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

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

geochemistry of ferromanganese nodule sediment pairs from central indian ocean basin abstract fourteen ferromanganese nodule sediment pairs from different sedimentary environments such as siliceous ooze 11 calcareous ooze two and red clay one from central indian ocean basin ciob were analysed for major trace and rare earth elements ree to understand the possible elemental relationship between them nodules from siliceous and calcareous ooze are diagenetic to early diagenetic whereas nodule from red clay is of hydrogenetic origin si al and ba are enriched in the sediments compared to associated nodules k and na are almost in the similar range in nodule sediment pairs and mn fe ti mg p ni cu mo zn co pb sr v y li and rees are all enriched in nodules compared to associated sediments siliceous and calcareous major portion of si al and k in both nodules and sediments appear to be of terrigenous nature the elements which are highly enriched in the nodules compared to associated sediments from both siliceous and calcareous ooze are mo 307 273 ni 71 125 mn 64 87 cu 43 80 co 23 75 pb 15 24 zn 9 11 and v 8 19 respectively these high enrichment ratios of elements could be due to effective diagenetic supply of metals from the underlying sediment to the nodule enrichment ratios of transition metals and rees in the nodule to sediment are higher in ciob compared to pacific and atlantic ocean nodule from red clay exhibit very small enrichment ratio of four with mn and ce while al fe ti ca na k mg p zn co v y and ree are all enriched in red clay compared to associated nodule this is probably due to presence of abundant smectite fish teeth micronodules and phillipsite in the red clay the strong positive correlation r 0 8 of mn with ni cu zn and mo and a convex pattern of shale normalized ree pattern with positive ce anomaly of siliceous ooze could be due to presence of abundant manganese micronodules none of the major trace and ree exhibits any type of inter elemental relationship between nodule and sediment pairs therefore it may not be appropriate to correlate elemental behaviour between these pairs

biogenic influence on the growth of ferromanganese micronodules in the central indian basin abstract in a 20 cm core collected from the central indian basin with increasing depth the abundance of ferromanganese micronodules decreases as their size increases and the surface texture changes from rough to smooth biological debris including radiolarian fragments diatom tests and bacterial cells were found associated with the micronodules dissolution of biological debris with increasing core depth was evident ferromanganese oxides are present as fine imprints and coarse lumpy growths on the biological debris they are also present in different crystal forms in vugs and cavities in the micronodules electron microprobe spot analyses indicate that the micronodules are particularly high in manganese and iron in the upper and lower levels of the sediment column respectively diagenetic effects may account for the metal enrichment it appears that biological debris play an important role in the growth of the micronodules

a study of cleaning procedures used for foraminiferal mg ca paleothermometry the various cleaning steps required for preparation of foraminiferal samples for mg ca and sr ca analysis are evaluated for their relative importance and effects on measured elemental ratios it is shown that the removal of silicate contamination is the most important step for the measurement of mg ca ratios in an example bulk sample mg ca decreases from 10 5 to 2 5 mmol mol 1 during clay removal oxidation of organic material causes a lowering of sample mg ca in the order of 10 or approximately 1 c when converted to temperature use of dilute acid leaching to remove adsorbed contaminants causes partial dissolution of the sample carbonate and a corresponding decrease in mg ca reductive treatment also causes dissolution of the sample and a decrease in the mg ca ratio of up to 10 15 sample preparation for sr ca analysis does not require the same degree of rigor as is necessary for mg ca work the within run reproducibility of the method described here for g ruber in a core top sample from the arabian sea was 1 8 mean sample ratio was 4 72 mmol mol 1 when converted to temperature this becomes 28 0 2 c the equivalent result for sr ca was 0 5 mean ratio 1 44 mmol mol 1

influence of sedimentation on enrichment of manganese and growth of ferromanganese micronodules bengal fan india abstract based upon down core variations in o mn ratio in sediment and in micronodules mn content organic carbon and abundance of micronodules in two box cores from high and low sedimentation regions of the bay of bengal 0 20 and 0 40 cm levels were identified as mn oxidation zone in the western and the eastern regions of the bay despite similarity in bottom water o 2 and organic carbon contents of the region a higher abundance of micronodules down to the deeper levels was observed in the area of low sedimentation but in the upper surfaces increased enrichment of mn was observed in core 1 located in the area of higher sediment accumulation rapid recycling of mn faster burial transfer to mn reduction zone mn dissolution and its upward diffusion re precipitation increasing upward flux of mn ii and associated higher consumption of o 2 limits the width of mn oxidation zone and appears to be responsible for enhanced enrichment of mn in the area of high sedimentation the results of the present study also suggest that though the availability of mn controls the formation of micronodules their resident time in mn oxic zone regulates their growth and influences their 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

the hydrogeologic information in cross borehole complex conductivity data from an unconsolidated conglomeratic sedimentary aquifer abstractaccurate estimation of the hydrological properties of near surface aquifers is important because these properties strongly influence groundwater flow and solute transport laboratory based investigations have indicated that induced polarization ip properties of porous media may be linked through either semiempirical or fully mechanistic models to hydrological properties including hydraulic conductivity therefore there is a need for field assessments of the value of ip measurements in providing insights into the hydrological properties of aquifers a cross borehole ip survey was carried out at the boise hydrogeophysical research site bhrs an unconsolidated fluvial aquifer that has previously been well studied with a variety of geophysical and hydrogeologic techniques high quality ip measurements were inverted with careful consideration of the data error structure to provide a 3d distribution of complex electrical conductivity values the inverted distribution was further simplified usin

