paleo seawater ree compositions and microbial signatures preserved in laminae of lower triassic ooids abstract signals indicative of paleo seawater rare earth element ree composition and microbial activity were identified in marine ooids from the lower triassic of south china using in situ laser ablation inductively coupled plasma mass spectroscopy la icp ms together with petrographic and isotope geochemical techniques quantitative trace element profiles were generated across successive growth laminae in the cortices of selected ooids the shale normalized ree and yttrium y data of these layers show 1 light rare earth element depletion mean la sn yb sn 0 36 0 14 2 positive la anomalies mean la la sn 2 02 1 25 and 3 high ratios of y ho mean 53 12 which are similar to modern seawater compositions and bahamian ooids these findings imply that ooids in the study samples faithfully record early triassic paleo seawater chemical signals such as ree y distributions petrographic observations revealed dark colored layers with intense fluorescence containing structures that resemble microbial filaments or extracellular polymeric substances these layers also possess more enriched ree compositions and higher concentrations of nutrient like elements e g zn and ba than adjacent recrystallized light colored laminae most ooid laminae contain negative ce anomalies indicative of a well oxygenated environment of formation but some laminae have minimal negative anomalies suggesting the influence of suboxic porewater conditions the present study provides a new perspective on the role of microbes in ooid genesis and on the utility of ooids as proxies for paleo seawater chemistry

precipitation of dolomite using sulphate reducing bacteria from the coorong region south australia significance and implications dolomite was successfully precipitated in culture experiments that simulated microbiogeochemical conditions prevailing during late stages of evaporation in ephemeral hypersaline dolomitic lakes of the coorong region south australia analyses of lake and pore water samples document rapid geochemical changes with time and depth in both dolomitic and non dolomitic lakes extremely high sulphate and magnesium ion concentrations in lake waters decline rapidly with depth in pore waters throughout the sulphate reduction zone whereas carbonate concentrations in pore waters reach levels up to 100 times those of normal sea water ultimately sulphate is totally consumed and no solid sulphate is recorded in the dolomitic lake sediments most probable number calculations of lake sediment samples record the presence of large populations of sulphate reducing bacteria whereas sulphur isotope analyses of lake water samples indicate microbial fractionation in all the lakes studied viable populations of microbes from the lake sediments were cultured in anoxic conditions in the laboratory samples were then injected into vials containing sterilized clastic or carbonate grains or glass beads immersed in a solution that simulated the lake water falls in the levels of sulphate and rising ph in positive vials were interpreted as indicating active bacterial sulphate reduction accompanied by increased concentrations of carbonate within 2 months sub spherical sub micron size crystals of dolomite identical to those of lake sediments were precipitated it is concluded that bacterial sulphate reduction overcomes kinetic constraints on dolomite formation by removing sulphate and releasing magnesium and calcium ions from neutral ion pairs and by generating elevated carbonate concentrations in a hypersaline strongly electrolytic solution the results demonstrate that bacterial sulphate reduction controls dolomite precipitation in both the laboratory experiments and lake sediments it is proposed that dolomite formation through bacterial sulphate reduction provides a process analogue applicable to thick platformal dolostones of the past where benthic microbial communities were the sole or dominant colonizers of shallow marine environments

equatorial zonal plasma drifts measured by the c nofs satellite during the 2008 2011 solar minimum 1 we use the measurements by the vector electric field investigation vefi on board the communication navigation outage forecasting system c nofs satellite to study the local time and seasonal and longitudinal dependent climatology of equatorial f region zonal plasma drifts during 2008 2011 these drifts are essentially westward during the day and eastward at night over jicamarca radio observatory the satellite measurements are in good agreement with incoherent scatter radar drifts our data show strong longitudinal variations particularly in the south american sector during the solstices the equinoctial data exhibit short lived and largely enhanced westward drifts near sunrise and wave 4 structures from the early afternoon to late night equinoctial periods the nighttime eastward drifts are largest near the western american sector at all seasons the june solstice postmidnight eastward drifts decrease sharply at longitudes of about 310 and have much smaller values in the entire eastern hemisphere we also briefly discuss the relationship between the longitude dependent vertical and zonal plasma drifts

microbial carbonates the geological record of the calcified bacterial algal mats and biofilms summary deposits produced by microbial growth and metabolism have been important components of carbonate sediments since the archaean geologically best known in seas and lakes microbial carbonates are also important at the present day in fluviatile spring cave and soil environments the principal organisms involved are bacteria particularly cyanobacteria small algae and fungi that participate in the growth of microbial biofilms and mats grain trapping is locally important but the key process is precipitation producing reefal accumulations of calcified microbes and enhancing mat accretion and preservation various metabolic processes such as photosynthetic uptake of co2 and or hco3 by cyanobacteria and ammonification denitrification and sulphate reduction by other bacteria can increase alkalinity and stimulate carbonate precipitation extracellular polymeric substances widely produced by microbes for attachment and protection are important in providing nucleation sites and facilitating sediment trapping microbial carbonate microfabrics are heterogeneous they commonly incorporate trapped particles and in situ algae and invertebrates and crystals form around bacterial cells but the main component is dense clotted or peloidal micrite resulting from calcification of bacterial cells sheaths and biofilm and from phytoplankton stimulated whiting nucleation interpretation of these texturally convergent and often inscrutable fabrics is a challenge conspicuous accumulations are large domes and columns with laminated stromatolite clotted thrombolite and other macrofabrics which may be either agglutinated or mainly composed of calcified or spar encrusted microbes stromatolite lamination appears to be primary but clotted thrombolite fabrics can be primary or secondary microbial precipitation also contributes to hot spring travertine cold spring mound calcrete cave crust and coated grain deposits as well as influencing carbonate cementation recrystallization and replacement microbial carbonate is biologically stimulated but also requires favourable saturation state in ambient water and thus relies uniquely on a combination of biotic and abiotic factors this overriding environmental control is seen at the present day by the localization of microbial carbonates in calcareous streams and springs and in shallow tropical seas and in the past by temporal variation in abundance of marine microbial carbonates patterns of cyanobacterial calcification and microbial dome formation through time appear to reflect fluctuations in seawater chemistry stromatolites appeared at 3450 ma and were generally diverse and abundant from 2800 to 1000 ma inception of a proterozoic decline variously identified at 2000 1000 and 675 ma has been attributed to eukaryote competition and or reduced lithification thrombolites and dendrolites mainly formed by calcified cyanobacteria became important early in the palaeozoic and reappeared in the late devonian microbial carbonates retained importance through much of the mesozoic became scarcer in marine environments in the cenozoic but locally re emerged as large agglutinated domes possibly reflecting increased algal involvement and thick micritic reef crusts in the late neogene famous modern examples at shark bay and lee stocking island are composite coarse agglutinated domes and columns with complex bacterial algal mats occurring in environments that are both stressed and current swept products of mat evolution ecological refugia sites of enhanced early lithification or all three

paleoproterozoic late orogenic and anorogenic alkaline granitic magmatism from northeast brazil abstract during the transamazonian cycle 2 0 0 2 ga two silica saturated alkaline granite suites were intruded along the border of the sao francisco craton northeastern brazil the couro de onca intrusive suite cois is late tectonic relative to major deformational events and the serra do meio suite sms postdates this event being interpreted as anorogenic type deformed during the brasiliano cycle 0 65 0 52 ga the cois encompasses alkali feldspar granites syenogranites monzogranites with dykes of similar composition and age 2 157 5 ma they are metaluminous rocks of alkaline affinity whose evolution was probably controlled by mineral fractionation processes involving mainly plagioclase amphibole and fe ti oxide the sms whose probable age is 2 01 ga is composed of metaluminous and peralkaline granites with associated quartz syenites with ti aegirine transformed during the brasiliano deformation to riebeckite titanite aenigmatite the temperatures of two stages of metamorphic transformation overprinted during the brasiliano event are estimated at about 550 and 400 450 c both magmatic suites are derived from enriched mantle sources the metaluminous and peralkaline trends observed in the sms characterized by high concentrations of hfs and re elements controlled mainly by f activity reflect the evolution of different primary magmas produced by successive melting of the same mantle sources in an anorogenic setting

aluminous granulites from the pulur complex ne turkey a case of partial melting efficient melt extraction and crystallisation abstract in the pulur complex ne turkey a heterogeneous rock sequence ranging from quartz rich mesocratic gneisses to silica and alkali deficient fe mg and al rich melanocratic rocks is characterized by granulite facies assemblages involving garnet cordierite sillimanite ilmenite spinel plagioclase quartz biotite corundum rutile and monazite textural evidence for partial melting in the aluminous granulites particularly leucosomes is largely absent or strongly obliterated by a late stage hydrothermal overprint however inclusion relations high peak p t conditions the refractory modes bulk and biotite compositions of the melanocratic rocks strongly support a model of partial melting the melt was almost completely removed from the melanocratic rocks and crystallised within the adjacent mesocratic gneisses which are silica rich bear evidence of former feldspar and show a large range in major element concentrations as well as a negative correlation of most elements with sio2 peak conditions are estimated to be 800 c and 0 7 0 8 gpa subsequent near isothermal decompression to 0 4 0 5 gpa at 800 730 c is suggested by the formation of cordierite coronas and cordierite spinel symplectites around garnet and in the matrix sm nd rb sr and 40ar 39ar isotope data indicate peak conditions at 330 ma and cooling below 300 c at 310 ma

comparison of zonal neutral winds with equatorial plasma bubble and plasma drift velocities 1 a one year dataset spanning march 2011 to march 2012 of coincident observations of nighttime thermospheric zonal neutral winds equatorial plasma bubble epb velocities and zonal plasma drifts is used to examine the relationship between the thermosphere and the ionosphere near the geomagnetic equator over peru thermospheric neutral winds are determined by using a bistatic fabry perot interferometer fpi experiment located at merihill and nazca in peru the ambient plasma drift velocities were obtained using the incoherent scatter radar at the jicamarca radio observatory in peru the epb zonal velocities were estimated utilizing images of the oi 630 0 nm emission recorded by a narrow field optical imaging system at the cerro tololo inter american observatory in chile the joint analysis of these datasets illustrates that the nighttime and night to night variations in the zonal neutral winds epb velocities and plasma drifts are well correlated this consistent result of the local time variations of the neutral winds with that of epb and plasma drifts illustrates that the f region dynamo is in general fully activated however at times the magnitude of the epb velocities and the plasma drifts are different from the neutral winds it is plausible that such a difference is due either to the effect of polarization electric fields developed inside the epb or due to the latitudinal gradient of the neutral winds and epb velocity measurements since the epb velocities are estimated at a higher latitude corresponding to an apex altitude of 400 km than the wind estimates which derive from an apex altitude of 250 km

