early diagenetic silica deposition in algal cysts and spores a source of sand in black shales abstract devonian black shales deposited on the north american craton contain abundant tasmanites cysts although these are typically flattened because of compaction a small proportion are filled with diagenetic silica the latter are spherical to ellipsoidal 0 1 0 5 mm and filled with chalcedony microquartz and megaquartz and single quartz crystals chalcedonic cyst fillings are preserved best in cheat and phosphate nodules whereas megaquartz and single quartz crystals are most common in shale matrix together with colloform textures this suggests that the various silica types originated from recrystallization of early diagenetic silica deposits thin sandstone beds in the chattanooga shale e g bransford sandstone contain abundant quartz sand that is much coarser than the detrital quartz component of the underlying black shales because of this their quartz component is thought to have been transported over considerable distances from the basin margin however because certain shale horizons contain as much as 10 silicified cysts that upon reworking could have yielded quartz grains of fine to coarse sand size the quartz component of these sandstone beds may actually have formed in situ indeed petrographic examination of the sandstone beds shows them to contain quartz grains with morphological and textural features of cyst quartz e g rounding sphericity chalcedony pyrite inclusions lobate grain margins thus silica deposition in algal cysts may provide a significant component of intrabasinal quartz sand in shale sequences distinction of this type of quartz from extrabasinal detrital quartz is important to the reconstruction of the depositional history of shale sequences

the role of hydrogeological base level in the formation of sub horizontal caves horizons example from the dead sea basin israel this paper deals with the hydrogeological relationship between base levels of saline lakes and the formation of sub horizontal caves the mechanism presented here suggests that many horizontal cave levels in carbonate sequences are created adjacent to the saline lakes shorelines because of the converging of the groundwater flow above the fresh saline water interface the main factors that control enhanced carbonate dissolution and cave formation are high groundwater flow velocities in the shallow phreatic zone during a relative long steady state of the water table high groundwater flow velocities are evident close to the dead sea due to the convergent fast flows above the shallow interface adjacent to the shoreline the same could prevail in the case of previous paleo lakes that existed in the basin the synergetic combination of the above preconditions for enhanced cave formation seems to be responsible for the formation of elevation controlled alignment of paleo near shore cave levels in the central and southern dead sea portion of the study area these are found on the western fault escarpment and basin margin in different stratigraphic horizons of carbonate lithology many of the cave levels can be linked to late quaternary holocene lake levels obtained from dated lake sediments within the basin the most common cave s elevation was found to be around 200 m below sea level which was the elevation of the lisan lake during part of its history on the other hand the hula basin in the northern part of the dead sea basin was not occupied by saline water bodies since its formation as a base level and thus the above preconditions for enhanced cave formation did not prevail indeed this is evident by the lack of horizontal cave levels on its western carbonate margins unlike the situation in the south

new isotopic evidence for the origin of groundwater from the nubian sandstone aquifer in the negev israel the geochemistry and isotopic composition h o s osulfate c sr of groundwater from the nubian sandstone kurnub group aquifer in the negev israel were investigated in an attempt to reconstruct the origin of the water and solutes evaluate modes of water rock interactions and determine mean residence times of the water the results indicate multiple recharge events into the nubian sandstone aquifer characterized by distinctive isotope signatures and deuterium excess values in the northeastern negev groundwater was identified with deuterium excess values of 16 which suggests local recharge via unconfined areas of the aquifer in the negev anticline systems the d 18 oh2o and d 2 h values 6 5 and 35 4 of this groundwater are higher than those of groundwater in the sinai peninsula and southern arava valley 7 5 and 48 3 that likewise have lower deuterium excess values of 10 based on the geochemical differences between groundwater in the unconfined and confined zones of the aquifer a conceptual geochemical model for the evolution of the groundwater in the nubian sandstone aquifer has been reconstructed the isotopic composition of shallow groundwater from the unconfined zone indicates that during recharge oxidation of pyrite to so4 d 34 sso4 13 d 18 oso4 7 7 and dissolution of caco3 87 sr 86 sr 0 70787 d 13 cdic 3 7 occur in the confined zone of the aquifer bacterial so4 reduction removes a significant part of dissolved so 2

direct measurements of floodwater infiltration into shallow alluvial aquifers the relationship between floodwater infiltration and groundwater recharge of a shallow alluvial aquifer in a hyper arid desert was studied in the arava valley israel the study implemented an experimental system that simultaneously monitors all three hydrological domains controlling the recharge process 1 floodwater stages on land surface 2 water content variations in the deep vadose zone and 3 groundwater response to the infiltration this experimental system makes use of a new technique for installing flexible time domain reflectometry probes for continuous monitoring of the vadose zone moisture profiles water infiltration was monitored in controlled infiltration experiments and during a natural flood the monitoring setup allowed real time tracking of the wetting front propagation velocities and assessment of water fluxes through the vadose zone the results revealed a complex infiltration process that includes matrix and preferential flow together with lateral flow

the relationship between current and paleo groundwater base levels abstract base levels are basically divided into two categories oceanic and marine base levels and continental terminal endorheic ones the marine domain serves as the ultimate base level for both surface and groundwater drainage systems continental inland depressions very often serve as terminal endorheic base levels to both surface drainage and groundwater systems many of the current both marine and inland base levels served also in the past as paleo base levels fluctuations of base level elevations affect the adjoined groundwater system in several ways such as changes in groundwater levels location of divides depths of fresh saline water interfaces and the amount of flow to the base levels this paper provides examples from many different parts of the world that describe the relationship between current and paleo base levels the examples include marine base levels as well as inland endorheic ones both currently above and below sea level close to and distant from the sea

lithologically influenced geomorphic responses to holocene climatic changes in the southern colorado plateau arizona a soil geomorphic and ecologic perspective abstract the semiarid landscape occupied by the navajo and hopi peoples on the colorado plateau in northeastern arizona in the southwestern united states is characterized by an extensive network of deeply incised arroyos since the early 20th century many researchers have proposed that the recent formation of arroyos in this region and also many attributes of modern vegetation communities were caused directly by overgrazing of vegetation by domestic livestock of the navajo other researchers however have proposed other causes for such features such as climatic change we believe that the landforms soils and vegetation of a small area located on antelope mesa in this region underlain by the highly erodible materials of the miocene bidahochi formation may have been more sensitive to minor climatic changes of the holocene than landscapes of massive mesozoic sandstones that dominate the colorado plateau in the antelope mesa area the presence of actively filling channels rather than arroyos in the upper parts of many drainage basins and associated soils and ecologic patterns indicate that the aggradation 1 was initiated in downstream reaches and within the past two centuries 2 may be linked to recently accelerated slope erosion and 3 is unrelated to past or ongoing grazing this suggests the ongoing aggradation may be related to recent minor climatic changes geochronologic and soil geomorphic evidence indicate that the most recent cycle of arroyo incision and filling may be a small scale analogue for larger magnitude older cycles that produced regionally recognizable paired terraces that are attributable to previous holocene climate changes we propose that climatic change and more specifically increases in precipitation caused an acceleration in the erosion of the steep typically minimally vegetated slopes of the bidahochi formation the beginning of the neoglacial period ca 2 3 ka effects of which are documented by other proxy records in this region may be the climatic change that triggered widespread deposition of a large mid holocene alluvial unit in this region alternating episodes of eolian activity and soil formation in the study area and in this general region provide independent evidence of holocene climatic changes our interpretations of the origin of the cut and fill cycles that emphasize the role of drainage basin lithology and differ significantly from previous interpretations emphasize the linkage of climatic changes groundwater levels and arroyo incision this study reveals the importance of integrating soil and ecologic studies with geomorphologic research such an approach may be critical in helping understand how anthropogenically induced climatic changes of the next century could impact geomorphic processes and the ecology of arid and semiarid regions

eolian sediment responses to late quaternary climate changes temporal and spatial patterns in the sahara abstract this paper presents a compilation of eolian based records of late quaternary climate changes in the sahara although the data are relatively sparse when viewed as a whole they reveal a general pattern of widespread eolian sediment mobilization prior to 11 000 cal years bp eolian sediment stabilization from 11 000 to 5000 cal years bp and a return to widespread eolian sediment mobilization after 5000 cal years bp furthermore an eolian based record from southern tunisia reveals the existence of millennial scale changes in eolian sediment behavior these millennial scale variations provide examples of eolian sediment responses to climate changes at a scale intermediate between seasonal and orbital milankovitch changes and they are also coincident with abrupt atmospheric and oceanic changes the general synchroneity of the eolian stratigraphic records and their coincidence with various oceanic and atmospheric changes suggest that global forcing mechanisms have influenced late quaternary eolian sediment behavior in the sahara

transformation of a subtropical river into a hyperhaline estuary the casamance river senegal paleogeographical implications abstract located in the south of senegal in the transitional guineo congolian soudanian zone the casamance system is composed of a small river supplied by a narrow drainage basin and followed by a 250 km long estuary the continuous rainfall decrease experienced by the region since the beginning of the century drastically affected the casamance river this climatic change suddenly accelerated during 1968 1970 which led to a four stage succession before 1968 1970 stage 1 rainfall 1300 mm the casamance estuary showed the customary negative upstream salinity gradient between 1968 1970 and 1978 stage 2 rainfall 1000 mm under decreasing rainfall the casamance estuary shifted to a hyperline inverse estuary it showed well defined physical chemical and biological zonations fresh groundwater resources supplying the upper reaches of the river during the dry season were progressively depleted between 1978 and 1986 1987 stage 3 the salinity peak of the end of the dry season progressively rose and shifted upward the ecological zonation showed the increasing marine influence until 1986 between 1986 1987 and 1990 stage 4 the dry season fresh water input had weakened with the depletion of groundwater resources a slight increase in rainfall was insufficient to repulse the hyperhaline waters and the restricted area extended upstream and downstream the physical chemical and biological zonations strongly widened and flattened in the future the return to stage 1 conditions by an increase in average rainfall would take decades inevitably it will be much longer than the transformation into a hyperhaline estuary thus a slight decrease of the average rainfall in the region provoked a drastic change of the hydrological and biological patterns of the ria the result seems to be a major crisis in the region and might be recorded in the fossil records we discuss these observations in terms of possible misreadings of paleoenvironments and in relation with long term climate trends

ca chloride brines at common outlets of the bet shean harod multiple aquifer system israel abstract the bet shean and harod valleys are regional recipients and mixing zones for groundwaters draining into them from a multiple aquifer system which includes carbonate and basalt aquifers and deep seated reservoirs of brine the outlets of the three aquifers are located at the mountain border separating the valleys from the gilboa and ramot issakhar mts the aquifers drain through two types of outlets unique and common the latter type is mainly conditioned by the occurrence of fault blocks acting as connecting media between the aquifers upon reaching the interconnecting zones fresh groundwater flowing from carbonate and basalt aquifers intermix losing their hydrochemical identities ca chloride brines originating from deep seated and confined reservoirs leak along the deep seated faults characterizing the common outlet zones and contaminate the relatively fresh mixing products originating from the three regional aquifers two types of dilute ca chloride brines were identified in the study area the devora type is a hot and hypersaline source brine which was identified at great depth and under very high hydrostatic pressures this brine could be the residual product of seawater that evaporated during the cambrian cretaceous continental interval and subsequent prolonged interaction with surrounding carbonate rocks the neve ur type brine seems to be genetically related to the neogene inland sdom sea that preceeded the contemporary dead sea

