palaeohydrogeological insights from natural tracer profiles in aquitard porewater great artesian basin australia 1 the value of using environmental tracer profiles in aquitards to quantify fluid flux and to reveal information about palaeohydrology is largely unknown for parts of the world that were not glaciated during the cenozoic we present deep continuous vertical profiles of aquitard pore water chloride concentration and 2h 18o composition from the western margin of the great artesian basin australia where upward leakage is the dominant groundwater discharge mechanism at the deeper of the two sites studied the cl and 2h profiles exhibit a distinctive s shape which we interpret as a shift in the upper concentration boundary condition over time numerical simulations are used to support an hypothesis that the shallow phreatic aquifer was more saline and more enriched in 2h compared to current conditions prior to 120 ka followed by an extended freshening phase from 120 to 20 ka then a saline phase similar to current conditions for the last 20 ka these timeframes correspond favorably with results of previous studies into the palaeohydrology of nearby playa lake eyre at the shallower site the tracer profiles decrease exponentially with depth we explore several models for the evolution of these profiles and adopt one of long term salt input at ground surface at both sites tracer concentrations for groundwater sampled from the underlying artesian aquifer provide conclusive evidence that recharge occurred within the last 10 20 ka chloride was a more useful tracer than 2h in this study primarily due to lack of recent glaciation in central australia to provide a dynamic 2h tracer signal

arid zone groundwater recharge and salinisation processes an example from the lake eyre basin australia in arid central australia the 1 14 m km2 endorheic lake eyre basin leb experiences sporadic floods and contains saline shallow groundwater in this basin where on ground physical and chemical data are very sparse new observations of major ion chemistry stable isotopes 2h 18o 13c radiogenic isotopes 3h 14c and remote sensing modis data were used to investigate groundwater recharge and salinisation processes in 2006 2007 in january 2007 there was a large and intense local rainfall event followed by flooding to the normally dry lake eyre resulting from heavy rainfall in the northern leb that took 2 months to arrive at lake eyre groundwater chemistry from this study show no evidence of recharge from the floodwaters or the local rainfall however this does not preclude the process low transit times and low infiltrating volumes may mean that the recharge event has not yet been detected over the longer term the stable isotope chemistry indicates that groundwater is predominantly diffusely recharged during heavy local rainfall events 100 150 mm month and radiogenic isotopes reflect an older shallow groundwater efficiently mixing with recent decadal recharge the high total dissolved solids tds of regional shallow groundwater up to 52 5 g l is intrinsically linked with these recharge processes where infiltrating diffuse rainfall is evaporated and heavy rainfall events transport saline pore water saline due to evaporation in the unsaturated zone to the groundwater system the high tds of shallow groundwater beneath the dry lake eyre bed up to 322 g l is also controlled by evaporation however although evaporite minerals are prolific in the lake area the non conservative behaviour of br in pore water limits analysis of the role of halite mineral dissolution and precipitation reactions controlling groundwater salinity evaporation driven salinisation of shallow groundwater in arid central australia is distinct from the transpiration driven salinisation of groundwater in the australian murray basin located in a semi arid climate and results in relatively high groundwater salinity values compared with many other large arid zone endorheic basins across the world

preseismic hydrogen gas anomalies caused by stress corrosion process preceding earthquakes simultaneous monitoring of he h2 ar n2 ch4 and rn in gas bubbles of groundwater from the 1 500 m deep nagashima well in the active yoro fault zone central japan reveals that three microearthquakes with m 1 6 2 6 in the fault zone are accompanied and preceded by increases of h2 as is a moderately large event with m 5 4 in the same fault zone all the focal distances of the earthquakes are within 25 km no comparable anomalies were seen in the gas species other than h2 we suggest that the selective and preseimic increases of h2 in groundwater gas bubbles are geochemical signals of the earthquake nucleation process of stress corrosion mechanism aseismic slips preceding earthquakes in the active fault zone are likely to have enhanced h2 production by mechanochemical reaction of fractured rock surface with water in pre existing fault planes as groundwater conduits

incomplete retention of radiation damage in zircon from sri lanka a suite of 18 zircon gemstones from placers in the highland southwestern complex sri lanka were subjected to a comprehensive study of their radiation damages and ages the investigation included x ray diffraction raman and pl spectroscopy electron microprobe pixe and hrtem analysis as well as u th he and shrimp u th pb age determinations zircon samples described in this study are virtually homogeneous they cover the range from slightly metamict to nearly amorphous generally concordant u th pb ages averaging 555 11 ma were obtained late ordovician zircon u th he ages scattering around 443 9 ma correspond reasonably well with previously determined biotite rb sr ages for rocks from the hswc slightly to moderately metamict zircon has retained the radiogenic he whereas only strongly radiation damaged zircon calculated total fluences exceeding 3 5 10 18 events g has experienced significant he loss when compared to unannealed zircon from other localities sri lanka zircon is about half as metamict as would correspond to complete damage accumulation over a 555 m y lasting self irradiation period suggesting significant annealing of the structural radiation damage insufficient consideration of this has often resulted in significant underestimation of radiation effects in zircon we suggest to estimate effective doses for sri lanka zircon by multiplying total fluences which were calculated using the zircon u th pb age by a correction factor of 0 55 this conversion may be applied to literature data as well because all gem zircon samples from sri lanka this work and previous studies seem to reveal the same general trends of property changes depending on the radiation damage the use of effective doses for sri lanka zircon contributes to more reliable quantitative estimates of radiation effects and makes possible direct comparison between natural and synthetic radiation damaged zircon

late mio pliocene chemical weathering of the yulong porphyry cu deposit in the eastern tibetan plateau constrained by goethite u th he dating implication for asian summer monsoon abstract chemical weathering has provided a potentially important feedback between tectonic forcing and climate evolution of the asian continent although precise constraints on the timing and history of weathering are only variably documented here we use goethite u th he and 4 he 3 he geochronology to constrain the timing and rates of chemical weathering at the yulong porphyry cu deposit on the eastern tibetan plateau goethite grains have u th he ages ranging from 6 73 0 51 to 0 53 0 04 ma that correlate with independent paleoclimatic proxies inferred from supergene mn oxides and loess deposits under variable tectonic regimes and vegetation zones over the southeastern asia this correlation indicates that regional climatic conditions especially monsoonal precipitation controlled chemical weathering and goethite precipitation in a vast area of southeastern asia the goethite ages suggest that the asian summer monsoon was relatively strong from 7 to 4 6 ma but weakened between 4 6 and 4 ma and then significantly intensified from 4 to 2 ma the precipitation ages of goethites collected along a 100 m thick weathering profile decrease with depth and indicate a downward propagation of the weathering front at rates of 53 5 10 8 and 4 8 0 6 m ma during the intervals of 7 4 4 2 and 2 0 7 ma respectively the rapid propagation of weathering front during 4 2 ma was caused by abrupt lowering of the water table which was possibly related to local surface uplift or reorganization of the river systems in southeastern tibet during this period

insolation values for the climate of the last 10 million years new values for the astronomical parameters of the earth s orbit and rotation eccentricity obliquity and precession are proposed for paleoclimatic research related to the late miocene the pliocene and the quaternary they have been obtained from a numerical solution of the lagrangian system of the planetary point masses and from an analytical solution of the poisson equations of the earth moon system the analytical expansion allows the direct determination of the main frequencies with their phase and amplitude numerical and analytical comparisons with the former astronomical solution ber78 are performed so that the accuracy and the interval of time over which the new solution is valid can be estimated the corresponding insolation values have also been computed this analysis leads to the conclusion that the new values are expected to be reliable over the last 5 ma in the time domain and at least over the last 10 ma in the frequency domain

