stromatolitic framework of carbonate mud mounds abstract mud mounds are an important phanerozoic reef type generally formed in deeper water on carbonate shelf to basin slopes they commonly contain radiaxial calcite spar filled depositional cavities stromatactis but lack abundant metazoan framebuilders mud mounds are often flanked by steeply dipping bioclastic grainstones and sometimes attained widths and depositional reliefs of over a hundred meters they occasionally occur as basal cores on which developed shallow water metazoan constructed reefs stromatactoid mud mounds are composed of a framework of submarine cemented crudely reticulate masses or a succession of laminar crusts surrounded by cement filled cavities these cavities developed when unconsolidated sediment around the framework was removed by winnowing mud mound frameworks of all ages show strong geometric and petrographic similarities to shallow water cryptalgal structures especially thrombolites unlaminated stromatolites which occur in many phanerozoic shallow water reefs both thrombolites and mud mound frameworks are largely composed of lime mudstone cemented on the sea floor and contain fenestral fabric and diagnostic cryptalgal microstructure their depositional surfaces were irregular not bored or burrowed and rarely encrusted stromatolitic lamina ion although commonly not well developed in the subtidal zone anyway occasionally occurs in mud mounds it is proposed that mud mounds accumulated from organic probably blue green algal binding of locally derived lime mud and bioclasts deposited relatively slowly from suspension patchy distribution of algal mats resulted in areas of both bound and unbound sediment sporadic floodlike episodes of rapid sedimentation however temporarily smothered the living algal mat and also left layers of unbound sediment periods of winnowing washed out unconsolidated unbound sediment and promoted synsedimentary cementation of resulting stromatactoid cavities and algal bound framework

temporal variation in calcification in marine cyanobacteria periods of widespread abundance of calcified cyanobacteria in marine environments are here termed cyanobacterial calcification episodes cces intense such episodes occurred in the cambrian early ordovician late devonian and mid late triassic mild episodes occurred during the early carboniferous and jurassic early cretaceous possible episodes during parts of the silurian and permian await confirmation cyanobacterial calcification is not obligate but is dependent upon environmental factors favouring carbonate precipitation cyanobacterial calcification episodes are therefore interpreted as reflecting periods of increased marine carbonate precipitation this is supported by the general abundance of marine carbonate cements and oolites during cyanobacterial calcification episodes cyanobacterial calcification episodes correspond with phanerozoic periods for which elevated global temperatures have been inferred they do not appear to correlate closely with inferred changes in aragonite calcite facilitation the sandberg curve and p co2 through time it is concluded that variations in the precipitation rates of abiotic and quasi abiotic marine carbonates through time have been controlled primarily by temperature the mineralogy of these precipitates appears instead to have been mainly influenced by p co2 and the mg ca ratio also linked to sea level through plate tectonic processes thus the controls on rate and mineralogy of precipitation were independent of one another

discrimination between earthquakes and chemical explosions by multivariate statistical analysis a case study for switzerland a data set of 43 confirmed earthquakes and 42 explosions 1 3 m l 3 8 is analyzed by multivariate statistical analysis the explosion events include quarry blasts and explosions detonated for seismic experiments as well as an explosion of an ammunition storage site the events of this training data set are mainly located in the alpine mountains and central switzerland with the seismic sources having excellent distance r 300 km and azimuthal coverage for the recording stations multivariate statistical analysis is used to derive general discriminant functions based on regional waveform data for the training set the discriminant functions are then tested for consistency on the events of the training data set with the result that 97 of these events are correctly identified by the multivariate discriminant functions of the total training data set 17 is classified as ambiguous cases based on marginal discriminant functions the method is subsequently applied to an extended data set including nighttime events from 1992 1996 which are hence regarded as earthquakes and a set of presumed explosions from the years 1984 1997 for central switzerland the events of the extended data set can clearly be identified with the discriminant functions derived from the training data set the identification rate is lower for other regions in switzerland which can be related to tectonic units for these regions considered to have a laterally homogeneous crust a linear correction term in the discriminant function providing for station corrections can be found that significantly decreases the misidentification rate online material table of earthquake and explosion events manuscript received 11 may 2001

fast numerical method for growth and retreat of subsurface ice on mars abstract subsurface water ice on mars evolves due to exchange of vapor with the atmosphere in the form of loss of ice to the atmosphere or in the form of the growth of interstitial ice described here is an accelerated numerical method for the long term evolution of subsurface ice this accelerated method is five orders of magnitude faster than explicit vapor transport calculations enabling fundamentally new types of climate models its speed matches that of purely thermal models the speedup is achieved primarily by solving time averaged equations for vapor transport and ice volume change processes incorporated are growth of interstitial pore ice retreat of pore ice retreat of an ice sheet and retreat of pore ice due to geothermal heating from below two example applications illustrate this numerical method s capabilities near the permafrost margin at 55 latitude ice is periodically depleted and slowly recharged leading to a pore ice layer estimated to be currently no more than a few meters thick at the phoenix landing site it shows the formation of a three layered structure whereby the layer of pore ice can be very thin

