geochemical and isotopic evidence for paleoredox conditions during deposition of the devonian mississippian new albany shale southern indiana the upper part of the new albany shale is divided into three members in ascending order these are 1 the morgan trail member a laminated brownish black shale 2 the camp run member an interbedded brownish black and greenish gray shale and 3 the clegg creek member also a laminated brownish black shale the morgan trail and camp run members contain 5 to 6 total organic carbon toc and 2 sulfide sulfur isotopic composition of sulfide in these members ranges from 5 0 to 20 0 c s plots indicate linear relationships between abundances of these elements with a zero intercept characteristic of sediments deposited in a non euxinic marine environment formation of diagenetic pyrite was carbon limited in these members the clegg creek member contains 10 to 15 toc and 2 to 6 sulfide sulfur isotopic compositions of sulfide range from 5 0 to 40 the most negative values occur in the uppermost clegg creek member and are characteristic of syngenetic pyrite formed within an anoxic water column abundances of carbon and sulfur are greater and uncorrelated in this member consistent with deposition in as euxinic environment in addition dop degree of pyritization values suggest that formation of pyrite was generally iron limited throughout clegg creek deposition but sulfur isotopes indicate that syngenetic water column pyrite becomes an important component in the sediment only in the upper part of the member at the top of the clegg creek member a zone of phosphate nodules and trace metal enrichment coincides with maximal toc values during euxinic deposition phosphate and trace metals accumulated below the chemocline because of limited vertical circulation in the water column increased productivity would have resulted in an increased flux of particulate organic matter to the sediment providing an effective sink for trace metals in the water column phosphate and trace metals released from organic matter during early diagenesis resulted in precipitation of metal rich phosphate nodules

geochemistry of sediments from the connection between the western and the eastern mediterranean sea strait of sicily odp site 963 abstract a geochemical and stable isotope geochemical study was carried out on sediments and pore waters from the strait of sicily at the connection between the western and the eastern mediterranean sea odp site 963 organic matter rich layers orls which are proposed to be time equivalent to eastern mediterranean sapropels only occur in sediments older than 550 kyr most likely because of a strong dilution of late pleistocene and holocene sediments by terrigenous material the orls have total organic carbon toc contents of up to 1 6 and are enriched in pyrite and trace metals toc pyrite ratios indicate the at least temporary presence of an anoxic water column during sediment formation which is in agreement with the observed sulfur isotope discrimination these conditions induced the enrichment in sulfide forming and redox sensitive trace elements trace metal enrichment is lower than at other sites in the mediterranean sea which may be attributed to a less reducing or a less stable anoxic environment that was less favorable for the accumulation of redox sensitive trace elements and organic matter however during sapropel events sedimentary conditions in the strait of sicily based on manganese and barium geochemistry must have been largely similar to those at other sites in the mediterranean sea according to elemental rock eval and stable carbon isotope analyses the organic matter in the orls is mainly of marine origin which appears to have been overprinted significantly during diagenesis a significant part of the organic matter in sediments from odp site 963 may also originate from uplifted land sections eroded during weathering and may primarily also be of marine origin the results of pore water analyses illustrate the presence of an active deep biosphere in the sediments of site 963 reflected for example by sulfate methane and iodine concentrations a brine probably originating from underlying messinian evaporites was detected but is only of minor influence

lack of evidence for enhanced preservation of sedimentary organic matter in the oxygen minimum of the gulf of california a test of the hypothesis that hydrogen rich organic matter accumulates preferentially in sediments under oxygen minima has been carried out by examining the composition of laminated and homogeneous diatomaceous sediments of the guaymas basin in the gulf of california the laminated sediments occur where an intense oxygen minimum intersects the slope around the margins of the basin above and below the depth of the oxygen minimum the sediments are homogenized by a burrowing infauna the two sediment types have very similar bulk chemical and mineral compositions and the organic matter is overwhelmingly marine the total organic carbon contents and rock eval parameters hydrogen and oxygen indices of the two sediment types are not significantly different whereas a road organic carbon maximum in the homogeneous sediments is centered at roughly 1200 m depth on the slope of the basin this maximum lies deeper than the core of the oxygen minimum thus both the concentration and the nature of the organic matter in the sediments of this highly productive marginal marine basin are not related to the concentration of dissolved oxygen in the bottom waters

sedimentary nitrogen isotopic ratio as a recorder for surface ocean nitrate utilization in two contrasting regions of the ocean the equatorial pacific and the southern ocean the 15n of core top sediments were strongly related to no3 in surface waters with distance from the equator in the equatorial pacific 15n increased from 7 to 16 as no3 decreased from 8 m to 0 1 m going from 60 to 30 s in the se indian ocean core top 15n increased from 5 to 11 as surface no3 decreased from 25 m to 0 1 m these results are strong evidence that sedimentary 15n in these regions is recording the increasing isotopic enrichment of near surface no3 with its depletion by phytoplankton in the case of the equatorial pacific 15n values for sinking particles collected at 150 m matched well the core top sediment values demonstrating little diagenetic alteration of the near surface generated isotopic signal these equatorial pacific data sets have variations with near surface no3 consistent with rayleigh fractionation kinetics for a fractionation factor u of 2 5 this value is substantially lower than previously found for temperate or polar regions perhaps as a result of differences in phytoplankton species assemblage or growth condition in the southern ocean south of the polar front comparison of 15n values for opal rich sediments south and sinking particles indicates an apparent 5 diagenetic enrichment relative to the surface generated signal that requires further investigation this exception aside our observations show that the surface water relationship of increasing 15n with increasing no3 depletion is generally transmitted to and preserved in the sediments an important requirement for further development and application of this important paleoceanographic tool

