graphical analysis of enthalpy composition relationships in mixed magmas enthalpy composition diagrams h x calculated from existing temperature composition t x phase diagrams and thermodynamic data provide a simple and effective means for evaluating the enthalpy temperature effects of magma mixing if athermal mixing is assumed adiabatic mixing lines on h x diagrams are straight lines because enthalpy unlike temperature is an extensive property of a system comparison of binary t x diagrams with their derivative h x diagrams shows that incorrect predictions can be obtained when t x diagrams are used to analyze mixing problems an h x diagram calculated using experimentally determined phase equilibria for anhydrous basalt rhyolite mixtures predicts that adiabatic mixing of basalt and rhyolite at their respective liquidus temperatures will result in small amounts of crystallization 2 wt because the phase equilibria of hydrous basalt rhyolite mixtures have not yet been determined an h x diagram for such mixtures cannot be constructed however existing hydrous phase equilibria can be used to predict whether adiabatic mixtures of anhydrous basalt and hydrous rhyolite will be super or subliquidus calculations at ptotal 200 mpa show that on an h x diagram a mixing chord drawn between anhydrous basalt and water saturated rhyolite at their respective liquidus temperatures lies below the enthalpy values calculated for a paricutin andesite and mt st helens dacite at their estimated liquidus temperatures this indicates that the liquidus for mixtures of anhydrous basalt and water saturated rhyolite is noticeably convex upward suggesting that larger amounts of crystallization will occur than in the anhydrous case

mo isotopic variations of a cambrian sedimentary profile in the huangling area south china evidence for redox environment corresponding to the cambrian explosion abstract the radiation of macroscopic animals in the early cambrian commonly be called as cambrian explosion had a close relationship with earth oxygenation these macrofossils are widely preserved within the early cambrian in the northern and western yangtze craton in order to show the casual relationship between animal evolution and earth redox environment mo content and isotopic composition analyses have been conducted on dolomites of the tianzhushan formation and the black shales of the shuijingtuo formation from the lowermost cambrian profile in the eastern huangling dome northern yangtze craton the calcitic dolostones from the tianzhushan formation display lower concentrations of mo contents 0 055 0 666 ppm than that of the black silty shales from the shuijingtuo formation 6 0 172 ppm this magnitude difference is most likely related to the different lithologies due to mo enrichment in shales the mo isotope values 98 95mo of the calcitic dolostones for the tianzhushan formation vary from 0 73 to 0 41 in comparison the black sandy shales from the shuijingtuo formation exhibit 98 95mo of 1 04 1 84 including 5 samples from the earliest shuijingtuo formation displaying systematically higher 98 95mo values 0 09 1 84 than those of the other 5 samples from upper layers 98 95mo 1 04 to 0 19 these geochemical data suggest that the redox environment of the early cambrian is fluctuating and the peak oxygenation of the ocean had already reached a level similar to modern environments according to the mo concentrations and 98 95mo data the sedimentary succession can be divided into five intervals which are closely correlated to the episodic evolution of early life in the cambrian together with the available published data from other profiles in the yangtze craton our new data reveal that the higher oxidation environment had a positive effect on the evolution of early life

gps and glonass observations of large scale traveling ionospheric disturbances during the 2015 st patrick s day storm using a comprehensive database of 5300 ground based gnss stations we have investigated large scale traveling ionospheric disturbances lstids during 17 18 march 2015 st patrick s day storm for the first time the high resolution two dimensional maps of the total electron content tec perturbation were made using not only gps but also glonass measurements several lstids originated from the auroral regions in the northern and southern hemispheres were observed simultaneously over europe north america and south america this storm is considered as a two step main phase storm during the first main phase lstids propagated over the whole daytime european region and over high latitudes of north america during the second main phase we report 1 intense lstids propagated equatorward in north america and europe 2 convergence of several lstids originated from the opposite hemispheres in the interference zone over geomagnetic equator in south america 3 super lstids with the wavefront length of more than 10000 km observed simultaneously in north america and europe lstids observed in three sectors had wavelength of 1200 2500 km and wave periods of 50 80 min during the recovery phase on the background of the negative ionospheric storm developed over north america we detect signatures of the stream like structures alongated within the latitudinal range of 29 n 42 n across the usa these structures persisted through the nighttime to the early morning from 04 ut till 13 ut on 18 march 2015 and they were associated with the subauroral polarization streams saps induced nighttime ionospheric flows

variations of redox conditions in the atmosphere and yangtze platform during the ediacaran cambrian transition constraints from cr isotopes and ce anomalies abstract the ediacaran cambrian transition was characterized by the evolution from ediacaran soft body to cambrian skeletal organisms and fluctuations of the marine carbon cycle marine redox changes should have played an essential role in both ecological and environmental evolutions however temporary changes and spatial distribution of redox conditions in the ediacaran cambrian oceans remain elusive and highly debated in this study we analyzed chromium cr isotope and cerium ce anomaly profiles in carbonates from the upper ediacaran lower cambrian dengying and zhujiaqing formations at the xiaotan section south china in an attempt to provide new insights helping unravel earth s surface redox changes during the ediacaran cambrian transition our results show that these carbonates record generally positive 53crauth values up to 1 15 with fluctuations and prominent negative ce anomalies ce ce values down to 0 35 implying a broad increase in oxygenation in the atmosphere and the inner shelf of the yangtze platform during the ediacaran cambrian transition the first appearance and subsequent diversification of the cambrian animals may have benefited from this oxygenation event the pronounced fluctuations of 53crauth and 13ccarb values can be explained by episodic oxidation of a deep water doc pool in a stratified water column across the chemocline through upwelling releasing light carbon isotopes and organic matter bound isotopically unfractionated cr iii into shallow waters

ocean chemistry during glacial time abstract measurements of co2 to air ratios in the gas trapped in bubbles in ice of glacial age suggest that the co2 content of the atmosphere was considerably lower during peak glacial time than during holocene time the purpose of this paper is to show that such a change must in all likelihood be the result of alterations in the nutrient element chemistry of sea water two possible scenarios are presented one involves alternate storage and erosion of phosphorous leaving residues from shelf sediments the other involves changes in the c p ratio in the organic debris falling to the deep sea means of verifying the nutrient cycle hypothesis are also given it is shown that the 13c record as we know it in planktonic and benthic foraminifera the oxygen record as inferred from benthic foraminifera species distributions and the early post glacial caco3 preservation event as recorded by aragonitic pteropods are consistent with both of the hypotheses presented only if an early post glacial spike in the 13c record for planktonic shells could be found would it be possible to eliminate one of these hypotheses i e that involving shelf storage the implications of these nutrient hypotheses to climate theory are as follows if shelf storage is responsible for the glacial to interglacial co2 increase then the co2 change must be considered an amplifier of some primary cause the reason is that sea level changes are needed to drive deposition on and erosion from the shelves on the other hand if changes in the c p ratio for falling debris are responsible then the co2 change could either be an amplifier or a primary cause for the major glacial to interglacial climatic cycle the latter is possible as self sustained oscillations in ocean chemistry might be driven by interactions between ocean ecology and ocean nutrient chemistry

