multi parametric climatological analysis associated with global significant volcanic eruptions during 2002 2017 in this work we search for physical and chemical climatological anomalies preceding major volcanic explosive eruptions mostly vei volcanic explosivity index 4 occurred from 2002 to 2017 by applying two specific algorithms i e capri and means the former algorithm has been already used for a multi climatological analysis of the amatrice norcia 2016 2017 earthquake preparatory phase piscini et al in pure appl geophys 174 3673 3688 2017 here we analyse some climatological parameters for a three month period before each volcanic explosive eruption then we compare the behavior with the typical one of the past the analysis is applied to an area with dimensions comparable to the volcano crater because it is the increase of the magmatic camera activity that in turn can cause a temperature increase whose evidence could be detected at the surface slezin in j volcanol geotherm res 122 1 2 7 50 2003 while the use of a larger area would provide a greater probability of occurrence of other events e g other volcano eruption meteorological storms etcetera therefore a smaller area of study reduces the risk to get false alarms in particular we considered thermal skin temperature skt and total water vapour content tcwv from ecmwf european centre and aerosol optical thickness aot sulphur dioxide so2 and atmospheric dimethylsulphide dms are obtained from nasa merra 2 global modeling and assimilation data archive the latter compound was added in the analysis to check the validity of the method since we did not expect significant anomalies from this parameter the models above described are used for their temporal spatial completeness allowing performing time series analyses and for a real time monitoring on a global scale by simultaneous analysis we found for almost all volcanic eruptions some anomalies in about all analyzed parameters that precede by 75 days to 20 days the explosion these anomalies are not always simultaneous but we find an interesting synchronicity that probably reveals a correlation among the different datasets in addition the agung volcano which has recently started an eruptive activity 25 november 2017 without reaching a vei4 explosion has also been investigated the data related to this volcano present a small number of anomalies much lower than all attributed to the other analyzed explosive volcanoes and this is in high agreement with the low explosive nature of the agung volcano eruption we find that the occurrence of thermal anomalies typically preceding stratovolcano caldera eruptions seems to take place some days after so2 emissions the climatological anomalies that precede eruptions at high latitudes usually surround the volcano in a wider area outside the volcanic edifice we verify that the number of positive anomalies is systematically greater in the year that precedes the investigated eruption with respect to a quiet year of comparison with accuracy from 91 to 100 suggesting that the applied methods detected climatological anomalies likely related to imminent volcanic eruptions

temperature limits for preservation of primary calcite clumped isotope paleotemperatures abstract solid state reordering of c o bonds in the calcite lattice can alter the clumped isotope composition of paleotemperature archives such as fossil brachiopod shells without inducing significant changes in shell microstructure and trace element concentrations metrics commonly used to gauge preservation quality to correctly interpret the paleoenvironmental significance of clumped isotope derived paleotemperatures it is necessary to understand the temperature time domain in which solid state c o bond reordering is important we address this question using a combination of laboratory and natural geological experiments on paleozoic brachiopod shells the laboratory experiments involve heating fossil brachiopod calcite at different temperatures and times to directly observe rates of 13 c 18 o bond reordering the resulting arrhenius parameters are indistinguishable from values previously determined for an optical calcite with similar trace element compositions we develop an alternative kinetic model for reordering that accounts for non first order reaction progress observed during the initial several hundred minutes of laboratory heating experiments and show that the simplified first order approximation model passey and henkes 2012 predicts reaction progress equally well for temperatures and timescales relevant to sedimentary basins we evaluate our laboratory based rate predictions by studying brachiopod calcite from several sedimentary basins with independently constrained burial temperature histories specifically we use the laboratory derived arrhenius parameters to predict the evolution of brachiopod calcite clumped isotope compositions during successive one million year time steps reflecting the burial and exhumation temperature paths of each basin while this exercise is limited by the relatively large uncertainties in the temperature histories of these basins we find general correspondence within error between predicted and observed clumped isotope values we present simplified temperature time diagrams for calcite showing domains where primary clumped isotope compositions will be preserved partially reordered and fully reordered in conclusion calcite samples dwelling at 100 c or lower for 10 6 10 8 year timescales should not be affected by solid state c o bond reordering

