youngest ambient inclusion trails from middle triassic phosphatized coprolites southwestern china new insights into an old intriguing phenomenon abstract copious microtubular structures are reported for the first time from the coprolites of early middle triassic guanling formation in luoping yunnan province southwestern china multiple salient characteristics of these microtubes including curved to coiled grooves with longitudinal striations angular turns cross cuttings and a terminal rounded pitting at one end of a groove support their strong affinities with ambient inclusion trails aits that are more commonly found in pre ediacaran sedimentary rocks these newly found microtubular structures are here interpreted to represent the youngest occurrence of aits in the geological record a review of all aits and similar microtubular structures reveals their common occurrences in ediacaran phosphorite and phanerozoic phosphatized fossil substrate similar to the aits found from the post ediacaran strata the aits from the luoping coprolites are also preserved in a phosphatized substrate we suggest that a microbial induced process might have contributed to the phosphogenesis of faeces and aits formation this process is interpreted to have involved the precipitation of phosphate minerals by microbial communities and the movement of pyrite through and within phosphatized substrate gel driven by fluid pressure this new interpretive model differs from the existing scenario invoked to explain the formation mechanism of pre ediacaran aits in which pyrite propulsion is thought to be more likely driven by metamorphism induced fluid pressure we thus hypothesize that the transformation in aits formative substrate from chert to phosphate as well as their formation mechanism might have been triggered by a significant change in ocean biogeochemistry linked to a phosphogenic event in the neoproterozoic

hydraulic conductivity of naturally sedimented and reconstituted clays interpreted from consolidation tests abstract the hydraulic conductivity of naturally sedimented and reconstituted clays is often interpreted using the settlement time curves measured from consolidation tests understanding the accuracy of the interpreted hydraulic conductivity is essential in geological and geotechnical engineering to the best knowledge of the authors such a work has been little reported up to now this study aims at investigating the errors of the interpreted hydraulic conductivity via the comparison between the interpreted values and the measurements the ratios of the interpreted values of hydraulic conductivity over the measurements are examined based on the data from the consolidation hydraulic conductivity tests performed in this study in conjunction with those published by our research team the investigated clays cover wide geological origins and depositional states the geological origins and depositional states are linked with the errors of the interpreted hydraulic conductivity for understanding the roles of these factors in the uncertainty of the interpreted hydraulic conductivity the causes responsible for the discrepancy in hydraulic conductivity between the interpretations and the measurements are identified the probability distribution of the errors of the interpreted hydraulic conductivity is also investigated

potential photosynthetic impact on phosphate stromatolite formation after the marinoan glaciation paleoceanographic implications abstract this study investigated the origin and the depositional age of phosphate stromatolites contained in the neoproterozoic salitre formation brazil the stromatolites exhibited columnar shapes and were intercalated with laminated dolostones their depositional environment was interpreted to have been an evaporitic ramp where erosion and reworking by waves prevailed laser ablation inductively coupled plasma mass spectrometry measurements of the stromatolites yielded a u pb age of 616 32 ma suggesting that they were deposited after the marinoan glaciation several types of filamentous structures were recognized in the stromatolites many of them were pseudofossil ambient inclusion trails but some were possibly microfossils to consider the general presence of photosynthetic microorganisms on the surface of shallow water stromatolites the involvement of microbial photosynthesis in phosphate stromatolite formation was expected numerical calculations determined that photosynthesis could have induced phosphate mineral precipitation at the time of deposition if the phosphorus concentration was above ca 5 m to achieve such high concentration at the shallow ocean globally elevated phosphorus concentration was considered to be the ultimate factor in addition to the local process es including upwelling and or evaporation therefore the phosphate stromatolites in the salitre formation are evidence of the development of a phosphorus rich ocean after the marinoan glaciation

new observations of ambient inclusion trails aits and pyrite framboids in the ediacaran doushantuo formation south china ambient inclusion trails aits are intriguing microtubular structures that commonly occur in association with pyrite in precambrian organic rich cherts and phosphorites they are thought to be created by the migration of pyrite or other crystal grains through a lithified substrate driven by pressure solution from the in situ thermal decomposition of organic matter new phosphorite samples of the ediacaran doushantuo formation south china contain abundant aits exhibiting diverse morphotypes which may be distinguished from filamentous microfossils and endolithic microborings with a suite of morphological criteria based on optical microscopy and scanning electron microscopy sem black shales of the baizhu section contains abundant pyrite framboids whose size distributions reveal significant temporal variations of redox conditions in shallow marine waters that probably promoted the formation of the doushantuo phosphorites aits in the phosphorites are categorized into three types and further into five subtypes i a i b ii a ii b and iii based on their morphologies and observed or interpreted associations with various kinds of terminal pyrite crystals among these subtype ii a single striated microtubes 2 10 m wide are interpreted to have resulted from migration of intact pyrite framboids those of subtype ii b dense clusters of outward radiating microtubes with consistent widths and inward facing cuspate ridges likely have formed by explosive disintegration and propulsion of pyrite framboids due to highly concentrated carbon dioxide gas during the oxidation of organic matter during early diagenesis formation of euhedral and framboidal pyrites involve a suite of biogeochemical and physical processes including non biological oxidation of organic matter and reduction of sulfate in the presence of ferrous iron following the burial of pyrites further oxidative degradation of organic matter produced abundant co2 gas which drives the pyrites to move through the solid but not yet fully lithified phosphatic gel composing granules this model explains the formation of previously reported but unexplained star burst type aits and it may be tested by experimental studies our new observations provide evidence for the widespread occurrence of aits in the doushantuo phosphorites and urge careful petrographic examinations and differentiation between aits and morphologically similar biogenic microstructures

the age of the nantuo formation and nantuo glaciation in south china a u pb sensitive high resolution ion microprobe shrimp age of 654 5 3 8 ma from an ash bed immediately below the nantuo formation in south china provides the lowest age constraint for the nantuo glaciation which has been correlated with the global marinoan glaciation a u pb shrimp age of 636 3 4 9 ma from a fallout tuff within the basal layer of the nantuo formation along with the existing age of 635 2 0 6 ma from its overlying doushantuo cap carbonate suggests that the traditionally defined nantuo formation may have been deposited in a short time period at the end of the nantuo glaciation in combination with available ages globally the data support a relatively short duration and rapid termination of marinoan glaciations

cooling induced strain localization in carbonate mylonites within a large scale shear zone glarus thrust switzerland abstract the glarus thrust switzerland offers a great field example of strain localization under retrograde conditions along the thrust mylonitic microfabrics are characterized by a temperature stress controlled balance of grain size reducing mechanisms and grain growth consequently mean grain sizes decrease along the thrust with decreasing metamorphic conditions and towards the thrust contact in an opposite manner calcite twin densities increase towards the contact cpos are strongest between 0 5 and 15 m away from the thrust but become generally weaker in the last centimeters where also cataclasites occur the cpo weakening and grain size reduction towards the shear zone point to a change from predominant dislocation creep to granular flow finally ending in cataclastic deformation the microfabric changes correlate with a decrease in 13c and 18o towards the thrust contact indicating the presence of fluids during cycles of brittle and plastic deformation based on the microfabric changes variations in stable isotopes and cross cut relationships a subdivision into a low and high temperature shear zone can be made the microfabric modifications resulted from changes in deformation conditions due to ongoing thrusting and exhumation induced cooling promoting further strain localization of an existing high strain shear zone

evolution of the raman spectrum of carbonaceous material in low grade metasediments of the glarus alps switzerland terra nova 22 354 360 2010 abstract the raman spectrum of carbonaceous material cm from advanced diagenesis 200 c to low grade metamorphism 320 c is documented in the helvetic flysch of the glarus alps switzerland the spectrum is complex with several defect bands at 1200 d4 1350 d1 1500 d3 and 1620 d2 cm 1 we document the evolution of these bands relative to the graphite g band with increasing metamorphic grade and we show that this qualitative evolution may be used as a proxy for temperature in the glarus alps we develop a robust peak fitting method and propose quantitative parameters that may be used as proxies for thermal metamorphism in this region further work in other geological contexts is needed to assess whether the spectral evolution observed in the glarus alps may be generalized and to critically assess the potential for calibrating a general empirical and quantitative thermometer based on the raman spectrum of cm in low grade rocks

variations in pyrite texture sulfur isotope composition and iron systematics in the black sea evidence for late pleistocene to holocene excursions of the o2 h2s redox transition time dependent variations in the physicochemical properties of pyrite were investigated in four sediment cores from the black sea in the laminated deep basin sediments of unit i and unit ii 86 of pyrite particles are present as fine grained framboidal aggregates in these sediments the dominance of pyrite framboids with a narrow size distribution and maximum size 18 m is evidence of syngenetic water column pyrite formation subjacent to the o2 h2s boundary sediments from the basin margin collected below the impingement of the o2 h2s boundary contain an increased proportion of fine grained euhedral grains of pyrite relative to framboidal aggregates suggesting increased additions of diagenetic pyrite below the sediment water interface the more efficient reduction and sulfidation of iron in the water column of the central region of the basin implies a more reactive source of iron there compared to the basin margins and is tied to increasing pyrite as framboids and greater degrees of pyritization dop in the basin center relative to the basin margins an evaluation of fe s c relations indicates that pyrite formation was limited by sulfate availability during deposition of the oldest lacustrine sediments of unit iii c limited for upper unit iii due to the input of sulfate rich mediterranean seawater and fe limited in the laminated organic carbon rich sediments of units i and ii these changes in pyrite limiting factors occurred within 4 m of compacted burial representing 15 ka sediment fabric and framboid size distributions at a shallow basin margin site suggest that during two extended periods of unit ii deposition the o2 h2s transition retreated to depths below 200 m however during these same intervals the 34s of pyrite remains uniform compared to overlying and underlying laminated sediments implying that this chemical signature may not be uniquely tied to the position of the o2 h2s boundary relative to the sediment water interface but rather is likely related to biogeochemical processes

