impact cratering in sandstone the memin pilot study on the effect of pore water abstract planetary surfaces are subjected to meteorite bombardment and crater formation rocks forming these surfaces are often porous and contain fluids to understand the role of both parameters on impact cratering we conducted laboratory experiments with dry and wet sandstone blocks impacted by centimeter sized steel spheres we utilized a 40 m two stage light gas gun to achieve impact velocities of up to 5 4 km s 1 cratering efficiency ejection velocities and spall volume are enhanced if the pore space of the sandstone is filled with water in addition the crater morphologies differ substantially from wet to dry targets i e craters in wet targets are larger but shallower we report on the effects of pore water on the excavation flow field and the degree of target damage we suggest that vaporization of water upon pressure release significantly contributes to the impact process

chemical modification of projectile residues and target material in a memin cratering experiment in the context of the memin project a hypervelocity cratering experiment has been performed using a sphere of the iron meteorite campo del cielo as projectile accelerated to 4 56 km s 1 and a block of seeberger sandstone as target material the ejecta collected in a newly designed catcher are represented by 1 weakly deformed 2 highly deformed and 3 highly shocked material the latter shows shock metamorphic features such as planar deformation features pdf in quartz formation of diaplectic quartz glass partial melting of the sandstone and partially molten projectile mixed mechanically and chemically with target melt during mixing of projectile and target melts the fe of the projectile is preferentially partitioned into target melt to a greater degree than ni and co yielding a fe ni that is generally higher than fe ni in the projectile this fractionation results from the differing siderophile properties specifically from differences in reactivity of fe ni and co with oxygen during projectile target interaction projectile matter was also detected in shocked quartz grains the average fe ni of quartz with pdf about 20 and of silica glasses about 24 are in contrast to the average sandstone ratio about 422 but resembles the fe ni ratio of the projectile about 14 we briefly discuss possible reasons of projectile melting and vaporization in the experiment in which the calculated maximum shock pressure does not exceed 55 gpa

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

geochemical processes between steel projectiles and silica rich targets in hypervelocity impact experiments abstract the possibility of fractionation processes between projectile and target matter is critical with regard to the classification of the impactor type from geochemical analysis of impactites from natural craters here we present results of five hypervelocity memin impact experiments poelchau et al 2013 using the cr v co mo w rich steel d290 1 as projectile and two different silica rich lithologies seeberger sandstone and taunus quartzite as target materials our study is focused on geochemical target projectile interaction occurring in highly shocked and projectile rich ejecta fragments in all of the investigated impact experiments whether sandstone or quartzite targets the ejecta fragments show i shock metamorphic features e g planar deformation features pdf and the formation of silica glasses ii partially melting of projectile and target and iii significant mechanical and chemical mixing of the target rock with projectile material the silica rich target melts are strongly enriched in the projectile tracer elements cr v and fe but have just minor enrichments of co w and mo inter element ratios of these tracer elements within the contaminated target melts differ strongly from the original ratios in the steel the fractionation results from differences in the reactivity of the respective elements with oxygen during interaction of the metal melt with silicate melt our results indicate that the principles of projectile target interaction and associated fractionation do not depend on impact energies at least for the selected experimental conditions and water saturation of the target partitioning of projectile tracer elements into the silicate target melt is much more enhanced in experiments with a non porous quartzite target compared with the porous sandstone target this is mainly the result of higher impact pressures consequently higher temperatures and longer reaction times at high temperatures in the experiments with quartzite as target material

paleomagnetism of the devonian kennett limestone and the rotation of the eastern klamath mountains california the devonian kennett limestone in the eastern klamath terrane in northern california has a stable magnetization that was acquired after the folding of the formation apparently in the very early cretaceous the mean paleomagnetic vector has the direction i 49 d 219 a95 7 2 and the parameters of the corresponding paleomagnetic pole are latitude 57 longitude 332 a95 7 4 all of the stably magnetized specimens have a single polarity we propose that the magnetization be associated with the emplacement of the shasta bally batholith during the m17 reversed interval at 134 ma the firmest conclusion that can be drawn from these data is that the eastern klamath terrane has undergone 70 11 of clockwise rotation since the early cretaceous this result does not support earlier tectonic models in which either the entire klamaths or terranes on the south side of the klamaths rotated in a counterclockwise sense the close agreement between the amount of clockwise rotation and that observed in the oregon coast range to the north of the klamaths suggests that both may reflect the same tectonic process the data may suggest a few hundred kilometers of northwestward translation of the terrane since the early cretaceous

pliocene pleistocene vegetational and climatic evolution of the south central mediterranean abstract the vegetational history of the south central mediterranean clearly reflects the major global climatic changes of the last four million years a mediterranean type climate characterized by strong seasonality and a dry summer may have existed in this region during the early pliocene a short term climatic cooling at approximately 3 2 ma resulted in the temporary establishment of a humidity demanding flora the onset of major northern hemisphere glaciation at approximately 2 4 ma initiated an alternation between humid glacial and dry interglacial conditions vegetational differences between this region and the north west mediterranean indicate that distinct latitudinal climatic gradients probably existed in the mediterranean during the pliocene early pleistocene

how old are young lunar craters 1 the accurate definition of the lunar cratering chronology is important for deriving absolute model ages across the lunar surface and throughout the solar system images from the lunar reconnaissance orbiter narrow angle cameras and wide angle camera and the selene kaguya terrain camera provide new opportunities to investigate crater size frequency distributions csfds on individual geological units at lunar impact craters we report new csfd measurements for the copernican aged craters north ray tycho and copernicus which are crucial anchor points for the lunar cratering chronology we also discuss possible reasons for an age discrepancy observed between the impact melt and ejecta units our csfds for north ray and tycho crater ejecta deposits are consistent with earlier measurements however for copernicus crater and one of its rays we find significantly lower cumulative crater frequencies than previous studies our new results for copernicus crater fit the existing lunar absolute chronologies significantly better than the previous counts our derived model ages of the ejecta blankets of north ray tycho and copernicus agree well with radiometric and exposure ages of the apollo 16 17 and 12 landing sites respectively and are generally consistent with a constant impact rate over the last 3 ga however small variations of the impact rate cannot be resolved in our data and require further investigations

on the use of a split hopkinson pressure bar in structural geology high strain rate deformation of seeberger sandstone and carrara marble under uniaxial compression abstract there is increasing evidence that seismogenic fractures can propagate faster than the shear wave velocity of the surrounding rocks strain rates within the tip region of such super shear earthquake ruptures can reach deformation conditions similar to impact processes resulting in rock pulverization the physical response of brittle rocks at high strain rates changes dramatically with respect to quasi static conditions rocks become stiffer and their strength increases a measure for the dynamic behavior of a rock and its strain dependency is the dynamic increase factor dif which is the ratio of the dynamic compressive strength to the quasi static uniaxial compressive strength to investigate deformation in the high strain rate regime experimentally we introduce the split hopkinson pressure bar technology to the structural geology community a method that is frequently used by rock and impact engineers we measure the stress strain response of homogeneous fine grained seeberger sandstone and carrara marble in uniaxial compression at strain rates ranging from 10 1 to 10 2 s 1 with respect to tangent modulus and dynamic uniaxial compressive strength we present full stress strain response curves of seeberger sandstone and carrara marble at high strain rates and an evaluation method to determine representative rates of deformation results indicate a rate dependent elastic behavior of carrara marble where an average increase of 18 could be observed at high strain rates of about 100 s 1 dif reaches a factor of 2 2 2 4 seeberger sandstone does not have a rate dependent linear stress strain response at high strain rates its dif was found to be about 1 6 1 7 at rates of 100 s 1 the onset of dynamic behavior is accompanied with changes in the fracture pattern from single to multiple fractures to pervasive pulverization for increasing rates of deformation seismogenic shear zones and their associated fragment size spectra should be carefully revisited in the light of dynamic deformation

scaling and reproducibility of craters produced at the experimental projectile impact chamber epic centro de astrobiologia spain the experimental projectile impact chamber epic is a specially designed facility for the study of processes related to wet target e g marine impacts it consists of a 7 m wide funnel shaped test bed and a 20 5 mm caliber compressed n2 gas gun the target can be unconsolidated or liquid the gas gun can launch 20 mm projectiles of various solid materials under ambient atmospheric pressure and at various angles from the horizontal to test the functionality and quality of obtained results by epic impacts were performed into dry beach sand targets with two different projectile materials ceramic al2o3 max velocity 290 m s 1 and delrin max velocity 410 m s 1 23 shots used a quarter space setting 19 normal 4 at 53 from horizontal and 14 were in a half space setting 13 normal 1 at 53 the experiments were compared with numerical simulations using the isale code differences were seen between the nondisruptive al2o3 ceramic and the disruptive delrin polymer projectiles in transient crater development all final crater dimensions when plotted in scaled form agree reasonably well with the results of other studies of impacts into granular materials we also successfully validated numerical models of vertical and oblique impacts in sand against the experimental results as well as demonstrated that the epic quarter space experiments are a reasonable approximation for half space experiments altogether the combined evaluation of experiments and numerical simulations support the usefulness of the epic in impact cratering studies

a mis 15 mis 12 record of environmental changes and lower palaeolithic occupation from valle giumentina central italy abstract an integrated geological study including sedimentology stable isotope analysis 18o 13c geochemistry micromorphology biomarker analysis 40ar 39ar geochronology and tephrochronology was undertaken on the quaternary infill of the valle giumentina basin in central italy which also includes an outstanding archaeological succession composed of nine human occupation levels ascribed to the lower and middle palaeolithic 40ar 39ar dating and other palaeoenvironmental and tephrochronological data constrain the sedimentary history of the whole succession to the mis 15 mis 12 interval between 618 13 ka and 456 2 ka palaeoenvironmental proxies suggest that over this time interval of about 150 ka sedimentary and pedogenic processes were mainly influenced by climatic changes in particular by the pulsing of local mountain glaciers of the majella massif specifically the valle giumentina succession records glacio fluvial and lacustrine sedimentation during the colder glacial periods and pedogenesis and or alluvial sedimentation during the warmer interglacial and or interstadial periods during this interval tectonics played a negligible role as a driving factor of local morphogenesis and sedimentation whereas the general regional uplift experienced in the middle pleistocene led to capture of the basin and its definitive extinction after mis 12 these data substantially improve previous knowledge of the chronology and sedimentary evolution of the succession providing for the first time a well constrained chronological and palaeoenvironmental framework for the archaeological and human palaeoecological record of valle giumentina

