sulfur record of rising and falling marine oxygen and sulfate levels during the lomagundi event carbonates from approximately 2 3 2 1 billion years ago show markedly positive 13c values commonly reaching and sometimes exceeding 10 traditional interpretation of these positive 13c values favors greatly enhanced organic carbon burial on a global scale although other researchers have invoked widespread methanogenesis within the sediments to resolve between these competing models and more generally among the mechanisms behind earth s most dramatic carbon isotope event we obtained coupled stable isotope data for carbonate carbon and carbonate associated sulfate cas cas from the lomagundi interval shows a narrow range of 34s values and concentrations much like those of phanerozoic and modern marine carbonate rocks the 34s values are a close match to those of coeval sulfate evaporites and likely reflect seawater composition these observations are inconsistent with the idea of diagenetic carbonate formation in the methanic zone toward the end of the carbon isotope excursion there is an increase in the 34s values of cas we propose that these trends in c and s isotope values track the isotopic evolution of seawater sulfate and reflect an increase in pyrite burial and a crash in the marine sulfate reservoir during ocean deoxygenation in the waning stages of the positive carbon isotope excursion

a pseudo genetic stochastic model to generate karstic networks summary in this paper we present a methodology for the stochastic simulation of 3d karstic conduits accounting for conceptual knowledge about the speleogenesis processes and accounting for a wide variety of field measurements the methodology consists of four main steps first a 3d geological model of the region is built the second step consists in the stochastic modeling of the internal heterogeneity of the karst formations e g initial fracturation bedding planes inception horizons etc then a study of the regional hydrology hydrogeology is conducted to identify the potential inlets and outlets of the system the base levels and the possibility of having different phases of karstification the last step consists in generating the conduits in an iterative manner using a fast marching algorithm in most of these steps a probabilistic model can be used to represent the degree of knowledge available and the remaining uncertainty depending on the data at hand the conduits are assumed to follow minimum effort paths in a heterogeneous medium from sinkholes or dolines toward springs the search of the shortest path is performed using a fast marching algorithm this process can be iterative allowing to account for the presence of already simulated conduits and to produce a hierarchical network the final result is a stochastic ensemble of 3d karst reservoir models that are all constrained by the regional geology the local heterogeneities and the regional flow conditions these networks can then be used to simulate flow and transport several levels of uncertainty can be considered large scale geological structures local heterogeneity position of possible inlets and outlets phases of karstification compared to other techniques this method is fast to account for the main factors controlling the 3d geometry of the network and to allow conditioning from available field observations

a quantitative method for the characterisation of karst aquifers based on spring hydrograph analysis this paper presents a method for characterizing flow systems in karst aquifers by acquiring quantitative information about the geometric and hydraulic aquifer parameters from spring hydrograph analysis numerical sensitivity analyses identified two fundamentally different flow domains depending on the overall configuration of aquifer parameters these two domains have been quantitatively characterized by deducing analytical solutions for the global hydraulic response of simple two dimensional model geometries during the baseflow recession of mature karst systems the hydraulic parameters of karst conduits do not influence the drainage of the low permeability matrix in this case the drainage process is influenced by the size and hydraulic parameters of the low permeability blocks alone this flow condition has been defined as matrix restrained flow regime mrfr during the baseflow recession of early karst systems and fissured systems as well as the flood recession of mature systems the recession process depends on the hydraulic parameters and the size of the low permeability blocks conduit conductivity and the total extent of the aquifer this flow condition has been defined as conduit influenced flow regime cifr analytical formulae demonstrated the limitations of equivalent models while equivalent discrete continuum models of early karst systems may reflect their real hydraulic response there is only one adequate parameter configuration for mature systems that yields appropriate recession coefficient consequently equivalent discrete continuum models are inadequate for simulating global response of mature karst systems the recession coefficient of equivalent porous medium models corresponds to the transition between matrix restrained and conduit influenced flow consequently equivalent porous medium models yield corrupted hydrographs both in mature and early systems and this approach is basically inadequate for modelling global response of karst aquifers

modeling flow in phreatic and epiphreatic karst conduits in the holloch cave muotatal switzerland the holloch cave is a site where the hydrodynamic behavior of a karst conduit network can be observed with a high degree of precision observed heads discharge rates conduit sizes and conduit lengths have been compiled into a simple hydrodynamic model in order to check their consistency it was possible to calibrate and satisfactorily fit the observed data model results show the following 1 flow models which are able to simulate turbulent flow in variably saturated conduit networks can adequately model conduit flow dominated karst systems 2 karst systems may be strongly nonlinear especially because of the presence of epiphreatic conduits 3 under certain circumstances storage in the epiphreatic conduits and in the fissured limestone matrix can be neglected 4 the typical effective hydraulic conductivity of karst conduits ranges between 1 and 10 m s 1 and the louis formula is adequate to calculate head losses in those conduits 5 indirect measurements of flow velocity using scallop size indicate values of 30 40 of the maximal annual discharge and velocity derived from pebble size indicates values of 150 of the maximal annual discharge

linear unit response functions as indicators of recharge areas for large karst springs abstract the delineation of groundwater recharge areas for karst springs is important for estimating groundwater supplies and for identifying sources and directions of contaminant movement this paper suggests the potential utility of spring discharge kernel functions analogous to instantaneous unit hydrographs for surface runoff in the identification of the recharge areas of large springs examples from southeastern missouri u s a show that when consistent methods are used for baseflow separation and excess precipitation determinations derived linear kernels are most physically realistic and have the least fitting error when the assumed spring recharge area is consistent with tracer study results

