relation between depositional environment and the elemental composition of early diagenetic siderite early diagenetic siderites from marine and fresh water depositional environments are characterized by distinctive compositional trends siderite from fresh water environments is often relatively pure i e greater than 90 mol feco sub 3 and commonly attains end member composition siderite from marine environments however is always extremely impure and has extensive substitution of mg up to 41 mol and to a lesser extent ca up to 15 mol for fe in the siderite lattice in addition marine siderite generally contains less mn and has a higher mg ca ratio than fresh water siderite this compositional variation appears to result from differences in the chemistry of early marine and meteoric pore waters inasmuch as early marine pore waters generally have a higher mg sup 2 ca sup 2 ratio and contain less mn sup 2 and fe sup 2 and more ca sup 2 and mg sup 2 than meteoric waters

seasonal variation of counterclockwise eddies downstream of the tsushima islands abstract the seasonal variation of counterclockwise eddies downstream of the tsushima islands in the tsushima straits was investigated from 2004 to 2008 using long term acoustic doppler current profiler adcp data eddy activity was high from summer to autumn july november the eddies were formed in short term intervals of 5 8 days almost corresponding to the formation cycle of karman vortices the eddy activity varied on a longer time period about 13 days the mean kinetic energy mke converted to eddy kinetic energy eke at current shears between the eastern and western channels of the tsushima straits the counterclockwise eddies that formed downstream of the tsushima islands were intensified and maintained by energy conversion from mke to eke at the northern shear of the current core in the eastern channel the countercurrent east of the tsushima islands from summer to autumn was intensified by energy conversion from eke to mke

siderite concretions from nonmarine shales westphalian a of the pennines england controls on their growth and composition back scattered electron microscopy has been used to examine the microstructure of nonmarine shale hosted siderite concretions the concretions are composed of 50 100 micrometer zoned crystallites which exhibit no noticeable center to edge variation within any individual concretion this indicates that siderite crystallites nucleated at virtually the same time across the entire concretion and that the concretions did not grow by radial addition of siderite layers around a central nucleus further siderite precipitation took place by crystal growth onto the nuclei the total proportion of siderite in any part of the concretion bears no simple relationship to the porosity of the enclosing shale at the time of precipitation and growth by passive precipitation in pore space is unlikely integration of microprobe data with bulk mineral chemical and stable isotope data suggests that the siderite crystallites are composed of an fe mn rich end member with a delta 13 c value of approximately 10 per mil and a mg ca rich end member with a delta 13 c value of approximately 0 per mil to 5 per mil the mineral chemical and stable isotope compositions of these concretions resulted from microbially mediated processes operating close 10 m to the sediment water interface during methanogenesis methanogenesis can generate low delta 13 c as well as high delta 13 c carbonate cements hence deep burial diagenetic reactions such as decarboxylation of organic matter need not be invoked to generate solutes for siderite precipitation

formation of siderite mg calcite iron sulphide concretions in intertidal marsh and sandflat sediments north norfolk england concretions cemented mainly by siderite mg calcite and iron monosulphide are common in late holocene marsh and sandflat sediments on parts of the north norfolk coast field experiments have shown that the concretions are actively forming in reduced sediments in which sulphate reducing bacteria are active 13c values ranging from 3 to 11 8 mean 5 9 0 suggest that the carbonate in the concretions is derived partly from marine sources and partly from microbial degradation of organic matter 18o values ranged from 6 4 to 0 8 mean 1 0 suggesting that carbonate precipitated in porewaters ranging from pure sea water to sea water diluted with meteoric water chemical analysis of porewaters showed no evidence of significant sulphate depletion at the depth of concretion formation some concretions have formed around fragments of wood or metal but others contain no apparent nucleus in field experiments siderite fes and mg calcite were precipitated around several different nuclei within a period of six months we suggest that siderite may form wherever the rate of iron reduction exceeds the rate of sulphate reduction such that insufficient dissolved sulphide is available to precipitate all the available dissolved ferrous iron

