anaerobic oxidation of methane in hypersaline messinian environments revealed by 13c depleted molecular fossils abstract the messinian sequence of evaporitic deposits in italy includes authigenic carbonates that have been suggested to derive from the microbial degradation of organic compounds but the biogeochemical mechanisms that led to their formation remained unknown to unravel these mechanisms 13 c depleted carbonate rocks including native sulphur bearing limestone calcare solfifero from two locations in sicily and bedded limestone from the northern apennines have been studied their 13 c values as low as 49 reflect incorporation of carbon derived from the oxidation of methane which was previously suggested to have been linked to bacterial sulphate reduction molecular fossils extracted from the limestones reveal that methane was indeed oxidized in an anaerobic process by archaea and sulphate reducing bacteria the observed biomarker patterns resemble those of methane seep carbonates which form as a consequence of the anaerobic oxidation of methane aom aom specific 13 c depleted archaeal biomarkers such as pmi 13 c 101 to 75 as well as compounds derived from sulphate reducing bacteria iso and anteiso fatty acids 13 c as low as 85 were identified in the messinian carbonates although the biomarker results clearly point to aom the compound inventory also revealed distinct differences to patterns found at marine methane seeps for example sn 3 hydroxyarchaeol is in some samples the only hydroxyarchaeol present something usually not found at seeps archaeol is less depleted in 13 c than pmi at most sites 13 c 55 to 30 pointing to the co occurrence of methanogenic or halophilic archaea with archaea involved in aom 1 the presence of calcite pseudomorphs after lenticular gypsum 2 18 o enrichment in carbonates and 3 the biomarkers o phytanyl o sesterterpanyl glycerolether extended archaeol tetrahymanol and possibly phytanylglycerol monoethers as well as non isoprenoidal macrocyclic glycerol diethers confirm that carbonate formation took place under evaporitic conditions aom has previously been shown to be inhibited in some brine pools on the modern seafloor our observations however demonstrate that aom functions in hypersaline environments as well

sedimentologic to metamorphic processes recorded in the high pressure low temperature mesozoic rosetta marble of anatolia anatolia s high pressure metamorphic belts are characterized in part by a neotethyan stratigraphic succession that includes a mid cretaceous hemi pelagic marble sequence this unit contains towards its stratigraphic top dm to m long radiating calcitic rods forming rosette like textures here we refer to these features as rosetta marble the remarkable textural similarity of non metamorphic selenite crystals and radiating calcite rods in the rosetta marble strongly suggests that these textures represent pseudomorphs after selenites metamorphosed hemi pelagic limestones dominated by rosetta selenite pseudomorphs are alternating with siliceous meta sediments containing relictic radiolaria tests this stratigraphic pattern is indicative of transient phases characterized by evaporites precipitated from basinal brines alternating with non evaporative hemi pelagic deposition from normal marine seawater the regional distribution of rosetta marble exposures over 600 km is indicative of basin scale evaporitic intervals high pressure low temperature metamorphism of these rocks is witnessed by sr rich up to 3500 ppm fibrous calcite pseudomorphs after aragonite and isolated aragonite inclusions in quartz peak metamorphic conditions of 1 2 gpa and 300 350 c are attested by high si white mica thermobarometry the rosetta marble case example examines the potential to unravel the complete history from deposition to diagenesis and metamorphism of meta sedimentary rocks

tectonics and sequence stratigraphy in messinian basins sicily constraints on the initiation and termination of the mediterranean salinity crisis deposits within the caltanissetta basin of central sicily have been important for developing the desiccating deep basin model for the messinian salinity crisis in the mediterranean linked structural and stratigraphic studies show that the sicilian depocenters are synclines related to underlying thrust structures of the frontal part of the maghrebian chain prior to the salinity crisis these basins were hydrodynamically linked through the foredeep to the mediterranean the precursor sediments terravecchia formation formed a delta sourced from the north early messinian regression acted on a range of paleobathymetries shallow in the north and progressively deeper in the south locally complicated by active thrust structures initial draw down of mediterranean base level is marked across the thrust belt by first cycle carbonates and evaporites on the structural highs and lows respectively vast accumulations of halite and potassium salts up to 1200 m are restricted to growing thrust synclines the different evaporite signatures may be related to different water conditions reflecting various meteoric and marine circulations across various subbasins with cyclicity reflecting high frequency variations in sea level a sequence stratigraphic model is developed to explain fractionation of evaporite facies between different paleobathymetric settings and to predict the temporal evolution of the successions in different subbasins thrusting provides accommodation space for evaporites and also controls the water pathways into the desiccating basins the intra messinian unconformity separating first and second cycle evaporites is a type 1 sequence boundary related to the forced regression associated with the acme of mediterranean desiccation an interpretation supported by local ravinement and incised valley fills the overlying second cycle evaporites are a combination of detrital reworked first cycle material and primary gypsum formed under brackish water regional onlap relationships and bed continuity suggest that this water body was of regional extent with a systematically rising base level these interpretations have several implications for messinian correlations in the mediterranean the deep basin evaporites correlate with an intra messinian unconformity that separates the two cycles on sicily and postdate the first cycle deposits regional base level was largely restored before the end of the salinity crisis

evaporite hosted native sulfur in trans pecos texas relations to late phase basin and range deformation major deposits of biogenic native sulfur are associated with narrow northeast trending grabens and normal faults that disrupt the gently tilted east dipping upper permian evaporite succession of the western delaware basin in trans pecos texas orebodies are restricted to geologic traps in the fractured and dissolution modified downfaulted blocks of the grabens other parallel regionally distributed grabens and normal faults are commonly the sites of noncommercial sulfur deposits and genetically related secondary replacement diagenetic limestone bodies the sulfur bearing structures probably formed during the later of two episodes of basin and range extension that have not previously been differentiated in texas but are well defined elsewhere in the western united states in texas several lines of evidence collectively support the existence of late phase northwest directed extension that was initiated in the middle miocene

bacterially mediated formation of diagenetic aragonite and native sulfur in zechstein carbonates upper permian central germany abstract neoformed diagenetic aragonite associated with organic rich aggregations and native sulfur occur within cavities of the ca2 and ca3 zechstein carbonates in central germany the cavities were formerly filled with gypsum bacterial sulfate reduction favored the precipitation of the carbonate phase this can be attributed to an increase in alkalinity accompanied with sulfate reduction the high sr concentrations of the neoformed aragonites compared to the low concentrations in the carbonate host rocks point to sulfate dissolution as the cation supplying process for the precipitation of aragonite low 13c values 10 pdb of the aragonite indicate that some of its carbon is derived from organic matter that has been oxidized by bacterial sulfate reduction aragonite inclusions bear rhomb shaped crystals of calcite replacing former dolomite elevated mg ca ratios due to this dedolomitization may have promoted the precipitation of aragonite instead of calcite the aragonite precipitated in the near surface meteoric vadose zone in recent times aragonite crystals display a platy habit sem analyses show that two types of micro rods are associated with these plates the mineralized micro rods are interpreted to be fossilized bacteria aragonite inclusions most of which contain organic rich aggregations yield a distinctive biomarker pattern high concentrations of specific unsaturated fatty acids are clearly indicative of newly produced organic matter and reflect the presence of a discrete microbial community being associated with the formation of the aragonite at one of the studied localities the aragonite is accompanied by native sulfur the formation of sulfur was mediated by h2s oxidizing bacteria this is corroborated by the presence of densely packed curved rods representing permineralized bacterial cells on and within the sulfur

