effects of asteroid and comet impacts on habitats for lithophytic organisms a synthesis asteroid and comet impacts can have a profound influence on the habitats available for lithophytic microorganisms using evidence from the haughton impact structure nunavut canadian high arctic we describe the role of impacts in influencing the nature of the lithophytic ecological niche impact induced increases in rock porosity and fracturing can result in the formation of cryptoendolithic habitats in some cases and depending upon the target material an increase in rock translucence can yield new habitats for photosynthetic cryptoendoliths chasmoendolithic habitats are associated with cracks and cavities connected to the surface of the rock and are commonly increased in abundance as a result of impact bulking chasmoendolithic habitats require less specific geological conditions than are required for cryptoendolithic habitats and their formation is likely to be common to most impact events impact events are unlikely to have an influence on epilithic and hypolithic habitats except in rare cases where for example the formation of impact glasses might yield new hypolithic habitats we present a synthetic understanding of the influence of asteroid and comet impacts on the availability and characteristics of rocky habitats for microorganisms

rock surface modeling as a tool to assess the morphology of inland notches mount carmel israel abstract inland notches are elongated c shape indentations carved into hard dense carbonate rocks of the mediterranean climate zone in recent years these unique features became of particular interest as geoindicators of denudation and slope erosion processes the study goals are to learn the processes acting upon the notches cavity by 1 examining the micromorphology of the backwall 2 identifying and classifying zones of erosion 3 learning the surface flow pattern and 4 proposing an erosion mechanism induced by exfoliation to this end a machine learning algorithm was designed using the microstructure texture streamlines formation and potential focal flow the workflow uses data from terrestrial laser scanning applies high resolution textural and curvature analyses and trains an artificial neural network to the different segments of the notch the reconstructed surface model shows division into three distinct belts within the cavity surface 1 the spalled belt sb 2 the transition zone belt tz and 3 the deposition belt db each belt owes its distinct microtopography implying on different geomorphic processes the newly developed methodology improves the recognition of streamline networks along the cavity backwall which mimic alluvial networks the organization of the reconstructed micro channels is similar to drainage basin systems where first order channels developed upstream converge into larger ones and diverge as distributaries as the gradient decreases depositing tufa along the notches base

endolithic biodegradation of cool water skeletal carbonates on scott shelf northwestern vancouver island canada abstract biodegradation of shell material is widespread in the cool water skeletal carbonate deposits on scott shelf northwestern vancouver island and is especially evident in the large aragonitic bivalves glycymeris and humilaria major primary sediment contributors ten types of endolithic microborings have been identified in the shells including representatives of green algae e g ostreobium quekettii blue green algae e g plectonema terebrans scytonema sp fungi bacteria and clionid sponges as well as macroborings of phoronids polychaetes and naticid gatropods microcrystalline carbonate is not precipitated in vacated bores boring physically weakens the shells rendering them more prone to mechanical abrasion during sediment transport and bioturbation and to biological abrasion by grazing benthos tumbling experiments demonstrate that the rate of carbonate mud production is much greater for bored as compared to fresh bivalve shells and that mud production rates decrease with tumbling time because most endolithic microborings are confined to the periphery of grains boring also increases significantly the porosity and surface area of skeletal grains and destroys their organic matrix making them susceptible to maceration and dissolution on cool water shelves fostered by the generally low rates of carbonate production and accumulation many aragonitic bivalve shells on scott shelf have become thoroughly degraded through a combination of endolithic microboring maceration and dissolution within about 1000 years in ambient sea water in geologic terms such selective taphonomic loss of skeletal material may be considerable in ancient temperate shelf limestones and should be evaluated when interpreting their paleoecology and paleoenvironments

colonization strategies of lithobiontic microorganisms on carbonate rocks biogenic weathering is caused by the action of lithobiontic organisms homogeneous carbonates are predominantly colonized by endolithic species that actively penetrate the rock substratum independent of already existing pores or fissures the organisms construct a system of ducts and cavities by active dissolution of the substratum a fresh noncolonized surface is penetrated by algae and ascomycetes in the first and second year after exposure to the environment the establishment of complex colonization patterns on and in the substratum by lichens takes several years in spite of the primary deteriorative effect on their substratum by the organisms long term endolithic growth also involves mechanisms that stabilize and preserve the rock surface morphology a tightly woven cellular network may strengthen the colonized stone this feature is of importance when natural and building stone are affected by biogenic weathering phenomena

haughton impact structure structural and morphological aspects haughton is a complex meteorite impact structure of tertiary age on devon island in the canadian arctic the 20 5 km diameter site was formed in essentially flat lying paleozoic carbonates roughly 1700 m in thickness overlying precambrian gneisses the structure comprises three concentric rings surrounding a central basin with interior peaks the outer ring diameter 20 5 km is an annulus of peaks separating the allen bay dolomites of the regional plateau from the same unit that has been downdropped towards the crater interior along a series of circumferential faults the middle ring of peaks diameter 14 15 km comprises both faulted allen bay dolomites and blocks of the underlying bay fiord formation uplifted 250 m hills of the inner elliptical ring 3 5 5 5 km in diameter are also formed from bay fiord formation and the underlying eleanor river formation brought up 600 m an interconnected series of normal faults occupies most of the annulus between the inner and outer rings within the central b

an extraordinary example of photokarren in a sandstone cave cueva charles brewer chimanta plateau venezuela biogeomorphology on a small scale a distinctive suite of small scale erosional forms that are oriented towards the light occur close to the entrance of cueva charles brewer a large cave in a sandstone tepui in se venezuela these are the third example of photokarren ever studied in the world the other two being from borneo and ireland they are the only photokarren ever described from sandstone and the only example from a non carbonate environment the host rock is a poorly lithified unit of the precambrian quartz arenite of the roraima supergroup the forms are all oriented towards the light at 30 regardless of rock surface orientation the primary negative erosional form is the tube coalescence of tubes results in the positive remnant forms of rods pinnacles and cones the final stage is a bumpy wavy surface of degraded cones the size of the features varies with erosion rate and details of the form vary with development stage the main population averages 4 4 cm in depth with 55 of the surface eroded this is divided into 10 tubes 70 rods 10 cones 5 linear valley and 5 wavy lowland the micro ecosystem includes many bacteria diatoms red algae green algae liverworts and oribatid mites but surprisingly no cyanobacteria the presence of a surface biofilm inside the forms but not on the remnant rock surface and in the non degraded forms the direct relationship of biomass with depth suggests that biological activity is the dominant control on development in addition direct bacterial corrosion was noted these same features occur to varying extents in the photokarren of borneo and ireland and the model for development that we present provides a unifying theory for all photokarren this study also includes the first published petrographic analysis of uppermost unit of the mataui formation

inland notches implications for subaerial formation of karstic landforms an example from the carbonate slopes of mt carmel israel abstract inland notches are defined herein as horizontal c shaped indentations developed on the carbonate slopes or cliffs in the mediterranean to semi arid zones the notches are shaped like half tubes that extend over tens or hundreds of meters along the stream valley slopes in mt carmel a series of 127 notches have been mapped on average their height and width are 2 2 5 m but they can reach 6 m in height and 9 5 m in width the geomorphic processes that create a notch combine chemical mechanical and biogenic weathering which act together to generate initial dissolution and later flake weathering exfoliation of the bed forming the notch cavity we propose an epikarstic subaerial mechanism for the formation and evolution of the notches the notches are unique landforms originating from the dissolution and disintegration of the rock under subaerial conditions by differential weathering of beds with different petrographic properties the notches follow specific beds that enable their formation and are destroyed by the collapse of the upper bed the formation and destruction alternate in cyclical episodes and therefore the notches are local phenomena that vary over time and space

investigation of young water inflow in karst aquifers using sf6 cfc 3h he 85kr 39ar and stable isotope components abstract karst aquifers are known for their wide distribution of water transfer velocities from this observation a multiple geochemical tracer approach seems to be particularly well suited to provide a significant assessment of groundwater flows but the choice of adapted tracers is essential in this study several common tracers in karst aquifers such as physicochemical parameters major ions stable isotopes and 13c to more specific tracers such as dating tracers 14c 3h 3h 3he cfc 12 sf6 and 85kr and 39ar were used in a fractured karstic carbonated aquifer located in burgundy france the information carried by each tracer and the best sampling strategy are compared on the basis of geochemical monitoring done during several recharge events and over longer time periods months to years this study s results demonstrate that at the seasonal and recharge event time scale the variability of concentrations is low for most tracers due to the broad spectrum of groundwater mixings the tracers used traditionally for the study of karst aquifers i e physicochemical parameters and major ions efficiently describe hydrological processes such as the direct and differed recharge but require being monitored at short time steps during recharge events to be maximized from stable isotopes tritium and cl contents the proportion of the fast direct recharge by the largest porosity was estimated using a binary mixing model the use of tracers such as cfc 12 sf6 and 85kr in karst aquifers provides additional information notably an estimation of apparent age but they require good preliminary knowledge of the karst system to interpret the results suitably the cfc 12 and sf6 methods efficiently determine the apparent age of baseflow but it is preferable to sample the groundwater during the recharge event furthermore these methods are based on different assumptions such as regional enrichment in atmospheric sf6 excess air and flow models among others 85kr and 39ar concentrations can potentially provide a more direct estimation of groundwater residence time conversely the 3h 3he method is inefficient in the karst aquifer for dating due to 3he degassing

weakening of gneiss surfaces colonized by endolithic lichens in the temperate climate area of northwest italy a role of lithobionts in geomorphological processes is increasingly argued but the spatio temporal scale of their impact is largely unexplored in many ecosystems this study first characterizes in the temperate zone northwest italy the relationships between lithobiontic communities including endolithic lichens and the hardness of their siliceous rock substrate villarfocchiardo gneiss the communities are characterized on humid and xeric quarry surfaces exposed for decades and natural outcrops exposed for centuries in terms of lichen and microbial constituents using a combined morphological and molecular approach and with regard to their development on and within the gneiss a lichen species belonging to acarosporaceae polysporina sarcogyne acarospora group needing taxonomic revision chasmoendolithically colonizes both the humid and xeric quarry surfaces on which epilithic cyanobacterial biofilms and epilithic pioneer lichens respectively occur light and electron microscopic observations show the development of the endolithic thalli within rock microcracks and the hyphal penetration along crystal boundaries down to depths of 1 to 3 mm more pronounced within the humid surfaces such colonization patterns are likely related to biogeophysical deterioration while no chemical alteration characterizes minerals contacted by the endolithic lichen by contrast on natural outcrops where the endolithic colonization is negligible a reddish rind below epilithic lichens indicates chemical weathering processes schmidt hammer measurements highlight that the endolithic lichens deeply affect the hardness of the gneiss down to 60 with respect to fresh controls and surfaces only colonized by cyanobacteria exerting a significantly higher weakening effect with respect to the associated epilithic lithobionts the phenomenon is more remarkable on humid than on xeric quarry surfaces and natural outcrops where epilithic lichens are likely involved in long term hardening processes supporting surface stabilization endolithic lichens are thus active biogeomorphological agents at the upper millimetric layer of siliceous rocks in temperate areas exerting their weakening action during the early decade scaled stages of surface exposure copyright 2015 john wiley sons ltd

