low temperature feldspar and illite formation through bioreduction of fe iii bearing smectite by an alkaliphilic bacterium abstract biogenic mineral assemblages that form from circumneutral microbial reduction of iron in smectite have been suggested as biosignatures in the geological record however mineralogical transformation of smectite mediated by microbes under extreme ph condition is still poorly known the objective of this study was to understand the reduction capacity of structural fe iii in iron rich smectite nontronite nau 2 by a novel anaerobic alkaliphile strain ccsd 1 isolated from the deep subsurface and associated mineralogical changes the experiments with ccsd 1 were conducted in a growth medium containing the electron shuttle anthraquinone 2 6 disulfonate aqds at ph 9 4 the fe ii concentration was monitored over the course of the experiment via wet chemistry and unreduced and reduced nontronites were characterized with x ray diffraction xrd and scanning and transmission electron microscopy sem and tem the results indicate that strain ccsd 1 utilizes proteinaceous substrates yeast extract and tryptone to reduce structural fe iii in smectite with the maximum reduction extent of 26 2 mineralogical analysis confirmed that biogenic plagioclase na ca feldspar and illite were formed after bioreduction our work shows that the interaction between alkaliphile and iron bearing smectite could account for low temperature feldspar and illite formation and these minerals may be used as biosignatures in sedimentary rocks

microbe clay mineral interactions clays and clay minerals are common components in soils sediments and sedimentary rocks and they play an important role in many environmental processes iron is ubiquitous in clays and clay minerals and its oxidation state in part controls the physical and chemical properties of these fine grained minerals the structural ferric iron in clay minerals can be reduced either chemically or biologically biological reductants include mesophilic and thermophilic microorganisms from diverse environments such as soils sediments sedimentary rocks and hydrothermal hot springs multiple clay minerals have been used for microbial reduction studies including dioctahedral smectiteillite series palygorskite chlorite and their various mixtures in natural soils and sediments all of these clay minerals are reducible by microorganisms under various conditions with smectite nontronite being the most reducible and illite the least the rate and extent of bioreduction depends on many experimental factors such as the type of microorganisms and clay minerals solution chemistry and temperature despite significant efforts current understanding of the mechanisms of microbial reduction of ferric iron in clay minerals is still limited whereas some studies have presented evidence for a solid state reduction mechanism others argue that the clay mineral structure partially dissolves when the extent of reduction is high this inconsistency may be related to several experimental conditions and their specific effects are discussed in this paper whereas past experiments have been largely conducted in well controlled laboratory systems recent efforts have attempted to transfer knowledge to the field to improve our understanding of more complex soil systems for better agricultural practices biologically reduced clay minerals are also important agents in remediating inorganic and organic contaminants in soil and groundwater systems this paper reviews the most recent developments and suggests some directions for future research

shock metamorphism of bosumtwi impact crater rocks shock attenuation and uplift formation shock wave attenuation rate and formation of central uplifts are not precisely constrained for moderately sized complex impact structures the distribution of shock metamorphism in drilled basement rocks from the 10 5 kilometer diameter bosumtwi crater and results of numerical modeling of inelastic rock deformation and modification processes during uplift constrained with petrographic data allowed reconstruction of the pre impact position of the drilled rocks and revealed a shock attenuation by 5 gigapascals in the uppermost 200 meters of the central uplift the proportion of shocked quartz grains and the average number of planar deformation feature sets per grain provide a sensitive indication of minor changes in shock pressure the results further imply that for moderately sized craters the rise of the central uplift is dominated by brittle failure

dynamic modeling suggests terrace zone asymmetry in the chicxulub crater is caused by target heterogeneity we investigate the cause of terrace zone asymmetry in the chicxulub impact crater using dynamic models of crater formation marine seismic data acquired across the crater show that the geometry of the crater s terrace zone a series of sedimentary megablocks that slumped into the crater from the crater rim varies significantly around the offshore half of the crater the seismic data also reveal that at the time of impact both the water depth and sediment thickness varied with azimuth around the impact site to test whether the observed heterogeneity in the pre impact target might have affected terrace zone geometry we constructed two end member models of upper target structure at chicxulub based on the seismic data at different azimuths one model representing the northwest sector had no water layer and a 3 km thick sediment layer the other model representing the northeast sector had a 2 km water layer above a 4 km sediment layer numerical models of vertical impacts into these two targets produced final craters that differ substantially in terrace zone geometry suggesting that the initial water depth and sediment thickness variations affected the structure of the terrace zone at chicxulub moreover the differences in terrace zone geometry between the two numerical models are consistent with the observed differences in the geometry of the terrace zone at different azimuths around the chicxulub crater we conclude that asymmetry in the pre impact target rocks at chicxulub is likely to be the primary cause of asymmetry in the terrace zone

numerical simulations of impact crater formation with dilatancy impact induced fracturing creates porosity that is responsible for many aspects of the geophysical signature of an impact crater this paper describes a simple model of dilatancy the creation of porosity in a shearing geological material and its implementation in the isale shock physics code the model is used to investigate impact induced dilatancy during simple and complex crater formation on earth simulations of simple crater formation produce porosity distributions consistent with observations dilatancy model parameters appropriate for low quality rock masses give the best agreement with observation more strongly dilatant behavior would require substantial postimpact porosity reduction the tendency for rock to dilate less when shearing under high pressure is an important property of the model pressure suppresses impact induced dilatancy in the shock wave at depth beneath the crater floor and in the convergent subcrater flow that forms the central uplift consequently subsurface porosity distribution is a strong function of crater size which is reflected in the inferred gravity anomaly the bouguer gravity anomaly for simulated craters smaller than 25 km is a broad low with a magnitude proportional to the crater radius larger craters exhibit a central gravity high within a suppressed gravity low lower crustal pressures on the moon relative to earth imply that impact induced dilatancy is more effective on the moon than earth for the same size impact in an initially nonporous target this difference may be mitigated by the presence of porosity in the lunar crust

a strain based porosity model for use in hydrocode simulations of impacts and implications for transient crater growth in porous targets numerical modelling of impact cratering has reached a high degree of sophistication however the treatment of porous materials still poses a large problem in hydrocode calculations we present a novel approach for dealing with porous compaction in numerical modelling of impact crater formation in contrast to previous attempts e g p alpha model snowplow model our model accounts for the collapse of pore space by assuming that the compaction function depends upon volumetric strain rather than pressure our new e alpha model requires only four input parameters and each has a physical meaning the model is simple and intuitive and shows good agreement with a wide variety of experimental data ranging from static compaction tests to highly dynamic impact experiments our major objective in developing the model is to investigate the effect of porosity and internal friction on transient crater formation we present preliminary numerical model results that suggest that both porosity and internal friction play an important role in limiting crater growth over a large range in gravity scaled source size

the formation of peak ring basins working hypotheses and path forward in using observations to constrain models of impact basin formation abstract impact basins provide windows into the crustal structure and stratigraphy of planetary bodies however interpreting the stratigraphic origin of basin materials requires an understanding of the processes controlling basin formation and morphology peak ring basins exhibiting a rim crest and single interior ring of peaks provide important insight into the basin formation process as they are transitional between complex craters with central peaks and larger multi ring basins new image and altimetry data from the lunar reconnaissance orbiter as well as a suite of remote sensing datasets have permitted a reassessment of the origin of lunar peak ring basins we synthesize morphometric spectroscopic and gravity observations of lunar peak ring basins and describe two working hypotheses for the formation of peak rings that involve interactions between inward collapsing walls of the transient cavity and large central uplifts of the crust and mantle major facets of our observations are then compared and discussed in the context of numerical simulations of peak ring basin formation in order to plot a course for future model refinement and development

