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

numerical modelling of impact melt production in porous rocks abstract melting of rocks by impact is a fundamental geologic process that results from shock wave compression and subsequent release from high pressure shock melted material is found in many terrestrial craters however most impact craters in sedimentary targets which are typically porous have been reported as containing significantly less melt than craters in nonporous crystalline targets to investigate the effect of porosity on shock melting we present a numerical modelling approach that combines a porosity compaction model with an equation of state for the solid component to demonstrate that our model accurately calculates shock pressures in porous materials we compare these results with hugoniot data for porous quartzite coconino sandstone and calcite our results show that the presence of porosity significantly reduces the critical pressure required for melting which enhances melt production we show that this effect is reduced but not totally diminished by faster shock wave decay in porous materials so that all other things being equal impact melt production is greater when target porosity is higher we conducted a series of simulations of impacts into targets of different material composition quartzite calcite dunite and porosity of up to 50 and varied the impact velocity between 6 and 50 km s we found a significant increase in the production of impact melt with increasing velocity in agreement with several previous studies and quantify the net increase in impact melt due to target porosity for the nonporous case our results agree well with estimated melt volumes at terrestrial impact craters over a range in size 7 90 km in diameter in porous targets our results contradict the widely cited observation of a melt deficiency in sedimentary target craters however our model results agree well with recently revised estimates of melt volumes at terrestrial craters formed in sedimentary or mixed sedimentary and crystalline targets this further strengthens the view that substantial volumes of impact melt should be produced during impacts into porous sedimentary targets and that the apparent paucity of impact melt in some sedimentary target craters may be due to difficulties in recognizing impact melts derived from sedimentary rocks

global distribution of lunar impact melt flows abstract in this study we analyzed the distribution and properties of 146 craters with impact melt deposits exterior to their rims many of these craters were only recently discovered due to their unusual radar properties in the near global mini rf data set we find that most craters with exterior deposits of impact melt are small 20 km and that the smallest craters have the longest melt flows relative to their size in addition exterior deposits of impact melt are more common in the highlands than the mare this may be the result of differing target properties in the highlands and mare the difference in titanium content or the greater variation of topography in the highlands we find that 80 of complex craters and 60 of simple craters have melt directions that are coincident or nearly coincident with the lowest point in their rim implying that pre existing topography plays a dominant role in melt emplacement this is likely due to movement during crater modification complex craters or breached crater rims simple craters we also find that impact melt flows have very high circular polarization ratios compared to other features on the moon this suggests that their surfaces are some of the roughest material on the moon at the centimeter to decimeter scale even though they appear smooth at the meter scale

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

observations at terrestrial impact structures their utility in constraining crater formation hypervelocity impact involves the near instantaneous transfer of considerable energy from the impactor to a spatially limited near surface volume of the target body local geology of the target area tends to be of secondary importance and the net result is that impacts of similar size on a given planetary body produce similar results this is the essence of the utility of observations at impact craters particularly terrestrial craters in constraining impact processes unfortunately there are few well documented results from systematic contemporaneous campaigns to characterize specific terrestrial impact structures with the full spectrum of geoscientific tools available at the time nevertheless observations of the terrestrial impact record have contributed substantially to fundamental properties of impact there is a beginning of convergence and mutual testing of observations at terrestrial impact structures and the results of modeling in particular from recent hydrocode models the terrestrial impact record provides few constraints on models of ejecta processes beyond a confirmation of the involvement of the local substrate in ejecta lithologies and shows that z models are at best first order approximations observational evidence to date suggests that the formation of interior rings is an extension of the structural uplift process that occurs at smaller complex impact structures there are however major observational gaps and cases e g vredefort where current observations and hydrocode models are apparently inconsistent it is perhaps time that the impact community as a whole considers documenting the existing observational and modeling knowledge gaps that are required to be filled to make the intellectual breakthroughs equivalent to those of the 1970s and 1980s which were fueled by observations at terrestrial impact structures filling these knowledge gaps would likely be centered on the later stages of formation of complex and ring structures and on ejecta

early stage ejecta velocity distribution for vertical hypervelocity impacts into sand the ejecta dynamics during main stage excavation flow in a cratering event have previously been well characterized particularly for vertical impacts in this experimental study we present new results addressing the early time low angle high speed component of the ejecta velocity distribution as a function of time for hypervelocity vertical impacts into sand although this regime represents a very small portion of total ejected mass in laboratory experiments it comprises a greater percentage of growth for larger craters

evidence of non extensive statistical physics of the lithospheric instability approaching the 2004 sumatran andaman and 2011 honshu mega earthquakes abstract in the present study we demonstrate in the frame of non extensive statistical physics significant deviations of the global seismic activity from a quasi stationary regime before sumatra andaman and honshu mega earthquakes suggesting the existence of a global scale intermediate term non extensive tectonic premonitory of impending mega earthquake processes in the lithosphere using non extensive statistical mechanics we describe the frequency moment the inter event time and distance distributions interpreting sumatran s 2004 and honshu 2011 earthquakes influence on these at a phenomenological level we find that global seismicity is described by non extensive statistical mechanics nesm and that the seismic moment and the earthquake inter event time distributions reflect a sub extensive system where long range interactions are important using the cross over formulation of nesm leads us to the conclusion that the seismic moment distribution of moderate events yields thermodynamic q values of qm 1 6 which seem to be constant for the duration of the sumatra and honshu earthquake preparation while rm which describes the seismic moment distribution of great events varies from 1 to 1 5 as we approach the mega events the inter event time and inter event distance distributions with q 1 5 and qd 0 3 respectively support the conclusion of non extensive spatio temporal duality suggesting that global shallow moderate seismicity with 5 5

succession in a jurassic marine cavity community and the evolution of cryptic marine faunas a cavity dwelling fauna from the middle jurassic of the western interior shows a succession controlled by increasing restriction of the cavities most likely by sediment infilling the succession proceeds from large and ubiquitous bivalves to smaller serpulids cyclostome bryozoans and thecideidine brachiopods there is a concurrent decrease in biomass and percent cover this jurassic fauna demonstrates that marine cavity dwelling faunas were specifically adapted to their environments at least 160 m y ago

structural geology of impact craters abstract the formation of impact craters is a highly dynamic and complex process that subjects the impacted target rocks to numerous types of deformation mechanisms understanding and interpreting these styles of micro meso and macroscale deformation has proved itself challenging for the field of structural geology in this paper we give an overview of the structural inventory found in craters of all size ranges on earth and look into the structures of craters on other planetary bodies structural features are discussed here that are caused by i extremely high pressures and temperatures that occur during the initial passage of the shock wave through the target rock and projectile ii the resulting flow field in the target that excavates and ejects rock materials and iii the gravitationally induced modification of the crater cavity into the final crater form a special focus is put on the effects that low angle impacting bodies have on crater formation we hope that this review will help both planetary scientists and structural geologists understand the deformation processes and resulting structures generated by meteorite impact