influence of water column anoxia on the elemental fractionation of carbon and phosphorus during sediment diagenesis abstract organic carbon oxidation and benthic total phosphorus flux measurements from sites covering a range of bottom water oxygen concentrations have been compiled the data show that p regeneration relative to carbon oxidation is much more extensive in sediments overlain by oxygen depleted waters these results are consistent with studies showing that low oxygen bottom water concentrations correlate with reduced total phosphorus burial efficiencies and enhanced organic carbon burial efficiencies based on these observations a positive feedback is proposed between water column anoxia enhanced benthic phosphorus regeneration and marine productivity this feedback may help explain the widespread accumulation of organic rich marine sediments from anoxic waters observed in the geologic record

geochemistry of ferromanganese nodules from domes site a northern equatorial pacific multiple diagenetic metal sources in the deep sea abstract the major and minor element composition of ferromanganese nodules from domes site a has been determined by x ray fluorescence methods three phases appear to control the bulk compositions mn and fe oxyhydroxides and aluminosilicates relatively wide compositional variations are evident throughout the area nodules with high mn fe ratios high cu mg mo ni and zn concentrations and high todorokite mno 2 ratios have granular surface textures and are confined to an east west trending depression with thin quaternary sediment cover nodules with low mn fe ratios high concentrations of as ca ce co la p sr ti v y and zr and low todorokite mno 2 ratios have smooth surfaces and are confined to shallower areas with relatively thick quaternary sediment to the north and south of the depression all nodules in the area have compositions which are influenced by diagenesis but those with the most marked diagenetic signature high mn fe and cu ni ratios low ce la ratios and more todorokite are found in areas of very slow or non existent sedimentation many of these nodules are actually in contact with outcropping tertiary sediment this paradox may be resolved by postulating by analogy with some shallow water occurrences that the nodules accrete from bottom waters which have enhanced particulate and dissolved metal contents derived from diagenetic reaction in areas remote from the site of nodule formation the metals are supplied in a bottom flow probably antarctic bottom water which also erodes or prevents modern sedimentation in the depression nodules on the flanks of the depression are not evidently affected by this flow and derive at least pan of their constituent metals from diagenetic reaction in the underlying quaternary sediment apparently abyssal diagenetic nodules can have an immediate and a remote diagenetic metal source metal fluxes derived from pore water dissolved metal gradients may not be relevant to particular accreting nodules if a significant fraction of their metals is derived from outside the area in which they form

evaluating nitrogen isotopes as proxies for depositional environmental conditions in shales comparing caney and woodford shales in the arkoma basin oklahoma abstract in this study we assessed the use of stable nitrogen isotopes 15 n to evaluate differences in water column conditions during the deposition of the woodford shale and caney shale in the arkoma basin in oklahoma by comparing bulk 15 n values the woodford shale was mainly deposited under anoxic bottom water column conditions whereas the caney shale shows evidence of deposition under a suboxic dysoxic deep water regime therefore these two units can be used to test the utility of 15 n as a proxy for the differentiation of these intervals based on depositional environment and post depositional processes and provide insights into differences that may impact their assessments as reservoir and source rocks we measured 15 n bulk organic carbon isotopes 13 c org total organic carbon toc and total nitrogen tn values from a core from the arkoma basin that contains sections of both caney shale and woodford shale bulk 15 n values are higher in the caney shale average 15 n bulk 9 5 0 8 than in the woodford shale average 15 n bulk 3 1 0 7 toc values in the woodford shale are slightly higher than those in the caney shale 6 2 and 4 2 respectively no significant differences were identified in the 13 c org and tn values between the two units given the depositional history of these units we suggest that the difference in 15 n between the caney shale and the woodford shale primarily reflects differences in depositional environment and that changes in 15 n bulk values due to diagenesis or catagensis are subordinate

sulfur isotopic trends and pathways of iron sulfide formation in upper holocene sediments of the anoxic black sea down core trends for extents of iron sulfidation in upper holocene microlaminated deposits of the black sea abyssal plain imply that most of the pyrite in these sediments is formed in the sulfidic water column and or very close to the sediment water interface sulfur isotopic data for pyrite within microlaminated muds from two localities in the deep basin show striking uniformity between sites and down core with a mean 34scdt value of 37 2 0 9 1 n 18 these isotopic trends support the hypothesis of early pyrite formation isotopic compositions of pyrite sulfur in the microlaminated bottom sediments are similar to those reported for particulate reduced sulfur collected in middepth sediment traps and to 34s values for water column dissolved sulfide within a narrow zone immediately below the o2 h2s interface these three sulfur reservoirs are distinctly different from the isotopic composition of ambient dissolved sulfide of the deep water column 175 m with 34s values for the deep dissolved sulfide reservoir being consistently lower by 2 to 4 these isotopic relationships suggest that iron sulfidation is occurring dominantly within a narrow shallow region at the top of the sulfidic water mass isotopic data from a fine grained turbidite collected in the deep basin and from rapidly accumulating iron monosulfide rich muds on the anoxic upper slope are enriched in34s relative to the microlaminated deposits the enrichments on the basin margin reflect a large component of iron sulfide formed during rapid burial a broad suite of geochemical data including sulfur isotopic results are consistent with an upper slope sediment source for the ubiquitous muddy turbidites of the deep basin the collective effects of reworking transport and redeposition result in a complete conversion of avs to pyrite with little additional iron sulfidation this conclusion is supported by a detailed isotopic mass balance the present isotopic study also highlights fundamental differences in the reactivities of the iron reservoirs distributed throughout the anoxic basin sediments of the upper slope and the genetically linked turbidites of the deep basin show similar extents of iron sulfidation that are significantly lower than those of the microlaminated deposits of the deep basin floor suggesting dramatically shorter timescales of iron reactivity for the microlaminated sediments of the deep basin importantly isotopic patterns from the modern black sea should assist greatly in the recognition and interpretation of ancient anoxia in the stratigraphic record

