valanginian isotope variation in glendonites and belemnites from arctic svalbard transient glacial temperatures during the cretaceous greenhouse oxygen and carbon isotope data from cretaceous valanginian glendonites and belemnites from arctic svalbard are presented oxygen isotope data from well preserved glendonites in conjunction with the ikaite to glendonite pseudomorph transition temperature are used to provide an estimate of the oxygen isotope composition of ambient seawater calculation of such a factor is essential for robust paleotemperature estimates using this methodology our paleotemperatures calculated from the oxygen isotope compositions of coexisting belemnites yield cool temperatures 4 7 c consistent with transient glacial polar conditions during the cretaceous greenhouse cool polar temperatures during the cretaceous help reconcile geologic data with the simulations of general circulation models nevertheless beyond this postulated and transient cool event within the valanginian the remainder of the isotope data are interpretable in terms of warm polar conditions during the cretaceous greenhouse

seismic anisotropy tracing plate dynamics in the mantle elastic anisotropy is present where the speed of a seismic wave depends on its direction in earth9s mantle elastic anisotropy is induced by minerals that are preferentially oriented in a directional flow or deformation earthquakes generate two seismic wave types compressional p and shear s waves whose coupling in anisotropic rocks leads to scattering birefringence and waves with hybrid polarizations this varied behavior is helping geophysicists explore rock textures within earth9s mantle and crust map present day upper mantle convection and study the formation of lithospheric plates and the accretion of continents in earth history

evidence from svalbard for near freezing temperatures and climate oscillations in the arctic during the paleocene and eocene until recently the arctic was assumed to be characterised by relatively warm conditions throughout the early cenozoic however recent investigations on deep sea drilling cores from northern high latitudes including the arctic ocean give apparently contradicting results here we report the intermittent occurrence of certain temperature indicators in the early tertiary sedimentary sequence on svalbard which may represent the first direct northern high latitude record of cold water temperatures for the early cenozoic glendonites calcite pseudomorphs after calcium carbonate hexahydrate and erratics in otherwise fine grained sediments require near freezing temperatures and the presence of at least seasonal sea ice this succession also contains coal seams and other warm climate indicators but not on the same stratigraphical levels these results imply the occurrence of cooling phases episodically during the warm background climate of the paleocene and eocene suggesting that arctic temperature variability was much greater than previously recognized

cenozoic biostratigraphy of the pogranichnyi region eastern sakhalin russia abstract diatom assemblages from the oligocene through late miocene siliceous and terrigenous formations of the pogranichnyi region of the east sakhalin basin are documented with particular attention given to the recognition of diatom zones from the oligocene and early miocene in the pilengskaya and borskaya formations improvements in the diatom biostratigraphic zonation scheme for the north pacific have made it possible to recognize oligocene rocks that may have previously been reported as unknown or as lower miocene deposits this paper is the first to more fully describe the evidence for more widespread oligocene and lower miocene siliceous deposits in the northwestern pacific than previously thought

glendonites and methane derived mg calcites in the sea of okhotsk eastern siberia implications of a venting related ikaite glendonite formation mg calcite cemented bioturbation traces glendonite aggregates of idiomorphic bi pyramidal crystals and porous amber colored carbonate concretions were recovered from a methane dominated cold vent area in 380 m water depth at the northern sakhalin slope sea of okhotsk bioturbation traces consist of mg calcite cemented sediment with 13c values between 37 and 46 peedee belemnite pdb which implicate methane as the carbon source glendonite a calcite pseudomorphosis after ikaite caco3 6h2o and amber colored concretions are both composed of varying amounts of calcite and mg calcite with 13c values between 19 and 34 pdb isotope analyses of an ikaite crystal recovered in the vicinity reveals 13c values between 20 and 22 pdb indicating organic matter as the carbon source microscopic investigations of glendonites and amber colored concretions show a porous fabric of a primary calcite phase that is overgrown by a secondary mg calcite cement as ikaite pseudomorphs to porous calcite and as carbon isotope values are the same for the ikaite and the high end member values of glendonite samples the primary calcite phase is suggested to be a former ikaite phase because they share the equal color fabric mineral and isotopic composition with glendonites the amber colored concretions are also suggested to represent calcite that transformed from ikaite a mixture of pseudomorph calcite 13c 20 pdb which originally formed as ikaite from degraded organic matter and mg calcite 13c 43 pdb which crystallized due to the anaerobic oxidation of methane can explain the varying carbon isotope data of the glendonites and the amber colored concretions the growth of ikaite the transformation of ikaite to calcite and the crystallization of mg calcite indicate changing geochemical conditions within a cold vent environment at different times ideal conditions for the ikaite formation are given during the establishment of a cold vent site when upward migrating methane rich fluids enhance the anaerobe decomposition of organic matter which again increases the phosphate and alkalinity concentrations near the sediment surface lower rates of organic matter decomposition during on going venting decrease these high phosphate but also sulphate concentrations and allows other carbonate phases as mg calcite to form this additional carbonate precipitation and the ikaite formation itself lower the high alkalinity and destabilize ikaite which pseudomorphs to porous calcite triggered by the further upward shifting so4 h2s boundary and increasing methane oxidation rates the typical cold vent methane derived carbonate genesis takes place which cements the sediment pore space and induces the secondary mg calcite crystallization within the glendonite fabric taking this scenario into account ikaite formation should be a common process in the beginning of methane dominated vent activity at cold bottom water temperatures glendonite pseudomorphs can be assumed to represent a typical manifestation at fossil and recent cold vents at high latitudes

a review and synthesis of glendonites pseudomorphs after ikaite with new data assessing applicability as recorders of ancient coldwater conditions abstract calcite pseudomorphs after ikaite glendonite are associated with coldwater depositional systems including glaciomarine and deepwater settings as dictated by the limited stability field of ikaite ikaite precipitation is favored by elevated alkalinity and dissolved phosphate conditions encountered commonly in association with organic rich marine sediments where methane oxidation is occurring the rapid recrystallization of ikaite to calcite during slight warming or pressure release results in considerable solid volume loss producing a highly porous crystal mesh preservation of the original ikaite crystal form requires precipitation of diagenetic calcite cement during early burial to prevent compaction and collapse of pseudomorph structures during later burial diagenesis remaining pore space may be filled with deeper burial calcite cement glendonites from the permian of the sydney basin occur in subtidal shelf facies containing glacial dropstones and a normal marine fauna stable oxygen isotope signatures of modern ikaite suggest carbonate precipitation in equilibrium with ambient seawater carbon signatures are usually strongly negative relative to normal marine carbonate consistent with derivation of carbonate from methane oxidation review of published data suggests that while holocene glendonite may provide reliable isotopic records of the conditions of ikaite precipitation precipitation of later calcite cement within the glendonite structure reduces the significance of the isotopic signature as an indicator of primary depositional conditions bulk glendonite samples from the permian sydney basin australia have a broad range of 18 o and 13c 18opdb 5 to 15 13c 8 to 16 in contrast to the narrow range for brachiopod carbonate 18opdb 1 to 5 13c 5 to 7 from the same strata handpicked separates of primary glendonite and secondary calcite also have a wide range of stable isotope values the data from sydney basin glendonites indicate that diagenetic precipitation of calcite has blurred the isotopic signature of primary ikaite replacement calcite at the scale of micosampling done in this study

extent of oceanic crust in the labrador sea1 this paper examines the mode of formation of the northern margins of the labrador sea observations of faulted and rotated crustal blocks across the northwest margin of greenland had led to the suggestion that this region is underlain by extended continental crust a detailed analysis of all geophysical data from this region presented here suggests on the contrary the possibility that it could have been formed by an excessively slow seafloor spreading process and ridge axis propagation this gave rise to rotated fault blocks at a time when spreading was mainly confined to the greenland side prior to its shift to the west supporting evidence for such a reconfiguration of the spreading axis comes from gravity and magnetic observations of this and neighbouring regions modelling of magnetic anomalies in the area based on the average rate of spreading for the entire labrador sea shows that a gradual shift of the ridge axis to the west started after the formation of anomaly 32 because the earliest seafloor spreading anomalies are highly attenuated in amplitudes other models like extended and intruded continental crust are possible if one only considers the magnetic anomalies however an extended continental crustal model poses problems in accounting for other geophysical observations based on a slow spreading model it is shown that oceanic crust extends fairly close to the foot of the slope with a narrow belt of extended continental crust along the west greenland margin while a much wider zone of perhaps attenuated continental crust extends off labrador breakup of the continental landmass occurred much closer to the west greenland coast than to labrador the applicability of a slow spreading model to other passive margins where similar geophysical observations have been reported is discussed

on using carbon and oxygen isotope data from glendonites as paleoenvironmental proxies a case study from the permian system of eastern australia abstract glendonites calcite pseudomorphs after ikaite caco3 6h2o feature prominently in fine grained glacially influenced permian marine strata of eastern australia which accumulated in a series of extensional basins that occupied polar to temperate latitudes along the southeastern margin of gondwana because ikaite formation in the marine environment requires near freezing temperatures high alkalinity and elevated concentrations of orthophosphate the presence of glendonites in ancient strata implies a particular array of paleoenvironmental conditions a petrographic and geochemical study was carried out to assess the veracity of isotopic data from glendonites as proxy indicators of ancient ocean chemistry sea floor temperature and diagenesis in thin section glendonites consist of inclusion zoned equant to bladed calcite crystals interpreted as the ikaite replacement phase enclosed in a matrix of calcite and minor chalcedony and pyrite cements carbon and oxygen isotope data show a negative covariance with 18o values ranging from 22 5 to 0 3 and 13c values from 27 7 to 4 5 v pdb of the calcite phases examined the ikaite replacement phase is the most enriched in 18o and most depleted in 13c enclosing cements possess lower 18o and higher 13c values and are interpreted to have formed during later stages of burial diagenesis the 18o values of the ikaite replacement phase do not correspond to formation with permian seawater at near freezing temperatures unless isotopic disequilibrium is assumed the 13c values are similar to the carbon isotope composition of bulk organic matter in the host sediment and suggest that the alkalinity and orthophosphate necessary for ikaite stability were generated in the zone of suboxic to anoxic diagenesis results indicate that although 18o and 13c values from glendonites are useful for understanding early to late diagenetic processes they are not ideal proxies for seawater chemistry and temperature

calcium carbonate as ikaite crystals in antarctic sea ice 1 we report on the discovery of the mineral ikaite caco3 6h2o in sea ice from the southern ocean the precipitation of caco3 during the freezing of seawater has previously been predicted from thermodynamic modelling indirect measurements and has been documented in artificial sea ice during laboratory experiments but has not been reported for natural sea ice it is assumed that caco3 formation in sea ice may be important for a sea ice driven carbon pump in ice covered oceanic waters without direct evidence of caco3 precipitation in sea ice its role in this and other processes has remained speculative the discovery of caco3 6h2o crystals in natural sea ice provides the necessary evidence for the evaluation of previous assumptions and lays the foundation for further studies to help elucidate the role of ikaite in the carbon cycle of the seasonally sea ice covered regions

ikaite abundance controlled by porewater phosphorus level potential links to dust and productivity abstractglendonites are pseudomorphs of the mineral ikaite caco3 6h2o after loss of hydration water and occur in distinctive euhedral crystalline forms sometimes clustered as rosettes of up to tens of centimeters in diameter while it is generally accepted that organic rich environments methane seeps and high phosphate levels are important for ikaite formation glendonite occurrences in ancient sedimentary sequences are widely considered to reflect near freezing temperatures even at high latitudes during periods of greenhouse climates to fully understand the paleoenvironmental significance of glendonites a comprehensive examination of the modern ikaite setting is necessary temperature is the most important parameter that has been quantitatively constrained for the presence of ikaite low bottom water temperature while a required condition for formation of the mineral is not adequate for its growth other controls are necessary to explain the absence of ikaite in many cold environments in this

