detection and monitoring of water filled voids using transient electromagnetic method a case study in shanxi china shanxi province is a major coal base for the rapid development in china but heavy production of coal resources has left abundant water filled voids creating significant geologic hazards around coal mines it is necessary to quickly investigate the position and distribution of voids with effective geophysical methods the feasibility of transient electromagnetic tem method in detecting and monitoring water filled voids is analyzed using 3d finite element numerical simulation results as well as a case study in this paper the case study was mainly to analyze and monitor the conditions around the site of a power transfer station under construction in the west of shanxi province where many water filled mined out voids existed central loop tem sounding was carried out three times from january 2010 to april 2011 around the building footprint the low resistivity abnormal area had been repeatedly located and the survey results showed that the area of voids increased with time which indicated that the ground at the site was in an unstable and dangerous state the surveys provided more detailed geological information to the government for further safety arrangement and building re design

mass occurrence of benthic coccoid cyanobacteria and their role in the production of neoarchean carbonates of south africa abstract the sparse archean fossil record is based almost entirely on carbonaceous remnants of microorganisms cellularly preserved due to their early post mortem silicification hitherto as an exception sedimentary carbonate rocks from the neoarchean nauga formation of south africa contain calcified microbial mats composed of microbiota closely resembling modern benthic colonial cyanobacteria chroococcales and pleurocapsales their remains visible under the scanning electron microscope sem after etching of polished rock samples comprise capsular envelopes mucilage sheaths and groups of cells mineralized by calcium carbonate with an admixture of al k mg fe silicates the capsular organization of the mucilaginous sheaths surrounding individual cells and cell clusters forming colonies and the mode of mineralization are the characteristic common features of the neoarchean microbiota described and their modern analogues the new findings indicate massive production of calcium carbonates by benthic coccoid cyanobacteria in the neoarchean and offer a solution to the problem of the origin of archean carbonate platforms stromatolites and microbial reefs

exploration of deep magnetite deposit under thick and conductive overburden with ex component of sotem a case study in china in northern china thick loess strata with low resistivity are widely present and can shield the deep induced electromagnetic field signal and influence the accuracy of deep targets while electromagnetic prospecting is being performed to achieve deep target exploration with high resolution a new technique known as the short offset transient electromagnetic method sotem is applied in this research area this method can be used to perform near source configuration surveys but shows no obvious difference between the deep magnetite deposit and low resistivity layer in this survey area therefore it cannot explore the magnetite deposit directly using the traditional magnetic component hz of sotem the ex component which can more effectively distinguish the high resistivity surrounding rock and overlying low resistivity layer than the hz component is used for exploration first 2d forward modeling and sensitivity analysis of the high resistivity body are carried out to determine the different responses of the ex and hz components respectively moreover to better determine the interface between the surrounding rock and low resistivity layer 1d occam inversion and the generalized inverse matrix inversion method are used furthermore aiming at the static effect of the ex component in field exploration joint inversion of the ex and hz components is carried out for comprehensive interpretation finally a field test is conducted and the drilling results are used for verification the research results can provide an effective geophysical model for the exploration of contact metasomatic magnetite deposits

low temperature feldspar and illite formation through bioreduction of fe iii bearing smectite by an alkaliphilic bacterium abstract biogenic mineral assemblages that form from circumneutral microbial reduction of iron in smectite have been suggested as biosignatures in the geological record however mineralogical transformation of smectite mediated by microbes under extreme ph condition is still poorly known the objective of this study was to understand the reduction capacity of structural fe iii in iron rich smectite nontronite nau 2 by a novel anaerobic alkaliphile strain ccsd 1 isolated from the deep subsurface and associated mineralogical changes the experiments with ccsd 1 were conducted in a growth medium containing the electron shuttle anthraquinone 2 6 disulfonate aqds at ph 9 4 the fe ii concentration was monitored over the course of the experiment via wet chemistry and unreduced and reduced nontronites were characterized with x ray diffraction xrd and scanning and transmission electron microscopy sem and tem the results indicate that strain ccsd 1 utilizes proteinaceous substrates yeast extract and tryptone to reduce structural fe iii in smectite with the maximum reduction extent of 26 2 mineralogical analysis confirmed that biogenic plagioclase na ca feldspar and illite were formed after bioreduction our work shows that the interaction between alkaliphile and iron bearing smectite could account for low temperature feldspar and illite formation and these minerals may be used as biosignatures in sedimentary rocks

geochemical and mineralogical studies of lake specchio di venere pantelleria island italy abstract isotopic and chemical investigations of lake specchio di venere on the island of pantelleria italy have been carried out in order to investigate the relationships existing between the lake water and the thermal springs feeding the lake with respect to the chemical composition of the thermal springs which discharge at the strand line the total content of dissolved solids of the lake water increases through an evaporative process under steady state conditions the lake water is depleted in ca mg sr total carbon and sio 2 on the basis of chemical and isotopic balances 35 of the recharge is lost by infiltration and the remaining 65 by evaporation the lacustrine sediments contain aragonite amorphous silica and dolomite the dolomite is formed either by direct precipitation or derived from aragonite by a dissolution reprecipitation process isotopic data relative to aragonite and dolomite are in good agreement with the mineralogical interpretation carbonate precipitation is caused by the rise of ph related to the loss of co 2 from spring water p co 2 1 2 atm ph 6 3 up to the final value observed in the lake water p co 2 10 2 7 atm ph 9 0 the conclusions drawn from chemical and isotopic data were tested by a mathematical equilibrium model in which evaporation is simulated allowing both co 2 outgassing and precipitation or dissolution of minerals the results of these calculations performed using the phreeqe computer program are in good agreement with the observations

iron and oxygen isotope fractionation during iron uv photo oxidation implications for early earth and mars abstract banded iron formations bifs contain appreciable amounts of ferric iron fe 3 the mechanism by which ferrous iron fe 2 was oxidized into fe 3 in an atmosphere that was globally anoxic is highly debated of the three scenarios that have been proposed to explain bif formation photo oxidation by uv photons is the only one that does not involve life the other two are oxidation by o 2 produced by photosynthesis and anoxygenic photosynthesis whereby fe 2 is directly used as electron donor in place of water we experimentally investigated iron and oxygen isotope fractionation imparted by iron photo oxidation at a ph of 7 3 the iron isotope fractionation between precipitated fe 3 bearing lepidocrocite and dissolved fe 2 follows a rayleigh distillation with an instantaneous 56 fe 54 fe fractionation factor of 1 2 such enrichment in the heavy isotopes of iron is consistent with the values measured in bifs we also investigated the nature of the mass fractionation law that governs iron isotope fractionation in the photo oxidation experiments i e the slope of the 56 fe 57 fe relationship the experimental run products follow a mass dependent law corresponding to the high t equilibrium limit the fact that a 3 8 gyr old bif sample if g from isua greenland falls on the same fractionation line confirms that iron photo oxidation in the surface layers of the oceans was a viable pathway to bif formation in the archean when the atmosphere was largely transparent to uv photons our experiments allow us to estimate the quantum yield of the photo oxidation process 0 07 iron atom oxidized per photon absorbed this yield is used to model iron oxidation on early mars as the photo oxidation proceeds the aqueous medium becomes more acidic which slows down the reaction by changing the speciation of iron to species that are less efficient at absorbing uv photons iron photo oxidation in centimeter to meter deep water ponds would take months to years to complete oxidation by o 2 in acidic conditions would be slower iron photo oxidation is thus likely responsible for the formation of jarosite hematite deposits on mars provided that shallow standing water bodies could persist for extended periods of time the oxygen isotopic composition of lepidocrocite precipitated from the photo oxidation experiment was measured and it is related to the composition of water by mass dependent fractionation the precipitate fluid 18 o 16 o isotope fractionation of 6 is consistent with previous determinations of oxygen equilibrium fraction factors between iron oxyhydroxides and water

near surface site investigation and imaging of karst cave using comprehensive geophysical and laser scanning a case study in shandong china the karst development of jiao dong peninsula in shandong province has formed a unique karst landform and has become one of the typical karst areas in the north of china karst collapse occurred during the construction of high speed railways and caused many environmental problems to reveal the development situation of karst area in shandong the conventional surface geophysical techniques were used for karst exploration and location of key area and the results of drilling verification were in good agreement with the results of geophysical exploration at the same time the new technology in the field of surveying and mapping 3d laser scanning technology is cited in the engineering geophysical exploration and the key issue is the shape and size of the karst it makes up for the shortcomings of traditional geophysical exploration technology that can only be qualitative and cannot be quantitatively analyzed it realizes the transformation of karst exploration from regional detection to single cave exploration and better implements the concept of information construction it has contributed to the smooth progress of the project and environmental protection

