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

the posidonia shale lower toarcian of sw germany an oxygen depleted ecosystem controlled by sea level and palaeoclimate abstract the lower toarcian posidonia shale is famous for its excellently preserved fossils and its high amount of organic matter up to 16 both quality of preservation and accumulation of organic matter have been explained by permanent anoxic bottom water conditions high resolution geochemical sedimentological and palaeoecological investigations of various sections of the posidonia shale in sw germany however indicate that oxygen availability was variable and ranged from short oxygenated periods to longer term anoxia the benthic macrofauna consists of nine fossil communities and was used in combination with geochemical data to reconstruct a time averaged oxygen curve anoxic conditions prevailed during the deposition of the toarcian black shales they were however punctuated by various short periods weeks to years with oxygenated bottom water conditions sedimentological e g distinctiveness of microlamination siliciclastic content and geochemical parameters e g organic matter content isotopic signatures 18o and 13c molecular redox parameters pristane phytane ratio arylisoprenoids exhibit a remarkable covariation and seem to be controlled by sea level fluctuations maximum oxygen depletion and an extreme negative shift of 13corg values 34 occurred during the early falciferum zone this is explained by the recycling of 12c enriched carbon derived from remineralization of organic matter on and within the substrate during low sea level stand and a highly elevated redox boundary including photic zone anoxia the subsequent transgression permitted enhanced water exchange with the tethyan ocean and caused improvement of living conditions at the end of the falciferum zone other important factors controlling the depositional environment are the overall palaeogeographic situation and climate the early jurassic is the latest period before break up of pangaea and probably was ruled by a strong meridional atmospheric circulation system with pronounced seasonal changes of prevailing trade and monsoon wind systems an estuarine circulation with a positive water balance and surface water with slightly reduced salinity in the summer alternated with an anti estuarine circulation and a negative water balance in the winter during the summer months a stratified water column with anoxic conditions below the halocline developed 18o data indicate low salinity in the surface water during the monsoon influenced summer high productivity was then located in the photic zone and the corresponding isotopically light 18o signal was fixed in the calcareous nannoplankton during the winter months a saline circulation system brought oxygen to the benthic environment favouring temporary benthic colonization especially during times of relative sea level high stand

carbon isotopic composition of hydrocarbons in ocean transported bitumens from the coastline of australia abstract bitumens stranding along the coastlines of the northern territory western australia south australia victoria and tasmania often have biomarker signatures which closely match those of oils of s e asian origin a suite of these bitumens was studied to determine the isotopic signatures of their alkanes and to compare them to similar oils from the central sumatra basin saturated hydrocarbons were separated into a fraction containing n alkanes and isoalkanes and one containing the multibranched cyclic components using adduction into silicalite gas chromatography isotope ratio mass spectrometry gc irms of the n alkanes revealed 13 c signatures covering a wide range of values from 25 5 to 29 pdb but generally falling between those of the botryococcane containing minas and duri oils from the central sumatra basin n alkanes of the minas oil are 3 4 lighter than their duri counterparts the isotopic compositions of pristane and phytane cover a similar range 13 c 24 to 27 botryococcane is consistently heavy with 13 c values in the range 11 to 14 one bitumen sample with no botryococcane but abundant bicadinanes showed n alkane 13 c values in the range 28 to 29 at the light extreme for waxy bitumens in our sample suite sample to sample differences in carbon isotopic signatures of n alkanes are attributed mainly to variations in primary source with weathering and biodegradation as minor causes instances of low precision for replicate analyses 2 are caused by the relative abundance of co eluting isoalkanes overall the isotopic patterns of waxy bitumens from the australian coastline provide independent confirmation of their similarity to central sumatran lacustrine oils on the other hand asphaltic bitumens from the southern australian coastline are isotopically light with n alkane 13 c values in the range 31 5 to 33 this distinctive feature may assist identification of their source

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

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

tectonics and sedimentation in the fohnsdorf seckau basin miocene austria from a pull apart basin to a half graben the miocene intramontane fohnsdorf seckau basin is situated at the junction of the sinistral mur murz fault system and the dextral pols lavanttal fault system the basin comprises a 2 400 m thick coal bearing fluviodeltaic lacustrine succession lower to middle miocene upper karpatian lower badenian which is overlain by a 1 000 m thick alluvio deltaic conglomeratic succession apfelberg formation middle upper badenian in the south a three stage model for the basin evolution has been reconstructed from structural analysis and basin fill geometries during a first pull apart phase subsidence occurred along ene trending sinistral strike slip faults of the mur murz fault system and ne sw to n s trending normal faults forming a composite pull apart basin between overstepping en echelon strike slip faults the seckau and fohnsdorf sub basins are considered as two adjacent pull aparts which merged into one basin during the second phase n s to nnw sse extension and normal faulting along the southern basin margin fault formed a half graben filled by wedge shaped alluvial strata apfelberg formation during the third phase after the end of basin sedimentation the dextral pols lavanttal fault system reshaped the western basin margin into a positive flower structure

guidelines for assessing the petroleum potential of coaly source rocks using rock eval pyrolysis abstract coaly source rocks are sufficiently different from marine and lacustrine source rocks in their organic matter characteristics to warrant separate guidelines for their assessment using rock eval pyrolysis the rank threshold for oil generation is indicated by the increase in bi s1 toc at rank sr 9 10 tmax 420 430 c ro 0 55 0 6 and the threshold for oil expulsion is indicated by the peak in qi s1 s2 toc at rank sr 11 12 5 tmax 430 440 c ro 0 65 0 85 the pronounced rank related increase in hi s2 toc prior to oil expulsion renders the use of immature samples inappropriate for source rock characterisation a more realistic indication of the petroleum generative potential and oil expulsion efficiency of coaly source rocks can be gained from samples near the onset of expulsion alternatively effective hi values i e his near the onset of expulsion can be estimated by translating the measured his of immature samples along the maturation pathway defined by the new zealand or other defined coal band coaly source rocks comprise a continuum of coaly lithologies including coals shaly coals and coaly mudstones determination of the total genetic potential of coaly source rock sequences is best made using lithology based samples near the onset of expulsion

