environmental isotopes meet 3d geological modelling conceptualising recharge and structurally controlled aquifer connectivity in the basalt plains of south western victoria australia summary to develop a conceptual model of recharge and inter aquifer connectivity for a complex aquifer system in southwestern victoria australia a three dimensional 3d geological model was constructed and used to examine the influence of the regional geology on groundwater composition and age as well as recharge mechanisms the major aquifers are three basalts differentiated on age and geomorphological features and an underlying palaeovalley deep lead system the upper fine grained sediments of the deep lead form an aquitard that separates the basalt from the permeable sands and gravels beneath recharge calculations chloride mass balance and water table fluctuation methods salinity stable isotope tritium and radiocarbon data show that volcanoes and the youngest basalts although volumetrically minor form preferential recharge areas for all the basalts up to 30 mm year and also recharge the deep lead sediments through volcanic necks that penetrate the aquitard infiltration through the thick clay rich soils on the older basalts is small typically 1 2 mm year and saline resulting in a progressive increase of groundwater salinity along the flow path in these basalts the comparison of fault location with groundwater age in the deep lead aquifer suggests that in some areas faults exert significant structural control on groundwater flow this study demonstrates the value of integrating geological hydrogeological and hydrochemical data to identify preferential recharge areas inter aquifer connectivity and the influence of faults on groundwater flow in a complex aquifer system

carbon mass balance isotopic tracers of biogenic methane and the role of acetate in coal beds powder river basin usa abstract a multi isotope c h o investigation of biogenic gas 13c ch4 13c co2 d ch4 and coal bed waters d 18o 13c dic 13c acetate was conducted along a 25 km basinward sampling transect in the powder river basin prb in wyoming and montana usa to address inconsistencies among isotope fingerprinting techniques and to apply mass balance isotope modeling to biogenic coalbed methane cbm results include the first published compound specific 13c acetate values from a natural biogenic cbm system providing new constraints on acetate s role in biogenic ch4 generation coal bed water chemistry is anoxic and dominated by na and hco3 with high alkalinity concentrations 14 8 33 0 meq l the deep basin interior environment contains sulfate free na hco3 dominated waters exhibiting signs of methanogenesis ch4 and co2 generally become 13c enriched from the shallow basin edge to the deep basin interior 13c ch4 78 2 to 56 2 and 13c co2 24 7 to 4 7 also compound specific 13c acetate is more positive in the basin interior compared to the basin edge setting range 34 3 to 15 1 using a steady state mass balance isotope model the observed variations in 13c ch4 and 13c co2 can be explained in terms of the favorability of methanogenesis fch4 relative to heterotrophic bacterially mediated non methanogenic pathways such as bacterial sulfate reduction which compete with methanogenesis for substrates at the basin interior fch4 exceeds 0 4 approaching its inferred limiting value hypothesized from the oxidation state of low molecular weight compounds detected in prb formation waters therefore methanogenesis is likely a dominant biogeochemical pathway consuming substrates in the deeper coal beds the basinward shift toward 13c enriched acetate broadly indicates linkage between acetate ch4 and co2 and likely records acetate synthesis effects modified by methanogenic fractionation these results suggest that acetate plays a role in methanogenesis in prb coal beds not necessarily a dominant role while other c isotope and microbial evidence suggests that hydrogenotrophic methanogenesis is also a significant methane producing pathway the results of this study broadly suggest multiple viable methanogenic pathways and c cycling that affects acetate a more complex view of coal bed geochemistry than implied by traditional c and h isotope fingerprinting of accumulated products ch4 co2 and coexisting water

structural and mechanical controls on intrusion related deposits of the tombstone gold belt yukon canada with comparisons to other vein hosted ore deposit types abstract intrusion related gold deposits at the clear creek scheelite dome and dublin gulch properties of the tombstone gold belt tgb yukon territory have dominantly e striking steeply dipping auriferous quartz extension veins within intrusions in adjacent metasedimentary rocks gold is hosted in subvertical nw to nnw striking sinistral faults as veins and breccias in e striking extension veins and locally in e to ene striking fault veins these structural relationships indicate low magnitude broadly e w directed shortening and n s extension during stock emplacement and gold mineralisation at 92 ma the lack of any deviation or deflection of the extension vein orientations in the country rocks with respect to their orientation within the stocks indicates consistent stress trajectories in both rock types these tgb deposits formed at 5 8 km depth where mean and differential stresses may be greater in magnitude than in shallower porphyry environments many porphyry systems feature magmatic related stresses that dominated the local stress field with more variable vein orientations the result conversely orogenic gold systems usually exhibit strong dimensionality in vein orientations fault hosted mineralisation in metasedimentary rocks of the tgb deposits in this study is comparable in geometry but generally smaller in size than in many orogenic gold systems intrusion related systems of the tgb exhibit intermediate structural styles of mineralisation that provide a useful bridge in understanding the diversity of mechanically controlled structural styles in otherwise mostly unrelated gold deposit types

magmatic hydrothermal evolution of highly fractionated granites evidence from the kuiqi miarolite in fujian province se china abstract the kuiqi miarolite a highly evolved alkaline granite pluton is situated in fujian province southeastern china quartz crystals from the kuiqi miarolite contain abundant inclusions which have preserved a complete record of the magmatic hydrothermal evolution five inclusion type were identified i e the melt m type melt fluid ml type daughter mineral bearing s type vapor rich v type and aqueous l type inclusions integrated petrographic microthermometric and laser raman spectroscopy studies demonstrate that the whole magmatic hydrothermal evolution at kuiqi comprises three stages i e the magmatic magmatic hydrothermal and hydrothermal stages the m type inclusions minimal trapping temperatures ca 710 800 c represent the melts entrapped at the magmatic stage of crystallization while the occurrence of euhedral prismatic arfvedsonites in these melt inclusions indicates that the granitic magma was probably volatile rich at the magmatic hydrothermal stage both the ml type inclusions t h ca 500 710 c and coexisting m and v type inclusions reflect the presence of late magmatic fluid circulation and melt volatile immiscibility exhibiting a transition toward the hydrothermal stage at the hydrothermal stage the pressure and temperature 700 485 c drop may have led to oversaturation of the primary saline fluids resulting in the phase separation a highly saline and a volatile rich fluid occurred accompanied by the widespread vapor brine immiscibility the l type inclusions in the miarolitic quartz display bimodal salinity distribution the t h and salinity of the inclusions at the bottom l 1 miarolitic quartz are ca 303 427 c and ca 6 6 17 9 wt nacl equiv respectively while that of the inclusions at the top l 2 are ca 165 232 c and ca 0 2 5 7 wt nacl equiv respectively this indicates a drop of fluid temperature and salinity during the miarolitic cavity formation moreover the low homogenization temperatures and salinities of the l type inclusions suggest an influx of meteoric water during the late hydrothermal evolution stage

chemical and isotopic tracers of the contribution of microbial gas in devonian organic rich shales and reservoir sandstones northern appalachian basin in this study the geochemistry and origin of natural gas and formation waters in devonian age organic rich shales and reservoir sandstones across the northern appalachian basin margin western new york eastern ohio northwestern pennsylvania and eastern kentucky were investigated additional samples were collected from mississippian berea sandstone silurian medina sandstone and ordovician trenton black river group oil and gas wells for comparison dissolved gases in shallow groundwaters in devonian organic rich shales along lake erie contain detectable ch4 0 01 50 55 mol with low 13c ch4 values 74 68 to 57 86 and no higher chain hydrocarbons characteristics typical of microbial gas nevertheless these groundwaters have only moderate alkalinity 1 14 8 72 meq kg and relatively low 13c values of dissolved inorganic c dic 24 8 to 0 6 suggesting that microbial methanogenesis is limited the majority of natural gases in devonian organic rich shales and sandstones at depth 168 m in the northern appalachian basin have a low ch4 to ethane and propane ratios 3 35 mol c1 c2 c3 and high 13c and d values of ch4 53 35 to 40 24 and 315 0 to 174 6 respectively which increase in depth reservoir age and thermal maturity the molecular and isotopic signature of these gases show that ch4 was generated via thermogenic processes despite this the geochemistry of co produced brines shows evidence for microbial activity high 13c values of dic 10 slightly elevated alkalinity up to 12 01 meq kg and low so4 values 1 mmole l in select devonian organic rich shale and sandstone formation water samples suggest the presence of methanogenesis while low 13c dic values 22 and relatively high so4 concentrations up to 12 31 mmole l in many brine samples point to so4 reduction which likely limits microbial ch4 generation in the appalachian basin together the formation water and gas results suggest that the vast majority of ch4 in the devonian organic rich shales and sandstones across the northern appalachian basin margin is thermogenic in origin small accumulations of microbial ch4 are present at shallow depths along lake erie and in western ny

geochemistry and origin of some natural gases in the plateau province central appalachian basin pennsylvania and ohio the appalachian plateau is a large elongate structural basin in the western part of the central appalachians in western pennsylvania and eastern ohio the plateau is a mostly wet gas mean c sub 2 c sub 5 c sub 1 c sub 5 6 08 district which has produced approximately one third of all the natural gas produced in the entire appalachian basin we sampled gases from 22 wells and 5 cores to determine the possible utility of stable isotope geochemistry for interpreting the origin of the gases and correlating them with their probable sources methane delta sup 13 c and delta c and delta d values range from 55 1 to 27 24 and 303 to 150 respectively corresponding ethane and propane values of selected samples range from 41 79 to 29 61 and 38 21 to 26 71 several gas samples exhibit isotopic reversals amoung the c sub 1 to c sub 3 hydrocarbons the isotope data provide some potential insight into the origin of these gases and the timing and direction of their migration into different reservoirs with few exceptions the gases we analyzed are secondary i e mixtures of gases varying origins or primary gases original gas from a single active source rock which were altered by geological processes most samples originated as associated thermogenic gases generated frommore types i ii kerogens at source rock maturities ranging from early mature to overmature coalbed gases and some upper devonian gases appear to be mixtures of thermogenic and microbial hydrocarbons we interpret several other gases from various cambrian through devonian reservoirs as mixtures of thermogenic gases less

organic matter production and preservation and evolution of anoxia in the holocene black sea dating of sediments collected in gravity cores during leg 1 of the 1988 r v knorr expedition to the black sea suggests that the onset of water column anoxia at 7 5 ka was virtually synchronous across the basin over a depth range of 200 2250 m a finely laminated organic carbon oc rich sapropel unit ii was produced as a result of this anoxia the trigger for increased oc production and development of anoxia was the spillover of saline waters through the bosporus that probably began at 9 0 ka and peaked between 7 0 and 5 5 ka this spillover enhanced vertical mixing and nutrient cycling and caused a short term 2 3 kyr burst in surface water productivity during the early part of unit ii deposition continued incursion of saline waters enhanced vertical stability and inhibited mixing of nutrients into surface waters thus limiting primary production and decreasing the oc flux to sediments beginning 5 5 ka concentration accumulation rate and degree of preservation of organic matter all decreased in the upper part of unit ii as a result of decreasing productivity but anoxia persisted throughout most of the water column the end of unit ii sapropel deposition was synchronous across the black sea as the result of the first blooms of the coccolith emiliania huxleyi which presumably marked an increase in surface water salinity above 11 and the beginning of unit i deposition the high coccolith carbonate fluxes that occurred during deposition of unit i diluted the oc concentration in the sediments but oc accumulation rates are about the same as those in upper part of unit ii

