a sulfate control on marine mid depth euxinia on the early cambrian ca 529 521 ma yangtze platform south china abstract given the high oxygen demands of complex metazoans a sound understanding of marine redox conditions is essential to reconstruct the factors that lead to the dramatic increases in ecosystem complexity and biological diversity in the early cambrian in this study we report new fe mo c s geochemical data from black shale rich strata of the early cambrian continental margin yangjiaping section in the yangtze platform south china integrated fe speciation and mo abundance data from the yangjiaping section in combination with previously reported data from shatan inner shelf songtao slope and longbizui basinal sections suggest mid depth euxinic waters coexisting with ferruginous deep waters and oxic surface waters this redox structure is similar to conditions previously suggested for the ediacaran yangtze platform and other proterozoic marine basins indicating that proterozoic layered ocean redox structure in some basins persisted into the early cambrian furthermore the fe mo data demonstrate that the mid depth euxinia was widespread during a marine transgression but shrank gradually along with widespread shelf oxygenation when the basin evolved into subsequent regression excess highly reactive iron fe hr in deep water with a hydrothermal origin may have had a control on the mid depth euxinia given geochemical and geological evidence for basinal hydrothermal activities on the other hand a sulfate limitation on bacterial sulfate reduction bsr and sulfide generation was suggested by a weak correlation r 2 0 22 between pyrite iron versus fe hr and total organic carbon toc form anoxic deep water sections and high toc averagely 6 in the deepest ferruginous water longbizui section furthermore a spatial gradient was observed in sulfur isotopic composition of pyrite averagely from 0 2 to 21 0 consistent with a lateral gradient of sulfate in concentration or and in isotope from shore to distal waters on the transgressive yangtze platform we accordingly proposed that two distinct sources riverine input and ocean reservoir provided sulfate for bsr dominantly in near shore and distal areas respectively and the euxinic retreat observed for the regression can be explained as a response to the progressive sulfate consumption of the ocean reservoir by intensive bsr and pyrite formation during preceding transgression therefore our results support a sulfate control on the spatiotemporal distribution of mid depth marine euxinia on the yangtze platform in early cambrian when complex metazoans rapidly evolved

terreneuvian small shelly faunas of east yunnan south china and their biostratigraphic implications the study discusses the detailed composition of terreneuvian small shelly fossil ssf assemblages of eastern yunnan province meishucun xianfeng and huize regions the described sections represent shallow water deposits of the yangtze platform that include a number of stratigraphical hiati the reported ssf assemblages can be assigned to the regional ssf biozones i iii anabarites trisulcatus protohertzina anabarica assemblage zone paragloborilus subglobosus purella squamulosa assemblage zone watsonella crosbyi assemblage zone zones ii and iii are slightly redefined based on new data two subzones of zone ii are proposed here namely annelitellus yangtzensis obtusoconus honorabilis subzone and maikhanella cambriana oelandiella korobkovi subzone claviconchella qianyii gen et sp nov and bubiites simplex gen et sp nov are reported here we also provide a critical revision of the ssf distribution for the well known meishucun section the correlation scheme for east yunnan documents the extent and duration of stratigraphical hiati the distribution of ssfs and the lithological characterization indicate three major events of exposure of the carbonate platform resulting in sedimentary breaks and possible karstification this prompts new consideration of the previously described stable isotope stratigraphy of shallow platform strata considering the complexity of the terreneuvian earth history as well as the uniqueness of ssf an integration of sedimentology geochemistry and paleontology is needed for future ssf study

synoptic systems interacting with the rocky mountain barrier observations and theories abstractusing a composite analysis for strong sea level pressure perturbations off the west coast of north america the evolution of large amplitude synoptic systems upstream of the rocky mountains is investigated for the winter season corresponding previous analyses are refined by avoiding multiple counting of events and extended by including potential vorticity vertical motion and deformation in the analysis cyclonic and anticyclonic anomalies behave similarly with weak local extrema forming in the lee of the mountain range southeast of the parent systems however neither the geopotential anomaly nor the associated potential vorticity anomaly cross the mountain range nevertheless these anomalies contribute to the sea level pressure anomaly in the lee for both positive and negative anomalies potential vorticity exhibits a bipolar structure with lobes over the reference point and over the cordillera respectively the relevance of several theories describing the interaction between synoptic syste

new constraint on the division of cambrian time a u pb zircon age of 530 7 0 9 ma for a volcanic ash in the lower placentian series of the avalonian terrane in southern new brunswick provides a precise point for calibration of early cambrian biologic evolution the ash is from the middle rusophycus avalonensis zone in saint john new brunswick this date is on subtrilobitic lower cambrian strata that may be approximately correlative with the sub tommotian manykaian stage of siberia and the lowest meishucunian stage of the south china platform this age when combined with published geochronologic data from the cambrian suggests that the manykaian stage may have lasted approximately 13 m y and that the tommotian may have been considerably shorter

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

multiple s isotopic constraints on paleo redox and sulfate concentrations across the ediacaran cambrian transition in south china abstract changes in oceanic chemical conditions are frequently invoked as a primary driver of biodiversification and mass extinction events in earth history during the ediacaran cambrian transition two major biological events including the extinction of the ediacaran biota and the cambrian explosion occurred approximately coincident with perturbations of the carbon and sulfur cycle these dramatic biological changes and coeval geochemical events are commonly thought to be linked but their causal relationships remain controversial here we present multiple s isotopic compositions of pyrite 34spy and 33spy from the xiaotan section spanning the ediacaran cambrian transition interval in south china our isotopic results show that negative 33spy values together with positive 34spy values occurred across the ediacaran cambrian boundary the negative 33spy data suggest mixing of sulfide from deep waters during the upwelling of sulfidic waters into oxygenated shallow waters the coincidence between the negative 33spy and the approximate timing of the extinction of the ediacaran biota implies that paleo redox perturbations may have contributed to the disappearance of the ediacaran biota negative 33spy values coupled with positive 34spy values were also observed in the cambrian zhongyicun member when the phosphorites were deposited suggesting a strong linkage between the upwelling of nutrient rich sulfidic deep waters and the deposition of the phosphorites in oxygenated shelf areas in addition using box models and stoichiometry calculations we quantitatively estimated elevated burial rates of organic matter and pyrite based on the parallel positive 13ccarb 34spy and 33spy excursions observed at xiaotan within cambrian stage 2 our mass balance modelling results provide an independent constraint on sulfate concentrations which were 4 mm or lower in the early cambrian oceans the probable increase in oxygen levels resulting from the enhanced burial of pyrite and organic matter could have provided a more habitable environment for early animals and thus paved the way for the radiation of early cambrian animals

