geochemical cycling of redox sensitive metals in sediments from lake malawi a diagnostic paleotracer for episodic changes in mixing depth changes in heat balance wind stress and lake level can affect the efficiency of mixing and depth of oxygen penetration in deep tropical lakes this study examines how transient changes in these parameters as reflected by the redox state of bottom waters are recorded in the sedimentary record of lake malawi we measured concentration profiles of redox sensitive metals across a layer of oxidized sediment deposited within a sequence composed of reduced sediments in a core taken at 298 m water depth 100 m below the present day chemocline by examining a range of metals that exhibit different geochemical behaviors mobilization under reducing fe mn versus oxidizing u conditions formation of insoluble sulfides cd mo pb zn susceptibility to scavenging onto fe or mn oxyhydroxide precipitates co mo pb v zn we are able to outline a sequence of events consistent with the formation of this feature 1 at some time before 11 ky bp there was an episode of penetration of oxygenated waters to depths close to or greater than that of this core i e substantially deeper in the lake basin than at present at this time diagenetically remobilized fe and mn were oxidized and precipitated in a near surface sediment horizon 2 fe and mn oxyhydroxides that precipitated from the water column as metal rich anoxic waters were mixed upward into oxygenated waters were deposited in an immediately overlying layer of the sediment such material continued to accumulate in surface sediments for a few hundred years until oxic conditions no longer prevailed in overlying waters 3 as the depth of the chemocline rose relative to the present day lake surface this authigenic material was in turn overlain by reducing sediments 4 subsequent diagenetic remobilization at the top and bottom of this redox sandwich resulted in formation of horizons enriched in u mo and sulfide forming metals notably cd along the redox gradients both above and to a lesser extent below the layer of oxidized sediment these enrichments immobilized under reducing conditions will remain as permanent markers of the episode of deepening of the chemocline even after reduction and remobilization of the oxidized fe and mn solids in addition such markers may be useful in determining whether observed episodic interruptions in deposition of varved sediments in the deep anoxic basins of lake malawi are due to bioturbation brought on by episodes of deeper oxygen penetration in the water column

distribution and significance of novel low molecular weight sterenes in an immature evaporitic sediment from the jinxian sag north china abstract an unusual series of c 22 c 27 monounsaturated sterenes and c 24 c 30 tetracyclic terpanes 17 21 seco hopanes were detected in relatively high concentrations in an immature evaporitic marl sediment of the jinxian sag bohai bay basin north china the site of unsaturation in these novel sterenes is assigned tentatively to the d ring on the basis of mass spectral interpretation which also distinguishes them from reported unsaturated sterenes other hydrocarbon biomarker or stable isotope characteristics are indicative of microbial e g methyl hopanes phytoplankton or higher plant depleted 13 c values of isoprenoids and hopanes inputs and an anoxic carbonate depositional environment hexacyclic hopanes tetracyclic terpanes the hydrocarbon composition showed no obvious biodegradation and the relatively high concentration of unsaturated terpenoids e g gammacerene and low values of other established maturity parameters t s t m 0 23 r o 0 44 t max 417 c are consistent with sediments of low maturity the novel low molecular weight sterenes and the tetracyclic terpanes may be early diagenetic products of microbial sources in a carbonate environment

geochemical effects of co2 sequestration in sandstones under simulated in situ conditions of deep saline aquifers abstract the geochemical effects of brine and supercritical co 2 scco 2 on reservoir rocks from deep 1500 2000 m saline aquifers were examined via experimental simulation at in situ conditions dry sandstone samples were mounted in a triaxial cell and autoclave system evacuated and saturated with 1 m nacl solution the brine rock system was allowed to react at 30 mpa confining pressure 15 mpa pore fluid pressure and 60 c while scco 2 was injected at a pressure gradient of 1 2 mpa the experiment was conducted for a period of 1496 h during which fluids were periodically sampled and analyzed the ph measured in partially degassed fluid samples at 25 c decreased from a starting value of 7 0 4 3 9 days and finally 5 1 after saturation with scco 2 fluid analyses indicate that most of the major e g ca mg fe mn and trace elements e g sr ba pb of the sandstone increase in concentration during the reaction with brine and scco 2 these results are supported by scanning electron microscopy which indicates dissolution of dolomite cement k feldspar and albite in addition to dissolution reactions the formation of montmorillonite was observed by adjusting surface area and reaction rates of dissolution and precipitation geochemical modeling of the experiments could reproduce long term trends in solution chemistry and indicated limited rates of dissolution as the system remained strongly undersaturated with most minerals including carbonates the geochemical models could not account for decreases in concentration of some elements changes in solution composition resulting from changes in imposed pressure gradient and the observed ca mg and si al ratios in solution

organic geochemical proxies of paleoceanographic paleolimnologic and paleoclimatic processes abstract organic matter constitutes a minor fraction of marine and freshwater sediments yet its important contribution to the sedimentary record can be used to reconstruct marine and continental paleoenvironments the organic matter content of sediments is the residue of past biota the amounts and types of organic matter present in sediments consequently reflect environmental conditions that impacted ecosystems at different past times general sources of the organic matter are inferred from bulk properties such as elemental compositions carbon and nitrogen stable isotope ratios rock eval pyrolysis data and organic petrography details of organic matter origins are refined by analyses of biomarker molecular compositions source changes are proxies for fluctuations in sea level oceanic surface currents and continental climates algal paleoproductivity rates are indicated by organic carbon mass accumulation rates and carbon and nitrogen stable isotopic compositions these parameters record past availability of nutrients and therefore are proxies of surface mixing in the oceans and amount of land runoff to lakes sea surface paleotemperatures are recorded by the number of carbon carbon double bonds in lipid biomarkers produced by marine algae larger proportions of the double bonds are proxies for the cooler surface waters that accompanied periods of global glaciation and intervals of enhanced upwelling the 13c and d values of plant organic matter record past concentrations of carbon dioxide in the atmosphere and changes in delivery of atmospheric moisture respectively diagenesis which causes the concentration and composition of organic matter in sedimentary settings to differ from those of the original biologically synthesized materials can bias organic geochemical paleoenvironmental records the magnitude of this potential source of misinformation must always be considered and evaluated comparison of multiple organic geochemical proxies of past conditions helps to compensate for the effects of diagenetic alterations and thereby to improve interpretations of paleoenvironmental change

diagenetic and catagenetic products of isorenieratene molecular indicators for photic zone anoxia a wide range of novel diagenetic and catagenetic products of the diaromatic carotenoid isorenieratene a pigment of the photosynthetic green sulphur bacteria chlorobiaceae has been identified in a number of sedimentary rocks ranging from ordovician to miocene compound identification is based on nmr mass spectrometry the presence of atropisomers and stable carbon isotopes atropisomers contain an axially chiral centre which in combination with other chiral centres results in two or more diastereomers that can be separated on a normal gc column chlorobiaceae use the reverse tca cycle to fix carbon so that their biomass is enriched in 13c high 13c contents of isorenieratene derivatives therefore support their inferred origins isorenieratene derivatives include c 40 c 33 and c 32 diaryl isoprenoids and short chain aryl isoprenoids with additional aromatic and or s containing rings c 33 and c 32 compounds are diagenetic products of c 33 and c 32 carotenoids formed from isorenieratene during early diagenesis through expulsion of toluene and m xylene respectively cyclisation of the polyene acyclic isoprenoid chain can proceed via an intramolecular diels alder reaction followed by aromatisation of the newly formed ring sulphurisation is also an important process during early diagenesis competing with expulsion and cyclisation sulphur bound isorenieratane is released during progressive diagenesis due to cleavage of relatively weak ss and cs bonds cleavage of c c bonds during aromatisation of newly formed rings and during catagenesis yields short chain compounds the inherent presence of a conjugated double bond system in carotenoids implies that similar diagenetic and catagenetic reactions can occur with all carotenoids chlorobiaceae live at or below the oxic anoxic boundary layer and require both light and h 2s the presence of isorenieratene or its diagenetic and catagenetic products in ancient sedimentary rocks and crude oils is therefore an excellent indication for photic zone anoxia in the depositional environment diagenetic and catagenetic products of isorenieratene are expected to find applications in reconstruction of palaeoenvironments and in oil oil and oil source rock correlation studies their presence in several petroleum source rocks suggests that anoxia is an important environmental parameter for the preservation of organic matter

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

chemostratigraphy of the posidonia black shale sw germany ii assessment of extent and persistence of photic zone anoxia using aryl isoprenoid distributions aquatic depositional environments where anoxic conditions extend from bottom waters into the photic zone occurred frequently during the geologic past periods of photic zone anoxia pza can be recognized by the presence of specific lipids produced exclusively by the green sulphur bacteria chlorobiaceae that are preserved in the sedimentary record chlorobiaceae perform anoxygenic photosynthesis that requires light penetration into h2s saturated waters sediment samples integrate paleoenvironmental conditions over time intervals ranging from at best a few decades to more commonly several millennia photic zone anoxia recognized in paleoenvironmental analyses is thus defined as episodic with no further interpretation on the duration and persistence of the anoxic events we provide here a high resolution multiproxy chemostratigraphy study for the toarcian posidonia black shale from the dotternhausen section in sw germany in order to assess duration and seasonal fluctuation of photic zone anoxia based on the relative abundance of derivatives of chlorobiaceae lipids we assess the variability in the degree and persistence of photic zone anoxia using an aryl isoprenoid ratio air obtained by calculating the proportion of the short chain c13 17 versus the intermediate chain c18 22 aryl isoprenoids higher relative abundance of the short chain analogues is interpreted as indicating more intensive aerobic degradation of aryl isoprenoids air varies between values of 0 5 indicative of persistent pza phases and 3 0 for short termed episodic pza events absolute concentration of aryl isoprenoids is negatively correlated with the air which is in agreement with a progressive diagenetic breakdown of aryl isoprenoids the air decreases are validated using independent palecological and geochemical redox indicators for the posidonia shale in sw germany d 2004 elsevier b v all rights reserved

deep water anoxia over the frasnian famennian boundary la serre france a tectonically induced oceanic anoxic event the frasnian famennian f f transition is well exposed in the basinal setting of la serre montagne noire france where oxygen deficient conditions prevailed in bottom environments in this paper we study the f f transition using inorganic geochemistry notably major elements redox sensitive and or sulphide forming trace metals and productivity proxies the results are compared with published data concerning the la serre section other f f sections and other geological formations also deposited in basinal settings the very high enrichment in redox and productivity tracers indicates that anoxic conditions prevailed across the f f boundary and that surface productivity was intense such deep water restricted conditions coupled with high productivity occurred in various places in late devonian oceans recycling alone cannot account for the intense nutrient supply and therefore the most probable source was via land runoff we discuss the eovariscan episode of uplift that stimulated rock weathering and hence long term nutrient supply to the seas

