sediment motion and velocity in a glacier fed stream current understanding of coarse sediment transport e g threshold for motion travel length and virtual velocity in mountain rivers is still quite limited and even less is known about glacial streams however the hydrological characteristics of these systems strong daily discharge fluctuations high water turbidity pose challenges to the use of tracers to monitor bed sediment dynamics as tagged clasts are usually located after bedload events when flow stage has receded e g by means of portable antennas in the case of passive integrated transponders pit the use of stationary antennas still scarcely in use worldwide to detect pit tagged particles has potential advantages in glacier fed streams if water discharge is monitored continuously a stationary antenna provides real time data on the actual discharge at the moment of tracer particles passage this study focuses on incipient motion and virtual velocity of bed particles measured by a stationary antennas system in a steep mountain channel saldur river drainage area 18 6 km2 italian alps where significant daily discharge fluctuations and bedload transport occur as a result of a nivo glacial regime four stationary antennas were installed 50 m apart in the study reach a total of 629 pit tagged clasts were inserted in the studied reach between 2011 and 2014 ranging in size from 35 mm to 580 mm with an overall recovery rate of around 44 critical discharge for sediment entrainment was obtained by detecting the movement of tracers placed immediately upstream of antennas virtual velocity was derived by knowing distances between the antennas and travel time of tracers results on initiation of motion show that the relationship between the size of transported tracers and the discharge measured at the time clasts were passing the stationary antenna is very weak the influence of antecedent flows on incipient motion was thus investigated by dividing the highest discharge recorded between each pit deployment and the subsequent entrainment by the actual critical discharge at the time of movement ratio qmax qc results show that approximately 50 of tracers moved at qmax qc 1 2 and that 73 of tracers moved at qmax qc 1 5 therefore about 30 of tracers had to previously experience a discharge substantially greater than the one that actually mobilized them also coarser particles moved at higher qmax qc ratios suggesting that higher antecedent flows may be needed to destabilize bed clustering results on the virtual velocity of the pit tagged clasts employed in the field show that the virtual velocity turned out to be highly variable ranging from 101 to 10 5 m min 1 and weakly related to either particle size or flow discharge however virtual velocity was well correlated with the highest flow discharge experienced by each tracer normalized by a percentile of the flow duration curve this evidence further stresses the importance of flow history on sediment entrainment and transport finally the pros and cons of the deployed monitoring technology are discussed

geochemical and mineralogical control of different genetic types of deep sea nodules from the pacific ocean deep sea nodules from the northeast pacific nodule belt and the southeast pacific sonne basin being formed in areas bordering the equatorial zone of high biological productivity accumulate by two basically different growth processes a early diagenetic growth by supply from pore water and b hydrogenetic growth by supply from near bottom sea water these growth processes lead to different genetic types of nodules early diagenetic type a hydrogenetic type b and mixed type ab a further type ac very rich in mn is being formed by increasing influence of early diagenesis these types can clearly be distinguished by their shapes surface textures mineral constituents of oxide fraction internal microstructures and geochemistry a genetical classification is being proposed on the basis of statistically computed interelement relationships todorokite very poor in fe is the main mn phase in the early diagenetic substance mno2 intimately intergrown with feooh xh2o is the main phase in the hydrogenetic substance consequently an important difference can be pointed out the metal supply for the growth of the early diagenetic nodules is based on an ionic solution of me2 e g mn2 ni2 cu2 zn2 whereas the supply for the hydrogenetic nodules is caused by transport of colloidal particles mobilization of mn2 and fractionation from fe is controlled by the amount of decomposing organic matter in the peneliquid layer of the sediments the main factor controlling the intensity of early diagenesis is the biological productivity in surface waters the crucial point of reversal at a mn fe ratio of about 5 obtained by hyperbolical regression of the analyses of nodules from the southeast pacific represents best concentrations in ni and cu mn fe quotients greater than 5 cause a decrease of ni and cu content nodules from the northeast pacific nodule belt generally contain higher concentrations in cu than nodules from the southeast pacific this can be explained by an additional supply of cu transported below ccd by siliceous plankton

surface based transport model for mixed size sediment we present a transport model for mixed sand gravel sediments fractional transport rates are referenced to the size distribution of the bed surface rather than subsurface making the model completely explicit and capable of predicting transient conditions the model is developed using a new data set of 48 coupled observations of flow transport and bed surface grain size using five different sediments the model incorporates a hiding function that resolves discrepancies observed among earlier hiding functions the model uses the full size distribution of the bed surface including sand and incorporates a nonlinear effect of sand content on gravel transport rate not included in previous models the model shares some common elements with two previous surface based transport models but differs in using the full surface size distribution and in that it is directly developed from a relatively comprehensive data set with unambiguous measurement of surface grain size over a range of flow transport rate and sediments

the infiltration of fine matrices into coarse grained alluvial sediments and its implications for stratigraphical interpretation traps designed to simulate the framework gravel of natural streams and installed in a coarse grained channel allow the identification and differentiation of the processes governing the infiltration of fines into bed interstices vertical patterns of matrix distribution reflect the relative importance of variables acting at both the surface of the channel bed and within the bed sediments differences in grain size and therefore pore size of the framework exercise a strong controlling influence an armour layer of coarse particles superimposed on comparatively finer sub surface bed material common to many coarse grained rivers is shown to encourage the clogging of near surface pores with matrix fines below the obstruction interstices may be protected from incursion and the gravel framework is often left open this is the reason for patchy concentrations of matrices often reported in the stratigraphical literature in contrast a uniform size grading of the bed sediment or an upwards fining leads to a more uniform packing of the interstices with matrix flood history is shown to be an important determinant of both the size distribution and the spatial distribution of matrices and is useful in providing a dynamic explanation of the variability of matrices observed from place to place in ancient deposits

a high temperature hydrothermal deposit on the east pacific rise near 7 n abstract a seabeam survey of the east pacific rise epr led to the selection of several sites having structural characteristics favorable for hydrothermal activity dredging of such an area located at 7 n on the epr resulted in the recovery of sulfides oxides and fresh basalt chemical analyses and isotopic compositions showed that the recovered pyrites were probably precipitated directly from hot vent hydrothermal waters chemical analyses and isotopic composition of manganese iron oxides indicated that they too were of hydrothermal origin 210 pb pb measurements yielded ages of 90 10years for the deposits this site may still be undergoing hydrothermal activity

geochemical features of fe mn micronodules in deep sea sediments of the western north pacific ocean potential for co product metal extraction from rey rich mud abstract rare earth element and yttrium rey rich mud around minamitorishima island japan in the western north pacific ocean has received significant attention as a novel rey resource in rey rich muds industrially critical metals such as co ni and mo occur in relatively high concentrations we show that fe mn micronodules separated from rey rich muds are significantly enriched in these elements we measured co contents of almost 3000 ppm and ni contents that exceed 39 000 ppm through experiments we demonstrated that reductive chemical leaching can be used to extract major portions generally 80 of the metals associated with fe mn oxyhydr oxides from rey rich muds the fe mn micronodules were of an oxic diagenetic origin a simple mass balance calculation indicated that the contribution of the fe mn micronodules to the bulk fe mn oxyhydr oxides in the sediment can amount to 8 50 median 18 the other metals associated with fe mn oxyhydr oxides seem to be hosted in mn microparticles probably of a hydrogenetic origin we estimate that the most promising site for rey rich mud development contains 9 3 0 6 102 t 1 6 0 1 103 t and 2 8 0 2 102 t of leachable co ni and mo respectively in 1 km2 0 10 m below seafloor these amounts account for 0 66 0 04 0 061 0 004 and 0 097 0 007 of present annual global productions of co ni and mo respectively the feasibility of extracting these metals as co products during rey rich mud development depends on the cost efficiency of the recovery process which ultimately depends on their market price in the near future

foraminiferal ooze from the galapagos rift area hydrothermal impact and diagenetic mobilization of elements abstract chemical changes during diagenesis in foraminiferal oozes have been studied in five cores from the hydrothermally active spreading centre of the galapagos rift shifts of concentrations of elements such as mn co cu ni zn and ba are related to changes of eh potential in the range from 0 33 to 0 07 v mn co and cu are strongly mobilized in the reduction zone and reprecipitated as hydroxides near the sediment water interface the ree distribution patterns of these oxide rich sediments are very similar to those in the base metal poor diagenetically formed mn nodules during diagenesis several elements ree co sb ba and zn were redistributed between carbonate and non carbonate phases whereas others were not fe sc th and cr although the composition of these sediments may be attributed to diverse sources convincing evidence supporting a hydrothermal impact comes from the sb concentrations

the effects of flood history on sediment transport in gravel bed rivers abstract the transport of coarse sediment during floods often exhibits hysteresis patterns from changes in flow fields channel geometry bedforms or sediment supply conditions flume experiments that simulate hydrographs tend to confirm that hysteresis is a consequence of the progressive organization of surface sediments in terms of grain protrusion imbrication orientation and roughness hysteretic patterns are also highly dependent on the kind of sediment supply conditions and the type of simulated hydrograph a factor that has not been investigated extensively is the effect of the timing and sequencing of floods on bedload transport depending on its magnitude and duration each flood leaves the channel bed in a different condition which influences the bedload transport of the next event representing the river bed s memory of past floods which can determine future responses to natural disturbances in this study i investigated the effects of different sequences of events i e the flood history on sediment transport through a series of flume experiments that simulated three types of stepped and symmetrical hydrographs ranging from short duration high magnitude to long duration low magnitude events under sediment recirculation conditions hydrographs were simulated as a sequence of the same event and with events in different sequences in order to explore the effects of different antecedent conditions on sediment transport the results show that a previous event decreases the rates of sediment transported by a certain hydrograph by around 40 if a high magnitude event precedes another one and around 70 if a low magnitude event precedes another event of similar magnitude a low magnitude event does not affect the rate of sediment transported by a subsequent high magnitude flood but a high magnitude event reduces the sediment transported by a subsequent long duration low magnitude event

growth rate variations of manganese nodules and crusts induced by paleoceanographic events time markers at about 3 ma 6 5 ma and 14 ma are common to 16 manganese nodules and crusts from different localities in the world oceans these time markers correspond to variations in the growth rates in the inner structure and in the chemistry of the samples the observed time markers could be related to 1 changes of the bottom water velocity and 2 variations in the manganese and iron contents in the deep ocean the time markers were determined by high resolution 10be dating applying the accelerator mass spectrometry facility at the eidgenossische technische hochschule zurich