varve calibrated records of carbonate and organic carbon accumulation over the last 2000 years in the black sea sedimentologic and geochemical studies of box and gravity cores recovered from the black sea during the first leg of a multileg international black sea expedition in 1988 allow reconstruction of the basinwide holocene environmental history of the black sea in the deeper parts of the basin box cores typically recovered a flocculent surface layer fluff laminated coccolith marls of unit i 25 45 cm thick and the upper 5 10 cm of finely laminated dark colored sapropels of unit ii fine grained homogeneous mud turbidites are interbedded with units i and ii over much of the basin but the stratigraphie position of these turbidites differs from site to site the deposition of individual turbidites up to 15 cm thick does not appear to have significantly disturbed underlying laminae sediment trap deployments in the black sea suggest that light and dark laminae couplets represent annual increments of sedimentation i e varves we have therefore constructed a varve chronology for the sequence in order to correlate and date distinctive sedimentation and paleoenvironmental events distinctive groups of laminae in unit i can be correlated across the entire deeper basin a distance of more than 1000 km this implies a remarkable homogeneity in production accumulation and preservation of biogenic material over much of the black sea during deposition of unit i the change from deposition of finely laminated organic carbon rich sapropels unit ii to laminated more calcareous coccolith rich marls unit i is thought to represent the crossing of a salinity threshold for emiliania huxleyi the varve chronology sets this change at about 1 63 ka 1633 100 yr b p but the record of magnetic secular variation measured in several cores produces an age estimate of about 2 0 ka for the base of unit i or about 1 2 times the varve age the average of six calibrated accelerator mass spectrometry radiocarbon ages for the base of unit i is 2 7 ka or about 1 7 times the varve age following the initial change to coccolith dominated sedimentation deposition of sapropel resumed for at least one significant period 1 56 1 25 ka since 1 25 ka cycles of carbonate deposition with quasi decadal periodicities have produced characteristic darker and lighter assemblages of laminae these cycles may have been climatically driven geochemical analyses coupled with the varve ages adopted herein indicate that accumulation rates of carbonate are nearly an order of magnitude higher in unit i averaging 35 45 g m 2 yr 1 than in sapropelic unit ii which contains primarily detrital carbonate the accumulation of lithogenic components in parts of unit i is only 1 5 times the rate in unit ii deepwater organic carbon accumulation rates are somewhat higher in unit i 3 5 4 5 g m 2 yr 1 than in the upper part of unit ii organic carbon accumulation rates in unit i are somewhat antithetic to those of carbonate and on the basis of this and additional constraints placed by pyrolysis and carbon isotopic analyses of organic material it appears that terrestrial organic matter is an important component perhaps 25 of total organic carbon burial in the basin unit i in the western part of the black sea has a higher terrestrial organic component and higher accumulation rates of terrigenous clastic material than unit i in the eastern part this difference between eastern and western black sea is to be expected because of the major rivers that empty into the western black sea from eastern europe ukraine and russia shallow slope sites but still within euxinic bottom waters have lower organic carbon accumulation rates and lower pyrolysis hydrogen indices than deepwater basinal sites suggesting selective resuspension and oxidation of organic matter at basin margins and focusing of organic matter deposition toward the basin center a comparison of the black sea data with those from several open ocean sites with similar water depths showed no significant difference between organic carbon accumulation rates under oxic and anoxic conditions for a given bulk accumulation rate the organic carbon accumulation rates normalized to primary productivity are about the same in both settings

microbial origin of australian coalbed methane bituminous coal seam gases from the permian sydney and bowen basins australia are characterized by 1 methane ethane ratios greater than or equal to 1000 2 dgr13c and dgrd values for methane of 60 10 pmil pdb and 217 17 pmil smow respectively 3 carbon dioxide contents of less than 5 and 4 dgr13c co 2 ch4 values of 55 10 pmil pdb these data suggest that microbial reduction of co2 rather than traditional thermogenic reactions is mainly responsible for gas composition invasions by co2 of deep seated external origins are readily recognized by their isotopic compositions 7 2 pmil pdb

structural control magmatic hydrothermal evolution and formation of hornfels hosted intrusion related gold deposits insight from the thaghassa deposit in eastern anti atlas morocco in the moroccan eastern anti atlas the thaghassa intrusion related gold deposit is hosted in hornfelsed metasedimentary rocks that lie adjacent to the ikniwn granodiorite fields studies reveal three tectono magmatic stages controlling the formation of the deposit i the first stage refers to the top to the south asymmetry and the syn kinematic ikniwn pluton emplacement controlled by a compressional or transpressional strain regime ii the second stage is characterized from older to younger and further away from the intrusion by metatexite with leucocratic stromatic bands aplo pegmatite sills intermediate veinlets composed of quartz k feldspar and muscovite and then gold bearing striped foliation veins all these features are assumed to have been emplaced during a large scale ene wsw dextral shearing process that results from an ese wnw shortening direction during transtensive tectonics we suggest that the progressive and continuous shearing was initiated since the aplo pegmatite stage and achieved during the hydrothermal phase the existence of intermediate veins characterized by quartz rich core and apatite muscovite feldspar rich rims demonstrates the progressive evolution from the magmatic to the hydrothermal stage and evidence for the persistence of the magmatic character at least until the onset of the hydrothermal process iii the late stage developed large volcanic dyke swarm and brittle faulting zircon u pb la icp ms dating yields a concordia age of 563 5 6 3 ma for the ikniwn granodiorite intrusion the fluid inclusions data besides the mineral thermometry indicate that two main types of fluids can been highlighted i a hot aquo carbonic h2o nacl co2 fluid with n2 and ch4 evolving from vapour rich n2 and ch4 inclusions for the magmatic stage 550 c to ch4 co2 biphased inclusions for the ongoing hydrothermal stage 450 300 c and ii an always secondary low t 200 c saline aqueous type probably nacl free from volatiles with very variable salinity eventually we highlight that in the hornfels hosted irg deposits fluid sources may originate from both magmatic processes and devolatization of the metamorphic host rocks

effects of oxidative weathering on the composition of organic matter in coal and sedimentary rock abstract the effect of oxidative weathering on the composition of sedimentary organic matter som of lignite subbituminous coal quartzose arenite siliceous mudstone siliceous shale and diatomaceous shale was investigated in hokkaido japan in a subarctic humid climate for 15 samples in total a humic substance extraction method was applied to divide som into lipid c humin c and alkali soluble c the alkali soluble c was further divided into fulvic acid fa c humic acid ha c and a smaller molecular size fraction smsf c which comprised organic molecules able to pass through a dialysis membrane

long distance tool stone transport in the argentine pampas abstract tools manufactured from a characteristic reddish siliceous rock are present in low frequencies in most early pampean assemblages in argentina they are bifacial tools including fishtail projectile points bipolar products and flakes they have been found in both excavated assemblages dated between 10 000 and 11 000 bp and in surface sites surface collections from uruguay also include fishtail projectile points manufactured on this rock petrographic analyses were carried out to determine stone provenance archaeological artifacts from the argentine pampas and macroscopically similar nodules obtained from secondary deposits in uruguay were analyzed the rock used for the artifacts is composed of a siliceous very fine homogeneous mass that is nearly isotropic and is characterized by recognizable remains of organisms including silicified gastropods the samples obtained from deposits in central and southern uruguay have similar microscopic characteristics many of these deposits were exploited as indigenous quarries therefore this reddish rock was transported from uruguay to the argentine pampas by societies who inhabited the region during the pleistocene holocene transition within this context we discuss the social meaning of this long distance tool stone transport and propose that it was a result of human interaction networks

the biogenic methane potential of european gas shale analogues results from incubation experiments and thermodynamic modelling abstract core samples from the lower jurassic posidonia shale lower toarcian wealden black shales both from the lower saxony basin northern germany and from the cambrian ordovician alum shale southern sweden have been investigated for their biogenic gas potential in incubation experiments the sample set represents all stages of thermal maturity from immature to overmature methane and to a higher degree carbon dioxide are generated from all samples by added microorganisms in general overmature samples rr 1 5 show lowest gas generation rates the highest generation rates for produced methane up to 89 mol g 1 day 1 and carbon dioxide 139 mol g 1 day 1 were detected in immature alum shale samples when different hydrocarbon degrading inocula where added whereas the lowest methane production rates were detected in wealden sediments the lightest 13c values for produced methane and carbon dioxide have been detected in posidonia shale samples of oil window maturity such samples are some of the most sensitive for gas generation and exhibit the strongest decreases of hydrogen indices after incubation hydrogeochemical modelling of methane generation fate and behaviour showed that methane formed during the early diagenesis got lost from posidonia shale the mainly investigated shale in this study as the mature posidonia shale is according to the incubation experiments still sensitive for gas generation a production scenario of generically generated methane due to oil degradation is simulated the basic conditions resemble the conditions in the antrim shale in the michigan basin gas production due to dewatering and pressure decrease results in an increase of the gas volumes coupled to a progressive enrichment of carbon dioxide in the produced gas moreover calcite scaling may be the consequence during progressive production similar to the antrim shale in the michigan basin such calcite precipitation has been demonstrated to predominantly occur in natural samples at oil window maturity

hematite in porous red clouded feldspars evidence of large scale crustal fluid rock interaction abstract transmission electron microscopy shows that red clouded alkali feldspars from granitic rocks contain numerous open pores up to several hundred nanometres in cross section and that almost every pore contains rosettes or needles of crystalline hematite in the samples described here the hematite forms at the reaction interfaces at which plagioclase feldspar is replaced by alkali feldspar these observations together with the fact that the origin of the porosity can be explained by the mechanism of sub solidus mineral fluid replacement processes indicate that hematite is a direct product of fluid rock interaction and is not a solid state exsolution product from the feldspar

pleistocene recharge to midcontinent basins effects on salinity structure and microbial gas generation the hydrogeochemistry of saline meteoric water interface zones in sedimentary basins is important in constraining the fluid migration history chemical evolution of basinal brines and physical stability of saline formation waters during episodes of freshwater recharge this is especially germane for interior cratonic basins such as the michigan and illinois basins although there are large differences in formation water salinity and hydrostratigraphy in these basins both are relatively quiescent tectonically and have experienced repeated cycles of glaciation during the pleistocene exploration for unconventional microbial gas deposits which began in the upper devonian age antrim shale at the northern margin of the michigan basin has recently extended into the age equivalent new albany shale of the neighboring illinois basin providing access to heretofore unavailable fluid samples these reveal an extensive regional recharge system that has profoundly changed the salinity structure and induced significant biogeochemical modification of formation water elemental and isotope geochemistry new formation water and gas samples were obtained from devonian mississippian strata in the illinois basin these included exploration wells in the new albany shale an organic rich black shale of upper devonian age and formation waters from over and underlying regional aquifer systems siluro devonian and mississippian age the hydrostratigraphic relations of major aquifers and aquitards along the eastern margin of the illinois basin critically influenced fluid migration into the new albany shale the new albany shale formation water chemistry indicates significant invasion of meteoric water with d values as low as 46 05 into the shale the carbon stable isotope system 13c values as high as 29 4 coupled with 18o d and alkalinity of formation waters alkalinity 24 08 meq kg identifies the presence of microbial gas associated with meteoric recharge regional geochemical patterns identify the underlying siluro devonian carbonate aquifer system as the major conduit for freshwater recharge into the fractured new albany shale reservoirs recharge from overlying mississippian carbonates is only significant in the southernmost portion of the basin margin where carbonates directly overlie the new albany shale recharge of dilute waters cl 1000 mm into the siluro devonian section has suppressed formation water salinity to depths as great as 1 km across the entire eastern illinois basin margin taken together with salinity and stable isotope patterns in age equivalent michigan basin formation waters they suggest a regional impact of recharge of 18o and d depleted fluids related to pleistocene glaciation devonian black shales at both basin margins have been affected by recharge and produced significant volumes of microbial methane this recharge is also manifested in different salinity gradients in the two basins because of their large differences in original formation water salinity given the relatively quiet tectonic history and subdued current topography in the midcontinent region it is likely that repeated cycles of glacial meltwater invasion across this region have induced a strong disequilibrium pattern in fluid salinity and produced a unique class of unconventional shale hosted gas deposits

a new model linking atmospheric methane sources to pleistocene glaciation via methanogenesis in sedimentary basins methane ch 4 is an important greenhouse gas and amplifier of climate change however the causes of atmospheric ch 4 variations over glacial interglacial cycles remain unresolved we propose that microbial methanogenesis along the shallow margins of sedimentary basins provides a source of atmospheric ch 4 temporally connected with both advance and retreat of continental ice sheets extensive biodegradation of hydrocarbons in the antrim shale formation michigan united states is associated with an active subsurface consortium of fermentative and methanogenic microorganisms this activity was initially stimulated when saline formation waters were diluted by meltwater derived from overriding pleistocene ice sheets during glaciation ch 4 produced by this community accumulated in the shale at a rate of 1 tg ch 4 per 1000 yr as a result of ice coverage and increased hydrostatic pressure we estimate that at present the antrim shale contains only 12 25 of the cumulative mass of ch 4 generated in the shale over the pleistocene indicating that ch 4 that had accumulated during glaciation was subsequently released following ice sheet retreat while release from the antrim shale represents only a small part of the global ch 4 budget when extended to other glaciated sedimentary basins subsurface methanogenesis may generate a substantial previously unrecognized source of atmospheric ch 4 during deglaciation

cause of shale gas geochemical anomalies and mechanisms for gas enrichment and depletion in high maturity shales abstract this article reviews the abnormal characteristics of shale gases natural gases produced from organic rich shales and discusses the cause of the anomalies and mechanisms for gas enrichment and depletion in high maturity organic rich shales the reported shale gas geochemical anomalies include rollover of iso alkane normal alkane ratios rollover of ethane and propane isotopic compositions abnormally light ethane and propane 13 c values as well as isotope reversals among methane ethane and propane these anomalies reflect the complex histories of gas generation and associated isotopic fractionation as well as in situ mixing and accumulation of gases generated from different precursors at different thermal maturities a model was proposed to explain the observed geochemical anomalies gas generation from kerogen cracking at relatively low thermal maturity accounted for the increase of iso alkane normal alkane ratios and ethane and propane 13 c values normal trend simultaneous cracking of kerogen retained oil and wet gas and associated isotopic fractionation at higher maturity caused decreasing iso alkane normal alkane ratios lighter ethane and propane 13 c and corresponding conversion of carbon isotopic distribution patterns from normal through partial reversal to complete reversal relatively low oil expulsion efficiency at peak oil generation low expulsion efficiency at peak gas generation and little gas loss during post generation evolution are necessary for organic rich shales to display the observed geochemical anomalies high organic matter richness high thermal maturity high degrees of kerogen gas and oil gas conversions and late stage the stage of peak gas generation and post generation evolution closed system accounted for gas enrichment in shales loss of free gases during post generation evolution may result in gas depletion or even undersaturation total gas content lower than the gas sorption capacity in high maturity organic rich shales

