diagenetic stabilization of the upper permian dalan formation persian gulf basin abstract the upper permian dalan formation is a supergiant gas reservoir in the persian gulf basin reservoir quality is controlled by the original facies type dolomitization and anhydrite cementation this study focuses on the texture petrographic analysis bulk stable isotope values and trace element composition in order to identify the original mineralogy of carbonate grains and cements and to assess the synsedimentary and diagenetic processes including the timing and setting of dolomitization the limestone data suggest that the initial precipitation of isopachous acicular to fibrous aragonite cements in the marine phreatic environment was followed by dissolution of aragonite grains and cements in the meteoric phreatic zone and neomorphism and low mg calcite cementation blocky and drusy crystals syntaxial overgrowths in the active freshwater phreatic zone the relatively pristine 18o and 13c values low mn and relatively high sr and na contents indicate that this meteoric diagenesis was relatively limited the remaining porous space was cemented by blocky calcite later during burial four types of dolomites are identified within a complex mixture of texturally and isotopically different dolomites dolomicrite dolomicrosparite dolosparite and saddle dolomite dolomicrite formed syndepositionally from the evaporated permian seawater or by reflux of dense evaporated brines during shallow burial the second major episode of dolomitization dolomicrosparite and dolosparite was driven by reflux of warmer and more saline fluids at greater depth which affected both previously non dolomitized and dolomitized sediments the final diagenetic stabilization during deep burial is associated with extensive pressure solution fracturing vein filling of calcite and dolomite cements and crystallization of saddle dolomite

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

an oscillating trend in phanerozoic non skeletal carbonate mineralogy textural and compositional data on ancient ooids and cements suggest the existence of an oscillating phanerozoic temporal trend in non skeletal carbonate mineralogy the trend shows good correlation with eustatic climatic oscillations proposed by others the most likely mechanism appears to be plate tectonically influenced oscillations in pco2 the vapour pressure of co2 rather than change in oceanic mg ca ratio

cementation in cold water bryozoan sand tasmania australia cold water 3 11 c carbonate is the predominant sediment on the tasmanian shelf calcitic skeletal grains bryozoa foraminifera echinoderms etc predominate over aragonitic gastropods etc ones non skeletal grains are mostly micritic intraclasts with some pellets fibrous spherulitic and rhombohedral calcite submarine cements range up to 90 in the bryozoan sand x ray analyses show that the bryozoan sand is characterized by a spectrum of calcites low to high magnesian and some aragonite a uniform spread of mg concentrations from 0 06 to 2 48 wt indicates 3 10 c ambient water temperatures the mn 10 360 ppm and fe 176 2499 ppm concentrations increase with increasing mg values due to the formation of impure caco3 phases the sr content in bryozoan sand bryozoa 3200 ppm sr decreases with increasing rhombohedral calcite cement as low mg calcite precipitating from 3 c sea water would have 1350 ppm sr the bryozoan sand grains with fibrous spherulitic calcite cements have high sr concentrations 4470 7000 ppm in the same range as in aragonitic detected only by x ray analyses bryozoan sand grains the spherulitic calcite cements are either pseudomorphs after original aragonite cements or these calcite cements and aragonite were inverted from fibrous spherulitic vaterite a predominant caco3 polymorph at temperatures 10 c

relative precipitation rates of aragonite and mg calcite from seawater temperature or carbonate ion control the temperature and degree of carbonate mineral supersaturation co3 2 ion concentration of seawater are the two most likely controlling variables on the compositions of recent marine carbonate cements the relative importance of these variables is difficult to assess in nature because they have similar trends with depth 0 1500 m and latitude in modern oceans we carried out laboratory experiments to investigate the relative growth rates of calcite mg calcite and aragonite in seawater as functions of both temperature 5 25 and 37 c and of carbonate ion concentration 2 5 to 15 times supersaturated with respect to calcite the precipitation rates of aragonite relative to those of calcite increase strongly with increasing temperature and are not affected greatly by changes in saturation state at 5 c calcite precipitation rates are nearly equivalent to those of aragonite regardless of the degree of saturation at both 25 and 37 c aragonite precipitation rates are much more rapid than those of calcite up to a factor of 4 except at very low saturation states calcite compositions vary from less than 5 mol mgco3 at 5 c to 14 mol mgco3 at 37 c our results suggest that the well documented shift toward precipitation of lower mol mg calcite and the decrease in abundance of aragonite cements with increasing oceanic depth and latitude can be attributed largely to lower temperatures