bed forms in bimodal sand gravel sediments laboratory and field analysis bed forms were studied in goodwin creek and a laboratory flume channel the bed sediment of the field site and flume had median diameters of 8ae3 modes of 0ae4 22ae6 mm and 1ae82 mm modes of 0ae5 5ae6 mm respectively the laboratory andfieldchannelshadsimilarvaluesofbimodalparameters ratiosofflowdepth to median bed material diameter and ratios of shear stress to critical shear stress and were judged to be comparable in the transport of bed load sediment and the resulting bed forms three groupings of bed forms from the laboratory flume experiments ripple like bed forms bed load sheets low relief bed waves were identified using the height and period of the bed forms for the range of flow depths and discharges investigated in the flume bed forms became higher and longer with increasing bed shear stress bed forms from goodwin creek were similar to those from theflume with comparable ratios between bed form length height and flow depth the bed forms in the flume provide a positive link between rate and size fluctuations measured in the field and the bed forms the smaller bed forms identified were sediment starved and are not considered to be dunes while the largest bed forms in which all of the bed material sizes were mobilized in the field and laboratory were judged to be dunes

the manganese nodules of the kane gap east atlantic indicators of sedimentation erosion changes manganese nodules from the kane gap a deep sea channel connecting the sierra leone and gambia basins off west africa were investigated chemically and dated by10be along cross sections comparing the nodule structure with the stratigraphy of the related sediments the following conclusions are drawn concerning the sedimentation processes during the last 4 to 6 106 years the growth of the nodules started about 4 to 4 5 ma before present during or near to the end of a period of erosion on a fossil free probably miocene sediment during the first phase of only a few hundred thousandyears the nodules grew very quickly 7 to 18 mm ma fe rich hydrogenetic material formed the internal sections of the nodules during this time slowing down of the bottom currents resulting in deposition of thin sediment covers for short intervals caused the character of the nodules to change to a more diagenetic composition the growth rates were reduced to about 1 to 2 mm ma the time of slowing is roughly 3 to 4 ma bp

sand dune geometry of large rivers during floods the geometry of lower regime bed forms in several large sand bed rivers is investigated during average and flood conditions the van rijn method is revised because it generally underpredicts the dune height of most large rivers around the world during floods in large sand bed rivers upper regime plane bed is not necessarily obtained when t 25 both parameters describing dune height and dune steepness do not decrease as the transport stage parameter t increases in the range 10 t 25 the analysis of bed form data during large floods on the meuse river and the rhine river branches indicates that both the dune height and length generally increase with discharge while dune steepness remains relatively constant a reasonable approximation of the wavelength is 6 5 h where h is the flow depth the dune height varies as a function of the depth h and median grain size d50 estimates can be obtained by 2 5 h 0 7d0 350

channel adjustments to a succession of water pulses in gravel bed rivers gravel bed rivers commonly exhibit a coarse surface armor resulting from a complex history of interactions between flow and sediment supply the evolution of the surface texture under single storm events or under steady flow conditions has been studied by a number of researchers however the role of successive floods on the surface texture evolution is still poorly understood an experimental campaign in an 18 m long 1 m wide flume has been designed to study these issues eight consecutive runs each one consisting of a low flow period of variable duration followed by a sudden flood water pulse lasting 1 5 h have been conducted the total duration of the experiment was 46 h the initial bed surface was created during a 280 h long experiment focused on the influence of episodic sediment supply on channel adjustments our experiments represent a realistic armored and structured beds found in mountain gravel bed rivers the armor surface texture persists over the duration of the experiment the experiment exhibits downstream fining of the bed surface texture it was found that sorting processes were affected by the duration of low flow between flood pulses since bed load transport is influenced by sediment sorting the evolution of bed load transport is impacted by the frequency of the water pulses short interpulse durations reduce the time over which fine material transported as bed load can be winnowed this in turn contributes to declining reduction of the bed load transport over time while the sediment storage increases

sediment supply limited bedforms in sand gravel bed rivers the stability of bedforms in mixtures of gravel and sand is not well understood two bedform types are characteristic flow parallel sand ribbons and flow transverse barchans flume experi ments and field data presented here show that gradual transitions exist from sand ribbons to barchans and from barchans to fully de veloped dunes barchans and sand ribbons occur when not enough transportable sediment is available for the formation of fully devel oped ripples or dunes the reason is that a part of the bed sediment is immobile e g with an armor layer which limits the sediment sup ply and thus the volume of sediment available for the formation of bedforms bedform stability diagrams are shown to be extendable to sedi ment supply limited bedforms in sand gravel sediment if the par ticle parameters of the diagrams are derived from the transported sediment instead of the bed sediment barchans and forms transi tional to fully developed dunes plot in the dune stability fields sand ribbons on the other hand plot in the ripple lower plane bed and dune fields in the case of sediment supply limitation bedforms are partly or completely related to the characteristics of the sediment supply from upstream the sediment underlying the bedforms may be a stable armor and the exchange of sediment between this armor and the bedforms may be small or non existent consequently bedform char acteristics in sand gravel mixtures in supply limited conditions often are not predictable from the local hydraulics and sediment charac teristics

real time measurements of sediment transport and bed morphology during channel altering flow and sediment transport events abstract real time measurements of bed changes over a reach are a missing piece needed to link bed morphology with sediment transport processes during unsteady flows when the bed adjusts quickly to changing transport rates or visual observation of the bed is precluded by fine sediment in the water column a new technique is presented that provides continuous measurement of sediment movement over the length of a flume a bedload monitoring system blms was developed that makes use of pressure pillows under a false flume bottom to measure sediment and water weights over discrete flume channel sections throughout a flow event this paper details the construction of the blms and provides examples of its use in a laboratory setting to reconstruct bed slopes during unsteady flows and to create a real time record of sediment transport rates across the flume channel bed during a sediment transporting flow data gathered from the blms compared well against techniques commonly in use in flume studies when the blms was analyzed in conjunction with bed surface dems and differenced dems a complete transport and bed adjustment picture was constructed the difference dems provided information on the spatial extent of bed morphology changes the blms supplied the data record necessary to reconstruct sediment transport records through the downstream channel including locations and time periods of temporary sediment storage and supply the blms makes it possible to construct a continuous record of the spatial distribution of sediment movement through the flume including areas of temporary aggradation and degradation exciting implications of future research that incorporates a blms include a more informed management of river systems as a result of improved temporal predictions of sediment movement and the associated changes in channel slope and bed morphology

rare earth element distribution and behaviour in buried manganese nodules from the central indian basin eight buried manganese nodules taken in the upper metre of a siliceous ooze sediment core in the central indian basin at 14 s and 74 e were analysed for major trace and rare earth ree elements interelemental correlation yields a strong positive association r 0 75 between fe p ti and ree suggesting a single carrier phase for ree in these nodules namely a titaniumrich ferriphosphate this correlation significantly improved r 0 90 when the influence of detrital fe is eliminated and only authigenic fe is considered the buried nodules appear to retain the mineralogical and geochemical characteristics including positive ce anomaly acquired during the accretion at the sediment water interface prior to their burial at 225 kyr b p the effect of burial is observed only in the depletion of heavy ree hree in a nodule buried at 23 5 cm depth where the environment is suboxic to anoxic middle ree mree in the nodules exhibit enrichment over light ree lree and hree while lree exhibit enrichment over hree compared to the ratios in shale nasc this enrichment pattern suggests an uptake sequence of the ree as mree lree hree in the manganese nodules

an integrated approach for identifying aquifers in transcurrent fault systems the najd shear system of the arabian nubian shield groundwater potentials were assessed for major transcurrent fault systems in basement complex terrains using the najd transcurrent shear system of the arabian nubian shield as a test case spatial analysis within a geographical information system environment of relevant data sets field remote sensing geophysical and digital elevation revealed a spatial correlation between existing well locations and distribution of najd transcurrent shear system structural elements i e faults shear zones melange dykes within highly fractured domains suggesting a causal relationship specifically at 1 intersection of najd brittle shear zones and fault systems 2 intersections of two or more fault systems 3 intersections of najd related dykes with the main streams within catchment areas and 4 within tectonic melange for each of the former aquifer types aquifer specific field and satellite based characteristics were identified and used in conjunction with complementary data e g watershed morphology precipitation soil moisture to target aquifers of similar settings postulated well locations were then successfully tested and refined using very low frequency technologies results could potentially highlight the important role of major transcurrent fault systems in providing settings conducive for hosting and transmitting groundwater and could potentially serve as a replicable model for regional assessment of groundwater potentials in similar tectonic and hydrologic settings

characterization and quantification of magnetofossils within abyssal manganese nodules from the western pacific ocean and implications for nodule formation this work was supported financially by southern university of science and technology sustech grant y01316111 to y m c the national key r d program of china 2016yfa0601903 to q s l the national natural science foundation of china 41430962 to q s l the australian research council dp160100805 and dp200100765 to a p r and the 13th five year plan project of international maritime resources investigation and development dy135 c1 1 06 and dy135 r2 1 01 to x m s and the guangdong provincial key laboratory of marine resources and coastal engineering we thank the guangzhou marine geological survey for supplying the samples

internal microfeatures of manganese nodules from the central indian ocean abstract the internal features of manganese nodules from abyssal hills ranging in height from 600 to 880 m and the nodules from abyssal plains in the central indian ocean have been studied nodules from the abyssal hills show mainly parallel laminations whereas nodules from the abyssal plains show prominent well developed columnar structures features such as botryoids and fractures filled with fe and mn oxides are more common in the nodules of abyssal plains whereas the clay content and clastic grains are more common in abyssal hill nodules compositional studies of layers within the nodules show that mn ni cu and zn increase from the nucleus to the outer layer while fe and co are inclined to decrease the innermost layer adjacent to the nucleus is hydrogenetic mn fe ratio of mn fe ratio of 4 2 5 4 and contain mainly todorokite with minor mno2 phillipsite and quartz a mixing model shows that the contribution of interstitial water to the outer diagenetic layers was about 75 and that of sea water was about 25