shallow water and hypersaline features from the middle proterozoic mt isa sequence fundamental differences of opinion exist about the depositional environment of sediments which host the middle proterozoic1 mt isa cu and pb zn deposits2 3 of northwestern queensland australia the copper host has been repeatedly interpreted as an algal reef2 4 and recently as a sabkha5 whilst models as diverse as saline lakes6 and deep oceanic basins3 7 9 have been proposed for the deposition of both the cu and pb zn ore bodies we now report the discovery of stromatolites halite casts large cross bedded channel deposits and flat pebble conglomerates in sediments closely associated with the ore deposit these sedimentary structures provide evidence of shallow water deposition with intermittent hypersaline and emergent conditions during deposition of the upper mt isa group3 6 sequence the assemblage of sedimentary structures strongly supports a shallow marine or shallow lacustrine depositional model either model is inconsistent with the previously postulated red sea type submarine exhalative mineralization model3 7 9 for mt isa instead we argue that mt isa ore formation took place in a shallow water system possibly aided by the action of evaporite derived brines

bicarbonate fluxes and co2 consumption by chemical weathering on the japanese archipelago application of a multi lithological model framework abstract prediction of co 2 consumption by chemical weathering is important to understand the global carbon cycle and island arcs are assumed to contribute significantly to the transfer of atmospheric soil co 2 to the oceans previous work established empirical functions for bicarbonate flux and co 2 consumption in dependence of runoff for five to six lithological classes these functions were applied in global studies however it has remained uncertain if improvements can be achieved by considering further factors or by an enhanced lithological classification scheme this study applies a new lithological map of japan with an enhanced lithological classification a hydrochemical data set representing 382 catchments covering 44 4 of the japanese archipelago and a multi lithological model approach to predict bicarbonate fluxes and co 2 consumption by chemical weathering because of significant carbonate contents in sediments different from carbonate sedimentary rocks acid plutonics and metamorphics firstly a bicarbonate flux model approach is established and secondly silicate and carbonate co 2 consumption is estimated based on the geochemical composition of rocks in accordance with previous studies on the catchment scale the most important factors controlling bicarbonate fluxes are lithology and runoff the anion ratio hco 3 so 4 2 cl is identified as the third most important predictor because anion sources and anion composition of river water have a great effect on bicarbonate concentrations and last but not least potential predictors such as gradient of slope temperature and physical erosion explain some part of the observed bicarbonate flux variation these potential predictors have been discussed in literature but quantification of the effects of these factors remains difficult due to their correlation with runoff and lithology however all tested models reproduce a total of observed bicarbonate fluxes within 10 on the regional scale including the simplest model which recognizes only lithology and runoff as predictors model results suggest that bicarbonate flux from the japanese archipelago is about 6 61 t c km 2 a 1 and co 2 consumption by chemical weathering is about 6 05 t c km 2 a 1 91 6 of bicarbonate flux this co 2 consumption rate is 3 2 times above the global average rate the silicate to carbonate co 2 consumption ratio is comparatively high it amounts to 9 9 which is above the global value the latter one being 1 to 1 5 carbonate sedimentary rocks contribute only 1 3 to bicarbonate fluxes due to their low areal proportion 0 2 acid volcanic rocks va show the lowest bicarbonate fluxes on average while basic and intermediate volcanics vb as well as pyroclastics py are in the range of the japanese average value the carbonate weathering contribution to bicarbonate fluxes from mixed sediments siliciclastic sediments metamorphics and acid plutonics is estimated to be 69 2 23 3 63 4 and 24 8 respectively only an average carbonate co 2 consumption per lithological class is calculated because no function based on typical predictors could be established to calculate carbonate weathering contribution to silicate dominated lithological classes this can be attributed to large spatial differences in carbonate content in rocks and to corresponding contributions to bicarbonatefluxes in the following results are compared to bicarbonate flux models of previous studies and identified differences are discussed in conclusion recognition of carbonate abundance in silicate dominated lithological classes including trace calcite is important to calculate silicate carbonate co 2 consumption ratios presented results are relevant for studies modelling co 2 consumption by chemical weathering in context of the global c cycle

temporal variation in calcification in marine cyanobacteria periods of widespread abundance of calcified cyanobacteria in marine environments are here termed cyanobacterial calcification episodes cces intense such episodes occurred in the cambrian early ordovician late devonian and mid late triassic mild episodes occurred during the early carboniferous and jurassic early cretaceous possible episodes during parts of the silurian and permian await confirmation cyanobacterial calcification is not obligate but is dependent upon environmental factors favouring carbonate precipitation cyanobacterial calcification episodes are therefore interpreted as reflecting periods of increased marine carbonate precipitation this is supported by the general abundance of marine carbonate cements and oolites during cyanobacterial calcification episodes cyanobacterial calcification episodes correspond with phanerozoic periods for which elevated global temperatures have been inferred they do not appear to correlate closely with inferred changes in aragonite calcite facilitation the sandberg curve and p co2 through time it is concluded that variations in the precipitation rates of abiotic and quasi abiotic marine carbonates through time have been controlled primarily by temperature the mineralogy of these precipitates appears instead to have been mainly influenced by p co2 and the mg ca ratio also linked to sea level through plate tectonic processes thus the controls on rate and mineralogy of precipitation were independent of one another

the earth s early hydrosphere the date at which the earth s hydrosphere came into existence is unknown although all current geological models for the very early precambrian predict or suppose a hydrosphere1 4 there are difficulties in reconciling this with geological and astronomical theories of planetary formation furthermore the effect of a substantial hydrosphere on the precambrian climatic environment is difficult to determine recent developments make it possible to synthesize a picture of this environment during the 700 myr preceding the deposition of the oldest known sediments5 we attempt such a synthesis here drawing together work on the dynamics of accretion from the proto planetary nebula6 7 and of planetary differentiation7 on the role of volatiles in impact cratering8 10 and on the composition11 22 isotope systematics23 25 and radiation climatology26 29 of the early hydrosphere we can reconcile these diverse contributions if the hydrosphere the inventory of excess volatiles1 is allowed to differentiate during accretion with most of the h2o and co2 going rapidly into oceans and sediments both gradual outgassing30 and a massive co2 atmosphere2 are unlikely and a reduced mantle beneath a neutral hydrosphere is not paradoxical1 3 17 results from both a one dimensional radiative convective 1d rc model and a general circulation model suggest that self regulating mechanisms are important in the climate of this early hydrosphere

siderite cannot be used as co2 sensor for archaean atmospheres abstract it was proposed to utilize siderite feco3 in mid to late archaean superior type banded as a proxy to constrain the co2 partial pressure of archaean atmospheres implicit in this proposition is that siderite was a primary carbonate mineral that crystallized directly from fe2 enriched archaean seawater in equilibrium with atmospheric co2 to our knowledge that proposition has not been demonstrated to be valid we test with water gas exchange experiments under controlled co2 partial pressures if siderite can be stabilized as a primary mineral in fe2 bearing seawater reduced seawater proxies enriched in fe2 and mn2 are equilibrated with reduced n2 ch4 co2 h2 gas phases with variable co2 the solid phases stabilized in fe2 enriched water compositions are amorphous ferrous iron hydroxy carbonates crystalline siderite feco3 is not found to be a stable phase the phases precipitating from mn2 enriched water include crystalline rhodochrosite mnco3 and possibly amorphous mn enriched phases based on these results we advise against using siderite in banded iron formations as a co2 sensor for the archaean atmosphere

the europium anomalies in banded iron formations and the thermal history of the oceanic crust abstract the ree rare earth element patterns in banded iron formations bif s from various sites in north america two sites in finland and three drillcores of the hamersley basin in western australia have been investigated using icp ms inductively coupled plasma mass spectrometry and inaa instrumental neutron activation analysis the results of this study as well as existing data show trends in the eu anomalies bif s older than 2 5 ga exhibit positive eu anomalies while younger ones exhibit none in chemical sediments between 2 5 and 2 3 ga both trends can be found because of the worldwide distribution of bif s this feature can be considered as a global change in the conditions controlling ree mobilization consideration of the redox conditions of bif formation in comparison with the calculated and measured eu redox equilibria suggests that a eu anomaly points to a dominantly hydrothermal source of ree s with solution temperatures above 175 c we suggest that the disappearance of the eu anomaly towards the proterozoic marks a change from mainly high temperature hydrothermal to dominantly low temperature alteration

researches on detection of 3 d underground cave based on tem technique because of unreasonable coal mining in china there are many unknown underground caves and the inhabited environment of humans is threatened by many geologic hazards such as cracking of the buildings ground subsidence etc to make the coal companies aware of the harmfulness of these hazards it is urgent to determine the reasons for the hazards in this paper transient electromagnetic method tem is used to detect the ground resistance caves instead of the time consuming and expensive direct drilling survey numerical results of the 3 d synthetic model and real field survey data are given the results showed that the tem method can be used to detect a complicated air filled underground 3 d cave and coincide with the results of direct drilling survey

