the current state of knowledge about shatter cones introduction to the special issue shatter cones are a fracture phenomenon that is exclusively associated with shock metamorphism and has also been produced in the laboratory in several shock experiments the occurrence of shatter cones is the only accepted meso to macroscopic recognition criterion for impact structures shatter cones exhibit a number of geometric characteristics orientation apical angles striation angles sizes that can be best described as varied from case to case possible links between geometric properties with impact or crater parameters have remained controversial and the lack of understanding of the mechanism of formation of shatter cones does not offer a physical framework to discuss or understand them a database of shatter cone occurrences has been produced for this introduction paper to the special issue of meteoritics and planetary science on shatter cones distribution of shatter cones with respect to crater size and lithology suggests that shatter cones do not occur in impact craters less than a few kilometers in diameter with a few currently questionable exceptions all pertinent hypotheses of formation are presented and discussed several may be discarded in light of the most recent observations the branching fracture mechanism and the interference models proposed respectively by sagy et al 2002 and baratoux and melosh 2003 require further evaluation new observations experiments or theoretical considerations presented in this special issue promise an important step forward based on a renewed effort to resolve the enigmatic origin of these important features

impact of mascarene high variability on the east african short rains the interannual variability of east african short rains easr and its link with the mascarene high mh variation are explored using observations and reanalysis data correlation and composite analyses for flood and drought events reveal that the easr variability is strongly linked to the mh zonal displacement in particular the zonal movement of the mh eastern ridge when the mh eastern ridge is anomalously displaced to the west east of its normal position the south east se trade winds over the south indian ocean sio anomalously strengthen weaken this enhances reduces the relatively cool and dry se trade winds and induces cold warm sea surface temperature anomaly in the sio as a result convection over the western equatorial sio is suppressed enhanced and leads to rainfall deficits excess over east africa droughts in east africa are associated with a westward migration of the mh eastern ridge while the relationship is less clear for flood events and their link to an eastward migration of the mh therefore the zonal migration of the mh eastern ridge provides a novel indicator for the easr extremes especially droughts this revelation has immense social application for rainfall forecast over east africa where rainfall deficits have become more prevalent against the background of deteriorating conventional forecasts for easr droughts

the search for fullerenes in rocks from the ries impact crater since their discovery fullerenes have been reported from various geological environments one group of these findings has been related to bolide impacts e g the sudbury crater and the k t and p t boundaries impact rocks of the ries crater germany including samples of suevites metamorphosed crystalline clasts and glass bombs have been collected in the otting altebrg and seelbronn quarries no fullerenes in concentrations above 1 ppb have been found in analyzed samples laser desorption time of flight mass spectrometry ld tof ms confirmed the absence of fullerenes in the analyzed samples these results support the concept that the ries impactor was a stony meteorite

seasonal variations in the southern hemisphere storm tracks and jet streams as revealed in a reanalysis dataset abstract regional characteristics of the climatological seasonal variations in southern hemisphere sh storm tracks are examined based on a reanalysis dataset when differences in vertical structure between the subpolar and subtropical jet streams spj and stj respectively are considered the regional characteristics can be interpreted reasonably well from a potential vorticity perspective of baroclinic eddy growth and downstream development of a baroclinic wave packet eddy activity in the upper and lower tropospheres is strongest in the core region of the spj over the eastern south atlantic and indian ocean throughout the year even in austral winter when the intense stj forms over the indian ocean and south pacific showing its eddy driven nature the spj accompanies the strong surface westerlies along a well defined baroclinic zone above an intense oceanic frontal zone in this core region of the storm track low level eddy activity is strongly correlated with the local near surface baroclinicity

reply to the comments on weathering plants and the long term carbon cycle some lichens can and do promote the weathering of their substrates the authors sole interest for purposes of carbon cycle modeling is the degree of that enhancement for calcium and magnesium silicates relative to both abiotic chemical weathering due to water rock interaction and the weathering that occurs beneath higher plants the work by jackson and keller 1970 had offered the most dramatic quantitative empirical evidence for weathering rate enhancement by a primitive terrestrial organism thus reassessment of their conclusions is of considerable importance in analyzing their samples the authors used the technique of back scattered electron imaging their results showed that the ferrihydrite rich gels created by stereocaulon vulcani were formed from wind supplied dust volcanic ash and detrital rock fragments not the lichen s immediate substrate

occurrence of natural fullerenes in low grade metamorphosed proterozoic shungite from karelia russia abstract we report on the occurrence of fullerenes in proterozoic shungite 2 ga from the shungite mine kondopoga karelia russia 62 12 n 34 17 e the presence of fullerenes has been confirmed by mass spectrometry with peaks at 360 and 720 amu atomic mass unit powder x ray diffraction showing ten diffraction peaks corresponding to the fullerite structure with a 1 4201 5 nm and 13 c nuclear magnetic resonance nmr spectroscopic studies showing a peak at 143 2 ppm in the kondopoga shungite mine fullerenes occur in silty shales that have experienced greenshist facies metamorphism