organic rich and manganese sedimentation during the cenomanian turonian boundary event in the outer carpathian basins a new record from the skole nappe poland abstract upper cenomanian lower turonian strata in the splawa section of the skole nappe outer carpathians poland provide a detailed palaeoenvironmental record of the oceanic anoxic event oae 2 from a deep water basin below the ccd at the northern margin of the western tethys the oae 2 succession consists of black parallel laminated radiolarian shales enriched in organic matter of mainly marine origin toc up to 8 organic carbon isotope variations together with microfossil datum events allowed to correlate the studied organic rich facies with other black shale successions along the outer carpathians and other areas of the western tethys the mean values of sedimentation rate 3 5 5 5 mm kyr and organic matter accumulation rate 0 5 g m2 year calculated for the oae 2 interval in the outer carpathian basins are comparable to the values from other deep water marginal basins in the western tethys the average redox sensitive trace metal contents and their enrichment factors indicate water column anoxia in the outer carpathian basins intensified during the interval of the largest shift in 13c values the periods of bottom anoxia were interrupted by intervals of variable eh conditions with sedimentation of hemipelagic green shales including poor agglutinated foraminiferal assemblages an increase in productivity of organic and siliceous plankton during the oae 2 is documented based on increased values of silica and barium enrichments this closely corresponds to an interval of the largest positive stable carbon isotope excursion related to the beginning of the largest sea level rise linked with intensive coastal upwelling extremely low sedimentation rate or even hiatuses and the increase in deep water circulation causing basin oxygenation resulted in precipitation of two ferromanganese layers their formation was related to changes in hydrodynamic conditions at the basin floor expressed by precipitation of fe mn carbonates some chemical indices seem to suggest that the primary metal enrichments could be related to hydrothermal activity however the concentrations of some elements show also on hydrogenic to diagenetic influences in these metalliferous sediments the precipitation of these fe mn sediments was probably synchronous with the manganese enrichment across the c t transition recorded in other western tethyan basins and in the adjacent epicontinental seas

formation of clay minerals during early diagenesis of a calcareous ooze abstract deep sea sediments from a basin in the southeast pacific are described in which strong carbonate dissolution and strong diagenetic migration of metals can be observed clay minerals of smectite type are formed in large quantities during the early diagenesis of this sediment in a first stage as an x ray amorphous phase which later crystallizes to smectite rb sc na and k become enriched during the process of clay mineral formation probably due to uptake of these elements from sea water to interlayer positions of smectite the unsolved question is what sort of mechanism connects the calcite dissolution with the formation of smectite the source of the al necessary for the formation of smectite is also unknown

experimental study of the coarse surface development effect on the bimodal bed load transport under unsteady flow conditions abstractgravel bed rivers display a surface layer that is coarser than the substrate lining below this armored surface the armored layer that is developed under certain flow conditions may be attributed as water worked sediment bed both the threshold of incipient motion and the bed load transport are affected by the presence of this layer in this study the coarse surface development and its effect on the sediment transport were investigated experimentally in a rectangular flume four antecedent flow rates were combined with an input hydrograph without sediment feeding the reference shear stress of individual fractions and the grain size distribution were determined after the development of the coarse surface due to the antecedent flow then a triangular shaped hydrograph was generated for both the intact surface and the coarse surface cases it was seen that the maximum bed load transport values obtained in unsteady flow experiments were highly dependent on the coarse surface formed by the anteceden

characteristics of manganese nodules from the central indian basin relationship with the sedimentary environment the hydrogenetic and diagenetic manganese nodules from the cib show an unequivocal genetic relationship with neogene sedimentological patterns hydrogenetic nodules were observed at the top of the sedimentary column and interstratified in thin sequences of biosiliceous sediments and underlying miocene red clays in cores from topographic highs early to late pliocene radiolarian fauna were found at the base of the biosiliceous deposits these condensed biosiliceous sediments are less than 4 0 m thick and periods of non deposition and or erosion may have occurred in the central deep area 11 15 s significant biogenic deposition began during the early to late pliocene as a result of the development of a high biogenic productivity belt to the south producing the favourable conditions for diagenetic accretionary processes for mn nodules this indicates growth of hydrogenetic nodules prior to the late pliocene and the subsequent inception of diagenetic accretion formation of the most recent diagenetic nodules is associated with higher rates of sedimentation in the deep sea troughs where the siliceous sediments are much thicker this should promote the diagenetic mobilization of mn and its precipitation under oxic and suboxic conditions nevertheless diagenetic nodules are restricted to the upper 40 cm of sediments younger than 400 000 years suggesting fast growing diagenetic nodules and the dissolution of buried nodules below the first 50 cm of siliceous oozes hydrogenetic nodules are formed by dense layers of mno2 fe oh 3 and amorphous silica and they show smooth texture and botryoidal shapes analysis of bulk and selected portions of layered crust or rind shows very low mnfe ratios 2 and relatively high co and ti contents in most cases the cores of hydrogenetic nodules are fragments of altered ash layers from the indonesian volcanic arc which is located more than 2500 km to the east the ash layers are also interstratified with miocene red clays diagenetic nodules show a granular texture and comprise concentric layers with dendritic or columnar structures mainly of 10 a manganate higher mn ni and cu contents are observed in this phase late diagenetic enrichment of these nodules is continuous within the upper 40 cm of recent ni that enhances the stability of early diagenetic 10 a manganate buserite and c the formation of todorokite some nodules referred to as mixed in the literature show hydrogenetic internal layers which grade outward to a diagenetic crust this transitional character suggests slow changes in the sedimentary environment as growth advances the nodules of the cib and the east equatorial pacific eep are similar in terms of both metallic composition and accretionary patterns however the nodules of the cib are considerably younger and present a continuous accretionary history the history of the manganese nodules from the cib is related to the post late miocene sedimentary and geodynamic evolution of this basin

mineralogy of polymetallic nodules and associated sediments from the central indian ocean basin abstract todorokite is the dominant mineral phase in the nodules of the northern central indian ocean basin these nodules are characterised by a rough surface texture are relatively rich in mn cu and ni and are associated with radiolarian sediments rich in montmorillonite chlorite and illite mno 2 is the dominant mineral phase in the nodules of the southern central indian ocean basin these nodules have a smooth surface texture are relatively rich in fe and co and are associated with pelagic clay sized sediments comprising keels of foraminifera zeolite and the clay minerals chlorite and illite the formation of these mineral phases and their composition in the nodules may have been controlled by the properties of associated sediments and the nucleus of the nodule does not influence the oxide layer mineralogy

the effect of hydrographs on bed load transport and bed sediment spatial arrangement 1 field measurements of sediment transport in gravel bed rivers often reveal hysteretic effects due to differences in sediment availability between the rising and falling limbs of a flood hydrograph however only a small number of flume studies have analyzed the dynamics of sediment transport during hydrographs three types of stepped hydrographs with contrasting durations and magnitudes are simulated here under sediment recirculation conditions bed load transport rate and grain size have been measured continuously the dynamic behavior of the surface armor layer has been explored by analyzing digital photographs and laser scanner surveys of the bed surface taken during hydrographs the results indicate that sediment transport during the falling limb was lower than during the rising limb in all of the three types of hydrographs this reduction is more evident for the low magnitude hydrographs the grain size of the bed remained virtually constant throughout the hydrographs but the grain size of transported sediments exhibited a counterclockwise hysteresis also a significant increase in the reference shear stress for sediment entrainment was measured during the falling limb of hydrographs additionally a detailed analysis of partial transport dynamics of the bed surface sediments reveals a reduction in sediment mobility during the falling limb of the hydrographs the difference in sediment entrainment and transport before and after the peak of the hydrographs appears to be caused by a change in the organization of the surface sediments an analysis of detailed laser scan bed surveys reveals a phase of bed restructuring lower vertical roughness clast rearrangement during the falling limb of hydrographs consequently changes in the degree of organization and complexity of the bed surface are likely the cause of the reduced mobility of sediments and thus of the reduced sediment transport rate during the falling limb of the hydrographs

copper nickel rich amalgamated ferromanganese crust nodule deposits from shatsky rise nw pacific 1 a unique set of ferromanganese crusts and nodules collected from shatsky rise sr nw pacific were analyzed for mineralogical and chemical compositions and dated using be isotopes and cobalt chronometry the composition of these midlatitude deep water deposits is markedly different from northwest equatorial pacific pcz crusts where most studies have been conducted crusts and nodules on sr formed in close proximity and some nodule deposits were cemented and overgrown by crusts forming amalgamated deposits the deep water sr crusts are high in cu li and th and low in co te and tl concentrations compared to pcz crusts thorium concentrations ppm are especially striking with a high of 152 mean 56 compared to pcz crusts mean 11 the deep water sr crusts show a diagenetic chemical signal but not a diagenetic mineralogy which together constrain the redox conditions to early oxic diagenesis diagenetic input to crusts is rare but unequivocal in these deep water crusts copper ni and li are strongly enriched in sr deep water deposits but only in layers older than about 3 4 ma diagenetic reactions in the sediment and dissolution of biogenic calcite in the water column are the likely sources of these metals the highest concentrations of li are in crust layers that formed near the calcite compensation depth the onset of ni cu and li enrichment in the middle miocene and cessation at about 3 4 ma were accompanied by changes in the deep water environment especially composition and flow rates of water masses and location of the carbonate compensation depth

manganese micronodules a possible indicator of sedimentary environments abstract manganese micronodule distribution size internal features and chemical composition as well as the composition of associated sediments have been determined in eight sediment cores taken from the siliceous ooze area of the central indian basin cib micronodule abundance expressed as the number of micronodules per gram of dried sediment 0 375 n g and size 75 1000 m show considerable variation with core depth and are directly related to each other the morphology surface texture and internal features of the micronodules are similar to those of surface macronodules from the same basin micronodules have high contents of mn 35 02 cu 1 6 ni 1 4 and zn 0 37 high mn fe ratios 5 101 and very low fe 1 8 al 2 o 3 1 3 tio 2 0 30 sio 2 2 7 and rare earth element 522 ppm contents compared to surface and buried macronodules micronodule abundance size and composition depend on the redox characteristics of the sedimentary environment and can therefore be used as indicators of the sedimentary environment

sedimentological geochemical and microfaunal responses to environmental changes around the cenomanian turonian boundary in the outer carpathian basin a record from the subsilesian nappe poland abstract sedimentological micropalaeontological and geochemical data from the upper cenomanian lower turonian zasan section outer carpathians subsilesian nappe poland provide new insights into the sedimentary environment and its changes in a basin at the northern margin of the western tethys a global oceanic event oae2 has been identified on the basis of lithology and radiolarian stratigraphic data this event is marked by a series of organic rich toc up to 5 non calcareous shales practically devoid of benthic microfossils indicative of bottom water anoxia the marine type of organic matter and the occurrence of radiolarian rich layers with abundant small opportunistic forms suggest that coastal upwelling was probably the main driving force for the accumulation of organic matter during the latest cenomanian the early diagenetic ferromanganese nodules followed by a 30 cm thick series of manganese rich non calcareous variegated shales and bentonites directly overlie the black facies of oae2 the fe mn nodules formed in two stages reflecting changes in bottom water dynamics across the c t boundary during the first stage the fe mn carbonate nodules were precipitated in presence of anoxic pore and or bottom water that could be episodically oxygenated later an increase in deep water circulation led to strong oxygenation of the bottom and pore water causing diagenetic modification of the nodule carbonate into ferromanganese oxides and hydroxides the manganiferous sediments recorded in the zasan section represent an isochronous horizon within the outer carpathian basin probably concurrent with manganese enrichments in many other epicontinental seas and deep water basins coinciding with the end of the carbon isotope excursion close to the base of the turonian the manganese event may have been related to increased deep water circulation associated with the maximum flooding of the late cenomanian early turonian transgression the mn event may have also been enhanced as a result of remobilization of mn 2 dissolved in anoxic bottom and pore waters in the organic rich sediments directly underlying the manganese sediments the lower turonian succession records increasing but not completed oxygenation of bottom water the oxygenation was interrupted by periods of anoxia marked by a few intervals of dark laminated black shales strongly enriched in organic matter toc up to 10 their marine origin and the occurrence of radiolarian rich layers demonstrate enhanced primary productivity and a low clastic supply during the sea level high stand frequency of radiolarian rich layers increases up section reflecting an increase in upwelling circulation at the northern margin of the carpathian basin during the early turonian

