fossils or sedimentary structures carbonaceous spheroids from the shale of the cryogenian nantuo formation in shengnongjia area south china abstract black shale of the cryogenian nantuo formation shennongjia area south china contains spheroids which co occur with fossils of macroalgae these three dimensional structures occur sparsely as isolated specimens or abundantly as clusters which show different types of boundaries between individuals they are generally circular on bedding surfaces and elliptical on transecting sections and range up to several millimeters in diameter both petrographic thin sections and scanning electron microscopy sem reveal that these spheroids are mostly organic carbon in composition and exhibit sharp well rounded external margins composed of microcrystalline clay minerals the carbonaceous nature of these spheroids and different elemental abundances between spheroids and matrix are also confirmed by raman spectroscopy and energy dispersive x ray spectroscopy eds organic carbon isotopic values of individual spheroids range from 28 55 to 28 83 with an average of 28 72 which show indistinguishable 13corg values with the surrounding sedimentary matrix but exhibit statistically significant difference to those of contemporaneous macroalgae a range of physical origins for these spheroids including concretions fluid escape structures raindrop impressions or bubble impressions are considered and cannot be entirely rejected alternatively biogenic origin is also a possible interpretation from observations of their morphological mineralogical geochemical and sedimentological characteristics although their nature remains unresolved the documentation of these new carbonaceous spheroids from the nantuo formation of shennongjia area adds to a growing list of fossil like structure records in the cryogenian period

enigmatic origin of the largest known carbon isotope excursion in earth s history carbonate rocks from the middle ediacaran period in locations all over the globe record the largest excursion in carbon isotopic compositions in earth history this finding suggests a dramatic reorganization of earth s carbon cycle named the shuram excursion for its original discovery in the shuram formation oman the anomaly closely precedes impressive events in evolution including the rise of large metazoans and the origin of biomineralization in animals instead of a true record of the carbon cycle at the time of sedimentation the carbon isotope signature recorded in the shuram excursion could be caused by alteration following deposition of the carbonate sediments a scenario supported by several geochemical indicators however such secondary processes are intrinsically local which makes it difficult to explain the coincident occurrence of carbon isotope anomalies in numerous records around the globe both possibilities are intriguing if the shuram excursion preserves a genuine record of ancient seawater chemistry it reflects a perturbation to the carbon cycle that is stronger than any known perturbations of the modern earth if however it represents secondary alteration during burial of sediments then marine sediments must have been globally preconditioned in a unique way to allow ordinary and local processes to produce an extraordinary and widespread response

mid latitude mesoscale variability neither homogeneous quasi geostrophic turbulence nor the effect of eddies on the interior ocean circulation remains the major focus of mesoscale research as was the case for much of the preceding 20 years following identification of the phenomena concentration on basin wide geographical exploration of eddy properties was rather well established by 1978 over the last few years a promising zero order description and rationalization of the mesoscale field has become available that is eddy energy is largest near strong flows intensification not only in western boundary currents but along their mid latitude open ocean extension roughly as indicated by gyre scale numerical models where eddies develop as a result of instability processes in the mid latitude jet and recirculation regimes and then propagate into the ocean interior our point of view is that mesoscale eddies drive recirculations but do not play a crucial role in the dynamics of the mean flow in the ocean interior in the north atlantic for example the idea is that the downstream increase in transport of the gulf stream is eddy driven but not the flow through the florida straits in addition the fluctuating response to forcing by variable winds may now be widely perceived as forming the horizontally homogeneous background signal in subtropical gyres the time dependent field associated with thermohaline flows at abyssal depths also has a special character

raman geothermometry of carbonaceous material in the basal ediacaran doushantuo cap dolostone the thermal history of extremely negative δ13c signatures in the aftermath of the terminal cryogenian snowball earth glaciation abstract extremely negative 13 c values as low as 48 of blocky calcite cements filling cavities sheet cracks and fractures in the basal ediacaran cap dolostone of the doushantuo formation in south china have been considered as evidence for methane release possibly associated with gas hydrate destabilization in the aftermath of the terminal cryogenian snowball earth glaciation alternatively these extremely negative 13 c values may have resulted from oxidation of thermogenic methane derived from localized hydrothermal activity long after the deposition of the doushantuo cap dolostone the latter interpretation was based on carbonate clumped isotope thermometry suggesting that the precipitation of extremely 13 c depleted calcite occurred at temperatures up to 476 c mean 378 c n 4 whereas carbonate fabrics with moderately negative 13 c values generally 10 were formed at much lower temperatures mean 112 c n 4 to assess these competing hypotheses we systematically investigated the petrography carbonate carbon and oxygen isotopes and carbonaceous material cm raman spectroscopy of the doushantuo cap carbonate raman geothermometry suggests that cm associated with different microfabrics and 13 c signatures including sedimentary fabrics with moderately negative 13 c values e g peloids stromatolite laminae microbial mat fragments diagenetic fabrics with moderately negative 13 c values e g some void filling or crack filling cements and diagenetic fabrics with extremely negative 13 c values e g void filling or crack filling blocky and bladed calcites experienced temperatures generally 13 c signatures and paleotemperatures whereas the origins of these extremely negative 13 c values remain unresolved the raman geothermometric data challenge the previous interpretation that they were derived from thermogenic methane related to localized hydrothermal activity at temperatures up to almost 500 c that only affected the thermal history of the calcite with extremely negative 13 c values instead the new data suggest that the analyzed microfabrics experienced the same peak temperatures

new material of the biomineralizing tubular fossil sinotubulites from the late ediacaran dengying formation south china abstract sinotubulites is a late ediacaran biomineralizing tubular fossil with a probable animal affinity it is characterized by millimeter to centimeter sized and multi layered tubes open at both ends the tube consists of two morphologically different walls a multi layered inner wall with weak ornamentations and a multi layered outer wall with transverse or oblique corrugations and sometimes longitudinal ridges the majority of previously published sinotubulites species are considered as synonymous with the type species s baimatuoensis three new species s triangularis n sp s pentacarinalis n sp and s hexagonus n sp are reported from the late ediacaran beiwan member of the dengying formation in southern shaanxi province south china the three new species are similar to the type species in having nested multilayered inner and outer tube walls however they are different in their polygonal cross sections and longitudinal ridges s baimatuoensis is more or less circular in cross section and lack longitudinal ridges on the outer tube wall whereas s triangularis s pentacarinalis and s hexagonus are respectively triangular pentagonal and hexagonal in cross section with three five and six longitudinal ridges on the exterior surface of the outer wall the new material adds to the diversity of late ediacaran biomineralizing animals the triradial pentaradial and hexaradial tubes of s triangularis s pentacarinalis and s hexagonus share some intriguing similarities in body symmetry with several early cambrian tubular fossils although these cambrian tubes are not open at both ends still it would be interesting to explore the tantalizing possibility of evolutionary continuity of triradial pentaradial and hexaradial tubular animals across the precambrian cambrian boundary

using sims to decode noisy stratigraphic δ13c variations in ediacaran carbonates abstract carbonate carbon isotope 13ccarb chemostratigraphy is a valuable tool in precambrian stratigraphic correlation the effectiveness of this tool rests on the assumption that 13ccarb data record global seawater signals however in some cases 13ccarb data exhibit rapid and noisy stratigraphic variations that may have been influenced by authigenic or diagenetic carbonate minerals to assess the contribution of non primary minerals towards bulk carbonate carbon isotope values we acquired sims secondary ion mass spectrometry 13ccarb data electron microscopic data and cl cathodoluminescence microscopic data from two ediacaran successions the lower member ii of the doushantuo formation in south china and the mooifontein member of the zaris formation in southern namibia the doushantuo samples came from a stratigraphic interval with noisy meter scale 13ccarb variations of up to 10 whereas the mooifontein member is characterized by consistent 13ccarb values with limited meter scale variations of less than 4 our data show that the meter scale stratigraphic variations in 13ccarb are also mirrored in the sims data at m mm scales in both doushantuo and mooifontein samples in the doushantuo samples sims 13ccarb values of authigenic calcite vary by up to 10 over m mm scales and can be either higher or lower than those of the co existing dolomite matrix which also appears to be affected by authigenic carbonate on the basis of petrographic observation bulk sample 13ccarb values measured on powders microdrilled from the same sims specimens are within the range of sims 13ccarb values thus we infer that bulk sample 13ccarb values of doushantuo samples represent mixtures of different carbonate components the doushantuo and mooifontein sims 13ccarb data validate the traditional method of using chemostratigraphic consistency to evaluate authigenic diagenetic alteration but given that secondary phases may be 13c enriched relative to matrix carbonate caution is warranted when taking maximum values to approximate primary chemostratigraphic trends

petrographic and sims pyrite sulfur isotope analyses of ediacaran chert nodules implications for microbial processes in pyrite rim formation silicification and exceptional fossil preservation abstract the lower ediacaran doushantuo formation in the yangtze gorges area contains exceptionally preserved microfossils including the earliest known animal resting eggs and embryos these fossils are preserved in cm sized chert nodules which typically have a microbial mat fragment in the center a silica cortex a pyrite rim and an outer rim of blocky calcite petrographic analysis indicates that the formation of the blocky calcite rim postdates that of the pyrite rim and silica cortex the pyrite rim grew centripetally during early diagenesis representing a reaction front that was determined by the dynamics between ambient fe2 and h2s the latter of which was derived from bacterial sulfate reduction bsr of mat fragment in nodule center the silica cortex was formed pervasively through replacement of carbonate sediments prior to compaction secondary ion mass spectroscopy sims sulfur isotopes of individual pyrite crystals 34spy sims in pyrite rims and matrices show highly positive values 15 2 39 8 the pyrite rims do not show an isotopic gradient between small crystals formed in outer rim during early diagenesis and large crystals formed in inner rim during subsequent overgrowth although rim pyrite in the same chert nodule has consistent 34spy sims values there are significant spatial and stratigraphic variations in 34spy sims values of both matrix and rim pyrite overall isotopic fractionation between pyrite and carbonate associated sulfate cas is small

high rate injection is associated with the increase in u s mid continent seismicity an unprecedented increase in earthquakes in the u s mid continent began in 2009 many of these earthquakes have been documented as induced by wastewater injection we examine the relationship between wastewater injection and u s mid continent seismicity using a newly assembled injection well database for the central and eastern united states we find that the entire increase in earthquake rate is associated with fluid injection wells high rate injection wells 300 000 barrels per month are much more likely to be associated with earthquakes than lower rate wells at the scale of our study a well s cumulative injected volume monthly wellhead pressure depth and proximity to crystalline basement do not strongly correlate with earthquake association managing injection rates may be a useful tool to minimize the likelihood of induced earthquakes

