seismic evidence for overpressured subducted oceanic crust and megathrust fault sealing water and hydrous minerals play a key role in geodynamic processes at subduction zones however there are few seismological constraints on the presence of water within the subducting plate audet et al model converted teleseismic waves to constrain the seismological properties of subducted oceanic crust from the cascadia continental margin to its intersection with the forearc mantle their observations suggest that water is pervasively present in fluid form at high pore pressures indicating that the megathrust is a low permeability boundary these results may hold important implications for our understanding of seismogenesis subduction zone structure and the mechanism of episodic tremor and slip this study models converted teleseismic waves to constrain the seismological properties of subducted oceanic crust from the cascadia continental margin to its intersection with the forearc mantle the observations suggest that water is pervasively present in fluid form at high pore pressures indicating that the megathrust is a low permeability boundary these results may hold important implications for our understanding of seismogenesis subduction zone structure and the mechanism of episodic tremor and slip water and hydrous minerals play a key part in geodynamic processes at subduction zones1 2 3 by weakening the plate boundary aiding slip and permitting subduction and indeed plate tectonics to occur4 the seismological signature of water within the forearc mantle wedge is evident in anomalies with low seismic shear velocity marking serpentinization5 6 7 however seismological observations bearing on the presence of water within the subducting plate itself are less well documented here we use converted teleseismic waves to obtain observations of anomalously high poisson s ratios within the subducted oceanic crust from the cascadia continental margin to its intersection with forearc mantle on the basis of pressure temperature and compositional considerations the elevated poisson s ratios indicate that water is pervasively present in fluid form at pore pressures near lithostatic values combined with observations of a strong negative velocity contrast at the top of the oceanic crust our results imply that the megathrust is a low permeability boundary the transition from a low to high permeability plate interface downdip into the mantle wedge is explained by hydrofracturing of the seal by volume changes across the interface caused by the onset of crustal eclogitization and mantle serpentinization these results may have important implications for our understanding of seismogenesis subduction zone structure and the mechanism of episodic tremor and slip

organic carbon burial rate and the molybdenum proxy theoretical framework and application to cenomanian turonian oceanic anoxic event 2 1 in this study the controls on organic carbon burial and molybdenum accumulation in ancient strata are investigated through an integration of biogeochemical modeling and data analysis critical aspects of the study are employment of a biogeochemical model for organic matter degradation to explore the controls on pore water sulfide generation and authigenic molybdenum accumulation and use of accumulation rate data for mo oc caco3 fe and ti to reconstruct organic matter remineralization processes the model results form a conceptual framework for the interpretation of primary production estimates and geochemical burial fluxes calculated on the basis of a high resolution orbital timescale for the cenomanian turonian c t oceanic anoxic event 2 interval in the western interior basin the results of this study suggest that the strong correlation between source rock development and intervals of transgression in the geologic record such as the c t could reflect a confluence of biogeochemical processes within sediments that obviates the need for large magnitude changes in primary production levels or oceanographic conditions such as prolonged periods of stable water column stratification

influence of water column anoxia and sediment supply on the burial and preservation of organic carbon in marine shales abstract previous work has suggested that the laminated organic rich and bioturbated organic poor shales of the camp run member of the late devonian early mississippian new albany shale formed under anoxic and oxygenated bottomwater conditions respectively and that the interbedding of the two facies was due to the vertical oscillation of a water column anoxic oxic boundary where it impinged on the basin margin we have extended this analysis by examining the chemical and mineralogical differences between the two shale facies in a single borehole core by seeking evidence for deposition of the laminated shales under bottom water oxia or anoxia and by determining whether the laminated shales formed when the carbon supply to the sea floor was higher the results of this study show that the laminated and bioturbated shales are mineralogically and chemically distinct relative to al an index of the aluminosilicate content si ti fe p na ba co cr cu mo ni v zn and zr are all higher whereas mn ca mg and sr are lower in the laminated compared with the bioturbated shales the differences are due to a higher quartz feldspar titanite ilmenite and zircon content in the laminated shales probably indicating a coarser grain size and the greater abundance of manganoan calcite in the bioturbated shales dissolved oxygen was present in bottom waters during the deposition of some of the laminated shale intervals because of the presence of manganoan calcite a phase that can only form in sediments with an oxic surface in addition the organic matter preserved in the two shale types is isotopically different 13corganic values are 1 9z permil lighter on average in the laminated compared with bioturbated intervals possibly indicating a larger fraction of terrestrial organic matter in the latter 15n values are 1 9z permil lighter on average in laminated compared with bioturbated intervals possibly indicating a larger fraction of terrestrial organic matter in the latter 15n values are 1 9z permil lighter on average in laminated compared with bioturbated intervals suggesting that nutrient drawdown was less during the deposition of the organic rich laminated shales the chemical mineralogical and isotopic contrasts between the two shale facies of the camp run member indicate that the conditions of sedimentation were different during their deposition the difference was possibly related to variations in sea level which would have caused the camp run shoreline to move closer to and farther from the core site causing in turn the deposition of coarser and finer grained sediments that contained different mixtures of marine and terrestrial organic matter bottomwater conditions were anoxic during deposition of most laminated intervals bottom water anoxia or dysoxia led to decreased burial and preservation of the essential nutrient phosphorus in the laminated organic rich shales relative to the rocks deposited beneath better oxygenated bottomwaters increased availability of phosphorus in the water column on long timescales leads to increased productivity and a higher settling flux of organic matter causing bottom water oxygen levels to fall this is consistent with the nitrogen isotope evidence suggesting that production was probably higher during the deposition of the organic rich shales thus production variations coupled with enhanced sedimentary regeneration of phosphorus from sediments related to low oxygen bottom water concentrations provide a general mechanism for the formation of the alternating facies of this member of the new albany shale

geochemistry of peruvian near surface sediments sixteen short sediment cores were recovered from the upper edge ueo within wo and below bo the oxygen minimum zone omz off peru during cruise 147 of r v sonne solids were analyzed for major trace elements total organic carbon total inorganic carbon total sulfur the stable sulfur isotope composition 34 s of pyrite and sulfate reduction rates srr pore waters were analyzed for dissolved sulfate sulfide and 34 s of sulfate in all cores highest srr were observed in the top 5 cm where pore water sulfate concentrations varied little due to resupply of sulfate by sulfide oxidation and or diffusion of sulfate from bottom water 34 s of dissolved sulfate showed only minor downcore increases strong 32 s enrichments in sedimentary pyrite to 48 vs v cdt are due to processes in the oxidative part of the sulfur cycle in addition to sulfate reduction manganese and co are significantly depleted in peruvian upwelling sediments most likely due to mobilization from particles settling through the omz whereas release of both elements from reducing sediments only seems to occur in near coastal sites cadmium mo and re are exceptionally enriched in wo sediments 600 m water depth high re and moderate cd and mo enrichments are seen in bo sediments 600 m water depth re mo ratios indicate anoxic and suboxic conditions for wo and bo sediments respectively cadmium and mo downcore profiles suggest considerable contribution to ueo wo sediments by a biodetrital phase whereas re presumably accumulates via diffusion across the sediment water interface to precipitation depth uranium is distinctly enriched in wo sediments due to sulfidic conditions and in some bo sediments due to phosphorites silver transfer to suboxic bo sediments is likely governed by diatomaceous matter input whereas in anoxic wo sediments ag is presumably trapped due to sulfide precipitation cadmium cu zn ni cr ag and t1 predominantly accumulate via biogenic pre concentration in plankton remains rhenium sb as v u and mo are enriched in accordance with seawater te availability lead and bi enrichment in ueo surface sediments is likely contributed by anthropogenic activity mining accumulation rates of toc cd mo u and v from peruvian and namibian sediments exceed those from the oman margin and gulf of california due to enhanced preservation off peru and namibia copyright 2004 elsevier ltd

hydrogen and oxygen isotope evidence for origin of mvt forming brines southern appalachians abstract hydrogen and oxygen isotope compositions of fluid inclusion hosted brines from mississippi valley type mvt deposits in the southern appalachians were analyzed to test whether the dominant water in the brines was seawater as suggested by previously reported na cl br relations measurements were made for deposits in the two main paleoaquifers in the area the lower cambrian shady and lower ordovician knox and included the large east tennessee ore field and the austinville district 18 o and d values for sphalerite hosted brines in the two main paleoaquifers cluster in separate fields those in the lower cambrian paleoaquifer form an elongate array that extends from 18 o 2 and d 41 to 18 o 5 and d 87 0 those in the lower ordovician paleoaquifer form a cluster at about 18 o 7 and d 35 stable isotope compositions of fluid inclusion hosted brines in fluorite from the lower ordovician paleoaquifer form an array that extends from the lower ordovician hosted sphalerite cluster toward the composition of modern formation waters in the lower ordovician paleoaquifer which plot along the meteoric water line stable isotope compositions of fluids in barite form an array that extends toward very low sd values typical of organic matter or gas these data permit but do not require the interpretation that the mineralizing brines contain seawater with hydrogen and oxygen isotope compositions that were modified by reaction with country rocks particularly with organic matter and or hydrocarbon gas when the appalachian data are plotted together with those from other mvt districts in the mid continent the combined data form a broad array that extends downward from hydrogen and oxygen isotope compositions typical of seawater toward low d values such as would form by fluid interaction with organic matter or gas consideration of published isotopic compositions of brines from other mvt deposits suggests that interaction with organic matter and or gas may be an important process in the evolution of ore forming brines

a major holocene enso anomaly during the medieval period 1 here we present a high resolution marine el nino flood record from peru a period of extreme drought without strong flooding occurred from a d 800 1250 anomalous precipitation patterns characterized the entire indo pacific enso domain with dry events in the northern arabian sea and the mid latitudes of both americas coinciding with wet periods in the atlantic cariaco basin the occurrence of contemporaneous moisture anomalies in other archives in the enso region highlights the role of el nino strength in global climate evolution during the late medieval period when temperature reconstructions show a rather heterogeneous pattern