chemical evolution of rare earth elements fractionation between colloidal and solution phases of filtered river water abstract within the dissolved fraction of connecticut river water there is large scale fractionation of rare earth elements between colloidal and solution phases colloidal particles carry a large part of the dissolved ree pool filtration through filters with progressively smaller pore size 0 45 0 22 and 0 025 m results in filtrates with lower absolute concentrations of ree and more fractionated compositions with decreasing pore size the filtrates have shale normalized abundances which become systematically more depleted in the lree relative to the hree hence both the solution and colloidal phases are significantly fractionated with respect to the dissolved fraction these conclusions are consistent with previous studies of ree in rivers estuaries and soils and with surface solution speciation models colloids play an important role in the aquatic geochemistry of rare earth elements they are responsible for the fractionation of ree during the estuarine removal of ree the removal of suspended and colloidal particles from river water leaves the solution phase of river water with compositions of ree as evolved as those of surface seawater hence the evolution of the composition of ree in river water and seawater is significantly influenced by colloid formation during chemical weathering on the continents

abiological origin of described stromatolites older than 3 2 ga the three well documented occurrences of three dimensional stromatolites older than 3 2 ga meet most criteria for biogenicity except the presence of fossil bacteria however they also show features more consistent with nonbiological origins small conical structures in the strelley pool chert in the upper part of the warrawoona group 3 5 3 2 ga western australia lack the structure typical of stromatolites and probably formed mainly through evaporitc precipitation a domal structure from the north pole chert warrawoona group formed by soft sediment deformation or originally flat layers laminated chert containing domal and pseudocolumnar structures in the onverwacht group 3 5 3 3 ga barberton greenstone belt south africa extends downward into veins and cavities where it formed through inorganic precipitation although bacterial communities were widespread on earth prior to 3 2 ga these particular three dimensional structures are probably abiotic in origin and do not provide information on the paleobiology or paleoecology of early organisms the paucity of archean stromatolites older than 3 2 ga probably reflects the paucity of known and possibly extant carbonate deposits of this age

the probable occurrence of interstitial al in hydrous f bearing and f free aluminosilicate melts experiments carried out on the system sio2 naalsi3o8 kalsi3o8 qz ab or at 1 kbar in the presence of h2o and f show that the quartz alkali feldspar field boundary is progressively displaced towards the feldspar join as f contents increase from 0 to 4 wt f increasing p h 2 o in the absence of f has already been shown to have a similar effect tuttle and bowen 1958 luth jahns and tuttle 1964 the increased size of the quartz field in the f bearing system compared to the hydrous system is believed to be caused by progressive removal of al from the tetrahedral network of the melt by complexing with f the residual network in the melt is thus enriched in si and this stabilizes precipitation of quartz rather than feldspar for certain bulk compositions the common presence of quench cryolite na3alf6 in certain experiments carried out with 4 wt f supports this interpretation and indicates that some al in the melt may be present in six fold coordination with f the effect of h2o in the absence of f may be similar with al being progressively removed from four fold coordination as more h2o is dissolved in the melt although a proportion of al in hydrous melts may occur in six fold coordination dry melts predominantly contain al in four fold coordination this major difference in al complexing may be one of the main causes for differences in the high pressure phase relations of wet and dry albearing silicate systems

neoproterozoic stratigraphy of the centralian superbasin australia abstract the basement of central australia includes the arunta block and the 1200 1100 ma musgrave block succeeded by 1075 1000 ma bimodal volcanic rifts and dolerite dykes a regional hiatus at 1000 800 ma interpreted as reflecting a central post volcanic underplated upland was followed at 800 ma by a second swarm of dykes in the musgrave block gawler craton and stuart shelf associated with the crustal sagging that initiated the centralian superbasin the centralian superbasin is defined here to encompass the neoproterozoic fill of the amadeus georgina ngalia officer and savory basins the intra cratonic superbasin was disrupted internally 540 600 ma ago petermann ranges orogeny by a central uplift and associated thrusts and by mid carboniferous 320 ma tectonism alice springs orogeny to form the structural basins listed above the stratigraphy and sedimentology of the relatively well known areas can be used as a basis for predicting those of the poorly known regions new results from acritarch biostratigraphy and isotope chemostratigraphy in conjunction with conventional lithostratigraphy and sequence analysis allow better stratigraphic resolution than previously possible field observations in the recently discovered savory basin in western australia provide a basis for correlations with the adjacent basins

microbialite development patterns in the last deglacial reefs from tahiti french polynesia iodp expedition 310 implications on reef framework architecture abstract the widespread occurrence of microbialites in the last deglacial reef frameworks 16 6 ka bp implies that the accurate study of their development patterns is of prime importance to unravel the evolution of reef architecture through time and to reconstruct the reef response to sea level variations and environmental changes the present study is based on the sedimentological and chronological analysis 14c ams dating of drill cores obtained during the iodp expedition 310 tahiti sea level on the successive terraces which typify the modern reef slopes from tahiti it provides a comprehensive data base to investigate the microbialite growth patterns i e growth rates and habitats to analyze their roles in reef frameworks and to reconstruct the evolution of the reef framework architecture during sea level rise the last deglacial reefs from tahiti are composed of two distinctive biological communities 1 the coralgal communities including seven assemblages characterized by various growth forms branching robust branching massive tabular and encrusting that form the initial frameworks and 2 the microbial communities developed in the primary cavities of those frameworks a few meters 1 5 to 6 m below the living coral reef surface where they heavily encrusted the coralgal assemblages to form microbialite crusts the dating results demonstrate the occurrence of two distinctive generations of microbialites the reefal microbialites which developed a few hundred years after coralgal communities in shallow water environments whereas the slope microbialites grew a few thousands of years later in significantly deeper water conditions after the demise of coralgal communities the development of microbialites was controlled by the volume and the shape of the primary cavities of the initial reef frameworks determined by the morphology and the packing of coral colonies the most widespread microbialite development occurred in frameworks dominated by branching thin encrusting tabular and robust branching coral colonies which built loose and open frameworks typified by a high porosity 50 in contrast their growth was minimal in compact coral frameworks formed by massive and thick encrusting corals where primary cavities yielded a low porosity 30 and could not host a significant microbialite expansion

the geochemistry of late archaean microbial carbonate implications for ocean chemistry and continental erosion history trace element concentrations and combined sr and nd isotope compositions were determined on stromatolitic carbonates microbialites from the 2 52 ga campbellrand carbonate platform south africa shale normalised rare earth element and yttrium patterns of the ancient samples are similar to those of modern seawater in having positive la and y anomalies and in being depleted in light rare earth elements in contrast to modern seawater and microbialite proxies the 2 52 ga samples lack a negative ce anomaly but possess a positive eu anomaly these latter trace element characteristics are interpreted to reflect anoxic deep ocean waters where unlike today hydrothermal fe input was not oxidised and scavenged and rare earth elements were not coprecipitated with fe oxyhydroxides the persistence of a positive eu anomaly in relatively shallow campbellrand platform waters indicates a dramatic reversal from hydrothermally dominated archaean to continental erosion dominated phanerozoic rare earth element flux ratio the dominant hydrothermal input is also expressed in the initial sr and nd isotope ratios there is collinear variation in sr nd systematics which range from primitive values 87sr 86sr of 0 702386 and end of 2 1 to more evolved crustal ratios mixing calculations show that the range in trace element ratios e g y ho and initial isotope ratios is not a result of contamination by trapped sediment but that the chemical and isotopic variation reflects carbonate deposition in an environment where different water masses mixed calculated nd flux ratios yield a hydrothermal input into the 2 52 ga oceans one order of magnitude larger than continental input such a change in flux ratio most likely required substantially reduced continental inputs which could in turn reflect a plate tectonic causation e g reduced topography or expansion of epicontinental seas

a rare earth element signature of bacteria in natural waters abstract this study shows that rare earth element ree distribution patterns between bacteria and water for five different bacterial strains bacillus subtilis escherichia coli alcaligenes faecalis shewanella putrefaciens and pseudomonas fluorescens exhibit a steep increase in the heavy ree hree part of the distribution pattern and a weak peak around the middle ree mree part though the ree patterns for b subtilis and e coli were already reported in our previous paper takahashi y ch tellier x hattori k h kato k fortin d 2005 adsorption of rare earth elements onto bacterial cell walls and its implication for ree sorption onto natural microbial mats chem geol 219 53 67 the present results clearly show that the characteristic ree pattern is commonly observed for various bacterial species in addition similar ree patterns were observed for bioflims containing neutrophilic iron oxidizers and other bacteria formed in a groundwater discharge area in the budo pond in hiroshima japan suggesting that the ree distribution pattern found in the laboratory experiments was reproduced in naturally occurring bacteria in fresh waters in addition the ree pattern characterized by a maximum at mree and an increase at hree was also observed in fe oxyhydroxide precipitates formed below the same biofilm which contained bacterial remnants these results show that the presence of bacteria in natural fe oxyhydroxides and possibly in other natural minerals can be reflected in the shape of ree patterns such results could potentially be extended to geological materials such as banded iron formation bif and used to discuss the effect of microbial activity on the formation of bif although there are still many problems related to the extrapolation of the results obtained for fe oxyhydroxides in modern water systems to bif such as abiotic processes and post depositional alteration of the ree patterns our study suggests that the ree pattern can be used as another tool to assess the role of bacteria in mineral formation in natural waters

mineral equilibrium modelling and calculated chemical potential relations of reaction textures in the ultrahigh temperature in ouzzal terrane in hihaou area western hoggar algeria

rare earth element geochemistry of late devonian reefal carbonates canning basin western australia confirmation of a seawater ree proxy in ancient limestones rare earth element and yttrium ree y concentrations were determined in 49 late devonian reefal carbonates from the lennard shelf canning basin western australia shale normalized sn ree y patterns of the late devonian samples display features consistent with the geochemistry of well oxygenated shallow seawater a variety of different ancient limestone components including microbialites some skeletal carbonates stromatoporoids and cements record seawater like ree y signatures contamination associated with phosphate fe oxides and shale was tested quantitatively and can be discounted as the source of the ree y patterns co occurring carbonate components that presumably precipitated from the same seawater have different relative ree concentrations but consistent ree y patterns clean devonian early marine cements n 3 display ree y signatures most like that of modern open ocean seawater and the highest y ho ratios e g 59 and greatest light ree lree depletion average nd sn yb sn 0 413 sd 0 076 however synsedimentary cements have the lowest ree concentrations e g 405 ppb non contaminated devonian microbialite samples containing a mixture of the calcimicrobe renalcis and micritic thrombolite aggregates in early marine cement n 11 have the highest relative ree concentrations of tested carbonates average total ree 11 3 ppm stromatoporoid skeletons unlike modern corals algae and molluscs also contain well developed seawater like ree patterns samples from an estuarine fringing reef have very different ree y patterns with lree enrichment nd sn yb sn 1 possibly reflecting inclusion of estuarine colloidal material that contained preferentially scavenged lree from a nearby riverine input source hence devonian limestones provide a proxy for marine ree geochemistry and allow the differentiation of co occurring water masses on the ancient lennard shelf although appropriate partition coefficients for quantification of devonian seawater ree concentrations from out data are unknown hypothetical devonian canning basin seawater ree patterns were obtained with coefficients derived from modern natural proxies and experimental values resulting devonian seawater patterns are slightly enriched in lree compared to most modem seawaters and suggest higher overall ree concentrations but are very similar to seawaters from regions with high terrigenous inputs our results suggest that most limestones should record important aspects of the ree geochemistry of the waters in which they precipitated provided they are relatively free of terrigenous contamination and major diagenetic alteration from fluids with high non seawater like ree contents hence we expect that many other ancient limestones will serve as seawater ree proxies and thereby provide information on paleoceanography paleogeography and geochemical evolution of the oceans copyright c 2004 elsevier ltd

