diagenetic fate of biogenic soft and hard magnetite in chemically stratified sedimentary environments of mamangua ria brazil d r and l j acknowledge funding from fapesp grants 2012 212123 and 2011 22018 3 respectively f a acknowledges funding from faperj cnpq and capes a p r acknowledges funding from the australian research council grants dp140104544 and dp160100805

determination of the stable iron isotopic composition of sequentially leached iron phases in marine sediments abstract reactive iron oxyhydr oxide minerals preferentially undergo early diagenetic redox cycling which can result in the production of dissolved fe ii the adsorption of fe ii onto particle surfaces and the formation of authigenic fe minerals the partitioning of iron in sediments has traditionally been studied by applying sequential extractions that target operationally defined iron phases here we complement an existing sequential leaching method by developing a sample processing protocol for 56fe analysis which we subsequently use to study fe phase specific fractionation related to dissimilatory iron reduction in a modern marine sediment carbonate fe was extracted by acetate easily reducible oxides e g ferrihydrite and lepidocrocite by hydroxylamine hcl reducible oxides e g goethite and hematite by dithionite citrate and magnetite by ammonium oxalate subsequently the samples were repeatedly oxidized heated and purified via fe precipitation and column chromatography the method was applied to surface sediments collected from the north sea south of the island of helgoland the acetate soluble fraction targeting siderite and ankerite showed a pronounced downcore 56fe trend this iron pool was most depleted in 56fe close to the sediment water interface similar to trends observed for pore water fe ii we interpret this pool as surface reduced fe ii rather than siderite or ankerite that was open to electron and atom exchange with the oxide surface common extractions using 0 5 m hcl or na dithionite alone may not resolve such trends as they dissolve iron from isotopically distinct pools leading to a mixed signal na dithionite leaching alone for example targets the sum of reducible fe oxides that potentially differ in their isotopic fingerprint hence the development of a sequential extraction fe isotope protocol provides a new opportunity for detailed study of the behavior of iron in a wide range of environmental settings

de glauconiarum origine the glauconitic facies is widespread on present day continental shelves from 50 s to 65 n and at water depths between 50 and 500 m and is in particularly great abundance on the upper slope and outer shelf between 200 and 300 m it is also common in many ancient rocks of post late precambrian age it occurs as sand to pebble sized essentially green particles granular facies but also as a surface coating on particles and hardgrounds and as a diffuse impregnation film and diffuse facies we suggest the replacement of the term glauconite which has been interchangeably used to designate a morphological form and a specific mineral by glaucony facies and glauconitic smectite and glauconitic mica as end members of the glauconitic mineral family the widely accepted model of burst and hower for glauconitization requires a degraded micaceous 2 1 layer lattice structure parent clay mineral however detailed analysis of numerous samples of recent glaucony reveals that such a parent substrate is exceptional the model therefore requires modification generally the parent material is carbonate particles argillaceous kaolinitic faecal pellets infillings of foraminiferal tests various mineral grains and rock fragments that pass gradually into the commonly occurring green grains we show that the process of glauconitization is achieved by de novo authigenic growth of automorphous crystallites in the pores of the substrate accompanied by progressive alteration and replacement of the substrate it is this two fold evolution that causes the verdissement of granular substrates macrofossils and hardgrounds the authigenic mineral is an iron rich and potassium poor glauconitic smectite while new smectites are growing into the remaining pore space the earlier smectites are modified by incorporation of potassium producing decreasingly expandable minerals with a non expandable glauconitic mica as the end member this mineralogical diversity of the glauconitic mineral family explains the highly variable physical and chemical properties of glaucony four categories nascent little evolved evolved and highly evolved glaucony are distinguished glauconitization appears to be controlled by a delicate balance between degree of physical confinement of a particle and the amount of ionic exchange between the micro environment and ambient open marine sea water the optimum conditions for glauconitization are those of semi confinement as a result the interior of a grain is more glauconitized than its less confined periphery similarly for identical substrate types large grains 500 m provide more favourable substrates for glauconitization than lesser confined small grains on a larger scale the formation of glaucony is governed by the availability of iron and potassium and the balance between detrital influx and winnowing low accumulation rates expose grains to the open marine environment for sufficiently long times 105 106 years for highly evolved glaucony

tectonic constraints on a deep seated rock slide in weathered crystalline rocks abstract deep seated rock slides dsrss recognised as one of the most important mass wasting processes worldwide involve large areas and cause several consequences in terms of environmental and economic damage they result from a complex of controlling features and processes dsrss are common in calabria southern italy where the complex geo structural setting plays a key role in controlling the geometry of the failure surface and its development this paper describes an integrated multi disciplinary approach to investigate a dsrs in palaeozoic high grade metamorphic rocks of the sila massif it focuses on the definition of the internal structure and the predisposing factors of the serra di buda landslide near the town of acri which is a paradigm for numerous landslides in this area an integrated interdisciplinary study based on geological structural and geomorphological investigations including field observations of weathering grade of rocks minero petrographic characterisations geotechnical investigations and in particular fifteen years of displacement monitoring is presented stereoscopic analysis of aerial photographs and field observations indicate that the serra di buda landslide consists of two distinct compounded bodies i an older and dormant body 7 ha and ii a more recent and active body 13 ha that overlies the previous one the active landslide shows movement linked to a deep seated translational rock slide block slide the velocity scale ranges from slow 1 6 m year during paroxysmal stages to extremely slow

cyclic 100 ka glacial interglacial migration of subseafloor redox zonation on the peruvian shelf the coupling of subseafloor microbial life to oceanographic and atmospheric conditions is poorly understood we examined diagenetic imprints and lipid biomarkers of past subseafloor microbial activity to evaluate its response to glacial interglacial cycles in a sedimentary section drilled on the peruvian shelf ocean drilling program leg 201 site 1229 multiple and distinct layers of diagenetic barite and dolomite i e minerals that typically form at the sulfate methane transition smt occur at much shallower burial depth than the present smt around 30 meters below seafloor these shallow layers co occur with peaks of 13c depleted archaeol a molecular fossil of anaerobic methane oxidizing archaea present day non steady state distributions of dissolved sulfate also suggest that the smt is highly sensitive to variations in organic carbon flux to the surface shelf sediments that may lead to shoaling of the smt reaction transport modeling substantiates our hypothesis that shallow smts occur in response to cyclic sediment deposition with a high organic carbon flux during interglacials and a low organic carbon flux during glacial stages long diffusion distances expectedly dampen the response of deeply buried microbial communities to changes in sediment deposition and other oceanographic drivers over relatively short geological time scales e g glacial interglacial periods however our study demonstrates how dynamically sediment biogeochemistry of the peru margin has responded to glacial interglacial change and how these changes are now preserved in the geological record such changes in subsurface biogeochemical zonation need to be taken into account to assess the role of the subseafloor biosphere in global element and redox cycling

modeling of calcite dissolution by oxic respiration in supralysoclinal deep sea sediments abstract pore water profiles of co2 ph ca2 and o2 in situ concentrations were measured at two stations on the upper continental slope off gabon the present study evaluates these measurements concerning their implications for the calcium carbonate system in deep sea sediments the model cotrem which was used to simulate the dynamics of this complex geochemical system revealed a strong dependence of calcite dissolution on oxic respiration at both sites all simulated calcite dissolution kinetics reached a dynamic equilibrium with almost equal calcite dissolution rates but different sub saturation states and ph values the latter are mainly dependent on boundary conditions and kinetic rate law parameters boundary conditions are of immense importance they define which ph deviations between measured data and the simulated equilibration instantaneous kinetics have still to be fitted by kinetic restrictions per rate law for the equilibration these ph deviations set up the range of possible values for rate constants in a given rate law to yield a well simulated ph a failure in the implementation of these boundary conditions may lead to non linearly flawed rate constants which fit only one usually the maximal ph deviation well the whole depth distribution of ph deviations has to be fitted very well by a kinetic rate law only this procedure secures that the used boundary conditions and rate laws constants are acceptable nevertheless several kinetic rate laws may be used for good ph fits featuring clear differences in parameter values for rate constants and reaction orders the connection between these rate laws with different parameters is examined and the dependence of the rate constant on the given form of the rate law is demonstrated this study achieves rate constants of 0 038 and 18 d for a dissolution rate law of 4 5th reaction order and sub saturation dependence from the term 1 these results are well within the range of rate constants obtained during former field studies for the same form of the dissolution rate law

kinematic behaviour and velocity characteristics of a complex deep seated crystalline rockslide system in relation to its interaction with a dam reservoir abstract this paper presents the geometry kinematics and temporal deformation characteristics of a deep seated rockslide system the hochmais atemkopf situated above the gepatsch dam reservoir in northern tyrol austria results from surface and subsurface geological investigations and deformation monitoring indicate that the hochmais atemkopf rockslide system involves several sliding masses one on top of the other characterized by different velocity characteristics with displacements being greater for the shallower slide bodies during the initial impounding phases of the gepatsch reservoir uplift forces beneath the foot of the slope led to the activation of one of these shallower slide bodies moving it more than 10 m downslope in 2 years after continuous deceleration of the sliding mass the deformation rates reduced to about 2 to 4 cm per year these were found to show seasonal fluctuations that correlated with reservoir levels and drawdown conditions with induced slope accelerations peaking when reservoir levels were at their lowest this suggests in part a controlling mechanism based on seepage forces where reservoir drawdown drives the episodic rockslide deformation behaviour together the data and analyses presented demonstrate the importance of integrating detailed geology and monitoring data to derive a basic understanding of the kinematics and controlling mechanisms of a deep seated rockslide system in advance of undertaking comprehensive numerical modelling

ferrimagnetic iron sulfide formation and methane venting across the paleocene eocene thermal maximum in shallow marine sediments ancient west siberian sea

reductive diagenesis magnetite dissolution greigite growth and paleomagnetic smoothing in marine sediments a new view abstract in many anoxic sedimentary environments the onset of sulfate reduction and pyritization of detrital iron bearing minerals leads to a precipitous decline in magnetic mineral concentration during early diagenesis the usefulness of the surviving paleomagnetic record in such environments is usually argued to depend on how much of the primary detrital magnetic assemblage survives diagenetic dissolution detailed rock magnetic and electron microscope analyses of rapidly deposited 7 cm kyr latest pleistocene holocene sediments from the continental margins of oman 22 22 4 n 60 08 0 e and northern california 38 24 8 n 123 58 2 w demonstrate that pyritization during early diagenesis also leads to the progressive down core growth of the ferrimagnetic iron sulfide greigite greigite growth begins with nucleation of large concentrations of superparamagnetic sp nanoparticles at the inferred position of the sulfate methane transition which can explain the apparently paradoxical suggestion that diagenetically reduced sediments contain enhanced concentrations of sp particles looping of hysteresis parameters on a day plot records the dissolution of single domain sd titano magnetite and the formation of sp greigite which then slowly and progressively grows through its sd blocking volume and acquires a stable paleomagnetic signal this looping trend is also evident in data from several published records oregon margin korea strait japan sea niger fan argentine margin and the ontong java plateau indicating that these processes may be widespread in reducing environments our observations have profound implications for paleomagnetic records from sulfate reducing environments the paleomagnetic signal recorded by greigite is offset from the age of the surrounding sediments by 10 s of kyr and ongoing growth of greigite at depth results in smoothing of the recorded signal over intervals of 10 s to 100 s of kyr we therefore expect the presence of greigite to compromise paleomagnetic records in a wide range of settings that have undergone reductive diagenesis