palaeoceanography of the early zechstein sea during kupferschiefer deposition in the lower rhine basin germany a reappraisal from stable isotope and organic geochemical investigations abstract in the study area of the lower rhine basin the permian kupferschiefer was deposited in a shallow water environment water exchange from this marginal basin with the zechstein sea was restricted by palaeohighs the burial depth of the shale did not exceed 1000 m during the depositional history of most parts of the basin maturation of the organic matter was governed only by the geothermal gradient not exceeding 68 c km during the late carboniferous due to minor thermal alteration of organic matter diagenetic effects on the biomarker composition and the light stable isotope ratios c h o n of organic matter and carbonates are of minor importance in the present study isotopic and organic geochemical data are interpreted with respect to palaeoceanographic aspects the data provide information about salinity variations the nature of organisms living in the water column and the importance of bacterial activity in the sediment during deposition from the degree of methylation of 2 methyl 2 trimethyl tridecylchromans mttc an euhaline to mesohaline 30 40 sea water salinity during kupferschiefer sedimentation can be inferred the high abundance of biomarkers derived from green purple sulphur bacteria suggests h2s saturation of the bottom waters and maximum water depths below 100 m in the basin because these organisms live near the boundary between the photic zone and the anoxic euxinic bottom water at a depth of 10 30 m primary production in the upper water column was dominated by photosynthetic cyanobacteria or green algae in the sediment sulphate reduction occurred due to the availability of abundant sulphate and organic detritus from the overlying water column furthermore methanogenesis was active mostly during early kupferschiefer deposition this is reflected by the light carbon isotopic composition of organic matter originating from recycling of co2 generated by methane oxidizing bacteria in the water column saccate pollen are the only morphologically preserved organic matter in the sediment

chlorine variations in the magma of soufriere hills volcano montserrat insights from cl in hornblende and melt inclusions the soufriere hills volcano in montserrat erupts a cl rich porphyritic andesite hcl degassing accompanies eruption and is dependent on the growth rate of the lava dome the magma contains hornblende phenocrysts that show repetitive zoning in most elements including cl on the basis of the zoning data cl oh ratios in the melt calculated from partitioning data increase rimward through each zone indicating that the phenocrysts formed under conditions of varying cl oh m an empirical relationship between a site occupancy in the hornblende and temperature implies that crystallisation of each zone is also accompanied by increasing temperature each zone ends at a resorption horizon and crystallisation recommences at lower temperature and cl oh m melt inclusion h2o and cl contents for the 8th january 2007 explosive eruption can be explained by closed system degassing with dclfl m between 5 and 30 or by open system degassing accompanied by a small amount of crystallisation however neither simple closed system degassing nor convective circulation of magma can explain the positive correlation of cl oh m with temperature we suggest that the zoning can be caused by accumulation of co2 rich vapour in the andesite probably as a result of mafic magma injection into the chamber decreasing h2o fugacity and or increasing clm result in increasing cl oh m while heat transferred with the volatiles causes the rise in temperature intermittently the accumulated fluid is lost to the surface possibly as a result of renewed eruptive activity this model requires the co2 rich fluid to be decoupled from the magma consistent with previous observations of continuous co2 emissions at the surface

an experimental study of phase equilibria in the system h 2 o co 2 nacl at 800 c and 9 kbar phase equilibria in the ternary system h2o co2 nacl were studied at 800 c and 9 kbar in internally heated gas pressure vessels using a modified synthetic fluid inclusion technique the low rate of quartz overgrowth along the b and a axes of quartz crystals was used to avoid fluid inclusion formation during heating prior to attainment of equilibrium run conditions the density of co2 in the synthetic fluid inclusions was calibrated using inclusions in the binary h2o co2 system synthesised by the same method and measured on the same heating freezing stage in the two phase field two types of fluid inclusions with different densities of co2 were observed using mass balance calculations these inclusions are used to constrain the miscibility gap and the orientation of two phase tie lines in the h2o co2 nacl system at 800 c and 9 kbar the equation of state of duan et al 1995 approximately describes the p t section of the ternary system up to about 40 wt of nacl at higher nacl concentrations the measured solubility of co2 in the brine is much smaller than predicted by the eos a salting out effect must be added to the equation of state to include coulomb interaction in the model of anderko and pitzer 1993 and pitzer and jiang 1996 the new experimental data together with published data up to 5 kbar shmulovich et al 1995 encompass practically all subsolidus crustal p t conditions a feature of the new experimental results is the large compositional range in the h2o co2 nacl system occupied by the stability fields of halite co2 rich fluid h2o nacl brine the prediction of halite stability in equilibrium with co2 rich fluid in deep crustal rocks is supported by recent petrological and fluid inclusion studies of granulites

