glass from the cretaceous tertiary boundary in haiti tektite like glasses preserved at the cretaceous tertiary boundary at beloc in haiti provide clear evidence of an impact event the glass composition suggests that the impact occurred on a continental shelf region generating a silica rich glass with chemical composition that reflects the melting of continental crustal rocks and a calcium rich glass produced by the fusion of marl sediments these findings indicate that catastrophic release to the atmosphere of 1015 moles of c02 from vaporized marl occurred during the impact

impacts into non polar ice rich paleodeposits on mars excess ejecta craters perched craters and pedestal craters as clues to amazonian climate history we compare three previously independently studied crater morphologies excess ejecta craters perched craters and pedestal craters each of which has been proposed to form from impacts into an ice rich surface layer our analysis identifies the specific similarities and differences between the crater types the commonalities provide significant evidence for a genetic relationship among the morphologies we use new surveys of excess ejecta and perched craters in the southern hemisphere in conjunction with prior studies of all of the morphologies to create a comprehensive overview of their geographic distributions and physical characteristics from these analyses we conclude that excess ejecta craters and perched craters are likely to have formed from the same mechanism with excess ejecta craters appearing fresh while perched craters have experienced post impact modification and infilling impacts that led to these two morphologies overwhelmed the ice rich layer penetrating into the underlying martian regolith resulting in the excavation of rock that formed the blocky ejecta necessary to armor the surface and preserve the ice rich deposits pedestal craters which tend to be smaller in diameter have the same average deposit thickness as excess ejecta and perched craters and form in the same geographic regions they rarely have ejecta around their crater rims instead exhibiting a smooth pedestal surface we interpret this to mean that they form from impacts into the same type of ice rich paleodeposit but that they do not penetrate through the icy surface layer and thus do not generate a blocky ejecta covering instead a process related to the impact event appears to produce a thin indurated surface lag deposit that serves to preserve the ice rich material these results provide a new basis to identify the presence of amazonian non polar ice rich deposits to map their distribution in space and time and to assess amazonian climate history specifically the ages distribution and physical attributes of the crater types suggest that tens to hundreds of meters of ice rich material has been episodically emplaced at mid latitudes in both hemispheres throughout the amazonian due to obliquity driven climate variations these deposits likely accumulated more frequently in the northern lowlands resulting in a larger population of all three crater morphologies in the northern hemisphere

preserved flora and organics in impact melt breccias impact cratering can destroy life from local to global scales and result in sudden turnovers of dominant genera and or species here we report that it can also preserve components of the local biology present at the time of impact we have investigated floral matter encapsulated within cenozoic era impact glasses produced by separate bolide impacts into the loessoid sediments of argentina that occurred between 9 2 ma miocene and 6 ka holocene the encapsulation preserved not only macro scale morphological biosignatures such as vascular bundles veins phytoliths and papillae but also structures down to the cellular level in the best preserved samples we also found evidence for organic matter while fossilization typically occurs over an extended time period as minerals slowly replace organic matter and the host rock lithifies under pressure the process documented here is instantaneous preservation of morphological and chemical biosignatures in impact events can provide snapshots of the ecology in environments that do not otherwise promote a diverse fossil record we suggest that this would provide a new strategy for identifying signs of possible early life on ancient mars where similar target conditions once existed

mars near infrared spectral reflectance of surface regions and compositional implications reflectance spectra 0 65 2 50 m are presented for 11 martian areas the spectral resolution is 1 and the spatial resolution is 1000 2000 km these are the first high quality spectrophotometric data at these wavelengths for regions on the surface spectral features previously observed are confirmed and better defined and a number of important spectral properties are characterized for the first time the spectra show water ice absorptions in the 1 5 and 2 0 m regions which if due to surface frost would imply the presence of 1 to 2 mg cm2 h2o however other studies have shown that the presence of an unprotected surface frost in late morning is unlikely water ice is stable at night even at the equator and might persist until late morning when the air is well undersaturated if it is intimately dispersed in weathering products especially if clays are present the dark region spectra indicate about 4 times less water ice than seen in bright regions since some bright material is present in dark regions there may be no water ice associated with the dark materials themselves this tends to confirm that weathering products thought to be more abundant in bright regions are involved in the mechanism that allows temporary persistance of unstable water ice the presence of weak 2 3 m features in many of the spectra are consistent with the presence of hydroxylated magnesium rich minerals such as sheet silicates serpentine talc and magnesian smectites or amphiboles anthophyllite the apparent absence of a 2 2 m absorption implies that montmorillonite may not be a major component of the martian regolith many of the spectra also show an apparent absorption at 1 9 m in the wing of the 2 0 m martian atmospheric co2 absorption which would indicate bound molecular water observed dark regions have distinctive near infrared spectral shapes previously not well determined which are characteristic of thin semi transparent alteration coatings overlying dark unaltered rock previously observed ferrous and ferric iron absorptions in the 1 m region are better defined by these new data clinopyroxene augite is definitely present but olivine is not spectrally apparent

late pleistocene holocene eolian deposits of the southern buenos aires province argentina a preliminary model abstract the aim is to reconstruct the sedimentological history of the late pleistocene holocene eolian deposits of southern buenos aires province hence a preliminary model is proposed in order to analyze the different stages of the sedimentological cycle the deposits include sandy loess fine sand sheets and dunefields the southern buenos aires province represents the depositional area whereas the source and transport environments are located in the northern patagonian andes and northern extra andean patagonia according to the mineralogical characteristics of the material explosive volcanism is considered the predominant process of particle formation particularly as generator of pyroclastic deposits which were reworked by different erosive processes glacial fluvial eolian during the late glacial maximum and the holocene alluvial deposits which were mainly generated by fluvial erosion of volcaniclastic sedimentary units were deposited along the floodplains of the colorado and negro rivers including those distal segments located in the emerged offshore platform the fluvial regime depended upon the regime of the glaciers hence it reflected the major glacial fluctuations which took place in the andes floodplains were deflated by southwest winds transporting the material towards the southern buenos aires province sandy loess and loessial sands and to la pampa province dunefields

deucalionis regio mars evidence for a new type of immobile weathered soil unit abstract a small equatorial region south of sinus meridiani deucalionis regio has been found spectrally distinct from other regions as seen in a high spectral resolution telescopic image of mars interpretations from a variety of other observations including infrared radiometric data historical occurrences of localized dust storms and general circulation wind modeling also suggest that the surface of deucalionis regio has properties that are different than those of nearby regions arabia acidalia sinus meridiani and oxia in terms of expression of color crystalline hematite content and perhaps pyroxene abundance and mineralogy the thermophysical and aeolian observations indicate that the soils in deucalionis regio are relatively immobile despite the likely occurrence of winds strong enough to move unconsolidated materials we propose that the soils in this region are indurated or crusted we predict that a mars observer class thermal emission spectrometer and gamma ray spectrometer will show the presence of crust forming minerals and elements in the soils of this region the spatial correlation between areas that have been previously proposed to be regional exposures of crust and areas that are spectrally similar to deucalionis regio may suggest a possible genetic relationship between the composition and the physical properties

mars definition and characterization of global surface units with emphasis on composition units of similar optical properties have been defined for a large part of the surface of mars using primarily viking 2 approach maps of red 0 59 m and violet 0 45 m normal albedo of available global data sets spectral albedo most closely relates to surface mineralogy the resultant unit map represents mars at the time the viking images were acquired ls 103 105 morning northern hemisphere summer in 1976 computer processing of these data reveals clusters of albedo values which relate to specific contiguous regions on the planet final unit definitions were determined by an interactive iterative process which included scientific judgment on the part of the researchers the results therefore are not the product of an unsupervised statistical classification some unit boundaries are of a gradational nature while others are more discrete certain of the units are temporal and relate to the presence of condensates at the time of observation other units by virtue of their redness and low albedo are almost certainly not affected by condensates a study of the albedo properties of analog materials measured in the laboratory and of telescopic spectrophotometry of mars indicates that both hydroxylated low temperature or secondary and hematitic high temperature or primary oxidized materials exist on the surface the most likely surface expression of global dust and or high albedo soils is in the classical bright region arabia this material is probably a low temperature hydrated oxidation product of mafic volcanic glass such as a palagonite or amorphous iron silica gel most low albedo features in the region studied have red and violet albedos consistent with a dark substrate such as basalt coated by or mixed with the fine grained alteration product mentioned above there may be no genetic relationship between these two components in this majority of low albedo surface materials certain of the other low albedo regions are also the most red highest r v areas observed on the planet these areas are consistent with a nonhydroxylated more hematitic material such as that produced by high temperature hydrothermal alteration of basalt some of these dark very red regions correlate with exposures of very ancient terrain at this spatial resolution 10 20 km pixel there is no evidence of surface exposures of uncoated or unweathered basaltic rock or glass comparisons of the unit map with other data sets available to us revealed no striking detailed correlations larger scale correlations certainly do exist however among the various albedo data sets and with thermal inertia data