modelling the hydrologic functions of a karst aquifer under active water management the lez spring a rainfall discharge model is applied to an aquifer characterized by active groundwater management the lez karst aquifer in the south of france groundwater is withdrawn by pumping in the main drain 400 m upstream from the main spring and 48 m below the aquifer overflow level a reservoir model was developed to characterize the functioning of this aquifer it is based on a conceptual model of the karst aquifer that takes into account flow through both the saturated zone and the unsaturated infiltration zone both rapid and slow flow in the infiltration zone and flow in the saturated zone are modelled since pumping withdraws groundwater from the main drain of the saturated zone modules characterizing various pumping practices are taken into account in the saturated zone reservoir the model simultaneously simulates spring discharge and water levels in the drain which characterize the saturated zone of the karst the groundwater reserves stored in the saturated zone can then be estimated the model can be used for water management since runoff and overflow from the aquifer feeding the lez river depend on the degree of saturation of the aquifer the model could be used for the flood management

sulfur and carbon isotopic evidence for metabolic pathway evolution and a four stepped earth system progression across the archean and paleoproterozoic abstract the earth s mantle has provided a ready redox gradient of sulfur compounds so2 h2s since the stabilization of the crust and formation of the ocean over 4 billion years ago and life has evolved a multitude of metabolic pathways to take advantage of this gradient these transitions are recorded in the sulfur and carbon isotope signals preserved in the rock record in the genomic records of extant microorganisms and in the changing mantle and crust structure composition and cycling here we have assembled approximately 20 000 sulfur 34s 33s 36s and carbon 13c isotope data points from scientific publications spanning over five decades of geochemical analyses on rocks deposited from 4 0 to 1 5 ga we place these data in the context of molecular clock and tectonic and surface redox indicators to identify overarching trends and integrate them into a holistic narrative on the transition of the earth s surface towards more oxidizing conditions the greatest extreme in 34s values of sulfide minerals 45 5 to 54 9 and sulfate minerals 13 6 to 46 6 as well as 13c values in carbonate minerals 16 8 to 29 6 occurred in the period following the great oxidation event goe while the greatest extremes in organic carbon 13c values 60 9 to 2 4 and sulfide and sulfate mineral 33s and 36s values 4 0 to 14 3 and 12 3 to 3 2 respectively occurred prior to the goe from our observations we divide transitions in earth s history into four periods period 1 4 00 to 2 80 ga during which geochemical cycles were initialized period 2 2 80 to 2 45 ga during which s and c isotope systems exhibit changes as conditions build up to the goe period 3 2 45 to 2 00 ga encompassing the goe and period 4 after 2 00 ga after which s and c isotopic systems remained relatively constant marking a time of earth system geochemical quiescence using these periods we link changes in s and c isotopes to molecular clock work to aid in interpreting emerging metabolic functions throughout earth s history while underscoring the need for better proxies for robust evolutionary analyses specifically results indicate 1 an early development of sulfide oxidation and dissimilatory sulfite reduction followed by disproportionation and then sulfate reduction to sulfite resulting in a fully biologically mediated sulfur cycle by 3 25 ga 2 support for the acetyl coenzyme a pathway as the most likely earliest form of biologically mediated carbon fixation following methanogenesis 3 an increasingly redox stratified ocean in the neoarchean with largely oxic surface water and euxinic bottom water during the first half of the paleoproterozoic and 4 that secular changes in earth system crustal cycling dynamics and continent formation likely played a key role in driving the timing of the goe finally based on geochemical data we suggest that the paleoproterozoic be divided into a new era of the eoproterozoic from 2 45 to 2 00 ga and the paleoproterozoic from 2 00 to 1 60 ga

regional stratigraphy of the zagros fold thrust belt of iran and its proforeland evolution the latest neoproterozoic through phanerozoic stratigraphy of the zagros fold thrust belt of iran has been revised in the light of recent investigations the revised stratigraphy consists of four groups of rocks each composed of a number of unconformity bounded megasequences representing various tectonosedimentary settings in the lowest group ranging in age from latest precambrian to devonian the uppermost neoproterozoic to middle cambrian rocks constitute a megasequence of evaporites siliciclastic deposits and interlayered carbonates which were deposited in pull apart basins that developed by the najd strike slip fault system this megasequence is overlain by a second one middle to late cambrian in age which consists of shallow marine siliciclastic and carbonate rocks representing deposition in an epicontinental platform the overlying shales siltstones and partly volcanogenic sandstones of ordovician silurian and devonian age are local remnants of stratigraphic units that were extensively eroded during development of several major unconformities the second group consists of two megasequences one permian and the other triassic composed of widespread transgressive basal siliciclastic rocks and overlying evaporitic carbonates of an equatorial epi pangean very shallow platformal sea the third group is composed of four megasequences formed of shallow and deep water carbonates with some siliciclastic and evaporite deposits which accumulated on a neo tethyan continental shelf during earliest jurassic through late turonian time the fourth group comprises siliciclastic and carbonate deposits of a largely underfilled nw to se trending forward and backward migrating late cretaceous to recent proforeland basin which has evolved as an integral part of the zagros orogen this last group consists of three megasequences ix x and xi with distinctive lateral and vertical facies variations which reflect specific tectonic events megasequence ix comprises uppermost turonian to middle maastrichtian prograding and retrograding siliciclastic and carbonate deposits whose accumulations reflect emplacement obduction of ophiolite slivers and subsequent collisional events in the zagros orogen megasequence x consists of uppermost maastrichtian to upper eocene siliciclastic and carbonate rocks which deposited first progradationally in front of the zagros orogenic wedge with reduced contractional tectonic activity and then retrogradationally due to intensified thrust stacking in the interior parts of the orogen megasequence xi consists of oligocene and lower miocene carbonate strata deposited retrogradationally shortly after a period of intensified late eocene thrust faulting in the deformational wedge and an overlying succession of upward coarsening northeasterly derived siliciclastic deposits of lower miocene to recent age which are composed of erosional byproducts of the southwest vergent zagros thrust sheets