pyrite formation in an anoxic estuarine basin in a shallow fjord like estuary the upper and lower basins of the pettaquamscutt river rhode island each contain water columns stratified into oxic and anoxic plus sulfidic layers both water columns contain iron monosulfides and pyrite from just below the oxic anoxic interface down to the sediment water interface concentrations of iron monosulfides increase with increasing depth in the water columns but concentrations of pyrite are relatively constant with depth suspended pyrite is present only as framboids whereas the underlying sediments contain dominantly framboids but also euhedral grains and infilled framboids based on pyrite textures s isotopic compositions of water column and sediment sulfides and settling rate calculations about 70 of the pyrite burial flux to the pettaquamscutt sediments is accounted for by framboids forming at the oxic anoxic interface and settling to the sediment water interface the remaining pyrite burial flux is secondary pyrite nucleation and growth within the sediments represented by euhedral grains and infilled framboids the s isotopic composition of pyrite in the pettaquamscutt sediments and presumably of pyrite in the sediments of other modern anoxic basins and analogous ancient sediments therefore contains a component originating near the oxic anoxic interface and a component added below the sediment water interface pyrite framboids form in the water column where there is high supersaturation with respect to pyrite and slight undersaturation with respect to the iron monosulfides we propose that framboid nucleation and growth occurs in the water column adjacent to and below the oxic anoxic interface where supplies of ferrous species sulfide species and suitable electron acceptors are available infilled and overgrown framboids from in the sediments as a result of surface nucleation and continued pyrite growth on framboids that originate above the sediment water interface

raman spectra of carbonaceous material in metasediments a new geothermometer metasedimentary rocks generally contain carbonaceous material cm deriving from the evolution of organic matter originally present in the host sedimentary rock during metamorphic processes this organic matter is progressively transformed into graphite s s and the degree of organisation of cm is known as a reliable indicator of metamorphic grade in this study the degree of organisation of cm was systematically characterised by raman microspectroscopy across several mesozoic and cenozoic reference metamorphic belts this degree of organisation including within sample heterogeneity was quantified by the relative area of the defect band r2 ratio the results from the schistes lustres western alps and sanbagawa japan cross sections show that 1 even through simple visual inspection changes in the cm raman spectrum appear sensitive to variations of metamorphic grade 2 there is an excellent agreement between the r2 values calculated for the two sections when considering samples with an equivalent metamorphic grade and 3 the evolution of the r2 ratio with metamorphic grade is controlled by temperature t along the tinos cross section greece which is characterised by a strong gradient of greenschist facies overprint on eclogite facies rocks the r2 ratio is nearly constant consequently the degree of organisation of cm is not affected by the retrogression and records peak metamorphic conditions more generally analysis of 54 samples representative of high temperature low pressure to high pressure low temperature metamorphic gradients shows that there is a linear correlation between the r2 ratio and the peak temperature t c 445 r2 641 whatever the metamorphic gradient and probably the organic precursor the raman spectrum of cm can therefore be used as a geothermometer of the maximum temperature conditions reached during regional metamorphism temperature can be estimated to 50 c in the range 330 650 c a few technical indications are given for optimal application

convective boundary layer structure in the presence of wind following swell the marine boundary layer is known to be influenced by fast long ocean swell waves travelling away from their generation area where they were initiated by momentum transferred to the ocean wave field during storms the atmospheric boundary layer during wind following swell and various stability states has been investigated using large eddy simulation les data the dominant energy containing motions in the near neutral atmospheric boundary layer over flat terrain are known to be dominated by near ground shear induced regions of high and low speed flow wind fields and momentum fluxes from les for swell dominated situations have been used to interpret field measurements suggesting that these motions are disrupted by effects related to the underlying wave field in the presence of swell waves statistical analysis and visualization are used to further describe the effects of stratification during swell for convective boundary layer winds and fluxes a mechanism for transport of momentum to the upper levels of the boundary layer is suggested from interpretation of les data coherent detached eddies from the directly wave induced motions near the surface are found to maintain an upward momentum transfer this mechanism is found to strengthen during stronger swell conditions and also during slightly convective conditions in this way it is argued that processes related to both the wave field and surface convection can have a significant influence on the global structure of neutral and convective boundary layers during swell this has implication for the turbulence length scales during wind following swell copyright 2012 royal meteorological society

filamentous fossil bacteria from the archean of western australia abstract four morphotypes of structurally preserved filamentous fossil bacteria have been discovered in petrographic thin sections of laminated carbonaceous cherts from the 3500 ma old warrawoona group of northwestern australia these tubular and septate microfossils are interpreted here as being syngenetic with warrawoona sedimentation as such they are apparently the oldest such fossils now known in the geological record the diversity of this assemblage and the evident complexity of its individual components suggest that the beginnings of life on earth may have appreciably pre dated the deposition of the warrawoona sediments

the structure of gradually transforming marine stratocumulus during the astex first lagrangian experiment summary an analysis of the mean and turbulent structure of the planetary boundary layer is presented using aircraft data obtained during the atlantic stratocumulus transition experiment e rst lagrangian experiment the analysis of the mean vertical structure relies mostly on slant proe le data however part of the analysis also uses socalled porpoise runs in the vicinity of the cloud top the analysis of the turbulence structure utilizes all of the data horizontal eight legs as well as slant proe les and presents both scaled turbulence statistics and a spectral analysis the purpose is to investigate details in the temporal development of the e rst lagrangian experiment and to study the turbulent structure in order to e nd scale relations that can be utilized in improved modelling of the stratocumulus capped boundary layer the hypothesis is that so called cloud decoupling has a signie cant impact on the turbulence scaling the measured cloud water is corrected to become consistent between the two participating aircraft the corrected maximum cloud water is more constant in time than in previous studies of the erst lagrangian it is suggested that previously analysed temporal variability may be an artefact of using two different instruments to measure cloud water the cloud top jump in equivalent potential temperature is positive in the erst three eights sufe ciently large for a stable cloud top but decreases and becomes negative for the last two eights in line with the breaking up of the cloud eeld the upper part of the boundary layer warms and dries more rapidly than the lower suggesting entrainment to be a dominant factor in the development of the cloud the analysis of the porpoise e ight legs illustrates how sharp features at the cloud top inversion are smoothed out while analysing several proe les eight legs or even entire eights rather than normalizing each proe le with the height to the local cloud top scaling of the turbulent e uxes and the velocity variances shows that the cloud layer is decoupled throughout almost the entire erst lagrangian it is also shown that while surface layer scaling is appropriate for the marine atmospheric boundary layer mabl the cloud layer turbulence scales with convective scaling the lowfrequency spectrum has no spectral gap with the exception of the vertical velocity and continues to increase with decreasing frequency with only a change in slope this indicates the presence of mesoscale motions the cospectra of the turbulent euxes are very noisy throughout when averaging several spectra into height intervals the scales of the turbulence as indicated by the peak in the averaged spectra appear to vary with height above the surface in the mabl but to be height independent in the cloud layer an attempt to calculate a dissipation length scale shows scatter but is consistent with a dissipation length scale increasing linearly with height in the mabl but being roughly constant or possibly parabolic with height in the cloud layer

biogenic versus metamorphic origins of diverse microtubes in 2 7 gyr old volcanic ashes multi scale investigations abstract titanite bearing microtubes in metabasalts have been interpreted as evidence for early microbial life thriving in the oceanic crust up to 3 5 ga ago based on similarities with microtubular pitting occurring in modern volcanic glass an alternative abiogenic origin as ambient inclusions trails aits has been debated but textural evidence such as the absence of diagnostic terminal inclusions was used to discard this possibility here we describe a variety of microtubes occurring in pyroclastic tuff of the 2 72 ga tumbiana formation western australia some of which resemble titanite filled microtubes reported in metamorphosed archean pillow basalts to assess the origin of the tumbiana microtubes we investigated their structure and chemistry and their root zone down to the sub micrometer scale using a combination of raman microspectroscopy scanning electron microscopy sem focused ion beam fib milling and scanning transmission electron microscopy stem coupled with energy dispersive x ray spectrometry edxs we report four types of microtubes type 1 comprises calcite microtubes type 2 comprises aits showing terminal pyrite and trails with negative crystal shapes type 3 comprises titanite microtubes in chlorite displaying morphologies similar to those reported in 3 5 ga old archean lavas at the sub micrometer scale they display a dendritic structure depending on their localization type 3 microtubes have been divided in three main sub types i type 3a extends in pores filled by chloritized cement ii type 3b occurs in pyroclasts and iii type 3c overgrows and thus post dates type 2 aits type 4 comprises titanite microtubes confined to quartz and calcite rims types 3 and 4 microtubes are terminated by sub micrometric carbonaceous and or mineral inclusions altogether these features suggest that the tumbiana titanite microtubes have formed as dendritic aits associated with displacement of mineral and or organic inclusions in pyroclasts and in surrounding void filling cements during recrystallization they are therefore unlikely to represent relics of the activity of early microbial life rather abiotic features formed in the presence of organic matter during burial metamorphism in that sense they may represent some sort of indirect evidence for life