circulation and low frequency variability near the chilean coast remotely forced fluctuations during the 1991 92 el nino results are reported from the first long recording current meter observations over the slope off chile these observations at 308s during the 1991 92 el nino event are analyzed together with observations of currents at a local deep sea site local wind and sea level sea level from the peru and chile coasts and wind temperature and currents from the equatorial pacific mean poleward flow of 12 cm s21 was observed within the peru chile undercurrent over the slope mean flow in the depth range of antarctic intermediate water was not distinguishable from zero in the presence of strong low frequency lf variability which dominated slope currents at all depths the strongest lf fluctuations had periods of about 50 days but periods of 10 and about 5 days were also observed significant local wind forcing of slope currents was only found in the period band 6 10 days and may be related to coastal trapped waves in the atmosphere our analysis shows that free coastal trapped waves in the ocean arriving from the north dominated the lf variability over the shelf and slope off northern and central chile during the 1991 92 el nino event strong 50 day period fluctuations there started their journey about two months earlier and 15 000 km farther up the coastal equatorial waveguide near the date line in the equatorial pacific as equatorial kelvin waves forced by westerly wind events of similar period upon reaching the south american coast these waves forced coastal trapped waves which propagated along the peru coast into the study region likewise a scenario of equatorial trapped waves forcing coastal trapped waves may explain 10 day as well as 6 day and 4 5 day period coastal trapped waves off chile stemming from mixed rossby gravity and inertia gravity waves trapped at the equator since the large 50 day period coastal trapped waves may strongly modify coastal upwelling source water such remotely forced waves may have a significant influence on the pelagic ecosystem off chile at least during el nino events

isotope geochemistry of fluid inclusions in permian halite with implications for the isotopic history of ocean water and the origin of saline formation waters abstract d and 18o values have been determined for fluid inclusions in 45 samples of permian halite the inclusions are enriched in 18o relative to the meteoric water line but are depleted in d relative to ocean water inclusions with the more positive values coincide with the isotopic composition expected for evaporating sea water which follows a hooked trajectory on a d 18o diagram inclusions with more negative values may represent more highly evaporated sea water but probably reflect synsedimentary or diagenetic mixing of meteoric water with evaporite brines the isotope systematics in these inclusions are sufficiently similar to those of a modern evaporite pan to indicate that permian sea water was isotopically similar to modern sea water connate evaporite brines can have negative values because of the probable hooked isotope trajectory of evaporating sea water and or synsedimentary mixing of evaporite brines with meteoric waters subsurface formation waters composed of mixtures of remnant primary evaporite brines and later meteoric waters may be more common than previous isotopic evidence has suggested

a viscoelastic coupling model for the cyclic deformation due to periodically repeated earthquakes at subduction zones vertical displacements due to periodic reverse faulting events in an elastic plate overlying a viscoelastic maxwell half space are obtained and compared with the observed deformation cycle coseismic strain release postseismic transients interseismic strain accumulation from japan the viscoelastic effects including the influence of buoyant restoring forces are obtained using the method developed by rundle and plate convergence and strain accumulation are incorporated following the procedure suggested by savage the resulting deformation cycle is compared with that of an analogous elastic half space dislocation model in which postearthquake effects are due to transient aseismic slip below the coseismic fault cyclic deformation is similar but not identical for the two models and observations from southwest japan suggest the superiority of the viscoelastic coupling model in particular inclusion of the effects of steady state flow in the asthenosphere overcomes a defect of the elastic half space model and results in agreement with the observed interseismic movement pattern several aspects of the postseismic deformation its landward migration and its transition to the interseismic phase of the cycle are explained as well but the short duration of near trench transients relative to those observed farther inland is not matched the success of a buried slip model in explaining early postseismic near trench movements and asthenospheric flow in accounting for cumulative postearthquake transient motions suggests the existence of a transition zone between lithosphere and asthenosphere whose behavior is brittle elastic in the short term and ductile for longer term deformation and such a modification may reconcile remaining discordant observations however reasonable variations in coupling model parameters cannot account for observed differences in the deformation cycle in other parts of japan and these regional differences remain unexplained

izmit earthquake postseismic deformation and dynamics of the north anatolian fault zone 1 we have modeled postseismic deformation from 1999 to 2003 in the region surrounding the 1999 izmit and duzce earthquake ruptures using a three dimensional viscoelastic finite element method our models confirm earlier findings that surface deformation within the first few months of the izmit earthquake is principally due to stable frictional afterslip on and below the izmit earthquake rupture a second deformation process is required however to fit the surface deformation after several months viscoelastic relaxation of lower crust and or upper mantle with a viscosity of the order of 2 to 5 1019 pa s improves the models fit to later gps site velocities however for a linear viscous rheology this range of values is inconsistent with highly localized interseismic deformation around the north anatolian fault zone nafz that was well observed prior to the earthquake sequence the simplest solution to this problem is to assume that the effective viscosity of the relaxing material increases with time after large earthquakes that is that it has a power law or burger s body transient rheology a burger s body rheology with two characteristic viscosities 2 to 5 1019 pa s and at least 2 1020 pa s in the mantle is consistent with deformation around the nafz throughout the earthquake cycle

origin and chemical evolution of formation waters from silurian devonian strata in the illinois basin usa abstract a suite of formation water samples from silurian devonian reservoirs in the illinois basin has been analyzed for major minor and trace element concentrations and for h o and sr isotopic compositions in order to interpret origin of salinity and geochemical evolution of brine compositions in this evaporite and shale poor cratonic basin although chloride concentrations range from 2000 to 137 000 mg l cl br ratios 291 18 are consistent with those of seawater or seawater evaporated short of halite saturation cl br 292 thus during silurian devonian time subaerially evaporated penesaline brine entered the subsurface where it was chemically modified through brine rock interactions cation br ratios and mineralogy of associated strata indicate that na and k were depleted through interaction with clay minerals ca was enriched and mg depleted by dolomitization and sr was enriched as a result of caco3 recrystallization and dolomitization although significant dilution of the modified brine with meteoric water is supported by d 18o covariance original marine waters have not been completely expelled from silurian devonian strata hydrogen and oxygen isotopes exhibit covariant relations with cation and anion concentrations implying that isotopic exchange between h2o and minerals has not greatly influenced the d 18o trend brine 87 sr 86 sr ratios range from 0 7092 to 0 7108 when these ratios are plotted versus 1 sr a two component mixing trend is suggested although sr concentrations have experienced local diagenetic modification a 87sr enriched fluid may have accompanied petroleum migration from new albany shales into adjacent silurian devonian carbonates where it mixed with remnant evaporated seawater this event probably preceded the influx of meteoric water as gdd and 18o are not correlated with sr isotopic compositions of formation waters

late holocene variability in pelagic fish scales and dinoflagellate cysts along the west coast of vancouver island ne pacific ocean fish stocks and dinoflagellates are essential components of the marine food chain sediment cores from a predominantly anoxic basin in effingham inlet vancouver island british columbia archive a late holocene 500 5300 years bp record of paleoproductivity in the north american coastal upwelling domain cud we present evidence that late holocene changes in the dinoflagellate cyst assemblages sedimentary record and fish stocks in the northeastern pacific ocean fluctuated at least partially in accordance with regional and global climate cycles principal components analysis pca and trend wavelet and spectral analyses were used to identify relationships cycles and trends in sediment grey scale values and the abundances of fish scales and dinoflagellate cysts on centennial to millennial time scales most observed cycles fluctuated in intensity over time particularly following transition of the regional climate to a higher rainfall phase that impacted coastal oceanic dynamics 3400f150 years ago correlation of the marine paleoproductivity records observed in effingham inlet with solar influenced climate proxy cycles observed in the north atlantic region indicates that solar forcing at different scales might have influenced the climate in the northeast pacific as well in particular an 1100 to 1400 year cycle in regional climate is well represented in the fish productivity proxy and sedimentological record it was also observed that colder water high productivity selenopemphix nephroides and anchovydominated banchovy regimeq ecosystems alternate with warmer water herring dominated bherring regimeq ecosystems at millennial time scales the fish scale record preserved in effingham inlet indicates that the ne pacific is now in transition from an danchovy t to a dherringt dominated regime d 2005 elsevier b v all rights reserved

accumulation and biological mixing of peru margin sediments abstract rates of sediment accumulation and biological particle mixing in eight cores from the peru shelf have been estimated by application of uranium series disequilibrium techniques and radiocarbon dating activities of 210pb 226ra 234th and 238u have been determined in closely spaced intervals in each sediment core biological particle mixing coefficients were determined via a two box advection diffusion steady state mixing model based on the distribution profiles of excess 210pb and in some cases excess 234th activities the sedimentation rates estimated were in the order of a few millimeters yr except for cores enriched in phosphatic components which displayed rates a few orders of magnitude slower bioturbation was significant in most cores studied with the exception of one core collected from within the middle of the oxygen minimum zone estimated biological mixing coefficients were in the order of 100 101 cm2 yr 1 for the surface mixed layer and 10 1 100 cm2 yr 1 for the layer below sediment slumping appears to have affected the 210pb distribution of two or three of our cores

saline groundwaters in the canadian shield a first overview abstract the chemical and isotopic compositions of saline groundwaters and brines in the canadian shield are described the occurrence of such waters is very widespread not related to any specific rock type or mineralization and generally can be expected at depths below 1 km the most saline brines have salinities exceeding 200 g l 1 dissolved solids and their chemistries tend to suggest that in the past saline waters penetrated the canadian shield the original chemistry of these solutions was subsequently modified through strong rock water interactions and it appears that their final chemical compositions are independent of the original chemistries stable isotope analyses indicate that these waters are not simple evaporated seawater sedimentary basin brines hydrothermal solutions or residual ore forming fluids although any of these could be a precursor of the brines secondary isotope exchange reactions and the hydration of primary silicates accompanied by the formation of clay minerals could have modified not only the primary isotopic composition but may have also profoundly influenced the chemistries of these brines to be effective these processes would have had to occur in closed systems

time dependent deformation of shale gas reservoir rocks and its long term effect on the in situ state of stress abstract laboratory testing of shale gas reservoir rocks reveal varying amounts of time dependent viscous deformation in response to applied differential stress the time dependent deformation is an inherent property of the dry rock as it occurs in the absence of pore fluid the contribution of the time dependent deformation is generally larger for rocks with more clay and organic content the time dependent behavior can be modeled as a power law function of time its magnitude is approximately linear with the magnitude of the applied differential stress and nearly insensitive to the confining pressure by applying linear viscoelastic theory and using laboratory constrained constitutive parameters we evaluated the effect of the time dependent deformation in modifying the in situ differential stress over time modeling suggests that a significant proportion of a differential stress change would be relaxed over time scales on the order of days because of this short time scale the composition of the rock as it influences the time dependent behavior may influence the in situ differential stress magnitudes stronger than the formation s geological loading history for these reservoirs