land atmosphere ocean interactions in the southeastern atlantic interannual variability land atmosphere ocean interactions in the southeastern south atlantic and their connections to interannual variability are examined using a regional climate model coupled with an intermediate level ocean model in austral summer zonal displacements of the south atlantic subtropical high sash can induce variations of mixed layer currents in the benguela upwelling region through surface wind stress curl anomalies near the namibian coast and an eastward shifted sash is related to the first pacific south american mode when the sash is meridionally displaced mixed layer vertically integrated ekman transport anomalies are mainly a response to the change of alongshore surface wind stress the latitudinal shift of the sash tends to dampen the anomalous alongshore wind by modulating the land sea thermal contrast while opposed by oceanic diffusion although the position of the sash is closely linked to the phase of el nino southern oscillation enso and the southern annular mode sam in austral summer an overall relationship between benguela upwelling strength and enso or sam is absent during austral winter variations of the mixed layer ekman transport in the benguela upwelling region are connected to the strength of the sash through its impact on both coastal wind stress curl and alongshore surface wind stress compared with austral summer low level cloud cover change plays a more important role although wintertime sea surface temperature fluctuations in the equatorial atlantic are strong and may act to influence variability over the northern benguela area the surface heat budget analysis suggests that local air sea interactions dominate

exploring sea country through high resolution 3d seismic imaging of australia s nw shelf resolving early coastal landscapes and preservation of underwater cultural heritage abstract almost 2 million square km of australia s continental shelf was flooded following the termination of the last glacial maximum and with it the cultural heritage of the first arrival and coastal occupation of australia beginning some 65 000 years ago in order to prospect for this missing cultural record we must first identify submerged coastal landscapes and landforms that likely provided favourable environments for occupation and resource use however this task is challenged by the sheer size of the australian continental margin to help address this we use industry 3d seismic datasets that cover vast areas of australia s continental shelf to map seafloor bathymetry at high resolution 10 25 m our study focuses an area of 6500 square km on the mid outer shelf regions proximal to barrow island the 3d seismic bathymetry revealed a highly complex and geomorphically mature coastal landscape preserved at depths of 70 75 m below sea level including coastal barrier dunes lagoonal systems tidal flats and estuarine channels based on the depth of the submerged shorelines and reconstructed sea level curves the age range of these coastal landforms is constrained to marine isotope stage 3 57 29 ka which overlaps with the known onset of occupation at barrow island and the wider carnarvon bioregion and the adjacent pilbara such feature preservation has significant geoheritage value but also allows for human behavioural ecology modelling and provides targets for future dating and site survey

annular modes in the extratropical circulation part i month to month variability the leading modes of variability of the extratropical circulation in both hemispheres are characterized by deep zonally symmetric or annular structures with geopotential height perturbations of opposing signs in the polar cap region and in the surrounding zonal ring centered near 458 latitude the structure and dynamics of the southern hemisphere sh annular mode have been extensively documented whereas the existence of a northern hemisphere nh mode herein referred to as the arctic oscillation ao has only recently been recognized like the sh mode the ao can be defined as the leading empirical orthogonal function of the sea level pressure field or of the zonally symmetric geopotential height or zonal wind fields in this paper the structure and seasonality of the nh and sh modes are compared based on data from the national centers for environmental prediction national center for atmospheric research reanalysis and supplementary datasets the structures of the nh and sh annular modes are shown to be remarkably similar not only in the zonally averaged geopotential height and zonal wind fields but in the mean meridional circulations as well both exist year round in the troposphere but they amplify with height upward into the stratosphere during those seasons in which the strength of the zonal flow is conducive to strong planetary wave mean flow interaction midwinter in the nh and late spring in the sh during these active seasons the annular modes modulate the strength of the lagrangian mean circulation in the lower stratosphere total column ozone and tropopause height over mid and high latitudes and the strength of the trade winds of their respective hemispheres the nh mode also contains an embedded planetary wave signature with expressions in surface air temperature precipitation total column ozone and tropopause height it is argued that the horizontal temperature advection by the perturbed zonal mean zonal wind field in the lower troposphere is instrumental in forcing this pattern a companion paper documents the striking resemblance between the structure of the annular modes and observed climate trends over the past few decades

origins of fullerenes in rocks this article is a technical comment and author response to the the discovery of naturally occuring fullerenes in shunga rock samples the commenting researchers did not find detectable amounts of fullerenes in a variety of carbon rich rocks they hypothesize that the fullerenes found in the shunga sample were probably a localized event the original researchers buseck and tsipursky provide a rebuttal with further comments including parallels to other minerological occurences all agreed that more data are needed 10 refs

