uranium isotopic evidence for groundwater chemical evolution and flow patterns in the eastern snake river plain aquifer idaho the isotopic composition and concentration of uranium and strontium in groundwater combined with solute concentration data provide important details regarding groundwater geochemical evolution and flow pathways in the eastern snake river plain aquifer the study was conducted in the vicinity of the idaho national engineering and environmental laboratory ineel idaho which has a long history of storing and disposing of radioactive waste some of which has entered the aquifer uranium concentrations in ineel groundwater range from 0 3 to 3 6 ppb and 234 u 238 u atomic ratios range between 0 000085 and 0 000168 activity ratios of 1 5 to 3 1 all of the samples have natural 235 u 238 u ratios and 236 u was not detected thus the trends delineated by the 234 u 238 u ratios reflect natural variations in the aquifer groundwater nearest the valleys that provides focused recharge to the snake river plain aquifer from the northwest has high 234 u 238 u ratios when compared to values of regional groundwater flowing southwestward in the aquifer mixing of these water masses can account for the intermediate uranium isotope ratios of some of the samples however water rock interaction must also be invoked to account for the observed trends in isotopic data uranium and 87 sr 86 sr isotope ratios are positively correlated and define a trend toward isotope ratios of the aquifer host rock these relations indicate that dissolution and or ion exchange are more important than alpha recoil or selective leaching in controlling 234 u 238 u ratios as a result 234 u 238 u ratios decrease along flow pathways toward the secular equilibrium values of the aquifer host rock uranium and strontium isotopic modification can be explained by incongruent dissolution of the host basalt lateral distributions of 234 u 238 u ratios indicate elongate zones of high 234 u 238 u ratios extending southward from the mouths of birch creek and the little lost river these elongate zones are interpreted as preferential flow paths two isolated pockets of groundwater located in the central and western parts of the study area have lower 234 u 238 u ratios than the adjacent aquifer water both of these zones are interpreted to contain stagnant waters that are relatively isolated from flow in the regional aquifer due to lower permeability physical and chemical evidence strongly suggests that the stagnant zones are dominated by water from the big lost river that infiltrated via flood control ponds spreading areas playas and the riverbed

a kinematic model for deformation of the lithosphere at subduction zones a subduction model that interprets the whole pattern of topography and gravity anomalies across the island arc trench system has been constructed on the basis of dislocation theory we model the lithosphere asthenosphere system by a gravitating stratified half space which consists of an elastic surface layer an intervening layer with maxwell viscoelasticily and an elastic substratum the steady subduction of the oceanic plate beneath the continental plate is represented by uniform slip at a constant rate over the plate interface which divides the elastic viscoelastic half space into two blocks using the limiting value theorem of the laplace transform we can show that the steady slip on the interface deeper than the lithosphere asthenosphere boundary does not contribute to surface deformation in the steady state accordingly the pattern of surface deformation associated with the steady state subduction depends only on the thickness of the lithosphere and the geometry of the plate interface shallower than the lithosphere asthenosphere boundary numerical results show that the pattern of vertical motion at subduction zones is characterized by steep uplift on the continental side sharp subsidence at the plate boundary and gentle uplift on the oceanic side this pattern bears a striking resemblance to the general pattern of topography across island arc trench systems the whole pattern of topography and gravity anomalies across the southern kurile arc is well matched by the subduction model with a lithosphere thickness of 50 km and a dip angle of 30 at depths

late eocene to early miocene ice sheet dynamics and the global carbon cycle paired benthic foraminiferal trace metal and stable isotope records have been constructed from equatorial pacific ocean drilling program site 1218 the records include the two largest abrupt 1 myr increases in the cenozoic benthic oxygen isotope record oi 1 in the earliest oligocene 34 ma and mi 1 in the earliest miocene 23 ma the paired mg ca and oxygen isotope records are used to calculate seawater 18o w calculated w suggests that a large antarctic ice sheet formed during oi 1 and subsequently fluctuated throughout the oligocene on both short 0 5 myr and long 2 3 myr timescales between about 50 and 100 of its maximum earliest oligocene size the magnitudes of these fluctuations are consistent with estimates of sea level derived from sequence stratigraphy the transient expansion of the antarctic ice sheet at mi 1 is marked in the benthic 18o record by two positive excursions between 23 7 and 22 9 ma each with a duration of 200 300 kyr bottom water temperatures decreased by 2 c over the 150 kyr immediately prior to both rapid 18o excursions however the onset of each of these phases of ice growth is synchronous within the resolution of the records with the onset of a 2 c warming over 150 kyr we suggest that the warming during these glacial expansions reflect increased greenhouse forcing prompted by a sudden decrease in global chemical weathering rates as antarctic basement silicate rocks became blanketed by an ice sheet this represents a negative feedback process that might have operated during major abrupt growth phases of the antarctic ice sheet

spatial and temporal variation of geochemical properties and paleoceanographic implications in the south korea plateau east sea during the late quaternary geochemical opal total organic carbon toc and caco3 analyses of three sediment cores from the south korea plateau in the east sea japan sea revealed that the late quaternary 190 kyr bp to the present paleoceanographic conditions are characterized by the orbital variations of geochemical properties that have recorded the changes of surface and bottom water conditions chronostratigraphy of the sediment cores was accomplished by the direct correlation of l values to the well dated core md01 2407 in oki ridge supplement to the ams 14c dates well known lithostratigraphic and tephrostratigraphic markers biogenic opal concentrations are high during marine isotope stage mis 1 and mis 5 5 and low during the glacial period suggesting that diatom production was enhanced during the warm period when the surface water exchange between the east sea and adjacent marginal seas was active in contrast glacial opal paleoproductivity appears to have been depressed probably because of insufficient nutrient availability resulting from limited vertical ventilation overall toc contents follow the orbital variations high during the interglacial and relatively low during the glacial time however high resolution toc fluctuations are independent of opal concentration which may be attributed more to the preservation of organic matter rather than to the surface water production the high toc contents in the thin dark mud i e tl layers may be due to the enhanced surface water production as well as the intensified bottom water anoxia on the other hand high caco3 contents associated with the tl layers during the glacial and stadial period may be attributed to the reduced dissolution the temporal variations of these geochemical properties are likely to follow the global orbital cycles indicating the significant changes of surface and bottom water properties due to the eustatic sea level fluctuations between the interglacial and glacial period the comparable values of these geochemical properties among the sediment cores suggest that the spatial paleoceanographic conditions in the south korea plateau were consistent and uniform during the late quaternary in spite of a little local discrepancy in amounts of properties and timing of events

pacific ocean and cenozoic evolution of climate 1 the pacific ocean has played a major role in climate evolution throughout the cenozoic 65 0 ma it is a fundamental component of global heat transport and circulation the dominant locus of primary productivity and consequently the largest reservoir for carbon exchange between the oceans and the atmosphere a satisfactory understanding of the cenozoic evolutionary history of the pacific and its impact on global climate is currently data limited nevertheless the large dynamic range of cenozoic conditions sets the stage to greatly expand our understanding of global climate and biogeochemical cycles past earth experiments are particularly useful to understand interactions between climate and geosystems under different greenhouse gas loads we highlight in this review four important problems in which the pacific played a major role the effect of changing geographic boundary conditions on ocean circulation interactions between the carbon cycle and climate the pacific ocean s influence on north american climate and its water cycle and the gradual evolution of climate systems

rapid stepwise onset of antarctic glaciation and deeper calcite compensation in the pacific ocean the ocean depth at which the rate of calcium carbonate input from surface waters equals the rate of dissolution is termed the calcite compensation depth at present this depth is 4 500 m with some variation between and within ocean basins the calcite compensation depth is linked to ocean acidity which is in turn linked to atmospheric carbon dioxide concentrations and hence global climate1 geological records of changes in the calcite compensation depth show a prominent deepening of more than 1 km near the eocene oligocene boundary 34 million years ago 2 when significant permanent ice sheets first appeared on antarctica3 4 5 6 but the relationship between these two events is poorly understood here we present ocean sediment records of calcium carbonate content as well as carbon and oxygen isotopic compositions from the tropical pacific ocean that cover the eocene oligocene boundary we find that the deepening of the calcite compensation depth was more rapid than previously documented and occurred in two jumps of about 40 000 years each synchronous with the stepwise onset of antarctic ice sheet growth the glaciation was initiated after climatic preconditioning7 by an interval when the earth s orbit of the sun favoured cool summers the changes in oxygen isotope composition across the eocene oligocene boundary are too large to be explained by antarctic ice sheet growth alone and must therefore also indicate contemporaneous global cooling and or northern hemisphere glaciation

