climate warming in the latest permian and the permian triassic mass extinction high resolution oxygen isotope records document the timing and magnitude of global warming across the permian triassic p tr boundary oxygen isotope ratios measured on phosphate bound oxygen in conodont apatite from the meishan and shangsi sections south china decrease by 2 in the latest permian translating into low latitude surface water warming of 8 c the oxygen isotope shift coincides with the negative shift in carbon isotope ratios of carbonates suggesting that the addition of isotopically light carbon to the ocean atmosphere system by siberian traps volcanism and related processes resulted in higher greenhouse gas levels and global warming the major temperature rise started immediately before the main extinction phase with maximum and harmful temperatures documented in the latest permian meishan bed 27 the coincidence of climate warming and the main pulse of extinction suggest that global warming was one of the causes of the collapse of the marine and terrestrial ecosystems in addition very warm climate conditions in the early triassic may have played a major role in the delayed recovery in the aftermath of the permian triassic crisis

new c isotope stratigraphy from southwest china implications for the placement of the precambrian cambrian boundary on the yangtze platform and global correlations a high resolution c isotope profile from a fossiliferous section spanning the precambrian cambrian pc c boundary on the yangtze platform southwest china is used to constrain c isotope chemostratigraphy and its global correlation the discovery of a strong negative c isotopic anomaly just below the china marker a indicates that this negative anomaly can be correlated globally and demonstrates that the pc c boundary of the chinese successions should be close to marker a on the basis of c isotope chemostratigraphic constraints and biostratigraphic data we find that c isotopic peak s2 also first reported here from the chinese successions can be correlated with c isotopic peak i in northern siberia and c isotope feature d in southwest mongolia by integrating the data from archaeocyaeothan fauna the c isotopic peak s3 in the middle dahai carbonates may be correlative with feature g in the mongolian section

nitrogen isotope chemostratigraphy of the ediacaran and early cambrian platform sequence at three gorges south china abstract the appearance of multicellular animals and subsequent radiation during the ediacaran cambrian transition may have significantly changed the oceanic ecosystem nitrogen cycling is essential for primary productivity and thus its connection to animal evolution is important for understanding the co evolution of the earth s environment and life here we first report on coupled organic carbon and nitrogen isotope chemostratigraphy from the entire ediacaran to early cambrian period by using drill core samples from the yangtze platform south china the results show that 15ntn values were high 6 until middle ediacaran gradually dropping down to 1 at the earliest cambrian then rising back to 4 in the end of the early cambrian organic carbon and nitrogen contents widely varied with a relatively constant c n ratio in each stratigraphic unit and do not apparently control the carbon and nitrogen isotopic trends these observations suggest that the 15ntn and c n trends mainly reflect secular changes in nitrogen cycling in the yangtze platform onset of the observed negative n isotope excursion coincided with a global carbon isotope excursion event shuram excursion before the shuram event the high 15n probably reflects denitrification in a nitrate limited oceanic condition also degradation of dissolved and particulate organic matter could be an additional mechanism for the 15n enrichment and may have been significant when the ocean was rich in organic matter at the time of the shuram event both 13ccarb and 15ntn values were dropped probably due to massive re mineralization of organic matter this scenario is supported by an anomalously low c n ratio implying that enhanced respiration resulted in selective loss of carbon as co2 with recycled organic nitrogen after the shuram event the 15n value continued to decrease despite that 13ccarb rose back to 4 the continued 15n drop appears to have coincided with a decreasing phosphorus content in carbonate this suggests that ocean oxygenation may have generated a more nitrate rich condition with respect to phosphorus as a limiting nutrient similar to the shuram event another negative 13ccarb event in the canglanpuan stage of the early cambrian is also characterized by carbon isotopic decoupling as well as the low c n ratio the results strongly support that the two stages of the decoupled negative 13ccarb excursions reflect a disappearance of a large organic carbon pool in the ocean the two events appear to relate with the appearance of new metazoan taxa with novel feeding strategies suggesting a link between ocean oxygenation nutrient cycling and the appearance and adaptation of metazoans the nitrogen isotope geochemistry is very useful to understand the link between the environmental ecological and biological evolutions

oceanic anoxia at the precambrian cambrian boundary the precambrian cambrian pc c boundary separates fossils representing two discrete evolutionary phases the neoproterozoic soft bodied ediacarian biotas and cambrian small shelly faunas the biological discontinuity is suspected to have been a result of mass extinction however recent discoveries of the ediacarian biotas in cambrian sediments have led to an understanding that the faunal change was gradual through the pc c transition th u ratios which are high in oxidizing conditions and low in reducing conditions show a considerable positive correlation with 13c values at all studied sites of the pc c boundary this correlation indicates that reported 13c variation across the pc c boundary from numerous localities corresponds to redox variation in the depositional environment the negative 13c anomaly that occurs worldwide at the pc c boundary therefore corresponds to the widespread development of an oxygen deficient shallow marine environment this finding suggests that widespread oceanic oxygen deficiency which has been interpreted to reflect phanerozoic mass extinction events also occurred immediately before the cambrian explosion

an iodine record of paleoproterozoic surface ocean oxygenation constraining oxygen levels in the early precambrian surface ocean has been a longstanding goal but efforts have been challenged by the availability of suitable proxies here we present a novel approach iodine geochemistry which broadens our perspective by providing constraints on shallow carbonate dominated marine settings iodate io 3 persists exclusively in oxic waters and is the sole iodine species incorporated into carbonate minerals allowing iodine to calcium ratios i ca in shallow carbonates to be used as a paleoredox indicator our data from a series of mesoarchean through paleoproterozoic carbonates deposited under shallow marine conditions reveal a progressive surface ocean oxygenation in the early paleoproterozoic these data seem to indicate that a largely anoxic surface ocean extended throughout the archean until the great oxidation event goe at ca 2 4 ga implying that previous inferences of pre goe oxygen production may reflect oxygen oases transient oxidation events or oxygen levels below those required for io 3 accumulation the data suggest formation and persistence of io 3 and consequently surface ocean oxygen concentrations of at least 1 m during the goe following the initial rise of oxygen carbonate associated iodine in globally extensive carbonate units deposited during the lomagundi positive carbon isotope excursion at ca 2 22 2 1 ga suggests a widespread aerobic iodine cycle beyond that operating prior to the event synchronous with high relative rates of organic carbon burial and apparent expansion of oxidative conditions

paired lunar meteorites mac88104 and mac88105 a new fan of lunar petrology abstract new lunar meteorite mac88104 5 represents an exciting new opportunity to study a potentially unsampled region of the moon we have analyzed six thin sections by electron microprobe and three bulk samples by instrumental neutron activation ina in order to determine the chemical characteristics of this new lunar sample lunar meteorite macs 8104 5 is dominated by lithologies of the ferroan anorthosite fan suite and contains abundant granulitized highland clasts devitrified glass beads of impact origin and two small clasts which appear to be of basaltic origin one of these asaltic clasts clast e in mac88105 84 is probably mesostasis material whereas the second larger clast clast g may be similar to the very low ti vlt or low ti high alumina mare basalts impact melt clasts mac88105 69 and 72 have major and trace element compositions similar to the bulk meteorite there is little evidence of any lkfm low k fra mauro or low k kreep contribution to this meteorite as mac88104 5 and other brecciated lunar meteorites are fe rich and poor in the incompatible elements relative to apollo 16 regolith and feldspathic breccias while the exact site of origin for the lunar meteorites cannot be pinpointed it is evident that they were derived from a relatively kreep free ferroan anorthosite terrain

petrogenesis of mesosiderites i origin of mafic lithologies and comparison with basaltic achondrites abstract new petrologic and trace element data on basaltic and gabbroic clasts in mesosiderites and basaltic achondrites combined with existing petrologic and trace element data have served as a basis for interpretation of the petrogenesis of mesosiderite clasts compared with the basaltic achondrites the mesosiderite basaltic and gabbroic clasts contain more abundant modal tridymite and merrillite and more commonly contain augite as a late magmatic phase their pyroxenes tend to be more mgo rich and have lower fe mn ratios which are positively correlated with the fe mg ratio some of the mesosiderite basaltic and gabbroic clasts contain xenocrystic plagioclase the basaltic clasts commonly show super chondritic eu sm ratios and slight lree depletions the cumulate gabbro clasts are extremely depleted in lil have very high eu sm ratios and high lu sm ratios all of these features can be explained by a model in which the mafic lithologies of mesosiderites were formed by remelting of a mixed basalt cumulate gabbro metal source region near the parent body surface reducing agents p c s from the metallic fraction reduce feo out of the silicate melt and result in the positive correlation of fe mn with fe mg observed in pyroxene analyses and the modal abundances of tridymite merrillite and augite xenocrystic plagioclase is a natural consequence of remelting a cumulate gabbro rich source as are the unique ree patterns observed

extinction of cloudina and namacalathus at the precambrian cambrian boundary in oman biostratigraphic carbon isotope and u pb zircon geochronological data from the ara group of oman indicate an abrupt last appearance of cloudina and namacalathus coincident with a large magnitude but short lived negative excursion in the carbon isotope composition of seawater that is globally coincident with the precambrian cambrian boundary u pb zircon age data from an intercalated ash bed directly define this negative excursion to be at 542 0 0 3 ma consistent with previous age constraints from siberia and namibia combined with the global biostratigraphic record these new data strengthen hypotheses invoking mass extinction within terminal proterozoic ecosystems at or near the precambrian cambrian boundary

