variations in the δd and δ18o compositions of illite smectites in a partly overpressured tertiary sequence from an offshore well texas gulf coast usa abstract argillaceous rocks from a partly overpressured tertiary sequence in an offshore well from the texas gulf coast show increasing illitization of illite smectites with depth of burial oxygen and hydrogen isotope analyses were performed on the illite smectite dominated 18 o with increasing illitization as would be expected from established illite smectite h 2 o isotope fractionation relationships local reversals in this trend to relatively more depleted d and enriched 18 o values do occur these reversals also appear to be coincident with the top of zones of overpressure calculation of the isotopic composition of formation water in equilibrium with the illite smectite suggests that the water in the overpressured zones was significantly more evolved i e d depleted 18 o enriched than water in the normally pressured zones water of this composition is unlikely to have been derived from smectite interlayer water released as a result of smectite dehydration or by membrane filtration in mudrocks coeval shifts in both the oxygen and hydrogen isotope compositions of the illite smectite also suggest that the dissolution of smectite and re precipitation of illite is the most likely mechanism of illitization in mudrocks

mass transfer and problems of secondary porosity creation in deeply buried hydrocarbon reservoirs abstract secondary porosity created by the post depositional leaching of detrital grains and cements can be of great economic importance the term secondary porosity is only descriptive and does not give any information on whether the porosity of the rock has been enhanced in reality there are two end member volumetric outcomes to the leaching process firstly the mineral can be completely dissolved and its components transported out of the system in such an instance the porosity of the rock will be enhanced secondly it is possible that a mineral will decompose and by product minerals will be precipitated which will occupy approximately the same volume as the original mineral the latter case is more likely where the pore waters are close to equilibrium with the majority of the minerals of the rock this will occur at elevated temperatures and or where the pore waters have been in contact with the rock for a long time these conditions are commonly met during intermediate to deep burial many metastable minerals such as high temperature feldspars probably decompose in this way a consequence of the decomposition of such metastable minerals is that primary porosity will be swapped for secondary and that older and more deeply buried rocks will contain a higher proportion of secondary porosity the mass transport equation may be used to examine the physico chemical environment where enhanced porosities most likely occur during leaching by using a simple non equilibrium mass transport model based on the silica system it is possible to demonstrate the relative importance of flow rate reaction rates specific surfaces and temperature in controlling the areal extent of leaching wide leaching zones are related to high flow rates which in turn promote a high throughput of undersaturated fluid and dispersion leaching over a wide area is also favoured by low reaction rates which will occur at low temperatures although it is true to say that less of a given silicate mineral can be dissolved by an undersaturated pore water at low temperature than at high temperature it is probable that pore fluids from deeply buried sediments are more likely to be close to equilibrium with a given mineral than for instance meteoric water thus the most likely environment for the production of widespread enhanced porosity is in the shallow subsurface the lower flow rates and higher temperatures that are encountered during deep burial diagenesis will result in far narrower more intense leaching zones as a result providing sufficient reactive mineral is present any undersaturated pore water will approach equilibrium in a short distance in order to transport undersaturated pore waters appreciable distances in the deep subsurface it is necessary to minimize their interaction with the host rock this could occur if the pore fluid were to move through a fracture system where it would interact with a far smaller surface area of reactive mineral than if it moved through the pore network

changing tectonic controls on the long term carbon cycle from mesozoic to present tectonic drivers of degassing and weathering processes are key long term controls on atmospheric co2 however there is considerable debate over the changing relative importance of different carbon sources and sinks existing geochemical models have tended to rely on indirect methods to derive tectonic drivers such as inversion of the seawater 87sr 86sr curve to estimate uplift or continental basalt area here we use improving geologic data to update the representation of tectonic drivers in the copse biogeochemical model the resulting model distinguishes co2 sinks from terrestrial granite weathering total basalt weathering and seafloor alteration it also distinguishes co2 sources from subduction zone metamorphism and from igneous intrusions we reconstruct terrestrial basaltic area from data on the extent of large igneous provinces and use their volume to estimate their contribution to degassing we adopt a recently published reconstruction of subduction related degassing and relate seafloor weathering to ocean crust creation rate revised degassing alone tends to produce unrealistically high co2 but this is counteracted by the inclusion of seafloor alteration and global basalt weathering producing a good overall fit to mesozoic cenozoic proxy co2 estimates and a good fit to 87sr 86sr data the model predicts that seafloor alteration and terrestrial weathering made similar contributions to co2 removal through the triassic and jurassic after which terrestrial weathering increased and seafloor weathering declined we predict that basalts made a greater contribution to silicate weathering than granites through the mesozoic before the contribution of basalt weathering declined over the cenozoic due to decreasing global basaltic area

re os isotope systematics and weathering of precambrian crustal rocks implications for the marine osmium isotope record the effects of weathering of freshly exposed precambrian rocks on the mobility of osmium were studied on soils developed on a chronosequence of glacial moraines from the western wind river range in wyoming the os budget of the precambrian granitoid source rocks is dominated by os rich trace phases such as magnetite amongst the major silicates biotite or a trace phase in biotite carries most of the os and re and is also the most radiogenic mineral with 187os 186os of 113 and 187re 186os of 2 000 re os isotope systematics of source rocks and soils indicate that rapid oxidation of magnetite mobilizes os with an isotopic composition similar to the isotopic composition of the bulk soils a very radiogenic fraction of os is mobilized through preferential weathering of biotite radiogenic runoff from precambrian shields inferred from osmium isotope analyses of freshwater fe mn nodules suggests that high latitude precambrian shields are important source areas of radiogenic os in seawater we propose that glacial scouring and weathering of glacial tills exposed after deglaciation of precambrian shields surrounding the north atlantic provides a mechanism for the slightly more radiogenic nature of north atlantic seawater compared to other seawater masses glacial interglacial variations in the osmium isotopic composition of seawater seem plausible and may be triggered by changes in weathering regimes on glacial interglacial time scales in high latitude shield areas surrounding the north atlantic

thermal anomalies associated with forced and free ground water convection in the dead sea rift valley the dead sea rift valley is a left lateral transform along which several rhombshaped grabens were formed at the sea of galilee which is one of these rhomb shaped grabens ambiguous heat fluxes were measured 70 80 mw m 2 at the central part of the lake 36 mw m 2 at the lake s southern coast 10 km apart and most surprising about 135 mw m 2 at the southern golan heights 6 8 km east of the graben margin a detailed geologic cross section traversing the entire sedimentary basin was constructed the hydrodynamics in this cross section were analyzed quantitatively using a two dimensional finite element code that solves the coupled variable density ground water flow and conductive convective heat transfer equations on the basis of numerical simulations different mechanisms of basin scale groundwater convection are suggested for the two sides of the rift that could influence the transport of heat 1 forced convection gravitydriven flow of hot brines from deeper aquifers to the land surface at the western side and 2 large scale free convection buoyancy driven flow of deep ground water at the eastern side the different heat fluxes within the rift valley are attributed to the different lithologies and to the locations of specific conduits through which the hot ground waters ascend from deeper horizons these simulations also explain the different salinities of the hot springs on the two sides of the rift

sandstone diagenesis in the pattani basin gulf of thailand history of water rock interaction and comparison with the gulf of mexico abstract in the pattani basin a failed rift basin extensive water rock interaction has occurred between subquartzose alluvial sandstones of miocene age and their pore fluids diagenetic rates and pathways have been strongly influenced by high geothermal gradients high co 2 fugacities and low pore water salinities depositional pore water was fresh to brackish depending on the depositional environment of the sediments chloride concentrations in modern formation water are believed primarily to reflect the proportions of river and sea water in the depositional environment however the concentration of other important solutes and the isotopic composition of the formation waters can not be explained by roportional mixing of these two end member waters dissolution of detrital plagioclase an 3 and k feldspar are reactions of major significance that are reflected chemically in the na cl and k cl ratios of the formation water despite the high temperature of the sandstones 120 200 c diagenetic albite does not occur geochemical calculations indicate the formation water is undersaturated with respect to both orthoclase and albite this style of feldspar diagenesis differs significantly from that of sandstones of similar composition in other basins and has probably influenced other aspects of silicate diagenesis important authigenic minerals are 1 locally abundant calcite cement 13 c 12 8 18 o 17 3 pdb an early diagenetic phase that formed at about 60 c 2 pore filling kaolinite 18 o 9 9 d 83 5smow that was closely associated with feldspar dissolution and formed over a range of temperatures and 3 fibrous pore lining and pore bridging illite 18 o 9 8 d 86 7 smow the last significant cement formed at temperatures of 120 to 150 c potassium argon dates on illite indicate that sandstone diagenesis took place during a period of rapid sedimentation in the first two thirds of the burial history comparison of pattani basin diagenesis with diagenesis of sandstones of similar age in other sedimentary basins demonstrates that chemical diagenesis relative to mechanical compaction has been especially rapid in the pattani basin this reflects the effect of high temperatures on reaction rates the net effect is a high average rate of porosity loss with burial 11 km

snowmelt runoff pathways in a boreal forest hillslope the role of pipe throughflow abstract on an instrumented slope of the lac laflamme basin we observed that during snowmelt season 1 the unsaturated matrix flow seems to be a negligible component of the downslope flow through the soil horizons 2 the groundwater flow from an aquifer in till a few meters thick is the major pathway for rain melt inputs and 3 when groundwater levels are high a turbulent pipe throughflow occurs at the mineral and organic soils interface gauging one of the subsurface streams showed that although its discharge is correlated and synchronized with nearby groundwater levels its hydrograph often reflected that of rain melt input according to our calculations pipe throughflow does not carry more than one fifth of the seasonal rain melt input during short periods hourly basis however it may become the main source of water input to the lake the water delivered by pipe throughflow forms a distinct 0 5 1 m thick acidic layer ph 4 4 4 8 that invades the lake just beneath the lake ice cover and is susceptible to affect the fish spawning ground

evolution of carbon cycle over the past 100 million years it is generally accepted that progressive cooling of global climate since the late cretaceous results from decreasing partial pressure of atmospheric co2 pco2 however details on how and why the carbon cycle evolved and how it would affect pco2 have not been fully resolved while the long term decline of pco2 might be caused by the decrease of volcanic degassing through the negative feedback between pco2 and silicate weathering seafloor spreading the major control of co2 degassing seems to have remained relatively constant alternative explanation known as uplift driven climate change hypothesis proposes that tectonic uplift may have enhanced the sink of atmospheric co2 by silicate weathering and thus produced the decline of pco2 however increasing weathering sink of co2 could deplete atmosphere all of its co2 within several million years while holding volcanic outgassing constant in this work major fluxes of long term carbon cycle are calculated based on a reverse model constrained by marine c sr and os isotopic records and the spreading rate of sea floor weathering of island basalt and continental silicate rocks are separated in the new model the results indicate a long term decline of island basalt weathering in consistent with the global cooling trend over the past 100 million years dramatic changes of the co2 fluxes associated continental silicate weathering reverse weathering volcanic degassing and the growth of organic carbon reservoir have been observed disturbance of atmospheric co2 cycle by these fluxes seems to be maintained by the concomitant adjustments of island basalt weathering that were sensitive to the pco2 controlled environment factors such as temperature and runoff the negative feedbacks between pco2 and weathering of island basalt might have played a significant role in stabilizing the long term carbon cycle