the early diagenesis of iron in pelagic sediments a multidisciplinary approach abstract biogeochemical reactions of iron within pelagic sediments from the eastern and western equatorial atlantic are investigated by means of pore water chemistry chemical leaching experiments and total elemental determinations color reflectance spectroscopy rock magnetic measurements and tem observations of the magnetic fraction results indicate that in the presence of nitrate ascorbate a weak reducing agent leachable iron decreased with depth from the sediment surface within this upper sediment region iron assimilation by bacteria is indicated as magnetosomes were found by tem observations throughout the whole core extractions with a strong reducing agent dithionite representing iron bound to iron oxides correlated linearly with the concentration of highly coercive magnetic minerals and with the reflection intensity of red color within the same iron redox zone the abrupt decrease of red color reflection intensity relative to the amount of iron oxides below the iron redox boundary is the result of a decrease in the specific surface area of iron oxyhydroxide oxides magnetic parameters imply a smaller average grain size of the magnetic fraction below the iron redox boundary arising from an increase in biogenic magnetite formed by magnetotactic assimilatory bacteria dissolution of very fine grained magnetite and the gradual decrease of coarser grained terrigenous titano magnetite with depth the early diagenetically formed magnetic fraction withstands subsequent dissolution and gives pronounced peaks of magnetic parameters within sediments with high carbonate and low terrigenous matter content

deep sulfate methane transition and sediment diagenesis in the gulf of alaska iodp site u1417 abstract sediment samples from the gulf of alaska goa iodp expedition 341 site u1417 have been analyzed to understand present and past diagenetic processes that overprint the primary sediment composition no sulfate methane transition zone smtz was observed at the zone of sulfate depletion but a 200 m thick sulfate and methane free sediment interval occurred between the depth of sulfate depletion 200 m and the onset of methanogenesis 440 m we suggest that this apparent gap in biogeochemical processing of organic matter is caused by anaerobic oxidation of methane fueled by sulfate which is released during dissolution of barites at the upper boundary of the methane rich layer beneath the methanogenic zone at 650 m depth pore water sulfate concentrations increase again indicating sulfate supply from greater depth feeding into a deep inverse smtz a likely explanation for the availability of sulfate in the deep sub seafloor at u1417 is the existence of a deep aquifer related to plate bending fractures which actively transports sulfate rich water to and potentially along the interface between sediments and oceanic crust such inverse diagenetic zonations have been previously observed in marine sediments but have not yet been linked to subduction related plate bending with the discovery of a deep inverse smtz in an intra oceanic plate setting and the blocking of upward methane diffusion by sulfate released from authigenic barite dissolution site u1417 provides new insights into sub seafloor pore fluid and gas dynamics and their implications for global element cycling and the deep biosphere

numerical modelling of slope damage in large slowly moving rockslides insights from the downie slide british columbia canada abstract the deformation of rock slopes is associated with the formation and accumulation of internal and external features such as tension cracks rock mass bulging and dilation rockfall etc that can be comprehensively referred to as slope damage in this paper we use a 3d distinct element numerical modelling approach to investigate the role of shear zone morphology and groundwater pressure on the displacement and slope damage accumulation at the downie slide a large extremely slowly moving rockslide in british columbia canada first we briefly review the external slope damage features that can be observed in an airborne laser scanner als dataset allowing four slope damage domains upper central northern and southern domain to be interpreted within the slide area based on the orientation and type of features using the same als dataset we construct a 3d model of the present day slope explicitly including the two shear zones along which displacements occur in order to investigate their role in the later stage of the landslide evolution we assign a strain softening constitutive model to the slide body in order to account for the decrease in material properties due to damage accumulation virtual inclinometers are also implemented in the model allowing for the comparison of simulated and observed displacement direction along the shear zones the progressive deformation and failure of the slope is then simulated both assuming dry and wet conditions in order to examine the role of pore water pressure and the morphology of the upper and lower shear zones on the magnitude orientation and distribution of displacements for each numerical model the simulated slope damage features are recorded by analyzing the zone volumetric strain and failure state and compared with the type and orientation of features observed in each of the interpreted slope damage domains thus allowing the numerical results to be better constrained and validated it is clearly demonstrated that the orientation and distribution of slope damage and displacements observed in both the surface als and the subsurface borehole inclinometer data can be well reproduced in the 3d numerical models numerical modelling results show that the principal factor controlling the spatial distribution of slope damage at the downie slide is the morphology of the lower shear zone whereas a negligible role is played by the upper shear zone morphology we also observe that models incorporating a groundwater table display larger displacements without significant effects on the orientation and distribution of simulated slope damage this paper demonstrates that an analysis of slope damage is very important for understanding the mechanisms underlying the behavior of large landslides and should be a fundamental step in the comprehensive characterization of any major slope failure

pyritization processes and greigite formation in the advancing sulfidization front in the upper pleistocene sediments of the black sea pyritization in late pleistocene sediments of the black sea is driven by sulfide formed during anaerobic methane oxidation a sulfidization front is formed by the opposing gradients of sulfide and dissolved iron the sulfidization processes are controlled by the diffusion flux of sulfide from above and by the solid reactive iron content two processes of diffusion limited pyrite formation were identified the first process includes pyrite precipitation with the accumulation of iron sulfide precursors with the average chemical composition of fesn n 1 10 1 29 including greigite elemental sulfur and polysulfides formed from h2s by a reductive dissolution of fe iii containing minerals serve as intermediates to convert iron sulfides into pyrite in the second process a direct pyrite precipitation occurs through prolonged exposure of iron containing minerals to dissolved sulfide methane driven sulfate reduction at depth causes a progressive formation of pyrite with a 34s of up to 15 0 the s isotopic composition of fes2 evolves due to contributions of different sulfur pools formed at different times steady state model calculations for the advancement of the sulfidization front showed that the process started at the pleistocene holocene transition between 6360 and 11 600 yr bp our study highlights the importance of anaerobic methane oxidation in generating and maintaining s enriched layers in marine sediments and has paleoenvironmental implications

long term investigation of a deep seated creeping landslide in crystalline rock part i geological and hydromechanical factors controlling the campo vallemaggia landslide slope movements of the deep seated campo vallemaggia landslide in the southern swiss alps have been reported for over 200 years surface and borehole investigations of the unstable mass reveal an u

deciphering the impact of diagenesis overprint on negative δ13c excursions using rock magnetism case study of ediacaran carbonates yangjiaping section south china rock magnetism is used here to investigate the genesis of one of the puzzling negative carbon isotopic excursions of the neoproterozoic in the yangtze platform south china a detailed characterization of the magnetic mineralogy which includes low temperature and high field magnetometry and classical magnetic measurement arm irm susceptibility was therefore performed along upper doushantuo and lower dengying formations outcropping in the yangjiaping section the derived magnetic parameters show variations that can be interpreted as variations in magnetic grains size and in oxide contents they show that the magnetic content is significantly reduced in samples presenting negative 13ccalcite values we interpret this as a result of magnetite dissolution and secondary carbonate precipitation during early diagenesis bacterial sulfate reduction combined with c and o isotopic data paleomagnetic techniques thus show that the upper doushantuo lower dengying negative excursion of the yangjiaping section is largely due to diagenesis although the preservation of a genuine 13c excursion of lower magnitude from 7 down to 0 instead of down to 9 as usually considered cannot be ruled out a corrected 13ccarbonate chemostratigraphic curve is therefore proposed the unambiguous identification of a strong diagenetic component for this excursion casts doubts on the primary nature of other potentially time equivalent negative excursions of the yangtze platform and thus to its correlation to negative excursions in other cratons i e shuram excursion more generally this study illustrates the potential of magnetic mineralogy characterization a low cost time efficient and non destructive technique as screening tool for diagenetic overprints of 13c and 18o

anaerobic methane oxidation and a deep h2s sink generate isotopically heavy sulfides in black sea sediments the main terminal processes of organic matter mineralization in anoxic black sea sediments underlying the sulfidic water column are sulfate reduction in the upper 2 4 m and methanogenesis below the sulfate zone the modern marine deposits comprise a ca 1 m deep layer of coccolith ooze and underlying sapropel below which sea water ions penetrate deep down into the limnic pleistocene deposits from 9000 years bp sulfate reduction rates have a subsurface maximum at the so42 ch4 transition where h2s reaches maximum concentration because of an excess of reactive iron in the deep limnic deposits most of the methane derived h2s is drawn downward to a sulfidization front where it reacts with fe iii and with fe2 diffusing up from below the h2s fe2 transition is marked by a black band of amorphous iron sulfide above which distinct horizons of greigite and pyrite formation occur the pore water gradients respond dynamically to environmental changes in the black sea with relatively short time constants of ca 500 yr for so42 and 10 yr for h2s whereas the fes in the black band has taken ca 3000 yr to accumulate the dual diffusion interfaces of so42 ch4 and h2s fe2 cause the trapping of isotopically heavy iron sulfide with 34s 15 to 33 at the sulfidization front a diffusion model for sulfur isotopes shows that the so42 diffusing downward into the so42 ch4 transition has an isotopic composition of 19 close to the 23 of h2s diffusing upward these isotopic compositions are however very different from the porewater so42 43 and h2s 15 at the same depth the model explains how methane driven sulfate reduction combined with a deep h2s sink leads to isotopically heavy pyrite in a sediment open to diffusion these results have general implications for the marine sulfur cycle and for the interpretation of sulfur isotopic data in modern sediments and in sedimentary rocks throughout earth s history

geochemical and sedimentological control of the magnetic properties of hemipelagic sediments owing to their high sedimentation rates and wide areal extent hemipelagic sediments along continental borderlands are potentially important high resolution recorders of geomagnetic secular variation to assess this possibility we studied suboxic hemipelagic muds from the oregon continental slope and anoxic laminated diatomaceous oozes from the gulf of california these sediments were rapidly deposited with average sedimentation rates of 121 and 135 cm kyr respectively bulk sediment sedimentological and geochemical analyses indicate that the two areas represent contrasting depositional regimes the remanence in both environments resides in fine grained magnetite particles although minor amounts of hematite were observed in the topmost gulf of california sediments despite first order differences the sediments from both areas show similar downcore patterns of systematic increases in solid sulfur mainly as pyrite dramatic decreases in natural nrm anhysteretic and isothermal remanent magnetization intensities and accompanying shifts in the magnetic stabilities these changes are consistent with reduction and dissolution of the ferrimagnetic iron oxides with depth due to early diagenesis of organic matter the magnetic grain size distribution first appears to rapidly coarsen downcore as the smallest and most abundant grains are removed then slowly grows finer as the remaining particles dissolve no evidence was observed for authigenic formation of magnetite provided sufficient concentration and stability of the detrital magnetic particles paleomagnetic directions can survive this dissolution diagenesis however relative paleointensity determinations based on normalization of nrm by concentration in related parameters will give erroneous estimates of paleofield behavior in such diagenetically altered sediments