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

multi elemental composition of authigenic carbonates in benthic foraminifera from the eastern bering sea continental margin international ocean discovery program site u1343 abstract bering sea sediments represent exceptional archives offering the potential to study past climates and biogeochemistry at a high resolution however abundant hydrocarbons of microbial origin especially along the eastern bering sea continental margin can hinder the applicability of palaeoceanographic proxies based on calcareous foraminifera due to the formation of authigenic carbonates nonetheless authigenic carbonates may also bear unique opportunities to reconstruct changes in the sedimentary redox environment here we use a suite of visual and geochemical evidence from single specimens of the shallow infaunal benthic foraminiferal species elphidium batialis saidova 1961 recovered from international ocean discovery program iodp site u1343 in the eastern bering sea to investigate the influence of authigenic carbonates on the foraminiferal trace metal composition our results demonstrate that foraminiferal calcite tests act as a nucleation template for secondary carbonate precipitation altering their geochemistry where organoclastic sulphate reduction and anaerobic oxidation of methane cause the formation of low and high mg calcite respectively the authigenic carbonates can occur as encrusting on the outside and or inside of foraminiferal tests in the form of recrystallization of the test wall or as banding along natural laminations within the foraminiferal test walls in addition to mg authigenic carbonates are enriched in u ca mn ca fe ca and sr ca depending on the redox environment that they were formed in our results demonstrate that site specific u ca thresholds are a promising tool to distinguish between diagenetically altered and pristine foraminiferal samples important for palaeoceanographic reconstructions utilising the primary foraminiferal geochemistry consistent with previous studies u mn ratios of foraminifera at iodp site u1343 increase according to their degree of diagenetic alteration suggesting a potential response of authigenic u mn to the microbial activity in turn linked to the sedimentary redox environment

gravel transport and morphological change in braided sunwapta river alberta canada the relation between morphological change and patterns of variation in bedload transport rate in braided streams was observed by repeated daily topographic surveys over a 25 day study period in a 60 m reach of the proglacial sunwapta river alberta canada there are two major periods of morphological change each lasting several days and each involving the complete destruction and reconstruction of bar complexes bar complex destruction was caused by redirection of the flow and by downstream extension of the confluence scour zone upstream reconstruction involved accretion of unit bars on bar head flank and tail and in one case was initiated by disection of a large lobate unit bar high rates of sediment movement measured from net scour and fill of the cross sections coincided with these morphological changes sediment was supplied from both bed and bank erosion and patterns and distances of transfer were highly variable rates of transport estimated by matching upstream erosional volumes with downstream deposition were much greater than those estimated from either a step length approach or a sediment budget measurements of scour and fill and observations of morphological change indicate that step lengths virtual transport distances were typically 40 100m during a diurnal discharge cycle shorter step lengths occurred when transfer was confined to a single anabranch and longer steps involved channel changes at the scale of the entire reach sediment budgeting was used to describe the spatial patterns of sediment transport associated with the morphological changes and to estimate minimum daily reach averaged transport rates mean bedload transport rates correlate with discharge but with considerable scatter the largest deviations from the mean relation can be tied to phases of channel incision bank erosion scour hole migration bar deposition and channel filling apparently controlled by changes and fluctuations in sediment supply from upstream independent of discharge these are interpreted as field evidence of autopulses or macropulses in bedload transport previously observed only in laboratory models of braided streams

tomogram based comparison of geostatistical models application to the macrodispersion experiment made site we propose a new framework to compare alternative geostatistical descriptions of a given site multiple realizations of each of the considered geostatistical models and their corresponding tomograms based on inversion of noise contaminated simulated data are used as a multivariate training image the training image is scanned with a direct sampling algorithm to obtain conditional realizations of hydraulic conductivity that are not only in agreement with the geostatistical model but also honor the spatially varying resolution of the site specific tomogram model comparison is based on the quality of the simulated geophysical data from the ensemble of conditional realizations the tomogram in this study is obtained by inversion of cross hole ground penetrating radar gpr first arrival travel time data acquired at the macro dispersion experiment made site in mississippi usa various heterogeneity descriptions ranging from multi gaussian fields to fields with complex multiple point statistics inferred from outcrops are considered under the assumption that the relationship between porosity and hydraulic conductivity inferred from local measurements is valid we find that conditioned multi gaussian realizations and derivatives thereof can explain the crosshole geophysical data a training image based on an aquifer analog from germany was found to be in better agreement with the geophysical data than the one based on the local outcrop which appears to under represent high hydraulic conductivity zones these findings are only based on the information content in a single resolution limited tomogram and extending the analysis to tracer or higher resolution surface gpr data might lead to different conclusions e g that discrete facies boundaries are necessary our framework makes it possible to identify inadequate geostatistical models and petrophysical relationships effectively narrowing the space of possible heterogeneity representations

abyssal sediment erosion in the central indian basin evidence from radiochemical and radiolarian studies abstract radiochemical analyses of three spade cores collected around 78 e between 10 s and 12 s from the abyssal depths in the central indian basin yield an average accumulation rate of 2 mm ka the ratios of 230th flux in the sediments to its production rate in the overlying water column fa fp are extremely low 0 2 this fact and the absence of collosphaera invaginata first appearance datum 150 200 ka an index radiolarian species of neogene radiolarian zone 1 indicate intense erosion and lateral transport of younger sediments from this region the radiochemical and radiolarian biostratigraphic evidence for nearly 175 ka of erosion of the chronological record of the sediments in this region has been attributed to the effect of turbulent antarctic bottom water entering the central indian basin through the northern saddles of the ninety east ridge