a growing sandstone type uranium district in south yili basin nw china as a result of extension of tien shan orogen evidences from geochronology and hydrology abstract the mesozoic yili basin of nw china represents the largest known concentration of u deposits in china and contains five major deposits namely from west to east the 512 kujie ertai 513 511 510 mengqiguer and 509 deposits pre mining resources within the explored sandstone type uranium deposits in this area are reportedly as much as 20 000 t contained u the mineralization is hosted by the middle lower jurassic shuixigou group which from base to top is divided into the badaowan sangonghe and xishanyao formations the u pb isotopic analysis of ores from the kujie ertai and mengqiguer deposits indicate that they contain high and variable amounts of initial common pb meaning that the only possible way to date these deposits is by using u pb isochrons two major stages of uranium mineralization have been identified by the u pb isotope dating of uranium ores in this region the kujie ertai deposit apparently formed between 23 4 3 3 and 20 18 0 49 ma corresponding to a period of crustal thickening and uplift within the tien shan orogen this event 35 21 ma accommodated the majority of the strain generated by the northward collision of the indian plate with the asian plate however the dating of samples from the mengqiguer deposit yielded much younger ages between 0 61 0 24 and 0 347 0 0048 ma the western tien shan mountains expanded until the pliocene as a result of the far field influence of continuous penetration of the indian plate into the asian plate this activated reverse faults and folds in the piedmont of the tien shan mountains and caused the continuous uplift of the southern flank of the yili basin the uplift caused the erosion of anticline hinge zones introducing significant amounts of oxidizing water into the shuixigou group generating a second stage of uranium mineralization hydrological sampling also suggests that the mengqiguer deposit continues to grow indicating a possible third stage of uranium mineralization 0 ma this also indicates that the u within these deposits is derived not only from u bearing sediments but from the tien shan mountains as a result of groundwater cycling the evolution of the u contents of groundwater that was initially derived from cold springs that flow into the mineralized units indicates that these cold springs have an essential role in mobilizing u from the tien shan mountains with rivers flowing through areas of outcropping mineralized units acting as a source of mineralizing fluids during the formation of the mengqiguer deposit

dark halo craters and the thickness of grooved terrain on ganymede dark halo craters in grooved terrain on ganymede represent potential probes of the subsurface geology these craters are surrounded by a broad diffuse low albedo annulus or halo halo radius is linearly proportional to crater radius indicating that the halo is related to the continuous ejecta deposit of the crater and is not removed by natural aging processes such as regolith development and exposure to the space environment the halos have orange violet albedo ratios that are intermediate between ratios associated with grooved terrain and cratered terrain we propose that halos result from the incorporation of cratered terrain material into crater ejecta in uruk sulcus only craters greater than 12 km in diameter have halos indicating that the cratered terrain material there forms a stratigraphic horizon buried at depth in the grooved terrain into which only larger craters can excavate this depth can be calculated from the transition diameter by reconstructing the transient crater we calculate a depth of excavation corresponding to the depth of burial of cratered terrain of 1 0 to 1 6 km this shallow burial is inconsistent with deep subsidence and burial stoping into the interior or lateral spreading apart of ancient cratered terrain units but is consistent with a filled graben model for grooved terrain where relatively clean ice has been emplaced over downdropped blocks of cratered terrain

shock barometry of the siljan impact structure sweden the siljan impact structure in sweden is the largest confirmed impact structure in western europe despite this the structure has been poorly studied in the past and detailed studies of shock metamorphic features in the target lithologies are missing here we present the results of a detailed systematic search for shock metamorphic features in quartz grains from 73 sampled localities at siljan at 21 localities from an area approximately 20 km in diameter located centrally in the structure the orientations of 2851 planar deformation feature sets in 1179 quartz grains were measured observations of shatter cones outside of the zone with shocked quartz extend the total shocked area to approximately 30 km in diameter the most strongly shocked samples recording pressures of up to 20 gpa occur at the very central part of the structure and locally in these samples higher pressures causing melting conditions in the affected rocks were reached pressures recorded in the studied samples decrease outwards from the center of the structure forming roughly circular envelopes around the proposed shock center based on the distribution pattern of shocked quartz at siljan the original transient cavity can be estimated at approximately 3238 km in diameter after correcting for erosion we conclude that the original rim to rim diameter of the siljan crater was somewhere in the size range 5090 km less

the role of bacterial extracellular polymeric substances in geomicrobiology abstract the last two decades have seen geomicrobiology evolve into a broad field encompassing a wide range of environmentally significant processes such as proton and metal adsorption onto cell surfaces and the effect of microbes on mineralisation redox cycling and contaminant transport within this sphere research groups have conducted studies using bacteria fungi diatoms and sludges all of which can play a part in geochemical processes here we review research on the role played by microbial extracellular polymeric substances eps focussing on bacterial and cyanobacterial eps we conclude by outlining future research directions in order to investigate unresolved questions in the field the effect of eps on metal adsorption is complex whereas some studies report an increase in metal adsorption when cells contain eps some report no differences yet others report a decrease these discrepancies may reflect differences in molecular and functional group composition of the eps eps provides a template for adsorption of metal cations to which carbonate ions are attracted to induce local mineral supersaturation this may be behind observed changes in both crystal polymorphism favouring formation of less stable polymorphs and crystal morphology where the presence of eps promotes the formation of rounded smoothed crystals or spheroids the role of eps in mineral dissolution bioleaching and corrosion is equivocal eps alone appears to have little effect on mineral dissolution bioleaching or biocorrosion instead it appears that eps increases rates of mineral weathering and leaching by forming complexes with metallic ions released by the mineral surface which may themselves catalyse bioleaching in the case of sulphides eps in biofilms forms effective barriers to the transport of particulate phases and exerts important controls on the transport and deposition of natural and engineered nanoparticles much less is known about the role of eps in the cycling of redox sensitive trace metals intuitively and as observed in microbial mats with sulphate reducing bacteria eps is a labile electron donor for microbial metabolism that could affect metal biogeochemistry but this remains to be conclusively demonstrated in laboratory experiments hence in this and other areas further studies are required to develop a mechanistic basis for including the effects of eps in biogeochemical models

