an ammonite zonation for the lower jurassic of canada and the united states the pliensbachian this is the first in a series of papers intended to establish a lower jurassic ammonite zonation that takes into account the biostratigraphic and biogeographic peculiarities of the north american succession its development has been spurred by the need for high resolution correlation between allochthonous terranes and the need for a standard to which microfossil sequences may be coupled in north america the lower boundary of the pliensbachian is drawn above the last echioceratids the lower pliensbachian is divided into in ascending order the imlayi whiteavesi and freboldi zones the upper pliensbachian into the kunae and carlottense zones the fannin bay section in the queen charlotte islands is designated the stratotype for the whiteavesi freboldi and kunae zones ideal stratotypes for the imlayi and carlottense zones are not presently known reference sections former illustrating the faunal associations that characterize all the zones are designated in western nevada the sunrise formation nor

a new late holocene sea level record from the mississippi delta evidence for a climate sea level connection abstract a detailed relative sea level rsl record was constructed for the time interval 600 1600 ad using basal peat to track sea level and containing 16 sea level index points that capture 60 cm of rsl rise the study area is in the mississippi delta where the spring tidal range is 0 47 m the impact of ocean currents on sea surface topography is limited and crustal motions are well constrained age control was obtained by ams 14 c dating and most ages represent weighted means of two subsamples sample elevations were determined by combining differential gps measurements with optical surveying all index points were plotted as error boxes using 2 confidence intervals for the ages plus all vertical errors involved in sampling and surveying as well as the indicative range of the samples a striking clustering of sea level index points between 1000 and 1200 ad suggests a possible acceleration in the rate of rsl rise removal of the long term trend 0 60 mm yr 1 allows for the possibility of a sea level oscillation with a maximum amplitude of 55 cm however given the size of the error boxes the possibility that oscillations did not occur cannot be entirely ruled out comparison of the new rsl record with various proxy climate records suggests that sea level in this area may have responded to hemispheric temperature changes including the medieval warm period and the little ice age however given the error margins associated with this reconstruction it is stressed that this causal mechanism is tentative and requires corroboration by high resolution sea level reconstructions elsewhere

stable nitrogen isotopes in angola basin surface sediments abstract sedimentary 15n contains a record of biogeochemical processes occurring in the water column stable nitrogen isotopes were measured in the bulk sedimentary matter of 18 surface sediment samples collected in three transects in the eastern angola basin perpendicular to the coast at 6 s 12 s and 17 s and two samples from the zaire estuary relative enrichment in 15n in sediments with distance from the coast was seen in each of the three transects off northern middle and southern angola values in the zaire fan northern angola and southern angola increased by 1 9 and 1 6 respectively from shallow 100 m to deep 4500 m water sediments and in middle angola by 2 5 water depth range 73 3809 m we propose that in the angola region the degree of fractionation of nitrogen isotopes in organic matter is a function of nutrient supply to sunlit waters the shift towards lighter isotopic values in shallow water signifies that the larger nitrate pool is not utilized as extensively as in water farther away from the coastal upwelling centers southern angola sediments were more than 1 lower average 15n 5 4 than the middle and northern transects average 15n 7 2 and 6 5 respectively this difference is attributed to higher nitrate concentrations in the surface water at 17 s for which there are two reasons one is that these sediments are located south of the angola benguela front at 16 s which demarcates the convergence of warm equatorial water with cold nutrient rich benguela current water the second cause is the intense namibian coastal upwelling zone extending northward up to the front comparisons of bulk 15n with 13corg and c n ratios show that the observed sedimentary 15n variations with water depth are due neither to water column diagenesis nor to mixing of terrestrial material with marine derived organic matter the two estuary sediment samples were mainly terrigenous in origin based on 13corg and c n ratios 15n values of these two samples were 7 0 and 7 6

postglacial land uplift patterns of south sweden and the baltic sea region comparison of the land uplift pattern for the last 10 300 years shown by studies of raised shorelines of the baltic ice lake with the pattern of present day land uplift of fennoscandia shows that significant regional changes of uplift pattern have taken place some of these changes seem to be related to a halt in ice retreat during the younger dryas cold stage it is also probable that some observed anomalies in the present uplift are not of glacio isostatic origin but are possibly related to structures in the lower lithosphere and upper mantle or large scale tectonics

burial of organic carbon and pyrite sulfur in sediments over phanerozoic time a new theory in present day marine sediments almost all of which are deposited in normal oxygenated seawater rates of burial of organic carbon c and pyrite sulfur s correlate positively and bear a constant ratio to one another c s 3 on a weight basis by contrast calculations based on the isotopic model of garrels and lerman 1981 indicate that at various times during the phanerozoic the worldwide burial ratio must have been considerably different than the present day value this ratio change is caused by the requirement that increases in the worldwide mass of organic carbon must be accompanied by equivalent decreases in the mass of sedimentary pyrite sulfur in order to maintain a roughly constant level of o2 in the atmosphere such apparently contradictory behavior can be explained if the locus of major organic carbon burial has shifted over time from normal marine environments as at present to non marine freshwater or to euxinic environments in the geologic past a shift to predominantly freshwater burial can help explain predicted high c s ratios in permo carboniferous sediments and a shift to euxinic environments can help explain predicted low c s ratios during the early paleozoic it is demonstrated that the three environments today exhibit distinguishably different average c s ratios

distribution and sources of bulk organic matter om on a tropical intertidal mud bank in french guiana from elemental and isotopic proxies the mobile french guiana coast is a shoreface region downdrift of the amazon river where enormous quantities of inorganic and organic materials are exchanged with the atlantic ocean the rapid accumulation of these materials forms highly unstable shore attached mud banks which can be temporally emerged and then rapidly colonized and stabilized by microphytobenthos and opportunistic mangroves i e avicennia germinans mud banks are preferential sites for the accumulation and significant remineralization of organic matter om due to intense erosion deposition cycles and potential biological colonization the distribution and sources of bulk sedimentary om were characterized by elemental and isotopic analyses of four sediment cores together with samples from three potential om sources mangrove plants suspended particulate matter spm and microphytobenthos all collected from the landward face of the macouria mud bank french guiana total organic carbon toc and nitrogen tn concentrations in the sediment cores showed that om sources were characterized by spatio temporal variations in this mud bank the relative contributions of mangrove plants spm and microphytobenthos were estimated using a three end member mixing model based on tn toc atomic ratios and 13c values sedimentary om is mostly controlled by spm associated with variable amounts of om derived from mangrove plants and microphytobenthos these variations could be explained by topography and bed elevation which decrease submersion time and increase desiccation higher contributions of microphytobenthos are associated with black om rich laminae identified in sedimentary cores and linked to temporal emersion phases of the mud bank which favor the growth of benthic microalgae this result is confirmed by the calculation of the average sediment accumulation rate around 36 7 14 8 cm yr 1 taking into account the emersion of the study site every spring tide a fortnightly cycle this value is within the range of the previous results from other mud banks in french guiana but is more than ten times greater than values generally obtained in other coastal contexts

mesozoic cenozoic deformation in the canadian cordillera the record of a continental bulldozer abstract a possible mesozoic cenozoic trajectory for the north american craton is outlined from latitude changes of the craton derived from a revised apparent polar wander path and from westward movement of the craton based on the assumption that africa has been the least mobile continent geographically since the latest paleozoic during each of five time intervals that span 220 million years the craton trajectory had a different vector each vector appears to be reflected in the canadian cordillera by the dominant style and orientation of structures formed during that interval for much of the past 220 million years the meridionally oriented western margin of the pangea laurasia north america plate has been the site of arc magmatism where weak arc back arc lithosphere sandwiched between strong ocean floor and craton lithospheres at times coupled across convergent or transform plate boundaries focused and recorded strain when the craton apparently moved due westward between 180 160 ma and 120 60 ma the dominant structures formed then record orogen normal compression and were accompanied by orogeny structures formed during the earlier episode are mainly in the eastern and interior cordillera and their formation shortly followed or coincided with accretion of most terranes to the craton margin in the later episode compressional structures span the entire cordillera which emerged as a tectonic and physiographic entity before and between these intervals when the craton apparently moved mostly northwestward mainly geological and paleomagnetic considerations indicate some terranes moved southward sinistrally relative to the craton after 60 ma southwestward movement of the craton was concurrent with large northward dextral strike slip faults that disrupted the newly established ancestral cordillera the coincidence between the age of structures that record dominant orogen normal compression at times when the craton apparently moved due westward and orogen parallel displacements when the craton had either northward or southward components of motion suggests the craton acting as a continental bulldozer was the primary driver of cordilleran deformation and orogenesis

