sedimentary pyrite formation an update sedimentary pyrite formation during early diagenesis is a major process for controlling the oxygen level of the atmosphere and the sulfate concentration in seawater over geologic time the amount of pyrite that may form in a sediment is limited by the rates of supply of decomposable organic matter dissolved sulfate and reactive detrital iron minerals organic matter appears to be the major control on pyrite formation in normal non euxinic terrigenous marine sediments where dissolved sulfate and iron minerals are abundant by contrast pyrite formation in non marine freshwater sediments is severely limited by low concentrations of sulfate and this characteristic can be used to distinguish ancient organic rich fresh water shales from marine shales under marine euxinic conditions sufficient h2s is produced that the dominant control on pyrite formation is the availability of reactive iron minerals calculations based on a sulfur isotope model indicate that over phanerozoic time the worldwide average organic carbon to pyrite sulfur ratio of sedimentary rocks has varied considerably high cs ratios during permo carboniferous time can be explained by a shift of major organic deposition from the oceans to the land which resulted in the formation of vast coal swamps at that time low cs ratios compared to today during the early paleozoic can be explained in terms of a greater abundance of euxinic basins combined with deposition of a more reactive type of organic matter in the remaining oxygenated portions of the ocean the latter could have been due to lower oceanic oxygen levels and or a lack of transportation of refractory terrestrial organic matter to the marine environment due to the absence of vascular land plants at that time

relationships between sulphur organic carbon and iron in the modern sediments of the black sea abstract the ratio of sedimentary s to organic c has been used as a diagnostic criterion for recognizing anoxic environments in the sedimentary record here we examine the relationship between pyrite s and organic c in the modern unit 1 sediments of the black sea to re evaluate this suggested relationship in box cores from shallow oxic or near oxic water pyrite s contents ranging from 0 1 and 2 5 by weight do not correlate with organic c contents in cores from the deep anoxic basin pyrite s concentrations range between 1 0 and 2 5 and are linearly related to organic c contents with an intercept that is not significantly different from zero the s c ratio is around 0 31 in these sediments which is somewhat lower than the ratio of 0 36 considered to be characteristic of normal marine oxic sediments thus the black sea anoxic sediments appear to be depleted in s relative to organic c the degree of pyritization dop of the sediments may be a better measure of anoxic conditions of sedimentation the dop values measured here show that pyrite formation is fe limited the correlation between organic c and pyrite s probably being induced by a positive correlation between fine grained sediment components the original fe source for pyrite formation in the sediments and organic matter such fe limitation is probably characteristic of anoxic basins where pyrite formation can take place in the water column and fe oxyhydroxides do not accumulate in the surface sediments the results on the sample set examined here are at variance with earlier data and interpretations for the black sea in particular the suggested s enrichment of anoxic black sea sediments was not found because of fe limitation

distribution and isotopic composition of sulfur in lake sediments of northern ontario sediments from unpolluted and highly polluted lakes in northern ontario have been fractionated into acid volatile sulfide hcl soluble sulfur elemental sulfur pyrite sulfur ester sulfate and carbon bonded sulfur and the isotopic composition of each fraction determined in general reduced inorganic s constitutes 25 50 of the total s in the polluted surficial sediments but is 20 in the unpolluted samples with pyrite formation being a minor process of s diagenesis in lake sediment ecosystems organic s in the form of ester sulfate and carbon bonded s predominates and both the c s ratios and the isotopic data suggest that in unpolluted lakes plant detritus can be a major contributor of organic s to the sediments the depth profiles observed suggest that the more labile ester sulfate is diagenetically converted to the carbon bonded form for the polluted sediments from the sudbury basin the isotopic data suggest that a the elemental s is derived from the oxidation of acid volatile sulfide in the aerobic surficial sediments and b the isotopically light reduced s species are incorporated into the organic material s diagenesis in lake sediments generally results in the release of 34s to the overlying water the suggestion is made that sulfate concentrations over 5 mg 1 accompanied by an enrichment of surficial sediments with isotopically different s may signal significant inputs of pollutant s into the lake and its basin