black shale deposition and faunal overturn in the devonian appalachian basin clastic starvation seasonal water column mixing and efficient biolimiting nutrient recycling integrated geochemical data suggest that black shale deposition in the devonian geneseo formation of western new york was initiated by the coincidence of siliciclastic starvation and the intensification of seasonal water column stratification and mixing once established however black shale deposition was maintained through efficient recycling of biolimiting nutrients which enhanced primary productivity recycling efficiency was achieved through a positive feedback loop of oscillating benthic redox conditions that enhanced n and p regeneration from sediments sustained high primary productivity by returning nutrients to the photic zone during mixing and ensured a downward flux of organic matter that drove or enhanced the episodic development of benthic anoxia during stratification this feedback was ultimately disrupted by rising siliciclastic influx which diluted organic matter and restored benthic redox stability the abrupt overturn of diverse long standing appalachian basin marine communities may have been the result of trophic resource destabilization during geneseo deposition

the source and origin of terrigenous sedimentary rocks in the mesoproterozoic ui group southeastern russia abstract arenites wackes and associated shales and siltstones of the ui group of riphcan age in southeastern siberia have been analyzed for petrographic major element and selected trace element compositions including the ree petrographic results suggest that the arenites may have been derived from granites and that the wackes may have been derived from more plagioclase rich rocks like tonalites or granodiorites the high quartz relative to other materials in many sandstones suggest that they may have been derived from intense chemical weathering or diagenesis so the mineralogic ratios may have been changed during these processes the shales and siltstones are composed mostly of illite and quartz in addition a cn k diagrams indicate that the wackes and associated shales and siltstones underwent k metasomatisim extrapolation of the shales and siltstones associated with the wackes back to the plagioclase alkali feldspar line in the a cn k diagram suggests a high average plagioclase to alkali feldspar ratio in the provenance tonalite to granodiorite extrapolation of shales and siltstones associated with the arenites suggest a low plagioclase to alkali feldspar ratio in the provenance granite in addition the index of compositional variability icv and chemical index of alteration cia parameters of the shales and siltstones suggest the weathering of the first cycle material was intense trace element ratios suggest all the sedimentary rocks were derived from mostly granitoids shales and siltstones were plotted as elemental ratios e g th sc vs eu eu these plots suggest a mix of a granodiorite tonalite source for the source of the shales and siltstones associated with the wackes with a granite source for the shales and siltstones associated with the arenites the arenites also contain lower eu eu and higher th co and th sc ratios than the wackes this as is consistent with the petrography suggests that the arenites were derived from a source with more granite and less granodiorite tonalite than the wackes

interaction between co2 rich sulfate solutions and carbonate reservoir rocks from atmospheric to supercritical co2 conditions experiments and modeling abstract a test site for co 2 geological storage is situated in hontomin burgos northern spain with a reservoir rock that is mainly composed of limestone during and after co 2 injection the resulting co 2 rich acid brine gives rise to the dissolution of carbonate minerals calcite and dolomite and gypsum or anhydrite at depth may precipitate since the reservoir brine contains sulfate experiments using columns filled with crushed limestone or dolostone were conducted under different p p co 2 conditions atmospheric 1 10 3 5 bar subcritical 10 10 bar and supercritical 150 34 bar t 25 40 and 60 c and input solution compositions gypsum undersaturated and gypsum equilibrated solutions we evaluated the effect of these parameters on the coupled reactions of calcite dolomite dissolution and gypsum anhydrite precipitation the crunchflow and phreeqc v 3 numerical codes were used to perform reactive transport simulations of the experiments within the range of p p co 2 and t of this study only gypsum precipitation took place no anhydrite was detected and this only occurred when the injected solution was equilibrated with gypsum under the p p co 2 t conditions the volume of precipitated gypsum was smaller than the volume of dissolved carbonate minerals yielding an increase in porosity up to 4 a decrease in t favored limestone dissolution regardless of p co 2 owing to increasing undersaturation with decreasing temperature however gypsum precipitation was favored at high t and under atmospheric p co 2 conditions but not at high t and under 10 bar of p co 2 conditions the increase in limestone dissolution with p co 2 was directly attributed to ph which was more acidic at higher p co 2 limestone dissolution induced late gypsum precipitation long induction time in contrast to dolostone dissolution which promoted rapid gypsum precipitation moreover owing to the slow kinetics of dolomite dissolution with respect to that of calcite both the volume of dissolved mineral and the increase in porosity were larger in the limestone experiments than in the dolostone ones under all p co 2 conditions 10 3 5 and 10 bar by increasing p co 2 carbonate dissolution occurred along the column whereas it was localized in the very inlet under atmospheric conditions this was due to the buffer capacity of the carbonic acid which maintains ph at around 5 and keeps the solution undersaturated with respect to calcite and dolomite along the column 1d reactive transport simulations reproduced the experimental data carbonate dissolution and gypsum precipitation for different p p co 2 t conditions drawing on reaction rate laws in the literature we used the reactive surface area to fit the models to the experimental data the values of the reactive surface area were much smaller than those calculated from the geometric areas

paleodepositional conditions in the orca basin as inferred from organic matter and trace metal contents abstract the orca basin located in the gulf of mexico is a highly stratified basin that collects sedimentary particles of clastic origin supplied by the mississippi river and of biogenic origin marine surface productivity the strong pycnocline induces anoxic bottom conditions that are expected to be favorable to organic matter om accumulation and prone to enrichment of sediments in redox sensitive trace metals here we report on om and trace metal contents in the upper 750 cm below sea floor cmbsf of core md02 2552 mostly holocene and deposited under permanently stratified bottom conditions the organic content is dominated by marine derived amorphous om contrary to expectations sedimentary om in the basin is highly degraded probably due to a long residence time of organic particles at the basin s basin s halocline at 2240 m also unexpected is the limited sedimentary enrichment of redox sensitive trace metals we suggest that the non enrichment in u and v could be explained by the so called basin reservoir effect that is limited metal availability because of low rates of water renewal in a strongly restricted subpycnoclinal water mass the non enrichment in cu could have the same cause plus the fact that the relatively degraded om may not readily form organometallic complexes however a marked enrichment is observed for mo and a moderate one for ni and cr which could be accounted for by sporadic presence of h 2 s in bottom waters such occurrences of h 2 s would not be sufficient to promote a detectable fes to fes 2 conversion but they would induce the capture of mo in the form of thiomolybdate and accessorily ni cr as ni cro 4 complexes

co2 percolation experiment through chlorite zeolite rich sandstone pretty hill formation otway basin australia underground co2 sequestration is highly recommended as an effective means of significantly decreasing co2 concentration in the atmosphere mineral storage is the more secure technology but requires the presence of high concentration of divalent cations in the pore fluid results from co2 percolation experiments through chlorite zeolite rich sandstone samples from the pretty hill formation otway basin australia are presented the dissolution of the laumontite 7 wt and chamosite 7 wt are the potential sources of calcium iron and magnesium required for carbonate precipitation the percolation experiment was setup to reproduce at laboratory scale the in situ temperature and pressure conditions t 95 degrees c and p 10 mpa the fluid injected at constant flow rate is a rock equilibrated brine subsequently enriched in co2 up to partial pressure of 6 mpa we observe feldspars laumontite and chamosite dissolution kaolinite and silica precipitation and a noticeable sink of co2 in the sample which is attributed to the precipitation of both amorphous carbon due to the reduction of co2 and fe rich carbonate permeability decreases of about one order of magnitude due to the localization of the kaolinite precipitation in the main flow paths while porosity increases the high reactivity of this sandstone makes this reservoir a valuable target for co2 mineralization but the associated permeability decrease may limit the injection rate and the spreading of the co2 in the reservoir

crocetane a potential marker of photic zone euxinia in thermally mature sediments and crude oils of devonian age abstract crocetane an irregular c 20 isoprenoid in sediments generally associated with gas hydrate settings is a molecular indicator for the anaerobic oxidation of methane green sulfur bacteria gsb are the main source for specific aromatic carotenoids e g isorenieratane in sedimentary environments and are molecular indicators of photic zone euxinia pze the present study comprises a detailed molecular and isotopic study of crocetane and gsb derived carotenoids in devonian sediments of the western canada sedimentary basin wcsb covering a range of thermal maturities in addition a series of oils generated from devonian source rocks of the basin have been analysed for crocetane crocetane was found in ten sediments from the wcsb and in seven devonian wcsb crude oils its abundance was found to increase with thermal maturity whereas the components derived from c 40 derived carotenoids decrease steadily we were not able to identify 2 6 10 15 19 pentamethylicosane pmi neither in the duvernay formation sediments nor in the wcsb crude oils consistent with previous findings the preferred proposed natural product precursor for crocetane is thus gsb derived carotenoids this is corroborated by their similar structural features and the 13 c value of combined crocetane and phytane in these samples however contributions from other carotenoids cannot be fully excluded crocetane can provide evidence for pze conditions in highly mature samples and crude oils of devonian age

temporal spatial reconstruction of the early frasnian late devonian anoxia in nw africa new field data from the ahnet basin algeria anoxic conditions were widespread in nw africa during the early frasnian late devonian that resulted in deposition of organic rich shales and limestones with total organic carbon toc values of up to 14 organic richness and thickness of these sediments vary laterally and organic rich vs organic poor facies boundaries are likely to have been diachronous a precise temporal spatial reconstruction of this anoxic phase in nw africa is complicated because the organic matter in outcrops is largely oxidised and biostratigraphic resolution in boreholes is generally low due to the lack of recoverable conodonts this contribution is based on eight outcrop sections at the margin of the central algerian ahnet basin where detailed spectral gammaray measurements were carried out using a handheld instrument the pre weathering organic richness in frasnian outcrop sections is approximated using the characteristic uranium enrichment in the anoxic facies that based on well studies is positively correlated with the total organic carbon content conodont biostratigraphic results from these sections suggest that the uraniumenriched interval the anoxic interval at the basin margin is most common in the basal frasnian conodont biozones 1 2 confirming previous results from the anti atlas in morocco in three of the eight localities studied the basal frasnian has not been deposited and the frasnian here commences with distinctly younger uranium enriched intervals including zones 4 11 well data from the eastern algerian berkine basin is interpreted to indicate a significantly longer anoxic phase there million yearscale diachroneities of the frasnian anoxia therefore clearly exist across the north africa shelf it is assumed that the palaeorelief might have been a major factor in controlling the onset duration and intensity of anoxia in the region d 2003 elsevier b v all rights reserved