a holocene record of marine fish remains from the northeastern pacific abstract ocean drilling program leg 169s retrieved a complete holocene sequence from saanich inlet british columbia canada fish and diatom remains were extracted from sediments at site 1034 very small fish bones teeth and scales were ubiquitous except in the lowermost glaciomarine clays scales degraded with depth in the identifiable fraction pacific herring were the most abundant with pacific hake and cartilaginous fish yielding significant fractions fish remains appear just before 12 000 bp but greatest diversity does not occur until about 6500 bp a smoothed abundance curve highlights two periods of maximal abundance at about 1500 and 6500 bp abundances in the last 1000 years are lower than the rest of the record a correlation with abundances of seven phytoplankton taxa is significant diatoms explain about a third of the variance this study demonstrates the use of fish and diatoms from the same paleosedimentary matrix to examine millennia scale correlations between primary and tertiary production

origin distribution and movement of brine in the permian basin u s a a model for displacement of connate brine na cl halite ca cl and gypsum ca cl brines with salinities from 45 to 300 g l are identified and mapped in four hydrostratigraphic units in the permian basin area beneath western texas and oklahoma and eastern new mexico providing spatial and lithologic constraints on the interpretation of the origin and movement of brine na cl brine is derived from meteoric water as young as 5 10 ma that dissolved anhydrite and halite whereas ca cl brine is interpreted to be ancient modified connate permian brine that now is mixing with and being displaced by the na cl brine displacement fronts appear as broad mixing zones with no significant salinity gradients evolution of ca cl brine composition from ideal evaporated sea water is attributed to dolomitization and syndepositional recycling of halite and bittern salts by intermittent influx of fresh water and sea water halite ca cl brine in the evaporite section in the northern part of the basin differs from gypsum ca cl brine in the south central part in salinity and na cl ratio and reflects segregation between halite and gypsum precipitating lagoons during the permian ca cl brine moved downward through the evaporite section into the underlying lower permian and pennsylvanian marine section that is now the deep basin brine aquifer mixing there withmore pre existing sea water buoyancy driven convection of brine dominated local flow for most of basin history with regional advection governed by topographically related forces dominant only for the past 5 to 10 ma 71 refs 11 figs less

evolution of saline waters and brines in the benue trough nigeria abstract hydrogeochemical assessment of 40 saline waters and brines from 20 locations within the lower southern and middle regions of the benue trough nigeria are presented and discussed in terms of genesis of the primary salinity and subsequent hydrochemical evolution the total dissolved ions range from 5263 to 88 800 mg l and 5148 to 47 145 mg l in the lower and middle region respectively the saline waters and brines are characteristically na cl type enriched in ca and sr on the one hand and depleted in mg and so 4 on the other relative to the seawater evaporation trend ionic ratios na cl br systematic and divalent cations suggest two likely sources of primary salinity a fossil seawater source and dissolution of halite however water rock interaction involving mg uptake by clay minerals and possibly dolomitization during diagenesis appear to be responsible for further modification of the primary chemistry a conceptualized hydrogeological flow model for the brines is presented

processes controlling colloid composition in a fractured and karstic aquifer in eastern tennessee usa abstract groundwater was sampled from a number of wells along recharge pathways between fractured shale and karstic formations to evaluate the chemical and hydrologic mechanisms controlling the nature and abundance of groundwater colloids the colloids recovered using low flow rate purging and sampling exhibited a composition and abundance consistent with lithology flow paths and effects of hydrology and aqueous chemistry on colloid mobilization and stability in general the larger size colloids and ca containing colloids were more abundant in the karstic lithologies while na containing colloids were more important in the shales the composition of the colloids reflected recharge pathways from the fractured shale and dolomite formations on the ridges into the limestone in the valley floor the mg colloids in the limestone reflect the possible contributions from the dolamite while the na k and si reflect possible contributions from the shale however it was not possible to use the colloid composition as a signature to demonstrate colloid transport from one lithology to another mixing of recharge water from the shale with groundwater within the limestone formation and precipitation dissolution reactions could account for the colloids present in the limestone without invoking transport of specific shale derived colloids into the limestone formation the abundance of colloids in groundwater appears to be controlled by both chemical factors affecting colloid stability as well as physical factors related to hydrology storm driven recharge and water velocities in general colloids were more abundant in wells with low ionic strength such as shallow wells in water table aquifers near sources of recharge at the top of the ridges increases in cation concentrations due to dissolution reactions along flow paths were associated with decreases in colloid abundance however in spite of elevated ionic strength colloid concentrations tended to be unexpectedly high in karstic wells that were completed in cavities or water bearing fractures the higher levels of colloids appear to be related to storm driven changes in chemistry or flow rates that causes resuspension of colloids settled within cavities and fractures

bone diagenesis and radiocarbon dating of fish bones at the shag river mouth site new zealand the shag river mouth site in southern new zealand has yielded a series of radiocarbon determinations from multiple sample types which suggest that the site was occupied briefly in the 14th century ad radiocarbon determinations of bone disclose a greater variation which has been attributed to problems of sample degradation contamination inadequate pretreatment or the use of sub fossil bones in prehistory we examined the dating of bone at the site using barracouta thyrsites atun fish bone in order to determine whether this material could be dated accurately we applied a series of analytical tests to ascertain the preservation state and the extent of post depositional contamination these data were used to predict which samples would be most useful for14c analysis the resultant ages with the exception of two problematic samples are consistent with those on other acceptable marine and estuarine shell carbonate samples based on the available results we suggest that barracouta fish bone from this site is well preserved and reliable for dating we re examined previous determinations of moa and rat bone from different parts of the site to evaluate their accuracy in the light of this new data

the trace metal content of recent organic carbon rich sediments implications for cretaceous black shale formation organic carbon rich sediments are enriched in several redox sensitive and stable sulfide forming trace metals tm and form an important sink in global tm cycles in today s ocean such sediments are deposited in coastal upwelling areas like those in the gulf of california off peru or off the namibian coast and euxinic basins like the black sea in an attempt to distinguish both environments by their specific tm patterns some important conclusions may be drawn 1 the tm enrichment seen in both environments broadly is rather similar 2 upwelling sediments are often enriched in cd and p and depleted in co and mn 3 sapropels have a tendency towards higher enrichments in ba and mo s re as cu ni sb and fe reflecting the strong sulfidation in an anoxic water column 4 upwelling systems cover a broad range of environmental settings where the steepness of the slope the proximity of h2s to the sediment seawater interface and the intensity of bio accumulation and regeneration play an important role for tm accumulation 5 the tm content of anoxic basins is mainly controlled by tm availability in the water column and sedimentation rate 6 enhanced bio productivity is the main switch turning an oxygenated into an anoxic environment cretaceous black shales oae 2 exhibit tm signatures of both coastal upwelling areas and sapropels the strong enrichments in cd mo tl v cu ni bi and sb demonstrate that bio accumulation and presence of h2s in the water column and associated sulfidation processes persisted during this time interval in large parts of the proto atlantic the usefulness of ba as a paleoproductivity proxy is obscured by diagenesis the extreme accumulation in ag and zn requires either an additional tm source for instance hydrothermal input or a different tm seawater composition during the cretaceous the geochemical data suggest that the major driving force for the widespread occurrence of c t black shales seems to be the increase in volcanic activity and associated co2 input throughout the cretaceous the ocean atmosphere system operated in a mode different from today during this time interval after conversion of the nutrient co2 into organic matter the system switched back into the normal operational mode

phosphate regeneration from sediments of the peru continental margin by dissolution of fish debris generally oxidative regeneration of phosphate from anoxic sediments is by microbially mediated sulfate reduction processes stoichiometric modelling of such reactions takes into consideration varying proportions of decomposable organically bound p to account for the ratios among nutrients in depth concentration profiles of near surface sediments new results of interstitial water composition from sediments underlying the water masses influenced by coastal upwelling of the eastern boundary current system off peru indicate that dissolution of phosphatic fish debris represents a mechanism for remineralization of phosphate comparable to or larger in magnitude than that by oxidative regeneration of organically bound p dissolved interstitial phosphate from fish debris is revealed by an excess amount of phosphate over that predicted from a simple stoichiometric oxidative regeneration model and by anomalously high dissolved interstitial fluoride concentrations phosphate flux estimates based on diffusion from the sediment suggest that this mechanism may generate up to 10 of the nutrient pool in the waters of the peru undercurrent partitioning of p among the two sources reveals further that fish debris phosphate is about four times more important than organically bound p in nutrient generation from sediments of the peru continental margin not only does this mechanism of regeneration affect the nutrient cycling but may also control widespread phosphorite formation in this area

thermal regime of the southwest japan subduction zone effects of age history of the subducting plate abstract during a mid miocene at about 15 ma tectonic reorganization an ocean spreading ridge perpendicular to the strike of the nankai trough subduction zone stopped spreading since that time there has been subduction of the cooling fossil spreading ridge in the present study we have developed a time dependent thermal subduction model for this region using the finite element method there are good seismological and geological constraints for the plate geometry and for the subduction history of the past 15 ma boundary conditions are specified so that the oceanic plate subducting at the nankai trough becomes cooler as it gets older the model results agree with the present heat flow trend that decreases landward and explain the paleothermal regime of high mid miocene temperatures inferred from land geological studies the tectonics of the region prior to 15 ma has some uncertainties assuming subduction of an active spreading ridge or an 80 ma old lithosphere prior to 15 ma give the same results for the present thermal regime of the seaward portion of the forearc but different results for the most landward region 250 km the thermal history of the forearc since 15 ma can be summarized as a rapid warming period as a consequence of ridge subduction followed by a cooling trend to the present as a result of the aging of the subducting plate the results illustrate the thermal consequences of one type of ridge subduction they also demonstrate that the thermal regime of a subduction zone depends critically on the age history of the subducting oceanic lithosphere especially if it is young as well as such parameters as the subducting plate dip angle and thickness of insulating sediments on the incoming oceanic crust this dependence is especially important when the thermal regime is used to constrain the seismogenic behaviour of the subduction thrust fault

alleghenian age of the upper mississippi valley zinc lead deposit determined by rb sr dating of sphalerite mississippi valley type mvt ore deposits in north america are generally thought to have formed from warm brines which migrated from sedimentary basins to sites of deposition in sedimentary strata of the neighbouring craton long after unification of the sediments1 3 when and how these migrations occurred is not well understood but recent geological evidence suggests that continental scale brine migration can be triggered by tectonic collisions4 6 indirect evidence7 9has suggested an association of north american mvt mineralization with the late palaeozoic alleghenian ouachita orogeny recently however nakai et al 10obtained a rb sr age of 377 29myr for sphalerites from the east tennessee mvt district which they linked to the middle palaeozoic acadian orogeny here we report rb sr dates for sphalerites from the mvt type section the upper mississippi valley umv zinc lead district rb sr data from two distinct sphalerite bands from the west hayden ore body yield two independent but indistinguishable isochrons of permian age 269 6 myr and 270 4 myr consistent with a brine migration episode initiated by the alleghenian ouachita orogeny in conjunction with the previous data indicating a link to the acadian orogeny10 11 our results indicate that north american mvt deposits formed in at least two distinct tectonic episodes