87sr 86sr chemostratigraphy of neoproterozoic dalradian carbonates below the port askaig glaciogenic formation scotland abstract the neoproterozoic cambrian dalradian supergroup of scotland contains three glaciogenic sedimentary units the port askaig formation the stralinchy reelan formation and the loch na cille boulder bed in ascending order although the idea that relatively cold climates occurred during the latest proterozoic is widely accepted the cause of the onset of glaciation is still controversial we use new carbonate 87 sr 86 sr data to better constrain this environmental change some dalradian limestones have high strontium contents 1000 ppm low manganese contents and mn sr ratios 87 sr 86 sr values of paleoseawater in the neoproterozoic the 87 sr 86 sr values of limestones of the islay formation ca 0 7067 sampled on the island of islay are similar to the values of previous studies however the 87 sr 86 sr values of limestones just below the port askaig formation ca 0 7064 collected on the island of garbh eileach have the lowest values recorded in the dalradian supergroup comparing these 87 sr 86 sr values with coeval 87 sr 86 sr values of other regions in the world such low 87 sr 86 sr i87 sr 86 sr ratio from the tonian through the cryogenian and ediacaran to the earliest cambrian the results show that the 87 sr 86 sr ratio of seawater decreased just before the older cryogenian glaciation that it increased by two steps in the early and middle ediacaran and that there were at least two abrupt positive excursions in the middle ediacaran and at the precambrian cambrian boundary the decline of the 87 sr 86 sr ratio of seawater just before the older cryogenian sturtian glaciation suggests that enhancement of weathering related to break up of the rodinia supercontinent and continental flood basalt volcanism was a likely driver for generating global cooling for the snowball earth conditions godderis et al 2003 donnadieu et al 2004

the polymict eucrites elephant moraine a79004 and a79011 and the regolith history of a basaltic achondrite parent body the achondrites elephant moraine a79004 and a79011 are closely related polymicteucrites of a type previously unrecognized in antarctica they contain an early metamorphically homogenized breccia containing clasts of great textural diversity very similar to those in howardites and a late injected mafic clast component that contains a suite of basalts that may in part be the result of impact melting rather than internal igneous processes the basaltic achondrite parent body bap of which they are regolith samples had a complex igneous history of 1 early igneous activity 2 brecciation to form polymict breccias 3 localized metamorphism resulting in partial homogenization of areas of the regolith 4 late igneous activity resulting from internal igneous or impact melting processes and 5 further brecciation and mixing of late formed mafic rocks with early breccias

silurian extension in the upper connecticut valley united states and the origin of middle paleozoic basins in the quebec embayment pre silurian strata of the bronson hill arch bha in the upper connecticut valley nh vt are host to the latest ludlow comerford intrusive suite consisting east to west of a mafic dike swarm with sheeted dikes and an intrusive complex the rocks are mostly mafic but with compositions ranging from gabbro to leucocratic tonalite the suite is truncated on the west by the monroe fault a late acadian thrust that carries rocks of the bha westward over silurian devonian strata of the connecticut valley gaspetrough cvgt dikes intrude folded strata with a pre intrusion metamorphic fabric taconian but they experienced acadian deforma tion twenty fractions of zircon and baddeleyite from three sample sites of gabbro diorite spanning nearly 40 km yield a weighted 207 pb 206 pb age of 419 1m a greenschist facies dikes sampled over a strike distance of 35 km were tholeiitic basalts formed by partial melting of asthenospheric mantle with little or no influence from mantle or crustal lithosphere the dike chemistry is similar to mid ocean ridge within plate and back arc basin basalts parent magmas originated in the astheno sphere and were erupted through severely thinned lithosphere adjacent to the cvgt extensive middle paleozoic basins in the internides of the appalachian orogen are restricted to the quebec embayment of the laurentian rifted margin and include the cvgt and the central maine trough cmt separated from the bha by a silurian tectonic hinge the ne trending comerford intrusions parallel the cvgt cmt and the tectonic hinge and indicate nw se extension during post taconian convergence the irregular margins of composite laurentia and avalon permitted continued colli sion in newfoundland st lawrence promontory and coeval extension in the quebec embayment extension may be related to hinge retreat of the northwest directed brunswick subduction complex and rise of the asthenosphere following slab break off an alternative hypothesis is that the basins originated as pull apart basins between northwest trending left stepping sinistral strike slip faults along the southern flanks of the new york and st lawrence promontories

oceanic redox conditions in the late mesoproterozoic recorded in the upper vazante group carbonates of sao francisco basin brazil evidence from stable isotopes and rees the vazante group consists of a late mesoproterozoic 1 0 1 1 ga carbonate dominated marine platform sequence in east central brazil the upper part of the sequence consists of a glaciomarine diamictite unit overlain by a cap carbonate the 13c profile of the upper vazante shows significant negative plunges one preglacial drop of 5 5 vpdb and two postglacial drops of 9 and 5 vpdb respectively the c isotope plunge in the preglacial carbonates is correlated with low th u ratios 0 1 1 4 and a negative ce ce shift 0 4 suggesting deposition under relative reducing conditions in contrast the c isotope plunges in the postglacial carbonates are associated with high th u ratios 2 and positive ce ce shifts up to 1 5 thus reflecting oxidizing conditions variations in the redox conditions of the late mesoproterozoic ocean reflected by changes in the th u and ce ce ratios are likely attributable to a combination of both global and local climatic and oceanographic changes similar to what has been inferred for the neoproterozoic oceans

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

seasonal dripwater mg ca and sr ca variations driven by cave ventilation implications for and modeling of speleothem paleoclimate records a 4 year study in a central texas cave quantifies multiple mechanisms that control dripwater composition and how these mechanisms vary at different drip sites we monitored cave air compositions in situ calcite growth dripwater composition and drip rate every 4 6 weeks three groups of drip sites are delineated groups 1 3 based on geochemical variations in dripwater composition quantitative modeling of mineral solution reactions within the host carbonate rock and cave environments is used to identify mechanisms that can account for variations in dripwater compositions the covariation of mg ca and sr ca and sr isotopes is key in delineating whether mg ca and sr ca variations are dictated by water rock interaction i e calcite or dolomite recrystallization or prior calcite precipitation pcp group 1 dripwater compositions reflects a narrow range of the extent of water rock interaction followed by varying amounts of prior calcite precipitation pcp group 2 dripwater compositions are controlled by varying amounts of water rock interaction with little to no pcp influence group 3 dripwater compositions are dictated by variable extents of both water rock interaction and pcp group 1 drip sites show seasonal variations in dripwater mg ca and sr ca whereas the other drip sites do not in contrast to the findings of most previous dripwater mg ca sr ca studies these seasonal variations at group 1 drip sites are independent of changes in water flux i e rainfall and or drip rate and instead significantly correlate with changes in cave air co2 concentrations these results are consistent with lower cave air co2 related to cool season ventilation of the cave atmosphere enhancing calcite precipitation and leading to dripwater geochemical evolution via pcp group 1 dripwater mg ca and sr ca seasonality and evidence for pcp as a mechanism that can account for that seasonality have two implications for many other regions where seasonal ventilation of caves is likely 1 speleothem trace element records may provide seasonal signals and 2 such records may be biased toward recording climate conditions during the season when calcite is depositing additionally we use our results to construct a forward model that illustrates the types of speleothem mg ca and sr ca variations that would result from varying controls on dripwater compositions the model provides a basis for interpreting paleodripwater controls from high frequency mg ca and sr ca variations for speleothems from caves at which long term monitoring studies are not feasible 2011 elsevier ltd all rights reserved

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

the paleoenvironmental evolution of the cambrian longwangmiao formation stage 4 toyonian on the yangtze platform south china petrographic and geochemical constrains abstract during the cambrian period stage 4 biodiversity and biomass declined rapidly and globally in an event known as the botomian toyonian crisis to gain a better understanding of the paleoenvironment in south china during this stage we present and interpret complex multi parameter carbonate analyses petrography carbon and oxygen isotopic composition and major trace and rare earth elements from the toyonian longwangmiao formation in the bandenggou section the longwangmiao formation comprises primarily carbonate deposits with massive detrital mineral occurrences in its lower middle sequence principal component analysis of the minerals and oxides leads to the definition of two intervals i and ii interval i is composed mainly of dolostones interbedded with sandstones and contains exceedingly high amounts of terrestrial original minerals and oxides as well as high ree y th and sc concentrations interval ii which is composed primarily of limestones has trace amounts of terrestrial original minerals and oxides and low ree y th and sc concentrations the 13c and 18o values show a significant positive shift from interval i to interval ii after eliminating the effects of diagenesis contributions through the analyses of diagenesis sensitive indexes 18o values mgo cao mn sr and fe sr ratios and the correlations of 13c 18o 18o eu eu eu eu ce ce and eu eu feo the sr and na concentrations of calcites in interval i are extremely high exceeding even the corresponding ranges of marine aragonites while calcites from interval ii have low sr and na concentrations that are within the range of marine low mg calcite however both show strong positive correlations between ca sr ca na and sr na the different calcite elemental behaviors in intervals i and ii suggest different carbonate precursors associated with seawater temperature and climate furthermore the sr ca ratios are negatively correlated with 13c and 18o values and the 13c values also negatively correlated with sio2 content these features indicate a significant change in the depositional environment during the cambrian toyonian stage from an early restricted marine environment under a warm and arid climate with massive terrestrial influxes to a later relatively open marine environment under a cool and humid climate with negligible terrestrial influxes this shift likely resulted in the observed changes in biomass and biodiversity

introduction to tectonics of china abstract the continental crust of china is a mosaic of cratonic blocks and orogenic belts containing small cratons and terranes with various tectonic settings they have diverse origins and complex histories of amalgamation and often suffered repeated reworking after multiple episodes of amalgamation in the last three decades extensive geological geochemical and geophysical investigations have been carried out on these cratonic blocks and intervening orogenic belts producing an abundant amount of new data and competing interpretations this provides important insights into understanding the formation and evolution of the chinese continents the papers assembled in this volume present a timely and comprehensive overview on major advancements and controversial issues related to the formation and evolution of continental crust in china complex tectonic histories were experienced not only by the large scale cratonic blocks and orogenic belts but also by small scale terranes and orogens between and inside these blocks nevertheless our understanding of lithotectonic units and geological processes has been greatly advanced by recent studies of zirconology and geochemistry for various rock types from major petrotectonic units in china it has been further advanced from integrated interpretations of geochemical and petrological data for petrogenesis of magmatic rocks an overview of these observations and interpretations provides new insights into understanding the continental plate tectonics and the chemical geodynamics of subduction zones

δ18o values 87sr86sr and sr mg ratios of late devonian abiotic marine calcite implications for the composition of ancient seawater abstract late devonian frasnian abiotic marine calcite has been microsampled and analyzed for 87 sr 86 sr ratios 18o and 13c values and minor element concentrations portions of marine cement crystals from the alberta and canning basins have escaped diagenetic alteration and preserve original marine 18o values 4 8 0 5 pdb 13c values 2 0 to 3 0 pdb 87 sr 86 sr ratios 0 70805 3 and sr mg weight ratios 0 04 to 0 05 marine 87 sr 86 sr ratios are globally consistent and can be correlated within the alberta basin and among the alberta canning and williston basins correlation of isotopic and chemical data strengthen the conclusion that marine cements from the leduc formation preserve original marine 18o values which are 3 to 4 lower than those of modern marine cements these low 18o values are best explained by precipitation from 18o depleted seawater and not by elevated seawater temperature or diagenetic alteration for comparison with devonian data analogous data were collected from holocene mg calcite and aragonite marine cements from enewetak atoll marshall islands mg calcite and aragonite marine cements are in isotopic equilibrium with ambient seawater and mg calcite cements are homogeneous with respect to sr and mg contents empirically derived homogeneous distribution coefficients for mg and sr in modern abiotic mg calcite from enewetak atoll are 0 034 and 0 15 respectively an equation describing the dependence of dsr on mg content was based on a compilation of sr and mg data from holocene abiotic marine calcite dsr 3 52 10 6 ppm mg 6 20 10 3 unlike that derived from experimental data this sr mg relation is consistent over a range of 4 to 20 mol mgco3 and may represent precipitation phenomena which are minimally controlled by kinetic effects comparison of sr and mg contents of analogous devonian and holocene marine cements suggests that the mg ca ratio of late devonian seawater was significantly lower and that the sr ca ratio was significantly higher than that of modern seawater