global anisotropy in the upper mantle inferred from the regionalization of phase velocities a data set of 2600 paths for rayleigh waves and 2170 paths for love waves was selected in order to resolve azimuthal anisotropy of surface waves in the period range 70 250 s the epicenters were chosen so that the paths provide uniform spatial and azimuthal coverage of earth a synthetic seismogram is computed for each path and compared to the observed seismogram in order to infer the phase velocity along each path to process such a large data set a new tomographic technique is designed a good correlation is found with surface tectonics in the whole period range for love waves and at shorter periods for rayleigh waves the directions of maximum velocities are also well correlated with plate tectonics motions for the 2 azimuthal term of rayleigh waves when the power spectrum of heterogeneities is computed it is found that for love waves the even orders are usually larger than the odd orders for rayleigh waves the degrees 2 and 6 dominate only at long periods suggesting a deep origin for these components

high temperature elasticity of iron bearing olivines the first high temperature data on the nine adiabatic elastic moduli for iron bearing olivine are reported these measurements are on two single crystal specimens of natural olivine at ambient pressure and from room temperature to a maximum of 1500 k the two specimens contain 8 and 9 modal percent fayalite which required the oxygen fugacity be controlled at high temperature to preserve their chemical stability the rectangular parallelepiped resonance apparatus was adapted to buffer the specimens from the atmosphere with a mixture of co and co2 gas a small increase 1 2 gpa in the adiabatic bulk modulus of each specimen over that of end member forsterite was found the data are high quality to extreme temperatures with good agreement found when comparing the temperature derivatives of the elastic moduli of the two specimens neither specimen exhibits measurable nonlinear temperature dependence in the computed isotropic bulk and shear moduli which is in contrast to published forsterite data the temperature derivatives of the isotropic bulk modulus ks are 1 69 1 80 10 2 gpa k 1 for the two olivine specimens and the shear modulus g derivatives are 1 38 1 36 10 2 gpa k 1 these derivatives are only slightly larger in magnitude than ks t p 1 56 10 2 and g t p 1 30 10 2 gpa k 1 found previously for iron bearing olivine over a very small temperature range there are also no significant differences between the temperature derivatives found here and the average derivatives of end member forsterite from data retrieved over a slightly larger temperature range several dimensionless parameters have been calculated from these results and are discussed in view of systematics which bear on high pressure phases in earth s transition zone one result from these systematics related to the seismic velocities in the earth and especially the shear wave velocities is that an olivine content of less than 50 is implied at the 400 km discontinuity if earth s upper mantle is isochemical furthermore the substitution of almost 10 iron for magnesium at the forsterite end of the olivine solid solution series has little effect on the dimensionless parameters or on the temperature derivatives of the elastic moduli at high temperature

shear wave polarization anisotropy and subduction induced flow in the mantle wedge of northeastern japan abstract shear wave polarization anisotropy in the central part of northeastern ne japan was investigated we analyzed s phases of 293 intermediate depth earthquakes recorded at 77 stations and obtained 1286 splitting parameters the obtained results show the systematic variation in splitting parameters across the arc the leading shear wave polarization directions fast direction obtained at stations in the western side of the study area are oriented nearly e w which is sub parallel to the direction of relative plate motion between the pacific plate and the north american okhotsk plate in contrast fast directions obtained at stations in the eastern side of the study area are oriented approximately n s stations in the western side have a larger average delay time compared to those in the eastern side these variations suggest that the nature of anisotropy is quite different between the eastern and the western sides both experimental studies on the deformation of olivine and numerical simulations of plate driven flow predict that the lattice preferred orientation of olivine causes the fast direction sub parallel to the flow direction for the conditions in the mantle wedge of ne japan we thus infer that the lattice preferred orientation of olivine generated by flow induced strain is the most likely candidate for anisotropy that produces splitting with e w fast direction three possible causes of anisotropy in the eastern side are considered deformation of water rich olivine in the mantle wedge trench parallel flow in the mantle wedge due to along strike dip variations in the slab and anisotropy in the crust and the slab we could not however determine which causes are dominant further systematic study is required to reveal the cause of anisotropy in the eastern side

b type olivine fabric in the mantle wedge insights from high resolution non newtonian subduction zone models several hypotheses have been proposed to explain trench parallel shear wave splitting in the mantle wedge of subduction zones these include 3 d flow effects parallel melt filled cracks and b type olivine fabric we predict the distribution of btype and other fabrics with high resolution thermal and stress models of subduction zones a composite viscous rheology is used that incorporates wet diffusion creep wet dislocation creep and a stress limiting approximated peierls creep law rheological parameters for dislocation and diffusion creep are based on deformation experiments the effects of variable viscous coupling between the slab and mantle are explored using kinematic boundary conditions that change along the top of the slab two end member models are observed which depend on the depth of partial viscous coupling between the slab and mantle 1 deep partial coupling which gives rise to cold high stress conditions in the forearc mantle and high temperature low stress conditions in the arc and back arc mantle 2 full viscous coupling at the base of a 40 km conducting lid which is characterized by high temperature and low stress the case with deep partial coupling which produces a better match with attenuation tomography and heat flow shows a large region with suitable conditions for b type fabric in the forearc mantle and a rapid transition toward the back arc to conditions that are more suitable for a c or e type fabrics full viscous coupling gives rise to high temperature low stress conditions unsuitable for b type fabric our modeling predicts that the best candidates for regions with b type fabric are the forearc mantle and a cold 10 15 km layer above the slab d 2005 elsevier b v all rights reserved

regulation of algal blooms in antarctic shelf waters by the release of iron from melting sea ice during summer 1995 96 we measured iron in the water column and conducted iron enrichment bottle incubation experiments at a station in the central ross sea 76 30 s 170 40 w first in the presence of melting sea ice and 17 days later in ice free conditions we observed a striking temporal change in mixed layer dissolved iron concentrations at this station from 0 72 2 3 nm with sea ice present to 0 16 0 17 nm in ice free conditions these changes were accompanied by a significant drawdown in macronutrients and an approximate doubling of algal diatom biomass our incubation experiments suggest that conditions were iron replete in the presence of sea ice and iron deficient in the absence of sea ice we surmise that bioavailable iron was released into seawater from the melting sea ice stimulating phytoplankton production and the biological removal of dissolved iron from the mixed layer until iron limited conditions developed these observations suggest that the episodic release of bioavailable iron from melting sea ice is an important factor regulating phytoplankton production particularly ice edge blooms in seasonally ice covered antarctic waters

deformation fabrics of the cima di gagnone peridotite massif central alps switzerland evidence of deformation at low temperatures in the presence of water we report a new observation of the olivine b type lattice preferred orientation lpo from the garnet peridotite at cima di gagnone switzerland the olivine b type fabric forms at low temperatures and or high stress in the presence of water and is of particular interest because it may be used to explain the trench parallel shear wave splitting that is often observed at subduction zones in conjunction with the olivine b type fabric we have found strong orthopyroxene lpo that is identical to those formed under water free conditions this suggests that water may not have a significant effect on orthopyroxene fabric from the olivine microstruc ture we determine that a stress of 22 8 mpa was applied during the deformation event that formed the olivine lpo using an olivine flow law and assuming geological strain rates we determine the temperature of deformation to be 800 175c this does not preclude an ultra deep origin for the ultramafic rocks at cima di gagnone but indicates that much of the deformation recorded in the microstructure occurred at modest temperatures

dehydration breakdown of antigorite and the formation of b type olivine cpo abstract peridotite formed by contact metamorphism and dehydration breakdown of an antigorite schist from the happo area central japan shows a strong olivine crystallographic preferred orientation ol cpo the lack of mesoscale deformation structures associated with the intrusion and the lack of microstructural evidence for plastic deformation of neoblastic grains suggest that olivine cpo in this area did not form as a result of solid state deformation instead the good correspondence between the original antigorite orientation and the orientation of the newly formed olivine implies the cpo formed by topotactic growth of the olivine after antigorite ol cpo is likely to develop by a similar process in subduction zone environments where foliated serpentinite is dragged down to depths where antigorite is no longer stable the happo ol cpo has a strong a axis concentration perpendicular to the lineation and within the foliation commonly referred to as b type ol cpo seismic fast directions parallel to the ocean trench are observed in many convergent margins and are consistent with the presence of b type ol cpo in the mantle wedge of these regions experimental work has shown that b type cpo can form by dislocation creep under hydrous conditions at relatively high stresses there are however several discrepancies between the characteristics of natural and laboratory samples with b type ol cpo 1 the formation conditions stress and temperature of some natural examples with b type cpo fall outside those predicted by experiments 2 in deformation experiments slip in the crystallographic c axis direction is important but has not been observed in natural examples of b type cpo 3 experimental work suggests the presence of h2o and either high shear stress or relatively low temperatures are essential for the formation of b type cpo these conditions are most likely to be achieved close to subduction boundaries but these regions are also associated with serpentinization which prevents strong olivine cpo patterns from forming we show b type ol cpo can form as a result of static topotactic growth of olivine after high temperature breakdown of foliated serpentinite these results resolve the discrepancies between experimental and natural examples of b type cpo and show the need to rethink the formation process of olivine cpo in convergent margins topotactic growth of olivine after antigorite can account for the inferred distribution of b type ol cpo in the mantle wedge more successfully than dislocation creep

geochemistry of ikaite formation at mono lake california implications for the origin of tufa mounds the mineral ikaite caco 3 6h 2 o not previously observed in lake environments precipitates seasonally along the shore of mono lake california where ca hco 3 spring water mixes with cold na co 3 lake water during the winter cold water temperatures and high concentrations of po 4 3 and organic carbon inhibit calcite precipitation allowing the metastable ikaite to form during the spring warming however ikaite decomposes to form calcium carbonate and water occasionally leaving pseudomorphs of the primary precipitate the identification of modern ikaite suggests that both pleistocene and holocene tufas in the mono basin originally precipitated as ikaite this mineral may also form in other lake environments but rapid recrystallization after warming destroys the physical chemical and isotopic evidence of formation and alters the geochemical record

constraints on subduction geodynamics from seismic anisotropy 1 much progress has been made over the past several decades in delineating the structure of subducting slabs but several key aspects of their dynamics remain poorly constrained major unsolved problems in subduction geodynamics include those related to mantle wedge viscosity and rheology slab hydration and dehydration mechanical coupling between slabs and the ambient mantle the geometry of mantle flow above and beneath slabs and the interactions between slabs and deep discontinuities such as the core mantle boundary observations of seismic anisotropy can provide relatively direct constraints on mantle dynamics because of the link between deformation and the resulting anisotropy when mantle rocks are deformed a preferred orientation of individual mineral crystals or materials such as partial melt often develops resulting in the directional dependence of seismic wave speeds measurements of seismic anisotropy thus represent a powerful tool for probing mantle dynamics in subduction systems here i review the observational constraints on seismic anisotropy in subduction zones and discuss how seismic data can place constraints on wedge slab and sub slab anisotropy i also discuss constraints from mineral physics investigations and geodynamical modeling studies and how they inform our interpretation of observations i evaluate different models in light of constraints from seismology geodynamics and mineral physics finally i discuss some of the major unsolved problems related to the dynamics of subduction systems and how ongoing and future work on the characterization and interpretation of seismic anisotropy can lead to progress particularly in frontier areas such as understanding slab dynamics in the deep mantle