hauptdolomit norian stratigraphy paleogeography and diagenesis abstract geochemical and carbonate petrographical methods were coordinated in facies investigations and environmental reevaluations related to the hauptdolomit hd main doimite formation norian of the northern calcareous alps it is practical to distinguish eight environmentally controlled facies units 1 8 and three geochemical groups i iii superimposed upon the environment pattern tidal complex lagoonal complex barrier bar and shoal complex is a predictable geochemical dolomitization and non carbonate distribution the vertical and lateral facies associations their waxing and waning in the geologic columns allow paleogeographic reconstructions especially important are clayey bituminous facies commonly known as seefeld facies which are interpreted to be of mainly intertidal to very shallow near shore rather than of deep water origin threefold stratigraphy can be substantiated and is found to be practicable for the hd formation in a large part of the northern calcareous alps in an attempt to explain some of the phenomena associated with dolomitization in the hd formation a model of anaerobic dolomitization has been considered outlining steps of early diagenetic dolomitization

new paleomagnetic results from the ediacaran doushantuo formation in south china and their paleogeographic implications abstract a new paleomagnetic pole is obtained from the top of member 3 of the doushantuo formation in the jiulongwan section of the yangtze gorges area in south china a total of 191 samples from 23 sites were collected and subjected to stepwise alternating field af and thermal demagnetization after the removal of a soft component sc of viscous magnetic remanence acquired in present geomagnetic field a high temperature component hc likely carried by magnetite was isolated the hc includes vectors from 147 samples using principal component analysis and arc constraints from 44 samples using remagnetization great circle analysis both the vectors only and the combined vectors and arc constraints of the hc passed a reversal test this is the first ediacaran paleomagnetic remanence from the south china block scb that passes a reversal test and it is interpreted as a primary remanence the hc vectors were thus used to calculate the paleomagnetic pole and in combination with arc constraints were used for polarity interpretation the vectors give a mean direction of d 75 2 i 41 0 95 2 5 n 147 after bedding correction and a corresponding paleomagnetic pole at 23 9 n 187 0 e dm dp 3 0 1 8 this pole differs significantly from previously published results of the doushantuo formation which may have been subjected to paleozoic remagnetization our results provide a 23 5 1 8 n paleolatitude for the yangtze gorges area of the scb and suggest several alternative paleogeographic options for the ediacaran cambrian amalgamation of east gondwana depending on chronostratigraphic correlations

massive formation of early diagenetic dolomite in the ediacaran ocean constraints on the dolomite problem paleozoic and precambrian sedimentary successions frequently contain massive dolomicrite camg co3 2 units despite kinetic inhibitions to nucleation and precipitation of dolomite at earth surface temperatures 100 c thus raising doubt about the validity of these deposits as archives of earth surface environments we present a high resolution 63 my long clumped isotope temperature t 47 record of shallow marine dolomicrites from two drillcores of the ediacaran 635 to 541 ma doushantuo formation in south china our t 47 record indicates that a majority 87 of these dolostones formed at temperatures of 100 c when considering the regional thermal history modeling of the influence of solid state reordering on our t 47 record further suggests that most of the studied dolostones formed at temperatures of 60 c providing direct evidence of a low temperature origin of these dolostones furthermore calculated 18o values of diagenetic fluids rare earth element plus yttrium compositions and petrographic observations of these dolostones are consistent with an early diagenetic origin in a rock buffered environment we thus propose that a precursor precipitate from seawater was subsequently dolomitized during early diagenesis in a near surface setting to produce the large volume of dolostones in the doushantuo formation our findings suggest that the preponderance of dolomite in paleozoic and precambrian deposits likely reflects oceanic conditions specific to those eras and that dolostones can be faithful recorders of environmental conditions in the early oceans