oxygen and carbon isotopic composition of ordovician brachiopods implications for coeval seawater one hundred and two articulate brachiopods and twenty one marine cements from ordovician strata were analyzed for oxygen and carbon isotopes these together with 200 previously published analyses of ordovician brachiopods mostly of upper ordovician age define a general trend of increasing 18o values with decreasing age from a minimum of 10 5 in the earliest ordovician to a maximum of 1 5 at the ordovician silurian boundary the 13c values show a general positive correlation with 18o and increase from 2 5 in the earliest ordovician to as high as 7 at the ordovician silurian boundary the magnitudes of ordovician excursions for both 18o and 13c are similar to those reported previously for the entire phanerozoic different genera of brachiopods from the same stratigraphie level did not yield any large differences in their isotopic compositions suggesting that vital effects did not influence decisively the isotope values of the studied skeletal parts petrographic examination and trace element analyses indicate that brachiopod shells from llandeilo to ashgill strata are well preserved and thus may have retained their primary isotopic signatures the same criteria for the tremadoc arenig and some llanvirn brachiopods suggest partial diagenetic alteration of 18o values in these samples but this does not preclude their utility as a recorder of a primary 13c signal the observed 18o trend for the well preserved portion of the record may reflect progressive cooling during ordovician perhaps complemented by a changing 18o values of seawater the latter could have been a consequence of a net increase in the rate of high temperature water rock interaction relative to its low temperature counterpart as indicated also by the large coeval decrease of marine 87sr86sr superimposed on the above long term 18o trend is a positive excursion of about 2 at the end of the ordovician probably reflecting a large expansion of polar ice caps the magnitude of this excursion indicates a degree of glaciation comparable to that at the height of the quaternary glacial episodes the secular 13c trend may reflect a progressive increase in marine organic productivity and or enhanced organic deposition in the ordovician oceans particularly noticeable at the time of the terminal ordovician glaciation

geochemical evidence from marine carbonate for enhanced terrigenous input into seawater during the ediacaran cambrian transition in south china abstract high resolution carbon and oxygen analyses along with residue contents major and trace element concentrations were carried out for marine dolostone from a profile through the upper ediacaran to the lower cambrian strata in south china the results provide geochemical evidence for enhanced input of terrigenous material into seawater in this period four positive and four negative carbon isotope excursions are identified in this profile the first remarkably negative 13c excursion exhibits the lowest value down to 2 at the ediacaran to cambrian boundary ecb in agreement with the global 13c and stratigraphy correlation the second remarkably negative 13ccarb excursion is as low as 1 81 subsequent to a positive 13ccarb excursion as high as 1 74 in the lower cambrian the ecb position in the stratigraphic profile is constrained by carbon isotope correlations the decreases of dolostone 18o and 13c values are synchronous across the ecb suggesting a change of the seawater composition at that time the increase of residue contents is concordant with decreases of y ho ratios and 18o values for the dolostone across the ecb suggesting the increase of terrigenous input in this period the relatively smooth ree y patterns of dolostone suggest its deposition in the environment of continental platform an integrated interpretation of these geochemical data including the major and trace element concentrations mn sr and mg ca ratios and the well preserved dolostone 13c and 18o values indicates that the terrigenous material from the continental weathering is rich in nutrients and 13c depleted organic matter which would have contributed to the negative 13ccarb excursion of dolostone at the stratigraphic boundaries the strong positive 13ccarb excursion in the lower cambrian may be linked to the biological radiation with lots of organic matter buried from the seawater in this period the fall and rise of sea level during different periods in the same region may result in differential input of terrigenous materials including freshwater into marine carbonates recording the coupling between regional tectonism and paleoclimatic change on the continental platform

a burial diagenesis origin for the ediacaran shuram wonoka carbon isotope anomaly marked negative 13c excursions in ediacaran age carbonate sediments have been identified in several sections globally but are not recognized in all sections of similar age the presence of 13ccarb values as low as 12 has been interpreted as recording fundamentally different processes in the global carbon cycle than those recognized today the 13ccarb anomalies are strongly correlated with 18ocarb values but are not represented in 13corg records while no primary depositional processes have been identified that can produce the correlated 18o 13c arrays simulations show that fluid rock interaction with high pco2 fluids is capable of producing such arrays at geologically reasonable pco2 and water rock ratios variations in the mg ca ratio and sulfate concentration of the altering fluid determine the extent of dolomite vs calcite and anhydrite in the resulting mineral assemblage incorporation of an initially aragonitic mineralogy demonstrates that high sr low mn sr and modest alteration of 87sr 86sr in ancient carbonates are all compatible with a burial diagenesis mechanism for generation of the 13c anomalies and do not necessarily imply preservation of primary values the profound ediacaran negative 13c anomalies can be adequately explained by well understood diagenetic processes conflated with the difficulty of correlating precambrian sections independently of chemostratigraphy they are not a record of primary seawater variations and need not have independent stratigraphic significance

the nature of the proterozoic cambrian transition in the northern amadeus basin central australia abstract the nature and completeness of the rock record is vital in determining whether evolution across the proterozoic cambrian boundary was episodic or explosive this study documents the nature of the neoproterozoic cambrian transition within the arumbera sandstone of the northern amadeus basin central australia and demonstrates an erosional surface close to this major stratigraphic boundary we are not able to recognise major facies differences between the largely unfossiliferous lower units i and ii and the rich trace fossil bearing beds of units iii iv horizons above and below the purported neoproterozoic cambrian transition were traced laterally and searched for both trace and body fossils in an attempt to locate a local boundary between the neoproterozoic and cambrian a single nonconformity bound sedimentary cycle above the major erosional surface dividing arumbera ii and iii is recognised the lowest sedimentary cycle of arumbera iii is devoid of trace fossils but at correlative levels in the ooraminna sub basin this horizon bears elements of the ediacara fauna reported for the first time herein we therefore suggest that contrary to previous studies the neoproterozoic cambrian transition is not coincident with the widespread seismic reflector but in areas of more complete sedimentation actually lies above it this study also presents new stratigraphic ichnological and palaeontological information from the neoproterozoic cambrian transition in central australia identifies areas of potentially continuous sedimentation and provides a basis for correlation of the arumbera sandstone with other neoproterozoic cambrian successions within australia and beyond

the origin of decoupled carbonate and organic carbon isotope signatures in the early cambrian ca 542 520 ma yangtze platform abstract the early cambrian ca 542 520 ma strata in south china record two prominent negative carbonate carbon isotope 13ccarb excursions of early nemakit daldynian n d and early tommotian ages across each of these excursions carbonate and organic carbon isotopes 13ccarb and 13corg are strongly decoupled regional correlation across a shelf to basin transect shows lateral heterogeneity of 13corg during the early middle n d but more homogenized 13corg values across the basin during the late n d and tommotian the temporal and lateral variations in 13corg suggest that decoupled 13ccarb and 13corg across the n d 13ccarb excursion were possibly caused by diagenetic alteration of organic matter and or amplification of detrital organic carbon isotope signature in low toc carbonates in contrast decoupled 13ccarb and 13corg of the upper n d and tommotian were likely resulted from chemoautotrophic methanotrophic biomass contribution to toc in organic rich black shale and carbonates the decoupled 13ccarb 13corg pattern from the lower n d strata ca 542 ma shows striking similarities with those from the basal ca 635 ma and upper ca 551 ma doushantuo formation in all three cases decoupled 13ccarb 13corg are seen in organic poor carbonates toc 0 1 and coupled 13ccarb 13corg occur in organic rich black shale and carbonates at the end of the negative 13ccarb excursion these similarities suggest that the shift from decoupled to coupled 13ccarb 13corg has no causal link with the terminal oxidation of a large oceanic doc reservoir given the pervasive anoxia euxinia in ediacaran early cambrian oceans local doc rich environments may have been common but a large oceanic doc reservoir capable of buffering the 13c of marine organic matter requires independent evidence

origin of ureilite meteorites and implications for planetary accretion although ureilites have been considered bizarre meteorites our analysis of their properties suggests that they formed by simple well known processes we conclude that 1 ureilites are the sole rock type in a major fraction of their parent body 2 they are partial melt residues and not cumulates 3 removal of 90 of the al in the basalts would largely stop radioactive heating if 26al was the heat source ensuring that large volumes of ureilite like material were generated 4 they formed in a large chondritic body that had a heterogeneous o isotopic composition 5 slow diffusion of o in solid and molten silicates ensured that partial melting did not homogenize the o isotopes of the residues 6 the puzzling absence of the basaltic melts that accompanied ureilite formation probably results from ejection into space by explosive volcanism together these conclusions provide a simple plausible origin for ureilites that accounts for most of their properties ureilites are residues from the partial melting of isotopically heterogeneous chondritic material we suggest that other meteorite parent bodies and planetesimals may have experienced similar histories and that ureilites provide important constraints on the accretionary and igneous histories of planets and asteroids

high resolution organic carbon isotope stratigraphy from a slope to basinal setting on the yangtze platform south china implications for the ediacaran cambrian transition organic carbon isotope data from two slope to basinal sections across the ediacaran cambrian transition on the yangtze platform south china record secular variations in delta c 13 data supplement highly comparable organic carbon isotope profiles from time equivalent shallow shelf and slope settings no environmentally determined carbon isotope gradient across the yangtze platform is discernible suggesting that a transgressive anoxic event provided an isotopically homogenous carbon source for primary productivity that originated from the deeper part of an anoxic and or sulfidic basin c 2011 elsevier b v all rights reserved

evolution of the composition of seawater through geologic time and its influence on the evolution of life abstract the redox state of the surface environment of the early earth is still controversial and a detailed and quantitative estimate is still lacking we carried out in situ analyses of major trace and rare earth elements of carbonate minerals in rocks with primary sedimentary structures in shallow and deep sea deposits in order to eliminate secondary carbonate and contamination of detrital materials and to estimate the redox condition of seawater through time based on the ce content and anomalies of the carbonate minerals at given parameters of atmospheric co2 content pco2 and ca content of seawater we calculated the oxygen contents of shallow and deep seawater respectively the results show that the oxygen content of the deep sea was low and constant until at least 1 9 ga the oxygen content of shallow seawater increased after 2 7 ga but fluctuated it became quite high at 2 5 and 2 3 ga but eventually increased after the phanerozoic in addition the calculation of a high pco2 condition shows that seawater was more oxic even in the archean than at present suggesting a relatively low pco2 through geologic time our detailed calculations from compositions of carbonate minerals in three gorge area south china show a low oxygen content of seawater after the snowball earth until the late ediacaran an increase in the late ediacaran and a significant decrease around the precambrian cambrian and nemakit daldynian tommotian boundaries these variations were possibly caused by global regression and dissolution of methane hydrates