petrology and palaeoenvironmental significance of authigenic iron rich clays carbonates and apatite in the claiborne group middle eocene ne texas the claiborne group eocene in north east texas consists of clayey sandstones and mudrocks both with variable proportions of dark green to brown clay pellets deposited in a marginal to open marine setting on the gulf coast margin the composition of concretionary carbonate and clay pellets from 5 localities has been investigated using a wide variety of analytical techniques our palaeontological sedimentological c s and stable isotope data support an interpretation of marginal marine facies with limited freshwater input for the claiborne group dark green mature pellets are predominantly associated with transgressive bioturbated marine sediments from the weches formation through to the youngest crockett formation there is a trend from pellets composed mostly of dark green serpentine rich mixed layer clay to those of mostly brown immature nontronite rich mixed layer clay the serpentine is intermediate between odinite and berthierine and may have been originally odinite that has undergone partial transformation to berthierine pellet maturity apparently corresponds with the degree of winnowing and sedimentation rate it does not appear to correspond with global temperature fluctuations though the serpentine rich rather than glauconite rich composition may do siderite cement mostly in the form of concretions post dates the iron rich clay pellets and pre dates calcite cement carbonate and apatite concretions show a wide range of mineral cement textures reflecting variation in sedimentary environment and early diagenetic processes based on water temperatures derived from verneriacardia bivalves a precipitation temperature of 20 c is assumed for the concretionary siderite using this temperature we surmise that the siderite precipitated from marine pore waters with intermittent meteoric water mixing

early diagenesis and its relationship to depositional environment and relative sea level fluctuations upper cretaceous marshybank formation alberta and british columbia early diagenesis of the upper cretaceous late coniacian to early santonian marshybank formation was controlled by depositional environment composition of depositional water fe and organic content of the sediment sedimentation rate proximity to the shoreline and influx of meteoric water related to relative sea level fall five depositional environments each characterized by a distinct early diagenetic mineral assemblage have been recognized offshore shelf sediments that were deposited in a dysaerobic environment are characterized by abundant framboidal pyrite and rare septarian concretions composed of early calcite and siderite intense sulphate reduction promoted by the dysaerobic depositional water was the primary influence on early diagenesis offshore shelf sediments deposited under aerobic conditions are characterized by abundant concretions composed of two generations of siderite s1 and s2 in this environment methanogenesis rather than sulphate reduction was more important early diagenesis of the inner shelf sands was generally limited however in sands deposited proximal to the shoreline mixing of marine and meteoric waters promoted crystallization of fe rich chlorite and siderite the shoreface was characterized by dissolution of detrital minerals in the upper portion and precipitation of kaolinite or illite smectite in the lower portion in the coastal plain environment brackish water and early reducing conditions resulted in formation of abundant euhedral pyrite ankerite rather than siderite is the typical early diagenetic carbonate the 18o values of the earliest cements i e early calcite siderite s1 inner shelf siderite indicate crystallization from a low 18o marine derived porewater assuming crystallization at 25 c a 18o value of about 7 smow can be estimated for the seaway during marshybank formation time similar calculations for the overlying dowling member puskwaskau formation suggest that the 18o value of the seaway increased to about 4 smow consistent with its transgressive nature very low 18o values are exhibited by siderite s2 these results indicate crystallization during intermediate diagenesis 60 c from meteoric water 15 smow that entered the marshybank formation during sea level lowstand

a new geochemical classification of sedimentary environments because of the relative constancy of ph in most subaqueous sediments and the general lack of measurability of eh these parameters are not practically useful for classifying sedimentary environments in their place a new classification is offered which derived from studies of modern sediments is based on the presence or absence of dissolved oxygen and dissolved sulfide in the sediments at the time of authigenic mineral formation sedimentary environments are first of all divided into oxic and anoxic depending upon the presence or absence of measurable dissolved oxygen anoxic environments in turn are divided into sulfidic and non sulfidic depending upon the presence of measurable dissolved sulfide anoxic nonsulfidic environments are further divided into postoxic or resulting from oxygen removal without sulfate reduction weakly reducing and methanic or resulting from complete sulfate reduction with consequent methane formation strongly reducing the environments are shown to succeed one another during early diagenesis in the order oxic post oxic sulfidic methanic iron and manganese minerals characteristic and stable in each environment are listed and discussed so that they may be used to distinguish the environments when studying the ancient geological record