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

evolution of a terminal neoproterozoic carbonate ramp system buah formation sultanate of oman effects of basement paleotopography the buah formation is a carbonate unit of late neoproterozoic age exposed in the jabal akhdar of northern oman and the huqf region of central oman the buah formation is interpreted as a distally steepened storm dominated ramp containing inner ramp tidally influenced oolitic shoal and back shoal lagoon fades and storm dominated mid ramp facies a slope break separates mid ramp facies from outer ramp facies characterized by accumulation of redeposited carbonates on gently inclined slopes 1 2 degrees combined facies stacking patterns and outcrop correlation via 1 3 c profiles suggest that buah carbonates formed as a highstand systems tract characterized by a general upward shallowing of facies and strong lateral progradation on a regional scale buah facies distributions across oman were controlled by the presence of basement highs defining areas of reduced subsidence which promoted lateral progradation of the buah carbonate ramp for tens of kilometers while the faster subsiding areas became sites of deep water deposition

precambrian microfossils from the sinian of south china the discovery of previously unknown microfossils from the sinian of western hubei province south china fig 1 is reported here the sinian there up to 1 000 m thick is naturally divisible into four formations fig 2 from the base upwards 1 the liantuo formation comprising feldspar quartz sandstones with basal conglomerates 2 the nantuo formation which is a tillite 3 the doushantuo formation which has micro dolomites intercalated with black shales and cherty beds with some siliceous or phosphatic nodules and 4 the dengying formation which is mainly dolomites the rock sample in which the microfossils were found was collected from the lower part of the doushantuo formation near the highway side 500 m east of liantuo yichang county fig 1 the doushantuo formation has been dated as 693 66 myr rb sr isochron age 1 pseudomorphs after gypsum sometimes occur in the lower part the microfossils are preserved in siliceous nodules particularly in the cherty portions the dark colour of the nodules is due to the high organic content

irreversible change of the oceanic carbon cycle in the earliest cambrian high resolution organic and inorganic carbon chemostratigraphy in the three gorges area south china the terminal neoproterozoic and its transition into the cambrian witnessed major evolutionary and geochemical changes large fluctuations in the carbon isotope ratio for inorganic carbon 13ccarb across the precambrian cambrian boundary pc c boundary indicate a significant change in the oceanic carbon cycle at that time this work presents the first high resolution 13corg chemostratigraphy of drill core samples across the pc c boundary in the three gorges area south china and discusses carbon cycles based on the relation between 13corg and 13ccarb we found that changes of 13corg and 13ccarb values were decoupled during the significant negative excursion of 13ccarb across the pc c boundary suggesting the presence of a huge organic carbon pool ocp previously the large ocp was inferred to have been established in the terminal proterozoic and to have disappeared at the end of the mid ediacaran shuram excursion in contrast our study suggests that the large ocp lasted until the early nemakit daldynian stage on the other hand in the middle nemakit daldynian to atdabanian the 13ccarb and 13corg changed in parallel as observed normally in the phanerozoic in order to evaluate these scenarios quantitatively we performed numerical simulations and calculated the time evolution of the 13ccarb masses of the inorganic and organic carbon pools and the fluxes between them as a result we show that the observed negative 13ccarb excursion with steady 13corg can be produced by enhanced primary productivity and remineralization of the large ocp if the rate constant for removal of organic carbon was considerably lower than that of today the end of the decoupled negative 13ccarb excursion is attributable to an increase in the removal rates of inorganic and organic carbon from the ocean the enhanced flux of organic carbon burials eliminated the large ocp so that the modern style carbon cycle was established by the early nemakit daldynian stage the inferred rapid increases of both organic and inorganic carbon burial rates in the middle nemakit daldynian stage were likely caused by the appearance of planktonic metazoans with guts making fecal pellets and by the first skeletal animals the biological innovations may have changed the oceanic carbon cycle irreversibly just after the pc c boundary

selenium arsenic and molybdenum variation and bio radiation in the ediacaran cambrian interval abstract the ediacaran early cambrian period is critical for the evolution of multicellular life however the distribution and enrichment patterns of biological trace elements and their correlations with the bio changes are not yet fully understood here we present the variation patterns of trace elements in the yangtze gorges area south china compared to the upper continental crust selenium se cadmium cd arsenic as and molybdenum mo are the most enriched and varied trace elements in the whole ediacaran and early cambrian formations the concentrations of which vary from 10 5 to 30 1 0 02 to 163 1 5 10 5 to 196 5 and 0 02 to 289 0 mg kg respectively with average values of 1 3 1 0 14 0 and 8 0 mg kg average enrichment factors ef of 27 0 10 7 9 7 and 5 4 and ef variations of 601 2 1663 6 131 0 and 192 6 respectively the significantly enriched ef 10 strata sequences of se and as mainly include the lower and upper ediacaran doushantuo member ii dst ii dst iv bottom and upper yanjiahe formation precambrian cambrian and shuijingtuo formation early cambrian mo displays similar significantly enriched strata with se and as from dst iv and above compared to the cryogenian nantuo formation se as and mo are enriched and concentrated in the whole ediacaran and early cambrian strata especially at the early ediacaran doushantuo formation the diachronous yanjiahe formation precambrian cambrian and the early cambrian shuijingtuo formation which are the horizons of the great bio changes moreover the significantly enriched strata of se as and mo are also consistent with intervals of great bio changes

carbon isotope excursions and the oxidant budget of the ediacaran atmosphere and ocean a possible global drop in marine carbon isotope values to as low as 12 peedee belemnite pdb recorded in the ediacaran shuram formation of oman has been attributed to the non steady state oxidation of oceanic dissolved organic carbon doc resulting from the rise in atmospheric oxygen to near modern values at the end of the precambrian geologic constraints indicate that the excursion lasted between 25 and 50 m y requiring a doc pool thousands of times to 10 000 times the modern inventory to conform with carbon isotope mass balance calculations for a 12 excursion at the consequent rates of doc oxidation oceanic sulfate and oxygen in the atmosphere and oceans are exhausted on a time scale of 800 k y oxidant depletion is incompatible with independent geochemical and biological indicators that show oceanic sulfate and oxygen levels were maintained or increased during the shuram excursion furthermore a doc driven excursion does not explain strong covariation between the carbon and oxygen isotope record these indicators show that negative isotope excursions recorded in the shuram and other ediacaran sections are unlikely to represent a global ocean signal