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

terrestrial organic carbon accumulation on the amazon deep sea fan during the last glacial sea level low stand abstract sediment cores from the amazon deep sea fan recovered during r v meteor cruise 16 2 show in detail the modern areal distribution of sedimentary organic carbon stable organic carbon isotopes of the organic matter om as well as variations in the depositional processes in addition we studied up to 300 m long drilled sediment records recovered during odp leg 155 which allow evaluation of temporal variations on the amazon fan our results reveal new evidence for a very rapid change of fan depositional processes and organic carbon source at times of sea level change over the middle and lower amazon fan to estimate the amount of terrestrial organic carbon stored in sediments from the last glacial in the amazon fan we used stable organic carbon isotopes of the om 13 c org organic carbon content corg and age models based on oxygen isotopes faunal data and magnetic excursions following our results the organic carbon accumulation on the amazon deep sea fan is controlled by glacio eustatic sea level oscillations interglacial sea level high stand sediments are dominated by marine om whereas during glacial sea level low stands terrestrial organic carbon is transported beyond the continental shelf through the amazon canyon and deposited directly onto the amazon deep sea fan glacial sediments of the amazon fan stored approximately 73 1015 g terrestrial corg in 20 000 years or 3 7 1012 g terrestrial corg yr 1 equivalent to 7 12 of the riverine organic carbon discharge assuming constant paleo discharge which is about the same amount of terrestrial organic carbon as deposited on the amazon shelf today 3 1 1012 g terrestrial corg yr 1 or 6 10 of the modern riverine organic carbon discharge

sulfate reduction related to the early diagenetic degradation of organic matter and black spot formation in tidal sandflats of the german wadden sea southern north sea stable isotope 13c 34s 18o and other geochemical results abstract a stable isotope geochemical investigation 34 s 32 s 13 c 12 c 18 o 16 o has been carried out to study the development of anoxic surface sediments black spots in the backbarrier tidal area of spiekeroog island southern north sea microbial sulfate reduction related to the degradation of mainly marine organic matter under anaerobic conditions led to the accumulation of hydrogen bisulfide up to 8 mm in the interstitial waters of the sandy sediments while the carbon isotopic composition of organic matter reflected the downcore preferential degradation of labile marine organic matter sulfur and oxygen isotope variations in the dissolved sulfur species provided information about the microbiologically mediated complex interactions between the sulfur carbon and oxygen cycles

a review of coastal palaeoclimate and relative sea level reconstructions using δ13c and c n ratios in organic material holocene reconstructions of relative sea level rsl and environmental change in the coastal zone have become progressively more numerous since the importance of assessing possible future sea level rises has become apparent traditionally this has been achieved using a combination of biological and physical indicators e g pollen diatoms foraminifera grain size etc in some circumstances microfossils can be rare or absent from holocene sediments and in these cases carbon isotope ratios 13c and organic carbon to total nitrogen ratios c n can be used because they have the potential to provide information as to the origin of organic material preserved in coastal environments the distinction in 13c and c n of the various sources of carbon to estuarine sediments has led to its wide use as a tracer of carbon pathways and storage in estuaries more recently these techniques have been applied to holocene sediments to decipher changes in palaeocoastal environments and thus position relative to sea level and or palaeoriver discharge which have direct relevance to palaeoclimate this paper reviews the studies that have utilised this technique and explores examples from a wide range of coastal environments saltmarshes estuaries lagoons isolation basins and fjords it also discusses the potential alteration of geochemical signatures as a result of decompositional processes organic matter decomposition has been shown to change sediment 13c and c n values and thus an understanding of the processes involved is necessary in order to have confidence in the palaeoenvironmental interpretation of holocene 13c and c n decompositional shifts in c n and particularly 13c can occur over a relatively short time period however it is the direction of change in 13c and c n rather than absolute values that is key for interpreting changes in relative sea level and thus such changes are commonly preserved

lower jurassic amaltheidae ammonitina in north america paleobiogeography and tectonic implications the amaltheids are restricted temporally to the late pliensbachian and geographically to the northern part of the northern hemisphere amaltheus stokesi is the only species that occurs in all areas of north america where amaltheids are found the craton north of the canada u s a border yields the most diverse amaltheid fauna including six of the seven taxa known in north america on quesnellia and stikinia there are no endemic amaltheids and diversity is low a stokesi increases in abundance northwards where in stikinia a margaritatus makes rare appearances wrangellia with its rich pliensbachian tethyan and east pacific faunas is almost devoid of amaltheids but its amaltheid fauna does include two specimens of a viligaensis an eastern russian species that is unknown elsewhere in north america cratonal amaltheid faunas have more in common with those of northwest europe than eastern eurasia suggesting that the arctic and northern north atlantic constituted the main dispersal route paleobiogeographic patterns on the major allochthonous terranes argue against terrane rotation and in support of post pliensbachian northward displacement relative to the north american craton in addition the presence of western pacific faunal elements on wrangellia suggests a more significant longitudinal displacement relative to the craton for this terrane compared to that for quesnellia and stikinia the chilliwack terrane of southwestern british columbia is a pliensbachian paleobiogeographic anomaly resume les amaltheides sont restreints dans le temps au pliensbachien et geographiquement a la partie septentrio nale de l hemisphere nord amaltheus stokesi est la seule espece qui se trouve dans toutes les regions de l amerique du nord ou on retrouve des amaltheides le craton au nord de la frontiere entre le canada et les etats unis fournit la faune amaltheide la plus diversifiee incluant six des sept taxons connus en amerique du nord a quesnellia et stiki nia il n y a pas d amaltheides endemiques et la diversite est faible a stokesi est de plus en plus abondant vers le nord ou a stikinia a margaritatus apparait rarement wrangellia avec ses riches faunes tethysiennes et du pacifique oriental pliensbachcien ne contient presque pas d amaltheides mais sa faune amaltheide comprend en effet deux specimens de a viligaensis une espece russe orientale inconnue ailleurs en amerique du nord les faunes cratonales amaltheides ont plus en commun avec celles de l europe du nord ouest que celles de l eurasie de l est suggerant que l arctique et l atlantique du nord septentrional etaient les principales voies de dispersion les patrons paleobiogeogra phiques sur les grands terranes allochtones plaident contre une rotation du terrane et en faveur d un deplacement relatif vers le nord par rapport au craton apres le pliensbachien de plus la presence d elements fauniques du pacifique ouest sur wrangellia suggere pour ce terrane un deplacement longitudinal plus important par rapport au craton que celui pour quesnellia et stikinia le terrane de chilliwack du sud ouest de la colombie britannique est une anomalie paleo biogeographique du pliensbachien traduit par la redaction 1449

early jurassic evolution of the northern stikinian arc evidence from the laberge group northwestern british columbia this study resolves fundamental questions concerning the age provenance and depositional history of laberge group strata in the whitehorse trough the jurassic inklin formation straddles the stikine and cache creek terranes along much of the length of the whitehorse trough ammonite biochronology indicates an age range of early sinemurian to late pliensbachian and provides the temporal framework for interpreting basin history strong temporal trends in both paleocurrent patterns and sandstone conglomerate petrofacies allow definition of three discrete phases in basin fill history stable tectonics characterized by relative volcanic quiescence and low sedimentation rates prevailed during the sinemurian sinemurian sandstone conglomerate petrofacies record a transitional arc provenance derived from erosion of the upper triassic volcanic pile flanking coastal sediments and arc roots of stikinia to the southwest during the early pliensbachian arc dissection was interrupted by a major magmatic episode wi

field observations of the isotopic composition of particulate organic carbon in the southern north sea and adjacent estuaries abstract the carbon isotopic composition of the organic matter in fluvial sediments and in fluvial suspended matter falls in the range valid for continental organic matter 25 to 28 the 13 c values in sediments from marine sedimentation areas and in marine suspended matter varies between 20 and 25 the rather low mean values for the deposited sediments of 13 2 suggest the presence of relatively large amounts of continental organic matter this may be a direct supply by the present day rivers and or organic matter derived from the erosion of peat layers even in the marine environment a distinction between these two sources of detrital continental organic matter is not possible with stable isotopes studies in the estuaries studied the organic matter contents decrease and the 13 c values of the organic matter increase in the seaward direction these changes are primarily caused by the mixing of fluvial and marine sediments

biogeochemical impact of submarine ground water discharge on coastal surface sands of the southern baltic sea this study evaluates the effect of submarine ground water discharge sgd on biogeochemical processes of sandy sediments of hel bight poland in the shallow southern baltic sea using stirred benthic chambers combined to seepage meters deep pore water profiles and a reactive transport model the main impacts of fresh anoxic groundwater seepage are due to 1 the efflux of methane 2 the efflux of phosphate and silicate 3 the efflux of dissolved organic carbon doc of aquifer origin methane from sgd is assumed to be only slightly oxidized within the sediments and potentially reach the atmosphere at a maximum rate of 30 mmol ch4 m 2 d 1 silicate and phosphate supplied by sgd promote a seep site net community production rate that is more than twice as compared to adjacent non seeping sites 70 and 30 mmol c m 2 d 1 respectively however oxygen uptake rates at the seep site during the night 30 mmol o2 m 2 d 1 are lower than those observed at the reference sites 50 mmol o2 m 2 d 1 we hypothesize that autogenic relatively labile doc is available at the reference site leading to higher oxygen uptake rates as compared to the seep sites where it is being replaced by less reactive doc originating from the ground water

cache creek terrane entrapment oroclinal paradox within the canadian cordillera exotic and far traveled oceanic crustal rocks of the cache creek terrane cc are bordered by less exotic quesnel qn and stikine st arc terranes to the east north and west all of these terranes are enveloped by an arcuate belt of displaced continental margin rocks the kootenay ko nisling ns and parts of the yukon tanana ytt terranes that have indirect ties to ancestral north america na initial 87sr 86sr isopleths conform to this arcuate pattern such a pattern of concentric belts presents a geological conundrum how did the qn st and cc come to be virtually enveloped by terranes with ties to na past and current models that explain assembly of the canadian cordillera are deficient in their treatment of this problem we propose that early mesozoic qn and st were joined through their northern ends as two adjacent arc festoons that faced south toward the cache creek ocean panthalassa oceanic plateau remnants within the cc today were transported from the tethyan realm and collided with these arcs during subduction of the cache creek ocean counterclockwise oroclinal rotation of st and ns terranes in the late triassic to early jurassic caused enclosure of the cc rotation continued until these terranes collided with qn in the middle jurassic paleomagnetic declination data provide support for this model in the form of large average anticlockwise rotations for permian to early jurassic sites in st but moderate clockwise rotations for sites in qn specific modern analogues for the cordilleran orocline include the yap trench where the caroline rise is colliding end on with the mariana arc and the banda arc located on the southeastern tail of the asian plate which is being deformed into a tight loop by interactions with the australian and pacific plates

