variation of co2 so2 ratio in volcanic plumes of miyakejima stable degassing deduced from heliborne measurements 1 heliborne measurements of co2 so2 ratio in a volcanic plume were performed at miyakejima volcano which has degassed intensively since september 2000 the repeated measurements started in october 2000 and showed constant molar co2 so2 ratio at 0 75 0 25 despite decreased so2 emission rate from 42 kt d in late 2000 to 16 kt d in late 2001 the co2 emission rate also decreased from 21 kt d in late 2000 to 8 kt d in late 2001 the co2 content in the magma is estimated to be 1200 ppm based on the mole ratio and s content in melt inclusions 1300 ppm the estimated co2 content corresponds to a saturation pressure of 280 mpa suggesting the presence of co2 rich bubbles in the magma chamber located at 4 km the constant co2 so2 ratio over the year implies a stable magma degassing process without a change in the composition of the degassing magma

using infrasound waves from eruption video to explain ground deformation preceding the eruption of suwanosejima volcano japan abstract combined video infrasound and seismic observations were conducted at suwanosejima volcano in august 2005 and the processes producing infrasound radiation at the onset of an eruption were examined based on the results of the observations infrasound waveforms were found to exhibit a slow weak pressure increase preceding phase 0 7 s before the large rapid main compression phase these pressure changes induced a subtle h2o phase change in steam discharged from the crater which could not be easily recognized in the normal video images however propagation of the pressure waves could be identified by image processing as luminance variations above the crater these variations coincided with the compression phase of the infrasound wave the origin time of the preceding phase estimated from the arrival times of an infrasound wave at two different stations and the luminance data was almost identical to the time when based on the seismic signals a vertical expansion occurred at a depth of about 0 5 km beneath the crater bottom considering the eruption processes of sakurajima volcano it was concluded that the preceding phase of the infrasound wave was caused by swelling of the ground surface at the crater bottom due to this expansion beneath the crater in the case of the suwanosejima eruption the volumetric change due this ground uplift was estimated to be 30 40 m3 the origin time of the subsequent main phase of the infrasound wave coincided with the onset of volcanic material ejection this suggests that the crater bottom which acted as a lid to the pressurized magma and gases before the eruption failed due to the expansion that occurred during the 0 7 s period prior to the eruption

the great extinction that never happened the demise of the dinosaurs considered the concept of a sudden extinction of the dinosaurs consequent upon the impact of some extraterrestrial object is so dramatic that it has taken hold upon the imaginations of many scientists as w

significant changes in land vegetation and oceanic redox across the cretaceous paleogene boundary abstract the impact of an extraterrestrial body 65 5 ma caused the so called cretaceous paleogene k pg event that resulted in a mass extinction and rapid changes in the surface environment on earth here we report changes in land vegetation and oceanic redox across the k pg boundary at caravaca southeastern spain using biomarkers the results reveal that the basal 3 mm thick layer of the k pg boundary clay is marked by a rapid increase in the concentration of terrestrial long chain n alkanes and dibenzofuran indicating the destruction of land vegetation and an increase in the supply of terrestrial organic matter into the marine environment during the deposition of the k pg boundary clay this layer also records a rapid increase in the concentration of dibenzothiophenes which indicates a change in redox conditions from oxic to anoxic euxinic conditions in the intermediate water over the seafloor the low oxygen conditions could have been caused by an increase in the influx of terrestrial organic matter into the ocean a rapid increase in the concentration of retene and retene cadalene occurred during the deposition of the upper part of the boundary clay 10 kyr after the mass extinction indicating the recovery of conifers which greatly decreased at the k pg boundary

the nature of volcanic earthquake swarm preceding the 2000 flank eruption at usu volcano hokkaido japan summary the 2000 eruption of usu volcano hokkaido occurred on the northwestern flank of volcano on march 31 at 13 07 local time after about 4 days of intensive seismic activity we study the seismic process prior to the eruption using the routine earthquake catalogue of the japan meteorological agency jma and the digital seismograms of the short period station nbbt jma earthquakes began beneath the summit and southern slope of the volcano then seismic foci clustered along two linear zones intersecting to the south of the initial epicentral zone the majority of earthquakes occurred at depth within the range between 4 and 7 km the magnitude range of located earthquakes varied between 0 8 and 4 4 the earthquake epicentres did not reach the sites of the forthcoming eruption they stopped at a distance of about 1 3 km the eruption began during the ceasing of seismic activity a study of the nature of the swarm was performed for a sample of 303 earthquakes with a magnitude interval from 2 5 to 3 4 that were representative of the swarm visual analysis allowed separating the earthquakes into two groups 286 volcano tectonic vt earthquakes and 17 long period lp earthquakes the spectral analysis of s wave so f274 vt earthquakes in the frame of brune s model showed that the vt earthquakes may be separated into two groups as characterized by high stress drops hsd and low stress drops lsd the swarm began with hsd earthquakes the lsd and lp earthquakes were recorded about 30 40 hr later simultaneously with the beginning of deformation of volcanic edifice and accompanied the hsd earthquakes up to the beginning of eruption we attribute the hsd earthquakes to the probable product of magmatic thermal fracturing of host rocks the relatively long lsd ruptures may be attributed to the slips along the pre existing fractures during magma movement