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

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

depositional environment sequence stratigraphy and geochemistry of lower cretaceous carbonates fahliyan formation south west iran abstract the fahliyan formation is a carbonate sequence of lower cretaceous berriasian hauterivian age and was deposited in the zagros sedimentary basin iran in this investigation the fahliyan formation at the type section and in the subsurface has been studied facies analysis and petrographic studies led to the recognition of 10 microfacies that were deposited in three facies belts lagoon shoal and open marine the observed facies patterns indicate a carbonate rimmed shelf depositional environment based on field observations microfacies analysis and sequence stratigraphic concepts two third order sequences in the type section and three third order sequences in the subsurface section were identified the transgressive deposits display a predominance of deep subtidal facies while highstand deposits show shallow subtidal facies some petrographic evidence such as an abundance of aragonite skeletal and non skeletal components shows that this formation was deposited in a sub tropical environment with original aragonite mineralogy geochemical evidence such as high sr na ratios also support original aragonite mineralogy 18o and 13c values suggests that alteration occurred during burial diagenesis in a closed system with low water rock interaction palaeotemperature calculation based on the heaviest oxygen isotope value in micritic samples of the fahliyan limestone shows that ambient water temperature was around 24 c during the deposition of this formation

submarine hydrothermal weathering global eustasy and carbonate polymorphism in phanerozoic marine oolites abstract the age and fabric of 347 phanerozoic marine oolites have been compiled in order to evaluate secular variations in the original mineralogy of these physicochemically precipitated sedimentary carbonates variation in the abundance of oolite correlates with positions of global sea level ooids were common during transgressions and regressions but were rare during lowstands and highstands the rarity of oolite during continental emergence early cambrian permo triassic late tertiary quaternary probably relates to a diminished areal extent of shallow carbonate environments causes for a similar paucity during continental submergence silurian devonian late cretaceous are more problematic higher atmospheric co2 and lower hydrospheric co3 concentration during highstands may have inhibited a biotic carbonate precipitation ooids coeval with highstands display a preponderance of fabrics evincing a primary calcite mineralogy ooids formed during lowstands are more diverse but record dominance of aragonite variations in cortical mineralogy relate more closely to flooded continental areas than to sea level elevations supporting the suggestion of mackenzie and pigott 1981 that variations in hydrospheric carbonate concentrations were more important in determining phanerozoic ooid mineralogy than were magnesium calcium concentrations these data on oolite abundance and mineralogy demonstrate that abiotic phanerozoic marine carbonates have been responsive to secular changes in atmospheric hydrospheric chemistry and global eustasy and suggest that these changes are directly related to past rates of submarine weathering and sea floor hydrothermal activity

diagenetic stabilization of aragonite and low mg calcite ii stable isotopes in rudists abstract cretaceous rudists having thick multilayered bimineralic aragonite and low mg calcite shells have been studied for the effects of phreatic vadose meteoric diagenesis on their microstructural and isotopic attributes rudist skeletal components with preserved original mineralogy of aragonite and low mg calcite and with preserved microstructures have isotopic signatures analogous to holocene marine bivalves this similarity argues for a comparable isotopic composition of the cretaceous and holocene seawater as well as for a similar mode of incorporation of stable isotopes into their shells diagenetic stabilization of rudist shells appears to have been a two stage process with low mg calcite diagenetic calcite lmc dlmc and particularly aragonite diagenetic calcite a dlmc transformation as the first step and cementation as a later development the direct a dlmc mineralogical transformation calcitization results in initial depletion in 18o of 2 and the subsequent diagenetic precipitation of ferroan calcite spar causes depletion in 13c as well as an additional decrease in 18o the former due to introduction of organically derived co2 into the diagenetic aquifer in contrast 13o and 13c isotopic depletions in the originally lmc skeletal components are both related to the precipitation of the late diagenetic ferroan sparry calcite cement the earlier calcitization stage being of subordinate importance only

kinetic control of morphology composition and mineralogy of abiotic sedimentary carbonates abstract conventional thinking has long held that the abiotic precipitation of calcium carbonate occurs with a causal relationship between fluid my ca ratios and crystal morphology crystal composition and carbonate mineralogy resulting in the formation of meteoric equant low magnesium calcite and marine acicular high magnesium calcite and aragonite problematically calcites with varying amounts of incorporated magnesium occur either as equant or acicular crystals and aragonite may coexist with calcite in either environment commonly however a systematic relation exists between crystal morphology composition mineralogy and rates of reactant supply to growing crystal surfaces for example equant rather than acicular crystals of calcite form in modern deep and or cold marine meteoric phreatic and deep burial settings where the degree of carbonate saturation and or rates of fluid flow are low in areas of higher saturation and or fluid flow such as in warm shallow marine and meteoric vadose environments acicular calcite may predominate this relation is also seen in systems in which aragonite and calcite form in intimate association aragonite precipitation is favored when rates of reactant supply are high calcite forms when rates are low such relations suggest that crystal morphology composition and mineralogy are controlled by the kinetics of surface nucleation and the amount of reactants principally carbonate ions at growth sites precipitating phases are the ones which can best accommodate such excess reactants ambient mg ca ratios only indirectly control the nature of inorganically precipitated carbonate phases