new biostratigraphic and chemostratigraphic data from the ediacaran doushantuo formation in intra shelf and upper slope facies of the yangtze platform implications for biozonation of acanthomorphic acritarchs in south china abstract carbon isotopic and microfossil records of the doushantuo formation in south china provide a valuable window onto major perturbations of the ediacaran carbon cycle and the evolution of morphologically complex acanthomorphic acritarchs both records exhibit significant geographic heterogeneity related to environmental taphonomic and diagenetic variations absolute 13 c carb values vary by as much as 10 between sections of the doushantuo formation the geographic and stratigraphic distribution of microfossils in the doushantuo formation is controlled by the occurrence of early diagenetic cherts and phosphorites that preserve microfossils early diagenetic cherts of the doushantuo formation have been investigated extensively at intra shelf sections around the huangling anticline but have been poorly documented elsewhere in south china here we present new petrographic and micropaleontological data from three doushantuo sections to the south of the huangling anticline including the wangzishi and huangjiaping sections representing intra shelf settings as well as the siduping section representing an upper slope setting we also present 13 c carb data from wangzishi petrographic observations indicate that some chert nodules at siduping were formed in situ whereas others were reworked and probably transported from the outer shelf along with olistostromes integrated lithostratigraphic and chemostratigraphic correlations suggest that the fossiliferous intervals at the three studied sections belong to the lower doushantuo formation the new micropaleontological data extend the geographic range of ediacaran acanthomorphs and suggest that elements of the tanarium conoideum hocosphaeridium scaberfacium hocosphaeridium anozos biozone recognized in the upper doushantuo formation around the huangling anticline specifically hocosphaeridium anozos and urasphaera nupta are also present in the lower doushantuo formation at the siduping section the data suggest that the first appearance of hocosphaeridium anozos may be in the 13 c carb chemostratigraphic feature ep1 and it is necessary to revise the acritarch biozonation developed in the yangtze gorges area this study highlights the importance of integrating 13 c carb chemostratigraphic and acritarch biostratigraphic data from multiple facies to develop ediacaran acanthomorph biozonation in south china and beyond

a new modular palaeopascichnid fossil curviacus ediacaranus new genus and species from the ediacaran dengying formation in the yangtze gorges area of south china non biomineralizing ediacaran macrofossils are rare in carbonate facies but they offer valuable information about their three dimensional internal anatomy and can broaden our view about their taphonomy and palaeoecology in this study we report a new ediacaran fossil curviacus ediacaranus new genus and species from bituminous limestone of the shibantan member of the dengying formation in the yangtze gorges area of south china curviacus is reconstructed as a benthic modular organism consisting of serially arranged and crescent shaped chambers the chambers are confined by chamber walls that are replicated by calcispars and are filled by micritic sediments such modular body construction is broadly similar to the co occurring yangtziramulus zhangii and other ediacaran modular fossils such as palaeopascichnus the preservation style of curviacus is similar to yangtziramulus although the phylogenetic affinities of both genera remain unresolved the new fossil adds to the diversity of ediacaran modular organisms

affirming life aquatic for the ediacara biota in china and australia the ediacara biota has been long championed as a snapshot of the marine ecosystem on the eve of the cambrian explosion providing important insights into the early evolution of animals fossiliferous beds in the eponymous ediacara member of south australia have been recently reinterpreted as paleosols and ediacara fossils as lichens or microbial colonies that lived on terrestrial soils this reinterpretation here dubbed the terrestrial ediacara hypothesis would fundamentally change our views of biological evolution just prior to the cambrian explosion we take a comparative paleobiology approach to test this hypothesis the ediacara member shares a number of forms with assemblages in ediacaran marine black shales in south china shales that show no evidence of pedogenesis thus the shared ediacara fossils and by extension other co occurring fossils are unlikely to have been terrestrial organisms a terrestrial interpretation is also inconsistent with functional morphological evidence some of the shared forms are not morphologically adapted to address the most critical challenges for terrestrial life e g mechanical support and desiccation thus the terrestrial ediacara hypothesis can be falsified on comparative paleobiological and functional morphological grounds and we urge paleopedologists to critically reevaluate evidence for pedogenesis in the ediacara member and other ediacaran successions

increasing seismicity in the u s midcontinent implications for earthquake hazard abstract earthquake activity in parts of the central united states has increased dramatically in recent years the space time distribution of the increased seismicity as well as numerous published case studies indicates that the increase is of anthropogenic origin principally driven by injection of wastewater coproduced with oil and gas from tight formations enhanced oil recovery and long term production also contribute to seismicity at a few locations preliminary hazard models indicate that areas experiencing the highest rate of earthquakes in 2014 have a short term one year hazard comparable to or higher than the hazard in the source region of tectonic earthquakes in the new madrid and charleston seismic zones

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

redox dependent distribution of early macro organisms evidence from the terminal ediacaran khatyspyt formation in arctic siberia abstract the ediacaran period witnessed the first appearance of macroscopic animal life in earth s history however the biogeochemical context for the stratigraphic occurrence of early metazoans is largely uncertain in part due to the dearth of integrated paleobiological and chemostratigraphic datasets in this study a comprehensive geochemical analysis was conducted on the fossiliferous khatyspyt formation in arctic siberia in order to gain insights into the ediacaran paleoenvironments this study was designed to specifically address the relationship between paleoredox conditions and ediacaran fossil occurrences in the khatyspyt formation our data reveal a dramatic shift in pyrite sulfur isotope compositions 34 s pyrite from ca 20 to ca 55 and this shift is intriguingly associated with the first occurrence of ediacara type macrofossils at the studied section suggesting a possible link between seawater redox conditions and distribution of early macroscopic organisms based on multiple lines of sedimentological and geochemical evidence we propose that the development of oceanic euxinia which may be widespread in the continental margins due to enhanced oxidative weathering in the terminal ediacaran period may have locally prohibited the colonization of ediacara type organisms and resulted in low 34 s pyrite values in the lower khatyspyt formation in the middle and upper khatyspyt formation progressive secular transition from euxinic to non euxinic and more habitable conditions may have allowed for the colonization of ediacara type and other macro organisms

probabilistic assessment of potential fault slip related to injection induced earthquakes application to north central oklahoma usa we utilize quantitative risk assessment qra to calculate the conditional probability of slip on mapped faults in response to injection related increases in pore pressure in north central oklahoma usa where widespread injection of produced saltwater has triggered thousands of small to medium sized earthquakes in the past 7 yr the conditional probability incorporates the uncertainty in each mohr coulomb parameter stress tensor pore pressure coefficient of friction and fault orientation through qra the result is a cumulative distribution function of the pore pressure required to cause slip on each fault segment the results can be used to assess the probability of induced slip on a known fault from a given injection related pore pressure increase after dividing north central oklahoma into six study areas we invert earthquake focal plane mechanisms in each area to constrain the orientation and relative magnitude of the principal stresses the qra identifies the potential for slip on the fault that produced the m 5 6 prague earthquake in 2011 and the northeastern extension of a mapped fault associated with the m 5 1 fairview earthquake sequence that occurred in early 2016 and had the 289 striking fault of the september 2016 m 5 8 pawnee event been mapped it would have been identified as potentially active

the biostratigraphic succession of acanthomorphic acritarchs of the ediacaran doushantuo formation in the yangtze gorges area south china and its biostratigraphic correlation with australia abstract abundant large acanthomorphic acritarchs from the ediacaran doushantuo formation in the yangtze gorges area south china are becoming useful tools for biostratigraphic subdivision and correlation of the ediacaran system despite limitations caused by facies control taphonomic bias and taxonomic problems based on thin section examination of chert samples collected from six sections of the doushantuo formation a clear stratigraphic distribution of acritarchs has allowed two assemblages of acanthomorphic acritarchs lower tianzhushania spinosa assemblage and upper tanarium anozos tanarium conoideum assemblage to be established these two assemblages which are found in the lower member ii and the upper member iii doushantuo formation respectively are constrained stratigraphically to the first and the second positive 13c excursions ep1 and ep2 respectively and are separated by a second negative 13c excursion en2 the lower t spinosa assemblage is dominated by the taxon t spinosa by comparison with the lower assemblage the upper t anozos t conoideum assemblage preserves more acanthomorphic acritarchs both in terms of number of individuals and in the diversity of the forms fifteen forms eotylotopalla delicata knollisphaeridium maximum echinosphaeridium maximum meghystrichosphaeridium magnificum schizofusa zangwenlongii sinosphaera rupina t anozos t conoideum tanarium irregulare variomargosphaeridium litoschum as well as the unnamed b c d e f and g forms are the predominant species in upper t anozos t conoideum assemblage among them the taxa t anozos and t conoideum occur in most great number and throughout the assemblage whereas the species t spinosa is presumed to have become extinct the upper t anozos t conoideum assemblage shares a number of species with the ediacaran complex acritarch palynoflora ecap in south and central australia including ceratosphaeridium glaberosum gyalosphaeridium pulchrum s zangwenlongii t conoideum t irregulare and v litoschum in addition the species t spinosa is not present in the ecap of australia hence the upper t anozos t conoideum assemblage of the doushantuo formation can be correlated with the ecap of south and central australia while the lower tianzhushania assemblage appears to be missing in south and central australia

methane derived authigenic carbonate from the lower doushantuo formation of south china implications for seawater sulfate concentration and global carbon cycle in the early ediacaran ocean authigenic carbonate associated with anaerobic oxidation of methane aom usually via microbial sulfate reduction msr or ferric iron reduction is generally characterized by extremely low 13c values 30 vpdb this has been used as one of the major diagnostic features for the recognition of hydrocarbon seep carbonate in the geological past previous reports on precambrian authigenic carbonates are rare limiting our understanding of the effects of their deposition on the earth s carbon isotopic mass balance in this study mainly based on petrographic features and pronounced negative 13c values as low as 38 1 we discovered authigenic calcite cement immediately above the cap dolostone in the basal ediacaran doushantuo formation in the jiulongwan section yangtze gorges area south china our observations not only provide direct evidence for the involvement of aom during carbonate precipitation in the early ediacaran 635 ma but also suggest that the seawater sulfate concentrations in the early ediacaran may have been higher than previously thought