chemical zoning and homogenization of pasamonte type pyroxene and their bearing on thermal metamorphism of a howardite parent body we studied thermal metamorphism in the surface layer of a eucrite parent body by examining pyroxene zoning ca mg fe zoning of pyroxenes in the pasamonte eucrite can be classified into three types type 1 with a core composition of ca5mg62fe32 and rim of ca41mg20fe4o type 2 with core of ca5mg62fe32 and rim of ca25mg34fe41 and type 3 with core of ca5mg66fe29 and rim of ca7mg32fe61 type 1 typically occurs adjacent to a mesostasis type 2 typically occurs adjacent to a surrounding plagioclase and type 3 is common in pyroxenes in the matrix pasamonte is less metamorphosed than previously believed because of the wide range of composition of zoned pyroxenes on the basis of ca mg fe variation data we have calculated the degree of homogenization of zoned pyroxenes by numerically solving the diffusion equation a pasamonte type pyroxene may yield a juvinas type pyroxene by thermal metamorphism the homogenization of juvinas pyroxene could not have taken place during initial cooling and may be related to reheating events although our calculation rests upon some assumptions

carbon isotope variability across the ediacaran yangtze platform in south china implications for a large surface to deep ocean δ13c gradient new isotope data obtained from relatively conformable carbonate rich strata of the ediacaran yangtze platform in south china reveal substantial 13 c variability in platform sections four negative 13 c anomalies with a nadir down to 8 pdb are present in the interval between the cap carbonate level 635 ma and the precambrian cambrian boundary 542 ma while in slope and basinal sections 13 c values are negative through the entire doushantuo formation 635 551 ma if these 13 c values are close to their primary seawater signature they imply a strong 10 surface to deep ocean 13 c gradient that is consistent with long term deep ocean anoxia and the presence of a large dissolved organic carbon doc reservoir the two prominent negative 13 c excursions within the doushantuo formation above the cap carbonate level are associated with shoaling and local exposure of the platform the anomalies may thus record remineralization of a large oceanic doc pool via sulfate reduction that transferred 13 c depleted carbon from the oceanic doc reservoir to the surface ocean during regression inconsistencies in ediacaran 13 c profiles globally and variations in south china in particular highlight the need for further evaluation of local departures in 13 c from an inferred average seawater signature

noble gas isotopic composition cosmic ray exposure history and terrestrial age of the meteorite allan hills a81005 from the moon we present a comprehensive study of the elemental and isotopic abundances of the noble gases he ne ar kr and xe in the meteorite allan hills a81005 from the moon in addition to a bulk sample five grain size fractions were analyzed chemical abundances relevant for the interpretation of the cosmic ray produced noble gases were determined and indicate that the grain size fractions are chemically uniform except for the fact that the trapped noble gas concentrations appear to be grain size correlated the isotopic and elemental pattern of the trapped solar wind noble gases in a81005 are very similar to those observed in lunar soils and breccias the a81005 material resided during 580 180 m y in the nuclear active zone of the lunar regolith at an average shielding depth of about 40 g cm2 from literature data we conclude that the moon earth transit time lasted less than a few million years finally a81005 was captured by the earth more than 140 000 years ago as obtained from the abundance of cosmic ray produced81kr

new carbon isotope stratigraphy of the ediacaran cambrian boundary interval from sw china implications for global correlation the yangtze platform preserves relatively thick carbonate successions and excellent fossil records across the ediacaran cambrian boundary interval the intensely studied meishucun section in east yunnan was one of the global stratotype section candidates for the precambrian cambrian boundary however depositional breaks were suspected in the section and the first appearance of small shelly fossils could not be verified the laolin section located in ne yunnan is more continuous and shows great potential for global correlation of carbon isotope features across the precambrian cambrian boundary however the stratigraphic framework and correlations were controversial we studied and systematically sampled the laolin section and present here new carbon isotope data for this section the laolin section consists of in ascending order the baiyanshao dolostone of the dengying formation the daibu siliceous dolostone zhongyicun dolomitic phosphorite lower dahai dolostone and upper dahai limestone of the zhujiaqing formation and the black siltstone of the shiyantou formation our data reveal a large negative 13 c excursion 7 2 l1 in the daibu member which matches the previously published data for the laolin section and a large positive excursion 3 5 l4 in the dahai member which was not shown in the published data the excursion l1 correlates well with the similarly large negative excursion near the first appearance of small shelly fossils in siberia and mongolia similar magnitude excursions are also known from morocco and oman for which there are no robust fossil constraints but from where volcanic ash beds have been dated precisely at 542 ma thus confirming a global biogeochemical event near the ediacaran cambrian boundary our data also indicate that deposition was more continuous at the laolin section compared with the meishucun section where there are no records of a comparable negative excursion near the ediacaran cambrian boundary nor any comparable positive excursion in the dahai member therefore the laolin section has proven potential to be a supplementary global stratotype section for the ediacaran cambrian boundary on the yangtze platform

petrology of alha81005 the first lunar meteorite petrography and mineral compositions show that alha81005 is a lunar highland regolith breccia and is the first known lunar meteorite lithic clasts are abundant and most are members of the anorthosite norite troctolite highland suite plagioclase compositions in lithic clasts and single grains are calcic an94 98 pyroxene compositions al ti and mno feo relationships support a lunar highland origin a non kreepy source region is indicated and the unexplored far side of the moon cannot be ruled out as a potential source

ree geochemistry of carbonates from the guanmenshan formation liaohe group ne sino korean craton implications for seawater compositional change during the great oxidation event abstract the worldwide 2 33 2 06 ga positive 13 c carb excursion has been correlated with the great oxidation event goe and termed as the lomagundi event the 2 3 1 85 ga guanmenshan formation in the liaohe group of the northeastern sino korean craton is characterized by positive 13 c carb excursion and is a potential candidate to evaluate the lomagundi event using rey rare earth element and yttrium ree y chemical fingerprints here we present major and trace element analysis of 42 samples from the guanmenshan formation which are pure marine chemical sediments and use the data to trace the seawater composition during 2 3 1 85 ga 15 least altered dolomicrite samples 600 m strata have ree values of 0 739 4 175 ppm 2 414 1 184 ppm and the y ho ratios of 34 5 56 6 44 1 5 7 they show uniform positive la sn la sn 1 04 0 27 and gd sn gd sn 1 64 0 40 anomalies and notable lree depletions indicated by nd sn yb sn values of 0 24 0 92 average 0 56 0 19 these features are consistent with the geochemistry of well oxygenated shallow ambient seawater and suggest that these samples provide a robust record of the primary rey signature of seawater during the lomagundi event the rey patterns of 15 silicified dolomites marbles locally with veinlets from the pb zn mining camps in the region with average eu cn eu cn 1 56 0 95 are identical to those of high temperature hydrothermal fluids 250 c characterized by a flat pattern and marked positive eu anomalies indicating that these rocks were subjected to metasomatism by hydrothermal fluids the guanmenshan formation shows average ce sn ce sn of 0 93 0 09 and sm cn yb cn of 1 which are higher than those of the archean 2 33 ga chemical sediments generally f o 2 and p co 2 the rey in the dolomicrite were mainly sourced from fluxes of solutes from terrestrial weathering and also from seafloor hydrothermal processes on a subordinate scale the guanmenshan dolomicrites have eu sn eu sn values of 1 34 2 55 i e around 1 53 indicating that they were deposited during 2 33 2 06 ga as the eu sn eu sn 1 53 can be used as a proxy for the 2 33 2 06 ga marine chemical sediments our study shows that the guanmenshan formation was formed at a critical turning point in earth history when the global atmosphere hydrosphere system witnessed a dramatic change from reducing to oxidizing conditions

rare earth elements in cold seep carbonates from the niger delta abstract the circulation of methane rich fluids at cold seeps often leads to precipitation of authigenic carbonates mediated by microbial activity which can be used as archives of fluid seepage on continental margins in this study we have investigated the potential of using rare earth element ree concentrations in authigenic carbonates for tracing fluid sources and providing information on associated biogeochemical processes at cold seeps we have examined various chemical procedures for the analysis of ree in authigenic carbonates and present a robust method using dilute acetic acid solution that allows the extraction of ree from carbonate phases with reduced contamination from fe mn oxides and detrital minerals using this method we analysed a series of carbonate samples collected at various deep sea sites of active fluid seepage on the niger delta for their ree and trace element concentrations 13c and 18o values and 87sr 86sr isotope compositions we show that the ree composition of cold seep carbonates is controlled primarily by that of the fluid from which they have precipitated our results also suggest that significant ree fractionation can occur during carbonate precipitation which can be related to various degrees of ree complexation by organic versus carbonate ligands in response to changing pore water chemical composition for parameters such as carbonate alkalinity

hydrogen sulphide release to surface waters at the precambrian cambrian boundary changes in environmental conditions at the precambrian cambrian transition around 542 million years ago have been suggested as a possible explanation for the apparent rapid increase in abundance of multicellular organisms known as the cambrian explosion the nature of the environmental changes is still a matter of debate however wille et al now report molybdenum isotope signatures of black shales from two stratigraphically correlated sample sets with a depositional age of about 542 million years with the help of a box model of the oceanic molybdenum cycle they find that intense upwelling of hydrogen sulphide rich deep ocean water best explains the observed early cambrian molybdenum isotope signal this suggests that the early cambrian animal radiation may have been triggered by a major change in ocean circulation following a long period during which the ocean was stratified with sulphidic deep water this paper reports molybdenum isotope signatures of black shales from two stratigraphically correlated sample sets with a depositional age of around 542 million years the findings suggest that the early cambrian animal radiation may have been triggered by a major change in ocean circulation terminating a long period during which the proterozoic ocean was stratified with sulphidic deep water animal like multicellular fossils appeared towards the end of the precambrian followed by a rapid increase in the abundance and diversity of fossils during the early cambrian period an event also known as the cambrian explosion 1 2 3 changes in the environmental conditions at the precambrian cambrian transition about 542 myr ago have been suggested as a possible explanation for this event but are still a matter of debate1 2 3 here we report molybdenum isotope signatures of black shales from two stratigraphically correlated sample sets with a depositional age of around 542 myr we find a transient molybdenum isotope signal immediately after the precambrian cambrian transition using a box model of the oceanic molybdenum cycle we find that intense upwelling of hydrogen sulphide rich deep ocean water best explains the observed early cambrian molybdenum isotope signal our findings suggest that the early cambrian animal radiation may have been triggered by a major change in ocean circulation terminating a long period during which the proterozoic ocean was stratified with sulphidic deep water

porites corals as recorders of mining and environmental impacts misima island papua new guinea abstract in 1989 open cut gold mining commenced on misima island in papua new guinea png open cut mining by its nature causes a significant increase in sedimentation via the exposure of soils to the erosive forces of rain and runoff this increased sedimentation affected the nearby fringing coral reef to varying degrees ranging from coral mortality smothering to relatively minor short term impacts the sediment associated with the mining operation consists of weathered quartz feldspar greenstone and schist these rocks have distinct chemical characteristics rare earth element patterns and high abundances of manganese zinc and lead and are entering the near shore environment in considerably higher than normal concentrations using laser ablation inductively coupled plasma mass spectrometry la icp ms we analyzed eight colonies two from high sedimentation two transitional two minor and two unaffected control sites for y la ce mn zn and pb all sites show low steady background levels prior to the commencement of mining in 1988 subsequently all sites apart from the control show dramatic increases of y la and ce associated with the increased sedimentation as well as rapid decreases following the cessation of mining the elements zn and pb exhibit a different behavior increasing in concentration after 1989 when ore processing began and one year after initial mining operations elevated levels of zn and pb in corals has continued well after the cessation of mining indicating ongoing transport into the reef of these metals via sulfate rich waters rare earth element ree abundance patterns measured in two corals show significant differences compared to coral sea seawater the corals display enrichments in the light and middle rees while the heavy rees are depleted relative to the seawater pattern this suggests that the nearshore seawater ree pattern is dominated by island sedimentation trace element abundances of misima island corals clearly record the dramatic changes in the environmental conditions at this site and provide a basis for identifying anthropogenic influences on corals reefs