the composition of sedimentary organic matter in relation to the dynamic features of a mangrove fringed coast in french guiana the sedimentary organic matter content of a series of 2 m deep cores was examined in relation to the evolution of mangrove forest on the basis of geochemical analyses and optical observations avicennia dominated forest deposits developing along the highly dynamic coastline of french guiana were collected in five stations based on stage of forest evolution the sedimentary organic matter in the upper sediment of the youngest mangrove swamp is mainly derived from algal mats with low carbon nitrogen ratios c n ratio from 6 to 8 and typical greyish amorphous organic flakes as observed in optical studies indeed rare young avicennia trees are present and effectively geochemical parameters do not give evidence of a litter made up of higher plant debris these rare debris being probably exported by the tides a slight increase with depth in the first decimetres of both total organic carbon toc content and c n ratio results from the development of the radial cable root system of the pioneer avicennia germinans early diagenetic conditions of this young forest are rather controlled by dominant suboxic processes as suggested by high eh values range 200 400 mv and local anoxic processes occurrence of pyrite in micro environments this is mainly due to the oxygen available by roots and crab bioturbation the organic content of the senescent mangrove sediment is mainly derived from higher plant debris in the uppermost 30 cm as indicated by relatively high c n ratios and the predominance of ligno cellulosic debris the strong decrease in hydrogen index values results from the degradation of the higher plant debris losing hydrogen bounds through decay processes moderately acidic ph values low ehs and the presence of pyrite framboids point towards the reducing decay processes in surficial layers of the senescent mangrove mediated by sulphate reducing bacteria whatever the stage of evolution of the forest the geochemical characteristics of the sediment below 30 cm are those of the shoreface one with opaque refractory debris derived from the amazon river detritus discharge the sediment collected from dead mangrove forests subsequently recolonized by pioneer mangroves contains organic markers which predate recolonization recording previous phases of erosion and accretion

evidence for active tilting of the nw german basin from correlations between fluvial landscape and geological subground the catchment basin of the river hunte lower saxony nw german basin was studied on a mesoscale length of 90 km to investigate the influence of the geological subground on modern morphology a geo information system gis was used to calculate linear correlation coefficients between the depth of geological strata base zechstein to base quaternary and the height of the modern landscape holocene alluvial plain lower weichselian terrace catchment basin and watershed high linear correlation coefficients between the base of tertiary and the height of the modern topography catchment basin r2 0 87 lower weichselian terrace r2 0 95 and holocene alluvial plain r2 0 95 indicate control of the modern topography by the depth of the geological subsurface via tilting of the entire basin most likely northward tilting of the nw german basin forces the river hunte to flow in a northerly direction by relative uplift of the hinterland wiehengebirge rhenish massif and subsidence of the north sea area

trace metals in holocene coastal peats and their relation to pyrite formation nw germany abstract three drill cores from the marshlands of nw germany which cover the entire holocene were analyzed at high resolution for bulk composition al fe selected trace metals and stable sulfur isotopes the drill cores contain two lithological types of peat i basal peats overlying pleistocene sands and ii intercalated peats situated between clastic sediments of predominantly marine origin the peat layers are characterized by distinct enrichments in pyrite due to microbial sulfate reduction under almost open system conditions with respect to seawater sulfate as shown by sulfur isotope partitioning the main fe source seems to be the freshwater environment the determination of dissolved and particulate fe of channels and small rivers close to the study area revealed a 50 fold higher fe content of the freshwater environment when compared with north sea water pyrite enrichments are explained by two scenarios i pyrite formation coincides with fen reed peat growth basal and intercalated under the influence of a brackish water zone salinity app 5 15 and ii pyrite was formed after peat growth in the lowest limnic basal peat intervals maximum pyrite accumulation ts 28 occurs in latter peats that contain thin clastic layers as a result of tidal channel activities after peat formation the occurrence of clastic layers may have favoured the inflow of saline groundwater the peat layers are also characterized by enrichments in redox sensitive trace metals as mo re u and cd whereas co cr cu mn ni pb tl and zn reflect the geogenic background leaching experiments have shown that as co cu mo re and tl are predominantly fixed as sulfides and or incorporated into pyrite the remaining trace metals show no distinct trends only cr reveals a strong relation to the lithogenic detritus seawater is the dominating source for as cd mo re and u the remaining trace elements seem to have a freshwater source similar to fe in contrast to the distribution of pyrite highest amounts of redox sensitive trace metals are seen in fen reed peats basal and intercalated that were formed under a direct influence of seawater and brackish water respectively therefore we suggest that saline groundwater entering the basal peats was probably depleted in redox sensitive trace metals e g owing to microbially induced reduction of trace metals and subsequent precipitation as sulfides or fixation by organic matter

half a century of dynamic coastal change affecting mangrove shorelines of french guiana a case study based on remote sensing data analyses and field surveys the mobile mud banks several kilometres wide and about 30 km long which form the sedimentary environment of the coast of the guianas are a consequence of the huge particulate discharge of the amazon these mud banks shift towards the northwest influenced by the combined action of accretion and erosion a process also affected by periodic variability because of this movement the coastline is unstable and continuously changing such changes determine the structure and composition of mangrove forests the only type of vegetation adapted to this dynamic environment the objectives of this study were to identify coastal changes that took place over the last 50 years and to relate them to natural processes of turnover and replenishment of mangrove forests these objectives have been achieved through a combination of remote sensing techniques aerial photographs and spot satellite images and field surveys in the area of the sinnamary estuary french guiana ground data were collected in representative mangrove forest stands chosen as a function of their growth stages and their structural features from pioneer and young stages to adult mixed and declining formations the coastline changes and the mangrove dynamics over the 1951 1999 period are analyzed through production of synthetic digital maps showing an alternation of net accretion 1951 1966 and erosion periods 1966 1991 followed by the present accretion phase based on this structural functional and historic information a global scenario of mangrove forest dynamics is proposed including a model of forest development forest gap processes and sedimentological dynamics the results of this research are discussed within the context of regional coastal amazonian area and global climate d 2004 elsevier b v all rights reserved

long wavelength heterogeneities in the upper mantle as seen by satellites abstract modern satellite methods have made it possible to study the gravity field of the earth with methods that primarily give increased information of the lower harmonics in a spherical harmonic expansion for areas covered with water we have recently obtained very interesting results from the seasat satellite earlier studies of the gravity field have mainly resulted in geophysical evaluations for the very low degrees which mostly reflect information from the core and the lower mantle now available studies seem to give evidence for geophysical activities which originate from convection currents as well as glacio isostatic uplifts most of this information is probably generated in the upper mantle methods for mapping of the terrestrial gravity field with satellite technique are presented and some of the problems with the geophysical evaluation are further discussed

cycling of trace metals mn fe mo u v cr in deep pore waters of intertidal flat sediments trace metals mn fe mo u cr v were studied in pore waters of an intertidal flat located in the german wadden sea the study system is an example of a permeable tidal flat system where pore water exchange is affected by tidal driven pressure gradients besides diffusion permanently installed in situ samplers were used to extract pore waters down to 5 m depth throughout one year the samplers were either located close to the tidal flat margin or in central parts of the tidal flat despite dynamic sedimentological and hydrological conditions the general trends with depth in deep tidal flat pore waters are remarkably similar to those observed in deep sea environments rates of trace metal cycling must be comparably large in order to maintain the observed pore water profiles trace metals further show similar general trends with depth close to the margin and in central parts of the tidal flat seasonal sampling revealed that v and cr vary concurrent with seasonal changes in dissolved organic carbon doc concentration this effect is most notable close to the tidal flat margin where sulphate doc and nutrients vary with season down to some metres depth seasonal variations of mn fe mo and u are by contrast limited to the upper decimetres of the sediment their seasonal patterns depend on organic matter supply redox stratification and particulate matter deposited on sediment surfaces pore water sampling within one tidal cycle provides evidence for pore water advection in margin sediments during low tide pore water flow towards the creekbank is generated by a hydraulic gradient suggesting that deep pore waters may be seeping out of creekbank sediments owing to the enrichment of specific elements like mn in pore water compared to sea water seeping pore waters may have an impact on the chemistry of the open water column mass balance calculations reveal that the impact of deep pore waters on the mn budget in the open water column is below 4 mn deep pore water discharge of the whole wadden sea is estimated to be about 9 of the total dissolved riverine mn input into the southern north sea

geochemical evidence for cryptic sulfur cycling in salt marsh sediments cryptic sulfur cycling is an enigmatic process in which sulfate is reduced to some lower valence state sulfur species and subsequently quantitatively reoxidized the rate and microbial energetics of this process and how prevalent it may be in the environment remain controversial here we investigate sulfur cycling in salt marsh sediments from norfolk england where we observe high ferrous iron concentrations with no depletion of sulfate or change in the sulfur isotope ratio of that sulfate but a 5 increase in the oxygen isotope ratio in sulfate indicating that sulfate has been through a reductive cycle replacing its oxygen atoms this cryptic sulfur cycle was replicated in laboratory incubations using 18o enriched water demonstrating that the field results do not solely result from mixing processes in the natural environment numerical modeling of the laboratory incubations scaled to represent the salt marsh sediments suggests that the uptake rate of sulfate during this cryptic sulfur cycling is similar to the uptake rate of sulfate during the fastest microbial sulfate reduction that has been measured in the natural environment the difference is that during cryptic sulfur cycling all of the sulfur is subsequently reoxidized to sulfate we discuss mechanisms for this pathway of sulfur cycling including the possible link to the subsurface iron cycle