the eocene oligocene preglacial glacial transition in the atlantic sector of the southern ocean odp site 690 abstract high resolution interdisciplinary analyses of the clay and coarse 40 m fractions of odp leg 113 site 690 eocene oligocene sediments on the flank of the maud rise provide information on paleoproductivity water masses paleoclimate and erosion in the antarctic range as well as on the cyclicity of these processes three time intervals are distinguished 1 1 the middle eocene characterized by a nearly pure smectites b productivity varying between relatively high values in the 42 44 ma interval to very low values after 42 ma and c cyclic variations which correspond to changes in clay mineral associations a warm saline deep water mass is inferred to have protected carbonate shells against dissolution at site 690 we interpret the abundant mica in the coarse fraction as distributed by intermediate currents 2 2 the latest middle eocene late eocene characterized by low productivity values increasing with time kaolinite and illite concentrations also increase since the middle late eocene boundary mixing in the water column which starts during a cooling event causes similar clay mineral assemblages at site 690 and at site 689 on top of maud rise 3 3 the oligocene separated from the eocene by a hiatus is characterized by high productivity highly increased amounts of illite and other minerals originating from erosion and physical weathering of antarctica and by cyclic variations of clay mineral indices which appear to be synchronous with productivity variations with a 400 450 kyr cyclicity six periods of strong carbonate dissolution associated with low productivity levels are attributed to incursions of cold carbonate aggressive bottom water of a proto aabw type

paleogene deepwater mass composition of the tropical pacific and implications for thermohaline circulation in a greenhouse world 1 the pacific ocean likely exerted the greatest marine influence on climate during the greenhouse interval of the paleogene the first step toward assessing the role of pacific deepwater circulation in global heat transport is a comprehensive reconstruction of deepwater mass composition and circulation patterns we present new deepwater mass nd isotope data from odp leg 199 sites 1215 1217 1219 and 1221 to augment the existing coverage provided by ferromanganese crust and fossil fish debris data the new data corroborate the notion that the pacific ocean operated in a bimodal pattern with deepwater sources in both the southern ocean and north pacific for much of the early to middle paleogene in addition the data indicate that there was little to no influence of atlantic waters on the deepwater composition of the tropical pacific the available deepwater nd isotope data provide refined constraints on the geographic and depth range of influence of both a southern ocean and north pacific deepwater mass from 65 to 45 ma the deep tropical pacific was the mixing location of deep waters sourced from the southern ocean and the north pacific the southern ocean deepwater mass extended from 1800 m to abyssal depths until 53 6 ma it circulated northward in the western pacific at least as far as the paleolocation of fe mn crust cld01 5 n paleolatitude and in the eastern portion of the pacific as far as site 1215 10 n paleolatitude a north pacific deepwater mass extended from at least 2400 m to 2900 m water depth from 65 to 54 ma south to shatsky rise paleolatitude 10 15 n and possibly as far as site 1215 700 km to the south of shatsky rise sites 1209 and 1211

impact of antarctic circumpolar current development on late paleogene ocean structure global cooling and the development of continental scale antarctic glaciation occurred in the late middle eocene to early oligocene 38 to 28 million years ago accompanied by deep ocean reorganization attributed to gradual antarctic circumpolar current acc development our benthic foraminiferal stable isotope comparisons show that a large 13c offset developed between mid depth 600 meters and deep 1000 meters western north atlantic waters in the early oligocene indicating the development of intermediate depth 13c and o2 minima closely linked in the modern ocean to northward incursion of antarctic intermediate water at the same time the ocean s coldest waters became restricted to south of the acc probably forming a bottom ocean layer as in the modern ocean we show that the modern four layer ocean structure surface intermediate deep and bottom waters developed during the early oligocene as a consequence of the acc

seamount loading and stress in the ocean lithosphere 2 viscoelastic and elastic viscoelastic models analytical solutions are presented for the deformation and stress state of a horizontally stratified earth subject to normal loads of size and wavelength that are characteristic of seamounts the models investigated include layered elastic plates homogeneous viscoelastic plates and elastic over viscoelastic models in all cases the composite models overlie an inviscid half space the principal advantage of the laminated elastic models over homogeneous elastic plates is that they can result in a substantial reduction in the maximum stress differences in those parts of the plate least capable of supporting large stress differences authors

viscosity structure of the oceanic lithosphere inferred from the differential late quaternary sea level variations for the southern cook islands summary late quaternary sea level variations for the southern cook islands such as rarotonga and mangaia provide information on the time dependent crustal movement due to viscoelastic arching in response to loading by the pleistocene volcanic island of rarotonga the lithospheric responses to both external and internal loads have been investigated to estimate the viscosity of the lower part of the lithosphere and to examine the initial stage of swell formation detailed observations of sea level variations for the past 125 kyr indicate that the crustal uplift for mangaia is greater than 10 m while rarotonga was apparently stable for this period the following geophysical implications for the lithospheric rheology and loading model are derived from these observations the observed differential crustal movement implies that the viscous relaxation associated with this volcanic loading is still proceeding in the lithosphere the layer supporting stresses has therefore been migrating with time from weaker lower zones into the stronger upper zones for a lithosphere with a depth dependent viscosity structure this fact provides an important constraint on the viscosity of the lower part of lithosphere the observation that rarotonga has been apparently stable for this period is indicative of a local buoyant internal load in the upper mantle this load may be related to small scale and secondary convection in the asthenosphere surface uplift due to an internal load is therefore required to cancel the subsidence by volcanic loading this problem has been examined for two simplified background density models one is a model in which the density of the lithosphere is equal to that of the asthenosphere for this model very large mass anomalies which are 10 times larger than the external load are required beneath the lithosphere in order to explain the observed differential crustal movement of the islands for an earth model for which the density of the lithosphere is greater than that of the asthenosphere which is possible for mature oceanic lithosphere the observed differential crustal movement is explained for an internal load model with density anomalies of less than 20 kg m j the volume of the internal load is at most twice the volume of the external load a high viscosity layer with an effective viscosity of pa s and with a thickness of greater than 60 km is required beneath the top elastic layer with a thickness of 10 15 km the thickness of thermal lithosphere estimated by the plate age of this region is approximately 80 90 km regardless of the age thickness relationship adopted it is therefore suggested that the major part of the thermal lithosphere is composed of a viscoelastic layer with an effective viscosity of

response of deep sea benthic foraminifera to miocene paleoclimatic events dsdp site 289 abstract changes in the miocene deep sea benthic foraminifera at dsdp site 289 closely correlate to the climatically induced variations in deep and bottom waters in the pacific ocean in early miocene time oxygen and carbon isotopes indicate that bottom waters were relatively warm and poorly oxygenated benthic foraminiferal assemblages are characterized by various species inherited from the oligocene expansion of the antarctic icecap in the early middle miocene 14 16 m y ago increased oxygen isotope values produced cold more oxygenated bottom waters and lead to a turnover in the benthic foraminifera an oligocene early miocene assemblage was replaced by a cibicidoid dominated assemblage some species became extinct and benthic faunas became more bathymetrically restricted with the increased stratification of deep waters in the ocean in mid miocene time epistominella exigua and e umbonifera indicative of young oxygenated bottom waters are relatively common at dsdp site 289 further glacial expansion 5 9 m y ago lowered sealevel increased oceanic upwelling and associated biological productivity and intensified the oxygen minima abundant hispid and costate uvigerines become a dominant faunal element at shallow depths above 2500 m as e umbonifera becomes common to abundant below 2500 m by late miocene time benthic faunas similar in species composition and proportion to modern faunas on the ontong java plateau had become established

stress modeling in the andes constraints on the south american intraplate stress magnitudes regions of high topography which exhibit both compressional and extensional deformation provide a natural laboratory to place constraints on horizontal intraplate stress magnitudes an elastic finite element analysis of the lithospheric stress field in the cordillera bianca region of peru has been used to evaluate the lithospheric stress state and constrain the south american intraplate stress magnitudes the orthogonal orientation of the andean high topography to the east west regional stress field in conjunction with the well documented change in deformation style from compression to extension across the cordillera provides a unique setting for the stress modeling a two dimensional finite element grid consisting of an assembly of isotropic elastic quadrilateral elements in a state of plane strain was used to represent the lithosphere an isostatically balanced crustal density model was used to calculate the stresses associated with the lateral density variations between the andean topography and the brazilian shield in some models horizontal stress was concentrated at midcrustal depths by including vertical variation in young s modulus the modeling results indicate bounds of 10 and 75 mpa for the magnitude of the average horizontal stress averaged over a 100 km thick lithosphere a preferred value of 25 mpa is obtained on the basis of fitting all of the data for the rheological models considered and predicting a transition from extension to compression near the 3000 m elevation contour such a far field average stress is consistent with a ridge push origin because the modeling performed in this study assumes that the topographic load is entirely compensated by the buoyancy of the deflected moho these estimates represent upper bounds the effect of incorporating thermal support for the topographic load of the cordillera bianca would be to further reduce our estimate of the intraplate stress magnitudes analysis of the distribution of calculated stress with depth indicates that previous assumptions about the vertical plane shear stress within the lithosphere being negligible are acceptable for the geometry of the andes