structure and mechanisms of the southern hemisphere summertime subtropical anticyclones abstract the three dimensional structure and dynamics of the climatological mean summertime subtropical anticyclones in the southern hemisphere sh are investigated as in the northern hemisphere nh each of the surface subtropical anticyclones over the south pacific south atlantic and south indian oceans is accompanied by a meridional vorticity dipole aloft exhibiting barotropic and baroclinic structures in its poleward and equatorward portions respectively in a manner that is dynamically consistent with the observed midtropospheric subsidence their dynamics are also similar to their nh counterpart it is demonstrated through the numerical experiments presented here that each of the sh surface anticyclones observed over the relatively cool eastern oceans can be reproduced as a response to a local near surface cooling heating couplet the cooling is mainly due to radiative cooling associated with low level maritime clouds and the heating to the east is due to sensible heat flux over the dry hea

testing for fullerenes in geologic materials oklo carbonaceous substances karelian shungites sudbury black tuff comment and reply reply buseck et al s 1992 1 discovery of fullerenes in fractures in a shungite sample enclosed in diabase from russian karelia has been followed by several substantiating reports see buseck 2002 2 p 785 as well as by conflicting reports e g ebbesen et al 1995 3 mossman et al

the keurusselka impact structure finland impact origin confirmed by characterization of planar deformation features in quartz grains although the meteorite impact origin of the keurusselkaimpact structure central finland has been established on the basis of the occurrence of shatter cones no detailed microscopic examination of the impactites from this structure has so far been made previous microscope investigations of in situ rocks did not yield any firm evidence of shock features raiskila et al 2008 kinnunen and hietala 2009 we have carried out microscopic observations on petrographic thin sections from seven in situ shatter cone samples and report here the discovery of planar fractures pfs and planar deformation features pdfs in quartz and feldspar grains the detection and characterization of microscopic shock metamorphic features in the investigated samples substantiates a meteorite impact origin for the keurusselkastructure the crystallographic orientations of 372 pdf sets in 276 quartz grains were measured using a universal stage u stage microscope for five of the seven distinct shatter cone samples based on our u stage results we estimate that investigated shatter cone samples from the keurusselkastructure have experienced peak shock pressures from approximately 2 gpa to slightly less than 20 gpa for the more heavily shocked samples the decoration of most of the pdfs with fluid inclusions also indicates that these originally amorphous shock features were altered by postimpact processes finally our field observations indicate that the exposed surface corresponds to the crater floor it is however difficult to estimate the exact diameter of the structure and the precise amount of material that has been eroded since its formation

a giant palaeoproterozoic deposit of shungite in nw russia genesis and practical applications abstract occurrences of 2 0 ga mature organic material from the lake onega area nw russia constitute one of the most remarkable accumulations of organic carbon from the palaeoproterozoic the deposit occurs in a 1000 m sedimentary volcanic succession developed over an area of 9000 km 2 with an estimated total carbon reserve exceeding 25 10 10 tonnes the organic material occurs in the form of the mineraloid shungite which is a black non crystalline semi metallic material that contains 98 wt c the shungite bearing rocks were accumulated within a volcanic continental rift setting in a non euxinic brackish water lagoonal environment developed on the rifted margin of the archaean craton the occurrences of shungite bearing rocks represent a combination of a petrified oil field petrified organosiliceous diapirs and oil spills these are exemplified by three types of deposit i in situ stratified ii migrated diapirs and iii redeposited clastic in situ stratified deposits are composed of metamorphosed oil shales 80 wt c diapiric deposits form non stratified cupolas or mushroom shaped bodies composed of shungite containing 35 75 wt sio 2 and 20 55 wt c these are considered to represent organosiliceous rocks originally gels or mud the shungite rocks show abundant shrinkage cracks cryptic fluidal textures and brecciation caused by multiple fluidisation processes the current data are consistent with either diapiric or mud volcanic origins occurrences of clastic shungite are hosted by lacustrine volcanoclastic greywackes deposited from turbiditic flows shungite occurs in rocks as shungite has a heterogeneous molecular structure in which carbon occurs as 10 nm globules irregularly distributed within carbon showing no structure the unusual physicochemical and structural properties of shungite are used in diverse industrial and environmental applications including metallurgy water purification thermolysis and organosynthesis of cyclic hydrocarbons shungite is an effective sorbent for removal of organic and inorganic substances pathogenic bacteria and heavy metals from contaminated water