control of sulfate pore water profiles by sedimentary events and the significance of anaerobic oxidation of methane for the burial of sulfur in marine sediments abstract gravity driven mass flow deposits proven by sedimentary and digital echosounder data are indicative for prevailing dynamic sedimentary conditions along the continental margin of the western argentine basin in this study we present geochemical data from a total of 23 gravity cores pore water so 4 is generally depleted within a few meters below the sediment surface by anaerobic oxidation of methane aom the different shapes of so 4 profiles concave kink and s type can be consistently explained by sedimentary slides possibly in combination with changes in the ch 4 flux from below thus mostly representing transient pore water conditions since slides may keep their original sedimentary signature a combined analysis and numerical modeling of geochemical physical properties and hydro acoustic data could be applied in order to reconstruct the sedimentary history we present first order estimates of the dating of sedimentary events for an area where conventional stratigraphic methods failed to this day the results of the investigated sites suggest that present day conditions are the result of events that occurred decades to thousands of years ago and promote a persisting mass transport from the shelf into the deep sea depositing high amounts of reactive compounds the high abundance of reactive iron phases in this region maintains low hydrogen sulfide levels in the sediments by a nearly quantitative precipitation of all reduced sulfate by aom for the total region we estimate a so 4 or ch 4 flux of 6 6 10 10 moles per year into the zone of aom projected to the global continental slope and rise area this may sum up to about 2 6 10 12 moles per year provided that the sulfur is completely fixed in the sediments it is about twice the global value of the recent global sulfur burial in marine sediments of 1 2 10 12 moles per year as previously estimated thus aom obviously contributes very significantly to the regulation of global sulfur reservoirs which is hitherto not sufficiently recognized this finding may have implications for global geochemical models as sulfur burial is an important control factor in the development of atmospheric oxygen levels over time

fluid flow methane fluxes carbonate precipitation and biogeochemical turnover in gas hydrate bearing sediments at hydrate ridge cascadia margin numerical modeling and mass balances a numerical model was applied to investigate and to quantify biogeochemical processes and methane turnover in gas hydrate bearing surface sediments from a cold vent site situated at hydrate ridge an accretionary structure located in the cascadia margin subduction zone steady state simulations were carried out to obtain a comprehensive overview on the activity in these sediments which are covered with bacterial mats and are affected by strong fluid flow from below the model results underline the dominance of advective fluid flow that forces a large inflow of methane from below 869 mumol cm 2 a 1 inducing high oxidation rates in the surface layers anaerobic methane oxidation is the major process proceeding at a depth integrated rate of 870 mumol cm 2 a 1 a significant fraction 14 of bicarbonate produced by anaerobic methane oxidation is removed from the fluids by precipitation of authigenic aragonite and calcite the total rate of carbonate precipitation 120 mumol cm 2 a 1 allows for the build up of a massive carbonate layer with a thickness of i m over a period of 20 000 years aragonite is the major carbonate mineral formed by anaerobic methane oxidation if the flow velocity of methane charge fluids is high enough greater than or equal to10 cm a 1 to maintain super saturation with respect to this highly soluble carbonate phase it precipitates much faster within the studied surface sediments than previously observed in abiotic laboratory experiments suggesting microbial catalysis the investigated station is characterized by high carbon and oxygen turnover rates approximate to1000 mumol cm 2 a 1 that are well beyond the rates observed at other continental slope sites not affected by fluid venting this underlines the strong impact of fluid venting on the benthic system even though the flow velocity of 10 cm a 1 derived by the model is relative low compared to fluid flow rates found at other cold vent sites non steady state simulations using measured fluid flow velocities as forcing demonstrate a rapid respond of the sediments within a few days to changes in advective flow moreover they reveal that efficient methane oxidation in these sediments prevents methane outflow into the bottom water over a wide range of fluid flow velocities 80 cm a 1 only at flow rates exceeding approximately 100 cm a 1 does dissolved methane break through the sediment surface to induce large fluxes of up to 5000 mumol ch4 cm 2 a 1 into the overlying bottom water

trench parallel flow beneath the nazca plate from seismic anisotropy shear wave splitting of s and sks phases reveals the anisotropy and strain field of the mantle beneath the subducting nazca plate cocos plate and the caribbean region these observations can be used to test models of mantle flow two dimensional entrained mantle flow beneath the subducting nazca slab is not consistent with the data rather there is evidence for horizontal trench parallel flow in the mantle beneath the nazca plate along much of the andean subduction zone trench parallel flow is attributale utable to retrograde motion of the slab the decoupling of the slab and underlying mantle and a partial barrier to flow at depth resulting in lateral mantle flow beneath the slab such flow facilitates the transfer of material from the shrinking mantle reservoir beneath the pacific basin to the growing mantle reservoir beneath the atlantic basin trenchparallel flow may explain the eastward motions of the caribbean and scotia sea plates the anomalously shallow bathymetry of the eastern nazca plate the long wavelength geoid high over western south america and it may contribute to the high elevation and intense deformation of the central andes

dynamics of gas hydrate case of the congo continental slope a numerical model is developed to study the temperature effect on stability and phase transformation of gas hydrate the model uses a mathematical formulation based on the enthalpy form of the conservation law of energy the use of the enthalpy form instead of the temperature form as often done in the literature has made the problem numerically simpler the model is then applied to describe the effect of sea bottom temperature variations on the stability of gas hydrate occurrences and on the seafloor reflectivity in sediments of the congo continental slope indeed a migrating seafloor reflectivity front is observed on 3d seimic images from two surveys performed 6 months apart and interpreted as a migrating gas hydrate stability zone seawater temperature variations were recorded over a 230 day period at the seafloor the amplitude of these variations could explain a 75 m shift in water depth of the upper limit of the gas hydrate stability zone however the response of the sediment to a perturbation applied at the seafloor is not immediate because of the effects of thermal diffusion and of latent heat of hydrate dissociation thermal modelling shows that the depth of penetration of these perturbations is around 2 m for the saturated sediment and around 6 m for hydrate bearing sediments hydrate fraction of 0 1 the switch between gas and gas hydrate generated by these temperature fluctuations concern only the first meter of sediment these appear too small to explain the migration of the seafloor reflectivity considering that the wavelength of the seismic signal is significantly larger around 10 m however for temperature fluctuations with larger wavelength the switch between gas and gas hydrate will be more important and consequently could explain the reflectivity contrast as a possible migrating gas or gas hydrate front

mantle flow at a slab edge seismic anisotropy in the kamchatka region the junction of the aleutian island and the kamchatka peninsula defines a sharp turn in the boundary of the pacific and north american plates terminating the subduction zones of the northwest pacific the regional pattern of shear wave birefringence near the junction indicates that trench parallel strain follows the seismogenic benioff zone but rotates to trench normal beyond the slab edge asthenospheric mantle is inferred to flow around and beneath the disrupted slab edge and may influence the shallowing dip of the benioff zone at the aleutian junction

the marine phosphorus cycle phosphorus introduced to the ocean must ultimately be removed if a steady state is to be maintained over geologic time aeolian input is insignificant and there is evidently no hydrothermal contribution rivers dominate p input to the ocean the fluvial p flux is poorly quantified due to the interactions of two factors 1 man s influence on river nutrient fluxes and 2 inherent complexities in understanding the biological and inorganic associations of p in estuarine and coastal waters our best estimate of the natural or pre man p input flux is about 10 x 10 sup 9 moles p cm sup 2 ocean surface year of the identified flux of phosphorus to the sediments about 90 percent is in the form of biogenic debris or its regeneration products the burial of phosphatic fish debris is negligible p removal by direct reaction of phosphate in seawater with sea floor basalts during mid ocean ridge hydrothermal circulation is insignificant p removal by processes such as sorption on clay surfaces or formation of authigenic fe and al phosphate phases is presently unquantified and remains a serious uncertainty in the phosphorus cycle the identified sources and sinks approximately balance yielding a residence time for p in the oceans of about 10 sup 5 yrs

cold climate in the eastern australian mid to late permian may reflect cold upwelling waters a suite of ice rafted dropstones and glendonites throughout the permian succession of eastern australia indicates the cold climate associated with the late paleozoic ice age persisted longest in this part of gondwana paradoxically these cold climate indicators are preserved in transgressive and highstand facies and formed at mid to high latitudes at a time when paleofloral and sedimentological data suggest equable onshore environments during the intervening lowstands and temperate conditions at the pole these apparent inconsistencies suggest that eastern australia was anomalously cold in the context of post sakmarian gondwanan climates and the distribution of sedimentary indicators could indicate localized cooling by oceanographic processes modern upwelling of cold abyssal waters produces the specific physiochemical conditions necessary for ikaite for mation and is likely to have contributed to the development of glendonites in the eastern australian permian system such upwelling would have locally lowered surface water temperatures such that seasonal sea or river ice could form which rafted debris across the marine shelf and a cold water fauna could develop this hypothesis is supported by coupled atmosphere ocean models for the permian which suggest that wind systems may have driven upwelling along this section of the gondwanan coast colder conditions dissipated with the onset of the hunter bowen contractional event and the transformation of the basin system from an open marine shelf to a foreland basin this new hypothesis reconciles the prolonged deposition of cold climate indicators in the eastern australian permian with an apparent post sakmarian warming elsewhere in gondwana

an olivine fabric database an overview of upper mantle fabrics and seismic anisotropy we present a unique database of 110 olivine petrofabrics and their calculated seismic properties the samples come from a variety of the upper mantle geodynamic environments ophiolites subduction zones and kimberlites with a wide range of micro structures a phenomenological relationship is established between p and s wave seismic anisotropy and the degree of crystal alignment fabric strength seismic anisotropy increases rapidly at low fabric strength before reaching a near saturation level of 15 to 20 for p waves and 10 to 15 for s waves despite a large variation in the symmetry of fabric patterns the average seismic properties of the different fabric micro structural and geodynamic settings have similar anisotropies in both magnitude and symmetry hence it would seem possible to determine some measure of fabric strength from seismic anisotropy if the dimensions of the anisotropic region are known but not geodynamic environment or details of the petrofabric pattern a simple pattern of seismic anisotropy characterises the average sample of the database which has the following features the polarisation plane of the fastest s wave is parallel or sub parallel to the foliation plane the maximum shear wave splitting is parallel to the y structural direction in foliation plane and normal to the lineation the maximum of the p wave velocity is parallel to the high concentration of 100 axes which is sub parallel to the lineation the 100 orientation distribution has the greatest influence on the p wave seismic anisotropy the 100 and 001 orientation distributions have the greatest influence on the symmetry of s wave anisotropy although the magnitude of anisotropy is influenced by the distribution of all three principal axes although the database only contains olivine petrofabrics this statistical study clearly shows that seismic anisotropy can be used to deduce the orientation of the structural frame in the upper mantle 1998 elsevier science b v all rights reserved

natural examples of olivine lattice preferred orientation patterns with a flow normal a axis maximum tectonic plate motion is thought to cause solid state plastic flow within the underlying upper mantle and accordingly lead to the development of a lattice preferred orientation of the constituent olivine crystals the mechanical anisotropy that results from such preferred orientation typically produces a direction of maximum seismic wave velocity parallel to the plate motion direction this has been explained by the existence of an olivine preferred orientation with an a axis maximum parallel to the induced mantle flow direction in subduction zones however the olivine a axes have been inferred to be arranged roughly perpendicular to plate motion which has usually been ascribed to localized complex mantle flow patterns recent experimental work suggests an alternative explanation under conditions of high water activity a b type olivine preferred orientation may form with the a axis maximum perpendicular to the flow direction natural examples of such b type preferred orientation are however almost entirely unknown here we document widespread b type olivine preferred orientation patterns from a subduction type metamorphic belt in southwest japan and show that these patterns developed in the presence of water our discovery implies that mantle flow above subduction zones may be much simpler than has generally been thought