a new method to determine the direction of impact asymmetry of concentric impact craters as observed in the field lockne on mars in experiments and simulations most impacts occur at an angle with respect to the horizontal plane this is primarily reflected in the ejecta distribution but at very low angle structural asymmetries such as elongation of the crater and nonradial development of the central peak become apparent unfortunately impact craters with pristine ejecta layers are rare on earth and also in areas with strong past or ongoing surface erosion on other planetary bodies and the structural analysis of central peaks requires good exposures or even on site access to outcrop however target properties are known to greatly influence the shape of the crater especially the relatively common target configuration of a weaker layer covering a more rigid basement one such effect is the formation of concentric craters i e a nested deeper inner crater surrounded by a shallow outer crater here we show that with decreasing impact angle there is a downrange shift of the outer crater with respect to the nested crater we use a combination of 1 field observation and published 3 d numerical simulation of one of the best examples of a terrestrial concentric impact crater formed in a layered target with preserved ejecta layer the lockne crater sweden 2 remote sensing data for three pristine concentric impact craters on mars with preserved ejecta layers further constraining the direction of impact as well as 3 laboratory impact experiments to develop the offset in crater concentricity into a complementary method to determine the direction of impact for layered target craters with poorly preserved ejecta layers

bioerosion in an equatorial middle jurassic coral sponge reef community callovian matmor formation southern israel abstract the matmor formation middle jurassic callovian 165 161 mya in southern israel contains abundant coral sponge patch reefs and large crinoids which have been extensively bioeroded by bivalves worms barnacles phoronids and others producing eight ichnospecies it is significant for the evolutionary history of bioerosion because this is the first equatorial middle jurassic boring ichnofauna to be documented when compared to contemporaneous ichnofaunas this assemblage is of average diversity and abundance but has only rare sponge borings and contains abundant specimens of oichnus paraboloides as shallow pits on crinoid stems the matmor formation surprisingly lacks carbonate hardgrounds which are otherwise abundant in subtropical and temperate equivalents

recurring cryptic ecosystems in lower to middle devonian carbonate mounds of hamar laghdad anti atlas morocco abstract exceptionally well preserved fossil cryptic communities have been discovered in submarine cavities of the lower and middle devonian emsian to givetian mud mounds in the hamar laghdad area anti atlas morocco the cryptic biota encrusted the roofs of the cavities and grew predominantly oriented upside down these unique coelobiotic communities were dominated by various solitary rugose corals which very often displayed a calice in calice growth pattern apart from the rugosans the cavities were inhabited by other sessile invertebrates tabulate corals cladochonids crinoids and lithistid sponges many of the skeletons were encrusted by microbial structures the high density of organisms overgrowing each other points to intensive competition for space in all studied devonian submarine crypts the late emsian to latest givetian cavities were colonised by various sets of coelobiotic inhabitants mostly originating from the surrounding deep water marine environments it is suggested that the local species pool was a decisive factor in determining the ecological succession and taxonomic structure of cryptic communities the changes in taxonomic composition and diversity over time and space were primarily related to variations in local physical environment consequently the communities in crypts affected by venting of high temperature fluids or hydrocarbon seepage were of low diversity and included endemic elements and characteristically small specimens

ages and stratigraphy of mare basalts in oceanus procellarum mare nubium mare cognitum and mare insularum accurate estimates of mare basalt ages are necessary to place constraints on the duration and the flux of lunar volcanism as well as on the petrogenesis of lunar mare basalts and their relationship to the thermal evolution of the moon we performed new crater size frequency distribution measurements in order to investigate the stratigraphy of mare basalts in oceanus procellarum and related regions such as mare nubium mare cognitum and mare insularum we used high resolution clementine color data to define 86 spectrally homogeneous units within these basins which were then dated with crater counts on lunar orbiter iv images our crater size frequency distribution measurements define mineralogical and spectral surface units and offer significant improvements in accuracy over previous analyses our data show that volcanism in the investigated region was active over a long period of time from 3 93 to 1 2 b y a total of 2 7 b y volumetrically most of the basalts erupted in the late imbrian period between 3 3 and 3 7 b y and we see evidence that numerous units have been resurfaced during the eratosthenian period significantly less basalt was erupted depending on the absolute model ages that one can assign to the lunar chronostratigraphic systems five units might be of copernican age younger basalts are generally exposed in the center of the investigated area that is closer to the volcanic centers of the aristarchus plateau and marius hills older basalts occur preferentially along the northwestern margin of oceanus procellarum and in the southeastern regions of the studied area i e in mare cognitum and mare nubium combining the new data with our previously measured ages for basalts in mare imbrium serenitatis tranquillitatis humorum australe and humboldtianum we find that the period of active volcanism on the moon lasted 2 8 b y from 4 b y to 1 2 b y on the basis of the basalts dated so far which do not yet include the potentially young basalts of mare smythii e g schultz and spudis 1983 we conclude that oceanus procellarum not only exhibits the widest range of ages of all investigated basins but probably also is the location of some of the youngest basalts on the lunar surface

stratigraphy and structural evolution of southern mare serenitatis a reinterpretation based on apollo lunar sounder experiment data the apollo lunar sounder experiment alse detected two subsurface reflecting horizons in southern mare serenitatis these horizons appear to be regolith layers 2 m thick which correlate with major stratigraphic boundaries in southeastern mare serenitatis our analysis differs from previous interpretations and implies that the lower horizon represents the interface between the earliest mare unit unit i 3 8 b y and the modified serenitatis basin material below the upper horizon represents the regolith developed by sustained impact bombardment of the unit i surface prior to the emplacement of the intermediate basalts unit ii 3 5 b y the latest volcanic episode unit iii 3 2 b y resulted in a very thin infilling 400 m deep in the southern portion of the basin and was undetected by alse profiles of the stratigraphic surfaces represented by the alse reflecting horizons are reconstructed for three stages in the basin filling history these reconstructions permit the timing and magnitude of various volcanic and tectonic events within the serenitatis basin to be assessed on the basis of comparison with orientale ring topography the large subsurface arch is interpreted to be the peak ring related topography of the serenitatis basin the thickness of mare basalts across the alse ground track is highly variable basalts are 400 m thick above the peak ring while they reach a maximum thickness of 2 5 km in the depression between the first and second basin rings comparison with orientale topography suggests that a major increase in basalt thickness of 6 km may occur 50 km inside the peak ring this region was unsampled by the alse traverse extensive load induced deformation occurred after the emplacement of unit i 1 2 km thick maximum this loading of the lithosphere resulted in graben formation along the margins of the basin major downwarping and tilting of the unit i surface and production of discrete zones of faulting buckling and subsidence pre mare topography exerted a strong control over the tectonic patterns in the basin topographic highs such as ring structures underwent 400 m of subsidence whereas intraring depressions underwent as much as 1 4 km of downwarping although the lithosphere was tectonically most active between the emplacement of units i and iii it continued to respond to the load of units i and ii after the emplacement of unit iii as evidenced by 600 m of postunit iii structural relief the association of all mare ridges transected by the alse ground track with distinct offsets or depth changes in the subsurface layering indicates that these surface features are tectonic in origin