ejecta from experimental impact craters particle size distribution and fragmentation energy abstract the particle size distribution psd of impact crater ejecta is an important parameter that is useful for understanding the formation of natural craters the distribution of space debris the influence of impact events on climate and energy partitioning in impact events 11 impact experiments into dry and water saturated sandstone were performed and analyzed the experiments span a range of impact velocities from 2 5 to 5 3 km s 1 using projectile sizes from 2 5 to 12 mm kinetic impact energies between 874 and 80 338 j were achieved ejecta of these experiments was collected and the psd was measured and quantified with power law fits the resulting power law exponents lie between 2 54 and 2 74 our results do not show an influence of impact energy or impact velocity on the psd of impact ejecta a significant increase in the psd values was found from dry to water saturated sandstone targets we suggest that water saturation of the target has multiple effects on ejecta fragmentation a comparison of our experimental data with data from the literature shows no correlation between the target material lithology and the ejecta psd interestingly literature data for disruption experiments revealed a strong influence imparted energy density on the d values psd values were used to calculate the energy spent for target fragmentation and show that the fraction of impact energy used for comminution is in the lower single digit percentage

island arc carbonates characterization and recognition in the ancient geologic record abstract carbonates of island arc origin that are preserved in paleozoic mesozoic terranes of the north american cordillera exhibit a distinctive suite of paleontologic and lithologic features and share a fundamental similarity with limestones forming in modern volcanic arcs this study provides the first detailed synthesis of carbonate depositional systems in island arcs and documents primary sedimentary constituents based on facies relationships and faunal communities models are developed that show patterns in the long term evolution of shallow marine organisms and the construction evolution and demise of carbonate platforms in island arcs a suite of criteria is identified that may be used to differentiate island arc carbonates from limestones that accumulated in other platform settings biogeographic isolation prolonged subsidence steep submarine slopes and tectonic instability of volcanic edifices contribute to the development of relatively high levels of species endemism impoverished normal marine faunas complex provincial affinities and relict biotas in limestones that are characterized by exceptionally thick platform and periplatform sequences fringing and barrier reefs at the shelf margin extensive lagoonal deposits and rapid lateral and vertical facies changes although destructive tectonic and geologic processes in island arcs may hinder determining the original size and extent of the carbonate platform and particular facies types may not be represented e g fringing and barrier reefs may be replaced by sand shoals at the platform margin many characteristics have potential value for identifying carbonates of island arc origin in the ancient rock record apart from being associated with calc alkaline volcanic and volcaniclastic assemblages the most valuable suite of features for recognizing island arc carbonates is marine biotas that exhibit elevated levels of endemism and mixed paleobiogeographic affinities extraordinary thicknesses of platform shallow marine and periplatform carbonates and rapid facies changes between volcanic and carbonate rocks and between shallow and deep water limestones recognizing that an ensemble of features is distinctive within island arc carbonates considerably enhances identification of volcanic arcs in the ancient geologic record and thus improves the likelihood of successfully unraveling the complex geologic history of ocean basins

shock wave profile study of tuff from the nevada test site shock wave equation of state and release behavior of tuff from the nevada test site were measured in the range 8 to 107 gpa by recording shock wave profiles produced by impact of projectiles accelerated by a two stage light gas gun shock wave profiles were measured with a fast optical interferometer hugoniot sound speed and effective gruneisen parameter data were determined from the profiles the specimen geometry allows direct observation of the shape of the leading edge of the shock in which complex compressive dynamics caused by pore crushing or phase transitions can manifest themselves the tuff specimens were tested in both a water saturated and semidry state hydration of the rock increases both the shock and sound speeds for a given compression the us up relation for our water saturated tuff is slightly nonlinear and can be approximated as us 2 00 1 42 up for 0 up 6 km s and us 2 29 1 29up for 0 up 3 km s for semidry tuff at pressures less than 18 gpa us 1 70 1 28up

climatic change evidence and lacustrine varves from maar lakes germany annually laminated non glacial lake sediments from lake holzmaar eifel western germany were investigated using large merkt thin sections the absolute age of varve intervals with variations in thickness and composition were correlated to climatic changes recorded by glacier fluctuations in the alps back to 8800 years vt varve time varve years before 1950 glacier advances coincide with sedimentation rate minima prior to 8800 years vt they coincide with sedimentation rate maxima the early and middle holocene sediments suggest a periodicity of about 1000 years for cold warm cycles a sequence of 512 varve thickness measurements was subjected to spectral analysis these provide apparent evidence for a 11 year sun spot cycle

late devonian to early carboniferous turbidite facies and basinal development of the eastern klamath mountains california abstract the late devonian to early carboniferous bragdon formation eastern klamath mountains california is a thick turbidite sequence deposited as a submarine fan complex within an arc related basin laminated mudstone and less abundant classical turbidites comprise most of the lower part of the bragdon and represent a lower fan environment amalgamated beds of normally graded to massive sandstone and pebbly sandstone occur throughout the bragdon but are most abundant in its upper half where they are associated with very thick channel fill beds of pebbly sandstone and conglomerate the upper half of the bragdon formation represents a mid fan to upper fan environment and it also includes closely interbedded classical turbidites interpreted as interchannel or levee deposits an upper slope facies of bioturbated mudstone with an early carboniferous fauna occurs at the top of the formation clastic material in the bragdon formation indicates little contemporaneous vulcanism and was probably derived from lower paleozoic metasediments which were uplifted to the north deposition of the bragdon was initiated by rifting and subsidence of an underlying middle devonian arc complex infilling of the resulting basin during the late devonian and early carboniferous is indicated by overlap of turbidite facies across middle devonian arc deposits and by an upward stratigraphic trend in the bragdon from lower fan to upper fan and slope environments

ries and chicxulub impact craters on earth provide insights for martian ejecta blankets terrestrial impact structures provide field evidence for cratering processes on planetary bodies that have an atmosphere and volatiles in the target rocks here we discuss two examples that may yield implications for martian craters 1 recent field analysis of the ries crater has revealed the existence of subhorizontal shear planes detachments in the periphery of the crater beneath the ejecta blanket at 0 9 1 8 crater radii distance their formation and associated radial outward shearing was caused by weak spallation and subsequent dragging during deposition of the ejecta curtain both processes are enhanced in rheologically layered targets and in the presence of fluids detachment faulting may also occur in the periphery of martian impacts and could be responsible for the formation of lobe parallel ridges and furrows in the inner layer of double layer and multiple layer ejecta craters 2 the ejecta blanket of the chicxulub crater was identified on the southeastern yucatn peninsula at distances of 3 0 5 0 crater radii from the impact center abundance of glide planes within the ejecta and particle abrasion both rise with crater distance which implies a ground hugging erosive and cohesive secondary ejecta flow systematic measurement of motion indicators revealed that the flow was deviated by a preexisting karst relief in analogy with martian fluidized ejecta blankets it is suggested that the large runout was related to subsurface volatiles and the presence of basal glide planes and was influenced by eroded bedrock lithologies it is proposed that ramparts may result from enhanced shear localization and a stacking of ejecta material along internal glide planes at decreasing flow rates when the flow begins to freeze below a certain yield stress

the various ages of occator crater ceres results of a comprehensive synthesis approach abstract the 90 5 km occator crater with its peculiar and unique bright spots is one of the most prominent and renowned feature on ceres occator attracted broad public attention in scientific media as it is proposed to exhibit signs of post impact cryovolcanic activity in order to understand the time sequence of deposition several attempts were made during dawn s primary mission by different research groups to date geomorphologic key units using superposed crater densities resulting absolute model formation ages for occator s ejecta and its interior lobate deposits range from 200 ma to 78 ma and about 100 ma to 6 9 ma but were based on different cratering chronology models measurements on image data at varying resolution and different statistical and methodological approaches here we present the results of a comprehensive approach of determining absolute model formation ages for occator this is achieved by using the best resolved framing camera image data by careful treatment of secondary crater admixture and the natural variability of crater detection and sizes by different crater analysts and by applying appropriate objective criteria for count area selection in this context we evaluate previously published model ages and explain why our results are likely to yield more consistent and robust information about the formation age of occator we also show that in contrast to previous publications csfds measured on occator s less competent ejecta blanket and its more competent cryovolcanic or impact melt related interior lobate deposits ilds are so similar to each other that the slight differences might rather be explained by different scaling parameters in different target materials or that the ilds have formed almost contemporaneously or only shortly after the occator forming impact

weichselian palynostratigraphy palaeovegetation and palaeoenvironment the record from lago grande di monticchio southern italy abstract the palynostratigraphic record from lago grande di monticchio s italy is presented an independent sedimentation rate based chronology provides an age of 101 530 calendar years bp for the lowermost sediments sampled this chronology enables assessment of the rapidity of vegetation changes during the last glacial contrary to widely held views the vegetation showed numerous large magnitude changes in periods of

structural chronology oroclinal deformation and tectonic evolution of the southeastern klamath mountains california devonian to jurassic volcanic sedimentary and minor intrusive rocks of the redding section rs accumulated in an intermittently active island arc setting general stratigraphic concordancy and the downsection continuity of metamorphic facies series indicate that these rocks shared a common postdepositional geologic history burial metamorphism produced secondary mineral assemblages of the zeolite prehnite pumpellyite pumpellyite actinolite and greenschist facies close correspondence between pressures calculated from existing stratigraphic overburden and those predicted from the observed metamorphic facies series indicates that less than 3 km of strata have been eroded from the presently exposed top of the early middle jurassic potem formation shortly after deposition of the potem formation compressional deformation f1 produced open to isoclinal folds foliations and small thrust faults k ar dates from post tectonic intrusions indicate that f1 deformation was completed before 168 ma this minimum age of f1 deformation is corroborated by a postfolding paleomagnetic overprint acquired at about 171 ma a second suite of intrusions dated at 120 130 ma provided a thermal pulse that variably reset the k ar system in f1 fabric defining celadonite and other relatively ar unretentive materials the nevadan orogeny late jurassic did not significantly deform rocks of the rs if at all nor is evidence for permo triassic sonoman deformation apparent the geometry of f1 structures varies systematically with location in the western bollibokka quadrangle bq f1 folds are upright with subvertical axial planes and associated foliations in the eastern bq f1 folds are overturned to the east with axial planes and associated foliations dipping as little as 40 to the west regional relationships suggest that f1 may have been a response to coeval tectonism in the western klamaths wherein crustal thickening during regional westward thrusting induced gravitational detachment of the rs from its partly serpentinized ophiolitic basement f1 structures subsequently were broadly warped about vertical axes producing variable paleomagnetic declination anomalies that range from 0 to greater than 100 clockwise the timing and cause of this f2 deformation event are as yet relatively unconstrained but were almost certainly post jurassic and may have been associated with development of the columbia embayment paleomagnetic data indicate north american paleolatitudes for the rs since at least the permian and apparently weigh against an allochthonous or exotic origin for this terrane paleontologic data indicate strong faunal similarities with north america and to a lesser extent with a tethyan province the significance of this apparent dual provinciality remains uncertain but extreme endemism of tethyan fusulinids corals brachiopods and pelecypods is questionable

