accelerator mass spectrometry radiocarbon dating of rock varnish accelerator mass spectrometry ams 14c dating off rock varnish provides minimum limiting ages for landforms and archaeological artifacts in arid and semiarid lands that are undatable by conventional radiocarbon methods experiments on sample collection the effect of different individuals preparing samples the influence of different chemical extraction procedures the incorporation of carbonate detritus possible contamination from rock underlying varnish the role of bio geochemical erosion of varnish and other influences reveal procedures that yield reproducible results conventional radiocarbon dates from charcoal beneath lava flows of hualalai volcano hawaii and from arid sites in western north america provide controls to test varnish radiocarbon dating ams radio carbon ages on the very bottom layer of varnishes are typically 10 younger than the 14c ages of these controls applications are illustrated here for fluvial aeolian peri glacial hillslope lacustrine and glacial geo morphology as well as rock art research in archaeology

cation leaching sites in rock varnish backscatter electron microscopy of subaerial rock varnish reveals porous textures that are sites of cation leaching with lowered k ca 2 ti 4 ratios and concentrations of manganese and iron laboratory studies show that rates of potassium and calcium leaching increase with temperature time and surface area and decrease when varnish interdigitates with coatings of amorphous silica only varnishes with continuous layering should be used in paleoenvironmental research and paleomagnetic studies not textures indicative of postdepositional modifications

infrasonic tremor in the diffraction zone 1 volcanic tremor signals recorded by an infrasound array 12 5 km from the active vent of k lauea volcano show clear diurnal amplitude variations and originate from a well defined direction pointing to the active pu u crater complex spectral amplitudes between 0 02 0 3 hz a proxy for wind speed increase when the wind speeds increase during the daytime spectral amplitudes between 0 5 3 hz where infrasonic tremor is concentrated increase when the wind speeds decrease at night power spectrum analysis shows that when ambient noise levels drop infrasonic tremor amplitudes rise array processing confirms this relationship and reveals tremor detections and amplitudes decrease during the day these changes in infrasonic tremor spectral amplitude and coherence are most likely due to diurnal variations in atmospheric boundary layers affecting infrasonic propagation within the diffraction zone recognition of these regional atmospheric patterns is necessary to permit robust infrasonic remote sensing of volcanic processes

models of rock varnish formation constrained by high resolution transmission electron microscopy nanometre scale transmission electron microscope imagery of manganiferous rock varnishes from death valley california peru antarctica and hawaii confirms prior infrared mineralogy studies the building blocks of rock varnish are clay minerals that are cemented to the rock by oxyhydroxides of manganese and iron rock varnish is layered on the scale of nanometres with the basic structure defined by the subparallel alignment of detrital clay minerals although only a few examples of bacteria were found possible cell wall encrustations are ubiquitous and aligned with the clay minerals mn fe oxides appear to be mobilized from bacterial casts and then reprecipitate on clay minerals that weather into monolayers these observations have implications for varnish dating and palaeoenvironmental techniques k ar and uranium series dating of rock varnish oxides can only yield minimum ages however this small spatial scale of mobilization would not alter the signal from micron scale microchemical laminations

revisiting alexander von humboldt s initiation of rock coating research abstractsecondary backscattered high resolution transmission and energy dispersive spectroscopy tools of electron microscopy reexamined alexander von humboldt s field site of brownish black crust s covering rocks along cataracts of the orinoco river modern tools confirm eighteenth century analysis that the basic composition includes an abundance of manganese iron and carbon additional major constituents include clay minerals calcium and sometimes barium and cobalt backscattered and secondary electron imaging confirms the 2 century old hypothesis of an accretionary nature of the orinoco coating the remarkable orinoco sheen is produced by a smooth lamellate micromorphology and high concentrations of manganese the same conditions required to produce lustrous varnishes formed in warm deserts although von humboldt deduced and we agree that coating constituents must derive from the orinoco electron microscope observations of mn enriched diatom fragments mn enriched cocci bacterial forms and