reconstructing the avalonia palaeocontinent in the cambrian a 519 ma caliche in south wales and transcontinental middle terreneuvian sandstones an early cambrian caliche on the st non9s formation emended is the base of the caerfai bay formation unit term changed at caerfai bay south wales subaerial exposure and the caliche mean the two formations were not genetically related units the st non9s is an older sand sheet likely tidalitic not delta related referred to avalonian depositional sequence ads 2 and the caerfai bay is a shallow mud basin unit refered to ads 4a the similar random formation upper ads 2 in north american avalonia has a basal age of c 528 ma and is unconformably overlain by red mudstones or sandstones in fault bounded basins on the avalonian inner platform coeval british sandstones lower hartshill wrekin st non9s brand hills are unconformably overlain by latest terreneuvian ads 3 or epoch 2 ads 4a units dates of 519 ma on caerfai bay ashes give an upper bracket on the late appearance of avalonian trilobites and suggest an ads 2 4a hiatus of several million years post st non9s and post random basin reorganization led to abundant caerfai bay formation volcanic ashes and sparse brigus formation ashes in newfoundland the broad extent of erosional sequence boundaries that bracket lithologically similar to identical units emphasize that east and west avalonia formed one palaeocontinent the inner platform in southern britain was larger than the midlands craton a tectonically defined later palaeozoic area unrelated to terminal ediacaran early palaeozoic depositional belts the cool water successions of early palaeozoic avalonia were distant from coeval west gondwanan carbonate platforms

early cambrian chronostratigraphy and geochronology of south australia abstract the most successful chronostratigraphic correlation methods enlist multiple proxies such as biostratigraphy and chemostratigraphy to constrain the timing of globally important bio and geo events here we present the first regional high resolution shelly fossil biostratigraphy integrated with 13c chemostratigraphy and corresponding 18o data from the traditional lower cambrian terreneuvian and provisional cambrian series 2 of south australia the global zhuce shice positive excursions ii and iii and the care are captured in lower cambrian successions from the arrowie and stansbury basins the south australian shelly fossil biostratigraphy has a consistent relationship with the 13c results bolstering interpretation identification and correlation of the excursions positive excursion ii straddles the boundary between the kulparina rostrata and micrina etheridgei zones and the care straddles the boundary between the m etheridgei and dailyatia odyssei zones peaking in the lower parts of the latter zone new ca tims zircon dates from the upper hawker group and billy creek formation provide geochronologic calibration points for the upper d odyssei zone and corresponding chemostratigraphic curve embedding the lower cambrian successions from south australia into a global chronostratigraphic context this multi proxy investigation demonstrates the power of integrated methods for developing regional biostratigraphic schemes and facilitating robust global correlation of lower cambrian successions from south australia part of east gondwana with coeval terranes on other cambrian palaeocontinents including south and north china siberia laurentia avalonia and west gondwana

numerical modeling of a coastal trapped disturbance part i comparison with observations abstract the coastal trapped disturbance ctd of 15 17 may 1985 represents an example of a strong mesoscale trapped event along the west coast of north america with abrupt transitions in many basic meteorological parameters in this study a comparison between observations and a numerical simulation of this event using the regional atmospheric modeling system rams is presented the model is shown to realistically reproduce ctd characteristics such as the coastal transition from northerly to southerly flow as a mesoscale coastal ridge of higher pressure with associated drops in marine layer temperature propagates northward along the west coast of north america simulated sea level pressure and temperature fields near the surface match well with observations especially at the synoptic scale the model realistically simulates mesoscale sea level pressure and 6 h pressure changes during the event the modeled hourly time evolution of sea level pressure and the southerly transitions at a series of coastal

a complex trace fossil from the spitskop member terminal ediacaran lower cambrian of southern namibia streptichnus narbonnei igen et isp nov a new trace fossil from the upper part of the spitskop member of the urusis formation southern namibia consists of clusters of unidirectionally curved radial elements in which individual elements typically are composed of imbricated sickle shaped segments somewhat comparable to those of treptichnus pedum such complex trace fossils generally are found only in cambrian or younger strata this opens to question the position of the ediacaran cambrian boundary in the nama group suggesting that it may locally be within the uppermost part of the urusis formation rather than at the base of the nomtsas formation

the large scale coastal wind field along the west coast of north america 1981 1982 we study the statistical properties of the coastal wind field along the west coast of north america for two summers 1981 and 1982 coastal ocean dynamics experiments 1 and 2 respectively and the intervening winter using measured winds and geostrophic winds calculated from fleet numerical oceanography center atmospheric pressure analyses summer wind fluctuations are driven primarily by the interaction between two relatively stationary pressure systems the north pacific subtropical high and southwest u s thermal low and by their interactions with propagating atmospheric systems to the north in particular propagating cyclones and associated fronts are often followed by a northeastward intensification of the high producing strong upwelling events along the california coast this summer event sequence occurs more frequently and is displaced farther to the south on average during summer 1981 winter wind fluctuations are primarily driven by propagating cyclones and anticyclones and they tend to have larger variance and space scales than in summer a preference for poleward equatorward propagation exists in summer winter and the largest time scales are observed in summer 1982 coastal atmospheric boundary layer processes substantially modify winds within 100 200 km of the coast consequently measured wind fluctuations are strongly polarized in the alongshore direction and have means and rms amplitudes that can vary considerably between nearby stations along the coast calculated wind fluctuations are less polarized in the alongshore direction and have alongshore correlation scales about 60 larger than those for measured winds they represent fluctuations with alongshore wavelengths of 900 km rather well but represent poorly those with smaller wavelengths and those due to coastal atmospheric boundary layer effects

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

interaction of a warm season frontal system with the coastal mountains of the western united states part i prefrontal onshore push coastal ridging and alongshore southerlies abstract observational analyses and numerical simulations are used to investigate the interaction between a warm season frontal system trough and the complex terrain of the western united states prior to frontal landfall synoptically driven offshore flow was associated with the northward development of a thermal trough and a coastal pressure ridge and associated southerly winds moved northward along the coasts of northern california oregon washington and southwestern british columbia this coastal pressure ridge coupled with the subsequent weakening of the offshore flow resulted in the onshore push of cool marine air approximately 24 h before frontal passage the onshore surge of cool marine air into warm dry continental air associated with the thermal trough produced a mesofront that moved over the coastal and cascade mountains diagnosis of a realistic simulation of the event shows that both solar heating and adiabatic warming from downslope flow over the rockies and the cascade mountains are i

chronology of early cambrian biomineralization data on the first appearances of major animal groups with mineralized skeletons on the siberian platform and worldwide are revised and summarized herein with references to an improved carbon isotope stratigraphy and radiometric dating in order to reconstruct the cambrian radiation popularly known as the cambrian explosion with a higher precision and provide a basis for the definition of cambrian stages 2 to 4 the lophotrochozoa and probably chaetognatha were first among protostomians to achieve biomineralization during the terreneuvian epoch mainly the fortunian age fast evolutionary radiation within the lophotrochozoa was followed by radiation of the sclerotized and biomineralized ecdysozoa during stage 3 the first mineralized skeletons of the deuterostomia represented by echinoderms appeared in the middle of cambrian stage 3 the fossil record of sponges and cnidarians suggests that they acquired biomineralized skeletons in the late neoproterozoic but diversification of both definite sponges and cnidarians was in parallel to that of bilaterians the distribution of calcium carbonate skeletal mineralogies from the upper ediacaran to lower cambrian reflects fluctuations in the global ocean chemistry and shows that the cambrian radiation occurred mainly during a time of aragonite and high magnesium calcite seas

an observational and numerical study of an intense landfalling cold front along the northwest coast of the united states during coast iop 2 abstract this paper presents an observational and numerical study of an intense wintertime cold front that made landfall along the northwest coast of the united states during iop 2 3 4 dec 1993 of the coastal observation and simulation with topography experiment observations suggest that the offshore frontal zone was associated with two transitions the first characterized by a substantial temperature gradient a nearly vertically oriented wind shift from southwesterly ahead to westerly behind and a convective rainband while the second transition had a slantwise wind shift zone from westerly ahead to northwesterly behind the frontal zone was quite narrow 5 km wide and nearly vertical below 850 mb and its width increased by 1 2 orders of magnitude above 850 mb well before the frontal landfall low level flow to the west of the olympics was associated with geostrophic balance in the cross shore direction and downgradient acceleration in the alongshore direction which contributed to the formation