different isotope and chemical patterns of pyrite oxidation related to lag and exponential growth phases of acidithiobacillus ferrooxidans reveal a microbial growth strategy abstract the solution chemistry during the initial slow increase of dissolved iron and sulfate and main stage rapid increase of dissolved iron and sulfate of pyrite leaching by acidithiobacillus ferrooxidans af at a starting ph of 2 05 shows significant differences during the initial stage ferrous iron fe 2 is the dominant iron species in solution and the molar ratio of produced sulfate so 4 2 and total iron fe tot is 1 1 thus does not reflect the stoichiometry of pyrite fes 2 during the main stage ferric iron fe 3 is the dominant iron species in solution and the so 4 2 fe tot ratio is with 1 9 close to the stoichiometry of fes 2 another difference between initial and main stage is an initial trend to slightly higher ph values followed by a drop during the main stage to ph 1 84 these observations raise the question if there are different modes of bioleaching of pyrite and if there are what those modes imply in terms of leaching mechanisms different oxygen and sulfur isotope trends of sulfate during the initial and main stages of pyrite oxidation confirm that there are two pyrite bioleaching modes the biochemical reactions during initial stage are best explained by the net reaction fes 2 3o 2 fe 2 so 4 2 so 2 g the degassing of sulfur dioxide so 2 acts as sink for sulfur depleted in 34 s compared to pyrite and is the cause of the so 4 2 fe tot ratio of 1 1 and the near constant ph during the exponential phase pyrite sulfur is almost quantitatively converted to sulfate according to the net reaction fes 2 15 4o 2 1 2h 2 o fe 3 2so 4 2 h we hypothesize that the transition between the modes of bioleaching of pyrite is due to the impact of the accumulation of ferrous iron which induces changes in the metabolic activity of af and may act as an inhibitor for the oxidation of sulfur species this transition defines a fundamental change in the growth strategy of af a mode where bacteria gain energy by oxidation of elemental sulfur to sulfite but show little growth is switched into a mode where bacteria gain a smaller amount of energy by the oxidation of ferrous iron but induce much faster pyrite leaching rates due to the production of ferric iron

microbe mineral interactions early carbonate precipitation in a hypersaline lake eleuthera island bahamas microbialites benthic microbial carbonate deposits were discovered in a hypersaline alkaline lake on eleuthera island bahamas from the edge towards the centre of the lake four main zones of precipitation could be distinguished 1 millimetre sized clumps of mg calcite on a thin microbial mat 2 thicker and continuous carbonate crusts with columnar morphologies 3 isolated patches of carbonate crust separated by a dark non calcified gelatinous mat and 4 a dark microbial mat without precipitation in thin section the precipitate displayed a micropeloidal structure characterized by micritic micropeloids strong autofluorescence surrounded by microspar and spar cement no fluorescence observations using scanning electron microscopy sem equipped with a cryotransfer system indicate that micrite nucleation is initiated within a polymer biofilm that embeds microbial communities these extracellular polymeric substances eps are progressively replaced with high mg calcite discontinuous eps calcification generates a micropeloidal structure of the micrite possibly resulting from the presence of clusters of coccoid or remnants of filamentous bacteria at high magnification the microstructure of the initial precipitate consists of 200 500 nm spheres no precipitation is observed in or on the sheaths of cyanobacteria and only a negligible amount of precipitation is directly associated with the well organized and active filamentous cyanobacteria in deeper layers of the mat indicating that carbonate precipitation is not associated with co2 uptake during photosynthesis instead the precipitation occurs at the uppermost layer of the mat which is composed of eps empty filamentous bacteria and coccoids gloeocapsa spp two dimensional mapping of sulphate reduction shows high activity in close association with the carbonate precipitate at the top of the microbial mat in combination these findings suggest that net precipitation of calcium carbonate results from a temporal and spatial decoupling of the various microbial metabolic processes responsible for caco3 precipitation and dissolution theoretically partial degradation of eps by aerobic heterotrophs or uv fuels sulphate reducing activity which increases alkalinity in microdomains inducing caco3 precipitation this degradation could also be responsible for eps decarboxylation which eliminates ca 2 binding capacity of the eps and releases ca 2 ions that were originally bound by carboxyl groups at the end of these processes the eps biofilm is calcified and exhibits a micritic micropeloidal structure the eps free precipitate subsequently serves as a substrate for physico chemical precipitation of spar cement from the alkaline water of the lake the micropeloidal structure has an intimate mixture of

formation of secondary carbonates and native sulphur in sulphate rich messinian strata sicily abstract microbially formed authigenic carbonates accompanied by native sulphur are present in the calcare solfifero below a thick succession of gypsum deposited during the messinian salinity crisis in sicily we sampled these carbonates and associated sulphur in five former sulphur mines to subject them to a detailed petrographic and geochemical study in order to explore their different modes of formation native sulphur formed in conjunction with microbial sulphate reduction which is reflected in its depletion in 34s 34s values as low as 2 vs v cdt and an enrichment of 34s in the residual sulphate 34s values as high as 61 the oxidation of organic matter by sulphate reduction increased alkalinity inducing precipitation of secondary carbonate minerals a set of authigenic limestones lacking sulphate minerals but characterized by pseudomorphs after gypsum and high 18o values as high as 9 vs v pdb reflects syngenetic mineral formation within evaporitic settings low 13c values as low as 52 vs v pdb reveal that these carbonate phases were formed by microbial sulphate reduction coupled to the oxidation of biogenic methane another set of authigenic carbonates that replaced sulphate minerals is typified by low 18o values as low as 4 these carbonates formed epigenetically during later diagenesis following compaction dissolution of gypsum or anhydrite by meteoric waters delivered the sulphate for microbial sulphate reduction low carbon isotope values of these carbonates 29 to 5 indicate that carbonate was derived from the oxidation of crude oil and possibly minor methane partly involving different degrees of admixture of dissolved carbonate from other sources although the studied rocks with their vast amounts of secondary carbonate minerals and sulphur seem to indicate a similar genesis at first glance having formed by biogeochemical transformations of sulphate and hydrocarbons this study reveals that these processes can occur at different times in variable geological environments