modeling complex flow in a karst aquifer abstract carbonate aquifers typically have complex groundwater flow patterns that result from depositional heterogeneities and post lithification fracturing and karstification various sources of information may be used to build a conceptual understanding of flow in the system including drilling data well tests geophysical surveys tracer tests and spring gaging these data were assembled to model flow numerically in germany s malm formation at a site where water disappears from the beds of ephemeral stream valleys flows through conduit systems and discharges to springs along surface water features modeling was performed by using a finite difference approach with drain networks representing the conduit component of flow laced throughout the porous medium along paths inferred on the basis of site data this approach represents an improvement over other karst models that attempt to represent a conduit by a single specialized model node at the spring location or by assigning a computationally problematic extremely high permeability to a zone by handling the conduit portion of this mixed flow system with drains a realistic interpretive flow model was created for this intricate aquifer

detrital record of mountain building provenance of jurassic foreland basin to the dabie mountains 1 the huangshi foreland basin developed on the southern margin of the dabie mountains as a result of tectonic loading during triassic collisional suturing between the north china and south china cratons modal and detrital zircon data for jurassic samples within the basin suggest a multicomponent source with input from both the south china craton and dabie orogen samples are predominantly quartz arenites derived on the basis of framework compositions from a recycled orogen source detrital zircons range in age from archean to triassic with a dominant component in the late paleoproterozoic between 1 9 1 7 ga and subsidiary components at 2 6 2 2 ga 0 8 0 7 ga 0 5 0 4 ga and 0 33 0 2 ga age data integrated with cathodoluminescence and trace element data for the zircons indicate that the archean and proterozoic detritus was derived from igneous and metamorphic sources that overlap with time equivalent pulses of such activity within the south china craton phanerozoic zircon ages overlap the times of the ordovician carboniferous and triassic high pressure metamorphism in the dabie mountains the provenance record integrated with paleocurrent and regional relations enables a paleogeographic reconstruction in which the huangshi basin was fed by a major axial flowing trunk river system carrying detritus from eastern and southern sources within the south china craton and was also fed by short south flowing tributaries supplying some detritus from the evolving dabie orogen the dominance of cratonic derived detritus within the provenance record of the huangshi basin contrasts with that of the hefei foreland basin that lies to the north of the dabie mountains which is dominated by neoproterozoic mesozoic detritus derived directly from the dabie mountains and lacks any significant older paleoproterozoic or archean components easterly extensions of the dabie sulu collisional suture and of the resultant huangshi basin occur in korea and japan over an along strike length of some 2000 km

constraints on timing of peak and retrograde metamorphism in the dabie shan ultrahigh pressure metamorphic belt east central china using u th pb dating of zircon and monazite abstract the dabie shan ultrahigh pressure metamorphic uhpm belt occupies the suture between the yangtze and sino korean blocks in east central china the timing of uhpm in the dabie belt is controversial and most recent data come from dating of zircons monazite has recently been recognized as useful for dating of multiple tectonic events due to its preservation of multiple growth zones and monazite growth has been documented to occur during prograde peak and retrograde metamorphism zircons and monazites from uhp mafic rocks from maowu and a uhp jadeite quartzite from shuanghe were imaged in thin sections and in mineral separates and dated using a high resolution ion microprobe maowu mafic rocks are unique in that they contain high light rare earth element concentrations and therefore contain abundant monazite maowu eclogites and garnet pyroxenites contain zircons with mean 206 pb 238 u age of 230 4 ma and monazites from a clinopyroxenite have 208 pb 232 th ages of 209 4 ma multiple lines of evidence suggest that the measured ages represent the timing of new growth and recrystallization and are not cooling ages i e they do not correspond to the cessation of diffusional pb loss as rocks cooled below the closure temperature during exhumation shuanghe jadeite quartzites contain zircons with cores that define a discordia with an upper intercept age 1921 22 ma and lower intercept age of 236 32 ma interpreted to represent the ages of the source rocks and of peak metamorphism respectively zircon rims contain jadeite inclusions that restrict growth to pressures greater than 1 5 gpa their pooled age of 238 3 ma agrees well with the lower intercept defined by cores suggesting that pb loss from cores and growth of new rims occurred during uhpm at 235 240 ma monazite records multiple events during retrograde metamorphism maowu clinopyroxenite and shuanghe jadeite quartzite experienced monazite growth at 209 ma interpreted to reflect regional amphibolite facies overprinting resulting from pervasive retrograde fluid infiltration only the jadeite quartzite records growth at 223 1 ma estimated exhumation rates for maowu are 7 8 km ma

monthly karstic spring flow forecasting using a sequential gaussian simulation technique analyzing groundwater hydrologic equations related to karstic aquifers and spring hydrograph simulation have become the focus of many researches having double or triple porosity structure mixed flow nature and varying conduit permeability have made these formations become complex heterogenic systems with great temporal and spatial hydrodynamic variability in this paper a conditional sequential gaussian simulation sgs is used to simulate monthly flow data of five karstic springs with different hydrogeological properties located in zagros mountain chain in western iran to evaluate the performance of the sgs algorithm the results are compared with those of an autoregressive integrated moving average arima model the results demonstrate the efficiency of the sgs model in simulation of monthly flows compared to the arima model they also show the suitability of this model for handling uncertainty associated with karstic spring flows through generation of several equally probable stochastic realizations