comparison of isotopic and geochemical characteristics of sediments from a gas and liquids prone wells in marcellus shale from appalachian basin west virginia abstract the middle devonian age marcellus shale contains one of the largest shale gas plays in north america hydrocarbon production in the eastern part of the play is mostly dry gas consisting of essentially pure methane production of natural gas liquids condensate increases toward the west which is the area currently being targeted by developers two marcellus shale cores from west virginia were analyzed to compare the isotopic and geochemical characteristics of a liquids prone well wv 7 in wetzel county with a gas prone well wv 6 in monongalia county the contrasts between the cores indicate that the conditions of the marcellus shale deposition were different between the two sites the dominant organic matter preserved in each core is isotopically different 13corg values are lighter on average in wv 6 compared with wv 7 a possible explanation is that a larger fraction of terrestrial organic matter was preserved in the wv 6 core whereas wv 7 may contain a greater percentage of marine organic matter clastic influx proxies e g ti al ca al and mg al also suggest that the wv 6 core site received a higher siliciclastic input compared to wv 7 consistent with a more proximal location to dry land and the delivery of greater amounts of terrestrial organic matter depleted 13ccarb values low concentrations of redox sensitive elements e g v cr ni and u and high variability 15n values in the wv 6 core all suggest the presence of higher dissolved oxygen concentration and short term shifts in an oxic anoxic boundary near the sediment water interface during deposition these lines of evidence indicate that the depositional conditions were favorable for the accumulation of predominantly gas prone type iii kerogen in the marcellus shale at the wv 6 site in contrast the marcellus shale at the wv 7 site was deposited in a more distal area that received a low terrestrial sediment supply organic matter primarily derived from marine algae and bottom water conditions that were dominantly anoxic such conditions were favorable for the accumulation of type ii kerogen that has a greater capacity to generate liquid hydrocarbons differences between the liquids prone and gas prone parts of the marcellus shale play have been largely ascribed to depth of burial and thermal maturation history this study indicates that depositional environment and sedimentary facies may have played significant roles as well

hydrographic conditions of the devono carboniferous north american seaway inferred from sedimentary mo toc relationships abstract deepwater anoxia developed widely within a series of silled intracratonic basins in north america during the middle devonian to early carboniferous but the hydrographic factors contributing to this development are virtually unknown the present study demonstrates that the degree of enrichment of strongly hydrogenous elements such as molybdenum mo in the organic rich shales that accumulated in these basins has the potential to provide information about paleohydrographic conditions most of the study units 49 of 55 exhibit significant positive covariation between elemental mo and toc concentrations yet there is substantial variation in the statistical parameters that define these relationships specifically the regression lines characterizing mo toc covariation have slopes m ranging from 2 to 65 10 4 although a majority of the study units yield m values between 10 and 25 10 4 the parameter m exhibits systematic stratigraphic variation within individual basins and geographic variation among basins suggesting that mo toc relationships were controlled by slowly evolving watermass characteristics of the devono carboniferous north american seaway a recent study of modern anoxic silled basins algeo t j lyons t w 2006 mo total organic carbon covariation in modern anoxic marine environments implications for analysis of paleoredox and paleohydrographic conditions paleoceanography 21 pa1016 doi 10 1029 2004pa001112 demonstrated that m is closely linked to the degree of restriction of the subpycnoclinal watermass as reflected in aqueous mo concentrations mo aq and deepwater renewal times dw these relationships reflect control of sedimentary mo enrichment by both the amount of sedimentary organic matter i e host phase availability and the concentration of aqueous mo i e source ion availability when applied to black shales of the devono carboniferous north american seaway these relationships permit both qualitative and quantitative inferences regarding the degree of restriction of deepwaters in cratonic basins and the evolution of hydrographic conditions through time black shales associated with early stages of sea level rise commonly exhibit low m values 1000 yr higher sea level stands resulted in more open marine conditions and enhanced deepwater renewal leading to deposition of black shales with m values up to 65 equivalent to mo aq 70 of the normal seawater concentration and dw

geochemical and climatic effects of increased marine organic carbon burial at the cenomanian turonian boundary perhaps the most significant event in the cretaceous record of the carbon isotope composition of carbonate1 2 other than the 1 2 5 negative shift in the carbon isotope composition of calcareous plankton at the cretaceous tertiary boundary3 is the rapid global positive excursion of 2 13c enrichment which took place between 91 5 myr and 90 3 myr late cenomanian to earliest turonian c t boundary event 1 4 5 this excursion has been attributed to a change in the isotope composition of the marine total dissolved carbon tdc reservoir resulting from an increase in rate of burial of 13c depleted organic carbon which coincided with a major global rise in sea level5 during the so called c t oceanic anoxic event oae 6 here we present new data from nine localities which demonstrate that a positive excursion in the carbon isotope composition of organic carbon at or near the c t boundary7 8 is nearly synchronous with that for carbonate and is widespread throughout the tethys and atlantic basins fig 1 as well as in more high latitude epicontinental seas the postulated increase in the rate of burial of organic carbon may have had a significant effect on co2 and o2 concentrations in the oceans and atmosphere and consequent effects on global climate and sedimentary facies