evidence of nonextensive statistical physics behavior of the hellenic subduction zone seismicity abstract the hellenic subduction zone hsz is the most seismically active region in europe many destructive earthquakes have taken place along the hsz in the past in this study we investigate the seismicity of the hsz based on the science of complex systems the spatiotemporal distributions of seismicity as well as the magnitude distribution are studied using the concept of nonextensive statistical physics nesp defining five seismic zones and forming an earthquake dataset that covers the period 1976 2009 we apply the nesp ideas to formulate the cumulative distribution functions of the inter event times and distances and the magnitude distribution along the hsz our results indicate that the nonextensive parameter qt which is related with the inter event time distribution presents almost similar values in each of the seismic zones and reflects the long term scale of the seismicity evolution in the hsz the qd parameter which is related with the inter event distance distribution presents a significant variation along the seismic zones this variation is related with the different degree of spatial earthquake clustering in each of the seismic zones of the hsz moreover in the framework of the fragment asperity model the thermostatistical parameter qm which is related with the frequency magnitude distribution could be used as an additional index to inform us about the physical state of each seismic zone along the hsz the variations of the qm parameter are related with the energy release rate in each seismic zone the models used fit rather well to the observed distributions implying the usefulness of nesp in investigating such phenomena exhibiting scale free nature and long range memory effects

morphometry of impact craters on mercury from messenger altimetry and imaging abstract data acquired by the mercury laser altimeter and the mercury dual imaging system on the messenger spacecraft in orbit about mercury provide a means to measure the geometry of many of the impact craters in mercury s northern hemisphere in detail for the first time the combination of topographic and imaging data permit a systematic evaluation of impact crater morphometry on mercury a new calculation of the diameter d t at which craters transition with increasing diameter from simple to complex forms and an exploration of the role of target properties and impact velocity on final crater size and shape measurements of impact crater depth on mercury confirm results from previous studies with the exception that the depths of large complex craters are typically shallower at a given diameter than reported from mariner 10 data secondary craters on mercury are generally shallower than primary craters of the same diameter no significant differences are observed between the depths of craters within heavily cratered terrain and those of craters within smooth plains the morphological attributes of craters that reflect the transition from simple to complex craters do not appear at the same diameter instead flat floors first appear with increasing diameter in craters at the smallest diameters followed with increasing diameter by reduced crater depth and rim height and then collapse and terracing of crater walls differences reported by others in d t between mercury and mars despite the similar surface gravitational acceleration on the two bodies are confirmed in this study the variations in d t between mercury and mars cannot be adequately attributed to differences in either surface properties or mean projectile velocity

the fractured moon production and saturation of porosity in the lunar highlands from impact cratering we have analyzed the bouguer anomaly ba of 1200 complex craters in the lunar highlands from gravity recovery and interior laboratory observations the ba of these craters is generally negative though positive ba values are observed particularly for smaller craters crater ba values scale inversely with crater diameter quantifying how larger impacts produce more extensive fracturing and dilatant bulking the bouguer anomaly of craters larger than 93 47 19 km in diameter is independent of crater size indicating that there is a limiting depth to impact generated porosity presumably from pore collapse associated with either overburden pressure or viscous flow impact generated porosity of the bulk lunar crust is likely in a state of equilibrium for craters smaller than 30km in diameter consistent with an 8km thick lunar megaregolith whereas the gravity signature of larger craters is still preserved and provides new insight into the cratering record of even the oldest lunar surfaces

martian subsurface properties and crater formation processes inferred from fresh impact crater geometries the geometry of simple impact craters reflects the properties of the target materials and the diverse range of fluidized morphologies observed in martian ejecta blankets are controlled by the near surface composition and the climate at the time of impact using the mars orbiter laser altimeter mola data set quantitative information about the strength of the upper crust and the dynamics of martian ejecta blankets may be derived from crater geometry measurements here we present the results from geometrical measurements of fresh craters 3 50 km in rim diameter in selected highland lunae and solis plana and lowland acidalia isidis and utopia planitiae terrains we find large resolved differences between the geometrical properties of the freshest highland and lowland craters simple lowland craters are 1 5 2 0 times deeper 5 o difference with 50 larger cavities 2 o compared to highland craters of the same diameter rim heights and the volume of material above the preimpact surface are slightly greater in the lowlands over most of the size range studied the different shapes of simple highland and lowland craters indicate that the upper 6 5 km of the lowland study regions are significantly stronger than the upper crust of the highland plateaus lowland craters collapse to final volumes of 45 70 of their transient cavity volumes while highland craters preserve only 25 50 the effective yield strength of the upper crust in the lowland regions falls in the range of competent rock approximately 9 12 mpa and the highland plateaus may be weaker by a factor of 2 or more consistent with heavily fractured noachian layered deposits the measured volumes of continuous ejecta blankets and uplifted surface materials exceed the predictions from standard crater scaling relationships and maxwell s z model of crater excavation by a factor of 3 the excess volume of fluidized ejecta blankets on mars cannot be explained by concentration of ejecta through nonballistic emplacement processes and or bulking the observations require a modification of the scaling laws and are well fit using a scaling factor of 1 4 between the transient crater surface diameter to the final crater rim diameter and excavation flow originating from one projectile diameter depth with z 2 7 the refined excavation model provides the first observationally constrained set of initial parameters for study of the formation of fluidized ejecta blankets on mars

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

diverse sclerozoan assemblages encrusting large bivalve shells from the callovian middle jurassic of southern poland a diverse sclerozoan assemblages consisting of both encrusting and boring biota are described from the large limid bivalves ctenostreon from the callovian hardground setting of zalas in southern poland at least 27 encrusting and seven bioerosion taxa are reported here which makes this assemblage not only one of the most diverse in the middle jurassic but the richest in encrusting taxa from the callovian the encrusters consist of cryptic biota of which sedentary polychaetes and cyclostome bryozoans dominate with respect to both species number and abundance the bioerosion traces are dominated by tiny pits referred to the ichnogenus oichnus probably made by some soft bodied biota in the present case followed by the borings of acrothoracican barnacles rogerella the first colonizers of the bivalve shells probably were borers as they only occur in the host shells the encrusting pioneers presumably were oysters and oyster like bivalves followed by opportunistic serpulid sabellid polychaetes and cyclostome bryozoans the last colonizers were calcisponges and thecideide brachiopods in comparison to the only known late callovian shallow and reef associated tropical sclerozoans of israel the assemblage from the open marine deeper setting of poland is much richer in encrusting taxa such a surprising high encruster diversity in the marine northern paleo latitude may have resulted from the deeper and calmer environment with a both reduced sedimentation rate and algal cover and without any significant salinity changes the factors that are thought to have impacted the tropical and shallow marine sclerozoans from israel

lunar mare basalt flow units thicknesses determined from crater size frequency distributions accurate lava flow unit thicknesses estimates are necessary to place constraints on volcanic flux estimates we refine the technique of using the shape of crater size frequency distribution csfd curves to estimate the thickness of individual lunar mare flow units we find that a characteristic knee often observed in csfd curves is reasonably interpreted to represent the presence of two lava flow units separated in time and that the diameter at which this knee occurs is related to the thickness of the overlying flow unit examination of 58 curves with this characteristic knee in several lunar nearside basins oceanus procellarum imbrium tranquillitatis humorum cognitum nubium and insularum allowed us to identify flow units that have not been detected in low sun images we found that the range of flow unit thickness is 20 220 m and the average is 30 60 m this technique expands considerably the ability to assess lava flow unit thicknesses and volumes on the moon and planets