the influence of weathering processes on riverine magnesium isotopes in a basaltic terrain this study presents major trace element and mg isotope data for the dissolved load and suspended particulates of icelandic rivers draining dominantly basaltic catchments including both glacier fed and direct runoff rivers these samples provide the opportunity to understand the behaviour of mg isotopes during chemical weathering where variations due to lithology are not extant given the significant role of mg in the carbon cycle such variations may provide important information on the regulation of earth s climate hydrothermal waters groundwater precipitation glacial ice basalt glass olivine and representative soils have also been analysed the dissolved load shows a wide range of 26mg compositions compared to the parent basaltic glass 26mg 0 29 ranging from 0 96 to 0 64 while precipitation and hydrothermal waters possess 26mg values of 0 83 and 0 85 respectively with lower mg concentrations than the dissolved load biomass activity in vegetation and organic material in soils and rivers colloids appear to have little effect on the mg isotope compositions rather the data suggest that mg elemental and isotopic variations are largely controlled by the formation and stability of secondary phases in response to differing hydrological conditions in some samples seawater in the form of direct precipitation or glacial runoff also appears to be an important source of mg glacier fed rivers groundwaters and some direct runoff rivers with a high ph have higher 26mg than basalt which is most likely due to the incorporation of light mg isotopes in secondary minerals in contrast those direct runoff rivers which have a relatively low ph have low 26mg relative to basalt consistent with preferential incorporation of heavy mg isotopes into secondary phases although it is not possible to rule out some contribution from precipitation riverine suspended particulates are depleted in mobile elements and have 26mg compositions values both higher and lower than unweathered basalt in the glacier fed and direct runoff rivers where the 26mg of the dissolved phase is heavy due to the formation of secondary phases the suspended load is light because it contains more of those phases the opposite is true for the remainder of the direct runoff rivers which have low ph this could be due to dissolution of secondary minerals enriched in light mg which are unstable at low ph or the formation of new secondary phases

a modeling case for high atmospheric oxygen concentrations during the mesozoic and cenozoic changes in atmospheric oxygen concentration over earth history are commonly related to the evolution of animals and plants but there is no direct geochemical proxy for o2 levels meaning that estimations rely heavily on modeling approaches the results of such studies differ greatly to the extent that today s atmospheric mixing ratio of 21 might be either the highest or lowest level during the past 200 m y long term oxygen sources such as the burial in sediments of reduced carbon and sulfur species are calculated in models by representation of nutrient cycling and estimation of productivity or by isotope mass balance imb a technique in which burial rates are inferred in order to match known isotope records studies utilizing these different techniques produce conflicting estimates for paleoatmospheric o2 with nutrient weathering models estimating concentrations close to or above that of the present day and imb models estimating low o2 especially during the mesozoic here we re assess the imb technique using the copse biogeochemical model imb modelling is confirmed to be highly sensitive to assumed carbonate 13c and when this input is defined following recent compilations predicted o2 is significantly higher and in reasonable agreement with that of non imb techniques we conclude that there is no model based support for low atmospheric oxygen concentrations during the past 200 m y high mesozoic o2 is consistent with wildfire records and the development of plant fire adaptions but links between o2 and mammal evolution appear more tenuous

andean sponges reveal long term benthic ecosystem shifts following the end triassic mass extinction abstract thick cherts and cherty dolomites in the basal jurassic aramachay formation of peru preserve a thriving continental shelf community dominated by siliceous sponges that followed the end triassic collapse of metazoan rich carbonate accumulation similar hettangian and sineumurian deposits from nevada u s a austria and morocco suggest that an early jurassic siliceous sponge takeover was a widespread phenomenon that persisted for 2 m y until metazoan driven carbonate sedimentation recovered the post extinction dominance of siliceous sponges likely resulted from the confluence of metazoan carbonate reef collapse removal of incumbents and geochemical conditions that fostered the success of the siliceous sponge dominated ecosystem simple mass balance calculations suggest the siliceous sponge takeover was likely permitted by an increased silica flux as a consequence of weathering central atlantic magmatic province camp basalts the camp basalts alone could supply all the silica needed to sustain the sponge takeover although contributions were also likely from increased hot climate weathering of other silicates and possible reductions in dissolved silica demand by radiolarians detailed sedimentological fossil and microfacies analyses were conducted at six field sites across a shallow shelf system recorded in the central peruvian andes yauli dome focusing on the metazoan contribution to sedimentation sedimentary structures at all six sites demonstrated on shelf deposition similar to the underlying upper triassic chambara formation in contrast to the black shale rich facies of the aramachay formation in other areas of peru examination of up to 147 m of cherty dolomite from the aramachay formation revealed a siliceous sponge dominated ecosystem including sponge body fossils compressed in situ sponge materials and abundant transported spiculite sediments siliceous sponges mostly demosponges and rare hexactinellids account for the chert lithology and apparently dominated the local ecology for approximately two million years the role of metazoan biocalcifiers in sediment production and ecological structure was profoundly reduced compared to the under and overlying formations representing a clear ecological state shift from pre extinction carbonate to post extinction siliceous dominated ecosystems before the carbonate system recovered 2 m y after the extinction

annual volcanic carbon dioxide emission an estimate from eruption chronologies continuing interest in the effects of carbon dioxide on climate has been promoted by the exponentially increasing anthropogenic production of co2 volcanoes are also a major source of carbon dioxide but their average input to the atmosphere is generally considered minor relative to anthropogenic input this study examines eruption chronologies to determine a new estimate of the volcanic co2 input and to test if temporal fluctuations may be resolved employing representative average values of 2 7 g cm 3 as density of erupted material 0 2 wt percent co2 in the original melt 60 percent degassing during eruption and an average volume of 0 1 km3 for each of the eruptions in the recently published eruption chronology of hirschboeck 1980 a volcanic input of about 1 5 1011 moles co2 yr 1 was determined for the period 1800 1969 the period 1800 1899 had a somewhat lower input than 1900 1969 which could well be related more to completeness of observational data than to a real increase in volcanic co2 this input is well below man s current co2 production of 4 5 1014 moles co2 yr 1

the strontium isotopic budget of himalayan rivers in nepal and bangladesh abstract himalayan rivers have very unusual sr characteristics and their budget cannot be achieved by simple mixing between silicate and carbonate even if carbonates are radiogenic we present sr o and c isotopic data from river and rain water bedload and bedrock samples for the western and central nepal himalaya and bangladesh including the monsoon season central himalayan rivers receive sr from several sources carbonate and clastic tethyan sediments high himalayan crystalline hhc gneisses and granitoids with minor marbles carbonates and metasediments of the lesser himalaya lh and miocene recent foreland basin sediment from the siwaliks group and the modern flood plain in the tethyan himalaya rivers have dissolved sr 6 mol l and 87sr 86sr 0 717 with a large contribution from moderately radiogenic carbonate rivers draining hhc gneisses are very dilute with sr 0 2 mol l and 87sr 86sr 0 74 lesser himalayan streams also have low sr 0 4 mol l and are highly radiogenic 87sr 86sr 0 78 highly radiogenic carbonates of the lh do not contribute significantly to the sr budget because they are sparse and have very low sr in large rivers exiting the himalaya sr systematics can be modeled as a mixture between tethyan rivers where slightly radiogenic carbonates mean 87sr 86sr 0 715 are the main source of sr and lesser himalaya waters where extremely radiogenic silicates 0 8 are the main source of sr hhc waters are less important because of their low sr rivers draining the siwaliks foreland basin sediments have sr 4 mol l and 87sr 86sr 0 725 weathering of silicates in the siwaliks and the flood plain results in a probably significant radiogenic 0 72 0 74 input to the ganges and brahmaputra g b but quantification of this flux is limited by uncertainties in the hydrologic budget the g b in bangladesh show strong seasonal variability with low sr and high 87sr 86sr during the monsoon sr in the brahmaputra ranges from 0 9 mol l and 0 722 in march to 0 3 mol l and 0 741 in august we estimate the seasonally weighted flux from the g b to be 6 5 108 mol yr with 87sr 86sr 0 7295

biogeochemical constraints on the triassic jurassic boundary carbon cycle event 1 the end triassic mass extinctions represent one of the five most severe biotic crises in earth history yet remain one of the most enigmatic ongoing debate concerns the environmental effects of the central atlantic magmatic province camp eruptions and their linkage with the mass extinction event across the triassic jurassic boundary there is conflicting paleo evidence for changes in atmospheric pco2 during the extrusion of the camp basalts studies on sediments from european and pacific localities have however identified a substantial negative isotopic anomaly up to 3 5 across the tr j boundary providing an important indicator of changes in the operation of the ancient global carbon cycle we sought to explain the paleo evidence by utilizing a carbon cycle model for the hothouse world of the end triassic that emphasizes the chemical weathering of silicate and carbonate rocks and the ocean carbonate chemistry we find that volcanic co2 outgassing fails to fully account for either a sufficient rise in atmospheric pco2 indicated by the stomata of fossil leaves or the sedimentary isotopic fingerprint instead the scenario that best fits all of the geologic evidence is a positive feedback loop in which warming due to a buildup of volcanically derived co2 triggers destabilization of seafloor methane hydrates and the catastrophic release of ch4 palfy et al 2001 we calculate that this carbon cycle perturbation was huge involving the release of 8000 9000 gt c as co2 during the camp basaltic eruptions and 5000 gt c as ch4 in the model the initial isotopic excursion is assumed to take place over 70 kyr while complete reequilibration of the ocean atmosphere system with respect to co2 is accomplished over 700 1000 kyr our results thus provide a preliminary theoretical explanation for the bioevents estimated pco2 changes and isotopic excursions observed in marine and continental sediments at this time

method of variable bias and its application to estimating subsurface temperature a method of obtaining variable bias estimates of physical quantities from noisy and incomplete data is introduced and its application to estimating subsurface temperature is illustrated by application to temperature data from the iberia salt dome in south louisiana

