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

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

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

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

inhomogeneous structure of the voronezh shield lithosphere from explosion seismology data abstract this paper presents the results of a seismological investigation of the voronezh shield the use of industrial quarry blasts as the most economic seismic energy source and telemetric arrays of the taiga type for deep seismic sounding observations has enabled the geophysical research group of the voronezh state university to obtain complete and valid information concerning the deep structure of the shield seismic records of refracted and reflected p and s phases from the intracrustal and subcrustal discontinuities allow the determination of independent and compatible velocity models v p z and v s z analysis of the travel time and amplitude curves derived from the deep seismic sounding data reveals a complex and inhomogeneous structure of the voronezh shield lithosphere the major discontinuities are found in the middle part of the consolidated crust several rather thick layers can be resolved which are separated by first order seismic boundaries in the consolidated crust beneath the southeastern part of the shield at depths from 6 7 to 11 13 km a low velocity layer is clearly established from the compressional wave data within the low velocity channel v p appears to decrease by 5 6 the low velocity channel in the uppermost consolidated crust is assumed to be due to metamorphogeneous granitization this is revealed by the precambrian basement structure poisson s ratio calculated from the compatible velocity models v p z and v s z shows a systematic increase down to the crustal basement and becomes discontinuous only in the low velocity channel at the top of the mantle poisson s ratio decreases on all the deep seismic sounding profiles the systematic variation of poisson s ratio is related to changes in the composition and mineralogy of the voronezh shield lithosphere

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

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

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

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

a data brief on magnesium isotope compositions of marine calcareous sediments and ferromanganese nodules 1 the magnesium isotope compositions of 26 ferromanganese nodules from various oceans and 22 calcareous sediment samples from ocean drilling program odp leg sites from the atlantic odp704 leg 114 and the pacific odp846 leg 138 have been analyzed by multicollector inductively coupled plasma mass spectrometer most nodules from the pacific and atlantic oceans have 26mg between 1 89 0 24 and 0 54 0 01 2 scatter around the average ocean water value of 0 86 0 12 indian ocean nodules display a large variation in 26mg ranging from 2 94 0 46 to 0 69 0 18 as for calcareous sediments 26mg variations range between 2 94 0 50 and 0 71 0 45 and between 4 00 0 31 and 1 63 0 09 for the atlantic and the pacific legs respectively this study allows the construction of a thread of global 26mg mapping in fe mn nodules and suggests that what controls the 26mg variations of marine calcareous sediments is complex and probably linked both to a mixture of different tests of micro organisms and to diagenesis

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

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

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

geochemical processes controlling the relationship between co mn and fe in early diagenetic deep sea nodules abstract early diagenetic manganese nodules from the northeast pacific nodule belt and from the southeast pacific peru basin show primary growth features of dendritic microtextures consisting of alternating laminae of crystalline 10 amanganate a1 substance and amorphous material which is composed of an intimate mixture of ferric hydroxide silicate and mno 2 a2 substance the formation of rhythmic sequences of a1 and a2 microlayers is explained by physico chemical changes in the peneliquid sediment layer and in the microenvironment of the accreting nodule surface a upward diffusion of mn 2 in the interstitial water as a result of decay of organic matter and mn mobilization b oxidation of mn 2 and formation of 10 amanganate in the upper part of the peneliquid sediment layer leading to ph depression in the microenvironment of the nodule surface which decreases the mobility of silicate resulting in formation of a2 layers c restoration of ph and renewed precipitation of 10 amanganate based on data of 171 bulk analyses and on electron microprobe investigations interelement relationships between co mn and fe are pointed out fe and co show a significant positive correlation r 0 84 while mn and co are poorly negatively correlated r 0 21 assuming linear regression the enrichment of co within the amorphous a2 phase is attributed to specific surface adsorption and subsequent oxidation of co 2 to co 3 in the strong electric field of si 4 robust complexes of co iii and feh 2 sio 4 prevent most of the co from being available for the 10 amanganate precipitation concerning the relation between mn and fe and co respectively the highest correlation coefficients are obtained using an inverse logarithmic regression under early diagenetic conditions the concentration and precipitation of mn 2 in the interstitial water depends on the redox gradient which is controlled by the amount of decomposing organic matter the nernst equation describes the relationship as a reciprocal logarithmic function however the quantities of colloidal ferric hydroxide and of dissolved silicate are not affected by variations of the redox potential these different characteristics in the precipitation of mn and the fe and si rich colloidal phase may cause the significantly negative logarithmic correlation of mn versus fe and co respectively