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

marine pore water sulfate profiles indicate in situ methane flux from underlying gas hydrate marine pore water sulfate profiles measured in piston cores are used to estimate methane flux toward the sea floor and to detect anomalous methane gradients within sediments overlying a major gas hydrate deposit at the carolina rise and blake ridge u s atlantic continental margin here sulfate gradients are linear implying that sulfate depletion is driven by methane flux from below rather than by the flux of sedimentary organic matter from above thus these linear sulfate gradients can be used to quantify and assess in situ methane flux which is a function of the methane inventory below

enhanced framboidal pyrite formation related to anaerobic oxidation of methane in the sulfate methane transition zone of the northern south china sea abstract many studies have confirmed that size distributions of framboidal pyrite can be an effective indicator of bottom water redox conditions in modern as well as ancient sedimentary environments however one environment in which production of framboidal pyrite has not been sufficiently studied to date is the sulfate methane transition zone smtz in which anaerobic oxidation of methane aom is coupled with microbial sulfate reduction msr to enhance iron sulfide mineral precipitation e g fes2 fes and fe3s4 here we document for the first time size distributions for pyrite framboids from the smtz based on data from two sites in the methane hydrate bearing region of the northern south china sea on the basis of framboid size pyrite concentration and sulfur isotope data we propose new insights into the formation process of authigenic pyrite framboids within the smtz we conclude that 1 enhanced anaerobic oxidation of methane aom not only plays a dominant role in the accumulation of 34s enriched pyrite but also is responsible for formation of highly variable and sometimes exceptionally large pyrite framboids in the smtz 2 most framboids occur in framboid clusters which commonly exhibit rod like shapes secondary overgrowths heavier 34s values and unusual size distributions e g mean size 20 m and standard deviation 3 0 m in the smtz 3 pyrite framboids formed in the smtz which have characteristics different from those formed in the sulfate reduction zone srz do not comment on redox conditions of the overlying water column and 4 framboid occurrences with similar characteristics in ancient marine deposits may be considered indicators of enhanced aom and mark the former position of the smtz in the paleo marine system in addition significant quantities of elemental sulfur were observed in the smtz possibly related to anaerobic oxidation of hydrogen sulfide and fluctuations of the smtz

sediment chemistry and magnetic properties in an anomalously reducing core from the eastern mediterranean sea abstract in core kc19c 19 6 m long recovered in the abyssal plain between crete and cyprus in the eastern mediterranean a large number of organic rich layers sapropels occur which correlate to maxima in the insolation curve in contrast to other sites in the eastern mediterranean porewaters contain sulfide below a few meters below seafloor mbsf geochemical analyses were performed on the porewaters ammonium alkalinity sulfate manganese iron bisulfide chloride eh ph and sediments organic carbon barium total sulfur total iron manganese pyrite dithionite extractable iron in addition a series of magnetic parameters and ratios nrm arm irm in arm irm s ratio arm 20mt arm in were determined in the top of the sediments fe and mn hydr oxides occur at the oxic suboxic boundary just above the youngest sapropel si2 these hydr oxides appear to be more easily demagnetized by means of alternating fields than deeper hydr oxides which presumably are of detrital origin the transition from suboxic to anoxic sediments is located at 2 mbsf sulfide is produced possibly during sulfate reduction through anoxic methane oxidation at 17 5 mbsf from 17 5 mbsf sulfide migrates upward titrating reactive fe resulting in pyrite formation in the entire sediment column up to 2 mbsf at this depth the upward sulfide flux has been totally consumed by reaction with solid phase fe and dissolved fe ii diffusing downward from the suboxic zone above from 2 mbsf downward magnetic intensities are significantly reduced indicating reductive dissolution of fe oxide minerals and pyrite formation as a consequence no reliable nrm data can be obtained in the lower half of the core

aspects of landslide activity in the mercantour massif and the french riviera southeastern france abstract landslides pose serious hazards in the mercantour massif and the french riviera in southeastern france the context for landslide development is a particularly favourable one both in terms of the geomorphic and structural setting of this alpine region and of the climatic hydrologic and seismic factors that trigger such failures high mountain relief and steep slopes constitute a very favourable setting for failures affecting massive basement rocks and a very heterogeneous sedimentary cover whose resistance has been weakened by weathering tectonic stresses and cambering due to gravity among trigger factors the important appears to be the precipitation regime rainfalls are commonly concentrated into short high intensity downpours or into bursts of sustained falls over periods of several days leading to soil saturation and lubrication of potential failure planes snowmelt also contributes to these lubrication processes earthquakes affecting this region are also a potentially important landslide trigger however while a lot of work has been done on the relationship between extreme climatic events and landslide activity much less is known of the trigger effects of earthquakes both the background factors that promote landslide development and the factors that trigger such failures are discussed within a time frame of landslide development progressive changes in soil strength due to weathering rock cambering and shattering processes lead to long term reduction in resistance superimposed on these progressive changes are episodic triggerings related to rainfall and snowmelt episodes or earthquakes landslides may occur as shallow low volume one time events or may be part of a progressive long term failure the former generally affect unconsolidated or clay rich sedimentary rocks especially on the coastal hillslopes of the french riviera a notable exception of a major voluminous one time event was the submarine landslide of the var delta in 1979 this landslide like numerous other smaller subaerial landslides onland was largely a result of human activities this landslide occurred following extensive modification of the var delta and notably reclamation of the steep fine grained delta front deforestation quarrying urbanisation and road network developments are various ways in which human activity has destabilized the coastal hillslopes favouring the development of numerous shallow landslides following each episode of heavy rainfall progressive landslides on the upper hillslopes of the mercantour massif have developed over long time spans order of 101 to 105 yrs and have involved more complex interactions between lithological controls slope characteristics and trigger factors the collelongue and bois de malbosc landslides have evolved into now stable failures buttressed by resistant migmatitic diorites or amphibolites the more voluminous and well monitored clapiere landslide is a relatively simple rotational landslide of the toe failure type this active landslide poses a serious to inhabitants and infrastructure in the tinee valley the importance of continued field monitoring modelling and mapping of landslides and their hazards is emphasised

paleo methane emissions recorded in foraminifera near the landward limit of the gas hydrate stability zone offshore western svalbard we present stable isotope and geochemical data from four sediment cores from west of prins karls forland ca 340 m water depth offshore western svalbard recovered from close to sites of active methane seepage as well as from shallower water depths where methane seepage is not presently observed our analyses provide insight into the record of methane seepage in an area where ongoing ocean warming may be fueling the destabilization of shallow methane hydrate the 13c values of benthic and planktonic foraminifera at the methane seep sites show distinct intervals with negative values as low as 27 8 that do not coincide with the present day depth of the sulfate methane transition zone smtz these intervals are interpreted to record long term fluctuations in methane release at the present day landward limit of the gas hydrate stability zone ghsz shifts in the radiocarbon ages obtained from planktonic foraminifera toward older values are related to methane derived authigenic carbonate overgrowths of the foraminiferal tests and prevent us from establishing the chronology of seepage events at shallower water depths where seepage is not presently observed no record of past methane seepage is recorded in foraminifera from sediments spanning the last 14 ka cal bp 14c ams dating 13c values of foraminiferal carbonate tests appear to be much more sensitive to methane seepage than other sediment parameters by providing nucleation sites for authigenic carbonate precipitation foraminifera thus record the position of even a transiently stable smtz which is likely to be a characteristic of temporally variable methane fluxes

simultaneous formation of iron rich layers at different redox boundaries in sediments of the amazon deep sea fan high resolution examinations of the solid phase have been performed on a gravity core that shows the typical amazon fan stratigraphy of the last 20 000 years the sedimentary record is characterized by two pronounced enrichments of solid phase fe the first fe peak from 0 34 to 0 37 m sediment depth consists of an indurated fe oxyhydroxide crust located close to the pleistocene holocene boundary this peak represents a widespread nonsteady state diagenetic feature on the fan the second fe peak is a pronounced enrichment of authigenic fe sulfides located between 6 15 and 6 45 m in the sediment the formation of this maximum is attributed to sulfate reduction that is mainly driven by anaerobic methane oxidation based on so42 pore water profiles and calculations of the time of formation of the fe sulfide enrichment we conclude that both fe rich layers formed more or less simultaneously the condition that caused both fe enrichments is a period of nonsteady state diagenesis induced by a pronounced decrease in sedimentation and organic carbon accumulation rates between the pleistocene and the holocene during this depositional change the redox boundaries and reaction fronts were fixed at particular sediment levels for a prolonged time thus producing higher concentrations of the authigenic minerals than possible under steady state diagenetic conditions

non steady state magnetic mineral reduction chemical lock in and delayed remanence acquisition in pelagic sediments abstract magnetic hysteresis data collected from pelagic sediment sites in the western equatorial pacific ocean define a progressive deepening of modern redox boundaries with decreased organic carbon input paleomagnetic data from the site with the highest organic carbon shows marked changes in the natural remanent magnetization at the modern fe redox boundary suggesting a type of chemical lock in process in which some magnetic grains form in situ above the boundary and freely orient in the field the depth of chemical lock in suggests paleomagnetic data will be smoothed on time scales ranging from less than 40 kyr to more than 425 kyr the higher values are compatible with models calling for a delayed remanence acquisition to account for the saw tooth pattern observed in some sedimentary paleointensity records

formation processes geomechanical characterisation and buttressing effects at the toe of deep seated rock slides in foliated metamorphic rock abstract in order to increase the understanding of deep seated rock slides in terms of formation processes kinematics and the impact of geometrical factors on slope stability and deformation behaviour a 300 m thick active rock slide located in austria was investigated results of geological and geodetic field surveys geophysical in situ investigations and numerical modelling are presented and analysed particular focus is given on the geomechanical characterisation of the rock slide mass progressive topographical slope changes due to initial rock slide formation processes internal rock mass deformation processes and back calculated strength properties of the basal shear zone back calculations considering the actual rock slide geometry yields a friction angle of the basal shear zone of about 24 rock slide volume balance analyses are performed in order to determine mass loss due to secondary slides and river erosion in relation to the pre failure topography the middle to upper part of the rock slide has lost zone of depletion and the foot of the slope has accumulated rock mass material zone of accumulation gis based estimations show an enormous volume imbalance between the depletion and accumulation zones given that the volume accumulation at the foot of the slope is nearly three times smaller than the volume depletion at higher elevations considerable erosion of the toe by the river has occurred the complex geological interaction of the rock slide with the alluvium at the toe of the slope was a key question of this study and thus the geomechanical impact of the alluvium on slope deformation and stability behaviour was studied by applying 2d discrete element modelling methods results show that the alluvium at the foot of the slope has a positive effect on the slope stability and the sensitivity of the stability behaviour

anaerobic methane oxidation on the amazon shelf anaerobic methane oxidation on the amazon shelf is strongly controlled by dynamic physical sedimentation processes rapidly accumulating physically reworked deltaic sediments characteristic of much of the shelf typically support what appear to be low rates of steady state anaerobic methane oxidation at depths of 5 8 m below the sediment water interface methane oxidation in these cases is responsible for 10 m methane charged sediment directly to seawater in this nonsteady state situation methane is a major source of recently produced co2 and an important reductant for sulfate these observations suggest that authigenic sedimentary carbonates derived from anaerobic methane oxidation may sometimes reflect physically enhanced nonsteady state exposure of methane to sulfate in otherwise biogeochemically unreactive deposits the concentration profiles of ch4 so 4 and co2 in the eroded deposit were reproduced by a coupled reaction transport model this area of the shelf was reexposed to seawater approximately 5 10 years ago based on the model results and the assumption that the erosion of the deposit occurred as a single event that has now ceased the necessary second order rate constant for anaerobic methane oxidation was 0 1 mm 1 d 1

viscous type sliding laws for landslides sliding of a moving soil mass along a basal surface is analyzed and viscous type sliding laws are presented they relate the relative sliding velocity at the base or at an interface to the state of stress at this surface examples of practical parameter determination illustrate the suitability of this approach two landslides in switzerland and in france provide the data for this purpose a third site la frasse switzerland serves as an example of three dimensional analysis of creeping slopes using the proposed formulation comparison of computed and measured velocity distributions shows the method to be promising key words landslides creep sliding law time dependence interface

twenty ninth canadian geotechnical colloquium the role of advanced numerical methods and geotechnical field measurements in understanding complex deep seated rock slope failure mechanisms the underlying complexity associated with deep seated rock slope stability problems usually restricts their treatment to phenomenological studies that are largely descriptive and qualitative quant