landscape evolution of the five islands of south louisiana scientific policy and salt dome utilization and management abstract the five islands of south central louisiana are piercement type salt domes uplifted from several kilometers depth as the surrounding strata experiences regional subsidence in general the domes are nearly circular in plan with maximum land surface elevations 23 52 m asl geomorphic evidence of salt induced uplift includes surface lineations aligned gullies excessively steep land surface topography and shear fractures in surficial sediments evidence of subsidence includes sinkhole ponds a few hectares in area broad topographic saddles over tens of hectares in size and kilometer scale collapse structures on each of the five islands peoria loess and silty colluvium bury a paleosol developed in the late pleistocene prairie complex of the lower mississippi valley the loess represents a single genetic unit of eolian origin is typically thickest on lower side slopes and is thin or absent on ridge crests the silty colluvium around the perimeter of the islands is a reworked loess derived from higher elevations shear fractures with high angle average dips occur in both peoria loess and the prairie complex conjugate shear pairs probably develop from extensional stress associated with vertical uplift of the underlying salt prairie complex deposition and initial soil development in a low relief alluvial plain of the mississippi river predates the latest emergence of the five islands loess and colluvial stratigraphy indicate that the domes were emergent during loess deposition gully incision shearing of quaternary sediments and the distribution of colluvium indicate continued uplift after loess deposition sinkholes and collapse structures are influenced by salt dissolution and corrasion whereas broad subsidence areas and topographic saddles form over areas of structural weakness within the salt five islands landscape evolution is controlled by the interaction of driving and resisting forces that operate over various time scales diapiric uplift is a driving force of net upwards motion and the external and internal salt dome hydrology are driving forces of solution and corrasion the structure and lithology of the internal salt stocks and the surrounding sediments are heterogeneous and have variable strength collectively this interaction produces both uplift and subsidence features across the salt dome landscape resource use at the five islands correlate with instability of both underground facilities and the surface landscape uplift of the five islands has continued since at least the late pleistocene is probably still active at present and periods of tectonic and geomorphic instability are possible in the future sediments overlying salt domes record discrete periods of surface uplift and periods of episodic and incremental subsidence that is common where salt domes pierce surficial sediment the rate magnitude and pattern of landscape modification by salt domes have implications for the safe utilization of mineral extraction and geostorage facilities geomorphic evaluation of salt dome landscapes can help to develop policies that ensure safe salt dome utilization salt dome resource planning should include detailed characterization of internal and external stratigraphy and structure modeling of geomorphic soil and rock mechanic and hydrologic processes routine and emergency planning at operating facilities and closure and post closure plans

the cenozoic evolution of the strontium and carbon cycles relative importance of continental erosion and mantle exchanges the past variations of the seawater 87sr86sr isotopic ratio are related to changes in the relative contribution of the mantle sr input to the ocean and the sr supply from continental weathering recently it has been postulated that the cenozoic increase in the seawater 87sr86sr isotopic ratio was associated with the uplift of the himalayan and andean mountains at that time these orogenies may have changed the sr isotopic ratio of the continental rocks undergoing weathering as a result of extensive metamorphism increased the river flux of sr through enhanced weathering in these regions and possibly caused the global climatic cooling trend of the cenozoic a model of the major geochemical cycles coupled to an energy balance climate model is used to explore the possible causes of the mesozoic cenozoic fluctuations in the seawater 87sr86sr isotopic ratio the contribution of the mantle exchanges at mid ocean ridges of the recycling of seafloor carbonates through plate margin volcanism and of the alteration of seafloor basalts to the fluctuations of the seawater 87sr86sr isotopic ratio are studied finally this model tentatively describes the impact of the himalayan orogeny on the geochemical cycles of sr and c some possible effects of the extensive metamorphism associated with the india asia collision and of the himalayan uplift are modelled the model reproduces the cenozoic increase of the seawater 87sr86sr isotopic ratio however the impact of the himalayan orogeny on the c cycle appears to be limited and insufficient to generate the global climatic cooling of the cenozoic rather in the model the cenozoic cooling is mostly due to the reduction of the co2 emission from mid ocean ridge volcanism and to changes in the chemical weathering rates in the rest of the world excluding the himalayas

regional variations in formation water chemistry major and minor elements frio formation fluids texas 1 spatial variation of major element content na ca and cl in formation waters in the oligocene frio formation texas show that mixing occurs vertically and that the chemistry of ca rich fluids varies from northern coastal to southern texas relative amounts of major and minor elements sr mg and k in ca rich fluids from south texas differ from those in other areas of texas and also are different from updip mesozoic fluids such differences seem to preclude the known mesozoic fluids as a source of ca in the south texas frio formation fluids barring complicated nonuniform water rock alteration changing the mesozoic fluid composition approximately coast parallel and strike parallel cross sections show that ca rich fluids in the frio are usually found at depth some anomalies occur where fluids are present near piercement structures and in a relatively large part of south texas in the latter region ca rich fluids exist above the top of geopressure suggesting that they may have been emplaced before geopressure became widespread 2 3 m y ago because there are no shallow ca rich fluids in the vicinity of major river systems in south texas meteoric fluids may have flushed ca rich fluids out of the areas near the rivers during past pluvial periods this process does not preclude the dilution of formation water by clay dehydration reactions another process that has been proposed to explain deep dilute formatio waters in gulf basin reservoirs

steady state analysis of unsaturated flow above a shallow water table aquifer drained by ditches the one dimensional pressure head profile above a fixed water table was studied for different steady infiltration rates as shown in previous studies when the infiltration rate qin is less than the soil saturated hydraulic conductivity ks this profile can be divided into two parts 1 from the water table surface z0 to an elevation z the pressure head varies from 0 to a value h such as k h qin 2 above the elevation z the pressure head is constant and equal to h above the water table the zone where the pressure head is variable has been called transition zone its height is shown to be highly variable and to depend on soil properties as well as on the infiltration rate this transition zone is not the capillary fringe as defined by gillham gillham r w 1984 the capillary fringe and its effect on water table response j hydrol 67 307 324 numerical experiments performed with hydrus 2d for the case of a water table drained by parallel ditches have shown that the height of the transition zone is similar in the one dimensional profile and in the two dimensional system as long as the local slope of the water table is small this result is important since in a two dimensional system the transition zone is the place where all the horizontal component of the unsaturated flow occurs the ratio of the horizontal component of the unsaturated flow vs the total horizontal flow in both the unsaturated and saturated zones has been computed for a given soil this ratio decreases as the infiltration rate increases for a given infiltration rate the soil with the thinnest transition zone transfers the largest amount of water above the water table

textural and isotopic development of marble assemblages during the barrovian style m2 metamorphic event naxos greece a detailed petrological analysis of the marble assemblages observed within the m2 metamorphic complex on naxos is presented two distinct periods of mineral growth are documented the first is associated with prograde m2 metamorphism and the second with retrograde m2 metamorphism occurring during ductile extensional thinning of the complex the textural and miner alogical characteristics and the carbon and oxygen isotope compositions of each generation are described and the p t xco2 conditions at which these two mineral generations were stable and the compositions of the fluids present during metamorphism are characterised whereas the low variance and stable isotope compositions of prograde siliceous dolomite assemblages are consistent with internally buffered fluid evolution the retrograde mineral generation is shown to have grown as a result of the infiltration of a water rich fluid phase that transported silica al2o3 na2o and feo into the host rocks this observation together with the stable isotope compositions of the retrograde calcite and the fact that occurrences of veins of this type are limited to marbles in the highest grade areas t 600 c of the metamorphic complex suggests that the fluids responsible for vein formation were generated during the crystallisation of melts as the metamorphic complex cooled from peak temperatures the existence of this second generation of minerals has significant implications for previous studies of heat transport by fluid flow on naxos because many of the unusually low 18o compositions of pelites at high grades may be ascribable to the effects of interaction with retrograde m2 fluids rather than with prograde fluids

evolution of cenozoic seawater lithium isotopes coupling of global denudation regime and shifting seawater sinks abstract the li isotopic record of seawater shows a dramatic increase of 9 over the past 60 million years here we use a model to explore what may have caused this change we focus particularly on considering how changes in the reverse weathering sinks that remove li from seawater can contribute to explain the observed increase our interpretation is based on dividing the oceanic sink which preferentially removes light li into two components i removal into marine authigenic clays in sediments at low temperatures with associated high fractionation factors and ii removal into altered oceanic basalt at higher temperatures and resulting lower fractionation factors we suggest that increases in the flux of degraded continental material delivered to the oceans over the past 60 ma could have increased removal of li into sedimentary authigenic clays versus altered basalt because altered basalt is associated with a smaller isotopic fractionation an increasing portion of the lower temperature authigenic clay associated sink could contribute to the rise of the seawater li isotope value this effect would moderate the extent to which the isotopic value of continental inputs must have changed in order to explain the seawater record over the cenozoic nonetheless unless the magnitude of fractionation during removal differs significantly from current understanding substantial change in the li 7 of inputs from continental weathering must have occurred our modeling suggests that dissolved riverine fluxes in the early eocene were characterized by li 7 of 0 to 13 with best estimates of 6 6 12 6 these values imply increases over the past 60 myrs of between 10 and 24 and we view a 13 increase as a likely scenario these changes would have been accompanied by increases in both the dissolved li flux from continental weathering and the removal flux from seawater into marine authigenic clays increases in li 7 of continental input are consistent with a change in the global denudation regime as a result of increasing continental erosion rate through the cenozoic changes in denudation may have meant increasing climate sensitivity of weathering over time but do not require globally supply limited and thus entirely climate insensitive weathering in the early cenozoic

porosity loss fluid flow and mass transfer in limestone reservoirs application to the upper jurassic smackover formation mississippi ooid grainstones of the upper jurassic smack over formation are buried to a depth of over 6 km and exposed to temperatures in excess of 200 c at black creek field mississippi combined effects of mechanical compaction intergranular pressure solution and cementation have reduced intergranular porosity of these ooid grainstones to 0 indicating that porosity reduction has gone to completion modal analysis of 24 samples lacking preburial cements indicates that from the original 40 porosity 13 porosity units range 4 to 21 were lost by mechanical compaction 15 porosity units range 8 to 23 were reduced by intergranular pressure solution and 12 porosity units range 1 to 26 were destroyed by cementation intergranular pressure solution caused an average of 28 range 15 to 51 vertical shortening in smackover ooid grainstones under ideal conditions the 28 vertical shortening will generate enough calcium carbonate to precipitate 10 calcite cement this is close to the measured volume of cements in smackover grainstones 12 suggesting that intergranular pressure solution provided most of the calcite cement present no external sources of calcium carbonate are required fine grained samples that experienced high degrees of intergranular pressure solution and contain only small amounts of cement occur at the top of the reservoir whereas coarse grained samples with abundant cement and low degrees of pressure solution occur in the middle and basal parts of the reservoir suggesting that the fine grained intervals acted as sources and the coarse grained intervals as sinks for calcium carbonate mass transfer of pressure solution generated calcium carbonate from the top of the unit to precipitation sites in the middle and basal parts of the reservoir could have occurred by a non rayleigh type convection cell due to calcite s reverse solubility with respect to temperature the cooling upward moving limb of the convection cell would become progressively more undersaturated and hence able to transport more dissolved calcium carbonate released by intergranular pressure solution in the upper portion of the reservoir pore fluids descending in the downward moving limb of the cell would become progressively more supersaturated and calcium carbonate would tend to precipitate as cement in the middle and basal parts of the reservoir as fluids become progressively hotter