rb sr dating of sphalerites from tennessee and the genesis of mississippi valley type ore deposits mississippi valley type mvt ore deposits commonly consist of some combination of lead zinc and iron sulphides accompanied by barite fluorite dolomite and calcite they are thought to form by fluid expulsion from sedimentary successions1 3 but their exact origin has remained controversial because of the scarcity of reliable geochronological data in a recent and widely quoted model the mvt deposits of the central and eastern united states formed as a result of large scale lateral fluid flow driven by the tectonic squeezing of sedimentary successions during the late palaeozoic alleghenian orogeny 330 250 myr 4 here we report the first direct rb sr dating of sphalerites from an mvt deposit and propose this as a useful geochronological technique for sulphide mineralization with poor age control rb sr data for sphalerites from coy mine east tennessee define an isochron age of 377 29 myr ruling out any genetic connection with the alleghenian orogeny instead mvt mineralization in the eastern united states was apparently generated from fluids expelled during thrusting associated with the older acadian orogeny 380 350 myr

stoichiometric saturation tests of nacl1 xbrx and kcl1 xbrx stoichiometric saturation is examined as a possible control on br contents of halite and sylvite during precipitation from binary salt solutions of nacl nabr and kcl kbr respectively experimental data at 25 c assumed to represent stoichiometric saturation were used to predict mole fractions of nabr in halite and kbr in sylvite in thermodynamic equilibrium with fluids as a function of aqueous activity ratios of br cl the predictions are based on the additional assumption that the aqueous activity product of the major salt component in the precipitated salt was independent of the trace br content in the salt lattice the extension of the predictions to diagenetic pressures and temperatures is discussed the predicted equilibrium br content of halite at initial halite saturation of evaporating seawater is in close agreement with that computed from the distribution coefficient of lutz 1975 measured in slowgrowth single crystal experiments fluid recrystallization of halite and sylvite at near surface temperatures is predicted to generally deplete the br contents in the solids bulk br contents in halite in cap rock of gulf coast salt domes generally agree with those predicted by the recrystallization of halite in the presence of evaporative concentrated seawater at a constant solution composition increasing temperature results in increasing the equilibrium br content of halite making less efficient br depletion in halite by recrystallization

geochemical characteristics of chilean upwelling sediments at 36 s abstract we examined the cycling of c s fe and the trace elements te ag cd mo mn re and se in chilean upwelling sediments from water depths of 127 2744 m at 36 s the sediments are clay rich with moderate total organic carbon toc and low biogenic caco3 contents for the shallow site within oxygen minimum zone omz which shows some thioploca biomass highest observed toc contents correspond to highest productivity induced toc flux and or enhanced preservation under o2 deficient conditions pyrite formation may be restricted by the concurrent presence of elemental s in thioploca and or the availability of reactive iron in the other sediments 370 m water depth pyrite formation is strongly restricted due to the low availability of metabolizable toc for sulfate reduction calculations of the degree of bacterially mediated remineralization suggest that more nitrogen than toc was remineralized by sulfate reduction than expected from redfield c n relationship manganese is significantly depleted due to reductive dissolution of mn hydr oxides within all sediments mo is only significantly enriched vs the lithogenic background in the shallow core implying anoxic conditions contents of re and mo as well as re mo ratios indicate suboxic conditions for the other cores cd and re contents decrease with increasing water depth reflecting decreasing reducing conditions in contrast authigenic ag contents increase with water depth suggesting enrichment controlled by seawater availability and or opaline input and not redox conditions elevated se contents in all cores may be either due to bio detrital input or diffusion from seawater accumulation rates of toc ts and te off chile are in the same order as those from the gulf of california and lower than those off peru distinct seasonality in upwelling and dilution of chilean sediments with terrigenous material lead to rather low metabolizable toc contents and lower te trapping capacity

distribution of various extracted phosphorus compounds in the interbedded turbiditic pelagic sediments of the madeira abyssal plain eastern north atlantic abstract a sequential extraction scheme was used to differentiate different p fractions in the interbedded turbiditic pelagic sediments of the madeira abyssal plain these fractions were carbonate associated exchangeable phosphate pex iron and aluminium associated phosphate poh calcium associated phosphate apatite phcl organic phosphorus porg and remaining phosphorus pr the pex forms a minor fraction of the total sedimentary phosphorus ptot whereas for most samples phcl represents near 80 of the ptot the amount of p in most fractions appears to be determined by the composition and provenance of the various turbidites the relatively high pex and the moderately high apatite p phcl for the sediment of turbidite e organicrich turbidite provenance group may point to a source area that is possibly upwelling related on the other hand the high phcl for the sediments of the turbidites b g n o p corresponds nicely to their volcanic and near coastal provenance area in contrast to this major impact of inherited p only a small contribution comes from p that is associated to post depositional re allocation of fe poh this results in a poh concentration that is slightly higher in the upper post depositionally oxidized layer of a turbidite than it is in the lower still un oxidized layer of the same turbidite in addition this postdepositional oxidation of the upper layer of a turbidite may also result in enhanced fe and p levels in the overlying pelagic interval the c p molar ratio for organic matter in these sediments is much higher than that reported for more recent sediments and for average marine plankton 1200 versus 500 and 106 respectively which may be caused by postdepositional differential decomposition of organic matter

assessment of the size of large and great historical earthquakes in peru a critical reappraisal of great historical earthquakes in peru is made in order to obtain quantitative estimates of rupture length seismic moment tsunami magnitude mt and moment magnitude mw newly collected information concerning several historical earthquakes permits the evaluation of macroseismic zones and from the size of these zones the estimation of length of rupture seismic moment and magnitude mw it is found that local tsunami data provide good quantitative estimates of mt and therefore an independent way of verifying macroseismic estimates of rupture length and seismic moment a space time diagram of great historical earthquakes shows the existence of three zones roughly corresponding to the segmentation of the nazca plate hasegawa and sacks 1981 subducting under peru the northern zone looks aseismic the central one is very complex it breaks either completely or in smaller segments and it may go through long quiescence periods the recurrence time for the southern segment the more regular one is of the order of one century

enhanced regeneration of phosphorus during formation of the most recent eastern mediterranean sapropel s1 phosphorus regeneration and burial fluxes during and after formation of the most recent sapropel s1 were determined for two deep basin low sedimentation sites in the eastern mediterranean sea organic c p ratios and burial fluxes indicate enhanced regeneration of p relative to c during deposition of sapropel s1 this is largely due to the enhanced release of p from organic matter during sulfate reduction release of p from fe bound p also increased but this was only a relatively minor source of dissolved p pore water hpo4 concentrations remained too low for carbonate fluorapatite formation an increased burial of biogenic ca p i e fish debris was observed for one site estimated benthic fluxes of p during sapropel formation were elevated relative to the present day 900 to 2800 vs 70 to 120 mol m 2 yr 1 the present day sedimentary p cycle in the deep basin sediments is characterized by two major zones of reaction 1 the zone near the sediment water interface where substantial release of hpo4 from organic matter takes place and 2 the oxidation front at the top of the s1 where upward diffusing hpo4 from below the sapropel is sorbed to fe oxides the efficiency of aerobic organisms in retaining p is reflected in the low organic c p ratios in the oxidized part of the sapropel burial efficiencies for reactive p were significantly lower during s1 times compared with the present day 7 to 15 vs 64 to 77 budget calculations for the eastern mediterranean sea demonstrate that the weakening of the antiestuarine circulation and the enhanced regeneration of p both contributed to a significant increase in deep water hpo 4 concentrations during sapropel s1 times provided that sufficient vertical mixing occurred enhanced regeneration of p at the seafloor may have played a key role in maintaining increased productivity during sapropel s1 formation copyright 2002 elsevier science ltd

inorganic geochemical indicators of glacial interglacial changes in productivity and anoxia on the california continental margin abstract evidence from sediments in cores collected from within the present oxygen minimum zone omz 600 1200 m on the central and northern california margins record several episodes during the last interstadial ois 3 ca 60 24 ka of deposition of laminated sediments containing elevated concentrations of several trace elements indicative of anoxic conditions e g mo ni zn and cu the presence of abundant well preserved organic matter as well as lack of bioturbation and the presence of elevated concentrations of mo and other trace elements all support the theory that the omz in the northeastern pacific ocean was more intense possibly anoxic at several times during the late pleistocene sediments of all ages in cores from the southern california margin contain elevated concentrations of mo suggesting that this area has always had higher rates of sulfate reduction than either the central or northern california areas most of the ba in sediments in all cores collected on the upper continental slope 200 2700 m off california and southern oregon is derived from detrital clastic material and this source did not change much in time however the amount of biogenic ba did vary with time and these variations closely follow the temporal variations in organic c corg mass accumulation rate using ba and corg mass accumulation rates as proxy variables for productivity all cores show that organic productivity under the california current upwelling system was highest during ois 3 and the holocene and lowest during the last glacial interval lgi ca 24 10 ka all paleoproductivity proxy variables indicate that the southern california area has always experienced higher productivity than other areas under the california current at least over the last 50 ky

spatial correlation of interseismic coupling and coseismic rupture extent of the 2011 mw 9 0 tohoku oki earthquake 1 imaging the extent to which the rupture areas of great earthquakes coincide with regions of pre seismic interplate coupling is central to understanding patterns of strain accumulation and release through the earthquake cycle both geodetic and seismic estimates of the coseismic rupture extent for the march 11 2011 mw 8 9 9 0 earthquake tohoku oki earthquake may be spatially correlated 0 26 0 05 to 0 82 0 05 with a region estimated to be partially to fully coupled in the interseismic period preceding the earthquake though there is substantial variation in the estimated distribution and magnitude of coseismic slip the 400 km long region estimated to have slipped 4 m corresponds to an area of the subduction zone interface that was coupled at 30 of long term plate convergence rate with peak slip near a region coupled 80 the northern termination of rupture is collocated with a region of relatively low 20 interseismic coupling near the epicenter of the 1994 mw 7 6 sanriku oki earthquake and near a region of potential long term low coupling or ongoing slow slip slip on the subduction interface beneath the coastline 40 50 km depth is best constrained by the land based gps data and least constrained on the shallowest portion of the plate interface due to the 230 km distance between geodetic observations and the japan trench