sedimentary evolution of a palaeozoic basin and ridge system the middle and upper devonian of the ahnet and mouydir algerian sahara the ahnet and mouydir regions of southern algeria are part of one of the world s largest almost undeformed exposures of palaeozoic rocks which exemplify a hitherto poorly known early variscan development of a devonian basin and ridge system this area includes a series of intracratonic basins along the northern margin of the west african craton which consists from w to e of the reggane basin azel matti ridge ahnet basin foum belrem ridge and mouydir basin the depositional and palaeogeographic interpretation is based on 71 sections in this region which for the first time were biostratigraphically calibrated by means of conodonts goniatites and brachiopods the structural evolution during devonian times was probably controlled by reactivation of ancient n s to nw se running faults in the precambrian basement which caused differential subsidence and uplift of a previously largely unstructured siliciclastic shelf a hiatus during emsian times indicates widespread emergence during this interval the entire area was flooded during the earliest eifelian when the first vestiges of the azel matti ridge become evident by stratigraphic condensation the palaeogeographic differentiation is most apparent during the givetian when a shoal with reduced carbonate sedimentation was established on the azel matti ridge passing towards the west and east into basinal environments of the reggane and ahnet basins respectively the foum belrem ridge is distinguished by increased subsidence during the early givetian and by revived uplift during the late givetian in the mouydir basin further east up to 1000 m of shales were deposited during the givetian the early frasnian is marked by the ubiquitous sedimentation of black shales and bituminous styliolinites these lithologies occur repeatedly already during the middle devonian and document intermittent anoxic conditions the basin and ridge topography is levelled by the shallowing up sequence of up to 1400 m thick upper frasnian and famennian shales which grade into a deltaic sequence of uppermost famennian tournaisian sandstones the up to now only vaguely discriminated lithostratigraphic formations of the devonian have been biostratigraphically defined in suitable type sections

testing provenance diagrams lessons from the well constrained cariaco basin abstract the fine grained sediments of the cariaco basin venezuela of the last 130 ky whose deposition history is well characterized were analyzed geochemically in order to test the validity of sediment bulk geochemistry as an indicator of detrital provenance several binary and ternary diagrams as well as the chemical index of alteration cia were tested for their capacity to discriminate the poorly contrasted detrital sources to the cariaco basin and to describe the temporal evolution of the contributions of these different sources most of the diagrams tested did not allow a good discrimination of sources or when sources were well discriminated did not allow an interpretation of the temporal variations consistent with the known history a relatively good discrimination of sources and a consistent interpretation of temporal variations were however obtained using hf vs th and la yb vs gd yb binary diagrams as well as ti zr th ti zr la and lu hf th ternary diagrams compared to the previous studies of the detrital content of the cariaco basin sediments the geochemical approach permitted the recognition of a sediment contribution eroded from the unare platform and gulf of cariaco during rapid sea level oscillations and the contribution of saharan eolian particles during the younger dryas preboreal and mis6 5 transition the choice of plotted elements was determined after considering carrier minerals so that different elements may be informative in different sedimentary contexts overall mineral sorting during transport appears as a major limit to quantitative estimation of the different contributions in particular mineral sorting leads to the selective enrichment of elements associated with clays al rb th and lree in sediments deposited in the basin unless the geochemical effect of mineral sorting can be measured it appears that quantitative provenance analysis should be performed on fractions of similar grain size instead of bulk sediment

anoxic events in the late frasnian causes of the frasnian famennian faunal crisis carbon isotope data collected from five frasnian famennian boundary sections in central europe show two positive 13 c excursions in the late frasnian 367 ma both anomalies coincided with the deposition of the bituminous lower and upper kellwasser horizons the carbon isotope patterns indicate two phases of enhanced burial and subsequent recycling of organic carbon a maximum formation of warm saline waters on the subtropical to tropical epicontinental shelves during late frasnian transgressive episodes may have induced oceanic oxygen deficits variations in the c org burial rates may have resulted in changes in the co 2 concentrations in the oceans and in the atmosphere culminating in global climatic changes we propose that the repeated co occurrences of sea level fluctuations anoxic conditions and global climatic changes during the late frasnian would affect especially the subtropical to tropical shallow water communities and reef ecosystems which were severely affected during the frasnian famennian faunal crisis

the late frasnian kellwasser horizons of the harz mountains germany two oxygen deficient periods resulting from different mechanisms in the harz mountains germany three late devonian sections aeketal huhnertal and kellwassertal were analyzed for major and trace element concentration the inorganic geochemical data were used to determine the environmental conditions associated with the deposition of the two late frasnian black kellwasser horizons in a submarine rise environment low ti al and zr al values and slight enrichment in nutrient and organic matter related trace elements e g ba cu and ni suggest that the kellwasser horizons were deposited during two periods of minimum detrital input but relatively elevated primary production enrichments in u v and mo in both black kellwasser horizons and values of redox indices including u th v cr and ni co indicate oxygen restricted conditions prevailed during the late frasnian times under oxygen depleted conditions reductive diagenesis caused precipitation of iron sulphides such as pyrite that are observed with sem however variations in major and trace element concentrations are not similar in the two kellwasser horizons particularly regarding redox markers the lower kellwasser horizon seems to be more o2 depleted than the upper kellwasser horizon in some german sections on the basis of these results we propose that the two kellwasser horizons are not caused by identical conditions the lower kellwasser horizon results from increased primary productivity enhanced by land derived nutrient loading and which triggered the anoxic conditions recorded in drowned platform setting in contrast the upper kellwasser horizon results from the onset of oxygen impoverished bottom water in the deepest part of the ocean due to episodic water stratification during maximum frasnian flooding oxygen depleted water may have impinged shallower environment during the linguiformis transgressive pulse nutrients would have been released from organic matter decay under reducing conditions and brought up to the photic zone during episodic water mixing

water column anoxia enhanced productivity and concomitant changes in δ13c and δ34s across the frasnian famennian boundary kowala holy cross mountains poland the investigation of the trace element and organic geochemistry of the frasnian famennian boundary section at kowala holy cross mountains poland shows that the lower water column was oxygen deficient during late frasnian and early famennian times the abundance and carbon isotopic composition of diaryl isoprenoids biomarkers indicative for green sulfur bacteria prove that euxinic waters reached into the photic zone at least episodically total organic carbon toc contents show two maxima that are time equivalent to the kellwasser horizons deposited in shallower water settings enhanced toc concentrations are explained by a higher primary productivity presumably as a consequence of an enhanced nutrient supply from the continent the increase in the abundance of hopanes and bituminite suggests that the bacterial contribution to toc increased at the frasnian famennian transition the sulfur isotopic composition of pyritic and organically bound sulfur shows a 27 excursion across the boundary the observation that the 34s values of organic bound sulfur closely resemble that of pyrite sulfur indicates a common sulfur source likely early diagenetic sulfide a change in the 13c of total dissolved inorganic carbon as a consequence of an enhanced burial of 12c enriched organic carbon is indicated by a 3 excursion measured for toc as well as for individual n alkanes and isoprenoids the burial of large amounts of organic carbon is expected to result in a decrease in pco2 and should affect the photosynthetic carbon isotope fractionation ep the fact that we observe no change in ep can be explained by the circumstance that ep was most probably at maximum values as a consequence of high atmospheric and oceanic dissolved co2 concentrations during the devonian

evaluation of the impact of co2 co contaminant gas aqueous fluid and reservoir rock interactions on the geologic sequestration of co2 lowering the costs of front end processes e g separation in the geologic sequestration of co2 can dramatically lower the overall costs one possible approach is to sequester less pure co2 waste streams that are less expensive or require less energy to separate from flue gas or a coal gasification process etc the objective of this research is to evaluate the impacts of co2 itself as well as an impure co2 waste stream on geologic sequestration using reaction progress models reactive transport simulators and analogous reactive transport experiments run in a plug flow reactor specifically we are investigating the potential for co injecting the sox nox and h2s present in coal fired waste streams along with the co2 we present here the results of reactive transport simulations made to investigate the long term impact of dissolved co2 h2s and so2 on carbon sequestration in the frio fm tx the results suggest that addition of relatively large amounts of h2s to a co2 injection should not adversely impact injectivity or sequestration compared to the injection of co2 alone the co injection of so2 however could produce significantly different results if conditions are such that so2 can oxidize to sulfate in the long term the simulations suggest that carbonate mineral formation can sequester a significant fraction of the injected carbon through the formation of calcite magnesite and dawsonite

experimental mineral dissolution in berea sandstone reacted with co2 or so2 co2 in nacl brine under co2 sequestration conditions a comparison of the geochemical changes induced in sandstone by either pure or impure co2 at geological co2 storage conditions was investigated samples of berea sandstone were batch reacted in 1 w v nacl brine saturated with pure co2 or mixed so2 co2 gas for 360 h at 50 degrees c and 10 mpa geochemical analysis of incremental water samples showed increases in the concentrations of elements such as calcium magnesium iron manganese and silicon throughout experiments likely being the products of carbonate and reactive silicate dissolution scanning electron microscope images taken of specific points of interest before and after batch reactions confirmed dissolution of carbonates but showed no reaction for minerals such as k feldspar the magnitude of apparent mineral reaction was higher for the mixed gas so2 co2 brine experiment with geochemical modelling also indicating greater dissolution of reactive silicates such as chlorite and potential precipitation of amorphous silica c 2014 elsevier b v all rights reserved

three series of rearranged hopanes in toarcian sediments northern italy abstract a suite of 36 shales and marls from the toarcian oceanic anoxic event section at three localities in northern italy was found to contain variable contents of three series of rearranged hopanes 17 diahopanes c 27 and c 29 34 and trace c 35 18 neohopanes c 27 and c 29 30 and an unidentified early eluting series c 27 and c 29 35 principal component analysis pca shows the 17 diahopanes and the early eluting rearranged hopanes to closely covary suggesting a related diagenetic mechanism for the formation of their rearranged skeletons a general covariance with diasteranes is also noted the 18 neohopanes show no covariance with diasteranes or the other two series of rearranged hopanes we also report 2 methyl analogues of the 17 diahopanes and early eluting rearranged hopanes we propose that the neohopanes may be at least partly derived from different biohopanoid precursors than the other two series of rearranged hopanes and that the diagenetic origin of the neohopane structure differs from that of the 17 diahopanes and the unidentified early eluting series