time reversal imaging of seismic sources and application to the great sumatra earthquake the increasing power of computers and numerical methods like spectral element methods allows continuously improving modelization of the propagation of seismic waves in heterogeneous media and the development of new applications in particular time reversal in the three dimensional earth the concept of time reversal hereafter referred to as tr was previously successfully applied for acoustic waves in many fields like medical imaging underwater acoustics and non destructive testing we present here the first application at the global scale of tr with associated reverse movies of seismic waves propagation by sending back long period time reversed seismograms we show that seismic wave energy is refocused at the right location and the right time of the earthquake when tr is applied to the sumatra andaman earthquake 26 dec 2004 the migration of the rupture from the south towards the north is retrieved therefore tr is potentially interesting for constraining the spatio temporal history of complex earthquakes

time reversal processing for source location in an urban environmenta a simulation study is conducted to demonstrate in principle that time reversal processing can be used to locate sound sources in an outdoor urban area with many buildings acoustic pulse propagation in this environment is simulated using a two dimensional finite difference time domain fdtd computation using the simulated time traces from only a few sensors and back propagating them with the fdtd model the sound energy refocuses in the vicinity of the true source location this time reversal numerical experiment confirms that using information acquired only at non line of sight locations is sufficient to obtain accurate source locations in a complex urban terrain a simulation study is conducted to demonstrate in principle that time reversal processing can be used to locate sound sources in an outdoor urban area with many buildings acoustic pulse propagation in this environment is simulated using a two dimensional finite difference time domain fdtd computation using the simulated time traces from only a few sensors and back propagating them with the fdtd model the sound energy refocuses in the vicinity of the true source location this time reversal numerical experiment confirms that using information acquired only at non line of sight locations is sufficient to obtain accurate source locations in a complex urban terrain

sound produced by the rapidly inflating santiaguito lava dome guatemala 1 vertical inflation of the caliente lava dome at santiaguito guatemala occurs coincidentally with the onset of explosive eruptions and produces infrasound that is generally peaked between 0 5 and 2 hz with amplitude of up to 5 pa at 1 km from vent inflation of up to 1 m progresses rapidly within 2 s and can encompass the entire surface of the 200 m diameter dome we use particle image velocimetry to quantify the time history of dome uplift and demonstrate that deflection of a volcano s solid surface can generate infrasound waves with amplitudes of a few pa the volumetric displacement history is used to model linear volumetric acoustic sources both compact and of finite extent synthetic waveforms match recorded infrasound in terms of timing and frequency content amplitude fit is very good for a station located 3 3 km from the vent and less good for stations shielded by near vent topography

time reverse location of seismic long period events recorded on mt etna we present the first application of a time reverse location method in a volcanic setting for a family of long period lp events recorded on mt etna results are compared with locations determined using a full moment tensor grid search inversion and cross correlation method from 2008 june 18 to july 3 50 broad band seismic stations were deployed on mt etna italy in close proximity to the summit two families of lp events were detected with dominant spectral peaks around 0 9 hz the large number of stations close to the summit allowed us to locate all events in both families using a time reversal location method the method involves taking the seismic signal reversing it in time and using it as a seismic source in a numerical seismic wave simulator where the reversed signals propagate through the numerical model interfere constructively and destructively and focus on the original source location the source location is the computational cell with the largest displacement magnitude at the time of maximum energy current density inside the grid before we located the two lp families we first applied the method to two synthetic data sets and found a good fit between the time reverse location and true synthetic location for a known velocity model the time reverse location results of the two families show a shallow seismic region close to the summit in agreement with the locations using a moment tensor full waveform inversion method and a cross correlation location method

baking black opal in the desert sun the importance of silica in desert varnish comment and reply reply we welcome the opportunity to reply to dorn 2007 who outlines the classical issues of desert varnish formation we agree that most previous research has suggested a biological mechanism bacterial enhancement of manganese in manganese rich coatings is intriguing however as we have published

manganese rich rock varnish does occur in antarctica abstract despite accounts to the contrary we have found that mn rich rock varnish is present in antarctica as others have before it is chemically and texturally similar to many varnishes found in lower latitudes antarctic varnishes show considerable potential as a dating and paleoenvironmental research tool