stable isotope mapping in messinian evaporative carbonates of central sicily mapping stable isotope isolines in both modern and ancient evaporative carbonate formations demonstrates that regional variations of 18 o values exist in the case of the messinian central sicilian basin an ancient evaporite basin the distribution pattern of the 18 o isolines can be related to the paleogeometry and paleohydrology of the basin isolines of equal 13 c values also show large regional variations possibly reflecting the domination of different bacterial processes oxidation sulfate reduction or methanogenesis in different regions the potential application for stable isotope mapping in evaporative carbonate formations deposited in both marine and lacustrine environments lies in its ability to predict the location of depositional centers in ancient evaporite basins

carbonate replacement of lacustrine gypsum deposits in two neogene continental basins eastern spain abstract bedded nonmarine gypsum deposits in the miocene teruel and cabriel basins eastern spain are partly replaced by carbonate the libros gypsum teruel graben is associated with fossiliferous carbonate wackestones and finely laminated organic matter rich mudstones which accumulated under anoxic conditions in a meromictic permanent lake the gypsum is locally pseudomorphed by aragonite or less commonly replaced by calcite low 13c values indicate that sulphate replacement resulted from bacterial sulphate reduction processes that were favoured by anacrobic conditions and abundant labile organic matter in the sediments petrographic evidence and oxygen isotopic composition suggest that gypsum replacement by aragonite occurred soon after deposition a subsequent return to oxidising conditions caused some aragonite to be replaced by diagenetic gypsum native sulphur is associated with some of these secondary gypsum occurrences the los ruices sulphate deposits cabriel basin contain beds of clastic and selenitic gypsum which are associated with limestones and red beds indicating accumulation in a shallow lake calcite is the principal replacement mineral bacterial sulphate reduction was insignificant in this basin because of a scarcity of organic matter stable isotope composition of diagenetic carbonate indicates that gypsum replacement occurred at shallow burial depths due to contact with dilute groundwaters of meteoric origin depositional environment evidently has a major influence upon the diagenetic history of primary sulphate deposits the quantity of preserved organic matter degradable by sulphate reducing bacteria is of particular importance and along with groundwater composition is the main factor controlling the mechanism of gypsum replacement by carbonate

diagenesis and porosity development in the first eocene reservoir at the giant wafra field partitioned zone saudi arabia and kuwait the first eocene reservoir at the wafra field produces heavy oil from very porous dolomites at depths of 300 to 400 m in the paleocene eocene umm er radhuma formation porosity is commonly 30 50 permeability is commonly 100 2000 md and those reservoir characteristics were determined largely by diagenesis early diagenesis is dominated by dolomitization dissolution associated with dolomitization and precipitation of sulfates petrographic and stable isotopic characteristics support dolomitization and sulfate precipitation in evaporated refluxing seawater during shallow burial the highest permeabilities occur in subtidal facies low permeability tidal flat facies stratify the reservoir heavy oil preferentially filled high permeability dolomites whereas low permeability tidal flat facies are commonly filled with water because their pore throats are too small to allow migration of viscous oil into the rock this reservoir s very high porosity is probably related to its shallow burial and early oil emplacement late stage diagenesis is dominated by bacterial sulfate reduction bsr that caused dissolution of sulfate nodules calcite cementation sulfur precipitation and oil biodegradation the bsr is indicated by very low compositions of calcite cements to peedee belemnite standard which require an organic carbon source probably oil the oxygen isotopic compositions of the calcites support precipitation from formation waters similar to those in the reservoir now the bsr probably started during initial oil emplacement and continues to the present the bsr was heterogeneous resulting in produced oils with gravities of 14 21 api even heavier oils are present that could not flow during primary production primary production was likely greatest in areas and intervals with lighter less viscous oil

messinian carbonate rich beds of the tertiary piedmont basin nw italy microbially mediated products straddling the onset of the salinity crisis abstract the seven messinian microbial carbonate rich layers cropping out in the pollenzo section tertiary piedmont basin nw italy are interbedded with a precession related cyclic succession composed of euxinic shale marl couplets and straddle the onset of the messinian salinity crisis msc a sharp change of sedimentological compositional and geochemical characteristics was observed from the onset of the msc onward suggesting strong differences in the mechanisms responsible for carbonate precipitation pre msc beds are mainly composed of dolomite and are interpreted as the product of early diagenesis formed by bacterial sulphate reduction in the shallow subsurface along the sulphate methane interface dolomite precipitation was temporarily enhanced by an upward flux of methane rich fluids possibly sourced by gas hydrate destabilisation conversely from the onset of the msc onward carbonate beds are thinly laminated and show abundant filaments interpreted as beggiatoa like bacteria while calcite and aragonite are the dominant authigenic phases these beds are interpreted as microbialites resulting from the lithification of chemotrophic bacterial mats dominated by sulphide oxidizing bacteria the carbonate necessary for their preservation was provided by bacterial sulphate reduction these microbialites that appear as the deeper water counterpart of bottom grown selenite layers deposited in the marginal part of the basin formed on an anoxic sea bottom under a density stratified water column the high sulphate concentration in the pore waters related to the presence of concentrated brines and to the regeneration of sulphate by sulphide oxidizing bacteria is considered as the driving factor controlling the mineralogical change from dolomite to calcite and aragonite finally the sharp shift towards negative 18 o values of carbonates observed from the onset of the msc onward was probably related to fractionation processes operated by sulphate reducing bacterial communities in the pore waters this suggests that care must be taken when dealing with microbial carbonates in the interpretation of the oxygen isotope values in terms of fluctuating salinity condition of the water mass in conclusion this study suggests that the onset of the msc had a strong impact on microbial populations governing carbonate precipitation in a sector of the basin dominated by depositional conditions not suitable for gypsum precipitation

petrographic and geochemical constraints on the formation and diagenesis of anhydrite cements smackover sandstones gulf of mexico abstract anhydrite cement is common in sedimentary rocks yet its origin is poorly understood the high concentration of sulfate in sea water and the lack of appreciable sulfate in most other natural waters suggests that anhydrite cement may have a marine origin but the relatively late timing of most anhydride cement tends to preclude sea water as the source of sulfate anhydrite cement is present in upper jurassic sandstones in the gulf of mexico as poikilotopic masses in which detrital grains are replaced and as smaller patches that have replaced single detrital grains anhydrite is a relatively late cement and postdates all other volumetrically significant authigenic phases including k feldspar dolomite quartz and most calcite cements the expected isotopic composition and trace element concentration of marine derived late jurassic anhydrite cement is predicted based on analyses of bedded anhydrite and on analyses found in the literature the expected chemical signature is 34s cdt 16 18o smow 14 87sr 86sr 0 7069 sr 1500 2500 ppm ba 200 ppm when geochemical analyses of smackover anhydrite cements are compared to the predicted composition it is apparent that most of the cement is not of marine origin two generations of anhydrite cement have been identified in the east texas basin on the basis of their strontium isotopic compositions and their strontium concentrations an early cement may have been derived from slightly modified late jurassic sea water whereas a second group of cements may have precipitated later in the burial history or may represent recrystallization of the first cement the chemistry of louisiana and mississippi basin anhydrite cements indicates that the sulfate was derived from dissolved bedded anhydrite and was reprecipitated in the sandstones from fluids that had undergone extensive water rock interaction after considerable burial this study suggests that late anhydrite cements in sedimentary rocks are most likely derived from remobilized calcium sulfate de osits