depth of investigation in electromagnetic sounding methods the time or frequency at which the electromagnetic em response of a buried inhomogeneity can first be measured is determined by its depth of burial and the average conductivity of the overlying section it is relatively independent of the type of source or receiver and their separation the ability to make measurements at this time or frequency however depends on the sensitivity and accuracy of the instrumentation the signal strength and the ambient noise level these factors affect different em sounding systems in surprisingly different ways for the magnetotelluric mt method it is possible to detect a buried half space under about 1 5 skin depths of overburden the maximum depth of investigation is virtually unbounded because of high signal strengths at low frequencies transient electromagnetic tem soundings on the other hand have a limited depth of penetration but are less affected by static shift errors for tem a buried inhomogeneity can be detected under about one diffusion depth of overburden for conventional near zone sounding in which induced voltage is measured impulse response the depth of investigation is proportional to the 1 5 power of the source moment and ground resistivity by contrast if the receiver is a magnetometer step response system the depth of investigation is proportional to the 1 3 power of source moment and is no longer a function of resistivity magnetic field measurements may therefore be superior for exploration in conductive areas such as sedimentary basins far zone or long offset tem soundings are traditionally used for deep exploration the depth of investigation for a voltage receiver is proportional to the 1 4 power of source moment and resistivity and is inversely proportional to the source receiver separation magnetic field measurements are difficult to make at long offsets because instrumental accuracy limits the measurement of the very slow decay of the magnetic field frequency domain controlled source systems are ideally suited for sounding at the very shallow depths needed for engineering archaeological and groundwater applications because of the relative ease of extending the measurements to arbitrarily high frequencies and also because geometric soundings can be made at low induction numbers

archaean phosphates a case study of transformation processes in apatite from the barberton greenstone belt multiple tools have been used to determine the sensitivity of phosphates from the early archaean barberton greenstone belt to transformation the assessment of the degree of transformation is crucial for verifying data about the parameters of the paleo environment from the obtained results three generations of phosphates can be distinguished group a is observed in cherts and banded iron formation bif early generation fluor hydroxyapatite that precipitated from seawater it is characterized by flat rare earth element ree patterns with a positive eu anomaly and high y ho ratio in the range of 54 70 apatites in this group lack any visible indicators of secondary alterations at the micro and nanoscales fourier transform infrared spectra indicate that these apatites are relatively rich in water and due to cationic substitution their oh stretching regions exhibit complex ordering and numerous component bands the characteristics observed in the cherts and silicified felsic volcaniclastics of group b imply advanced metasomatic alteration they exhibit light and heavy ree depletion and an absence of water in the halogen site nanoscale investigations reveal cracks pores nanofluid inclusions and nanochannel like structures as well as inclusions group c is represented by igneous derived apatites that partially reflect their igneous origin the phosphates are predominantly fluorapatite with typical magmatic apatite ree distribution patterns imaging at the micro and nanoscales indicates that they partially preserve the signature of igneous origin it seems that some of the analyzed apatite partially preserved their primordial features therefore they might be used for the reconstruction of archaean abiotic systems

detecting shallow caverns in china using tem to detect shallow anomalies under certain conditions electromagnetic methods can be more effective in reconnaissance surveying than high resolution surface seismic this case study describes the results of the transient electromagnetic method tem in an environment where initial field trials showed that surface seismic was difficult to employ effectively and expensive to implement

timing of the descent into the last ice age determined by the bipolar seesaw we present planktonic foraminiferal fauna and isotope records from the se atlantic that highlight the nature of millennial scale variability over the last 100 kyr we derive an hypothesis driven age model for our records based on the empirical link between variations in greenland temperature ocean circulation and carbonate preservation in the deep se atlantic our results extend earlier findings of an anti phase seesaw relationship between north and south for the largest abrupt events of marine isotope stage mis 3 2 and the last deglaciation in particular we find that heinrich stadials were paralleled by inferred southward shifts of the thermal subtropical front these were followed by pronounced rebounds of the front with the return to interstadial conditions in the north our results also shed light on the mechanism of glaciation in contrast to the last deglaciation which was a globally symmetric change superposed by interhemispheric asynchronicity we find that the descent into full glacial conditions at the onset of mis 4 70 ka displayed interhemispheric synchrony we suggest that this globally synchronous descent into glacial mis 4 was preconditioned by orbital changes but that the timing was ultimately determined by abrupt changes in ocean atmosphere circulation patterns i e the bipolar seesaw

appraisal of an array tem method in detecting a mined out area beneath a conductive layer the transient electromagnetic method has been extensively used for the detection of mined out area in china for the past few years in the cases that the mined out area is overlain by a conductive layer the detection of the target layer is difficult with a traditional loop source tem method in order to detect the target layer in this condition this paper presents a newly developed array tem method which uses a grounded wire source the underground current density distribution and the responses of the grounded wire source tem configuration are modeled to demonstrate that the target layer is detectable in this condition the 1d occam inversion routine is applied to the synthetic single station data and common middle point gather the result reveals that the electric source tem method is capable of recovering the resistive target layer beneath the conductive overburden by contrast the conductive target layer cannot be recovered unless the distance between the target layer and the conductive overburden is large compared with inversion result of the single station data the inversion of common middle point gather can better recover the resistivity of the target layer finally a case study illustrates that the array tem method is successfully applied in recovering a water filled mined out area beneath a conductive overburden

cave detection in limestone using ground penetrating radar ground penetrating radar gpr is becoming a more common component of the standard array of geophysical techniques that are used by archaeologists in this paper we report on the use of gpr to survey an area of archaeologically important karst topography at kitley caves in devon u k we describe the use of gpr to detect voids within a limestone outcrop as an aid to locating cave systems which might contain sediments suitable for excavation the performance of the gpr equipment is analysed and the results compared to those obtained with an electrical resistance survey carried out at the same location in particular the depth of penetration of the gpr is estimated and we report discernible echo signals from a much greater depth than is usually reported in archaeological applications of gpr

b_na rich palaeoproterozoic aravalli metasediments of evaporitic association nw india a new repository of gold mineralization we report field observations and preliminary petrochemical and stable isotopic compositions of the host rock and sulfide minerals for a recently discovered sulfide hosted gold deposit from the palaeoproterozoic aravalli rocks in northwestern india gold occurs associated with feascu co sulfides in lithofacies of diverse mineralogical composition dominated by amphibole bearing dolomitic marble and albite rich quartzo feldspathic rocks qfr the presence of vugs believed to be after dissolution of halite patches coupled with the development of scapolite bearing assemblages in dolomite marble occurrence of tourmaline rich mineralized rocks and very high na content of carbonates and qfr indicate hypersaline depositional environment for the host rock a narrow spread of 34 scdt values from 10 5 to 12 8 for stratiform arsenopyrite and remobilized pyrrhotite corroborates hypersaline to evaporitic depositional environment the 13 c values for gold bearing carbonates show bimodal distribution one population mean 0 4 v pdb is close to the sea water carbonate values while the other 3 l indicates probable mantle affinity the 18 o values for carbonates mean 18 4 v smow are not discriminative as they appear to have been modified by subsequent metamorphism and hydrothermal activity interpretation of mantellic source for carbon is borne out from the absence of biogenic activity and incompatibility of significantly negative 13 c values in the evaporitic setting of deposition of bhukia rocks we suggest that nab rich fluids channeled through rift related faults were responsible for creating hypersaline conditions that eventually evolved into an evaporitic environment mantle carbon through some still deeper faults was probably responsible for the gold transport and its subsequent deposition in an otherwise uncommon evaporitic repository of carbonates and qfr 2002 elsevier science b v all rights reserved

geochemistry of bolivian salars lipez southern altiplano origin of solutes and brine evolution abstract the southern bolivian altiplano is a volcanic area which contains numerous undrained basins occupied by playas and saline lakes locally named salars solutes carried by springs and rivers into the salars originate mostly from the alteration of the volcanic rocks and the re solution of ancient buried evaporites both weathering and hydrothermal alteration lead to na hco 3 inflow waters of similar composition high contents of lithium and boron are not specifically related to hydrothermal activity evaporite leaching leads to na cl inflow waters of higher salinity atmospheric precipitation contributes only a small amount of ca and so 4 and very little na or cl the calculated evaporative evolution of the inflow waters shows that about half of them should become highly alkaline brines and the other half should end as near neutral brines however alkaline soda lakes are rare in this region most lake brines are of the na cl and na cl so 4 types to understand this anomaly one characteristic sequence of evaporating waters was studied in detail precipitation of calcite and mg smectites accounts only partially for the reduction of alkalinity a further loss of alkalinity is probably related to the oxidation of wind blown native sulfur in peripheral ponds wind blown sulfur is also deposited around the lakes on the drainage basins in the rainy season ephemeral streams carry along sulfur particles in permanent pools of the preconcentration areas a hydrologic control of brine chemistry is suspected inflow waters that should become alkaline appear to evolve to neutral brines if they remain in contact with atmospheric dust and peripheral colluvium for a long time on the contrary inflow waters to soda lakes are generally close to the shore and have only minimal contact with atmospheric dust and peripheral sediments presently all lakes are at relatively low levels and inflow waters often drain an important area of the drainage basin before reaching the topographic low in the past lakes were at higher levels and less interaction occurred between inflow waters atmospheric dust and peripheral sediments as a result the chemistry of some lakes may have changed during the quaternary