erosion rates on mars and implications for climate change constraints from the pathfinder landing site the observation that the mars pathfinder landing site looks very similar to its appearance after it was deposited by catastrophic floods around 1 8 3 5 ga allows quantitative constraints to be placed on the rate of change of the site since that time the abundance of erosional features such as an exhumed former soil horizon sculpted wind tails ripplelike and other tag deposits and ventifacts fluted and grooved rocks all suggest the site has undergone net deflation or loss of 3 7 cm of material the presence of barchan dunes and ventifacts argues for erosion by saltating crystalline sand size particles entrained in the wind most ventifacts probably formed soon after the catastrophic flood which likely introduced a large fresh supply of sand size particles distributed across the rocky plain the strongest winds blew toward the northwest during this time resulting in the sculpting of ventifacts deflation of the surface collections of dunes within big crater and other lows and possibly preferentially eroding small crater rims the predominant wind direction changed to blow toward the southwest similar to today these winds further deflated the surface completed the deposition of sand size material in dunes and ultimately trapped these dunes in lows the erosional features observed by pathfinder indicate extremely low long term deflation rates of 0 01 0 04 nm yr since the end of the hesperian 1 8 3 5 ga similar to less precise rates of 1 nm yr based on the preservation of craters at the viking 1 and pathfinder landing sites short term redistribution rates deposition and removal of atmospheric dust at the pathfinder landing site and preexisting dust and sand at other locations on mars are up to 10 5 nm yr estimates of erosion rates on mars show a rapid decrease by 3 6 orders of magnitude from 10 2 10 4 nm yr in noachian terrains characterized by rimless flat floored craters and valley networks to the exceedingly slow rates 10 2 10 nm yr operating during the hesperian and amazonian noachian erosion rates comparable to low continental denudation rates on earth are consistent with erosion by running water and perhaps a more clement climate the rapid decrease in erosion rates is consistent with a major climatic change during the noachian at the tail end of heavy bombardment and a cold dry desiccating climate similar to today s since that time

pedestal crater heights on mars a proxy for the thicknesses of past ice rich amazonian deposits abstract mid latitude pedestal craters on mars offer crucial insights into the timing and extent of widespread ice rich deposits during the amazonian period our previous comprehensive analysis of pedestal craters strongly supports a climate related formation mechanism whereby pedestals result from impacts into ice rich material at mid latitudes during periods of higher obliquity the ice from this target deposit later sublimates due to obliquity changes but is preserved beneath the protective cover of the armored pedestal as such the heights of pedestals act as a proxy for the thicknesses of the paleodeposits in this analysis our measurement of 2300 pedestal heights shows that although pedestals can reach up to 260 m in height 82 are shorter than 60 m and only 2 are taller than 100 m mean pedestal heights are 48 0 m in the northern mid latitudes and 40 4 m in the southern mid latitudes with the tallest pedestals located in utopia planitia acidalia planitia and malea planum we use these data in conjunction with prior climate model results to identify both regional and global trends regarding ice accumulation during obliquity excursions our data provide evidence for multiple episodes of emplacement and removal of the mid latitude ice rich deposit based on stratigraphic relationships between pedestal craters and the close proximity of pedestals with significantly different heights

a search for basaltic to intermediate glasses on mars assessing martian crustal mineralogy multiple datasets have demonstrated that the crust of mars is fundamentally basaltic however spectral libraries used to interrogate thermal infrared spectra of martian dark regions through spectral deconvolution have heretofore lacked mafic glasses despite the importance of amorphous phases or phases with amorphous like spectral signatures in martian mineralogy to establish the presence and importance of basaltic to intermediate glasses in martian lithologies we created five such glasses obtained their thermal infrared spectra and included the spectra in a library used to deconvolve nine regional thermal emission spectrometer spectra from mars we employed the nonnegative least squares nnls deconvolution method which yields deconvolved phase abundances and the uncertainties associated with those abundances the basaltic to intermediate glasses do not appear in the deconvolution solutions indicating they are not globally or regionally important phases because martian igneous or impact processes are capable of basaltic to intermediate glass formation the lack of such glasses in the deconvolved mineralogies suggests either the glasses did not form in detectable quantities or they or their signatures have been removed the masking or replacement of basaltic to intermediate glasses through alteration is supported by the appearance in the deconvolution solutions of amorphous phases e g silica rich glasses opal or phases with amorphous like spectral signatures e g clays zeolites that commonly form through aqueous alteration of mafic glasses the glasses may still be important to local scale thermal infrared studies given the basaltic nature of mars and the variety of local scale lithologies detected by various missions the regional mineralogies derived from the nnls deconvolution analysis divide into five statistically separable groups which provide insight into regional trends in mineralogy

a global view of martian surface compositions from mgs tes thermal emission spectrometer tes data from the mars global surveyor mgs are used to determine compositions and distributions of martian low albedo regions two surface spectral signatures are identified from low albedo regions comparisons with spectra of terrestrial rock samples and deconvolution results indicate that the two compositions are a basaltic composition dominated by plagioclase feldspar and clinopyroxene and an andesitic composition dominated by plagioclase feldspar and volcanic glass the distribution of the two compositions is split roughly along the planetary dichotomy the basaltic composition is confined to older surfaces and the more silicic composition is concentrated in the younger northern plains

mapping of spectral variations on the surface of mars from high spectral resolution telescopic images abstract we analyze a high spectral resolution r 200 visible and near infrared 0 44 1 02 m telescopic spectral image of mars to explore surface material variations across the observed face of the planet which is centered on sinus meridiani two independent analysis methods are employed linear mixture modeling and supervised spectral pattern classification with an artificial neural network four endmember type regions are identified with linear mixing further refinement is achieved with the nonlinear neural network classification algorithm separating eight units of geological significance differences in spectral features among the mapped units are characterized among the medium to high albedo units northern lowlands typified by chryse planitia show far less evidence of bulk crystalline hematite than western arabia or any other highland regions the relationship of these bright units to the globally distributed aeolian dust is not yet clear within our image low albedo regions with the most pronounced crystalline hematite signature primarily correlate with the classic dark regions with the exception of acidalia planitia spectral evidence for pyroxenes also correlates well with most of the classic low albedo regions but again acidalia planitia is the major exception significant spectral anomaly is also found in an equatorial region deucalionis regio a companion paper in this issue discusses the soil properties of deucalionis our data and analysis support a compositional trend that is consistent with the global geologic crustal dichotomy of mars namely that the younger northern lowlands contain less bulk crystalline hematite than southern highlands

the plio pleistocene record of the central eastern pampas buenos aires province argentina the chapadmalal case study abstract the plio pleistocene record of central eastern pampas argentina is preserved in loess like sediments exposed in the sea cliffs south of mar del plata the uplift of the andes during miocene triggered the deposition of wind blown material the source areas are located about 1000 km away in western argentina volcanic ashfalls play a significant role in the formation of eolian sediments which were reworked and redeposited by aqueous transport in a flat low relief landscape under varying climatic conditions vertebrate fossil assemblages document warm and wetter pliocene and early pleistocene climates during montehermosan and uquian land mammal ages more arid and cooler conditions alternating with humid and warmer intervals prevailed during the middle to late pleistocene in ensenadan and lujanian land mammal ages the chapadmalal locality is the best exposed and most complete section almost all the units have been modified by pedogenesis truncated paleosols as well as pedogenic and non pedogenic calcretes are very frequent throughout the stratigraphic succession several paleosurfaces with prominent paleosols and calcretes suggest that sedimentation was an episodic process with numerous depositional gaps recording relatively long lasting intervals of landscape stability the depositional events represent alternations of fluvial and eolian sedimentation low frequency catastrophic episodes played an important role in the sedimentation process

dust and ice deposition in the martian geologic record abstract the polar layered deposits of mars demonstrate that thick accumulations of dust and ice deposits can develop on the planet if environmental conditions are favorable these deposits appear to be hundreds of millions of years old and other deposits of similar size but of greater age in nonpolar regions may have formed by similar processes possible relict dust deposits include from oldest to youngest noachian intercrater materials including arabia mantle deposits noachian to early hesperian south polar pitted deposits early hesperian hellas and argyre basin deposits late hesperian electris deposits and the amazonian medusae fossae formation these deposits typically are hundreds of meters to a couple kilometers thick and cover upward of a million or more square kilometers the apparent persistence of dust sedimentation at the south pole back to the early hesperian or earlier and the early growth of tharsis during the late noachian and perhaps earlier indicates that extensive polar wandering is unlikely following the middle noachian a scenario for the overall history of dust and perhaps ice deposition on mars includes widespread voluminous accumulations perhaps planetwide during the noachian as impacts volcanism and surface processes generated large amounts of dust the arabia deposits may have formed as ice availability and dust accumulation waned during the early hesperian thick dust sedimentation became restricted to the south pole and the deep hellas and argyre basins the north polar sedimentary record prior to the amazonian is largely obscured deposits at electris and medusae fossae may have resulted from local sources of fine grained material perhaps volcanic eruptions

dark aeolian sediments in martian craters composition and sources our research focuses on the mineralogical characteristics of dark sediment deposits in martian craters dunes dune fields and sand sheets and their local sediment sources carried out on the basis of 70 selected localities morphological analyses reveal dark layers exposed in a number of crater walls showing indications of material transport from the layers downwall to the intracrater deposits additional sites show dark sediment emerging from several craters floors suggesting a dark material source beneath the crater floor spectral analyses of omega and crism data showed for the first time that a direct mineralogical connection exists between the dark layers in the crater walls and the intracrater dune and sand sheet material based on these findings it is shown that these layers are the local sources for the dark aeolian sediment inside the craters spectral analyses further indicate that all deposits are nearly of the same mafic mineralogical composition hinting at a similar origin we conclude that the mineralogical composition points to a volcanic origin of the material the dark layers which we infer to be the material sources might represent layers of volcanic ash almost globally deposited in early noachian times and subsequently covered by regolith groundwater impact erosion and crustal movement led to the highly fragmented situation of the dark layers today however burial protected the layers of dark sediment from chemical alteration caused by surficial fluvial processes impact erosion after the wet periods on mars led to the exposure and mobilization of the material today