measurements of thermal properties of icy mars regolith analogs in a series of laboratory experiments we measure thermal diffusivity thermal conductivity and heat capacity of icy regolith created by vapor deposition of water below its triple point and in a low pressure atmosphere we find that an ice regolith mixture prepared in this manner which may be common on mars and potentially also present on the moon mercury comets and other bodies has a thermal conductivity that increases approximately linearly with ice content this trend differs substantially from thermal property models based of preferential formation of ice at grain contacts previously applied to both terrestrial and non terrestrial subsurface ice we describe the observed microphysical structure of ice responsible for these thermal properties which displaces interstitial gases traps bubbles exhibits anisotropic growth and bridges non neighboring grains we also consider the applicability of these measurements to subsurface ice on mars and other solar system bodies

trilobite associations taphonomy lithofacies and environments of the silurian reefs of north greenland abstract llandovery silurian reefs in north greenland have yielded extensive collections of remarkably well preserved trilobites dominated by scutelluids these collections provide a unique opportunity to analyse the reefs and their trilobite faunas in a palaeoenvironmental context and the study highlights the importance of pre existing collections to which further scientific value can be added counts of trilobite sclerites from thirteen reef localities are analysed using cluster and correspondence analyses to identify trilobite associations and taphonomic signatures lithofacies analysis allows these to be understood in a detailed palaeoenvironmental context seven trilobite associations are identified scutelluid illaenimorph scutelluid scutelluid cheirurid scutelluid harpetid proetid encrinurid and illaenimorph the number of associations highlights the variable distribution of taxa within the reefs which is partly a reflection of intense hydrodynamic sorting in reef environments trilobites are predominantly associated with a cement rich microbial lithofacies it is apparent that microbial processes were the principal contributors to the production of carbonate mud and played a significant role in the development of the greenland reefs the observed associations comprise time averaged event beds in an otherwise low energy and slow sedimentation regime and possibly result from storm activity remobilising sclerites and depositing them within depressions and cavity fills within the reef surface correspondence analysis reveals two distinct taphonomic signatures within the reef and transport distance is the primary influence on these the proetid association is readily separated from the others by its taphonomic attributes representing the least amount of transport and suggesting the taxa involved took advantage of the more sheltered niches within the reef this is the first study of reef dwelling trilobites to take advantage of multivariate techniques to identify associations and describe their taphonomic attributes in particular the effectiveness of correspondence analysis in recognising taphonomic signatures is demonstrated

exposed h2o rich areas detected on ceres with the dawn visible and infrared mapping spectrometer abstract h2o rich materials are locally exposed at the surface of ceres as discovered from infrared reflectance spectra of the visible and infrared mapping spectrometer vir of the dawn mission nine locations on ceres exhibit diagnostic absorption bands of the h2o molecule at 2 00 1 65 and 1 28 m the detections are all consistent with h2o ice mixed with low albedo components all the reported h2o exposures occur at latitudes poleward of 30 in fresh craters near rim shadows have a surface area

taphonomic signatures of turbid zone reef development examples from paluma shoals and lugger shoal inshore central great barrier reef australia numerous coral reefs and coral communities occur along the nearshore regions of the central great barrier reef australia coastline these develop under conditions of episodically high wave induced sediment resuspension and turbidity and terrigenoclastic sediment accumulation cores recovered from two such reefs at paluma shoals and lugger bay are used to assess the taphonomic features and processes associated with framework development in such settings reef framework development is dominated by the accumulation of mainly rubble coral and isolated in situ coral colonies the reef fabric varies from clast to matrix supported in character and the matrix comprises poorly sorted mixed terrigenoclastic carbonate sediments taphonomic signatures from the different reef sites and facies show little variability and thus a distinct suite of taphonomic criteria indicative of nearshore turbid zone reef development are delineated the degree of both calcareous encrustation and internal bioerosion exhibits a high degree of between clast variability and many clasts are preserved in near pristine condition where present calcareous encrustation is restricted to thin isolated crusts comprising mainly of the coralline algae lithoporella or lithothamnion and isolated serpulid worms and cemented bivalves no biological binding of framework constituents occurs bioerosion is dominated by traces of entobia sp sponge borings and locally gastrochaenolites sp bivalve traces although only a limited suite of bioerosion trace morphologies is present there is little or no cementation of the reef framework and only isolated acicular aragonite or peloidal micrite cements occur within intra skeletal cavities significant occlusion of primary and secondary skeletal porosity by uncemented fine grained mainly terrigenous sediment is however common throughout the reef sequence the taphonomic criteria identified all have good preservation potential and should be readily identifiable within core sections such criteria thus have potential for aiding the recognition of reefs that either developed under similar environmental conditions of high turbidity and terrigenous sediment accumulation or which were subject to similar conditions during more short lived phases of reef accretion

an early silurian herefordshire myodocope ostracod from greenland and its palaeoecological and palaeobiogeographical significance here we record the occurrence of a new species of the herefordshire lagerstatte ostracod genus pauline from the lower silurian upper telychian of north greenland pauline nivisis sp nov was recovered from a limestone boulder pentamerus bjerge formation collected south of kap schuchert washington land it is reasonable to transpose the palaeobiology known from the herefordshire pauline avibella body limbs including swimming antennae lateral eyes gills and alimentary system into the carapace of the greenland species which represents the oldest cylindroleberidid myodocopid and almost the oldest known myodocope and is the first record of a herefordshire lagerstatte genus from outside the welsh borderland locality morphological sedimentological and faunal evidence suggest that the greenland species was nektobenthic this is compatible with the notion that ostracods specifically myodocopids did not invade the water column until later in the silurian in the wenlock and ludlow epochs pauline is an early silurian link between baltic british and north laurentian ostracod faunas endorsing the idea that the uk and greenland were in close geographical proximity near a remnant iapetus ocean during late llandovery time