chronology of pleistocene glacial advances in the central rocky mountains the distribution and ages of moraines in the wyoming type localities for pre pinedale rocky mountain glacial deposits are not well known through morphostratigraphic mapping river terrace longitudinal profile analysis and tephrochronology we place the age of sacagawea ridge moraines in the dinwoody lakes type area at about 660 ka outwash and river terrace deposits in the bull lake type area previously considered to be sacagawea ridge are actually older by one or two glacial cycles in the bull lake type locality 15 individual moraines are divided into 4 groups on the basis of relative age criteria using 36cl 10be cosmogenic dating of boulders the two older groups must be 130 ka the younger groups are given age ranges of 130 to 100 ka and 120 to 95 ka a terrace along wind river can be morphostratigraphically traced to the youngest of these moraine groups 36cl dating of boulders on the terrace provides an age range of 125 to 100 ka the combined relative age and cosmogenic nuclide chronology is consistent with previously published evidence from yellowstone national park demonstrating that mountain glaciers advanced not only prior to and during the later portion of marine isotope stage 6 but also during marine isotope stage 5d in contrast with some other areas of the rocky mountains we found no evidence for advances during marine isotope stage 4 at bull lake pinedale moraines that have a 36cl 10be age range of 23 to 16 ka suggest that glacial advances were limited to the later part of marine isotope stage 2 a river terrace that can be traced to these moraines has an age range of 23 to 16 ka a possible glacial advance during early marine isotope stage 2 is indicated by a river terrace whose age range is estimated by incision rate modeling at 46 to 28 ka but no moraines were identified along wind river there are eight terrace levels capped with outwash that are older than sacagawea ridge although the terraces are the record of early to middle pleistocene climatic cycles there are no correlative moraines preserved at the land surface

geochemistry of some gases in hydrothermal fluids from the southern juan de fuca ridge five samples of hydrothermal fluids from two vent areas on the southern juan de fuca ridge were analyzed for dissolved gases concentrations in the end member hydrothermal fluid of h2 270 527 mol kg ch4 82 118 mol kg and co2 3920 4460 mol kg are well above values in ambient seawater and are similar to concentrations reported for other ridge crest hydrothermal systems the carbon isotopic ratios of the ch4 13c 17 8 to 20 8 and co2 13c 3 6 to 4 7 suggest that at least some of the ch4 and co2 in the fluids is basalt derived the range of 13c values for the basalt derived co2 is 6 8 to 9 7 calculated by assuming conservation of recharge co2 during hydrothermal circulation apparent temperatures of equilibration between the ch4 and the basalt derived co2 range from 640 c to 750 c small amounts of ethane c2h6 ch4 0 9 10 3 2 2 10 3 propane and butane detected in the samples may also have formed in the basalt one sample of almost pure 95 5 hydrothermal fluid contained a significant fraction up to 63 and 74 respectively of the recharge ar and n2 this suggests that the fluid has not undergone extensive vapor liquid phase separation

origin and spatial distribution of gas at seismogenic depths of the san andreas fault from drill mud gas analysis abstract data are presented on the molecular composition of drill mud gas from the lower sedimentary section 1800 3987 m of the safod san andreas fault observatory at depth main hole measured on line during drilling as well as c and h isotope data from off line mud gas samples hydrocarbons h 2 and co 2 are the most abundant non atmospheric gases in drill mud when drilling seismogenic zones gas influx into the well at depth is related to the lithology and permeability of the drilled strata larger formation gas influx was detected when drilling through organic rich shales and permeable sandstones the saf san andreas fault encountered between approximately 3100 m and 3450 m borehole depth is generally low in gas but is encompassed by two gas rich zones 2700 2900 m and below 3550 m at the fault margins with enhanced 222 rn activities and distinct gas compositions within the fault two interstratified gas rich lenses 3150 3200 m and 3310 3340 m consist of co 2 and hydrocarbons upper zone but almost exclusively of hydrocarbons lower zone the isotopic composition indicates an organic source of hydrocarbons and co 2 in the entire sedimentary section of the well hydrocarbons in sedimentary strata are partly of microbial origin down to 2500 m borehole depth the contribution of thermogenic gas increases between 2500 m and 3200 m below 3200 m hydrocarbons fully derive from thermal degradation of organic matter the lack of h 2 in the center of the fault and the high concentration of h 2 in the fractured zones at the fault margins are consistent with h 2 formation by interaction of water with fresh silica mineral surfaces generated by tectonic activities however this needs to be verified by laboratory experiments based on these studies it is concluded that the fault zone margins consist of strata with enhanced permeability separated by a low permeability fault center

late cenozoic uplift of mountain ranges and global climate change chicken or egg the high altitudes of most mountain ranges have commonly been ascribed to late cenozoic uplift without reference to when crustal thickening and other tectonic processes occurred deep incision and recent denudation of these mountain ranges abundant late cenozoic coarse sediment near them and palaeobotanical evidence for warmer climates where high mountain climates today are relatively cold have traditionally been interpreted as evidence for recent uplift an alternative cause of these phenomena is late cenozoic global climate change towards lower temperatures increased alpine glaciation a stormier climate and perturbations to humidity vegetative cover and precipitation

some observations on the origins of large volumes of carbon dioxide accumulations in sedimentary basins large volumes of carbon dioxide i e up to 90 v v have been encountered in sedimentary basins from various geological settings but their origins remain enigmatic evidence from carbon and noble gas isotope analyses indicate a variety of interpretations for the origins of the co2 including mantle degassing metamorphic reactions or magmatic processes the formation of large accumulations of large volumes of co2 in sedimentary basins is discussed with specific reference to published data from the pannonian basin hungary the cooper eromanga basin australia and the south viking graben north sea these basins have occurrences of large volumes i e over 15 v v of isotopically heavy carbon dioxide thought to be of inorganic origin and although they differ somewhat in terms of sedimentary fill all have major structural features close to the gas accumulations the available geochemical data are currently neither sufficient to confirm the specific origin s of the co2 e g mantle derived carbonate metamorphism nor unscramble co2 mixed from two or more sources ongoing studies especially those involving noble gas analyses should provide fuller answers

the siljan deep well helium isotope results the siljan ring impact structure in sweden is the scene of current deep drilling exploration for methane trapped in a crustal reservoir the initial hole drilled to a depth of 6100 m through precambrian granite has been augmented by three branching side track holes beginning at 4700 m that have extended the drilled depth to 6957 m forty four gas samples extracted from the circulating drilling fluid have been analyzed for he ne and 3he4he ratios granite chips recovered from the well and eight natural gas seeps from the siljan ring and other localities in sweden have also been analyzed to provide ambient helium comparisons the 3he4he ratios in the well gases are mixtures of three components 1 atmospheric helium dissolved in recirculated drilling fluid 2 carrier he used for well site gas chromatography that contaminated some of the samples taken for he isotope analysis and 3 a crustal radiogenic component from the granite with a 3he4he ratio of 0 015 times the atmospheric ratio 1 40 10 6 although helium concentrations are generally low throughout the hole up to 4800 ppm hydrofracturing at the termination of drilling in side track hole 3 yielded gas with 23 100 ppm of helium and the crustal isotope ratio for siljan granite fluids isotope ratios in the gas seeps are in agreement with the deep crustal value but the granite itself has lower 3he4he ratios due to preferential extraction of 3he from li bearing micas no evidence of a mantle helium component is observed in the isotopic data an upper limit calculation based on the difference between he isotope ratios in the granite and in the formation waters gives a maximum of 0 15 of more helium in the well gas helium