permian triassic boundary ptb in the lower yangtze region southeastern china a new discovery of deep water archive based on organic carbon isotopic and u pb geochronological studies abstract the lower yangtze region of southeastern china is an important area for the study of permian triassic boundary ptb in this region many well known ptb sections e g meishan have been investigated widely and extensively however these sections are dominantly in shallow water settings and data from deep water areas are lacking to fill the gap we conducted a field survey recently and found a deep water ptb section with relatively continuous deposition using integrated organic carbon isotopic and u pb geochronological studies this well exposed and fresh section is located at niushan xuancheng city anhui province 90 km west of the well known meishan section which is the ptb global boundary stratotype section and point the organic carbon isotope curve of the section contains three positive excursions pcies and two negative excursions ncies which can be well correlated with other ptb sections as well as with wuchiapingian changhsingian boundary wcb sections worldwide they archive the original ptb and wcb signatures further u pb dating of magmatic zircons in volcanic ashes validates this new finding i e the ptb interval between 252 49 0 76 ma and 251 74 0 77 ma carbon isotopes of ptb sections in south china reflect the regional paleogeography the two ncies ncie 2 and ncie 3 across the ptb transition are most likely caused by widespread large scale volcanic activity in contrast the ncie 1 near the wcb is possibly related to an increase in the productivity of organic matter as a result of transgression and a change in the organic matter type from terrigenous to marine

geochemical changes in the early cambrian interval of the yangtze platform south china implications for hydrothermal influences and paleocean redox conditions abstract the possible triggering mechanisms of the ediacaran cambrian transition in south china have been debated for many years in this study 80 samples from liuchapo niutitang and mingxinsi formations were collected from well yk 1 located in southeastern chongqing a high resolution chemostratigraphic study including evaluation of rare earth elements rees and trace elements was used to elucidate the paleoenvironments of the upper yangtze platform margin the mingxinsi gray shale and the liuchapo formation exhibit flat post archean australian normalized ree patterns with weakly negative ce anomalies which is typical of detritus obvious positive eu anomalies in chert samples of the basal niutitang formation imply a short term influence of hydrothermal fluid the ree patterns of the basal niutitang phosphatic rocks show significant enrichment of heavy rees significantly negative ce anomalies and positive y anomalies similar to the ree distribution pattern in seawater demonstrating that these sediments were produced under oxic seawater conditions moderately positive eu anomalies and positive y anomalies of the lower niutitang shales may indicate mixing of hydrothermal fluids and seawater the flat ree patterns with weak eu anomalies of the upper niutitang shale may have been generated by hydrothermal inputs diluted by detrital materials dramatic increases of ce anomalies in the basal niutitang formation reveal a significant decrease of the oxygen level in seawater trace elements such as ba u v u cu cr zn ni and sr are commonly enriched in these formations compared to the upper continental crust authigenic abundances of al normalized u and al normalized v as well as ratios of th u and v sc are used as indicators of redox conditions these distributions demonstrate that the redox conditions of the bottom water during the ediacaran cambrian transition abruptly changed from oxic in the nemakit daldynian age to anoxic in the early tommotian age and gradually became less reducing in the late tommotian age and the atdabanian age a strong correlation between total organic carbon toc concentrations and ratios of u al and v al in the entire section except in the phosphatic rocks implies non sulfidic conditions most trace elements cannot be used as proxies for redox conditions associated with the phosphatic rocks in the basal niutitang formation because abundant trace elements were especially absorbed in apatite the toc concentrations correlated well with the redox conditions of bottom water we infer that the section deposited in the platform margin was influenced by episodic hydrothermal activities that began at the beginning of the tommotian age and these activities may have terminated at the beginning of the atdabanian age enrichments of organic matter that were mainly derived from the photic zone were controlled by the redox conditions of the bottom water

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

glacial interglacial co2 change the iron hypothesis several explanations for the 200 to 280 ppm glacial interglacial change in atmospheric co2 concentrations deal with variations in southern ocean phytoplankton productivity and the related use or nonuse of major plant nutrients an hypothesis is presented herein in which arguments are made that new productivity in today s southern ocean 7 4 1013g yr 1 is limited by iron deficiency and hence the phytoplankton are unable to take advantage of the excess surface nitrate phosphate that if used could result in total southern ocean new production of 2 3 1015 g c yr 1 as a consequence of fe limited new productivity holocene interglacial co2 levels preindustrial are as high as they were during the last interglacial 280 ppm in contrast atmospheric dust fe supplies were 50 times higher during the last glacial maximum lgm because of this fe enrichment phytoplankton growth may have been greatly enhanced larger amounts of upwelled nutrients may have been used and the resulting stimulation of new productivity may have contributed to the lgm drawdown of atmospheric co2 to levels of less than 200 ppm background information and arguments in support of this hypothesis are presented

nitrogen cycle perturbations linked to metazoan diversification during the early cambrian abstract the rapid diversification of metazoans during the late ediacaran early cambrian is one of the most remarkable evolutionary events in earth history however the triggering mechanism remains highly contentious particularly concerning the relationship of this biological event to contemporaneous changes in ocean redox and nutrient cycling in this study we report new bulk nitrogen isotope 15n and organic carbon isotope 13corg data from the lower cambrian niutitang formation in two deep water sections in south china to provide a better understanding of the relationship of the nitrogen cycle ocean redox and biological evolution during this key period the 15n data from two study sections are characterized by consistently low values 1 to 2 throughout the niutitang formation despite large variations in 13corg we interpret these low 15n values to have resulted from assimilation of recycled ammonium nh4 and n2 fixation compilation of available 15n data reveals large temporal and spatial 15n variations from 1 to 7 in time equivalent strata in south china such 15n variations imply the co existence of aerobic and anaerobic n cycles and highly heterogeneous ocean redox conditions during the early cambrian in south china which is consistent with inferences from other geochemical proxies temporal fluctuations and spatial heterogeneity in ocean redox conditions may have controlled the distribution and evolution of metazoans during the early cambrian