nonuniform cratering of the moon and a revised crater chronology of the inner solar system abstract we model the cratering of the moon and terrestrial planets from the present knowledge of the orbital and size distribution of asteroids and comets in the inner solar system in order to refine the crater chronology method impact occurrences locations velocities and incidence angles are calculated semi analytically and scaling laws are used to convert impactor sizes into crater sizes our approach is generalizable to other moons or planets the lunar cratering rate varies with both latitude and longitude with respect to the global average it is about 25 lower at 65 n 90 e and larger by the same amount at the apex of motion 0 n 90 w for the present earth moon separation the measured size frequency distributions of lunar craters are reconciled with the observed population of near earth objects under the assumption that craters smaller than a few kilometers in diameter form in a porous megaregolith varying depths of this megaregolith between the mare and highlands is a plausible partial explanation for differences in previously reported measured size frequency distributions we give a revised analytical relationship between the number of craters and the age of a lunar surface for the inner planets expected size frequency crater distributions are calculated that account for differences in impact conditions and the age of a few key geologic units is given we estimate the orientale and caloris basins to be 3 73 ga old and the surface of venus to be 240 ma old the terrestrial cratering record is consistent with the revised chronology and a constant impact rate over the last 400 ma better knowledge of the orbital dynamics crater scaling laws and megaregolith properties are needed to confidently assess the net uncertainty of the model ages that result from the combination of numerous steps from the observation of asteroids to the formation of craters our model may be inaccurate for periods prior to 3 5 ga because of a different impactor population or for craters smaller than a few kilometers on mars and mercury due to the presence of subsurface ice and to the abundance of large secondaries respectively standard parameter values allow for the first time to naturally reproduce both the size distribution and absolute number of lunar craters up to 3 5 ga ago and give self consistent estimates of the planetary cratering rates relative to the moon

complex craters relationship of stratigraphy and rings to impact conditions one of the key issues associated with the understanding of large scale impacts is how the observable complex crater structural features e g central peaks and pits flat floors ring shaped ridges and depressions stratigraphic modifications and faults relate to the impactor s parameters e g radius velocity and density and the nonobservable transient crater measures e g depth of penetration and diameter at maximum penetration we have numerically modeled large scale impacts on planets for a range of impactor parameters gravity and planetary material strengths from these we found that the collapse of the transient cavity results in the development of a tall transient central peak that oscillates and drives surface waves that are arrested by the balance between gravitational forces and planetary strength to produce a wide range of the observed surface features in addition we found that the underlying stratigraphy is inverted outside of the transient cavity diameter overturned flap region but not inside this change in stratigraphy is observable by remote sensing drilling seismic imaging and gravity mapping techniques we used the above results to develop scaling laws and to make estimates of the impact parameters for the chicxulub impact and also compared the calculated stratigraphic profile with the internal structure model developed by hildebrand et al 1998 using gravity seismic and other field data for a stratigraphy rotation diameter of 90 km the maximum depth of penetration is 43 km the impactor diameter was also calculated from the scaling relationships we get for a 2 7 g cm 3 asteroid impacting at 20 km s or a 1 0 g cm 3 comet impacting at 40 km s an impactor diameter of 13 km and for a comet impacting at 60 km s an impactor diameter of 10 km

hydrocode modeling of the sierra madera impact structure we present the first hydrocode simulations of the formation of the sierra madera structure west texas usa which was caused by an impact into a thick sedimentary target sequence we modeled sierra madera using the isale hydrocode and here we present two best fit models 1 a crater with a rim final crater diameter of 12 km in agreement with previous authors interpretations of the original structure and 2 a crater 16 km in diameter with increased postimpact erosion both models fit some of the geologic observational data but discrepancies with estimates of peak shock pressure extent of deformation and stratigraphic displacement remain this study suggests that sierra madera may be a larger crater than previously reported and illustrates some of the challenges in simulating impact deformation of sedimentary lithologies as many terrestrial craters possess some amount of sedimentary rocks in the target sequence numerical models of impacts into sedimentary targets are essential to our understanding of target rock deformation and the mechanics of crater formation

experimental constraints on shock induced microstructures in naturally deformed silicates abstract planar deformation features pdfs in various minerals have long been accepted as evidence of impact induced deformation the uniqueness of this association was challenged in the context of the k t boundary extinction debate after mosaicism and microstructures similar to pdfs were reported from the products of explosive volcanism as a result of this debate a significant volume of new experimental and observational data on the development of shock induced microstructures has become available over the last ten years the results reveal that factors such as pre shock temperature pulse duration and crystallographic orientation of target minerals to the shock wave have a primary influence on how these microstructures develop data from diamond anvil cell and high pressure friction experiments reveal that the same solid state amorphization process that produces shock induced pdfs at low temperatures also occurs at much lower strain rates in static experiments the experimental data indicate that the amorphization process is thermally activated and that the character of the resulting pdfs is a function of the applied strain rate shock induced amorphization occurs along those crystallographic planes that are most readily transformed to the high pressure phase during very short pulse durations and produces pdfs that are visible at the optical scale lower strain rate deformation produces tem scale amorphization with orientations that are more homogeneously distributed throughout the target mineral and produces no optically visible pdfs the data confirm the uniqueness of multiple intersecting sets of optically visible pdfs as a diagnostic indicator of hypervelocity impact the data also support the hypothesis that the amorphization process can occur at a wide range of strain rates and that the limiting pressure for the process is controlled by the phase stability of the target mineral under the applied loading conditions not by the hel the data also suggest that the onset pressure the maximum pressure and the pressure range for producing optically visible pdfs decrease with increasing temperature and decreasing strain rate as the pressure range for optically visible pdf formation decreases it is replaced by homogeneous amorphization as observed in the anvil cell experiments thus the uniqueness of multiple intersecting sets of optically visible pdfs to hypervelocity impact is not due to a unique process but rather to a specific set of loading conditions that produce an optically visible microstructure likewise single sets of microdeformations observed in volcanic rocks are produced by the same process but at different loading conditions that preclude the development of multiple intersecting sets of pdfs the data also indicate that shock mosaicism which occurs above the hel represents a plastic response of the target mineral to loading rates that are too large to be accommodated by crystal plastic mechanisms observational data for some naturally deformed samples from the k t boundary the vredefort dome and volcanic rocks along with the experimental observations are used to constrain the range of conditions under which the natural microstructures form and to understand the differences between microstructures produced by impact volcanic and other natural processes finally some possible mechanisms for producing the microstructures observed in volcanic rocks are proposed

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

rock fluidization during peak ring formation of large impact structures large meteorite impact structures on the terrestrial bodies of the solar system contain pronounced topographic rings which emerged from uplifted target crustal rocks within minutes of impact to flow rapidly over large distances these target rocks must have weakened drastically but they subsequently regained sufficient strength to build and sustain topographic rings the mechanisms of rock deformation that accomplish such extreme change in mechanical behaviour during cratering are largely unknown and have been debated for decades recent drilling of the approximately 200 km diameter chicxulub impact structure in mexico has produced a record of brittle and viscous deformation within its peak ring rocks here we show how catastrophic rock weakening upon impact is followed by an increase in rock strength that culminated in the formation of the peak ring during cratering the observations point to quasi continuous rock flow and hence acoustic fluidization as the dominant physical process controlling initial cratering followed by increasingly localized faulting

reduction of structural fe iii in nontronite by thermophilic microbial consortia enriched from hot springs in tengchong yunnan province china abstract iron redox cycling provides one of the most important energy sources supporting microorganisms in terrestrial hot springs in order to understand microbial fe iii reduction processes in hot springs fe iii reducing bacterial consortia were successfully retrieved from seven acidic hot springs in tengchong county yunnan province china a temperature range from 40 6 c to 74 7 c and a ph range from 2 64 to 4 72 these fe iii reducing consortia were mainly composed of sulfate reducing bacteria srb including desulfotomaculum thermodesulfobacterium and desulfomicrobium and organic matter fermenting bacteria thermoanaerobacterium and thermoanaerobacter with each consortia having specific composition depending on the physio chemical conditions of the studied hot springs the obtained consortia were capable of dissimilatory reduction of fe iii in nontronite nau 2 ferruginous smectite with 20 8 to 29 8 reduction extent and initial reduction rate of 0 011 0 023 mm fe iii g nau 2 h these extents and rates were comparable to those by mesophilic fe reducers in the presence of electron shuttles both high temperature and the possible presence of electron shuttles in hot springs may have accounted for these observed high reduction extents and rates various secondary minerals formed during nau 2 bioreduction including fe sulfides and oxides silicates and silica in one spring illitization and kaolinization of smectite were observed suggesting that fe reducers play important roles in mineral transformation in geothermal environments