subtropical dipole modes simulated in a coupled general circulation model the growth and decay mechanisms of subtropical dipole modes in the southern indian and south atlantic oceans and their impacts on southern african rainfall are investigated using results from a coupled general circulationmodeloriginallydevelopedforpredictingtropicalclimatevariations thesecond most dominant mode of interannual sea surface temperature sst variations in the southern indian south atlantic ocean represents a northeast southwest oriented dipole now called subtropical dipole mode the positive negative sst interannualanomalypole startsto grow in australspring and reachesits peakin february in austral late spring the suppressed enhanced latent heat flux loss associated with the variations in the subtropical high causes a thinner thicker than normal mixed layer thickness that in turn enhances reduces the warming of the mixed layer by the climatological shortwave radiation the positive negative pole gradually decays in austral fall because the mixed layercooling by the entrainmentis enhanced reduced mostlyowing to the larger smaller temperature difference between the mixed layer and the entrained water the increased decreased latent heat loss due to the warmer colder sst also contributes to the decay of the positive negative pole although furtherverification using longerobservational data is required the present coupled model suggests that the south atlantic subtropical dipole may play a more important role in rainfall variations over the southern african region than the indian ocean subtropical dipole

subtropical sst dipole events in the southern indian ocean sea surface temperature sst anomalies in the subtropical southern indian ocean show interannual dipole events that are seasonally phase locked to the austral summer a positive phase of the event is characterized by cold sst anomalies in the eastern part i e off australia and warm sst anomalies in the southwestern part south of madagascar such an event is found to produce above normal rainfall over many regions in south central africa the cooling of sst in the eastern part is mainly caused by the enhanced evaporation this is associated with stronger winds along the eastern edge of the subtropical high which is strengthened and shifted slightly to the south during the event on the other hand relative decrease in the seasonal latent heat loss due to reduced evaporation dominates the warming in the southwestern part evolution of such subtropical dipole events shows quite a contrast to that of the tropical dipole events discovered recently in the indian ocean

shock induced melting and vaporization of shatter cone surfaces evidence from the sudbury impact structure analytical scanning electron microscopy has been used to investigate the surface textures and compositions of newly exposed shatter cones from the 1 85 ga sudbury impact structure canada unusual surface microstructures are observed at the micron scale including silicate melt smears melt fibres and melt splats silicate and ni rich spherules up to 5 m in diameter adorn earlier formed surface features and we interpret these to be condensates formed due to shock induced vaporization of the shatter cone surfaces the development of striations on the shatter cones is attributed to shock related fracture and slip formation of melts and spherules indicates that the highest ranks of shock metamorphism stages iv and v were realized but only on a very localized scale shatter cone surfaces are therefore likely sites for the development of high pressure polymorphs and if the chemistry is appropriate fullerenes as such they may be equivalent to type a pseudotachylytes and shock veins in meteorites

stability of atmospheric co2 levels across the triassic jurassic boundary the triassic jurassic boundary 208 million years ago is associated with widespread extinctions in both the marine and terrestrial biota the cause of these extinctions has been widely attributed to the eruption of flood basalts of the central atlantic magmatic province this volcanic event is thought to have released significant amounts of co2 into the atmosphere which could have led to catastrophic greenhouse warming but the evidence for co2 induced extinction remains equivocal here we present the carbon isotope compositions of pedogenic calcite from palaeosol formations spanning a 20 myr period across the triassic jurassic boundary using a standard diffusion model we interpret these isotopic data to represent a rise in atmospheric co2 concentrations of about 250 p p m across the boundary as compared with previous estimates of a 2 000 4 000 p p m increase the relative stability of atmospheric co2 across this boundary suggests that environmental degradation and extinctions during the early jurassic were not caused by volcanic outgassing of co2 other volcanic effects such as the release of atmospheric aerosols or tectonically driven sea level change may have been responsible for this event

shatter cone and microscopic shock alteration evidence for a post paleoproterozoic terrestrial impact structure near santa fe new mexico usa article i nfo field mapping morphologic description and petrographic analysis of recently discovered shatter cones within paleoproterozoic crystalline rocks exposed over an area n 5k m 2 located 8 km northeast of santa fe new mexico usa give robust evidence of a previously unrecognized terrestrial impact structure herein we provisionally name this the santa fe impact structure the shatter cones are composed of nested sub conical curviplanar and flat joint surfaces bearing abundant curved and bifurcating striations that strongly resemble the multiply striated joint surfaces msjs documented from shatter cones at vredefort dome the cones occur as a penetrative feature in intrusive igneous and supracrustal metamorphic rocks are unusually large up to 2 m long and 0 5 m wide at the base display upward pointing apices and have subvertical northeastward plunging axes that crosscut regional host rock fabrics key characteristics of superficially similar but non shock generated conical and striated features are inconsistent with the properties of the santa fe cones in thin section sub millimeter scale dark semi opaque to isotropic veneers on cone surfaces and veinlets within cone interiors closely resemble previously described shock induced melt features microscopic grain alteration restricted generally to within 1 mm of the cone surfaces includes random fractures fluid micro inclusions sericite replacement in feldspar rare kink bands in mica optical mosaicism and decorated planar fractures pfs and planar deformation features pdfs in quartz the pfs and pdfs are dominated by a basal 0001 crystallographic orientation which indicate a peak shock pressure of 5 10 gpa that is consistent with shatter cone formation regional structural and exhumation models together with anomalous breccia units that overlie and crosscut the shatter cone bearing rocks may provide additional age constraints for the impact event the observed shatter cone outcrop area suggests that the minimum final crater diameter of the santa fe impact structure was 6 13 km