iron deficiency limits phytoplankton growth in antarctic waters enrichment experiments were performed in the ross sea to test the hypothesis that iron deficiency is responsible for the phytoplankton s failure to use up the luxuriant major nutrient supplies found in these and all other offshore antarctic ocean waters nitrate uptake rates in the controls without added trace elements ranged from 0 58 to 1 22 mol kg 1 d 1 the addition of 1 to 5 nmol of unchelated fe per liter resulted in rates that were 2 to 10 times higher 2 54 to 6 00 mol no3 kg 1 d 1 rates in bottles with 2 nmol mn added were identical to those in the controls 0 57 to 1 04 mol no3 kg 1 d 1 total decreases in no3 were balanced by increases in particulate organic n these results suggest that fe deficiency is the primary reason that the present day southern ocean biological pump is shut off in contrast iron was 50 times more abundant during the last glacial maximum greater fe availability may have stimulated the biological pump and contributed to the ice age drawdown of atmospheric c02 these results also imply that large scale southern ocean fe fertilization is feasible at least in terms of the total amounts of fe required i e 100 000 to 500 000 tons yr 1

neoproterozoic to early cambrian small shelly fossil assemblages and a revised biostratigraphic correlation of the yangtze platform china abstract small shelly fossils ssfs occur widely on the yangtze platform and have great potential for biostratigraphic subdivision of pre trilobitic early cambrian strata based on the ssf record of the shallow water realm five biozones can be recognized for the meishucunian stage in ascending order the biozones are anabarites trisulcatus protohertzina anabarica assemblage zone paragloborilus subglobosus purella squamulosa assemblage zone watsonella crosbyi assemblage zone formerly heraultipegma yunnanensis zone poorly fossiliferous interzone sinosachites flabelliformis tannuolina zhangwentangi assemblage zone in addition one ssf biozone is recognized for the overlying qiongzhusian stage pelagiella subangulata taxon range zone the formerly used siphogonuchites triangularis paragloborilus subglobosus zone and heraultipegma yunnanensis zone are discussed and redefined approximately 80 species of ssfs were screened for their spatial and temporal distribution on the yangtze platform variations in lithofacies and biofacies can be recognized throughout the yangtze platform extending over an area of 2000 900 km in a deeper water shelf setting the first zone is represented by the protohertzina anabarica kaiyangites novilis assemblage zone while younger zones are not recognized in the southern region at the northern platform margin the qiongzhusian is represented by the ninella tarimensis cambroclavus fangxianensis assemblage zone and the rhombocorniculum cancellatum taxon range zone the southeastern shaanxi western hubei region followed a slightly different lithological and faunal development than the rest of yangtze platform indicating a stronger similarity with parts of east gondwana some taxa such as w crosbyi p subangulata r cancellatum microdictyon effusum a trisulcatus protohertzina unguliformis and p anabarica occur nearly worldwide and support an international correlation of early cambrian sequences between the yangtze platform and smaller west gondwanan blocks siberia newfoundland and australia the six investigated zones of the yangtze platform comprise an interval spanning the early nemakit daldynian to the late atdabanian early botoman stage on the siberian platform palaeobiogeographic analysis revealed a strong taxic similarity between the yangtze platform and the tarim platform a smaller number of species are shared with other west gondwanan platform fragments such as india and iran palaeobiogeographic results do not support the previously reported position of the south china block between australia and siberia during the early cambrian

an empirical model of the earth s horizontal wind fields hwm07 1 the new horizontal wind model hwm07 provides a statistical representation of the horizontal wind fields of the earth s atmosphere from the ground to the exosphere 0 500 km it represents over 50 years of satellite rocket and ground based wind measurements via a compact fortran 90 subroutine the computer model is a function of geographic location altitude day of the year solar local time and geomagnetic activity it includes representations of the zonal mean circulation stationary planetary waves migrating tides and the seasonal modulation thereof hwm07 is composed of two components a quiet time component for the background state described in this paper and a geomagnetic storm time component dwm07 described in a companion paper

paired carbonate and organic carbon isotope variations of the ediacaran doushantuo formation from an upper slope section at siduping south china abstract intensive carbon isotope analyses from the doushantuo formation ca 635 551 ma in south china reveal decoupled carbonate and organic carbon isotopes 13ccarb and 13corg that have been interpreted as recording a large dissolved organic carbon doc reservoir in the ediacaran ocean or chemoautotrophic methanotrophic recycling modification of organic matter in a redox stratified ocean existing paired 13ccarb 13corg data however are mostly from sections of an intrashelf lagoon near the yangtze gorges area where basin restriction may have resulted in local isotope departure from the open ocean to better understand the spatial and temporal variations of the ediacaran 13c excursions we have conducted high resolution paired 13ccarb 13corg analyses of the doushantuo formation from an upper slope section at siduping hunan province south china the data reveal three negative 13ccarb excursions at the basal middle and upper doushantuo formation two prominent negative 13corg anomalies are also observed in black shales and shaly dolostones at the base and top of the doushantuo formation for the majority of the doushantuo formation however 13ccarb and 13corg values are decoupled similar to those observed in the yangtze gorges area both 13ccarb and 13corg show large up to 10 variations among shallow and deep water sections that are consistent with a large carbon isotope gradient in a stratified ediacaran ocean the large 13ccarb gradient between shallow and deep water sections implies the availability of sulfate in deep water environments where the addition of authigenic carbonate films cements into surface ocean derived carbonate particles in anoxic water column or pore water led to more negative 13ccarb values significant spatial 13corg variations suggest that the decoupled 13ccarb 13corg may not have been resulted from direct buffering of a large doc reservoir but from recycling of organic matter by chemoautotrophs and methanotrophs compilation of available paired 13ccarb 13corg data from the yangtze platform reveals alternating intervals of coupled and decoupled 13ccarb 13corg values up to the early cambrian 520 ma intervals with coupled 13ccarb and 13corg coincide with evidence for ocean oxygenation events this phenomenon may be explained by episodic growth and oxidation of a moderate doc reservoir 6 12 times of the modern ocean the upper doushantuo 13ccarb anomaly temporally crosses a major stratigraphic unconformity indicating that part of the upper doushantuo shuram 13ccarb excursion was formed during sea level regression large spatial and temporal variations of the upper doushantuo 13ccarb excursion may record a mixed signature of open ocean seawater overprinted by facies dependent isotope variation stratigraphic truncation and authigenic diagenetic modification along the unconformity the real primary 13ccarb excursion may be shorter lived than previously thought

