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

diagenetic cycling of arsenic in amazon shelf sediments in order to help elucidate major natural controls on the diagenetic behavior of as vertical profiles of total dissolved and solid phase as were measured in amazon shelf deposits a deltaic region little influenced by human activity arsenic distributions are typically characterized by subsurface porewater maxima and surficial solid phase enrichment maximum porewater as concentrations 2 4 m are an order of magnitude greater than levels reported in most other coastal marine environments and elevated concentrations extend several meters below the sediment surface dissolved as varies inversely with easily leachable as 40 140 nmol g 1 in the solid phase and directly with increases in solid phase fe ii these patterns reflect a strong redox coupling with fe whereby oxidized as is associated with fe oxyhydroxides in surface sediments then subsequently reduced and released upon burial in the extensive suboxic zone upward diffusion and intense physical reworking of sediments presumably releases the dissolved arsenic fraction to the water column or allows for re adsorption in surface sediments arsenic porewater concentrations generally increase away from the river in some cases regular seasonal variations are evident apparently corresponding to nonsteady state ingrowth of diagenetic profiles following extensive sediment reworking during rising river flow the massive cycling of as in amazon shelf sediments is likely due to the combined effects of intense chemical weathering in regions of the drainage basin production of oxides and a turbulent physical regime present on the shelf both of which promote sedimentary cycling of fe and coupled elements during early diagenesis

dental wash a problematic method for extracting microfossils from teeth abstract a variety of microfossils originating from plant foods become trapped in the dental calculus matrix processing of dental calculus allows extraction of these microfossils the resulting data can be used to reconstruct diet at the individual and population levels as the identification of microfossils like starch grains and phytoliths to the generic level and sometimes to the species level is possible however in some archaeological sites dental calculus deposits do not preserve well enough to be processed to prevent the loss of information in such cases we present a technique called dental wash it permits extracting microfossils from cryptic dental calculus deposits in the two experimental archaeological cases presented herein we identified phytoliths starch grains as well as a diatom fragment with this method whereas in a control sample no microfossils were found moderate damage to the teeth was detected when they were already friable due to poor preservation minor damage to the surface of well preserved teeth was observed this indicates that the proposed method is efficient in recovering microfossils but unacceptable because of damage to teeth if the method can be refined it will expand the potential of dental calculus analysis to a greater range of archeological sites

zur systematik der kohlenstoff schwefel eisen verhaltnisse in auftriebssedimenten abundances of organic carbon sulfur and reactive iron in sediments of three upwelling environments peru oman and benguela suggest that organic carbon reduced sulfur ratios c s ratios in this category of marine sediments deviate considerably from previously established empirical ratios in normal marine sediments to clarify the discrepancies we investigated those components of the diagenetic system that limit the formation of pyrite sulfate concentrations and reduction rates in pore waters availability of reactive iron and the quantity and quality of organic matter all three limitations are evident in our sample pools the results suggest that c s ratios in recent and fossil marine sediments rich in organic matter may be unsuitable as paleoenvironmental indicators

stratigraphic evolution of the late holocene ganges brahmaputra lower delta plain sediment cores from the ganges brahmaputra delta in bangladesh were examined for sedimentological character clay mineralogy elemental trends c n s and 14c geochronology to develop a model for the sedimentary sequence resulting from lower delta plain progradation in the late holocene a widespread facies succession from muddy sand to interbedded mud records progradation of shoal island complexes and the transition from subtidal to intertidal conditions mangrove vegetated islands and peninsulas represent the final phase of progradation a mottled mud that is deposited by penetration of turbid coastal water into the mangroves during high water events organic matter preservation is generally low 1 toc in most of these well drained deposits that are characterized by a permeable silt dominated granulometry clay mineralogy in the cores records the relative influence of smectite and kaolinite rich ganges sediments and illite and chlorite rich brahmaputra material the lower delta plain west of the modern river mouths was deposited as a ganges dominated delta in three phases since 5000 cal years bp with brahmaputra influence confined to the meghna estuary area and to the supratidal section of western delta deposits evolution of the lower delta plain in the late holocene was influenced by regional subsidence patterns in the tectonically active bengal basin which controlled distributary channel avulsion and migration and the creation of accommodation space

the geochemical study of fluvio lacustrine aquifers in the kathmandu basin nepal and the implications for the mobilization of arsenic the geochemical analyses of fluvial lacustrine aquifer sediments of the kathmandu valley have been made as a step in assessing the environment for the mobilization of arsenic in groundwater elements measured by x ray fluorescence xrf include 4 major oxides fe2o3 tio2 cao p2o5 and 14 trace elements as pb zn cu ni cr v sr y nb zr th sc and ts elution tests of 15 selected core samples were also carried out to determine the potential leaching of arsenic from the sediments the xrf results show that average bulk concentrations of the major oxides and trace elements are similar to modern unconsolidated sediments and average upper continental crust however the abundance of elements varies with grain size with higher concentrations in finer size grades variations in elemental abundances within the basin are strongly controlled by sediment facies the elution tests show that greater amounts of arsenic are generally eluted from the fine sediments although the rates are variable the results overall suggest that as concentrations in the bulk sediments are not a controlling factor for elevated as in the kathmandu basin groundwater and the roles of other factors such as redox conditions and organic matter contents are likely to be more significant

mobility of arsenic and trace element inventories in sediment cores from masuda city southwestern japan the vertical distribution of arsenic and other trace and major elements has been studied in four sediment cores from masuda city nagashima and okite in the shimane prefecture of southwestern japan the sediment cores were also subjected to leaching techniques and 14c dating the stratigraphic sequences in the cores consist of silt and sandy silt at top passing downward into gray to black clays elevated values of as pb zn cu ni cr and v are present in several horizons while abundances of these elements tend to be higher in the black and gray clays probably due to adsorption onto clay sediments higher concentrations of fe and total sulfur ts occur in black clays the correlations of the trace metals with iron suggest their adsorption onto fe oxy hydroxides whereas correlations with sulfur in some cores indicate that they were precipitated as fe sulfides age determinations suggest that clay horizons at 5 m depth were deposited at around 5 000 and 6 000 years bp 14c ages during the transgressive phase of sea level change the results of the leaching techniques in the core samples show that higher amounts of as were extracted with deionized water even at neutral ph as can be released from sediments to groundwater and therefore groundwater pollution is a concern in masuda city and the surrounding area

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

sedimentological characteristics heavy metal distribution and magnetic properties in subtidal sediments ria de pontevedra nw spain the rias of nw spain are coastal ecosystems of high biological productivity and great economic importance they are intensively exploited by man for fish and shellfish there are a number of important centres of population and industrial activity along their margins which serve as sources of contamination in this context it is desirable to achieve the best possible understanding of the physico chemical processes that control spatial and temporal variations in the geochemical mineralogical and sedimentological characteristics of near surface sediments in the ria de pontevedra and in particular the distribution and mobility of heavy metal contaminants thus adequate environmental planning can be achieved for this site and understanding gained for comparable contexts core samples were examined from the inner middle and outer parts of the ria grain size distributions reflect the presence of two main populations one dominated by silt and clay derived mainly from terrestrial sources and the other by fine sand to coarse silt which is derived mainly from continental shelf and ria mouth sources mineralogical analysis shows an abundance of terrestrial intensive weathering products near the ria head a dominance of shelf derived sediment towards the mouth and the presence of several diagenetic minerals whose nature varies with location within the ria in the inner ria the near surface sediments are slightly enriched in pb cu and zn from anthropogenic sources these sediments are fine grained and have a high organic content hence they have a higher potential to sorb contaminants than the coarser grained less organic rich sediments of the mid and outer ria the estimated sedimentation rates for the fine grained organic rich sediments from the inner part of the ria are about 1 mm year 1 the dominant authigenic minerals in the inner ria are iron sulphides whereas in the mid and outer ria iron silicates and oxyhydroxides are more important these differences in authigenic iron mineralogy are clearly reflected by the magnetic properties of the sediments

depositional environment of oil shale within the second member of permian lucaogou formation in the santanghu basin northwest china abstract the non marine santanghu basin in northwest china hosts one of the richest and thickest permian lacustrine source rock intervals in the world conventional oil in jurassic sandstone reservoirs and tight oil in the tuffaceous permian tiaohu formation were sourced from mudrocks in the underlying second member of lucaogou formation which also have tight oil potential proved by recent commercial discoveries based on inorganic and organic geochemistry organic petrography and stable isotope geochemistry the depositional environment and the tight oil potential of the second member of permian lucaogou formation were investigated the data imply a gradual evolution of the depositional environment from a stratified saline to a freshwater lake the succession can be subdivided into a lower middle and an upper unit each characterized by decreasing water salinity high bioproductivity has been caused by the bloom of algae and photosynthetic cyanobacteria water column stratification accelerated the activity of methanothrophs as indicated by low 13c values of hopanes biomarker composition provides evidence for decreasing contributions of cyanobacteria to the biomass and increasing abundance of prasinophytae compared to other algae with decreasing salinity enhanced terrigenous organic matter input appeared during periods of high freshwater inflow low total organic carbon toc contents in the lower unit are most likely caused by rapid sedimentation rate high bioproductivity and excellent preservation conditions resulted in high toc contents in the middle unit terrigenous organic matter input increased together with fresh water inflow in the upper unit resulting in high toc values during periods of possibly low sedimentation rates in a deep water column the samples of the second member exhibit a good to very good potential to generate conventional oil high toc and extractable organic matter yields together with the thickness of the fine grained sediments show that the middle and upper units of the second member of lucaogou formation hold significant tight oil potential mineralogical composition of this dolomite rich shale with respect to abundance of brittle minerals including quartz and carbonates and rare clay testifies a good tight oil potential

sediment water interaction acidity and other water quality parameters in a subtropical setting pimpama river southeast queensland the geological setting and landuse activities of the pimpama river catchment are typical for many drainage systems in southeast queensland the river originates in coastal ranges of late paleozoic age crosses a floodplain developed during the late pleistocene holocene sea level fluctuations and flows into the southern part of the moreton bay the formation of sedimentary pyrite associated with the mid holocene transgression is an important feature of this coastal setting the oxidation and hydrolysis of pyrite and the consequent production of sulfuric acid are controlled by the amount and seasonality of rainfall and influenced locally by landuse activities the acid production and the leaching of dissolved metals from river alluvium and estuarine sediments impact substantially on land and aquatic habitats the water quality of the pimpama river and its tributaries reflects the lithology of the bedrock and can vary largely depending on season tidal regimes sediment lithology local topography and agricultural activities