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

northerly surface winds over the eastern north pacific ocean in spring and summer 1 persistent spring and summer northerly surface winds are the defining climatological feature of the western coast of north america especially south of the oregon coast northerly surface winds are important for upwelling and a vast array of other biological oceanic and atmospheric processes intermittence in northerly coastal surface wind is characterized and wind events are quantitatively defined using coastal buoy data south of cape mendocino on the northern california coast the defined wind events are then used as a basis for composites in order to explain the spatial evolution of various atmospheric and oceanic processes wind events involve large scale changes in the three dimensional atmospheric circulation including the eastern north pacific subtropical anticyclone and southeast trade winds composites of qscat satellite scatterometer wind estimates from 1999 to 2005 based on a single coastal buoy indicate that wind events typically last 72 96 h and result in anomalies in surface wind and ekman pumping that extend over 1000 km from the west coast of north america it may be useful to consider ocean circulation and dependent ecosystem dynamics and the distribution of temperature moisture and aerosols in the atmospheric boundary layer in the context of wind events defined herein

the dynamic evolution of the palaeozoic geography of eastern asia abstract new palaeogeographical reconstructions are presented for eleven time intervals through the palaeozoic of the eastern asia region from the middle cambrian at 510 ma to the end of the permian at 250 ma they centre on the continental blocks of north china south china and annamia indochina and their relationships with northeastern gondwana which was united to form part of pangea from the late carboniferous onwards also shown is the continent of tarim during the lower palaeozoic as well as the hutag uul songliao and khanka jiamasu bureya terranes both of which straddle the russian mongolian and chinese borders today from silurian times onwards we conclude that annamia and south china were united as a single continent throughout the lower palaeozoic and early devonian and were translocated by major strike slip faulting along the northeastern gondwana margin during that period from off afghanistan to outboard of the sibumasu and australian sectors of the superterrane they left the gondwana marginal area together during the lower devonian opening of the palaeotethys ocean but very shortly afterwards they themselves divided into the two separate continental blocks that we recognise today not to reunite until the triassic the various cambrian to permian rocks found in japan largely represent active volcanic arcs which originally lay to the southeast of south china although the carboniferous was more quiescent there the neotethys ocean opened during the permian dividing sibumasu and the tibetan terranes from gondwana and the palaeotethys ocean started to close progressively in the upper palaeozoic as most of the east asian continents and smaller terranes moved towards siberia the positions of the various continents and terranes have been deduced from a mixture of palaeomagnetic and faunal data the positions of large igneous provinces and kimberlites and the need to provide kinematic continuity between maps of successive ages however many uncertainties remain

carbon isotope stratigraphy and the problem of a pre tommotian stage in siberia carbon isotopic oscillations are useful to elucidate the stratigraphy and biogeochemical events around the precambrian cambrian transition new isotopic data from the manykaj and emyaksin formations of the eastern anabar uplift siberia help to correlate the lower cambrian and neoproterozoic cambrian transitional beds across the siberian platform the similarity of trends and amplitudes of the carbon isotopic curves together with biostratigraphic and sequence stratigraphic markers from the anabar uplift provide a precise correlation with the southern part of the siberian platform diagenesis of argillaceous limestones of the emyaksin formation has appar ently not affected the primary isotopic variations the resulting curve is nearly identical in sections about 100 km apart in the tommotian atdabanian portion of the formation relatively frequent and pronounced isotopic oscillations in the lower beds of the emyaksin formation fit between features i and ii of the southern siberian isotopic reference scale but are undetected therein owing to the deposi tional hiatus at the base of the tommotian stage in its type section this confirms the transgressive onlap from the north suggested by previous studies and makes the appearance of the cambrian skele tal fossils on the siberian platform less abrupt the hiatus in the south appears to embrace at least two biostratigraphic zones as recognized in the north the case is strengthened for a pre tommotian cambrian stage in siberia the biostratigraphic framework for which has been elaborated earlier

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

watsonella crosbyi from the lower cambrian terreneuvian stage 2 normanville group in south australia correlation of lower cambrian strata is often confounded by provincialism of key fauna the widespread occurrence of the micromollusc watsonella crosbyi grabau 1900 is therefore an important biostratigraphic signpost with potential for international correlation of lower cambrian successions previous correlations of w crosbyi from australia normanville group suggested an atdabanian to botoman equivalent age however in the upper part of the mount terrible formation stratigraphic ranges of w crosbyi and aldanella sp cf golubevi overlap prior to the incoming of vertically burrowed piperock which is indicative of an age no earlier than cambrian stage 2 the stratigraphic range of w crosbyi in the normanville group south australia correlates with the ranges of the taxon in china france mongolia and siberia though not newfoundland the new australian data add further support for considering the first occurrence of w crosbyi a good potential candidate for defining the base of cambrian stage 2 the stratigraphic range of w crosbyi through the lower cambrian normanville group has been determined based on collections from measured sections although rare w crosbyi is part of an assemblage of micromolluscs including bemella sp parailsanella sp cf murenica and a sinistral form of aldanella a sp cf a golubevi other fauna present include australohalkieria sp eremactis mawsoni chancelloriids and cupitheca sp

sequence stratigraphy and sedimentology of the neoproterozoic kuibis and schwarzrand subgroups nama group southwestern namibia abstract the kuibis and schwarzrand subgroups of the nama group form a succession of shallow marine and minor fluvial sedimentary rocks that is exposed over much of central and southern namibia ediacaran type body fossils and the stratigraphic carbon isotope variability indicate a vendian age for much of these strata the precambrian cambrian boundary is in the uppermost part of the schwarzrand subgroup radiometric dating of abundant volcanic ash beds which span much of the vendian and extend into the cambrian part of the section could make the nama group the best calibrated reference section for vendian chronostratigraphy here we describe the sedimentology and sequence stratigraphy of exposures of the kuibis and schwarzrand subgroups in southwestern namibia we place tighter environmental constraints on the paleontology and geochemistry and we identify seven depositional sequences the boundaries of the depositional sequences correspond to the more important disconformities in the kuibis and schwarzrand subgroups their identification is crucial for defining rates of organism evolution and isotopic differentiation

the characteristics and significance of conventional and unconventional sinian silurian gas systems in the sichuan basin central china abstract oil and gas discoveries within proterozoic cambrian strata and the majority of shale gas production occurs in relatively stable tectonic regions and characterised by moderate thermal maturity r o o 2 5 the system comprises two components namely a conventional sinian cambrian dolomite hosted gas resource and an unconventional cambrian silurian shale gas deposit both represent trillion cubic meter accumulations the migration accumulation type sinian cambrian gas system is a result of numerous processes including 1 paleo high trapping within a relatively stable tectonic setting 2 appropriate source materials located in a paleo rift trough 3 large scale dolomite grainstone reservoirs located near the paleo high 4 adequate gas produced from in situ crude oil cracking and 5 gypsum salt and shale cap rock preservation the self contained source reservoir cambrian silurian shale gas system is localized by deepwater organic rich shelf facies characterized by high silicon and calcium contents the recent discovery of these two massive gas fields in old and over matured sedimentary strata has effectively extended the upper maturity limit of r o over 3 0 which may indicate the efficacy of broadening current natural gas exploration areas thus potentially increasing global natural gas resources significantly furthermore the discovery may spark interest in natural gas exploration in widely distributed old strata thus encouraging co development of conventional and unconventional petroleum accumulations