reconstruction of paleoceanic redox conditions of the lower cambrian niutitang shales in northern guizhou upper yangtze region abstract the paleoceanic redox conditions and the vertical and spatial distribution of organic matter rich lower cambrian niutitang shales are varied in the upper yangtze region china an integrated approach including organic geochemistry major and trace elemental geochemistry and x ray diffraction xrd mineralogy was used to characterize changes in redox conditions and to determine key controls on organic matter accumulation during deposition of the lower cambrian niutitang shales a 202 m long cored well located in kaiyang county in northern guizhou china was thoroughly characterized by the integrated approach in this study vertically total organic carbon toc rich siliceous and argillaceous black shales were developed in the lower and middle niutitang formation and toc lean silty shales were found in the upper niutitang formation the toc content in the lower and middle niutitang shales ranges from 0 27 to 6 7 with an average value of 2 1 and it decreases from 0 30 to 0 11 in the upper niutitang formation shales the toc rich siliceous shales in the lower niutitang formation were characterized by high total sulfur content enrichment in redox sensitive trace elements high corg p ratios and high authigenic mo u covariation indicating they were deposited under persistent anoxic conditions most organic rich shales from the middle niutitang formation were deposited under anoxic conditions whereas a few intervals having low toc contents were deposited in a predominantly oxic depositional environment in contrast the upper niutitang formation were deposited under fully oxic conditions a combination of high primary productivity and enhanced organic preservation under euxinic water column conditions is the key control on organic matter accumulation in the lower niutitang formation shales however a coupling of redox depositional environment and terrestrial mineral dilution plays an important role in organic matter accumulation and preservation in the middle niutitang formation similar organic matter abundance distribution and carbon isotope excursion of organic matter in the sediments deposited at different depositional facies on the yangtze platform suggest regional isotopically homogenous organic carbon input due to the widespread transgressive event with deep basinal waters being transported into the shallow shelf environments at the base of the lower cambrian as a result 13corg distribution patterns can be used as a stratigraphic correlation marker in the upper yangtze region

longitudinal variations of the topside ionosphere at low latitudes satellite measurements and mathematical modelings the longitudinal variations of the topside ionosphere at low latitudes observed by the hinotori satellite during equinoctial periods at high solar activity are studied using the sheffield university plasmasphere ionosphere model supim the model values show that both the neutral wind and e b drift velocities make important contributions to the observed longitudinal variations in the topside ionosphere the displacement of the geographic and magnetic equators and the magnetic declination angle which give rise to conjugate hemisphere differences in the neutral wind in the magnetic meridian are the principal causes of the observed north south asymmetries in the electron density about the magnetic equator a comparison of the modeled and observed electron densities shows that the modeled longitudinal variations are in general in qualitative agreement with the observations when the neutral winds are taken from the hwm90 thermospheric wind model improved agreement in the magnitudes is achieved if hwm90 is modified so that at low latitudes 1 the eastward component of the zonal wind is increased during the day and decreased at night and 2 the diurnal variations of the meridional wind in the northern hemisphere at eastern longitudes and the equatorward wind at around midnight at western longitudes are reduced the model reproduces the observed longitudinal variations in the development of the equatorial peak electron density during the day and in the equatorial trough and associated crests during the afternoon and postsunset periods the trough and crests are most prominent at around 2000 lt where the crest to trough ratio varies from about 1 15 at eastern longitudes to about 2 0 at western longitudes model calculations show that the longitudinal differences of these features can arise from a longitudinal variation in the vertical e b drift velocity

ionospheric electron content within the equatorial f 2 layer anomaly belt this paper describes some new results on the day to day behavior of the location of the equatorial anomaly in the columnar electron content the measurements were made from a unique network of stations covering dip latitudes from 0 n to 25 n during the period in 1975 1976 near sunspot minimum when the ats 6 satellite was visible from india the latitudinal distribution of the total electron content on a particular day was found to depend only on the strength of the electrojet current as determined by the difference of the horizontal magnetic field at stations on the magnetic equator and another outside the equatorial electrojet rather than on the horizontal magnetic field measured only at the equatorial station during magnetically disturbed periods the presence or absence of the anomaly was also found to depend only upon the strength of the electrojet current the varying electrojet current that is the equatorial electric field is very effective in moving the ionization to the anomaly latitudes of 15 20 but the columnar electron content over the magnetic equator remains relatively constant

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

climate ocean control on the depositional watermass conditions and organic matter enrichment in lower cambrian black shale in the upper yangtze platform abstract the lower cambrian sediments including the qiongzhusi and maidiping formations in the sichuan basin are generally considered as the main source rocks of precambrian cambrian petroleum system a comprehensive study integrated with multiple geochemical methods was conducted on 119 lower cambrian drillcore samples collected from the upper yangtze platform the results show that the fluctuation of sea level and climate during the deposition of the qiongzhusi and maidiping formations act as the critical factors controlling the watermass conditions and thus om accumulation during the deposition of upper maidiping formation 1m the paleoclimate was arid and sea level was relatively low in the study area the depositional environment indexes uef moef gammacerane index carotane and vef suggested that the upper 1m was deposited in a strong restricted marine setting with high water salinity and anoxic water conditions in ziyang weiyuan area however during the early qiongzhusi formation period the paleoclimate became humid and sea level rose in the study area high paleoproductiviy caused by high concentrations of nutrients brought by seawater and freshwater plays an important role in om accumulation in the basal part of the qiongzhusi formation 1q furthermore the model of paleoproductivity promotion caused by the coordinated control of climate and extensive transgression in the lower part of 1q may also be applicable to interpret the origin of high organic carbon abundance in the strata deposited in the same period with the 1q such as shiyantou shuijingtuo and niutitang formations in other parts of the upper yangtze platform

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

carbonate carbon isotope chemostratigraphy and u pb zircon geochronology of the liuchapo formation in south china constraints on the ediacaran cambrian boundary in deep water sequences abstract the ediacaran cambrian transition was one of the most significant intervals in geological history witnessing the origin of the metazoans and major environmental changes establishing a precise chronostratigraphic framework for the ediacaran cambrian transition has great significance for understanding the geological and evolutionary processes during this transition an integrated study on carbonate carbon isotopes and u pb zircon dating was conducted within the liuchapo formation in the sifangjing section in northeastern guizhou province south china to recognize the ediacaran cambrian boundary in slope facies of the yangtze block a substantial negative carbonate carbon isotope excursion was recognized within the lower part of the liuchapo formation moreover a weighted mean u pb zircon age of 540 7 3 8 6 6 ma was obtained from a tuffaceous interlayer approximately 2 m above the interval of the negative carbon isotope excursion the carbon isotope and age dating results indicate that the ediacaran cambrian boundary within the sifangjing section should be placed in the lower part of the liuchapo formation additionally in the sifangjing section a distribution of horodyskia minor extends up to the basal cambrian while the last appearance datum lad of palaeopascichnus jiumenensis correlates to the large negative carbon isotope excursion within the liuchapo formation this relationship indicates that the lad of the palaeopascichnus jiumenensis is a potential tool for the stratigraphic correlation of the ediacaran cambrian boundary successions in slope and deep water basin settings of the yangtze block