organic geochemistry of the lower miocene oberdorf lignite styrian basin austria its relation to petrography palynology and the palaeoenvironment abstract in the oberdorf trough at the northwestern margin of the styrian basin austria an up to 36 m thick lower miocene ottnangian lignite seam occurs within the fluvial koflach voitsberg formation previous results indicate that the lignite originated in a topogenous mire within a wet forest swamp palaeoenvironment differences in soluble organic matter som yield of borehole samples from the lignite seam are related to free lipids present in plant waxes or resins and the presence of thermally labile polymers indicated by the contents of liptinite macerals i e resinite suberinite and liptodetrinite the n alkane distribution patterns are dominated by high molecular weight lipids with marked odd over even predominance originating from plant waxes a contribution of algae to the even numbered short chain lipids observed in considerable amounts in the footwall sediments is proposed terpenoid biomarkers characteristic for conifers and angiosperms were detected consistent with palynomorphic spectra which are dominated by forest swamp pollen taxodiaceae cupressaceae and pollen from plants living in a mixed mesophytic forest excellent relationships between higher plant biomarker composition and palynologic data indicate that the organic geochemical results reflect the varying inputs of coniferales vs angiosperms the data further imply that cuparene may be used for taxonomical differentiation of coniferales families organic geochemical data provide evidence that the content of land plant derived biomarkers is controlled by the input of resin rich conifers concentrations of hopanoids dominated by hop 17 21 ene generally increase towards the top of the lignite a section characterised by high extents of aromatisation of triterpenoid biomarkers the results suggest that the aromatisation of angiosperm derived biomarkers may be governed by the activity of anaerobic rather than by aerobic bacteria however changes in the depositional environment and palynologic facies during peat formation probably influenced the origin and fate of angiosperm derived triterpenoids the results indicate how biomarker composition may contribute to the evaluation of environmental changes cross correlations of organic geochemical parameters with palynological data and petrography based facies indicators will provide further insights in the peat forming vegetation and biogeochemical activities in the mire

the identification of an active fault by a multidisciplinary study at the archaeological site of sagalassos sw turkey abstract the archaeological site of sagalassos sw turkey is located in a region characterized by the absence of any significant recent seismic activity contrary to adjacent regions however the assessment of earthquake related damage at the site suggests that the earthquakes that have been demonstrated to have struck this pisidian city in ca ad 500 and in the middle or second half of the 7th century ad are characterized by an msk intensity of at least viii and occurred on a fault very close to the city different investigation techniques archaeoseismology remote sensing and geomorphology surface geology and structural data 2d resistivity imaging and palaeoseismological trenching have been applied at the archaeological site and its direct surroundings in search for the causative fault of these earthquakes this multidisciplinary approach shows that each of the different approaches independently provides only partial non conclusive information with respect to the fault identification integration is imperative to give a conclusive answer in the search for the causative fault this study has indeed revealed the existence of a to date unknown active normal fault system passing underneath ancient sagalassos i e the sagalassos fault a historical coseismic surface rupture event on this fault could be identified this event possibly corresponds to the devastating sagalassos earthquakes of ca ad 500 and the middle or second half of the 7th century ad finally this study demonstrates that in the particular geodynamic setting of sw turkey archaeological sites with extensive earthquake related damage form an important tool in any attempt to asses the seismic hazard

the neogene fohnsdorf basin basin formation and basin inversion during lateral extrusion in the eastern alps austria the evolution of the early middle miocene fohnsdorf basin has been studied using borehole data reflection seismic lines and vitrinite reflectance the basin is located along the sinistral mur murz fault system and probably formed as an asymmetric pull apart basin which was subsequently modified by halfgraben tectonics as a consequence of eastward lateral extrusion sedimentation started with the deposition of fluvio deltaic sediments thick coal accumulated in the northwestern basin thereafter subsidence rates increased dramatically with the formation of a lake several hundred meters deep the lake was filled mainly from the north with more than 1500 m of sediments showing a coarsening upward trend due to southward prograding deltaic lobes a sequence of more than 1000 m of boulder gravels blockschotter in the southeastern part of the basin are interpreted as the upper part of a coarse grained fan delta succession which accumulated along a normal fault along the southern basin margin fan deltas reached the central basin only during the early stages of sedimentation and during the late stages of basin formation miocene heat flow was approximately 65 70 mw m2 which is significantly lower than in other basins along the mur murz fault system the present day southwestern basin margin is a recent feature which is related to transpression along the dextral pols lavanttal fault system it is formed by reverse faults constituting the northeastern part of a flower structure miocene sediments in the feeberg valley are preserved along its southwestern part uplift of the central part of the flower structure was at least 2 4 km north south compression resulted in the deformation of the basin fill uplift of the e w trending basement ridge separating the fohnsdorf and seckau basins and in the erosion of 1750 m of sediments along the northern basin margin

rare earth elements distribution in granulite facies marbles a witness of fluid rock interaction abstract the rare earth element ree distribution of marbles from tranomaro se madagascar shows that the marbles have interacted with syn metamorphic fluids during the panafrican granulite facies metamorphism the tranomaro area is characterized by an extensive development of pyroxenites skarns variably mineralized in uranothorianite and enriched in ree zr across a meter scale marble pyroxenite contact the ree content increases from the most remote marble sample to the contact with the pyroxenite la from 19 8 to 129 ppm ree patterns in enriched marbles display a strong negative eu anomaly similar to those of pyroxenites this peculiar type of ree distribution results from fluid infiltration on a regional scale some marbles have similar ree characteristics progressive development of eu anomaly together with ree enrichment showing that some of them have interacted with fluids infiltration was hardly recognizable using c and o isotopic signatures because large isotopic variations were introduced during the pre granulitic history then ree distribution in high grade marble may be helpful in monitoring syn metamorphic fluid flow in the present case it is a more reliable tracer of fluid infiltration than stable isotopic compositions

