seismic tomography a window into deep earth abstract the goal of this paper is to provide an overview of the current state of the art in seismic tomography and trace its origins from pioneering work in the early 1970s to its present status as the pre eminent tool for imaging the earth s interior at a variety of scales due to length limitations we cannot hope to cover every aspect of this diverse topic or include mathematical derivations of the underlying principles rather we will provide a largely descriptive coverage of the methodology that is targeted at readers not intimately familiar with the topic the relative merits of local versus global parameterization ray tracing versus wavefront tracking backprojection versus gradient based inversion and synthetic testing versus model covariance are explored a variety of key application areas are also discussed including body wave traveltime tomography surface wave tomography attenuation tomography and ambient noise tomography established and emerging trends many of which are driven by the ongoing rapid increases in available computing power will also be examined including finite frequency tomography full waveform tomography and joint tomography using multiple datasets several practical applications of seismic tomography including body wave traveltime attenuation and surface waveform are presented in order to reinforce prior discussion of theory

environmental perturbations caused by the impacts of asteroids and comets we review the major impact associated mechanisms proposed to cause extinctions at the cretaceous tertiary geological boundary we then discuss how the proposed extinction mechanisms may relate to the environmental consequences of asteroid and comet impacts in general our chief goal is to provide relatively simple prescriptions for evaluating the importance of impacting objects over a range of energies and compositions but we also stress that there are many uncertainties we conclude that impacts with energies less than about 10 mt are a negligible hazard for impacts with energies above 10 mt and below about 104 mt i e impact frequencies less than one in 6 104 years corresponding to comets and asteroids with diameters smaller than about 400 m and 650 m respectively blast damage earthquakes and fires should be important on a scale of 104 or 105 km which corresponds to the area damaged in many natural disasters of recent history however tsunami excited by marine impacts could be more damaging flooding a kilometer of coastal plain over entire ocean basins in the energy range of 104 105 mt intervals up to 3 105 years corresponding to comets and asteroids with diameters up to 850 m and 1 4 km respectively water vapor injections and ozone loss become significant on the global scale in our nominal model such an impact does not inject enough submicrometer dust into the stratosphere to produce major adverse effects but if a higher fraction of pulverized rock than we think likely reaches the stratosphere stratospheric dust causing global cooling would also be important in this energy range thus 105 mt is a lower limit where damage might occur beyond the experience of human history the energy range from 105 to 106 mt intervals up to 2 106 years corresponding to comets and asteroids up to 1 8 and 3 km diameter is transitional between regional and global effects stratospheric dust sulfates released from within impacting asteroids and soot from extensive wild fires sparked by thermal radiation from the impact can produce climatologically significant global optical depths of the order of 10 moreover the ejecta plumes of these impacts may produce enough no from shock heated air to destroy the ozone shield between 106 and 107 mt intervals up to 1 5 107 years corresponding to comets and asteroids up to 4 and 6 5 km diameter dust and sulfate levels would be high enough to reduce light levels below those necessary for photosynthesis ballistic ejecta reentering the atmosphere as shooting stars would set fires over regions exceeding 107 km and the resulting smoke would reduce light levels even further at energies above 107 mt blast and earthquake damage reach the regional scale 106 km tsunami cresting to 100 m and flooding 20 km inland could sweep the coastal zones of one of the world s ocean basins fires would be set globally light levels may drop so low from the smoke dust and sulfate as to make vision impossible at energies approaching 109 mt 108 years the ocean surface waters may be acidified globally by sulfur from the interiors of comets and asteroids the cretaceous tertiary impact in particular struck evaporate substrates that very likely generated a dense widespread sulfate aerosol layer with consequent climatic effects the combination of all of these physical effects would surely represent a devastating stress on the global biosphere

the pre quaternary history of fire abstract although evidence for land vegetation comes from the silurian and maybe even earlier the first record of fossil charcoal fusain is from the late devonian for this period there are only one or two isolated records not until the early carboniferous is there a record of extensive charcoal deposits mainly preserved in near shore clastic sediments which provide evidence of significant and widespread wildfires by the late carboniferous charcoal was common or abundant in a wide range of facies including tropical wetland peats wildfire played an important role in shaping the environment at this time the latest palaeozoic and early mesozoic records of charcoal are fewer whereas important deposits of late mesozoic age are found worldwide the occurrence of charcoal at the cretaceous tertiary boundary has been highlighted as evidence for a global fire following a meteorite impact but this interpretation is questionable charcoal has been widely reported from tertiary sediments and its appearance in the quaternary and recent is not solely as a result of human impact through the past 400 million years there have been major changes in atmospheric oxygen levels that affected fire intensity and frequency fire systems thus have a long history and their impact on shaping the environment is assessed

magma reflection imaging in krafla iceland using microearthquake sources the details of magma plumbing beneath active volcanoes remain a major challenge in geochemistry geophysics and volcanic hazard evaluation here we apply a relatively novel variation of seismic interferometry which we call virtual reflection seismic profiling vrsp to produce a high resolution image of a known crustal magma body the technique takes advantage of recent advances in both seismic instrumentation dense arrays and seismic analysis seismic interferometry we have applied this technique to data recently acquired at an iconic volcanic system krafla which lies on the mid atlantic ridge as exposed in northern iceland what make this particular site exceptional are encounters with rhyolitic magma in two drillholes k 39 and iceland deep drilling project 1 iddp 1 these known magma bodies represent a unique calibration opportunity for surface geophysical measurements of magma distribution at depth in this study we produced a stacked seismic reflection section by applying common depth point processing techniques to virtual shot gathers derived from interferometry of p waves from microearthquakes generated by tectonic magmatic and or geothermal activity we observe a strong coherent reflection on the seismic section at a travel time corresponding to the depth at which magma was encountered in the iddp 1 wellbore we interpret this reflection to be from magma or magma related fluids additional coherent reflections may correspond to other components of the magma plumbing beneath krafla these results represent a promising new technique for structural imaging with natural sources that can be applied to a wide array of geologic and energy problems that involve natural or induced seismic clusters

fireball passes and nothing burns the role of thermal radiation in the cretaceous tertiary event evidence from the charcoal record of north america high soot contents have been reported in cretaceous tertiary k t sedimentary rocks leading to the suggestion that the amount of thermal power delivered from the chicxulub impact was sufficient to have ignited wildfires soot cannot be used to indicate fire location however as soot from one large fire could spread globally sources other than biomass burning could also yield soot charcoal in nonmarine sedimentary rocks here quantified in situ in polished blocks provides a unique tool to record the distribution of wildfires and therefore assess the extent of any thermal radiation associated with the impact at chicxulub the k t and lowermost tertiary sedimentary rocks of six nonmarine sequences colorado to saskatchewan contain no charcoal or below background levels of charcoal and a significant quantity of noncharred organic materials revealing that there was no distinctive wildfire across the north american continent related to the k t event this finding indicates that the k t impact cannot have delivered a peak irradiance of 95 kw m 2 of thermal power to the atmosphere and 19 kw m 2 to the ground therefore the thermal power delivered from the impact to north america did not have the destructive potential previously predicted high amounts of thermal radiation were not responsible for the environmental perturbations or extinctions associated with the k t event

proximal cretaceous tertiary boundary impact deposits in the caribbean trace element isotopic and mineralogic studies indicate that the proposed impact at the cretaceous tertiary k t boundary occurred in an ocean basin although a minor component of continental material is required the size and abundance of shocked minerals and the restricted geographic occurrence of the ejecta layer and impact wave deposits suggest an impact between the americas coarse boundary sediments at sites 151 and 153 in the colombian basin and 5 to 450 meter thick boundary sediments in cuba may be deposits of a giant wave produced by a nearby oceanic impact on the southern peninsula of haiti a approximately 50 centimeter thick ejecta layer occurs at the k t boundary this ejecta layer is approximately 25 times as thick as that at any known k t site and suggests an impact site within approximately 1000 kilometers seismic reflection profiles suggest that a buried approximately 300 km diameter candidate structure occurs in the colombian basin

constraints on the thermal energy released from the chicxulub impactor new evidence from multi method charcoal analysis it has been suggested by various workers that an extraterrestrial impact at the k t boundary delivered sufficient thermal power to ignite globally extensive wildfires numerous models have sought to predict the amount of thermal power released by the impact but none have considered the distribution of wildfire indicators in k t rocks probably the most distinctive product from combustion of biomass is charcoal the abundance of charcoal across the k t boundary at eight non marine sites in north america stretching from colorado in the south to saskatchewan in the north is recorded using three separate methods that allow quantitative analyses of microscopic to macroscopic charcoal particles this study not only provides the first extensive study of charcoals across the k t boundary but also uses the presence or absence of charred material to predict the extent and severity of the thermal pulse released by the k t impact across the area predicted to have suffered the most extreme environmental effects the k t rocks contain on average between four and eight times according to the method used less charcoal than the cretaceous rock record and non charred plant remains are abundant in the k t rocks the below background charcoal abundance and the high proportion of noncharred material in the k t and lowermost tertiary rocks across the western interior of north america suggest that there were no significant wildfires in this area associated with the k t event although soot and polyaromatic hydrocarbons pahs have been reported in the k t rocks we suggest that the soot morphology and pah types are more consistent with a source from the vaporization of hydrocarbons rather than biomass for spontaneous ignition of vegetation temperatures 545 c are necessary whereas smouldering will begin at 325 c the below background levels of charcoal in the k t rocks allow the ground temperatures following the k t impact to be constrained to between no more than 545 c at any point and not above 325 c for any significant period this implies a maximum irradiance of 2 at the ground surface and that no more than 6 kw m 2 of thermal power was delivered to the ground for more than a few hours therefore our results show that the fossil record indicates that the impact at chixculub did not generate sufficient thermal power to ignite extensive wildfires

the stability of zincian spinels in sulfide systems and their potential as exploration guides for metamorphosed massive sulfide deposits zincian spinel zn fe mg al 2 o 4 is found in a variety of geologic settings including metamorphosed massive sulfide deposits aluminous metasediments pegmatites and marbles many spinels in and near metamorphosed massive sulfides have formed by desulfidation and oxidation reactions that involve members of the system zn fe al si s o experimental reversals of the simplified reaction zns fes 2al 2 o 3 o 2 znal 2 o sub 4 feal 2 o 4 s 2 using hydrothermal techniques have been obtained at 2 and 5 kb and various temperatures using fe sub 1 x s fes 2 fe 3 o 4 as a buffer calculated positions of the spinel sphalerite equilibria in f sub o 2 f sub s 2 x space for ideal behavior along the znal 2 o 4 feal 2 o 4 join as is suggested by octahedral site preference energies agree with experimental results and theoretical calculations depending on the choice of the free energy of formation of hercynite the compositions of spinels in equilibrium with sphalerite and either pyrite or pyrrhotite become more zn enriched with increasing f sub s 2 and f sub o 2 values and can be used as a measure of f sub o 2 during metamorphism spinel associated with metamorphosed massive sulfide deposits marbles and aluminous metasediments is enriched in the gahnite znal 2 o 4 spinel mgal 2 o 4 and hercynite feal 2 o 4 molecules respectively whereas spinel associated with pegmatites is depleted in the spinel molecule such variability in composition constitutes a potential exploration guide for metamorphosed massive sulfide deposits