δ13c depth profiles from paleosols across the permian triassic boundary evidence for methane release stable carbon isotopic analyses of organic carbon 13 c in individual paleosol profiles from permian triassic sequences of antarctica reveal systematic isotopic variations with profile depth these variations are in many cases analogous to those in modern soils which are functions of redox conditions soil development and degree and type of microbial decay in modern soils these isotopic depth functions develop independently from vegetation changes c 3 versus c 4 vegetation and can be diagnostic of soil orders this study shows that soil intrinsic functions can be preserved in the 13 c values of paleosols as old as 260 ma and constitute valuable data for paleoecological interpretations a large carbon isotopic offset of as much as 10 in whole paleosol profiles across the permian triassic boundary indicates significant changes in the soil biogeochemistry and the soil atmosphere system early triassic paleosols are distinctive in their extremely low 13 c values to 42 and often show an anomalous 13 c depth distribution compared to both permian paleosols and modern soils highly depleted 13 c values as the ones in early triassic paleosols are suggested to be associated with microbial methane oxidation methanotrophy this hypothesis implies increased methane concentrations in the early triassic soil atmosphere system increased atmospheric methane was probably partly responsible for the global carbon isotopic shift documented in marine and terrestrial sediments across the permian triassic boundary

seawater ph and isotopic paleotemperatures of cretaceous oceans abstract stable oxygen isotope ratios 18 o of foraminifera are widely used to reconstruct the climatic history of earth it is well known that temperature reconstructions based on 18 o are complicated by factors such as the unknown isotopic composition of the ocean in addition recent experimental and theoretical work has shown that the seawater ph has a marked effect on the 18 o of foraminifera here i employ this effect to demonstrate that reconstructions based on 18 o of foraminifera may underestimate sea surface temperatures in the geological past ocean surface temperatures for the mid cretaceous are estimated to have been 2 3 5 c higher than previously thought

ree patterns of eucrites and their genetic implications abstract rare earth element ree abundances in eucrites were precisely determined on juvinas pasamonte cachari stannem and antarctic eucrites y 74450 63 d g y 75015 20 e f y 75011 73 y 790007 61 f y 75011 84 d 1 and y 790007 61 e 4 the last two samples are eucrite clasts from polymict eucrites the other antarctic eucrite samples are matrix from polymict eucrites like the stannern eucrite all of the antarctic eucrites have relatively high ree abundances ree abundances in two clast samples are higher than those in the stannern and matrix samples of the antarctic eucrites when ree abundances in the antarctic eucrites and the stannem eucrite are normalized by the ree abundance suite of the juvinas or pasamonte eucrites highly linear ree patterns are obtained for the juvinas or pasamonte normalized ree patterns of the antarctic and stannern eucrites the inclination of the linear ree patterns increases with increasing ree abundances these observations suggest that the eucrites with larger ree abundances such as the stannern and antarctic eucrites were produced as residual liquid in a fractional crystallization process from the main group of eucrites e g the juvinas eucrite on the other hand the moore county cumulate eucrite is considered to be a solid phase formed in this process

early earth snowballs limited by weathering a series of extreme cooling episodes starting 750 million years ago could have repeatedly turned the planet into an ice covered snowball carbon cycle modelling suggests that the timing of the glaciations can be explained by chemical weathering rates

climate controlled mass extinctions facies and sea level changes around the devonian carboniferous boundary in the eastern anti atlas se morocco abstract detailed sedimentological and biostratigraphical studies of successions in the eastern anti atlas se morocco focused on changing depositional environments and reconstructions of sea level changes during the late famennian to middle tournaisian the investigations cover a transect from the central maider to the easternmost and southern tafilalt regions near the moroccan algerian border the moroccan data are compared with the standard succession of the german rhenish massif and with the regional and global stratigraphic record the results testify to high frequency sea level changes including two global transgressive and anoxic events the main hangenberg event hangenberg black shale level at the top of the wocklumeria zone upper devonian vi e and the lower alum shale event at the lower middle tournaisian lower carboniferous i ii boundary regionally both anoxic intervals coincided with mass extinctions followed by rapid radiation especially of pelagic biota a significant shallowing and regression occurred just below the devonian carboniferous boundary at the northern margin of gondwana and caused the sudden n nw progradation of a large deltaic complex over 300 500 km thick siliciclastic successions filled fast subsiding synsedimentary troughs of the maider and amessoui syncline southern tafilalt correlation with the glacial phases of southern gondwana south america south africa indicates a glacial eustatic origin of sea level changes and a major sea level fall in the scale of 100 m or more coinciding with the main regressive phase of the extended hangenberg crisis interval the new results are in accord with the hypothesis of an episode of cool humid climate at the end of the devonian that allowed contemporaneous glacial buildup in high latitudes and extensive clastic discharge in the middle latitudes of nw africa

dissolution methods for strontium isotope stratigraphy guidelines for the use of bulk carbonate and phosphorite rocks diverse carbonate dissolution methods have been applied to bulk carbonate rocks in order to target least altered components for strontium isotope stratigraphy sis this is especially important for precambrian and cambrian studies for which no suitable skeletal material is available one proven method for bulk limestones involves the removal of up to a third of the powdered sample using an acid pre leach before partial dissolution of the rest of the sample using a weak acid or acid buffer solution we applied a similar technique to dissolve a range of lithologies limestone dolostone and phosphorite and compared the strontium isotopic composition of various leaches to contemporaneous seawater our results vindicate this approach and allow us to conclude that some dolomitic and phosphatic rock components may retain a near primary seawater 87sr 86sr composition once contaminant strontium from secondary calcite and other phases has been removed commonly applied trace element e g mn sr mg ca and isotopic c o screening cut offs were also examined in the light of these results and proved unreliable particularly in the case of dolostones and partially dolomitized limestones we recommend that rigid sample selection and sequential leaching procedures be applied to all sis studies of bulk materials and propose a general protocol for strontium isotope studies on marine authigenic rocks which may also be applicable to rare earth element and other geochemical studies of marine authigenic minerals in the future

the estuarine geochemistry of rare earth elements and indium in the chao phraya river thailand abstract a new filtration method using a 0 04 m hollow fiber filter was applied to the river estuarine and coastal waters in the chao phraya estuary for geochemical investigation the filtered waters were analyzed for all the lanthanides y and in by using inductively coupled plasma mass spectrometry icpms the dissolved concentrations of rare earth elements rees are significantly lower than those reported previously for other rivers presumably because of effective removal of river colloids by the ultra filtration the variation of dissolved rees in the estuary is dependent on the season the light rees vary considerably in the low salinity s 3 show almost conservative trends being consistent with some of the previous works europium is strongly enriched in the river and estuarine waters compared to the south china sea waters thus the ree source of the chao phraya river must be fractionated and modified in entering to the south china sea dissolved in and ce in the high salinity s 20 25 zone of the estuary are lower than those of the offshore waters and therefore the dissolved flux of the chao phraya river cannot account for the higher concentrations of dissolved in and ce in the surface waters of the south china sea the negative ce anomaly is progressively developed with increasing salinity being consistent with continued oxidation of ce iii to ce iv in the estuary fractionation of the light to heavy rees seems to take place whereas the y ho fractionation is unclear in the estuarine mixing zone

oxygen isotope fractionation during synthesis of camg carbonate and implications for sedimentary dolomite formation hydrous camg carbonate was synthesized at temperatures of 40 degrees 60 degrees and 80 degrees c in the laboratory this material has very similar mineralogical characteristics to natural disordered dolomite from the coorong region in south australia besides the dolomite variable amounts of amorphous carbonate are present in all samples the oxygen isotope compositions of synthesized bulk carbonate samples e g amorphous carbonate plus dolomite plot significantly lower than the northrop and clayton 1966 dolomite water equilibrium fractionated degassing of the samples however revealed relatively low oxygen isotope values for fast reacting using 100 h3po4 amorphous carbonate in contrast slow reacting dolomite has more positive oxygen isotope values and calculated carbonate water oxygen isotope fractionation values are close to strongest known dolomite water oxygen isotope fractionation published earlier on variations of reaction stabilization temperatures during synthesis gave evidence for dolomite formation from hypersaline solutions by a dissolution reprecipitation process it is likely that amorphous carbonate has been a problem in defining the dolomite water fractionation in the past moreover dolomite associated amorphous carbonate contents probably led to incorrect speculations about lower oxygen isotope fractionation in a so called protodolomite water system copyright c 2005 elsevier ltd

cerium anomaly variations in ediacaran earliest cambrian carbonates from the yangtze gorges area south china implications for oxygenation of coeval shallow seawater abstract the late neoproterozoic ocean witnessed the naissance of animals which is believed to have been stimulated by an increase in oxygen levels in the ocean however apart from the emergence of animal fossils little supporting evidence has been found for the rise of oxygen in shallow seawater here we present ce anomaly data a redox proxy with a higher reduction potential than many other redox proxies for carbonates from well preserved marine successions the doushantuo formation dengying formation and lower yanjiahe formation of the ediacaran period and the upper yanjiahe formation of early cambrian on the neoproterozoic yangtze platform in the yangtze gorges area in order to constrain the redox evolution of the shallow marine environment calculated ce anomalies were screened using the following criteria al 36 in acetic acid leached carbonate to target samples that preserve primary seawater ree features and ce anomalies the samples satisfying this screening show seawater like ree distribution patterns in leached carbonates and may have recorded ce anomalies of the seawater from which the carbonates precipitated these data show that the doushantuo formation has ce ce values between 0 92 and 0 71 the dengying formation between 0 90 and 0 40 and the yanjiahe formation between 0 52 and 0 72 the ce ce values of the doushantuo formation suggest that shallow waters during the doushantuo stage 635 551 ma were anoxic to suboxic from the bottom to the top of the dengying formation ce ce values decrease systematically which cannot be explained by a change in depositional depth of the carbonate but suggests that the shallow waters became more oxygenated during the dengying stages from 551 ma to ediacaran cambrian boundary these results may provide direct evidence for an increase in oxygen levels in the shallow marine environment during the ediacaran period