syn depositional alteration of coral reef framework through bioerosion encrustation and cementation taphonomic signatures of reef accretion and reef depositional events the development of coral reef framework and the preservational character of both in situ and rubble coral is strongly influenced by a range of physical chemical and biologically mediated taphonomic processes these operate at or just below the reef framework water interface and can be defined as having either a constructive or destructive effect upon primary reef framework i e coral constituents constructional activities add additional calcium carbonate to the primary framework structure via secondary framework growth and early cementation destructive processes which remove or degrade primary and secondary framework carbonate are associated with the effects of either physical mainly storm disturbance or biological erosion termed bioerosion key bioeroding groups include the grazing fish and echinoid groups as well as the activities of an array of infaunal borers these include specific groups of sponges bivalves and worms termed macroborers as well as cyanobacteria chlorophytes rhodophytes and fungi termed microborers the relative importance of each process and the rates at which they operate vary spatially across individual reef systems in addition many of these processes leave distinctive signatures on or in the coral framework in some cases e g calcareous encrusters these are the skeletons of the organisms themselves whilst in other cases the organism may leave behind a trace of their activity e g macro and microborers these represent useful palaeoenvironmental tools firstly because they often have good preservation potential and secondly because the range and extent of many of the individual species groups and processes involved exhibit reasonably well constrained environment and or depth related distributions as a result these taphonomically important organisms or processes can be used to delineate between reef environments in core or outcrop and to aid the interpretation of reef depositional processes and events this review summarises current understanding regarding the distribution of these species processes within contemporary reef settings and considers the suites of taphonomic signatures that may aid in the recognition and interpretation of depositional environments and events

impact induced impoverishment and transformation of a sandstone habitat for lithophytic microorganisms sandstones are a common habitat for lithophytic microorganisms including cryptoendoliths we describe laboratory experiments on the colonization of impact metamorphosed sandstones from the haughton impact structure canadian high arctic colonization experiments with the coccoid cyanobacterium chroococcidiopsis sp and the motile gram positive bacterium bacillus subtilis show that in contrast to initially low porosity crystalline target rocks which can become more porous as a result of impact bulking by closing pore spaces the sedimentary cryptoendolithic habitat can be impoverished by impact however the heterogeneous distribution of collapsed pores melt phases and subsequent recrystallization results in heterogeneous colonization patterns cavities and vesicles formed during melting can yield new habitats for both cryptoendoliths and chasmoendoliths manifested in the natural cryptoendolithic colonization of shocked sandstones by contrast post impact thermal annealing and recrystallization of impact melt phases destroys the cavities and vesicles in extreme cases complete recrystallization of the rock fabric makes the material suitable only for epilithic and potentially hypolithic colonists these experiments further our understanding of the influence of the target lithology on the effects of asteroid and comet impacts on habitats for lithophytic microorganisms

geophysical research on the kardla impact structure hiiumaa island estonia the 4 km wide and 500 m deep circular kardla impact structure in hiiumaa island estonia of middle ordovician age 455 ma is buried under upper ordovician and quaternary sediments to constrain the geophysical models of the structure petrophysical properties such as magnetic susceptibility natural remanent magnetization nrm density electrical conductivity porosity and p wave velocity were measured on samples of crystalline and sedimentary rocks collected from drill cores in different parts of the structure and the surrounding area the results were used to interpret the central gravity anomaly of 3 mgal and the magnetic anomaly of 100 nt and also the surrounding weak positive anomalies revealed by high precision survey data the unshocked granitic rocks outside the structure have a mean density of 2630 kgm 3 their shocked counterparts have densities of 2400 kgm 3 at a depth of 500 m increasing up to 2550 kgm 3 at a depth of 850 m porosity and electrical conductivity decrease but p wave velocity increases as density increases away from the impact point thus the gradual changes in the physical properties of the rocks as a function of radial distance from the crater centre are consistent with an impact origin for kardla as in many other impact structures the magnetization of the shocked rocks are also clearly lower than those of unshocked target rocks a new geophysical and geological model of the kardla structure is presented based on geophysical field measurements and data on gradual changes in petrophysical parameters of the shocked target and overlying rocks together with structural data from numerous boreholes an important feature of this model is the lack of an observable geophysical signature of the central uplift observed in drillcores

underground renewal time and mixing of the main mineral waters of tunisia a multi tracer study bottled waters are increasingly popular in tunisia most of them come from groundwaters thus raising the question of the long term availability of the mineral groundwater resources water collected from production springs or wells of eleven mineral waters of tunisia among the main commercial brands were analyzed for tritium 3h helium 3 sf6 cfcs and carbon 14 tracer tracer plots indicate that all of the groundwaters of our data set are a mixture of modern rainwater with older groundwater flow waters that are beyond the time scale of the transient tracers 14c data suggest that the age of these old waters which constitute the main water reservoir is of the order of radiocarbon half life or more most of the studied sites have groundwater renewal times in the range 50 150 years for the sites where tracer concentrations are the most diluted by old waters this value logically increase to several centuries

diurnally modulated cumulus moistening in the preonset stage of the madden julian oscillation during dynamo abstractatmospheric soundings radar and air sea flux measurements collected during dynamics of the madden julian oscillation dynamo are employed to study mjo convective onset i e the transition from shallow to deep convection in the tropical indian ocean the findings indicate that moistening of the low midtroposphere during the preonset stage of the mjo is achieved by simultaneous changes in the convective cloud population and large scale circulation namely cumuliform clouds deepen and grow in areal coverage as the drying by large scale subsidence and horizontal westerly advection wane the reduction of large scale subsidence is tied to the reduction of column radiative cooling during the preonset stage which ultimately links back to the evolving cloud population while net column moistening in the preonset stage is tied to large scale circulation changes a new finding of this study is the high degree to which the locally driven diurnal cycle invigorates convective clouds and cumulus moiste

residence time mineralization processes and groundwater origin within a carbonate coastal aquifer with a thick unsaturated zone this study aims at establishing groundwater residence times identifying mineralization processes and determining groundwater origins within a carbonate coastal aquifer with thick unsaturated zone and lying on a granitic depression a multi tracer approach major ions sio2 br ba sr2 18o 2h 13c 3h ne ar combined with a groundwater residence time determination using cfcs and sf6 allows defining the global setting of the study site a typical mineralization conditioned by the sea sprays and the carbonate matrix helped to validate the groundwater weighted residence times from using a binary mixing model terrigenic sf6 excesses have been detected and quantified which permits to identify a groundwater flow from the surrounding fractured granites towards the lower aquifer principally the use of cfcs and sf6 as a first hydrogeological investigation tool is possible and very relevant despite the thick unsaturated zone and the hydraulic connexion with a granitic environment

the lithobiontic ecological niche with special reference to microorganisms abstract revised terminology is proposed that describes the ecological niches of microorganisms within hard mineral substrates organisms attached to the external surfaces of the rock are termed epiliths while those in the interior of the rock are all termed endoliths the latter are called chasmoendoliths if they inhabit fissures in rocks cryptoendoliths if they dwell within structural cavities and euendoliths if they actively penetrate calcareous substrates

bathymetric zonation of modern microborers in dead coral substrates from new caledonia implications for paleodepth reconstructions in holocene corals abstract microboring endoliths were studied in dead modern corals collected at various depths and in growth position on la surprise atoll in new caledonia eight taxa of microborers were regularly observed three cyanobacteria hyella caespitosa mastigocoleus testarum and plectonema terebrans two chlorophytes ostreobium quekettii and phaeophila dendroides and three fungal forms dodgella priscus and two unidentified fungi the relative abundance of each taxon was determined in the modern corals throughout the studied sampling interval from 0 down to 40 m water depth this allowed us to propose for the first time a bathymetric model based on microendolith assemblages colonizing in situ hard substrates of corals in this model the occurrence of the cyanobacteria hyella and mastigocoleus indicates a bathymetric range from 0 down to a water depth of 3 and 6 m respectively the chlorophyta o quekettii associated with the cyanobacterium p terebrans and fungi is dominant from 10 to 40 m depth which is the lower limit of our sampling the distribution ranges of individual taxa observed in the dead coral substrates from new caledonia are much narrower than those reported in the literature for other substrates the bathymetric model based on distribution of microborers in modern corals was then applied to interpret the trace assemblages of microborers observed in holocene corals collected by drilling on two reef sites of new caledonia la surprise islet in the vicinity of the sampling sites of the modern corals and the barrier reef of bayes on the ne coast of grande terre the paleodepth interpretations performed at various levels along the cores allow identification of several shallowing upward sequences during the last 7000 years of reef growth in new caledonia differences in the thickness of these sequences between la surprise and bayes sites were interpreted as differences in the space available for accommodation between the two sites in turn related to the differential subsidence that affected new caledonia during holocene times the use of the microendolith trace assemblages in paleodepth reconstructions of holocene reefs from new caledonia allowed detection of relative sea level variations finer than those deduced from changes in coralgal assemblages

geological overview and cratering model for the haughton impact structure devon island canadian high arctic the haughton impact structure has been the focus of systematic multi disciplinary field and laboratory research activities over the past several years regional geological mapping has refined the sedimentary target stratigraphy and constrained the thickness of the sedimentary sequence at the time of impact to 1880 m new 40ar 39ar dates place the impact event at 39 ma in the late eocene haughton has an apparent crater diameter of 23 km with an estimated rim final crater diameter of 16 km the structure lacks a central topographic peak or peak ring which is unusual for craters of this size geological mapping and sampling reveals that a series of different impactites are present at haughton the volumetrically dominant crater fill impact melt breccias contain a calcite anhydrite silicate glass groundmass all of which have been shown to represent impact generated melt phases these impactites are therefore stratigraphically and genetically equivalent to coherent impact melt rocks present in craters developed in crystalline targets the crater fill impactites provided a heat source that drove a post impact hydrothermal system during this time haughton would have represented a transient warm wet microbial oasis a subsequent episode of erosion during which time substantial amounts of impactites were removed was followed by the deposition of intracrater lacustrine sediments of the haughton formation during the miocene present day intracrater lakes and ponds preserve a detailed paleoenvironmental record dating back to the last glaciation in the high arctic modern modification of the landscape is dominated by seasonal regional glacial and niveal melting and local periglacial processes the impact processing of target materials improved the opportunities for colonization and has provided several present day habitats suitable for microbial life that otherwise do not exist in the surrounding terrain