lithospheric response to volcanic loading in the southern cook islands abstract the response of the ocean lithosphere to volcanic island loading has been investigated for the southern cook islands of rarotonga mangaia and the aitutaki mauke group using 1 estimates of the change with distance from the load of uplift of islands located on the flexure created arch 2 geoid height perturbations as observed with the geos 3 and seasat radar altimeters and 3 bathymetric evidence for the moat and arch about the island loads the effective flexural rigidity for rarotonga is found to be higher than for the older and nearby islands of mangaia and aitutaki this together with an earlier result for tahiti 1 suggests that stress relaxation of the lithosphere has occurred and that this layer behaves as a viscoelastic material with an effective viscosity of about 5 10 10 25 poise the observations for the flexural rigidity do not indicate any dependence on the age of the lithosphere at the time the loading occurred this suggests that there are no significant differences in lithospheric properties for plates in the age range of 6 7 10 7 years altimeter passes to the east of mauke indicate that there may be an uncharted submarine extension of the aitutaki mauke chain

cyclic crustal movement steady uplift of marine terraces and evolution of the island arc trench system in southwest japan summary in southwest japan where the philippine sea plate is descending beneath the eurasian plate at the nankai trough we can observe cyclic crustal movement related to the periodic occurrence of interplate earthquakes with the time interval of 102 yr steady uplift of the marine terraces formed by eustatic sea level changes for the last 105 yr and gradual evolution of the island arc trench system through the last 4 x 106 yr we demonstrate that these phenomena with very different characteristic time scales can be consistently explained by a single plate subduction model in our model the lithosphere asthenosphere system is represented by a stratified viscoelastic half space under gravity consisting of a high viscosity surface layer and a low viscosity substratum and interaction between oceanic and continental plates by steady slip motion over the whole plate boundary and its perturbation associated with the periodic occurrence of earthquakes the effects of accretion of oceanic sediments at plate boundaries erosion on land and sedimentation on inner trench walls are also considered in the model from comparison of theoretical results with observed data we obtained the following conclusions valid for young subduction zones observed deformation cycles cannot be explained by a simple rebound model in which the effect of steady plate subduction is ignored the steady plate subduction brings about steady uplift of marine terraces the present patterns of surface topography and gravity anomalies are held nearly stable by the balance of erosion sedimentation rates and substantial growth rates

modern deep sea benthic foraminifera a brief review of their morphology based biodiversity and trophic diversity most fossil deep sea foraminifera are multichambered and have relatively robust calcareous or agglutinated shells modern assemblages on the other hand include many fragile monothalamous single chambered forms and komokiaceans a superfamily of protist currently placed within the foraminifera with soft test walls these groups are poorly known and most of the hundreds of morphospecies recognized in deep sea samples are undescribed the relative abundance of robust and fragile taxa varies with water depth and food supply calcareous and other hard shelled species tend to predominate in relatively eutrophic areas particularly on continental margins but decrease as a proportion of the entire live fauna i e including soft shelled species with increasing water depth even above the ccd carbonate compensation depth most of the species on which the foraminiferal proxies used in palaeoceanography are based live in these bathyal regions at abyssal depths and particularly below the ccd faunas are largely agglutinated and dominated by monothalamous forms these assemblages have a much lower fossilization potential than those found on continental margins in addition to carbonate dissolution these patterns probably reflect adaptations to increasingly oligotrophic conditions on the ocean floor with increasing depth and distance from land bathyal species include herbivores and opportunistic deposit feeders omnivores that consume labile organic material in addition to deep infaunal deposit feeders and must contribute significantly to carbon cycling many abyssal monothalamous foraminifera in constrast accumulate stercomata waste pellets composed of fine sediment particles and probably ingest sediment associated bacteria and more refractory organic matter some monothalamous species without stercomata may be bacteriovores although they probably process organic carbon at a slower rate than calcareous species the shear abundance of monothalamous taxa at abyssal depths suggests that they are important in carbon cycling on a global scale the loss of a substantial proportion of foraminiferal biomass and biodiversity from the fossil record should be considered when using foraminifera to reconstruct palaeoproductivity for example by using the benthic foraminiferal accummulation rate bfar different dietary preferences among calcareous species have implications for the stable carbon isotope signal preserved in their shell

groundwater fast paths in the snake river plain aquifer radiogenic isotope ratios as natural groundwater tracers preferential flow paths are expected in many groundwater systems and must be located because they can greatly affect contaminant transport the fundamental characteristics of radiogenic isotope ratios in chemically evolving waters make them highly effective as preferential flow path indicators these ratios tend to be more easily interpreted than solute concentration data because their response to water rock interaction is less complex we demonstrate this approach with groundwater sup 87 sr sup 86 sr ratios in the snake river plain aquifer within and near the idaho national engineering and environmental laboratory these data reveal slow flow zones as lower sup 87 sr sup 86 sr areas created by prolonged interaction with the host basalts and a relatively fast flowing zone as a high sup 87 sr sup 86 sr area

the influence of microhabitats on the carbon isotopic composition of deep sea benthic foraminifera we report 13c and 18o values for rose bengal stained benthic foraminifera from a set of box cores from continental margin environments in the atlantic and pacific oceans these isotopic results are compared with foraminiferal distribution data and pore water 13c profiles to evaluate the importance of environmental microhabitat effects on the carbon isotopic composition of benthic foraminifera the 13c values of infaunal taxa are consistently lower than those of epifaunal taxa suggesting that microhabitat effects on test composition do exist the 13c differences between foraminiferal carbonate and bottom water dissolved inorganic carbon are not correlated with the 18o differences between benthic foraminifera tests and equilibrium calcite but they do correlate with variations in the chemistry of sediment pore waters however interspecific 18o differences as well as 13c differences between species with similar vertical distributions in the sediments indicate that taxon specific vital effects also influence test composition

behaviour of the oceanic lithosphere at subduction zones plastic yield strength from a finite element method abstract using the finite element method to study the deflection of the oceanic lithosphere at subduction zones shows that deflection of an elastic plastic model agrees with observed bathymetry data except for 2 examples kermadec and mariana where the lithospheric behaviour remains elastic seaward of the trench seven of the cases we studied could be easily fitted and enabled us to compute an effective yield strength the average value of which is about 3 8 to 4 8 kbar and seems to be the same in every case

late pleistocene crustal uplift and gravity anomaly in the eastern part of kyushu japan and its geophysical implications the miyazaki plain eastern part of kyushu japan is characterized by both significant negative gravity anomalies and aseismic crustal uplifting 1 mm year in the late pleistocene and holocene we examine the relationship between these two phenomena which may provide important constraints on the interaction between the collision and or subduction of the kyushu palau ridge and the forearc we estimate the mass deficiency below 11 km depth by using the gravity anomalies and p wave velocity structure of the upper crust the onset of the load accumulation 0 5 0 4 ma is inferred from the movement of the fluvial terraces considering the tephrochronology the loading history is assumed to be a linear function of time we evaluate the crustal rebound by assuming a viscoelastic plate deformation with an underplating load existing at 20 or 30 km depth the predicted crustal movement for models with a lithospheric crustal viscosity of 1023 1024 pa s can explain the observed altitudes of the shoreline of the marine terraces formed at the last interglacial of about 125 kyr bp and the middle holocene of 5 6 kyr bp although we cannot restrict the origin of the buoyant body the subduction of the kyushu palau ridge remnant arc associated with back arc opening of the shikoku basin may be related to the buoyancy for the uplifting region examined here on the other hand the buoyant body off the miyazaki plain probably plays an important role in the interaction between the subducting oceanic slab and the overriding forearc crust thus the observed lateral variation of the interplate coupling on the convergent boundary along the nankai trough may be attributed to the existence of the buoyant body