aquifer characterization using shallow geophysics in the keritis basin of western crete greece effective management of groundwater resources is a well known problem in several areas around the world it is especially important to areas suffering from an intrinsic lack of fresh water such as islands detailed study of available aquifers is of particular interest in the highly touristic greek island of crete the increasing water demand makes water resources management extremely important for sustainable development this is the case in the prefecture of chania in western crete where there has been a lack of success of many different groundwater management plans that have been produced over the years and submitted for application to water management authority the inefficiency of the management plans is verified by the continuous water shortage reported every year which forces the public authorities to transfer water from far away sources and wells until today there are only geological data as well as information from the borehole logs therefore the current work is focused to study in detail the tectonic and hydrogeological characteristics of the keritis watershed to make a correlation of the available geoenvironmental information with the geophysical data of the study aquifer transient electromagnetic soundings were conducted to obtain detailed information about the tectonic hydrogeological hydrolithological and geometrical characteristics of the aquifer under investigation in addition optimum areas of water well drilling were identified to minimize the uncertainty and the total cost economical managerial etc of future groundwater surveys

rapid incision of a small coarse and steep fan delta in response to base level fall the case of nahal qedem the dead sea israel the dead sea has been continuously dropping 0 4 1 0 m yr 1 since the middle of the 20th century and thus provides a unique field laboratory for studying in real time the response of drainage systems to a non tectonic base level fall the aim of this work is to study the short term ongoing erosive response to a rapid base level drop in a small steep fronted erodible fan delta setting the work explores the controls of the steep qedem fan delta guided by its clinoform structure on its incision longitudinal profiles of the fan delta and of its entrenched channel were measured in the field sedimentary facies changes fluviatile shallow lacustrine and beach were followed along exposures the existence of large boulders provided an opportunity to examine the uncertain role of armouring and boulder flux on incision the field study was combined with digital elevation models dems that were extracted from pairs of overlapping aerial photos maps of erosion and deposition were prepared using a change detection algorithm the longitudinal profile of the entrenched channel was found to be steep and linear the outlet temporarily hangs elevated and ungraded above the retreating lake level indicating years without incision flow events which cause lags in response to the rapid lake level drop in spite of the large boulders the small drainage basin and precipitation volume over the basin of the qedem the recorded vertical incision rates in the unconsolidated sediments are as high as 0 8 m yr 1 i e similar to those of the largest wadis draining to the dead sea the steep front of the fan delta is suggested to be a main factor controlling the efficient incision a unique transport mechanism of rolling boulders following undercutting contributed to the entrenchment efficiency copyright 2010 john wiley sons ltd

the circulation of the dead sea brine in the regional aquifer abstract ca chloride brines have circulated between the lakes and the adjacent aquifers throughout the history of the dead sea lacustrine hydrology system the ein qedem eq hydrothermal saline springs system discharging at the western shores of the modern dead sea is the modern manifestation of this essential and continuous process the eq springs comprise the most significant source of ca chloride brine that currently discharges into the lake the chemical composition of eq brine has remained virtually uniform during the past ca 40 yr indicating that the brine represents a large groundwater reservoir the eq brine evolved from ancient ca chloride brine that occupied the tectonic depression of the dead sea basin during the quaternary during this period the composition of lake s brine was affected by mixing with freshwater and formation of primary minerals based on chronological and geochemical data we argue that the eq brine comprises the epilimnetic solution of last glacial lake lisan that penetrated and circulated through the adjacent judea group aquifer 14c and 81kr dating indicates recharge ages spanning the time interval of 40 20 ka coinciding with the period when the lake reached its highest stand of 200 30 m below msl at 31 17 4 ka and maintained a stable layered stratified configuration for a period of several ten thousand years the presented evidence suggests that the circulation of the ca chloride brine involves penetration into the aquifer during high stands eq brine recharge and its discharge back into the lake during the modern low stands 400 to 430 m below msl accordingly the mechanism of brine circulation between the lake and the marginal aquifers is related to the long term hydro climate history of the dead sea basin and its vicinity

identifying recharge processes into a vast fossil aquifer based on dynamic groundwater 81kr age evolution abstract water in deep aquifers in arid regions is often considered to be fossil when modern recharge rates are negligible relative to the reservoir capacity over the past five decades the nubian sandstone aquifer nsa in the arid region of the sinai peninsula egypt and the negev desert israel has been considered to contain fossil water based on 14c dating which revealed 14c ages of about 30 kyr over most of the aquifer however this relatively homogeneous age distribution contradicts the expected increase in groundwater age in the direction of decreasing piezometric head along the flow trajectories here dating results with the longer lived 81kr radioisotope t1 2 229 11 kyr are presented highlighting a wide age range of 40 kyr to 630 kyr in the confined sections of the aquifer all with very low 14c activity

rare earth major and trace element composition of monterey and dsdp chert and associated host sediment assessing the influence of chemical fractionation during diagenesis abstract chert and associated host sediments from monterey formation and deep sea drilling project dsdp sequences were analyzed in order to assess chemical behavior during diagenesis of biogenic sediments the primary compositional contrast between chert and host sediment is a greater absolute sio2 concentration in chert often with final sio2 98 wt this contrast in sio2 and si al potentially reflects precursor sediment heterogeneity diagenetic chemical fractionation or both sio2 concentrations and si al ratios in chert are far greater than in modern siliceous oozes however and often exceed values in acid cleaned diatom tests compositional contrasts between chert and host sediment are also orders of magnitude greater than between multiple samples of the host sediment calculations based on the initial composition of adjacent host observed porosity reductions from host to chert and a postulated influx of pure sio2 construct a chert composition which is essentially identical to observed sio2 values in chert thus precursor heterogeneity does not seem to be the dominant factor influencing the current chert composition for the key elements of interest in order to assess the extent of chemical fractionation during diagenesis we approximate the precursor composition by analyzing host sediments adjacent to the chert the sio2 concentration contrast seems caused by biogenic sio2 dissolution and transport from the local adjacent host sediment and subsequent sio2 reprecipitation in the chert along with sio2 other elements are often added with respect to al to monterey and dsdp chert during silicification although absolute concentrations decrease the two monterey quartz chert nodules investigated in contrast to the opal ct and quartz chert lenses formed primarily by extreme removal of carbonate and phosphate thereby increasing relative sio2 concentrations dsdp chert formed by both carbonate phosphate dissolution and sio2 addition from the host manganese is fractionated during chert formation resulting in mno al 2 o 3 ratios that no longer record the depositional signal of the precursor sediment ree data indicate only subtle diagenetic fractionation across the rare earth series ce ce values do not change significantly during diagenesis of either monterey or dsdp chert eu eu decreases slightly during formation of dsdp chert la n yb n is affected only minimally as well during formation of one monterey opal ct chert lens ree al ratios show subtle distribution changes at gd and to a lesser extent near nd and ho ree compositional contrasts between diagenetic states of siliceous sediment and chert are of a vastly smaller scale than has been noted between different depositional environments of marine sediment indicating that the paleoenvironmental ree signature is not obscured by diagenetic overprinting

diagenetic cycling of nutrients in seafloor sediments and the carbonate silica balance in a paleozoic cool water carbonate system sverdrup basin canadian arctic archipelago abstract seafloor processes are often destructive of biogenic remains while at the same time promoting growth of authigenic minerals such as hematite fluorapatite glauconite and chalcedony middle to late permian sedimentary rocks in the sverdrup basin are cool water marine sandstones shales limestones and cherts rich in carbonate and siliceous biotic components the authigenic minerals hematite fluorapatite glauconite and chalcedony are abundant from the interactions of nutrient elements silica phosphorus and iron with carbonate and siliceous biotas in ramp environments of variable energy and sediment accumulation rate these authigenic phases represent in part faunas that are no longer preserved and should not be viewed simply as diagenetic products early middle permian siliciclastic rocks the assistance formation contain carbonate heterozoan biotas with widespread siderite and hematite and local void filling phosphate deposited under moderate sediment accumulation rates sponge spicules were dissolved unless encased in hematite or siderite and incorporated in silica cement in contrast more slowly deposited younger middle permian inboard cherty limestones the lower trold fiord formation underwent frequent physical and biological reworking resulting in dissolution of biogenic silica and precipitation of glauconite and carbonate fluorapatite sediment reworking also excavated and produced rounded glauconite and phosphate clasts much of the glauconite was then oxidized to hematite on the seafloor again unless encased in phosphate sponge spicules were dissolved and the silica precipitated as glauconite or chalcedony coeval deeper water phosphatic cherty limestones the degerbols formation do however contain sponge spiculites reduced sediment reworking led to retention of silica in pore fluids and slowed dissolution of sponge spicules resulting in local preservation of sponge spiculite facies late permian organic rich cherts the lindstrom formation with prolific siliceous sponges and a less plentiful carbonate biota accumulated relatively slowly sponge spicules were preserved and carbonate biota partially dissolved in these organic rich deposits implying that the biota had to be overwhelmingly dominated by siliceous components to overcome ambient silica undersaturation in pore fluids each succession has a distinct composition depending upon the rate of sediment accumulation the original benthic biota and the nature and abundance of silica phosphate and iron in seawater at any given time these characteristics controlled the formation of authigenic minerals and the preservation or dissolution of carbonate and silica biotas

compositional controls on early diagenetic pathways in fine grained sedimentary rocks implications for predicting unconventional reservoir attributes of mudstones diagenesis significantly impacts mudstone lithofacies processes operating to control diagenetic pathways in mudstones are poorly known compared to analogous processes occurring in other sedimentary rocks selected organic carbon rich mudstones from the kimmeridge clay and monterey formations have been investigated to determine how varying starting compositions influence diagenesis the sampled kimmeridge clay formation mudstones are organized into thin homogenous beds composed mainly of siliciclastic detritus with some constituents derived from water column production e g coccoliths s depleted type ii kerogen as much as 52 6 total organic carbon toc and others from diagenesis e g pyrite carbonate and kaolinite the sampled monterey formation mudstones are organized into thin beds that exhibit pelleted wavy lamination and are predominantly composed of production derived components including diatoms coccoliths and foraminifera in addition to type iis kerogen as much as 16 5 toc and apatite and silica cements during early burial of the studied kimmeridge clay formation mudstones the availability of detrital fe iii and reactive clay minerals caused carbonate and silicate buffering reactions to operate effectively and the pore waters to be fe ii rich these conditions led to pyrite iron poor carbonates and kaolinite cements precipitating preserved organic carbon being s depleted and sweet hydrocarbons being generated in contrast during the diagenesis of the sampled monterey formation mudstones sulfide oxidation coupled with opal dissolution and the reduced availability of both fe iii and reactive siliciclastic detritus meant that the pore waters were poorly buffered and locally acidic these conditions resulted in local carbonate dissolution apatite and silica cements precipitation natural kerogen sulfurization and sour hydrocarbons generation differences in mud composition at deposition significantly influence subsequent diagenesis these differences impact their source rock attributes and mechanical properties