biomarker and isotope evidence for microbially mediated carbonate formation from gypsum and petroleum hydrocarbons along the western coast of the gulf of suez large amounts of evaporitic gypsum of miocene age have been microbially transformed into carbonates and elemental sulfur in the presence of petroleum similar diagenetic transformations have been described from numerous sites worldwide but the role of petroleum specifically as a carbon source for the sulfate reducing microbial community remains elusive we carried out a geochemical investigation of microbial carbonates from the gulf of suez that suggests the presence of a community of sulfate reducing bacteria thriving on carbon substrates contained in petroleum specifically a set of non isoprenoidal macrocyclic glycerol diethers mcgds that we tentatively ascribe to sulfate reducing bacteria have a stable carbon isotope composition close to that of petroleum n alkanes associated with the carbonates the presence of archaeol that is 13c enriched relative to bacterial lipids suggests that archaea are present but either indirectly involved or not involved in the transformation of petroleum derived carbon the lipid biomarker pattern we observe is distinct from those observed in settings where sulfate reduction is coupled to the anaerobic oxidation of methane our results suggest that petroleum migration has triggered the microbial transformation of gypsum into carbonates in the gulf of suez by extension the involvement of petroleum in the microbial transformation of gypsum into carbonates in other settings which was suggested by more indirect geological and inorganic geochemical evidence seems very likely

biotic and abiotic processes in the formation and diagenesis of permian dolomitic stromatolites zechstein group ne england abstract the crinkly bed of the upper permian zechstein group succession roker formation hauptdolomit z2c in northeast england is a distinctive 1 4 meter thick unit that has been interpreted as a stromatolite of microbial origin or alternatively as the result of purely abiotic precipitation close examination of this stratigraphically significant unit shows that it is the result of both physical and microbial processes and was deposited in hypersaline shallow water immediately following lowstand evaporite deposition within the zechstein basin the internal structure of the crinkly bed consists of fine millimeter scale laminae of alternating clotted peloidal or aphanitic micritic layers and granular laminae composed of silt size peloids with rare hollow spheroids the lamination is extremely regular in thickness and laterally persistent for up to 4 meters a microbial community composed of coccoid and filamentous microorganisms inferred from fossil evidence colonized the original sediment surface it is suggested that this biofilm was responsible for the precipitation of both the micrite laminae and most of the peloids of the granular laminae the peloids are consequently interpreted as autochthonous this interpretation of a microbial origin is consistent with the microstructure and geochemical signatures of the micritic dolomite which constitutes both the continuous micritic laminae and the peloids themselves primary dolomite precipitation is hypothesized to have taken place from marine to slightly hypersaline waters mediated by bacterial metabolism similar to the process that operates in modern intertidal microbial mats the crinkly bed shows macro structures that vary along a continuum from symmetrical to asymmetrical centimeter scale ripple like structures some showing interference patterns through to domical and conical structures more typical of stromatolites the more ripple like structures have a lamination of microbial origin identical to that within the domal conical stromatolites there is no internal cross lamination their origin is equivocal they could be the result of physical current or wave induced deformation of a surficial biofilm or their form could be inherited from true mechanically deposited ripples not observed that provided a template for biofilm growth changes in the nature and strength of the wave and or current regime and possibly in the community structure of the microbial mat produced this array of microbially induced macrostructures miss the latter plus the absence of desiccation features indicative of intertidal to supratidal deposition suggest subtidal sedimentation at a depth of several meters intergranular gypsum cement precipitated during early diagenesis and ferroan sparry dolomite precipitated during burial tertiary uplift and the consequent exposure to meteoric waters resulted in the precipitation of calcite cements that replaced gypsum and pre existing dolomite probably via the biological mediation of heterotrophic bacteria the interpretation of this distinctive stratigraphic unit illustrates the difficulty in distinguishing between biotic and abiotic processes in the sedimentary record

a neogene seawater sulfur isotope age curve from calcareous pelagic microfossils abstract until now our knowledge of the sulfur isotopic composition of seawater through geologic time has depended on stable isotopic analysis of sulfate from evaporites owing to the sporadic occurrence of evaporites through time the secular sulfur isotope age curve contains many gaps with little or no data in order to fill in some of these gaps particularly the neogene we have analyzed the sulfur isotopic composition of carbonate associated sulfate in carbonate tests of planktonic foraminifera other investigators have shown that sulfate may occur in biogenic calcites either lattice bound as micro fluid inclusions in adsorbed phases or as protein polysaccharides whatever the origin the sulfur isotopic composition of this sulfate appears to be representative of that of the water in which the organism lived as shown by results on recent calcareous foraminifera and macrofossils using this approach for study of miocene to recent pelagic marine sediments supplemented by new data for miocene marine evaporites from the gulf of suez we have found that the 34 s of seawater has decreased about 2 5 over the past 25 m y and that most of the decrease has occurred over the past 5 m y parallelling a decrease in the 13 c of dissolved oceanic bicarbonate from the same interval sedimentary redox models based on isotope records suggest that organic carbon and sulfide burial have both decreased over the past 5 m y alternatively an increase in weathering rates over the past 5 m y would not require a decrease in organic carbon or sulfide burial as long as the isotopic effect of the increased river input exceeds the isotopic effect of the burial of the reduced species in either case the net result would be a decrease in atmospheric p o 2