the 2016 mw5 1 fairview oklahoma earthquakes evidence for long range poroelastic triggering at 40 km from fluid disposal wells abstract wastewater disposal in the central u s is likely responsible for an unprecedented surge in earthquake activity much of this activity is thought to be driven by induced pore pressure changes and slip on pre stressed faults which requires a hydraulic connection between faults and injection wells however direct pressure effects and hydraulic connectivity are questionable for earthquakes located at large distances and depths from the injectors here we examine triggering mechanisms of induced earthquakes which occurred at more than 40 km from wastewater disposal wells in the greater fairview region northwest oklahoma employing numerical and semi analytical poroelastic models the region exhibited few earthquakes before 2013 when background seismicity started to accelerate rapidly culminating in the mw5 1 fairview earthquake in february 2016 injection rates in the 2 2 5 km deep arbuckle formation started to increase rapidly in 2012 about two years before the start of seismicity increase most of the injection activity was concentrated toward the northeast of the study region generating a relatively cohesive zone of pressure perturbations between 0 1 and 1 mpa much of the near injection seismicity was likely triggered by pressure effects and fault assisted pressure diffusion to seismogenic depth outside of the high pressure zone we observed two remarkably detached linear seismicity clusters which occurred at 20 to 50 km distance from the initial seismicity and 10 to 40 km from the nearest high rate injector semi analytical models reveal that poroelastically induced coulomb stress changes surpass pore pressure changes at these distances providing a plausible triggering mechanism in the far field of injection wells these results indicate that both pore pressures and poroelastic stresses can play a significant role in triggering deep and distant earthquakes by fluid injection and should be considered for seismic hazard assessment beyond the targeted reservoir

estimates of the geostrophic stream function in the western north pacific from xbt surveys the upper ocean temperature and dynamic height fields are correlated in the western north pacific ocean this relationship can be used to map a relative geostrophic stream function of the kuroshio extension using temperature data from expendable bathythermograph xbt surveys we have examined the ability of the north pacific ship of opportunity xbt program known as transpac to carry out this procedure estimates of 600 1200 dbar geostrophic shear were generated from the xbt data utilizing objective mapping techniques these estimates were compared with measured currents at 600 m relative to 1200 m along 152 e from 27 n to 42 n the estimated and measured relative currents are positively correlated with an rms error of 6 cm s over a measured dynamic range of 30 cm s however the xbt estimated shears consistently underestimate the measured values by a factor of 2 to 3 the underestimate of the amplitude is the result of both undersampling and mapping produres that eliminate high wavenumber contributions of the dynamic height variability these factors appear to be responsible for previous differences in amplitude between directly measured and transpac xbt estimated values of relative eddy kinetic energy and reynolds stress the transpac xbt survey can only monitor qualitatively the dynamic topography of the kuroshio extension meanders and rings the variability outside of the extension with a temperature range of 3 c cannot be resolved because of inaccuracies in the temperature dynamic height relationship to monitor the kuroshio extension variability in the future it is recommended that transpac xbt resources in the western north pacific concentrate on obtaining a denser sample of the field during the fall and winter seasons because of incomplete ship track coverage in spring and summer

the use of earthquake rate changes as a stress meter at kilauea volcano stress changes in the earth s crust are generally estimated from model calculations that use near surface deformation as an observational constraint but the widespread correlation of changes of earthquake activity with stress has led to suggestions that stress changes might be calculated from earthquake occurrence rates obtained from seismicity catalogues although this possibility has considerable appeal because seismicity data are routinely collected and have good spatial and temporal resolution the method has not yet proven successful owing to the non linearity of earthquake rate changes with respect to both stress and time here however we present two methods for inverting earthquake rate data to infer stress changes using a formulation for the stress and time dependence of earthquake rates application of these methods at kilauea volcano in hawaii yields good agreement with independent estimates indicating that earthquake rates can provide a practical remote sensing stress meter

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

revised neoproterozoic and terreneuvian stratigraphy of the lena anabar basin and north western slope of the olenek uplift siberian platform abstract the early to mid neoproterozoic pre glacial sedimentary succession of the lena anabar basin northeast siberian platform records protracted faulting and subsidence possibly as part of the widespread continental rifting and the break up of rodinia there is a significant stratigraphic unconformity separating the pre glacial neoproterozoic strata and the overlying upper ediacaran succession in the lena anabar basin with the terreneuvian strata most likely to be deposited in a foreland of the central taimyr accretionary belt the cryogenian sensu strictum i e younger than 720 ma and lower ediacaran deposits are missing in the area in this study we assess the palaeontological content of the precambrian and terreneuvian strata of the lena anabar basin and the adjacent north western slope of the olenek uplift and revise the chronostratigraphy of the region with special emphasis to biostratigraphic index taxa for the pre glacial neoproterozoic section we establish the new tukulan kulady taimylyr formations and redefine the khastakh formation we also refine the ediacaran and terreneuvian stratigraphy by formalising the maastakh khatyspyt and turkut formations of the khorbusuonka group whereas the kessyusa formation is raised to group rank and subdivided into the syhargalakh oppokun mattaia and chuskuna formations the proposed stratigraphic correlation scheme is based upon depositional unity and is consistent both lithologically and biostratigraphically providing a robust framework for future stratigraphic sedimentological and palaeobiological studies

acanthomorphic acritarchs of the doushantuo formation from an upper slope section in northwestern hunan province south china with implications for early middle ediacaran biostratigraphy abstract doushantuo pertatataka acritarchs dpas are abundant and well preserved in the ediacaran doushantuo formation in south china not only do they provide insights into the marine ecosystem immediately after a neoproterozoic global glaciation they also afford us an ideal tool for ediacaran stratigraphic subdivision and correlation however previous reports of dpas in south china are mostly from the yangtze gorges area in intra shelf basin and from weng an in shelf margin environments while data from localities in slope and basinal facies are lacking here we present lithostratigraphy carbon and strontium isotope chemostratigraphy and acritarch biostratigraphy of the doushantuo formation from an upper slope section at lujiayuanzi in northwestern hunan province south china five dpa genera and eight species are preserved in the doushantuo formation chert nodules with the uppermost two dpa horizons occurring above a 13 c negative excursion that is correlated with the en3 shuram excursion based on integrated litho and chemostratigraphic correlation our new findings reveal a broader temporal and spatial distribution of dpas in south china and further support their biostratigraphic potential in the early middle ediacaran subdivision and correlation

beyond the stony veil reconstructing the earth s earliest large animal traces via computed tomography x ray imaging abstract trace fossils are superb lines of evidence for examining the ancient biologic world because they offer an opportunity to infer behavioral ecology of organisms however traces can be difficult to parse from their matrix which leads to the loss of important morphological and behavioral data this is especially true for the earliest marine animal traces from the ediacaran period 635 541 ma which are usually small

carbonate hosted avalon type fossils in arctic siberia avalon type fossils are crucial to understanding the origin of phanerozoic ecosystems but their usual occurrence in volcaniclastic and siliciclastic facies greatly limits their paleobiological resolution the unique carbonate hosted assemblage of the khatyspyt formation on the olenek uplift of north central siberia promises a much enhanced anatomical and paleo ecological view of these enigmatic organisms avalon type fossils are preserved by authigenic carbonate cementation in intervals of finely laminated nodular limestones khatyspyt type taphonomic window interbedded silicified calcareous mudstones yield diverse carbonaceous compressions occasionally with taphonomic phantoms of avalon type taxa miaohe type taphonomic window styles of moldic preservation do not appear to be taxon selective and therefore cannot alone be responsible for the morphological distinctiveness of ediacaran macrofossils and the profound disparity in the taxonomic composition between fossil assemblages on the other hand the exclusion of avalon type fossils from carbonaceous compressions miaohe type preservational window is a real taphonomic signal that provides an important constraint on the properties of certain ediacaran tissues

a comparison of the mid latitude eddy fields in the western north atlantic and north pacific oceans abstract latitudinal distributions of estimates of eddy kinetic energy and off diagonal component of the horizontal reynolds stresses are demonstrated to have similar shapes at corresponding generally western locations but at much different depths in the mid latitude north atlantic and north pacific oceans this comparison is based on direct current measurements at abyssal depths in the north atlantic along 55 w and on indirect estimates of upper level velocity differences in the vertical for the north pacific between the izu or izu ogasawara or south honshu ridge and the shatsky rise these sections span the more energetic segments of the kuroshio extension and gulf stream systems

stable carbon isotopes of sedimentary kerogens and carbonaceous macrofossils from the ediacaran miaohe member in south china implications for stratigraphic correlation and sources of sedimentary organic carbon abstract ediacaran stratigraphic correlation depends on the integration of paleontological and 13ccarb data however these data often come from different lithologies e g shales vs carbonates making it difficult to directly link biostratigraphic and chemostratigraphic markers ediacaran successions in south china consist of mixed carbonates and shales offering an opportunity for integrated biostratigraphic and chemostratigraphic investigations black shales of the ediacaran miaohe member in the yangtze gorges area contain macroalgae and ediacara type macrofossils both preserved as carbonaceous compressions the miaohe member has been traditionally regarded as an equivalent to member iv of the uppermost doushantuo formation that records part of the shuram negative 13ccarb excursion in south china thus the miaohe member may have the potential to clarify the stratigraphic relationship between ediacara type fossils and the shuram excursion recently however the miaohe member has been partially correlated with the shibantan member of the dengying formation the a correlation or partially with member iv the z correlation these correlations have different implications for the relationship between the miaohe member and the shuram excursion here we test these two correlations using 13c data of sedimentary kerogen or total organic carbon 13corgtoc taking advantage of the distinct 13corgtoc values between the shibantan member and member iv our data show that 13corgtoc of the miaohe member is more similar to that of member iv than to shibantan member providing tentative support for the z correlation in addition we also analyzed 13corg of individual carbonaceous compression fossils 13corgtaxon which have lower carbon isotope values than toc the data suggest that oxygenic photosynthesizers e g macroalgae cyanobacteria and eukaryotic phytoplankton were not the only contributors to sedimentary toc methylotrophs photoautotrophs and chemoautotrophs living in anoxic waters or at the oxycline may have fixed recycled co2 derived from organic carbon remineralization thus contributing a significant amount of 13c depleted organic carbon to sedimentary kerogen in the miaohe member

trace fossil evidence for ediacaran bilaterian animals with complex behaviors abstract distinguishing ediacaran trace fossils from tubular body fossils can be a challenge and several ediacaran fossils previously interpreted as animal traces have been shown to be tubular body fossils nonetheless true ediacaran trace fossils are present but they are relatively few and morphologically simple dominated by horizontal trails and shallow burrows such simple morphologies have been taken as evidence for a modest behavioral complexity and limited geobiological impact of animal bioturbators before the cambrian explosion here we report three types of trace fossils horizontal tunnels surface tracks trails and vertical traces from the latest ediacaran dengying formation 551 541 ma in the yangtze gorges area of south china cross cutting tunnels and the presence of scratch marks indicate that these traces are unlikely tubular body fossils instead these three types of traces likely represent animal activities related to under mat feeding epibenthic locomotion and temporary dwelling respectively we show that these three types of traces were constructed by the same bilaterian animals that had moderately complex interactions with microbial mats to exploit nutrients and o 2 resources these animals heralded a new age in ecosystem engineering animal sediment interaction and biogeochemical cycling