evidence for late devonian vertical movements and extensional deformation in northern africa and arabia integration in the geodynamics of the devonian world 1 the upper paleozoic geodynamic evolution is discussed at the scale of a wide part of gondwana from north africa to arabia with the aim of giving an integrated tectonic scenario for the study domain we revisit six key areas namely the anti atlas belt morocco the bechar basin west algeria the hassi r mel high central algeria the talemezane arch south tunisia the western desert egypt and finally the high zagros belt iran below the so called hercynian unconformity which is in reality a highly composite discontinuity surface and subsurface data display a well known arch and basin geometry with basement highs and intervening paleozoic basins we show that this major feature results mainly from a late devonian event and can no longer be interpreted as a far effect of the variscan orogeny this event is characterized by a more or less diffuse extensional deformation and accompanied either by subsidence in the western part of the system or by an important uplift of probable thermal origin followed by erosion and peneplanation by the end of the devonian the whole region suffered a general subsidence governed by the progressive cooling of the lithosphere such a primary configuration is preserved in arabia with typical sag geometry of the carboniferous and permian deposits but strongly disturbed elsewhere by the conjugated effects of the variscan orogeny during the carboniferous and or by subsequent uplifts linked to the central atlantic and neo tethys rifting episodes in conclusion we try to integrate this new understanding in the geodynamics of the late devonian which at world scale is characterized by the onset of the variscan orogeny on the one hand and by magmatism rifting and basement uplift on the other hand

deciphering the upper famennian hangenberg black shale depositional environments based on multi proxy record abstract presented for the first time in this paper are the results of a detailed multi proxy investigation conducted on the hangenberg black shale hbs from the polish part of the laurussian shelf which provide details about the environmental conditions in existence during deposition of the shale and the role played by anoxic conditions in the mass extinction events that occurred at the end of the devonian times inorganic and organic redox indicators indicate that bottom water redox conditions changed periodically from being mainly anoxic euxinic to oxic or being partially depleted in oxygen u th values above 1 25 ni co values above 7 and v v ni values above 0 8 recorded from the lower part of the hbs all point to anoxic euxinic conditions being present as do high total organic carbon contents toc above 10 and degree of pyritisation dop values around 0 75 however the presence of benthic fauna over the lower part of the hbs attests to opportunistic colonisation of the seafloor during oxic episodes evidence for similar episodes has also been recognised over the middle part of the hbs e g u th values below 1 25 ni co values below 4 v v ni values below 0 8 toc values of 3 to 5 5 and dop values of 0 4 to 0 75 plus the common occurrence of benthic fauna anoxic conditions returned during the deposition of the upper part of the hsb though they were not as well developed as when the lower part of the shale was laid down of interest is the presence of small pyrite framboids and isorenieratene biomarkers in all the analysed samples which suggest that euxinic conditions persisted in the photic zone of the water column a twenty centimetre thick layer of volcanogenic deposits tuffites is present in the middle part of the hbs the geochemical characteristics of which are typical of ocean floor basalts the occurrence of volcanogenic material below and within the hbs together with an absence of calcium carbonate over its upper part the presence of abundant tetrads just above the black shale and a drastic decrease in faunal frequency in the upper part of the hbs imply that volcanism may have caused oceanic acidification or hypercapnia that in turn potentially may have influenced the hangenberg mass extinction event

diagenetic versus detrital origin of the magnetic susceptibility variations in some carbonate frasnian famennian boundary sections from northern africa and western europe implications for paleoenvironmental reconstructions to provide a new insight into the diagenetic versus detrital origin of the magnetic susceptibility variations in ancient carbonate sequences a study was conducted within four frasnian famennian platform carbonate sections from germany france and morocco the study includes along section magnetic susceptibility and carbonate content measurements complemented by analyses of magnetic hysteresis parameters inorganic geochemistry and clay mineralogy our results show that the magnetic susceptibility evolution is dominantly controlled by the variations in the concentration of low coercivity ferromagnetic magnetite grains and to a lesser extent of paramagnetic clays in more detail hysteresis ratios suggest the coexistence of two magnetite populations with significantly different grain size 1 a dominantly coarse grained detrital fraction including a mixture of multi domain and single domain particles 2 an authigenic fine grained fraction composed of a mixture of single domain and superparamagnetic particles despite a diagenetic imprint on the clay assemblages no relationship is established between magnetic susceptibility and illite crystallinity therefore discarding a noticeable distortion of primary within section magnetic susceptibility evolution the overall inherited character of the magnetic susceptibility fluctuations is corroborated by a significant correlation of magnetic susceptibility with terrigenous proxies zr th the poorer correlation of magnetic susceptibility with the fe content is consistent with the existence of a very fine grained authigenic magnetite component that possibly induces a global magnetic susceptibility increase at the section scale but no distortion of the within section evolution the magnetic susceptibility curves presented here provide a general record of climate driven detrital influx and carbonate productivity through frasnian lower famennian times

a new ecological severity ranking of major phanerozoic biodiversity crises a new ecological severity ranking of the major phanerozoic biodiversity crises is proposed in which the capitanian crisis is ranked lesser than the frasnian late devonian but greater than the serpukhovian end mississippian and the famennian end devonian crisis is ranked as equal in ecological impact to the hirnantian end ordovician two new decouplings between taxonomic severity and ecological severity are revealed in these analyses the capitanian and famennian crises in which the ecological impact of the biodiversity loss was markedly different from the magnitude of the biodiversity loss these analyses also reveal that the great devonian interchange gdi invasive species event in the givetian biodiversity crisis may provide an important palaeoecological analog for the study of present day extinction and homogenization in ecosystems produced by modern invasive species

biomarkers reveal the role of photic zone euxinia in exceptional fossil preservation an organic geochemical perspective photic zone euxinia pze has proven important for elucidating biogeochemical changes that occur during oceanic anoxic events including mass extinction and conditions associated with unique fossil preservation organic geochemical analyses of a 380 ma invertebrate fossil which included well preserved soft tissues from the gogo formation canning basin western australia showed biomarkers and stable isotopic values characteristic of pze and a consortium of sulfate reducing bacteria which lead to exceptional fossil and biomarker preservation the carbonate concretion contained phytoplankton green sulfur bacteria chlorobi and sulfate reducing bacteria biomarkers with an increasing concentration toward the nucleus where the fossil is preserved the spatial distribution of cholestane unequivocally associated with the fossilized tissue and its high relative abundance to the total steranes suggest that the fossil is a crustacean the presence of an active sulfur cycle in this devonian system including sulfate reduction and the resulting pze played a pivotal role in the preservation of soft tissue from the fossil and its associated low maturity biomarker ratios

chemostratigraphic reconstruction of biofacies molecular evidence linking cyst forming dinoflagellates with pre triassic ancestors new data from numerous detailed mass spectrometric studies have detected triaromatic dinosteroids in precambrian to cenozoic rock samples triaromatic dinosteroids are organic geochemicals derived from dinosterols compounds known in modern organisms to be the nearly exclusive widely occurring products of dinoflagellates we observed the ubiquitous occurrence of these dinosteroids in 49 late triassic through cretaceous marine source rocks and the absence of them in 13 permian carboniferous source rocks synergistic with the dinoflagellate cyst record however finding dinosteroids in lower paleozoic and precambrian strata presents challenging results for molecular paleontologists evolutionary biologists palynologists and especially for those concerned with the food web at various times of biological crisis other than the few species known as parasites and symbionts many other dinoflagellate species are important as primary producers the presence of precambrian to devonian triaromatic dinosteroids gives chemostratigraphic evidence of dinoflagellates or other organisms with similar chemosynthetic capabilities in rocks significantly older than the oldest undisputed dinoflagellate fossils dinoflagellate cysts from the middle triassic 240 ma and older than the putative silurian 420 ma dinocyst arpylorus antiquus calandra sargent from tunisia this systematic chemostratigraphic approach can shed light not only on lineages of dinoflagellates and their precursors but potentially on many other lineages especially bacteria algae plants and possibly some metazoans

experimental evaluation of the impact of the interactions of co2 so2 brine and reservoir rock on petrophysical properties a case study from the ketzin test site germany the objective of this study is to evaluate the impact of impure co2 on a possible co2 repository here we present experimental data on the simulation of the injection of pure co2 and co2 and cocontaminant so2 into a saline aquifer long term exposure experiments with pure co2 reveal no significant changes in the petrophysical properties electrical resistivity elastic wave velocity and permeability in contrast for the injection of co2 and cocontaminant so2 1 vol we have observed significant and irreversible changes of all monitored physical parameters on the one hand the decrease of p wave velocity and the increase of electrical resistivity indicate a dissolution of some framework material on the other hand the decrease of permeability points to the mobilization and redistribution of fines these data might be relevant for subsequent modeling and estimations about tolerable concentration limits regarding the contaminants of co2 to be stored

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

environmental analysis of paleoceanographic systems based on molybdenum uranium covariation abstract modern low oxygen marine systems exhibit patterns of molybdenum uranium covariation that can be linked to specific attributes and processes of the depositional system including 1 variation in benthic redox conditions 2 the operation of particulate shuttles within the water column and 3 the evolution of watermass chemistry the importance of these factors in each depositional system can be assessed both from the degree of enrichment of authigenic molybdenum mo auth and uranium u auth and from the mo u auth ratio of the sediment relative to the seawater mo u molar ratio of 7 5 7 9 in open ocean systems with suboxic bottomwaters u auth enrichment tends to exceed that of mo auth owing to onset of u auth accumulation at the fe ii fe iii redox boundary resulting in sediment mo u auth ratios less than that of seawater as bottomwaters become increasingly reducing and at least occasionally sulfidic the rate of accumulation of mo auth increases relative to that of u auth and sediment mo u auth ratios equal or exceed that of seawater in restricted marine systems with permanently sulfidic deepwaters the relative enrichment of mo auth and u auth depends on additional factors in the cariaco basin which has an aqueous mo u ratio similar to that of seawater the operation of a particulate mn fe oxyhydroxide shuttle serves to accelerate the transfer of mo to the seafloor leading to strong enrichments in mo auth relative to u auth in the black sea the chemistry of the deep watermass has evolved to the point where its aqueous mo u ratio is only 0 04 that of seawater as a consequence of which sediments deposited under deepwater influence are depleted in mo auth relative to u auth these mo u covariation patterns can be used to gain a better understanding of the watermass attributes and processes of ancient low oxygen marine systems analysis of anoxic facies from two north american paleomarine systems the late pennsylvanian midcontinent sea lpms and the late devonian seaway lds reveals authigenic mo u relationships similar to those of the modern marine environments above implying similar redox and hydrographic controls the observed patterns are consistent with laterally unconfined circulation and strong watermass exchange within the lpms and with markedly restricted deepwater circulation in silled basins of the lds patterns of authigenic mo u covariation may prove useful in analysis of other paleoceanographic systems to reveal aspects of watermass composition and environmental dynamics