non conservative behavior of bromide in surface waters and brines of central andes a release into the atmosphere abstract the transfer of reactive bromine into the atmosphere was recently observed by honninger et al honninger g bobrowski n palenque e r torrez r platt u 2004 reactive bromine and sulfur emission at salar de uyuni bolivia geophys res lett 31 doi 10 1029 2003gl018818 in a large salt pan of the bolivian altiplano the salar de uyuni however bromide is considered to be an excellent conservative tracer which leads to the questioning of its actual conservation in surficial geochemical processes the relation between bromide and lithium thought to be a conservative component in waters and brines of the central andes points to a depletion of br relative to li in uyuni brines of about 50 300 kg day a flux close to that measured by honninger et al 2004 200 kg day such values are very low in regard to the size of the salar 5 30 g km 2 day salt efflorescences have a much higher surface area than a flat salt crust which should enhance the release of bromine leach solutions of salt efflorescences in closed basins of northern chile are compared to their parent waters conservative components should have the same concentration ratios in both solutions actually a strong depletion in br is observed in the leach solutions which could suggest a significant release of br from the salt into the atmosphere during the rainy season efflorescences are leached and their dissolved components brought in saline lakes and salars evaporative profiles show a slight but noticeable fractionation between li and br which could be due to the contribution of br depleted leach solutions of salt efflorescences therefore bromide does not behave conservatively in surface waters and brines of the central andes if the loss of br is really due to its transfer into the atmosphere then the flux would be much higher than that estimated for the salar de uyuni alone numerous salt pans saline lakes and widespread efflorescences covering large land surfaces would contribute significantly more reactive bromine into the atmosphere

evolution of the eastern tropical pacific through plio pleistocene glaciation a tropical pacific climate state resembling that of a permanent el nino is hypothesized to have ended as a result of a reorganization of the ocean heat budget 3 million years ago a time when large ice sheets appeared in the high latitudes of the northern hemisphere we report a high resolution alkenone reconstruction of conditions in the heart of the eastern equatorial pacific eep cold tongue that reflects the combined influences of changes in the equatorial thermocline the properties of the thermocline s source waters atmospheric greenhouse gas content and orbital variations on sea surface temperature sst and biological productivity over the past 5 million years our data indicate that the intensification of northern hemisphere glaciation 3 million years ago did not interrupt an almost monotonic cooling of the eep during the plio pleistocene sst and productivity in the eastern tropical pacific varied in phase with global ice volume changes at a dominant 41 000 year obliquity frequency throughout this time changes in the southern hemisphere most likely modulated most of the changes observed

geologic history of natural coal bed fires powder river basin usa abstract coal bed fires ignited by natural processes have baked and fused overlying sediments to form clinker a hard red or varicolored rock through much of the northern great plains of the united states usa the gently dipping coal beds in the region burn when regional downwasting brings them above the local water table the resulting clinker forms a rim along the exposed edge of the coal bed in an ongoing process through geologic time the resistant clinker is left capping buttes and ridges after the softer unbaked strata erode away clinker outcrops cover more than 4100 km2 in the powder river basin prb which lies in wyoming wy and montana mt the clinker in place records tens of billions of tons of coal that have burned releasing gases into the atmosphere the amount of clinker that has eroded away was at least an order of magnitude greater than the clinker that remains in place fission track and uranium thorium helium ages of detrital zircon crystals in clinker and paleomagnetic ages of clinker show that coal beds have burned naturally during at least the past 4 million years ma the oldest in place clinker that has been dated collected from a high isolated clinker capped ridge has a fission track age of 2 8 0 6 ma evidence of erosion and downcutting is also preserved by clinker clasts in gravel terraces one clinker boulder in a terrace 360 m above the yellowstone river has a fission track age of 4 0 0 7 ma coal bed fires are caused by lightning wildfires spontaneous combustion or human activity on coal outcrops and in mines miners government agencies and ranchers have extinguished thousands of coal bed fires but natural ignition continues where fresh coal has access to air at any given time hundreds of fires mostly small are burning in the powder river basin the total amount of coal burned by natural fires in the last 2 ma is one to two orders of magnitude greater than the total amount of coal removed by mining in the past century however current annual rates of coal mining are three to four orders of magnitude greater than estimated prehistoric annual rates of coal consumption by natural fires

anomalous hydrogen emissions from the san andreas fault observed at the cienega winery central california we began continuous monitoring of h2 concentration in soil along the san andreas and calaveras faults in central california in december 1980 using small h2 o2 fuel cell sensors ten monitoring stations deployed to date have shown that anomalous h2 emissions take place occasionally in addition to diurnal changes among the ten sites the cienega winery site has produced data that are characterized by very small diurnal changes a stable baseline and remarkably distinct spike like h2 anomalies since its installation in july 1982 a major peak appeared on 1 10 november 1982 and another on 3 april 1983 and a medium peak on 1 november 1983 the occurrences of these peaks coincided with periods of very low seismicity within a radius of 50 km from the site in order to methodically assess how these peaks are related to earthquakes three h2 degassing models were examined a plausible correlational pattern was obtained by using a model that 1 adopts a hemicircular spreading pattern of h2 along an incipient fracture plane from the hypocenter of an earthquake 2 relies on the feo h2o reaction for h2 generation and 3 relates the accumulated amount of h2 to the mass of serpentinization of underlying ophiolitic rocks the mass was tentatively assumed to be proportional to the seismic energy of the earthquake

correlation of late pleistocene glaciation in the western united states with north atlantic heinrich events a survey of the chronology of late pleistocene glaciers in the western united states indicates a record of glacier advances during the last glaciation which is more variable than that predicted by orbital forcing numerical dating of late pleistocene deposits from the puget lobe of the cordilleran ice sheet and alpine glaciers and ice caps in the rocky mountains and cascade range suggests that advances and retreats of these glaciers were in phase with episodes of growth and collapse of the laurentide ice sheet associated with the north atlantic heinrich events specifically the existing chronologies indicate that these glaciers were advancing to their terminal areas up to several thousand years before a heinrich event and retreated shortly thereafter because midlatitude glaciers respond relatively rapidly to climate change this complex record of glacial fluctuations suggests mechanisms of climate forcing in western north america that are in some way tied to heinrich events one possible mechanism involves southerly and northerly displacement of the jet stream across the western united states in response to growth and collapse of the laurentide ice sheet

empirical evidence of climate s role in rocky mountain landscape evolution 1 climate may be the dominant factor affecting landscape evolution during the late cenozoic but models that connect climate and landscape evolution cannot be tested without precise ages of landforms zircon u th he ages of clinker metamorphosed rock formed by burning of underlying coal seams provide constraints on the spatial and temporal patterns of quaternary erosion in the powder river basin of wyoming and montana the age distribution of 86 sites shows two temporal patterns 1 a bias toward younger ages because of erosion of older clinker and 2 periodic occurrence of coal fires likely corresponding with particular climatic regimes statistical t tests of the ages and spectral analyses of the age probability density function indicate that these episodes of frequent coal fires most likely correspond with times of high eccentricity in earth s orbit possibly driven by increased seasonality in the region causing increased erosion rates and coal exhumation correlation of ages with interglacial time periods is weaker the correlations between climate and coal fires improve when only samples greater than 50 km from the front of the bighorn range the site of the nearest alpine glaciation are compared together these results indicate that the interaction between upstream glaciation and downstream erosion is likely not the dominant control on quaternary landscape evolution in the powder river basin particularly since 0 5 ma instead incision rates are likely controlled by the response of streams to climate shifts within the basin itself possibly changes in local precipitation rates or frequency magnitude distributions with no discernable lag time between climate changes and landscape responses clinker ages are consistent with numerical models in which stream erosion is driven by fluctuations in stream power on thousand year timescales within the basins possibly as a result of changing precipitation patterns and is driven by regional rock uplift on million year timescales