petrography trace elements and oxygen and carbon isotopes of gordon group carbonates ordovician florentine valley tasmania australia gordon group carbonates are a thick 2 km stratigraphically continuous ordovician sequence that ranges in age from the arenig to the ashgill they were deposited in subtidal intertidal supratidal and channel depositional environments at a paleolatitude of about 10 n the biota is similar to modern tropical chlorozoan assemblages with abundant corals oncolites calcareous algae and stromatolites non skeletal grains are abundant and are predominantly intraclasts and pellets with some oolites and aggregates micrite is abundant with some sparry calcite cement dolomite which commonly replaces micrite extensive burrows and mud cracks formed mostly during early diagenesis by marine to mixed marine waters the gordon group limestones are characterized by high sr na ratios 2 6 4 6 similar to modern aragonitic carbonates the stratigraphic variations of sr na and mn are related to depositional environments diagenesis and dolomitization the low mn concentrations indicate oxidizing peritidal depositional environments with high rates of carbonate deposition na varies with salinity and the sr varies with facies the largest sr concentrations are in corals and micrites the sr na and mn concentrations have been affected by two stage meteoric diagenetic stabilization the first stage involves marked depletion of sr and na with no appreciable gain of mn due to inversion of aragonite to low mg calcite the second stage involves no significant change in sr and na with appreciable gain of mn which is due to recrystallization of low mg calcites and addition of spar cement in a semi closed diagenetic system sr concentrations decrease whereas mn and fe concentrations increase with increasing mg concentrations due to dolomitization in predominantly marine waters with some influx of meteoric waters the 18o and 13c isotopic fields of calcites and dolomites partly overlap and the dolomites are enriched relative to co existing calcites by 2 to 3 in 18o and by about 1 in 13c similar to modem marine and mixed marine dolomites low mn and fe concentrations indicative of least meteoric diagenetic change correspond to 5 0 0 5 18o and 1 0 05 13c suggesting that these values were the original late ordovician marine calcite values in tasmania these isotopic values are similar to the least altered late ordovician brachiopods and marine calcite cements from other areas the middle ordovician 18o and 13c values of marine cements are 7 and 0 respectively and these values match the marine cement values of the same age from other areas this shift towards heavier isotopic values from middle to late ordovician is probably due to both glaciation in the higher latitudes of gondwana and a slight drop in temperature 4 c depletion in 13c 18o sr and na and enrichment in mn in the lower and upper most part of the late ordovician tasmanian limestones indicative of pronounced meteoric diagenesis coincide with a major australia wide marine regressions

microfacies and geochemistry of the middle cretaceous sarvak formation in zagros basin izeh zone sw iran abstract the sarvak formation albian to cenomanian forming part of the bangestan group comprises a thick succession of carbonate rocks in the zagros basin of southern iran the sarvak formation forms one of the main hydrocarbon reservoirs of this region three sections in the northern 252 m thickness and southern flanks 348 m thickness of the mish and anneh anticlines 245 m thickness in the izeh zone of sw iran were selected for this study petrographic analysis led us to define 10 microfacies units deposited in four facies belts i tidal flat ii lagoonal iii shoal and iv open marine all of these form part of a platform ramp environment geochemical investigations limited to outcrops of the mish anticline aided in understanding geochemical and diagenetic characteristics of carbonate rocks from the sarvak formation variations of oxygen and carbon isotope data from limestones of the sarvak formation indicate near primary marine phreatic and partially meteoric digenesis for both flanks of the mish anticline respectively lower abundances of mn and fe suggest that the carbonates at both sites appear to have stabilized under mainly oxic conditions the sarvak carbonates from the north flank of the mish anticline indicate higher rock water interaction and a closed diagenetic system in comparison to the south flank of the mish anticline vertical and lateral variations in stratigraphic thicknesses in selected outcrops can be related to the presence of syn sedimentary faults in the zagros basin that resulted in regional instability or due to rates of sedimentation with lower rates of deposition in the basin during middle cretaceous times

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

guadalupian cool versus warm water deposits in central iran a record of the capitanian kamura events arefifardcapitanian cooling event in iran

diagenetic evolution of the eocene ramp carbonates a paradigm from the nile valley egypt petrographical and geochemical attributes abstract carbonate rocks of east nile valley in egypt have been investigated as a paradigm for revealing the diagenetic evolution of the eocene ramp carbonates the integration of petrographical elemental geochemical and stable isotopic data revealed that the studied carbonates have been influenced by a sequence of diagenetic processes which are included in three diagenetic episodes i e eogenesis mesogenesis and telogenesis and are related to four diagenetic environments i e marine phreatic meteoric phreatic burial and uplifting environments the paragenetic sequence of the studied carbonates commences with the eodiagenetic episode which includes the marine and meteoric phreatic diagenetic environments the marine phreatic diagenetic environment comprises micritization glauconitization pyritization marine cementation fibrous calcite and syntaxial overgrowth rim cements early dolomitization formation of fine crystalline matrix replacive dolomites and early stages of mechanical compaction before significant burial the meteoric phreatic diagenetic environment includes the neomorphism dissolution meteoric cementation earlier phases of sparry calcite cements and precipitation of megaquartz in the void spaces of the peritidal carbonates during the mesogenesis episode the studied carbonates were exposed to burial diagenesis the shallow burial diagenesis resulted in the creation of point tangenetial contacts between the allochemical constituents and the precipitation of a medium coarse crystalline dolomite cement filling the dissolved fossils and dissolution pores the deep burial diagenetic processes embody the chemical compaction condensed fitted interpeneteration and pressure dissolution fabrics fracturing and burial cementation the telodiagenesis represents the last episode in the diagenetic history of the studied carbonates it witnessed the fracturing meteoric vadose cementation and hematitization processes