contrasting molybdenum cycling and isotopic properties in euxinic versus non euxinic sediments and sedimentary rocks refining the paleoproxies abstract the redox sensitive transition element molybdenum is present in the earth s crust at trace concentrations but is abundant in seawater marine sediments and ancient sedimentary rocks these occurrences have led to the development of a suite of paleoredox proxies based on the bulk concentration of mo its isotopic composition and the covariation of mo with total organic carbon toc in ancient black shales however these proxies have almost exclusively targeted the identification and interpretation of euxinic environments where bottom waters are both anoxic and sulfidic here we present a discussion of the mo geochemistry of non euxinic sediments where hydrogen sulfide is sometimes present yet always restricted to pore waters we propose a new paleoredox application that uses mo concentrations to help distinguish between environments where sulfide was present in the bottom waters and environments where sulfide was restricted to pore waters under ideal conditions it is also possible to infer the presence of mn oxides recycling in non euxinic paleoenvironments based on the mo isotope composition of ancient black shales providing a critical constraint on bottom water oxygenation

mo total organic carbon covariation in modern anoxic marine environments implications for analysis of paleoredox and paleohydrographic conditions 1 sedimentary molybdenum mo s has been widely used as a proxy for benthic redox potential owing to its generally strong enrichment in organic rich marine facies deposited under oxygen depleted conditions a detailed analysis of mo s total organic carbon toc covariation in modern anoxic marine environments and its relationship to ambient water chemistry suggests that 1 mo s while useful in distinguishing oxic from anoxic facies is not related in a simple manner to dissolved sulfide concentrations within euxinic environments and 2 patterns of mo s toc covariation can provide information about paleohydrographic conditions especially the degree of restriction of the subchemoclinal water mass and temporal changes thereof related to deepwater renewal these inferences are based on data from four anoxic silled basins the black sea framvaren fjord cariaco basin and saanich inlet and one upwelling zone the namibian shelf representing a spectrum of aqueous chemical conditions related to water mass restriction in the silled basin environments increasing restriction is correlated with a systematic decrease in mo s toc ratios from 45 5 for saanich inlet to 4 5 1 for the black sea this variation reflects control of mo s by mo aq which becomes depleted in stagnant basins through removal to the sediment without adequate resupply by deepwater renewal the basin reservoir effect the temporal dynamics of this process are revealed by high resolution chemostratigraphic data from framvaren fjord and cariaco basin sediment cores which exhibit long term trends toward lower mo s toc ratios following development of water column stratification and deepwater anoxia mo burial fluxes peak in weakly sulfidic environments such as saanich inlet owing to a combination of greater mo aq availability and enhanced mo transport to the sediment water interface via fe mn redox cycling and are lower in strongly sulfidic environments such as the black sea and framvaren fjord these observations demonstrate that at timescales associated with deepwater renewal in anoxic silled basins decreased sedimentary mo concentrations and burial fluxes are associated with lower benthic redox potentials i e more sulfidic conditions these conclusions apply only to anoxic marine environments exhibiting some degree of water mass restriction e g silled basins and are not valid for low oxygen facies in open marine settings such as continent margin upwelling systems

the response of benthic foraminifera to productivity cycles in the eastern equatorial pacific faunal and geochemical constraints on glacial bottom water oxygen levels the stage 2 glacial maximum in eastern equatorial pacific ocean sediments is characterized by a pronounced increase in the organic carbon content which has been attributed either to increased upwelling and higher production along the equatorial divergence during the last glacial period or to enhanced preservation as a consequence of a lower concentration of dissolved o2 in glacial bottom water several lines of evidence are presented based on data from two gravity cores collected from the central panama basin which support the former interpretation first both the abundance and the size of benthic foraminifera of the genus uvigerina increase in stage 2 coincident with the increase in organic carbon concentration most probably because of the greater availability of organic detritus during the glacial period the increase in foraminiferal size and associated greater requirement of oxygen for respiration argues against the probability that oxygen was substantially depleted in the upper centimeter where uvigerina spp are thought to live second the number of meiofaunal faecal pellets increases markedly during the stage 2 maximum indicating a more populous and active infauna which again argues against oxygen depletion third there is no significant decrease in the iodine organic carbon i corg ratio in the stage 2 sediments because iodine is depleted relative to carbon in anoxic basins but enriched in association with organic matter in oxic environments the absence of a depletion in the i corg ratio in stage 2 is evidence that bottom water remained oxygen replete during the last glacial fourth molybdenum is not enriched in sediments deposited in stage 2 the presence of anoxic or dysaerobic bottom water or shallow pore waters during that time would have been recorded by the addition of mo to the sediments via coprecipitation with authigenic iron sulphides the combined faunal and geochemical data are consistent with the notion that panama basin deep waters remained oxygen replete during the last glacial maximum it is concluded that the late stage 2 carbon enrichment in the eastern equatorial pacific more probably reflects higher productivity rather than enhanced preservation