assessing compositional variability and migration of natural gas in the antrim shale in the michigan basin using noble gas geochemistry abstract this study uses stable noble gases he ne ar kr xe volume fractions and isotopic ratios from antrim shale natural gas to assess compositional variability and vertical fluid migration within this reservoir in addition to distinguishing between the presence of thermogenic versus biogenic methane r ra values where r is the measured 3he 4he ratio and ra is the atmospheric value of 1 384 0 013 10 6 vary from 0 01 to 0 34 suggesting a largely dominant crustal 4he component with minor atmospheric and mantle contributions crustal 21ne 40ar and 136xe contributions are also present but the atmospheric component is largely dominant for these gases crustal contributions for 21ne 40ar and 136xe vary between 1 1 and 12 5 between 0 7 and 19 and between 0 1 and 2 7 respectively a few samples present higher than atmospheric 20ne 22ne ratios pointing to the presence of a small mantle ne component high horizontal and vertical variability of noble gas signatures in the antrim shale are observed these are mainly due to variable noble gas input from deep brines and to a smaller extent variable in situ production within different layers of the antrim shale in particular the lachine and norwood members estimated 4he ages considering external 4he input for antrim shale water vary between 0 9 ka and 238 2 ka and match well for most samples with the timing of the major wisconsin glaciation suggesting that antrim shale water was influenced by glaciation induced recharge consistency between measured and predicted 40ar 36ar ratios assuming ar release temperatures 250 c supports a thermogenic origin for most of the methane in these samples this thermogenic methane is likely to originate at greater depths either from the deeper portion of the antrim shale in the central portion of the michigan basin or from deeper formations given that the thermal maturity of the antrim shale in the study area is rather low

geochemical constraints on the genesis of the scheelite dome intrusion related gold deposit tombstone gold belt yukon canada the scheelite dome intrusion related gold deposit western selwyn basin yukon is hosted in hornfelsed metasedimentary strata that lie adjacent to the exposed apices of a monzogranite to quartz monzonite plutonic complex of the mid cretaceous tombstone tungsten magmatic belt tintina gold province alaska and yukon a variety of mineralization styles occur throughout a 10 3 km east trending corridor and include reduced au and w rich skarns au w and ag pb zn sb rich quartz tension vein arrays and multiphase fault veins and isolated zones of au rich sericite carbonate altered rock integrated u pb shrimp data for magmatic zircon and ar ar data for magmatic and hydrothermal biotite indicate that gold mineralization occurred within 1 to 2 m y of magma emplacement fluid inclusion oxygen isotope and arsenopyrite geothermometry data indicate that hydrothermal minerals formed at depths of 6 to 9 km over a temperature range from 550 c high temperature au rich skarns formed at 400 c whereas vein hosted mineralization formed at 280 to 380 c in skarns au is strongly associated with enrichments of bi te w and as whereas a variety of au rich veins occur with as rich type 1 and te and w rich type 2 end members silver pb zn sb veins are typically au poor and represent the latest and lowest temperature phase in the hydrothermal paragenesis the fluid inclusion data indicate that all mineralization styles were formed from low salinity 4 wt nacl equiv aqueous carbonic fluids consistent with the composition of fluid inclusions within infilled miarolitic cavities in the intrusive rocks however the nonaqueous fluid was predominantly ch 4 in skarn co 2 in au te and au w veins and a fluid with roughly equal amounts of co 2 ch 4 and n 2 in au as and ag pb zn sb veins oxygen isotope data are consistent with a mineralizing fluid of predominantly magmatic origin that was variably modified to more positive 18 o values during interaction with 18 o enriched metasedimentary strata sulfur isotope data suggest two possible sources of sulfur a magmatic source characterized by 34 s values of approximately 5 to 0 per mil and sulfur from the metasedimentary country rocks characterized by more negative 34 s values of approximately 15 to 10 per mil collectively the data indicate that gold at scheelite dome was deposited from a magmatic hydrothermal system interaction of magmatic fluids with graphitic hornfels rocks resulted in reduction of the ore fluids higher ch 4 co 2 ratios and modification of the oxygen and sulfur isotope values of the ore fluids toward those of the metasedimentary hornfels progressive reduction and cooling of hydrothermal fluids in addition to phase separation in vein hosted mineralization were the mechanisms for gold deposition compared to other intrusion related gold deposits associated with the tombstone tungsten magmatic belt magmatism exposed mineralization at scheelite dome is predominantly hosted by hornfelsed metasedimentary rocks this results in more diverse mineralization styles and a greater spread of isotope and fluid inclusion data

methane and climate during the precambrian era abstract the sun was substantially less bright in the distant past yet earth s surface temperature remained above freezing higher concentrations of the greenhouse gases co 2 and ch 4 were likely responsible for keeping the early climate warm ch 4 concentrations of 1000 ppm or higher are predicted for the late archean paleoproterozoic atmosphere prior to the rise of o 2 photolysis of this ch 4 may have created an optically thin organic haze during much of this time the rise of o 2 at 2 3 ga eliminated most of the methane and probably triggered the paleoproterozoic glaciations ch 4 concentrations could have remained elevated throughout much of the proterozoic however as a consequence of low concentrations of dissolved o 2 and sulfate in the deep oceans and a corresponding increase in organic matter recycling by fermentation and methanogenesis

pleistocene hydrology of north america the role of ice sheets in reorganizing groundwater flow systems 1 while the geomorphic consequences of pleistocene megafloods have been known for some time it has been only in the past 2 decades that hydrogeologists and glaciologists alike have begun to appreciate the important impact that ice sheet aquifer interactions have had in controlling subsurface flow patterns recharge rates and the distribution of fresh water in confined aquifer systems across north america in this paper we document the numerous lines of geochemical isotopic and geomechanical evidence of ice sheet hydrogeology across north america we also review the mechanical thermal and hydrologic processes that control subsurface fluid migration beneath ice sheets finite element models of subsurface fluid flow permafrost formation and ice sheet loading are presented to investigate the coupled nature of transport processes during glaciation deglaciation these indicate that recharge rates as high as 10 times modern values occurred as the laurentide ice sheet overran the margins of sedimentary basins the effects of ice sheet loading and permafrost formation result in complex transient flow patterns within aquifers and confining units alike using geochemical and environmental isotopic data we estimate that the volume of glacial meltwater emplaced at the margins of sedimentary basins overrun by the laurentide ice sheet totals about 3 7 104 km3 which is about 0 2 of the volume of the laurentide ice sheet subglacial infiltration estimates based on continental scale hydrologic models are even higher 5 10 of meltwater generated these studies in sum call into question the widely held notion that groundwater flow patterns within confined aquifer systems are controlled primarily by the water table configuration during the pleistocene rather groundwater flow patterns were likely much more complex and transient in nature than has previously been thought because pleistocene recharge rates are believed to be highly variable these studies have profound implications for water resource managers charged with determining sustainable pumping rates from confined aquifers that host ice sheet meltwater

evolution and origin of deep reservoir water at the activo luna oil field gulf of mexico mexico petroleum wells of the activo de produccion luna oil field at the mexican gulf coast are partially invaded by formation water at a production depth between 5000 and 6000 m measured 14c activities between less than 0 9 and 13 7 modern carbon reflect a homogenous late pleistocene early holocene age 40 10 ka for the regional infiltration of meteoric and marine water into the reservoir before infiltration both components were partially affected by atmospheric evaporation which explains the hypersaline composition of some formation waters very positive d18o values up to 12 5 of the formation waters are caused by strong secondary water rock interaction processes and reflect close to equilibrium conditions between the carbonate host rock and the fluids the formation of biogenic and or thermocatalytic methane in some parts of the petroleum reservoir is indicated by d13c values up to 20 4 southwest northeast directed hydraulic migration of the deep aquifer between camps sen and escuintle pijije caparroso is indicated by interference tests and pressure drawdown characteristics whereas northwest southeast trending thrust faults restrict communication toward the luna and tizon camps in the most northeastern part of the oil field on a local scale vertical zonation trends of the fluids with decreasing salinity toward upper parts of the common aquifer are related to separation processes by gravity and or by the rising of condensed vapor the migration of the fluids is mainly related to southwest northeast trending fractures and microfractures whereas northwest southeast and northeast southwest trending reverse and normal faults respectively behave irregularly as barrier or as flow conduits recently the extraction of petroleum caused an increased mobilization of the hydrodynamic aquifer system begin page 458

a late cretaceous tin metallogenic event in nanling w sn metallogenic province constraints from u pb ar ar geochronology at the jiepailing sn be f deposit hunan china abstract the jiepailing deposit located in southern hunan province china is a giant sn be f deposit in the nanling w sn province the sn be f mineralization is spatially associated with the jiepailing granite porphyry la mc icp ms zircon u pb dating of the jiepailing granite porphyry yielded a weighted mean 206 pb 238 u age of 90 5 0 9 ma mswd 0 32 which is interpreted as the emplacement age of the granite porphyry hydrothermal muscovite yields a plateau 40 ar 39 ar age of 92 1 0 7 ma mswd 0 9 which is well consistent with the zircon u pb age of the jiepailing granite porphyry responsible for the sn be f mineralization indicating a temporal link between the emplacement of the jiepailing granite porphyry and the sn be f mineralization our new high precise geochronological data suggest that the jiepailing giant sn be f deposit and related granite formed during the early late cretaceous 92 90 ma which provided convincing evidence for a previously unrecognized metallogenic event related to late cretaceous granitic magmatism in nanling region the occurrence of the late cretaceous sn metallogenic event identified in southern hunan province further highlights the importance of systematic metallogenic studies of the nanling w sn province integrated with high precise geochronological data obtained previously it is suggested that the nanling region mainly experienced three tectonomagmatic activities and lithospheric thinning events during mesozoic which are responsible for three sn w metallogenic events to form the world class nanling w sn metallogenic province

hydrogeochemistry and coal associated bacterial populations from a methanogenic coal bed abstract biogenic coalbed methane cbm a microbially generated source of natural gas trapped within coal beds is an important energy resource in many countries specific bacterial populations and enzymes involved in coal degradation the potential rate limiting step of cbm formation are relatively unknown the u s geological survey usgs has established a field site birney test site in an undeveloped area of the powder river basin prb with four wells completed in the flowers goodale coal bed one in the overlying sandstone formation and four in overlying and underlying coal beds knoblach nance and terret the nine wells were positioned to characterize the hydraulic conductivity of the flowers goodale coal bed and were selectively cored to investigate the hydrogeochemistry and microbiology associated with cbm production at the birney test site aquifer test results indicated the flowers goodale coal bed in a zone from about 112 to 120 m below land surface at the test site had very low hydraulic conductivity 0 005 m d compared to other prb coal beds examined consistent with microbial methanogenesis groundwater in the coal bed and overlying sandstone contain dissolved methane 46 mg l average with low 13 c values 67 average high alkalinity values 22 meq kg average relatively positive 13 c dic values 4 average and no detectable higher chain hydrocarbons no 3 or so 4 2 bioassay methane production was greatest at the upper interface of the flowers goodale coal bed near the overlying sandstone pyrotag analysis identified aeribacillus as a dominant in situ bacterial community member in the coal near the sandstone and statistical analysis indicated actinobacteria predominated coal core samples compared to claystone or sandstone cores these bacteria which previously have been correlated with hydrocarbon containing environments such as oil reservoirs have demonstrated the ability to produce biosurfactants to break down hydrocarbons identifying microorganisms involved in coal degradation and the hydrogeochemical conditions that promote their activity is crucial to understanding and improving in situ cbm production

