magmatic precursors to the 18 may 1980 eruption of mount st helens usa perhaps the most difficult task facing volcanologists today is that of distinguishing between low level volcanic restlessness and activity that presages a full scale eruption we illustrate these difficulties by reexamining the sequence of events that led to the 18 may 1980 eruption of mount st helens activity that is often presented as a classic example of early phreatic explosions leading to a magmatic eruption this interpretation is problematic however given the known ascent of juvenile magma to within 250 m of the surface prior to the climactic event reexamination of ash samples from several precursory events shows that small amounts of juvenile material were erupted as early as 28 march 1980 just two weeks after the first seismic signals of reawakening and that the juvenile content of the ash had probably increased by early may the magmatic component of these eruptions was not recognized at the time because of the high crystallinity of the juvenile material a signature of extensive degassing induced crystallization during magma ascent identification of juvenile material in the precursory ash from mount st helens has important implications for initiation of eruptive activity

palaeoscolecids from the balang fauna of the qiandongian cambrian series 2 guizhou china wronascolex is a taxon of palaeoscolecids it is commonly represented by isolated button like microfossils or compressed individuals which are found worldwide in strata ranging from the cambrian series 2 to series 3 the earliest representative of wronascolex is known from the sinsk formation of the lower cambrian of the siberian platform other species occur in burgess shale type biotas of cambrian age from australia spain and north america new palaeoscolecid material from the balang fauna of the cambrian series 2 of eastern guizhou represents a new species of wronascolex w geyiensis sp nov and extends the geographic and stratigraphic distribution of wronascolex as well as providing additional evidence for understanding its morphology based upon correlation of body configuration and cuticular ornaments

a review on phreatic eruptions and their precursors abstract an analysis of the reported information on 132 historical phreatic events indicates that most of these 115 were not followed by a magmatic or phreatomagmatic eruption only in 18 cases precursory phenomena are reportedly lacking whereas they are recognized for the majority 72 of the considered cases these precursors have been analyzed as a function of the kind of phreatic event and of its possible triggering mechanism unfortunately the quality of the available information is poor however data suggest that anomalous seismicity ground deformation changes in the output chemistry and temperature of fumaroles and thermal springs are potential mid term precursors whereas seismic tremor is a common short term precursor

a new early cambrian konservat lagerstatte expands the occurrence of burgess shale type deposits on the yangtze platform abstract we report the fandian biota a new konservat lagerstatte from the cambrian stage 3 yuxiansi and jiulaodong formations in sichuan south china with close faunal links to the chengjiang biota in yunnan the biodiversity of the fandian biota includes total group euarthropods radiodonts bivalved forms acercostracans trilobites non biomineralized trilobitomorphs armoured lobopodians palaeoscolecids pedunculate brachiopods hyoliths chancelloriids sponges and filamentous algae benthic dwellers dominate the fossil community e g trilobitomorphs brachiopods sponges with rare instances of nektonic radiodonts bivalved euarthropods and infaunal palaeoscolecids organisms the fandian biota contains soft bodied taxa that were only known from chengjiang and xiaoshiba until now namely primicaris acercostracan xandarella non trilobite trilobitomorph and mafangscolex palaeoscolecid expanding the distribution of these previously endemic taxa beyond yunnan to the northern yangtze platform during the cambrian stage 3 our findings provide a more comprehensive understanding of early cambrian biodiversity that inhabited the yangtze platform over a substantially greater palaeobiogeographic distribution than previously considered

deep sea fragmentation style of havre revealed by dendrogrammatic analyses of particle morphometry in 2012 the eruption of deep sea volcano havre produced an abundance of fine ash at a depth of 1000 m below sea level in this study the 2d shapes of havre ash grains retrieved from the seafloor were compared quantitatively with those of particles generated in a suite of different fragmentation experiments which used remelted rhyolitic rock and pumice from the eruption site a new statistical data analysis technique denoted as dendrogrammatic analysis of particle morphology dapm is introduced it is designed to compare large numbers of morphometric data sets containing shape information for a set of ash particles to group them by morphological similarities and to visualize these clusters in a dendrogram further steps involve t tests and equivalence tests and reveal morphometric differences as well as matching features the dapm suggests that the majority of havre ash was thermohydraulically produced by induced fuel coolant interaction a subset of ash particles features an elongated tube morphology their morphometry matches that of particles that were experimentally produced by a combination of shearing and quenching and we infer that the natural particles were formed by synextrusive ash venting

thermohydraulic explosions in phreatomagmatic eruptions as evidenced by the comparison between pyroclasts and products from molten fuel coolant interaction experiments 1 thermohydraulic explosions were produced by molten fuel coolant interaction mfci experiments using remelted shoshonitic rocks from vulcano italy the fragmentation history and energy release were recorded the resulting products were recovered and analyzed with the scanning electron microscope fine particles from experiments show shape and surface features that result from melt fragmentation in brittle mode these clasts relate to the thermohydraulic phase of the mfci where most of the mechanical energy is released they are here called active particles the total surface area of such particles is proportional to the energy of the respective explosions other particles from experiments show shape and surface features that result from melt fragmentation in a ductile regime these fragments called passive particles form after the thermohydraulic phase during the expansion phase of the mfci in order to verify thermohydraulic explosions in volcanic eruptions we compared experimental products with samples from phreatomagmatic base surge deposits of vulcano ash particles from the experiments show features similar to those from the deposits suggesting that the experiments reproduced the same fragmentation dynamics to achieve discrimination between active and passive particles we calculated shape parameters from image analysis the mass of active particles in base surge deposits was calculated as the material properties for the natural samples are identical to the experimental ones the energy measurements and calculations of the experiments can be applied for a single phreatomagmatic eruption at vulcano a maximum mechanical energy release of 2 75 1013 j was calculated representing a tnt analogue of 6 5 kt