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

estimation of intraplate strain accumulation in the new madrid seismic zone from repeat gps surveys the new madrid seismic zone nmsz a region within the eastern portion of the north american plate where great earthquakes occurred in 1811 1812 provides a type example of large earthquakes within a relatively stable continental interior assessing the scale and causes of deformation in such regions as well estimation of the recurrence interval for the large earthquakes within them has long been recognized as an important but challenging issue for which the advent of space based geodesy provides an important new tool here we report initial results from two global positioning system gps surveys of a geodetic network spanning the new madrid seismic zone because the expected strain signal is small the data were analyzed in three different ways first site velocities were estimated and analyzed for spatial gradients parallel and perpendicular to the trend of the major strike slip faults inferred from seismicity this analysis suggests but does not require a few millimeters per year of right lateral shear across the southern portion of the seismic zone consistent with the earthquake focal mechanisms second we divided the network into near field subnetworks and found possibly significant shear associated with approximately e w shortening within the southern nmsz and possible n s shortening across the left step connecting the presumed strike slip faults third we compared the strain observed along individual baselines to that predicted from the results of earlier near field surveys which combined gps and triangulation data in the southern part of the seismic zone we found general agreement with the earlier study although our data suggest lower strain rates hence after only 2 years of measurements the gps data suggest but do not yet require detectable strain accumulation however given that great earthquakes occur in the area and that our results are reasonably consistent with the results of other geodetic studies using different data and with earthquake mechanisms it seems likely that we are seeing strain accumulation in the southern nmsz a simple interpretation of the data as showing about 3 to 5 mm yr 1 of right lateral fault parallel motion implies a 1000 to 3300 year recurrence for great earthquakes with 5 to 10 m slip assuming all the accumulating strain is released seismically this recurrence interval may be an underestimate if the observed strains are largely postseismic effects of the 1811 1812 earthquakes a possibility suggested by the observation that plate wide data show less motion across the nmsz future surveys should resolve this issue as the longer measurement spans yield more precise velocity estimates

aftershocks halted by static stress shadows the role of permanent versus transient crustal stress changes in triggering earthquakes is debated analysis of the stress imparted by the joshua tree and nearby landers earthquakes in california in 1992 implies that a permanent drop in stress can halt aftershocks so such static stress changes should be incorporated into seismic hazard assessments

triggered earthquakes suppressed by an evolving stress shadow from a propagating dyke the role of static versus dynamic stresses in earthquake clusters is unclear analysis of earthquakes triggered by a dyke intrusion at an icelandic volcano unambiguously demonstrates that static stresses are important for earthquake clustering large earthquakes can generate small changes in static stress increases that trigger aftershock swarms or reductions that create a region of reduced seismicity a stress shadow1 2 however seismic waves from large earthquakes also cause transient dynamic stresses that may trigger seismicity3 4 this makes it difficult to separate the relative influence of static and dynamic stress changes on aftershocks dyke intrusions do not generate dynamic stresses so provide an unambiguous test of the stress shadow hypothesis here we use gps and seismic data to reconstruct the intrusion of an igneous dyke that is 46 km long and 5 m wide beneath bar arbunga volcano central iceland in august 2014 we find that during dyke emplacement bursts of seismicity at a distance of 5 to 15 km were first triggered and then abruptly switched off as the dyke tip propagated away from the volcano we calculate the evolving static stress changes during dyke propagation and show that the stressing rate controls both the triggering and then suppression of earthquake rates in three separate areas adjacent to the dyke our results imply that static stress changes help control earthquake clustering similar small static stress changes may be important for triggering seismicity near geothermal areas regions being hydrofractured and deflating oil and gas fields

evaluation of ground motion models for usgs seismic hazard forecasts induced and tectonic earthquakes in the central and eastern united statesevaluation of gmms for usgs seismic hazard forecasts

eddy momentum flux and its contribution to the southern ocean momentum balance a large amount of momentum is transferred to the southern ocean by strong westerly winds analytical and numerical models have suggested that transient eddies may be important in transporting this momentum away from the region of wind forcing either horizontally1or vertically downwards where it is balanced by bottom topographic drag2 5 there are however few long term in situ observations of horizontal eddy momentum flux6 8 and no large scale measurements of vertical eddy fluxes to test these models as a result the momentum balance of the antarctic circumpolar current acc remains uncertain and the role of eddies controversial here we use geosat satellite altimeter data to resolve directional eddy kinetic energy and horizontal eddy momentum flux in the acc on fine spatial and temporal scales the complex spatial distribution of surface eddy momentum flux is strongly influenced by bottom topography the horizontal eddy momentum flux tends generally to concentrate the mean flow although some regions of divergence are observed our results show that the zonally averaged horizontal eddy momentum flux from transient eddies is an order of magnitude too small and in the wrong direction to directly balance the eastward momentum input from wind1

evidence from the ad 2000 izu islands earthquake swarm that stressing rate governs seismicity magma intrusions and eruptions commonly produce abrupt changes in seismicity far from magma conduits that cannot be associated with the diffusion of pore fluids or heat such swarm seismicity also migrates with time and often exhibits a dog bone shaped distribution the largest earthquakes in swarms produce aftershocks that obey an omori type exponential temporal decay but the duration of the aftershock sequences is drastically reduced relative to normal earthquake activity here we use one of the most energetic swarms ever recorded to study the dependence of these properties on the stress imparted by a magma intrusion a 1 000 fold increase in seismicity rate and a 1 000 fold decrease in aftershock duration occurred during the two month long dyke intrusion we find that the seismicity rate is proportional to the calculated stressing rate and that the duration of aftershock sequences is inversely proportional to the stressing rate this behaviour is in accord with a laboratory based rate state constitutive law suggesting an explanation for the occurrence of earthquake swarms any sustained increase in stressing rate whether due to an intrusion extrusion or creep event should produce such seismological behaviour

recent long term moored instrument observations in the western north pacific selected results based on the first deployment duration was 298 324 days depending on specific location of an array of 38 current temperature meters on 10 moorings along 152 e from 28 n to 41 n are discussed abyssal eddy kinetic energies along 152 e near the kuroshio extension are a factor of 2 to possibly 5 lower than those previously observed at similar depths close to the energetic regions of the gulf stream the thermocline kinetic energy frequency distribution at 28 n 152 e is similar in shape to that observed at a site near 31 n 70 w but not 28 n 70 w although the total energy levels are quite different however the distance from the corresponding strong current regimes is nearly the same the largest scale latitudinal distribution of the off diagonal component of horizontal reynolds stress has a characteristic general shape that is negative to the south and positive to the north of the gulf stream or kuroshio extension or mid latitude jet at all depths for all longitudes where such data are available in both oceans and in the numerical experiments examined

organic composition and diagenetic mineralization of microfossils in the ediacaran doushantuo chert nodule by raman and petrographic analyses abstract we studied microfossils and their embedding matrix minerals from chert nodules in the ediacaran doushantuo formation of the yangtze gorges area in south china using raman spectroscopy as well as transmitted and polarized light microscopy the microfossils are composed of organic carbonaceous material with weak structural organization ordering which indicates a low degree of thermal maturation and alteration raman spectral disparity of carbonaceous material among different portions vesicle inclusion of microfossils reveals some differences in organic composition and structure of their precursor biological matters the mineral phases of silica matrix that entombs the microfossils are recognized as opal ct cryptocrystalline quartz and their transitional phases overall raman spectral analyses and petrographic observations document a complete and continuous sequence of silica phase transformation from opal ct to quartz when reconstructing the diagenetic history of sediments and mineralization process of microfossils in a localized microenvironment the silica in pore waters precipitated preferentially at the periphery of microorganisms in the form of opal gradually decreasing in abundance as it transformed into more stable cryptocrystalline quartz the recrystallization took place in cryptocrystalline quartz to form grains authigenic fluorapatite readily precipitated in the vicinity of some microfossils and within their degraded organic fragments while apatite was crystallizing around organisms and their biostructures silica precipitated in the surrounding voids inhibiting the space of potential apatite crystallization the silicification and phosphatization of microfossils occurred in the microbial sulfate reduction msr zone of the sediment column and both were driven by the localized ph change resulting from msr and pyrite precipitation in the microenvironment thus facilitating the exceptional fossil preservation in the doushantuo chert nodules

frictional slip of granite at hydrothermal conditions sliding on faults in much of the continental crust likely occurs at hydrothermal conditions i e at elevated temperature and elevated pressure of aqueous pore fluids yet there have been few relevant laboratory studies to measure the strength sliding behavior and friction constitutive properties of faults at hydrothermal conditions we slid laboratory granite faults containing a layer of granite powder simulated gouge velocity stepping experiments were performed at temperatures of 23 to 600 c pore fluid pressures ph2o of 0 dry and 100 mpa wet effective normal stress of 400 mpa and sliding velocities v of 0 01 to 1 m s 0 32 to 32 m yr conditions were similar to those in earlier tests on dry granite to 845 c by lockner et al 1986 the mechanical results define two regimes the first regime includes dry granite up to at least 845 and wet granite below 250 c in this regime the coefficient of friction is high 0 7 to 0 8 and depends only modestly on temperature slip rate and ph2o the second regime includes wet granite above 350 c in this regime friction decreases considerably with increasing temperature temperature weakening and with decreasing slip rate velocity strengthening these regimes correspond well to those identified in sliding tests on ultrafine quartz we infer that one or more fluid assisted deformation mechanisms are activated in the second hydrothermal regime and operate concurrently with cataclastic flow slip in the first cool and or dry regime is characterized by pervasive shearing and particle size reduction slip in the second hot and wet regime is localized primarily onto narrow shear bands adjacent to the gouge rock interfaces weakness of these boundary shears may result either from an abundance of phyllosilicates preferentially aligned for easy dislocation glide or from a dependence of strength on gouge particle size major features of the granite data set can be fit reasonably well by a rate and temperature dependent three regime friction constitutive model chester this issue we extrapolate the experimental data and model fit in order to estimate steady state shear strength versus depth along natural slipping faults for sliding rates as low as 31 mm yr we do this for two end member cases in the first case pore pressure is assumed hydrostatic at all depths shallow crustal strength in this case is similar to that calculated in previous work from room temperature friction data while at depths below about 9 13 km depending on slip rate strength becomes less sensitive to depth but sensitive to slip rate in the second case pore pressure is assumed to be near lithostatic at depths below 5 km strength is low at all depths in this case 20 mpa in agreement with observations of weak faults such as the san andreas the predicted depth of transition from velocity weakening to velocity strengthening lies at about 13 km depth for a slip rate of 31 mm yr in rough agreement with the seismic aseismic transition depth observed on mature continental faults these results highlight the importance of fluid assisted deformation processes active in faults at depth and the need for laboratory studies on the roles of additional factors such as fluid chemistry large displacements higher concentrations of phyllosilicates and time dependent fault healing