neoproterozoic early cambrian isotopic variation and chemostratigraphy of the lesser himalaya india eastern gondwana the rodinia supercontinent had fragmented by 750 ma and east gondwana india australia and antarctica separated from west laurentia baltica africa and south america occupied other side of the rodinia neoproterozoic rifting breakup of rodinia low latitude glaciation and global warming events have been recorded from the lesser himalaya of india chemostratigraphy of the blaini krol tal succession indicates precambrian cambrian transition lies in the lower tal formation 13 c 4 pdb the krol belt in the lesser himalaya is characterized by positive 13 c values 1 to 6 pdb the appearance of multicelluler ediacaran life in the upper krol is consistent with hypothesis that increase in atmospheric oxygen played a major role in metazoan evolution and cambrian diversification of life on earth the base of the terminal proterozoic system in the lesser himalaya is established in the blaini formation the pink cap carbonate of the blaini formation shows negative 13 c value 3 pdb and this blainian glaciation is correlated with marinoan glacial event other regions of the eastern gondwana and south china parts of siberia and north africa neoproterozic early cambrian chemostratigraphy in the lesser himalaya is consistent in the isotopic variation where there is carbon isotopic similarity between neoproterozoic bambui group in central brazil south america and the krol formation of the lesser himalaya india in the northeastern lesser himalaya india the neoproterozoic sedimentary succession shows well developed carbonate the buxa dolomite shows significantly positive c isotope ratios 13 c 3 7 to 5 4 pdb the o isotopic data also shows remarkable consistency with the 18 o values fluctuating within a narrow range between 8 9 and 7 2 vpdb these isotopic results from the eastern lesser himalaya correspond to the terminal proterozoic c isotopic evolution followed by oscillations during the precambrian cambrian transition in the lesser himalaya in eastern gondwana

an explanation of the effect of seawater carbonate concentration on foraminiferal oxygen isotopes abstract stable oxygen isotope ratios of foraminiferal calcite are widely used in paleoceanography to provide a chronology of temperature changes during ocean history it was recently demonstrated that the stable oxygen isotope ratios in planktonic foraminifera are affected by changes of the seawater chemistry carbonate system the 18 o of the foraminiferal calcite decreases with increasing co 3 2 concentration or p h this paper provides a simple explanation for seawater chemistry dependent stable oxygen isotope variations in the planktonic foraminifera orbulina universa which is derived from oxygen isotope partitioning during inorganic precipitation the oxygen isotope fractionation between water and the dissolved carbonate species s h 2 co 3 hco 3 co 3 2 decreases with increasing p h provided that calcium carbonate is formed from a mixture of the carbonate species in proportion to their relative contribution to s the oxygen isotopic composition of caco 3 also decreases with increasing p h the slope of shell 18 o vs co 3 2 of orbulina universa observed in culture experiments is 0 0022 mol kg 1 1 spero et al 1997 whereas the slope derived from inorganic precipitation is 0 0024 mol kg 1 the theory also provides an explanation of the nonequilibrium fractionation effects in synthetic carbonates described by kim and o neil 1997 which can be understood in terms of equilibrium fractionation at different p h the results presented here emphasize that the oxygen isotope fractionation between calcium carbonate and water does not only depend on the temperature but also on the p h of the solution from which it is formed

the vendian cambrian δ13c record north iran evidence for overturning of the ocean before the cambrian explosion continuous fossilliferous successions across the precambrian cambrian pc c boundary in the elburz mountains of northern iran show a remarkable negative 13c excursion just below the pc c boundary high concentrations of manganese phosphorus barium and high abundances of fossil phytoplankton and black shale coincide with the excursion worldwide stratigraphic correlation shows that the isotopic anomaly is a global event the initial metazoan diversification coupled with13c enrichment occurs stratigraphically just above the excursion we propose the following scenario for oceanic environmental changes before the cambrian faunal explosion based on new data from iran a global warm climate following the last precambrian glaciation resulted in a generally stagnant oceanic condition so that surface water was oxic deep water was dysoxic depleted in13c and enriched in nutrients massive upwelling of deep water vertical advection of nutrients and13c depleted co2 caused enhanced phytoplankton productivity and a sharp drop in 13c in shallow water carbonate and organic carbon we conclude that latest cryptozoic overturning of ocean stratification preceded the cambrian explosion

comparison of yamato and victoria land polymict eucrites a view from mineralogical and isotopic studies new interior samples of four yamato polymict eucrites y74159 y74450 y75011 and y75015 have been studied by electron microprobe transmission electron microscope and x ray diffraction techniques and compared with several samples of the victoria land polymict eucrites these same samples have been analysed using rb sr and nd sm isotopic systematics several grains of inverted pigeonite with blebby augite similar to those in binda and moama have been identified in all four yamato eucrites coarse grained mesostasis rich subophitic basalts which contain mg rich pigeonite with fe rich olivine veinlets zoned outward to a subcalcic ferroaugite rims have also been found these unique clasts were not found in alh76005 77302 78040 78158 and 78165 and eet eucrites the tight grouping of rb sr and sm nd ratios and similar modal compositions of the yamato group indicate that they are most likely to be pieces from a single fall and distinct from the alh and eet groups however the yamato allan hills and elephant moraine groups may sample a few distinct magmas or similar but different source regions on the same parent body

biogenic and abiogenic low mg calcite blmc and almc evaluation of seawater ree composition water masses and carbonate diagenesis the ree and shale normalized paas reesn values of modern brachiopods biogenic low mg calcite blmc represented by several species from high to low latitudes from shallow to deep waters and from warm and cold water environments define three distinct average seawater trends the warm and cold water brachiopods define two indistinguishable p 0 050 groups that mimic open ocean seawater ree chemistry exhibiting the typical lree enrichment with a slightly positive to negative ce anomaly followed by an otherwise invariant series other recent brachiopods from an essentially siliciclastic seabed environment are distinct in both ree and reesn trends from the previous two populations showing a slight enrichment in the mrees and an increasing trend in the hrees other groups of modern brachiopods are characterized by elevated reesn trends relative to the normal groups as well as by complexity of the series trends the most characteristic feature is the decrease in the hrees in these brachiopods from areas of unusual productivity i e such as upwelling currents fluvial input and aerosol dust deposition preserved brachiopods from the eocene and silurian exhibit reesn trends and ce anomalies similar to that of the open ocean modern brachiopods although their enriched ree concentrations suggest precipitation of blmc influenced by extrinsic environmental conditions preservation of the blmc was tested by comparing the ree and reesn trends of preserved eocene brachiopods to those of oligocene brachiopods that were altered in an open diagenetic system in the presence of phreatic meteoric water the altered blmc is enriched by approximately one order of magnitude in both ree and reesn trends relative to that in blmc of their preserved counterparts similarly the ree and reesn of preserved silurian brachiopod blmc were compared to those of their enclosing altered lime mudstone which exhibits features of partly closed system phreatic meteoric water diagenesis despite these differences in the diagenetic alteration systems and processes the rees and reesn trends of the blmc of altered brachiopods and of originally mixed mineralogy lime mudstones now diagenetic low mg calcite are enriched by about one order of magnitude relative to those observed in the coeval and preserved blmc in contrast to the changes in ree and reesn of carbonates exposed to phreatic meteoric water diagenesis are the ree compositions of late burial calcite cements precipitated in diagenetically open systems from burial fluids the ree and reesn trends of the burial cements mimic those of their host lime mudstone with all showing slight lree enrichment and slight hree depletion exhibiting a chevron pattern of the reesn trends the overall enrichment or depletion of the cement reesn trends relative to that of their respective host rock material reflects not only the openness of the diagenetic system but also strong differences in the elemental and ree compositions of the burial fluids evaluation of the ce ce sn and la pr pr sn anomalies suggests precipitation of the burial calcite cements essentially in equilibrium with their source fluids

precambrian cambrian transition death valley united states the death valley region contains one of the best exposed and often visited precambrian cambrian successions in the world but the chronostratigraphic framework necessary for understanding the critical biologic and geologic events recorded in these sections has been inadequate the recent discovery of treptichnus phycodes pedum within the uppermost parasequence of the lower member of the wood canyon formation allows correlation of the precambrian cambrian boundary to this region and provides a necessary global tie point for the death valley section new carbon isotope chemostratigraphic profiles bracket this biostratigraphic datum and record the classic negative carbon isotope excursion at the boundary for the first time biostratigraphic chemostratigraphic and lithostratigraphic information from pretrilobite strata in this region can be directly compared with similar data from other key sections that record the precursors of the cambrian explosion few precambrian cambrian boundary sections contain both the facies restricted boundary fossil t pedum and carbon isotope data as found in death valley thus the death valley succession provides a critical link toward our understanding of the correlation between siliciclastic dominated and carbonate dominated precambrian cambrian transition sections

seep carbonates and preserved methane oxidizing archaea and sulfate reducing bacteria fossils suggest recent gas venting on the seafloor in the northeastern south china sea seep carbonates formed by the synergistic metabolism of methane oxidizing archaea moa and sulfate reducing bacteria srb have been found in many places worldwide but have not been found to date in the south china sea mud volcanoes and shale diapirs have been reported in the south china sea however and microscope and geochernical analysis of carbonates dredged where bottom simulating reflectors bsr suggest the presence of gas hydrate on the northeastern continental slope of the south china sea suggest that the carbonates are hydrocarbon seep related carbonates the carbonates we dredged are chimney like and preserve moa srb fossils their very light carbon isotopic compositions 51 25 to 51 76 parts per thousand suggest that their carbon was derived from microbial methane oxidization these seep carbonates and their preserved moa srb fossils imply gas venting has occurred recently on the seafloor in the northeastern continental slopes in the south china sea c 2005 elsevier ltd all rights reserved

the neoproterozoic cambrian record in australia a stable isotope study abstract shallow intracratonic basins developed across a large area of the central part of the australian craton during the neoproterozoic and continued to accumulate marine sedimentary successions until well into the early palaeozoic a half billion year sedimentary record carbonate successions ranging in age from neoproterozoic cryogenian to ostensibly early ordovician have been sampled at eleven sites across four of the northernmost of these basins amadeus georgina wiso and daly basins a total of 996 samples were then analyzed for stable carbon 13 c carb and oxygen 18 o carb isotopes to develop a regional secular stable carbon isotopic curve the curve complements earlier work and provides an important framework for global correlation at a critical time in earth history during which the biosphere and atmosphere were evolving rapidly at one site in the amadeus basin diagenesis proved to have significantly modified the isotopic composition of the carbonates and the data were eliminated analysis of the remaining samples suggests that they reflect the global secular stable carbon isotope curve and tie well with established palaeontological timescales in particular key isotopic excursions can be identified in the earliest part of the neoproterozoic succession notably the negative excursion following the sturtian glaciation in the early palaeozoic record a major excursion during ordian early templetonian 509 506 ma time can be identified across the region as can the so called spice excursion which has been associated globally with the steptoean stage of laurentia 497 5 495 ma a smaller late templetonian floran 506 503 ma positive excursion has also been recognized the stable carbon isotope record provides a strong regional correlation in both fossiliferous and unfossiliferous neoproterozoic and early palaeozoic successions and allows a global correlation to be established