baking black opal in the desert sun the importance of silica in desert varnish comment and reply comment perry et al 2006 1 contribute a fourth alternative of silica binding to three prior hypotheses of varnish formation 1 abiotic mn fe enhancement e g engel and sharp 1958 2 2 biotic mn fe enhancement e g dorn and oberlander 1982 3 allen et al 2004 4 and 3 a

desert varnish and environmental change near broken hill western new south wales abstract desert varnish is widespread in arid australia and occurs as a thin often discontinuous manganese enriched surface coating near broken hill western new south wales radiocarbon dating of calcium carbonate associated with this varnish indicated that major varnishing took place before about 10 000 years b p with varnish forming conditions continuing during the holocene small patches of varnish on secondary carbonate on non varnished rock and sometimes on existing varnish suggest that current environmental conditions allow for some varnish formation loss of varnish has resulted from within channel abrasion weathering by lichens minor breakdown of varnish substrates and localized weathering possibly related to a previously higher soil surface

spatial temporal and geographic considerations of the problem of rock varnish diagenesis article i nfo the rock varnish literature hosts an abundance of prima facie contradictory empirical data past and perhaps future empirical contradictions however can be resolved by theoretical considerations of different spatial and temporal scales of varnish diagenesis as well as the geomorphic position of different types of varnishes for example twentieth century contamination by lead and other heavy metals has led to claims of accumulation rates in the last century far more rapid than prior published empirical studies a consideration of spatial scales resolves this contradiction nanoscale processes allow migration of lead into varnish deposited well before the twentieth century time of heavy metal pollution evidence of nanometer scale disequilibrium in three samples led to claims that varnish cannot be used in paleoclimatic research these data rest in contrast to replicable patterns in varnish deposition observed by dr tanzhuo liu and others in over ten thousand micro sedimentary basins this contraction can be resolved by understanding that the types of varnishes studied differ and that processes differ substantially between the nanoscale and the micron scale a lack of evidence of mn oxidizers in genetic analyses contrasts with culturing studies and in situ evidence of mn enhancement by bacteria this contradiction has a likely resolution in vastly different temporal scales dna material analyzed may be no older than 200 years but in situ fossilized remains of bacteria may be preserved for thousands of years recording palaeoecological conditions favoring growth of mn enhancing bacteria

diversity of rock varnish bacterial communities from black canyon new mexico 1 scientists vigorously debate the degree to which rock varnish is formed through the actions of microorganisms to investigate this enigma we utilized a three pronged approach that combined 1 culture independent molecular methods to characterize bacterial communities associated with varnish that coats the rhyolitic volcanic rocks of black canyon new mexico and rocks with no visible varnish 2 culturing of varnish in media supplemented with reduced forms of manganese and or iron and no or low amounts of carbon to isolate bacteria capable of precipitating iron and or manganese oxides and 3 scanning electron microscopy sem of varnish and nearby rock that lacks macroscopically visible varnish our culture independent studies revealed significant differences between varnish and nonvarnish communities chloroflexi and ktedobacteria dominated one varnish site while the other varnish site was dominated by cyanobacteria the nonvarnish sites were dominated by actinobacteria and to a lesser extent cyanobacteria and were the only samples to contain deinococcus thermus sequences approximately 65 of varnish cultures produced visible manganese precipitates most culture isolates were not closely related to known manganese oxidizers with the exception of bacillus spp sem revealed microbial morphologies and two types of varnish morphologies 1 relatively smooth layers and 2 patches of botryoidal pinnacles which were often associated with increased manganese concentrations bare rock showed evidence of incipient varnish these results have important implications for the detection of life on extraterrestrial planets such as mars where putative varnish coatings have been observed and represent some of the first culture independent characterizations of varnish communities

syncontractional crustal anatexis and deformation during emplacement of 1435 ma plutons western needle mountains colorado mesoproterozoic deformation and biomodal magmatism in southwest colorado offer important insight into the nature and tectonic regime of 1 4 ga magmatism in the western united states we document syncontractional emplacement of coeval gabbroic and granitic plutons in the middle crust at 1435 ma in the western needle mountains this is incompatible with extension dominated anorogenic models proposed for the generation of 1 4 ga plutonic rocks in the southwest but lends further support for synkinematic intracontinental magmatism in response to regional tectonic strains created by transpressive or compressive plate margin interactions between 1500 1300 ma intrustion of the 1435 ma electra lake gabbro and eolus granite into paleoproterozoic rocks caused local crustal anatexis and extensive thermal metamorphism in the needle mountains deformation of paleoproterozoic country rocks at 1435 ma is widespread but is concentrated in pluton aureoles where thermally softened crust accommodated the strain we int