the timescale and mechanism of granulite formation at kurunegala sri lanka incipient charnockite formation at kurunegala in sri lanka is characterized by the growth of orthopyroxene at the expense of amphibole and biotite in an originally homogeneous gneiss mineral equilibria in the charnockite assemblage record pressure temperature p t conditions of 738 60 c and 6 9 1 2 kbar at 17 0 1 2 log fo2 and ah2o 0 18 0 16 wholerock trace element and isotopic measurements show that charnockite formation was accompanied by a systematic depletion of sm rb pb u sr nd with a fractionation of rb sr sm nd and th u ratios and crystallization of the charnockite assemblage at 535 5 ma major element fe mg ca and sm nd equilibration between minerals occurred at 524 9 ma whereas pb and rb sr underwent continued exchange to 501 5 ma and 486 1 ma respectively trace element data for both amphibolite and charnockite minerals show that depletion on a whole rock scale can be accounted for either by changes in mineral modes or trace element abundances within the immediate area of dehydration the fractionation of sm nd on a whole rock scale is controlled by the breakdown of amphibole without the growth of a major new host phase for sm in the charnockite rubidium and sr are dependent on the relative behaviour of biotite plagioclase and alkali feldspar modelling of dehydration melting involving the breakdown of amphibole biotite and alkali feldspar reproduces the observed sm nd and rb sr fractionation and indicates the loss of small melt fractions on a cm scale from the charnockite these observations suggest that partial melting is the most plausible means of effecting both the dehydration and depletion that accompanies charnockite formation

free thermohaline convection in sediments surrounding a salt column complex groundwater convection patterns are possible near salt domes because groundwater is subject to both lateral heat and salinity gradients in order to assess the mechanisms responsible for driving convection near salt domes we use dimensional analysis and numerical simulations to investigate coupled heat and salt transport in homogeneous sediments surrounding a cylindrical salt column the dimensional analysis does not require the boussinesq assumption the coupled heat solute and groundwater transport equations are controlled by three dimensionless parameters the rayleigh number the lewis number and the buoyancy ratio the buoyancy ratio is the ratio of salinity to temperature effects on groundwater density and it directly affects the groundwater flow equation a finite difference numerical multigridding algorithm is used to iteratively solve the coupled transport equations the multigridding technique was about 3 times faster than a point wise successive overrelaxation solution boundary conditions for the numerical simulations were adjusted to represent different contrasts in the thermal gradient between the salt and the overlying sediments the contrast in thermal gradient is parameterized by the thermal conductivity ratio and is responsible for isotherms being elevated near the salt the analysis suggests that a wide range of convective flow patterns are possible with flow occurring either up or down along the salt flank the sense of convection is dependent mainly on the value of the buoyancy ratio and how sharply isotherms are pulled up near the salt these factors in turn depend on the regional salinity variation the time since diapirism and the thermal conductivity of water saturated sediments while this analysis provides useful insight into the mechanisms driving free convection near salt domes the assumptions about medium and fluid properties may limit the applicability of dimensional analysis in simulating flow in specific geologic settings

the phanerozoic δ88 86sr record of seawater new constraints on past changes in oceanic carbonate fluxes the isotopic composition of phanerozoic marine sediments provides important information about changes in seawater chemistry in particular the radiogenic strontium isotope 87sr 86sr system is a powerful tool for constraining plate tectonic processes and their influence on atmospheric co2 concentrations however the 87sr 86sr isotope ratio of seawater is not sensitive to temporal changes in the marine strontium sr output flux which is primarily controlled by the burial of calcium carbonate caco3 at the ocean floor the sr budget of the phanerozoic ocean including the associated changes in the amount of caco3 burial is therefore only poorly constrained here we present the first stable isotope record of sr for phanerozoic skeletal carbonates and by inference for phanerozoic seawater 88 86srsw which we find to be sensitive to imbalances in the sr input and output fluxes this 88 86srsw record varies from 0 25 to 0 60 vs srm987 with a mean of 0 37 the fractionation factor between modern seawater and skeletal calcite 88 86srcc sw based on the analysis of 13 modern brachiopods mean 88 86sr of 0 176 0 016 2 standard deviations s d is 0 21 and was found to be independent of species water temperature and habitat location overall the phanerozoic 88 86srsw record is positively correlated with the ca isotope record 44 40casw but not with the radiogenic sr isotope record 87sr 86sr sw a new numerical modeling approach which considers both 88 86srsw and 87sr 86sr sw yields improved estimates for phanerozoic fluxes and concentrations for seawater sr the oceanic net carbonate flux of sr f sr carb varied between an output of 4 7x1010mol myr and an input of 2 3x1010mol myr with a mean of 1 6x1010mol myr on time scales in excess of 100myrs the f sr carb is proposed to have been controlled by the relative importance of calcium carbonate precipitates during the aragonite and calcite sea episodes on time scales less than 20myrs the f sr carb seems to be controlled by variable combinations of carbonate burial rate shelf carbonate weathering and recrystallization ocean acidification and ocean anoxia in particular the permian triassic transition is marked by a prominent positive 88 86srsw peak that reflects a significantly enhanced burial flux of sr and carbonate likely driven by bacterial sulfate reduction bsr and the related alkalinity production in deeper anoxic waters we also argue that the residence time of sr in the phanerozoic ocean ranged from 1myrs to 20myrs

kilometre scale thermohaline overturn of pore waters in the louisiana gulf coast convincing evidence exists for the large scale convection of sea water through the upper oceanic crust even at considerable distances from mid ocean ridges1 2 there has been considerable interest in verifying the existence of convective overturn of pore fluid in large sedimentary basins a mass transport process which could profoundly influence the transport of heat hydrocarbons metals and diagenetically reactive dissolved constituents3 4 the existence of fluid convection in sediments of the united states gulf coast has been inferred on the basis of the large volumes of fluid necessary to account for the observed diagenetic alteration5 and the existence of thermal anomalies that cannot be explained by simple conductive transport of heat3 6 theoretical rayleigh darcy calculations6 7 support the notion that thermally driven convection is possible here i present geochemical and physical evidence for the existence of density inversions in gulf coast pore fluids sufficient to drive large scale convective fluid flow at rates conceivably as high as metres per year the density inversions are caused in part by the dissolution of salt diapirs and the formation of dense saline brines at shallow depths

numerical analysis of seawater circulation in carbonate platforms ii the dynamic interaction between geothermal and brine reflux circulation density driven seawater circulation may occur in carbonate platforms due to geothermal heating and or reflux of water of elevated salinity in geothermal circulation lateral contrasts in temperature between seawater and platform groundwa ters warmed by the geothermal heat flux result in upward convective flow with colder seawater drawn into the platform at depth with reflux circulation platform top waters concentrated by evaporation flow downward displacing less dense underlying ground waters we have used a variable density groundwater flow model to examine the pattern magnitude and interaction of these two different circulation mechanisms for mesosaline platform top waters 50 and brines concentrated up to saturation with respect to gypsum 150 and halite 246 geothermal circulation most active around the platform margin becomes restricted and eventually shut off by reflux of brines from the platform interior towards the margin the persistence of geothermal circulation is dependent on the rate of brine reflux which is proportional to the concentration of platform top brines and also critically dependent on the magnitude and distribution of permeability low permeability evaporites can severely restrict reflux whereas high permeability units in hydraulic continuity enhance brine transport reduction in permeability with depth and anisotropy of permeability kv kh focuses flow laterally in the shallow subsurface 1 km resulting in a horizontally elongated brine plume aquifer porosity and dispersivity are relatively minor controls on reflux platform brines can entrain surficial seawater when brine generating conditions cease but the platform top remains submerged a variant of reflux we term latent reflux brines concentrated up to gypsum saturation have relatively long residence times of at least 100 times the duration of the reflux event they thus represent a long term control on post reflux groundwater circulation and conse quently on the rates and spatial patterns of shallow burial diagenesis such as dolomiti zation

geologic constraints on the glacial amplification of phanerozoic climate sensitivity the long term carbon cycle depends on many feedbacks silicate weathering consumes atmospheric co2 but is also enhanced by the increased temperatures brought about by this important greenhouse gas the long term sensitivity t2x of climate to co2 doubling modulates the strength of this negative feedback we update the model experiment of royer and others 2007 by estimating an empirical probability density function pdf of t2x for the phanerozoic by using an improved geocarbsulf carbon cycle model to predict a larger recalibrated set of proxy co2 measurements from the present day to 420 ma the new geocarbsulf parameterizes the rapid weathering of volcanic rocks relative to plutonic rocks updates to the carbon cycle model and the proxy co2 data set induce opposing model responses as a result our experiment maintains an agreement with t2x estimates based on numerical climate models and late cenozoic paleoclimate for a climate sensitivity t2x that is uniform throughout the phanerozoic the most probable value is 3 to 4 c geocarbsulf fits the proxy co2 data equally well and with far more parameter choices if t2x is amplified by at least a factor of two during the glacial intervals of the paleozoic 260 340 ma and cenozoic 0 40 ma relative to non glacial intervals of earth history for glacial amplification of two the empirical pdfs for glacial climate sensitivity predict t2x g 2 0 c with 99 percent probability t2x g 3 4 c with 95 percent probability and t2x g 4 4 c with 90 percent probability the most probable values are t2x g 6 to 8 c this result supports the notion that the response of earth9s present day surface temperature will be amplified by the millennial and longer term waxing and waning of ice sheets

water table shapes and drain flow rates in shallow drainage systems abstract a relationship between drain flow rate elevation and shape of the water table and recharge intensity in shallow drainage systems is developed from an analytical spatial integration of the boussinesq equation in transient conditions drain flow rates are shown to be the sum of three terms the first one is proportional to the maximum water table elevation and more generally to the steady state flow rate at the same water table elevation the second one is a fraction of the recharge rate of the water table depending on the water table shape the third one accounts for possible changes in water storage in the water table due to its shape changes drain flow rates in shallow drainage systems are shown to be fully predicted by one unique variable that is a function of a combination of the hydraulic conductivity k the drainable porosity f and the drain spacing 2l namely k f2l2 this variable also determines the dynamics of changes in the water table shape and in turn the respective parts of the three terms in the equation it is shown that drainage systems with values of 1 m 1 h 1 respond very fast to recharge events water table shape changes occur very quickly so that the third component of the drain flow can be neglected in that case the equation results in a simplified analytical relationship the reliability of the complete and simplified equations to predict drain flow rates in transient conditions is discussed in relation to in situ measurements