application of nondestructive testing methods to study the damage zone underneath impact craters of memin laboratory experiments within the framework of the multidisciplinary experimental and modeling impact research network memin research group the damage zones underneath two experimentally produced impact craters in sandstone targets were investigated using several nondestructive testing ndt methods the 20 20 20 cm sandstones were impacted by steel projectiles with a radius of 1 25 mm at approximately 5 km s 1 resulting in craters with approximately 6 cm diameter and approximately 1 cm depth ultrasound us tomography and vibrational analysis were applied before and after the impact experiments to characterize the damage zone and micro computer tomography l ct measurements were performed to visualize subsurface fractures the newly obtained experimental data can help to quantify the extent of the damage zone which extends to about 8 cm depth in the target the impacted sandstone shows a local p wave reduction of 18 below the crater floor and a general reduction in elastic moduli by between approximately 9 and approximately 18 depending on the type of elastic modulus the results contribute to a better empirical and theoretical understanding of hypervelocity events and simulations of cratering processes

vegetation history and palaeoclimate of the last glacial period at lago grande di monticchio southern italy a high resolution palynological study of a 51 m core from lago grande di monticchio southern italy has provided a palaeonvironmental record for the last glacill a annual lamination based chronology supported by radiometric and tephrochronological dates provides an absolute timescale for this record that spans 76 300 years correlations are established between the pollen stratigraphy the grip ice core 18o record and foraminiferal assemblages from atlantic core v23 81 both dansgaard oeschger and heinrich events are reflected by changes in the pollen stratigraphy revised dates are estimated for heinrich events h1 h6 a quantitative palaeoclimate reconstruction based upon the pollen data provides evidence of the climate changes in southern italy associated with these and other fluctuations during the last glacial

hypervelocity impacts on dry and wet sandstone observations of ejecta dynamics and crater growth this study deals with the investigation of highly dynamic processes associated with hypervelocity impacts on porous sandstone for the impact experiments two light gas accelerators with different calibers were used capable of accelerating steel projectiles with diameters ranging from 2 5 to 12 mm to several kilometers per second the projectiles impacted on dry and water saturated seeberger sandstone targets the study includes investigations of the influence of pore water on the shape of the ejecta cloud as well as transient crater growth the results show a significant influence of pore water on ejecta behavior steeper ejecta cone angles are observed if the impacts are conducted on wet sandstones the transient crater grows at a faster rate and reaches a larger diameter if the target is water saturated in our experiments target porosity leads to smaller crater sizes compared with nonporous targets water within the pore space reduces porosity and counteracts this process power law fits were applied to the crater growth curves the results show an increase in the scaling exponent with increasing pore space saturation

the carancas meteorite impact crater peru geologic surveying and modeling of crater formation and atmospheric passage the recent carancas meteorite impact event caused a worldwide sensation an h4 5 chondrite struck the earth south of lake titicaca in peru on september 15 2007 and formed a crater 14 2 m across it is the smallest youngest and one of two eye witnessed impact crater events on earth the impact violated the hitherto existing view that stony meteorites below a size of 100 m undergo major disruption and deceleration during their passage through the atmosphere and are not capable of producing craters fragmentation occurs if the strength of the meteoroid is less than the aerodynamic stresses that occur in flight the small fragments that result from a breakup rain down at terminal velocity and are not capable of producing impact craters the carancas cratering event however demonstrates that meter sized stony meteoroids indeed can survive the atmospheric passage under specific circumstances we present results of a detailed geologic survey of the crater and its ejecta to constrain the possible range of impact parameters we carried out numerical models of crater formation with the isale hydrocode in two and three dimensions depending on the strength properties of the target the impact energies range between approximately 100 1000 mj 0 024 0 24 t tnt by modeling the atmospheric traverse we demonstrate that low cosmic velocities 12 1 4 kms 1 and shallow entry angles 20 are prerequisites to keep aerodynamic stresses low 10 mpa and thus to prevent fragmentation of stony meteoroids with standard strength properties this scenario results in a strong meteoroid deceleration a deflection of the trajectory to a steeper impact angle 40 60 and an impact velocity of 350 600 ms 1 which is insufficient to produce a shock wave and significant shock effects in target minerals aerodynamic and crater modeling are consistent with field data and our microscopic inspection however these data are in conflict with trajectories inferred from the analysis of infrasound signals

impact experiments in low temperature ice new results of low velocity impact experiments in cubic and cylindrical 20 cm water ice targets initially at 257 and 81 k are reported impact velocities and impact energies vary between 0 1 and 0 64 km sec and 10 9 and 10 10 ergs respectively observed crater diameters range from 7 to 15 cm and are two to three times larger than values found for equal energy impacts in basaltic targets crater dimensions in ice targets increase slightly with increasing target temperatures crater volumes of strength controlled ice craters are about 10 to 100 times larger than those observed for craters in crystalline rocks based on similarity analysis general scaling laws for strength controlled crater formation are derived and are applied to crater formation on the icy galilean and saturnian satellites this analysis indicates that surface ages based on impact crater statistics on an icy crust will appear greater than those for a silicate crust which experienced the same impact history the greater ejecta volume for cratering in ice versus cratering in silicate targets leads to accelerated regolith production on an icy planet

formation of a small impact structure discovered within the agoudal meteorite strewn field morocco a relic impact structure was recognized within the strewn field of the agoudal iron meteorite the heavily eroded structure has preserved shatter cones in a limestone basement and remnants of autochthonous and allochthonous breccias fragments of iron incorporated into the allochthonous breccia have a chemical composition ni 5 16 wt ir 0 019 ppm similar to that of the agoudal meteorite supporting a syngenetic origin of the strewn field and the impact structure the total recovered mass of agoudal meteorite fragments is estimated at approximately 500 kg the estimated size of the se nw oriented strewn field is 6 2 km model calculations with minimal preatmospheric size show that a similar meteorite strewn field plus one small crater with observed shock effects could be formed by fragmentation of a meteoroid approximately 1 4 m in diameter with an impact angle of approximately 60 from the horizontal however the most probable is an impact of a larger 3 4 m diameter meteoroid resulting a strewn field with approximately 10 craters 10 30 m in diameter each plus numerous meteorite fragments the calculated scattering area of meteorite shrapnel ejected from these impact craters could completely cover the observed strewn field of the agoudal meteorite

palaeoclimate chronology and vegetation history of the weichselian lateglacial comparative analysis of data from three cores at lago grande di monticchio southern italy abstract palynological and chronological data are presented for the lateglacial from three cores taken at different locations in the basin of lago grande di monticchio plant macrofossil data from one core provide complementary evidence of the palaeovegetation quantitative palaeoclimate reconstructions are made from the pollen data using pollen climate response surfaces the chronological framework for late glacial events as well as the palaeoclimate are compared with other sources of evidence of lateglacial palaeoenvironments surface conditions in the north atlantic appear to be more directly linked to climatic conditions in italy than is the temperature in greenland nonetheless the palynological record exhibits high frequency variability that reflects high frequency climatic changes paralleling those seen in the ice core records from greenland

the memin research unit scaling impact cratering experiments in porous sandstones the memin research unit multidisciplinary experimental and modeling impact research network is focused on analyzing experimental impact craters and experimental cratering processes in geological materials memin is interested in understanding how porosity and pore space saturation influence the cratering process here we present results of a series of impact experiments into porous wet and dry sandstone targets steel iron meteorite and aluminum projectiles ranging in size from 2 5 to 12 mm were accelerated to velocities of 2 5 7 8 km s 1 yielding craters with diameters between 3 9 and 40 cm results show that the target s porosity reduces crater volumes and cratering efficiency relative to nonporous rocks saturation of pore space with water to 50 and 90 increasingly counteracts the effects of porosity leading to larger but flatter craters spallation becomes more dominant in larger scale experiments and leads to an increase in cratering efficiency with increasing projectile size for constant impact velocities the volume of spalled material is estimated using parabolic fits to the crater morphology yielding approximations of the transient crater volume for impacts at the same velocity these transient craters show a constant cratering efficiency that is not affected by projectile size

a meteorite crater on earth formed on september 15 2007 the carancas hypervelocity impact on september 15 2007 a bright fireball was observed and a big explosion was heard by many inhabitants near the southern shore of lake titicaca in the community of carancas peru a 13 5 m crater and several fragments of a stony meteorite were found close to the site of the impact the carancas event is the first impact crater whose formation was directly observed by several witnesses as well as the first unambiguous seismic recording of a crater forming meteorite impact on earth we present several lines of evidence that suggest that the carancas crater was a hypervelocity impact an event like this should have not occurred according to the accepted picture of stony meteoroids ablating in the earths atmosphere therefore it challenges our present models of entry dynamics we discuss alternatives to explain this particular event this emphasizes the weakness in the pervasive use of average parameters such as tensile strength fragmentation behavior and ablation behavior in current modeling efforts this underscores the need to examine a full range of possible values for these parameters when drawing general conclusions from models about impact processes

island arc sedimentation in the middle devonian kennett formation eastern klamath mountains california the kennett formation is a unit of intra arc sediments which was deposited during the final stages of early to middle devonian island arc construction in the eastern klamath mountains california nearshore bioturbated volcaniclastics with a shallow marine fauna also contain rare debris of land plants indicating island source areas these sediments grade to volcaniclastic turbidites of slope origin which in turn grade to thin bedded siliceous mudstone representing a basin floor environment limestone lenses at the top of the kennett are debris deposits with matrix supported intraclasts and overturned colonial skeletons which were derived from shallow carbonate banks sedimentary facies of the kennett indicate a mature arc topography of islands submerged highs and intra arc basins basins were probably developed by tectonic extension of the arc during the early devonian