exploring for a record of ancient martian life the immediate task facing exopaleontology is to define a strategy to explore mars for a fossil record during the decade long exploration program that lies ahead consideration of the quality of paleontological information preserved under different geological conditions is important if we are to develop a strategy with broad applicability the preservation of microbial fossils is strongly influenced by the physical chemical and biological factors of the environment which acting together determine the types of information that will be captured and retained in the rock record in detrital sedimentary systems preservation is favored by rapid burial in fine grained clay rich sediments in chemical sedimentary systems preservation is enhanced by rapid entombment in fine grained chemical precipitates for long term preservation host rocks must be composed of stable minerals that are resistant to chemical weathering and that form an impermeable matrix and closed chemical system to protect biosignatures from alteration during subsequent diagenesis or metamorphism in this context host rocks composed of highly ordered chemically stable mineral phases like silica e g cherts or phosphate e g phosphorites are especially favored such lithologies tend to have very long crustal residence times and along with carbonates and shales are the most common host rocks for the precambrian microfossil record on earth although we make the defensible assumption that mars was more like the earth early in its history clearly the geological and historical differences between the two planets are many such differences must be carefully considered when adapting an earth based strategy to mars

the shear convergence and thermohaline structure of a front abstract with the objective of measuring convergence directly to confirm previous observations of frontal subduction a seaward upwelling jet off central california was studied using satellite infrared images hydrographic sections ship drift and clusters of surface drifters the cyclonic front of the jet was sharper than 1 km resulting in a shear several times larger than f a cross frontal convergence of 7 cm s 1 over the width of the front equivalent to 0 8f was visible as a 20 m wide accumulation of debris the sharpness of the front lasted at least for a day away from the cyclonic front the divergence of the flow was small and the shear was less than 0 6f thermohaline layers originating at the front were interleaving along isopycnals suggesting water subduction it is proposed that the asymetry between anticyclonic and cyclonic sides of the jet and the strong convergence at the cyclonicfront resulted from a frictionally driven ageostrophic secondary circulation superimposed on the geostr

tectonics of complex crater formation as revealed by the haughton impact structure devon island canadian high arctic the results of a systematic field mapping campaign at the haughton impact structure have revealed new information about the tectonic evolution of mid size complex impact structures these studies reveal that several structures are generated during the initial compressive outward directed growth of the transient cavity during the excavation stage of crater formation 1 sub vertical radial faults and fractures 2 sub horizontal bedding parallel detachment faults and 3 minor concentric faults and fractures uplift of the transient cavity floor toward the end of the excavation stage produces a central uplift compressional inward directed deformation results in the duplication of strata along thrust faults and folds it is notable that haughton lacks a central topographic peak or peak ring the gravitational collapse of transient cavity walls involves the complex interaction of a series of interconnected radial and concentric faults while the outermost concentric faults dip in toward the crater center the majority of the innermost faults at haughton dip away from the center complex interactions between an outward directed collapsing central uplift and inward collapsing crater walls during the final stages of crater modification resulted in a structural ring of uplifted intensely faulted sub vertical and or overturned strata at a radial distance from the crater center of 5 0 6 5 km converging flow during the collapse of transient cavity walls was accommodated by the formation of several structures 1 sub vertical radial faults and folds 2 positive flower structures and chaotically brecciated ridges 3 rollover anticlines in the hanging walls of major listric faults and 4 antithetic faults and crestal collapse grabens oblique strike slip i e centripetal movement along concentric faults also accommodated strain during the final stages of readjustment during the crater modification stage it is clear that deformation during collapse of the transient cavity walls at haughton was brittle and localized along discrete fault planes separating kilometer size blocks

calcite filled borings in the most recently deposited skeleton in live collected porites scleractinia implications for trace element archives abstract skeletons of the scleractinian coral porites are widely utilized as archives of geochemical proxies for among other things sea surface temperature in paleoclimate studies here we document live collected porites lobata specimens wherein as much as 60 of the most recently deposited skeletal aragonite i e the part of the skeleton that projects into the layer of living polyps and thus is still in direct contact with living coral tissue has been bored and replaced by calcite cement calcite and aragonite were identified in situ using raman microspectroscopy the boring filling calcite cement has significantly different trace element ratios sr ca mmol mol 6 3 1 4 mg ca mmol mol 12 0 5 1 than the host coral skeletal aragonite sr ca mmol mol 9 9 1 3 mg ca mmol mol 4 5 2 3 the borings appear to have been excavated by a coccoid cyanobacterium that dissolved aragonite at one end and induced calcite precipitation at the other end as it migrated through the coral skeleton boring activity and cement precipitation occurred concomitantly with coral skeleton growth thus replacing skeletal aragonite that was only days to weeks old in some cases although the cement filled borings were observed in only 20 of sampled corals their occurrence in some of the most recently produced coral skeleton suggests that any corallum could contain such cements irrespective of the coral s subsequent diagenetic history in other words pristine skeletal aragonite was not preserved in parts of some corals for even a few weeks although not well documented in coral skeletons microbes that concomitantly excavate carbonate while inducing cement precipitation in their borings may be common in the ubiquitous communities that carry out micritization of carbonate grains in shallow carbonate settings thus such phenomena may be widespread and failure to recognize even very small quantities of early cement filled borings in corals used for paleoclimate studies could compromise high resolution paleotemperature reconstructions the inability to predict the occurrence of cement filled borings in coralla combined with the difficulty in recognizing them on polished blocks highlights the great care that must be taken in vetting samples both for bulk and microanalysis of geochemistry

the nature of the groundmass of surficial suevite from the ries impact structure germany and constraints on its origin surficial suevites from the ries impact structure have been investigated in the field and using optical and analytical scanning electron microscopy the groundmass of these suevites comprises calcite clay minerals impact melt glass crystallites plagioclase garnet and pyroxene francolite and ba phillipsite the latter zeolite is a secondary phase abundant textures have been observed intricate flow textures between the various groundmass phases globules of each phase in the other phases spheroids of pyrrhotite in calcite the budding off of clay globules into silicate glass and or calcite euhedral overgrowths of francolite on apatite clasts and quench textured crystallites in the groundmass groundmass forming calcite displays higher feo mno and sio2 contents than limestone target material the composition of suevite clay minerals is highly variable and not always consistent with montmorillonite three types of glasses are distinguished in the groundmass type 1 glasses are sio2 rich and are clearly derived from sandstones in the sedimentary cover while the protoliths of the other two glass types remains unclear analytical data and micro textures indicate that the calcite silicate glass francolite and clay minerals of the groundmass of the ries suevites represent a series of impact generated melts that were molten at the time of and after deposition on cooling plagioclase pyroxene and garnet crystallized from the groundmass these results are at variance with the current traditional descriptive definition of suevite given that ries is the original type occurrence of suevite some modification to the traditional definition may be in order as the results of this study are most consistent with the groundmass of ries surficial suevites representing a mix of several types of impact generated melts we suggest that a possible origin for these suevites is as some form of impact melt flow s that emanated from different regions of the evolving crater

precambrian endoliths discovered the earliest known microborings have now been found in late precambrian ooids upper riphean1 vendian2 570 700 myr of the eleonore bay group of eastern greenland the ooids were originally carbonaceous and underwent silicification after boring occurred the finding establishes that the habit of microbial boring evolved before the appearance of skeleton bearing metazoans in the geological record

mg silica precipitation in fossilization mechanisms of sand tufa endolithic microbial community mono lake california abstract the detection of mg silica associated with endolithic biofilms of cyanobacteria and bacterial communities living in lake shore sand tufa formations in mono lake california has been observed using scanning electron microscopy with backscattered electron imaging sem bse and energy dispersive x ray spectroscopy eds mg accumulated in cell walls of living cyanobacteria is interpreted to promote mg silicification with structural preservation while non cyanobacterial prokaryotes are not fossilized however extracellular polymeric substances around the living communities were prominent as nucleation sites for authigenic mineral precipitation a mg silicate served to stabilize the biofilm remains further diagenesis of these textures resulted in occlusion of the cytoplasm pore spaces by carbonate precipitates this precipitate damaged the microfossil structures but the mg silica fabric was still present the paleontological significance of mg silica precipitates as a possible biosignature of the former presence of endolithic biofilms is addressed

biogeological signatures of microboring cyanobacterial communities in marine carbonates from cabo rojo puerto rico abstract the occurrence of carbonate boring organisms in marine and continental environments is well known and accounts for substantial rates of sediment and sedimentary rock reworking at the geological scale many case studies have documented the importance of cyanobacteria in near surface environments but nearly all have relied upon morphological descriptions in this study we applied a polyphasic approach to evaluate euendolithic cyanobacterial assemblages from a variety of carbonaceous marine substrates using electron microscopy cultivation and molecular genetic techniques the limitations and biases of the different methods became evident none could be deemed optimal and each failed to detect much or some of the extant diversity in the samples in general sem tended to underestimate the diversity of morphologically simple community members and cultivation yielded a very biased view of the community all approaches however congruently detected differences in community structure between soft substrates and hard substrates with the latter displaying communities of higher complexity in spite of these differences the geological and sedimentary imprints of the boring community exemplified in the formation of well structured micritic envelopes of re worked carbonate were uniform throughout the samples implying that the mechanism of action is common and most likely universal our results speak for the merits of a multidisciplinary approach and provide cautionary implications for paleoenvironmental reconstructions

cryptoendolithic alteration of antarctic sandstones pioneers or opportunists 1 the cryptoendolithic habitat of the antarctic dry valleys has been considered a good analogy for past martian ecosystems if life arose on the planet yet cryptoendoliths are thought to favor the colonization of rocks that have a preexisting porous structure e g sandstones this may weaken their significance as exact analogues of potential rock colonizing organisms on mars given our current understanding of the dominant volcanic nature of martian geology however the production of oxalic acid by these lichen dominated communities and its weathering potential indicate that it could be an aid in rock colonization enabling endoliths to inhabit a wider variety of rock types utilizing icp aes and scanning electron microscope techniques this study investigates elemental and mineralogical compositions within colonized and uncolonized layers in individual sandstone samples this is in order to determine if the weathering of mineral phases within the colonized layers causes an increase in the amount of pore space available for colonization the results show that colonized layers are more weathered than uncolonized deeper portions of the rock substrate layers within uncolonized samples have uniform compositions differences between the colonized and uncolonized layers also occur to varying extents within colonized rocks of different mineralogical maturities the results confirm that cryptoendoliths modify their habitat through the production of oxalic acid and suggest that over time this directly increases the porosity of their inhabited layer potentially increasing the biomass it can support

shape free inference of hyporheic traveltime distributions from synthetic conservative and smart tracer tests in streams 1 the hyporheic zone has been identified as important for river ecology natural biogeochemical turnover filtration of particles degradation of dissolved pollutants and thus for the self cleaning capacity of streams and for groundwater quality good estimation of the traveltime distribution in the hyporheic zone is required to achieve a better understanding of transport in the river system the transient storage model has been accepted as an appropriate tool for reach scale transport in rivers undergoing hyporheic exchange but the choice of the best parametric function for the hyporheic traveltime distribution has remained unclear we present an approach to obtaining hyporheic traveltime distributions from synchronous conservative and smart tracer experiments that does not rely on a particular functional form of the hyporheic traveltime distribution but treats the latter as a continuous function nonnegativity of the hyporheic traveltime distribution is enforced by the application of lagrange multipliers a smoothness parameter needed for regularization and uncertainty bounds are obtained by the expectation maximization method relying on conditional realizations the shape free inference provides the opportunity for capturing unconventional shapes e g multiple peaks in the estimation we test the approach by applying it to a virtual test case with a bimodal hyporheic traveltime distribution which is recaptured in the inversion of noisy data