manganese ores in tunisia genetic constraints from trace element geochemistry and mineralogy abstract northern and central tunisia hosts few small scale stratiform and stratabound mn deposits low to medium in grade mn

growth of a manganese nodule from peru basin a radiochemical anatomy abstract attempts have been made to study the entire growth history of a manganese nodule from the northern part of peru basin in the pacific using radiochemical profiles of 230 th 232 th 227 th 230 th and 10 be 9 be combined with the observations on fe mn contents and textural variation the radiochemical data indicate that the nodule grew more or less concentrically throughout most of its existence since it formed 1 5 my ago receiving mn from both bottom water and pore water this condition appeared to have changed about 180 ky ago when the growth became asymmetric in that the top and bottom sides became fixed in their relative positions on the sea floor since then the bottom side accreted with a fast rate of close to 200 mm my apparently fueled by the supply of diagenetically remobilized mn in pore water from the sediment substrate in the meantime the top side accumulated at about 6 mm my a value which is in the normal range for deep sea nodules having their mn supplied from the hydrogenous source

origin of hysteresis in bed form response to unsteady flows 1 field and laboratory studies indicate that changes in riverbed morphology often lag changes in water discharge this lagged response produces hysteresis in the relationship between water discharge and bed form geometry to understand these phenomena we performed flume experiments to observe the response of a sand bed to step increases and decreases in water discharge for an abrupt rise in discharge we observed that bed forms grew rapidly by collision and merger of bed forms migrating with different celerities growth rate slowed as bed forms approached equilibrium with the higher discharge regime after an abrupt discharge drop bed form decay occurred through formation of smaller secondary bed forms in equilibrium with the lower discharge which cannibalized the original relict features we present a simple model framework to quantitatively predict time scales of bed form adjustment to flow changes based on equilibrium bed form heights lengths and celerities at low and high flows for rising discharge the model assumes that all bed form collisions result in irreversible merger due to a dispersion of initial celerities for falling discharge we derive a diffusion model for the decay of relict high stage features our models predict the form and time scale of experimental bed form adjustments additional experiments applying slow and fast triangular flood waves show that bed form hysteresis occurs only when the time scale of flow change is faster than the modeled and measured bed form adjustment time we show that our predicted adjustment time scales can also be used to predict the occurrence of bed form hysteresis in natural floods

dike rock generation and magma interactions in the bir safsaf igneous complex south west egypt implications for the pan african evolution in north east africa the geological setting ages petrography and geochemistry of late pan african 580 ma calc alkaline and tholeiitic dike rocks in the bir safsaf igneous complex of south west egypt are discussed these basaltic to rhyolitic dikes intruded contemporaneously and shortly after the intrusion of granitoids the major and trace element data sr and nd isotope relations in combination with textural observations confirm complex interactions between most of the intermediate calcalkaline dike melts and plutonic melts with different degrees of mixing assimilation replenishment and tapping of magma chambers trachytic and rhyolitic dikes are strongly differentiated melts from the granitic pluton the tholeiitic dikes evolved dominantly by fractional crystallization processes it is inferred that open system and closed system processes operated in calc alkaline magma chambers and that the calc alkaline melts came from a garnet and amphibole bearing mantle modified by a subduction component tholeiitic rocks were formed later by fractional crystallization and assimilation processes magma ascent of both dike types took place in an extensional environment and the presumed subduction zone has to be seen in connection with the atmur delgo suture zone

petrogenesis of ferromanganese nodules from east of the chagos archipelago central indian basin indian ocean abstract deep sea ferromanganese nodules occur over a large area and on many different sediment types of the central indian basin indian ocean selected samples were studied to determine their chemical and mineralogical compositions and microstructural features repeated laminations of variable thickness alternately dominated by todorokite and vernadite are characteristic of these nodules these laminae show on electron microprobe line scans corresponding interlaminar partitioning of mn cu ni and fe co the bulk chemical compositions of these nodules plot in both the hydrogenetic and early diagenetic fields on the fe mn ni cu co 10 ternary diagram the binary diagram depicting the covariation of mn ni cu against fe co shows two distinct parallel regression lines one delineated by nodules from terrigenous siliceous ooze and siliceous ooze terrigenous sediments and the other by nodules from red clay siliceous ooze red clay and calcareous ooze red clay an increasing diagenetic influence in the nodules with the nature of the host sediment types was observed in the sequence terrigenous siliceous ooze and red clay siliceous calcareous ooze red clay a negative correlation between mn fe ratio and co and a positive correlation between mn fe ratio and ni cu was established the nodules show dendritic laminated and globular microstructures formed by primary growth of fe mn oxide laminae depositional hiatuses in the primary microstructures indicate that the growth of these nodules was episodic the oxide laminations show extremely complex growth patterns scattered biogenic remains and mineral grains acted as accessory seeds for growth of oxide layers in addition to the main nuclei none of the primary microstructures can be uniquely linked to a particular growth process or growth rate radial cracks cutting across primary microstructures are often filled by todorokite of a later generation post depositional modifications of the nodules were largely controlled by accreted biogenic remains as indicated by their progressive dissolution with increasing depth from nodule surfaces their pseudomorphic replacement by todorokite and the later growth of phillipsite and todorokite in the microfossil molds the growth patterns of the in filled oxides are often controlled entirely by the cavity walls and are discordant with the primary growth fabric primary todorokite was recrystallized to coarser grains of different chemical composition later generation veins of todorokite cut across and chaotically disrupted primary laminae

tectonic and paleoceanographic conditions during the formation of ferromanganese nodules from the northern south china sea based on the high resolution geochemistry mineralogy and isotopes abstract deep water ferromanganese fe mn nodules cumulate trace elements from the underlying sediment pore water and seawater during the concentric mineral layers growth process over millions of years they can record long term tectonic movements and paleoceanographic changes to systematically ascertain paleoceanographic evolution of the deep south china sea scs since the last 3 2 ma we comprehensively investigated microstructure mineralogy geochemical element concentrations as well as sr nd and pb isotopic compositions in the fe mn nodules nearby the dongsha islands in the northern scs results indicate that these deposits were formed in a continental marginal environment by a mixture of diagenetic and hydrogenetic processes overall the studied nodules can be divided into three stages with different microstructures and chemical compositions which indicate different formation environments stage 1a is the innermost and oldest layer with a porous mottled texture and has the lowest mn fe ratio cu ni and zn which implies comparatively high oxidization conditions in contrast the mn mineralogy of stage 2 shows conditions similar to those of buserite formed under less oxidative conditions between stage 1a and 2 stage 1b represents a mixture of stage 1a and 2 and has inhomogeneous growth structures based on the nd and sr isotopic composition of the detrital phases and pb isotopes three potential terrigenous source regions including south china luzon and taiwan that discharge into the northern scs from 3 2 ma to 1 06 ma after 1 06 ma the terrigenous fraction in the fe mn deposits on the northern slope of the scs is a two end members mixture of fluvial input from taiwan islands and eolian dusts from the chinese loess our study indicates that scs bottom water variation occurred at 3 2 ma 2 1 ma and 1 06 ma respectively which could be attributed to global cooling and the influence of luzon arc forearc uplift

ferromanganese nodules from manop sites h s and r control of mineralogical and chemical composition by multiple accretionary processes abstract the chemical composition of ferromanganese nodules from the three nodule bearing manop sites in the pacific can be accounted for in a qualitative way by variable contributions of distinct accretionary processes these accretionary modes are 1 1 hydrogenous i e direct precipitation or accumulation of colloidal metal oxides in seawater 2 2 oxic diagenesis which refers to a variety of ferromanganese accretion processes occurring in oxic sediments and 3 3 suboxic diagenesis which results from reduction of mn 4 by oxidation of organic matter in the sediments geochemical evidence suggests processes 1 and 2 occur at all three manop nodule bearing sites and process 3 occurs only at the hemipelagic site h which underlies the relatively productive waters of the eastern tropical pacific a normative model quantitatively accounts for the variability observed in nearly all elements zn and na however are not well explained by the three end member model and we suggest that an additional accretionary process results in greater variability in the abundances of these elements variable contributions from the three accretionary processes result in distinct top bottom compositional differences at the three sites nodule tops from h are enriched in ni cu and zn instead of the more typical enrichments of these elements in nodule bottoms in addition elemental correlations typical of most pelagic nodules are reversed at site h the three accretionary processes result in distinct mineralogies hydrogenous precipitation produces mno2 oxic diagenesis however produces cu ni rich todorokite and suboxic diagenesis results in an unstable todorokite which transforms to a 7 a phase birnessite upon dehydration the presence of cu and ni as charge balancing cations influence the stability of the todorokite structure in the bottoms of h nodules which accrete dominantly by suboxic diagenesis na and possibly mn 2 provide much of the charge balance for the todorokite structure limited growth rate data for h nodules suggest suboxic accretion is the fastest of the three processes with rates at least 200 mm 106 yr oxic accretion is probably 10 times slower and hydrogenous 100 times slower since these rates predict more suboxic component in bulk nodules than is calculated by the normative analysis we propose that suboxic accretion is a non steady state process variations in surface water productivity cause pulses of particulate flux to the sea floor which result in transient mn reduction in the surface sediments and reprecipitation on nodule surfaces