growth dynamics and ecology of upper jurassic mounds with comparisons to mid palaeozoic mounds the mid palaeozoic including the late jurassic was a time of both widespread coral reef growth and pronounced mound formation a comparison of mound features and their general setting highlights despite all differences general similarities in overall growth dynamics mound formation was frequently driven by discontinuous patterns particularly by background sedimentation in many examples episodes of mound stabilisation by early lithification growth of microbolite crusts and winnowing of fines was followed by growth episodes of benthic fauna under reduced to negligible background sedimentation this pattern of variable sedimentation and organic buildups may have occurred in different orders and magnitudes inducing a fractal pattern in some mound complexes a composite approach in estimating growth rates of mounds demonstrates that highfrequency oscillations necessary for growth of most mounds might have ranged from a few thousand years to 4th and 5th order milankovich cycles that were superimposed by autocyclic factors d 2001 elsevier science b v all rights reserved

analysis of high frequency pg lg ratios from nts explosions and western u s earthquakes the high frequency pg lg discriminant is studied between frequencies of 0 5 and 10 hz using 294 nts explosions and 114 western u s earthquakes recorded at four broadband seismic stations operated by lawrence livermore national laboratory the stations are located at distances of about 200 to 400 km from the nevada test site nts event magnitudes ranged from about 2 5 to 6 5 and propagation paths for the earthquakes range from approximately 175 to 1300 km the discriminant is shown to be very effective and displays improved separation between earthquakes and explosions as frequency is increased because of propagation effects it is important to apply distance corrections directly to the amplitude ratios or to the magnitude corrected amplitudes prior to computing the ratios multivariate discrimination analysis using both maximum likelihood gaussian classifiers and a backpropagation neural network show that approximately 95 of the events can be correctly identified both classification procedures were designed to handle missing data filled in using a nearest neighbor algorithm except for a few notable exceptions most of the earthquake misclassifications occur for mb 4 which is expected for events having reduced signal to noise ratios all of the explosion misclassifications occur for mb 4 suggesting a source or near source effect rather than an effect of poor signal to noise ratio the explosions that were misclassified were typically of magnitude large enough to be classified correctly by mb ms or love wave energy the main drawback of the pg lg discriminant is that because of signal to noise considerations and propagation effects the number of measurements are reduced considerably at higher frequencies it is expected that the problem will be amplified as magnitudes are reduced and event receiver distances are increased

characteristic microseismicity during the development process of intermittent rockburst in a deep railway tunnel abstract during deep tunnel excavation more than one rockburst sometimes occur in a particular area which seriously threatens construction safety in this work the characteristic microseismicity occurring during the development process of intermittent rockburst more than one rockburst occurring in a particular area and single rockburst only one rockburst occurring in a particular area and the associated mechanism of formation are studied data was collected during the construction of a railway tunnel in southwestern china microseismicity was recorded and analyzed before and after each rockburst for both intermittent and single rockbursts the schmidt number declines heavily with time the cumulative apparent volume rises sharply with time and the seismic activity is high before the rockburst however this characteristic microseismicity can also be found with no rockburst occurrence between each rockburst in an intermittent rockburst the ms events mostly have low ms energy i e whose logarithm measured in joules is smaller than 3 5 and the energy stored in the rockmass of the rockburst zone is not adequately released therefore there is likely to be another rockburst after the blast when high in situ stress is present after the last rockburst of an intermittent rockburst and the single rockburst some ms events of high ms energy i e whose logarithm measured in joules is larger than 3 5 occur in the deep surrounding rockmass and the energy stored in the rockmass of the rockburst zone is gradually released to a certain degree the stress is transferred to the deep surrounding rockmass whose stability is relatively high as a result a subsequent rockburst is hardly likely to occur again

earthquake hazard after a mainshock in california after a strong earthquake the possibility of the occurrence of either significant aftershocks or an even stronger mainshock is a continuing hazard that threatens the resumption of critical services and reoccupation of essential but partially damaged structures a stochastic parametric model allows determination of probabilities for aftershocks and larger mainshocks during intervals following the mainshock the probabilities depend strongly on the model parameters which are estimated with bayesian statistics from both the ongoing aftershock sequence and from a suite of historic california aftershock sequences probabilities for damaging aftershocks and greater mainshocks are typically well constrained after the first day of the sequence with accuracy increasing with time

characteristics of coal mining microseismic and blasting signals at qianqiu coal mine the signal waveforms caused by blasting events which are similar to the microseismic ms signal waveforms caused by mining activities are very common during the ms monitoring at coal mines however these blasting signals are not useful for monitoring and early warning of the coal or rock dynamic disasters by ms monitoring technique to distinguish between the coal mining ms signals and the blasting signals we studied the differences between these waveforms by analyzing the dominant frequency signal duration following peak attenuation and multifractal parameters and f the main results are the coal mining ms signals have lower dominant frequency below 80 hz and longer vibration duration more than 2 s than the blasting signals dominant frequency above 80 hz and duration less than 2 s the following peak envelope curves of the two types of signals fit a power function moreover the power exponent and fitting accuracy were obtained to describe the attenuated speed and stabilities of the ms signals the coal mining ms signals attenuate slower and the coda waves are more complex than the blasting signals the dividing line of the power exponent between the mining ms and the blasting signals is 8 according to the multifractal theory the mining ms signals have smaller spectral width below 1 2 and f below 0 3 than the blasting signals above 1 2 and f above 0 3 the research results lay a foundation for the automatic identification of mining ms signals and blasting signals recorded in coal mines