chemical evolution of saline waters in the jordan dead sea transform and in adjoining areas the ca mg relationship in groundwaters strongly points to the overall dolomitization and local albitization the mg ca ratios reveal two trends by which saline waters develop increase of mg ca ratio by evaporation and decreasing mg ca ratios due to dolomitization and albitization br cl vs na cl ratios demonstrate that albitization does not play a major role which leaves dolomitization to be the main source for decreasing mg ca ratios in saline waters in the eastern and southern region of lake kinneret salinization occurs by mixing with a ca mg molar ratio 1 dominates which developed by the albitization of plagioclase in abundant mafic volcanics and the dolomitization of limestones the most saline groundwater of the tabgha fuliya and tiberias clusters could be regional derivatives of at least two mother brines in diluted form one is represented by ha on water the other is a na rich brine of the zemah type additionally a deep seated ca dominant brine may ascend along the fractures on the western side of lake kinneret which is absent on the eastern side groundwaters of the lower jordan valley are chemically different on both sides of the jordan river indicating that the exchange of water is insignificant all saline waters from the dead sea and its surroundings represent a complex mixture of brines and precipitation and local dissolution of halite and gypsum many wells of the arava araba valley pump groundwater from the upper cretaceous limestone aquifer the origin of the water is actually from the lower cretaceous kurnub group sandstones groundwater drawn from the quaternary alluvial fill either originates from kurnub group sandstones eilat 108 yaalon 117 or from altered limestones of the judea group the origin of these waters is from floods flowing through wadis incised into calcareous formations of the judea group on the other hand as a result of step faulting hydraulic contact is locally established between the kurnub and the judea groups aquifers facilitating the inter aquifer flow of the confined kurnub paleowater into the karstic formations of the judea group two periods of neogene brine formation are considered the post messinan inland lagoon resulting in drying up of the sdom sea and the evaporation of the pleistocene samra lake which went further through the stage of lake lisan to the present dead sea for the first period major element hydrochemistry suggests that the saline waters and brines in the jordan dead sea arava valley transform evolved from the gradual evaporation of an accumulating mixture of sea ground and surface water due to the precipitation of carbonates gypsum and halite such an evaporating primary water body was strongly enriched in mg br and b and shows high molar ratios of br cl b cl and mg ca but low na cl ratios the development of the br cl ratio is chemically modelled showing that indeed brine development is explicable that way along with the evaporation brine evaporites formed which are leached by infiltrating fresh water yielding secondary brines with na cl ratios of 1 when primary brines infiltrated the sub surface they were subjected to mg ca exchange in limestones dolomitization and to chloritization and albitization in basic igneous rocks turning them into ca cl brines these tertiary brines are omnipresent in the rift the brines of the late lisan and dead sea were generated by evaporating drainage waters which leached halite gypsum and carbonates from the soil and from the sub surface all these brines are still being flushed out by meteoric water resulting in saline groundwaters this flushing is regionally enhanced by intensive groundwater exploitation in variable proportions the neogene and late lisan lake and recent dead sea brines have to be considered as the most serious sources of salinization of groundwaters in the rift deep seated pre sdom brines cannot strictly be excluded but if active they play a negligible role only

primary silica precipitate at the precambrian cambrian boundary in the south oman salt basin sultanate of oman abstract an organic rich laminated chert silicilyte consisting of up to 90 microcrystalline quartz that formed at the precambrian cambrian boundary acts as a light oil reservoir in the subsurface of the south oman salt basin sultanate of oman fully encased in salt domes it was first discovered during the 1990 s hydrocarbon exploration activities of petroleum development oman because of the economic significance and the unconventional reservoir characteristics there is great interest in understanding the origin of the laminated chert its source of silica and mode of precipitation in an anoxic sulphur rich stagnant and highly saline basin the homogeneous distribution and high values of stable si isotope composition avg 30 si 0 83 0 28 coupled with a low molar ge si ratio 6 of the microcrystalline matrix quartz clearly reveal dissolved silica in the seawater as the si source whereas hydrothermal or biogenic e g sponge derived silica can be excluded silica precipitation from seawater was likely the result of a dramatic increase in salinity in response to salt dissolution atop and adjacent to the edges of transtensional depressions on the deep basin floor thus markedly reducing the solubility of amorphous silica in these brine filled seawater depressions this saturation triggered the formation of silica gel which accumulated at the basin floor forming a soft silica rich layer on bacterial mats giving rise to a laminated sediment the mean number of laminae is ca 32 per year suggesting that layering is non annual and controlled by processes such as fluctuations in nutrient supply lunar driven re mixing or diagenetic segregation the transformation of the silica gel to microcrystalline quartz occurred below 45 c indicating a less than 4 5 18 o composition of the pore water during microcrystalline quartz formation

rare earths and yttrium hydrostratigraphy along the lake kinneret dead sea arava transform fault israel and adjoining territories rare earth elements and y rey have been analysed in 49 groundwaters from localities in the areas of lake kinneret and the jordan and arava valleys these waters originate from various aquifers and the rey abundances are expected to be controlled by the aquifer rocks the rey pattern allow one to distinguish interaction of waters with basalts basalt limestone interaction zones silicified limestones limestones from the judea and avdat groups upper cretaceous and eocene respectively and sandstones of the lower cretaceous kurnub group groundwater from the quaternary alluvial fill dead sea group are either controlled by judea group limestone or kurnub group sandstone the rey patterns show characteristic features for each group in hydrogeological systems the rocks of natural replenishment areas are usually not the same as rock units from which the waters are collected this becomes evident by comparing the lithostratigraphic groups from which the waters were collected and the hydrochemical grouping according to rey patterns with their characteristic trends and anomalies in many cases there is a correspondence between the lithostratigraphic and the hydrochemical grouping in other cases the 2 groupings disagree this disagreement proves inter aquifer flow of groundwater in some cases the geologically derived aquifers rocks of origin differ from those indicated by rey patterns thus applying the rey grouping new fundamental information for hydrological models can be given and sources of salinisation can be elucidated

catastrophic arid episodes in the eastern mediterranean linked with the north atlantic heinrich events the response of continental climate to the well documented climate oscillations during the last glacial period has been a subject of intense interest yet much less is known about the influence on regional continental climates than in the marine or polar realms of earth the detailed lake level history of the closed lake lisan paleo dead sea in the middle east has been reconstructed from shoreline indications and high resolution u th and 1 4 c chronologies thus providing data on the response of the lake s catchment area to the climate changes during the corresponding period we present a correlation between the newly developed lake lisan level curve for the past 55 k y and the north atlantic heinrich events the correlation indicates a closely connected climate response between these north atlantic events and the hydrologic conditions that prevailed in the eastern mediterranean our findings show that although the generally cooler conditions that prevailed during the last glaciation favored high levels of the lake catastrophic events in the north atlantic which are associated with maximum cooling have been responsible for droughts in the eastern mediterranean we infer that cold water input to the mediterranean originating in the collapse of the north atlantic deep water circulation caused the reduction of evaporation and less precipitation in the eastern mediterranean

reply to comment on ben dor y et al varves of the dead sea sedimentary record quaternary science reviews 215 2019 173 184 abstract in the comment on varves of the dead sea sedimentary record quaternary science reviews 215 ben dor et al 2019 173 184 by r bookman two recently published papers are suggested to prove that the interpretation of the laminated sedimentary sequence of the dead sea deposited mostly during mis2 and holocene pluvials as annual deposits i e varves is wrong in the following response we delineate several lines of evidence which coalesce to demonstrate that based on the vast majority of evidence including some of the evidence provided in the comment itself the interpretation of these sediments as varves is the more likely scientific conclusion we further discuss the evidence brought up in the comment and its irrelevance and lack of robustness for addressing the question under discussion

hypersaline brine diagenesis and evolution in the dead sea lake lisan system israel abstract water soluble salts were extracted from 57 aragonite and detrital laminae sampled from the pleistocene lake lisan sediments the solutions and solids were analysed for ca mg na k sr cl so 4 and bicarbonate average na cl mg ca sr ca mg cl ca cl sr cl k cl k na and k mg ratios calculated for seven stratigraphie elevations in the lisan column indicate that the dead sea rift sediment brine system has remained practically closed for 70000 years the soluble salts reflect both the hydrologie evolution of the lake as well as diagenetic processes mg ca ratios systematically decrease in younger sediments and this decline is accompanied by a 1 5 4 fold sr enrichment in aragonite solubles relative to salts extracted from detrital laminae the major process responsible for these observations is dolomitization of sr rich aragonite by interstitial brine diagenesis was triggered by slow desiccation of the lake s sediments after the lisan waters started to recede due to a change in climate very sharp chemical gradients which developed in the sediments after deposition have been preserved because further diagenesis was quenched by the advancing dry out h 2 o loss by evaporation induced difrusional migration of na and cl from aragonite laminae into adjacent detrital layers this lowered the na cl ratio in the aragonite and raised it in the detritus relative to the initial dead sea na cl ratio of 0 26 the early lisan brine was similar in its chemical composition and total salinity to that of the present dead sea

middle upper ordovician radiolarians in hunan and jiangxi provinces south china implications for the sedimentary environment and nature of the nanhua basin abstract the yanxi and duiershi formations of the middle upper ordovician in south china are composed of black grayish black and dark gray thin bedded cherts and siliceous slates rich in carbonaceous materials and pyrite horizontal beddings are developed the strata contain randomly distributed fossils radiolarians are discovered in the loudi yongzhou hengyang ji an and ganzhou sections the radiolaria from two sections are identified as protoentactinia sp abundances of radiolarian in the central area of hunan and jiangxi provinces are higher than in the southern area the strata become thickened while the amounts of siliceous materials are decreased and argillaceous contents are increased from northwest to southwest for the yanxi and duiershi formations the lithology gradually changes from carbonate rocks in the north to clastic rocks in the south 30si values of chert and siliceous slate range from 0 6 to 1 18 with al2o3 al2o3 fe2o3 mno tio2 lan cen ce ce and la yb n ratios of 0 65 0 97 0 01 0 16 0 99 1 27 0 85 1 10 and 0 91 1 66 respectively the sio2 and tio2 average contents are 89 08 and 0 27 the sio2 contents decrease while the tio2 increase from northwest to southeast they have similar the ree concentration with no obvious eu anomalies the yanxi and duiershi formations were deposited predominately in a bathyal environment on the continental slope basin and the seawater was stagnant in the middle early late ordovician the nanhua basin occupied a rather large area and sedimentary rocks in the region around hengyang ji an were deposited in the basin center with terrigenous source derived from the southeast

uranium and rare earth elements in hazm el jalamid phosphate saudi arabia concentrations and geochemical patterns comparison this work was carried out to analyze and compare hazm el jalamid phosphate ores saudi arabia with other ores for their uranium u and rare earth elements ree abundance and geochemical pattern fifteen representative phosphate ore samples were collected from three phosphate mines hazm el jalamid and umm wu al in saudi arabia and el sibayia egypt and analyzed for some elements si al fe ca mg na k cr ti mn p sr and ba u and rees using inductively coupled plasma mass spectrometry detailed studies of the hazm el jalamid phosphorite samples were conducted using scanning electron microscopy sem and energy dispersive x ray spectroscopy edx the average u contents in the hazm el jalamid samples were considerably lower than those of other phosphate ores from different origins and countries the sem edx analyses reveal the presence of uranium bearing minerals apatite and uranyl vanadate minerals carnotite k2 uo2 2 vo4 the highest ree concentration values were recorded for la in all samples followed by ce and nd the lowest ree concentrations were recorded for tm in all samples hazm el jalamid phosphate samples are highly enriched in heavy rees hrees and depleted in light rees lrees except for la the rees exhibit the same behavior in the phosphate deposits of hazm el jalamid umm wu al el sibayia florida and morocco and the opposite behavior in the phosphate deposits from jordon and kola which are enriched in lrees except for la and depleted in hrees