origin and in situ concentrations of hydrocarbons in the kumano forearc basin from drilling mud gas monitoring during iodp nantroseize exp 319 abstract nantroseize exp 319 of the integrated ocean drilling program iodp was the first cruise in the history of scientific ocean drilling with drilling mud circulation through a riser drilling mud was pumped through the drill string and returned to the drill ship through the riser pipe during drilling of hole c0009a from 703 to 1604 mbsf meter below sea floor and hole enlargement from 703 to 1569 mbsf during riser drilling gas from returning drilling mud was continuously extracted sampled and analyzed in real time to reveal information on the gas composition and gas concentrations at depth hydrocarbons were the only formation derived gases identified in drilling mud and reached up to 14 vol of methane and 48 ppmv of ethane the chemical and isotopic compositions of hydrocarbons exhibit a microbial origin hydrocarbons released from drilling mud and cuttings correlate with visible allochthonous material wood lignite in drilling cuttings at greater depth addition of small but increasing amounts of hydrocarbons probably from low temperature thermal degradation of organic matter is indicated the methane content is also tightly correlated with several intervals of low poisson s ratio from vp vs observed in sonic velocity logs suggesting that the gas is situated in the pore space of the rock as free gas the gas concentrations in the formation determined from drilling mud gas monitoring reaching up to 24 lgas lsediment for methane in hole c0009a in line with gas concentrations from interpreted downhole sonic logs

chemical openness and potential for misinterpretation of the solute environment of coastal sabkhat abstract sabkha deposits in the geologic record are commonly used to interpret the environmental conditions of deposition implicit in this use is the assumption that the solute system is chemically closed that is the authigenic minerals represent the composition of the fluids in their environment of origin thermodynamic and mass balance calculations based on measurements of water and solute flux of contemporary abu dhabi coastal sabkha system however demonstrate that the system is open for sodium and chloride where nearly half of the input is lost but closed for sulfur where nearly 100 is retained sulfur and chloride isotopes were consistent with this observation if these sabkha deposits were preserved in the geologic record they would suggest a solute environment rich in sulfate and poor in chloride yet the reverse is true in most coastal sabkha environments capillary forces bring solutes and water to the surface where the water evaporates and halite carnallite sylvite and other soluble minerals are precipitated retrograde minerals such as anhydrite calcite dolomite and gypsum however precipitate and accumulate in the capillary zone beneath the surface of the coastal sabkha because they possess relatively low solubility and are below the surface these retrograde minerals are protected from dissolution and physical erosion occurring from infrequent but intense rainfall events thus they are more likely to be preserved in the geological record than highly soluble minerals formed on the surface

real time fluid analysis during drilling of the wenchuan earthquake fault scientific drilling project and its responding features abstract the wenchuan earthquake fault scientific drilling project was established shortly after the wenchuan earthquake several on site laboratories were built to perform the real time fluid analysis during drilling simultaneously the concentrations of argon methane hydrogen carbon dioxide helium nitrogen oxygen and radon in drilling mud gas were determined during the entirely process of drilling the setup for real time fluid analysis was stability for long time the mud gas such as methane and radon yielded low concentrations above the principal slip zone psz whereas yielded high concentrations under the psz the real time fluid data might provide the real time information for identifying and validating of the psz in the deep fault zone the gas concentration showed abnormal fluctuation during the ms 4 0 earthquake on april 27 2010 the abnormality occurred one hour before the earthquake and ended half an hour after the earthquake the real time fluid analysis during drilling might have captured the signal of the ms 4 0 earthquake at a quarter past six on april 27 one strong and nearest aftershock

stable isotope and hydrochemical evolution of groundwater in the semi arid hamersley basin of subtropical northwest australia summary the hamersley basin in the semi arid pilbara region of northwest australia is currently subject to increasing pressure from altered hydrology associated with mining activities as well as water abstraction for regional development sustainable water management across the region must be underpinned by an understanding of the factors that constrain water supply in arid zones we measured the amount and isotopic signature of individual rainfall events over three consecutive years 2009 2011 to determine the likely processes that control surface water pools in streams and groundwater recharge across the hamersley basin we also measured concentrations of ions in particular bromide and chloride to define and quantify sources of major recharge stable isotope composition of precipitation across the basin forms a local meteoric water line lmwl defined by the equation 2h 7 03 0 17 18o 4 78 1 45 thus the slope of the lmwl was similar to the global meteoric water line gmwl however the intercept of the lmwl was significantly different to the gmwl which is attributable to the amount or rainout effect the stable isotope composition of rainfall events was highly variable and dependent on event size however the 2h and 18o values of fresh groundwater from the alluvium and fractured aquifers were similar and characterised by a very narrow range alluvium aquifer 18o 8 02 0 83 2h 55 6 6 0 n 65 fractured aquifer 18o 8 22 0 70 2h 56 9 5 0 n 207 our findings suggest that intense rainfall events of 20 mm with limited evaporation prior to infiltration contribute most to recharge in contrast the 2h and 18o values and chemical composition of the relatively saline groundwater in the terminal fortescue marsh suggest a combination of evaporation and cyclic drying and wetting of the marsh surface prior to recharge saline groundwater samples were more 18o enriched than fresh groundwater 2h and 18o values shifted to the right of the lmwl forming a straight line with a slope of 3 58 0 20 and an intercept of 25 55 0 71 r2 0 95 p

shallow soil co2 flow along the san andreas and calaveras faults california 1 we evaluate a comprehensive soil co2 survey along the san andreas fault saf in parkfield and the calaveras fault cf in hollister california in the context of spatial and temporal variability origin and transport of co2 in fractured terrain co2 efflux was measured within grids with portable instrumentation and continuously with meteorological parameters at a fixed station in both faulted and unfaulted areas spatial and temporal variability of surface co2 effluxes was observed to be higher at faulted saf and cf sites relative to comparable background areas however 13c 23 3 to 16 4 and 14c 75 5 to 94 4 values of soil co2 in both faulted and unfaulted areas are indicative of biogenic co2 even though co2 effluxes in faulted areas reached values as high as 428 g m 2 d 1 profiles of soil co2 concentration as a function of depth were measured at multiple sites within saf and cf grids and repeatedly at two locations at the saf grid many of these profiles suggest a surprisingly high component of advective co2 flow spectral and correlation analysis of saf co2 efflux and meteorological parameter time series indicates that effects of wind speed variations on atmospheric air flow though fractures modulate surface efflux of biogenic co2 the resulting areal patterns in co2 effluxes could be erroneously attributed to a deep gas source in the absence of isotopic data a problem that must be addressed in fault zone soil gas studies