late pleistocene and halocene sea level changes in japan implications for tectonic histories and mantle rheology abstract it is very important to separate the tectonic and glacial isostatic components in the observed holocene and late pleistocene sea level changes in tectonically active areas such as japan for studying tectonic processes and for constraining mantle rheology the separation can be achieved by considering the spatial dependence of the relative sea level on the geometry of the coastline around the site where sea level is evaluated in fact the relative sea level caused by the last deglaciation at sites in the embayment such as tokyo and osaka has a sea level curve with a high stand at mid holocene and that site situated on the tip of peninsula has a sea level curve culminating towards the present the geometric effect also causes the regional difference of the sea level variations in the late glacial phase in the japanese islands the regional difference of the predicted relative sea level is about 5 m at 6000 years ago 20 m at 10 000 years ago and 30 m at 18 000 years ago comparison between observations and predictions indicates that the observations at several sites in japan are consistent with the predicted sea level variations more systematic data is required for the period 18 000 years ago to the present in order to examine tectonic processes and mantle rheology

geology and geochemistry of the sediment hosted cheshmeh konan redbed type copper deposit nw iran the several hundred m thick miocene upper red formation in northwestern iran hosts stratiform and fault controlled copper mineralization copper enrichment in the percent range occurs in dm thick carbonaceous sandstone and shale units within the clastic redbed sequence and consists of fine grained disseminated copper sulfides chalcopyrite bornite chalcocite and supergene alteration minerals covellite malachite and azurite the copper mineralization formed after calcite cementation of the primary rock permeability copper sulfides occur mainly as replacement of diagenetic pyrite which in turn replaced organic matter electron microprobe analysis on bornite chalcocite and covellite identifies elevated silver contents in these minerals up to 0 12 0 72 and 1 21 wt respectively whereas chalcopyrite and pyrite have only trace amounts of silver 0 26 and 0 06 wt respectively microthermometric data on fluid inclusions in authigenic quartz and calcite indicate that the cu mineralization is related to a diagenetic fluid of moderate to low temperature th 96 160 c but high salinity 25 38 wt cacl2 equiv the range of 34s in pyrite is 41 9 to 16 4 average 31 4 where framboidal pyrite shows the most negative values between 41 9 and 31 8 and fine grained pyrite has relatively heavier 34s values 29 2 to 16 4 consistent with a bacteriogenic derivation of the sulfur the cu sulfides chalcopyrite bornite and chalcocite show slightly heavier values from 14 6 to 9 0 and their sulfur sources may be both the precursor pyrite s and the bacterial reduction of sulfate bearing basinal brines carbonates related to the ore stage show isotopically light values of 13cv pdb from 8 2 to 5 1 and 18ov pdb from 10 3 to 7 2 indicating a mixed source of oxidation of organic carbon ca 20 and hco3 from seawater porewater ca 0 the copper mineralization is mainly controlled by organic matter content and paleopermeability intragranular space to large fracture patterns enhanced by feldspar and calcite dissolution the cheshmeh konan deposit can be classified as a redbed type sediment hosted stratiform copper ssc deposit

diagenetic cycling of arsenic in the sediments of eutrophic baldeggersee switzerland sedimentation and benthic release of as was determined in baldeggersee a eutrophic lake in central switzerland sediment traps recorded as sedimentation during 1994 including a flood event in spring diagenetic processes were studied using porewater profiles at the sediment water interface and in deeper sediment strata deposited in the mesotrophic lake before 1885 sediment cores were used to calculate the accumulation and to construct the balance of sedimentation and remobilisation the results showed that the lake sediment acts as an efficient sink for as only 22 of the particulate as flux reaching the sediment surface was remobilised at the sediment water interface the as accumulation in the recent varved section of the eutrophic lake was 40 mg as m 2 a 1 iron reduction in older sediment caused a remobilisation of 1 2 mg as m 2 a 1 this upward flux from the deeper sediment was quantitatively immobilised in the recent sulfidic sediments the flood event in spring contributed about 34 of the yearly sediment load and led to distinct peak profiles of dissolved as in the porewater this evidence for rapid remobilisation disappeared within months

c s fe relationships and the isotopic composition of pyrite in the new albany shale of the illinois basin u s a the relationship between pyritic sulfur content spyr and organic carbon content corg of shales analyzed from the new albany group depends upon corg for samples of 6 wt no spty corg correlation is apparent the degree of fe pyritization dop shows similar relationships to corg these c s fe relationships suggest that pyrite formation was limited by the availability of metabolizable organic carbon in samples where corg 6 wt apparent sulfur isotope fractionations relative to contemporaneous seawater sulfate 34s for pyrite formation average 40 for non calcareous shales and 25 for calcareous shales 34s values become smaller with increasing corg spyt and dop for all corg poar 6 wt and some corg nch 6 wt shales these trends suggest that pyrite formation occurred in a closed system or that instantaneous bacterial fractionation for sulfate reduction decreased in magnitude with increasing organic carbon content the isotopic trends observed in the new albany group are not necessarily representative of other shales having a comparable range of organic carbon content e g cretaceous shales and mudstones from the western interior of north america gautier 1986 34s values in the remainder of the corg rich new albany group shales are relatively large 38 to 47 and independent of corg spyr and dop which suggests that pyrite in these shales formed mostly at or above the sediment water interface by precipitation from an isotopically uniform reservoir of dissolved h2s

tracing bottom water redox conditions during deposition of lower and upper jurassic organic rich sedimentary rocks in the lusitanian basin portugal insights from inorganic geochemistry abstract the lower jurassic agua de madeiros am fm and vale das fontes vf fm formations and the upper jurassic cabacos formation cab fm are considered the most important units with petroleum source rock potential in the lusitanian basin and the likely sources for its widespread hydrocarbon occurrences nonetheless the bottom water redox conditions during their deposition remain debatable to resolve this controversy we investigated whole rock inorganic geochemical data of the most significant organic rich levels of the am vf and cab fms cropping out at basin scale significant variations in toc ts and redox sensitive elements contents and their ratios are evident within and between the organic rich levels of the studied units a positive covariation between primary productivity proxies toc enrichment and paleo redox proxies for the lower jurassic units clearly suggest an interdependence between enhanced primary productivity organic matter accumulation and bottom water redox conditions for the am fm the paleo redox proxies indicate that the black shales deposition took place beneath bottom waters that ranged from suboxic to strongly euxinic conditions with a clear predominance of the latter a toc threshold of 6 7 wt clearly separates samples deposited under suboxic to anoxic conditions from those deposited under true euxinic conditions and is interpreted as the minimum amount of organic matter om accumulation within sediments required to sustain h2s production at rates that outpaced its consumption through precipitation of sulphides and or om sulphurization allowing the diffusion of h2s to the bottom waters for the vale das fontes fm the paleo redox proxies suggest a prevalence of suboxic to anoxic bottom waters despite all black shales displaying toc contents greater than the above threshold the less reducing conditions relative to the am fm euxinic black shales are attributed to i a larger proportion of continental om ii lower reactivity of the om reaching the sediment water interface decreasing oxygen consumption and iii higher availability of reactive iron increasing the buffer effect to h2s produced through om remineralization by sulphate reducing bacteria both units display mo ef vs u ef covariation patterns that deviate from the field of sediments deposited under unrestricted open marine conditions towards higher mo enrichment relative to that of u indicating an accelerated transport of aqueous mo to the sediments consistent with the operation of a metal oxyhydroxide particulate shuttle linked to mn and fe redox cycling within the water column in a weakly restricted basin the mo cot regression line slope indicates a moderate degree of bottom water mass restriction with mo aq concentration of 60 70 of the present day seawater value and bottom water renewal times of 10 20 years akin to the present day cariaco basin the redox conditions of the cab fm organic rich levels are dependent on the location of the depositional environment in the basin with deposition taking place beneath oxygenated bottom waters at cabo mondego and under suboxic conditions at vale de ventos and pedrogao the latter denoting a larger degree of oxygen depletion than the former in this context the overall potential for om preservation should increase from cabo mondego to vale de ventos and pedrogao

carbon sulphur iron variations and sulphur isotope patterns of silurian graptolite shales black shale horizons graptolithenschiefer in silurian and lower devonian strata of the franconian thuringian highlands frankenwald thuringer wald of germany have high metal concentrations e g u v mo organic carbon sulphur and iron contents degree of pyritization dop and sulphur isotope ratios from the lower graptolite shales along with faunal and sedimentological evidence show that the depositional environment was anoxic although some data e g c s plots do not suggest completely euxinic conditions the dop versus c plot indicates a black sea type environment from the sulphur isotope data the environment fluctuated between open and closed with respect to sulphate supply with higher carbon contents reflecting an increased bacterial reduction of the available sulphate diagenetic effects were responsible for somewhat unusual plots of c s ratios though iron availability may have been influential

microwave radiometric measurements of sea surface temperature from the seasat satellite first results initial results from the seasat scanning multichannel microwave radiometer indicate that the sea surface temperature can be measured with a root mean square sensitivity of 1 2 c or better the first microwave map of sea surface temperature for the entire pacific has been produced

clues to stone tool function re examined comparing starch grain frequencies on used and unused obsidian artefacts the identification of plant residues observed on prehistoric stone artefacts has often been used to inform on tool function without adequate consideration of potential contamination due to post depositional processes the paper redresses this balance by proposing a methodology which combines use wear and residue analyses with systematic testing of depositional context to distinguish residues formed during tool use from accidental contamination a case study involving obsidian artefacts from an open site in papua new guinea is used to illustrate the new approach starch grains a class of residue which has had little attention outside australia were chosen as the focus of study because of their abundance at this site the frequency of starch grains extracted from residues on stone artefacts was compared with those in sediments adhering to and adjacent to the artefact a use wear study conducted as a blind test provided an independent measure of whether the artefacts had been used the frequency of starch grains was shown to be significantly correlated with used artefacts and not correlated with unused artefacts or the sediments the case study demonstrates the importance of testing for contamination and also illustrates the benefit of studying starch grains as a class of plant residue