early cambrian priapulid worms buried with their lined burrows five specimens of the priapulid maotianshania cylindrica preserved inside their lined burrows were described from the lower cambrian chengjiang deposits near kunming southern china the exceptional preservation suggests that this worm made a dwelling tube by lining within the uppermost sediment layers this seems to be unique among priapulids in comparison with the cambrian selkirkia and paraselkirkia as well as some modern priapulid larvae and loriciferans taphonomic evidence indicates that the burrow and worm specimens are not buried in situ but were moved by storm tsunami or turbidity generated currents that are thought to have brought sedimentary material intermittently

evolution of fluid geochemistry at the turrialba volcano costa rica from 1998 to 2008 turrialba 10 02 n 83 45 w is a 3 349 m high stratovolcano belonging to the holocene cordillera central volcanic belt of costa rica the summit consists of three ew oriented craters east central and west since its last eruptive phase 1864 1866 the central and west craters have displayed modest fumarolic activity with outlet temperatures clustering around 90 c in 2001 seismic swarms ground deformation and increasing fumarolic activity occurred from 2005 to 2008 new fumarolic vents opened between and within the central and west craters and along the western and southwestern outer flanks of the volcanic edifice these physical changes were accompanied by a drastic modification in the gas chemistry that can be divided in three stages 1 hydrothermal from 1998 to autumn 2001 characterized by the presence of h2o co2 h2s and to a very minor extent hcl and hf 2 hydrothermal magmatic autumn 2001 2007 with the appearance of so2 and a significant increase of hcl and hf and 3 magmatic dominated 2007 2008 characterized by increased so2 content so2 h2s 100 and temperatures up to 282 c accordingly gas equilibrium in the co2 ch4 h2 system suggests a progressive evolution of the deep fluid reservoir toward higher temperatures and more oxidizing conditions the chemical physical modifications of turrialba in the last decade can be interpreted as part of a cyclic mechanism controlling the balance between the hydrothermal and the magmatic systems nevertheless the risk of rejuvenation of the volcanic activity cannot be excluded and an appropriate seismic ground deformation and geochemical monitoring program is highly recommended turrialba lies at a distance of 35 and 15 km from san jose and cartago respectively the two largest cities in costa rica

bioturbation in burgess shale type lagerstatten case study of trace fossil body fossil association from the kaili biota cambrian series 3 guizhou china abstract cruziana gordia planolites rusophycus and trichophycus are common ichnological elements of the kaili biota new discoveries based on the examination of 323 specimens include eldoniids echinoderms trilobites monoplacophorans and non biomineralizing arthropods that are associated with trace fossils based on the observed effects of bioturbation on the preservation of five different animal groups it is clear that infaunal scavengers deposit feeders were periodically active on the kaili sea floor and were able to reach historic layers yielding exceptionally preserved fossils in general the average level of infaunal activity is absent to moderate ichnofabric index i i 1 to 3 in the kaili substrate by contrast the phycodes beds are completely disturbed by infaunal activity i i 5 observed burrow diameter ranges from diminutive 0 2 mm to normal up to 4 2 mm computed tomography allows us to visualize the precise geometry of the trace fossil body fossil association in three dimensions we concluded that although some kaili infaunal animals could bore through the biomineralized echinoderms they did not appear to have scavenged upon these echinoderms based on our three dimensional reconstruction furthermore kaili burrowers can reach the historic layers containing exceptionally preserved fossils without altering soft tissue preservation on the other hand we used conventional techniques to reveal that one burrow is filled with fecal pellets 100 200 m at its terminal end because most burrows are filled with yellow brown coarse sediment and because there is no compositional difference between the fecal pellets and the surrounding coarse sediment within the burrow the origin of the yellow brown coarse sediment is interpreted here as parautochthonous and or autochthonous and as a result of sediment reworking by deposit or suspension feeders the relative scarcity of soft part preservation in the kaili biota compared to the older chengjiang biota and the younger burgess shale biota may be the result of post burial bio disturbance due to the relatively high intensity of local bioturbation it is plausible that oxygenation in deeper sediments facilitated by bioturbation allowed carcasses in the kaili biota to undergo a more extensive period of normal decay prior to final burial than in other cambrian konservat lagerstatten