long term soil erosion derived from in situ 10be and inventories of meteoric 10be in deeply weathered soils in southern brazil abstract meteoric 10 be is commonly used as a geochemical tracer of soil erosion and regolith residence time over long time scales 10 3 yr the acidic conditions of tropical soils are less favorable for meteoric 10 be retention and make a translation of meteoric 10 be inventories into surface erosion rates complex in this empirical study we evaluate the potential loss of meteoric 10 be in the weathering zone along a toposequence in southern brazil three regolith profiles were sampled to explore the mobility of be in the soil system the sequential chemical extractions of four reactive fractions indicate that the amorphous oxy hydroxide and crystalline oxide fractions are the main carriers of meteoric 10 be our data from the brazilian toposequence reveal significantly higher inventories of meteoric 10 be in the slope concavities compared to the upslope positions this demonstrates that chemical leaching and deep percolation of meteoric 10 be within the soil profile leads to vertical and lateral redistribution of meteoric 10 be across the hillslope our data show that more than 50 of the delivered meteoric 10 be is leached from the upslope regolith profiles after correcting the inventories for incomplete retention of meteoric 10 be surface erosion rates are derived for the slope convexities upslope erosion rates are below 5 mm kyr and agree with the in situ 10 be derived denudation rates our results suggest that soil and sediment fluxes can accurately be derived from meteoric 10 be inventories in well developed soils when the meteoric 10 be mobility is constrained using differential mass balances

the dynamics and thermodynamics of volcanic clouds theory and observations from the april 15 and april 21 1990 eruptions of redoubt volcano alaska on april 15 1990 and april 21 1990 two relatively small explosive eruptions occurred at redoubt volcano alaska lasting about 4 and 8 minutes respectively on both occasions the erupted material travelled as a pyroclastic flow down an ice canyon on the north flank of the volcano using slow scan television recordings of the eruption and the seismic record in both the near and far field we deduce that after a few minutes the upper parts of these pyroclastic flows became buoyant and a large and hot ash cloud ascended off the flow these thermals rose to a height of about 12 km at which point they began to spread laterally as umbrella clouds using a simple thermodynamic model we estimate that the clouds had a temperature in the approximate range 600 700 k as they rose buoyantly from the flow after entraining and heating air and melting and vaporizing ice we also estimate that in each eruption approximately 109 kg of fine ash was injected into the atmosphere during the april 15 eruption a slow scan television camera recorded the ascent of the cloud these observations are described analysed and compared with the predictions of a new model for the dynamics governing the ascent of such clouds in accord with the observations our model predicts that the cloud initially ascended rather sluggishly since it is only just buoyant on rising from the pyroclastic flow as it ascends it entrains and heats up more air and hence generates more buoyancy therefore it accelerates upwards only much higher in the cloud does the velocity decrease again as the thermal energy of the cloud becomes exhausted the model also predicts that the height of rise of such coignimbrite thermals is a function of the initial mass and temperature of the cloud but is almost independent of the initial velocity during the april 21 eruption a sequence of photographs recorded the lateral spreading of the umbrella cloud during an interval of about 10 minutes after the eruption these photographs are analysed and successfully compared with a simple model for the spreading of the umbrella cloud as a gravity current in a stratified environment using an avhrr satellite image of the air fall deposit from the april 15 eruption combined with a simple model we suggest that the primary mechanism of ash dispersal was transport by the ambient wind

kinematic features of isolated volcanic clouds revealed by video records 1 ascent processes of small volcanic clouds are analyzed using video records obtained for some eruptive events at asama and miyakejima volcanoes japan in this analysis each segment of the volcanic cloud is treated as an isolated thermal i e a spherical body ascending independently by its buoyancy our kinematic analysis reveals simple relationships among the ascent velocity radius and height of volcanic clouds the applicability of the entrainment hypothesis and the relation that was obtained from a dimensional analysis by scorer is examined for natural volcanic clouds the empirical dimensionless constants characterizing the entrainment hypothesis and the scorer s relation are more or less scattered and their mean values are about 0 36 and 0 6 respectively these empirical relations can be used to evaluate kinematic features of volcanic clouds approximately without thermodynamic consideration