sterane biomarkers as indicators of palaeozoic algal evolution and extinction events abstract algae are among the oldest organisms known to inhabit the earth s biosphere with a record dating back some 2 7 ga only few marine algae produce hard parts that can be preserved over geologic time and consequently their fossil record is incomplete molecular fossils or biomarkers add complementary information to the fossil palynomorph record steroids are important constituents of eukaryotic cell membranes and are preserved in sediments as steranes c28 and c29 steranes are indicators for the presence of green and c27 steranes for the presence of red algae respectively the relative abundance of steranes allows the investigation of the fossil record for palaeozoic algal diversification and evolution in this study 500 palaeozoic rock samples representing a broad facies variety from the upper ordovician to the p t boundary were investigated for sterane compositions in addition three profiles covering the hirnantian the f f and the hangenberg event were analyzed for possible shifts in the sterane distribution associated with extinction events a sharp increase of the c28 c29 sterane ratio from 0 70 at the devonian carboniferous boundary implies a fundamental change in the green algae assemblage from more primitive mainly c29 sterane producing algae to modern c28 sterane producing algae for all investigated extinction events a pronounced but short lived rise in the c28 sterane content occurs that is attributed to an episodic increase in prasinophytes the gradual radiation of algae may have been triggered by frequent mass extinctions in the upper devonian culminating with the massive decline of acritarchs at the d c boundary the coeval rise in the c28 c29 sterane ratio indicates the presence of an non encysting algal group and coincides with the global augmentation of numerous filamentous codiacea siphonales and the rise of euspondyle and metaspondyle dasycladales

the whole rock cerium anomaly a potential indicator of eustatic sea level changes in shales of the anoxic facies abstract the whole rock cerium anomaly tested for outer shelf upper slope stratigraphic sections from the middle ordovician through the lower silurian of scotland is proposed as an empirical technique to develop a eustatic 3rd order or finer scale sea level curve this interval was chosen as it straddles the well documented late ordovician glaciation and can be defined by graptolite zones the anomaly is calculated from neutron activation analysis of low carbonate phosphate free fossil free field identified shales of the graptolite facies by comparison of the normalized cerium content with the linearized trend of the normalized composition of other rare earth elements in order of atomic number for sections originally deposited in the main pycnocline below the surface mixed layer values of the anomaly for a given sample would indicate its position on the redox curves developed for the early paleozoic by wilde 1987 changes in the anomaly that are positive with time would indicate a lowering of sea level as the apparent depth on the redox curve would reflect more oxic conditions relative changes negative with time would indicate a rise in sea level as the apparent depth reflects more anoxic conditions depending on the vertical sample spacing and the time interval sampled resolution of the order of 1 m y might be achieved thus the vail et al 1977 curves of the 3rd order 1 to 10 m y or of finer scale could be obtained by this technique with the proper choice of section accordingly for the early through middle paleozoic when the main pycnocline was anoxic this geochemical technique could be used to develop eustatic sea level curves and additionally offer an independent calibration for seismic stratigraphy as well as an indicator of glacial interglacial climatic sequences or eustatic changes due to fluctuations in global ridge crest volumes

effect of dissolved h2so4 on the interaction between co2 rich brine solutions and limestone sandstone and marl abstract the effect of pure and impure carbon dioxide co 2 on geological storage is uncertain oxidation of impurities such as sulfur dioxide so 2 and hydrogen sulfide h 2 s which may be catalyzed by co injected oxygen or nitrogen oxides leads to the formation of sulfuric acid h 2 so 4 and a decrease in ph of the formation water we investigated the effect of 0 005 mol l 1 h 2 so 4 corresponding to a worst case of 0 4 so 2 in the flue gas anticipating total conversion of so 2 into h 2 so 4 on the reactivity of the reservoir limestone and sandstone and cap marl rocks of hontomin spain at p pco 2 10 bar and 60 c during 24 days using flow through column experiments aqueous element concentrations were measured from fluid extracts obtained periodically throughout the experiments to infer fluid rock reactions over time results were modeled with the crunchflow reactive transport code the added h 2 so 4 lowered the ph of the injected brine by 1 5 ph units with respect to the ph of 3 6 of the h 2 so 4 free brine in both h 2 so 4 free and h 2 so 4 rich brine calcite dissolution fostered gypsum precipitation a comparison between the reactivity of the rocks reacted in h 2 so 4 free and h 2 so 4 rich brine showed that calcite dissolution and gypsum precipitation rates were increased by 27 48 and 25 75 respectively in h 2 so 4 rich brine overall rock porosity increments in h 2 so 4 rich brine were 2 9 3 6 3 7 4 8 and 2 1 2 7 for sandstone limestone and marl respectively porosities in h 2 so 4 rich brine were 6 23 and 250 higher respectively than under pure co 2 modeled porosity increments in the acid inlet zone in h 2 so 4 rich brine for sandstone limestone and marl were 28 29 44 45 and 24 28 respectively corresponding to an increase of 1 250 and 25 respectively relative to h 2 so 4 free brine gypsum precipitation was consistently higher in marl than in limestone and sandstone indicating kinetically favorable conditions for gypsum precipitation within the cap rock our results provide relevant data for long term storage simulations of impure co 2 injection

the role of sea level change and marine anoxia in the frasnian famennian late devonian mass extinction johnson et al johnson j g klapper g sandberg c a 1985 devonian eustatic fluctuations in euramerica geological society of america bulletin 96 567 587 proposed one of the first explicit links between marine anoxia transgression and mass extinction for the frasnian famennian f f late devonian mass extinction this cause and effect nexus has been accepted by many but others prefer sea level fall and cooling as an extinction mechanism new facies analysis of sections in the usa and europe france germany poland and comparison with sections known from the literature in canada australia and china reveal several high frequency relative sea level changes in the late frasnian to earliest famennian extinction interval a clear signal of major transgression is seen within the early rhenana zone e g drowning of the carbonate platform in the western united states this is the base of transgressive regressive cycle iid of the johnson et al johnson j g klapper g sandberg c a 1985 devonian eustatic fluctuations in euramerica geological society of america bulletin 96 567 587 eustatic curve this was curtailed by regression and sequence boundary generation within the early linguiformis zone recorded by hardground and karstification surfaces in sections from canada to australia this major eustatic fall probably terminated platform carbonate deposition over wide areas especially in western north america the subsequent transgression in the later linguiformis zone recorded by the widespread development of organic rich shale facies is also significant because it is associated with the expansion of anoxic deposition known as the upper kellwasser event johnson et al s johnson j g klapper g sandberg c a 1985 devonian eustatic fluctuations in euramerica geological society of america bulletin 96 567 587 original transgression anoxia extinction link is thus supported although some extinction losses of platform carbonate biota during the preceeding regression cannot be ruled out conodont faunas suffered major losses during the upper kellwasser event with deep water taxa notably affected this renders unreliable any eustatic analyses utilising changes in conodont biofacies claims for a latest frasnian regression are not supported and probably reflect poor biostratigraphic dating of the early linguiformis zone sequence boundary

supercritical carbon dioxide brine rock reactions in the madison limestone of southwest wyoming an experimental investigation of a sulfur rich natural carbon dioxide reservoir abstract the madison limestone on the moxa arch southwest wyoming usa is a sulfur rich natural co 2 reservoir a series of hydrothermal experiments was performed to evaluate multi phase co 2 h 2 o brine rock reactions and processes in this reservoir and to test the hypothesis that this reservoir is a natural analog for geologic carbon sulfur co sequestration idealized madison limestone dolomite calcite anhydrite pyrite and na cl so 4 2 brine i 0 5 molal reacted at 110 c and 25 mpa for approximately 81 days 1940 h supercritical co 2 was then injected and the experiment continued for approximately 46 days 1100 h a parallel experiment was performed without supercritical co 2 to provide a basis of understanding for the interaction of supercritical co 2 with the brine rock system two additional experiments were conducted in the same manner but without anhydrite in the starting mineral assemblage to examine supercritical co 2 sulfur reactivity injection of supercritical co 2 decreases ph by 2 5 to 3 3 units increases eh by 0 19 to 0 23 v and drives reaction pathways along the pyrite anhydrite saturation boundary of an eh ph diagram the dolomite calcite anhydrite mineral assemblage and reaction textures that are produced are consistent with those observed in the natural co 2 reservoir the mineral assemblage does not change following emplacement of supercritical co 2 instead minerals dissolve mobilize and re precipitate anhydrite precipitates in the dolomite calcite pyrite experiment following injection of supercritical co 2 and provides a mineral trap for sulfur anhydrite precipitation decreases so 4 2 activity ultimately leading to mineralization of co 2 experimental results support the hypothesis that the madison limestone on the moxa arch is a natural analog for geologic carbon sulfur co sequestration

mountain building enhanced continental weathering and organic carbon burial as major causes for climatic cooling at the frasnian famennian boundary c 376 ma the late devonian was a period of drastic environmental changes as exemplified by a major biotic crisis at the frasnian famennian boundary ffb and the onset in famennian times of glaciations across southern gondwana worldwide evidence for the coeval development of the major acadian eovariscan belt led us to propose a model relating the late frasnian famennian environmental perturbations to extensive continental uplift through two atmospheric co2 depleting mechanisms 1 the intensification of silicate weathering on the continental areas as attested by a major rise in the 87 sr 86 sr composition of sea water at the ffb and 2 the massive burial of organic carbon kellwasser events in partially confined basins due to the collisional induced reduction of equatorial oceanic communications between the palaeotethysian and panthalassic oceans this process is also suggested to have been controlled by an important primary productivity connected to an increased nutrient availability triggered by the enhanced continental run off

epipelagic chitinozoan biotopes map a steep latitudinal temperature gradient for earliest late ordovician seas implications for a cooling late ordovician climate abstract the early mid ordovician has long been considered a super greenhouse world based largely on high relative global sea levels and light stable oxygen isotope data from bulk carbonates an alternative and largely untested hypothesis has suggested that at least in equatorial palaeolatitudes there was a steady cooling trend through the early ordovician reaching the range of modern equatorial sea surface temperatures by the mid ordovician this hypothesis though controversial is supported by palaeobiogeographical studies of the early late ordovician sandbian zooplankton graptolite biotopes these are comparable to the modern planktonic foraminifera provinces and suggest a latitudinal temperature gradient that is similar to the modern one chitinozoans are also an important group of palaeozoic marine microfossils but with a poorly known biological affinity here we present an analysis of chitinozoan species palaeobiogeography for the early late ordovician sandbian c 460 ma which confirms that these microfossils and likely their parent organisms were epipelagic unlike the graptolites chitinozoans had their highest diversity and abundance south of 35 s during this time which strongly suggests adaptation to temperate to cold waters the distribution of chitinozoan biotopes during the gracilis time slice allows us to identify the austral subtropical subpolar and polar belts key oceanographic boundaries are identified as the subtropical subpolar transition at 35 s and tentatively the polar front at 55 70 s again these are in a similar position to those in the modern southern ocean chitinozoan biotopes also map a steep latitudinal faunal gradient that is comparable to that of the graptolites and that of modern plankton this likely indicates a steep latitudinal temperature gradient for early late ordovician seas and questions the notion that this interval of earth history had a greenhouse climate