geological characterization of the ina shield volcano summit pit crater on the moon evidence for extrusion of waning stage lava lake magmatic foams and anomalously young crater retention ages ina a distinctive 2 3 km d shaped depression is composed of unusual bulbous shaped mounds surrounded by optically immature hummocky blocky floor units the crisp appearance optical immaturity and low number of superposed impact craters combine to strongly suggest a geologically recent formation for ina but the specific formation mechanism remains controversial we reconfirm that ina is a summit pit crater vent on a small shield volcano 3 5 billion years old following detailed characterization we interpret the range of ina characteristics to be consistent with a two component model of origin during the waning stages of summit pit eruption activities the ina pit crater floor is interpreted to be dominated by the products of late stage low rise rate magmatic dike emplacement magma in the dike underwent significant shallow degassing and vesicle formation followed by continued degassing below the solidified and highly microvesicular and macrovesicular lava lake crust resulting in cracking of the crust and extrusion of gas rich magmatic foams onto the lava lake crust to form the mounds these unique substrate characteristics highly porous aerogel like foam mounds and floor terrains with large vesicles and void space exert important effects on subsequent impact crater characteristics and populations influencing 1 optical maturation processes 2 regolith development and 3 landscape evolution by modifying the nature and evolution of superposed impact craters and thus producing anomalously young crater retention ages accounting for these effects results in a shift of crater size frequency distribution model ages from

lago grande di monticchio southern italy a long record of environmental change illustrated by sediment geochemistry abstract bulk geochemical analysis has been carried out on a 51 m sediment core from lago grande di monticchio in southern italy the record which may extend from the present back through more than one glacial cycle displays major variations in indicators of palaeoproductivity such as organic carbon and biogenic silica the most prominent change occurs at the holocene boundary lower in the sequence zones of moderately enhanced productivity highlight either interstadial or interglacial periods c n ratios and hydrogen indices provide possible indications of the sources and diagenetic state of the bulk organic matter but must be interpreted carefully as it is difficult to isolate the effects of these two factors changes in the clastic fraction e g na al ratio suggest that tephra deposition in the lake and its catchment has significantly altered the sedimentation this may also have influenced the biological productivity of the system

laboratory impacts into dry and wet sandstone with and without an overlying water layer implications for scaling laws and projectile survivability scaling laws describing crater dimensions are defined in terms of projectile velocity and mass densities of the materials involved strength of the target and the local gravity here the additional importance of target porosity and saturation and an overlying water layer are considered through 15 laboratory impacts of 1 mm diameter stainless steel projectiles at 5 km s 1 into a an initially uncharacterized sandstone porosity 17 and b coconino sandstone porosity 23 the higher porosity dry sandstone allows a crater to form with a larger diameter but smaller depth than in the lower porosity dry sandstone furthermore for both porosities a greater volume of material is excavated from a wet target than a dry target by 27 30 comparison of our results with pi scaling dimensionless ratios of key parameters characterizing cratering data over a range of scales suggests that porosity is important for scaling laws given that the new data lie significantly beneath the current fit for ice and rock targets on a v versus 3 plot v gives cratering efficiency and 3 the influence of target strength an overlying water layer results in a reduction of crater dimensions with larger craters produced in the saturated targets compared to unsaturated targets a water depth of approximately 12 times the projectile diameter is required before craters are no longer observed in the targets previous experimental studies have shown that this ratio varies between 10 and 20 gault and sonett 1982 in our experiments 25 of the original projectile mass survives the impact

late pleistocene climatic variations as recorded in two italian maar lakes lago di mezzano lago grande di monticchio abstract sediment profiles from two maar lakes lago di mezzano central italy and lago grande di monticchio southern italy were investigated with respect to their minerogenic and biogenic sediment accumulation rates for a time window spanning the final 20 000 yr of the last glaciation the chronological framework is provided by calibrated radiocarbon ages varve counting calculation of sedimentation rates and tephrochronology in the time slice between 34 000 and 14 000 cal bp periods of increased minerogenic input are observed in both lacustrine records interrupted by periods of low minerogenic input these cyclic variations have an average recurrence time of 1785 yr for lago di mezzano and 2875 yr for lago grande di monticchio comparing well with marine and ice core data explanations for these pulses of increased minerogenic sedimentation include enhanced erosion and runoff the higher precipitation evaporation ratio required for this interpretation was possibly restricted to winter months as earlier published pollen analyses on sediments from lago grande di monticchio show a contemporary development of steppe vegetation an indicator for cool dry climatic conditions this may be connected with a southward shift of the westerlies and a reinforced jet stream agreement of lacustrine data from italy with late pleistocene glacial events in central italy with events recorded in marine archives from the north atlantic heinrich events and with oxygen isotope data from greenland ice cores is interpreted as evidence for the late pleistocene climate in europe being influenced by north atlantic climatic forcing which may be related to dansgaard oeschger cycles

evolution of the late quaternary san gregorio magno tectono karstic basin southern italy inferred from geomorphological tephrostratigraphical and palaeoecological analyses tectonic implications the pantano di san gregorio magno is a 4 7 km 2 large tectono karstic basin located in the axial belt of the southern apennines an area affected by intense seismicity the basin was formed in the middle pleistocene and is presently undissected it is filled by lacustrine sediments clays silts and pyroclastic sands passing laterally into alluvial fan deposits geomorphological investigations were integrated with tephrostratigraphical palynological and palaeoecological analyses of a 61 m thick core not reaching the bedrock the multiproxy analysis of the s gregorio magno record shows that over the last 200k yr the basin hosted a freshwater lake with an oscillating level age constraints provided by the tephrostratigraphic record allowed estimation of the sedimentation rate which varied strongly through time evolution of the basin resulted from the complex combination of tectonic subsidence karst processes and changing amounts of sedimentary inputs the latter was influenced by allogenic contributions related both to primary and reworked volcanoclastic inputs and was climate driven the overall evidence which indicates that in the long term the accumulation rate substantially counterbalanced the accommodation space created by faulting suggests that the basin evolution was also modulated by changing subsidence rates copyright 2006 john wiley sons ltd

a reconnaissance rb sr sm nd u pb and k ar study of some host rocks and ore minerals in the west shasta cu zn district california the copley greenstone balaklala rhyolite and mule mountain stock in the west shasta cu zn district california have rb sr sm nd u pb and k ar systematics that indicate they are a cogenetic suite of ensimatic island arc rocks about 400 m y pervasive alteration and mineralization of these rocks for the most part was syngenetic and the major component of the mineralizing fluid was devonian seawater k ar ages of quartz sericite concentrates from ore horizons and rb sr systematics of a few rock and ore specimens record a later thermal and mineralizing event in the district of about 260 m y contamination of some rocks with pelagic sediments is indicated by the sm nd data

dispersed remnants of a northeast pacific fringing arc upper paleozoic terranes of permian mccloud faunal affinity western u s two fragmentary subparallel belts of terranes within the western north american cordillera contain upper paleozoic rocks and are characterized by contrasting lithotectonic assemblages and contrasting permian faunal affinity these two belts are a volcanic arc related successions of permian mccloud faunal affinity mccloud belt and b subduction related accretionary complexes of permian tethy an faunal affinity cache creek belt this paper supports the hypothesis that the fragmentary terranes of the mccloud belt once constituted parts of a northeast pacific fringing arc system and in constrast to some earlier interpretations concludes that the volcanic arc evolved above an eastward dipping subduction zone the absolute distance between this arc and western north america during the late paleozoic cannot be constrained however there is little evidence to suggest closure of a major 10 km ocean basin or protracted periods of westward dipping subduction parts of devonian to permian volcanic island arc sequences of the western u s cordillera are represented in the northern sierra eastern klamath bilk creek grindstone and chilliwack terranes these scattered volcanic arc remnants share several fundamental characteristics 1 the sequences were constructed across continental affinity basement assemblages 2 they underwent similar tectonic evolution during late paleozoic time such as coeval pulses in volcanism and related depositional histories 3 they contain early permian mccloud type fauna of distinctive biogeographic affinity 4 mccloud belt terranes are spatially and possibly genetically related to westward lying accretionary complexes of the cache creek belt which contain fragments of upper triassic blueschist and permian limestone blocks bearing tethyan permian fusulinids and corals based on the presence of distinctive early permian mccloud fauna the island arc remnants discussed in this paper are referred to as the mccloud belt the similarities between mccloud belt terranes suggest that they were once parts of a long lived late paleozoic volcanic arc complex the stratigraphy of these terranes records the tectonic evolution of the volcanic arc volcanism within the paleozoic arc began as early as the early devonian and was succeeded or accompanied by carbonate and epiclastic sedimentation during the middle and late devonian an influx of detritus derived from sedimentary and metasedimentary rocks during the late devonian and mississippian records the uplift and erosion of arc basement sequences an event that was at least locally accompanied by ongoing volcanism a pulse in volcanism during the pennsylvanian and coeval uplift led to the establishment of shallow marine and deltaic volcanogenic and carbonate sedimentation and locally subaerial exposure which persisted into the early early permian elsewhere during the early permian shallow water carbonate deposition was established with only minor influx of volcanogenic debris during the late permian and locally as early as late early permian a major pulse in volcanism occurred and is now represented by voluminous sequences of volcanogenic debris and lavas most of these sequences are overlain by upper triassic carbonate platformal sequences arc volcanism was recorded at least locally until the middle jurassic paleomagnetic data are used to constrain a schematic pre cretaceous reconstruction of these volcanic arc sequences and their associated subduction assemblages the inferred paleogeography of island arc sequences and the adjacent accretionary terranes suggests that volcanism occurred above an east dipping subduction zone with a long lived paleogeographic relation to north america the current structural position of these terranes is largely the result of mesozoic and locally younger deformation

devonian intra oceanic arc rift sedimentation facies development in the gamilaroi terrane new england orogen eastern australia abstract silurian devonian rocks within the gamilaroi terrane part of the new england orogen of eastern australia provide a well preserved on land example of the development of an intra oceanic arc rift ten sedimentary facies represent different phases in the evolution of the gamilaroi rift and are typified by predominantly volcaniclastic conglomerates and mudstones with minor sandstones all of which were deposited by debris flows and turbidity currents subordinate facies include limestones crystal rich volcaniclastic sandstones volcanic breccias and olistostromes the facies are distributed throughout a succession of six lithostratigraphic units each of which represents a distinct phase in the history of the arc rift felsic volcanic and volcaniclastic rocks at the base of the section represent part of the original arc and are overlain by volcaniclastic sandstones and mudstones deposited within an arc basin lower devonian emsian limestones underwent rapid subsidence concurrent with an influx of volcaniclastic sediments indicating initiation of rift related faulting a thick conglomerate succession was deposited rapidly on a debris apron system adjacent to the steep sided rift walls overlying tuffaceous mudstones indicate a decrease in clastic input later in the history of the rift basin thick intervals of massive and pillowed basalts at the top of the succession indicate a major period of volcanism within the rift oceanic island arc rift sequences are characterised by highly variable sedimentary facies distribution facies distribution over the 400 km extent of the gamilaroi terrane is also highly variable modern arc rift zones are divided into a series of smaller separate elongate basins providing an explanation for the high facies variability observed in the field