chemical and physical responses to deformation in micaceous quartzites from the tauern window eastern alps micaceous quartzites from a subvertical shear zone in the tauern window contain abundant quartz clasts derived from dismembered quartz tourmaline veins bulk plane strain deformation affected these rocks at amphibolite facies conditions shape changes suggest net shortening of the clasts by 11 64 with a mean value of 35 quartz within the clasts accommodated this strain largely via dislocation creep processes on the high stress flanks of the clasts however quartz was removed via solution mass transfer pressure solution processes the resulting change in bulk composition allowed growth of porphyro blastic staurolite chlorite kyanite on the clast flanks matrix sio2 contents decrease from c 83 wt away from the clasts to 49 58 in the selvages on the clast flanks the chemical changes are consistent with c 70 volume loss in the high stress zones calculated shortening values within the clast flanks are similar to the volume loss estimates and are greatly in excess of the shortening values calculated from the clasts themselves flow laws for dislocation creep versus pressure solution imply large strain rate gradients and or differential stress gradients between the matrix and the clast selvages in a rock containing a large proportion of semirigid clasts weakening within the clast flanks could dominate rock rheology in our samples however weakening within the selvages was self limiting 1 growth of strong staurolite porphyroblasts in the selvages protected remaining quartz from dissolution and 2 overall flattening of the quartz clasts probably decreased the resolved shear stress on the flanks to values near those of the matrix which would have reduced the driving force for solution transfer creep extreme chemical changes nonetheless occurred over short distances the necessity of maintaining strain compatibility may lead to significant localized dissolution in rocks containing rheologic heterogeneities and overall weakening of the rocks may result solution transfer creep may be a major process whereby weakening and strain localization occur during deep crustal metamorphism of polymineralic rocks

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

hydraulics morphology and energy dissipation in an alpine step pool channel 1 to investigate the relationship between hydraulics and channel morphology in step pool channels we combined three dimensional velocity measurements with an acoustic doppler velocimeter and topographic surveys in a steep step pool channel the rio cordon italy measurements were organized around step pool and tread units and occurred within a range of 36 57 of bankfull discharges as flow moved from steps to their downstream pools in our study reach an average of approximately two thirds of the total energy was dissipated as measured by relative head loss through step pool sequences much of this head loss was achieved by elevation potential energy loss rather than velocity reductions although an overall expected pattern of flow acceleration toward step crests and deceleration in pools was present pool velocities were high especially where upstream step crests were irregular and where residual pool depths were low many steps were porous or leaky with irregular cross channel bed and water surface topography producing high velocity jets and less flow resistance than channel spanning dammed steps longitudinal variations in hydraulics are thus often overshadowed by lateral variations arising from morphologic complexities velocity and turbulence characteristics in the rio cordon show marked differences from data we have collected in a more stable and wood rich channel in the colorado rockies in which ponded steps are more prevalent and pools are slower and more turbulent comparison of these channels illustrates that step pool structure and hydraulics are strongly influenced by flow regime sediment supply lithology time since the last step forming flood and availability of in stream wood

crystal chemical characterization of tourmalines from the english lake district electron microprobe analyses and mossbauer spectroscopy electron microprobe analyses empa and mossbauer spectra ms have been acquired for natural tourmalines sampled near crummock water and haweswater english lake district in the former the dravite schorl series is prevalent whereas in the latter the dravite species is dominant all tourmaline samples presently studied are chemically disordered the compositional and ms data give an insight into the thermal and fluid evolution experienced by the tourmalinite rocks the tourmalines from crummock water crystallized in a closed low f o 2 environment under the influence of a magmatic fluid the tourmalines from haweswater are of hydrothermal origin and were formed under low variable t and low f o 2 conditions from a fluid of constant composition