transport driven by eddy momentum fluxes in the gulf stream extension region the importance of the gulf stream extension region in climate and seasonal prediction research is being increasingly recognised here we use satellite derived eddy momentum fluxes to drive a shallow water model for the north atlantic ocean that includes the realistic ocean bottom topography the results show that the eddy momentum fluxes can drive significant transport sufficient to explain the observed increase in transport of the gulf stream following its separation from the coast at cape hatteras as well as the observed recirculation gyres the model also captures recirculating gyres seen in the mean sea surface height field within the north atlantic current system east of the grand banks of newfoundland including a representation of the mann eddy

eight armed ediacara fossil preserved in contrasting taphonomic windows from china and australia we report the preservation of the eight armed ediacara fossil eoandromeda octobrachiata as carbonaceous compressions in the doushantuo black shale of south china and as casts and molds in the rawnsley quartzite in south australia the contrasting preservational styles in two taphonomic windows indicate that e octobrachiata may have had a relatively recalcitrant organic integument which rules out its close comparison with giant agglutinated foraminifers such as xenophyophores its octaradial symmetry and dextrally spiraling arms suggest that it may be a diploblastic grade animal sharing some features with cnidarians and ctenophores although its phylogenetic affinity remains open it is the first and only unambiguously identified ediacaran macrofossil that occurs in two drastically different taphonomic windows thus bridging the conventional biological and taxonomic gaps between the ediacara and miaohe biotas which collectively record the earliest known macroscopic and complex life

hydromechanical controls on the spatiotemporal patterns of injection induced seismicity in different fault architecture implication for 2013 2014 azle earthquakes

activation of optimally and unfavourably oriented faults in a uniform local stress field during the 2011 prague oklahoma sequence the orientations of faults activated relative to the local principal stress directions can provide insights into the role of pore pressure changes in induced earthquake sequences here we examine the 2011 m 5 7 prague earthquake sequence that was induced by nearby wastewater disposal we estimate the local principal compressive stress direction near the rupture as inferred from shear wave splitting measurements at spatial resolutions as small as 750 m we find that the dominant azimuth observed is parallel to previous estimates of the regional compressive stress with some secondary azimuths oriented subparallel to the strike of the major fault structures from an extended catalogue we map ten distinct fault segments activated during the sequence that exhibit a wide array of orientations we assess whether the five near vertical fault planes are optimally oriented to fail in the determined stress field we find that only two of the fault planes including the m 5 7 main shock fault are optimally oriented both the m 4 8 foreshock and m 4 8 aftershock occur on fault planes that deviate 20 29 from the optimal orientation for slip our results confirm that induced event sequences can occur on faults not optimally oriented for failure in the local stress field the results suggest elevated pore fluid pressures likely induced failure along several of the faults activated in the 2011 prague sequence

a long term earthquake rate model for the central and eastern united states from smoothed seismicity abstract i present a long term earthquake rate model for the central and eastern united states from adaptive smoothed seismicity by employing pseudoprospective likelihood testing l test i examined the effects of fixed and adaptive smoothing methods and the effects of catalog duration and composition on the ability of the models to forecast the spatial distribution of recent earthquakes to stabilize the adaptive smoothing method for regions of low seismicity i introduced minor modifications to the way that the adaptive smoothing distances are calculated across all smoothed seismicity models the use of adaptive smoothing and the use of earthquakes from the recent part of the catalog optimizes the likelihood for tests with m 2 7 and m 4 0 earthquake catalogs the smoothed seismicity models optimized by likelihood testing with m 2 7 catalogs also produce the highest likelihood values for m 4 0 likelihood testing thus substantiating the hypothesis that the locations of moderate size earthquakes can be forecast by the locations of smaller earthquakes the likelihood test does not however maximize the fraction of earthquakes that are better forecast than a seismicity rate model with uniform rates in all cells in this regard fixed smoothing models perform better than adaptive smoothing models the preferred model of this study is the adaptive smoothed seismicity model based on its ability to maximize the joint likelihood of predicting the locations of recent small to moderate size earthquakes across eastern north america the preferred rate model delineates 12 regions where the annual rate of m 5 earthquakes exceeds 2 10 3 although these seismic regions have been previously recognized the preferred forecasts are more spatially concentrated than the rates from fixed smoothed seismicity models with rate increases of up to a factor of 10 near clusters of high seismic activity online material figures of minimum magnitude determination b value estimation and maps of earthquake rate and forecasts and tables of optimized neighbor numbers and smoothing distances

uranium and molybdenum isotope evidence for an episode of widespread ocean oxygenation during the late ediacaran period abstract to improve estimates of the extent of ocean oxygenation during the late ediacaran period we measured the u and mo isotope compositions of euxinic anoxic and sulfidic organic rich mudrocks orm of member iv upper doushantuo formation south china the average 238 u of most samples is 0 24 0 16 2sd relative to standard crm145 which is slightly higher than the average 238 u of 0 02 0 12 for restricted black sea deep water unit i euxinic sediments and is similar to a modeled 238 u value of 0 2 for open ocean euxinic sediments in the modern well oxygenated oceans because 238 u is preferentially removed to euxinic sediments compared to 235 u expanded ocean anoxia will deplete seawater of 238 u relative to 235 u ultimately leading to deposition of orm with low 238 u hence the high 238 u of member iv orm points to a common occurrence of extensive ocean oxygenation ca 560 to 551 myr ago the mo isotope composition of sediments deposited from strongly euxinic bottom waters h 2 s aq 11 m either directly records the global seawater mo isotope composition if mo removal from deep waters is quantitative or represents a minimum value for seawater if mo removal is not quantitative near the top of member iv 98 mo approaches the modern seawater value of 2 34 0 10 high 98 mo points to widespread ocean oxygenation because the preferential removal of isotopically light mo to sediments occurs to a greater extent in o 2 rich compared to o 2 deficient marine environments however the 98 mo value for most member iv orm is near 0 relative to standard nist srm 3134 0 25 suggesting extensive anoxia the low 98 mo is at odds with the high mo concentrations of member iv orm which suggest a large seawater mo inventory in well oxygenated oceans and the high 238 u hence we propose that the low 98 mo of most member iv orm was fractionated from contemporaneous seawater possible mechanisms driving this isotope fractionation include 1 inadequate dissolved sulfide for quantitative thiomolybdate formation and capture of a seawater like 98 mo signature in sediments or 2 delivery of isotopically light mo to sediments via a particulate fe mn oxyhydroxide shuttle a compilation of mo isotope data from euxinic orm suggests that there were transient episodes of extensive ocean oxygenation that break up intervals of less oxygenated oceans during late neoproterozoic and early paleozoic time hence member iv does not capture irreversible deep ocean oxygenation instead complex ocean redox variations likely marked the transition from o 2 deficient proterozoic oceans to widely oxygenated later phanerozoic oceans

interactions between ediacaran animals and microbial mats insights from lamonte trevallis a new trace fossil from the dengying formation of south china abstract a new ichnogenus and ichnospecies lamonte trevallis is formally described from the shibantan member limestone of the upper ediacaran dengying formation yangtze gorges area south china it is characterized by horizontal tunnels connected with short vertical burrows and surface trails the horizontal burrows are elliptical or bilobed in transverse cross section preserved in full relief and filled with carbonate intraclasts micrites as well as calcite and silica cements they occur exclusively in silty crinkled and microlaminated layers that are interpreted as amalgamated cyanobacterial microbial mats no burrows have been found in intraclastic layers adjacent to the microlaminated layers the vertical traces are filled with the same material as the burrows but they typically project through the crinkled microlaminae and are exposed on the bedding surface the surface tracks are always preserved in negative epirelief or positive hyporelief and consist of two parallel series of either sharp scratch marks or small knobs the burrow infill has 18ocarb and 13ccarb values distinct from but intermediate between microlaminated and intraclastic layers consistent with petrographic observation that burrow infill consists of a mixture of early carbonate cements intraclasts and micrites bedding plane bioturbation intensity 20 40 measured as percentage of bedding plane area covered by l trevallis traces is comparable to similar measurements in pre trilobite cambrian carbonates the exclusive occurrence of l trevallis within microbial mats may have both taphonomic and ecological significance these mats may have provided firm substrates and localized geochemical conditions that contributed to the structural integrity of the burrows and they may have also facilitated early diagenetic cementation of burrow infill thus facilitating burrow preservation the close association of these burrows with microbial mats implies that the trace producers actively mined cyanobacterial mats to exploit oxygen or nutrient resources the trace makers of l trevallis were better able to utilize the resources around them than many other ediacaran trace makers and provide an ichnological record of a flourishing benthic ecology in late ediacaran oceans at the dawn of the agronomic revolution

carbonaceous biosignatures of diverse chemotrophic microbial communities from chert nodules of the ediacaran doushantuo formation the ediacaran doushantuo formation dst is renowned for exceptionally preserved precambrian fossils including metazoans some of these fossils particularly microfossils such as multicellular algae and acanthomorphic acritarchs are preserved in dst chert nodules to better understand the geomicrobiological processes that contributed to the authigenic formation of dst chert nodules and facilitated exceptional fossil preservation we analyzed organic matter in these chert nodules and the surrounding matrix calcareous mudstone using multiple in situ techniques confocal laser raman spectroscopy micro fourier transform infrared spectroscopy ftir and secondary ion mass spectroscopy sims we found strong ultrastructural chemical and isotopic heterogeneities in the organic matter as indicated by the raman spectral parameter i 1350 1600 ranging from 0 49 to 0 88 the infrared spectral index r3 2 from 0 12 to 0 90 and an estimated 13corg sims range of 44 v pdb these micron scale heterogeneities imply that the organic matter preserved in the dst chert nodules is derived from different carbonaceous sources in a diverse microbial ecosystem including eukaryotic and or prokaryotic photoautotrophs as well as chemotrophs involved in the fermentation and probably anaerobic oxidation of organic remains thus the microbial ecosystems in ediacaran ocean waters and sediments were more complex than previously thought and these microbial processes controlled dynamic micro environments in dst sediments where chert nodules were formed and fossils were mineralized the results also show that variations in the relative abundances activities and interactions of co existing microorganisms in dst sediments may have modulated 13corg shifts causing local decoupling between 13corg and 13ccarb as measured in bulk samples