erosion of deccan traps determined by river geochemistry impact on the global climate and the 87sr 86sr ratio of seawater abstract the impact of the deccan traps on chemical weathering and atmospheric co2 consumption on earth is evaluated based on the study of major elements strontium and 87sr 86sr isotopic ratios of the main rivers flowing through the traps using a numerical model which describes the coupled evolution of the chemical cycles of carbon alkalinity and strontium and allows one to compute the variations in atmospheric pco2 mean global temperature and the 87sr 86sr isotopic ratio of seawater in response to deccan trap emplacement the results suggest that the rate of chemical weathering of deccan traps 21 63 t km2 yr and associated atmospheric co2 consumption 0 58 2 54 106 mol c km2 yr are relatively high compared to those linked to other basaltic regions our results on the deccan and available data from other basaltic regions show that runoff and temperature are the two main parameters which control the rate of co2 consumption during weathering of basalts according to the relationship f r f c 0 exp ea r 1 t 1 298 where f is the specific co2 consumption rate mol km2 yr rf is runoff mm yr c0 is a constant 1764 mol l ea represents an apparent activation energy for basalt weathering with a value of 42 3 kj mol determined in the present study r is the gas constant and t is the absolute temperature k modelling results show that emplacement and weathering of deccan traps basalts played an important role in the geochemical cycles of carbon and strontium in particular the traps led to a change in weathering rate of both carbonates and silicates in carbonate deposition on seafloor in sr isotopic composition of the riverine flux and hence a change in marine sr isotopic composition as a result deccan traps emplacement was responsible for a strong increase of atmospheric pco2 by 1050 ppmv followed by a new steady state pco2 lower than that in pre deccan times by 57 ppmv implying that pre industrial atmospheric pco2 would have been 20 higher in the absence of deccan basalts pco2 evolution was accompanied by a rapid warming of 4 c followed after 1 myr by a global cooling of 0 55 c during the warming phase continental silicate weathering is increased globally since weathering of continental silicate rocks provides radiogenic sr to the ocean the model predicts a peak in the 87sr 86sr ratio of seawater following the deccan traps emplacement the amplitude and duration of this spike in the sr isotopic signal are comparable to those observed at the cretaceous tertiary boundary the results of this study demonstrate the important control exerted by the emplacement and weathering of large basaltic provinces on the geochemical and climatic changes on earth

was the antarctic glaciation delayed by a high degassing rate during the early cenozoic abstract the cenozoic is a period of major climatic changes marked by the formation of the antarctic ice sheet at the eocene oligocene e o boundary the opening of the southern ocean seaways and the decrease in atmospheric co2 are two processes generally evoked to explain this e o cooling the debate is still ongoing but modeling studies tend to demonstrate that the decrease in atmospheric co2 is the main driver of the cooling however uncertainties persist on what drove the decrease in atmospheric co2 during the cenozoic in this study we investigate the impact of continental drift lithology distribution and volcanic degassing rates on the atmospheric carbon dioxide concentration over the cenozoic within a coupled climate carbon model geoclim in the model the continental drift results in driving low atmospheric co2 levels during the eocene and the oligocene the dispersed configuration and the location of a large continental area north africa northern south america within the inter tropical convergence zone itcz promote co2 consumption by weathering forcing co2 to remain low icehouse conditions are also promoted by the drifting of india and the weathering of the deccan basalts in the itcz during the eocene and by the weathering of the ethiopian traps during the oligocene to prevent the building up of the antarctic ice sheet at the eocene the model needs enhanced solid earth degassing flux by 50 so that atmospheric co2 levels stay above the glacial threshold 750 ppm we find that the decrease in atmospheric co2 from the eocene to the oligocene is probably due to a reduction in the source of volcanic co2 rather than an increase in silicate weathering the model results furthermore suggest that during the miocene period the northward drifting of both the african plate and india including the deccan traps might have decreased the continental surface exposed to chemical weathering therefore generating higher co2 values finally the uplift of the tibetan plateau from the miocene to the present day induces in the model an increase in silicate weathering through the intensification of the south eastern asian monsoon causing atmospheric co2 to come back to a pre industrial value

a numerical model for the formation of saline waters due to diffusion of dissolved nacl in subsiding sedimentary basins with evaporites abstract numerical modeling by a finite difference method incorporating the effects of vertical variations in pressure temperature salinity and porosity shows that mass transport by diffusion may be a major brine forming process in sedimentary basins containing halite beds vertical fluxes of dissolved nacl are greatest when the subsidence rate is slow at subsidence rates of 20 m m y 1 more than 250 m of salt can be dissolved over 150 m y at rapid subsidence rates such as 500 m m y 1 pore waters are advected downward so rapidly that although a diffusion front develops above the evaporite this front moves downward as the evaporite subsides and diffusive fluxes at shallow depths are thus low however under such conditions the pore water column becomes gravitationally unstable as a result of thermally induced density inversions and the potential for convective overturn is enhanced with accompanying advective salt flux upward although dissolution and diffusion of nacl are important processes in the burial history of evaporites they are not adequate by themselves to produce the regional salinity versus depth profiles that are actually observed in some sedimentary basins diffusion induced gradients progressively increase with depth whereas gradients actually observed in sedimentary basins tend to decrease with depth the difference is presumably due to the activity of other mass transport mechanisms such as advection convection and dispersion

modelling the phanerozoic carbon cycle and climate constraints from the 87sr 86sr isotopic ratio of seawater a numerical model describing the coupled evolution of the biogeochemical cycles of carbon sulfur calcium magnesium phosphorus and strontium has been developed to describe the long term changes of atmospheric carbon dioxide and climate during the phanerozoic the emphasis is on the effects of coupling the cycles of carbon and strontium various interpretations of the observed phanerozoic history of the seawater 87sr 86sr ratio are investigated with the model more specifically the abilities of continental weathering volcanism and surface lithology in generating that signal are tested and compared it is suggested that the observed fluctuations are mostly due to a changing weatherability over time it is shown that such a conclusion is very important for the modelling of the carbon cycle indeed it implies that the conventional belief that the evolution of atmospheric carbon dioxide and climate on a long time scale is governed by the balance between the volcanic input of co2 and the rate of silicate weathering is not true rather carbon exchanges between the mantle and the exogenic system are likely to have played a key role too further the increase of the global weathering rates with increasing surface temperature and or atmospheric co2 pressure usually postulated in long term carbon cycle and climate modelling is also inconsistent with the new model other factors appear to have modulated the weatherability of the continents through time such as mountain building and the existence of glaciers and ice sheets based on these observations a history of atmospheric carbon dioxide and climate during phanerozoic time consistent with the strontium isotopic data is reconstructed with the model and is shown to be compatible with paleoclimatic indicators such as the timing of glaciation and the estimates of cretaceous paleotemperatures

continental flood basalt weathering as a trigger for neoproterozoic snowball earth abstract atmospheric co2 levels and global climate are regulated on geological timescales by the silicate weathering feedback however this thermostat has failed multiple times in earth s history most spectacularly during the cryogenian c 720 635 ma snowball earth episodes the unique middle neoproterozoic paleogeography of a rifting low latitude supercontinent likely favored a globally cool climate due to the influence of the silicate weathering feedback and planetary albedo under these primed conditions the emplacement and weathering of extensive continental flood basalt provinces may have provided the final trigger for runaway global glaciation weathering of continental flood basalts may have also contributed to the characteristically high carbon isotope ratios 13 c of neoproterozoic seawater due to their elevated p contents in order to test these hypotheses we have compiled new and previously published neoproterozoic nd isotope data from mudstones in northern rodinia north america australia svalbard and south china and sr isotope data from carbonate rocks the nd isotope data are used to model the mafic detrital input into sedimentary basins in northern rodinia the results reveal a dominant contribution from continental flood basalt weathering during the ca 130 m y preceding the onset of cryogenian glaciation followed by a precipitous decline afterwards these data are mirrored by the sr isotope record which reflects the importance of chemical weathering of continental flood basalts on solute fluxes to the early middle neoproterozoic ocean including a pulse of unradiogenic sr input into the oceans just prior to the onset of cyrogenian glaciation hence our new data support the hypotheses that elevated rates of flood basalt weathering contributed to both the high average 13 c of seawater in the neoproterozoic and to the initiation of the first sturtian snowball earth

origin and evolution of halite based on stable isotopes δ37cl δ81br δ11b and δ7li and trace elements in tuz golu basin turkey abstract the tuz golu basin located in central anatolia contains ancient miocene and recent evaporite deposits the aim of this study is to determine the origin and evolution of the ancient halite deposits in the basin particularly whether there is a marine origin for this purpose the mineralogical geochemical and isotopic properties of halite samples taken from three different drillings at the southern part of the tuz golu basin were determined halite samples in the tuz golu basin are characterized by cl 60 20 61 00 na 39 00 39 40 and br 5 637 ppm contents the cl br ca mg2 so42 and k values and cl br 948 86428 ratios indicated that during the formation of the ancient halites in the tuz golu basin the mixture of solutions had different compositions origins and that the dissolution recrystallization and dedolomitization mechanisms were effective the 81br 37cl 7li and 11b isotopic compositions of the pure halites range from 0 06 to 0 82 0 80 to 1 28 0 70 to 30 60 and 14 70 to 11 60 respectively the low 37cl from 0 06 to 0 06 low 81br from 0 03 to 0 95 high 11b from 6 40 11 60 and high 7li from 26 00 to 30 60 values clearly indicate that the brine involved in the formation of the halites of the tuz golu basin was largely derived from seawater during the mid miocene climatic optimum mmco period additionally the cl br ca2 mg2 and so42 contents as well as the intermediate 81br 0 34 0 95 values of the tuz golu samples indicated that the origin of the ancient halites in the basin is not only a marine composition but also a mixture of solutions having different compositions ratios or origins e g seawater or saline water and groundwater fresh water

the impact of life on climate stabilization over different timescales surface life has been argued to be crucial in keeping a planet habitable in the long term biologically enhanced weathering compensates for increasing solar luminosity and temperature dependent plant productivity weakens climate perturbations furthermore a reduced calcification rate of marine organisms provides a negative feedback to rising atmospheric co2 here i present a model of the long term carbon cycle including biological enhancement of weathering and marine calcification climate oscillations of periods from thousands to millions of years arise from a simple model of mountain uplift and erosion i systematically study the influence of the biologically driven feedbacks on damping these oscillations for oscillations of periods 0 5 myr these findings are sensitive to the ratio of land to oceans however furthermore the mantle carbon degassing rate plays a role since the temperature dependence of biological primary productivity may be smaller at higher temperatures altogether life can be argued to stabilize the climate on timescales longer than some 100 kyr while details depend on the geological state of the planet

perched brine plumes above salt domes and dewatering of geopressured sediments previous studies have shown that there is a brine plume with more than 160 g l 1 total dissolved solids tds in the subsurface perched above welsh salt dome in south louisiana the occurrence of this plume has been postulated to be due to the expulsion of geopressured fluids up a fault on the flank of welsh dome the process that resulted in formation of the anomalous brine plume near welsh dome is of importance because hydrocarbon production is approximately coincident with the brine plume in map plan although in cross sections the brine plume actually occurs a few hundred meters above hydrocarbon production zones using a variable density groundwater flow model sutra we tested the hypothesis that a pulse of fluid flow up the fault could result in brine formation near the top of the dome when the permeability of the geopressured zone was very low in our simulations brine formation in the hydropressured zone occurred entirely by brine density flow and flow was downward along the fault flanking the dome above a certain threshold permeability for the geopressured zone between 10 7 darcy and 10 5 darcy in the vertical direction geopressured fluids were forced up the fault and brine formation occurred above the dome rather than on the flank brines can theoretically form above salt domes in very short geologic times 10 1 ma by expulsion of waters from the geopressured zone below but the fluid effluxes required are gigantic and appear to be unsustainable over large time intervals such as 10 ma

salinization problems in the negb results from thermohaline simulations the occurrence of salty waters close to the surface is a well known problem in the north east german basin previous numerical simulations showed that near surface brine occurrences are due to the interaction of hydrostatic and thermally induced forces mixed convection the influence of hydraulic permeabilities and thermal conductivities on the observed patterns remained an open question based on a hydro geochemical dataset thermohaline simulations are carried out in order to quantify the impact of these physical parameters on brine migration the results indicate that the salinity and temperature profiles are strongly controlled by hydraulic permeabilities and can locally be influenced by thermal conductivities