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

multivariate statistical analysis of geochemical data as indicative of the hydrogeochemical evolution of groundwater in a sedimentary rock aquifer system summary the study of groundwater hydrogeochemistry of the paleozoic basses laurentides sedimentary rock aquifer system in quebec produced a large geochemical dataset groundwater samples were collected at 153 sites over a 1500 km2 study area and analyzed for major and minor ions the large number of data can lead to difficulties in the integration interpretation and representation of the results two multivariate statistical methods hierarchical cluster analysis hca and principal components analysis pca were applied to a subgroup of the dataset to evaluate their usefulness to classify the groundwater samples and to identify geochemical processes controlling groundwater geochemistry this subgroup consisted of 144 samples and 14 parameters ca2 mg2 na k hco 3 cl so 4 2 fe2 mn2 br sr2 f ba2 hs seven geochemically distinct clusters c1 c7 resulted from the hca samples from clusters c3 c4 c6 and c7 are mostly located in preferential recharge areas the majority of these samples have ca mg hco3 recharge groundwater c3 c6 c7 and na hco3 evolved groundwater c4 samples from the other three clusters c1 c2 c5 are characteristic of an aquifer system under confined conditions the majority of these samples have na hco3 evolved groundwater c1 c5 and na cl ancient groundwater that exhibits elevated concentrations in br c2 in addition to recognizing the importance of hydrogeological conditions on groundwater geochemistry the distribution of clusters also showed the importance of the geological formations on minor and trace elements such as fe2 mn2 sr2 f and ba2 the first five components of the pca account for 78 3 of the total variance in the dataset component 1 is defined by highly positive loadings in na cl and br and is related to groundwater mixing with champlain sea water and solute diffusion from the marine clay aquitard the high positive loadings in ca2 and mg2 of component 2 suggest the importance of dissolution of carbonate rocks in this aquifer system from their characteristic loadings the first two components are defined as the salinity and hardness components respectively components 3 5 are related to more local and geological effects the integration of the hca and the pca with conventional classification of groundwater types as well as with the hydrogeological and geological contexts allowed the division of the region into four main geochemical areas providing an improved regional picture of the aquifer system dynamics and hydrogeochemical evolution of groundwater the following factors were recognized as influencing the evolution of groundwater identified in every geochemical area 1 geological characteristics including sedimentary rock type and till mineralogy 2 hydrogeological characteristics represented by the level of confinement and the hydraulic gradient and 3 the geological history including the latest glaciation and the champlain sea invasion with its integrated approach this hydrogeochemical study contributes to the characterization and understanding of complex groundwater flow systems and provides an example of the long term geochemical evolution of hydrogeological systems after a major perturbation in this case seawater invasion

an introductory perspective on non tropical shelf carbonates abstract this brief account introduces the topic of non tropical shelf carbonate deposits both modern and ancient specific aspects of which are described and discussed in the 22 accompanying papers in this special issue of sedimentary geology non tropical shelves are loosely defined as lying poleward of the present limit of development of hermatypic coral reefs or beyond the mean annual surface water isotherm of about 20 c typically near 30 latitude most geoscientists have traditionally regarded shallow water carbonate formation as a low latitude phenomenon however wherever the rate and extent of terrigenous sediment dilution is small the potential exists for extensive deposits of skeletal carbonate to accumulate on shelves beyond the sub tropics the facies attributes of the modern non tropical carbonates are distinctive and contrast significantly with the structural lithological faunal floral mineralogical and diagenetic character of their tropical counterparts in the rock record non tropical limestones probably occur throughout the phanerozoic but generally remain to be identified and or interpreted as such they are presently described mainly from the ordovician permian and tertiary quaternary periods of major continental glaciations and accentuated latitudinal thermal gradients a uniformitarian approach to the recognition and interpretation of ancient shallow marine limestones requires acceptance of both tropical and non tropical carbonate facies models

petrographic and geochemical evidence for original aragonite mineralogy of upper jurassic carbonates mozduran formation sarakhs area iran abstract diverse skeletal and non skeletal grains with abundant red and blue green calcareous algae evaporites and early diagenetic dolomites in the mozduran carbonates are similar to those of modern warm water shallow marine carbonates isopachous and fibrous intragranular sparry calcite cements resemble modern aragonite morphologies concentric and radial ooids are like modern aragonitic forms which are formed in turbulent and in low energy environments respectively deformed ooids shattered micritic envelopes and spalled ooids indicate aragonite dissolution during meteoric diagenesis meteoric cements are equant mosaic to drusy calcites burial cements only occur as vein fillings sr and na covariance with mn supports evidence of inversion of aragonite to calcite with subsequent open phreatic diagenesis fe concentrations are a magnitude higher than mn due to a reducing phreatic environment high sr na ratios suggest original aragonite mineralogy the 18 o and 13 c field of mozduran limestone lies at the edge of the modern shallow marine field indicating a range from marine to meteoric cements differences in 18 o values between marine calcites and meteoric derived calcites is similar to that in the modern tropics the surface marine diagenetic trend line that passes through shallow marine modern whole carbonates cuts the mozduran limestone isotope field due to their formation in warm shallow marine waters given that atmospheric co 2 levels were similar to those at present increasing mn and fe values decreasing na and uniform sr values with increasingly lighter values of both 18 o and 13 c are exlained by extensive meteoric diagenesis the least altered marine calcite 18 o value of 2 6 pdb corresponds to 29 or 24 c depending on whether 0 of present seawater and 1 2 of ancient seawater with no ice caps are taken as a base an original calcite mineralogy postulated for some jurassic limestones is related to a non tropical origin