geochemical and sedimentological responses of arctic glacial lake ilirney chukotka far east russia to palaeoenvironmental change since 51 8 ka bp abstract palaeoenvironmental reconstructions with temporal coverages extending beyond marine isotope stage mis three are scarce within the data sparse region of chukotka far east russia the objective of this paper is to infer palaeoenvironmental variability from a 10 76 m long osl and 14c dated sediment core from lake ilirney chukotka 67 21 n 168 19 e we analysed high resolution sediment geochemistry xrf sedimentology tc tn toc grain size mineralogy xrd and preliminary micropalaeontological data diatoms and pollen from the core as well as acoustic sub bottom profiling data from the lake basin our results affirm the application of xrf based sediment geochemical proxies as effective tracers of palaeoenvironmental variability within arctic lake systems our study reveals that a lake formed during mis3 from 51 8 4 1 ka bp following extensive mis4 glaciation catchment palaeoenvironmental conditions during this time remained harsh associated with the continued presence of a catchment glacier until 36 2 2 6 ka bp partial amelioration reflected by increased diatom catchment vegetation and lake organic productivity and clastic sediment input from mixed sources from 36 2 2 6 ka bp resulted in a lake high stand 15 m above present and is interpreted as evidence of a more productive palaeoenvironment coincident with the mis3 interstadial optimum a transitional period of deteriorating palaeoenvironmental conditions occurred 30 27 9 ka bp and was superseded by periglacial glacial conditions from 27 9 0 8 ka bp during the last glacial maximum deglaciation as marked by sediment geochemical proxies commenced at 20 2 0 8 ka bp our findings are compared with lacustrine yedoma and river bluff records from across beringia and potentially yield limited support for a marked younger dryas cooling in the study area

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

geochemical and sedimentological studies of a box core from the western sector of the peru basin abstract the distribution of sediments micronodules and manganese nodules which has been studied in a number of cores from the peru basin is clearly related to the proximity of the basin to the c c d and to the equatorial high productivity zone one core from the peru basin has been looked at in considerable detail in this core an extensively bioturbated calcareous siliceous rich upper sedimentary unit is underlain by an overconsolidated dark brown clay characteristic differences in mineralogy and chemistry are observed in the composition of these sediment types with the dark brown clays having higher contents of mn fe co ni cu zn and p than the sediments of the upper horizon in addition these dark brown clays contain montmorillonite as the principal clay mineral whereas the sediments of the upper sediment horizon consist of montmorillonite kaolinite and illite micronodules are much more abundant in the coarse fraction 40 m of the dark brown clay horizon than in the upper sedimentary unit and are characterized by higher mn fe ratios and higher ni and cu contents than those from the upper sediment horizon this reflects the fact that these overconsolidated sediments are well oxidized and that element remobilization from the micronodules has not taken place within this sediment type in the upper sedimentary unit there is a sharp drop in the mn fe ratio and ni and cu contents of the micronodules immediately beneath the sediment surface reflecting the selective migration of mn and other transition elements such as ni and cu from the micronodules buried managanese nodules are found at two horizons within the sediment column these nodules show characteristic differences in their surface texture compared to surface nodules but no marked difference in composition the buried nodules are not associated with any well defined feature such as a sedimentary hiatus it is suggested that nodules are maintained at the sediment surface by bioturbation buried nodules are simply those nodules that have failed to be maintained at the sediment water interface

estimating the in situ porosity of sandy soils sampled in boreholes abstract this paper deals with sandy aquifers it explains how to use parameters of borehole samples and data of mechanical tests performed in boreholes to assess the in situ values of porosity the concepts of maximum and minimum void ratios emax and emin are presented with the results of studies trying to predict their values predictive equations are proposed to link the values of emax and emin to that of the coefficient of uniformity cu of the grain size distribution curve and the roundness factor rf of solid particles once the values of emax and emin have been estimated those of the in situ void ratio e and porosity n can be assessed from the data of in situ mechanical tests for example split spoon tests an example evaluation is presented for an unconfined sand aquifer which was investigated using boreholes field tests laboratory tests slug tests in monitoring wells and a long term pumping test

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

on the occurrence of ferromanganese micronodules from the sediments of the bengal fan a high terrigenous sediment input region studies of 13 samples 10 surface sediments and 3 cores from across the middle fan region of the bay of bengal reveal the presence of micronodules area 0 22 million km2 over the entire bay these micronodules have two dominant morphological forms botryoidal in the eastern bay and spheroidal in the central and the western regions of the bay the abundance of the micronodules was found to be higher in the eastern region of the bay in the cores the micronodules were generally found to decrease in abundance down core the core from the eastern region had micronodules down to deeper levels than the western side todorokite is the manganese mineral present in the micronodules associated mineral phases are quartz feldspar and phillipsite these micronodules have high mn 19 20 32 13 rather low fe 1 20 1 83 ni 0 10 1 14 zn 0 10 0 30 and co 0 01 0 04 and their mnfe ratio ranges from 10 55 to 25 42 the contents of mn ni cu and zn and the mnfe ratio decrease down core based upon the variations in the abundance morphology mnfe ratio of the micronodules and the elemental distributions and the omn ratio in the sediments remobilization of mn from deeper levels and its precipitation at the upper surfaces of the sediment column in an oxic environment is suggested the results of the present study also suggest that a high rate of sedimentation is not a limiting factor for the formation of micronodules although it might affect their growth