atmospheric effects on ejecta emplacement laboratory experiments allow the investigation of complex interactions between impacts and an atmosphere although small in scale they can provide essential first order constraints on the processes affecting late stage ballistic ejecta and styles of ejecta emplacement around much larger craters on planetary surfaces the laboratory experiments involved impacting different fine grained particulate targets under varying atmospheric pressure and density different gas compositions during crater formation ballistic ejecta form the classic cone shaped profile observed under vacuum conditions as atmospheric density increases for a given pressure however the ejecta curtain bulges at the base and pinches above this systematic change in the ejecta curtain reflects the combined effects of deceleration of ejecta smaller than a critical size and entrainment of these ejecta within atmospheric vortices created as the outward moving wall of ejecta displaces the atmosphere additionally a systematic change in emplacement style occurs as a function of atmospheric pressure largely independent of density contiguous ejecta rampart superposing ballistically emplaced deposits 0 06 to 0 3 bar ejecta flow lobes 0 3 to 0 7 bar and radial patterns 0 8 bar underlying processes controlling such systematic changes in emplacement style were revealed by observing the evolution of the ejecta curtain by changing target materials including layered targets and low density particulates by varying atmospheric density by changing impact angle and by comparing the ejecta run out distances with first order models of turbidity flows three distinct ejecta emplacement processes can be characterized ejecta ramparts result from coarser clasts sorted and driven outward by vortical winds behind the outward moving ejecta curtain this style of wind modified emplacement represents minimal ejecta entrainment and is enhanced by a bimodal size distribution in the ejecta such eddy supported flows are observed to increase in run out distance scaled to crater size with increasing atmospheric pressure by analogy with turbidity flows this scaled distance should increase as r1 2 for a given atmospheric pressure and degree of entrainment ejecta flows with much greater run out distances develop as the turbulent power in atmospheric response winds increase such flows overrun and scour the inner ejecta facies thereby producing distinct inner and outer facies the degree of ejecta entrainment depends on the dimensionless ratio of drag to gravity forces acting on individual ejecta and the intensity of the winds created by the outward moving curtain entrainment increases with increasing atmospheric density and ejection velocity crater size but decreases with ejecta density and size the intensity of curtain generated winds increases with ejection velocity crater size the dimensionless drag ratio characterizing the laboratory experiments can be applied to mars since the reduced atmospheric density is offset by the increased ejection velocities for kilometer scale events for a given crater size ejection velocity and atmospheric conditions a wide range of nonballistic ejecta emplacement styles could occur simply by varying ejecta sizes even without the presence of water alternatively the onset crater diameter for nonballistic emplacement styles can reflect the range of ejecta sizes possible from the diverse martian geologic history massive basalts to fine grained aeolian deposits scaling considerations further predict that ejecta run out distances scaled to crater size on mars should increase as r1 2 hence long run out flows dependent on crater diameter need not reflect depth to a buried reservoir of water on venus however the dense atmosphere maximizes entrainment and results in ejecta flow densities approaching a constant fraction of the atmospheric density under such conditions ejecta run out distances should decrease as r 1 2

the chemical composition of martian soil and rocks returned by the mobile alpha proton x ray spectrometer preliminary results from the x ray mode the alpha proton x ray spectrometer apxs on board the rover of the mars pathfinder mission measured the chemical composition of six soils and five rocks at the ares vallis landing site the soil analyses show similarity to those determined by the viking missions the analyzed rocks were partially covered by dust but otherwise compositionally similar to each other they are unexpectedly high in silica and potassium but low in magnesium compared to martian soils and martian meteorites the analyzed rocks are similar in composition to terrestrial andesites and close to the mean composition of earth s crust addition of a mafic component and reaction products of volcanic gases to the local rock material is necessary to explain the soil composition

spectral evidence for weathered basalt as an alternative to andesite in the northern lowlands of mars mineral abundances derived from the analysis of remotely sensed thermal emission data from mars have been interpreted to indicate that the surface is composed of basalt surface type 1 and andesite surface type 2 1 the global distribution of these rock types is divided roughly along the planetary dichotomy which separates ancient heavily cratered crust in the southern hemisphere basalt from younger lowland plains in the north andesite 1 but the existence of such a large volume of andesite is difficult to reconcile with our present understanding of the geological evolution of mars here we reinterpret martian surface rock lithologies using mineral abundances from previous work1 and new mineralogies derived from a spectral end member set representing minerals common in unaltered and low temperature aqueously altered basalts our results continue to indicate the dominance of unaltered basalt in the southern highlands but reveal that the northern lowlands can be interpreted as weathered basalt as an alternative to andesite the coincidence between locations of such altered basalt and a suggested northern ocean basin implies that lowland plains material may be composed of basalts weathered under submarine conditions or weathered basaltic sediments transported into this depocentre

mass movement slope streaks imaged by the mars orbiter camera narrow fan shaped dark streaks on steep martian slopes were originally observed in viking orbiter images but a definitive explanation was not possible because of resolution limitations pictures acquired by the mars orbiter camera moc aboard the mars global surveyor mgs spacecraft show innumerable examples of dark slope streaks distributed widely but not uniformly across the brighter equatorial regions as well as individual details of these features that were not visible in viking orbiter data dark slope streaks as well as much rarer bright slope streaks represent one of the most widespread and easily recognized styles of mass movement currently affecting the martian surface new dark streaks have formed since viking and even during the mgs mission confirming earlier suppositions that higher contrast dark streaks are younger and fade brighten with time the darkest slope streaks represent 10 contrast with surrounding slope materials no small outcrops supplying dark material or bright material for bright streaks have been found at streak apexes digitate downslope ends indicate slope streak formation involves a ground hugging flow subject to deflection by minor topographic obstacles the model we favor explains most dark slope streaks as scars from dust avalanches following oversteepening of air fall deposits this process is analogous to terrestrial avalanches of oversteepened dry loose snow which produce shallow avalanche scars with similar morphologies low angles of internal friction typically 10 30i for terrestrial loess and clay materials suggest that mass movement of low cohesion martian dusty air fall is possible on a wide range of gradients martian gravity presumed low density of the air fall deposits and thin unresolved by moc failed layer depths imply extremely low cohesive strength at time of failure consistent with expectations for an air fall deposit of dust particles as speed increases during a dust avalanche a growing fraction of the avalanching dust particles acquires sufficient kinetic energy to be lost to the atmosphere in suspension limiting the momentum of the descending avalanche front the equilibrium speed where rate of mass lost to the atmosphere is balanced by mass continually entrained as the avalanche front descends decreases with decreasing gradient this mechanism explains observations from moc images indicating slope streaks formed with little reserve kinetic energy for run outs on to valley floors and explains why large distal deposits of displaced material are not found at downslope streak ends the mass movement process of dark and bright slope streak formation through dust avalanches involves renewable sources of dust only leaving underlying slope materials unaffected areas where dark and bright slope streaks currently form and fade in cycles are closely correlated with low thermal inertia and probably represent regions where dust currently is accumulating not just residing

hematite pyroxene and phyllosilicates on mars implications from oxidized impact melt rocks from manicouagan crater quebec canada visible and near ir reflectivity mossbauer and x ray diffraction data were obtained on powders of impact melt rock from the manicouagan impact crater located in quebec canada the iron mineralogy is dominated by pyroxene for the least oxidized samples and by hematite for the most oxidized samples phyllosilicate smectite contents up to 15 wt were found in some heavily oxidized samples nanophase hematite and or paramagnetic ferric iron is observed in all samples no hydrous ferric oxides e g goethite lepidocrocite and ferrihydrite were detected which implies the alteration occurred above 250 c oxidative alteration is thought to have occurred predominantly during late stage crystallization and subsolidus cooling of the impact melt by invasion of oxidizing vapors and or solutions while the impact melt rocks were still hot the near ir band minimum correlated with the extent of aleration fe3 fetot and ranged from 1000 nm high ca pyroxene to 850 nm bulk well crystalline hematite for least and most oxidized samples respectively intermediate band positions 900 920 nm are attributed to low ca pyroxene and or a composite band from hematite pyroxene assemblages manicouagan data are consistent with previous assignments of hematite and pyroxene to the 850 and 1000 nm bands observed in martian reflectivity spectra manicouagan data also show that possible assignments for intermediate band positions 900 920 nm in martian spectra are pyroxene and or hematite pyroxene assemblages by analogy with impact melt sheets and in agreement with observables for mars oxidative alteration of martian impact melt sheets above 250 c and subsequent erosion could produce rocks and soils with variable proportions of hematite both bulk and nanophase pyroxene and phyllosilicates as iron bearing mineralogies if this process is dominant these phases on mars were formed rapidly at relatively high temperatures on a sporadic basis throughout the history of the planet the manicouagan samples also show that this mineralogical diversity can be accomplished at constant chemical composition which is also indicated for mars from analyses of soil at the two viking landing sites

gale crater and impact processes curiosity s first 364 sols on mars abstract impact processes at all scales have been involved in the formation and subsequent evolution of gale crater small impact craters in the vicinity of the curiosity msl landing site and rover traverse during the 364 sols after landing have been studied both from orbit and the surface evidence for the effect of impacts on basement outcrops may include loose blocks of sandstone and conglomerate and disrupted fractured sedimentary layers which are not obviously displaced by erosion impact ejecta blankets are likely to be present but in the absence of distinct glass or impact melt phases are difficult to distinguish from sedimentary volcaniclastic breccia and conglomerate deposits the occurrence of individual blocks with diverse petrological characteristics including igneous textures have been identified across the surface of bradbury rise and some of these blocks may represent distal ejecta from larger craters in the vicinity of gale distal ejecta may also occur in the form of impact spherules identified in the sediments and drift material possible examples of impactites in the form of shatter cones shocked rocks and ropy textured fragments of materials that may have been molten have been observed but cannot be uniquely confirmed modification by aeolian processes of craters smaller than 40 m in diameter observed in this study are indicated by erosion of crater rims and infill of craters with aeolian and airfall dust deposits estimates for resurfacing suggest that craters less than 15 m in diameter may represent steady state between production and destruction the smallest candidate impact crater observed is 0 6 m in diameter the observed crater record and other data are consistent with a resurfacing rate of the order of 10 mm myr considerably greater than the rate from impact cratering alone but remarkably lower than terrestrial erosion rates