note on lag in bedload discharge it is postulated that movable sediment beds comprise of two types of grains termed undisturbed and disturbed grains the probability of entrainment by flow of the latter is higher than that of the former the lag in bedload transport is due to the difference in the entrainment probabilities of the two types of grains a model is developed to predict lag in bedload transport the spatial and temporal lag coefficients are functions of both the inner and outer variables the 50 of the equilibrium bedload discharge is attained within about 26 of the total lag distance or lag time the lag model was verified by conducting laboratory experiments and using experimental data of bagnold the proposed model agrees with the experimental data both the lag distance and lag time decrease with increasing equilibrium bedload discharge the findings of the model can be used to improve the einstein formula for the equilibrium bedload discharge

unit stream power equation for gravel the basic assumptions used in the derivation of bedload or gravel transport equations are reviewed and examined to determine their validities laboratory data indicate that unit stream power is mor

diagenetic mobilization of manganese in peru basin sediments abstract the mn contents and sedimentation rates of two cores from different areas of the peru basin have been determined the southern core is associated with mn nodules of conventional slow accretion rates mm 106 yr while the northern one accompanies nodules with very high growth rates 102 mm 106 yr the depletion of mn observed within the top 40 cm of the cores is interpreted as resulting from a diagenetic remobilization of mn 2 due to the oxidative characteristics of the sedimentary column in both cores the calculated flux of mn provided by the sediment is higher than the total mn recovered in the overlying nodules this indicates that the mn content of the peru basin nodules can be supplied by diagenetic processes from the sediment not only for the slowly growing nodules but also for the extremely fast growing concretions found in the north of the basin

sediment concentration versus water discharge during single hydrologic events in rivers relations between sediment concentration c and water discharge q for a hydrologic event such as a flood are studied qualitatively by analyzing smoothed temporal graphs discharge and concentration vs time in terms of mode spread and skewness comparing cq ratios at a given discharge on the rising and falling limbs of the discharge hydrograph provides a consistent reliable method for categorizing c q relations five common classes of such relations are single valued straight or curved clockwise loop counterclockwise loop single valued plus a loop and figure eight temporal graph mode and skewness influence the type of relation whereas temporal graph spread affects the details of the particular c q relation its graphical breadth shape orientation and plotted location field examples of the various types of relations are given including varieties that heretofore have received little attention such as the figure eight explanations for each type of c q relation are discussed

sediment feed and recirculating flumes fundamental difference two standard modes of laboratory sediment transport flume operation are sediment feed and recirculating in the case of uniform sediment the final equilibriums achieved in the two modes are equivalent and independent of initial conditions even though the specified flow and sediment constraints differ when the sediment consists of a mixture of sizes however this symmetry breaks down in a sediment feed flume both the feed rate and size distribution are specified by the user and must be identical to those of the bed load at final equilibrium the final state thus becomes independent of initial conditions in a recirculating flume however the equilibrium size distribution of neither the bed load nor the bed surface material can be specified in advance as a result the final state depends on the initial conditions and can include the possibility of partial transport the equilibriums themselves are equivalent in that they obey the same laws of flow and sediment transport their ia priori n predictability however differs due to the difference in governing constraints when fractional transport is scaled by the bulk size distribution the two flume modes may produce very different transport relations even for the same sediment a consistent approach requires that the transport be scaled by the size distribution of the bed surface

growth history of manganese nodules and crusts of the peru basin abstract in the nodule field of the peru basin situated south of the zone of high bioproductivity a relatively high flux of biogenic matter explains a distinct redox boundary at about 10 cm depth separating very soft oxic surface sediments from stiffer suboxic sediments maximum abundance 50 kg m 2 of diagenetic nodules is found near the calcite compensation depth ccd currently at 4250 m there the accretion rate of nodules is much higher 100 mm ma 1 than on ridges 5 mm ma 1 highest accretion rates are found at the bottom of large nodules that repeatedly sink to a level immediately above the redox boundary there distinct diagenetic growth conditions prevail and layers of dense laminated mn oxide of very pure todorokite are formed the layering of nodules is mainly the result of organisms moving nodules within the oxic surface sediment from diagenetic to hydrogenetic environments the frequency of such movements is much higher than that of climatic changes two types of nodule burial occur in the peru basin large nodules are less easily moved by organisms and become buried consequently buried nodules generally are larger than surface nodules this type of burial predominates in basins at ridges where smaller nodules prevail burial is mainly controlled by statistical selection where some nodules are not moved up by organisms

co evolution of coarse grain structuring and bed roughness in response to episodic sediment supply in an experimental aggrading channel this is the accepted version of the following article hassan m a saletti m zhang c ferrer boix c johnson j p l muller t and von flotow c 2020 co evolution of coarse grain structuring and bed roughness in response to episodic sediment supply in an experimental aggrading channel earth surf process landforms 45 948 961 https doi org 10 1002 esp 4788 which has been published in final form at https onlinelibrary wiley com doi abs 10 1002 esp 4788

atmur delgo suture a neoproterozoic oceanic basin extending into the interior of northeast africa field and remote sensing data have enabled identification of a previously unrecognized discontinuous belt of ophiolitic nappe remnants in northeastern sudan the belt crops out for 200 km in a west southwest to southwest direction from the western margin of the arabian nubian shield into the gneissic terrane previously accepted as part of the archean to paleoproterozoic nile craton although highly dismembered and metamorphosed the belt contains all the components of a phanerozoic type ophiolite the ophiolite belt is interpreted as a suture zone atmur delgo suture manifesting collision 700 ma between a passive margin terrane in the south with an island arc terrane in the north following the consumption of an oceanic basin along a north dipping subduction zone our results indicate that previously recognized crustal provinces in northeastern africa must be reassessed critically

atypical ferromanganese nodules from pelagic areas of the central indian basin equatorial indian ocean abstract two box core samples one each from red clay and siliceous ooze sediment provinces from the central indian basin indian ocean were studied both cores contained ferromanganese nodules at their tops the red clay sediment also hosts buried nodules at a depth of 82 cm chemical characterization of the sediments indicates that early diagenetic remobilization of transitional metals is pronounced in the siliceous ooze sediment while in the red clay no such effect is discernible this is further corroborated by the abundance and dissolution patterns of microorganisms and ferromanganese micronodules occurring in the two sediment columns bulk chemical analyses indicate that all the nodules are of the hydrogenetic b type vernadite and todorokite are the major minerals both of which constitute laminated nondirectional colloform and cuspate microstructures petrographic studies yield evidence of recrystallization of todorokite and partial transformation of vernadite to todorokite the former process being more advanced in buried nodules microprobe analyses revealed that primary todorokite has a lower mn fe ratio and higher ni content than recrystallized todorokite in the same sample the mineralogical reconstitution in the nodules is attributed to postdepositional intranodule diagenesis the present study does not reveal the correlation between mineralogy and microstructure in the nodules which has been suggested for the nodules from the pacific neither can any mineral or microstructure be considered specific for any particular genetic model the studied nodules are therefore atypical the mineralogical and chemical reordering in these ferromanganese nodules raises the question of the viability of radiometric methods in determining growth rates of such nodules

experiments on the effect of hydrograph characteristics on vertical grain sorting in gravel bed rivers 1 desert ephemeral gravel bed streams typically have bed surfaces that are relatively unarmored compared to the substrate below while gravel bed streams in humid and snowmelt areas typically have well armored surfaces the degree of armoring can be characterized in terms of an armor ratio defined as the ratio of the surface median size to the substrate median size a set of field data shows desert ephemeral gravel bed streams with armor ratios ranging from 0 5 to 2 4 and with an average value of 1 2 the armor ratio of snowmelt fed gravel bed streams in the same set ranges from 2 to 7 with an average value of 3 4 the reason for this difference is sought in terms of differing hydrological characteristics and sediment supply regimes thirteen experiments were conducted to study the formation of armoring under a range of hydrological conditions the experiments have two limiting cases a relatively flat hydrograph that represents conditions produced by continuous snowmelt and a sharply peaked hydrograph that represents conditions associated with flash floods all constant hydrograph experiments developed a well armored structured surface while short asymmetrical hydrographs did not result in substantial vertical sorting all symmetrical hydrographs show some degree of sorting and the sorting tended to become more pronounced with longer duration sediment supply appears to be a first order control on bed surface armoring while the shape of the hydrograph plays a secondary role

local variations in distribution and composition of ferromanganese nodules in the clarion clipperton nodule province abstract local variations in nodule distribution and composition are discussed based on investigations in seven areas surveyed during five soviet expeditions beteween 1968 and 1988 to the clarion clipperton nodule province variations in nodule abundance are related to seafloor topography and to local changes in sedimentation rates caused both by bottom current activity and by carbonate dissolution below the lysocline and ccd most variations in nodule composition can be attributed to the two principal mechanisms of nodule growth hydrogenetic and diagenetic which create three genetic types of nodules differing in morphology mineralogy inner structure and chemistry hydrogenetic nodules relatively enriched in fe co and pb poor in mn cu ni and mo and with low mn fe ratios were found both on abyssal hills where they are associated with siliceous marly ooze and on the abyssal basin floor where they are associated with radiolarian ooze rugged bottom topography favours their occurrence and high abundance hydrogenetic nodules are though to be formed under distinct stable bottom current conditions diagenetic nodules enriched in mn cu ni and mo and with a high mn fe ratio occur on clayey radiolarian ooze on the abyssal basin floor below the ccd these nodules are deposited in high densities and are found predominantly on gentle slopes where upper quaternary clayey radiolarian ooze is only a few tens of centimetres thick and is unconformably underlain by pre quaternary pelagic clay we assume that the diagenetic growth of hydroxides is favoured by long term oscillations of bottom currents which lead to periodical redeposition of the soft unstable diagenetically active surface layer of radiolarian ooze the latter serves as a direct source of metals for nodule growth

a systematic analysis of eight decades of incipient motion studies with special reference to gravel bedded rivers data compiled from eight decades of incipient motion studies were used to calculate dimensionless critical shear stress values of the median grain size t c 50 calculated t c 50 values were stratified by initial motion definition median grain size type surface subsurface or laboratory mixture relative roughness and flow regime a traditional shields plot constructed from data that represent initial motion of the bed surface material reveals systematic methodological biases of incipient motion definition t c 50 values determined from reference bed load transport rates and from visual observation of grain motion define subparallel shields curves with the latter generally underlying the former values derived from competence functions define a separate but poorly developed field while theoretical values predict a wide range of generally higher stresses that likely represent instantaneous rather than time averaged critical shear stresses the available data indicate that for high critical boundary reynolds numbers and low relative roughnesses typical of gravel bedded rivers reference based and visually based studies have t c50 ranges of 0 052 0 086 and 0 030 0 073 respectively the apparent lack of a universal t 50 for gravel bedded rivers warrants great care in choosing defendable t c50 values for particular applications