investigating the strength and trend of seismic anisotropy in the western part of makran subduction zone and southeast of iran abstract the makran subduction zone located in southeastern iran and southern pakistan extends approximately 900 km along the eurasian arabian plate boundary where the arabian oceanic plate subducts beneath the eurasian plate using broadband seismic data recorded in the western part of makran in the southeast of iran seismic anisotropy was studied to better understand geodynamic processes of this subduction zone we analyzed shear wave splitting of core refracted shear wave phases sks skks and pks recorded by 17 broadband stations located in the western makran and southeast of iran from 542 earthquakes mw 6 0 that occurred between 2004 and 2017 at epicentral distances between 90 145 few stations close to the trench line exhibit a trench oblique trend in the west to a trench prependicular trend to the east the magnitude of splitting delay times suggests a mantle source of anisotropy our findings show that the majority of the fast axes of seismic anisotropy at farthest stations in the backarc region are oriented in the nw se direction with delay times created by crust and mantle varying between 0 8 and 1 3 s the orientations of these fast directions are almost parallel to surface structural features for stations near the minab strike slip fault system the transition from the makran subduction zone to the zagros collision zone the fast directions are sub parallel to the strike of this fault system indicating that simple shear is likely the main source of anisotropy

geochemistry of early carbonate cements in the cardium formation central alberta abstract authigenic minerals and diagenetic textures in the marine conglomerates and sandstones of the cretaceous cardium formation in the northeast pembina area preserve a complex sequence of diagenetic events textural relationships observed in thin section and under the scanning electron microscope were used to determine the relative timing of diagenetic events in these marine sediments paragenetic sequences are similar for the conglomerate sandstone and siderite nodules in the enclosing shales extensive cementation by siderite and calcite occurred early in the diagenetic history before any significant compaction the geometry and distribution of lithofacies in the cardium may have influenced the diagenesis and internal stratigraphy of the conglomerate overlying shale matrix conglomerate may have trapped upward migrating fluids increased in buoyancy by dissolved co2 produced by decay of organic matter in the enclosing shales these fluids could have infiltrated the upper portion of open matrix conglomerate causing cementation petrographic evidence shows alternating precipitation of siderite and pyrite implying fluctuating activities of dissolved carbonate and hydrogen sulfide probably caused by bacterially mediated processes during early diagenesis early sequences of siderite and pyrite precipitation can be related to zones of iron reduction sulfate reduction and possibly decarboxylation during diagenesis carbon and oxygen isotopic data indicate a systematic change in the isotopic compositions of calcite and siderite from 25 to 3013c and 018o for cements early in the paragenetic sequence to 0 to 513c and 15 18o for cements which are interpreted to occur later in the paragenetic sequence this observation is consiste t with the influence of meteoric water on later stages of cement deposition in the cardium a unit considered to be marine and deposited well offshore on a shallow marine shelf the intrusion of meteoric water far offshore may be related to changes in sea level many variables must be accounted for but it is feasible using the estimated regional dip of the cardium at the time of deposition 0 005 for a 1 m drop in sea level to push the freshwater seawater interface seaward on the order of 100 km

oxygen and carbon isotopic composition of marine carbonate concretions an overview abstract compilation of stable isotope data 18o and 13c for marine calcite siderite and dolomite concretions from a large number of studies reveals consistent and unanticipated isotopic trends although many of the dolomites have 18o values that are compatible with precipitation from unaltered seawater at low temperatures most of the calcites and siderites are far too depleted in 12o for such an origin this is surprising as most of the concretions appear to have formed very early in the diagenetic history of the sediments often within several meters of the sediment water interface the most likely cause of the anomalously depleted oxygen values is a decrease in pore water 18o values during early diagenesis a result perhaps of a significant influx of meteoric water into the marine shelf environment or water mineral interaction e g precipitation of 18o enriched minerals the carbon isotopic field for dolomite is quite different from that for calcite and siderite highly positive 13c values are fairly common only for dolomites this indicates that while dolomite concretions often form in sediments where methanogenesis is rapid precipitation of calcite and siderite concretions is restricted to sediments where either n methanogenesis takes place or where methanogenesis is not extensive enough to generate highly positive pore fluid 13c values this variation in carbon isotopic composition among the different minerals suggests that the rates of organic carbon oxidation and sedimentation may control the mineralogy of carbonate concretions high organic carbon oxidation rates favor dolomite and lower oxidation rates favor calcite or siderite