sulfate reduction in surface sediments of the southeast atlantic continental margin between 15 38 s and 27 57 s angola and namibia sulfate reduction rates in the surface sediments from 17 stations from an along slope transect 1 300 m and from a cross slope transect 855 4 766 m were determined in the continental margin sediments of the benguela upwelling system profiles at all sites in the upwelling area showed increasing sulfate reduction rates from near zero at the surface to a peak at 2 5 cm up to 29 nmol cm 23 d 21 and then decreasing exponentially with depth to near background rates at 10 20 cm depth 2 nmol cm 23 d 21 depth integrated sulfate reduction rates were greatest at 1 300 m and decreased exponentially with water depth along the transect following the 1 300 m isobath depthintegrated sulfate reduction rates were highest in the north cape basin 1 16 6 0 23 mmol m 22 d 21 decreased over the walvis ridge 0 67 6 0 02 mmol m 22 d 21 and were lowest in the south angola basin 0 31 6 0 23 mmol m 22 d 21 depth integrated sulfate reduction rates were consistent with the known pattern of coastal upwelling intensities and were also strongly correlated with surface organic carbon concentrations sulfate reduction rates both as a function of depth and in comparison with sediment trap data indicated that lateral downslope transport of organic carbon occurs sulfate reduction was estimated to account for 20 90 of the published rates of total oxygen consumption for the sediments at 1 300 m depth and 3 16 of sediments from 2 000 to 3 000 m depth comparison of the sulfate reduction rate profiles with the published diffusive oxygen uptake rates showed that the kinetics of oxygen utilization in the surface sediments are much faster than those for anaerobic organic carbon remineralization although the underlying cause of the difference was not clear

a comparison of benthic nutrient fluxes from deep sea sediments off namibia and argentina abstract benthic fluxes of nitrate phosphate silicate and oxygen estimated c org input to the sea floor and c org content of surface sediments at various stations in the argentine basin and the cape basin south atlantic were used to characterize the benthic mineralization pattern in these areas diffusive benthic fluxes across the sediment water interface reveal very intense subsurface biodegradation of organic matter and dissolution of biogenic silica across the namibian continental margin diffusive benthic fluxes generally decrease with increasing water depth but a considerable site to site variation exists along the 1300 m isobath mineralization patterns indicate that the input flux of organic matter seems to be significantly controlled by vertical transport through the water column a nearly reverse pattern can be observed in the western argentine basin intense nutrient release is observed even at locations on the deeper slope for this whole area a dependence of nutrient release and water depth is not observed an exception is the rio de la plata region where stations between 1800 and 3500 m water depth reveal the highest nitrate and phosphate fluxes decreasing towards the shelf and into the deeper basin silicate fluxes off the rio de la plata increase continuously with water depth below 4000 m water depth this is probably due to the input of antarctic diatoms by the antarctic bottom water mineralization processes on the continental margin of the argentine basin do not correlate with the estimated organic matter input from surface waters in accordance with previous sedimentological studies we conclude that intense sediment mass flows from the shelf are the main source for the input of reactive organic matter to the deeper parts of the continental margin

kinematics and rheology of a major landslide based on signal analysis a detailed geodetic record which is over 23 years old and describes the kinematics of the mandria or left bank upstream landslide a major deep seated landslide close to the polyphyton dam greece was analysed on the basis of advanced signal analysis techniques without any geotechnical constraints it was found that all points share the same pattern of displacement which characterises both short and longer records the overall behaviour of the landslide can be described as viscoelastic and viscous or elastoviscous with multi annual periodic effects superimposed on the creep as the results of spectral analysis indicate the landslide seems insensitive to seasonal variations of precipitation and to annual fluctuations of the reservoir level although the first filling of the reservoir is likely to have had an important role in its movement there is a lack of subsurface information but the available data indicate that the landslide corresponds to a rigid mass dominated by brittle behaviour and int

magnetite diagenesis in marine sediments from the oregon continental margin the magnetochemistry of sediments from the oregon continental margin is examined to determine the effects of iron sulfur diagenesis on the paleomagnetic record magnetic mineral dissolution and transformation into iron sulfides are a common feature in these suboxic to anoxic lutites these processes are evidenced in rapid decreases in natural remanent magnetization intensities and stabilities systematic changes in other rock magnetic properties and increases in solid phase sulfur concentrations with depth hysteresis measurements are used to evaluate downcore changes in magnetite concentration and grain size magnetite abundances decrease downcore from initial values of about 0 1 and nominal grain diameters lie within a narrow pseudosingle domain range of 0 08 to 0 6 m a first order surface area reaction model da dt ka is proposed to explain the magnetite dissolution mechanism where a is the total magnetite surface area and k is the rate constant the solution of this equation predicts that the surface area and concentration decrease exponentially and the concentration in addition depends on grain size application of this model in two cores where grain size varies with depth successfully explains the downcore profiles of both concentration and surface area despite extensive magnetite destruction magnetic directions in such sediments appear to reliably record long wavelength trends of the geomagnetic field

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

impact of iron release by volcanic ash alteration on carbon cycling in sediments of the northern hikurangi margin abstract we present geochemical data collected from volcanic ash bearing sediments on the upper slope of the northern hikurangi margin during the rv sonne so247 expedition in 2016 gravity coring and seafloor drilling with the marum mebo200 allowed for collection of sediments down to 105 meters below seafloor mbsf release of dissolved sr2 with isotopic composition enriched in 86sr 87sr 86sr minimum 0 708461 at 83 5 mbsf is indicative of ash alteration this reaction releases other cations in the 30 70 mbsf depth interval as reflected by maxima in pore water ca2 and ba2 concentrations in addition we posit that fe iii in volcanogenic glass serves as an electron acceptor for methane oxidation a reaction that releases fe2 measured in the pore fluids to a maximum concentration of 184 m several lines of evidence support our proposed coupling of ash alteration with fe mediated anaerobic oxidation of methane fe aom beneath the sulfate methane transition smt which lies at 7 mbsf at this site in the 30 70 mbsf interval we observe a concurrent increase in fe2 and a depletion of ch4 with a well defined decrease in 13 c ch4 values indicative of microbial fractionation of carbon the negative excursions in 13 c values of both dic and ch4 are similar to that observed by sulfate driven aom at low so 4 2 concentrations and can only be explained by the microbially mediated carbon isotope equilibration between ch4 and dic mass balance considerations reveal that the iron cycled through the coupled ash alteration and aom reactions is consumed as authigenic fe bearing minerals this iron sink term derived from the mass balance is consistent with the amount of iron present as carbonate minerals as estimated from sequential extraction analyses using a numerical modeling approach we estimate the rate of fe aom to be on the order of 0 4 mol cm 2 yr 1 which accounts for 12 of total ch4 removal in the sediments although not without uncertainties the results presented reveal that fe aom in ash bearing sediments is significantly lower than the sulfate driven ch4 consumption which at this site is 3 0 mol cm 2 yr 1 we highlight that fe iii in ash can potentially serve as an electron acceptor for methane oxidation in sulfate depleted settings this is relevant to our understanding of c fe cycling in the methanic zone that typically underlies the smt and could be important in supporting the deep biosphere

carbon sulfur iron relationships in sedimentary rocks from southwestern taiwan influence of geochemical environment on greigite and pyrrhotite formation the importance of the magnetic iron sulfide minerals greigite fe3s4 and pyrrhotite fe7s8 is often underappreciated in geochemical studies because they are metastable with respect to pyrite fes2 based on magnetic properties and x ray diffraction analysis previous studies have reported widespread occurrences of these magnetic minerals along with magnetite fe3o4 in two thick plio pleistocene marine sedimentary sequences from southwestern taiwan different stratigraphic zones were classified according to the dominant magnetic mineral assemblages greigite pyrrhotite and magnetite dominated zones greigite and pyrrhotite are intimately associated with fine grained sediments whereas magnetite is more abundant in coarse grained sediments we measured total organic carbon toc total sulfur ts total iron fet 1n hcl extractable iron fea and bulk sediment grain size for different stratigraphic zones in order to understand the factors governing the formation and preservation of the two magnetic iron sulfide minerals the studied sediments have low ts fea weight ratios 0 03 0 2 far below that of pyrite 1 15 which indicates that an excess of reactive iron was available for pyritization observed low ts 0 05 0 27 is attributed to the low organic carbon contents toc 0 25 0 55 which resulted from dilution by rapid terrigenous sedimentation the fine grained sediments also have the highest fet and fea values we suggest that under conditions of low organic carbon provision the high iron activity in the fine grained sediments may have removed reduced sulfur so effectively that pyritization was arrested or retarded which in turn favored preservation of the intermediate magnetic iron sulfides the relative abundances of reactive iron and labile organic carbon appear to have controlled the transformation pathway of amorphous fes into greigite or into pyrrhotite compared to pyrrhotite dominated sediments greigite dominated sediments are finer grained and have higher fea but lower ts we suggest that diagenetic environments with higher supply of reactive iron lower supply of labile organic matter and consequently lower sulfide concentration result in relatively high eh conditions which favor formation of greigite relative to pyrrhotite

geological and morphological study of the daguangbao landslide triggered by the ms 8 0 wenchuan earthquake china abstract landslides are one of the most significant geomorphic processes in mountainous regions recently a gigantic landslide daguangbao dgb landslide with a volume of 1 2 109 m3 was triggered by the ms 8 0 wenchuan earthquake china and has attracted widespread attention this landslide 28 38 16 93 e 104 06 02 35 n is located 85 km north northeast nne of the epicenter and on the hanging wall side 4 km away from the surface rupture zone of the earthquake our long term 2008 present study which includes topographic interpretation and geological and geomorphological investigations allows us to define the geological model of the dgb landslide and estimate the initiation and traveling mechanisms the topography was studied by using high resolution digital elevation models arial images and abundant photos at different scales are used to performed geomorphological analysis the geology in the landslide area was studied by exploratory trenches a tunnel and terrestrial laser scanning tls the results show that the mass movement destabilized a folded slope along a deep seated average depth of 400 m bedding fault developed in the dolomite of the sinian formation the morphology of the landslide main scarp is characterized by steep 55 75 and high up to 730 m release surfaces resulting from the linkage of three joint sets an excess pore water pressure dependent loss of shear strength at the basal layer during the earthquake is assumed to have favored landslide initiation an internal shear running subparallel to the stratification surface is confirmed to have dominated the longitudinal mobility of the landslide and driven landslide mass thrusting to a height of 500 m on the slopes on the other side of the valley the dgb landslide as a transient destabilization and morphogenesis event has largely contributed to erosion in the study area

pliocene glacial cyclicity in a deep sea sediment drift antarctic peninsula pacific margin abstract giant deep sea sediment drifts are widespread features along the continental rise of the west antarctic peninsula representing the most proximal continuous sedimentary recorders for west antarctic ice events and glacial interglacial cyclicity sediment physical geochemical records and x ray images derived from odp leg 178 site 1095 sediment drift 7 show characteristics in glacial interglacial cyclicity and associated sedimentary processes during early pliocene two boundary types dividing half cycles have been recognized 1 interglacial to glacial transitions that are distinct and characterized by a sharp boundary and abrupt change in lithology 2 glacial to interglacial transitions that are diffuse and characterized by a gradual decline of sediment physical and geochemical values with a marked reduction in sedimentation rates the boundaries defined in conjunction with magneto and biostratigraphic tie points form the framework for the calculation of relative sedimentation and accumulation rates used for reconstructing early pliocene paleoproductivity and terrigenous flux to the drift warm early pliocene climate conditions for west antarctic peninsula region are indicated by open ocean conditions in glacials short residence times of the grounded ice sheet at the shelf edge with sporadic fluctuations as well as periodic collapses of the ice sheet front we propose a 5 phase drift sedimentation model for the early pliocene and postulate a highly dynamic ice sheet likely reduced in thickness resulting in oscillations which lie closer to the shelf edge than was the case during the late quaternary