distribution biomass and diversity of benthic foraminifera in relation to sediment geochemistry in the arabian sea the distribution biomass and diversity of living rose bengal stained deep sea benthic foraminifera 30 mu m were investigated with multicorer samples from seven stations in the arabian sea during the intermonsoonal periods in march and in september october 1995 water depths of the stations ranged between 1916 and 4425 m the distribution of benthic foraminifera was compared with dissolved oxygen organic carbon calcium carbonate ammonium silica chloroplastic pigment equivalents sand content pore water content of the sediment and organic carbon flux to explain the foraminiferal patterns and depositional environments a total of six species communities comprising 178 living species were identified by principal component analysis the seasonal comparison shows that at the western stations foraminiferal abundance and biomass were higher during the spring intermonsoon than during the fall intermonsoon the regional comparison indicates a distinct gradient in abundance biomass and diversity from west to east and for biomass from north to south highest values are recorded in the western part of the arabian sea where the influence of coastal and offshore upwelling are responsible for high carbon fluxes estimated total biomass of living benthic foraminifera integrated for the upper 5 cm of the sediment ranged between 11 mg corg m 2 at the southern station and 420 mg corg m 2 at the western station foraminifera in the size range from 30 to 125 mu m the so called microforaminifera contributed between 20 and 65 to the abundance but only 3 to 28 to the biomass of the fauna highest values were found in the central and southern arabian sea indicating their importance in oligotrophic deep sea areas the overall abundance of benthic foraminifera is positively correlated with oxygen content and pore volume and partly with carbon content and chloroplastic pigment equivalents of the sediment the distributional patterns of the communities seem to be controlled by sand fraction dissolved oxygen calcium carbonate and organic carbon content of the sediment but the critical variables are of different significance for each community

some aspects of viscous stress relaxation and intraplate seismicity abstract considerable evidence suggests that the lithosphere has a maxwellian rheology with an effective viscosity of 1026 poise or less in a maxwellian lithosphere viscous stress dissipation limits the maximum attainable stresses due to mechanisms providing a constant stress buildup to a value max given by the product of stress buildup rate c and viscous relaxation time max c where is the ratio of viscosity to rigidity the effectiveness of several intraplate stress building mechanisms in a maxwellian lithosphere was analysed with the following results 1 1 the maximum stress produced by the latitudinal drift of lithospheric plates is 27 bars or less 2 2 the maximum stress produced by the cooling of uplifted eroded regions is 90 bars or less 3 3 lithospheric flexure due to isostatic rebound causes maximum stresses of 68 bars or less for the appalachian rebound and approximately 150 bars for the laurentide rebound it is concluded that none of the mechanisms considered are likely to cause earthquakes if the mechanical strength of the lithosphere is on the order of 1 kb if the strength of the lithosphere is on the order of 100 bars then intraplate earthquakes may result from the laurentide deglaciation as well as from the cooling of uplifted eroded regions but if the lithospheric viscosity is on the order of 1025 poise then only the laurentide deglaciation may produce adequate stresses the fact that a stress buildup rate of 74 bars 200 yrs along the san andreas fault generates earthquakes requires a minimum lithospheric viscosity on the order of 1022 poise

effects of the quaternary sea level change on the subsidence of a sedimentary basin a case study of the osaka bay sedimentary basin japan abstract surface load redistribution related to the quaternary ice age may play an important role on the formation of quaternary sedimentary basin the basin is in fact formed by tectonic processes but the quaternary sea level change may effect the subsequent evolution of the basin in particular the subsidence history thus the time dependent surface load and its concomitant sediment loading produce a maximum crustal subsidence of about 100 m if the following conditions are satisfied 1 maxwell relaxation time of relatively thin lithosphere is less than the period of the glacial and interglacial cycle of 10 5 yr and 2 sediments are sufficiently supplied into the deformed areas by the water loading crustal subsidence of 100 m corresponds to about 20 for the depression of osaka bay basin during the past 1 2 myr these two conditions seem to be satisfied in active island arcs with relatively weak lithosphere and osaka bay sedimentary basin formed in the quaternary is a suitable place to test this mechanism and or to examine its effect on the crustal subsidence related to the sedimentary basin

recent benthic foraminifera from the eastern south atlantic ocean dependence on food supply and water masses abstract sixty surface sediment samples from the eastern south atlantic ocean including the walvis ridge the angola and cape basins and the southwest african continental margin were analysed for their benthic foraminiferal content to unravel faunal distribution patterns and ecological preferences live stained with rose bengal and dead faunas were counted separately and then each grouped by q mode principal component analysis into seven principal faunal end members then multiple regression technique was used to correlate recent assemblages with available environmental variables and to finally differentiate between four principal groups of environmental agents acting upon the generation of benthic foraminiferal assemblages 1 seasonality of food supply and organic carbon flux rates together with oxygen content in the pore and bottom waters 2 lateral advection of deep water masses 3 bottom water carbonate corrosiveness and 4 energetic state at the benthic boundary layer and grain size composition of the substrate food supply and corresponding dissolved oxygen contents in the pore and bottom waters turned out to be the most important factors which control the distribution pattern of the recent benthic foraminifera at the continental margin in the zone of coastal upwelling and its mixing area benthic foraminiferal assemblages are dominated by stenobathic high productivity faunas characterized by elevated standing stocks low diversities and a large number of endobenthic living species at the continental shelf and upper continental slope the live assemblages are characterized by rectuvigerina cylindrica uvigerina peregrina s 1 uvigerina auberiana and rhizammina spp while the dead assemblages are characterized by cassidulina laevigata bolivina dilatata bulimina costata and b mexicana at the lower continental slope strong influence of high organic matter fluxes on the species composition is restricted to the area off the cunene river mouth where the live assemblage is dominated by uvigerina peregrina s 1 the corresponding dead assemblage by melonis barleeanum and m zaandamae in the adjacent areas of the lower continental slope the biocoenosis is characterized by reophax bilocularis and epistominella exigua which becomes dominant in the corresponding dead assemblage at the walvis ridge and in the abyssal angola and cape basins where organic matter fluxes are low and highly seasonal benthic foraminiferal assemblages reflect both the oligotrophic situation and the deep and bottom water mass configuration the top and flanks of the walvis ridge are inhabited by the rhizammina psammosphaera and r bilocularis live assemblages the corresponding dead assemblages are dominated by g subglobosa on the ridge top and e exigua on the flanks within the highly diverse e exigua dead assemblage several associated epibenthic species coincide with the core of nadw between about 1600 and 3700 m water depth these species include osangularia culter cibicidoides kullenbergi melonis pompilioides bolivinita pseudothalmanni and bulimina alazanensis the assemblages of the abyssal cape and angola basins are characterized by nuttallides umbonifer and a high proportion of agglutinated species these species are adapted to very low organic matter fluxes and a carbonate corrosive environment

effects of a viscoelastic lithosphere on the isostatic bedrock response abstract the lithosphere responds to loading by elastic flexure which is followed by viscous relaxation the amount of which depends on the stress duration this study compares results of an earth model in which the lithosphere is modelled as a purely elastic layer and as a more general viscoelastic solid overlain by a rigid crust it shows the emergence of a noticeable difference in the short wavelength 1 102 5 102 km component of the bedrock deformation after loading durations of the order of 105 106 yr assuming a lower lithosphere viscosity of the order of 1023 1024 pa s in particular for the long term loading hypothesised to be imposed by the east antarctic ice sheet we find that a viscoelastic lithosphere yields a more local deformation pattern to which ice sheet dynamics are highly sensitive it confirms that modelling of the antarctic long term evolution would benefit from a fully coupled ice bedrock approach in which the lithosphere would be represented by a viscoelastic solid

flexural response of the oceanic lithosphere at an arc arc junction implication for the subduction of aseismic ridges abstract the deformation of the oceanic lithosphere subducting at the junction of two trenches is studied by means of a three dimensional finite element analysis results show that the existence of a junction i e a change in trend of the trench axis yields a specific shape of the outer topographic rise in a convex junction area such as the japan and kuril trenches the topographic bulge presents a dome whereas in a concave junction area such as the java and sumatra trenches this bulge is less pronounced these theoretical results are confirmed by the bathymetry seaward of the junctions of the japan and kuril trenches and of the peru chile trench moreover the existence of the abnormal topographic dome in front of a convex junction contributes to the creation of normal faults which help the subduction of seamounts or of other bathymetric features in such areas

evolution of atlantic thermohaline circulation early oligocene onset of deep water production in the north atlantic the flow of deep water masses is a key component of heat transport in the modern climate system yet the role of deep ocean heat transport during periods of extreme warmth is poorly understood the present mode of meridional overturning circulation is characterized by deep water formation in both the north atlantic and the southern ocean however a different mode of meridional overturning circulation operated during the extreme greenhouse warmth of the early cenozoic during which time the southern ocean was the dominant region of deep water formation the combination of general global cooling and tectonic evolution of the atlantic basins over the past 55 m y ultimately led to the development of a mode of overturning circulation characterized by both southern ocean and north atlantic deep water sources the change in deep water circulation mode may in turn have affected global climate however unraveling the causes and consequences of this transition requires a better understanding of the timing of the transition new nd isotope data from the southeastern atlantic ocean indicate that the initial transition to a bipolar mode of deep water circulation occurred in the early oligocene ca 33 ma the likely cause of significant deep water production in the north atlantic was tectonic deepening of the sill separating the greenland norwegian sea from the north atlantic