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

a new equatorial very shallow marine sclerozoan fauna from the middle jurassic late callovian of southern israel abstract tropical jurassic sclerozoan faunas are poorly known yet they are critical to our understanding of jurassic biogeography and the evolution of hard substrate communities a diverse assemblage of hard substrate fossils is here described from subunits 53 and 54 of the upper matmor formation callovian of hamakhtesh hagadol in the negev desert of southern israel this region was on or very near the equator during the middle jurassic the fauna is dominated by flat platter shaped sponges actostroma and scleractinian corals microsolena some of which have the depressed centers and raised rims of microatolls which form today in the shallowest subtidal zone associated with reef systems the coral and calcareous sponge platters are encrusted on their top surfaces by one species of serpulid worm and many small coral and sponge recruits with narrow attachments and mushroom shaped or conical skeletons growing upwards the undersurfaces of the platters are encrusted by another serpulid species at least two calcareous sponges rare cyclostome bryozoans oysters plicatulid bivalves and numerous thecideide brachiopods the first known from the jurassic of the region the upper and undersurfaces of the platters are often bored by bivalves forming the ichnospecies gastrochaenolites torpedo these borings were occasionally reoccupied by a nestling mytilid bivalve on the undersurfaces of the skeletal platters this encrusting fauna of the matmor formation apparently lived in a shallow lagoon on the landward side of a coral reef the fossils in the surrounding muddy sediments are primarily echinoids oysters and rhynchonellid and terebratulid brachiopods this sclerozoan fauna is an evidence that jurassic tropical hard substrate faunas were serpulid rich and bryozoan poor as predicted but more diverse at twelve species than expected this community was also ecologically divided into open and cryptic assemblages like its jurassic equivalents in the temperate and subtropical waters of europe and north america

grail gravity constraints on the vertical and lateral density structure of the lunar crust we analyzed data from the gravity recovery and interior laboratory grail mission using a localized admittance approach to map out spatial variations in the vertical density structure of the lunar crust mare regions are characterized by a distinct decrease in density with depth while the farside is characterized by an increase in density with depth at an average gradient of 35 kg m 3 km 1 and typical surface porosities of at least 20 the apollo 12 and 14 landing site region has a similar density structure to the farside permitting a comparison with seismic velocity profiles the interior of the south pole aitken sp a impact basin appears distinct with a near surface low density porous layer 2 3 times thinner than the rest of the farside this result suggests that redistribution of material during the large sp a impact likely played a major role in sculpting the lunar crust

igneous rocks formed by hypervelocity impact abstract igneous rocks are the primary building blocks of planetary crusts most igneous rocks originate via decompression melting and or wet melting of protolith lithologies within planetary interiors and their classification and compositional petrographic and textural characteristics are well studied as our exploration of the solar system continues so too does the inventory of intrusive and extrusive igneous rocks settings and processes the results of planetary exploration have also clearly demonstrated that impact cratering is a ubiquitous geological process that has affected and will continue to affect all planetary objects with a solid surface whether that be rock or ice it is now recognized that the production of igneous rocks is a fundamental outcome of hypervelocity impact the goal of this review is to provide an up to date synthesis of our knowledge and understanding of igneous rocks formed by hypervelocity impact following a brief overview of the basics of the impact process we describe how and why melts are generated during impact events and how impact melting differs from endogenic igneous processes while the process may differ we show that the products of hypervelocity impact can share close similarities with volcanic and shallow intrusive igneous rocks of endogenic origin such impact melt rocks as they are termed can display lobate margins and cooling cracks columnar joints and at the hand specimen and microscopic scale such rocks can display mineral textures that are typical of volcanic rocks such as quench crystallites ophitic porphyritic as well as features such as vesicles flow textures and so on historically these similarities led to the misidentification of some igneous rocks now known to be impact melt rocks as being of endogenic origin this raises the question as to how to distinguish between an impact versus an endogenic origin for igneous like rocks on other planetary bodies where fieldwork and sample analysis may not be possible and all that may be available is remote sensing data while the interpretation of some impact melt rocks may be relatively straightforward e g for clast rich varieties and those with clear projectile contamination we conclude that distinguishing between impact and endogenic igneous rocks is a non trivial task that ultimately may require sample investigation and analysis to be conducted caution is therefore urged in the interpretation of igneous rocks on planetary surfaces

differentiating induced and natural seismicity using space time magnitude statistics applied to the coso geothermal field a remarkable characteristic of earthquakes is their clustering in time and space displaying their self similarity it remains to be tested if natural and induced earthquakes share the same behavior we study natural and induced earthquakes comparatively in the same tectonic setting at the coso geothermal field covering the preproduction and coproduction periods from 1981 to 2013 we analyze interevent times spatial dimension and frequency size distributions for natural and induced earthquakes individually these distributions are statistically indistinguishable determining the distribution of nearest neighbor distances in a combined space time magnitude metric lets us identify clear differences between both kinds of seismicity compared to natural earthquakes induced earthquakes feature a larger population of background seismicity and nearest neighbors at large magnitude rescaled times and small magnitude rescaled distances local stress perturbations induced by field operations appear to be strong enough to drive local faults through several seismic cycles and reactivate them after time periods on the order of a year

deep impact craters in the isidis and southwestern utopia planitia regions of mars high target material strength as a possible cause using themis moc and mola data we havefound 51 craters in the diameter range 6 11 8 km withinsouthwestern utopia planitia and isidis planitia that aresignificantly deeper than typical fresh craters in the northernlowlands of mars the restricted geographic distribution ofthese craters their simple morphology and data fromimpact and explosion crater studies suggest that unusuallystrong target materials as much as a factor of 2 greater thanaverage materials in the martian lowlands are the cause ofthe excessive crater depth we propose that the greater targetmaterial strength acts to delay gravity dominated collapse tolarger crater sizes furthermore we suggest that a regional olivine rich mafic to untramafic rock unit identified by tesand themis is a reasonable candidate for these strongmaterials the unit is exposed on the southern edge of isidisbasin and in crater ejecta within the basin and forms layersthat dip toward the isidis basin center

cryptic encrusting communities in a middle devonian mesophotic paleoenvironment of the holy cross mountains poland abstract the middle devonian givetian chaetetid sponges and alveolitid tabulate corals that inhabited mesophotic paleoenvironments of the southern shelf of laurussia holy cross mountains poland have been studied with respect to encrustation patterns these epibiotic communities are characterized by modest diversity and high dominance and show distinct polarization with respect to the exposed and cryptic sides of the host s skeletons the most abundant davidsoniid brachiopods and microconchids show strong preferences toward the lower cryptic sides while auloporid tabulate corals dominate on the exposed sides of the hosts the remaining and much rarer epibionts cornulitids and rugose corals show no clear preferences in some shallow water silurian paleoenvironments auloporids are known to dominate the cryptic sides of the hosts thus considering the auloporid tabulates as photosymbiotic corals their absence or rarity in the middle devonian cryptic habitats might have resulted from insufficient irradiance levels in otherwise depleted light conditions as a result the available space and lack or lower competition for the area with faster growing colonial auloporids enabled solitary encrusters to colonize the cryptic niches the scarce bioerosion traces and rather low diversity of epibionts in our case may indicate that these mesophotic reefs developed in a nutrient poor oligotrophic habitats the davidsoniid dominated cryptic encrusting communities were widespread in some paleoenvironments during the middle devonian being known from both laurussia and south china craton however such mesophotic cryptic communities characterized by distinct polarization in comparison to open surface environments contrast with other givetian deep water aphotic cryptic communities reported so far where such polarization is hardly visible