geochemistry of ferromanganese micronodules and associated mn and trace metals diagenesis at high terrigenous depositional site of middle fan region bay of bengal abstract the influence of sedimentation on the morphology growth and geochemistry of the micronodules and on mn enrichment in the sediments of the bay of bengal has been evaluated mn accumulation is 307 219 mg cm2 kyr 1 in cores having 20 17 cm kyr 1 sedimentation rate but drops to 34 17 7 mg cm2 kyr 1 in cores with 3 4 cm kyr 1 sedimentation rates however mn enrichment zone becomes thinner with increased sedimentation the abundance of the micronodules increases and they have been observed down to the deeper levels with higher contents of mn ni cu and zn from the areas of the lower sedimentation the results of the present study reveal that though the higher sedimentation may be conducive for higher mn accumulation in the upper surfaces of the sediments the growth abundance and enrichment of mn ni cu and zn in the micronodules are mostly regulated by their residence time within mn oxidation zone the influence of residence time on the morphology and the internal structures of the micronodules are also evaluated

composition and formation of fossil manganese nodules in jurassic to cretaceous radiolarites from the nicoya ophiolite complex nw costa rica horizons of several types of upper jurassic to lower cretaceous manganese nodules occur locally in sequences of radiolarian cherts within the nicoya ophiolite complex nw costa rica field studies x ray diffraction analysis petrographic chemical and experimental studies give evidence of a sedimentary early diagenetic origin of the nodules in contrast to earlier suggestions smooth discoidal compact and very dense nodules with diameters of some mm to 9 cm dominate they are characterized by braunite hollandite pyrolusite and quartz as well as 39 61 mn 0 9 1 6 fe 5 26 sio2 1 3 1 9 a12o3 1 5 3 0 ba 460 5400 ppm cu 85 340 ppm ni and 40 130 ppm co among others it is suggested that the original mineralogy todorokite was altered during thermometamorphic braunite and hydrothermal hollandite pyrolusite events petrographic similarities between the fossil nodules and modern deep sea nodules are striking using standard hydrothermal techniques in an experimental study it is shown that under special conditions braunite can be produced from modern nodule material

stabilization of 10a manganates by interlayer cations and hydrothermal treatment implications for the mineralogy of marine manganese concretions abstract experimental substitutions of transition and alkaline earth cations into synthetic 10a na manganate show that cation uptake and the stability of the cation substituted mineral increase with stability of the hydroxide of the cation hydrothermal treatment of synthetic 10a manganates with different metal contents as well as marine diagenetic and hydrothermal 10a manganates shows that the stabilities of their structures are enhanced with increasing temperature the stabilization is due to reinforcement of the tunnel walls supporting the mn4 o2 6 octaheral layers the diagenetic 10a manganates have initially unstable buserite like structures with each interlayer wall composed of two mn2 o2 3 x oh 3 x octahedra 0 x 3 with either a na o2 2x oh n 2x unit n 6 and or 8 or less frequently a mn2 o2 2x oh 2 2x octahedron in between some of these cations in the walls are post depositionally substituted by highly hydrated divalent metal cations particularly cu2 and ni2 while some of the mn2 ions are slowly oxidized to mn4 these interlayer changes result in higher crystal field stabilization energy and shifts from interlayer van der waal s forces and weak coordination links to strong coordination links which stabilize the mineral structures low temperature hydrothermal 10a manganates have todorokite like structures with tunnel walls constructed predominantly of mn2 o2 3 x oh 3 x and mn2 o2 2x oh 6 2x octahedra high temperature hydrothermal 10a manganates have stable todorokite structures with the walls constructed of mn4 o2 6 octahedra the positive correlation between the formation or post depositional alteration temperatures and the mineral stability is due to the increase in oxidation rate of interlayer mn2 ions with increasing temperature of the hydrothermal fluids marine 10a manganates can be used as genetic indicators for manganese concretions and the sediments in which they occur and as a geothermometer in the search of ancient and modern hydrothermal vents where massive sulphide deposits are often found

bed topography and sediment sorting in channel bend with unsteady flow bed topography and transverse sediment sorting in an alluvial channel bend were investigated under unsteady flow conditions with nonuniform sediment five experiments each having the same initial sediment size gradation but a different inflow hydrograph were done in a 180 channel bend with a constant radius of curvature in addition bed elevations across various sections of the bend were measured and bed surface sediment were sampled at the peak and end of the hydrograph in each experiment experimental results indicated that the characteristics of the hydrograph have prominent influences on bed topography and transverse sediment sorting those cases with a higher ramping rate of the hydrograph have greater deposition heights near the inner bank and larger scour depths near the outer bank furthermore the sediment is finer near the inner bank and coarser near the outer bank in cases with a higher ramping rate the bed deformation and sediment size variation correlated well with the unsteady flow par

simplicity and complexity of bed load response during flash floods in a gravel bed ephemeral river a 10 year field study 1 a decade of data for the nahal eshtemoa an unarmored gravel bed ephemeral river reveals that bed load flux during rain fed flash floods is a simple function of channel average boundary shear stress however the relation is inadequately described by a power function of the type commonly used in predictive bed load equations and a linear function gives a much better fit the success of a linear function is related to the unarmored nature of the bed material typical of ephemeral gravel bed rivers and the ready availability of sediment at all levels of transport stage bed load response to changing shear stress is largely undifferentiated as flash floods wax or wane however while most data conform to a simple relation between bed load and hydraulic stress some for individual floods or flood segments do not reflecting variability in sediment supply and texture three type behaviors are identified that assist in explaining both the general simple pattern and the limited scatter of the bed load shear stress plot type 1 provides the majority of the data giving the general linear relation between bed load flux and boundary shear stress type 2 is rare given the flashy nature of the hydrograph but represents comparatively steady flows well above the entrainment threshold during which bed load sheets or the breakup of grain clusters lead to spasmodic changes in bed load flux type 3 shows a weak relation between shear stress and bed load flux representing flow conditions just above the entrainment threshold

sediments and micronodules in the northern and central peru basin the mineralogy and composition of sediments and manganese micronodules from the northern and central sectors of the peru basin are discussed because of the proximity of the basin to the carbonate compensation depth c c d surface sediments vary between calcareous oozes and siliceous muds besides biogenic components clay minerals are important by far the most abundant clay mineral is smectite which is thought to be of diagenetic origin on a carbonate free basis the surface sediments are rather uniform in composition throughout the basin and are similar in composition to those of the equatorial pacific sedimentation rates for the uppermost core sections are in the range of 3 to 5 mm 1000 yr

mineralogy and crystal chemistry of mn fe co ni and cu in a deep sea pacific polymetallic nodule minor element concentrations in marine ferromanganese nodules are primarily controlled by the mineralogy which itself depends on redox conditions at the sediment water interface results are presented for the first in depth x ray microstructural and microspectroscopic investigation of a mixed hydrogenetic diagenetic nodule which is representative of ferromanganese deposits on abyssal plains the measurements were conducted by micro x ray diffraction and x ray absorption spectroscopy both xanes and exafs on hydrogeneous and diagenetic regions of the nodule the hydrogenetic diagenetic interface was imaged by x ray microfluorescence after which regions of interest were chosen to represent mineralogical and chemical transformations that occurred at the early stage of suboxic diagenesis in the hydrogenetic nodule oxic environment mn is speciated as fe vernadite a nanocomposite material composed of intergrown feroxyhite feooh and monodispersed phyllomanganate layers having no interlayer mn vernadite in the diagenetic nodule suboxic environment mn is speciated dominantly as mg rich 10 a vernadite which consists of a random intergrowth of vernadite and its transformation product todorokite the authigenic 10 a vernadite precipitated from the components of vernadite in fe vernadite that were dissolved in suboxic microenvironments of the sediment direct evidence supporting a redox driven dissolution reaction is provided by the valence composition of mn as measured by micro xanes which is 0 69mn4 0 24mn3 0 07mn2 average 3 62 0 04 v u for fe vernadite and 0 61mn4 0 23mn3 0 16mn2 average 3 28 0 04 v u for 10 a vernadite ni and cu derived mainly from dissolved vernadite and oxidized organic matter replace structural mn3 4 in both the mno2 layer and todorokite domains of 10 a vernadite pure todorokite in highly diagenetic regions of the nodule has an average formula of mg2 0 167 mn4 0 783 mn3 0 099co3 0 002ni2 0 076cu2 0 040 o2 n h2o with an atomic ratio of cu ni co mn 0 13 which is slightly lower than 0 167 1 6 the maximum metal uptake capacity reported for marine nodules by analogy with synthetic todorokites we infer that mg2 which has a hydrated diameter close to that of the 3 3 tunnel size of todorokite and mn3 and cu2 which prefer jahn teller distorted octahedra play a crucial role in templating the topotactic transformation of 10 a vernadite to todorokite and stabilizing todorokite in suboxic marine sediments

sediment transport part i bed load transport a method is presented which enables the computation of the bed load transport as the product of the saltation height the particle velocity and the bed load concentration the equations of motions for a solitary particle are solved numerically to determine the saltation height and particle velocity experiments with gravel particles transported as bed load are selected to calibrate the mathematical model using the lift coefficient as a free parameter the model is used to compute the saltation heights and lengths for a range of flow conditions the computational results are used to determine simple relationships for the saltation characteristics measured transport rates of the bed load are used to compute the sediment concentration in the bed load layer a simple expression specifying the bed load concentration as a function of the flow and sediment conditions is proposed a verification analysis using about 600 alternative data shows that about 77 of the predicted bed load transport rates are within 0 5 and 2 times the observed values

physical complexity to model morphological changes at a natural channel bend this study developed a two dimensional 2 d depth averaged model for morphological changes at natural bends by including a secondary flow correction the model was tested in two laboratory scale events a field study was further adopted to demonstrate the capability of the model in predicting bed deformation at natural bends further a series of scenarios with different setups of sediment related parameters were tested to explore the possibility of a 2 d model to simulate morphological changes at a natural bend and to investigate how much physical complexity is needed for reliable modeling the results suggest that a 2 d depth averaged model can reconstruct the hydrodynamic and morphological features at a bend reasonably provided that the model addresses a secondary flow correction and reasonably parameterize grain sizes within a channel in a pragmatic way the factors such as sediment transport formula and roughness height have relatively less significance on the bed change pattern at a bend the study reveals that the secondary flow effect and grain size parameterization should be given a first priority among other parameters when modeling bed deformation at a natural bend using a 2 d model