isotope stratigraphy of the ediacarian neoproterozoic iii of the adelaide rift complex australia and the overprint of water column stratification abstract this study establishes a high resolution 13c chemostratigraphic framework for the type ediacarian terminal proterozoic section in the adelaide rift complex a framework that contributes to the emerging global chronostratigraphic synthesis of a period that saw momentous changes in the earth s surface environment only 15 m of the 3 5 km thick type section consists of shallow water carbonates of the kind that have formed the basis of most previous studies of neoproterozoic chemostratigraphy however the organic 13corg record reveals a surprising richness of information and shows excellent utility in correlation between sections in the adelaide rift complex lateral variations in 13corg profiles correspond to expected diachronous patterns of basin fill with the addition of 87sr 86sr data correlation can also be made to the officer and amadeus basins consistent with known lithostratigraphic and sequence stratigraphic constraints sublittoral micritic carbonates of the upper nuccaleena formation cap dolostone and lower and middle wonoka formation show strong basinwide 13c depletion 13ccarb 3 to 10 despite compelling evidence for preservation of depositional 13ccarb such as good textural preservation evidence for sea floor lithification and in the wonoka formation pristine 87sr 86sr and low mn sr associated with the depleted carbonates are rare subaqueous evaporite relatively heavy 13corg and anomalously 13c depleted organic carbon of benthic microbial mat origin and a common cause salinity stratification of the water column is postulated the indicated palaeogeographic setting an evaporative mediterranean like basin tenuously connected to the world ocean is entirely consistent with previous suggestions of one or more messinian type desiccation events to explain very deep 1 km incised valleys or canyons in the adelaide rift complex and officer basin at horizons within the wonoka formation and correlates positive excursions in 13corg during basin stratification may in part be due to 12c depletion of surface waters by photosynthetic carbon fixation despite the proposed semi isolation of australian ediacarian basins from the world ocean major 13c excursions which can to some extent be differentiated by the monotonic rise in ediacarian marine 87sr 86sr appear to be correlatable to the upper windermere supergroup northwest canada

shift in limiting nutrients in the late ediacaran early cambrian marine systems of south china abstract the ediacaran to cambrian periods are characterized by the diversification and extinction of metazoans carbon cycle perturbation and ocean oxygenation ocean nutrient cycles play a major role in the primary production and productivity driven shallow water anoxia that was responsible for mass extinction in some phanerozoic intervals however the relationships between these cycles and primary production and biological events during the ediacaran to cambrian periods have not previously been well explored this study presents stratigraphic profiles of nitrogen and organic carbon isotopes for sections belonging to the shelf and deep basin regions of the yangtze platform south china the nitrogen isotope profiles for these two regions share a similar trend showing 1 relatively stable 15n values of 5 6 in the early middle ediacaran 635 ma ca 560 ma and 2 a shift towards lower 15n values 3 4 since the shuram 13ccarb excursion the 15n values in the shelf section experienced a two stage decrease from the late ediacaran to cambrian stage 2 of the terreneuvian series down to 1 and then an increase from 1 to 4 across the cambrian stage 2 3 boundary i e the terreneuvian cambrian series 2 boundary at 521 ma these data in combination with previously reported nutrient profiles 15n p and mo allow the following new conclusions to be drawn 1 the early middle ediacaran ocean was characterized by n mo colimitation of primary production on a geological timescale that is different from the p limitation on long term primary production in the modern ocean 2 a shift in the ultimate limiting nutrient from n and mo to p likely occurred in late ediacaran early cambrian marine systems this shift may have been a prerequisite for the extinction of small shelly fossils in response to the development of photic zone anoxia for several million years in cambrian stage 2 which was followed by the third and most prominent phase of metazoan diversification

cambrian small skeletal fossil and carbon isotope records of the southern huangling anticline hubei china and implications for chemostratigraphy of the yangtze platform abstract rich small skeletal fossil assemblages are described from the yanjiahe formation and tianzhushan member of southern huangling anticline the anabarites trisulcatus protohertzina anabarica assemblage zone small skeletal fossil zone 1 is recognized in the middle to upper yanjiahe formation while the thin topmost conglomeratic limestone unit yielded a mixed assemblage resulting from reworking and redeposition of source material of small skeletal fossil zones 1 to 3 including anabarites trisulcatus protohertzina anabarica p unguliformis watsonella crosbyi aldanella attleborensis anabarella plana our revised biostratigraphic correlation indicates the existence of longer hiatuses in the yanjiahe formation and between the yanjiahe and shuijingtuo formations the obtained 13ccarb values in our profile deviate in some details from those of some previous reports based on the new biostratigraphic correlation the 13ccarb trend records values oscillating between 3 to 4 4 in the upper anabarites trisulcatus protohertzina anabarica assemblage zone which is unusual for the yangtze platform this interval of positive 13ccarb values in the upper yanjiahe formation and the dahai member of eastern yunnan are here interpreted to reflect the impact of a local aquafacies moreover it is here argued that the selection of a carbon isotope peak as a primary index tool in the laolin section for defining the cambrian stage 2 must be treated with caution as this isotope excursion is influenced by a regional water mass and does not reflect an open marine seawater signature underlining other technical and theoretic concerns on the general application of chemostratigraphy in cambrian shallow water carbonate platforms overall we suggest that chemostratigraphic correlations need to be supported by biostratigraphic tools

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

sedimentary evolution of the ediacaran yangtze platform shelf hubei and hunan provinces central china abstract the development of the ediacaran doushantuo formation 635 551 ma on the yangtze platform is studied to analyse the environmental changes on this platform accompanying the ediacaran bioradiation in this study we will present a detailed facies analysis and propose a tentative stratigraphic analysis of seven selected sections that are located predominantly on the platform shelf situated in the hubei province the doushantuo yangtze platform displays two major depositional environments a rimmed carbonate platform and an open shelf the shift from one depositional model to another may be related to the paleotopography in horsts and grabens inherited from previous extensional movements the strata observed in the shelf deposits of the doushantuo formation are organised in three stacked facies successions these shallowing upward facies successions may be correlatable with other ediacaran sections worldwide