a nonhydrostatic mesoscale simulation of the 10 11 june 1994 coastally trapped wind reversal abstract during the summer months the california coast is under the influence of persistent northwesterly flow several times each summer this regime is disrupted by coastally trapped wind reversals ctwr in which the northwesterly flow is replaced by southerlies in a narrow zone along the coast controversy exists as to the physical mechanisms responsible for initiation and maintenance of ctwrs while it is clear that coastal terrain is important in creating the trapped response the precise role played by terrain is unclear in the present study these issues are investigated using a nonhydrostatic mesoscale model to simulate the 10 11 june 1994 ctwr event the results show that the model successfully reproduces many of the observed features of this event including anomalous vertical structure involving the relatively shallow boundary layer with a warm nearly neutral layer above the northward propagation of southerly flow in advance of a tongue of coastal stratus fog and a substantial reduction i

paleo marine environments of the early cambrian yangtze platform abstract previous studies have generated conflicting interpretations of the nature of oceanographic conditions on the early cambrian yangtze platform we investigated paleo environmental conditions there through an analysis of major elements and redox sensitive trace elements in the lower cambrian niutitang formation from two new drillcores ry1 and ry2 in guizhou province high toc and excess ba concentrations record elevated productivity in the study area redox variation was documented based on enrichment factors efs for redox sensitive trace elements mo u v cr ni and co and c org p ratios these proxies indicate that the lower unit of the niutitang formation was deposited under fluctuating but mostly anoxic conditions whereas the upper unit was deposited under predominantly suboxic conditions mo toc ratios suggest persistently moderate to strong basinal restriction although mo u covariation patterns show no evidence for operation of a particulate shuttle despite the semi restricted anoxic nature of the deep watermass episodic deep water oxygenation events occurred within the yangtze platform sea and longer term secular variation may record eustatic influences additionally patterns of trace metal enrichment record evidence of submarine hydrothermal inputs we propose an integrated paleoenvironmental model to account for the observed productivity redox and hydrographic patterns in the early cambrian yangtze platform on the basis of paleo marine environmental analysis we ascribe the scarcity of trace fossils in the bottom to oxygen deficiency and deny considering the songlin biota as the onset of the intense biogenic evolution after global atmospheric and oceanic oxygenation

marine redox variations and nitrogen cycle of the early cambrian southern margin of the yangtze platform south china evidence from nitrogen and organic carbon isotopes the early cambrian is a crucial interval during which the marine environment encountered significant perturbations alongside key biological innovations the nitrogen isotopic composition of ancient sediments has the potential to record co variation between the marine ecosystem and environmental conditions here we report bulk nitrogen and organic carbon isotopic compositions accompanied by mo concentration data a proxy for redox conditions for a shelf marginal drill core section sancha and a deep basinal outcrop section yuanjia in hunan province south china for the cambrian fortunian stage variable delta n 15 bulk values 4 to 2 parts per thousand and low delta c 13 org values 35 parts per thousand to 33 from the yuanjia section indicate that anoxic waters shoaled into the photic zone with ammonia assimilation competing with anammox in the basinal area in the late cambrian stage 2 low delta n 15 bulk and delta c 13 org values together with high mo bulk concentrations delta n 15 bulk 5 to 0 parts per thousand delta c 13 org 33 5 to 31 0 parts per thousand 100 ppm mo bulk in sancha section and delta n 15 bulk 0 parts per thousand delta c 13 org similar to 33 parts per thousand 100 ppm mo bulk in yuanjia section reflect intense n 2 fixation accompanied by intermittent ammonia assimilation under expanded euxinic condition with shoaling chemocline possibly into the photic zone in the early cambrian stage 3 relatively high delta n 15 bulk values alongside positive delta c 13 org excursions at both sections indicate an increasing contribution from n 15 enriched nitrate assimilation and hence more oxic conditions shelf margin sediments from the middle and late parts of cambrian stage 3 are characterized bylaw delta n 15 bulk values similar to 0 parts per thousand being lowest in the basinal area 3 to 0 parts per thousand in combination with high mo bulk concentration 100 ppm and high mo tocbulk ratios averaging similar to 18 in deep basinal sediments these data suggest that the photic zone became anoxic again but that sulfidic conditions occurred in the basinal area only compared with stage 2 euxinia was less extensive during this interval with photosynthetic biomass dominating over chemoautotrophic biomass at both localities based on a combination of delta n 15 data from this study and published data from studies on contemporaneous sections in yunnan province and the three gorges area it is possible to reconstruct the spatial variability and temporal evolution of redox conditions in the various marine environments along the southern margin of the yangtze platform the basinal area appears to have been dominated by anoxia and intermittent euxinia in the photic zone during most of the early cambrian fortunian stage to stage 3 with the exception of more oxic conditions during early stage 3 on the platform oxygenated shallow water prevailed with the exception of the notable cambrian stage 2 anoxic event the outer shelf area experienced anoxia from stage 2 to stage 3 of the early cambrian although of possibly limited areal extent the high mo bulk concentrations and mo tocbulk ratios suggest that the south china basin was well connected with the considerably oxygenated open ocean and that the mean low delta n 15 bulk values similar to 1 6 parts per thousand from the basin may reflect generally lower delta n 15 composition for seawater nitrate in the early cambrian compared with modern value c 2015 elsevier b v all rights reserved

sims u pb zircon ages and ni mo pge geochemistry of the lower cambrian niutitang formation in south china constraints on ni mo pge mineralization and stratigraphic correlations abstract in comparison with previous studies on the ni mo pge ore deposits within the deep water lower cambrian black shales of the niutitang formation around hunan and guizhou provinces this study focused on the shallow water ni mo pge enriched layer of the niutitang formation around hubei province by means of an integrated geochronological pge ree and trace element geochemical study the results suggest the ni mo pge enriched layer has a dominant seawater origin whereas the ni mo pge ore deposits have mixed seawater hydrothermal and terrigenous origins trace metals precipitated from ambient seawater under anoxic suboxic settings at exceedingly slow sedimentation rates with episodic injections of fresh oxidized seawater organic matter played an important role in sourcing transporting and precipitating trace metals however decay of organic material by means of sulfate reducing reactions and or fluid reworking overprinted primary relationships with trace metal contents however the positive linear relationships are clearly shown between organic carbon and trace metal contents new sims u pb ages constrained the depositional age of the ni mo pge enriched layer to be 532 527 ma which argues against previous assumption that the anoxic event recorded in the ni mo pge took place at the ediacaran cambrian boundary furthermore new radiometric ages suggest the shuijingtuo niutitang formation could be correlated with shiyantou formation dahai and upper zhongyicun members whereas yanjiahe formation correlated with daibu and lower zhongyicun members in yunnan province respectively