geochemical characteristics in the longmaxi formation early silurian of south china implications for organic matter accumulation abstract the organic rich early silurian sediments longmaxi formation on the yangtze platform are considered to be one of the main source rocks in south china in order to investigate the mechanism of organic accumulation multiple geochemical proxies including redox parameters s c and trace element ratios productivity indices p and ba contents and clastic influx indicator ti al ratios are presented here from the hehua section yichang hubei province the longmaxi sediments have high toc contents 3 00 10 85 avg 5 63 low pyrite sulfur contents 0 42 1 14 avg 0 59 high p 0 02 0 44 avg 0 12 and ba contents 576 65 2542 43 ppm avg 1592 17 ppm calculated s c th u ni co v cr and v v ni ratios are 0 05 0 24 avg 0 12 0 23 9 86 avg 2 30 2 65 46 24 avg 15 46 0 27 14 42 avg 3 75 and 0 36 0 96 avg 0 75 respectively s c and trace element ratios together with pyrite morphology suggest dysoxic anoxic conditions prevailed during deposition of the longmaxi intervals which was mainly caused by a worldwide marine transgression after the melting of gondwana glaciation productivity proxies indicate that the organic rich longmaxi sediments were deposited in moderate to high primary productivity water columns the consistent ti al ratios suggest a rather homogeneous nature for the detrital supply geochemical data provide a good constraint on the accumulation of organic matter and relevant oceanic environment anoxic conditions together with relatively high productivity were likely responsible for the accumulation of organic rich sediments during the longmaxi interval

cova del rinoceront castelldefels barcelona a terrestrial record for the last interglacial period mis 5 in the mediterranean coast of the iberian peninsula abstract the cova del rinoceront a site in ne iberia contains a thick sedimentary fill preserving a faunal archive from the penultimate glacial and the the last interglacial periods layers i to iii have been dated to between 74 and 147 ka coinciding with mis 5a to 5e a period poorly represented in the mediterranean terrestrial record the results from cova del rinoceront are of broader interest for the reconstruction of ecological dynamics during warm stages and the understanding of the evolution and geographical variation of several taxa the palaeoecological evidence suggests a landscape dominated by mixed wooded vegetation with mild climatic conditions slightly more humid than today several vertebrate taxa including haploidoceros mediterraneus stephanorhinus hundsheimensis and glis glis are documented for the first time in the early upper pleistocene of europe showing that these species persisted across the region for longer than previously thought in addition the recovery of a small lithic assemblage indicates human presence in the surroundings of the site the 11 m thick stratigraphic section also provides an ideal setting in which to compare several geochronological methods u th dating of the flowstones that cap the deposit of speleothems formed along the cave walls and of speleothems buried by the deposit at different elevations provides minimum and maximum ages of 74 and 175 ka respectively for the accumulation the ages obtained by luminescence electron spin resonance esr amino acid racemisation aar palaeomagnetism and u series dating of bone are in good agreement with each other and are stratigraphically consistent this well dated faunal succession presents a unique opportunity to assess changes in the pleistocene fauna of the mediterranean coast over an interval of more than 100 ka

the use of operationally defined sequential fe extraction methods for mineralogical applications a cautionary tale from mossbauer spectroscopy abstract reactive iron minerals are crucial components of global nutrient cycles directly controlling carbon transport and storage in marine sediments sequential selective extraction is frequently used for quantitatively characterising and chemically isolating individual fe mineral phases reagent specific mineral solubility is fundamental to the success of any sequential extraction but is strongly affected by the varying physical and chemical morphology intrinsic to natural mineral samples natural sediment rock and soil samples often contain a mineral mixture which further modifies solvent efficacy 57fe mossbauer spectroscopy only probes the hyperfine interactions between next nearest neighbouring atomic nuclei in the crystal lattice and is less affected by variation in mineral grain size and crystallinity than conventional x ray based methods in this study we used mossbauer spectroscopy in a novel context to cross calibrate and optimise a popular but frequently misused sequential fe extraction protocol our results showed that incomplete and premature removal of the target fe minerals could occur at nearly every stage of the extraction and in many cases the leachate fe content did not represent the target phase at all crystalline natural siderite and amorphous synthetic goethite were detected in the mossbauer spectrum of the ammonium oxalate extraction for magnetite after which all reactive fe minerals should have been removed consistent with previous studies and unlike many other clay minerals nontronite was extracted as part of the highly reactive fe pool and in fact our data indicate that this mineral was extracted by the initial na acetate extraction that targets carbonate bound fe matrix effects appeared to cause variable yield efficiencies synthetic goethite was successfully removed when present as an individual mineral yet persisted beyond its target extraction when present in an fe mineral mixture although suitable for the quantification of operationally defined fe pools we caution the unverified use of sequential fe extraction protocols for mineral specific applications the application of sequential fe extractions to define the reactive fe pools as a paleoredox proxy of depositional conditions appears relatively robust the premature removal of 2 line ferrihydrite observed in this study due to the use of the more aggressive na acetate extraction for crystalline siderite does not limit the quantitative use of the sequential fe extraction in ancient sediments where such easily reducible oxides are unlikely to persist in contrast attributing the outcomes of operationally defined fe pools to specific fe minerals is precarious and potentially entirely erroneous where fe mineral specificity or separation is required we recommend post extraction validation by another secondary technique mossbauer spectroscopy offers such a method that can independently verify extraction stages and assess mineral specificity

spatial distribution of major and trace elements in shallow reservoir sediments an example from lake waco texas sediment geochemistry of a shallow 6 m average reservoir lake waco was evaluated for the spatial distribution of major and trace elements sixty bottom and core samples along a 21 km transect within the reservoir 18 overbank sediment samples and 8 rock types in the drainage area were collected and analyzed for major al ca fe and trace elements as ba cr cu hg mn ni pb sr v zn elemental concentrations in the reservoir sediments closely correspond to concentrations in the regional rocks and represent a mixture of overbank sediment composition of the tributaries elemental concentrations were statistically regressed against al concentrations in order to establish regional baseline levels and thereby distinguish natural from anthropogenic sources spatial geochemical trends considered in terms of element to al ratio versus v to al ratio relate to the natural and anthropogenic sources contributing to the elemental concentrations the spatial elemental distribution in the reservoir which receive sediments from two mineralogically contrasting basins reflect textural and mineralogical transition within the reservoir and suggest a progressive mixing of sediment from the tributaries the spatial elemental distribution and sediment texture suggest that the sediment source which determines the sediment type has a greater influence on the major and trace element distributions in shallow reservoir sediments than bathymetry

geochemical and petrographic investigation of triassic and late miocene organic rich intervals from onshore cyprus eastern mediterranean abstract in order to improve the understanding of potential petroleum systems in the still underexplored eastern mediterranean sea two field campaigns were performed to investigate potential source rocks onshore cyprus elemental data total organic toc and inorganic carbon tic total sulfur ts fe ni v rock eval pyrolysis biomarker and microscopic analysis organic petrography random vitrinite reflectance vrr palynofacies of the obtained mesozoic to cenozoic samples have proven the existence of organic matter om rich deposits within the following two geological formations 1 the triassic vlambouros formation fm of the mamonia complex comprises frequently occurring few centimeter thin clay layers interbedded between meter thick sandstone units the clay layers of this formation are characterized by toc contents of about 1 wt representing a type iii kerogen showing hydrogen index hi values of 48 mg hc g toc on average vrr values of 0 5 to 0 6 as well as several biomarker ratios indicate low thermal maturity the formation was deposited at the northern margin of gondwana and similar strata may be present in the basement of the levant basin and the eratosthenes seamount there thermal maturity would be higher and such rocks might contribute to thermogenic gas systems 2 in the miocene pakhna fm om bearing intervals are mainly present in the upper part of the formation in outcrops east of the troodos mountain while organic rich intervals are very scarce to absent in the south and southwest of the island the eastern outcrops show abundant fine grained marly mud to wackestones interbedded with coarser grained carbonates the fine grained intervals have toc contents of about 4 wt representing mainly type ii iii kerogen with hi values of 238 mg hc g toc on average the om is immature as indicated by vrr values between 0 3 and 0 5 ts toc 2 8 and several biomarker ratios indicate oxygen depleted even anoxic conditions during deposition a negative correlation between the toc and tic indicates that such conditions were reached during enhanced primary bioproductivity controlled by local and regional clastic derived nutrient input similar conditions may have been present along the southeastern margin of the eratosthenes seamount south of cyprus presence of abundant organic matter and high sedimentation rates during the miocene were favorable for microbial gas generation in the deeper parts of the basins

tropical and mid latitude north pacific sea surface temperature variabililty from the seasat smmr sea surface temperature sst data from the scanning multichannel microwave radiometer smmr for the entire seasat mission july 6 to october 10 1978 was obtained from the seasat project office and has been analyzed for the mid latitude north pacific 20 n 50 n 145 e 130 w and the eastern tropical pacific 10 s 20 n 95 w 145 w systematic cross scan sst biases were observed in the smmr data strongly dependent upon latitude solar elevation time of day and month the cross scan biases are ascribed to incomplete accounting for faraday rotation of polarized microwave energy propagating upward through the ionosphere a second systematic sst bias occurred between data of ascending and descending passes nearly 12 hours apart the bias increased steadily through the mission as the seasat orbit moved from 6 a m p m to 12 a m p m local sun time coverage the ascending descending bias is ascribed to measurements being made at different times in the diurnal cycle of sst corrections for the two systematic effects were derived and applied to the smmr data to produce maps of sst in mid latitude 10 and 30 day maps of smmr sst were compared with similar maps produced from routine shipboard sst observations mostly engine injection temperatures the monthly smmr and shipbased maps agreed at the 0 5 0 7 c rms level in july and september but exhibited a 0 5 c rms scatter about a significant 1 0 c bias in august the august bias may be a reflection of true midsummer vertical differences in temperature between the 1 cm depth of smmr observations and the typically 5 m depth of ship observations monthly sst anomalies deviation from climatology for smmr and ship exhibited similar patterns but the smmr maps appear superior because of their better spatial data coverage in the eastern tropical pacific a sequence of 15 8 day interval maps were constructed the maps reproduce known climatological features in particular the cold tongue of water along the equator week to week variations occur in the intensity of the cold tongue in addition wave like patterns occur along the meridional gradient just north of the equator having 1000 km wavelength and propagating west at about 42 km day