petrology and genesis of karelian shungite high rank coal abstract shungites are highly carbonaceous highly metamorphosed rocks associated with several stratigraphic levels of the lower proterozoic in karelia being a complex material shungite is very important also as oldest accumulations of concentrated organic matter the nature of shungite is still unclear despite its more than a century long study by russian and western scientists a chemical coal petrographic study of shungite has been conducted using a specially designed technique the etching of polished surfaces it is found that the shungite bed near shunga village is a coal seam with a typical set of megascopic features rather than an accumulation of bitumen this bed consists not only of sapropelic but of humic organic matter as well unlike other biogenic structures from precambrian coal such as the huron series michigan lake the structures established in shungite near shunga village have a more complex plant composition organic matter from various types of shungite bearing rocks show different petrographic and chemical properties thus organic matter of sapropelic nature from silicate rocks with traces of stromatolite texture differs from the coal matter composing the shunga bed shungites are the most metamorphosed coals among all those known at present and they are assigned here to metaanthracite rank the results obtained show a new insight into the biogenic remains composing an ancient coal bed and in terms of the present stratigraphic scale allow the beginning of coal accumulation to be placed in the proterozoic although the possibility of a non precambrian age cannot be ruled out

vredefort shatter cones revisited shatter cones have been described from a number of circular and polygonal structures worldwide the origin of which has been alternatively ascribed to the impacts of large extraterrestrial projectiles or to catastrophic endogenic processes despite their association with enigmatic catastrophic processes the nature of shatter cones and the physics involved in their formation have not been comprehensively researched results of detailed field and laboratory studies of shatter cones from three areas in the collar of the vredefort dome in south africa are presented vredefort shatter cones are directly related to a widely displayed fracture phenomenon termed multiply striated joint sets msjs msjs are planar to curviplanar fractures occuring at spacings of 1 to several millimeters the joint sets have a fractal character when a new measurement protocol is used in the field involving study of all joint surfaces and all steps and striae exposed on these surfaces new information is gained on the genesis and significance of the msjs and on their relationship to striated conical fractures the internal constitution of a rock specimen with msjs was examined in detail by documenting the precise geometry of many fractures in a suite of parallel thin sections transecting the specimen the steps and striae on shatter cone surfaces have the characteristics of displacement fractures microfaults along which evidence of melting is observed shatter cone and msjs surfaces are often covered with glassy films we evaluate whether these fracture phenomena are linked to the formation of pseudotachylitic friction melt our field and petrographic observations can be interpreted as consistent with the generation of shatter cones msjs relatively late in the formation of the vredefort structure this scenario contrasts sharply with the widely held view that shatter cones are formed during the early compression phase of a shock event that affected horizontal strata

testing for fullerenes in geologic materials oklo carbonaceous substances karelian shungites sudbury black tuff comment and reply the presence of low concentrations of fullerenes has been reported from numerous terrestrial and meteoritic sources buseck 2002 1 in a recent paper mossman et al 2003 2 present mass spectra of carbonaceous substances using laser desorption ionization ldi and high resolution electron

an antarctic circumpolar wave in surface pressure wind temperature and sea ice extent the southern ocean is the only oceanic domain encircling the globe it contains the strong eastward flow of the antarctic circumpolar current and is the unifying link for exchanges of water masses at all depths between the world s major ocean basins1 as these exchanges are an important control on mean global climate the southern ocean is expected to play an important role in transmitting climate anomalies around the globe interannual variability has been often observed at high southern latitudes and observations of sea ice extent suggest that such features propagate eastwards around the southern ocean2 3 here we use data from a variety of observational techniques to identify significant interannual variations in the atmospheric pressure at sea level wind stress sea surface temperature and sea ice extent over the southern ocean these anomalies propagate eastward with the circumpolar flow with a period of 4 5 years and taking 8 10 years to encircle the pole this system of coupled anomalies which we call the antarctic circumpolar wave is likely to play an important role in climate regulation and dynamics both within and beyond the southern ocean