late early oligocene deep sea benthic foraminifera and their faunal response to paleoceanographic changes in the eastern equatorial pacific abstract we documented new data on the late early oligocene benthic foraminifera and sediment geochemistry in the eastern equatorial pacific ocean eep from integrated ocean drilling program exp 320 site u1334 paleo water depth 3650 to 3850 m with some published data on those from ocean drilling program leg 199 sites 1218 3850 to 4000 m and 1219 4270 to 4370 m in order to understand the response of abyssal benthic foraminifera to paleoceanographic conditions during the interval 32 28 ma the relative abundances of nuttallides umbonifer were distinctly different between sites 1218 and 1219 during 31 0 to 29 9 ma although other major taxa e g globocassidulina subglobosa cibicidoides spp and oridorsalis umbonatus showed no marked changes the characteristics e g shannon wiener h of the benthic foraminiferal fauna are affected by the abundance of a few dominant species rather than by the change in the number of species in the eep based on multi dimensional scaling mds two mds axes were recognized mds axis 1 characteristic taxa n umbonifer and cibicidoides sp a and mds axis 2 characteristic taxa g subglobosa and bolivina huneri the tendency of both mds axes 1 and 2 showed a distinct depth gradient among the three sites after 28 6 ma whereas the tendency was different from 31 0 to 28 6 ma especially at site 1218 increased abundance of n umbonifer in the eep after 29 ma was similar to that in the atlantic ocean after the expanded distribution of this species to shallower depths was finished the faunal change at 28 6 ma might be related to the change of deep water circulation possibly with the influences of the southern component water scw and or northern component water in the south atlantic ocean in contrast the faunal change at 31 0 ma might be related to the formation of the scw and or meridional overturning circulation in the southern ocean in particular mds axis 1 exhibited the opposite tendency between sites 1218 and 1219 around the oi 2 event whereas the depth gradient was clearly observed among the sites around the oi 2 event the opposite tendency of mds axis 1 around the oi 2 event might be explained by the varying influences of the scw on different depths of the eep especially in terms of carbonate undersaturation the influence of the scw on benthic foraminifera in the eep was different among the depths of the three sites in the oi 2 event however the depth gradient of the scw influence was gradually intensified in the oi 2 event and the 28 6 28 0 ma interval

response of abyssal benthic foraminifera to mid oligocene glacial events in the eastern equatorial pacific ocean odp leg 199 abstract we investigated oligocene and early miocene benthic foraminiferal faunas 105 m in size from ocean drilling program leg 199 site 1218 4826 m water depth and 3300 to 4000 m paleo water depth and site 1219 5063 m water depth and 4200 to 4400 m paleo water depth to understand the response of abyssal benthic foraminifera to mid oligocene glacial events in the eastern equatorial pacific ocean two principal factor assemblages were recognized the factor 1 assemblage common nuttallides umbonifer is related to either an influx of the southern component water scw possibly carbonate undersaturated or a decrease in seasonality of the food supply from the surface ocean the factor 2 assemblage is characterized by typical deep sea taxa living under variable trophic conditions possibly with a seasonal component in food supply the occurrence of abyssal benthic foraminifera faunas during the mid oligocene depends on either the effect of scw or the seasonality of food resources the factor 1 assemblage was most common near 76ol c11r 73ol c10rn and 67ol c9n ca 30 2 29 1 and 26 8 ma respectively by palike et al 2006 this indicates that the effect of scw increased or the seasonal input of food from the surface ocean to benthic environments was weakened close to these glacial events in contrast the huge export flux of small biogenic carbonate particles close to these glacial events might be responsible for carbonate rich sediments buffering carbonate undersaturation changes in deep water masses or the periodicity of food supply from the surface ocean and variation in surface carbonate production affected by orbital forcing had an impact on the mid oligocene faunas of abyssal benthic foraminifera around the intervals of glacial events in the eastern equatorial pacific ocean the factor 1 assemblage decreased sharply at 30 ma 29 8 ma by palike et al 2006 30 0 ma by ck95 and returned to dominance after 29 ma 28 6 ma by palike et al 2006 28 8 ma by ck95 it is likely that the effect of scw possibly carbonate undersaturated has intensified since the late oligocene the faunal transition of benthic foraminifera in the eastern equatorial pacific ocean at 29 ma might be attributable to the influence of northern component water ncw input to the southern ocean and the subsequent formation of scw at about that time

constraints on yield strength in the oceanic lithosphere derived from observations of flexure summary the wavelength and amplitude of outer rises seaward of sub duction zones and arches surrounding islands and seamounts are used to parameterize flexure profiles in terms of the moment and curvature at the first zero crossing the data show the clear age dependence in the mechanical thickness of the lithosphere up to 60 100myr saturation of moment at large curvature is interpreted in terms of a depth dependent yield strength for the lithosphere using relations adopted from laboratory experiments of rock deformation a comparison of theoretical curves with observed moments indicates that old oceanic lithosphere has no long term strength below about 40 km depth with no difference between 100 and 165 myr old crust moderate axial loading forces 200 mpa can explain most variations in the moment curvature observations except in the case of the kuril trench which appears anomalous given the age of the crust regional tension causes greater variability in moment as compared to regional compression because of the greater slope in the brittle failure envelope under tension the observations point to a lithosphere weaker than the prediction from experimental deformation of rocks of the possible weakening mechanisms elevated pore fluid pressure on faults does not predict the correct age dependence and is incompatible with earthquake focal mechanisms our favoured explanation is that the activation energy q appropriate for ductile flow at geological strain rates is lower than the values derived from laboratory extrapolations of dry olivine data taken at high temperatures if recent oceanic geotherms are reliable q in the lower lithosphere must be lower than 100kcal mol 1 the method used here is most appropriate for trench profiles with curvatures greater than 10 7m 1 for lower curvatures such as along seamount profiles small errors in the curvature estimate cause large changes in rheological parameters

outer slope faulting associated with the western kuril and japan trenches summary elongated fault escarpments on the outer slopes of the western kuril and japan trenches have been investigated through detailed swath bathymetric mapping numerous horsts and grabens formed by these escarpments were identified distinct n70 e linear alignment of the escarpments parallel to the magnetic anomaly lineations was revealed on the outer slope of the western kuril trench in the japan trench north of 39 00aen most of the escarpments are parallel to the trench axis and oblique to the magnetic lineations a zig zag pattern of faulting exists south of 39 00aen each topographic profile was decomposed by computer analysis into two curves representing 1 the smoothed long wavelength slope of the subducting ocean crust surface and 2 the short wavelength 10 km roughness of plateaus and valleys edged by outwardand inward facing fault escarpments throughout the surveyed areas escarpment heights increase from the crest of the trench outer swell down to a depth of about 6000 m on the slope of the outer trench wall but with no distinct increase below that depth no significant diverence is recognized in fault throws towards and away from the trench it can be concluded that these elongated escarpments originate from normal faults on the upper layer of the oceanic crust under extensional stress in a direction perpendicular to the trench axis which is caused by downward bending of the subducting lithosphere the relationship of escarpment height to escarpment length is similar to that obtained from normal fault escarpments in the east pacific rise crest the maximum length and height of escarpments are small in the kuril trench compared with those in the japan trench implying a diverence in mechanical strength depending on the fault orientation the crust is weakest along the inherited spreading fabric second weakest probably along the non transform ovset direction and strongest in directions very oblique to these orientations seamounts appear to be more rigid than normal ocean crust with no particular weak orientations resulting in fewer but larger faults along the axis of plate bending as most clearly represented in the subducting daiichi kashima seamount

geochemistry and stratigraphic correlation of basalt lavas beneath the idaho chemical processing plant idaho national engineering laboratory thirty nine samples of basaltic core were collected from wells 121 and 123 located approximately 1 8 km apart north and south of the idaho chemical processing plant at the idaho national engineering laboratory samples were collected from depths ranging from 15 to 221 m below land surface for the purpose of establishing stratigraphic correlations between these two wells elemental analyses indicate that the basalts consist of three principal chemical types two of these types are each represented by a single basalt flow in each well the third chemical type is represented by many basalt flows and includes a broad range of chemical compositions that is distinguished from the other two types basalt flows within the third type were identified by hierarchical k cluster analysis of 14 representative elements fe ca k na sc co la ce sm eu yb hf ta and th cluster analyses indicate correlations of basalt flows between wells 121 and 123 at depths of approximately 38 40 m 125 128 m 131 137 m 149 158 m and 183 198 m probable correlations also are indicated for at least seven other depth intervals basalt flows in several depth intervals do not correlate on the basis of chemical compositions thus reflecting possible flow margins in the sequence between the wells multi element chemical data provide a useful method for determining stratigraphic correlations of basalt in the upper 1 2 km of the eastern snake river plain