alteration of oceanic volcanic glass textural evidence of microbial activity the subsurface biosphere may constitute as much as 50 percent of earth9s biomass direct and indirect evidence suggests that an extensive biosphere exists in the rocks below the sea floor this survey of basalts of the atlantic pacific and indian oceans supports the hypothesis that bacteria have colonized much of the upper oceanic crust which has a volume estimated at 1018 cubic meters although this is the largest habitat on earth its low abundance of bacteria constitutes much less than 1 percent of earth9s biomass

image processing and roughness analysis of exposed bedrock fault planes as a tool for paleoseismological analysis results from the campo felice fault central apennines italy abstract morphologic investigations along the campo felice cf fault central apennines italy have been made in order to develop a procedure for the paleoseismological analysis of bedrock fault scarps the cf fault has been responsible for the formation of an impressive limestone fault scarp geomorphologic work on the cf basin and related fault indicated that the scarp originated from tectonic fault displacements three morphologic units have been distinguished along the fault scarp and defined as morphosome m1 lowest part of the scarp m2 and m3 the uppermost part these units display different karstic features which are the result of their different duration of exposure to weathering micromorphologic analyses focused on the morphosome m1 along which the cf fault plane is exposed for a height ranging between 4 and 7 m these analyses were aimed at defining differently weathered bands located at various heights and parallel to the fault scarp top and base the presence of these bands suggests repeated fault movements the exposed fault surface displays a low grade biokarstic weathering due to the action of epilithic and endolithic organisms the biokarst distribution is however inhomogeneous and conditioned by the presence of nourishing elements moisture and by light intensity an area preferentially affected by the biokarstic processes develops as a band at the bedrock soil contact at the base of the scarp roughness and colour analyses were made to identify uplifted bands which previously formed at the bedrock soil contact the roughness analysis was made using a microroughness meter along 20 cm long horizontal transects repeated each 20 cm of fault height for the entire morphosome m1 at various sites along the scarp the roughness variance data plotted vs the fault height failed to identify differently weathered bands of paleoseismological interest this result is probably due to the complex distribution of biokarst along the investigated fault plane more reliable results have been obtained by areal analysis of the variation of the colour rendering of the rocks exposed along the fault plane at different sites photographic images of large portions of fault surfaces have been processed with standard graphic computer programs the variations of colour indicated the presence of bands at various heights along the fault plane two uplifted bands have been recognised at all the investigated sites suggesting two displacement events e1 and e2 a preliminary chronological framework for these two events the youngest of which affected the cf fault can be derived from the paleoseismological data available for the southernmost branch of the regional fault system that includes the cf fault according to these data e1 may have occurred between 860 and 1300 ad while e2 may have occurred at about 1900 bc work is in progress to define surface exposure ages of different parts of the fault plane by means of in situ produced cosmogenic 36 cl this procedure will give further chronological constraints for the age of e1 and e2 and will also permit to test the validity of the micromorphologic analysis of bedrock fault scarps for paleoseismological aims

biologically initiated rock crust on sandstone mechanical and hydraulic properties and resistance to erosion abstract biocolonization on sandstone surfaces is known to play an important role in rock disintegration yet it sometimes also aids in the protection of the underlying materials from rapid erosion there have been few studies comparing the mechanical and or hydraulic properties of the birc biologically initiated rock crust with its subsurface as a result the overall effects of the birc are not yet well understood the objective of the present study was to briefly characterize the birc from both the mineralogical and biological points of view and especially to quantify the effect of the birc upon the mechanical and hydraulic properties of friable sandstone the mineralogical investigation of a well developed birc showed that its surface is enriched in kaolinite and clay to silt sized quartz particles total organic carbon increases with the age of the birc based on dna sequencing and microscopy the birc is formed by various fungi including components of lichens and green algae using the method of drilling resistance by measuring tensile strength and based on water jet testing it was determined that a birc is up to 12 times less erodible and has 3 35 times higher tensile strength than the subsurface friable sandstone saturated hydraulic conductivity of the studied birc is 15 300 times lower than the subsurface and was measured to also decrease in capillary water absorption 2 33 times water vapor diffusion is not significantly influenced by the presence of the birc the birc thus forms a hardened surface which protects the underlying material from rain and flowing water erosion and considerably modifies the sandstone s hydraulic properties exposing the material to calcination 550 c and experiments with the enzyme zymolyase indicated that a major contribution to the surface hardening is provided by organic matter in firmer sandstones the birc may still considerably decrease the rate of weathering as it is capable of providing cohesion to strongly weathered and disintegrated sandstone surfaces however only a near surface zone of the sandstone is stabilized by the birc and additional sources of stabilization gravity induced stress inorganic cement etc contribute to the resistance of the subsurface zone of sandstone exposures

impact induced microbial endolithic habitats asteroid and comet impacts on earth are commonly viewed as agents of ecosystem destruction be it on local or global scales however for some microbial communities impacts may represent an opportunity for habitat formation as some substrates are rendered more suitable for colonization when processed by impacts we describe how heavily shocked gneissic crystalline basement rocks exposed at the haughton impact structure devon island nunavut arctic canada are hosts to endolithic photosynthetic microorganisms in significantly greater abundance than lesser shocked or unshocked gneisses two factors contribute to this enhancement a increased porosity due to impact fracturing and differential mineral vaporization and b increased translucence due to the selective vaporization of opaque mineral phases using biological ultraviolet radiation dosimetry and by measuring the concentrations of photoprotective compounds we demonstrate that a covering of 0 8 mm of shocked gneiss can provide substantial protection from ultraviolet radiation reducing the inactivation of bacillus subtilis spores by 2 orders of magnitude the colonisation of the shocked habitat represents a potential mechanism for pioneer microorganisms to invade an impact structure in the earliest stages of post impact primary succession the communities are analogous to the endolithic communities associated with sedimentary rocks in antarctica but because they occur in shocked crystalline rocks they illustrate a mechanism for the creation of microbial habitats on planetary surfaces that do not have exposed sedimentary units this might have been the case on early earth the data have implications for the microhabitats in which biological signatures might be sought on mars

application of artificial neural networks as a tool for moisture prediction in microbially colonized halite in the atacama desert the atacama desert is the driest and one of the most life limiting places on earth despite the extreme conditions microbial endolithic communities have been found inside halite rocks the presence of these microbial communities is possible due to the hygroscopic properties of evaporitic rocks composed of sodium chloride it is important to elucidate every possible water source in such a hyperarid environment therefore in the present study an artificial neural network ann based model has been designed to predict the presence of liquid water on the surface of halite pinnacles the model predicts the moisture formation using two basic meteorological variables air temperature and air relative humidity anns have been successfully employed for the first time as a tool for predicting the appearance of liquid water a key factor for the endolithic microbial communities living in the driest part of the atacama desert the model developed is able to correctly predict the formation of water on the surface of the halite pinnacles 83 of the cases we anticipate the future application of this model as an important tool for the prediction of the water availability and therefore potential habitability of lithic substrates in extreme environments on earth and perhaps elsewhere

evidence for chlorine recycling hydrosphere biosphere atmosphere in a forested wet zone on the canadian shield abstract the ability to measure environmental levels of 36 cl by accelerator mass spectrometry and 3 h by 3 he ingrowth mass spectrometry has made it possible to use the pulses of these two isotopes released into the atmosphere during nuclear weapons testing as tracers of cl and water movement in soils and groundwater the authors have investigated the movement of these tracers below a forested wet zone and have found that both are retarded to a differing extent in the near surface because of vegetative uptake and recycling adsorption by clay particles followed by slow release to the groundwater may also be significant the data accumulated in this region of near vertical recharge have gone a considerable distance towards explaining the anomalously low concentrations of 36 cl measured in the 5 laurentian great lakes as well as indicating possible mechanisms for large scale cl recycling in the atmosphere and biosphere identification of the near term non conservative behaviour of the cl is significant since such a phenomenon could introduce errors in many watershed calculations e g water residence times evaporation rates and mixing calculations

a paleozoic age for the tunnunik impact structure we report paleomagnetic directions from the target rocks of the tunnunik impact structure as well as from lithic impact breccia dikes that formed during the impact event the target sedimentary rocks have been remagnetized after impact related tilting during a reverse polarity interval their magnetization is unblocked up to 350 degrees c the diabase dikes intruding into these sediments retained their original magnetization which unblocks above 400 degrees c the impact breccia records a paleomagnetic direction similar to that of the overprints in the target sedimentary rocks the comparison of the resulting virtual geomagnetic pole for the tunnunik impact structure with the apparent polar wander path for laurentia combined with biostratigraphic constraints from the target sedimentary rocks is most consistent with an impact age in the late ordovician or silurian around 430 450 ma soon after the deposition of the youngest impacted sedimentary rocks our results from the overprinted sedimentary rocks and diabase dikes imply that the postimpact temperature of the studied rocks was about 350 degrees c

the distribution of meteoric cl 36 in precipitation across europe in spring 2007 abstract the cosmogenic isotope 36 cl is a valuable tool for understanding many earth system processes but an improved knowledge of its spatial distribution at the earth s surface is critical for several applications meteoric 36 cl fallout reflects complex interactions between atmospheric production transport and deposition processes and predictive models require experimental validation this study investigates for the first time in a systematic way the spatial distribution of meteoric 36 cl on a continental scale within the european landmass using precipitation samples collected during spring 2007 36 cl cl ratios increase with distance inland and the new data exhibit a strong exponential relationship with 18 o values of precipitation r s 0 75 yielding a useful predictive framework for future studies precipitation events in central european regions are characterised by high 36 cl cl ratios with a maximum measured in lyon france of 746 134 10 15 the new data confirm models for the dependence of 36 cl fallout on latitude with the highest mean springtime fallout 53 6 atoms m 2 s 1 occurring in the 40 50 n latitudinal band with sharp decreases in fallout in high latitude regions and more gradual decreases towards the lower latitudes the 36 cl bomb pulse introduced by thermonuclear weapon testing predominantly in the 1950 s has persisted in the environment for c 50 years but the new data indicate that 36 cl fallout has now essentially returned to natural pre bomb values

exogenous carbonaceous microstructures in early archaean cherts and bifs from the isua greenstone belt implications for the search for life in ancient rocks abstract the microstructure of hf etched samples of early archaean banded iron formations bifs and cherts from the 3 7 b y old isua greenstone belt southwestern greenland was investigated using high resolution scanning electron microscopy equipped with an electron diffraction system capable of analysing light elements the rocks contain both endogenous of internal origin and exogenous of external origin carbonaceous microstructures the former consist of inclusions of graphite and possibly small amorphous carbonaceous particles both embedded in metacherts however further in situ tem studies are needed to verify the endogeneity of the amorphous particles moreover these rocks also contain endolithic microorganisms i e inhabiting cracks in rocks as well as undifferentiated carbonaceous matter that occur in fractures and cracks between grains the microorganisms include cyanobacteria filamentous microorganisms such as fungal hyphae and possibly bacteria as well as large unidentified cells or spores most of the microorganisms appear to have been fossilised the endoliths are evidently younger than the host rock but must have infiltrated at different periods most likely after the inland ice retreated 8000 years ago the presence of endolithic carbonaceous matter in cracks and microfissures in these rocks will affect any analyses of bulk samples such as carbon isotopes and chemical biomarkers as well as analyses of acid macerated residues thus previous isotope measurements made on bifs and cherts from isua may reflect younger contamination rather than an endogenous original signal likewise some of the previously described isuan microorganisms probably represent recent endolithic contamination