conditions for sublimating water ice to supply ceres exosphere dawn at ceres guest investigator program award nnx15ai29g nsf graduate research fellowship award dge 1143653

predictions of depth to ice on asteroids based on an asynchronous model of temperature impact stirring and ice loss abstract water ice near the surface of main belt asteroids is gradually lost to space a mantle of low thermal conductivity causes large surface temperature amplitudes and thus increased cooling by thermal re radiation lowering temperatures well below the fast rotator limit a computational barrier for modeling this ice loss is the multi scale character of the problem accurate temperatures require many time steps within a solar day but ice retreats slowly over billions of years this barrier is overcome with asynchronous coupling models of temperature ice loss and impact stirring each use their own time steps and are coupled with one another the model is applied to 1 ceres and 7968 elst pizarro on ceres ice can be expected in the top half meter poleward of 60 latitude on both hemispheres even if excursions of the axis tilt took place and even in the presence of impact gardening at the poles ice can be expected within a centimeter of the surface the retreating ice crust leads to emission of water from the surface mainly at the equator the gradually retreating ice supplies a water exosphere less dense than has been observed by the herschel telescope for main belt comet elst pizarro depths to ice depend on the properties of the surface mantle for a dust mantle estimated depths are on the order of a decimeter for a rocky surface the depth at the pole is on the order of one meter hence it could have been activated by a small impact that exposed buried ice

pitted terrains on 1 ceres and implications for shallow subsurface volatile distribution prior to the arrival of the dawn spacecraft at ceres the dwarf planet was anticipated to be ice rich searches for morphological features related to ice have been ongoing during dawn s mission at ceres here we report the identification of pitted terrains associated with fresh cerean impact craters the cerean pitted terrains exhibit strong morphological similarities to pitted materials previously identified on mars where ice is implicated in pit development and vesta where the presence of ice is debated we employ numerical models to investigate the formation of pitted materials on ceres and discuss the relative importance of water ice and other volatiles in pit development there we conclude that water ice likely plays an important role in pit development on ceres similar pitted terrains may be common in the asteroid belt and may be of interest to future missions motivated by both astrobiology and in situ resource utilization

thermal stability of ice on ceres with rough topography the dwarf planet ceres may have an ice rich crust and subsurface ice exposed by impacts or endogenic activity would be subject to sublimation we model surface and subsurface temperatures on ceres to assess lifetimes of water ice and other volatiles topographic shadowing allows a small but non negligible fraction 0 4 of ceres surface to be perennially below the 110 k criterion for 1 gyr of stability these areas are found above 60 latitude other molecules ch3oh nh3 so2 co2 may be cold trapped in smaller abundances a model for the transport gravitational escape and photoionization of h2o molecules suggests net accumulation in the cold traps buried ice is stable within a meter for 1 gyr at latitudes higher than 50 an illuminated polar cap of water ice would be stable within a few degrees of the poles only if it maintained a high albedo 0 5 at present obliquity if the obliquity exceeded 5 in the geologically recent past then a putative polar cap would have been erased at latitudes 0 30 ice is stable under solar illumination only briefly 10 100 yr unless it has high albedo and thermal inertia in which case lifetimes of 104 yr are possible finally a small hemispheric asymmetry exists due to the timing of ceres perihelion passage which would lead to a detectable enhancement of ice in the northern hemisphere if the orbital elements vary slowly relative to the ice accumulation rate our model results are potentially testable during the dawn science mission

distribution patterns of upper devonian phacopid trilobites paleobiogeographical and paleoenvironmental significance phacopid trilobites are relatively widespread in devonian deposits after a maximum diversity in the middle devonian most phacopids were severely affected by repeated sea level eustatic changes especially in the frasnian and it was during that time that the main groups of reduced eye or blind phacopids arose the aim of this investigation was to evaluate the distribution patterns of upper devonian phacopids at a global level through a clustering analysis in a paleogeographical and paleoenvironmental framework in order to understand their fluctuations in time and space the phacopid biodiversity is represented in this study by 22 taxa from the frasnian to the late famennian additionally four main time intervals frasnian i famennian post i famennian ii iii and famennian iv vi have been explored to complete the clustering analysis two ordering methods i e a seriation routine and a detrended correspondence analysis have been performed respectively to reveal chronological sequences and to identify indirect paleoenvironmental gradients analyses enabled us to establish 1 bathymetrical gradients showing some taxa such as omegops restricted to shallower environments and other taxa such as ductina or dianops to deeper environments and 2 paleobiogeographical affinities showing exchanges along the margins of north gondwana and avalonia baltica and probable connections along the margin of north east gondwana after the major mid givetian taghanic transgression