evidence for fullerenes in solid bitumen from pillow lavas of proterozoic age from mitov bohemian massif czech republic abstract andesitic pillow lavas containing biogenic solid bitumen sb are a constituent of a neoproterozoic volcanosedimentary sequence tepla barrandian unit bohemian massif in the mitov area of the czech republic a black shale formation that is crosscut by these andesitic basalts is 565 ma old carbon disulfide extracts of two powdered samples of sb contain 0 2 and 0 3 ppm of c 60 respectively as determined by high pressure liquid chromatography the peak assignment based on retention time is fully supported by high resolution electron ionization mass spectrometry ei ms no c 70 was detected nor was c 60 found in two other sb samples from this locality other investigated carbonaceous samples from bohemia coals and anthracites of upper paleozoic age and anthraxolite graphitoids and graphite of upper proterozoic age did not contain fullerenes at concentrations above the detection limit of 0 01 ppm the absence of c 60 in these samples was confirmed by ei ms the proposed mechanism of fullerene formation involves a primary algal phase generation of a hydrocarbonaceous mixture in the course of thermal evolution of the sedimentary series and their high temperature transformation related to the extrusion of basalt an important feature for fullerene conservation was the enclosure of fullerenes in sb with a structure similar to glasslike carbon where the fullerene was protected against oxidation

micro shock deformation adjacent to the surface of shatter cones from the beaverhead impact structure montana petrographic and transmission electron microscopy tem study reveals that planar fractures pseudotachylite pst veinlets and planar deformation features pdf in quartz and k feldspar grains are developed only within 2 mm of the surface of shatter cones in proterozoic arkosic sandstones from the beaverhead montana impact structure this unique association reinforces the impact shock origin attibuted to all these shock metamorphic features no high pressure sio 2 polymorphs were found in the pst but possibly this is because these cones formed far from the center of the impact structure in a shock pressure zone below the stability field of the high pressure polymorphs

the nature distribution and genesis of the coesite and stishovite associated with the pseudotachylite of the vredefort dome south africa abstract the vredefort dome represents the uplift centre of a well known 2 00 ga old impact structure of unusually large magnitude shock features like shatter cones planar features and high pressure silica polymorphs are common the present study deals with the description mode of occurrence field distribution and post shock metamorphic alteration of coesite and stishovite which were poorly documented up to now these minerals occur as unusually large crystals in the quartzite of the wall rock in contact with very thin pseudotachylite veins in the pseudotachylite itself which can be interpreted as a friction and or a shock recovery melt fine needles of kyanite are ubiquitous it is proposed that these thin pseudotachylites a type formed during the transit of the shock wave they preceded the development of thick pseudotachylite and microbreccia veins b type which formed during the tensional period which immediately followed from comparison with the model of formation of high pressure polymorphs in porous sandstone it is suggested that higher pressure and stress was concentrated along the a type veins at the arrival of the shock front at this time the quartz was transformed into a high pressure phase which was probably poorly crystalline behind the shock front that is during the rarefaction the pressure was progressively released and the polymorphs crystallized from this initial high pressure phase stishovite crystallized first followed by coesite the high pressure conditions may have lasted an unusually long time due to the magnitude of the vredefort impact this long time probably about one second may account for the large size of the coesite and stishovite crystals most of the high pressure silica polymorphs are corroded to a variable degree by secondary quartz and preserved only in a restricted area of the impact structure this alteration is attributed to post shock metamorphism due to the temperature of the rock before impact plus the heat left after shock recovery some of the evidence put forward by authors against the impact model is discussed according to the facts arising from this investigation it is concluded that an origin by impact remains the simplest and most realistic model to explain the origin of the vredefort dome

enso modoki impact on the southern hemisphere storm track activity during extended austral winter 1 impacts of the recently discovered enso modoki phenomena on extended winter storm track activity in the southern hemisphere are examined using the observed rainfall sea surface temperature and reanalyzed upper air circulation data for the period 1979 2004 the partial correlation technique is utilized to distinguish the impact of enso modoki events from those of the enso and indian ocean dipole iod el nino modoki events introduce an anomalous blocking over central eastern australia which suppresses the storm track activity from southwest till centraleast reducing the storm associated rainfall in southeastern tip and portions of the southeast on the other hand the storm track activity in central argentina is enhanced owing to the strengthened upper air westerlies in this region the impacts from the enso modoki events are apparently stronger than the individual impacts from the enso and iod events