cdw photogrammetry of low relief fluvial features accuracy and implications for reach scale sediment budgeting terrestrial photogrammetry enables rapid survey to be undertaken in the fluvial environment a crucial factor when assessing highly dynamic features in addition it permits the generation of terrain surfaces at a level of detail which given equal time constraints in the field far exceeds the detail permitted by conventional tacheometric survey this study details the levels of accuracy that can be achieved using the rolleimetric close range digital workstation cdw photogrammetric survey technique on a variety of low relief fluvial geomorphic features lateral point and mid channel bars ranging from 10 m 2 to 100 m 2 the cdw software processes image data from an array of photographs and establishes a set of three dimensional co ordinates for the photographed object the accuracies achieved across all bar surfaces were well within the resolution defined by the maximum size of the gravel on the bar surface mean errors were between 0 026 and 0 057 m the use of cdw photogrammetry does not require experienced personnel however care must be taken during the survey to minimize edge effects and to ensure that target density is sufficient to produce a terrain model that is accurate to within the limits of the surface sediment size guidance on target density as a function of terrain roughness is given to aid the user a methodology is suggested that will allow cdw to be incorporated into sediment budgeting techniques improving the level of achievable accuracy 1998 john wiley sons ltd

compositional variations in manganese micronodules a possible indicator of sedimentary environments manganese micronodules from various environments were analyzed with the electron microprobe chemical characteristics of marine manganese nodules were examined in relation with their depositional environments and compared with those of manganese macronodules the compositional variation has a connection with accumulation rates and chemical features of the associated sediments mg and ti tend to be enriched in micronodules relative to the host sediments these elements may produce authigenic mineral phases in micronodules these observations show that manganese micronodules are chemically formed under approximately the same condition as that for macronodules but coexisting pairs of micronodules and macronodules collected from the same sediments suggest that oxic diagenesis plays a more important role in the formation of micronodules than that of macronodules the chemical features of manganese micronodules collected from several marine environments such as a marginal sea hemipelagic regions and the cent

evolution of ocean temperature and ice volume through the mid pleistocene climate transition earth s climate underwent a fundamental change between 1250 and 700 thousand years ago the mid pleistocene transition mpt when the dominant periodicity of climate cycles changed from 41 thousand to 100 thousand years in the absence of substantial change in orbital forcing over this time an increase occurred in the amplitude of change of deep ocean foraminiferal oxygen isotopic ratios traditionally interpreted as defining the main rhythm of ice ages although containing large effects of changes in deep ocean temperature we have separated the effects of decreasing temperature and increasing global ice volume on oxygen isotope ratios our results suggest that the mpt was initiated by an abrupt increase in antarctic ice volume 900 thousand years ago we see no evidence of a pattern of gradual cooling but near freezing temperatures occur at every glacial maximum

early diagenetic processes affecting nutrients in the pore waters of central indian ocean cores abstract pore water nutrients nitrite nitrate phosphate silicate ph and solid phase organic carbon were analysed for one core from the arabian sea and three cores from the manganese nodule area in the central indian ocean basin possible denitrification and unoxidized organic carbon are observed in the arabian sea core while nitrification with intermediate low nitrate and high organic carbon are found in the mottled zones of the pelagic cores mobilization of iron host oxyhydroxides and peaked profiles of organic carbon are related to a gradual increase in the phosphate profiles the asymptotic silica values are less than the 100 saturation levels of amorphous silica and they fall outside the stability field of sepiolite

do manganese nodules grow or dissolve after burial results from the central indian ocean basin abstract fifty buried manganese nodules at different depth intervals were recovered in 12 sediment cores from the central indian ocean basin ciob a maximum of 15 buried nodules were encountered in one sediment core aas 22 gc 07 and the deepest nodule was recovered at 5 50 m below seafloor in core aas 04 gc 5a approximately 80 of the buried nodules are small in size 2 cm diameter in contrast to the atlantic ocean and peru basin pacific ocean where the majority of the buried nodules are large 8 cm and 6 cm respectively buried nodule size decreases with core depth and this distribution appears to be similar to the phenomenon of brazil nut effect buried nodules exhibit both smooth and rough surface textures and are ellipsoidal elongated rounded sub rounded irregular and polynucleated buried nodules from siliceous ooze are enriched in mn cu ni zn mo ga v and rb whereas those from red clay are enriched in fe co ti u th y cr nb and rare earth elements ree buried nodules from siliceous ooze suggest their formation under hydrogenetic early digenetic and diagenetic processes whereas those from red clay are of hydrogenetic origin ree are enriched more than 1 5 times in buried nodules from red clay compared to siliceous ooze however the mode of incorporation of ree into buried nodules from both sedimentary environments is by a single authigenic phase consisting of fe ti p shale normalized ree patterns and ce anomalies suggest that nodules from siliceous ooze formed under more oxidizing conditions than those from red clay nodules buried at depths between 1 5 and 2 5 m are diagenetic mn fe ratio 10 15 formed in highly oxic environments large positive ce anomalies and record aeolian dust high eu anomalies chemical composition surface texture and morphology of buried nodules are similar to those of surface nodules from the same basin furthermore buried nodule compositions do not exhibit any distinct patterns within the core depth suggesting that buried nodules neither grow nor dissolve after their burial in the sediment column