submillennial environmental fluctuations during marine oxygen isotope stage 2 a comparative analysis of diatom and pollen evidence from lago grande di monticchio south italy high temporal resolution pollen and diatom analyses carried out on sediments from lago grande di monticchio span the interval 23 700 21 200 calendar yr bp a brief interstadial during marine oxygen isotope stage 2 both records exhibit marked changes that are interpreted as responses to climatic changes the diatoms and terrestrial vegetation appear to respond at the same time any relative lag in the response of the vegetation was less than the ca 60 yr resolution of the two records the interval coincides at least in part with the campo imperatore stade when the gran sasso ice sheet reached its maximum extent and water level was high in the fucino lake correlation of the marked environmental oscillation with one of the dansgaard oeschger events recorded by stable oxygen isotope records from the greenland ice cap is proposed this follows an interval interpreted as having a cold dry climate and correlated with a heinrich event in the north atlantic together the two records enable a multifactorial interpretation of the palaeoclimate changes that characterise the oscillation providing additional insight to that obtained from studies of ice and ocean sediment cores especially with respect to the seasonality of temperature and precipitation copyright 1999 john wiley sons ltd

the extra large light gas gun of the fraunhofer emi applications for impact cratering research abstract the extra large light gas gun xllgg at the fraunhofer ernst mach institut emi efringen kirchen germany is a two stage light gas gun that can accelerate projectile masses of up to 100 g up to velocities of 6 km s 1 the accelerator s set up allows various combinations of pump and launch tubes for applications in different fields of hypervelocity impact research in the framework of the memin multidisciplinary experimental and modeling impact research network program the xllgg is used for mesoscale cratering experiments with projectiles made of steel and of iron meteorites and targets consisting of sandstone and other rocks the craters produced with this equipment reach a diameter of up to 40 cm a size unique in laboratory cratering research with the implementation of neural networks the acceleration process is being optimized currently yielding peak velocities of 7 8 km s 1 for a 100 g projectile here we summarize technical aspects of the xllgg

quantitative analysis of impact induced seismic signals by numerical modeling we quantify the seismicity of impact events using a combined numerical and experimental approach the objectives of this work are 1 the calibration of the numerical model by utilizing real time measurements of the elastic wave velocity and pressure amplitudes in laboratory impact experiments 2 the determination of seismic parameters such as quality factor q and seismic efficiency k for materials of different porosity and water saturation by a systematic parameter study employing the calibrated numerical model by means of numerical experiments we found that the seismic efficiency k decreases slightly with porosity from k 3 4 10 3 for nonporous quartzite to k 2 6 10 3 for 25 porous sandstone if pores are completely or partly filled with water we determined a seismic efficiency of k 8 2 10 5 which is approximately two orders of magnitude lower than in the nonporous case by measuring the attenuation of the seismic wave with distance in our numerical experiments we determined the seismic quality factor q to range between 35 for the solid quartzite and 80 for the porous dry targets for water saturated target materials q is much lower 10 the obtained values are in the range of literature values translating the seismic efficiency into seismic magnitudes we show that the seismic magnitude of an impact event is about one order of magnitude smaller considering a water saturated target in comparison to a solid or porous target obtained seismic magnitudes decrease linearly with distance to the point of impact and are consistent with empirical data for distances closer to the point of impact the seismic magnitude decreases more rapidly with distance for a water saturated material compared to a dry material

interaction of aluminum projectiles with quartz sand in impact experiments formation of khatyrkite cual 2 and reduction of sio 2 to si abstract we analyzed the interaction of spherical 6 36 mm diameter cu bearing aluminum projectiles with quartz sand targets in hypervelocity impact experiments performed at nasa ames vertical gun range impact velocities and inferred peak shock pressures varied between 5 9 and 6 5 km s and 41 and 48 gpa respectively shocked particles impact melt particles coated with thin crusts of molten projectile material were recovered from the floors of the ca 33 cm diameter craters and the respective ejecta blankets through petrographic and chemical optical microscopy fe empa sem edx and xrf analysis we show that these particles have a layered structure manifested in distinct layers of decreasing shock metamorphism these can be characterized by the following physical and chemical reactions and alteration products i complete melting and subsequent recrystallization of the projectile forming a distinct crystallization texture in the fused metal crust ii projectile target mixing involving a redox reaction between cu bearing al alloy und sio 2 leading to formation of khatyrkite cual 2 al 2 o 3 melt euhedral silicon crystals and spherical droplets of silicon iii melting of quartz to lechatelierite and formation of planar deformation features in relic quartz grains and iv shock lithification of quartz grains with fracturing of grains grain boundary melting planar deformation features and complete loss of porosity to our knowledge this is the first report of khatyrkite formed experimentally in hypervelocity impact experiments these results have implications for the understanding of a similar redox reaction between al cu metal and siliceous impact melt recently postulated for the khatyrka cv3 carbonaceous chondrite moreover these results bear on the processes that lead to layers of regolith on the surfaces of planetary bodies without atmospheres such as asteroids in the main belt e g 4 vesta and on the moon specifically impacts of mm sized projectiles at velocities between 4 and 6 km s into regolith covered asteroidal surfaces in the main belt should yield similar impact melt particles that feature a continuum of shock effects i e partially to completely molten projectile remnants adhering to impact melted regolith agglomerates as well as projectile contaminated impact melts and local shock melting along grain boundaries

a crater and its ejecta an interpretation of deep impact we apply recently updated scaling laws for impact cratering and ejecta to interpret observations of the deep impact event an important question is whether the cratering event was gravity or strength dominated the answer gives important clues about the properties of the surface material of tempel 1 gravity scaling was assumed in pre event calculations and has been asserted in initial studies of the mission results because the gravity field of tempel 1 is extremely weak a gravity dominated event necessarily implies a surface with essentially zero strength the conclusion of gravity scaling was based mainly on the interpretation that the impact ejecta plume remained attached to the comet during its evolution we address that feature here and conclude that even strength dominated craters would result in a plume that appeared to remain attached to the surface we then calculate the plume characteristics from scaling laws for a variety of material types and for gravity and strength dominated cases we find that no model of cratering alone can match the reported observation of plume mass and brightness history instead comet like acceleration mechanisms such as expanding vapor clouds are required to move the ejected mass to the far field in a few hour time frame with such mechanisms and to within the large uncertainties either gravity or strength craters can provide the levels of estimated observed mass thus the observations are unlikely to answer the questions about the mechanical nature of the tempel 1 surface

paleozoic and lower mesozoic magmas from the eastern klamath mountains north california and the geodynamic evolution of northwestern america abstract the paleozoic to early mesozoic geology of the eastern klamath mountains n california is characterized by three major magmatic events of ordovician late ordovician to early devonian and permo triassic ages the ordovician event is represented by a calc alkalic island arc sequence lovers leap butte sequence developed in the vicinity of a continental margin the late ordovician to early devonian event consists of the 430 480 ma old trinity ophiolite formed during the early development of a marginal basin and a series of low k tholeiitic volcanic suites lovers leap basalt keratophyre unit copley and balaklala formations belonging to intraoceanic island arcs finally the permo triassic event gave rise to three successives phases of volcanic activity nosoni dekkas and bully hill represented by the highly differentiated basalt to rhyolite low k tholeiitic series of mature island arcs the permo triassic sediments are indicative of shallow to moderate depth in an open warm sea the geodynamic evolution of the eastern klamath mountains during paleozoic to early mesozoic times is therefore constrained by the geological petrological and geochemical features of its island arcs and related marginal basin a consistent plate tectonic model is proposed for the area consisting of six main stages 1 1 development during ordovician times of a calc alkalic island arc in the vicinity of a continental margin 2 2 extrusion during late ordovician to silurian times of a primitive basalt andesite intraoceanic island arc suite which terminated with boninites the latter suggest rifting in the fore arc followed by the breakup of the arc 3 3 opening and development of the trinity back arc basin around 430 480 ma ago 4 4 eruption of the balaklala rhyolite either in the arc or in the fore arc ending in early devonian time with intrusion of the 400 ma mule mountain stock 5 5 break in volcanic activity from the early devonian to the early permian and 6 6 development of a mature island arc from the early permian to the late triassic the eastern klamath mountains island arc formations and ophiolitic suite are part of the cordilleran suspect terranes considered to be gondwana margin fragments that have undergone large northward translations before final collision with the north american craton during late mesozoic or cenozoic times these eastern klamath mountains island arcs could be associated with the paleo pacific oceanic plate that led to accretion of these allochthonous terranes to the american margin

regional setting and new information on some critical geologic features of the west shasta district california the west shasta massive sulfide district is in the easternmost of a series of accreted island arc and oceanic crust terranes that comprise the klamath mountains a sequence of submarine volcanic rocks of predominantly early devonian age is the principal component of the island arc terrane in which the sulfide deposits are hosted the copley greenstone consisting mainly of andesitic and basaltic pillow lavas and breccias totaling at least 1 800 m in thickness is the oldest rock unit in the sequence it is overlain and also intruded by dikes of the balaklala rhyolite northeast of the west shasta district greenstone also overlies the balaklala rhyolite suggesting that a major greenstone unit may overlie potentially mineralized rhyolite east of the district however recent studies have shown that the complex relations in that area can be explained by folding the balaklala sequence consists of silicic flows breccias and tuffs having a maximum thickness somewhat in excess of 1 000 m the balaklala has been divided by kinkel et al 1956 into three units a lower nonporphyritic to slightly porphyritic unit containing large amounts of breccia and tuff a middle unit characterized by rhyolite containing quartz phenocrysts 1 to 4 mm in diameter but also containing a complex assortment of tuff breccia and pyritic massive sulfide bodies in its upper part and an upper unit typically containing dark quartz phenocrysts in excess of 4 mm in diameter much of the lower part of the upper unit is pyroclastic material whereas most of the upper part of the unit appears to be a massive volcanic flow rock at least half a dozen eruptive centers for the balaklala rhyolite are identified three of them within an area measuring 17 x 3 km that constitutes the limits of the former mining district the youngest unit in the arc sequence is the kennett formation consisting of black shale and chert containing radiolarians which indicate fairly deep water deposition in its lower part and limestone containing a shallow water fauna of probable middle devonian age in the upper part a 400 m y old trondhjemite stock named the mule mountain stock intrudes the copley greenstone and balaklala rhyolite and is considered to be essentially coeval with these volcanic units the pyritic massive sulfide deposits occur in clusters of individual bodies owing in large part to disruption by postmineral faults the deposits are stratigraphically confined to the upper part of the subhorizontal middle unit of the balaklala and their horizontal distribution is here interpreted to have been controlled by an extensional tectonic regime that prevailed during early devonian time the major geologic evidence for such a regime is the marked preferred elongations exhibited by the distribution of the afore mentioned eruptive centers the eight or nine massive sulfide clusters in the district and the geometrically similar distribution of the clusters in relation to each other the preferred directions of elongation in both the detailed and broader senses may be generalized to n 20 degrees to 25 degrees e n 37 degrees e n 60 degrees to 80 degrees e and n 40 degrees to 60 degrees w the three northeast trends dominate throughout the district whereas the northwest trend is evident mainly in the northern part and is more speculative the major deposit clusters fall at intersections of the major trends some of which may have been grabens trend intersections having no known deposits may be good exploration targets in localities where the stratigraphically favorable middle unit of the balaklala is still present