geochemistry of cobalt rich ferromanganese crusts from the perth abyssal plain e indian ocean abstract geochemistry of cobalt rich ferromanganese crusts from the as yet unexplored dirck hartog ridge dhr a linear bathymetric feature of poorly understood origin located in the centre of the perth abyssal plain pap is described for the first time based on 3 samples analyzed with xrf icp ms and epma mean bulk concentrations of fe and mn were 20 8 and 18 4 wt respectively individual crust layers however proved chemically variable the mean concentration of metals of the highest economic potential cu ni co was 0 69 wt the mean total rare earth elements ree and yttrium rey contents in the samples 1908 mg kg proved moderate the crusts showed strong positive ce anomalies negative y anomalies and a low y sn hosn ratio mean 0 56 observations on the texture and chemical composition of the crust samples studied allowed us to distinguish two major and two subtypes of representative colloform structures built of laminae the type i colloform structures showed the mn fe ratio to range from 0 86 to 5 69 the ranges in type ii colloform structures being 0 49 2 47 subtype ii 1 and 6 91 221 42 subtype ii 2 the subtype ii 2 colloform structures were enriched in ni up to 7 31 wt the co and cu concentrations showed a high variability 0 03 1 64 and 0 03 0 22 wt respectively according to the current genetic models and discrimination diagrams the crusts studied were classified as hydrogenetic although individual laminae and groups of laminae could be regarded as diagenetic or hydrothermal

the morphodynamics of fluvial sand dunes in the river rhine near mainz germany ii hydrodynamics and sediment transport the dynamics of large isolated sand dunes moving across a gravel lag layer were studied in a supply limited reach of the river rhine during daylong surveys suspended sediment concentration bedload transport rate water depth flow velocity turbulence intensity near bed shear stress and water temperature were recorded over individual isolated dunes this paper considers the hydrodynamic environment and sediment transport over the dunes a companion paper details the sedimentology and morphology of the dunes flow over the flat gravel lag upstream of large dunes is more uniform than that over dunes and gravels are rarely entrained by in bank discharges unsteady and non logarithmic velocity profiles are common within the boundary layer above the stoss side of large dunes and the near bed flow demonstrates evidence of large scale coherent low frequency flow structures these may reflect stacked sequences of separated boundary layers generated by secondary dunes however the low amplitude morphology of large dunes does not affect the statistical properties of turbulence production over the stoss sides bed roughness and near bed shear stress commonly increase steadily over the stoss of dunes but may decrease near the crest especially where a crestal platform exists that is devoid of secondary bedforms bed roughness scales with the physical size of bed roughness elements however variability in roughness lengths is large owing to the composite nature of bed roughness bedload transport over stoss slopes is spatially variable but often shows an increase with increasing bed shear stress over the stoss well formed wakes only develop downstream of lee slopes which are close to the angle of repose otherwise separation is weak and suspension and settling of fine sediments is of little consequence to dune evolution wake flow is characterized by turbulence production one order of magnitude greater than over the stoss side which may be related to vortex shedding from the dune however wake current speeds are extremely low and variable in direction reverse flow is not sustained and no retrogressive bedforms occur in the lee of large dunes near bed shear stress and bed roughness are usually low within the wake reflecting low current speeds weak wake flow reattachment occurs at a variable distance downstream up to several times the duneform height a two dimensional numerical model for flow over dune topography calibrated using average parameter values provided a reasonable description of the flow upstream and over the backs of large dunes as far as the crestal region wake flow could not be modelled however the temporal and spatial complexity of natural three dimensional flow over the dunes resulted in variance in parameter estimates this variance precluded modelling of flow and bedload transport consequently it was not possible to model dune evolution in a deterministic sense

neogene oceanographic variations recorded in manganese nodules from the somali basin abstract a detailed study of a nodule from the somali basin dated by 230 th excess was correlated with the paleoceanographic events recorded in site 236 leg 24 deep sea drilling project dsdp cores tentative indications are that the phase of nodule accretion starting with the development of pillar structure at a depth of 20 mm in the nodule around 13 ma coincides with increased antarctic bottom water aabw flow and an elevated calciumcarbonate compensation depth ccd the late miocene lowering of the ccd is represented by the mottled zones between 8 and 18 mm in the nodule is characterised by an abundant silicate component 20 of aeolian origin the miocene pliocene boundary 5 ma occurs at a depth of about 8 mm and is represented by the development of pillar structure and a minimum of aeolian dust 10 3 the increased biological productivity of the somali surface water since the middle miocene is demonstrated by the increasing c org content of the nodule from 0 11 to 0 19 towards its surface

biogenic signature and ultra microfossils in ferromanganese nodules of the central indian ocean basin abstract theories related to the precipitation mechanism of the metallic elements in marine manganese nodules have remained controversial between two schools of thoughts 1 chemical oxidation abiotic origin and 2 deposition of the metals through microbial enzymatic processes biogenic origin one of the most important evidence in support of the biogenic origin is the occurrence of fossilized microbes however well documented literature in this regard is either lacking or very scanty in case of indian ocean nodules using high resolution feg sem we have recorded various biogenic signatures and ultra microfossils in the ferromanganese nodule samples from central indian ocean basin ciob that are presented in this paper the microfossils are mostly protozoans belonging to varieties of bacteria diatoms and foraminifera some of the features recorded in this study have perhaps never been reported before from any manganese nodules the chemical compositions of these ultra microfossils indicate a high level of manganese precipitation in and around them in comparison to the distant surrounding areas while clumpy microbes are enriched with nickel the rod shaped bacteria are rich in copper up to 4 70 wt nickel and 5 31 wt cu have been recorded in the fossilized microbe bodies the high abundance of biogenic features as well as microfossils in the ferromanganese nodules and their chemical compositions support arguments in favor of a dominant role of the microorganisms in the construction of the nodules of the ciob

sedimentary processes and manganese nodule formation in the korea deep ocean study kodos area western part of clarion clipperton fracture zones northeast equatorial pacific abstract in the southern part of the korea deep ocean study kodos area the western part of the clarion clipperton fracture zones abundant nodules occur in the oligocene to miocene radiolarian bearing smectitic clay the nodules are generally concentrated in patchy pavements more than 5 kg m2 on the hilly seafloor with sediment waves they are either rare or abundant on the seamounts and are generally rare in the abyssal plain the nodules can be classified into three types based on distinct surface texture the s type nodules occur in intensely bioturbated sediment of the abyssal hill and seamount areas in the abyssal plain the r type nodules are dominant embedded within the topmost quaternary sediment layer in the southeastern part where pliocene sediment occurs they are in an incipient stage of growth the s type nodules are rich in fe and co in columnar structures of mno2 whereas the r types contain abundant mn ni cu and zn in dendritic and massive 10a manganate layers the t type nodules occur together with either the r or s type showing intermediate composition regardless of the type and shape the bottoms of nodules contain more abundant mn ni cu zn and 10a manganate than the tops as the mn fe ratio increases in the nodules the abundance of ni cu and zn increases up to a constant value about 11 of mn southward in the underlying sediment however it decreases northward manganese and these minor metals are concentrated in the lowermost tertiary sediment as much as 2 to 3 times than those in the topmost sediment layer which is intensely bioturbated iron and co are relatively uniform downcore manganese ni and cu are abundant in micronodules whereas fe is concentrated in smectite redistributional processes of bottom currents seem to be most responsible for the re generation and concentration of nodules in patchy pavements by excavating buried nodules these processes result in an inverse relation of nodule abundance to the thickness of uppermost sedimentary layer which comprises the radiolarian ooze of clipperton formation in the seamount areas sediment slumping has also contributed to the concentration of nodules the fragmentation of old nodules also enhances the nodule re generation activities of benthic animals cause the nodules to be lifted upward onto the seafloor mostly during the quiescent periods of bottom currents the growth of nodules by resedimentation processes results in the large discrepancy in composition not only between the types but also the tops and bottoms controlled by the burial rates of nodules within the topmost sediment layer where the diagenesis takes place diagenetic growth of nodules occurs by utilizing mn and minor metals remobilized from micronodules during biomixing and decomposition of organic materials within tertiary sediment nodule growth is more active southward toward the equator latitudinal variations of nodule size distribution abundance and composition result from the change in surface water productivity and the timing of nodule nucleation as the pacific plate migrates northwestward

ferromanganese oxide deposits from the central pacific ocean ii nodules and associated sediments bulk chemical mineralogical and selective leach analyses have been made on a suite of abyssal ferromanganese nodules and associated sediments from the s w equatorial pacific ocean compositional relations between nodules sediment oxyhydroxides and nearby ferromanganese encrustations are drawn assuming that the crusts represent purely hydrogenetic ferromanganese material crusts mno2 rich nodules and sediment oxyhydroxides are compositionally similar and distinct from diagenetic todorokitebearing nodules compared to fe mn crusts sediment oxyhydroxides are however slightly enriched relative to mn and ni in fe cu zn ti and al and depleted in co and pb reflecting processes of non hydrogenous element supply and diagenesis mno2 nodules exhibit compositions intermediate between fe mn crusts and sediment oxyhydroxides and thus are considered to accrete oxides from both the water column and associated sediments deep ocean vertical element fluxes associated with large organic aggregates biogenic calcite silica and soft parts have been calculated for the study area fluxes associated with organic aggregates are one to three orders of magnitude greater than those associated with the other phases considered are in good agreement with element accumulation rates in sediments and are up to four orders of magnitude greater than element accumulation rates in nodules metal release from labile biogenic material in surface sediments can qualitatively explain the differences between the composition of fe mn crusts and sediment oxyhydroxides todorokite rich diagenetic nodules are confined to an eastwards widening equatorial wedge it is proposed that todorokite precipitates directly from interstitial waters since the transition metal chemistry of interstitial waters is controlled dominantly by reactions involving the breakdown of organic carbon the supply and degradation rate of organic material is a critical factor in the formation of diagenetic nodules the wide range of trace metal mn ratios observed in marine todorokite reflects a balance between the release of trace metals from labile biogenic phases and the reductive remobilisation of mn oxide both of which are related to the breakdown of organic carbon

linking bed morphology changes of two sediment mixtures to sediment transport predictions in unsteady flows flume experiments were conducted to measure bed morphology adjustments in sand gravel and sand silt sediment mixtures during repeated hydrographs and to link these changes to sediment transport patterns over multiple time scales sediment composition and hydrograph flow magnitude greatly influenced channel morphology which impacted sediment yield hysteresis and transport predictions bed load yields were larger and more variable for the sand silt mixture as gravel in the sand gravel sediment inhibited grain entrainment limited bed form growth and acted to stabilize the bed hysteresis patterns varied due to bed form and surface structure adjustments as well as the stabilizing effect of antecedent low flows using half the data set a dimensionless fractional transport equation was derived based on excess shear stress dimensionless reference shear stresses were estimated in two ways as bulk values from all transport measurements and by applying a separate limb approach in which values were estimated for each limb of each hydrograph for the other half of the data set transport predictions with the separate limb approach were more accurate than those from six existing transport equations and the fractional relationship applied with bulk reference shear stresses thus hydrograph limb dependent dimensionless reference shear stress links changing bed morphology and sediment transport providing a parameter to improve transport predictions during individual flood events and in unsteady flow regimes this approach represents a framework with which to develop site specific transport relationships for varying flow regimes particularly in cases where detailed bed morphology measurements are not feasible and heterogeneous sediment complicates bed structure over time