high resolution aquifer characterization using crosshole gpr full waveform tomography comparison with direct push and tracer test data limited knowledge about the spatial distribution of aquifer properties typically constrains our ability to predict subsurface flow and transport here we investigate the value of using high resolution full waveform inversion of cross borehole ground penetrating radar gpr data for aquifer characterization by stitching together gpr tomograms from multiple adjacent crosshole planes we are able to image with a decimeter scale resolution the dielectric permittivity and electrical conductivity of an alluvial aquifer along cross sections of 50 m length and 10 m depth a logistic regression model is employed to predict the spatial distribution of lithological facies on the basis of the gpr results vertical profiles of porosity and hydraulic conductivity from direct push flowmeter and grain size data suggest that the gpr predicted facies classification is meaningful with regard to porosity and hydraulic conductivity even though the distributions of individual facies show some overlap and the absolute hydraulic conductivities from the different methods direct push flowmeter grain size differ up to approximately one order of magnitude comparison of the gpr predicted facies architecture with tracer test data suggests that the plume splitting observed in a tracer experiment was caused by a hydraulically low conductive sand layer with a thickness of only a few decimeters because this sand layer is identified by gpr full waveform inversion but not by conventional gpr ray based inversion we conclude that the improvement in spatial resolution due to full waveform inversion is crucial to detect small scale aquifer structures that are highly relevant for solute transport

fe mn oxyhydr oxides as an indicator of rey enrichment in deep sea sediments from the central north pacific abstract nowadays pelagic sediments are globally explored as a potential resource of rare earth elements and yttrium termed as rey and have received unprecedented attention however the formation mechanism of rey rich deep sea mud remains controversial the fe mn oxyhydr oxides are ubiquitous in oxic marine sediments and potentially beneficial for the rey enrichment the research of them is important for understanding the ore formation of rey rich mud and thus can help to evaluate the role of marine sediments in global rey cycles in this contribution using advanced in situ analytical techniques we provide new results on the nanoscale mineralogy and geochemistry of fe mn oxyhydr oxides that are recovered from rey rich deep sea sediments in central north pacific ocean in situ x ray diffraction analyzer and scanning electron microscope reveal that the fe mn minerals e g vernadite birnessite and todorokite occur as overgrowths on the surface of nuclei to form fe mn micronodules transmission electron microscope tem imaging reveals that these fe mn minerals are composed of nanocrystals with high intercrystalline porosity indicating a potential strong adsorption capacity the tem observations also imply a mineral phase transformation from birnessite vernadite to todorokite during the oxic diagenesis accompanied by corresponding changes in geochemical compositions laser ablation inductively coupled plasma mass spectrometry demonstrates that fe mn oxyhydr oxides contain high rey concentrations varying from 439 to 1 654 ppm with an average of 790 ppm and can be regarded as an important host of rey furthermore the paas normalized and seawater normalized rey patterns both infer that the rey contents of fe mn oxyhydr oxides are ultimately derived from seawater and characterized by preferential scavenging of ce overall fe mn oxyhydr oxides not only contribute a moderate proportion of rey but also provide specific information for understanding geochemical processes related to rey enrichment in deep sea sediments

thorium and radium isotopic relationships in manganese nodules and sediments at manop site s abstract relationships among th and ra isotopes in nodule sediment and water phases at manop site s establish the most likely source for th in the nodules the frequency of nodule turning and the similarity of micro and macro nodules manganese nodules and bottom waters have 230 th 232 th activity ratios considerably higher than other phases at this site suggesting that sea water is the likely source of th for the nodules similar 230 th 232 th activity ratios in nodule tops and bottoms and in certain cases departure from expected 226 ra 230 th activity ratios in nodule tops and bottoms indicate that the nodules rotate every one to ten thousand years the micro nodules have diffusion coefficients of ra similar to macro nodule bottoms i suggest that they may act as a carrier phase for transporting metals through oxic sediments to nodules

negative correlation between porosity and hydraulic conductivity in sand and gravel aquifers at cape cod massachusetts usa although it may be intuitive to think of the hydraulic conductivity k of unconsolidated coarse grained sediments as increasing monotonically with increasing porosity f studies have documented a negative correlation between these two parameters under certain grain size distributions and packing arrangements this is confirmed at two sites on cape cod massachusetts usa where groundwater investigations were conducted in sand and gravel aquifers specifically to examine the interdependency of several aquifer properties using measurements from four geophysical well logs along with k and f the electrical resistivity r0 and the natural gamma activity g of saturated deposits were determined as functions of depth qualitative examination of results from the first site implies a negative correlation between k and f that is substantiated by a rigorous multivariate analysis of log data collected from the second site a principal components analysis describes an overdetermined system of inversion equations with approximately 92 of the cumulative proportion of the total variance being accounted for by only three of the four eigenvectors a subsequent r mode factor analysis projects directional trends among the four variables k f r0 and g and a negative correlation between k and f emerges as the primary result q 2005 elsevier b v all rights reserved