the sulfur system in anoxic subsurface brines and its implication in brine evolutionary pathways the ca chloride brines in the dead sea area abstract important elements in the evolutionary history of saline groundwater might be overlooked when they involve both sulfate removal through reduction and input of sulfate via dissolution these two simultaneous and apparently contrasting processes can result in a negligible net effect on the sulfate concentration isotopic composition of sulfur in sulfate and sulfide can be applied to identify the bacterial sulfate reduction bsr though the extent of the process is difficult to quantify saturation with respect to gypsum may suggest that gypsum dissolution also occurs however a more definite identification of these processes and their quantification can be achieved through the use of ammonium concentration in the anoxic brines this approach assumes that the ammonium is derived only from the oxidation of organic matter through bsr and it requires that the c n ratio in the oxidized organic matter be known a minimum estimate for the sulfate reduction can be obtained when the redfield c n ratio 106 16 is assumed several calculation methods are presented to identify the extent of sulfate reduction prior to concomitant with or following gypsum dissolution that are based on combining sulfur isotopic compositions rayleigh distillation equation and calculated gypsum saturation indices the required assumptions are presented and their validation is discussed the subsurface hypersaline ca chloride brines in the vicinity of the dead sea are taken as a case study here sulfur isotope compositions of sulfate and sulfide and high ammonium concentrations indicate bsr occurs in the subsurface the sulfur isotopic composition of the sulfate makes it possible to distinguish between two major groups of brine and their recent evolutionary histories 1 the qedem shalem thermal brines 34 s so4 21 24 which emerge as springs along the shores and are slightly undersaturated with respect to gypsum 2 dsif tappuah brines 34 s so4 30 60 which are found in shallow boreholes and are saturated to oversaturated with respect to gypsum calculations based on their ammonium content suggest that both groups of brine require apparent unreasonably high oversaturations with respect to gypsum prior to the onset of the reduction this implies that the groundwater systems were open with respect to sulfate and that the sulfate reservoir was replenished continuously or intermittently during the bsr the dsif tappuah brines continue to dissolve gypsum during their bsr the dissolving sulfate is derived from relatively isotopically enriched gypsums 34 s so4 20 such as found in the lisan formation these brines approach the steady state isotopic composition 34 s ss dictated by the combination of the 34 s of the dissolving gypsum and the fractionation factor accompanying bsr the sulfur isotopic composition of the qedem shalem brines implies that most of their ammonium content is derived from an earlier phase of bsr and that the last phase of bsr takes place during the brines rapid ascent to the surface prior to this stage they evolved through either 1 dissolution of gypsum with 34 s so4 20 which occurred after the main bsr in the subsurface 2 a previous phase in which the brines were part of a lake and later percolated to the subsurface as such their isotopic composition and ammonium content were determined by the combined effect of freshwater sulfate input to the lake and bsr in the stratified lake

a review of the source behaviour and distribution of arsenic in natural waters the range of as concentrations found in natural waters is large ranging from less than 0 5 g l 1 to more than 5000 g l 1 typical concentrations in freshwater are less than 10 g l 1 and frequently less than 1 g l 1 rarely much higher concentrations are found particularly in groundwater in such areas more than 10 of wells may be affected defined as those exceeding 50 g l 1 and in the worst cases this figure may exceed 90 well known high as groundwater areas have been found in argentina chile mexico china and hungary and more recently in west bengal india bangladesh and vietnam the scale of the problem in terms of population exposed to high as concentrations is greatest in the bengal basin with more than 40 million people drinking water containing excessive as these large scale natural as groundwater problem areas tend to be found in two types of environment firstly inland or closed basins in arid or semi arid areas and secondly strongly reducing aquifers often derived from alluvium both environments tend to contain geologically young sediments and to be in flat low lying areas where groundwater flow is sluggish historically these are poorly flushed aquifers and any as released from the sediments following burial has been able to accumulate in the groundwater arsenic rich groundwaters are also found in geothermal areas and on a more localised scale in areas of mining activity and where oxidation of sulphide minerals has occurred the as content of the aquifer materials in major problem aquifers does not appear to be exceptionally high being normally in the range 1 20 mg kg 1 there appear to be two distinct triggers that can lead to the release of as on a large scale the first is the development of high ph 8 5 conditions in semi arid or arid environments usually as a result of the combined effects of mineral weathering and high evaporation rates this ph change leads either to the desorption of adsorbed as especially as v species and a range of other anion forming elements v b f mo se and u from mineral oxides especially fe oxides or it prevents them from being adsorbed the second trigger is the development of strongly reducing conditions at near neutral ph values leading to the desorption of as from mineral oxides and to the reductive dissolution of fe and mn oxides also leading to as release iron ii and as iii are relatively abundant in these groundwaters and so4 concentrations are small typically 1 mg l 1 or less large concentrations of phosphate bicarbonate silicate and possibly organic matter can enhance the desorption of as because of competition for adsorption sites a characteristic feature of high groundwater as areas is the large degree of spatial variability in as concentrations in the groundwaters this means that it may be difficult or impossible to predict reliably the likely concentration of as in a particular well from the results of neighbouring wells and means that there is little alternative but to analyse each well arsenic affected aquifers are restricted to certain environments and appear to be the exception rather than the rule in most aquifers the majority of wells are likely to be unaffected even when for example they contain high concentrations of dissolved fe

phyllosilicates and zeolite assemblages in the carbonate periplatform of the great bahama bank origin and relation to diagenetic processes odp leg 166 sites 1006 and 1007 abstract the western flank of the great bahama bank drilled during odp leg 166 at seven sites represents a prograding carbonate sequence from late oligocene to holocene eberli et al proc odp init reports 166 1997 the signatures of the detrital input and of diagenetic alteration are evident in clay enriched intervals from the most distal sites 1006 and 1007 in the straits of florida mineralogical and chemical investigations xrd tem sem icp ms run on bulk rocks and on the clay fractions enable the origin and evolution of silicate parageneses to be characterized plio pleistocene silt and clay interbeds contain detrital clay assemblages comprising chlorite illite interstratified illite smectite smectite kaolinite and palygorskite the greater smectite input within late pliocene units than in pleistocene oozes may relate either varying source areas or change in paleoclimatic conditions and weathering intensity the clay intervals from miocene upper oligocene wackestone sections are fairly different with prevalent smectite in the fine fraction whose high crystallinity and mg contents that point towards an authigenic origin the lower miocene section below 1104 mbsf at depths where compaction features are well developed is particularly characterized by abundant authigenic na k clinoptilolite filling foraminifer tests the authigenic smectite and clinoptilolite paragenesis is recorded by the chemical trends both of the sediment and the interstitial fluid this diagenetic evolution implies si and mg rich fluids circulating in deeper and older sequences for lack of any local volcaniclastic input the genesis of zeolite and the terms of water rock interaction are discussed the location of the diagenetic front correlates with that of the seismic sequence boundary p2 dated as 23 2 ma this correspondence may allow the chronostratigraphic significance of some specific seismic reflections to be reassessed

natural enrichment of arsenic in loch lomond sediments abstract concentrations of arsenic in surface or near surface sediment in 12 of 13 cores from the three major basins of loch lomond are substantially enhanced up to 675 mg kg compared with background values of 15 50 mg kg sedimentary as profiles are attributed to post depositional enrichment processes since there are no recent significant sources of environmental as contamination anthropogenic or natural in the loch lomond area the enrichments can be interpreted in terms of post depositional diagenetic remobilization processes in sediment reducing zones followed by upward migration of as through interstitial waters and oxidation adsorption precipitation reactions in near surface oxidizing layers confirmation of the diagenetic adsorption hypothesis is provided directly by the analysis of as species 1 5 81 g l in pore water and indirectly via comparison with sedimentary phosphorus

deposition of coal and oil shale in ne china the eocene huadian basin compared to the coeval fushun basin abstract the huadian and fushun basins located along the dunmi fault zone ne china are filled with non marine coal and oil shale bearing sediments of eocene age despite similar tectonic setting the habitat of coal and oil shale differs significantly during this study the depositional environment of organic rich sediments in the huadian basin and factors controlling differences between both basins were investigated early in the history of the huadian basin thin coaly and bituminous mudstones accumulated in shallow lake environments pyrite member water depth increased during deposition of the oil shale member but did not exceed a few tens of meters preventing stable water column stratification moreover deposition of fan delta sediments interrupted accumulation of fine grained rocks nevertheless algal blooms and oxygen depleted conditions resulted in accumulation of 13 thin high subsidence rates in the fushun basin favored deposition of thick coal during the transgressive stage and of oil shale in a deep lake in contrast minor subsidence in the huadian basin resulted in a lake with moderate water depth and deposition of several oil shale layers with varying quality in this basin economic coal developed only during the regressive stage

framboidal and idiomorphic pyrite in the upper maastrichtian sedimentary rocks at gabal oweina nile valley egypt formation processes oxidation products and genetic implications to the origin of framboidal pyrite abstract the upper maastrichtian organic rich sediments studied at gabal oweina egypt are moderately enriched in syngenetic and diagenetic pyrite pyrite occurs mostly as layers or bands group of lamina lenses diagenetic intercalated pockets burrow fills and disseminated individual pyrite framboids and crystals within the host sediments the pyritic thin bands and lamina consist mostly of unconsolidated to compact oriented pyrite oriented along the bedding planes in gypsiferous clayey matrix and less common as poorly oriented pyrite crystallites in several cases pyrite crystals of the latter type depict zoning fracturing and micro concretions pyritic burrow fills are composed mainly of pyrite phosphatic ooids microfossils glauconitic grains poorly graphitized carbon and native sulfur pyrite replaces minerals other than gypsum sulfur or carbon it also replaces microfossils thus turning some of the phosphatic ooids and microfossils to pyritized pseudomorphs none of the studied phosphate ooids or framboids contains any mackinawite pyrrhotite or greigite based on the microscopic and sem observations of the micro textures of disseminated pyrite found at gabal oweina section four morphological forms of primary pyrite could be identified 1 grouped multiple framboids 2 individual framboids 3 pyrite idiomorphic crystal overgrowths on framboids and 4 single and aggregates of euhedral pyrite crystals the multiple framboid formation may have emerged from three successive processes nucleation and growth of individual aggregates of the microcrystals to form combined micro framboids the growth of framboids and followed by grouping of the several pyrite framboids direct pyrite nucleation shell formation crystallization and aggregation processes might complete a single framboid the disseminated single and aggregated euhedral pyrite crystals bear evidence indicating that their formation was via nucleation and growth of pyrite crystallites and their aggregation to individual framboids infilling in the interstices by additional pyritic material compaction and homogenization of all these materials furthermore we encounter for the first time in nature idiomorphic pyrite crystals that integrated numerous framboids using them as their nucleation and growth sites without erasing or modifying their pristine morphology elemental sulfur contains minor concentration of sb ni cd and cu strongly suggesting their presence as submicron sulfide crystallite inclusions sem and microprobe investigations revealed that goethite is present as a weathering product in all morphological types of pyrite however only an iron sulfate presumably melanterite was encountered as oxidation product of the multi framboids and the euhedral aggregate crystals the upper maastrichtian sediments not only contain a menagerie of pyrite morphologies but probably a complete record of the formation process and the geochemical conditions of the growth of framboids single pyrite crystals pyrite burrows pyritized mn fe oxide framboids and finally their weathered products the various pyrite forms strongly suggest a multistage process that led to their formation without any evidence for mackinawite pyrrhotite or greigite precursors there is also no evidence in the oweina sediments for post pyrite formation of mackinawite pyrrhotite or greigite the presence of elemental sulfur containing minor concentrations of sb ni cd and cu with pyrite framboids indicates that the pore solutions were geochemically supersaturated in sulfur thus inhibiting the crystallization of any iron sulfide other than pyrite this cast considerable doubt on the assumed mackinawite or greigite precursors as prerequisite for formation of pyrite framboids