quantitative experiments on phreatomagmatic explosions abstract an experimental set up for controlled generation of thermal explosions fuel coolant interactions has been built by an interdisciplinary research group of volcanologists physicists and engineering scientists the tee haus thermal explosion experiment during the last 3 years more than 500 experimental runs were performed aim of the project was not to build a mini volcano but to produce igniteable mixtures of water and hot melt on a small scale in order to investigate basic physical aspects such small scale mixtures however most probably also occur during phreatomagmatic events in nature mixtures of water and magma on a large scale may be modelled by combination of small elements earlier experimental studies of thermal explosions were carried out with the use of metal melts nearly exclusively therefore a carbonate melt approx 0 3 kg of 1 1 mass ratio na2co3 k2co3 was used for initial experimental series because of easy handling and more magma similarity by injection of water into this melt explosive mixtures were produced and ignited self triggering explosive interactions occurred in a wide melt temperature range 720 to 1040 c at melt temperatures exceeding 1000 c co2 increasingly degassed presence of non condensible gas bubbles in the melt strongly reduced the explosivity the intensity of explosions only slightly increased with higher melt temperatures but strongly increased with higher water injection velocities because of more intensive mixing a minimum injection velocity was found to be approx 0 7 m s 1 experiments with silicate melts derived from diverse remelted volcanic rocks were carried out with a slightly modified set up explosions were ignited by an additional trigger a shock wave of approx 8 j in volcanic systems shock waves of this magnitude are abundant volcanic tremor etc strong explosions with silicate melts were produced at melt temperatures between 1350 and 1750 c the produced explosions exerted repulsion forces of up to 24 000 n with a typical pulse duration of 1 ms carbonate melt resp 1 5 ms silicate melts the ejection velocity was found to be in a range between 200 and 400 m s 1 explosion energy values up to 500 j were calculated the maximum explosion pressure was calculated to be in the range between 10 and 100 mpa only part of the melt so called interactive melt reacts explosively with injected water most of the melt is passively ejected by and after the thermal explosion different fragmentation processes result in specific grain size and grain shape populations that can be distinguished from each other particles resulting from the fine fragmentation process that precedes and causes the thermal explosion are characterized by angular to subrounded shapes and grain sizes ranging from 20 m to 180 m the amount of interactive melt is proportional to the intensity of the explosion the maximum amount of water vapourized at the explosive interaction so called interactive water was estimated thus the water melt mass ratio for explosive interactions could be calculated the values range between 1 25 and 1 35 carbonate melt resp between 1 6 and 1 25 silicate melts

mechanisms of hydrovolcanic pyroclast formation grain size scanning electron microscopy and experimental studies pyroclasts produced by explosive magma water interactions are of various sizes and shapes data from analysis of over 200 samples of hydrovolcanic ash are interpreted by comparison with experimentally produced ash grain size and scanning electron microscopy sem reveal information on the formation of hydrovolcanic pyroclasts strombolian explosions result from limited water interaction with magma and the pyroclasts produced are dominantly centimeter sized with increasing water interaction hydrovolcanism increases in explosivity to surtseyan and vulcanian activity these eruptions produce millimeter to micron sized pyroclasts the abundance of fine ash 63 m diameter increases from 5 to over 30 percent as water interaction reaches an explosive maximum this maximum occurs with interactions of virtually equal volumes of melt and water five dominant pyroclast shape types determined by sem result from hydrovolcanic fragmentation 1 blocky and equant 2 vesicular and irregular with smooth surfaces 3 moss like and convoluted 4 spherical or drop like and 5 plate like types 1 and 2 dominate pyroclasts greater than 100 m in diameter types 3 and 4 are typical of fine ash type 5 pyroclasts characterize ash less than 100 m in diameter resulting from hydrovolcanic fragmentation after strong vesiculation fragmentation mechanisms observed in experimental melt water interactions result from vapor film generation expansion and collapse fragments of congealed melt are products of several alternative mechanisms including stress wave cavitation detonation waves and fluid instability mixing all result in rapid heat transfer these mechanisms can explain the five observed pyroclast shapes stress wave fracturing cavitation of the melt results from high pressure and temperature gradients at the melt water interface simultaneous brittle fracture and quenching produces type 1 pyroclasts type 2 develops smooth fused surfaces due to turbulent mixing with water after fracture and before quenching fluid instabilities promote turbulent mixing of melt and water and produce fine ash this kind of fragmentation occurs during high energy explosions the increased melt surface area due to fine fragmentation promotes high efficiency heat exchange between the melt and water shapes of resulting pyroclasts are determined by maximum surface area type 3 and surface tension effects type 4 type 5 pyroclasts result from nearly simultaneous vesicle burst and melt water fragmentation

cambrian burgess shale type deposits share a common mode of fossilization although cambrian burgess shale type bst biotas are fundamental to understanding the radiation of metazoans the nature of their extraordinary preservation remains controversial there remains disagreement about the importance of the role of early mineral replication of soft tissues versus the conservation of primary organic remains most prior work focused on soft bodied fossils from the two most important bst biotas those of the burgess shale canada and maotianshan shale chengjiang china fossils from these two deposits do not provide ideal candidates for specimen level taphonomic study because they have been altered the burgess shale by greenschist facies metamorphism and the maotianshan shale by intensive subsurface weathering elemental mapping of soft bodied fossils from 11 other bst deposits worldwide demonstrates that bst preservation represents a single major taphonomic pathway that may share a common cause wherever it occurs the conservation of organic tissues and not early authigenic mineralization is the primary mechanism responsible for the preservation of bst assemblages early authigenic mineral replacement preserves certain anatomical features of some specimens but the preservation of non biomineralized bst fossils requires suppression of the processes that normally lead to the degradation of organic remains in marine environments

eruptive activity at turrialba volcano costa rica inferences from 3he 4he in fumarole gases and chemistry of the products ejected during 2014 and 2015 a new period of eruptive activity started at turrialba volcano costa rica in 2010 after almost 150 years of quiescence this activity has been characterized by sporadic explosions whose frequency clearly increased since october 2014 this study aimed to identify the mechanisms that triggered the resumption of this eruptive activity and characterize the evolution of the phenomena over the past 2 years we integrate 3he 4he data available on fumarole gases collected in the summit area of turrialba between 1999 and 2011 with new measurements made on samples collected between september 2014 and february 2016 the results of a petrological investigation of the products that erupted between october 2014 and may 2015 are also presented we infer that the resumption of eruptive activity in 2010 was triggered by a replenishment of the plumbing system of turrialba by a new batch of magma this is supported by the increase in 3he 4he values observed since 2005 at the crater fumaroles and by comparable high values in september 2014 just before the onset of the new eruptive phase the presence of a number of fresh and juvenile glassy shards in the erupted products increased between october 2014 and may 2015 suggesting the involvement of new magma with a composition similar to that erupted in 1864 1866 we conclude that the increase in 3he 4he at the summit fumaroles since october 2015 represents strong evidence of a new phase of magma replenishment which implies that the level of activity remains high at the volcano this article is protected by copyright all rights reserved