estimating depth of investigation in dc resistivity and ip surveys in this paper the term depth of investigation refers generically to the depth below which surface data are insensitive to the value of the physical property of the earth estimates of this depth for dc resistivity and induced polarization ip surveys are essential when interpreting models obtained from any inversion because structure beneath that depth should not be interpreted geologically we advocate carrying out a limited exploration of model space to generate a few models that have minimum structure and that differ substantially from the final model used for interpretation visual assessment of these models often provides answers about existence of deeper structures differences between the models can be quantified into a depth of investigation doi index that can be displayed with the model used for interpretation an explicit algorithm for evaluating the doi is presented the doi curves are somewhat dependent upon the parameters used to generate the different models but the results are robust

paleoproterozoic stark formation athapuscow basin northwest canada record of cratonic scale salinity crisis abstract the paleoproterozoic stark formation a thick breccia unit formed during the transition from marine to non marine foreland basin fill in the athapuscow basin northwest territories canada four types of breccia occur in the stark formation 1 bedded breccias at the base of the unit overlying the basinal facies of the underlying pethei group are interpreted as debris flows 2 massive chaotic breccias occur in the lower part of the stark formation throughout the basin and these are interpreted to be evaporite collapse breccias 3 siltstone and mudstone breccia occurs in the upper part of the stark formation and is also interpreted as evaporite collapse breccia though much less evaporite was involved in its formation than the underlying chaotic breccia and 4 laminar accretionary breccia consisting of laminar carbonate clasts commonly with flat bottoms and convex up upper surface geometries these clasts occur in lenticular pods and are interpreted to form in caves following dissolution of evaporites or carbonates the widespread presence and abundance of evaporite pseudomorphs especially halite in all breccia types the stratigraphic restriction of the stark formation and irregular filling above this unit indicates that all but the bedded breccia formed by the dissolution and collapse of evaporites chaotic breccia directly above underlying pethei group shallow water and deep water carbonates indicates the evaporates formed across the platform and adjacent deep basin foundered megaclasts up to 1 5 km long and 40 m thick in basinal settings suggest cumulative evaporite thicknesses on the order of a few tens to a few hundreds of meters carbonate clasts in all the breccias contain abundant wave ripples planar laminations stromatolites and ooids these structures along with a paucity of subaerial exposure features indicates nearly all carbonate deposition in the stark was subaqueous thus by inference the evaporites in the stark formation were also partially subaqueous displacive halite pseudomorphs are common throughout all facies in the stark formation silicified and dolomite filled halite pseudomorphs are common along the contact between the evaporite collapse breccia and underlying carbonate platform pethei group and surrounding large clasts in basinal settings silicified hopper crystal casts within deep water rhythmites of the uppermost pethei group indicate precipitation of halite over deep waters gypsum pseudomorphs are exceedingly rare and anhydrite pseudomorphs were not observed the dominance of halite features in this basin and two penecontemporaneous basins kilihigok basin and wopmay orogen surrounding the slave craton suggests that relative to the present day seawater at 1 9 to 1 8 ga was oversaturated with respect to calcium carbonate had higher hco3 concentration and possibly was depleted in so42 the dearth of extensive thick bedded marine gypsum in the archean and early paleoproterozoic can be explained by low atmospheric oxygen content prior to 2 ga in conjunction with increased carbonate saturation before 1 6 ga

nitrogen isotope evidence for alkaline lakes on late archean continents abstract nitrogen isotope ratios in ancient sedimentary rocks are generally interpreted as a proxy for metabolic nitrogen pathways and the redox state of the water column fractionation processes occurring under anoxic alkaline conditions during the dissociation of nh 4 to h and volatile nh3 are frequently overlooked although this mechanism imparts large isotopic fractionations here we propose that nh3 volatilization is largely responsible for 15n values of up to 50 at high c n ratios in the late archean tumbiana formation this sequence of sedimentary rocks represents a system of lakes that formed on subaerial flood basalts and were partly filled by basaltic volcanic ash aqueous alteration of volcanic glass followed by evaporative concentration of ions should have led to the development of high alkalinity with a ph of 9 or higher as in modern analogues in this sedimentologically unusual setting nitrogen isotope ratios thus provide indirect evidence for the oldest alkaline lake system in the rock record these very heavy lacustrine 15n values contrast markedly with those of archean marine sedimentary rocks making a precambrian soda ocean unlikely today alkaline lakes are among the most productive ecosystems on earth some nutrients in particular molybdenum are more soluble at high ph and certain prebiotic reactions would likely have been favored under alkaline conditions in similar settings earlier in earth s history hence alkaline lakes in the archean could have been significant for the origin and early evolution of life

secular variations in precambrian seawater chemistry and the timing of precambrian aragonite seas and calcite seas an extension of the seawater secular variation model that successfully predicted the observed timing of phanerozoic mgso 4 vs kcl marine evaporites and aragonite seas vs calcite seas has been applied to the prediction of the secular variations in the major ion chemistry of seawater and aragonite seas vs calcite seas during the precambrian testing of the predictions was based on those precambrian seafloor carbonate precipitates that have been interpreted by others to have formed originally as aragonite of 16 examples of precambrian seafloor aragonite 14 fall within the 6 periods of aragonite seas predicted for the late archean proterozoic by the model 1 falls on the transition between an aragonite sea and calcite sea and 1 falls in a period of calcite seas this strong correlation supports the following predictions of the model 1 precambrian seawater was a saline nacl water with ca hco 3 since at least the late archean 2 the major ion compositions of precambrian seawater chemistry and their secular variations are in the same ranges as those of phanerozoic seawater 3 the mg ca mole ratio in seawater has controlled the types of caco 3 polymorphs that have precipitated from earth9s oceans throughout the phanerozoic and most if not all of the precambrian

the composition of the precambrian ocean waters abstract the composition of the precambrian oceans was different from the present composition this is a direct consequence of a co2 atmosphere depleted in oxygen at the beginning the mineralization was lower the oceans waters were chloro dicarbonated with a lower tenor of chlorine richer in phosphates and they were depleted in sulphates sulphur was in the reduced state of sulphides the abundance of phosphates supported the expansion of life the cations na and mg2 coexisted with ca2 fe2 and ba2 whose levels were higher than they are today the main trends of the evolution are schematized in the figure

hydrogeochemistry of lake turkana kenya mass balance and mineral reactions in an alkaline lake abstract lake turkana in northwestern kenya is a closed basin alkaline ph 9 2 lake of moderate salinity tds 2500 ppm principal ions are na hco 3 and ci the lake is essentially polymictic in the northern basin and little compositional variation occurs in surface waters the omo river is the principal influent providing some 80 90 of water input to the lake chloride has an apparent accumulation time of about 2500 years after accounting for burial of interstitial water the bottom sediments are predominantly detrital and fine grained yet mineral water reactions are very important for the geochcmical budget ca 2 is precipitated as calcite na is removed as an exchangeable cation on smectite mg 2 is probably incorporated into a mg silicate phase most likely poorlycrystalline smectite as it enters the lake water k may be used in illite regradation cation exchange is a very important process in the mass balance of this lake over 40 of incoming na is removed as an exchangeable cation after cation exchange and interstitial water burial na has a response time of 2650 years which compares favorably with that of chloride these processes seem to occur rapidly within the water mass of the lake other reactions may be important in regulating interstitial water compositions several changes occur in the upper 3m of sediment interstitial water ph drops to 8 3 and alkalinity increases slightly with depth so 2 4 decreases slightly and amorphous silica saturation is approached these changes are a response to organic matter oxidation and the dissolution of unstable silicates rather than a reversal of reactions occurring in the lake water high rates of sedimentation up to 1 cm per year may minimize the effects of diffusion between the interstitial waters and the lake water although burial of interstitial water assumes considerable importance

a new method for geoelectrical investigations underwater1 a new electrical method is proposed for determining the apparent resistivity of multi earth layers located underwater the method is based on direct current geoelectric sounding principles a layered earth model is used to simulate the stratigraphic target the measurement array is of pole pole type it is located underwater and is orientated vertically this particular electrode configuration is very useful when conventional electrical methods cannot be used especially if the water depth becomes very important the calculated apparent resistivity shows a substantial quality increase in the measured signal caused by the underwater targets from which little or no response is measured using conventional surface electrode methods in practice however different factors such as water stratification underwater streams or meteorological conditions complicate the interpretation of the field results a case study is presented where field surveys carried out on lake geneva were interpreted using the calculated apparent resistivity master curves