coupling between sedimentary dynamics early diagenetic processes and biogeochemical cycling in the amazon guianas mobile mud belt coastal french guiana coastal french guiana lies within the vast mobile mudbelt that characterizes much of the s american inner shelf downdrift of the amazon river approximately 15 20 of the amazon sediment outfall moves nw along the guianas in part as a series of 20 25 coastal mud waves seasonal studies of a representative migrating mudwave located between kourou and sinnamary french guiana demonstrate that diagenetic properties and biogeochemical cycling are closely coupled to sedimentary dynamics and the refluxing of reduced components between the seabed coastal facies and well oxygenated overlying water an unsteady two zone diagenetic regime is typically present in the shallow subtidal and low intertidal regions a surficial layer usually 0 5 1 m thick is nonsulfidic highly reactive and dominated by fe mn cycling this suboxic layer unconformably overlies more consolidated sediment in which net so42 reduction is often observed and contracts shoreward toward the mangrove fringe as sediments stabilize and become bioturbated the relatively stable intertidal flats are also sites of significant benthic primary production despite suboxic conditions over extensive intervals anaerobic remineralization rates are high co2 0 2 0 6 mm day 1 and often show little evidence of attenuation with depth integrated co2 fluxes are 20 235 mmol m 2 day 1 wet dry season average 120 far exceeding diffusive o2 fluxes into the bottom high reactivity 0 08 day 1 and low c n remineralization release ratios 5 3 of decomposing material imply fresh substrate of marine origin most reduced solid phase fe is present as nonpyritic authigenic fe minerals 20 fe ii is in pyrite and low sedimentary c s ratios 6 8 reflect the generally nonsulfidic conditions a broad range of tracers e g 234th t1 2 24 days 210pb t1 2 22 years seasonal cl profiles and nonsteady state diagenetic models of pore water concentrations and oxidant reductant relationships demonstrate that the upper 0 1 1 m of deposits are reworked and exchanged with overlying water on timescales of 10 days to seasonally thus the seafloor acts as a massive suboxic batch reactor entraining and processing reactive marine plankton regenerating fe mn oxides exchanging metabolites and nutrients with the oxygenated water column and generating suites of nonsulfidic authigenic minerals the apparent paradoxical properties of high remineralization rate low reductant content corg 630 mol g 1 and dominance of suboxic metal cycling are a direct consequence of frequent entrainment of highly reactive organic substrate and simultaneous regeneration of the major fe oxidants in oxygenated water the amazon guianas mobile mudbelt is a zone of extraordinarily intense sedimentary and biogeochemical recycling greatly exceeding stable coastal systems such as salt marshes in material exchange with the sea

the diagenesis of phosphorus in a nearshore marine sediment abstract chemical analyses have been made for total inorganic phosphorus total organic phosphorus and organic carbon in plankton and in anoxic sediments from long island sound u s a when combined with laboratory experiments the measurements of other studies on the same sediments and mathematical modelling the results indicate that 1 1 a large proportion of dissolved phosphate in the upper 10 cm of sediment zone of bioturbation is provided by the release of adsorbed phosphate during the reduction of ferric oxyhydroxides 2 2 below the zone of bioturbation phosphate is liberated to solution solely via organic matter decomposition and the release is stoichiometrically coupled to bacterial sulfate reduction and ammonia formation 3 3 a steady state diagenetic model can be used to predict the profile of organic phosphorus from that of dissolved phosphate at depths below the zone of bioturbation 4 4 the flux of dissolved phosphate out of the sediment must arise largely from phosphate liberation occurring very close 5 5 there is a large preferential loss of phosphorus relative to carbon from organic matter at the time of or prior to burial whereas after burial phosphorus is not lost preferentially at this location

new lower jurassic ammonite faunas from the fernie formation southern canadian rocky mountains new ammonite faunas are described from sections along bighorn and scalp creeks in central western alberta where lower jurassic parts of the fernie formation are exposed the first record of the upper sinemurian obtusum zone from the fernie is based on the occurrence of asteroceras cf stellare and epophioceras cf breoni in the basal pebbly coquina on bighorn creek the overlying red deer member has yielded amaltheus cf stokesi representing the upper pliensbachian margaritatus zone in immediately superjacent strata the first north american examples of amauroceras occur together with protogrammoceras and aveyroniceras in the basal parts of the overlying poker chip shale a fauna including harpoceras cf falciferum harpoceratoides polyplectus cf subplanatus hildaites cf serpentiniformis and dactylioceras cf athleticum is correlated with the lower toarcian falciferum zone the upper parts of the poker chip shale on fording river in southeastern british columbia contain a fauna representing some pa

preservation of elemental and isotopic source identification of sedimentary organic matter the amount and type of organic matter in the sediments of lakes and oceans contribute to their paleoenvironmental and paleoclimatological records only a small fraction of the initial aquatic organic matter survives destruction and alteration during sinking and sedimentation selective degradation modifies the character of the surviving small fraction of organic matter which becomes incorporated in bottom sediments organic matter alterations can continue to sub bottom depths of hundreds of meters corresponding to millions of years source and paleoenvironmental information nonetheless remains preserved in the molecular elemental and isotopic compositions of organic matter c n and 13c values of total organic matter in particular appear to retain paleoenvironmental information for multi myr time periods

a review of postglacial emergence on svalbard franz josef land and novaya zemlya northern eurasia the pattern of postglacial emergence in the barents sea is pivotal to constraining the timing of deglaciation and extent and thickness of the last ice sheet in northern eurasia this review unites records of holocene relative sea level from svalbard franz josef land and novaya zemlya to better understand the geometries of past ice sheet loads emergence data from northern eurasia confine the maximum area of glacier loading to the northwestern barents sea where 100 m of emergence is measured on kongs ya deglacial unloading commenced on western and northern spitsbergen c 13 12 14 c ka ago and by c 10 5 14 ck a on eastern svalbard and more distal sites on franz josef land and novaya zemlya the marine limit phase c 13 12 14 c ka on western and northern spitsbergen is characterized by the construction of spits indicating a dominance of long shore drift over stormgenerated fetch reflecting extensive sea ice coverage of coastal areas at sites in proximity to the ice sheet margin on western and northern spitsbergen there is evidence for a transgressive regressive cycle c 6 4 14 c ka possibly reflecting back migration of displaced mantle material a modern transgression is inferred from the marine erosion of 17th century cultural features and 14 c ages of whalebone and terrestrial peat buried by modern storm gravels that place sea level at its present position by c 2 to 1 ka ago the greatest observed emergence on franz josef land occurs on bell island with a marine limit at 49 m aht formed c 10 14 c ka available emergence data since 9 ka show rising strandlines toward the southwest at b0 3 m km the northern limit of emergence on franz josef land is poorly constrained because relative sea level data is sparse north of 80 30 0 n in contrast to svalbard and franz josef land the marine limit on northern novaya zemlya is only 10 15 m above high tide and formed between 6 5 and 5 0 14 c ka when global sea level was stabilizing all sites show little apparent emergence during the past 2 ka with the youngest raised landforms at identical heights to storm beaches this minimal glacio isostatic signature on novaya zemlya and on vaygach island where deglaciation commenced 10 ka ago indicates ice sheet thicknesses of o1 5 km the spatial variation in emergence for the barents sea indicates that western and northern spitsbergen and novaya zemlya were near the reactive margin of the ice sheet and these areas sustained the briefest ice coverage 2 6 ka and were probably not in isostatic equilibrium in contrast central and eastern svalbard and southern franz josef land were beneath a substantial ice load and probably sustained this load for c 10 14 c ka and achieved isostatic equilibrium isostasy residual from an ice sheet model portrays well the general pattern of uplift and load response at the centre of ice sheets but deviates substantial at the ice sheet margin or areas covered by thin ice like novaya zemlya

holocene relative sea level history of novaya zemlya russia and implications for late weichselian ice sheet loading abstract we present six new radiocarbon dated emergence curves that provide a detailed record of postglacial emergence of northern novaya zemlya and ages which constrain the emergence of vaygach island in the southern archipelago radiocarbon ages on hiatella sp from a lateral moraine in russkaya gavan and abundances of foraminifea in a marine core from nordenskiold bay 300 km south of our study area indicate that coastal deglaciation occurred prior to 10 000 cal yr b p however postglacial emergence commenced 7000 cal yr b p with stabilization of global sea level the total emergence is 13 11 m above sea level asl with apparent uplift rates of 1 2 mm yr for the past 2000 yr indicating modest glacier loads 11 000 cal yr b p deglaciation or both the isobase pattern showing no east west tilt across novaya zemlya and offshore moraines suggest a separate ice dispersal center over novaya zemlya for the later stages of the late weichselian glacial cycle and possibly earlier

pore water dissolved inorganic carbon sources and cycling in the shallow sediments of the haima cold seeps south china sea abstract pore water geochemical compositions provide the insights into seafloor cold seep activities and biogeochemical processes of methane derived carbon in sediments in this study six sediment push cores were collected by manned submersible at the center and edge of the active haima cold seeps and a nearby background site pore water compositions of the so42 ca2 mg2 sr2 nh4 dissolved inorganic carbon dic and 13c dic at each sediments core were measured the very shallow depths of sulfate methane transition zone smtz suggest that high methane flux and significant anaerobic oxidation of methane aom activities occur in the shallow sediments reaction transport modelling results show that the relative contributions of aom and organoclastic sulfate reduction osr consuming sulfate are 84 1 and 15 9 at site hm 2 6 and 94 6 and 5 4 at site hm 3 3 respectively furthermore extremely low 13c dic values at the central sites hm 2 6 45 67 and hm 3 3 53 87 indicate an external methane derived dic based on the 13c mass balance we quantify the proportions of pore water dic derived from organic matter degradation and aom as 24 7 and 65 3 at site hm 2 6 and 9 3 and 80 7 at site hm 3 3 respectively an increase in pore water dic concentration leads to carbonate precipitation plots of sr ca vs mg ca ratios reveal that the carbonate phases in sediments are dominantly high mg calcite in this region our study demonstrates that aom can serve as a dominant biogeochemical process through incorporation of methane derived carbon into dissolved and solid inorganic carbon phases significantly influencing dic cycling within the shallow sediments of the haima cold seep area