mesozoic basin development and tectonic evolution of the dabieshan orogenic belt central china 1 the dabieshan orogenic belt is a zone of long lived shortening with late stage extension that formed during mesozoic time in central china regional basin analysis coupled with structural cross sections provides a means of reconstructing the paleogeography of the region from triassic continental collision through early tertiary extension the overall distribution of different basin types in the orogenic belt indicates that there was a prolonged period of shortening throughout the mesozoic that became less intense over time meanwhile extension became more common from jurassic into tertiary time either compression or extension was isochronous but limited to different geographic regions and or crustal levels or alternated repeatedly orogen wide through time nonetheless the orogen underwent gradual transition from overall shortening and crustal thickening to dominantly extension and rift basin formation although these events overlapped in time from the jurassic through early cretaceous penecontemporaneous compression and extension across the orogen may reflect long term 100 m y shortening and crustal thickening leading to gravitational spreading of the resultant thick crustal welt we suspect that this prolonged history of shortening across two nearby 100 km apart suture zones played some role in the exhumation of ultrahigh pressure rocks from beneath the dabieshan

the behavior of molybdenum and its isotopes across the chemocline and in the sediments of sulfidic lake cadagno switzerland abstract molybdenum mo isotope studies in black shales can provide information about the redox evolution of the earth s oceans provided the isotopic consequences of mo burial into its major sinks are well understood previous applications of the mo isotope paleo ocean redox proxy assumed quantitative scavenging of mo when buried into sulfidic sediments this paper contains the first complete suite of mo isotope fractionation observations in a sulfidic water column and sediment system the meromictic lake cadagno switzerland a small alpine lake with a pronounced oxygen sulfide transition reaching up to h 2 s 200 m in the bottom waters or about 300 m total sulfide s 2 h 2 s hs s 2 we find that mo behaves conservatively in the oxic zone and non conservatively in the sulfidic zone where dissolved mo concentrations decrease from 14 nm to 2 8 nm across this transition dissolved mo in the upper oxic waters has a 98 mo oxic 0 9 0 1 which matches that of the riverine input 98 mo river 0 9 0 1 in the deeper sulfidic waters a subaquatic source delivers mo at 1 55 0 1 but the dissolved mo is even heavier at 98 mo sulfidic 1 8 sediment traps in the sulfidic zone of the lake collect particles increasingly enriched in mo with depth with 98 mo values significantly fractionated at 0 8 to 1 2 both near the chemocline and in the deepest trap suspended particulates in the sulfidic waters carry lighter mo than the ambient dissolved mo pool by 0 3 1 5 sedimentary mo concentrations correlate with total organic carbon and yield mo levels which are two orders of magnitude higher than typical crustal values found in rocks from the catchment area solid phase mo in the sediment shows a slightly positive 98 mo trend with depth from 98 mo 1 2 to 1 4 while the pore waters show dramatic enrichments of mo 2000 nm with a relatively light isotope signature of 98 mo 0 9 1 0 these data are explained if mo is converted to particle reactive oxythiomolybdates in the sulfidic waters and is fractionated during removal from solution onto particles isotope fractionation is expressed in the water column despite the high sulfide concentrations because the rate of mo removal is fast compared to the slow reaction kinetics of thiomolybdate formation however elemental and isotopic mass balances show that mo is indeed quantitatively removed to the lake sediments and thus the isotopic composition of the sediments reflects sources to the sulfidic water this efficient mo drawdown is expected to occur in settings where h 2 s is very much in excess over mo or in a restricted setting where the water renewal rate is slow compared to the mo burial rate we present a model for the mo isotope fractionation in sulfidic systems associated with the slow reaction kinetics and conclude that quantitative removal will occur in highly sulfidic and restricted marine systems

rainfall runoff relations for karstic springs part i convolution and spectral analyses karstic basins contain large reserves of subsurface water in this paper three karstic systems located in the pyrenees mountains ariege france are studied long records of rainfall and discharge rates for these karstic springs are available sampled at different rates daily hourly and half hourly this study aims at illustrating and assessing the capabilities and limitations of linear black box methods for analysing rainfall runoff type relationships and reconstructing runoffs from rainfall rate data using such systems in this study precipitation and discharge rates are considered as two autocorrelated and cross correlated stochastic processes a linear and stationary rainfall runoff model is adopted which is used for identification and simulation purposes different versions are analysed including a model based on a convolution integral between the precipitation rate p and a transfer function h t which can be thought of as the unit impulse response of the system it is shown that this linear stochastic model i e the statistical version although accurate in some respects does not represent the hydraulic behaviour of the system very well during low flow episodes and floods it is also shown that the use of fourier analysis alone does not lead to a satisfactory reconstitution of observed runoff sequences for these reasons the use of non linear random process input output models based on volterra integral series is proposed and discussed

molybdenum in the northeast pacific ocean1 the concentration of dissolved molybdenum has been determined in several profiles from the northeast pacific ocean the salinity normalized concentration is essentially constant in all open ocean samples 107 nm 1 2 5 nm the dissolved distribution is not significantly affected by biological cycling