observations and experiments on the origin and formation of inertinite group macerals the inertinite group macerals include fusinite semifusinite inertodetrinite macrinite micrinite and funginite and secretinite which together replace sclerotinite the macrolithotype fusain comprises fusinite and semifusinite and is now widely accepted as charcoal formed by wildfire activity however alternative origins for fusinite and semifusinite are still claimed this paper considers the use of the terms pyrofusinite degradofusinite rank fusinite and primary fusinite misleading while the definitions of the terms funginite and secretinite are also considered problematic observations made on modern wildfire derived and volcanogenic charcoal assemblages using reflectance and scanning electron microscopy together with experimental charcoalification studies demonstrate that most if not all inertinite macerals have acquired their optical and physical characteristics through the action of elevated temperatures the criteria for the identification of charcoals produced by wildfire and volcanic activity are outlined and the role of the petrographic nomenclature system is discussed

early paleogene wildfires in peat forming environments at schoningen germany wildfire activity in early paleogene greenhouse conditions can be used as an analogue to gauge the effect of future warming trends on wildfire in the current climate system inertinite fossil charcoal in coal from 11 autochthonous early paleogene lignite seams from the schoningen mine germany was quantified using macerations in situ pillars and industry standard crushed samples a new three transect method was developed to quantify in situ charcoal the combination of in situ pillars and crushed samples accounts for temporal and spatial variation in charcoal through a stratigraphically oriented pillar whilst maintaining comparability with industry standards and previous work charcoal occurs as a range of randomly distributed particle sizes indicating that fires were burning locally in the schoningen peat forming environment and in the surrounding areas but according to petrological data not in an episodic or periodic pattern although charcoal abundance is low relative to previous high fire worlds such as the cretaceous three quantitative and semi quantitative methods show increased wildfire activity relative to the modern world in the warmest parts of the early paleogene as atmospheric oxygen levels stabilised to modern values and precipitation and humidity became the main control on wildfire increased rainfall followed by drier intervals would have created an environment rich in dry fuel in which wildfires could easily propagate if humidity was low enough in the later part of the early eocene ypresian charcoal abundance fell to levels similar to those found in modern peats this indicates that the transition to the modern low fire world occurred within the early eocene earlier than previous records suggest

paleoatmospheric pco2 fluctuations across the cretaceous tertiary boundary recorded from paleosol carbonates in ne china abstract a dramatic change in atmospheric composition has been postulated because of global carbon cycle disruption during the cretaceous k tertiary t transition following the chicxulub impact and deccan trap eruptions here pedogenic carbonates were collected from drill core of a borehole sk 1 n straddling the late cretaceous and early paleocene strata in the songliao basin northeast china to reconstruct atmospheric co 2 concentrations using a paleosol paleobarometer our estimates for atmospheric pco 2 from paleosol carbonates range between 277 115 ppmv and 837 164 ppmv between 67 8 ma and 63 1 ma one large 66 65 5 ma and several small co 2 spikes 64 7 64 2 ma during the latest maastrichtian to earliest danian are reported here and incorporated with previously published pco 2 estimates also estimated from paleosol carbonates these co 2 spikes are attributed to one million year long emplacement of the large deccan flood basalts along with the extraterrestrial impact at the k t boundary

observations on the nature and origin of fusain abstract evidence for a wildfire origin of fusain is examined charcoal produced by natural fires and artificial charring resembles fossil fusain both in physical size and shape and in optical reflectance artificially charred leaves and naturally burnt wood are illustrated using the sem reflectance studies on modern charcoals suggest that much semifusinite may be produced by pyrolysis the ecological implications of a wildfire origin of fusain are discussed and it is concluded that fires have been a feature of terrestrial ecosystems from at least the late devonian

retrograde evolution in the central vosges mountains northeastern france implications for the metamorphic history of high grade rocks during the variscan orogeny abstract metamorphism in the vosges massif is characterized by rocks formed under a wide range of pressures and temperatures high pressure rocks garnet peridotites and eclogites facies rocks are found together with low pressure rocks garnetcordierite stability field hitherto metamorphism has been interpreted within the framework of an identical p t evolution for all rock types corresponding to either two separate geotectonic events or a unique p t evolution from high pressure to low pressure conditions we studied gneisses from the vosges massif in order to constrain the p t t path they followed p t estimation indicates that gneisses equilibrated between 5 and 7 kbar during peak metamorphism time rocks later experienced cooling from temperatures above 650 c down to 550 c it is possible that the entire p t evolution of the gneisses took place within the lower part of the amphibolite facies which is inconsistent with the p t evolution of the high pressure rocks the noteworthy absence of muscovite staurolite assemblages is attributed to conditions of low h2o and low o2 activity the consequences for the geodynamics in the vosges massif are that at least two separate geotectonic events are required in order to explain the juxtaposition of high pressure rocks with low pressure amphibolite facies rocks

geologic framework of nonmarine cretaceous tertiary boundary sites raton basin new mexico and colorado iridium concentrations are anomalously high at the palynological cretaceous tertiary boundary in fluvial sedimentary rocks of the lower part of the raton formation at several localities in the raton basin of new mexico and colorado the iridium anomaly is associated with a thin bed of kaolinitic claystone in a discontinuous carbonaceous shale and coal sequence

carbon isotopic evidence for biomass burning at the k t boundary a new interpretation of existing carbon isotopic data combined with results from a biogeochemical model suggests that burning of terrestrial biomass occurred on a global scale at the cretaceous tertiary k t boundary carbon isotopic ratios from planktonic and benthic microfossils across the k t boundary reveal not only a breakdown in the normal surface water to deep water gradient of 13 c 12 c but also a reversal at the boundary this reversal cannot be explained by the cessation off primary production alone we propose that combustion of terrestrial biomass with subsequent transfer of isotopically light carbon to surface waters is the most likely cause of this anomaly a biogeochemical model is used to quantify the extent of burning at the boundary combustion of roughly 25 of the above ground biomass at the end of the cretaceous is necessary to account for the observed isotopic signal

probabilistic earthquake relocation in three dimensional velocity models for the yellowstone national park region wyoming recorded seismicity for the yellowstone national park region comprising 25 267 earthquakes from november 1972 to december 2002 has been relocated using three dimensional velocity models and probabilistic earthquake location in addition new coda magnitudes for earthquakes between 1984 and 2002 were computed by using an improved coda magnitude equation three dimensional velocity models for earthquake location were computed by inverting subsets of high quality data of three different periods 1973 1981 1984 1994 and 1995 2002 for hypocenter locations and seismic velocities earthquakes were relocated by using a nonlinear probabilistic solution to the earthquake location problem fully nonlinear location uncertainties included in the probabilistic solution allow a better and more reliable classification of earthquake locations into four quality classes earthquake locations show an improvement in location accuracy with time which we attribute to improved network geometry and more precise timing of arrival times no large systematic shifts of the relocated earthquake locations are observed except a systematic shift of 2 km to greater depth the new relocated earthquake locations show tighter clustering of epicenters and focal depths when compared with original earthquake locations the most intense seismicity in terms of number of earthquakes and cumulative seismic moment release in the yellowstone national park region occurs northwest of the yellowstone caldera between hebgen lake and the northern rim of the caldera seismicity within the yellowstone caldera is diffuse and shallow individual clusters of earthquakes can be associated with major hydrothermal areas

towards understanding the puzzling lack of acid geothermal springs in tibet china insight from a comparison with yellowstone usa and some active volcanic hydrothermal systems abstract explanations for the lack of acid geothermal springs in tibet are inferred from a comprehensive hydrochemical comparison of tibetan geothermal waters with those discharged from yellowstone usa and two active volcanic areas nevado del ruiz colombia and miravalles costa rica where acid springs are widely distributed and diversified in terms of geochemical characteristic and origin for the hydrothermal areas investigated in this study there appears to be a relationship between the depths of magma chambers and the occurrence of acid chloride rich springs formed via direct magmatic fluid absorption nevado del ruiz and miravalles with magma at or very close to the surface less than 1 2 km exhibit very acidic waters containing hcl and h2so4 in contrast the tibetan hydrothermal systems represented by yangbajain usually have fairly deep seated magma chambers so that the released acid fluids are much more likely to be fully neutralized during transport to the surface the absence of steam heated acid waters in tibet however may be primarily due to the lack of a confining layer like young impermeable lavas at yellowstone to separate geothermal steam from underlying neutral chloride waters and the possible scenario that the deep geothermal fluids below tibet carry less h2s than those below yellowstone

characterization of a fractured granitic pluton p and s waves seismic tomography and uncertainty analysis abstract a detailed characterization of the physical properties of a granitic pluton including a three dimensional reconstruction of the fractures network and its surrounding are obtained by high resolution seismic tomography of p and s waves the input p and s wave travel times were picked from three component offset and azimuth variable seismic profile ovsp acquired in a 500 m deep vertical borehole the travel time inversion resulted in two three dimensional p and s wave velocity models and the uncertainty robustness and sensitivity are estimated by performing a monte carlo type analysis and checkerboard test this study provides an indicator of the uniqueness of the determined model the 500 m deep borehole was continuously cored and extensively surveyed by geophysical techniques thus the detailed surface geological mapping fracture index logs borehole televiewer images and p and s wave velocities derived from sonic logs provide solid constraints for the interpretation of the tomographic images the three dimensional tomographic images reveal fracture zones mapped at surface that intersect the borehole at different depths and they can be identified in the core descriptions and in the borehole televiewer images the fractures identified on the cores feature relatively low values for the sonic p and s wave velocities and high values for poisson s ratio for single type lithologies the distribution of poisson s ratio differentiates fractured and altered granite from fresh unfractured domains within the rock poisson s ratios close to 0 3 correlate with fractured volumes consistent with fracture index and sonic logs otherwise poisson s ratio values close to 0 25 are related to unaltered and unfractured rock

global fire at the cretaceous tertiary boundary cretaceous tertiary k t boundary clays from five sites in europe and new zealand are 102 104 fold enriched in elemental c mainly soot which is isotopically uniform and apparently comes from a single global fire the soot layer coincides with the ir layer suggesting that the fire was triggered by meteorite impact and began before the ejecta had settled

three dimensional p wave velocity structure in the upper crust beneath kuju volcano central kyushu japan kuju volcano lies near aso caldera at the center of kyushu island western japan after a few hundred years of dormancy a phreatic explosion accompanied by a small ash eruption occurred on 11 october 1995 this study was undertaken to determine the subsurface seismic velocity structure associated with the active magmatic regime in the kuju volcanic region the three dimensional upper crustal p wave velocity structure beneath kuju volcano was determined using methods for the simultaneous inversion of p wave arrival times from local earthquakes in and around the kuju volcanic region for velocities and hypocentral parameters results reveal two shallower low velocity anomalies located in the northern and southern parts of kuju volcano consistent with the presence of significant negative bouguer gravity anomalies in addition a high velocity anomaly is located approximately 5 km northwest of mt kuju one of the domes in kuju volcano beneath this high velocity anomaly a low velocity anomaly is present this velocity structure suggests a magmatic regime that has a lid consisting of cooled solid material overlying a chamber of partially molten material