sedimentary carbonates through phanerozoic time plate tectonic processes play a critical role in the origin and distribution of sedimentary carbonates through phanerozoic time the phanerozoic age distribution of sedimentary properties like calcite dolomite ratio inferred ooid and cement mineralogy and survival rate of continental carbonates is cyclic the cycles appear to be coupled to plate tectonic processes that give rise to global sea level change and changes in the properties of the ocean atmosphere system first order changes in sea level are driven by the accretion of mid ocean ridges high accretion rate high sea level low accretion rate low sea level although correlations between sea level and sedimentary carbonate properties are not strong high sea level over an extended period of time appears to be correlated with low calcite dolomite ratios lack of inferred aragonite ooids and cements and maxima in the survival rate of continental carbonates the opposite is true for extended periods of low mid ocean ridge accretion rates and global sea levels the lack of strong correlations may reflect an insufficient data base and the possibility of lags between sea level change and change in carbonate properties furthermore the survival rate of continental carbonates appears to be affected by differential cycling and therefore may not be directly related to accumulation rate it appears that the environmental conditions for early dolomitization and calcite ooid and cement formation are best met during extended times of high sea level when atmospheric co2 levels are high and the saturation state of seawater with respect to carbonate minerals relatively low during low sea levels early dolomitization is less favored and aragonite precipitates are more abundant because of low atmospheric co2 levels and enhanced seawater carbonate saturation states differential cycling has modified the phanerozoic sedimentary carbonate mass age distribution because of erosion of younger units within continental carbonate cycles it may be difficult to derive an unequivocal record of the partitioning of carbonate between the deep sea and shallow water realms of deposition during the phanerozoic this difficulty must be considered in further quantification of geochemical models describing the geologic history of atmospheric co2 and climate change

criteria for recognition of cold water carbonate sedimentation berriedale limestone lower permian tasmania australia abstract the permian berriedale limestone is an alternating sequence of limestone and calcareous shale associated with marine glacial terrigenous sediments it was deposited at a paleolatitude near 80 s during the gondwanan permo carboniferous ice age dropstones commonly disrupt laminae range widely in size and composition and reveal glacially derived shapes and textures under the sem there is a lower diversity of fauna mostly bryozoans brachiopods and pelecypods and non skeletal grains mostly intraclasts than in warm water limestones the vertical variation in depositional microfacies through shale limestone shale beds indicates that the shallow marine limestones formed during the lowering of sea level in colder periods as the sea level rose during warmer periods a shower of dropstones preceded shale deposition for this mason dropstones are more numerous around the contacts between limestone beds and overlying shale beds but rare in the middle or base of limestone beds icebergs calved from adjacent glaciers were floating and the surface water temperature was near freezing during limestone deposition upwelling cold currents provided nutrients and maintained calcium carbonate at saturation well developed rhombs in micrite microspar and spar and length slow elongate rhombs and poikilotopic rhombic plates both formed by accretion of rhombohedra indicate low mg calcite precipitated from seawater at a temperature of 3 c these cements are overlain by micrite marine mud dropstones and geopetal fillings of well sorted internal sediments and are cut by borings all proving both synsedimentary ages and submarine origin of these cements the calcium carbonate content in these cold marine waters fluctuated ranging from undersaturated destructive diagenesis pits etchings rhombic pores and dissolution features to saturated constructive diagenesis as the sea level rose during warmer periods large volumes of melt waters mixed with marine waters the mixing zone cements succeeding marine cements are cloudy inclusion rich coarse plates up to a few mm these crystals grew embedding or nucleating over early formed crystals and previously cemented both fillings and encrustations bioclasts the mixing zone cementation is preceded by erosion of early formed crystals the eroded crystals now occur as inclusions in mixing zone cements the field microfacies and diagenetic criteria evolved in this study might be used for recognition of a wide spectrum of cold water carbonates temperate subpolar and glacio marine

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

microfacies and geochemistry of the ilam formation in the tang e rashid area izeh s w iran abstract the ilam formation santonian campanian in age part of the bangestan group is disconformably overlain by the sarvak formation and underlain by the gurpi formation in the tang e rashid peyon area izeh zagros southwest of iran facies analyses indicate that the ilam carbonates formed in four microfacies belts tidal flat lagoon shoal and open marine in a platform ramp environment major and minor elements and carbon and oxygen isotope values were used to determine the original carbonate mineralogy of the ilam formation petrographic evidence and elemental and oxygen and carbon isotope values indicate that aragonite was the original carbonate mineralogy in the ilam formation the elemental and isotopic compositions of the ilam carbonates also illustrate that they have stabilized in the marine phreatic environment variations of sr ca and 18 o values versus mn suggest that diagenetic alteration occurred in a closed system temperature calculation based on the oxygen isotope value of the least altered sample indicates that the very early shallow burial fluid temperature was around 28 c recognition of the exact boundary between the ilam and sarvak formations is difficult due to similar lithologies and the absence of the surgah formation in the study area however elemental and oxygen and carbon isotope analysis were used to determine the boundary between these formations the 18 o and 13 c values along with elemental results clearly indicate a subaerial exposure surface below which meteoric diagenesis affected the sediments