bryozoans in transition the depauperate and patchy jurassic biota bryozoans were profoundly affected by the end permian and probably also by the end triassic mass extinction events their recovery in terms of diversity and disparity during the jurassic was slow and geographically patchy critical compilation of data from the published literature reveals only 172 valid species 160 cyclostomes 10 ctenostomes and 2 cheilostomes some as yet not formally named however the rate of description of new jurassic bryozoan species during the last two hundred years implies that many more species remain to be discovered and described the jurassic is the only geological period during which cyclostomes were the dominant order and is also important in having the oldest cheilostome bryozoan the first representative of the order that dominates the modern bryozoan biota species diversity peaked in the bathonian where local assemblages may contain up to 33 species encrusters account for 124 73 of the 172 jurassic species among which small sheet like forms especially those assigned to the form genus berenicea are the most numerous the overwhelming predominance in the jurassic of weeds with runner ribbon or sheet colony forms is striking unlike the triassic and cretaceous large tree like or frondose erect colonies are uncommon and species with fenestrate articulated and free living colonies are unknown of 92 geographically categorized entries for jurassic bryozoans in the zoological record 1937 2003 80 87 are european records outside europe diversity appears to have remained low throughout the jurassic and non weedy species are particularly scarce compared with the cretaceous jurassic bryozoans show no adaptations that can be interpreted as related to the increased predation pressure associated with the mesozoic marine revolution the jurassic bryozoan biota shares characteristics with both the stenolaemate dominated palaeozoic triassic biota and the cheilostome dominated cretaceous recent biotas

contemporary uplift of the sierra nevada western united states from gps and insar measurements modern space geodesy has recently enabled the direct observation of slow geological processes that move and shape earth s surface including plate tectonics and crustal strain accumulation that leads to earthquakes more elusive has been the direct observation of active mountain growth because geodetic measurements have larger uncertainties in the vertical direction while mountain growth is typically very slow for the sierra nevada of california and nevada western united states the history of elevation is complex exhibiting features of both ancient 40 60 ma and relatively young 3 ma elevation here we exploit the complementary strengths of high precision three component point positions from the gps and blanket coverage line of sight measurements from interferometric synthetic aperture radar insar to show that contemporary vertical motion of the sierra nevada is between 1 and 2 mm yr the motion is upward with respect to earth s center of mass and with respect to a relatively stable eastern nevada indicating generation of relief and uplift against gravity uplift is distributed along the entire length of the range between latitude 35 n and 40 n and is not focused near localized seismically imaged mantle downwellings these results indicate that the modern episode of sierra nevada uplift is still active and could have generated the entire modern range in 3 m y

terrace width variations in complex lunar craters the widths of terrace structures in complex craters on the moon are compared to existing theoretical models of their origin terrace widths in an individual crater increase monotonically outward toward the crater rim similarly the width w of the terraces lying closest to the rim of a crater of diameter d increases monotonically obeying a least squares power law relation w km 0 09d0 87 km a simple model of slumping that ignores inertial forces and assumes a constant bedrock yield strength is in good agreement with the observations

topographic characterization of lunar complex craters 1 we use lunar orbiter laser altimeter topography data to revisit the depth d diameter d and central peak height hcp diameter relationships for fresh complex lunar craters we assembled a data set of young craters with d 15 km and ensured the craters were unmodified and fresh using lunar reconnaissance orbiter wide angle camera images we used lunar orbiter laser altimeter gridded data to determine the rim to floor crater depths as well as the height of the central peak above the crater floor we established power law d d and hcp d relationships for complex craters on mare and highlands terrain our results indicate that craters on highland terrain are on average deeper and have higher central peaks than craters on mare terrain furthermore we find that the crater depths for both mare and highlands craters are significantly deeper than previously reported this likely reflects the inclusion of transitional craters and or older and or modified craters in previous work as well as the limitations of the stereophotogrammetric and shadow length data sets used in those studies there is substantial variability in the depths and the central peak heights for craters in a given diameter range we suggest that the differences in mean d and hcp as a function of crater diameter for highlands and mare craters result from differences in bulk physical properties of the terrain types whereas the variability in d and hcp at a given diameter may reflect variations in impactor properties and impact parameters

precursory seismic activation and critical point phenomena in this paper we relate the behavior of seismicity prior to a characteristic earthquake to the excitation in proximity to a spinodal instability we illustrate the spinodal instability as the upper limit of superheated water prior to a steam explosion we draw an analogy between the steam explosion and a characteristic earthquake and show that the power law activation associated with the spinodal instability is essentially identical to the power law increase in benioff strain observed prior to characteristic earthquakes we find that theory and actual data give very similar results

testing the viability of topographic relaxation as a mechanism for the formation of lunar floor fractured craters historically two modes of origin for lunar floor fractured craters have been proposed subcrater laccolith emplacement and topographic relaxation to test the viability of the topographic relaxation model we employ an elastoviscoplastic finite element model and ductile rheology measurements of a devolatilized terrestrial diabase an analog to lunar crustal materials trials were run under two situations 1 under extreme conditions e g high heat flow to determine the maximum degree of relaxation that the model can accommodate and 2 under more nominal conditions in order to resolve how much relaxation can be expected to occur under more plausible lunar conditions we find that in the extreme case topographic relaxation is a viable means only for explaining the observed shallowing of the largest floor fractured craters 100 km in diameter results from the less extreme case demonstrate that lunar materials are simply too rigid to experience degrees of relaxation as large as those observed in the floor fractured crater population these results indicate that topographic relaxation is not the primary mechanism for the formation of floor fractured craters because the topographic relaxation model does not apply for the vast majority of floor fractured craters i e those with diameters less than 60 km we conclude that the laccolith intrusion model is a more viable alternative

palaeoecology and evolution of marine hard substrate communities abstract marine organisms have occupied hard substrates since the archaean shells rocks wood and sedimentary hardgrounds offer relatively stable habitats compared to unconsolidated sediments but the plants and animals which inhabit them must develop means to gain and defend this premium attachment space hard substrate communities are formed by organisms with a variety of strategies for adhering to and or excavating the substrates they inhabit while mobile grazers organically attached and even soft bodied organisms may leave evidence of their former presence in ancient hard substrate communities a superior fossil record is left by sessile encrusters with mineralised skeletons and by borers which leave trace fossils furthermore encrusters and borers are preserved in situ retaining their spatial relationships to one another and to the substrate spatial competition ecological succession oriented growth and differential utilisation of exposed vs hidden substrate surfaces can all be observed or inferred hard substrate communities are thus excellent systems with which to study community evolution over hundreds of millions of years here we review the research on modern and ancient hard substrate communities and point to some changes that have affected them over geological time scales such changes include a general increase in bioerosion of hard substrates particularly carbonate surfaces through the phanerozoic this is at least in part analogous to the infaunalisation trends seen in soft substrate communities encrusting forms show an increase in skeletalisation from the palaeozoic into the mesozoic and cenozoic which may be a response to increasing levels of predation hard substrate communities considering borers and encrusters together show a rough increase in tiering through the phanerozoic which again parallels trends seen in soft substrate communities this extensive review of the literature on living and fossil hard substrate organisms shows that many opportunities remain for large scale studies of trends through time at the community and clade levels palaeontologists will especially benefit by closer integration of their work with that of neontologists particularly in aspects of ecology such as larval recruitment competition and succession