monohydrocalcite in the arctic ikka fjord sw greenland first reported marine occurrence abstract monohydrocalcite mhc has previously been known only from fresh water and terrestrial environments however as documented in the present paper mhc is a common mineral up to 55 in debris fragments from submarine ikaite caco3 6h2o tufa columns in the cold marine ikka fjord sw greenland the columns form where alkaline fresh water from submarine springs mixes with cold seawater and precipitates ikaite petrographical and geochemical data indicate that mhc represents a transitional diagenetic phase in the recrystallization process of metastable ikaite to final calcite the stable isotope data 13c and 18o document a closer relationship of mhc with the precursor ikaite than with calcite replacement of ikaite by mhc is suggested to take place by dissolution and precipitation in a semi closed pore water system dominated by alkaline spring water and with only limited access of seawater in this environment nucleation of calcite is inhibited by phosphate ions apart from calcite aragonite and hydrous mg carbonates were also observed in the tufa debris the mg carbonates represent late diagenetic phases probably formed from recrystallization of mch in normal seawater environments

anisotropy and flow in pacific subduction zone back arcs we have obtained constraints on the strength and orientation of anisotropy in the mantle beneath the tonga southern kuril japan and izu bonin subduction zones using shear wave splitting in s phases from local earthquakes and in teleseismic core phases such as sks the observed splitting in all four subduction zones is consistent with a model in which the lower transition zone 520 660 km and lower mantle are isotropic and in which significant anisotropy occurs in the back arc upper mantle the upper transition zone 410 520 km beneath the southern kurils appears to contain weak anisotropy the observed fast directions indicate that the geometry of back arc strain in the upper mantle varies systematically across the western pacific rim beneath izu bonin and tonga fast directions are aligned with the azimuth of subducting pacific plate motion and are parallel or sub parallel to overriding plate extension however fast directions beneath the japan sea western honshu and sakhalin island are highly oblique to subducting plate motion and parallel to present or past overriding plate shearing models of back arc mantle flow that are driven by viscous coupling to local plate motions can reproduce the splitting observed in tonga and izu bonin but further three dimensional flow modeling is required to ascertain whether viscous plate coupling can explain the splitting observed in the southern kurils and japan the fast directions in the southern kurils and japan may require strain in the back arc mantle that is driven by regional or global patterns of mantle flow

effect of water and stress on the lattice preferred orientation of olivine the influence of water and stress on the lattice preferred orientation lpo of olivine aggregates was investigated through large strain shear deformation experiments at high pressures and temperatures p 0 5 2 1 gpa t 1470 1570 k under both waterpoor and water rich conditions the specimens are hot pressed synthetic olivine aggregates or single crystals of olivine water was supplied to the sample by decomposition of a mixture of talc and brucite deformation experiments were conducted up to shear strain 6 using the griggs apparatus where water fugacity was up to 13 gpa at the pressure of 2 gpa the water content in olivine saturated with water increases with increasing pressure and the solubility of water in olivine at p 0 5 2 gpa was 400 1200 ppm h si several new types of lpo in olivine are found depending on water content and stress samples deformed in waterpoor conditions show a conventional lpo of olivine where the olivine 100 axis is subparallel to the shear direction the 010 plane subparallel to the shear plane type a however we identified three new types type b c and e of lpo of olivine depending on the water content and stress the type b lpo of olivine which was found at relatively high stress and or under moderate to high water content conditions is characterized by the olivine 001 axis subparallel to the shear direction the 010 plane subparallel to the shear plane the type c lpo which was found at low stress and under water rich conditions is characterized by the olivine 001 axis subparallel to the shear direction the 100 plane subparallel to the shear plane the type e lpo which was found under low stress and moderate water content is characterized by the olivine 100 axis subparallel to the shear direction the 001 plane subparallel to the shear plane observations by transmission electron microscopy tem and scanning electron microscopy sem show that the dislocations in water poor samples type a are curved and both b 100 and b 001 dislocations have a similar population numerous subgrains are seen in water poor samples in backscattered electron images in contrast water rich samples both type b and type c contain mostly b 001 dislocations and dislocations are straight and sub grain boundaries are rare compared to those in water poor samples these observations suggest that 1 dominant slip systems in olivine change with water fugacity and stress and 2 grain boundary migration is enhanced in the presence of water seismic anisotropy corresponding to the fabrics under water rich condition is significantly different from that under water poor condition consequently the relationship between seismic anisotropy and flow geometry in water rich regions is expected to be

effect of temperature on the b to c type olivine fabric transition and implication for flow pattern in subduction zones abstract the effect of temperature on the b to c type fabric transition in olivine was investigated by large strain shear deformation experiments a new series of deformation experiments was conducted at 1273 1373 k 2 0 gpa and strain rates ranging from 3 8 10 4 to 3 2 10 5 s 1 under water saturated conditions and combined with previous results at 1473 k the influence of temperature on deformation fabrics was investigated two types of olivine fabrics were identified one in which the olivine 0 0 1 axis is subparallel to the shear direction and the 0 1 0 plane is parallel to the shear plane b type and another one in which the 0 0 1 axis is parallel to the shear direction and the 1 0 0 plane is parallel to the shear plane c type the b type olivine fabric occurs at higher stress than the c type but the stress magnitude at which the b to c type fabric transition occurs decreases significantly with decreasing temperature the temperature dependence of the transition stress is parameterized using a range of exponential flow law that is constrained by the experimental study when the experimental results are extrapolated to lower temperatures the fabric transition between b and c type is predicted to occur at 1 mpa and 1000 k this prediction is consistent with the olivine fabrics in naturally deformed peridotites found in plate convergent regions the present study indicates that when some amounts of water 200 ppm h si are present the b type fabric will dominate in low temperature regions of the upper mantle whereas the c type or e type fabric will dominate at high temperatures the complex seismic anisotropy in subduction zones can be explained by changes in the dominant type of olivine fabrics caused by spatial variations in physical and chemical variables such as temperature and water content rather than by complexities in mantle wedge flow pattern

a preliminary assessment of the hydrocarbon potential of the larsen basin antarctica abstract the larsen basin on the northwest margin of the weddell sea formed as a mesozoic ensialic basin during gondwana breakup deposition was either in half grabens on the extending weddell sea margin or in a restricted back arc basin at the northern end of this basin 5 6 km of sedimentary rock crop out on james ross island exposing elements of a large potential hydrocarbon system aeromagnetic and outcrop data suggest that the basin structure inferred from james ross island can be recognised at least as far south as 70 s upper jurassic anoxic marine strata deposited prior to the main phase of arc development form a rich potential source t o c up to 3 5 with both marine and terrestrial kerogens arc derived volcaniclastic sediments of barremian oligocene age form a regressive megasequence basal strata represent slope apron and rudaceous submarine fan deposits proximal to the margin fan conglomerates form lenticular bodies hundreds of metres thick and tens of kilometres across enveloped in slope apron mudstones late cretaceous fault reactivation and uplift led to dramatic shallowing of the basin with deposition of shelf facies although there are many potentially attractive reservoir targets there may be problems of pore occlusion due to the abundant labile volcanic grains however there is evidence of more quartzose sandstone towards the top of the section and inferentially toward the basin centre in the larsen basin there is moderate potential for oil generated from upper jurassic source rocks and reservoired in cretaceous and tertiary sandstones and conglomerates in large stratigraphic or structural traps caused by partial basin inversion during deposition

calcium carbonate hexahydrate from organic rich sediments of the antarctic shelf precursors of glendonites large euhedral crystals of calcium carbonate hexahydrate were recovered from a shelf basin of the bransfield strait antarctic peninsula at a water depth of 1950 meters and sub zero bottom water temperatures the chemistry mineralogy and stable isotope composition of this hydrated calcium carbonate phase its environment of formation and its mode of precipitation confirm the properties variously attributed to hypothetical precursors of the glendonites and thereby greatly expand their use in paleoceanographic interpretation

importance of submarine landslides for non steady state conditions in pore water systems lower zaire congo deep sea fan abstract most concentration profiles of sulfate in continental margin sediments show constant or continuously increasing gradients from the benthic boundary layer down to the deep sulfate reduction zone however a very marked change in this gradient has been observed several meters below the surface at many locations which has been attributed to anoxic sulfide oxidation or to non local transport mechanisms of pore waters the subject of this study is to investigate whether this feature could be better explained by non steady state conditions in the pore water system to this end data are presented from two gravity cores recovered from the zaire deep sea fan the sediments at this location can be subdivided into two sections the upper layer about 10 m thick consists of stratified pelagic deposits representing a period of continuous sedimentation over the last 190 kyr it is underlain by a turbidite sequence measuring several meters in thickness which contains large crystals of authigenic calcium carbonate ikaite caco3 6h2o ikaite 13c values are indicative of a methane carbon contribution to the co2 pool radiocarbon ages of these minerals as well as of the adjacent bulk sediments provide strong evidence that the pelagic sediments have overthrust the lower section as a coherent block therefore the emplacement of a relatively undisturbed sediment package is postulated pore water profiles show the depth of the sulfate methane transition zone within the turbiditic sediments by the adaptation of a simple transport reaction model it is shown that the change in the geochemical environmental conditions resulting from this slide emplacement and the development towards a new steady state are fully sufficient to explain all features related to the pore water profiles particularly so42 and dissolved inorganic carbon dic the model shows that the downslope transport took place about 300 yr ago

carbonate sedimentation in a permian high latitude subpolar depositional realm queensland australia high latitude carbonate rocks that formed in subpolar paleozoic oceans contain critical information about past climate but they are neither well documented nor fully understood lower and middle permian limestones that were deposited in such paleoenvironments at 45 s to 55 s along the southeastern margin of gondwana are now exposed in eastern australia such carbonates constitute a small but important and well preserved part of the siliciclastic glacigene succession in the bowen basin from southern and central queensland cleanest limestones accumulated on topographic highs in the eastern seaward parts of the basin that were isolated from siliciclastic sediment input from the western craton shallow water deposits are composed of large eurydesmid bivalves spiriferid and productid brachiopods bryozoans infaunal and epifaunal benthic foraminifers calcareous sponge spicules and abundant crinoids in the form of locally cross bedded rudstones and grainstones deeper water muddy carbonates are dominated by bryozoans crinoids and productids shells and spines deepest water sediments are argillaceous floatstones or shales containing fenestrate bryozoans thin walled productids and siliceous sponge spicules when integrated with recent studies of coeval sedimentary rocks along the 2000 km long paleocontinental margin a clear pattern of sedimentation emerges wherein deposition took place in similar settings during three discrete periods of deglaciation late sakmarian late artinskian and wordian all of the carbonates are distinguished by a low diversity high abundance heterozoan biota with no phototrophs and express a recurring deepening upward stratigraphic motif that is interpreted to reflect rising sea level accompanying glacial meltdown they also record a strong poleward gradient of increasing ice rafted debris increasing skeleton size decreasing invertebrate diversity decreasing epifaunal calcareous benthic foraminifers and reduction in crinoids glendonites are confined to siliciclastic sediments deposited during glacial periods comparison with coeval northern hemisphere carbonates indicates a strong parallelism of facies and depositional systems this study helps to establish these deposits as a template for a global paleozoic high latitude carbonate facies model