dolomite abundance and stratigraphic age constraints on rates and mechanisms of phanerozoic dolostone formation increasing dolomite abundance with age relative to limestone has long been accepted as one of the general truisms of sedimentary geology a relationship which suggests that dolomitization is a cumulative process occurring slowly over the full burial history of a carbonate sequence however reevaluation of data in support of this assumption indicates that although relative dolomite abundances do change significantly throughout phanerozoic carbonate sequences no data set demonstrates any direct correlation between dolomite content and age whereas tabulation of available data does suggest greater amounts of dolomite formation during periods of continental flooding global mass balance calculations of potential magnesium sources also indicate that most dolomite has formed from marine or marine derived fluids at the earth9s surface this conclusion is indirectly supported by significant short term period scale changes in phanerozoic dolomite abundance a variation which would be more attenuated if dolomitization were dominantly a burial process dolomitization may be enhanced during times of global transgression higher atmospheric pco 2 and lower calcite saturation state in shallow marine settings

hydrothermal alteration of the ediacaran doushantuo formation in the yangtze gorges area south china abstract the geochemical and fossil record preserved in the ediacaran age 635 551 ma doushantuo formation of south china has been extensively examined to explore the impact of changing climate and the oxidation state of the oceans on the development and distribution of early multicellular life in the yangtze gorges area this formation shows many of the geochemical trends and features thought to typify global ocean chemistry in the ediacaran period but there are indications that post sedimentary processes modified these signals this study of clay minerals and organic matter builds a more detailed picture of the type and degree of post sedimentary alteration at different stratigraphic levels of the formation and focuses on how this alteration influenced stable carbon and oxygen isotope records in the cratonward jiulongwan and huajipo sections of the doushantuo formation its lower part members 1 and 2 consists largely of dolomitic shale rich in authigenic saponite that crystallized in an alkaline sedimentary basin saponite has been altered to chlorite via corrensite across tens of meters of strata in lower member 2 with increased alteration downward toward the cap dolostone the greater chloritization is accompanied by lower 18 o and higher d values of trioctahedral clays this pattern of alteration of trioctahedral clays is likely due to hydrothermal fluid activity in the underlying relatively permeable nantuo formation and cap dolostone a concomitant increase of solid bitumen reflectance toward the base of the formation supports this idea in the uppermost part of the formation in the yangtze gorges area member 4 a typical open water marine dolomitic shale rich in illite and organic matter increases in the methylphenanthrenes ratio index and solid bitumen reflectance correlate with decrease of the bulk rock k al ratio upward providing evidence for hot fluid migration above the nearly impermeable shale clay from the upper part of the formation is enriched in 18 o but not in d relative to clay from the lower parts indicating progressive 18 o enrichment of hydrothermal fluids that percolated upward and laterally through permeable 18 o rich carbonates a maximum hydrothermal alteration temperature of 200 c is estimated from a calibration curve for illitization during burial diagenesis but given that the hydrothermal activity probably occurred in short pulses the temperature could have been much higher k ar ages are consistent across different size fractions of fine illite from member 4 shale 430 ma and from a k bentonite bed near the base of member 2 in the jiuqunao section 325 ma 25 km from jiulongwan and huajipo these age values show that the diagenetic illite of the doushantuo formation is a product of either deep burial diagenesis overprinted by spatially limited hydrothermal activity or of two localized hydrothermal events patterns of carbonate 13 c and 18 o depletion in the basal doushantuo formation are similar to chloritization trends and 18 o variation in diagenetic clay minerals given independent evidence for 13 c depletion of hydrothermal fluids these trends indicate carbonate fluid isotope exchange commensurate with the degree of post sedimentary alteration supporting a model of lithologically controlled differential diagenesis induced by hydrothermal fluids as the main control on c and o isotope variability in this stratigraphic interval this model could potentially explain other notable 13 c excursions higher up in member 3

high temperature environments of human evolution in east africa based on bond ordering in paleosol carbonates many important hominid bearing fossil localities in east africa are in regions that are extremely hot and dry although humans are well adapted to such conditions it has been inferred that east african environments were cooler or more wooded during the pliocene and pleistocene when this region was a central stage of human evolution here we show that the turkana basin kenya today one of the hottest places on earth has been continually hot during the past 4 million years the distribution of 13c 18o bonds in paleosol carbonates indicates that soil temperatures during periods of carbonate formation were typically above 30 c and often in excess of 35 c similar soil temperatures are observed today in the turkana basin and reflect high air temperatures combined with solar heating of the soil surface these results are specific to periods of soil carbonate formation and we suggest that such periods composed a large fraction of integrated time in the turkana basin if correct this interpretation has implications for human thermophysiology and implies a long standing human association with marginal environments