scheelite apatite calcite and tourmaline compositions from the late archean hutti orogenic gold deposit implications for analogous two stage ore fluids abstract gold mineralization at hutti southern india has occurred in two stages stage 1 mineral assemblage comprises biotite chlorite plagioclase calcite epidote actinolite tourmaline arsenopyrite pyrite pyrrhotite and gold whereas the stage 2 mineral assemblage is represented by sericite chlorite calcite scheelite tourmaline apatite titanite pyrrhotite arsenopyrite and gold we report here the occurrence of scheelite from the stage 1 assemblage and compare major and trace element compositions of scheelite fluorapatite f 4 wt calcite and tourmaline from the two stages with an emphasis on the second stage in which they are best represented scheelite displays three types of ree patterns these are the type i middle ree mree enriched with negative eu anomaly type ii heavy ree hree enriched with minor positive negative eu anomaly and type iii that varies from slightly mree enriched to mree depleted with correspondingly increasing positive eu anomaly the stage 1 scheelites display type i pattern while stage 2 scheelites display type ii and type iii patterns textural and compositional evidence suggest asynchronous precipitation of scheelite fluorapatite and calcite in the stage 2 mineralization indicating precipitation from cyclic fluid flow the occurrence of rare minute scheelite grains in the stage 1 mineralization assemblage is most likely because of prevalent high temperature 350 477 c whereas during the stage 2 mineralization abundant scheelite precipitation evidenced by the presence of scheelite rich carbonate quartz veins was favored by the decrease in temperature 300 c additionally repeated fluid pressure fluctuations due to fault valve mechanism would have further enhanced precipitation of scheelite in stage 2 the fewer scheelites in stage 1 mineralization resulted in their mree enriched pattern with high ree the mree depleted patterns of stage 2 scheelites on the other hand do not necessarily indicate a compositionally different fluid but are due to rapid removal of mree in early formed mree enriched scheelites making them less and less available in the fluid for later crystallizing scheelites this is supported by the observation that except for the slight remobilization of lree the rees are conserved in the altered rocks trace element ratios y ho zr hf nb ta in fluorapatite and calcite are chondritic indicating little fractionation of these element pairs and cannot be diagnostic of fluid composition tourmalines from both the stages record equally low contents of na liles and hfses and comparably low fe 3 fe 2 ratios suggesting very similar nature of the two fluids which were low in salinity trace element poor and reducing in nature indicating a metamorphic parentage

jet and hydraulic jump near bed stresses below a horseshoe waterfall 1 horseshoe waterfalls are a common but unexplained feature of bedrock rivers as a step toward understanding their geomorphology a six component force torque sensor was used to evaluate clear water scour mechanisms in a 0 91 m broad crested horseshoe waterfall built into a 2 75 m wide flume to measure longitudinal lateral and temporal profiles of the near bed spatially averaged stress vector jet impact caused moderate near bed stress downstream of the impact point the stress vector shifted into a much more forceful upthrust with peak stress beyond the boil crest instantaneous fluctuations in near bed lift exceeded drag by 5 10 times and occurred over a wider range of frequencies suggesting a larger role for particle entrainment predictions of bed stress significantly underestimated actual conditions these results show that horseshoe waterfalls have an extended region of high scour along their centerline corresponding with the three dimensional convergent dynamics associated with both jet impact and jump enhanced lift fluctuations