paleomagnetism of the late paleozoic slide mountain terrane northern and central british columbia paleomagnetic samples were collected from mid pennsylvanian to lower permian red argillaceous cherts at two localities of the slide mountain terrane 18 sites from the sylvester allochthon in northern british columbia and 11 sites from sliding mountain in central british columbia a secondary component of natural remanent magnetization in the sylvester samples yields a paleomagnetic pole that can be brought into coincidence with the jurassic portion of the north american apparent polar wander path by inferring vertical axis rotation during obduction of the allochthon both localities yield a characteristic component chrm with unblocking temperatures from 650 to 680 c after structural correction for bedding tilt all inclinations of chrm are negative consistent with magnetization during a reversed polarity interval in the northern hemisphere site mean chrm directions show consistent inclinations but distinct stratigraphic groupings of declinations inclination only statistics indicate that the chrm p

geochemical fractionation between porcellanite and host sediment abstract to reveal chemical fractionation during porcellanitization we have examined chemical compositions of porcellanite clasts and their host sediments from dsdp sites 164 and 166 porcellanite is an intermediate product during chert formation distinctly higher si ti ratios are observed in porcellanite relative to the host sediment indicating si transfer from the host sediment however ti normalized values of al fe mn ca na k p rare earth elements sc rb y cs pb th and cr in porcellanite are similar to those of the host sediment showing that these elements are affected by only very limited fractionation during porcellanitization and retain information about the sedimentary environment the si ti p ti and al ti ratios in dsdp clayey samples fluctuate synchronously with their sedimentation ages because the si ti and p ti ratios in clayey sediment reflect the contribution of biogenic siliceous and phosphatic debris respectively their high values in cenozoic clayey sediments indicate

last glacial holocene temperatures and hydrology of the sea of galilee and hula valley from clumped isotopes in melanopsis shells abstract the carbonate clumped isotope 47 thermometer was applied to fresh water snails melanopsis spp grown in the waters of the sea of galilee and hula valley in the north of israel modern shells grown at known temperatures agree with the 47 t calibration of zaarur et al 2013 fossil melanopsis shells from 2 locations gesher bnot ya aqov at the southern tip of the hula valley and the sea of galilee provide a temperature record for the region during the time interval of the past 20 kyrs glacial temperatures are 5 c cooler than mid holocene and 3 c cooler than modern similar to other records in the region these 47 derived temperatures are combined with 18o of the shell carbonate to calculate the oxygen isotopic composition of the habitat waters contrary to global trends and other regional records reconstructed 18owater values increase from the late glacial through the holocene this reversed signal reflects a decrease in the relative contribution of snowmelt to the watershed post lgm and a transition to a more rain dominated inflow a fairly constant difference in 18owater values between the hula valley and sea of galilee waters suggests that the hydrological relationship of the two water bodies had remained constant with the temperature changes playing only a minor role in the extent of evaporation of the sea of galilee relative to the hula

alteration adsorption and nucleation processes on clay water interfaces mechanisms for the retention of uranium by altered clay surfaces on the nanometer scale abstract nano scale processes on the solid water interface of clay minerals control the mobility of metals in the environment these processes can occur in confined pore spaces of clay buffers and barriers as well as in contaminated sediments and involve a combination of alteration adsorption and nucleation processes of multiple species and phases this study characterizes nano scale processes on the interface between clay minerals and uranyl bearing solution near neutral ph samples of clay minerals with a contact ph of 6 7 are collected from a u mill and mine tailings at key lake saskatchewan canada the tailings material contains cu as co mo ni se bearing polymetallic phases and has been deposited with a surplus of ca oh 2 and na2co3 slaked lime small volumes of mill process solutions containing sulfuric acid and u are occasionally discharged onto the surface of the tailings and are neutralized after discharge by reactions with the slaked lime transmission electron microscopy tem in combination with the focused ion beam fib technique and other analytical methods sem xrd xrf and icp oes are used to characterize the chemical and mineralogical composition of phases within confined pore spaces of the clay minerals montmorillonite and kaolinite and in the surrounding tailings material alteration zones around the clay minerals are characterized by different generations of secondary silicates containing variable proportions of adsorbed uranyl and arsenate species and by the intergrowth of the silicates with the uranyl minerals cuprosklodowskite cu uo2 2 sio3oh 2 h2o 6 and metazeunerite cu uo2 aso4 2 h2o 8 the majority of alteration phases such as illite illite smectite kaolinite and vermiculite have been most likely formed in the sedimentary basin of the u ore deposit and contain low amounts of fe 10 at formed most likely in the limed tailings at high contact ph 10 5 and their structure is characterized by a low degree of long range order adsorption of u and nucleation of metazeunerite and cuprosklodowskite are strongly controlled by the presence of the adsorbed oxy anion species arsenate and silica on the fe enriched silicates heterogeneous nucleation of nano crystals of the uranyl minerals occurs most likely on adsorption sites of binary uranyl arsenate and silica complexes as well as on ternary uranyl arsenate or uranyl silicate complexes the uranyl minerals occur as aggregates of misoriented nano size crystals and are the result of supersaturated solutions and a high number of nucleation sites that prevented the formation of larger crystals through oswald ripening the results of this study provide an understanding of interfacial nano scale processes between uranyl species and altered clay buffers in a potential nuclear waste repository as similar alteration conditions of clays may occur in a multi barrier system

clay mineral weathering and contaminant dynamics in a caustic aqueous system ii mineral transformation and microscale partitioning microscopic and spectroscopic studies were conducted to assess mineral transformation processes in aqueous suspensions of illite il vermiculite vm and montmorillonite mt that were subjected to weathering in a simulated high level radioactive tank waste leachate 0 05 m alt 2 m na 1 m no3 p h 14 cs and sr 2 present as co contaminants time series 0 to 369 d experiments were conducted at 298 k with initial cs 0 and sr 0 concentrations from 10 5 to 10 mol kg incongruent clay dissolution resulted in an accumulation of secondary aluminosilicate precipitates identified as nitrate sodalite nitrate cancrinite and zeolite x by molecular spectroscopy and electron microscopy xrd ir nmr sem eds and tem eds contaminant fate was dependent on competing uptake to parent clays and weathering products tem eds results indicated that high il affinity for cs was due to adsorption at frayed edge sites the il system also comprised sr rich aluminous precipitates after 369 d reaction time in mt systems cs and sr were co precipitated into increasingly recalcitrant spheroidal precipitates over the course of the experiment whereas contaminant association with montmorillonite platelets was less prevalent in contrast cs and sr were found in association with weathered vm particles despite the formation of spheroidal aluminosilicate precipitates that were comparable to those formed from mt dissolution copyright 2005 elsevier ltd

stream incision and terrace development in frijoles canyon bandelier national monument new mexico and the influence of lithology and climate abstract the record of stream incision and terrace development in frijoles canyon nm was investigated to examine the controls on channel evolution in this region frijoles canyon developed after deposition of the voluminous ignimbrites of the tshirege member of the bandelier tuff at ca 1 22 ma which provides excellent temporal constraints on canyon evolution base level fall along the rio grande the master drainage in the region contributed to initial incision of the stream development of a major knickpoint in basalt near the rio grande however has effectively isolated most of the stream channel from direct effects of this base level change since the early or middle pleistocene late quaternary evolution of the channel has included development of strath and fill terraces that record the effects of climatic variations and local lithologic variations within the tuff on channel processes a fill terrace underlain by up to 13 m of coarse gravelly alluvium records significant aggradation in the early to middle holocene following a major regional climate change aggradation probably resulted from large increases in sediment supply in the holocene relative to the late pleistocene which was perhaps related to variations in intense summer rains rapid incision in the middle to late holocene has stranded the underlying strath up to 21 m above the modern channel and local rates of incision of up to 4 m ka are more than 10 times the average rates since 1 22 ma holocene incision displays great spatial variability associated with local lithologic variations and results in a stream profile that has evolved rapidly in the last 10 000 years the high rates of incision occur where easily eroded nonwelded tuff is exposed in the canyon bottom whereas a more resistant vapor phase altered tuff unit upstream has impeded incision incision may also have been affected by migration of knickpoints within the tuff paired strath terraces record periods of local base level stability and lateral erosion that were terminated by episodes of downcutting the downcutting was probably controlled by rare high magnitude floods capable of stripping the pervasive gravel armor and exposing nonwelded tuff beneath the stream bed no tectonic influence on late quaternary terrace development or stream incision has been recognized despite frijoles canyon being crossed by the pajarito fault zone a major bounding structure of the rio grande rift instead climatic influences on sediment supply and flood characteristics mediated by lithologic variations in the canyon bottom have controlled late quaternary stream profile evolution

the chemical evolution of kurnub group paleowater in the sinai negev province a mass balance approach abstract the chemical evolution of the kurnub group paleowater was studied starting from rainwater in recharge areas of the sinai and along groundwater flowpaths leading to the natural outlets of this regional aquifer this was achieved by investigating the chemical composition of groundwater ionic ratios degrees of saturation with common mineral species normative analysis of dissolved salts and by modeling of rock water interaction and mixing processes occurring along groundwater flow paths the initial groundwater composition used is from the nakhel well in sinai it evolves from desert rainwater percolating through typical kurnub group lithology in sinai this rainwater dissolves mainly gypsum halite and dolomite together with smaller amounts of marine aerosol and k feldspar at the same time it precipitates calcite sio 2 smectite and degasses co 2 between the area of nakhel and the northern negev the chemistry of kurnub group waters is influenced by dissolution of halite and lesser amounts of gypsum of surficial origin in recharge areas small amounts of feldspars and of dolomite cement in sandstones eroded from the arabo nubian igneous massif of sinai and organic degradation derived co 2 concomitantly there is precipitation of calcite smectite sio 2 and probably analcime characteristic of sediments in continental closed basins north of the negev the kurnub group fluids are diluted and altered by mixing with judea group aquifer groundwaters on the e there is mixing with residual brines from the water body ancestral to the dead sea prior to discharge into the arava valley rock water interaction indicated by netpath and phreeqc modeling is in agreement with lithology and facies changes previously observed in the kurnub group sequence

lithification of biogenic siliceous sediments evidence from neogene diatomaceous sequences of northeast japan abstract biogenic siliceous deposits are a significant component of neogene stratigraphic sequences of the northeast japan arc field observations demonstrate that the siliceous rocks are classified into five lithologic types diatomite opaline porcelanite opaline chert quartzose porcelanite and black shale stratigraphic data suggest that the siliceous formations were deposited continuously from the middle miocene to early pliocene diatomite occurs throughout the sedimentary sequences and changes laterally into chert and porcelanite multivariate statistical analysis of geochemical data indicates that lithification and mineralogical transformation of silica rich deposits was governed not only by compaction and cementation during burial but also by sorting of grains by biological sediment seawater mixing diatomite is composed of frustules without fine ornamentations and delicate structures fine and delicate tests were more susceptible to dissolution than coarse and solid ones and dissolved in the course of biological sediment disturbance ubiquitous occuerences of diatomite in the stratigraphic sequences are attributed to residual frustules which were more resistant to the diagenetic dissolution precipitation reaction of silica biogenic silica is the main source of silica to form chert diagenetic precipitation of silica in diatomaceous beds through progressive sediment burial formed porcelanitic rocks with opaline porcelanite being the precursor of quartzose porcelanite chert was not subjected to biological sediment reworking and fragile shells were preserved during accumulation silicification of precursor deposits of chert was promoted by intraformational dissolution precipitation reaction of silica with increasing sediment compaction and dehydration

