hydrocarbon biomarkers of neoproterozoic to lower cambrian oils from eastern siberia the neoproterozoic era is of widespread geobiological interest because it marks the critical transition from a world of microbes to one where animals become an established feature of the landscape much research into this time period has focused on the ventilation of the oceans as this is widely considered a primary factor driving the diversification of complex multicellular life in this study proterozoic to cambrian aged oils from eastern siberia were analyzed for their hydrocarbon biomarker contents and compound specific carbon isotopes in order to further our understanding of the prevailing environment and its microbial and metazoan communities geochemically these oils are broadly comparable to those of the ediacaran cambrian sedimentary rocks and oils of the south oman salt basin organic matter in the source sedimentary rocks included significant contributions from green algae demosponges and bacteria including cyanobacteria and methanotrophic proteobacteria although the ages of the siberian oils and putative parent source rock intervals are poorly constrained the geochemical similarities between the ediacaran oman huqf and nepa botuoba katanga family of siberian oil samples are impressive leading to the inference that their source rocks are coeval on the other hand oils from the baykit high are distinctive likely older and possibly of cryogenian age

the anomalous ca cycle in the ediacaran ocean evidence from ca isotopes preserved in carbonates in the three gorges area south china abstract the ediacaran cambrian was one of the most important periods for the evolution of life recent studies have provided detailed chemostratigraphies that decipher the linkages between ambient surface environmental changes and biological evolution the occurrence of skeletal fossils in ediacaran rocks suggests that the possible onset of ca biomineralization started in the latest neoproterozoic molecular clocks also predict the emergence of animals containing ca carbonate spicules in the neoproterozoic therefore it is important to estimate the transition of the ca cycle in seawater ancient ca cycles in the oceans are estimated from the calcium isotopic compositions of carbonate rocks however the lack of continuous ca isotopic data in the ediacaran leaves the ca cycle unresolved the almost continuously exposed ediacaran and cambrian strata in south china mainly comprise carbonate rocks with subordinate black shales and sandstones which contain many fossils suitable for the study of environmental and biological changes we conducted drilling from the liantuo via the nantuo doushantuo dengying and yanjiahe to the shuijingtuo formation at four sites in the three gorges area in order to obtain continuous fresh samples without surface alteration and oxidation we analyzed 44 ca 42 ca ratios in carbonate rocks with a multiple collector inductively coupled plasma mass spectrometer mc icp ms screened for diagenetic alteration the resultant 44 42 ca ratios exhibit a smooth curve the values of 44 42 ca are anomalously high relative to those in the phanerozoic and they gradually decrease towards the end of the ediacaran our new ca isotope chemostratigraphy suggests that a different ca cycle had existed during the ediacaran the long term high 44 42 ca is not simply explicable by changes in temperature differences in carbonate mineralogy or changes in the input output fluxes of ca to the ocean we propose three possible explanations for the observed high 44 42 ca ratios in the ediacaran high 44 42 ca ratios of ca inputs potential undiscovered sinks of ca with low 44 42 ca values and negligible isotope fractionation between carbonate and seawater we consider that one or all of these contributed to the high 44 42 ca ratios of these we prefer the small isotope fractionation which implies that the ca concentration in seawater was initially low in the early ediacaran and increased throughout that period

rewriting the climatology of the tropical north atlantic and caribbean sea atmosphere abstract the jordan mean tropical sounding has provided a benchmark reference for representing the climatology of the tropical north atlantic and caribbean sea atmosphere for over 50 years however recent observations and studies have suggested that during the months of the north atlantic hurricane season this region of the world is affected by multiple air masses with very distinct thermodynamic and kinematic characteristics this study examined 6000 rawinsonde observations from the caribbean sea region taken during the core months july october of the 1995 2002 hurricane seasons it was found that single mean soundings created from this new dataset were very similar to c l jordan s 1958 sounding work however recently developed multispectral satellite imagery that can track low to midlevel dry air masses indicated that the 1995 2002 hurricane season dataset and likely jordan s dataset as well was dominated by three distinct air masses moist tropical mt saharan air layer sal and midlatit

biomarker evidence for photosynthesis during neoproterozoic glaciation laterally extensive black shales were deposited on the sao francisco craton in southeastern brazil during low latitude neoproterozoic glaciation 740 to 700 million years ago these rocks contain up to 3 0 weight organic carbon which we interpret as representing the preserved record of abundant marine primary productivity from glacial times extractable biomarkers reflect a complex and productive microbial ecosystem including both phototrophic bacteria and eukaryotes living in a stratified ocean with thin or absent sea ice oxic surface waters and euxinic conditions within the photic zone such an environment provides important constraints for parts of the snowball earth hypothesis

