what is diatomite different types of biogenic remains ranging from siliceous algae to carbonate precipitates accumulate in the sediments of lakes and other aquatic ecosystems unicellular algae called diatoms which form a siliceous test or frustule are an ecologically and biogeochemically important group of organisms in aquatic environments and are often preserved in lake or marine sediments when diatoms accumulate in large numbers in sediments the fossilized remains can form diatomite in sedimentological literature diatomite is defined as a friable light coloured sedimentary rock with a diatom content of at least 50 however in the quaternary science literature diatomite is commonly used as a description of a sediment type that contains a large quantity of diatom frustules without a precise description of diatom abundance here we pose the question what is diatomite what quantity of diatoms define a sediment as diatomite is it an uncompacted sediment or a compacted sediment we provide a short overview of prior practices and suggest that sediment with more than 50 of sediment weight comprised of diatom sio2 and having high 70 porosity is diatomaceous ooze if unconsolidated and diatomite if consolidated greater burial depth and higher temperatures result in porosity loss and recrystallization into porcelanite chert and pure quartz less

formation of willemite in hydrothermal environments willemite zinc silicate is the main zinc mineral in some carbonate hosted ore deposits e g franklin new jersey vazante brazil beltana south australia kabwe zambia recent interest in these unconventional zinc deposits has increased because of high zinc grades that exceed 40 wt percent relatively low environmental impact of ore processing owing to the lack of acid generating sulfides in the waste and advances in ore processing technologies in the past most metallogenic studies proposed formation of willemite deposits by supergene or hypogene alteration of preexisting sulfide deposits however recent data on the vazante beltana and kabwe deposits indicate willemite crystallization at temperatures in excess of 150 c raising the possibility of primary precipitation from hydrothermal fluids we use numerical geochemical modeling to examine the formation of willemite under hydrothermal conditions activity activity diagrams reveal that in the presence of dissolved sulfur and quartz willemite instead of sphalerite will precipitate under oxidizing e g hematite stable sulfate predominant and alkaline ph higher than k feldspar muscovite quartz conditions willemite also becomes more stable relative to sphalerite at high temperature and willemite can coexist with magnetite at 300 c the stabilities and solubilities of sphalerite willemite smithsonite hydrozincite and zincite were calculated for wide ranges of temperature 25 300 c chloride concentration dissolved sulfur and carbon concentrations ph quartz saturation and oxidation potential plots of the solubility of the different minerals as a function of two variables e g temperature and redox state ph and redox state allow us to predict the effects of changing chemical conditions which in turn permits an estimate of the efficiency of particular precipitation processes cooling is an effective process for precipitating sphalerite but not willemite whereas ph increase e g by acidic fluids reacting with carbonates is effective for precipitating willemite but not sphalerite dynamic geochemical models that simulate physicochemical processes are used to understand the formation of the beltana willemite deposit in the adelaide geosyncline of south australia this small high grade deposit 850 000 t at 36 zn is hosted in dolomite of the cambrian ajax limestone next to a tectonic contact with the diapiric halite bearing clastic sediments of the callanna group the orebody is associated with hematite alteration and is characterized by the total absence of sulfides willemite is the only zinc ore mineral and the arsenate hedyphane ca 2 pb 3 aso 4 3 cl is the main lead mineral the model results show that willemite will precipitate in response to water rock interaction and fluid mixing processes at temperatures above 120 c the presence of arsenate in the hydrothermal fluid is likely to have been important at beltana in arsenate absent models sulfate is reduced to sulfide by the precipitation of ferrous iron as hematite resulting in the precipitation of sphalerite and galena in contrast in models including arsenate the reduction of sulfate to sulfide is inhibited and willemite is predicted to precipitate

the stable isotopic composition of modern soil carbonate and its relationship to climate the oxygen isotopic composition of modern soil carbonate is well correlated with the isotopic composition of local meteoric water the carbon isotopic cycle for co 2 in soils can be described in terms of the proportion of biomass using the c 4 photosynthetic pathway and the co 2 respiration rate of the soil at low soil respiration rates significant atmospheric co 2 mixing can occur in general the carbon isotopic composition of soil carbonate is related to the proportion of c 4 biomass present in soil but soils that freeze to the depth of carbonate formation often have a significant atmospheric component this suggests that freezing of the soil solution should be considered as another important mechanism for soil carbonate formation because of these relationships the isotopic composition of soil carbonate may be a paleoclimatic and paleoecologic indicator in cases in which diagenetic alteration has not occurred

the calamine nonsulfide zn pb deposits of belgium petrographical mineralogical and geochemical characterization abstract the belgian nonsulfide zn deposits represent the historical basis for the zinc mining and smelting industry in europe the zinc ores were called calamines and consist of a mixture of zn carbonates smithsonite hydrozincite and zn silicates hemimorphite willemite and zn clays with a variable content of pb minerals the calamines are considered to be oxidation products of primary sulfide ores the most important was the la calamine orebody more than 600 000 tons of zn metal that was continuously exploited for several centuries nonsulfide ores were also exploited at schmalgraf engis dickenbusch fossey rocheux oneux welkenraedt and in other smaller deposits all no longer accessible for study where the calamines extended from the surface to an average depth of 40 to 50 m the primary zn pb sulfide mineralization consists of post variscan hydrothermal veins and replacement bodies mostly occurring in the dinantian visean limestones the sulfides intersect the paleozoic rocks and are truncated and unconformably covered by late cretaceous sediments santonian aachen fm the same setting has been observed for the nonsulfide ores suggesting an early to mid cretaceous weathering consistent with other geological and geochronological data on paleoweathering in europe the extensive occurrence of willemite that appears to be the first deposited nonsulfide mineral is a striking particularity of the belgian calamines most fluid inclusions in willemite 80 and all inclusions in smithsonite are monophase aqueous ice melting temperatures suggest salinities between 0 and 5 wt nacl equiv homogenization temperatures of rare two phase inclusions liquid vapor in willemite display a large variation between 80 and 190 an interval matching the temperature ranges of other willemite ores throughout the world so far considered of hydrothermal origin the stable isotope variation of belgian smithsonites and cerussites is very similar to the range measured in other supergene nonsulfide deposits similar to those of sw sardinia belgian smithsonites exhibit a limited range of 18o values from 27 1 to 30 6 averaging 28 4 0 8 v smow this limited range points to a relatively uniform isotope composition of the oxidizing waters and constant temperatures of smithsonite crystallization carbon isotope values even from the same mine show a considerable range from 11 6 to 1 6 this extensive range indicates at least two carbon sources 13c depleted carbon derived from the organic matter in the soils and 13c enriched carbon originating from marine carbonate host rocks cerussites have oxygen isotope values ranging from 16 8 to 19 3 averaging 17 8 1 0 and carbon isotope values of 18 4 to 14 7 the metallic deposits of eastern belgium have undergone a polyphase history which started with a possibly jurassic sulfide mineralization followed by oxidation under high silica activities and consequently by supergene weathering owing to structure and mineralogical association we do not consider the high homogenization temperatures as reliable minimum temperature estimates of willemite formation however it is possible that the willemite concentrations could have been derived from low temperature localized hydrothermal processes caused by deeply reaching oxidizing fluids smithsonite and hemimorphite often developed at the expenses of willemite have all the characteristics of supergene oxidation products