combining ash analyses with remote sensing to identify juvenile magma involvement and fragmentation mechanisms during the 2018 19 small eruption of peteroa volcano southern andes abstract the planchon peteroa volcanic complex ppvc is located on the border of chile and argentina and is one of the most active volcanic systems in the andes holocene activity has included magma water interaction with an evolving series of crater lakes mainly sourced from peteroa volcano this study examines data from the 2018 19 eruption together with the volcanic history of the ppvc to elucidate the complex interplay between magmatic activity and summit water and ice from february 2016 to mid 2019 three seismic swarms occurred in the ppvc preceding the explosive eruption from september 2018 to april 2019 the activity originated from a small vent nested within the easternmost crater the most active portion of the complex peteroa the explosions interacted with a crater lake producing ash plumes up to 2 km above the crater and building a small tephra cone to investigate the eruption mechanisms we performed remote sensing analysis of plume dispersal thermal anomalies and ground deformation and characterized the volcanic products including grain size componentry morphology internal textures composition and mineralogy our results suggest that the precursory seismicity beginning in 2016 was related to the intrusion of a new magma batch that reached the surface during the 2018 19 eruption the eruption was also preceded by thermal anomalies geomorphic changes and increased hydrothermal activity at the surface though without any ground deformation recognized through radar interferometry insar the eruption initially produced predominantly recycled ash phreatic activity then evolved to increasing proportions of juvenile magma phreatomagmatic by april 2019 the juvenile clasts had a trachyandesite composition 59 wt sio2 with vesicular and dense scoria containing plagioclase and pyroxene the ash surfaces show external quenching cracks and step fractures consistent with phreatomagmatic fragmentation within the active crater lake textural characteristics also point to a slowly ascending batch of magma that was relatively viscous by the time it interacted with water in the crater lake notably these juvenile particles are distinctive from the pre 2018 products ash erupted from 2010 11 did not contain recognizable juvenile material and is inferred to have been a mainly phreatic eruption our findings suggest that the interplay between phreatic and phreatomagmatic eruptions fed by small magma batches intruding at shallow levels characterize much of the eruptive behavior of the ppvc during the last three decades multi parametric assessment is a powerful tool to discriminate between phreatic and phreatomagmatic eruptions

a strengthened impact of november arctic oscillation on subsequent tropical pacific sea surface temperature variation since the late 1970s the connection between november arctic oscillation ao and the following spring summer tropical pacific sea surface temperature sst experienced a pronounced enhancement around the late 1970s the connection was weak before but strong after the late 1970s the present study investigates the plausible reasons for the connection change after the late 1970s significant anomalous cyclone appears over subtropical north pacific and pronounced anomalous westerly winds occur over tropical western pacific in the positive phase of november ao as such november ao could exert a significant influence on the subsequent spring summer tropical pacific sst variation by contrast before the late 1970s anomalous cyclone and associated anomalous westerly winds to its south are weak and shift northward thereby the connection between november ao and tropical pacific sst is weak further analyses suggest that the interdecadal change in the anomalous cyclone over the subtropical north pacific may be related to the change in the november ao s pacific component and the strength of feedback of synoptic scale eddy to mean flow specifically after the late 1970s november ao s pacific component displays a zonally elongated structure which is favorable for the formation of easterly wind anomalies over the mid latitude north pacific and related wave mean flow interaction in addition feedback of synoptic eddy to mean flow is enhanced after the late 1970s which is partly related to the intensification of the north pacific storm track this may also contribute to enhancement of the anomalous cyclone over the subtropical pacific

identifying magma water interaction from the surface features of ash particles the deposits from explosive volcanic eruptions those eruptions that release mechanical energy over a short time span1 are characterized by an abundance of volcanic ash2 3 this ash is produced by fragmentation of the magma driving the eruption and by fragmenting and ejecting parts of the pre existing crust host rocks interactions between rising magma and the hydrosphere oceans lakes and ground water play an important role in explosive volcanism4 5 because of the unique thermodynamic properties of water that allow it to very effectively convert thermal into mechanical energy although the relative proportion of magma to host rock fragments is well preserved in the pyroclastic rocks deposited by such eruptions it has remained difficult to quantitatively assess the interaction of magma with liquid water from the analysis of pyroclastic deposits2 3 4 5 here we report the results of a study of natural pyroclastic sequences combined with scaled laboratory experiments we find that surface features of ash grains can be used to identify the dynamic contact of magma with liquid water the abundance of such ash grains can then be related to the water magma mass ratios during their interaction