impact of diagenesis and low grade metamorphosis on isotope δ26mg δ13c δ18o and 87sr 86sr and elemental ca mg mn fe and sr signatures of triassic sabkha dolomites abstract dolomite is a common rock forming mineral in the geological record but its value as archive of ancient seawater 26 mg signatures and their variations in time is at present underexplored unknown factors include the sensitivity of 26 mg ratio to processes in the diagenetic and low grade metamorphic domain this paper documents and discusses the first detailed 26 mg data set from early diagenetic and burial dolomites samples come from the upper triassic hauptdolomit dolomia principale the dolomites italy and include coeval dolomicrites that underwent differential burial diagenesis and low grade metamorphosis in a temperature range between about 100 and more than 350 c magnesium isotope data are complemented by dolomite 13 c 18 o and 87 sr 86 sr isotope ratios as well as ca mg mn fe and sr elemental abundances and data on the dolomite crystal structure as indicated by dolomicrite 87 sr 86 sr ratios and petrographic evidence sabkha calcian d1 dolomites precipitated from evaporated seawater and stabilized at an early marine pore water diagenetic stage to d2 dolomites analysed here with increasing burial temperature dolomite 26 mg ratio scatter in the data set decreases with increasing mg ca ratio and degree of order specifically 26 mg ratio variability is reduced from 0 36 2 at burial temperatures beneath 100 c to about 0 14 2 at temperatures in excess of 350 c respectively with mean 26 mg values ranging constantly near 1 9 this suggests that at least for the rock buffered system investigated here dolomicrite 26 mg proxy data are conservative and preserve near pristine values even at elevated burial temperatures at present the main element of uncertainty is the mg isotope fractionation factor between evaporated seawater and dolomite a possible solution to this problem includes the compilation of data from modern sabkha environments including pore water and calcian dolomite 26 mg isotope signatures

carbonate clumped isotope bond reordering and geospeedometry carbonate clumped isotope thermometry is based on the preference of 13c and 18o to form bonds with each other at elevated temperatures such bond ordering is susceptible to resetting by diffusion of c and o through the solid mineral lattice this type of bond reordering has the potential to obscure primary paleoclimate information but could also provide a basis for reconstructing shallow crustal temperatures and cooling rates we determined arrhenius parameters for solid state reordering of c o bonds in two different calcites through a series of laboratory heating experiments we find that the calcites have different susceptibilities to solid state reordering reaction progress follows a first order rate law in both calcites but only after an initial period of non first order reaction that we suggest relates to annealing of nonequilibrium defects when the calcites are first heated to experimental temperature we show that the apparent equilibrium temperature equations or closure temperature equations for carbonate clumped isotope reordering are analogous dodson s equations for first order loss of daughter isotopes for each calcite the sensitivity of apparent equilibrium temperature to cooling rate is sufficiently high for inference of cooling rates within a factor of 5 or better for cooling rates ranging from tens of degrees per day to a few degrees per million years however because the calcites have different susceptibilities to reordering each calcite defines its own cooling rate apparent equilibrium temperature relationship the cooling rates of carrara marble inferred from carbonate clumped isotope geospeedometry are 10 6 10 3 degrees per annum and are in broad agreement with rates inferred from thermochronometric methods cooling rates for 13c depleted calcites from the late neoproterozoic doushantou cap carbonates in south china are on the order of 102 104 degrees per annum consistent with rapid cooling following formation of these calcites by a short lived hydrothermal event bristow et al 2011 nature v 474 p 68 71 most of the uncertainty in these estimates relates to uncertainty in arrhenius parameters for different calcites thus while the carbonate clumped isotope geospeedometer shows promise for recording cooling rates in settings and lithologies where other geospeedometers may not be applicable the uncertainty in cooling rate will be large without independent knowledge of the reordering kinetics of each study material thus the full potential of the method will only be realized if reordering kinetics can be accurately determined for each study material or predicted on the basis of mineral composition texture or other observable parameters