glendonites from an early jurassic methane seep climate or methane indicators abstract an early jurassic late pliensbachian section margaritatus to spinatum ammonite zone northeast of cremlingen germany revealed three horizons with abundant glendonites calcite pseudomorphs after ikaite caco3 6h2o as well as authigenic carbonates these pseudomorphs have previously been used as indicators for organic and phosphate rich paleoenvironments with near freezing bottom water temperatures stable isotope measurements clearly show that the ikaite glendonite was precipitated at a methane seep location with methanotrophic sulfate reduction as the triggering geochemical process for ikaite formation at the sulfate methane interface the termination of methane seepage probably led to the disintegration of the primary mineral ikaite and successive pseudomorph formation reconstructed paleo bottom water temperatures ca 10 c from belemnites and ostracods indicate temperatures well above the previously observed range of ikaite stability near freezing raising the question if methane seeps are distinct geochemical sites promoting ikaite formation at higher temperatures

upper mantle anisotropy beneath japan from shear wave splitting in this study we utilize data from 64 broadband seismic stations of the japanese f net network to investigate the threedimensional pattern of anisotropy in the subduction system beneath japan we have compiled a database of approximately 1900 high quality splitting measurements selected by visual inspection of over 25 000 records of s sks and skks phases at f net stations covering a wide range of incidence angles incoming polarization angles and backazimuths analysis of the variations of measured splitting parameters with these parameters allows us to consider complexities in structure such as multiple anisotropic layers dipping symmetry axes and small scale lateral variations in anisotropic properties here we focus on the presentation of the splitting measurements themselves a detailed interpretation in terms of tectonics and mantle flow is beyond the scope of this paper in the southern part of the f net array along the ryukyu arc we find that fast directions are consistently trench parallel with splitting times of 1 s or more moving northward along the array the measured splitting patterns become more complicated with significant variations in apparent splitting parameters that indicate complex anisotropic structure additionally measured fast directions vary significantly over short length scales and stations separated by less than 100 km often exhibit very different splitting behavior this increase in complexity of anisotropic structure coincides geographically with the complicated slab morphology of the subducting pacific plate at stations on hokkaido to the north and kyushu to the south we see some evidence that the fast direction of anisotropy may rotate from trench parallel close to the trench to subduction parallel further away from the trench which may correspond either to a change in stress conditions and or volatile content or to a change in flow regime 2005 elsevier b v all rights reserved

a complex pattern of mantle flow in the lau backarc shear wave splitting analysis of local events recorded on land and on the ocean floor in the tonga arc and lau backarc indicate a complex pattern of azimuthal anisotropy that cannot be explained by mantle flow coupled to the downgoing plate these observations suggest that the direction of mantle flow rotates from convergence parallel in the fiji plateau to north south beneath the lau basin and arc parallel beneath the tonga arc these results correlate with helium isotopes that map mantle flow of the samoan plume into the lau basin through an opening tear in the pacific plate

variable microstructure of peridotite samples from the southern mariana trench evidence of a complex tectonic evolution abstract we retrieved samples of peridotite from a dredge haul kh92 1 d2 collected during cruise kh92 1 undertaken by the research vessel r v hakuho in 1992 at the landward trench slope of the southern mariana trench 11 41 16 n 143 29 62 e depth 6594 7431 m which is the deepest ocean in the world ten of 30 retrieved samples possessed both a foliation and lineation as assessed from 46 thin sections of various orientations and observations of hand samples the samples showed marked variation in microstructure ranging from coarse 5 mm equigranular and intensely elongated textures to finer

black shale formation in the late paleocene early eocene arctic ocean and paleoenvironmental conditions new results from a detailed organic petrological study abstract the study of particulate organic matter om in arctic ocean sediments from the late cretaceous to the eocene iodp expedition 302 has revealed detailed information about the aquatic marine om fluxes biological sources preservation and export of terrestrial material here we present detailed data from maceral analysis vitrinite reflectance measurements and organic geochemistry during the campanian paleocene fluxes of land derived om are indicated by reworked and oxidized macerals vitrinite inertinite and terrigenous liptinite cutinite sporinite in the early eocene drastic environmental changes are indicated by peaks in aquatic om up to 40 45 lamalginite telalginite liptodetrinite dinoflagellate cysts and amorphous om up to 50 bituminite these events of increased aquatic om flux similar to conditions favoring black shale deposition correlate with the global 13c events paleocene eocene thermal maximum petm and elmo event freshwater discharge and proximity of the source area are documented by freshwater algae material pediastrum botryococcus and immature land plant material corphuminite textinite we consider that erosion of coal bearing sediments during transgression time lead to humic acids release as a source for bituminite deposited in the early eocene black shales

quantification of diffusive benthic fluxes of nitrate phosphate and silicate in the southern atlantic ocean pore water data from surface sediments and bottom water data at 180 locations were used to create distribution maps of diffusive benthic release rates of nitrate phosphate and silicate in the southern atlantic ocean for water depths 1000 m geostatistical methods of variogram analysis and kriging were used for data interpolation since benthic fluxes are controlled by organic matter degradation and dissolution processes and therefore by the supply of organic matter to the sediment surface the distribution pattern of all investigated constituents should reflect a general coupling to surface water productivity this seems to be true for the most part of the oligotrophic central south atlantic and the upwelling area off southwest africa striking regional differences in this regard however exist for the eastern equatorial region where unexpectedly low fluxes were calculated and the argentine basin where benthic fluxes are very high the argentine basin obviously receives a higher input of degradable dissolvable material whereas in the eastern equatorial region the low benthic fluxes are possibly due to intense nutrient recycling within the water column estimated fluxes vary considerably over the entire region no3 10 180 mmol m 2 yr 1 po4 2 11 mmol m 2 yr 1 and si 0 0 65 mol m 2 yr 1 areas of highest release rates are the continental margins off southwest africa and off argentina the investigated area comprises a total of approximately 32 106 km2 between 8 n and 40 50 s our estimations reveal benthic release rates of 1 55 l012 mol no3 yr 1 3 5 l010 mol po4 yr 1 and 2 1 1012 mol si yr 1 open ocean areas with middle to low fluxes contribute about 70 80 of the total estimated fluxes the release of phosphate is probably underestimated because of core recovery artifacts and is therefore based on the assumption that fluxes are not lower than 0 25 mmol m 2 yr 1 at any location of the studied area the investigated area represents about one tenth of the world deep ocean without the arctic ocean assuming the south atlantic to be representative we calculate annual global release rates of 15 l012 mol no3 32 l010 mol po4 and 20 1012 mol si if our estimates are correct about 4 6 of silicate 3 4 of nitrate and 1 of phosphate annually produced in the surface waters are remineralized in surface sediments from water depths 1000 m

arc parallel flow within the mantle wedge evidence from the accreted talkeetna arc south central alaska 1 residual mantle exposures in the accreted talkeetna arc alaska provide the first rock analog for the arc parallel flow that is inferred from seismic anisotropy at several modern arcs the peridotites exposed at the base of the jurassic talkeetna arc have a moho parallel foliation and indicate dislocation creep of olivine at temperatures of 1000 to 1100 c slip occurred chiefly on the 001 100 slip system which has only rarely been observed to be the dominant slip system in olivine stretching lineations and olivine 100 slip directions are subparallel to the long axis of the talkeetna arc for over 200 km indicating that mantle flow was parallel to the arc axis the alignment of the olivine 100 axes yields a calculated s wave anisotropy with the fast polarization direction parallel to the arc thus 1 the fast polarization directions observed parallel to some modern arcs now have an exposed geological analog 2 arc parallel fast polarization directions can be caused by anisotropic peridotites and do not require the presence of fracture zones fluid filled pockets or glide on the 010 001 h2o induced slip system 3 seismic anisotropy beneath modern arcs may be due to slip on 001 100 with a horizontal foliation rather than slip on 010 100 with a vertical foliation and 4 the observed dominance of the 001 100 slip system may be due to high h2o concentrations suggesting that strain in the oceanic upper mantle may be accommodated dominantly by 001 100 olivine slip

authigenic ferrimagnetic iron sulfide preservation due to nonsteady state diagenesis a perspective from perseverance drift northwestern weddell sea we document magnetic mineral diagenesis with high resolution magnetic susceptibility hysteresis isothermal remanent magnetization and other rock magnetic measurements through a shallow sulfate m

the evidence and implications of polar ice during the mesozoic abstract the mesozoic perhaps representing the longest period of warmth during phanerozoic earth history contains in general sparse and frequently equivocal evidence for polar ice although this time is undoubtedly punctuated by oscillations in climate whether sufficient to lead to polar cooling and the formation of polar ice an inviting mechanism to account for faunal and floral distribution patterns and large scale sea level change has been widely debated mesozoic evidence for glacial conditions includes abraded rock surfaces generally unsorted stone rich beds and the presence of dropstones rafted by ice within a finer grained host sediment faunal and floral evidence has also been utilised to determine the presence or absence of cold or sub freezing polar conditions together with more indirect evidence for glacial conditions derived from general circulation model gcm simulations of climate the analysis of clay mineral distributions glendonite abundance and palaeontological and sedimentological evidence for globally synchronous sea level change the extent of possible glacial environments during the mesozoic has been established by plotting published reports of glacial sediments on palaeogeographic reconstructions the general clustering of evidence at high palaeolatitudes suggests that the extent of polar ice during the mesozoic is likely to have been approximately one third the size of the present day based on such evidence a number of episodes of cold or sub freezing polar climates during the bajocian bathonian tithonian volgian valanginian and aptian are recognised evidence exists possibly also for a cold episode during the early jurassic pliensbachian although poorly constrained owing to limited biostratigraphical control the longevity of these events may be represented by a cold snap within a stage although undoubtedly the possible smearing of ages may have had the effect of lengthening and hence promoting the importance of these proposed events the climate regime of the earth during these times may be hypothesised to be characterised by a relatively steep pole to equator temperature gradient where low latitude regions are as warm or warmer than today the evidence to support such reasoning includes sharp increases in the areal distribution of both glendonites and deposits with affinities to glacial tillites and dropstones for these times coincidental falls of sea level arid events and an increased bipolarity of faunas at these times imparts further confidence that these events were of a magnitude to effect the earth as a whole

silicified glendonites in the ediacaran doushantuo formation south china and their potential paleoclimatic implications the ediacaran period is punctuated by the ca 580 ma gaskiers glaciation in newfoundland however paleoclimatic data are scarce in ediacaran successions in south china where abundant geochemical and paleobiological data are shaping current understanding of ediacaran evolutionary and environmental history here we report the occurrence of silicified glendonites in the ediacaran doushantuo formation deposited in an inner shelf environment on the south china block petrographic evidence suggests that these silicified glendonites are pseudomorphs after syndepositional or early authigenic ikaites formed at near freezing temperatures the glendonite bearing stratigraphic interval is characterized by positive 13c values it predates both the negative 13c excursion en3 widely believed to be an equivalent of the shuram negative excursion and excursion en2 although alternative interpretations may be possible these glendonites may be related to and correlated with the gaskiers glaciation if confirmed this correlation suggests that the shuram event postdates the gaskiers glaciation thus having important implications for ediacaran climate changes carbon cycles and biological evolution