black carbon in soils and sediments analysis distribution implications and current challenges this review highlights the ubiquity of black carbon bc produced by incomplete combustion of plant material and fossil fuels in peats soils and lacustrine and marine sediments we examine various definitions and analytical approaches and seek to provide a common language bc represents a continuum from partly charred material to graphite and soot particles with no general agreement on clear cut boundaries formation of bc can occur in two fundamentally different ways volatiles recondense to highly graphitized soot bc whereas the solid residues form char bc both forms of bc are relatively inert and are distributed globally by water and wind via fluvial and atmospheric transport we summarize chronologically the ubiquity of bc in soils and sediments since devonian times differentiating between bc from vegetation fires and from fossil fuel combustion bc has important implications for various biological geochemical and environmental processes as examples bc may represent a significant sink in the global carbon cycle affect the earth s radiative heat balance be a useful tracer for earth s fire history build up a significant fraction of carbon buried in soils and sediments and carry organic pollutants on land bc seems to be abundant in dark colored soils affected by frequent vegetation burning and fossil fuel combustion thus probably contributing to the highly stable aromatic components of soil organic matter we discuss challenges for future research despite the great importance of bc only limited progress has been made in calibrating analytical techniques progress in the quantification of bc is likely to come from systematic intercomparison using bcs from different sources and in different natural matrices bc identification could benefit from isotopic and spectroscopic techniques applied at the bulk and molecular levels the key to estimating bc stocks in soils and sediments is an understanding of the processes involved in bc degradation on a molecular level a promising approach would be the combination of short term laboratory experiments and long term field trials

frontolysis by surface heat flux in the agulhas return current region with a focus on mixed layer processes observation and a high resolution cgcm detailed mechanisms for frontogenesis frontolysis of the agulhas return current arc front defined as the maximum of the meridional sea surface temperature sst gradient at each longitude within the arc region 40 50 e 55 35 s are investigated using observational datasets due to larger smaller latent heat release to the atmosphere on the northern southern side of the front the meridional gradient of surface net heat flux nhf is found throughout the year in austral summer surface warming is weaker stronger on the northern southern side and thus the nhf tends to relax the sst front the weaker stronger surface warming at the same time leads to the deeper shallower mixed layer on the northern southern side this enhances the frontolysis because deeper shallower mixed layer is less more sensitive to surface warming in austral winter stronger weaker surface cooling on the northern southern side contributes to the frontolysis however deeper shallower mixed layer is induced by stronger weaker surface cooling on the northern southern side and suppresses the frontolysis because the deeper shallower mixed layer is less more sensitive to surface cooling therefore the frontolysis by the nhf becomes stronger weaker through the mixed layer processes in austral summer winter the cause of the meridional gradient of mixed layer depth is estimated using diagnostic entrainment velocity and the monin obukhov depth furthermore the above mechanisms obtained from the observation are confirmed using outputs from a high resolution coupled general circulation model causes of model biases are also discussed

search for extractable fullerenes in clays from the cretaceous tertiary boundary of the woodside creek and flaxbourne river sites new zealand abstract when fullerenes were first discovered to form spontaneously in condensing carbon vapors kroto et al 1985 it was suggested that they might be widely distributed in the universe searches for fullerenes in meteorites see devries et al 1993 were unsuccessful but c 60 and c 70 were reported to occur on earth in samples of shungite a meta anthracite from a deposit near shunga russia buseck et al 1992 and in fulgurite a substance formed when lightning strikes certain soils or rocks daly et al 1993 the occurrence of fullerenes in shungite is particularly surprising since fullerene synthesis in the laboratory has always involved gas phase chemistry at temperatures over 1000 c such conditions may be attained during lightning strikes but shungite is believed to have formed from carbonaceous material creeping into fissures of a precambrian rock which metamorphosed under extreme pressures if the original carbonaceous material did not already contain fullerenes perhaps from wildfires they must have formed during the metamorphism by as yet unknown solid or liquid phase mechanisms

subtropical indian ocean sst dipole events and southern african rainfall an atmospheric general circulation model agcm is used to examine how the regional atmospheric circulation and rainfall over southern africa respond to a recently observed dipole in subtropical sea surface temperature sst over the south indian ocean observations suggest that when sst is warm to the south of madagascar and cool off western australia increased summer rains occur over large areas of southeastern africa the model results suggest that this sst pattern leads to increased rainfall via enhanced convergence of moister than average air over the region increased evaporation occurs over the warm pole in the south west indian ocean and this moist air is advected towards mozambique and eastern south africa as a result of the low pressure anomaly generated over this pole which strengthens the onshore flow

testing for fullerenes in geologic materials oklo carbonaceous substances karelian shungites sudbury black tuff fullerenes have been reported from diverse geologic environments since their discovery in shungite from karelian russia our investigation is prompted by the presence of onionskin like structures in some carbonaceous substances associated with the fossil nuclear fission reactors of oklo gabon the same series of extractions and the same instrumental techniques laser desorption ionization and high resolution mass spectroscopy electron impact mass spectroscopy were employed to test for fullerenes in samples from three different localities two sites containing putative fullerenes sudbury basin and russian karelia and one new location oklo gabon we confirm the presence of fullerenes c 6 0 and c 7 0 in the black tuff of the onaping formation impact breccia in the sudbury basin but we find no evidence of fullerenes in shungite samples from various locations in russian karelia analysis of carbonaceous substances associated with the natural nuclear fission reactors of oklo yields no definitive signals for fullerenes if fullerenes were produced during sustained nuclear fission at oklo then they are present below the detection limit 100 fmol or they have destabilized since formation contrary to some expectations geologic occurrences of fullerenes are not commonplace