hydrocode simulations of chicxulub crater collapse and peak ring formation we use hydrocode modeling to investigate dynamic models for the collapse of the chicxulub impact crater our aim is to integrate the results from numerical simulations with kinematic models derived from seismic reflection and wide angle velocity data to further our understanding of the formation of large impact craters in our simulations we model the collapse of a 100 km diameter bowlshaped cavity formed in comprehensively fractured crustal material to facilitate wholesale collapse we require that the strength of the target be significantly weakened in the present model we achieve this using acoustic fluidization where strong vibrations produced by the expanding shock wave cause extreme pressure fluctuations in the target at times and positions where the overburden pressure is sufficiently counteracted the frictional resistance is reduced enabling the rock debris to flow our simulations produce a collapsed crater that contains most of the features that we observe in the seismic data at chicxulub in particular we observe a topographic peak ring formed as material that is originally part of the central uplift collapses outward and is thrust over the inwardly collapsing transient crater rim this model for peak ring generation has not been previously demonstrated by numerical simulations and predicts that the peak ring is composed of deeply derived material and that the stratigraphy within the peak ring is overturned c 2002 elsevier science usa

mid sized complex crater formation in mixed crystalline sedimentary targets insight from modeling and observation large impact crater formation is an important geologic process that is not fully understood the current paradigm for impact crater formation is based on models and observations of impacts in homogeneous targets real targets are rarely uniform for example the majority of earth s surface is covered by sedimentary rocks and or a water layer the ubiquity of layering across solar system bodies makes it important to understand the effect target properties have on the cratering process to advance understanding of the mechanics of crater collapse and the effect of variations in target properties on crater formation the first bridging the gap workshop recommended that geological observation and numerical modeling focussed on mid sized 15 30 km diameter craters on earth these are large enough to be complex small enough to be mapped surveyed and modelled at high resolution and numerous enough for the effects of target properties to be potentially disentangled from the effects of other variables in this paper we compare observations and numerical models of three 18 26 km diameter craters formed in different target lithology ries germany haughton canada and el gygytgyn russia based on the first order assumption that the impact energy was the same in all three impacts we performed numerical simulations of each crater to construct a simple quantitative model for mid sized complex crater formation in a subaerial mixed crystalline sedimentary target we compared our results with interpreted geological profiles of ries and haughton based on detailed new and published geological mapping and published geophysical surveys our combined observational and numerical modeling work suggests that the major structural differences between each crater can be explained by the difference in thickness of the pre impact sedimentary cover in each case we conclude that the presence of an inner ring at ries and not at haughton is because basement rocks that are stronger than the overlying sediments are sufficiently close to the surface that they are uplifted and overturned during excavation and remain as an uplifted ring after modification and post impact erosion for constant impact energy transient and final crater diameters increase with increasing sediment thickness

rb sr dating of the impact melt from east clearwater quebec the rb sr composition of eight melt rock and three basement samples from the east clearwater impact structure quebec and two basement samples from the west clearwater structure has been determined the whole rock 87sr 86sr ratios of the melt samples 0 7167 0 7253 are within the range of the basement samples 0 7054 0 7322 and provide further evidence that the melt rocks represent shock melted basement a mineral isochron obtained from a relatively coarse grained melt rock gives an age of 287 26 ma for the crystallization age of the melt this is equivalent to k ar whole rock ages of 285 30 ma and 300 30 ma and a rb sr age of 266 15 ma obtained on melt rocks from west clearwater and confirms the previously generally held assumption that the east and west clearwater structures resulted from the simultaneous impact of two bodies at 285 300 ma ago

dynamical weakening of faults by acoustic fluidization when a fault slips seismically some of the energy released may excite strong short wavelength vibrations near the fault core such vibrations can temporarily reduce the normal stress on the fault allowing it to slip at lower shear stresses than predicted by laboratory coefficients of friction this phenomenon of acoustic fluidization provides an alternative to theories that invoke pressurized fluids as an explanation for why some faults appear to be so weak

a loading model for an owc caisson based upon large scale measurements wave energy is one of the most promising marine energy resources in terms of the scale of the resource but there remains little technology convergence and costs remain at near prohibitive levels of many wave energy converter wec concepts that have been developed over the years the oscillating water column owc stands out for its simplicity and low maintenance cost quite some experience of actual owc operation has been gained to date from small stand alone pilot schemes one way to reduce costs is the integration of an owc wec into a breakwater enabling some degree of cost sharing between energy and harbour or coastal defence functions a major problem encountered during the design of an owc wec scheme remains the uncertainty in the wave loads with their critical influence upon capital cost a model to estimate forces acting on an owc chamber in a caisson breakwater is proposed in this paper horizontal forces on the front curtain wall and the rear in chamber wall are predicted in addition and unlike a conventional caisson breakwater vertical forces acting on the caisson chamber ceiling will have considerable effect on sliding and overturning characteristics of the breakwater structure the proposed model enables the prediction of chamber pressures which in turn influence the chamber vertical force the new model has been compared with results from large scale physical model measurements from tests carried out in the very large wave channel gwk in hannover germany forces under both regular and irregular wave conditions were measured the comparisons show that the model fits well with the test results to the factor of 1 0 2 for the regular wave cases and to the factor of 0 8 0 2 for irregular wave cases this model will enable the structural design of caisson breakwater integrated owcs to be approached with uncertainties reduced to those comparable with conventional caisson design

insights into the morphology of the serra da cangalha impact structure from geophysical modeling forward modeling is commonly applied to gravity field data of impact structures to determine the main gravity anomaly sources in this context we have developed 2 5 d gravity models of the serra da cangalha impact structure for the purpose of investigating geological bodies structures underneath the crater interpretation of the models was supported by ground magnetic data acquired along profiles as well as by high resolution aeromagnetic data ground magnetic data reveal the presence of short wavelength anomalies probably related to shallow magnetic sources that could have been emplaced during the cratering process aeromagnetic data show that the basement underneath the crater occurs at an average depth of about 1 9 km whereas in the region beneath the central uplift it is raised to 0 5 1 km below the current surface these depths are also supported by 2 5 d gravity models showing a gentle relief for the basement beneath the central uplift area geophysical data were used to provide further constraints for numeral modeling of crater formation that provided important information on the structural modification that affected the rocks underneath the crater as well as on shock induced modifications of target rocks the results showed that the morphology is consistent with the current observations of the crater and that serra da cangalha was formed by a meteorite of approximately 1 4 km diameter striking at 12 km s 1