black shale deposition in an upper ordovician silurian permanently stratified peri glacial basin southern jordan abstract the lower palaeozoic upper ordovician silurian succession of north africa contains one of the world s most prolific black shale source rocks yet the origin of these rocks remains contentious the black shale of the batra formation in jordan was deposited at high palaeolatitude during rapid hirnantian to early silurian deglaciation here we report geological and organic geochemical results that provide evidence for an increase in photic zone primary productivity during ice melting the decay of this organic matter through oxidative respiration resulted in euxinia which enhanced the potential for organic matter preservation the occurrence of isorenieratane in all samples indicates euxinia extended from the photic zone to the sediment water interface the stratified basins and fjords of east antarctica provide a likely modern analogue

a chronology of paleozoic sea level changes sea levels have been determined for most of the paleozoic era 542 to 251 million years ago but an integrated history of sea levels has remained unrealized we reconstructed a history of sea level fluctuations for the entire paleozoic by using stratigraphic sections from pericratonic and cratonic basins evaluation of the timing and amplitude of individual sea level events reveals that the magnitude of change is the most problematic to estimate accurately the long term sea level shows a gradual rise through the cambrian reaching a zenith in the late ordovician then a short lived but prominent withdrawal in response to hirnantian glaciation subsequent but decreasingly substantial eustatic highs occurred in the mid silurian near the middle late devonian boundary and in the latest carboniferous eustatic lows are recorded in the early devonian near the mississippian pennsylvanian boundary and in the late permian one hundred and seventy two eustatic events are documented for the paleozoic varying in magnitude from a few tens of meters to 125 meters

aliphatic and aromatic biomarkers from gondwanan sediments of late ordovician to early devonian age an early terrestrialization approach abstract twenty one core samples of late ordovician to early devonian age from sections in southern tunisia north african platform gondwana and containing marine and terrestrial organic matter with microbial input were investigated to link the aliphatic and aromatic hydrocarbon distributions with the terrestrial and marine palynomorph content e g acritarchs prasinophytes chitinozoans cryptospores and trilete spores in addition to several biomarkers of algal bacterial origin long chain n alkanes that might be derived from land plants as well as the terrestrial diterpane norabietane were found several land plant derived biomarkers such as retene cadalene simonellite tetrahydroretene and c19 isohexylalkyl naphthalene were observed in the aromatic fractions while these terrestrial biomarkers could be clearly recognized in the middle silurian lower devonian samples their presence in the upper ordovician lower silurian sediments is more doubtful because of much lower relative abundances the land plant biomarkers show a fairly good correlation with the occurrence and abundance of cryptospores and trilete spores derived from bryophytes and tracheophytes which covered the emerged areas around the ghadamis basin during the silurian and devonian the early tracheophytes e g cooksonia lycophytes and zosterophylls are therefore suggested as a new terrestrial source for most of the saturated and aromatic biomarkers found in sediments of middle silurian to early devonian age

palynofacies around the frasnian famennian boundary in the holy cross mountains southern poland abstract palynofacies have been analysed in two representative frasnian famennian f f localities kowala quarry and agow plucki trench in the holy cross mountains poland with the aim of reconstructing sedimentary conditions and palynofloral history over the extinction boundary interval leiospheres are the most common palynomorphs taxonomically impoverished acritarch assemblages and a low proportion of land derived material indicate offshore sedimentation in a mid shelf environment with some evidence of an earliest famennian regression increased productivity of phytoplankton near the f f boundary was possibly related to eutrophication of the epeiric seas thus causing anoxic conditions close to and on the seafloor no significant changes in palynofacies have been observed through the f f boundary deposits in these laurussian shelf basins in agreement with data from other parts of the devonian world

molecular characterization of organic matter in sediments from the keg river formation elk point group western canada sedimentary basin abstract distributions of free and sulfur bound biomarkers in organic rich sediments from the lower and upper keg river formation elk point group western canada reveal deposition of these sediments under reducing conditions in agreement with the geological data the predominance of aryl isoprenoids of chlorobiaceae origin indicates that photic zone anoxia occurred during time of deposition a series of novel aryl isoprenoids with a carboxylic acid function was identified by gc ms and the structure of the predominant 3 methyl 5 2 3 6 trimethylphenyl pentanoate was proven by synthesis of an authentic standard the occurrence of these acids gives evidence that oxidative breakdown at least partially accounts for the diagenetic fate of aromatic carotenoids li etnh 2 desulfurization of two kerogen concentrates yielded only low amounts of sulfur bound hydrocarbons and suggests that either sulfur sequestration was not a predominant process or more probably that a major part of the hydrocarbons initially sulfurized were released upon maturation giving further evidence that poly sulfide bonds are cleaved at relatively low levels of thermal stress

chlorobiaceae in palaeozoic seas revealed by biological markers isotopes and geology biomarker hydrocarbons in oils and sediments have considerable potential for assessing the nature of biological processes in the past but only a few can be uniquely related to particular organisms reef hosted oils in the silurian of the michigan basin canada and the devonian of western canada have high abundances of 1 alkyl 2 3 6 trimethylbenzenes their precise structures suggest that they are diagenetic products of aromatic carotenoids of the green sulphur bacteria individual components are enriched in 13c by 7 8 relative to the saturated hydrocarbons of the same oil an isotopic anomaly of this magnitude and direction correlates with a component of photosynthetic carbon assimilation by the reductive tricarboxylic acid cycle these results together with data on palaeoenvironments provide compelling evidence for the existence in ancient restricted seas of microbial communities containing chlorobiaceae organisms with distinctive biochemistry which leave morphologically identifiable remains

an organic geochemical perspective on terrestrialization the colonization of land required new strategies for safe gamete diaspore dispersal and to cope with desiccation harmful radiation fire and gravity accordingly the morphology behaviour and physiology of the organisms changed here we explore to what extent physiological adaptations reflected in the molecular content of the sediments add to our understanding of the terrestrialization many compounds considered characteristic of land organisms do not provide valuable information from the fossil record since 1 they were not preserved 2 they occur or correspond to substances that evolved prior to the terrestrialization e g cutan vs algaenan cellulose or 3 they have been changed diagenetically and or catagenetically the latter leads to geo macro molecules without a chemical fingerprint relating them to their original bio macro molecules despite sometimes excellent morphological preservation of the organic remains nevertheless some molecular markers and their stable isotopes provide independent information on the terrestrialization process the odd predominance of n alkane surface waxes is a feature already apparent in early land plants and could with caution be used as such furthermore fossil terpenoids and their derivatives are valuable for reconstructing the evolution of major plant groups the radiation of the phenylpropanoid pathway with for example sporopollenin and lignin seems to be closely related to the evolution of land plants as for other disciplines occupied with unravelling past life and environment organic geochemistry relies heavily on the paradigm that the present provides a key to the past for organic geochemistry the biosynthetic pathways of living organisms provide such a key the biosynthetic differences between organisms provide insight into the evolution of biosynthetic pathways and this can be applied to and calibrated against the fossil record evolution also implies adaptation and by linking species ecology to their biochemistry the adaptive value of the biosynthetic pathways and the biomolecules produced may be resolved this biosynthetic link to environment can also be applied to the past for instance the notion that oxygen is required in steroid and non hopanoid triterpenoid synthesis implies that analysis of steroids in ancient sediments may help to unravel the early evolution of the atmosphere summons et al 2006 analogous to the oxygenation of the earth s atmosphere terrestrialization also required major adaptations of the terrestrializing organisms to the living conditions on land the conquest of land required the development or strengthening of supportive structures such as skeletons stems and roots to withstand earth s gravity without the support of water and to resist wind it also demanded water saving strategies such as arthropod and plant cuticles vertebrate skin and cork to survive low humidity environments and sometimes fire as well as the development of water conducting tissues in plants roots tracheids finally the higher exposure to harmful radiation required sunscreens such as pigments aromatic and other substances as uv filters whereas the endoand exoskeletal adaptations are intrinsically based on the formation of large biopolymers water saving and uv protection may be also realized by means of smaller molecules our working hypothesis is that the major changes in biosynthetic pathways which accompanied the terrestrialization of organisms are reflected in the molecular composition of the organic matter present in palaeozoic sedimentary rocks for instance a minor change in the biosynthesis of sporopollenin may have led to lignin in return we can expect the changes in composition of the organic matter om in palaeozoic rocks to help determine following evolutionary trends the question being asked is to what extent is our working hypothesis valid and what does this provide us with to understand terrestrialization we restrict ourselves to primary producers and arthropods since they have a rich fossil record both organic geochemically and as microand macroscopic remains we exclude other terrestrial heterotrophic life forms worms snails vertebrates etc since they do not usually leave a chemically characteristic signature in the sediments from vecoli m clement g meyer berthaud b eds the terrestrialization process modelling complex interactions at the biosphere geosphere interface geological society london special publications 339 11 36 doi 10 1144 sp339 3 0305 8719 10 15 00 the geological society of london 2010 organic matter analysis lipids and

the global frasnian famennian kellwasser event during the uppermostp gigas conodont zone p linguiformis zone the stepwise frasnian extinction culminates in the global transgressive regressive frasnian famennian kellwasser event most pelagic organisms of the tropical marine environment are more or less affected by this mass extinction during the early upper devonian extinction rates are clearly related to the deposition of black shales and the storage of a great amount of organic carbon in the shelf sediments contemporaneous positive excursions of the 13c recorded from pelagic limestones of europe and australia prove a worldwide change in the co2 content of the oceans surface water which is in balance with the atmosphere if the climate is controlled by the co2 content of the atmosphere a cyclic operation process might have developed with the succession transgression high organic production deposition of organic carbon lowering of co2 in the atmosphere icehouse effect polar glaciation regression erosion of organic carbon and re supply of co2 to the ocean and atmosphere greenhouse effect deglaciation transgression during the change from a greenhouse to an icehouse effect an overturn of the anoxic oceans probably was one of the causes for the mass killing of low latitude marine organisms

