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

development of cleavage in limestones of a fold thrust belt in eastern new york abstract tectonic cleavage has developed in lower devonian limestones of the hudson valley fold thrust belt in new york state morphology and distribution of cleavage in these limestones is controlled by the amount of clay quartz matrix present and by strain only limestones with greater than 10 clay quartz matrix developed widespread cleavage x ray diffraction analyses indicate that the clay matrix was altered during deformation the width of the 001 illite peak in cleaved lime wackestone is less than that in uncleaved lime wackestone from the same stratigraphic level a minimum of 10 clay is necessary to provide interconnectivity between sites of dissolution and the free fluid system preliminary analyses of bulk chemistry indicate that calcite is removed from the local rock system during cleavage development supporting proposals that circulation of fluid through the rock plays a major role in the development of cleavage textural evidence suggests that both pressure solution and free face dissolution contribute to the removal of ions at grain boundaries cross cutting relations indicate that cleavage was initiated early during the development of the fold thrust belt but continued to develop during the late stages of folding

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

deformation volume and cleavage development in metasedimentary rocks from the ballarat slate belt psammites from the ballarat slate belt in se australia exhibit well developed differentiated or spaced cleavage defined by alternating phyllosilicate and quartz rich domains termed p and q domains respectively strain estimates derived from independent microstructural and chemical observations suggest that the p q fabrics developed in response to plane strain deformation dominated by solution transfer with the principal finite shortening in the p domains approximately twice that in the adjacent q domains significant finite extensions are indicated by ubiquitous quartz albite chlorite overgrowths in both p and q domains while pressure shadow development around syntectonic pyrite porphyroblasts suggest finite extension of at least 100 this estimate is comparable with the extension predicted for constant volume deformation and consequently there appears to have been no significant bulk material loss or gain on the hand specimen scale these observations are consistent with solute transfer scales as little as a few centimetres via diffusion in a stationary fluid and do not require although do not necessarily preclude large scale advective fluid transport through the slate belt during cleavage formation as suggested in previous studies

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

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

preeruption history of the grande ronde formation lavas columbia river basalt group american northwest evidence from phenocrysts basaltic andesite lavas belonging to the grande ronde formation constitute 87 of the columbia river basalt group although these lavas are chemically evolved they generally contain 5 phenocrysts two hypotheses have been proposed to explain this observation the first hypothesis suggests that grande ronde lavas were near primary melts generated by large scale melting of eclogite from the inferred yellowstone plume the alternative hypothesis proposes that grande ronde magmas were extremely hydrous and rose rapidly from the mantle such that the dissolved water kept the magmas close to their liquidi we present new information on textures and mineral chemistry of phenocrysts in two well characterized field sections through the grande ronde formation the new data lead us to conclude that at least some of the grande ronde primary magmas were highly hydrous however they all underwent extensive fractionation magma mixing and degassing in a shallow intrusive network prior to eruption as lava

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

cleavage geometry and the development of the church bay anticline co cork ireland abstract the church bay anticline is one of a series of e w trending hercyman folds in southern ireland the fold has a crudely axial planar cleavage which was initiated early in the buckling history the cleavage was deformed subsequently by a number of discrete bedding parallel shear zones as the fold continued to amplify this has resulted in a characteristically sigmoidal cleavage geometry in the fold profile plane the cleavage also displays kink bands and sharp angular changes across bedding planes in the fold hinge as a result of shearing within these sheared zones the cleavage is intensified indicating that conditions for cleavage formation were maintained throughout the development of the fold no new cleavage has formed despite the rotation of the cleavage during the deformation history

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

interrelations of mesoscopic structures and strain across a small regional fold virginia appalachians abstract small regional folds such as the clover hollow anticline of the narrows thrust sheet in southwest virginia u s a are considered to be large buckle folds expressing lateral shortening above a subsurface decollement cleavage mesoscopic and regional folds and contraction faults have developed in these rocks under anchimetamorphic conditions in a single protracted deformation during thrust sheet emplacement the contraction faults dominate the structure at all scales three fault associations isolated contraction faults contraction faults in series and complex fault zones with intense folding determine the pattern and intensity of local structures regional displacement transfer of strain along and across faults has produced local variations in structural style duplex like systems of second order faults terminate laterally into zones of intense folding and third order faulting fold tightness cleavage intensity strain magnitude and total longitudinal strain e t are maximum in these regions contraction faults in this thrust sheet have propagated along zones of high strain rate associated with mesoscopic folding and intense cleavage regional hinge migration and greater structural complexity along the southeast limb of the clover hollow anticline are considered to be due to emplacement of the adjacent thrust sheet