turbulent metal silicate mixing fragmentation and equilibration in magma oceans abstract much of the earth was built by high energy impacts of planetesimals and embryos many of these impactors already differentiated with metallic cores of their own geochemical data provide critical information on the timing of accretion and the prevailing physical conditions but their interpretation depends critically on the degree of metal silicate chemical equilibration during core mantle differentiation which is poorly constrained efficient equilibration requires that the large volumes of iron derived from impactor cores mix with molten silicates down to scales small enough to allow fast metal silicate mass transfer here we use fluid dynamics experiments to show that large metal blobs falling in a magma ocean mix with the molten silicate through turbulent entrainment with fragmentation into droplets eventually resulting from the entrainment process in our experiments fragmentation of the dense fluid occurs after falling a distance equal to 3 4 times its initial diameter at which point a sizable volume of ambient fluid has already been entrained and mixed with the dense falling fluid contrary to previous assumptions we demonstrate that fragmentation of the metallic phase into droplets may not be required for efficient equilibration turbulent mixing by drastically increasing the metal silicate interfacial area may result in fast equilibration even before fragmentation efficient re equilibration is predicted for impactors of size small compared to the magma ocean depth in contrast much less re equilibration is predicted for large impacts in situations where the impactor core diameter approaches the magma ocean thickness

late cretaceous to early paleocene climate and sea level fluctuations the tunisian record abstract climate and sea level fluctuations across the cretaceous tertiary k t transition in tunisia were examined based on bulk rock and clay mineralogies biostratigraphy and lithology in five sections el melah el kef elles ain settara and seldja spanning from open marine to shallow inner neritic environments late campanian to early danian trends examined at el kef and elles indicate an increasingly more humid climate associated with sea level fluctuations and increased detrital influx that culminates at the k t transition this long term trend in increasing humidity and runoff in the tethys region is associated with middle and high latitude cooling results of short term changes across the k t transition indicate a sea level lowstand in the latest maastrichtian about 25 100 ka below the k t boundary with the regression marked by increased detrital influx at el kef and elles and a short hiatus at ain settara a rising sea level at the end of the maastrichtian is expressed at elles and el kef by deposition of a foraminiferal packstone a flooding surface and condensed sedimentation mark the k t boundary clay which is rich in terrestrial organic matter the p0 p1a transition is marked by a sea level lowstand corresponding to a short hiatus at ain settara where most of p0 is missing and a period of non deposition and erosion in the lower part of p1a 64 95 ma at seldja p0 and possibly the topmost part of cf1 are missing these sea level fluctuations are associated with maximum humidity these data suggest that in tunisia long term environmental stresses during the last 500 ka before the k t boundary and continuing into the early danian are primarily related to climate and sea level fluctuations within this long term climatic trend the pronounced warm and humid event within the latest maastrichtian zone cf1 may be linked to greenhouse conditions induced by deccan volcanism the absence of any significant clay mineral variations at or near the k t boundary and ir anomaly suggests that the bolide impact had a relatively incidental short term effect on climate in the tethys region

carbon isotope evidence for the timing of the cretaceous palaeogene macrobenthic colonisation at the agost section southeast spain abstract the cretaceous palaeogene k t boundary section of agost southeast spain one of the most complete sections existing contains a well developed trace fossil assemblage composed of dark and light filled trace fossils registered in the uppermost cretaceous maastrichtian plummerita hantkeninoides biozone sediments the trace fossil assemblage reveals that significant macrobenthic colonisation occurred around the k t boundary interval however difficulties in recognising trace fossils affecting the k t boundary layer as well as in biostratigraphically characterising these trace fossils hindered a conclusive interpretation on the timing of this macrobenthic colonisation with the aim of this characterisation we determined the 13c of the carbonate fraction of dark and light filling materials from the trace fossils since the carbon isotope compositions of uppermost cretaceous and lowermost palaeogene materials are clearly different the data compiled provide evidence for a significant distinction between light filled trace fossils with 13c values higher than 1 6 peedee belemnite pdb and dark filled trace fossils with 13c values between 0 21 and 1 2 pdb most of these being lower than 0 7 pdb the comparison of these values with those from the uppermost maastrichtian to the lowermost danian sediments reveals that the macrobenthic colonisation occurred in different phases across the k t boundary interval