ejection behavior characteristics in experimental cratering in sandstone targets within the frame of the memin research unit multidisciplinary experimental and numerical impact research network impact experiments on sandstone targets were carried out to systematically study the influence of projectile mass velocity and target water saturation on the cratering and ejection processes the projectiles were accelerated with two stage light gas guns ernst mach institute onto fine grained targets seeberger sandstone with about 23 porosity collection of the ejecta on custom designed catchers allowed determination of particle shape size distribution ejection angle and microstructures mapping of the ejecta imprints on the catcher surface enabled linking of the different patterns to ejection stages observed on high speed videos the increase in projectile mass from 0 067 to 7 1 g correlates with an increase in the total ejected mass ejecta angles however are similar in range for all experiments the increase in projectile velocity from 2 5 to 5 1 km s 1 correlates with a total ejecta mass increase as well as in an increase in comminution efficiency and a widening of the ejecta cone a higher degree of water saturation of the target yields an increase in total ejecta mass up to 400 with respect to dry targets higher ejecta velocity and a steeper cone these data in turn suggest that the reduced impedance contrast between the quartz grains of the target and the pores plays a primary role in the ejecta mass increase while vaporization of water determines the ejecta behavior concerning ejecta velocity and particle distribution

the plumbotectonics of the west shasta mining district eastern klamath mountains california the tectonic setting comprising the west shasta mining district has often been compared with that of primitive island arcs concentrations of uranium thorium and lead and lead isotope compositions were determined for devonian ores and rocks of the west shasta district eastern klamath mountains california to help evaluate the tectonic classification the lead isotope pattern is found to be complex from comparison of the data with those on younger ores and rocks in the region and with those isotopic patterns found in modern tectonic terranes however a number of conclusions are possible a lead isotope point for the devonian oceanic mantle is now well established from this study on the west shasta district this isotopic composition is in agreement with that suggested by slawson in 1983 i e from a sample of massive sulfide ore from the golinsky deposit with a 206 pb 204 pb of 17 830 a 207 pb 204 pb of 15 450 and a 208 pb 204 pb of 37 313 if the devonian mantle is analogous to the modern mantle the determined value is probably at the more radiogenic end of the devonian oceanic mantle array some samples of volcanic rocks and ores that have elevated values of 207 pb 204 pb and 208 pb 204 pb indicate that subducted pelagic sediments or interaction of the magmas with other sediments downsection have been involved to varying degrees in the generation of magmas the high ratios were not attained by addition of lead to the volcanic rocks or ores during subsequent magmatic events such as intrusion of the permian pit river stock to the east or of the cretaceous shasta bally batholith that crops out to the south and west and may underlie part of the district some values of 207 pb 204 pb are sufficiently high as to suggest that west shasta may have developed nearer a continent than was previously supposed lead isotope data for quaternary volcanic rocks are somewhat more radiogenic than for cretaceous ores and plutonic rocks permo triassic ores are again a bit less radiogenic the isotopic differences between the permo triassic and quaternary data could be accounted for by a value for 238 u 204 pb of 10 42 in common source material using this value of 238 u 204 pb to calculate even further back to 400 m y the resulting ratios are found to fall very close to the best value for the lead isotope mixing line between the devonian mantle and pelagic sediments we interpret this intersection to be the mean value for the assimilated devonian sediment lead 18 250 for 206 pb 204 pb and 15 582 for 207 pb 204 pb as deduced for the lead isotope composition for the devonian mantle at this location the pelagic sediment lead isotope composition also is toward the more radiogenic end of the values expected for pelagic sediments in the devonian lack of sediments in the observed volcanic section of the west shasta district suggests a submerged volcanic arc setting as interpreted by others for the troodos and samail ophiolites rather than an island arc situation such as the green tuff area of japan or an incipient spreading ridge setting that might have grown to be a subaerial iceland the elevated values of 207 pb 204 pb for some samples suggest a submerged volcanic are whereas the exceedingly low values of thorium which is not easily mobilized during alteration events for both basaltic andesites and plagiorhyolites is suggestive of depleted source material such as is found for most oceanic spreading centers elevated values of 207 pb 204 pb are exceedingly rare in midocean ridge basalts and low contents of thorium are known in island arcs so a submerged volcanic arc is the preferred interpretation some similarity exists between the 206 pb 204 pb values of devonian ores having elevated values of 207 pb 204 pb and those of the permo triassic ores of the east shasta district as mentioned by slawson in 1983 this similarity is now confirmed to be a coincidence we find it due first of all to some incorporation of sediment lead in the magmas followed later by some migration of radiogenic lead probably locally derived into the ores during subsequent events because there was some postdepositional lead migration into the ores some migration of copper also into the ores cannot be excluded lead especially radiogenic lead however is more mobile than copper as the migrating lead is deduced to have been locally derived from the observed section rather than exotically derived any copper added was probably locally derived also

a long pollen record from laghi di monticchio southern italy a preiminary account a pollen diagram from lake monticchio a volcanic crater lake in s central italy east of naples shows a long vegetation record for the holocene and the later portion of the last weichselian glacial period the upper 735 cm of a 2550 cm core is assigned to the holocene it begins with expansion of betula birch and quercus oak followed by fagus beech tilia lime and other mesic trees in the next phase the flora is dominated by oak with an increase in herb pollen in the later holocene the flora is again diversified by the appearance of abies fir curpinus hornbeam and other trees in the latest pleistocene portion of the core the vegetation is dominated by grasses artemisia sage brush and chenopods indicating a treeless environment the base of the core shows continued dominance by steppe like vegetation with 9interstadial9 episodes in which trees especially oak beech and fir were abundant the climatic interpretation is that the late pleistocene was very dry at least in the summer growing season and probably although not necessarily colder than now in the holocene increased precipitation favoured expansion of tree populations for a brief period there was a return of water stress in the growing season marked by a loss of tree species diversity and an increase in herbs in the later holocene a progressive diversification of tree species indicates a return to a more humid and perhaps cooler climate the vegetation history and climatic inferences are closely similar to records available from greece the available radiocarbon dates which show a consistent pattern indicate that the core is much older than 40000 years at the base but not old enough to include the major post eemian interstadials the 9holocene9 birch expansion began nearly 20000 years ago these dates appear to be systematically too old in the light of present knowledge the preliminary character of the study is emphasized further radiocarbon dates especially of the 9holocene9 section are needed as are more detailed studies of sedimentation processes and tephra occurrences

velocity scaling of impact craters in water ice over the range 1 to 7 3 km s 1 the impact cratering behavior of polycrystalline ice at a temperature of 259 3 k has been investigated by 16 impacts with 1 mm aluminum 2017 alloy spheres density 2790 kg m 3 over the velocity range 1 to 7 3 km s 1 using a two stage light gas gun crater cross sectional profiles and diameter depth and volume data are presented it is found that there is no significant difference in power law energy exponents for scaling of crater diameter and volume between these data and previous low velocity 1 km s 1 ice impact data dimensionless pi group scaling was also found to scale the data in a way which can be readily combined with earlier lower velocity data and data at a lower ice temperature

is the linne impact crater morphology influenced by the rheological layering on the moon s surface insights from numerical modeling linne is a simple crater with a diameter of 2 23 km and a depth of 0 52 km located in northwestern mare serenitatis recent high resolution data acquired by the lunar reconnaissance orbiter camera revealed that the shape of this impact structure is best described by an inverted truncated cone we perform morphometric measurements including slope and profile curvature on the digital terrain model of linne finding the possible presence of three subtle topographic steps at the elevation of 20 100 and 200 m relative to the target surface the kink at 100 m might be related to the interface between two different rheological layers using the isale shock physics code we numerically model the formation of linne crater to derive hints on the possible impact conditions and target physical properties in the initial setup we adopt a basaltic projectile impacting the moon with a speed of 18 km s 1 for the local surface we consider either one or two layers in order to test the influence of material properties or composite rheologies on the final crater morphology the one layer model shows that the largest variations in the crater shape take place when either the cohesion or the friction coefficient is varied in particular a cohesion of 10 kpa marks the threshold between conical and parabolic shaped craters the two layer model shows that the interface between the two layers would be exposed at the observed depth of 100 m when an intermediate value 200 m for the upper fractured layer is set we have also found that the truncated cone morphology of linne might originate from an incomplete collapse of the crater wall as the breccia lens remains clustered along the crater walls while the high albedo deposit on the crater floor can be interpreted as a very shallow lens of fallout breccia the modeling analysis allows us to derive important clues on the impactor size under the assumption of a vertical impact and collision velocity equal to the mean value and on the approximate large scale preimpact target properties observations suggest that these large scale material properties likely include some important smaller scale variations disclosed as subtle morphological steps in the crater walls furthermore the modeling results allow advancing some hypotheses on the geological evolution of the mare serenitatis region where linne crater is located unit s14 we suggest that unit s14 has a thickness of at least a few hundreds of meters up to about 400 m