millennial scale climate instability during the early pleistocene epoch climate proxy records of the past 100 000 years show that the earth s climate has varied significantly and continuously on timescales as short as a few thousand years 1 7 similar variability has also recently been observed for the interval 340 500 thousand years ago8 these dramatic climate shifts expressed most strongly in the north atlantic region may be linked to and possibly amplified by alterations in the mode of ocean thermohaline circulation4 5 6 7 8 9 here we use sediment records of past iceberg discharge and deep water chemistry to show that such millennial scale oscillations in climate occurred over one million years ago this was a time of significantly different climate boundary conditions not only was the early pleistocene epoch generally warmer but global climate variations were governed largely by changes in earth s orbital obliguity our results suggest that such millennial scale climate instability may be a pervasive and long term characteristic of earth s climate rather than just a feature of the strong glacial interglacial cycles of the past 800 000 years

dependence of the climatological axial latitudes of the tropospheric westerlies and storm tracks on the latitude of an extratropical oceanic front 1 major storm tracks where migratory cyclones and anticyclones recurrently develop are observed around midlatitude oceanic frontal zones with strong meridional gradient of sea surface temperature sst a set of atmospheric general circulation model experiments is performed with zonally uniform sst prescribed at the model lower boundary the latitudinal sst profile for each hemisphere is characterized by a single front the frontal latitude is varied systematically from one experiment to another while the intensity of the frontal gradient is kept unchanged though idealized the experiments reveal a climatological tendency for a low level storm track to be organized along or slightly poleward of the sst front if located in the subtropics or midlatitudes as a surface manifestation of an eddy driven polar front jet pfj surface westerly axis tends to form on the poleward flank of the front this anchoring effect of the sst front is also hinted at upper levels but the climatological positions of the storm track and pfj are less sensitive to the frontal latitude for the sst front at subpolar latitude the joint primary axes of the upper level storm track and pfj form in midlatitudes away from the sst front their positions correspond to their counterpart simulated with a particular sst profile from which frontal gradient has been removed suggesting that the anchoring effect of a subpolar sst front on the storm track and pfj is overshadowed by atmospheric internal dynamics namely the self maintenance mechanism of a midlatitude storm track and pfj through their interactions

zonal movement of the mascarene high in austral summer temporal variations in the mascarene high mh defined by the sea level pressure slp maximum within the region of 40 120 e 50 10 s in austral summer november january were investigated using atmospheric reanalysis datasets the mh longitudinal position has a dominant timescale at about 6 years which appears to be independent of the mh intensity variation the mh longitudinal movement is caused by a combination of slp variations in the eastern south indian ocean esio and in the western south indian ocean wsio as follows 1 pressure variations in the esio region are confined to the lower atmosphere up to the mid troposphere and are associated with the el nino southern oscillation events 2 pressure variations in the wsio region characterized by a quasi barotropic structure throughout the troposphere are related to the meridional movement of storm track sea surface temperature anomalies associated with the longitudinal movement of the mh show a southwest northeast dipole structure but this is shifted 10 westward in longitude compared with that associated with the mh intensity

geological fullerenes review and analysis abstract fullerenes have been reported from numerous terrestrial and meteoritic sources but only at low concentrations the occurrences are associated with localized energetic events such as lightning impacts of extraterrestrial objects and wildfires great interest has also been generated by a series of papers that report noble gases with anomalous isotopic compositions encapsulated within fullerenes in spite of all of the published work many unresolved questions remain about the identity and formation of fullerenes in geological environments

exogenic and endogenic breccias a discussion of major problematics abstract pseudotachylitic breccias impact melt rock ultra cataclasites and even ultramylonites may macroscopically be of very similar appearance even detailed optical microscopic work may not suffice to identify the actual type of melt rock studied the difficulties to distinguish different tectonically produced breccias fault rocks and impact breccias for which no uniformly accepted nomenclature exists are examined and the various formational processes friction melting or shock melting at the macro and micro scales are discussed special emphasis is placed on the occurrence of different and multiple breccia types within impact structures where not only impact induced friction melt and impact melt may occur but where tectonically produced fault rocks that are not related to the impact event may further complicate the breccia situation melting on shatter cone surfaces and its likely formation the proposed origin as distal impact breccia of certain diamictites and problems with carbonate breccias and caused by metamorphic overprint on breccias are discussed it is cautioned not too easily to reach generalized conclusions for example with regard to the usage of the a and b type pseudotachylite terminology areas in need of further breccia studies if possible in close collaboration between impact and tectonic researchers are emphasized