formation of pyrite in freshwater sediments implications for c s ratios abstract the vertical distribution of pyrite acid volatile sulphide avs carbon and total s st were determined directly in the sediments of three lakes of different trophic status the results showed that freshwater pyrite formation reflects the redox status of the sediment or overlying waters it appears to form chiefly in reducing sediments which are subject to oxidizing influences by either a low turnover of organic carbon or periodic incursions of oxygen although there are high concentrations of avs in the near surface sediments of productive lakes very little is diagenetically converted to pyrite the feasibility of using sulphur ratios to diagnose whether rocks were formed in marine or freshwater environments is assessed new values for fes 2 fes of 0 5 5 show that this ratio does not provide a reliable test values of c sp where sp represents pyrite sulphur lie within the range of 160 700 and are much higher than previously measured ratios of c s t of 1 50 these new determinations show that if pyrite sulphur is unequivocally measured c s ratios may be a more sensitive indicator of salinity than had been previously thought

magnetic iron nickel sulphides in the pliocene and pleistocene marine marls from the vrica section calabria italy abstract the rock magnetic properties of the late pliocene and early pleistocene open marine marls from the vrica section in calabria italy point to magnetic sulphide as the main magnetic mineral and remanence carrier the maximum blocking temperatures however are between 340 and 360 c which is too high for stoichiometric monoclinic pyrrhotite magnetic concentrates of the sediment are rich in iron sulphide grains and iron nickel sulphide grains microprobe observations show that most of the grains are of the order of 1 m in size and attached to iron bearing clay flakes microprobe analyses of the sulphides yield a large range of compositions ranging from pyrite through greigite pyrrhotite to sulphur deficient monosulphides and with ni contents varying from zero to a few atom percent in the pyrite grains and from zero to as much as 35 atm in the monosulphides the high ni content of many of the grains is extraordinary and has not been reported before in marine sediments most of the compositions cannot be directly connected with a known mineral phase the marine depositional environment of the marls imposes an authigenic origin for the sulphides and this is supported by several observations the great number of sulphide grains in the magnetic concentrates suggests that at least one of the sulphide compositions must have a ferrimagnetic structure possibly the sulphides with a metal to sulphur ratio close to that of monoclinic pyrrhotite and between 25 and 35 of the fe replaced by ni the ni substitution could possibly be the cause of the high blocking temperatures

role of organic matter and sulphate reducing bacteria for metal sulphide precipitation in the bahloul formation at the bou grine zn pb deposit tunisia abstract the origin of the bou grine zn pb deposit of tunisia was investigated during a geochemical study of the cretaceous bahloul formation the inorganic and organic chemical compositions of the bituminous marls and limestones as well as the light stable isotope ratios of organic carbon and carbonates were measured closely spaced samples were collected along two profiles at different distances from the enrichments in zn and pb which are best developed near the bou grine diapir the organic geochemical data suggest sulphide precipitation at the bou grine deposit by sulphate reducing bacteria srb srb utilized hydrocarbons derived both from the bahloul sediments and from external source rocks production of s ii by the bacteria was most probably limited by the availability of sulphate although sulphate was available to the bacteria in high concentrations in close proximity to the triassic salt dome ground waters evolved to hypersaline basinal brines by dissolution of salt and anhydrite at the contact of the diapir these brines would have been capable of leaching metals from the sedimentary sequences adjacent to the salt dome the triassic series has often been advocated as the source of the metals and the cretaceous sediments themselves are carriers of metallic elements ore deposition apparently resulted when metal bearing solutions that migrated upward into the roof zone of the diapir mixed with s ii bearing solutions those formed when srb oxidized the high amounts of hydrocarbons within the bahloul sediments and in the brines using so 4 2 from sulphate rich waters in the anhydrite caprock as an oxidant

processes responsible for the development of soft sediment deformation structures ssds in the paleoproterozoic gordon lake formation huronian supergroup canada abstract an exposure of the paleoproterozoic gordon lake formation in the bruce mines area ontario canada contains abundant soft sediment deformation structures ssds including load casts convolute bedding pseudonodules ball and pillow structures flame structures and one dewatering pipe these features are developed in siltstone to fine grained sandstone beds and are between 1 and 120 cm in width and 3 78 cm high the primary trigger mechanism is interpreted to be storm or tsunami activity however seismic shock overloading brought about by density inversions or a combination of these processes may have influenced the formation of ssds to a lesser degree several beds also contain flat to wavy carbonaceous laminae locally with a botryoidal texture and concentrations of heavy minerals which are interpreted as relicts of microbial mats microbial mats may have played a minor role in the formation of ssds but do not appear to have been a prominent driving mechanism soft sediment deformation structures observed in the baie fine flack lake and cobalt plains regions of ontario are smaller and not as abundant as in the study area suggesting that the deposits in the study area were either affected by local events or different magnitudes of sedimentary processes in contrast to the tidal flat paleoenvironment interpreted for the gordon lake formation in the flack lake area the stratigraphically lower beds at the studied outcrop more closely resemble shallow shelf deposits

early diagenetic greigite as an indicator of paleosalinity changes in the middle miocene paratethys sea of central europe the miocene epicontinental paratethys sea of central eurasia has experienced multiple restriction and reconnection events to the open ocean magnetostratigraphy is an important dating tool to better understand the temporal and spatial paleoenvironmental variations associated with these changes magnetostratigraphy in the paratethys domain however is complicated by the presence of greigite fe3s4 here we report rock magnetic and x ray fluorescence data of the tisa section romania which was previously magnetostratigraphically dated at the middle miocene base at 12 8 ma and top at 12 2 ma this section comprises the badenian sarmatian extinction event bsee which is marked by a major salinity change from marine to brackish environments related to the opening of the connection between the central and the eastern paratethys basins in the marine badenian sediments below the bsee the pyritization process is shown to be complete because of abundant sulfate supply in the brackish sarmatian deposits four intervals with early diagenetic greigite are observed and linked to insufficient sulfate in the water column these four greigite intervals appear to correspond to maxima in the 100 kyr eccentricity cycle we propose that increased fresh water from the eastern paratethys basin during eccentricity maxima restricted the sulfate availability in the tisa area leading to a reduced hs production and enhanced greigite preservation the early diagenetic formation of greigite enables a quasi syn depositional recording of the paleomagnetic field which allows reliable paleomagnetic dating in this section our results further suggest greigite as a potential indicator for salinity changes during marine brackish transitions

climate control of sulfate influx to lake hovsgol northwest mongolia during the last glacial postglacial transition constraints from sulfur geochemistry abstract changes in sulfur cycles in lake hovsgol northwest mongolia are discussed on the basis of total organic carbon toc total sulfur ts concentrations and stable sulfur isotope ratios 34 s in two sediment cores x104 and x106 covering the last glacial to the present correlation plots of toc and ts c s plots of the sediment cores indicate dissolved sulfate enrichment in sediment pore water and high sulfate reducing bacteria srb activity during the climate transition from the last glacial to postglacial period lg pg transition from ca 21 to 11 6 cal ka bp in addition positive shifts of 34 s values from 3 7 to 32 6 were observed during the lg pg transition these results suggest a large influx of 34 s rich dissolved sulfate into the lake during this period the 34 s rich dissolved sulfate may have accumulated on the shore wetlands and marshes of lake hovsgol during the last glacial period owing to the increase in atmospheric precipitation and lake level rise during the lg pg transition the 34 s rich dissolved sulfate may have been supplied from the shore to the lake increased sulfate influx during the lg pg transition has also been observed in a lake baikal sediment core our new sulfur geochemical data shows past environmental changes particularly moisture changes within continental asia during the climate transition

organic geochemistry of an anoxic cycle a case history from the oligocene section hungary total organic carbon extractable organic matter sulfur content kerogen type and saturated hydrocarbons have been determined in 25 core samples from an approximately 100 m thick section of the oligocene tard clay near budapest the tard clay records a five million year long anoxic cycle initiated by isolation of the sea development of a positive water balance and resulting density stratification and terminated by the re opening of access to the sea the lower non and moderately laminated shales record the build up of anoxia they contain 0 5 5 0 of organic carbon and type iii kerogen their saturated hydrocarbon fractions show high abundance of phyllocladanes biomarkers characterising coniferae derived organic matter the overlying moderately and strongly laminated sediments containing 1 5 5 0 organic carbon a predominance of hopanes over the n alkanes and type ii kerogen show the imprint of increased planktonic productivity the nutrients needed for this high productivity were liberated by alteration processes of contemporaneous volcanic glass the upper part of the strongly laminated shales containing a maximum of 2 organic carbon and type iii kerogen deposited after the termination of volcanic ash falls records a drop of planktonic productivity at the top of the tard clay the weak lamination and the low content 1 of organic carbon signifies the end of the bottom water oxygen depletion due to the destruction of density stratification of the water column

trace metals in lacustrine and marine sediments a case study from the gulf of carpentaria northern australia abstract sediment cores taken from the shallow the data form remarkably linear covariation trends suggesting physical mixing of two sedimentary components as the predominant process controlling the compositions of both lacustrine and marine sediments one component has high ca sr and mn suggestive of biogenic carbonate the other component contributes virtually all of the sedimentary budget of the other elements and is probably terrigenous clay either water borne or aeolian minor contributions from heavy minerals such as zircon may account for the higher values of zr and y for some horizons in the core anomalously high concentrations of zircon may have been brought into the gulf as dust particles during episodes of increased aeolian activity carbonate is most abundant in the marine sediments resulting in the higher observed ca and sr concentrations v and mn seem to be the metallic elements most sensitive to depositional environment and water chemistry environmental conditions had little or no effect on sedimentation of the other metals v and mn were delivered to the lacustrine sediments more efficiently than to the marine sediments probably reflecting changes in solubility as slightly acid lacustrine waters gave way to more neutral oceanic conditions metal organic complexing was not an important process in these oxidised sediments