time reverse modeling of low frequency microtremors application to hydrocarbon reservoir localization 1 time reverse modeling is applied to synthetic and real low frequency microtremors measured at the earth surface with synchronized seismometers in contrast to previous time reverse applications no single event or first arrival time identification is applied for microtremor localization synthetic low frequency microtremors are numerically generated within a small underground area and modeled with a finite difference algorithm simulating two dimensional elastic wave propagation time reverse modeling using synthetic microtremors shows that small underground source areas can be accurately located different source characteristics which emit mainly p waves or s waves vertically influence the localization accuracy time reverse modeling is applied to two real microtremor data sets acquired 16 months apart above known oil reservoirs nearby voitsdorf austria to investigate whether spectral anomalies observed above the reservoirs originate from the reservoirs time reverse modeling indicates that low frequency microtremor signals originate from the reservoir locations and provides a possible method for reservoir localization

an overview of volcano infrasound from hawaiian to plinian local to global abstract volcano infrasound is an increasingly useful technique for detecting locating characterizing and quantifying eruptive activity and can be used to constrain eruption source parameters in recent years studies of infrasound data from active volcanoes have shown clear progress towards mitigating volcanic hazards and understanding volcanic source processes volcano acoustic sources are shallow or aerial thus volcano infrasound data provide valuable information on eruption dynamics and are readily combined with direct and remote observations of gas ash and other eruptive phenomena the infrasound signals produced by volcanoes are indicative of the eruption style and dynamics here we review the diversity of infrasound signals generated by a wide variety of volcanic eruptions from hawaiian to plinian and the physical processes inferred to produce them we place particular emphasis on regional 15 250 km distance and global 250 km distance volcano infrasound studies as recent work in this area has made significant advances in monitoring and characterizing remote and difficult to monitor eruptions long range infrasonic detection of explosive volcanic eruptions is possible due to the energetic source mechanisms involved minor atmospheric attenuation at low frequencies and the existence of waveguides in the atmosphere however accurate characterization of the atmosphere and its spatiotemporal variability is required for reliable long range sound propagation modeling and correct interpretation of global infrasound recordings conversely because volcanic explosions are energetic and sometimes repetitive infrasound sources they can be used to validate atmospheric and acoustic propagation models

hrtem investigation of trilling todorokite and nano phase mn oxides in manganese dendrites we characterized manganese dendrites on three different substrate rocks rhyolite clayey siltstone and limestone using high resolution transmission electron microscopy manganese dendrites are mainly composed of nanometer scale mn hydr oxides fe oxy hydroxide sulfate and clay minerals including hollandite todorokite birnessite goethite amorphous fe hydroxide smectite illite and gypsum each sample has a different main manganese phase two dendrite samples have more than one manganese phase todorokite crystals on a limestone sample from altmuhl valley germany showed trilling intergrowths chain width disorder and chain termination occur in todorokite the sum of the numbers of octahedral wall layers and octahedral chains were equal at both sides beyond the termination the chain termination rule was explained by the geometry of octahedral chains and the octahedral wall layer the trilling intergrowths of todorokite might be formed by transforming the structure from birnessite to todorokite or by multiple epitaxial todorokite nucleations on octahedral wall layer of todorokite or birnessite based on chain width disorder in the todorokite we suggest that the todorokite might have been transformed from birnessite

characterizing complex eruptive activity at santiaguito guatemala using infrasound semblance in networked arrays abstract we implement an infrasound semblance technique to identify acoustic sources originating from volcanic vents and apply the technique to the generally low amplitude infrasound