tomographic inversion of p wave velocity and q structures beneath the kirishima volcanic complex southern japan based on finite difference calculations of complex traveltimes summary we estimate the p wave velocity and attenuation structures beneath the kirishima volcanic complex southern japan by inverting the complex traveltimes arrival times and pulse widths of waveform data obtained during an active seismic experiment conducted in 1994 in this experiment six 200 250 kg shots were recorded at 163 temporary seismic stations deployed on the volcanic complex we use first arrival times for the shots which were hand measured interactively the waveform data are fourier transformed into the frequency domain and analysed using a new method based on autoregressive modelling of complex decaying oscillations in the frequency domain to determine pulse widths for the first arrival phases a non linear inversion method is used to invert 893 first arrival times and 325 pulse widths to estimate the velocity and attenuation structures of the volcanic complex wavefronts for the inversion are calculated with a finite difference method based on the eikonal equation which is well suited to estimating the complex traveltimes for the structures of the kirishima volcano complex where large structural heterogeneities are expected the attenuation structure is derived using ray paths derived from the velocity structure we obtain 3 d velocity and attenuation structures down to 1 5 and 0 5 km below sea level respectively high velocity pipe like structures with correspondingly low attenuation are found under the summit craters these pipe like structures are interpreted as remnant conduits of solidified magma no evidence of a shallow magma chamber is visible in the tomographic images

gahnite chrysoberyl and beryl co occurrence as accessory minerals in a highly evolved peraluminous pluton the belvis de monroy leucogranite caceres spain abstract gahnite znal 2 o 4 chrysoberyl beal 2 o 4 and beryl be 3 al 2 si 6 o 18 have been found as accessory minerals in the external highly fractionated leucogranitic unit within the hercynian reversely zoned belvis de monroy pluton westernmost part of the montes de toledo batholith caceres spain the highly felsic sio 2 72 wt and peraluminous acnk 1 2 character of this leucogranite together with the high content of some incompatible elements f li b and p seems to be a primary consequence of fractional crystallization in a magmatic closed system the high be contents and zn fe total ratio 0 01 are relevant factors which have favoured the precipitation of these minerals moreover the si al p b and f activities might be high favouring the magmatic crystallization of such exotic mineral phases together with be rich cordierite f rich micas sillimanite and al rich phosphates in fact the interplay between the silica and alumina activities likely controls the stabilization and the preferential crystallization of gahnite chrysoberyl or beryl chrysoberyl assemblages in mm sized microdomains the p t crystallization conditions are constrained by the muscovite and sillimanite stability fields and the minimum granite al 2 o 3 saturated solidus and have been estimated at temperatures between 670 and 700 c and pressures between 1 and 2 kbar

experiments in waterlogging and sedimentology of charcoal results and implications abstract fossil charcoal has a sporadic occurrence in sedimentary rocks since devonian time it is moderately common as a component of the organic material found in a wide variety of facies but there are also some notable concentrations which occur locally these occurrences have considerable palaeobotanical and palaeoecological value because the process of charring may result in excellent preservation of plant tissue if assemblages of charred material are to be used to interpret palaeoenvironments it is important to understand the behaviour of charcoal during transport from the site of the fire charcoal is an unusual sedimentary material because most fresh material floats but with prolonged immersion becomes waterlogged and sinks we carried out a series of waterlogging experiments on uncharred material and charcoal from a range of different plant types and tissues these show considerable variations in the rates of waterlogging of different charred and uncharred plant tissues and it is suggested that buoyancy contrasts are likely to result in separation during transport and deposition furthermore experiments in a flume tank have shown that the process of deposition of charcoal in sand is controlled by the rate of migration of bedforms which is in turn determined by depth flow velocity and sediment supply allochthonous assemblages of charred and uncharred plant debris will most probably be biased and not fully representative of the contemporaneous plants or vegetation the presence of charcoal concentrations may be used as an aid in interpreting palaeohydraulic conditions

evidence of neogene wildfires in central chile charcoal records from the navidad formation abstract mediterranean type climate mtc ecosystems are characterized by recurrent wildfires although the majority of wildfires are human ignited non anthropogenic i e natural wildfires are common in all mtc regions except central chile the low frequency of natural wildfires in this chilean region is explained by the scarcity of non anthropogenic ignition sources basically thunderstorm induced lightning and volcanic activity however from a geological perspective the current relative absence of non anthropogenic wildfires in central chile is a recent phenomenon in the transition from the early to middle miocene the climate in the region was likely warm and seasonally dry such climate conditions would allow the growth of fuel during the spring becoming flammable during the dry season this fire prone landscape would likely have been ignited by the high volcanic activity that concomitantly occurred with the orogeny of the andes to evaluate this hypothesis we sampled rocks from the three locations at the navidad formation considering the fossil plant evidence deposited during this warm and seasonally dry period we found a high concentration of charcoal in playa navidad coinciding with the global warming event reported between 17 and 15 ma the predominance of microscopic charcoal particles between 125 and 250 m only allows us to infer the occurrence of neogene fires at a regional scale the fused cell walls preserved in the charcoal anatomy likely suggest that such fire events were highly severe the presence of pumice associated with the high charcoal concentrations supports the hypothesis of volcanic ignition sources very little charcoal was found in punta perro late oligocene early miocene or in cerro los pololos late middle miocene where fire may have been limited by fuel humidity and ignition sources respectively although changes in the depositional environment would also help explain differences in the fire record throughout the navidad formation in conclusion our results provide the first quantitative neogene charcoal record for south america the evidence of fire occurrence in central chile during the neogene will contribute to understanding the evolution of the mediterranean type flora

upper crustal structure of the yellowstone caldera from seismic delay time analyses and gravity correlations the 1978 yellowstone snake river plain seismic experiment provided detailed refraction data that were recorded across a two dimensional array of seismographs in yellowstone national park a delay time analysis was applied to 173 crystalline basement pg arrivals from these data to determine the three dimensional distribution of velocities and the layer configuration of the upper crust beneath the yellowstone caldera the p wave velocity structure of the caldera is characterized by a surface layer of combined sediments and rhyolite flows averaging 2 8 km s that range in thickness from 1 5 to 2 0 km adjacent to the caldera the crystalline upper crustal layer has a velocity of 6 05 0 01 km s but this layer decreases by 6 to 5 70 km s beneath the caldera and extends northeast 15 km beyond the caldera smaller zones of very low p velocity 4 0 km s a 30 velocity reduction compared to the 6 05 km s layer occur in the upper crust beneath the northeastern caldera rim and beneath the southwest caldera in the vicinity of the upper and midway geyser basins a three dimensional gravity interpretation based upon densities derived from the seismic model suggests that the regional gravity low of 60 mgal over the caldera correlates directly with 1 the surface layer of combined sediments and rhyolite flows 2 the low velocity 5 7 km s upper crustal layer and 3 the 4 0 km s low velocity zone beneath the northeastern caldera rim an interpretation of the seismic velocities and densities based on experimental data and theoretical models suggests that the 6 05 km s 2 70 g cm3 regional pg velocity is characteristic of crystalline basement rocks such as the precambrian granitic gneisses that are exposed north and south of the yellowstone caldera the 5 7 km s velocity layer 2 65 g cm3 is interpreted to be a 10 km thick hot body of granitic composition the 4 0 km s low velocity body 2 40 g cm3 beneath the northeastern caldera rim is associated with a local 20 mgal gravity anomaly with a range of interpretations from a large steam dominated system to a felsic body of 10 to 50 partial melt the postulated 4 0 km s low velocity layer beneath the southwestern caldera does not have a corresponding gravity signature and may reflect a zone of high seismic attenuation attributed to a saturated fracture zone this seismic velocity model of the yellowstone caldera suggests that the source of the quaternary silicic volcanic rocks corresponds to the 5 7 km s layer in the upper crust that appears to contribute the principal source of heat to the yellowstone hydrothermal systems the anomalous low velocity body in the northeastern caldera rim area may be a cupola of partial melt with an overlying vapor dominated carapace and may represent the waning stages of the third cycle of quaternary volcanism or the beginning of a new cycle of volcanism that will continue the northeastward progression of the silicic volcanism of the yellowstone snake river plain propagating system

k pg extinction reevaluation of the heat fire hypothesis 1 the global debris layer created by the end cretaceous impact at chicxulub contained enough soot to indicate that the entire terrestrial biosphere had burned preliminary modeling showed that the reentry of ejecta would have caused a global infrared ir pulse sufficient to ignite global fires within a few hours of the chicxulub impact this heat pulse and subsequent fires explain the terrestrial survival patterns in the earliest paleocene because all the surviving species were plausibly able to take shelter from heat and fire underground or in water however new models of the global ir heat pulse as well as the absence of charcoal and the presence of noncharred organic matter have been said to be inconsistent with the idea of global fires that could have caused the extinctions it was suggested that the soot in the debris layer originated from the impact site itself because the morphology of the soot the chain length of polycyclic aromatic hydrocarbons and the presence of carbon cenospheres were said to be inconsistent with burning the terrestrial biosphere these assertions either are incorrect or have alternate explanations that are consistent with global firestorms we show that the apparent charcoal depletion in the cretaceous paleogene layer has been misinterpreted due to the failure to correct properly for sediment deposition rates we also show that the mass of soot potentially released from the impact site is far too low to supply the observed soot however global firestorms are consistent with both data and physical modeling

charcoal recognition taphonomy and uses in palaeoenvironmental analysis abstract charcoal predominantly the product of wildfires is abundant in many sedimentary rocks deposited in a wide range of environments from terrestrial to marine it also occurs in some volcanic rocks this paper outlines aspects of charcoal formation both natural and experimental and briefly considers the taphonomic processes leading to a final assemblage this is done using examples from recent fires and through experimentation the ways in which charcoal assemblages are recognized in the field and extraction in the laboratory are also considered methods of charcoal identification are presented the range of charcoalified plant organs that can be found is discussed and a wide range of study methods outlined including light microscopy dark field light microscopy reflectance microscopy scanning electron microscopy and synchrotron radiation x ray tomographic microscopy emphasis in this paper is on the study of macro and meso charcoal above180 m finally there is a consideration of the broad use of charcoal from plant evolution studies fire history studies vegetation studies anatomical studies climate and atmospheric studies and the wider importance of charcoal for the earth and biological sciences charcoal is information rich but yet is an under utilized resource