petrogenesis of a type granitoids from the alto moxoto and alto pajeu terranes of the borborema province ne brazil constraints from geochemistry and isotopic composition abstract a type granitoids 512 ma either intruded into paleoproterozoic gneiss of the alto moxoto terrane prata complex and serra da engabelada pluton or into early neoproterozoic metavolcanic metasedimentary sequence of the alto pajeu terrane serrote santo antonio pluton constitute a small proportion of brasiliano pan african granitoids in the central tectonic domain of the borborema province northeastern brazil the prata complex consists of syenogranites monzogranites mafic enclaves of diorites and norites the felsic and mafic members are not genetically related through fractionation mingling and mixing were extensive processes within the prata complex the granites evolution appears to have involved fractionation of alkali feldspar biotite apatite and sphene without significant wall rock assimilation the serra da engabelada and serrote santo antonio plutons consist of biotite syenogranites with rare mafic enclaves the studied granitoids are dominantly metaluminous characterized by fe rich biotite and fe hornblende high total alkalis y nb and ree and low cao mgo and sr abundances and high feo feo mgo ratios characterize these granitoids chondrite normalized ree patterns show enriched lree moderate to strong negative eu anomalies and more or less flat heavy ree the studied granitoids and diabase from dykes and enclaves show negative end 512ma values 14 to 10 high incompatible elements such as lile hfse and ree suggesting important contribution of paleoproterozoic crust the origin of the granites is thought to have involved partial melting of granodioritic or tonalitic lower crust such isotopic signature of the diabase from the dykes also reflects a paleoproterozoic enriched lithospheric mantle in the area the intrusion of the studied granitoids contemporary with sub volcanic bimodal magmatism and deposition of many cambrian pull apart basins in the north and central tectonic domain of the borborema province suggest intrusion during post tectonic relaxation of the brasiliano orogeny following the assembly of west gondwana

fluorine geochemistry of basaltic rocks from continental and oceanic regions and petrogenetic application fluorine contents in about 300 samples of various types of basalts and related rocks from continental southwestern u s a zaire deccan and south africa and oceanic regions hawaii and mid atlantic ridge between 23 n and 40 n were determined by a selective ion electrode method

giant subtidal stromatolites forming in normal salinity waters we report here the discovery of giant lithified subtidal columnar stromatolites 2 m high growing in 7 8 m of clear oceanic water in current swept channels between the exuma islands on the eastern bahama bank they grow by trapping ooid and pelletal carbonate sand and synsedimentary precipitation of carbonate cement within a field of giant megaripples the discovery is important to geologists and biologists because similar organo sedimentary structures built by a combination of cementation and the trapping of sediment by microbes were the dominant fossil types during the precambrian stromatolites are thought to have been responsible for the production of free oxygen and thus the evolution of animal life1 2 until the discovery of small lithified subtidal columnar stromatolites in the bahamas3 the only subtidal marine examples known to be living while undergoing lithification were in the hypersaline waters of hamelin pool at shark bay western australia4 7 shark bay stromatolites range from intertidal to the shallow subtidal with the larger columns reaching 1 m in height the shark bay stromatolites have strongly influenced geological interpretation by analogy many ancient stromatolites have been considered to have grown in intertidal and or hypersaline conditions8 although hypersalinity was not a necessity for growth during the precambrian because grazing metazoan life had not then evolved

ultra high temperature metamorphism and multistage decompressional evolution of sapphirine granulites from the palni hill ranges southern india sapphirine granulites from a new locality in the palni hill ranges southern india occur in a small enclave of migmatitic highly magnesian metapelites mg 85 72 within massive enderbitic orthogneiss they show a variety of multiphase reaction textures that partially overprint a coarse grained high pressure assemblage of bt opx ky grt pl qtz the sequence of reactions as deduced from the corona and symplectite assemblages together with petrogenetic grid considerations records a clockwise p t evolution with four distinct stages 1 equilibration of the initial high p assemblage in deep overthickened crust 12 kbar 800 900 c was followed by a stage of near isobaric heating presumably as a consequence of input of extra heat provided by the voluminous enderbitic intrusives during heating kyanite was converted to sillimanite and biotite was involved in a series of vapour phase absent melting reactions which resulted in the ultra high temperature assemblage opx crd kfs spr sil grt qtz bt coexisting with melt equilibration at c 950 1000 c 11 10 kbar 2 subsequently as a result of decompression of the order of 4 kbar at ultra high temperature a sequence of symplectite assemblages opx sil spr spr crdopx spr crdopx crdopx crd spl crd spl developed at the expense of garnet orthopyroxene and sillimanite this stage of near isothermal decompression implies rapid ascent of the granulites into mid crustal levels possibly due to extensional collapse and erosion of the overthickened crust 3 development of late biotite through back reaction of melt with residual garnet indicates a stage of near isobaric cooling to c 875 c at 7 8 kbar i e relaxation of the rapidly ascended crust to the stable geotherm 4 a second period of near isothermal exhumation up to c 6 5 kbar 850 c is indicated by the partial breakdown of late biotite through volatile phase absent melting reactions available isotope data suggest that the early part of the evolutionary history stages 1 3 is presumably coeval with the early proterozoic metamorphism in the extended granulite terrane of the nilgiri biligirirangan and shevaroy hills to the north while the exhumation of the granulites from mid crustal levels stage 4 occurred only during the pan african thermotectonic event which led to the accretion of the kerala khondalite belt to the south

microbial biomineralization processes forming modern ca mg carbonate stromatolites abstract modern ca mg carbonate stromatolites form in association with the microbialmat in the hypersaline coastal lagoon lagoa vermelha brazil thestromatolites although showing diversi ed fabrics characterized by thin orcrude lamination and or thrombolitic clotting exhibit a pervasive peloidalmicrofabric the peloidal texture consists of dark micritic aggregates of veryhigh mg calcite and or ca dolomite formed by an iso oriented assemblage ofsub micron trigonal polyhedrons and organic matter limpid acicular crystalsof aragonite arranged in spherulites surround these aggregates unlike thearagonite crystals organic matter is present consistently in the dark micriticcarbonate comprising the peloids this organic matter is observed as sub micron at and lamentous mucus like structures inside the interspaces of thehigh mg calcite and ca dolomite crystals and is interpreted as the remains ofdegraded extracellular polymeric substances moreover many fossilizedbacterial cells are associated strictly with both carbonate phases these cellsconsist mainly of 0ae2to4lm in diameter sub spherical rod like and lamentous forms isolated or in colony like clusters the co existence offossil extracellular polymeric substances and bacterial bodies associated withthe polyhedrons of ca mg carbonate implies that the organic matter andmicrobial metabolism played a fundamental role in the precipitation of theminerals that form the peloids by contrast the lack of extracellular polymericsubstances in the aragonitic phase indicates an additional precipitationmechanism the complex processes that induce mineral precipitation in themodern lagoa vermelha microbial mat appear to be recorded in the studiedlithi ed stromatolites sub micron polyhedral crystal formation of high mgcalcite and or ca dolomite results from the coalescence of carbonatenanoglobules around degraded organic matter nuclei sub micron polyhedralcrystals aggregate to form larger ovoidal crystals that constitute peloids subsequent precipitation of aragonitic spherulites around peloids occurs asmicro environmental water conditions around the peloids change keywords bacterial fossils biomineralization microbialite nanoglobules peloids stromatolites

fine grained agglutinated elongate columnar stromatolites tieling formation ca 1420 ma north china the mesoproterozoic tieling formation near jixian northern china contains thick beds of vertically branched laterally elongate columnar stromatolites carbonate mud is the primary component of both the stromatolites and their intervening matrix its abundance is attributed to water column whiting precipitation stimulated by cyanobacterial photosynthesis neomorphic microspar gives the stromatolites a streaky microfabric and small mud flakes are common in the matrix the columns consist of low relief mainly non enveloping laminae that show erosive truncation and well defined repetitive lamination in plan view the columns form disjunct elongate ridges 10 cm wide separated by narrow matrix filled runnels the stromatolite surfaces were initially cohesive rather than rigid and prone to scour and are interpreted as current aligned microbial mats that trapped carbonate mud the pervasive ridge runnel system suggests scale dependent biophysical feedback between i carbonate mud supply ii current duration strength and direction and iii growth and trapping by prolific mat growth together these factors determined the size morphology and arrangement of the stromatolite columns and their laminae as well as their branching patterns alignment and ridge runnel spacing ridge runnel surfaces resemble ripple mark patterns but whether currents were parallel and or normal to stromatolite alignment remains unclear the formation and preservation of tieling columns required plentiful supply of carbonate mud mat building microbes well adapted to cope with this abundant sediment and absence of both significant early lithification and bioturbation these factors were time limited and tieling stromatolites closely resemble coeval examples in the belt purcell supergroup of laurentia the dynamic interactions between mat growth currents and sediment supply that determined the shape of tieling columns contributed to the morphotypical diversity that characterizes mid late proterozoic branched stromatolites this article is protected by copyright all rights reserved