variation of chemical index of alteration cia in the ediacaran doushantuo formation and its environmental implications abstract the ediacaran period 635 541 ma witnessed rapid turnovers of marine organisms that eventually led to the early cambrian radiation the ediacaran doushantuo formation ca 635 551 ma serves as one of the most important and intensively studied stratigraphic units for understanding the co evolution of life and environment during this critical time interval to better understand the early middle ediacaran climate change we reconstruct a temporal variation curve of chemical index of alteration cia from a drill core and an outcrop of the doushantuo formation in combination with previously published cia data from segments of time equivalent strata the results show three distinct decreases in cia values that correlate well with the positive carbon isotope 13c excursion at the low doushantuo formation ep1 and the negative 13c excursion at the middle en2 and upper en3 doushantuo formation the decline of cia in ep1 is consistent with occurrence of glendonites at the same stratigraphic interval that suggests a cooling event the low cia values in en2 and en3 also suggest relatively colder periods that are consistent with evidence from strontium isotope 87sr 86sr and oxygen isotope 18o data with existing bio and chemostratigraphic constraints the cooling event associated with en2 might be synchronous with the gaskiers glaciation the other two cold periods associated with ep1 and en3 however have not been documented from other successions globally which needs to be tested in future studies

aeolian sediment transport and deposition in a modern high latitude glacial marine environment aeolian sand and dust in polar regions are transported offshore over sea ice and released to the ocean during summer melt this process has long been considered an important contributor to polar sea floor sedimentation and as a source of bioavailable iron that triggers vast phytoplankton blooms reported here are aeolian sediment dispersal patterns and accumulation rates varying between 0 2 g m 2 yr 1 and 55 g m 2 yr 1 over 3000 km2 of sea ice in mcmurdo sound south west ross sea adjacent to the largest ice free area in antarctica sediment distribution and the abundance of southern mcmurdo volcanic group derived glass show that most sediment originates from the mcmurdo ice shelf and nearby coastal outcrops almost no sediment is derived from the extensive ice free areas of the mcmurdo dry valleys due to winnowed surficial layers shielding sand sized and silt sized material from wind erosion and because of the imposing topographic barrier of the north south aligned piedmont glaciers southerly winds of intermediate strength ca 20 m sec 1 are primarily responsible for transporting sediment northwards and offshore the results presented here indicate that sand sized sediment does not travel more than ca 5 km offshore but very fine sand and silt grains can travel 100 km from source for sites 10 km from the coast the mass accumulation rate is relatively uniform 1 14 0 57 g m 2 yr 1 three orders of magnitude above estimated global atmospheric dust values for the region this uniformity represents a sea floor sedimentation rate of only 0 2 cm kyr 1 well below the rates of 9 cm kyr 1 reported for biogenic dominated sedimentation measured over much of the ross sea these results show that even for this region of high windblown sediment flux aeolian processes are only a minor contributor to sea floor sedimentation excepting areas proximal to coastal sources

new type of olivine fabric from deformation experiments at modest water content and low stress a new type of olivine fabric was found by high strain simple shear deformation experiments in the presence of trace amounts of water at 0 5 2 2 gpa and 1470 1570 k in this fabric called e type fabric the olivine 100 axis is subparallel to the shear direction and the 001 plane is parallel to the shear plane this geometry suggests that the 100 001 slip system makes the dominant contribution to total strain this fabric is dominant at a modest water content 200 coh 1000 h 10 6 si at low stresses and high temperatures some mylonites from peridotite massifs show this type of olivine fabric which suggests the presence of water during the shear localization the seismic anisotropy caused by this fabric is qualitatively similar to that by dry fabric a type but the magnitudes of anisotropy are different between the two types for horizontal flow the amplitude of vsh vsv anisotropy is weaker but the amplitude of shear wave splitting is stronger for the e type fabric than for the a type dry fabric seismic anisotropy in the oceanic upper mantle may be due to the olivine e type fabric

seismic anisotropies of the songshugou peridotites qinling orogen central china and their seismic implications abstract though extensively studied the roles of olivine crystal preferred orientations cpos or fabrics in affecting the seismic anisotropies in the earth s upper mantle are rather complicated and still not fully known in this study we attempted to address this issue by analyzing the seismic anisotropies e g p wave anisotropy avp s wave polarization anisotropy avs radial anisotropy and rayleigh wave anisotropy g of the songshugou peridotites dunite dominated in the qinling orogen in central china based on our previously reported olivine cpos the seismic anisotropy patterns of olivine aggregates in our studied samples are well consistent with the prediction for their olivine cpo types and the magnitude of seismic anisotropies shows a striking positive correlation with equilibrium pressure and temperature p t conditions significant reductions of seismic anisotropies avp max avs and g are observed in porphyroclastic dunite compared to coarse and fine grained dunites as the results of olivine cpo transition from a d type in coarse grained dunite through ag type like in porphyroclastic dunite to b type like in fine grained dunite and strength variation weakening a d type ag type like strengthening ag type like b type like during dynamic recrystallization the transition of olivine cpos from a d type to b ag type like in the forearc mantle may weaken the seismic anisotropies and deviate the fast velocity direction and the fast s wave polarization direction from trench perpendicular to trench oblique direction with the cooling and aging of forearc mantle depending on the size and distribution of the peridotite body such as the songshugou peridotites b and ag type like olivine cpos can be an additional despite minor local contributor to the orogen parallel fast velocity direction and fast shear wave polarization direction in the orogenic crust such as in the songshugou area in qinling orogen

an ikaite record of late holocene climate at the antarctic peninsula abstract calcium carbonate can crystallize in a hydrated form as ikaite at low temperatures the hydration water in ikaite grown in laboratory experiments records the 18 o of ambient water a feature potentially useful for reconstructing 18 o of local seawater we report the first downcore 18 o record of natural ikaite hydration waters and crystals collected from the antarctic peninsula ap a region sensitive to climate fluctuations we are able to establish the zone of ikaite formation within shallow sediments based on porewater chemical and isotopic data having constrained the depth of ikaite formation and 18 o of ikaite crystals and hydration waters we are able to infer local changes in fjord 18 o versus time during the late holocene this ikaite record qualitatively supports that both the medieval warm period and little ice age extended to the antarctic peninsula

effects of water on dynamically recrystallized grain size of olivine abstract recrystallized grain size versus stress relationship for olivine has been determined under water poor and water rich conditions we found that when the water content in olivine exceeds 800 ppm h si the size of recrystallized grains is about two to three times larger than under water poor conditions compared at the same stress level microstructural observations of deformed samples show that the ratio of recrystallized grain size to that of subgrains increases significantly with water content and that the volume fraction of grains containing subgrain boundaries is smaller under water rich conditions than under water poor conditions these observations suggest that the enhancement of grain boundary mobility by water is more significant than that of dislocation recovery leading to a larger size of recrystallized grains under water rich conditions

intermediate depth earthquake faulting by dehydration embrittlement with negative volume change earthquakes are observed to occur in subduction zones to depths of approximately 680 km even though unassisted brittle failure is inhibited at depths greater than about 50 km owing to the high pressures and temperatures it is thought that such earthquakes particularly those at intermediate depths of 50 300 km may instead be triggered by embrittlement accompanying dehydration of hydrous minerals principally serpentine a problem with failure by serpentine dehydration is that the volume change accompanying dehydration becomes negative at pressures of 2 4 gpa 60 120 km depth above which brittle fracture mechanics predicts that the instability should be quenched here we show that dehydration of antigorite serpentinite under stress results in faults delineated by ultrafine grained solid reaction products formed during dehydration this phenomenon was observed under all conditions tested pressures of 1 6 gpa temperatures of 650 820 degrees c independent of the sign of the volume change of reaction although this result contradicts expectations from fracture mechanics it can be explained by separation of fluid from solid residue before and during faulting a hypothesis supported by our observations these observations confirm that dehydration embrittlement is a viable mechanism for nucleating earthquakes independent of depth as long as there are hydrous minerals breaking down under a differential stress

seismic anisotropy of serpentinite from val malenco italy 2015 american geophysical union all rights reserved serpentinites deformed in mantle subduction zones are thought to contribute significantly to seismic anisotropy of the upper mantle and have therefore been of great interest with studies on deformation preferred orientation and elastic properties here we present a combined study of a classical sample from val malenco italy investigating the microstructure and texture with state of the art synchrotron x ray and neutron diffraction methods and measuring ultrasonic velocities both with a multi anvil apparatus and a novel instrument to measure 3 d velocities on spheres both results from diffraction methods and velocity measurements are compared discussing advantages and disadvantages from spherical velocities elastic tensor properties can be derived by inversion also from quantitative texture measurements elastic properties can be modeled by self consistent averaging good agreement between the velocity and microstructural models is observed

holocene climate and glacial history of the northeastern antarctic peninsula the marine sedimentary record from a long shaldril core abstract a high resolution record of holocene deglacial and climate history was obtained from a 77 m sediment core from the firth of tay antarctic peninsula as part of the shaldril initiative this study provides a detailed sedimentological record of holocene paleoclimate and glacial advance and retreat from the eastern side of the peninsula a robust chronostratigraphy was derived from thirty three radiocarbon dates on carbonate material this chronostratigraphic framework was used to establish the timing of glacial and climate events derived from multiple proxies including magnetic susceptibility electric resistivity porosity ice rafted debris content organic carbon content nitrogen content biogenic silica content and diatom and foraminiferal assemblages the core bottomed out in a stiff diamicton interpreted as till gravelly and sandy mud above the till is interpreted as proximal glaciomarine sediment that represents decoupling of the glacier from the seafloor circa 9400 cal yr bp and its subsequent landward retreat this was approximately 5000 yr later than in the bransfield basin and south shetland islands on the western side of the peninsula the firth of tay core site remained in a proximal glaciomarine setting until 8300 cal yr bp at which time significant glacial retreat took place deposition of diatomaceous glaciomarine sediments after 8300 cal yr bp indicates that an ice shelf has not existed in the area since this time the onset of seasonally open marine conditions between 7800 and 6000 cal yr bp followed the deglacial period and is interpreted as the mid holocene climatic optimum open marine conditions lasted until present with a minor cooling having occurred between 6000 and 4500 cal yr bp and a period of minor glacial retreat and or decreased sea ice coverage between 4500 and 3500 cal yr bp finally climatic cooling and variable sea ice cover occurred from 3500 cal yr bp to near present and it is interpreted as being part of the neoglacial the onset of the neoglacial appears to have occurred earlier in the firth of tay than on the western side of the antarctic peninsula the medieval warm period and little ice age were not pronounced in the firth of tay the breadth and synchroneity of the rapid regional warming and glacial retreat observed in the antarctic peninsula during the last century appear to be unprecedented during the holocene epoch

glendonites as a paleoenvironmental tool implications for early cretaceous high latitude climates in australia glendonites calcite pseudomorphs after the metastable mineral ikaite caco3 6h2o occur in the late aptian interval of the bulldog shale in the eromanga basin australia and in other early cretaceous basins at high paleolatitudes ikaite precipitation in the marine environment requires near freezing temperatures not higher than 4 c high alkalinity increased levels of orthophosphate and high pco2 the rapid and complete transformation of ikaite to calcite at temperatures between 5 and 8 c provides an upper limit on the oxygen isotopic composition of the pore waters 2 6 w 3 4 smow if it is assumed that these pore waters are representative of the shallow eromanga basin the calculated w can be used to reassess belemnite fossil oxygen isotopic paleotemperatures temperature recorded by fauna living in the basin at the time of ikaite precipitation data previously reported as 11 to 16 c assuming w 0 0 smow yield paleotemperatures ranging from 1 to 5 c squarely in the range of ikaite stability the low w indicates hyposaline conditions most likely caused by mixing high latitude meteoric waters with seawater the 18o depleted low temperature waters suggest that the region was at least seasonally colder than previously accepted