the carbonate hosted willemite prospects of the zambezi metamorphic belt zambia zambian willemite zn2sio4 deposits occur in the metasedimentary carbonate rocks of the proterozoic katangan supergroup the most important orebodies are located around kabwe and contain both sulphides and willemite in dolomites of low metamorphic grade the star zinc and excelsior prospects lusaka area discovered in the early 1920s occur in the metamorphic lithotypes of the late proterozoic zambezi supracrustal sequence which were deposited in a transtensional basin formed during the oblique collision of the kalahari and congo cratons the deposits are hosted by the limestone and dolomitic marbles of the cheta and lusaka formations structural analysis indicates that several fracture sets host the deposits which may be genetically related to the pan african mwembeshi dislocation zone a major geotectonic boundary between the lufilian arc and the zambezi belt in both prospects willemite replaces the marbles and is found along joints and fissures with open space filling textures and locally may develop colloform and vuggy fabrics as well silver as well as traces of germanium and cadmium have been detected within the willemite ore and lead or zinc sulphides are scarce or absent calcite locally replaces willemite willemite is associated with specular hematite and franklinite and post dates the zn spinel gahnite in the paragenesis genthelvite zn4be3 sio4 3s occurs as a minor phase in irregular aggregates the willemites from the lusaka area though mn poor show green cathodoluminescence colours and bright green fluorescence in short wave uv as the high temperature willemites in usa thermometric analyses of primary fluid inclusions in willemite yield homogenization temperatures that range from 160 c to 240 c and salinities of 8 16 wt equiv nacl the homogenization temperatures suggest a hypogene hydrothermal origin for the willemite concentrations the geochemistry of fluid inclusion leachates suggests that the hydrothermal fluids were brines derived from highly evaporated seawater precise age constraints are currently lacking for the lusaka area deposits though the deposits are not deformed indicating that they post date the lufilian orogeny 520 ma the possibility of precursor ores exists the gahnite franklinite willemite deposits could have been derived from a metamorphosed primary sulphide or even nonsulphide concentration that has subsequently been completely destroyed however there is no real evidence of such a primary source for the willemite mineral association the lusaka zinc ores may have been produced by an extensive hydrothermal system with fluids discharging along basinal fracture zones controlled by the pre pan african rifting stage a paragenesis similar to that of the lusaka prospects has been proposed to be a vector towards massive sulphide ores in several parts of the world therefore it is possible that these small willemite showings in zambia may be part of a much bigger and still unexplored zinc province

nanodiamond rich layer across three continents consistent with major cosmic impact at 12 800 cal bp abstracta major cosmic impact event has been proposed at the onset of the younger dryas yd cooling episode at 12 800 150 years before present forming the yd boundary ydb layer distributed over 50 million km2 on four continents in 24 dated stratigraphic sections in 10 countries of the northern hemisphere the ydb layer contains a clearly defined abundance peak in nanodiamonds nds a major cosmic impact proxy observed nd polytypes include cubic diamonds lonsdaleite like crystals and diamond like carbon nanoparticles called n diamond and i carbon the nd abundances in bulk ydb sediments ranged up to 500 ppb mean 200 ppb and that in carbon spherules up to 3700 ppb mean 750 ppb 138 of 205 sediment samples 67 contained no detectable nds isotopic evidence indicates that ydb nds were produced from terrestrial carbon as with other impact diamonds and were not derived from the impactor itself the ydb layer is also marked by abundance peaks in other impact related proxies including

fire across the k t boundary initial results from the sugarite coal new mexico usa abstract it has been hypothesized that major global fires occurred following a bolide impact at the cretaceous tertiary boundary evidence for this has been mainly from soot or black carbon at a number of marine boundary sites as well as the occurrence of inertinites fusinite in coals above the boundary in addition the occurrence of fossil charcoal inertinites in potential tsunami deposits has been used to strengthen this idea however fire is known to have been widespread throughout the cretaceous based on the distribution of fossil charcoal and it is necessary to evaluate the claims for a global fire at the k t boundary within the context of this more extensive record of ancient fires the occurrence of the k t boundary within the sugarite coal sequence in the raton basin new mexico offers the opportunity to assess the incidence of fire in local peat forming vegetation in the latest cretaceous across the cretaceous tertiary boundary interval and in the earliest tertiary the distribution of fire products i e fossil charcoal is assessed using a combination of inertinite group macerals in polished blocks of coal and plant particles released by chemical maceration of coal inertinite group macerals fusinite semifusinite inertodetrinite which represent fossil charcoal and particles of charcoal in maceration residues are abundant throughout the sugarite coal sequence both before during and after the k t boundary event samples from below the boundary yield inertinites that constitute more than 20 of the coal three horizons are inertinite rich 50 fire was obviously an important element of the terrestrial environment during the latest cretaceous high inertinite values and abundant charcoal particles characterize the latest cretaceous part of the coal the carbonaceous shale just below the boundary the boundary interval itself and tertiary coals and carbonaceous shales above the boundary charcoal in mineral rich units of the latest cretaceous immediately below the boundary in the boundary interval and in the tertiary is dominated by small inertodetrinite particles these might have been wind blown from regional fires or they may reflect reworking during erosion which led to sediment input into the mire in either case the charcoal signature in these units is the same irrespective of their position in the sequence our data combined with that from two other sites in terrestrial sequences in north america show that fires were an integral part of mire ecosystems through the latest cretaceous and into the early tertiary therefore evidence for distinctive global wildfires at the cretaceous tertiary boundary would have to be sought from careful consideration of other aspects of charcoal deposition including flux rates for charcoal and soot

fire storms and erosional events in the idaho batholith in late december 1996 the south fork payette river basin in west central idaho experienced a prolonged storm that culminated on january 1 1997 with intense rain on melting snow that triggered slide failures producing debris flows and sediment charged floods failures occurred in saturated cohesionless grussy colluvium derived from weathered idaho batholith granitic rocks many failures along the south fork payette river originated in ponderosa pine forests burned in the 1989 stand replacing lowman fire an example is the 0 49 km 2 jughead creek basin where a single large colluvial failure produced almost 40 of the total volume eroded from the basin and generated a massive and rapid debris flow failures also occurred in steep unburned and unforested drainages such as hopkins creek in this south facing 0 58 km 2 basin 15 colluvial hollows failed but no single failure produced more than 10 of the total eroded volume sediment transport in hopkins creek occurred by prolonged sediment charged sheetflooding despite vegetation differences sediment yields from the geomorphically similar hopkins creek 42 000 mg km 2 and jughead creek 44 000 mg km 2 basins were quite similar these 1997 erosion events are equivalent to several thousand years of sediment yield at low rates 2 7 30 mg km 2 year 1 measured by short term sediment trapping and gauging in idaho batholith watersheds if similar large events were solely responsible for sediment export recurrence intervals ris of several hundred years would account for higher sediment yields averaged over 10 4 year from idaho batholith watersheds dating of small fire induced sheetflooding events in an early holocene tributary junction fan of jughead creek indicates that frequent small sedimentation events ri 33 80 year occurred between 7400 and 6600 cal year bp with an average yield not greatly exceeding 16 mg km 2 year 1 compared with the holocene average erosion rates during that 800 year period were unusually low suggesting that sediment yields have not been constant over time and that climatic variations and related fire regime changes may exert a strong influence on the probability of major erosional events copyright 2001 john wiley sons ltd

three dimensional p and s wave velocity structure of redoubt volcano alaska the three dimensional p and s wave structure of redoubt volcano alaska and the underlying crust to depths of 7 8 km is determined from 6219 p wave and 4008 s wave first arrival times recorded by a 30 station seismograph network deployed on and around the volcano first arrival times are calculated using a finite difference technique which allows for flexible parameterization of the slowness model and easy inclusion of topography and source receiver geometry the three dimensional p wave velocity structure and hypocenters are determined simultaneously while the three dimensional s wave velocity model is determined using the relocated seismicity and an initial s wave velocity model derived from the p wave velocity model assuming an average vp vs ratio of 1 78 convergence is steady with approximately 73 and 52 reduction in p and s wave arrival time rms respectively after 10 iterations the most prominent feature observed in the three dimensional velocity models derived for both p and s waves is a relative low velocity near vertical pipelike structure approximately 1 km in diameter that extends from 1 to 6 km beneath sea level this feature aligns axially with the bulk of seismicity and is interpreted as a highly fractured and altered zone encompassing a magma conduit the velocity structure beneath the north flank of the volcano between depths of 1 and 6 km is characterized by large lateral velocity variations high velocities within this region are interpreted as remnant dikes and sills and low velocities as regions along which magma migrates no large low velocity body suggestive of a magma chamber is resolved in the upper 7 8 km of the crust

metamorphosed proterozoic zn pb ag mineralization in the foster river area northern saskatchewan canada metamorphosed zn pb occurrences fable lake george sito south sito southwest sito west sito east robyn lake and mackie lake with high zn pb ratios occur in the foster river area northern saskatchewan on the southeast margin of the paleoproterozoic wollaston domain the sito east prospect the largest of these occurrences contains 50 000 tonnes of 4 5 zn with one drill intercept containing 11 m of 4 2 zn and 0 6 pb most prospects are hosted in a thin areally extensive metaquartzite within a thick sequence of metasiltstones and metaquartzites in the middle of the paleoproterozoic wollaston group occurrences in metaquartzites and metaarkoses which locally contain gahnite spessartine and or graphite are spatially associated with metaexhalites iron formation and quartz garnetite and strata bound metamorphosed hydrothermal alteration zones nodular sillimanite rock post archean australian shale normalized rare earth element ree patterns of all three rock types are characterized by light ree enrichment positive ce anomalies neutral to strongly negative eu anomalies and heavy ree depletion consistent with an environment of deposition distinguished by a high 30 wt continental detrital component and formation from or interaction with low temperature 250 c near neutral ph and high fo2 fluids sulfur isotope compositions of sulfides at foster river are highly enriched in 34s 34s 26 2 38 1 n 20 and resulted from microbial reduction of partially reduced seawater sulfate in a restricted basin the spatial association of spessartine and gahnite bearing lithologies and silicate facies iron formation with paleoproterozoic base metal sulfides in a psammopelitic host sequence implies similarities between sulfide mineralization in the foster river area and broken hill type pb zn ag deposits however the markedly enriched 34ssulfide compositions low pb pb zn and ag pb zn ag ratios low ag contents and apparent absence of metavolcanic and metavolcaniclastic rocks in the dominantly clastic rock sequence hosting the sulfides in the foster river area suggest that these occurrences are part of a metamorphosed sedimentary exhalative system with broken hill type affinities similar to that associated with the formation of the gamsberg zn south africa kanmantoo group pb zn south australia and sullivan pb zn canada deposits

chicxulub crater a possible cretaceous tertiary boundary impact crater on the yucatan peninsula mexico we suggest that a buried 180 km diameter circular structure on the yucatan peninsula mexico is an impact crater its size and shape are revealed by magnetic and gravity field anomalies as well as by oil wells drilled inside and near the structure the stratigraphy of the crater includes a sequence of andesitic igneous rocks and glass interbedded with and overlain by breccias that contain evidence of shock metamorphism the andesitic rocks have chemical and isotopic compositions similar to those of tektites found in cretaceous tertiary k t ejecta a 90 m thick k t boundary breccia also containing evidence of shock metamorphism is present 50 km outside the crater s edge this breccia probably represents the crater s ejecta blanket the age of the crater is not precisely known but a k t boundary age is indicated because the crater is in a thick carbonate sequence shock produced co2 from the impact may have caused a severe greenhouse warming

ore textures and remobilization mechanisms of the hongtoushan copper zinc deposit liaoning china abstract the hongtoushan copper zinc deposit is a volcanic associated massive sulfide deposit in the archean greenstone belt in liaoning china polymetamorphism has resulted in changes to the composition and textures of minerals in the deposit along with remobilization during metamorphism the original alteration minerals that formed with the ore minerals such as chlorite and sericite were transformed into cordierite anthophyllite and phlogopite after further remobilization new minerals such as gahnite and actinolite were formed in this process the original textures were destroyed and new textures were formed including recrystallization and growth textures brittle and ductile deformation textures durchbewegung textures replacement textures chalcopyrite disease and retrograde textures the ore forming components underwent two periods of remobilization in the first early stage mechanical remobilization was important and formed a high grade cu zn au ag ore pillar along the vertical hinge of a synformal fold in the second late stage the mixed hydrothermal mechanical remobilization affected the ores and was typically characterized by matrix sulfides together with silicate minerals moving from the matrix into individual fractured pyrite metablasts and replacing them to varying degrees