tectonics of the southern portion of the ribeira belt apiai domain abstract the name ribeira belt was originally used in a reference to a broad belt of deformed crust which strikes subparallel to the southeastern brazilian coastline it was originally believed to be neoproterozoic brasiliano panafrican but present investigations indicate that this age seems to be mainly related to the extensive arc related plutonism and tectono metamorphism that affected its most representative formations whereas the time of deposition of the supracrustals would be significantly older in this study the main tectono stratigraphic features of the apiai domain of the ribeira belt are described the lithostratigraphy is reviewed as well the paleogeographic structural geochemical and radiometric data and their implications for the tectonic evolution models for the region the marine sediments of the apiai domain were laid down on the borders of the parana and luis alves cratons and on an intervening mesoproterozoic 1 8 1 1 ga ocean crust they were intensively deformed by ocean closure and collision of the cratonic fragments and they constitute the majority of the local supracrustals designated as the acungui supergroup symmetrical continental passive margin deposits are represented to the northwest by a more proximal facies itaiacoca group probably related to the parana paleocontinent and by the capiru formation to the southeast between them lies the central domain formed by the votuverava group characterized by the remains of gradually deepening carbonatic platform sediments of the lajeado subgroup which grade eastward into distal turbiditic sequences of the ribeira subgroup where ocean floor and immature island arc magmatic rocks are present during the neoproterozoic the apiai domain behaved as a single continental mass into which basic rocks were intruded between 1 1 and 0 85 ga between 0 7 and 0 6 ga the apiai domain evolved into a cordilleran type magmatic arc related to the evolution of a subduction zone possibly situated to the southeast of the luis alves cratonic fragment this subduction caused metamorphism and migmatization of the supra and infra crustal rocks of the region and produced the extensive calc alkaline granitoid plutonism between 0 6 and 0 45 ga the majority of the southeastern continental blocks amalgamated during closure of the adamastor ocean followed by development of a system of regional dextral transcurrent shear zones related to oblique collision and or escape tectonics pull apart basins opened up and were filled with molasse sequences the region was intruded by post tectonic granitoids and then underwent regional cooling

the utility of methane clumped isotopes to constrain the origins of methane in natural gas accumulations methane clumped isotope compositions provide a new approach to understanding the formational conditions of methane from both biogenic and thermogenic sources under some conditions these compositions can be used to reconstruct the formational temperatures of the gas and this capability can be applied to common subsets of both biogenic and thermogenic systems additionally there are examples in which clumped isotope compositions do not reflect gas formation temperatures but instead mixing effects and kinetic phenomena such kinetic effects also occur in common and recognizable subtypes of biogenic and thermogenic gases here we review the use of methane clumped isotope measurements for understanding the origin of methane in the subsurface we review methane clumped isotope measurements from numerous biogenic and thermogenic natural gas reservoirs we then place these measurements in the context of common frameworks for identifying the formational conditions of methane including the use of methane 13 c and d values and c 1 c 2 3 ratios finally we propose a framework for how methane clumped isotopes can be used to identify the origin of methane accumulations

biogenic methane and carbon dioxide generation in organic rich shales from southeastern brazil abstract brazilian shale formations are potential biogenic gas systems that are still poorly understood organic rich shales from ponta grossa devonian parana basin irati permian parana basin and tremembe paleogene taubate basin formations were analyzed in order to evaluate their biogenic methane ch 4 generation potential and to constrain environmental and geological conditions that may affect methanogenic metabolism additionally the generation potential of carbon dioxide co 2 was evaluated in combination with ch 4 to constrain brazilian organic rich shales as sources of greenhouse gas to the atmosphere twenty four shale samples were used for batch incubations in dry and wet conditions and after headspace refilling and acetic acid addition during one year physico chemical parameters such as total organic carbon toc specific surface area and pore volume were characterized in order to understand general geologic controls on ch 4 and co 2 production biogenic gas generation rates in dry tests reached up to 3 17 ml t d milliliter per ton of shale per day for ch 4 and 2 45 10 3 ml t d for co 2 during the first 30 days with wet samples producing about 54 more ch 4 and 151 more co 2 than dry samples headspace refilling did not demonstrate significant changes on production rates while acetic acid addition restarted or increased ch 4 and co 2 production rates in several microcosms shales from the irati formation showed the highest methane production rates for both dry and wet tests with unusual ranges of 13 c ch4 and 13 c co2 that may be linked to hydrocarbon biodegradation the studied shale formations have different pore volume and specific surface area but without significant influence over biogenic methane generation

processes that control mineral and element abundances in shales abstract a shale s composition can be used to infer physical chemical and biological processes that have acted on it over its life history and this knowledge is used to surmise conditions at the time when each process was active this review lists the most important processes that control shale mineral and element abundances during each of the five stages of its life history 1 during weathering transport and deposition the most important processes are chemical weathering hydraulic sorting and mixing adsorption reverse weathering and incorporation of organic matter and biominerals 2 during early diagenesis the most important processes are exchange across the water sediment interface compaction microbial respiration mineral transformations and concretion formation 3 during burial diagenesis the most important processes are compaction catagenesis and metagenesis and mineral transformations 4 during exhumation the most important processes are decompaction brine invasion groundwater penetration and microbial respiration 5 during weathering the most important processes are organic matter oxidation mineral oxidation and hydrolysis groundwater transport and disaggregation this classification of processes provides a way to envision how concurrent and consecutive processes that occurred over a shale s life history have affected its mineralogy and chemical composition

geochemistry and mineralogy of the 2 45 ga pronto paleosols ontario canada abstract the ontario canada pronto paleosols which formed around 2 45 ga on archean granite were studied through field observation mineralogical study by microscope and microprobe and chemical analyses of major and 45 trace elements including rare earth elements rees since the first full description of its mineralogy and chemistry of major elements by gay and grandstaff gay a l grandstaff d e 1980 chemistry and mineralogy of precambrian paleosols at elliot lake ontario canada precambrian res 12 349 373 the pronto paleosols are among the most cited paleosols of the archean early proterozoic era though several questions have been raised as to whether they are true in place ancient soils results of this study show that the studied section meets the criteria for being in place paleosols furthermore the profile has no explicit traces of being strongly affected by hydrothermal alteration the ree containing accessory minerals were destroyed through weathering and secondary phosphate minerals with rees formed all of these observations support the weathering origin of the pronto paleosols however the profile should be identified as a saprolith rather than paleosol as even the uppermost samples exhibit the granitic texture of the parent rock the samples in this study were collected mainly from two sites site i and site ii saprolith samples from site i show the retention of fe and increases of the fe iii fe ii ratios and the chemical index of alteration cia values toward the unconformity as for the site ii samples the fe ti ratios show slight decreases with increasing cia values in the upper part of section whereas these samples also show the same trend of increasing fe iii fe ii ratios as the samples from site i microprobe analyses show that fe from the parent rock distributes mainly in mafic minerals as hornblende biotite or chlorite which were completely destroyed during the early stages of weathering in the saprolith section fe is present in sericite aggregates in the form of obscure patches of iron oxide tens of micrometers in size all these characteristics indicate that i the fe was not lost during soil formation at site i and slight amount of fe was lost at site ii and ii ferrous fe was quantitatively transformed to ferric fe i e oxidation during soil formation in the samples from both sites the ratios of al ti and si ti decrease toward the top of the profile together with the destruction of minerals toward the unconformity such as apatite biotite and chlorite the depletion of al and si suggests that the parental granite was weathered by an acidic weathering solution during the archean early proterozoic era the high atmospheric partial pressure of co 2 p co 2 is the most probable candidate for producing the acidic weathering solution

structural setting style and timing of vein hosted gold mineralization at the pogo deposit east central alaska gold bearing veins within the liese zone of the pogo deposit display a two stage evolutionary history that records temporal variation in kinematics fluid chemistry and temperature several stacked shallow northwest dipping shear veins are developed at pogo and collectively comprise the liese zone veins consist of 1 early narrow biotite bearing shear veins 2 white quartz veins with pyrite arsenopyrite bands referred to as main stage quartz veins that have sericite fe mg carbonate alteration envelopes and which exploit the early shear veins and 3 extension veins that form as steeper offshoots from the main stage veins the presence and orientation of oblique fabrics developed in the older biotite bearing shear veins are indicative of top to the south displacement under ductile to semi brittle conditions at higher temperatures in contrast the orientation of the extension veins and local sigmoidal shapes indicate a component of top to the northwest normal displacement on the main stage veins in their present orientation and brittle to semi brittle conditions of formation dolomite sericite alteration surrounding main stage veins may represent late to post mineral hydrothermal fluid exploitation of vein margins during ongoing normal displacement along vein systems all types of veining overprint 107 106 ma post metamorphic granitic dykes molybdenite in main stage quartz assemblages has returned re os ages of 104 2 1 1 ma significantly older than 96 to 91 ma 40ar 39ar ages obtained from vein alteration assemblages that may reflect thermal resetting during post mineral fault related hydrothermal activity magmatism and or retrograde cooling of the lithologic sequence unlike typical mesothermal shear vein hosted gold systems pogo is temporally and tectonically separated from metamorphic deformation events and has a comparable kinematic and geometric architecture to cretaceous plutonic gold deposits in the region we interpret the deposit to have formed during a regional cretaceous extensional event during multi stage exploitation of extensional fault surfaces by hydrothermal fluid from a cooling magmatic source

extensive microbial modification of formation water geochemistry case study from a midcontinent sedimentary basin united states the upper devonian antrim shale in the michigan basin is an economically significant source of microbially produced methane along the basin margins where meteoric recharge has been focused oxygen and hydrogen stable isotope compositions of antrim formation waters show that fresh waters recharged from pleistocene glaciation and modern precipitation suppressed basinal brine salinity to great depths and enhanced methanogenesis this paper presents results of integrated elemental and isotope analyses of antrim shale formation waters from the margins and center of the michigan basin focusing on solute sources and geochemical modifications associated with regionally extensive microbial methanogenesis cl br na systematics reveal that salinity is controlled not only by mixing between variable amounts of basinal brine and meteoric water but also by halite dissolution where fluids recharged through underlying devonian carbonate aquifers with localized evaporite deposits divalent cations carbonate system parameters and carbon isotope compositions of dissolved inorganic carbon have been systematically and profoundly altered by microbial methanogenesis large decreases in formation water ca mg and ca sr ratios accompany increasing carbonate alkalinity values in areas with high rates of microbial gas production thermodynamic and reaction path modeling show that these changes are consistent with calcite precipitation during progressive microbial methanogenesis similar variations in fluid chemistry are evident in databases from other sedimentary basins containing black shales and coal beds associated with microbial gas microbial methanogenesis may play an important role in the geochemical evolution of divalent cation relationships in crustal fluids and should be considered in models of formation water origin and evolution

the role of discontinuous magma inputs in felsic magma and ore generation for a long time granites have been considered as passive bodies ascending under intrinsic negative density and viscosity contrasts with their host rocks chemical variations within a granitic body resulted from in situ differentiation and crystal fractionation since the mid 1980s this global view has been significantly modified by i shifting melting from water saturated conditions to fluid absent reactions ii increasing the role played by the mantle during granite generation iii reassessing the rheology of partially molten rocks iv demonstrating stepwise segregation and ascent of magmas by analogue and numerical models v combining structural geophysical and geochemical studies to reveal the internal structures in granitic plutons it results that a granitic body is built up by a discontinuous accumulation of successive magma intrusions the discontinuous nature of magma emplacement has also significant consequences for its ability to generate ore the processes that lead to ore deposits are examined with a brief review of the magmatic and fluid phases that concentrate ore forming elements examples are taken from crustal derived granites and porphyry type deposits those are considered as the two end members of magmatic and hydrothermal ore deposits the source characteristics of the magma the emplacement mechanisms and magma mixing processes are the frame that controls the potential to carry base metals with the magma the distribution of elements is controlled by diffusion partition between minerals and melt solubility and redox conditions variations of those parameters are examined by considering their activation energy which controls the exponential dependence with temperature a characteristic length depending on the activation energy temperature variation and time is estimated for a characteristic time lag of 30 ka the intrusion of a magma into a magma chamber of similar composition hence temperature has few effects on diffusion partition coefficient and redox conditions because of a too low temperature contrast the intrusion of a mafic magma into a felsic one induces a variation of 300 c in both magmas the characteristic length of diffusion may vary by up to two orders of magnitude whereas the variation of partition coefficients is only one order of magnitude the redox conditions are about 2 5 log unit in the mafic magma but they can vary by 7 log units in the felsic magma hence a strong decrease in d values is observed in porphyry type deposits the effect is a removal of the elements with higher activation energy w sn zr from the mafic to the felsic magma deformation during the late stages of emplacement also controls ore formation

submagmatic microfractures in granites microstructures in hercynian granite plutons of the pyrenees indicate fracturing of plagioclase crystals in the presence of melt this is represented mainly by quartz and or feldspar that fills fractures electron microprobe analyses demonstrate that in compositional agreement with the rims of the zoned plagioclase the feldspar infillings are more sodic with decreasing melt fraction fracturing resulted from concentration of stress at contacts between grains while the granite was submagmatic i e when the melt was below the critical fraction for magmatic flow material compositionally far from eutectic is petrologically the best candictate to develop submagmatic fractures because during cooling the volume fraction of melt remains low for a large temperature range a strong tendency for microfractures to be oblique to flow foliation may constitute a new criterion for shear sense in magmas