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

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

microscopic deformation mechanisms associated with mica film formation in cleaved psammitic rocks abstract at islesboro maine cleavage is well developed in low greenschist facies siltstones and interbedded pelites of early paleozoic age the siltstones contain a spatial sequence of mica film structures that corresponds to increasing intensity of mesoscopic cleavage in the most weakly foliated rocks cleavage is defined by the preferred orientation of individual mica particles in siltstones displaying slightly higher strain these particles are accompanied by short discontinuous mica film segments thought to have formed by the recrystallization of early pore space layer silicates in moderately cleaved rocks these segments link up to form lengthened mica films by a process thought to include intergranular fracture transgranular fracture and layer silicate crystallization in strongly cleaved rocks the lengthened mica films become longer and thicken appreciably by solution transfer of quartz and residual accumulation of layer silicates and opaque minerals layer silicate crystallization is evident at all stages of mica film development but is especially marked by the growth of decussate mica inside late stage thick mica rich layers this sequence of mica film development is probably characteristic of fine grained psammitic rocks and may not necessarily occur in carbonate rich or mica rich rocks

the role of pressure solution and intermicrolithon slip in the development of disjunctive cleavage domains a study from helvick head in the irish variscides the offset of sedimentary laminae bedding surfaces veins and other passive markers across disjunctive cleavage domains has commonly been attributed solely to pressure solution a detailed study of disjunctive cleavage within siltstones and sandstones from helvick head co waterford on the eastern margin of the irish variscides indicates that the cleavage domains were initially formed by pressure solution processes however the study also revealed features which cannot be explained by pressure solution alone the cleavage domains represent planes of weakness within otherwise relatively homogeneous rock during fold tightening they were rotated out of parallelism with the principal xy plane of the finite strain ellipsoid thus enabling shear movement between the microlithons it is considered that this intermicrolithon slip caused a rotation of the elongate quartz grains within the cleavage domains resulting in an asymmetry of their long axes with respect to the cleavage domain margin grain microfracturing and occasionally slickensides on cleavage surfaces intermicrolithon slip is unlikely to be a localized phenomenon but is probably widespread throughout the irish variscides and other orogenic belts

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

a microstructural and microchemical study of cleavage lamellae in a slate abstract the results of a detailed microstructural and microchemical study of a slate from the chewton area victoria australia are reported in which it was found that cleavage developed from microcrenulations phyllosilicates in p domains differed in their chemistry from those in q domains and were concentrated in the p domains by localized metamorphic reactions which were aided by mechanical rotation and solution processes wide dark cleavage lamellae often taken as evidence for the passive concentration of insoluble minerals appear to have had a similar origin the p domains exhibited two types of microstructure one which was consistent with annealing and the other with deformation within the domain cataclasites had formed along some p domains suggesting that they had become preferential sites for late phase brittle deformation