the role of carbonates in the evolution of early martian oceans central to the question of life on mars is whether there has been liquid water on the martian surface and how the planet could have evolved from possible initial warm and wet conditions to the cold and dry present state virtually all models for this climatic evolution rely strongly on the removal of an initial thick carbon dioxide atmosphere by precipitation of carbonate minerals from surface waters that may have been quite similar to those of hadean eon earth s oceans in order for this to occur a hydrologic cycle would be necessary in which chemical weathering of silicate rocks consumes co2 that precipitates as carbonates in an acidic martian ocean which probably had a very high alkalinity the consumption of atmospheric co2 by this process would result in a gradual decrease of the atmospheric greenhouse influence and cooling of the climate once the surface of mars became cold enough so that freezing conditions prevailed the hydrologic cycle would largely cease and the uptake of co2 by silicate rock weathering would greatly diminish the alkalinity of the freezing seawater would probably be sufficient to result in the removal of all calcium as calcium carbonate some magnesium and sodium would also likely be removed as carbonates as well the removal of these cations as carbonates has a major influence on the final temperature at which liquid brines would be able to persist on the surface of mars during the period of freezing the oceans would act as a source of co2 rather than a sink further slowing the rate of climate change on mars

weathering of pumice in the sediments as a possible source of major ions for the waters of lake taupo new zealand abstract the mass flows of major ions na k ca mg so 4 cl and hco 3 into lake taupo with the surface waters draining the lake catchment are less than the mass flows of major ions leaving the lake some of these differences are the result of geothermal fluid entering the lake and the mass contributions from this fluid are estimated from the li budget for the lake an accurate hydrological balance for the lake suggests a groundwater inflow of 8 m 3 s 1 by assuming that this groundwater has the same composition as spring waters entering the lake from pumice aquifers the mass contributions from groundwater are included in the majorion budgets combination of all these mass flows in the budgets still leaves unexplained differences between the quantities of major ions entering the lake and the quantities leaving the lake despite the water budget being complete it is shown that the remaining mass flows in the budgets could be due to the dissolution of pumice within the lake na concentrations in the interstitial waters of lake sediments are higher than in the overlying lake water and the calculated flux of na ions from the sediment into the lake water would satisfy the mass budget for na it is concluded that the dissolution of pumice in lake sediments could contribute major ions to the waters of some lakes in volcanic regions

chemistry and stromatolites of the sea linked satonda crater lake indonesia a recent model for the precambrian sea abstract the abundance of in situ calcified stromatolites in the precambrian paleontological record and their absence from modern seas is still an enigma we report on the discovery of the first recent in situ calcified stromatolites growing in a sea linked environment the stromatolites are produced by coccoid cyanobacteria and started to grow 4000 yr ago in the crater lake of satonda island indonesia compared to seawater the lake has gained alkalinity and lost ca its ph 8 45 as well as its saturation with respect to calcite is significantly higher than in seawater the additional alkalinity is provided by biogenic co2 and subsequent weathering of volcanic silicates satonda crater lake may provide an analogue to the stromatolite sustaining precambrian marine environments which therefore may have been more alkaline than present day seawater this conclusion is congruent with the recently advanced hypothesis of an early soda ocean

europa s crust and ocean origin composition and the prospects for life abstract we have considered a wide array of scenarios for europa s chemical evolution in an attempt to explain the presence of ice and hydrated materials on its surface and to understand the physical and chemical nature of any ocean that may lie below we postulate that following formation of the jovian system the europan evolutionary sequence has as its major links a initial carbonaceous chondrite rock b global primordial aqueous differentiation and formation of an impure primordial hydrous crust c brine evolution and intracrustal differentiation d degassing of europa s mantle and gas venting e hydrothermal processes and f chemical surface alteration our models were developed in the context of constraints provided by galileo imaging near infrared reflectance spectroscopy and gravity and magnetometer data low temperature aqueous differentiation from a carbonaceous ci or cm chondrite precursor without further chemical processing would result in a crust ocean enriched in magnesium sulfate and sodium sulfate consistent with galileo spectroscopy within the bounds of this simple model a wide range of possible layered structures may result the final state depends on the details of intracrustal differentiation devolatilization of the rocky mantle and hydrothermal brine reactions could have produced very different ocean crust compositions e g an ocean crust of sodium carbonate or sulfuric acid or a crust containing abundant clathrate hydrates realistic chemical physical evolution scenarios differ greatly in detailed predictions but they generally call for a highly impure and chemically layered crust some of these models could lead also to lateral chemical heterogeneities by diapiric upwellings and or cryovolcanism we describe some plausible geological consequences of the physical chemical structures predicted from these scenarios these predicted consequences and observed aspects of europa s geology may serve as a basis for further analys is and discrimination among several alternative scenarios most chemical pathways could support viable ecosystems based on analogy with the metabolic and physiological versatility of terrestrial microorganisms

organic synthesis during fluid mixing in hydrothermal systems hydrothermal circulation can lead to fluid mixing on any planet with liquid water and a source of heat aqueous fluids with differing compositions especially different oxidation states are likely to be far from thermodynamic equilibrium when they mix and provide a source of free energy that can drive organic synthesis from co 2 and h 2 and or supply a source of geochemical energy to chemolithoautotrophic organisms results are presented that quantify the potential for organic synthesis during unbuffered fluid mixing in present submarine hydrothermal svstems as well as hypothetical systems that may have existed on the early earth and mars dissolved hydrogen present in submarine hydrothermal fluids owing to the high temperature reduction of h 2 o as seawater reacts with oceanic crustal rocks provides the reduction potential and the thermodynamic drive for organic synthesis from co 2 or bicarbonate as hydrothermal fluids mix with seawater the potential for organic synthesis is a strong function of the h 2 content of the hydrothermal fluid which is in turn a function of the prevailing oxidation state controlled by the composition of the rock that hosts the hydrothermal system hydrothermal fluids with initial oxidation states at or below those set by the fayalite magnetite quartz mineral assemblage show the greatest potential for driving organic synthesis these calculations show that it is thermodynamically possible for 100 of the carbon in the mixed fluid to be reduced to a mixture of carboxylic acids alcohols and ketones in the range 250 50 c as cold seawater mixes with the hydrothermal fluid as the temperature drops larger organic molecules are favored which implies that fluid mixing could drive the geochemical equivalent of a metaholic system this enormous reduction potential probably drives a large portion of the primary productivity around present seafloor hydrothermal vents and would have been present in hydrothermal systems on the early earth or mars the single largest control on the potential for organic synthesis is the composition of the rock that hosts the hydrothermal system

constraints on ocean carbonate chemistry and pco2 in the archaean and palaeoproterozoic one of the great problems in the history of earth s climate is how to reconcile evidence for liquid water and habitable climates on early earth with the faint young sun predicted from stellar evolution models possible solutions include a wide range of atmospheric and oceanic chemistries with large uncertainties in boundary conditions for the evolution and diversification of life and the role of the global carbon cycle in maintaining habitable climates increased atmospheric co 2 is a common component of many solutions but its connection to the carbon chemistry of the ocean remains unknown here we present calcium isotope data spanning the period from 2 7 to 1 9 billion years ago from evaporitic sedimentary carbonates that can test this relationship these data from the tumbiana formation the campbellrand platform and the pethei group exhibit limited variability such limited variability occurs in marine environments with a high ratio of calcium to carbonate alkalinity we are therefore able to rule out soda ocean conditions during this period of earth history we further interpret this and existing data to provide empirical constraints for carbonate chemistry of the ancient oceans and for the role of co 2 in compensating for the faint young sun