sedimentological evaluation of general circulation model simulations for the greenhouse earth cretaceous and jurassic case studies abstract conceptual climate models based on the workings of the present day climate system provided a first order approach to ancient climate systems they are potentially very subjective in character their main drawback was that they involved the relocation of continents beneath a stable atmospheric circulation modelled upon that of the present general circulation models gcms use the laws of physics and an understanding of past geography to simulate climatic responses they are objective in character however they require super computers to handle vast numbers of calculations nonetheless it is now possible to compare results from different gcms for a range of times and over a wide range of parameterisations gcms are currently producing simulated climate predictions which compare favourably with the distributions of climatically sensitive facies e g coals evaporites and palaeosols they have been used effectively in the prediction of oceanic upwelling sites and the distribution of petroleum source rocks and phosphorites parameterisation is the main weakness in gcms e g sea surface temperature orography cloud behaviour sensitivity experiments can be run on gcms which simulate the effects of milankovitch forcing and thus provide insights into possible patterns of climate change both globally and locally i e provide predictions that can be evaluated against the rock record future use of gcms could be in the forward modelling of sequence stratigraphic evolution and in the prediction of the diagenetic characteristics of reservoir units in frontier exploration areas the sedimentary record provides the only way that gcms may themselves be evaluated and this is important because these same gcms are being used currently to predict possible changes in future climate

an iron shuttle for deepwater silica in late archean and early paleoproterozoic iron formation iron formations are typically thinly bedded or laminated sedimentary rocks containing 15 or more of iron and a large proportion of silica commonly 40 in the ca 2590 2460 ma campbellrand kuruman complex transvaal supergroup south africa iron formation occurs as a sediment starved deepwater facies distal to carbonates and shales iron minerals primarily siderite define the lamination the silica primarily occurs as thin beds and nodules of diagenetic chert now microcrystalline quartz filling pore space and replacing iron formation minerals and co occurring deepwater lithologies mechanisms proposed to explain precipitation of the iron component of iron formation include photosynthetic oxygen production anoxygenic photosynthesis abiotic photochemistry and chemoautotrophy using fe ii as an electron donor the origin and mechanism of silica precipitation in these deposits have received less attention here we present a conceptual model of iron formation that offers insight into the deposition of silica the model hinges on the proclivity of dissolved silica to adsorb onto the hydrous surfaces of ferric oxides soluble ferrous iron is oxidized in the surface ocean to form ferric hydroxides which precipitate fe oh 3 binds silica and sinks from the surface ocean along with organic matter shuttling silica to basinal waters and sediments fe iii respiration in the sediments returns the majority of iron to the water column but also generates considerable alkalinity in pore waters driving precipitation of siderite from fe2 and respiration influenced co2 silica liberated during iron reduction becomes concentrated in pore fluids and is ultimately precipitated as diagenetic mineral phases this model explains many of the mineralogical textural and environmental features of late archean and earliest paleo proterozoic iron formation

definition of groundwater flow patterns by environmental tracers in the multiple aquifer system of southern arava valley israel abstract the present paper describes a model for identification and semi quantitative evaluation of the different water bodies replenishing groundwater in the southern arava rift valley the potential sources of recharge into the alluvial aquifer of the valley were assessed by multivariable cluster analysis of environmental tracers such as dissolved ions and stable isotopes this data was also used to determine the flow pattern to the valley and within its alluvial aquifer to the natural outlet of the red sea spatial variations in the chemical compositions of groundwater and of their isotopic ratios are explained as the result of differential rates of replenishment of various water bodies flowing to the arava the alluvial aquifer of the southern arava valley is recharged by the following water bodies 1 lateral subsurface flow caused by infiltration of water from flash floods occurring in the neighbouring mountain massifs 2 upward and lateral groundwater flow from sandstone and carbonate aquifers in the negev and edom mountains and 3 leakage from deep seated brine reservoirs a complete groundwater flow pattern based upon hydrological hydrochemical and isotopic data is presented in a compartmental configuration

quantitative assessment of the flow pattern in the southern arava valley israel by environmental tracers and a mixing cell model abstract this paper demonstrates the implementation of a novel mathematical model to quantify subsurface inflows from various sources into the arid alluvial basin of the southern arava valley divided between israel and jordan the model is based on spatial distribution of environmental tracers and is aimed for use on basins with complex hydrogeological structure and or with scarce physical hydrologic information however a sufficient qualified number of wells and springs are required to allow water sampling for chemical and isotopic analyses environmental tracers are used in a multivariable cluster analysis to define potential sources of recharge and also to delimit homogeneous mixing compartments within the modeled aquifer six mixing cells were identified based on 13 constituents a quantitative assessment of 11 significant subsurface inflows was obtained results revealed that the total recharge into the southern arava basin is around 12 52 10 6 m 3 year 1 the major source of inflow into the alluvial aquifer is from the nubian sandstone aquifer which comprises 65 75 of the total recharge only 19 24 of the recharge but the most important source of fresh water originates over the eastern jordanian mountains and alluvial fans

sedimentary environments of the middle permian phosphorite chert complex from the northeastern yangtze platform china the gufeng formation a continental shelf radiolarian chert abstract radiolarian chert deposited on a continental shelf occurs in the middle permian gufeng formation on the northeastern yangtze platform china the sedimentary environments of radiolarian cherts from accretionary complexes have been well studied however there are few studies about radiolarian chert deposited on continental shelves therefore we have completed a sedimentological and geochemical study of the gufeng formation the gufeng formation is subdivided into the phosphate nodule bearing mudstone member pnmm and the siliceous rock member srm in ascending order the basal pnmm consists of glauconite bearing mudstone which indicates deposition under aerobic shallow marine conditions whereas the upper pnmm is composed of mudstone including abundant phosphate nodules suggesting deposition near the outer shelf in suboxic conditions the srm consists mainly of alternating beds of black chert mudstone and siliceous mudstone with minor tuffaceous mudstone and porous chert beds the black chert contains abundant radiolarians sponge spicules and organic matter framboidal pyrite occurs in the black chert porous chert in the srm includes abundant rhombohedral cavities which are dolomite moulds surrounded by quartz suggesting dolomitization before silicification during early diagenesis the gufeng chert is characterized by high si mo ni cu and zn contents and extremely low mn content the gufeng chert has high normal paraffin concentrations with petroleum like markers these geochemical features suggest that the gufeng chert was deposited under sulfate reducing conditions and is not hydrothermal but rather biogenic in origin the sedimentological and geochemical data suggest that the gufeng formation was deposited mainly on the outer shelf in suboxic anoxic conditions caused by organic matter produced during upwelling the upwelling probably led to high radiolarian productivity abundant silica and organic matter were deposited in the gufeng basin compared with chert from other sites the gufeng chert shows many similarities with chert from platformal basins but not with chert from accretionary complexes especially with respect to age rock type stratigraphy and geochemical features the chert of the gufeng formation is similar to that of the phosphoria formation in the western u s a which is a world class phosphorite giant these similarities suggest that upwelling occurred around the eastern margins of panthalassa and the paleotethys concurrently during the middle permian in general shelf type radiolarian chert represented by the gufeng chert usually shows some of the following features dark color lack of rhythmical bedding association with phosphorite platformal limestone felsic tuff abundant organic matter and sulfides shelf type radiolarian chert is deposited in a poorly aerated restricted basin or in an oxygen minimum zone

the relationship between saline groundwater within the arava rift valley in israel and the present and ancient base levels as detected by deep geoelectromagnetic soundings the time domain electromagnetic tdem geophysical method was employed to detect saline groundwater bodies within and in the close margins of the arava rift valley the arava valley aquifers are known to occupy fresh to saline groundwater the lateral subsurface inflow to the arava from west and east is characterized by fresh to brackish waters the results of the present study indicate that salination of groundwater is controlled by both present day and ancient base levels namely by the dead sea in the north and by the gulf of elat in the south the configuration obtained by the tdem survey exhibits interfaces and palaeo interfaces between fresh to brackish waters and underlying seawater or diluted seawater intruded inland from both base levels as well as brines intruded from the northern base level the central arava structural and hydrological divide seems to escape seawater or brine encroachment at least to the considerable depth of the tdem measurements

strontium isotopic chemical and sedimentological evidence for the evolution of lake lisan and the dead sea precise strontium isotope ratios combined with chemical analyses and sedimentological information are used to monitor the water sources and the evolution of the dead sea and its late pleistocene precursor lake lisan 70 18 kyr b p the materials analyzed include bulk aragonite water leached soluble salts and residual aragonite and gypsum from the lisan formation in the perazim valley near the sw shore of the dead sea the residual aragonite and the associated soluble salts display systematic fluctuations in 17sr86sr ratios between 0 70803 and 0 70806 and from 0 70805 to 0 70807 respectively in individual soluble salt residual aragonite pairs the soluble salt displays a higher 87sr86sr ratio gypsum samples yield 17sr86sr ratios similar to the soluble salts from adjacent layers in the section this shows that in individual samples the source of sr in aragonite was distinct from that in soluble salts and the gypsum the sterility of the lisan sediments their strictly nonbioturbated fine lamination and their high content of chloride salts indicate that lake lisan was a saline or even hypersaline water body in the absence of alternative sources of hco3 and s042 the abundance of primary aragonite and gypsum in the lisan column reflects an import of very large volumes of freshwater into the otherwise saline lake resulting in a density stratification of this water body the history of the upper water layer and that of the lower brine is reflected in the chemical and strontium isotope composition of the aragonite and in that of the associated soluble salts and in the gypsum samples respectively whereas the bicarbonate and much of the ca2 required for aragonite crystallization were supplied by the freshwater the complementary ca2 and sr 2 were added by the lower brine the upper water layer of lake lisan acted as a so42 capacitor during the lake s rise periods it was removed therefrom as prominent gypsum beds upon climatic induced drier period mixing or even complete overturn of the lake the evolution of lake lisan took place between two distinct modes the first was characterized by an extensive supply of freshwater and resulted in a rise of the lake s level a density layered structure and precipitation of aragonite the second mode was marked by a diminishing freshwater input resulting in mixing or complete overturn of its water and precipitation of gypsum these two modes reflect the climatic evolution of the region in the late pleistocene which fluctuated between drier and wetter periods the transition to the holocene is accompanied by the dry up of lake lisan and its contraction to the present dead sea

calibration of the 14c time scale to 40 ka by 234u 230th dating of lake lisan sediments last glacial dead sea a new comparison of 14c dates with 234u 230th ages is presented of aragonites from lake lisan the last glacial dead sea between 20 52 cal ka bp the lisan data are coincident with the coral based 14c calendar age calibration through the continuous portion of the curve to 23 5 cal ka bp and with the additional checkpoints at 30 and 40 cal ka bp the agreement with the corals provides evidence for the accuracy of the u th and 14c ages and indicates that lisan aragonites can potentially be used to generate a nearly continuous record of the atmospheric 14c variations through this crucial time interval the lisan data are compared with other records older than 25 cal ka bp from lake suigetsu japan north atlantic foraminifera south african cave deposits and tufa from spain over some age intervals the records show broad agreement over other intervals they diverge all agree that 14c ages were 2 5 0 5 ka younger than calendar ages between 20 32 cal ka bp for ages 32 cal ka bp the lake suigetsu data indicate small differences between 14c ages and calendar ages of less than 1 5 ka the other records broadly agree that 14c ages are too young by 3 1 ka from 32 39 cal ka bp at 40 cal ka bp the foraminifera show equal 14c and calendar ages while the corals lisan aragonites and the spanish tufa indicate a large age difference of 4 5 ka a recent paleomagnetic study of the lisan formation indicates that the high calendar 14c age difference at 40 cal ka bp may be associated with the laschamp paleomagnetic excursion