on the seismic response of deep seated rock slope instabilities insights from numerical modeling abstract earthquake induced landslides constitute a critical component of seismic hazard in mountainous regions while many seismic slope stability analysis methods exist with varying degrees of complexity details of interactions between seismic waves and incipient landslides are not well understood and rarely incorporated in particular for deep seated slope instabilities we present a series of 2d distinct element numerical models aimed at clarifying interactions between earthquakes and large rock slope instabilities the study has two main goals 1 to explore the role of amplification in enhancing co seismic slope deformation a relationship widely discussed in literature but rarely tested quantitatively and 2 to compare our numerical results with the well established newmark method which is commonly used in seismic slope stability analysis we focus on three amplification phenomena 1 geometric topographic amplification 2 amplification related to material contrasts and 3 amplification related to compliant fractures slope height topography seismic velocity contrasts and internal strength and damage history were varied systematically in a series of models with a relatively simple scalable geometry for each model we compute the spatial amplification patterns and displacement induced by real earthquake ground motions we find that material contrasts and internal fracturing create both the largest amplification factors and induced displacements while the effect of geometry is comparably small newmark type sliding block methods underestimate displacements by not accounting for material contrasts and internal fracturing within the landslide body both common phenomena in deep seated slope instabilities although larger amplification factors tend to be associated with greater displacements we did not identify a clear link between ground motion frequency content spectral amplification and induced displacement nevertheless observation of amplification patterns can play an important role in seismic slope stability analyses as 1 strong amplification related to material contrasts or compliant fractures is an indicator of potentially large co seismic displacements and 2 amplification patterns can be used to constrain geological and numerical models used for seismic stability analysis the complexity of wave slope interactions as well as the potential to severely underestimate hazard using newmark type methods motivates use of rigorous numerical modeling for quantitative seismic hazard and risk assessment of large landslides

diagenetic alteration of magnetic signals by anaerobic oxidation of methane related to a change in sedimentation rate geochemical and rock magnetic investigations of sediments from three sites on the continental margin off argentina and uruguay were carried out to study diagenetic alteration of iron minerals driven by anaerobic oxidation of methane aom the western argentine basin represents a suitable sedimentary environment to study nonsteady state processes because it is characterized by highly dynamic depositional conditions mineralogic and bulk solid phase data document that the sediment mainly consists of terrigenous material with high contents of iron minerals as a typical feature of these deposits distinct minima in magnetic susceptibility are observed pore water data reveal that these minima in susceptibility coincide with the current depth of the sulfate methane transition smt where hs is generated by the process of aom the released hs reacts with the abundant iron oxyhydr oxides resulting in the precipitation of iron sulfides accompanied by a nearly complete loss of magnetic susceptibility modeling of geochemical data suggest that the magnetic record in this area is highly influenced by a drastic change in mean sedimentation rate sr which occurred during the pleistocene holocene transition we assume that the strong decrease in mean sr encountered during this glacial interglacial transition induced a fixation of the smt at a specific depth the stagnation has obviously enhanced diagenetic dissolution of iron oxyhydr oxides within a distinct sediment interval this assumption was further substantiated by numerical modeling in which the mean sr was decreased from 100 cm kyr 1 during glacial times to 5 cm kyr 1 in the holocene and the methane flux from below was fixed to a constant value to obtain the observed geochemical and magnetic patterns the smt must remain at a fixed position for 9000 yrs this calculated value closely correlates to the timing of the pleistocene holocene transition the results of the model show additionally that a constant high mean sr would cause a concave up profile of pore water sulfate under steady state conditions copyright 2005 elsevier ltd

geochemical evidence of a massive slide in the southern norwegian sea during the 1981 cruise of the ms tyro to the southern norwegian basin several piston cores were collected for sedimentological research some of these were available for geochemical study fig 1 in laboratory analyses the pore water composition of one of these cores showed evidence of input of non saline water whereas pore water in other cores from the same basin did not give any indication of dilution with fresh water careful examination of the chemical constituents of the pore water and some parameters of the sediment gives convincing evidence for the origin of the fresh water the presence of non saline water can be attributed to a massive slide of a coastal fresh to brackish sediment slab with preservation of structural and pore water composition this sliding is thought to have taken place about 12 000 to 15 000 years bp

sequence stratigraphic significance of miocene to pliocene glauconite rich layers on and offshore of the us mid atlantic margin glauconite is generally agreed to be a reliable indicator of low sedimentation rate but little systematic work has been done to specify the role of glauconite in a sequence stratigraphic framework ocean drilling program leg 174a recovered a good record of late tertiary sediments along the shelf edge of the new jersey us atlantic margin and glauconite was present in many intervals of the cores sometimes in vertical proximity to sequence boundaries leg 174a glauconite was analyzed with binocular microscope xrd and sem to determine the percent of potassium and degree of maturity in order to relate occurrence to depositional environment seismic data were used to locate sequence boundaries and percent glauconite was visually estimated glauconite samples from site 1073 were found to have formed within a lowstand systems tract lst and as part of a distal condensed section cs within a transgressive systems tract tst these results are comparable to those from nearby site 903 of leg 150 which indicate a similar depositional setting for glauconite glauconites at shelf sites 1071 and 1072 likely formed in the tst as well onshore glauconite occurs mainly in transgressive systems tracts the miocene appears to be the upper limit of glauconite formation onshore as the magnitude of sea level change decreased present onshore locations became too nearshore to maintain sediment free environments and the zone of glauconite deposition moved seaward the same process did not occur offshore until the plio pleistocene low subsidence rate margins such as the us atlantic are subject more to the variations of sea level than to changes in sediment supply tectonics or other factors influencing their depositional patterns although glauconite occurrence is widespread in the stratigraphic record this study demonstrates that for low subsidence rate margins primary deposition of glauconite is largely restricted to the tst

a data driven model of the global calcite lysocline gridded maps of sediment calcium carbonate calcite concentration and overlying water saturation state archer 1996 are combined with maps of benthic oxygen fluxes and sediment accumulation rates from jahnke 1996 and cweink 1986 to drive a diagenetic model of calcium carbonate preservation in deep sea sediments the only model input for which we cannot draw a detailed map is the rain rate of calcite to the seafloor so i use the model to calculate the calcite rain rate required to simulate the observed distribution of calcite concentration on the seafloor the predictive power of the model can be checked by searching for input parameters to which the model is sensitive and comparing the model requirements with independent data the model is sensitive to the ratio of organic carbon to calcite rain rates the rain ratio and within the constraint of pelagic sediment trap rain ratio data is unable to reproduce the calcite field without respiratory dissolution the promotion of calcium carbonate dissolution by the oxic degradation of organic carbon however relative to variability in sediment trap data the required model rain ratio is insensitive to the extent of anoxic respiration the stoichiometric ratio of o c during respiration the bioturbation rate the dissolution rate constant the effect of borate chemistry and small offsets in the saturation state for caco3 the model is sensitive to the accumulation rate of non caco3 material and predicts an atlantic pacific difference in non caco3 rain rate which is consistent with observations the model predicts that the dissolution flux of caco3 from sediments is 25 40 1012 mol yr 1 roughly half of the total deep sea caco3 dissolution rate estimated from the water column alkalinity distribution broecker and peng 1987 archer and maier reimer 1994 wollast 1994 the model also predicts that only 20 30 of the flux of caco3 to the seafloor globally escapes dissolution

deep sulfate reduction completely mediated by anaerobic methane oxidation in sediments of the upwelling area off namibia abstract porewater concentrations of sulfate methane and other relevant constituents were determined on four sediment cores from the high productivity upwelling area off namibia which were recovered from the continental slope at water depths of 1300 and 2000 m at all four stations a distinct sulfate methane transition zone was observed several meters below the seafloor in which both sulfate and methane are consumed nutrient porewater concentration profiles do not show gradient slope changes at the depths of the transition zones flux calculations carried out on the basis of the determined porewater profiles revealed that anaerobic methane oxidation accounts for 100 of deep sulfate reduction within the sulfate methane transition zone and consumes the total net diffusive sulfate flux a significant contribution of organic carbon oxidation to the reduction of sulfate at these depths could therefore be excluded we state that porewater profiles of sulfate with constant gradients above the transition zones are indicative for anaerobic methane oxidation controlling sulfate reduction

the impact of diffusive transport of methane on pore water and sediment geochemistry constrained by authigenic enrichments of carbon sulfur and trace elements a case study from the shenhu area of the south china sea abstract sulfate driven anaerobic oxidation of methane sd aom controls methane release from marine sediments to the ocean a variety of authigenic precipitates within sediments has been widely used to identify past occurrences of sd aom however the lack of a systematic evaluation of the formation conditions of these precipitates sometimes impedes the recognition of sd aom in past environments characterized by diffusive transport of methane carbon sulfur and trace element geochemistry of pore water and sediments was investigated at a site affected by upward methane diffusion in the shenhu area of the south china sea here the sulfate methane transition zone smtz is located 7 6 m below the seafloor based on sulfate and methane concentrations the slope of 34s vs 18o values of sulfate is consistent with diffusive transport of methane concentration and isotope profiles of pore water species point to diffusive rather than advective transport of solutes enhanced sulfate reduction inferred from 34s values of sulfate agrees with the local occurrence of relatively abundant 34s enriched iron sulfide minerals the time required to produce the observed authigenic iron sulfides around the smtz is estimated to be 1 1 ka based on the amount of iron sulfide minerals and the present diffusive flux of sulfate no enrichment of authigenic carbonate barium ba and molybdenum mo was detected in the studied sediments this observation is consistent with the calculation that the current fluxes of pore water calcium magnesium ba and mo are too low to allow for authigenic enrichments the low fluxes are largely controlled by diffusion which facilitates the formation of 34s enriched iron sulfide minerals the observed enrichment patterns unlike those of sediments affected by advective seepage are expected to be prevalent in modern and ancient continental margin sediments and may contribute to the identification of past methane rich zones and overlying sd aom zones as sinks for methane in the geological record

oceanographic control of biogenic opal and diatoms in surface sediments of the southwestern atlantic based on 66 surface sediment samples collected in the sw atlantic ocean between 27 and 50 s this study presents an overview of the spatial distribution of biogenic opal and diatom concentrations and diatom assemblages biogenic opal has highest values in the deepest pelagic stations and decreases toward the slope diatoms closely follow the spatial trend of opal diatom assemblages reflect the present day dominant hydrographical features antarctic diatoms are the main contributors to the preserved diatom community in core top sediments with coastal planktonic and tropical subtropical diatoms as secondary components dominance of antarctic diatoms between 35 and 50 s in the pelagic realm mirrors the northward displacement of antarctic source water masses characterized by high nutrient content and low salinity northward of ca 35 s the highest contribution of tropical subtropical pelagic diatoms typical for nutrient poor and high salinity waters matches the main southward path of the brazil current mixing of antarctic and tropical waters down up to 45 s is clearly illustrated by the diatom assemblage concentrations of biogenic opal and diatoms rather reflect the path of predominant water masses but are less correlated with surface water productivity in the sw atlantic

oxidative sulfur cycling in the deep biosphere of the nankai trough japan the existence of oxidative microbial sulfur cycling in the deep biosphere has been postulated but it is difficult to identify because isotope effects of reductive sulfur cycling generally overprint those of oxidative sulfur cycling in the sediments at integrated ocean drilling program iodp site c0007 holes a c drilled and sampled during iodp expedition 316 at the nankai trough japan sulfur and oxygen isotope compositions of dissolved and solid phase sulfur compounds show evidence for a discrete zone of deep oxidative sulfur cycling the sulfate concentration profile and isotope values show two distinct sulfate reduction regimes one for downward diffusing sulfate in the uppermost 36 m of sediment unit i and another zone below 90 m where sulfate diffuses upward from a deep subsurface fluid the sulfur and oxygen isotope composition of sulfate and a dramatic change in solid phase iron geochemistry indicate that oxidative sulfur cycling occurs at depth the highly dynamic sedimentary and tectonic regime at nankai trough has created an environment in the subsurface where geochemical gradients can sustain deep oxidative sulfur cycling over long durations of time