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

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

regional variability in ferromanganese nodule composition northeastern tropical pacific ocean abstract ferromanganese nodules are products of both direct and indirect precipitation in the marine environment therefore they potentially posses an important record of the oceanographic conditions under which they have grown previous attempts to extract useful paleoceanographic interpretations from ferromanganese nodules have been hampered by the scarcity of data and analytical inconsistencies which make the separation of locally controlled versus regionally controlled variations in nodule composition difficult between 1978 and 1981 the ocean minerals company omco conducted extensive surveys in the northeastern tropical pacific ocean during this time the average bulk geochemistry of nodules from 4657 grab samples collected from an area of approximately 1 5 million km2 was determined using highly uniform and closely controlled analytical protocols because of its broad areal coverage large sample size and the consistency of the analytical techniques employed this data set is ideally suited to quantitatively examine longstanding hypotheses concerning the factors that control the regional scale variability of nodule compositions a combination of geostatistical techniques have been employed to achieve this objective the results of a q mode factor analysis of the geochemical data indicate that the nodules are composed of a two component mixture of material acquired from both sediment and seawater sources via diagenetic and hydrogenetic accretionary processes respectively linear modeling of these results determined that diagenetic accretion is the predominant accretionary processes in this region of the pacific finally a kriging analysis was employed to examine the spatial variability of nodule composition contour maps of the kriging results suggest that variations in primary productivity levels and sedimentation rates are the primary influences on the regional scale variability of nodule composition and that the influence of diagenetic accretion is maximally approaching the equatorial zone of high productivity the nodules examined in this study are likely oligocene to miocene in age the probable paleolocations of these nodules at that time as determined by backtracking from the inferred northwesterly movement of the pacific plate would still place the nodules well within the zone of equatorial high productivity consequently while these nodules may have been subject to variations in the magnitudes of primary productivity and sedimentation rate during their active growth phase the observed compositional trends suggest that the overall spatial pattern of productivity has remained essentially the same

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

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

geochemistry of polymetallic nodules from the central indian ocean basin abstract polymetallic nodules dredged at fourteen stations between 12 15 s and 76 80 e in the central indian ocean basin ciob display wide variations in shape size texture mineral phases and chemical composition among the thirteen different types of nodules present only spherical and ellipsoidal nodules ranging in size from in the ciob the nodules of a particular size range have common morphological mineralogical and chemical properties compared to the larger nodules the smaller nodules are enriched in mn cu and ni have higher growth rates and higher cu ni ce la and ce fe ratios and todorokite as the major mineral phase the smaller nodules also show enrichment in heavy rees and exhibit a negative ce anomaly comparison of the average cu ni co content in the different sized nodules indicates that only smaller nodules have grades 2 61 3 04 for nodules different sized nodules from the ciob suggest formation at different places and indicate movement due to bottom currents from the place of formation to the deeper water regions three models are suggested to explain the observed morphological mineralogical and geochemical variations with respect to nodule size 1 in the ccd model the smaller nodules 4 cm which have high fe and moisture and low todorokite contents are formed mainly by hydrogenesis 3 the mixing model indicated shifting of the smaller nodules formed close to the ccd to deep sea regions and mixing with larger nodules formed from hydrogenous precipitation

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

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

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

growth of diagenetic ferromanganese nodules in an oxic deep sea sedimentary environment northeast equatorial pacific abstract to study the accretion mechanism of diagenetic ferromanganese nodules formed in an oxic deep sea sedimentary environment manganese nodules sediments and pore waters were sampled in the northeast equatorial pacific diagenetic ferromanganese nodules are ellipsoidal to discoidal in shape rough in surface texture enriched in cu ni and 10 a manganite and are ubiquitous on the abyssal plain hydrogenetic nodules are polynucleated irregular in shape smooth in surface texture enriched in co and mno 2 and occur dominantly on seamounts numerous microlayers with diagenetic or hydrogenetic characteristics occur successively in the nodules concentration of nitrate in sediment pore waters indicates that overall redox conditions are oxic however mn oxide grains on the walls of burrows and worm tubes are interpreted to be reprecipitated metal ions supplied from oxygen depleted microenvironments that formed in the oxic sediment column by decomposition of organic matter active mixing of bottom sediments by benthic fauna and bottom currents is indicated by ubiquitous burrows worm tubes and tracks and trails high values in sediment mixing coefficients 1 cm 2 yr and scattering of data points in depth profiles of pore water nitrate concentrations we suggest that diagenetic ferromanganese nodules in an oxic deep sea sedimentary environment grew from remobilized metal ions as well as reprecipitated mn oxide grains which were supplied to the nodules episodically during the stirring of bottom sediments by benthic fauna and intermittent strong bottom current flow

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

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

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

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

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

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