experiments on turbulent metal silicate mixing in a magma ocean we compare the results of laboratory fluid dynamics experiments with theoretical models of turbulent entrainment in two phase buoyant plumes and thermals to estimate the amount of mixing between the iron core of a planetesimal or planetary embryo and the molten silicates in a magma pool formed by its impact with a growing planet during accretion we demonstrate experimentally that turbulent plumes in immiscible fluids fragment into droplets and that the envelope of the droplet distribution is indistinguishable from the envelope of a turbulent plume in a single phase fluid under the same dynamical conditions implying that turbulent entrainment concepts are applicable to immiscible fluids mixing a series of experiments are made on the time evolution of a two phase turbulent thermal representing a planetesimal core falling under its own negative buoyancy in a spherical fluid representing an impact produced magma pool two stages of mixing are observed in these experiments the first corresponding to turbulent entrainment during free fall of the thermal the second corresponding to entrainment in turbulent gravity currents that form after the thermal reaches the base of the magma pool we demonstrate that the amount of mixing between metals and silicate liquids in a magma pool depends on the rouse number of the metal fragments and increases rapidly with the radius of the proto planet we derive a similarity model for metal silicate mixing in a spherical magma pool assuming a constant entrainment coefficient for the turbulent liquid metal phase this model supports our experimental finding that a small metal core of an impactor will become diluted i e mix within a deep magma pool but a large impacting core will not fully dilute before reaching the base of the magma pool

crustal structure of northern spitsbergen along the deep seismic transect between the molloy deep and nordaustlandet a deep seismic sounding experiment was performed during the expedition arktis xv 2of the rv polarstern and the polish ship eltanin in 1999 in the continent ocean transitionzone of northwestern svalbard along the 430 km long profile awi 99200 the profile runsfrom the molloy deep in the vicinity of an active spreading axis in the northern atlantic tonordaustlandet seismic energy airgun andtntshots was recorded by seismic land onshore stations obss and hydrophone systems with airgun shots recorded up to 200 km onshore and50 km offshore the data recorded along the entire profile provide an excellent database fora detailed seismic modelling of the crustal p wave velocity field along the profile track aminimal depth of about 6 km to the moho discontinuity was found east of the molloy deep here the upper mantle exhibits a p wave velocity of about 7 9 km s 1 and the crustal thicknessdoes not exceed 4 km the continent ocean transition zone to the east is characterized by acomplex seismic velocity structure the moho interface reaches a maximum depth of 28 kmbeneath the continental part of the profile with a p wave velocity in the upper mantle of8 15 km s 1 the continental crust consists of three layers with p wave velocities of about5 5 5 9 6 0 and 6 2 6 6 km s 1 respectively in addition we have found two reflectors in themantle lithosphere at depths of 14 42 and 40 50 km dipping ne the evolution of the regionappears to be within a shear rift tectonic setting the continent ocean transition zone is mostlydominated by extension so the last stage of the development of this margin can be classifiedas rifting the uplifted moho boundary close to the molloy deep can be interpreted as thesouthwestern end of the molloy ridge

stable isotope and foraminiferal changes across the cretaceous tertiary boundary at stevns klint denmark arguments for long term oceanic instability before and after bolide impact event abstract stable isotope and planktic and benthic foraminiferal analyses of the k t boundary transition at stevens klint denmark indicate a 100 500 kyr long period of instability in oceanic bottom water temperature and sea level during the latest maastrichtian from 2 7 m below and up to the k t boundary bottom water temperatures gradually cooled about 1 5 c as surface water temperatures remained constant at the k t boundary bottom water temperatures decreased additionally 3 c and then returned to pre boundary values just above the boundary interval coincident with the onset of the first temperature decrease there was a prominent sea level fall estimated between 50 100 m as observed in benthic and planktic foraminiferal assemblages as well as in a decreasing surface to bottom 13 c gradient about 40 cm below the iridium rich k t boundary clay sea level began to rise poor preservation of foraminifera above the k t boundary allows only tentative interpretation of danian events at stevns klint however sea level generally continued to rise interrupted by short sea level falls associated with the observed sea level changes are three important hiatuses at the contact between the white chalk and overlying grey white bryozoan chalk about 2 7 m below the k t boundary at or near the top of the fish clay zone pla parvularugoglobigerina eugubina missing and at the contact of the cerithium limestone and overlying bryozoan limestone about 60 cm above the k t boundary part of zone plc missing these unconformities are coeval with hiatuses observed in many continental shelf sections and indicate a global eustatic rather than regional isostatic response notable is that at stevns klint the episode of oceanic instability is registered over approximately the same stratigraphic interval in which supposed extraterrestrial amino acids occur a circumstance that may indicate a connection a gradual positive shift in 13 c is registered in both benthic and planktic foraminiferal assemblages in the upper maastrichtian at stevns klint the positive shift is followed by a prominent negative 13 c shift 1 3 at the k t boundary an upper maastrichtian positive 13 c excursion followed by a negative 13 c anomaly at or near the k t boundary has previously been observed in deep sea cores from the pacific ocean and the weddell sea antarctica implying a global event previous suggestions of a relation between the uppermost maastrichtian positive 13 c excursion and sea level variation are not supported by the data for stevns klint