sorption of cs to micaceous subsurface sediments from the hanford site usa the sorption of cs was investigated over a large concentration range 10 9 10 2 mol l on subsurface sediments from a united states nuclear materials site hanford where high level nuclear wastes hlw have been accidentally released to the vadose zone the sediment sorbs large amounts of radiocesium but expedited migration has been observed when hlw a nano3 brine is the carrier cs sorption was measured on homoionic sediments na k ca2 with electrolyte concentrations ranging from 0 01 to 1 0 mol l in na electrolyte concentrations were extended to near saturation with nano3 s 7 0 mol l the sediment contained nonexpansible biotite muscovite and expansible vermiculite smectite phyllosilicates the sorption data were interpreted according to the frayed edge planar site conceptual model a four parameter two site high and low affinity numeric ion exchange model was effective in describing the sorption data the high affinity sites were ascribed to wedge zones on the micas where particle edges have partially expanded due to the removal of interlayer cations during weathering and the low affinity ones to planar sites on the expansible clays the electrolyte cations competed with cs for both high and low affinity sites according to the trend k na ca2 at high salt concentration cs adsorption occurred only on high affinity sites na was an effective competitor for the high affinity sites at high salt concentrations in select experiments silver thiourea agtu was used as a blocking agent to further isolate and characterize the high affinity sites but the method was found to be problematic mica particles were handpicked from the sediment contacted with cs aq and analyzed by electron microprobe to identify phases and features important to cs sorption the microprobe study implied that biotite was the primary contributor of high affinity sites because of its weathered periphery the poly phase sediment exhibited close similarity in ion selectivity to illite which has been well studied although its proportion of high affinity sites relative to the cation exchange capacity cec was lower than that of illite important insights are provided on how na in hlw and indigenous k displaced from the sediments may act to expedite the migration of strongly sorbing cs in subsurface environments

constraining groundwater flow residence times inter aquifer mixing and aquifer properties using environmental isotopes in the southeast murray basin australia environmental isotopes particularly d 18 o d 2 h and d 13 c values 87 sr 86 sr ratios and a 14 c constrain geochemical processes recharge distribution and rates and inter aquifer mixing in the riverine province of the southern murray basin due to methanogenesis and the variable d 13 c values of matrix calcite d 13 c

changes in lead and zinc lability during weathering induced acidification of desert mine tailings coupling chemical and micro scale analyses desert mine tailings may accumulate toxic metals in the near surface centimeters because of low water through flux rates along with other constraints metal toxicity precludes natural plant colonization even over decadal time scales since unconsolidated particles can be subjected to transport by wind and water erosion potentially resulting in direct human and ecosystem exposure there is a need to know how the lability and form of metals change in the tailings weathering environment a combination of chemical extractions x ray diffraction micro x ray fluorescence spectroscopy and micro raman spectroscopy were employed to study pb and zn contamination in surficial arid mine tailings from the arizona klondyke state superfund site initial site characterization indicated a wide range in ph 2 5 to 8 0 in the surficial tailings pile ligand promoted dtpa extractions used to assess plant available metal pools showed decreasing available zn and mn with progressive tailings acidification aluminum shows the inverse trend and pb and fe show more complex ph dependence since the tailings derive from a common source and parent mineralogy it is presumed that variations in ph and bioavailable metal concentrations result from associated variation in particle scale geochemistry four sub samples ranging in ph from 2 6 to 5 4 were subjected to further characterization to elucidate micro scale controls on metal mobility with acidification total pb ranging from 5 13 g kg 1 was increasingly associated with fe and s in plumbojarosite aggregates for zn both total 0 4 6 g kg 1 and labile fractions decreased with decreasing ph zinc was found to be primarily associated with the secondary mn phases manjiroite and chalcophanite the results suggest that progressive tailings acidification diminishes the overall lability of the total pb and zn pools

characterizing a large shear zone with seismic and magnetotelluric methods the case of the dead sea transform 1 seismic tomography imaging of seismic scatterers and magnetotelluric soundings reveal a sharp lithologic contrast along a 10 km long segment of the arava fault af a prominent fault of the southern dead sea transform dst in the middle east low seismic velocities and resistivities occur on its western side and higher values east of it and the boundary between the two units coincides partly with a seismic scattering image at 1 4 km depth the boundary is offset to the east of the af surface trace suggesting that at least two fault strands exist and that slip occurred on multiple strands throughout the margin s history a westward fault jump possibly associated with straightening of a fault bend explains both our observations and the narrow fault zone observed by others

geophysical images of the dead sea transform in jordan reveal an impermeable barrier for fluid flow 1 high resolutionseismictomography and magneto telluric mt soundings of the shallow crust show strong changes in material properties across the dead sea transform fault dst in the arava valley in jordan 2d inversion results of the mt data indicate that the dst is associated with a strong lateral conductivity contrast of a highly conductive layer at a depth of approximately 1 5 km cut off at a position coinciding with the surface trace of the dst at the same location we observe a sharp increase of p wave velocities from 5 km s to the east the high velocities in the east probably reflect precambrian rocks while the high electrical conductivity west of the dst is attributed to saline fluids within the sedimentary filling in this sense the dst appears to act as an impermeable barrier between two different rock formations such a localized fluid barrier is consistent with models of fault zone evolution but has so far not been imaged by geophysical methods the situation at the dst is remarkably different from active segments of the san andreas fault which typically show a conductive fault core acting as a fluid conduit

lake levels and sequence stratigraphy of lake lisan the late pleistocene precursor of the dead sea lake lisan the late pleistocene precursor of the dead sea existed from 70 000 to 15 000 yr b p it evolved through frequent water level fluctuations which reflected the regional hydrological and climatic conditions we determined the water level of the lake for the time interval 55 000 15 000 cal yr b p by mapping offshore nearshore and fan delta sediments by application of sequence stratigraphy methods and by dating with radiocarbon and u series methods during the studied time interval the lake level fluctuated between 340 and 160 m below mean sea level msl between 55 000 and 30 000 cal yr b p the lake evolved through short term fluctuations around 280 290 m below msl punctuated at 48 000 43 000 cal yr b p by a drop event to at least 340 m below msl at 27 000 cal yr b p the lake began to rise sharply reaching its maximum elevation of about 164 m below msl between 26 000 and 23 000 cal yr b p then it began dropping and reached 300 m below msl at 15 000 cal yr b p during the holocene the lake corresponding to the present dead sea stabilized at ca 400 m below msl with minor fluctuations the hypsometric curve of the basin indicates that large changes in lake area are expected at above 403 and 385 m below msl at these elevations the lake level is buffered lake lisan was always higher than 380 m below msl indicating a significantly large water contribution to the basin the long and repetitious periods of stabilization at 280 290 m below msl during lake lisan time indicate hydrological control combined with the existence of a physical sill at this elevation crossing this sill could not have been achieved without a dramatic increase in the total water input to the lake as occurred during the fast and intense lake rise from 280 to 160 m below msl at 27 000 cal yr b p

estimation of spatial recharge distribution using environmental isotopes and hydrochemical data ii application to aravaipa valley in southern arizona u s a abstract in part i a mathematical model was developed to estimate the spatial distribution of annual recharge rates into an aquifer using environmental isotopes and hydrochemical data in part ii the model is applied to real data from the aravaipa valley in southern arizona these data suffer from a paucity of hydrologic information but contain numerous isotopic and hydrochemical analyses the model is able to extract from the available data both qualitative and quantitative information about recharge into and flow through the shallow unconfined aquifer in the valley the model shows that this aquifer is replenished primarily by lateral recharge from the pediments and the tributary stowe gulch basin as well as by upward leakage from the underlying confined aquifer recharge from the aravaipa creek is relatively minor lateral recharge from the eastern pediments into the unconfined aquifer exceeds that from the western pediments by a factor of two the western pediments are a major source of recharge for the confined aquifer these results are tentative because independent means to verify them are currently lacking we are encouraged however that the mass balance errors of water and dissolved constituents do not exceed 4 and that the flow rate obtained from darcy s law at one location within the unconfined aquifer in which transmissivity is known agrees with model prediction while chemical reactions are ignored in the model some of the isotopic and chemical species show sufficient spatial variability due to mixing to justify the approach this is supported by analyses of equilibrium water mineral interactions conducted by wateqf

a mixed seawater and hydrothermal origin of superior type banded iron formation bif hosted kouambo iron deposit palaeoproterozoic nyong series southwestern cameroon constraints from petrography and geochemistry abstract the kouambo iron deposit contains banded iron formations bifs and is located in the northwestern margin of the congo craton the bifs are hosted in palaeoproterozoic nyong series a dominantly metasedimentary formations which were metamorphosed into greenschist to granulite facies the kouambo bifs are medium to coarse grained banded rocks consisting of alternation of si rich and fe rich mesobands and belong to oxide facies iron formations geochemistry analyses reveal that these iron formations are composed of 96 wt fe2o3 and sio2 and have low concentrations of al2o3 tio2 and trace hfse suggesting chemical precipitates of silica and iron moreover these bifs have low concentrations of al2o3 tio2 and trace hfses high field strength elements e g zr hf ta pb and th suggesting that terrigenous detrital materials contributed insignificantly to the sedimentation the post archean australian shale paas normalized ree y patterns display seawater like profile minor lree depletion and hree enrichment positive y anomalies however they display positive eu and negative ce anomalies and low y ho ratio average 29 which suggest the influence of the hydrothermal fluids the weak positive eu eu paas ratio average 1 5 associated with the low v 17 5 ppm co 6 1 ppm and ni 27 5 ppm contents similar to other superior type bifs worldwide are consistent with the deposition of the kouambo bifs in continental marginal sea or back arc basin environment in summary the kouambo bifs show a seawater like ree y signature however the positive eu anomalies and reduced y ho ratios relative to seawater indicates a possible mixing with hydrothermal fluids 0 5

diagenetic formation of bedded chert implications from a rock magnetic study of siliceous precursor sediments abstract bedded chert is a distinctive rock type characterized by a rhythmic alternation of quartz rich chert beds and clay rich interbeds the origin of the lithologic variations is not well understood a rock magnetic study of a sequence of alternating bands of radiolarian rich and clay rich bands recovered by odp leg 129 which is considered to be the best known analog for the bedded chert precursor sediments shows that the relative abundances and characteristics of magnetic phases are similar in both sediment types with only a minor 1 5 times on average increase in bulk concentration in clay rich bands comparison with magnetic properties of the diagenetically mature chert shale couplets suggests that siliceous precursor sediments undergo strong differential diagenetic modification a simple silica transfer model with dissolution of silica in proto shale donor beds and deposition in proto chert receiver beds indicate that the known features of the bedded chert sequences such as the difference in thickness cosmic dust content between chert and shale can be reproduced in case of donor beds having initially lower clay higher biogenic silica content compared to receiver beds while contrary to the current depositional model explaining chert beds formation by episodic radiolarian bloom on a background of slow accumulation of clays an association of proto shale beds with high productivity episodes is supported by an independent paleoproductivity proxy their higher al ti values and is in full agreement with the known silica diagenesis trends particularly with the retarding influence of detrital minerals on silica transformations the impetus for diagenetic silica segregation is provided by initial variability in clay content within a siliceous sedimentary succession silica dissolution starts in clay poor intervals when diffusing silica encounters clay rich beds adsorption to clay lowers dissolved silica content below the saturation level of the higher solubility phases and leads to deposition of low solubility quartz early deposition of quartz cement prevents significant compaction of chert layers while the loss of silica in donor beds leads to their compaction and concomitant increase in non reactive clay and cosmic dust particles severe distortion of primary environmental signals during differential diagenesis questions the use of bedded chert sequences for cyclostratigraphic studies