marine redox stratification on the earliest cambrian ca 542 529 ma yangtze platform abstract in order to explore the marine redox structure on the earliest cambrian ca 542 529 ma yangtze platform south china new fe mo c s geochemical data from the slope xugongping section for the liuchapo and the base of niutitang formation are reported here integrated fe speciation and mo abundance data from the xugongping section in combination with previously published data from slope basinal longbizui section and others suggest oxic surface waters and ferruginous deep waters coexisting with occasional mid depth euxinic waters during the fortunian stage and with widespread euxinic waters during the early stage 2 marine transgression a compilation of new and published sulfur isotope data of pyrite for the liuchapo and the base of niutitang formations presents high isotopic values mostly 10 and distinctly different spatiotemporal gradient characteristics during the fortunian stage and the beginning of the stage 2 we propose that redox stratification developed in the earliest cambrian protected basin and eustatic change and the connectivity of the protected basin with the open ocean controlled the materials supply from riverine input and open ocean reservoir and thus spatiotemporal variability of ocean chemistry

early cambrian ocean mixing recorded by phosphorite successions in the nanhua basin south china abstract phosphorite successions in the nearshore meishucun section and the offshore gezhongwu section of the nanhua basin south china were investigated to decipher the circulation pattern of the early cambrian ocean the 539 535 ma phosphorites from the meishucun section contain authigenic phosphorus rich mineral aggregates collophanite grains with much lower bio limiting elements zn cd and ni than those from the gezhongwu section in contrast collophanite grains in the 535 526 ma phosphorites from both sections have similar concentrations of these elements this change indicates that the ocean likely transformed from a chemically stratified state to a homogeneous state at 535 ma phosphorites from both sections have constant 87sr 86sr ratios and end t values supporting the interpretation of a relatively constant terrestrial input into the nanhua basin between 539 ma and 526 ma instead negative 13c excursions and similar 208pb 204pb ratios of the 535 526 ma phosphorites are indicative of an extensive upwelling of the deep oceanic water in combination with previous studies of deep ocean oxygenation our work provides evidence for the vertical mixing of the ocean between 535 ma and 526 ma which introduced o2 rich water at the ocean bottom to promote early cambrian biodiversity

nitrogen isotope evidence for redox variations at the ediacaran cambrian transition in south china abstractnitrogen isotope 15n analyses of the early cambrian ca 542 520 ma strata in the yangtze gorges area south china reveal a prominent positive 15n excursion 8 concurrent with a negative shift in organic carbon isotopes 13corg at the early nemakit daldynian or early fortunian stage this positive 15n excursion in combination with the previously reported paired 13ccarb 13corg at this interval can be interpreted as resulting from denitrification with large isotopic fractionation subsequent 15n from early nemakit daldynian to early tommotian stage 2 are dominated by stable values fluctuating between 2 and 2 close to that of atmosphere n2 0 accompanied by the low and stable 13corg 33 and decoupled 13ccarb 13corg we argue that the relatively low and invariant 15n values from this interval likely resulted from enhanced n fixation with limited isotopic fractionation enhanced n fixation is generally associated with significant nutrient n loss mainly through denit

improved horizontal wind model hwm07 enables estimation of equatorial ionospheric electric fields from satellite magnetic measurements 1 horizontal neutral winds play an important role in low latitude ionospheric e and f region dynamics in particular the zonal winds have strong effects on the local structure of the low latitude ionospheric current system accurate wind specification is therefore essential for modeling these currents in order to investigate the retrieval of eastward electric fields from satellite derived equatorial electrojet eej profiles we consider a provisional horizontal wind model hwm07 and its implications for the meridional structure of the eej we find that eej current profiles predicted using hwm07 agree better with champ magnetometer derived current profiles than eej profiles predicted using the older hwm93 model the improved wind model opens exciting new possibilities of determining the day side eastward electric field in the equatorial ionosphere from satellite magnetic field measurements

nitrogen and organic carbon isotope stratigraphy of the yangtze platform during the ediacaran cambrian transition in south china abstract n and corg isotope results are presented from six sections along a west east transect in the south china basin scb covering both shallow and deeper domains in order to investigate biogeochemical cycling stratigraphic correlation and isotope systematics over the crucial ediacaran cambrian transition 15n bulk values range between 3 and 7 while 13corg values range between 21 and 39 similar isotopic trends have been identified for both these proxies across the basin although hiatuses differences in depositional setting and syn depositional bacterial fermentation may have caused some inconsistencies a trend towards negative n isotope values can be recognized above the pc c boundary in both shallow and deeper basin realms across the yangtze platform this negative 15n excursion is probably a response to photic zone anoxia and intense nitrogen fixation assimilation by diazotrophic cyanobacteria and green purple sulfur bacteria gsb and psb the xiaotan section and a composite section from the yangtze gorges area show meaningful similarities in their nitrogen isotope trends interpreted as chemocline fluctuations in the water column that testify to rapid mixing of water overlying the shallow platform using carbon isotope stratigraphy we correlate boundary strata across the platform to test the wider significance of nitrogen isotopic variations increased bioturbation and food chain complexity across the ediacaran cambrian transition probably led to more frequent variations in nitrate isotope composition and related pool dimension during the early cambrian reflecting the beginning of a new more biologically controlled era

carbon isotope geochemistry and palaeontology of neoproterozoic to early cambrian siliciclastic successions in the east european platform poland a well preserved stratigraphic record of the organic carbon isotopic composition across the precambrian cambrian transition has been obtained from a sequence of entirely detrital rocks underlying the lublin slope east european platform poland the observed 13 c pattern for organic carbon is comparable to isotope data determined for coeval carbonate platform sequences elsewhere these results underline the truly global nature of these secular variations within the carbon cycle during the terminal proterozoic and early cambrian largely independent of host lithology and facies the direct combination of micropalaeontological and geochemical results from sedimentary organic matter allows a detailed interpretation of the isotope record as probably caused by secular changes in the net balance of burial and erosion rates of repositories of organic carbon furthermore these variations appear to be directly correlatable with changes in the diversity and abundance of the biota and radiation extinction events

east west coast differences in total electron content over the continental us 1 total electron content tec measurements made by a network of dense gps receivers over the continental us are used to investigate ionospheric longitudinal differences we find that the evening tec is substantially higher on the us east coast than on the west and vice versa for the morning tec the longitudinal difference displays a clear diurnal variation through an analysis of morning evening variability in the east west tec difference minimum variability is found to coincide with the longitudes of zero magnetic declination over the continental us we suggest that these new findings of longitudinal differences in ionospheric tec at midlatitudes are caused by the longitudinal difference in magnetic declination combined with the effects of thermospheric zonal winds which are subject to directional reversal over the course of a day this study indicates that longitudinal variations in tec measurements contain critical information on thermospheric zonal winds the proposed declination zonal wind mechanism may also provide a new insight into longitude ut changes at midlatitudes on a global scale as well as into some geospace disturbances