the 1978 yellowstone eastern snake river plain seismic profiling experiment data and upper crustal structure of the yellowstone region eleven in line refraction profiles recorded to distances of 300 km and one azimuthal fan plot were constructed from data recorded with a 150 station array in the yellowstone national park area during the 1978 yellowstone snake river plain seismic experiment interpretations of the data suggest that the crustal p wave velocity model for the yellowstone region is characterized by 1 an averaged 10 km thick upper crustal layer v sub p 6 0 km s 2 an average crustal velocity of 6 3 km s and 3 a total crustal thickness of 44 km velocity models are presented for profiles that emphasize the upper crust and show 1 a decrease in the depth to the top of the upper crustal crystalline basement from 5 km in southwestern yellowstone near island park to 1 km at the northeast side of the yellowstone plateau that is interpreted as a progressive thinning of the silicic surface volcanic layer to the northeast and 2 evidence for a large lateral inhomogeneity interpreted to be a low velocity body with a decrease of at least 10 in p wave velocity located beneath the northeast corner of the yellowstone plateau the low velocity zone coincides with a local 30 mgal residual gravity anomaly and is located beneath partmore of the sour creek resurgent dome and part of the hot springs basin the largest hydrothermal system in yellowstone the low velocity body has a maximum depth to the top of 3 km and a minimum depth to the bottom of 9 km and may represent a zone of partial melt in comparison to the thermally undisturbed upper crust of the surrounding rocky mountains the upper crust of the northeastern yellowstone plateau appears laterally inhomogeneous in velocity and layer thickness suggesting effects of thermal and magma intrusion whereas the lower crust appears relatively homogeneous less

the crustal magma chamber of the katla volcano in south iceland revealed by 2 d seismic undershooting summary results of a 2 d seismic undershooting experiment on the katla central volcano in south iceland are reported large localized traveltime anomalies 0 4 s are observed on an array within the katla caldera the traveltimes are forward modelled using a wavefront tracker developed in appendix a thus non linear effects encountered in traveltime tomography are avoided as well as common problems with ray tracing in the presence of strong lateral heterogeneity an extreme variation in compressional velocity is required to extend over a significant volume in order to model the data the resulting model is not unique but constraints on the allowable range of velocities 2 5 6 0 km s render the basic features well constrained a clear s wave shadow is closely associated with delays in traveltime due to a shallow slow anomaly low amplitude p waves go hand in hand with early arrivals due to thin structural features flanking the slow anomaly the model is interpreted in terms of a magma chamber containing extensively molten rock the magma chamber is shallow with a bottom at a depth of about 1 5 km below sea level 3 0 km below surface and measures about 5 km across the depth of the chamber is roughly at the level of buoyant equilibrium for basaltic melt in the crust owing to poor vertical resolution at shallow depths in the undershooting geometry the top of this shallow magma chamber is not well resolved on the other hand the bottom of the chamber is well resolved the chamber is underlain by rocks of average or high velocity for that depth the magma chamber is a persistent feature big enough 10 km3 to supply magma for large eruptions and to supply heat to permit remelting of hydrated basaltic crust to produce silicic magmas at shallow levels the chamber is fed by magma fracturing from below the model agrees with phenomenological models of magma chambers in iceland based on geological observations and provides a quantification of those models in terms of depth and size on the other hand it is fundamentally different from recent models of magma chambers at mid ocean ridges which may be more akin to the pervasive region of partial melt at depth beneath iceland this underlines the important effect of the icelandic hotspot on tectonics and volcanism in iceland and implies a substantially different crustal and thermal structure in iceland from that of normal mid ocean ridges

revisiting wildfires at the k pg boundary 1 the discovery of large amounts of soot in clays deposited at the cretaceous paleogene k pg boundary and linked to the 65 ma chicxulub impact crater led to the hypothesis that major wildfires were a consequence of the asteroid impact subsequently several lines of evidence including the lack of charcoal in north american sites were used to argue against global wildfires close to the impact site fires are likely to be directly ignited by the impact fireball whereas globally they could be ignited by radiation from the reentry of hypervelocity ejecta to date models of the latter have yet to take into account that ejection and thus the emission of thermal radiation is asymmetric and dependent on impact angle here we model 1 the impact and ejection of material 2 the ballistic continuation of ejecta around a spherical earth and 3 the thermal pulse delivered to the earth s surface when ejecta reenters the atmosphere we find that thermal pulses in the downrange direction are sufficient to ignite flora several thousand kilometers from chicxulub whereas pulses at most sites in the uprange direction are too low to ignite even the most susceptible plant matter our analyses and models suggest some fires were ignited by the impact fireball and ejecta reentry but that the nonuniform distribution of thermal radiation across the surface of the earth is inconsistent with the ignition of fires globally as a direct and immediate result of the chicxulub impact instead we propose that the desiccation of flora by ejecta reentry as well as the effects of postimpact global cooling darkness left much of the terrestrial flora prone to fires and that the volume of soot in the global k pg layer is explained by a combination of syn and postimpact wildfires

survival in the first hours of the cenozoic for several hours following the chicxulub impact the entire earth was bathed with intense infrared radiation from ballistically reentering ejecta the global heat pulse would have killed unsheltered organisms directly and ignited fires at places where adequate fuel was available sheltering underground within natural cavities or in water would have been a necessary but not always sufficient condition for survival survival through sheltering from an initial thermal pulse is not adequately considered in literature about cretaceous tertiary nonmarine extinctions we compare predicted intense short term thermal effects with what is known about the fossil record of nonmarine vertebrates and suggest that paleontological evidence of survival is compatible with theoretical results from bolide physics

relationship between impact crater size and severity of related extinction episodes abstract how large must an extraterrestrial impact be to cause a peak episode of increased extinctions of life impact energies 3 107 mt tnt associated with terrestrial impact craters with final diameters 100 km seem to be required to generate significant widespread climatic effects from sub micron dust and soot in the atmosphere leading to a distinct extinction episode 15 extinction of marine genera impacts creating craters smaller than 100 km in final diameter in the 106 to 107 mt tnt range are capable of mostly regional destruction with minimal impact on global climate or biota these results are supported by the fact that the ages of the four known 100 km diameter craters of the last 260 my popigai chicxulub morokweng and manicouagan are all correlative with times of documented extinction episodes whereas smaller craters are not the largest crater the 180 km diameter chicxulub crater a 108 mt tnt event is associated with the more severe major mass extinction event 45 extinction of genera at the end of the cretaceous the percent species extinctions show a significant linear relationship with final crater diameter and impact energy the very large chicxulub impact lies close to the predicted curve of percent extinction versus impact crater diameter and energy but the low angle of impact an unusual composition of the target area with thick sediments rich in carbonates sulfates and organic material and a large excavated transient crater may have led to the generation of unusually large amounts of co2 widely distributed dust soot and sulfate aerosols and a uniquely severe impact related environmental disaster chicxulub may thus be the only large body impact associated with a major mass extinction in the phanerozoic target sensitivity may apply to large impacts into ocean crust having only a thin cover of organic poor and carbonate poor pelagic sediments and thus even large oceanic impacts which are still unknown may not produce enough dust soot and aerosols to cause environmental crises leading to global extinction peaks above background levels

inversion for crustal structure using reflections from the passcal ouachita experiment an interface inversion has been tested and applied to wide angle reflection data from the 1986 passcal ouachita experiment an interface corrugation with a relief of 10 km and a width of 30 km was successfully imaged in a test of the interface inversion velocity depth curves derived for shot points 14 19 using the tail sum method are similar to an average one dimensional velocity model from forward modeling using travel time correlations from southern profiles 14 19 the similarity of these velocity depth curves positioned over the southern half of the passcal experiment suggests that crustal structure in this region is approximately laterally homogeneous lower crustal velocities are not well resolved due to the recording on most profiles of only small segments of the travel time triplications a two dimensional velocity structure was derived by using the average one dimensional velocities for the deeper crustal layers and formally inverting for depth to interfaces the final inversion model is found to be consistent with previous refraction interpretations south of the ouachita orogenic trend and concurrent interpretations of the passcal data set inversion results for the central and southern portion of the passcal profile indicate a depth of 10 12 km for a midcrustal layer which thins southward from approximately 10 km to about 4 km a lower crustal layer with an average thickness of 12 km and a moho depth of approximately 29 5 km are also determined interface depths are in agreement with a normal moveout stack of the passcal data set in particular the shallowing of the moho to a depth of 30 km over the northern 50 km of the profile matches previous interpretations of the data set and has been interpreted here and in previous studies as the location of the paleozoic continental margin geophysical studies of the modern atlantic continental passive margin provide the simplest comparison to the crustal structure derived here the lower crustal layer found south of the shallowing of the moho to 30 km beneath the passcal profile is analogous in thickness and position to rift stage lower crust however other tectonic interpretations are possible given the uncertainties in velocity and lithology relationships

p and s velocity structure of the yellowstone volcanic field from local earthquake and controlled source tomography the three dimensional p and s velocity from vp vs ratios distribution and improved hypocenters for the yellowstone volcanic field have been determined from inversion of first arrival times from 7942 local earthquakes and 16 controlled source explosions the p velocity model has an rms residual of 0 09 s whereas the vp vs ratio model calculated from 511 earthquakes has an rms residual of 0 29 s high p and s velocities outside the yellowstone caldera represent thermally undisturbed basement and sedimentary rocks a caldera wide 15 decrease from regional p velocities at depths of 6 to 12 km is coincident with a 60 mgal gravity anomaly and is interpreted as a hot subsolidus granitic batholith with a quasi plastic rheology localized 30 reductions from regional seismic velocities and higher vp vs ratios 8 km beneath yellowstone s resurgent domes are interpreted as partial melts and vestigial magma systems associated with youthful less than 2 ma silicic volcanism additional low seismic velocities and vp vs ratios and a 20 mgal gravity low less than 4 km beneath the northeast caldera rim are interpreted as a hydrothermal fracture zone thermally driven by underlying partial melt hypocenters relocated with the three dimensional p velocity model show subparallel alignment with nw se trending postcaldera volcanic vents and normal faults northwest of the caldera focal depths of relocated earthquakes decrease from more than 11 km outside the caldera to less than 6 km within the caldera reflecting thinning and heating of the seismogenic crust

crustal structure in tengchong volcano geothermal area western yunnan china abstract based upon the deep seismic sounding profiles carried out in the tengchong volcano geothermal area tvga western yunnan province of china a 2 d crustal p velocity structure is obtained by use of finite difference inversion and forward travel time fitting method the crustal model shows that a low velocity anomaly zone exists in the upper crust which is related to geothermal activity two faults the longling ruili fault and tengchong fault on the profile extend from surface to the lower crust and the tengchong fault likely penetrates the moho moreover based on teleseismic receiver functions on a temporary seismic network s wave velocity structures beneath the geothermal field show low s wave velocity in the upper crust from results of geophysical survey the crust of tvga is characterized by low p wave and s wave velocities low resistivity high heat flow value and low q the upper mantle p wave velocity is also low this suggests presence of magma in the crust derived from the upper mantle the low velocity anomaly in upper crust may be related to the magma differentiation the tengchong volcanic area is located on the northeast edge of the indian eurasian plate collision zone away from the eastern boundary of the indian plate by about 450 km based on the results of this paper and related studies the tengchong volcanoes can be classified as plate boundary volcanoes