how complete are cretaceous tertiary boundary sections a chronostratigraphic estimate based on graphic correlation cogent interpretations of data bearing on the cretaceous tertiary k t extinction controversy depend on the existence of accurate chronostratigraphic models for the various k t boundary sections we have employed the graphic correlation technique to summarize biostratigraphic and lithostratigraphic data from 15 intensively sampled k t boundary sections within a common chronostratigraphic model our results indicate that almost all of these sections along with 13 additional boundary sections not used to construct the model contain prolonged and in many cases multiple hiatuses of these 28 boundary sections only six were found to contain a continuous record of sediment accumulation across the k t boundary itself these six k t complete sections are el kef tunisia agost spain caravaca spain and three sections along the brazos river texas a comparative analysis of hiatus distributions among these 28 k t boundary sections also reveals the presence of systematic differences between continental shelf and deep sea depositional environments the lower danian interval immediately following the k t boundary and extending into biochronozones p0 and p1a is typically missing from the deep sea whereas boundary sections deposited in shallower middle neritic to upper slope environments are in most cases complete across the k t boundary these shallow neritic boundary sections however are in many instances disrupted by hiatuses at the p0 p1a boundary and again in the upper part of zone p1a these differential patterns of hiatus distribution between deep sea and continental shelf depositional settings appear to be linked to sea level fluctuations our data suggest that the apparently sudden mass extinction of planktonic foraminifera and anomalies in the occurrence of geochemical tracers that are characteristic of the k t boundary in deep sea sections may be artifacts of a temporally incomplete deep sea stratigraphic record

relationship between infrasound derived and buoyancy derived eruption plume volume estimates volume estimations for discrete plumes accompanying short lived eruptions are potentially possible using infrasound signals plumes emitted during short lived discrete eruptions have been modeled as discrete thermals or rooted thermals based on the one dimensional model for the rise of a discrete thermal the initial buoyancy f0 of a spherical thermal can theoretically be estimated from the maximum plume height and a vertical profile of ambient air density we here examine the relationship between infrasound derived volume vinf and the buoyancy derived volume vb as derived from f0 which depends on gravity acceleration and the difference in density between the thermal and surrounding air to understand how vinf relates to the dynamics of the eruption plume we analyze infrasound data accompanying vulcanian and phreatic eruptions at aso shinmoedake and lokon empung volcanoes to estimate vinf and consider vinf from other volcanoes we obtain a representative ratio of vb vinf of 16 by examining 53 events because the analyzed infrasound signals share a prominent pressure pulse at the onset we regard vinf as the volume of the plume at initiation i e as a jet instead we consider vb as the thermal volume when it has entrained a sufficient amount of the surrounding air and obtains f0 comparison of the bulk density of the jet and the discrete thermal yields a rate of volume change between both regimes by a factor of 1 8 32 which is consistent with the ratio of vb vinf our result provides an effective index to constrain erupted plume volume using infrasound data with real time monitoring systems

explosive volcanic eruptions v observations of plume dynamics during the 1979 soufriere eruption st vincent summary during the 1979 eruption of the soufritre of st vincent west indies a 14min period of explosive activity occurred on april 22 the first three minutes of this activity were filmed five individual explosions formed distinct plumes which fed an eruption column which eventually ascended to a height of over 18 km the ascent velocities of the fronts of these plumes ranged from 8 5 to 61 7m s the half angle of spreading of the plume fronts ranged from 21 5 to 24 one of the plumes was observed to 8 km height and decelerated steadily from 5 1 5 to 23 m s l the main column fed by individual explosions was however observed to accelerate from 8 5 to 58 m s l in the same height interval a theoretical treatment of volcanic plume motion is presented measurements of dimensions velocities and spreading rates from the film are used to estimate plume parameters such as temperature particle content and volume discharge rate of magma from the theoretical relationships these calculations show that the individual plumes became hotter and richer in juvenile ash with time the acceleration of the main eruption column was the result of being fed by increasingly hotter and more ash rich explosions an average volume discharge rate of 12600m3s is estimated from the analysis of the plume motions this value agrees closely with an estimate of discharge rate based on the heat flux required to form an 18 km high column this agreement suggests that theories of convective motions in plumes can be successfully adapted to the volcanic case as long as the effect of hot entrained ash particles is considered