flat pebble conglomerate its multiple origins and relationship to metre scale depositional cycles carbonate flat pebble conglomerate is an important component of precambrian to lower palaeozoic strata but its origins remain enigmatic the upper cambrian to lower ordovician strata of the snowy range formation in northern wyoming and southern montana contain abundant flat pebble conglomerate beds in shallow water cyclic and non cyclic strata several origins of flat pebble conglomerate are inferred for these strata in one case all stages of development of flat pebble conglomerate are captured within stormdominated shoreface deposits of hummocky cross stratified hcs fine carbonate grainstone a variety of synsedimentary deformation structures records the transition from mildly deformed in situ stratification to buckled beds of partially disarticulated bedding to fully developed flat pebble conglomerate these features resulted from failure of a shoreface and subsequent brittle and ductile deformation of compacted to early cemented deposits failure was induced by either storm or seismic waves and many beds failed along discrete slide scar surfaces centimetre scale laminae within thick amalgamated hcs beds were planes of weakness that led to the development of platy clasts within partly disarticulated and rotated bedding of the buckled beds in some cases buckled masses accelerated downslope until they exceeded their internal friction completely disarticulated into clasts and transformed into a mass flow of individual cm to dm scale clasts this transition was accompanied by the addition of sand sized echinoderm rich debris from local sources which slightly lowered friction by reducing clast clast interactions the resulting dominantly horizontal clast orientations suggest transport by dense viscous flow dominated by laminar shear these flows generally came to rest on the lower shoreface although in some cases they continued a limited distance beyond fairweather wave base and were interbedded with shale and grainstone beds the clasts in these beds show no evidence of extensive reworking i e not well rounded or condensation i e no rinds or coatings a second type of flat pebble conglomerate bed occurs at the top of upward coarsening metre scale cycles the flat pebble conglomerate beds cap these shoaling cycles and represent either lowstand deposits or in some cases may represent transgressive lags the clasts are well rounded display borings and have iron rich coatings the matrix to these beds locally includes glauconite these beds were considerably reworked and represent condensed deposits thrombolites occur above the flat pebble beds and record microbial growth before initial transgression at the cycle boundaries a third

compositional variability of terrestrial mantle apatites thermodynamic modeling of apatite volatile contents and the halogen and water budgets of planetary mantles abstract apatites in ultramafic xenoliths from hawaii kamchatka nunivak island lunar crater volcanic field and the navajo volcanic field have variable volatile f cl oh compositions that correlate with their petrogenesis apatites in metasomatized lherzolite harzburgite xenoliths are relatively cl rich whereas apatites in igneous pyroxenite and amphibolite xenoliths are relatively f rich our results support the generalization of o reilly and griffin 2000 that metasomatic apatites tend to be cl rich and magmatic apatites tend to be f rich mantle metasomatism may largely be the consequence of devolatilization of cl rich fluids from subducted lithosphere however the occurrence of metasomatic xenoliths far removed from subduction zones e g bullenmerri as well as the geochemistry of cl in some plume basalts and diamonds indicates that not all metasomatism is subduction triggered thermodynamic modeling of the influence on apatite compositions of variable f cl h2o and p abundances as well as temperature is consistent with the idea that terrestrial mantle fluids are h2o rich and that halogen enrichment in terrestrial apatites need not represent large absolute halogen abundances in the fluids the models indicate that the occurrence of volatile poor calcium phosphate merrillite whitlockite in the martian and terrestrial mantles is facilitated by halogen and phosphorus rich and water poor environments the rarity of this assemblage in the terrestrial mantle compared to mars is consistent with the relatively wet and halogen and phosphorus poor nature of the terrestrial mantle compared to that of mars

reversed experiments on biotite quartz feldspar melting in the system kmash implications for crustal anatexis melting temperatures of biotite quartz and biotite quartz feldspar assemblages in the system k 2 o mgo al 2 o 3 sio 2 h 2 o have been determined in the pressure range 0 5 18 kbar the subsolidus dehydration of biotite quartz also has been investigated from 300 to 500 bars the melting equilibria studied are phlogopite quartz sanidine vapor liquid o phlogopite quartz vapor enstatite liquid k phlogopite quartz enstatite liquid k v and phlogopite quartz sanidine enstatite liquid v at 10 kbar the o reaction occurs at 700 720 c the k reaction at 780 790 c the k v reaction at 815 850 c and the v reaction at 800 850 c vapor saturated reactions were reversed isobarically in two stage experiments in which the starting assemblage was held at a temperature 10 above the temperature of previously observed melting for a duration equivalent to an initial melting experiment followed by lowering of the temperature below the temperature of initial mel

anorogenic alkaline granites from northeastern brazil major trace and rare earth elements in magmatic and metamorphic biotite and na mafic minerals abstract the anorogenic alkaline silica oversaturated serra do meio suite is located within the riacho do pontal fold belt northeast brazil this suite assumed to be paleoproterozoic in age encompasses metaluminous and peralkaline granites which have been deformed during the neoproterozoic collisional event preserved late magmatic to subsolidus amphiboles belong to the riebeckite arfvedsonite and riebeckite winchite solid solutions riebeckite winchite is frequently rimmed by ti aegirine ti aegirine cores are strongly enriched in nb y hf and ree which significantly decrease in concentrations towards the rims ree patterns of ti aegirine are strikingly similar to ti pyroxenes from the ilimaussaq peralkaline intrusion recrystallisation of mineral assemblages was associated with deformation although some original grains are still preserved magmatic annite was converted into magnetite and biotite with lower fe fe mg ratios recrystallised amphibole is pure riebeckite magmatic ti na bearing pyroxene was converted to low ti aegirine titanite astrophyllite aenigmatite the reaction riebeckite quartz aegirine magnetite quartz fluid is also observed biotite and na mafic minerals recrystallised under metamorphic oxidising conditions corresponding to temperatures of 600 c between the ninio and hm buffers

dehydration melting phenomena in leptynitic gneisses and the generation of leucogranites a case study from the kerala khondalite belt southern india

fluid absent melting of f rich phlogopite rutile quartz fluid absent melting is believed to be an important process in the generation of melts m the lower crust and upper mantle breakdown of phlogopite makes h 0 available and thus controls the conditions at which fluid absent melting occurs both f2andti in biotite ha e been shown to affect strongly the thermal stability of biotite to model better the fluid absenti eltmg of a ssemblagescontaining phlogopite the reaction f phlogopite quartz rutile enstatite melt has been studied experimentally experiments were pe o med at 7 10 and 15 kbar using a natural f rich phlogopite with a starting com os tion off f oh 0 43 and mg mg fe in molar proportions 0 94 results mdlcate that the therma l stability of f rich phlogopite quartz rutile is extended by as much as 450 c relative to the kmash system and by 300 c relative to the ti free f kmash system approach to equilibrium in the experiments was assessed by convergence of results of melting and crystallization experiments phlogopite compositions from e penmental products show that although f rich phlogopite incorporates relatively little ti 3 wt i02 the combination of f and ti increases the stability of phlogopite to considerably higher temperatures 300 0c than that of either component alone melts formed by the fluid absent melting off rich phlogopite quartz rutile at temperatures 1000 care anitic and stro g1yperaluminous the compositions of these melts suggest that the formationofmetalummous to peralkaline a type granites by fluid absent melting of halogen enriched sources is unlikely

archaean ttgs as sources of younger granitic magmas melting of sodic metatonalites at 0 6 1 2 gpa two natural low k2o na2o ttg tonalitic gneisses one hornblende bearing and the other biotite bearing were partially melted at 0 8 1 2 gpa fluid absent the chief melting reactions involve the breakdown of the biotite and hornblende the hornblende tonalite is slightly less fertile than the biotite tonalite but melt volumes reach around 30 at 1 000 c this contrasts with results of most previous work on more potassic ttgs which generally showed much lower fertility though commonly producing more potassic melts garnet is formed in biotite bearing tonalitic protoliths at p 0 8 gpa and at 1 0 gpa in hornblende bearing tonalitic protoliths all fluid absent experiments produced peraluminous granitic to granodioritic melts typically with sio2 70 wt for the biotite tonalite increasing t formed progressively more melt with progressively lower k2o na2o however the compositions of melts from the hornblende tonalite do not vary significantly with t with increasing p melts from the biotite tonalite become less potassic due to the increasing thermal stability of biotite for the hornblende tonalite again there is no consistent trend fluid absent melting of sodic ttgs produces melts with insufficient k2o to model the magmas that formed the voluminous late potassic granites that are common in archaean terranes reconnaissance fluid present experiments at 0 6 gpa imply that h2o saturated partial melting of ttgs is also not a viable process for producing magmas that formed these granites the protoliths for these must have been more potassic and less silicic nevertheless at granulite facies conditions sodic ttgs will produce significant quantities of broadly leucogranodioritic melt that will be more potassic than the protoliths upward abstraction of this melt would result in some lile depletion of the terrane younger k rich magmatism is unlikely to represent recycling of ttg crust on its own and it seems most likely that evolved crustal rocks and or highly enriched mantle must be involved

rare earth element and nd isotopic variations in regionally extensive dolomites from the burlington keokuk formation mississippian implications for ree mobility during carbonate diagenesis abstract marine carbonates of the burlington keokuk fm miss of the midcontinent region have been subject to two major episodes of regionally extensive 100 000 km2 dolomitization previous studies of the cathodoluminescent petrography sr c and o isotopic compositions and sr fe mn and ca concentrations of burlington keokuk dolostones outline a diagenetic history in which lime mud was pervasively dolomitized by a seawater dominated fluid at many localities this early dolomite generation dolomite i was recrystallized by nonmarine diagenetic fluids at shallow burial depths to produce dolomite ii dolomites i and ii have similar rare earth element ree patterns and abundances and a narrow range of initial 143nd 144nd isotope ratios of 0 511906 0 000025 1 this consistency in the nd isotope ratios and ree patterns along with the presence of anomalously low abundances of cerium in the dolomites cherts glauconite pellets fish apatite and crinoids suggests that 1 seawater derived ree dominated the system and 2 the extensive water rock interaction that produced profound textural and compositional changes during the formation of dolomite ii did not significantly alter the ree patterns or nd isotopic signatures of the dolomites the results of quantitative modeling of isotopic and trace lement exchange during water rock interaction in carbonate systems indicate that extremely large water rock ratios are required to alter the ree signatures of diagenetic carbonates such large water rock ratios can reflect either 1 large extents of fluid flow during carbonate recrystallization or 2 minimal interaction between diagenetic fluids and host rocks during carbonate cement crystallization late vug filling calcite and dolomite have low sm nd and high ce nd n ratios relative to the dolostones such distinct ree signatures probably reflect limited interaction between late diagenetic fluids and burlington keokuk host rocks penecontemporaneous clastic sediments have similar initial 143nd 144nd isotope ratios 0 511857 0 511877 and lower sm nd ratios compared to the dolomites suggesting 1 a common crustal source of ree for the clastics and carbonates and 2 ree fractionation during the formation of carbonate apatite glauconite and other authigenic phases in the marine environment

