and surface processes these themes were energized in the final decades of the twentieth century and may become increasingly important in the first decades of this millennium this review paper provides a historical perspective on the development of ideas in the fields of geomorphology quaternary geology vs sedimentary geology and then summarizes key processes that operate to produce alluvial stratigraphic records over time scales of 103 106 years of particular interest are changes in discharge regimes sediment supply and sediment storage en route from source terrains to sedimentary basins as well as changes in sea level and the concept of accommodation late quaternary stratigraphic records from the loire france mississippi usa colorado texas usa and rhine meuse the netherlands rivers are used to illustrate the influences of climate change on continental interior rivers as well as the influence of interacting climate and sea level change on continental margin systems the paper concludes with a look forward to a bright future for studies of fluvial response to climate and sea level change at present empirical field based research on fluvial response to climate and sea level change lags behind a the global change community s understanding of the magnitude and frequency of climate and sea level change b the sequence stratigraphic community s desire to interpret climate and especially sea level change as forcing mechanisms and c the modelling community s ability to generate numerical and physical models of surface processes and their stratigraphic results a major challenge for the future is to catch up which will require the development of more detailed and sophisticated quaternary stratigraphic sedimentological and geochronological frameworks in a variety of continental interior and continental margin settings there is a particular need for studies that seek to document fluvial responses to allogenic forcing over both shorter 102 103 years and longer 104 106 years time scales than has commonly been the case to date as well as in larger river systems from source to sink studies of quaternary systems in depositional basin settings are especially critical because they can provide realistic analogues for interpretation of the pre quaternary rock record

sm nd dating of fig tree clay minerals of the barberton greenstone belt south africa sm nd isotopic data from carbonate derived clay minerals of the 3 22 3 25 ga fig tree group barberton greenstone belt south africa form a linear array corresponding to an age of 3102 64 ma making these minerals the oldest dated clays on earth the obtained age is 120 160 m y younger than the depositional age determined by zircon geochronology nd model ages for the clays range from approximately 3 39 to 3 44 ga and almost cover the age variation of the barberton greenstone belt rocks consistent with independent evidence that the clay minerals are derived from material of the belt the combined isotopic and mineralogical data provide evidence for a cryptic thermal overprint in the sediments of the belt however the highest temperature reached by the samples since the time of clay mineral formation was 300 degrees c lower than virtually any known early archean supracrustal sequence

climate forcing of the pb isotope record of terrigenous input into the equatorial atlantic abstract pb isotopic compositions of bulk sediment cores from the tropical atlantic are used here to infer variations in the provenance of terrigenous input to the tropical atlantic during pleistocene climate cycles the 200 ka high precision 2 100 ppm pb isotope records of the ceara rise western atlantic and sierra leone rise eastern atlantic cores show a clear glacial interglacial cyclicity reflected by alternating unradiogenic pb and radiogenic pb in both cores the glacial interglacial pb isotopic contrast is also observed in pb pb space and can be explained in terms of binary mixing variations along the mixing lines reflecting changes in the relative proportions of the glacial unradiogenic and interglacial radiogenic pb source s the pleistocene pb isotopic variability of the terrigenous input to the ceara rise can be linked to changes in the weathering styles in the amazon basin and as a result in the amazon river discharge these changes are reflected by a greater contribution from the highlands andes pb source during glacial times and strengthening of the lowlands shield pb source during interglacials on the other hand pb isotopic variations in the sierra leone rise core indicate increased pb inputs from the saharan dust plume during glacial times in agreement with the wind patterns over africa furthermore this result bears some implications on the cause of the enhanced glacial terrigenous fluxes to the tropical atlantic which we infer to be due to increase in winter wind transport rather than glacial hyperaridity the cyclicity of the ceara rise and sierra leone rise pb isotopic records together with changes in the proportions of mixing sources throughout the last 200 ka monitor changes in the hydrological cycle over south america and the wind systems over africa respectively both of which are linked to the seasonal latitudinal migration of the intertropical convergence zone the correlation found between pb isotope cycles and other paleoclimate proxies suggests that pb isotopes may be responding to variations in earth s orbital parameters

infragravity waves and nearshore bars in protected storm dominated coastal environments abstract field measurements of run up oscillations were conducted on fetch restricted storm wave dominated beaches in denmark experiments took place under conditions with breaker heights of 1 5 3 m and wave periods of 5 7 s statistically significant spectral peaks were identified in the infragravity regime the frequencies of these peaks were compared to frequencies predicted by the edge wave cut off model originally proposed by huntley j geophys res 81 1976 and it was found that the waves were probably cut off mode edge waves with the mode number corresponding to the number of nearshore bars at the locality in question the waves were usually standing alongshore but during an experiment in which a very high energy level prevailed the edge waves were probably progressive the selection of only one or two cut off modes may be the result of an interrelationship between the topographic cut off and offshore wave groups the nearshore region was surveyed following storms it was found that there was generally a good correlation between bar positions and rhythmic dimensions and the theoretical cross shore and longshore structure of the recorded edge waves it is concluded that infragravity waves may be important in the formation migration and morphology of nearshore bars with the number of bars depending on the edge wave mode number