boron isotopic constraints on the petrogenesis of hematitic phyllite in the southern serra do espinhaco minas gerais brazil abstract metasiliciclastic rocks predominate in the lower units of the palaeo mesoproterozoic espinhaco supergroup in the southern serra do espinhaco minas gerais brazil the lower units also comprise rocks with locally preserved igneous fabrics but which have very unusual chemistries these rocks collectively known as hematitic phyllite are characterised by abundant fine grained muscovite i e sericite and variable amounts of titaniferous hematite rutile and tourmaline currently the hematitic phyllite has been interpreted as a metamorphosed palaeosol after basaltic rocks and as such has been used as a palaeoclimatic indicator however the lateritic nature of the hematitic phyllite cannot unambiguously be determined because of the k metasomatism hematitisation and tourmalinisation recorded in the hematitic phyllite and in the arenaceous country rocks here we report the b isotopic and chemical compositions of tourmaline from the hematitic phyllite our 11b data are in the range between 15 and 4 the tourmaline compositions fall along the povondraite oxy dravite join which defines a meta evaporitic tourmaline trend a meta evaporitic b source is constrained by the b isotopic data as non marine our model for the hematitic phyllite suggests that b and k rich brines were derived from the metamorphic dewatering of non marine evaporites such brines extensively altered volcanic rocks of basaltic and rhyolitic compositions leading to tourmaline bearing hematite sericite assemblages of the hematitic phyllite

a rare garnet tourmaline sillimanite biotite ilmenite quartz assemblage from the granulite facies region of south central massachusetts a rare lithology consisting of garnet tourmaline sillimanite biotite ilmenite quartz has been found within the granulite facies region of south central massachusetts the homogeneous ti rich oxy dravitic tourmaline x mg mg mg fe 0 72 0 77 falls into the alkali group and is similar in composition to lower grade tourmaline found in corresponding metapelitic rocks in maine charge balancing calculations and binary diagrams suggest that like biotite in the region tourmaline has undergone deprotonation by means of the exchange vectors alor 1 oh 1 and tio 2 r 1 oh 2 where r represents fe mg the restriction of a concordant tourmaline rich horizon in otherwise tourmaline free rocks of this granulite facies region suggests that either 1 b released during prograde fluid absent dehydration reactions of muscovite and biotite was locally available in a fluid phase or melt for later crystallization near the peak of granulite facies metamorphism along pathways that provided a conduit for fluid migration or 2 that this is simply a b rich compositional horizon tourmalinite that survived anatexis and granulite facies metamorphism and that records the incipient conditions of tourmaline breakdown and subsequent recrystallization near or post peak metamorphism

biogeochemical cycling in an organic rich coastal marine basin 8 a sulfur isotopic budget balanced by differential diffusion across the sediment water interface abstract the sulfur isotopic composition of the sulfur fluxes occurring in the anoxic marine sediments of cape lookout bight n c u s a was determined and the result of isotopic mass balance was obtained via the differential diffusion model seasonal pore water sulfate 34 s measurements yielded a calculated sulfate input of 0 6 sulfate transported into the sediments via diffusion appeared to be enriched in the lighter isotope because its concentration gradient was steeper due to the increase in the measured isotopic composition of sulfate with depth similarly the back diffusion of dissolved sulfide towards the sediment water interface appeared enriched in the heavier isotope the isotopic composition of this flux was calculated from measurements of the 34 s of dissolved sulfide and was determined to be 15 9 the isotopic composition of buried sulfide was determined to be 5 2 and the detrital sulfur input was estimated to be 6 2 an isotope mass balance equation based upon the fluxes at the sediment water interface successfully predicted the isotopic composition of the buried sulfur flux within 0 5 thus confirming that isotopes diffuse in response to their individual concentration gradients