guidelines for evaluating petroleum source rock using programmed pyrolysis rock eval pyrolysis is used to rapidly evaluate the petroleum generative potential and thermal maturity of rocks accurate conclusions require programs every 30 60 ft 9 18 m understanding of interpretive pitfalls and supporting data such as visual kerogen vitrinite reflectance and elemental analyses the generative potential of coals is commonly overestimated by pyrolysis and is best determined by elemental analysis and organic petrography most coals show high s2 s3 5 and low hi values 300 mg hc g toc migrated oil and mud additives which alter rock eval data can sometimes be removed by special processing for immature rocks bimodal s2 peaks and pi values over 0 2 indicate contamination pyrolysis downgrades organic poor clay rich rocks which show lower hi and higher tmax values than isolated kerogen because of adsorption of pyrolyzate on the clays tmax values for small s2 peaks 0 2 mg hc g toc are unreliable tmax is affected by maturation organic matter type contamination and the mineral matrix s3 is sensitive to inorganic and adsorbed carbon dioxide and to instrumentation problems acidification of carbonate rich samples and proper maintenance improves s3 measurement constant sample weights 100 mg are recommended below a threshold weight tmax increases by up to 10 c and other parameters decrease organic rich samples which overload the detector can be diluted with carbonate detector linearity is determined by pyrolyzing various weights of an organic rich rock

co2 h2s cos s8 alo oh bearing fluid inclusions in ruby from marble hosted deposits in luc yen area north vietnam abstract fluid inclusions have been studied in rubies from marble hosted deposits in the luc yen mining district north vietnam raman and infrared spectroscopy combined with microthermometry investigations on primary and secondary fluid inclusions provided evidence of co 2 h 2 s cos s 8 alo oh bearing fluids with native sulphur and diaspore daughter minerals without visible water diaspore appeared as a nonvisible film of 2 3 m coating the wall of the fluid inclusion cavity and native sulphur was generally nucleated during raman irradiation the presence of diaspore and cos in the fluid inclusions indicates that water was present in the paleofluid the mole fractions of h 2 o and co 2 are around 10 2 and the expected concentration of water in the fluid inclusions is in the 1 10 mol range crush leach identified sulphates and chlorides that are assigned to the presence of anhydrite and na ca cl salts found by sem in the ruby crystals the co 2 rich inclusions which do not coexist with an aqueous phase by immiscibility process demonstrate that ruby grew from this co 2 rich and water poor fluid at equilibrium with na ca cl salts thermal reduction of evaporitic sulphates based on an initial assemblage of anhydrite calcite and graphite originating from the metamorphism of organic matter is proposed to explain the original fluid chemistry of these marble hosted rubies the marbles acted as a closed system and the carbonic composition of the parent fluids in ruby indicates that aluminium can be transported in co 2 rich fluids at high p t

coal deposition in the noric depression eastern alps raised and low lying mires in miocene pull apart basins abstract pull apart basins often form during the late stage of continental collision provided appropriate climatic conditions these basins may contain thick coal seams two such examples are the leoben and fohnsdorf basins in austria which formed in miocene times during the post collisional stage of the alpine orogene both basins contain more than 10 m of sub bituminous coal despite similar ages tectonic settings and similar stratigraphic position of the seams within the sedimentary sequence the properties of the coals differ significantly the leoben coal is quite clean whereas fohnsdorf coal is rich in ash and sulfur petrographical and geochemical methods were applied to reconstruct the environmental factors that controlled coal properties in these basins coal formation in the leoben basin commenced in an eutrophic low lying mire this was followed by deposition of the main body of coal which formed in an ombrotrophic raised mire coal deposition was only shortly interrupted by deposition of volcanic ashes due to an acid paleo environment the volcanic material within the raised mire was altered to kaolinite thick vitrain bands representing large trees are found in the lower part of the seam only siderite is the main inorganic constituent in the main coal body lakes within the raised mire were present during late stages of peat accumulation and were filled with sapropelic coal the high ash yields of this facies are due to abundant siliceous sponges siliceous crusts and tuffogenic minerals finally high subsidence rates caused the flooding of the raised mire and sapropelic shales were deposited in the newly formed lake the iron which formed siderite in the raised mire and biogenic and abiogenic silica present in the lakes within the raised mire are derived from volcanic ashes the high ash fohnsdorf coal was formed in a low lying mire close to a brackish lake the seam geometry is controlled by the progradation of a fluvio deltaic system into the brackish lake and its subsequent drowning the roof of the seam is formed by coquinoidal limestones and sapropelic shales the brackish influence reduced the acidity of the mire which resulted in the transformation of volcanic glass into montmorillonite the low acidity also promoted high bacterial activity which together with the high sulfate content of brackish waters explains the high sulfur and pyrite content of the coal its high content of biogenic methane is probably another effect of bacterial activity low ash low sulfur coal is restricted to thin layers these might represent local raised mires which formed after the withdrawal of a fluvial system

evolution of lacustrine systems along the miocene mur murz fault system eastern alps austria and implications on source rocks in pull apart basins tectonically controlled lakes developed during miocene lateral extrusion of the eastern alps mineralogy and the inorganic and organic geochemistry of rocks from three boreholes were investigated to reconstruct the evolution of lake ingering and lake groisenbach and to study the distribution of source rocks in pull apart basins gas prone coal and oil prone sapropelic shale accumulated during the initial shallow stages of lake ingering thereafter the lake deepened rapidly 125 m thick prodelta shale containing a type ii kerogen was deposited in the brackish several hundred meter deep hydrologically closed lake afterwards decreasing subsidence allowed the filling of the lake by prograding deltas during the advance of the deltaic systems the lake became shallower hydrologically open and the brackish influence terminated source rock quality decreased significantly during the filling stage of the lake a consequence of dilution of autochthonous organic matter and of enhanced input of land plants despite its considerable dimensions formation and filling of lake ingering lasted only two million years lake groisenbach was considerably smaller and more susceptible to high frequency changes in lake chemistry although the water body was temporarily oligosaline brackish conditions did not occur high sulphur contents were due to anoxic events and the inflow of ca rich waters abundant dissolved silica favoured diatoms blooms