characterization of gases in sedimentary formations through monitoring during drilling and core leaching balazuc borehole deep geology of france programme abstract continuous analysis of the drilling fluids and core sampling formed a major part of the ardeche theme of the deep geology of france programme when drilling the balazuc 1 borehole in 1991 the analyses of gas concentrations in the drilling fluids are compared to those of core leaching both data sets show good agreement although higher concentrations are obtained in the drilling fluids the drilling to core ratio shows a relatively constant value these higher concentrations are due to crushing of the rock during drilling and the influence of the sediments surrounding the borehole the characterization of the gases with depth indicates 3 different zones 1 the jurassic carbonates with high ch 4 and co 2 concentrations 2 the triassic upper sandstone and middle evaporitic units with average concentrations of he co 2 n 2 and low ch 4 and 3 the triassic lower sandstone unit and the carboniferous silts with high he n 2 and low co 2 and ch 4 concentrations these trends indicate that diffusion is not a major process at balazuc and that the formations remained relatively independent from each other nitrogen and co 2 which are the main constituents show a reverse correlation the high co 2 zones are related to the carbonate formations in the hettangian carbonates a zone of black shales has preserved a high hydrocarbon content due to its very low permeability whilst in the other formations any hydrocarbons originally present have escaped the he record in the continuous measurement mainly reflects the fractured levels and the paleoporous zones this is correlated to major fluid transfer in the formations of the lower part of the borehole along the uzer fault

real time mud gas logging during drilling of the safod pilot hole in parkfield ca 1 the real time mud gas monitoring during drilling of the 2 2 km deep safod pilot hole has proved successful a nearly complete depth profile was obtained for methane radon helium and with limitations for carbon dioxide within the sedimentary section 0 768 m mud gas yielded the highest ch4 co2 and 222rn concentrations whereas he was comparably low four major gas rich zones were identified methane is a mixture of microbial and thermogenic origin mud gas concentrations of ch4 and rn are much lower in the underlying granitic rocks and the average background level of he is higher in addition to several gas rich zones two shear zones inferred from geophysical measurements are also indicated by increased mud gas concentrations gas results permit speculation that one major shear zone is hydraulically connected to the sedimentary section above up to 9 of the helium is of mantle origin which is probably a lower limit

origin of hydrogen and carbon dioxide in fault gases and its relation to fault activity gases occluded in fracture zones of active faults are characterized by a high concentration of h 2 and or co 2 a predominant gas species h 2 or co 2 is related to the lithofacies which the fault cuts carbon dioxide concentration in sediments fluctuates with temperature this evidence and sigma 13 c of co 2 about 20 suggests that co 2 originates from organic materials carbon dioxide with sigma 13 c of 5 to 17 in brecciated gneiss containing marble may have been produced by interaction between organically derived co 2 and the marble or alternatively may have been magmatically derived hydrogen usually occurs in sheared silicate rocks and its concentration fluctuates a great deal the concentration of h 2 from active faults associated with historical earthquakes usually amounts to as high as several percent in maximum whereas the concentration of h 2 from quaternary faults not associated with historical earthquakes is at most 1

constraints on paleofluid sources using the clumped isotope thermometry of carbonate veins from the safod san andreas fault observatory at depth borehole abstract the san andreas fault observatory at depth safod near parkfield california is a borehole drilled through two active deforming zones of the san andreas fault the southwest deforming zone sdz and the central deforming zone cdz these zones accommodate displacement by seismic slip and aseismic creep elevated fluid pressures and fluid rock interactions have been proposed to explain the low apparent strength and aseismic creep observed but the origin of the fluids and existence of high fluid pressures remains uncertain we use clumped isotope thermometry and 18o 13c compositions of calcite in veins to constrain the origin of paleofluids and compare these results to the isotopic composition of modern day pore fluids from the safod borehole and nearby areas we observe that 1 calcite vein temperatures vary from 81 to 134 c which overlaps the current ambient borehole temperatures of 110 115 c at sampled depths 2 vein calcite is not in carbon isotope equilibrium with modern day pore fluids 3 the 18o values of paleofluids close to the sdz and cdz calculated from vein 18o and temperature data are not in equilibrium with local modern day pore waters but approach equilibrium with modern pore waters far from these zones and 4 syntectonic vein calcite is only in c and o isotopic equilibrium with their host rocks within the sdz and cdz spatial patterns of 18o and 13c show little evidence for across fault fluid flow clumped isotope temperatures are consistent with locally derived fluid sources but not with continuous or episodic replenishment of fluids from shallow sedimentary brines or deep fluid sources our findings are compatible with flow of meteoric fluids from the southwestern damage zone into the sdz and cdz which would have favored the formation of weak phyllosilicates and contributed to the present day weakness of the two actively deforming zones

abiogenic methanogenesis in crystalline rocks isotopically anomalous ch4 rich gas deposits are found in mining sites on both the canadian and fennoscandian shields with 13cch4 values from 22 4 to 48 5 and dch4 values from 133 to 372 these methane deposits cannot be accounted for by conventional processes of bacterial or thermogenic methanogenesis compositionally the gases are similar to other ch4 rich gas occurrences found in canadian and fennoscandian shield rocks sherwood lollar et al 1993 however the isotopically anomalous gases of this study are characterized by unexpectedly high concentrations of h2 gas ranging from several volume percent up to 30 vol the h2 gases are consistently depleted in the heavy isotope with dh2 values of 619 to 659 3h 4he ratios in the range of 0 4 10 8 to 4 4 sx 10 8 indicate that there is no resolvable component of mantle derived he in these deposits based on these results a mantle derived source for the c bearing gases is unlikely several lines of evidence support an alternative abiogenic origin for the gases from sudbury canada and juuka and pori finland the d depleted h2 gas and calculated d ch4 h2 equilibration temperatures of 110 170 c at all three sites are in good agreement with results obtained for abiogenically produced ch4 and h2 in ophiolite sequences in oman and the philippines serpentinization and the hydration of ultramafic rocks are the proposed mechanisms for ch4 and h2 production in these ophiolite sequences the widespread occurrence of serpentinized and altered ultramafic rocks at juuka and at a number of other sites in both canada and finland implies that similar mechanisms may be involved in gas production at at least three sites on the shields the origin of the gases at the remaining shield sites is discussed alternative hypothesis include 1 production of the rest of the shield gases by mixing between abiogenic endmembers and bacterially generated hydrocarbon gas such as identified elsewhere on the canadian and fennoscandian shields sherwood lollar et al 1993 and 2 production of a series of isotopically distinct abiogenic ch4 endmembers at each site due to variability in the isotopic composition of available carbon sources we cannot conclusively distinguish between the alternative scenarios based on existing data however the evidence for an abiogenic ch4 endmember at at least three sites emphasizes the need for substantial revision of current theories of methanogenesis abiogenic processes of ch4 production may be considerably more widespread than previously anticipated

paleogeographic and paleotectonic setting of laramide sedimentary basins in the central rocky mountain region in the rocky mountain region between central montana and central new mexico sedimentologically isolated nonmarine basins were produced by basement deformation during the laramide orogeny within the area formerly occupied by a broad late cretaceous foreland basin in which laterally continuous marine facies had accumulated previously laramide structures of varying trend and scale reflect heterogeneity of crustal strain caused by shear between the continental lithosphere and an underlying subhorizontal slab of subducted oceanic lithosphere laramide basins include perimeter basins along the cratonic periphery of the arcuate laramide province axial basins along a north south intramontane trend and ponded basins located farther west closer to the overthrust belt twelve specific stratigraphic and sedimentologic criteria for the onset duration and termination of laramide deformation allow the chronology of basin development to be inferred independently for each basin maastrichtian initiation of laramide deformation was approximately synchronous throughout the laramide province but termination of laramide deformation was systematically diachronous from north to south between early and late eocene time widespread eocene erosion surfaces truncate syntectonic laramide sequences and are overlain by largely volcanic and volcaniclastic post laramide strata of eocene age in the north and oligocene age in the south fluvial depositional systems draining toward the great plains were dominant in perimeter and axial basins but ponded basins were occupied at times by large lakes that served as regional sediment traps paleocene drainages from ponded basins also led eastward toward the continental interior but partly interconnected lakes that developed within several ponded basins by mid eocene time were either closed hydrologically or else they drained westward into the tyee paleoriver of the pacific northwest