distribution and sources of particulate organic matter in the water column and sediments of the fly river delta gulf of papua papua new guinea suspended particles from surface and bottom waters and surficial sediments from the seabed were collected throughout the fly river subaqueous delta region during the monsoon season in january 2003 because of the unusually low river discharge associated with a strong el nino water column salinities were relatively high 10 to 32 throughout most of the delta with brackish salinities 4 wt relatively high organic carbon nitrogen molar ratios oc n 20 mol mol and quite depleted stable isotopic compositions of organic carbon 13coc 27 in contrast surface sediments in the seabed displayed spatially uniform compositions that were characterized by markedly lower oc contents 1 1 0 8 wt lower oc n ratios 17 9 mol mol and relatively enriched 13coc compositions 25 5 1 1 the radioisotopic compositions of oc from a selected set of seabed samples 14coc of 408 82 indicate om in surface sediments is old 14c ages of 2800 to over 6000 years before present the ratios of organic carbon to mineral surface area exhibited by these sediments are within the typical mono layer equivalent ranges characteristic of shelf sediments and do not reflect the preferential removal of terrigenous om overall these compositions indicate that while water column pom appears to be derived mainly from terrigenous vascular plant debris and riverine estuarine phytoplankton the source of most of the sedimentary pom is aged soil oc ultimately derived from c3 vegetation we speculate that the concentrations and sources of suspended pom in the water column of the fly river delta region reflect the conditions of low river discharge low wave energy and neap tides encountered at the time of sampling in contrast pom compositions in surface sediments are consistent with the transport and deposition of old mineral bound oc most likely eroded from the upland regions of the fly river watershed which is characterized by steep slopes high precipitation and c3 tropical forests and grasslands

the determination of rates of land uplift in norway it is the task and the responsibility of the geodetic section within the geographical survey of norway to establish and maintain the national horizontal and vertical geodetic primary control networks of that country provided that relative crustal movements take place within norway they will cause deformations to these networks there is no geodetic proof that any horizontal deformations of the surface layer of the crust take place in continental norway and there is no established geological evidence of such movements either in 1984 a small geodetic control network was established and measured for the first time across a possibly active fault it is not expected that horizontal movements will cause any serious problems in the maintenance of the horizontal network vertical movements of the ground however are causing us problems both in the establishment and in the maintenance of a national height system

pelagic molybdenum concentration anomalies and the impact of sediment resuspension on the molybdenum budget in two tidal systems of the north sea the seasonal dynamics of molybdenum mo were studied in the water column of two tidal basins of the german wadden sea sylt romo and spiekeroog between 2007 and 2011 in contrast to its conservative behaviour in the open ocean both losses of more than 50 of the usual concentration level of mo in seawater and enrichments up to 20 were observed repeatedly in the water column of the study areas during early summer mo removal by adsorption on algae derived organic matter e g after phaeocystis blooms is postulated to be a possible mechanism mo bound to organic aggregates is likely transferred to the surface sediment where microbial decomposition enriches mo in the pore water first 98 95mo data of the study area disclose residual mo in the open water column being isotopically heavier than momo mean ocean molybdenum during a negative mo concentration anomaly whereas suspended particulate matter shows distinctly lighter values based on field observations a mo isotope enrichment factor of e 0 3 has been determined which was used to argue against sorption on metal oxide surfaces it is suggested here that isotope fractionation is caused by biological activity and association to organic matter pelagic mo concentration anomalies exceeding the theoretical salinity based concentration level on the other hand cannot be explained by replenishment via north sea waters alone and require a supply of excess mo laboratory experiments with natural anoxic tidal flat sediments and modelled sediment displacement during storm events suggest fast and effective mo release during the resuspension of anoxic sediments in oxic seawater as an important process for a recycling of sedimentary sulphide bound mo into the water column

a u pb and 40ar 39ar time scale for the jurassic published time scales provide discrepant age estimates for jurassic stage boundaries and carry large uncer tainties the u pb or 40 ar 39 ar dating of volcaniclastic rocks with precisely known stratigraphic age is the preferred method to improve the calibration a radiometric age database consisting of fifty u pb and 40 ar 39 ar ages was com piled to construct a revised jurassic time scale accepted ages have a precision of 5 ma 2 or better and are con fined to no more than two adjacent stages the majority of these calibration points result from integrated bio and geochronologic dating in the western north american cordillera and have not been previously used in time scales di rect dates are available only for the triassic jurassic boundary and the initial boundary of the crassicosta chron and the callovian stage the chronogram method was used to estimate all early and early middle jurassic zone boundaries attempted here for the first time late middle jurassic substage boundaries and late jurassic stage boundaries signif icant improvement is achieved for the pliensbachian and toarcian where six consecutive zone boundaries are deter mined the derived zonal durations are disparate varying between 0 4 and 1 6 ma the latest jurassic isotopic database remains too sparse therefore chronogram estimates are improved using interpolation based on magnetochronology the initial boundaries of jurassic stages are proposed as follows berriasian jurassic cretaceous 1418 18

carbon and nutrient accumulation in tropical mangrove creeks amazon region abstract the marapanim river estuary mre is part of the amazon estuarine system located in northern brazil which is characterized as having extensive mangrove forests given that previous studies reported co2 and ch4 fluxes from mangrove creeks in this region here we investigate the potential organic carbon sequestration of the creek mudflats to get a better understanding of the carbon cycling through these systems sediment accumulation rates derived from 210pb dating indicated that sampled cores represent the previous 24 4 yr the approximately 24 year total organic carbon toc total nitrogen tn and total phosphorus tp burial rates were estimated to be 192 5 43 5 15 3 4 1 and 3 2 0 8 g m 2 yr 1 respectively a binary source mixing model based on carbon stable isotopes 13c revealed that the sedimentary organic matter om is mainly influenced by marine phytoplankton input 49 to 95 furthermore the toc accumulation rates found here were slightly higher than the global averages estimated for within mangrove forests suggesting that these unaccounted carbon sinks along creek mudflat environments are relevant for carbon budgets in mangrove colonized coastal zones the highest contents stocks and accumulation rates were found in the tidal creek sediments that are most influenced by nearby mangroves and are more protected than sediments from major river margins our results indicate that the creek mudflats play a major role in carbon and nutrients sequestration directly related to grain size and om sources

isotopic analysis of sulfur cycling and gypsum vein formation in a natural co2 reservoir abstract in order to assess the long term security of geologic carbon storage it is crucial to study the geochemical behavior of sulfur in reservoirs that store co2 fossil fuel combustion may produce mixtures of carbon dioxide and sulfur gases and the geochemical effects of sulfur co2 cosequestration are poorly understood this study examines sulfur mineralization from a core drilled in a stacked sequence of natural co2 reservoirs near the town of green river utah these reservoirs include the entrada and navajo sandstone which are separated by the carmel formation caprock and transected by a system of co2 degassing normal faults through which saline co2 charged brines discharge our objective in this study is to evaluate the mechanisms and timing of secondary mineral formation particularly gypsum formation in the co2 reservoirs and intervening caprock the carmel formation contains beds of gypsum within a fault zone secondary veins of gypsum exist throughout the entrada sandstone and carmel formation we report sulfur and oxygen isotope data 34sso4 and 18oso4 respectively measured in gypsum and 34s measured in pyrite and the oxygen and hydrogen isotope composition 18o and d respectively of gypsum hydration water the multiple isotope approach allows us to trace the sources of sulfur in the reservoirs and when combined with structural and petrological evidence the progress of fluid rock reactions and relative timing of vein mineralization the secondary gypsum veins in the carmel formation derive from mixing of fluids with two isotopically distinct sulfate sources sulfate from the gypsum beds within the carmel formation and sulfate rich brines that originate from evaporites in the underlying carboniferous paradox formation the gypsum veins in the entrada sandstone have a relatively wide range of 18oso4 both isotopically more enriched in 18o and more depleted in 18o than the primary gypsum sources we suggest that some aqueous sulfate in the entrada sandstone may cycle through multiple valence states as it undergoes reduction and reoxidation resulting in the replacement of its oxygen atoms and allowing the occasional formation of gypsum with anomalous low 18oso4 our data from gypsum hydration water indicates that groups of gypsum veins formed at two different times gypsum veins in the entrada sandstone and some veins in the carmel formation likely formed during quaternary co2 charged brine discharge events while other veins located close to the gypsum beds in the carmel formation formed earlier likely during cycles of dehydration and rehydration associated with the laramide age 40 mya faulting we conclude that calcium sulfate mineral formation in brine filled fractures may play an important role in inhibiting fluid migration in geologic reservoirs that contain co2

organic matter budget in the southeast atlantic continental margin close to the congo canyon in situ measurements of sediment oxygen consumption abstract a study of organic carbon mineralization from the congo continental shelf to the abyssal plain through the congo submarine channel and angola margin was undertaken using in situ measurements of sediment oxygen demand as a tracer of benthic carbon recycling two measurement techniques were coupled on a single autonomous platform in situ benthic chambers and microelectrodes which provided total and diffusive oxygen uptake as well as oxygen microdistributions in porewaters in addition sediment trap fluxes sediment composition org c tot n caco3 porosity and radionuclide profiles provided measurements of respectively input fluxes and burial rate of organic and inorganic compounds the in situ results show that the oxygen consumption on this margin close to the congo river is high with values of total oxygen uptake tou of 4 0 6 3 6 0 5 mmol m 2 d 1 at 1300 and 3100 m depth respectively and between 1 9 0 3 and 2 4 0 2 mmol m 2 d 1 at 4000 m depth diffusive oxygen uptakes dou were 2 8 1 1 2 3 0 8 0 8 0 3 and 1 2 0 1 mmol m 2 d 1 respectively at the same depths the magnitude of the oxygen demands on the slope is correlated with water depth but is not correlated with the proximity of the submarine channel levee system which indicates that cross slope transport processes are active over the entire margin comparison of the vertical flux of organic carbon with its mineralization and burial reveal that this lateral input is very important since the sum of recycling and burial in the sediments is 5 8 times larger than the vertical flux recorded in traps transfer of material from the congo river occurs through turbidity currents channelled in the congo valley which are subsequently deposited in the lobe zone in the congo fan below 4800 m ship board measurements of oxygen profiles indicate large mineralization rates of organic carbon in this zone which agrees with the high organic carbon content 3 and the large sedimentation rate 19 mm y 1 found on this site the lobe region could receive as high as 19 mol c m 2 y 1 1 3 being mineralized and 2 3 being buried and could constitute the largest depocenter of organic carbon in the south atlantic