the role of microorganisms and biofilms in the breakdown and dissolution of quartz and glass three different types of silica 1 quartz sand 2 crystalline scepter quartz and 3 commercial glass subjected to biological growth were investigated for evidence of biologically induced breakdown the results of laboratory experiments with biofilms on quartz sand and glass were compared with material from the field microscopic optical and sem analysis of quartz sand weathered in vitro by a microbial community of cyanobacteria diatoms and heterotrophic bacteria demonstrate grain diminution of a sand fraction of north sea sediment the microbial community changes the minerals in the vicinity of the living cells which leave their mark on the quartz surface in form of imprints depressions and pits subsequently microbial growth on the surface brought about a general decrease of the grain size in the layer beneath a biofilm imprints of diatoms on glass surfaces colonized by diatoms and heterotrophic bacteria confirm the chemical etching activity of these organisms mixed cultures of diatoms and bacteria show depressions corresponding to the shape of individual cells our experiments confirm that diatoms heterotrophic bacteria and cyanobacteria from natural biofilms can actively attack quartz and glass microscopic analysis of an idiomorphic scepter quartz crystal from a tepui weathering environment reveals that the associated biofilms can create a local shift in the ph from 3 4 ph of water on the tepui to evidently higher than 9 necessary for quartz dissolution the quartz covered with a biofilm is partially perforated to a depth of more than 4 mm we conclude that biofilm growth in marine sub aquatic and terrestrial sub aerial conditions can significantly increase the breakdown of silica in the amorphous glass sub crystalline chert crystalline and granular forms of quartz microbial growth may therefore substantially modify the processes of transformation of a major rock forming mineral of great chemical and physical resistance

wave driven wind jets in the marine atmospheric boundary layer abstract the interaction between ocean surface waves and the overlying wind leads to a transfer of momentum across the air sea interface atmospheric and oceanic models typically allow for momentum transfer to be directed only downward from the atmosphere to the ocean recent observations have suggested that momentum can also be transferred upward when long wavelength waves characteristic of remotely generated swell propagate faster than the wind speed the effect of upward momentum transfer on the marine atmospheric boundary layer is investigated here using idealized models that solve the momentum budget above the ocean surface a variant of the classical ekman model that accounts for the wave induced stress demonstrates that although the momentum flux due to the waves penetrates only a small fraction of the depth of the boundary layer the wind profile is profoundly changed through its whole depth when the upward momentum transfer from surface waves sufficiently exceeds the downward turbulent momen

apatite glaucony association in the ediacaran doushantuo formation south china and implications for marine redox conditions abstract major phosphogenic events took place in the late paleoproterozoic and the ediacaran both of which followed an episode of atmospheric oxygenation these apparent coincidences have led to suggestions that the precambrian phosphorus cycle was partly regulated by oceanic redox conditions although direct evidence is lacking in this paper we report the discovery of glaucony in drill cores from the phosphorite rich ediacaran doushantuo formation at weng an south china which provides new insights into redox conditions and geochemical cycles during the deposition and early diagenesis of the lower doushantuo formation the presence of flaser and lenticular bedding in the sandstones suggests deposition in a tidally influenced shallow water environment apatite is present as millimeter scale flasers in sandstones but more commonly as intraclastic grains glaucony typically occurs as interstitial aggregates cementing and replacing detrital minerals and phosphatic grains with an upsection decrease in abundance the doushantuo glauconies have consistently high k2o 7 6 9 6 wt in particular phosphorite hosted glaucony has generally higher total iron tfe2o3 than sandstone hosted glaucony consistent with al3 fe3 substitution in the octahedral site as supported by raman peaks slightly shifted towards lower wavenumbers for higher fe content a decrease in detrital input probably resulted in limited al availability during early diagenesis which in turn led to the waning of glaucony upsection the phosphate grains do not show any negative ce anomalies consistent with precipitation of authigenic apatite in suboxic environments with insignificant preferential remobilisation of ce during deposition and early diagenesis ree y features show variable diagenetic ree enrichment in phosphorites but identical concave down patterns the wide occurrence of glaucony cement further documents the presence of a generally suboxic early diagenetic environment on the seafloor which was in active exchange with bottom seawater slight fluctuations of redox states in the porewater and bottom water would have promoted the cycling of fe enrichment of phosphate and ree and extensive glaucony authigenesis therefore the glaucony bearing phosphorites in the doushantuo formation are a direct result of fe redox driven diagenesis apatite glaucony association likely forms in suboxic environments and is considered as a useful mineralogical proxy for paleoredox conditions on the precambrian ocean floors

introducing surface waves in a coupled wave atmosphere regional climate model impact on atmospheric mixing length 1 the marine atmospheric boundary layer is strongly influenced by the moving surface in the presence of surface waves the impact depends on the wave conditions and the interaction with the atmosphere previous studies using measurements as well as numerical simulations with large eddy simulations have shown that surface waves propagating faster than the wind swell alter the surface exchange as well as turbulence properties in the atmosphere this impact is here introduced in a coupled wave atmosphere regional climate model with a so called e l turbulence scheme where e is the turbulent kinetic energy and l is a mixing length a wave age dependent coefficient here called wmix is added to the mixing length in the turbulence parameterization this acts similarly to inducing additional convection with larger mixing length and increased eddy diffusivity when we have near neutral stratification and strong swell for shallow boundary layers the regional coupled climate model shows a larger response to the introduced wave coupling with increased near surface wind speed and smaller wind gradient between the surface and middle part of the boundary layer the impact for the studied areas is relatively minor for parameters averaged over 1 year but for limited periods and specific situations the impact is larger one could expect a larger impact in areas with stronger swell dominance we thus conclude that the impact of swell waves on the mixing in the boundary layer is not insignificant and should be taken into account when developing wave atmosphere coupled regional climate models or global climate models

the permeability of an intact granite the permeability of intact barre granite is determined by conducting transient hydraulic pulse tests that induce radial flow in saturated granite cylinders containing a water filled co axial cavity saturated specimens of granite are also subjected to uniform heating on the outer cylindrical surface and the permeability of the granite is measured at the termination of a heating sequence the theoretical basis for the use of simplified analytical solutions for evaluating the decay of the pressure pulse is examined and the permeability of the granite in the pre heating and post heating states is inferred from the results of pulse tests the reported investigations document one of the limited numbers of large scale laboratory tests conducted to determine the permeability characteristics of intact granite the results of the permeability measurements indicate the absence of any appreciable influences of micro structural alterations in the fabric of the granite due to its heating in a saturated condition at an average temperature of 140 celsius

terminal proterozoic cyanobacterial blooms and phosphogenesis documented by the doushantuo granular phosphorites ii microbial diversity and c isotopes an unprecedented period of phosphogenesis along with massive deposition of black shales major perturbations in the global carbon cycle and the rise of atmospheric oxygen occurred in the terminal proterozoic in the aftermath of the marinoan glaciation although causal links between these processes have been postulated evidence remains challenging correlated in situ micro analyses of granular phosphorites from the ediacaran doushantuo formation in yichang south china suggested that cyanobacteria and associated extracellular polymeric substances eps might have promoted aggregated granule growth and subsequent phosphatization she et al 2013 here we present new paleontological data for the doushantuo phosphorites from yichang which combined with raman microspectroscopy and carbon isotope data further document links between the biology of cyanobacteria and phosphogenesis mapping of microfossils in thin section shows that most phosphatic granules contain microfossils that are dominated by colonies of myxococcoides along with several filamentous genera generally considered to represent cyanobacterial sheaths in addition the phosphorites and associated rocks have 13corg values in the range of 26 0 to 29 7 vpdb consistent with photoautotrophic carbon fixation with the rubisco enzyme close association of phosphorites with the marinoan tillites in stratigraphic level supports a genetic link between deglaciation and phosphogenesis at least for the doushantuo occurrence our new data suggest that major cyanobacterial blooms probably took place in the terminal proterozoic which might have resulted in rapid scavenging of bioavailable phosphorus and massive accumulations of organic matter om within a redox stratified intra shelf basin the om bound phosphorus could have liberated by microbial sulfate reduction and other anaerobic metabolisms and subsequently concentrated by fe redox pumping below the chemocline upwelling of the bottom waters or upward fluctuation of the chemocline might have brought p enriched waters to the photic zone where it was again scavenged by cyanobacteria through their eps to be subsequently precipitated as francolite the feedbacks between enhanced continental weathering cyanobacterial blooms carbon burial and accelerated phosphorus cycle thus controlled the marine biogeochemical changes which led to further oxygenation of the atmosphere and oceans ultimately paving the way for the rise of metazoans