global deep sea extinctions during the pleistocene ice ages the dark near freezing environment of the deep oceans is regarded as one of the most stable habitats on earth and this stability is generally reflected in the slow turnover rates extinctions and appearances of the organisms that live there by far the best fossil record of deep sea organisms is provided by the shells of benthic foraminifera protista a little known global extinction of deep sea benthic foraminifera occurred during the pleistocene ice ages in the southwest pacific it caused the disappearance of at least two families 15 genera and 48 species 15 25 of the fauna of dominantly uniserial elongate foraminifera with distinctive apertural modifications these forms progressively died back and became extinct during glacial periods in the late pliocene to middle pleistocene ca 2 5 0 6 ma most extinctions occurred between 1 0 and 0 6 ma at the time of the middle pleistocene climatic revolution this first high resolution study of this extinction event indicates that it was far more significant for deep sea diversity loss than previously reported 10 species the middle pleistocene extinction was the most dramatic last phase of a worldwide decline in the abundance of these elongate forms a phase that began during cooling near the eocene oligocene boundary and continued during the middle miocene clearly these taxa declined when the world cooled but the reason is yet to be resolved

mixing primitive and evolved olivine tholeiite magmas in the eastern snake river plain idaho abstract butte 5206 a small monogenetic olivine tholeiite basalt otb shield in the eastern snake river plain esrp erupted during late pleistocene time along the arco big southern butte volcanic rift zone geochemical data from butte 5206 and other basalts that erupted in the vicinity including correlated samples from coreholes are evaluated for possible mechanisms of magma evolution in the esrp thermodynamic and mass balance models demonstrate that the evolution of butte 5206 magmas reflect a two stage process 1 fractional crystallization of relatively primitive magma possibly at multiple crustal levels and 2 mixing of primitive and evolved liquids in a shallow reservoir prior to eruption application of this model to other basalts and local eruptive centers in the region suggest that similar processes are active during the petrogenesis of many esrp basalts and that the process of intrusion and mixing is cyclic throughout pleistocene to holocene time

the accuracy of some lithospheric bending parameters summary a procedure is described for iterative least squares inference of bending parameters from lithospheric deflection profiles the method is applied to several bathymetric profiles seaward of subduction zones and used to study the accuracy with which these parameters and related ones such as plate thickness and moment curvature relations can be determined the presence of typical bathymetric undulations particularly at wavelengths of the order of the flexural wavelength and greater prevents the inference of effective elastic thickness from single profile data to better than 12 km 2 mixing of elastic and inelastic model estimates of effective thickness further increases scatter it is found that the sensitivity of inferred bending moments on the outer trench wall to typical uncertainties of regional bathymetric slope is substantial and inferred estimates of inelastic behaviour need to be interpreted with caution

paleoproductivity from benthic foraminifera abundance glacial to postglacial change in the west equatorial pacific surface productivity is correlated with the rate of accumulation of benthic foraminifera on the deep sea floor as a rule of thumb for each 1 mg of organic carbon arriving at the sea floor one benthic foram shell 150 m is deposited the correlation can be used to reconstruct organic flux to the sea floor in the past and hence the productivity of past oceans applying the appropriate equations to box core data from the ontong java plateau in the western equatorial pacific we found that productivity during the last glacial maximum exceeded present productivity by a factor of between 1 5 and 2 0 with intermediate values for the mid transition period accumulation of benthic foraminifera was depressed on top of the plateau during the glacial and transitional period presumably because increased winnowing removed part of the food supply

evidence for deep water production in the north pacific ocean during the early cenozoic warm interval the deep ocean circulation is responsible for a significant component of global heat transport in the present mode of circulation deep waters form in the north atlantic and southern oceans where surface water becomes sufficiently cold and dense to sink polar temperatures during the warmest climatic interval of the cenozoic era approximately 65 to 40 million years myr ago were significantly warmer than today and this may have been a consequence of enhanced oceanic heat transport however understanding the relationship between deep ocean circulation and ancient climate is complicated by differences in oceanic gateways which affect where deep waters form and how they circulate here i report records of neodymium isotopes from two cores in the pacific ocean that indicate a shift in deep water production from the southern ocean to the north pacific approximately 65 myr ago the source of deep waters reverted back to the southern ocean 40 myr ago the relative timing of changes in the neodymium and oxygen isotope records indicates that changes in cenozoic deep water circulation patterns were the consequence not the cause of extreme cenozoic warmth

state of stress in the oceanic lithosphere in response to loading summary flexure studies of the oceanic lithosphere constrained by bathymetry and gravity data suggest that the lithosphere behaves elastically over geological time scales for loads to be supported however large bending stresses approaching 10 kb in some cases are required at the top and bottom of the elastic plate these stress differences can be significantly reduced by introducing more complex rheologies we propose a model of layered lithosphere consisting of a purely elastic upper layer a transition zone with viscosity varying with depth and a perfectly plastic lower layer the transition layer is grossly centred at the bottom of the elastic plate such a model results in a noticeable reduction of stress differences reaching 60 per cent for flow laws representing creep mechanisms in olivine when applied to a number of seamount loads this model leads to maximum stress differences which do not exceed 1 2kb the approach used in this study allows us to follow stress relaxation over time taking account of the thermal cooling of the lithosphere we show that the elastic thickness of the lithosphere is stabilized after a given time while the time required for stabilization is found to be of the order 5 6 per cent of the age of the lithosphere at the date of loading

benthic foraminiferal assemblages from the eastern weddell sea between 68 and 73 s distribution ecology and fossilization potential surface sediment samples taken with a vented box corer from the eastern weddell sea on four profiles perpendicular to the continental margin have been investigated for their benthic foraminiferal content the live fauna was differentiated from empty tests comprising the foraminiferal death assemblage based on the dead assemblages potential fossil assemblages were calculated to facilitate the analogy with late neogene core material five distinct live assemblages inhabit the continental margin today six dead assemblages and five potential fossil assemblages respectively correspond to these biocoenoses a predominantly calcareous live fauna dominated by trifarina angulosa is correlated with strong bottom currents and sandy sediments at the shelf break and on the uppermost continental slope below this on the upper slope down to 2000 m water depth the predominantly calcareous bulimina aculeata assemblage coincides with the core of warm 0 c weddell deep water and with fine and more organic rich sediments these calcareous live assemblages completely change composition during early diagenesis because of calcite dissolution within the uppermost sediment which depends largely on the grain size distribution of the sediment and the fluxes of organic matter therefore a still calcareous t angulosa dominated fossil assemblage indicates the sandy substrates on the shelf break and the upper slope whereas the deeper slope with hemipelagic calm sedimentation and with high fluxes of organic matter is indicated by martinottiella nodulosa the characteristic arenaceous fossil remnant of the former predominantly calcareous live b aculeata fauna on a continental terrace between 2500 and 3500 m water depth cribrostomoides subglobosus dominates the live fauna but because of rapid disintegration of the empty tests of this agglutinated species a predominantly calcareous fauna characterized by oridorsalis umbonatus and epistominella exigua comprises the dead assemblage and the potential fossil assemblage respectively on the lower continental slope between the carbonate lysocline 3500 m and the carbonate compensation depth 4000 m tests of nuttallides umbonifer are the characteristic dead and potential fossil remnants of a former predominantly arenaceous live fauna which is associated with the lower part of the antarctic bottom water aabw this corroborates earlier investigations suggesting a relationship between the carbonate corrosiveness of water masses and the distribution of n umbonifer this is important for inferring paleo routes and estimates of paleo production rates of aabw during the neogene

evolution of cenozoic seaways in the circum antarctic region abstract a complete circum antarctic seaway did not open until both the south tasman rise cleared the oates land coast of east antarctica and drake passage opened between the southern tip of south america and the northern end of the antarctic peninsula major plate motions based on dated seafloor spreading anomalies and distinct fracture zone lineations constrain the age of the opening of a seaway between the south tasman rise and antarctica as very close to the eocene oligocene boundary with an unrestricted opening deeper than 2000 m dating from 32 ma timing of the opening of drake passage is more circumstantial because the exact motions of certain micro continental fragments are not known the motion of africa with respect to south america as well as the motion of east antarctica with respect to africa are well constrained for the cenozoic these major plate motions are used with the reasonable assumption of no cenozoic motion of the antarctic peninsula with respect to east antarctica to constrain the location of the antarctic peninsula with respect to the southern tip of south america for the critical period of late eocene to late oligocene uncertainty of motion of the south georgia and south orkney microcontinents and other possible continental fragments make an exact time for opening of drake passage difficult to ascertain even so the early oligocene position of the antarctic peninsula with respect to south america requires a through going deep water seaway to have been open at drake passage prior to 28 ma even given the unconstrained motion of various high standing crustal fragments in the scotia sea with reasonable assumptions concerning motion of the crustal fragments in the western and central scotia sea it is likely that drake passage or passage through powell basin was open to deep water circulation by 31 2 ma