evidence for a paleoaquifer from early diagenetic siderite of the cardium formation alberta canada abstract the sedimentology and stratigraphy of the cretaceous cardium formation are generally interpreted as indicating an offshore shallow marine shelf environment of deposition however geochemical and isotopic data suggest that porewater salinity varied widely during early diagenesis for much of the cardium in cases with little or no evidence of subaerial exposure of the sediments this apparent conflict can be resolved by postulating infiltration of early meteoric water into these nearshore sediments behind a mobile mixing zone infiltration of meteoric water and movement of the interface may have been possible during any phase of basin formation whether transgression regression or stillstand evidence for the presence of this paleoaquifer is found in data from the early diagenetic s derite cements of the raven river allomember and carrot creek member of the cardium formation

a numerical study of barotropic instability associated with the soya warm current in the sea of okhotsk abstract numerical model experiments have been carried out in an attempt to elucidate the generation mechanism of the eddy or wave street in the soya warm current we use a barotropic model incorporating bottom topography under realistic conditions the model produces waves whose properties are within range of the observed ones the generation mechanism of the waves proposed in this experiment is as follows when the current is driven by the mean water level difference between the japan sea and the sea of okhotsk the flow separates from the cape in the soya strait in the region of the flow separation strong positive vorticity is produced by the frictional torques occurring as the water flows through the strait and by vortex stretching as the water is pushed out to deeper depths this strong vorticity or horizontal shear induces barotropic instability in which the waves are generated in brief the system of the soya warm current accompanied by an eddy street is interpreted as a good geophysical ex

petrology and palaeoenvironmental significance of glaucony in the eocene succession at whitecliff bay hampshire basin uk following the investigations of odin and others into the distribution of green granules glaucony has been widely assumed to be a reliable indicator of a fully marine open shelf environment with a low sedimentation rate we have investigated the value of glaucony as a palaeoenvironmental indicator through an investigation of the pellets and their distribution and reworking in the predominantly brackish to shallow marine tertiary sediments of the hampshire basin together with a re evaluation of the sedimentology glaucony has apparently formed in situ in all lithofacies from shallow marine to estuarine of the three highest glaucony concentrations all dominated by in situ glaucony two occur within highstand system tracts the third is at a sequence boundary several important surfaces do not have more than a few percent glaucony with very variable proportions of mature and in situ pellets the correlation between glaucony concentration and sequence stratigraphy is most obvious in the london clay and wittering formations where least reworking of pellets has occurred in the barton group there are no major concentrations of glaucony at any of the important stratal surfaces we believe this more random glaucony distribution is due to limited glaucony formation and reworking of older glaucony in these sediments ideal conditions for glaucony formation are interpreted to have been fully marine 10 30 m water depth a warm temperature plus low sedimentation rate with periodic winnowing to concentrate the pellets although most of these conditions for glaucony formation occurred in the selsey formation and barton group a factor or factors mitigated against glauconitization we suggest that this was lowering of the water temperature the london clay and wittering formations were deposited relatively rapidly 50 60 m ma 1 and include intervals of estuarine sedimentation both factors that we believe inhibited glaucony formation glaucony maturity reflects the minimum length of time spent in surface sediments close to the oxic sub oxic interface point count data and chemical data for glaucony indicate widespread reworking and an overall increase in reworking with time possibly due to uplift on the isle of wight monocline the apparently wide range of conditions in which glaucony will form and the frequency with which it is reworked suggest that it is a less useful indicator palaeo environmental indicator than is commonly supposed

geochemistry of carbonate cements in the sag river and shublik formations triassic jurassic north slope alaska implications for the geochemical evolution of formation waters carbonate cements calcite siderite dolomite and ankerite formed throughout the diagenetic history of the sag river and shublik formations the trace element and isotopic geochemistry of these cements varies as a function of the timing of precipitation earliest calcites formed prior to significant compaction of the sediment are relatively enriched in mg up to 4 4 mol and have 87sr 86sr values mean 0 707898 compatible with the original marine pore waters later calcites are relatively fe rich up to 5 0 mol and are characterized by increasing 87sr 86sr values up to 0 712823 and sr content with decreasing age the fe content of zoned siderite and dolomite ankerite rhombs increases towards the outside of the rhombs i e increasing fe content with decreasing age these geochemical variations appear principally to result from changes in pore water chemistry during diagenesis the increase in 87sr 86 sr and sr content of the cements is most likely due to interaction between pore waters and 87 sr rich clay and possibly feldspar in ellesmerian mudrocks whole rock 87sr 86 sr signatures for the mudrocks are 0 716 pore water fe2 concentration was probably controlled by diagenetic alterations involving fe bearing minerals e g pyrite precipitation a reconnaissance examination of carbonate cements in the overlying kingak shale indicates that similar alterations occurred in the kingak the low 18 o value of some calcite cements 11 96 pdb suggests that an influx of meteoric water may have occurred in the mid neocomian though the low value could also result from an abnormally high geothermal gradient associated with mid neocomian rifting