modelling of gas generation in coals of the zonguldak basin northwestern turkey abstract the generation of gas in selected coal seams of the zonguldak basin northwestern turkey has been modelled by incorporating laboratory derived non isothermal reactions kinetics into the geothermal histories of the coal bearing strata kinetic parameters have been determined by programmed temperature open system pyrolysis of a low maturity 0 5 r 0 coal at three linnear heating rates of 0 1 0 7 and 5 0 k min the mathematical analysis of the bulk hydrocarbon evolution profiles assuming 25 first order reactions with activation energies regularly spaced between 46 and 70 kcal mol and a single pre exponential factor a yielded a value of a 3 17 10 16 min 1 and a rather broad hydrocarbon potential vs activation energy distribution with a maximum at 55 kcal mol geological time temperature relationships have been reconstructed by use of the basin modelling technique depending on the location within the basin of the wells studied and on the geological history of the coal bearing sediments the simulation procedure resulted in a predicted gas generation of up to 40 mg per g of coal

impact melts and glasses on mars 1 dark mobile materials on mars are widely considered to be volcanically derived windblown particulates such a conclusion is consistent with the large volcanic edifices on mars and the assumption that a volatile rich crust would not favor significant impact melt generation several post viking discoveries however provide new perspectives for reconsidering alternative origins not only for some of the mobile dark veneers but also certain materials at the pathfinder and viking landing sites first certain dark materials on mars do not exhibit the expected mafic absorption features in their reflectance spectra second the pathfinder mission revealed unexpected feldspathic compositions of vesicular blocks that lead to a preliminary conclusion that they represent andesites or basaltic andesites rather than basalts third recent discoveries of holocene to miocene impacts in argentine loessoid deposits provide new insights for the nature of melts generated from eolian sediments fourth global dispersal of impact melt products are now recognized in the terrestrial record throughout the cenozoic consequently the generation and preservation of impact glass on mars should be reconsidered possible occurrences include possible tektite like strewnfields downrange from recent oblique impacts dark avalanches emerging from backwasting cliffs of easily eroded unconformable deposits global dispersal of glassy ejecta from hesperian and amazonian craters of chicxulub scale and dark mobile veneers emerging from noachian craters we propose that the mobile dark materials comprising many of the named features of mars as well as some blocks at the pathfinder viking landing sites may represent impact melt products

a 3 3 ma impact in argentina and possible consequences enigmatic glassy materials escorias and red bricklike materials tierras cocidas occur at a restricted stratigraphic level the top of the chapadmalal formation materials from one locality near mar del plata are attributed to a mid pliocene impact event with a radiometric and magnetostratigraphic age of 3 3 million years ago ma an extinction of endemic fauna including the glyptodonts and flightless cariamid birds correlates with the unit containing the impact glasses moreover the age of the glasses is coincident within dating uncertainties with a pulselike change in the oxygen isotope marine record in the atlantic and pacific oceans just before the late pliocene deterioration of the climate

effects of glass content and oxidation on the spectra of snc like basalts applications to mars remote sensing 1 we have investigated the effects of crystallization and oxidation on the visible and near infrared visnir and mid infrared mid ir spectra of materials with a shergotty nakhla chassigny snc basaltic composition in order to investigate potential links between martian visnir spectra martian mid ir spectra and snc meteorite data snc basalt samples of varying crystallinities were synthesized and subsequently oxidized in air at 700 c for 1 7 days and reflectance spectra of both fine 75 m and coarse 75 500 m basalt samples were obtained before and after oxidation the effects of crystallization on the spectral properties are readily observed in the unoxidized products in the visnir increasing crystallization is accompanied by an increasing influence of pyroxene absorptions and decreasing influence of glass absorptions in the mid ir changes in spectral properties with crystallization are due to the variations in relative amounts of glass pyroxene and plagioclase oxidation alters the glass and pyroxenes within the samples leading to changes in visnir and mid ir spectral shapes although distinct signatures of oxidation products are not always observed both spectral and electron microscopy data indicate that hematite is the dominant oxidation product in the pigeonite and glass of the samples in pigeonite hematite is present in nanophase form and leads to the diminishment of the diagnostic 1 and 2 m pyroxene absorptions in the visnir as well as pyroxene absorptions expressed between 800 and 1100 cm 1 in the mid ir in glass hematite forms a near surface layer that is detected with varying efficiencies in the visnir and mid ir depending on the crystallinity and particle size of the analyzed sample oxidized snc basalt samples of various crystallinities and fine grain sizes provide the best analogs to mars remote sensing data in the visnir and mid ir in the visnir partially crystalline oxidized snc basalts can reproduce martian dark region characteristics in the mid ir similarities exist between the spectra of a partially crystalline oxidized snc basalt and the basalt lithology detected by the thermal emission spectrometer tes the andesite lithology detected by tes is best matched by the spectrum of a fully crystalline oxidized snc basalt these results imply that plagioclase rich lithologies are not required by tes data and that observed variations in spectral character of dark regions across the martian surface can be explained by snc basalts influenced by oxidation coupled with variations in degree of crystallization

shocked plagioclase signatures in thermal emission spectrometer data of mars abstract the extensive impact cratering record on mars combined with evidence from snc meteorites suggests that a significant fraction of the surface is composed of materials subjected to variable shock pressures pressure induced structural changes in minerals during high pressure shock events alter their thermal infrared spectral emission features particularly for feldspars in a predictable fashion to understand the degree to which the distribution and magnitude of shock effects influence martian surface mineralogy we used standard spectral mineral libraries supplemented by laboratory spectra of experimentally shocked bytownite feldspar johnson j r horz f christensen p lucey p g 2002b j geophys res 107 e10 doi 10 1029 2001je001517 to deconvolve thermal emission spectrometer tes data from six relatively large 50 km impact craters on mars we used both tes orbital data and tes mosaics emission phase function sequences to study local and regional areas near the craters and compared the differences between models using single tes detector data and 3 2 detector averaged data inclusion of shocked feldspar spectra in the deconvolution models consistently improved the rms errors compared to models in which the spectra were not used and resulted in modeled shocked feldspar abundances of 15 in some regions however the magnitudes of model rms error improvements were within the noise equivalent rms errors for the tes instrument hamilton v personal communication this suggests that while shocked feldspars may be a component of the regions studied their presence cannot be conclusively demonstrated in the tes data analyzed here if the distributions of shocked feldspars suggested by the models are real the lack of spatial correlation to crater materials may reflect extensive aeolian mixing of martian regolith materials composed of variably shocked impact ejecta from both local and distant sources

mars surface mineralogy from hubble space telescope imaging during 1994 1995 observations calibration and initial results visible to near infrared observations of mars were made with the hubble space telescope hst during 1994 1995 with the goals of monitoring seasonal variability of the surface and atmosphere and mapping specific spectral units to constrain the planet s surface mineralogy this paper presents the details of the collection and calibration of the data concentrating specifically on the near ir data that were obtained exclusively for the surface mineralogy aspect of our hst mars observing program we also present some initial results from the calibrated data set our calibration procedures included the standard pipeline processing steps supplemented by special procedures required for use with the linear ramp filters on the wide field planetary camera 2 instrument and an additional point spread function deconvolution procedure applied in order to realize the full potential spatial resolution of the images 23 to 64 km pixel between august 1994 and august 1995 the calibration results in a set of images projected onto a standard map grid and presented in radiance factor i f units having an estimated 5 photometric accuracy based on the performance of hst and comparisons with previous ground based and spacecraft mars spectra initial scientific analyses of these data reveal 1 distinct red blue color units within the classical bright regions similar to those seen in viking orbiter images and possibly related to variations in nanophase and or crystalline ferric mineral abundance 2 near ir spectral slope variations correlated with albedo on a large scale darker is bluer near ir slope but exhibiting wider variations among many of the small scale features visible in the data 3 an absorption at 860 nm that occurs in all regions but which is 3 to 5 stronger in many of the classical dark regions than in the bright regions possibly because of a greater abundance of a well crystalline ferric phase like hematite or a very low ca pyroxene or opx cpx mixture and 4 an absorption from pyroxene at 953 nm with a band depth that is inversely correlated with albedo bright regions 0 to 5 deep dark regions 7 to 15 deep and which shows the highest band depth values in individual craters calderas and other small geologic units that are resolved in the images

seeing through the dust martian crustal heterogeneity and links to the snc meteorites through the application of new analytical techniques to high spatial resolution imaging spectrometer data the ferrous mineralogy of major volcanic terrains on mars is shown to consist of significant fractions of both low and high calcium pyroxene changes in the relative abundances of these pyroxenes are observed for units of different age and morphology even in regions with higher degrees of alteration and contamination from dust volcanic rocks with these characteristics are uncommon on earth but are typical of the basaltic snc meteorites shergottites nakhlites and chassignites thought to be from mars thus it is possible to infer even through the veil of dust that the snc meteorites have mineralogic affinities to major volcanic provinces on mars and are therefore truly representative of the heterogeneity observed on the surface of the red planet

results from the mars pathfinder camera images of the martian surface returned by the imager for mars pathfinder imp show a complex surface of ridges and troughs covered by rocks that have been transported and modified by fluvial aeolian and impact processes analysis of the spectral signatures in the scene at 440 to 1000 nanometer wavelength reveal three types of rock and four classes of soil upward looking imp images of the predawn sky show thin bluish clouds that probably represent water ice forming on local atmospheric haze opacity 0 5 haze particles are about 1 micrometer in radius and the water vapor column abundance is about 10 precipitable micrometers