saline groundwater in israel its bearing on the water crisis in the country abstract one of the major causes for the deterioration of water quality bearing heavily on the water crisis in israel is the ongoing contamination of its water resources by saline water bodies the present paper reviews the geochemical processes forming saline water lists and explains certain chemical and isotopic parameters which enable understanding these processes and describes the saline groundwater bodies and various salinization phenomena occurring in the country s various aquifers deterioration of groundwater in israel is caused by numerous natural processes such as encroachment of sea water migration of connate highly pressurized brines penetrating into fresh groundwater by subsurface dissolution of soluble salts originating in surrounding country rocks and by water rock interaction in addition to sea water two saline water bodies were identified as the main factors causing salinization of fresh groundwater a ca chloride brines encountered in the jordan dead sea rift valley in various parts of the negev and of the coastal plain and b na chloride saline water identified in the subsurface of the negev and in the southern part of the coastal plain intensive exploitation of groundwater in israel has disturbed the natural equilibrium which prevailed between fresh and saline water the newly established groundwater flow regimes have facilitated the migration of saline water bodies their participation in the active hydrological cycle and the progressive contamination of fresh groundwater these processes which were not anticipated by planners and water resources managers emphasize that large scale groundwater exploitation was undertaken without giving sufficient consideration to the occurrence and subsurface migration of saline water and brines

geochemistry of the lisan and damya formations in jordan and implications for palaeoclimate abstract geochemical mineralogical and sedimentological investigations carried out on the lacustrine lisan and damya formations of the jordan rift valley reveal three major and several minor transgressive depositional cycles all terminating with massive gypsum precipitation the highest level of lake lisan is reported in the literature at 130 m below mean sea level b s l from 70 45 calibrated ka bp the lisan formation is characterised by a high gypsum aragonite ratio and a low lithogenic content implying a regression of an initially high water level caused by reduced water input in the following interval ca 45 36 cal ka bp two low water stands are marked by higher salt concentrations after recovery and a period of higher water level the lake lisan era ends with a strong regression at around 16 cal ka bp this date coincides with the period when lake van eastern turkey also fell dry thus marking a strong drought signal in the entire near east the overlying damya formation containing more lithogenics records lake level fluctuations at around 300 m b s l the existence of a north south precipitation gradient as present today is indicated by increasing sr ca ratios in aragonite and a decreasing lithogenic content in a n s direction secondary gypsum formed diagenetically and aragonite and low mg calcite was transformed into high mg fe calcite

anomalously low al2o3 tio2 values for archean cherts from the pilbara block western australia possible evidence for extensive chemical weathering on the early earth geochemical sedimentological and mineralogical features of 3 0 ga archean cherts and intercalated bifs from the pilbara block western australia were studied chert layers that are well exposed at point samson 20 km north northeast of roebourne consist of various types of chert white light gray chert brownish yellow chert gray chert dark gray chert massive black chert and light gray chert the cherts other than brownish yellow chert consist mostly of microcrystalline quartz with a minor amount of fine silicate minerals and carbonates the brownish yellow chert is characterized by a high concentration of goethite most cherts contain thin layers characterized by high concentrations of ti bearing minerals such as rutile anatase fe ti aggregates and fine tio2 grains accordingly al2o3 tio2 values in some samples are very low 1 0 indicating that these samples contain more tio2 than al2o3 this geochemical feature is attributed mainly to the supply of detrital materials with high ti bearing minerals to the site of deposition because the ti bearing minerals are generally associated with detrital quartz and zircon ti enriched detrital materials are possibly formed by al ti fractionation during 1 extensive chemical weathering or 2 hydrothermal alteration of the source rocks in the first hypothesis which we prefer it is suggested that low ph values 4 of meteoric waters accelerated the decomposition of rock forming minerals and prevented precipitation of dissolved al3 such low ph values of meteoric waters could have been attributed to more violent volcanic activities issuing acid materials e g h2s and hcl and or a higher concentration of atmospheric co2 in the archean than today

redox change in sedimentary environments of triassic bedded cherts central japan possible reflection of sea level change middle triassic radiolarian bedded cherts in the mino belt central japan include a sequence showing an abrupt facies change from the lower to the upper where grey black bedded cherts enriched in carbonaceous matter and framboidal pyrite are overlain by brick red hematitic bed ded cherts brownish yellow chert enriched in goethite and purple red chert occur at the boundary between the grey black bedded cherts and the brick red bedded cherts this facies change is in accor dance with stratigraphic variations of geochemical characteristics the lower section grey black bedded cherts compared with the upper section brick red bedded cherts are enriched in ctot and stot and are characterized by lower mno tio 2 higher feo fe 2 o 3 total iron as fe 2 o 3 and more variable fe2o3 tio2 values some of the lower section samples in addition are characterized by an enrich ment in some transition metals ni cu and zn the covariation of mineralogical and geochemical characteristics indicates that sedimentary environments and diagenetic processes were different between the lower and the upper section bedded cherts during the deposition of the lower section bedded cherts the sedimentary environment was anoxic and bacterial sulphate reduction occurred during the early diagenetic stage in contrast the upper section bedded cherts were subjected to less reducing diagenetic processes active sulphate reduction did not occur the change of sedimentary environment and diagenetic process at the site of deposition is likely to be attributed to the fluctuated concentration of dissolved oxygen in the water mass of a semi closed marginal ocean basin which was potentially caused by sea level change that occurred during middle triassic time

varves in marine sediments a review the global compilation of reported marine varved sedimentary records throughout the quaternary contains 52 sites marine varve deposition and preservation typically depend on environmental and sedimentological conditions such as a sufficiently high sedimentation rate severe depletion of dissolved oxygen in bottom water to exclude bioturbation by macrobenthos and a seasonally varying sedimentary input to yield a recognizable rhythmic varve pattern additional oceanographic factors include the strength and depth range of the oxygen minimum zone omz and regional anthropogenic eutrophication from point sources such as large polluted rivers quaternary marine varves are not only found in those parts of the open ocean that comply with these conditions but also in fjords embayments and estuaries with thermohaline density stratification and nearshore marine lakes with strong hydrologic connections to ocean water this review critically describes settings and sedimentological characteristics of marine sites where varves have been reported broader applications of marine varve records are discussed for example in terms of radiocarbon calibration on high resolution time scales constraining paleoceanographic variability and global change teleconnections diagnosing factors affecting modern fish population dynamics based on past performance detailing biogeochemical cycles and deciphering complex factors influencing marine productivity varves in saline water bodies without hydrologic connection to the global ocean are not included in this review and instead pertain to the companion review on lacustrine varves where also general and fundamental principles of varve deposition classification and dating are covered zolitschka et al 2015 the postulated occurrence of varves in pre quaternary rocks is critically discussed in this review with representative examples in the case of non evaporitic laminations in fine grained ancient marine rocks such as banded iron formations and black shales laminations may not be varves but instead may have multiple alternative origins such as event beds or formation via bottom currents that transport and sort silt sized particles clay floccules and organic mineral aggregates in the form of migrating bedload ripples

differential compaction and subsidence in sedimentary basins due to silica diagenesis a case study the conversion of opal a to opal ct is a thermochemical diagenetic process that can cause kilometer scale differential compaction and differential subsidence within clastic sedimentary basins this is demonstrated for an opal a to opal ct conversion imaged by three dimensional seismic data on the northeastern atlantic margin this diagenetic front has a circular to polygonal ridge depression morphology the ridges have a relief of 10 50 m and separate circular to polygonal depressions that have diameters of 1 2 km some of which link up to form interconnected networks this morphology initially developed because the host sediments mantled an underlying polygonal fault system and the front tracked deformed stratigraphy ridges formed above the tips of the underlying faults and depressions formed between them ridge relief and width then progressively increased due to earlier opal a to opal ct conversion above ridges as well as conversion laterally along beds or bed sets this caused compaction and concomitant subsidence in the overburden and the development of a circular to polygonal network of overburden troughs aligned with the ridge system a positive feedback loop was established where additional overburden sediment above the growing ridges reached the depth of conversion ahead of adjacent areas driving more compaction and differential subsidence this paper provides the first insights into the large scale morphological characteristics of opal a to opal ct diagenetic fronts it demonstrates the potential for a local stratigraphic control on diagenetic front development and morphology and lastly highlights the potential utility of seismic reflection data for understanding diagenetic processes

diagenetic formation of bedded chert evidence from chemistry of the chert shale couplet theories concerning the formation of bedded chert traditionally have emphasized either depositional or diagenetic processes major and rare earth element data from franciscan assemblage mesozoic and claremont formation miocene bedded chert sequences along with physical observations such as the presence of rare and highly corroded radiolarians in shale interbeds are most consistent with a dominantly diagenetic origin of chert shale couplets and are incompatible with many depositional theories chemical distributions between franciscan and claremont bedded chert shale closely match chemical fractionations recorded by monterey formation and deep sea drilling project sampled cherts formed by diagenetic sio sub 2 dissolution transport and reprecipitation suggesting that diagenetic migration of sio sub 2 from proto shale to proto chert is also largely responsible for chert shale couplets identical ce anomalies ce ce found in immediately adjacent chert shale layers indicate that turbidites or other transport mechanisms are not responsible for the alternating beds neither the chemistry of the chert shale couplet nor the overall stratigraphy of the sequences is consistent with couplet formation being caused by productivity fluctuations chemical mass balance calculations reconstructing the total bulk sediment composition suggest that modern siliceous sequences do not contain enough labile biogenic sio sub 2 to form entire stratigraphies of bedded chert

from diatom opal a δ18o to chert δ18o in deep sea sediments abstract 18o signature of marine deep sea cherts was previously used to reconstruct past ocean temperature and oceanic bottom water 18o through the cenozoic and mesozoic periods oxygen isotopes in deep sea cherts which were never exposed to meteoric water exhibit a wide range of values indicating that the evolution and maturation of biogenic amorphous opal opal a to opal ct and microquartz chert is accompanied by isotopic changes we measured 18o of diatom opal a opal ct and microquartz chert in downcore profiles of sediment cores odp 795 and 799 from the sea of japan diatom opal a opal ct and microquartz chert were separated and purified from the bulk sediment this was followed by xrd sem eds and xps to identify and quantify the mineral phases the qualitative elemental concentrations and the amounts of authigenic clays diatom opal a transforms to opal ct and microquartz chert when it is deposited in sediment originally rich in diatoms relative to other lithologic constituents such as clay diatom opal a 18o is in the range of 34 38 18o of opal ct is 25 at the first phase transformation at 330 mbsf in odp 795 and 420 mbsf in odp 799 this phase transformation occurs at a temperature of about 40 c 18o of opal ct remains essentially unchanged until it undergoes the second phase transformation to microquartz chert at 470 mbsf in odp 795 and at 580 mbsf in odp 799 at which point its 18o decreases abruptly to 20 this phase transformation occurs at a temperature of about 60 c the 18o values of opal ct and microquartz chert appear to reflect equilibrium formation temperatures of silica corresponding to the geothermal gradient and the local porewater 18o the 18o of opal ct and microquartz chert are controlled by the geothermal temperatures and compositions of pore waters during polymorphic transformations deep within the sediment indicating that the 18o of these phases cannot be used to determine temperature or composition of seawater during diatom growth