a stable isotope study of pyrite formation in the late pleistocene and holocene sediments of the black sea the abundance and isotopic composition of total and pyrite sulphur have been determined in a core in the central black sea pyrite varies in concentration from roughly 2 wt in the sapropel unit 2 to 0 8 wt in the modern horizon unit 1 and ca 0 1 wt in the lowermost horizons of unit 3 lake beds an intermediate mud flow horizon and the upper part of the lake beds have similar values to those in the modern sediments the degree of pyritization dop is lowest 0 05 in the lower lake beds and highest 0 55 in unit 1 the sapropel has values of ca 0 48 34spyrite varies from a minimum of 37 in the sapropel to 33 in unit 1 up to 15 in the upper lake beds and 0 in the lower lake beds the unit 1 and sapropel values are similar to the 34s values reported by fry et al 1991 of dissolved sulphide immediately below the water column oxic anoxic interface 36 to 38 but significantly heavier than those in the deep waters of the basin ca 41 these results are interpreted as a reflection of the presence of four different types of pyrite in the sediments of the black sea 1 pyrite in units 1 and 2 that is formed within the upper part of the water column immediately below the oxic anoxic interface where 34s of dissolved sulphide is 36 2 pyrite in the mud flow layer lying between unit 1 and the sapropel unit 2 with a significantly heavier isotopic composition that was formed around the margins of the basin under conditions that were probably more closed with respect to dissolved sulphate than those in which the pyrite in units 1 and 2 were formed 3 pyrite in the upper part of the lake beds unit 3 that was formed under closed system conditions by reaction between excess reducible fe remaining in these freshwater sediments and downward diffusing sulphate and or sulphide from the overlying organic rich sapropel and 4 pyrite in the lower part of the unit 3 representing a phase formed from the ambient sulphate in the freshwaters of the late pleistocene lake the isotopic information supports earlier suggestions that pyrite in the modern sediments of the black sea forms mainly in the water column with only minor amounts forming in the sediment because of the severe fe limitation of the bottom sediments that accumulate 2 000 m below the main fe and hs reaction zone at the oxic anoxic interface at shallow depths in the water column

organic rich transitional facies in silled basins response to sea level change high resolution profiles of organic carbon delta sup 13 c sub org sulfur delta sup 38 s and some trace elements in cores from two silled basins kau bay indonesia and the black sea allow division of the sedimentary record into three distinct units representing a pleistocene fresh water brackish water facies unit 3 a holocene transitional facies unit 2 and a modern fully marine facies unit 1 the geochemical characteristics of these units are strikingly similar for both basins the sediments form unit 3 are characterized by the predominance of terrestrial organic matter mo and u concentrations at crustal abundance and positive delta sup 34 s values the transitional sediments unit 2 are strongly enriched in marine organic matter and mo v and u and have intermediate delta sup 34 s values sediments from the modern marine facies unit 1 are moderately organic carbon rich and slightly enriched in mo and u and have negative delta sup 34 s values the organic carbon rich sediments from unit 2 were formed by increased production during the transition from the pleistocene isolated fresh water brackish water environment to the modern open marine facies this temporarily higher productivity was caused by displacement of nutrients from the deep water into the euphotic zone owing to the gradual infilling by marine waters

carbon sulfur iron systematics of the uppermost deep water sediments of the black sea box cores recovered during leg 4 of the 1988 r v knorr black sea oceanographic expedition from deep water regions of the basin were dominated by coccolith rich microlaminated unit 1 sediment and muddy gray turbidite layers both organic carbon oc and pyrite sulfur values for unit 1 display narrow ranges with mean concentrations of 5 3 1 1 1 wt and 1 3 0 3 wt respectively unit 1 is not enriched in pyrite s relative to sediments deposited under oxygenated bottom waters normal marine sediments with comparable oc concentrations carbon sulfur relationships evaluated on a calcium carbonate free basis to avoid spurious correlations resulting from dilution effects demonstrate that oc and pyrite s are essentially decoupled these observations combined with the persistence of elevated pore water sulfide to depth and a strong correlation between pyrite s and the detrital fe component argue strongly for limitation of pyrite formation in unit 1 by the availability of reactive fe unit 1 fe limitation is further indicated by degree of pyritization dop studies a measure of the extent to which the original potentially reactive fe has been transformed to pyrite these studies show sulfidation of reactive fe ranging from 57 to 78 with dop values independent of oc concentration unit 1 dop profiles suggest that the majority of the pyrite is formed in the sulfidic water column and or very close to the sediment water interface pyrite s concentrations of unit 1 when compared with the particulate reduced sulfur fluxes measured in time series sediment traps are compatible with predominantly water column pyrite formation because of the limitations in the supply of reactive fe associated with the comparatively high supply of oc the microlaminated sediment is characterized by c s ratios greater than those typical of holocene oxically deposited sediments the turbidite muds of the deep basin display high reduced s values relative to holocene normal marine sediments in samples with low oc concentrations low c s ratios this reflects pyrite formation under anoxic sulfidic bottom water conditions in a probable upper slope source region as well as during transport and final deposition intermediate dop values for the turbidites in part a product of their rapid rate of deposition reveal that fe limitation is ultimately not a factor and that further pyrite should form during burial however the very rapid rate at which unit 1 pyrite forms suggests fundamental differences between the overall reactivities of the fe phases associated with the microlaminated and turbiditic sediments the signature of water column anoxia with regard to sedimentary pyrite formation is clearly indicated by the high dop values of unit 1 and the comparatively high levels of s associated with the low concentrations of oc of the turbidite muds this agrees with similar conclusions based on studies of ancient sedimentary rocks