reconstruction of early cambrian ocean chemistry from mo isotopes the neoproterozoic cambrian transition was a key time interval in the history of the earth especially for variations in oceanic and atmospheric chemical composition however two conflicting views exist concerning the nature of ocean chemistry across the precambrian cambrian boundary abundant geochemical evidence suggests that oceanic basins were fully oxygenated by the late ediacaran while other studies provide seemingly conflicting evidence for anoxic deep waters with ferruginous conditions fe ii enriched persisting into the cambrian here two early cambrian sedimentary platform and shelf slope sections in south china were investigated to trace early cambrian ocean chemistry from mo isotopes the results reveal that early cambrian sediments deposited under oxic to anoxic euxinic conditions have 98 95mo values ranging from 0 28 to 2 29 which suggests that early cambrian seawater may have had 98 95mo values of at least 2 29 similar to modern oceans the heaviest and relatively homogeneous 98 95mo values were recorded in siltstone samples formed under completely oxic conditions which is considered that mn oxide free shuttling was responsible for such heavy 98 95mo value further combined with fe species data and the accumulation extent of mo and u the variation of 98 95mo values in the two studied sections demonstrate a redox stratified ocean with completely oxic shallow water and predominantly anoxic even euxinic deeper water having developed early on which eventually became completely oxygenated this suggests that oceanic circulation at the time became reorganized and such changes in oceanic chemistry may have been responsible for triggering the cambrian explosion of biological diversity

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

geochronological constraint on the cambrian chengjiang biota south china the cambrian chengjiang biota of south china provides compelling fossil evidence for the rapid appearance of metazoan phyla in earth history the cambrian explosion however the timing of the chengjiang biota is poorly constrained owing to lack of datable rock materials within the maotianshan shale that yields the fossils here we integrate secondary ion mass spectrometry sims and chemical ablation isotope dilution thermal ionization mass spectrometry ca id tims u pb analyses of detrital zircons from the maotianshan shale to provide high precision geochronological constraint on the chengjiang biota the youngest group of sims u pb detrital zircon dates yields an age peak at 520 ma six zircons from this group are further dated by the ca id tims u pb technique but suggesting that they were not formed from a single zircon growth event thereby neither the age peak nor the weighted mean age defined by the youngest sims u pb dates could represent the maximum depositional age of the maotianshan shale instead the youngest ca id tims u pb date 518 03 0 69 0 71 ma 2 analytical uncertainty incorporates u pb tracer calibration uncertainty provides the first robust maximum age of the chengjiang biota this new geochronological constraint on the chengjiang biota indicates that the cambrian explosion reached its major phase around 518 03 0 69 0 71 ma demonstrating a protracted process 22 myr for the cambrian explosion supplementary material sims and ca id tims zircon u pb data are available at https doi org 10 6084 m9 figshare c 4024849

evaluating episodic hydrothermal activity in south china during the early cambrian implications for biotic evolution abstract the early cambrian 541 514 ma was a crucial interval for the evolution of life on earth popularly known as the cambrian explosion here we report the timing of changes in hydrothermal and depositional inputs as well as paleo redox state which may have influenced biogeochemical changes according to high resolution petrology fossil distributions isotopic records and inorganic geochemistry the lower cambrian of the south china can be subdivided into four intervals the lowermost cambrian zhujiaqing formation cam i the cambrian stage 2 shiyantou formation cam ii the lower part of the cambrian stage 3 yu anshan formation cam iii and the mid upper cambrian stage 3 and the middle upper part of the yu anshan formation continuing into the canglangpu formation cam iv hydrothermal events are detected during the early cam i cam ii and cam iii intervals during the early cam i and cam ii intervals these events coincided with extensive bottom water euxinia which in turn may have restricted the spread or proliferation of ediacaran fauna and small shelly fauna through the whole cam iii interval further hydrothermal events occurred concurrently with euxinic and ferruginous conditions probably within a single spatially stratified water column again plausibly restricting the spread of aerobic organisms in conjunction with the cessation of hydrothermal events and the gradual lowering of sea level during the late cam iii oxic water environments gradually spread into relatively deep water regions concurrent with the emergence of the chengjiang and qingjiang faunas these data suggest that periodic hydrothermal events may have had a significant impact on the spread radiation and extinction of macroscopic fauna during the early cambrian in south china

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

evidence for marine redox control on spatial colonization of early animals during cambrian age 3 c 521 514 ma in south china the early cambrian period was a key interval in earth history with regard to changes in both ocean chemistry and animal evolution although increasing ocean ventilation has been widely assumed to have played a key role in the rapid appearance diversification and spatial colonization of early animals this relationship is in fact not firmly established here we report a high resolution fe c s al ti geochemical study of the lower cambrian wangjiaping section from an outer shelf setting of the yangtze sea of south china iron speciation data document a redox transition from dominantly euxinic to ferruginous conditions during cambrian age 3 c 521 514 ma interpretation of coexisting pyrite sulphur isotope 34 s py records from wangjiaping reveals relatively high marine sulphate availability at wangjiaping furthermore wangjiaping section shows lower 34 s py 2 1 5 3 and lower toc 2 4 1 1 values but higher positive correlation r 2 0 66 p 0 01 between toc and fe py fe hr relative to deeper sections reported previously suggesting that euxinia developed at wangjiaping in response to increasing marine productivity and organic matter sinking fluxes our reconstructed redox conditions and fossils at wangjiaping in comparison with previously well studied strata in the inner shelf xiaotan and shatan sections suggest that planktonic and benthic planktonic trilobites with bioturbation appeared in the oxic water columns whereas only planktonic trilobites without bioturbation occurred within the anoxic even euxinic water columns during cambrian age 3 this finding indicates that spatial heterogeneity of redox conditions in the shelves had an important effect on early animal distribution in the yangtze block

an observational and numerical study of a cold front interacting with the olympic mountains during coast iop5 abstract this paper documents the three dimensional flow and precipitation structures associated with a weak cold front interacting with the olympic mountains and the subsequent development of a puget sound convergence zone this study utilizes data collected during coast iop5 the fifth intensive observing period of the coastal observation and simulation with topography field experiment that took place on 11 12 december 1993 one of the most important data sources was a noaa p 3 aircraft which provided flight level data radar reflectivity and doppler winds as it circumnavigated the olympics initially frontal passage along the western foothills of the olympics was accompanied by a 2 3 c temperature drop a rapid wind shift to northwesterlies and an intense line of precipitation 35 45 dbz however the wind shift and associated precipitation structures attenuated when the front began to ascend the windward slopes of the olympics surface and p 3 observations document the deformation of the front

the west coast thermal trough mesoscale evolution and sensitivity to terrain and surface fluxes abstractdespite the significant impacts of the west coast thermal trough wctt on west coast weather and climate questions remain regarding its mesoscale structure origin and dynamics of particular interest is the relative importance of terrain forcing advection and surface heating on wctt formation and evolution to explore such questions the 13 16 may 2007 wctt event was examined using observations and simulations from the weather research and forecasting wrf model an analysis of the thermodynamic energy equation for these simulations was completed as well as sensitivity experiments in which terrain or surface fluxes were removed or modified for the may 2007 event vertical advection of potential temperature is the primary driver of local warming and wctt formation west of the cascades the downslope flow that drives this warming is forced by easterly flow associated with high pressure over british columbia canada when the terrain is removed from the model the wctt does not form and high