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

transient processes in stromboli s shallow basaltic system inferred from dolerite and magmatic breccia blocks erupted during the 5 april 2003 paroxysm we describe the mineralogy geochemistry and mesomicrostructure of fresh subvolcanic blocks erupted during the 5 april 2003 paroxysm of stromboli aeolian islands italy these blocks represent 50 vol of the total erupted ejecta and consist of fine to medium grained basaltic lithotypes ranging from relatively homogeneous dolerites to strongly or poorly welded magmatic breccias the breccia components are represented by angular fragments of dolerites entrapped in a matrix of vesiculated lava like to scoriae crystal rich cr basalt all of the studied blocks are cognates with the cr basalt of the normal strombolian activity or lavas and they are often coated by a few centimeter thick layer of crystal poor cp basaltic pumice erupted during the paroxysm we suggest that they result from the rapid increase of pressure and related subvolcanic rock failure that occurred shortly before the 5 april 2003 explosion when the uppermost portion of the edifice inflated and suffered brecciation as the result of the sudden rise of the gas rich cp basalt that triggered the eruption dolerites and magmatic matrix of the breccias show major and trace element compositions that match those of the cr basalts erupted during normal strombolian activity and effusive events at stromboli volcano dolerites consist of a phenocrysts normally found in the cr basalts and b late stage magmatic minerals such as sanidine an60 28 plagioclase fe mn rich olivines fo68 48 phlogopite apatite and opaque mineral pairs magnetite and ilmenite most of which are never found both in lava flows and scoriae erupted during the persistent explosive activity that characterizes typical strombolian behavior subvolcanic crystallization of the stromboli cr magma leading to slowly cooled equivalents of basalts could result from transient drainage of the magma from the summit craters to lower levels fingering and engulfing of the material that collapsed from the summit crater floor into the shallow basaltic system during the late evening of 28 december 2002 coupled with the short break in the summit persistent explosions between december 2002 and march 2003 permitted the cr magma pockets to solidify as dolerites which were confined to the uppermost portion of the system and thus not involved in the ongoing flank effusive activity crystal size distribution of the basaltic blocks and crystallization of the finer grained 0 1 mm mafic minerals of the dolerites over a time interval of 100 days closely agrees with the above interpretation vesicle filling miarolitic cavities locally found in some dolerites with minerals deposited as vapor phase crystallization is a result of continuous gas percolation through the rocks of the uppermost portion of the volcanic system poorly welded magmatic breccias formed during syn eruptive processes of 5 april 2003 when the paroxysm strongly shattered the shallow subvolcanic system and many dolerite fragments were entrapped in the cr magma in contrast the high degree of welding between the dolerite clasts and the cr basaltic matrix in the strongly welded magmatic breccias provides a snapshot of subvolcanic intrusions of the cr basalt into the dolerite when after a 2 month break in activity cr magmas started to rise again to the summit craters blocks similar to these subvolcanic ejecta of 5 april 2003 were also erupted during previous paroxysms e g 1930 suggesting that changes in the usual strombolian activity e g short breaks in the persistent mild explosions and or flank effusive activity lead to transient crystallization of dolerites in the shallow plumbing system

the effects of feo on the system cmas at low pressure and implications for basalt crystallization processes the common occurrence of olivine clinopyroxene and plagioclase in natural basalts may suggest that crystallization of these phases exerts important controls on the evolution of natural basalts at low pressure in order to understand the effects of such an assemblage on the evolution of basalt an experimental study of the divariant assemblage 1 an cpx ol in the system cmas feo was undertaken at 1 bar and under very reducing conditions experiments have been performed along three isothernal sections detailed electron microprobe data have been collected on all the coexisting phases combining these data with available data in the system cmas the compositions of all the coexisting phases have been described as functions of temperature and cao content in the melt by applying a multiple linear regression method this allows a quantitative characterization of the divariant assemblage 1 an epx ol in the system cmas feo from 1275 c to 1160 c with liquid compositions ranging from mg 1 to mg 0 28 knowing the composition temperature relationships the basic t x configuration of the assemblage 1 an cpx ol has been analysed and mass balance calculations have been performed to examine the feo effect on different crystallization processes addition of feo to the system cmas transforms the thermal divide in the assemblage 1 an cpx ol to a thermal ridge and shifts the spine of the thermal ridge towards sio2 poor compositions with decreasing temperature this indicates that tholeiitic basalts can be relatively silica poor and evolve towards slightly more silica poor compositions with increasing feo content pigeonite replaces ortheonstatite as a crystallizing phase along the silica rich boundary of the assemblage 1 an cpx ol in some iron and silica rich composition olivine possibly terminates its crystallization or even starts resorption prior to pigeonite precipitation this suppresses silica enrichment in the melt crystallization paths of the assemblage 1 an cpx ol are determined by the detailed t x relations of the thermal ridge with the melt evolving away from the spine the liquid evolution trend depends strongly on the initial compositions a tholeiitic liquid can follow a moderate silica enrichment path at the same very reducing condition of there is a high modal proportion of olivine a fenner mechanism therefore is at work at the same place as a bowen mechanism