palynological and bulk geochemical constraints on the paleoceanographic conditions across the frasnian famennian boundary new albany shale indiana abstract a down core record of stable isotope and geochemical results is integrated with palynofacies kerogen data from the new albany shale indiana to reconstruct environmental changes that occurred across the frasnian famennian boundary preliminary interpretations are focused on developing several multiproxy linkages that will potentially lead toward a more robust understanding of the occurrence and significance of phytoplankton assemblage variations during the late devonian a time of widespread black shale formation development of such linkages will potentially provide a more comprehensive assessment of the various controls on 1 primary production and 2 carbon sequestration in a large low paleolatitude intracratonic basin an abrupt change in the geochemical and biotic proxies for particulate organic matter across the frasnian famennian boundary coincides with a distinct lithological change characterized by laminated brownish black famennian mudstones unconformably overlying alternating bioturbated greenish gray and non bioturbated dark gray frasnian mudstones elemental and isotopic profiles reflect different patterns of production degradation and removal of organic carbon in the two shale facies a shift from acritarch to prasinophyte dominated waters across the boundary indicates the overall importance of bathymetric fluctuations chemico physical conditions and nutrient availability related to eustatic sea level change a positive 13 c v pdb shift of 1 1 across the boundary is interpreted to be correlative with the global upper kellwasser event a preliminary model is proposed to explain the sustainable primary production during times of maximum flooding thereby enhancing organic preservation during black shale formation

application of curvatures to airborne gravity gradient data in oil exploration abstractwe apply equipotential surface curvatures to airborne gravity gradient data the mean and differential curvature of the equipotential surface the curvature of the gravity field line the zero contour of the gaussian curvature and the shape index improve the understanding and geologic interpretation of gravity gradient data their use is illustrated in model data and applied to falcon airborne gravity gradiometer data from the canning basin australia

a new model for the kellwasser anoxia events late devonian shallow water anoxia in an open oceanic setting in the central asian orogenic belt the frasnian famennian mass extinction event devastated tropical marine ecosystems and ranks in the top six in taxonomic and ecological severity the close stratigraphic association between the extinction and the kellwasser anoxia events support a link between oceanographic anoxia and extinction the upper and lower kellwasser horizons have been identified in epicontinental and basinal settings in laurussia gondwana siberia and south china the hongguleleng formation late devonian in northwestern xinjiang china contains both the frasnian famennian boundary and the rebound from the frasnian famennian extinction event in a highly fossiliferous shallow marine setting associated with a devonian oceanic island arc complex part of the central asian orogenic belt or caob here we show that the hongguleleng formation also records the upper kellwasser anoxia event through analysis of multiple geochemical proxies in contrast to previous studies asserting that the kellwasser events were restricted to epicontinental seaways and basins our results indicate that it occurred not only along the shallow continental margins of the closing rheic ocean but also in shallow water in the open oceanic part of paleotethys previous explanations for the kellwasser events from epicontinental margins and basins call for the migration of deep anoxic bottom water into shallow water environments as a kill mechanism for shallow marine ecosystems or attribute it to sea level rise and subsequent stagnation there is no evidence that the devonian oceans completely overturned during the kellwasser events similarly many transgressive events in the devonian are not associated with black shales we therefore suggest an alternative mechanism for the kellwasser events based on new evidence from the caob where anoxia is driven by episodic eutrophication of surface waters

geochemical effects of an oxycombustion stream containing so2 and o2 on carbonate rocks in the context of co2 storage this paper describes the effects of the injection of a co2 dominated gas mixture into a geologic reservoir rock through experimental work in the context of limiting greenhouse gas emissions into the atmosphere the injected gas mixture consists of the exhaust fumes from an oxyboiler without desulphurisation with the following mole fraction composition co2 0 82 so2 0 04 o 2 0 04 n 2 0 04 and ar 0 06 corresponding experiments using pure co2 and n 2 were performed as a benchmark the rock sample was obtained by drilling to a depth of 4600 m into a low porosity dolostone reservoir containing micrometric to centimetric fractures in the south west of france northern pyrenees the fracture network represents the primary volume available for co2 storage and is partly filled with dolomite separated from the rock matrix by a thin layer of calcite covering the wall rocks experimental reactivity of the rock was tested in 2 cm 3 batch reactors in the presence of saline water 25 g l nacl and a gas phase pure n 2 pure co2 and gas mixture chemical analyses of the reacting solutions indicated that the mineralogic assemblage during exposure to pure co2 was in equilibrium with the aqueous solution raman analyses of the gas phase revealed only the presence of co2 optical and electronic microscopy of the resultant solid phases indicated partial dissolution of carbonates and oxidation of the pyrite surfaces in the presence of the gas mixture important mineralogic alteration occurred together with the consumption of half of the o 2 and total consumption of the so2 this high reactivity with the gas mixture leads to the complete dissolution of calcite and partial dissolution of dolomite and the precipitation of anhydrite and barite particularly in the zones where the calcite was initially present similarly pyrite was completely oxidised to hematite analyses of the rock samples indicated partial alteration of the clay minerals in the matrix to potassic beidellite in the experiment involving pure co2 and solely to vermiculites in the gas mixture experiment in conclusion the presence of so2 in the injection stream associated with the presence of o 2 results in an early strong acidification of the water which was buffered by the significant reactivity of the carbonates dissolution of all of the calcite and 6 of the dolomite and partial alteration of the clay minerals 87 of illite and 100 of smectite to vermiculites pyrite and aqueous fe from clays were completely oxidised by o 2 resulting in hematite and fe3 the mineralogic alteration and consequent volume changes under experimental conditions led to a slight increase in the porosity of the dolomite matrix and an average pore volume loss of 11 in the fractures caused by the replacement of calcite with anhydrite due to its high reactivity with carbonate so2 can react early during the injection phase the spatial distribution of calcite in the fractures of the reservoir has to be considered as one of the primary parameters controlling the evolution of the reservoir in terms of injectivity and petrophysical properties particularly in the zone near the injection wellbores the integrity of the calcite rich caprock is however ensured due to its thickness more than 1000 m and its calcite content which leads to ph buffering and anhydrite precipitation which in turn induces a porosity reduction and a possible coating of the rock formation

organic matter deposition in the ghadames basin libya during the late devonian a multidisciplinary approach the organic rich deposits of late devonian age are the second most important petroleum source rocks in the ghadames basin libya from available stratigraphy the peak of organic matter deposition corresponding to a level of radioactive shales easily recognized in gamma ray logs occurred at the frasnian famennian transition the present study was focused on samples from borehole d1 26 located in the central part of the ghadames basin belonging to the aouinet ouenine iii and iv formations frasnian to famennian the mineral and organic content of the rocks were analyzed in order to determine the origin of organic matter accumulation and estimate if the organic matter enrichment could be related to the well known upper kellwasser event the results indicate that during the frasnian the planktonic primary productivity was moderate but anoxic conditions reaching the euphotic zone were frequent and allowed efficient preservation of the organic matter at the frasnian famennian transition the deposition of the radioactive shales level can be related to a eustatic rise which allowed incursion of nutrient rich water in the basin leading to increase in primary productivity and photic zone anoxia during the famennian the conditions changed associated with a relative sea level fall and or a progradation of detrital sediments originating from the south photic zone anoxia was only episodic and plankton derived organic matter was poorly preserved nevertheless the important influx of organic matter of terrestrial origin allowed significant enrichment of the sediment in organic matter several indications suggest the radioactive shales interval could be coeval with the upper kellwasser level nevertheless further stratigraphic work is needed to confirm this hypothesis

on the interaction of pure and impure supercritical co2 with rock forming minerals in saline aquifers an experimental geochemical approach abstract the aim of this experimental study was to evaluate and compare the geochemical impact of pure and impure co2 on rock forming minerals of possible co2 storage reservoirs this geochemical approach takes into account the incomplete purification of industrial captured co2 and the related effects during injection and provides relevant data for long term storage simulations of this specific greenhouse gas batch experiments were conducted to investigate the interactions of supercritical co2 brine and rock forming mineral concentrates albite microcline kaolinite biotite muscovite calcite dolomite and anhydrite using a newly developed experimental setup after up to 42 day 1000 h experiments using pure and impure supercritical co2 the dissolution and solution characteristics were examined by xrd xrf sem and eds for the solid and icp ms and ic for the fluid reactants respectively experiments with mixtures of supercritical co2 99 5 vol and so2 or no2 impurities 0 5 vol suggest the formation of h2so4 and hno3 reflected in ph values between 1 and 4 for experiments with silicates and anhydrite and between 5 and 6 for experiments with carbonates these acids should be responsible for the general larger amount of cations dissolved from the mineral phases compared to experiments using pure co2 for pure co2 a ph of around 4 was obtained using silicates and anhydrite and 7 8 for carbonates dissolution of carbonates was observed after both pure and impure co2 experiments anhydrite was corroded by approximately 50 wt and gypsum precipitated during experiments with supercritical co2 no2 silicates do not exhibit visible alterations during all experiments but released an increasing amount of cations in the reaction fluid during experiments with impure co2 nonetheless precipitated secondary carbonates could not be identified

aryl isoprenoids and diaromatic carotenoids in paleozoic source rocks and oils from the western canada and williston basins abstract aryl isoprenoids in the range c13 c31 have been identified in source rock bitumens and oils from several paleozoic age petroleum systems in the western canada and williston basins the principal compounds possess the 2 alkyl 1 3 4 trimethyl substitution pattern characteristic of diaromatic carotenoids found in the chlorobiaceae family of photosynthetic sulfur bacteria two c40 perhydrodiaromatic carotenoids which are structurally related to the presumed precursors of the aryl isoprenoids have also been identified in oils and source rock bitumens of the duvernay late devonian petroleum system pyrolysis gas chromatograms of kerogens isolated from several paleozoic source rocks show an unusual abundance of 1 2 3 4 tetramethylbenzene it is proposed that this compound arises from cleavage of diaromatic carotenoid moieties which have been incorporated into the kerogen structure with increasing maturation concentrations of the aryl isoprenoids in duvernay source rock bitumens increase to a point whereas the c40 perhydrodiaromatic carotenoids decrease steadily previous studies have suggested that aryl isoprenoids may be indicators of enhanced salinity environments this is not supported by the present work which shows high concentrations in source rocks associated with presumed normal marine salinities there is however a general association with intervals of condensed clastic or mixed clastic carbonate sedimentation within carbonate depositional systems from the association found and from parallels to modern habitats of photosynthetic bacteria it can be inferred that these biomarkers indicate prolific bacterial growth in a stratified water column at and below the oxic anoxic boundary layer in sub tropical to tropical marine environments