evidence for late paleozoic brine migration in cambrian carbonate rocks of the central and southern appalachians implications for mississippi valley type sulfide mineralization abstract many lower paleozoic limestones and dolostones in the valley and ridge province of the central and southern appalachians contain 10 to 25 weight percent authigenic potassium feldspar this was considered to be a product of early diagenesis however 40 ar 39 ar analyses of overgrowths on detrital k feldspar in cambrian carbonate rocks from pennsylvania maryland virginia and tennessee yield late carboniferous early permian ages 278 322 ma simple mass balance calculations suggest that the feldspar could not have formed isochemically but required the flux of multiple pore volumes of fluid through the rocks reflecting regional fluid migration events during the late paleozoic alleghanian orogeny microthermometric measurements of fluid inclusions in overgrowths on detrital k feldspar and quartz grains from unmineralized rocks throughout the study area indicate homogenization temperatures from 100 to 200 c and freezing point depressions of 14 to 18 5 c 18 21 wt nacl equiv the apparent similarity of these fluids to fluid inclusions in ore and gangue minerals of nearby mississippi valley type mvt deposits suggests that the regional occurrences of authigenic k feldspar and mvt mineralization may be genetically related this hypothesis is supported by the discovery of authigenic k feldspar intergrown with sphalerite in several mines of the mascot jefferson city district e tennessee regional potassic alteration in unmineralized carbonate rocks and localized occurrences of mvt mineralization are both explainable by a gravity driven flow model in which deep brines migrate towards the basin margin under a hydraulic gradient established during the alleghanian orogeny the authigenic k feldspar may reflect the loss of k during disequilibrium cooling of the ascending brines mvt deposits are probably localized manifestations of the same migrating fluids occurring where the necessary physical and chemical traps are present

pore water fluoride in peru continental margin sediments uptake from seawater abstract fluoride analyses display downward decreasing pore water gradients in peru shelf phosphatic muds that require diffusion from the overlying seawater into the sediment column and removal by reaction within the upper few tens of centimeters presumably by incorporation into carbonate fluorapatite the profiles can be modeled as first order f removal with rate constants of 3 yr 1 and asymptotic f concentrations deep in the cores of 35 45 m almost one half the seawater value the integrated flux of fluoride from seawater into organic rich shelf sediments in coastal upwelling zones phosphatic muds yields a contemporaneous global f burial of 0 54 10 10 mol f yr 1 about one fifth the burial in other sinks mostly carbonates and opal the associated burial flux of phosphorus in shelf phosphorites is about 1 6 10 10 mol p yr 1 comparable to p burial in the deep sea with organic matter 1 4 10 10 mol yr 1 and biogenic carbonates 1 4 10 10 mol yr 1 thus phosphorite formation on the peru shelf is a significant contemporaneous process

the use of sedimentary fish remains for interpretation of long term fish population fluctuations abstract the varved marine sediments of saanich inlet british columbia retain a detailed record of fish remains we examine methods to process and interpret sedimentary fish remains and explore sources of bias in transfer and preservation through time in high resolution box cores spanning the last 130 years scales outnumber vertebrae a consistent record across replicates is recognizable once outliers are removed pacific herring and hake remains make up over 90 of the identifiable remains cores from odp leg 169s covered the entire holocene scale recovery is poor so the record is based on fragmented bones bones associated with the backbone gill arches and fins yield the best taxonomic information in both core sets low frequency signals are resolved using a five sample running mean because the data series in the short cores are autocorrelated spectral analysis is the best approach to identify high frequency signals that explain much variance in the scale data high cross spectral coherencies confirm a basin wide signal in scale deposition the herring scale deposition data are compared to recent fishery biomass estimates and confirm similarities in timing of low frequency trends and signals experiments with herring in large tanks explore the transfer of scales from fish to the ocean floor shedding and predation are found to provide a regular rain of scales to the sediments overall the sedimentary fish remains record in basins with good preservation shows promise as a means to identify generalized long term fish histories through the holocene as well as a more specific pacific herring and hake story over the last century

compressive sensing of the tohoku oki mw 9 0 earthquake frequency dependent rupture modes 1 compressive sensing cs is a technique for finding sparse signal representations to underdetermined linear measurement equations we use cs to locate seismic sources during the rupture of the 2011 tohoku oki mw9 0 earthquake in japan from teleseismic p waves recorded by an array of stations in the united states the seismic sources are located by minimizing the l2 norm of the difference between the observed and modeled waveforms penalized by the l1 norm of the seismic source vector the resulting minimization problem is convex and can be solved efficiently our results show clear frequency dependent rupture modes with high frequency energy radiation dominant in the down dip region and low frequency radiation in the updip region which may be caused by differences in rupture behavior more intermittent or continuous at the slab interface due to heterogeneous frictional properties

brines in the carboniferous sydney coalfield atlantic canada abstract formation waters within upper carboniferous sandstones in the sub sea prince and phalen coal mines nova scotia originated as residual evaporative fluids probably during the precipitation of windsor group lower carboniferous salts which underlie the coal measures salinity varies from 7800 to 176 000 mg l and the waters are na ca cl brines enriched in ca sr and br and depleted in na k mg and so4 relative to the seawater evaporation curve br cl and na cl ratios suggest that the brine composition corresponds to an evaporation ratio of as much as 30 the brines lie close to the meteoric line on h o isotopic plots but with a compositional range of 18o from 4 18 to 6 99 and of d from 42 4 to 23 5 distant from modern meteoric or ocean water mine water composition contrasts with that of nearby salt spring brines which are inferred to have originated through dissolution of windsor group evaporites by modern meteoric waters however a contribution to the mine waters from halite dissolution and from br in organic matter cannot be ruled out present concentrations of several elements in the brines can be explained by water rock interaction the original windsor brines probably moved up into the overlying coal measure sandstones along faults prior to the late triassic the high salinity and irregular salinity distribution in the phalen sandstones suggests that the brines have undergone only modest dilution and are virtually immobile in contrast prince waters show a progressive increase in salinity with depth and are inferred to have mixed with surface waters basinal brines from which these modern formation fluids were derived may have been important agents in base metal and ba mineralisation from the mid carboniferous onwards as saline fluid inclusions are common in zn pb sulphide deposits in the region

spatiotemporal evolution of a fault shear stress patch due to viscoelastic interseismic fault zone rheology abstract we conducted numerical studies to explore how shear stress anomalies on fault planes shear stress patches evolve spatiotemporally during the interseismic period under the influence of viscoelastic rheology assigned to fault zones of finite thickness 2 d viscoelastic models consisting of a fault zone and host rock were sheared to simulate shear stress accumulation along fault zones due to tectonic loading no fault slip along a distinct fault planes is implied in the model thus all fault shear motion is accommodated by distributed deformation in the viscoelastic fault zone results show that magnitudes of shear stress patches evolve not only temporally but also spatially especially when the stress anomaly is created by a geometrical irregularity asperity along the interface of an elastic host rock and viscoelastic fault zone such shear stress anomalies diffuse spatially so that the spatial dimension of the shear stress patch appears to grow over time models with varying fault zone viscoelastic properties and varying fault zone viscosity both show that such spatial diffusion of shear stress is enhanced by increasing the contribution of the viscous behavior the absolute rate at which shear stress patches grow spatially is generally not influenced by the size of the shear stress patch therefore shear stress patches with smaller dimensions will appear to grow quicker in the relative sense compared to larger stress patches these results suggest that the minimum dimensions of shear stress patches that can exist along a fault could be governed by the effective viscosity of the fault zone therefore patterns of accumulated shear stress could vary along faults when viscous properties are heterogeneous for instance due to depth or material heterogeneity which has implications on how earthquake rupture behavior could vary along faults

the impact of sediment provenance on barium based productivity estimates abstract biogenic barium in marine sediments has been suggested to be a reliable proxy of export productivity from the surface ocean and algorithms have been developed to link these properties however problems arise when the proposed algorithms are applied to predominantly terrigenous sediments a major source of error is incorrect estimates of the terrigenous ba al ratio in normative calculations of the amount of biogenic barium in the sediment compared to an often used global average ba al ratio much better results can be obtained by estimating the terrigenous ba al ratio from exponential regression of the ba al ratios of surface sediments obtained from continental slope transects this method has been applied to surface sediments from the chilean continental slope the calculated regional terrigenous ba al ratios could be verified with purely terrigenous samples from chilean rivers the resulting accumulation rates of biogenic barium on the chilean continental slope reliably reproduce the regional pattern of primary productivity in the southern peru chile current indicating the potential of biogenic barium as a useful paleo productivity proxy

anchovy population and ocean climatic fluctuations in the humboldt current system during the last 700 years and their implications a marine sedimentary record collected from 87 m water depth in a coastal environment of the humboldt current system mejillones bay 23 s northern chile was used to reconstruct the past 700 years of ocean climatic conditions and to study the influence of any changes on anchovy population dynamics we analyzed quartz organic carbon total nitrogen alkenones and fish scales four stratigraphic units in the sediment column correspond with fluctuations in these and other proxies low scale deposition rate sdr values from 1330 to 1420 suggest a low abundance of anchovy in this coastal environment three subsequent cycles of ca 170 years each showed an increase and decrease of anchovy populations which is in agreement with changes in the wind regime sea surface temperature and primary productivity since ca 1840 marked fluctuations of sdr have been observed probably as a consequence of the onset of a different oceanographic regime characterized by intensified southern winds and upwelling colder surface waters higher primary productivity and enhanced la nina like interdecadal variability an increase of the anchovy population was observed until halfway through the 20th century followed by a decrease even though water temperature decreased and primary productivity increased this situation is likely the consequence of the increased fishery activity that developed in this zone during the last 60 years after analyzing the results obtained for anchovy sdr we can determine that there is a relation between the abundance of this species and phases of the pacific decadal oscillation pdo in which an increase in the sdr coincides with a pdo cold phase while a decline coincides with a warm phase fast fourier transformation analysis applied to the time series obtained from the mejillones sediment core and to the north atlantic oscillation nao the pdo and the solar irradiance index time series shows three different decadal cycles 80 100 years 61 75 years and 45 48 years approximately furthermore the results of this study suggest that both the pdo and the nao and the biogeochemical markers of mejillones exhibit periodicities that fall within the 80 to 100 year gleissberg solar cycle indicating that global solar radiation plays a key role in the local ocean climatic processes and confirming teleconnection linkages between widely separated regions

the brine underlying the oak ridge reservation tennessee usa characterization genesis and environmental implications abstract the deep hydrogeologic system underlying the oak ridge atomic reservation contains brine its origin was assessed using existing and newly acquired chemical and isotopic data the proposed model which best fits the data is modification of residual brine from which halite has been precipitated potential sources for this brine are in the appalachian mountains in the east where bedded halite is documented and where the hydraulic gradient needed to move the residual brine exists other models such as ultrafiltration and halite dissolution were also evaluated in places contaminants such as radionuclides heavy metals nitrates and organic compounds have reached the deep system the chemical and isotopic features of the brine were examined with respect to its potential discharge contaminated in places into shallow freshwater systems the observations suggest that whereas the origin of the salts in the brine may be very old influx of recent water takes place consequently the brine is not isolated in terms of recharge and discharge from the overlying active and fresh water bearing units