a revised calibration of the clumped isotope thermometer abstract a growing number of materials and environmental settings are studied using the carbonate clumped isotope 47 thermometer the method has been applied in both biogenic and non biogenic carbonate systems in marine and terrestrial settings over a wide range of geological timescales the current 47 temperature calibration gives good temperature estimates for most biogenic materials however systematic biases are commonly observed at low temperatures in this study we report additional calibration data that covers a wider temperature range at more evenly distributed temperatures and are measured at higher analytical precision than the original calibration combining these data with the original calibration yields a 47 t relationship that is similar to the original calibration though slightly less steep 47 0 0526 0 0025 10 6 t 2 0 0520 0 0284 this revised calibration is in better agreement with biogenic carbonates including those grown at low temperatures the difference between the original and revised calibrations is significant for carbonates forming below 16 c or above 49 c 47 values of 0 68 and 0 56 additionally we include a comprehensive analysis of the sources of error associated with 47 measurements and estimated temperatures and recommend measurement strategies for obtaining the desired precision as an illustration we apply the revised calibration and uncertainty analysis to 3 previously published studies at low temperatures the revised calibration results in significant differences from the original calibration and hence affects the interpretation of the environmental signal recorded in light of our 47 errors analysis in cases where the temperature signals are small we find that replicate analyses are critical to identify a temperature signal

a study of the uppermost inner core from pkkp and p p differential traveltimes summary we have assembled a data set of pkkpdf pkkpbc pkkpdf bc and pkppkpdf pkkpbc differential traveltimes this data set is used to study the earth s uppermost inner core in the western hemisphere data from the eastern pacific are recorded at the canadian yellowknife array and travel through the inner core twice once perpendicular to the earth s rotation axis and once parallel to the rotation axis our polar paths sample a similar region to paths from the south sandwich islands to alaska an important path geometry for inner core anisotropy studies our data set has the potential to be an independent source of information on the structure of the inner core and to be a good supplement to past pkp studies differential time residuals relative to isotropic inner core models of up to several seconds are found the differential traveltimes show significant scatter up to 6 s making it difficult to attribute them to inner core anisotropy alone alternatively strong heterogeneity in the inner core and along the mantle paths may contribute to observations

dolomite occurrence evolution and economically important associations abstract dolomite is not a simple mineral it can form as a primary precipitate a diagenetic replacement or as a hydrothermal metamorphic phase all that it requires is permeability a mechanism that facilitates fluid flow and a sufficient supply of magnesium dolomite can form in lakes on or beneath the shallow seafloor in zones of brine reflux and in early to late burial settings it may form from seawater from continental waters from the mixing of basinal brines the mixing of hypersaline brine with seawater or the mixing of seawater with meteoric water or via the cooling of basinal brines bacterial metabolism may aid the process of precipitation in settings where sulfate reducing species flourish and microbial action may control primary precipitation in some hypersaline anoxic lake settings dolomite is a metastable mineral early formed crystals can be replaced by later more stable phases with such replacements repeated a number of times during burial and metamorphism each new phase is formed by the partial or complete dissolution of an earlier dolomite this continual re equilibration during burial detracts from the ability of trace elements to indicate depositional conditions and resets the oxygen isotope signature of the dolomite at progressively higher temperatures because subsurface dolomite evolves via dissolution and reprecipitation a bed of dolomite can retain or create porosity and permeability to much greater burial depths and into higher temperature realms than a limestone counterpart dolomitization also creates new crystals with new rhomb growth following the dissolution of less stable precursors repetition of this process without complete pore cementation can generate intercrystalline porosity a number of times in the rock s burial history intercrystalline porosity is a highly interconnected style of porosity that gives dolomite reservoirs their good fluid storage capacity and efficient drainage the fact that many dolomite reservoirs formed via brine reflux means that they sit beneath an evaporite seal in both platform and basinwide evaporite settings the same association of evaporites sulfate source and entrained hydrocarbons means that burial conditions are also suitable for thermochemical sulfate reduction and the precipitation of base metals this tends to occur at higher temperatures 60 c 80 c and so the resulting dolomites tend to be ferroan and consist of saddle shaped crystals