stable isotope geochemistry of coal bed and shale gas and related production waters a review coal bed and shale gas can be of thermogenic microbial or of mixed origin with the distinction made primarily on the basis of the molecular and stable isotope compositions of the gases and production waters methane ethane carbon dioxide and nitrogen are the main constituents of coal bed and shale gases with a general lack of c2 hydrocarbon species in gases produced from shallow levels and more mature coals and shales evidence for the presence of microbial gas include 13c ch4 values less than 50 covariation of the isotope compositions of gases and production water carbon and hydrogen isotope fractionations consistent with microbial processes and positive 13c values of dissolved inorganic carbon in production waters the co2 reduction pathway is distinguished from acetate methyl type fermentation by somewhat lower 13c ch4 and higher d ch4 but can also have overlapping values depending on the openness of the microbial system and the extent of substrate depletion crossplots of 13c ch4 versus 13c co2 and d ch4 versus 13c h2o may provide a better indication of the origin of the gases and the dominant metabolic pathway than the absolute carbon and hydrogen isotope compositions of methane in the majority of cases microbial coal bed and shale gases have carbon and hydrogen isotope fractionations close to those expected for co2 reduction primary thermogenic gases have 13c ch4 values greater than 50 and 13c values that systematically increase from c1 to c4 and define a relatively straight line when plotted against reciprocal carbon number although coals and disseminated organic matter in shales represent a continuum as hydrocarbon source rocks current data suggest a divergence between these two rock types at the high maturity end in deep basin shale gas reversals or rollovers in molecular and isotopic compositions are increasingly reported in what is effectively a closed shale system as opposed to the relative openness in coal measure environments detailed geochemical studies of coal bed and shale gas and related production waters are essential to determine not only gas origins but also the dominant methanogenic pathway in the case of microbial gases

the late pleistocene early holocene archaeological record in brazil a geo referenced database abstract between 13 000 and 8000 14c bp eastern south america was settled by a stable and diversified population of hunter gatherers archaeological excavation in the past twenty years has yielded increasingly consistent evidence of occupation in different regions of brazil since the end of the pleistocene with dates at least contemporary to the clovis horizon in north america this is addressed by documenting and analysing the quantity quality and distribution of archaeological 14c dates from brazil during this period a total of 277 dates from 90 sites are tabulated mapped and included in the analysis during the late pleistocene there was a pioneer phase of human colonization with dispersal inland through the major river systems subsequently the early holocene saw the first phase of established settlement of brazil s interior there seems to be an archaeological threshold reached at ca 10 500 years 14c bp numbers of sites increase there is evidence of settlement of all major biomes and there is clear evidence of inter regional cultural diversity

palaeoindian occupation of the atacama desert northern chile palaeoindian occupation of the atacama desert in northern chile has been found between 12 600 and 10 200 cal yr bp the new site at salar punta negra 24 28 s 60 53 w 2976 m includes about 1000 classifiable mostly unifacial artefacts and uniquely three different diagnostic types of early projectile points two of the lateglacial early holocene projectile types have wide distribution and are known from different geographical areas in south america the palaeoindian fell fish tail point mainly from the southern cone of south america and the triangular tuina points typical of the puna of the south central andes in northern chile and northwestern argentina in addition we found a third type a stemmed point typical for the salar punta negra filling a large geographical gap of fell occupation the site at salar punta negra provides evidence for generally much higher mobility and diversity of early cultures and supports an andean pacific route for early human exploration of south america to the south through the desert at intermediate altitudes contemporaneous high amplitude climatic changes were fundamental preconditions to provide adequate environments and habitats and to make palaeoindian hunting gathering occupation possible in the atacama desert copyright 2005 john wiley sons ltd

release fault a variety of cross fault in linked extensional fault systems in the sergipe alagoas basin ne brazil abstract two types of cross faults are herein recognized transfer faults and the newly termed release faults transfer faults form where cross faults connect distinct normal faults and horizontal displacements predominate over vertical ones in contrast release faults form where cross faults associated with individual normal faults die out within the hangingwall before connecting to other normal faults and have predominantly vertical displacements release faults are geometrically required to accommodate variable displacements along the strike of a normal fault thus they form to release the bending stresses in the hangingwall and do not cut normal fault planes nor detachment surfaces at depth release faults have maximum throws adjacent to normal faults and may be nearly perpendicular or obliquely oriented to the strike of the latter such geometry appears not to depend upon pre existing weaknesses but such variable orientation to normal faults is an inherent property of release faults release faults commonly appear as simple normal faults in seismic sections without implying extension along the strike of rift and basins three dimensional strain deformation occurs in the hangingwall only between the terminations of an individual normal fault but regionally release faulting is associated with plane strain deformation in linked extensional fault systems

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

building an island arc crustal section time constraints from a la icp ms zircon study geochronological studies of samples from continuous crustal sections of fossil intra oceanic arcs are paramount for determining the precise timing of major processes that took place during the building of an oceanic island arc crust in this study laser ablation icp ms u pb zircon and conventional rb sr analyses pinpoint the timing of major events responsible for crustal growth of the kohistan paleo island arc northern pakistan inheritance in magmatic rocks is evidence for recycling of intra arc material and indicates that the kohistan arc may have formed as early as 135 4 ma one older inherited grain indicates that the arc developed on a young oceanic lithosphere whose remnants include a c 175 ma old component an interesting consequence is that intra oceanic arc magmas can yield inherited zircons which can be much older than the arc system itself without requiring recycling back into the mantle by subduction processes in the case of the kohistan arc ante arc neotethys oceanic lithosphere was tapped by arc magmas during their way upward into the arc crust the oldest magmatic ages measured in this study fall in the range 101 102 ma 100 9 0 6 and 102 1 0 4 ma this period corresponds to arc build up and thickening of the arc crust leucogranitic melts dated at 89 9 0 4 ma and 90 9 1 0 ma are considered as produced by dehydration melting reaction accompanying granulitisation of the thickened lower arc crust a maximum age for this event is 97 7 0 7 ma the age of emplacement of a garnet meta tonalite affected by granulite facies metamorphism magmatic activity was still ongoing during and after the granulitisation as testified by emplacement of a diorite and a gabbro dated at 89 1 0 6 and 88 2 0 9 ma respectively the upper part of the metaplutonic sequence contains diorite samples dated at 84 6 0 5 ma and 84 3 0 5 ma and as young as 81 1 0 7 ma during this period and based on the present day outcropping sequences the mean crustal growth rate varied from 32 to 65 km 3 km ma volume per unit width along the strike of the arc which is comparable to the range for present day arcs of the western pacific region the correspondence of crustal growth rates observed for present day island arcs and the good preservation of the crustal section in the kohistan arc make this area an exceptional natural laboratory to study arc related processes and to check models of continental crust formation by arc accretion

reply to comments by h d holland on the oxygen geochemical cycle dynamics and stability geochim cosmochim acta 66 361 381 2002

palaeoproterozoic evaporites in fennoscandia implications for seawater sulphate the rise of atmospheric oxygen and local amplification of the δ13c excursion this paper addresses global oxygenation and establishment of a marine sulphate reservoir in the palaeoproterozoic we report syn depositional marine anhydrite containing pseudomorphs after ca sulphates as widespread throughout the tulomozero formation in the se fennoscandian shield implying that surface waters were oxidized and a large so42 marine reservoir was developed as early as 2100 ma the ca sulphates and associated magnesite and halite precipitated syn depositionally from oxidized evolved and modified seawater in coastal playa sabkha and intertidal flat settings sr 87 sr 86 and delta 13 c of associated c 13 rich stromatolitic dolostones were environmentally controlled with the highest ratios occurring in playa and sabkha carbonates the results imply that the palaeoproterozoic delta 13 c carb excursion was amplified by 8 by local environmental factors and calls into question many observations of putative delta 13 c global signals reported previously from similar palaeoproterozoic evaporitic dolostones the local environmental amplification can explain a large regional and intercontinental delta 13 c discrepancy observed in synchronous carbonates

lower and upper neoproterozoic magmatic records in itaiacoca belt parana brazil zircon ages and lithostratigraphy studies abstract the itaiacoca belt is a sequence of metavolcanic and metasedimentary rocks that crop out east of parana and southeast of sao paulo states in southern brazil this geologic geochronologic study supports division of the itaiacoca belt into two major lithologic sequences the older is a carbonate platform sequence dolomitic meta limestones metamarls calc phyllites carbonate phyllites with minimum deposition ages related to the end of the mesoproterozoic beginning of the neoproterozoic 1030 908 ma u pb zircon of metabasic rocks the younger sequence contains mainly clastics deposits meta arkoses metavolcanics metaconglomerates metapelites with deposition ages related to the neoproterozoic 645 628 ma u pb zircon of metavolcanic rocks these ages are quite close to k ar ages fine fraction of the 628 610 ma interval associated with metamorphism and cooling of the itaiacoca belt the contact between the dolomitic meta limestones and meta arkoses is marked by intense stretching and high angle foliation suggesting that the discontinuity between these associations resulted from shearing it is proposed here that the term itaiacoca sequence should represent the dolomitic meta limestones and the term abapa sequence represents the meta arkoses metavolcanics phyllites in a major tectonic context these periods are related to the break up of rodinia supercontinent 1030 908 ma and the amalgamation of the gondwana supercontinent 645 628 ma

organic carbon accumulation in the holocene sapropel of the black sea the modern laminated coccolith marl unit 1 of the black sea containing 2 6 wt organic carbon overlies a finely laminated sapropel unit 2 containing 5 20 wt organic carbon however the accumulation rate of organic carbon in the sapropel is not significantly different from that in unit 1 in contrast the accumulation rates of either caco 3 or lithogenous matter clay are significantly lower in the sapropel compared with unit 1 thus the sapropel has very high organic carbon contents because of lesser dilution of the organic fraction by the other bulk components because the accumulation rate of organic carbon in the sapropel is similar to that in unit 1 which is not significantly different from accumulation rates in oxygenated environments in similar settings the black sea sapropel is not necessarily characteristic of anoxic basins

isotope techniques for tracing migration of gases in sedimentary basins the isotopic composition of methane is primarily dependent on the stage of maturation of organic matter present in the hydrocarbon source rocks and is not changed during migration the isotopic composition of in situ methane can be estimated from the maturity of the source organic matter migrated methane from deeper more mature sources is recognized by its relative 13 c enrichment compared to indigenous methane examples are presented in this paper to evaluate the migration pattern of gases in sedimentary basins

comparison of fluid geochemistry and microbiology of multiple organic rich reservoirs in the illinois basin usa evidence for controls on methanogenesis and microbial transport abstract microbial methane in sedimentary basins comprises approximately 20 of global natural gas resources yet little is known about the environmental requirements and metabolic rates of these subsurface microbial communities the illinois basin located in the midcontinent of the united states is an ideal location to investigate hydrogeochemical factors controlling methanogenesis as microbial methane accumulations occur 1 in three organic rich reservoirs of different geologic ages and organic matter types upper devonian new albany shale up to 900 m depth pennsylvanian coals up to 600 m depth and quaternary glacial sediments shallow aquifers 2 across steep salinity gradients and 3 with variable concentrations of so 4 2 for all three organic rich reservoirs aqueous geochemical conditions are favorable for microbial methanogenesis with near neutral ph so 4 2 concentrations 80 c in nutrient poor environments necessitating the re introduction of microbes into the subsurface via groundwater transport

distribution of total dissolved solids in mcmurray formation water in the athabasca oil sands region alberta canada implications for regional hydrogeology and resource development total dissolved solids tds concentrations of 258 lower cretaceous mcmurray formation water samples in the athabasca oil sands region 54 to 58 n and 110 to 114 w were mapped using published data from recent government reports and environmental impact assessments mcmurray formation waters varied from nonsaline 240 mg l to brine 279 000 mg l with a regional trend of high salinity water approximately following the partial dissolution front of the devonian prairie evaporite formation the simplest hydrogeological explanation for the observed formation water salinity data is that devonian aquifers are locally connected to the mcmurray formation via conduits in the sub cretaceous karst system in the region overlying the partial dissolution front of the prairie evaporite formation the driving force for upward formation water flow is provided by the pleistocene glaciation events that reversed the regional devonian flow system over the past 2 m y in the athabasca region this study demonstrates that a detailed approach to hydrogeological assessment is required to elucidate tds concentrations in mcmurray formation waters at an individual lease area scale the observed heterogeneity in formation water tds and the potential for present day upward flow has implications for both mining and in situ oil sands resource development