three dimensional viscoelastic finite element model for postseismic deformation of the great 1960 chile earthquake 2 5 10 19 pa s for the continental upper mantle the model well explains the gps observations numerical tests suggest that the continental mantle viscosity value is reasonably well constrained the model shows the prolonged postseismic seaward motion of the inland area to be a unique feature of earthquakes with very long rupture along strike and large coseismic fault slip for short rupture and small coseismic slip the motion will stop very quickly after the earthquake explaining why this phenomenon is not more commonly observed with an oceanic mantle viscosity of 10 20 pa s the model also provides an explanation for tide gauge constrained postseismic uplift 200 km from the trench that had previously been explained using a model of prolonged afterslip of a deep segment of the chile subduction fault index terms 1236 geodesy and gravity rheology of the lithosphere and mantle 8160 1242 geodesy and gravity seismic deformations 7205 3230 mathematical geophysics numerical solutions 7209 seismology earthquake dynamics and mechanics 7260 seismology theory and modeling keywords postseismic deformation viscoelastic stress relaxation gps finite element modeling chile subduction zone upper mantle viscosity

br cl ratios and o h c and b isotopic constraints on the origin of saline waters from eastern canada saline groundwaters were recovered from undisturbed restigouche deposit and active brunswick 12 mine zn pb volcanogenic massive sulfide deposits in the bathurst mining camp bmc northern new brunswick canada these groundwaters along with fresh to brackish meteoric ground and surface waters from the bmc have been analyzed to determine their major trace element and stable isotopic o h c and b compositions saline groundwaters total dissolved solids 22 45 g l are characterized by relatively high na ca ratios compared to brines from the canadian shield and low na clmolar and d 11 b isotopic compositions 2 5 to 11 1 compared to seawater although saline waters from the canadian shield commonly have oxygen and hydrogen isotopic compositions that plot to the left of the global meteoric water line those from the bmc fall close to the water line fracture and vein carbonate minerals at the restigouche deposit have restricted carbon isotopic compositions of around 5 to 6 the carbon isotopic compositions of the saline waters at the restigouche deposit 12 d 13 cdic are the result of fractionation of dissolved inorganic carbon by methanogenesis we suggest that unlike previous models for shield brines the composition of saline waters in the bmc is best explained by prolonged water rock reaction with no requirement of precursor seawater we suggest that elevated br cl ratios of saline waters compared to seawater may be explained by differential uptake of br and cl during groundwater evolution through water rock reaction 2007 elsevier ltd all rights reserved

2010 maule earthquake slip correlates with pre seismic locking of andean subduction zone analysis of seismic data and global positioning system gps observations from the region around the site of the recent magnitude 8 8 maule earthquake in chile have been combined with modelling of the andean subduction zone to build up a detailed image of the event the earthquake occurred at a seismic gap part of the fault that has not experienced a major earthquake since 1835 and it seems to have released most of the stress accumulated since that time the observations suggest that coseismic slip heterogeneity at the scale of single asperities and therefore the seismic potential of future great earthquakes might be anticipated by geodetic observations these authors show evidence for a high coherence between the slip distribution inferred from the 2010 maule earthquake chile and the patchwork of interseismic locking distribution derived from global positioning system observations during the previous decade their work suggests that coseismic slip heterogeneity at the scale of single asperities should indicate the seismic potential of future earthquakes which thus might be anticipated by geodetic observations the magnitude 8 8 maule chile earthquake of 27 february 2010 ruptured a segment of the andean subduction zone megathrust that has been suspected to be of high seismic potential1 2 3 4 5 6 it is the largest earthquake to rupture a mature seismic gap in a subduction zone that has been monitored with a dense space geodetic network before the event this provides an image of the pre seismically locked state of the plate interface of unprecedentedly high resolution allowing for an assessment of the spatial correlation of interseismic locking with coseismic slip pre seismic locking might be used to anticipate future ruptures in many seismic gaps6 7 8 9 10 11 12 given the fundamental assumption that locking and slip are similar this hypothesis however could not be tested without the occurrence of the first gap filling earthquake here we show evidence that the 2010 maule earthquake slip distribution correlates closely with the patchwork of interseismic locking distribution as derived by inversion of global positioning system gps observations during the previous decade the earthquake nucleated in a region of high locking gradient and released most of the stresses accumulated in the area since the last major event in 1835 two regions of high seismic slip asperities appeared to be nearly fully locked before the earthquake between these asperities the rupture bridged a zone that was creeping interseismically with consistently low coseismic slip the rupture stopped in areas that were highly locked before the earthquake but where pre stress had been significantly reduced by overlapping twentieth century earthquakes our work suggests that coseismic slip heterogeneity at the scale of single asperities should indicate the seismic potential of future great earthquakes which thus might be anticipated by geodetic observations

low velocity damaged structure of the san andreas fault at parkfield from fault zone trapped waves 1 we used dense linear seismic arrays across and along the san andreas fault saf at parkfield california to record fault zone trapped waves generated by explosions and microearthquakes in 2002 prominent trapped waves appeared at stations close to the saf main fault trace while some energy was trapped in the north strand at the array site observations and 3 d finite difference simulations of trapped waves at 2 5 hz show evidence of a damaged core zone on the main saf the zone from the surface to seismogenic depths is marked by a low velocity waveguide 150 m wide in which q is 10 50 and shear velocities are reduced by 30 40 from wall rock velocities with the greatest velocity reduction at shallow depth we interpret that this distinct low velocity zone on the main saf is a remanent of damage due to past large earthquakes on the principal fault plane at parkfield a less developed low velocity zone may be evident on the north strand that experienced minor breaks in the 1966 m6 event

biogenic barium and the detrital ba al ratio a comparison of their direct and indirect determination biogenic barium concentrations obtained from direct determination by a three step sequential extraction procedure are compared to those obtained from the widely used indirect normative calculation based on total digestion a comparison of the biogenic barium from the direct sequential extraction and the indirect normative calculation clearly shows that the detrital ba al ratio is the critical factor in the normative approach and that erroneous assumptions based on this ratio may introduce significant errors to the calculated biogenic barium overall the crustal average ba al ratio of 0 005 0 01 is much higher than our directly determined global average of 0 0037 this would result in an underestimation of the biogenic barium and thus of the primary productivity calculated using the ba flux obtained from the normatively calculated ba record using our ba al det ratio of 0 0037 leads to normatively calculated biogenic barium results that are in reasonable agreement with the biogenic barium from sequential extraction for samples of the atlantic pacific and indian ocean our directly determined regional ba al det ratios deviate from those calculated or assumed from hinterland ratios and our global average ba al det is lower than the one commonly reported therefore in sediments with a significant terrigenous fraction the sequential extraction technique is always required

salt diffusion in interstitial waters and halite removal from sediments examples from the red sea and illinois basins abstract large thicknesses of bedded halite can be removed in subsiding sedimentary basins by vertical diffusion of dissolved salt in interstitial waters over geologic time scales calculations show that at least 10 m to 40 m of halite may have dissolved and diffused through the red sea sediments overlying the salt beds since cessation of salt deposition approximately 5 3 million years ago the total amount of salt diffused out of the sediment column over geologic time is five to twenty times the amount of salt that currently exists in the porewater column if upward flow in the past occurred at even small rates 10 3 m yr the amount of halite removed could have been ten times as great 500 m unlike the red sea basin no halite beds are known in the illinois basin in spite of the fact that interstitial waters with as much as 200 tds approximately 220 g l occur calculations show that if a halite bed had been deposited at the base of the illinois basin in cambrian time it would have been completely removed from the stratigraphic record had it initially been less than 60 m to 130 m in thickness a significant thickness of halite deposited in sedimentary basins may thus be removed during active burial of salt beds and before exhumation and exposure of the salt beds to shallow meteoric waters

high velocity frictional properties of gabbro high velocity friction experiments have been performed on a pair of hollow cylindrical specimens of gabbro initially at room temperature at slip rates from 7 5 mm s to 1 8 m s with total circumferential displacements of 125 to 174 m and at normal stresses to 5 mpa using a rotary shear high speed friction testing machine steady state friction increases slightly with increasing slip rate at slip rates to about 100 mm s velocity strengthening and it decreases markedly with increasing slip rate at higher velocities velocity weakening steady state friction in the velocity weakening regime is lower for the non melting case than the frictional melting case due perhaps to severe thermal fracturing a very large peak friction is always recognized upon the initiation of visible frictional melting presumably owing to the welding of fault surfaces upon the solidification of melt patches frictional properties thus change dramatically with increasing displacement at high velocities and such a non linear effect must be incorporated into the analysis of earthquake initiation processes

phosphogenesis and active phosphorite formation in sediments from the arabian sea oxygen minimum zone in this study porewater chemistry solid phase analysis and microscopic observations were combined to evaluate phosphogenesis in three boxcores located within the intensive oxygen minimum zone of the arabian sea three parameters namely a decrease of the dissolved phosphate and fluoride concentrations with depth saturation with respect to carbonate fluorapatite and the presence of a solid phase ca phosphate mineral all indicate that phosphogenesis is currently taking place at all three sites authigenic apatite precipitation rates vary between 0 076 and 1 04 molp cm 2 yr 1 and are of the same order of magnitude as reported for other high productivity areas precipitation of an intermediate precursor precedes francolite formation in the continental slope sediments on the karachi margin results of a diagenetic p model indicate that phosphogenesis is induced by high rates of organic matter degradation dissolution of fish debris is likely to provide a substantial additional source of phosphate redox iron cycling does not influence phosphogenesis in these environments model results suggest that sediment mixing is essential in promoting early diagenetic phosphogenesis the highest rate of francolite formation was observed in a boxcore taken on the oman margin where it contributes to the formation of a holocene phosphorite deposit this observation contrasts with previous reports of only old phosphorites in this area phosphorites are presently forming on the oman margin as a result of a deposition of older reworked material from the continental shelf which has undergone an earlier phase of phosphogenesis b a high input of reactive p fish debris and degradable organic matter c a relatively low sediment accumulation rate and d the absence of winnowing on this location holocene phosphorite deposits may be less common on the oman margin than in other coastal upwelling areas because of the narrowness of the shelf and the steepness of the slope which limit the area where phosphorite formation may occur