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

observational evidence of crystalline iron oxides on mars visible to near ir 0 4 1 0 mu m spectral reflectance observations of mars during the 1988 opposition were performed at mauna kea observatory using a circular variable filter spectrometer at a spectral resolution r lambda delta lambda approx 80 on august 13 and 14 1988 ut 41 regions 500 600 km in diameter were observed on mars the data have been reduced both to reflectance relative to solar analog mars 16 cyg b and to relative reflectance spot spot the spectra show the strong near uv reflectance dropoff characteristic of mars as well as absorptions at 0 62 0 72 mu m and 0 81 0 94 mu m both seen here clearly for the first time these absorption features are interpreted as fe sup 3 electronic transition bands that indicate the presence of crystalline ferric oxide or hydroxide minerals on the martian surface comparison of these data with laboratory spectra obtained by other workers supports the conclusion that a single iron oxide phase most likely hematite could account for all of the observed spectral behavior of the martian surface soils and airborne dust in the 0 4 1 0 mu m region this possibility must be reconciled with data from other possible spectral analogs and other wavelength regions as well as geochemical and mineral stability considerations to arrive at amore more complete understanding of the role of ferric minerals in martian surface mineralogy and weathering less

the spatial distribution of rocks on mars abstract the spatial distribution of rocks exposed at the surface of mars has been mapped using viking infrared thermal mapper irtm observations overall there are no regions on the surface of mars at a scale of 1 1 in latitude and longitude that are rock free the modal value of rock abundance is 6 areal coverage with no areas having more than 30 35 rock cover the model developed to determine rock abundance relates the thermal emission in each of the four surface sensing irtm bands to temperature contrasts within the field of view non unit thermal emissivity due to absorption bands in the surface materials and the absorption and scattering of the outgoing energy by atmospheric dust and water ice each of these effects produce characteristic spectral and diurnal signatures allowing them to be separated the temperature contrasts provide a means to determine both the abundance of exposed rocks and the fine component thermal intertia rock abundance alone does not produce the observed variation in bulk thermal inertia of the surface low inertia fine bright surfaces have fewer rocks exposed than do high inertia coarse dark surfaces rock abundance does not correlate well with the rms slope nor reflectivity determined from delay doppler radar measurements there is however a possible correlation between rms slope determined from continuous wave radar observations dual polarization radar measurements which provide the best radar measure of small scale roughness indicate that the tharsis volcanic region is very rough whereas thermal measurements indicate very few rocks and a covering of dust together these observations suggest an approximately 1 m thick mantle of fines covering a very rough subsurface this fine material may be an aeolian deposit of dust storm fallout valles marineris together with several major channels and chaotic terrains have high rock abundances as does the acidalia planitia basin this observed distribution may reflect the initial deposition of coarse material associated with channel formation syrtis major is unique in having a high inertia but a very low rock abundance together with low radar roughness these observations are consistent with mantling of rocks by sand the observed distribution of rocks and fines indicates that aeolian processes both erosional and depositional play a dominant role in shaping the present martian surface

absence of silicic volcanism on mars implications for crustal composition and volatile abundance on earth eruptions of silicic magmas with volumes of 1 100 km3 are generally associated with stratovolcanoes or composite cones whereas larger 100 1000 km3 ignimbrite deposits are erupted from resurgent calderas and related structures small volumes of silicic rocks are generated by differentiation within basic magma chambers associated with stratovolcanoes but large silicic deposits are largely confined to areas where the granitic crust is thicker than 25 km as mantle derived magmas rise through the thick granitic crust fractional crystallization and assimilation of hydrous crustal rocks concentrate volatiles and sio2 in the magma yielding explosive silicic eruptions on mars under similar chemical conditions ignimbrite eruptions could take place over a broader range of physical conditions than on earth but no large volume ignimbrite deposits can be identified positively explosive basic to ultrabasic eruptions may be responsible for small cinder conelike features on mars and perhaps for the ancient flank scoured paterae such eruptions may have been driven by near surface water ice magma interactions or volatile rich magmas the paterae represent a unique style of volcanism that stopped 2 b y ago we suggest that the volatiles associated with these features were derived from mantle sources and that the cessation of patera formation may coincide with the termination of the period of maximum planetary degassing volcanism since 2 b y ago has been dominantly effusive except for minor explosive ash events such as those which blanketed part of the summit of hecates tholus we propose that such eruptions were driven by volatiles generated by differentiation of a magma chamber similar to icelandic explosive eruptions the apparent lack of large scale silicic volcanism on mars is circumstantial evidence that mars is deficient in volatiles and lacks a granitic crust

pliocene pedosedimentary cycles in the southern pampas argentina well developed bt horizons of five palaeosols p1 p5 have been recorded previously within a 20 m thick succession of pliocene siltstones and clayey siltstones in the southern part of the buenos aires province of argentina this paper reports a detailed field and micromorphological thin section investigation of a 6 m portion of the sequence encompassing p2 and p3 large scale faunal burrow infillings occur throughout other bioturbation features in the form of channel and spongy microstructures are mainly confined to the siltstones the intervening clayey siltstones bt horizons have been affected more by shrink swell disruption as evidenced by slickensides and a range of striated b fabrics in thin sections clay coatings indicative of illuvial accumulation of clay translocated in suspension from overlying a or e horizons occur in both the siltstones and clayey siltstones the types microstratigraphic associations and depth functions of features are interpreted in terms of changing interactions balances and dominances between sedimentary pedogenic and erosional processes over time thus providing the basis for the pedosedimentary reconstruction of landscape evolution in the region during part of the pliocene represented by the whole p1 p5 sequence 4 5 ma bp it is envisaged that this period was dominated by aeolian deposition although fluvial and mass movement processes probably led to reworking and redistribution of some of the materials overall rates of subaerial deposition however were not substantial pedogenic processes were active throughout the balance between sedimentation and pedogenesis varying over time in a cyclical fashion phases of reduced deposition and establishment of relatively stable land surfaces were marked by the development of argillic soil profiles with clearly defined eluvial and illuvial horizons intervening periods of more rapid accumulation of coarser material were characterized by accretionary soil development and welding of new pedological features on existing soils as the surface accreted first transforming existing eluvial horizons into bct ae horizons siltstones and then encouraging the syndepositional upward extension of these complex horizons the primary basis of the alternating units of siltstones bct ae horizons and clayey siltstones bt horizons lies in the cyclical change in size of particles deposited although pedogenic translocation processes enhanced these textural differences the underlying driving mechanism behind the pedosedimentary cycle can only be speculated upon although it is tempting to relate the sedimentation pattern to climatic fluctuations linked to glacial advances and retreats in the patagonian andes during the pliocene

initiation of run out flows on venus by oblique impacts abstract a hypervelocity oblique impact results in a downrange moving vapor cloud a significant fraction of which is derived from the projectile since the vapor cloud expands to great extent and becomes very tenuous quickly on a planet with a thin or no atmosphere it does not leave a well defined geologic expression the thick atmosphere of venus however is sufficient to contain such a rapidly expanding vapor cloud as a result of atmospheric interactions impact vapor condenses and contributes to run out flows around craters on venus previous results of both laboratory experiments and simple semi analytical calculations indicate that an impact vapor origin can account for the morphology of run out flows on venus most consistently however the detailed dynamics and geologic record of downrange moving impact vapor clouds in venus s atmosphere are not understood quantitatively to approach these problems we carried out two dimensional hydrocode calculations parametric studies of these hydrocode calculations yield simple scaling laws for both the total downrange travel distance and the final temperature of impact vapor clouds under conditions on venus under typical impact conditions impact vapor clouds travel downrange more than a crater radius prior to the completion of crater formation furthermore the scaling law for the total travel distance is compared with observations for the downrange offset of the source regions of run out flows around oblique craters the results of this comparison suggest that energy momentum partitioning processes other than pure shock coupling may play important roles in hypervelocity impact at planetary scales the results of hydrocode calculations also indicate that the terminal temperature of the impact vapor is close to the condensation temperatures of silicates suggesting that two scenarios are possible for expected range of impact conditions 1 impact vapor condenses and forms run out flows 2 impact vapor fails to condense and leaves no run out flows consequently natural variation in impact angle velocity and projectile composition may account for partial occurrence of run out flows around impact craters on venus

crater ejecta scaling laws fundamental forms based on dimensional analysis a model of crater ejecta is constructed using dimensional analysis and a recently developed theory of energy and momentum coupling in cratering events general relations are derived that provide a rationale for scaling laboratory measurements of ejecta to larger events specific expressions are presented for ejection velocities and ejecta blanket profiles in two limiting regimes of crater formation the so called gravity and strength regimes in the gravity regime ejecta velocities at geometrically similar launch points within craters vary as the square root of the product of crater radius and gravity this relation implies geometric similarity of ejecta blankets that is the thickness of an ejecta blanket as a function of distance from the crater center is the same for all sizes of craters if the thickness and range are expressed in terms of crater radii in the strength regime ejecta velocities are independent of crater size consequently ejecta blankets are not geometrically similar in this regime for points away from the crater rim the expressions for ejecta velocities and thickness take the form of power laws the exponents in these power laws are functions of an exponent that appears in crater radius scaling relations thus experimental studies of the dependence of crater radius on impact conditions determine scaling relations for ejecta predicted ejection velocities and ejecta blanket profiles based on measured values of are compared to existing measurements of velocities and debris profiles

impact origin of the chesapeake bay structure and the source of the north american tektites seismic profiles drill core samples and gravity data suggest that a complex impact crater 35 5 million years old and 90 kilometers in diameter is buried beneath the lower chesapeake bay the breccia that fills the structure contains evidence of shock metamorphism including impact melt breccias and multiple sets of planar deformation features shock lamellae in quartz and feldspar the age of the crater and the composition of some breccia clasts are consistent with the chesapeake bay impact structure being the source of the north american tektites

widespread weathered glass on the surface of mars low albedo sediments cover 10 7 km 2 in the northern lowlands of mars but the composition and origin of these widespread deposits have remained ambiguous despite many previous investigations here we use near infrared spectra acquired by the mars express omega observatoire pour la mineralogie l9eau les glaces et l9activite imaging spectrometer to show that these sediments exhibit spectral characteristics that are consistent with both high abundances of iron bearing glass and silica enriched leached rinds on glass this interpretation is supported by observations of low albedo soil grains with possible rinds at the phoenix mars lander landing site in the northern lowlands by comparison with the extensive glass rich dune fields and sand sheets of iceland we propose an explosive volcanic origin for these glass rich sediments we also propose that the glassy remnant rinds on the sediments are the result of postdepositional alteration as these rinds are commonly formed in arid terrestrial volcanic environments during water limited moderately acidic leaching these weathered glass rich deposits in the northern lowlands are also colocated with the strongest concentrations of a major global compositional surface type previously identified in mid infrared spectra suggesting that they may be representative of global processes our results provide potential confirmation of models suggesting that explosive volcanism has been widespread on mars and also raise the possibilities that glass rich volcaniclastics are a major source of eolian sand on mars and that widespread surficial aqueous alteration has occurred under amazonian climatic conditions