deformation fabrics of olivine in val malenco peridotite found in italy and implications for the seismic anisotropy in the upper mantle abstract an exhumed huge body of ultramafic rocks is preserved in val malenco italy in this study petrofabrics and deformation microstructures of olivine in the val malenco peridotite were examined and new observations of lattice preferred orientation lpo of olivine such as type b and type e lpo in the peridotite are reported three types depending on the grain size of olivine fabrics were observed type a fabric exhibiting the 010 100 slip system in the large relic grain area and type b and type e fabrics exhibiting the 010 001 and 001 100 slip systems respectively in the widely distributed recrystallized grain area the slips occurred mainly on 010 001 and the 001 100 slip system has only rarely been reported to be the dominant slip system of olivine found in natural rocks further seismic velocities and seismic anisotropies were calculated for the three types of fabrics found the seismic anisotropies in the upper mantle can be attributed to the type b type e or type a lpos of olivine moreover the anomaly in seismic low velocity in the mantle wedge can be attributed to the serpentinization as well as the mixed fabrics of the type a type b and type e

the influence of plate motions on three dimensional back arc mantle flow and shear wave splitting both the polarization direction of the fast shear waves and the types of deformation within overriding plates vary between the back arc basins of western pacific subduction zones the goal of this study is to test the possibility that motions of the overriding plates may control the patterns of seismic anisotropy and therefore the observed shear wave splitting we calculated three dimensional models of viscous asthenospheric flow driven by the motions of the subducting slab and overriding plates shear wave splitting was calculated for polymineralic anisotropy within the back arc mantle wedge assuming that the anisotropy was created by flow induced strain predicted splitting may differ substantially depending on whether anisotropy is computed directly using polycrystalline plasticity models or is based on the orientation of finite strain a parameter study shows that both finite strain and textural anisotropy developed within three dimensional plate coupled asthenospheric flow models are very heterogeneous when back arc shearing occurs within the overriding plate therefore predicted shear wave splitting varies strongly as a function of plate motion boundary conditions and with ray path through the back arc asthenosphere flow models incorporating plate motion boundary conditions for the tonga southern kuril and eastern aleutian subduction zones produce splitting parameters consistent with observations from each region trench parallel flow generated by small variations in the dip of the subducting plate may be important in explaining observed fast directions of anisotropy sampled within the innermost corner of the mantle wedge

wide but not ubiquitous distribution of glendonite in the doushantuo formation south china implications for ediacaran climate abstract glendonites are pseudomorphs of syndepositional or early authigenic ikaite caco3 6h2o that often forms at near freezing temperatures silicified glendonite has been reported from inner shelf deposits of the lower ediacaran doushantuo formation at a single stratigraphic section in south china where they are stratigraphically associated with the positive 13c excursion ep1 but predate the negative 13c excursion en3 shuram excursion indicating a period of cool climate somewhere between 609 ma and 551 ma this interpretation predicts a wider geographic distribution of ediacaran glendonites in equivalent strata in the yangtze block of south china to test this prediction we conducted a regional survey of doushantuo formation and found that although glendonites are not universally present they occur in expected stratigraphic intervals and in association with ep1 at two new sections representing inner shelf and intrashelf basin facies the wide but not ubiquitous distribution of doushantuo glendonites indicates that ikaite precipitation and glendonite formation was controlled by both regional climatic and local geochemical factors glendonites at the new localities are stellate clusters pseudomorphed by calcite spar and sometimes are rimmed with silica the calcite spar is characterized by highly variable and mostly negative 13c values as low as 37 indicating that diagenetic transformation of precursor ikaite to calcitic glendonite may be related to anaerobic oxidation of organic matter or methane in sediment the new data suggest an early ediacaran cold period prior to en3 or the shuram excursion and facilitation of glendonite ikaite formation by both climatic and local geochemical conditions such as redox conditions and phosphate concentrations

a review of the geodynamic evolution of flat slab subduction in mexico peru and chile abstract subducting plates around the globe display a large variability in terms of slab geometry including regions where smooth and little variation in subduction parameters is observed while the vast majority of subduction slabs plunge into the mantle at different but positive dip angles the end member case of flat slab subduction seems to strongly defy this rule and move horizontally several hundreds of kilometers before diving into the surrounding hotter mantle by employing a comparative assessment for the mexican peruvian and chilean flat slab subduction zones we find a series of parameters that apparently facilitate slab flattening among them trench roll back as well as strong variations and discontinuities in the structure of oceanic and overriding plates seem to be the most important however we were not able to find the necessary and sufficient conditions that provide an explanation for the formation of flat slabs in all three subduction zones in order to unravel the origin of flat slab subduction it is probably necessary a numerical approach that considers also the influence of surrounding plates and their corresponding geometries on 3d subduction dynamics

a laboratory model of subduction zone anisotropy abstract measurements of split seismic shear waves near pacific subduction zones show that fast polarization directions are primarily trench parallel in the seaward side mantle beneath a subducting slab and variable in the mantle wedge beneath back arc basins it is generally accepted that the azimuth of the fast polarization direction defines the average orientation of the crystallographic a axis in olivine here we use laboratory experiments to determine the orientation of the olivine a axis in the upper mantle in the vicinity of a subducting slab a laboratory analog for olivine a axis motion during creep deformation is developed using small cylinders whiskers suspended in a viscous fluid subduction beneath a stationary overriding plate variable dip angles and realistic rollback and down dip plate kinematics are examined plate rollback produces strong plate parallel whisker alignments for all dip angles examined alignment in the wedge occurs in three layers a layer of dip parallel alignment above the downgoing plate a layer of subhorizontal alignment beneath the overriding plate and a core of intermediate orientations the amount of alignment beneath the overriding plate and the wedge core decreases with increasing dip angle our results indicate that olivine a axis orientation in the seaward side mantle is controlled by the amount of slab rollback and that orientations in the mantle wedge depend upon slab dip angle

margin segmentation of baffin bay davis strait eastern canada based on seismic reflection and potential field data abstract the continental margin of baffin island was interpreted from a compilation of seismic reflection and potential field data based on these data it was divided into volcanic and non volcanic segments in the northernmost area coast parallel grabens and continental basement highs are superseded beneath the slope by irregular basement topography in combination with the velocities from refraction data and the lack of a magnetic slope anomaly we propose a non volcanic margin in the central region the seismic data show a limited region with a seaward dipping reflector sequence that may be intercalated with a sedimentary section both north and south of cape dyer extensive volcanic rocks are interpreted at and below seabed consistent with a volcanic margin in the southern region the depth to basement drops rapidly offshore a thick prograding sedimentary wedge produces a high amplitude long wavelength free air gravity anomaly that was previously confused with the continent ocean boundary although some volcanic rocks are mapped in the region this area is adjacent to the non volcanic labrador sea margin and is interpreted to be of similar structure segmentation of the margin by major faults can explain the abrupt transitions from volcanic to non volcanic margin segments the continent ocean boundary for the region is determined based on the potential field and seismic data along the greenland plate in davis strait the continent ocean boundary coincides with the ungava fault zone the continent ocean boundary is used in conjunction with published poles of rotation to evaluate plate reconstructions at chrons 33n and 27n the earlier reconstruction produces an extensive overlap of boundaries in the north the later reconstruction shows a gap in the southern region thus additional information is required to refine the reconstructions

upper mantle seismic anisotropy resulting from pressure induced slip transition in olivine seismic anisotropy in the oceanic lithosphere results from flow induced crystallographic preferred orientation of dry olivine during lithosphere creation recent experiments however showed that high water activity changes the flow mechanisms of olivine and hence the crystallographic preferred orientation better explaining the seismic anisotropy in the mantle wedge above subduction zones whether changes in the crystallographic preferred orientation of olivine are unique to the effects of water has become controversial and is critical to resolve here we report low stress high strain experiments on typical dry mantle rock at high pressures and temperatures showing that at 3 gpa pressure induces the same profound transition in olivine crystallographic preferred orientation that is produced by high water activity at lower pressure one important consequence for global tectonics is that alignment of fast seismic waves parallel to trenches beneath subducting slabs probably reflects entrainment of sub lithospheric mantle in the direction of subduction rather than trench parallel flow as interpreted at present from the large variety of crystallographic preferred orientations in olivine in both experiments and natural rocks we infer that in addition to the pressure induced changes in olivine slip systems implied here there are probably further changes in slip systems at higher pressure and temperature seismic anisotropy in earth s oceanic lithosphere and in the mantle wedge above subduction zones is associated with crystallographic preferred orientations of olivine experiments at high pressure and temperature suggest that a pressure of 3 gpa can induce the same changes in the crystal structure of olivine as high water activity at lower pressures

the solubility and stabilization of ikaite caco3 6h2o from 0 to 25 c environmental and paleoclimatic implications for thinolite tufa we determined the solubility of ikaite from 0 to 25 c to model its saturation state in natural waters and test the hypothesis that it is the precursor of the calcite pseudomorphs in thinolite tufa of quaternary lake lahontan reversible solubility at buffered p co 2 yields the following expression for the dissolution constant of ikaite log k ikaite 0 15981 2011 1 t where t circ k and 0 circ c leq t leq 25 circ c derived standard state properties are delta g ikaite circ 2541 9 kjmol 1 pm 0 66 delta h ikaite circ 2973 4 kjmol 1 pm 1 02 s ikaite circ 306 6 jt 1 mol 1 pm 1 2 modeling shows that ikaite is undersaturated at all temperatures in seawater and in alkaline lakes but that it rapidly approaches saturation near 0 c its precipitation in near freezing marine sediments requires large additions of hco 3 to pore fluids from the diagenetic decomposition of organic matter its crystallization in tufas of alkaline lakes howeve

tectonosedimentary evolution of the deep iberia newfoundland margins evidence for a complex breakup history most of the conceptual ideas concerning sedimentary architecture and tectonic evolution of deep rifted margins are based on either intracontinental rift basins or proximal margins both of which underwent only small amounts of crustal thinning in this paper we investigate the tectonosedimentary and morphotectonic evolution related to continental breakup of the highly extended deep iberia newfoundland margins our results show that continental breakup is a complex process distributed in time and space on the basis of mapping of dated seismic units and borehole data we are able to identify two major phases of extension during a first phase dated as tithonian to barremian 145 128 ma deformation is related to exhumation of mantle rocks basins become younger oceanward and fault geometry changes from upward to downward concave resulting in complex sedimentary structures and basin geometries a second phase dated as latest aptian 112 ma overprints previously exhumed mantle and accreted juvenile oceanic crust over more than 200 km leading to the formation of basement highs the observed complex breakup history challenges classical concepts of rifting and leads to new interpretations for the tectonosedimentary evolution of deep rifted margins

submarine columns of ikaite tufa in the small ikka fjord in southwestern greenland we have studied remarkable submarine tufa columns forming over alkaline springs by abiotic precipitationof the metastable cold water mineral ikaite caco3 6h2o 1 3 the columns which support a rich marine life are up to 20 m high with annual growth of more than 50 cm we wish to nominate the locality which seems to be unique for classification as a geological world heritage site