conditions of meteoric calcite formation along a variscan fault and their possible relation to climatic evolution during the jurassic cretaceous two calcite cements filling karst cavities and replacing lower carboniferous limestones at the variscan front thrust were precipitated after mid jurassic cimmerian uplift and subsequent erosion but before late cretaceous strike slip movement the first calcite stage a is nonferroan and crystals are coated by hematite and or goethite these minerals also occur as inclusions along growth zones the calcite lattice contains 0 07 mol fe but mn concentrations can be as high as 0 72 mol in bright yellow luminescent zones primary originally one phase all liquid aqueous inclusions have a final melting temperature between 0 2 and 0 2 c indicating a meteoric origin of the ambient water the 13c and 18o values of the calcites are between 7 3 and 6 3 7 8 and 5 5 on the vienna peedee belemnite vpdb scale respectively the second calcite stage b consists of ferroan 0 13 0 84 mol fe blocky crystals with mn concentrations between 0 34 and 0 87 mol primary single phase aqueous fluid inclusions indicate precipitation from a meteoric fluid below 50 c the 13c values of stage b calcites vary between 7 3 and 2 1 vpdb and the 18o values between 7 9 and 7 2 vpdb a precipitation temperature below 50 c for the stage a calcites and the presence of iron oxide hydroxide inclusions in the crystals indicate near surface precipitation conditions within this setting the geochemistry of the nonferroan stage a calcites reflects precipitation under oxic to suboxic conditions the ferroan stage b calcites precipitated in a reducing environment the evolution from the stage a to stage b calcites and the associated geochemical changes are interpreted to be related to the change from semiarid to humid conditions in western europe during late jurassic cretaceous times a change in humidity can explain the evolution of groundwater from oxic suboxic to reducing conditions during calcite precipitation the typically higher 13c values of the stage b compared to the stage a calcites can be explained by a smaller contribution of carbon derived from soil zone processes than from carbonate dissolution in the groundwater under humid conditions the small shift to lower 18o between stage a and b calcites may be caused by a higher precipitation temperature or a decrease in the 18o value of the meteoric water this decrease could have been caused by a change in the source of the air masses or by an increase in the amount of rainfall during the early mid cretaceous although the latter interpretation is preferred it cannot be proven

palaeoenvironmental significance of palustrine carbonates and calcretes in the geological record interest in palustrine carbonates and calcretes has increased over the last 20 years since they contain significant environmental information much of the work performed in this area has focused on either of two types of terrestrial carbonate palustrine carbonates or calcretes pedogenic and groundwater yet their simultaneous study shows there may be a gradual transition from one form to the other revealing the interplay between pedogenic sedimentary and diagenetic processes three main factors control the formation of these carbonates the position of the water table the host rock and the period of sub aerial exposure in pedogenic calcretes precipitation of carbonate takes places mostly in the vadose zone above the water table and within a previous host rock or sediment in groundwater calcretes the precipitation of carbonate also occurs within a previous host rock and around the groundwater table in palustrine carbonates however the precipitation of lime mud occurs in a lacustrine water body palustrine carbonates necessarily form on previous lacustrine mud whereas both types of calcretes may form on any type of sediment or soil the sub aerial exposure time needed to form palustrine carbonates may by relatively short even a season whereas pedogenic calcretes need more time several years to millions of years groundwater calcretes do not form on the topographic surfaces so there is no need of sub aerial exposure however stable surfaces favour the development of thick groundwater calcretes small fluctuations in the water table cause gradual transitions of these three types of terrestrial carbonates and the subsequent mixture of their characteristic features causing difficulties in the interpretation of these carbonates the formation of these carbonates is controlled by palaeoenvironmental factors both commonly form in semi arid climates arid climates are also suitable for calcretes but sub humid conditions are more suitable for palustrine carbonates more indications of climatic conditions may be obtained through the analysis of the d18o content of both calcretes and palustrine carbonates and from the depth of the horizon containing carbonate nodules in pedogenic calcretes vegetation is also important in the formation of these types of carbonates data on the prevailing vegetation can be obtained from the analysis of the micro and macrofabric as well as from the d13c signal of the primary carbonates which in pedogenic carbonates has also been used to estimate atmospheric pco2 during the phanerozoic these terrestrial carbonates are widely distributed on floodplains and distal areas of alluvial basins their presence and characteristics can be used as indicators of aggradation subsidence or accommodation rates and therefore as indicators of different tectonic regimes even though the study of these carbonates has notably increased in recent years much less is known about them than about marine carbonates presently there is much emphasis on obtaining a general model for sequence stratigraphy in terrestrial basins with a need to include the carbonates analysed in this paper

equilibrium oxygen hydrogen and carbon isotope fractionation factors applicable to geologic systems as demonstrated by the chapters in this short course stable isotope techniques are an important tool in almost every branch of the earth sciences central to many of these applications is a quantitative understanding of equilibrium isotope partitioning between substances indeed it was harold urey s 1947 thermodynamically based estimate of the temperature dependence of 18o 16o fractionation between calcium carbonate and water and a recognition of how this information might be used to determine the temperatures of ancient oceans that launched the science of stable isotope geochemistry the approach pioneered by urey has since been used to estimate temperatures for a wide range of geological processes e g emiliani 1955 anderson et al 1971 clayton 1986 valley this volume in addition to their geothermometric applications equilibrium fractionation data are also important in the study of fluid rock interactions including those associated with diagenetic hydrothermal and metamorphic processes baumgartner and valley this volume shanks this volume finally a knowledge of equilibrium fractionation is a necessary first step in evaluating isotopic disequilibrium a widespread phenomenon that is increasingly being used to study temporal relationships in geological systems cole and chakraborty this volume in the fifty four years since the publication of urey s paper equilibrium fractionation data have been reported for many minerals and fluids of geological interest these data were derived from 1 theoretical calculations following the methods developed by urey 1947 and bigeleisen and mayer 1947 2 direct laboratory experiments 3 semi empirical bond strength models and 4 measurement of fractionations in natural samples each of these methods has its advantages and disadvantages however the availability of a variety of methods for calibrating fractionation factors has led to a plethora of calibrations not all of which are in agreement in this chapter we evaluate the major methods for determining fractionation factors

oxygen isotope fractionation during smithsonite formation from aqueous solutions abstract oxygen isotope fractionation between carbonate minerals and water is used as an environmental proxy to estimate mineral formation temperatures or isotopic composition of precipitating fluids to date no experimental data on the oxygen isotope fractionation factor between smithsonite znco3 and water 18o smithsonite water 18o 16o smithsonite 18o 16o water exist therefore in the present study experimental work on smithsonite synthesis in the temperature range between 25 and 80 c is coupled with ab initio based theoretical calculations laboratory precipitation experiments took place in titanium reactors at elevated pco2 10 atm in order to induce the formation of smithsonite from hydrozincite zn5 co3 2 oh 6 which is the precursor phase initially formed at 25 c and low pco2 ph 6 8 the constant 18o smithsonite water 1000 18osmithonite 1000 18owater value reached at a reaction time 10 000 min 7 days suggests near equilibrium conditions based on the experimentally obtained temperature relation of 18o smithsonite water at 25 40 60 and 80 c the integrated equation can be linearly described by the function 10 3 ln 18 o smithsonite water 2 79 10 6 t 2 0 95 0 06 10 6 t 2 0 60 where the temperature is in kelvin the ab initio calculations suggest that this relation can be described in the temperature range from 0 to 100 c as 10 3 ln smithsonite liquid water 3 21 10 6 t 2 3 63 0 025 10 6 t 2 0 90 the 18o smithsonite water values from the experimental approach fit within error to the theoretical relationship from the literature and the above ab initio calculations difference in slope between the experiment and theoretical obtained equation likely reflects modeling inaccuracies whereas kinetic effects cannot be completely ruled out in the experimental approach the obtained 18o smithsonite water values match with the general sequence of zn2