evidence for a widespread basaltic breccia component in the martian low albedo regions from the reflectance spectrum of northwest africa 7034 northwest africa nwa 7034 is the first breccia meteorite from mars and unlike the shergottite nakhlite and chassignite snc martian meteorites it matches the estimated chemical composition of martian crust here we show that the visible infrared reflectance spectrum of nwa 7034 is unique compared to other sncs and is more similar than them to remotely sensed data from mars suggesting the martian regolith may contain significant brecciated material produced during heavy bombardment of the crust

in situ compositions of martian volcanics implications for the mantle the primary objective of this analysis is to determine the mineralogic composition of relatively pristine terrains exposed on the surface of mars this analysis is conducted using imaging spectrometer data acquired in 1989 by the imaging spectrometer for mars ism instrument that was onboard the phobos ii spacecraft the ism instrument acquired some of the highest spectral 64 channels between 0 77 and 3 14 m and spatial resolution 22 km pixel observations to date of mars focused on the equatorial region relatively unaltered surfaces were identified in these data on the basis of their spectral properties low albedo weak spectral slope absence of ferric absorptions and were found in volcanic terrains of syrtis major valles marineris ophir planum and sinus meridiani oxia palus spectra representative of the diversity among terrains were extracted for detailed analysis using the modified gaussian model to determine the primary mafic mineralogy it was determined that the mafic mineralogy of the regions investigated is dominated by low calcium and high calcium pyroxene lcp hcp and that there was homogeneity within a given region but some heterogeneity between regions in the relative abundance of lcp to hcp the two pyroxene mineralogy is consistent with the mineralogies of the basaltic snc meteorites believed to have originated on mars two pyroxene volcanic mineralogies are indicative of large degrees of partial melting e g komatiites or a mantle source depleted in aluminum integration of these findings with previous studies of mars and the snc meteorites indicates that 1 the snc mineralogies are representative of large volcanic regions of mars with surface ages as old as 2 3 ga 2 the martian mantle was depleted in aluminum at least as long ago as the oldest terrain analyzed ophir planum and 3 there has been little evolution in the composition of mantle source regions as the 180 ma snc mineralogies are comparable to those of the oldest terrains analyzed

temporal changes in the cerberus region of mars mariner 9 and viking comparisons abstract as in seen from comparisons of mariner 9 images obtained in 1972 and viking orbiter 1 images obtained in 1978 several changes have occurred in the cerberus region of mars changes in the boundary of the low albedo feature resulted in an increase of the total area of cerberus by slightly more than 1 although the southwestern boundary had shifted as much as 90 km relative darkening of cerberus has resulted in a more uniform tone and is accompanied by the disappearance of dark filamentary markings although several bright streaks within cerberus changed in length neither lengthening nor shortening of the streaks predominated however changes in streak direction indicate a clockwise rotation of mean streak azimuth between 1972 and 1978 these changes in the outline and appearance of cerberus can best be explained by eolian redistribution and removal of bright material during major dust storms volcanic flow fronts which show through the albedo feature indicate that the contrast between cerberusand the surrounding light plains is not due to a difference in lithology but to the distribution of surficial deposits because of local topographic influences on the regional atmospheric circulation patterns it is probable that cerberus will retain a similar appearance and location

the formation of infilled craters on mars evidence for widespread impact induced decompression of the early martian mantle flat floored craters have long been recognized on mars with early work hypothesizing a sedimentary origin more recently high resolution thermal inertia measurements show that these craters contain some of the rockiest materials on the planet inconsistent with poorly consolidated sedimentary materials in this study the distribution physical properties morphology and thermal inertia and composition of these craters are thoroughly investigated over the entire planet the majority of the 2800 rocky crater floors identified are concentrated in the low albedo 0 1 0 17 cratered southern highlands these craters were infilled at 3 5 ga and are associated with the highest thermal inertia values and some of the most mafic materials identified on the planet although several processes may have led to the formation of the crater floors the most likely scenario is volcanic infilling through fractures created by the impact event the primitive magma source directly results from decompression melting of the martian mantle by the removal of the crustal material excavated by the impactor volcanic infilling of craters by decompression melting appears to only have occurred in early martian history when the lithosphere was still relatively thin and the thermal gradient was high this process was widespread and responsible for the eruption of significant volumes of primitive material inside and likely outside of craters impact induced decompression melting of the martian mantle accounts for the unusual infilling of martian craters and is a widespread planetary process that has gone previously undocumented

atmospheric effects on ejecta emplacement and crater formation on venus from magellan the venus cratering record provides a unique environment for assessing the effects of both gravity and an atmosphere on impact crater formation this contribution uses surface signatures of energy partitioning as a framework for testing extrapolations from laboratory experiments and other planetary settings seven general conclusions can be drawn first the dense lower atmosphere of venus takes on the role of a low density target for bodies smaller than about 4 km in diameter air blasts created by cratering in the atmosphere create distinctive surface signatures that allow the derivation of an independent assessment of impactor energy at the limit of break up second dynamic pressures during entry of larger bodies will exceed their strength limit but may not prevent penetration of the atmosphere due to aerodynamic reshaping that minimizes the drag coefficient such a process may account for the formation of unusually small craters 1 3 km third the dense atmosphere of venus preserves signatures of early time cratering processes on the surface that are typically lost on atmosphere free surfaces such signatures not only provide another estimate of impactor energy but also include a distinctive record of the impactor i e comet versus asteroid in distinctive run out flows created before the crater has finished formation strong winds and turbulence associated with the atmospheric disturbance at later times create wind streaks behind topographic barriers fourth ballistic ejection of excavated debris occurs from craters on venus just as it does on planets without an atmosphere thereby underscoring the fundamental mechanical transfer of energy from impactor to target fifth ejecta emplacement is nonballistic due to the large dynamic forces acting on the advancing curtain and its constituent ejecta the outward moving ejecta curtain induces strong response winds that entrain ejecta and drive a ground hugging debris flow outward without returning to the cavity flow separation creates an overriding run out ejecta flow further sustained by atmospheric turbulence and identified as radar dark lobate lobes sixth radar dark parabolas are proposed to be late time fallout deposits created as the downrange fireball evolves aloft perhaps analogous to terrestrial tektite strewn fields and seventh the response of crater formation to the atmosphere is conversely expressed by a reduction in cratering efficiency as revealed by the unusually large central peak complexes and the unexpected diameter depth relations of craters hence surface ages may be significantly underestimated

analysis of terrestrial and martian volcanic compositions using thermal emission spectroscopy 2 application to martian surface spectra from the mars global surveyor thermal emission spectrometer atmospherically corrected thermal infrared spectra of large regions of the martian surface from the mars global surveyor thermal emission spectrometer mgs tes previously have been interpreted to represent two general spectral classes one class represents a basalt to basaltic andesite composition and the other class represents a basaltic andesite to andesite composition we have performed new linear deconvolutions of the two martian surface type spectra with an end member set tailored to represent volcanic rock types our preparatory study of laboratory spectra of terrestrial volcanic rocks acquired at 2 cm 21 sampling convolved to tes spectral sampling 10 cm 21 shows little degradation in deconvolution results when compared to results acquired using the higher spectral resolution data indicating that the deconvolution technique is valid for analyzing data at tes resolution our spectral fits to the martian data agree well with previous models and do not exhibit any notable deviations from the martian spectra that would indicate the absence of any significant end members in our model modal mineralogies obtained with these new spectral fits also compare favorably within the previously stated uncertainties to prior results the newly derived modal mineralogies are used with new and traditional classification schemes for volcanic igneous rocks introduced in a companion paper wyatt et al this issue to classify the martian compositions our results substantiate the previously proposed hypothesis that these two spectral classes on the martian surface represent volcanic compositions with distinguishable differences in silica content ranging from basalt to andesite

tektite bearing deep water clastic unit at the cretaceous tertiary boundary in northeastern mexico the hypothesis of cretaceous tertiary k t boundary impact on yucatan mexico predicts that nearby sites should show evidence of proximal impact ejecta and disturbance by giant waves an outcrop along the arroyo el mimbral in northeastern mexico contains a layered clastic unit up to 3 m thick that interrupts a biostratigraphically complete pelagic marl sequence deposited at more than 400 m water depth the marls were found to be unsuitable for determining magnetostratigraphy but foraminiferal biostratigraphy places the clastic unit precisely at the k t boundary we interpret this clastic unit as the deposit of a megawave or tsunami produced by an extraterrestrial impact the elastic unit comprises three main subunits 1 the basal spherule bed contains glass in the form of tektites and microtektites glass spherules replaced by chlorite smectite and calcite and quartz grains showing probable shock features this bed is interpreted as a channelized deposit of proximal ejects 2 a set of lenticular massive graded laminated beds contains intraclasts and abundant plant debris and may be the result of megawave backwash that carried coarse debris from shallow parts of the continental margin into deeper water 3 at the top several thin ripple beds composed of fine sand are separated by clay drapes they are interpreted as deposits of oscillating currents perhaps a seiche an iridium anomaly 921 23 pg g is observed at the top of the ripple beds our observations at the mimbral locality support the hypothesis of a k t impact on nearby yucatan