3700 ma pre metamorphic dolomite formed by microbial mediation in the isua supracrustal belt w greenland simple evidence for early life chemical meta sedimentary rocks in the amphibolite facies 3700 ma isua supracrustal belt w greenland are mostly strongly deformed so there is only a small chance of the survival of features such as stromatolites or microfossils that would be direct proof of a 3700 ma biosphere therefore the search for evidence of 3700 ma life in isua rocks has focused on chemical signatures particularly c isotopes the new approach presented here is based on whole rock chemistry rather than isotopic signatures isua chemical sedimentary rocks have ca mg fe bulk compositions that coincide with ferroan dolomite siderite fe oxide mixtures most have low al2o3 tio2 contents 0 5 and 0 05 wt respectively showing minimal contamination from terriginous materials identical seawater like ree y shale normalised trace element signatures with la ce eu and y positive anomalies are found in magnetite rich banded iron formation bif such as the geochemical standard if g dolomite rich rocks and quartz carbonate calcsilicate rocks additionally from a rare small area of low deformation in isua there are 3700 ma pillow lava interstices consisting of quartz tremolite calcite derived from pre metamorphic dolomite silica thus the dolomite in the chemical sediments and the pillow interstice was part of the pre metamorphic assemblage and was deposited from seawater and or low temperature groundwater as shown by the ree y chemistry therefore at least some isua carbonate rocks are sedimentary or diagenetic in origin rather than being formed by metasomatism at 600 500

dolomite mountains and the origin of the dolomite rock of which they mainly consist historical developments and new perspectives beginning in the late 18th century the dolomite mountains in northern italy have been the location for major sedimentological developments from the discovery of the mineral dolomite to the formulation of the coral reef hypothesis to explain the origin of the massive dolomite structures that define the splendid scenery of the region further the dolomite mountains have inspired voluminous research into the origin of dolomite questioning whether dolomite is a primary precipitate or a secondary replacement product recently with the recognition that microbes can mediate dolomite precipitation a new geomicrobiological approach combining the study of modern natural environments with bacterial culture experiments is now being used to calibrate or interpret microbial evidence derived from the dolomite rock record this three pronged methodology applied to the study of dolomite formation holds great promise for future research into the dolomite problem and provides a new impetus to revisit the dolomite mountains in the 21st century

paleoclimate reconstruction using carbonate clumped isotope thermometry carbonate clumped isotope thermometry is a relatively new paleotemperature proxy based on measurements of the degree of ordering of 13 c and 18 o into bonds with each other making the 13 c 18 o 16 o 2 2 ion group in lattices of carbonate minerals this technique has several unusual properties that complement existing methods of paleoclimate reconstruction most importantly it is based on a homogeneous isotope exchange equilibrium and thus constrains temperature independent of the isotopic composition of waters from which carbonates grew this method also appears to be generally insensitive to vital effects that compromise many other paleothermometers based on the chemical properties of biominerals or organic matter at least for those organisms that have been subjected to systematic study to date corals and foraminifera however discrepancies among some calibrations particularly at low temperatures may point toward the existence of vital effects in mollusks and other organisms this review discusses the principles and calibrations of the technique its uses in combination with conventional stable isotope measurements to constrain the 18 o of past waters preservation of paleotemperatures in ancient materials as well as current problems in our understanding of calibrations and interlaboratory data comparisons

neoproterozoic aragonite dolomite seas widespread marine dolomite precipitation in cryogenian reef complexes the extraordinary abundance of dolomite in the proterozoic challenges our understanding of precambrian marine environments here we show that synsedimentary marine dolomite precipitation was pervasive within cryogenian reef complexes from the adelaide fold belt south australia although these reefs are composed of dolomite textural evidence indicates an originally aragonitic mineralogy for depositional components in common with many other neoproterozoic carbonates allochthonous slope debris from the reefs invariably contains both limestone and dolomite clasts indicating synsedimentary dolomitization in the reefs we describe several new forms of fibrous marine dolomite cement from the reefs that have a length slow optical character these fascicular slow radial slow and rhombic dolomite cements have finely preserved cathodoluminescent growth zones and optical characteristics that indicate they originally precipitated as dolomite rather than replacing calcite or aragonite cements abundant early marine dolomite precipitation implies a radically different seawater chemistry for the cryogenian perhaps these aragonite dolomite seas are associated with extreme neoproterozoic glacial events and or ocean anoxia