a case study of air sea interaction during swell conditions air sea interaction data from a situation with pronounced unidirectional swell have been analyzed measurements of turbulence at three levels 10 18 and 26 m above mean sea level together with directional wave buoy data from the site ostergarnsholm in the baltic sea were used the situation which lasted for 48 hours appeared in the aftermath of a gale the wind direction during the swell situation turned slowly within a 90 sector both during the gale phase and the swell phase the over water fetch was 150 km the wind speed during the swell phase was typically 4 m s 1 during the swell phase a wind maximum near or below the lowest wind speed measuring level 10 m was observed the net momentum flux was very small resulting in cd values 0 7 10 3 throughout the lowest 26 m covered by the tower measurements turbulence intensities in all three components remained high despite the low value of the kinematic momentum flux u w resulting in a reduction of the correlation coefficient for the longitudinal and vertical velocity from its typical value around 0 35 to between 0 2 and 0 and with some positive values at the higher measuring levels appearing abruptly at wave age c0 u10 equal to 1 2 turbulence spectra of the horizontal components were shown not to scale with height above the water surface in contrast to vertical velocity spectra for which such a variation was observed in the low frequency range in addition spectral peaks in the horizontal wind spectra were found at a frequency as low as 10 3 hz from a comparison with results from a previous study it was concluded that this turbulence is of the inactive kind being brought down from the upper parts of the boundary layer by pressure transport

observations on the genus huroniospora barghoorn implications for paleoecology of the gunflint microbiota abstract examination of exceptionally well preserved thin sections of gunflint chert reveals new morphological criteria which are utilized for a critical evaluation of the genus huroniospora the shape varies from spheroidal to ellipsoidal one third of the specimens examined have either simple circular apertures or breaks in the vessel wall wall structure and surface texture appear to vary with quality of preservation these and other features lead to the conclusion that huroniospora represents a spore or encysted cell rather than a vegetative cell the presence of huroniospora in the schreiber beach assemblage does not constitute direct evidence for the primary photosynthetic nature of the interlaminar community

compression behaviour of reconstituted soils at high initial water contents oedometer tests starting from a very small effective vertical stress of 0 5 kpa were performed on three reconstituted clays with different liquid limits the soils were prepared at various initial water contents ranging from 0 7 to 2 0 times their corresponding liquid limits it is observed that the e log v compression curves show an inverse s shape due to suction pressure resisting deformation similar to that of soft natural clays caused by consolidation yield stress the suction pressure s of the reconstituted clays can be correlated with the ratio of initial void ratio to void ratio at liquid limit e0 el the suction pressure curve defined by a unique relationship between suction pressure s and the normalised void ratio at suction pressure es el is also proposed to distinguish between the pre suction and the post suction states in addition burland s concept of the intrinsic compression line is adopted for correlating the compression curves of various reconstituted clays at high initia

ambient inclusion trails in palaeozoic crustaceans phosphatocopina and ostracoda abstract hollow microtubular structures with pyrite grains at their termini have been found in phosphatocopines hesslandona toreborgensis and hesslandona cf angustata from the late cambrian of northern poland and in the metacopine ostracod cytherellina submagna from the early devonian of podolia ukraine the cambrian phosphatocopines are secondarily phosphatised and microtubes 5 20 m in diameter are preserved inside the phosphatized bivalved shield visible on the shield surface as half open microstructures with pyrite grains at their terminal end they are visible only where an external coating layer has peeled off in the devonian ostracod c submagna microtubes c 1 8 m in diameter occur within the phosphatized internal mould steinkern and are visible on the surface of the mould due to the dissolution of the calcite carapace during extraction of the limestone samples these microtubular structures are here interpreted as ambient inclusion trails aits due to the presence of terminal pyrite crystals of equivalent diameter to the microtube polygonal microtube cross sections plus longitudinal striations on the microtube walls that record the movement of the migrating angular pyrite crystal aits are thought to form when mineral crystals typically pyrite are impelled to migrate through a fine grained mineral matrix under increased fluid gas pressure our new materials provide the first record of exceptionally preserved aits occurring in crustaceans and only the third reported occurrence of aits in the palaeozoic the intimate occurrence of aits with phosphatized crustacean body fossils supports the hypothesis that aits are likely driven by increases in gas pressure due the decomposition of soft tissue in the case of cytherellina submagna our calculations suggest that as little as 20 g of organic matter decaying within a volume of 0 06 mm3 encased by an impermeable outer carapace may have been sufficient to produce a large number 100 of aits

evolution of stable internal boundary layers over a cold sea the situation studied in this paper relates to air flow from a heated land surface out over a water surface with much lower temperature observations from the baltic sea where this kind of situati

marine boundary layer structure for the sea fog formation off the west coast of the korean peninsula marine boundary layer mbl structure for the formation of sea fogs off the west coast of the korean peninsula are examined for the investigation period from january 2002 to august 2006 using the meteorological data measured at a buoy and the vertical sounding data measured at an island in this region there is the total of 3 294 vertical soundings during the investigation period based on these vertical soundings the mbl structure is classified as convective boundary layer cbl when inversion exists aloft but at altitudes lower than 3 km 1 618 soundings stable boundary layer sbl when inversion base is at the surface 655 soundings or near neutral boundary layer nnbl when there is no inversion or inversion base is higher than 3 km altitude 1 021 soundings under the cbl condition the most frequently formed lower level cloud is stratocumulus but fogs do form in spring and summer months mostly as warm sea fogs tsst t sst 0 are the most frequently found lower level clouds the effects of turbulence advection and radiation on sea fog formation vary with turbulence strength represented by bulk richardson number r b for cold sea fog cases in the highly turbulent regime r b 0 30 regimes the effects of turbulence decrease dramatically and so do the advection effects but radiative cooling is still strong again making it the crucial reason for the successful formation of cold sea fogs on the other hand the turbulent moisture supply from the warmer sea surface is the crucial factor for the formation of warm sea fogs while turbulent warming and radiative cooling largely cancel each other out and the advection effects are negligibly small

terminal proterozoic cyanobacterial blooms and phosphogenesis documented by the doushantuo granular phosphorites i in situ micro analysis of textures and composition abstract in order to ascertain the origin of granular phosphorites and the roles of microorganisms in phosphogenesis we conducted comprehensive petrographic surveys and correlated in situ micro analyses of granular phosphorites from the doushantuo formation near yichang south china phosphatic granules display organically zoned internal structures often associated with abundant cyanobacteria like microfossils the internal ultrastructure of the granules as documented by raman microspectroscopy scanning electron microscopy sem and transmission electron microscopy tem is characterized by randomly oriented apatite nano crystals embedded with ubiquitous carbonaceous particles in the apatite groundmass these represent primary textures formed by the rapid growth of apatite provided with abundant nucleation sites within microbial biofabrics nanosims elemental mapping revealed close correspondence of carbon and nitrogen with microfossil structures at the cellular and sub cellular level we propose that the doushantuo granules themselves were formed by microbially mediated accretionary growth followed by rapid phosphatization occurring at the sediment water interface extracellular polymeric substances eps produced by cyanobacteria would have played crucial roles in these processes by promoting aggregated granule growth in addition to providing nucleation sites for apatite crystallization while previous studies have suggested a dominant role of sulfur metabolizing microorganisms in the precipitation of phosphate in phosphorites new observations indicate that the emplacement of most sulfur bearing minerals in the doushantuo phosphorites postdate phosphatization itself our new model of phosphorite formation thus places cyanobacterial eps as an earlier key component of the mineralization of the doushantuo granular phosphorites

proprietes caracteristiques des argiles de l est du canada the compilation of numerous geotechnical data has allowed the definition of the main physical mechanical and hydraulic properties of marine and lacustrine clays of eastern canada as well as the establishment of correlations between some of these properties the possible uses of these correlations are described this study shows that the clays of eastern canada exhibit a behaviour similar to that of other clays but that they are characterized by a higher degree of structuration keywords physical properties mechanical properties hydraulic properties clays canada correlations journal translation

uncovering framboidal pyrite biogenicity using nano scale cnorg mapping framboidal pyrite has been used as a paleo redox proxy and a biomarker in ancient sediments but the interpretation of pyrite framboids can be controversial especially where later overgrowths have obscured primary textures here we show how nano scale chemical mapping of organic carbon and nitrogen cn org can detect relict framboids within precambrian pyrite grains and determine their formation mechanism pyrite grains associated with an ediacaran fossil lagerstatte from newfoundland ca 560 ma hold significance for our understanding of taphonomy and redox history of the earliest macrofossil assemblages they show distinct chemical zoning with respect to cn org relict framboids are revealed as spheroidal zones within larger pyrite grains whereby pure pyrite microcrystals are enclosed by a mesh like matrix of pyrite possessing elevated cn org replicating observations from framboids growing within modern biofilms subsequent pyrite overgrowths also incorporated cn org from biofilms with concentric cn org zoning showing that the availability of cn org progressively decreased during later pyrite growth multiple framboids are commonly cemented together by these overgrowths to form larger grains with relict framboids only detectable in cn org maps in situ sulfur isotope data 34 s 24 to 15 show that the source of sulfur for the pyrite was also biologically mediated most likely via a sulfate reducing microbial metabolism within the biofilms relict framboids have significantly smaller diameters than the pyrite grains that enclose them suggesting that the use of framboid diameters to infer water column paleo redox conditions should be approached with caution this work shows that pyrite framboids have formed within organic biofilms for at least 560 m y and provides a novel methodology that could readily be extended to search for such biomarkers in older rocks and potentially on other planets