analytical 1d dual porosity equivalent solutions to 3d discrete single continuum models application to karstic spring hydrograph modelling abstract one dimensional analytical porosity weighted solutions of the dual porosity model are derived providing insights on how to relate exchange and storage coefficients to the volumetric density of the high permeability medium it is shown that porosity weighted storage and exchange coefficients are needed when handling highly heterogeneous systems such as karstic aquifers using equivalent dual porosity models the sensitivity of these coefficients is illustrated by means of numerical experiments with theoretical karst systems the presented 1d dual porosity analytical model is used to reproduce the hydraulic responses of reference 3d karst aquifers modelled by a discrete single continuum approach under various stress conditions simulation results show the relations between the dual porosity model coefficients and the structural features of the discrete single continuum model the calibration of the equivalent 1d analytical dual porosity model on reference hydraulic responses confirms the dependence of the exchange coefficient with the karstic network density the use of the analytical model could also point out some fundamental structural properties of the karstic network that rule the shape of the hydraulic responses such as density and connectivity

proterozoic ocean redox and biogeochemical stasis the partial pressure of oxygen in earth s atmosphere has increased dramatically through time and this increase is thought to have occurred in two rapid steps at both ends of the proterozoic eon 2 5 0 543 ga however the trajectory and mechanisms of earth s oxygenation are still poorly constrained and little is known regarding attendant changes in ocean ventilation and seafloor redox we have a particularly poor understanding of ocean chemistry during the mid proterozoic 1 8 0 8 ga given the coupling between redox sensitive trace element cycles and planktonic productivity various models for mid proterozoic ocean chemistry imply different effects on the biogeochemical cycling of major and trace nutrients with potential ecological constraints on emerging eukaryotic life here we exploit the differing redox behavior of molybdenum and chromium to provide constraints on seafloor redox evolution by coupling a large database of sedimentary metal enrichments to a mass balance model that includes spatially variant metal burial rates we find that the metal enrichment record implies a proterozoic deep ocean characterized by pervasive anoxia relative to the phanerozoic at least 30 40 of modern seafloor area but a relatively small extent of euxinic anoxic and sulfidic seafloor less than 1 10 of modern seafloor area our model suggests that the oceanic mo reservoir is extremely sensitive to perturbations in the extent of sulfidic seafloor and that the record of mo and chromium enrichments through time is consistent with the possibility of a mo n colimited marine biosphere during many periods of earth s history

rise in seawater sulphate concentration associated with the paleoproterozoic positive carbon isotope excursion evidence from sulphate evaporites in the 2 2 2 1 gyr shallow marine lucknow formation south africa past oceanic sulphate concentration is important for under standing how the oceansredox state responded to atmospheric oxygen levels the absence of extensive marine sulphate evaporites before 1 2 gyr probably reflects low seawater sulphate and or higher carbonate concentrations sulphate evaporites formed locally during the 2 22 2 06 gyr lomagundi positive d 13 c excursion however the 2 2 2 1 gyr lucknow formation south africa provides the first direct evidence for seawater sulphate precipitation on a carbonate platform with open ocean access and limited terrestrial input these marginal marine deposits contain evidence for evaporite molds pseudomorphs after selenite gypsum and solid inclusions of ca sulphate in quartz carbon and sulphur isotope data match the global record and indicate a marine source of the evaporitic brines the apparent precipitation of gypsum before halite requires 2 5 mm l 1 sulphate concentration higher than cur rent estimates for the paleoproterozoic during the lomagundi event which postdates the 2 32 gyr initial rise in atmospheric oxygen seawater sulphate concentration rose from archean values of 200 lm l 1 but dropped subsequently because of higher pyrite burial rates and a lower oceanic redox state

conceptualization and classification of groundwater surface water hydrodynamic interactions in karst watersheds case of the karst watershed of the coulazou river southern france summary over the last two decades groundwater systems and surface water bodies are being more and more considered as a same entity which constitutes a single resource within the hydrologic system understanding groundwater surface water gw sw interactions is necessary to effectively manage the water resources concepts methods of analysis and classifications of these hydrodynamic interactions have thus been developed mostly in case of porous aquifer today gw sw interactions are still often poorly understood in many watersheds particularly in the case of complex aquifers like karst aquifers this study focuses on the influence of groundwater on the genesis and propagation of surface floods in the case of a highly karstified watershed gw sw hydrodynamic interactions are analysed i at a local scale focussing on hydrodynamic interactions between the karst aquifer in the vicinity of the river and the river and ii at a larger scale focussing on hydrodynamic interactions between a karst spring and sinkholes in the riverbed hydrodynamic time series are described using the karst watershed of the coulazou river western montpellier france as a case study results are used to adapt gw sw classifications that are usually devoted to porous media in case of the studied karst aquifer it is shown that the initial groundwater level may be used to forecast the type of hydraulic connection between the river and the saturated zone during flood however initial water level in the karst aquifer does not give any information about the flow direction gaining or losing stream during a flood the latter is found to be also controlled by the limited discharge capacity of karst conduits a conceptual model of karst river interactions during flood is given with concepts that are derived from the analysis of the coulazou watershed but that can be easily applied to most of the karst watersheds

semi distributed lumped model of a karst system under active management summary in this paper inverse modeling is used to characterize the regime of a karst aquifer subjected to extensive pumping in a conduit located upstream of its main outlet the systemic approach uses a transfer model that is based on computing the convolution integral of up to several signals e g efficient rainfall pumping to simulate flow rates and groundwater levels in both the karst conduit and the carbonate matrix at the aquifer outlet and in several parts of the catchment area the model is a semi distributed lumped model which simulates the hydrological response of a heterogeneous karst aquifer made up of different hydrologic compartments and is applied to the lez karst system france groundwater is abstracted near the system s major outlet at a higher rate than the low water spring discharge thereby mobilizing stored groundwater during low water periods active management the model s results are very satisfactory especially for the karst system outlet where the water levels are particularly well reproduced the model can also simulate the natural i e non pumping state of the karst system and thereby estimate the impact of active management on the water resource