secular oscillations in the carbonate mineralogy of reef building and sediment producing organisms driven by tectonically forced shifts in seawater chemistry the primary mineralogy of oolites and early marine carbonate cements led sandberg nature 305 1983 19 22 to divide the phanerozoic eon into three intervals of aragonite seas and two intervals of calcite seas hardie geology 24 1996 279 283 has shown that these oscillations together with synchronous oscillations in the mineralogy of marine potash evaporites can be explained by secular shifts in the mg ca ratio of seawater driven by changes in spreading rates along mid ocean ridges the hardie model also predicts that high mg calcite should precipitate along with aragonite as it does in today s aragonite sea we have uncovered oscillations in the carbonate mineralogy of hypercalcifying organisms ones that have produced massive skeletons large reefs or voluminous bodies of sediment that correspond to sandberg s aragonite seas and calcite seas and that are predicted by the hardie model particular groups of corals sponges and algae appear to have been dominant reef builders only when favored by an appropriate mg ca ratio in seawater in early and middle paleozoic calcite seas calcite i reefs were dominated by calcitic tabulate heliolitid and rugose corals and calcitic stromatoporoids in contrast during the period of late paleozoic early mesozoic aragonite seas aragonite ii aragonitic groups of sponges scleractinian corals and phylloid algae as well as high mg calcitic red algae were principal reef builders during late cretaceous time at the acme of calcite ii massive rudists displaced aragonitic hermatypic corals in today s aragonite sea aragonite iii scleractinian corals are again dominant reef builders along with high mg calcitic coralline algae major sediment producing algae exhibit temporal patterns similar to those of reef builders calcitic receptaculitids flourished during calcite i whereas aragonitic dasycladaceans did not become dominant rock formers until aragonite ii during calcite ii calcitic nannoplankton formed massive coccolith chalks in warm shallow seas of the late cretaceous after the mg ca ratio of seawater had reached a very low value and calcium concentration a very high value as the mg ca ratio of seawater rose and calcium concentration fell during the cenozoic era individual coccoliths on average became less massive and encrusted cells less thickly by pliocene time during aragonite iii the prominent genus discoaster secreted only narrow rayed coccoliths that covered less than 25 of the cell surface also during aragonite iii the aragonitic green alga halimeda emerged as the dominant skeletal sediment producer in reef tracts the influence of seawater chemistry on skeletal secretion appears to have been especially strong for morphologically simple taxa that exert relatively weak control over their own calcification such groups include algae sponges corals and bryozoans morphological simplicity also permits these groups to adopt vegetative or colonial modes of growth that confer success in competition for space on reefs this linkage in addition to the basic chemical demands of hypercalcification has given the mg ca ratio of seawater strong control over the success of individual reef building taxa more generally this ratio appears to have strongly influenced evolutionary changes in the skeletal mineralogy of sponges and cheilostome bryozoans throughout their history we conclude that throughout phanerozoic time a chain of causation has extended from mid ocean ridge processes via seawater chemistry to the mineralogical and biological composition of reef communities and bioclastic carbonate deposits

carbonate minerals major and minor elements and oxygen and carbon isotopes and their variation with water depth in cool temperate carbonates western tasmania australia cool temperature bryomol carbonates predominate on shallow shelves around western tasmania many samples are bored and encrusted due to the occurrence of submarine hardgrounds and to slow rates of sedimentation intragranular caco3 cementation is common tasmanian whole carbonates are mainly mixtures of high mg calcite hmc and low mg calcite lmc with minor amounts of aragonite hmc and aragonite contents decrease while lmc content increases with increasing water due to a decrease in water temperature mg concentrations in calcite correspond to temperatures of 10 c sr and na concentrations in bryozoa decrease due to calcite cementation whereas their concentrations increase with aragonite content mn and fe concentrations are higher than in warm shallow marine counterparts and increase with increasing aragonite percentage sr and na concentrations in calcite slightly increase with increasing lmc percentage due to decreasing water temperatures mn and fe values in calcite are independent of water temperature hmc percentage and hmc lmc ratios decrease while lmc percentage increases with increasingly heavier 18o values due to decreasing temperatures lmc is a marine mineral and not a product of meteoric diagenesis unusually high concentrations of sr na mn and fe in aragonite are due either to the tendency of aragonite formed in cold seas to incorporate more of these elements or to aragonite formation by transformation of metastable cold water caco3 minerals such as vaterite or hydrous calcite sr contents decrease with increasing water depth due to a decrease in aragonite and increase in low mg calcite na values increase with increasing water depth due to increasing salinity mn and fe concentrations decrease with increasing water depth due to decreasing continental terrigenous input depth related variations in mg sr na mn and fe are due to marine diagenesis and are unrelated to meteoric diagenesis 18o and 13c values are positively correlated and this isotopic field is bisected by the diagenesis trend line for upwelling water that passes through the point 1 18o 0 13c the 18o values become heavier and mg values decrease with increasing water depth due to decreasing temperatures from about 17 to 6 c for normal seawater and from 13 to 2 c for upwelling water these temperatures are lower than measured summer values because of the strong seasonal effect of surface waters influx of subantarctic water in winter and mixing of cold upwelling waters in the bottom water as carbonates in upwelling regions are in equilibrium with upwelling water having 18o values of 1 in paleotemperature determinations seawater values that are lower by 1 than those postulated for different geological periods should be considered for those carbonates suspected of being non tropical in origin on the basis of geological and geochemical evidence originally calcitic limestonesare abundant in ancient sequences and their temperatures of formation and diagenesis can be better understood by using the data base provided by this study