cryptic coral crinoid hanging gardens from the middle devonian of southern morocco an unusual and exceptionally well preserved cryptic community of cnidarians crinoids sponges and microbes developed in a submarine cavity of middle devonian age in the hamar laghdad area morocco the biota encrusted the cavity roof and grew predominantly in an upside down position forming spectacular hanging gardens the investigated assemblage differs strikingly from both its paleozoic and modern analogues it constitutes one of a very few known examples of fossil cryptic assemblages developed in relatively deep water settings and is the first report of a cryptic paleoecosystem dominated by rugose corals the results support the view that during the middle paleozoic there was no distinct polarization between open surface and cryptic faunas in deep water environments but keen competition for space already existed in devonian cryptic assemblages the regional species pool seems to have been the main determinant of the ecological succession and structure of this cryptic community

lunar radar sounder observations of subsurface layers under the nearside maria of the moon observations of the subsurface geology of the moon help advance our understanding of lunar origin and evolution radar sounding from the kaguya spacecraft has revealed subsurface layers at an apparent depth of several hundred meters in nearside maria comparison with the surface geology in the serenitatis basin implies that the prominent echoes are probably from buried regolith layers accumulated during the depositional hiatus of mare basalts the stratification indicates a tectonic quiescence between 3 55 and 2 84 billion years ago mare ridges were formed subsequently the basalts that accumulated during this quiet period have a total thickness of only a few hundred meters these observations suggest that mascon loading did not produce the tectonics in serenitatis after 3 55 billion years ago global cooling probably dominated the tectonics after 2 84 billion years ago

on the nature and dynamics of the seismogenetic systems of north california usa an analysis based on non extensive statistical physics abstract we examine the nature of the seismogenetic system in north california usa by searching for evidence of complexity and non extensivity in the earthquake record we attempt to determine whether earthquakes are generated by a self excited poisson process in which case they obey boltzmann gibbs thermodynamics or by a critical process in which long range interactions in non equilibrium states are expected correlation and the thermodynamics deviate from the boltzmann gibbs formalism emphasis is given to background seismicity since it is generally agreed that aftershock sequences comprise correlated sets we use the complete and homogeneous earthquake catalogue published by the north california earthquake data centre in which aftershocks are either included or have been removed by a stochastic declustering procedure we examine multivariate cumulative frequency distributions of earthquake magnitudes interevent time and interevent distance in the context of non extensive statistical physics which is a generalization of extensive boltzmann gibbs thermodynamics to non equilibrating non extensive systems our results indicate that the seismogenetic systems of north california are generally sub extensive complex and non poissonian the background seismicity exhibits long range interaction as evidenced by the overall increase of correlation observed by declustering the earthquake catalogues as well as by the high correlation observed for earthquakes separated by long interevent distances it is also important to emphasize that two subsystems with rather different properties appear to exist the correlation observed along the sierra nevada range walker lane is quasi stationary and indicates a self organized critical fault system conversely the north segment of the san andreas fault exhibits changes in the level of correlation with reference to the large loma prieta event of 1989 and thus has attributes of critical point behaviour albeit without acceleration of seismic release rates soc appears to be a likely explanation of complexity mechanisms but since there are other ways by which complexity may emerge additional work is required before assertive conclusions can be drawn

mass wasting features on the moon how active is the lunar surface abstract mass wasting features have long been noticed on the moon but there has been no systematic studies for their morphological geometrical or distribution characteristics the effect of mass wasting on topographic evolution and surface erosion on the moon is not fully understood using high resolution image and topography data obtained from the lunar reconnaissance orbiter spacecraft we found that mass wasting has been globally and continuously occurring on the moon meteor impacts and moonquakes are the two major triggering mechanisms in forming lunar mass wasting features we selected over 300 examples of lunar mass wasting features and classified them as falls flows slides slumps and creeps after studying their morphology potential mode of emplacement and sizes of displaced materials the slope and age distributions for their host terrains are studied to estimate the topographic evolutionary sequence of the lunar surface under the effect of mass wasting due to continuous reshaping by mass wasting surface topographies on the moon tend to become smoother with time with fewer mass wasting events occurring on older surfaces pre nectarian surfaces may represent the final stage of surface topographic evolution on slope angles regarding the effect of mass wasting crater densities on lunar surfaces vary with slope angles because the surface erosion rate and regolith production rate on slopes are larger than those on flat areas

the geology of 433 eros the global high resolution imaging of asteroid 433 eros by the near earth asteroid rendezvous near shoemaker spacecraft has made it possible to develop the first comprehensive picture of the geology of a small s type asteroid eros displays a variety of surface features and evidence of a substantial regolith large scale facets grooves and ridges indicate the presence of at least one global planar structure directional and superposition relations of smaller structural features suggest that fracturing has occurred throughout the object as with other small objects impact craters dominate the overall shape as well as the small scale topography of eros depth diameter ratios of craters on eros average 0 13 but the freshest craters approach lunar values of 0 2 ejecta block production from craters is highly variable the majority of large blocks appear to have originated from one 7 6 km crater shoemaker the interior morphology of craters does not reveal the influence of discrete mechanical boundaries at depth in the manner of craters formed on lunar mare regolith and on some parts of phobos this lack of mechanical boundaries and the abundant evidence of regolith in nearly every high resolution image suggests a gradation in the porosity and fracturing with depth the density of small craters is deficient at sizes below 200 m relative to predicted slopes of empirical saturation this characteristic which is also found on parts of phobos and lunar highland areas probably results from the efficient obliteration of small craters on a body with significant topographic slopes and a thick regolith eros displays a variety of regolith features such as debris aprons fine grained ponded deposits talus cones and bright and dark streamers on steep slopes indicative of efficient downslope movement of regolith these processes serve to mix materials in the upper loose fragmental portion of the asteroid regolith in the instance of ponded materials and crater wall deposits there is evidence of processes that segregate finer materials into discrete deposits the near observations have shown us that surface processes on small asteroids can be very complex and result in a wide variety of morphologic features and landforms that today seem exotic future missions to comets and asteroids will surely reveal still as yet unseen processes as well as give context to those discovered by the near shoemaker spacecraft