paleoclimatic implications of u series dates for lake sediments and travertines in the arava rift valley israel abstract the sayif travertines and lacustrine limestones cropping out in the northern arava valley a region of extreme aridity have been dated by the 230 th 234 u disequilibrium method the consistency between the stratigraphic position and the apparent ages at each of the sampling sites strongly supports the reliability of the ages most of the ages fall within two clusters that are coincident with ages representative of oceanic oxygen isotope stages 5 and 7 the colder intervening stage 6 was not a period of substantial travertine formation during the warmer global episodes of isotopic stages 5 and 7 the arid south of israel apparently was considerably wetter than at present

u th dating of lake lisan late pleistocene dead sea aragonite and implications for glacial east mediterranean climate change u series dating can be an effective means to obtain accurate and precise ages on quaternary carbonates however most samples require a correction for u and th in admixed detritus this complication is often addressed through generation of u th isochrons requiring analyses of several coeval samples in addition presence of water derived hydrogenous th in the carbonate can cause inaccuracies in isochron ages this study reports a high resolution u series chronology of sediments deposited by lake lisan the last glacial precursor of the dead sea the strategy employed combines multiple measurements from a few stratigraphic heights and fewer analyses from many heights in a single described and measured section the resulting chronology is based on ages at 22 heights in a 40 m thick section covering the interval of 70 14 calendar ka bp the effects of admixed detritus are evaluated using trace elements nearly pure aragonite samples indicated by very low abundances of insoluble elements such as nb and zr were found to contain hydrogenous th which causes the uncorrected u 230th age of a modern sample to be 2 5 ka nevertheless accurate ages have been obtained by correcting for the detrital and aqueous interferences the resulting ages are in stratigraphic order and their accuracy is evidenced by consistency of lisan formation u series and 14c ages with the coral based calendar radiocarbon age calibration the u th ages provide a context to unravel the limnological history of lake lisan boundaries between the lower middle and upper stratigraphic units correspond to the mis 4 3 and 3 2 transitions respectively during mis 2 and 4 the lake generally showed a stable two layer configuration and a positive fresh water balance reflected by deposition of laminated aragonite detritus dry intervals during mis 2 and 4 are indicated by thick gypsum layers and an inferred depositional hiatus which are temporally associated with heinrich events h1 at 17 ka and h6 at 65 ka respectively during mis 3 the lake level was unstable with intermittent dry periods indicated by abundant clastic layers and a significant hiatus between 43 49 ka clastic layers are associated with dansgaard oeschger events during mis 3 and indicate lake level declines during abrupt northern hemisphere warmings overall the climate of the eastern mediterranean region shows a strong linkage to the northern hemisphere climate with increasing lake size and stability during cold periods and fluctuations and dessication during warmings and heinrich events

proposed sources of methane along the dead sea transform abstract the concentrations and isotopic compositions of methane higher alkanes dissolved inorganic carbon dic and co 2 were studied in fresh groundwater brines and springs along the dead sea transform dst from the hula valley in the north to the dead sea ds basin in the south although the occurrence of methane along the dst was documented before this is the first time that comprehensive research was conducted on the methane provenance and the post genetic reactions involved the methane stable carbon isotopic composition 13 c ch4 shows a distinct geographic pattern in the northern part of the dst studied in the hula valley and lake kinneret where recent marshy and lacustrine environments exist the methane source seems to be related to intense shallow depth methanogenesis this microbial methane shows low 13 c values in the range of 13 c ch4 between 58 and 72 and high alkane ratios c 1 c 2 c 3 between 100 and 1000 the isotope fractionation co2 ch4 of 1 065 suggests the domination of hydrogenotrophic methanogenesis rather than acetoclastic methanogenesis in the waters of hammat gader and tiberias hot spring whose source is the cretaceous aquifer 13 c ch4 has high values of 28 and 56 respectively with low alkane ratios of 40 in both sites the high 2 h ch4 values of hammat gader in addition to the isotopic composition of the dic and the difference between co 2 and ch 4 reject the possibility of local microbially produced methane and suggest a sub surface thermogenic source of an initial stage of thermal degradation of bituminous chalk of senonian age similarly methane in groundwater from the ds basin is also interpreted to be of thermogenic origin in accordance with the local geology context in the ds basin of buried asphalt and due to the low geothermal gradient in the region it is speculated that methane is produced from slight heating of the asphalts in general it seems that there is a thermogenic methane contribution along the entire dst which is locally masked by high microbial activity in shallow organic rich environments such as lake kinneret and the hula basin

southward migration of rain tracks during the last glacial revealed by salinity gradient in lake lisan dead sea rift abstract the paleosalinity of the late pleistocene lake lisan during its highstand between 27 000 and 15 000 years b p is evaluated from biological data diatoms cyanobacteria fish and ostracods and chemical data sr ca and na ca ratios in authigenic aragonite the data indicate a zone of maximum salinity at the southern part of the lake in the vicinity of the present dead sea basin while most of the freshwater input to lake lisan originated from the jordan river in the north and runoff from the eastern and western parts of the drainage basin our analysis indicates a significant additional contribution from a southern freshwater source at present the contribution of the southern source to the dead sea is minimal hence it appears that in addition to the prevailing rain originating from the mediterranean an additional southern source of rain was more active during the last glacial than today this may be explained by migration of rain tracks whose moisture originated in the atlantic from the mediterranean southwards

palaeosols and late pleistocene rainfall fluctuations in the negev desert the existence of a series of palaeosols in the present day desert region of southern israel the northern negev desert 1 2 indicates recurring periods of wetter climate in the past up to seven well developed palaeosols occur within a section and each has a horizon containing soft calcium carbonate nodules 3 15 mm in diameter the palaeosols are developed within loess or fluvially redeposited loess consisting of silty clay or clayey silt the 14c ages of the uppermost three calcic horizons average 13 000 yr bp calcic horizon ch i 28 000 yr bp ch ii and 37 000 yr bp ch iii drier phases occurred between these periods of pedogenesis especially during the last glacial maximum centred at 18 000 yr bp when extensive erosion occurred analysis of the 13c content of nodule carbonates points to the occurrence of strong north south rainfall gradients during each period of calcic horizon formation which excludes the possibility of monsoonal rains contributing to the increased rainfall during these periods the palaeosols correspond to global warm phases of the last glacial period

chemical transport to the seafloor of the equatorial pacific ocean across a latitudinal transect at 135 w tracking sedimentary major trace and rare earth element fluxes at the equator and the intertropical convergence zone we have analyzed the major trace and rare earth element composition of surface sediments collected from a transect across the equator at 135 w longitude in the pacific ocean comparing the behavior of this suite of elements to the caco3 opal and corg fluxes which record sharp maxima at the equator previously documented at the same sampling stations enables us to assess the relative significance of the various pathways by which trace elements are transported to the equatorial pacific seafloor the 1 1 high biogenic source at the equator associated with equatorial divergence of surface water and upwelling of nutrient rich water and 2 2 high aluminosilicate flux at 4 n associated with increased terrigenous input from elevated rainfall at the intertropical convergence zone itcz of the tradewinds are the two most important fluxes with which elemental transport is affiliated the biogenic flux at the equator transports ca and sr structurally bound to carbonate tests and mn primarily as an adsorbed component trace elements such as cr as pb and the rees are also influenced by the biogenic flux at the equator although this affiliation is not regionally dominant normative calculations suggest that extremely large fluxes of ba and p at the equator are carried by only small proportions of barite and apatite phases the high terrigenous flux at the itcz has a profound effect on chemical transport to the seafloor with elemental fluxes increasing tremendously and in parallel with ti normative calculations however indicate that these fluxes are far in excess of what can be supplied by lattice bound terrigenous phases the accumulation of ba is greater than is affiliated with biogenic transport at the equator while the p flux at the itcz is only 10 less than at the equator this challenges the common view that ba and p are essentially exclusively associated with biogenic fluxes many other elements including mn pb as and rees also record greater accumulation beneath the itcz than at the equator thus adsorptive scavenging by terrigenous paniculate matter or phases intimately associated with them appears to be an extremely important process regulating elemental transport to the equatorial pacific seafloor these findings emphasize the role of vertical transport to the sediment and provide additional constraints on the paleochemical use of trace elements to track biogenic and terrigenous fluxes

evolution of brackish groundater in a typical arid region northern arava rift valley southern israel brackish groundwater in the northern arava valley south of the dead sea is characterized by salinities up to 4000 mg l this groundwater originates from two main aquifers the first is a relatively shallow aquifer composed of clastic and carbonates of the neogene recent hazeva and arava fill formations the second aquifer occurs usually within a depth of 700 1500 m and is composed of lower cretaceous sandstones of the kurnub group no significant differences could be discerned between the concentrations and ionic ratios of these two main groundwater bodies the chemical evolution of the groundwater is the result of two major processes 1 dissolution groundwater flowing through the kurnub group beyond the boundaries of the arava rift valley and through part of the hazeva and arava fill aquifers is characterized by typical ratios na cl 1 and by ca hco3 so4 0 75 the chemical composition of this groundwater indicates a contribution of salts derived from ancient cacl brines such brines are known to have evolved since the neogene in the arava rift valley they are encountered throughout the whole sedimentary succession in the dead sea and northern arava rift valley area intermixing to various degrees with brackish or fresh groundwater the stratigraphic relation between the brackish and saline groundwater bodies is not consistent usually the less concentrated groundwater overlies the more saline there are however cases of transposition possibly indicating the occurrence of unflushed pockets of cacl brines brackish groundwater derived from the two main aquifers is characterized by an excess of mg and so4 such an excess may have evolved from residual salts precipitated as the result of recent or subrecent fractional evaporation of rain and or floodwater under arid conditions water which precipitated crusts of calcite gypsum and halite became enriched in mg and so4 and to a lesser degree in k and na another possible explanation for the excess mg and so4 is the complete evaporation of surface water resulting in the precipitation of kmg sulphates subsequent dissolution by freshflood water would then preferentially dissolve and mobilize these highly soluble minerals

chert spheroids of the monterey formation california usa early diagenetic structures of bedded siliceous deposits chert spheroids are distinctive early diagenetic features that occur in bedded siliceous deposits spanning the phanerozoic these features are distinct in structure and genesis from similar concentrically banded wood grain or onion skin chert nodules from carbonate successions in the miocene monterey formation of california usa chert spheroids are irregular concentrically banded nodules which formed by a unique version of brittle differential compaction that results from the contrasting physical properties of chert and diatomite during shortening there is brittle fracture of diatomite around and horizontally away from the convex surface of strain resistant chert nodules unlike most older siliceous deposits the monterey formation still preserves all stages of silica diagenesis thus retaining textural mineralogical and geochemical features key to unravelling the origin of chert spheroids and other enigmatic chert structures chert spheroids found in opal a diatomite form individual nodules composed of alternating bands of impure opal ct chert and pure opal ct or chalcedony with increased burial diagenesis surrounding diatomite transforms to bedded porcelanite or chert and spheroids no longer form discrete nodules yet still display characteristic concentric bands of pure and impure microcrystalline quartz and chalcedony petrographic observations show that the purer silica bands are composed of void filling cement that precipitated in curved dilational fractures and do not reflect geochemical growth banding in the manner of liesegang phenomena invoked to explain concentrically banded chert nodules in limestone chertification of bedded siliceous sediment can occur more shallowly 100 m and rapidly 1 myr than the bulk silica phase transitions forming porcelanite or siliceous shale in the monterey formation and other hemipelagic pelagic siliceous deposits early diagenesis is indicated by physical properties deformational style and oxygen isotopic composition of chert spheroids early formed cherts formed by pore filling impregnation of the purest primary diatomaceous beds along permeable fractures and in calcareous siliceous strata