surface heating and patchiness in the coastal ocean off central california during a wind relaxation event the field work was funded by the u s office of naval research onr coasta i sciences program code i 122cs as part of the coastal transition zone project s r r re ceived additional support from direct research funding at the u s naval postgraduate school nps the portion of this work carried out at the jet propulsion laboratory california institute of technology was sponsored by onr and the national aeronautics and space administration model simulatiotis were conducted by the oceanic planetary boundary layer laboratory sponsored by onr and funded by nps the boom probe was designed and built by the oceanography department support staff at the naval postgraduate school paul jessen assisted with the data collection and processing the satellite image was provided by toby garfield and the nps interactive digital environmental analysis idea laboratory

amplitude and horizontal structure of a large diurnal sea surface warming event during the coastal ocean dynamics experiment abstract intense diurnal warming of the ocean surface was observed in april 1982 off california using a combination of mooring hydrographic and satellite infrared and satellite pigment measurements the event corresponded to a spatial and temooral minimum of the wind stress the diurnal surface temperature amplitude exceeded 6 6 c locally despite a 490 nm optical depth of 20 m suggesting that phytoplankton was not responsible for the shallow heat trapping coherent horizontal temperature streaks at least 50 km long and 4 8 km wide formedduring the subsequent erosion of the shallow warm layers it is hypothesized that thcfr scale was set by planetary boundary layer circulations

noble gas tracers for characterisation of flow dynamics and origin of groundwater a case study in switzerland summary the grenchen aquifer system in the swiss plateau was extensively investigated in order to determine the extent of groundwater contamination and to assess the natural attenuation capacity environmental tracer data were applied to estimate groundwater travel times mixing ratios and evaluate groundwater origin recharge is basically possible in two distinct topographical areas the immediate vicinity of the town of grenchen and the elevated plateau of the first jura mountain ridge groundwater dating was performed with the 3 h 3 he dating method and supplemented by 85 kr measurements stable isotope data 18 o 2 h and dissolved noble gas concentrations allow the determination of the recharge temperature which is correlated to the recharge elevation noble gas temperatures ngt decrease in the direction of groundwater flow and range from 10 to 13 c in the upstream area of the town to 7 9 c in the downstream river plain this trend could suggest the admixture of water from the underlying limestone aquifer recharged under cooler infiltration conditions e g at higher recharge elevations however it is shown in this study that the difference in ngt does not require such a recharge rather increasing air temperatures over the last 40 years and the urban heat island effect could possibly explain most of the observed temperature shift furthermore it is concluded that the downstream river plain is hydrologically disconnected from the upstream town area consequently most water from the town area is drained by the creek witibach and recharge in the river plain is higher than previously assumed

ecological perspectives on rock surface weathering towards a conceptual model a wide range of information is now available on the ecology of rock surface microorganisms including bacteria fungi and algae and lichens and their role in weathering in particular locations external environmental conditions as well as rock characteristics determine the type of rock surface community and thus the style of biological weathering a simple preliminary conceptual model can be drawn which relates biological weathering activity to an environmental stress gradient and which is applicable at a range of scales further research needs carrying out to test and extend this model in order to make some progress towards the important goal of assessing the overall importance of biological weathering to geomorphology

the effects of meteorite impacts on the availability of bioessential elements for endolithic organisms meteorite impacts one of the most ubiquitous processes in the solar system have the ability to destroy as well as create habitats for life the impact process can increase the translucency and porosity of the target substrate as well as mobilize biologically relevant elements within the substrate for endolithic organisms this process has important implications especially in extreme environments where they are forced to seek refuge in the interior of rocks here we show that unshocked target rocks and rocks that have experienced pressures up to about 80 gpa from the haughton impact structure devon island canada possess a small but discernible change in bulk chemistry within the major oxide analysis however changes in the distribution of elements did occur with increasing shock level for both the sedimentary and crystalline target both the crystalline and sedimentary target rocks contain significant amounts of glasses at higher shock levels up to about 95 by volume which would improve the availability of these elements to potential microbial endoliths as glasses are more easily dissolved by organic acids the implication that impact events do not impoverish their capacity to serve as a substrate through volatilization is important with respect to analogous impact structures on mars after the deleterious effects of the direct meteorite impact any microorganisms on mars would have benefited from the input of heat the mobilization of a possible frozen groundwater system as well as increased translucency porosity and trace nutrient availability of the target substrate

rock magnetic and paleomagnetic study of the keurusselka impact structure central finland abstract there are 31 proven impact structures in fennoscandia one of the most densely crater populated areas of the earth the recently discovered keurusselka impact structure 62 08 n 24 37 e is located within the central finland granitoid complex which formed 1890 1860 ma ago during the svecofennian orogeny it is a deeply eroded complex crater that yields in situ shatter cones with evidence of shock metamorphism e g planar deformation features in quartz new petrophysical and rock magnetic results of shocked and unshocked target rocks of various lithologies combined with paleomagnetic studies are presented the suggested central uplift with shatter cones is characterized by increased magnetization and susceptibility the presence of magnetite and pyrrhotite was observed as carriers for the remanent magnetization four different remanent magnetization directions were isolated 1 a characteristic svecofennian target rock component a with a mean direction of d 334 8 i 45 6 95 14 9 yielding a pole plat 51 1 plon 241 9 a95 15 1 2 component b d 42 4 i 64 1 95 8 4 yielding a pole plat 61 0 plon 129 1 a95 10 6 3 component c d 159 5 i 65 4 95 10 7 yielding a pole plat 21 0 plon 39 3 a95 15 6 and 4 component e d 275 5 i 62 0 95 14 4 yielding a pole plat 39 7 plon 314 3 a95 19 7 components c and e are considered much younger possibly neoproterozoic overprints compared with the components a and b the pole of component b corresponds with the 1120 ma pole of salla diabase dyke and is in agreement with the 40ar 39ar age of 1140 ma from a pseudotachylitic breccia vein in a central part of the structure therefore component b could be related to the impact and thus represent the impact age

impactites of the haughton impact structure devon island canadian high arctic contrary to the previous interpretation of a single allochthonous impactite lithology combined field optical and analytical scanning electron microscopy sem studies have revealed the presence of a series of impactites at the haughton impact structure in the crater interior there is a consistent upward sequence from parautochthonous target rocks overlain by parautochthonous lithic monomict breccias through allochthonous lithic polymict breccia into pale grey allochthonous impact melt breccias the groundmass of the pale grey impact melt breccias consists of microcrystalline calcite silicate impact melt glass and anhydrite analytical data and microtextures indicate that these phases represent a series of impact generated melts that were molten at the time of and following deposition impact melt glass clasts are present in approximately half of the samples studied consideration of the groundmass phases and impact glass clasts reveal that impactites of the crater interior contain shock melted sedimentary material from depths of 920 to 200 to 760 m and are interpreted as remnants of the continuous ejecta blanket the pale grey impact melt breccias although similar to the impact melt breccias of the crater interior are more carbonate rich and do not appear to have incorporated clasts from the crystalline basement thus the spatial distribution of the crater fill impactites at haughton the stratigraphic succession from target rocks to allochthonous impactites the recognition of large volumes of impact melt breccias and their probable original volume are all analogous to characteristics of coherent impact melt layers in comparatively sized structures formed in crystalline targets

ignimbrite as a substrate for endolithic life in the hyper arid atacama desert implications for the search for life on mars the hyper arid core of the atacama desert in chile is considered the driest and most life limited place on earth with few habitats capable of sustaining an active microbial ecosystem as such it is one of the best terrestrial analogues of the extreme arid conditions on mars and an ideal environment to explore survival and biological adaptation strategies as the environment becomes increasingly dry here we show that weakly welded rhyolitic ignimbrites in this desert are abundantly colonized by endolithic cyanobacteria and associated heterotrophic bacteria we propose that the porous ignimbrite interior provides protection from damaging uv radiation and excessive levels of visible light rock porosity also favors cell hydration through water retention after scarce rainfall events even when the surrounding environment remains stubbornly dry this is the first known example of an endolithic microbial community colonizing ignimbrite rocks in an extremely dry environment the existence of a habitat capable of supporting abundant phototrophic and heterotrophic communities in an environment that precludes most life forms suggests that if similar deposits are found on mars these should be considered important targets in the search for life indeed ignimbrite rocks have been tentatively identified in gale crater the landing site of the mars science laboratory msl mission and could be directly analyzed by its rover curiosity

geophysical aspects of meteorite impact craters in eroded shield environment with special emphasis on electric resistivity abstract the traditional geophysical methods of magnetics and gravity as applied to meteorite impact crater studies are shortly reviewed their optimal resolution power with respect to crater size and pre existing structures is discussed the morphology of some typical impact craters is illustrated to show the character of the post impact deformation a new geophysical method in impact crater studies the in situ measurement of electrical resistivity is introduced and illustrated with case studies from simple and complex craters it is concluded that the resistivity method represents a useful tool for mapping the extent of authigenic brecciation in crater structures and their surroundings the method constitutes in combination with detailed elevation data gravity and magnetic measurements a powerful tool for constraining the classification of impact craters in crystalline shield environments the resistivity measurements have revealed a complex brecciation pattern in large central uplift structures consisting of a central less brecciated core surrounded by a ring of more intense brecciation typical impact brecciated crystalline rocks have resistivities between 2000 and 8000 ohm m the crater structures treated in this paper are bjorko dellen siljan and uppland all located in sweden

estimating recharge in fractured aquifers of a temperate humid to semiarid volcanic island jeju korea from water table fluctuations and cl cfc 12 and 3h chemistry summary groundwater table fluctuations wtf chloride mass balance cmb apparent groundwater chlorofluorocarbon cfc 12 ages and tritium 3 h mean residence times were used to assess recharge rates on jeju island korea where groundwater is the main source of potable water given the limitations of various techniques and the respective data the methods yield median values of 687 mm yr wtf 429 mm yr cmb 423 mm yr cfc 12 and 394 mm yr 3 h which are lower than the multi annual 1993 2002 average value calculated using the soil water budget swb method 911 mm yr these underestimates are mainly due to most groundwater samples used for the analyses being located in the more arid lowland areas of the island all methods yield highest recharge rates in the southern and eastern districts of jeju implying a strong control of rainfall on the spatial recharge distribution the spatial variability of recharge at the catchment scale is caused by spatially and temporally variable rainfall and evapotranspiration as well as the wide range in effective porosity and specific yield values of the aquifer lithologies the wtf method yields reliable results in the coastal regions where low hydraulic gradients prevail the cmb technique underestimates the recharge values of the swb in all geographic districts probably as a result of anthropogenic cl additions to groundwater and unaccounted for atmospheric cl dry deposition median recharge estimates from the cfc 12 and 3 h data show the lowest spatial correlation with those from the swb mainly as a result of vertical anisotropies and uncertainties in the determination of effective aquifer thicknesses particularly in the perched high level areas the here applied methods are useful for local calibration and validation of swb estimates in lower parabasal regions where thin unsaturated zones prevail however due to their inability to predict recharge in the more remote upslope areas from which as of yet no groundwater data could be obtained they cannot be applied to predict average recharge values representative for the whole island