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

structural evolution of the irish variscides the effects of the variscan orogeny on the upper palaeozoic succession are recognizable throughout central and southern ireland the deformation can be zoned using structural styles and trends which illustrate a northward decrease in deformation intensity coupled with increasing control by pre variscan structures in the basement the most intense deformation occurs to the south of the dingle dungarvan line where shortening approaches 50 as a result of layer parallel shortening followed by buckling and finally thrusting the deformation is considered to have developed above a shallow dipping sole thrust which has been located offshore by the swat seismic reflection profiles cross faults which are common throughout the orogen resulted from n s shear couples this is consistent with their origin as accommodation structures due to differential shortening along strike the original shape of the munster basin has exerted a control on the distribution and overall facing of the major structures the sole thrust extends to the north of the dingle dungarvan line and the structural zonation of the orogen is due to variations in the stratigraphic level of this thrust the leinster massif is considered to be essentially autochthonous slip on the sole thrust decays towards the massif which acted as a rigid passive block and was partially responsible for the arcuate trend of the orogen

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

the problem of shearing along axial plane foliations abstract the structural significance of axial plane foliations cannot be understood unless we make a distinction between rotation of the material plane foliation and rotation of the geometrically defined x y plane of the strain ellipsoid if the foliation rotates as a material plane at any stage of deformation then its final orientation will be different from that of the x y plane it is suggested that reorientation of foliation takes place by some combination of the formation of foliation e g recrystallization along the x y plane and passive rotation of the material plane foliation in the same continuous deformation the deviation between the foliation and the x y plane is then much less than 5 degrees however because of this deviation a considerable amount of shear strain may develop along the foliation the analysis thus explains how a foliation can be approximately parallel to the x y plane and yet be a plane of shearing

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

development of slaty cleavage in a mudstone unit from the cantabrian mountains northern spain abstract a 200 m thick mudstone unit in the carboniferous of the cantabrian mountains northern spain exhibits an increase in intensity of the slaty cleavage from top to bottom which appears to be correlated with a decrease in the mean grain size average bed thickness and quartz mica ratio anastomosing cleavage domains formed by pressure solution and by kinking and rotation of the detrital micas become closer spaced wider and more continuous towards the finer grained base of the unit growth of strongly oriented new micas within the cleavage domains also appears to be correlated with the intensity of the domain development and hence with the initial lithology clay minerals have been completely replaced throughout the mudstone by muscovite paragonite and pyrophyllite during low grade metamorphism the growth of an oriented mica fabric however is restricted to samples with well developed cleavage domains

bundled slaty cleavage in laminated argillite north central minnesota abstract exceptional bundled slaty cleavage defined herein has been found in drill cores of laminated folded weakly metamorphosed argillite at several localities in the early proterozoic animikie basin of north central minnesota the cleavage domains are more closely spaced within the cleavage bundles than outside them the mean tectosilicate grain size of siltstone layers measured normal to cleavage is less in the cleavage bundles than outside them and the cleavage bundles are enriched in opaque phases and phyllosilicates relative to extra bundle segments these facts suggest that pressure solution was a major factor in bundle development if it is assumed that opaque phases have been conserved during pressure solution the modal differences in composition between intra bundle and extra bundle segments of beds provide a means for estimating bulk material shortening normal to cleavage argillite samples from the central part of the animikie basin have been shortened a minimum of about 22 as estimated by this method these estimates are similar to the shortening values derived from other strain markers in other rock types interbedded with the argillite and are also consistent with the regional pattern of deformation

the palaeoenvironment and deformation of beaconites like burrows in the old red sandstone at gortnabinna sw ireland the gortnabinna area contains a number of well preserved deformed burrows within the fluviatile old red sandstone of s ireland detailed logging of the local succession enables subdivision into four facies facies 1 represents sheet flood deposits facies 2 ephemeral stream channels facies 3 marginal sheet flood deposits and facies 4 low energy settling of fines the burrows occur in facies 1 and 4 the sediments are now folded into a large upright westward plunging anticline the fold has a well developed axial planar cleavage and is extended along strike by listric normal faults the burrows in facies 1 were originally circular and orthogonal to bedding and reveal a n s layer parallel shortening strain of 2 1 followed by a shear strain of 1 48 during folding these burrows have a bimodal distribution of diameters with peaks in the ranges 50 80 and 110 170 mm the burrows of facies 4 are sub parallel to the bedding plane and are generally curved with a maximum width of 180 mm and lengths of up to 2 3 m these burrows display passive infill following abandonment the burrows are morphologically similar though distinct from beaconites barratti which has been described from elsewhere in the old red sandstone and are tentatively interpreted as lungfish burrows