a reconstruction of archean biological diversity based on molecular fossils from the 2 78 to 2 45 billion year old mount bruce supergroup hamersley basin western australia abstract bitumens extracted from 2 7 to 2 5 billion year old ga shales of the fortescue and hamersley groups in the pilbara craton western australia contain traces of molecular fossils based on a combination of molecular characteristics typical of many precambrian bitumens their consistently and unusually high thermal maturities and their widespread distribution throughout the hamersley basin the bitumens can be characterized as probably of archean age accepting this interpretation the biomarkers open a new window on archean biodiversity the presence of hopanes in the archean rocks confirms the antiquity of the domain bacteria and high relative concentrations of 2 methylhopanes indicate that cyanobacteria were important primary producers oxygenic photosynthesis therefore evolved 2 7 ga ago and well before independent evidence suggests significant levels of oxygen accumulated in the atmosphere moreover the abundance of cyanobacterial biomarkers in shales interbedded with oxide facies banded iron formations bif indicates that although some archean bif might have been formed by abiotic photochemical processes or anoxygenic phototrophic bacteria those in the hamersley group formed as a direct consequence of biological oxygen production biomarkers of the 3 methylhopane series suggest that microaerophilic heterotrophic bacteria probably methanotrophs or methylotrophs were active in late archean environments the presence of steranes in a wide range of structures with relative abundances like those from late paleoproterozoic to phanerozoic sediments is convincing evidence for the existence of eukaryotes in the late archean 900 ma before visible fossil evidence indicates that the lineage arose sterol biosynthesis in extant eukaryotes requires molecular oxygen the presence of steranes together with biomarkers of oxygenic photosynthetic cyanobacteria suggests that the concentration of dissolved oxygen in some regions of the upper water column was equivalent to at least 1 of the present atmospheric level pal and may have been sufficient to support aerobic respiration

relationship between petroleum composition and depositional environment of petroleum source rocks crude oils of nonmarine source can be distinguished from those of marine shale source and from oils originating in marine carbonate sequences by using a battery of geochemical parameters as demonstrated with a sample suite of nearly 40 oils a novel parameter based on the presence of c30 steranes in the oil was found to be a definitive indication of a contribution to the source from marine derived organic matter a second novel parameter based on monoaromatized steroid distributions was effective in helping to distinguish nonmarine from marine crudes and can be used to gauge relative amounts of higher plant input to oils within a given basin sterane distributions were similarly useful for detecting higher plant input but were less effective than monoaromatize steroid distributions for making marine versus nonmarine distinctions concentrations of high molecular weight paraffin can also be effective nonmarine indicators but are influenced by maturation and biodegradation processes certain algal derived nonmarine oils may show little high molecular weight paraffin response oils from carbonate sources with a few exceptions can be distinguished by having low pristane phytane ratios low carbon preference indexes and high sulfur contents gammacerane indexes and carbon isotope ratios of the whole crude are not effective in distinguishing these types of environmental differences on a global basis

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

a simulation of the development of successive cells along a cold outflow boundary abstract a three dimensional numerical simulation is presented in which five new cells clouds develop in succession over a 4 h period the cells that develop have common characteristics including a lifetime of 40 min they form at 30 min intervals in a convergent region along the cold outflow boundary that is established by previous cells the propagation of the cloud system is several meters per second faster than individual cell movement due to the discrete development of new cells on the right flank of previous ones analysis of the simulation indicates that the most pronounced changes near the surface are due to downdraft development in contrast there is only a weak signature of new updraft development near the surface in the convergence field each new updraft develops along the cold outflow boundary which moves slowly away from the previous cell the air participating in the generation of a new cell appears to have originated 1 1 5 km below cloud base 2 6 km as the cell grows and rain begins

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

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

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

the variability and predictability of axisymmetric hurricanes in statistical equilibrium abstractthe variability and predictability of axisymmetric hurricanes are determined from a 500 day numerical simulation of a tropical cyclone in statistical equilibrium by design the solution is independent of the initial conditions and environmental variability which isolates the intrinsic axisymmetric hurricane variability variability near the radius of maximum wind is dominated by two patterns one associated primarily with radial shifts of the maximum wind and one primarily with intensity change at the time mean radius of maximum wind these patterns are linked to convective bands that originate more than 100 km from the storm center and propagate inward bands approaching the storm produce eyewall replacement cycles with an increase in storm intensity as the secondary eyewall contracts radially inward a dominant time period of 4 8 days is found for the convective bands which is hypothesized to be determined by the time scale over which subsidence from previous bands suppresses convection a

some aspects of hurricane inner core dynamics and energetics abstract the energy cycle of the mature hurricane resides in the secondary circulation that passes through the storm s eyewall by equating the generation of energy in this cycle to boundary layer dissipation an upper bound on wind speed is derived this bound depends on the degree of thermodynamic disequilibrium between the tropical ocean and atmosphere on the difference between sea surface and outflow absolute temperatures and also on the ratio between the enthalpy exchange and surface drag coefficients such a bound proves to be an excellent predictor of maximum wind speeds in two different axisymmetric numerical models and does not appear to depend on the existence of the hurricane eye but further consideration of the detailed dynamics of the eye and eyewall show that the intensification of hurricanes is accelerated by feedbacks associated with a component of eye subsidence forced by radial turbulent diffusion of momentum this radial momentum diffusion is an inevitable by product of the strong fr