anatomy of a modern open ocean carbonate slope northern little bahama bank the open ocean carbonate slope north of little bahama bank consists of a relatively steep 4 upper slope between water depths of 200 and 900 m and a more gentle 1 2 lower slope between depths of 900 and 1300 m the upper slope is dissected by numerous small submarine canyons 50 150 m in relief that act as a line source for the downslope transport of coarse grained carbonate debris the lower slope is devoid of any well defined canyons but does contain numerous small 1 5 m hummocks of uncertain origin and numerous larger 5 40 m patchily distributed ahermatypic coral mounds sediments along the upper slope have prograded seaward during the cenozoic as a slope front fill seismic facies of fine grained peri platform ooze surface sediments show lateral gradation of both grain size and carbonate mineralogy with the fine fraction derived largely from the adjacent shallow water platform near surface sedimentary facies along the upper slope display a gradual downslope decrease in the degree of submarine cementation from well lithified hardgrounds to patchily cemented nodular ooze to unlithified peri platform ooze controlled by lateral variations in diagenetic potential and or winnowing by bottom currents submarine cementation stabilizes the upper part of the slope allowing upbuilding of the platform margin and controls the distribution of submarine slides as well as the headward extent of submarine canyons where unlithified sediments are heavily bioturbated and are locally undergoing dolomitization upper slope sediments are also conditioned eustatically resulting in vertical cyclic sequences of diagenetically unstable aragonite and magnesian calcite rich and stable calcite rich carbonates that may explain the well bedded nature of ancient peri platform ooze sequences lower slope sediments have prograded seaward during the cenozoic as a chaotic fill seismic facies of coarse grained carbonate turbidites and debris flow deposits with subordinate amounts of peri platform ooze coarse clasts are internally derived from fine grained upper slope sediments via incipient cementation submarine sliding and the generation of sediment gravity flows gravity flows bypass the upper slope via a multitude of canyons and are deposited along the lower slope as a wedge shaped apron of debris parallel to the adjacent shelf edge consisting of a complex spatial arrangement of localized turbidites and debris flow deposits a proximal apron facies of thick mud supported debris flow deposits plus thick coarse grained ta turbidites grades seaward into a distal apron facies of thinner grain supported debris flow deposits and thinner finer grained ta b turbidites with increasing proportions of peri platform ooze both the geomorphology and sedimentary facies relationships of the carbonate apron north of little bahama bank differ significantly from the classic submarine fan model as such a carbonate apron model offers an alternative to the fan model for palaeoenvironmental analysis of ancient open ocean carbonate slope sequences

the effect of target properties on transient crater scaling for simple craters the effects of the coefficient of friction and porosity on impact cratering are not sufficiently considered in scaling laws that predict the crater size from a known impactor size velocity and mass we carried out a systematic numerical study employing more than 1000 two dimensional models of simple crater formation under lunar conditions in targets with varying properties a simple numerical setup is used where targets are approximated as granular or brecciated materials and any compression of porous materials results in permanent compaction the results are found to be consistent with impact laboratory experiments for water low strength and low porosity materials e g wet sand and sands using this assumption we found that both the friction coefficient and porosity are important for estimating transient crater diameters as is the strength term in crater scaling laws i e the effective strength the effects of porosity and friction coefficient on impact cratering were parameterized and incorporated into group scaling laws and predict transient crater diameters within an accuracy of 5 for targets with friction coefficients f 0 4 and porosities 0 30 moreover 90 crater scaling relationships are made available and can be used to estimate transient crater diameters on various terrains and geological units with different coefficient of friction porosity and cohesion the derived relationships are most robust for targets with 10 15 applicable for a lunar environment and could therefore yield significant insights into the influence of target properties on cratering statistics

revision and recalibration of existing shock classifications for quartzose rocks using low shock pressure 2 5 20 gpa recovery experiments and mesoscale numerical modeling a combination of shock recovery experiments and numerical modeling of shock deformation in the low shock pressure range from 2 5 to 20 gpa for two dry sandstone types of different porosity a completely water saturated sandstone and a well indurated quartzite provides new insights into strongly heterogeneous distribution of different shock features 1 for nonporous quartzo feldspathic rocks the traditional classification scheme stoffler 1984 is suitable with slight changes in pressure calibration 2 for water saturated quartzose rocks a cataclastic texture microbreccia seems to be typical for the shock pressure range up to 20 gpa this microbreccia does not show formation of pdfs but diaplectic quartz glass sio2 melt is formed at 20 gpa 1 vol 3 for porous quartzose rocks the following sequence of shock features is observed with progressive increase in shock pressure 1 crushing of pores 2 intense fracturing of quartz grains and 3 increasing formation of diaplectic quartz glass sio2 melt replacing fracturing the formation of diaplectic quartz glass sio2 melt together with sio2 high pressure phases is a continuous process that strongly depends on porosity this experimental observation is confirmed by our concomitant numerical modeling recalibration of the shock classification scheme results in a porosity versus shock pressure diagram illustrating distinct boundaries for the different shock stages

late pliocene northern hemisphere glaciations the continental and marine responses in the central mediterranean abstract detailed pollen analyses and oxygen isotope records of three foraminiferal species globigerina bulloides uvigerina peregrina and cibicides pachyderma from the semaforo and vrica composite sections crotone southern italy have been compared to the global climatic changes depicted by late pliocene early pleistocene foraminiferal 18o records of site 607 in the north atlantic and hole 653a in the tyrrhenian basin west mediterranean major overturns in the mid altitude vegetation are shown near isotopic stages 82 60 58 and 50 at about 2 03 ma 1 6 ma and 1 37 ma according to the raymo et al 1989 and ruddiman et al 1989 timescales at the same dates glacial 18o maxima either became higher or display step increases in the western mediterranean or in the open ocean as well this suggests that size increases of northern hemisphere ice sheets were the driving factor for regional or local marine and continental environmental changes within the mediterranean basin near isotopic stages 62 60 close to the conventional plio pleistocene boundary the climatic conditions severed enough within the mediterranean basin to modify the continental environment as depicted by a sudden increase of artemisia percentages while the first significant southward migration of the north polar front may have been recorded by an influx of left coiling neogloboquadrina pachyderma in the central mediterranean it also appears that boreal guests entered the mediterranean during phases of 18o enrichment of foraminiferal calcite there does not seem to be any discrepancy between the climatic concept of the pliocene pleistocene boundary and its chronostratigraphic definition

in situ measurements of impact induced pressure waves in sandstone targets in the present study we introduce an innovative method for the measurement of impact induced pressure waves within geological materials impact experiments on dry and water saturated sandstone targets were conducted at a velocity of 4600 m s using 12 mm steel projectiles to investigate amplitudes decay behavior and speed of the waves propagating through the target material for this purpose a special kind of piezoresistive sensor capable of recording transient stress pulses within solid brittle materials was developed and calibrated using a split hopkinson pressure bar experimental impact parameters projectile size and speed were kept constant and yielded reproducible signal curves in terms of rise time and peak amplitudes pressure amplitudes decreased by 3 orders of magnitude within the first 250 mm i e 42 projectile radii the attenuation for water saturated sandstone is higher compared to dry sandstone which is attributed to dissipation effects caused by relative motion between bulk material and interstitial water the proportion of the impact energy radiated as seismic energy seismic efficiency is in the order of 10 3 the present study shows the feasibility of real time measurements of waves caused by hypervelocity impacts on geological materials experiments of this kind lead to a better understanding of the processes in the crater subsurface during a hypervelocity impact

the first memin shock recovery experiments at low shock pressure 5 12 5 gpa with dry porous sandstone as part of the memin research program this project is focused on shock deformation experimentally generated in dry porous seeberger sandstone in the low shock pressure range from 5 to 12 5 gpa special attention is paid to the influence of porosity on progressive shock metamorphism shock recovery experiments were carried out with a high explosive set up that generates a planar shock wave and using the shock impedance method cylinders of sandstone of average grain size of 0 17 mm and porosity of about 19 vol and containing some 96 wt sio2 were shock deformed shock effects induced with increasing shock pressure include 1 already at 5 gpa the entire pore space is closed quartz grains show undulatory extinction on average 134 fractures per mm are observed dark vesicular melt glass of the composition of the montmorillonitic phyllosilicate component of this sandstone occurs at an average amount of 1 6 vol 2 at 7 5 gpa quartz grains show weak but prominent mosaicism and the number of fractures increases to 171 per millimeter two additional kinds of melt both based on phyllosilicate precursor could be observed a light colored vesicular melt and a melt containing large iron particles the total amount of melt all types increased in this experiment to 2 4 vol raman spectroscopy confirmed the presence of shock deformed quartz grains near the surface 3 at 10 and 12 5 gpa quartz grains also show weak but prominent mosaicism the number of fractures per mm has reached a plateau value of approximately 200 and the total amount of the different melt types has increased to 4 8 vol diaplectic quartz glass could be observed locally near the impacted surface in addition local shock effects most likely caused by multiple shock wave reflections at sandstone container interfaces occur throughout the sample cylinders and include locally enhanced formation of pdf as well as shear zones associated with cataclastic microbreccia diaplectic quartz glass and sio2 melt overall findings from these first experiments have demonstrated that characteristic shock effects diagnostic for the confirmation of impact structures and suitable for shock pressure calibration are rare so far they are restricted to the limited formation of pdf and diaplectic quartz glass at shock pressures of 10 gpa and above

weathering behaviour and construction suitability of dimension stones from the drei gleichen area thuringia germany the construction suitability of a dimension stone depends on its weathering properties along with the petrology and the petrophysical properties the aim of this study was to evaluate the suitability of the dimension stones from the drei gleichen area for construction and replacement purposes in total six sandstones ingersleben wachsenburg hindfelden seeberg rohnberg gleichenberg upper triassic as well as two carbonates wachsenburg sinter quaternary wandersleben dolomite middle triassic were analysed the results from our laboratory and on site studies of the dimension stones show that rocks from the same stratigraphic layer like the sandstones from the upper triassic can show major differences in their petrophysical and weathering properties these differences are attributed to their different diagenesis resulting e g in varying pore space water balance and strength properties the pore size distribution can be divided into four different groups based on their occurring maxima and micropore content the determined water balance properties as well as moisture expansion and salt attack depend on these groups next to this the mineralogical composition significantly influences the weathering resistance sandstones with a high content of altered lithoclasts show a high amount of moisture expansion low strength and in consequence a low weathering resistance against salt attack based on the results of the present study an evaluation of construction suitability could be accomplished from the analysed sandstones only the seebergen sandstone is suitable for construction purposes due to its good availability good strength properties high compressive and tensile strength low softening degree as well as a low porosity furthermore the wachsenburg sandstone also shows good petrophysical and petrological properties but exploitable deposits are too sparse to be of commercial interest from the carbonates the wachsenburg sinter shows very suitable rock parameters but only sparse outcrops occur which are not appropriate for mining

land snails from the last glacial maximum on andikithira southern greece and their palaeoclimatic implications an assemblage of land snails from an aeolianite deposit on the coast of the southern greek island of andikithira is shown to date to 16 000 yr bp and thus represents the period of the last glacial maximum lgm oxygen isotope stage 2 the assemblage has no modern analogue five of the ten species are extinct on the island and some of these now live only at high elevations 950 m significantly cooler temperatures some 5 8 c below present and slightly drier moisture conditions lower rainfall partially offset by reduced evapotranspiration at the lower temperature are inferred the large temperature depression at the lgm well documented in northern and central europe extended also to the mediterranean climate of southern europe late quaternary climatic changes had a considerable impact on the fauna of this isolated island