hydrothermal system beneath aso volcano as inferred from self potential mapping and resistivity structure abstract we conducted self potential sp surveys sequentially from part to part over the central cones of aso volcano since august 1998 by december 2001 the compiled sp map revealed large sp anomalies on the central cones the main feature of the sp map is a w shaped profile along the ns transect over the central cones it is probable that this characteristic sp profile is produced by the combination of hydrothermal upwelling in the middle and topographic effect a positive anomaly showing a large concentric pattern has appeared after correcting the topographic effect to evaluate this sp anomaly we implemented a numerical code that calculates electric potential produced by arbitrarily positioned current sources and sinks in any three dimensional resistivity structure a layered structure obtained from a time domain electromagnetic tdem field experiment was used for the resistivity model the estimated current source is 300 a being located in a conductive layer around the sea level meanwhile sinks were estimated to sit on a circular area corresponding to the marginal part of the conductive layer water and heat budget study gives a lower limit of water mass transfer from depth to the bottom of the crater lake of nakadake this value was used to estimate the equivalent current in either case of electro kinetic ek mizutani h ishido t 1976 a new interpretation of magnetic field variation associated with the matsushiro earthquakes j geomag geoelectr 28 179 188 or rapid fluid disruption rfd process johnston m j s byerlee j d lockner d 2001 rapid fluid disruption a source for self potential anomalies on volcanoes j geophys res 106 b3 4327 4335 this comparison suggests that the former process is preferable to explain the observed sp anomaly from these results we infer a large scale hydrothermal system beneath the central cones of aso volcano in which the fluid flow initiates from the surrounding area converging to the central vent to transport the heat and materials up to the crater lake of nakadake through a vapor filled conduit

biochemostratigraphy of an upper albian turonian succession from the southeastern neo tethys margin sw iran abstract a neo tethyan upper albian turonian hemi pelagic carbonate succession sarvak formation accessible in outcrop in the zagros sw iran was investigated using sedimentology microfacies analysis planktonic foraminifera biostratigraphy and carbon isotope stratigraphy the succession contains six biozones including thalmanninella th appenninica th globotruncanoides rotalipora cushmani whiteinella archaeocretacea helvetoglobotruncana helvetica and marginotruncana schneegansi some of these biozones show variable stratigraphic positions throughout the tethyan and boreal realms that hinder correlation of the studied iranian section with european reference sections therefore the correlation of the existing biostratigraphic framework was complemented by carbonate carbon isotope stratigraphy based on bulk carbonate material despite the low resolution of the presented carbon isotope record pronounced global events including the late turonian events cenomanian turonian boundary ctb event oae 2 and albian cenomanian boundary acb event can be distinguished the 13c excursions provide global synchronous time lines for correlation the distinguished biozones were compared among the sections regarding their stratigraphic positions relative to these time lines the correlation tentatively suggests that the biostratigraphic datum marking the acb is diachronous with an se nw trend first appearance datum fad of th appenninica varies from the upper albian to the lower cenomanian the fad of th globotruncanoides is also variable from the upper albian to the lower cenomanian however the middle cenomanian turonian biozones including rotalipora cushmani and whiteinella archaeocretacea zones are synchronous elevated pco2 contributed to the gradual increase of the sst sea surface temperature during the cenomanian and the dramatic climax at the earliest turonian this trend closely correlates with the change from the diachronous acb biozones to synchronous ctb biozones possibly increasing ssts provided temperature tolerance range for the species throughout different latitudes and assisted their rapid distribution moreover the warming raised the sea level from the latest albian to turonian that inundated landbridges resulting in an enhanced marine circulation and faster distribution of planktonic species throughout the neo tethys ocean

continent ocean transition on the voring plateau ne atlantic derived from densely sampled ocean bottom seismometer data 1 a 180 km long seismic wide angle profile was acquired across the voring plateau ne atlantic using a tuned air gun array and three component ocean bottom seismometers deployed with 5 km spacing the seismic p wave data have been modeled by ray tracing inversion and the model has been constrained by s wave and gravity modeling the data and modeling have allowed us to depict the crustal structure and nature of the continent ocean transition cot in a classical volcanic margin case the p wave velocity near the top of the main crustal layer is estimated to 6 0 km s landward of the 25 km wide cot the seaward increase to 6 5 km s in the cot is conformable with heavily intruded continental crust within this zone farther seaward the velocity increase to 6 9 km s in the same layer suggests the presence of oceanic crust the abundant magmatism landward of and within the cot is primarily observed as extrusives forming wedges of seaward dipping reflectors and mafic lower crustal intrusions underplating the maximum thickness of the oceanic crust is measured to 23 5 km at the seaward termination of the cot