marine geology of the gulf of trieste northern adriatic geochemical aspects abstract geochemical analyses of surficial sediment in the gulf of trieste in terms of organic carbon total nitrogen and phosphorus 13c composition of sedimentary organic matter the trace metals hg pb cr cu zn cd ni mn and fe and the radionuclides 137cs and 210pb were carried out the higher values of organic carbon total nitrogen and phosphorus are restricted to the clayey silty sediments of the small bays of koper piran muggia and panzano and around the river isonzo outflow on the basis of 13c values the sedimentary organic matter is of entirely marine origin in the central part of the gulf which is bordered by two areas of greater terrigenous influence with the exception of hg and pb the areal distribution of the trace metals is similar to that of carbon nitrogen and phosphorus with higher contents in the clayey silty and silty sediments the mercury and pb contents exhibit a gradual decrease from the mouth of the isonzo river towards the southern part of the gulf riverine inputs also provide the most important sources of 137cs in the sediments of the gulf high 137cs activities in the uppermost layer of the cores indicate the chernobyl signal and in contrast to 210pb the vertical profiles show its occurrence in deeper layers which is attributed to diffusion of the 137cs distribution studies of the biogenic elements carbon nitrogen and phosphorus and the trace metals in the surficial and subsurficial layers of the 40 m deep borehole mk 6 in koper bay shows practically no enrichment in the former but an increase in the hg and pb contents this would not indicate a rapid increase in eutrophication in the gulf or that the sediments are an important sink for biogenic elements

structural effects of tidal exposures on mudflats along the french guiana coast wetting and drying cycles on intertidal mudflats vary considerably with altitude modifying the physical characteristics of surface sediment in ways favoring or not plant colonization in this context sediment properties were investigated by means of laboratory experiments and field surveys on a wide range of fluid to desiccated muds from the highly dynamic coastline of french guiana changes in physical parameters such as sediment erodability yield stress water loss and pore water salinity indicated a long term compaction of mudflats as well as fluctuations related to the successive wetting and drying cycles mudcracks constituted a spectacular feature representative of the contractional stress they re opened after a few days of dewatering and re healed during the subsequent wetting from the analysis of field data the trapping of avicennia germinans propagules in ephemeral mudcracks turned out to be responsible of 95 of the sprouting on the coastal fringe thus desiccation process usually considered as a typical feature of erosion revealed herein to be a major mechanism of colonization this mechanism undoubtedly affects the 1600 km long amazon coastal system and is believed to exist in many other tropical environments submitted to important siltation

sulfate reduction and formation of iron sulfide minerals in nearshore sediments from qi ao island pearl river estuary southern china abstract sulfate reduction usually leads to the formation of iron sulfide minerals in marine sediments and strongly influences the global coupled carbon iron sulfur biogeochemical cycles in marine sediments here we report sulfate reduction and pyrite formation from the coastal sediments near qi ao island pearl river estuary using a combination of sedimentary pore water and solid sediment geochemical analyses strong enrichments in reactive iron 276 8 358 2 mol g were observed especially at the sites located near the river outlets high contents of reactive iron and low values of the degree of iron pyritization dop indicate that the limiting effect of reactive iron on pyrite formation can be excluded at these sites in the upper sedimentary layer conservative mixing of river water and marine water reinforces the fact that sulfate reduction is not appreciable the limited sulfate supply and low sulfate reduction rates lead to not enough dissolved sulfide available for formation of iron sulfide minerals however below this dilution mixing layer pore water geochemical profiles indicate that a fraction of sulfate consumption is mediated by upward diffusing methane an additional sulfide is produced from anaerobic oxidation of methane aom and later reacts with reactive iron resulting in enhancement of pyrite formation in the sediments by contrast it appears that sulfate concentration is a primary factor controlling for pyrite formation in these estuarine environments our study highlights the need in future work for an integrated analysis of the hydrologically driven change in the bottom seawater sulfate concentrations to better understand the regulation factors of global sulfur reservoirs in coastal sediments of estuarine environments as sulfur burial is an important factor in determining the past atmospheric oxygen level

origin and composition of organic matter in tidal flat sediments from the german wadden sea abstract two sediment cores of up to 550 cm length from an intertidal flat of the german wadden sea near the island of spiekeroog were investigated for the quantity and composition of fossil organic matter om the lowermost parts of the cores are dominated by grey mud of a salt marsh facies containing mainly terrestrial om estimated to account for 60 75 of the total om based on 13 c values and the ratio of short to long chain n alkanols the terrigenous origin of the dominant fraction is indicated among others by high proportions of c 29 sterols and long chain n alkanes typical of plant waxes coarse shell beds overlying the grey mud at 2 2 5 m depth represent a flooding and erosion event possibly related to heavy storm floods in the middle ages within the intertidal sand dominated sediments in the upper parts of the cores total organic carbon toc contents are generally low ranging from 0 1 to 0 5 and correlate well with the amount of mud fraction r 2 0 90 at the surface marine om has not undergone intense diagenetic alteration and so is the dominant fraction eroded peat particles are common throughout most of the sequence and values of the phragmites peat indicator ppi 5 indicate an origin from reed peat due to a high relative abundance of the n c 24 alkane changes in the composition of microbial communities over the depth interval investigated are documented by varying compositions of unsaturated fatty acids with 16 and 18 carbons eicosapentaenoic acid epa was detected along the entire cores and indicates the presence of epa producing bacterial strains

sedimentation rates in relation to sedimentary processes of the yangtze estuary china radioisotope analysis and digital elevation model dem method were combined to examine sedimentation rates and associated sedimentary processes in the yangtze river estuary the major depocenter is validated at the delta front sedimentary facies above the normal wave base nwb where accumulation exceeds erosion this alternated sedimentation does not accommodate pb 210 and cs 137 measurement although sedimentation rates of less than 0 2 5 0 cm yr 1 were recorded in the fine grained silty sediments which were interbedded with coarse grained sandy sediments however historical dem data provide more detailed information on sedimentation in the delta front facies where accumulation is dominant in the sandy shoals 1 73 8 30 cm yr 1 and delta front slope 5 22 cm yr 1 facies the dem data also show that erosion 1 61 7 32 cm yr 1 dominates in the northern estuarine distributaries and accumulation 3 01 4 97 cm yr 1 prevails in the southern ones primarily owing to the superimposed runoff and ebb tidal currents pb 210 and cs 137 measurements reveal sedimentation rate from 2 0 cm yr 1 to 6 3 6 6 cm yr 1 in the delta front slope facies which progressively decreases to 0 8 cm yr 1 in the prodelta facies and is unmeasurable in the delta shelf transition zone dem analysis detects minor erosion in the delta front slope and prodelta facies although accumulation predominates there the present sedimentological database will be useful for estuarine environmental assessment after the three gorges dam is completed in 2009

physical processes and fine grained sediment dynamics coast of surinam south america abstract the prograding holocene mud wedge between the amazon and orinoco rivers in the trade wind belt of northeastern south america provides a modern day example of muds accumulating under moderate wave energy conditions gigantic shore attached mudbanks 10 km 20 km composed partly of thixotropic fluid mud gel front this coast every 30 60 km to form a buffer to wave attack and a temporary storage for fine grained sediments this mesotidal coast tide range 2 0 m with gentle offshore slope 0 0006 allows the exposure twice a day of extensive tidal flat deposits which are backed by mangrove swamps on a well developed chenier plain complex field experiments were conducted in surinam du ing 1975 and 1977 to provide new information on process form relationships in this interesting but unusual muddy environment simultaneous measurements of waves currents tide elevation suspended sediment concentration and variations in mud density show that soft intertidal and subtidal muds are suspended at both tide and wave frequency suspended sediment concentrations typically exceed 1 000 mg l at the surface as incoming solitary like waves partially disperse fluid mud into overlying water on a falling or rising tide redeposition of mud may occur near time of high tide the strong attenuation of shallow water waves by these muds provides conditions that are favorable for further sedimentation high concentrations of suspended fluid mud together with solitary like waves from the northeast throughout the year can lead to extraordinarily high net sediment transport rates in the nearshore zone calculations based on solitary wave theory and on data obtained from this study indicate that 15 65 106 m3 of mud can move along shore each year without involving breaking waves the concept of radiation stress and a nearshore circulation cell or bedload transport farther offshore outside the zone of wave dominance wind driven currents and the guiana current combine to transport muds to the northwest consistent with the observed direction of mudflat migration

protogrammoceras paltum buckman a late pliensbachian jurassic ammonite from axel heiberg island canadian arctic archipelago ammonites collected from red weathering sandstones lying between the heiberg and savik formations north of wolf fiord on southeastern axel heiberg island are identified as protogrammoceras paltum buckman these strata are probably latest pliensbachian in age spinatum standard zone early jurassic and are tentatively correlated with the jaeger formation