ca sr and 87sr 86sr ratios as tracers of ca and sr cycling in the rio icacos watershed luquillo mountains puerto rico abstract we investigated ca and sr cycling in a humid tropical forest by analyzing ca sr ratios and 87sr 86sr ratios in soil minerals soil exchangeable cations soil porewater and plant roots wood and leaves and calculating the relative contributions of sr from atmospheric inputs and weathering of local bedrock an unexpectedly large contribution of bedrock derived sr and presumably ca is cycled through the vegetation reflecting the important role of geological processes in controlling the cycling of base cation nutrients even in a system with intensely weathered soil this is surprising because over 99 of the ca and sr that was originally in the bedrock is leached out of the soil and saprolite during early stages of weathering at this site and because there are large atmospheric inputs to the site of both sea salt and saharan dust substantial differences in ca and sr cycling are seen on small spatial scales between a ridgetop and an adjacent steep hillslope site measured ca sr ratios reflect fractionation between these elements during biogeochemical cycling fractionation was particularly evident between wood and foliar tissue but fractionation during soil exchange processes is also likely in comparing the ca sr ratios of plants exchangeable cations and bulk soils we found that foliar ca sr ratios were greater than exchangeable cation ca sr ratios which in turn were greater than soil ca sr ratios similar to patterns observed at other highly weathered tropical sites

the antarctic achondrite alha 76005 a polymict eucrite abstract alha 76005 is a basaltic achondrite containing few if any orthopyroxenes its bulk major and trace element composition is like that of a non cumulate eucrite and unlike that of a howardite it contains a variety of igneous clasts which differ in their textures pyroxene plagioclase ratios and pyroxene and plagioclase compositions one clast no 4 was found to have the ree pattern of a cumulate eucrite and an oxygen isotopic composition different from that of the bulk meteorite both the chemical and oxygen isotopic composition of clast no 4 suggest that it was derived from a source different from its host these observations lead to the conclusion that alha 76005 is a polymict eucrite

rare earth elements in authigenic methane seep carbonates as tracers for fluid composition during early diagenesis abstract authigenic carbonates forming at an active methane seep on the makran accretionary prism mainly consist of aragonite in the form of microcrystalline cryptocrystalline and botryoidal phases the 13 c carbonate values are very negative 49 0 to 44 0 v pdb agreeing with microbial methane as dominant carbon source the 18 o carbonate values are exclusively positive 3 0 to 4 5 v pdb and indicate precipitation in equilibrium with seawater at bottom water temperatures the content of rare earth elements and yttrium ree y determined by laser ablation inductively coupled plasma mass spectrometry la icp ms and solution icp ms varies for each aragonite variety with early microcrystalline aragonite yielding the highest cryptocrystalline aragonite intermediate and later botryoidal aragonite the lowest ree y concentrations shale normalised ree y patterns of different types of authigenic carbonate reflect distinct pore fluid compositions during precipitation microcrystalline aragonite shows high contents of middle rare earth elements mree reflecting ree patterns ascribed to anoxic pore water cryptocrystalline aragonite exhibits a seawater like ree y pattern at elevated total ree y concentrations indicating higher concentrations of rees in pore waters which were influenced by seawater botryoidal aragonite is characterised by seawater like ree y patterns at initial growth stages followed by an increase of light rare earth elements lree with advancing crystal growth reflecting changing pore fluid composition during precipitation of this cement conventional sample preparation involving micro drilling of carbonate phases and subsequent solution icp ms does not allow to recognise such subtle changes in the ree y composition of individual carbonate phases to be able to reconstruct the evolution of pore water composition during early diagenesis an analytical approach is required that allows to track the changing elemental composition in a paragenetic sequence as well as in individual phases high resolution analysis of seep carbonates from the makran accretionary prism by la icp ms reveals that pore fluid composition not only evolved in the course of the formation of different phases but also changed during the precipitation of individual phases

basaltic fragments in lunar feldspathic meteorites connecting sample analyses to orbital remote sensing abstract the feldspathic lunar meteorites contain rare fragments of crystalline basalts we analyzed 16 basalt fragments from four feldspathic lunar meteorites allan hills alha 81005 macalpine hills mac 88104 88105 queen alexandra range que 93069 miller range mil 07006 and utilized literature data for another dhofar dho 1180 we compositionally classify basalt fragments according to their magma s estimated tio2 contents which we derive for crystalline basalts from pyroxene tio2 and the mineral melt ti distribution coefficient overall most of the basalt fragments are low ti basalts 1 6 tio2 with a significant proportion of very low ti basalts 10 tio2 and 6 10 tio2 respectively this distribution of basalt tio2 abundances is nearly identical to that obtained from orbital remote sensing of the moon both uv vis from clementine and gamma ray from lunar prospector however the distribution of tio2 abundances is unlike those of the apollo and luna returned samples we observe a paucity of high ti basalts the compositional types of basalt differs from meteorite to meteorite which implies that all basalt subtypes are not randomly distributed on the moon i e the basalt fragments in each meteorite probably represent basalts in the neighborhood of the meteorite launch site these differences in basalt chemistry and classifications may be useful in identifying the source regions of some feldspathic meteorites some of the basalt fragments probably originate from ancient cryptomaria and so may hold clues to the petrogenesis of the moon s oldest volcanism

survey and evaluation of eucrite bulk compositions the purpose of this survey is to establish reference bulk elemental abundances for the eucrites and thereby provide the basis to test core formation models as well as partial melting fractional crystallization and magma ocean theories for the eucrite parent body in order to evaluate bulk elemental abundances for the eucrites 296 peer reviewed articles monographs theses or books and 143 abstracts dating from 1938 to 1997 were surveyed of the 101 eucrites having at least one set of elemental abundance analyses reported in the literature 20 were selected for in depth examination the selection criteria of our sample were based on the total number of analyses available for a given eucrite and the total number of elements for which data exist the mean bulk elemental abundance 1 standard deviation and the percent deviation were calculated for each element in a given eucrite in order to evaluate the quality of the mean abundances the elements were then grouped according to availability of data and percent deviations possible reasons for the different deviations in the different groups are briefly discussed from the major element abundances the normative cipw composition the molar compositions of pyroxene olivine and plagioclase and the bulk densities were calculated and compared to petrographic observations the calculated norms for the noncumulates agree well with the observations while the norms for the cumulates do not possible reasons for this are discussed unfortunately analyses of many elements are poorly represented in the literature and many bulk analyses suffer from unacceptable levels of uncertainty therefore future work requires bulk elemental analyses for some of the more poorly characterized elements in eucrites especially those of key elements used for planetary modeling

elevated pco2 leading to late triassic extinction persistent photic zone euxinia and rising sea levels the late triassic mass extinction event is the most severe global warming related crisis to have affected important extant marine groups such as scleractinian corals and offers potential insights into climate change scenarios here we present evidence from chlorobi derived biomarkers of episodic and persistent photic zone euxinia from biomarkers and stable carbon isotopes we present evidence of rapid mixing of atmospheric and oceanic carbon reservoirs global versus regional trends are resolved in kerogen organic matter type carbonate 13c and bulk and pyrite 34s this suite of data demonstrates for the first time a comprehensive organic and stable isotope geochemical reconstruction of events leading up to the late triassic extinction event and its aftermath the cascade of events prior to during and after the extinction is remarkably similar to those reported for the late permian extinction the largest extinction event of the phanerozoic we predict that similar conditions will have occurred during all past episodes of rapid global warming and biotic crisis that are associated with similar rises in p co2

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

tectonic and regional metamorphic implications of the discovery of middle ordovician conodonts in cover rocks east of the green mountain massif vermont middle ordovician late arenigian early caradocian conodonts were recovered from a dolostone lens in carbonaceous schist 30 m below the base of the pinney hollow formation in the eastern cover sequence near west bridgewater vermont these are the first reported fossils from the metamorphic cover sequence rocks east of the green mountain berkshire and housatonic massifs of western new england the conodonts are recrystallized coated with graphitic matter thermally altered to a color alteration index cai of at least 5 and tectonically deformed the faunule is nearly monospecific consisting of abundant periodon aculeatus hadding and rare protopanderodus the preponderance of periodon and the absence of warm shallow water species characteristic of the north american midcontinent conodont province suggest a slope or basin depositional setting the conodont bearing carbonaceous schist is traceable 3 km southeast to the plymouth area where it had been designated the uppermost member of the plymout

the δ13c excursions spanning the cambrian explosion to the canglangpuian mass extinction in the three gorges area south china abstract a remarkable increase of the animal genera and a subsequent mass extinction in the late early cambrian are well known as the cambrian explosion and the botomian toyonian crisis a composite global curve of the carbon isotope ratios for inorganic carbon 13ccarb shows multiple fluctuations during the evolution events and it indicates significant changes of the oceanic carbon cycle at that time this study reveals a new continuous isotopic chemostratigraphy for inorganic carbon 13ccarb from the bottom of the shipai to the base of the shilongdong formations in three gorges area south china this section covers the canglangpuian to the longwangmiaoian stages in the lower cambrian the 13ccarb variation exhibits three negative excursions a remarkably negative excursion down to ca 12 in the middle canglangpuian stage a negative excursion to ca 1 0 in the upper canglangpuian stage and a negative excursion to ca 1 0 in the longwangmiaoian stage respectively the largest negative 13ccarb excursion and a positive excursion before the excursion are definitely consistent with the 13ccarb negative shift aece during the mass extinction and the 13ccarb positive values mice during the increase of animal genera respectively however the minimum values of the negative shifts among south china siberia and canada sections are different from each other the positive 13ccarb excursion at the bottom of the canglangpuian stage indicates that primary productivities and organic carbon burial were enhanced a sea level rise in the qiongzhusian to bottom of the canglangpuian stages in south china corresponds to the sinsk transgression event in siberia and canada a eutrophication due to higher continental weathering during the transgression after the long term retrogression enhanced the high primary production and consequently promoted the significant increase of animal diversity on the other hand deposition of laminated black shales without bioturbation signatures and a decline of trilobite diversity are observed during the negative 13ccarb excursion in the canglangpuian stage indicating that the shallow water environment became anoxic at that time the negative 13ccarb shift indicates an influx of abundant 12co2 due to oxidation of organic carbons in seawater the difference of the minimum values among sections implies the local difference in size of the organic carbon reservoirs and extent of the degradation of the carbons the largest 13c anomaly in south china suggests the presence of the largest ocps due to higher activity of primary production and high degree of oxidation of the ocps because of higher activity of animals the coincidence of the timing of the negative 13c excursions in the canglangpuian stage among the sections indicates a global event and suggests that the onset was caused by increase of oxygen contents of seawater and atmosphere abundant oxygen yielded by the increased primary productivity in the atdabanian and the qiongzhusian stages caused onset of the oxidation of ocp and possibly led to the shallow water anoxia and the mass extinction of benthic animals in the botomian and the canglangpuian stage