source of solutes to the coastal sabkha of abu dhabi an ascending brine model is proposed to address the observed isotope geochemistry solute composition and solute and water fluxes in the coastal sabkha of the emirate of abu dhabi mass balance measurements document that 95 of the solutes are derived from ascending continental brines minor amounts are derived from rainfall and from groundwater entering from up gradient areas nearly 100 of the annual water loss is from evaporation and not lateral discharge direct rainfall on the sabkha and subsequent recharge to the underlying aquifer account for 90 of the annual water input to the system the remaining 10 comes from both lateral and ascending groundwater flow thus the water and solutes in this system are from different sources solute concentrations of conservative i e nonreactive elements in the coastal sabkha covered aquifer are consistent with the fluid pore volumes of ascending brine calculated from hydrologic properties calcium to sulfate ratios and sulfur isotopes are consistent with this source of solute from the underlying tertiary formations recharging rainwater dissolves halite and other soluble minerals on the surface causing the solution to become more dense and sink to the bottom of the aquifer where it vertically mixes with less dense ascending brines solutes are returned to the surface by capillary forces and recycled or lost from the system by eolian or fluvial processes thus the system becomes vertically mixed consistent with the presence of tritium throughout the aquifer but there is essentially no horizontal mixing of seawater with groundwater the observed seawater solutes in the supratidal zone come from interstitial seawater trapped by the rapid progradation of the sediments into the arabian gulf and are not refluxed or laterally mixed the ascending brine model contrasts significantly with both the seawater flooding and evaporative pumping models previously proposed as a source of solutes to the coastal sabkha of the emirate of abu dhabi use of these earlier models leads to incorrect conclusions and raises serious questions about their applicability in the evaluation of sabkhat in the geologic record

numerical modeling of fluvial strath terrace formation in response to oscillating climate many river systems in western north america retain a fluvial strath terrace rec ord of discontinuous downcutting into bedrock through the quaternary their importance lies in their use to interpret climatic events in the headwaters and to determine long term incision rates terrace formation has been ascribed to changes in sediment supply and or water discharge produced by late quaternary climatic fluctuations we use a one dimensional channel evolution model to explore whether temporal variations in sediment and water discharge can generate terrace sequences the model includes sediment transport vertical bedrock erosion limited by alluvial cover and lateral valley wall erosion we set limits on our modeling by using data collected from the terraced wind river basin two types of experiments were performed constant period sinusoidal input histories and variable period inputs scaled by the marine 18 o rec ord our simulations indicate that strath terrace formation requires input variability that produces a changing ratio of vertical to lateral erosion rates straths are cut when the channel floor is protected from erosion by sediment and are abandoned and terraces formed when incision can resume following sediment cover thinning high sediment supply promotes wide valley floors that are abandoned as sediment supply decreases in contrast wide valleys are promoted by low effective water discharge and are abandoned as discharge increases widening of the valley floors that become terraces occurs over many thousands of years the transition from valley widening to downcutting and terrace creation occurs in response to subtle input changes affecting local divergence of sediment transport capacity formation of terraces lags by several thousand years the input changes that cause their formation our results suggest that use of terrace ages to set limits on the timing of a specific event must be done with the knowledge that the system can take thousands of years to respond to a perturbation the incision rate calculated in the field from the lowest terrace in these systems will likely be higher than the rate calculated by using older terraces because the most recent fluvial response in the field is commonly downcutting associated with declining sediment input since the last glacial maximum this apparent increase in incision rates is observed in many river systems and should not necessarily be interpreted as a response to an increase in rock uplift rate

geophysical properties within the san andreas fault zone at the san andreas fault observatory at depth and their relationships to rock properties and fault zone structure 1 we examine the relationships between borehole geophysical data and physical properties of fault related rocks within the san andreas fault as determined from data from the san andreas fault observatory at depth borehole geophysical logs cuttings data and drilling data from the region 3 to 4 km measured depth of the borehole encompass the active part of the san andreas fault the fault zone lies in a sequence of deformed sandstones siltstone shale serpentinite bearing block in matrix rocks and sheared phyllitic siltstone the borehole geophysical logs reveal the presence of a low velocity zone from 3190 to 3410 m measured depth with vp and vs values 10 30 lower than the surrounding rocks and a 1 2 m thick zone of active shearing at 3301 3303 m measured depth seven low velocity excursions with increased porosity decreased density and mud gas kick signatures are present in the fault zone geologic data on grain scale deformation and alteration are compared to borehole data and reveal weak correlations and inverse relationships to the geophysical data in places vp and vs increase with grain scale deformation and alteration and decrease with porosity in the fault zone the low velocity zone is associated with a significant lithologic and structural transition to low velocity rocks dominated by phyllosilicates and penetratively foliated sheared rocks the zone of active shearing and the regions of low sonic velocity appear to be associated with clay rich rocks that exhibit fine scale foliation and higher porosities that may be a consequence of the fault related shearing of foliated and fine grained sedimentary rocks

h2 generation by reaction between h2o and crushed rock an experimental study on h2 degassing from the active fault zone granite and quartz were crushed under moist conditions in the temperature range of 25 270 c in order to obtain the information on the mechanism operative for h2 degassing along active faults it was found that the amounts of h2 gas released by crushing granite and quartz increased with temperature up to around 200 c and then decreased suddenly the results indicate that h2 gas is generated by a chemical reaction between water and such radicals as si and si o formed on the fresh surfaces when the si o si bonds are destroyed by crushing and that the existence of a maximum for amount of h2 gas is due to the decrease of the lifetime of si o radical at the temperature higher than about 200 c the results lend credence to the possibility that h2 gas is generated in the temperature range of 25 270 c along the active fault through the reaction between groundwater and the fresh surfaces of underground rocks formed by the fault movements

distinguishing seawater from geologic brine in saline coastal groundwater using radium 226 an example from the sabkha of the uae article sabkhat salt flats are common geographic featuresof low lyingmarinecoastalareas thatdevelopunder hyper aridclimaticconditions theyare characterizedby thepresenceof highlyconcentratedsalinesolutions and evap oritic minerals and have been cited in the geologic literature as present day representations of hyper arid regional paleohydrogeology paleoclimatology coastal processes and sedimentation in the geologic record it is therefore important that a correct understanding of the origin and development of these features be achieved knowledge of the source of solutes is an important first step in understanding these features historically two theories have been advanced as to the main source of solutes in sabkha brines an early concept entailing seawa ter as the obvious source and a more recent and dynamic theory involving ascending geologic brine forced upward into the base of the sabkha by a regional hydraulic gradient in the underlying formations ra 226 coulduniquely distinguish betweenthese sourcesunder certain circumstances asitistypically present atelevat ed activity of hundreds to thousands of bq m 3 becquerels per cubic meter in subsurface formation brines at exceedingly low activities in open ocean and coastal water and not significantly supplied to water from recently formed marine sedimentary framework material the coastal marine sabkha of the emirate of abu dhabi was used to test this hypothesis the distribution of ra 226 in 70 samples of sabkha brine mean 700 bq m 3 7 sam ples of underlying deeper formation brine mean 3416 bq m 3