oncoids as environmental indicators in the much wenlock limestone formation of the english midlands the much wenlock limestone formation of the west midlands was deposited in a mid shelf setting and is divisible into three members the upper and lower quarried limestone members being separated by the more argillaceous nodular limestone member oncoids composed predominantly of micritic fabrics with rothpletzella and girvanella occur commonly in the lower quarried limestone member these oncoids vary from subspherical bodies up to 5 mm in diameter to forms with a highly irregular and branched upper surface which reach 70 mm across each form is indicative of a different depositional environment which is also reflected in the sediment enclosing the oncoid equidimensional oncoids in peloidal packstones were formed by continuous rolling whereas the larger branched forms enclosed in loosely packed wackestones developed in quieter conditions below wave base the distribution of oncoid morphotypes in the lower quarried limestone member shows that small variations in relative sea level were superimposed on the overall middle to late wenlock regressive episode during which the much wenlock limestone formation was deposited the uniformity of the formation throughout the west midlands indicates that the sea floor was essentially planar over a large area vertical variation of oncoid morphology within the lower quarried limestone member can be traced throughout the area allowing accurate correlation of relative sea level variations

extensive submarine lithification in a cave in the belize barrier reef platform abstract extensive deposits of submarine cements discovered in a submerged pleistocene cave in the outer barrier reef platform off belize central america occur in an unusual setting on and within countless calcareous projections formed by serpulid worms on the ceiling of the cave the cements are predominantly dense submicrocrystalline and microcrystalline to porous chalky or submicrosucrosic magnesium calcite approximately 15 mole mgco3 and they contain minor amounts of acicular aragonite which generally forms a lining inside the aragonitic serpulid tubes radiocarbon dates three year artificial substrate experiments and evidence of the ceiling s original relief indicate a low rate of accumulation for the serpulid cement projections the characteristic 20 60 m peloidal texture associated with magnesium calcite submarine cements is well developed here and there within the projections these peloids are physiochemical precipitates having formed during the development of the submarine cement deposits which accumulated preferentially on substrates that have a slow rate of accumulation and that experience little or no disturbance of their sediment cover artificial substrates placed on the ceiling of the cave for three years revealed that the initial stage of precipitation of magnesium calcite from seawater is in the form of a submicrocrystalline magnesium calcite dust

aftershock characteristics as a means of discriminating explosions from earthquakes abstract the behavior of aftershock sequences around the nevada test site nts in the southern great basin is characterized as a potential discriminant between explosions and earthquakes the aftershock model designed by reasenberg and jones 1989 1994 allows for a probabilistic statement of earthquakelike aftershock behavior at any time after the mainshock we use this model to define two types of aftershock discriminants the first defines m x or the minimum magnitude of an aftershock expected within a given duration after the mainshock with probability x of the 67 earthquakes with m 4 in the study region 63 of them produce an aftershock greater than m 99 within the first 7 days after a mainshock this is contrasted with only six of 93 explosions with m 4 that produce an aftershock greater than m 99 for the same period if the aftershock magnitude threshold is lowered and the m 90 criteria is used then no explosions produce an aftershock greater than m 90 for durations that end more than 17 days after the mainshock the other discriminant defines n x or the minimum cumulative number of aftershocks expected for a given time after the mainshock with probability x similar to the aftershock magnitude discriminant five earthquakes do not produce more aftershocks than n 99 within 7 days after the mainshock however within the same period all but one of the explosions produce fewer aftershocks than n 99 one explosion is added if the duration is shortened to 2 days after the mainshock the cumulative number aftershock discriminant is more reliable especially at short durations but requires a low magnitude of completeness for the given earthquake catalog these results at nts are quite promising and should be evaluated at other nuclear test sites to understand the effects of differences in the geologic setting and nuclear testing practices on its performance

ceres predictions for near surface water ice stability and implications for plume generating processes this paper will constrain the possible sources and processes for the formation of recently observed h2o vapor plumes above the surface of the dwarf planet ceres two hypotheses have been proposed 1 cryovolcanism where the water source is the mantle and the heating source is still unknown or 2 comet like sublimation where near surface water ice is vaporized by seasonally increasing solar insolation we test hypothesis 2 comet like near surface sublimation by using a thermal model to examine the stability of water ice in the near surface for a reasonable range of physical parameters thermal inertia surface roughness and slopes we find that water ice is only stable at latitudes higher than 40 60 these results indicate that either a the physical properties of ceres are unlike our expectations or b an alternative to comet like sublimation such as the cryovolcanism hypothesis must be invoked

carbonaceous chondrites as analogs for the composition and alteration of ceres the mineralogy and geochemistry of ceres as constrained by dawn s instruments are broadly consistent with a carbonaceous chondrite cm ci bulk composition differences explainable by ceres s more advanced alteration include the formation of mg rich serpentine and ammoniated clay a greater proportion of carbonate and lesser organic matter amounts of magnetite sulfide and carbon that could act as spectral darkening agents and partial fractionation of water ice and silicates in the interior and regolith ceres is not spectrally unique but is similar to a few other c class asteroids which may also have suffered extensive alteration all these bodies are among the largest carbonaceous chondrite asteroids and they orbit in the same part of the main belt thus the degree of alteration is apparently related to the size of the body although the ammonia now incorporated into clay likely condensed in the outer nebula we cannot presently determine whether ceres itself formed in the outer solar system and migrated inward or was assembled within the main belt along with other carbonaceous chondrite bodies