origin and mechanisms of k si metasomatism of ca 3 4 3 3ga volcaniclastic deposits and implications for archean seawater evolution examples from cherts of kittys gap pilbara craton australia and msauli barberton greenstone belt south africa abstract the effects of k si metasomatism during the formation of early archean replacement cherts have been quantified in this study by the investigation of two well known stratigraphic sections the msauli chert mc barberton greenstone belt south africa and the kittys gap chert kgc pilbara craton western australia the kgcs have a dacitic precursor similar to duffer formation dacites pilbara craton while the mcs are derived from al depleted komatiites similar to those from the weltevreden formation barberton greenstone belt mass balance calculations reveal that the volcaniclastic deposits had initial porosities of up to 85 vol for the kgc and of 65 vol for the mc secondary porosities 27 vol mc 8 vol kgc produced during k metasomatism are proportional to the dissolution of fe ca mg rich glass and precursor minerals komatiites have a higher chemical exchange potential than dacites each gram releasing 1 2 mmol fe2 2 8 mmol mg2 1 4 mmol ca2 and 1 1 mmol na to seawater together with 4 4 mmol o2 k metasomatism of 1 g of komatiite further implies an uptake of 0 67 mmol of k and 2 7 mmol of h the highest silica uptake is achieved for the kgc 82 mmol g of precursor this silica enrichment most likely operated in the water column and at the sediment water interface by sorption mechanisms on the surface of detrital particles and particulate organic matter as a result of seawater silica saturation acidic conditions ph 5 5 6 5 and hot temperatures 70 c favored the formation of k rich phyllosilicates by interaction with seawater during the early diagenetic alteration of the volcaniclastic particles the widespread occurrence of k si metasomatism in volcanic and sedimentary rocks can be regarded as a general alteration process of the early archean seafloor with a major influence on seawater composition the highly k selective metasomatism confirms previous studies suggesting that the archean ocean was acidic and probably in equilibrium with a co2 rich atmosphere

an early soda ocean in analogy to modern soda lakes commonly associated with volcanic regions it is postulated that the ancient sea had a high alkalinity a high ph and low ca and mg concentrations the change towards nacl dominance as observed in the present day ocean can best be explained by a series of mineral equilibria crustal differentiation and life processes in principle hydrothermal leaching of chlorine from the oceanic crust caused this ion to accumulate in the sea while at the same time dissolved carbonates became gradually removed by organisms and carbonates the switch from a soda to a halite ocean was accomplished 1 ga ago critical biochemical events marking the chemical evolution of the precambrian sea and their implications for the pco2 in air will be discussed

microbialite formation in seawater of increased alkalinity satonda crater lake indonesia abstract the crater lake of the small volcanic island satonda indonesia is unique for its red algal microbial reefs thriving in marine derived water of increased alkalinity the lake is a potential analogue for ancient oceans sustaining microbialites under open marine conditions current reef surfaces are dominated by living red algae covered by non calcified biofilms with scattered cyanobacteria and diatoms minor caco3 precipitates are restricted to the seasonally flooded reef tops which develop biofilms up to 500 m thick dominated by the cyanobacteria pleurocapsa calothrix phormidium and hyella microcrystalline aragonite patches form within the biofilm mucilage and fibrous aragonite cements grow in exopolymer poor spaces such as the inside of dead lysed green algal cells and reef framework voids cementation of lysed hadromerid sponge resting bodies results in the formation of wetheredella like structures hydrochemistry data and model calculations indicate that co2 degassing after seasonal mixis can shift the carbonate equilibrium to cause caco3 precipitation increased concentrations of dissolved inorganic carbon limit the ability of autotrophic biofilm microorganisms to shift the carbonate equilibrium therefore photosynthesis induced cyanobacterial calcification does not occur instead passive diffusion controlled eps mediated permineralization of biofilm mucus at contact with the considerably supersaturated open lake water takes place in contrast to extreme soda lakes the release of ca2 from aerobic degradation of extracellular polymeric substances does not support caco3 precipitation in satonda because the simultaneously released co2 is insufficiently buffered subfossil reef parts comprise green algal tufts encrusted by microstromatolites with layers of fibrous aragonite and an amorphous unidentified mg si phase the microstromatolites probably formed when lake satonda evolved from seawater to ca2 depleted raised alkalinity conditions because of sulfate reduction in bottom sediments and pronounced seasonality with deep mixing events and strong co2 degassing the latter effect caused rapid growth of fibrous aragonite while mg si layers replaced the initially mg calcite impregnated biofilms this could be explained by dissolution of siliceous diatoms and sponge spicules at high ph followed by mg calcite dissolution and mg silica precipitation at low ph due to heterotrophic activity within the entombed biofilms

rare earth element systematics of the chemically precipitated component in early precambrian iron formations and the evolution of the terrestrial atmosphere hydrosphere lithosphere system irrespective of provenance age and metamorphic grade the chemically precipitated component in early precambrian 2 3 ga iron formations ifs displays smyb cn 1 which reflects the corresponding ratios of contemporaneous seawater in conjunction with end if end shale jacobsen and pimentel klose 1988a b this rare earth element ree signature reveals that the ree distribution in early precambrian ifs must be explained by mixing between a marine bottom and a surface water component and that the rees and by analogy the fe cannot be derived from weathering of a continental source eusm n ratios of detritus free ifs are controlled by the marine bottom water component where eusm cn 1 results from ree input from high temperature high t hydrothermal fluids which received their ree signature during high t alteration of oceanic crust at spreading centres decreasing eusm cn of ifs with decreasing depositional age reflect the vaning importance of high t compared to low t 200 c hydrothermal fluids hence oceanic crust alteration for the ree budget of marine bottom waters and are related to decreasing upper mantle temperatures smyb n ratios of detritus free ifs are controlled by the marine surface water component whose ree distribution is affected by the same processes which operate today in the entire ocean mixing calculations reveal that smyb cn in early precambrian marine surface waters was significantly lower than it is today to explain this difference two mechanisms are discussed on the basis of higher pco2 and lower po2 levels of the precambrian atmosphere 1 1 higher co32 in precambrian river and coastal waters and 2 2 redox cycling of the rees at an oceanwide chemocline which separated anoxic and oxic water masses however these processes are synergetic and could have operated in unison the ree distribution in precambrian ifs is described as a result of mixing in a multicomponent system where high t and low t hydrothermal fluids contributed to the marine bottom water and ree input from the dissolved ree pool in river waters after some modification in estuaries dominated the ree distribution in marine surface waters after mixing of bottom and surface waters their combined ree load was quantitatively scavenged onto precipitating iron oxihydroxides or iron carbonates and deposited with the chemically precipitated component after addition of variable amounts of clastic detritus this eventually resulted in the ree distribution observed in precambrian ifs

diversity and origin of quartz cements in continental carbonates example from the lower cretaceous rift deposits of the south atlantic margin abstract silica precipitation in continental carbonates is a common process occurring during sedimentation and diagenesis the lower cretaceous rift deposits of the south atlantic equatorial margin which are intensively explored by petroleum companies provide good examples of such silicifications in carbonates exhibiting a wide diversity of petrographic habit of early to late quartz cements in order to understand the palaeoenvironmental and diagenetic conditions leading to this diversity we integrated detailed petrography of diagenetic sequences and quartz habit with 18oquartz measurements by sims of individual cements observed in samples from the offshore and onshore basins of the west african margin the petrographic description highlights the omnipresence of early fibrous microquartz cements exhibiting either length fast or length slow habit in addition to laminated microquartz and micro or mega quartz forms amongst the isotopic analysis the 18oquartz data show that length slow cements are generally strongly enriched in 18o 18oquartz ranging from 31 to 37 smow whereas length fast forms show less elevated values 25 c and

two opposing effects of sulfate reduction on carbonate precipitation in normal marine hypersaline and alkaline environments reply abstractsulfate reduction has been suggested as a mechanism to induce precipitation of calcium and magnesium carbonates in marine sediments and microbial mats through most of earth s his tory however sulfate reduction also causes a drop in ph that favors dissolution rather than precipitation of carbonates model results obtained in this study show that in modern seawa ter modern hypersaline water and assumed precambrian alkaline seawater sulfate reduction initially lowers the saturation of carbonates due to a rapid decrease in ph with continu ing sulfate reduction the ph stabilizes between 6 5 and 7 and carbonate saturation slowly increases as a result of increasing dissolved inorganic carbon concentration however sulfate reduction in surface microbial mats is not suf cient to cause such an increase in saturation with increasing salinity sulfate reduction becomes even less ef cient to induce carbonate pre cipitation in an alkaline precambrian ocean where large amounts of carbonate were formed induction through sulfate reduction was entirely ineffective other metabolic pathways or abi otic factors must be responsible for inducing carbonate formation in microbial mats through earth s history

use of transient electromagnetics to define local hydrogeology in an arid alluvial environment to characterize a local groundwater system in an arid alluvial environment a transient electromagnetic tem survey was performed with a dense station spacing along intersecting profiles structural features of significance to groundwater development were clearly evident in the color modulated apparent resistivity versus time pseudosections that were used to display the apparent resistivity data modeling results in conjunction with pseudosections were used to determine exploratory drill sites comparing the modeled results with electric logs from test holes demonstrated that 1 d modeling is not suitable for areas where rapid lateral change occurs these areas are easily identified in the apparent resistivity versus time pseudosections sites not located in fault zones with a resistivity greater than a few tens of ohm m were considered to be preferred locations for production wells hydraulic testing confirmed this interpretation philosophy the survey demonstrates the utility of closely spaced tem sound