integrated ediacaran sinian chronostratigraphy of south china abstract the ediacaran period was a critical time in the history of life and earth understanding the complex interactions between geological and biological events during this interval requires high resolution chronostratigraphy thanks to its uniquely favorable palaeogeographic setting south china is an ideal region for constructing a framework for global chronostratigraphic correlation of ediacaran strata here continuous ediacaran successions contain both siliciclastic and carbonate rocks that range from shallow to deep marine and contain rich fossil assemblages showing a variety of preservation styles as part of the present study 62 reference sections distributed throughout the yangtze platform were investigated analyses of the sedimentary facies and sequence stratigraphy of more than 40 sections revealed four major sequences in the shallow marine facies three major sequence boundaries occur respectively in the middle and upper parts of the doushantuo formation and in the middle part of the dengying formation subdivision and correlation of the ediacaran successions of the yangtze platform based on sequence stratigraphy is congruent with the carbon isotope chemostratigraphy of 12 reference sections 1075 samples the sequence boundary sb2 in the middle part of the doushantuo formation is suggested here as the lower xiadongian upper yangtzean series boundary of the ediacaran which coincides with several globally recognizable events namely 1 the end of the neoproterozoic glaciations 2 the first appearance of animals 3 the sudden increase in the diversity of acanthomorphic acritarchs and 4 a negative 13 c excursion the ediacaran system of south china may be subdivided into five stages furthermore the criteria for defining these stages may be applicable throughout the world also the composite carbon isotope profile of the ediacaran of south china can be used as a global reference for chronostratigraphic subdivision and correlation in addition to the globally recognizable negative 13 c excursion in the cap carbonate at the base of the ediacaran the negative 13 c excursion in the uppermost doushantuo wonoka shuram interval represents another globally correlatable major excursion the positive 13 c excursion immediately following the uppermost doushantuo excursion and ending at 548 ma is also useful for global correlation current ediacaran chronostratigraphy and global correlations indicate that the upper doushantuo wonoka shuram negative 13 c excursion ranges from ca 560 ma to 551 ma and therefore coincides with the evolutionary renovation of life feedback between evolutionary innovation and geochemical cycling was the key mechanism for this unique and most strongly negative 13 c excursion in earth history our chronostratigraphic correlations also imply that the earliest known metazoan biotas namely the weng an and characteristic ediacaran biotas do not constitute two temporally separate evolutionary lineages as proposed previously but represent two parallel evolutionary pathways preceding the cambrian explosion of animal life

in situ stress and active faulting in oklahoma abstract appreciable injection induced seismicity has been occurring in north central oklahoma since 2009 to better understand these earthquakes we have compiled new information on the state of stress in the state to compare it with both mapped faults and faults inferred from earthquake epicenters and focal plane mechanisms seventy five new in situ stress orientations are available from wellbores throughout the state in the north central part of the state where the induced seismicity is occurring stress orientation and relative magnitude from focal mechanism inversions show excellent agreement with the wellbore stress orientations all of the data show remarkably uniform stress directions the azimuth of s hmax the maximum horizontal stress is about n85 5 e strike slip faulting is occurring in central oklahoma with strike slip normal and normal faulting observed in northern oklahoma and southern kansas as very few of the thousands of m 2 5 earthquakes that have recently occurred are located on or near already mapped faults we utilize the stress information to interpret the likely fault planes associated with over 300 well constrained focal plane mechanisms in the vicinity of the january 2016 sequence of magnitude 4 and 5 earthquakes in the fairview oklahoma region we illustrate how knowledge of the stress field can be used to identify the faults responsible for the seismicity and better evaluate the potential hazard associated with possible future earthquakes in the area the september 2016 m w 5 8 pawnee event occurred on an unmapped n70 w trending strike slip fault expected to be active in the local stress field

fault stability inferred from granite sliding experiments at hydrothermal conditions seismicity on crustal faults is concentrated in the depth interval 1 3 to 12 15km tse and rice 1986 suggested that the lower bound on seismicity is due to a switch with increasing temperature from velocity weakening destabilizing to velocity strengthening stabilizing friction they inferred this transition from friction data for dry granite however pore fluids exist at elevated temperatures throughout the crust and may strongly influence strength and sliding behavior we present new data from sliding experiments on granite at elevated t 23 to 600 plus elevated ph2o 100 mpa our results show velocity strengthening at room temperature but velocity weakening from 100 to 350 c except at 250 from 350 to 600 there are systematic trends from velocity weakening to strong velocity strengthening and from high to low friction neither trend was seen in tests on dry granite the velocity dependence data imply the potential for unstable slip in the interval 100 to 350 using a geotherm to map temperature to depth this interval closely matches the observed earthquake distribution

was the ediacaran shuram excursion a globally synchronized early diagenetic event insights from methane derived authigenic carbonates in the uppermost doushantuo formation south china abstract the ediacaran period is characterized by the most profound negative carbon isotope 13c excursion in earth history the shuram excursion various hypotheses including the massive oxidation of dissolved organic carbon doc in the oceans the weathering of terrestrial organic carbon or the release and oxidation of methane hydrates and or expelled petroleum from the subsurface have been proposed as sources of the 13c depleted carbon more recently it has been suggested that global scale precipitation of early authigenic carbonates driven by anaerobic microbial metabolism in unconsolidated sediments may have caused the shuram excursion but empirical evidence is lacking here we present a comprehensive analysis of a shuram associated interval from the uppermost doushantuo formation in south china our study reveals petrographic evidence of methane derived authigenic calcite formed as early diagenetic cements and nodules that are remarkably depleted in 13c suggesting a buildup of alkalinity in pore fluids through the anaerobic oxidation of methane aom and systematically depleted in 18o relative to co occurring dolomite early authigenesis of these minerals is likely to be driven by increased microbial sulfate reduction triggered by enhanced continental weathering in the context of a marked rise in atmospheric oxygen levels in light of the finding of methane derived authigenic carbonates at zhongling and based on our basin scale stratigraphic correlation we hypothesize that the marked 13c and 18o depletion including their co variation noted worldwide in the shuram excursion may reflect an episode of authigenesis occurring within a sulfate methane transition zone smtz if true the shuram excursion was then a global biogeochemical response to enhanced seawater sulfate concentration in the ediacaran ocean driven by the neoproterozoic oxidation of surface environments this paleo oceanographic transition may have therefore paved the way for subsequent evolution and diversification of animals our study highlights the significance of an integrated approach that combines petrography mineralogy and texture specific micro drilling geochemistry in chemostratigraphic studies

identifying potentially induced seismicity and assessing statistical significance in oklahoma and california we develop a statistical method for identifying induced seismicity from large datasets and apply the method to decades of wastewater disposal and seismicity data in california and oklahoma the study regions are divided into gridblocks we use a longitudinal study design seeking associations between seismicity and wastewater injection volume along time series within each gridblock in each gridblock we find the maximum likelihood estimate for a model parameter that relates induced seismicity hazard to total volume of wastewater injected each year to assess significance we compute likelihood ratio test statistics in each gridblock and each state california and oklahoma resampling with permutation and random temporal offset of injection data is used to estimate p values from the likelihood ratio statistics we focus on assessing whether observed associations between injection and seismicity occur more often than would be expected by chance we do not attempt to quantify the overall incidence of induced seismicity the study is designed so that under reasonable assumptions the associations can be formally interpreted as demonstrating causality wastewater disposal is associated with other activities that can induce seismicity such as reservoir depletion therefore our results should be interpreted as finding seismicity induced by wastewater disposal and all other associated activities in oklahoma the analysis finds with extremely high confidence that seismicity associated with wastewater disposal has occurred in california the analysis finds moderate evidence that seismicity associated with wastewater disposal has occurred but the result is not strong enough to be conclusive

stratigraphic position of the ediacaran miaohe biota and its constrains on the age of the upper doushantuo δ13c anomaly in the yangtze gorges area south china abstract the siliceous shale unit that hosts the ediacaran miaohe biota in the yangtze gorges area commonly referred to as the miaohe member has an age of 551 0 7 ma this unit is thought to be time equivalent with the doushantuo member iv which marks the top of the upper doushantuo negative 13 c excursion new bio sequence and chemostratigraphic studies presented here demonstrate that the miaohe member is significantly younger than the doushantuo member iv most likely time equivalent with the lower shibantan member of the dengying formation the new findings indicate that the top of the doushantuo formation i e the top of the upper doushantuo shuram 13 c excursion should be much older than 551 ma likely 560 ma the ocean oxygenation event documented from the doushantuo member iv black shales should also be older than 560 ma and predate the miaohe biota for more than 10 ma

wind influence on the mesoscale activity along the gulf stream and the north atlantic currents two independent data sets are used to diagnose the wind effect on the mesoscale activity in the north atlantic ocean the oceanic surface variability is described with topex poseidon sea surface height measurements from october 1992 to september 1997 spatial extensions and temporal variations of high mesoscale activity are compared with the zonal and meridional components of the ers 1 wind stress the ekman pumping and the zonal sverdrupian velocity regions with high mesoscale surface variability seem to be correlated to regions with eastward sverdrupian velocities when the sverdrupian velocity is eastward and increases with time the mesoscale activity is intensified indicating a growth of instability rates theoretical and numerical results based on the interplay of barotropic eastward sverdrup flows and westward propagation of long rossby waves suggest that the wind controls western regions where baroclinic instability is favored interactions between the eddy field and the mean circulation are therefore analyzed to try to extract the instability mechanism responsible for the growth of the mesoscale activity along the gulf stream and the north atlantic current our results seem to suggest that the seasonal changes of mesoscale activity associated with eastward currents are linked to seasonal changes of the eastward sverdrupian velocity

injection induced seismicity poroelastic and earthquake nucleation effects the standard model of injection induced seismicity considers changes in coulomb strength due solely to changes in pore pressure we consider two additional effects full poroelastic coupling of stress and pore pressure and time dependent earthquake nucleation we model stress and pore pressure due to specified injection rate in a homogeneous poroelastic medium stress and pore pressure are used to compute seismicity rate through the dieterich 1994 model for constant injection rate the time to reach a critical seismicity rate scales with t r2 cfc where r is distance from the injector c is hydraulic diffusivity and fc is a factor that depends on mechanical properties and weakly on r the seismicity rate decays following a peak consistent with some observations during injection poroelastic coupling may increase or decrease the seismicity rate depending on the orientation of the faults relative to the injector if injection induced stresses inhibit slip abrupt shut in can lead to locally sharp increases in seismicity rate tapering the flux mitigates this effect the maximum magnitude event has been observed to occur postinjection we suggest the seismicity rate at a given magnitude depends on the nucleation rate the size distribution of fault segments and if the background shear stress is low the time varying volume of perturbed crust this leads to a rollover in frequency magnitude distribution for larger events with a corner that increases with time larger events are absent at short times but approach the background frequency with time larger events occurring post shut in are thus not unexpected