alteration of magnetic mineralogy at the sulfate methane transition analysis of sediments from the argentine continental slope on the argentine continental slope off the rio de la plata estuary the sulfate methane transition smt has been encountered at shallow depths of a few meters below the seafloor at around this horizon where sulfate diffusing downward from the bottom water is met and reduced by methane rising from deeper in the sediment column intense alteration affects the detrital magnetic mineral assemblage less than 10 of the dominant primary low coercivity ferrimagnetic titano magnetite remains after alteration in the upper part of the suboxic environment underlying the iron redox boundary which is located at a depth of 0 1 m approximately 60 of the finer grained detrital fraction is already dissolved while the high coercivity minerals are relatively unaffected in the suboxic environment large portions 40 are diagenetically dissolved in the sulfidic smt zone nevertheless the characteristics of the magnetic residue are entirely controlled by a high coercivity mineral assemblage unlike common observations that diagenetic alteration produces coarser magnetic grain sizes in suboxic milieus a distinct overall fining is found in the sulfidic zone different factors should contribute to this effect scanning electron microscope analysis combined with x ray microanalysis identified fine grained titano magnetite preserved as inclusions in silicates and between high ti titanohematite lamellae and possibly of prime importance a comprehensive fragmentation of larger grains in the course of maghemitization the only secondary iron sulfide mineral detected is pyrite which is present as clusters of euhedral crystals or directly replaces titano magnetite the thermomagnetic measurements did not provide evidence for the presence of ferrimagnetic sulfides such as greigite different from other studies reporting a marked magnetic enhancement at around the smt due to the precipitation and preservation of such metastable ferrimagnetic sulfides a complete pyritization process will cause a distinct magnetic depletion like in the present case 2005 elsevier b v all rights reserved

modelling the efficiency of a drainage gallery work for a large landslide with respect to hydrogeological heterogeneity this study describes transient hydrogeological and geomechanical models realized jointly in 2006 by the geolep office geologie de l ecole polytechnique of the polytechnical school of lausanne epfl and geomod sa within the framework of the stabilization work of the la frasse landslide vaud switzerland these models evaluate the impact of a deep drainage gallery with subvertical drainage boreholes towards the surface in terms of reduction of the deformation velocities and increase of the landslide s factor of safety the paper presents the effect of different pipe spacing of the drainage system considering the local heterogeneities the results show that a mean spacing between the drainage boreholes of the order of 10 m is sufficient to control the temporal head fluctuations between the wells within a range of a few metres moreover this solution induces a strong diminution of the predicted displacements during a specific crisis from 101 cm for the model without drainage to around 14 cm for the drained model and a significant gain of stability from a factor of safety fos of 1 05 to 1 30

long term investigation of a deep seated creeping landslide in crystalline rock part ii mitigation measures and numerical modelling of deep drainage at campo vallemaggia for more than 200 years the villages of campo vallemaggia and cimalmotto have been slowly moving on top of a deep seated landslide in the southern swiss alps numerous mitigation measures have bee

characterization of the origin of coalbed gases in southeastern illinois basin by compound specific carbon and hydrogen stable isotope ratios abstract coalbed gases and waters from exploratory and production gas wells in the southeastern illinois basin were sampled to assess geochemically the origin of coalbed gases with an emphasis on the springfield and seelyville coal members that are commercially targeted for coalbed methane production in indiana on line analyses of hydrocarbon gases methane to butanes c 1 c 2 c 3 n c 4 i c 4 and co 2 yielded gas concentrations plus d and 13 c values the low thermal maturity of indiana coals with vitrinite reflectance r 0 0 6 is in agreement with an overwhelmingly biogenic isotopic signature of coalbed gases containing 96 methane generated via bacterial co 2 reduction in contrast thermogenic gas was generated in the stratigraphically equivalent coal beds in western kentucky s rough creek graben zone where higher maturities of up to r 0 0 8 were reached owing to tectonic and hydrothermal activity no secondary biogenic methane was observed in more mature western kentucky coal beds where greater burial depth limits the recharge of meteoric water biogenic and thermogenic coalbed gases represent two end members that are compositionally and isotopically distinct microbial biodegradation of thermogenic c 2 hydrocarbon gases in indiana coal beds preferentially targets c 3 and introduces isotope fractionation whereby remaining c 3 is enriched in deuterium and 13 c

deep seated gravitational slope deformations in the european alps abstract deep seated gravitational slope deformations dsgsd are widespread phenomena recognized in different mountain ranges worldwide the distribution of such phenomena at the scale of a mountain belt has rarely been systematically analysed in the past aim of the paper is to present and discuss an inventory map of dsgsd at the scale of the entire european alps in order to review existing knowledge and investigate general controls on these phenomena the criteria adopted for their classification and distinction are presented a total of 1033 dsgsds ranging in size between 0 03 and 108 km 2 have been mapped the inventory has been validated against available local or regional landslide inventories at different scales and prepared by different authors using different approaches the frequency area relationship for the mapped features is presented the spatial distribution of the mapped dsgsd has been quantified by discretizing the study area into regular square grids with different resolution and analysed with respect to a variety of geological geomorpohological and morphometric variables and of their clustering discriminant principal component and cluster analyses have been performed to define the most important controlling and predisposing factors results suggest that the occurrence of foliated metamorphic rocks lgm ice thickness local relief and related parameters slope size drainage density and river stream power are the local parameters most positively correlated to dsgsd occurrence the impact of these phenomena on slope morphology in terms of hypsometry and slope gradient adjustment is also discussed

integrated multi temporal analysis of the displacement behaviour and morphology of a deep seated compound landslide cerentino switzerland abstract deep seated gravitational slope deformations dsgsds are complex slope instabilities commonly involving long term evolution with significant spatial and temporal variations in slope kinematics the cerentino compound landslide in southern switzerland exemplifies the long term evolution of dsgsds as well as short term movements causing substantial damage to infrastructure using an integrated analysis of surface geomorphology displacement monitoring data borehole core and cosmogenic nuclide dating we discuss the preconditioning and driving factors kinematic behaviour and long term evolution of the instability we demonstrate that foliation orientation and lithological boundaries together with slope geometry and alpine faults likely played significant roles in preconditioning the slope for failure based on morphology mapping and hierarchical clustering analysis of 2007 2018 detrended surface displacement data we show that the landslide is separated into up to eight compartments at surface revealing differences in kinematic behaviour from very active at the toe to insignificant movements in the upper region of the landslide above the village of cerentino these surficial compartments likely correspond to secondary sliding zones within the landslide mass the analysis of data from inclinometer and fibre optic strain sensors installed in a new deep borehole 230 m provided insight into movement within the landslide mass results show vertical heterogeneity in total displacement which appears to be controlled by an active discrete shear zone located at 107 m by shallower secondary sliding surfaces and by distributed movement particularly in the upper 20 m of the instability extrapolation of cosmogenic nuclide dating results from five samples taken on the exposed upper sliding scar reveals a possible age of failure initiation of 5 6 ka with long term decelerating movement trends these generally slow averaged movements show multi annual responses to long term changes in precipitation and locally rapid responses to strong recharge events the rare combination of dating and detailed analysis of displacement allows us to demonstrate the behaviour of dsgsds at long and short timescales with implications for hazard assessment and mitigation of these complex failures

cyclostratigraphy of the reference section for the cretaceous white chalk of northern germany lagerdorf kronsmoor a late campanian early maastrichtian orbital time scale new carbonate records of the upper campanian lower maastrichtian white chalk of northern germany at lagerdorf kronsmoor represent a continuous succession suitable for time series analysis the boreal chalk succession is characterized by several intervals of reduced carbonate content in the basiplana spiniger polyplocum upper langei and upper grimmensis granulosus to pseudoobtusa boreal macrofossil zones which are mainly related to periods of increased detrital supply results of spectral analysis on the carbonate time series allow the detection of the periodicities of long and short eccentricity the long eccentricity signal can be extended to the entire upper campanian comprising a total of 15 25 long eccentricity cycles a minimum time span of 6 2 ma and an age of 77 5 0 4 ma for the lower upper campanian boundary the long eccentricity cycles detected from chalk carbonate contents correlate with long eccentricity cycles detected in self potential logs of boreholes proving their significance within different depositional settings and rates of subsidence in the north german basin the biostratigraphic consistent occurrence of long eccentricity cycles provides evidence for the completeness of the sedimentary record the long term intervals of increased detrital supply are the expression of increased progradation of clay minerals related to a long term sea level fall with superimposed short sea level falls within a 2 5 million year interval spanning the campanian maastrichtian boundary it cannot be decided from the present state of knowledge if this signal is controlled by increased erosion due to uplift of inverted structures by eustatic sea level fall or a combination of both the detection of the long eccentricity suggests an orbital forcing superimposed on a long term regressive trend

kinematics of a giant slow moving landslide in northwest china constraints from high resolution remote sensing imagery and gps monitoring abstract slow moving landslides generally are long lived and characterized by continuous movement with some fluctuation in sliding rate following changes of environmental factors such as rainfall and earthquake analysis on kinematics of this type of landslide is essential for understanding its mechanism and identifying causal factors controlling its movement behavior this paper presents a study on kinematics of a giant slow moving landslide in northwest china called the xieliupo landslide which is about 72 10 6 m 3 in volume and has been slowly moving for more than 100 years this study is conducted using archival high resolution remote sensing images from multi sources over a period about 43 years and the data from 15 month gps monitoring six sets of multi source remote sensing images in 1969 1971 2004 2008 2010 and 2012 with spatial resolution higher than 2 5 m were used and gps monitoring data were recorded from september 2012 to december 2013 obvious geomorphologic changes identified from the images in 1971 and 2004 confirm that this landslide did move slowly in the past quantitative analysis reveals that movement of the landslide was persistent and behaved in a block by block mode with the greatest and the least velocities in its middle and lower parts respectively distance measurement between the homologous point pairs on the orthorectified images in 2005 2010 and 2012 indicates that annual ground displacement of the landslide ranged from 0 52 m to 6 54 m in the seven years gps monitoring data shows that the landslide ground displacement in the 15 months varied from 0 49 m to 2 91 m and annually between 0 39 m and 2 33 m with a rather uniform movement pattern as identified using the remote sensing images gps monitoring results also reveal that the landslide movement is intermittent inter annually it is further discussed that movement behavior of the landslide is largely controlled by its topography with great influence of the active fault along its left hand flank and river erosion at its toe rainfall may affect inter annual movement behavior of the landslide

contradictory magnetic polarities in sediments and variable timing of neoformation of authigenic greigite abstract in several recent published studies paleomagnetic results from greigite bearing sediments reveal characteristic remanences that are anti parallel to those carried by coexisting detrital magnetic minerals and polarities that are opposite to those expected for the age of the rock unit these observations have important implications for the reliability of paleomagnetic data from greigite bearing sediments we have investigated the origin of such contradictory magnetic polarities by studying the formation mechanisms of greigite in mudstones from the lower gutingkeng formation southwestern taiwan scanning electron microscope observations indicate that the gutingkeng greigite has three modes of occurrence including nodular framboidal and matrix greigite microtextural observations including transection of bedding by iron sulfide nodules with no deviation of sediment textures the presence of partially dissolved edges around detrital and early diagenetic phases and neoformation of greigite and fe rich clays around detrital phyllosilicates indicate that all three types of greigite have a diagenetic origin that post dates early diagenetic pyrite in addition paleomagnetic data yield contradictory polarities even for greigite bearing sister samples from the same stratigraphic horizon the data are collectively interpreted to indicate that neoformation of the gutingkeng greigite occurred after partial dissolution of syngenetic or early diagenetic pyrite the timing of greigite formation can apparently vary enough to give contradictory polarities for different greigite components even within a single stratigraphic horizon direct petrographic observation of authigenic magnetic iron sulfide phases as carried out in this study can provide important constraints on formation mechanisms and timing of remanence acquisition for these minerals and suggests that care should be taken when interpreting magnetostratigraphic data from greigite bearing sediments