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

distinctive hydrocarbon biomarkers from fossiliferous sediment of the late proterozoic walcott member chuar group grand canyon arizona abundant extractable hydrocarbons in association with well preserved kerogen have been recognised in a dolostone from the chuar group approx 850 ma the biomarkers present include c15 c30 acyclic isoprenoids c26 c28 steranes c27 c35 hopanes and extended tricyclic terpanes among the striking characteristics of the distributions are the dominance of steranes and methyl steranes lacking side chain alkylation and the presence of putative c29 c35 neohopanes and gammacerane the high abundance of steranes is consistent with the presumed eukaryotic affinities of several types of microfossils including chuaria present in associated mudstones this stratum is the oldest in which gammacerane has been found and suggests contributions from protozoa to the depositional environment which appears to have been hypersaline there is a strong correlation between the carbon isotopic composition of the kerogen and that of the various polarity fractions of the bitumens chemical degradation and pyrolysis of the kerogens yielded n alkanes with similar characteristics to the bitumens but there are differences in the patterns of distribution of the acyclic isoprenoid sterane and triterpane biomarkers

self stratification of tropical cyclone outflow part i implications for storm structure extant theoretical work on the steady state structure and intensity of idealized axisymmetric tropical cyclones relies on the assumption that isentropic surfaces in the storm outflow match those of the unperturbed environment at large distances from the storm s core these isentropic surfaces generally lie just above the tropopause wheretheverticaltemperaturestructureisapproximatelyisothermal soithas beenassumedthat the absolute temperature of the outflow is nearly constant here it is shown that this assumption is not justified at least when applied to storms simulated by a convection resolving axisymmetric numerical model in whichmuchofthe outflowoccursbelowtheambienttropopauseanddevelopsits ownstratification unrelated to that of the unperturbed environment the authors propose that this stratification is set in the storm s core by the requirement that the richardson number remain near its critical value for the onset of small scale turbulence this ansatz is tested by calculating the richardson number in numerically simulated storms and then showing that the assumption of constant richardson number determines the variation of the outflow temperature with angular momentum or entropy and thereby sets the low level radial structure of the storm outside its radius of maximum surface winds part ii will show that allowing the outflow temperature to vary also allows one to discard an empirical factor that was introduced in previous work on the intensification of tropical cyclones

potential vorticity diagnosis of a simulated hurricane part ii quasi balanced contributions to forced secondary circulations although the forced secondary circulations fscs associated with hurricane like vortices have been previously examined understanding is still limited to idealized axisymmetric flows and forcing functions in this study the individual contributions of latent heating frictional and dry dynamical processes to the fscs of a hurricane vortex are separated in order to examine how a hurricane can intensify against the destructive action of vertical shear and how a warm cored eye forms this is achieved by applying a potential vorticity pv inversion and quasi balanced omega equations system to a cloud resolving simulation of hurricane andrew 1992 during its mature stage with the finest grid size of 6 km it is shown that the latent heating fsc tilting outward with height acts to oppose the shear forced vertical tilt of the storm and part of the upward mass fluxes near the top of the eyewall is detrained inward causing the convergence aloft and subsidence warming in the hurricane eye the friction fsc is similar to that of the ekman pumping with its peak upward motion occurring near the top of the planetary boundary layer pbl in the eye about 40 of the pbl convergence is related to surface friction and the rest to latent heating in the eyewall in contrast the dry dynamical forcing is determined by vertical shear and system relative flow when an axisymmetric balanced vortex is subjected to westerly shear a deep countershear fsc appears across the inner core region with the rising sinking motion downshear upshear and easterly sheared horizontal flows in the vertical the shear fsc is shown to reduce the destructive roles of the large scale shear imposed as much as 40 including its forced vertical tilt moreover the shear fsc intensity is near linearly proportional to the shear magnitude and the wavenumber 1 vertical motion asymmetry can be considered as the integrated effects of the shear fscs from all the tropospheric layers the shear fsc can be attributed to the laplacian of thermal advection and the temporal and spatial variations of centrifugal force in the quasi balanced omega equation and confirms the previous finding of the development of wavenumber 1 cloud asymmetries in hurricanes hurricane eye dynamics are presented by synthesizing the latent heating fsc with previous studies the authors propose to separate the eye formation from maintenance processes the upper level inward mass detrainment forces the subsidence warming and the formation of an eye the surface pressure fall and increased rotation in the eyewall this increased rotation will induce an additional vertical pressure gradient force to balance the net buoyancy generated by the subsidence warming for the maintenance of the hurricane eye in this sense the negative vertical shear in tangential wind in the eyewall should be considered as being forced by the subsidence warming and maintained by the rotation in the eyewall

diamondoid hydrocarbon ratios novel maturity indices for highly mature crude oils abstract diamondoid hydrocarbons have been identified in oil and source rock samples from the tarim yinggehai qiongdongnan and other chinese basins two diamondoid hydrocarbon ratios have been used as novel high maturity indices to evaluate the maturation and evolution of crude oils and condensates in these chinese basins the two ratios 1 ma 1 ma 2 ma mai methyl adamantane index and 4 md 1 md 3 md 4 md mdi methyl diamantane index were found to increase with increasing vitrinite reflectance the initial values for the ratios are ca 50 and 30 respectively diamondoid hydrocarbons are products of rearrangement of polycyclic hydrocarbons and their ratios are found to be affected by organic input to a minor extent based on this study crude oils from the tarim basin are generally believed to be very mature ro 1 1 the cambrian ordovician source beds are the major source rocks of crude oils and natural gases in this basin condensates from the tarim yinggehai and qiongdongnan basins have higher maturities equivalent to ro values of 1 6 2 0 gases and condensates from the yinggehai and qiongdongnan basins are generated mainly from tertiary source rocks below 4000 5000 m