influence of organic matter on smectite illitization a comparison between red and dark mudstones from the dongying depression china interactions between organic matter om and clay minerals have received considerable attention in previous studies the influence of om on smectite illitization has been analyzed primarily in simulation experiments rather than in diagenetic studies the present study explores the influence of om on smectite illitization during diagenesis thirty red and dark mudstone samples from the dongying depression were analyzed x ray diffraction xrd analyses revealed that the illite percentages in mixed layer illite smectite i s of both types of samples were dispersive above 3100 m and more convergent below this depth the stacking mode of i s in dark mudstones above 3100 m remained primarily at r0 r0 5 ordering with the average number of layers nave dispersively distributed between 2 and 4 5 in red mudstones the i s changed from the r0 to r0 5 mode with the nave increasing from 2 to 5 over this range the smectite illitization in dark mudstones was slower than that in red mudstones below 3100 m the i s stacking mode of dark mudstones changed from r0 5 to r3 ordering with the nave increasing sharply from 4 to 8 in red mudstones the i s displayed r1 5 and r3 ordering with the nave varying between 4 5 and 6 5 over this range the smectite illitization in dark mudstones accelerated rapidly whereas the process in red mudstones was retarded additionally the red mudstone samples contained little om whereas the dark mudstone samples contained abundant total organic carbon 0 17 4 43 thermo xrd near infrared nir as well as mid infrared mir spectroscopy analyses suggested that the om in dark mudstones exhibited a significant transition at 3100 m coincident with the illitization change above 3100 m the smectite illitization in dark mudstones was delayed due to the om pillar effect in the interlayer spaces of smectite below 3100 m the interlayer om became varied and desorbed discharging organic acid this led to the dissolution of smectite structural layers consequently illitization in the dark mudstone was accelerated this study revealed that the existence and occurrence of om could influence the smectite illitization in diagenesis further study on the interactions between om and clay minerals is needed to facilitate our understanding on the mechanism of smectite illitization as well as its geological applications

how big was the chesapeake bay impact insight from numerical modeling the chesapeake bay impact structure virginia is the largest impact crater in the united states the important question of how large the impactor was that formed the crater remains unanswered this is primarily due to peculiarities of the crater structure revealed by seismic exploration that complicate comparisons with other terrestrial and extraterrestrial craters one potential explanation for the unusual structure of the chesapeake bay crater is that the cratering process was affected by rheologic variations in the target at the time of impact using numerical modeling we find that for a sufficient contrast in material strength between the sedimentary and crystalline units at the chesapeake bay impact site we can produce a model of the final crater that is consistent with observational constraints and hence we can infer the energy released during the impact 1 75 3 10 6 mt in the absence of target strength variations the final crater diameter is likely to have been 40 km rather than the observed 80 90 km

shock metamorphism of quartz in nature and experiment ii significance in geoscience the occurrence of shock metamorphosed quartz is the most common petrographic criterion for the identification of terrestrial impact structures and lithologies its utility is due to its almost ubiquitous occurrence in terrestrial rocks its overall stability and the fact that a variety of shock metamorphic effects occurring over a range of shock pressures have been well documented these shock effects have been generally duplicated in shock recovery experiments and thus serve as shock pressure barometers after reviewing the general character of shock effects in quartz the differences between experimental and natural shock events and their potential effects on the shock metamorphism of quartz are explored the short pulse lengths in experiments may account for the difficulty in synthesizing the high pressure polymorphs coesite and stishovite compared to natural occurrences in addition post shock thermal effects are possible in natural events which can affect shock altered physical properties such as refractive index and cause annealing of shock damage and recrystallization the orientations of planar microstructures however are unaffected by post impact thermal events except if quartz is recrystallized and provide the best natural shock barometer in terms of utility and occurrence the nature of planar microstructures particularly planar deformation features pdfs is discussed in some detail and a scheme of variations in orientations with shock pressure is provided the effect of post impact events on pdfs is generally limited to annealing of the original glass lamellae to produce decorated pdfs resulting from the exsolution of dissolved water during recrystallization basal 0001 pdfs differ from other pdf orientations in that they are multiple mechanical brazil twins which are difficult to detect if not partially annealed and decorated the occurrence and significance of shock metamorphosed quartz and its other phases namely coesite stishovite diaplectic glass and lechatelierite are discussed for terrestrial impact structures in both crystalline non porous and sedimentary porous targets the bulk of past studies have dealt with crystalline targets where variations in recorded shock pressure in quartz have been used to constrain aspects of the cratering process and to estimate crater dimensions at eroded structures in sedimentary targets the effect of pore space results in an inhomogeneous distribution in recorded shock pressure and temperature which requires a different classification scheme for the variation of recorded shock compared to that in crystalline targets this is discussed along with examples of variations in the relative abundances of planar microstructures and their orientations which are attributed to textural variations in sedimentary target rocks examples of the shock metamorphism of quartz in distal ejecta such as at the k t boundary and from nuclear explosions are illustrated and are equivalent to that of known impact structures except with respect to characteristics that are due to long term post shock thermal effects finally the differences between the deformation and phase transformation of quartz by shock and by endogenic tectonic and volcanic processes are discussed we confirm previous conclusions that they are completely dissimilar in character due to the vastly different physical conditions and time scales typical for shock events compared to tectonic and volcanic events well characterized and documented shock effects in quartz are unequivocal indicators of impact in the natural environment

microbially mediated iron redox cycling of subsurface sediments from hanford site washington state usa abstract iron bearing clay minerals are predominant in soils and sediments and they undergo oxidation reduction cycles as a result of natural processes such as wetting drying cycles and plant root respiration however the kinetics and mechanisms of multiple redox cycles of iron in clay rich sediments and consequences of such cycling on sediment properties are poorly understood the objective of this study was to understand how multiple redox cycles of fe in clay rich sediment affect the rate and extent of fe bioreduction and the physicochemical properties of the sediment a natural sediment sample containing fe bearing montmorillonite from hanford washington usa was size fractionated 2 0 to 0 5 m hanford c and 0 5 to 0 02 m hanford f and redox cycled for four times bioreduction was achieved utilizing geobacter sulfurreducens and re oxidization was performed with sparged air time course change of total fe ii was monitored to measure the rate and extent of fe iii bioreduction redox cycled sediments were characterized to determine the physicochemical changes both the initial rate and extent of bioreduction fluctuated across the four redox cycles but they ultimately decreased from 5 3 mol g 1 h 1 and 22 9 to nearly zero by the fourth cycle these fluctuation patterns were likely due to a combined effect of reductive dissolution of small poorly crystalline clay particles by 3 5 and clay mineral structural changes as evidenced by redox induced changes of aqueous chemistry surface area cation exchange capacity mineralogy and mossbauer parameters once these small poorly crystalline clay particles were dissolved structural fe in residual larger and more crystalline clay particles was largely reversible across additional redox cycles as revealed by mossbauer spectroscopy through the first three cycles

microbial dissolution of clay minerals as a source of iron and silica in marine sediments interactions between microbes and minerals have the potential to contribute significantly to the global cycles of various elements and serve as a link between the geosphere and life in particular the microbially mediated cycle of iron within marine sediments is closely tied to the carbon cycle the dissolved iron that serves as a nutrient is thought to be primarily drawn from well known pools of highly reactive bioavailable iron and iron complexes iron contained within the crystal lattice of clay minerals the most abundant materials found at the earth s surface is not thought to be part of this pool here we analyse the mineral composition of middle cambrian aged mudstones from the western united states we find intergrown mineral aggregates of quartz pyrite and calcite on the basis of mineral phase relationships and temperatures of crystallization derived from stable isotopes of oxygen we infer that mineral dissolution driven by microbes released iron and silica to the surrounding sediment pore waters and led to the subsequent precipitation of the observed minerals the microbial extraction of structurally coordinated fe3 from clay minerals after their deposition in marine sediments may liberate a fraction of iron previously considered unavailable and may be important in iron and silica cycling in marine sediments interactions between microbes and minerals are evident in modern global elemental cycles relationships between minerals in cambrian mudstones indicate that such interactions may have released otherwise unavailable mineral bound iron and silica into the ancient oceans