redox and paleoenvironmental conditions of the devonian carboniferous sappington formation southwestern montana and comparison to the bakken formation williston basin abstract the sappington formation outcrops in southwestern montana and spans the upper devonian lower mississippian transition it consists of two carbonaceous shale intervals one upper and one lower and a middle dolomitic siltstone and silty sandstone it was deposited in a relatively small basin with the central montana uplift separating the sappington basin from the williston basin to the east which contains the economically important bakken formation previous biostratigraphic and lithostratigraphic comparisons have identified the sappington and bakken formations as depositionally contemporaneous and due to the subsurface nature of the bakken the sappington has emerged as a useful outcrop analogue this study presents new geochemical data from the sappington formation providing a comparison to the bakken and insight into paleo redox conditions during the devonian carboniferous on the western laurentian margin geochemical signals in the sappington formation outcrop samples are partially obscured by oxidative weathering but similar to the lower bakken shale the lower sappington shale appears to record dominantly euxinic conditions albeit with intervals when the water column was suboxic to ferruginous and with an absence of organic or inorganic geochemical evidence for photic zone euxinia the upper sappington shale appears to have been deposited in ferruginous to dysoxic conditions thus the sappington appears to be an excellent analogue to the bakken on a lithostratigraphic level but the geochemical environment for black shales source rock deposition appears less reducing closer proximity to the open ocean and consequent lower levels of restriction may have been responsible for these redox differences however sappington core samples and an increased focus on integrating geochemical data into the regional stratigraphic record will be necessary to further understand paleoceanographic and biogeochemical drivers

modeling of storm responses in conduit flow aquifers with reservoirs abstract in aquifers containing large voids such as karst aquifers with caves or basaltic aquifers with lava tubes hydrographs at wells or springs are used to analyze the structure and response of the hydrogeological system numerical modeling of hydrograph response is commonly based on either inverse techniques or postulated flow geometries however the range of mechanisms for generating hydrograph responses have not been fully investigated physical modeling of these complex non darcian systems permits better understanding of the storm responses that conduit systems may generate using a numerical model of conduit flow systems which incorporates turbulent flow some of the mechanisms that can alter storm pulses were investigated by treating them as combinations of pipes that connect reservoirs the results indicate that the response of a conduit flow aquifer can range from what has been called diffuse or steady to conduit or flashy without employing a diffusive component a full range of behavior can be the result of changes from phreatic to epiphreatic conditions in a conduit changes in conduit geometry or multiple springs draining the same system the results provide a quantitative tool to assess spring and well hydrographs and illustrate mechanisms that can generate observed responses which have previously been qualitatively interpreted

molybdenum isotope evidence for widespread anoxia in mid proterozoic oceans how much dissolved oxygen was present in the mid proterozoic oceans between 1 8 and 1 0 billion years ago is debated vigorously one model argues for oxygenation of the oceans soon after the initial rise of atmospheric oxygen 2 3 billion years ago recent evidence for h 2 s in some mid proterozoic marine basins suggests however that the deep ocean remained anoxic until much later new molybdenum isotope data from modern and ancient sediments indicate expanded anoxia during the mid proterozoic compared to the present day ocean consequently oxygenation of the deep oceans may have lagged that of the atmosphere by over a billion years

pyrite formation in the water column and sediments of a meromictic lake we compared concentrations of organic carbon partitioning of iron and sulfur stable isotopic ratios of major sulfur species and pyrite morphologies in the water column and sediments of oxic and euxinic portions of a sulfate rich meromictic lake green lake near fayetteville new york in order to examine the effects of euxinic conditions on pyrite formation and sedimentary fe s c relations about 15 of the pyrite in sediments of the euxinic basin of green lake forms in the water column the bulk of pyrite in both euxinic and oxic sediments forms in the upper 10 cm of the sediment and is limited by availability of reactive iron oxic and euxinic sediments in green lake cannot be clearly distinguished on the basis of concentrations of organic carbon or pyrite degree of pyritization or sulfur isotopic ratios of pyrite but can be distinguished by using size distributions of pyrite framboids therefore fe s c relations in ancient shales must be used with caution when attempting to reconstruct paleoenvironmental redox conditions

modern iron isotope perspective on the benthic iron shuttle and the redox evolution of ancient oceans the increase in atmospheric oxygen ca 2 4 ga had a significant impact on the geochemical cycling of fe the history of environmental oxygenation may be recorded in the fe isotope composition of archean and proterozoic sediments but this record cannot be interpreted accurately until we understand the mechanisms causing isotope variations here we present fe isotope data and iron aluminum ratios from the black sea oxic shelf and euxinic basin the isotope data demonstrate that shelf fe is depleted in the lighter isotope compared to both the detrital weathering input and the sediments of the euxinic basin we propose that there is net transport of isotopically light fe from sediments of the shelf to those of the distal anoxic basin consistent with enrichments in reactive fe seen in the deep basin the low 56 fe benthic fe flux is generated during the coupling of microbial fe iii reduction or sulfidization with fe 2 aq oxidation low 56 fe values reported previously from late archean sedimentary pyrites may be an isotopic fingerprint of analogous fe redox cycling in the late archean oceans this interpretation implies shallow water fe redox recycling in the late archean we predict that the light isotopic compositions of the late archean will prove to be distinct from those of the early archean before fe redox cycling became an important process and we infer that this difference may be related to the presence of oxygen in the surface ocean