statistical mechanics and scaling of fault populations with increasing strain in the corinth rift scaling properties of fracture fault systems are studied in order to characterize the mechanical properties of rocks and to provide insight into the mechanisms that govern fault growth a comprehensive image of the fault network in the corinth rift greece obtained through numerous field studies and marine geophysical surveys allows for the first time such a study over the entire area of the rift we compile a detailed fault map of the area and analyze the scaling properties of fault trace lengths by using a statistical mechanics model derived in the framework of generalized statistical mechanics and associated maximum entropy principle by using this framework a range of asymptotic power law to exponential like distributions are derived that can well describe the observed scaling patterns of fault trace lengths in the rift systematic variations and in particular a transition from asymptotic power law to exponential like scaling are observed to be a function of increasing strain in distinct strain regimes in the rift providing quantitative evidence for such crustal processes in a single tectonic setting these results indicate the organization of the fault system as a function of brittle strain in the earth s crust and suggest there are different mechanisms for fault growth in the distinct parts of the rift in addition other factors such as fault interactions and the thickness of the brittle layer affect how the fault system evolves in time the results suggest that regional strain fault interactions and the boundary condition of the brittle layer may control fault growth and the fault network evolution in the corinth rift

spatial distribution of aftershocks and background seismicity in central california we examine the spatial distribution of earthquake hypocenters in four central california areas the aftershock zones of the 1 1984 morgan hill 2 1979 coyote lake and 3 1983 coalinga earthquakes as well as 4 the aseismically creeping area around hollister the basic tool we use to analyze these data are frequency distributions of interevent distances between earthquakes these distributions are evaluated on the basis of their deviation from what would be expected if earthquakes occurred randomly in the study areas we find that both background seismic activity and aftershocks in the study areas exhibit nonrandom spatial distribution two major spatial patterns clustering at small distances and anomalies at larger distances are observed depending on tectonic setting while both patterns are seen in the strike slip environments along the calaveras fault morgan hill coyote lake and hollister aftershocks of the coalinga event a thrust earthquake seem to be characterized by clustering only the spatial distribution of earthquakes in areas gradually decreasing in size does not seem to support the hypothesis of a self similar distribution over the range of scales studied here regardless of tectonic setting spatial distributions are independent of magnitude for the coalinga aftershocks but events in strike slip environments show increasing clustering with increasing magnitude finally earthquake spatial distributions vary in time showing different patterns before during and following the end of aftershock sequences

crustal stress field in southern california and its implications for fault mechanics we present a new high spatial resolution image of stress orientation in southern california based on the inversion of earthquake focal mechanisms we use this image to study the mechanics of faulting in the plate boundary region the stress field contains significant spatial heterogeneity which in some cases appears to be a result of the complexity of faulting and in other cases appears to be a cause temporal changes in the stress field are also observed primarily related to major earthquakes the observed 15 10 rotation of the stress axes due to the 1992 m7 3 landers mainshock implies that the deviatoric stress magnitude in the crust is low of the order of 10 mpa this suggests that active faults in southern california are weak the maximum principal stress axis near the san andreas fault is often at 50 to the fault strike indicating that the shear stress on the fault is comparable to the deviatoric stress the san andreas in southern california may therefore be a weak fault in a low strength crust

geometric relationships of pristine martian complex impact craters and their implications to mars geologic history 1 based on the depths of pristine complex craters on mars we have estimated the final post modification phase depth dr to diameter d function of martian complex craters we suggest that the dr d function determined here holds globally for complex craters 12 km diameter the global nature of this function may be due to the stability of slopes in the highly fractured rock that makes up the steep interior walls of post modification phase craters the stability of such slopes should be controlled mainly by such factors as the nature of the fractures and not target strength this function is an essential benchmark for studies that utilize crater geometry as their basis for example the function can be used in gradation history of mars to predict the magnitude of degradation for instance an example 20 km diameter middle early noachian age crater that initially formed in the mid latitudes of mars with a depth of 1800 m instead of 1404 m as predicted by the fresh craters function has lost 1450 m of its depth over its history 350 m in the noachian 400 m during an intense episode of degradation at the end of the noachian and 700 m thereafter no evidence of the period of intense degradation is found in the high latitudes although those regions appear to have been affected by a process that reduced crater depth soon after they form

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

impact induced seismic activity on asteroid 433 eros a surface modification process high resolution images of the surface of asteroid 433 eros revealed evidence of downslope movement of a loose regolith layer as well as the degradation and erasure of small impact craters less than 100 meters in diameter one hypothesis to explain these observations is seismic reverberation after impact events we used a combination of seismic and geomorphic modeling to analyze the response of regolith covered topography particularly craters to impact induced seismic shaking applying these results to a stochastic cratering model for the surface of eros produced good agreement with the observed size frequency distribution of craters including the paucity of small craters

microbialite morphology structure and growth a model of the upper jurassic reefs of the chay peninsula western france abstract during the early kimmeridgian the northern margin of the aquitaine basin western france is characterised by a significant development of coral reefs the reef formation of the chay peninsula comprises two main reefal units in which the microbial structures can contribute up to 70 of framework the microbial crusts which played an important role in the stabilisation and growth of the reef body show the characteristic clotted aspect of thrombolitic microbialites corals are the main skeletal components of the build ups the bioconstructions of the chay area are thus classified as coral thrombolite reefs four main morpho structural types of microbial crusts are distinguished 1 pseudostalactitic microbialites on the roof of intra reef palaeocaves 2 mamillated microbialites found either on the undersides or on the flanks of the bioherms 3 reticular microbialites in marginal parts of the reefs and between adjacent bioconstructed units and 4 interstitial microbialites in voids of bioclastic deposits thrombolitic crusts developed on various substrates such as corals bivalves or bioclasts the thrombolites formed a dense clotted and or micropeloidal microbial framework in which macro and micro encrusters also occur variations in accumulation rate strongly influenced the reef morphology in particular its relief above the sediment surface the coalescence of the coral microbialite patches created numerous intra reef cavities of metre scale dimensions the direction of microbial growth which defined the macroscopic microbialite forms strongly depended on the position within the reef framework but was also controlled by water energy accumulation rate and light availability

cratering history and lunar chronology the moon is exceptional and important because it is the only planetary body besides the earth for which we have both a detailed stratigraphic history and datable rock samples that can be related to specific geomorphologic units fig 5 1 the moon has preserved much of its magmatic and impact record of at least the last 4 billion years while its endogenic history is of great interest for the fundamentals of planetary interiors and surfaces the moon has become a calibration plate for the cratering record of the earth moon system and by extrapolation of the entire inner solar system if one assumes a heliocentric origin for impactor populations these populations range from asteroids through long and short period comets to interplanetary dust and cover a size range from hundreds of kilometers to micrometers figure 5 1 telescopic view of the nearside of the earth s moon with landing sites of the apollo and luna missions this chapter reviews the presently available data sets in support of this paradigmatic assumption as follows 1 the phenomenology of lunar impact craters 2 the terrestrial record of the impact cratering process and the interpretation of terrestrial impactites as far as this ground truth is relevant for the interpretation of lunar impact craters and datable lunar impact breccias and melt rocks 3 the theory and numerical simulation of the cratering process and the characteristics of the earth moon crossing population of impactors asteroids and comets 4 the principles of relative age dating of lunar surface units and the general lunar stratigraphy 5 the stratigraphic significance and ages of lunar samples impactites and basalts and based on this data set the absolute ages of lunar surface units 6 the cratering rate of the moon as a function of time and 7 the time calibration of this cratering rate based on the