geologic characteristics of relatively high thermal inertia intracrater deposits in southwestern margaritifer terra mars 1 twenty one craters in southwestern margaritifer terra exhibit unusually warm interior deposits in nighttime thermal emission imaging system themis infrared images these deposits exhibit nighttime temperatures as high as 223 k and are 5 18 warmer than the surrounding plain thermal inertia values derived from thermal emission spectrometer tes data are greater for the deposits than the plains with maximum values between 455 and 675 j m 2 k 1 s 1 2 analysis of themis thermal inertia data having nearly an order of magnitude better spatial resolution shows that the deposits can have a thermal inertia as high as 1060 j m 2 k 1 s 1 2 albedo and dust cover index values suggest that both the deposits and the surrounding region are generally dust free compositional analysis with tes and themis data show that though a small number of the deposits may have isolated compositional differences the majority of the deposits have a composition similar to that of the surrounding plains the geomorphology of the craters as viewed from mars orbiter camera moc images shows that the deposits are coherent units rather than sand deposits an observation that is consistent with the relatively high thermal inertia values if these deposits are coherent rock units as the results of our study suggest possible methods of formation include emplacement of primary igneous material or lithification of sediments from surrounding terrain

ground truth for oblique impact processes new insight from the rio cuarto argentina crater field new evidence for an impact origin of oblong rimmed depressions near rio cuarto cordoba province argentina includes shocked silicate phases e g diaplectic glass thermal decomposition of high temperature mineral clasts e g baddeleyite from zircon rapid quenching very low water contents 0 1 wt and generation of identical glasses in hypervelocity laboratory impact experiments the results indicate that glasses with a wide range in major element concentrations can form from a single target type in a relatively small impact event impact glasses with the greatest volatile loss typically exhibit the greatest meteoritic contamination as defined by cr ni and ir abundances the different impact glass types and the different degrees of impactor contamination are proposed to reflect proximity to the projectile target interface during shallow penetration in an oblique impact consistent with laboratory simulations and planetary analogues

geochemical evidence for an impact origin for a late archean spherule layer transvaal supergroup south africa a late archean layer rich in sand sized spherules of former silicate melt in the monteville formation transvaal supergroup south africa has ir concentrations as high as 6 4 ppb and is clearly enriched in ir relative to associated tuffs carbonates and shales the monteville spherule layer is also enriched in other siderophile elements including the platinum group elements pges the pges in the spherule layer produce a flat meteorite like pattern when they are normalized to chondritic abundances the abundances of ir and other siderophile elements are similar to broadly contemporaneous spherule layers in the hamersley basin of western australia that the mineral compositions textures and sedimentary structures of the spherule layers in the transvaal supergroup and hamersley basin are also very similar suggests that they were all formed by the same processes we think that the best way to explain the high ir concentrations and other characteristics of the monteville spherule layer is that it represents distal impact ejecta there are however significant differences between the monteville spherule layer and early archean spherule layers in the barberton greenstone belt including much higher average and maximum concentrations of ir in the latter the data presented here clearly show that each precambrian spherule layer is unique and needs to be characterized individually as is true for the impact spherule layers of the phanerozoic

decameter scale pedestal craters in the tropics of mars evidence for the recent presence of very young regional ice deposits in tharsis abstract global climate models predict that ice will be deposited in tropical regions during obliquity excursions from the current mean obliquity of 25 to 35 but no geological evidence for such deposits has been reported we document the presence of very small decameter scale pedestal craters in the tropics of mars the daedalia planum tharsis region that are superposed on an impact crater dated to 12 5 ma ago the characteristics abundance and distribution of these small pedestal craters provide geological evidence that meters thick ice accumulations existed in the tropical tharsis region of mars in the last few million years when mean obliquity was 35 5 15 ma before it transitioned to a mean of 25 0 3 ma a reconnaissance survey reveals similar small pedestal crater examples superposed on the older amazonian arsia mons tropical mountain glacier deposit suggesting that ice can accumulate in these tropical regions without initiating large scale glacial conditions these results support the predictions of general circulation models that ice can migrate to the equatorial regions during periods of moderate obliquity and then serve as a source for mid latitude deposits

latitude dependence of martian pedestal craters evidence for a sublimation driven formation mechanism we report on the results of a survey to document and characterize pedestal craters on mars equatorward of similar to 60 degrees n and 65 degrees s latitude the identification of 2696 pedestal craters reveals a strong latitude dependence with the vast majority found poleward of 33 degrees n and 40 degrees s this latitudinal extent is correlated with many climate indicators consistent with the presence of an ice rich substrate and with climate model predictions of where ice is deposited during periods of higher obliquity in the amazonian we have measured key physical attributes of pedestal craters including the farthest radial extents of the pedestals pedestal heights and the circularity of the pedestal margins in conjunction with the geographic distribution our measurements strongly support a sublimation related formation mechanism this is in contrast to previous hypotheses which have relied on eolian deflation to produce the elevated plateaus the identification of marginal pits on the scarps of some pedestal craters interpreted to be sublimation pits provide direct evidence for the presence of ice rich material underlying the armored surface of pedestal craters on the basis of our findings we propose a formation mechanism whereby projectiles impact into a volatile rich dust snow ice substrate tens to hundreds of meters thick overlying a dominantly fragmental silicate regolith the area surrounding the resulting crater becomes armored pedestals extend to a distance of multiple crater radii farther than typical ejecta deposits necessitating an armoring mechanism that is capable of indurating the surface to a distance greater than the reach of the ejecta return to low obliquity causes sublimation of the volatile rich layer from the intercrater plains lowering the elevation of the regional terrain this yields generally circular pedestal craters elevated above the surrounding plains as a result the armored surfaces of pedestal craters have preserved a significant record of amazonian climate history in the form of ice rich deposits

chemical multispectral and textural constraints on the composition and origin of rocks at the mars pathfinder landing site rocks at the mars pathfinder site are probably locally derived textures on rock surfaces may indicate volcanic sedimentary or impact generated rocks but aeolian abration and dust coatings prevent unambiguous interpretation multispectral imaging has resolved four spectral classes of rocks gray and red which occur on different surfaces of the same rocks pink which is probably soil crusts and maroon which occurs as large boulders mostly in the far field rocks are assigned to two spectral trends based on the position of peak reflectance the primary spectral trend contains gray red and pink rocks maroon rocks constitute the secondary spectral trend the spatial pattern of spectral variations observed is oriented along the prevailing wind direction the primary spectral trend arises from thin ferric coatings of aeolian dust on darker rocks the secondary spectral trend is apparently due to coating by a different mineral probably maghemite or ferrihydrite a chronology based on rock spectra suggests that rounded maroon boulders constitute the oldest petrologic unit a flood deposit succeeded by smaller cobbles possibly deposited by impact and followed by aeolian erosion and deposition nearly linear chemical trends in alpha proton x ray spectrometer rock compositions are interpreted as mixing lines between rock and adhering dust a conclusion supported by a correlation between sulfur abundance and red blue spectral ratio extrapolations of regression lines to zero sulfur give the composition of a presumed igneous rock the chemistry and normative mineralogy of the sulfur free rock resemble common terrestrial volcanic rocks and its classification corresponds to andesite igneous rocks of this composition may occur with clastic sedimentary rocks or impact melts and breccias however the spectral mottling expected on conglomerates or breccias is not observed in any apxs analyzed rocks interpretation of the rocks as andesites is complicated by absence of a 1 m pyroxene absorption band plausible explanations include impact glass band masking by magnetite or presence of calcium and iron rich pyroxenes and olivine which push the absorption band minimum past the imager s spectral range the inferred andesitic composition is most similar to terrestrial anorogenic icelandites formed by fractionation of tholeiitic basaltic magmas early melting of a relatively primitive martian mantle could produce an appropriate parent magma supporting the ancient age of pathfinder rocks inferred from their incorporation in hesperian flood deposits although rocks of andesitic composition at the pathfinder site may represent samples of ancient martian crust inferences drawn about a necessary role for water or plate tectonics in their petrogenesis are probably unwarranted

iron mineralogy of the surface of mars from the 1 μm band spectral properties 1 we study the 1 m absorption from omega mex spectra to map martian iron mineralogy at a global scale this band is covered on the left by the vnir visible and near infrared omega channel and on the right by the swir short wavelengths infrared one we first perform a systematic spatial coregistration of the two channels after an improvement of the vnir radiometric calibration the update of the vnir instrumental transfer function itf and the internal stray light estimation is based on the spectra of the phobos red units and of the water ice north polar cap of mars which have been fitted according to an iterative process the level of the signal in the blue wavelength range previously systematically overestimated due to a stray light residual and the general shape of the spectrum for 0 7 m are improved global maps of the 1 m signature have been derived from 9 new spectral indices the largest values of the 1 m band integral are found in noachian terrains and in the dunes around the north polar cap in the south polar region an area centered at 155 w and 83 s is mapped as a distinctive spectral unit dominated by pyroxene the northern lowlands of mars together with other dark terrains located in the northern hemisphere show very low values of some spectral indices due to the negative spectral slope in the nir this behavior is consistent with the presence of weathered basalts with a possible glassy or amorphous component among the hydrated terrains the only ones that can be isolated by studying the 1 m band are those located in terra meridiani aram chaos and capri chasma enriched in sulfate and hematite on the other hand the sulfates of the dark dunes surrounding the northern polar cap and the phyllosilicates of the bright hydrated deposits of mawrth vallis cannot be isolated combining the parameters used in this study this suggests that their distinctive mineralogy does not affect the 1 m band remaining similar to the global martian average shape

tidal dynamics in the south china sea summary the tidal dynamics of the south china sea are examined by the use of a two dimensional non linear hydrodynamic finite difference model which has been run separately for the m2 and k1 tidal constituents the models are tuned through the open boundary conditions to fit the observed coastal tides cotidal charts for the two constituents are presented and compared with earlier charts based on coastal observations alone the flow of tidal energy is studied and it is concluded that the strength of the diurnal tide in the sea is due largely to the resonant diurnal response of the gulfs of tonkin and thailand an energy budget reveals that for both constituents direct tidal forcing within the sea is significant and that tidal energy which enters through the open boundary is in fact lost back to the earth moon orbital system by this means