major and trace element chemistry of gahnite as an exploration guide to broken hill type pb zn ag mineralization in the broken hill domain new south wales australia gahnite bearing rocks are common throughout the proterozoic broken hill domain new south wales australia where they are spatially associated with broken hill type pb zn ag mineralization including the supergiant broken hill deposit in the past such rocks have been utilized as exploration guides to ores of this type but their presence has had mixed success in discovering new occurrences of sulfide mineralization major element chemistry of gahnite has previously been used to define a compositional range associated with metamorphosed massive sulfides deposits including broken hill type deposits but it fails to distinguish sulfide rich from sulfide poor occurrences major and trace element data from la icp ms and electron microprobe analyses were obtained for gahnite from twelve broken hill type deposits to determine whether or not gahnite chemistry may be used to distinguish prospective exploration targets from nonprospective occurrences major and trace element data were discriminated using a principal component analysis and in a bivariate plot of zn fe versus ni cr v to distinguish gahnite associated with the broken hill deposit from that associated with sulfide poor lode pegmatite and sillimanite gneiss bivariate plots of zn fe versus trace element contents e g ga co mn co ni v cd suggest gahnite from the broken hill deposit has a relatively restricted compositional range that overlaps with some minor broken hill type occurrences based on the ore grade wt pb zn of rocks hosting gahnite at each locality gahnite in the highest grade mineralization from minor broken hill type deposits possess compositions that plot within the field for gahnite from the broken hill deposit which suggests that major and trace element chemistry e g zn fe 2 4 vs co 10 110 ppm ga 110 400 ppm mn 500 2 250 ppm and co 25 100 ppm vs ga 125 375 ppm may be used as an exploration guide to high grade ore

an experimental assessment of the ignition of forest fuels by the thermal pulse generated by the cretaceous palaeogene impact at chicxulub a large extraterrestrial body hit the yucatan peninsula at the end of the cretaceous period models suggest that a substantial amount of thermal radiation was delivered to the earth s surface by the impact leading to the suggestion that it was capable of igniting extensive wildfires and contributed to the end cretaceous extinctions we have reproduced in the laboratory the most intense impact induced heat fluxes estimated to have reached different points on the earth s surface using a fire propagation apparatus and investigated the ignition potential of forest fuels the experiments indicate that dry litter can ignite but live fuels typically do not suggesting that any ignition caused by impact induced thermal radiation would have been strongly regional dependent the intense but short lived pulse downrange and at proximal and intermedi ate distances from the impact is insufficient to ignite live fuel however the less intense but longer lasting thermal pulse at distal locations may have ignited areas of live fuels because plants and ecosystems are generally resistant to single localized fire events we conclude that any fires ignited by impact induced thermal radiation cannot be directly responsible for plant extinctions implying that heat stress is only part of the end cretaceous story received 3 july 2014 revised 10 october 2014 accepted 10 october 2014

sequential palynological changes across the composite cretaceous tertiary k t boundary claystone and contiguous strata western canada and montana u s a the boundary claystone in the western canada basin is composed of three intimately associated layers with a regional distribution a basal brownish grey hackly claystone a middle brownish black sa

self shielding of thermal radiation by chicxulub impact ejecta firestorm or fizzle as hypervelocity ejecta from the chicxulub yucatan mexico impact fell back to earth the surface may have received a deadly dose of thermal radiation sufficient to ignite global wildfires using a two phase fluid flow code which includes ejecta and air opacities in a radiative transfer calculation we modeled the atmospheric reentry of spherules arriving at distal sites the models predict a pulse of thermal radiation at the surface peaking at 5 15 kw m 2 analogous to an oven set on broil 260 c previous calculations which ignored spherule opacity yielded 10 kw m 2 sustained over 20 min and such an extended pulse is thought to be required for wood ignition however the new modeling suggests that fluxes only exceed the solar norm for 30 min and are only 5 kw m 2 for a few minutes previous models failed to consider the self shielding effect of settling spherules which block an increasing proportion of downward thermal radiation emitted by the later arriving spherules such self shielding may have prevented widespread wildfire ignition although the thermal pulse may have been sufficient to ignite localized fires and kill fauna lacking temporary shelter an opaque cap of submicron dust in the upper atmosphere could however override the self shielding effect

anthracology and taphonomy from wood gathering to charcoal analysis a review of the taphonomic processes modifying charcoal assemblages in archaeological contexts abstract a discussion on the representativeness of charcoal from archaeological contexts and their potential for palaeoecological reconstruction is presented the charcoal deposits studied are the result of human activities and natural processes difficult to separate on the basis of their effects only this is why taphonomy should not be limited to the study of charcoal after the extinction of fire as a result our questioning has been widened to include the entire succession of processes from past vegetation to the anthracological diagram we propose a review of the taphonomic processes affecting anthracological assemblages in archaeological contexts from wood gathering to the analysis of charcoal results human practices appear clearly as the first filter determining or conditioning the assemblage the combustion process can induce a double filter by limiting the taxonomic information and by falsifying the initial quantity of burned wood post depositional agents represent a third level of filters between the vegetation and the anthracological assemblage finally sampling and quantification methods can also induce a distortion of the assemblage the aim of this paper is to present the state of the discipline today the problems already solved and the questions that remain to be studied

spike of pyrosynthetic polycyclic aromatic hydrocarbons associated with an abrupt decrease in δ13c of a terrestrial biomarker at the cretaceous tertiary boundary at caravaca spain the first vertical high resolution record of polycyclic aromatic hydrocarbons pahs of pyrosynthetic origin and the corresponding 13 c profile of a terrestrial biomarker across the cretaceous tertiary k t boundary at caravaca spain reveals the following in comparison with adjacent cretaceous marlstones the first thin horizon 0 to 0 5 cm 0 the k t boundary of the boundary clay layer is 1 enriched as much as 112 to 154 fold in typical pyrosynthetic pahs such as coronene benzo g h i perylene and benzo e pyrene and 2 shows an abrupt 13 c decrease of 1 4 1 8 in terrestrial higher plant derived n c 29 alkane the spike of pyrosynthetic pahs associated with an abrupt decrease in 13 c value of a terrestrial biomarker is interpreted to reflect the prevalence of extensive fires with subsequent 13 c decrease in atmospheric co 2 it is estimated that the geologically instantaneous combustion of 18 24 of the terrestrial above ground biomass would be necessary to account for the measured negative isotopic shift at the k t boundary on the basis of carbon mass balance between terrestrial above ground biomass and atmosphere

trajectories and distribution of material ejected from the chicxulub impact crater implications for postimpact wildfires 1 the trajectories of low and high energy ejecta from the chicxulub impact crater have been computed using a numerical code and compared with analyses of debris deposited in k t boundary sections these calculations indicate that low energy ejecta produces centimeter to meter thick deposits within 4000 km of the point of impact although its azimuthal distribution depends on the incident angle of the projectile with the surface of the earth the high energy ejecta or vapor plume rises through the atmosphere and isotropically expands at the top of the atmosphere the velocity of this ejecta increases as it rises approximately 12 of the high energy ejecta is lost because it reaches escape velocities while 25 of the material reaccretes within 2 hours 55 reaccretes within 8 hours and 85 reaccretes within 72 hours this ejecta is distributed globally but it is concentrated around the chicxulub impact site and at the antipode corresponding to india and the indian ocean 65 million years ago it is also slightly smeared in a longitudinal direction because of earth s rotation because this debris does not reaccrete all at once the collisional shock heating of the atmosphere will be drawn out over a period of a few days and will occur in pulses this could be an important factor when calculating postimpact chemical reactions in the stratosphere the calculations also indicate the ejecta would have ignited wildfires on several continents around the world although the distribution of those fires depends partly on the trajectory of the projectile

metasomatic rocks with greisenization associated with the ore bearing zones in the iron mountains železne hory mountains eastern bohemia czechoslovakia in the central iron mountains the ore mineralized deformation zones represent deep reaching faults which possibly reach the upper mantle during geological history they were used by ascending magmas fluids and barren and ore hydrothermal solutions it can be shown that the metasomatism provoked by acid fluids bears the character of greisenization the type of the original greisenized rocks here can be determined on the basis of elements that were immobile during greisenization especially si ti sc and ree after or even during greisenization the metasomatic rocks were affected by shearing metamorphism corresponding in its pt conditions to the middle zone of the almandine amphibolite facies it was possibly in this period that the enigmatic skarn body of sama ov originated owing to its similarity to the dyke skarn of kraskov its similar origin could be assumed the deposition of skarn minerals from circulating fluids which were perhaps released during greisenization

impact dust not the cause of the cretaceous tertiary mass extinction most of the 3 mm thick globally distributed chicxulub ejecta layer found at the cretaceous tertiary k t boundary was deposited as condensation droplets from the impact vapor plume a small fraction of this layer 14 g was submicrometer size dust the global mass and grain size distribution of the clastic debris indicate that stratospheric winds spread the debris from north america over the pacific ocean to europe and little debris reached high southern latitudes these findings indicate that the original k t impact extinction hypothesis the shutdown of photosynthesis by submicrometer size dust is not valid because it requires more than two orders of magnitude more fine dust than is estimated here furthermore estimates of future impact hazards which rely upon inaccurate impact dust loadings are greatly overstated

models of lithosphere and asthenosphere anisotropic structure of the yellowstone hot spot from shear wave splitting 1 teleseismic shear wave splitting measured at 56 continuous and temporary seismographs deployed in a 500 km by 600 km area around the yellowstone hot spot indicates that fast anisotropy in the mantle is parallel to the direction of plate motion under most of the array the average split time from all stations of 0 9 s is typical of continental stations there is little evidence for plume induced radial strain suggesting that any contribution of gravitationally spreading plume material is undetectably small with respect to the plate motion velocity two stations within yellowstone have splitting measurements indicating the apparent fast anisotropy direction is nearly perpendicular to plate motion these stations are 30 km from stations with parallel to plate motion the 70 rotation over 30 km suggests a shallow source of anisotropy however split times for these stations are more than 2 s we suggest melt filled stress oriented cracks in the lithosphere are responsible for the anomalous orientations within yellowstone stations southeast of yellowstone have measurements of oriented nnw to wnw at high angles to the plate motion direction the archean lithosphere beneath these stations may have significant anisotropy capable of producing the observed splitting