a giant underwater encrusted stalactite from the blue hole lighthouse reef belize revisited a complex history of biologically induced carbonate accretion under changing meteoric and marine conditions a late pleistocene to holocene submerged and encrusted speleothem exhibits a complex history including a meteoric phase and two marine phases a combined study using petrography mineralogy and inorganic and organic geochemistry as well as geochronology has shown that phototrophic and heterotrophic biological activity impacted carbonate precipitation during all phases of carbonate accretion the stalactite formed ca 30 m below modern sea level at a marginal overhang in the blue hole of lighthouse reef atoll unlike purely meteoric speleothems the belize example consists of a meteoric core a marine aragonite crust and a serpulid micrite rich outer crust as a result of postglacial flooding of the karst cave the core of the stalactite has a tufaceous texture containing algal or microbial remains and consists entirely of low magnesium calcite formed 19 55 10 68 kyr bp the texture suggests that the stalactite formed at the cave entrance and hence the former cave ceiling had apparently collapsed earlier during the pleistocene oxygen 18o and carbon 13c isotopes across the core suggest a trend towards drier conditions and reduced soil and plant cover after the last glacial maximum the marine aragonite crust consists of stacked botryoids in which individual crystals up to 700 lm have dark terminations enriched in high magnesium calcite this crust accreted from 10 82 to 9 95 kyr bp in warm shallow water during the early holocene thermal optimum carbonate accretion rates were considerable and averaged 125 m yr the crust has a dense laminated texture on one side and a porous shrubby texture on the other the presence of n c16 1 5 n c17 1 6 and 10me c16 fatty acids in the laminated crust suggests that sulfate reducing bacteria contributed to aragonite formation in an environment that was less open than the formation environment of the porous crust where these biomarkers are lacking n c16 1 5 n c17 1 6 or are less abundant 10me c16 enrichment of 34s and 18o in carbonate associated sulfate cas relative to seawater sulfate also suggests sulfate reduction during carbonate formation the greater contribution of heterotrophic processes to aragonite precipitation in the laminated crust is also reflected in 13c values as low as 1 3 whereas no such depletion is observed in the aragonite of the porous crust 13c values as low as 0 0 a pronounced isotopic variability and excursions to positive 13c values as high as 3 5 0 in the inner half of the laminated crust indicate an episodic local impact of photosynthesis on aragonite precipitation whereas the lack of such excursions in the porous crust 13c values as high as 1 5 0 is again best explained by a more open environment of formation after a ca 5 kyr hiatus from 4 39 kyr bp a biogenic crust of abundant serpulids and finely crystalline microbial and detrital carbonate consisting of high magnesium calcite and aragonite accreted on the outer surface of the stalactite outermost crust accretion was probably influenced by the inundation of the lighthouse reef lagoon that started to shed abundant fine grained carbonate sediment into the blue hole the stalactite broke off the cave ceiling either before or after the formation of the outermost crust likely due to seismic movements along the nearby plate boundary the study demonstrates that like speleothems from the terrestrial realm submerged stalactites may have had complex histories with great potential as paleoenvironmental archives

the origin of evaporitive limestones an example from the messinian of sicily italy a good example of an extensive evaporative carbonate deposit which has altered little since formation is found in the messinian upper miocene evaporites of sicily in this study these messinian carbonates the calcare di base are examined through a combination of field observations together with petrologic mineralogic and stable isotope studies these evaporitic carbonates are found in massive nearly featureless beds both calcite and aragonite commonly composed of automorphic breccias and or weakly layered micrite additionally fine scale features are observed within the carbonates such as small algal stromatolites and algally controlled laminae petrologic study of thin sections reveals ubiquitous algal filaments and grumeleuse to pelletal micrites as the primary components this suggests by analogy to modern hypersaline environments that the original calcium carbonate precipitated as algally controlled aragonite in a hypersaline environment displacive and interbedded halite still present within the deposit in the subsurface in some areas has been leached in others leaving residual breccias cubic voids and halite pseudomorphs the carbonate has been partially calcitized during one or more phases of early diagenesis the diagenetic systems which affected these sediments were not wholly open the halite was removed in some areas early in the sediment s history but after partial lithification probably synsedimentary as indicated by breccias containing well preserved halite voids these breccias lie within a nonhalite bearing micritic matrix later alteration has removed more of the halite leaving cubic void spaces porous layers and halite pseudomorphs filled with calcite celestite and strontianite the presence in some areas of considerable amounts of unaltered aragonite and in other regions of secondary strontium minerals indicate that the systems which affected these sediments were not open ones based on the oxygen isotope values obtained from the unaltered aragonites it appears that the large volumes of calcium carbonate in this deposit were derived from a combination of continual influx of seawater together with a probable contribution from continental sources coming into a restricted hypersaline environment at the margins of the basin the isotopic composition of the altered carbonates suggests that meteoric waters participated in the diagenesis while secondary bacterial processes oxidation sulfate reduction and methanogenesis contributed carbonate ions depleted in carbon 12 to the final product

chronology causes and progression of the messinian salinity crisis the messinian salinity crisis is widely regarded as one of the most dramatic episodes of oceanic change of the past 20 or so million years 1 3 earliest explanations were that extremely thick evaporites were deposited in a deep and desiccated mediterranean basin that had been repeatedly isolated from the atlantic ocean1 2 but elucidation of the causes of the isolation whether driven largely by glacio eustatic or tectonic processes have been hampered by the absence of an accurate time frame here we present an astronomically calibrated chronology for the mediterranean messinian age based on an integrated high resolution stratigraphy and tuning of sedimentary cycle patterns to variations in the earth s orbital parameters we show that the onset of the messinian salinity crisis is synchronous over the entire mediterranean basin dated at 5 96 0 02 million years ago isolation from the atlantic ocean was established between 5 59 and 5 33 million years ago causing a large fall in mediterranean water level followed by erosion 5 59 5 50 million years ago and deposition 5 50 5 33 million years ago of non marine sediments in a large lago mare lake sea basin cyclic evaporite deposition is almost entirely related to circum mediterranean climate changes driven by changes in the earth s precession and not to obliquity induced glacio eustatic sea level changes we argue in favour of a dominantly tectonic origin for the messinian salinity crisis although its exact timing may well have been controlled by the 400 kyr component of the earth s eccentricity cycle

holocene dolomitization of calcium carbonate sediments from the coastal sabkhas of abu dhabi u a e a stable isotope study secondary dolomitization of holocene calcium carbonate sediments occurs beneath the coastal sabkhas of abu dhabi u a e a stable isotope study of the sabhka sediments and brines indicates that the

reply to the comment on carbonate deposition and diagenesis in evaporitic environments the evaporative and sulphur bearing limestones during the settlement of the messinian salinity crisis in sicily and calabria by caruso et al 2015 palaeo3 429 136 162 abstract manzi et al in press took the opportunity offered by our paper to repeat again all the set of ideas supporting an interpretative model of the messinian salinity crisis msc a model they assert to be valid for the whole mediterranean basin what emerges from reading this long comment may be summarized in one criticism of our article we have not systematically applied their interpretative model to our data the aim of our paper was not to promote their ideas but to submit the results of more than 20 years of field studies and petrographical and geochemical analyses on sicilian and calabrian sequences of the messinian calcare di base it is out of our purpose to enumerate again in this reply the data and interpretations we have developed in our paper which disagree with their model and rule out most of their propositions thus we will not reply in detail to this repetitive stream of ideas supporting their model but we want to respond to some general and unfair comments which are often far away from objectivity and rectify some inaccurate assertions about the description of some sections