sulphur and iron geochemistry of holocene coastal peats nw germany a tool for palaeoenvironmental reconstruction abstract a drill core from the marshlands of nw germany covering the entire holocene was analysed at high resolution by geochemical xrf cirm ms and microfacies methods diatoms thin sections sem in order to provide information about the palaeoenvironmental development in addition microbial experiments were carried out with sulphate reducing bacteria srb and cellulose fermenting fungi in seawater using peat as substrate the core contains an intercalated reed peat layer 2 73 3 02 m and a basal peat 5 78 6 42 m the basal peat consists in the lowest part of fen woodland and raised bog peat while the upper part is formed by a reed peat bed the peat layers are characterised by a distinct enrichment of pyrite with negative bulk sediment 34 s values av 11 5 range 2 6 to 26 7 reflecting microbial sulphate reduction in some peat intervals under almost open system conditions with respect to the input of seawater sulphate pyrite occurs exclusively with framboidal texture in close vicinity to the organic matter which indicates localised pyrite formation at the decay site in microenvironments with high concentrations of dissolved fe microbial experiments reveal that peat does not represent an appropriate substrate for srb and that srb have to rely on the preceding decomposition of peat by other microorganisms in microenvironments the total sulphur content of the peat layers averages to 7 8 wt with a maximum value of 28 2 wt unusually found within the basal peat at the transition of fen woodland and raised bog peat the pyrite enrichments can be explained by two different scenarios which are related to the intensity of the sea level rise the first scenario applies to a moderate sea level rise and is decisive for the reed peats where pyrite formation coincides with peat growth a brackish zone is assumed for the peat forming environment which is influenced by iron rich freshwater and sulphate rich seawater as the freshwater forms the major fe source the amounts of pyrite increase to a certain degree with decreasing salinity in this environment the palaeosalinity is estimated by the investigation of littoral and pelagic diatoms the second scenario applies to the extensive pyrite formation within the basal peat at the transition of fen and bog peat this pyrite was likely formed after peat growth favoured by a steep sea level rise thin sections of this peat interval reveal clastic layers 1 3 mm with completely pyritised interfaces as these clastic layers contain marine pelagic diatoms e g paralia sulcata we propose that they are caused by tidal channel activities during a phase of a steep sea level rise the marine incursion led to a partial buoyancy of the basal peat at weak transition zones i e the transition from fen to bog peat as a result of the bouyancy marine suspended particulate matter can be introduced laterally in between the peat sections when the peat settles down a clastic layer remains whose interface with the peat may have favoured the inflow of waters of higher salinity therefore an enhanced formation of pyrite was possible due to the combination of sulphate rich ground water and iron rich peatland waters

offset of an upper pliensbachian geographic zonation in the north american cordillera by transcurrent movement the north to south climatic zonation of upper pliensbachian ammonites known in europe has been recognized in the north american cordillera this simple geographic arrangement has been disrupted by northwest trending dextral transcurrent faults with further documentation the amount of offset of these zones should provide a measure of the amount of movement on these faults since pliensbachian time and further document the allochthoneity of the western part of the cordillera

the pliensbachian toarcian early jurassic extinction a global multi phased event abstract during the pliensbachian toarcian interval of the early jurassic there is a well known second order marine extinction that is observable at the species and genus levels ammonite diversity data from successions throughout europe and parts of the arctic suggest that this extinction may have been multi phased with diversity declining over six separate intervals the main phase of decline begins at the pliensbachian toarcian boundary and extends into the lower toarcian to a level that is correlative with the tenuicostatum serpentinum zone boundary to date only the main phase of extinction has been demonstrated as being global in extent and affecting multiple taxonomic groups this multi phased extinction has been attributed to regional and global controlling mechanisms that are associated with the volcanic greenhouse scenario which links the eruption of the karoo ferrar large igneous province lip to global warming and mass extinction we compare stratigraphic ranges of ammonite and foraminiferal species in pliensbachian toarcian successions of western north america to the record in europe and parts of the arctic in order to test the geographic extent of the multiple phases of extinction our results show six intervals of species level decline that correlate with those recognized in europe 1 middle of the lower pliensbachian middle whiteavesi middle freboldi zones 2 middle of the upper pliensbachian upper kunae lower carlottense zone 3 pliensbachian toarcian boundary into the lower toarcian upper carlottense middle kanense zones 4 middle toarcian upper planulata lower crassicosta zones 5 upper middle lower upper toarcian middle crassicosta hillebrandti zones and 6 upper toarcian lower yakounensis zone recognition of this multi phased event in three separate ocean basins paleo pacific paleo arctic and tethys oceans in at least two taxonomic groups greatly expands the known geographic extent of this multi phased event and argues for a controlling mechanism that is global in its reach in relation to the volcanic greenhouse scenario our study shows that four of the six pulses of extinction occur within the main phase of karoo magmatism the decline in the early pliensbachian previously thought to be separate from this event occurs within error range of the onset of karoo magmatism and the decline in the late toarcian coincides with the later stages of magmatism these observations extend the known duration of this multi phased extinction event to the early pliensbachian and support the volcanic greenhouse scenario specifically the eruption of the karoo ferrar lip as a preeminent factor driving the multi phased extinction of the pliensbachian toarcian

isotope fractionation during nitrogen remineralization ammonification implications for nitrogen isotope biogeochemistry abstract the 15 n 14 n isotopic ratio of marine particulate organic matter usually increases as a consequence of preferential 14 n remineralization ammonification during decay in the oxic water column and at the oxic seafloor however a fractionation factor 15 e of sediment ammonification in natural environments has not been determined yet here the 15 e of sedimentary ammonification is calculated in a set of seven sapropel containing sediment cores two subrecent sediment cores and four sediment trap deployments from the eastern mediterranean sea data clearly reveal rayleigh type isotope fractionation and a fractionation factor 15 e between 1 43 and 2 3 hence sediments and probably sinking particulate organic matter as well can be important sources of isotopically depleted reactive nitrogen the knowledge of 15 e further enables to reconstruct paleo export fluxes from sediment cores if original and actual 15 n as well as n accumulation rates are known

trade wind waves and mud dynamics on the french guiana coast south america input from era 40 wave data and field investigations the south american coast between brazil and venezuela is affected by longshore migrating mud banks derived from the fine grained amazon sediment discharge onshore mud migration prevails over shallow bank areas alternating alongshore with deeper inter bank areas the transport on the inner shelf and attachment to the shoreline of this migrating mud has been attributed mainly to wind waves however the lack of in situ data on waves hampers understanding of the relationship between waves and mud dynamics a 44 yr record 1960 2004 of the era 40 wave dataset generated by the european centre for medium range weather forecasts ecmwf was used in conjunction with field investigations in french guiana to define both event scale and longer term patterns of mud mobilisation induced by waves the ratio h03 t2 combining wave height h and period t and the angle of wave incidence were singled out as the most relevant parameters for describing wave forcing typical bank and inter bank profiles and corresponding mud densities and a 3 month record of changes in the thickness of the fluid mud layer in an estuarine navigation channel were monitored by echo sounding from october 2002 to january 2003 an 80 day record of bed level changes in the intertidal zone was obtained from august to november 2004 using a pressure transducer the results on the wave regime of french guiana confirm a distinctly seasonal pattern and highlight an increase in h03 t2 over the 44 yr period related to an increase in trade wind velocities determined from corresponding trends in atlantic wind pseudo stress off the south american coast wave forcing over bank areas leads to the liquefaction of a 1 3 m thick layer of mud that is transported onshore and alongshore by the longshore component of wave energy the episodic nature of high wave energy events generally results in the formation of mud bar features from the shoreward mobilisation of gel like fluid mud the effect of waves on mud is particularly marked following long periods of low energy and especially at the onset of the high wave energy season october to may when even moderate wave energy events can lead to significant mobilisation of mud significant phases of increased wave energy are attended by higher long term annual rates of longshore mud bank migration but the correlation is rather poor between the wave forcing parameter h03 t2 and migration rates because stronger wave forcing is generally associated with low angles of wave incidence this suggests a complementary role of other hydrodynamic mechanisms such as geostrophic and tidal currents in longshore mud bank migration

submarine slide scars and mass movements in karmsundet and skudenesfjorden southwestern norway morphology and evolution abstract shallow seismic sections multibeam bathymetric images and geotechnical investigations of the seafloor in karmsundet and skudenesfjorden sw norway have revealed the occurrence of large slide scars and associated mass movement deposits the slide escarpments are up to 30 40 m high and 8 km long with up to 20 10 6 m 3 of sediment released during a single event of retrogressive sliding the slide scars show a range of associated seafloor topography reflecting various modes of sediment displacement the variation in the escarpment morphology and sediment deformation style can be attributed to the varied intensity of liquefaction sliding involved mud deposits of allerod younger dryas to early holocene age but partly also deposits older than ca 12 000 14 c years bp the sediment failures were probably triggered by seismic reactivation of a local fault by postglacial regional isostatic rebound prior to failure the seafloor deposits were undercompacted and metastable due to high pore pressure the presence of shallow gas and the relatively steep local slope created by the formation of a major scour trough by sea currents minor gravitational sliding may still occur along some of the escarpments although engineering slope stability analysis indicates that the deposits can be regarded as stable in the present day conditions of static load and the anticipated weak sporadic earthquakes with an occurrence likelihood of 10 4 year and a peak acceleration of 0 25 g

isotopic and microbiological signatures of pyrite driven denitrification in a sandy aquifer denitrification driven by pyrite oxidation can play a major role in the removal of nitrate from groundwater systems as yet limited information is available on the interactions between the micro organisms and aqueous and mineral phases in aquifers where pyrite oxidation is occurring in this study we examine the groundwater and sediment composition along a well characterized redox gradient in a heavily nitrate polluted pyritic sandy aquifer in oostrum the netherlands to identify the sequence of steps involved in denitrification coupled to pyrite oxidation multi isotope analyses 15n no3 18o no3 34s so42 18o so42 and 34spyrite confirm that pyrite is the main electron donor for denitrification at this location enrichment factors derived from the observed changes in nitrate isotopic composition range from 2 0 to 10 9 for e15n and from 2 0 to 9 1 for e18o the isotopic data indicate that pyrite oxidation accounts for approximately 70 of the sulfate present in the zone of denitrification solid phase analyses confirm the presence of pyrite and organic matter rich clay lenses in the subsurface at oostrum in addition sulfur xanes and iron xas results suggest the presence of a series of intermediate sulfur species elemental sulfur and so32 that may be produced during denitrification consistent with geochemical analysis 16s rrna gene sequencing revealed the presence of bacteria capable of sulfide oxidation coupled to nitrate reduction and that are tolerant to high aqueous metal concentrations 2012 elsevier b v