redox architecture of an ediacaran ocean margin integrated chemostratigraphic δ13c δ34s 87sr 86sr ce ce correlation of the doushantuo formation south china abstract early diagenetic silicification and phosphatization of the ediacaran doushantuo formation ca 635 to 551 ma in south china offer extraordinary taphonomic windows into the early evolution of multicellular eukaryotes including various algal groups and potentially animals in order to understand how the ecological and taphonomic distribution of these ediacaran eukaryotes was controlled by oceanic redox conditions it is critical to reconstruct the redox architecture of the sedimentary basin recently two alternative redox models have been proposed to account for the geochemical and sedimentary features of the doushantuo formation one argues that the unit was deposited on a continental margin where a metastable sulfidic wedge was dynamically maintained by a sulfate concentration gradient between shelf and basinal environments the other contends that the sulfidic water mass was largely restricted to the intra shelf basin behind a rimmed margin these two models make different predictions about the stratigraphic completeness and correlation of the doushantuo formation to test these predictions we generated high resolution time series trends of multiple isotopic and elemental tracers including 34s 87sr 86sr and ce ce to facilitate an integrated chemostratigraphic correlation between inner shelf xiaofenghe intra shelf jiulongwan and outer shelf yangjiaping and zhongling sections our correlations suggest that both the inner and outer shelf sections are stratigraphically incomplete relative to the intra shelf section the euxinic wedge model should be reconsidered insofar as it is based on a miscorrelation between sections viewed from our revised chemostratigraphic framework euxinic conditions on the platform appear to have been largely restricted to the intra shelf basin carbonates in the upper doushantuo formation at jiulongwan and their stratigraphic equivalents are characterized by a profound negative carbon isotope anomaly i e the shuram excursion coincident with a drop in pyrite sulfur isotope values and a significant rise in 87sr 86sr from 0 7080 to 0 7090 the integrated stratigraphic data from south china suggest that the onset of the shuram excursion is associated with enhanced oxidative continental weathering that delivered radiogenic strontium as well as sulfate to the ediacaran basin

observational study of marine atmospheric boundary layer characteristics during swell abstract by combining simultaneous data from an instrumented air sea interaction spar asis buoy and a 30 m tower profiles of wind and turbulence characteristics have been obtained at several heights from about 1 to 30 m above the water surface during swell conditions five cases formed as averages over time periods ranging from 2 5 to 9 5 h representing quasi steady conditions have been selected they represent a range of typical wave age and include wind following swell cases and cross swell cases for relatively large wave age the wind profile exhibits a well defined maximum in the height range 5 10 m for more modest wave age this maximum turns into a sharp knee in the wind profile below the maximum or knee the wind increases rapidly with height above that point the wind is very nearly constant up to the highest measuring level on the tower 30 m analysis of balloon data from one day with swell indicates that the layer with constant wind in fact extends to the top of the boundary layer

simulation of the observed evening transition and nocturnal boundary layers large eddy simulation large eddy simulations are performed of two observed cases of evening transition boundary layers over land although generally similar to the observations the simulations have a poor match to the ageostrophic wind above the boundary layer and overestimate the nocturnal 4 m wind speed for one case the nocturnal phase is also simulated using a close match to observations in the early evening reproducing well the early morning boundary layer and jet this is achieved with a moderate resolution 5 m and also demonstrates the importance of a good initial wind state in a numerical weather prediction context these findings motivate improved wind profile observations around transition and a better representation of the ageostrophic wind by the boundary layer parametrization copyright 2006 crown copyright

wave induced wind in the marine boundary layer recent field observations and large eddy simulations have shown that the impact of fast swell on the marine atmospheric boundary layer mabl might be stronger than previously assumed for low to moderate winds blowing in the same direction as the waves swell propagates faster than the mean wind the momentum flux above the sea surface will then have two major components the turbulent shear stress directed downward and the swell induced stress directed upward for sufficiently high wave age values the wave induced component becomes increasingly dominant and the total momentum flux will be directed into the atmosphere recent field measurements have shown that this upward momentum transfer from the ocean into the atmosphere has a considerable impact on the surface layer flow dynamics and on the turbulence structure of the overall mabl the vertical wind profile will no longer exhibit a logarithmic shape because an acceleration of the airflow near the surface will take place generating a low level wave driven wind maximum a wind jet as waves propagate away from their generation area as swell some of the wave momentum will be returned to the atmosphere in the form of wave driven winds a model that qualitatively reproduces the wave following atmospheric flow and the wave generated wind maximum as seen from measurements is proposed the model assumes a stationary momentum and turbulent kinetic energy balance and uses the dampening of the waves at the surface to describe the momentum flux from the waves to the atmosphere in this study simultaneous observations of wind profiles turbulent fluxes and wave spectra during swell events are presented and compared with the model in the absence of an established model for the linear damping ratio during swell conditions the model is combined with observations to estimate the wave damping for the cases in which the observations showed a pronounced swell signal and almost no wind waves the agreement between observed and modeled wind profiles is remarkably good the resulting attenuation length is found to be relatively short which suggests that the estimated damping ratios are too large the authors attribute this at least partly to processes not accounted for by the model such as the existence of an atmospheric background wind in the model this extra momentum must be supplied by the waves in terms of a larger damping ratio

evaluation of a roughness length model and sea surface properties with data from the baltic sea abstract the exchange of momentum between the oceans and atmosphere is important for many atmospheric and oceanic processes and is mainly governed by the roughness of sea surface the roughness can be expressed by a roughness length z0 a roughness length model based on the concept that z0 is determined by stochastic wave breaking is presented the model performance is evaluated using measurements from the ostergarnsholm site in the baltic sea and pertinent information from other recent investigations the wave field and the roughness length variations are investigated during various sea state conditions dominated by wind driven waves it is found that several parameters describing the characteristics of the wave field are dependent on the amount of energy that long waves have relative to the energy of short wind driven waves of the sea spectrum called the swell ratio the impact of swell ratio on z0 can explain the discrepancies found in various results among relevant investigations the roughne

on the volumetric strain time curve patterns of dredged clays during primary consolidation thirteen one dimensional consolidation tests with step loading were performed on dredged clays reconstituted at different initial water contents both vertical deformation and pore pressure were measured during primary consolidation which refers to the time dependent compression process associated with the dissipation of pore pressure the pore pressure changes were investigated by considering the maximum and the residual values the development of compression during pore pressure dissipation was analysed to identify the change patterns in volumetric strain time curves three types of change patterns were found during the primary consolidation and the remoulded yield stress was found to be the key factor in classifying the change patterns the inflexion point is absent for types 1 and 2 indicating that the end of primary consolidation cannot be determined by the commonly used taylor and casagrande methods type 3 shows an inverse s shape suggesting that the end of primary consolidation determined ba

hydraulic conductivity of clays in confined tests under low hydraulic gradients clay barriers normally function at hydraulic gradients much lower than are commonly used in laboratory tests for hydraulic conductivity this paper describes low gradient tests on compacted illite

sedimentary phosphorites an example phosphoria formation southeastern idaho u s a the phosphorous cycle filters through both the biological and geological worlds and sedimentary phosphates exist at the interface between these two portions of the global phosphorous cycle sedimentary phosphates form only when the proper physical conditions and biological activity coincide once deposited the phosphate po43 crystallizes into the mineral carbonate fluorapatite cfa this mineral with substitution of co32 for po43 compositionally falls between the familiar forms of fluorapatite found in igneous and metamorphic rocks and the apatites found in biological material including our own bones and teeth finally through mining and processing it is these sedimentary phosphates that are used as fertilizers and additives for food production and other activities and are subsequently returned to the biosphere the unique settings in which phosphorites form those areas where phosphate is concentrated millions of times above normal and sedimentation rates are drastically slowed are not fully understood and have been the subject of sometimes intense scientific debate over the last century and a half furthermore the mineralogy of these deposits is unique difficult to study and contentious because of our dependence on phosphate for use in fertilizers and other agricultural and chemical uses these deposits are interesting not only from a scientific viewpoint but from an economic standpoint as well however like many mining operations phosphate mining has environmental problems that must be addressed this chapter provides an overview of the salient points in phosphorite formation mineralogy and mining and puts into context the current work being undertaken on the phosphoria formation in southeastern idaho this chapter does not provide a full description of all the sedimentalogical mineralogical and industrial work that has been done on sedimentary phosphates indeed numerous full volumes have been published on phosphorites and more will undoubtedly follow for large scale phosphorites to

correlations between index tests and the properties of remoulded clays correlations have been developed which relate the compressibility undrained shear strength and permeability of remoulded clays to their atterberg limits and activity the relationships can be used to model a hydraulic fill such as fine grained dredged material or mine tailings prior to deposition they can also be used to estimate the engineering properties of normally consolidated natural clay such as marine sediments the correlations cover a wide range of plasticity index and liquidity index for a wide variety of clays it was found that the activity plays a major role in the compressibility and undrained shear strength and is thus also related to the sensitivity of clays the activity apparently does not affect the permeability but other factors remain to be investigated because compressibility undrained shear strength and permeability are interrelated it can be concluded that if one is known then the other two can be derived hence these three engineering properties are seen as different

the transition from downward to upward air sea momentum flux in swell dominated light wind conditions fifteen hours of consecutive swell data from the experiment flux etat de la mer et teledetection en condition de fetch variable fetch in the mediterranean show a distinct upward momentum flux