challenges in defining the base of cambrian series 2 and stage 3 formal subdivision of the cambrian system into four series and ten stages is in progress the base of cambrian stage 3 provisional which is conterminous with the base of cambrian series 2 provisional is expected to be placed at a horizon close to the first appearance of trilobites which marks the onset of the largest phase of the cambrian explosion conceptually an ideal boundary position would be marked by a significant and globally recognizable bioevent that divides the lower part of the cambrian system into a sub trilobitic terreneuvian series and a trilobite dominated series 2 if the level is to be identified principally through biostratigraphic means its position also needs to be recognizable using non biostratigraphic means and its correlation potential should be tested through detailed investigation of several continuous successions embracing the critical interval major difficulties in identifying a suitable horizon include strong biotic provincialism a plethora of regional unconformities and facies changes on different paleocontinents in the cambrian terreneuvian series 2 boundary interval levels that provide potential for intercontinental correlation include the first appearance position of trilobites and the approximately equivalent first appearance positions of certain small shelly fossil and acritarch species in addition a non biostratigraphic marker such as a stable carbon isotopic excursion may be useful as a correlation level cambrian series 2 and stage 3 are provisional stratigraphic units and their conterminous base was previously suggested to coincide to the appearance of trilobites compared to other potential chronostratigraphic indicators the first appearance of trilobites still has advantages for recognizing and correlating the base of stage 3 and should remain as the provisional primary marker for the boundary position

further shrimp geochronology on the early cambrian of south china zircon 206pb 238u ages are reported for bentonites from two cambrian sections in south china the meishucun and the fandian the analyzed zircons vary widely in age because of the presence of detrital and altered grains spot ages were corrected for calibration drift during analysis and the age of reference zircon sl13 was calibrated as 580 ma against other standards using sims use of mixture modeling was essential to resolve the different age components and to identify the volcanic ages two age groups occur within the meishucun bed 5 bentonite of which the larger at 518 7 2 5 ma is interpreted as a post depositional zircon growth event and the other at 539 4 2 9 ma as the volcanic age bentonites from the meishucun bed 9 and its fandian equivalent have two age groups 526 5 1 1 ma and 540 2 1 0 ma we interpret the younger of these as the tuff magmatic age and the older as detrital small shelly fossils indicate meischucunian bed 5 is an equivalent of the late nemakit daldynian and its 539 4 2 9 ma age both closely times the base of the cambrian and is a maximum for the basal tommotian the 526 5 1 1 ma for bed 9 and its equivalents approximates the close of the tommotian

effects of coastal orography on landfalling cold fronts part i dry inviscid dynamics abstract in this study the interaction of cold fronts with idealized coastal terrain typical of the western united states and canada is considered two issues are examined first what are the factors that determine the strength of the coastal winds and second what are the orographic effects on the frontal evolution to address these issues the authors utilize a two dimensional boussinesq terrain following coordinate numerical model in which a uniform prescribed flow is forced to move over a plateau the resultant across mountain velocities are characterized by a zone of strongly decelerated flow upstream of the windward slope and a train of inertia gravity waves downstream a barrier jet oriented parallel to the mountain is produced by the coriolis force the variations of the magnitude of the upstream deceleration and the barrier jet over a wide range of froude numbers and rossby numbers are described steady linear theory applied to flow over a plateau shows that the upstream deceleration is dete

early cambrian bioconstructions in the zavkhan basin of western mongolia the neoproterozoic cambrian succession in the zavkhan basin of western mongolia preserves early cambrian bioconstructions of nemakit daldynian to botomian age as elsewhere siberia morocco the nemakit daldynian bioconstructions in the upper tsagaan oloom formation to lower bayan gol formation interval were purely calcimicrobial spectacular calcimicrobial patch reefs of presumed tommotian age are present in the lower bayan gol formation in contrast late atdabanian early botomian bioconstructions are varied and well developed in the upper salaany gol formation including in addition to calcimicrobial bioherms gordonophyton razumovskia crusts radiocyathan archaeocyathan bioherms and thickets of the ramose archaeocyath cambrocyathellus these latter zavkhan basin buildups show some ecological and sedimentological features in common with coeval bioconstructions in south australia which also developed under a tectonically active regime

the neoproterozoic lower cambrian in northern govi altay western mongolia regional setting lithostratigraphy and biostratigraphy this paper provides a framework for the stratigraphy and correlation of key sections through the neoproterozoic lower cambrian of the govi altay area western mongolia studied by members of igcp project 303 dzabkhan formation volcanic rocks at the base of the succession are suggested to have formed during rifting of the baydrik tarbagatay microcontinent in the baykalian interval c 850 650 ma pre vendian accretion transformed this rift and adjacent microcontinental fragments into a marginal marine back arc basin in which accumulated relatively uninterrupted neoproterozoic and earliest palaeozoic sediments lithostratigraphy for the latter is defined with detailed maps at five sections bayan gol northern and southern blocks tsagaan gol salaany gol and tayshir the tsagaan oloom formation lower member contains two diamictites of possible sturtian age middle and upper carbonates are compared with the yudomian vendian of siberia the former ending with a unit of boxonia grumulosa stromatolites in the upper member phosphorite shale is followed mainly by limestones with the earliest skeletal fauna the bayan gol formation comprises siliciclastic limestone intercalations with increasingly diverse invertebrate biota correlation of lithological marker beds across the study area produces a composite stratigraphic section to which the earliest skeletal fossil occurrences are tied the anabarites trisulcatus zone of the nemakit daldynian stage begins near the base of the tsagaan oloom formation upper member unit 11 the purella antiqua zone begins near the base of the bayan gol formation unit 18 assemblages typical of the nochoroicyathus sunnaginicus zone base of the tommotian stage range through units 19 to 23 elements typical of the dokidocyathus regularis zone middle tommotian appear in unit 24 near the top of the bayan gol formation

tsunami sedimentation associated with the 1923 kamchatka earthquake abstract the kuril kamchatka region is notorious for the occurrence of earthquake tsunamis and historical documents show that they have caused repeatedly considerable damage since the 1750s the great tsunami generated in april 1923 around the northern kamchatka trench flooded the coast of ust kamchatsk depositing a thin sand layer which is traceable up to 3 km or more inland beyond the present coastline local government documents indicate that the 1923 tsunami flooded low lying coastal areas covered by thick snow the unusual process of tsunami run up without loss of tractive load is interpreted to have resulted from the smoothing of fields by the ice covered surface we conclude that the tsunami flooded snowfields and deposited an extensive sheet of sand a mixture of snow and seawater flooded over the area and caused damage to vegetation