characterization of environmental conditions during microbial mg carbonate precipitation and early diagenetic dolomite crust formation brejo do espinho rio de janeiro brazil

alteration of early formed dolomite during shallow to deep burial mississippian mission canyon formation central to southwestern montana dolomite in the mississippian mission canyon formation osagean to middle meramecian of central and southwestern montana precipitated during multiple episodes of dolomitization and or recrystallization the earliest generation of dolomite most likely precipitated from evaporated sea water in near surface diagenetic environments when the mission canyon platform intermittently aggraded to sea level this dolomite has relatively positive delta sup 18 o values minus 1 5 to 7 5 and typically is nonstoichiometric and trace element enriched a second generation of dolomite has very negative delta sup 18 o values minus 11 2 to minus 1 5 and always is stoichiometric and trace element depleted dolomite with delta sup 18 o values minus 6 8 is in the upper 100 180 m of the mission canyon formation beneath a regional post mission canyon unconformity and karst surface that extends across the entire study area dolomite depleted in sup 18 o may have 1 precipitated initially in a regional mixing zone during post mission canyon subaerial exposure and karstification 2 precipitated at elevated temperatures during later diagenesis or 3 recrystallized from an earlier generation of dolomite during later shallow to deep burial diagenesis very negative delta sup 18 o values and low trace element contents for the second generation of dolomite suggest that diagenetic solutions were dominated by meteoric water whereas delta sup 13 c values indicate that diageneticmore fluids were buffered by osagean carbonate rocks 54 refs 10 figs less

precambrian dolomites petrographic and isotopic evidence that they differ from phanerozoic dolomites dolomites are more common in precambrian than in phanerozoic rocks and from a petrographic isotopic study of the middle to upper proterozoic beck spring dolomite of eastern california it is suggested that precambrian dolomites are different from those of the phanerozoic petrographically all fabric details of precambrian dolomites studied are preserved just as if they were limestones and isotopically they show the same trend as limestones increasingly negative i8 o and to a lesser extent increasingly light i8 c from depositional components through early fibrous dolomite cements to later dolomite spar cements the data suggest that in precambrian time dolomite was the principal carbonate mineral precipitated from seawater and during diagenesis and this implies that precambrian seawater was different from that of the phanerozoic

evolution of neoproterozoic wonoka shuram anomaly aged carbonates evidence from clumped isotope paleothermometry the wonoka shuram anomaly represents the largest negative carbon isotope excursion recognized in the geologic record and is associated with the emergence and diversification of metazoan life ca 580 million years ago ma the origin of the anomaly is highly debated with interpretations ranging from primary to diagenetic each having unique and potentially transformative implications for early life here we apply carbonate clumped isotope thermometry to three sections expressing the anomaly in order to constrain mineral formation temperatures and thus directly calculate water oxygen isotope compositions 18ow with which carbonate minerals equilibrated with 18ow known it is possible to address previous hypotheses for the origin of the anomaly in each section precipitation temperatures correlate positively with reconstructed 18ow previous hypotheses based on the covariance of 18ocarb vs 13ccarb uncorrected for temperature effects suggested a meteoric diagenetic origin for the anomaly however reconstructed 18ow values do not covary with carbon isotope compositions 13ccarb within anomaly facies rather the oxygen isotope and temperature data are consistent with carbonate recrystallization and equilibration under increasingly rock buffered conditions based on simple modeling and comparison to modern formation fluids recrystallization may have occurred in an environment far removed from the initial depositional or early diagenetic regime in addition although clumped isotope temperatures vary significantly and reach elevated values consistent with burial diagenesis it is unclear to what degree if at all carbon isotope values were reset during recrystallization ultimately these new data indicate that wonoka shuram aged carbonates experienced equilibration with fluids under increasingly closed system conditions the clumped isotope data do not provide a means to distinguish previous hypotheses outright but provide additional context for the evaluation of geochemical signatures within these ancient carbonate rocks