the passa tres lode gold deposit parana state brazil an example of structurally controlled mineralisation formed during magmatic hydrothermal transition and hosted within granite abstract the passa tres granite is a nne ssw elongated shape intrusion located in the parana state southern brazil this intrusion was emplaced within metapelites of the mesoproterozoic votuverava group which are part of the n040 e trending lancinha shear zone gold mineralisation within the passa tres granite is held by meter scale quartz veins forming orebodies with variable massive banded sheared and or brecciated internal textures structural data indicate the existence of two orthogonal directions of structures n s and e w dipping 60 75 w and 45 70 s respectively mineralised veins contain in addition to the quartz of the gangue and in chronological order fluorite pyrite chalcopyrite gold aikinite molybdenite muscovite carbonate and baryte gold occurs as native grains within fractures that affect pyrite commonly associated with chalcopyrite and aikinite quartz veins are sometimes bordered by aplitic dykes additionally some of the veins exhibit a thin margin of k feldspar minerals that could represent the early stage of vein formation these observations the presence of unidirectional solidification textures ust along with abundant expression of pegmatite rich pockets within granite that crops out close to the surface allow the reconstruction of the granite architecture in terms of late magmatic evolution magmatic hydrothermal transition and position of the cupola n s and e w systems are interpreted to be contemporaneous and conjugate normal displacements are predominant and main mineralised veins are essentially located within extensional pull apart structures the structural model suggests that the normal faults were initiated along former low angle planes associated with aplite and or early quartz veins that subsequently controlled the opening of the pull apart structures that represent the economic orebodies zircon from the granite and muscovite grains from mineralised veins were dated by u pb and ar ar methods respectively zircons from the main facies medium grained gem and microgranite gef provided undistinguishable ages which were pooled to give an age of 611 9 3 6 ma a less abundant leucocratic facies white granite geb yielded a significantly younger age of 592 8 7 1 ma muscovites from quartz veins gave ar ar ages of 612 9 2 to 608 8 2 ma transitional vein with a k feldspar border 611 7 2 to 608 8 2 ma mineralised veins and 608 4 2 ma barren quartz vein thus the passa tres granite and its gold mineralisation appear to represent a unique example of an intrusion related gold system in which the mineralisation concentrates in the core of the magmatic intrusion in the form of meter scale veins strongly controlled by tectonics

localization and possible social aggregation in the late pleistocene and early holocene on the north coast of peru abstract early circular living structures made of rough field stone radiocarbon dated between 10 800 and 8300 bp and probably affiliated with the paijan culture on the north coast of peru are discussed in terms of possible proto household economies that are localized and socially aggregated in compressed environmental zones along the lower western slopes of the andes the technological settlement and economic data recovered from several sites in the zana and jequetepeque valleys are discussed briefly their broader implications are presented as well

tracing the magmatic hydrothermal transition in regional low strain zones the role of magma dynamics in strain localization at pluton roof implications for intrusion related gold deposits structural controls are critical during magmatic to hydrothermal transition in the formation of intrusion related gold deposits they may explain why only some parts of intrusions are mineralized and why only very few intrusions host large deposits moreover most of these gold deposits postdate peak regional metamorphism and were formed in zones of relatively low strain indeed the efficiency of structural gold traps is highest along favourably oriented intrusion host rock contacts where mechanical instability maintains high permeability in the cracked thermal aureole this may be reinforced by melt injections from an underlying root zone we present a structural analysis of the deformation features of a granite pluton roof large scale dykes and a network of gold veins are intensively developed in this roof recording a succession of mechanical instabilities our gravity survey underlines the presence of a pluton feeder zone located just beneath the mineralized network it is argued that interferences between regional stress and melt injection in the feeder zone favoured the development of the network by strain located close to the granite roof this stresses the role of mechanical instabilities triggered by the combined effects of regional stress and melt dynamics in determining the location and size of this type of gold deposit

noble gas tracing of groundwater coalbed methane interaction in the san juan basin usa the san juan basin natural gas field located in northwestern new mexico and southwestern colorado in the usa is a case type coalbed methane system groundwater is thought to play a key role in both biogenic methane generation and the co2 sequestration potential of coalbed systems we show here how noble gases can be used to construct a physical model that describes the interaction between the groundwater system and the produced gas we collected 28 gas samples from producing wells in the artesian overpressured high production region of the basin together with 8 gas samples from the underpressured low production zone as a control stable isotope and major species determination clearly characterize the gas in the high production region as dominantly biogenic in origin and the underpressured low producing region as having a significant admix of thermogenic coal gas 3he 4he ratios increase from 0 0836ra at the basin margin to 0 318ra towards the center indicating a clear but small mantle he signature in all gases coherent fractionation of water derived 20ne 36ar and crustal 4he 40ar are explained by a simple rayleigh fractionation model of open system groundwater degassing low 20ne concentrations compared to the model predicted values are accounted for by dilution of the groundwater associated gas by desorbed coalbed methane this rayleigh fractionation and dilution model together with the gas production history allows us to quantify the amount of water involved in gas production at each well the quantified water volumes in both underpressured and overpressured zones range from 1 7 103 m3 to 4 2 105 m3 with no clear distinction between over and underpressured production zones these results conclusively show that the volume of groundwater seen by coal does not play a role in determining the volume of methane produced by secondary biodegradation of these coalbeds there is no requirement of continuous groundwater flow for renewing the microbes or nutrient components we furthermore observe strong mass related isotopic fractionation of 20ne 22ne and 38ar 36ar isotopic ratios this can be explained by a noble gas concentration gradient in the groundwater during gas production which causes diffusive partial re equilibration of the noble gas isotopes it is important for the study of other systems in which extensive groundwater degassing may have occurred to recognize that severe isotopic fractionation of air derived noble gases can occur when such concentration gradients are established during gas production excess air derived xe and kr in our samples are shown to be related to the diluting coalbed methane and can only be accounted for if xe and kr are preferentially and volumetrically trapped within the coal matrix and released during biodegradation to form ch4

release of biodegradable dissolved organic matter from ancient sedimentary rocks 1 sedimentary rocks contain the largest mass of organic carbon on earth yet these reservoirs are not well integrated into modern carbon budgets here we describe the release of dissolved organic matter dom from om rich sedimentary rocks under simulated weathering conditions results from column experiments demonstrate slow sustained release of dom from ancient sedimentary rocks under simulated weathering conditions 1h nmr analysis of shale derived dom reveals a highly aliphatic carbohydrate poor material distinct from other natural dom pools shale derived dom is rapidly assimilated and biodegraded by aerobic heterotrophic bacteria consequently no compositional signature of shale derived dom other than 14c depletion is likely to persist in rivers or other surface reservoirs combined these efforts show that dissolution provides a mechanism for the conversion of refractory kerogen into labile biomass linking rock weathering with sedimentary om oxidation and the delivery of aged om to rivers and ocean margins

zircon u pb molybdenite re os and muscovite ar ar isotopic dating of the xitian w sn polymetallic deposit eastern hunan province south china and its geological significance the xitian tungsten tin w sn polymetallic deposit located in eastern hunan province south china is a recently explored region containing one of the largest w sn deposits in the nanling w sn metallogenic province the mineral zones in this deposit comprise skarn greisen structurally altered rock and quartz vein types the deposit is mainly hosted by devonian dolomitic limestone at the contact with the xitian granite complex the xitian granite complex consists of indosinian late triassic 230 215 ma and yanshanian late jurassic early cretaceous 165 141 ma granites zircons from two samples of the xitian granite dated using laser ablation inductively coupled mass spectrometer la icpms u pb analysis yielded two ages of 225 6 1 3 ma and 151 8 1 4 ma representing the emplacement ages of two episodic intrusions of the xitian granite complex molybdenites separated from ore bearing quartz veins yielded a re os isochron age of 149 7 0 9 ma in excellent agreement with a weighted mean age of 150 3 0 5 ma two samples of muscovites from ore bearing greisens yielded 40ar 39ar plateau ages of 149 5 1 5 ma and 149 4 1 5 ma respectively these isotopic ages obtained from hydrothermal minerals are slightly younger than the zircon u pb age of 151 8 1 4 ma of the yanshanian granite in the xitian area indicating that the w sn mineralization is genetically related to the late jurassic magmatism the xitian deposit is a good example of the early yanshanian regional w sn ore forming event 160 150 ma in the nanling region the relatively high re contents 8 7 to 44 0 ppm average of 30 5 ppm in molybdenites suggest a mixture of mantle and crustal sources in the genesis of the ore forming fluids and melts based upon previous geochemical studies of early yanshanian granite and regional geology we argue that the xitian w sn polymetallic deposit can be attributed to back arc lithosphere extension in the region which was probably triggered by the break off of the flat slab of the palae pacific plate beneath the lithosphere

microbial generation of economic accumulations of methane within a shallow organic rich shale although methane of bacterial origin is ubiquitous in marine and freshwater sediments economic accumulations of bacterial gases occur mainly at depths of several kilometres in tertiary basins that had high sedimentation rates1 2 here we present an integration of geochemical and isotopic data from gas and water extracted from the upper devonian antrim shale along the northern margin of the michigan basin which demonstrates that significant volumes of bacterial gas have been generated in organic rich shales at depths of less than 600 metres the antrim shale is mainly a self sourced reservoir in contrast to conventional gas deposits that have migrated from a source to a reservoir and has become one of the most actively exploited gas reservoirs3 in the united states the gas forming processes operating at shallow depths in the antrim shale are not unique4 and an understanding of these processes should lead to the identification and development of other economic non conventional gas deposits around the world

discussion of the article by a c lasaga and h ohmoto on the oxygen geochemical cycle dynamics and stability geochim cosmochim acta 66 361 381 2002

syenite associated disseminated gold deposits in the abitibi greenstone belt canada a distinct group of gold deposits in the abitibi greenstone belt is spatially associated with quartz monzonite to syenite stocks and dikes the deposits occur mainly along major fault zones in association with preserved slivers of alluvial fluvial timiskaming type sedimentary rocks the deposits consist of disseminated sulfide replacement zones with variably developed stockworks of quartz carbonate k feldspar veinlets within zones of carbonate albite k feldspar and sericite alteration the syenitic intrusions are broadly contemporaneous with deposition of timiskaming sedimentary rocks and together with disseminated gold mineralization they have been overprinted by subsequent regional folding and related penetrative cleavage disseminated gold orebodies occur within composite syenitic stocks or along their margins along satellite dikes and sills and along faults and lithologic contacts away from intrusions orebodies in these different positions are interpreted to represent proximal to distal components of large magmatic hydrothermal systems centered on and possibly genetically related to composite syenitic stocks

fluid inclusion characteristics of intrusion related gold mineralization tombstone tungsten magmatic belt yukon territory canada intrusion hosted low sulfide sheeted vein systems are common within many plutons and stocks of the middle cretaceous tombstone tungsten magmatic belt yukon territory and host significant gold mineralization fluid inclusion characteristics of five such systems namely emerald lake dublin gulch scheelite dome mike lake and mactung constrain the vein forming fluid composition formation temperatures and pressures hydrothermal fluid processes and potential fluid sources the veins contain a wide range of fluid inclusion types ubiquitous type 1a and 1b inclusions are low salinity 1a xnacl 1 kbar at emerald lake and dublin gulch and 2 kbar at mactung and scheelite dome that potentially control fluid composition and evolution a variety of fluid processes may have been responsible for gold precipitation including immiscibility and or release of an evolving magmatic fluid

absolute timing of sulfide and gold mineralization a comparison of re os molybdenite and ar ar mica methods from the tintina gold belt alaska new re os molybdenite dates from two lode gold deposits of the tintina gold belt alaska provide direct timing constraints for sulfide and gold mineralization at fort knox the re os molybdenite date is identical to the u pb zircon age for the host intrusion supporting an intrusive related origin for the deposit however 40ar 39ar dates from hydrothermal and igneous mica are considerably younger at the pogo deposit re os molybdenite dates are also much older than 40ar 39ar dates from hydrothermal mica but dissimilar to the age of local granites these age relationships indicate that the re os molybdenite method records the timing of sulfide and gold mineralization whereas much younger 40ar 39ar dates are affected by post ore thermal events slow cooling and or systemic analytical effects the results of this study complement a growing body of evidence to indicate that the re os chronometer in molybdenite can be an accurate and robust tool for establishing timing relations in ore systems

living on the river edge the tigre site k 87 new data and implications for the initial colonization of the uruguay river basin abstract this paper presents new data on the initial settlement of the southeastern region of south america based on recent research conducted at the tigre archaeological site k87 located in the middle uruguay river basin near the uruguayan border with brazil and argentina the current archaeological excavations carried out in this open air site confirmed that it is a multicomponent site a new series of 20 radiocarbon dates refined the chronology of recurrent human occupations at this site during the late pleistocene 13 260 cal bp the pleistocene holocene transition 12 920 11 750 cal bp the early holocene 11 300 9300 cal bp and the late holocene 1180 cal bp demonstrating the strategic importance of this site during the prehistory of the region in this paper we describe the archaeological and stratigraphic contexts of the site and analyze the artifact assemblage of the early components tigre points recovered from the archaeological excavations confirm that this is a paleoamerican point design that circulated in the region between 12 000 11 100 cal bp in addition associated with these points bifaces fractured preforms and a type of asymmetric biface with a crescent half moon shape were recovered these crescent artifacts show a high standardization in form size and knapping technique which is described in this paper finally we discuss the geographic distribution of the tigre points the blade technology present in the uruguay river basin the presence of prestige artifacts during the settlement and the chronology of the umbu tradition of southern brazil in relation to the previous and recent data obtained in the tigre site