carbonate deposition and diagenesis in evaporitic environments the evaporative and sulphur bearing limestones during the settlement of the messinian salinity crisis in sicily and calabria abstract the depositional and diagenetic processes involved in the formation of carbonates in the evaporitic environment of the messinian salinity crisis are investigated in southern italy sicily and calabria strong differences are observed between the studied sections that reflect specific depositional and diagenetic evolution in the interconnected sub basins resulting from the syn sedimentary tectonic fragmentation of the central sicilian and calabrian domains these carbonates formed diachronously in restricted perched sub basins between the tripoli formation and the hypersaline settings of the msc the calcare di base cdb that can be interbedded with gypsum layers occurs rhythmically at the transition between the upper part of the tripoli formation and the massive gypsum and at places synchronously with the deposition of the lower gypsum unit it deposited initially as primary peloidal and microbial limestones but their original structure and mineral composition were modified by the superimposition of early to late diagenetic processes the first diagenetic step was the development of interstitially grown gypsum and halite crystals from trapped saturated brines that locally led to the formation of salt beds the sulphur limestone sl resulted from the activity of sulphate reducing bacteria that occurred locally in the deeper parts of the various basins where anoxic bottom waters favoured microbial processes fuelled by biogenic methane and crude oil and caused the carbonate replacement of gypsum and the formation of native sulphur the migration of hydrocarbon and h 2 s rich fluids caused the epigenetic dissemination of sulphur and a late diagenetic carbonate replacement of the gypsum later influxes of continental fresh waters were responsible for the dissolution of the halite crystals and their replacement by sparry calcite the vugs formed during both the gypsum calcite conversion and the halite dissolution either remained empty or were filled with calcite celestine fibrous silica anhydrite secondary gypsum and native sulphur the initial accumulation of fine grained carbonate and gypsum sediments was strongly destabilised by volumetric changes resulting from mineral replacements and fluidisation processes their superimposition explains the vuggy and boxwork like textures in situ brecciation and lateral displacement which are responsible for the chaotic organisation without necessarily involving basin scale re sedimentation in the form of debris flows

periglacial paleosols and cryogenian paleoclimate near adelaide south australia abstract late cryogenian deformation of the reynella siltstone near hallett cove south australia has been interpreted as shallow marine methane seeps which were furthermore proposed to have played a role in deglaciation from snowball earth re examination and new analyses of these same outcrops confirms an earlier interpretation of this intrastratal deformation as periglacial paleosols which are evidence that even at maximum extent late cryogenian glaciers did not cover all continental lowlands let alone the world ocean known miocene and pliocene methane seeps of california examined for this study are very different in their gray color rounded nodules and clayey host rock compared with red highly deformed and silty to pebbly reynella siltstone of hallett cove stable isotopic composition of nodular carbonate in the reynella siltstone fails to show extreme carbon isotopic depletion or the meteoric oxygen lines characteristic of known methane seeps and sphaerosideritic waterlogged paleosols but instead shows covariance of carbon and oxygen isotopic composition comparable with that in pedogenic and subaerial carbonate of well drained soils mass balance geochemical analyses show modest weathering compatible with sand wedge structures and evaporitic pseudomorphs indicative of arid and frigid paleoclimate outcrops of reynella siltstone near hallett cove represent frigid low latitude floodplains not submarine methane seeps nor global glaciation

changes in sources and storage in a karst aquifer during a transition from drought to wet conditions summary understanding the sources and processes that control groundwater compositions and the timing and magnitude of groundwater vulnerability to potential surface water contamination under varying meteorologic conditions is critical to informing groundwater protection policies and practices this is especially true in karst terrains where infiltrating surface water can rapidly affect groundwater quality we analyzed the evolution of groundwater compositions major ions and sr isotopes during the transition from extreme drought to wet conditions and used inverse geochemical modeling phreeqc to constrain controls on groundwater compositions during this evolution spring water and groundwater from two wells dominantly receiving diffuse and conduit flow termed diffuse site and conduit site respectively in the barton springs segment of the edwards aquifer central texas usa and surface water from losing streams that recharge the aquifer were sampled every 3 4 weeks during november 2008 march 2010 during this period water compositions at the spring and conduit sites changed rapidly but there was no change at the diffuse site illustrating the dual nature i e diffuse vs conduit of flow in this karst system geochemical modeling demonstrated that within a month of the onset of wet conditions the majority of spring water and groundwater at the conduit site was composed of surface water providing quantitative information on the timing and magnitude of the vulnerability of groundwater to potential surface water contamination the temporal pattern of increasing spring discharge and changing pattern of covariation between spring discharge and surface water steam recharge indicates that that there were two modes of aquifer response one with a small amount of storage and a second that accommodates more storage

microbial mediated pre salt carbonate deposition during the messinian salinity crisis calcare di base fm southern italy abstract a multi scale analysis of sedimentary carbonate facies and post sedimentary diagenetic features of the calcare di base formation the precursor to evaporites in upper messinian successions of northern calabria and central sicily has revealed their microbial bio mediated origin massive to laminated microbial boundstones represent the most common sedimentary facies forming flat to low relief cm to m scale stromatolitic and thrombolitic bodies the fabric of the micrite varies from peloidal to aphanitic and almost always preserves filamentous bacteria which characterized the original microbial mat the mat was dominated by sulphur oxidizing bacteria belonging to the thiotrichaceae but there is evidence for a more complex community with sulphate and or nitrate reducing bacteria all being responsible for the mediation of the carbonate precipitation microbial boundstones are rich in pseudomorphs of ca sulphate and halite which formed during the deposition of the microbial carbonate layers of primary gypsum are interbedded locally with carbonates suggesting the presence of restricted marine conditions the stable o and c isotopic composition of the carbonates that vary from dolomite to aragonite and calcite suggests a complex interplay between arid to humid climatic changes expressed cyclic interbedding of the carbonate with marl marlstone later diagenetic events mainly consist of phreatic meteoric recrystallization and cementation although considered as diachronous the microbial carbonates can be mapped out over a distance of more than 500 km across southern italy this indicates near constant environmental conditions upon the central mediterranean shelf at the beginning of the salinity crisis deposition of the extensive subaqueous microbial deposit that largely comprises the calcare di base is envisaged to have taken place across a shallow to moderate depth platform with local slopes into deeper water areas where some resedimentation occurred