organic molecular evidence in the late neoproterozoic tillites for a palaeo oceanic environment during the snowball earth era in the yangtze region southern china abstract the upper neoproterozoic nantuo and jiangkou formations in southern china have commonly been identified as the deposits of glaciations dating back to 600 ma and 720 ma belonging to the marinoan and sturtian ice ages respectively or the so called snowball earth events in the present study 44 typical upper neoproterozoic to lower cambrian sedimentary rock samples including 16 diamictites have been collected from 12 stratigraphic sections in hubei hunan shanxi chongqing guizhou and yunnan provinces in the yangtze region southern china and analyzed by routine organic geochemical techniques except for the diamictites and cap carbonates most of these rocks have middle to high toc values of up to 0 16 6 50 in the cambrian and 0 12 9 37 in the upper neoproterozoic rock samples by contrast the diamictites and cap carbonates have a toc range only from 0 01 to 0 13 1 2 orders of magnitude lower than those in most of the non glacial sedimentary rocks indicating very limited organic productivity in the palaeo oceanic environment during the snowball earth era phytane and pristane which are derivatives of chlorophyll a and various steranes which are biomarkers of eukaryotes were detected in all the rock samples there is a tendency for positive correlation between toc and the concentrations of phytane and or pristane therefore it implies that photosynthetic autotrophs should have been the primary organisms contributing to the sedimentary organic matter in the yangtze palaeo ocean moreover the concentrations of phytane plus pristane range from 0 024 ng g to 0 446 ng g in most non glacial sedimentary rocks and from 0 005 ng g to 0 076 ng g in diamictites the unusually low concentrations of phytane and pristane reveal a very weak photosynthetic process a restricted euphotic zone and quite limited sunlight within the palaeo oceanic water column even though the productivity of photosynthetic organisms was very low it can still be inferred that photosynthetic process never ceased in the late neoproterozoic palaeo oceanic environment this evidence suggests that the palaeo ocean in the yangtze region during the snowball earth was either covered by a thin sea ice sheet or was covered by a thicker sea ice sheet that included polynyas or areas of open water both these possibilities would have allowed the survival of photosynthetic eukaroytes and other organisms

the formation of moist vortices and tropical cyclones in idealized simulations abstractthe upscale aggregation of convection is used to understand the emergence of rotating coherent midtropospheric structures and the subsequent process of tropical cyclone formation the cloud model version 1 cm1 is integrated on an f plane with uniform sea surface temperature sst and prescribed uniform background flow deep convection is maintained by surface fluxes from an ocean with uniform surface temperature convection begins to organize simultaneously into moist and dry midtropospheric patches after 10 days after 20 days the patches begin to rotate on relatively small scales moist cyclonic vortices merge eventually forming a single dominant vortex that subsequently forms a tropical cyclone on a realistic time scale of about 5 days radiation that interacts with clouds and water vapor aids in forming coherent rotating structures using the path to genesis provided by the aggregated solution the relationship between thermodynamic changes within the vortex and changes in the character

pu xe u xe u pb chronology and isotope systematics of ancient zircons from western australia the presence of xenon isotopes from in situ spontaneous fission of short lived 244 pu has been confirmed in a suite of 16 hadean detrital zircons from western australia in order to investigate the effects of xenon loss on estimates of the inferred pu u ratio we have irradiated the zircons with thermal neutrons to generate xe from 235 u neutron fission 131 xe 134 xe and 132 xe 134 xe ratios have been used to calculate the relative contributions from spontaneous fission of 244 pu and 238 u and neutron fission of 235 u and hence compare nominal pu u ratios and xenon retention ages u xe ages are typically lower than the pb pb ages indicating that xenon loss is common we show how the ternary mixing diagram can be used to place constraints on the timing and extent of this loss and to generate a corresponding pu u xe isochron although the zircons investigated in this study were extracted from the same metasedimentary unit the timing of xenon loss is variable this suggests that the loss may be the result of variable degrees of metamictization from grain to grain inferred pu u o ratios show a general decrease with the discordancy between pb pb and u xe ages for the least discordant samples we infer pu u o 0 008 which is close to the widely adopted chondritic value while we cannot completely exclude the effects of pu u fractionation in magmatic and other processes between formation of the earth and crystallisation of the zircons we conclude that they have been relatively small bfactor 2 and reflect the compatible behaviour of pu and u in the 4 valence state 2007 elsevier b v all rights reserved