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

an experimental study of phase equilibria in the systems h 2 o co 2 cacl 2 and h 2 o co 2 nacl at high pressures and temperatures 500 800 c 0 5 0 9 gpa geological and geophysical applications phase equilibria in the ternary systems h2o co2 nacl and h2o co2 cacl2 have been determined from the study of synthetic fluid inclusions in quartz at 500 and 800 c 0 5 and 0 9 gpa the crystallographic control on rates of quartz overgrowth on synthetic quartz crystals was exploited to prevent trapping of fluid inclusions prior to attainment of run conditions two types of fluid inclusion were found with different density or co2 homogenisation temperature th co2 a co2 rich phase with low th co2 and a brine with relatively high th co2 the density of co2 was calibrated using inclusions in the binary system h2o co2 mass balance calculations constrain tie lines and the miscibility gap between brines and co2 rich fluids in the h2o co2 nacl and h2o co2 cacl2 systems at 500 and 800 c and 0 5 and 0 9 gpa the miscibility gap in the cacl2 system is larger than in the nacl system and solubilities of co2 are smaller cacl2 demonstrates a larger salting out effect than nacl at the same p t conditions in ternary systems homogeneous fluids are h2o rich and of extremely low salinity but at medium to high concentrations of salts and non polar gases fluids are unlikely to be homogeneous the two phase state of crustal fluids should be common for low fluid rock ratios the cation compositions of crustal fluids are buffered by major crustal minerals feldspars and micas in pelites and granitic rocks calcite dolomite in carbonates and pyroxenes and amphiboles in metabasites fluids in pelitic and granitic rocks are na k rich while for carbonate and metabasic rocks fluids are ca mg fe rich on lithological boundaries between silicate and carbonate rocks or between pelites and metabasites diffusive cation exchange of the salt components of the fluid will cause the surfaces of immiscibility to intersect leading to unmixing in the fluid phase dispersion of acoustic energy at critical conditions of the fluid may amplify seismic reflections that result from different fluid densities on lithological boundaries

experimental studies in model fluid systems numerous observations provide strong evidence that fluid fluid coexistence is a widespread phenomenon in many geological processes i oceanic hydrothermal fluids display a wide range in salinity which clearly indicates fluid phase separation of the circulating seawater see foustoukos and seyfried 2007a ii selective enrichment of certain elements and coeval entrapped inclusions of different co existing fluids highlight the role immiscible fluids play in ore formation see heinrich 2007a iii trace element and stable isotope characteristic as well as equilibrium mineral assemblages in contact aureoles prove immiscible fluids to be a ubiquitous feature in most contact metamorphism see heinrich 2007b iv small scale fluid heterogeneity in eclogitic rocks indicate fluid immiscibility to occur in metamorphic rocks up to high or even ultra high pressure see heinrich 2007b unfortunately fluids are principally non quenchable phases and direct quantitative information on fluid properties at p and t is in most cases not available experimental studies are thus central in studying geologic fluids in general and co existing fluids in particular they are still the primary source of quantitative information on physicochemical properties of co existing crustal fluids they allow e g determine i fluid phase relations as function of p t and x ii physical fluid properties like density and viscosity and iii trace element and isotope fractionation between co existing fluids but also between co existing fluids and solids the experimental data can then be used as input in forward modeling approaches the results and or predictions of which may then be tested in natural systems see driesner and geiger 2007 experimental data on co existing fluids in systems of geological relevance already date back to the flrst half of last century e g keevil 1942 since the 1960ies numerous systematic experimental studies on fluid fluid phase relations at crustal p and t conditions were performed e g sourirajan and kennedy

fluid inclusions in epidote minerals and fluid development in epidote bearing rocks the widespread occurrence of epidote minerals in metamorphic and igneous rocks as well as in many ore deposit types makes it a promising candidate for fluid inclusion studies apart from high to very high temperature and low to intermediate pressure conditions epidote minerals are stable over a wide range of pressure and temperature in the continental and oceanic crust e g poli and schmidt 1998 yet fluid inclusion studies on epidote minerals are surprisingly scarce even in fluid saturated environments like certain vein type deposits or hydrothermal volcanic vugs and druses for example epidote minerals are not mentioned in the subject index of roedder s 1984 outstanding summary and review of fluid inclusion studies and occurrences which lists more than sixty different host minerals for fluid inclusions nonetheless more recent studies showed fluid inclusions in epidote minerals to be the only direct witness of the physiochemical and compositional fluid evolution during certain geodynamic processes mainly found in fossil geothermal systems ore deposits and high pressure to ultra high pressure rocks the aim of this review is to outline and summarize some aspects and interpretations of geodynamic processes which are based on temperature t pressure p molar volume v and composition x data from fluid inclusions in epidote minerals as well as associated host minerals from various geological environments the review starts with a chapter on some typical mixed volatile solid fluid equilibria involving epidote minerals which are relevant for the here discussed environments this is followed by a short introduction into the basic concepts of fluid inclusion research and the role of epidote minerals the next section covers fluid inclusion studies on epidote minerals from active and fossil geothermal systems as well as low grade metamorphic rocks and constraints on the p t x properties of the fluids present in these systems this is followed by a short introduction