precambrian cambrian trace fossils from the yangtze platform south china and the early evolution of bilaterian lifestyles abstract siliciclastic carbonaceous and phosphoritic shallow marine sediments from several neoproterozoic ediacaran and precambrian cambrian pc c boundary sections on the yangtze platform south china contain remarkable trace fossil assemblages the present paper provides a general overview on the distribution and the possible palaeobiological and palaeoenvironmental significance of these trace fossil assemblages from selected pc c boundary sections on the passive yangtze platform margins comparative investigations of the typology of neoproterozoic ediacaran ichnofaunas as well as of the related sedimentary environments accompanying the ichnoassemblages demonstrate in general correspondence with other studies worldwide that the neoproterozoic ichnofaunas are mainly composed of slightly curved to straight and unbranched horizontal traces which are usually related to the occurrence of shallow marine softgrounds sealed by microbial mats rare traces show ichnomorphological patterns that indicate developments toward a more effective horizontal exploitation of the feeding ground during the late neoproterozoic and earliest cambrian the majority of these traces appear to represent undermat miners with simple feeding strategies during the earliest phanerozoic early meishucunian stage equivalent to the nemakit daldynian stage of siberia the oxic shallow water environments along the ancient continental passive margins of the yangtze platform were populated by large as yet unknown arthropods which produced rusophycus type trace fossils the late precambrian to early phanerozoic sediments of the yangtze platform generally provide excellently preserved trace fossil records which together with the presence of index fossils ssf from the nemakit daldynian stage provide a more detailed insight into the development of pc c palaeoenvironments and the evolution of lifestyles among early bilaterian metazoans a preliminary comparison of the neoproterozic biotas occurring on the yangtze platform and in other time equivalent ediacaran habitats demonstrates general similarities but also some striking differences probably due to palaeoenvironmental variations the data presented here from south china are critically discussed in the light of current palichnological approaches and theories

wide but not ubiquitous distribution of glendonite in the doushantuo formation south china implications for ediacaran climate abstract glendonites are pseudomorphs of syndepositional or early authigenic ikaite caco3 6h2o that often forms at near freezing temperatures silicified glendonite has been reported from inner shelf deposits of the lower ediacaran doushantuo formation at a single stratigraphic section in south china where they are stratigraphically associated with the positive 13c excursion ep1 but predate the negative 13c excursion en3 shuram excursion indicating a period of cool climate somewhere between 609 ma and 551 ma this interpretation predicts a wider geographic distribution of ediacaran glendonites in equivalent strata in the yangtze block of south china to test this prediction we conducted a regional survey of doushantuo formation and found that although glendonites are not universally present they occur in expected stratigraphic intervals and in association with ep1 at two new sections representing inner shelf and intrashelf basin facies the wide but not ubiquitous distribution of doushantuo glendonites indicates that ikaite precipitation and glendonite formation was controlled by both regional climatic and local geochemical factors glendonites at the new localities are stellate clusters pseudomorphed by calcite spar and sometimes are rimmed with silica the calcite spar is characterized by highly variable and mostly negative 13c values as low as 37 indicating that diagenetic transformation of precursor ikaite to calcitic glendonite may be related to anaerobic oxidation of organic matter or methane in sediment the new data suggest an early ediacaran cold period prior to en3 or the shuram excursion and facilitation of glendonite ikaite formation by both climatic and local geochemical conditions such as redox conditions and phosphate concentrations

second order moment of central california seismicity 1969 1982 the second order moment cross correlation function of earthquakes in the u s geological survey central california catalog between 1969 and 1982 was calculated with respect to a magnitude threshold m 4 0 over interevent distances up to 80 km and interevent times up to 320 days the statistical procedure results in a representation of the spatial temporal structure of the catalog associated with m 4 0 earthquakes and is capable of revealing patterns too weak to be detected in the space time distribution of seismicity for individual earthquake sequences a method is introduced for identifying aftershocks based on a physical two parameter model of the earthquake interaction process the results show that the aftershock process dominates the second order moment and may even obscure the statistical expression of a precursory process a concentration of foreshocks within 15 km and 3 days of m 4 0 main shocks exhibits an apparent migration toward the main shock loci with velocity 2 6 5 3 km d this concentration may be related to an observed tendency for m 4 0 events to cluster auto correlate over this interevent range with the identified aftershocks removed the residual catalog is poissonion in space and time when two m 4 0 earthquakes occur within 80 km and 40 days of each other aftershock productivity appears to be relatively enhanced in the earlier sequence this suggests that aftershock populations are not solely dependent on their main shocks and that unusually productive aftershock sequences may be predictors of future moderate earthquakes

horizontal reynolds stresses in the central equatorial pacific seven 13 month long current records from the north pacific experiment hawaii to tahiti shuttle experiment during 1979 1980 were analyzed to investigate eddy energetics of the upper ocean within 75 km of the equator profiling current meter data from the experiment were also used in an attempt to relate the eddy motions to the mean zonal flow the current fluctuations are highly anisotropic with zonal current dominating after removal of a linear trend plus annual and semiannual harmonics the residual high frequency current fluctuations are much more nearly isotropic the high frequency eddy kinetic energy decreases by a factor of 2 over the upper 250 m and at 100 m has a relative minimum on the equator the seasonal time scale eddy kinetic energy shows a much more dramatic decrease below the thermocline with the exception of tidal peaks the spectra of zonal current are red while meridional current spectra show a flattening at the lowest resolvable frequencies meridional current was non stationary with an energetic packet of 10 to 15 day period oscillations occurring in early 1980 the off diagonal component of the reynolds stress tensor u calculated from the high frequency residuals is everywhere positive decreasing from north to south and with depth the implied cross equatorial flux of zonal momentum is at odds with eddy viscosity parameterizations which relate u to the mean meridional shear of the zonal current the observed distribution of reynolds stresses might be explained by radiation of energy from an instability of the portion of the south equatorial current north of the equator in all cases the high frequency u time series are significantly skewed toward positive values and show no evidence of periodicity indicating that the process es responsible is are intermittent and broadband this is consistent with the instability mechanism

investigation of injection induced seismicity using a coupled fluid flow and rate state friction model we describe a numerical investigation of seismicity induced by injection into a single isolated fracture injection into a single isolated fracture is a simple analog for shear stimulation in enhanced geothermal systems egs during which water is injected into fractured low permeability rock triggering slip on preexisting large scale fracture zones a model was developed and used that couples 1 fluid flow 2 rate and state friction and 3 mechanical stress interaction between fracture elements based on the results of this model we propose a mechanism to describe the process by which the stimulated region grows during shear stimulation which we refer to as the sequential stimulation ss mechanism if the ss mechanism is realistic it would undermine assumptions that are made for the estimation of the minimum principal stress and unstimulated hydraulic diffusivity we investigated the effect of injection pressure on induced seismicity for injection at constant pressure there was not a signifi

the effect of loading rate on static friction and the rate of fault healing during the earthquake cycle the seismic cycle requires that faults strengthen heal between earthquakes and the rate of this healing process plays a key role in determining earthquake stress drop1 2 3 4 rupture characteristics5 6 and seismic scaling relations2 3 4 7 frictional healing as evidenced by increasing static friction during quasi stationary contact between two surfaces1 8 9 10 11 12 is considered the mechanism most likely to be responsible for fault strengthening2 3 13 14 previous studies however have shown a large discrepancy between laboratory and seismic field estimates of the healing rate2 3 4 14 15 in the laboratory rock friction changes by only a few per cent per order of magnitude change in slip rate whereas seismic stress drop increases by a factor of 2 to 5 per order of magnitude increase in earthquake recurrence interval but in such comparisons it is assumed that healing and static friction are independent of loading rate here i summarize laboratory measurements showing that static friction and healing vary with loading rate and time as expected from friction theory16 17 18 applying these results to seismic faulting and accounting for differences in laboratory seismic and tectonic slip rates i demonstrate that post seismic healing is expected to be retardedfor a period of several hundred days following an earthquake in agreement with recent findings from repeating earthquakes13 14 19 20

likelihood testing of seismicity based rate forecasts of induced earthquakes in oklahoma and kansas likelihood testing of induced earthquakes in oklahoma and kansas has identified the parameters that optimize the forecasting ability of smoothed seismicity models and quantified the recent temporal stability of the spatial seismicity patterns use of the most recent 1 year period of earthquake data and use of 10 20 km smoothing distances produced the greatest likelihood the likelihood that the locations of january june 2015 earthquakes were consistent with optimized forecasts decayed with increasing elapsed time between the catalogs used for model development and testing likelihood tests with two additional sets of earthquakes from 2014 exhibit a strong sensitivity of the rate of decay to the smoothing distance marked reductions in likelihood are caused by the nonstationarity of the induced earthquake locations our results indicate a multiple fold benefit from smoothed seismicity models in developing short term earthquake rate forecasts for induced earthquakes in oklahoma and kansas relative to the use of seismic source zones

earthquake hypocenters and focal mechanisms in central oklahoma reveal a complex system of reactivated subsurface strike slip faulting the sharp increase in seismicity over a broad region of central oklahoma has raised concern regarding the source of the activity and its potential hazard to local communities and energy industry infrastructure since early 2010 numerous organizations have deployed temporary portable seismic stations in central oklahoma in order to record the evolving seismicity in this study we apply a multiple event relocation method to produce a catalog of 3639 central oklahoma earthquakes from late 2009 through 2014 regional moment tensor rmt source parameters were determined for 195 of the largest and best recorded earthquakes combining rmt results with relocated seismicity enabled us to determine the length depth and style of faulting occurring on reactivated subsurface fault systems results show that the majority of earthquakes occur on near vertical optimally oriented ne sw and nw se strike slip faults in the shallow crystalline basement these are necessary first order observations required to assess the potential hazards of individual faults in oklahoma

seismic strain rates in the central and eastern united states seismic strain rates for the entire central and eastern united states are estimated from historical seismicity and from several seismicity models typical strain rates are estimated to be the on the order of 10 12 to 10 11 per year except near historical sites of large earthquakes where higher rates pertain uncertainties in strain rates are large deformation caused by strain rates less than 10 10 yr 1 is very small compared to average denudation rates denudation and deposition may control the rate of earthquake occurrence in some parts of the central and eastern united states by modifying the vertical stress due to load a simple quantitative model predicts the earthquake occurrence rate in the appalachian mountains from an estimate of the regional denudation rate