raman spectrum of carbonaceous material a possible metamorphic grade indicator for low grade metamorphic rocks raman spectral analyses of carbonaceous material cm extracted from pelitic samples along two sections traversing the metamorphic belt of taiwan were carried out in the present study the results show similar spectral variations of cm with metamorphic grade as those documented in the literature however continuous sampling from zeolite facies through prehnite pumpellyite facies to greenschist facies metamorphic rocks in the present study does reveal some interesting features on the raman spectra of cm that were not noted before both the raman d disordered o ordered peak area i e integrated intensity ratio and the d o peak width i e full width at half maximum fwhm ratio of the cm decrease with progressive metamorphism but the most prominent change in the d o peak area ratio occurs in samples of lower greenschist facies metamorphic grade while the most significant decrease in the d o peak width ratio occurs in samples near the boundary of prehnite pumpellyite facies and greenschist facies this phenomenon is interpreted as a result of the decoupling of the changing rates of in plane crystallite size and degree of defects of cm with progressive metamorphism it is postulated that the raman spectrum of cm can serve as a metamorphic grade indicator to distinguish samples of prehnite pumpellyite facies metamorphic grade from those of greenschist facies metamorphic grade

evidence for sulfidic deep water during the late permian in the east greenland basin a detailed study of the size distribution of framboidal pyrites in the black shales of the upper permian ravnefjeld formation was performed to evaluate the redox state of the late permian ocean in contrast to framboidal pyrites in bioturbated sediments the smaller and less variable size distribution of pyrite framboids in the laminated shales of the ravnefjeld formation provides persuasive evidence for sulfidic h 2 s rich bottom water conditions in the east greenland basin however the s isotope compositions of both pyrite populations show a similar distribution the widespread 3 4 s values of pyrites 41 2 to 28 2 in the black shales of the ravnefjeld formation indicate a large fractionation up to 52 7 relative to seawater sulfate and may record different pathways of sulfur cycling in sulfidic water columns as well as within sediments the new data from the east greenland basin indicate that environmental stress such as widespread sulfidic conditions could have caused the biotic crisis in the late permian

influence of metal ions and ph on the hydraulic properties of potential acid sulfate soils acid sulfate soils ass cover extensive areas of east australian coastal floodplains upon oxidation these hydromorphic pyritic sediments produce large quantities of sulfuric acid in addition due to their geographic location these soils may also come in contact with high ionic strength estuarine tidal waters as a result there is typically a large variation in acidity ph and cation concentrations in soil porewaters and adjacent aquatic systems e g agricultural field drains rivers estuaries etc acid sulfate soils especially from the unoxidized gelatinous deeper layers contain a relatively high proportion of montmorillonite which is wellknown for its shrink swell properties variations in cation concentrations including h3o can influence montmorillonite platelet interactions and may thus also significantly affect the hydraulic conductivity of materials containing this clay in this paper we report on the effect of four common cations at reasonable environmental concentrations on the hydraulic properties of potential unoxidized acid sulfate soil materials the natural system was simplified by examining individually the effects of each cation h ca2 fe2 and na on a soil water suspension in a filtration cell unit moisture ratio hydraulic conductivity and the consolidation coefficient of the deposited filter cakes were calculated using material coordinates theory the results indicate that the hydraulic conductivity of potential acid sulfate soils increases at low ph and with cation concentration although an increase in the charge of amphoteric edge groups on montmorillonite clays may result in some aggregation between individual clay platelets we conclude that the extent of these changes are unlikely to cause significant increases in the transportation of acidity and contaminants through potential acid sulfate soils as the hydraulic conductivity of these materials remain low 10 9 m s at ph and ionic conditions normally experienced in the field

integrated chemostratigraphy of the doushantuo formation at the northern xiaofenghe section yangtze gorges south china and its implication for ediacaran stratigraphic correlation and ocean redox models abstract the ediacaran doushantuo formation in the yangtze gorges of south china plays an important role in our understanding of biological evolution global correlation and ocean redox conditions because of the availability of high resolution paleontological and geochemical data and numerous radiometric dates however integrated study has been focused on the jiulongwan section that was largely deposited below wave base in a restricted shelf lagoon jiang et al 2011 zhu et al 2011 studies of shallower water successions are lacking and this presents a challenge to test ediacaran stratigraphic correlation and ocean redox models to fill this knowledge gap we conducted a high resolution integrated study of the doushantuo formation at the northern xiaofenghe nxf section approximately 35 km to the northeast and paleogeographically updip of the jiulongwan section with the exception of the basal 20 m nxf sediments were deposited above normal wave base integrated biostratigraphic and chemostratigraphic data indicate that the 140 m thick nxf section correlates with the lower doushantuo formation member i and much of member ii i e the lower ca 70 m of the formation at jiulongwan geochemical data from nxf and other doushantuo sections indicate that euxinic conditions may have been limited to a shelf lagoon represented by the jiulongwan section that was restricted between the proximal inner shelf and a distal shelf margin shoal complex at least during early doushantuo time following the deposition of the doushantuo cap dolostone further integrated studies are necessary to test whether euxinic conditions existed in open marine shelves in south china and elsewhere during the ediacaran period

microborings in early cambrian phosphatic and phosphatized fossils abstract a small proportion of phosphatic and phosphatized fossils mostly microfossils extracted from lower cambrian qiongzhusian lime mudstones of deeper water aspect belonging to the yu anshan and shuijingtuo formations of south china is perforated by microborings these microborings are present in bradoriid and phosphatocopine arthropod carapaces lingulid brachiopod valves microdictyon plates and tommotiid sclerites their absence in co occurring phosphatized eodiscid trilobite exoskeletons and palaeoscolecid worm trunk fragments indicates a substrate specificity that suggests the boring microorganism was heterotrophic extracting particular residual organic compounds present in only certain bioclast types microborings occur as meandering tunnels and grooves on bioclast surfaces and most are 10 20 m wide and circular in cross section the euendoliths were thus able to live partly exposed as well as within the substrate tunnel and groove walls bear a distinct longitudinal sculpture of straight striae separated by cuspate ridges 1 2 m apart that parallel the microboring never twisting the microborings accord with the ichnotaxon microptychoites fuquanensis dong in dong et al dong y ji q wang s 1984 the discovery of microscopic trace fossils in the sinian doushantuo formation in southwestern china scientia geologica sinica 346 347 in chinese the fluted sculpture appears to have no modern analogue but may have arisen by localized secretions at the tip of a bundle of filaments this kind of microboring had been previously reported from phosphatic substrates of ediacaran earliest cambrian middle cambrian and probably early devonian age but appears to have no recent counterpart

use of nanosims in the search for early life on earth ambient inclusion trails in a c 3400 ma sandstone ambient inclusion trails ait are enigmatic microtubular structures created by the migration of mineral crystals through a lithified substrate the decomposition of organic material has been suggested as the driving force for the crystal migration but has yet to be rigorously tested ait may hold potential as a biosignature for investigating early life on earth if the associated organic material can be shown to be biological this paper attempts to test the formation mechanism and biogenicity of ait from the c 3400 ma strelley pool sandstone of western australia using nanosims technology in doing so we demonstrate the unique ability of the nanosims to combine sub micron scale imaging with in situ chemical and isotopic data thereby enhancing our ability to evaluate the biogenicity criteria for archaean microstructures enrichments of a suite of major elements c n p s and trace elements co fe ni zn often associated with biological processes are found within several ait in this sandstone c and n enrichments are most common along ait margins and correlate with depletions of si o ca and mg indicating that this material is indeed organic in nature 13 c values of this carbonaceous material average 26 petrographic observations show that some of the ait occur in the centre of detrital sandstone grains where they were sealed from later fluid flow and therefore preserve primary archaean bio geochemistry in contrast ait found around the outer edges of sandstone grains may contain more recent organic material introduced by later fluid migration and are an unreliable biosignature using the petrographic and geochemical data a multi stage model for ait formation and subsequent diagenetic modification is proposed the possible sources of the primary organic material are discussed and we conclude that the data are consistent with a biological origin for these ait an abiogenic origin is more difficult to sustain but cannot yet be completely excluded for ait in general

on conducting the modified slug test in tight formations the method introduced by bredehoeft and papadopulos 1980 for conducting a modified slug test in tight formations does not assure the condition of approximate equilibrium necessary at the start of the test in addition compressibility in the shut in well can be significantly larger than the compressibility of water which bredehoeft and papadopulos indicate should be used in the calculations errors that may result from using the original test procedure are discussed and a modified procedure and testing arrangement are presented

turbulence adjustment and scaling in an offshore convective internal boundary layer a casper case study abstractthe characteristics of a convective internal boundary layer cibl documented offshore during the east coast phase of the coupled air sea processes and electromagnetic ducting research cas

euendoliths versus ambient inclusion trails from early cambrian kuanchuanpu formation south china abundant microstructures have been discovered in small skeletal fossils ssfs and embryo like fossils collected from the lower cambrian kuanchuanpu formation ca 535 ma in xixiang county shaanxi province china these involve two co occurring structures 1 long unbranched cylindrical filaments which are comparable to phosphatic casts of microborings constructed by euendolithic cyanobacteria endoconchia lata in morphology and preservation pathway and 2 meandering micro tubes or grooves on fossil moulds and steinkerns of a wide range of sizes and morphological diversities perceived as ambient inclusion trails aits herein we also report a new occurrence of organic carbon spherules as ait propelled material which is rare in comparable fossils from direct comparison of endolith fossils and aits we propose a mechanism to account for their notably different preservation and further attempt to offer an explanation for their co occurrence their differential preservation suggests a chronological taphonomic sequence of their formation we interpret that e lata microborings formed prior to phosphate sedimentation whereas aits are likely generated in a later phase of or after phosphorite precipitation but before calcareous re cementation dissecting the sequence of formation of these structures in conjunction with detailed morphological observations assists in distinguishing true biologically produced endoliths from otherwise abiogenically produced microstructures