determination of the h3bo3 concentration in fluid and melt inclusions in granite pegmatites by laser raman microprobe spectroscopy a method of determining the boric acid h3bo3 concentration in fluid inclusions and volatile rich glasses using laser raman microprobe spectroscopy is described the h3bo3 content of melt and fluid inclusions is determined with good accuracy and precision in the concentration range of 0 to 20 wt and with a minimum detection limit mdl of 0 05 wt h3bo3 the method is applicable to complex solutions that contain components such as nacl kcl rbcl or cscl which do not form stable hydrated borates with boric acid at room temperature this raman study demonstrates that boric acid is an abundant component in volatile rich melt inclusions and in genetically linked primary and pseudosecondary fluid inclusions particularly in tourmaline bearing granites and boron rich pegmatites in quenched pegmatite melt boron occurs predominantly as a trigonal coordinated b oh 3 complex the analytical method is applied to a series of melt and fluid inclusions from different localities and geological environments namely hydrothermal tin and tungsten deposits granite pegmatites and rhyolites special emphasis is given to the analysis of fluorine phosphorus and boron rich pegmatites of the variscan ehrenfriedersdorf complex central erzgebirge germany in this pegmatite system boron in combination with water fluorine and phosphorous is responsible for immiscibility of two coexisting silicate melts a silicate rich h2o poor melt and a silicate poor h2o rich melt accompanied by strong element fraction ation between the two boron fractionates into the water rich silicate melt by factors between 1 8 at 500 c and 1 0 at 712 c if at low pressure a vapor phase is additionally formed boron is partitioned into the vapor phase the utility of the developed method was also quantitatively tested by experiments with a hydrothermal diamond anvil cell

raman spectroscopic densimeter for pure co2 and co2 h2o nacl fluid systems over a wide p t range up to 360 c and 50 mpa abstract density of fluid inclusions is one of the most important parameters to reconstruct the p t conditions of entrapment of geo fluids co existing with microthermometry methods raman spectroscopy also became a useful tool to determine the density of co2 bearing inclusions via fermi diad splitting in this study a new co2 densimeter which takes into account the effects of temperature pressure and h2o nacl on fermi diad splitting was built from experiments using a high pressure optical cell raman spectra of co2 were collected in the range 20 to 360 c and 0 51 to 50 mpa i e a density range from 0 0057 to 1 1600 g cm 3 our results show that temperature and pressure have significant impact on density relationship with lower by up to about 0 5 cm 1 with increasing pressure and temperature at a given density on the contrary dissolved h2o nacl had no effect on the density relationship so the function defined for pure co2 system can also be applied to calculate the density of co2 h2o nacl system up to 360 c 50 mpa and 20 35 wt nacl the new densimeters presented in this study provide a useful tool to determine the pressure of co2 rich fluid inclusions all along the isochoric path for any water concentration

diverse sedimentary conditions during deposition of coal and oil shale from the meihe basin eocene ne china the meihe basin in northeastern china is a normal fault controlled basin filled with eocene nonmarine deposits the sediments assigned to the meihe formation sediment grain sizes core study well log analysis and micropetrographic study combined with sedimentary facies analysis indicate that the main sedimentary facies of the meihe basin represent fan delta lake and turbidite deposits thick coal seams that are mainly distributed in the eastern part of the studied area were deposited in the swamp facies of the lower coal bearing member oil shale was mainly deposited in the deep lake represented by the mudstone member and is mainly distributed in the southern part of the studied area in the lower coal bearing member organic rich sediments are characterized by toc content between 0 6 wt and 43 1 wt and contain type ii and iii kerogen the thick coal seams are the result of high landplant productivity and good preservation conditions thin coal seams in the fan delta plain resulted from the migration and erosion of the fan delta channel in the shallow lake and fan delta front limited productivity coupled with dilution by inorganic matter resulted in lower organic matter content in themudstonemember oil shale and mudstone rich in organic matter were deposited in a deep lake with an average toc content of 3 4 wt the origin of the organic matter was mainly algae and aquatic plants mixed with land plants the improved preservation conditions and high bioproductivity in this environment resulted in three oil shale layers in the lower part of this sedimentary succession three coal bearing and oil shale bearing fault basins lie adjacent to the dunhua mishan fault zone among which the fushun basin is located in the southwest the meihe basin is in themiddle and thehuadian basin is in the southeast from the fushun basin to the huadian basin the oil shale and coal seams have distinct sedimentation characters laterally vertically in each basin the organic matter sources all have the same variation trend from land plants to land plants mixed with algae to algae then to algae mixed with land plants and the toc content also shows a similar trend from high to medium high then to low in each basin

botanical control on banding character in two new zealand coal beds abstract two new zealand coal beds were examined using a palaeobotanical approach to determine controls on banding characteristics the morley cretaceous coal is thickly 5 to 1 or 32 to 2 mm and well 25 banded whereas the brunner eocene coal is essentially non banded palynological analyses indicate that the morley was formed from a gymnosperm dominated vegetation with a secondary component of angiosperms in contrast the brunner was dominated by angiosperm vegetation with only a minor component of gymnosperms however it was found that any xylite vitrain bands 1 mm in either coal bed were comprised exclusively of secondary xylem of probable gymnosperm origin the presence of gymnosperm wood i e secondary xylem forming the larger bands in both coals can be related to the relative resistance of this material to chemical and physical decay as compared to all other plant tissues an absence of angiosperm wood in either the morley or brunner coal beds may be the result of the relative chemical degradability of angiosperm wood as compared to gymnosperm wood alternatively angiosperms in either of the two palaeo mires may have been shrubby and thus did not produce abundant woody tissue in either case the banded nature of the morley coal bed is the result of the presence of gymnosperm wood and the non banded nature of the brunner is the result of being dominated by a flora angiosperm which is easily degraded