moist convection and the injection of volcanic ash into the atmosphere if unsaturated water vapor is carried upward by a volcanic eruption column it may eventually become saturated owing to the decrease in temperature of the column as it expands through decompression and transfers heat to entrained air heat released as a result of the subsequent condensation of water vapor causes the air within the column to expand we show that this increases the buoyancy and therefore the total height of rise of the column the increase in height is significant in relatively small sub plinian and strombolian eruptions in which mass eruption rates lie in the range 103 to 106 kg s in such eruptions the latent heat released as the entrained water vapor condenses may provide the main source of heat which drives the ash and clasts upward the height of rise then becomes relatively insensitive to the mass flux erupted at the vent and depends primarily upon the vapor loading of the atmosphere in a moist atmosphere ash may rise several kilomtres higher than in an eruption of comparable strength in a dry environment moist convection leads to much wider ash dispersal particularly from very small eruptions subsequently rain flushing of ash from umbrella clouds may result from the water which forms through the condensation of entrained vapor the ash provides natural condensation nuclei for some of this entrained vapor whose mass may be much greater than that of the ash in small columns 107 kg s the latent heat released by condensation of vapor is relatively small in comparison with the thermal energy provided by the hot clasts and therefore moisture has no significant effect upon the eruption column dynamics furthermore the mass of water vapor originating from the erupted volatiles is usually comparable to or greater than that entrained from the ambient air our model also shows that if the erupting mixture becomes buoyant then the eruption columns associated with phreatomagmatic eruptions ascend nearly as high as plinian columns with the same mass eruption rate this is because the water which is vaporized by the hot ash at the source condenses higher in the column and thereby restores its latent heat to the ascending ash

the cretaceous tertiary boundary event in ecuador reduced biotic effects due to eastern boundary current setting a multidisciplinary study of a new cretaceous tertiary k t boundary section near guayaquil ecuador reveals an unusually cool water low diversity planktic foraminiferal fauna and a high diversity radiolarian fauna similar to those found in southern high latitude k t sequences despite the fact that this section was deposited near the cretaceous equator the k t boundary is located by planktic foraminifera within a narrow interval bounded by last appearances of tropical cretaceous species and first appearances of tertiary species including parvularugoglobigerina eugubina as in southern high latitudes there is no major mass extinction of either planktic foraminifera or radiolarians at this level a major radiolarian faunal discontinuity occurs some 6 m higher in the section within foraminiferal zone plc some 300 500 kyr after the k t event 13c values from bulk carbonates show both high and low latitude characteristics similarly to low latitudes there is a 3 negative 13c excursion at the k t boundary which is generally interpreted as a major decrease in primary productivity but unlike the low latitudes recovery occurs within a few thousand years as compared with 300 500 kyr and suggests rapid nutrient influx from the antarctic region via a current similar to the humboldt current today similarly to high latitude k t sequences a negative 13c shift occurs in the early danian zone plb about 300 kyr after the k t boundary sedimentologic and mineralogic data indicate a late maastrichtian with relatively low biogenic quartz and high carbonate followed by increasing biogenic quartz 50 and decreasing carbonate 5 during the early danian this suggests intensified atmospheric and oceanic circulation and upwelling off ecuador during the early danian the k t transition is marked by increased volcanic activity continental erosion and terrigenous influx but this also occurs in the early danian zone at the p1ap1b zonal transition and is thus not unique to the k t boundary we suggest that the catastrophic biotic effects normally observed at the k t boundary in low latitudes are greatly reduced or absent in the eastern equatorial pacific because this region was dominated then as now by upwelling and current transport of nutrient rich waters from the antarctic ocean as a result the biotic patterns are characteristic of southern high latitudes whereas the 13c pattern combines ameliorated low latitude effects with predominantly high latitude trends

caldera collapse during the 2000 eruption of miyakejima volcano japan a collapsed caldera 1 6 km in diameter and 450 m in depth was formed at the summit of miyakejima volcano during the 2000 eruption the collapsed caldera appeared on 8 july with a minor phreatic eruption 12 days after seismic activity and magma intrusion occurred northwest of the volcano growth of the caldera took from 8 july to the middle of august with seismic swarms associated with the continuous intrusion of magma northwest of the volcano the growth rate of the caldera was about 1 4 107 m3 day and the final volume of the collapsed caldera was about 6 108 m3 major phreatomagmatic eruptions produced a total of about 1 6 1010 kg 1 1 107 m3 of volcanic ash after caldera growth the caldera structure and the nature of the eruptive materials of the first collapse on 8 july suggest that the surface subsidence was caused by the upward migration of a steam filled cavity with stoping of the roof rock above the magma reservoir the diameter of the stoping column was estimated to be 600 700 m from circumferential faults that developed in the caldera floor and the collapse of the caldera wall enlarged the diameter of the caldera to 1 6 km the total volume of the caldera and the horizontal diameter of the stoping column gave a subsidence of the caldera floor of 1 6 2 1 km