fluorine end member micas and amphiboles the near end member minerals fluorphlogopite xf 0 96 and fluortremolite xf 0 82 have been found in grenville marbles near balmat new york these micas and amphiboles like other fluorine rich minerals reported in the literature are extremely low in iron the substitution of f for oh is partly responsible for stabilizing these minerals in the granulite facies marbles of the adirondacks fluorine rich amphiboles and micas are more common than generally recognized a literature review shows that many amphiboles and micas have more than fifty percent of the interlayer site occupied by fluorine this degree of solid solution qualifies these phases as independent minerals but they are not currently recognized by the i m a we propose that fluorbiotite fluorphlogopite fluoractinolite fluorarfvedsonite fluoredenite fluorhastingsite fluorpargasite fluorrichterite fluorriebeckite fluortremolite fluoredenitic hornblende fluorhastingsitic hornblende fluorpargasitic hornblende fluortremolitic hornblende fluorferro edenite and fluormagnesio arfvedsonite be formally applied as mineral names for these phases identification of the mineralogically and petrologically important solid solution of fluorine for hydroxyl is currently obscured by use of names that imply hydroxyl end members

f rich phlogopite stability in ultra high temperature metapelites from the napier complex east antarctica fluorine rich phlogopite f content up to 8 wt f f oh 0 9 in ultra high temperature metapelitic granulites from the napier complex east antarctica is associated with aluminous orthopyroxene osumilite sapphirine garnet and quartz textural relationships imply that some of the phlogopite is of primary origin and stable under ultra high temperature conditions this is in accord with recent experimental evidence on the stability of f rich phlogopite because the f rich phlogopite also occurs as rounded inclusions in aluminous orthopyroxene al 2 o 3 up to 12 8 wt sapphirine osumilite and garnet it is inferred that the ultra high temperature mineral assemblages which includes these minerals formed during prograde partial melting reactions at the expense of phlogopite at a depth of less than 30 km thus the coarse grained peak metamorphic assemblages formed below 9 kbar and there is no evidence the rocks underwent any significant degree of decompression during or soon after peak metamorphic conditions the phlogopite breakdown reactions we suggest on the basis of textural arguments differ from those postulated from experiments on f free systems

high energy coralgal stromatolite frameworks from holocene reefs tahiti french polynesia drill cores from holocene reefs on tahiti french polynesia reveal a framework composed of massive branching acroporids encrusted by coralline algae associated with sessile vermetid gastropods and arborescent foraminifers laminated micritic crusts form coatings over coral branches or more commonly over related encrusting organisms throughout the cored reef sections these crusts appear as a major structural and volumetric component of the reef framework the microbial nature of these micritic crusts is inferred from their typical organic growth forms and geometry the occurrence of microbial remains and stable isotope measurements the reef communities accumulated at depths less than 5 m below mean sea level in a high energy environment throughout vertical growth from 7140 170 yr bp to the present the nature of the involved benthic communities stable isotope data and high calcification rates of microbially encrusted corals strongly suggest that local environmental conditions have been optimal for reef development for the last 7000 years the causes of the predominance of microbial communities over actual encrusters red algae foraminifers remain problematic and could be related to short term fluctuations in ecological parameters microbial micritic crusts seemingly played a prominent role in protecting the coralgal colonies from bioeroders and grazers and possibly in strengthening the framework due to rapid lithification the record of similar microbial crusts in other quaternary reef tracts suggests that microbial communities may have played a more prominent role in quaternary reefs than presently recognized

inferred syngenetic textural evolution in holocene cryptic reefal microbialites heron reef great barrier reef australia cryptic microbialites in the heron reef framework occur as crusts of fingerlike microcolumns or branching dendrolites rarely more than 1 cm long microstructure of the most recently growing microbialite surfaces consists of coalesced 3 m scalenohedra that are indistinguishable from previously described mg calcite abiotic cement the transformation from submicrometer anhedral crystallites to 3 m scalenohedra is inferred to have occurred only during active microbialite accretion beneath a biofilm this syngenetic change from primary biologically induced microstructures to microstructures that are indistinguishable from abiotic cement has important implications for the recognition and interpretation of early marine microcrystalline carbonates and cements

regional scale grenvillian age uht metamorphism in the mollendo camana block basement of the peruvian andes the mollendo camana block mcb is a 50 150 km precambrian inlier of the andean belt that outcrops along the pacific coast of southern peru it consists of stromatic migmatites of paleoproter ozoic heritage intensely metamorphosed during the grenville event c 1 ga u pb and u th pb ages on zircon and monazite in the migmatites aluminous mesosomes fmas and quartzofeldspathic leucosomes kfmash contain various amounts of k feldspar kfs orthopyroxene xmg opx 0 86 plagioclase pl sillimanite sil exceptionally kyanite ky ilmenite ilm magnetite mag quartz qtz and minor amounts of garnet xmg grt 0 60 sapphirine xmg spr 0 87 cordierite xmg crd 0 92 and biotite xmg bt 0 83 the ubiquitous peak mineral assemblage is opx sil kfs qtz grt in most of the mcb which together with the high al content of orthopyroxene 10 al2o3 and the local coexistence of sapphirine quartz attest to regional uht metamorphism 900 c at pressures in excess of 1 0 gpa fluid absent melting of biotite is responsible for the massive production of orthopyroxene that proceeded until exhaustion of biotite and most of the garnet in the southern part of the mcb mollendo cocachacra areas in this area a first stage of decompression from 1 1 1 2 to 0 8 0 9 gpa at temperatures in excess of 950 c is marked by the breakdown of sil opx to spr opx crd assemblages according to several bivariant fmas reactions high t decompression is also shown by mg rich garnet being replaced by crd spr and crd opx bearing symplectites and reacting with quartz to produce low al opx sil symplectites in quartz rich migmatites neither osumilite nor spinel quartz assemblages being formed isobaric cooling at about 0 9 gpa probably followed the initial decompression and proceeded with massive precipitation of melts towards the os invariant point as demonstrated by bt qtz pl symplectites in quartz rich migmatites melt opx sil bt grt kfs qtz finally opx rims around secondary biotite attest to late fluid absent melting compatible with a second stage of decompression below 900 c the two stages of decompression are interpreted as due to rapid tectonic denudation whereas the regional extent of uht metamorphism in the area probably results from large scale penetration of hot asthenospheric mantle at the base of an over thickened crust

titanium substitution in biotite an empirical model with applications to thermometry o2 and h2o barometries and consequences for biotite stability abstract an empirical model for solution of ti in biotite is developed and calibrated on the basis of various equilibria among biotite and ti saturating assemblages sources of data used for the calibration include both experimental products and published analyses of natural assemblages ti solution in biotite can be satisfactorily modelled by means of the exchange component tife 2 whose non ideal behavior can be approximated empirically by means of a linear function of the relative concentrations of ti and octahedral al in biotite within assemblages which fix the chemical potential of the exchange component tife 2 the concentration of this component in biotite is very sensitive to temperature and oxygen fugacity making it possible to use biotite oxide assemblages to obtain reliable t and f o 2 estimates in igneous and metamorphic rocks in assemblages which also contain alkali feldspar it is possible to use breakdown equilibria of ti additive components in biotite to estimate h 2 o fugacity such uses are likely to find important applications in rocks in which other assemblages sensitive to temperature f o 2 and or f h 2 o are absent in general rocks containing a single oxide phase plus biotite as the only mafic silicate phase alkali feldspar the empirical model for solution of ti in biotite also allows to calculate the loci of various terminal reactions for the assemblage titanian biotite quartz which by comparison with equivalent equilibria in ti free systems provide insight into the effect of ti on the stability of biotite solubility of ti in biotite increases with temperature in a strongly non linear fashion as a consequence calculations predict that the effect of ti on the stability of biotite is very small up to conditions typical of the beginning of the granulite facies of metamorphism but beyond those conditions ti concentration increases markedly and biotite is rendered very refractory at mid to deep crustal pressures 10 kbar the vapor absent solidus of biotite quartz in rocks containing ti saturating phases is likely to exceed 900 c even in bulk compositions with subequal concentrations of fe and mg

titanium aluminum and interlayer cation substitutions in biotite from high grade gneisses west greenland detailed electron microprobe study pelitic to mafic metamorphic rocks from two localities higher ti k k na and possible k na similar al iv and lower al vi in granulite vs amphibolite grade samples modified journal abstract

mid neoproterozoic biostratigraphy and isotope stratigraphy in australia abstract palynomorph and stromatolite assemblages from mid neoproterozoic strata of australia appear highly significant when collated with results obtained from isotope stratigraphy and allow correlation across the centralian superbasin and adelaide rift complex the majority of palynomorphs from the lower mid neoproterozoic 830 ma have limited biostratigraphic value although a few apparently have restricted ranges carbonates at this stratigraphic level contain the distinctive stromatolite acaciella australica and other taxa of the acaciella australica stromatolite assemblage these carbonates have 13ccarb values of between 4 and 0 and associated anhydrite has 87sr 86sr ratios of 0 7069 these depleted 13ccarb values are immediately preceded by values of 6 1 in the western officer and amadeus basins of the centralian superbasin similar c and sr isotopic features are seen in the similarly aged upper shaler supergroup of canada upper mid neoproterozoic 760 ma carbonates contain the distinctive stromatolite baicalia burra and other stromatolites of the baicalia burra stromatolite assemblage siliciclastic horizons in the same interval contain the acritarch cerebrosphaera buickii and have 13ccarb values of between 0 and 8 the highest mid neoproterozoic 13ccarb values of between 6 7 and 8 1 occur within the stratigraphic range of c buickii in australia in the western officer basin and adelaide rift complex the mid neoproterozoic 13ccarb peaks are preceded by values of ca 0 the apparently restricted range of c buickii in australia suggests the need for reinterpretation of the stratigraphic position of its occurrence in the svanbergfjellet formation akademikerbreen group spitsbergen which was previously considered a post sturtian glacial deposit

nb and zr behavior in rutile during high grade metamorphism and retrogression an example from the ivrea verbano zone abstract detailed textural observations and in situ analyses emp sims and la icp ms are used to characterize trace element behavior during prograde and retrograde metamorphic reactions involving rutile the ivrea verbano zone is a classic granulite area and rocks from the strona and d ossola valleys are an example of the amphibolite to granulite facies transition although different rock types occur in the area detailed sampling and petrographic work show that rutile only occurs in granulite facies paragneisses these rocks show a rich inventory of textures that allow not only for the investigation of trace element behavior in response to prograde rutile growth but also for the effect of post peak processes on rutile chemistry nb concentrations in rutile from lower grade samples show a larger spread from 500 to 5000 ppm within one sample when compared to those from higher grades this pattern can be modeled using prograde rutile growth formed from biotite breakdown zr concentrations in rutile are characterized by an anomalously large spread and a bimodal distribution maximum zr concentrations increase according to the general metamorphic gradient known for this area temperatures from zr in rutile thermometry although feasible are considerably higher than previous calculations increasing from ca 850 to 930 c a second cluster of zr concentrations in rutile occurs at rather constant concentrations ca 1000 ppm for all localities and is interpreted to be related to intense fluid influx at high temperature and or to post peak diffusional resetting favored by slow cooling rates alteration textures characterized by a complex network of micro veins are evidence for the late fluid influx the fluid strongly affected the rutiles which is evidenced by corrosion of older rutile grains and formation of rutile veinlets