origin of toasted quartz in terrestrial impact structures quartz present in the target rocks at impact sites and as clasts within impact melt rocks and some pseudotachylytes commonly exhibits a brown nonpleochroic grainy appearance in plane and cross polarized light known as toasted quartz this variety of quartz also possesses a higher albedo in hand sample than colorless examples despite the intense coloration no compositional origin for the browning is evident a high proportion of exceptionally small typically submicron scale fluid inclusions which are typically too small to be observed with the petrographic microscope is considered to be the cause these fluid inclusions are predominantly located along decorated planar deformation features and they enhance scattering of transmitted light and reflect larger quantities of incident light statistically lower sio 2 and total oxide contents present in toasted quartz relative to untoasted quartz are consistent with increased surface electron scattering during microprobe analysis by fluid inclusions intersecting the surface

ecology and spatial pattern of cyanobacterial community island patches in the atacama desert chile 1 plant landscape ecology studies have been carried out for decades and are fundamental to biological research in contrast few corollary spatial landscape studies exist for microorganisms particularly in extreme environments to address this gap we mapped the abundance and spatial distribution of photoautotrophs colonizing translucent rocks in several sites in the atacama desert including the hyperarid core cyanobacterial communities at all sites are predominantly 75 perilithic confined to the periphery of rocks and occur in non random spatial patterns island patches at multiple scales cyanobacterial patches typically contain 1 5 colonized rocks but in some cases support much higher numbers a high resolution mapping of a single 18 m2 rock cluster at the aguas calientes study site 25 s 69 w revealed colonization of 5 2 49 of 948 quartz rocks and showed colonized rocks to be much larger 2x than the available mean rock size ripley s k and point pattern analyses show that quartz rocks are not selected or occupied by cyanobacteria randomly but that non random processes distinct from those creating the background rock pattern must be invoked to explain microbial patchiness in the atacama desert these processes include physical controls rock size orientation microtopography that reflect resource water limitations and biological dispersal via rainfall fog and wind

36cl in modern groundwater dated by a multi tracer approach 3h 3he sf6 cfc 12 and 85kr a case study in quaternary sand aquifers in the odense pilot river basin denmark abstract 36 cl produced by thermonuclear bomb testing has been proposed as an additional tool to date or at least to identify recent groundwater components in order to investigate the behaviour of 36 cl in shallow groundwater a multi tracer approach 3 h 3 he sf 6 cfc 12 and 85 kr was used to characterise and date the groundwater of a quaternary sands aquifer which is located on the island of funen near the city of odense denmark recharge to the semi confined shallow aquifer occurs through permeable sand windows and fractured tills at the surface locally however mixing with older pre bomb water from the underlying limestone aquifer may occur the integrated analyses of the available tracer data allowed a well constrained age structure determination of the investigated water system the 36 cl cl ratios measured in groundwater were used to reconstruct the fallout rates for radioactive 36 cl at odense the calculated fallout values exceeded the fallout estimated based on data from the dye 3 ice core in greenland recycling of the bomb peak fallout seems to be the most probable reason of the high values measured the local extent of this process is difficult to quantify which impedes the use of 36 cl for dating

evidence for the shock melting of sulfates from the haughton impact structure arctic canada abstract sulfate minerals can form an important component of the matrix to carbonate rich impact melt breccias at the 24 km diameter 23 ma haughton impact structure arctic canada the textural and chemical features of the matrix forming sulfates indicate that these phases in addition to co existing carbonates and silicates crystallized directly from an impact generated melt evidence for this includes 1 the matrix supported nature of the crater fill lithologies 2 sulfate carbonate silicate liquid immiscible textures 3 possible quench textures in anhydrite and 4 flow textures developed between anhydrite and silicate rich glasses further supporting evidence includes the presence of si al and mg in the anhydrite structure which were probably trapped by quenching from a melt irregular blebs and globules of shock melted carbonates within anhydrite also suggest a common origin for the two phases field studies reveal that clasts of anhydrite bearing target material are also present in the crater fill deposits several clasts of anhydrite quartz lithologies exhibit evidence for incipient shock melting in both phases previous assumptions about the response of sulfates and carbonates to hypervelocity impact i e lack of melting may therefore be incorrect

what controls seasonal variations of the diurnal cycle of sea surface temperature in the eastern tropical indian ocean abstractrecent in situ buoy observations revealed interesting seasonal features of the diurnal sea surface temperature cycle dsst in the eastern tropical indian ocean composite analysis shows that areas away from the equator exhibit stronger seasonal variations of dsst while weaker seasonal variations appear near the equator the most interesting characteristic is the distinctive contrast of the seasonal variations of dsst between the bay of bengal bob and the region south of the equator particularly around 12 s while the range of dsst is weakest in the bob during boreal summer it has its largest range around 12 s in austral summer furthermore bob dsst exhibits two peaks that occur during the monsoon transitions march april and october whereas dsst south of the equator shows only a single peak in its annual cycle using a one dimensional oceanic mixed layer model the authors examined the cause of the distinctive annual cycles of dsst north and south of the equator two parallel experiment

the terrestrial impact cratering record approximately 130 terrestrial hypervelocity impact craters are currently known due to variations in preservation and in geologic knowledge this sample is biased towards young x 20 km craters on the cratons of australia europe including the former u s s r and north america the rate of discovery of new craters is 3 5 craters per year although modified by erosion terrestrial impact craters exhibit the range of morphologies observed for craters on other terrestrial planetary bodies such as the moon terrestrial craters provide essential ground truth data on the geologic effects of impact and the subsurface structure of impact craters which can be used to constrain interpretations of lunar samples and models of crater formation due to erosion and its effects on form terrestrial craters are recognized primarily by the occurrence of shock metamorphic effects these include shatter cones microscopic planar deformation features solid state and fusion glasses high pressure polymorphs and whole rock melting and vaporization shock recovery experiments indicate that these features occur over shock pressures of 5 gpa to x 100 gpa terrestrial craters have a set of geophysical characteristics which are largely the result of the passage of a shock wave and impact induced fracturing they include gravity and magnetic lows and reductions in seismic velocity the gravity anomalies are seldom greater than 30 mgal due to the limiting effects of lithostatic pressure on fracturing at large complex craters the gravity signature may include a central relative gravity high due to uplift and short wavelength central magnetic anomalies due to a variety of processes much current work is focused on the effects of impact on earth evolution previous work on shock metamorphism and the contamination of impact melt rocks by meteoritic siderophile elements provides a basis for the interpretation of the physical and chemical evidence from cretaceous tertiary boundary sites as resulting from a major impact suggestions that other biological boundaries in the stratigraphie record are due to periodic impacts are not supported by time series analysis of the terrestrial cratering record by analogy with the lunar record and modelling of the effects of very large impacts it has been proposed that biological and atmospheric evolution of the earth could not stabilize before the end of the late heavy bombardment 3 8 ga ago the present terrestrial cratering rate is 5 4 2 7 10 15 km 2a 1 for a diameter 20 km this represents a local threat on historic time scales on a global scale a major impact sufficient to cripple human civilization severely will occur on time scales of 106 a

fluid inclusion analysis of twinned selenite gypsum beds from the miocene of the madrid basin spain implication on dolomite bioformation this research work is centred on continental lacustrine gypsum deposits of miocene age cropping out in the easternmost part of the madrid basin these gypsum deposits accumulated in a continental saline lake are characterized by a spectacular distinctive christmas tree morphology and a peculiar dolomite replacement a combination of microscopic petrography and scanning electron microscopy and analytical techniques fluid inclusion microthermometry x ray energy dispersive spectroscopy and x ray diffractometry was used in order to study the crystallographic distribution and the composition of the fluid inclusions within the gypsum the objectives were to characterize the continental brine from which the mineral precipitated and to detect mineral and element traces that could indicate early diagenetic processes altering the gypsum deposits data from primary fluid inclusions indicated that gypsum precipitated from an aqueous fluid lake water of low to moderate total salinity between 20 and 90 g l nacl secondary fluid inclusions represent interstitial lake brine in contact with gypsum slightly enriched in total salt content as crystal formation proceeded textural ultrastructural and microanalytical analysis indicate that the presence of dolomite precipitates inside the gypsum layers is related to the microbial colonization of the gypsum deposits and the biomineralization of the cell walls and extracellular polymeric substances around the cells our investigation emphasizes necessity of a multidisciplinary approach to assess geobiological processes

impact generated carbonate melts evidence from the haughton structure canada evidence is presented for the melting of dolomite rich target rocks during formation of the 24 km diameter 23 ma haughton impact structure on devon island in the canadian high arctic field studies and analytical scanning electron microscopy reveal that the s 200 m thick crater fill deposit which currently covers an v60 km 2 area in the center of the structure comprises fragmented target rocks set within a carbonate silicate matrix the silicate component of the matrix consists of si al mg rich glass the carbonate component is microcrystalline calcite containing up to a few wt si and al the calcite also forms spherules and globules within the silicate glass with which it develops microtextures indicative of liquid immiscibility dolomite clasts exhibit evidence of assimilation and may show calcite and rare dolomite overgrowths some clasts are penetrated by calcite and silicate injections along with the carbonate silicate glass textures the presence of pigeonite and spinifex textured diopside suggests that the matrix to the crater fill deposit was originally molten and was rapidly cooled this indicates that the impact event that generated haughton caused fusion of the predominantly dolomitic target rocks it appears that the ca mg component of the dolomite may have dissociated with mg entering the silicate melt phase while the ca component formed a caco3 dominant melt the silicates were derived by the fusion of lower paleozoic sandstones siltstones shales and impure dolomites evidence for melting is corroborated by a review of theoretical and experimental work which shows that caco3 melts at s 10 gpa and s 2000 k instead of dissociating to release co2 this work indicates that carbonate rich sedimentary targets may also undergo impact melting and that the volume of co2 released into the atmosphere during such events may be considerably less than previously estimated fl 2001 elsevier science b v all rights reserved