molecular fossils extracted from the early cambrian section in the three gorges area south china abstract environmental investigation of the early cambrian is assessed through molecular fossils based from three core samples drilled in the three gorges area south china the core samples record environmental information dating from the earliest part of the early cambrian to nearly the end of the early cambrian making this investigation unique from previous investigations because a more far reaching temporal record is assessed this record includes unusually high abundance of longer chain n alkanes lca around n c 27 having been recognized in the earliest cambrian strata based on no odd even preference of the lca and comparisons to hydrocarbons in cultured cells of microorganisms the lca may be derived from hydrocarbons of sulfate reducing bacteria on the other hand a phototrophic origin of the sca is supported by a clear positive correlation with pristane the relative abundance of lca to sca increased in the earliest cambrian suggesting predominance of sulfate reducers against phototrophs this lca abundance with simultaneous decrease of pristane phytane may indicate a euxinic condition where sulfate reducers remineralize organic carbon in the water column this is consistent with the concomitant decrease of the 13 c carb value probably due to a massive reoxidation of organic carbon the inferred reducing condition is further supported by the enhanced appearance of squalane that could be derived from an archeal lipid our results suggest the euxinia of the yangtze platform in the earliest cambrian that may relate to the emergence of the large nektonic animals which require sufficient level of free oxygen

intensity and structure changes during hurricane eyewall replacement cycles abstracta flight level aircraft dataset consisting of 79 atlantic basin hurricanes from 1977 to 2007 was used to develop an unprecedented climatology of inner core intensity and structure changes associated with eyewall replacement cycles ercs during an erc the inner core structure was found to undergo dramatic changes that result in an intensity oscillation and rapid broadening of the wind field concentrated temporal sampling by reconnaissance aircraft in 14 of the 79 hurricanes captured virtually the entire evolution of 24 erc events the analysis of this large dataset extends the phenomenological paradigm of ercs described in previous observational case studies by identifying and exploring three distinct phases of ercs intensification weakening and reintensification in general hurricanes intensify sometimes rapidly when outer wind maxima are first encountered by aircraft the mean locations of the inner and outer wind maximum at the start of an erc are 35 and 106 km from storm center respe

a three dimensional analysis of the outflow layer of supertyphoon flo 1990 abstract isentropic coordinate analyses of rawinsondes and cloud motion wind vectors derived from geostationary satellite imagery are employed to describe the three dimensional upper tropospheric and lower stratospheric circulation attending western north pacific supertyphoon flo during september 1990 outflow from the storm is concentrated in several evolving channels in the horizontal in terms of vertical structure net outflow evaluated at 6 latitude 666 km radius is found to occur at higher levels and over an increasing range of potential temperature as the tropical cyclone intensifies outflow on the equatorward side of the tropical cyclone tends to occur at greater values higher altitudes than poleward outflow potential vorticity also decreases within the corresponding isentropic layers associated with the outflow the implications of the vertical variability of outflow structure in terms of the interactions between storm and environment and effects on storm structural changes are consi

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

possible animal body fossils in pre marinoan limestones from south australia the neoproterozoic era was punctuated by the sturtian about 710 million years ago and marinoan about 635 million years ago intervals of glaciation in south australia the rocks left behind by the glaciations are separated by a succession of limestones and shales which were deposited at tropical latitudes here we describe millimetre to centimetre scale fossils from the trezona formation which pre dates the marinoan glaciation these weakly calcified fossils occur as anvil wishbone ring and perforated slab shapes and are contained within stromatolitic limestones the trezona formation fossils pre date the oldest known calcified fossils of this size by 90 million years and cannot be separated from the surrounding calcite matrix or imaged by traditional x ray based tomographic scanning methods instead we have traced cross sections of individual fossils by serially grinding and scanning each sample at a resolution of 50 8 m from these images we constructed three dimensional digital models of the fossils our reconstructions show a population of ellipsoidal organisms without symmetry and with a network of interior canals that lead to circular apertures on the fossil surface we suggest that several characteristics of these reef dwelling fossils are best explained if the fossils are identified as sponge grade metazoans the trezona formation of south australia pre dates the 635 million year old marinoan glaciation fossils found at this location are up to several millimetres in size and share morphological characteristics with sponge grade animals

a molecular and isotopic geochemical study of meso to neoproterozoic 1 73 0 85 ga sediments from the jixian section yanshan basin north china abstract this paper systematically describes the molecular and isotopic characteristics of meso to neoproterozoic 1 73 0 85 ga sediments from the jixian section yanshan basin north china a correlation is made between molecular fingerprints and paleoenvironmental and paleontologic data acquired from these strata the agreement between these parameters suggest that the biomarkers preserved in these proterozoic sediments are good indicators of the evolution of the paleoenvironment and early life in the yanshan basin the fact that extended regular isoprenoids c20 were detected in most of the studied samples suggest a sustained lipid input to sedimentary organic matter from halophiles and other possible archaebacteria through meso to neoproterozoic two dehydroabietin isomers i e 18 and 19 norabieta 8 11 13 trienes were unexpectedly present in these samples which provides evidence suggesting that the compounds with abieta structure could be derived from primitive organisms such as algae the stable carbon isotope characteristics of kerogen and coexisting carbonate show a rapid decline in atmospheric co2 concentration from 1 73 to1 58 ga and a stable concentration afterwards the difference c in isotopic composition between carbonate and associated kerogen lies in zonal variations along the stratigraphic sequence which can be attributed to the alternations of marine transgressions and regressions that occurred in the yanshan basin during the proterozoic the carbon isotope relationships between kerogen and alkanes from these strata are consistent with the hypothesis that before 1 4 ga both n alkanes and isoprenoids had been derived mainly from heterotrophic halophiles and other archaebacteria but after that only isoprenoids originated from archaebacteria whereas n alkanes were possibly derived from photosynthetic organisms changes in the source of n alkanes around 1 4 ga may suggest a decline of heterotrophic reworking to primary lipids which can be related to the formation of a quiet shallow water environment of an epicontinental sea at this stage in the yanshan basin