rock engraving chronologies and accelerator mass spectrometry radiocarbon age of desert varnish abstract it has been proposed that the minimum age of rock engravings can be established from dating organic carbon associated with desert varnish a naturally occurring coating on rocks in arid regions in this study five radiocarbon ages were obtained from organic carbon in previously undated varnishes from the pilbara western australia four varnish samples were scraped from dull black coatings and one from patchy shiny black varnish all radiocarbon ages were younger than 2800 years bp ages were younger at the rock varnish interface than in overlying varnish a reversal of expected stratigraphic relations these results highlighted a number of difficulties associated with the interpretation of varnish radiocarbon ages including the potential absence of a link between organic carbon age and varnish deposition age linkages are complicated by the time transgressive nature of varnish formation its weathering over time and the probable mixed ages of dated organic carbon engraving chronologies based solely on radiocarbon ages of varnish should be treated with extreme caution

systematic mn fluctuations in laminated rock varnish developed on coeval early holocene flint artifacts along a climatic transect negev desert israel abstract this study presents an assessment of the potential application of mn content in rock varnish laminae as a paleoclimate indicator to investigate the environmental controls on varnish formation we determined mn composition in rock varnish formed on flint artifacts produced during the earliest holocene from eight coeval prehistoric sites in the negev desert israel these sites lie along a north south annual rainfall transect ranging between 120 and 30 mm yr 1 the varnish is 100 times enriched in mn relative to the content in the desert dust source material chemical profiles across the varnish display 4 6 distinct mn peaks in all sampled sites pointing to systematic fluctuations within the varnish along a wide range of environmental settings the mean mn contents in the various sites range between 10 7 and 15 6 at yet within this range the mn content in the negev varnish does not show a correlation with mean annual rainfall as moisture is needed for mn mobility wetting cycles by dew or light rain which are not adequately represented by the mean annual rainfall amounts but control the number of wetting drying cycles may explain the variance within the results from the arid and hyperarid negev varnish

influence of near source volcano topography on the acoustic wavefield and implication for source modeling in near source conditions 5 km the atmosphere is often assumed to be fully transparent to acoustic waves and to have a small effect on the acoustic wavefield as a consequence the propagation of the acoustic waves in the atmosphere near the source is often neglected and waveform is compensated only in amplitude by the inverse of the distance from the source however the amplitude distribution at five infrasonic stations deployed around the active craters of the stromboli volcano reveals anomalous decay up to 11 db larger than expected which cannot be explained in terms of energy loss for geometrical spreading the distribution of amplitude decay changes for different source positions suggesting a strong relationship with the source to receiver path geometry by using 2d fdtd modeling we show that the anomalous amplitude distribution of the acoustic waves at stromboli is not necessarily due to the source radiation pattern but it is strongly influenced by the topography of the ground atmosphere interface diffraction and reflection of topography contaminate the acoustic wavefield and have a strong effect in reducing the amplitude and altering the waveform our work demonstrates that line of sight conditions are quite difficult to be achieved in acoustic experiments and that a detailed knowledge of the topography along the crater receiver path is necessary whenever infrasound waveforms are used to invert for the source process

volcano infrasound a review abstract exploding volcanoes which produce intense infrasound are reminiscent of the veritable explosion of volcano infrasound papers published during the last decade volcano infrasound is effective for tracking and quantifying eruptive phenomena because it corresponds to activity occurring near and around the volcanic vent as opposed to seismic signals which are generated by both surface and internal volcanic processes as with seismology infrasound can be recorded remotely during inclement weather or in the dark to provide a continuous record of a volcano s unrest moreover it can also be exploited at regional or global distances where seismic monitoring has limited efficacy this paper provides a literature overview of the current state of the field and summarizes applications of infrasound as a tool for better understanding volcanic activity many infrasound studies have focused on integration with other geophysical data including seismic thermal electromagnetic radiation and gas spectroscopy and they have generally improved our understanding of eruption dynamics other work has incorporated infrasound into volcano surveillance to enhance capabilities for monitoring hazardous volcanoes and reducing risk this paper aims to provide an overview of volcano airwave studies from analog microbarometer to modern pressure transducer and summarizes how infrasound is currently used to infer eruption dynamics it also outlines the relative merits of local and regional infrasound surveillance highlights differences between array and network sensor topologies and concludes with mention of sensor technologies appropriate for volcano infrasound study