pyrite framboid study of marine permian triassic boundary sections a complex anoxic event and its relationship to contemporaneous mass extinction size analysis of pyrite framboids has been undertaken on epicontinental permian triassic boundary sections throughout the world in order to evaluate the intensity and duration of anoxia mid paleolatitude sections from the margins of the boreal spitsbergen greenland and neotethyan oceans western australia reveal intense anoxia throughout the permian triassic boundary interval with euxinic conditions frequently developing and dysoxia encountered even in relatively shallow water settings above storm wave base at equatorial paleolatitudes weakly oxygenated dysoxic conditions are widely developed in a broad range of water depths including those shallow enough to produce oolite deposition although euxinia was rare western and eastern tethyan locations re veal a complex and unstable redox history anoxia in the hindeodus praeparvus zone was replaced by oxygenated facies in the permian triassic boundary interval h changxingensis to h parvus zones oxygen poor deposition returned during the succeeding isarcicella isarcica zone the more persistent and intense development of oxygen restriction in cooler water mid paleolatitude sections argues against warming and dissolved oxygen decline as the key cause of permian triassic bound ary anoxia in higher paleolatitudes the ben thic invertebrate extinctions occurred during a prolonged phase of oxygen poor deposition while in equatorial tethyan locations benthic losses occurred at the end of the fi rst anoxic phase in the late h praeparvus zone

permeability of a bentonite crushed granite rock mixture using different experimental techniques the use of bentonite based mixtures as a sealing material for deep geologic repositories is common to many different concepts for isolating nuclear fuel waste in this context saturated hydraulic conductivity becomes a fundamental parameter when analysing the long term behaviour of these facilities despite that measurement of hydraulic conductivity is still far from being routine for very low permeability materials a mixture of 30 sodium bentonite and 70 crushed granite rock is being considered as a sealing material in a future repository in sweden this paper describes the experimental programme carried out to determine the permeability of this mixture constant head tests pulse tests and oedometer tests have been used for that purpose but because of the characteristics of the material large grain size and very low permeability special test procedures and equipments had to be developed the paper also presents the analysis of the results including a numerical simulation of the pulse test by usin

thermal mesoscale circulations on the baltic coast 1 numerical case study a three dimensional mesoscale numerical model is utilized to investigate a well documented seabreeze event taken from experimental data the simulations are not set up as a model validation instea

use of conventional stability parameters during swell the situation with swell is of climatological importance over the baltic sea since swell is present during as much as 40 of the time in this study two periods with unstable and two periods with stable stratification and wind following swell are investigated data are taken at a small flat island in the baltic sea during unstable stratification the turbulent structure shows great resemblance to the free convective boundary layer and scales with the boundary layer height since surface heat flux is too small to support the high levels of turbulence present inactive turbulence is probably the dominating source for the stably stratified layer there are smaller differences between data with and without swell the turbulence is mainly transported upward into the atmosphere with the aid of pressure fluctuations induced by the waves for most of the data with swell the gradients are smaller than for growing sea during unstable conditions the wind gradients are negative indicating the presence of a wave driven wind the gradients increase with increasing height above the surface the drag coefficient is smaller than is usually found for both stable and unstable stratification and varies very little with wind and stratification there are only small variations in the heat transfer coefficients with changing stratification but they are significantly different for stable and unstable stratification

ancient graphite in the eoarchean quartz pyroxene rocks from akilia in southern west greenland i petrographic and spectroscopic characterization because all known eoarchean 3 65 ga volcano sedimentary terranes are locked in granitoid gneiss complexes that have experienced high degrees of metamorphism and deformation the origin and mode of preservation of carbonaceous material in the oldest metasedimentary rocks remain a subject of vigorous debate to determine the biogenicity of carbon in graphite in such rocks carbonaceous material must be demonstrably indigenous and its composition should be consistent with thermally altered biogenic carbon as well as inconsistent with abiogenic carbon here we report the petrological and spectroscopic characteristics of carbonaceous material typically associated with individual apatite grains but also with various other minerals including calcite in a 3 83 ga granulite facies ferruginous quartz pyroxene unit qp rock from the island of akilia in southern west greenland in thin sections of the fine grained parts of akilia qp rock sample g91 26 mapped apatites were found to be associated with graphite in about 20 of the occurrences raman spectra of this carbonaceous material had strong g band and small d band absorptions indicative of crystalline graphite three apatite associated graphites were found to contain curled graphite structures identified by an anomalously intense second order d band or 2d band raman mode these structures are similar to graphite whiskers or cones documented to form at high temperatures raman spectra of apatite associated graphite were consistent with formation at temperatures calculated to be between 635 and 830 c which are consistent with granulite facies metamorphic conditions three graphite targets extracted by focused ion beam fib methods contained thin graphite coatings on apatite grains rather than inclusions sensu stricto as inferred from transmitted light microscopy and raman spectroscopy tem analyses of graphite in these fib sections showed a 0 0 0 2 interplanar spacing between 3 41 and 3 64 a for apatite associated graphite which is larger than the spacing of pure graphite 3 35 a and may be caused by the presence of non carbon heteroatoms in interlayer sites samples analyzed by synchrotron based scanning transmission x ray microscopy stxm also confirmed the presence of crystalline graphite but abundances of n and o heteroatoms were below detection limit for this method graphite in the akilia qp rock was also found to occur in complex polyphase mineral assemblages of hornblende calcite sulfides magnetite that point to high temperature precipitation from carbon bearing fluids these complex mineral assemblages may represent another generation of graphitization that could have occurred during the amphibolite facies metamorphic event at 2 7 ga several observations point to graphitization from high temperature fluid deposition for some of the akilia graphite and our results do not exclude a biogenic source of carbon in graphite associated with apatite but ambiguities remain for the origin of this carbon

swell impact on wind stress and atmospheric mixing in a regional coupled atmosphere wave model over the ocean the atmospheric turbulence can be significantly affected by swell waves change in the atmospheric turbulence affects the wind stress and atmospheric mixing over swell waves in thi

end of primary consolidation parameters using inflection point method this note describes a faster and complete consolidation testing procedure using the inflection point method so as to obtain the void ratio consolidation curve at the end of primary consolidation an

variability in the summertime coastal marine atmospheric boundary layer off california usa an analysis of boundary layer structure and surface layer turbulence from measurements off the california coast is presented from data collected by research aircraft during two field experiments the coastal waves 1996 cw96 and the monterey area ship track mast experiments cw96 covers the near coast region in particular in the vicinity of major headlands whereas mast extends offshore along the us west coast coastal modification of the along coast flow occurs on two main horizontal scales firstly a large scale variability is due to the interplay between the shallow near coast marine atmospheric boundary layer mabl and the coastal terrain typically higher than the mabl depth the mabl depth decreases smoothly towards the coast while the wind speed increases to a coastal jet in response to the sloping mabl inversion secondly the flow is affected by supercritical flow dynamics as the wind speed increases and the mabl depth decreases towards the coast the mabl flow becomes supercritical in a shallow water sense as supercritical shallow water flow interacts with major headlands expansion fans form affecting both the wind speed and the mabl depth the combination of cw96 and mast data reveals significant differences between the flow along the coast and that far offshore mabl winds are stronger near the coast whereas aloft the winds are weaker than offshore the near coast mabl is also better mixed turbulence increases towards the coast while the sensible heat flux decreases and often changes sign leading to stable stratification near the coast a length scale determining the across coast influence of the expansion fans is defined from simple inviscid and irrotational shallow water theory data from four days of the cw96 experiment show that this simple theory describes the low level wind speed adequately surface layer turbulence also scales with this simple length scale but the results are complicated by upwelling of cold water giving rise to strong internal boundary layers from terms in the turbulent energy budgets it appears that dissipation of turbulence exceeds local production copyright 2004 royal meteorological society

high phosphate availability as a possible cause for massive cyanobacterial production of oxygen in the paleoproterozoic atmosphere abstract the deposition of major precambrian phosphorites was restricted to times of global change and atmospheric oxygenation at both ends of the proterozoic phosphorites formed after highly positive carbon isotope excursions in carbonates deposited during the paleoproterozoic lomagundi jatuli event and the neoproterozoic cryogenian and ediacaran periods the correlative step wise rise in atmospheric oxygen over the proterozoic has been linked to changes in the carbon cycle however the postulated relations between carbon isotope events phosphorites and atmospheric oxygenation remain unexplained paleoproterozoic carbonates of the aravalli supergroup india preserve evidence for cyanobacterial blooms in the form of tightly packed stromatolitic columns in the world s oldest significant sedimentary phosphate deposit restricted basins of the lower aravalli group with stromatolitic phosphorites in jhamarkotra udaipur jhabua and sallopat exhibit near zero 13 c carb values and large ranges of 13 c org values between 33 3 and 10 1 indicative of a complex carbon cycle because phosphate accumulates primarily in oxic sediments these eutrophic microbial ecosystems likely developed within the photic zone of the shallow oxygenated marine realm this is consistent with deposition during the time of increasingly more oxidizing conditions after the great oxidation event goe approximately contemporaneous basins without phosphate deposits from ghasiar karouli negadia umra and babarmal exhibit a range of positive 13 c carb excursions some with values up to 11 2 that suggest high rates of organic carbon burial and others with moderately high 13 c carb values around 6 or 3 that suggest smaller carbon cycle perturbations the 15 n values of all these rocks vary between 0 7 and 3 4 and are consistent with the predominance of nitrogen fixation during cyanobacterial blooms in all basin types such low nitrogen isotope values are interpreted to have arisen from the biological response to high phosphate availability we conclude that increased phosphate availability during and after the paleoproterozoic lomagundi jatuli event likely caused cyanobacterial blooms and was a key factor in the oxygenation of earth s atmosphere increasing oxygenation of the shallow ocean seafloor favored the removal of excess phosphate as authigenic apatite thus dampening effects of weathering increases on organic burial and marine 13 c carb after about 2 0 ga