introduction to special section preparing for the san andreas fault observatory at depth 7209 seismology earthquake dynamics andmechanics 7230seismology seismicityandseismotectonics 8010structural geology fractures and faults citation hickman s m zoback and w ellsworth 2004 introduction to specialsection preparing for the san andreas fault observatory atdepth geophys res lett 31 l12s01 doi 10 1029 2004gl020688

pleistocene incision rates in the western united states calibrated using lava creek b tephra the lava creek b ash bed erupted from the yellowstone caldera ca 0 64 ma provides a datum for measuring long term fluvial incision west of the mississippi river the ash is widely preserved due to its substantial volume broad initial dispersal and the aggrading environment into which the ash fell drainages incised soon after lava creek b deposition isolating the ash from fluvial erosion and preserving it in fill terraces calculated rates of incision since ca 0 60 ma range from 2 to 30 cm k y 1 rates are high in most areas near the rocky mountains and downstream along rivers draining mountainous terrain and are lowest east of the high plains and along the snake river incision rates along many rivers decrease downstream rates of downcutting increased in the late pleistocene along several major rivers indicating that climate change altered sediment budgets regional and temporal data suggest that fluvial incision records increased middle and late pleistocene runoff from the southern rocky mountains rather than epeirogenic uplift but regional rock uplift cannot be excluded as a significant factor

atmospheric bromine flux from the coastal abu dhabi sabkhat a ground water mass balance investigation 1 a solute mass balance study of ground water of the 3000 km2 coastal sabkhat salt flats of the emirate of abu dhabi united arab emirates documents an annual bromide loss of approximately 255 metric tons 0 0032 gmoles or 85 kg km2 this value is an order of magnitude greater than previously published direct measurements from the atmosphere over an evaporative environment of a salar in bolivia laboratory evidence consistent with published reports suggests that this loss is by vapor transport to the atmosphere if this bromine flux to the atmosphere is representative of the total earth area of active salt flats then it is a significant and generally under recognized input to the global atmospheric bromide flux

gas geochemistry applied to earthquake prediction an overview terrestrial gases in groundwater and soil air have been extensively studied in recent years in seismically active areas especially in ussr china japan and united states in search of premonitory changes that might be useful for earthquake prediction concentrations of radon helium hydrogen mercury carbon dioxide and several other volatiles have been found generally to be anomalously high along active faults suggesting that the faults may be paths of least resistance for the terrestrial gases generated or stored in the earth to escape to the atmosphere temporal gas concentration changes with durations of a few hours to many months have been observed before many large earthquakes at a relatively small number of favorably situated stations at epicentral distances of up to several hundreds of kilometers these sensitive stations are generally located along active faults especially at intersections or bends of faults or some other structurally weak zones possibly because of tectonic strain concentration at such places however gas concentrations especially those measured at or near the ground surface may also be significantly affected by meteorological hydrological and other nontectonic changes in the environment the nontectonically induced variations must be carefully eliminated or recognized in the search of true earthquake related anomalies

origin of nitrogen rich natural gases in the california great valley evidence from helium carbon and nitrogen isotope ratios abstract dry natural gases produced from the sacramento and northern san joaquin basins contain up to 87 nitrogen 15n measurements for gases with n2 8 vary from 0 9 to 3 5 methane 13c values vary from 61 to 15 3 he 4 he ratios indicate the presence of mantle derived helium in addition to radiogenic crustal helium and suggest that the gases may originate from mixing between three principal components a hydrocarbon rich gas with 3 he 4 he 0 1r a derived from the microbial and thermogenic alteration of sedimentary organic matter a hydrocarbonrich gas with 3 he 4 he 2 75r a derived from the localized pyrolysis of sediments by magmatic volatiles and a nitrogenrich gas with 3 he 4 he 1r a the nitrogen rich component is characterized by methane 13c less negative than 25 and n 2 ar ratios as high as 22 000 nitrogen concentrations tend to increase towards the basement along the shallow eastern margin of the valley suggesting that the nitrogen rich component is derived from metasedimentary rocks deep within the crust the coast ranges fraciscan complex which was thrust well beneath the great valley during late mesozoic and early cenozoic subduction appears to be the most likely source

dating fluvial terraces with and profiles application to the wind river wyoming abstract fluvial strath terraces provide a record of river incision and the timing of climatic perturbations to the fluvial system dating depositional surfaces like terraces that are older than the range of 14 c however is difficult we employ a cosmogenic radionuclide crn profile technique that addresses a major problem of crn dating on such surfaces nuclide inheritance by measuring 10 be and 26 al profiles we constrain the exposure age and the mean crn inheritance for the deposit the crn profile also yields a self check on the assumptions underlying the method we report our attempts to date terraces along the wind river wy like many sequences of western north american fluvial terraces these are inferred to reflect oscillation between glacial and interglacial conditions in the headwaters previous dating of some of these terraces and the associated terraces and glacial deposits makes this a unique location to compare dating methods dates from five sites along the bull lake glacial correlative terrace wr 3 are 118 125 ka which agrees with dates on bull lake age moraines and independent age estimates on the terrace and is consistent with the model of terrace glacial relationship crn inheritance is significant and highly variable requiring it be considered despite the additional sampling complexity assuming all inheritance in wr 3 deposits arises during exhumation in the headwaters we obtain minimum mean rates of exhumation of 13 130 m my for the source rocks alternatively assuming the crns are inherited during clast transport the time of fluvial transport from source to terrace is 10 ka it increases downstream and is lower for sand than cobbles the crn ages for older terraces wr 7 300 ka and wr 15 510 ka are lower by 50 than previous estimates based on tephrochronology the most plausible explanation is eolian deflation of a once thicker loess cover on the terrace surfaces mean thicknesses of loess of 0 5 1 5 m are required to reconcile these concentrations of crn with the previous estimates of age difficulty in dating the older terraces emphasizes that geologic caution independent estimates of age and multiple sample sites should still be part of dating depositional surfaces with crns even when employing the inheritance correction technique