changes in the pelagic fine fraction carbonate sedimentation during the cretaceous paleocene transition contribution of the separation technique to the study of bidart section abstract the bidart section southwestern france displays an almost complete late maastrichtian early danian transition as the cretaceous paleocene k p crisis mainly affects carbonate producers the aim of this study is to precisely evaluate the evolution of pelagic sediments composition across the boundary a new protocol for separation of fine carbonates into discrete size fractions was used 1 to precisely evaluate in weight of carbonate and not only number of particles per gram of rock the contribution of each carbonate component type foraminifera calcareous nannofossils and nonbiogenic carbonates calcite microparticles and calcareous macrocrystals and 2 to measure their isotopic signature and thus constrain the origin of these carbonate particles the maastrichtian pelagic carbonates are mostly biogenic 70 of the bulk carbonate but also contain nonbiogenic carbonates calcite microparticles 4 m due to their isotopic signature calcite microparticles cannot result from fragmentation and partial dissolution of biogenic remains and the most likely origin appears to be early diagenetic processes and or export from shallow water platforms the calcareous macrocrystals derive from an early diagenetic process the lowermost danian sediments are dominated by nonbiogenic carbonates between 50 and 80 of the bulk carbonate nevertheless two kinds of biogenic components are present thoracosphaera operculata and maastrichtian like calcareous nannofossils thoracosphaera operculata is an opportunistic calcareous dinoflagellate which frequently occurs at high abundances in basal danian sediments and is certainly in situ this is confirmed by it showing a danian isotopic signature the maastrichtian like calcareous nannofossils are nannofossils of taxa that indisputably occur in the maastrichtian but which do not occur consistently in later danian strata they show a maastrichtian type isotopic signature which strongly supports the inference that they are mainly reworked from the maastrichtian this study shows that nonbiogenic carbonates are important components of the pelagic carbonate even during periods of normal sedimentation in the crisis interval the biogenic carbonate production drops sharply while calcite microparticles and carbonate macrocrystals remain almost unaffected and represent the major part of the carbonate in the earliest danian sediments finally the sediments return to a composition similar to that of the maastrichtian in m pseudobulloides foraminifera zone

near k t age of clastic deposits from texas to brazil impact volcanism and or sea level lowstand near k t boundary clastic deposits from texas mexico haiti guatemala and brazil often described as impact generated tsunami deposits are stratigraphically below well defined k t boundary horizons and appear not to be causally related to the k t boundary event stratigraphic evidence indicates that their deposition began during the last 170 200 kyr of the maastrichtian coincident with a major eustatic sea level lowstand that lowered sea level by as much as 70 100 m clastic deposition ended a few tens of thousands of years before the k t boundary during a rapidly rising sea level the presence of glass in clastic deposits in haiti northeastern mexico and yucatan suggests that the sea level lowstand coincided with a time of major volcanism or pre k t boundary bolide impact

chicxulub impact spherules in the north atlantic and caribbean age constraints and cretaceous tertiary boundary hiatus the chicxulub impact is commonly believed to have caused the cretaceous tertiary boundary mass extinction and a thin impact spherule layer in the north atlantic and caribbean is frequently cited as proof we evaluated this claim in the seven best north atlantic and caribbean cretaceous tertiary boundary sequences based on high resolution biostratigraphy quantitative faunal analyses and stable isotopes results reveal a major cretaceous tertiary boundary unconformity spanning most of danian subzone p1a 1 and maastrichtian zones cf1 cf2 400 ka in the nw atlantic bass river core odp sites 1049a 1049c and 1050c in the caribbean odp sites 999b and 1001b the unconformity spans from the early danian zone p1a 1 through to zones cf1 cf4 3 ma only in the demerara rise odp site 1259b is erosion relatively minor and restricted to the earliest danian zone p0 and most of subzone p1a 1 150 ka in all sites examined chicxulub impact spherules are reworked into the early danian subzone p1a 1 about 150 200 ka after the mass extinction a similar pattern of erosion and redeposition of impact spherules in danian sediments has previously been documented from cuba haiti belize guatemala south and central mexico this pattern can be explained by intensified gulf stream circulation at times of climate cooling and sea level changes the age of the chicxulub impact cannot be determined from these reworked impact spherule layers but can be evaluated based on the stratigraphically oldest spherule layer in ne mexico and texas which indicates that this impact predates the cretaceous tertiary boundary by about 130 150 ka