metamorphic p t conditions of the kerala south india khondalite belt a granulite facies supracrustal terrain the khondalite belt of southernmost india is an immense section of granulite facies metasediments of probable early proterozoic age dominant rock types are migmatized khondalites garnet sillimanite pm cordierite metapelites acid biotite garnet graphitic gneisses and charnockites quartzofeldspathic gneisses with orthopyroxene throughout much of southern kerala the biotite gneisses are in a state of arrested conversion to charnockite partially decrepitated co 2 inclusions in quartz at the ponmudi mixed biotite gneiss charnockite quarry have significant ch 4 and or n 2 and are texturally late the probable sequence of events in metasediments was 1 migmatization 2 charnockite formation 3 symplectitic cordierite formation and 4 late co 2 entrapment phase equilibrium diagrams of anatexis in aluminous systems and fe mg exchange between garnet and biotite indicate metamorphic temperatures of 650 850 c for the khondalites temperatures based on garnet orthopyroxene

rare earth elements and yttrium in seawater icp ms determinations in the east caroline coral sea and south fiji basins of the western south pacific ocean abstract using inductively coupled plasma mass spectrometry icp ms vertical profiles of yttrium and all the rare earth elements rees in seawater were obtained at three locations in the western south pacific the east caroline coral sea and south fiji basins based on the data we have analyzed the inter ree iii relationships and found that ree iii s heavier than dy and particularly close neighbors show strong coherencies in their oceanic behavior considering that the heavy ree iii s are less particle reactive than the light and middle ree iii s and that they have very tight correlations with regressions passing almost through the origin the neighboring element ratios of the heavy ree iii s behave virtually conservatively and are suitable as tracers of water masses the dy ho er system is practically good because its dynamic range signal to noise ratio is large in the ocean the highest ho dy ratios 0 31 are found in intermediate and deep waters throughout the western south pacific which overlie the antarctic bottom water with a low ho dy ratio 0 27 these high ho dy waters are probably formed in the polar and subantarctic frontal zone and advect northward ree iii data provide better insights into the deep water recirculation in the south pacific than those discussed based upon the regular oceanographic properties alone

establishing criteria to distinguish oil seep from methane seep carbonates hydrocarbon seeps harbor copious chemosynthesis dependent life the traces of which are preserved in the fossil record within authigenic carbonates these environments are mostly characterized by seepage of methane rich fluids yet numerous crude oil dominated seeps have been discovered in recent years oil seepage has a profound influence on the local fauna but recognizing such seeps in the rock record remains elusive this study presents new geochemical data that will allow for a more confident identification of ancient oil seep deposits geochemical data from modern and ancient seep limestones reveal that oil dominated seep carbonates are enriched in rare earth elements and uranium compared to their methane dominated counterparts these trace element patterns have the potential to serve as a basis for an improved understanding of the adaptation of chemosynthetic life to oil seepage and to better constrain the marine carbon cycle in the geologic past

nucleation of calcium carbonate on bacterial nanoglobules nucleation of calcium carbonate on microbial cell material may have been the dominant mode of microbial carbonate formation during most of earth s history current knowledge predicts that nucleation takes place on the cell surface or on extracellular polymeric substances however the initial nucleation steps have not been described in detail and the process remains elusive here we describe the bacterial nucleation of calcium carbonate at the nanometer scale in our precipitation experiment with sulfate reducing bacteria srb the bulk of calcium carbonate precipitates on hundreds of individual globules 60 200 nm in diameter globules originate from the srb cell surface but calcify significantly only when released to the culture medium similar globules have been observed albeit at a much larger scale in other bacterial precipitation experiments and in many natural microbial carbonates suggesting that the process we describe could be an important step in microbial calcification

3 43 billion year old stromatolite reef from the pilbara craton of western australia ecosystem scale insights to early life on earth abstract the 3 43 billion year old strelley pool chert pilbara craton western australia contains compelling evidence of early archaean life in the form of kilometre sized remnants of an ancient stromatolitic carbonate platform reviewing and building on earlier studies we examine the fossilized remains of the platform to seek ecosystem scale insights to earth s early biosphere examining the evidence for biosedimentation and the importance and effect of different environmental processes on biological activity both vertical and lateral trends show that stromatolite abundance and diversity are greatest in the area interpreted as an isolated partially restricted peritidal marine carbonate platform or reef where there is virtually no trace of hydrothermal or terrigenous clastic input in contrast stromatolites are poorly developed or absent among hydrothermal volcaniclastic or terrigenous clastic sedimentary facies and are absent in deeper marine settings that are laterally equivalent to shallow marine stromatolitic facies hydrothermal veins some of which were previously interpreted as vents that exhaled fluids from which the stromatolitic structures precipitated are shown to postdate the stromatolites on the platform stromatolite facies associations varied between different palaeoenvironments but some stromatolite types occurred across different palaeoenvironments highlighting the combined influence of biological and environmental processes on stromatolite formation the regional distribution of stromatolites in the palaeoenvironment suggests a biological response to variations in water depth sediment influx and hydrothermal activity with stromatolite formation favoured by relatively normal shallow marine environments with low clastic chemical sedimentation rates and no direct input from high temperature hydrothermal systems the lithology structure and fabrics of the stromatolites and their close association with abundant evaporite crystal pseudomorphs indicate that evaporitic precipitation was probably the dominant non biological process that contributed to stromatolite formation the study supports a biological interpretation for the origin of the stromatolites and reveals compelling evidence for the conditions that favoured biological activity on the early earth and formation of macroscopic biosignatures that could be preserved for most of earth s history

high temperature metamorphism and the role of magmatic heat sources at the rogaland anorthosite complex in southwestern norway the rogaland complex covers 1000 km in southwestern norway and consists mainly of anorthosite massifs and the layered bjerkreim sokndal lopolith bsl these rocks intrude charnockitic migmatites containing intercalated marbles and garnetiferous migmatites high temperature mineral isograds pigeonite osumilite and orthopyroxene in the metamorphic basement are subparallel to and increase in grade towards the intrusive complex p t estimates from the country rocks show a roughly linear increase in temperature towards the bsl consistent with the distribution of isograds the peak p t conditions at 20 and 2 5 km from the contact at 5 kbar range from 700 to 41000 c field relations and age determinations link the high t metamorphism and the magmatism the two dimensional thermal modelling indicates that heat from a single magmatic cooling unit is not sufficient to produce the array of isograds and the peak metamorphic temperatures two magmatic episodes separated by 3myr however can account for the high temperature metamorphism in this model the emplacement and crystallization of the anorthosite produces a regional thermal gradient from 750 to 600 c after a brief hiatus a second smaller body bsl provides an additional thermal input that results in an array of high temperature isograds and country rock temperatures 41000 c

microscale observations of sulfate reduction correlation of microbial activity with lithified micritic laminae in modern marine stromatolites we report for the first time micrometer scale correlation of geologic and microbial processes in modern marine stromatolites precipitation of micritic laminae in these stromatolites was studied by comparing microstructure as observed in petrographic thin sections with microbial sulfatereduction activity two dimensional mapping of sulfate reduction rates was implemented by incubating a vertical section of a stromatolite face on silver foil coated with 35 so 4 2 our results show that sulfate reduction activity is high in zones of caco 3 precipitation and indicate that microbial activity produces lithified micritic laminae near the surface of the stromatolites similarities with micritic laminae in ancient stromatolites suggest that sulfate reduction may also have been an important mechanism of carbonate precipitation in these fossilized structures

the solubility of fluorite in h2o and h2o nacl at high pressure and temperature abstract the solubility of fluorite in h2o and h2o nacl has been measured at 600 1000 c 0 5 2 0 gpa in a piston cylinder apparatus fluorite dissolves congruently at all conditions investigated the data indicate that the concentration of fluorite dissolved in h2o is low at 600 c and 0 5 gpa 0 0014 mol kg h2o but increases strongly with temperature t and pressure p to 0 247 mol kg h2o at 1000 c 2 gpa the data were fit with the equation log mcaf2 6 587 2 774p1 2 2 266 10 3 4 699 10 4p t where mcaf2 is molality of caf2 t is in kelvin and p is in gpa fluorite solubility was also measured in h2o nacl fluids at 800 c and 1 0 gpa results indicate a strong increase in dissolved fluorite concentration with increasing nacl content from 0 028 mol kg h2o at xnacl 0 to 1 673 mol kg h2o at xnacl 0 486 where xnacl is the mole fraction of nacl in the fluid the data were fit to mcaf2 0 01035 1 141xnacl 4 694xnacl2 the results indicate that f mobility will be further enhanced by saline brines in high p t igneous and metamorphic environments high f solubility in h2o and h2o nacl in the deep crust and upper mantle can promote mobilization of high field strength elements rare earth elements u and th through transport as f bearing complexes

stromatolites in precambrian carbonates evolutionary mileposts or environmental dipsticks stromatolites are attached lithified sedimentary growth structures accretionary away from a point or limited surface of initiation though the accretion process is commonly regarded to result from the sediment trapping or precipitation inducing activities of microbial mats little evidence of this process is preserved in most precambrian stromatolites the successful study and interpretation of stromatolites requires a process based approach oriented toward deconvolving the replacement textures of ancient stromatolites the effects of diagenetic recrystallization first must be accounted for followed by analysis of lamination textures and deduction of possible accretion mechanisms accretion hypotheses can be tested using numerical simulations based on modern stromatolite growth processes application of this approach has shown that stromatolites were originally formed largely through in situ precipitation of laminae during archean and older proterozoic times but that younger proterozoic stromatolites grew largely through the accretion of carbonate sediments most likely through the physical process of microbial trapping and binding this trend most likely reflects long term evolution of the earth s environment rather than microbial communities

biochemical and ultrastructural evidence for the origin of whitings a biologically induced calcium carbonate precipitation mechanism we propose that bahamian whitings floating patches of lime mud are in part the result of biological precipitation of calcium carbonate induced by picoplankton and cellular components the cells may act as nucleation sites for crystallization from seawater supersaturated with caco3 our model represents a new hypothesis concerning bahamian whiting formation and is based on several lines of evidence biochemical data suggest that the macromolecules from carbonate suspended in bahama banks whitings are distinct from those found in the lime mud sediment producer penicillus and from bottom sediment direct ultrastructural evidence indicates that mineralization occurs on the surfaces of picoplankton cells and degrading organic cellular components the organic constituents include but are not restricted to whole and fragmented algal cells and composite structures 20 30 m in diameter the observed calcium carbonate crystals are distinct from skeletal debris because of the magnitude of the whiting phenomenon calculations of carbonate sediment production budgets should include the potential contribution of calcium carbonate produced by epicefular precipitation knowledge of carbonate mud genesis is critical to interpretation of ancient occurrences of lime mud as well as to understanding ancient and global carbon cycles