localized sources of water vapour on the dwarf planet 1 ceres the largest asteroid of the solar system 1 ceres has been thought to have an icy surface here it is observed to be emitting water vapour the presence of hydrated minerals on the surface of ceres the largest body in the solar system s main asteroid belt suggested that there may be water there too now infrared spectra obtained by esa s herschel space observatory provide unambiguous evidence that there is water ice at or near the surface of ceres water vapour is issuing at a rate of at least 1026 molecules per second from sources on ceres localized to mid latitude regions the water evaporation could be due to comet like sublimation or to cryo volcanism in which volcanoes erupt volatiles such as water instead of molten rocks this finding supports models that propose that the icy bodies such as comets may have migrated into the asteroid belt from beyond the notional snowline dividing the early solar system into a dry inner and icy outer regions the snowline conventionally divides solar system objects into dry bodies ranging out to the main asteroid belt and icy bodies beyond the belt models suggest that some of the icy bodies may have migrated into the asteroid belt1 recent observations indicate the presence of water ice on the surface of some asteroids2 3 4 with sublimation5 a potential reason for the dust activity observed on others hydrated minerals have been found6 7 8 on the surface of the largest object in the asteroid belt the dwarf planet 1 ceres which is thought to be differentiated into a silicate core with an icy mantle9 10 11 the presence of water vapour around ceres was suggested by a marginal detection of the photodissociation product of water hydroxyl ref 12 but could not be confirmed by later more sensitive observations13 here we report the detection of water vapour around ceres with at least 1026 molecules being produced per second originating from localized sources that seem to be linked to mid latitude regions on the surface14 15 the water evaporation could be due to comet like sublimation or to cryo volcanism in which volcanoes erupt volatiles such as water instead of molten rocks

taphonomy and palaeoecology of the emuellid trilobite balcoracania dailyi early cambrian south australia monospecific assemblages of the trilobite balcoracania dailyi occur in lower cambrian strata within the adelaide geosyncline in south australia biostratinomic data from single bedding plane assemblages within the warragee and coads hill members of the billy creek formation and white point conglomerate reveal a range of taphonomic signatures from census to within habitat timeaveraged assemblages these assemblages are interpreted as having inhabited protected shallow marginal marine environments size frequency distributions coupled with taphonomic data show that the warragee member census assemblage represents a living population in a physically stressful environment within a tidally influenced lagoon while the original population structure of the coads hill member and white point conglomerate assemblages has been lost due to varying degrees of taphonomic overprinting integration of taphonomic stratigraphic and sedimentological data supports the interpretation of b dailyi as representing an opportunistic species a preserved body cluster from the warragee member assemblage is considered to characterise a congregation formed for the purpose of synchronous reproduction and ecdysis representing one of the oldest examples of gregarious behaviour in the arthropod fossil record furthermore by analogy with modern horseshoe crabs the high number of juveniles i e protaspides and early meraspides within the same assemblage are believed to be constituents of a nursery within the intertidal zone with adults migrating into the shallows to copulate and spawn preserved moult ensembles from the coads hill member and white point conglomerate have enabled the description of exuviation techniques for b dailyi 2007 elsevier b v all rights reserved

discrimination of chemical explosions and earthquakes in central europe a case study both natural and artificial seismicity is observed in the vogtland area at near regional distance 180 km from the geress array this setting offers the opportunity to test various discrimination criteria using a uniform data set of 39 earthquakes and 22 chemical explosions strip mine and quarry blasts from a single epicentral region mostly eliminating wave path and distance effects discriminants used include lg pg and lg rg maximum amplitude ratios spectral peaks and slopes extracted by autoregressive moving average arma modeling master event correlation and the search for time independent frequency structures in sonograms although no single discrimi nant achieves a perfect separation of the two populations a joint discrimination scheme employing simple majority voting reduces misclassifications to 2 future research will focus on possible generalization and the physical basis of the discriminants

application of correspondence analysis to palaeobathymetric reconstruction of cenomanian and turonian cretaceous rocks of eastern algeria abstract the vertical succession of facies is used to characterize the hierarchy of stratigraphic cycles depositional sequences and systems tracts in upper cretaceous rocks of the aures mountains eastern algeria correspondence analysis was used to identify the main palaeontological associations and the systems tracts linked to them resulting in a tentative reconstruction of the changing palaeobathymetry through the succession the results were corroborated by comparison with a eustatic curve and subsidence data comparisons of bathymetric and eustatic curves can help calibrate and scale regional bathymetric curves and verify if the water depths derived by other palaeoecological methods agree with those determined from correspondence analysis

discrimination of earthquakes and explosions in southern russia using regional high frequency three component data from the iris jsp caucasus network high frequency regional records from small earthquakes magnitude 4 5 and comparable magnitude chemical explosions are analyzed to find a reliable seismic discriminant in southern russia near kislovodsk the digital three compo nent seismograms recorded during 1992 by the caucasus network operated by la mont doherty earth observatory since 1991 in the distance ranges 15 to 233 km are used mean vertical component pg lg spectral amplitude ratios in the band 8 to 18 hz are about 1 3 and 3 2 for earthquakes and explosions respectively in this region we find that the vertical component pg lg spectral ratio in the frequency band 8 to 18 hz serves quite well for classifying these events a linear discriminant function analysis indicates that the pg lg spectral ratio method provides discrimination power with a total misclassification probability of about 7 the pg lg spectral ratios of rotated three component regional records improve the discrimination power of the spectral ratio method over the vertical component pg lg ratios preliminary analysis indicates that distance corrected vertical component pg lg ratios improve the dis crimination power by about 4 over uncorrected ratios but we find that an even better discriminant is the pg lg spectral ratio of the three component regional records corrected for the free surface effect in the frequency band 8 to 18 hz the free surface corrected three component pg lg spectral ratio provides discrimination power with a total misclassification probability of only 2 6 free surface corrected and network averaged pg lg spectral ratios provide transportability of the spectral ratio method to various regions worldwide