distribution of major trace and rare earth elements in surface sediments of the wharton basin indian ocean bulk chemical analyses of eighteen surface sediments taken on an east west transect lat 15 40 s in the wharton basin indian ocean were analysed for major trace and rare earth elements ree by inductively coupled plasma atomic emission spectrometry icp aes the relationship between al and k suggests in situ formation of authigenic phillipsite the relationship between p and ca suggests accumulation of biogenic apatite fish bone debris from high biological productivity waters which is confirmed by the linear relationship with p and cu a strong positive correlation among redox sensitive metals mn fe cu ni and zn suggests that they are incorporated into a ferromanganese oxide phase probably micronodules calcareous oozes from the transect have low ree abundance la 8 ppm with a very strong negative cece value 0 41 siliceous oozes have high ree abundance la 28 ppm with moderate positive cece 1 24 and red clays have highest ree abundance la 66 ppm with a weak positive 1 05 to moderate negative cece 0 73 shale normalized ree patterns and layb n ratios record similar enrichment of heavy ree hree relative to light ree lree in all sediment types this might be due to retention of the bottom water ree pattern and the presence of fish bone debris correlation coefficient and r mode factor analyses suggest a very strong positive association r2 0 9 of ree with p and thus most likely with biogenic apatite fish bone debris as p is directly associated with biological activity it is thus related to surface primary productivity ree in the wharton basin sediments appear to reflect a combination of surface water effects and diagenetic processes

chemistry of surface sediment along a north south transect across the equator in the central indian basin an assessment of biogenic and detrital influences on elemental burial on the seafloor nineteen surface sediment samples collected along a north south transect across the equator in the central indian basin cib were analysed for their major minor and rare earth element ree composition in absence of the element flux data we demonstrate here the association of various elements and their preferential sinks using inter elemental associations in sediment exhibiting latitudinal dissimilarity biogenic sedimentation north of the equator 1 to 4 n latitudes is dominated by carbonate ooze whereas south of the equator 4 to 14 s latitudes is dominated by siliceous ooze carbonate ooze deposition 60 caco3 above 4400 m and its drastic reduction to 80 of their respective total content in all the three sediment zones these observations suggest a close link between ba and a mn oxide phase on the other hand nearly overlapping latitudinal trends of alxs with carbonate in areas north of the equator and opal south of the equator strong positive correlation of alxs with opal r 0 8 similar ratios between carbonate free opal and alxs 16 in both biogenic sediments suggest a close link between productivity and alxs the alxs proportion in both biogenic sediment types is around 28 of the total al suggesting nearly the same level of primary productivity along the transect 4 n to 14 s which supports the estimates of berger berger w h 1989 global maps of the ocean productivity in w h berger v s smetacek g wefer eds productivity of the ocean present and past dahlem workshop reports wiley chichester pp 429 455 and kabanova kabanova j g 1968 primary production of the northern part of the indian ocean oceanology 8 214 255 i e 70 g cm 2 y 1 the rees exhibit mutual coherence in the sediment r 0 7 however they display an increasing affinity towards mn r increases from 0 6 to 0 8 and decreasing affinity towards ti r decreases from 0 8 to 0 3 with increasing atomic number such a subtle but systematic variation within ree group suggests preferential burial of heavy ree by mn oxide phase and light ree by detrital phase

rare earth element geochemistry of standard sediments a study using inductively coupled plasma spectrometry the rare earth elements ree and y have been determined in 15 international standard sediments from france german democratic republic canada and the u s a samples were prepared using conventional rock dissolution techniques and the ree and y were separated from other constituents using cation exchange chromatography the ree la ce pr nd sm eu gd dy ho er yb lu and y were analysed simultaneously by inductively coupled plasma atomic emission spectrometry results indicate that u s g s standard shale sco 1 cody shale is a good reference material to use for the normalisation of the ree distributions of sediments data normalised to sco 1 are more readily interpreted than those normalised to existing estimates of average shale the ree patterns of standard sediments vary considerably in shape span an order of magnitude in absolute concentration and provide valuable reference values for the ree analysis of other sedimentary materials

rare earth element geochemistry of oceanic ferromanganese nodules and associated sediments abstract analyses have been made of ree contents of a well characterized suite of deep sea 4000 m principally todorokite bearing ferromanganese nodules and associated sediments from the pacific ocean ree in nodules and their sediments are closely related nodules with the largest positive ce anomalies are found on sediments with the smallest negative ce anomalies in contrast nodules with the highest contents of other rare earths 3 ree are found on sediments with the lowest 3 ree contents and vice versa 143 nd 144 nd ratios in the nodules 0 51244 point to an original seawater source but an identical ratio for sediments in combination with the ree patterns suggests that diagenetic reactions may transfer elements into the nodules analysis of biogenic phases shows that the direct contribution of plankton and carbonate and siliceous skeletal materials to ree contents of nodules and sediments is negligible inter element relationships and leaching tests suggest that ree contents are controlled by a p rich phase with a ree pattern similar to that for biogenous apatite and an fe rich phase with a pattern the mirror image of that for sea water it is proposed that 3 ree concentrations are controlled by the surface chemistry of these phases during diagenetic reactions which vary with sediment accumulation rate processes which favour the enrichment of transition metals in equatorial pacific nodules favour the depletion of 3 ree in nodules and enrichment of 3 ree in associated sediments in contrast ce appears to be added both to nodules and sediments directly from seawater and is not involved in diagenetic reactions

using electrical resistivity logs and short duration pumping tests to estimate hydraulic conductivity profiles abstract hydraulic conductivity profiles hcps are of crucial importance for 3 dimensional flow and transport groundwater models easy and inexpensive methods for the estimation of such profiles increase their availability and strengthen the efficiency of the models in this study a method is presented which combines the electrical resistivity er measured over the depth of the aquifer in a borehole and the response of the aquifer to the short duration pumping from the borehole the hydraulic conductivity profile is calculated from the kozeny carman equation in which the profiles of the porosity and the mean grain size mgs are required porosity is calculated from archie s law using the intrinsic formation factor which results from the er mgs is calculated from the porosity using a relationship between them the initial form of this relationship is obtained from literature data and is then adjusted to the conditions of each particular case the adjustment is achieved by calibrating a modflow based groundwater model so that it sufficiently simulates the temporal variation of the water level measured in the borehole during the short pumping the method is applied to the estimation of the hcp in an unconsolidated alluvial aquifer in greece the sensitivity of the results to the parameters and assumptions used in the method is investigated and discussed