organic matter origin and distribution in suspended particulate materials and surficial sediments from the western adriatic sea italy abstract in this study organic carbon oc total nitrogen tn stable carbon isotopic 13 c oc and cuo reaction product compositions were used to identify the sources of organic matter om and to quantify the relative importance of allochthonous and autochthonous contributions to the western adriatic sea italy suspended particulate material 195 samples and surficial sediments 0 1 cm 70 samples from shallow cross shelf transects were collected in february and may 2003 respectively vertical water column profiles were acquired along the same transects data include depth potential temperature salinity density and chlorophyll fluorimetry along the western adriatic shelf in the near shore region the phytoplankton growth was influenced by dynamics of the buoyant plumes from the po and appennine rivers a small amount of very fine terrigenous material remained suspended within the coastal current and was exported southward along the shelf to the slope high variability in the bulk composition was detected in the po prodelta surficial sediments whereas the western adriatic shelf although a larger area exhibited a narrower range of values a significant decoupling was observed between suspended particles in the water column and surficial deposits the organic material collected in the water column was compositionally heterogeneous with contributions from marine phytoplankton riverine estuarine phytoplankton and soil derived om frequent physical reworking of surficial sediments likely leads to the efficient oxidation of marine oc resulting in the observed accumulation and preservation of refractory soil derived oc delivered by the po and appennine rivers

mechanisms of land sea interactions the distribution of metals and sedimentary organic matter in sediments of a river dominated mediterranean karstic estuary this paper examines disposal of metals and the origin characteristics and distribution of sedimentary organic matter som in a mediterranean karstic estuary in the north eastern adriatic this environment offers a real time small model system for studies of geochemical processes in microtidal mediterranean estuaries that are infilling with sediments and classified as river dominated disequilibrium estuaries the results have shown that the longitudinal distribution of heavy metals in sediments follows the sedimentation dynamics and deposition pattern of river borne clay mineral particles the highest concentration of metals was found in the restricted upper part of the estuary characterized by rapid deposition of clay particles and terrestrial sedimentary organic matter and decreases toward the open sea the vertical distribution of metals in sediment cores depends on the prevailing ph and eh conditions significant increases of the concentrations of metals in the uppermost strata are the result of recent anthropogenic inputs the share of the terrestrial component in

a multilayered water column in the ediacaran yangtze platform insights from carbonate and organic matter paired δ13c abstract large carbon isotope fluctuations have been systematically reported for ediacaran carbonate rocks the meaning of which remains controversial in order to better understand the mechanisms behind such variations we present new paired 13c data on carbonates 13ccarb and their associated organic matter 13corg from a shelf margin section yangjiaping of the doushantuo formation in this section the doushantuo formation starts with cap dolostones presenting 13ccarb values around 5 and 13corg values between 30 3 and 27 6 up section phased variations in 13ccarb and 13corg describe positive and negative excursions while their difference 13cdol org 13ccarb 13corg remains around 29 2 these new data allow the first reconstruction of lateral variations of 13ccarb 13corg and 13ccarb org for a shelf to basin cross section of the yangtze platform south china after integration with results reported previously for two other sections across the yangtze platform the isotope signals reveal strong lateral heterogeneities with complex variations of 13ccarb and 13cdol org in the inner shelf section phased variations in the shelf margin section with positive 13ccarb and 13cdol org close to 29 and dominantly negative 13ccarb with 13corg as low as 35 in the basin these variations are incompatible with the idea that the 13ccarb can systematically be used as a proxy of ocean surface waters assuming that 13ccarb are acquired in bottom waters and or upper sediments we show that the heterogeneous 13ccarb and 13cdol org are compatible with a stratified water column composed of up to three layers i an oxic surface layer where dissolved inorganic carbon dic is probably in isotope equilibrium with the atmosphere ii an intermediate euxinic layer with a lower 13cdic due to organic matter oxidation by ongoing sulphate reduction iii a bottom euxinic layer that seems to be restricted to the inner shelf lagoonal facies lacking sulphate containing methane and with a higher 13cdic due to dic production by methanogenesis if our model holds true it suggests that not only negative but also positive ediacaran carbon isotope excursions may reflect ocean stratification the positive excursion possibly recording a sulphate free methanogenic layer at the bottom of restricted basins

hydrochemical mineralogical and isotopic investigation of arsenic distribution and mobilization in the guandu wetland of taiwan summary this study explores the distribution and mobilization of as in the ecosystem of the guandu wetlands taiwan the chemical parameters chemical sequential extraction mineralogical compositions and sulfur isotopic compositions i e d 34 s so4 and d 18 s so4 of porewater and two sediment core samples s2 and s5 locate in the inner and outer sites of the guandu wetland were analyzed to characterize as spatial distribution the crucial mechanisms of the biogeochemical processes that control as mobility in wetland ecosystems were inferred based on factor analysis and cluster analysis the vertical distributions of the redox zones in s2 and s5 were classified as oxidizing transitional and reducing zones respectively the mineralogical characteristics showed that adsorption and desorption are the major processes which control as retention in the surface sediment under cyclic aerobic anaerobic conditions aqueous as and fe were restrained because of oxidation whereas aqueous fe precipitated as amorphous metal oxides i e feo feooh and fe2o3 subsequently aqueous as was adsorbed onto the surfaces of fe hydr oxides resulting in a high solid as content in the oxidizing zone the high aqueous as content in the boundary of the transitional and reducing zones was caused by the reductive dissolution of highly dissolved fe compounds through the microbial respiration of organic matter om in the reducing zone as 3 can be constrained by the formation of fes2 in sediment during bacterial sulfate reduction that is governed by the relative enrichment of the d 34 s so4 and d 18 s so4 values sulfur disproportionation and the redox of ele

regional patterns of tectonic stress in europe nearly 1500 stress orientation determinations are now available for europe the data come from earthquake focal mechanisms overcoring measurements well bore breakouts hydraulic fracturing measurements and young fault slip studies and sample the stress field from the surface to seismogenic depths three distinct regional patterns of maximum compressive horizontal stress shmax orientation can be defined from these data a consistent nw to nnw shmax stress orientation in western europe a wnw ese shmax orientation in scandinavia similar to western europe but with a larger variability of shmax orientations and a consistent e w shmax orientation and n s extension in the aegean sea and western anatolia the different stress fields can be attributed to plate driving forces acting on the boundaries of the eurasian plate locally modified by lithospheric properties in different regions on average the orientation of maximum stress in western europe is subparallel to the direction of relative plate motion between africa and europe and is rotated 17 clockwise from the direction of absolute plate motion the uniformly oriented stress field in western europe coincides with thin to medium lithospheric thickness approximately 50 90 km and high heat flow values 80 m w m2 in western europe a predominance of strike slip focal mechanisms implies that the intermediate principal stress is vertical the more irregular horizontal stress orientations in scandinavia coincide with thick continental lithosphere 110 170 km and low heat flow 50 m w m2 the cold thick lithosphere in this region may result in lower mean stresses associated with far field tectonic forces and allow the stress field to be more easily perturbed by local effects such as deglaciation flexure and topography the stress field of the aegean sea and western anatolia is consistent with n s extension in a back arc setting behind the hellenic trench subduction zone the stress field is influenced in places by regional geologic structures e g in the western alps where shmax directions show a slight tendency toward a radial stress pattern not all major geologic structures however appear to affect the shmax orientation e g in the vicinity of the rhine rift system horizontal stress orientations are continuous

sulfidization of lacustrine glacial clay upon holocene marine transgression arkona basin baltic sea abstract towards the end of the last deglaciation more than 13 500 years ago the southern baltic sea was a freshwater lake the baltic ice lake for several thousand years during which iron rich organic poor clay was deposited the modern brackish marine stage started about 8600 years ago with the deposition of organic rich mud which is today characterized by high rates of sulfate reduction and high concentrations of free sulfide we studied the iron sulfur diagenesis in gravity cores from the arkona basin sw baltic sea to track the progressing sulfidization front in the buried ice lake sediment the geochemical zonation was unusual as the sulfate concentration dropped steeply by two thirds below which it increased again due to a deep sulfate reservoir the reservoir had been established during the early holocene marine period as sulfate and other seawater ions diffused down into the lake sediment for several thousand years sulfur isotope analyses confirmed its origin as seawater sulfate while its oxygen isotope composition indicated a microbially catalyzed equilibration with ambient interstitial water decoupled from net sulfate reduction today hydrogen sulfide diffuses from the marine mud down into the lake sediment where a black band with high magnetic susceptibility and high iron monosulfide greigite and elemental sulfur content shows progressing sulfidization of the large pool of solid phase reactive iron dissolved iron from the deep ice lake sediment diffuses up to the sulfide front and provides a small supplement to the solid fe iii pool as a sulfide sink pyrite formation at the sulfidization front may involve surface bound zero valent sulfur while above the front polysulfides are in equilibrium with the system hydrogen sulfide polysulfide rhombic sulfur and may not be important for further pyrite formation the holocene iron sulfur diagenesis observed in the arkona basin represents an important transitional state for post glacial transgressions with organic rich marine sediment overlying lacustrine clay such as in other areas of the baltic sea or in the black sea