a unified interpretation of vertical movement in himalaya and horizontal deformation in tibet on the basis of elastic and viscoelastic dislocation theory abstract the present day convergence rate between the indian and the eurasian plates has been estimated to be about 50 mm year at the collision boundary extending along the himalayas about 40 of the total convergence is consumed by the subduction of the indian plate beneath the eurasian plate the rest of about 60 is consumed by the internal deformation of the eurasian plate the present crustal movement in this region is characterized by rapid uplift along the high himalayas and large scale horizontal deformation in and around tibet the fundamental causes of these two different types of crustal movement are the same interaction between the indian and the eurasian plates in this study we represent the plate interaction by steady increase in tangential displacement discontinuity dislocation across the interface that divides a surface layer overlying a viscoelastic half space into the indian and the eurasian plates first given a steady slip of 20 mm year at the plate interface with a ramp shaped undulation below the high himalayas we computed the profile of surface uplift rates along a line perpendicular to the himalayan arc the result accords with observed free air gravity anomalies and the intermediate and short term uplift rates estimated respectively from the present heights of river terraces and levelling data this means that the rapid uplift of the high himalayas is due to the steady slip along the ramp shaped plate interface below it second given the steady slips of 20 mm year along the 2000 km long collision boundary and 50 mm year along the remaining portions of the india eurasia plate boundary we computed the increase rates of horizontal deformation in and around tibet the result accords with the observed strikes and slip rates of major quaternary active faults this means that the horizontal deformation in and around tibet is due to the slip deficits of 30 mm year at the collision boundary from these two results we can conclude that the present rapid uplift of the high himalayas and large scale horizontal deformation in and around tibet are consistently explained by a single plate interaction model based on elastic and viscoelastic dislocation theory this study sheds new light on the driving mechanism of the crustal deformation in the india eurasia collision zone as follows the plate interaction on single plate interface consists of coexisting two different physical mechanisms 1 slip along the ramp undulation spatial changes in slip direction 2 slip deficit at the collision boundary spatial changes in slip rates as a consequence the two different types of crustal deformation in the india eurasia collision zone are driven by these two different physical mechanisms

stress and relaxation time in the viscoelastic lithosphere inferred from the outer topographic rise the deformation of a thin viscoelastic plate is usually analyzed by use of an equation that is derived with an artificial assumption of the poisson s ratio equal to 1 2 it is shown in this paper that a simple treatment applicable to an arbitrary value of poisson s ratio is possible by introducing a new variable that represents the pressure gradient between the top and bottom of the plate in this treatment a one dimensional stationary deformation of moving plate is given by a simple analytic equation this equation is used to analyze the bathymetry of the outer topographic rise seaward of the deep sea trenches the analysis reveals that the lithosphere in the western pacific trenches is subject to an extensional horizontal force of 100 mpa or greater the horizontal force may be much less or even compressive in the eastern pacific trenches to prevent horizontal force and bending stress from being extraordinarily large the maxwell relaxation time of the plate must be 1 m y or shorter and the effective viscosity must be 1024 pa s or less

deep sea benthic foraminiferal assemblage response to a surface ocean productivity gradient a test a transect of samples from the eastern equatorial pacific where surface ocean productivity is the only changing environmental variable was used to test the response of benthic foraminiferal assemblages to an open ocean productivity gradient the transect runs along the east pacific rise from the highly productive waters near the equator to the oligotrophic south pacific subtropical gyre surface sediment benthic assemblages show progressive change along the transect with strong compositional shifts corresponding to the rapid productivity gradient near the equator and to the position of the southern convergence near 18 19 s the relationship of the assemblages to surface ocean productivity was tested by statistical regression of quantitative estimates of productivity on the assemblage principal component scores calculated for each sampling location the regression yielded an r squared of 0 87 demonstrating a clear relationship between surface ocean productivity and deep sea benthic foraminiferal assemblage composition the species most important to this relationship display a consistent response to oceanic productivity for long stretches of geologic time this conservative behavior and the results of the regression analysis indicate that benthic foraminiferal assemblages can be used to estimate surface ocean productivity for the geologic past

oligocene climate dynamics a planktonic and benthic foraminiferal stable isotope stratigraphy of the oligocene equatorial pacific ocean drilling program site 1218 was generated at 6 kyr resolution between magnetochrons c9n and c11n 2n 26 4 30 ma on a newly developed astronomically calibrated timescale our data allow a detailed examination of oligocene paleoceanography the evolution of the early cryosphere and the influence of orbital forcing on glacioeustatic sea level variations spectral analysis reveals power and coherency for obliquity 40 kyr period and eccentricity 110 405 kyr orbital bands with an additional strong imprint of the eccentricity and 1 2 myr obliquity amplitude cycle driving ice sheet oscillations in the southern hemisphere planktonic and benthic foraminifera 18o are used to constrain the magnitude and timing of major fluctuations in ice volume and global sea level change glacial episodes related to obliquity and eccentricity variations occurred at 29 16 27 91 and 26 76 ma corresponding to glacioeustatic sea level fluctuations of 50 65 m alteration of high latitude temperatures and antarctic ice volume had a significant impact on the global carbon burial and equatorial productivity as cyclic variations are also recorded in the carbon isotope signal of planktonic and benthic foraminifera the water column carbon isotope gradient and estimated percent carbonate of bulk sediment we also investigate the implications of a close correspondence between oxygen and carbon isotope events and long term amplitude envelope extrema in astronomical calculations during the oligocene and develop a new naming scheme for stable isotope events on the basis of the 405 kyr eccentricity cycle count

geological and geochemical constraints on the genesis of the huachanggou gold deposit western qinling region central china the huachanggou gold deposit is located in lueyang county shaanxi province central china it is situated in the mian lue sutural zone in the western qinling orogen and controlled by a wnw striking ductile shear zone the ore deposit is developed in spilite limestone and phyllite in the middle lower devonian sanhekou group and the wall rocks show evidence of deformation pyrite is the main gold bearing mineral and the native gold is either visible or microscopic the huachanggou gold deposit is considered to be an orogenic gold deposit controlled by a ductile shear zone related to the indosinian qinling orogenic event the ores show a strong enrichment in au ag and as but exhibit a simple assemblage of au and ag that are strongly correlated together gold was deposited from a moderate to low salinity salt solution co2 hydrothermal fluid at medium temperature variations in s pb c and o isotopic composition indicate that the sulfur was derived from the reduction of seawater sulfate in the wall rocks the lead was derived mainly from the wall rocks the carbon was derived from the dissolution of marine carbonate the variations in h and o isotopic composition indicate that the ore forming fluids were derived originally from metamorphic fluid with meteoric water mixing in later stages au migrated mainly in the form of au hs 2 to form the deposit boiling of the fluid triggered the precipitation of the metal sulfides that contain the gold

hydrothermal alteration and ore forming fluids associated with gold tellurium mineralization in the dongping gold deposit china abstract the dongping gold deposit hosted in syenites is one of the largest hydrothermal gold deposits in china and composed of ore veins in the upper parts and altered zones in the lower parts of the ore bodies pervasive potassic alteration and silicification overprint the wall rocks of the ore deposit the alteration minerals include orthoclase microcline perthite quartz sericite epidote calcite hematite and pyrite with the quartz pyrite and hematite assemblages closely associated with gold mineralization the phases of hydrothermal alteration include i potassic alteration ii potassic alteration silicification iii silicification epidotization hematitization iv silicification sericitization pyritization and v carbonation mass balance calculations in potassic altered and silicified rocks reveal the gain of k2o na2o sio2 hfses and transition elements tes and the loss of rees most major elements were affected by intense mineral reactions and the ree patterns of the ore are consistent with those of the syenites gold silver and tellurium show positive correlation and close association with silicification fluid inclusion homogenization temperatures in quartz veins range from 154 c to 382 c peak at 275 c 325 c with salinities of 4 9 wt nacl equiv at temperatures of 325 c the fluid is estimated to have ph 3 70 5 86 log fo2 32 4 to 28 1 with au and te transported as au hs 2 and te22 complexes the ore forming fluids evolved from high ph and fo2 at moderate temperatures into moderate low ph low fo2 and low temperature conditions the fineness of the precipitated native gold and the contents of the oxide minerals e g magnetite and hematite decreased followed by precipitation of au and ag bearing tellurides the hydrothermal system was derived from an alkaline magma and the deposit is defined as an alkaline rock hosted hydrothermal gold deposit