biofilm related calcification sediment trapping and constructive micrite envelopes a criterion for the recognition of ancient grass bed environments micrite envelopes are a common feature in carbonate sediments and are typically associated with the micrite filling of borings produced by microendolithic organisms these are referred to as destructive micrite envelopes and have long been recognized as reflecting an important early diagenetic process recent analysis of sediments collected from back reef environments at discovery bay north jamaica however has demonstrated envelope formation on the surfaces of carbonate grains clearly distinct from the micrite filling of microborings such constructive envelopes occur almost exclusively in sediments from grass bed environments and are always intimately associated with biofilms comprising abundant mucilage cyanobacteria bacteria and diatoms it is suggested that these envelopes represent a product of both biologically mediated micrite precipitation occurring within the biofilm mucilage and around the biofilm components i e cyanobacteria and diatoms and associated trapping of carbonate mud and fine grained sediment their recognition only within grass bed sediments may enable their use as a diagnostic feature of grass bed environments or vegetation stabilized substrates in the rock record

exploiting regional amplitude envelopes a case study for earthquakes and explosions in the korean peninsula abstract we introduce a new method to use narrowband regional amplitude envelopes for event analysis building on the success of the coda wave method we construct synthetic template envelopes that attempt to fit the entire waveform including multiple direct phases and their coda across a broad frequency band the method makes use of our understanding of earthquake and explosion source models regional wave propagation and the relationship between direct amplitudes and their respective codas we demonstrate the power of the method by examining earthquake and nuclear explosions in the korean peninsula at regional distance stations mdj mudangjing china and tjn taejon south korea in order to implement the method however we need to account for propagation through the use of an attenuation model for the region which we have developed in addition to an empirical correction to provide for unaccounted effects in the direct to coda transfer functions under the assumption that our explosion and attenuation models and the empirically obtained p to p coda and s to s coda transfer functions are correct we determine that the 2006 test by the democratic people s republic of korea dprk is consistent with a yield between 200 and 800 tons and a depth between 20 and 300 m with our best fit at 500 tons at a depth of 100 m similarly the 2009 dprk test is consistent with a yield range of 1 5 kt and a depth range of 70 600 m with our best fit at 2 kt at a depth of 200 m

the permanently shadowed regions of dwarf planet ceres ceres has only a small spin axis tilt 4 and craters near its rotational poles can experience permanent shadow and trap volatiles as is the case on mercury and on earth s moon topography derived from stereo imaging by the dawn spacecraft is used to calculate direct solar irradiance that defines the extent of the permanently shadowed regions psrs in the northern polar region psrs cover 1800 km2 or 0 13 of the hemisphere and most of the psrs are cold enough to trap water ice over geological time periods based on modeling of the water exosphere water molecules seasonally reside around the winter pole and ultimately an estimated 0 14 of molecules get trapped even for the lowest estimates of the amount of available water this predicts accumulation rates in excess of loss rates and hence there should be fresh ice deposits in the cold traps

multivariate data analysis in palaeoecology and palaeobiogeography a review abstract palaeoecologists and palaeobiogeographers are often confronted with large multivariate data sets from which fossil communities assemblages or associations or faunal provinces are to be recognized the complex multidimensional nature of these data sets the recognition of the enormous variation of communities and environments both in space and time and the difficulties of dealing with these problems by the human mind justify the use of multivariate statistical methods in palaeoecology and palaeobiogeography concepts and basic procedures of several commonly used multivariated statistical methods of palaeoecology and palaeobiogeography are reviewed in the wider context of quantitative community ecology and biogeography basic assumptions about data structure and theoretical and practical limitations are discussed the emphasis is on evaluation of binary similarity coefficients and two multivariate approaches cluster analysis and ordination thirty nine binary similarity coefficients are evaluated against nine criteria jaccard s coefficient of community is found most suitable as a similarity measure between samples under the conditions tested algorithmic procedures of cluster analysis especially the agglomerative hierarchical cluster analysis techniques and indirect ordinations particularly polar ordination principal component analysis principal coordinate analysis correspondence analysis detrended correspondence analysis and nonmetric multidimensional scaling are outlined and their applicability to palaeoecological and palaeobiogeographical data is discussed where the data are appropriate an integration of cluster analysis and ordination is suggested to be applied to the same data

seismic source summary for all u s below surface nuclear explosions a summary of information is presented for all u s nuclear tests detonated below the earth s surface the data include explosion times locations yields and depths of burial as well as geophysical information about working point media and for the underground explosions data about surface collapse subsidence phenomena this summary is intended to furnish available and up to date data useful for studies of seismic and hydroacoustic sources as well as for studies of the seismic and hydroacoustic transmission characteristics of the earth manuscript received 2 july 2001