early season depletion of dissolved iron in the ross sea polynya implications for iron dynamics on the antarctic continental shelf 1 the ross sea polynya is among the most productive regions in the southern ocean and may constitute a significant oceanic co2 sink based on results from several field studies this region has been considered seasonally iron limited whereby a winter reserve of dissolved iron dfe is progressively depleted during the growing season to low concentrations 0 1 nm that limit phytoplankton growth in the austral summer december february here we report new iron data for the ross sea polynya during austral summer 2005 2006 27 december 22 january and the following austral spring 2006 16 november 3 december the summer 2005 2006 data show generally low dfe concentrations in polynya surface waters 0 10 0 05 nm in upper 40 m n 175 consistent with previous observations surprisingly our spring 2006 data reveal similar low surface dfe concentrations in the polynya 0 06 0 04 nm in upper 40 m n 69 in association with relatively high rates of primary production 170 260 mmol c m 2 d 1 these results indicate that the winter reserve dfe may be consumed relatively early in the growing season such that polynya surface waters can become iron limited as early as november i e the seasonal depletion of dfe is not necessarily gradual satellite observations reveal significant biomass accumulation in the polynya during summer 2006 2007 implying significant sources of new dfe to surface waters during this period possible sources of this new dfe include episodic vertical exchange lateral advection aerosol input and reductive dissolution of particulate iron

early permian seasonality from bivalve δ18o and implications for the oxygen isotopic composition of seawater oxygen isotope values of sequentially microsampled accretionary carbonate from the thick shelled calcitic bivalve eurydesma from the early permian of southeastern australia vary seasonally over 6 yr of growth paleotemperature constraints derived from coeval glendonite and ice rafted clasts in combination with published biome data indicate near freezing winter conditions however paleotemperatures calculated from oxygen isotope data are too warm unless the 18 o value of seawater approached 4 associated stenohaline brachiopods and lack of covariance with 13 c argue against significantly reduced salinity and published 18 o data from across australia suggest that conditions recorded by this bivalve were typical of the gondwanan high latitudes the negative 18 o value of seawater implied by these data reflects in part the expected meridional gradient in marine seawater composition related to latitudinal variation in evaporation and precipitation in permian oceans but is also consistent with previous suggestions of a secular increase in the oxygen isotopic composition of ocean water through the phanerozoic

mapping seismic anisotropy using harmonic decomposition of receiver functions an application to northern apennines italy 1 isotropic and anisotropic seismic structures across the northern apennines italy subduction zone are imaged using a new method for the analysis of teleseismic receiver functions rfs more than 13 000 p wave coda of teleseismic records from the 2003 2007 retreating trench extension and accretion tectonics retreat experiment are used to provide new insights into a peculiar subduction zone between two continental plates that is considered a focal point of mediterranean evolution a new methodology for the analysis of receiver functions is developed which combines both migration and harmonic decomposition of the receiver function data set the migration technique follows a classical common conversion point scheme and helps to focus on a crucial depth range 20 70 km where the mantle wedge develops harmonic decomposition of a receiver function data set is a novel and less explored approach to the analysis of p to s converted phases the separation of the back azimuth harmonics is achieved through a numerical regression of the stacked radial and transverse receiver functions from which we obtain independent constraints on both isotropic and anisotropic seismic structures the application of our method to the retreat data set succeeds both in confirming previous knowledge about seismic structure in the area and in highlighting new structures beneath the northern apennines chain where previous studies failed to clearly retrieve the geometry of the subducted interfaces we present our results in closely spaced profiles across and along the northern apennines chain to highlight the convergence of the tyrrhenian and the adriatic microplates which differ in their crustal structure where the adriatic microplate subducts beneath tuscany and the tyrrhenian sea a signature of the dipping adriatic moho is clearly observed beneath the tyrrhenian moho in a large portion of the forearc region in the area where the two mohos overlap our new analysis reveals the presence of an anisotropic body above the subducted moho there is a strong ps converted phase with anisotropic characteristics from the top of the adriatic plate to a depth of at least 80 km because the ps conversion occurs much deeper than similar ps phases in cascadia and japan dehydration of oceanic crust seems unlikely as a causative factor rather the existence of this body trapped between the two interfaces supports the hypothesis of lower crustal delamination in a postsubduction tectonic setting

tectonostratigraphic evolution of the labrador margin atlantic canada abstract the labrador continental margin provides a rich source of data with which to study the relationships between stratigraphy tectonics and paleoenvironment we have completed a regional seismic interpretation and integrated this with new biostratigraphic data based on analyses of palynomorphs from wells in the hopedale and saglek basins which occur on this margin our results are summarized in a tectonostratigraphic chart which displays new and consistent age control for the major lithostratigraphic units and provides more precise evaluation of their depositional and paleoenvironmental history we have identified and dated six regional unconformities in the wells and we can recognize several others on the seismic data the older unconformities cretaceous are related to the tectonics of rifting and seafloor spreading and may delineate the onset of different stages of the rift process in the paleocene early eocene unconformity development was influenced by episodic volcanism due to the passage of the proto iceland hotspot to the north and to a major change in spreading direction in the labrador sea many of these unconformities are also identified in offshore southwest greenland and the grand banks suggesting widespread controlling mechanisms during the post seafloor spreading stage the effects of mass wasting and slumping and of paleoenvironmental controls on the stratigraphy were more pronounced we discuss the petroleum potential of the hopedale basin in terms of the structures we see on the seismic data and highlight the bjarni formation which likely contains the most prospective source and reservoir rocks in this basin

seismic anisotropy produced by serpentine in mantle wedge abstract trench parallel seismic anisotropy has been observed in many subduction zones in the upper mantle in this study the crystal preferred orientation cpo and seismic anisotropy of natural serpentine from val malenco in northern italy and punta bettolina in western italy are studied it is found that the 001 axes are aligned subnormal to the foliation but the 010 axes of the serpentine are aligned subparallel to the lineation which is significantly different from that produced in a recent high pressure experiment cpos of serpentine found herein can be used to explain the trench parallel seismic anisotropy in a cold mantle wedge for serpentine deformed not only at angles greater than 45 but also at low angles such as in horizontal shear from the surface indicating the broader implications of the cpo of serpentine for interpreting seismic anisotropy than previously thought it is also found that seismic anisotropy caused by the cpo of serpentine depends on the degree of serpentinization and flow geometry the seismic anisotropy increases with antigorite volume fraction the seismic anisotropy of shear waves is large i e 23 36 for samples with an antigorite volume fraction of 40 93 current data suggest that the trench parallel seismic anisotropy with a delay time of 1 2 s in the forearc mantle wedge can be attributed to the cpo of antigorite having 010 axes aligned subparallel to the flow direction and 001 axes subnormal to the flow plane

ikaite pseudomorphs in the zaire deep sea fan an intermediate between calcite and porous calcite translucent brown aggregates of calcium carbonate crystals have been found in cores from the zaire deep sea fan west equatorial africa the aggregates are well preserved but very friable upon storage they become yellowish white and cloudy and release water chemical mineralogical xrd petrographical crystal morphological and stable isotope data demonstrate that the crystals have passed through three phases 1 an authigenic carbonate phase probably calcium carbonate which is represented by the external habit of the present crystals 2 a translucent brown ikaite phase caco 3 6h 2 o unstable at temperatures above 5 c and 3 a phase consisting of calcite microcrystals that are poorly cemented and form a porous mass within the crystal form of the morphologically unchanged first phase the transformation from the first phase into ikaite was probably a kinetic replacement the transformation from ikaite into the third phase occurred because of storage at room temperature the presence of ikaite is indicative of a low temperature anaerobic organic carbon rich marine environment ikaite is probably the precursor of a great number of porous calcite pseudomorphs and possibly also of many marine authigenic microcrystalline carbonate nodules

complex rifted continental margins explained by dynamical models of depth dependent lithospheric extension observations from a number of rifted margins e g south atlantic salt basin mid norwegian margin exmouth plateau reveal wide regions of extremely attenuated crust and depositional environments that indicate depth dependent lithospheric extension although the one dimensional thermal kinematic consequences of depth dependent extension are understood no comprehensive process based explanation for the complex style of these margins exists here we present self consistent numerical models of passive margin formation that explain the depth dependent extension the width of the margin its characteristic tripartite nature and why such margins are prone to deposition of evaporites under appropriate climatic conditions some features that are important to reproducing the observed characteristics include decoupling between upper and lower parts of the lithosphere during stretching contrasting wide and narrow extensional styles above and below the decoupling level and progressive focusing of crustal extension toward the rift axis

shear wave splitting beneath the southwestern kurile arc and northeastern japan arc a new insight into mantle return flow 1 shear wave splitting in the southwestern part of the kurile arc and the northeastern ne japan arc is investigated using the waveforms from local earthquakes for both arcs observed shear wave splitting shows clear evidence for a striking rotation of fast direction across the arc suggesting the different feature of anisotropy between the fore arc and back arc sides trench parallel fast directions are observed in the fore arc side which is consistent with the anisotropy expected from the deformation of the b type olivine fabric as well as the anisotropy in the slab fast directions observed in the back arc side show approximately e w and ese wnw in the ne japan arc and n s in the southwestern kurile arc which are characterized by the local maximum dip direction of the subducted pacific plate not by the direction of plate convergence this relationship suggests that the direction of the mantle return flow is governed by the local slab geometry

u th systematics and ages of authigenic carbonates from hydrate ridge cascadia margin recorders of fluid flow variations uranium u concentrations and activity ratios 234u of authigenic carbonates are sensitive recorders of different fluid compositions at submarine seeps of hydrocarbon rich fluids cold seeps at hydrate ridge off the coast of oregon usa the low u concentrations mean 1 3 0 4 g g and high 234u values 165 317 of gas hydrate carbonates reflect the influence of sedimentary pore water indicating that these carbonates were formed under reducing conditions below or at the seafloor their 230th 234u ages span a time interval from 0 8 to 6 4 ka and cluster around 1 2 and 4 7 ka in contrast chemoherm carbonates precipitate from marine bottom water marked by relatively high u concentrations mean 5 2 0 8 g g and a mean 234u ratio of 166 3 their u isotopes reflect the 234u ratios of the bottom water being enriched in 234u relative to normal seawater simple mass balance calculations based on u concentrations and their corresponding 234u ratios reveal a contribution of about 11 of sedimentary pore water to the bottom water from the u pore water flux and the reconstructed u pore water concentration a mean flow rate of about 147 68 cm a can be estimated 230th 234u ages of chemoherm carbonates range from 7 3 to 267 6 ka 230th 234u ages of two chemoherms alvin and se knoll chemoherm correspond to time intervals of low sealevel stands in marine isotope stages mis 2 4 5 6 7 and 8 this observation indicates that fluid flow at cold seep sites sensitively reflects pressure changes of the hydraulic head in the sediments the 18o pdb ratios of the chemoherm carbonates support the hypothesis of precipitation during glacial times deviations of the chemoherm 18o values from the marine 18o record can be interpreted as to reflect temporally and spatially varying bottom water and or vent fluid temperatures during carbonate precipitation between 2 6 and 8 6 c

glendonites in neoproterozoic low latitude interglacial sedimentary rocks northwest canada insights into the cryogenian ocean and precambrian cold water carbonates stellate crystals of ferroan dolomite in neritic siliciclastic and carbonate sedimentary rocks between sturtian and marinoan glaciations in the mackenzie mountains are interpreted as replaced glendonites these pseudomorphs after ikaite indicate that shallow seawater at that time was near freezing stromatolites verify that paleoenvironments were in the photic zone and physical sedimentary structures such as hummocky cross bedding confirm that the seafloor was repeatedly disturbed by storms glendonites within these low latitude continental shelf to coastal sedimentary deposits imply that global ocean water during much of cryogenian time was likely very cold such an ocean would easily have cooled to yield widespread sea ice and through positive feedback growth of low latitude continental glaciers in this situation gas hydrates could have formed in shallow water cold shelf sediment but would have been particularly sensitive to destabilization as a result of sea level change co occurrence of pisolites and glendonites in these rocks additionally implies that some ooids and pisoids might have been unlike phanerozoic equivalents characteristic of cold water sediments