cl deposition rate reconstruction from bomb pulse until present a study based on groundwater records the radioactive isotope 36 cl with a half life of 301 ka is a valuable chronometer for estimation of groundwater residence time up to 2 millions of years aerial thermonuclear fission bomb tests performed during the late 1950s injected a massive amount of this isotope into the atmosphere which exceeded the natural fallout signal since this bomb pulse atmospheric 36 cl deposition tends to return to natural fallout rate the monitoring of this attenuation can provide a good opportunity to extend the use of this chro nometer to shorter time spans venice s lagoon alimentation zone shows groundwaters with residence times distributed over last fifty years this permits the estimation of a continuous 36 cl deposition curve free from latitudinal and seasonal variations of the signal three old groundwater samples with residence times comprised in the range a900 to a8000 bp allow the estimation of a mean natural deposition of 49 at m a2 s a1 and are in good agreement with 36 cl fallout observed for the last 40 000 years by plummer et al 1997 for the bomb pulse period a fallout of 5300 at m a2 s a1 was calculated this was followed by a strong attenuation period taking place until the 1980s during which the fallout reached values ranging between 167 and 354 at m a2 s a1 the attenuation reached then a plateau it experienced a slower lowering until the actual deposition with fallout values calculated between 124 and 252 at m a2 s a1 this persistence of high deposition rate was classically attributed to biological and atmo spherical recycling processes or underestimation of the natural atmospheric production of the 36 cl additional source of 36 cl production has been envisaged through the activation of chlorine radicals from stratospherical cfcs leading to a 36 cl production rate comparable with that of ar spallation from the first approximation lastly the latitudinal factor of the attenuation of the fallout rate is discussed and the impact of the jet streams is proposed as an explanation for the discrepancies in the attenuation rate

lee region of gran canaria the mountainous canary islancls present obstacles to the trade wincls ancl to the canary current flowing equatorwarc past them in situ observations of hydrographic properties ancl surface wincls south of gran canaria together with advancecl very high resolution racliometer ancl synthetic aperture racial images e uring 2 weeks in summer 1995 are analyzecl a cyclonic edcly shecl l rom the west of the islancl c1riftecl southwestwarcl at 5 s j while the southeast coast was approachecl by an upwelling filament originating off nw africa a wincllee region bounclecl by intense horizontal shear lines hacl a weak return islandwarcl wincl in its center the lee formee a triangulai c1iurnally varying war111 water 001 with two sea surface temperature maxima separatecl by lower temperatures below the return wincl shallow temperature stratification occurrecl behincl the islancl in contrast to the l1niform surface mixecllayer in exposecl regions upwelling ancl clownwelling of 10 20 111 were indicatecl on the cyclonic ancl anticyclonic sicles of the lee region in the sar la u lines of strong current shear along a temperature front between the cyclonic eclcly the upwelling filament were iclentifiable i iowever the racial images were clominatecl atmospheric phenomena including mountain lee wave paclcets winclrows and wincl lines estimation of the wincl field l rom the sar backscatter intensity revealed ex structure and intensification on the eclges of the warm lee

late ordovician brachiopod distribution and ecospace partitioning in the tvaren crater system sweden abstract patterns of distribution and ecospace utilization of late ordovician brachiopods in a recently formed contemporary meteorite crater are described and analyzed rhynchonelliformean brachiopod communities dominated by a wide range of orthides and strophomenides colonized the newly formed crater at the crater rim communities were established early on although the crater depression was not inhabited until deposition of the upper third of the remaining crater fill the crater formed a protected but restricted microenvironment where sediments four times the thickness of the nearby basinal succession accumulated within this narrow space environments varied from shallow water to deeper waters about 200 m in depth and from well oxygenated to hypoxic such varied environments generated a rough ecological landscape facilitating niche partitioning across a relatively small geographic area analysis of the guild structure of the fauna permits explanation of a local biodiversity hotspot in otherwise low diversity strata elsewhere in the scandinavian region the tvaren impact event had an important palaeobiologic effect upon the fossil record as it served as a local pump and reservoir for biodiversity moreover the development of new community types and narrowly defined niches helped further drive both and biodiversity during a critical phase of the great ordovician biodiversification event

biodegradation of temperate water skeletal carbonates by boring sponges on the scott shelf british columbia canada abstract boring sponges are a major agent of shell destruction and in the process an important contributor of fine grained carbonate detritus in temperate skeletal carbonate deposits on scott shelf northwestern vancouver island intensive boring is encouraged by the generally low rates of carbonate production and sedimentation skeletal grains become considerably weakened by sponge boring and break preferentially along the directions of sponge excavated tunnels and galleries within the shell boring also facilitates shell dissolution by significantly increasing the surface area weight ratio of shells and by breaking down the organic matrix of shells the large aragonitic bivalves glycymeris and humilaria appear especially susceptible to sponge biodegradation and have become thoroughly bored and corroded within about 1000 years in ambient shelf waters thus their preservation potential is low selective loss of aragonitic biota from ancient cool water shelf skeletal carbonate deposits is anticipated and is evident in many temperate latitude occurrences of new zealand cenozoic limestones

limestone biopitting in coastal settings a spatial morphometric sem and molecular microbiology sequencing study in the mallorca rocky coast balearic islands western mediterranean abstract biological agency on rock coasts has been widely recognised over recent decades this study deals with the distribution and morphometric characteristics of microforms features developed by cyanobacteria rivularia sp on coastal limestone outcrops these coastal microforms known as biopits have a small rounded basin shape a few millimetres in size environmental and geological data were collected from 100 random rock surface spots from punta des farallo cape mallorca western mediterranean from which major controls on the spatial distribution of biopits were established additionally morphological data on 382 biopits determined the diagnostic morphometry of these features and their enlargement mechanisms the results indicated that biopits exhibit a preferential location in shaded exposures and sheltered areas from prevailing winds and waves avoiding direct insolation and desiccation other major controls on these microforms location and development were variables such as the rock surface slope and the distance to the coast i e influence of splash and spray shadow spots displayed higher biopits density than other locations according to the patterns determined by environmental and geomorphological factors at the study site morphometric analyses showed that biopits have a width twice their depth the average width of the microforms was 6 49 2 40 mm and the average depth 2 46 1 09 mm most frequently the width depth ratio was 2 or larger this characteristic shape ratio was an additional factor that plays a role in maintaining the necessary humidity for microorganisms associated with biopits

diurnal warm layer events in the western mediterranean and european shelf seas we characterize near surface ocean diurnal warm layer events using satellite observations and fields from numerical weather forecasting the study covers april to september 2006 over the area 11 degrees w to 17 degrees e and 35 degrees n to 57 degrees n with 0 1 degrees cells we use hourly satellite ssts from which peak amplitudes of diurnal cycles in sst dssts can be estimated with error similar to 0 3 k the diurnal excursions of sst observed are spatially and temporally coherent the largest dssts exceed 6 k affect 0 01 of the surface and are seen in the mediterranean north and irish seas there is an anti correlation between the magnitude and the horizontal length scale of dsst events events wherein dsst exceeds 4 k have length scales of 40 km from the frequency distribution of different measures of wind speed minima we infer that extreme dsst maxima arise where conditions of low wind speed are sustained from early morning to mid afternoon

do periglacial landscapes evolve under periglacial conditions polar and alpine periglacial areas are traditionally regarded as necessarily submitted to very efficient frost driven processes that control the holocene and ongoing geomorphic activity during the last decade the validity of this academic view has been increasingly questioned among the international scientific community the search for the real past and present processes responsible for landform evolution in cold nonglaciated areas is based mainly on more and more refined monitoring protocols relying upon sophisticated equipment to assess the representativeness and significance of monitoring data collected in restricted sites it appears necessary however to widen the perspective by adopting a twofold multiscale approach as proposed in the present paper 1 in space by integrating various scales from the general slope system to the bioclimatic nanoenvironment and 2 in time by taking into account the landscape history from tertiary inherited features to recent process changes induced by the contemporary warming reintegrating the historical approach should help both to place the ongoing processes within a succession and or combination of interoperating processes and to avoid misinterpretations of features considered wrongly as emblematic of frost action overall both the historical and monitoring approaches tend to reduce the geomorphic efficiency of frost derived processes instead the role of noncold related processes such as chemical thermal biogenic and rainfall induced ones is being emphasized of special interest would be an interdisciplinary discussion between geomorphologists and various disciplines of biological sciences including biochemistry and ecology studying processes of primary successions

comparison of airborne synthetic aperture radar imagery with in situ surface slope measurements across gulf stream slicks and a convergent front synthetic aperture radar sar imagery showing two types of features near the inshore edge of the gulf stream are compared with nearly simultaneous estimates of the sea surface slope field derived from optical shipboard measurements one class of feature consists of a set of narrow dark lines having radar signal modulations of about 10 db at l band these modulations are comparable to those observed in the in situ wave slope data over wavenumbers corresponding to the radar resonant bragg waves these modulations are also predicted by a simplified equilibrium wave spectrum model using a surface elasticity of about 25 mn m as determined from in situ measurements of surface tension and a wind friction velocity of about 10 cm s from buoy and shipboard measurements these results support lyzenga and marmorino s 1998 inference that the gulf stream dark lines represent relatively passive biogenically derived surfactant slicks that are advected and strained by the large scale surface flow field the second class of feature consists of a pair of bright dark signatures over the shallow continental shelf region near cape hatteras north carolina these features are characterized by signal modulations of about 4 and 4 db in both the l band sar and in situ data these modulations appear to be due to the interaction of surface waves with the current convergence and divergence regions associated with a rotary circulation in a shallow convergent front model calculations of this interaction by lyzenga 1998 indicate that the positive perturbations associated with current convergence should be relatively independent of the wavenumber which is in approximate agreement with the in situ measurements of the present paper the model also indicates that the negative perturbations associated with the region of current divergence should decrease for wavenumbers higher than l band that trend is observed in the sar data but not in the in situ data which show significant perturbations at higher wavenumbers it is conjectured that this is due to the effects of surfactants and either along front or time variability in the frontal dynamics which are not included in the model additional comparisons of this kind should be useful to further test and improve physical models of near surface phenomena

microborer ichnocoenoses in quaternary corals from new caledonia reconstructions of paleo water depths and reef growth strategies in relation to environmental changes abstract coral reef growth and development depend on several environmental factors including tectonic and climatic parameters and local ecological drivers reef growth is especially sensitive to sea level variations paleo water depth reconstructions are essential tools used to determine reef growth patterns during different periods of reef growth assemblages of corals and or coralline algae have been commonly used in such paleodepth reconstructions this study shows that using microendolith ichnocoenoses can sometimes provide better accuracy than traditional coralgal analyses particularly in the depth range 0 10 m where coralgal assemblages usually show broad distribution ranges holocene and pleistocene cores from two barrier reef sites on the west coast of grande terre in new caledonia are examined here holocene reef development at these sites feature examples of microendolith ichnocoenoses that document rapid environmental changes and small sea level variations of about 2 5 m in amplitude and record these changes with more accuracy than coral and coralline algae assemblages which are highly dependant on the hydrodynamic energy of the setting during the pleistocene which was less chronologically constrained the microendolith ichnocoenoses also reflect paleo water depths and reef growth patterns at different periods of reef history