tectonic controls of phanerozoic sedimentary rock cycling the cyclic nature of the phanerozoic sedimentary rock distribution carbon sulphur coupling and material transfer among sedimentary reservoirs appears to be controlled by tectonic factors the distribution of preserved sedimentary mass in terms of rock mass remaining u geologic age shows a minimum c 300 350 ma ago which separates two subcycles of erosion and deposition of sedimentary rocks the older subcycle was interrupted because of the major continental collisions of the devonian and late carboniferous these collisions resulted in a reduction of outcrop areas of rocks of the older cycle relative to their masses leading to a decline in the probability of destruction and an increase in half life of these older sediments a strong correlation exists between the long term cyclicity in the phanerozoic global sea level curve and the distribution of carbon and sulphur among their major exogenic reservoirs this correlation is related to two principal tectonic modes of the phanerozoic oscillatory and submergent it is postulated that the submergent mode of active plate convergence obduction and subduction of sediments large ridge volume and high sea level gave rise to low erosion and sedimentation rates less restricted environments of carbonate deposition and relatively high atmospheric co 2 levels high temperatures resulting from an increased rate of production of co 2 from diagenetic and metamorphic reactions at subduction zones as sea level rose carbon was transferred from the sedimentary reservoir of reduced organic carbon to that of oxidized inorganic carbon in limestones whereas sulphur moved from the oxidized sulphate reservoir to the reduced sulphide reservoir as sea level fell reservoir transfers were opposite to those above culminating in the oscillatory mode of generally elevated continental interiors these reservoir transfers are consistent with secular changes observed in the distribution of 13 c and 34 s in sedimentary materials during the phanerozoic petrographic examination of phanerozoic oolite formations shows that ooids with preserved calcitic relict textures are characteristic of pre carboniferous carbonate rocks whereas ooids with relict textures indicative of initial aragonite mineralogy are dominant in rocks of younger age these changes in ooid mineralogy may be interpreted as reflecting changes in co 2 levels of the ocean atmosphere system consistent with the above tectonic considerations atmospheric co 2 levels were higher prior to carboniferous time favouring formation of calcitic ooids and skeletal parts after the carboniferous co 2 levels fell and aragonite and mg calcites of greater than 8 mol mg increased in abundance as precipitates

a warm equable cretaceous the nature of the problem abstract the nature of the problem of warm equable paleoclimates is defined by investigating the mid cretaceous period the problem consists of three components 1 defining precisely the climatic state during any specified interval of geologic time 2 specifying the external climatic forcing factors which may have been important and 3 understanding the climatic response to any specific modifying influence these components are characterized by limitations of critical importance in understanding paleoclimates the nature of the problem of a warm cretaceous is defined both qualitatively and quantitatively within these limits

dolomitization and dolomite neomorphism in the back reef facies of the bonneterre and davis formations cambrian southeastern missouri the back reef facies of the bonneterre and davis formations consists of dolomitized cryptalgalaminates and partially dolomitized peloid mudstones these subfacies were deposited on tidal flats and in shallow lagoons that existed in the st francois mountains of southeast missouri during late cambrian time the back reef facies is bounded on the seaward side by dolomitized algal bioherms and grainstone banks which host the southeast missouri mississippi valley type mvt lead zinc copper ore deposits cryptalgalaminates are replaced by both fine crystalline planar dolomite and coarse crystalline nonplanar dolomite peloid mudstones are partially replaced but mainly by coarse crystalline nonplanar dolomite planar dolomite replacing cryptalgalaminates shows gradational transitions into coarse crystalline nonplanar dolomite the transitions are accompanied by progressive increase in average crystal size and an increased skewness toward the coarse size fraction planar dolomite is enriched in 18 o relative to stratigraphically equivalent marine limestones coarse crystalline nonplanar dolomite which replaces both cryptalgalaminates and peloid mudstones has delta 13 c and delta 18 o values transitional between those of planar dolomite and late dolomite cements associated with mvt mineralization fluid inclusion analysis of nonplanar dolomite and associated dolomite cements indicates precipitation at elevated temperatures 60 to 114 degrees c by saline basinal fluids these data indicate that the back reef facies was subjected to a complex diagenetic history involving both early and late diagenetic dolomitization and dolomite neomorphism fine crystalline planar dolomite was formed during early diagenetic dolomitization of the cryptalgalaminate subfacies by a fluid approaching seawater composition coarse crystalline nonplanar dolomite was formed as a result of neomorphism of pro existing planar dolomite and dolomitization of peloid mudstones after burial accompanying mvt mineralization in southeast missouri