glacial interglacial variability in the eastern tropical north pacific oxygen minimum zone recorded by redox sensitive trace metals 1 changes in the intensity of the oxygen minimum zone omz in the eastern tropical north pacific over the past 140 kyr are recorded as enrichments and depletions of redox sensitive metals in sediments of two piston cores one within and one below the modern omz from the continental margin off mazatlan mexico 22 41 n 106 28 w concentrations of al 7 7 0 6 ti 0 37 0 03 fe 3 1 0 25 mn 320 31 ppm and ba 560 82 ppm in core nh15p within the omz at 420 m water depth were relatively constant over the last 110 kyr in contrast concentrations of cd 4 8 2 ppm cu 29 8 9 1 ppm u 9 1 3 7 ppm mo 12 1 5 0 ppm v 138 2 51 9 ppm and re 45 8 25 5 ppb were all at least 30 higher in interglacial stages compared to glacial stages concentrations of al 7 4 0 3 ti 0 35 0 03 fe 3 5 0 4 and mn 385 77 ppm in core nh22p below the omz at 2025 m water depth were comparable to those in core nh15p while concentrations of ba 1662 292 ppm were about a factor of three higher in contrast concentrations of cd 0 9 0 3 ppm u 6 6 0 9 ppm mo 3 2 1 2 ppm v 81 8 10 1 ppm and re 25 4 12 ppb were lower in sediments of comparable age than the concentrations of these same metals in the omz core and the differences in their concentrations over glacial interglacial cycles were less pronounced than those in shallower core comparison of the nonlithogenic fraction of metals in the sediments with their estimated contribution from plankton suggests that organic matter is probably the major source of cu ba and perhaps cd to the sediment whereas the indirect effects of organic carbon and low bottom water oxygen concentrations on sediment redox state appear to be more important controls on the distributions u re mo and v changes in the depth at which re and mo precipitated in the sediments and in the re mo ratio suggest that the redox state of the surface sediment and overlying water at both core depths varied over time re and mo removal depths were shallower and re mo ratios were lower at the omz site than in deeper water suggesting that a more reducing environment prevailed over time at the shallower site although the redox state of the waters and sediment at both sites varied over glacial interglacial cycles the omz likely was never anoxic in the last 140 kyr this variability in redox state could be attributed to changes in regional export productivity changes in ocean circulation or a combination of both processes a paleoproductivity reconstruction from biogenic ba data suggests that glacial productivity was considerable lower than it was during interglacial stages model results suggest that the oxygen penetration depth an indicator of sediment redox state changed less than 1 cm as a result of the change in productivity changes in oxygen penetration depth estimated from re and u removal depths are significantly larger suggesting that changes in ventilation are a more important control on sediment redox state overall trace metal results confirm the tight coupling between ocean circulation marine productivity and global change

barium accumulation in the arabian sea controls on barite preservation in marine sediments in this study a new sequential extraction technique is used to investigate the particulate barium ba phases in sediments from the arabian sea to determine the processes controlling ba accumulation in marine sediments the total solid phase ba concentration in arabian sea surface sediments increases with water depth from 200 ppm at 500 meters below sea surface mbss to 1000 ppm at 3000 mbss the sedimentary ba composition consists of three major fractions barite ba incorporated in aluminosilicates and ba associated with mn fe oxides accumulation of barite which is the most important ba fraction in sediments located below 2000 mbss increases gradually with water depth the ba al ratio of the terrigenous fraction varies significantly across the arabian basin as the result of differences in grain size and provenance of the terrigenous sediment ba associated with mn oxides is a relatively minor fraction compared with bulk ba concentrations and it only accumulates in well oxygenated sediments below the present day oxygen minimum zone the water depth dependent accumulation of barite in the arabian sea is not related to the continuous formation of barite in settling organic particles or ba scavenging by mn oxyhydroxides but is primarily controlled by differences in ba preservation upon deposition a good correlation between the barite saturation index and the barite accumulation rate in the upper 2000 m of the water column may indicate that the degree of barite saturation of the bottom water is the main environmental factor regulating the burial efficiency of barite organic matter degradation bioturbation diagenetic mn cycling and the crystallinity of the accumulating barite may play additional roles copyright 2001 elsevier science ltd

transuranic nuclides in two coastal marine sediments off peru the fluxes of plutonium isotopes as well as their depth profiles are similar for northern and southern hemispheric varved sediments taken off western american coasts the inventories are in excess of the values predicted for atmospheric fallout in these anoxic sediments there is a general increase in concentration from depths to the near surface these observations are explainable on the bases that anoxic deposits have a substantially higher retentivity of sedimented materials compared to that of their bioturbated oxic counterparts and that there are inputs of resuspended materials previously deposited in the marine environment the 241am distributions are explained by ingrowth from 241pu assuming a substantial input of the parent from the u s thermonuclear tests during the 1950 s and the immobilization of both pu and am in the deposits

a novel chemical method to quantify fish debris in marine sediments burial of fish bones which consist primarily of hydroxyapatite has been recognized as a mechanism to remove reactive phosphorus from the oceans in this study a new method is presented which differentiates p associated with biogenous apatite pfish from other p fractions the method consisting of a sequential chemical extraction with 2 m nh4cl has been successfully tested on standard materials it enables us for the first time to quantify fish debris in sediment records and to assess their importance for the marine phosphorus cycle the nh4cl extraction has been applied to sediment samples from the arabian sea preservation of fish debris is significantly higher in sediments located above 1 200 m water depth than it is for deeper sediments the distribution of pfish contents in surface sediments is predominantly governed by the extent of fish debris regeneration which is related to differences in water depth and sedimentation rates in addition a good correlation between high sedimentary pfish contents and low oxygen bottom water concentrations suggests that the presence of the intense oxygen minimum zone may account for the enhanced preservation of fish debris in continental slope sediments

authigenic molybdenum formation in marine sediments a link to pore water sulfide in the santa barbara basin pore water and sediment mo concentrations were measured in a suite of multicores collected at four sites along the northeastern flank of the santa barbara basin to examine the connection between authigenic mo formation and pore water sulfide concentration only at the deepest site 580 m where pore water sulfide concentrations rise to 0 1 mm right below the sediment water interface was there active authigenic mo formation at shallower sites 550 430 and 340 m where pore water sulfide concentrations were consistently 0 05 mm mo precipitation was not occurring at the time of sampling a sulfide concentration of 0 1 mm appears to be a threshold for the onset of mo fe s co precipitation a second threshold sulfide concentration of 100 mm is required for mo precipitation without fe possibly as mo s or as particle bound mo mass budgets for mo were constructed by combining pore water and sediment results for mo with analyses of sediment trap material from santa barbara basin as well as sediment accumulation rates derived from 210 pb the calculations show that most of the authigenic mo in the sediment at the deepest site is supplied by diffusion from overlying bottom waters there is however a non lithogenic particulate mo associated with sinking particles that contributes 15 to the total authigenic mo accumulation analysis of sediment trap samples and supernant brine solutions indicates the presence of non lithogenic particulate mo a large fraction of which is easily remobilized and perhaps associated with mn oxides our observations show that even with the very high flux of organic carbon reaching the sediment of santa barbara basin active formation of sedimentary authigenic mo requires a bottom water oxygen concentration below 3 mm however small but measurable rates of authigenic mo accumulation were observed at sites where bottom water oxygen ranged between 5 and 23 mm indicating that the formation of authigenic mo occurred in the recent past but not at the time of sampling copyright 2000 elsevier science ltd

vertical and horizontal extension of the oxygen minimum zone in the eastern south pacific ocean recent hydrographic measurements within the eastern south pacific 1999 2001 were combined with vertically high resolution data from the world ocean circulation experiment high resolution profiles and bottle casts from the world ocean database 2001 and the world ocean atlas 2001 in order to evaluate the vertical and horizontal extension of the oxygen minimum zone 600 m off peru between 5 and 13 s and to about 1000 km offshore its upper boundary is shallowest 150 m off peru shoaling towards the coast and extending well into the euphotic zone in some places offshore the thickness and meridional extent of the oxygen minimum zone decrease until it finally vanishes at 140 w between 2 and 8 s moving southward along the coast of south america the zonal extension of the oxygen minimum zone gradually diminishes from 3000 km 15 s to 1200 km 20 s and then to 25 km 30 s only a thin band is detected at 37 s off concepcion chile simultaneously the oxygen minimum zone s maximum thickness decreases from 300 m 20 s to less than 50 m south of 30 s the spatial distribution of ekman suction velocity and oxygen minimum zone thickness correlate well especially in the core off chile the eastern south pacific intermediate water mass introduces increased vertical stability into the upper water column complicating ventilation of the oxygen minimum zone from above in addition oxygen enriched antarctic intermediate water clashes with the oxygen minimum zone at around 30 s causing a pronounced sub surface oxygen front the new estimates of vertical and horizontal oxygen minimum zone distribution in the eastern south pacific complement the global quantification of naturally hypoxic continental margins by helly and levin 2004 global distribution of naturally occurring marine hypoxia on continental margins deep sea research i 51 1159 1168 and provide new baseline data useful for studies on the role of oxygen in the degradation of organic matter in the water column and the related implications for biogeochemical cycles coastal upwelling zones along the eastern pacific combine with general circulation to provide a mechanism that allows renewal of upper pacific deep water the most oxygen poor and oldest water mass of the world oceans

the origin and evolution of saline formation water lower cretaceous carbonates south central texas u s a abstract land l s and prezbindowski d r 1981 the origin and evolution of saline formation water lower cretaceous carbonates south central texas u s a in w back and r letolle guest editors symposium on geochemistry of groundwater 26th international geological congress j hydrol 54 51ndash 74 systematic chemical variation exists in formation water collected from a dip section through lower cretaceous rocks of south central texas chemical variation can be explained by an interactive water rock diagenetic model the cyclic lower cretaceous shelf carbonates of the edwards group dip into the gulf of mexico coast geosyncline and can be considered to a first approximation as part of a complex aquifer contained by paleozoic basement beneath and by relatively impermeable upper cretaceous clay and chalk above the hydrodynamic character of this carbonate system is strongly controlled by major fault systems major fault systems serve as pathways for vertical movement of basinal brines into the lower cretaceous section formation water movement in this sytem has strong upfault and updip components the parent na ca cl brine originates deep in the gulf of mexico basin at temperatures between 200 and 250 c by the reaction halite detrital plagioclase quartz water albite brine other dissolved components originate by reaction of the fluid with the sedimentary phases k feldspar calcite dolomite anhydrite celestite barite and fluorite significant quantities of pb zn and fe have been mobilized as well as the brine moves updip out of the overpressured deep gulf of mexico basin and encounters limestones of the stuart city reef trend the buried platform margin small amounts of galena precipitate in late fractures continuing to rise upfault and updip the brine becomes progressively diluted on encountering significant quantities of dolomite in the backreef facies the ca rich brine causes dedolomitization although thermochemical consideration suggests that small amounts of several authigenic phases should precipitate most have yet to be found minor amounts of several kinds of calcite spar are present however as the brine evolves by dilution and by cooling no systematic changes in any cation cl ratio occur except for regular updip gain in mg as a result of progressive dedolomitization the formation water highly diluted by meteoric water eventually discharges along faults as hot mineral water