geochemistry and mineralogy of marine and non marine namurian black shales from the tansley borehole derbyshire the namurian black shales studied have a good palaeontological control pyrite illite and organic matter are higher in the marine shales and siderite and kaolinite are higher in the non marine shales the distribution of the diagenetic iron minerals is attributed to anionic activities controlled by salinity the same control could account for the observed clay mineral distribution by differential flocculation the major element geochemistry closely reflects the above mineral variation mn and zr are higher in the non marine shales due to siderite and zircon respectively co cr rb y and ba are not significantly different and a detrital source mainly clay minerals is suggested in the marine shales the elements pb cu v ni sr and zn are significantly higher using a discriminant function analysis the palaeosalinity groups are separated and the contribution of each element to the separation is calculated the present element locations are thought from correlation analysis to be pyrite and organic matter by analogy with experimental work and modern environments the element enrichment is mainly attributed to reactions involving organic matter and oxyhydroxide material in environments in which salinity and slow rates of sedimentation were important factors the element enrichment cannot be related directly to seawater concentrations unlike some black shales and the accumulation rates for pb and cu are thought to be unusually high

formation of secondary pyrite and carbonate minerals in the lower williams lake tailings basin elliot lake ontario canada the lower williams lake tailings which resulted from u milling operations during the late 1950s and early 1960s cover an area of 2 ha in a small bog under partial water cover the tailings are underlain by a sand unit containing decaying organic material above the natural base consisting of sand till and gravel the tailings are composed predominantly of quartz muscovite k feldspar plagioclase and clinochlore residual pyrite grains displaying angular to subangular particles measuring less than 1 to 250 m occur in concentrations ranging from trace to approximately 6 wt framboidal pyrite has formed within the tailings basin in association with organic rich material the appearance of framboidal pyrite in the tailings indicates a reversal of the oxidation process and reprecipitation of fe sulfides in addition the tailings include calcite calcian siderite fe oxyhydroxides and fe si oxyhydroxides as secondary precipitates and replacement products groundwaters in the tailings and the underlying units are saturated with respect to gypsum and siderite these and the other saturation indices calculated for calcite goethite and barite are consistent with the secondary mineralogy of the tailings conditions promoting the formation of pyrite can be described as neutral to weakly alkaline and reducing assisted by microbial activity this study provides the first account of secondary carbonates and framboidal pyrite in the elliot lake tailings the existing environmental conditions at the site are favorable for the desired site rehabilitation

the magnetic structure and palaeomagnetic recording fidelity of sub micron greigite fe3s4 abstract we present the results of a finite element micromagnetic model of 30 nm to 300 nm greigite fe3s4 grains with a variety of equant morphologies this grain size range covers the magnetic single domain sd to pseudo single domain psd transition and possibly also the psd to multi domain md transition the sd psd threshold d 0 is determined to be 50 nm d 0 56 nm depending on grain shape the nudged elastic band method was used to determine the room temperature energy barriers between stable states and thus the blocking volumes it is found that in the absence of interparticle magnetostatic interactions the magnetisation of equant sd greigite is not stable on a geological scale and only psd grains 70 nm can be expected to carry a stable magnetisation over billion year timescales i e all non interacting sd particles are essentially superparamagnetic we further identify a mechanism for the psd to multi domain md transition which is of a continuous nature from psd nucleation up to 300 nm when structures typical of md behaviour like closure domains begin to form

geochemistry of cu co ni zn cd and cr in the surficial sediments of a tropical estuary southwest coast of india a granulometric approach geochemical characteristics of six trace metals cu co ni zn cd and cr in the bulk sediment and sand silt and clay fractions of a tropical estuary on the southwest coast of india have been studied and discussed in bulk sediment the trace metal concentration is controlled mainly by the textural composition of the sample mud sandy mud and sandy silt register higher concentrations of trace metals than that in sand dominant sediments the granulometric partitioning studies also re affirmed the role of particle size in enriching the trace metals the silt and clay fractions exhibit 7 8 times the enrichment of cu and cd compared to that in sand the enrichment factors of zn cr ni and co in the silt and clay fractions compared to that in sand are 5 6 4 5 2 5 and 2 3 times respectively the trace metals in the sand fraction particularly ni and cr exhibit strong positive correlation with the heavy mineral content of the samples it clearly indicates a heavy mineral pathway to the trace metals in the sand fraction cu and co in silt and clay fractions exhibit a marked decrease towards the high saline zones of the estuary this is attributed to the desorption of cu and co from particulate phases during estuarine mixing contrary to cu and co the content of zn in the clay fraction shows a marginal increase towards the estuarine mouth this could be explained by the influx of zn rich contaminant discharges from zn smelting industries located slightly north of the estuarine mouth the released zn will effectively be held in the lattices of the clay mineral montmorillonite which also exhibits a marked increase towards the estuarine mouth the anomalously high values of cd in some places of the central vembanad estuary is attributed to the local pollution

pollen concentration analysis of ancestral pueblo dietary variation previous coprolite research on the colorado plateau has shown that macrofossils are a useful way of statistically demonstrating prehistoric dietary variation of ancestral pueblos anasazi up until now pollen concentration from human coprolites has not been used for comparative statistical study we present here the statistical anal ysis of pollen concentration values of coprolites from two ancestral pueblo sites salmon ruin and antelope house the data show that although most pollen types do not show statistically significant variation there are some types that show how different ancestral pueblo populations adapted to plant resources in different environ ments the analysis indicates that future work should focus more on pollen concentration analysis of coprolites

kerogen origin evolution and structure kerogen commonly defined as the insoluble macromolecular organic matter om dispersed in sedimentary rocks is by far the most abundant form of om on earth this fossil material is of prime importance as the source of oil and natural gas moreover kerogen can provide essential information on major topics such as past environments climates and biota this review reports the main advances in kerogen studies since the comprehensive synthesis edited by durand durand b ed kerogen insoluble organic matter from sedimentary rocks editions technip paris 1980 it is organized into eight sections the first two are concerned with the successive definitions of kerogen and the definition used here the different techniques used for kerogen isolation without loss or degradation and basic kerogen analysis the third and fourth focus on sedimentary om sources and preservation processes in relation to depositional environment including sedimentation conditions favourable for kerogen accumulation and extrapolation to past geological time great strides have been made in the latter topics over the last 25 years owing to a combination of classical studies in organic geochemistry and studies in other domains such as biogeochemistry oceanography hydrology and soil science along with the development of powerful analytical tools the next two sections deal with the different kerogen classifications by type and kerogen evolution and maturation upon burial in sediments structural modelling of coal and kerogen based on physical and or chemical structural analysis is described in the following section although only statistical the models thus derived provide a synthetic view of the main structural resemblances and differences among various samples in relation to source maturity or physicochemical properties finally the last section explores some of the advances in kerogen understanding expected for the near future the review includes a list containing about 500 references

methanotrophs regulated atmospheric sulfur isotope anomalies during the mesoarchean tumbiana formation western australia abstract the 2 73 billion year old tumbiana formation of the fortescue group in the pilbara craton western australia preserves one of the best records of the fortescue negative carbon isotope excursion with organic 13 c values as low as 60 the prevailing environmental conditions at this biological excursion are not well understood here we present an integrated carbon 12 c 13 c and multiple sulfur 32 s 33 s 34 s 36 s isotopes study of a pristine diamond drill core through the tumbiana formation collected at meentheena by the pilbara drilling project our results show centimeter to meter scale heterogeneities in sulfur and carbon contents and isotope compositions organic 13 c values vary at the meter scale and display a bimodal distribution with peaks at about 44 and 34 this bimodal distribution is interpreted to reflect variations in the contribution of methanotrophic metabolism to the biomass the 34 s v cdt values of sedimentary pyrite vary from 5 73 to 2 75 sulfur isotopes sulfur contents and s c ratios are variable suggesting a complex local biotic sulfur cycling sedimentary pyrite preserves mass independent fractionation of sulfur mif s with 33 s v cdt ranging between 0 25 and 1 64 average 0 47 corresponding to the characteristic dampened mesoarchean anomalies positive correlation between sulfide mif s and a 13 c depletion of organic matter argues for a causal link between methanotrophs activity and the preservation of mif s anomalies in the rock record

a simplified microwave model and its application to the determination of some oceanic environmental parametric values using multichannel microwave radiometric observations this paper proposes a simplified microwave model linerized by taylor expansion and incorporating observed fundamental microwave emissive properties and discusses its application along with the least square method for determining some oceanic environmental parametric values from multichannel observation data as a case study microwave radiometric observations were made in vertical and horizontal polarizations at 6 7 and 18 6 ghz at incidence angles from 200 to 700 at steps of 100 and sea surface temperature wind speed and sky brightness temperatures at the above dual frequencies at zenith angles from 200 to 700 were determined from a set of observed data at each incidence angle the algorithm derived results were compared with observed ones and showed good agreements within 10 percent of errors at incidence angles from 200 to 600 however no good agreement was attained at large incidence angles such as 70 except sky brightness temperature at 6 7 ghz this disagreement may be attributed mainly to the difficulty and incompleteness in corrections such as estimation of reflected sky radiation and antenna characteristics both for retrieval of the antenna temperature averaged over the main lobe and observation errors this fact however may also suggest that observations at such larger incidence angles are of less utility

iron species determination to investigate early diagenetic reactivity in marine sediments iron speciation was determined in hemiplegic sediments from a high productivity area to investigate systematically the early diagenetic reactivity of fe a combination of various leaching agents 1 m hci dithionite buffered in citrate acetic acid hf h2so4 acetic cr ii was applied to sediment and extracted more than 80 of total fe subsequent fe species determination defined specific mineral fractions that are available for fe reduction and fractions formed as products of fe diagenesis to determine the fe speciation of sheet silicates we explored an extraction procedure hf h2so4 and verified the procedure by application to standard rocks variations of fe speciation of sheet silicates reflect the possible formation of fe bearing silicates in near surface sediments the same fraction indicates a change in the primary input at greater depth which is supported by other parameters the fe ii fe iii ratio of total sediment determined by extractions was compared with mossbauer spectroscopy at room temperature and showed agreement within 10 m6ssbauer spectroscopy indicates the occurrence of siderite in the presence of free sulfide and pyrite supporting the importance of microenvironments during mineral formation the occurrence of other fe ii bearing minerals such as ankerite ca fe mg carbonate can be presumed but remains speculative