an isotopic biogeochemical study of neoproterozoic and early cambrian sediments from the centralian superbasin australia abstract organic matter from neoproterozoic and early cambrian sediments of the amadeus and officer basins of the centralian superbasin australia has been studied for biomarker distributions and the carbon isotopic compositions of kerogen and individual hydrocarbons these sediments represent both shallow and deep water marine facies in the older sections and marine and saline lacustrine carbonate deposits in the cambrian hydrocarbon biomarker patterns were found to be quite consistent with the known sedimentary environments and provide valuable insights into the biogeochemical changes which accompanied the transition from a microbially dominated ocean to the early stages of metazoan radiation in particular carbon isotopic data for n alkyl and isoprenoid lipids presented here and in earlier studies showed a reversal in carbon isotopic ordering between the proterozoic and phanerozoic by comparison with the 13c of kerogen n alkyl lipids from deep water proterozoic sediments were enriched in 13c and appear to be derived mainly from heterotrophs whilst open marine phanerozoic counterparts are 13c depleted and evidently derived mainly from autotrophs data from the samples studied here are consistent with a model invoking a change in the redox structure of the ocean possibly aided by the innovation of faecal pellets

inertial waves in axisymmetric tropical cyclones abstractthe heat engine model of tropical cyclones describes a thermally direct overturning circulation outflowing air slowly subsides as radiative cooling to space balances adiabatic warming a p

origin of petroleum in the neoproterozoic cambrian south oman salt basin abstract the south oman salt basin sosb is host to the world s oldest known commercial deposits most of the south oman oils have been proven to be associated with the source rocks of the neoproterozoic to cambrian huqf supergroup but the assignment of oils to specific huqf intervals or facies has been hampered by the geochemical similarity of the organic matter across the entire huqf sequence possibly as a consequence of limited change in the local palaeoenvironment and biota over the time of its deposition this study was conducted to establish improved correlations between organic rich rock units and reservoir fluids in the sosb through detailed molecular and isotopic analysis of the huqf supergroup with special emphasis directed towards understanding the ara carbonate stringer play unusual biomarkers tentatively identified as a norsteranes show distinctive patterns among carbonate stringer oils and rocks different from those observed in nafun sediments and ara rocks from the athel basin these putative a norsteranes form the basis for new oil source correlations in the sosb and provide for the first time geochemical evidence of a self charging mechanism for the carbonate stringer play the paucity of markers specific to the nafun group shuram buah and masirah bay formations confounds attempts to quantify their respective contributions to huqf oil accumulations nafun inputs can only be determined on the basis of subtle differences between nafun and ara biomarker ratios the most useful geochemical characteristics delineating nafun group organic matter from ara group intra salt source rocks included low relative abundance of mid chain monomethyl alkanes x compounds low relative abundance of gammacerane 28 30 dinorhopane 25 28 30 trinorhopane and 2 methylhopanes low c 22 t c 21 t and high c 23 t c 24 t cheilanthanes ratio values based on these parameters molecular evidence for major contributions of liquid hydrocarbons from nafun group sediments shuram buah and masirah bay formations is lacking our results suggest that the majority of sosb hydrocarbon accumulations originate from within the ara group either from the carbonate stringers or from the package of sediments that comprises the thuleilat athel silicilyte and u shale formations subtle aspects of the composition of some carbonate stringer and post salt huqf oils could suggest some degree of sourcing from the nafun rocks but stronger evidence is needed to confirm this

quadruple sulfur isotope analysis of ca 3 5 ga dresser formation new evidence for microbial sulfate reduction in the early archean abstract multiple sulfur isotope system is a powerful new tracer for atmospheric volcanic and biological influences on sulfur cycles in the anoxic early earth here we report high precision quadruple sulfur isotope analyses 32s 33s 34s 36s of barite pyrite in barite and sulfides in related hydrothermal and igneous rocks occurring in the ca 3 5 ga dresser formation western australia our results indicate that observed isotopic variations are mainly controlled by mixing of mass dependently md and non mass dependently fractionated non md sulfur reservoirs based on the quadruple sulfur isotope systematics 34s 33s 36s for these minerals four end member sulfur reservoirs have been recognized 1 non md sulfate 34s 5 2 33s 3 1 2 md sulfate 34s 10 3 3 non md sulfur 34s 6 33s 4 and 4 igneous md sulfur 34s 33s 0 the first and third components show a clear non md signatures thus probably represent sulfate and sulfur aerosol inputs the md sulfate component 2 is enriched in 34s 10 3 and may have originated from microbial and or abiotic disproportionation of volcanic s or so2 our results reconfirm that the dresser barites contain small amounts of pyrite depleted in 34s by 15 22 relative to the host barite these barite pyrite pairs exhibit a mass dependent relationship of 33s 34s with slope less than 0 512 which is consistent with that expected for microbial sulfate reduction and is significantly different from that of equilibrium fractionation 0 515 the barite pyrite pairs also show up to 1 difference in 36s values and steep 36s 33s slopes which deviate from the main archean array 36s 33s 0 9 and are comparable to isotope effects exhibited by sulfate reducing microbes 36s 33s 5 to 11 these new lines of evidence support the existence of sulfate reducers at ca 3 5 ga whereas microbial sulfur disproportionation may have been more limited than recently suggested