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

comparative study of major element geochemistry of gypsum ghost limestones and selenite lithofacies from the miocene of northern carpathian foredeep implication to the model of massive replacement of solid sulphates by calcium carbonates abstract gypsum ghost limestones and selenite gypsum facies commonly believed to be as lithological equivalents caused by massive replacement of selenites by limestones occur in the same miocene evaporitic series of the northern carpathian foredeep southern poland and differ considerably with regard to their sedimentological features and major element compositions the differences dealing with variation of contents ranges means patterns of distribution correlations and interelement ratios of the major elements clearly do not indicate any geochemical similarities between the gypsum ghost limestones and the selenite gypsum lithofacies mass balance chemistry shows a deficit of calcium and sulphur contents in the limestones compared to the composition of the selenitic gypsum and implies that the gypsum ghost limestones system was open to mass transfer and cannot be related to simple and regionally extended replacement of solid sulphate rocks by limestones plus native sulphur the major element geochemistry of the gypsum ghost limestones and the selenites represent their original compositions which in turn reflect original depositional settings rather than pore water chemistry during replacive diagenesis both the lithological units developed in co eval depositional domains carbonate and sulphate constituting an evaporitic system but corresponding to different sedimentary settings of the system the gypsum ghost limestones reflect the unique situation of simultaneous formation of carbonate and selenites in a sedimentary transitional milieu between the carbonate and gypsum domains where bottom calcium carbonate deposition was alternating with the growth of selenite crystals the results are clearly inconsistent with the epigenetic model of formation of the polish sulphur deposits which assumes massive and regionally extended replacement of sulphate deposits by carbonates

calibration of seawater intrusion models inverse parameter estimation using surface electrical resistivity tomography and borehole data electrical resistivity tomography ert can be used to constrain seawater intrusion models because of its high sensitivity to total dissolved solid contents tds in groundwater and its relatively high lateral coverage however the spatial variability of resolution in electrical imaging may prevent the correct recovery of the desired hydrochemical properties such as salt mass fraction this paper presents a sequential approach to evaluate the feasibility of identifying hydraulic conductivity and dispersivity in density dependent flow and transport models from surface ert derived mass fraction in the course of this study geophysical inversion was performed by using a smoothness constraint tikhonov approach whereas the hydrological inversion was performed using a gradient based levenberg marquardt algorithm two synthetic benchmarks were tested they represent a pumping experiment in a homogeneous and heterogeneous coastal aquifer respectively these simulations demonstrated that only the lower salt mass fraction of the seawater freshwater transition zone can be recovered for different times this ability has here been quantified in terms of cumulative sensitivity and our study has further demonstrated that the mismatch between the targeted and the recovered salt mass fraction occurs from a certain threshold we were additionally able to explore the capability of sensitivity filtered ert images using ground surface data only to recover in both synthetic cases the hydraulic conductivity while the dispersivity is more difficult to estimate we attribute the latter mainly to the lack of ert derived data at depth where resolution is poorer as well as to the smoothing effect of the ert inversion

carbonate replacements after sulfate evaporites in the middle miocene of egypt abstract massive zones of diagenetic carbonate which replace sulfate deposits are observed in the middle miocene evaporites in several outcrops along the egyptian coast of the gulf of suez these carbonates display marked similarities of morphology lithofacies and stable isotope composition to diagenetic carbonates described in some portions of messinian gessoso solfifera formation of sicily and in the castiles of the upper permian castile formation of the delaware basin the mechanism of mineral transformation is basically bacterial sulfate reduction because the low 13c values of these carbonates argue for the organic origin of carbon the 18o values fall i to two distinct groupings indicating that the carbonates were crystallized during two different diagenetic stages the early diagenetic stage occurred soon after deposition in pore waters of marine origin and at different levels of evaporation organic matter used by bacteria was produced in situ the late diagenetic stage occurred when the tectonic or halokinetic uplift of the sequence caused flushing of the sediments by groundwaters of the phreatic aquifer and hydrocarbon migration furthermore to explain the very low 18o values of these carbonates it is inferred that locally ambient temperatures reached more than 35 c due to the large quantities of energy released during the bacterial sulfate reduction

diagenetic gypsum related to sulfur deposits in evaporites libros gypsum miocene ne spain abstract the libros gypsum is the thickest evaporite unit of the miocene infill of the teruel basin in ne spain during the deposition of this unit intense bacterial sulfate reducing bsr activity in the lake depocenter generated a native sulfur deposit diagenetic gypsum resulted from subsequent sulfur oxidation the different processes involved in these transformations were first investigated by anadon et al 1992 the present paper is concerned with this diagenetic gypsum from the stratigraphic petrographic isotopic and genetic points of view diagenetic gypsum occurs mainly as continuous or discontinuous layers individual levels or lenses irregular masses nodules and micronodules and veins its main textures are coarse crystalline anhedral and fine grained alabastrine both of which can replace any former lithology carbonate gypsum and sulfur the following sequence of processes and mineral textural transformations is deduced primary gypsum deposition bsr and biodiagenetic carbonate h 2 s production growth of native sulfur growth of diagenetic gypsum partial recrystallization of the diagenetic gypsum textures the gypsification of the native sulfur generated two types of banded structures in the diagenetic gypsum 1 concentric structures of centripetal growth and 2 expansive roughly concentric structures in the first type the gypsification operated from the outer boundaries towards the inner parts in the second type part of the carbonate hosting the sulfur was also gypsified replaced cemented in the diagenetic gypsum the 34 s values are in agreement with a native sulfur and h 2 s provenance the 18 o sulfate values however enable us to differentiate two main groups of values one with positive values and the other with negative values in the group of positive values interstitial evaporated solutions participated in the sulfur oxidation this process presumably occurred in a first oxidation stage during shallow to deeper burial of the libros gypsum unit in the group of negative values however only meteoric waters participated in the oxidation which presumably occurred in a second oxidation stage during the final exhumation of the unit a third group of values is characterized by very high sulfur and oxygen values suggesting that bsr residual solutions also participated in the oxidation processes locally during the two oxidation stages both the textural characteristics and the isotopic composition of the diagenetic gypsum indicate that gypsification operated as a multistadic process

a new facies model for the upper gypsum of sicily italy chronological and palaeoenvironmental constraints for the messinian salinity crisis in the mediterranean the upper gypsum unit of the caltanissetta basin sicily records the last phase of the messinian salinity crisis comprising the so called lago mare event a new facies analysis study recognizes nine to ten depositional cycles consisting of seven rhythmically interbedded primary gypsum bodies and two to three sandstone bodies separated by marly terrigenous horizons showing laterally persistent vertical organization a basal thin gypsum bed is overlain by a cluster of five thicker gypsum bodies a marly interval containing two distinct sandstone horizons separates this cluster from the overlying uppermost seventh gypsum body the terrigenous arenazzolo formation in turn followed by the lower pliocene trubi formation is considered here to form the uppermost part of the upper gypsum unit the rhythmic alternation in the sandy marls and gypsum sandstone bodies records the response of sediments from shelfal to deltaic systems to precession driven arid wet climate fluctuations causing cyclical changes of both base level and water concentration during wet climate phases at insolation maxima marl and sandstone were deposited in a hypohaline environment as suggested by i the typical lago mare faunal assemblage and ii the negative 18o values during arid phases at insolation minima the reduced meteoric supply recorded by higher 18o values in the carbonate caused the development of a negative hydrological budget leading to evaporite precipitation at a basinal scale the upper gypsum unit unconformably overlies a mainly clastic evaporite unit containing carbonate breccia the so called calcare di base and or clastic gypsum towards the basin centres where the basal contact becomes conformable a primary gypsum cumulate horizon is present this layer is interpreted as a possible lateral equivalent of the halite unit present only in the deepest depocentres based on astronomical calibration of the depositional cycles the upper gypsum unit including the arenazzolo formation spans the interval between 5 33 and 5 53 ma this new age calibration allows the deposition of the halite unit to be dated between 5 6 ma top of the lower evaporites and 5 55 ma base of the upper evaporites corresponding to isotopic stages tg12 and or tg14