ground motions induced by mining seismic events with different focal mechanisms abstract it is essential to quantify the ground motions induced by seismic events with different focal mechanisms in underground mine to quantitatively calculate the induced ground motions we expressed the motions as the convolution of the seismic source and the wave propagation path using seismological method firstly we investigated the theoretical ground motion patterns using four idealized focal mechanisms results show that the pure compressional failure source and the pure tensional failure source induced the same ground motion patterns the vibrations they induced attenuate extremely fast the pure shear failure source shows closely azimuth related pattern with four quadrants around the source the pure explosive failure source induces vibrations attenuating toward all directions away from the source but the vibrations are not attenuated gradually with the increasing distance then we investigated the ground motions under complicated focal mechanisms using recorded fault slip events cavity collapse events and tensional failure events the fault slip events show a four quadrants ground motion distribution in the horizontal plane and a two quadrants distribution in the vertical plan but the cavity collapse events show a two quadrants distribution in the horizontal plane and a four quadrants distribution in the vertical plane it is concluded that the induced ground motion at a certain location is controlled by the dual effects of the azimuth and the source focal mechanism as well as the distance and the source magnitude

post impact cryo hydrologic formation of small mounds and hills in ceres s occator crater the intimate mixture of ice and silicate within the uppermost few kilometres of ceres influences its geology and the evolution of its subsurface both ground ice and cryovolcanic processes have been hypothesized to form geologic terrains on ceres including within occator crater where they have been suggested to influence the post impact surface evolution both types of processes involve the presence and expression of volatiles and brines such that distinguishing between them could be difficult here we use images and topography data from the nasa dawn mission to investigate the morphology age and distribution of mounds and hills within occator crater and infer their origin the shapes and relative ages of many of these features suggest that they formed as impact induced water rich flows that covered the crater floor refroze in a manner similar to the formation of periglacial ice cored mounds on earth called pingos we suggest that impacts on ceres produced hydrologic conditions for surface changes in the absence of cryovolcanic processes our findings imply that cryo hydrologic processes extend beyond earth and mars and have been active on ceres in the geologically recent past mounds within ceres s occator crater may have formed by freezing of water rich impact induced melt by a process analogous to that of pingo formation on earth according to an analysis of data from nasa s dawn mission

geophysical evolution of the themis family parent body 1 we model the geophysical evolution of the themis family parent body this study is motivated by the recent detection of water ice at the surface of 24 themis the first detection of free water on the surface of an asteroid the themis family members display a variety of spectral properties and densities a possible indication that their parent was differentiated at the time of break up differentiation of the parent body is better explained if it accreted as a mixture of ice within a few my after the production of cais from these models we highlight a number of issues that provide a strong rationale for further ground based and future space exploration of that family

episodes of particle ejection from the surface of the active asteroid 101955 bennu introduction active asteroids are small bodies in the solar system that show ongoing mass loss such as the ejection of dust which may be caused by large impacts volatile release or rotational acceleration studying them informs our understanding of the evolution and destruction of asteroids and the origin of volatile materials such as water on earth the osiris rex origins spectral interpretation resource identification and security regolith explorer spacecraft has rendezvoused with the near earth asteroid 101955 bennu the selection of bennu as the osiris rex target was partially based on its spectral similarity to some active asteroids observations designed to detect mass loss at bennu were conducted from earth and during the spacecraft s approach but no signs of asteroid activity were found however when the spacecraft entered orbit in january 2019 we serendipitously observed particles in the vicinity of bennu that had apparently been ejected from its surface rationale we analyzed the properties and behavior of particles ejected from bennu to determine the possible mechanisms of ejection and provide understanding of the broader population of active asteroids images obtained by the spacecraft indicate multiple discrete ejection events with a range of energies and resultant particle trajectories we characterized three large ejection events that respectively occurred on 6 january 19 january and 11 february 2019 tracking of individual particles across multiple images by means of optical navigation techniques provided the initial conditions for orbit determination modeling by combining these approaches we estimated the locations and times of ejection events and determined initial velocity vectors of particles we estimated the particle sizes and the minimum energies of the ejection events using a particle albedo and density consistent with observations of bennu results particles with diameters from 3 m s 1 estimated energies ranged from 270 mj for the 6 january event to 8 mj for the 11 february event the three events arose from widely separated sites which do not show any obvious geological distinction from the rest of bennu s surface however these events all occurred in the late afternoon between about 15 00 and 18 00 local solar time in addition to discrete ejection events we detected a persistent background of particles in the bennu environment some of these background particles have been observed to persist on temporary orbits that last several days in one case with a semimajor axis 1 km the orbital characteristics of these gravitationally bound objects make it possible to determine the ratio of their cross sectional area to their mass combined with their photometric phase functions this information constrains the parameter space of the particles diameters densities and albedos conclusion plausible mechanisms for the large ejection events include thermal fracturing volatile release through dehydration of phyllosilicates and meteoroid impacts the late afternoon timing of the events is consistent with any of these mechanisms bennu s boulder geology indicates that thermal fracturing perhaps enhanced by volatile release could occur on the asteroid surface smaller events especially those that occur on the night side of bennu could be attributable to reimpacting particles our observations classify bennu as an active asteroid active asteroids are commonly identified by major mass loss events observable with telescopes on scales much greater than we observed at bennu our findings indicate that there is a continuum of mass loss event magnitudes among active asteroids