a comparative study of the rare earth element ree distributions within the lower cretaceous dolomites and limestones of central tunisia ree distribution strontium content and oxygen isotopic composition have been studied in the lower cretaceous dolomites and their interbedded and or parental limestones of central tunisia dolomites as indicated by previous sedimentologic geochemical and isotopic study are different in origin environments of dolomite formation include evaporitic sabkha deep phreatic karst and lacustrine with the exception of the sabkha environment dolomitizing fluids presumably have been essentially meteoric the comparison between ree distributions in dolomites and limestones clearly suggests that the general shapes of the ree patterns are preserved during dolomitization nevertheless the total ree amounts are somewhat lowered in dolomites comparatively to parental limestones moreover within the dolomites the total ree contents are positively correlated to the sr and 18o contents thus indicating that the decrease in ree sr and 18o contents is related to a decrease in the salinity of dolomitizing fluids in addition dolomites associated with emergence surfaces karst are the most impoverished in ree furthermore they are relatively enriched in light ree indicating a more or less important fractionation with the ree distributions this enrichment has been related to the influence of the inorganic complexes which favours the greatest solubility of the heavy ree in basic solution with respect to the lightest members of the ree group

geochemistry of late archaean stromatolites from zimbabwe evidence for microbial life in restricted epicontinental seas we report comprehensive trace element and sr isotope data for microbial carbonates from the archaean mushandike limestone masvingo greenstone belt zimbabwe the stromatolites have very coherent ree y patterns and share the essential shale normalised characteristics of other archaean marine precipitates positive la and gd anomalies absence of a negative cc anomaly and a strongly superchondritic y ho ratio mixing models constrain the maximum amount of shale contamination to 0 25 1 and calculated detritus free carbonate ree y systematics require precipitation from seawater in terms of light ree over heavy ree depletion however the studied samples are very different from all other known archaean marine precipitates in shale normalised plots the mushandike samples yield a negative slope a very restricted regional input source of the dissolved load is indicated because normalisation with locally occurring tonalite gneiss ree y data yields a pattern closely resembling typical shale normalised archaean marine chemical sediments the disappearance of a negative eu anomaly when patterns are normalised with local tonalite gneiss strengthens this interpretation sr isotope ratios are strongly correlated with trace element contents and ratios which explains the modest scatter in sr isotope ratios as representing minor clastic contamination importantly even the least contaminated samples have very radiogenic initial sr 87 sr 86 ratios 0 7184 implying sr input from an ancient high rb sr source such as the early archaean gneisses of south central zimbabwe a local ancient 3 5 3 8 ga source is also indicated by previously published pb isotope datasets for the mushandike stromatolites this is entirely compatible with the occurrence of 3 7 3 8 ga zircons in quartzites and metapelites from comparably old greenstone belts within less than 150 km of the studied locality comparison of the pb isotope ratios of the mushandike stromatolites with 2 7 and 2 6 ga old stromatolites from the neighbouring belingwe greenstone belt demonstrates differences in initial isotope composition that relate to the extent of exchange with the open ocean the development of numerous basins on old continental crust with water masses variably restricted from the open ocean suggests a lack of strong vertical topography on this late archaean craton c 2004 elsevier b v all rights reserved

geochemical and stable isotope signatures of proterozoic stromatolitic carbonates from the vempalle and tadpatri formations cuddapah supergroup india implications on paleoenvironment and depositional conditions abstract spectacular stromatolitic dolomites with varied morphological features are preserved in the vempalle and tadpatri formations of the proterozoic cuddapah basin eastern dharwar craton they exhibit stratifera columnar conical domal and spheroidal lobate morphologies in which columns are branched at some places in tadpatri formation based on their trace elements such as rey and stable isotope compositions carbon and oxygen the vempalle stromatolites have been classified as three types vempalle i stromatolites exhibit pronounced positive eu anomalies with small scale positive ce anomalies whereas vempalle ii counterparts have slight negative to positive eu feeble positive ce and positive gd anomalies vemaplle iii stromatolites display positive ce eu and gd anomalies the tadpatri formation stromatolites have pronounced gd anomalies with low order positive ce and eu anomalies significant depletion in 18o is observed in vempalle ranging from 10 70 to 7 07 and 20 73 to 11 87 in tadpatri formations the tadpatri stromatolites display negative 13c varying from 4 56 to 1 26 contrarily the vempalle stromatolites recorded both positive and negative 13c ranging from 0 24 to 2 00 thereby reflecting their deviation from the popular belief of the boring billion concept of displaying midproterozoic 13c stasis the flat ree patterns along with ce eu and gd anomalies chondritic to superchondritic y ho ratios collectively reflect on marine water conditions for their deposition with variable inputs of siliciclastic terrigenous materials and hydrothermal signatures these cherty dolomitic stromatolites were deposited in subtidal intertidal supratidal zones of a shallow shelf of proterozoic open ocean under warm alkaline and anoxic conditions

melt producing and melt consuming reactions in the achankovil cordierite gneisses south india migmatitic cordierite gneisses within the achankovil zone az of southern pan african india record melt producing and subsequent melt consuming mineral reactions early mineral assemblages bt sil qtz and bt sil spl deduced from inclusion textures in garnet prophyroblasts break down via successive dehydration melting reactions to high t phase assemblages e g grt crd liq opx liq spl crd liq later back reactions between the restite and the in situ crystallizing melt resulted in thin cordierite coronas separating garnet from the leucosome and partial resorption of garnet to opx crd or crd bt qtz symplectites leucosomes generally display a moderate low strain gneisses to strong high strain gneisses depletion of alkali feldspar attributed to mineral melt back reactions partly controlled by the degree of melt segregation using a kfmash partial petrogenetic grid that includes a melt phase and qualitative pseudosections for microdomains of high and low al si ratios the successive phase assemblages and reaction textures are interpreted in terms of a clockwise p t path culminating at about 6 7 kbar and 900 950 c this p t path is consistent with but more detailed than published results which suggests that taking a melt phase into account is not only a valid but also a useful approach comparing p t data and lithological and isotopic data for the az with adjacent east gondwana fragments suggests the presence of a coherent metasedimentary unit exposed from southern madagascar via south india az and sri lanka wanni complex to the lutzow holm bay in eastern antarctica

characterization and origin of a compositionally zoned aluminous a type granite from south india the pan african ambalavayal granite intrudes the high grade metamorphic terrain of northern kerala south india and is spatially associated with the moyar and calicut lineaments the pluton was aligned nearly parallel to the northeast southwest and east west faults in the basement consistent with magma ascent along pre existing deep crustal lineaments in an extensional tectonic regime the pluton is characterized by the presence of iron rich hydrous mafic minerals primary magnetite f o2 above the ni nio buffer and high initial emplacement temperatures near 1000 c modal and textural analyses reveal two probable compositional zones within the pluton outer and inner major element variations support this zoning and point to a peralkaline to metaluminous outer zone and a metaluminous to slightly peraluminous inner zone both zones exhibit major and trace element characteristics of the a type granites with the outer zone belonging to the a1 subtype and the inner zone to the a2 subtype of eby the trace element trends observed from outer zone to the inner zone suggests that crystal fractionation may have been the dominant process in the generation of high levels of the incompatible elements in the case of inner zone samples the high initial 87sr 86sr ratio 0 7135 and high y nb ratios y nb 1 2 are in the range expected for rocks derived from crustal protoliths a petrogenetic model involving partial melting of a charnockitic mafic to intermediate lower crust followed by limited fractional crystallization of the magma in a high level magma chamber is proposed the enrichment of hfse and ree except eu in the inner zone is considered the ultimate product of crystal melt and volatile activity during the final stage of crystallization in a highly silicic sio2 74 magma chamber

an empirical model of the drift velocity of equatorial plasma depletions 1 the far ultraviolet imager on the image spacecraft image fuv has been used to observe o plasma depletions in the post sunset equatorial ionosphere small scale density irregularities associated with such depletions are believed to adversely affect trans ionospheric radio signals such as gps prediction of the motion of these plasma depletions is a necessary component of the ability to forecast the occurrence of such radio signal interference an automated method has recently been developed to identify and track the position and zonal drift velocity of these depletions here we use this method to create a large database of the zonal drift velocities of these depletions we present an empirical model based on these observations that describes the observed drift velocities as a function of both local time and magnetic latitude which is essential to represent their behavior a comparison of the observed drift velocities with zonal winds from both an empirical model horizontal wind model hwm07 and a first principles model the tiegcm reveals that the plasma depletions drift velocities have a latitudinal gradient that cannot be explained solely by the f region dynamo in the post sunset period at least by these climatological models this suggests that these plasma depletions may not simply drift with the background f region plasma it has previously been suggested that vertical polarization electric fields associated with the plasma depletions are responsible for their zonal drifts exceeding the background flow which may explain the previously observed discrepancy in the drift velocities and the discrepancy in their gradients reported here

discriminating stromatolite formation modes using rare earth element geochemistry trapping and binding versus in situ precipitation of stromatolites from the neoproterozoic bitter springs formation northern territory australia stromatolites consist primarily of trapped and bound ambient sediment and or authigenic mineral precipitates but discrimination of the two constituents is difficult where stromatolites have a fine texture we used laser ablation inductively coupled plasma mass spectrometry to measure trace element rare earth element ree y and th concentrations in both stromatolites domical and branched and closely associated particulate carbonate sediment in interspaces spaces between columns or branches from bioherms within the neoproterozoic bitter springs formation central australia our high resolution sampling allows discrimination of shale normalised ree patterns between carbonate in stromatolites and immediately adjacent fine grained ambient particulate carbonate sediment from interspaces whereas all samples show similar negative la and ce anomalies positive gd anomalies and chondritic y ho ratios the stromatolites and non stromatolite sediment are distinguishable on the basis of consistently elevated light rees lrees in the stromatolitic laminae and relatively depleted lrees in the particulate sediment samples additionally concentrations of the lithophile element th are higher in ambient sediment samples than in stromatolites consistent with accumulation of some fine siliciclastic detrital material in the ambient sediment but a near absence in the stromatolites these findings are consistent with the stromatolites consisting dominantly of in situ carbonate precipitates rather than trapped and bound ambient sediment hence high resolution trace element ree y th geochemistry can discriminate fine grained carbonates in these stromatolites from coeval non stromatolitic carbonate sediment and demonstrates that the sampled stromatolites formed primarily from in situ precipitation presumably within microbial mats biofilms rather than by trapping and binding of ambient sediment identification of the source of fine carbonate in stromatolites is significant because if it is not too heavily contaminated by trapped ambient sediment it may contain geochemical biosignatures and or direct evidence of the local water chemistry in which the precipitates formed