evolution of the fossa cone vulcano abstract in decreasing order of abundance the principal emplacement mechanisms for deposits of the fossa edifice of vulcano include dry surge wet surge pyroclastic fall lahar lava flow pyroclastic flow and epiclastic processes most samples from pyroclastic beds on fossa contain two grain size populations the coarser mode at 0 5 1 5 resulted from modified ballistic transport whereas the finer mode at 2 5 3 5 is related to surge transport reconstruction of the entire stratigraphy of the cone permits the beds to be grouped into five principal eruptive cycles all of which postdate the lower pilato ash of lipari dated at 11 000 to 8 500 y b p pte nere cycle palizzi cycle commenda cycle pietre cotte cycle and the modern cycle additional cycles may be present but exposures on the cone are insufficient for their adequate definition all cycles follow a similar stochastic pattern starting with surge eruptions and ending with effusion of lava from the crater rim the frequency of pyroclastic fall events increases with time throughout each cycle this progressive decrease in the efficiency of water melt interaction through the duration of each cycle may be due to a gradual rise of each new magma column coupled with an increase in magmatic volatiles tectonism and magma mixing both play a role in triggering eruptions on fossa the present crater lies at the intersection of two prominent tectonic trends a nnw fracture system parallels the main eruptive centers and an ene set aligns with the migration of minor vents the silicic lavas of fossa contain a mixture of two components xenocrysts of plagioclase augite and olivine surrounded by a dark glass are intimately dispersed into an evolved rhyolitic matrix

seaweeds through time morphological and ecological analysis of proterozoic and early paleozoic benthic macroalgae abstract benthic marine macroalgae or seaweeds are key ecological players in oceans today and have been since the proterozoic to date however morphological and evolutionary patterns for precambrian macroalgae have been documented only in rather broad terms to refine our understanding in this critical interval we updated a dataset of proterozoic to early paleozoic noncalcified macroalgal fossils preserved as macroscopic carbonaceous compressions the data were analyzed using non parametric multidimensional scaling nmds and functional form group ffg approaches in order to characterize morphological and ecological evolutionary patterns of these macroalgae at the broadest scale the results show progressive increases in thallus size morphospace range and aspects of ecological complexity such as canopy heights surface area volume ratios and functional form groups through time these trends however are not always monotonous in particular significant increases in proterozoic macroalgal morphological diversity and maximum size appear to have occurred in the neoproterozoic tonian and ediacaran periods respectively analysis of ediacaran macroalgal assemblages shows that macroalgae broadly follow the ediacara like fossil assemblages with a significant drop in most studied metrics in the terminal ediacaran stage 550 539 ma the latter event occurs during the kotlinian crisis experienced by ediacara type macro organisms highlighting the possibility that this extinction event during the ediacaran cambrian transition affected both macroalgae and ediacara type macro organisms our analysis also confirms an ordovician increase in the morphological and ecological diversity of macroalgae

burgess shale type biotas were not entirely burrowed away burgess shale type biotas occur globally in the cambrian record and offer unparalleled insight into the cambrian explosion the initial phanerozoic radiation of the metazoa deposits bearing except

spatial variation in the diversity and composition of the lower cambrian series 2 stage 3 chengjiang biota southwest china abstract strata hosting the lower cambrian series 2 stage 3 chengjiang biota maotianshan shale member yu anshan formation occur throughout the eastern part of yunnan province southwest china in this study literature based faunal inventories from 10 areas representing 34 localities together with 22 038 new specimens collected at three localities from three of the 10 areas were analyzed quantitatively to assess large scale spatial variation in taxonomic diversity and composition our analyses show substantial co variation between local paleoenvironmental settings and species diversity and suggest the presence of three general taphofacies in the maotianshan shale member from west to east low diversity 26 species characterizes the wuding area where fossiliferous strata have undergone extensive bioturbation high diversity 215 species characterizes the chengjiang haikou anning areas where fossiliferous strata consist of stacked couplets of thin event and background mudstone layers moderate diversity 55 species characterizes the malong area where fossiliferous strata consist of indistinctly bedded shale showing fewer single event layers but abundant background layers in spite of variations in sampling effort between sites spatial patterns in species diversity and community composition were controlled primarily by variation in depositional environments along a proximal offshore to lower shoreface gradient which influenced both ecological and taphonomic factors the offshore settings haikou chengjiang anning areas show relatively high species diversity and exceptional preservation of soft bodied fossils reflecting rapid burial in distal tempestites relatively high degrees of bioturbation time averaging and hydrodynamic disturbance caused a substantial decrease in the quality of preservation and number of soft bodied species in the wuding and malong areas arthropods are the most diverse group in most localities followed by priapulids poriferans brachiopods lobopods and hyoliths this study shows that the chengjiang biota lends itself very well to high resolution characterization of spatial variation in taxonomic diversity faunal composition and fossil preservation furthermore the chengjiang biota may provide a unique opportunity to assess the roles of environmental factors taphonomy and ecological controls on species diversity at local to regional spatial scales

carbon isotope systematics of turrialba volcano costa rica using a portable cavity ring down spectrometer over the past two decades activity at turrialba volcano costa rica has shifted from hydrothermal to increasingly magmatic in character with enhanced degassing and eruption potential we have conducted a survey of the 13c signatures of gases at turrialba using a portable field based crds with comparison to standard irms techniques our 13c results of the volcanic plume high temperature vents and soil gases reveal isotopic heterogeneity in the co2 gas composition at turrialba prior to its recent phase of eruptive activity the isotopic value of the regional fault system falla ariete 3 4 0 1 is in distinct contrast with the central crater gases 3 9 0 1 and the 2012 high temperature vent 4 4 0 2 an indication that spatial variability in 13c may be linked to hydrothermal transport of volcanic gases heterogeneities in the source composition or magmatic degassing isotopic values of co2 samples collected in the plume vary from 13c of 5 2 to 10 0 indicative of mixing between atmospheric co2 9 2 0 1 and a volcanic source we compare the keeling method to a traditional mixing model hyperbolic mixing curve to estimate the volcanic source composition at turrialba from the plume measurements the predicted source compositions from the keeling and hyperbolic methods 3 0 0 5 and 3 9 0 4 respectively illustrate two potential interpretations of the volcanic source at turrialba as of the 29 october 2014 turrialba has entered a new eruptive period and continued monitoring of the summit gases for 13c should be conducted to better understand the dominant processes controlling 13c fractionation at turrialba