new 40ar 39ar dating of the clearwater lake impact structures quebec canada not the binary asteroid impact it seems abstract the two clearwater lake impact structures quebec canada are generally interpreted as a crater doublet formed by the impact of a binary asteroid here arguments are presented that raise important questions about the proposed double impact scenario new 40 ar 39 ar dating of two virtually fresh impact melt rock samples from the 36 km west clearwater lake impact structure yielded two statistically robust early permian plateau ages with a weighted mean of 286 2 2 2 2 6 ma 2 mswd 0 33 p 0 57 in contrast 40 ar 39 ar results for two chloritized melt rocks from the 26 km east clearwater lake impact structure produced disturbed age spectra suggestive of a distinct extraneous argon component although individually weakly robust age spectra corrected for the trapped argon component and inverse isochron plots for the east clearwater melt rocks consistently yielded apparent ages around 460 470 ma no permian signal was found in either of these melt aliquots our new 40 ar 39 ar results reproduce earlier 40 ar 39 ar plateau ages 283 ma and 465 ma respectively for the two impact structures by bottomley et al 1990 and are in conflict with a previous statistically non robust rb sr age of 287 293 26 ma for east clearwater the combined cluster of apparent ages of 460 470 ma derived from four different samples across the impact melt sheet is very unlikely to represent a false age effect due to the incorporation of extraneous argon into the melt instead it strongly favors a middle ordovician age for the east clearwater impact and impact induced hydrothermal chloritization moreover the clearwater impact structures are characterized by different natural remanent magnetizations testifying to separate geologic histories an effect unexpected in the case of a permian double impact whereas the west clearwater impact affected ordovician carbonates incorporated into the impact breccia drill core reports from the 1960s concluded that clasts of ordovician sedimentary rocks are seemingly absent in the impact breccia lens of the east clearwater lake impact structure which is overlain by 100 m of post impact sandstones shales and carbonates no resolvable impactor contamination has so far been detected in the west clearwater impact melt rocks whereas east clearwater carries a distinct ordinary possibly l chondritic impactor signature in its melt rocks east clearwater lake might thus represent one among a long list of ordovician impact structures in north america and northern europe that were presumably formed in response to the l chondrite asteroid breakup event 470 ma ago paleogeographic reconstructions show that the ordovician east clearwater impact probably occurred in a near coastal to shallow marine setting while the permian west clearwater impact hit continental pangaea along with the new 40 ar 39 ar data the paleomagnetic sedimentologic and geochemical findings suggest that the close spatial arrangement of the two clearwater lakes is most likely pure coincidence the two impact structures seem to represent a false doublet struck by impacts separated by 180 million years in time the new results for the clearwater lake impact structures have major implications for the reliable identification of doublet impact craters and the rate of binary asteroid impacts on earth and on other planetary bodies in the inner solar system

shock metamorphic features and their zoning and orientation in the precambrian rocks of the manicouagan structure quebec canada abstract the manicouagan structure of impact origin is located in eastern quebec about 300 km north of the st lawrence river the complex is of triassic age the shock deformation of the more important rock forming minerals of the autochthonous or at least parautochthonous rocks within the structure is described four zones of shock metamorphism are delineated based on the deformation features of plagioclase 1 plagioclase without planar features 2 plagioclase with planar features 3 first occurrence of plagioclase with partial isotropization and 4 first occurrence of plagioclase with total isotropization these four zones are more or less concentric and indicate a general increase in the grade of shock metamorphism towards the centre of the structure however several small areas probably underlain by allochthonous rocks appear not to fit this general picture biotite and garnet show evidence of a shock orientation of their deformation features an impact origin for the structure is favoured the impact possibly triggering volcanism

complex crater formation insights from combining observations of shock pressure distribution with numerical models at the west clearwater lake impact structure large impact structures have complex morphologies with zones of structural uplift that can be expressed topographically as central peaks and or peak rings internal to the crater rim the formation of these structures requires transient strength reduction in the target material and one of the proposed mechanisms to explain this behavior is acoustic fluidization here samples of shock metamorphosed quartz bearing lithologies at the west clearwater lake impact structure canada are used to estimate the maximum recorded shock pressures in three dimensions across the crater these measurements demonstrate that the currently observed distribution of shock metamorphism is strongly controlled by the formation of the structural uplift the distribution of peak shock pressures together with apparent crater morphology and geological observations is compared with numerical impact simulations to constrain parameters used in the block model implementation of acoustic fluidization the numerical simulations produce craters that are consistent with morphological and geological observations the results show that the regeneration of acoustic energy must be an important feature of acoustic fluidization in crater collapse and should be included in future implementations based on the comparison between observational data and impact simulations we conclude that the west clearwater lake structure had an original rim final crater diameter of 35 40 km and has since experienced up to 2 km of differential erosion

estimating average shock pressures recorded by impactite samples based on universal stage investigations of planar deformation features in quartz sources of error and recommendations planar deformation features pdfs in quartz are the most widely used indicator of shock metamorphism in terrestrial rocks they can also be used for estimating average shock pressures that quartz bearing rocks have been subjected to here we report on a number of observations and problems that we have encountered when performing universal stage measurements and crystallographically indexing of pdf orientations in quartz these include a comparison between manual and automated methods of indexing pdfs an evaluation of the new stereographic projection template and observations regarding the pdf statistics related to the c axis position and rhombohedral plane symmetry we further discuss the implications that our findings have for shock barometry studies our study shows that the currently used stereographic projection template for indexing pdfs in quartz might induce an overestimation of rhombohedral planes with low miller bravais indices we suggest based on a comparison of different shock barometry methods that a unified method of assigning shock pressures to samples based on pdfs in quartz is necessary to allow comparison of data sets this method needs to take into account not only the average number of pdf sets grain but also the number of high miller bravais index planes both of which are important factors according to our study finally we present a suggestion for such a method which is valid for nonporous quartz bearing rock types which consists of assigning quartz grains into types a e based on the pdf orientation pattern and then calculation of a mean shock pressure for each sample less

diachroneity of the clearwater west and clearwater east impact structures indicated by the u th he dating method the u th he method has been applied to constrain the formation ages of the clearwater west and east impact structures of quebec canada zircons were separated from impact melt samples derived from a surface exposure at clearwater west 32 km diameter and from a drill core at clearwater east 26 km diameter the u th he results indicate ages of 280 27 ma 2 n 7 for clearwater west and 450 56 ma 2 n 8 for clearwater east our u th he date for clearwater west supports the findings of previous rb sr 266 15 ma 2 and 40ar 39ar 280 4 ma and 283 8 2 2 ma 2 impact melt studies our u th he date for clearwater east also overlaps with previously published 40ar 39ar dating results which yielded u shaped spectra with maximum and best estimate dates of 460 470 ma our results support the contention previously based solely on 40ar 39ar data that the clearwater west and east impact structures do not comprise an impact doublet that formed coevally from a binary asteroid pair