characterization of the reactivity of riverine heterogeneous sediments using a facies based approach the rhine meuse delta the netherlands large groundwater resources are found in densely populated lowland areas which consist often of young unconsolidated and reduced sediments when anthropogenic activities lead to oxygenation of the aquifer breakdown of the main reduced fractions i e sedimentary organic matter som and pyrite could lead to severe groundwater deterioration such as acidification heavy metal mobilization and increased hardness the characterization of the reactive properties of these sediments is important in predicting groundwater deterioration but is often complicated by the high degree of heterogeneity of these sediments in this study the potential reduction capacity prc based on som and pyrite content the potential buffer capacity pbc based on carbonate content potential acidification capacity pac based on the potential acid production by sulfide oxidation and the measured reduction capacity mrc of five facies which are typical of the riverine sediments in the rhine meuse delta the netherlands were determined a universal facies classification model was used to classify the deposits into more homogeneous sub units based on lithologic and geogenic properties with a further sub division into oxic or anoxic redox environment based upon groundwater data and field observations the bulk chemical data show strong variation across facies for the median values of prc 186 9093 mmol o2 kg 1 pbc 17 132 mmol o2 kg 1 and pac 36 1530 mmol h kg 1 the mrc was measured as reactivity to molecular o2 exposure and was 0 5 567 3 mmol o2 kg 1 steady state oxidation rates were in the wide range of 0 001 10 355 mmol o2 kg 1 day 1 but were typically about 3 8 times faster in fine facies than in coarse facies both the prc and mrc depend strongly on grain size but also on the syn post depositional environment and redox conditions the main part of the prc consists of som but pyrite reactivity is higher than som reactivity as shown by the relative depletion of pyrite in oxic subfacies and the preferential oxidation during the oxidation experiments some facies are very prone to acidification because the pac is higher than the pbc but the oxidation experiments also show that acidification could already start before the prc is fully exhausted this study is one of the few that combines bulk chemical data groundwater data and reactivity measurements and shows that a facies based approach is a practical tool in characterizing the reactivity of heterogeneous deposits 2007 elsevier ltd all rights reserved

distribution of arsenic iii arsenic v and total inorganic arsenic in porewaters from a thick till and clay rich aquitard sequence saskatchewan canada abstract inorganic arsenic species were measured in the porewaters collected from eighteen piezometers installed between 3 and 91 4 m below ground in a thick till and clay rich aquitard sequence located in southern saskatchewan to investigate the distribution of and controls on arsenic speciation in the sequence aqueous concentrations of as v as iii and total as are in the range of 0 31 97 0 71 21 and 3 2 98 ppb respectively profiles of as iii and as v concentration distribution with depth broadly track that of total as erratic increases to 15 2 m then more uniform concentrations to 88 m aqueous arsenic is accumulated at the upper redox transition zone 6 14 m the alkaline porewater at 91 4 m contains the highest concentrations of as v and total as which might result from the facilitated desorption of arsenate from the host solid due to decrease of positive surface charge of the oxides in alkaline solution the ratio of as v as iii is greater than unity in the uppermost oxidized porewater 3 m less than unity from 4 6 to 71 6 m and greater than unity in the lowest four porewaters 76 2 to 91 4 m in the 3 m porewater low as iii but high as v as iii is due to the oxidized nature of the near surface weathered till the high as v as iii in the deepest porewater at 91 4 m likely results from the enhanced and heterogeneous oxidation of as iii to as v on clay mineral surfaces in the alkaline solution total as and arsenic speciation may not be controlled by as fe or mn concentrations in the host till or clay dissolved as v and total as positively covary with aqueous chloride whereas dissolved as iii is independent of aqueous chloride aqueous as iii and to a less extent as v and total as are positively correlated with dissolved mn in the till in the clay aqueous as v and total as show strong negative covariation with mn however aqueous as iii as v and total as exhibit almost no correlation with total dissolved fe in the till the as v as iii ratio has strong negative correlation with dissolved mn but positive covaration with dissolved chloride generally good agreement between the redox potentials eh calculated from aqueous as v and as iii concentrations and those measured by a pt electrode throughout most of the unoxidized till suggests the suitability of using as v as iii redox couple as a redox indicator for the studied aquitard system however large negative bias of the calculated eh from the measured eh in the oxidized till upper unoxidized till and the clay is attributed to errors associated with the field measurements of eh

reducing marine and warm climate conditions during the late cretaceous and their influence on organic matter enrichment in the oil shale deposits of north jordan abstract late cretaceous oil shales located in the yarmouk sub basin north jordan were analysed using techniques of organic and inorganic geochemistry coupled with a microfossil study results of this study were used to reconstruct the paleoenvironmental and paleoclimatic conditions during the late cretaceous and to investigate their influence on organic matter enrichment of the oil shale deposits the analysed oil shales have high toc and s total content values in the ranges of 2 11 12 85 wt and 1 83 8 81 wt respectively the high s total content and its relation with toc values indicate that the sulfur is associated with organic matter and that the oil shales were deposited in a marine environment under reducing conditions this is shown by petrographic observation and supported by biomarker distributions the microscopic investigation indicated that the oil shales contain abundant liptinitic materials i e alginite and amorphous organic matter and planktonic foraminifera the presence of these sapropelic materials and planktonic foraminifera assemblages further suggests a marine origin biomarker distributions are also known to reflect dominantly marine plankton algal and microorganisms source input water column stratification and low oxygen reducing conditions are indicated by narrow pr ph values relatively high v ni elemental ratios and the presence of gammacerane reducing conditions contribute to preservation of organic matter warm water periods during the late cretaceous are also indicated by dominant occurrences of warm water index microfossil taxa the warm climate combined with elevated phosphorus p are the major causes of excessive algae growth and led to enhanced biological productivity within the photic zone of the water column during deposition of the oil shale deposits this increased bio productivity in combination with good preservation of organic matter are the main mechanisms of organic matter enrichment within the late cretaceous oil shales in the north jordan

organic geochemistry of the lower toarcian posidonia shale in nw europe abstract a suite of core and outcrop samples of the lower toarcian posidonia shale and time equivalent deposits was collected from multiple locations including southern germany swabian alb and franconian alb northern germany the east coast of great britain the netherlands and luxembourg in order to study major differences and similarities with respect to depositional environment and redox potential based on molecular geochemical data all samples are immature or in the early oil window with the highest thermal maturity occurring in the profile from great britain about 0 7 vitrinite reflectance molecular geochemical maturity parameters were used to quantify maturation in detail during shale deposition in the west cleveland basin great britain h 2 s was immediately consumed in the water column by terrigenous input supplying abundant reactive iron to form pyrite these samples are characterized by low dibenzothiophene phenanthrene ratios 95 of 2 and h 2 s in contrast sulfidic euxinic bottom waters possibly with enhanced salinity and stratified water column prevailed due to a more restricted iron supply in luxembourg northern germany and the franconian alb of southern germany a more oxygenated dysoxic bottom water column associated with anoxic sediments i e anoxic dysoxic boundary close to the sediment water interface prevailed in the swabian alb of southern germany despite observed changes within each vertical profile at each site large scale regional trends in depositional conditions can be clearly identified for the early toarcian

oceanography from space active and passive spaceborne instruments that can observe the sea are discussed attention is given to satellite observations of ocean surface temperature and heating wind speed and direction ocean currents wave height ocean color and sea ice specific measurements now being made from space are described the accuracy of various instruments is considered and problems associated with the analysis of satellite data are examined it is concluded that the satellites and techniques used by different nations should be sufficiently standard that data from one satellite can be directly compared with data from another and that accurate calibration and overlap of satellite data are necessary to confirm the continuity and homogeneity of the data

geochemical study of organic matter rich cycles from the kimmeridge clay formation of yorkshire uk productivity versus anoxia abstract in this contribution we study two meter scale cycles from the kimmeridge clay formation cored near marton yorkshire which shows cyclic organic matter om distribution our aim is to try to understand the factors responsile for om accumulation the first cycle called lower cycle shows a total organic carbon toc content between 1 and 10 whereas the second called upper cycle shows a toc content varying between 5 and 35 the geochemical composition major elements and trace elements the organic geochemistry toc hi palynofacies and mineralogy of the sediments have been determined in both cycles the cyclicity is expressed through variations in the nature and in the relative abundance of the various types of organic matter constituents furthermore dilution effects by inorganic components of the sediment cannot account for the toc cyclicity for lower cycle the mo v and u content is low and little variable as is the intensity of the oxidation which om suffered from this indicates that variations in phytoplanktonic productivity may be held responsible for the cyclicity in steady and mildly reducing redox conditions in the upper cycle cyclicity also appears to depend on productivity but variations in the concentration of mo v and u and in the oxidation state of the om suggest the environment was temporarily more reducing it is proposed that larger amounts of h 2 s were released into marine bottom waters as a result of initial om decomposition forced the oxic anoxic boundary to rise in the water column and thus favoured om storage the main driving force for variations in the om concentration was the productivity of organic matter walled phytoplankton redox conditions of the depositional environment could have had a positive action but only by acting as a positive feedback effect

magnetic properties of pelagic marine carbonates abstract pelagic carbonates are deposited far from continents usually at water depths of 3000 6000 m at rates below 10 cm kyr and are a globally important sediment type recent advances with recognition of widespread preservation of biogenic magnetite the inorganic remains of magnetotactic bacteria have fundamentally changed our understanding of the magnetic properties of pelagic carbonates we review evidence for the magnetic minerals typically preserved in pelagic carbonates the effects of magnetic mineral diagenesis on paleomagnetic and environmental magnetic records of pelagic carbonates and what magnetic properties can tell us about the open ocean environments in which pelagic carbonates are deposited we also discuss briefly late diagenetic remagnetisations recorded by some carbonates despite recent advances in our knowledge of these phenomena much remains undiscovered we are only at early stages of understanding how biogenic magnetite gives rise to paleomagnetic signals in sediments and whether it carries a poorly understood biogeochemical remanent magnetisation recently developed techniques have potential for testing how different magnetotactic bacterial species which produce different magnetite morphologies respond to changing nutrient and oxygenation conditions future work needs to test whether it is possible to develop proxies for ancient nutrient conditions from well calibrated modern magnetotactic bacterial occurrences a tantalizing link between giant magnetofossils and paleogene hyperthermal events needs to be tested much remains to be learned about the relationship between climate and the organisms that biomineralised these large and novel magnetite morphologies rather than being a well worn subject that has been studied for over 60 years the magnetic properties of pelagic carbonates hold many secrets that await discovery