statistical analysis of textural data from complex pyroclastic sequences implications for fragmentation processes of the agnano monte spina tephra 4 1 ka phlegraean fields southern italy the agnano monte spina eruption 4 1 ka generated pyroclastic deposits with complex internal stratigraphy that reflects variations in eruptive style to obtain constraints on the fragmentation processes we analysed grain size and scanning electron microscopy sem data by means of multivariate statistical techniques of the cluster and factor analysis types the results allow the identification of end member deposits related to either pure magmatic activity or pure phreatomagmatic activity in addition some deposits show evidence of the contemporaneous operation of both end member fragmentation modes the presence of the two contrasting fragmentation processes during the various phases of explosive activity is tentatively interpreted to be a function in inhomogeneities in gas exsolution processes within the magma column that feeds the eruption

a preliminary note on the dispersal of the cambrian burgess shale type faunas abstract the common or similar elements of faunas shared by the early cambrian chengjiang fauna and the middle cambrian burgess shale fauna are listed in a generic level so as to have a better understanding of the palaeogeographic relationship between the south china block and laurentia the burgess shale type faunas probably had a worldwide distribution during the interval ranging from the late tommotian to atdabanian the geographic and biological contributions to the cosmopolitan geographic distribution of the burgess shale type faunas are discussed however newly developed pelagic larvae in many phyla which probably acquired their first bloom in the cambrian might have promoted the dispersal

are the ashes from the latest eruptions 2010 2016 at turrialba volcano costa rica related to phreatic or phreatomagmatic events abstract the initial eruptive episodes of explosive eruptions are classified as phreatic if the amount of juvenile material scoria glass pumice is null and the amount of fresh accidental lithics and hydrothermally altered lithics is substantial phreatic eruptions have been in some cases recognized as precursory events preceding phreatomagmatic and magmatic eruptive phases usually the lithological features of tephra deposits are investigated and sampled in the field investigation of ash samples under binocular microscope or by back scattered electron bse microscope images of polished sections is usually considered sufficient to typify the fragmentation mechanism of the eruption the opening eruptive phases at turrialba volcano together with the formation of new intracraters i e 2010 2012 2014 and the enlargement of the western crater 29 october 2014 to present were classified in previous papers and internal reports as phreatic we studied a series of ash samples erupted from 2010 to 2016 with the aim of understanding the fragmentation processes characterizing the vent opening phases we used sem eds analyses in addition to field and microscopic investigation results showed a composition of accidental lithics of fresh to hydrothermally altered clasts and secondary minerals 82 98 besides juvenile andesite fragments 2 18 which leads us to revisit the classification of the initial eruptive phases of turrialba as phreatomagmatic our method allowed the detection of a juvenile component directly involved in an effective magma water interaction which was possible only by a scrutinous examination of the glass surface textures by sem in the range size between 3 and 3 5 phi we recommend such a type of investigation when the identification of fresh magma in a new eruption is crucial for the preparedness and hazard evaluation at active volcanoes

preservational modes in the ediacaran gaojiashan lagerstatte pyritization aluminosilicification and carbonaceous compression abstract burgess shale type bst fossils often are preserved as two dimensional carbonaceous compressions sometimes aided by two mineralization processes pyritization and aluminosilicification defined by a thin and sometimes localized coating of authigenic pyrite or aluminosilicate minerals on the carbonaceous materials here we report similar mineralization modes within the late ediacaran gaojiashan lagerstatte of southern shaanxi province south china examination of two common gaojiashan fossils conotubus hemiannulatus and gaojiashania cyclus hereafter referred by generic names only indicates that pervasive pyritization is the primary taphonomic pathway in this deposit responsible for the preservation of 80 of the collected fossils pervasive pyritization of gaojiashan fossils results in their three dimensional preservation as opposed to two dimensional carbonaceous compression with thin pyrite coatings seen in some bst lagerstatte however microscale investigation using environmental scanning electron microscopy esem and energy dispersive x ray spectroscopy eds shows that some flattened specimens of conotubus and gaojiashania are preserved as carbonaceous compressions which are in some cases associated with aluminosilicate minerals rare compressed specimens of conotubus are replicated by greenish clay minerals which are interpreted as diagenetic products of aluminosilicate precursors our taphonomic analysis shows that pervasive authigenic pyritization tends to replicate more labile tissues than aluminosilicate aided carbonaceous compression but both pyritization and aluminosilicification processes can facilitate the replication and preservation of soft bodied organisms in siliciclastic sediments building upon this conclusion we propose that multiple taphonomic processes including kerogenization or polymerization of organic molecules pyritization and aluminosilicification can contribute to the mode of bst preservation viewed in this light various siliciclastic hosted lagerstatten that are facilitated by kerogenization pyritization and aluminosilicification can be plotted on a ternary diagram based on the relative importance of these taphonomic processes