convergence history across zagros iran constraints from collisional and earlier deformation the zagros orogen provides a unique opportunity within the alpine system to evaluate the interplay between a young tertiary collision and earlier subduction obduction processes within the crush zone and the sanandaj sirjan internal zone separating the zagros fold belt from central iran we document several major tectonic events taking place at the end of the cretaceous of the eocene and from the mio pliocene onwards ca 20 15 ma contrary to recent interpretations our data cross sections and description of the overall deformation style strongly suggest that the main zagros thrust mzt is deeply rooted possibly to moho depths and that the suture zone effectively runs along the mzt field observations show that the final resorption of the oceanic domain took place slightly after 35 ma and that collision must have started before ca 23 25 ma in northern zagros the shortening rate across the crush zone since the mid miocene 20 15 ma is estimated at a minimum 3 4 mm year shear movements in the crush zone during the eocene oligocene period and extensional strike slip movements in the internal zones during the late cretaceous point to an oblique setting early in the convergence history a geotectonic scenario for convergence from the time of obduction to the present is finally proposed

simple procedure to simulate karstic aquifers a procedure to simulate karstic aquifers is presented it is based on a simulation of spring discharge using precipitation and where necessary temperature as input data the karstic aquifer system is considered to be divided into three zones the surface zone the unsaturated zone uz and the saturated zone sz each of these is described by a transfer function that determines the water supplied from the overlying zone water loss through evapotranspiration is calculated empirically and subtracted from the total precipitation in order to obtain the effective infiltration into the uz the transfer function characterizing the uz can be expressed as a convolution function the uz acts as a buffer delaying effective infiltration into the sz water discharge from the sz is described by the recession function of the spring and this becomes the transfer function that characterizes the emergence of water from the sz the model permits the simulation of the influence of pumped abstractions from the system by a simple modification of the transfer functions involved copyright 2007 john wiley sons ltd

the behavior of biologically important trace elements across the oxic euxinic transition of meromictic fayetteville green lake new york usa abstract trace elements are central components of enzymes that catalyze many of the essential reactions mediated by life the redox sensitive nature of trace elements also permits their use as a record of ancient ocean conditions preserved in the geologic record trace element geochemistry in modern stratified systems is often used as a proxy for the redox state of the ancient oceans which are thought to have been largely anoxic in the present study we examined trace element behavior of simultaneously collected samples at a heretofore unprecedented depth resolution 1 0 25 m intervals throughout the redox stratified water column of fayetteville green lake n y fgl a 53 m deep meromictic lake under euxinic conditions similar to those thought to have been prevalent in proterozoic oceans among characterized proterozoic ocean analogs fgl represents an understudied proxy in terms of trace elements with characteristics of low salinity and high sulfate in the fgl water column spikes in the concentration of dissolved mn fe and co are coincident with the transition from oxic to euxinic conditions and are associated with a decrease in dissolved mo concentration in contrast the concentration of dissolved ni did not vary across this transition despite the dramatic shift in redox state from these data we present a one dimensional model for element transport and cycling through the water column to the sediments collectively this comprehensive analysis of water column geochemistry provides insight into the effects of biogeochemical cycling in stratified systems on dissolved trace element concentrations in the water column this study in concert with characterization of other early earth analogs will greatly enhance the use of trace elements in interpreting the geologic record

carboniferous and triassic eclogites in the western dabie mountains east central china evidence for protracted convergence of the north and south china blocks shrimp u pb dating and laser ablation icp ms trace element analyses of zircon from four eclogite samples from the north western dabie mountains central china provide evidence for two eclogite facies metamorphic events three samples from the huwan shear zone yield indistinguishable late carboniferous metamorphic ages of 312 5 307 4 and 311 17 ma with a mean age of 309 3 ma one sample from the hong an group 1 km south of the shear zone yields a late triassic age of 232 10 ma similar to the age of ultra high pressure uhp metamorphism in the east qinling dabie orogenic belt ree and other trace element compositions of the zircon from two of the huwan samples indicate metamorphic zircon growth in the presence of garnet but not plagioclase namely in the eclogite facies an interpretation supported by the presence of garnet omphacite and phengite inclusions zircon also grew during later retrogression zircon cores from the huwan shear zone have ordovician to devonian 440 350 ma ages flat to steep heavy ree patterns negative eu anomalies and in some cases plagioclase inclusions indicative of derivation from north china block igneous and low pressure metamorphic source rocks cores from hong an group zircon are neoproterozoic 780 610 ma consistent with derivation from the south china block in the western dabie mountains the first stage of the collision between the north and south china blocks took place in the carboniferous along a suture north of the huwan shear zone the major triassic continent continent collision occurred along a suture at the southern boundary of the shear zone the first collision produced local eclogite facies metamorphism in the huwan shear zone the second produced widespread eclogite facies metamorphism throughout the dabie mountains sulu terrane and a lower grade overprint in the shear zone