effects of sources and diagenesis on the isotopic and chemical composition of carbon and sulfur in cretaceous shales abstract the cretaceous lea park formation of south central saskatchewan contains organic matter from marine and terrestrial sources in proportions that vary as a result of deposition during the campanian claggett transgressive regressive cycle in the western interior seaway of north america the relative proportions of organic matter from these sources were determined using a terrestrial index ti that compares n alkanes considered to be of terrestrial origin n c25 to n c59 to those considered to be of marine origin n c15 to n c22 the c isotopic composition of cretaceous marine organic matter is found to be near 32 o while terrestrial organic matter is near 24 the lower 13c values of marine organic matter from the lea park formation as compared with those of recent marine organic matter are similar to the relation observed in other cretaceous rocks 13c values of terrestrial organic matter however are similar to those of the present during the miocene 13c values of marine organic matter became similar to recent values and this change in isotopic composition may be related to the development of deep cold water associated with the formation of antarctic ice sheets consequences of the formation of deep cold water may include improved exchange of co2 between atmosphere and oceans reduced pco2 levels and co2 concentrations in the photic zone of the oceans and environmental changes sufficient to produce an alternate metabolic pathway in phytoplankton all of these processes potentially result in higher 13c values in marine organic matter pyrite formation in the lea park mudstones was limited by the availability of metabolizable organic matter with the greatest amount of pyrite typically associated with organic matter having the lowest ti values 34spy values range nearly 30 and vary directly with the composition of associated organic matter variations in the supply of metabolizable organic matter were more important than differences in sedimentation rate in producing the range of 34spy values a34s values 534sseawater 34spyrite vary with the composition of organic matter and become larger when associated with more metabolizable organic matter

geochemical relationships of late paleozoic carbon rich shales of the midcontinent usa a compendium of results advocating changeable geochemical conditions abstract previous studies have shown that pennsylvanian black shales of the midcontinent us possess a more complex geochemical history than was once thought vine and tourtelot econ geol 65 1970 253 and coveney and glascock appl geochem 4 1989 347 note that the widespread nature of metalliferous pennsylvanian black shales and the diverse geological environments across the midwestern us pose the likelihood that metals contained in the black shales are of complex origins detailed geochemical and statistical representations using characteristics of numerous black shale members have shown that water depth may not have been uniformly deep as previously inferred by numerous workers earlier suggestions that these black shales were associated exclusively with anoxic depositional conditions have been challenged by a more realistic theory of multifaceted fluctuating environmental conditions a wide range of major and trace element concentrations combined with widely varying characteristics and diverse types of organic matter indicate the presence of fluctuating geochemical settings the presumption is that numerous associated chemical reactions occurred syngenetically one geochemical index degree of pyritization dop suggests a dysaerobic to aerobic setting for many of the shales whereas some other geochemical proxies i e v v ni indicate punctuated episodes of bottom water anoxia schieber abstr programs geol soc am 33 6 2001 a102 notes that in some black shales pyrite enrichment due to intermittent organic reworking explains the high dop values once thought to equate with extreme euxinic depositional conditions it seems likely therefore that even during apparent euxinic periods as indicated by bulk geochemistry oxygen deprived events were apparently short lived the seemingly euxinic fingerprint as shown by geochemical characteristics may result through time averaging abstr programs geol soc am 33 6 2001 a102 of intermittent euxinic events providing a misleading indication of dominant euxinic conditions thus detailed microstratigraphic sampling is necessary to delineate short punctuated occurrences of intermittent sub oxic episodes the midcontinent pennsylvanian shales may reflect a complex array of bottom water oxygenation variations and water depth fluctuations in response to climatic and localized events hatch j r and leventhal j s 1992 relationship between inferred redox potential of the depositional environment and geochemistry of the upper pennsylvanian missourian stark shale member of the dennis limestone wabaunsee county kansas usa in meyers p a pratt l m nagy b eds geochemistry of metalliferous black shales chem geol 99 65 82 complicated by post depositional events appl geochem 4 1989 347 this research examines the previous exclusively anoxic origin for midcontinent pennsylvanian black shales from a geochemical perspective and offers an alternative supported by detailed statistical presentations with the hypothesis that events of anoxia were punctuated by short lived dysaerobic or even near oxic events

sea surface temperature mapping with the seasat microwave radiometer sea surface temperature data from the seasat scanning multichannel microwave radiometer smmr has been mapped for the period july 7 to august 6 1978 in the western north pacific 20 n 50 n 140 e 180 and compared against similar maps constructed from all available ship observations the temperature difference between the smmr and ship maps has a standard deviation of 0 75 c about a mean bias of 0 22 c smmr being warmer the average standard deviation of all individual observations about the mapped values is 1 51 c and 2 10 c for smmr and ship respectively both the smmr and ship maps exhibit the known major climatological features for the region in addition both data types yield similar maps of sea surface temperature anomaly departure from climatology with large scale 500 km anomaly features of 1 3 c aside from having a lower noise level the smmr data is superior to the ship data for constructing large scale maps because it is more uniformly distributed in space and time

ediacaran cambrian ordovician silurian and permian shales of the upper yangtze platform south china deposition thermal maturity and shale gas potential abstract for many years the yangtze platform has been successfully explored and exploited for petroleum the lower silurian longmaxi shale proved to contain commercial quantities of gas but several other formations might also have a high potential for shale hosted gas exploration this paper comprises of geochemical petrographical petrophysical and mineralogical information on the major proterozoic and paleozoic gas shales in the upper yangtze area which provides insights on the depositional environment the thermal maturity of organic matter shale gas storage capacity and the fracability of these rocks the total organic carbon toc content varies from 0 1 to 22 5 with an average value of 2 7 and most of these shales were deposited in an oxygen depleted marine environment equivalent vitrinite reflectance vrr values range from 2 20 to 4 25 indicating that all samples are in the gas generation window and lost a large amount of primary organic carbon porosity varies between 1 5 and 13 6 with an average value of 5 8 while the excess sorption capacity ranges from 0 10 to 0 22 mmol g rock minerology data show that quartz is the predominant mineral except for the upper permian longtan formation in which clay minerals account for 29 to 84 new data were combined with those from other publications and compared to information on other well studied shale hosted gas systems

microfabric mineralogy and early diagenetic history of the whitby mudstone formation toarcian cleveland basin u k the whitby mudstone formation in northeast england contains three shale facies normal restricted and bituminous which have previously been differentiated on the basis of sedimentary structures and faunal assemblages this paper shows that the three facies can also be differentiated by mineralogical geochemical and microtextural criteria determined using bsem edxra xrd and xrf the bituminous shale facies consists of finely laminated shales containing an early diagenetic mineral assemblage dominated by pyrite calcite and dolomite the weakly laminated restricted facies shales contain an early diagenetic assemblage dominated by pyrite the normal facies shales are very weakly laminated and contain siderite in addition to pyrite the geochemical conditions which left a dominant early diagenetic imprint on the three facies are interpreted to be carbon rich sulphidic carbon poor sulphidic and very carbon poor sulphidic respectively

weathering of the ganga alluvial plain northern india implications from fluvial geochemistry of the gomati river abstract in the northern part of the indian sub continent the ganga alluvial plain gap feeds its weathering products to the ganga brahmaputra river system one of the world s largest fluvial systems the authors present a geochemical study of the gap weathering products transported by the gomati river the ganga river tributary to understand weathering processes of an alluvial plain in a humid sub tropical climate a total of 28 sediment samples were collected during the monsoon season and were analysed by x ray fluorescence spectrometry for 25 major and trace elements bulk chemistry of the channel flood and suspended sediments mostly consists 90 80 and 75 respectively of three elements al si and fe major element concentrations normalised with respect to upper continental crust ucc show strong depletion of highly mobile elements na ca and enrichment of immobile elements ti si silica enrichment in the sand fraction is probably caused by chemical weathering of feldspar mineral sorting during fluvial transportation acts as the single important factor that controls the geochemistry of these weathering products and also strongly influences major and trace element distribution in the individual sediment samples trace element ba cr cu nb ni pb v and zn concentrations were strongly correlated with major element si al fe mn and k concentrations indicating that the abundance of trace elements is controlled by the same processes that control the major element distribution in these sediments the gap weathering products were geochemically distinguished as arkose to litharenite in rock classification chemical mobility normalised with respect to tio 2 in ucc indicates that si na zr ba and sr mainly derived from feldspar muscovite and biotite are lost during weathering iron and zn remained immobile during weathering and were strongly adsorbed by phyllosilicates and concentrated in fine grained sediment fractions the chemical index of alteration indicates that the gap has experienced chemical weathering of incipient to moderate intensity the gap weathering products also demonstrated a progressive incomplete alteration in the alluvial sequence made up of the himalayan derived sediments a model has been proposed to better understand weathering processes and products of the gap in temporary storage of 50 ka in a humid sub tropical climate

early diagenesis of the upper devonian escuminac formation in the gaspe peninsula quebec sedimentological and geochemical evidence abstract clay mineral investigations pyrolysis of organic matter and microscopic observation of palynomorphs are used to interpret the diagenetic conditions of the upper devonian escuminac formation quebec canada pyrolysis of kerogen vitrinite reflectance and the presence of smectite show that the sediments of this formation have been subjected only to a shallow burial diagenesis hence the geochemical signatures are informative on the palaeoenvironment concretions are observed in the escuminac formation sedimentological and geochemical evidence suggest that these concretions were formed during early diagenesis from biodegradation of organic matter the well known fish fauna of the escuminac formation show good preservation due in part to extensive early diagenetic carbonate cementation the occurrence of calcite cements and fibrous calcite is attributed to the early diagenetic transformation of pre existing organic matter

control of the preservation of organic matter by productivity and sulphate reduction in kimmeridgian shales from dorset uk abstract the kimmeridgian shales of dorset uk have a very wide range of total organic carbon toc content and hydrogen index hi these cyclic changes of organic carbon accumulation are usually interpreted in terms of biomass changes induced by variations in productivity the influence of such variations on the intensity of sulphate reduction and consequently on the preservation of organic carbon were studied the pyrite content does not reflect the full extent of sulphate reduction for sediments with a toc content greater than 10 when easily reducible iron is no longer available h 2 s is preferentially fixed as organic compounds in algal bodies a sulphate reduction index sri initial c org residual c org was calculated for each sediment on the basis of the sulphate reduction reaction stoichiometry and a drastic change in sulphate reduction intensity was seen for toc contents of about 10 above this value the sri is low and decreases with increasing toc content the sediments are rich in organic carbon composed of well laminated stacked algal bodies and were probably deposited at an oxygen depleted water sediment interface in this instance the quality and the amount of organic matter buried depends directly on the organic fluxes towards the redox interface it is assumed that the high relative input of organic matter which can be metabolized exceeds the availability of sulphate in the pore waters so that part of it escapes sulphate reduction and is probably degraded by other processes methanogenesis for toc contents less than 10 the sri is higher and variable the sediments show traces of burrowing and the depositional conditions are thought to be dysaerobic it is proposed that under such conditions bioturbation brings both sulphate and reducible iron into the sediment and that sulphate reduction mainly expressed by the presence of pyrite consumes all the available organic matter which can be metabolized the strong variability in the intensity of sulphate reduction depends on various parameters such as the genetic type of planktonic organic matter the method of transportation to the sediment and possibly the earlier oxic degradation during transportation