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

sediment carbon nitrogen and phosphorus cycling in an anoxic fjord effingham inlet british columbia sediment geochemistry as well as benthic exchange of nutrients was investigated in effingham inlet a fjord located on the west coast of vancouver island in barkley sound the effect of bottom water oxygenation on sediment carbon nitrogen and phosphorus cycling was compared at sites overlain by oxic and anoxic bottom waters the sites separated by only 3 kilometers were similar in terms of key diagenetic parameters including mass accumulation rate and bulk sediment organic carbon content thus allowing a focus on diagenetic effects attributable to depositional oxygen availability benthic flux chamber incubations sulfate reduction rate measurements measurements of solid phase and pore water chemical profiles were compared for the sites these comparisons reveal that diagenetic processes in the site overlain by oxic waters act to retain more phosphorus in the sediment relative to the anoxic site differences in phosphorus benthic fluxes and burial between the two sites most likely result from differences in organic matter cycling under aerobic versus anaerobic conditions and are not strongly influenced by cycling of p associated with metal oxide phases

role of alternating redox conditions in the formation of organic rich interval in the middle devonian marcellus shale appalachian basin usa abstract geochemical isotopic and petrographic analyses were performed on a 30 m core of the marcellus shale obtained from greene county pennsylvania to understand the dominant controls on organic matter deposition in the black shale study units our study suggests that the regeneration of nutrients such as nitrogen n and phosphorous p may have played a key role in the formation of organic carbon oc rich intervals in the marcellus shale the decomposition of organic matter is likely to have released n and p into the water column and the episodic upward mixing of these nutrient enriched waters enhanced primary production the ratios of corg nbulk and corg ptot are significantly higher in the oc rich zone of the core i e defined as toc 4 and located between 2393 and 2406 5 m depth the high corg ptot and corg nbulk ratios of the preserved organic matter may reflect the release of n and p by microbial processes indicating the recycling of nutrients during deposition of the oc rich interval in addition our data show a positive relationships between the corg ptot and corg nbulk ratios and the organic carbon content which indicate that the recycled nutrients may have promoted primary productivity resulting in higher oc accumulation in some intervals the geochemical and stable isotopic results also suggest that the alternating redox conditions in the water mass were favorable for nutrient regeneration highly variable trace metal concentrations e g u mo and v in the oc rich zone and a wide range of 15n and 34spyr values towards the top of the oc rich zone suggest fluctuations between anoxic and suboxic water conditions finally sedimentary features and agglutinated benthic foraminifera in the oc rich zone support the existence of short term fluctuations between suboxic and anoxic conditions near the sediment water interface multiple lines of evidence suggest that nutrient regeneration due to alternating redox conditions may have played an important role in the formation of oc rich intervals in the marcellus shale

multiple controls on the preservation of organic matter in devonian mississippian marine black shales geochemical and petrographic evidence geochemical and petrographic analysis of an interval of black shales between the huron shale member of the new albany shale upper devonian famennian and the sunbury shale lower mississippian tournaisian suggests that multiple controls influenced the accumulation of organic matter stratigraphic trends were determined following detailed analysis of a core from the central appalachian basin d6 montgomery county ky specifically c s fe relationships mo v v ni ni co and v cr were used to assess paleo redox conditions during sediment accumulation the role of clastic input was evaluated using ti al k al and si al and c p was used as a proxy for paleoproductivity the terrestrial to marine maceral ratio t m vitrinite plus inertinite alginite plus bituminite was used to evaluate changes in om source c s fe relationships and trace element ratios suggest anoxic conditions prevailed during deposition of much of the upper part of this interval however bottom water conditions were intermittently dysoxic during accumulation of the huron shale member and possibly dysoxic to marginally oxic during accumulation of the lowermost huron shale member productivity appears to have been an important factor in the accumulation of corg and high c p ratios are consistent with a productivity anoxia feedback mechanism in addition nutrients from increased terrestrial weathering may have contributed to enhanced productivity variations in sediment influx may also have influenced corg concentrations through sediment starvation one of the more significant observations in this work is an increase in terrestrial om inertinite and vitrinite up section which may reflect vegetative changes occurring on land during this time interval most of this increase is due to inertinite much of which appears to be fusinitic in origin and hence may be fossil charcoal this latter observation has implications for the expansion of land plants into drier niches and for late devonian atmospheric oxygen levels introduction of more resistant terrestrial om to anoxic basins may have been an important factor in the preservation of high carbon 10 intervals especially in the cleveland member of the new albany shale upper devonian famennian and the sunbury shale lower mississippian tournaisian

corrosion patterns of seep carbonates from the eastern mediterranean sea terra nova 23 206 212 2011 abstract porous seep carbonates are exposed at mud volcanoes in the eastern mediterranean sea the 13c depleted aragonitic carbonates formed as a consequence of the anaerobic oxidation of methane in a shallow sub surface environment besides the macroscopically visible cavernous fabric extensive carbonate corrosion was revealed by detailed analysis after erosion of the background sediments the carbonates became exposed to oxygenated bottom waters that are periodically influenced by the release of methane and upward diffusion of hydrogen sulphide we suggest that carbonate corrosion resulted from acidity locally produced by aerobic oxidation of methane and hydrogen sulphide in the otherwise with respect to aragonite oversaturated bottom waters although it remains to be tested whether the mechanisms of carbonate dissolution suggested herein are valid this study reveals that a better estimate of the significance of corrosion is required to assess the amount of methane derived carbon that is permanently fixed in seep carbonates