a global assessment of zn isotope fractionation in secondary zn minerals from sulfide and non sulfide ore deposits and model for fractionation control abstract we investigated extent and direction of zn isotope fractionation in secondary zinc minerals formed during low temperature hydrothermal and or supergene oxidation of primary sulfide deposits zinc isotope data have been obtained from non sulfide zinc mineral separates willemite zn2sio4 smithsonite znco3 hemimorphite zn4 si2o7 oh 2 h2o hydrozincite zn5 co3 2 oh 6 and sauconite na0 3zn3 si al 4o10 oh 2 4h2o collected from several zn deposits in ireland belgium poland namibia peru yemen and zambia the data are compared with zn isotope compositions measured on zn sulfides collected in the same areas and or derived from the existing literature to establish the controls of direction and likely extent of any fractionations we find that willemite has the greatest compositional variability with measured 66znjcm lyon values ranging from 0 42 to 1 39 spanning the entire range of terrestrial variation in zn isotopes recorded to date overall significant fractionations in positive and negative directions are recorded relative to the precursor phase primary sphalerite or an earlier secondary phase with primary sphalerite falling in a relatively narrow range of isotopic values approximately 0 1 to 0 4 most of the data observed on willemite hemimorphite and hydrozincite can be explained with a model of isotopic fractionation in which partial dissolution of primary sphalerite is followed by precipitation of an initial secondary phase that preferentially incorporates heavy zn isotopes smithsonite instead preferentially incorporates light zn isotopes this reflects the variation in the zn x bond strengths of these secondary phases with respect to the original sulfides we also observed that isotope compositions do not depend only on the difference between the fractionation factors of the involved phases but also on the amount of the secondary mineral precipitated after dissolution of primary sulfide and that the greatest fractionations occur when only small amounts of secondary mineral are precipitated progressive precipitation from migrating fluids that form phases enriched in heavy zinc isotopes would lead to a gradual decrease in the 66zn values of such phases and the fluids involved in time and space strong negative isotopic shifts are almost only observed for late crystallizing phases such as those in vugs these are interpreted to reflect precipitation from residual isotopically light fluids that are the inevitable highly fractionated product of the above described process where a more complete replacement of primary sulfide has occurred such as in the high grade core of non sulfide zinc orebodies there is limited net isotopic fractionation because dissolved primary zinc is nearly quantitatively reprecipitated locally in addition in only one case yanque peru we observed that the fringes of non sulfide zinc deposit were characterized by isotopically fractionated compositions with highly negative values implying extensive precipitation earlier or elsewhere of isotopically heavy secondary phases the higher grade ore zones where complete breakdown of primary sulfides and quantitative reprecipitation of zinc have occurred show instead less fractionated compositions

a cold supergene zinc deposit in alaska the reef ridge case the reef ridge deposit is a typical supergene nonsulfide zinc mineralization located in the yukon koyukuk region of west central alaska usa it is hosted in sedimentary rocks of the farewell terrane a continental fragment sandwiched between the siberian and laurentian cratons during the early paleozoic the mineralization occurs in lower middle devonian shallow water dolomite of a paleozoic carbonate platform succession belonging to the nixon fork tectonic unit the mineralization consists of oxidized minerals associated with minor remaining sulfides pyrite marcasite and sphalerite in the oxidation zone smithsonite is the predominant mineral mixed with fe hydr oxides goethite and hematite a complete petrographic and mineralogical study was performed samples were analyzed by x ray diffraction inductively coupled plasma mass spectrometry and emission spectrometry energy dispersive scanning electron microscopy and qemscan quantitative evaluation of minerals by scanning electron microscopy the most abundant mineral in the nonsulfide ore is smithsonite similar to other nonsulfide zn deposits worldwide the first generation of smithsonite has replaced both primary sphalerite and the host carbonates a second smithsonite generation precipitated as cement in vugs cavities and fractures minor zinc amounts also occur in the fe hydr oxides and zinc traces have been identified in clay minerals the carbon and oxygen isotope values of smithsonite at reef ridge vary from 0 7 to 2 1 relative to vienna peedee belemnite vpdb and 19 1 to 21 9 relative to vienna standard mean ocean water vsmow the 13 c values are similar to those of the host rock suggesting that the predominant carbon source for smithsonite was the host carbonates with only a limited contribution from organic carbon the oxygen isotope ratios of reef ridge smithsonite are more depleted in 18 o compared to supergene nonsulfides from other parts of the world formed under warm humid temperate or semiarid climates the oxygen isotope fractionation between water and smithsonite which relates the 18 o value of the mineralizing solution the formation temperature of smithsonite and its 18 o composition indicates that the 18 o composition of reef ridge smithsonite is related to very low formation temperatures 10 c and strong depletion in 18 o of the precipitating waters the 18 o smithsonite composition the strong 18 o depletion and the relationship of the formation of the reef ridge nonsulfide deposit with the development of the sleetmute upland surface which started in the late tertiary and continues to the present indicate that the formation of the reef ridge nonsulfide deposit is probably related to cold humid weathering episodes during a period comprised between late tertiary and holocene the traditional interpretation on the genesis of zn nonsulfide deposits in warm humid temperate or semiarid conditions should be questioned where other climate zones are indicated

stable isotope geochemistry of ground and surface waters associated with undisturbed massive sulfide deposits constraints on origin of waters and water rock reactions abstract stable isotopes h o c were determined for ground and surface waters collected from two relatively undisturbed massive sulfide deposits halfmile lake and restigouche in the bathurst mining camp bmc new brunswick canada additional waters from active and inactive mines in the bmc were also collected oxygen and hydrogen isotopes of surface and shallow groundwaters from both the halfmile lake and restigouche deposits are remarkably uniform 13 to 14 and 85 to 95 for 18ovsmow and 2hvsmow respectively these values are lighter than predicted for northern new brunswick and combined with elevated deuterium excess values suggest that recharge waters are dominated by winter precipitation recharged during spring melting deeper groundwaters from the restigouche deposit and from active and inactive mines have heavier 18ovsmow ratios up to 10 8 than shallow groundwaters suggesting recharge under warmer climate or mixing with shield type brines some of the co variation in cl concentrations and 18ovsmow ratios can be explained by mixing between saline and shallow recharge water end members carbon isotopic compositions of dissolved inorganic carbon dic are variable ranging from 15 to 5 13cvpdb for most ground and surface waters much of the variation in the carbon isotopes is consistent with closed system groundwater evolution involving soil zone co2 and fracture zone carbonate minerals calcite dolomite and siderite average 6 5 13cvpdb the dic of saline restigouche deposit groundwater is isotopically heavy 12 13cvpdb indicating carbon isotopic fractionation from methanogenesis via co2 reduction consistent with the lack of dissolved sulfate in these waters and the observation of ch4 degassing during sampling

geochemistry of holocene cryptotephras from the north iceland shelf md99 2269 intercalibration with radiocarbon and palaeomagnetic chronostratigraphies tephra grain counting morphology and geochemistry in the 150 1000 m size fraction were used to identify 22 individual tephra horizons and one visible tephra layer saksunarvatn from postglacial sediment of the north iceland shelf core md99 2269 66 37 53 n 20 51 16 w water depth 365 m length 2533 cm from the reykjafjardarall basin is constrained at the base by the vedde tephra c 12 000 cal yr bp geochemical analyses and stratigraphical position of the 22 tephra horizons were used to identify the following cryptotephras kol 1372 ad 1372 hekla 1104 ad 1104 snaefellsnes 1 c 1790 cal yr bp hekla 3 c 2970 cal yr bp hekla 4 c 4230 cal yr bp tv 5 c 6860 cal yr bp and suduroy c 8070 cal yr bp a tephra of the same geochemistry as kol 1372 was found near the base of the core and is here named kol3 2269 11 000 cal yr bp eleven additional cryptotephras were geochemically typed to their respective icelandic volcanic centres of origin and their ages constrained four teph