nature and environmental significance of microbialites in quaternary reefs the tahiti paradox drill cores from the bamer reef edge of tahiti exhibit 85 93 m thick coralgal sequences recording at least 13 500 years of continuous reef growth in optimal environmental conditions the cored reef sequences form an overall shallowingupward succession with assemblages of branching or massive colonies of porires at the base overlain by a robust branching community acropom gr dmmi robirstn heavily encrusted by coralline algae sessile vermetid gastropods and arborescent foraminifers which grew at depths less than 6 m microbialites generally form the last stage of encrustation of coral colonies or more commonly of related encrusting organisms thus appearing as a major structural component of the reef sequence where they may locally form 809 of the rock by volume they developed in an open cavity system of the reef framework with freely circulating normal marine water microbialites include laminated crusts and clotted micritic masses commonly associated in compound crusts probably feflecting differences in the composition of the involved biological communities and in biomineralization processes that controlled the accretion of the crusts the isotopic composition of the microbialites 2 05 to 3 92 i they underwent also indivitlual processes of biominrlali2ation besicles the overall decrease in lizht and enqy conditions rttlecting progressive burial by conil growth the widespread development of microbialites within the reef framework may be related to increased alkalinity and niitrient availability in interstitial waters due to temstrial groundwwr seepage and puiodic runoffs the tlevelopment of micrubialites in the cryptic niches of the reef framework ceased about 6000 years

fluid absent melting behavior of a two mica metapelite experimental constraints on the origin of black hills granite we have studied experimentally the vapor absent melting behavior introduction of a proterozoic metapelite hp 60 1 from the black hills south peraluminous leucogranites such as the miocene granites dakota to assess whether the high do tourmaline bearing granites of the himalaya and tourmaline granites of the harney of the harney peak suite resulted from muscovite dominated depeak suite in south dakota are widely considered to be hydration melting at 10 kbar samples were sealed with no added the product of muscovite dehydration melting yet few h2o in gold capsules then run in a 0 5 inch 1 27 cm pistonexperimental studies of muscovite dehydration melting cylinder apparatus over the temperature interval 812 975 c reactions have been performed because the low temexperiments were conducted at 10 kbar to allow comparison with peratures of the reactions hinder the approach to equiother metapelite melting studies mass balance calculations imply librium in addition melt fractions generated are typically the melting reaction muscovite biotite plagioclase quartz low resulting in small melt pockets which are very difficult melt alkali feldspar aluminosilicate garnet until to analyze with the electron microprobe in this study muscovite is exhausted 812 c then the reaction biotite we assess the possible genetic relationship between the plagioclase quartz alkali feldspar aluminosilicate tourmaline bearing granites of the harney peak suite melt garnet the inferred muscovite reaction is completed below and the aluminous metasediments these granites intrude 812 c and produces 1 2 wt melt melt production of the although the attempt to investigate the muscovite decontinuous biotite reaction increases steadily with rising temperature hydration melting reaction was hindered by the surto 32 wt in our highest temperature run the low melt prisingly low melt productivity we were able to infer a productivity of the muscovite reaction at 10 kbar suggests that balanced reaction illuminating the dominantly peritectic melting at lower pressures may be necessary to generate mobile melt nature of fluid absent muscovite breakdown under the fractions by muscovite dominated reactions in our starting material conditions investigated in addition melts of hp 60 1 are considerably more mafic than isotopic and trace element studies indicate a genetic the tourmaline bearing granites with average combined tio2 relationship between s type granites and aluminous metamgo feo contents of 1 85 wt and 0 84 wt respectively sediments in the black hills of south dakota where the in particular melts of hp 60 1 are enriched in ti and would harney peak granite hpg intruded proterozoic and probably stabilize biotite rather than tourmaline upon cooling archean schists and metagreywackes undergoing regional arguing against hp 60 1 as a potential source rock for the metamorphism the timing and mode of emplacement of tourmaline granites the hpg and the deformation and regional metamorphic

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

whitings a sedimentologic dilemma whitings drifting clouds of water milky because of suspended carbonate have been claimed to originate from either the action of bottom feeding fish or direct precipitation of calcium carbonate five cruises during different seasons were made to the great bahama bank to collect data pertinent to the controversy measurements of particulate concentrations average 10 mg liter with a maximum of 20 mg liter of carbonate sediment suspended in whiting water compared with an average of 1 5 mg liter for clear water outside the whitings the particles are dominantly acicular aragonite but mg calcite composes as much as 20 percent of some whitings sedimentation rates measured with fixed and drifting sediment traps were as great as 34 g m 2 hr sediment suspended in whitings aggregated into silt and sand size fioccules and settled to the bottom of settling tanks within six hours even on a rocking ship sediment in artificial whitings created by stirring sediment from the bottom with a shrimp trawl settled to the bottom in about the same time natural whitings on the other hand were never observed to dissipate because sedimentation from whitings occurs at rates sufficient to cause dissipation of the whitings within six hours we conclude that the natural whitings are continually replenished by direct precipitation the search for fish in whitings utilized sidescan sonar and fathometer imaging shrimp trawls rotenone remote video and direct scuba observation these methods and 25 years of casual observations leading to this study indicate that fish are not involved in the formation of most bahamian whitings several whitings were found over rocky or sandy bottoms where there was no mud available for fish to suspend the distance of these whitings from areas of muddy bottom precluded their having been made elsewhere by fish stable carbon and oxygen isotopic analyses and delta 14 c activity are interpreted to indicate that the suspended sediment in whitings contains some precipitated calcium carbonate and is not merely bottom sediment stirred into suspension estimates indicate that the amount of new carbonate produced in whitings on the great bahama bank is substantially higher than that arising from algal production consequently the amount of sediment transported to deep water may be much greater than previously thought

petrology and geochemistry of paleoproterozoic a type granite at kanigiri in the nellore khammam schist belt andhra pradesh india abstract the kanigiri pluton 6 2 2 1 km 2 995 ma occurs close to a major fault and is intrusive into the meta volcanics in the western margin of the nellore khammam schist belt in andhra pradesh india the dominantly metaluminous pluton displays geochemical characteristics of a type granites including high abundances of nb zr y ta and ree except eu and low concentrations of sc ba sr and eu displaying distinct variation trends with increasing silica content it has less fractionated ree patterns and large negative eu anomalies the cluster analyses of major and trace elements indicate three main associations a a primary magmatic association characterized by the presence of la ce fe ti mn k ba and sr b ore related association consisting of zr hf nb y and c a volatile association with rb ta li and cs systematic variation in sr rb sr rb ba ratios along with and low k rb ratios reflects fractionation of feldspars variations in sc and ta result from fractionation of ferromagnesian silicates removal of zircon and allanite affected the hf ta and ce yb ratios limited variation in source sensitive y nb and yb ta ratios is consistent with the results of melting experiments and indicates that metaluminous granitoids of this pluton were probably derived through melting of lower crustal sources geochemical field and petrological data for the kanigiri granite suggest that the granite is a partial melting product of mafic rocks like gabbros that are also present in the study region

contribution of microbialites to the development of coral reefs during the last deglacial period case study from vanuatu south west pacific coral reefs have grown continuously during the last 24 ka on the island of espiritu santo vanuatu south west pacific in a setting characterized by frequent tectonic uplifts related to subduction of the australia plate beneath the vanuatu island arc sedimentological and geochemical studies of two neighbouring areas having much different mean uplift rates and environmental settings provides an opportunity to analyze the environmental factors that promoted the widespread development of microbialite crusts from about 24 to 6 ka b p nutrient supplies and probably the rapidity of the sea level rise are critical to an explanation of the distinctive distribution of microbialites in reef cores nutrient flux has been related to terrigenous fluxes in the tasmaloum reef system that fringed the south west uplifting coast of espiritu santo and possibly to upwelling in the urelapa sequence that was isolated from the main island during its growth a peak in microbialite abundance occurred between 16 and 10 ka b p a time window characterized by increasing erosional processes and or more intense upwelling during a very rapid rise in sea level

effects of solar and geomagnetic activities on the zonal drift of equatorial plasma bubbles equatorial plasma bubbles are mostly generated in the postsunset sector and then move in the zonal direction plasma bubbles can last for several hours and move over hundreds of kilometers even more than 1000 km in this study we use measurements of ion density by the communication navigation outage forecasting system satellite to determine the orbit averaged drift velocity of plasma bubbles the objective of the study is to identify the dependence of the bubble drift on the solar radio flux and geomagnetic activities in total 5463 drift velocities are derived over may 2008 to april 2014 and a statistical analysis is performed the average pattern of the bubble drift is in good agreement with the zonal drift of the equatorial f region plasma the zonal drift velocity of plasma bubbles increases with the solar radio flux however the increase shows different features at different local times geomagnetic activities cause a decrease of the eastward drift velocity of plasma bubbles equivalent to the occurrence of a westward drift through disturbance dynamo process in particular the decrease of the eastward drift velocity appears to become accelerated when the dst index is smaller than 60 nt or kp is larger than 4

fluorine and chlorine behaviour during progressive dehydration melting consequences for granite geochemistry and metallogeny dehydration melting of biotite is the main control on crustal differentiation in the mid to lower continental crust because this reaction produces the most voluminous and most mobile granitic melts biotite breaks down over a broad temperature interval so the partitioning behaviour of elements between biotite and melt is likely to vary it has been hypothesized that fluorine may stabilize biotite to higher melting temperatures because biotite is typically f rich in ultra high temperature uht metamorphic rocks if true f would be an important influence on crustal differentiation because not only would it broaden the temperature range of melting but also elevated f concentration decreases melt viscosity furthermore ligand partitioning between biotite and melt may be an important influence on the metallogeny of magmas this study used electron microprobe analysis of biotite in rocks from the ballachulish and rogaland metamorphic aureoles to investigate the concentration of f and cl in biotite heated to 600 1 000 c results show a broad increase in biotite f content up to 5 04 f with temperature until 850 920 c beyond which f content decreases 2 5 f chlorine concentrations in biotite are consistently lower 1 cl and show a progressive decrease after the onset of partial melting it was found that mg content and the processes that control mg distribution are most strongly correlated with f and cl concentration in biotite calculations based on these results indicate that f enriched biotite could be a significant source of f for continental crust derived melts generation of a hot f rich melt at uht conditions could be important for transporting lower crustal metals to the upper crust