pyrite morphology and redox fluctuations recorded in the ediacaran doushantuo formation abstract recent geochemical studies of the doushantuo formation ca 635 551 ma in south china suggested that the ediacaran ocean was strongly stratified with an oxic surface layer above a euxinic wedge that was sandwiched within ferruginous deep waters this ocean redox model however was derived largely from the data obtained from stratigraphic sections in the yangtze gorges area that according to recent paleogeographic reconstruction were deposited in a restricted intrashelf lagoon in order to test the redox conditions in open ocean deep water environments we have conducted a detailed morphological analysis of authigenic pyrites from the upper to lower slope sections of the doushantuo formation in analogy to modern euxinic basins such as the black sea framboidal pyrites with smaller and less variable size distribution are taken as evidence for sulfide precipitation in euxinic water column while larger and more variable framboidal and euhedral pyrites are formed or diagenetically altered in sediments with an overlying oxic dysoxic water column except for a few brief intervals pyrites from the doushantuo formation in upper slope sections siduping and taoying sections are mainly of early diagenetic origin and do not record water column euxinia during deposition in contrast pyrites from the doushantuo formation in the lower slope section wuhe section are dominated by fine grained framboids indicative of pervasive water column euxinia below chemocline in both upper and lower slope sections temporal changes in genetic pyrite types occur at centimeter to decameter scales suggesting frequent chemocline fluctuations the overall decrease in abundance of framboidal pyrites toward the upper doushantuo formation in upper slope sections suggests increasing water column oxygenation and deepening of the chemocline macroalgae and metazoan fossils are found mainly from shale intervals without syngenetic pyrites in upper slope sections indicating the sensitivity of macroscopic eukaryotes to the ocean chemocline the redox fluctuations recorded by the doushantuo pyrites compels for comprehensive geochemical data in deep water successions to further test the existing paleoceanographic models of the ediacaran ocean

large eddy simulations and observations of atmospheric marine boundary layers above nonequilibrium surface waves abstract winds and waves in marine boundary layers are often in an unsettled state when fast running swell generated by distant storms propagates into local regions and modifies the overlying turbulent fields a large eddy simulation les model with the capability to resolve a moving sinusoidal wave at its lower boundary is developed to investigate this low wind fast wave regime it is used to simulate idealized situations with wind following and opposing fast propagating waves swell and stationary bumps les predicts momentum transfer from the ocean to the atmosphere for wind following swell and this can greatly modify the turbulence production mechanism in the marine surface layer in certain circumstances the generation of a low level jet reduces the mean shear between the surface layer and the pbl top resulting in a near collapse of turbulence in the pbl when light winds oppose the propagating swell turbulence levels increase over the depth of the boundary layer and the surface drag increases

fluctuation of shelf basin redox conditions in the early ediacaran evidence from lantian formation black shales in south china abstract finely laminated pyrite and organic rich black shales that bear a euxinic interpretation dominate the ediacaran lantian formation in southern anhui south china however these black shales preserve benthic sessile algae and possible metazoans in situ suggesting that the lantian shelf basin may have had at least episodically oxidized bottom water during the early ediacaran period redox conditions of the fossiliferous lantian black shales were examined by petrological analysis pyrite framboid and 34s measurements and redox sensitive trace element rste analysis lamina by lamina pyrite framboid measurements show that lantian black shales were deposited under fluctuating redox conditions the 34s values of pyrites range from 20 5 to 2 3 for different laminae and display less negative values than the earliest ediacaran black shales supporting a return to a relatively low seawater sulfate concentration after the early ediacaran oxidation event similarly the lantian black shale rste concentrations e g mo u and v are low compared to previously published results from the early ediacaran and constant from lamina to lamina suggesting a drop in ocean wide rste concentrations occurring independently of frequent local redox condition changes these frequent redox condition changes in the lantian shelf basin may have facilitated the productivity and preservation of macroscopic lantian biota

precambrian microbe like pseudofossils a promising solution to the problem of various problems that have hindered progress in documenting the precambrian history of life the difficulty in distinguishing between bona fide microbial fossils and nonbiological microscopic pseudofossils has been among the most serious though errors in the interpretation of putative precambrian fossil microbes have diminished greatly over recent years mistakes continue to be made we suggest that such errors can be avoided by the use of a multifaceted strategy based on a specified series of biologically definitive characteristics that document the presence of interrelated biological morphology and biologically derived chemistry to illustrate this promising approach we use optical microscopy confocal laser scanning microscopy and raman spectroscopy together to distinguish between authentic microbial fossils and microscopic look alikes both coccoidal and filamentous rock embedded in five proterozoic and two archean geological units bona fide fossils of the 800 ma bitter springs formation of central australia and 3050 ma farrel quartzite of northwestern australia and objects we regard to be pseudofossils from the 770 ma chanda limestone of southern india 800 ma myrtle springs formation of south australia 1020 ma lakhanda formation of southeastern siberia 1700 ma vempalle formation of central india and 2629 ma marra mamba iron formation of northwestern australia the results demonstrate that no single criterion by itself is sufficient to establish the biological origin of such objects instead as shown here this problem appears solvable by the use of an interdisciplinary approach that combines the data and techniques of geology biology and chemistry

the fetch experiment an overview the flux etat de la mer et teledetection en conditions de fetch variable fetch was aimed at studying the physical processes associated with air sea exchanges and mesoscale oceanic circulation in a coastal region dominated by frequent strong offshore winds the experiment took place in march april 1998 in the northwestern mediterranean sea gulf of lion observations were collected with the r v l atalante with an air sea interaction spar asis buoy with waverider buoys and with research aircraft equipped for in situ and remote sensing measurements the present paper is an introduction to the following special section which groups 12 papers including this one presenting results on turbulent flux measurements at the ocean surface on the behavior of the marine atmospheric boundary layer on the ocean waves characteristics on the ocean circulation and on remote sensing of surface parameters this overview presents the background and objectives of fetch the experimental setup and operations and the dominant atmospheric and oceanic conditions and introduces the different papers of the special section

early diagenesis of organic matter in peru continental margin sediments phosphorite precipitation abstract pore water chemistry total dissolved co 2 nh 4 no 3 no 2 po 4 si oh 4 ca mg fe mn so 4 h 2 s and f and titration alkalinity solid phase chemistry c org p org c tot n tot f si opal and s ii and sediment characteristics porosity dry bulk density and formation factors were determined on a centimeter scale spacing in the upper 20 40 cm of sediments under intense upwelling areas on the peru continental shelf these data demonstrate that carbonate fluorapatite cfa is precipitating from pore waters in the upper few centimeters of a gelatinous mud with high organic carbon content up to 20 c org very high porosity 0 96 ml cm 3 and very low dry bulk density 3 dissolved phosphate concentrations at the sediment water interface range from 20 to 100 m orders of magnitude higher than bottom water concentrations and much higher than predicted from regeneration of organic matter the mechanism of this interfacial phosphate release is unclear but is apparently uncoupled from carbon and nitrogen metabolism and thus may be linked either to dissolution of fish debris or to the presence of a microbial mat in surficial sediments fluoride is incorporated into cfa by diffusion from the overlying seawater and carbonate ions are provided from pore water alkalinity magnesium concentrations in this reaction zone are not significantly different from those of seawater suggesting that magnesium depletion is not a necessary prerequisite for cfa precipitation the environment of precipitation is interface linked rather than driven by organic diagenesis of phosphorus deeper in the sediment most of the cores display a wide range of diagenetic characteristics below the immediate interfacial region but almost all show the precipitation signature near the interface this interface linked early diagenetic porewater environment for the precipitation of cfa explains many of the geochemical characteristics of phosphorites and provides a testable model to compare the modern phosphogenic analog with ancient phosphorite deposits two of the cores display very high solid phase phosphorus and fluoride contents reflecting the presence of apparently modern pelletal apatites

the near neutral marine atmospheric boundary layer with no surface shearing stress a case study abstract data from a marine coastal experiment over the baltic sea comprising airborne measurements and mast measurements have been used to highlight the turbulence dynamics of a case with most unusual flow characteristics the boundary layer had a depth of about 1200 m the thermal stratification was near neutral with small positive heat flux below 300 m and equally small negative heat flux above the entire situation lasted about 6 hours turbulence levels were unexpectedly high in view of the fact that momentum flux was negligible in fact positive in the layers near the surface and buoyancy flux was also small the turbulence was found to scale with the height of the boundary layer giving rise to velocity spectra having the shape of those characteristic of convectively mixed boundary layers analysis of the turbulence budget for the entire planetary boundary layer pbl revealed that energy was produced from shear instability in the uppermost parts of the pbl and was distributed to the lower par