the flow system in the japan sea caused by a sea level difference through shallow straits we investigate how the current system through the japan sea is driven and what determines the volume transport we suppose that a part of the difference in geopotential anomaly between the subtropical and subpolar gyre is converted into a barotropic sea level difference across the three shallow straits which connect the japan sea with the pacific and that this difference is the primary driving force of the current system then we examine the flow under the condition that there is a constant sea level difference between two oceans connected through a shallow strait we found that the strait acts as a source of arrested shelf waves or steady coastal flows for the timescale beyond the inertial period in the northern hemisphere steady flows are established along the shelves with the coast to the right left in the ocean of low high sea level we apply this notion to the current system through the japan sea the tsushima nearshore branch the tsugaru coastal mode and the soya current can all be interpreted as a coastally trapped flow whose source is the upstream strait further a series of northeastward flows along the south and east china seas shelves should be interpreted as coastally trapped flows whose source is the downstream tsushima strait numerical model experiments incorporating the realistic topography also simulate the observed flow fields the volume flux through each strait being limited geostrophically relations between the sea level difference and volume transport can be represented by simple formulas

spherulitic siderites in the holocene coastal deposits of korea eastern yellow sea elemental and isotopic composition and depositional environment abstract siderite concretions are recovered from both freshwater unit ii and tidal unit i deposits in the holocene macrotidal flat of kyunggi bay west coast of korea siderites from both units show a spherulitic and well rounded texture and well developed equant rhombs on the external surfaces the size of the concretions in unit ii 50 150 m in diameter is normally larger than that in unit i 10 20 m the siderites in unit ii are chemically pure and highly enriched in fe whereas those of unit i are relatively impure and distinctly zoned demarcating high mn up to 69 1 mol in the core and high fe up to 75 9 mol in the margin within siderites of unit i substitution for fe by ca and mg reaches up to 20 3 mol mean 15 1 mol and 16 1 mol mean 12 6 mol respectively bulk 18 o values 0 7 to 1 3 peedee belemnite pdb for siderites in unit i are relatively higher than those 7 1 to 0 5 pdb in unit ii regardless of units siderite 13 c values 21 3 to 11 2 pdb are persistently low indicating microbially mediated precipitation at shallow burial depth extensive mn ca and mg substitution coupled with enrichment of 18 o in the siderites of unit i seems to reflect marine influence during the holocene transgression the occurrence of early diagenetic siderites provides supporting evidence on the depositional environment marine vs non marine of the holocene muddy coastal deposits of korea eastern yellow sea

geochemistry of early siderite cements from the eocene succession of whitecliff bay hampshire basin u k abstract siderite cements in the eocene of whitecliff bay hampshire basin u k occur in a range of depositional facies and morphological associations most siderites are associated with in situ glaucony or occur beneath conspicuous lithological breaks these associations illustrate the importance of slow deposition for early diagenetic carbonate precipitation siderite in the eocene sediments of whitecliff bay is impure and in many cases comprises zoned crystals with an overall decrease in substitution of ca mg and mn for fe from crystal core to rim trends in ca mg and mn from early to later siderite vary between samples with no evident environmental control siderite concretions without calcite cement occur only beneath lithological breaks where meteoric water may have been introduced precipitation temperatures have been calculated from siderite 18o data and are based on the assumption that precipitation occurred from seawater these temperatures are reasonable for typical microbial siderite precipitated in marine sediment but are slightly low for marine siderite where there may have been meteoric overprinting if the precipitation temperature for siderite cements is assumed from 18o data for time equivalent biogenic carbonate rather than the composition of the precipitating fluid the calculated isotopic composition of the precipitating fluid is generally compatible with the inferred marginal marine depositional environments