crater morphology in sandstone targets the memin impact parameter study hypervelocity 2 5 7 8 km s 1 impact experiments into sandstone were carried out to investigate the influence of projectile velocity and mass target pore space saturation target projectile density contrast and target layer orientation on crater size and shape crater size increases with increasing projectile velocity and mass as well as with increasing target pore space saturation craters in water saturated porous targets are generally shallower and larger in volume and in diameter than craters from equivalent impacts into dry porous sandstone morphometric analyses of the resultant craters 5 40 cm in diameter reveal features that are characteristic of all of our experimental craters regardless of impact conditions i a large central depression within a fragile light colored central part and ii an outer spallation zone with areas of incipient spallation two different mechanical processes grain fragmentation and intergranular tensile fracturing are recorded within these crater morphologies zone i approximates the shape of the transient crater formed by material compression displacement comminution and excavation flow whereas ii is the result of intergranular tensile fracturing and spallation the transient crater dimensions are reconstructed by fitting quadric parabolas to crater profiles from digital elevation models the dimensions of this transient and of the final crater show the same trends both increase in volume with increasing impact energy and with increasing water saturation of the target pore space the relative size of the transient crater in percent of the final crater volume decreases with increasing projectile mass and velocity signifying a greater contribution of spallation on the final crater size when projectile mass and velocity are increased

early devonian volcanism in the eastern klamath mountains california evidence for an immature island arc the early devonian volcanic sequence of the eastern klamath mountains northern california consists of the copley greenstone a basalt andesite series overlain by the balaklala rhyolite all the rocks are metamorphosed to the greenschist facies the copley greenstone consists of massive flows and pyroclastic deposits in the lower part that are overlain by pillow lavas no sediments are interlayered in the volcanic pile except in the easternmost outcrop area where sandstones with granitic debris and shaly tuffs are interbedded in the uppermost flows high mg andesites occur only near the top of the basic volcanic succession the balaklala rhyolite is formed of massive flows breccias and tuffs the copley volcanic rocks poor in titanium belong to a low k tholeiitic suite formed in an island arc geodynamic environment the occurrence of olivine with chromium spinels in almost all the lava types the enrichment in magnesium chromium and nickel and the depletion in hygromagmaphile elements suggest that

diaplectic quartz glass and sio2 melt experimentally generated at only 5 gpa shock pressure in porous sandstone laboratory observations and meso scale numerical modeling abstract a combination of shock recovery experiments and numerical modeling of shock deformation in the low pressure range from 2 5 to 17 5 gpa in dry porous seeberger sandstone provides new significant insights with respect to the heterogeneous nature of shock distribution in such important upper crustal material for which to date no pressure calibrated scheme for shock metamorphism exists we found that pores are already completely closed at 2 5 gpa shock pressure whole quartz grains or parts of them are transformed to diaplectic quartz glass and or sio 2 melt starting already at 5 gpa whereas these effects are not observed below shock pressures of 30 35 and 45 gpa respectively in shock experiments with quartz single crystals the appearance of diaplectic glass or melt is not restricted to the zone directly below the impacted surface but is related to the occurrence of pores in a much broader zone the combined amount of these phases increases distinctly with increasing shock pressure from 0 03 vol at 5 gpa to 80 vol at 17 5 gpa in accordance with a previous shock classification for silica phases in naturally shocked coconino sandstone from meteor crater that was based on varied slopes of the coconino sandstone hugoniot curve our observations allow us to construct a shock pressure classification for porous sandstone consistent with shock stages 1b 4 of the progressive shock metamorphism classification of kieffer 1971 numerical modeling at the meso scale provides the explanation for the discrepancy of shock deformation in porous material and single crystal quartz in keeping with our experimental results it confirms that pore space is completely collapsed at low nominal pressure and demonstrates that pore space collapse results in localized pressure amplification that can exceed 4 times the initial pressure this provides an explanation for the formation of diaplectic quartz glass and lechatelierite as observed in the low shock pressure experiments the numerical models predict an amount of sio 2 melt similar to that observed in the shock experiments this also shows that numerical models are essential to provide information beyond experimental capabilities

the role of substrate characteristics in producing anomalously young crater retention ages in volcanic deposits on the moon morphology topography subresolution roughness and mode of emplacement of the sosigenes lunar irregular mare patch lunar irregular mare patches imps comprise dozens of small distinctive and enigmatic lunar mare features characterized by their irregular shapes well preserved state of relief apparent optical immaturity and few superposed impact craters imps are interpreted to have been formed or modified geologically very recently 100 ma braden et al 2014 however their apparent relatively recent formation modification dates and emplacement mechanisms are debated we focus in detail on one of the major imps sosigenes located in western mare tranquillitatis and dated by braden et al 2014 at 18 ma the sosigenes imp occurs on the floor of an elongate pit crater interpreted to represent the surface manifestation of magmatic dike propagation from the lunar mantle during the mare basalt emplacement era billions of years ago the floor of the pit crater is characterized by three morphologic units typical of several other imps i e 1 bulbous mounds 5 10 m higher than the adjacent floor units with unusually young crater retention ages meters thick regolith and slightly smaller subresolution roughness than typical mature lunar regolith 2 a lower hummocky unit mantled by a very thin regolith and significantly smaller subresolution roughness and 3 a lower blocky unit composed of fresh boulder fields with individual meter scale boulders and rough subresolution surface texture using new volcanological interpretations for the ascent and eruption of magma in dikes and dike degassing and extrusion behavior in the final stages of dike closure we interpret the three units to be related to the late stage behavior of an ancient dike emplacement event following the initial dike emplacement and collapse of the pit crater the floor of the pit crater was flooded by the latest stage magma the low rise rate of the magma in the terminal stages of the dike emplacement event favored flooding of the pit crater floor to form a lava lake and co gas bubble coalescence initiated a strombolian phase disrupting the cooling lava lake surface this phase produced a very rough and highly porous with both vesicularity and macroporosity lava lake surface as the lake surface cooled in the terminal stage of the eruption dike closure with no addition of magma from depth caused the last magma reaching shallow levels to produce viscous magmatic foam due to h2 o gas exsolution this magmatic foam was extruded through cracks in the lava lake crust to produce the bulbous mounds we interpret all of these activities to have taken place in the terminal stages of the dike emplacement event billions of years ago we attribute the unusual physical properties of the mounds and floor units anomalously young ages unusual morphology relative immaturity and blockiness to be due to the unusual physical properties of the substrate produced during the waning stages of a dike emplacement event in a pit crater the unique physical properties of the mounds magmatic foams and hummocky units small vesicles and large void space altered the nature of subsequent impact cratering regolith development and landscape evolution inhibiting the typical formation and evolution of superposed impact craters and maintaining the morphologic crispness and optical immaturity accounting for the effects of the reduced diameter of craters formed in magmatic foams results in a shift of the crater size frequency distribution age from 100 myr to billions of years contemporaneous with the surrounding ancient mare basalts we conclude that extremely young mare basalt eruptions and resulting modification of lunar thermal evolution models to account for the apparent young ages of the imps are not required we suggest that other imp occurrences both those associated with pit craters atop dikes and those linked to fissure eruptions in the lunar maria may have had similar ancient origins

vegetation response to upper pliocene glacial interglacial cyclicity in the central mediterranean abstract new detailed pollen analysis of the lower part of the upper pliocene semaforo section crotone italy documents cyclic behavior of vegetation at the beginning of the northern hemisphere glaciations the competition between four vegetation units subtropical humid forest deciduous temperate forest altitudinal coniferous forest and open xeric assemblage probably reflects modifications of vegetation belts at this montane site several increases in herbaceous open vegetation regularly alternate with subtropical humid forest which expresses rapid climatic oscillations the complete temporal succession deciduous forest rich in quercus followed by subtropical humid forest taxodiaceae and cathaya then altitudinal coniferous forest tsuga cedrus abies and picea and finally herbaceous open vegetation graminae compositae and artemisia displays the climatic evolution from warm and humid interglaciation to cold and dry glaciation it also suggests an independent variation of temperature and humidity the two main climatic parameters the vegetation history of southern calabria recorded in the semaforo section have been correlated with the 18o signal established in the atlantic ocean

non intrusive measurements of crater growth abstract an experimental technique to measure crater growth is presented whereby a high speed video captures profiles of a crater forming after impact obtained using a vertical laser sheet centered on the impact point unlike previous so called quarter space experiments where projectiles were launched along a transparent plexiglas sheet so that growth of half a crater could be viewed the use of the laser sheet permits viewing changes in crater shape without any physical interference to the cratering process this technique indicates that for low velocity impacts 300 m s into 220 m glass beads that are without cohesion and where the projectile is not disrupted craters initially grow somewhat proportionally but that later their depths remain essentially constant while their diameters continue to expand in addition these experiments indicate that as the impact velocity increases the rate of growth and the transient depth to diameter ratio at the end of ejecta excavation decreases these last two observations are probably due to the large time of penetration of the projectile which becomes a significant fraction of the time of crater formation this is contrary to the expectations for the scaling rules which assumes a point source very high curtain angles 45 are also seen and could be due to the low friction angle of the target significant crater modification which is rarely seen in quarter space experiments is also observed and appears to be controlled by the dynamic angle of repose of the target these latter observations indicate that differences in target friction angles may need to be considered when determining near rim ejecta mass distributions and large scale crater modification processes on the planets

review of close range three dimensional laser scanning of geological hand samples abstract the morphological study of geological hand samples has a wide variety of applications in the geosciences which is conventionally accomplished by measuring the distance between features of interest on the sample s surface close range three dimensional 3d laser scanners provide an opportunity to study the form and shape of geological samples in a digital environment and have been increasingly utilized in fields such as paleontology rock mechanics and sedimentology with some uptake in planetary sciences and structural geology for paleontological studies primary applications are in quantitative analysis of fossil morphology and integration into 3d animated models for understanding species movements in the field of rock mechanics typical uses of 3d digital geological hand sample models include quantifying joint roughness coefficient jrc determining the surface roughness of rock samples and assessing morphological changes over time due to processes such as weathering in the field of sedimentology such models are incorporated to characterize the shape of sediment particles and to calculate key parameters such as bulk density this paper aims to provide a comprehensive review of established literature that includes substantial use of digital geological hand samples acquired from 3d close range