facies sequences on a carbonate ramp the carboniferous limestone of south wales during early carboniferous times a major sea level rise led to the development of an extensive carbonate ramp over what is now south wales differential subsidence and sea level changes resulted in distinctive facies sequences in the ramp succession and a model is offered which recognizes three distinct geomorpho tectonic settings inner mid and outer ramp the inner ramp zone occurs in the more landward part of the province and was an area undergoing little or no subsidence the sequence is dominated by oolitic grainstones and peritidal limestones representing shoal and back shoal environments the peritidal units are transgressive deposits consisting of stacked asymmetrical shallowing up cycles the sequence contains many subaerial breaks and tectonic uplift resulted in base level changes and fluvial incision the mid ramp zone sequence is intermediate in thickness between the inner and outer ramp successions and consists mainly of bioclastic limestones deposited below fairweather wave base sedimentation periodically exceeded sea level rise and subsidence and regressive progradational oolitic sand bodies developed the thickest of which are stacked units with up to four individual sand bodies storm processes were of major importance in this setting the outer ramp zone is represented by a thick sequence of muddy bioclastic limestones deposited below storm wave base and major waulsortian reef mounds also developed none of the shallowing phases seen in the other ramp zones can be detected in this sequence subsidence and eustatic sea level rise seem to have been the major controls on deposition but the recognition of eustatic sea level falls is difficult the detailed facies model for ramp carbonates presented here may be applicable elsewhere in the geological record

major minerals elemental and isotopic composition in modern temperate shelf carbonates eastern tasmania australia implications for the occurrence of extensive ancient non tropical carbonates eastern tasmanian shelf sediments range from siliciclastics mixed carbonates to pure carbonates carbonates consist mainly of skeletal bryozoa hashes with variable amounts of intragranular caco3 cement minerals detected by xrd are mainly mixtures of low to high mg calcites and quartz with variable amounts of aragonite four factors account for 95 of total variance of mineral components and elemental composition and are related to elements in carbonate fraction factor 1 positive relationship between mn and mg with latitude factor 2 to calcite types from d spacing variation factor 3 and to longitudinal i e distance from coast variation of carbonate and siliciclastic contents factor 4 factorial plots indicate residue carbonate plane with elements associated with them and that mg mn and aragonite contents and calcite d spacings are related to latitude and vary with water temperatures ca values reflect variable amounts of carbonate mg content indicates water temperatures of 10 c sr and na are positively correlated and increase with both calcite and aragonite contents and the ratio of srna is 1 unlike high ratios found in warm water carbonates mn concentrations are higher than in warm shallow marine carbonates and similar range of sr and na contents in both calcite and aragonite may be due to the formation of impure phases of caco3 the 18o and 13c values are positively correlated and tend to fall between the trend lines of seafoor diagenesis and upwelling water positive correlation between 13c and sr and na is due to both calcite and aragonite contents or due to the occurrence of vaterite the 18o values of whole sediments indicate water temperature from 14 to 8 c normal seawater or 10 4 c upwelling water these temperatures are slightly higher than those obtained from 18o of eastern tasmanian brachiopods originally calcitic ancient carbonates are abundant in stratigraphic sequences and can be better understood by comparison with modern temperature calcitic carbonates rather than with aragonitic modern tropical carbonates many of these ancient originally calcitic carbonates are of non tropical origin as coeval tropical aragonitic carbonates occur elsewhere low srna ratios and high mn contents are indicative of temperate origin heavy 13c values can be used in calculating water temperatures the non tropical carbonates form at low co2 levels in regions of upwelling waters which maintain saturation of caco3 and provide nutrients for a luxuriant growth of fauna

calcareous dunes of the united arab emirates and noah s flood the postglacial reflooding of the persian arabian gulf abstract aeolian dunes cover most of the united arab emirates and a large part of the eastern arabian peninsula although these sands as well as older aeolianites are largely composed of quartz there is a high percentage of detrital carbonate in them south of the persian arabian gulf for more than 40 km this percentage decreases inland these carbonate grains consist mainly of marine bioclastic fragments and calcareous ooids and were derived from the floor of the persian gulf which was exposed during low sea level of the last glacial period the postglacial rise in sea level rapidly reflooded the floor of the persian gulf cutting off the source for these aeolian sediments between 12 and 6 ka the sea transgressed more than 1000 km inundating the extended route of the tigris euphrates river and forcing people living on the exposed floor of the gulf to abandon their settlements because of the varying rate of eustatic sea level rise these waters at times flooded across the flat floor of the persian gulf at more than a kilometer per year we proposed that the stories of a great flood recorded in the bible as noah s flood and in babylonian history on clay tablets excavated in the tigris euphrates delta as the epic of gilgamesh are a record of this rapid postglacial flooding of the floor of the persian gulf