an evaluation of hurricane superintensity in axisymmetric numerical models abstractpotential intensity pi is an analytical bound on steady inviscid axisymmetric hurricane wind speed studies have shown that simulated hurricane azimuthal wind speed can greatly exceed a

tropical cyclone eye thermodynamics in intense tropical cyclones sea level pressures at the center are 50 100 hpa lower than outside the vortex but only 10 30 hpa of the total pressure fall occurs inside the eye between the eyewall and the center warming by dry subsidence accounts for this fraction of the total hydrostatic pressure fall convection in the eyewall causes the warming by doing work on the eye to force the thermally indirect subsidence soundings inside hurricane eyes show warm and dry air aloft separated by an inversion from cloudy air below dewpoint depressions at the inversion level typically 850 500 hpa are 10 30 k rather than the 100 k that would occur if the air descended from tropopause level without dilution by the surrounding cloud the observed temperature and dewpoint distribution above the inversion can however be derived by 100 hpa of undilute dry subsidence from an initial sounding that is somewhat more stable than a moist adiabat it is hypothesized that the air above the inversion has remained in the eye since it was enclosed when the eyewall formed and that it has subsided at most a few kilometers the cause of the subsidence is the enclosed air s being drawn downward toward the inversion level as the air below it flows outward into the eyewall shrinkage of the eye s volume is more than adequate to supply the volume lost as dry air is incorporated into the eyewall or converted to moist air by turbulent mixing across the eye boundary the moist air below the inversion is in thermodynamic contact with the sea surface its moisture derives from evaporation of seawater inside the eye frictional inflow of moist air under the eyewall and from moist downdrafts induced as condensate mixes into the eye the moist air s residence time in the eye is much shorter than that of the dry air above the inversion the height of the inversion is determined by the balance between evaporation inflow and inward mixing on one hand and loss to the eyewall updrafts on the other

an examination of the thermodynamic impacts of western north pacific tropical cyclones on their tropical tropospheric environment abstractthe present study examines the tropospheric thermodynamic anomalies induced by western north pacific tropical cyclone tc passage using storm relative composites negative moist static energy mse anomalies containing embedded westward propagating anomalies generally occur only following larger tcs for two months following tc passage in a region extending from the domain center to 3000 km to its west larger tcs force negative mse anomalies likely because of feedbacks from stronger broader tc induced negative sea surface temperature sst anomalies and the excitation of tc induced rossby waves to the southeast of the tc the negative mse anomalies are composed of lower and midtropospheric negative latent energy anomalies with smaller contributions from boundary layer and upper tropospheric negative sensible heat anomalies the lower and midtropospheric negative mse anomalies are forced by the tc whereas the upper tropospheric negative mse anomalies are forced by the madden julian oscillatio

methyl diamantane index mdi as a maturity parameter for lower palaeozoic carbonate rocks at high maturity and overmaturity diamantanes were identified in extracts from the lower ordovician majiagou formations o1m5 of the central gas field shanganning basin china at 3100 3800 m corresponding to ro 1 9 3 9 the mdi methyl diamantane index 4 md 1 md 3 md 4 md ranges from 40 to 65 for the source rock extracts changes in the mdi index in the very mature sections ro 2 0 are relatively small and no linear correlation between mdi and ro o r mdi and depth is noted as previously reported suggesting the possibility that the mdi may have limited applicability in maturity determinations 2000 elsevier science ltd all rights reserved

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

new chronological constraints for cryogenian to cambrian rocks in the three gorges weng an and chengjiang areas south china abstract the neoproterozoic and cambrian were two of the most dramatic periods in the history of the earth because large multi cellular animals first appeared then in the so called cambrian explosion to better understand this event many paleontological and geochemical studies now focus on rocks in south china because of the fossiliferous succession and good exposure since the recognition of the yangtze gorges and chengjiang area as type localities of the sinian ediacaran and meishucunian early cambrian systems both sections have been intensively investigated in order to decipher the relationships between the evolution of life and surface environmental changes it is necessary to understand their paleontological geochemical and geo chronological constraints this study presents new chronological constraints for the cryogenian to cambrian rocks in the three gorges weng an and chengjiang areas south china we discovered two tuff layers one at the base of the shuijingtuo fm at three gorges and the other at the bottom of the dahai member in chengjiang in addition we collected sandstones from neoproterozoic strata in the three gorges chengjiang and weng an areas for provenance analysis zircons separated from the tuff layers provide new nano sims u pb ages of 526 4 5 4 ma at the base of the shuijingtuo fm and 523 9 6 7 ma at the bottom of the dahai member the tuffaceous beds occur at an unconformity and nodules are common in the three gorges meishucun and taoying sections indicating that major and relatively wide scale volcanic and sedimentological events occurred at ca 525 ma moreover carbonate carbon isotope chemostratigraphies at morocco siberia three gorges and meishucun display different characteristics during the tommotian one possibility is that the south china ocean was separated from an outer ocean at that time detrital zircons in sandstones have age populations at ca 2 7 1 8 1 6 1 0 and from 0 9 to 0 75 ga indicating that the paleo hinterland of the nanhua and kangdian rift basins was geologically complex despite the lack of ca 1 6 ga rocks in the yangtze and cathaysia blocks these data are nevertheless interpreted to indicate derivation of the zircons from basement rocks in the yangtze craton