compositional asymmetry in replacement tourmaline an example from the tauern window eastern alps tourmaline partially replacing pre existing tourmaline from a tectonically dismembered tourmalinite vein has developed distinctive compositional asymmetry that reflects influx of reactive fluids the tourmalinite clast enclosed in a quartzite from the tauern window eastern alps experienced a clockwise p t t path with maximal burial depths of 35 40 km 10 11 kbar peak temperatures of 550 c and major deformation preceding peak thermal conditions the primary tourmaline of the tourmalinite clast generation 1 is texturally and compositionally heterogeneous ranging from schorl to dravite mg mg fe 0 27 0 61 with highly variable al consistent with combinations of the x oal nar 1 and alo r oh 1 exchange vectors where x o represents x site vacancy and r is fe 2 mn mg generation 2 tourmaline is manifest as distinctive compositionally asymmetric bands of colorless foitite zone 1 and blue schorl zone 2 replacing generation 1 tourmaline replacement takes place along a scalloped margin and advances preferentially towards the analogous pole c of generation 1 tourmaline the two zones of generation 2 range from foitite to schorl with a restricted ratio of mg mg fe of 0 32 0 41 but with variable x o al na and r predominantly reflecting x oal nar 1 post deformational generation 3 tourmaline ranges from schorl to foitite and partially pseudomorphs generations 1 and generations 2 tourmaline deformation and fracturing of primary tourmaline generation 1 from the tourmalinite clast provided access to reactive fluids with adequate chemical affinity to produce partial tourmaline replacement it is likely that the reactive fluid was a neutral to alkaline aqueous fluid phase with relatively low na contents

tourmaline as a petrogenetic indicator in the pfitsch formation western tauern window eastern alps abstract tourmaline is a common accessory mineral in the metasedimentary pfitsch formation located in the pfitscher joch passo de vizze area in the tauern window of the eastern alps these post variscan metasedimentary units experienced peak metamorphic conditions of 550 c 1 0 gpa during the alpine orogeny tourmaline is most abundant in a 25 m thick unit of feldspathic gneiss 20 200 g g b where it occurs as idiomorphic crystals typically 10 mm in length the abundance and size of the tourmaline crystals increase near coarse grained quartzofeldspathic segregations 1200 g g b reflecting the mobilization and concentration of b by metamorphic fluids near segregations individual tourmaline crystals have up to three growth zones recording pro 350 500 c 0 7 1 0 gpa and retrograde 400 c 0 2 gpa growth as determined by combining textural information and sector zoning thermometry retrograde tourmaline occurs as individual crystals as well as overgrowths on prograde tourmaline crystals especially on the surface of extensional fractures formed by e w extension during regional decompression tourmaline in the pfitsch formation is dravitic with a variable fe content that correlates with the fe content of its respective host unit charge balance calculations suggest that a significant proportion of fe in tourmaline is ferric supporting the interpretation of a subaerial continental sedimentary protolith tourmaline near segregations has the highest inferred ferric iron content which decreases across growth zones potentially reflecting a reduction of the fluid during metamorphism the mg mg fe ratio increases with prograde tourmaline growth and decreases in retrograde overgrowths in contrast the ca ca na ratio increases gradually from 0 05 to 0 20 with prograde growth and continues to increase up to 0 25 in the retrograde overgrowths recording the maximum ca ca na ratio of the fluid during alpine metamorphism the metasediments of the pfitsch formation have very low and variable whole rock 11 b values 14 1 to 33 6 with the highest values 17 7 to 14 1 found in b rich samples 165 1200 g g b containing abundant tourmaline and the lowest values 24 2 to 33 6 in b depleted samples 21 40 g g which lack tourmaline this observation supports preferential loss of 11 b from the rocks during prograde metamorphism zoned tourmaline crystals in the pfitsch formation show successively decreasing b isotope ratios from 7 8 to 11 2 in their cores and 17 3 to 20 3 in their rims as supported by a rayleigh fractionation model the b isotope values of the host rocks and the tourmaline crystals are most easily explained by the internal redistribution of b from a b rich precursor mineral e g mica to the tourmaline during alpine metamorphism