paleomagnetism and rock magnetism of east and west clearwater lake impact structures the east and west cleawater lake impact structures wiy sh kimi lake quebec 26 and 32 km in diameter respectively have been proposed to represent an impact doublet we investigated their pale

coupling of fe ii oxidation in illite with nitrate reduction and its role in clay mineral transformation abstract in pedogenic and diagenetic processes clay minerals transform from pre existing phases to other clay minerals via intermediate interstratified clays temperature pressure chemical composition of fluids and time are traditionally considered to be the important geological variables for clay mineral transformations nearly ten years ago the role of microbes was recognized for the first time where microbial reduction of structural fe iii in smectite resulted in formation of illite under ambient conditions within two weeks however the opposite process the oxidation of structural fe ii in illite has not been studied and it remains unclear whether or not this process would result in the back reaction e g from illite to smectite the overall objective of this study was to investigate biological oxidation of structural fe ii in illite coupled with nitrate reduction and the effect of this process on clay mineral transformation laboratory incubations were set up where structural fe ii in illite served as electron donor nitrate as electron acceptor and pseudogulbenkiania sp strain 2002 as mediator solution chemistry and gas composition were monitored over time mineralogical transformation resulting from bio oxidation was characterized with x ray diffraction and scanning and transmission electron microscopy our results demonstrated that strain 2002 was able to couple oxidation of structural fe ii in illite with reduction of nitrate to n 2 with nitrite as a transient intermediate this oxidation reaction resulted in transformation of illite to smectite and ultimately to kaolinite illite smectite kaolinite transformations this study illustrates the importance of fe redox process in mediating the smectite illite mineral cycle with important implications for fe redox cycling and mineral evolution in surficial earth environments

phase relations among smectite r1 illite smectite and illite a variety of smectitic and illitic clays were studied by tem and aem following ex pansion by l r white resin to define phase relations for clay minerals undergoing di genesis and low grade metamorphism samples included a prograde shale sequence from the gulf coast a hydrothermal bentonite from zempleni hungary and shales from the nankai trough japan michigan and the welsh sedimentary basin all samples were dominated by various proportions of only three kinds of clay minerals smectite having no 10 alayers r1 illite smectite i s 50 illite and illite with only small proportions of smectite like interlayers mixed layer phases with intermediate ratios of i s were observed only as minor components of other layer sequences lattice fringe images show that the common layer spacing of r1 i s is 21 aand that it has 0 7 0 8 k pfu its properties are not an average of those of smectite and illite which is consistent with the uniqueness of the r1 i s structure a prograde sequence of clay mineral transitions in the studied samples can be charac terized by five stages with different combinations of the three major phases i e smectite r1 i s and illite corresponding to different grades the sequence from low to high grade is 1 pure smectite 2 smectite with small proportions of discrete r1 i s and illite 3 r1 i s with small proportions of smectite and illite 4 illite with some r1 i s and smectite and 5 illite common exceptions to this scheme are inferred to be caused by the inherent metastability of all phases in occurrences that are rate or path dependent

contrasting meteoritic signatures within the clearwater east and clearwater west impact structures the view from osmium isotopes abstract osmium isotopes provide a powerful tool for identifying meteoritic signatures in impactites we apply the osmium isotope method to impact melt and country rocks from the clearwater east and clearwater west craters located in quebec canada impact melts from clearwater east have 187 os 188 os ratios of 0 1281 0 1285 these values indicate a significant meteoritic component which exceeds that in impact melts at all terrestrial craters studied to date except morokweng such findings align with earlier results from chromium isotopes and platinum group elements in contrast impact melts from clearwater west have 187 os 188 os ratios between 6 604 and 59 12 these highly radiogenic ratios are indistinguishable from the 187 os 188 os ratios in country rocks hence osmium isotopes provide no evidence for a meteoritic component in impact melts at clearwater west the clearwater craters formed in almost identical targets therefore target effects cannot readily explain the stark difference between the two clearwater craters if melt sheet heterogeneity is similar at the two craters the probability that melts at clearwater west host an undetected chondritic component is 1 may best explain the unusually strong meteoritic signature although the signature or its nondetection at each crater may be related to asymmetric preservation of the impactor component the results presented here provide further evidence that clearwater east and clearwater west were temporally separate impact events

three component mixed layer illite smectite kaolinite i s k minerals in hydromorphic soils south china to understand clay mineral transformations in hydromorphic conditions in the red earth sediments in xuancheng south china clay mineralogy was investigated using x ray diffraction xrd and high resolution transmission electron microscopy hrtem the xrd results indicated that clay minerals in the hydromorphic soils were illite kaolinite smectite vermiculite and mixed layer illite smectite and illite smectite kaolinite changes of the kaolinitic reflections under the various conditions suggested that the kaolinitic phase is a mixed layer structure having kaolinite layers randomly interstratified with illite and smectite layers hrtem observation showed that 10 a illite layers interstratified with both 15 a smectite layers and 7 a kaolinite layers in clay particles confirming the occurrence of illite smectite kaolinite i s k three component mixed layer clays the lattice fringes of the i s k clays appeared corrugated and vanishing and also exhibited variable thickness along a lattice fringe which were consistent with changes from illite to smectite from smectite to kaolinite and from illite to kaolinite respectively hydromorphic conditions in the xuancheng soils led simultaneously to the direct transformation of illite to kaolinite and the transformation of illite to smectite to kaolinite in the pedogenic processes and the formation of i s k three component mixed layer clays as intermediate products of these processes

the transition from complex crater to peak ring basin on the moon new observations from the lunar orbiter laser altimeter lola instrument impact craters on planetary bodies transition with increasing size from simple to complex to peak ring basins and finally to multi ring basins important to understanding the relationship between complex craters with central peaks and multi ring basins is the analysis of protobasins exhibiting a rim crest and interior ring plus a central peak and peak ring basins exhibiting a rim crest and an interior ring new data have permitted improved portrayal and classification of these transitional features on the moon we used new 128 pixel degree gridded topographic data from the lunar orbiter laser altimeter lola instrument onboard the lunar reconnaissance orbiter combined with image mosaics to conduct a survey of craters 50 km in diameter on the moon and to update the existing catalogs of lunar peak ring basins and protobasins our updated catalog includes 17 peak ring basins rim crest diameters range from 207 km to 582 km geometric mean 343 km and 3 protobasins 137 170 km geometric mean 157 km several basins inferred to be multi ring basins in prior studies apollo moscoviense grimaldi freundlich sharonov coulomb sarton and korolev are now classified as peak ring basins due to their similarities with lunar peak ring basin morphologies and absence of definitive topographic ring structures greater than two in number we also include in our catalog 23 craters exhibiting small ring like clusters of peaks 50 205 km geometric mean 81 km one humboldt exhibits a rim crest diameter and an interior morphology that may be uniquely transitional to the process of forming peak rings a power law fit to ring diameters d ring and rim crest diameters dr of peak ring basins on the