rock varnish in the sonoran desert microbiologically mediated accumulation of manganiferous sediments rock varnish occurs in virtually all environments most commonly in arid and semi arid climates including antarctica rock varnish consists of thin layers of intimately mixed aeolian and chemical sediments often showing botryoidal and more rarely stromatolite like morphologies typical rock varnish samples collected at twin peak mountain park near phoenix arizona consist of abundant quartz with plagioclase illite and a mixed layer fe clay mineral probably corrensite eds sem bse and tem analyses revealed that the typical mn fe minerals occur as minute particles some of these particles and other mineral grains are attached to filaments xrd and electron diffraction showed that the mn fe bearing particles are poorly crystalline the filaments based on morphological criteria are virtually indistinguishable from fungal filaments most filaments are fragments probably broken by scraping during sample collection coccoid and rod shaped forms resembling cyanobacteria and other bacteria respectively are also present unlike definitive minerals these filaments disintegrated in the concentrated energy of the sem electron beam at the instrumental and experimental conditions used in addition no filamentous rod shaped or coccoid forms were observed in samples hydrolysed with 6 n hcl for 24 h at 100 c bacteria and fungi in powdered rock varnish were cultured on four media incubated aerobically in the dark at 25 c the culture media yielded dense growths of spore forming bacteria and filamentous fungi one fungus and two bacillus isolates oxidized and concentrated manganese control experiments revealed that fungi and bacteria are present on and below the surfaces of rock varnish free and hydrolysed peptide protein bound amino acids were identified in the rock varnish amino acids showed virtually no racemization with the exception of d l asp 0 1 relatively high molecular weight humic matter was also separated from the rock varnish high resolution mass spectrometry revealed non hydrocarbon moieties similar to a suwannee river fl humic acid standard micro organisms and their original biochemical compounds do not seem to be preserved for long in the accreting varnish layer the studies showed that the filaments helped to trap mineral particles of rock varnish and that bacteria and fungi abetted mn concentration some structures in the layers of rock varnish resemble stromatolites and present definitions would allow them to be termed as such

time reversal location of glacial earthquakes in 2003 ekstrom et al reported the detection and location of a new class of earthquakes occurring in the polar regions of the earth the proposed source mechanism involves large and sudden sliding motions of glaciers which gave the name glacial earthquakes to these events in this study we localize some of these earthquakes with a time reversal mirror trm algorithm which contrary to ordinary back projection methods does not involve testing each possible source location in trm localization an earthquake is located on the basis of only one 3 d spectral element simulation of seismic wave propagation by using the full complexity of recorded data as simultaneous time reversed sources we show that on the basis of this approach even glacial earthquakes with a faint signal can be correctly localized and that the pattern of the time reversed wavefield is coherent with the motion of glaciers down their valley

mapping complex vent eruptive activity at santiaguito guatemala using network infrasound semblance pyroclastic laden explosive eruptions from santiaguito volcano guatemala are vented from the 200 m diameter caliente dome summit and result in a superposition of spatially extensive and temporally sustained tens of seconds to minutes acoustic sources a network of infrasonic microphones distributed on various sides of the volcano record distinct waveforms which are poorly correlated across the network and suggestive of acoustic interference from multiple sources presuming the infrasound wavefield is a linear superposition of spatially and temporally distinct sub events we introduce a semblance mapping technique to recover the time history of the spatially evolving sources during successive time windows coincident high resolution video footage corroborates that both rapid dome uplift and individual explosive pulses are likely sources of high semblance infrasound that are identifiable during short 2 s time windows this study suggests that complex and network variable infrasound waveforms are produced whenever a volcanic vent source dimension is large compared to the wavelength of the sound being produced non compact infrasound radiators are probably commonplace at silicic volcanic systems where venting often occurs across a dome surface