a 70 kyr sea surface temperature record off southern chile ocean drilling program site 1233 1 we present the first high resolution alkenone derived sea surface temperature sst reconstruction in the southeast pacific ocean drilling program site 1233 covering the major part of the last glacial period and the holocene the record shows a clear millennial scale pattern that is very similar to climate fluctuations observed in antarctic ice cores suggesting that the southern hemisphere high latitude climate changes extended into the midlatitudes involving simultaneous changes in air temperatures over antarctica sea ice extent extension of the antarctic circumpolar current and westerly atmospheric circulation a comparison to other midlatitude surface ocean records suggests that this antarctic millennial scale pattern was probably a hemisphere wide phenomenon in addition we performed sst gradient reconstructions over the complete latitudinal range of the pacific eastern boundary current system for different time intervals during the last 70 kyr the main results suggest an equatorward displaced subtropical gyre circulation during marine isotope stages 2 and 4

thermal stability of amino acids in siliceous ooze under alkaline hydrothermal conditions abstract hydrothermal systems have been suggested as being favourable environments for the origin and evolution of life on the primitive earth to test this hypothesis it is necessary to investigate under hydrothermal conditions the behaviour of biomolecules such as amino acids aas a major component of organisms in contrast to submarine hydrothermal systems hot springs in the rift valley in eastern africa on the thick continental crust often have a high ph alkaline conditions as a result of enrichment via na 2 co 3 and volatile gases we reacted siliceous ooze with an aqueous solution of nacl and na 2 co 3 at elevated temperature 100 300 c to evaluate the thermal stability of the aas under alkaline hydrothermal conditions the aas in the sediment in peptide form were released to the liquid phase and decomposed through hydrolysis of peptide bonds comparison of the results with those from similar experiments using the same sediment sample under neutral conditions reveals that the rates of decomposition of the aas are significantly inhibited under alkaline conditions moreover aas remained in both the solid and liquid phases even after heating at 300 c for 240 h our results indicate that aas are more thermally stable in alkaline solution indicating that these hydrothermal conditions are more favourable for the evolution of primitive life on the thick continental crust they also imply that alkaline hydrothermal systems on other planets might be plausible places for extraterrestrial life

debate about ironstone has solute supply been surficial weathering hydrothermal convection or exhalation of deep fluids ironstone is any chemical sedimentary rock with 15 fe an iron formation is a stratigraphic unit which is composed largely of ironstone the solutes which have precipitated to become ironstone have dissolved from the earth s surface from the upper crust e g the basaltic layer of oceanic crust or from deeper within the earth genetic modellers generally choose between surficial weathering e g soil formation and hydrothermal fluids which have convected through the upper kilometre of oceanic crust most genetic modellers attribute cherty laminated iron formations to hydrothermal convection and noncherty oolitic iron formations to surficial weathering however both types of iron formations are attributable to the exhalation of fluids from a source region too deep for convection of seawater evidence for a deep source of ferriferous fluids comes from a comparison of ancient ironstone with modern ferriferous sediment in coastal venezuela a deep source origin for ironstone has wide ranging implications for the origins of other chemical sedimentary ores e g phosphorite manganostone bedded magnesite sedimentary uranium ore various karst filling ores and even petroleum preliminary study of a modern oolitic iron deposit described herein suggests that the source of iron and silica to iron formations may have been even deeper than envisioned within most hydrothermal convection models

influence of ph and dissolved si on fe isotope fractionation during dissimilatory microbial reduction of hematite microbial dissimilatory iron reduction dir has been identified as a mechanism for production of aqueous fe ii that has low 56 fe 54 fe ratios in modern and ancient suboxic environments that contain ferric oxides or hydroxides these studies suggest that dir could have played an important role in producing distinct fe isotope compositions in precambrian banded iron formations or other marine sedimentary rocks however the applicability of experimental studies of fe isotope fractionation produced by dir in geochemically simple systems to ancient marine environments remains unclear here we report fe isotope fractionations produced during dissimilatory microbial reduction of hematite by geobacter sulfurreducens in the presence and absence of dissolved si at neutral and alkaline ph hematite reduction was significantly decreased by si at alkaline but not neutral ph presumably due to si polymerization at the hematite surface the presence of si altered fe isotope fractionation factors between aqueous fe ii or sorbed fe ii and reactive fe iii reflecting changes in bonding environment of the reactive fe iii component at the oxide surface despite these changes in isotopic fractionations our results demonstrate that microbial fe iii oxide reduction produces fe ii with negative d 56 fe values under conditions of variable ph and dissolved si similar to the large inventory of negative d 56 fe in neoarchean and paleoproterozoic age marine sedimentary rocks

precambrian atmospheric oxygen and banded iron formations a delayed ocean model abstract evidence and arguments increasingly in favor of free oxygen in the earth s early atmosphere renew the constraints on the environmental significance of precambrian banded iron formations an early moist greenhouse atmosphere with a delay in and gradual growth of the world oceans offers a mechanism to provide a geochemically and mechanically segregated source of iron and silica for banded iron formation while simultaneously cannibalizing evidence for early archean red beds the model supports the high rates of weathering necessary to remove initially outgassed co2 quickly favors continuity in early biogenic evolution provides a mechanism for hydrogen and strontium isotope partitioning and is consistent with iron oxide facies that are devoid of organic carbon or stromatolites that are not encrusted by iron oxide

calcium and magnesium limited dolomite precipitation at deep springs lake california dolomite ca mg co3 2 precipitation from supersaturated ionic solutions at earth surface temperatures is considered kinetically inhibited because of the difficulties experienced in experimentally reproducing such a process nevertheless recent dolomite is observed to form in hypersaline and alkaline environments such recent dolomite precipitation is commonly attributed to microbial mediation because dolomite has been demonstrated to form in vitro in microbial cultures the mechanism of microbially mediated dolomite precipitation is however poorly understood and it remains unclear what role microbial mediation plays in natural environments in the study presented here simple geochemical methods were used to assess the limitations and controls of dolomite formation in deep springs lake a highly alkaline playa lake in eastern california showing ongoing dolomite authigenesis the sediments of deep springs lake consist of unlithified clay fraction dolomite ooze based on d 18 o equilibria and textural observations dolomite precipitates from oxygenated and agitated surface brine the na so4 dominated brine contains up to 500 mm dissolved inorganic carbon whereas mg 2 and ca 2 concentrations are ca 1 and 0ae 3m m respectively precipitation in the subsurface probably is not significant because of the lack of ca 2 below 0ae01 mm under such highly alkaline conditions the effect of microbial metabolism on supersaturation by ph and alkalinity increase is negligible a putative microbial effect could however support dolomite nucleation or support crystal growth by overcoming a kinetic barrier an essential limitation on crystal growth rates imposed by the low ca 2 and mg 2 concentrations could favour the thermodynamically more stable carbonate phase which is dolomite to precipitate this mode of unlithified dolomite ooze formation showing d 13 c values near to equilibrium with atmospheric co2 ca 3 contrasts the formation of isotopically light organically derived hard lithified dolomite layers in the subsurface of some less alkaline environments inferred physicochemical controls on dolomite formation under highly alkaline conditions observed in deep springs lake may shed light on conditions that favoured extensive dolomite formation in alkaline precambrian oceans as opposed to modern oceans where dolomites only form diagenetically in organic c rich sediments

a geological study of lake van eastern turkey lake van is a lake with a volume of 607 km3 and a maximum depth of 451 m in a tectonically active zone in eastern anatolia it may be divided into three physiographic provinces lacustrine shelf sublacustrine slope and lake basin the shelf is largely made up of submerged fluvial valleys and alluvial plains as evidenced by the local occurrence of karst like topography buried leveed river valleys and sediment wedges interpretable as relict deltas the shelf and basinal deposits are characterized by an alternating succession of well stratified and chaotically reflecting layers consisting of turbidites and slump deposits respectively this thick sequence of unconsolidated to consolidated sediments is underlain by a paleozoic metamorphic or upper cretaceous limestone basement

precambrian dolomites petrographic and isotopic evidence that they differ from phanerozoic dolomites dolomites are more common in precambrian than in phanerozoic rocks and from a petrographic isotopic study of the middle to upper proterozoic beck spring dolomite of eastern california it is suggested that precambrian dolomites are different from those of the phanerozoic petrographically all fabric details of precambrian dolomites studied are preserved just as if they were limestones and isotopically they show the same trend as limestones increasingly negative i8 o and to a lesser extent increasingly light i8 c from depositional components through early fibrous dolomite cements to later dolomite spar cements the data suggest that in precambrian time dolomite was the principal carbonate mineral precipitated from seawater and during diagenesis and this implies that precambrian seawater was different from that of the phanerozoic