organic carbon sulphur and iron in recent semi euxinic sediments of kau bay indonesia kau bay island of halmahera eastern indonesia is a 470 m deep basin separated from the pacific ocean by a sill that is at present only 40 m below sea level during weichselian time the sea level dropped below the depth of the sill and freshwater sediments were deposited these sediments are rich in organic matter corg 2 6 wt with terrigenous isotope characteristics 13corg 28 to 30 and are also rich in sulphur s 4 wt this sulphur enrichment is interpreted to be a late diagenetic feature related to diffusion of dissolved sulphate and sulphide from the marine sediments into the freshwater sediments the sulphur in these sediments has a 34s value of 15 the overlying holocene sediments consist of marine muds deposited in alternating low oxygen and h2s bearing bottom waters the marine sediments are also rich in organic matter corg 2 6 wt but of mixed terrigenous and marine origin 13c 25 to 19 moreover the sulphur content of these holocene sediments is lower s 1 2 wt and isotopically lighter 34s 20 in addition to pyrite large amounts of acid volatile sulphur avs compounds accumulate in kau bay the reactive iron content of the sediment limits the amount of iron that is sulphidized while the supply of oxidants controls the limited conversion of avs to pyrite total and reactive iron contents are strongly correlated with the amount of terrigenous organic matter as a consequence of their common provenance and depositional histories the marine sediments in kau bay show no simple relation between organic carbon and sulphur

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

a study of sulphur enrichment in the humic fraction of marine sediments during early diagenesis abstract the evolution of the sulphur content of humic acids extracted from a near shore sediment core was investigated special attention was taken to avoid s contamination of the humic materials during extraction the s c ratios increased continuously with depth to values which strongly suggest s addition to the humic matrix during early diagenesis by reactions between organic matter and h2s or its oxidation products their light isotopic composition supports this view however subsequent isotopic exchange has obscured the mechanism initially involved since a large fraction of the enrichment occurred above the sulphidic zone redox boundaries such as the interface of anoxic microniches within more oxidized zones or the sulphidic suboxic boundary of the sediment column must have been important sites for s addition bioturbation by increasing the contact between sedimentary zones of a different redox regime will likely enhance such processes

transition from hydraulic jump to open channel flow this technical note presents the results of a laboratory study of the transition region from the end of a hydraulic jump to fully developed open channel flow the velocity profile changes from that of a wall jet to the semilogarithmic form of open channel flow in this region the bed shear stress continues to decrease rapidly to eventually become constant the intensity of flow on the centerplane decreases continuously to attain the relevant open channel value the length of this transition region was found to be approximately equal to 10 times the tailwater depth for the range of froude numbers studied which varied from 3 87 to 10 48