new insights into the genesis of iocg deposits from a case study of the yinachang deposit in sw china abstract the yinachang fe cu au u ree deposit is hosted by the lower part of the paleoproterozoic kunyang group in the central yunnan province of sw china in an area known to contain iron oxide cu au mineralisation the deposit includes i the sulphide assemblage chalcopyrite pyrite magnetite cobaltite molybdenite cassiterite ii rare earth element assemblage bastnaesite parasite fergusonite xenotime monazite iii the uranyl hydroxide mineral vandendriesscheite iv gold commonly hosted by ankerite and v the gangue mineral assemblage apatite biotite fluorspar quartz calcite the ore is commonly massive disseminated banded or in calcite veins the banded mineralisation contains high concentration of au co mo u fe cu and ree and the vein type mineralisation has abundant ree minerals of bastnaesite parisite fergusonite and xenotime monazite exists as inclusions in apatite or as discrete grains on the surface of magnetite and the uranium is associated with chalcopyrite the mineralising process can be divided into an initial na alteration followed by the ore forming assemblages of fe ree and cu au u ree mineralisation the average 18oh2o values in the quartz and calcite change are between 3 5 and 10 7 with dv smow values ranging between 98 2 and 47 7 the calcite siderite and ankerite have 13c isotope composition ranges from 14 to 1 and 18o compositions of 6 9 to 22 the h o c isotope systematics indicate that the mineralising fluids have mixed magmatic and metamorphic sources whereas the carbon is sourced from marine carbonate and the low temperature alternation of polyphase mantle material in situ 34s sulphide value ranges between 1 1 and 11 9 and the bulk 34s value ranges between 4 7 and 10 5 in situ pb isotopes of sulphide samples have 206pb 204pb values of 18 58 18 76 207pb 204pb values of 15 51 15 66 and 208pb 204pb values of 37 47 38 06 these values plot in the upper crust pb evolution curve indicative of a complex source of pb in the deposit the pb is interpreted to have a deep seated magmatic source with a contribution from the crust it is also proposed that the ree mineralised fluids are derived from a late stage of alkaline magma differentiation the 40ar 39ar biotite date indicates that the precambrian rocks in the kangdian region were regionally metamorphosed at ca 900 ma the yinachang fe cu au u ree deposit is interpreted as an iocg deposit based on geological and isotopic studies the banded ore and vein type ore are the main exploration targets for uranium gold and ree this study helps us better understand iocg deposits in china

ocean overturning since the late cretaceous inferences from a new benthic foraminiferal isotope compilation 1 benthic foraminiferal oxygen isotopic d 18 o and carbon isotopic d 13 c trends constructed from compilations of data series from multiple ocean sites provide one of the primary means of reconstructing changes in the ocean interior these records are also widely used as a general climate indicator for comparison with local and more specific marine and terrestrial climate proxy records we present new benthic foraminiferal d 18 o and d 13 c compilations for individual ocean basins that provide a robust estimate of benthic foraminiferal stable isotopic variations to 80ma andtentatively to 110ma first order variations ininterbasinal isotopicgradients delineate transitions from interior ocean heterogeneity during the late cretaceous 65 ma to early paleogene 35 65 ma homogeneity and a return to heterogeneity in the late paleogene early neogene 35 0 ma we propose that these transitions reflect alterations in a first order characteristic of ocean circulation the ability of winds to make water in the deep ocean circulate we document the initiation of large interbasinal d 18 o gradients in the early oligocene and link the variations in interbasinal d 18 o gradients from the middle eocene to oligocene with the increasing influence of wind driven mixing due to the gradual tectonic opening of southern ocean passages and initiation and strengthening of the antarctic circumpolar current the role of wind driven upwelling possibly associated with a tethyan circumequatorial current in controlling late cretaceous interior ocean heterogeneity should be the subject of further research

benthic foraminiferal assemblages from the eastern south atlantic polar front region between 35 and 57 s distribution ecology and fossilization potential abstract surface sediment samples taken with a multiple corer from the polar front region along two profiles in the eastern south atlantic sector between 35 and 57 s have been investigated for their benthic foraminiferal content live fauna was differentiated from the death assemblage based on the dead assemblages potential fossil assemblages dead fauna reduced by non resistant agglutinants were calculated for comparison with upper neogene core material the distribution of the potential fossil assemblages defined byq mode principal component analysis mirrors the recent hydrographic as well as the trophic situation in the eastern south atlantic ocean circulation and productivity two southern component bottom water faunas reflect the northward flow of antarctic bottom water aabw and lower circum polar deep water lcdw an assemblage dominated by the arenaceousmultifidella nodulosa below the calcite compensation depth ccd and anuttallides umbonifer dominated assemblage above the ccd in the region of highest bio silicious primary productivity south of the polar front and north of the winter sea ice limit these faunas are overprinted by a southern high productivity fauna dominated by infaunal species such aspullenia bulloides melonis pompilioides andm zaandamae north atlantic deep water nadw meets the circum polar deep water cdw at intermediate depth as reflected in the distribution of the northern component deep water fauna dominated byepistominella exigua the high productivity assemblage overprinting this fauna the northern high productivity fauna is dominated by the shallow endobenthicbulimina aculeata a strong bottom current fauna dominated byangulogerina angulosa characterizes areas between 400 and 900 m water depth with sandy sediment independent from water mass characteristics and food supply

a kinematic model for evolution of island arc trench systems summary plate subduction zones are typically characterized by the patterns of surface topography and gravity anomalies consisting of island arc high trench low and outer rise gentle high these patterns are stable on the time scale of 106 107 yr at some subduction zones regardless of its age steady uplift of marine terraces formed by eustatic sea level changes during the last lo5 yr can be also observed the stable patterns of topography and gravity anomalies and the steady uplift of marine terraces seem to contradict each other we constructed a kinematic model which could explain the evolution process of island arc trench systems and demonstrated that this puzzle could be solved by considering the effect of accretion at plate boundaries in our model the lithosphere asthenosphere system is represented by a stratified visco elastic half space under gravity which consists of a high viscosity surface layer and a low viscosity substratum the rheological properties of both layers are assumed to be a maxwell fluid in shear and an elastic solid in bulk interaction between oceanic and continental plates is represented by the steady increase of discontinuity in tangential displacement across the plate boundary the other essential factors considered in our model are accretion of oceanic sediments at plate boundaries erosion on land and sedimentation on inner trench wall we computed the evolution process of island arc trench systems by using the kinematic model and obtained the following results the island arc trench systems grow at nearly constant rates in the early stage of plate subduction therefore at young subduction zones we can generally expect the steady uplift of marine terraces the stable patterns of topography and gravity anomalies are formed within several million years after the initiation of plate subduction when the accretion process continuously proceeds at plate boundaries these stable patterns gradually migrate seaward as a whole in such a case we can expect the steady uplift of marine terraces even at old subduction zones we demonstrate that our model can consistently explain the observed surface topography gravity anomalies and uplift rates of marine terraces at subduction zones

recent deep sea benthic foraminiferal distributions in the south china and sulu seas thirty nine surface sediment samples collected from the south china and sulu seas were examined to determine the bathymetric distribution of benthic foraminifera in these two basins and the factors responsible for these distributions the benthic foraminiferal faunas of both basins are highly diverse but have low absolute abundances benthic number and species diversity systematically decrease with increasing water depth four faunal assemblages were identified for each basin byq mode principal component analysis theglobocassidulina subglobosa uvigerina assemblage 1500 m and theuvigerina assemblage 1400 m represent the shallowest assemblages in the south china sea and sulu sea respectively and are found within the oxygen minimum zone of each basin where the sedimentary organic carbon content is highest and the pore water oxygen penetration depth zo is shallowest thebulimina aculeata assemblage occurs at water depths between 1700 and 2000 m in the southeastern south china sea and is also associated with relatively high sedimentary organic carbon content theastrononion pusillum assemblage is found in south china sea at the depths between 1500 and 3200 m below the lysocline 3200 m in the south china sea this assemblage is replaced by the agglutinatedrhabdammina abyssorum assemblage this assemblage reflects the presence of a water mass that is highly undersaturated with respect to calcite in the sulu sea thepyrgo murrhina assemblage occupies water depths from 1400 to 2200 m below 2200 m two deep water assemblages are present that are both dominated byoridorsalis umbonatus a correlation between various environmental and benthic foraminiferal variables indicates that salinity temperature sediment grain size water depth and bottom water oxygen concentration are not key factors controlling the benthic foraminiferal distribution in either the south china sea or the sulu sea rather organic carbon content and oxygen penetration depth in sediments appear to play important roles in determining the distribution of benthic foraminifera in both basins