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

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

graphical analysis of the orthopyroxene pigeonite augite plagioclase equilibrium at liquidus temperatures and low pressure there are both natural and experimental observations of the coexistence of three pyroxenes orthopyroxene opx pigeonite pig augite aug with plagioclase pl commonly the assemblage occurs as an intermediate product in the following fractionation trend of a mafic magma opx aug pl opx aug pig pl aug pig pl to clarify the phase equilibria constraints on the existence of this mineral assemblage we have graphically analyzed the change in topology of an isobaric isoplethic section ol aug pl qtz with fe 25 50 where fe fe fe mg and an 50 arising from an increase in the fe value of silicate liquid the analysis shows that the stability field of the mineral assemblage opx aug pig pl is restricted and can onlycrystallize in the interval between two invariant points t 4 1 ol opx pig aug pl l and t 4 2 qtz opx pig aug pl l that emerge successively during expansion of a liquidus volume of pigeonite within the isobaric isoplethic section ol aug pl qtz at fe values lower than t 4 1 the 3 pyroxene assemblage cannot exist due to the absence of a contact surface between the primary volumes of plagioclase and pigeonite at fe values greater than t 4 2 the assemblage is unstable due to separation of the primary volumes of orthopyroxene and augite

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

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

estimation of volume changes by comparative chemical analyses in heterogeneously deformed rocks folds with mass transfer abstract this paper presents a method for calculating the volume change between the various sectors of the same heterogeneously deformed layer fold shear zone by comparing the chemical composition of deformed sectors with that of a reference sector the principle consists of considering some minerals as being insoluble illite chlorite and passively concentrated in deformed zones because of the loss of more soluble minerals quartz calcite dolomite by pressure solution simple observations can be used to test the validity of the assumptions required to calculate volume change in the analysis of a slaty matrix around a ptygmatic fold a map of values is drawn and these values are shown to be compatible with the general strain pattern for several limb hinge pairs of straight limbed folds the relations between volume change elongation parallel to limb layering l l o and the angle between limb and hinge are determined the influence of various parameters such as temperature pressure initial composition and structure of the rock on these relations is also pointed out

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

the origin of basic ultrabasic sills with s d and i shaped compositional profiles by in situ crystallization of a single input of phenocryst poor parental magma an attempt is made to develop an in situ crystallization model based on the concept of soret fractionation to explain the origin of commonly observed s d and i shaped compositional profiles in sills formed from a single pulse of phenocryst poor parental magma the model envisages that the various compositional profiles observed in sills can be interpreted in terms of different combinations of four principal units basal zone and layered series forming the floor sequence and top zone and upper border series constituting the roof sequence the basal and top zones represent mirror images of the layered and upper border series respectively and therefore are referred to as basal and top reversals it is proposed that the formation of basal and top reversals takes place through the non equilibrium soret differentiation of liquid boundary layers which form as a consequence of the temperature gradient imposed by the cold country rock in contrast the layered and upper border series originate predominantly through the crystal liquid boundary layers developing in equilibrium conditions the model permits the production of s d and i shaped compositional profiles from the same magma composition all that is necessary to produce a specific shape of compositional profile is an appropriate temperature gradient imposed by the cold country rock on the liquid boundary layers of a parental magma of a given composition

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

origin and significance of compositional layering in late precambrian sediments blue ridge province north carolina u s a abstract basal arkosic sandstones of the late precambrian grandfather mountain formation contain smallscale deformation zones usually 1 mm thick and spaced 5 to 10 mm apart the deformation zones are composed of green phengitic muscovite which concentrated in the deformation zones during pressure solution removal of quartz assuming plane strain the deformation zones have lost 34 of their area due to solution of quartz and axial ratios of strain ellipses are on the order of 16 1 in the principal plane the deformation zones and associated tight to isoclinal folds in the basal arkoses form a structural style which is transitional between ductile deformation zones in the crystalline basement and kink style folding in the interbedded siltstones and arkoses of the upper grandfather mountain formation since deformation zones may be more common in sedimentary rocks and low grade metasediments than previously realized one should exercise caution when using penetrative fabrics to unravel the structural history of multiply deformed rocks small scale deformation zones can be misinterpreted as a crenulation cleavage cutting an earlier penetrative fabric

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

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

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

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