do archean chemical sediments record ancient seawater rare earth element patterns rare earth elements ree concentrations of archean and proterozoic chemical sediments are commonly used as proxies to study secular trends in the geochemistry of precambrian seawater in addition similarities in the ree signatures of archean chemical sediments and modern seawater have led researchers to argue that some archean rocks originated as biochemical precipitates i e microbial carbonates in shallow marine e g peritidal environments however terrestrial waters including river water and groundwater also commonly exhibit ree fractionation patterns that resemble modern seawater here we present the seawater like ree data for ground

on the late neoproterozoic early cambrian transition events in parts of east gondwanaland abstract the east gondwanaland evolved as a result of break up of the rodinia supercontinent the late neoproterozoic early cambrian geochemical events documented in the rocks of the east gondwanaland and siberia suggest variations in the c s and sr isotopic compositions of the contemporary seawater and systematic distribution of phosphorite and evaporite deposits the geochemical records in the peninsular india himalaya south china iran and oman regions have been discussed and used for establishing late neoproterozoic links of these widely separated sedimentary basins

multiple δ13c excursions spanning the cambrian explosion to the botomian crisis in siberia new high resolution 13 c data through the lower cambrian of siberia reveal multiple positive excursions coincident with phases in the explosion of invertebrate phyla nemakit daldynian to middle botomian stages comparison of the 18 o and trace element mg fe mu sr chemistry indicate that six new 13 c cycles are primary rather than diagenetic features with potential for global correlation positive 13 c excursions up to 3 indicate that fractional organic carbon burial rates were high but variable through the cambrian explosion values for 13 c dropped sharply from around 2 2 to 1 6 in botomian time coincident with mass extinction of the archaeocyathan reef biota the rapid fluctuation of the 13 c signal and the temporal coincidence of the pronounced negative shift with the extinction event hint that the 13 c record may record productivity variations during the early cambrian radiation

dissolution methods for strontium isotope stratigraphy whole rock analysis the preparation of samples for strontium isotope stratigraphy sis by whole rock dissolution results in contributions of sr from contaminant phases as well as from the target carbonate phase here we highlight and quantify the errors in 87sr 86sr values that might result when calcium carbonate is dissolved using an inappropriate method we report the variation in 87sr 86sr value of sr released from four samples of differing calcite content and degrees of cementation when subject to different methods of dissolution we show that errors of up to 0 000076 in 87sr 86sr which correspond to errors of 3 68 ma in age can be avoided by careful preleaching of the samples

mineralogy geochemistry and 40ar 39ar geochronology of lunar granulitic breccia northwest africa 3163 and paired stones comparisons with apollo samples abstract the lunar meteorites northwest africa nwa 3163 4881 and 4483 are paired stones classified as granulitic breccias at 2 4 kg these three stones constitute one of the largest known lunar meteorite masses here we describe the petrography mineralogy and chemistry of nwa 3163 4881 and 4483 and present 40 ar 39 ar data for two of the meteorites two pyroxene thermometry indicates that the rocks equilibrated at 1050 50 c which represents the high temperature low pressure event that generated their characteristic recrystallization textures and reset their ar systematics stepped heating in situ infrared laser microprobe 40 ar 39 ar geochronology yields a mean age of 3327 29 ma for nwa 3163 and a more disturbed release spectrum for nwa 4881 nwa 4881 shows an upward trending pattern suggesting that it may have had a 40 ar 39 ar age of 3 0 ga but that it was partially reset at 2 6 ga nwa 3163 et al exhibit shock effects including maskelynitized plagioclase shock veins and melt pockets which are absent in the apollo granulitic breccias although the apollo and meteorite samples are texturally similar and have comparable bulk compositions and equilibration temperatures their trace and siderophile element contents point to distinct parental lithologies derived from different regions of the moon based on mineralogical and geochemical differences between the apollo and meteorite samples we conclude that the parent rock s of the paired nwa meteorites came from an area outside the imbrium region and that they underwent high temperature granulite event metamorphism long after the late heavy bombardment

marine carbonate records of terrigenous input into paleotethyan seawater geochemical constraints from carboniferous limestones a combined study of trace elements carbon and oxygen isotopes was carried out for carboniferous marine limestones from the lower yangtze platform in south china the results provide insights into the influence of terrigenous input to paleotethyan seawater from which pure and impure carbonates precipitated in terms of the correlations between the concentrations of elements with different properties variable extents of two component mixing are evident between seawater and terrigenous detritus this is quantitatively dictated by such parameters as the calcite seawater partition coefficients dx and the seawater continental upper crust partition coefficients kx water soluble elements with high and medium kx values such as na mg p v cr ni cu zn sr mo and u are susceptible to incorporation into carbonate lattices and thus their concentrations represent the geochemical composition of paleoseawater in contrast water insoluble elements with low kx values such as be al sc co ga cs ree hf and th cannot be incorporated into carbonate lattices thus providing a proxy for contributions from terrigenous material the carboniferous marine limestones from a stratigraphic profile exhibit three positive and three negative d 13 c excursions from the late visean to gzhelian these d 13 c excursions generally match those of contemporaneous carbonates elsewhere in the world which can be linked to the alternative occurrences of cold and warm paleoclimates in the carboniferous the lowest d 13 c values in the profile are generally associated with the lowest values of y ho and the highest values of nd yb paas th sc and insoluble residue this indicates a significant contribution from the terrigenous material to the negative d 13 c excursions the effect from the warm paleoclimate is also indicated by high chemical indices of alteration for the insoluble residue from the three intervals of high terrigenous input on the other hand the positive d 13 c excursions are associated with the decreases of terrigenous input therefore the incorporation of terrigenous material into the epicontinental seawater is temporally linked to the paleoclimatic change on continental margins adjacent to the paleotethyan seawater

interpreting carbon isotope excursions carbonates and organic matter abstract variations in the carbon isotopic compositions of marine carbonate and organic carbon provide a record of changes in the fraction of organic carbon buried through time and may provide clues to changes in rates of weathering and sources of organic carbon paired carbonate and organic carbon isotope determinations provide a possibility of interpreting not only changes in the global carbon cycle through time but changes in atmospheric pco2 as well interpretations of these types of data are typically rather qualitative a quantitative basis is required to develop a better understanding of changes in the carbon cycle for this purpose we employ a simple model of the global carbon cycle which is subjected to a number of different perturbations each lasting 500 ky i e much longer than the residence times of carbon and phosphorus in the ocean atmosphere system in addition to standard considerations of carbon mass and isotopic fluxes to the ocean atmosphere system from weathering and volcanism and fluxes of organic carbon and carbonate carbon to sediments the model incorporates sensitivity of the photosynthetic carbon isotope effect to changes in pco2 the inclusion of this parameter leads to unexpected carbon isotope responses to forcing that causes increased rates of organic carbon burial a series of simple to more complex simulations illustrates the significant effects of varying differences between the carbon isotopic composition of sedimented carbonate and organic carbon b with constant b a 50 increase in organic carbon burial produces a parallel increase in carbonate and organic carbon isotopic compositions however the same simulation with b responsive to pco2 changes produces an initial parallel 13 c increase but this is followed by an even greater 13 c enrichment in organic carbon because pco2 falls in response to increased organic carbon burial the counterintuitive overall result of the enhanced organic carbon burial event is that the carbonate carbon isotopic composition actually decreases because of the more substantial increase in 13 c org in addition we illustrate the effects on carbon isotopic compositions of the oceanic inorganic carbon reservoir and buried organic matter of a 50 increase in volcanic co2 outgassing a 50 increase in weathering rate with coupled phosphate and riverine carbon flux responses a 50 decrease in shale associated organic carbon weathering a 50 decrease in silicate weathering rate and the possible effects of the rise in abundance of c4 plants in the late miocene to recent we compare the model simulated carbon isotopic responses for some of these experiments to paired carbonate and organic carbon records to illustrate how these records might be interpreted in light of the model response

geochemical changes across the proterozoic cambrian transition in the durmala phosphorite mine section mussoorie hills garhwal himalaya india abstract the transition from the neoproterozoic nemakit daldynian 1 krol e dolomite to the tommotian lower tal phosphorite chert black shale sequence denotes a period of drastic change in the depositional environment and the chemical milieu of the sedimentation basin these changes are reflected by a marked negative excursion of carbon isotopes phosphorus enrichment trace metal content high organic carbon burial and notably the first appearance of prolific small shelly fauna and burrowing organisms recent studies have documented these changes along several stratigraphic profiles in the mussoorie hills of the garhwal himalaya for which a single profile from the durmala phosphorite mine provides a key section discussed here

the puerto lapice eucrite puerto lapice is a new eucrite fall castilla la mancha spain 10 may 2007 in this paper we report its detailed petrography magnetic characterization mineral and bulk chemistry oxygen and noble gas isotope systematics and radionuclide data study of four thin sections from two different specimens reveal that the meteorite is brecciated in nature and it contains basaltic and granulitic clasts as well as recrystallized impact melt and breccia fragments shock veins are ubiquitous and show evidence of at least three different shock events bulk chemical analyses suggest that puerto lapice belongs to the main group of basaltic eucrites although it has a significantly higher cr content oxygen isotopes also confirm that the meteorite is a normal member of the hed suite noble gas abundances show typical patterns with dominant cosmogenic and radiogenic contributions and indicate an average exposure age of 19 2 ma and a pu fission xe age well within typical eucrite values cosmogenic radionuclides suggest a preatmospheric size of about 20 30 cm in diameter

glendonites in neoproterozoic low latitude interglacial sedimentary rocks northwest canada insights into the cryogenian ocean and precambrian cold water carbonates stellate crystals of ferroan dolomite in neritic siliciclastic and carbonate sedimentary rocks between sturtian and marinoan glaciations in the mackenzie mountains are interpreted as replaced glendonites these pseudomorphs after ikaite indicate that shallow seawater at that time was near freezing stromatolites verify that paleoenvironments were in the photic zone and physical sedimentary structures such as hummocky cross bedding confirm that the seafloor was repeatedly disturbed by storms glendonites within these low latitude continental shelf to coastal sedimentary deposits imply that global ocean water during much of cryogenian time was likely very cold such an ocean would easily have cooled to yield widespread sea ice and through positive feedback growth of low latitude continental glaciers in this situation gas hydrates could have formed in shallow water cold shelf sediment but would have been particularly sensitive to destabilization as a result of sea level change co occurrence of pisolites and glendonites in these rocks additionally implies that some ooids and pisoids might have been unlike phanerozoic equivalents characteristic of cold water sediments