a new high resolution holocene tephra stratigraphy in eastern iceland improving the icelandic and north atlantic tephrochronology a new and improved holocene tephra stratigraphy and tephrochronological framework for eastern and northern iceland is presented investigations of a sediment sequence from lake logurinn have revealed a comprehensive tephra record spanning the last 10 200 years a total of 157 tephra layers have been identified whereof 149 tephra layers have been correlated to its source volcanic system using geochemistry stratigraphy and age fifteen layers have chemical composition of two affinities that possibly represent two very closely spaced eruptions thus these 157 tephra layers are believed to represent 172 explosive eruptions nineteen tephra marker layers have been identified in the lake logurinn record g1922 a1875 v1477 v1410 h1636 k1625 o1362 g1354 k1262 v874 hrafnkatla sn 1 grakolla hy h3 h4 ho ll1755 and reitsvik 8 tephra markers new potential tephra markers are the silicic askja l 9400 cal bp the low titanium basalt layers ll 1774 10 150 cal bp and ll 1755 9990 cal bp assigned to veidivotn bardarbunga and the tephra layers ll 1527 8 7850 cal bp ll 911 2 2370 cal bp ll 908 4 2350 cal bp ll 781 9 1930 cal bp ll 644 4 1480 cal bp not yet correlated to a source volcanic system a silicic tephra marker layer reitsvik 8 correlated to the fosen tephra in norway has been identified in lake logurinn the lake logurinn tephra record has been connected and integrated with the icelandic terrestrial tephrochronology and stratigraphy through 102 tephra layers the marine tephra stratigraphy through 39 layers and overseas through 9 tephra layers this record is the first high resolution tephra stratigraphical and chronological framework for the holocene in eastern iceland as well as the most detailed and continuous record and has considerable potential to serve as a key section or a stratotype for the holocene in eastern iceland and the north atlantic

a precisely dated lake level rise marked by diatomite formation in northeastern ireland the intercorrelation of palaeoclimate events from various studies is often hindered by a lack of precise chronological control tephra isochrons can overcome this problem by providing direct site linkages this paper outlines a study of holocene peat and diatomite deposits that accumulated within the floodplain of lough neagh northern ireland the icelandic hekla 4 tephra has been identified at the base of diatomite deposits at a number of sites and provides firm dating evidence for a widespread flooding event in the area at ca 2300 bc the evidence is consistent with other studies in ireland and elsewhere for increased wetness at this time the results demonstrate that the terrestrial deposits around lough neagh contain an important record of holocene lake level change dendrochronological evidence from the lough neagh area provides additional information about lake level fluctuations over the past two millennia copyright 2004 john wiley sons ltd

river response to rapid holocene environmental change evidence and explanation in british catchments macklin m g jones a f lewin j 2010 river response to rapid holocene environmental change evidence and explanation in british catchments quaternary science reviews 29 13 14 1555 1576 sponsorship welsh assembly government and the higher education funding council for wales for funding this study through its support of the centre for catchment and coastal research at aberystwyth university

stable isotope geochemistry of copper carbonates at the northwest extension deposit morenci district arizona implications for conditions of supergene oxidation and related mineralization stable isotope analyses were performed on 39 copper carbonate samples from the las terrazas fault zone of the northwest extension copper oxide deposit morenci district arizona the 18 o values of azurite 23 3 25 5 smow and malachite 21 0 23 5 smow indicate formation in supergene conditions from meteoric water oxygen isotope thermometry suggests oxidation occurred at temperatures between 20 and 34 c with lower temperatures representing ambient air temperatures and higher temperatures reflecting minor heat production by exothermic oxidation of sulfides for malachite a relationship between higher temperatures and higher local oxide copper grade suggests in situ formation from oxidizing copper sulfides whereas for azurite the lack of such a relationship and field evidence suggest formation from copper transported along major structures azurite 13 c values range from 4 2 to 10 7 per mil and exhibit isotopic enrichment with increasing height above the supergene enrichment blanket paleowater table this evidence suggests that azurite samples received significant amounts of organic carbon resulting from the oxidation of bacteria known to be instrumental in supergene sulfide enrichment processes adjoining the water table with upward diffusive enrichment producing the observed enrichment in 13 c with height above the water table malachite 13 c values range from 9 6 to 11 1 per mil and suggest a carbon source from oxidation of surface vegetation and or dissolution of primary or secondary carbonate by a rising water table during supergene processes detailed investigation of millimeter scale isotopic profiles across azurite veins suggests a carbon source that is initially lighter than whole vein sample measurements with progressive isotopic enrichment of the carbon source or reservoir during vein formation this as well as the fact that partial pressures of co 2 must exceed atmospheric levels for azurite formation indicates that these veins formed in a system that was at least partially closed to the atmosphere oxygen isotope thermometry indicates many of the veins formed at temperatures up to 10 c above ambient temperatures with a drop to ambient temperatures during final vein growth isotopic and field evidence indicate that the northwest extension oxide deposit formed when a shallow early stage copper sulfide enrichment blanket was stranded above the water table relatively low temperature oxidation of these sulfides produced copper rich solutions that were transported along major structures and azurite formed when the fluids intersected pockets of high p co 2 possibly produced by seasonal oxidation of supergene related bacteria above the water table over time oxidation and related mineralization reduced permeability along major structures and bacterial populations waned as deeper sulfide enrichment processes slowed lower p co 2 and reduced transport potential produced in situ and highly localized oxidation centered on the high grade zones of the early sulfide blanket remaining in the oxidation zone with malachite as a dominant phase

hypogene zn carbonate ores in the angouran deposit nw iran the world class angouran nonsulfide zn pb deposit is one of the major zn producers in iran with resources estimated at about 18 mt at 28 zn mainly in the form of the zn carbonate smithsonite this study aims to characterize these carbonate ores by means of their mineralogy and geochemistry which has also been extended to the host rocks of mineralization and other local carbonate rock types including the prominent travertines in the angouran district as well as to the local spring waters petrographical chemical and stable isotope o h c sr data indicate that the genesis of the zn carbonate ores at angouran is fairly distinct from that of other classical nonsulfide zn deposits that formed entirely by supergene processes mineralization occurred during two successive stages with the zinc being derived from a preexisting sulfide ore body a first main stage of zn carbonates stage i carbonate ore is associated with both preexisting and subordinate newly formed sulfides whereas a second stage is characterized by supergene carbonates zn and minor pb coexisting with oxides and hydroxides stage ii carbonate ore the coprecipitation of smithsonite with galena pyrite and arsenopyrite as well as the absence of fe and mn oxides hydroxides and of any discernible oxidation or dissolution of the sphalerite rich primary sulfide ore shows that the fluids responsible for the main stage i carbonate ores were relatively reduced and close to neutral to slightly basic ph with high fco2 smithsonite 18ovsmow values from stage i carbonate ore range from 18 3 to 23 6 while those of stage ii carbonate ore show a much smaller range between 24 3 and 24 9 the 13c values are fairly constant in smithsonite of stage i carbonate ore 3 2 6 0 but show a considerable spread towards lower 13cvpdb values 4 6 to 11 2 in stage ii carbonate ore this suggests a hypogene formation of stage i carbonate ore at angouran from low temperature hydrothermal fluids probably mobilized during the waning stages of tertiary quaternary volcanic activity in an environment characterized by abundant travertine systems throughout the whole region conversely stage ii carbonate ore is unambiguously related to supergene weathering as evidenced by the absence of sulfides the presence of fe mn oxides and arsenates and by high 18o values found in smithsonite ii the variable but still relatively heavy carbon isotope values of supergene smithsonite ii suggests only a very minor contribution by organic soil carbon as is generally the case in supergene nonsulfide deposits

determining terrestrial paleotemperatures using the oxygen isotopic composition of pedogenic carbonate abstract quantifying terrestrial paleotemperatures has proven to be a challenging endeavor this paper explores the use of the oxygen isotopic composition of pedogenic calcite for terrestrial paleotemperature reconstructions we generate three paleotemperature equations two of them derived by simultaneous solution of equations that describe the fractionation of oxygen isotopes in the exogenic cycle while the third equation is derived using a linear regression through modern 18occ mat oxygen isotopic composition of pedogenic calcite versus mean annual temperature data we use the paleotemperature equations to evaluate climate change across the k t boundary by analyzing the oxygen isotopic composition of pedogenic carbonates from a series of stacked paleosols in west texas the fabrics in the calcite nodules were evaluated in order to identify soil carbonate components that have the best chance of containing isotopic information that represents ancient pedogenic conditions the average temperature for west texas during the time period studied is 18 0 5 c two temperature excursions are recognized prior to the k t boundary in which terrestrial temperatures increase by about 4 c for relatively short periods of time these short greenhouse events documented in west texas correlate with changes in marine temperatures as well as terrestrial temperatures in north dakota during the same time period latitudinal temperature gradients generated using the west texas and north dakota data indicate that the spatial simultaneous solution yields the most reliable temperature reconstructions of the three equations considered in this study