geochronological constraints on stratigraphic correlation and oceanic oxygenation in ediacaran cambrian transition in south china the continuous late ediacaran early cambrian deep water successions of south china archive the complete evolution of seawater chemical conditions in the deep ocean during this critical time interval however the geochemical data from these poorly fossiliferous and condensed successions lack high resolution stratigraphic constraints hampering their interpretation for the spatio temporal evolution of the sweater chemistry in this time interval in this study we report a new sims and ca id tims zircon u pb age 545 76 0 66 ma total uncertainty for an ash bed at the lower liuchapo formation in the deep water longbizui section in western hunan province the new age suggests that the lower and the middle upper parts of the liuchapo formation in the deep water facies can be correlated with the lower dengying formation and the upper dengying lower zhujiaqing formations in the shallow water facies respectively this correlation implies that the correlative horizon of the ediacaran cambrian boundary in the deep water facies in south china is likely located near the base of a widespread negative 13corg excursion at the upper liuchapo formation based on our new geochronological framework the compilations of fe speciation mo and u data indicate that the deep ocean was characterized by widespread anoxic ferruginous water with intermittent euxinic water impinged on the middle lower slope in ediacaran cambrian transition and significant oxygenation events occurred in 533 520 ma the compilations do not support any significant oceanic oxygenation events in 551 535 ma

new u pb zircon ages of the ediacaran cambrian boundary strata in south china the ediacaran cambrian transition is a critical interval marking drastic biological oceanic and geochemical co evolutions in geological history but it is poorly constrained geochronologically in south china we here present two new sets of sims u pb zircon ages from ediacaran cambrian boundary strata dengying liuchapo and niutitang formations deposited in the slope basin environments of carbonate platforms two weighted mean u pb ages of 542 1 5 0 ma and 542 6 3 7 ma in the basal and mid upper liuchapo formation respectively in slope and basinal settings provide the first direct age set for the ediacaran cambrian boundary in south china another two u pb ages of 524 2 5 1 ma and 522 3 3 7 ma from the base of the overlying niutitang formation indicate that this widespread unit in south china was deposited about 20 ma after the onset of the cambrian

new u pb age from the basal niutitang formation in south china implications for diachronous development and condensation of stratigraphic units across the yangtze platform at the ediacaran cambrian transition abstract the black shale dominated niutitang formation covers a large portion of the early cambrian yangtze platform in south china the base of this unit has been traditionally taken as the ediacaran cambrian boundary ca 542 ma recent radiometric ages from the basal niutitang formation and its correlative units however are significantly younger than 542 ma and raise questions about the diachrony of stratigraphic units across the yangtze platform at the ediacaran cambrian transition here we report a new u pb sensitive high resolution ion microprobe shrimp age of 522 7 4 9 ma from a tuffaceous bed of the basal niutitang formation in a deep water section in taoying guizhou province of south china this age in combination with existing ages and biostratigraphic data suggests that the base of the niutitang formation is of tommotian or upper meishucunian age and the ediacaran cambrian boundary is most likely within the liuchapo formation the depositional age of the unusual metal enriched ni mo pge sulfide deposits which are approximately 1 m above the ca 523 ma tuffaceous bed should be early tommotian upper meishucunian rather than early nemakit daldynian lower meishucunian regional correlation confirms the diachronous development and condensation of stratigraphic units across the early cambrian yangtze platform and provides important information for understanding the paleogeography and paleoceanographic events at the ediacaran cambrian transition in south china

cambrian evolutionary radiation context correlation and chronostratigraphy overcoming deficiencies of the first appearance datum fad concept abstract use of the first appearance datum fad of a fossil to define a global chronostratigraphic unit s base can lead to intractable correlation and stability problems fads are diachronous they reflect species evolutionary history dispersal biofacies preservation collection and taxonomy the cambrian evolutionary radiation is characterised by diachronous fads biofacies controls and provincialism of taxa and ecological communities that confound a stable lower cambrian chronostratigraphy cambrian series and stage definitions require greater attention to assemblage zone successions and non biostratigraphic particularly carbon isotope correlation techniques such as those that define the ediacaran system base a redefined basal cambrian trichophycus pedum assemblage zone lies above the highest ediacaran type biotas vendobionts putative metazoans and calcareous problematica such as cloudina and the basal asteridium tornatum comasphaeridium velvetum zone acritarchs this definition and the likely close correspondence of evolutionary origin and local fad of t pedum preserves the fortune head newfoundland gssp of the cambrian base and allows the presence of sub cambrian branched ichnofossils the sub tommotian equivalent base of stage 2 a suggested laolinian stage should be defined by the i l4 zhuce 13 c positive peak bracketed by the lower ranges of watsonella crosbyi and aldanella attleborensis molluscs and the skiagia ornata fimbrioglomerella membranacea zone acritarchs the w crosbyi and a attleborensis fads cannot define a stage 2 base as they are diachronous even in the newfoundland type w crosbyi zone the series 2 base cannot be based on a species fad owing to the provincialism of skeletalised metazoans in the terreneuvian series 2 boundary interval and global heterochrony of the oldest trilobites a series 2 and stage 3 a suggested lenaldanian series and zhurinskyan stage new gssp base is proposed at the siberian lower atdabanian 13 c iv peak which correlates into south china avalonia and morocco and assigns the oldest trilobites to the terminal terreneuvian series

the storegga slides evidence from eastern scotland for a possible tsunami abstract the second storegga slide on the continental slope off western norway has been dated at between 8000 and 5000 yrs b p a prominent sand layer in flandrian holocene deposits along the coast of eastern scotland and dated at approximately 7000 yrs b p may have been deposited by a tsunami generated by the slide the altitude and stratigraphy of the layer allow estimates to be made of the magnitude of the earthquake which initiated the slide

controls on organic matter accumulation on the early cambrian western yangtze platform south china abstract the origin of widespread organic rich shales on the early cambrian yangtze platform of nanhua basin south china has been attributed to high primary productivity to test this hypothesis we generated multiple paleoproductivity ocar and par paleoredox corg p ratios upwelling restriction coef mnef co ppm mn mo toc and cd mo ratios and terrigenous flux proxies al and unreactive fe feu for the lower cambrian niutitang formation in the outer shelf jinsha section which records a typical transition from the organic rich black shales to overlying organic lean mudstones or siltstones these new data were integrated with published paleoredox proxies iron speciation and redox sensitive trace metals for the same section our results suggest that the organic rich toc 4 6 1 8 lower member lm 0 37 m of the niutitang formation records ferruginous conditions high productivity levels and low siliciclastic fluxes and that the organic poor toc 0 1 0 1 upper member um 37 329 m was characterized by dominantly oxic conditions declining productivity levels and high siliciclastic fluxes our results suggest a redox shift from ferruginous to oxic conditions and enhanced terrigenous fluxes in response to falling sea level from the lm to the um secular variations in primary productivity and redox conditions are strongly correlated which is consistent with a positive feedback high primary productivity led to increasing water column anoxia which enhanced organic p recycling stimulating further productivity variations in primary productivity may reflect variable upwelling intensity in a semi restricted shelf setting linked to sea level changes taken together these findings suggest that a combination of primary productivity redox conditions and terrigenous fluxes driven by sea level changes played a key role in organic matter accumulation on the early cambrian western yangtze platform