the phanerozoic carbon cycle co2 and o2 by robert a berner the phanerozoic carbon cycle co2 and o2 by robert a berner new york oxford university press 2004 158 pages 99 50 a major focus of modern earth science research has come to be upon the subject of this book by robert berner of yale university that much remains to be understood of the

geothermal convection in the tengiz carbonate platform kazakhstan reactive transport models of diagenesis and reservoir quality a fundamental challenge in carbonate reservoir characterization is predicting the spatial distribution of diagenesis we used a reactive transport model to investigate the viability of geothermal convection and associated patterns of diagenetic porosity modification in the tengiz isolated carbonate platform reservoir before burial forced convection generates significant calcite dissolution locally up to 45 toward the platform center minor calcite cementation up to 0 4 in the slope and moderate calcite dissolution and cementation up to 1 6 in serpukhovian boundstone convective cells the patterns and rates of diagenesis proved critically sensitive to specified vertical permeability after burial with 200 m 660 ft of salt modeled subsurface temperature contrasts drive platform scale free convection flow is hydraulically closed but significant dissolution up to 7 3 after 20 m y occurred in the serpukhovian and visean platform interior and minor cementation up to 0 7 occurred toward the margin a shale filled salt withdrawal basin 500 m 1640 ft deep significantly modifies the subsurface temperature distribution and free convective flow ascending groundwaters beneath the withdrawal basin created a zone of calcite dissolution up to 24 5 in 20 m y with a mushroom geometry and minor cementation up to 2 3 in 20 m y in the distal platform interior and margin rates of diagenesis are dramatically reduced with increasing overburden as compaction retards convective flow from a generic perspective free convection persists if the salt overburden is substituted with shale although flow is reversed resulting in a different distribution of diagenesis simulations of geothermal convection provide a physically viable model for the integration of direct diagenetic observations to augment predictions of reservoir quality in tengiz and other carbonate platform reservoirs

origin of an anhydrite sheath encircling a salt diapir and implications for the seismic imaging of steep sided salt structures egersund basin northern north sea the ingress of meteoric fluids into the crests of salt structures typically results in the formation of anhydrite dominated caprock the migration of connate fluids up the margins of salt structures has also been documented although the products related to this are rarely sampled in the deep subsurface we use 3d seismic reflection and borehole data to document the geometry and lithology of a salt diapir seismic data suggest that a weld is developed along the diapir stem although borehole data indicate that the stem consists of an inner c 1500 m thick halite dominated zone and an outer c 250 m thick anhydrite dominated sheath the anhydrite may have formed early in the basin history as a depositional anhydrite or crestal caprock an alternative interpretation is that the anhydrite represents lateral caprock which formed late in the basin history in response to the migration of nacl poor fluid up the margins of the diapir and dissolution of halite the possibility that lateral caprock may form adjacent to salt structures has implications for understanding the patterns and vigour of groundwater flow in sedimentary basins furthermore our study shows the margins of steep sided salt structures may be misidentified by several hundred metres if time migrated seismic reflection data are used

density driven groundwater flow near salt domes active halite dissolution occurs around numerous salt domes in louisiana forming brines with as much as 300 g l 1 tds tds total dissolved solids most of which is na and cl we numerically modeled the possible dynamics of 1 brine density flow induced by solute concentration gradients and 2 thermal convection induced by temperature gradients around hypothetical salt domes calculated maximum flow velocities due to brine density flow range from 0 01 to 1 m yr 1 even in low permeability sediments much greater than velocities due to thermal convection immense quantities of halite can be dissolved by brine density flow up to 3 km3 myr 1 and formation of brine plumes can occur very rapidly in some cases requiring 1 myr maximum flow velocities increase with bulk permeability and decrease with increasing anisotropy geopressured waters bleeding upward into the hydropressured zone may affect brine formation in the hydropressured zone provided permeability of the geopressured zone is sufficiently high

formation water geochemistry of the sverdrup basin implications for hydrocarbon development in the high arctic abstract the sverdrup basin holds significant reserves of discovered and undiscovered petroleum that have not been produced to date given its remote arctic setting loss of perennial sea ice increases the prospects for producing reserves from this region potential renewed drilling and production requires knowledge of formation water geochemistry to aid both exploration as well as regulatory development historic data shows formation waters typically have a seawater origin although there is high variability in formation water geochemistry salt diapirs lead to localized brine generation with salinities over an order of magnitude higher than average for the basin evidence also shows fresh water influx occurred along the basin margins that initiated biogenic gas generation

subduction flux modulates the geomagnetic polarity reversal rate abstract ascertaining the cause of variations in the frequency of geomagnetic polarity reversals through the phanerozoic has remained a primary research question straddling paleomagnetism and geodynamics for decades numerical models suggest the primary control on geomagnetic reversal rates on 10 to 100 ma timescales is the changing heat flux across the core mantle boundary and that this is itself expected to be strongly influenced by variations in the flux of lithosphere subducted into the mantle a positive relationship between the time dependent global subduction flux and magnetic reversal rate is expected with a time delay to transmit the thermal imprint into the lowermost mantle we perform the first test of this hypothesis using subduction flux estimates and geomagnetic reversal rate data back to the early paleozoic subduction area flux estimates are derived from global full plate tectonic models and are evaluated against independent subduction flux proxies based on the global age distribution of detrital zircons and strontium isotopes a continuous phanerozoic reversal rate model is built from pre existing compilations back to 320 ma plus a new reversal rate model in the data sparse mid to early paleozoic cross correlation of the time dependent subduction flux and geomagnetic reversal rate series reveals a significant correlation with a time delay of 120 ma with reversals trailing the subduction flux this time delay represents a value intermediate between the seismologically constrained time expected for a subducted slab to transit from the surface to the core mantle boundary 150 300 ma and the much shorter lag time predicted by some numerical models of mantle flow 30 60 ma while the reason for this large discrepancy remains unclear it is encouraging that our novel estimate of lag time represents a compromise between them although important uncertainties in our proposed relationship remain these results cast new light on the dynamic connections between the surface and deep earth and will help to constrain new models linking mantle convection the thermal evolution of the lowermost mantle and the geodynamo

cenozoic carbon cycle imbalances and a variable weathering feedback abstract the long term stability of earth s climate and the recovery of the ocean atmosphere system after carbon cycle perturbations are often attributed to a stabilizing negative feedback between silicate weathering and climate however evidence for the operation of this feedback over million year timescales and in response to tectonic and long term climatic change remains scarce for example the past 50 million years of the cenozoic era are characterized by long term cooling and declining atmospheric co2 p co 2 during this interval constant or decreasing carbon fluxes from the solid earth to the atmosphere suggest that stable or decreasing weathering fluxes are needed to balance the carbon cycle in contrast marine isotopic proxies of weathering i e 87sr 86sr 7 li and 187os 188os are interpreted to reflect increasing weathering fluxes here we evaluate the existence of a negative feedback by reconstructing the imbalance in the carbon cycle during the cenozoic using the surface inventories of carbon and alkalinity only a sustained 0 25 0 5 increase in silicate weathering is necessary to explain the long term decline in p co 2 over the cenozoic we propose that the long term decrease in p co 2 is due to an increase in the strength of the silicate weathering feedback i e the constant of proportionality between the silicate weathering flux and climate rather than an increase in the weathering flux this increase in the feedback strength which mirrors the marine isotope proxies occurs as transient 1 million year timescales remains invariant to match the long term inputs of carbon over the cenozoic this results in stable long term weathering fluxes even as p co 2 decreases we attribute increasing feedback strength to a change in the type and reactivity of rock in the weathering zone which collectively has increased the reactivity of the surface of the earth increasing feedback strength through the cenozoic reconciles mass balance in the carbon cycle with the marine isotopic proxies of weathering and may explain why there are periods when the earth system is more sensitive to carbon cycle perturbations

pipe flow in james bay coastal wetlands pipes are common along the banks of streams that drain the wetlands of the james bay coast the primary source of water to the pipes is overland flow which responds very quickly to rainfall events pipe flow therefore becomes insignificant shortly after the termination of surface runoff an assessment of the relative contributions of pipe flow and darcy s groundwater flow to a small coastal creek shows that whereas groundwater flow contributed less than 1 to summer stormflow pipes provided about 10 of stream runoff

chemical weathering response to tectonic forcing a soils perspective from the san gabriel mountains california abstract what controls the chemical weathering of soils in tectonically active landscapes recent field and modeling studies suggest that tectonic forcing and associated increases in erosion rates may either promote or hinder soil chemical weathering these competing trajectories are dependent on two primary controls the availability of fresh minerals and their residence time on the landsurface here we explore rates and extents of soil weathering in the san gabriel mountains of california where previous work has measured clear tectonic fingerprints on rates of long term exhumation hillslope erosion and landscape morphology we quantify chemical weathering across this landscape by elemental analysis of soils saprolites and bedrock on six sites that bracket the low gradient hillslopes of the relict upland plateau and the high gradient hillslopes at the margins of the tectonically driven incising landscape average chemical depletion fractions which measure weathering losses from soil relative to unweathered parent material decrease with increasing elevation and decreasing temperature reflecting a combination of climate influence and potential dust inputs from the mojave desert weathering fluxes from non dust affected sites with similar elevations climates and lithology correlate with both erosion rates and hillslope gradient on low gradient hillslopes 25 weathering intensities and rates both decrease as erosion rates increase and soils thin at the highest denudation rates 300 t km 2 y 1 saprolite production is outpaced and soils are produced directly from fractured rock these patterns are consistent with those predicted by a previously published model for denudation weathering relationships based on mineral weathering kinetics variable weathering extents in soils indicate that weathering in the sgm is largely kinetically limited this study is the first to quantify decreases in both rates and extents of soil chemical weathering with increasing erosion rates and suggests tectonic uplift in rapidly eroding and incising landscapes may not stimulate increased silicate weathering

a model for atmospheric co 2 over phanerozoic time a new model has been constructed for calculating the level of atmospheric co sub 2 over phanerozoic time which is much simpler mathematically than the blag model but more complex geologically and biologically results suggest that there has been a notable pattern of varying atmospheric co sub 2 level over the past 570 my with high levels during the mesozoic and early paleozoic and low levels during the permo carboniferous and late cenozoic sensitivity analysis shows that within reasonable limits of the principal governing parameters this qualitative trend of varying co sub 2 is relatively insensitive to the actual values chosen for these parameters causes of the co sub 2 variation are multiple and no single geological or biological process can be called upon to explain all co sub 2 variation for all time the calculated trend of co sub 2 over time agrees well with independent estimations of paleoclimates thus the greenhouse theory of paleoclimate on a long geological time scale is supported by the results of the present study