observations and predictions of the behaviour of large slow moving landslides in schist clyde dam reservoir new zealand abstract major remedial works involving toe buttressing pumped drainage gravity drainage and or infiltration protection were undertaken at nine of the seventeen large landslides along the clyde dam reservoir margins prior to lake filling in 1992 1993 all 17 landslides continue to be routinely monitored and inspected as part of the dam safety assurance programme undertaken by contact energy movement of the landslides is monitored by a combination of inclinometers extensometers and survey and is correlated with controlling events including lake filling storms floods prolonged wet periods and earthquakes most monitoring records extend over periods of 15 years with some histories as long as 25 years over 100 years of rainfall records are available for nearby locations very small deformation responses attributable to lake filling occurred at four of the stabilized slides slightly accelerated movement occurred at one slide that had not been stabilized and minor reactivation was detected at three others two landslides have demonstrated movement rate sensitivity to rainfall events neither slide was significantly affected by lake filling monitoring records show that movement of a known active part of the brewery creek landslide is triggered when a key piezometer reaches or exceeds a critical threshold level movement continues until the piezometer drops below that level movement of part of ripponvale landslide increases following prolonged rainfall events the slide was barely affected by lake filling and has not responded to subsequent transient increases in toe inundation levels floods data from zone a of the slide mass which is entirely above the lake shows the slide to be very sensitive to the effects of prolonged wet periods movement rates increase over a period of months and then gradually reduce based on the records to date it can be predicted that the slide will exhibit an increased movement rate when the cumulative rainfall over a period of 3 to 4 months exceeds about 300 mm

early diagenesis of iron and sulfur in bornholm basin sediments the role of near surface pyrite formation abstract pyrite formation in marine sedimentary environments plays a key role in the global biogeochemical cycles of carbon sulfur and iron regulating earth s surface redox balance over geological time scales the sulfur isotopic composition of pyrite is one of the major geochemical tools for investigating early diagenetic processes in modern marine sediments and substantive changes to the earth s surface environment in ancient sedimentary rocks we studied sulfur iron diagenesis and the sulfur isotopic evolution in sediments of the bornholm basin southwestern baltic sea to track the formation of pyrite in the near surface sediments pyrite accumulation is observed with depth over the uppermost 100 cm before the extent of pyritization of the highly reactive iron pool fepy fehr stays constant at ca 0 9 suggesting that the use of a single iron speciation parameter as a proxy for anoxic and sulfidic conditions needs to be supported by other independent indicators in sedimentary records stable sulfur isotopic analysis demonstrates that the bulk pools of elemental sulfur and iron monosulfide do not exchange isotopes completely with aqueous sulfide we suggest that the reactions with polysulfide and aqueous sulfide are probably restricted to the surface of the solid phase sulfur and iron sulfur aggregates although pyrite is growing throughout the uppermost sediment column the pyrite at depth has a sulfur isotopic composition similar to that of pyrite formed near the sediment surface to understand the isotopic discrepancy between pyrite and aqueous sulfide in the deeper sediments we developed a simple diagenetic model which reproduces the observed sulfur isotopic composition of pyrite well our results suggest that much of the pyrite is rapidly formed near the sediment water interface and its 34s is not as influenced by the 34s enriched pool of aqueous sulfide in the deeper part of the sediment allowing 32s enriched pyrite to be preserved in deeper sediments this near surface diagenesis and the associated isotopic pattern are possibly of relevance for many marine sediments with high organic matter content and high aqueous sulfide but low reactive iron availability moreover our sulfur isotopic data demonstrate that extremely slow pyritization is ongoing in the deep lacustrine clay sediments these results have implications for the interpretation of sulfur iron geochemical data in both modern and ancient settings as well as for improving reconstructions of ancient depositional environments and a better understanding of the marine sulfur cycle throughout earth s history

diagenetic formation of ferrimagnetic iron sulphide minerals in rapidly deposited marine sediments south island new zealand abstract detailed magnetostratigraphic studies of late neogene siliciclastic sediments of the awatere group south island new zealand 41 45 s 174 05 e have revealed a wide range of palaeomagnetic behaviour examination of rock magnetic properties was undertaken using conventional palaeomagnetic techniques and thermomagnetic x ray diffraction and electron microprobe analyses these analyses indicate that the ferrimagnetic iron sulphide minerals greigite and pyrrhotite are responsible for a stable and intense magnetic remanence in fine grained sediments whereas titanomagnetite is the only remanence bearing mineral identified in coarser grained sediments which are less strongly and less stably magnetised than the fine grained sediments detrital titanomagnetite grains are likely to have undergone dissolution during early diagenesis as a result of iron sulphide formation which occurs commonly in rapidly deposited anoxic sediments that support active sulphate reduction and h 2 s formation preservation of greigite and pyrrhotite is inferred to result from the arrest of the pyritisation process probably due to the low permeability of the fine grained sediments and consumption of available h 2 s before full reaction to pyrite occurred relative palaeomagnetic instability and weak remanence intensities in coarser grained sediments is likely to be due to low titanomagnetite concentrations resulting from titanomagnetite dissolution

tectonic and gravity induced deformation along the active talas fergana fault tien shan kyrgyzstan abstract this paper shows by field palaeoseismological data the holocene activity of the central segment of the intracontinental talas fergana fault tff and the relevance of possible future seismic shaking on slope stability around a large water reservoir the fault striking nw se is marked by a continuous series of scarps deflected streams and water divides and prehistoric earthquakes that offset substrate and holocene deposits fault movements are characterised by right lateral strike slip kinematics with a subordinate component of uplift of the ne block structural geological and geomorphological field data indicate that shallow and deep landslides are aligned along the tff and some of them are active where the tff runs close to the reservoir the fault trace is obscured by a series of landslides affecting rock and soil materials and ranging in size from small slope instabilities to deep seated gravity induced slope deformations dgsds the largest of these which does not show clear evidence of present day activity involves a volume of about 1 km3 and is associated with smaller but active landslides in its lower part with volumes in the order of 2 5 104 m3 to 1 106 m3 based on the spatial and temporal relations between landslides and faults we argue that at least some of these slope failures may have a coseismic character stability analyses by means of limit equilibrium methods lems and stress strain analysis by finite difference numerical modelling fdm were carried out to evaluate different hazard scenarios linked to these slope instabilities the results indicate concern for the different threats posed ranging from the possible disruption of the m 41 highway the main transportation route in central asia to the possible collapse of huge rock masses into the reservoir possibly generating a tsunami

evidence for the submarine weathering of silicate minerals in black sea sediments possible implications for the marine li and b cycles 1 the role of sediment diagenesis in the marine cycles of li and b is poorly understood because li and b are easily mobilized during burial and are consumed in authigenic clay mineral formation their abundance in marine pore waters varies considerably exchange with the overlying ocean through diffusive fluxes should thus be common nevertheless only a minor li sink associated with the low temperature alteration of volcanic ash has been observed we describe a low temperature diagenetic environment in the black sea dominated by the alteration of detrital plagioclase feldspars fluids expelled from the odessa mud volcano in the sorokin trough originate from shallow 100 400 m deep sediments which are poor in volcanic materials but rich in anorthite these fluids are depleted in na k li b and 18o and enriched in ca2 and sr2 indicating that anorthite is dissolving and authigenic clays are forming using a simple chemical model we calculate the ph and the partial pressure of co2 pco2 in fluids associated with this alteration process our results show that the ph of these fluids is up to 1 5 ph units lower than in most deep marine sediments and that pco2 levels are up to several hundred times higher than in the atmosphere these conditions are similar to those which favor the weathering of silicate minerals in subaerial soil environments we propose that in black sea sediments enhanced organic matter preservation favors co2 production through methanogenesis and results in a low pore water ph compared to most deep sea sediments as a result silicate mineral weathering which is a sluggish process in most marine diagenetic environments proceeds rapidly in black sea sediments there is a potential for organic matter rich continental shelf environments to host this type of diagenesis should such environments be widespread this new li and b sink could help balance the marine li and li isotope budgets but would imply an apparent imbalance in the b cycle

pore water profiles and authigenic mineralization in shallow marine sediments above the methane charged system on umitaka spur japan sea umitaka spur situated on an unusual collisional plate boundary along the eastern margin of the japan sea hosts gas seeps pock marks collapse structures and gas hydrates piston cores were recovered from this ridge to understand carbon cycling pore fluid gradients and authigenic mineralization above a methane charged system we present the chemistry of fluids and solids from three cores adjacent to seep locations high fluxes of ch4 and alkalinity transport carbon from a deep zone of methanogenesis toward the seafloor methane however reacts with so42 across a shallow sulfate methane transition smt which generates additional alkalinity and hs a fraction of these ch4 oxidation products form authigenic carbonate and pyrite these minerals are not readily apparent from visual inspection of split cores because they exist as micritic coatings on microfossils or as framboidal pyrite they are however readily observed in chemical analyses as peaks of labile ca sr ba or s in sediment at or near the smt carbon inputs and outputs nicely balance across the smt in all three cores if one considers four relevant fluxes loss of alkalinity to the seafloor addition of methane from below addition of alkalinity from below and carbonate precipitation importantly in all cores the magnitude of the fluxes decreases in this order although some carbon rising from depth forms authigenic carbonate most 80 escapes to the ocean as alkalinity nonetheless authigenic fronts in sediment on umitaka spur are a significant reservoir of inorganic carbon given calculated pore fluid fluxes for ca and sr the fronts require tens of thousands of years to form suggesting that the present state and loss of carbon represent long lived processes

nutrient leakage from the north pacific to the bering sea iodp site u1341 following the onset of northern hemispheric glaciation 1 intergrated ocean drilling program expedition 323 recovered a sediment record covering the last 4 3 ma from the bering sea integrated ocean drilling program site u1341 bowers ridge 2177 m water depth to resolve pliocene pleistocene paleoenvironmental changes in this marginal basin 190 sediment samples were analyzed for their bulk element composition aluminium contents in bowers ridge sediments are variable but overall higher toward younger sediments probably related to the intensification of the northern hemispheric glaciation and increasing sea ice transport in the bering sea the gradual increase of terrigenous input is mirrored by decreasing sio2 and excess si sixs contents but the overall si enrichment of the deposits reflects continuous opal deposition since the pliocene at bowers ridge unlike in the north pacific the sixs record at site u1341 does not support a dramatic decrease in opal export following the onset of the northern hemispheric glaciation around 2 7 ma but sio2xs have higher accumulation rates up to 8 g cm2 ka between 2 6 and 1 8 ma bp during this period the major oceanic opal deposition centers shifted globally from open marine high latitude regions to upwelling areas we here discuss how the onset of north pacific stratification at 2 7 ma bp may have caused leakage of nutrient rich deep intermediate north pacific water into the bering sea via the deep kamtchatka strait leading to increased opal deposition and likely reactive organic matter export at bowers ridge as a result magnetic and geochemical records were overprinted by intensified diagenesis significantly affecting their applications as paleoceanographic proxies