perils in distinguishing phreatic from phreatomagmatic ash insights into the eruption mechanisms of the 6 august 2012 mt tongariro eruption new zealand abstract the weak geophysical precursors of the 6 august 2012 te maari eruption of mt tongariro and a lack of obvious juvenile components in its proximal ballistic deposits imply that the eruption was caused by the sudden decompression of a sealed hot hydrothermal system strong magmatic signals in pre and post eruption gas emissions indicate that fresh magma had intruded to shallow levels shortly before this eruption here we examine the volcanic ash produced during the august eruption with the aim of determining whether juvenile magma was erupted or not the widely applied criteria for identifying fresh juvenile pyroclasts provided inconclusive results the te maari ash sorting and trend towards a unimodal grain size distribution increase with distance along the dispersal axis proximal to intermediate sites showing polymodal grain size distributions can be related to the re fragmentation of different pre existing lithologies overlapped erupted pulses and transport mechanisms and to particle aggregation between 69 and 100 vol of particles coarser than 3 and 45 75 vol of grains finer than 3 were sourced from the pre existing commonly hydrothermally altered vent area lavas and pyroclasts free crystals pyroxene plagioclase magnetite pyrite make up 0 23 vol of particles coarser than 3 and 22 41 vol of grains finer than 3 brown to black fragments of fresh glass are a small 1 15 vol but notable component under sem these blocky glassy particles are poorly vesicular and irregularly shaped some with fluidal or bubble wall surfaces and others with fragmented stepped surfaces and fine adhering ash in thin section they contain variable amounts of microlites within an isotropic groundmass the range in silica content of the microprobe analysed glass is very wide 56 77 wt and cannot be correlated to any specific particle textural type these chemically and texturally diverse glassy fragments are identical to mechanically broken pieces of country rock lavas and pyroclasts both their diversity and their match with vent country rocks argue strongly against a juvenile origin for the glassy fragments we conclude that rising magma provided only heat and gas into the overlying sealed vapour dominated hydrothermal system a landslide from this area led to a rapid decompression and ash was produced by top down hydrothermal explosions careful attention must be paid to the combination of compositions and textures of fine ash particles in such situations as well as to the context of their source vent in order to be confident that new magma has reached the surface

multi stage chaotic magma mixing at turrialba volcano abstract after a century of quiescence turrialba a quaternary stratovolcano in the costa rican volcanic front started a new eruptive cycle in 2010 that is ongoing to this date july 3rd 2019 violent eruptions began in 2014 producing columns of ash that reached 4 km above the summit of the volcano here we provide new major and trace element data from fresh glassy fragments basaltic to rhyolitic and mineralogical data for feldspars olivines and pyroxenes from ash fallout collected from 2016 and 2017 eruptions we investigate the composition of the magma replenishing the system as well as the different juvenile components involved in the latter phase of this renewed eruption cycle we find a range of mafic to felsic compositions in every eruptive event sampled our new geochemical data coupled with monte carlo binary mixing simulations indicate that magmas at turrialba volcano are influenced by the input of a back arc type strongly high field strength element enriched 20 60 ppm component generated by decompression melting from subduction driven corner flow thermodynamic modeling using melts software suggests that fractional crystallization alone fails to explain the compositional range of turrialba s eruptive products we instead propose that a complex multi stage magma mixing process produced renewed activity at turrialba based on the trace element variability the dominant intermediate magmatic compositions observed and the results of our multi element mixing simulations this mixing process occurs upon injection of new mantle derived melts into turrialba s fractionated magmatic reservoirs and is governed by chaotic dynamics induced by gradients in temperature and viscosity

stratigraphic controls of soft bodied fossil occurrences in the cambrian chengjiang biota lagerstatte maotianshan shale yunnan province china abstract the early cambrian maotianshan shale exposed near kunming china is one of the oldest and best preserved konservat lagerstatten containing the chengjiang biota although the fossils have been well studied the depositional processes and stratigraphic relationships amongst the fossil bearing localities are poorly understood largely due to limited continuous exposures and structural complexity in this area in this study we use a detailed facies and stacking pattern analysis to delineate the depositional history and stratigraphic relationship of the maotianshan sedimentologic observations from five prolific fossil localities of the chengjiang biota have yielded six distinct facies within the maotianshan shale the three coarse grained facies composed of siltstones and very fine sandstones f1 f3 contain sedimentary structures including hummocky cross stratification and combined flow ripples that are consistent with deposition within storm wave base the fine grained facies composed of interbedded silty mudstones and clay rich mudstones f4 f6 were deposited below the wave base and represent episodes of lower storm frequency and pelagic sedimentation these six facies have specific stacking patterns indicating the presence of five distinct depositional units each of those depositional units is bound on its upper and lower contact by a flooding surface fining upward successions near the base of each stratigraphic unit are interpreted as short lived marine transgressions these are overlain by coarsening upward stacked facies interpreted as a period of shoreline progradation the fossils of the chengjiang fauna are exclusively found in the coarsening upward part of the depositional units the oldest fossil bearing intervals are associated with the most westerns sections in the study area in contrast the youngest fossil bearing intervals are found in the most eastern sections this time transgressive relationship is interpreted to reflect a genetic relation between distinct sedimentary processes and environments and the burial and preservation of the chengjiang biota

mechanism for burgess shale type preservation exceptionally preserved fossil biotas of the burgess shale and a handful of other similar cambrian deposits provide rare but critical insights into the early diversification of animals the extraordinary preservation of labile tissues in these geographically widespread but temporally restricted soft bodied fossil assemblages has remained enigmatic since walcott s initial discovery in 1909 here we demonstrate the mechanism of burgess shale type preservation using sedimentologic and geochemical data from the chengjiang burgess shale and five other principal burgess shale type deposits sulfur isotope evidence from sedimentary pyrites reveals that the exquisite fossilization of organic remains as carbonaceous compressions resulted from early inhibition of microbial activity in the sediments by means of oxidant deprivation low sulfate concentrations in the global ocean and low oxygen bottom water conditions at the sites of deposition resulted in reduced oxidant availability subsequently rapid entombment of fossils in fine grained sediments and early sealing of sediments by pervasive carbonate cements at bed tops restricted oxidant flux into the sediments a permeability barrier provided by bed capping cements that were emplaced at the seafloor is a feature that is shared among burgess shale type deposits and resulted from the unusually high alkalinity of cambrian oceans thus burgess shale type preservation of soft bodied fossil assemblages worldwide was promoted by unique aspects of early paleozoic seawater chemistry that strongly impacted sediment diagenesis providing a fundamentally unique record of the immediate aftermath of the cambrian explosion