basaltic volcanism and mass extinction at the permo triassic boundary environmental impact and modeling of the global carbon cycle the siberian traps represent one of the most voluminous continental flood basalt provinces on earth the mass extinction at the end of the permian was the most severe in the history of life in the present paper these two major concurrent events that occurred are analysed and a geochemical model coupled with an energy balance model is used to calculate their environmental impact on atmospheric co2 oceanic 13c and marine anoxia the latitudinal temperature gradient is reduced relative to today resulting in warmer temperatures at high latitudes the warmer climate and the presence of fresh basaltic provinces increase the weatherability of the continental surfaces resulting in an enhanced consumption of atmospheric co2 through weathering first the eruption of the siberian traps is accompanied by a massive volume of 13c depleted co2 degassed from the mantle and added to the ocean through silicate weathering thus lowering marine 13c second the rapid collapse in productivity induces a strong decrease in the global organic carbon burial this too tends to increase the proportion of light carbon in the ocean these two effects can explain the low 13c values across the pt boundary and methane release need not be invoked to explain the 13c fluctuations it is proposed that the phosphorus cycle which drives primary production in the model plays an important role on the recovery of productivity and the 13c variations

thickness of the chemical weathering zone and implications for erosional and climatic drivers of weathering and for carbon cycle feedbacks quantitative understanding of variability in weathering fluxes on the modern earth is limited because little is known about where the most important weathering reactions take place this is partly because the locus of weathering is difficult to measure empirically inverse analysis of a parametric model presented here provides first order constraints on variability in the thickness of the zone of active weathering results suggest that the effective thickness of the weathering zone varies relatively little across several orders of magnitude of denudation rate at low to moderate denudation rates reactions in soils may dominate weathering fluxes at the catchment scale but the contribution from soil weathering decreases at higher denudation rates consequently increased erosion leads to higher weathering fluxes sustained by progressively greater contributions from weathering in bedrock the effect of climate temperature and runoff on weathering fluxes is apparently weaker at low denudation rates than at high denudation rates such that erosion and potentially associated bedrock weathering may be important for maintaining climate stabilizing feedbacks in earth s carbon cycle

modeling subsurface flow in sedimentary basins groundwater flows that arise in sedimentary basins from the effects of topographic relief buoyant convection sediment compaction erosional unloading and combinations of these driving forces can be described using quantitative modeling techniques models can be constructed to consider the effects of heat and solute transport petroleum migration and the chemical interaction of water and rocks the accuracy of model predictions however is limited by the difficulty of predicting hydrologic properties of sediments on regional dimensions estimating past conditions such as topographic relief and knowledge of how physical and chemical processes interact over gelogic time scales progress in basin modeling will accelerate as hydrologic research efforts are better integrated with those of other specialities such as sedimentology rock mechanics and geochemistry

inclusion of the weathering of volcanic rocks in the geocarbsulf model the carbon cycle model geocarbsulf is extended by dividing the weathering of silicates into volcanic and non volcanic rocks the proportion of volcanic weathering is calculated as a function of time from the oceanic record of 87sr 86sr the volcanic proportion is then used to modify the equations for calculating atmospheric co2 by the addition of a new non dimensional volcanic weathering factor the effect of uplift and physical erosion on weathering is also modified by using only the distribution over time of the abundance of sandstones and shales and not sr isotopic data that had been used previously results indicate moderate change from geocarbsulf in the distribution of atmospheric co2 over phanerozoic time this includes an increased minimum in co2 during the late ordovician in agreement with the presence of a continental glaciation at that time and a shift of maximum mesozoic values from the jurassic to the early cretaceous

analytical solutions for two dimensional groundwater flow with subsurface drainage tiles summary the tile drainage problem in an unconfined aquifer was investigated a mathematical model was established that describes two dimensional groundwater flow in an unconfined aquifer near a river with a linearized boussinesq equation time dependent sources and a sloped tile analytical solutions for groundwater level and discharge were derived and used to compare hydrologic conditions in a system with and without tile natural drainage we found that the spatial and temporal variations of groundwater level and discharge were significantly altered by the presence of drainage tile in an aquifer with tile drainage the groundwater level was lower and total groundwater discharge to the river increased compared to an aquifer with no tile application of the solutions to a synthetic case demonstrates that the analytical solutions derived can be used to quantify effect of tiles on nitrate loads in the baseflow of a river and assess the effectiveness of various conservation practices

evolution of the cenozoic carbon cycle the roles of tectonics and co2 fertilization cenozoic carbon fluxes associated with rock weathering sediment burial and volcanic degassing are calculated from the mass balance equations coupling marine isotopic records of carbon both organic and inorganic strontium and osmium the result is confirmed by the good match between modeled carbonate sedimentation rates and carbonate sedimentation rates previously integrated from ocean basins worldwide the coevolution between weathering and burial of carbonate suggests that marine carbonate accumulation was regulated mainly by the recycling of carbonate rocks which mediated the bicarbonate ion concentration of the oceans a reduction in co2 effusion to the atmosphere caused by reduced volcanic degassing from 52 to 15 ma and tectonically enhanced organic rock exhumation since 15 ma is also observed these changes in co2 effusion are balanced by concomitant changes in co2 sequestration by silicate weathering and organic carbon burial importantly we demonstrate a clear decoupling of modeled silicate weathering rates from global climate over the last 15 ma this observation is inconsistent with temperature mediated mineral dissolution acting as the key mechanism facilitating the co2 silicate weathering feedback process however we instead observe a clear coupling positive correlation between modeled silicate weathering organic carbon burial and atmospheric co2 concentration we suggest that co2 fertilization effects on terrestrial biomass productivity and plant weathering could have represented a major negative feedback process helping to balance atmospheric co2 at least during the cenozoic ice house periods

basin dewatering near salt domes and formation of brine plumes a previous study noted the occurrence of a subsurface brine plume with more than 160 g l sodium chloride perched above welsh salt dome in southwestern louisiana plumes of saline groundwaters have been reported above other gulf coast salt domes as well the u s geological survey code sutra was used to model the formation of brine plumes around a generic salt dome by basin dewatering along the flanks of the dome and also to study the gravitational instability of a brine plume initially perched above a dome in the absence of an externally impressed driving force for upwelling the simulations take into account the effect of salt concentration gradients on brine density the first set of simulations showed that a brine plume initially perched above a salt dome sank rapidly in the absence of an overpressured section where observed perched brine plumes above salt domes must therefore be either 1 young 2 ma if formed by basin dewatering and vertical fluid expulsion along the flanks of salt domes or 2 formed by a continuous mechanism the second set of simulations modeled the dewatering of a thick initially overpressured sedimentary section extending from a depth of 3 km to a depth of 10 km the deflation rate of the overpressured section profoundly depended on whether or not a permeable conduit along the flank of the dome existed which could collect water expelled radially inward to the flank of the dome from the overpressured sediments and focus it upward along the flank of the dome in most simulations the volume of compaction water was limited to only 10 of the total volume of overpressured sediment around the dome and there was an ample amount of compaction water for a perched brine plume to form in fact when a perched brine plume formed it formed very quickly in 0 01 m y after a negligible degree of deflation of the overpressured section it is conceivable that if cycles of conduit sealing and seal rupturing occurred perched brine plumes could be formed several times during deflation conditions necessary for the formation of a perched brine plume are as follows 1 waters must be focused laterally toward the dome within in the overpressured section 2 there must be a conduit of sediment with relatively high vertical permeability along the flank of the dome and 3 sediments above the dome must be more permeable than sediments along the flank of the dome for some simulations the average linear velocity of upward flow along the flanks of the dome was 3 m yr possibly of large enough magnitude to cause a thermal anomaly if perched brine plumes form by basin dewatering the thermal buoyancy effects associated with such a thermal anomaly may make the plumes rise to depths shallower than indicated in the simulations here the inability of the code sutra to simultaneously model heat and solute transport did not permit an evaluation of this

reconstructing first order changes in sea level during the phanerozoic and neoproterozoic using strontium isotopes the eustatic sea level curves published in the seventies and eighties have supported scientific advances in the earth sciences and the emergence of sequence stratigraphy as an important hydrocarbon exploration tool however validity of reconstructions of eustatic sea level based on sequence stratigraphic correlations has remained controversial proposed sea level curves differ because of site to site changes in local tectonics depositional rates and long wavelength dynamic topography resulting from mantle convection in particular the overall amplitude of global phanerozoic long term sea level is poorly constrained and has been estimated to vary between 400 m above present day sea level to 50 m below present day sea level to improve estimates of past sea level we explore an alternative methodology to estimate global sea level change we utilise the phanerozoic neoproterozoic 87sr 86sr record which at first order represents the mix of inputs from continental weathering and from mantle input by volcanism by compensating for weathering with estimates of runoff from a 3d climate model geoclimtec a corrected 87sr 86sr record can be obtained that solely reflects the contribution of strontium from mantle sources at first order the flux of strontium from the mantle through time is due to increases and decreases in the production of oceanic crust through time therefore the changing levels of mantle derived strontium can be used as a proxy for the production of oceanic lithosphere by applying linear oceanic plate age distributions we compute sea level and continental flooded area curves we find that our curves are generally within the range of previous curves built on classical approaches a phanerozoic first order cyclicity of 250 myr is observed that may extend into the neoproterozoic the low frequency i e on the order of 10 to 100 my sea level curve that we propose while open for improvement may be used as baseline for refined sequence stratigraphic studies at a global and basin scale

influence of slope on subsurface drainage of hillsides hillside drainage was investigated using numerical solutions to the two dimensional form of the richards equation for combined unsaturated and saturated flow the objectives of the study were to examine the influence of slope on drain flow rates and water table depths in the center regions of sloping hillsides solutions were obtained for slopes 135 m long containing parallel drains spaced 30 m apart and located l m below the surface in 3 and 7 m deep profiles drainage under steady infiltration and for transient conditions was simulated on slopes of up to 0 40 m m using two soils small slopes 0 15 m m were found to have little effect on drain flow rates and water table depths in the center of the region indicating that drainage theory developed for flat land can be used for interior parallel drains on these slopes

evidence for co2 infiltration in granulite facies marbles from lofoten vesteralen norway abstract lofoten vesteralen comprises an amphibolite to granulite facies terrain metamorphosed in the granulite facies at 1 8 ga amphibolite facies marbles retain close to premetamorphic carbon and oxygen isotopic signatures 13 c 10 pdb 18 o 26 smow the margins of marbles near the amphibolite granulite transition and granulite facies marbles show large shifts to much lighter carbon and oxygen to 13 c 7 pdb and 18 o 10 smow these shifts imply exchange with a co 2 bearing fluid large co 2 rock weight ratios were achieved in granulite facies marbles and this could reflect large scale infiltration of co 2 into the granulite facies crust the occurrence of carbonic metamorphism in at least some granulite terrains could be a reflection of high mantle co 2 degassing rates in the precambrian or the recycling of carbon in a subduction related environment