large depth hydrogeological detection in the north china type coalfield through short offset grounded wire tem the north china type coalfield is the most important coalfield in china with the development of chinese economy shallow coal resources 600 m have been exhausted and large depth detection is being conducted water inrush is disastrous for coal mining however large depth 600 1200 m detection of water filled zones in the north china type coalfield is a difficult geophysical task due to its low resistivity coverage the traditional loop source transient electromagnetic method tem cannot realize large depth detection on the other hand high resolution detection of lotem is limited by the problem of recording points and large volume effect to explore the large depth targets with high resolution short offset grounded tem sotem was applied in the north china type coalfield sotem is one branch of grounded wire tem the response of sotem is calculated using superposing dipole method rather than the direct dipole approximation which is used in the calculation of the response of lotem this paper analyzes the comparison of the resolution and detection depth between sotem and loop source tem at first compared to the loop source tem with frequently used parameters the detection depth of sotem with the usual setup parameters is about twice of magnitude and the resolution capability of sotem at large depth is higher than that of loop source tem then the resolution capability and detection depth between lotem and sotem are analyzed for the grounded wire tem offsets are strictly related to the detection depth so the detection depth of lotem with larger receiver transmitter offset will be greater however at the depth of 600 1200 m the resolution capability to conductive targets of sotem is higher than that of lotem at last sotem with a 1000 m long source and 1000 2000 m offset is applied to the 1200 m depth exploration of water filled zones in the north china type coalfield the induced voltage is observed and transformed into magnetic field then the data is inverted using the least mean fourth algorithm the distribution of water on the top and bottom surface of the large depth no 4 coal seam is given and is verified by the drilling result

injection of mantle type helium into lake van turkey the clue for quantifying deep water renewal helium neon and tritium concentrations have been measured to study long term vertical mixing and deep water renewal in lake van eastern turkey the largest soda lake on earth helium excesses were found in the water column of lake van although neon concentrations were close to air saturation the excesses of both isotopes are strictly correlated and increase with depth in the bottom water 4he supersaturation is about 20 and the corresponding 3he concentration is 2 5 times the air saturation value the mean excess 3he 4he ratio of 1 1 2 10 5 is slightly higher than the morb ratio found in lake nemrut a neighbouring volcanic crater lake in which a large input of mantle helium was detected mantle helium accounts for the majority of the helium excesses in lake van although part of the 3he excess is attributed to the presence of tritium a one dimensional lake model was used which describes tritium input vertical mixing and gas exchange to reconstruct the evolution of the helium isotopes and the tritium as a conclusion the model based on the measured 3he and 4he profiles shows that 1 the vertical exchange of deep water occurs within 1 2 yr 2 the flux of mantle helium into the lake averaged over the total cross section of lake van is 0 23 0 35 cm3 stp m 2 yr 1 2 3 1011 atoms m 2 s 1 the present estimate of the global mantle helium flux averaged over the total surface area of the earth is 3 9 109 atoms m 2 s 1 the flux into lake van would account for at least 0 04 0 06 of this

predicting riverine dissolved silica fluxes to coastal zones from a hyperactive region and analysis of their first order controls silicate weathering and resulting transport of dissolved matter influence the global carbon cycle in two ways first by the uptake of atmospheric soil co2 and second by providing the oceanic ecosystems via the fluvial systems with the nutrient dissolved silica dsi previous work suggests that regions dominated by volcanics are hyperactive or even hot spots concerning dsi mobilization here we present a new approach for predicting dsi fluxes to coastal zones emphasizing first order controlling factors lithology runoff relief land cover and temperature this approach is applied to the japanese archipelago a region characterized by a high percentage of volcanics 29 1 of surface area the presented dsi flux model is based on data of 516 catchments covering approximately 56 7 of the area of the japanese archipelago the spatial distribution of lithology one of the most important first order controls is taken from a new high resolution map of japan results show that the japanese archipelago is a hyperactive region with a dsi yield 6 6 times higher than the world average of 3 3 t sio2 km 2 a 1 but with large regional variations approximately 10 of its area exceeds 10 times the world average dsi yield slope constitutes another important controlling factor on dsi fluxes besides lithology and runoff and can exceed the influence of runoff on dsi yields even though the monitored area on the japanese archipelago stretches from about 31 to 46 n temperature is not identified as a significant first order model variable this may be due to the fact that slope runoff and lithology are correlated with temperature due to regional settings of the archipelago and temperature information is substituted to a certain extent by these factors land cover data also do not improve the prediction model this may partly be attributed to misinterpreted land cover information from satellite images implications of results for earth system and global carbon cycle modeling are discussed

fluids during diagenesis and sulfate vein formation in sediments at gale crater mars we model the fluids involved in the alteration processes recorded in the sheepbed member mudstones of yellowknife bay ykb gale crater mars as revealed by the mars science laboratory curiosity rover investigations we compare the gale crater waters with fluids modeled for shergottites nakhlites and the ancient meteorite alh 84001 as well as rocks analyzed by the mars exploration rovers and with terrestrial ground and surface waters the aqueous solution present during sediment alteration associated with phyllosilicate formation at gale was high in na k and si had low mg fe and al concentrations relative to terrestrial groundwaters such as the deccan traps and other modeled mars fluids and had near neutral to alkaline ph ca and s species were present in the 10 3 to 10 2 concentration range a fluid local to gale crater strata produced the alteration products observed by curiosity and subsequent evaporation of this groundwater type fluid formed impure sulfate and silica rich deposits veins or horizons in a second separate stage of alteration partial dissolution of this sulfate rich layer in yellowknife bay or beyond led to the pure sulfate veins observed in ykb this scenario is analogous to similar processes identified at a terrestrial site in triassic sediments with gypsum veins of the mercia mudstone group in watchet bay uk

rare earth and trace elements of microbialites in upper jurassic coral and sponge microbialite reefs major trace y zr pb th and u rare earth element ree and sm nd isotope analyses were carried out on microbialites and detrital carbonate sediments collected in upper jurassic coral and sponge microbialite reef settings selected bioconstructions developed in various palaeogeographic settings and depositional environments on northwestern tethys and eastern atlantic margins pure carbonate lagoon carbonate dominated deep shelf to epicontinental basin and mixed carbonate siliciclastic shallow ramp and lagoon the proximity to terrigenous sources directly controlled ree patterns of carbonate samples lateral and intrareef sediments and to a lesser degree stromatolitic microbial crusts are more susceptible to contamination by terrigenous material than are microbialites of thrombolitic fabric in mixed carbonate siliciclastic settings microbialites display a flat shale normalized ree pattern in pure carbonate lagoonal settings microbialites have shale normalized ree patterns similar to those of modern seawaters with a negative ce anomaly ce ce up to 0 14 positive la and gd anomalies and light ree depletion relative to heavy ree these data imply that similar ree chemistry than modern seawater already occurred on the northwestern tethys margin at the upper jurassic strong negative ce anomalies b0 4 imply microbialite formation in well oxygenated seawaters both in coral reefs of pure carbonate lagoonal environments pagny sur meuse and sponge bioherms of deep shelf settings plettenberg absence of positive ce anomalies rules out an influence of alkaline and high ph seawaters thus ree patterns and nd isotopic signatures which are in perfect agreement with existing results for tethysian seawater confirm that microbialites can be used as proxies of palaeoenvironmental seawater chemical characteristics

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

archean cherts derived from chemical biogenic and clastic sedimentation in a shallow restricted basin examples from the gorge creek group in the pilbara block the 3ae0 ga chert sequence of the gorge creek group is exposed at ord ranges about 50 km east of port hedland in the pilbara block the chert sequence examined in this study is 15 m thick and consists of oxide rich laminated chert grey chert silicified clastic rock carbonaceous black chert and carbonate rich laminated chert although the cherts have undergone postdepositional silica enrichment such as cementation and metasomatic silicification primary precipitation of silica at the site of deposition is indicated by abundant microstructures mosaic and spherulitic structures other primary to early diagenetic components were carbonates sulphates gypsum and anhydrite and organic matter although these mineral associations on the whole correspond to those of modern marine evaporites they are different from modern equivalents with respect to abundant precipitation of amorphous silica and presumed primary precipitation of iron carbonate siderite this feature is a possible manifestation of peculiar physicochemical conditions in the water mass from which the chemical sediments were precipitated compared with modern ocean waters the concentrations of fe and si were significantly higher and the ph value might have been lower these conditions could be obtained by contributions of fe and si enriched hydrothermal solutions and continental run off to the site of deposition grey cherts contain detrital quartz and altered fe ti oxides and were formed in a period of input of terrigenous detrital materials they are characterized by higher concentrations of tio2 a l 2 o 3 cr ni zn rb and zr compared with the other types of chert and by very low 4 al2o3 tio2 values these features are attributed to the supply of terrigenous detrital materials that contain abundant fe ti oxides ilmenite and titanomagnetite and fine tio2 particles such detrital materials might have been formed by extensive chemical alteration of source rocks and residual enrichment of ti relative to al