isotopically heavy oxygen containing siderite derived from the decomposition of methane hydrate authigenic siderite from the miocene and pliocene sediments of the blake outer ridge formed in a methane fermentation zone in equilibrium with anomalously heavy oxygen water as evidenced by its heavy carbon 1 6 to 12 5 13c and heavy oxygen 0 1 to 7 9 18o values blake outer ridge sediments are impregnated with methane hydrate which is generally enriched in 18o relative to ambient water this suggests that decomposition of methane hydrate and subsequent release of large amounts of methane and heavy oxygen water affected the formation of the 18o enriched siderite gas hydrate reaction in sediments is an important process for causing a dramatic variation of oxygen isotopic composition of the interstitial water and of authigenic carbonates formed during burial diagenesis

distribution and formation of okhotsk sea intermediate water an analysis of isopycnal climatological data 1 in order to clarify the distribution and formation of okhotsk sea intermediate water osiw an isopycnal climatological data set based on all of the available historical observations is developed and examined the isopycnal maps clearly show that there are two direct ventilation sources for osiw dense shelf water dsw with cold and fresh properties influenced by sea ice formation in the northwest shelf region and forerunner of soya warm current water fscw which has warm and saline properties originating in the japan sea the cold and fresh water extends southward from the northwest shelf to the shelf slope off sakhalin island it suggests that dsw is transported southward by the east sakhalin current the dsw enters the kuril basin and mixes with fscw and western subarctic water wsaw originating from the north pacific to form osiw the annual mean production rate of dsw estimated from the total volume of dsw over the shelf in spring and summer is 0 67 sv 1 sv 106 m3 s the annual mean volume transport of fscw is estimated to be 0 08 sv on the basis of its cross section area and the current speed assumption of isopycnal mixing yields a mixing ratio of 1 1 0 1 among dsw wsaw and fscw to form osiw we estimate the annual production rate of osiw to be 1 4 sv the corresponding osiw s renewal time is 7 years continued assumption of isopycnal mixing yields a mixing ratio of 0 6 0 4 between wsaw and osiw to form oyashio intermediate water oyiw

microbial influence on the oxygen isotopic composition of diagenetic siderite abstract numerous early diagenetic siderite concretions previously described have been interpreted as the results of microbially mediated reactions interpretation of oxygen isotope data for such material requires an understanding of the effect of temperature on fractionation processes however whilst equilibrium fractionation of oxygen isotopes between siderite and water has been measured down to 33 c extrapolation to lower temperatures may be invalid furthermore inorganic measurements may not be applicable to microbial systems the specific iron reducing microorganism geobacter metallireducens has been cultured anaerobically in the laboratory using acetate as an organic substrate and amorphous feooh as an electron acceptor the acetate is oxidised to co2 with concurrent iron reduction and extracellular siderite precipitation rhombohedral siderite crystals up to 25 m in size have been precipitated over a range of temperatures 18 40 c stable isotopic analysis of these crystals and the solutions from which they precipitate shows that this microbial precipitation of siderite has an associated isotopic fractionation different from the published equilibrium and which is not simply a function of temperature in all cases 18o values of siderite are lower than predicted by inorganic equilibrium fractionation data this may explain the numerous anomalously low 18o values reported for early diagenetic marine siderites and previously attributed to mechanisms such as mixing with meteoric water sediment water interaction recrystallisation or variable isotopic fractionation despite a lack of supporting evidence

winter and summer temperatures of the early middle eocene of france from turritella δ18o profiles the mean annual range of temperature is from a climatological point of view at least as important as the mean annual temperature in order to examine intra annual temperature variations in the warm early cenozoic we have analyzed stable oxygen and carbon isotopes along the transect of growth on excellently preserved specimens of the gastropod turritella imbricataria and the bivalve venericardia imbricata from sedimentary rocks of early middle eocene age ca 46 ma in the paris basin turritella shell growth is fast throughout the year and the isotopic records give the first detailed information about early middle eocene seasonal variations the oxygen isotope profiles indicate winter temperatures of about 14 c and summer temperatures of up to 28 c i e a seasonality indistinguishable from the present situation but an annual temperature some 10 c higher our results contradict the opinion that the climate during this period was more equable than that of today