stable isotope geochemistry of the lower cambrian sekwi formation northwest territories canada implications for ocean chemistry and secular curve generation abstract three curves delineating 13 c variations across the early cambrian sekwi formation carbonate ramp mackenzie mountains northwest territories canada are incorporated into a biostratigraphic and sequence stratigraphic framework that provides a higher resolution temporal and spatial framework for the sekwi formation the three 13 c curves were correlated across a range of depositional environments from tidal flat to deep subtidal on the sekwi carbonate ramp eight 13 c cycles in the curves a h were correlated across the basin complimenting the sequence stratigraphic framework the most complete 13 c curve from the sekwi formation correlates well with a composite early cambrian 13 c curve from the siberian platform however the differing magnitude and absolute timing of some of the correlative isotopic excursions records the influence of regional tectonism sea level changes and diagenesis on the sekwi ramp additionally the sekwi formation 13 c curve has more high frequency variations than the siberian curve due in part to the higher sample density used to construct the sekwi curve the early middle cambrian boundary was not sampled in this study but a large negative isotopic excursion in the very latest early cambrian coincides with a regional drowning that may be correlative throughout western laurentia but recognizing this event globally is problematic

organic compositions of the embryo bearing lowermost cambrian kuanchuanpu formation on the northern yangtze platform china abstract we investigated the origin of organic matter and paleoceanographic conditions of the embryo bearing lowermost cambrian kuanchuanpu formation in shaanxi province china in terms of sedimentary facies fossil morphometry and organic geochemistry including biomarker compositions the results indicated the abundance of algae and eukaryotic phytoplankton that fueled a diverse ecosystem including cnidarians and small shelly fossils the water column contained enough oxygen to provide habitat for benthic cnidarians such as olivooides on the other hand low pristane phytane ratios detection of squalane and hopane composition indicate reductive conditions within the sediments and that the redox front was likely near the water sediment interface common occurrences of pyrite and barite indicate that redox reactions of sulfur species were activated at the water sediment interface such circumstances and the high phosphate concentration in ambient water may recall the presence of sulfur oxidizing bacteria that promoted the phosphatization of animal embryos as suggested for in the neoproterozoic doushantuo formation nitrogen was the limiting nutrient for primary productivity and the high phosphate concentration in the ocean promoted the phosphatization of animal embryos at the reductive water sediment interface

revisiting the relationship between eyewall contraction and intensification abstractin the widely accepted convective ring model of tropical cyclone intensification the intensification of the maximum winds and the contraction of the radius of maximum winds rmw occur simultaneously this study shows that in idealized numerical simulations contraction and intensification commence at the same time but that contraction ceases long before peak intensity is achieved the rate of contraction decreases with increasing initial size while the rate of intensification does not vary systematically with initial size utilizing a diagnostic expression for the rate of contraction it is shown that contraction is halted in association with a rapid increase in the sharpness of the tangential wind profile near the rmw and is not due to changes in the radial gradient of the tangential wind tendency it is shown that a number of real storms exhibit a relationship between contraction and intensification that is similar to what is seen in the idealized simulations in particular the statistical

diamondoid hydrocarbon ratios as indicators of biodegradation in australian crude oils the effect of biodegradation on diamondoid distributions in petroleum has been investigated on a series of crude oils reservoired in two australian sedimentary basins the gippsland basin and the carnarvon basin the ratio of methyladamantanes to adamantane rises with increasing biodegradation significant changes in the ratio occur at extreme levels indicating that diamondoids can be indicators of petroleum biodegradation especially when most other hydrocarbons have been removed the methyladamantane adamantane ratio can also be used to assess the composition of crude oils that are comprised of a mixture of severely biodegraded and non biodegraded oil

an air sea interaction theory for tropical cyclones part ii evolutionary study using a nonhydrostatic axisymmetric numerical model abstract in part i of this study an analytical model for a steady state tropical cyclone is constructed on the assumption that boundary layer air parcels are conditionally neutral to displacements along the angular momentum surfaces of the hurricane vortex the reversible thermodynamics implied by this assumption allows the mature storm to be thought of as a simple carnot engine acquiring heat at the high temperature ocean surface and losing heat near the low temperature tropopause although the oceanic heat source is universally recognized as the sine qua non for the mature hurricane there is also wide acceptance of conditional instability of the second kind cisk which makes no specific reference to surface heat fluxes as the formative mechanism this ambivalence is seen in that all numerical simulation studies find it essential to have transfer from the ocean surface yet all start from a conditionally unstable atmosphere the hypothesis put forward in part i based on the steady state theory is t