infrasonic monitoring at stromboli volcano during the 2003 effusive eruption insights on the explosive and degassing process of an open conduit system 1 stromboli is an open conduit volcano characterized by persistent conduit degassing and explosive dynamics during the 2003 effusive eruption we monitored this activity with a five element array deployed at 450 m from the active craters the array allows us to track in real time changes of explosive activity in terms of source position and excess pressure release infrasonic monitoring located the new active vents in the same preeruptive position revealing that the collapse of the crater terrace has not changed the geometry of the shallow feeding system elevation of the infrasonic source is stable at 750 m above sea level coincident with the elevation of the crater terrace this suggests a shallow position of the magma column or if the source is embedded in the conduit diffraction at the crater rim at the end of the eruption back azimuth analysis indicates that explosive activity was progressively reestablished at all of the craters following a ne toward sw direction along the collapsed trench the array detected significant small amplitude 1 pa infrasonic activity occurring at a rate of approximately one pulse every 2 s and generally located in only one vent at a time this persistent activity is not related to strombolian explosion but we infer it is reflecting the overpressurized degassing of the magma column amplitude distribution of 7 million infrasonic signals shows that this degassing is 1 order of magnitude more energetic than the explosions besides infrasonic amplitude distribution presents a decay with a double slope indicating that explosions and degassing are driven by conduit dynamics acting at two different rates

nanometer scale layering in rock varnish implications for genesis and paleoenvironmental interpretation manganiferous rock varnish collected from death valley and antarctica contains the smallest known terrestrial sedimentary deposits with some layers only a few nanometers thick irregularities in these nanometer scale layers are consistent with shrinking cracking and weathering of clay minerals in the death valley rock varnish very different high resolution transmission electron microscope hrtem textures coexist that may be related to climatic change hrtem observations contradict previous microbial models of mn fe enhancement requiring a new three step model of biomineralization and diagenesis for varnish formation

stable carbon isotope ratios of rock varnish organic matter a new paleoenvironmental indicator stable carbon isotope ratios of organic matter in rock varnishes of holocene age from western north america and the middle east show a strong association with the environment this isotopic variability reflects the abundance of plants with different photosynthetic pathways in adjacent vegetation analyses of different layers of varnish on late pleistocene desert landforms indicate that the carbon isotopic composition of varnish organic matter is a paleoenvironmental indicator

finite difference time domain modeling of transient infrasonic wavefields excited by volcanic explosions 1 numerical modeling of waveform diffractions along the rim of a volcano vent shows high correlation to observed explosion signals at karymsky volcano kamchatka russia the finite difference modeling assumed a gaussian source time function and an axisymmetric geometry a clear demonstration of the significant distortion of infrasonic wavefronts was caused by diffraction at the vent rim edge data collected at karymsky in 1997 and 1998 were compared to synthetic waveforms and variations of vent geometry were determined via grid search karymsky exhibited a wide range of variation in infrasonic waveforms well explained by the diffraction and modeled as changing vent geometry rim diffraction of volcanic infrasound is shown to be significant and must be accounted for when interpreting source physics from acoustic observations

characteristics and origin of rock varnish from the hyperarid coastal deserts of northern peru abstract the characteristics of a new type of rock varnish from the hyperarid coastal deserts of northern peru combined with laboratory experiments on associated soil materials provide new insights into the formation of rock varnish the peruvian varnish consists of an fe rich mn poor component covering up to 95 of a varnished surface and a fe rich mn rich component found only in pits and along cracks and ridges the alkaline soils plus the catalytic fe oxyhydroxides that coat much of the varnish surfaces make the peruvian situation ideal for physicochemical precipitation of mn however the low mn content of the dominant fe rich mn poor component suggests that such precipitation is minor this plus the presence of abundant bacteria in the mn rich varnish and the recorded presence of mn precipitating bacteria in varnish elsewhere suggests that bacteria are almost solely responsible for mn precipitation in rock varnish a set of experiments involving peruvian soil samples in contact with water co2 solutions indicates that natural fogs or dews release mn but not fe when they come in contact with eolian materials on rock surfaces this mechanism may efficiently provide mn to bacteria on varnishing surfaces the lack of fe in solution suggests that a large but unknown proportion of fe in varnish may be in the form of insoluble fe oxyhydroxides sorbed onto the clay minerals that form the bulk of rock varnish the results of this study do not substantively change r i dorn s paleoenvironmental interpretations of varnish mn fe ratios but they do suggest areas for further inquiry