stream curvature and bank erosion a model based on the momentum equation based on the momentum equation of flow the force per unit area which the flow exerts radially on the outer bank of a stream bend is expressed by an equation in which the force is explicitly related to the curvature ratio r w curve radius channel width a dimensionless curvature coefficient c alpha is defined which is dependent on r w and the coefficient of dynamic bedload friction tan alpha exploring the changes of c alpha with r w reveals a functional relationship which for the known values of tan alpha shows maximal values of c alpha for r w values between 2 and 4 the theoretical results agree with field measurements of the relationship between r w and the rate of channel migration

sm nd isotope systematics in deep sea sediments clay size versus coarser fractions sm nd studies were carried out on last glacial and holocene sediments from the labrador sea three grain size fractions were analyzed for each sediment the clay size fraction 2 m the fine cohesive silts 2 10 m and the coarse silts 10 63 m in most cases sm nd s ignatures are different from one grain size to anot her in addition different sm nd signatures are derived fr om the clay size fractions compared to the cohesive silt fraction indicating that the cohesive fraction is heterogeneous and that distinct origins in terms of source areas are implied silt fractions record the influence of supplies from the north american precambrian shield whereas clay size fractions 2 m are more sensitive to s edimentary input from the eastern basins in relati on with deep currents coupling sm nd studies on silt and c lay fractions may be a powerful tool to unravel the evolution of deep circulations versus detrital supplies

sortable silt and fine sediment size composition slicing parameters for palaeocurrent speed and palaeoceanography fine sediment size 63 ixm is best measured by a sedimentation technique which records the whole size distribution repeated size measurement with intermediate steps of removal of components by dissolution allows inference of the size distribution of the removed component as well as the residue in this way the size of the biogenic and lithogenic noncarbonate fractions can be determined observations of many size distributions suggest a minimum in grain size frequency curves at 8 to 10 ixm the dynamics of sediment erosion deposition and aggregate breakup suggest that fine sediment behavior is dominantly cohesive below 10 1xm grain size and noncohesive above that size thus silt coarser than 10 ixm displays size sorting in response to hydrodynamlc processes and its properties may be used to infer current speed silt that is f mer than 10 ixm behaves in the same way as clay 2 xm useful parameters of the distribution are the 10 63 ixm mean size and the percentage 10 63 ixm in the fine fraction we cannot use size distributions to distinguish the nature of the currents therefore to infer water mass advection speeds i e the mean kinetic energy of the flow ku regions of high eddy kinetic energy ke must be avoided at the present such abyssal regions lie under the high surface k e of major current systems gulf stream kuroshio agulhas antarctic circmpolar current and brazil falldand currents in the argenthe basin this is probably a satisfactory guide for the pleistocene with regard to the carbonate subfraction of the size spectrum size modes due to both cocco iths and foramlnlferal fragments can be recognized and analyzed with the boundary between them again at about 10 lm the flux of less than 10 lm carbonate at pelagic sites above the lysocline is another candidate for a productivity indicator

the production of north atlantic deep water sources rates and pathways updating an earlier account by dickson et al 1990 this paper reviews the initial development phase of north atlantic deep water nadw production from the points where the dense inflows from nordic seas cross the greenland scotland ridge to the point off south greenland where the buildup of new production appears almost complete in particular three long term current meter arrays totaling 91 instruments and set at 160 km intervals south from the denmark strait sill are used to validate earlier short term arrays by others and in combination with these earlier arrays to describe the downstream evolution of mean speed depth and entrainment the variability of the overflow current in space and time and the likely contribution of the other three main constituents of nadw production at densities greater than 27 8 from the points of overflow 5 6 sv the transport within this range increases by entrainment and confluence with other contributory streams to around 13 3 sv at cape farewell while recirculating elements prevent us from determining the net southgoing transport a nadw transport of this order appears consistent with recent estimates of net abyssal flow passing south through the north and south atlantic

genesis of the permian karstic pingguo bauxite deposit western guangxi china more than 0 5 billion tons of late permian bauxite overlies the karstic topography of the maokou formation of western guangxi in china here we provide new mineralogical geochemical sr nd pb isotopic and pyrite s isotope and trace element compositional data for the pingguo bauxite deposit aiming to further our understanding of the genesis of permian bauxite the pingguo bauxite contains three distinct layers a lower layer dominated by ferric clay or weathered iron ore a middle layer of cryptocrystalline and oolitic bauxite ore and an upper layer dominated by argillaceous bauxite the bauxite ore is mainly diaspore pyrite chamosite and anatase whereas the argillaceous bauxite contains diaspore kaolinite pyrophyllite pyrite and anatase two types of pyrite have been identified within the bauxite fine grained and framboidal pyrite py1 occurring in aggregates and coarse grained and euhedral pyrite py2 py1 is enriched in trace elements and is thought to have a diagenetic origin whereas py2 is deficient in trace elements and is considered to have formed by later recrystallization the s isotopic composition of pyrite 34 11 to 18 91 and visible ovoid microorganisms within the bauxite provide evidences of microbial activity during bauxite formation the sr nd pb isotopic composition of the bauxite indicates that these ores were generated by the weathering of basalts belonging to the emeishan large igneous province lip and limestones of the maokou formation microorganisms were likely to have enhanced the dissolution and weathering of the parent rock and facilitated the precipitation of diaspore under near surface conditions