tricyclic terpanes in precambrian bituminous sandstone from the eastern yanshan region north china a bituminous sandstone at the base of the xiamaling formation precambrian is a fossil oil pool which was thermally altered into reservoir bitumen 760 ma ago this reservoir bitumen was extracted fractionated and analyzed for biomarkers a novel series of extended tricyclic terpanes c18 c23 with a 13 n alkyl side chain configuration was identified by co injection of two standards c18 c20 and gc ms analysis some bicyclic sesquiterpanes c18 norditerpanes regular extended tricyclic terpanes c18 c24 no c22 and alkylcyclohexanes were also detected the source of the organic matter its alteration in the sandstone reservoir and the origin of its novel tricyclic terpanes are all inferred to be microbial

rearranged des e hopanoid hydrocarbons in sediments and petroleum abstract two tetracyclic triterpene derived hydrocarbons des e d c friedo 25 norhopa 5 7 9 triene 1 and des e d c friedohop 8 ene 8 have been isolated from an italian triassic black shale and identified by ms and nmr spectroscopy their structure the occurrence in the sediment of their ring a methylated counterparts as well as carbon isotopic data indicate that these compounds originate from bacterial hopanoids their formation most probably involves a sedimentary rearrangement of a functionalised des e hopane intermediate this hypothesis was further substantiated by experiments in which 8 was formed from 18 h des e hopan 17 ol 10 by treatment with k 10 montmorillonite clay in addition some minor unsaturated hydrocarbons formed as by products are also present in sediments

changes of palaeoenvironmental conditions recorded in late devonian reef systems from the canning basin western australia a biomarker and stable isotope approach abstract although the late devonian extinctions were amongst the largest mass extinction events in the phanerozoic the causes nature and timing of these events remain poorly restrained in addition to the most pronounced biodiversity loss at the frasnian famennian f f boundary and the end famennian there were also less extensively studied extinction pulses in the middle to late givetian and the frasnian here we used a combination of palynological elemental molecular and stable isotope analyses to investigate a sedimentary record of reef systems from this time period in the canning basin western australia the acquired data generally showed distinct variations between sediments from i the time around the givetian frasnian g f boundary and ii later in the frasnian and indicated a distinct interval of biotic stress particularly for reef builders in the older sediments alterations of pristane phytane ratios gammacerane indices chlorobi biomarkers dkerogen and chroman ratios describe the change from a restricted marine palaeoenvironment with an anoxic euxinic hypolimnion towards a presumably open marine setting with a vertically mixed oxic to suboxic water column simultaneous excursions in 13c profiles of carbonates organic matter om and hydrocarbons in the older sediments reflect the stratification induced enhancement of om recycling by sulfate reducing bacteria alterations in sterane distributions and elevated abundances of methyltrimethyltridecylchromans mttcs and perylene indicate an increased terrigenous nutrient input via riverine influx which would have promoted stratification phytoplankton blooms and the development of lower water column anoxia the detected palaeoenvironmental conditions around the g f boundary may reflect a local or global extinction event our data furthermore suggest a contribution of the higher plant expansion and photic zone euxinia to the late devonian extinctions consistent with previous hypotheses furthermore this work might contribute to the understanding of variations in devonian reef margin and platform top architecture relevant for petroleum exploration and development in the global devonian hydrocarbon resources

the frasnian famennian mass extinction insights from high resolution sequence stratigraphy and cyclostratigraphy in south china two sequences sfr sfa each 1 1 2 myr in duration are recognised in the strata across the frasnian famennian f f transition both in carbonate platform and interplatform basinal successions in south china the sequence boundary between the two sequences is placed a little below the top of the frasnian the sequences are basically composed of coarsening upward bed thickness increasing upward cycles and shallowing upward cycles parasequences in basinal and platform deposits respectively which stack into cycle sets typically six to eight cycles 10 and 12 cycle sets are identified in sequences sfr and sfa respectively these cycle sets can be further grouped into larger scale composite cycle sets herein termed mesocycle and megacycle sets with two and four cycle sets respectively this vertical cycle stacking pattern and the hierarchy of cyclicity suggest a milankovitch style of forcing such that the cycles and cycle sets were formed in response to the orbital perturbations of precession 16 18 kyr and eccentricity v100 kyr in duration respectively in the basinal cycles smaller scale rhythmic stratification beds typically six to eight beds in a cycle are extensive and were likely caused by millennial scale climatic forcing in the lower sequence sfr the latest highstand deposits consist of calciturbidites and debrites in deep water strata and fenestral limestones in shallow water strata representing a major third order sea level fall within these deposits four cycle sets are further identified in both coeval deep water and platform successions succeeding deeper water organic rich facies within which three cycles occur are the transgressive deposits of the overlying famennian sequence sfa these cycles represent three higher frequency 16 18 kyr sea level fluctuations and accompanying anoxia superimposed on a major third order sea level rise the f f boundary is placed at the top of the first cycle based on conodont data thus a major sea level fall and then a rise occurred in the f f transitional period faunal and sedimentological data reveal a massive biotic decline in concert with the major sea level fall and a further biotic demise coinciding with the major sea level rise and its three superimposed higher frequency sea level fluctuations and accompanying anoxia the f f biotic crisis was therefore characterised by two episodes of step down extinction on the basis of milankovitch orbital rhythms the first major biotic extinction took place over v400 kyr and the subsequent event was v50 kyr in duration i e v450 kyr for the entire event at the same time as the massive decline of normal marine fossils during the latest frasnian sea level fall there was widespread cyanobacterial growth and a thriving of planktonic calcispheres suggesting eutrophic conditions this situation could have caused a severe biotic loss as a result of the deterioration of surface water clarity and formation of anoxic bottom waters due to over

extent and duration of marine anoxia during the frasnian famennian late devonian mass extinction in poland germany austria and france the intensity and extent of anoxia during the two kellwasser anoxic events has been investigatedinarangeofeuropeanlocalitiesusingamultidisciplinaryapproach pyriteframboidassay gamma ray spectrometry and sediment fabric analysis the results reveal that the development of the lower kellwasser horizon in the early late rhenana zone frasnian stage in german type sections does not always coincide with anoxic events elsewhere in europe and in some locations seafloor oxygenation improves during this interval thus this anoxic event is not universally developed in contrast the upper kellwasser horizon developed in the late linguiformis zone frasnian stage in germany correlates with a european wide anoxic event that is manifest as an intensification of anoxia inbasinallocationstothepointthatstableeuxinicconditionsweredeveloped forexample inthebasins of the holy cross mountains poland the interval also saw the spread of dysoxic waters into very shallow water for instance reefal locations and it seems reasonable to link the contemporaneous demise of many marine taxa to this phase of intense and widespread anoxia in basinal locations euxinic conditions persisted into the earliest famennian with little change of depositional conditions only in the continental margin location of austria was anoxia not developed at any time in the late devonian consequently it appears that the upper kellwasser anoxic event was an epicontinental seaway phenomenon caused by the upward expansion of anoxia from deep basinal locales rather than an oceanic anoxic event that has spilled laterally into epicontinental settings

chemical effects of sulfur dioxide co injection with carbon dioxide on the reservoir and caprock mineralogy and permeability in depleted gas fields the most suitable candidates for subsurface storage of co2 are depleted gas fields their ability to retain co2 can however be influenced by the effect which impurities in the co2 stream e g h2s and so2 have on the mineralogy of reservoir and seal in order to investigate the effects of so2 we carried out laboratory experiments on reservoir and cap rock core samples from gas fields in the northeast of the netherlands the rock samples were contained in reactor vessels for 30 days in contact with co2 and 100 ppm so2 under in situ conditions 300 bar 100 degrees c the vessels also contained brine with the same composition as in the actual reservoir furthermore equilibrium modeling was carried out using phreeqc software in order to model the experiments on caprock samples after the experiments the permeability of the reservoir samples had increased by a factor of 1 2 2 2 as a result of dissolution of primary reservoir minerals analysis of the associated brine samples before and after the experiments showed that concentrations of k si and al had increased indicative of silicate mineral dissolution in the caprock samples composed of carbonate and anhydrite minerals permeability changed by a factor of 0 79 23 the increase in permeability is proportional to the amount of carbonate in the caprock with higher carbonate content in comparison with anhydrite the permeability increase is higher due to the additional carbonate dissolution this dependency of permeability variations was verified by the modeling study hence caprock with a higher anhydrite content in comparison with carbonate minerals has a lower risk of leakage after co injection of 100 ppmv so2 with co2 c 2015 elsevier ltd all rights reserved

supercritical carbon dioxide and sulfur in the madison limestone a natural analog in southwest wyoming for geologic carbon sulfur co sequestration article i nfo the madison limestone on the moxa arch southwest wyoming usa contains large volumes 65 95 of supercritical co2 that it has stored naturally for 50 million years this reservoir also contains supercritical h2s aqueous sulfur complexes so4 2 and hs and sulfur bearing minerals anhydrite and pyrite although so2 is not present these sulfur bearing phases are known products of so2 disproportionation in other water rock systems the natural co occurrence of so4 2 s 2 supercritical co2 and brine affords the opportunity to evaluate the fate of a carbon sulfur co sequestration scenario mineralogic data was obtained from drill core and aqueous geochemical data from wells outside and within the current supercritical co2 sulfur brine rock system in addition to dolomite calcite and accessory sulfur bearing minerals the madison limestone contains accessory quartz and the aluminum bearing minerals feldspar illite and analcime dawsonite naalco3 oh 2 predicted as an important carbon sink in sequestration modeling studies is not present after confirming equilibrium conditions for the madison limestone system reaction path models were constructed with initial conditions based on data from outside the reservoir addition of supercritical co2 to the madison limestone was simulated and the results compared to data from inside the reservoir the model accurately predicts the observed mineralogy and captures the fundamental changes expected in a madison limestone brine system into which co2 is added ph decreases from 5 7 to 4 5 at 90 c and to 4 0 at 110 c as expected from dissolution of supercritical co2 creation of carbonic acid and buffering by the carbonate rock the calculated redox potential increases by 0 1 v at 90 c and 0 15 v at 110 c due to equilibrium among co2 anhydrite and pyrite final calculated eh and ph match conditions for the co existing sulfur phases present in produced waters and core from within the reservoir total dissolved solids increase with reaction progress mostly due to dissolution of calcite with an accompanying increase in dissolved bicarbonate the madison limestone is a natural example of the thermodynamic end point that similar fluid rock systems will develop following emplacement of a supercritical co2 sulfur mixture and is a natural analog for geologic carbon sulfur co sequestration