effective sediment transporting discharge from magnitude frequency analysis the long term effectiveness of a geomorphic event of a particular magnitude is the product of the effect of a single event of that magnitude times the frequency with which it recurs magnitude frequency analysis if discharge frequency of a stream is assumed to be log normally distributed and if sediment transport rate is assumed to be a power function of discharge then transport effectiveness attains a maximum value at some discharge termed here the effective discharge that moves the most sediment over the long term the effective discharge and its recurrence interval may be predicted if both assumptions are correct analysis of 55 u s streams demonstrates that the observed and the predicted recurrence intervals of the effective discharge are in poor agreement this lack of agreement results from the failure of the power function of discharge to predict adequately the sediment transport rate above some high discharge threshold or thresholds the observed recurrence interval of the effective discha

paleoproductivity from benthic foraminifera abundance glacial to postglacial change in the west equatorial pacific surface productivity is correlated with the rate of accumulation of benthic foraminifera on the deep sea floor as a rule of thumb for each 1 mg of organic carbon arriving at the sea floor one benthic foram shell 150 m is deposited the correlation can be used to reconstruct organic flux to the sea floor in the past and hence the productivity of past oceans applying the appropriate equations to box core data from the ontong java plateau in the western equatorial pacific we found that productivity during the last glacial maximum exceeded present productivity by a factor of between 1 5 and 2 0 with intermediate values for the mid transition period accumulation of benthic foraminifera was depressed on top of the plateau during the glacial and transitional period presumably because increased winnowing removed part of the food supply

nitrogen cycling during the cretaceous cenomanian turonian oceanic anoxic event ii low 15n values ranging from 1 2 to 3 9 and atomic carbon nitrogen c n ratios of 25 50 are characteristic of black shales deposited during the cenomanian turonian boundary interval and oceanic anoxic event ii oae ii an observed antithetic relationship between c n ratios and 15n could suggest a predominance of terrestrially derived organic matter or a diagenetic control on 15n variability shifting bulk 15n values lower however hydrogen indices hi generally 450 and a positive correlation of hi with c n mitigates against a significant terrestrial organic matter fraction high c n values are likely the result preferential degradation of labile n rich compounds during early diagenesis and loss of n as ammonium from sediments through time a hypothetical model that considers the degradation of a 15n enriched labile protein fraction yields only small 1 2 negative shifts in 15n however 15n depletion during diagenesis is contrary to normal isotope kinetics which should result in 15n enrichment of bulk organic matter therefore we conclude that the bulk 15n values in this study reflect primary changes in the nitrogen cycle the 15n data support the hypothesis of expanded nitrogen fixation driven by upwelling of nutrient nitrogen poor phosphorus replete waters during oae ii and from the mid cenomanian to santonian at demerara rise the low 15n values which are significantly lower than bulk 15n values in modern regions where nitrogen fixation is known to be important probably result from a more significant fraction of dissolved inorganic nitrogen being produced by nitrogen fixation during the peak of oae ii a marked shift to lower 15n values is observed this shift possibly reflects greater utilization of 15n depleted ammonium during a chemocline upward excursion cue dominance of low 15n values from other periods of more widespread marine anoxia is likely the result of similar processes

terrestrial organic carbon contributions to sediments on the washington margin elemental and stable carbon isotopic compositions and biomarker concentrations were determined in sediments from the columbia river basin and the washington margin in order to evaluate geochemical approaches for quantifying terrestrial organic matter in marine sediments the biomarkers include an homologous series of long chain n alkanes derived from the surface waxes of higher plants phenolic and hydroxyalkanoic compounds produced by cuo oxidation of two major vascular plant biopolymers lignin and cutin all marine sediments including samples collected from the most remote sites in cascadia basin showed organic geochemical evidence for the presence of terrestrial organic carbon using endmember values for the various biomarkers determined empirically by two independent means we estimate that the terrestrial contribution to the washington margin is 60 for shelf sediments 30 for slope sediments and decreases further to 15 in basin sediments results from the same geochemical measurements made with depth in gravity core 6705 7 from cascadia seachannel suggest that our approach to assess terrestrial organic carbon contributions to contemporary deposits on the washington margin can be applied to the study of sediments depositing in this region since the last glacial period

nitrogen isotope and productivity variations along the northeast pacific margin over the last 120 kyr surface and subsurface paleoceanography 1 glacial interglacial changes in sedimentary 15n over the last 120 kyr display a remarkably similar pattern in timing and amplitude in core records extending from the denitrification zone in the eastern tropical north pacific etnp where subsurface denitrification is active to the oregon margin where no denitrification occurs today low 15n values 4 6 generally characterize glacial stages 2 and 4 and higher 15n values 7 10 are representative of the holocene millennial scale periods within stage 3 and stage 5 the inferred synchroneity of 15n variations along the entire margin implies that the nitrate isotopic signal produced in the oxygen poor subsurface waters in the etnp is rapidly advected northward and recorded at sites far beyond the boundaries of the modern denitrification zone similar to 15n primary production indicators percent corg ba al and percent opal show glacial interglacial as well as millennial scale variations along the ne pacific margin with higher primary production during warm periods however the relative phasing between 15n and paleoproduction tracers within individual records changes latitudinally whereas 15n and primary production vary approximately synchronously in the midlatitudes production lags 15n in the etnp by several kiloyears this lag calls for a new understanding of the processes driving denitrification in the etnp we suggest that oxygen input by the equatorial undercurrent as well as local organic matter flux controls denitrification rates in the etnp moreover the differences in relative timing point to a time transgressive development of upwelling favorable winds along the ne pacific margin after the last glaciation with those in the north developing several kiloyears earlier