geophysical geochemical and geodetical signals of reawakening at turrialba volcano costa rica after almost 150 years of quiescence article i nfo turrialba is a basaltic andesitic stratovolcano 3340 masl in the cordillera volcanica central in costa rica after the last eruption 1864 1866 volcanic manifestations were limited to weak fumarolic discharge continuous since 1980 from the summit from 1996 onward the degassing activity has progressively been increasing reaching its climax after 2005 new fumaroles have appeared in the central and west summit craters the latter now being the most active and in the fracture system in between showing sulphur deposits and progressively increasing degassing rate in 2004 fumaroles and new fissures have appeared on the sw outer and ssw distal flanks the latter being located along a major ne oriented tectonic lineament fumarolic temperatures at the bottom of the west crater have increased from 88 to 282 c in early 2008 changes in chemical and isotopic compositions of discharged fluids have shown a progressive enhancing of the magmatic signature since 2001 since late 2007 so2 flux measured with mini doas has increased two orders of magnitude 1 t day in 2002 to 740 t day in january 2008 the enhanced gas discharge at turrialba volcano has caused significant interference on tropospheric o3 measurements at 2 3 km altitude 50 km w from the volcano seismic swarms followed an increasing trend consistent with that of the fumaroles the maximum seismic activity to date up to thousands of events day was recorded in mid 2007 an inflationary trend was observed in the crater area in this paper we present for the first time all the available data on the activity of turrialba volcano new geophysical geodetical and geochemical data and published geophysical and geochemical data are presented and discussed as a whole the multidisciplinary approach indicated that from 1996 to 2009 three stages deriving by the delicate equilibrium between the hydrothermal and the magmatic reservoirs were recognized the magmatic dominated phase is still prevailing as evidenced by the fact that while completing the present paper on the 4th of january 2010 at 16 57 gmt a loud explosion occurred at the west crater and was followed by three others spaced out every 10 min these events were interpreted as associated with phreatic eruptions

a new macroalgal assemblage from the xiaoshiba biota cambrian series 2 stage 3 of southern china abstract exquisitely preserved burgess shale type fossils from the xiaoshiba lagerstatte in the cambrian series 2 hongjingshao formation of southern china provide remarkable perspective on early metazoans but have never been reported with plants here we first recognize a new assemblage of highly mineralized macroalgae from this biota based on morphological differences there are three new genera and four new species identified doulia rara gen et sp nov eolaminaria simigladiola sp nov singulariphyca ramosa gen et sp nov and rugophyca longa gen et sp nov relative to the other three species s ramosa is widely distributed among the beds which may indicate a dominat species in this community this new discovery fills part of the long gap in the detailed record of macroalgae between the chengjiang biota and the kaili biota representing a localized macroalgal flourish at the end of cambrian stage 3 the assemblage that shows morphological characters similar to some macroalgae found in the precambrian and primitive to those of the cambrian stage 5 lays the basis for revealing the evolutionary biology of early macroalgae and understanding the precambrian cambrian transition questions taphonomic study of this fossiliferous bed indicates that some well preserved macroalgae are preserved within their original habitats through analyzing the depositional environments of the known cambrian macroalgae we suggest that macroalgae tend to be preserved in relatively deep marine environments with less disturbance

experimental rapid alteration of basaltic glass implications for the origins of atmospheric particulates glassy microspherules collected from the plume of etna volcano show a surprising compositional variability with sio 2 from 48 to 90 wt despite a very homogeneous basaltic source magma sio 2 48 this same variability is also observed in individual microspherules from their inner to outer parts the most plausible hypothesis concerning these compositional variabilities is the interaction of the microspherules with the volcanic gases inside the crater prior to their atmospheric dispersal in order to study this compositional variability we experimentally exposed basaltic glass to volcanic gases at etna the resulting glass composition documents a fundamental alteration mechanism involving an apparent leaching process that can rapidly form nearly pure silica because microspherules erupted directly into the air from lava fountains remain unaltered the duration of microspherules within a gas plume can explain the chemical variability of glass alteration a major implication for the origin of glassy atmospheric particulates is that chemical compositions cannot be used as a reliable indicator of their source e g meteoric volcanic anthropogenic

image processing analysis in reconstructing fragmentation and transportation mechanisms of pyroclastic deposits the case of monte pilato rocche rosse eruptions lipari aeolian islands italy abstract a quantitative study of particle morphology of samples from monte pilato rocche rosse deposits lipari aeolian islands italy shows a significant variability in particle structure and texture the study consisted of image processing techniques and multivariate statistical methods in analysis of the quantitative particle morphology data with the goal of identifying the genetic processes responsible for the formation of the deposits from these investigations we numerically define the form of the clasts thus avoiding subjectivity in the classification of clast morphology starting from this clast definition we then construct diagrams in which clasts due to different genetic processes i e magmatic vs hydromagmatic fragmentation are discriminated based on simple nondimensional parameters the application of the methods used seems to be of general interest in discriminating the fragmentation and transportation dynamics responsible for the formation of pyroclastic deposits