wave loadings acting on innovative rubble mound breakwater for overtopping wave energy conversion abstract the overtopping breakwater for energy conversion obrec is an overtopping type wave energy converter totally embedded into traditional rubble mound breakwaters the device consists of a reinforced concrete front reservoir designed with the aim of capturing the wave overtopping in order to produce electricity the energy is extracted through low head turbines using the difference between the water levels in the reservoir and the sea water level this paper investigates the nature and magnitude of wave loadings exerting on various parts of the structure the results improve the overall knowledge on the device behavior completing the highlights from the complementary test campaign carried out in the same wave flume in 2012 vicinanza et al 2014 the formulas provided have been used to design the first obrec prototype breakwater in operation since january 2016 at naples harbour italy

wave loads on a land based dual chamber oscillating water column wave energy device abstract wave energy is one of renewable energy resources with great potential due to the mechanical and structural simplicity oscillating water column owc wave energy converter wec is considered to be one of the most promising marine renewable energy devices however owc remains not commercialized mainly due to its complex hydrodynamic performance and uncertainty in wave loads in the present study based on potential flow theory and time domain higher order boundary element method hobem a fully nonlinear numerical model is developed and used to investigate the wave induced force and bending moment on a land fixed dual chamber owc device the bernoulli equation is used to calculate the wave force and bending moment the equation is modified by accounting for the pneumatic pressure in the air chamber and the viscosity effect and then solved using an acceleration potential method the numerical model was compared with the experiment carried out in a wave current flume at the state key laboratory of coastal and offshore engineering dalian university of technology china and good agreement between the simulation and experimental results was observed the horizontal components of wave forces on the two curtain walls of the dual chamber owc wec were found to be much larger than the corresponding vertical components the seaside curtain wall suffered much larger wave loads in comparison with the inner curtain wall therefore the wave force on the seaside curtain wall is the dominant force the largest wave induced bending moment occurs at the joint of device and seabed the effects of the sub chamber width ratio and curtain wall draft on the wave induced force and bending moment are investigated the dominant wave force and moment increase with curtain wall draft and the peak wave loads can be reduced by moving the internal curtain wall close to the seaside curtain wall

innovative rubble mound breakwaters for overtopping wave energy conversion abstract this paper intends contributing to the development of an economically and environmentally sustainable coastal infrastructure which combines rubble mound breakwaters with wave energy converters wec the energy is produced by collecting wave overtopping in a front reservoir which is returned to the sea through turbines wave loadings and average wave overtopping rate at the rear side of the rubble mound breakwater and in the front reservoir are discussed on the basis of physical 2 d model tests carried out at aalborg university dk the experiments have been analyzed and compared with results from model tests and wave load design formulae by norgaard et al 2013 for traditional rubble mound crown walls the existing prediction methods seem unable to predict the hydraulic performances and loadings on the front reservoir and thus new prediction formulae are proposed based on the new experiments the formulae are provided with the aim to be of direct use to engineers in the preliminary design of a first prototype of combined breakwater and wave energy converter

combining shock barometry with numerical modeling insights into complex crater formation the example of the siljan impact structure sweden siljan central sweden is the largest known impact structure in europe it was formed at about 380 ma in the late devonian period the structure has been heavily eroded to a level originally located underneath the crater floor and to date important questions about the original size and morphology of siljan remain unanswered here we present the results of a shock barometry study of quartz bearing surface and drill core samples combined with numerical modeling using isale the investigated 13 bedrock granitoid samples show that the recorded shock pressure decreases with increasing depth from 15 to 20 gpa near the present surface to 10 15 gpa at 600 m depth a best fit model that is consistent with observational constraints relating to the present size of the structure the location of the downfaulted sediments and the observed surface and vertical shock barometry profiles is presented the best fit model results in a final crater rim to rim diameter of 65 km according to our simulations the original siljan impact structure would have been a peak ring crater siljan was formed in a mixed target of paleozoic sedimentary rocks overlaying crystalline basement our modeling suggests that at the time of impact the sedimentary sequence was approximately 3 km thick since then there has been around 4 km of erosion of the structure

shock metamorphism and shock barometry at a complex impact structure slate islands canada the slate islands archipelago is believed to represent the central uplifted portion of a complex impact structure planar microstructures in quartz and feldspars and shock vitrification of rocks are the most common shock metamorphic features encountered no diaplectic quartz was identified in the exposed rocks but minor maskelynite is present shatter cones occur on all islands of the archipelago suggesting minimum pressures of 4 2 gpa the relative frequency of low index planar microstructures of specific optically determined crystallographic orientations in quartz are correlated with results from shock barometric experiments to estimate peak shock pressures experienced by the exposed target rocks in general there is a decrease in shock pressure recorded in the target rocks from about 20 25 gpa in east central patterson island to about 5 10 gpa at the western shore of this island and on mortimer island the shock attenuation gradient is 4 5 gpa km across this section of the island group however the shock attenuation has a roughly concentric plan only over the western part of the archipelago there is no distinct shock center and there are other deviations from circularity this is probably the result of 1 the shock wave not having expanded from a point or spherical source because of the 1 0 to 1 5 km size of the impactor 2 differential movement of large target rock blocks during the central uplift and crater modification phases of the impact process the orientation of planar deformation features in quartz appears to be independent of the shock wave direction suggesting that crystal structure exerts the primary control on microstructure development based on the results of xrd analyses residual post impact temperatures were high enough to cause annealing of submicroscopic damage in shocked quartz

wave power extraction from multiple oscillating water columns along a straight coast the integration of oscillating water column owc wave energy converters into a coastal structure breakwater jetty pier etc or more generally their installation along the coast is an effective way to increase the accessibility of wave power exploitation in this paper a theoretical model is developed based on the linear potential flow theory and eigenfunction matching method to evaluate the hydrodynamic performance of an array of owcs installed along a vertical straight coast the chamber of each owc consists of a hollow vertical circular cylinder which is half embedded in the wall the owc chambers in the theoretical model may have different sizes i e different values of the radius wall thickness and submergence at the top of each chamber a wells turbine is installed to extract power the effects of the wells turbine together with the air compressibility are taken into account as a linear power take off system the hydrodynamic and wave power extraction performance of the multiple coast integrated owcs is compared with that of a single offshore coast integrated owc and of multiple offshore owcs more specifically we analyse the role of the incident wave direction chamber size i e radius wall thickness and submergence spacing between owcs and number of owcs by means of the present theoretical model it is shown that wave power extraction from the coast integrated owcs for a certain range of wave conditions can be significantly enhanced due to both the constructive array effect and the constructive coast effect

structural evidence from shock metamorphism in simple and complex impact craters linking observations to theory the structure of canadian impact craters formed in crystalline rocks is analyzed using shock metamorphism and evidence for movement along shear zones the analysis is based on an interpretation that beyond the near field region shock pressure attenuates down axis as p r 2 in agreement with nuclear test and computed results and as p r 3 near the surface in both simple and complex craters the transient cavity is defined by the limit of fragmentation due to direct and reflected shock waves the intersection of the transient cavity with hemispheric shock isobars indicates that the transient cavity has a parabolic form weakening by dilation during early uplift allows late stage slumping of the walls of simple craters this is controlled by a spheroidal primary shear of radius rs 2dt where dt is the depth of the transient crater due to excavation and initial compression with increasing crater diameter the size of the transient cavity decreases relative to the shock imprint suggesting that fragmentation and excavation is limited by progressively earlier collapse of the margins under gravity central peak formation in complex craters may be initiated by relaxation of the shock compressed central parautochthone so the primary shear lubricated by friction melting meets below the crater floor and drives the continuing upward motion