tracking euxinia in the ancient ocean a multiproxy perspective and proterozoic case study the evolution and extinction of life are tied intimately to the oxygen state of the ocean and particularly to the presence of anoxic and h2s containing euxinic water on a global scale anoxia and euxinia were more common in the past relative to today s 0 5 euxinic seafloor we are able to constrain the distributions of these conditions through a combination of indirect numerical modeling methods and more direct geochemical proxies with particular emphasis on fe s mo analysis of fine grained siliciclastic rocks for the latter establishing the spatiotemporal pattern of oceanic redox is more difficult with very old rocks because of the limited availability of well dated well preserved materials that span shallow and deep environments across time lines despite these difficulties the multiple approaches synthesized in our case study point to global oxygen deficiency in the deep ocean and perhaps euxinia during most if not all of the proterozoic and likely extending into the early paleozoic

cretaceous tertiary convergence and continental collision sanandaj sirjan zone western iran abstract the sanandaj sirjan zone contains the metamorphic core of the zagros continental collision zone in western iran the zone has been subdivided into the following from southwest to northeast an outer belt of imbricate thrust slices radiolarite bisotun ophiolite and marginal sub zones which consist of mesozoic deep marine sediments shallow marine carbonates oceanic crust and volcanic arc respectively and an inner complexly deformed sub zone late palaeozoic mesozoic passive margin succession rifting and sea floor spreading of tethys occurred in the permian to triassic but in the sanandaj sirjan zone extension related successions are mainly of late triassic age subduction of tethyan sea floor in the late jurassic to cretaceous produced deformation metamorphism and unconformities in the marginal and complexly deformed sub zones deformation climaxed in the late cretaceous when a major southwest vergent fold belt formed associated with greenschist facies metamorphism and post dated by abundant palaeogene granitic plutons in the southwest of the zone a late cretaceous island arc passive margin collision occurred with ophiolite emplacement onto the northern arabian margin similar to that in oman final closure of tethys was not completed until the miocene when central iran collided with the northeast arabian margin

identification of a karst system s intrinsic hydrodynamic parameters upscaling from single springs to the whole aquifer for water management purposes information about an entire aquifer system is generally more important than information about a specific spring since a karstic aquifer system might drain to several outlets conclusions derived from a single spring can be misleading for characterization and modeling in this study we apply a conceptual model to an alpine dolomite karst system in austria the particular challenge was that several small springs with strongly varying hydrological behavior and diffuse flow into surrounding streams drain this system instead of applying the model to a single spring it was calibrated simultaneously to several observations within the system aiming to identify the karst system s intrinsic hydrodynamic parameters parameter identification is supported by modeling the transport of water isotopes 18o the parameters were transferred to the whole system with a simple upscaling procedure and a sensitivity analysis was performed to unfold influence of isotopic information on parameter sensitivity and simulation uncertainty the results show that it is possible to identify system intrinsic parameters but the sensitivity analysis revealed that some are hardly identifiable only by considering uncertainty reasonable predictions can be provided for the whole system including isotopic information increases the sensitivity of some intrinsic parameters but it goes along with a sensitivity decrease for others however a possible reduction of prediction uncertainty by isotopic information is compensated by deficiencies in the transport modeling routines

significance and origin of very large regulating power of some karst aquifers in the middle east implication on karst aquifer classification summary karst aquifers are the main groundwater resource in lebanon as well as in most mediterranean countries most of them are not exploited in a sustainable way partly because their characteristics remain unknown karst aquifers are so complex that the assessment of their resource and their exploitable storage requires an analysis of their whole functioning particularly by analysing the spring hydrograph among all various methods the method proposed by mangin aims to characterize at the same time the recharge conditions and the storage and recession of the saturated zone by analyzing the spring hydrograph this method defines two parameters the infiltration delay i and the regulating power k which are the roots of a classification of karst systems this classification makes the distinction between karst and porous aquifers considering the value of the regulating power k is assumed to be lower than 0 5 in karst and between 0 5 and 1 for all other aquifers 1 being the upper limit the study of karst aquifers in lebanon shows values of k 0 5 and even 1 former data from the literature show that other karst springs in middle east have comparable characteristics in fact what is not considered by mangin and others k is equivalent to a mean residence time in years of water in the saturated zone so long residence times are normally observed in poorly karstified aquifers or containing abandoned not functioning karstification the geological framework in which the studied springs are located in fact shows that these aquifers have been subject to a long complex evolution as a consequence of the base level rising this rising produced the flooding of the successive karst drainage network which does not really function anymore and provides a large storage capacity to the aquifer the very interesting properties of these aquifers make them prime targets for fulfilling the increasing needs of water

manganese and iron geochemistry in sediments underlying the redox stratified fayetteville green lake abstract manganese and iron are redox sensitive elements that yield clues about biogeochemistry and redox conditions both in modern environments and in the geologic past here we investigated mn and fe bearing minerals preserved in basin sediments underlying fayetteville green lake a redox stratified lake that serves as a geochemical analogue for paleoproterozoic oceans synchrotron source microprobe techniques xrf xanes and xrd and bulk geochemical analyses were used to examine the microscale distribution and speciation of mn fe and s as a function of depth in the top 48 cm of anoxic lake sediments manganese was primarily associated with calcite grains as a manganese rich carbonate that precipitated in the chemocline of the water column and settled through the euxinic basin to collect in lake sediments iron was preserved in framboidal iron sulfides that precipitated in euxinic bottom waters and underwent transformation to pyrite and marcasite in the sediments previous studies attribute the formation of manganese rich carbonates to the diagenetic alteration of manganese oxides deposited in basins underlying oxygenated water our study challenges this paradigm by providing evidence that mn bearing carbonates form in the water column and accumulate in sediments below anoxic waters consequently manganoan carbonates preserved in the rock record do not necessarily denote the presence of oxygenated bottom waters in ocean basins