evidence for cryptoendolithic life in devonian pillow basalts of variscan orogens germany abstract late devonian frasnian pillow basalts from the frankenwald and thuringer wald within the saxothuringian zone in germany were found to contain abundant putative biogenic filaments indicating that the volcanic rocks once harbored microbial life the mineralized filaments are found in calcite filled amygdules former vesicles where they started to form on internal surfaces of vesicles after seawater ingress the filaments postdate an early fibrous carbonate cement but predate later equant calcite spar revealing syngenetic formation a biogenic origin of filaments is indicated by their size and morphology resembling modern microorganisms their independence of crystal faces and cleavage plans complex branching patterns and internal segmentation the filamentous microorganisms represent cryptoendoliths that lived in structural cavities of the basalt they became preserved upon microbial clay authigenesis similar to the encrustation of modern prokaryotes in iron rich environments filaments consist of clay minerals with the endmember composition berthierine chamosite and illite glauconite based on the discovery of fossilized filamentous microorganisms in late devonian pillow basalts of the saxothurigian zone that are similar to filaments previously found in middle devonian pillow basalts of the rhenohercynian zone it is apparent that cryptoendolithic life was more widespread than previously recognized structural cavities within seafloor basalt may thus represent a common perhaps universal niche for life in the oceanic crust

endolithic microorganisms in the antarctic cold desert in the frigid desert of the antarctic dry valleys there are no visible life forms on the surface of the soil or rocks yet in certain rock types a narrow subsurface zone has a favorable microclimate and is colonized by microorganisms dominant are lichens of unusual organization they survive not by physiological adaptation to lower temperatures but by changing their mode of growth being able to grow between the crystals of porous rocks their activity results in mobilization of iron compounds and in rock weatherning with a characteristic pattern of exfoliation this simple ecosystem lacks both higher consumers and predators

the fossil record of igneous rock abstract a growing awareness of life in deep igneous crust expands our appreciation for life s distribution in the upper geosphere through time and space and extends the known inhabitable realm of earth and possibly beyond for most of life s history until plants colonized land in the ordovician the deep biosphere was the largest reservoir of living biomass this suggests that deep crustal habitats played an important role in the evolution and development of the biosphere paradoxically the paleo perspective of deep life has been largely neglected in the exploration of the deep biosphere as well as in paleontology as a whole here we review the collective understanding of the fossil record in igneous crust with the aim to highlight a rising research field with great potential for substantial findings and progress in the near future we include new results that emphasize the importance of direct or indirect dating of fossils and introduction of new techniques into the field currently an incoherent record of morphological fossils and chemofossils stretching from present to 2 4 ga implies the presence of an abundant and rich yet largely unexplored fossil record further investigations of deep paleo environments will most certainly result in substantial insights into the distribution and development of biospheres throughout life s history the early evolution of prokaryotes and eukaryotes and earth s early biogeochemical cycles we emphasize the fossil record of igneous rock to give it the same status as the fossil record in sedimentary rocks and to implement fossil investigations as standard procedures in future international drilling campaigns

facilitation of endolithic microbial survival in the hyperarid core of the atacama desert by mineral deliquescence 1 the hyperarid core of the atacama desert is considered the dry limit for life on earth soils in this region have very low abundance of heterotrophic bacteria and are practically barren of photosynthetic microorganisms because of the extreme dry conditions 2 mm a 1 rainfall however relatively abundant endolithic communities of cyanobacteria chroococcidiopsis occur within halite crusts in paleolake evaporitic deposits by means of continuous monitoring of the microclimate conditions temperature relative humidity water vapor density wetness and photosynthetically active radiation inside and around the halite crusts we demonstrate here that water vapor condenses within the pore space of the halite at relative humidity rh levels that otherwise hinder the occurrence of liquid water in the surrounding environment water condensation occurs at rh 75 which corresponds to the deliquescence point of halite we have estimated a total of 57 deliquescence events i e water condensation within the halite crusts as opposed to only 1 liquid water event outside these wet events resulted in a total of 213 8 h of potential photosynthetic activity for the endolithic microorganisms versus only 6 h for organisms outside the halite crusts halite crusts may therefore represent the last available niche for photosynthetic activity in extreme arid environments on earth

intra crater sedimentary deposits at the haughton impact structure devon island canadian high arctic detailed field mapping has revealed the presence of a series of intra crater sedimentary deposits within the interior of the haughton impact structure devon island canadian high arctic coarse grained well sorted pale gray lithic sandstones reworked impact melt breccias unconformably overlie pristine impact melt breccias and attest to an episode of erosion during which time significant quantities of impact melt breccias were removed the reworked impact melt breccias are in turn unconformably overlain by paleolacustrine sediments of the miocene haughton formation sediments of the haughton formation were clearly derived from pre impact lower paleozoic target rocks of the allen bay formation which form the crater rim in the northern western and southern regions of the haughton structure collectively these field relationships indicate that the haughton formation was deposited up to several million years after the formation of the haughton crater and that they do not therefore represent an immediate post impact crater lake deposit this is consistent with new isotopic dating of impactites from haughton that indicate an eocene age for the impact event sherlock et al 2005 in addition isolated deposits of post miocene intra crater glacigenic and fluvioglacial sediments were found lying unconformably over remnants of the haughton formation impact melt breccias and other pre impact target rock formations these deposits provide clear evidence for glaciation at the haughton crater the wealth and complexity of geological and climatological information preserved as intra crater deposits at haughton suggests that craters on mars with intra crater sedimentary records might present us with similar opportunities but also possibly significant challenges

beachrock formation via microbial dissolution and re precipitation of carbonate minerals cementation of beach sand in the intertidal zone produces beachrock such as that found on heron island heron reef great barrier reef australia although common to coastlines in many low latitude beach environments the cause of cementation is not fully understood in this investigation electron and x ray fluorescence microscopy were used to characterize previously undocumented features of beachrock two generations of beachrock were examined as a means of understanding the progression of cementation meniscus shaped attachments at point contacts appear to be the first cements to form in biofilms near the beachrock surface this is followed by isopachous fringe cements within the now enclosed beachrock composed of aragonite needles that are enriched in strontium and contain extracellular polymeric substances eps cement precipitation is driven by locally high concentrations of cations in solution undoubtedly generated via microbial dissolution of the detrital carbonate grains binding to negatively charged bacterial eps retains these cations within beachrock microenvironments the metabolism of cyanobacteria and associated heterotrophs induce the supersaturating conditions needed for cement precipitation deeper within beachrock mm to cm below the surface abundant microbialites are found on the edges of grains and contain trapped and bound detrital material these structures are laminated enriched in strontium in some layers and contain microfossils the results of this investigation clearly demonstrate a biological influence in the precipitation of aragonite cement involving internal recycling of cations through microbial dissolution and precipitation of carbonate minerals

quantifying paleorecharge in the continental intercalaire ci aquifer by a monte carlo inversion approach of 36cl cl data abstract past variations of the recharge is estimated in the atlas mountains the main recharge area of the continental intercalaire ci aquifer one of the major saharan aquifers over the last 775 kyr in this mediterranean climatic context continental archives generally record single humid events grouped in hypothetical time interval and do not offer continuous chronicles of precipitation we propose to use spatially distributed 36 cl cl data as a temporal constraint to infer the past recharge in the atlas area based on a simplified but robust climatic scenario assuming a piston model we apply a markov chain monte carlo mcmc inversion approach to attribute a specific recharge to the last nine interglacial periods and an undifferentiated recharge to the glacial periods the interglacial recharge values vary from a few mm yr 1 to more than 60 mm yr 1 glacial recharge is less than 1 mm yr 1 these values are then analyzed in terms of intensity and allow questioning some initial hypothesis especially the generally accepted value of the initial 36 cl cl value around 133 10 15 at at 1 our analysis suggests a higher value around 175 10 15 at at 1 this approach allows us to bring out paleoclimatic information retained in these continental archives especially computed recharges provide reliable evidence that marine isotope stage mis 5 was more humid than the holocene period in agreement with marine archives that document wet condition in the north sahara during that period

carbonate silicate liquid immiscibility upon impact melting ries crater germany the 24 km diameter ries impact crater in southern germany is one of the most studied impact structures on earth the ries impactor struck a triassic to upper jurassic sedimentary sequence overlying hercynian crystalline basement at the time of impact 14 87 0 36 ma storzer et al 1995 the 350 m thick malm limestone was present only to the south and east of the impact site to the north and west the malm had been eroded away exposing the underlying dogger and lias the largest proportion of shocked target material is in the impact melt bearing breccia suevite the suevite had been believed to be derived entirely from the crystalline basement calcite in the suevite has been interpreted as a postimpact hydrothermal deposit from optical inspection of 540 thin sections of suevite from 32 sites i find that calcite in the suevite shows textural evidence of liquid immiscibility with the silicate impact melt textural evidence of liquid immiscibility between silicate and carbonate melt in the ries suevite includes carbonate globules within silicate glass silicate globules embedded in carbonate deformable and coalescing carbonate spheres within silicate glass sharp menisci or cusps and budding between silicate and carbonate melt fluidal textures and gas vesicles in carbonate schlieren a quench crystallization sequence of the carbonate spinifex textured quenched carbonate separate carbonate spherules in the suevite mineral fragment matrix and inclusions of mineral fragments suspended in carbonate blebs given this evidence of liquid immiscibility the carbonate in the suevite therefore has like the silicate melt a primary origin by impact shock melting evidence of carbonate silicate liquid immiscibility is abundant in the suevites from the southwest to east of the ries crater the rarer suevites to the west to northeast of the crater are nearly devoid of carbonate melts this correspondence between the occurrence of outcropping limestones at the target surface and the formation of carbonate melt indicates that the malm limestones are the source rocks of the carbonate impact melt this correspondence shows that the suevites preserve a compositional memory of their source rocks from the regional distribution of suevites with or without immiscible carbonate melts it is inferred that the ries impactor hit the steep albtrauf escarpment at its toe in an oblique impact from the north

the bosumtwi meteorite impact structure ghana a magnetic model abstract a magnetic model is proposed for the bosumtwi meteorite impact structure in ghana africa this relatively young 1 07 ma structure with a diameter of 10 5 km is exposed within early proterozoic birimian tarkwaian rocks the central part of the structure is buried under postimpact lake sediments and because of lack of drill cores geophysics is the only way to reveal its internal structure to study the structure below and beyond the lake a high resolution low altitude 70 m airborne geophysical survey across the structure was conducted which included measurements of the total magnetic field electromagnetic data and gamma radiation the magnetic data show a circumferential magnetic halo outside the lakeshore 12 km in diameter the central north part of the lake reveals a central negative magnetic anomaly with smaller positive side anomalies north and south of it which is typical for magnetized bodies at shallow latitudes a few weaker negative magnetic anomalies exist in the eastern and western part of the lake together with the northern one they seem to encircle a central uplift our model shows that the magnetic anomaly of the structure is presumably produced by one or several relatively strongly remanently magnetized impact melt rock or melt rich suevite bodies petrophysical measurements show a clear difference between the physical properties of preimpact target rocks and impactites suevites have a higher magnetization and have low densities and high porosities compared to the target rocks in suevites the remanent magnetization dominates over induced magnetization koenigsberger ratio 3 preliminary palaeomagnetic results reveal that the normally magnetized remanence component in suevites was acquired during the jaramillo normal polarity epoch this interpretation is consistent with the modelling results that also require a normal polarity magnetization for the magnetic body beneath the lake the reverse polarity remanence component superimposed on the normal component is probably acquired during subsequent reverse polarity events