the cretaceous tertiary biotic transition mass extinctions are recognized through the study of fossil groups across event horizons and from analyses of long term trends in taxonomic richness and diversity both approaches have inherent flaws and data that once seemed reliable can be readily superseded by the discovery of new fossils and or the application of new analytical techniques herein the current state of the cretaceous tertiary k t biostratigraphical record is reviewed for most major fossil clades including calcareous nannoplankton dinoflagellates diatoms radiolaria foraminifera ostracodes scleractinian corals bryozoans brachio pods molluscs echinoderms fish amphibians reptiles and terrestrial plants macrofossils and palynomorphs these reviews take account of possible biasing factors in the fossil record in order to extract the most comprehensive picture of the k t biotic crisis available results suggest that many faunal and floral groups ostracodes bryozoa ammonite cephalopods bivalves archosaurs were in decline throughout the latest maastrichtian while others diatoms radiolaria benthic foraminifera brachiopods gastropods fish amphibians lepidosaurs terrestrial plants passed through the k t event horizon with only minor taxonomic richness and or diversity changes a few microfossil groups calcareous nannoplankton dinoflagellates planktonic foraminifera did experience a turnover of varying magnitudes in the latest maastrichtian earliest danian however many of these turnovers along with changes in ecological dominance patterns among benthic foraminifera began in the latest maastrichtian improved taxonomic estimates of the overall pattern and magnitude of the k t extinction event must await the development of more reliable systematic and phylogenetic data for all upper cretaceous clades

an integrated 3d velocity inversion joint hypocentral determination relocation analysis of events in the northridge area abstract a subset of 3371 events recorded in the northridge area by the southern california seismic network during january to april 1994 was relocated with the joint hypocentral determination jhd technique this analysis showed two unexpected results a the jhd locations are shifted about 3 9 km on average in a northwest direction with respect to the locations determined using a single event location sel program and b the station corrections vary between 0 55 and 1 26 sec a rather large range in addition the jhd locations are less scattered than the sel locations for each station the weighted average of the arrival time residuals obtained when the events are located with the sel program which does not apply distance or error weighting are generally smaller than the corresponding jhd corrections the locations determined with sel and using the weighted average residuals as station corrections do not differ much from the sel locations but on average the rms residuals become as small as those corresponding to the jhd locations as the magnitude of the station corrections indicates the presence of large lateral velocity variations a 3d velocity model for the area was determined using the arrival times of 1012 events recorded by at least 17 stations the initial velocity model was that used routinely by the southern california earthquake center the first two layers 5 5 and 10 5 km thick were subdivided into 100 blocks each 12 12 km these layers show a pronounced low velocity anomaly 24 and 16 respectively immediately to the northwest of the epicentral area this low velocity zone coincides with the west ventura basin another pronounced low velocity zone to the southeast of the epicentral area reflects the presence of the los angeles basin the locations obtained with the 3d velocity model are consistently to the southeast of the jhd locations 2 4 km on average to establish the effect of these pronounced lateral velocity variations on the sel and jhd locations synthetic travel times were analyzed the synthetic times were generated for event locations determined by jhd shifted by various amounts and the 3d velocity model and were subsequently treated as the actual data the most important result of this analysis is that the jhd locations are affected by a quasi systematic shift in a northwest direction up to about 2 7 km on average depending on the initial shift but that the relative locations are well preserved therefore both the velocity inversion of the actual data and the analysis of the synthetic data indicate that the jhd locations determined for the actual data are quasi systematically mislocated to account for this mislocation an overall shift of 2 5 km to the southeast was applied to all the jhd locations one of the most important implications of the shifted locations is the possibility that the northeasterly dipping santa susana fault to the northwest of the epicentral area was seismically active during the aftershock sequence this feature is more diffuse in other published locations

the 1978 yellowstone eastern snake river plain seismic profiling experiment crustal structure of the yellowstone region and experiment design in 1978 a major seismic profiling experiment was conducted in the yellowstone eastern snake river plain region of idaho and wyoming fifteen shots were recorded that provided coverage to distances of 300 km in this paper travel time and synthetic seismogram modeling was used to evaluate an average p wave velocity and apparent q structure of the crust from two seismic profiles reversed across the yellowstone national park region this area includes the well known hydrothermal features of yellowstone national park geysers fumeroles etc a large collapse caldera and extensive silicic volcanism of quaternary age features attributed to shallow crustal sources of magma the averaged crustal structure for this region as interpreted from the seismic data consists of 1 a highly variable near surface layer approximately 2 km thick with variable velocities of 3 0 to 4 8 km s and a low apparent q of 30 that is interpreted to be composed of weathered rhyolites and sedimentary infill 2 an upper crustal layer 3 to 4 km thick with variable velocities of 4 9 to 5 5 km s and apparent q of 50 to 200 that is thought to represent the accumulation of the pleistocene quaternary rhyolite flows ash flow tuffs and possible paleozoic and precambrian metamorphic equivalents 3 the crystalline upper crust that is characterized by a laterally inhomogeneous layer that varies in velocity from 4 0 to 6 1 km s averaging 5 km thick with a q of 300 this layer appears to be a cooling but still hot body of granitic composition beneath the yellowstone caldera it is thought to be a remnant of the magma chambers that produced the quaternary silicic volcanic rocks of the yellowstone plateau and may still be a major contributor to the high heat flow 4 a laterally homogeneous intermediate crustal layer 8 to 10 km thick with a velocity of 6 5 km s and apparent q of 100 to 300 5 a homogeneous 25 km thick lower crust with a velocity of 6 7 to 6 8 km s and an apparent q of 300 and 6 a total crustal thickness of 43 km the upper crustal layer 5 5 to 6 0 km s is thought to be the thermally altered equivalent of the continental crystalline basement that is normally 15 to 20 km thick in the surrounding thermally undisturbed archean crust an interpretation from these results suggests that mafic melts from the mantle have penetrated the lower crust without significant variations in the velocity structure but produce the main source of heat that drives the volcanic and hydrothermal systems of yellowstone the high apparent attenuation and large lateral velocity variations in the upper crust are consistent with a model in which partial fractionation partial melting and metamorphism differentiate the original upper crust to produce silicic melts that were extruded as rhyolites and ash flow tuffs across the yellowstone plateau this seismic model is consistent with the evidence for a systematic northeastward propogation of silicic volcanic centers along the eastern snake river plain to their present location beneath the yellowstone hydrothermal system while these findings do not bear directly on the origin and source of the heat i e mantle lumes lithospheric fractures mantle radiogenetic heat basal lithospheric shearing etc they provide a constraint on the configuration and lateral extent of crustal layers that reflect thermal and compositional boundaries

copper gold and silver enrichment in ore mylonites within massive sulphide orebodies at hongtoushan vhms deposit n e china abstract the hongtoushan archaean cu zn volcanic hosted massive sulphide vhms deposit occurs in the hunbei granite greenstone terrane liaoning province of ne china the ores were metamorphosed 3 0 2 8 ga to upper amphibolite facies at temperatures between 600 and 650 c and underwent three phases of deformation the deformation has transposed the stratiform orebodies into a y shaped configuration ore minerals in the deposit were originally composed of pyrite pyrrhotite chalcopyrite and sphalerite prograde metamorphism obliterated almost all the sedimentary textures in the ores and the present ore textures were formed substantially during peak and post peak metamorphism intensive remobilisations have occurred in the hongtoushan deposit at various scales there are more than 30 oreshoots inside the main massive sulphide orebodies the oreshoots range from 2 to 30 m in length 0 1 to 1 5 m in width and 2 to 30 m in depth extension most run parallel or sub parallel to the strike of the massive sulphide ore layers with only a few being developed in metamorphic rocks in the immediate vicinity of the sulphide orebodies almost all the sulphide and gangue minerals in the oreshoots have been affected by intense shearing pyrite is characterised by cataclastic flow pyrrhotite chalcopyrite and sphalerite exhibit strong plasticity hydrothermal alteration minerals in the oreshoots are dominated by deformation free hornblende actinolite epidote clinozoisite biotite muscovite albite carbonate and quartz cu au and ag in the ore mylonites average 11 wt 1 74 and 235 g t respectively compared to the massive sulphide ores these oreshoots show remarkable enrichment of these elements with enrichment coefficients of 5 3 5 0 and 4 6 respectively we draw the conclusion that these oreshoots are actually ore mylonites overprinted by late stage fluids the presence of annealing textures in pyrrhotite and the absence in pyrite suggest that formation and succeeding annealing of the ore mylonite took place over the temperature range from 550 to 450 c such a temperature range combined with the geology and mineralogy indicates that these ore mylonites and the derivative oreshoots were formed during upper greenschist facies retrograde metamorphism similarity of the ore mylonites to the massive ores in metal varieties and lead isotope ages suggest that cu au and ag of the overprinting fluids on the ore mylonites were derived mainly from the nearby massive sulphide ores however lead isotope compositions of the ore mylonites also suggest that an external source such as the metamorphic host rocks has also contributed to their metal budget

a process for fire related debris flow initiation cerro grande fire new mexico in this study we examine factors that pertain to the generation of debris flows from a basin recently burned by wildfire throughout the summer 2000 thunderstorm season we monitored rain gauges channel cross sections hillslope transects and nine sediment runoff traps deployed in a steep 0 15 km 2 basin burned by the may 2000 cerro grande fire in new mexico debris flows were triggered in the monitored basin during a rainstorm on july 16 2000 in response to a maximum 30 min rainfall intensity of 31 mm h 1 return period of approximately 2 years eleven other storms occurred before and after the july storm these storms resulted in significant runoff but did not generate debris flows the debris flows generated by the july 16 storm initiated on a broad open hillslope as levee lined rills the levees were composed of gravel and cobble sized material supported by an abundant fine grained matrix debris flow deposits were observed only on the hillslopes and in the first and second order drainages of the monitored basin no significant amounts of channel incision were measured following the passage of the debris flows indicating that most of the material in the flows originated from the hillslopes sediment runoff concentrations of between 0 23 and 0 81 kg l 1 with a mean of 0 42 kg l 1 were measured from the hillslope traps following the debris flow producing storm these concentrations however were not unique to the july 16 storm the materials entrained by the july 16 storm contained a higher proportion of silt plus clay sized materials in the 2 mm fraction than the materials collected from storms that produced comparable sediment runoff concentrations but not debris flows the difference in materials demonstrates the critical role of the availability of fine grained wood ash mantling the hillslopes in the runoff dominated generation of post wildfire debris flows the highest sediment runoff concentrations again not unique to debris flow production were produced from maximum 30 min rainfall intensities greater than 20 mm h 1

simultaneous inversion for lateral velocity variations and hypocenters in the yellowstone region using earthquake and refraction data a three dimensional upper crustal p wave velocity structure of the yellowstone region was determined by simultaneous inversion using pg refracted arrival times and earthquake generated direct p wave arrival times the velocity structure was modeled by a two layer block configuration with the velocity of the surface layer fixed the inversion was performed on a 14 4 km thick second layer 5 6 blocks using an optimal block size of 21 2 18 3 km and incorporated the method of separation of parameters results show volumes of higher velocities approximately 6 3 km s north of the yellowstone caldera that correlate with gravity anomaly highs and are interpreted to be associated with near surface crystalline basement the upper crust beneath the caldera showed an average velocity of 5 8 km s with prominent low velocity zones of 4 9 and 5 2 km s in the northeast and southwest portions of the caldera respectively the 4 9 km s low velocity layer in the northeast corner of the caldera coincides with a localized 20 mgal bouguer gravity low and the largest area of hydrothermal activity in yellowstone national park relocating earthquakes with the new velocity model showed a systematic migration of epicenters radially toward the caldera by an average of 1 2 km relative to locations using a homogeneous velocity model