experimental constraint on grain scale fluid connectivity in subduction zones abstract the dihedral angle between olivine and aqueous fluid is a critical parameter in identifying the grain scale fluid connectivity which controls the distribution and migration of aqueous fluids in subduction zones besides physical properties of mantle wedges recent magnetotelluric observations have suggested the occurrence of significant fluid circulation in deep fore arc regions which can be explained by infiltration of saline fluid with a low in the mantle wedge huang et al 2019 along with the salt component non polarized gas such as co2 is a crucial constituent of subduction zone fluids co2 is known to increase the olivine fluid under conditions in which the olivine does not react with co2 which is in contrast to the effect of nacl on for a better understanding of the connectivity of multicomponent fluid in the mantle wedge we experimentally constrained in olivine h2o co2 fluid and olivine h2o co2 nacl multicomponent fluid systems at 1 4 gpa and 800 1100 c for the h2o co2 system we found that co2 tends to increase at 1 gpa and 800 1100 c and at 2 gpa and 1100 c in contrast co2 reduced even below 60 at relatively high pressure p and low temperature t conditions in which the olivine partly reacts with co2 to form magnesite and orthopyroxene opx the consumption of non wettable co2 components in aqueous fluid alone cannot explain lower than those in a pure h2o system additional experiments on olivine magnesite h2o and olivine opx h2o systems showed that the presence of magnesite or opx decreased the olivine fluid which implies that coexisting minerals affect the olivine fluid interfacial energy by changing the fluid chemistry the results of the multicomponent system showed that the effect of nacl on is much more significant than that of co2 strikingly was smaller than 60 in all the magnesite and opx bearing multicomponent systems our results suggest that slab derived fluid can infiltrate into the deep fore arc mantle wedge through an interconnected network even in a co2 bearing multicomponent system at pressures above 2 gpa which facilitates significant fore arc fluid circulation the contrasting effects of aqueous fluid and silicate melt on the seismic wave velocity in a wide condition may allow for the possibility of mapping partial melt in the mantle wedge

characteristics of the middle jurassic marine source rocks and prediction of favorable source rock kitchens in the qiangtang basin of tibet we have evaluated the hydrocarbon bearing potential of middle jurassic marine source rocks in the qiangtang basin tibet through a comprehensive study of samples from a large number of surface outcrops in different structural units and from the qiang d2 well in the southern qiangtang depression data that were acquired including the depositional environment thickness of sedimentary units and organic geochemistry are used to identify the principal controlling factors and predict the location of favorable hydrocarbon kitchens the source rocks are mainly platform limestone of the middle jurassic buqu formation this formation comprises a suite of intra platform sag marls micrites and black shales that were deposited in a deep water and restricted depositional environment the marls form hydrocarbon rich source rocks with organic matter that is mainly type ii and in the mature to highly mature stage in the dongco hulu lake and tupoco baitan lake deep sags limestone also forms a medium level source rock in the qiangtang basin limestone is the favorable source rock kitchen and is more significant in this regard than mudstone the results provide important constraints on evaluating the hydrocarbon potential of jurassic marine source rocks and for locating petroleum resources in the qiangtang basin

stable isotope composition of siderite as an indicator of the paleoenvironmental history of oil shale lakes the sediments of two eocene oil shale lakes messel graben and eckfeld maar west germany were analyzed with respect to the distribution chemical and stable isotope composition of siderite the data allow a reconstruction of different stages in the sedimentary and early diagenetic history of the lakes in the messel lake siderite formation started when the sedimentation of laminated sapropelic corg rich sediments was already established the early stage of oil shale sedimentation was characterized by pyrite precipitation in the siderite stage the stable isotope composition of the carbonate suggests methanogenesis to have been an important process at the sediment water boundary layer in the eckfeld lake siderite formation started even before sedimentation of the first sapropelic laminae the stable isotopic composition of the carbonate again indicates an anoxic sediment water boundary layer and strong methanogenesis with the expansion of this environment into the deep water mass sapropel sedimentation became established for both sequences the chemistry and stable isotope composition of the siderites correlates with petrographic and paleontological information about climate dependent fluctuations in the ecological chemical and early diagenetic environment the strong relationship of siderite formation to methanogenesis may be explained by the rate of microbial organic matter degradation which governed both methanogenesis and pco2

fluid immiscibility in metamorphic rocks evidence of fluid immiscibility in metamorphic rocks comes in the best of all worlds from fluid inclusion observations in fact fluid immiscibility should be anticipated over the full range of metamorphic conditions provided that appropriate bulk fluid compositions are present in a review paper entitled metamorphic fluids the evidence from fluid inclusions crawford and hollister 1986 summarized the role of fluid immiscibility in metamorphism was only recognized after serious study of fluid inclusions in metamorphic rocks was underway in the late 1970s and has yet to attract the attention of more than a handful of petrologists studying metamorphic rocks since then tremendous progress has been made a huge amount of fluid inclusion studies have convincingly shown that immiscible fluids can be present in rocks of all bulk compositions and at all p t conditions thermodynamic databases of minerals solid solutions and fluid mixtures along with the development of gibbs free energy minimization programs now allow for detailed prediction of the evolution of phase assemblages and mineral compositions in p t space significant progress has also been made in understanding reaction kinetics diffusional and convective mass transport and the interpretation of fluid rock interaction during metamorphism given the vast fluid inclusion evidence of immiscibility it would appear however that phase petrology and mass transport in any specific rock where fluids are involved are not correctly interpreted if possible or proven immiscibility is not considered relatively few studies directly link mineral reactions with immiscible fluids therefore this review aims at working out the effects of fluid immiscibility on the progress of metamorphic reactions and fluid transport over a wide range of conditions questions arise directly from the fluid inclusion record in metamorphic rocks this chapter however is organized the other way round at first it summarizes phase relations of fluid systems pertinent to