paleo environmental conditions of the early cambrian niutitang formation in the fenggang area the southwestern margin of the yangtze platform southern china evidence from major elements trace elements and other proxies abstract the precambrian cambrian transition was a key time in earth history especially for marine biological evolution and oceanic chemistry the redox stratification with oxic shallow water and anoxic even euxinic deeper water in the early cambrian yangtze sea which gradually became completely oxygenated has been suggested as a possible trigger for the cambrian explosion of biological diversity however for some areas in northern guizhou where the exploration and research are lacking identifying this pattern of redox stratification by paleo environmental analysis from borehole data is still in need here we report a remarkable variation range in trace elements mo v u ni th co sc zn and cu molar corg p ratios and pyrite morphology from 27 core samples from one new drill hole xy1 located in the fenggang area northern guizhou on the yangtze platform south china high levels of ba from 3242 ppm to 33 800 ppm and total organic carbon toc from 4 to 9 36 in 15 core samples in the lower member lm of the niutitang formation indicated elevated primary productivity in the study area redox change was recorded based on enrichment factors efs for rstes mo u and v redox proxies v v ni ni co v sc and th u corg p ratios and particle size of framboidal pyrite these signatures demonstrate that the lm was deposited under anoxic conditions with sulfidic episodes whereas the upper member um of the niutitang formation was deposited under suboxic oxic conditions with intermittently anoxic episodes mo toc ratios from 3 72 to 39 86 mean 18 76 suggest weak moderate water mass restriction mo u covariation patterns strong but variable enrichment of mo and u moef ranging from 31 45 to 257 97 uef ranging from 4 68 to 39 07 in the lm show alternation of particulate shuttling and redox conditions occurred in the early cambrian yangtze sea whereas mo u covariation patterns moderate mo enrichment but depletion or non enrichment of u mean moef 7 29 mean uef 0 95 in the um may indicate the combined influence of particulate shuttling and diagenetic diffusion of u via bioactivities which result in low u values and an anoxic signature from frambiodal pyrite particle size mean 4 556 m median 4 41 m additionally excess ba baxs concentration 33 800 ppm and 32 500 ppm and association patterns of trace metal enrichment in the lm indicate the existence of submarine hydrothermal events in addition during deposition of the um bioactivities indicated by mo u systematics and oxic conditions indicated by redox sensitive trace elements rstes and multiple proxies may be a cause of biological diversification recorded in the early cambrian finally data in this record a progressive transition from anoxic bottom waters with euxinic episodes to overwhelming oxic conditions during early cambrian

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

the onshore surge of marine air into the pacific northwest a coastal region of complex terrain abstract many coastal locations around the world experience rapid transitions from warm dry continental air to cool moist marine air these onshore pushes or surges of marine air can be accompanied by strong winds large temperature drops and a substantial increase in low clouds a detailed case study of a typical pacific northwest event as well as a composite of several events are presented it is shown that all major surges are initiated by synoptic scale changes and that the mesoscale topography of the region amplifies the synoptic signal annual monthly and diurnal climatologies are discussed this paper also discusses the origin of associated west coast phenomena such as heat troughs and narrow coastal pressure ridges

spatiotemporal evolution and causes of marine euxinia in the early cambrian nanhua basin south china abstract marine redox conditions and their dynamic variations in the early cambrian are thought to have strongly influenced the evolution of early animals however the patterns and mechanisms of contemporaneous marine redox variation remain poorly understood the nanhua basin south china was a failed rift basin located between the yangtze block nw margin and cathaysia block se margin in the early cambrian in this study we conducted a comprehensive study of marine redox conditions sulfur cycling and chemical weathering intensity of source areas for the lower cambrian shales of the qingxi formation in the basinal shimensuidao section which was geographically close to the cathaysia block we integrated these results with previously published data from the nearby silikou section as well as the coeval inner shelf xiaotan upper slope daotuo lower slope longbizui and basinal zhalagou sections where were closer to the yangtze block at shimensuidao iron species and redox sensitive trace element data suggest dominantly euxinic conditions for the organic rich black shale interval lower member lm and variable redox conditions oxic ferruginous euxinic for the overlying organic lean shales upper member um of the qingxi formation integrated redox results show a similar lessening of euxinic conditions from lm to um across the entire basin and that euxinia developed along both the yangtze and cathaysia basin margins but it was mainly in upper slope areas e g daotuo on the yangtze margin and reached basinal areas e g silikou and shimensuidao on the cathaysia margin a decline of 34spy from lm to um was observed at shimensuidao and other sections which can be explained by decreasing microbial sulfate reduction rates due to decreasing organic availability and increasing riverine sulfate flux at study sections lower 34spy values in shallow marine relative to deep marine areas suggest increased terrestrial sulfate availability to the shallower sites chemical index of alteration cia values at shimensuidao are uniformly high for both the lm ciacorr1 82 5 0 4 ciacorr2 88 6 0 5 and um ciacorr1 80 2 2 3 ciacorr2 86 2 2 5 compared with the low to moderate values at daotuo ciacorr2 61 9 3 9 for lm 71 3 4 8 for um this pattern is consistent with intense chemical weathering of source areas on the cathaysia block and weaker chemical weathering of source areas on the yangtze block based on these observations we propose that strong chemical weathering of the cathaysia block led to regionally high terrigenous sulfate fluxes resulting in expansion of mid depth euxinia into deep basinal areas on the cathaysia margin of the nanhua basin in contrast weak chemical weathering of the yangtze block yielded lower terrigenous sulfate fluxes limiting euxinia to upper slope areas on the yangtze margin of the basin weaker euxinia during um deposition may have been due to its decreasing organic availability and or small seawater sulfate reservoir caused by persistent euxinic consumption during lm deposition our results highlight the complex controls and the key role of continental weathering and resulting terrigenous sulfate fluxes in marine euxinic variations in early cambrian marginal seas providing new insights into the co evolution of continents oceans and early animals

the west coast thermal trough climatology and synoptic evolution abstractalthough the west coast thermal trough wctt is the most important mesoscale feature over the u s west coast during the warm season its initiation evolution and structure are not well understood originating in the southwest united states this inverted trough can extend northward into oregon washington and british columbia with large impacts on temperature wind humidity and air quality using ncep s north american regional reanalysis narr annual and diurnal climatologies of wctts reaching the northwest united states were constructed for the entire year wctts are most frequent along the coast near the california oregon border with weaker maxima west of the cascade and coastal mountains over the coastal region they occur most often during autumn while east of the cascade mountains the highest frequency is during summer there is strong diurnal variability in wctt frequency during the summer with little diurnal variation in winter though compositing revealed important seasonal d

biostratigraphy of the vendian cambrian beds and the lower cambrian boundary in siberia general agreement exists that the position of the base of the cambrian precambrian cambrian boundary should coincide with a biostratigraphic marker that can be widely traced and is linked to the evolution of the small shelly fauna on the siberian platform the presence of distinct facies during the vendian cambrian interval has made biostratigraphic correlation based on palaeontological data highly contentious a solution to this problem appears to exist with the recognition of an almost uninterrupted profile in the aldan uchur watershed where key sections expose the eastern and transitional facial region on this basis we present a general biostratigraphic scheme for the vendian cambrian across the southern siberian platform that connects separate facies further correlation with key sections in northern siberia leads to the recognition of three biostratigraphic zones for the vendian cambrian interval these are anabarites trisulcatus zone purella antiqua zone aldanocyathus sunnaginicus zone the abundance of chinese type small shelly fossils in the region of the eastern facies suggest correlation of the a sunnaginicus zone with the siphogonuchites paragloborilus zone of china and the p antiqua zone with the circotheca anabarites protohertzina zone in places at the base of the circotheca anabarites protohertzina zone in china analogies to the a trisulcatus zone can be identified it is proposed that in siberia the base of the a sunnaginicus zone base of tommotian stage be taken as the base of the cambrian this would correspond with marker b of the meishucunian in china