quantitative evaluation of the biostratigraphic distribution of acanthomorphic acritarchs in the ediacaran doushantuo formation in the yangtze gorges area south china abstract doushantuo acanthomorphic acritarchs are large morphologically complex organic walled microfossils broadly constrained between the 635 ma nantuo glaciation and the 551 ma miaohe biota they are potential biostratigraphic tools for subdivision and correlation of the ediacaran system in south china however major variations in sedimentary facies and stratigraphic thickness present challenges in understanding the spatial and temporal distribution of these acritarchs further the distribution of acritarchs in the doushantuo formation is associated with the presence of early diagenetic chert and phosphate implying a certain degree of preservational bias and or environmental control the purpose of this paper is to document the stratigraphic distribution of doushantuo acritarchs and to quantitatively evaluate their biostratigraphic significance and possible taphonomic environmental biases based on high resolution paleontological data from six sections over 100 km in the yangtze gorges area south china a total of 1082 acritarch fossils were recorded from 84 chert horizons in the six sections of the study area these chert horizons are not uniformly distributed throughout the doushantuo formation thus the presence absence of early diagenetic chert does play a role in controlling the distribution of acritarchs the sampled chert horizons can be grouped into two stratigraphic intervals in the lower and upper doushantuo formation respectively based on regional stratigraphic correlation quantitative analysis shows that the two intervals are distinct taxonomically and largely independent of taphonomic or facies controls thus the two intervals can be regarded as assemblage biozones the lower biozone biozone 1 is numerically dominated by tianzhushania spinosa n 587 68 3 and meghystrichosphaeridium magnificum n 74 8 6 whereas the upper biozone biozone 2 is dominated by ericiasphaera rigida n 104 47 1 and tianzhushania spinosa n 34 14 1 the three most common genera meghystrichosphaeridium tianzhushania and ericiasphaera have been identified in all sections correspondence analysis ca detrended correspondence analysis dca discriminant analysis da and pairwise comparisons of samples spearman rank coefficient and jaccard chao index all consistently support biostratigraphic zonations thus the distribution of the doushantuo acanthomorphs is primarily controlled by biostratigraphic position of samples with facies and taphonomic differences playing a secondary role our case study suggests that acanthomorphic acritarchs can offer a viable tool for regional correlation of the ediacaran system

carbon isotope chemostratigraphy and sedimentary facies evolution of the ediacaran doushantuo formation in western hubei south china abstract the doushantuo formation of south china consisting of intercalated siliciclastic and carbonate rocks which exhibit considerable variation in thickness and sedimentary facies is one of the key sedimentary units in the world for understanding ediacaran geobiological processes however stratigraphic correlation and sedimentary facies evolution of the doushantuo formation remain controversial sedimentary facies analysis of the well known sections of the yangtze gorges area and new sections in northern yichang western hubei indicate that the doushantuo succession in the yangtze gorges area was deposited in an offshore intra shelf basin within the yangtze platform in contrast the doushantuo formation in the northern yichang area which is characterized by one or a few phosphate rich horizons represents deposition on the subtidal or intertidal shelf and so is similar to the succession in the weng an area central guizhou province the carbon isotope profiles of the different sections exhibit significant variation which is interpreted to result from facies differences sequence and high resolution carbon isotope stratigraphy have clarified problematic correlations and the temporal relationship between fossil assemblages of the doushantuo formation on the yangtze platform the results confirm that a prominent negative 13ccarb excursion baince nadir down to 5 in the middle portion of the second sequence of the doushantuo formation is a widely traceable event baince together with three other 13ccarb excursions namely cance at the base wance near the first sequence boundary near the middle and dounce at the top of the doushantuo formation constitute a complete carbon isotope profile for the doushantuo formation that reflects contemporaneous seawater and so serves as a reference chemostratigraphic profile for global stratigraphic correlation and for evaluating the chemical evolution of seawater during the ediacaran period

coping with earthquakes induced by fluid injection large areas of the united states long considered geologically stable with little or no detected seismicity have recently become seismically active the increase in earthquake activity began in the mid continent starting in 2001 1 and has continued to rise in 2014 the rate of occurrence of earthquakes with magnitudes m of 3 and greater in oklahoma exceeded that in california see the figure this elevated activity includes larger earthquakes several with m 5 that have caused significant damage 2 3 to a large extent the increasing rate of earthquakes in the mid continent is due to fluid injection activities used in modern energy production 1 4 5 we explore potential avenues for mitigating effects of induced seismicity although the united states is our focus here canada china the uk and others confront similar problems associated with oil and gas production whereas quakes induced by geothermal activities affect switzerland germany and others

a constitutive law for rate of earthquake production and its application to earthquake clustering seismicity is modeled as a sequence of earthquake nucleation events in which the distribution of initial conditions over the population of nucleation sources and stress ing history control the timing of earthquakes the model is implemented using solutions for nucleation of unstable fault slip on faults with experimentally derived rate and state dependent fault properties this yields a general state variable constitutive formulation for rate of earthquake production resulting from an applied stressing history to illustrate and test the model some characteristics of seismicity following a stress step have been explored it is proposed that various features of earthquake clustering arise from sensi tivity of nucleation times to the stress changes induced by prior earthquakes the model gives the characteristic omori aftershock decay law and interprets aftershock parameters in terms of stress change and stressing rate earthquake data appear to support a model prediction that aftershock duration defined as the time for rates to return to the back ground seismicity rate is proportional to mainshock recurrence time observed spatial and temporal clustering of earthquake pairs arises as a consequence of the spatial depen dence of stress changes of the first event of the pair and stress sensitive time dependent nucleation applications of the constitutive formulation are not restricted to the simple stress step models investigated here it may be applied to stressing histories of arbitrary complexity the apparent success at modeling clustering phenomena suggests the possibil ity of using the formulation to estimate short to intermediate term earthquake probabil ities following occurrence of other earthquakes and for inversion of temporal variations of earthquake rates for changes in driving stress

phosphogenesis associated with the shuram excursion petrographic and geochemical observations from the ediacaran doushantuo formation of south china abstract the ediacaran period witnessed one of the largest phosphogenic events in earth s history coincidently some phosphorite deposits in south china are associated with the largest known carbon isotope negative excursion i e shuram excursion suggesting an intimate coupling of the biogeochemical carbon and phosphorous cycles however the geomicrobiological linkage between these anomalies remain poorly understood in this study we investigated the phosphorite samples from the uppermost doushantuo formation in south china carbon isotope compositions of authigenic calcite cements and nodules in the phosphorites are as low as 34 vpdb petrographic and geochemical investigations indicate that the 13 c depleted carbonates likely formed as the result of microbial sulfate and iron reduction that released phosphorous from iron oxyhydroxide concentrating phosphorous in pore waters and thereby promoting phosphate mineralization the timing of this event appears to coincide with enhanced sulfate delivery to seawater through continental weathering the basin scale distribution of doushantuo phosphorites suggests a redox control on the availability of iron oxyhydroxide and the recycling of pore water phosphorous both inner and outer shelf regions were likely characterized by an oxic water column and were the main loci for phosphogenesis on the contrary intra shelf and slope regions which are lean in phosphorite were subjected to euxinic or ferruginous water column conditions the intimate coupling between ediacaran phosphogenesis and the shuram excursion suggests strong links among seawater redox conditions c s p fe cycling and fossil phosphatization increased microbial sulfate reduction driven by enhanced sulfate reservoir in the ediacaran ocean may have played an essential role on these biogeochemical events

acanthomorphic acritarchs from the ediacaran doushantuo formation at zhangcunping in south china with implications for the evolution of early ediacaran eukaryotes abstract microfossil assemblages preserved in the ediacaran doushantuo formation phosphorites i e the weng an biota and chert nodules in south china provide key evidence for the diversification of marine eukaryotes in the aftermath of cryogenian global glaciation two biozones i e the lower tianzhushania spinosa biozone and the upper hocosphaeridium anozos biozone have been proposed on the basis of acanthomorphic acritarchs preserved in the doushantuo formation chert nodules in the yangtze gorges area strata containing the weng an biota at weng an have been correlated either with the upper acritarch biozone based mainly on chemostratigraphic data or with the lower acritarch biozone according to the occurrence of tianzhushania spinosa in both assemblages these alternative correlations need to be resolved in order to improve our understanding of the evolutionary pattern of microscopic eukaryotes after the marinoan glaciation to address this problem we carried out an integrated litho bio and chemostratigraphic study of the doushantuo formation in the zhangcunping area where the microfossil assemblage resembles the weng an biota at weng an in both taxonomic composition and biostratigraphic ranges our study supports the litho and chemostratigraphic correlation of the doushantuo formation between the zhangcunping and yangtze gorges areas thus the doushantuo formation at zhangcunping provides a link between the weng an and yangtze gorges areas together with published paleontological and stratigraphic data the present study favors a correlation between the fossiliferous strata at zhangcunping and the upper part of the t spinosa biozone recognized in the yangtze gorges area the strata yielding the weng an biota at weng an can be at least partially correlated with the t spinosa biozone supporting the idea that the weng an microfossil assemblage is biostratigraphically transitional between the lower and upper acanthomorphic assemblages this correlation is consistent with the fact that several taxa that used to be regarded characteristic of the h anozos biozone may actually range downsection into the t spinosa biozone thus supporting an earlier diversification of doushantuo acanthomorphs these results call for more detailed investigation on the taxonomic composition and biostratigraphic ranges of acanthomorphs in the t spinosa biozone and re consideration of acanthomorphic biozonation of the doushantuo formation in the yangtze gorges area

the stratigraphic complexity of the middle ediacaran carbon isotopic record in the yangtze gorges area south china and its implications for the age and chemostratigraphic significance of the shuram excursion abstract the middle ediacaran shuram excursion represents the most pronounced negative carbon isotopic shift in earth history and has been considered as evidence for a profound disturbance to the global carbon cycle and proposed as a key chemostratigraphic marker for ediacaran stratigraphic subdivision and global correlation previous study has revealed a pronounced negative 13c shift en3 in the upper doushantuo formation of south china which has been interpreted as an equivalent of the shuram excursion detailed 13c investigation of multiple sections of the ediacaran doushantuo formation around the huangling anticline western hubei province south china indicates that the 13c variation in the upper doushantuo formation is more complex than previously reported in the western region of the huangling anticline a moderately positive 13c excursion here termed the diaoyapo positive excursion bisects two strongly negative 13c excursions here termed the jiuqunao negative excursion and the younger miaohe negative excursion with a 551 ma ash bed capping the miaohe negative excursion in the central region there is only one negative 13c excursion whereas in the eastern region the negative 13c excursion is absent the variable stratigraphic expression of these 13c excursions is most parsimoniously interpreted as reflecting local facies variation diagenesis and or a cryptic unconformity the more complete but more complex 13c chemostratigraphic record in the western region of huangling anticline implies that depending on how this record is correlated with the shuram excursion the latter may be significantly older than 551 ma if it does represent a global chemostratigraphic marker