the chemistry and origin of zincian spinel associated with the aggeneys cu pb zn ag deposits namaqualand south africa zincian spinel or gahnite zn fe mg al2o4 occurs in metamorphosed sulphide rich rocks garnet quartzites quartz magnetite rocks aluminous metasediments barite magnetite rocks quartz veins and pegmatites associated with the aggeneys base metal deposits namaqualand south africa zincian spinel in sulphide bearing rocks is considered to have formed predominantly by desulphurization reactions involving a member of the system fe s o and sphalerite with sillimanite or garnet gahnite in sulphide free garnet quartzites quartz magnetite rocks and barite magnetite rocks probably formed from zn and al that were hydrothermally derived whereas gahnite in aluminous metasediments was derived from the metamorphism of metalliferous shales in which zn may originally have been linked to organic material gahnite is zn rich in sulphide bearing rock but is fe rich in sulphide free garnet quartzites and quartz magnetite rocks although zn rich spinels represent guides to ore in the aggeneys area and elsewhere in the namaqualand metamorphic complex fe rich spinels should not be discounted because zn rich and fe rich spinels occur within metres of sulphides at aggeneys

simultaneous inversion for hypocenters and lateral velocity variations an iterative solution with a layered model an iterative inversion technique has been developed that uses the direct p and s wave arrival times from local earthquakes to compute simultaneously a three dimensional velocity structure and relocated hypocenters crustal structure is modeled by subdividing flat layers into rectangular blocks an interpolation function is used to smoothly vary velocities between blocks allowing ray trace calculations of travel times in a three dimensional medium tests using synthetic data from known models show that solutions are reasonably independent of block size and spatial distribution but are sensitive to the choice of layer thicknesses application of the technique to observed earthquake data from north central utah shows the following 1 lateral velocity variations in the crust as large as 7 occur over 30 km distances 2 earthquake epicenters computed with the three dimensional velocity structure were shifted an average of 3 0 km from locations determined assuming homogeneous flat layered models and 3 the laterally varying velocity structure correlates with anomalous variations in the local gravity and aeromagnetic fields suggesting that the new velocity information can be valuable in acquiring a better understanding of crustal structure

combustion of fossil organic matter at the cretaceous paleogene k p boundary recognition of elevated concentrations of aciniform soot in cretaceous paleogene k p boundary sediments worldwide led to the hypothesis that global scale forest wildfires could have been generated by the k p boundary bolide impact and might have contributed directly to the extinction event the wildfires are estimated to have injected 10 13 t of co 2 into the atmosphere resulting in an interval of greenhouse warming yet minimal amounts of charred plant remains and abundant noncharred material occur in various k p boundary locations across north america this refutes the inference that wildfires occurred on a global scale and requires an alternative explanation for the aciniform soot here we describe significant concentrations of carbon cenospheres in k p boundary sediments from new zealand denmark and canada carbon cenospheres are thought to derive solely from incomplete combustion of pulverized coal or fuel oil droplets which suggests that the impact may have combusted organic rich target crust the chicxulub impact crater is located adjacent to the cantarell oil reservoir one of the most productive oil fields on earth this indicates that abundance of organic carbon in the chicxulub target crust was likely to have been above global mean values but even if we discount chicxulub9s organic rich locality the global mean crustal abundance for fossil organic matter is more than adequate to account for observed concentrations of both carbon cenospheres and aciniform soot therefore making the global wildfire hypothesis unnecessary

palaeobotanical evidence for a june impact winter at the cretaceous tertiary boundary a large bolide impact such as that thought to have occurred at the cretaceous tertiary k t boundary should produce large amounts of light attenuating debris thereby causing an impact winter 1 3 because of thermal buffering in the oceans evidence for a brief 1 2 months2 4 impact winter would be found only in terrestrial environments aquatic leaves in the k t boundary section near teapot dome wyoming preserve structural deformation that can be duplicated experimentally in extant aquatic leaves by freezing reproductive stages reached by the fossil aquatic plants at the time of death suggest that freezing took place in approximately early june both the existence of the structurally deformed plants and the high abundance of fern spores occur in a horizon containing sparse impact debris but below the horizon containing abundant impact debris i therefore suggest that the lower horizon represents debris and effects from a large distant bolide impact and the upper horizon represents a small nearby bolide impact

systematics of hydrothermal alteration at the falun base metal sulfide deposit and implications for ore genesis and exploration bergslagen ore district fennoscandian shield sweden the paleoproterozoic falun zn pb cu au ag pyritic sulfide deposit in the bergslagen ore district sweden is enveloped by hydrothermally altered rocks metamorphosed to the lower amphibolite facie

fireball passes and nothing burns the role of thermal radiation in the cretaceous tertiary event evidence from the charcoal record of north america comment and reply reply the suggestion that globally extensive wildfires were ignited as part of the cretaceous tertiary k t boundary events e g robertson et al 2004 1 melosh et al 1990 2 kring and durda 2002 3 ignores the following 1 absence of above background levels of charcoal 2 absence of

high resolution palaeofire signals from christina lake alberta a comparison of the charcoal signals extracted by two different methods abstract two high resolution palaeofire signals were extracted from the annually laminated sediment of christina lake in the boreal forest of alberta canada a charcoal curve focusing on large charcoal fragments 125 m was extracted by the sieving method described by whitlock and millspaugh a carbon curve which includes all size fractions of charcoal was extracted by a method modified from winkler s chemical assay method modifications included increasing the duration of nitric acid treatment to 2 h and using a total carbon analyser tca rather than standard loss on ignition these adjustments resulted in a carbon curve which is unaffected by clay water losses and subtle changes in sedimentology which were problematic in the original gravimetric technique the sensitivity of the tca allowed subtle shifts in carbon i e charcoal abundance to be detected in lake sediments with low levels of charcoal when compared with the known fire history near the lake since 1900 the sieved charcoal curve was most responsive to fires known to burn near the shore of the lake and less responsive to fires burning elsewhere in the watershed the tca carbon curve was somewhat more sensitive than the sieved charcoal curve for detecting fires in the drainage basin which did not burn to the lake edge the tca carbon curve was strongly correlated with sediment influx suggesting stream inputs of charcoal are the dominant influence on this signal the peak in response of the tca curve to known fire events was sometimes lagged by several years suggesting that it can take several seasons for the bulk of stream transported charcoal to make its way from the watershed to its final deposition site in the lake very large fires burning just outside the drainage basin of the lake were not detected by either method suggesting that both of the methods used are sensitive only to fires burning in the watershed and that long distance aerially dispersed charcoal is insignificant at this site

earthquake locations and three dimensional crustal structure in the coyote lake area central california previous work on the simultaneous inversion method has been improved and extended to incorporate iterative solution for earthquake locations and laterally heterogeneous structure approximate ray tracing and parameter separation are important elements of the improved method application of the method to p wave arrival time data recorded by stations of the u s geological survey central california network yields a three dimensional model for the velocity structure of the upper crust in an area encompassing the rupture zone of the coyote lake earthquake of august 1979 very strong correlations between the velocity model and the geology and gravity and magnetic anomalies are observed improved estimates of the locations of earthquakes in the study area are also determined the relocation of explosions indicates epicentral accuracies of the order of a kilometer or better based on the revised hypocentral locations it is concluded that the san andreas fault is vertical in this area with no actual offset between the epicenters and the fault trace in contrast the calaveras has two or more active fault surfaces one nearly vertical and another dipping 75 to the northeast

developing a post fire flood chronology and recurrence probability from alluvial stratigraphy in the buffalo creek watershed colorado usa stratigraphic and geomorphic evidence indicate floods that occur soon after forest fires have been intermittent but common events in many mountainous areas during the past several thousand years the magnitude and recurrence of these post fire flood events reflects the joint probability between the recurrence of fires and the recurrence of subsequent rainfall events of varying magnitude and intensity following the may 1996 buffalo creek colorado forest fire precipitation amounts and intensities that generated very little surface runoff outside of the burned area resulted in severe hillslope erosion floods and streambed sediment entrainment in the rugged severely burned 48 km 2 area these floods added sediment to many existing alluvial fans while simultaneously incising other fans and alluvial deposits incision of older fans revealed multiple sequences of fluvially transported sandy gravel that grade upward into charcoal rich loamy horizons we interpret these sequences to represent periods of high sediment transport and aggradation during floods followed by intervals of quiescence and relative stability in the watershed until a subsequent fire occurred an alluvial sequence near the mouth of a tributary draining a 0 82 km 2 area indicated several previous post fire flood cycles in the watershed dendrochronologic and radiocarbon ages of material in this deposit span approximately 2900 years and define three aggradational periods the three general aggradational periods are separated by intervals of approximately nine to ten centuries and reflect a millennium scale geomorphic response to a closely timed sequence of events severe and intense watershed scale stand replacing fires and subsequent rainstorms and flooding millennium scale aggradational units at the study site may have resulted from a scenario in which the initial runoff from the burned watershed transported and deposited large volumes of sediment on downstream alluvial surfaces and tributary fans subsequent storm runoff may have produced localized incision and channelization preventing additional vertical aggradation on the sampled alluvial deposit for several centuries two of the millennium scale aggradational periods at the study site consist of multiple gravel and loam sequences with similar radiocarbon ages these closely dated sequences may reflect a multidecade scale geomorphic response to more frequent but aerially limited and less severe fires followed by rainstorms of relatively common recurrence

mid holocene charcoal stratigraphy fire history and palaeoecology at north gill north york moors uk abstract small peat mires are a favourable medium for the preservation of charcoal records that can be correlated more precisely with past fire history as part of multi proxy palaeoecological studies the north york moors upland has many suitable peat deposits with a well researched palaeoenvironmental history that offer the potential for high precision palaeofire studies we have examined the charcoal and pollen stratigraphy at the north gill site at a range of spatial and temporal resolutions for the mid holocene period between about 7k and 4 5k radiocarbon years ago in an individual core three size class charcoal records large small and microscopic reflect the scale and location of local fire events although the micro charcoal curve contains a background regional signal of about 10 of the charcoal pollen ratio most micro charcoal is generated locally and deposited close to its source at the site scale spatial comparison of four cores shows a variable relationship between tree pollen and micro charcoal concentrations which is an index of the size and intensity of local fire phases individual fires cannot be distinguished fine resolution sampling at the millimetre scale resolves major burning phases into discrete sub phases that may reflect the effects of individual fires at this fine temporal scale this multi scale research indicates that detailed charcoal stratigraphies at varying resolutions are capable of interpretation in terms of local regional and intermediate fire history

fireball passes and nothing burns the role of thermal radiation in the cretaceous tertiary event evidence from the charcoal record of north america comment and reply comment belcher et al 2003 1 reported that at six locations across north america quantities of charcoal in the cretaceous tertiary k t boundary clay are about an order of magnitude below background levels they interpreted this absence of charcoal as evidence for the absence of a global

hst imaging of atmospheric phenomena created by the impact of comet shoemaker levy 9 hubble space telescope hst images reveal major atmospheric changes created by the collision of comet shoemaker levy 9 with jupiter plumes rose to 3000 kilometers with ejection velocities on the order of 10 kilometers second 1 some plumes were visible in the shadow of jupiter before rising into sunlight during some impacts the incoming bolide may have been detected impact times were on average about 8 minutes later than predicted atmospheric waves were seen with a wave front speed of 454 20 meters second 1 the hst images reveal impact site evolution and record the overall change in jupiter s appearance as a result of the bombardment