stable isotope characterization of the thermal profile and subsurface biological activity during oxidation of the great australia deposit cloncurry queensland australia the application of stable isotope thermometry and phase relations was used to examine the thermal evolution of oxidation and secondary mineralization at the great australia cu au co deposit cloncurry queensland australia results show that early secondary mineralization consisted of djurleite crystallization at temperatures 93 c followed by calcite mineralization at 66 to 75 c the secondary mineralization paragenesis continued with azurite that formed at about 51 c followed by malachite crystallization at 41 to 38 c and malachite after azurite at 34 c the final stage of secondary mineralization consists of calcite that formed at 25 to 30 c followed by goethite the general trend observed is for early oxidation and supergene enrichment at apparent temperatures less than 93 c and between 66 and 75 c cooling to ambient surface temperatures late in the period of mineralization a correlation is observed between decreasing isotope thermometry temperatures and increasing 13c values as oxidation and supergene enrichment progressed this is interpreted to result from exothermic sulfide oxidation and associated subsurface thermophilic bacterial oxidation within the oxidation front over the period of oxidation and supergene enrichment temperatures decreased and 13c values increased recording in the secondary minerals the passing of the oxidation front and a diminishing subsurface bacterial carbon source

hydrothermal alteration and mineralization in the neves corvo volcanic hosted massive sulfide deposit portugal ii oxygen hydrogen and carbon isotopes the oxygen hydrogen and carbon isotope compositions of hydrothermally altered rocks and minerals from massive and stockwork ores of the neves corvo volcanic hosted massive sulfide deposit have been used to infer its thermal history and the origins of the hydrothermal fluids quartz and cassiterite separated from the stringer and massive cassiterite ores of the corvo orebody tin corridor have 18o values of 12 5 to 13 6 and 1 4 to 0 4 per mil respectively quartz cassiterite oxygen isotope fractionation indicates temperatures of 174 to 207 c avg 191 c for precipitation of this mineral pair the calculated oxygen isotope composition of the fluid 18oh2o 0 4 to 0 7 avg 0 1 suggests that cassiterite precipitation resulted from extensive mixing of a tin bearing fluid with seawater at sea floor hydrothermal vents the whole rock oxygen isotope composition of the hydrothermally altered felsic volcanic rocks hosting the sulfide stockwork of the corvo orebody varies from the central stockwork chloritic alteration zone i 18o 8 7 9 6 to the peripheral zones sericitic and paragonitic alteration zones iia 18o 11 6 13 1 and iib 18o 11 0 14 1 the 18o values of quartz also increase from alteration zone i avg 13 9 to alteration zone iia avg 14 4 to alteration zone iib avg 15 0 quartz from the hanging wall jasper unit yielded higher 18o values of 15 5 to 17 9 per mil chlorite from alteration zone i has 18o values of 6 1 to 8 4 per mil avg 7 4 sericite has 18o and d values that vary slightly from 18o 9 3 to 10 1 per mil avg 9 9 and d 59 to 47 per mil avg 53 in alteration zone i to 18o 9 8 to 11 4 per mil avg 10 5 and d 50 per mil in alteration zone iia to 18o 9 4 to 11 7 per mil avg 10 6 and d 61 to 36 per mil avg 45 in alteration zone iib siderite associated with waning hydrothermal activity has low 13c values 11 1 to 5 8 suggesting the incorporation of oxidized organic carbon from the footwall sequence and or the addition of magmatic carbon in alteration zone i quartz chlorite fractionation indicates temperatures of 249 to 402 c avg 335 c and 18oh2o values of 6 1 to 10 2 per mil avg 8 3 quartz sericite pairs gave isotopic equilibrium temperatures of 250 to 289 c avg 269 c and 18oh2o values of 5 8 to 7 0 per mil avg 6 4 in alteration zone iia and 170 to 318 c avg 223 c and 18oh2o 1 4 to 8 3 per mil avg 4 5 in alteration zone iib the oxygen isotope data show that in the core of the feeder system alteration zone i the temperature and the 18oh2o values were very high the d values calculated for the ore fluids d 37 to 11 are also significantly lower than seawater outward from the central stockwork alteration zones iia and iib the ore fluid was depleted in 18o and the temperatures were lower the oxygen hydrogen and carbon isotope signatures of the neves corvo ore fluids are best explained by incorporation of magmatic and or metamorphic fluids into a seawater dominated hydrothermal system magmatic fluids in particular were a likely source for the tin and much of the copper in the neves corvo ores

extreme 34s depletions in zns at the mike gold deposit carlin trend nevada evidence for bacteriogenic supergene sphalerite we identified submicrometer sized framboidal sphalerite zns below the base of supergene oxidation in a carlin type gold deposit of eocene age in nevada united states where the framboidal sphalerite forms a blanket like body containing 400 000 metric tons of zinc framboidal sphalerite 0 1 mum in diameter formed in the early miocene ranges from 0 1 to 0 35 mol fes the delta 34 s values range from 25 to w 70 the lowest values measured in a marine or terrestrial environment these s isotope data demonstrate the involvement of sulfate reducing bacteria and provide the first documentation that sphalerite can form significant supergene sulfide enrichment blankets

stable isotope geochemistry of carbonate minerals in supergene oxidation zones of zn pb deposits abstract the 18 o 16 o and 13 c 12 c ratios of carbonate minerals formed by supergene oxidation of zn pb deposits and submarine alteration of ancient slags were studied in order to constrain isotope fractionation factors for smithsonite cerussite and phosgenite and to characterize conditions of nonsulfide ore formation we present new isotope data of carbonate hosted ores from the iglesiente district sardinia italy and vila ruiva portugal as well as from the silicate hosted ores of the broken hill district new south wales australia and freihung germany and review previously published isotope data the temperature dependence of oxygen isotope fractionation between pb and zn carbonate minerals and water below 240 c for cerussite and below 100 c for smithsonite and phosgenite can be expressed as 1000ln cerussite water 2 29 10 6 t 2 3 56 1000ln smithsonite water 3 10 10 6 t 2 3 50 1000ln phosgenite water 2 55 10 6 t 2 3 50 with t in kelvin the carbon isotope fractionation between smithsonite phosgenite hydrozincite and calcite is less than about 2 while cerussites are strongly depleted in 13 c by about 10 as compared to the former minerals oxygen isotope variations of individual carbonate minerals within a deposit are relatively small indicating constant formation temperatures and a single meteoric fluid source average formation temperatures of the studied deposits are calculated at 20 5 c using the estimated isotope compositions of local paleometeoric waters we observe a linear relationship between the isotope values of estimated paleometeoric waters and supergene carbonates thus base metal carbonate minerals from supergene deposits may provide paleoclimatic information the carbon isotope values are in most carbonate hosted deposits highly variable more than 10 suggesting at least two isotopically distinct carbon sources the isotopically light component can be related to oxidation of c3 plants soil derived carbon and or microbes that take active part in sulfide oxidation while the isotopically heavy component originates from carbonate carbon from wall rocks and or atmospheric carbon the 13 c enriched component is less dominant in silicate hosted deposits