mechanisms driving groundwater flow near salt domes groundwater flow near salt domes is complex because groundwater is subject to a variety of driving forces including the release of geopressured fluids large lateral density gradients and regional hydraulic head gradients the complexity of this environment is born out by recent geochemical and geophysical observations that indicate the occurrence of upward groundwater flow near some salt domes in order to evaluate the relative importance of different mechanisms driving groundwater flow near salt domes the authors have developed a numerical model that couples groundwater flow heat transport and transport of dissolved salt and accounts for salt diapirism the calculations indicate that upward groundwater flow can occur as the result of thermal convection when the regional background salinity is greater than 15 weight percent a value typical of many areas of the south louisiana salt dome province for lower background salinities dissolution causes salt laden groundwater near the dome to sink leading to depressed isotherms while the release of geopressured fluids is difficult to quantify it remains a likely mechanism for driving upward groundwater flow near some salt domes

geocarbsulf a combined model for phanerozoic atmospheric o2 and co2 abstract a model for the combined long term cycles of carbon and sulfur has been constructed which combines all the factors modifying weathering and degassing of the geocarb iii model berner r a kothavala z 2001 geocarb iii a revised model of atmospheric co2 over phanerozoic time am j sci 301 182 204 for co2 with rapid recycling and oxygen dependent carbon and sulfur isotope fractionation of an isotope mass balance model for o2 berner r a 2001 modeling atmospheric o2 over phanerozoic time geochim cosmochim acta 65 685 694 new isotopic data for both carbon and sulfur are used and new feedbacks are created by combining the models sensitivity analysis is done by determining 1 the effect on weathering rates of using rapid recycling rapid recycling treats carbon and sulfur weathering in terms of young rapidly weathering rocks and older more slowly weathering rocks 2 the effect on o2 of using different initial starting conditions 3 the effect on o2 of using different data for carbon isotope fractionation during photosynthesis and alternative values of oceanic 13c for the past 200 million years 4 the effect on sulfur isotope fractionation and on o2 of varying the size of o2 feedback during sedimentary pyrite formation 5 the effect on o2 of varying the dependence of organic matter and pyrite weathering on tectonic uplift plus erosion and the degree of exposure of coastal lands by sea level change 6 the effect on co2 of adding the variability of volcanic rock weathering over time berner r a 2006 inclusion of the weathering of volcanic rocks in the geocarbsulf model am j sci 306 in press results show a similar trend of atmospheric co2 over the phanerozoic to the results of geocarb iii but with some differences during the early paleozoic and for variable volcanic rock weathering lower co2 values during the mesozoic atmospheric oxygen shows a major broad late paleozoic peak with a maximum value of about 30 o2 in the permian a secondary less broad peak centered near the silurian devonian boundary variation between 15 and 20 o2 during the cambrian and ordovician a very sharp drop from 30 to 15 o2 at the permo triassic boundary and a more or less continuous rise in o2 from the late triassic to the present

on the role of chemical weathering of continental arcs in long term climate regulation a case study of the peninsular ranges batholith california usa abstract the long term stability of atmospheric pco2 is dominantly determined by the balance between the rate of co2 input from magmatic metamorphic degassing and the efficiency of co2 uptake by silicate weathering via eventual precipitation as marine carbonate and by organic carbon burial silicate weathering is thought to represent a negative feedback to changes in atmospheric pco2 the late cretaceous early cenozoic was characterized by elevated atmospheric pco2 and greenhouse climate widely thought to be due to increased magmatic flux from mid ocean ridges flood basalts and continental arcs of interest here is the role of continental arcs in modulating long term atmospheric co2 contents and climate continental arc magmatism is accompanied by rapid uplift and erosion due to magmatic tectonic thickening of the crust thus the development of continental arcs might also enhance the global efficiency of silicate weathering in turn increasing the efficiency of carbon sequestration to assess the contribution of continental arcs to global carbon sinks we conducted a case study in the cretaceous peninsular ranges batholith prb and associated forearc basin in southern california usa representing one segment of a mesozoic circum pacific continental arc system arc magmatism occurred between 170 85 ma peaking at 100 ma erosion occurred during magmatism and continued well into the early eocene with forearc sediments representing the products of this protracted unroofing of the arc by calculating the depletion of ca in forearc sediments relative to their arc protoliths we estimate chemical weathering fluxes in equivalent co2 to be 106 mol km 2 yr 1 near the end of magmatism decreasing to 105 mol km 2 yr 1 by the early eocene integrated over the entire magmatic and post magmatic history of the batholith the total amount of co2 consumed through chemical weathering is comparable to that degassed however during magmatism the regional degassing flux exceeds the regional weathering flux even though the efficiency of weathering is increased due to magmatic and tectonic uplift after magmatism ends continued erosion from remnant topography causes the arc to transition into a net regional sink increasing the global efficiency of chemical weathering and amplifying cooling after magmatism ends understanding how atmospheric co2 and climate vary over long timescales requires an understanding of how magmatic orogenies enhance degassing but also increase the strength of the global silicate weathering feedback

modelling investigation of water partitioning at a semiarid ponderosa pine hillslope the effects of vegetation root distribution on near surface water partitioning can be two fold on the one hand the roots facilitate deep percolation by root induced macropore flow on the other hand they reduce the potential for deep percolation by root water uptake processes whether the roots impede or facilitate deep percolation depends on various conditions including climate soil and vegetation characteristics this paper examines the effects of root distribution on deep percolation into the underlying permeable bedrock for a given soil profile and climate condition using hydrus modelling the simulations were based on previously field experiments on a semiarid ponderosa pine pinus ponderosa hillslope an equivalent single continuum model for simulating root macropore flow on hillslopes is presented with root macropore hydraulic parameterization estimated based on observed root distribution the sensitivity analysis results indicate that the root macropore effect dominates saturated soil water flow in low conductivity soils kmatrix below 10 7 m s while it is insignificant in soils with a kmatrix larger than 10 5 m s consistent with observations in this and other studies at the ponderosa pine site the model with simple rootmacropore parameterization reasonably well reproduces soil moisture distribution and some major runoff events the results indicate that the clay rich soil layer without root induced macropores acts as an impeding layer for potential groundwater recharge this impeding layer results in a bedrock percolation of less than 1 of the annual precipitation without this impeding layer percolation into the underlying permeable bedrock could be as much as 20 of the annual precipitation this suggests that at a surface with low permeability soil overlying permeable bedrock the root penetration depth in the soil is critical condition for whether or not significant percolation occurs copyright 2010 john wiley sons ltd

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

siberian gas venting and the end permian environmental crisis abstract the end of the permian period is marked by global warming and the biggest known mass extinction on earth the crisis is commonly attributed to the formation of the siberian traps large igneous province although the causal mechanisms remain disputed we show that heating of tunguska basin sediments by the ascending magma played a key role in triggering the crisis our conclusions are based on extensive field work in siberia in 2004 and 2006 heating of organic rich shale and petroleum bearing evaporites around sill intrusions led to greenhouse gas and halocarbon generation in sufficient volumes to cause global warming and atmospheric ozone depletion basin scale gas production potential estimates show that metamorphism of organic matter and petroleum could have generated 100 000 gt co2 the gases were released to the end permian atmosphere partly through spectacular pipe structures with kilometre sized craters dating of a sill intrusion by the u pb method shows that the gas release occurred at 252 0 0 4 million years ago overlapping in time with the end permian global warming and mass extinction heating experiments to 275 c on petroleum bearing rock salt from siberia suggests that methyl chloride and methyl bromide were significant components of the erupted gases the results indicate that global warming and ozone depletion were the two main drivers for the end permian environmental crisis we demonstrate that the composition of the heated sedimentary rocks below the flood basalts is the most important factor in controlling whether a large igneous provinces causes an environmental crisis or not we propose that a similar mechanism could have been responsible for the triassic jurassic 200 ma global warming and mass extinction based on the presence of thick sill intrusions in the evaporite deposits of the amazon basin in brazil

field scale modeling of subsurface tile drained soils using an equivalent medium approach research conducted for the last 35 years has shown that subsurface drainage has a significant impact on hydrology and contaminant transport this can be observed at the field scale and also at the watershed scale impacts are always associated with modifying otherwise natural flow paths most computer model representations of drainage have been drawn at the field scale these models require relatively precise data that are usually unavailable when simulating hydrology and water quality in large watersheds we believe that in this case drainage representation should be simplified and yet closely match observations as a first step towards incorporating drainage systems into large scale hydrological models we propose an equivalent representation of drains buried in a soil profile by using a homogeneous anisotropic porous medium without drains this representation is based on a self consistent approach and on geometrical considerations simplification is such that calculating the equivalent hydraulic conductivity requires only information on the main length and spacing of the tile drains and not on their precise location this approach also provides a much simpler discretisation of the domain because of the absence of internal boundary conditions on the drainage pipes compared to other methods that have simplified drainage representation in existing watershed models it requires no parameter fitting two alternatives to the method are presented in the first one the soil profile equipped with the actual drain pipes is represented by an equivalent horizontally layered system with no pipes in the second the layered system has been replaced with an equivalent homogeneous profile the efficiency of these approaches was tested against a classical representation of tile drains using the swms 3d code which solves the richards equation for a typical drained plot configuration the equivalent medium approach appears to give satisfying results for global water outflow and mean water table elevation

origin and evolution of formation waters from oil fields on the norwegian shelf abstract stable isotopes of h and o and chemical analyses of formation waters from upper triassic jurassic clastic reservoirs and cretaceous carbonate reservoirs offshore norway are employed to interpret the origin and evolution of these waters in both types of reservoir the formation waters become progressively enriched in total dissolved solids and the heavy isotope of o with increasing depth whereas deuterium varies erratically between 20 and 40 smow bromine analyses and stable isotope data indicate that the formation waters are mixtures of a brine end member formed by evaporation of sea water beyond the point of halite saturation and meteoric water the chemical and isotopic composition of the formation waters and general geological considerations suggest that the brines originated as connate waters in permian evaporites and were later expelled into overlying strata there is a disequilibrium stable isotope distribution between the bulk chalk formations and the formation waters and only minor diagenetic modification of the formation waters appears to have taken place in these reservoirs the formation waters from the clastic reservoirs on the other hand are modified by diagenetic reactions

sensitivity of stream aquifer seepage to spatial variability of the saturated hydraulic conductivity of the aquifer abstract in this paper the sensitivities of stream aquifer seepage flow and the state of connection or disconnection between stream and aquifer to spatial variability in the aquifer saturated hydraulic conductivity are studied with the variably saturated modelling programme swms 2d using a monte carlo technique a simple stream aquifer flow system is used with a rectangular stream with a clogging layer on its perimeter partially penetrating an alluvial aquifer a 2d nearest neighbour method is used to generate fields of log normally distributed saturated conductivity for the alluvial aquifer for a specific set of degree of heterogeneity and the nearest neighbour autoregressive parameters seven different cases are studied five of these investigate the effect of the nearest neighbour parameters and three cases investigate the effect of aquifer water table level the results show that the nearest neighbour parameters and the aquifer degree of heterogeneity significantly affect the modelling of stream seepage pressure heads and the state of connection disconnection between stream and aquifer particularly when the water table is some distance below the streambed moreover comparisons of these results with a purely deterministic model show good agreement when the stream and the aquifer are connected or disconnected but with a high water table however there are significant differences between the deterministic and stochastic models when the water table is well below the streambed