using environmental isotopes and dissolved methane concentrations to constrain hydrochemical processes and inter aquifer mixing in the galilee and eromanga basins great artesian basin australia summary groundwater recharge processes water rock interaction and the hydraulic connectivity between aquifers of the galilee and eromanga basins in central queensland australia were investigated using stable 2 h 18 o 13 c and 87 sr 86 sr and radiogenic 36 cl isotopes and dissolved methane concentrations complemented by major ion chemistry the central eromanga and the upper sequence of the galilee basins are both sub basins of the great artesian basin gab and the coal seams of the galilee basin are currently explored for their potential as commercial coal seam gas deposits in order to understand the potential influence of depressurisation of coal seams required to release the gas on adjacent aquifers a detailed understanding of recharge processes and groundwater hydraulics of these basins prior to any development is required each of the different isotope systems were used in this study to provide different information on specific processes for example the assessment of 13 c and 87 sr 86 sr ratios suggested that carbonate dissolution is one of the major processes controlling the water chemistry within some aquifers in addition the combined assessment of 2 h 18 o and major ion chemistry indicates that transpiration is the primary process controlling the solute concentration in the gab recharge area whereas evaporation appears to be less significant groundwaters in the galilee basin recharge area outside the limits of the gab are different to any groundwater within the gab units this difference is attributed to the dissolution of potassium bearing micas which are absent in the gab groundwater age estimates based on 36 cl cl ratios suggest that there is a steady increase along the flow paths and this lack of anomalous age estimates from the recharge areas to the deeper parts of the basin indicates that there is no evidence for regional inter aquifer mixing based in isotopes only however dissolved methane concentrations and groundwater chemistry near faults indicates the potential mix of gas and or water from the coal seams into the gab groundwaters suggesting that there may be local influence of faults as gas water conduits

early human occupation of uruguay radiocarbon database and archaeological implications abstract the early human occupation of the territory between the uruguay river and the atlantic coast occurred from ca 11 ka to 7 ka bp in four millennia environmental and cultural changes occurred with better conditions for human life and the end of the megamammal extinction process the climate became warmer and more humid the lowlands covered very extensive areas and the sea level and coastlines changed producing ecotonal zones with high productivity this process originated the la plata river of today environmental conditions and social processes are well combined in this successful human colonization corporate groups of dynamic hunter gatherers built an extended social interaction sphere and produced new tool kits for human work the emergence of variability in lithic projectile points is the material correlation of the technological adaptation to a new environmental condition the radiocarbon database for uruguay is adequate although a little limited for the atlantic coast there are several independent lines of evidence toward discussion of hunter gatherer modes of production and a dispersal model for the atlantic side of south america this paper explores information about covariant transformations in landscape occupation and in way of life as well as analyzing the role played by the atlantic coast in human expansion

composition and stable isotope geochemistry of natural gases from kansas midcontinent u s a abstract more than 28 1012 ft 3 79 1010 m3 of natural gas and 5 3 109 bbl 8 4 108 m3 of oil have been produced in kansas u s a from paleozoic carbonate and sandstone reservoirs on structural uplifts and shallow embayments along the northern margin of the anadarko basin a heavily explored geologically well characterized state kansas is an excellent place to study hydrocarbon migration and to test geochemical models for the origin of natural gases immature to marginally mature rocks of eastern kansas cherokee and forest city basins produce mixed microbial and thermogenic gases gases in this region have wetness 0 03 51 methane 13c 65 to 43 and methane d 260 to 150 gases from central and western kansas nemaha uplift to hugoton embayment are entirely thermogenic and have wetness 4 51 methane 13c 48 to 39 and methane d 195 to 140 ethane and propane 13c values throughout kansas vary from 38 to 28 and from 35 to 24 respectively mature thermogenic gas generated from source rocks in southwestern kansas and the anadarko basin with 1 0 ro 1 4 is recognized throughout the state lateral migration into shallow reservoirs on the central kansas and northern nemaha uplifts and in the cherokee basin probably occurred along basal pennsylvanian conglomerates and weathered lower paleozoic carbonates at the regional sub pennsylvanian unconformity early thermogenic gas generated by local source rocks with ro 0 7 is recognized in isolated fields in the salina and forest city basins in ordovician reservoirs beneath the sub pennsylvanian unconformity in the cherokee basin and in reservoirs generally above the unconformity in the cherokee and sedgwick basins the eastern central kansas uplift and the hugoton embayment

coal weathering and the geochemical carbon cycle abstract the weathering rate of sedimentary organic matter in the continental surficial environment is poorly constrained despite its importance to the geochemical carbon cycle during this weathering complete oxidation to carbon dioxide is normally assumed but there is little proof that this actually occurs knowledge of the rate and mechanisms of sedimentary organic matter weathering is important because it is one of the major controls on atmospheric oxygen level through geologic time we have determined the aqueous oxidation rates of pyrite free bituminous coal at 24 and 50 c by using a dual cell flow through method coal was used as an example of sedimentary organic matter because of the difficulty in obtaining pyrite free kerogen for laboratory study the aqueous oxidation rate obtained in the present study for air saturated water 270 m o2 was found to be on the order of 2 10 12 mol o2 m2 s at 25 c which is fast compared to other geologic processes such as tectonic uplift and exposure through erosion the reaction order with respect to oxygen level is 0 5 on a several thousand hour time scale for both 24 and 50 c experiments activation energies determined under 24 and 50 c conditions were 40 kj mol o2 indicating that the oxidation reaction is surface reaction controlled the oxygen consumption rate obtained in this study is two to three orders of magnitude smaller than that for pyrite oxidation in water but still rapid on a geologic time scale aqueous coal oxidation results in the formation of dissolved co2 dissolved organic carbon doc and solid oxidation products which are all quantitatively significant reaction products

archaeology of the pleistocene holocene transition in uruguay an overview abstract in uruguay evidence of early human occupation comes from different archaeological regions including the basin of uruguay and cuareim rivers basin of negro mid river and the atlantic littoral this paper presents a synthesis and overview of the poorly known archaeology of the pleistocene holocene transition of uruguay including archaeological sedimentological and palaeontological information related to the early human occupation in this region the ancient human settlements occurred in various environmental settings including riverbanks hilltops and maritime landscapes new fell type or fishtail projectile points and preliminary results of the current research in pay paso locality are presented evidence from pay paso site 1 indicates that during early holocene the shore of the cuareim river was a paleosurface that was occupied by early human groups a new and previously unpublished type of projectile point from early hunter gatherers ca 9300 9100 yr bp was recovered from excavation of pay paso site 1 finally some comments and observations about culture material and lithic technology for early people of uruguay are explored

genetic and temporal relations between formation waters and biogenic methane upper devonian antrim shale michigan basin usa abstract controversy remains regarding how well geochemical criteria can distinguish microbial from thermogenic methane natural gas in most conventional deposits has migrated from a source rock to a reservoir rarely remaining associated with the original or cogenetic formation waters we investigated an unusual gas reservoir the late devonian antrim shale in which large volumes of variably saline water are coproduced with gas the antrim shale is organic rich of relatively low thermal maturity extensively fractured and is both source and reservoir for methane that is generated dominantly by microbial activity this hydrogeologic setting permits integration of chemical and isotopic compositions of coproduced water and gas providing a unique opportunity to characterize methane generating mechanisms the well developed fracture network provides a conduit for gas and water mass transport within the antrim shale and allows invasion of meteoric water from overlying aquifers in the glacial drift steep regional concentration gradients in chemical and isotopic data are observed for formation waters and gases dilute waters grade into dense brines 300 000 ppm over lateral distances of less than 30 km radiogenic 14c and 3h and stable isotope 18o and d analyses of shallow antrim shale formation waters and glacial drift groundwaters indicate recharge times from modern to 20 000 yr bp carbon isotope compositions of methane from antrim shale wells are typical of the established range for thermogenic or mixed gas 13c 47 to 56 however the unusually high 13c values of co2 coproduced with methane 22 and dissolved inorganic carbon dic in formation waters 28 require bacterial mediation the d values of methane and coproduced formation water provide the strongest evidence of bacterial methanogenesis methane ethane propane ratios and 13c values for ethane indicate 1 the presence of a thermogenic gas component that increases basinward and 2 progressive bacterial oxidation of ethane as the antrim shale subcrop is approached multiple episodes of pleistocene glaciation over northern michigan appear critical to the development of these gas deposits loading of thick ice sheets may have provided hydraulic head that enhanced dilation of preexisting fractures and influx of meteoric water the physical erosion cycle of repeated glacial advances and retreats exhumed the antrim shale around the northern margin of the michigan basin subjecting it to near surface physiochemical and biochemical processes the chemical and hydrologic relations demonstrated in the antrim shale reservoir suggest a dynamic connection between pleistocene glacial history of the midcontinent region and development of recoverable microbially generated natural gas reserves

the khopik porphyry copper prospect lut block eastern iran geology alteration and mineralization fluid inclusion and oxygen isotope studies abstract the khopik porphyry copper au mo prospect in eastern iran is associated with a succession of middle to late eocene i type high k calc alkaline to shoshonite monzonitic to dioritic subvolcanic porphyry stocks emplaced within cogenetic volcanic rocks laser ablation u pb zircon ages indicate that the monzonite stocks crystallized over a short time span during the middle eocene 39 0 0 8 ma to 38 2 0 8 ma as result of subduction of the afghan block beneath the lut block porphyry copper mineralization is hosted by the monzonitic intrusions and is associated with a hydrothermal alteration that includes potassic sericitic potassic quartz sericite carbonate pyrite qscp quartz carbonate pyrite qcp and propylitic zones mineralization occurs as disseminated to stockwork styles and as minor hydrothermal breccias some mineralization occurs in fault zones as quartz sulfide veins telescoped onto the porphyry system the main ore minerals are chalcopyrite and bornite with minorpyrite and magnetite and the highest cu 0 01 0 9 wt au 2 ppm and mo unidirectional pre ore stage solidification texture ust represented by comb quartz layers within the potassic alteration zone formed from a hypersaline brine 57 73 wt nacl equiv low density vapor rich fluids 4 22 wt nacl equiv at temperatures of 482 c to over 600 c the isotopic composition of oxygen 18 o water 8 7 8 9 suggests that the quartz layers crystallized from magmatic hydrothermal fluids that exsolved in the upper part of the monzonitic intrusions potassic alteration formed from high salinity fluids 51 73 wt at temperatures between 432 592 c and low salinity vapor rich solutions with 11 19 wt nacl equiv later veinlets in the qscp zone formed from lower salinity fluids 18 o water 9 9 3 for potassic and 7 3 for qscp also indicate a magmatic origin for the ore fluids the widespread presence of middle eocene to lower oligocene magmatism and mineralization in eastern iran suggests the presence of another important porphyry copper belt in addition to the northwest southeast urumieh dokhtar copper belt of iran

magmatic hydrothermal evolution of the cretaceous duolong gold rich porphyry copper deposit in the bangongco metallogenic belt tibet evidence from u pb and 40ar 39ar geochronology abstract the duolong gold rich porphyry copper deposit was recently discovered and represents a giant prospect inferred resources of 4 5 mt fine cu with a grade of 0 72 cu 30 50 t fine gold with a grade of 0 23 g t au in the bangongco metallogenic belt tibet zircon shrimp and la icp ms u pb geochronology shows that the multiple porphyritic intrusions were emplaced during two episodes the first at about 121 ma bolong mineralized granodiorite porphyry bmgp and barren granodiorite porphyry bgp and the second about 116 ma duobuza mineralized granodiorite porphyry dmgp moreover the basaltic andesites also have two episodes at about 118 ma and 106 ma respectively one andesite yields an u pb zircon age of 111 9 1 9 ma indicating it formed after the multiple granodiorite porphyries by contrast the 40ar 39ar age of 115 2 1 1 ma hydrothermal k feldspar vein hosted in dmgp reveals the close temporal relationship of ore bearing potassic alteration to the emplacement of the dmgp the sericite from quartz sericite vein hosted in dmgp yields a 40ar 39ar age of 115 2 1 2 ma therefore the ore forming magmatic hydrothermal evolution probably persisted for 6 m y additionally the zircon u pb ages 106 121 ma of the volcanic rocks and the porphyries suggest that the neo tethys ocean was still subducting northward during the early cretaceous

age and depositional environment of the draa sfar massive sulfide deposit morocco the draa sfar mineralization consists of two main stratabound orebodies sidi m barek and tazacourt located north and south of the tensift river oued tessift respectively each orebody is comprised by at least two massive sulfide lenses the hosting rocks are predominantly black shales although minor rhyolitic rocks are also present in the footwall to the southern orebody shales rhyolitic volcanic rocks and massive sulfides are all included into the sarhlef series which is recognized as one of the main stratigraphic units of the moroccan variscan meseta hydrothermal activity related with an anomalous thermal gradient together with a high sedimentation rate in a tectonically driven pull apart marine basin favored the accumulation of organic rich mud in the deepest parts of the basin and the sedimentary environment suitable for massive sulfide deposition and preservation this took place by replacement of the hosting unlithified wet mud below the sediment water interface geochemical data suggest a sedimentary environment characterized by oxic water column and anoxic sediment pile with the redox boundary below the sediment water interface the low oxygen availability within the sediment pile inhibited oxidation and pyritization of pyrrhotite biostratigraphic analysis based on the palynological content of the hosting black shales restricts the age of the sulfides to the asbian substage mid mississippian this age is consistent with earlier geochronological constraints