submillimeter life positions of bacteria protists and metazoans in laminated sediments of the santa barbara basin to provide insights into the biogeochemistry of environments where steep chemical gradients place anaerobes microaerophiles and aerobes in close proximity it might be necessary to survey biotic distributions on scales that are not possible using conventional ecological approaches to overcome such limitations we adapted sedimentological and cell biological methods to examine the life positions of microbes within sediments this fluorescently labeled embedded core flec technique was used to survey the submillimeter distributions of eukaryotic nanobiota and meiofauna plus co occurring prokaryotes inhabiting laminated sediments of the bathyal santa barbara basin sbb 34 13 n 120 02 w although sbb sediments were vertically structured on the scale of millimeters i e as laminae and microelectrode profiles suggested vertically distinct oxygenated and anoxic sulfidic layers the distributions of aerobes microaerophiles and sulfide tolerant anaerobes were not concomitantly structured unprecedented associations were observed among microorganisms for example relatively deep in the sediments where high sulfide concentrations were expected flagellates were intimately associated with beggiatoa ciliates were typically solitary whereas flagellates were often aggregated in nearly monomorphotypic swarms of 3 104 mm 3 such aggregations could significantly affect geochemical pore water processes at scales 1 l our observations indicate that a mosaic of chemically heterogeneous microhabitats exist in both vertical and horizontal dimensions suggesting that biogeochemical processes in the sbb are more complex than predictions based on standard biotic assessments and microelectrode profiling

organic matter accumulation and preservation controls in a deep sea modern environment an example from namibian slope sediments the luderitz upwelling cell is presently the most productive area of the benguela current system and abundant organic matter om accumulates on the adjacent slope sediments even at great water depth om from two cores taken on the slope and covering the last 280 kyear was analysed in terms of petroleum quality rock eval chemical features ftir eds and petrographic composition light microscopy and tem these data indicate that the om is more oxidized at 3606 m water depth than on the upper slope sediments 1029 m although the petroleum quality of the om throughout the deep water core remains surprisingly high for hemipelagic deep sea sediments hi 200 400 mg g the petroleum quality of om accumulated on the upper slope is consistently high hi averages 450 mg g two petrographic types of om are distinguishable from microscopic observation each ascribed to distinctive preservation mechanisms 1 granular amorphous om which dominates in the deep water core is formed by organo mineral aggregates aggregation appears to be the primary preservation mode at this depth although is quantitatively limited maximum toc value of 4 wt of bulk sediment obtained through this process the ultrastructure of the aggregates highlights an intimate association pattern between sedimentary om and clays 2 gel like nannoscopically amorphous om naom largely dominates at 1000 m water depth and contains sulfur thus early diagenetic sulfurization was probably involved in the preservation of this om but a contribution from the classical degradation recondensation pathway cannot be ruled out moreover selective preservation occurred at both sites but represents an insignificant part of the om organic fluxes mainly control the occurrence and extent of sulfurisation at both water depths by determining the redox conditions at the sea floor aggregate formation is limited by both organic and mineral fluxes at the lower slope whereas om supply is never limiting on the upper slope although consistently operating through time at both depths preservation by organo mineral association is limited by mineral availability and thus accounts for a relatively minor portion of the om accumulated on this organic rich slope in the case of large organic fluxes sulfurisation and or degradation recondensation is required to obtain toc contents above 4 wt of bulk sediment in the area

a model for uranium rhenium and molybdenum diagenesis in marine sediments based on results from coastal locations abstract the purpose of this research is to characterize the mobilization and immobilization processes that control the authigenic accumulation of uranium u rhenium re and molybdenum mo in marine sediments we analyzed these redox sensitive metals rsm in benthic chamber pore water and solid phase samples at a site in buzzards bay massachusetts usa that has high bottom water oxygen concentrations 230 300 mol l and high organic matter oxidation rates 390 mol c cm2 y the oxygen penetration depth varies from 2 to 9 mm below the sediment water interface but pore water sulfide is below detection release of rsm to pore waters during the remineralization of solid phases occurs near the sediment water interface at depths above the zone of authigenic rsm formation this release occurs consistently for mo at both sites but only in the winter for re in buzzards bay and intermittently for u at the buzzards bay site re removal to the solid phase extends to the bottom of the profile while the zone of removal is restricted to 2 9 cm for u and mo authigenic re formation is independent of the anoxic remineralization rate which is consistent with an abiotic removal mechanism the rate of authigenic u formation and its modeled removal rate constant increase with increasing anoxic remineralization rates and is consistent with u reduction being microbially mediated authigenic mo formation is related to the formation of sulfidic microenvironments the depth and extent of mo removal from pore water is closely associated with the balance between iron and sulfate reduction and the consumption of pore water sulfide via iron sulfide formation pore water rsm reach constant asymptotic concentrations in sulfidic sediments but only pore water re is constant at depth in buzzards bay the increases in pore water u at the buzzards bay site are consistent with addition via irrigation and subsequent upward diffusion to the removal zone deep pore water mo concentrations exceed its bottom water concentration due to irrigation induced oxidation and remobilization from the solid phase in sulfidic sediments there is no evidence for higher pore water u or mo concentrations at depth due to the absence of irrigation and or the presence of more stable authigenic rsm phases there are good correlations between benthic fluxes and authigenic accumulation rates for u and mo in sulfidic sediments however results from buzzards bay suggest irrigation ultimately results in the partial loss of u and mo from the solid phase with accumulation rates that are 20 30 of the modeled flux irrigation can augment re possibly u or compromise u mo authigenic accumulation in sediments and is important when determining burial rates in continental margin sediments