the indian ocean nodule field petrotectonic evolution and ferromanganese deposits abstract the indian ocean nodule field ionf is significant from several points of view roughly bordered by 10 s to 16 30 s and 72 e to 80 e and located within the central indian ocean basin ciob the field hosts the world s second largest and second high grade manganese nodule deposit after the equatorial nodule belt in the north pacific ocean moreover the crust underlying this field is characterised by unique morphotectonic signatures owing to its formation between 60 and 49 ma under three variable spreading conditions fast intermediate and slow from the indian ocean ridge system iors the nodule field has been surveyed both extensively more than 0 4 million km2 area and intensively comprising of a large geophysical data set and geological sample inventory during the last two decades several morphotectonic features such as seamounts hills ridge normal lineaments and ridge parallel lineations have disturbed the apparently smooth topographic gradient 1 7000 of the seafloor here variations in the rate of spreading and formation of new oceanic crust along the ridge crest during more than one episode of india eurasia collision are imprinted in the ionf based on the nature of the ridge parallel lineations which are related to the rate of crustal accretion the field is divided in to four sectors a b c and d from north to south sectors a and c were formed at a fast rate of spreading 90 95 mm year half rate and sectors b and d were formed at an intermediate 55 mm year and slow 26 mm year rates respectively the predominance of tensional stress in sectors a and c caused asymmetrical flexuring of the seafloor resulting in widely spaced faults and folds with low amplitude and large wavelength in contrast the seafloor flexuring in sector d are closely spaced long symmetrical and of high amplitude the timing and intensity of the collision of india with eurasia is constrained by the variable intensity of these flexures suggesting probably a soft touch at 58 ma and the hard collision at about 51 ma the nodule field hosts several seamounts both as isolated entities and in linear chains which are arranged parallel to the flow lines along the direction of absolute motion of the indian plate the distribution morphology and growth patterns of a majority of these seamounts are related to spreading rate suggesting their formation at the ridge crest however many of the seamounts show more than one stage of growth with local intraplate volcanism contributing to the enlargement of the larger ancient seamounts varieties of volcanics such as tholeiitic basalts spilites ferrobasalts and pumice occur within the ionf the alteration of some of these volcanics has resulted in palagonitisation of the glass and formation of zeolites subsequently during its journey away from the ridge crest to the abyssal areas the crust underlying the nodule field witnessed intraplate volcanism this is evident from the addition of younger rocks at the base of the ancient seamounts inconsistent growth of volcanoes eruption of ferrobasalt corresponding to the areas of high amplitude magnetic zones and presence of volcanogenic hydrothermal materials vhm of 10 ka age these findings collectively hint that the ionf is geodynamically unstable and may have been volcanically active in the recent past during the last 8 ma growth of authigenic ferromanganese deposits in the form of manganese nodules and crusts has occurred in the nodule field the deposits occur at an average water depth of 5000 m the basinal geomorphology intraplate tectonic deformations and volcanic eruptions considerably influence the formation development morphology mineralogy and composition of these deposits the data show that the large seamounts reverse faults and fracture zones fzs supply rock fragments as seeds for the nodule formation the hydrogenous precipitation from the overlying water column is the primary source of metal accumulation in the nodules the secondary relatively weak intraplate eruptions along the base of ancient seamounts or lineaments subsurface igneous activity and diagenetic remobilisation of metals have also played significant role in the growth and enrichment of the deposit based on a large data set we estimate the contribution of various physico chemical parameters and model the probable conditions of formation of the ferromanganese deposits in the ionf the model also hints at the location where the resource exploitation should be rewarding

the measurement of river bank erosion and lateral channel change a review a detailed review and chronological survey is presented of the various techniques which have been used for the measurement of river bank erosion and channel change the techniques are classified according to the time scales involved long intermediate and short and each is discussed with respect to accuracy and repeatability the methods covered include sedimentological evidence botanical evidence historical sources planimetric resurvey repeated cross profiling erosion pins and terrestrial photogrammetry prospects for future developments are also discussed

recognition of units in coarse unconsolidated braided stream deposits from geophysical log data with principal components analysis returns from drilling in unconsolidated cobble and sand aquifers commonly do not identify lithologic changes that may be meaningful for hydrogeologic investigations vertical resolution of saturated quaternary coarse braided stream deposits is significantly improved by interpreting natural gamma g epithermal neutron n and electromagnetically induced resistivity ir logs obtained from wells at the capital station site in boise idaho interpretation of these geophysical logs is simplified because these sediments are derived largely from high gamma producing source rocks granitics of the boise river drainage contain few clays and have undergone little diagenesis analysis of g n and ir data from these deposits with principal components analysis provides an objective means to determine if units can be recognized within the braided stream deposits in particular performing principal components analysis on g n and ir data from eight wells at capital station 1 allows the variable system dimensionality to be reduced from three to two by selecting the two eigenvectors with the greatest variance as axes for principal component scatterplots 2 generates principal components with interpretable physical meanings 3 distinguishes sand from cobble dominated units and 4 provides a means to distinguish between cobble dominated units