reactive iron in marine sediments abstract a combined field laboratory study has been undertaken to explore the mineralogy concentrations and reactivity towards sulfide of iron in marine sediments also considered is the importance of bacterial fe liberation in regulating pore water chemistry two contrasting marine environments are included one is the relatively fe poor foam site and the other is the fe rich sediment of the subaqueous mississippi delta results show that oxide minerals are the most important fe phases in early diagenetic pyrite formation however viewed separately lepidocrocite and ferrihydrite are more reactive towards sulfide than goethite and hematite when fe oxides are present in relatively high concentrations dissolved sulfide is nearly absent from sediment pore waters with concomitant high concentrations of dissolved fe even in the presence of active sulfide production by sulfate reduction a combination of experimental results and diagenetic modelling shows that in some sediments pore water fe finds it origin in the bacterial reduction of iron oxides this seems the case even though greater amounts of fe are reduced by reaction of sulfide with iron oxides it appears that distinct microenvironments may exist in marine sediments where in one microenvironment sulfide reacts with fe oxides locally precipitating fe sulfide minerals in another fe reduced and solubilized by microorganisms migrates freely into solution

a comparative study of iron and manganese diagenesis in continental slope and deep sea basin sediments off uruguay sw atlantic pore water and solid phase from surface sediments of the continental slope off uruguay and from the argentine basin southwestern atlantic were investigated geochemically to ascribe characteristic early diagenetic reactions of iron and manganese solid phase iron speciation was determined by extractions as well as by mossbauer spectroscopy both methods showed good agreement 6 deviation for total fe speciation the proportion of easy reducible iron oxyhydroxide relative to total fe oxides decreased from the continental slope to the deep sea which is attributed to an increase in crystallinity during transport as well as to a general decrease of iron mobilization the product of iron reoxidation is fe oxyhydroxide which made up less than 5 of total fe in addition to this fraction a proportion of smectite bound iron was found to be redox reactive this fraction made up to 10 of total fe in sediments of the argentine basin and was quantitatively extracted by 1 n hcl the redox reactive fe ii fraction of smectite was almost completely reoxidized within 24 h under air atmosphere and may therefore considerably contribute to iron redox cycling if bioturbation occurs in the case of the slope sediments we found concurrent iron and manganese release to pore water it is not clear whether this is caused by dissimilatory iron and manganese reduction at the same depth or dissimilatory iron reduction alone inducing mn iv reduction by abiotic reaction with released fe2 the argentine basin sediment showed a significant manganese solid phase enrichment above the denitrification depth despite the absence of a distinct pore water gradient of mn this implies a recent termination of manganese mobilization and thus a non steady state situation with respect to sedimentation or to organic carbon burial rate

dissolution and pyritization of magnetite in anoxie marine sediments concentrations of magnetite were determined with depth in sediments of varying h2s content taken from long island sound foam nwc and sachem sites and from a site in the rapidly depositing subaqueous portion of the mississippi delta for the three long island sound sites dissolution of magnetite during burial is clearly demonstrated and for all four sites the rate of magnetite dissolution is proportional to the concentration of dissolved pore water sulfide by combining magnetite depth distributions with sedimentation rate data and measurements of dissolved sulfide we find that magnetite dissolution is well described by the following rate law dcmagdt 1 1 10 5c0 5bcmagamag where cmag is the concentration of magnetite grams per gram of sediment cs is the concentration of dissolved sulfide mm and amag is the specific surface area of magnetite in the sediment cm2 per gram of magnetite this equation means that for a typical range of magnetite surface areas and dissolved sulfide concentrations the half life of magnetite in anoxic marine sediments ranges from about 50 to 1000 years sem observations of magnetite grains from the different sediment sites reveal that magnetite dissolution may be accompanied by extensive replacement by pyrite this only occurs if magnetite is in contact with high concentrations of h2s 1 mm for relatively long periods of time several hundred years with low concentrations of h2s 1 mm magnetite dissolution occurs without identifiable pyrite replacement we suggest that this feature of magnetite diagenesis may prove to be a useful paleosulfide indicator

diagenesis of magnetic minerals in recent haemipelagic sediments rapidly deposited sediments from marine and lake environments are being used increasingly to study decadal to millennial fluctuations in the earth s magnetic field the objectives are to gain more fundamental understanding of the geodynamo and to establish a new dating technique for sediments while lacustrine sections are generally restricted to temperate latitude glacial lakes 20 000 yr old rapidly deposited marine sediments along continental margins potentially offer continuous high resolution yet long term records of geomagnetic secular variation however to interpret the sedimentary magnetic record accurately geochemical processes that affect the reliability of the magnetic signal must be understood we now report downcore magnetic profiles from undisturbed kasten cores taken in rapidly deposited laminated sediments from the gulf of california and in bioturbated haemipelagic muds on the oregon continental slope which give apparently reliable directions but show dramatic decreases in the intensities of natural nrm and artificial arm irm remanences with depth downcore porewater and solid sulphur analyses show concave down decreases in porewater sulphate and systematic increases in pyrite and metastable monosulphides the maximum curvature of the sulphide profile occurs directly below the high magnetization zone combined with other compositional and mineralogical analyses these data suggest that due to oxidative decomposition of organic matter magnetites and other iron oxides become progressively reduced and subsequently sulphidized and pyritized with depth iron reduction seems to occur before sulphide formation changes in magnetic stability parameters are consistent with selective dissolution of the finer sized grains causing downcore coarsening of the magnetic fraction

magnetic anomalies in the imbrium and schrodinger impact basins orbital evidence for persistence of the lunar core dynamo into the imbrian epoch approximate maps of the lunar crustal magnetic field at low altitudes in the vicinities of the three imbrian aged impact basins orientale schrodinger and imbrium have been constructed using lunar prospector and kaguya orbital magnetometer data detectable anomalies are confirmed to be present well within the rims of imbrium and schrodinger anomalies in schrodinger are asymmetrically distributed about the basin center while a single isolated anomaly is most clearly detected within imbrium northwest of timocharis crater the subsurface within these basins was heated to high temperatures at the time of impact and required long time periods up to 1 myr to cool below the curie temperature for metallic iron remanence carriers 1043 k therefore consistent with laboratory analyses of returned samples a steady long lived magnetizing field i e a former core dynamo is inferred to have existed when these basins formed the asymmetrical distribution within schrodinger suggests partial demagnetization by later volcanic activity when the dynamo field was much weaker or nonexistent however it remains true that anomalies within imbrian aged basins are much weaker than those within most nectarian aged basins the virtual absence of anomalies within orientale where impact melt rocks the maunder formation are exposed at the surface is difficult to explain unless the dynamo field was much weaker during the imbrian period

impact of climate change on the magnetic mineral assemblage in marine sediments from izu rear arc nw pacific ocean over the last 1 myr abstract a rock magnetic study was conducted on upper pleistocene marine sediments from international ocean discovery program expedition 350 site u1437 in order to highlight the paleoenvironmental changes in the nw pacific ocean influenced by the east asian monsoon regime remanent magnetization analyses hysteresis properties first order reversal curves and low temperature magnetic measurements were carried out along with electron microscope observations the results indicate that coarse grained titano magnetite is the dominant magnetic phase in the magnetic mineral assemblage time series analysis supports that this assemblage is modulated by global climate changes over the last 1 myr during the interglacial stages magnetic minerals are more abundant and are dominated by coarse grained titano magnetite of both terrigenous likely from mainland china and volcanic izu arc front japan origin during the glacial stages the magnetic mineral content is lower probably reflecting partial dissolution of ti magnetite and the magnetic assemblage is composed of terrigenous coarse grained titano magnetite and of higher coercivity presumably finer eolian particles likely hematite as a result of the enhancement of the winter monsoon in continental asia the magnetic mineral assemblage reflects a superimposition of volcanic and global climate signals bulk organic geochemical analyses for total and organic carbon as well as nitrogen and sulfur contents confirm a climatic signature in the composition of the sediments with more oxygenated water masses being present during glacial periods additional x ray fluorescence measurements on bulk samples indicate various origins of the sediment particles with both proximal and distal sources

rock magnetic and geochemical evidence for authigenic magnetite formation via iron reduction in coal bearing sediments offshore shimokita peninsula japan iodp site c0020 sediments recovered at integrated ocean drilling program iodp site c0020 in a forearc basin offshore shimokita peninsula japan include numerous coal beds 0 3 7 m thick that are associated with a transition from a terrestrial to marine depositional environment within the primary coal bearing unit 2 km depth below seafloor there are sharp increases in magnetic susceptibility in close proximity to the coal beds superimposed on a background of consistently low magnetic susceptibility throughout the remainder of the recovered stratigraphic sequence we investigate the source of the magnetic susceptibility variability and characterize the dominant magnetic assemblage throughout the entire cored record using isothermal remanent magnetization irm thermal demagnetization anhysteretic remanent magnetization arm iron speciation and iron isotopes magnetic mineral assemblages in all samples are dominated by very low coercivity minerals with unblocking temperatures between 350 580 c that are interpreted to be magnetite samples with lower unblocking temperatures 300 400 c higher arm higher frequency dependence and isotopically heavy 56fe across a range of lithologies in the coal bearing unit between 1925 1995 mbsf indicate the presence of fine grained authigenic magnetite we suggest that iron reducing bacteria facilitated the production of fine grained magnetite within the coal bearing unit during burial and interaction with pore waters the coal peat acted as a source of electron donors during burial mediated by humic acids to supply iron reducing bacteria in the surrounding siliciclastic sediments these results indicate that coal bearing sediments may play an important role in iron cycling in subsiding peat environments and if buried deeply through time within the subsequent deep biosphere

plio pleistocene magnetic polarity stratigraphies and diagenetic magnetite dissolution at odp leg 177 sites 1089 1091 1093 and 1094 abstract magnetic polarity stratigraphies from odp leg 177 high resolution sites indicate brunhes sedimentation rates in the 12 25 cm kyr range with a trend of decreasing sedimentation rates with increasing age magnetite is the principal remanence carrying mineral downcore alteration of magnetite and authigenic growth of iron sulfides introduces a high coercivity diagenetic remanence carrier pyrrhotite the change in pore water sulfate with depth in the sediment tends to be in step with the decrease in magnetization intensity indicating the link between sulfate reduction and magnetite dissolution shipboard pass through magnetometer data are generally very noisy due to a combination of weak magnetization intensities drilling related core deformation and the influence of authigenic iron sulfides post cruise progressive demagnetization of discrete samples aids the magnetostratigraphic interpretation as these measurements are less influenced by low magnetization intensities and drilling related deformation the magnetostratigraphic interpretations provide much needed calibration for biostratigraphic events in the high latitude southern oceans apart from the odp hole 745b kerguelen plateau published plio pleistocene magnetostratigraphies from odp sites in the southern ocean are poorly constrained for this reason we compare interpolated ages of 11 radiolarian events and one diatom event that occur at hole 745b and leg 177 sites

progressive dissolution of titanomagnetites at odp site 653 tyrrhenian sea abstract magnetic properties microscopy and ferrous ferric iron ratio document increasing down core alteration of titanomagnetite to iron sulfide at odp site 653 leg 107 tyrrhenian sea changes in magnetic properties are interpreted to indicate a grain size increase in titanomagnetite to 40 m below seafloor bsf and a grain size decrease from this level to about 150 m bsf as dissolution affects first the fine grained and then the coarser grained magnetite the availability of dissolved sulfate from underlying messinian evaporites may account for the sulfide supply at depth and hence for the prolonged dissolution process dissolution at leg 107 sites adjacent to site 653 is less pronounced possibly by the availability of organic matter that can be metabolised by sulfate reducing bacteria