cainozoic stratigraphy palaeoenvironments and geological evolution of the lake eyre basin abstract for a large part of inland australia weathering and erosion prevailed from the cenomanian to the late paleocene subsidence commencing in the late paleocene produced a depocentre the lake eyre basin in which sedimentation occurred in three main phases 1 fluviolacustrine sand silt clay and carbonaceous horizons from latest paleocene to middle eocene 2 dolomite and magnesium rich clay and sand deposited in extensive shallow alkaline lakes from latest oligocene miocene and 3 red clay silt and sand were deposited in fluvial lacustrine and aeolian settings during the pliocene and quaternary widespread weathering and silicification of sediments occurred in the late eocene oligocene and again in the pliocene the latter also accompanied by ferruginisation the silcrete sheets were folded into broad domes during the oligocene and again in the pliocene when faulting marginal to the southern ranges also occurred from the late paleocene to early eocene the basin supported rainforest growing in megathermal to mesothermal conditions by the middle eocene vegetation had changed to localised riparian forest in valley bottoms and more open sclerophyllous woodland in the hinterland indicating monsoonal conditions for most of this early tertiary interval deposition was by broad braidstreams flowing northwards in the miocene scattered elements of megathermal forest still existed but open woodland was far more extensive strong climatic seasonality and elevated temperatures promoted the deposition of thick dolomites in giant alkaline lakes the lakes and the diverse vegetation were home to a rich aquatic and terrestrial fauna by the pliocene climate was semiarid and vegetation mainly open casuarinaceae dominated woodland with very rare stands of forest confined to edaphically suitable sites increasing aridity during the quaternary was punctuated by pluvial intervals vast lakes formed during the interglacials largely as a result of higher rainfall in queensland drier windier conditions during the glacials particularly the last led to the development of extensive dunefields

deuterium oxygen 18 and tritium in stripa groundwater deuterium oxygen 18 and tritium determinations show that groundwaters in the fractures of the stripa granite are of meteoric origin not affected by secondary isotope effects evaporation or isotope exchange deep ground waters have lower 18o and 2h contents than recent shallow groundwaters the differences are most likely due to recharge during cooler climatic conditions however no age information can be derived because recharge could have occurred before the last major climatic improvement following the last deglaciation during minor climatic variations during the more recent past or could be the result of regional groundwater flow low 18o contents are paralleled by increasing salinities with highest salinities limited to a narrow fracture zone at a depth of about 800 m below ground surface most saline waters sampled appear to represent mixtures of a saline component with an isotopically depleted water and local fresh water the presence of young groundwaters is indicated by bomb produced 3h all surface boreholes contain tritium indicating residence times 35 years however tritium is also found in some boreholes drilled at the 300 m mine levels and its presence may be due to flows induced in response to heater tests low but detectable 3h contents about 0 1 to 1 tu in v2 at about 850 m below groundsurface are discussed either as subsurface production and or as a result of admixtures of small amounts of recent water to old groundwater

oxygen isotopes in meteoric calcite cements as indicators of continental paleoclimate because meteoric water 18 o values decrease with decreasing ambient temperature and increasing latitude 18 o values of meteoric calcite cement should exhibit a similar relation with paleolatitude and be an indicator of continental paleotemperatures to test this we compiled isotopic and paleolatitude data for 20 meteoric cements and nine speleothems ranging in age from devonian to modern and in paleolatitude from 3 5 to 83 mean 18 o values for meteoric cements and speleothems both show the same negative correlation with paleolatitude the 18 o vs latitude trend for these carbonates is almost identical to that predicted for modern inland environments but differs from the trend for coastal environments this suggests that the ground water controlling the ultimate composition of meteoric cement is derived predominantly from inland recharge if it is assumed that the modern meteoric water 18 o vs temperature relation is valid for the past and that insignificant evaporation occurred prior to carbonate precipitation then coastal and inland paleotemperatures can be calculated from the 18 o values of meteoric calcite 18 o mcl and seawater 18 o sw by using the equations t coastal 13 3 32 6 0 231 0 0613 18 o mcl 18 o sw and t inland 17 8 16 2 0 572 0 1233 18 o mcl 18 o sw where t is temperature in c calcite precipitated from coastal meteoric water at temperatures between 0 and 25 c will exhibit a narrow range in 18 o 6 to 4 where 18 o sw 0 the 18 o of calcite precipitated from inland meteoric water will be sensitive to paleotemperature ranging from 14 to 5 where 18 o sw 0 for temperatures of 0 to 25 c

miocene biofacies development and geological history of the gulf of suez egypt abstract miocene sediments of the gulf of suez were deposited in a rapidly subsiding rift which became active during late oligocene and early pliocene tectonic episodes complex lithological variations associated with the variable submarine structure commonly preclude detailed correlation of drilled subsurface successions thick middle to late miocene evaporites and their geometry obscure seismic interpretation of prospective sub evaporitic early and middle miocene sequences the thick miocene sediments are believed to have significantly furnished the source as well as the reservoirs and seals for the oil discovered in the gulf of suez over four billion barrels of oil have been established as recoverable reserves in miocene reservoirs a new gulf wide detailed correlation scheme is established based upon a series of newly defined microfaunal assemblage zones these zones are based on holistic analysis of microfauna utilizing planktonic and benthonic foraminifera diatoms otoliths and pteropods dating by planktonic foraminifera and calcareous nannofossils indicates the zones are isochronous vertical and lateral variations in assemblage characteristics have been identified mapped and are concluded to be the results of vertical and lateral differences in salinity water depth water clarity lithological variation and oxygen availability the correlative applicability of this scheme within the gulf of suez provides potential for it to serve as a reference for drilled sequences in the red sea where thicker evaporite sequences make sub evaporitic stratigraphic correlation even more difficult owing to the greater seismic attenuation isochronous palaeoenvironmental variations are detected utilizing the zonation scheme both within the gulf of suez and the red sea region which will assist in the correlation and mapping of stratigraphic sequences of hydrocabon potential detection confirmation and the degree of displacement of faults is also improved by the application of the scheme

multi proxy evidence for holocene lake level and salinity changes at an loch mor a coastal lake on the aran islands western ireland abstract curves for holocene lake levels and salinity changes are presented for an loch mor a small oligohaline lake on the aran islands off the west coast of ireland based on palaeoecological investigations of a 12 m long lake sediment core new insights are also provided into holocene sea level change in the galway bay region particular emphasis has been placed on the ostracod fauna both past and present salinity and lake level changes were reconstructed from the fossil ostracod assemblages based on the known tolerances of individual species and on the assemblages as a whole additional evidence was provided by other proxies including strontium isotope ratios derived from ostracod shells and other carbonates plant macrofossil and pollen analyses and sedimentological changes the early holocene pre boreal i e 11 5 10 ka was characterised by low lake levels and slightly elevated salinity values probably the result of high evapotranspiration and low precipitation rather than elevated sea levels early holocene plant and animal migration to the island does not seem to have been impeded but relative sea levels were not necessarily so low below 40 m a s l that landbridges were present to the mainland between ca 10 and 8 5 ka relatively high lake levels prevailed at 8 3 and 7 5 ka minor fluctuations lowering of the lake level occurred that are assumed to relate to early holocene abrupt events beginning at 7 05 ka lake levels declined sharply a general trend towards rising lake levels started at ca 6 4 ka and accelerated at ca 5 6 ka as runoff increased as a result of neolithic clearances at ca 4 8 ka lake levels began to rise once again probably in response to changes in rainfall and or evapotranspiration and runoff lower lake levels during the first half of the 1st millennium ad were probably a response to decreased runoff as a result of a drier climate coupled with regeneration of woody vegetation the sharpest rise in both lake levels and salinity began during the ninth century ad which is attributed to a rapid rise in relative sea level