molecular fossils and other organic markers as palaeoenvironmental indicators of the messinian calcare di base formation normal versus stressed marine deposition rossano basin northern calabria italy a multidisciplinary study has been carried out on the late miocene messinian calcare di base formation in northern calabria italy with the aim of understanding the depositional conditions of these enigmatic carbonate sediments that have been interpreted as evaporitic or diagenetic limestone the research has been developed through sedimentological microfacies organic petrography and geochemical analyses palynofacies rock eval pyrolysis and gas chromatography mass spectrometry the carbonates studied preserve their original mineralogy aragonite and microstructure the prevailing microfacies consists of clotted peloidal micrite with antigravitative fabric larger and darker cylindrical subcylindrical micritic grains attributable to faecal pellets are more or less randomly dispersed in the peloidal micrite the faecal pellets have been ascribed to copepods because zooclasts of these arthropods were observed in the palynofacies bright epifluorescence characterizes the faecal pellets and peloidal micrite indicating their high content of organic matter detrital and stromatolitic microfacies occur rarely around a few percent the detrital microfacies is characterized by silt sized grains organized in thin sometimes bioturbated graded laminae the stromatolitic microfacies shows planar to gently curved wrinkled laminae organized in dark and light couplets the associated sedimentary organic matter shows low maturity and preserves the original signatures of the source organisms rock eval pyrolysis revealed a transitional composition between type ii and type iii kerogen suggesting a mixture of marine and terrigenous organic matter input the molecular biogeochemical data indicate three main biological signatures algae bacteria and higher plants organic markers together with sedimentary evidence indicate a marine depositional scenario influenced by freshwater input rather than evaporitic concentration we conclude that the most probable bacterial process involved in carbonate precipitation of the calcare di base considering the freshwater input and consequent probable enrichment in organic matter and ca2 ions is ammonification of amino acids in aerobic conditions

behavior of carbonate associated sulfate during meteoric diagenesis and implications for the sulfur isotope paleoproxy abstract although carbonate associated sulfate cas is used widely as a proxy for the sulfur isotope composition of ancient seawater little is known about the effects of diagenesis on retention of primary 34 s signals our case study of the key largo limestone pleistocene florida is the first systematic assessment of the impact of meteoric diagenesis on cas properties geochemical and petrographic data show that meteoric diagenesis has affected the exposed coralline facies to varying degrees yielding differences now expressed as sharp reaction fronts between primary and secondary carbonate minerals within individual coral heads specifically analyses across high resolution transects in the key largo limestone show that concentrations of strontium and sodium decrease across the recrystallization front from original aragonite to meteoric low magnesium calcite by factors of roughly 5 and 10 respectively predictably 18 o values decrease across these same fronts the 13 c relationships are more complex with the most depleted values observed in the latest formed calcite such trends likely reflect carbon isotope buffering capacity that decreased as reaction progressed as well as protracted development of soil profiles and the associated terrestrial biomass and thus depleted 13 c during sea level lowstand conversely 34 s values of cas vary within a narrow buffered range from 20 6 to 22 6 compared to 20 8 22 0 of coeval pleistocene seawater across the same mineralogical transition despite sulfate concentrations that drop in the diagenetic calcite by an average factor of 12 collectively these data point to robust preservation of primary 34 s for carbonates that have experienced intense meteoric diagenesis which is encouraging news for those using the isotopic composition of cas as a paleoceanographic proxy at the same time the vulnerability of cas concentrations to diagenetic resetting is clear

ediacaran gaskiers glaciation of newfoundland reconsidered newly discovered palaeosols in the gaskiers formation of newfoundland provide a new perspective on its palaeoenvironment and are evidence that it was not a deep submarine tillite nor an anoxic deep sea floor nor a cap carbonate from extreme geochemical perturbation of the global ocean discovery of oxidized palaeosols and re evaluation of sedimentary facies and stratigraphic relationships now suggest reinterpretation as a coastal plain with glacial moraines in the forearc basin of a continental volcanic arc like modern japan ediacaran palaeosols of the gaskiers formation lack large root traces but show soil profile differentiation clay enrichment and depletion of alkali and alkaline earth elements at the expense of feldspar and rock fragments and diagnostic soil structures blocky peds argillans sepic plasmic fabric these palaeosols are evidence of a humid temperate climate and marked marine regression accompanying the gaskiers glaciation of the early ediacaran 580 ma geochemical weathering trends in the palaeosols especially phosphorus depletion are characteristic of biologically active soils ediacaran microbial earth ecoystems may have been responsible for filamentous disruption of bedding in the palaeosols

carbonate stromatolites from a messinian hypersaline setting in the caltanissetta basin sicily petrographic evidence of microbial activity and related stable isotope and rare earth element signatures lower messinian stromatolites of the calcare di base formation at sutera in sicily record periods of low sea level strong evaporation and elevated salinity thought to be associated with the onset of the messinian salinity crisis overlying aragonitic limestones were precipitated in normal to slightly evaporative conditions occasionally influenced by an influx of meteoric water evidence of bacterial involvement in carbonate formation is recorded in three dolomite rich stromatolite beds in the lower portion of the section that contain low domes with irregular crinkly millimetre scale lamination and small fenestrae the dominant microfabrics are i peloidal and clotted dolomicrite with calcite filled fenestrae ii dolomicrite with bacterium like filaments and pores partially filled by calcite or black amorphous matter and iii micrite in which fenestrae alternate with dark thin wispy micrite the filaments resemble beggiatoa like sulphur bacteria under scanning electron microscopy the filaments consist of spherical aggregates of dolomite interpreted to result from calcification of bacterial microcolonies the dolomite crystals are commonly arranged as rounded grains that appear to be incorporated or absorbed into developing crystal faces biofilm like remains occur in voids between the filaments the dolomite consistently shows negative d 13 c values down to 11ae3 and very positive d 18 o mean value 7ae9 that suggest formation as primary precipitate with a substantial contribution of organic co2 very negative d 13 c values down to 31ae6 of early diagenetic calcite associated with the dolomite suggest contribution of co2 originating by anaerobic methane oxidation the shale normalized rare earth element patterns of sutera stromatolites show features similar to those in present day microbial mats with enrichment in light rare earth elements and m type tetrad effects enrichment around pr coupled to a decline around nd and a peak around sm and eu taken together the petrography and geochemistry of the sutera stromatolites provide diverse and compelling evidence for microbial influence on carbonate precipitation