rock varnish in new york an accelerated snapshot of accretionary processes abstract samples of manganiferous rock varnish collected from fluvial bedrock outcrop and erie barge canal settings in new york state host a variety of diatom fungal and bacterial microbial forms that are enhanced in manganese and iron use of a dual beam focused ion beam scanning electron microscope to manipulate the varnish in situ reveals microbial forms that would not have otherwise been identified the relative abundance of mn fe enriched biotic forms in new york samples is far greater than varnishes collected from warm deserts moisture availability has long been noted as a possible control on varnish growth rates a hypothesis consistent with the greater abundance of mn enhancing bioforms sub micron images of incipient varnish formation reveal that varnishing in new york probably starts with the mortality of microorganisms that enhanced mn on bare mineral surfaces microbial death results in the adsorption of the mn rich sheath onto the rock in the form of filamentous networks clay minerals are then cemented by remobilization of the mn rich material thus the previously unanswered question of what comes first clay mineral deposition or enhancement of mn can be answered in new york because of the faster rate of varnish growth in contrast very slow rates of varnishing seen in warm deserts of microns per thousand years make it less likely that collected samples will reveal varnish accretionary processes than samples collected from fast accreting moist settings

characteristics of desert varnish from nanometer to micrometer scale a photo oxidation model on its formation abstract rock varnish is a widespread mn rich rock coating commonly developed in arid environments but the mechanism for its formation is still under debate in this study rock varnish and adjacent soil dust collected from gobi desert were analyzed for exploring the possible abiotic oxidation mechanism of mn oxides the occurrence of rock varnish shows a direct and close relationship with strong irradiation of sunlight giving the first evidence of photochemical genesis abundant caves and tunnels with average diameter of 1 5 m are observed on varnish surface regions which facilitate the penetration of sunlight and water metal oxyhydr oxides including birnessite hematite goethite rutile and anatase account for the major components of rock varnish which are all solar light responsive semiconducting minerals the trace elements enrichment patterns revealed by la icp ms provide the indication of an aqueous origin the positive ce anomalies in varnish in contrast to the rock substrate as well as the positive correlation between ce and mn suggest a strong oxidizing environment in the genesis of rock varnish therefore the photo generated holes and reactive oxygen species ross on metal oxides in varnish can promote mn ii oxidation which are further demonstrated from thermodynamic and kinetic considerations ross including 1o2 and oh with strong oxidizing capability are detected by epr in varnish suspension providing the direct evidence for mn ii oxidation laboratory experimental simulations show the photocatalysis of metal oxides in rock varnish greatly promote mn ii oxidation by 2 10 7 97 times in comparison with homogenous solution oxidation all these lines of evidence suggest that light induced abiotic process may play important roles in the formation of rock varnish together with other abiotic and biotic pathways which can even provide implications for the evolution of mn oxides on surface of terrestrial planets

microtextures in mudrocks as revealed by backscattered electron imaging abstract this report is one of the first attempts to examine polished mudrock sections with backscattered scanning electron microscopy bse in order to image characterize and understand their microtextures as well as to help reconstruct sedimentary and diagenetic environments over 180 polished thin sections of mudrocks from precambrian to early middle tertiary age were examined in this study using bse seven common microtextures have been identified in the samples examined with bse microlaminations fossil forms pyrite clay minerals and micas chemical and physical alteration glauconization and porosity microlaminations have been examined at the single grain level foraminifera in the gulf coast tertiary reflect a sequence of preservation relations from shallow depths to a few thousand meters fecal pellets in a black mudrock from spitsbergen of upper jurassic age contain what appear to be well preserved fossil vertebrates replaced by pyrite the chemical and physical variations within micas and clay minerals seem to be the result of selective alteration along cracks and defects in the minerals and these have been imaged mineral growth and dissolution at the submicron level can be imaged particularly in the clay minerals quartz and feldspar glauconite growth conditions geochemical complexities of carbonate formation and the size shape and orientation of micron sized pore spaces in shales have been obtained thus the microtextural analysis of mudrocks not only is possible but can be accomplished in great detail with existing techniques