the magellan pb deposit western australia a new category within the class of supergene non sulphide mineral systems abstract the magellan pb deposit is located in an outlier of the palaeoproterozoic earaheedy group overlying the southeast yerrida basin a feasibility study of the magellan prospect was completed in 2001 with at that time proven and probable ore reserves of 8 5 mt grading 7 12 pb the deposit is currently exploited from two open pits magellan and cano the lead orebodies are hosted in a silicified dolomitic collapse breccia and underlying altered and weathered sandstone and siltstone the host succession comprises from top to bottom a lateritic unit overlying a zone of silicified silcretized quartz clay breccia overlying saprolitic clay breccia and siltstone palaeoproterozoic earaheedy group and basin the footwall consists of black shales of the maraloou formation palaeoproterozoic yerrida basin magellan is a non sulphide mineral system with cerrusite and anglesite as the major ore minerals and plattnerite coronadite pyromorphite and plumbogummite as minor to negligible ore components the lack of sulphides and the sole presence of oxide minerals suggest that the ore was formed under physico chemical conditions conducive to the precipitation of pb carbonate and pb sulphate it is proposed that the magellan lead deposit represents the supergene modified residue from mississippi valley type mvt mineralisation hosted in the sweetwaters member of the yelma formation of the earaheedy group that underwent prolonged weathering which led to dissolution volume reduction and oxidation of the galena and sphalerite as well as leaching out of highly mobile zn leaving behind the pb carbonate and sulphate mineralisation the magellan mineral system likely represents a new category within the non sulphide class of ore deposits

defining the potential source region of volcanic ash in northwest europe during the mid to late holocene abstract far travelled volcanic ash fine grained tephra clouds pose economic and societal risks largely through their potential impact on the aviation industry a long view of ash clouds extending over northwest europe assembled from the study and geochemical characterisation of cryptotephra i e tephra invisible to the naked eye in sedimentary records can help inform the understanding of the frequency of such events and the nature of eruptions that generate them here we review the records of cryptotephra deposition in northwest europe during the mid to late holocene the last eight millennia to gain insights into the sources of volcanic ash reaching this region we consider almost 500 published and unpublished datasets for cryptotephras recorded in sedimentary sequences ranging from ireland to latvia and on the basis of their major element geochemical composition we identify 90 unique ash horizons and their likely provenance the majority 72 of the cryptotephras derive from icelandic eruptions but a large proportion 24 originates from other volcanic regions including alaska the cascades kamchatka mexico the azores and possibly the mediterranean although moderate magnitude eruptions in iceland may potentially disperse ash clouds over europe it appears that only large magnitude events in more distant regions have generally had this capacity and then only when suitable meteorological conditions prevailed nevertheless the cryptotephra records demonstrate that ash clouds from most volcanic regions capable of producing large explosive eruptions in the northern mid to high latitudes particularly those to the west of europe as well as in tropical north america have the potential to extend to northwest europe volcanic ash forecasts for this region need therefore to take into account possible risks posed not only by icelandic eruptions but also by any large magnitude eruptions in north america or the north pacific area

stable isotope geochronology of the australian regolith australian regolith profiles can be assigned to one of three post palaeozoic age groups on the basis of the oxygen isotope composition of authigenic clay minerals developed in the profile systematic variations in the isotopic composition of meteoric waters and therefore of the authigenic regolith minerals that formed in equilibrium with them are a result of the continent s drift from high to low latitudes and changes in global climate residual clays collected in situ from regolith profiles of post mid tertiary age have 18o values between 17 5 and 21 3 with the exception of samples from northern australia north of approximately 20 s which have anomalously low values because meteoric waters in northern australia are largely derived from monsoonal rain the high 18o values of post mid tertiary residual clays are consistent with australia s northward drift to low warm latitudes during this time compared with the much higher latitudes it occupied for most of its post palaeozoic history late tertiary residual clays have 18o values that are indistinguishable from all other post mid tertiary clays indicating that further subdivision of the sample groups is not feasible on a continent wide scale comparison with hypothetical modern clays in equilibrium with modern meteoric waters confirms that there has been very little change in the isotopic composition of meteoric waters in australia since the mid tertiary pre mid tertiary clays have lower 18o values between 10 0 and 17 5 which are consistently lower than post mid tertiary clays 18o values of less than 14 to 15 are thought to reflect weathering events during much earlier geologic periods perhaps early or mid mesozoic when australia was at high latitude and the australian climate was humid and cool to cold several workers have documented the existence of very old regolith profiles and land surfaces in australia and support for the above hypothesis comes from three analyses of clays from profiles of stratigraphically demonstrable pre late mesozoic age which have 18o values between 10 2 and 12 3 regolith profiles composed of low 18o clays 15 are widespread in australia and it is possible that a much greater part of the modern landscape than previously recognized developed in the early or mid mesozoic the 18o values of transported i e sedimentary kaolinites reveals that the major source for many tertiary kaolinitic sediments was this postulated pre late mesozoic low 18o regolith the stableisotope evidence that much of the australian regolith formed in comparatively cold conditions suggests that contrary to some traditional interpretations lateritization and deep weathering phenomena are not solely the result of weathering in tropical or sub tropical climates the hydrogen isotope composition of the clays range from 115 to 50 however it is inferred that the majority of clays have undergone some post formational hydrogen isotope exchange which renders their d composition unsuitable for dating purposes

abrupt climatic changes and an unstable transition into a late holocene thermal decline a multiproxy lacustrine record from southern sweden the transition from a middle holocene relatively warm and stable climate to a cooler and unstable late holocene climate is reconstructed using sediments from lake igelsjon south central sweden this multiproxy study illustrates local regional and global scale responses to climatic change by focusing on a previously identified abrupt hydrological shift to cooler and or wetter conditions around 4000 cal yr bp the results suggest that between ca 4600 and ca 3400 cal yr bp the environment around and within the lake responded in two major well defined steps the first between 4450 and 4350 cal yr bp and the second between 4000 and 3800 cal yr bp a series of rapid fluctuations of short duration were superimposed on the general cooling trend with the most severe aquatic response peaking at ca 3800 cal yr bp pollen percentage and influx values show forest composition and pollen productivity changes and a distinct decline in total and corylus pollen influx in the period of 4000 3500 cal yr bp stomatal based reconstruction of atmospheric co2 concentration produced a tenuous decrease with a minimum between 3650 and 3500 cal yr bp copyright 2005 john wiley sons ltd

geology of the skorpion supergene zinc deposit southern namibia the skorpion zinc deposit in southwestern namibia comprises a significant nonsulfide orebody 24 6 mt at 10 6 zn and subordinate amounts of primary base metal sulfide mineralization which structurally underlies the nonsulfide ores at depth the host rocks of the blind nonsulfide orebody and relict sulfide mineralization consist of a mixed volcano sedimentary sequence of neoproterozoic age that has formed in an initial continental rift system between the kalahari cratonic province and the rio de la plata cratonic province the metavolcanic and subvolcanic rocks display a distinct bimodal geochemical composition of within plate affinity and have been emplaced under an extensional crustal regime zircons from a rhyolitic vesicular flow extruded approximately contemporaneously with the volcanic hosted sulfide mineralization have been dated by shrimp u pb analysis and yield an age of 751 9 5 5 ma the basin that hosts the skorpion deposit has been shaped by horst and half graben tectonics which also controlled the sedimentary deposition of siliciclastic and carbonate sediments within both shallow and deeper water environments the rock sequence was affected by a major tectono metamorphic event the pan african brasiliano orogeny at approximately 550 to 545 ma metamorphism reached uppermost greenschist to lowermost amphibolite facies and the complex deformational style of the region is the result of intense faulting folding and thrusting the skorpion orebody is hosted by arkosic metaarenites and subordinately by volcaniclastic metasedimentary rocks it is irregularly shaped transgressive to sedimentary layering and has a relatively flat top which is covered by a blanket of unmineralized overburden consisting of calcrete boulder beds and recent sand dunes at depth the orebody has a relatively sharp contact with a barren marble unit on the east and south and a more gradational boundary within the siliciclastic host rocks on the west and north the nonsulfide ore minerals comprise predominantly sauconite zn smectite substantial amounts of hemimorphite and smithsonite and subordinate amounts of scholzite tarbuttite atacamite hydrozincite and hetearolite the ore minerals are mainly euhedral and subhedral crystals and occur as open space fillings in intergranular voids fractures and breccias and as replacements of feldspar and mica the metasedimentary host rocks of the nonsulfide ore contain abundant iron hydroxide pseudomorphs after disseminated sulfides and stringers and after rare semimassive stratiform layers of sulfides gossanous manganese and iron hydroxide rich siliciclastic metasedimentary rocks are common in the western and northwestern vicinity of the nonsulfide orebody alteration of the supergene mineralized host rocks includes removal of calcite cement and the breakdown of detrital albite rich plagioclase and of minor orthoclase local alteration phenomena also include silicification and rare secondary barite both a result of the alteration and breakdown of feldspar minor base metal sulfide mineral deposits occur in metarhyolitic flows and felsic hyaloclastic rocks structurally below the nonsulfide orebody the primary sulfide minerals comprise pyrite pyrrhotite sphalerite minor chalcopyrite and galena as well as secondary chalcocite and colloidal sphalerite brunckite the volcanic hosted sulfide ore minerals are deformed and partly recrystallized and thus of premetamorphic and predeformation origin in contrast the skorpion nonsulfide zinc deposit is of postmetamorphic origin as shown by two hydrous low p low t ore assemblages the secondary assemblages occur at least partly as delicate euhedral and subhedral crystals in secondary pore space open fractures veins and breccias the nonsulfide ore contains pseudomorphs from in situ oxidation and replacement of preexisting sulfides and ore and also from the remobilization or precipitation of base metals the skorpion nonsulfide zinc deposit is of supergene origin and formed from the oxidation of sulfide protore by circulating meteoric water as suggested by textural evidence and by initial stable isotope data the timing of ore formation is still undefined but lies within the large age bracket between 545 ma peak metamorphism and subsequent partial exhumation and the deposition of the nonmineralized overburden of namib desert gravels 21 ma and dune sands