geochronology of the baye mn oxide deposit southern yunnan plateau implications for the late miocene to pleistocene paleoclimatic conditions and topographic evolution 40ar 39ar laser incremental heating analyses of supergene k mn oxides from weathering profiles at the baye mn deposit southern yunnan plateau sw china were carried out to place constraints on the timing of weathering and derive insights into local paleoclimatic and landscape evolution weathering profiles in the baye mn mine are dominated by 20 30 m thick saprolites which are locally covered by unconsolidated alluvial deposits we analyzed 70 grains from 35 hand samples collected from four sites located at distinct elevations in most cases different grains from the same hand sample and different samples from the same site have reproducible 40ar 39ar plateau ages the plateau ages of individual grains are also consistent with the respective isochron integrated and ideogram ages this age consistency attests to the reliability of the geochronological results as numerical constraints on the formation and evolution of these weathering profiles sixty four grains from 32 hand samples collected from weathering profiles at four sites a to d yield well defined plateau or pseudoplateau ages ranging from 2 98 0 07 to 0 16 ma 2 the age results show that mn oxides become progressively younger towards lower elevations samples collected from the highest elevation site 1855 m a s l have the oldest ages at 2 98 0 07 to 2 83 0 13 ma samples from intermediate elevations 1821 to 1815 m a s l yield ages ranging from 2 91 0 10 to 2 08 0 11 ma and those from the lowest sites 1768 to 1753 m a s l are younger than 1 25 0 08 ma the age versus elevation relationship indicates fast downward propagation of weathering front since the late pliocene and permits estimating the weathering rates at 3 3 3 8 6 6 1 2 and 11 1 1 9 m myr 1 during the time periods of 2 98 2 83 2 91 2 08 and 1 25 to 0 16 ma respectively the average river incision rates estimated from the surface exposed ages range from 235 10 to 416 19 m myr 1 during the past 3 million years the incision rate calculated from minimum exposed ages at sites b d is 33 2 m myr 1 for the time period of 2 91 1 25 ma which is consistent with the slow incision of streams on the ridges over the yunnan plateau since the early pleistocene three mn oxide pebbles contained in the alluvial deposits overlying the saprolite dominated weathering profiles at the two highest sites provided additional information on the timing of weathering four grains from two pebbles yield plateau ages of 6 32 0 19 to 5 27 0 10 ma whereas the other two grains from the third pebble indicate the minimum formation ages of 8 2 0 4 and 9 3 0 3 ma these ages confirm the existence of older weathering profiles now dismantled in the region manganese oxide 40ar 39ar ages of the baye deposit when combined with results from other localities indicate that lateritic weathering and supergene mn enrichment and by inference warm and humid climates conducive to intense weathering have prevailed over the plateau since the middle to late miocene the climatic conditions inferred from the weathering geochronology are consistent with multiple independent marine and terrestrial sedimentary and paleontological records confirming that supergene mn oxides can be used as a useful proxy for past climate age clusters of mn oxides at 2 9 2 4 1 2 0 8 and 0 6 0 4 ma are broadly coincident with and thus likely reflect intensification events of the indian summer monsoon that brings moisture and abundant precipitation to the yunnan plateau these clusters also coincide with the periods of significant surface uplift in the yunnan plateau demonstrating a causal link between topographic evolution plateau uplift and intensification of the monsoonal climate

orbital control climate seasonality and landscape evolution in the quaternary rocky mountains abstract while climate has long been implicated in the extensive erosion of eocene through miocene aged basin fills in the rocky mountains lack of precise high temporal density datasets of landform ages has made it difficult to detail the mechanisms by which climate increased relief a dense dataset of u th he dates from the powder river basin wyoming and montana usa indicates correspondence between elevated exhumation and peaks in orbital eccentricity here we use an atmospheric general circulation model to investigate the potential role of eccentricity in enhancing erosion in the rocky mountains we find that with high orbital eccentricity 0 05767 elevated seasonality the moving vernal equinox of perihelion mvelp 270 results in 10 100 more summer precipitation and surface runoff than low seasonality mvelp 90 under low orbital eccentricity 0 0034 precipitation and runoff changes across a precession cycle are negligible these results suggest that elevated eccentricity could indeed be associated with more intense summer precipitation and runoff which could then drive higher landscape erosion rates this finding could explain the occurrence of 100 kyr cyclicity in powder river basin landform ages and provides a clear non glacial link between climate variability and landscape evolution in the rocky mountains in this and other low to mid latitude sedimentary basins runoff volume and not glacier dynamics may be the variable that exerts primary control on landscape evolution

helium isotope variations in turkey relationship to tectonics volcanism and recent seismic activities the distribution of helium isotope ratios in the various tectonic provinces of turkey is examined through a synthesis of previously published data and the results of a recent survey along the north anatolian fault zone nafz following the catastrophic 1999 earthquakes the r ra values where r sample 3he 4he and ra air 3he 4he cover a wide range from 0 05 to 7 87 and the mantle derived helium is clearly identified in most locations the mantle derived component is high 50 of total he in a regions of central and eastern anatolia both of which are associated with historically active volcanoes and b the seismically active west to central segment of nafz while the mantle contribution reaches a maximum at nemrut volcano in eastern anatolia a region of dominantly compressional tectonics and with moderate enthalpy geothermal fields it is relatively low 50 in the western anatolian extensional province even though this region has the highest geothermal potential the average 3he enthalpy ratios estimated for the different provinces suggest lithospheric stretching and rise of the geotherm as the major mechanism of high heat flow yet limited intrusive activity in western anatolia is suggested as the reason for the comparatively low he additions and consequently low 1 7 106 atoms j 3he enthalpy ratios a more extensive magmatic activity appears to be responsible for the greater input of both heat and helium in eastern and central anatolia with intra province 3he enthalpy variations from 3 1 106 atoms j in eastern to 0 25 106 atoms j in central anatolia reflecting the ageing of hydro magmatic systems the relatively high 3he concentrations in low enthalpy waters of northern anatolia 2 8 106 atoms j are particularly significant since there is no evidence of volcanic activity associated with the strike slip motion along the seismically active segment of nafz continuous monitoring of he isotope compositions along nafz should lead to a better understanding of this apparent anomaly as well as the relationship if any between he isotope variations and seismic activities in this region

identification of pathways for hydrogen gas migration in fault zones with a discontinuous heterogeneous permeability structure and the relationship to particle size distribution of fault materials previous studies have reported that high concentrations of h2 gas are released from active fault zones experimental studies suggest that the h2 gas is derived from the reaction of water with free radicals formed when silicate minerals are fractured at hypocenter depths during fault activities however the pathways for migration of deep seated fluids to surface are still unknown in this study we performed quick multipoint h2 gas measurements across a fault zone using a portable gas monitor and a hand drill the fault zone studied includes a smectite rich fault core dividing two clearly distinguishable damage zones granite cataclasite and welded tuff fault breccia the measurements show that h2 gas emissions collected in 2 3 h sampling periods from start of measurement range from 320 3 to 446 2 ppm min in the granite cataclasite and 60 5 to 137 8 ppm min in the welded tuff fault breccias negligible quantities of h2 gas could be collected from the fault core particle size distribution analyses of fault rocks indicate that the granite cataclasite tends to be rich in particles that are finer i e less cohesive and easy to disaggregate which leads to the inference that the granite cataclasite has high permeability based on the h2 gas measurements and the particle size distribution analyses the h2 gas is considered to have migrated in permeable damage zones mostly by advection with groundwater multipoint h2 gas measurement will be effective in qualitative delineation of variations in permeability of regional structures

climate control on quaternary coal fires and landscape evolution powder river basin wyoming and montana late cenozoic stream incision and basin excavation have strongly influenced the modern rocky mountain landscape but constraints on the timing and rates of erosion are limited the geology of the powder river basin provides an unusually good opportunity to address spatial and temporal patterns of stream incision numerous coal seams in the paleocene fort union and eocene wasatch formations within the basin have burned during late cenozoic incision as coal was exposed to dry and oxygen rich near surface conditions the topography of this region is dominated by hills capped with clinker sedimentary rocks metamorphosed by burning of underlying coal beds we use u th he ages of clinker to determine times of relatively rapid erosion with the assumption that coal must be near earth s surface to burn ages of 55 in situ samples range from 0 007 to 1 1 ma clinker preferentially formed during times in which eccentricity of the earth s orbit was high times that typically but not always correlate with interglacial periods our data therefore suggest that rates of landscape evolution in this region are affected by climate fluctuations because the clinker ages correlate better with eccentricity time series than with an oxygen isotope record of global ice volume we hypothesize thatmore variations in solar insolation modulated by eccentricity have a larger impact on rates of landscape evolution in this region than do glacial interglacial cycles less