on the equatorial anomaly of the ionospheric total electron content near the northern anomaly crest region daily contour charts of the ionospheric total electron content in latitude versus local time coordinates have been used to study the behavior of the development of the equatorial anomaly around the northern anomaly crest region the daily development of the equatorial anomaly shows quite large day to day variabilities not only on magnetically disturbed days but also on quiet days the daily maximum anomaly crest moves poleward as the magnitude of the total electron content of the daily maximum anomaly crest increases the increase of the equatorial electrojet strength also results in a poleward movement of the anomaly crest no significant correlation exists between the anomaly crest and the magnetic ital ap index the monthly mean diurnal development of the equatorial anomaly shows a remarkable seasonal difference with the anomaly largest in equinoxes and slightly larger in winter than in summer copyright american geophysical union 1989

ree and trace element patterns from organic rich rocks of the ediacaran cambrian transitional interval abstract it has been established that important changes in the marine environment and the biosphere occurred during the cambrian however the relationships between the so called cambrian explosion and the concomitant environmental changes are not yet fully understood this study presents new geochemical data from the black shale successions from different facies belts of the yangtze platform in south china variations in the concentrations of ree and trace elements varying ce ce th u v sc and v cr ratios in kerogen as well as in bulk rocks from different depositional environments along a transect from platform to basin indicate two oxidation events which led to the oxygenation of the water column in shallow marine environments and euxinic conditions weak correlation between toc v u and mo in the deeper sea during the first oxidation event in the late terreneuvian anoxic conditions in bottom waters rapidly changed to euxinic conditions subsequently the second oxidation event during the early epoch 2 of the cambrian led to oxic suboxic conditions in deeper seawater

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

chemostratigraphic and sedimentological framework of the largest negative carbon isotopic excursion in earth history the neoproterozoic shuram formation nafun group oman abstract oman records in its neoproterozoic nafun group huqf supergroup an essentially complete carbonate rich ediacaran succession the nafun group overlies the presumed marinoan rift related fiq member ca 635 ma and ends just below the precambrian cambrian boundary 542 ma tectonic subsidence caused by thermal contraction following fiq aged rifting allowed the preservation of about 1 km of postrift stratigraphy with no major stratigraphic breaks the nafun group above the marinoan cap carbonate hadash formation represents two siliciclastic to carbonate grand cycles both initiated by significant transgressions these cycles comprise the masirah bay khufai formations and the shuram buah formations the khufai shuram boundary is associated with the start of a major carbon isotope perturbation the uppermost ramp carbonates of the khufai formation record a smooth decrease in 13c from about 4 to values around 0 followed by two descending steps across which values plunge to a nadir of 12 in the overlying red siltstones and shales interbedded with thin limestones of the shuram formation this fall in isotopic values is temporally rapid and coincident in both shallow and deep water sections in the time span of a single parasequence the 13c nadir is then followed by 50 million years of monotonic recovery the shuram shift represents the largest 13c inorganic carbon negative excursion in earth history although the snowball earth theory links periods of depleted carbon isotopic ratios with periods of global glaciation the non glaciated context of the shuram formation suggests that the causal relationship between global glaciation and negative carbon isotopic excursions is non unique although the precise mechanism driving this major perturbation of the carbon cycle remains enigmatic the long term remineralization of an isotopically depleted organic carbon reservoir in ocean water is a promising candidate

in situ analyses of phosphorus contents of carbonate minerals reconstruction of phosphorus contents of seawater from the ediacaran to early cambrian abstract the ediacaran and cambrian periods were one of the most important periods for the evolution of life the biodiversity drastically expanded in the period however the origins are still ambiguous because surface environmental changes through the time have not been well understood yet we conducted in situ analyses of the phosphorus contents of carbonate minerals with a laser ablation inductively coupled plasma mass spectrometer la icp ms to estimate the phosphorus contents of seawater from the ediacaran to the early cambrian carbonate rocks contain not only the carbonate minerals but also detrital and authigenic materials such as silicate and phosphate minerals therefore the whole rock compositions of carbonate rocks are not directly related with seawater composition to avoid the influence of the involvement of the phosphate minerals we performed the microscopic observation elemental mapping of si ca mg fe and p contents with an electron probe microanalyzer epma and investigation of time profiles of signal intensities of ca sr mn p la and ba with the la icp ms especially samples with low mn sr ratios and primary textures such as oolites are suitable to estimate the primary phosphorus contents of the carbonates the chemostratigraphy of the phosphorus contents of carbonates from the drill core and outcrop samples displays that the phosphorus contents decrease from ca 400 ppm in the ediacaran through ca 200 ppm around the terminal ediacaran and the beginning of the cambrian to ca 50 ppm in the early cambrian previous works on 87sr 86sr chemostratigraphy from the ediacaran to the cambrian sections suggested relatively high continental influx in the middle ediacaran and around the precambrian cambrian pc c boundary the high phosphorus content in the ediacaran was possibly due to the high continental flux on the other hand previous works on chemostratigraphy of carbon isotope values of carbonate carbon from the ediacaran to the cambrian sections showed some large negative anomalies in the ediacaran and around the precambrian cambrian pc c boundary and suggested that the negative anomalies were caused by remineralization and respiration of dissolved organic matter the degradation of the organic matter also accounts for the high phosphorus contents in the ediacaran the high phosphorus content of seawater favors enhancement of primary productivity and formation of phosphorites the high phosphorus contents in the seawater possibly led to the emergence of the large and motile organism through the enhancement of primary productivity and the consequent increase of oxygen content of the seawater

an integrated chemostratigraphic δ13c δ18o 87sr 86sr δ15n study of the doushantuo formation in western hubei province south china abstract high resolution isotopic analyses were conducted on core samples from the ediacaran doushantuo formation at the wangjiapeng section western hubei province in south china whereby two laterally traceable negative 13ccarb excursions en1 and en3 were recognized the magnitude and duration of these excursions permit intra basinal and inter basinal correlation which indicates that they probably represent a global change in seawater composition the occurrence of decoupled 13ccar 13corg with almost invariable 13corg values at wangjiapeng zhongling yangjiaping sections is consistent with remineralization of a dissolved organic carbon doc pool by means of sulfate reduction as recorded in en3 the synchronous presence of en3 a shift to higher 87sr 86sr and decrease of mn and fe contents and 15n values together points to a glacial influence whereby oxygenation and remineralization of reduced carbon produced 13c depleted dic glaciations cause a drop in sea level which itself leads to increased continental shelf area to be exposed to surface weathering and ultimately to enhanced delivery of radiogenic 87sr the increase of 87sr 86sr ratios sulfate and phosphate are consequences of surface runoff into oceanic environments and such perturbations induce biogeochemical changes

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

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