low frequency and high frequency changes in temperature and effective humidity during the holocene in south central sweden implications for atmospheric and oceanic forcings of climate an integrated use of independent palaeoclimatological proxy techniques that reflect different components of the climate system provides a potential key for functional analysis of past climate changes here we report a 10 000 year quantitative record of annual mean temperature tann based on pollen climate transfer functions and pollen stratigraphical data from lake flarken south central sweden the pollen based temperature reconstruction is compared with a reconstruction of effective humidity as reflected by a 18o record obtained on stratigraphy of lacustrine carbonates from lake igelsjon c 10 km from lake flarken which gives evidence of pronounced changes in effective humidity the relatively low tann and high effective humidity as reflected by a low evaporation inflow ratio suggest a maritime early holocene climate 10 000 8 300 cal year bp seemingly incompatible with the highly seasonal solar insolation configuration we argue that the maritime climate was due to the stronger than present zonal flow enhanced by the high early holocene sea surface temperatures in the north atlantic the maritime climate mode was disrupted by the abrupt cold event at 8 200 cal year bp followed at 8 000 cal year bp by a stable holocene thermal maximum the latter was characterized by tann values about 2 5 c higher than at present and markedly dry conditions indicative of stable summer time anti cyclonic circulation possibly corresponding with modern blocking anticyclonic conditions the last 4 300 year period is characterized by an increasingly cold moist and unstable climate the results demonstrate the value of combining two independent palaeoclimatic proxies in enhancing the reliability generality and interpretability of the palaeoclimatic results further methodological refinements especially in resolving past seasonal climatic contrasts are needed to better understand the role of different forcing factors in driving millennial scale climate dynamics

the correlation between 18o 16o ratios of meteoric water and surface temperature its use in investigating terrestrial climate change over geologic time abstract correlations between mean annual temperature mat and the weighted average oxygen isotope composition of yearly precipitation 18opt are well known but the utility of modern relations to make reliable estimates of temperature change over geological time is uncertain this question has been addressed by using seasonal subsets of the global data base of temperature and isotopic measurements to represent two different climate modes a comparison of middle to high latitude 18opt temperature relations for each climate mode reveals 1 a significant offset between them and 2 a difference in the strength of their correlations the offset in relations is due to differences in temperature and water vapor budget in the tropics and can lead to serious underestimates of temperature change differences in the strength of correlations arise from the influence of climate mode specific non temperature factors on 18opt the overall result is that no single relation can be used in all cases to make unambiguous temperature estimates using a temporal record of 18opt values one way to overcome these problems is to reconstruct 18opt temperature relations for the time periods being investigated if an appropriate proxy for 18opt is available it may also be possible to estimate temperature without relying on 18opt temperature relations a promising alternative to these options is to use records of 18opt to test predictions of global climate models an approach that may allow a reliable and more complete reconstruction to be made of climate change over geologic time

carbon and oxygen isotopic covariations in hydrothermal calcites isotopic covariations of carbon and oxygen in hydrothermal calcites are quantitatively modeled in terms of the following three mixing processes 1 mixing between two different fluids which leads to the precipitation of calcite 2 mixing between fluid and rock a calcite precipitation due to fluid rock interaction b secondary alteration of primary calcite by interaction with a subsequent fluid the models are derived from mass balance equations a distinction among the three mixing processes can be made on a 13c vs 18o diagram which places important constraints on the genesis of hydrothermal mineralization the variables which control the ultimate isotopic composition of hydrothermal calcites include the composition of the initial fluid and the wallrock temperature and dissolved carbon species owing to significant temperature dependent fractionation effects during equilibrium precipitation of calcite from a hydrothermal fluid the mixing processes may be distinguished by telltale patterns of isotopic data in 13c vs 18o space in particular caution must be exercised in postulating the fluid mixing as the cause for mineral deposition this is demonstrated for hydrothermal pb zn deposits in the western harz mountains germany a positive correlation between 13c and 18o values is observed for calcites from the bad grund deposit in the upper harz two sample profiles through calcite veins show similar correlations with the lowest values at the center of the veins and the highest values at the vein margins because the correlation array has a greater slope than for calcite precipitation at equilibrium in a closed system and because fluid mixing may not proceed perpendicular to the vein strike it is assumed that a fluid rock interaction is responsible for the observed correlation and thus for the precipitation of calcite a deep seated fluid is inferred with a 13c value of 7 and a 18o value of 10 as well as h2co3 as the dominant dissolved carbon species precipitation temperatures of the calcites are estimated to be about 280 170 c quite different isotopic distributions are observed for calcites from the st andreasberg deposit in the middle harz an alteration model is suggested based mainly on the isotopic distribution through a calcite vein in addition to a primary fluid which has the same isotopic composition as that in the bad grund deposit and thus seems to be responsible for the precipitation of calcite associated with sulfides an evolved hco 3 dominant subsurface fluid with 13c about 20 15 and 18o 0 is deduced to alter the primary calcite at low temperatures of 70 40 c

d h evidence for the timing of kaolinization in northeast bavaria germany the dsmow values of sedimentary kaolins from the western border of the bohemian massif northeast bavaria that did not suffer a deep burial less than 1000 m nor a hydrothermal overprint change systematically from late triassic 50 to mid jurassic and late cretaceous 56 to 66 to upper oligocene mid miocene 77 to 90 all analyzed clays are far from hydrogen isotope equilibrium with present day meteoric waters combined oxygen and hydrogen isotope data of selected samples indicate low temperatures of formation 30 c and no evidence for preferential d h exchange with younger waters the hydrogen isotopic evolution of kaolins is interpreted as reflecting a systematic isotopic change of paleo meteoric waters in that region this can be related mainly to the northward drift of stable europe after the break up of gondwana increasing continentality surface uplift and global cooling are additional factors responsible for decreasing dsmow values since the mid cretaceous kaolinite hydrogen isotope ratios of two large residual economic deposits tirschenreuth dsmow 80 to 76 hirschau schaittenbach dsmow 70 to 63 can be used in combination with additional geological evidence to constrain the timing of weathering in these areas a late early cretaceous kaolinization age is suggested for the early triassic sandstone hosted deposits near hirschau schnaittenbach whereas a late oligocene to mid miocene age is indicated for the carboniferous granite hosted tirschenreuth deposits