the distribution of rare earth elements in manganese micronodules and sediments from the equatorial and southwest pacific abstract thirty three manganese micronodules and 38 associated sediments from selected areas in the equatorial and southwest pacific have been analyzed for ree significant variations in composition of both micronodules and sediments between the areas are observed in general the avarage ree abundance in manganese modules in a given area is higher than that of the associated micronodules but the ce la ratio of the micronodules is in some cases higher than that of the nodules the avarage ce la ratio of the micronodules is always higher than that of the associated sediment but the ree abundance is lower in several cases the ce anomaly is dominantly positive for micronodules and negative for sediments negative ce anomalies are however found in micronodules from the crest of the east pacific rise epr where metallogenesis is taking place positive ce anomalies occur in sediments from the southwestern pacific basin between the epr and new zealand the highest ce la ratios of both micronodules and sediments are found in this region reflecting the well oxidized conditions prevailing there

concept of hydraulic porosity and experimental investigation in nonlinear flow analysis through rubble mound breakwaters summary this paper aims to cast light on findings of experimental results and theoretical findings that evaluate hydraulic coefficients for non linear flow through coarse aggregates experimental pilot made use of a physical model consisting of a flume of 13 m in length being controlled by an electro mechanical device to create different types of flow regimes in this regard two different relatively uniform aggregates ranging in size from 2 to 19 mm at first and 2 to 25 mm at second materials have been selected the physical characteristics such as size distribution porosity and fluid viscosity have been measured for each material to create a set of the reliable hydraulic gradient vs bulk velocity data tests have been conducted on the materials a non linear mathematical model based on the extended forchheimer s equation efe has been employed in developing necessary equations needed for the assessments findings indicate in determination of flow velocity within the pores of the media the porosity term exponent may depend upon the nature of the flow regime in addition the proposed general equation for non darcy unsteady flow through coarse porous media seems to be a more reliable tool for modeling purposes and engineering applications

fe mn micronodules born in the metalliferous sediments of two spreading centres the east pacific rise and mid atlantic ridge abstract a geochemical study of fe mn micronodules associated with the metalliferous sediments at two spreading centres has shown that their composition depends on the site of micronodule formation close to the hydrothermal mounds they exhibit significant variation in elemental content related to the type of hydrothermal discharge low or high temperature the nature of primary hydrothermal matter plume fall out oxidised sulfides and the extent of diagenesis in this environment three types of micronodules can be distinguished although not observed as pure end members 1 diagenetic micronodules 2 micronodules formed generally from the plume fall out of oxyhydroxide matter and 3 micronodules grown on the oxidised sulfide grains supplied to the sediments by slumping or fall out of nearby buoyant plume away from the active spreading centre the hydrothermal signatures of primary precipitates are gradually masked and hydrogenous diagenetic processes lead the micronodule formation composition of micronodules becomes less variable well pronounced deep rift valleys confine the hydrothermal plume which brings the hydrothermal suspension into contact with restricted volumes of seawater and consequently weakens the hydrogenous influence on the primary hydrothermal matter shallow rift valleys do not confine hydrothermal plumes which are scattered over hundreds of kilometres by bottom currents this brings the hydrothermal suspended matter into contact with large volumes of seawater extensive scavenging occurs which masks the hydrothermal signal away from the spreading axis and enhances the hydrogenous one thus the ridge crest morphology defined by the spreading rate is supposed to play a certain role though indirect in the chemical composition of the primary precipitates and consequently in the composition of the micronodules formed

the oxidation state of manganese in ferromanganese nodules and deep sea sediments from the central indian ocean abstract ferromanganese nodules from different sediment facies including siliceous ooze pelagic clay sediments from transition zone of siliceous and pelagic clay and seamount crusts from the central indian ocean were analysed for chemical composition mineralogy and bulk oxidation state of mn by the iodometric method despite considerable variation in chemical composition mn fe ratio times from 1 35 to 7 42 and mineralogy the o mn ratio or mno x solid hydrous manganese oxide does not vary much from 1 73 to 1 81 suggesting most of the mn in the manganese nodules in mn iv the oxidised upper zone in the sediment cores decreases in thickness from 15 cm in the north 5 s to 11 cm in the southern part 14 s of the central indian ocean iodometric titration of deep sea sediments yields o mn ratios of 1 29 1 95 sediments from the manganese nodule field have maximum solid mn concentrations and lower o mn ratios in the core top 0 3 cm with minimum mn and o mn ratios at 11 cm depth and thus may reflect the mechanism controlling the supply of diagenetic mn to the nodules in contrast sediments from the non manganese nodule field have comparatively low solid phase mn concentrations in the core top 0 3 cm and almost uniform o mn ratios with depth indicating that mn is not preserved in the sediments but may be remobilised and deposited somewhere else

compressional velocity and porosity in sand clay mixtures laboratory measurements of porosity and compressional velocity were conducted on unconsolidated brine saturated clean ottawa sand pure kaolinite and their mixtures at various confining pressures a peak in p velocity versus clay content in unconsolidated sand clay mixtures at 40 percent clay by weight was found the peak in velocity is 20 30 percent higher than for either pure clay or clean sand a minimum in porosity versus clay content at 20 40 percent clay by weight is also observed such behavior is explained using a micro geometrical model for mixtures of sand and clay in which two classes of sediments are considered 1 sands and shaley sands in which clay is dispersed in the pore space of load bearing sand and thus reduces porosity and increases the elastic moduli of the pore filling material and 2 shales and sandy shales in which sand grains are dispersed in a clay matrix for these sediments the model reproduces the extrema in velocity and porosity and accounts for much of the scatter in