microbial methane in the shallow paleozoic sediments and glacial deposits of illinois u s a abstract methane formed by the microbial decomposition of buried organic matter is virtually ubiquitous in the groundwaters of illinois chemical and carbon isotopic compositions are reported for gas samples collected from over 200 private and municipal water wells and from 39 small gas wells completed in glacial deposits drift gas wells carbon and hydrogen isotopic data for methane carbon dioxide and water show that these gases were formed by the carbon dioxide reduction pathway the same mechanism which has been previously shown to be responsible for microbial methane formation in the marine environment the isotopic composition of methane in these samples can be closely correlated with the chemical composition of the gas and with water chemistry the data are interpreted as indicating that isotopically very light methane is found in waters where the residence time of groundwater in the methanogenesis zone was very short relative to the methane production rate

identification of source carbon for microbial methane in unconventional gas reservoirs a method is proposed for identifying the carbon source for methane generated by carbonate reduction microbial methanogenesis using the isotopic and compositional mass balance of carbon in cogenerated carbon dioxide co2 and methane microbial methanogenesis from bitumen or petroleum generates more methane than co2 so the carbon isotopic compositions of methane and co2 are relatively heavy and similar to the carbon isotopic composition of thermogenic methane microbial methanogenesis that uses kerogen or recent organic matter as a carbon source generates relatively more co2 than methane therefore methane and co2 have the light carbon typical of shallow microbial methane this concept was quantified and tested against three literature examples to determine if the relative amount of co2 generation could be estimated with sufficient resolution to predict source carbon type and generation temperature in gas shales and coalbed methane antrim shale michigan gases are demonstrated to be derived mainly from immature bitumen in the shale at modern reservoir temperatures and cooler temperatures fruitland coal gases in the western san juan basin are derived mainly from bitumen in oil window maturity coals at modern temperature southwest indiana coal gases are derived mainly from thermally immature kerogen at modern and warmer temperatures identification of the methane carbon source and temperature helps delineate microbial methane resource fairways where fairways are limited by microbial gas generation temperatures may help determine if microbial methane is actively generated today or a relict from earlier microbial generation

microbial production and modification of gases in sedimentary basins a geochemical case study from a devonian shale gas play michigan basin an expanded data set for gases produced from the antrim shale a devonian black shale in the michigan basin united states has allowed for a detailed examination of the related chemical and isotopic compositional changes in the solid gas liquid systems that discriminate between microbial and thermogenic gas origin in the antrim shale economic microbial gas deposits are located near the basin margins where the shale has a relatively low thermal maturity and fresh water infiltrates the permeable fracture network the most compelling evidence for microbial generation is the correlation between deuterium in methane and coproduced water along the basin margins there is also a systematic enrichment in 13c of ethane and propane with decreasing concentrations that suggests microbial oxidation of these thermogenic gas components microbial oxidation accounts not only for the shift in 13c values for ethane but also in part for the geographic trend in gas composition as ethane and higher chain hydrocarbons are preferentially removed this oxidation is likely an anaerobic process involving a syntrophic relationship between methanogens and sulfate reducing bacteria the results of this study are integrated into a predictive model for microbial gas exploration based on key geochemical indicators that are present in both gas and coproduced water one unequivocal signature of microbial methanogenesis is the extremely positive carbon isotope values for both the dissolved inorganic carbon in the water and the coproduced co2 gas in contrast the 13c value of methane is of limited use in these reservoirs as the values typically fall between the commonly accepted fields for thermogenic and microbial gas in addition the confounding isotopic and compositional overprint of microbial oxidation increasing the values to typically thermogenic values may obscure the distinction between methanogenic and thermogenic gas

p t fluid deformation regime of the ediacaran serra do cavalo magro orogenic gold deposit ribeira belt brazil abstract the serra do cavalo magro orogenic gold deposit is located in the southern ribeira belt brazil gold quartz veins are hosted in calymmian 1500 1450 ma metasedimentary and metabasic rocks and ediacaran 610 600 ma granitic rocks geochronological data available in previous literature and structural petrological relationships with host rocks and shear zones indicate that the gold mineralization was formed within 580 540 ma during the late stage evolution of the brasiliano pan african orogeny related with gondwana supercontinent assembly petrological modeling indicates peak metamorphic conditions from 560 c and 7 kbar chlorite biotite phyllite to 625 c and 6 8 kbar garnet biotite phyllite recorded in immediate host rocks gold mineralization occurs in quartz shear and extensional veins structurally controlled by ne trending second and third order sinistral transcurrent shear zones the nnw trending subvertical and subhorizontal extensional veins are oriented 55 85 in relation to the fault planes indicating the shear zones were severely misoriented to frictional reactivation deformation within the shear zones was accommodated by bulging recrystallization of quartz aggregates while feldspar aggregates from the granitic protolith underwent cataclastic flow or were replaced by sericite epidote producing phyllonites gold precipitated during stages of vein deformation within microfractures in shear and extensional veins with quartz previously subjected to bulging recrystallization metamorphic ore bearing fluids are recorded in distinct assemblages of low to moderate salinities 1 18 wt nacleq h2o nacl cacl2 and h2o co2 n2 nacl cacl2 fluid inclusions and co2 n2 inclusions microthermometric data indicate entrapment conditions of 250 350 c and 0 3 2 3 kbar recording hydrostatic to supralithostatic fluid pressures in post peak metamorphic stages sharp fluid pressure fluctuations 0 4 1 6 kbar resulted from earthquake rupture events and the fault valve behavior induced circulation of fluids from distinct sources with limited partial fluid mixing favoring the gold transportation and precipitation

the dublin gulch intrusion hosted gold deposit tombstone plutonic suite yukon territory canada the dublin gulch intrusion is a member of the tombstone plutonic suite a linear belt of middle cretaceous intrusions that extend across the yukon territory like many of the intrusions in this suite the dublin gulch intrusion is associated with several different zones of gold and tungsten mineralization within and immediately adjacent to the intrusion the eagle zone 50 3 mt 0 93 g t gold located in the southwestern part of the dublin gulch intrusion hosts the most significant concentration of gold in the area the gold occurs in a broadly east west striking steeply south dipping series of sheeted veins the veins consist of early quartz scheelite pyrrhotite pyrite arsenopyrite and are associated with k feldspar albite alteration envelopes these grade out to and are overprinted by sericite carbonate chlorite alteration the same assemblage also occurs in veinlets that refracture sheeted quartz veins and contain the majority of the gold the gold occurs with molybdenite lead bismuth antimony sulfosalts galena and bismuthinite gold correlates strongly with bismuth r 2 0 9 a relationship common to several intrusion related gold deposits but has a poor correlation with all other elements tungsten and molybdenum have a weak inter element correlation r 2 0 55 and paragenetically pre date the majority of gold precipitation lead zinc copper silver antimony and arsenic have moderate to strong inter element correlations 0 58 to 0 93 the change from tungsten bearing mineralization through to gold bismuth rich ores with elevated syn to post ore lead zinc copper silver antimony and arsenic can be grossly correlated with a change in hydrothermal fluid composition early scheelite bearing quartz contains primary co2 rich fluid inclusions which are post dated by secondary inclusions with higher salinities up to 15 wt nacl equiv and less co2 these latter inclusions are interpreted to coincide with the later gold bismuth and base metal mineralization the favored genetic model is one in which early co2 rich fluids exsolved from a magma with an initially high co2 content but progressively became more saline and h2o rich as the system evolved

origin and formation of methane in groundwater of glacial origin from the cambrian vendian aquifer system in estonia abstract groundwater in the cambrian vendian aquifer system in estonia is characterised by the most depleted isotopic composition known in europe 18o down to 23 the water most likely originates from glacial meltwater recharge from the fennoscandian ice sheet in the pleistocene the aquifer system is characterised by relative high methane concentrations up to 50 of dissolved gases estimated absolute concentration up to 1600 mol l 1 the origin of which has so far remained unclear in this paper we focus on the origin of methane the factors controlling its spatial distribution and its isotope geochemistry in the aquifer system the data reveal a large spatial variability in methane concentration 13cch4 and 2hch4 values from 6 to 105 and from 220 to 420 respectively we show that local oxidation processes rather than different pathways of methane formation have affected the initial isotopic composition of methane using the least modified 13cch4 values from 85 to 105 we conclude that methane most likely originates from the organic material overridden by the fennoscandian ice shield during the late weichselian glaciation that was carried into the aquifer system with infiltrating glacial meltwater the estimated 18o values of the water where the methane was formed are 17 1 5 supporting the inference that the methane was formed during the middle weichselian interstadial the study shows that groundwater of glacial origin in the cambrian vendian aquifer system can serve as an alternative palaeoenvironmental archive to be used for studying the variations in climatic and environmental conditions in northern europe during glacial interglacial cycles of the pleistocene

dynamic model constraints on oxygen 17 depletion in atmospheric o2 after a snowball earth a large perturbation in atmospheric co2 and o2 or bioproductivity will result in a drastic pulse of 17o change in atmospheric o2 as seen in the marinoan oxygen 17 depletion mosd event in the immediate aftermath of a global deglaciation 635 mya the exact nature of the perturbation however is debated here we constructed a coupled four box and quick response biosphere atmosphere model to examine both the steady state and dynamics of the mosd event our model shows that the ultra high co2 concentrations proposed by the snowball earth hypothesis produce a typical mosd duration of less than 106 y and a magnitude of 17o depletion reaching approximately 35 both numbers are in remarkable agreement with geological constraints from south china and svalbard moderate co2 and low o2 concentration e g 3 200 parts per million by volume and 0 01 bar respectively could produce distinct sulfate 17o depletion only if postglacial marine bioproductivity was impossibly low our dynamic model also suggests that a snowball in which the ocean is isolated from the atmosphere by a continuous ice cover may be distinguished from one in which cracks in the ice permit ocean atmosphere exchange only if partial pressure of atmospheric o2 is larger than 0 02 bar during the snowball period and records of weathering derived sulfate are available for the very first few tens of thousands of years after the onset of the meltdown in any case a snowball earth is a precondition for the observed mosd event

late pleistocene human occupation of the hyperarid core in the atacama desert northern chile abstract few archeological sites in south america contain uncontroversial evidence for when the first peopling of the continent occurred largely ignored in this debate extreme environments are assumed either as barriers to this early wave of migration or without potential for past habitability here we report on a rare 12 13 ka human occupation from quebrada mani site qm12 a plantless near rainless landscape 1240 m asl and 85 km from the pacific ocean located in the hyperarid core of the atacama desert this location harbored wetlands and riparian woodlands that were fed by increased rainfall further east in the central andes during the latest pleistocene excavations at qm12 yielded a diverse cultural assemblage of lithics burned and cut bones marine gastropods pigments plant fibers and wooden artifacts alongside a prepared fireplace sixteen radiocarbon dates from site qm12 on charcoal marine shells animal dung plant remains and wood reveal that the occupation took place between 12 8 and 11 7 ka these results demonstrate that the atacama desert was not a barrier to early american settlement and dispersal and provide new clues for understanding the cultural complexity and diversity of the peopling of south america during the last glacial interglacial transition

predicting co2 occurrence on a regional scale southeast asia example abstract prediction of co 2 occurrence in natural gases is difficult owing to the interplay among basinal sources e g volcanic emanations carbonate hydrolysis and metamorphism organic diagenesis and maturation reservoir processes e g mineralogical transformations and poorly understood physicochemical phenomena e g differential solubility of gas components carbonate buffering phase segregation published approaches to assessing co 2 risk are based either on circumstantial evidence of basinal influences or statistical analysis of reservoir attributes the present study presents the results of empirical statistical and neural network analysis of co 2 abundance in natural gas and discusses potentially influential basinal and reservoir attributes to quantify risk factors for anomalous co 2 occurrences in southeast asia the results of this study indicate that tectonic setting including basement crustal age basement fault density reservoir temperature and reservoir pressure are key elements controlling co 2 abundance assignment of co 2 risk at the basin level can be roughly approximated using the results of this study more accurate assessments of co 2 risk at the basin play field and reservoir levels require more comprehensive geological and geochemical data as well as consideration of potentially influential physico chemical processes

methanogenic microbial community of the eastern paris basin potential for energy production from organic rich shales abstract shallow thermally immature organic rich shales represent considerable resources in the paris basin france we investigated the presence of methanogenic consortia i e syntrophic bacteria and methanogens in the lower toarcian paper shales formation to link geochemical and lithological properties of the rocks to the spatial distribution of microbial communities the presence of methanogenic microbial populations demonstrated via their growth in enrichment cultures occurs throughout most of the rock layers and may be explained by the transport of organics and microorganisms within the formation the enriched consortia were able to utilize the organic matter of the rock as sole carbon source in microcosm indicating a strong potential of these microbial communities for methanogenesis in situ