pvtx properties of h2o co2 salt at ptx conditions applicable to carbon sequestration in saline formations among the many scenarios that have been proposed to reduce the amount of carbon dioxide co2 emissions to the atmosphere carbon capture and storage ccs in geological reservoirs represents the method most technologically feasible and capable of accommodating the large amounts of co2 that are generated on an annual basis by combustion of fossil fuels ipcc 2005 geological environments and processes that have been proposed for ccs include deep unmineable coal seams depleted oil and gas reservoirs organic rich shale basins deep saline formations and mineral carbonation of basalts of these various options the one that is most attractive owing to its widespread distribution and capacity to store large amounts of co2 is deep saline formations with the u s department of energy reporting that saline formations in the united states could potentially store more than 2 100 20 000 billion metric tons of co2 doe 2012 a recently released assessment of geologic carbon dioxide storage potential usgs 2013 estimates a capacity ranging from 2 400 to 3 700 billion metric tonnes gt of co2 which corresponds to the low end of the doe estimate when supercritical co2 scco2 is injected into a saline formation it may be stored in various ways initially the co2 will be stored by structural and stratigraphic trapping whereby scco2 is trapped beneath an impermeable confining layer that prohibits the upward migration of the more buoyant scco2 some scco2 may also be stored by residual trapping in pores via capillary forces in the discussion to follow we include residual trapping with structural stratigraphic trapping as all of these processes involve the storage of a scco2 phase and as such the volume requirements are assumed to be identical for these storage mechanisms for a given mass of co2 over time

interpreting rock eval pyrolysis data using graphs of pyrolizable hydrocarbons vs total organic carbon kerogen the major organic component of sedimentary rocks is commonly analyzed by rock eval pyrolysis plotting the data on a graph of s 2 vs total organic carbon toc and determining the regression equation is the best method for determining the true average hydrogen index and measuring the adsorption of hydrocarbon by the rock matrix such a plot also indicates the type of kerogen present and avoids the problem of increasing hydrogen index with total organic carbon content with the s 2 vs toc diagram the organic component of different suites of samples may be compared and their petroleum generation potentials established as an example the diagrams are used to evaluate the sedimentary environments and petroleum potential of the paleogene evaporitic sediments of the mulhouse basin alsace france

depositional environment of the lower cretaceous muling formation of the laoheishan basin ne china implications from geochemical and petrological analyses abstract the laoheishan basin located in northeastern china is filled with non marine coal and oil shale oil prone mudstone sediments of the lower cretaceous muling formation based on petrological mineralogical and geochemical methods the depositional environment during organic matter om accumulation is investigated for the first time the coal is subbituminous in rank petrological and bulk geochemical data indicate sapropelic coal deposited in low lying mire under freshwater conditions high pristane phytane ratios provide evidence for a land plant origin of om and oxic conditions during deposition a neutral to slightly alkaline ph is reflected by the presence of carbonate high liptinite contents and terpenoid biomarker composition indicate high amounts of resinous om during oil shale deposition a raised water table was favorable for om preservation under oxic to dysoxic conditions the oil shales in the lower unit of the succession not associated with coal are characterized by high hydrogen index and resinite contents interpreted to reflect deposition at elevated water depths in contrast to the findings of previous studies on oil shales in china indicating its origin from algal om a predominance of terrigenous om rich in waxy and resinous lipids is implied from biomarker and maceral composition the lower cretaceous oil shale and coal in the laoheishan basin contain high amounts of land plant derived terpenoid biomarkers derived from coniferales e g pinaceae cupressaceae taxodiaceae araucariaceae podocarpaceae and ferns the results are in agreement with palynological data the data highlight the potential of resinous and waxy om to form excellent hydrocarbon source rocks

sesqui and diterpenoid biomarkers preserved in taxodium rich oligocene oxbow lake clays weisselster basin germany several diterpenoids of the abietane pimarane and phyllocladane type and three cadalanetype sesquiterpenoids have been identified in the organic solvent extracts of lower oligocene clay sediments haselbach strata saxony germany the sediment contains needles and cone scales of a fossil taxodium species which represents the only conifer in the samples a clear correlation between the observed conifer biomarkers and taxodium is evident apart from diterpenoids detected previously in other sediments a new diaromatic totarane diterpenoid is reported in isolated fossil and recent taxodium needles and cone scales as well as in the haselbach clays a phenolic diterpenoid of the abietane type ferruginol has been identified the results indicate that the taxodium rich clay samples contain several diterpenoids which so far have been used as biomarkers for other conifer families and thus the chemotaxonomical use of diterpenoid biomarkers for the differentiation of fossil conifer families has to be revised

organic geochemical and stable carbon isotopic investigation of coals formed in low lying and raised mires within the eastern alps austria abstract up to 16 m thick coal seams formed in miocene pull apart basins within the eastern alps in low lying and raised mires despite similar rank sub bituminous stage coal quality differs significantly coals from low lying mires e g fohnsdorf are characterized by significantly higher ash yields and sulfur contents than coals from raised mires e g leoben organic geochemical and carbon isotope investigations were performed to assess the differences in facies the fohnsdorf coals are characterized by higher yields of soluble organic matter som slightly higher proportions of hydrocarbons in the som generally lower pristane phytane ratios and the occurrence of high corg normalized n alkane concentrations only n alkane patterns in the leoben samples show a marked odd over even predominance these differences are indicative of a more intensive dys to anaerobic biochemical degradation of plant material within the fohnsdorf mire terpenoid biomarkers characteristic of conifers and angiosperms were detected in the leoben coals whereas the latter are missing in the fohnsdorf samples in the leoben coals higher saturated to aromatic diterpenoid ratios were detected than in the fohnsdorf coals because of similar rank enhanced aromatisation in the fohnsdorf basin is probably related to microbial activity despite this the fohnsdorf coals are characterized by lower hopane concentrations the results imply that the aromatisation of terpenoid biomarkers is governed by the activity of anaerobic rather than aerobic bacteria an overall negative correlation between 13c of organic matter and the degree of aromatisation of diterpenoid biomarkers is observed it is suggested that the carbon isotopic composition results from different extents of microbial degradation of the biomass the fohnsdorf coals are rich in sulfur high contents of coalbed methane were encountered during mining suggesting high activities of anaerobic bacteria in a nearly neutral sulfate bearing brackish environment of the low lying mire and methanogenesis during or after coalification sulfate reduction and methanogenesis are known to increase 13c values of residual organic matter