effects of an emergent vegetation patch on channel reach bathymetry and stability during repeated unsteady flows while research into the interaction between in channel vegetation flow and bed sediment has increased in recent years there is still a need to understand how unsteady flows affect these processes particularly in terms of channel bed adjustments in this study flume experiments tested two flood hydrograph sizes run over sand gravel and sand silt beds to evaluate reach scale impacts of a mid channel vegetation patch of variable stem density on channel bathymetry and stability alternating flood hydrographs with periods of low steady flow created flow sequences reflective of an extended unsteady flow regime thereby simulating time scales consisting of multiple flood events digital elevation models provided detailed measurements of channel change following each flood event to enable analysis over each unsteady flow sequence the vegetation patch created characteristic channel bathymetries dependent on sediment mixture and patch density that in all cases resulted in a more variable bed structure than channels without a patch reach scale stability quantified based on net volumetric bed change only occurred with a sparse patch in the low flood sequence corresponding with little variation in surface composition and structure in most other cases scour measured at the patch prevented stability at the reach scale especially in the finer substrate overall findings show that a channel may only adjust to a stable bathymetry upon addition of a mid channel vegetation patch within a limited range of flow regimes and patch stem densities and that for the experimental conditions tested here in stream patches generally did not enhance reach scale bed stability this article is protected by copyright all rights reserved

fine scale study of major and trace elements in the fe mn nodules from the south china sea and their metallogenic constraints abstract many marine fe mn polymetallic nodules may contain high concentrations of mn cu ni zn co and rare earth elements plus yttrium rey to determine the occurrence and enrichment processes of these metals in the fe mn nodules we conducted high resolution mineralogical and geochemical studies on the fe mn nodules collected from the south china sea in situ epma and la icp ms analyses and elemental imaging were performed on individual microlayers of the nodules to reveal the major and trace element distributions the whole rock mineralogical and chemical compositions of the fe mn nodules indicate a hydrogenetic origin the mn mineral phases are mainly composed of nanocrystalline vernadite with interlayered 10 a and 7 a phyllomanganates such as todorokite birnessite and buserite fe ti oxides hydroxides are intergrown and essentially x ray amorphous feroxyhyte and goethite we recognize two main types of microlayers type a layer suboxic diagenetic precipitates containing a high mn fe ratio and high concentrations of cu ni zn ba li and mg and type b layer oxic hydrogenetic accretions with low fractionation of mn and fe and high contents of co rey ti sr and pb furthermore elemental mapping indicates that the enrichments of co and rey are mainly associated with fe mineral phases rather than mn ones which are enriched in mg cu ni zn li and ba two mineralization processes and metal distributions in the individual microlayers are identified in the fe or mn mineral phases the occurrence of 10 a and 7 a phyllomanganates in type a layers are commonly enriched in trace metals such as ni cu zn li ba and mg whereas the metals for the type b layers include co ti pb sr rey which may be carried by the intergrowing fe ti oxyhydroxides and vernadite thus hydrogenesis and diagenesis facilitate the enrichment of fe co ti sr pb rey and mn ni zn cu li ba mg respectively during the mineralization of the south china sea nodules

flume and field based calibration of surrogate sensors for monitoring bedload transport bedload transport assessment is important for geomorphological engineering and ecological studies of gravel bed rivers bedload can be monitored at experimental stations that require expensive maintenance or by using portable traps which allows measuring instantaneous transport rates but at a single point and at high costs and operational risks the need for continuously measuring bedload intensity and dynamics has therefore increased the use and enhancement of surrogate methods this paper reports on a set of flume experiments in which a japanese acoustic pipe and an impact plate have been tested using four well sorted and three poorly sorted sediment mixtures additional data were collected in a glacierized high gradient andean stream estero morales using a portable bunte type bedload sampler results show that the data provided by the acoustic pipe which is amplified on 6 channels having different gains can be calibrated for the grain size and for the intensity of transported sediments coarser than 9 mm r2 0 93 and 0 88 respectively even if the flume based calibration is very robust upscaling the calibration to field applications is more challenging and the bedload intensity could be predicted better than the grain size of transported sediments r2 0 61 and 0 43 respectively the inexpensive impact plate equipped with accelerometer could be calibrated for bedload intensity quite well in the flume but only poorly in the field r2 0 16 and could not provide information on the size of transported sediments

geochemical variations of ferromanganese nodules and crusts from different provinces of the pacific ocean and their genetic control abstract the chemical composition of nodule samples from the northeast pacific nodule belt and from the northern part of the nazca plate in the southeast pacific have been investigated ni and cu contents increase with increasing mn fe ratio up to a value of 5 in samples from both provinces the nodules from the southeast pacific show a decrease in ni and cu contents when the mn fe ratio increases above a value of 5 nodules with a mn fe ratio of 5 have the highest concentrations of ni and cu a similar relationship cannot clearly be observed in nodules from the northeast pacific where the mn fe ratio does not exceed values of 7 4 the observed decrease in the ni and cu contents at mn fe ratios greater than 5 is a consequence of an enhanced supply of mn2 ions within the pore water environment of the upper centimeters to decimeters of the sediment column this leads to the incorporation of mn2 ions instead of ni2 and cu2 ions in the intermediate layers of the todorokite lattice increased amounts of organic matter in the sediment deposits below the equatorial zone of high biological productivity result in a decrease in the redox potential within the uppermost part of the sediment column which promotes the mobilization of mn nodules grow faster under these conditions and are enriched in mn and depleted in ni and cu the co contents of the nodules from the southeast pacific decrease in general with rising mn fe ratio considering three phase diagrams the geochemical discrimination of different genetic types of nodules is possible plotting only co vs mn and fe in a three phase diagram it can be elucidated that ferromanganese deposits richest in co only occur at mn fe ratios between 1 and 2 however the individual co values show a great range of variation in the case of early diagenetic nodules the samples from the southeast pacific show on the average lower concentrations of co than the nodules from the northeast pacific

an experimental study into the geometry of supply limited dunes the relationship between dune geometry and the volume of mobile sediment was studied in flume experiments in these flume experiments the volume of mobile sediment on top of an immobile coarse sediment layer was increased stepwise and the bedform characteristics were observed a strong relationship was found between the volume that is mobile and therefore available for bedform formation and the dune dimensions and regularity if the sediment supply is limited dunes are smaller and more regular series of experiments with a decreasing supply limitation were conducted for different flow velocities and water depths the relationship between the dune dimensions and the available volume is different for each series the observed relationships between dune dimensions and layer thickness collapse to one relationship for height and one for length if scaling parameters are introduced current models for bedform dimensions under alluvial conditions can be extended to partial transport conditions using this relationship

experimental evidence for the effect of hydrographs on sediment pulse dynamics in gravel bedded rivers 1 gravel augmentation is a river restoration technique applied to channels downstream of dams where size selective transport and lack of gravel resupply have created armored relatively immobile channel beds augmentation sediment pulses rely on flow releases to move the material downstream and create conditions conducive to salmon spawning and rearing yet how sediment pulses respond to flow releases is often unknown here we explore how three types of dam releases constant flow small hydrograph and large hydrograph impact sediment transport and pulse behavior translation and dispersion in a channel with forced bar pool morphology we use the term sediment pulse generically to refer to the sediment introduced to the channel the zone of pronounced bed material transport that it causes and the sediment wave that may form in the channel from the additional sediment supply which can include input sediment and bed material in our experiments we held the volume of water released constant which is equivalent to holding the cost of purchasing a water volume constant in a stream restoration project the sediment pulses had the same grain size as the bed material in the channel we found that a constant flow 60 greater than the discharge required to initiate sediment motion caused a mixture of translation and dispersion of the sediment pulse a broad crested hydrograph with a peak flow 2 5 times the discharge required for entrainment caused pulse dispersion while a more peaked hydrograph 3 times the entrainment threshold discharge caused pulse dispersion with some translation the hydrographs produced a well defined clockwise hysteresis effecting sediment transport as is often observed for fine sediment transport and transportlimited gravel bed rivers the results imply a rational basis for design of water releases associated with gravel augmentation that is directly linked to the desired sediment behavior

bed topography and sand transport responses to a step change in discharge and water depth abstractat base flow conditions ephemeral streams with mobile beds may inherit bed topography caused by previous higher flow events resulting in bed topography that is not in equilibrium with flow conditions major flow events can generate large bedforms that result in hydrodynamics and sediment transport that are not in equilibrium with subsequent lower flow conditions to simulate a large storm runoff driven stream flow followed by lower base flow conditions changes in sand bed topography and sand transport caused by a simultaneous reduction in discharge and flow depth in a laboratory flume with an equilibrium sand bed and steady approximately uniform flow were investigated bed topography was evaluated using second order structure functions semivariograms and statistical analyses sediment transport responded rapidly to a near instantaneous negative step in mean flow depth and discharge the relative contributions of reduced bedform height and celerity to the decreased transport rate are quantif

the incidence and nature of bedload transport during flood flows in coarse grained alluvial channels a continuous record reveals that the incidence of bedload in a coarse grained river channel changes from flood to flood long periods of inactivity encourage the channel bed to consolidate sufficiently so that bedload is largely confined to the recession limb of the next flood wave but when floods follow each other closely the bed material is comparatively loose and offers less resistance to entrainment in this case substantial amounts of bedload are generated on the rising limb this is confirmed by values of bed shear stress or stream power at the threshold of initial motion which can be up to five times the overall mean in the case of isolated floods or those which are the first of the season this produces a complicated relationship between flow parameters and bedload and explains some of the difficulties in establishing bedload rating curves for coarse grained channels besides this the threshold of initial motion is shown to occur at levels of bed shear stress three times those at the thresholds of final motion this adds further confusion to attempts at developing predictive bedload equations and clearly indicates at least one reason why equations currently in use are unsatisfactory bedload is shown to be characterized by a series of pulses with a mean periodicity of 1 7 hours in the absence of migrating bedforms it is speculated that this well documented pattern reflects the passage of kinematic waves of particles in a slow moving traction carpet the general pattern of bedload including pulsations is shown to occur more or less synchronously at different points across the stream channel