discovery of agglutinated benthic foraminifera in devonian black shales and their relevance for the redox state of ancient seas abstract agglutinated foraminifera are benthic organisms that occur in marginal marine to bathyal environments though some taxa can live in oxygen deficient environments they require at least some oxygen in order to persist at the seafloor the discovery that they occur widely in late devonian black shales has a bearing on the boundary conditions required for episodes of extensive carbon sequestration in marine sediments and their connection to atmospheric composition and global climate devonian black shales of the eastern us have been studied extensively to determine the fundamental controls on carbon burial and a range of mechanisms has been proposed finding agglutinated benthic foraminifera in these black shales refocuses the debate about their origin and points to limitations of earlier models

plate tectonic trigger of changes in pco2 and climate in the oxfordian late jurassic carbon isotope and modeling evidence abstract the transition from the middle to the late jurassic was characterized by significant changes in oceanography and climate and by changes in global carbon cycle as shown in the c isotope record a prominent mid oxfordian positive excursion in bulk carbonate carbon isotope values 13 c carb with an amplitude of more than 1 has been documented from many sections in the northern tethys realm in this study we present new bulk organic matter c isotope data 13 c org from northwestern tethys that do not record the mid oxfordian positive excursion in carbonate carbon on the contrary 13 c org decreases during the interval of the most rapid increase in 13 c carb we demonstrate that this decrease is not due to a changing marine terrestrial organic carbon partitioning but that the contrasting isotope trends record peculiar environmental and climate changes which occurred near the beginning of the late jurassic using a simple carbon cycle model we show that an increase in atmospheric p co 2 starting at modern levels could be the cause of contrasting trends in 13 c carb and 13 c org we suggest that a reorganisation of ocean currents related to the opening and or widening of the tethys atlantic pacific seaway and a massive spread of shallow sea carbonate production led to higher p co 2 model simulations indicate that this increase in p co 2 may have triggered changes in the biological carbon pump and in organic carbon burial that can explain the middle oxfordian c isotope record

equatorial dynamics observed by rocket radar and satellite during the cadre malted campaign 2 mean and wave structures coherence and variability we present an analysis of the wind and temperature measurements made by rocket radar and satellite instrumentation in the equatorial and subtropical middle atmosphere accompanying the malted cadre campaign conducted at alcantara brazil during august 1994 measured mean winds and temperatures extended from 10 to 110 km exhibited general consistency between instruments and revealed an oscillatory nature of the mean zonal wind with altitude at equatorial latitudes mf radar measurements of tidal structures showed these to exhibit variability on 8 and 16 day periods but to be largely uncorrelated in time two day wave structures displayed the same periodicities but were well correlated among sites at northern and equatorial latitudes rocket and radar measurements at smaller scales of motion revealed inertia gravity waves having significant temporal coherence quadrature correlations between components indicating clear directions of propagation and momentum flux and mean wind correlations indicative of gravity wave filtering processes rocket estimates of diurnal tidal amplitudes suggest that the diurnal tide achieves convectively unstable amplitudes in the upper equatorial mesosphere

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

preservation of organic matter and alteration of its carbon and nitrogen isotope composition during simulated and in situ early sedimentary diagenesis abstract the carbon and nitrogen isotope composition of organic matter has been widely used to trace biogeochemical processes in marine and lacustrine environments in order to reconstruct past environmental changes from sedimentary organic matter it is crucial to consider potential alteration of the primary isotopic signal by bacterial degradation in the water column and during early diagenesis in the sediments in a series of oxic and anoxic incubation experiments we examined the fate of organic matter and the alteration of its carbon and nitrogen isotopic composition during microbial degradation the decomposition rates determined with a double exponential decay model show that the more reactive fraction of organic matter degrades at similar rates under oxic and anoxic conditions however under oxic conditions the proportion of organic matter resistent to degradation is much lower than under anoxic conditions within three months of incubation the 13c of bulk organic matter decreased by 1 6 with respect to the initial value the depletion can be attributed to the selective preservation of 13c depleted organic compounds during anoxic decay the 15n values continuously decreased to about 3 below the initial value the decrease probably results from bacterial growth adding 15n depleted biomass to the residual material in the oxic experiment 15n values increased by more then 3 before decreasing to a value indistinguishable from the initial isotopic composition the dissimilarity between oxic and anoxic conditions may be attributed to differences in the type timing and degree of microbial activity and preferential degradation in agreement with the anoxic incubation experiments sediments from eutrophic lake lugano are on average depleted in 13c 1 5 and 15n 1 2 with respect to sinking particulate organic matter collected during a long term sediment trap study

mass wasting on the submarine lomonosov ridge central arctic ocean a total of seven arcuate transverse troughs 5 6 km wide 7 9 km long and 150 200 m deep are present on both sides of the crest of the central part of lomonosov ridge arctic ocean the troughs occur within a restricted ridge length of ca 65 km trough morphology and disrupted piecewise continuous sub bottom reflections down to a common stratigraphic horizon below the troughs indicate lateral spread of progressively disintegrating sediment blocks above a glide plane lomonosov ridge is aseismic but the spatially restricted mass waste occurrences suggest sediment instability induced by earthquake loading another possibility is a pressure wave from a possible impact of an extraterrestrial object on alpha ridge about 500 km away the slide event s is likely to be pre late pleistocene as sediment deposition within one of the slide scars appears continuous over the last c 600 ka 2007 elsevier b v all rights reserved