chemical constraints and origins of four groups of gulf coast reservoir fluids pitzer s method for computing activity coefficients has been applied to reported fluid compositions in four groups of gulf coast reservoirs the mississippi and arkansas smackover formation the texas edwards group the texas frio formation and the louisiana miocene sequence the activity quotients in fluids from carbonate reservoirs imply a reaction relation between calcite and disordered dolomite in which ordering increases at higher temperatures this relationship indicates that an increasing mg ca molality ratio with decreasing temperature does not necessarily imply dolomite dissolution by an updip moving fluid instead it may reflect an approach to equilibrium between calcite and metastable dolomite activity quotients in fluids from clastic reservoirs imply a rea tion relation between chlorite illite potassium feldspar and quartz at temperatures above 100 c 212 f present fluid compositions in the smackover and the edwards appear to be related to the updip movement of louann brines from the gulf coast basin accompanied by dolomitization in particular bromide plots for the edwards fluids indicate simple dilution of louann brines with interstitial fluids similar plots for fluids from the smackover show the complicating effects of illite formation sylvite dissolution and halite recrystallization albitization may have occurred during fluid movement through clastics prior to entering the smackover and edwards present fluid compositions in the frio and miocene are apparently not related to louann brines the compositional data reflect the effects of halite dissolution the subsequent albitization of plagioclase and potassium feldspar and the dissolution of carbonates during secondary porosity formation

the evaporation path of seawater and the coprecipitation of br and k with halite brines and salt were sampled at the morton bahamas solar salt production facility on great inagua island in the bahamas the brines were analyzed by ion chromatography to define more precisely than heretofore the evaporation path of seawater to the end of the halite facies at inagua calcium carbonate begins to precipitate at a brine concentration factor of 1 8 times that of seawater gypsum begins to precipitate at a brine concentration of 3 8 times seawater and halite at a concentration factor of 10 6 three of the most concentrated brines from inagua 40 times seawater were evaporated further in the laboratory magnesium sulfate first precipitated at brine concentrations about 70 times those of seawater and potassium bearing phases began to precipitate for these brines at concentrations greater than 90 times those of seawater the distribution of coefficients of br and k between brines and halite were determined by combining analytical data for the inagua brines with measurements of the br and k content of halites from inagua and of halite which had precipitated from inagua brines during storage the observed average value of dbr is 0 032 in good agreement with some of the previous measurements the measured values of dk are highly variable 0 001 to 0 021 dk for halite precipitated early in the halite facies is in the vicinity of 0 015

processes controlling forms of phosphorus in surficial sediments from the eastern arabian sea impinged by varying bottom water oxygenation conditions abstract the surficial sediments from the upper continental slope of the eastern arabian sea impinged by the oxygen minimum zone omz 150 1200 m water depth show varying concentrations of the biogenic element phosphorus p 0 1 0 2 in the northern and southern areas even though total organic carbon concentrations are relatively constant toc 2 5 prakash babu et al 1999 to understand this discordance 17 surface sediment samples from shelf slope and deep sea of the eastern arabian sea were investigated using a five step sequential extraction scheme to delineate the process responsible for p enrichment in omz high fractions of organic phosphorus porg 10 26 biogenic phosphorus pbio 36 48 relatively low molar corg porg ratios 322 447 and corg preactive ratios close to redfield ratio in omz sediments of the se arabian sea suggest accumulation under high surface production and low residence time of labile forms of p due to high sedimentation rates despite higher productivity in surface waters low fractions of porg 8 13 less than deep sea sediments of the study area 12 13 pbio 25 33 relatively high molar corg porg ratios 341 508 and corg preactive ratios less than redfield ratio in omz sediments from the ne arabian sea may indicate a higher degree of regeneration and diagenetic transformation of labile forms of p to other phases authigenic phosphorus paut fraction varies by a factor of 2 8 in sediments from the omz when compared to well oxygenated deep sea sediments of the study area while the ptotal remains constant significant p transformation seems to occur in ne arabian sea which is suggested by high paut fraction 50 compared to low paut fraction 10 39 in the se arabian sea sediments supply rates of phosphorus variable rates of p dissolution under varying dissolved oxygen contents in the bottom waters and early diagenetic transformation of p within the sediments seem to influence p geochemistry in sediments overlain by the omz in the eastern arabian sea

pleistocene meteoric pore water in dated marine sediment cores off callao peru abstract during cruise so 147 of the german research vessel sonne a large decrease in salinity with depth was found in the pore water at a site about 10 sea miles off callao lima peru the origin of this freshening was investigated in a multidisciplinary approach using geochemical geochronological and isotope hydrological methods the methodology applied is a possible strategy to deal with anomalous pore water freshenings and if necessary to put them into the general framework of submarine groundwater discharge concentrations of the major and conservative elements e g na k cl b br decrease at the same ratios deuterium d and oxygen 18 18o data reveal the meteoric origin of the fresh water end member indicating a mixture of 30 seawater and 70 fresh water at a depth in sediment of about 10 m 210pb and 137cs sedimentation rates determined by gamma spectrometry range between 2 and 4 5 mm y for the last century whereas values derived from ams 14c for the last millennia give mean rates smaller than 1 mm y this indicates strongly varying sedimentation conditions nevertheless from the geochronological data it can be concluded that the origin of the fresh water end member is situated in sediments of pleistocene age literature data of the isotope signature of modern water in the nearby lima aquifer are clearly different from the calculated values for the fresh water end member in the pore waters on the basis of the isotopic altitude effect described in the literature the isotopic signature of the fresh pore water end member can be explained as rain water directly infiltrated into the lima aquifer in contrast this infiltration is negligible there under present day arid climatic conditions theoretical considerations on pore water advective and diffusive transport give further indications that the fresh pore water end member is entrapped paleowater of pleistocene origin the observed pore water freshening and the geochemical and geochronological data can be conclusively explained by diffusive mixing of seawater with meteoric water which infiltrated during the last sea level low stand and stayed entrapped during transgression and sedimentation

the march 11 2011 tohoku oki earthquake and cascading failure of the plate interface 1 a continuous back projection analysis using data recorded in north america between march 9 2011 and april 7 2011 is applied to the mw 9 0 2011 tohoku oki earthquake and the foreshocks and aftershocks of this event as with the mw 8 8 2010 maule chile earthquake back projection results of the mainshock show variations in rupture behavior when data filtered to different frequency ranges are used in particular there is a relationship between the frequency of data used and the position along the dip direction of the energy release with the highest frequency result imaging energy at the down dip edge of the rupture and progressively lower frequencies showing a continuous shift updip in addition these results show that late in the rupture 200 seconds after the hypocentral time energy at all frequencies is imaged very close to the trench at about 37 n which with the energy imaged near and updip of the epicenter may have acted as a tsunami source comparing the mainshock rupture area to the area that ruptured during m 6 foreshocks and aftershocks between march 9th and april 7th shows that total failure of the plate interface nearly doubled compared to the mainshock alone building upon the idea that the mainshock occurred through interactions between multiple segments the results imply that the total failure area of the interface may represent the area that can rupture during a single event as a series of in phase interface segments

frequency dependent energy radiation and fault coupling for the 2010 mw8 8 maule chile and 2011 mw9 0 tohoku japan earthquakes 1 we carried out back projections of teleseismic data filtered in different frequency bands for the 2010 maule chile and the 2011 tohoku japan earthquakes for the maule earthquake there were differences along strike of the fault with the high frequency energy mainly originating from an area 200 km northeast of the epicenter whereas low frequency energy came from a location closer to the epicenter the tohoku earthquake shows strong frequency dependence in the dip direction high frequency sources were located about 100 km west of the epicenter while low frequency sources were around epicenter near the japan trench we compare the spatial distributions of energy with estimates of seismic coupling before the earthquakes areas of high frequency radiation seem correlated with regions that were strongly coupled before the earthquakes areas of high coupling may be associated with fault properties that are more heterogeneous and or have overall higher stress producing higher frequency seismic waves

fish scales in sediments from off callao central peru abstract we study fish scales as a proxy of fish abundance and preservation biases together with phosphorus from fish remains p fish in a sediment core retrieved off callao peru 12 1 s 77 42 w water depth 179 m core length 52 cm we interpret our results as a function of changing redox conditions based on ratios of redox sensitive trace elements cu al mo al ni al zn al v al terrigenous indicators fe in clays ti al and biogenic proxies caco 3 biogenic opal total nitrogen organic carbon barite ba the core covers roughly 700 years of deposition based on 210 pb activities extrapolated downcore and 14 c dating at selected intervals our fish scale record is dominated by anchovy engraulis ringens scales followed by hake merluccius gayii scales the core presented an abrupt lithological change at 17 cm corresponding to the early 19th century above that depth it was laminated and was more organic rich 10 15 organic carbon than below where the core was partly laminated and less organic rich fish p total ratios were also observed within the upper 17 cm of the core the behavior of biogenic proxies and redox sensitive trace elements was similar more reduced conditions corresponded to higher contents of caco 3 c org total nitrogen and fish scales suggesting that these proxies might convey an important preservation signal

origin and evolution of formation waters from oil fields on the norwegian shelf abstract stable isotopes of h and o and chemical analyses of formation waters from upper triassic jurassic clastic reservoirs and cretaceous carbonate reservoirs offshore norway are employed to interpret the origin and evolution of these waters in both types of reservoir the formation waters become progressively enriched in total dissolved solids and the heavy isotope of o with increasing depth whereas deuterium varies erratically between 20 and 40 smow bromine analyses and stable isotope data indicate that the formation waters are mixtures of a brine end member formed by evaporation of sea water beyond the point of halite saturation and meteoric water the chemical and isotopic composition of the formation waters and general geological considerations suggest that the brines originated as connate waters in permian evaporites and were later expelled into overlying strata there is a disequilibrium stable isotope distribution between the bulk chalk formations and the formation waters and only minor diagenetic modification of the formation waters appears to have taken place in these reservoirs the formation waters from the clastic reservoirs on the other hand are modified by diagenetic reactions