cretaceous tertiary chicxulub impact angle and its consequences the chicxulub impact structure exhibits asymmetries in its geophysical signatures that closely resemble asymmetries produced by oblique impacts in laboratory experiments and recognized on planetary surfaces these asymmetric signatures suggest a trajectory for the chicxulub bolide from the southeast to the northwest at a 20 30 angle from the horizontal as a result biotic extinctions may have been most severe and catastrophic in the northern hemisphere geographic variation in the magnitude of the cretaceous tertiary k t fern spike and palynofloral extinctions are consistent with the proposed trajectory

the surface of syrtis major composition of the volcanic substrate and mixing with altered dust and soil syrtis major is an old low relief volcanic plateau near the equatorial regions of mars it is a persistent low albedo feature on the planet and is thought to contain a high abundance of exposed bedrock and or locally derived surface material and debris spatially resolved variations in surface spectral properties and therefore composition are investigated with data from the imaging spectrometer for mars ism instrument ism obtained 128 wavelength channel spectra from 0 76 to 3 16 m for contiguous pixels approximately 22 22 km in size across much of the plateau the value and spatial distribution of four primary spectral variables albedo continuum slope wavelength of the ferric ferrous band minimum area of the ferric ferrous absorption are mapped and coregistered to viking digital photomosaics analysis of these maps shows that although there is a high degree of overall spectral variability on the plateau the key indicators of mafic mineralogy are relatively homogeneous detailed examination of reflectance spectra from representative areas across the plateau indicate the volcanic surface is dominated by augite bearing basalts and the pyroxene composition in the basalts is estimated to be 0 275 0 075 ca ca fe mg and 0 3 0 1 fe fe ca mg additional mineral components may include olivine feldspar and glass most of the spectral variability on the plateau is interpreted to result from mixing of volcanic bedrock and or locally derived surface material and debris with highly altered dust and soil in western syrtis major the altered material is a transient component on the surface or occurs in large spatially coherent patches e g crater rims in eastern syrtis major it is apparent that the dust components are firmly fixed to the basaltic substrate as a stable oxide rind or coating

spectral properties of martian and other planetary glasses and their detection in remotely sensed data thirty silicate glasses were synthesized as realistic analogs to those expected to exist on mars the moon and mercury samples were measured using visible near infrared and mossbauer spectroscopy to determine the effects of varying bulk chemistry oxygen fugacity and temperature on spectral properties for martian glasses the fo2 during fusion strongly affects absorption band intensities in the spectra while bulk chemistry has noticeable secondary effects on absorption band positions titanium and iron content drive spectral changes in lunar glasses where fe3 is effectively absent iron free mercury analog glasses have much higher albedos than all other samples and their spectral shape is a close match to some pyroclastic deposits on mercury synthetic glass spectra were used as inputs into a spectral unmixing model applied to remote orbital datasets to test for the presence of glass the model is validated against physical laboratory mixture spectra as well as previous detections of glass rich pyroclastic deposits on the moon remote data were then used from suspected impact deposits and possible pyroclastic deposits on mars as a new application of the model the results reveal spatially coherent glass rich material and the strong spectral match of the synthetic glasses to these remotely sensed data gives new insights into the presence and character of glasses on the martian surface the large library of glass spectra generated here acquired from consistently synthesized and measured samples can serve as a resource for further studies of volcanic and impact processes on planetary bodies

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

geographic variation in australasian microtektite concentrations implications concerning the location and size of the source crater geographic variations in the concentration of australasian microtektites in 42 cores from the indian ocean western equatorial pacific ocean and the philippine celebes and sulo seas were used to predict the location of the australasian tektite source crater and to estimate its size the location that seems to best explain the geographic variations in microtektite concentrations is located in central cambodia at about 12 n latitude and 106 e longitude the diameter of the source crater is estimated to be between 32 and 114 km based on thickness of the microtektite layer at each site and distance from the predicted source area in cambodia the large range in estimated size of the source crater is due to a lack of knowledge about the value of the exponent that describes the radial decrease in ejecta thickness additional microtektite ejecta bearing sites closer to the source region could help resolve this problem

assumptions about the presence of natural glasses on mars natural glasses occur not only on earth but also in lunar rocks and in some meteorites on geological grounds natural glasses could be expected on the surface of mars and their presence would have important implications for the weathering and alteration of the near surface layer ultramafic and mafic magmatism rich in iron and some volatiles appears to have been important on mars as has been impact cratering volcanism and possibly hydrothermal alteration available data indicate that we can presume the past or present existence of volcanic basaltic glasses impact glasses formed by thermal fusion of meteorite impact targets and diaplectic mainly maskelynite glasses conditions appear unsuitable for the formation of tektites on the martian surface and the production of measurable amounts of fulgurite or combustion glass seems improbable prospects for the remote and in situ identification of martian glasses and their subsequent weathering products are discussed and include orbital reflectance and thermal emission spectroscopic measurements and mossbauer spectroscopy from a surface lander

mid infrared spectroscopy of impactites from the nordlinger ries impact crater abstract this study is part of an effort to build a mid infrared database 7 14 m of spectra for mertis mercury radiometer and thermal infrared spectrometer an instrument onboard of the esa jaxa bepicolombo space probe to be launched to mercury in 2017 mercury was exposed to abundant impacts throughout its history this study of terrestrial impactites can provide estimates of the effects of shock metamorphism on the mid infrared spectral properties of planetary materials in this study we focus on the nordlinger ries crater in southern germany a well preserved and easily accessible impact crater with abundant suevite impactites suevite and melt glass bulk samples from otting and aumuhle as well as red suevite from polsingen were characterized and their reflectance spectra in mid infrared range obtained in addition in situ mid infrared spectra were made from glasses and matrix areas in thin sections the results show similar but distinguishable spectra for both bulk suevite and melt glass samples as well as in situ measurements impact melt glass from aumuhle and otting have spectra dominated by a reststrahlen band at 9 3 9 6 m bulk melt rock from polsingen and bulk suevite and fine grained matrix have their strongest band between 9 4 and 9 6 m there are also features between 8 5 and 9 m and 12 5 12 8 m associated with crystalline phases there is evidence of weathering products in the fine grained matrix such as smectites mercury endured many impacts with impactors of all sizes over its history so spectral characteristics observed for impactites formed only in a single impact like in the ries impact event can be expected to be very common on planetary bodies exposed to many more impacts in their past we conclude that in mid infrared remote sensing data the surface of mercury can be expected to be dominated by features of amorphous materials

the oblique impact hale and its consequences on mars 1 highly oblique impacts represent a rare and special class of impact events manifested as elliptical craters preserved on present day planetary surfaces crater excavation in highly oblique impacts differs from that of standard vertical impacts due to early time asymmetries imparted by the downrange directed coupling of energy between the projectile and target such asymmetries are preserved as scouring and mobilized surface materials produced by high velocity low angle ejecta and blast winds along the initial impact trajectory axis downrange subsequent deposition of resulting melt rich products occurs in the form of concentrated strewnfields located downrange from the impact the distinct nature of these distal strewnfields is separate from later time more proximal ejecta accumulations and generally allows connecting these specific deposits with their parent crater the present study involves a three dimensional computational impact simulation modeled using the cth shock physics hydrocode of an event similar to the impact that produced the elliptical hale impact crater on mars 125 km 150 km diameter crater located at 36 s 36 w results generally capture the predicted patterns indicative of highly oblique impacts evidence is presented for correlated distal strewnfields located downrange from hale that coincide with prominent low albedo surface deposits and wind streaks on the present day martian surface thereby providing implications for possible identification for other dark glassy strewnfields as well as impact generated winds on mars

effect of planetary rotation on distal tektite deposition on mars 1 the rapid rotation of mars creates a significant pseudoforce known as the coriolis force that greatly modifies the flight paths and subsequent deposition of distal ejecta ejecta with launch velocities of 3 km s and greater an accurate depiction of the effects of the coriolis force requires the integration of the coriolis terms directly into a series of spherical ballistic equations applied within a rotating reference frame the resulting landing positions of radially ejected particles tend to form distinct wrapping patterns that are focused to specific areas in the hemisphere opposite from the source crater around the pole for high latitude craters 45 in latitude and above and in an equatorial band for low latitude craters below 45 latitude consequently particular locations on the surface receive deposits in stages direct delivery of ejecta followed by deposits of higher velocity ejecta this staged deposition leads to regions of enhanced ejecta accumulations where meters of material collect millimeters would be predicted in nonrotational radial decay models thus high latitude craters could supply a considerable amount of distal products tektites and melts to polar locations perhaps contributing to the dark circumpolar materials

effect of volatiles and target lithology on the generation and emplacement of impact crater fill and ejecta deposits on mars impact cratering is an important geological process on mars and the nature of martian impact craters may provide important information as to the volatile content of the martian crust terrestrial impact structures currently provide the only ground truth data as to the role of volatiles and an atmosphere on the impact cratering process recent advancements based on studies of several well preserved terrestrial craters have been made regarding the role and effect of volatiles on the impact cratering process combined field and laboratory studies reveal that impact melting is much more common in volatile rich targets than previously thought so impact melt rocks melt bearing breccias and glasses should be common on mars consideration of the terrestrial impact cratering record suggests that it is the presence or absence of subsurface volatiles and not the presence of an atmosphere that largely controls ejecta emplacement on mars furthermore recent studies at the haughton and ries impact structures reveal that there are two discrete episodes of ejecta deposition during the formation of complex impact craters that provide a mechanism for generating multiple layers of ejecta it is apparent that the relative abundance of volatiles in the near surface region outside a transient cavity and in the target rocks within the transient cavity play a key role in controlling the amount of fluidization of martian ejecta deposits this study shows the value of using terrestrial analogues in addition to observational data from robotic orbiters and landers laboratory experiments and numerical modeling to explore the martian impact cratering record