a depth versus diameter scaling relationship for the best preserved melt bearing complex craters on mars abstract we use topographic data to show that impact craters with pitted floor deposits are among the deepest on mars this is consistent with the interpretation of pitted materials as primary crater fill impactite deposits emplaced during crater formation our database consists of 224 pitted material craters ranging in size from 1 to 150 km in diameter our measurements are based on topographic data from the mars orbiter laser altimeter mola and the high resolution stereo camera hrsc we have used these craters to measure the relationship between crater diameter and the initial post formation depth depth was measured as maximum rim to floor depth d r but we also report the depth measured using other definitions the database was down selected by refining or removing elevation measurements from problematic craters affected by processes and conditions that influenced their d r d such as pre impact slopes topography and later overprinting craters we report a maximum deepest and mean scaling relationship of d r 0 347 0 021 d 0 537 0 017 and d r 0 323 0 017 d 0 538 0 016 respectively our results suggest that significant variations between previously reported mola based d r vs d relationships may result from the inclusion of craters that 1 are influenced by atypical processes e g highly oblique impact 2 are significantly degraded 3 reside within high strength regions and 4 are transitional partially collapsed by taking such issues into consideration and only measuring craters with primary floor materials we present the best estimate to date of a mola based relationship of d r vs d for the least degraded complex craters on mars this can be applied to crater degradation studies and provides a useful constraint for models of complex crater formation

gullies and landslides on the moon evidence for dry granular flows 1 high resolution images from chandrayaan 1 terrain mapping camera and lunar reconnaissance orbiter camera reveal landslides and gully formation on the interior wall of a 7 km diameter simple crater emplaced in schrodinger basin on the farside of the moon these features occur on the steep upper crater wall where the slope is 35 the gullies show a typical alcove channel fan morphology some gullies incise bedrock where impact related faults are present slope failure along the concentric faults also led to formation of landslides dark slope streaks are abundant at the bright gully regions especially near the fan and channel deposits spectral characteristics inferred from data obtained by hyperspectral imager and moon mineralogy mapper on board chandrayaan 1 show that the gullies and landslides are characterized by high optical immaturity and devoid of prominent spectral absorption features related to water or hydroxyl molecules suggesting youthful dry granular flows mass movements on the crater wall led to the formation of arcuate ridges and ponding of fine grained sediments on the crater floor runout flows from small impact craters on the slopes indicate that impact induced seismic shaking was responsible for the downslope mass movements crater size frequency distributions suggest a minimum age of 18 2 ma for the gullies and 2 ma for the landslides while age of the host crater ejecta was inferred to be about 175 ma the gullies and landslides also occur on the interior wall of other impact craters elsewhere on the moon and probably formed by similar processes

the layered structure of lunar maria identification of the hf radar reflector in mare serenitatis using multiband optical images abstract comparison of the lunar radar sounder lrs data to the multiband imager mi data is performed to identify the subsurface reflectors in mare serenitatis the lrs is fm cw radar 4 6 mhz and the 2 mhz bandwidth leads to the range resolution of 75 m in a vacuum whereas the sampling interval in the flight direction is about 75 m when an altitude of the spacecraft with polar orbit is nominal 100 km horizontally continuous reflectors were clearly detected by lrs in limited areas that consist of about 9 of the whole maria the typical depth of the reflectors is estimated to be a few hundred meters layered structures of mare basalts are also discernible on some crater walls in the mi data of the visible bands vis the vis range has nine wavelengths of 415 750 900 950 and 1000 nm and their spatial resolution is 20 m pixel at a nominal altitude the stratigraphies around bessel and bessel h craters in mare serenitatis are examined in this paper it was revealed that the subsurface reflectors lie on the boundaries between basalt units with different chemical compositions in addition model calculations using the simplified radar equation indicate that the subsurface reflectors are not compositional interfaces but layer boundaries with a high porosity contrast these results suggest that the detected reflectors in mare serenitatis are regolith accumulated during so long hiatus of mare volcanisms enough for chemical composition of magma to change not instantaneously therefore combination of the lrs and mi data has a potential to reveal characteristics of a series of magmatism forming each lithostratigraphic unit in mare serenitatis and other maria

nonuniform cratering of the terrestrial planets article history we estimate the impact flux and cratering rate as a function of latitude on the terrestrial planets using a model distribution of planet crossing asteroids and comets bottke w f morbidelli a jedicke r petit j m levison h f michel p metcalfe t s 2002 icarus 156 399 433 after determining the planetary impact probabilities as a function of the relative encounter velocity and encounter inclination the impact positions are calculated analytically assuming the projectiles follow hyperbolic paths during the encounter phase as the source of projectiles is not isotropic latitudinal variations of the impact flux are predicted the calculated ratio between the pole and equator is 1 05 for mercury 1 00 for venus 0 96 for the earth 0 90 for the moon and 1 14 for mars over its long term obliquity variation history by taking into account the latitudinal dependence of the impact velocity and impact angle and by using a crater scaling law that depends on the vertical component of the impact velocity the latitudinal variations of the cratering rate the number of craters with a given size formed per unit time and unit area is in general enhanced with respect to the equator the polar cratering rate is about 30 larger on mars and 10 on mercury whereas it is 10 less on the earth and 20 less on the moon the cratering rate is found to be uniform on venus the relative global impact fluxes on mercury venus the earth and mars are calculated with respect to the moon and we find values of 1 9 1 8 1 6 and 2 8 respectively our results show that the relative shape of the crater size frequency distribution does not noticeably depend upon latitude for any of the terrestrial bodies in this study nevertheless by neglecting the expected latitudinal variations of the cratering rate systematic errors of 20 30 in the age of planetary surfaces could exist between equatorial and polar regions when using the crater chronology method

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

the effect of target lithology on the products of impact melting impact cratering is an important geological process on the terrestrial planets and rocky and icy moons of the outer solar system impact events generate pressures and temperatures that can melt a substantial volume of the target however there remains considerable discussion as to the effect of target lithology on the generation of impact melts early studies showed that for impacts into crystalline targets coherent impact melt rocks or sheets are formed with these rocks often displaying classic igneous structures e g columnar jointing and textures for impact structures containing some amount of sedimentary rocks in the target sequence a wide range of impactgenerated lithologies have been described although it has generally been suggested that impact melt is either lacking or is volumetrically minor this is surprising given theoretical constraints which show that as much melt should be produced during impacts into sedimentary targets the question then arises where has all the melt gone the goal of this synthesis is to explore the effect of target lithology on the products of impact melting a comparative study of the similarly sized haughton mistastin and ries impact structures suggests that the fundamental processes of impact melting are basically the same in sedimentary and crystalline targets regardless of target properties furthermore using advanced microbeam analytical techniques it is apparent that for the structures under consideration here a large proportion of the melt is retained within the crater as crater fill impactites for impacts into sedimentary bearing target rocks thus it is suggested that the basic products are genetically equivalent but they just appear different that is it is the textural chemical and physical properties of the products that vary